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Ketogenic Diet Disrupts the Circadian Clock and Increases Hypofibrinolytic Risk by Inducing Expression of Plasminogen Activator Inhibitor-1
Abstract
Metabolic disorders such as diabetes and obesity are considered risk factors for cardiovascular diseases by increasing levels of blood plasminogen activator inhibitor-1 (PAI-1). Ketogenic diets (KDs) have been used as an approach to weight loss in both obese and nonobese individuals. We examined circadian changes in plasma PAI-1 and its mRNA expression levels in tissues from mice fed with a KD (KD mice), to evaluate its effects on fibrinolytic functions.
Two weeks on the kDa increased plasma levels of free fatty acids and ketones accompanied by hypoglycemia in mice. Plasma PAI-1 concentrations were extremely elevated in accordance with mRNA expression levels in the heart and liver, but not in the kidneys of KD mice. Circadian expression of PAI-1 mRNA was phase-advanced for 4.7, 7.9, and 7.8 hours in the heart, kidney, and adipose tissues, respectively, as well as that of circadian genes mPer2 and DBP in KD mice, suggesting that peripheral clocks were phase-advanced by ketosis despite feeding ad libitum under a periodic light-dark cycle. The circadian clock that regulates behavioral activity rhythms was also phase-advanced, and its free-running period was significantly shortened in KD mice.
Our findings suggest that ketogenic status increases hypofibrinolytic risk by inducing abnormal circadian expression of PAI-1.
... Such diets mimic the metabolic conditions of fasting or caloric restriction and are based on theoretical concepts of the effects of dietary component ratios on energy expenditure [6]. We previously demonstrated that circadian clock gene expression is disrupted in peripheral tissues of hypothermic mice fed with a KD (KD mice) [7][8][9]. We examined the temporal expression profiles of Cirbp mRNA in mice under KD feeding and fasting to elucidate the regulation mechanism of CIRBP expression in vivo. ...
... The phase of circadian gene expression was obviously advanced both in the KD mouse liver and heart as described [8,9]. We demonstrated the phase-advancing effects of a KD on the biological clock that governs rhythmic behavioral activity as well as the rhythmic expression of circadian genes in mouse peripheral tissues [8,9]. ...
... The phase of circadian gene expression was obviously advanced both in the KD mouse liver and heart as described [8,9]. We demonstrated the phase-advancing effects of a KD on the biological clock that governs rhythmic behavioral activity as well as the rhythmic expression of circadian genes in mouse peripheral tissues [8,9]. Therefore, chronic KD feeding seems to affect the circadian phase of the central nervous systems. ...
Cold-inducible RNA-binding protein (CIRBP) induced by cold stress modulates the molecular circadian clock in vitro. The present study examines the effect of a ketogenic diet (KD) and fasting on Cirbp expression in the mouse liver. Chronic KD administration induced time-dependent Cirbp expression with hypothermia in mice. The circadian expression of clock genes such as Bmal1 and Clock was phase-advanced and augmented in the liver of mice fed with a KD. Transient food deprivation also induced time-dependent Cirbp expression with hypothermia in mice. These findings suggest that hypothermia is involved in the increased expression of Cirbp under ketogenic or fasting conditions.
... Notably, starvation or a ketogenic diet (low-carbohydrate and high-fat) that mimics starvation, advances the onset of daily behavioral rhythms in mice. 51,52) Consuming a high-salt diet (4% or 8% NaCl) for more than two weeks advances liver, kidney, and lung clocks in mice. 53) Because the rhythms of feeding and drinking behaviors are not affected by high-salt diets, the central clock is not affected. ...
... Factors that alter metabolic states would also affect the circadian system at the behavioral level. A ketogenic diet that promotes lipolysis and body weight loss through mimicking starvation signals, advances the onset of behavioral rhythms, 51) whereas a high-fat diet with carbohydrate that imitates satiation signals, prolongs the circadian period. 43) Moreover, food factors regulating PPARs might modulate the circadian clock systems like bezafibrate. ...
Daily activity rhythms that are dominated by internal clocks are called circadian rhythms. A central clock is located in the suprachiasmatic nucleus of the hypothalamus, and peripheral clocks are located in most mammalian peripheral cells. The central clock is entrained by light/dark cycles, whereas peripheral clocks are entrained by feeding cycles. The effects of nutrients on the central and peripheral clocks have been investigated during the past decade and much interaction between them has come to light. For example, a high-fat diet prolongs the period of circadian behavior, a ketogenic diet advances the onset of locomotor activity rhythms, and a high-salt diet advances the phase of peripheral molecular clocks. Moreover, some food factors such as caffeine, nobiletin, and resveratrol, alter molecular and/or behavioral circadian rhythms. Here, we review nutrients and food factors that modulate mammalian circadian clocks from the cellular to the behavioral level.
... A high-fat diet in mice leads to changes in the period of the locomotor activity rhythm and alterations in the expression and cycling of canonical circadian clock genes, nuclear receptors that regulate clock transcription factors, and clock-controlled genes involved in fuel utilization in the hypothalamus, liver, and adipose tissue (Kohsaka et al., 2007). Ketogenic diet, used for weight loss disrupts the circadian clock (phaseadvanced) and increases hypofibrinolytic risk by inducing expression of plasminogen activator inhibitor-1 (Oishi et al., 2009). High salt diet advances the phase of clock gene expression by about 3 h in the liver, kidney, and lung, without altering circadian feeding, drinking, and locomotor rhythms in mice. ...
... The interplay between circadian clock, nutrition, and metabolism. (With information ofFroy, 2007;Kohsaka et al., 2007;Oishi et al., 2009;Oike et al., 2010;Leone et al., 2015;Oike, 2017;Tahara et al., 2018). ...
Background
The circadian clock is an evolved autonomous timekeeping system that aligns body functions to the solar course, by anticipating/coordinating the required metabolic activities; such internal clock responds to several exogenous stimuli (Zeitgebers) able to synchronize the endogenous rhythm. A disrupted circadian rhythm leads to several neurodegenerative and metabolic illness such as obesity, diabetes, and psychiatric disorders.
Scope and approach
Circadian rhythm disorders have no current medical treatment, but chrononutrition has emerged as an important tool to enhance metabolic and nutritional health in sleep disorders. This review highlights the effects of meal timing, food types, nutrients and several bioactive xenobiotic compounds (chronobiotics) on circadian clocks. The potential application of diet therapies is discussed particularly to deal with certain metabolic disorders related to circadian misalignment.
Key findings and conclusions: The desynchronization of circadian rhythms negatively influences health necessitating the development of molecular modulators of circadian rhythms including food components, meal timing, or different diet types that can help correct circadian disorders attenuating the burden of chronic diseases. However, there is limited research on the chronobiotic effect of specific foods/compounds in clinical trials. Animal studies evaluating the chronobiological response, resulting from the ingestion of a particular food, are also limited; most available studies (in vitro and animal models) report the effect of a single nutrient (e.g., caffeine, palmitate, among others) which is difficult to translate to real-life situations. This review offers the perspective of a chronobiotic-based approach, identifying targets for health improvement, which are current lifestyle-associated issues.
... The effects of a ketogenic diet on clock gene expression have been recently investigated in mouse models, and these studies showed that KD is able to influence circadian rhythm. Oishi et al. (2009Oishi et al. ( , 2013 fed mice with KD or normal chow for 2 weeks, and observed that KD induced a phase-advance in peripheral clocks and behavioral activity, despite a maintained light-dark cycle and feeding ad libitum. The phase-advance effect was greater in the heart, kidney, and adipose tissue, than in the liver. ...
Circadian rhythms underpin most physiological processes, including energy metabolism. The core circadian clock consists of a transcription-translation negative feedback loop, and is synchronized to light-dark cycles by virtue of light input from the retina, to the central clock in the suprachiasmatic nucleus in the hypothalamus. All cells in the body have circadian oscillators which are entrained to the central clock by neural and humoral signals. In addition to light entrainment of the central clock in the brain, it now emerges that other stimuli can drive circadian clock function in peripheral tissues, the major one being food. This can then drive the liver clock to be misaligned with the central brain clock, a situation of internal misalignment with metabolic disease consequences. Such misalignment is prevalent, with shift workers making up 20% of the working population. The effects of diet composition on the clock are not completely clarified yet. High-fat diet and fasting influence circadian expression of clock genes, inducing phase-advance and phase-delay in animal models. Ketogenic diet (KD) is able to induce a metabolic switch from carbohydrate to fatty acid oxidation, miming a fasting state. In recent years, some animal studies have been conducted to investigate the ability of the KD to modify circadian gene expression, and demonstrated that the KD alters circadian rhythm and induces a rearrangement of metabolic gene expression. These findings may lead to new approaches to obesity and metabolic pathologies treatment.
... Consequently, under these hypocaloric conditions, nocturnal animals become partially diurnal. A ketogenic diet is another nutritional condition that leads not only to body mass loss and lipid mobilisation, but also to a phase-advanced rhythm of locomotor activity (Oishi et al. 2009). ...
Daily brain rhythmicity, which controls the sleep-wake cycle and neuroendocrine functions, is generated by an endogenous circadian timing system. Within the multi-oscillatory circadian network, a master clock is located in the suprachiasmatic nuclei of the hypothalamus, whose main synchroniser (Zeitgeber) is light. In contrast, imposed meal times and temporally restricted feeding are potent synchronisers for secondary clocks in peripheral organs such as the liver and in brain regions, although not for the suprachiasmatic nuclei. Even when animals are exposed to a light-dark cycle, timed calorie restriction (i.e. when only a hypocaloric diet is given every day) is a synchroniser powerful enough to modify the suprachiasmatic clockwork and increase the synchronising effects of light. A daily chocolate snack in animals fed ad libitum with chow diet entrains the suprachiasmatic clockwork only under the conditions of constant darkness and decreases the synchronising effects of light. Secondary clocks in the brain outside the suprachiasmatic nuclei are differentially influenced by meal timing. Circadian oscillations can either be highly sensitive to food-related metabolic or reward cues (i.e. their phase is shifted according to the timed meal schedule) in some structures or hardly affected by meal timing (palatable or not) in others. Furthermore, animals will manifest food-anticipatory activity prior to their expected meal time. Anticipation of a palatable or regular meal may rely on a network of brain clocks, involving metabolic and reward systems and the cerebellum.
... Restricted daytime feeding by nocturnal animals obviously shifts their peripheral clocks [4,5]. Specific nutritional diets such as high-fat and ketogenic diets affect circadian oscillators despite feeding ad libitum [6,7], suggesting that food quality and not simply the timing of caloric intake, is also a factor in the entrainment of circadian clocks. These diets affect the metabolic status of mice, and probably alter their circadian clocks. ...
Dietary compounds influence the expression of various genes and play a major role in changing physiological and metabolic states. However, little is known about the role of food ingredients in the regulation of circadian gene expression. Here, we show that feeding mice with a high-salt (HS) diet ad libitum for over 2weeks advanced the phase of clock gene expression by about 3h in the liver, kidney, and lung, but did not change circadian feeding, drinking, and locomotor rhythms. Focused DNA microarray analysis showed that the expression phase of many genes related to metabolism in the liver was also advanced. Immediately before phase advancement in peripheral tissues, the mRNA expression of sodium-glucose cotransporter 1 (Sglt1) and glucose transporter 2 (Glut2), that are responsible for glucose absorption, was increased in the jejunum. Furthermore, blood glucose uptake increased more rapidly after consuming the HS diet than the control diet. Moreover, phloridzin, a specific inhibitor of SGLT1, prevented the increased glucose transporter expression in the jejunum and phase advancement in the livers of mice on the HS diet. These results suggest that increased glucose absorption induced by dietary HS alters the food entrainment of peripheral molecular circadian rhythms.
... Rev-ErbA suppresses plasminogen activator inhibitor type 1 gene expression and is therefore a major determinant of the circadian plasminogen activator inhibitor type 1 variation and may influence the susceptibility to myocardial infarction in the early morning (49). Experimental findings in mice suggest that ketogenic status increases hypofibrinolytic risk by inducing abnormal circadian expression of plasminogen activator inhibitor type 1 (50). ...
OBJECTIVE:: Circadian rhythms are intrinsic timekeeping mechanisms that allow for adaptation to cyclic environmental changes. Increasing evidence suggests that circadian rhythms may influence progression of a variety of diseases as well as effectiveness and toxicity of drugs commonly used in the intensive care unit. In this perspective, we provide a brief review of the molecular mechanisms of circadian rhythms and its relevance to critical care. DATA SOURCES, STUDY SELECTION, DATA EXTRACTION, AND DATA SYNTHESIS:: Articles related to circadian rhythms and organ systems in normal and disease conditions were searched through the PubMed library with the goal of providing a concise review. CONCLUSIONS:: Critically ill patients may be highly vulnerable to disruption of circadian rhythms as a result of the severity of their underlying diseases as well as the intensive care unit environment where noise and frequent therapeutic/diagnostic interventions take place. Further basic and clinical research addressing the importance of circadian rhythms in the context of critical care is warranted to develop a better understanding of the complex pathophysiology of critically ill patients as well as to identify novel therapeutic approaches for these patients.
... 107,108 A ketogenic diet is another example of negative energy balance leading to body mass loss, lipid mobilization, and phase-advanced sleep-wake cycle. 109 Nocturnal mice, that have to work for getting food with increasing levels of workload over days, become also partially diurnal. Interestingly, the switch from nocturnal to diurnal pattern of activity coincides with a gradual shift toward a negative energy balance. ...
Circadian rhythmicity that has been shaped by evolution over millions of years generates an internal timing controlling the sleep-wake and metabolism cycles. The daily variations between sleep/fasting/catabolism and wakefulness/feeding/anabolism are coordinated by a master hypothalamic clock, mainly reset by ambient light. Secondary clocks, including liver and adipose tissue, are normally synchronized by the master clock, but they are also sensitive to feeding time, especially when meals take place during the usual resting period. Cellular metabolism and circadian clocks are tightly interconnected at the molecular levels. Although the suprachiasmatic clock is not shifted by mealtime under light-dark conditions, nutritional cues can feedback onto it and modulate its function under hypo- and hypercaloric (high-fat) conditions. Food-related reward cues are other modulators of the master clock. Circadian disturbances (e.g., desynchronization induced by shift work or chronic jet lag) are frequently associated with metabolic dysfunctions (chronobesity) and vice versa. Pharmacological tools and natural synchronizers (i.e., light and mealtime) can be useful as chronotherapeutic treatments to limit the occurrence of metabolic risk factors.
... More in detail, Al-Zaid et al., 11 found that a low carbohydrate ketogenic diet enhances the cardiac tolerance to global ischemia in rats with global ischemic injury, thus suggesting that the low carbohydrate ketogenic diet is functionally cardio-protective. On the contrary, Oishi et al., 12 found that the ketogenic status in mice fed with the ketogenic diet increases hypofibrinolytic risk by inducing abnormal circadian expression of plasminogen activator inhibitor-1. ...
Purpose
The present study aimed to assess the impact of the ketogenic diet on arterial morphology and endothelial function of the big vessels of the neck and on cardiac diastolic function, in a cohort of epileptic children and young adults treated with the ketogenic diet.
Methods
Patients were recruited based on the following inclusion criteria: 1) patients who were or had been on the ketogenic diet for a time period of at least six months. Each patient underwent measurement of carotid intima media thickness, carotid artery stiffness, echocardiography, and diastolic function assessment. Patients with drug resistant epilepsy, matched for number, age and sex and never treated with ketogenic diet, were recruited as controls.
Results
The population study was composed by 43 epilepsy patients (23 males), aged between 19 months and 31 years (mean 11 years). Twenty-three patients were or had been treated with ketogenic diet, and 20 had never been on it (control group). Subjects treated with the ketogenic diet had higher arterial stiffness parameters, including AIx and β-index and higher serum levels of cholesterol or triglycerides compared to those who had never been on the diet (control group) (p < 0.001).
Conclusions
Arterial stiffness is increased in children and young adults treated with the ketogenic diet, before the increase of the intima media thickness. This supports that arterial stiffness is an early marker of vascular damage.
... Both nutrients and meal timing can affect the clock system, thus " chrononutrition " has two aspects: 1) nutrients/food components regulate the clock system, e.g., caffeine prolongs the period of circadian clocks and the locomotor activity rhythm, and high-fat diets alter the rhythms of lipogenesis, circulating lipids, locomotor activity, and feeding behavior; 2) meal-timing affects output of the clock system, e.g., skipping breakfast and nocturnal eating increases risk of obesity, whereas time-restricted feedings prevent metabolic disorders induced by high-fat diets. Regular/time-restricted feedings synchronize and amplify the rhythms of clock system, whereas irregular/unusual feedings cause desynchronization and attenuate the rhythms, probably leading to metabolic disorders rhythm of clock and clock-controlled genes are phaseadvanced in peripheral tissues under a normal light/ dark condition [40]. Interestingly, ketogenic diets were designed to mimic the physiological response to starvation , and hypocaloric conditions induce a phaseadvance in circadian locomotor activity rhythms [41]. ...
Circadian clocks that comprise clock genes exist throughout the body and control daily physiological events. The central clock that dominates activity rhythms is entrained by light/dark cycles, whereas peripheral clocks regulating local metabolic rhythms are determined by feeding/fasting cycles. Nutrients reset peripheral circadian clocks and the local clock genes control downstream metabolic processes. Metabolic states also affect the clockworks in feedback manners. Because the circadian system organizes whole energy homeostasis, including food intake, fat accumulation, and caloric expenditure, the disruption of circadian clocks leads to metabolic disorders. Recent findings show that time-restricted feeding during the active phase amplifies circadian clocks and improves metabolic disorders induced by a high-fat diet without caloric reduction, whereas unusual/irregular food intake induces various metabolic dysfunctions. Such evidence from nutrition studies that consider circadian system (chrononutrition) has rapidly accumulated. We review molecular relationships between circadian clocks and nutrition as well as recent chrononutrition findings.
... Calorie restriction with ultradian feeding schedules induces phase-advances in wheel-running and body temperature rhythms [22,23]. Bezafibrate-induced activation of PPARa [24,25] and ketogenic diets [26,27] that mimic the metabolic conditions of fasting or caloric restriction without time cues can also advance the phase of circadian behavior, core Tb and hepatic clock gene expression. Various metabolic changes such as those associated with diabetes and obesity tissue-dependently affect peripheral clock gene expression. ...
Behavioral and physiological circadian rhythms are controlled by endogenous oscillators in animals. Voluntary wheel-running in rodents is thought to be an appropriate model of aerobic exercise in humans. We evaluated the effects of chronic voluntary exercise on the circadian system by analyzing temporal profiles of feeding, core body temperature, plasma hormone concentrations and peripheral expression of clock and clock-controlled genes in mice housed under sedentary (SED) conditions or given free access to a running-wheel (RW) for four weeks. Voluntary wheel-running activity advanced the circadian phases of increases in body temperature, food intake and corticosterone secretion in the mice. The circadian expression of clock and clock-controlled genes was tissue- and gene-specifically affected in the RW mice. The temporal expression of E-box-dependent circadian clock genes such as Per1, Per2, Nr1d1 and Dbp were slightly, but significantly phase-advanced in the liver and white adipose tissue, but not in brown adipose tissue and skeletal muscle. Peak levels of Per1, Per2 and Nr1d1 expression were significantly increased in the skeletal muscle of RW mice. The circadian phase and levels of hepatic mRNA expression of the clock-controlled genes that are involved in cholesterol and fatty acid metabolism significantly differed between SED and RW mice. These findings indicated that endogenous clock-governed voluntary wheel-running activity provides feedback to the central circadian clock that systemically governs behavioral and physiological rhythms.
... It has been shown that peripheral clocks were phase-advanced by ketosis despite feeding ad libitum under lightedark conditions. The circadian clock that regulates behavioral activity rhythms was also phase-advanced, and its free-running period was significantly shortened in KD mice (Oishi et al., 2009(Oishi et al., , 2013. However, our gene analyses were performed under total darkness, which is a more accurate assessment, considering the masking effect of light. ...
Ketogenic diet (KD) is used for weight loss or to treat epilepsy. KD leads to liver AMP-activated protein kinase (AMPK) activation, which would be expected to inhibit gluconeogenesis. However, KD leads to increased hepatic glucose output. As AMPK and its active phosphorylated form (pAMPK) show circadian oscillation, this discrepancy could stem from wrong-time-of-day sampling. The effect of KD was tested on mouse clock gene expression, AMPK, mTOR, SIRT1 and locomotor activity for 2 months and compared to low-fat diet (LFD). KD led to 1.5-fold increased levels of blood glucose and insulin. Brain pAMPK/AMPK ratio was 40% higher under KD, whereas that in liver was not affected. KD led to 40% and 20% down-regulation of the ratio of pP70S6K/P70S6K, the downstream target of mTOR, in the brain and liver, respectively. SIRT1 levels were 40% higher in the brain, but 40% lower in the liver of KD-fed mice. Clock genes showed delayed rhythms under KD. In the brain of KD-fed mice, amplitudes of clock genes were down-regulated, whereas 6-fold up-regulation was found in the liver. The metabolic state under KD indicates reduced satiety in the brain and reduced anabolism alongside increased gluconeogenesis in the liver.
... Similarly, streptozotocin-induced insulin-deficient mice, which have high blood glucose levels, showed a phase-advanced peripheral clock phase (178). In contrast, ketogenic diets, accompanied by hypoglycemia, caused phase-advanced peripheral clocks (179). However, this effect was caused by a shortened circadian free-running period of the SCN and a behavioral phase in the normal light-dark cycle. ...
The circadian clock system in mammals drives many physiological processes including the daily rhythms of sleep-wake behavior, hormonal secretion, and metabolism. This system responds to daily environmental changes, such as the light-dark cycle, food intake, and drug administration. In this review, we focus on the central and peripheral circadian clock systems in response to drugs, food, and nutrition. We also discuss the adaptation and anticipation mechanisms of our body with regard to clock system regulation of various kinetic and dynamic pathways, including absorption, distribution, metabolism, and excretion of drugs and nutrients. "Chrono-pharmacology" and "chrono-nutrition" are likely to become important research fields in chrono-biological studies.
... 56 Altered circadian expression of a major regulator of fibrinolysis appears to influence susceptibility to myocardial infarction. 57 Circadian dysrhythmia alters metabolic function, with derangements in lipid and glucose homeostasis leading to obesity and glucose intolerance. 58 A mutation in one clock gene triggers a metabolic switch towards fatty acid oxidation and increased myocardial oxygen consumption, inhibiting the ability of cells to meet metabolic demands under stress conditions. ...
Many physiological and cellular processes cycle with time, with the period between one peak and the next being roughly equal to 24 h. These circadian rhythms underlie ‘permissive homeostasis’, whereby anticipation of periods of increased energy demand or stress may enhance the function of individual cells, organ systems or whole organisms. Many physiological variables related to survival during critical illness have a circadian rhythm, including the sleep/wake cycle, haemodynamic and respiratory indices, immunity and coagulation, but their clinical significance remains underappreciated. Critically ill patients suffer from circadian dysrhythmia, manifesting overtly as sleep disturbance and delirium, but with widespread covert effects on cellular and organ function. Environmental and pharmacological strategies that ameliorate or prevent circadian dysrhythmia have demonstrated clinical benefit. Harnessing these important biological phenomena to match metabolic supply to demand and bolster cell defenses at the apposite time may be a future therapeutic strategy in the intensive care unit.
... Per2 is a direct regulator of Cpt1a expression, a rate-limiting enzyme that transfers long-chain fatty acids to the inner mitochondrial membrane for ß-oxidation, and is an indirect regulator of Hmgcs2, the rate-limiting enzyme for ketogenesis from the resulting acetyl-CoA (154). The KD may also increase transcriptional activation of CCG's by the CLOCK:BMAL1 complex (peaking at ZT8-12); the KD diet has been shown to upregulate the clock output gene Dbp in the liver, heart, kidney, and adipose tissue (155). ...
The molecular circadian clock regulates metabolic processes within the cell, and the alignment of these clocks between tissues is essential for the maintenance of metabolic homeostasis. The possibility of misalignment arises from the differential responsiveness of tissues to the environmental cues that synchronize the clock (zeitgebers). Although light is the dominant environmental cue for the master clock of the suprachiasmatic nucleus, many other tissues are sensitive to feeding and fasting. When rhythms of feeding behavior are altered, for example by shift work or the constant availability of highly palatable foods, strong feedback is sent to the peripheral molecular clocks. Varying degrees of phase shift can cause the systemic misalignment of metabolic processes. Moreover, when there is a misalignment between the endogenous rhythms in physiology and environmental inputs, such as feeding during the inactive phase, the body's ability to maintain homeostasis is impaired. The loss of phase coordination between the organism and environment, as well as internal misalignment between tissues, can produce cardiometabolic disease as a consequence. The aim of this review is to synthesize the work on the mechanisms and metabolic effects of circadian misalignment. The timing of food intake is highlighted as a powerful environmental cue with the potential to destroy or restore the synchrony of circadian rhythms in metabolism.
... Diet is known to strongly impact the phase and amplitude of clock gene expression in metabolic tissues. Calorie restriction, ketogenic diets, and time-restricted feeding protocols typically lead to an increase in the amplitude of clock gene expression (Dong et al., 2010;Girotti et al., 2009;Hara et al., 2001;Katewa et al., 2016;Oishi et al., 2009Oishi et al., , 2012Patel et al., 2016), whereas a dampened rhythm of clock gene expression is observed when animals are given a high-fat diet or a calorie-surplus diet (Kohsaka et al., 2007). Furthermore, pharmaceutical interventions that are protective against the metabolic effects of a high-fat diet, such as metformin, are associated with increases in the amplitude and phase of clock gene expression in metabolic tissues (Barnea et al., 2012;Um et al., 2007). ...
Temperature rhythms can act as potent signals for the modulation of the amplitude and phase of clock gene expression in peripheral organs in vitro, but the relevance of the circadian rhythm of core body temperature (Tc) as a modulating signal in vivo has not yet been investigated. Using calorie restriction and cafeteria feeding, we induced a larger and a dampened Tc amplitude, respectively, in male Wistar rats, and investigated the circadian expression profile of the core clock genes Bmal1, Per2, Cry1, and Rev-erbα, the heat-responsive genes heat shock protein 90 (Hsp90) and cold-inducible RNA binding protein (Cirbp), and Pgc1α, Pparα/γ/δ, Glut1/4, and Chop10 in the liver, skeletal muscle, white adipose tissue (WAT), and adrenal glands. Diet-altered Tc rhythms differentially affected the profiles of clock genes, Hsp90, and Cirbp expression in peripheral tissues. Greater Tc amplitudes elicited by calorie restriction were associated with large amplitudes of Hsp90 and Cirbp expression in the liver and WAT, in which larger amplitudes of clock gene expression were also observed. The amplitudes of metabolic gene expression were greater in the WAT, but not in the liver, in calorie-restricted rats. Conversely, diet-altered Tc rhythms were not translated to distinct changes in the amplitude of Hsp90, Cirbp, or clock or metabolic genes in the skeletal muscle or adrenal glands. While it was not possible to disentangle the effects of diet and temperature in this model, taken together with previous in vitro studies, our study presents novel data consistent with the notion that the circadian Tc rhythm can modulate the amplitude of circadian gene expression in vivo. The different responses of Hsp90 and Cirbp in peripheral tissues may be linked to the tissue-specific responses of peripheral clocks to diet and/or body temperature rhythms, but the association with the amplitude of metabolic gene expression is limited to the WAT.
... However, the amplitude of CCGs is not drastically altered in the intestine (Tognini et al., 2017). KD also caused phase-advanced of circadian rhythm and shorten its free-running period in mice, increased hypofibrinolytic risk by inducing expression of plasminogen activator inhibitor-1 (Oishi et al., 2009). Fig. 3 shows dietary styles regulating circadian rhythm. ...
The circadian rhythm regulates the daily cycles of various physiological activities. Accumulating evidences revealed that circadian rhythm plays an important role in regulating metabolic homeostasis, and disruptions of circadian rhythms resulting in metabolic disorder. Peripheral clocks are not only controlled by the central clock but also entrained by external cues. Dietary pattern and compounds derived from food are found to play multiple roles in regulating metabolic processes through resetting peripheral clocks. Here we review the recent advance of effects and mechanisms of dietary pattern and compounds modulating peripheral clocks and regulating metabolic processes. Multiple molecular mechanisms linked dietary pattern and compounds with circadian rhythm and metabolism were summarized. Elaboration of crosstalk between diet and circadian rhythm may provide targets for the prevention of metabolic disorder. The exact mechanisms that feeding pattern and dietary compounds linked metabolic process and circadian rhythm need to be further investigated.
... In this respect, it is interesting that restricted daytime feeding, when food is only available for a few hours during the day (a time when nocturnal rat and mouse do not normally eat), uncouples peripheral clocks from the SCN and shifts these clocks to the timing of food availability [12,73]. Similarly, dietary interventions such as a high-fat diet [74] or a ketogenic diet [75,76] have profound effects on oscillations of the peripheral clocks. These findings suggest that both timing of the diet and its quality may entrain the circadian clock and alter pharmacokinetic profiles of drugs, which are substrates of ABC and SLC transporters. ...
Introduction: SLC and ABC transporters expressed in the intestine, liver, and kidney, determine the absorption, distribution, and excretion of drugs. In addition, most molecular and cellular processes show circadian rhythmicity controlled by circadian clocks that leads to diurnal variations in the pharmacokinetics and pharmacodynamics of many drugs and affects their therapeutic efficacy and toxicity.
Area covered: This review provides an overview of the current knowledge on the circadian rhythmicity of drug transporters and the molecular mechanisms of their circadian control. Evidence for coupling drug transporters to circadian oscillators and the plausible candidates conveying circadian clock signals to target drug transporters, particularly transcription factors operating as the output of clock genes, is discussed.
Expert opinion: The circadian machinery has been demonstrated to interact upon the uptake and efflux of various drug transporters. The evidence supports the concept that diurnal changes that affect drug transporters may influence the pharmacokinetics of the drugs. However, more systematic studies are required to better define the timing of pharmacologically important drug transporter regulation and determine tissue- and sex-dependent differences. Finally, the transfer of knowledge based on the results and conclusions obtained primarily from animal models will require careful validation before it is applied to humans.
... During the daily period of fasting, therefore, the metabolic modulation of photic phase shifting may be mediated, in part, by these fuels derived from lipid stores. It is worth mentioning here that mice fed a ketogenic diet not only display an expected loss of body mass and lipid mobilisation, but also show a phase-advanced rhythm of locomotor activity ( Oishi et al. 2009). ...
Daily variations in behaviour and physiology are controlled by a circadian timing system consisting of a network of oscillatory structures. In mammals, a master clock, located in the suprachiasmatic nuclei (SCN) of the hypothalamus, adjusts timing of other self-sustained oscillators in the brain and peripheral organs. Synchronisation to external cues is mainly achieved by ambient light, which resets the SCN clock. Other environmental factors, in particular food availability and time of feeding, also influence internal timing. Timed feeding can reset the phase of the peripheral oscillators whilst having almost no effect in shifting the phase of the SCN clockwork when animals are exposed (synchronised) to a light-dark cycle. Food deprivation and calorie restriction lead not only to loss of body mass (>15%) and increased motor activity, but also affect the timing of daily activity, nocturnal animals becoming partially diurnal (i.e. they are active during their usual sleep period). This change in behavioural timing is due in part to the fact that metabolic cues associated with calorie restriction affect the SCN clock and its synchronisation to light.
... Intake of a high-fat diet also attenuates the amplitude of day/night feeding and clock gene expression rhythms in the liver and adipose tissues (Eckel-Mahan et al. 2013) and may induce a phase-advance of liver clocks and altered feeding rhythms (Pendergast et al. 2013). In addition, intake of a ketogenic diet (with a higher proportion of fat and a very low proportion of carbohydrates) alters circadian locomotor activity rhythm and results in a phase advance of the clock genes, even under a normal light/ dark cycle (Oishi et al. 2009). These alterations could be related with free fatty acids that are increased by a ketogenic diet in plasma (Shirai et al. 2007;Gutman et al. 2012). ...
Chrononutrition proposes that nutrients or meal timing per se could affect the circadian clock system, and that the desynchronization of biological rhythms could negatively influence timing and food choices. Research in this area has suggested that mealtime, energy distribution throughout the day, nocturnal eating and food ingestion frequency may influence nutrient metabolism, being associated with metabolic and nutritional diseases. Given the growing amount of evidence linking the circadian clock system to metabolic and nutritional health, circadian organization seems to be clinically important in the understanding of diseases such as obesity and, maybe, in the nutritional treatment of them. Thus, chrononutrition emerges as an important tool to enhance the metabolic and nutritional health of particular population groups (e.g. shift workers) and in the treatment of diseases such as obesity. For this reason, the area needs to be further explored.
... We reveal a tissue-specific cyclic signature in response to a KD regimen that leads to a dramatic increase in b-oxidation and consequent ketosis (Paoli et al., 2015). While the impact of KD on the circadian clock has been noted (Genzer et al., 2015;Oishi et al., 2009), the molecular mechanisms underlying its action have not been satisfactorily explored. Our study represents the first exhaustive analysis of how KD influences rhythmic genomic reprogramming. ...
The circadian clock orchestrates rhythms in physiology and behavior, allowing organismal adaptation to daily environmental changes. While food intake profoundly influences diurnal rhythms in the liver, how nutritional challenges are differentially interpreted by distinct tissue-specific clocks remains poorly explored. Ketogenic diet (KD) is considered to have metabolic and therapeutic value, though its impact on circadian homeostasis is virtually unknown. We show that KD has profound and differential effects on liver and intestine clocks. Specifically, the amplitude of clock-controlled genes and BMAL1 chromatin recruitment are drastically altered by KD in the liver, but not in the intestine. KD induces nuclear accumulation of PPARα in both tissues but with different circadian phase. Also, gut and liver clocks respond differently to carbohydrate supplementation to KD. Importantly, KD induces serum and intestinal β-hydroxyl-butyrate levels to robustly oscillate in a circadian manner, an event coupled to tissue-specific cyclic histone deacetylase (HDAC) activity and histone acetylation.
Plasminogen activator inhibitor-1 (PAI-1), the primary physiological inhibitor of plasminogen activators, is an important contributor to hypofibrinolysis in the presence of metabolic disorders such as diabetes and obesity. The C57BLKS/J (BKS) inbred mouse strain is a popular animal model of type 2 diabetes. We previously described that food deprivation (FD) induces adipose PAI-1 expression in both lean BKS mice and BKS-db/db mice carrying a mutation in the leptin receptor gene. To evaluate the effects of the background of mouse strains, we examined FD-induced PAI-1 expression in the liver, heart and epididymal adipose tissues of BKS, C57BL/6J (B6), C3H/HeN and ICR mice. We found that PAI-1 expression is significantly induced in the heart and liver of fasted mice, although levels of expression in adipose tissues are strain-dependent. The effect of FD on plasma PAI-1 levels is also strain-dependent. Genetic background seems to be an important factor that should be considered when investigating thrombosis and fibrinolysis relative to metabolic changes in mice.
Fibroblast growth factor 21 (FGF21) is a key metabolic regulator that is induced by peroxisome proliferator-activated receptor alpha (PPARalpha) activation in response to fasting. We recently reported that bezafibrate, a pan-agonist of PPARs, decreases body temperature late at night through hypothalamic neuropeptide Y (NPY) activation and others have shown that mice overexpressing FGF21 are prone to torpor.
We examined whether FGF21 is essential for fasting-induced hypothermia using FGF21 knockout (KO) mice.
Acute fasting decreased body temperature late at night accompanied by the induction of hepatic FGF21 and hypothalamic NPY expression in wild-type mice. A deficiency of FGF21 affected neither fasting-induced hypothermia nor hypothalamic NPY induction. Fasting enhanced locomotor activity in both genotypes. On the other hand, a deficiency of FGF21 significantly attenuated chronic hypothermia and hypoactivity induced by a ketogenic diet (KD).
Our findings suggest that FGF21 is not essential for the hypothermia that is associated with the early stages of fasting, although it might be involved in the adaptive response of body temperature to chronic starvation.
Cardiovascular functions, including blood pressure and vascular functions, show diurnal oscillation. Circadian variations have been clearly shown in the occurrence of cardiovascular events such as acute myocardial infarction. Circadian rhythm strongly influences human biology and pathology. The identification and characterization of mammalian clock genes revealed that they are expressed almost everywhere throughout the body in a circadian manner. In contrast to the central clock in the suprachiasmatic nucleus (SCN), the clock in each tissue or cell is designated as a peripheral clock. It is now accepted that peripheral clocks have their own roles specific to each peripheral organ by regulating the expression of clock-controlled genes (CCGs), although the oscillation mechanisms of the peripheral clock are similar to that of the SCN. However, little was known about how the peripheral clock in the vasculature contributes to the process of cardiovascular disorders. The biological clock allows each organ or cell to anticipate and prepare for changes in external stimuli. Recent evidence obtained using genetically engineered mice with disrupted circadian rhythm showed a novel function of the internal clock in the pathogenesis of endothelial dysfunction, hypertension and hemostasis. Loss of synchronization between the central and peripheral clock also contributes to the pathogenesis of cardiovascular diseases, as restoration of clock homeostasis could prevent disease progression. Identification of CCGs in each organ, as well as discovery of tools to manipulate the phase of each biological clock, will be of great help in establishing a novel chronotherapeutic approach to the prevention and treatment of cardiovascular disorders.
Cardiovascular functions such as heart rate and blood pressure show 24h variation. The incidence of cardiovascular diseases including acute myocardial infarction and arrhythmia also exhibits diurnal variation. The center of this circadian clock is located in the suprachiasmatic nucleus in the hypothalamus. However, recent findings revealed that each organ, including cardiovascular tissues, has its own internal clock, which has been termed a peripheral clock. The functional roles played by peripheral clocks have been reported recently. Since the peripheral clock is considered to play considerable roles in the processes of cardiac tissues, the identification of genes specifically regulated by this clock will provide insights into its role in the pathogenesis of cardiovascular disorders. In addition, the discovery of small compounds that modulate the peripheral clock will help to establish chronotherapeutic approaches. Understanding the biological relevance of the peripheral clock will provide novel approaches to the prevention and treatment of cardiovascular diseases.
Objective:
The ketogenic diet (KD) has been referred to as an "effective therapy with side effects" for children with intractable epilepsy. Among the most recognized adverse effects, there are cardiac conduction abnormalities, vascular and myocardial dysfunction. However, very limited and controversial data are available regarding the effects of the KD on cardiac functions. We sought to analyze the mid-term effect of ketogenic diet on cardiac functions in patients with intractable epilepsy who received a ketogenic diet for at least 12months using conventional and relatively new imaging techniques.
Methods:
This prospective study included 61 patients with intractable epilepsy who received ketogenic diet for at least 12months. Clinical examinations, serum carnitine and selenium levels as well as electrocardiographic and echocardiographic examinations were scheduled prior to the procedure and at 1, 3, 6 and 12months. We utilized two-dimensional, M-mode, colored Doppler, spectral Doppler and pulsed wave tissue Doppler imaging techniques to investigate ventricular systolic and diastolic functions of this subgroup of patients.
Results:
In our study, there was no significant difference after 1year of KD therapy compared to baseline values-except a significantly decreased A wave velocity-in terms of pulse wave Doppler echocardiographic measurements of the diastolic function. The tissue Doppler measurements obtained from the lateral wall of tricuspide and mitral annuli were not different at baseline and at month 12 of the treatment, as well.
Conclusion:
The ketogenic diet appears to have no disturbing effect on ventricular functions in epileptic children in the midterm.
Daily restricted feeding entrains the circadian rhythm of mouse clock gene expression in the central nervous system, excluding the suprachiasmatic nucleus (SCN), as well as in the peripheral tissues such as the liver, lung, and heart. In addition to entrainment of the clock genes, daily restricted feeding induces a locomotor activity increase 2-3h before the restricted feeding time initiates. The increase in activity is called the food-anticipatory activity (FAA). In addition to FAA, daily restricted feeding can also entrain peripheral circadian clocks in other organs such as liver, lung, and heart. This type of oscillator is called the food-entrainable peripheral oscillator (FEPO). At present, the mechanisms for restricted feeding-induced entrainment of locomotor activity (FAA) and/or peripheral clock (FEPO) are still unknown. In this review, we describe the role of the central nervous system and peripheral tissues in FAA performance and also in the entrainment of clock gene expression. In addition, the mechanism for entrainment of circadian oscillators by the abuse of drugs, such as methamphetamine, is discussed.
An increased level of plasminogen activator inhibitor-1 (PAI-1) is considered a risk factor for cardiovascular diseases, and PAI-1 gene expression is under the control of molecular circadian clocks in mammals. We recently showed that PAI-1 expression is augmented in a phase-advanced circadian manner in mice fed with a ketogenic diet (KD). To determine whether peroxisome proliferator-activated receptor α (PPARα) is involved in hypofibrinolytic status induced by a KD, we examined the expression profiles of PAI-1 and circadian clock genes in PPARα-null KD mice. Chronic administration of bezafibrate induced the PAI-1 gene expression in a PPARα-dependent manner. Feeding with a KD augmented the circadian expression of PAI-1 mRNA in the hearts and livers of wild-type (WT) mice as previously described. The KD-induced mRNA expression of typical PPARα target genes such as Cyp4A10 and FGF21 was damped in PPARα-null mice. However, plasma PAI-1 concentrations were significantly more elevated in PPARα-null KD mice in accordance with hepatic mRNA levels. These observations suggest that PPARα activation is dispensable for KD-induced PAI-1 expression. We also found that hyperlipidemia, fatty liver, and the hepatic expressions of PPARγ and its coactivator PCG-1α were more effectively induced in PPARα-null, than in WT mice on a KD. Furthermore, KD-induced hepatic PAI-1 expression was significantly suppressed by supplementation with bisphenol A diglycidyl ether, a PPARγ antagonist, in both WT and PPARα-null mice. PPARγ activation seems to be involved in KD-induced hypofibrinolysis by augmenting PAI-1 gene expression in the fatty liver.
Scheduled food access during the daytime for nocturnal mice or rats entrains the food-entrainable oscillator (FEO) in the brain and the food-entrainable peripheral oscillator (FEPO) in the peripheral tissues. FEO and FEPO are not regulated by the central clock, which is in the suprachiasmatic nucleus. FEO produces food anticipatory activity (FAA) 2-3 h before the scheduled feeding time initiates. FEPO produces entrainment in the rhythm of peripheral clock gene expression and in the rhythm of food-metabolic functions in peripheral organs. At present, the mechanisms of the FEO and FEPO are not completely understood, despite many studies that have been performed in this field. In addition, circadian clocks affect metabolism of nutrition (absorption, distribution, metabolism, excretion). In this review, we describe and review the characteristics and biological implications of FEO and FEPO and the mechanism of metabolism of nutrition with day-night differences. We call this relationship between nutrition and chronobiology –Chrono-nutrition,— which is an important study field to understand how our body clocks contribute to our health throughout the day.
Insulin resistance in patients with type II diabetes has recently been treated with thiazolidinediones, a class of peroxisome proliferator-activated receptor γ (PPARγ) agonists. However, these compounds are possibly associated with a significant increase in the risk of cardiovascular events. We examined the effect of the PPARγ agonist rosiglitazone on the expression of plasminogen activator inhibitor-1 (PAI-1) that is the primary inhibitor of fibrinolysis in the liver of diabetic mice and cultured mouse and human hepatocytes. Concentrations of plasma PAI-1 and levels of its mRNA expression in the liver were significantly elevated in accordance with hepatic PPARγ1 and PPARγ2 mRNA accumulation in genetically diabetic db/db mice. An intraperitoneal injection of rosiglitazone significantly increased plasma PAI-1 concentrations in parallel with hepatic, but not with adipose mRNA levels in db/db mice, and did not affect these parameters in wild-type mice. Rosiglitazone as well as the PPARα agonist bezafibrate significantly induced PAI-1 mRNA expression in cultured mouse hepatocytes. Furthermore, both rosiglitazone and pioglitazone significantly induced, whereas bezafibrate did not affect PAI-1 mRNA expression in the human liver carcinoma cell line HepG2. The transient induction of PAI-1 gene expression mediated by PPARγ in the fatty liver might be involved in the increased risk of cardiovascular events associated with thiazolidinediones in diabetic patients through decreasing fibrinolytic activity.
Fibroblast growth factor 21 (FGF21) is a key metabolic regulator that is induced by fasting and starvation, and its expression is thought to be regulated by the circadian clock in the liver. To evaluate the functional role of FGF21 in the circadian regulation of physiology and behavior, we examined the temporal expression profiles of Fgf21 and circadian clock genes in addition to behavioral activity rhythms under adlibitum feeding (ALF) and time-imposed restricted feeding (RF) in mice. Four hours of daily restricted feeding during the daytime induced over an 80-fold increase in feeding-dependent rhythmic Fgf21 mRNA expression in epididymal white adipose tissue (eWAT), although the expression levels were continuously increased 10-fold in the liver of wild-type (WT) mice. Refeeding subsequent to transient fasting revealed that refeeding but not fasting remarkably induces Fgf21 expression in eWAT, although fasting-induced hepatic Fgf21 expression is completely reversed by refeeding. The free-running period of locomotor activity rhythm under ALF and the food anticipatory activity (FAA) under RF remained intact in Fgf21 knockout (KO) mice, suggesting that FGF21 is dispensable for both the central clock in the suprachiasmatic nucleus (SCN) and the food-entrainable oscillator that governs the FAA. Temporal expression profiles of circadian genes such as mPer2 and BMAL1 were essentially identical in both tissues between WT and Fgf21 KO mice under RF. The physiological role of the refeeding-induced adipose Fgf21 expression remains to be elucidated.
Recent studies have demonstrated that metabolic changes in mammals induce feedback regulation of the circadian clock. The present study evaluates the effects of a low-carbohydrate high-protein diet (HPD) on circadian behavior and peripheral circadian clocks in mice. Circadian rhythms of locomotor activity and core body temperature remained normal in mice fed with the HPD diet (HPD mice), suggesting that it did not affect the central clock in the hypothalamus. Two weeks of HPD feeding induced mild hypoglycemia without affecting body weight, although these mice consumed more calories than mice fed with a normal diet (ND mice). Plasma insulin levels were increased during the inactive phase in HPD mice, but increased twice, beginning and end of the active phase, in ND mice. Expression levels of the key gluconeogenic regulatory genes PEPCK and G6Pase were significantly induced in the liver and kidneys of HPD mice. The HPD appeared to induce peroxisome proliferator-activated receptor α (PPARα) activation, since mRNA expression levels of PPARα and its typical target genes, such as PDK4 and Cyp4A10, were significantly increased in the liver and kidneys. Circadian mRNA expression of clock genes, such as BMAL1, Cry1, NPAS2, and Rev-erbα, but not Per2, was significantly phase-advanced, and mean expression levels of BMAL1 and Cry1 mRNAs were significantly elevated, in the liver and kidneys of HPD mice. These findings suggest that a HPD not only affects glucose homeostasis, but that it also advances the molecular circadian clock in peripheral tissues.
Mesial Temporal Lobe Epilepsy (mTLE) characterized by progressive development of complex partial seizures originating from the hippocampus is the most prevalent and refractory type of epilepsy. One of the remarkable features of mTLE is the rhythmic pattern of occurrence of spontaneous seizures, implying a dependence on the endogenous clock system for seizure threshold. Conversely, circadian rhythms are affected by epilepsy too. Comprehending how the circadian system and seizures interact with each other is essential for understanding the pathophysiology of epilepsy as well as for developing innovative therapies that are efficacious for better seizure control. In this review, we confer how the temporal dysregulation of the circadian clock in the hippocampus combined with multiple uncoupled oscillators could lead to periodic seizure occurrences and comorbidities. Unraveling these associations with additional research would help in developing chronotherapy for mTLE, based on the chronobiology of spontaneous seizures. Notably, differential dosing of antiepileptic drugs over the circadian period and/or strategies that resynchronize biological rhythms may substantially improve the management of seizures in mTLE patients.
The discrepancy about the role of estrogens in hepatic fibrogenesis and lack of studies addressed of ketogenic diet (KD) on hepatic stellate cells (HSC), prompted us to investigate the activity of HSC in control, KD- and tioacetamide (TAA)-administrated rats with different plasma concentration of estradiol (E2). HSC were isolated by the collagenase perfusion methods and separated by the Percoll gradient centrifugation. After the 4(th) and 8(th) day of incubation, lysates of HSC and the media were collected for further analysis. The HSC derived from KD-rats released remarkably more transforming growth factor (TGF)-β1 than cells obtained from animals fed with a standard diet. The ovarectomy of KD-rats markedly intensified the secretion of this fibrogenic cytokine on the 8(th) day of incubation (201.33±17.15 pg/ml). In HSC of rats exposed to E2, the TGF-β1 concentration did not exceed 157±34.39 pg/ml. In respect to the collagen type I, the HSC obtained from ovarectomised KD-rats released an augmented amount of this ECM protein after the 8(th) day of culture (1.83±0.14 U/ml). In the same time, higher quantities of ASMA appeared in the KD rats (1.41±0.3 pg/mg protein). Exposition of rats to E2 did not markedly decrease the amount of ASMA. In summary, KD was able to induce morphological and functional changes in HSC, especially derived from rats deprived of ovarian estrogens. However, the preservation of E2 in ovarectomised rats didn't substantially alter the activation of HSC.
The hematologic system performs a number of essential functions, including oxygen transport, the execution of the immune response against tumor cells and invading pathogens, and hemostasis (blood clotting). These roles are performed by erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets), respectively. Critically, circadian rhythms are evident in the function of all 3 cell types. In this review, we describe these oscillations, explore their mechanistic bases, and highlight their key implications. Since erythrocytes are anucleate, circadian rhythms in these cells testify to the existence of a nontranscriptional circadian clock. From a clinical perspective, leukocyte rhythms could underlie daily variation in the severity of allergic reactions, the symptoms of chronic inflammatory diseases, and the body's response to infection, while the rhythmic properties of thrombocytes may explain daily fluctuations in the incidence of heart attack and stroke. Consequently, the efficacy of treatments for these conditions is likely to depend on the timing of their administration. Last, we outline preliminary evidence that circadian disruption in the hematologic system could contribute to the deleterious effects of poor diet, shift work, and alcohol abuse on human health.
© 2015 The Author(s).
The circadian clock is one of the most conserved systems in mammals. It is an important regulator of many biological processes, such as the sleep-wake cycle, hormone secretion, and body temperature, which can influence both cellular and organ-level metabolic functioning. At the molecular level, the circadian system consists of autoregulatory feedback loop that dictates the timing of behavioral and physiological processes. This molecular clock is persistent in all of the central and peripheral tissues. Metabolism can also affect the circadian clock via feeding, or by metabolites which expression is controlled by food intake. Therefore, the current chapter emphasizes the cross-talk between the circadian system and metabolism at the molecular level, and its physiological outcome.
The expression rhythms of clock genes, such as Per1, Per2, Bmal1, and Rev-erb α, in mouse peripheral clocks, are entrained by a scheduled feeding paradigm. In terms of food composition, a carbohydrate-containing diet is reported to cause strong entrainment through insulin secretion. However, it is unknown whether human diets entrain peripheral circadian clocks. In this study, we used freeze-dried diets for type 2 diabetes (DB) and chronic kidney disease (CKD), as well as low-carbohydrate diets. After 24 h of fasting, PER2::LUC knock-in mice were given access to food for 2 days during inactive periods, and bioluminescence rhythm was then measured using an in vivo imaging system. AIN-93M, the control mouse diet with a protein:fat:carbohydrate (PFC) ratio of 14.7:9.5:75.8, caused a significant phase advance (7.3 h) in the liver clock compared with that in 24 h fasted mice, whereas human diets caused significant but smaller phase advances (4.7–6.2 h). Compared with healthy and high fat/sucrose-induced DB mice, adenine-induced CKD mice showed attenuation of a phase-advance with a normal diet. There were no significant differences in phase-advance values between human diets (normal, DB, and CKD). In addition, a normal-carbohydrate diet (PFC ratio of 20.3:23.3:56.4) and a low-carbohydrate diet (PFC ratio of 36.4:42.9:20.7) caused similar phase advances in peripheral clocks. The present results strongly suggest that scheduled feeding with human diets can cause phase advances in the peripheral clocks of not only healthy, but also DB and CKD mice. This discovery provides support to the food-induced entrainment of peripheral clocks in human clinical trials.
Objective: To clarify the relationship between a stress-related marker, plasminogen
activator inhibitor (PAI)-1, and a history of alcohol abuse in the childhood home.
Methods: We compared the serum levels of PAI-1 between individuals with a history of
alcohol abuse in the childhood home (N=53) and controls without such a history (N=96)
in a population-based sample of adults with a high level of mental symptoms.
Results: Subjects who experienced alcohol abuse in the childhood home had lower levels
of PAI-1 (p=0.011) and more often a diagnosis of major depressive disorder (MDD) (p <
0.001) when compared with the controls. In multivariate analyses, lowered levels of
PAI-1 were associated with an approximately doubled likelihood of belonging to the
group with alcohol abuse in the childhood home in three different models with
adjustments for age, gender, body mass index, MDD, coronary heart disease and
cholesterol medication (ORs 2.19-2.43; p ≤ 0.05 in all models).
Conclusion: A history of alcohol abuse in the childhood home was independently
associated with lowered levels of PAI-1, a substance with neuroprotective qualities.
Lowered PAI-1 in individuals who experience alcohol abuse in the childhood home may
increase their vulnerability to neuronal pathology closely related to psychiatric
symptoms.
Numerous long-term studies have investigated the circadian clock system in mammals, which organizes physiological functions, including metabolism, digestion, and absorption of food, and energy expenditure. Food or nutrition can be a synchronizer for the circadian clock systems, as potent as the external light-dark signal can be. Recent studies have investigated different kinds of food, frequency of consumption, and time of consumption for optimizing body clock and ensuring healthy habits. In this review, we discuss recent studies investigating chronobiology and nutrition, and then summarize available information as "Chrono-nutrition" for the development of a new standardized research strategy.
Glucose is molecule usually studied in relation to metabolism. Except for this traditional view, it is known that under certain conditions glucose can serve as a signal molecule for the circadian system. The circadian system is entrained by relevant synchronizing cues that can be tissue-dependent. Central oscillator is synchronized mainly by light-dark cycle, while peripheral oscillators can be entrained by food intake. Glucose transport in the organism is controlled by insulin dependent and independent mechanism. Therefore, we employed streptozotocin-induced diabetes to elucidate the influence of metabolic changes on glucose transporter (glut1, glut4) 24-h expression profile in peripheral oscillators in tissues, inside (frontal cortex, cerebellum) and outside (heart) the blood-brain barrier. Diabetes was induced by streptozotocin injection. Seventeen days later, sampling was performed during a 24-h cycle. Gene expression was measured using real-time PCR. We observed down-regulation of glut1 and glut4 expression in the heart of diabetic rats. The expression of glut1 and glut4 in brain areas was not down-regulated, however, we observed trend to phase advance in glut1 expression in the cerebellum. These results may indicate higher glucose levels in diabetic brain, which might influence regulation of clock gene expression in different manner in brain compared to periphery.
Locomotor activity is affected by a range of factors in addition to experimental treatment, including the breeding environment. Appropriate convalescence and acclimation are important for animal experiments, because environmental changes and physical burden can result from surgery, transportation, and cage exchange. However, the duration that locomotor activity is affected by these factors is currently unclear, because it has traditionally been difficult to measure locomotor activity in multiple group-housed animals in any location other than the analysis room. In the present study, we analyzed the locomotor activity of group-housed rats using a nano tag® after surgery, transportation, and cage exchange. The nano tag®, a new device for analyzing activity, can measure locomotor activity in laboratory animals with no limitation on the number of animals in same cage. Any type of cage can be used for analysis, at any time of day, and in any location. Nano tags® were subcutaneously implanted in male rats (F344/NSlc, 6 weeks of age) and locomotor activity was continuously measured after surgery, transportation, and cage exchange. Significant activity changes were observed in rats after transportation and cage exchange, 9 days and 3 h after the event, respectively. The results suggest that continuous measurement of locomotor activity with nano tags® can be used to monitor changes in activity induced by environmental changes, and will be helpful for designing animal experiments analyzing locomotor activity.
The circadian rhythm controls many physiological functions, such as feeding, motor activity, endocrine secretion and autonomic nerve. Regular feeding pattern can entrain the peripheral circadian clock, whereas peripheral clock systems can control the absorption distribution, metabolism and excretion of nutrients, suggesting mutual interactions between circadian clocks and nutrition/food. The interactions were so-called by "chrono-nutrition", and bigger meals for breakfast were good for entrainment of peripheral clock and protection of obesity. Similar to chrono-nutrition the timing of exercise ("chrono-exercise") is important for both entrainment signals and energy expenditure. Evening exercise and/or feeding then exercise was good timing exercise for protection of obesity. Taken all, it is suggested that timing of feeding and exercise is now one of key factors for metabolic syndrome.
Circadian rhythms are manifested as a series of autonomous and endogenous oscillators and are generated by the molecular circadian clock system in order to coordinate the internal time with the exogenous environmental changes in a 24 hour (h) daily cycle. In mammals, Suprachiasmatic nucleus (SCN) is regarded as the master clock, as it is entrained by the environmental cues and in turn synchronizes the peripheral clocks. Desynchronization between master clock and peripheral clocks give rise to many cellular, physiological and pathological alterations. In recent years, the focus is on establishing dietary regimes as therapeutic interventions. Ketogenic diet (KD) is one such dietary regimen characterized by relatively higher fat and protein proportions in diet than the carbohydrates, which recapitulates certain metabolic aspects of fatty acid metabolism and production of ketone bodies (KBs). KD which is comprised of saturated triglycerides polyunsaturated fatty acids (PUFAs) appears to be beneficial in improving age associated perturbations. This chapter focuses on the therapeutic effects of KD on healthy aging as well as unravelling the connection between KD and circadian rhythm, hence further establishing rationale for the KD regime as a therapeutic intervention.
We evaluated associations between obesity induced by a high-fat diet (HFD) and the environmental light-dark (LD) cycle that entrains the master circadian clock located in the suprachiasmatic nucleus of mammals. Mice were fed normal diet or HFD for 6 weeks in individual cages with running wheels under a normal 12 h light-12 h dark cycle (LD 12 : 12) or an ultradian 3 h light-3 h dark cycle (LD 3 : 3) that might perturb the central clock. Circadian behavioral rhythms in mice fed both diets were disrupted by light-induced direct suppression of the behavior (masking effect) under LD 3 : 3. The ultradian LD cycle reduced the total daily activity of wheel running and enhanced body weight gain in the mice fed the HFD. Secondary effects such as obesity are probably not associated with inactivity induced under these circumstances because wheel-running activity decreased markedly within a few days of transfer from LD 12 : 12 to LD 3 : 3. Food consumption was significantly suppressed under LD 3 : 3 in mice fed the HFD. These findings suggest that the aberrant LD cycle induced physical inactivity and enhanced weight gain depending on dietary fat consumption. This might help to explain the higher incidence of obesity among shift workers.
The circadian system allows organisms to remain synchronized with rhythmic environmental changes with a 24-h period. The molecular mechanism of circadian oscillations is based on the rhythmic expression of clock genes organized in feedback loops. Alterations in the circadian system contribute to the development of several pathological conditions including diabetes, but the exact mechanisms responsible for such alterations are not known. Therefore, we employed streptozotocin-induced diabetes to elucidate the influence of metabolic changes on clock gene (clock, npas2, per2) expression in peripheral oscillators in tissues inside (frontal cortex, cerebellum) and outside (heart, kidney) the blood-brain barrier. Diabetes was induced by streptozotocin injection. Seventeen days later, sampling was performed during a 24-h cycle. Gene expression was measured using real-time PCR. We observed a phase advance in rhythmic clock gene expression in the heart and kidney of diabetic rats. The study also focused on the possible role of npas2 in locomotor activity regulation in diabetic animals. The most pronounced changes were observed in the frontal cortex, which displayed up-regulation of npas2 expression. A change in locomotor activity was observed in diabetic rats during the dark phase of the 24-h cycle. We suggest that the altered function of the frontal cortex induced by diabetes might contribute to the modified behavior of diabetic rats.
https://www.thieme-connect.com/DOI/DOI?10.1055/s-0033-1349123
An essential component of energy homeostasis lies in an organism's ability to coordinate daily patterns in activity, feeding, energy utilization and energy storage across the daily 24-h cycle. Most tissues of the body contain the molecular clock machinery required for circadian oscillation and rhythmic gene expression. Under normal circumstances, behavioural and physiological rhythms are orchestrated and synchronized by the suprachiasmatic nucleus (SCN) of the hypothalamus, considered to be the master circadian clock. However, metabolic processes are easily decoupled from the primarily light-driven SCN when food intake is desynchronized from normal diurnal patterns of activity. This dissociation from SCN based timing demonstrates that the circadian system is responsive to changes in energy supply and metabolic status. There has long been evidence for the existence of an anatomically distinct and autonomous food-entrainable oscillator (FEO) that can govern behavioural rhythms, when feeding becomes the dominant entraining stimulus. But now rapidly growing evidence suggests that core circadian clock genes are involved in reciprocal transcriptional feedback with genetic regulators of metabolism, and are directly responsive to cellular energy supply. This close interaction is likely to be critical for normal circadian regulation of metabolism, and may also underlie the disruption of proper metabolic rhythms observed in metabolic disorders, such as obesity and type-II diabetes.
Plasminogen activator inhibitor-1 (PAI-1) controls the regulation of the fibrinolytic system in blood by inhibiting both urokinase-type and tissue-type plasminogen activators. Enhanced levels of PAI-1 are found in patients with type 2 diabetes mellitus which is associated with a dysbalance in glucose and lipid homeostasis. Especially a defective insulin response in the liver contributes to the development of hyperglycemia, dyslipidemia and peripheral insulin resistance and may contribute to hepatic over-expression of PAI-1 in diabetes type 2. Furthermore, a substantial upregulation of PAI-1 expression has also been shown in a variety of liver injury models. Thus, the liver appears to be not only a major site of PAI-1 synthesis in response to hormonal changes, but also in response to a variety of other pathological events. PAI-1 expression in liver largely depends on activation of signalling pathways and transcriptional regulators which may be the basis for a new level of cross-talk between different signalling pathways and thus may represent attractive therapeutic candidates. This article will primarily focus on the regulation of PAI-1 expression in liver cells and discuss potential cross-talks between metabolic, hormonal and environmental signals.
The onset of myocardial infarction occurs frequently in the early morning, and it may partly result from circadian variation
of fibrinolytic activity. Plasminogen activator inhibitor-1 activity shows a circadian oscillation and may account for the
morning onset of myocardial infarction. However, the molecular mechanisms regulating this circadian oscillation remain unknown.
Recent evidence indicates that basic helix-loop-helix (bHLH)/PAS domain transcription factors play a crucial role in controlling
the biological clock that controls circadian rhythm. We isolated a novel bHLH/PAS protein, cycle-like factor (CLIF) from human
umbilical vein endothelial cells. CLIF shares high homology with Drosophila CYCLE, one of the essential transcriptional regulators of circadian rhythm. CLIF is expressed in endothelial cells and neurons
in the brain, including the suprachiasmatic nucleus, the center of the circadian clock. In endothelial cells, CLIF forms a
heterodimer with CLOCK and up-regulates the PAI-1 gene through E-box sites. Furthermore, Period2 and Cryptochrome1, whose
expression show a circadian oscillation in peripheral tissues, inhibit the PAI-1 promoter activation by the CLOCK:CLIF heterodimer.
These results suggest that CLIF regulates the circadian oscillation of PAI-1 gene expression in endothelial cells. In addition,
the results potentially provide a molecular basis for the morning onset of myocardial infarction.
Ketogenic diets have been used to treat seizure disorders of children and recently it was shown to increase the drug-induced seizure threshold in rats. Protein phosphorylation is a major regulatory mechanism of signal transduction that has been implicated in modulating neuronal excitability. We investigated the basal protein phosphorylation in microslices from different brain regions (hippocampus, cerebral cortex and cerebellum) of young rats fed a ketogenic diet, and we evaluated the effect of this diet on weight development and health of these rats based on serum biochemistry. Thirty-day-old rats consumed ad libitum ketogenic (high fat) or control diets for 8 wk. Rats consuming the high fat diet had ketonemia without signs of undernutrition or illness. Microslices were incubated in media containing (32)P-phosphate, and (32)P-phosphoprotein content was analyzed by one- or two-dimensional electrophoresis followed by autoradiography. Basal protein phosphorylation was greater in brain slices from ketogenic rats. Different increments of synapsin I, GAP-43 and GFAP phosphorylation were observed in two-dimensional autoradiography. A ketogenic diet induced metabolic changes affecting the basal status of protein phosphorylation. This change could affect the mechanisms of signal transduction in neural cells involved in the increase in the seizure threshold.
We reviewed recent progress in the study of the chronobiological aspects of the cardiovascular system.
Medline was used as the main search tool, and the full texts of selected papers were obtained.
More than 300 references were found, and 52 of them, representing the major findings in this field, were included in the reference list. Results of these studies confirm that most cardiovascular physiological parameters (such as heart rate, blood pressure, electrocardiogram indices) and pathophysiological events (myocardial ischemia/infarction, sudden cardiac death) show circadian rhythms. Results also suggest that consideration of these rhythms is important for the diagnosis and treatment of cardiovascular disorders and that restoration of normal circadian rhythms may be associated with clinical improvement.
The study of circadian rhythms in the cardiovascular system is emerging as an important area of investigation because of its potential implications for patient management.
In recent years, restriction of carbohydrate intake for weight loss has become widespread. Our research group began studying physiological responses to very-low-carbohydrate ketogenic diets (VLCKDs) in the late 1990s because we felt there was a significant void in the literature and limited understanding of metabolic responses to VLCKDs. This launched us into a line of research examining the physiological effects of VLCKDs. In this paper, we briefly overview nine studies we have published on isoenergetic and hypoenergetic VLCKDs in men and women. These studies have focused on blood lipid responses to VLCKDs, but we have also addressed changes in body weight, body composition, and hormones. Compared with low-fat diets, short-term VLCKDs consistently result in improvements in fat loss, fasting and postprandial triacylglycerols, high-density lipoprotein-cholesterol, the distribution of low-density lipoprotein-cholesterol subclasses, and insulin resistance. These are the key metabolic abnormalities of metabolic syndrome, a problem of epidemic proportions in the United States. There is substantial variability in total cholesterol and low-density lipoprotein-cholesterol responses to VLCKD. The factors responsible for this variability are not known, and studies designed to identify methods to predict blood lipid responses to VLCKD and other dietary approaches represent critical areas for nutrition researchers. Further research is warranted to validate the physiological effects of VLCKD over longer periods of time, including studies that modify the quality of macronutrients (i.e., the type of fat and protein) and the interaction with other interventions (e.g., exercise, dietary supplements, drugs).
Low-carbohydrate diets have become increasingly popular for weight loss. However, evidence from individual trials about benefits and risks of these diets to achieve weight loss and modify cardiovascular risk factors is preliminary.
We used the Cochrane Collaboration search strategy to identify trials comparing the effects of low-carbohydrate diets without restriction of energy intake vs low-fat diets in individuals with a body mass index (calculated as weight in kilograms divided by the square of height in meters) of at least 25. Included trials had to report changes in body weight in intention-to-treat analysis and to have a follow-up of at least 6 months. Two reviewers independently assessed trial eligibility and quality of randomized controlled trials.
Five trials including a total of 447 individuals fulfilled our inclusion criteria. After 6 months, individuals assigned to low-carbohydrate diets had lost more weight than individuals randomized to low-fat diets (weighted mean difference, -3.3 kg; 95% confidence interval [CI], -5.3 to -1.4 kg). This difference was no longer obvious after 12 months (weighted mean difference, -1.0 kg; 95% CI, -3.5 to 1.5 kg). There were no differences in blood pressure. Triglyceride and high-density lipoprotein cholesterol values changed more favorably in individuals assigned to low-carbohydrate diets (after 6 months, for triglycerides, weighted mean difference, -22.1 mg/dL [-0.25 mmol/L]; 95% CI, -38.1 to -5.3 mg/dL [-0.43 to -0.06 mmol/L]; and for high-density lipoprotein cholesterol, weighted mean difference, 4.6 mg/dL [0.12 mmol/L]; 95% CI, 1.5-8.1 mg/dL [0.04-0.21 mmol/L]), but total cholesterol and low-density lipoprotein cholesterol values changed more favorably in individuals assigned to low-fat diets (weighted mean difference in low-density lipoprotein cholesterol after 6 months, 5.4 mg/dL [0.14 mmol/L]; 95% CI, 1.2-10.1 mg/dL [0.03-0.26 mmol/L]).
Low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered.
Ketogenic diets have been used as an approach to weight loss on the basis of the theoretical advantage of a low-carbohydrate, high-fat diet. To evaluate the physiological and metabolic effects of such diets on weight we studied mice consuming a very-low-carbohydrate, ketogenic diet (KD). This diet had profound effects on energy balance and gene expression. C57BL/6 mice animals were fed one of four diets: KD; a commonly used obesogenic high-fat, high-sucrose diet (HF); 66% caloric restriction (CR); and control chow (C). Mice on KD ate the same calories as mice on C and HF, but weight dropped and stabilized at 85% initial weight, similar to CR. This was consistent with increased energy expenditure seen in animals fed KD vs. those on C and CR. Microarray analysis of liver showed a unique pattern of gene expression in KD, with increased expression of genes in fatty acid oxidation pathways and reduction in lipid synthesis pathways. Animals made obese on HF and transitioned to KD lost all excess body weight, improved glucose tolerance, and increased energy expenditure. Analysis of key genes showed similar changes as those seen in lean animals placed directly on KD. Additionally, AMP kinase activity was increased, with a corresponding decrease in ACC activity. These data indicate that KD induces a unique metabolic state congruous with weight loss.
The persistence of an epidemic of obesity and type 2 diabetes suggests that new nutritional strategies are needed if the epidemic is to be overcome. A promising nutritional approach suggested by this thematic review is carbohydrate restriction. Recent studies show that, under conditions of carbohydrate restriction, fuel sources shift from glucose and fatty acids to fatty acids and ketones, and that ad libitum-fed carbohydrate-restricted diets lead to appetite reduction, weight loss, and improvement in surrogate markers of cardiovascular disease.
Background We reviewed recent progress in the study of the chronobiological aspects of the cardiovascular system. Methods Medline was used as the main search tool, and the full texts of selected papers were obtained. Results More than 300 references were found, and 52 of them, representing the major findings in this field, were included in the reference list. Results of these studies confirm that most cardiovascular physiological parameters (such as heart rate, blood pressure, electrocardiogram indices) and pathophysiological events (myocardial ischemia/infarction, sudden cardiac death) show circadian rhythms. Results also suggest that consideration of these rhythms is important for the diagnosis and treatment of cardiovascular disorders and that restoration of normal circadian rhythms may be associated with clinical improvement. Conclusion The study of circadian rhythms in the cardiovascular system is emerging as an important area of investigation because of its potential implications for patient management.
Context: The scarcity of data addressing the health effects of popular diets is an important public health concern, especially since patients and physicians are interested in using popular diets as individualized eating strategies for disease prevention. Objective: To assess adherence rates and the effectiveness of 4 popular diets (Atkins, Zone, Weight Watchers, and Ornish) for weight loss and cardiac risk factor reduction. Design, Setting, and Participants: A single-center randomized trial at an academic medical center in Boston, Mass, of overweight or obese (body mass index: mean, 35; range, 27-42) adults aged 22 to 72 years with known hypertension, dyslipidemia, or fasting hyperglycemia. Participants were enrolled starting July 18, 2000, and randomized to 4 popular diet groups until January 24, 2002. Intervention: A total of 160 participants were randomly assigned to either Atkins (carbohydrate restriction, n=40). Zone (macronutrient balance, n=40), Weight Watchers (calorie restriction, n=40), or Ornish (fat restriction, n=40) diet groups. After 2 months of maximum effort, participants selected their own levels of dietary adherence. Main Outcome Measures: One-year changes in baseline weight and cardiac risk factors, and self-selected dietary adherence rates per self-report. Results: Assuming no change from baseline for participants who discontinued the study, mean (SD) weight loss at 1 year was 2.1 (4.8) kg for Atkins (21 [53 %] of 40 participants completed, P=.009), 3.2 (6.0) kg for Zone (26 [65%] of 40 completed, P=.002), 3.0 (4.9) kg for Weight Watchers (26 [65%] of 40 completed, P<.001), and 3.3 (7.3) kg for Ornish (20 [50%] of 40 completed, P=.007). Greater effects were observed in study completers. Each diet significantly reduced the low-density lipoprotein/high-density lipoprotein (HDL) cholesterol ratio by approximately 10% (all P<.05), with no significant effects on blood pressure or glucose at 1 year. Amount of weight loss was associated with self-reported dietary adherence level (r=0.60; P<.001) but not with diet type (r=0.07; P= .40). For each diet, decreasing levels of total/HDL cholesterol, C-reactive protein, and insulin were significantly associated with weight loss (mean r=0.36, 0.37, and 0.39, respectively) with no significant difference between diets (P= .48, P= .57, P= .31, respectively). Conclusions: Each popular diet modestly reduced body weight and several cardiac risk factors at 1 year. Overall dietary adherence rates were low, although increased adherence was associated with greater weight loss and cardiac risk factor reductions for each diet group.
Relationships between energy intake and fibrinolytic functions have been documented in detail. We evaluated food deprivation (FD) as a means of modulating fibrinolytic activity in genetically obese and diabetic db/db mice and in their lean counterparts. Twelve hours of FD induced considerable gene expression of plasminogen activator inhibitor-I (PAW) in both epididymal (3.8-fold, p<0.05) and intestinal (2.4-fold, p<0.05) adipose tissues without affecting plasma PAI-1 levels in db/db mice, whereas the FD did not affect these parameters in wild-type mice. Importantly, 24 hours of FD increased the plasma PAI-1 content in wild-type (1.9-fold, p<0.01) but not in db/db mice, although adipose PAW mRNA levels were significantly increased in db/db mice. The plasma PAI-1 content significantly correlated with hepatic PAI-1 mRNA levels in wild-type (r=0.84, p<0.01) and in db/db (r=0.63, p<0.0 1) mice. However, plasma PAI-1 did not correlate with adipose PAI-1 expression in db/db mice, although adipose tissue in general is thought to be the principal site of PAI-1 production in obesity. Hepatic PAI-1 expression was closely correlated with serum levels of free fatty acids in wild-type (r=0.72, p<0.0 1), but not in db/db mice.Adipose PAI- 1 expression significantly correlated with serum corticosterone levels in both genotypes (wild-type, r=0.52,P<0.05; db/db, r=0.5 1, p<0.0 1), suggesting that adipose PAI-1 expression is up-regulated by fastingi-nduced glucocorticoids. The present findings suggested that fasting differentially affects fibrinolytic activity in obese and lean subjects and that PAW expression in the liver as well as in adipose tissues comprises an important determinant of increased risk for cardiovascular disease in obesity.
We studied the effect of thiazolidinediones (TZDs) on the regulation of plasminogen activator inhibitor 1 (PAI-1) gene expression during 3T3-L1 adipocyte differentiation. Treatment of the cells with pioglitazone and insulin shortened the time for differentiation from 9 d to 3 d, which resulted in a dramatic increase in PAI-1 mRNA as well as PAI-1 antigen secreted into the culture medium. Insulin or pioglitazone alone had relatively little effect on the rate of cell differentiation and did not alter PAI-1 mRNA levels. A number of other TZDs (e.g., troglitazone, ciglitazone) also induced PAI-1 gene expression in the presence of insulin, and the magnitude of induction was approximately proportional to the ability of these molecules to activate the nuclear receptor, peroxisome proliferator-activated receptor- γ. We also studied the mechanism of induction of PAI-1 mRNA by pioglitazone/insulin. Although the half-life of adipocyte PAI-1 mRNA was not changed upon treatment with pioglitazone/insulin, this treatment induced PAI-1 promoter activity 10-fold. These results indicate that PAI-1 mRNA and protein are up-regulated by TZDs in an insulin-dependent manner and that these effects result from an increase in the rate of transcription of the PAI-1 gene. The increase in PAI-1 occurs in parallel with the induction of adipogenesis, which suggests that the two processes are related.
Ketogenic diets (KDs) are effective treatments for epilepsy. The mechanisms of action are poorly understood. In some experimental seizure models, calorie restriction and hypoglycemia may augment the antiseizure effects of KDs. In addition, inhibiting glycolysis or diverting glucose from the glycolytic pathway inhibits seizures and possibly epileptogenesis, suggesting an interaction between energy regulation and the anticonvulsant actions of these interventions. Children on KDs frequently exhibit poor weight gain and have lower blood glucose levels compared to children on standard, balanced diets. Young rodents on a KD also exhibit slow weight gain, lower blood glucose and insulin levels, and elevated leptin levels. This review considers the possibility that calorie restriction, low serum glucose, and KDs share common cell signaling pathways to alter brain excitability. AMP-activated protein kinase (AMPK) is an attractive candidate signaling protein that could link energy balance to gene expression in such a way so as to reduce brain excitability.
Peroxisome proliferator-activated receptor alpha (PPARalpha) is a drug/fatty acid-activated trans cription factor involved in the starvation response, and is thus relevant to the ketogenic diet (KD). This article summarizes research indicating the role of PPARalpha in central and peripheral nervous system function with particular reference to downstream targets relevant to anticonvulsant action.
Fasting and other dietary regimens have been used to treat epilepsy since at least 500 BC. To mimic the metabolism of fasting, the ketogenic diet (KD) was introduced by modern physicians as a treatment for epilepsy in the 1920s. For two decades this therapy was widely used, but with the modern era of antiepileptic drug treatment its use declined dramatically. By the end of the twentieth century this therapy was available in only a small number of children's hospitals. Over the past 15 years, there has been an explosion in the use, and scientific interest in the KD. This review traces the history of one of the most effective treatments for childhood epilepsy.
An increased level of obesity-induced plasma plasminogen activator inhibitor-1 (PAI-1) is considered a risk factor for cardiovascular disease. To determine whether the circadian clock component PERIOD2 (PER2) is involved in the regulation of PAI-1 gene expression, we performed transient transfection assays in vitro, and generated transgenic (Tg) mice overexpressing PER2. We then compared PAI-1 expression in Tg and wild-type (WT) mice with or without obesity induced by a high-fat/high-sucrose diet. PER2 suppressed CLOCK:BMAL1- and CLOCK:BMAL2-dependent transactivation of the PAI-1 promoter in vitro. Furthermore, nuclear translocation is dispensable for PER2 to suppress CLOCK:BMAL1-dependent transactivation of the PAI-1 promoter, because functional loss of the nuclear localization domain did not affect either the interaction with BMAL1 or the suppressive role of PER2. The diurnal expression of clock and clock-controlled genes was disrupted in a gene-specific manner, whereas that of PAI-1 mRNA was significantly damped in the hearts of PER2 Tg mice fed with a normal diet. Obesity-induced plasma PAI-1 increase was significantly suppressed in Tg mice in accordance with cardiac PAI-1 mRNA levels, whereas body weight gain and changes in metabolic parameters were identical between WT and Tg mice. Endogenous PAI-1 gene expression induced by transforming growth factor-beta1 was significantly attenuated in embryonic fibroblasts derived from Tg mice compared with those from WT mice. Our results demonstrated that PER2 represses PAI-1 gene transcription in a BMAL1/2-dependent manner. The present findings also suggest that PER2 attenuates obesity-induced hypofibrinolysis by downregulating PAI-1 expression independently of metabolic disorders.
The mammalian timing system is composed of a bodywide web of cell-autonomous and self-sustained oscillators. A master clock in the SCN synchronizes peripheral clocks through yet poorly understood molecular signaling pathways. In this lecture I shall present some of the experimental approaches we are employing to elucidate signaling routes through which the SCN may phase entrain peripheral clocks. These attempts unveiled several candidate pathways worth pursuing in future studies, including signaling through nuclear receptors, cytoskeleton components, Ca(2+), fibroblast growth factors, ubiquitin ligases, Sirtuin 1 (a redox-sensing histone deacetylase), RNA binding proteins, and body temperature.
By inhibiting plasminogen activators uPA and tPA, inducing uPA-uPAR internalization and interfering with the interaction between extracellular matrix protein vitronectin and alphavbeta3 integrin, plasminogen activator inhibitor type 1 (PAI-1) is active in the regulation of various biological processes involving extracellular proteolysis and tissue remodeling. PAI-1 is expressed in many cell types under the control of a variety of signals, depending on cell type. The most prominent and important of these signals are TGFbeta, hypoxia and insulin. Although the signaling pathways were largely elucidated, recent investigations have revealed more complicated aspects. The pathways interact at the level of both transcription factors and regulatory elements on the promoter. Furthermore, the engagement of negative factors in these pathways has been shown to be important, adding complexity and versatility to PAI-1 gene regulation.
Peroxisome proliferator-activated receptor alpha (PPARalpha) is a nuclear receptor that regulates the expression of genes associated with lipid metabolism. Recent studies have suggested that the expression of PPARalpha-dependent fibroblast growth factor 21 (FGF21) plays important roles in adaptation to fasting, such as lipolysis and ketogenesis. We found that a nighttime injection of bezafibrate, a ligand of PPARalpha, effectively induced FGF21 expression, whereas a daytime injection did not affect it. Furthermore, bezafibrate-induced circadian FGF21 expression was abolished in PPARalpha-deficient mice. These observations suggest that bezafibrate-induced circadian FGF21 expression is due to circadian variations in the responsiveness of the PPARalpha system in the liver.
Recent evidence from randomized controlled trials of hypocaloric low carbohydrate diets in people without diabetes has shown that they promote significant weight loss over the short term. There is very little evidence for any effects of reduced carbohydrate intakes on body weight, glycaemia and cardiovascular risk in people with type 2 diabetes.
An electronic search was performed using MEDLINE (1966 to March 2007), EMBASE (1988 to March 2007) and Cochrane Central Register of Controlled Trials (1991 to March 2007) using the keywords low carbohydrate, type 2 diabetes and weight loss. Studies including subjects with type 2 diabetes who adopted a reduced carbohydrate weight loss diet were identified. Data were extracted on study design, weight loss, effects on glycaemia and cardiovascular risk and potential adverse effects.
Six studies investigating the effects of hypocaloric reduced carbohydrate diets in people with type 2 diabetes were identified. The studies were heterogenous and most included small numbers, were short-term and provided varying amounts of carbohydrate. No studies were identified that were both low carbohydrate (<50 g day(-1)) and also designed as randomized controlled trials. All studies reported reductions in both body weight and glycated haemoglobin, with no deleterious effects on cardiovascular risk, renal function or nutritional intake.
Conclusions are limited by study design and small numbers, but it appears that reduced carbohydrate diets are safe and effective over the short term for people with type 2 diabetes.
The pharmacokinetics of human recombinant plasminogen activator inhibitor-1 (rPAI-1) was studied in rabbits. Latent rPAI-1 (0-2 units of tissue-type plasminogen activator neutralizing activity per microgram protein); reactivated rPAI-1 (approximately 150 units/micrograms); and chloramine T-oxidized, nonreactivatable rPAI-1 (approximately 0.7 units/microgram) were studied. The pharmacokinetic parameters for the disposition of rPAI-1 antigen after an intravenous bolus injection of 1.0 or 2.5 mg/kg rPAI-1 were very similar for all three forms: the initial volume of distribution was approximately 60 ml/kg, the initial half-life in plasma was 6 minutes, and the plasma clearance was approximately 4 ml/kg/min. The disposition of PAI activity after injection of reactivated rPAI-1 was similar to that of rPAI-1 antigen. Injection of latent rPAI-1 was associated with a nearly threefold increase in the specific activity of circulating PAI-1 from 2 units/micrograms to 5.0 +/- 1.1 units/micrograms (p less than 0.01) within 1 minute, followed by a cumulative 25-fold increase in specific activity over 1 hour (p = 0.01). In contrast, the specific activity of oxidized or reactivated preparations of rPAI-1 did not increase in the first several minutes after injection. These findings support the existence of a fast-acting but low-capacity mechanism for the reactivation of rPAI-1 in vivo.
This study investigated the possible effect(s) of prolonged fasting and subsequent ad lib refeeding on the circadian organization of rats kept in constant darkness. Free-running rhythms of wheel-running activity and body temperature were studied in rats fasted during a 7-day interval followed with ad lib refeeding started either at subjective midday, i.e., CT6 (circadian time 6) or subjective midnight, i.e., CT18. Phase-shifts of temperature acrophases were similar to those of activity acrophases. During fasting, phase-shifts were phase-advanced (1 circadian h on the average) in most cases. During refeeding, they were mostly phase-delays (2 circadian h on the average) independently of the circadian time of refeeding, i.e., ad lib refeeding did not act as a Zeitgeber. In conclusion, prolonged fasting and subsequent refeeding induce opposite effects on the circadian organization.
To test whether circadian responses to light are modulated by decreased glucose availability, we analyzed photic phase resetting of the circadian rhythm of locomotor activity in mice exposed to four metabolic challenges: 1) blockade of glucose utilization induced by 2-deoxy-D-glucose (2-DG), 2) fasting (food was removed for 30 h), 3) insulin administration, and 4) insulin treatment after fasting. In mice housed in constant darkness, light pulses applied during early subjective night induced phase delays of the rhythm of locomotor activity, whereas light pulses applied during late subjective night caused phase advances. There was an overall reduction of light-induced phase shifts, with a more pronounced effect for delays, in mice pretreated with 500 mg/kg ip 2-DG compared with mice injected with saline. Administration of glucose with 2-DG prevented the reduction of light-induced phase delays. Furthermore, phase delays were reduced in fed mice pretreated with 5 IU/kg sc insulin and in fasted mice injected with saline or insulin compared with control fed mice. These results show that circadian responses to light are reduced when brain glucose availability is decreased, suggesting a metabolic modulation of light-induced phase shifts.
The increased expression of plasminogen activator inhibitor type-1 (PAI-1) is associated with increased concentrations of fatty acids in blood and may accelerate atherogenesis in diabetes. The present study was designed to define mechanisms by which nonesterified (free) fatty acids (FFAs) augment the expression of PAI-1. FFAs increased PAI-1 protein and mRNA expression by HepG2 cells. To identify potential regulatory elements, we constructed chimeric genes by fusing 1313, 853, 610, or 328 bp of human PAI-1 5'-flanking DNA to a luciferase reporter (PAI-LUC). A 2-fold increase in luciferase activity was seen when cells were transfected with PAI-LUC 1313, 863, or 610 and exposed to FFAs. No response to FFAs was seen with PAI-LUC 328 and after deletion of a 72-bp (-599 to -528) fragment from PAI-LUC 1313. This 72-bp fragment conferred FFA responsiveness to a different (simian virus 40) promoter. Two footprinted regions were demonstrated by DNase I analysis. Gel mobility shift assays indicated specific binding of extracted proteins to an FFA response element: 5'-TG(G/C)(1-2)CTG-3'. This sequence is repeated 4 times and is similar to an Sp1-binding site. Sp1 consensus oligonucleotides inhibited binding of extracted proteins to the regulatory elements. Accordingly, FFA-induced increased expression of PAI-1 in HepG2 cells is mediated by the binding of a transcription factor or factors to the repeated fatty acid response element, 5'-TG(G/C)(1-2)CTG-3', that is highly homologous to an Sp1-binding site.
In mammals, a master circadian "clock" resides in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. The SCN clock is composed of multiple, single-cell circadian oscillators, which, when synchronized, generate coordinated circadian outputs that regulate overt rhythms. Eight clock genes have been cloned that are involved in interacting transcriptional-/translational-feedback loops that compose the molecular clockwork. The daily light-dark cycle ultimately impinges on the control of two clock genes that reset the core clock mechanism in the SCN. Clock-controlled genes are also generated by the central clock mechanism, but their protein products transduce downstream effects. Peripheral oscillators are controlled by the SCN and provide local control of overt rhythm expression. Greater understanding of the cellular and molecular mechanisms of the SCN clockwork provides opportunities for pharmacological manipulation of circadian timing.
High-fat ketogenic diets are used to treat intractable seizures in children, but little is known of the mechanism by which these diets work or whether fats rich in n-3 polyunsaturates might be beneficial. Tissue lipid and fatty acid profiles were determined in rats consuming very high fat (80 weight%), low-carbohydrate ketogenic diets containing either medium-chain triglyceride, flaxseed oil, butter, or an equal combination of these three fat sources. Ketogenic diets containing butter markedly raised liver triglyceride but had no effect on plasma cholesterol. Unlike the other fats, flaxseed oil in the ketogenic diet did not raise brain cholesterol. Brain total and free fatty acid profiles remained similar in all groups, but there was an increase in the proportion of arachidonate in brain total lipids in the medium-chain triglyceride group, while the two groups consuming flaxseed oil had significantly lower arachidonate in brain, liver, and plasma. The very high dietary intake of alpha-linolenate in the flaxseed group did not change docosahexaenoate levels in the brain. Our previous report based on these diets showed that although ketosis is higher in rats consuming a ketogenic diet based on medium-chain triglyceride oil, seizure resistance in the pentylenetetrazol model is not clearly related to the degree of ketosis achieved. In combination with our present data from the same seizure study, it appears that ketogenic diets with widely differing effects on tissue lipids and fatty acid profiles can confer a similar amount of seizure protection.
Time in the biological sense is measured by cycles that range from
milliseconds to years. Circadian rhythms, which measure time on a scale of
24 h, are generated by one of the most ubiquitous and well-studied
timing systems. At the core of this timing mechanism is an intricate molecular
mechanism that ticks away in many different tissues throughout the body.
However, these independent rhythms are tamed by a master clock in the brain,
which coordinates tissue-specific rhythms according to light input it receives
from the outside world.
Circadian variation in plasminogen activator inhibitor-1 (PAI-1) production likely contributes to increased risk of myocardial infarction and decreased efficacy of thrombolytic therapy during the morning. In this study, we characterize the abilities of fundamental molecular components of intrinsic circadian clocks to regulate the human PAI-1 promoter in transfected endothelial cells. Both CLOCK:BMAL1 and CLOCK:BMAL2 heterodimers activate the PAI-1 promoter through requisite proximal (-565 to -560 bp) and distal (-680 to -675 bp) E-box enhancers. Although the distal E-box overlaps the 4G/5G polymorphism of the PAI-1 promoter, allelic variation at this site does not influence CLOCK:BMAL1-and CLOCK:BMAL2-mediated transactivation. Together, CLOCK:BMAL1 and CLOCK:BMAL2 make additive contributions to PAI-1 gene transcription. While the abilities of these heterodimers to activate gene expression differ by twofold, the susceptibilities of these circadian activators to inhibition by period and cryptochrome proteins are equivalent and redox independent. Given that BMAL1 and BMAL2 differ in their spatiotemporal distributions, such distinctions may allow intrinsic circadian clocks to modulate the amplitudes of their oscillators, while maintaining circadian periodicity. In this way, fundamental circadian clock components may drive circadian variation in PAI-1, which in turn influences the pathogenesis, timing, and treatment of acute atherothrombotic events.
Because obesity and insulin resistance (IR) are strongly associated with liver steatosis (LS), we investigated the relation between the degree of LS and plasminogen activator inhibitor-1 (PAI-1) in ob/ob mice, in C57/BL6 mice with alcoholic LS, and in severely obese humans.
In both mouse models, plasma PAI-1 levels were associated with PAI-1 expression in the liver and with the degree of LS. Liver PAI-1 antigen was associated with the tumor necrosis factor receptor-II (TNFRII) antigen, whereas association with TNF antigen content was found in ob/ob mice only. No significant correlation between plasma PAI-1 and PAI-1 expression in adipose tissue of ob/ob mice was observed. Furthermore, the relation between plasma PAI-1 levels and body weight was positive in ob/ob mice but negative in C57/BL6 mice (both P<0.001). In humans, PAI-1 levels were correlated with the degree of LS, and 26% of plasma PAI-1 activity was independently explained by LS and serum insulin levels.
Plasma PAI-1 levels are more closely related to fat accumulation and PAI-1 expression in the liver than in adipose tissue. In steatotic liver, PAI-1 antigen content is associated with those of TNF and TNFRII. Therefore, we suggest that TNF pathway dysregulation in LS could be involved in increased plasma PAI-1 in obesity with IR.
This review outlines the molecular sensors that reprogram cellular metabolism in response to the ketogenic diet (KD). Special emphasis is placed on the fasting-, fatty acid- and drug-activated transcription factor, peroxisome proliferator-activated receptor alpha (PPARalpha). The KD causes a switch to ketogenesis that is coordinated with an array of changes in cellular lipid, amino acid, carbohydrate and inflammatory pathways. The role of both liver and brain PPARalpha in mediating such changes will be examined, with special reference to the anti-epileptic effects not only of the KD but a range of synthetic anti-epileptic drugs such as valproate. Finally, the implications of the KD and activated brain PPARalpha will be discussed in the context of their potential involvement in a range of disorders of neuro-degeneration and neuro-inflammation.
Context:
The Atkins diet books have sold more than 45 million copies over 40 years, and in the obesity epidemic this diet and accompanying Atkins food products are popular. The diet claims to be effective at producing weight loss despite ad-libitum consumption of fatty meat, butter, and other high-fat dairy products, restricting only the intake of carbohydrates to under 30 g a day. Low-carbohydrate diets have been regarded as fad diets, but recent research questions this view.
Starting point:
A systematic review of low-carbohydrate diets found that the weight loss achieved is associated with the duration of the diet and restriction of energy intake, but not with restriction of carbohydrates. Two groups have reported longer-term randomised studies that compared instruction in the low-carbohydrate diet with a low-fat calorie-reduced diet in obese patients (N Engl J Med 2003; 348: 2082-90; Ann Intern Med 2004; 140: 778-85). Both trials showed better weight loss on the low-carbohydrate diet after 6 months, but no difference after 12 months. WHERE NEXT?: The apparent paradox that ad-libitum intake of high-fat foods produces weight loss might be due to severe restriction of carbohydrate depleting glycogen stores, leading to excretion of bound water, the ketogenic nature of the diet being appetite suppressing, the high protein-content being highly satiating and reducing spontaneous food intake, or limited food choices leading to decreased energy intake. Long-term studies are needed to measure changes in nutritional status and body composition during the low-carbohydrate diet, and to assess fasting and postprandial cardiovascular risk factors and adverse effects. Without that information, low-carbohydrate diets cannot be recommended.
The scarcity of data addressing the health effects of popular diets is an important public health concern, especially since patients and physicians are interested in using popular diets as individualized eating strategies for disease prevention.
To assess adherence rates and the effectiveness of 4 popular diets (Atkins, Zone, Weight Watchers, and Ornish) for weight loss and cardiac risk factor reduction.
A single-center randomized trial at an academic medical center in Boston, Mass, of overweight or obese (body mass index: mean, 35; range, 27-42) adults aged 22 to 72 years with known hypertension, dyslipidemia, or fasting hyperglycemia. Participants were enrolled starting July 18, 2000, and randomized to 4 popular diet groups until January 24, 2002.
A total of 160 participants were randomly assigned to either Atkins (carbohydrate restriction, n=40), Zone (macronutrient balance, n=40), Weight Watchers (calorie restriction, n=40), or Ornish (fat restriction, n=40) diet groups. After 2 months of maximum effort, participants selected their own levels of dietary adherence.
One-year changes in baseline weight and cardiac risk factors, and self-selected dietary adherence rates per self-report.
Assuming no change from baseline for participants who discontinued the study, mean (SD) weight loss at 1 year was 2.1 (4.8) kg for Atkins (21 [53%] of 40 participants completed, P = .009), 3.2 (6.0) kg for Zone (26 [65%] of 40 completed, P = .002), 3.0 (4.9) kg for Weight Watchers (26 [65%] of 40 completed, P < .001), and 3.3 (7.3) kg for Ornish (20 [50%] of 40 completed, P = .007). Greater effects were observed in study completers. Each diet significantly reduced the low-density lipoprotein/high-density lipoprotein (HDL) cholesterol ratio by approximately 10% (all P<.05), with no significant effects on blood pressure or glucose at 1 year. Amount of weight loss was associated with self-reported dietary adherence level (r = 0.60; P<.001) but not with diet type (r = 0.07; P = .40). For each diet, decreasing levels of total/HDL cholesterol, C-reactive protein, and insulin were significantly associated with weight loss (mean r = 0.36, 0.37, and 0.39, respectively) with no significant difference between diets (P = .48, P = .57, P = .31, respectively).
Each popular diet modestly reduced body weight and several cardiac risk factors at 1 year. Overall dietary adherence rates were low, although increased adherence was associated with greater weight loss and cardiac risk factor reductions for each diet group.
Stroke is the culmination of a heterogeneous group of cerebrovascular diseases that is manifested as ischemia or hemorrhage of one or more blood vessels of the brain. The occurrence of many acute cardiovascular events--such as myocardial infarction, sudden cardiac death, pulmonary embolism, critical limb ischemia, and aortic aneurysm rupture--exhibits prominent 24 h patterning, with a major morning peak and secondary early evening peak. The incidence of stroke exhibits the same 24 h pattern. Although ischemic and hemorrhagic strokes are different entities and are characterized by different pathophysiological mechanisms, they share an identical double-peak 24 h pattern. A constellation of endogenous circadian rhythms and exogenous cyclic factors are involved. The staging of the circadian rhythms in vascular tone, coagulative balance, and blood pressure plus temporal patterns in posture, physical activity, emotional stress, and medication effects play central and/or triggering roles. Features of the circadian rhythm of blood pressure, in terms of their chronic and acute effects on cerebral vessels, and of coagulation are especially important. Clinical medicine has been most concerned with the prevention of stroke in the morning, when population-based studies show it is of greatest risk during the 24 h; however, improved protection of at-risk patients against stroke in the early evening, the second most vulnerable time of cerebrovascular accidents, has received relatively little attention thus far.
Since the dawn of civilization, carbohydrate has comprised the largest source of energy in the diet for most populations. The source of the carbohydrate has been from plants in the form of complex carbohydrate high in fiber. Only in affluent cultures has sugar contributed so much of the total energy. When carbohydrate is consumed as a major component of a plant-based diet, a high-carbohydrate, low-fat diet is associated with low plasma levels of total and low-density lipoprotein cholesterol, less coronary heart disease, less diabetes, and less obesity. Very low-carbohydrate (ketogenic) diets may provide short-term solutions but do not lead to a long-term solution for most people.
Recent evidence has emerged that peroxisome proliferator-activated receptor alpha (PPARalpha), which is largely involved in lipid metabolism, can play an important role in connecting circadian biology and metabolism. In the present study, we investigated the mechanisms by which PPARalpha influences the pacemakers acting in the central clock located in the suprachiasmatic nucleus and in the peripheral oscillator of the liver. We demonstrate that PPARalpha plays a specific role in the peripheral circadian control because it is required to maintain the circadian rhythm of the master clock gene brain and muscle Arnt-like protein 1 (bmal1) in vivo. This regulation occurs via a direct binding of PPARalpha on a potential PPARalpha response element located in the bmal1 promoter. Reversely, BMAL1 is an upstream regulator of PPARalpha gene expression. We further demonstrate that fenofibrate induces circadian rhythm of clock gene expression in cell culture and up-regulates hepatic bmal1 in vivo. Together, these results provide evidence for an additional regulatory feedback loop involving BMAL1 and PPARalpha in peripheral clocks.
There are conflicting reports regarding circadian variation in the onset of acute myocardial infarction (MI) among patients with diabetes. We therefore, studied the circadian pattern of the incidence of acute MI in patients (n = 3,882) who were enrolled in the Onset Study stratified by the presence, type, and duration of diabetes. The Onset Study was conducted at 64 U.S. medical centers between August 1989 and September 1996. We used harmonic regression model to evaluate the circadian variation of MI symptom onset in patients with and without diabetes. Subgroup analysis was performed according to the presence, type, and duration of diabetes by the chi(2) test (dividing the day into four 6-h intervals). Patients without diabetes exhibited a prominent morning peak in the incidence of acute MI symptom onset (P < 0.001). In contrast, patients with type 1 diabetes and type 2 diabetes > or =5 years had a marked attenuation of the morning peak. Patients who had type 2 diabetes diagnosed within the previous 5 years had a pattern of onset of acute MI similar to patients without diabetes. Patients with type 1 diabetes and those with type 2 diabetes > or =5 years have an attenuation of the morning peak in acute MI. Inconsistency in observation of such an effect in patients with diabetes in the past may well have been due to difference in the duration of diabetes and thus the variable extent of underlying autonomic dysfunction.
Robust biological rhythms have been shown to affect life span. Biological clocks can be entrained by two feeding regimens, restricted feeding (RF) and caloric restriction (CR). RF restricts the time of food availability, whereas CR restricts the amount of calories with temporal food consumption. CR is known to retard aging and extend life span of animals via yet-unknown pathways. We hypothesize that resetting the biological clock could be one possible mechanism by which CR extends life span. Because it is experimentally difficult to uncouple calorie reduction from temporal food consumption, we took advantage of the murine urokinase-like plasminogen activator (alphaMUPA) transgenic mice overexpressing a serine protease implicated in brain development and plasticity; they exhibit spontaneously reduced eating and increased life span. Quantitative real-time PCR analysis revealed that alphaMUPA mice exhibit robust expression of the clock genes mPer1, mPer2, mClock, and mCry1 but not mBmal1 in the liver. We also found changes in the circadian amplitude and/or phase of clock-controlled output systems, such as feeding behavior, body temperature, and enteric cryptdin expression. A change in the light-dark regimen led to modified clock gene expression and abrogated circadian patterns of food intake in wild-type (WT) and alphaMUPA mice. Consequently, food consumption of WT mice increased, whereas that of alphaMUPA mice remained the same, indicating that reduced food intake occurs upstream and independently of the biological clock. Thus we surmise that CR could lead to pronounced and synchronized biological rhythms. Because the biological clock controls mitochondrial, hormonal, and physiological parameters, system synchronicity could lead to extended life span.
PAI-1 is expressed and secreted by adipose tissue which may mediate the pathogenesis of obesity-associated cardiovascular complications. Evidence is presented in this report that PAI-1 is not expressed by preadipocyte, but significantly induced during 3T3-L1 adipocyte differentiation and the PAI-1 expression correlates with the induction of peroxisome proliferator-activated receptor gamma (PPARgamma). A peroxisome proliferator responsive element (PPRE)-like cis-element (-206TCCCCCATGCCCT-194) is identified in the mouse PAI-1 gene promoter by electrophoretic mobility shift assay (EMSA) combined with transient transfection experiments; the PPRE-like cis-element forms a specific DNA-protein complex only with adipocyte nuclear extracts, not with preadipocyte nuclear extracts; the DNA-protein complex can be totally competed away by non-labeled consensus PPRE, and can be supershifted with PPARgamma antibody. Mutation of this PPRE-like cis-element can abolish the transactivation of mouse PAI-1 promoter mediated by PPARgamma. Specific PPARgamma ligand Pioglitazone can significantly induce the PAI-1 expression, and stimulate the secretion of PAI-1 into medium.
An increased level of obesity-induced plasma plasminogen activator inhibitor-1 (PAI-1) is considered a risk factor for cardiovascular disease.
The present study investigates whether the circadian clock component CLOCK is involved in obesity-induced PAI-1 elevation.
We examined plasma PAI-1 and mRNA expression levels in tissues from leptin-deficient obese and diabetic ob/ob mice lacking functional CLOCK protein.
Our results demonstrated that plasma PAI-1 levels were augmented in a circadian manner in accordance with the mRNA expression levels in ob/ob mice. Surprisingly, a Clock mutation normalized the plasma PAI-1 concentrations in accordance with the mRNA levels in the heart, lung and liver of ob/ob mice, but significantly increased PAI-1 mRNA levels in adipose tissue by inducing adipocyte hypertrophy in ob/ob mice. The Clock mutation also normalized tissue PAI-1 antigen levels in the liver but not in the adipose tissue of ob/ob mice.
These observations suggest that CLOCK is involved in obesity-induced disordered fibrinolysis by regulating PAI-1 gene expression in a tissue-dependent manner. Furthermore, it appears that obesity-induced PAI-1 production in adipose tissue is not closely related to systemic PAI-1 increases in vivo.
The present study investigated the influence of linoleic acid and fenofibrate on plasminogen activator inhibitor-1 (PAI-1) expression in HepG2 cells and the mechanism possibly involved. Using gene recombination techniques, chloromycetin acetyltransferase (CAT) reporter gene plasmids containing nuclear factor-kappaB response element deletion (del1-PAI-pCAT) or very-low-density lipoprotein/fatty acid response element deletion (del2-PAI-pCAT) in the PAI-1 promoter were constructed and transiently transfected into HepG2 cells, respectively. Linoleic acid and fenofibrate were added to induce the transfected cells. The PAI-1 expression in mRNA and protein level was significantly induced by linoleic acid, but suppressed by fenofibrate. In the HepG2 cells transfected with PAI-pCAT plasmid, the PAI-1 transcription activity was significantly induced by linoleic acid, but suppressed by fenofibrate. Under transfection with del1-PAI-pCAT, both linoleic acid and fenofibrate increased the PAI-1 transcriptional activity; whereas in those cells transfected with del2-PAI-pCAT, fenofibrate significantly reduced PAI-1 transcriptional activity but no change was found with linoleic acid stimulation. Peroxisome proliferator-activated receptor alpha may be one of transcription factors playing a role in the upregulation of PAI-1 gene expression by linoleic acid in HepG2 cells. The inhibition of the nuclear factor-kappaB signaling pathway may be involved in the downregulation of PAI-1 gene expression by fenofibrate.
Delayed sleep phase syndrome (DSPS) is very often seen among patients with sleep-wake rhythm disorders. Humans with the 3111C allele of the human Clock gene tend to demonstrate a higher evening preference on the morningness-eveningness (ME) preference test. DSPS is thought to be an extreme form of this evening preference. Clock-mutant mice have been proposed as an animal model of evening preference. In this study, we looked at whether constant light (LL) housing of Clock-mutant mice during lactation would result in evening preference and/or DSPS. Housed under light-dark (LD) or constant dark (DD) conditions during the lactation period, both wild-type and Clock-mutant mice did not show a phase-delay in the locomotor activity measured under light-dark conditions, whereas constant light housing during lactation significantly caused a delayed onset. The magnitude of the delay during the light-dark cycle was positively associated with free-running period measured during constant darkness. Among wild, heterozygote, and homozygote pups born from heterozygous dams, only homozygote pups showed a delayed onset. Constant light-housed Clock-mutant mice exhibited a lower number and delayed peak of phospho-MAPK-immunoreactive cells in core regions of the suprachiasmatic nucleus (SCN) compared to light-dark housed wild-type or Clock-mutant mice. Activity onset returned to normal with daily melatonin injection at the lights-off time for 5 days. The present results demonstrate that Clock-mutant mice exposed to constant light during lactation can function as an animal model of DSPS and can be used to gain an understanding of the ethological aspects of DSPS as well as to find medication for its treatment.
Recent progress at the molecular level has revealed that nuclear receptors play an important role in the generation of mammalian circadian rhythms. To examine whether peroxisome proliferator-activated receptor alpha (PPARalpha) is involved in the regulation of circadian behavioral rhythms in mammals, we evaluated the locomotor activity of mice administered with the hypolipidemic PPARalpha ligand, bezafibrate. Circadian locomotor activity was phase-advanced about 3h in mice given bezafibrate under light-dark (LD) conditions. Transfer from LD to constant darkness did not change the onset of activity in these mice, suggesting that bezafibrate advanced the phase of the endogenous clock. Surprisingly, bezafibrate also advanced the phase in mice with lesions of the suprachiasmatic nucleus (SCN; the central clock in mammals). The circadian expression of clock genes such as period2, BMAL1, and Rev-erbalpha was also phase-advanced in various tissues (cortex, liver, and fat) without affecting the SCN. Bezafibrate also phase-advanced the activity phase that is delayed in model mice with delayed sleep phase syndrome (DSPS) due to a Clock gene mutation. Our results indicated that PPARalpha is involved in circadian clock control independently of the SCN and that PPARalpha could be a potent target of drugs to treat circadian rhythm sleep disorders including DSPS.
The master clock located in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus regulates circadian rhythms in mammals. The clock is an intracellular, transcriptional mechanism sharing the same molecular components in SCN neurons and in peripheral cells, such as the liver, intestine, and retina. The circadian clock controls food processing and energy homeostasis by regulating the expression and/or activity of enzymes involved in cholesterol, amino acid, lipid, glycogen, and glucose metabolism. In addition, many hormones involved in metabolism, such as insulin, glucagon, adiponectin, corticosterone, leptin, and ghrelin, exhibit circadian oscillation. Furthermore, disruption of circadian rhythms is involved in the development of cancer, metabolic syndrome, and obesity. Metabolism and food intake also feed back to influence the biological clock. Calorie restriction (CR) entrains the SCN clock, whereas timed meals entrain peripheral oscillators. Furthermore, the cellular redox state, dictated by food metabolism, and several nutrients, such as glucose, ethanol, adenosine, caffeine, thiamine, and retinoic acid, can phase-shift circadian rhythms. In conclusion, there is a large body of evidence that links feeding regimens, food components, and the biological clock.
Metformin is one of the most commonly used first line drugs for type II diabetes. Metformin lowers serum glucose levels by
activating 5′-AMP-activated kinase (AMPK), which maintains energy homeostasis by directly sensing the AMP/ATP ratio. AMPK
plays a central role in food intake and energy metabolism through its activities in central nervous system and peripheral
tissues. Since food intake and energy metabolism is synchronized to the light-dark (LD) cycle of the environment, we investigated
the possibility that AMPK may affect circadian rhythm. We discovered that the circadian period of Rat-1 fibroblasts treated
with metformin was shortened by 1 h. One of the regulators of the period length is casein kinase Iϵ (CKIϵ), which by phosphorylating
and inducing the degradation of the circadian clock component, mPer2, shortens the period length. AMPK phosphorylates Ser-389
of CKIϵ, resulting in increased CKIϵ activity and degradation of mPer2. In peripheral tissues, injection of metformin leads
to mPer2 degradation and a phase advance in the circadian expression pattern of clock genes in wild-type mice but not in AMPK
α2 knock-out mice. We conclude that metformin and AMPK have a previously unrecognized role in regulating the circadian rhythm.
A sufficient energy supply is essential for life; consequently, multiple mechanisms have evolved to ensure both energy availability and conservation during fasting and starvation. Two reports in this issue of Cell Metabolism (Badman et al., 2007; Inagaki et al., 2007) demonstrate that FGF21, a circulating protein produced in the liver in response to the PPARalpha transcription factor, is a "missing link" in the biology of fasting, inducing adipose tissue lipolysis, liver ketogenesis, and metabolic adaptation to the fasting state.
This study examined circadian variation in coagulation and fibrinolytic parameters among Jcl:ICR, C3H/HeN, BALB/cA, and C57BL/6J strains of mice. Plasma plasminogen activator inhibitor 1 (PAI-1) levels fluctuated in a circadian manner and peaked in accordance with the mRNA levels at the start of the active phase in all strains. Fibrinogen mRNA levels peaked at the start of rest periods in all strains, although plasma fibrinogen levels remained constant. Strain differences in plasma antithrombin (AT) activity and protein C (PC) levels were then identified. Plasma AT activity was circadian rhythmic only in Jcl:ICR, but not in other strains, although the mRNA levels remained constant in all strains. Levels of plasma PC and its mRNA fluctuated in a circadian manner only in Jcl:ICR mice, whereas those of plasma prothrombin, factor X, factor VII, prothrombin time (PT), and activated partial thrombin time (APTT) remained constant in all strains. These results suggest that genetic heterogeneity underlies phenotypic variations in the circadian rhythmicity of blood coagulation and fibrinolysis. The circadian onset of thrombotic events might be due in part to the rhythmic gene expression of coagulation and fibrinolytic factors. The present study provides fundamental information about mouse strains that will help to understand the circadian variation in blood coagulation and fibrinolysis.