Kari Kalliokoski

• PhD, MSc
• Research Service Manager at University of Turku

Exercise improves health and well-being across diverse organ systems, and elucidating mechanisms underlying the beneficial effects of exercise can lead to new therapies. Here, we show that transforming growth factor-β2 (TGF-β2) is secreted from adipose tissue in response to exercise and improves glucose tolerance in mice. We identify TGF-β2 as an e...

The endogenous μ-opioid receptor (MOR) system regulates motivational and hedonic processing. We tested directly whether individual differences in MOR are associated with neural reward responses to food pictures in humans. We scanned 33 non-obese individuals with positron emission tomography (PET) using the MOR-specific radioligand [11C]carfentanil....

Type 2 diabetes mellitus (T2DM) is associated with reduced myocardial glucose uptake (GU) and increased free fatty acid uptake (FFAU). Sprint interval training (SIT) improves physical exercise capacity and metabolic biomarkers, but effects of SIT on cardiac function and energy substrate metabolism in diabetic subjects are unknown. We tested the hyp...

We investigated the effects of sprint interval training (SIT) and moderate‐intensity continuous training (MICT) on glucose uptake (GU) during hyperinsulinemic euglycemic clamp and fatty acid uptake (FAU) at fasting state in thigh and arm muscles in subjects with type 2 diabetes (T2D) or prediabetes. Twenty‐six patients (age 49, SD 4; 10 women) were...

The effects of sprint interval training (SIT) on intramyocellular (IMCL) and extramyocellular (EMCL) lipid accumulation are unclear. We tested the effects of SIT and moderate‐intensity continuous training (MICT) on IMCL and EMCL accumulation in a randomized controlled setting in two different study populations; healthy untrained men (n 28) and subj...

Metabolic syndrome increases the risk of developing noncommunicable diseases such as metabolic dysfunction-associated steatotic liver disease. The aim was to investigate the effects of sedentary behavior (SB) reduction on liver glucose uptake (LGU), endogenous glucose production (EGP), liver fat content (LFC), and liver enzyme levels (alanine amino...

Context Postprandial hepatic glycogen synthesis and glycolysis are reduced in hepatic insulin resistance. However, the physiologic interpretation of the reduction in hepatic glucose uptake (GU) during the gold-standard measurement of insulin sensitivity, hyperinsulinemic euglycemic clamp, in insulin resistance is unclear. This is because the periph...

A first-in-human phase I clinical study aimed to assess the safety profile, radiation dosimetry, and biodistribution of a potential cardiac PET myocardial perfusion imaging tracer, [18F]SYN2 (18F-labeled acridine derivative), in healthy subjects. Methods: [18F]SYN2 intravenous administration with PET imaging was performed on healthy volunteers, and...

Purpose: The associations between work time, leisure-time, and non-workday physical activity (PA) and sedentary behavior (SED) and 24 h ambulatory blood pressure (BP) are not well known. Therefore, the aim of this study was to evaluate the associations between domain-specific activity behavior and 24 h blood pressure. Methods: A hundred and fifty-s...

The aim of this study was to investigate whether a reduction in accelerometer-measured sedentary behavior (SB) improves blood lipids in inactive adults with metabolic syndrome (MetS). Sixty-four participants were randomly assigned into intervention (INT, n = 33) and control (CONT, n = 31) groups. The INT group was instructed to reduce SB by 1 h/day...

The heart depends critically on continuous blood supply, but it is unknown whether cancer itself affects myocardial blood flow (MBF). This study investigated MBF in cancer patients and cardiac morphology in a cancer mice model. MBF was quantified with [¹⁵O]H2O positron emission tomography at rest in recently diagnosed breast cancer patients and age...

Objectives Sedentary behaviour (SB) is a plausible intervention target for back pain mitigation. Therefore, this study aimed to investigate the effects of a 6-month SB reduction intervention on back pain and related disability outcomes, and paraspinal muscle (ie, erector spinae and transversospinales separately) insulin sensitivity (glucose uptake,...

Backgrounds Obesity is associated with alterations in bone turnover markers (BTMs). However, the association between regional fat distribution and bone metabolism has received less attention. This study therefore aimed to identify which specific fat compartments (i.e., abdominal and femoral subcutaneous fat, intra- and extraperitoneal fat, and tota...

Background Obesity is associated with impaired glucose metabolism and hepatic insulin resistance. The aim was to investigate the associations of hepatic glucose uptake (HGU) and endogenous glucose production (EGP) to sedentary behavior (SB), physical activity (PA), cardiorespiratory fitness, dietary factors, and metabolic risk markers. Methods For...

Background Fatty acid uptake can be measured using PET and 14-(R,S)‐[¹⁸F]fluoro‐6‐thia‐heptadecanoic acid ([¹⁸F]FTHA). However, the relatively rapid rate of [¹⁸F]FTHA metabolism significantly affects kinetic modeling of tissue uptake. Thus, there is a need for accurate chromatographic methods to analyze the unmetabolized [¹⁸F]FTHA (parent fraction)...

Background The effects of reducing sedentary behaviour (SB) on cardiac structure and function remain unknown, yet reducing SB may have potential for heart failure prevention. Purpose The aim of this study was to investigate whether reducing SB could lead to healthy cardiac remodelling. Methods Sixty-four physically inactive adults with metabolic...

Context Increased standing time has been associated with improved health, but the underlying mechanism is unclear. Objectives We herein investigate if increased weight loading increases energy demand and thereby glucose uptake (GU) locally in bone and/or muscle in the lower extremities. Methods In this single-center clinical trial with randomized...

Physical activities and sedentary behaviors take place in different contexts. This study aimed to determine if the context, total score, and leisure-time MET-index assessed by the Baecke questionnaire associate with each other or with sedentary behavior and physical activity outcomes from a 4-week accelerometer measurement in physically inactive ad...

Metabolic flexibility (MetFlex) describes the ability to respond and adapt to changes in metabolic demand and substrate availability. The relationship between physical (in)activity and MetFlex is unclear. This study aimed to determine whether sedentary time, physical activity (PA), and cardiorespiratory fitness associate with MetFlex. Sedentary tim...

Evidence on the long-term effects of reducing sedentary behaviour (SB) on blood pressure (BP) is scarce. Therefore, we performed a sub-analysis of the BP effects of a six-month intervention that aimed at reducing SB by 1 h/day and replacing it with non-exercise activities. Sixty-four physically inactive and sedentary adults with metabolic syndrome...

Background and aims: Clinical management of critical limb-threatening ischemia (CLTI) is focused on prevention and treatment of atherosclerotic arterial occlusions. The role of microvascular pathology in disease progression is still largely unspecified and more importantly not utilized for treatment. The aim of this explorative study was to charac...

Sedentary behavior (SB) and physical inactivity associate with impaired insulin sensitivity. We investigated whether an intervention aimed at a 1h reduction in daily SB during 6 months would improve insulin sensitivity in the weight-bearing thigh muscles. Forty-four sedentary inactive adults [mean age 58 (SD 7) years; 43% men] with metabolic syndro...

Objective: Cannabinoid type 1 receptors (CB1R) modulate feeding behavior and energy homeostasis, and the CB1R tone is dysgulated in obesity. This study aimed to investigate CB1R availability in peripheral tissue and brain in young men with overweight versus lean men. Methods: Healthy males with high (HR, n = 16) or low (LR, n = 20) obesity risk...

Background: Changes in fatty acid metabolism are an important component of the pathogenesis of type 2 diabetes mellitus (T2DM). Fatty acid uptake in tissues can be measured with positron emission tomography (PET) imaging, employing the fatty acid analogue 18F-FTHA radiotracer. We aimed to evaluate the repeatability of assessments of fatty acid upta...

Introduction Poor cardiorespiratory fitness (CRF) is associated with adverse health outcomes. Previous observational and cross‐sectional studies have suggested that reducing sedentary behavior (SB) might improve CRF. Therefore, we investigated the effects of a 6‐month intervention of reducing SB on CRF in 64 sedentary inactive adults with metabolic...

Objective To investigate the associations of sedentary time, physical activity, and cardiorespiratory fitness with skeletal muscle glucose uptake (GU). Methods Sedentary time and physical activity were measured with accelerometers, and VO2max with cycle ergometry in 44 sedentary adults with metabolic syndrome. Thigh muscle GU was determined with [...

Purpose: To investigate whether a reduction in daily sedentary behavior (SB) improves insulin sensitivity in adults with metabolic syndrome in 6 months, without adding intentional exercise training. Methods: Sixty-four sedentary inactive middle-aged adults with overweight and metabolic syndrome [mean age 58 (SD 7) years, mean BMI 31.6 (SD 4.3) k...

Objective: To investigate whether alterations in brain glucose uptake (BGU), insulin action in the brain-liver axis, and whole-body insulin sensitivity occur in young adults in pre-obese state. Methods: Healthy males with either high (HR, n = 19) or low risk (LR, n = 22) for developing obesity were studied with [18F]fluoro-D-glucose ([18F]FDG) - po...

Objectives The aim was to investigate if reducing sedentary behavior (SB) improves cardiometabolic biomarkers in adults with metabolic syndrome (MetS). Design Randomized controlled trial. Methods Sixty-four sedentary middle-aged adults with MetS were randomized into intervention (INT; n = 33) and control (CON; n = 31) groups. INT was guided to li...

Purpose: The muscle perfusion response to post-exercise cold water immersion (CWI) is not well understood. We examined the effects of graded post-exercise CWI upon global and regional quadriceps femoris muscle perfusion using positron emission tomography (PET) and [15O]H2O. Methods: Using a matched-group design, 30 healthy men performed cycle er...

Introduction: Central μ-opioid receptors (MORs) modulate affective responses to physical exercise. Individuals with higher aerobic fitness report greater exercise-induced mood improvements than those with lower fitness, but the link between cardiorespiratory fitness and the MOR system remains unresolved. Here we tested whether maximal oxygen uptak...

Background Obesity is a pressing public health concern worldwide. Novel pharmacological means are urgently needed to combat the increase of obesity and accompanying type 2 diabetes (T2D). Although fully established obesity is associated with neuromolecular alterations and insulin resistance in the brain, potential obesity-promoting mechanisms in th...

Background: This study evaluated tracer uptake and lesion detectability with the novel radiopharmaceutical 18F-radiohybrid (rh)PSMA-7.3 in patients with prostate cancer (PCa). Materials and Methods: Ten patients (three with high-risk primary localized PCa [Cohort A], three with hormone-sensitive metastatic PCa [Cohort B], and four with castration-r...

Background: Cardiorespiratory fitness (CRF) has been inversely associated with insulin resistance and clustering of cardiometabolic risk factors among overweight and obese individuals. However, most previous studies have scaled CRF by body mass (BM) possibly inflating the association between CRF and cardiometabolic health. We investigated the asso...

Purpose This phase 1 open-label study evaluated the uptake kinetics of a novel theranostic PET radiopharmaceutical, ¹⁸ F-rhPSMA-7.3, to optimise its use for imaging of prostate cancer. Methods Nine men, three with high-risk localised prostate cancer, three with treatment-naïve hormone-sensitive metastatic disease and three with castration-resistan...

Eating behavior varies greatly between individuals, but the neurobiological basis of these trait-like differences in feeding remains poorly understood. Central μ-opioid receptors (MOR) and cannabinoid CB1 receptors (CB1R) regulate energy balance via multiple neural pathways, promoting food intake and reward. Because obesity and eating disorders hav...

Objectives To determine how components of accelerometer-measured sedentary behavior (SB) and physical activity (PA), and fitness are associated with insulin sensitivity in adults with metabolic syndrome. Design Cross-sectional. Methods Target population was middle-aged (40-65 years) sedentary adults with metabolic syndrome. SB, breaks in SB, stan...

Accelerometry is a commonly used method to determine physical activity in clinical studies, but the duration and timing of measurement have seldom been addressed. We aimed to evaluate possible changes in the measured outcomes and associations with insulin resistance during four weeks of accelerometry data collection. This study included 143 partici...

Short-term exercise training programs that consist of moderate intensity endurance training or high intensity interval training have become popular choices for healthy lifestyle modifications, with as little as two weeks of training being shown to improve cardiorespiratory fitness and whole-body glucose metabolism. An emerging concept in exercise b...

Objective To study the pathophysiological cascade of pressure ulcer (PU) development consisting of tissue deformation, inflammation and hypoxia. Method In this crossover study, deformation was measured with computerised tomography (CT) linked with contact area reflecting immersion and envelopment. Inflammation and hypoxia were measured using subep...

Seasonal rhythms influence emotion and sociability. The brain μ-opioid receptor (MOR) system modulates a multitude of seasonally varying socioemotional functions, but its seasonal variation remains elusive with no previously reported in vivo evidence. Here, we first conducted a cross-sectional study with previously acquired human [11C]carfentanil P...

Eating behavior varies greatly between healthy individuals, but the neurobiological basis of these trait-like differences in feeding remains unknown. Central mu-opioid receptors (MOR) and cannabinoid CB1-receptors (CB1R) regulate energy balance via multiple neural pathways, promoting food intake and reward. Because obesity and eating disorders have...

Central μ-opioid receptors (MORs) modulate affective responses to physical exercise. Individuals with higher aerobic fitness report greater exercise-induced mood improvements than those with lower fitness, but the link between cardiorespiratory fitness and the MOR system remains unresolved. Here we tested whether maximal oxygen uptake (VO 2peak ) a...

The aim of this study was to examine the associations of cardiometabolic health markers with device-measured sedentary behavior (SB) duration and different intensities of physical activity (PA) among overweight working-aged adults with low self-reported PA levels. This cross-sectional analysis included 144 subjects (42 men) with mean age of 57 (SD...

Purpose Rac1 and its downstream target PAK1 are novel regulators of insulin and exercise-induced glucose uptake in skeletal muscle. However, it is not yet understood how different training intensities affect the expression of these proteins. Therefore, we studied the effects of high-intensity interval training (HIIT) and moderate-intensity continuo...

This first-in-humans study investigated the safety, biodistribution, and radiation dosimetry of a novel 18F-labeled radiohybrid prostate-specific membrane antigen (rhPSMA) PET imaging agent, 18F-rhPSMA-7.3. Methods: Six healthy volunteers (3 men, 3 women) underwent multiple whole-body PET acquisitions at scheduled time points up to 248 min after th...

Context Exercise training improves bone mineral density, but little is known about the effects of training on bone marrow (BM) metabolism. BM insulin sensitivity has been suggested to play an important role in bone health and whole-body insulin sensitivity. Objective To study the effects of exercise training on BM metabolism. Design Randomized co...

Introduction We investigated the effects of a supervised progressive sprint interval training (SIT) and moderate-intensity continuous training (MICT) on adipocyte morphology and adipose tissue metabolism and function; we also tested whether the responses were similar regardless of baseline glucose tolerance and sex. Research design and methods 26...

Background and Aims Computed tomography (CT)-derived adipose tissue radiodensity represents a potential noninvasive surrogate marker for lipid deposition and obesity-related metabolic disease risk. We studied the effects of bariatric surgery CT-derived adipose radiodensities in abdominal and femoral areas and their relationships to circulating meta...

Major depressive disorder is associated with lowered mood, anxiety, anhedonia, sleep problems, and cognitive impairments. Many of these functions are regulated by μ-opioid receptor (MOR) system. Preclinical, in vivo, and post-mortem studies have however yielded inconclusive results regarding the role of the MOR in depression and anxiety. Moreover,...

Seasonal rhythms influence mood and sociability. The mu-opioid receptor (MOR) system modulates a multitude of seasonally varying socioemotional functions, but seasonal variation in the MOR system remains elusive. We used positron emission tomography (PET) imaging with [11C]carfentanil, a high affinity MOR radioligand, to repeatedly measure in vivo...

Alterations in the brain’s μ-opioid receptor (MOR) system have been associated with several neuropsychiatric diseases. Also healthy individuals vary considerably in MOR availability. Multiple epidemiological factors have been proposed to influence MOR system, but due to small sample sizes the magnitude of their influence remains inconclusive. We co...

We examined the influence of graded cold-water immersion (CWI) on global and regional quadriceps muscle perfusion using positron emission tomography (PET) and [ ¹⁵ O]H 2 O. In thirty healthy males (33±8 yrs; 81±10 kg; 184±5 cm; percentage body fat: 13±5%; V̇O 2peak : 47±8 mL·kg ⁻¹ ·min ⁻¹ ) quadriceps perfusion, thigh and calf cutaneous vascular co...

Purpose Abnormal lipoprotein and amino acid profiles are associated with insulin resistance and may help to identify this condition. The aim of this study was to create models estimating skeletal muscle and whole-body insulin sensitivity using fasting metabolite profiles and common clinical and laboratory measures. Material and methods The cross-s...

The brain's mu-opioid receptors (MORs) are involved in analgesia, reward and mood regulation. Several neuropsychiatric diseases have been associated with dysfunctional MOR system, and there is also considerable variation in receptor density among healthy individuals. Sex, age, body mass and smoking have been proposed to influence the MOR system, bu...

Inrtroduction: Intestinal metabolism and microbiota profiles are impaired in obesity and insulin resistance. Moreover, dysbiotic gut microbiota has been suggested to promote systemic low-grade inflammation and insulin resistance through the release of endotoxins particularly lipopolysaccharides. We have previously shown that exercise training impr...

Aims: Simultaneous measurement of right (RV) and left ventricle (LV) myocardial blood flow (MBF), oxygen extraction fraction (OEF), and oxygen consumption (MVO2) non-invasively in humans would provide new possibilities to understand cardiac physiology and different patho-physiological states. Methods: We developed and tested an optimized novel meth...

Objective Skeletal muscle is unique among organs in that its blood flow, thus oxygen supply that is critical for muscular function, can change over a remarkably large range. Compared to the rest, muscle blood flow can increase over 20-fold during intense exercise. Positron emission tomography (PET) and [15O]-H2O tracer provide a unique tool for the...

Human bone marrow is a metabolically active tissue that responds to acute low intensity exercise by having increased glucose uptake. Here we studied whether bone marrow glucose uptake increases more with increased exercise intensities. Femoral bone marrow glucose uptake was measured using positron emission tomography and 18F-fluoro-deoxyglucose in...

Intrinsic factors related to muscle metabolism may explain the differences in mechanical efficiency (ME) during exercise. Therefore, this study aimed to investigate the relationship between muscle metabolism and ME. Totally 17 healthy recreationally active male participants were recruited and divided into efficient (EF; n = 8) and inefficient (IE;...

Aims/hypothesis: Pancreatic fat accumulation may contribute to the development of beta cell dysfunction. Exercise training improves whole-body insulin sensitivity, but its effects on pancreatic fat content and beta cell dysfunction are unclear. The aim of this parallel-group randomised controlled trial was to evaluate the effects of exercise train...

Physical exercise modulates food reward and helps control body weight. The endogenous µ‐opioid receptor (MOR) system is involved in rewarding aspects of both food and physical exercise, yet interaction between endogenous opioid release following exercise and anticipatory food reward remains unresolved. Here we tested whether exercise‐induced opioid...

Objective: Insulin resistance is reflected by the rates of reduced glucose uptake (GU) into the key insulin-sensitive tissues, skeletal muscle, liver and adipose tissue. It is unclear whether insulin resistance occurs simultaneously in all these tissues or whether insulin resistance is tissue specific. Design and methods: We measured GU in skele...

Aim: We aimed to investigate the effect of bariatric surgery on lipid metabolism in supraclavicular brown adipose tissue in morbidly obese women. We hypothesized that lipid metabolism improves after surgery-induced weight loss. Materials and methods: Twenty-three morbidly obese women (BMI 42.1 ± 4.2 kg/m2 ; age 43.8 ± 9.8 years) were studied bef...

The mechanisms that regulate bone blood flow (BBF) in humans are largely unknown. Animal studies suggest that nitric oxide (NO) could be involved and in the present study we investigated the effects of inhibition of nitric oxide synthase (NOS) alone and in combination with inhibition of cyclooxygenase (COX) enzyme, thus prostaglandin (PG) synthesis...

Brain insulin-stimulated glucose uptake (GU) is increased in obese and insulin resistant subjects but normalizes after weight loss along with improved whole-body insulin sensitivity. Our aim was to study whether short-term exercise training (moderate intensity continuous training (MICT) or sprint interval training (SIT)) alters substrates for brain...

Introduction: The aim of this study was to investigate affective responses to repeated sessions of sprint interval training (SIT) in comparison with moderate-intensity continuous training (MICT) in insulin resistant subjects. Methods: Twenty-six insulin resistant adults (age: 49 (4) years, 10 women) were randomized into SIT (n=13) or MICT (n=13)...

Central opioidergic mechanisms may modulate the positive effects of physical exercise such as mood elevation and stress reduction. How exercise intensity and concomitant affective changes affect central opioidergic responses is unknown. We studied the effects of acute physical exercise on the cerebral μ-opioid receptors (MOR) of 22 healthy recreati...

Purpose: Animal studies suggest that the inhibition of nitric oxide synthase (NOS) affects blood flow differently in different skeletal muscles according to their muscle fibre type composition (oxidative vs glycolytic). Quadriceps femoris (QF) muscle consists of four different muscle parts: vastus intermedius (VI), rectus femoris (RF), vastus medi...

Aims: Little is known about the effects of exercise training on brown adipose tissue (BAT) metabolism in humans. We tested the hypothesis that high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) improve BAT insulin sensitivity. Materials and methods: Healthy middle-aged men (n = 18, age 47 [CI: 49, 43] years...

Similar to muscles, the intestine is also insulin resistant in obese subjects and subjects with impaired glucose tolerance. Exercise training improves muscle insulin sensitivity, but its effects on intestinal metabolism are not known. We studied the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT)...

Purpose Epicardial (EAT) and pericardial (PAT) fat masses and myocardial triglyceride content (MTC) are enlarged in obesity and insulin resistance. We studied whether the high-intensity interval (HIIT) and moderate intensity continuous training (MICT) similarly decrease ectopic fat in and around the heart and whether the decrease is similar in heal...

Adipose tissue metabolism and circulation play an important role in human health. It is well-known that adipose tissue mass is increased in response to excess caloric intake leading to obesity and further to local hypoxia and inflammatory signaling. Acute exercise increases blood supply to adipose tissue and mobilization of fat stores for energy. H...

Key points: High-intensity interval training (HIIT) has become popular, time-sparing alternative to moderate intensity continuous training (MICT), although the cardiac vascular and metabolic effects of HIIT are incompletely known. We compared the effects of 2-week interventions with HIIT and MICT on myocardial perfusion and free fatty acid and glu...

Despite the recent studies on structural and functional adaptations of the right ventricle (RV) to exercise training, adaptations of its metabolism remain unknown. We investigated the effects of short-term, high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on RV glucose and fat metabolism. Twenty-eight untrai...