A Lochner

Stellenbosch University, Stellenbosch, Western Cape, South Africa

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Publications (211)764.12 Total impact

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    Yolandi Espach · Amanda Lochner · Hans Strijdom · Barbara Huisamen ·
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    ABSTRACT: The ataxia-telangiectasia mutated (ATM) protein kinase is well known to play a significant role in the response to double stranded DNA breaks in the nucleus. Recently, it has become apparent that ATM is also involved in a large number of cytoplasmic processes and responses, some of which may contribute to metabolic and cardiovascular complications when disrupted. Due to its involvement in these processes, therapeutic activation of ATM could potentially be a novel approach for the prevention or treatment of cardiovascular disease. However, relatively little is currently known about the cardiovascular role of ATM. In this review, we highlight studies that have shed some light on the role of ATM in the cardiovascular context, namely in oxidative stress, atherosclerosis and metabolism, insulin resistance and cardiac remodeling.
    Cardiovascular Drugs and Therapy 02/2015; 29(1). DOI:10.1007/s10557-015-6571-z · 3.19 Impact Factor
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    Amanda Lochner · Frederic Nduhirabandi ·
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    ABSTRACT: Melatonin treatment has been shown to prevent the harmful effects of diet-induced obesity and reduce myocardial susceptibility to ischaemia-reperfusion injury (IRI) when administered from the onset of obesity. However, the exact mechanism whereby it exerts its beneficial actions on the heart in obesity and insulin resistance is unknown. In this study we investigated the effects of relatively short-term melatonin treatment on the heart in a rat model of diet-induced obesity. Control (C) and diet-induced obese (D) Wistar rats (fed for 20 weeks (wks)) were divided into 3 groups receiving drinking water with or without melatonin (4mg/kg/day) for the last 6 or 3 wks of experimentation. Isolated hearts were perfused in the working mode, subjected to regional (35min) or global ischaemia (15min) and reperfusion (2h); others were non-perfused (baseline). Myocardial infarct sizes as well as baseline and post-ischaemic activation of PKB/Akt, ERK42/44, GSK-3B and STAT-3 were determined. Blood was collected for study of metabolic parameters. Diet-induced obesity caused significant increases in body weight gain (14.5%), visceral adiposity (70.3%), fasting blood glucose (20%), serum insulin (55.6%) and triglyceride (84.2%) levels with a concomitant increase in post-ischaemic myocardial infarct size (41%) and a reduced cardiac output (12.7%). Melatonin treatment (both 3 and 6 wks) decreased serum insulin levels and the HOMA-index in the D group only (3 wks % reduction: 39%; 47.2%, p<0.05 vs untreated D respectively) with no effect on body weight gain, visceral adiposity, serum triglycerides and glucose levels. It also increased serum adiponectin levels in the D group (113% p<0.05 vs untreated D), reduced myocardial infarct sizes in both groups (3 wks %reduction: C 42.4%; D 61.6%) and activated baseline myocardial STAT-3, PKB/Akt, ERK42/44 and GSK-3< after 10 min reperfusion. Short-term melatonin administration to obese and insulin resistant rats reduced insulin resistance and protected the heart against ex vivo myocardial IRI independently of body weight gain and visceral adiposity. Melatonin-induced cardioprotection was associated with concomitant activation of the RISK and SAFE pathways. Published conference paper
    Circulation 11/2014; 130:A18554. DOI:10.13140/2.1.4173.9841 · 14.43 Impact Factor
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    ABSTRACT: Chronic melatonin treatment has been shown to prevent the harmful effects of diet-induced obesity and reduce myocardial susceptibility to ischaemia-reperfusion injury (IRI). However, the exact mechanism whereby it exerts its beneficial actions on the heart in obesity/insulin resistance remains unknown. Herein, we investigated the effects of relatively short-term melatonin treatment on the heart in a rat model of diet-induced obesity. Control and diet-induced obese Wistar rats (fed a high calorie diet for 20 weeks) were each subdivided into 3 groups receiving drinking water with or without melatonin (4mg/kg/day) for the last 6 or 3 weeks of experimentation. A number of isolated hearts were perfused in the working mode, subjected to regional or global ischaemia-reperfusion; others were non-perfused. Metabolic parameters, myocardial infarct sizes, baseline and post-ischaemic activation of PKB/Akt, ERK42/44, GSK-3β and STAT-3 were determined. Diet-induced obesity caused increases in body weight gain, visceral adiposity, fasting blood glucose, serum insulin and triglyceride levels with a concomitant cardiac hypertrophy, large post-ischaemic myocardial infarct sizes and a reduced cardiac output. Melatonin treatment (3 and 6 weeks) decreased serum insulin levels and the HOMA-index (p<0.05) with no effect on weight gain (after 3 weeks), visceral adiposity, serum triglyceride and glucose levels. It increased serum adiponectin levels, reduced myocardial infarct sizes in both groups and activated baseline myocardial STAT-3 and PKB/Akt, ERK42/44 and GSK-3β during reperfusion. Overall, short-term melatonin administration to obese/insulin resistant rats reduced insulin resistance and protected the heart against ex vivo myocardial IRI independently of body weight change and visceral adiposity.
    Journal of Pineal Research 09/2014; 57(3). DOI:10.1111/jpi.12171 · 9.60 Impact Factor
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    Ruduwaan Salie · Barbara Huisamen · Amanda Lochner ·
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    ABSTRACT: Background Although obesity is still considered a risk factor in the development of cardiovascular disorders, recent studies suggested that it may also be associated with reduced morbidity and mortality, the so-called “obesity paradox”. Experimental data on the impact of diabetes, obesity and insulin resistance on myocardial ischaemia/reperfusion injury are controversial. Similar conflicting data have been reported regarding the effects of ischaemic preconditioning on ischaemia/reperfusion injury in hearts from such animals. The aim of the present study was to evaluate the susceptibility to myocardial ischaemia/reperfusion damage in two models of diet-induced obesity as well as the effect of ischaemic and pharmacological preconditioning on such hearts. Methods Three groups of rats were fed with: (i) normal rat chow (controls) (ii) a sucrose-supplemented diet (DIO) (iii) a high fat diet (HFD). After 16 weeks, rats were sacrificed and isolated hearts perfused in the working mode and subjected to 35 min regional ischaemia/60 min reperfusion. Endpoints were infarct size and functional recovery. Infarct size was determined, using tetrazolium staining. Activation of PKB/Akt and ERKp44/p42 (RISK pathway) during early reperfusion was determined using Western blot. Statistical evaluation was done using ANOVA and the Bonferroni correction. Results Infarct sizes of non-preconditioned hearts from the two obese groups were significantly smaller than those of the age-matched controls. Ischaemic as well as pharmacological (beta-adrenergic) preconditioning with a beta2-adrenergic receptor agonist, formoterol, caused a significant reduction in infarct size of the controls, but were without effect on infarct size of hearts from the obese groups. However, ischaemic as well as beta-preconditioning caused an improvement in functional performance during reperfusion in all three groups. A clear-cut correlation between the reduction in infarct size and activation of ERKp44/p42 and PKB/Akt was not observed: The reduction in infarct size observed in the non-preconditioned hearts from the obese groups was not associated with activation of the RISK pathway. However, beta-adrenergic preconditioning caused a significant activation of ERKp44/p42, but not PKB/Akt, in all three groups. Conclusions Relatively long-term administration of the two obesity-inducing diets resulted in cardioprotection against ischaemia/reperfusion damage. Further protection by preconditioning was, however, without effect on infarct size, while an improvement in functional recovery was observed.
    Cardiovascular Diabetology 07/2014; 13(1):109. DOI:10.1186/s12933-014-0109-8 · 4.02 Impact Factor
  • I Webster · A Smith · A Lochner · B Huisamen ·
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    ABSTRACT: Aims In isolated rat heart perfusion experiments, drug administration occurs via retrograde perfusion. This can be done in the non-recirculating mode (coronary effluent is discarded), or recirculating mode (coronary effluent is collected and reused). It was recently observed in our lab while using sanguinarine, an MKP-1 inhibitor, that there were differences in outcomes depending on the mode of recirculation used. Methods and Results Hearts from control (C); diet-induced obese (DIO) Wistar rats and their age matched controls (AMC) were perfused on the rig. Hearts received buffer (control) , insulin, sanguinarine, insulin + sanguinarine combination or methanol (vehicle) for 15mins pre- and 10mins post-ischemia in either a non- or re-circulating manner. Hearts were subjected to 15mins global ischemia and 30mins reperfusion. Mechanical function was documented pre- and post-ischemia . When not-recirculated , sanguinarine alone and in combination with insulin in C, DIO and AMC groups, caused a significant decrease in functional recovery during reperfusion. However, when the coronary effluent was recirculated, hearts perfused with sanguinarine or sanguinarine + insulin exhibited a significant recovery in function when compared with their non-recirculation counterparts (p < 0.01). No differences were seen with either control, insulin nor vehicle hearts. Conclusion Sanguinarine elicited a vast improvement in perfusion outcomes when recirculated compared to non-recirculation . Since this was seen during perfusion only when sanguinarine was present, it is possible that recirculating reperfusion of the drug caused profound changes in its composition. More investigation is needed into the mechanisms involved. Thus caution should be exercised by researchers when designing a perfusion protocol for drug research.
    Cardiovascular Drugs and Therapy 07/2014; 28(5). DOI:10.1007/s10557-014-6543-8 · 3.19 Impact Factor
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    Frederic Nduhirabandi · Amanda Lochner ·
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    ABSTRACT: The ongoing worldwide obesity epidemic is paralleled by an elevated incidence of the metabolic syndrome, a disorder referred to as a clustering of metabolic abnormalities that increase the risk for cardiovascular disease and type 2 diabetes. Considered as a multifunctional molecule, the pineal gland hormone melatonin is also involved in body fat mass and energy metabolism regulation. A large body of evidence supports the beneficial effects of melatonin on the cardiovascular function in normal and pathophysiological conditions. However, melatonin’s role in cardiovascular risk factors such as obesity and other related disorders including the metabolic syndrome needs further investigations, particularly in humans. This chapter will address the effects of melatonin on the metabolic syndrome focusing on obesity and insulin-resistant conditions. Since cardiovascular disease is the primary outcome of the metabolic syndrome, the effects of melatonin on cardiovascular function will be also described focusing on normal and pathological conditions. In view of the current knowledge, we aim to reveal the potential clinical relevance of melatonin or melatonin receptor agonists in the setting of obesity-induced metabolic syndrome.
    Melatonin and Melatonergic Drugs in Clinical Practice, 2014 edited by Srinivasan V.; Brzezinski A.; Oter S.; Shillcutt S.D., 01/2014: chapter Melatonin and the metabolic syndrome: pages 6:71-95; Springer., ISBN: ISBN 978-81-322-0824-2 & 978-81-322-0825-9
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    Hans Strijdom · Nontuthuko Chamane · Amanda Lochner ·
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    ABSTRACT: Since it was identified as the elusive endothelium-derived relaxing factor (EDRF) in the 1980s, nitric oxide (NO) has rapidly gained status as one of the most important signalling molecules in the cardiovascular system. Now, 20 years later, NO is regarded by most to be a ubiquitous mediator of cardioprotection. However, due to various complex underlying cellular mechanisms, the actions of NO often seem to be contradictory. This article sheds light on some of the mechanisms that may influence the variable actions of NO in the heart. Its role in conditions of oxygen deprivation (ischaemia and hypoxia) in particular is relevant to basic scientists and clinicians alike, since the prevalence of ischaemic heart disease is on the rise (in both the developed and the developing worlds) and novel therapeutic options are in constant demand. NO is a promising candidate molecule that could find therapeutic application. For this to be achieved, a sound understanding of this simple molecule and its complex actions is required.
    Cardiovascular journal of Africa 10/2013; 20(5):303-10. · 0.79 Impact Factor
  • T B Flepisi · Amanda Lochner · Barbara Huisamen ·
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    ABSTRACT: Glycogen synthase kinase-3 (GSK-3) is a serine-threonine protein kinase, discovered as a regulator of glycogen synthase. GSK-3 may regulate the expression of SERCA-2a potentially affecting myocardial contractility. It is known to phosphorylate and inhibit IRS-1, thus disrupting insulin signalling. This study aimed to determine whether myocardial GSK-3 protein and its substrate proteins are dysregulated in obesity and insulin resistance, and whether chronic GSK-3 inhibition can prevent or reverse this. Weight matched male Wistar rats were rendered obese by hyperphagia using a special diet (DIO) for 16 weeks and compared to chow fed controls. Half of each group was treated with the GSK-3 inhibitor CHIR118637 (30 mg/kg/day) from week 12 to16 of the diet period. Biometric and biochemical parameters were measured and protein expression determined by Western blotting and specific antibodies. Ca(2+)ATPase activity was determined spectrophotometrically. Cardiomyocytes were prepared by collagenase perfusion and insulin stimulated 2-deoxy-glucose uptake determined. DIO rats were significantly heavier than controls, associated with increased intra-peritoneal fat and insulin resistance. GSK-3 inhibition did not affect weight but improved insulin resistance, also on cellular level. It had no effect on GSK-3 expression but elevated its phospho/total ratio and elevated IRS-2 expression. Obesity lowered SERCA-2a expression and activity while GSK-3 inhibition alleviated this. The phospho/total ratio of phospholamban underscored inhibition of SERCA-2a in obesity. In addition, signs of myocardial hypertrophy were observed in treated control rats. GSK-3 inhibition could not reverse all the detrimental effects of obesity but may be harmful in normal rat hearts. It regulates IRS-2, SERCA-2a and phospholamban expression but not IRS-1.
    Cardiovascular Drugs and Therapy 07/2013; 27(5). DOI:10.1007/s10557-013-6467-8 · 3.19 Impact Factor
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    Amanda Lochner · Barbara Huisamen · Frederic Nduhirabandi ·
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    ABSTRACT: Melatonin (N-acetyl-5-methoxytryptamine) has been shown by several workers to protect the heart against ischaemia/reperfusion damage. Melatonin, both in the picomolar and micromolar range, significantly reduces infarct size and improves functional recovery during reperfusion. This may be due to its free radical scavenging and anti-oxidant effects, while the melatonin receptor and its marked anti-adrenergic actions may also be involved. The latter is mediated by nitric oxide (NO), guanylyl cyclase and protein kinase C (PKC). Melatonin-induced cardioprotection is associated with activation of protein kinase B (PKB), extracellular signal-regulated kinase (ERK1/2) (the Reperfusion Injury Salvage Kinase (RISK) pathway) and signal activator and transducer 3 (STAT-3) (the Survivor Activating Factor Enhancement (SAFE) pathway) during reperfusion and inhibition of the mitochondrial permeability transition pore (MPTP). Very little is known about the effect of melatonin on myocardial substrate metabolism. Melatonin was demonstrated to be involved in the regulation of whole body glucose homeostasis via its effects on pancreatic insulin secretion and may thus indirectly affect myocardial substrate metabolism in a circadian manner.
    Frontiers in bioscience (Elite edition) 01/2013; E5(1):305-315. DOI:10.2741/E617
  • Ruduwaan Salie · Johannes A Moolman · Amanda Lochner ·
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    ABSTRACT: The aim of this study was to investigate the mechanism of beta-adrenergic preconditioning (BPC). The roles of adenosine and its receptor subtypes, the generation of oxygen free radicals (ROS) and activation of the K(ATP) channels as well as the phosphoinositide-3-kinase (PI(3)K)/PKB/Akt and extracellular signal-regulated kinase (ERK) signal transduction pathways during the triggering and mediation phases were evaluated. Using the isolated working rat heart, BPC was elicited by administration of denopamine (beta1 adrenergic receptor agonist, 10(-7) M), isoproterenol (beta1/beta2 adrenergic receptor agonist, 10(-7) M) or formoterol (beta2 adrenergic receptor agonist, 10(-9) M) for 5 min followed by 5 min washout. Index ischaemia was 35 min regional ischaemia and infarct size determined using the tetrazolium method. The role of adenosine was studied using adenosine deaminase and selective antagonists as well as the PI(3)K and ERK inhibitors, wortmannin and PD98,059, bracketing the triggering and mediating phases. Involvement of ROS, PKC, the mitochondrial K(ATP) channels, release of endogenous opioids and bradykinin was studied by administration of N-acetyl cysteine (NAC), bisindolylmaleimide, the K(ATP) channel blocker 5-hydroxydecanoate (5-HD), naloxone or HOE140, respectively. Activation of PKB/Akt and ERKp44/p42 during triggering and reperfusion was determined by Western blot. Preconditioning with all three beta-adrenergic receptor agonists caused a reduction in infarct size and an improvement in postischaemic function. BPC preconditioning with isoproterenol, denopamine or formoterol was abolished by the adenosine A3 receptor antagonist MRS1191 during both the triggering and mediation phases. Isoproterenol-induced preconditioning (beta1/beta2 PC) was attenuated by MRS1754, an adenosine A(2B) receptor antagonist, during the triggering phase and abolished during reperfusion. The mediation phase of beta1/beta2 PC was also abolished by ZM241385, an adenosine A(2A) antagonist. The free radical scavenger NAC caused a significant attenuation of cardioprotection induced by isoproterenol when administered during both trigger and mediation phases, while being effective during the trigger phase with denopamine and during reperfusion in formoterol preconditioned hearts. The mitochondrial K(ATP) channel blocker, 5-HD, was without effect on beta1/beta2 PC during both triggering and mediation phases. BPC in rat hearts is dependent on activation of the A(3) adenosine receptors by endogenously produced adenosine and production of free radicals during the triggering and mediation phases while the A(2A) and A(2B) adenosine receptors participate mainly during reperfusion. The mitochondrial K(ATP) channels do not contribute to cardioprotection at any stage. Activation of ERK and PI3K/PKB/Akt during the triggering and reperfusion phases is associated with cardioprotection.
    Archiv für Kreislaufforschung 09/2012; 107(5):281. DOI:10.1007/s00395-012-0281-5 · 5.41 Impact Factor
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    I Webster · E F Du Toit · B Huisamen · A Lochner ·
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    ABSTRACT: To investigate the effects of dietary creatine supplementation alone and in combination with exercise on basal cardiac function, susceptibility to ischaemia/reperfusion injury and mitochondrial oxidative function. There has been an increase in the use of creatine supplementation among sports enthusiasts, and by clinicians as a therapeutic agent in muscular and neurological diseases. The effects of creatine have been studied extensively in skeletal muscle, but not in the myocardium. Male Wistar rats were swim-trained for 8 weeks, 5 days per week. Hearts were excised and either freeze-clamped for biochemical analysis or perfused on the isolated heart perfusion system to assess function and ischaemia/reperfusion tolerance. Mechanical function was documented in working heart and retrograde mode. The left coronary artery was ligated and infarct size determined. Mitochondrial oxidative capacity was quantified. Aortic output recovery of hearts from the sedentary controls (CSed) was significantly higher than those from creatine-supplemented sedentary (CrSed), creatine-supplemented exercised (CrEx) as well as control exercised (CEx) groups. Ischaemic contracture of hearts from CrEx was significantly higher than that of CSed. There were no differences in infarct size and mitochondrial oxygen consumption. This study suggests that creatine supplementation has no effects on basal cardiac function but reduces myocardial tolerance to ischaemia in hearts from exercise-trained animals, by increasing the ischaemic contracture and decreasing reperfusion aortic output. Exercise training alone also significantly decreased aortic output recovery. However, the exact mechanisms for these adverse myocardial effects are unknown and need further investigation.
    Acta Physiologica 06/2012; 206(1):6-19. DOI:10.1111/j.1748-1716.2012.02463.x · 4.38 Impact Factor
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    ABSTRACT: The metabolic syndrome is recognized as a cluster of disturbances associated with obesity, type 2 diabetes and hypertension. Over the past two decades, the number of people with the metabolic syndrome has increased at an alarming rate. This increase is associated with the global epidemic of both obesity and diabetes. Cardiovascular mortality is increased among diabetics and obesity-related insulin-resistant patients, and obesity is currently recognized as independent risk factor for cardiovascular disease. We aimed to establish the effects of a short period of an altered diet on the heart using a rat model of hyperphagia-induced obesity (diet supplemented with sucrose and condensed milk for 8 weeks = DIO) compared to age-matched controls. Isolated, perfused hearts were subjected to global or regional ischaemia/reperfusion. Function on reperfusion was recorded and infarct size determined. A plasma lipid profile was established via HPLC-based methods and proteins involved in metabolic signalling determined either by western blotting or RT-PCR. 8 weeks of diet resulted in whole-body but not myocardial insulin resistance, increased plasma triglyceride and phospholipid levels as well as increased lipid peroxidation. Despite the similar baseline function, hearts from DIO animals showed significantly poorer postischaemic recovery than controls (41.9 % RPP recovery vs 57.9 %, P < 0.05, n = 7-11/group) but surprisingly, smaller infarct size (24.95 ± 1.97 vs 47.26 ± 4.05 % of the area at risk, P < 0.005, n = 8/group). Basal phosphorylation of PKB/Akt was elevated but IRS-1 and SERCA-2 expression severely downregulated. In conclusion, after only 8 weeks of a slight change in diet, the rat heart shows signs of metabolic remodelling. Some of these changes may be protective but others may be detrimental and eventually lead to maladaptation.
    Molecular and Cellular Biochemistry 05/2012; 368(1-2):37-45. DOI:10.1007/s11010-012-1340-9 · 2.39 Impact Factor
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    Mashudu Mudau · Amanda Genis · Amanda Lochner · Hans Strijdom ·
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    ABSTRACT: Since the discovery in the 1980s that nitric oxide (NO) is in fact the elusive endothelium-derived relaxing factor, it has become evident that NO is not only a major cardiovascular signalling molecule, but that changes in its bioavailability are crucial in determining whether atherosclerosis will develop or not. Sustained high levels of harmful circulating stimuli associated with cardiovascular risk factors such as diabetes mellitus elicit responses in endothelial cells that appear sequentially, namely endothelial cell activation and endothelial dysfunction (ED). ED, characterised by reduced NO bioavailability, is now recognised by many as an early, reversible precursor of atherosclerosis. The pathogenesis of ED is multifactorial; however, oxidative stress appears to be the common underlying cellular mechanism in the ensuing loss of vaso-active, inflammatory, haemostatic and redox homeostasis in the body’s vascular system. The role of ED as a pathophysiological link between early endothelial cell changes associated with cardiovascular risk factors and the development of ischaemic heart disease is of importance to basic scientists and clinicians alike.
    05/2012; 23(4):222-31. DOI:10.5830/CVJA-2011-068
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    ABSTRACT: Melatonin plays an important role in body weight regulation and glucose homeostasis. However its metabolic actions on the heart remain unknown. The present study examined the effects of short-term melatonin (Mel) administration on glucose uptake stimulated with or without insulin (Ins) in isolated adult cardiomyocytes. Hearts were isolated from 3 groups of male rats: normal control (NC), control diet (C), and obese (D) groups (high-calorie diet: 65% carbohydrates, 19% protein and 16% fat). Hearts from the latter two groups were studied after 16 to 20 weeks of feeding and compared with those from normal control rats weighing 200-220 g. Rats were weighed, blood collected and cardiomyocytes were isolated. Cardiomyocytes were incubated with Mel (10 to 100 nM), Luzindole (Luz) (5 uM) or Ins (1 nM) and glucose uptake was initiated by addition of 2-deoxy-D-[3H] glucose (1.8 uM) and incubated for 30 min. The high-calorie diet caused significant increases in body weight (p<0.05), visceral adiposity (p<0.01), HOMA index and cardiac hypertrophy (p<0.05). While cardiomyocytes from both groups (16-19 weeks) had no significant difference in Ins stimulation, after 20- 23 weeks Ins stimulation was reduced in the D group compared to their age matched control group [fold stimulation: 1.75±0.09 (C) versus 1.45±0.1 (D), p<0.05]. In all groups, melatonin alone did not affect the glucose uptake compared to basal levels. In cardiomyocytes isolated from NC rats, the presence of melatonin enhanced Ins stimulated glucose uptake [fold stimulation: 2.48±0.2 (Ins), 3.36±0.4 (Ins+Mel); p<0.05). After 16-19 weeks, melatonin enhanced Ins stimulation as a trend [p<0.052 (C), p<0.06 (D)], however, after 20-23 weeks, this trend disappeared in both groups (p>0.5). Luz with or without Ins, in the presence of Mel, attenuated the glucose uptake. Acute melatonin administration may enhance insulin action in normal but not in insulin resistant isolated adult cardiomyocytes. In addition, short-term melatonin treatment does not stimulate glucose metabolism in the heart, the results suggest that melatonin receptors may play a role in its effect on glucose uptake Key words: Melatonin, cardiomyocytes, glucose uptake. Published abstract http://www.academicjournals.org/journal/SRE/article-full-text-pdf/C66E8FF33765.
    Scientific research and essays 04/2012; 7(58):18. · 0.45 Impact Factor
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    Gerald Maarman · Erna Marais · Amanda Lochner · Eugene F du Toit ·
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    ABSTRACT: By increasing circulating free fatty acids and the rate of fatty acid oxidation, obesity decreases glucose oxidation and myocardial tolerance to ischemia. Partial inhibition of fatty acid oxidation may improve myocardial tolerance to ischemia/reperfusion (I/R) in obesity. We assessed the effects of oxfenicine treatment on post ischemic cardiac function and myocardial infarct size in obese rats. Male Wistar rats were fed a control diet or a high calorie diet which resulted in diet induced obesity (DIO) for 16 weeks. Oxfenicine (200 mg/kg/day) was administered to control and DIO rats for the last 8 weeks. Isolated hearts were perfused and infarct size and post ischemic cardiac function was assessed after regional or global ischemia and reperfusion. Cardiac mitochondrial function was assessed and myocardial expression and activity of CPT-1 (carnitine palmitoyl transferase-1) and IRS-1 (insulin receptor substrate-1) was assessed using Western blot analysis. In the DIO rats, chronic oxfenicine treatment improved post ischemic cardiac function and reduced myocardial infarct size after I/R but had no effect on the cardiac mitochondrial respiration. Chronic oxfenicine treatment worsened post ischemic cardiac function, myocardial infarct size and basal mitochondrial respiration in control rat hearts. Basal respiratory control index (RCI) values, state 2 and state 4 respiration rates and ADP phosphorylation rates were compromised by oxfenicine treatment. Chronic oxfenicine treatment improved myocardial tolerance to I/R in the obese rat hearts but decreased myocardial tolerance to I/R in control rat hearts. This decreased tolerance to ischemia of oxfenicine treated controls was associated with adverse changes in basal and reoxygenation mitochondrial function. These changes were absent in oxfenicine treated hearts from obese rats.
    Cardiovascular Drugs and Therapy 03/2012; 26(3):205-16. DOI:10.1007/s10557-012-6377-1 · 3.19 Impact Factor
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    F Nduhirabandi · E.F. du Toit · A Lochner ·
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    ABSTRACT: The metabolic syndrome (MetS) is a cluster of metabolic abnormalities associated with increased risk for cardiovascular diseases. Apart from its powerful antioxidant properties, the pineal gland hormone melatonin has recently attracted the interest of various investigators as a multifunctional molecule. Melatonin has been shown to have beneficial effects in cardiovascular disorders including ischaemic heart disease and hypertension. However, its role in cardiovascular risk factors including obesity and other related metabolic abnormalities is not yet established, particularly in humans. New emerging data show that melatonin may play an important role in body weight regulation and energy metabolism. This review will address the role of melatonin in the MetS focusing on its effects in obesity, insulin resistance and leptin resistance. The overall findings suggest that melatonin should be exploited as a therapeutic tool to prevent or reverse the harmful effects of obesity and its related metabolic disorders.
    Acta Physiologica 01/2012; 205(2):209-23. DOI:10.1111/j.1748-1716.2012.02410.x · 4.38 Impact Factor
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    ABSTRACT: PKCε is central to cardioprotection. Sub-proteome analysis demonstrated co-localization of activated cardiac PKCε (aPKCε) with metabolic, mitochondrial, and cardioprotective modulators like hypoxia-inducible factor 1α (HIF-1α). aPKCε relocates to the mitochondrion, inactivating glycogen synthase kinase 3β (GSK3β) to modulate glycogen metabolism, hypertrophy and HIF-1α. However, there is no established mechanistic link between PKCε, p-GSK3β and HIF1-α. Here we hypothesized that cardiac-restricted aPKCε improves mitochondrial response to hypobaric hypoxia by altered substrate fuel selection via a GSK3β/HIF-1α-dependent mechanism. aPKCε and wild-type (WT) mice were exposed to 14 days of hypobaric hypoxia (45 kPa, 11% O(2)) and cardiac metabolism, functional parameters, p-GSK3β/HIF-1α expression, mitochondrial function and ultrastructure analyzed versus normoxic controls. Mitochondrial ADP-dependent respiration, ATP production and membrane potential were attenuated in hypoxic WT but maintained in hypoxic aPKCε mitochondria (P < 0.005, n = 8). Electron microscopy revealed a hypoxia-associated increase in mitochondrial number with ultrastructural disarray in WT versus aPKCε hearts. Concordantly, left ventricular work was diminished in hypoxic WT but not aPKCε mice (glucose only perfusions). However, addition of palmitate abrogated this (P < 0.05 vs. WT). aPKCε hearts displayed increased glucose utilization at baseline and with hypoxia. In parallel, p-GSK3β and HIF1-α peptide levels were increased in hypoxic aPKCε hearts versus WT. Our study demonstrates that modest, sustained PKCε activation blunts cardiac pathophysiologic responses usually observed in response to chronic hypoxia. Moreover, we propose that preferential glucose utilization by PKCε hearts is orchestrated by a p-GSK3β/HIF-1α-mediated mechanism, playing a crucial role to sustain contractile function in response to chronic hypobaric hypoxia.
    Journal of Cellular Physiology 09/2011; 226(9):2457-68. DOI:10.1002/jcp.22592 · 3.84 Impact Factor
  • B Loos · A Lochner · A-M Engelbrecht ·
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    ABSTRACT: Autophagy is a conserved catabolic process for long-lived proteins and organelles and is primarily responsible for nonspecific degradation of redundant or faulty cell components. Although autophagy has been described as the cell's major adaptive strategy in response to metabolic challenges, its influence on the cell's energy profile is poorly understood. In the myocardium, autophagy is active at basal levels and is crucial for maintaining its contractile function. Defects in the autophagic machinery cause cardiac dysfunction and heart failure. In this paper we propose that (1) autophagy contributes significantly to the metabolic balance sheet of the heart. (2) Increased autophagy contributes to an improved myocardial energy profile through changing the cardiac substrate preference. (3) Substrates generated through autophagy give rise to an alternative for ATP production with an oxygen-sparing effect. These elements identify autophagy in a new context of myocardial metabolic interregulation, which we discuss in the settings of myocardial infarction, heart failure and the diabetic heart. It is hoped that the hypothesis presented can lead to new insights aimed at exploiting autophagy to improve existing metabolic-based therapy in heart disease.
    Medical Hypotheses 07/2011; 77(1):52-7. DOI:10.1016/j.mehy.2011.03.021 · 1.07 Impact Factor

Publication Stats

3k Citations
764.12 Total Impact Points


  • 1969-2015
    • Stellenbosch University
      • • Department of Biomedical Sciences
      • • Division of Medical Physiology
      • • Department of Medicine
      • • Division of General Internal Medicine
      Stellenbosch, Western Cape, South Africa
  • 1975-2008
    • University of Cape Town
      • Department of Medicine
      Kaapstad, Western Cape, South Africa
  • 2001
    • St. Boniface Hospital Research
      • Institute of Cardiovascular Sciences
      Winnipeg, Manitoba, Canada
  • 1993
    • Hadassah Medical Center
      • Department of Pathology
      Yerushalayim, Jerusalem, Israel
  • 1988
    • University of the Free State
      • Department of Chemical Pathology
      Bloemfontein, Free State, South Africa