Dietary methionine restriction attenuates renal ischaemia/reperfusion-induced myocardial injury by activating the CSE/H2S/ERS pathway in diabetic mice.

Methionine restrictive diet may alleviate ischaemia/reperfusion (I/R)-induced myocardial injury, but its underlying mechanism remains unclear. HE staining was performed to evaluate the myocardial injury caused by I/R and the effect of methionine-restricted diet (MRD) in I/R mice. IHC and Western blot were carried out to analyse the expression of CSE, CHOP and active caspase3 in I/R mice and hypoxia/reoxygenation (H/R) cells. TUNEL assay and flow cytometry were used to assess the apoptotic status of I/R mice and H/R cells. MTT was performed to analyse the proliferation of H/R cells. H2S assay was used to evaluate the concentration of H2S in the myocardial tissues and peripheral blood of I/R mice. I/R-induced mediated myocardial injury and apoptosis were partially reversed by methionine-restricted diet (MRD) via the down-regulation of CSE expression and up-regulation of CHOP and active caspase3 expression. The decreased H2S concentration in myocardial tissues and peripheral blood of I/R mice was increased by MRD. Accordingly, in a cellular model of I/R injury established with H9C2 cells, cell proliferation was inhibited, cell apoptosis was increased, and the expressions of CSE, CHOP and active caspase3 were dysregulated, whereas NaHS treatment alleviated the effect of I/R injury in H9C2 cells in a dose-dependent manner. This study provided a deep insight into the mechanism underlying the role of MRD in I/R-induced myocardial injury.

Dietary Calanus oil recovers metabolic flexibility and rescues postischemic cardiac function in obese female mice.

The aim of this study was to find out whether dietary supplementation with Calanus oil (a novel marine oil) or infusion of exenatide (an incretin mimetic) could counteract obesity-induced alterations in myocardial metabolism and improve postischemic recovery of left ventricular (LV) function. Female C57bl/6J mice received high-fat diet (HFD, 45% energy from fat) for 12 wk followed by 8-wk feeding with nonsupplemented HFD, HFD supplemented with 2% Calanus oil, or HFD plus exenatide infusion (10 µg·kg-1·day-1). A lean control group was included, receiving normal chow throughout the whole period. Fatty acid and glucose oxidation was measured in ex vivo perfused hearts during baseline conditions, while LV function was assessed with an intraventricular fluid-filled balloon before and after 20 min of global ischemia. HFD-fed mice receiving Calanus oil or exenatide showed less intra-abdominal fat deposition than mice receiving nonsupplemented HFD. Both treatments prevented the HFD-induced decline in myocardial glucose oxidation. Somewhat surprising, recovery of LV function was apparently better in hearts from mice fed nonsupplemented HFD relative to hearts from mice fed normal chow. More importantly however, postischemic recovery of hearts from mice receiving HFD with Calanus oil was superior to that of mice receiving nonsupplemented HFD and mice receiving HFD with exenatide, as expressed by better pressure development, contractility, and relaxation properties. In summary, dietary Calanus oil and administration of exenatide counteracted obesity-induced derangements of myocardial metabolism. Calanus oil also protected the heart from ischemia, which could have implications for the prevention of obesity-related cardiac disease. NEW & NOTEWORTHY This article describes for the first time that dietary supplementation with a low amount (2%) of a novel marine oil (Calanus oil) in mice is able to prevent the overreliance of fatty acid oxidation for energy production during obesity. The same effect was observed with infusion of the incretin mimetic, exanatide. The improvement in myocardial metabolism in Calanus oil-treated mice was accompanied by a significantly better recovery of cardiac performance following ischemia-reperfusion. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/dietary-calanus-oil-energy-metabolism-and-cardiac-function/ .

Aged (Black) versus Raw Garlic against Ischemia/Reperfusion-Induced Cardiac Complications.

Recent evidence from studies suggests that aged black garlic also has an effect on health. The major aim of the present study is to compare the effect of raw and aged black garlic on postischemic cardiac recovery. Male Sprague Dawley rats were randomly divided into three groups. Animals of the first group were fed with raw garlic, animals of the second group received aged black garlic, while the third group served as vehicle-treated controls. Upon conclusion of the treatment, isolated hearts were undertaken to ischemia/reperfusion. Heart function and infarct size were measured and the level of HO-1 and iNOS were studied. Superior postischemic cardiac function and reduced infarct size in both garlic treated groups compared to the drug-free control group, indicated cardioprotective effects. However, no significant differences between the garlic treated groups were observed. Western blot analysis revealed that raw garlic enhanced the level of HO-1 before ischemia, while in ischemic samples, we found elevated HO-1 expression in both garlic treated groups. The level of iNOS was the same before ischemia in all groups, however, a markedly reduced iNOS level in ischemic/reperfused hearts originating from control and raw garlic treated animals was observed. Samples from aged black garlic treated animals demonstrated that the level of iNOS was not significantly reduced after ischemia/reperfusion. Taken together these results indicate that not only raw but also aged black garlic possess a cardioprotective effect.

Molecular Pathways Involved in the Amelioration of Myocardial Injury in Diabetic Rats by Kaempferol.

There is growing evidence that chronic hyperglycemia leads to the formation of advanced glycation end products (AGEs) which exerts its effect via interaction with the receptor for advanced glycation end products (RAGE). AGE-RAGE activation results in oxidative stress and inflammation. It is well known that this mechanism is involved in the pathogenesis of cardiovascular disease in diabetes. Kaempferol, a dietary flavonoid, is known to possess antioxidant, anti-apoptotic, and anti-inflammatory activities. However, little is known about the effect of kaempferol on myocardial ischemia-reperfusion (IR) injury in diabetic rats. Diabetes was induced in male albino Wistar rats using streptozotocin (70 mg/kg; i.p.), and rats with glucose level >250 mg/dL were considered as diabetic. Diabetic rats were treated with vehicle (2 mL/kg; i.p.) and kaempferol (20 mg/kg; i.p.) daily for a period of 28 days and on the 28th day, ischemia was produced by one-stage ligation of the left anterior descending coronary artery for 45 min followed by reperfusion for 60 min. After completion of surgery, rats were sacrificed and the heart tissue was processed for biochemical, morphological, and molecular studies. Kaempferol pretreatment significantly reduced hyperglycemia, maintained hemodynamic function, suppressed AGE-RAGE axis activation, normalized oxidative stress, and preserved morphological alterations. In addition, there was decreased level of inflammatory markers (tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and NF-κB), inhibition of active c-Jun N-terminal kinase (JNK) and p38 proteins, and activation of Extracellular signal regulated kinase 1/2 (ERK1/2) a prosurvival kinase. Furthermore, it also attenuated apoptosis by reducing the expression of pro-apoptotic proteins (Bax and Caspase-3), Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive cells, and increasing the level of anti-apoptotic protein (Bcl-2). In conclusion, kaempferol attenuated myocardial ischemia-reperfusion injury in diabetic rats by reducing AGE-RAGE/ mitogen activated protein kinase (MAPK) induced oxidative stress and inflammation.

Indispensable role of endothelial nitric oxide synthase in caloric restriction-induced cardioprotection against ischemia-reperfusion injury.

Caloric restriction (CR) confers cardioprotection against ischemia-reperfusion injury (IRI). We previously found that treatment with N(G)-nitro-l-arginine methyl ester completely abrogates CR-induced cardioprotection and increases nuclear sirtuin 1 (Sirt1) expression. However, it remains unclear whether endothelial nitric oxide (NO) synthase (eNOS) plays a role in CR-induced cardioprotection and Sirt1 activation. We subjected eNOS-deficient (eNOS(-/-)) mice to either 3-mo ad libitum (AL) feeding or CR (-40%). Isolated perfused hearts were subjected to 25-min global ischemia followed by 60-min reperfusion. The degree of myocardial IRI in AL-fed eNOS(-/-) mice was more severe than that in AL-fed wild-type mice. Furthermore, CR did not exert cardioprotection in eNOS(-/-) mice. eNOS(-/-) mice exhibited elevated blood pressure and left ventricular hypertrophy compared with wild-type mice, although they underwent CR. Although nuclear Sir1 content was increased, the increases in cardiac Sirt1 activity with CR was absent in eNOS(-/-) mice. In eNOS(-/-) mice treated with hydralazine, blood pressure and left ventricular weight became comparable with CR-treated wild-type mice. However, CR-induced cardioprotection was not observed. Resveratrol enhanced cardiac Sirt1 activity but failed to mimic CR-induced cardioprotection in eNOS(-/-) mice. Finally, combination therapy with resveratrol and hydralazine attenuated myocardial IRI and reduced infarct size in eNOS(-/-) mice, and their effects were comparable with those observed in CR-treated wild-type mice. These results demonstrate the essential roles of eNOS in the development of CR-induced cardioprotection and Sirt1 activation during CR. The combination of a relatively low dose of resveratrol with an adequate vasodilator therapy might be useful for managing patients with endothelial dysfunction associated with impaired NO bioavailability.

Acute consumption of a high-fat diet prior to ischemia-reperfusion results in cardioprotection through NF-κB-dependent regulation of autophagic pathways.

Previous studies have demonstrated improvement of cardiac function occurs with acute consumption of a high-fat diet (HFD) after myocardial infarction (MI). However, no data exist addressing the effects of acute HFD upon the extent of injury after MI. This study investigates the hypothesis that short-term HFD, prior to infarction, protects the heart against ischemia-reperfusion (I/R) injury through NF-κB-dependent regulation of cell death pathways in the heart. Data show that an acute HFD initiates cardioprotection against MI (>50% reduction in infarct size normalized to risk region) after 24 h to 2 wk of HFD, but protection is completely absent after 6 wk of HFD, when mice are reported to develop pathophysiology related to the diet. Furthermore, cardioprotection after 24 h of HFD persists after an additional 24 h of normal chow feeding and was found to be dependent upon NF-κB activation in cardiomyocytes. This study also indicates that short-term HFD activates autophagic processes (beclin-1, LC-3) preischemia, as seen in other protective stimuli. Increases in beclin-1 and LC-3 were found to be NF-κB-dependent, and administration of chloroquine, an inhibitor of autophagy, abrogated cardioprotection. Our results support that acute high-fat feeding mediates cardioprotection against I/R injury associated with a NF-κB-dependent increase in autophagy and reduced apoptosis, as has been found for ischemic preconditioning.

High carbohydrate and high fat diets protect the heart against ischaemia/reperfusion injury.

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.

Nicotinamide-rich diet protects the heart against ischaemia-reperfusion in mice: a crucial role for cardiac SUR2A.

It is a consensus view that a strategy to increase heart resistance to ischaemia-reperfusion is a warranted. Here, based on our previous study, we have hypothesized that a nicotinamide-rich diet could increase myocardial resistance to ischaemia-reperfusion. Therefore, the purpose of this study was to determine whether nicotinamide-rich diet would increase heart resistance to ischaemia-reperfusion and what is the underlying mechanism. Experiments have been done on mice on control and nicotinamide-rich diet (mice were a week on nicotinamide-rich diet) as well as on transgenic mice overexpressing SUR2A (SUR2A mice), a regulatory subunit of cardioprotective ATP-sensitive K(+) (K(ATP)) channels and their littermate controls (WT). The levels of mRNA in heart tissue were measured by real-time RT-PCR, whole heart and single cell resistance to ischaemia-reperfusion and severe hypoxia was measured by TTC staining and laser confocal microscopy, respectively. Nicotinamide-rich diet significantly decreased the size of myocardial infarction induced by ischaemia-reperfusion (from 42.5+/-4.6% of the area at risk zone in mice on control diet to 26.8+/-1.8% in mice on nicotinamide-rich diet, n=6-12, P=0.031). The cardioprotective effect of nicotinamide-rich diet was associated with 11.46+/-1.22 times (n=6) increased mRNA levels of SUR2A in the heart. HMR1098, a selective inhibitor of the sarcolemmal K(ATP) channels opening, abolished cardioprotection afforded by nicotinamide-rich diet. Transgenic mice with a sole increase in SUR2A expression had also increased cardiac resistance to ischaemia-reperfusion. We conclude that nicotinamide-rich diet up-regulate SUR2A and increases heart resistance to ischaemia-reperfusion.

Low carbohydrate ketogenic diet enhances cardiac tolerance to global ischaemia.

UNLABELLED: The cardio-protective effects of a low carbohydrate ketogenic diet following global ischaemic injury as compared to rats fed a normal and high carbohydrate diet for a period of 19 weeks, were investigated. The reperfusion recovery of coronary flow was highly significant in the low carbohydrate ketogenic diet group. Although the initial reperfusion recovery of the pressure developed in the left ventricle, Pmax was similar in all groups, after 15 minutes, the momentum for faster recovery was maintained in the low carbohydrate ketogenic diet group. Ultrastructural observations of the cardiac muscles have shown that there was a decrease in the number of mitochondria in rats fed a high carbohydrate diet and an increase in the number of mitochondria in those fed a low carbohydrate ketogenic diet as compared to the normal diet group. This study demonstrates that a low carbohydrate ketogenic diet is cardio-protective functionally. INTRODUCTION: Ischaemia and reperfusion lead to cell death. These pathways are regulated and hence are subjected to therapeutic intervention. Previously, we have shown that a low carbohydrate ketogenic diet (LCKD) reduces the risk factors for heart disease in obese patients. This study is aimed at understanding the cardio-protective effects of LCKD following global ischaemic injury in rats. MATERIALS AND METHODS: Rats weighing 190-250 g were divided into normal diet (ND), LCKD and high carbohydrate diet (HCD) groups consisting of six animals in each group. Specific diets were given to each group for a period of 19 weeks. Changes in body weight, ultrastructure of the cardiac muscles and the cardio-protective effects of the LCKD group as compared to the ND and HCD groups were investigated in rats following global ischaemic injury. RESULTS: Electron microscopic studies have shown that there was a decrease in the number of mitochondria in rats fed a high carbohydrate diet and an increase in the number of mitochondria in those fed a low carbohydrate ketogenic diet as compared to the normal diet group. Rats on LCKD had a remarkable tolerance to ischaemia and a faster recovery of cardiac function following reperfusion. The initial reperfusion recovery of the pressure developed in the left ventricle, Pmax was similar in all groups. However, after 15 minutes, the momentum for faster recovery was significantly maintained in the LCKD group (P < 0.05). The reperfusion recovery of coronary flow was highly significant (P < 0.05) in the LCKD regime. The increase in left ventricle end diastolic pressure, coronary vascular resistance and the changes in body weight were not significant between the experimental groups. DISCUSSION AND CONCLUSION: This is a unique study showing ultrastructural variation in cardiac muscle in relation to cardio-protective function in rats fed a low carbohydrate ketogenic diet. This study suggests that the LCKD is cardio-protective functionally. The underlying mechanism of the cardio-protective effect of an LCKD needs to be elucidated.

Dietary red palm oil improves reperfusion cardiac function in the isolated perfused rat heart of animals fed a high cholesterol diet.

It has been shown that dietary red palm oil (RPO) supplementation improved reperfusion function. However, no exact protective cellular mechanisms have been established. Our aim was to search for a possible cellular mechanism and a role for fatty acids. Rats were fed a standard rat chow, plus cholesterol and/or RPO-supplementation for 6 weeks. Functional recovery, myocardial phospholipid and cAMP/cGMP levels were determined in isolated rat hearts subjected to 25 min of normothermic total global ischaemia. Dietary RPO in the presence of cholesterol improved aortic output (AO) recovery (63.2+/-3.06%, P<0.05) vs. cholesterol only (36.5+/-6.2%). The improved functional recovery in hearts supplemented with RPO vs. control was preceded by an elevation in the cGMP levels early in ischaemia (RPO 132.9+/-36.3% vs. control 42.7+/-24.4%, P<0.05). Concurrently, cAMP levels decreased (RPO -8.3+/-6.9% vs. control 19.9+/-7.7%, P<0.05). Our data suggest that dietary RPO-supplementation improved reperfusion AO through mechanisms that may include activation of the NO-cGMP and inhibition of the cAMP pathway.

Hyperhomocysteinemia abrogates fasting-induced cardioprotection against ischemia/reperfusion by limiting bioavailability of hydrogen sulfide anions.

UNLABELLED: Elevated plasma homocysteine levels are considered an independent risk factor for cardiovascular diseases. Experimental evidence has shown that hydrogen sulfide anion (HS(-)) protects the myocardium from ischemia/reperfusion (IR) injury. Both homocysteine levels and endogenous HS(-) production are mainly regulated by two transsulfuration enzymes, cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CTH). We hypothesized that the transsulfuration pathway plays essential roles in the development of cardiac adaptive responses against ischemia, and investigated the roles of homocysteine, HS(-), and transsulfuration enzymes in fasting-induced cardioprotection against IR injury utilizing hyperhomocysteinemic Cbs (-/-) and Cth (-/-) mice. Langendorff-perfused hearts were subjected to 25-min global ischemia, followed by 60-min reperfusion. Two-day fasting ameliorated left ventricular dysfunction after reperfusion via propargylglycine- and glibenclamide-sensitive pathways in wild-type mice but not in Cbs (-/-) or Cth (-/-) mice, although fasting induced cardiac expression of several Nrf2 target antioxidant genes in both wild-type and Cth (-/-) mice. Intraperitoneal administration of sodium hydrosulfide (a HS(-) donor) at 24 h prior to IR improved myocardial recovery in wild-type mice but not in Cth (-/-) or high-methionine-diet-fed (thus intermediately hyperhomocysteinemic) wild-type mice. Quantitative analysis of reactive sulfur species using monobromobimane derivatization methods revealed that homocysteine efficiently captures HS(-) to form homocysteine persulfide in the hearts as well as in the in vitro reactions. Here we propose a novel molecular and pathophysiological basis for hyperhomocysteinemia; excessive circulatory homocysteine interferes with HS(-)-related cardioprotection against IR injury by capturing endogenous HS(-) to form homocysteine persulfide. KEY MESSAGE: Two-day fasting of mice ameliorates ischemia/reperfusion injury in Langendorff hearts. H2S-producing enzymes, CBS and CTH, are essential in fasting-induced cardioprotection. Administration of a H2S donor (NaHS) confers cardioprotection against IR injury. NaHS effects are absent in Cth (-/-), Cbs (-/-), and dietary hyperhomocysteinemic mice. Homocysteine captures cardioprotective HS(-) to form homocysteine persulfide.

Impact of specific substrate supply on efficiency of cardiac function: an update.

Investigations of the mechanisms that modulate energy generation during states of altered cardiac metabolism have reached a point where there is both need and demand for novel approaches. The evidence discussed here strongly suggests that both energy generation and utilization in these states may be effectively strengthened by nutritional manipulation. Compared with standard treatments for ischemia/reperfusion injury or heart failure, nutritional therapy may present an important and less toxic approach by affecting the mechanisms of energy utilization during compromised cardiac states. We provide not only a conceptual framework for further experimental studies of myocardial metabolism during ischemia and reperfusion injury but also a basis for developing clinically applicable nutrients designed to improve deranged cardiac function. The use of traditional energy substrates, in conjunction with those that may be conditionally important during compromised cardiac states, potentially offers a useful therapeutic modality in the treatment of the cardiac patient.

Ischemic preconditioning: the role of mitochondria and aging.

Aging represents a triple threat for myocardial infarction (MI). Not only does the incidence of MI increase with age, but the heart becomes more susceptible to MI induced damage and protective interventions such as ischemic preconditioning (IPC) become less effective. Therefore, any rational therapeutic strategy must be built around the ability to combat the detrimental effects of ischemia in aged individuals. To accomplish this, we need to develop a better understanding of how ischemic damage, protection, and aging are linked. In this regard, mitochondria have emerged as a common theme. First, mitochondria contribute to cell damage during ischemia-reperfusion (IR) and are central to cell death. Second, the protective signaling pathways activated by IPC converge on mitochondria, and the opening of mitochondrial ion channels alone is sufficient to elicit protection. Finally, mitochondria clearly influence the aging process, and specific defects in mitochondrial activity are associated with age-related functional decline. This review will summarize the effects of aging on myocardial IR injury and discuss relevant and emerging strategies to protect against MI with an emphasis on mitochondrial function.

Dietary red palm oil supplementation protects against the consequences of global ischemia in the isolated perfused rat heart.

Activation of the NO-cGMP pathway is associated with myocardial protection against ischemia. During ischemia, function of this pathway is disturbed. Little is known about the effects of supplements such as Red Palm Oil (RPO) on the myocardial NO- cGMP- signalling pathway. RPO consists of saturated (SFAs), mono-unsaturated (MUFAs) and polyunsaturated (PUFAs) fatty acids and is an antioxidant rich in natural B-carotene and vitamin E (tocopherols and tocotrienols). This study determined whether dietary RPO-supplementation protects against the consequences of ischemia and identified a possible mechanism for this protection. Long-Evans rats were fed a control diet or control diet plus 7 g RPO per kg diet for six weeks. Hearts were excised and mounted on a working heart perfusion apparatus. Cardiac function was measured before and after hearts were subjected to 25 minutes of global ischemia. Left ventricular systolic (LVSP) and diastolic pressure (LVDP), coronary flow (CF), heart rate (HR) and aortic output (AO) were measured. To assess NO-cGMP pathway activity, hearts subjected to the same conditions, were freeze-clamped and analysed for tissue cAMP and cGMP levels using a RIA method. Furthermore, composition of myocardial phospholipid fatty acids by gas chromatography and blood samples were collected for serum lipid determinations. The percentage aortic output recovery of hearts supplemented with RPO was 72.9 +/-3.43% vs 55.4 +/-2.48% for controls (P< 0.05). Ten minutes into ischemia the cGMP levels of the RPO-supplementation group were significantly higher than the control group (26.5+/-2.78 pmol/g vs 10.1+/-1.78 pmol/g. Total myocardial PUFA content in hearts supplemented with RPO increased from 54.45+/-1.11% before ischemia to 59.03 +/- 0.30% after ischemia P<0.05). Results demonstrated that RPO-supplementation protected hearts against the consequences of ischemia/reperfusion injury. These findings suggest that dietary RPO protects via the NO-cGMP pathway and/or changes in PUFA composition during ischemia/reperfusion.

Cardiac Ca(2+) regulation and the tuna fish sandwich.

Following myocardial ischemia and reperfusion, there is a risk of fatal arrhythmias that result from damage to cellular Ca(2+) homeostasis mechanisms. n-3 Polyunsaturated fatty acids seem to protect against these arrhythmias by mechanisms involving the sarcoplasmic reticulum and the sarcolemma.

Effect of dietary sunflower seed oil on the severity of reperfusion-induced arrhythmias in anesthetized rats.

Myocardial ischemia followed by reperfusion was produced in artificially respirated, open-chest rats. Coronary artery ligation for 6 min rarely evoked arrhythmias; however, reperfusion after this period rapidly produced severe dysrhythmias in all control animals. Reperfusion after 12 min of ischemia produced less frequent dysrhythmias than after coronary occlusion for 6 min. Feeding of a linoleic acid-rich diet, applying 12% sunflower seed oil in rat food pellet for 4 weeks, decreased the incidence of reperfusion-induced ventricular fibrillation both after 6 min (2/15 vs. 7/11) and 12 min (0/11 vs. 2/8) of myocardial ischemia and the incidence of other arrhythmias was also decreased. The number of animals developing no arrhythmias during reperfusion was increased (8/15 after 6 min of ischemia, 4/11 after 12 min of ischemia vs. 0/11 and 0/8 in controls, respectively). Our results indicate that increased dietary consumption of linoleic acid decreased the occurrence of life-threatening arrhythmias both during the acute phase of myocardial ischemia and during reperfusion in anesthetized rats.

Manipulation of myocardial alpha-tocopherol levels fails to affect reperfusion arrhythmias or functional recovery following ischemic challenge in the rat heart.

Antioxidants that act as free radical scavengers have the potential to inhibit lipid peroxidation. It has previously been proposed that a relationship exists between free radicals, lipid peroxidation and reperfusion-induced arrhythmias. We have therefore examined the ability of the lipid-soluble antioxidant, alpha-tocopherol, to decrease the incidence of reperfusion-induced arrhythmias. We have shown that the myocardial alpha-tocopherol content can be significantly increased from its control value of 65.3 +/- 5.6 nmoles/g wet wt of heart to 115.0 +/- 15.6 nmoles/g wet wt of heart (p less than 0.01) by chronic intraperitoneal pretreatment and that it can be decreased, to 21.1 +/- 3.7 nmoles/g wet wt of heart (p less than 0.01), by chronic dietary manipulation. Rat hearts isolated from either of these groups, or from placebo-treated control animals, were subjected to 5 or 10 min coronary artery occlusion and were subsequently reperfused; there were no significant differences between the incidence and duration of VF and VT or the incidence and number of VPBs in these three groups. The effect of alpha-tocopherol manipulation on metabolic and functional recovery of working hearts subjected to 20 min global ischemia was subsequently examined and no significant changes were observed. Cardiac output recovered to 82 +/- 4, 81 +/- 6 and 76 +/- 5% of its preischemic value in the control, enriched and depleted groups, respectively. In conclusion, myocardial alpha-tocopherol content appears to bear no relation to the severity of reperfusion-induced arrhythmias or to the resistance of the heart to ischemic injury.

Prevention of cardiac arrhythmia by dietary (n-3) polyunsaturated fatty acids and their mechanism of action.

The role of marine fish oil (n-3) polyunsaturated fatty acids in the prevention of fatal ventricular arrhythmia has been established in experimental animals. Prevention of arrhythmias arising at the onset of ischemia and reperfusion is important because if untreated, they result in sudden cardiac death. Animals supplemented with fish oils in their diet developed little or no ventricular fibrillation after ischemia was induced. Similar effects have also been observed in cultured neonatal cardiomyocytes. Several mechanisms have been proposed and studied to explain the antiarrhythmic effects of fish oil polyunsaturated fatty acids, but to date, no definite mechanism has been validated. The sequence of action of these mechanisms and whether more than one mechanism is involved is also not clear. Some of the mechanisms suggested to explain the antiarrhythmic action of fish oils include the incorporation and modification of cell membrane structure by (n-3) polyunsaturated fatty acids, their direct effect on calcium channels and cardiomyocytes and their role in eicosanoid metabolism. Other mechanisms that are currently being investigated include the role of (n-3) polyunsaturated fatty acids in cell signalling mediated through phosphoinositides and their effect on various enzymes and receptors. This article reviews these mechanisms and the antiarrhythmic studies using (n-3) polyunsaturated fatty acids.

Effect of combined supplementation with vitamin E and alpha-lipoic acid on myocardial performance during in vivo ischaemia-reperfusion.

Reactive oxygen species (ROS) contribute significantly to myocardial ischaemia-reperfusion (I-R) injury. Recently the combination of the antioxidants vitamin E (VE) and alpha-lipoic acid (alpha-LA) has been reported to improve cardiac performance and reduce myocardial lipid peroxidation during in vitro I-R. The purpose of these experiments was to investigate the effects of VE and alpha-LA supplementation on cardiac performance, incidence of dysrhythmias and biochemical alterations during an in vivo myocardial I-R insult. Female Sprague-Dawley rats (4-months old) were assigned to one of the two dietary treatments: (1) control diet (CON) or (2) VE and alpha-LA supplementation (ANTIOXID). The CON diet was prepared to meet AIN-93M standards, which contains 75 IU VE kg-1 diet. The ANTIOXID diet contained 10 000 IU VE kg(-1) diet and 1.65 g alpha-LA kg(-1) diet. After the 14-week feeding period, significant differences (P<0.05) existed in mean myocardial VE levels between dietary groups. Animals in each experimental group were subjected to an in vivo I-R protocol which included 25 min of left anterior coronary artery occlusion followed by 10 min of reperfusion. No group differences (P>0.05) existed in cardiac performance (e.g. peak arterial pressure or ventricular work) or the incidence of ventricular dysrhythmias during the I-R protocol. Following I-R, two markers of lipid peroxidation were lower (P<0.05) in the ANTIOXID animals compared with CON. These data indicate that dietary supplementation of the antioxidants, VE and alpha-LA do not influence cardiac performance or the incidence of dysrhythmias but do decrease lipid peroxidation during in vivo I-R in young adult rats.