The effect of different dietary lipid supplements on the nonesterified fatty acid composition of normoxic rat hearts: A link between nutrition and cardiac arrhythmia

Omega-3 polyunsaturated fatty acids and ventricular fibrillation: the possible involvement of eicosanoids

Increased dietary omega-3 polyunsaturated fatty acids (PUFAs) reduce the incidence and severity of ventricular fibrillation (VF) in laboratory animals subjected to partial ischaemia and reduce the risk of cardiac arrest in humans after myocardial infarction. In whole animals there is considerable evidence which suggests that incorporation of these fatty acids into cardiac membrane phospholipids influences the production of a variety of eicosanoids having opposing arrhythmogenic or anti-arrhythmogenic properties, and that the balance of these actions is shifted in favour of an anti-arrhythmogenic state by feeding fish oil dietary supplements rich in omega-3 PUFA. However, differences in eicosanoid biosynthesis between species, between tissues of the same species and even between different intracellular sites within cells of the same tissue could influence experimental outcomes. The importance of further studies with the most appropriate whole animal models or tissues is emphasized, as is the difference between the structural integrity of cardiac muscle and cardiomyocytes in vitro.

Specific modifications of phosphatidylinositol and nonesterified fatty acid fractions in cultured porcine cardiomyocytes supplemented with n-3 polyunsaturated fatty acids

Mechanisms for the antiarrhythmic effect of n-3 polyunsaturated fatty acids (PUFA) are currently being investigated using isolated cardiac myocytes. It is still not known whether the incorporation of n-3 PUFA into membrane phospholipids is a prerequisite for its protective action or if n-3 PUFA exert antiarrhythmic effects in their nonesterified form as demonstrated by recent studies. Adult porcine cardiomyocytes were grown in media supplemented with arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). After 24 h, analysis of total lipids showed that the myocytes were enriched with the respective fatty acids compared to control cells. Large proportions of all three fatty acids supplemented (69% AA, 72% DHA, and 66% EPA) remained unesterified. Fatty acid analyses of total phospholipids (PL) revealed that the incorporation of EPA and DHA, though small, was significantly different (P<0.05) from that of the control cells. The PL fraction was further separated into phosphatidylinositol (PI), phosphatidylethanolamine, phosphatidylcholine, and phosphatidylserine to study the pattern of incorporation of the fatty acids in these fractions. It became apparent that EPA and DHA were selectively incorporated into the PI fraction. This study demonstrates that in adult porcine cardiomyocytes, the n-3 PUFA supplementation selectively modulates two important lipid fractions, nonesterified fatty acid and PI, which were implicated in the mechanisms of prevention of cardiac arrhythmias.

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.

Effects of eicosapentaenoic acid and docosahexaenoic acid diet supplement on tolerance to the cardiotoxicity of epirubicin and to ischaemia reperfusion in the isolated rat heart

We compared the effects of 2 weeks dietary supplement of docosahexaenoic acid, eicosapentaenoic acid or olive oil on myocardial tolerance to the cardiotoxicity of the anthracycline epirubicin and to ischaemia reperfusion. Isolated rat hearts from the dietary groups were perfused at a constant flow rate of 12.5 ml/min. The hearts were subjected to a 20 min. period of epirubicin infusion by a side arm of the perfusion system at a rate of 0.2 mg/min. or a 20 min. period of global ischaemia. After 10 min. of epirubicin infusion a significantly (P < 0.05) higher aortic pressure (an index of coronary resistance during constant flow perfusion) was observed in the olive oil group; 130 +/- 22% (mean +/- S.D.) compared to hearts in the docosahexaenoic acid; 108 +/- 9% (mean +/- S.D.), and eicosapentaenoic acid; 105 +/- 7% (mean +/- S.D.), group. Hearts from docosahexaenoic acid-fed rats showed a significantly increased left ventricular end-diastolic pressure (an index of contracture); of 66 +/- 30 mmHg (mean +/- S.D.) after 15 min. of global ischaemia compared to eicosapetaenoic acid fed rats; 37 +/- 18 mmHg (mean +/- S.D.), and significantly higher release of lactate dehydrogenase during the following 30 min. period of reperfusion compared to olive oil-fed rats. We conclude that eicosapentaenoic acid and docosahexaenoic acid could be useful during epirubicin infusion and that docosahexaenoic acid could be harmful during ischaemia reperfusion.

Comparison of the effects of a range of dietary lipids upon serum and tissue lipid composition in the rat

Since the type of fat consumed in the diet may play a role in the development of several disorders, it is important to ascertain the effects of different dietary fats upon parameters such as serum lipid levels and adipose deposition. The aim of this study was to determine the effects of feeding rats a range of fats with differing fatty acid compositions. Weanling male rats were fed for 10 weeks on a low fat (LF) diet or on one of five high fat diets, which contained 20% by weight of either hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Food intake, animal growth, tissue weights at sacrifice, serum and liver lipid concentrations and serum, heart, brain and adipose tissue fatty acid compositions were studied. The food intake of the LF-fed animals was greater than that of animals fed on the high fat diets; there were no differences in food intake between animals fed the high fat diets. The total energy intake was lower for animals fed on the HCO diet than for those fed on the LF, OO, EPO or MO diets; there were no other differences in energy intake between the groups. Animals fed the different diets had almost identical rates of weight gain up to 5 weeks; after this period of rapid growth, the increase in weight was slower in all groups but especially in the LF-fed animals. The LF-fed rats had a lower total weight gain and smaller final weights than rats fed on the high fat diets. Animals fed on the MO diet had a greater weight gain than those fed on the OO or EPO diets and their final weights were greater. The MO diet resulted in greatly increased liver weight compared with each of the other diets. The HCO, OO and EPO diets also increased liver weight compared with the LF diet. The total lipid content of the livers from rats fed the high fat diets was greater than that of those from rats fed the LF diet; the livers from animals fed the MO diet contained more lipid than those from animals fed each of the other diets. MO feeding increased the free cholesterol, cholesterol ester and triacylglycerol contents of the liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipids and cardiac arrhythmia

In any discussion of lipids and heart disease it is beneficial from the outset to recognise that at least three different pathological processes may be involved. The first of these is atherosclerosis which involves the deposition of "fat" in the coronary vessels, another is thrombogenesis which describes the formation of blood clots in the coronary vessels, and the third is arrhythmia which refers to disorders in the beating of the heart which may become sufficiently serious to cause sudden cardiac death (SCD). Also it is this disturbance in the rhythmic beating of the heart which is responsible for much of the mortality from 'heart attacks' which occur 'outside-of-hospital' in societies like U.S.A., U.K. and Australia. It is this latter condition of cardiac arrhythmia which is the major concern of this review. Because it is often difficult to differentiate the role of lipids in 'heart disease' in man, it has frequently been assumed that all dietary fatty acids have similar effects on the different processes involved, and many unwarranted generalisations have been made which have led to conflicts of opinion amongst physicians and confusion in the lay public. From the animal studies discussed in this review, it is apparent that dietary fatty acids have an important role to play in determining the vulnerability of the myocardium to develop serious ventricular fibrillation (VF) and potentially lethal cardiac arrhythmia. In general, diets rich in saturated fatty acids promote a state of myocardial vulnerability, whilst diets rich in PUFA significantly diminish the probability of developing lethal disorders in cardiac rhythm when the heart is placed under pharmacological (or emotional) stress, or deprived of sufficient blood flow and supply of oxygen. Very recent experiments with the monounsaturated fatty acid (MUFA) oleic acid clearly demonstrate that, at least in rats subjected to ligation of their coronary artery, this acid is not 'neutral' as has been suggested by some for its role in atherosclerosis, but in fact is indistinguishable from saturated fatty acids in its effect in promoting arrhythmia during either regional ischaemia or reperfusion arrhythmia in this animal model of SCD.(ABSTRACT TRUNCATED AT 400 WORDS)

Infusion of EPA and DHA lipid emulsions: effects on heart lipids and tolerance to ischaemia-reperfusion in the isolated rat heart

The aim of the present study was to examine the effect of acute infusion of lipid emulsions enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) on heart lipids, tolerance to infusion and to ischaemia-reperfusion. Isolated rat hearts were subjected to a 10 min lipid infusion period prior to 25 min of total global ischaemia and 30 min of reperfusion. Effects on physiology and metabolism were recorded during infusion and reperfusion. A more than doubled increase of DHA and a 12-fold increase of EPA in terms of relative concentration was demonstrated in the free fatty acid fraction after infusion with the respective triglyceride emulsions, without any profound change in physiology. High levels of DHA were associated with a reduced recovery of left ventricular developed pressure (LVDP) and increased release of lactate dehydrogenase (LDH) during reperfusion, while the hearts infused with the EPA-emulsion showed a recovery comparable to the control group. Heart lipid peroxidation, evaluated by release of thiobarbituric acid reactive substances (TBARS) in effluate, was about 4-fold higher in the DHA-group compared to the EPA-group during start of reperfusion and may in part explain the reduced recovery observed in these hearts. The present study demonstrates enrichment of DHA and EPA in the free fatty acid fraction after a short period of infusion. Protective effects of the emulsions were not found, instead the data indicate harmful effects of DHA during ischaemia-reperfusion. However, the presence of TBARS in this emulsion could have influenced the results.