Dietary fatty acids and myocardial function

Novel Pharmacological Interventions to Maintain Sinus Rhythm after DC Cardioversion

Despite the availability of potentially curative interventions for atrial fibrillation, there remains an important role for conventional anti-arrhythmic therapy and anti-coagulation combined with direct current cardioversion. Unfortunately, the latter approach is disturbed by high recurrence rates of atrial fibrillation. In recent years, several adjunctive therapies have emerged which may facilitate the maintenance of sinus rhythm. These novel therapies and their potential mechanisms of action are reviewed in this article.

Chronic hypoxia alters fatty acid composition of phospholipids in right and left ventricular myocardium

Adult male Wistar rats were exposed to intermittent high altitude hypoxia of 7000 m simulated in a hypobaric chamber for 8 h/day, 5 days a week; the total number of exposures was 25. The concentration of individual phospholipids and their fatty acid (FA) profile was determined in right (RV) and left (LV) ventricles. Adaptation to hypoxia decreased the concentration of diphosphatidytglycerol (DPG) in hypertrophied RV by 19% and in non-hypertrophied LV by 12% in comparison with normoxic controls. Chronically hypoxic hearts exhibited lower phospholipid n-6 polyunsaturated FA(PUFA) content mainly due to decreased linoleic acid (18:2n-6), which was opposed by increased n-3 PUFA mainly due to docosahexaenoic acid (22:6n-3) in phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI). The content of arachidonic acid (20:4n-6) was unchanged in total phospholipids, but in PC it was increased in both ventricles (by 22%) and in PE decreased in LV only (by 20%). Chronic hypoxia increased the un-saturation index of PC and PE in both ventricles. The content of monounsaturated FA (MUFA) was increased and 18:2n-6 decreased in DPG. The proportion of saturated FA was increased in PC and PI of hypoxic RV but not LV. The FA composition of phosphatidylserine was not altered in hypoxic ventricles. It is concluded that chronic hypoxia led to only minor changes in individual phospholipid concentration in rat ventricular myocardium, but markedly altered their FA profile. These changes, in particular the greater incorporation of n-3 PUFA into phospholipids and increased un-saturation index, may lead to a better preservation of membrane integrity and thereby contribute to improved ischemic tolerance of chronically hypoxic hearts.

Influence of phospholipid long chain polyunsaturated fatty acid composition on neonatal rat cardiomyocyte function in physiological conditions and during glucose-free hypoxia-reoxygenation

There is evidence that dietary polyunsaturated fatty acids (PUFA) may protect against cardiovascular diseases, but the involvement of the cardiac muscle cell in this beneficial action remain largely unknown. The present study compared the respective influence of n-3 and n-6 PUFA on the function of cultured neonatal rat cardiomyocytes (CM). Cells were grown for 4 days in media enriched either n-3 (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) or n-6 (arachidonic acid, AA) PUFA. The PUFA n-6/n-3 ratio in the phospholipids was close to 1 and 20 in the n-3 and n-6 cells, respectively. The transmembrane potentials were recorded using microelectrodes and the contractions were monitored with a photoelectric device. In physiological conditions, the increase of n-6 PUFA level in the phospholipids resulted in a significant decrease in the maximal rate of initial depolarization (-16%). In opposition, the action potential amplitude and duration were not altered, and the cell contraction outline was not affected. Ischemia was simulated in vitro using a substrate-free, hypoxia-reoxygenation procedure in a specially designed gas-flow chamber. The progressive loss of electrical activity induced by the substrate-free, hypoxic treatment was affected by the n-6/n-3 ratio, since the n-6 rich CM displayed a slower depression of the AP amplitude and duration parameters. Conversely, the recovery of the resting potential (MDP) during reoxygenation was faster in n-3 CM, whereas the recovery of the contraction parameters was unaffected by the fatty acid composition of the cells. These results suggested that, in physiological conditions, the modification of long chain PUFA balance in the phospholipids of cardiac muscle cells may modulate the initial AP upstroke, which is governed by sodium channels. Moreover, the presence of n-3 PUFA appeared to accelerate the electrical depression during substrate-free hypoxia but in turn to allow a faster recovery upon reoxygenation.

Polyunsaturated fatty acids and signalling via phospholipase C-beta and A2 in myocardium

Dietary n-6 and n-3 polyunsaturated fatty acids (PUFAs) have potent biological effects on the blood(cells), the vasculature and they myocardium. In the epidemiological studies in which the benefit from the regular ingestion of n-3 PUFAs was reported, the responsible mechanisms remain obscure. A great deal of the PUFA-effect can be explained by the known interference with the eicosanoid metabolism. Many processes, believed to be involved in atherogenesis such as adhesion and infiltration of bloodcells (in)to the vasculature, platelet aggregation, secretion of endothelium-derived factors and mitogenic responses of vascular smooth muscle cells are partially mediated by receptor-activated phospholipases C-beta and A2. As PUFAs take part at many steps of the signalling pathways, the latter could represent important action sites to beneficially interfere with atherogenesis. In this brief review, we have discussed the results of studies on the influence of alteration of PUFA composition of the membrane phospholipids or of exogenously administered non-esterified PURAs on phospholipid signalling. For convenience, we have mainly focused our discussion on those studies available on the myocardium. By changing the PUFA composition of the phospholipids, the endogenous substrates for the membrane-associated phospholipase C-beta and A2 are changed. This is accompanied by changes in their hydrolytic action on these substrates resulting in altered products (the molecular species of 1,2-diacylglycerols and the non-esterified PUFAs) which on their turn evoke changes in events downstream of the signalling cascades: activation of distinct protein kinase C isoenzymes, formation of distinct eicosanoids and non-esterified PUFA effects on Ca2+ channels. It has also become more clear that the membrane physicochemical properties, in terms of fluidity and cholesterol content of the bilayer, might undergo changes due to altered PUFA incorporation into the membrane phospholipids. The latter effects could have consequences for the receptor functioning, receptor-GTP-binding protein coupling, GTP-binding protein-phospholipase C-beta or A2 coupling as well. It should be noted that most of these studies have been carried out with cardiomyocytes isolated from hearts of animals on PUFA diet or incubation of cultured cardiomyocytes with non-esterified PUFAs in the presence of albumin. Studies need to be performed to prove that the PUFA-diet induced modulations of the phospholipid signalling reactions do occur in vivo and that these effects are involved in the mechanism of beneficial effects of dietary PUFAs on the process of atherosclerosis.

Alterations in phospholipid N-methylation of cardiac subcellular membranes due to experimentally induced diabetes in rats

Phosphatidylethanolamine N-methylation was examined in cardiac subcellular membranes after inducing chronic experimental diabetes in rats (65 mg streptozotocin/kg, i.v.). The incorporation of radiolabeled methyl groups from S-adenosyl-L-methionine in diabetic sarcolemma was significantly depressed at all three catalytic sites (I, II, and III) of the methyltransferase system. An increase in methyl group incorporation was evident at site I without any changes at sites II and III in diabetic sarcoplasmic reticulum and mitochondria. Similar changes were also seen for the individual N-methylated lipids (monomethyl-, dimethylphosphatidylethanolamine, and phosphatidylcholine) specifically formed at each catalytic site in all cardiac membranes from diabetic animals. These alterations in N-methylation were reversible by a 14-d insulin therapy to the diabetic animals. In the presence of 10 microM ATP and 0.1 microM Ca2+, N-methylation was maximally activated at site I in both control and diabetic sarcolemma and sarcoplasmic reticulum, but not in mitochondria. Incubation of cardiac membranes with of S-adenosyl-L-methionine showed that Ca2(+)-stimulated ATPase activities in both sarcolemma and sarcoplasmic reticulum were augmented; however, the activation of diabetic sarcolemma was lesser and that of diabetic sarcoplasmic reticulum was greater in comparison with the control preparations. These results identify alterations in phosphatidylethanolamine N-methylation in subcellular membranes from diabetic heart, and it is suggested that these defects may be crucial in the development of cardiac dysfunction in chronic diabetes.

The effects of dietary mackerel oil on the recovery of cardiac function after acute ischaemic events in the pig

To investigate the effects of fish oil nutrition on cardiac haemodynamics and the biochemical response to ischaemia-reperfusion, young pigs (5 weeks old) were fed a 9% lard fat diet or a mixed diet of 4.5% mackerel oil and 4.5% lard fat for 16 weeks. In the mackerel oil fed pigs plasma cholesterol and triglyceride levels decreased by 22% and 58% (both p less than 0.05), respectively, while levels in the animals which received only lard fat did not change. The n-6 fatty acids present in cardiac and platelet membrane phospholipids underwent a partial replacement by n-3 fatty acids in the mackerel oil fed pigs. Under anaesthesia, multiple coronary artery occlusions (5 min) were interrupted by 10 min of reperfusion. The extent of recovery of cardiac function and reduction of adenine nucleotide levels were similar for both dietary groups. The incidence of reperfusion arrhythmias was significantly lower and the reactive hyperaemic responses were of longer duration in the mackerel oil fed animals. These effects cannot be explained by diet-induced alterations in thromboxane B2/6-keto-PGF1 alpha ratio, although a marked reduction in absolute levels of both prostaglandins was seen in the mackerel oil fed pigs (p less than 0.05). In conclusion, dietary fish oil caused changes in membrane fatty acid composition and plasma prostaglandin levels, although these did not affect alterations of cardiac performance during and after short periods of ischaemia.