Cardiac performance and plasma lipids of omega-3 fatty acid-treated streptozocin-induced diabetic rats

Dietary α-Linolenic Acid Counters Cardioprotective Dysfunction in Diabetic Mice: Unconventional PUFA Protection

Whether dietary omega-3 (n-3) polyunsaturated fatty acid (PUFA) confers cardiac benefit in cardiometabolic disorders is unclear. We test whether dietary -linolenic acid (ALA) enhances myocardial resistance to ischemia-reperfusion (I-R) and responses to ischemic preconditioning (IPC) in type 2 diabetes (T2D); and involvement of conventional PUFA-dependent mechanisms (caveolins/cavins, kinase signaling, mitochondrial function, and inflammation). Eight-week male C57Bl/6 mice received streptozotocin (75 mg/kg) and 21 weeks high-fat/high-carbohydrate feeding. Half received ALA over six weeks. Responses to I-R/IPC were assessed in perfused hearts. Localization and expression of caveolins/cavins, protein kinase B (AKT), and glycogen synthase kinase-3 β (GSK3β); mitochondrial function; and inflammatory mediators were assessed. ALA reduced circulating leptin, without affecting body weight, glycemic dysfunction, or cholesterol. While I-R tolerance was unaltered, paradoxical injury with IPC was reversed to cardioprotection with ALA. However, post-ischemic apoptosis (nucleosome content) appeared unchanged. Benefit was not associated with shifts in localization or expression of caveolins/cavins, p-AKT, p-GSK3β, or mitochondrial function. Despite mixed inflammatory mediator changes, tumor necrosis factor-a (TNF-a) was markedly reduced. Data collectively reveal a novel impact of ALA on cardioprotective dysfunction in T2D mice, unrelated to caveolins/cavins, mitochondrial, or stress kinase modulation. Although evidence suggests inflammatory involvement, the basis of this "un-conventional" protection remains to be identified.

Sarcolemmal dependence of cardiac protection and stress-resistance: roles in aged or diseased hearts

Disruption of the sarcolemmal membrane is a defining feature of oncotic death in cardiac ischaemia-reperfusion (I-R), and its molecular makeup not only fundamentally governs this process but also affects multiple determinants of both myocardial I-R injury and responsiveness to cardioprotective stimuli. Beyond the influences of membrane lipids on the cytoprotective (and death) receptors intimately embedded within this bilayer, myocardial ionic homeostasis, substrate metabolism, intercellular communication and electrical conduction are all sensitive to sarcolemmal makeup, and critical to outcomes from I-R. As will be outlined in this review, these crucial sarcolemmal dependencies may underlie not only the negative effects of age and common co-morbidities on myocardial ischaemic tolerance but also the on-going challenge of implementing efficacious cardioprotection in patients suffering accidental or surgically induced I-R. We review evidence for the involvement of sarcolemmal makeup changes in the impairment of stress-resistance and cardioprotection observed with ageing and highly prevalent co-morbid conditions including diabetes and hypercholesterolaemia. A greater understanding of membrane changes with age/disease, and the inter-dependences of ischaemic tolerance and cardioprotection on sarcolemmal makeup, can facilitate the development of strategies to preserve membrane integrity and cell viability, and advance the challenging goal of implementing efficacious 'cardioprotection' in clinically relevant patient cohorts. Linked Articles This article is part of a themed section on Molecular Pharmacology of G Protein-Coupled Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.20/issuetoc.

Cardiac mitochondrial alterations induced by insulin deficiency and hyperinsulinaemia in rats: targeting membrane homeostasis with trimetazidine

The present study investigated the ability of trimetazidine (TMZ) to maintain cardiac mitochondrial function during the development of insulin deficiency and hyperinsulinaemia. The anti-ischaemic drug TMZ is known to increase phospholipid synthesis in cardiac membranes and to have a cardioprotective effect. Insulin deficiency was obtained by streptozotocin injection and hyperinsulinaemia was achieved via a fructose diet. Trimetazidine was incorporated into the diet (7.8 mg/day) and mitochondrial function was evaluated in skinned cardiac fibres. Insulin deficiency decreased mitochondrial affinity for ADP and the index of creatine kinase functional activity. This last alteration was partially prevented by TMZ treatment. Insulin deficiency strongly decreased n-3 polyunsaturated fatty acids, especially the docosahexaenoic acid (DHA) content, in cardiac and mitochondrial membranes, inducing a strong increase in the n-6/n-3 ratio. Trimetazidine treatment limited the increase in the n-6/n-3 ratio and prevented the decrease in DHA content in mitochondrial membranes. Insulin deficiency decreased glutamate- and palmitoylcarnitine-supported respiration. Hyperinsulinaemia affected neither mitochondrial affinity for ADP nor the index of creatine kinase functional activity. Hyperinsulinaemia slightly and significantly affected mitochondrial fatty acid composition, by a small increase the n-6/n-3 ratio. Trimetazidine did not modify membrane-bound mitochondrial function but increased the n-6/n-3 ratio. Moreover, hyperinsulinaemia decreased glutamate-supported respiration. In conclusion, modification of membrane homeostasis with TMZ partially prevented the alterations in fatty acid composition and function in cardiac mitochondria induced by insulin deficiency. Three months of hyperinsulinaemia did not modify membrane-bound mitochondrial function and had only slight effects on fatty acid composition.

Docosahexaenoic acid affects insulin deficiency- and insulin resistance-induced alterations in cardiac mitochondria

The effect of docosahexaenoic acid (DHA) intake on cardiac mitochondrial function was evaluated in permeabilized fibers in insulin deficiency and insulin resistance in rats. The insulin-deficient state was obtained by streptozotocin injection 2 mo before investigations. Insulin resistance was obtained by feeding a 62% fructose diet for 3 mo. DHA was incorporated in the diet to modify the fatty acid composition of cardiac membranes, including mitochondria. Insulin deficiency decreased mitochondrial creatine kinase (mi-CK) activity and mitochondrial sensitivity to ADP. DHA intake prevented these alterations. Moreover, the insulin-deficient state significantly decreased n-3 polyunsaturated fatty acids (PUFA) and slightly increased n-6 PUFA in both cardiac and mitochondrial membranes, inducing a significant increase in the n-6-to-n-3 ratio. DHA intake maintained high myocardial and mitochondrial DHA content. Insulin deficiency also decreased glutamate- and palmitoylcarnitine-supported mitochondrial respiration, but DHA intake did not prevent these effects. In contrast, insulin resistance did not affect mi-CK activity or sensitivity to ADP. However, insulin resistance influenced the myocardial fatty acid composition with decreased n-6 and n-3 PUFA contents and increased monounsaturated fatty acid content. Only slight alterations were observed in mitochondrial fatty acid composition, and they were corrected by DHA intake. Moreover, insulin resistance decreased the glutamate-supported respiration, and DHA intake did not influence this effect. In conclusion, the impairment of cardiac mitochondrial function was more pronounced in the insulin-deficient state than in insulin resistance. The modification of fatty acid composition of cardiac and mitochondrial membranes by DHA partially prevented the mitochondrial alterations induced in the two models.

Diabetic cardiomyopathy

Diabetic cardiomyopathy as a distinct entity was first recognized by Rubler et al. in diabetics with congestive heart failure (CHF), who had no evidence of coronary atherosclerosis. The Framingham study showed a 2.4-fold increased incidence of CHF in diabetic men and a 5.1-fold increase in diabetic women over 18 years. Pathological studies show left ventricular hypertrophy and fibrosis with varying degrees of small vessel disease, the functional significance of which is uncertain. Hypertension was recognized as an important cofactor in the development of fatal congestive heart failure in diabetics. On cardiac catheterization, in patients symptomatic of heart failure, either congestive or restrictive patterns have been observed. In contrast, asymptomatic diabetics had decreased left ventricular compliance but normal systolic function on hemodynamic study. Noninvasive studies show alterations in systolic and especially diastolic function, particularly in diabetics with microvascular complications and/or coexistent hypertension. Using load-independent measures of contractility, however, systolic function was generally found to be normal in asymptomatic normotensive diabetics. Experimental studies have focused on the mildly diabetic dog and the severely diabetic rat. Decreased left ventricular compliance and increased interstitial connective tissue were observed in chronically diabetic dogs. In contrast, ventricular myocardium from diabetic rats exhibits a reversible decrease in the speed of contraction, prolongation of contraction, and a delay in relaxation. These mechanical changes are associated with a decreased myosin ATPase, a shift in myosin isoenzyme distribution, alterations in a variety of Ca2+ fluxes, and changes in responses to alpha- and beta-adrenergic and cholinergic stimulation. These biochemical changes may be secondary to alterations in carbohydrate, lipid, and adenine nucleotide metabolism in the diabetic heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiomyopathy associated with noninsulin-dependent diabetes

Cardiovascular disease represents the major cause of morbidity and mortality in noninsulin-dependent diabetic patients. While it was once thought that atherosclerotic vascular disease was responsible for all of these adverse effects, recent studies support the notion that one of the major adverse complications of diabetes is the development of a diabetic cardiomyopathy characterized by defects in both diastolic and systolic function. Contributing to the development of the cardiomyopathy is a shift in myosin isozyme content in favor of the least active V3 form. Also defective in the noninsulin-dependent diabetic heart is regulation of calcium homeostasis. While transport of calcium by the sarcolemmal and sarcoplasmic reticular calcium pumps are minimally affected by noninsulin-dependent diabetes, significant impairment occurs in sarcolemmal Na(+)-Ca2+ exchanger activity. This defect limits the ability of of the diabetic heart to extrude calcium, contributing to an elevation in [Ca2+]i. Also promoting the accumulation of calcium by the diabetic cell is a decrease in Na+, K+ ATPase activity, which is known to increase [Ca2+]i secondary to a rise in [Na+]i. In addition, calcium influx via the calcium channel is stimulated. Although the molecular mechanisms underlying these defects are presently unknown, the possibility that they may be related to aberrations in glucose or lipid metabolism are considered. The evidence suggests that classical theories of glucose toxicity, such as excessive polyol production or glycosylation, appear to be insignificant factors in heart. Also insignificant are defects in lipid metabolism leading to accumulation of toxic lipid amphiphiles or triacylglycerol. Rather, the major defects involve membrane changes, such as phosphatidylethanolamine N-methylation and protein phosphorylation, which can be attributed to the state of insulin resistance.

Diabetic heart muscle disease

Diabetic patients may have various abnormalities in left ventricular systolic and diastolic function not attributable to coronary heart disease, hypertension or other known cardiac disease. Although the exact causes of this diabetic heart muscle disease or "diabetic cardiomyopathy" are still incompletely understood, several mechanisms may contribute to it including disturbed myocardial energy metabolism, microvascular changes, structural changes in collagen, increased myocardial fibrosis, and cardiac autonomic neuropathy. Perhaps the most typical feature of diabetic heart muscle disease is an abnormal filling pattern of the left ventricle, suggesting reduced compliance or prolonged relaxation. Left ventricular systolic function is commonly normal at rest in asymptomatic diabetic patients, but it frequently becomes abnormal during exercise. The abnormalities in left ventricular systolic function may be partly reversible along with an improvement of metabolic control of diabetes. It is not known how frequently subclinical abnormalities in left ventricular function in diabetic patients result in clinically manifest heart failure.