Dietary fish oil reverses lipotoxicity, altered glucose metabolism, and nPKCepsilon translocation in the heart of dyslipemic insulin-resistant rats

Comparative effects of nanoemulsions loaded with duck oil and lard oil on palmitate-induced lipotoxicity

The effects of duck oil and lard oil on lipotoxicity induced by saturated long-chain fatty acids were evaluated in HepG2 cells. Lipotoxicity triggered by palmitate, a saturated fatty acid, was inhibited more by duck oil-loaded nanoemulsion (DO-NE) than by lard oil-loaded nanoemulsion (LO-NE) and control nanoemulsion (NE) in HepG2 cells. Accumulation of reactive oxygen species and lipid vacuoles in HepG2 cells induced by palmitate treatment was inhibited by DO-NE but not by LO-NE. Consistently, treatment of HepG2 cells with DO-NE, but not with NE or LO-NE, significantly reduced the expression levels of peroxisome proliferator-activated receptor-γ2 and sterol regulatory element-binding protein-1, which are key regulatory proteins in hepatic lipid accumulation. In addition, the cleavage of poly (ADP-ribose) polymerase and caspase-3 were reduced more by DO-NE than by LO-NE, indicating that DO-NE directly attenuates cellular damage induced by palmitate. Collectively, these results imply that the biological activity of duck oil against palmitate-induced cellular damage is more potent than that of lard oil. PRACTICAL APPLICATIONS: Accumulated lipids in nonadipose tissues, especially the liver, cause lipotoxicity, a pathologic feature of hepatic disorders, by inducing oxidative stress. A nanoemulsion loaded with duck oil, which is a functional food widely consumed by Korean people, inhibited lipotoxicity by suppressing lipid accumulation in HepG2 cells exposed to palmitate, which mimic nonalcoholic fatty liver disease. Thus, we propose that duck oil can be used as a functional food to improve lipid-induced hepatic disorders.

Dietary soya protein improves intra-myocardial lipid deposition and altered glucose metabolism in a hypertensive, dyslipidaemic, insulin-resistant rat model

This study investigates the effects of replacing dietary casein by soya protein on the underlying mechanisms involved in the impaired metabolic fate of glucose and lipid metabolisms in the heart of dyslipidaemic rats chronically fed (8 months) a sucrose-rich (62·5 %) diet (SRD). To test this hypothesis, Wistar rats were fed an SRD for 4 months. From months 4 to 8, half the animals continued with the SRD and the other half were fed an SRD in which casein was substituted by soya. The control group received a diet with maize starch as the carbohydrate source. Compared with the SRD-fed group, the following results were obtained. First, soya protein significantly (P<0·001) reduced the plasma NEFA levels and normalised dyslipidaemia and glucose homoeostasis, improving insulin resistance. The protein levels of fatty acid translocase at basal state and under insulin stimulation and the protein levels and activity of muscle-type carnitine palmitoyltransferase 1 were normalised. Second, a significant (P<0·001) reduction of TAG, long-chain acyl CoA and diacylglycerol levels was observed in the heart muscle. Third, soya protein significantly increased (P<0·01) GLUT4 protein level under insulin stimulation and normalised glucose phosphorylation and oxidation. A reduction of phosphorylated AMP protein kinase protein level was recorded without changes in uncoupling protein 2 and PPARα. Fourth, hydroxyproline concentration decreased in the left ventricle and hypertension was normalised. The new information provided shows the beneficial effects of soya protein upon the altered pathways of glucose and lipid metabolism in the heart muscle of this rat model.

Dietary Salba (Salvia hispanica L) improves the altered metabolic fate of glucose and reduces increased collagen deposition in the heart of insulin-resistant rats

This study reports the effects of dietary Salba (chia) seeds on the mechanisms underlying impaired glucose metabolism in the heart of dyslipemic insulin-resistant rats fed a sucrose-rich diet (SRD). Wistar rats were fed a SRD for 3 months. Afterwards, half the animals continued with the SRD; in the other half's diet chia seeds replaced corn oil (CO) for three months (SRD+chia). In the control group, corn starch replaced sucrose. The replacement of CO by chia seeds in the SRD restored the activities of key enzymes involved in heart glucose metabolism decreasing fatty acid oxidation. Chia seeds normalized insulin stimulated GLUT-4 transporter, the abundance of IRS-1 and pAMPK, changed the profile of fatty acid phospholipids, reduced left-ventricle collagen deposition and normalized hypertension and dyslipidemia. New evidence is provided concerning the effects of dietary chia seeds in improving the altered metabolic fate of glucose in the heart of dyslipemic insulin-resistant rats.

Mechanisms Involved in the Improvement of Lipotoxicity and Impaired Lipid Metabolism by Dietary α-Linolenic Acid Rich Salvia hispanica L (Salba) Seed in the Heart of Dyslipemic Insulin-Resistant Rats

This study explores the mechanisms underlying the altered lipid metabolism in the heart of dyslipemic insulin-resistant (IR) rats fed a sucrose-rich diet (SRD) and investigates if chia seeds (rich in α-linolenic acid 18:3, n-3 ALA) improve/reverse cardiac lipotoxicity. Wistar rats received an SRD-diet for three months. Half of the animals continued with the SRD up to month 6. The other half was fed an SRD in which the fat source, corn oil (CO), was replaced by chia seeds from month 3 to 6 (SRD+chia). A reference group consumed a control diet (CD) all the time. Triglyceride, long-chain acyl CoA (LC ACoA) and diacylglycerol (DAG) contents, pyruvate dehydrogenase complex (PDHc) and muscle-type carnitine palmitoyltransferase 1 (M-CPT1) activities and protein mass levels of M-CPT1, membrane fatty acid transporter (FAT/CD36), peroxisome proliferator activated receptor α (PPARα) and uncoupling protein 2 (UCP2) were analyzed. Results show that: (a) the hearts of SRD-fed rats display lipotoxicity suggesting impaired myocardial lipid utilization; (b) Compared with the SRD group, dietary chia normalizes blood pressure; reverses/improves heart lipotoxicity, glucose oxidation, the increased protein mass level of FAT/CD36, and the impaired insulin stimulated FAT/CD36 translocation to the plasma membrane. The enhanced M-CPT1 activity is markedly reduced without similar changes in protein mass. PPARα slightly decreases, while the UCP2 protein level remains unchanged in all groups. Normalization of dyslipidemia and IR by chia reduces plasma fatty acids (FAs) availability, suggesting that a different milieu prevents the robust translocation of FAT/CD36. This could reduce the influx of FAs, decreasing the elevated M-CPT1 activity and lipid storage and improving glucose oxidation in cardiac muscles of SRD-fed rats.

Ceramide-mediated depression in cardiomyocyte contractility through PKC activation and modulation of myofilament protein phosphorylation

Although ceramide accumulation in the heart is considered a major factor in promoting apoptosis and cardiac disorders, including heart failure, lipotoxicity and ischemia-reperfusion injury, little is known about ceramide's role in mediating changes in contractility. In the present study, we measured the functional consequences of acute exposure of isolated field-stimulated adult rat cardiomyocytes to C6-ceramide. Exogenous ceramide treatment depressed the peak amplitude and the maximal velocity of shortening without altering intracellular calcium levels or kinetics. The inactive ceramide analog C6-dihydroceramide had no effect on myocyte shortening or [Ca(2+)]i transients. Experiments testing a potential role for C6-ceramide-mediated effects on activation of protein kinase C (PKC) demonstrated evidence for signaling through the calcium-independent isoform, PKCε. We employed 2-dimensional electrophoresis and anti-phospho-peptide antibodies to test whether treatment of the cardiomyocytes with C6-ceramide altered myocyte shortening via PKC-dependent phosphorylation of myofilament proteins. Compared to controls, myocytes treated with ceramide exhibited increased phosphorylation of myosin binding protein-C (cMyBP-C), specifically at Ser273 and Ser302, and troponin I (cTnI) at sites apart from Ser23/24, which could be attenuated with PKC inhibition. We conclude that the altered myofilament response to calcium resulting from multiple sites of PKC-dependent phosphorylation contributes to contractile dysfunction that is associated with cardiac diseases in which elevations in ceramides are present.

Fish oil selectively improves heart function in a mouse model of lipid-induced cardiomyopathy

Fish oil (FO) supplementation may improve cardiac function in some patients with heart failure, especially those with diabetes. To determine why this occurs, we studied the effects of FO in mice with heart failure either due to transgenic expression of the lipid uptake protein acyl CoA synthetase 1 (ACS1) or overexpression of the transcription factor peroxisomal proliferator-activated receptor (PPAR) γ via the cardiac-specific myosin heavy chain (MHC) promoter. ACS1 mice and control littermates were fed 3 diets containing low-dose or high-dose FO or nonpurified diet (NPD) for 6 weeks. MHC-PPARγ mice were fed low-dose FO or NPD. Compared with control mice fed with NPD, ACS1, and MHC-PPARγ, mice fed with NPD had reduced cardiac function and survival with cardiac fibrosis. In contrast, ACS1 mice fed with high-dose FO had better cardiac function, survival, and less myocardial fibrosis. FO increased eicosapentaenoic and docosahexaenoic acids and reduced saturated fatty acids in cardiac diacylglycerols. This was associated with reduced protein kinase C alpha and beta activation. In contrast, low-dose FO reduced MHC-PPARγ mice survival with no change in protein kinase C activation or cardiac function. Thus, dietary FO reverses fibrosis and improves cardiac function and survival of ACS1 mice but does not benefit all forms of lipid-mediated cardiomyopathy.

Age-dependent effects of high fat-diet on murine left ventricles: role of palmitate

Obesity-associated heart disease results in myocardial lipid accumulation leading to lipotoxicity. However, recent studies are suggestive of protective effects of high-fat diets (HFD). To determine whether age results in differential changes in diet-induced obesity, we fed young and old (3 and 18 months) male C57Bl/6 mice control diet, low-fat diet (both 10 kcal% fat) or HFD (45 kcal% fat) for 16 weeks, after which we analyzed LV function, mitochondrial changes, and potential modifiers of myocardial structure. HFD or age did not change LV systolic function, although a mildly increased BNP was observed in all old mice. This was associated with increased myocardial collagen, triglyceride, diacylglycerol, and ceramide content as well as higher caspase 3 activation in old mice with highest levels in old HFD mice. Pyruvate-dependent respiration and mitochondrial biogenesis were reduced in all old mice and in young HFD mice. Activation of AMPK, a strong inducer of mitochondrial biogenesis, was reduced in both HFD groups and in old control or LFD mice. Cardiomyocytes from old rats demonstrated significantly reduced AMPK activation, impaired mitochondrial biogenesis, higher ceramide content, and reduced viability after palmitate (C16:0) in vitro, while no major deleterious effects were observed in young cardiomyocytes. Aged but not young cardiomyocytes were unable to respond to higher palmitate with increased fatty acid oxidation. Thus, HFD results in cardiac structural alterations and accumulation of lipid intermediates predominantly in old mice, possibly due to the inability of old cardiomyocytes to adapt to high-fatty acid load.

Fish oil supplementation for two generations increases insulin sensitivity in rats

We investigated the effect of fish oil supplementation for two consecutive generations on insulin sensitivity in rats. After the nursing period (21 days), female rats from the same prole were divided into two groups: (a) control group and (b) fish oil group. Female rats were supplemented with water (control) or fish oil at 1 g/kg body weight as a single bolus for 3 months. After this period, female rats were mated with male Wistar rats fed on a balanced chow diet (not supplemented). Female rats continued to receive supplementation throughout gestation and lactation periods. The same treatment was performed for the next two generations (G1 and G2). At 75 days of age, male offspring from G1 and G2 generations from both groups were used in the experiments. G1 rats did not present any difference with control rats. However, G2 rats presented reduction in glycemia and lipidemia and improvement in in vivo insulin sensitivity (model assessment of insulin resistance, insulin tolerance test) as well as in vitro insulin sensitivity in soleus muscle (glucose uptake and metabolism). This effect was associated with increased insulin-stimulated p38 MAP kinase phosphorylation and lower n-6/n-3 fatty acid ratio, but not with activation of proteins from insulin signaling (IR, IRS-1 and Akt). Global DNA methylation was decreased in liver but not in soleus muscle. These results suggest that long-term fish oil supplementation improves insulin sensitivity in association with increased insulin-stimulated p38 activation and decreased n-6:n-3 ratio in skeletal muscle and decreased global DNA methylation in liver.

Role of FAT/CD36 in novel PKC isoform activation in heart of spontaneously hypertensive rats

Disruption to the sensitive balance of long-chain fatty acids and glucose in the heart could cause cardiovascular diseases. Searching for a possible role of novel protein kinase C (nPKC) in heart with disrupted energy balance, we compared the insulin-resistant spontaneously hypertensive rats (SHR), which carry a nonfunctional variant of the fatty acid transporter FAT/CD36, with the less insulin-resistant congenic strain SHR-4 that is genetically identical except for a segment on chromosome 4 including a wild-type gene for a functional FAT/CD36. We analyzed expression of the nPKC-δ and -ε isoforms plus triacylglycerols (TAG) content in the myocardium of both FAT/CD36 strains and after a high sucrose diet (HSD). Two weeks before killing, males of both strains were randomly divided into two groups and fed either a standard laboratory chow or an HSD. PKC was determined by Western blotting in particulate and cytosolic fractions from left ventricles. The SHR-4 rats exhibited lower serum levels of insulin and free fatty acids than did SHR rats and higher amounts of PKC-ε in the heart particulate fraction. HSD caused accumulation of heart TAG in SHR but not in SHR-4. HSD increased PKC-δ and decreased PKC-ε expression in particulate fraction from left ventricles of SHR-4 while having no effects in SHR. These results demonstrate that reduced insulin resistance in SHR-4 rats with wild-type FAT/CD36 is associated with the insulin signaling pathway involving nPKCs.

Long-term high-fat diet-induced obesity decreases the cardiac leptin receptor without apparent lipotoxicity

AIMS

Leptin resistance has been associated with cardiac lipotoxicity; however, whether leptin resistance is a risk factor associated with cardiac lipotoxicity at different time points in diet-induced obesity is unclear. The objective of this study was to evaluate this relationship.

MAIN METHODS

Male Wistar rats were fed a normal chow diet (12% from fat) or a high-fat diet (49% from fat) for 15 and 45 weeks, respectively. The adiposity index, body weight and co-morbidities were evaluated. Heart lipotoxicity was assessed by analyzing cardiac function and morphological changes as well as cardiac triglyceride, ceramide and lipid hydroperoxide accumulations. Cardiac apoptosis was examined using the TUNEL method. Leptin function was determined by examining plasma leptin levels, cardiac leptin receptors (OB-R) and related phosphorylations of AMP-activated kinase protein (AMPK) and Acetyl CoA carboxylase (ACC).

KEY FINDINGS

The diet-induced obesity was characterized by an elevated adiposity index, body weight and leptin levels at both 15 and 45 weeks. There was no difference between groups in the cardiac triglyceride or lipid hydroperoxide levels. Interestingly, ceramide levels decreased in obese animals in both experimental periods. The cardiac morphological and functional parameters were not altered. Although down-regulation of OB-R has occurred in chronic obesity, it did not adversely affect AMPK or ACC phosphorylation.

SIGNIFICANCE

The development of obesity via long-term feeding of a high-fat diet to rats does not result in cardiac lipotoxicity but promotes the down-regulation of OB-R. However, this does not result in altered levels of AMPK or ACC phosphorylations in this animal model.

Cardiovascular effects of edible oils: a comparison between four popular edible oils

Edible oils form an essential part of the modern diet. These oils play a role as an energy source, and provide the diet with many beneficial micronutrients. Although a popular conception may be that fat should be avoided, certain edible oils as a dietary supplement may play an important role in the improvement of cardiovascular health. CVD has become one of the leading causes of death worldwide. Dietary supplementation with different oils may have beneficial effects on cardiovascular health. While olive oil and sunflower-seed oil are known to reduce serum cholesterol, fish oil has become well known for reducing potentially fatal cardiac arrhythmias. Recently, red palm oil research has shown beneficial effects on cardiac recovery from ischaemia-reperfusion injury. It is clear that dietary supplementation with edible oils may play a vital role in reducing the mortality rate due to heart disease. The specific benefits and disadvantages of these oils should, however, be explored in greater depth. The present review will attempt to identify the benefits and shortcomings of four popular edible oils, namely olive oil, sunflower-seed oil, fish oil and palm oil. Additionally the present review will aim to reveal potential areas of research which could further enhance our understanding of the effects of edible oils on cardiovascular health.

Creating and curing fatty hearts

PURPOSE OF REVIEW

Diseases associated with ectopic disposition of lipids are becoming an increasingly important medical problem as the incidence of type 2 diabetes and obesity increases. One of the organs affected by lipotoxicity is the heart and this review presents an update on human and animal studies of this problem.

RECENT FINDINGS

Human studies have clearly correlated heart dysfunction with the content of triglyceride. More recently human heart samples have been used to assess gene changes associated with altered lipid accumulation. Genetically altered mice have been created that develop lipotoxic cardiomyopathies and newer investigations are attempting to delineate curative therapies.

SUMMARY

Human studies will confirm the metabolic changes associated with lipotoxic cardiomyopathy and, hopefully, animal studies will guide treatment options.

Lipogenic enzyme activities and glucose uptake in fat tissue of dyslipemic, insulin-resistant rats: effects of fish oil

OBJECTIVE

The purposes of the present work were twofold: (1) investigate same mechanisms involved in the development of fat cell hypertrophy in the experimental model of dyslipidemia and whole-body insulin resistance induced in rats chronically fed a sucrose-rich diet (SRD); and (2) analyze the possible beneficial effect of fish oil on these mechanisms.

METHODS

For 6 mo, male Wistar rats received a sucrose-rich diet (62.5% w/w sucrose, 8% corn oil) or a control diet in which sucrose was replaced by starch. After this period, the sucrose-fed animals were divided randomly into two groups: the first one continued with the same diet up to 8 mo and the second one received the same diet, but with corn oil replaced by 7% fish oil+1 % corn oil. Rats were fed with this diet for the next 2 mo.

RESULTS

Although an enlarged fat cell lipolysis and an impaired insulin-stimulated glucose uptake were present in the fat cells of SRD-fed rats, an increase of several key enzymes of the novo lipogenesis could be one of the possible mechanisms involved in visceral adiposity. The addition of dietary fish oil restored or improved the above abnormalities.

CONCLUSION

This study shows possible mechanisms conditioning the influence of nutrients on the development and management of dyslipidemia, insulin sensitivity, and fat cell accretion, all abnormalities present in the metabolic syndrome.