Increased translocation of cardiac protein kinase C beta2 accompanies mild cardiac hypertrophy in rats fed saturated fat

Polyunsaturated ω3 fatty acids prevent the cardiac hypertrophy in hypertensive rats

It has been demonstrated that supplementation with the two main omega 3 polyunsaturated fatty acids (ω3 FAs), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), leads to modifications in the cardiac physiology. ω3 FAs can affect the membrane's lipid composition, as well as proteins' location and/or function. The Na⁺/H⁺ exchanger (NHE1) is an integral membrane protein involved in the maintenance of intracellular pH and its hyperactivity has been associated with the development of various cardiovascular diseases such as cardiac hypertrophy. Our aim was to determine the effect of ω3 FAs on systolic blood pressure (SBP), lipid profiles, NHE1 activity, and cardiac function in spontaneously hypertensive rats (SHR) using Wistar rats (W) as normotensive control. After weaning, the rats received orally ω3 FAs (200 mg/kg body mass/day/ 4 months). We measured SBP, lipid profiles, and different echocardiography parameters, which were used to calculate cardiac hypertrophy index, systolic function, and ventricular geometry. The rats were sacrificed, and ventricular cardiomyocytes were obtained to measure NHE1 activity. While the treatment with ω3 FAs did not affect the SBP, lipid analysis of plasma revealed a significant decrease in omega-6/omega-3 ratio, correlated with a significant reduction in left ventricular mass index in SHR. The NHE1 activity was significantly higher in SHR compared with W. While in W the NHE1 activity was similar in both groups, a significant decrease in NHE1 activity was detected in SHRs supplemented with ω3 FAs, reaching values comparable with W. Altogether, these findings revealed that diet supplementation with ω3 FAs since early age prevents the development of cardiac hypertrophy in SHR, perhaps by decreasing NHE1 activity, without altering hemodynamic overload.

Are exercise-induced changes of fatty acids associated with cardiac hypertrophy in athletes? A pilot study

Study aim: In this study, we evaluated the effects of acute and chronic exercise on the plasma FAs and their association with cardiac hypertrophy indices.

Material and methods: In this pilot study, 15 sedentary and 15 athlete women underwent acute and long-term water aerobic exercise and their plasma FA levels and a number of electrocardiographic parameters, such as left ventricular end-diastolic diameter index (LVEDDI), left ventricular ejection fraction (LVEF), left ventricular mass index (LVMI), and wall thickness were evaluated before and after the exercise program.

Results: The acute exercise significantly increased palmitic and oleic acid levels in non-athletes and stearic acid in both groups. However, the same type of exercise decreased linoleic acid only in non-athlete women (p < 0.05). The water aerobics training caused a significant decrease in the levels of palmitic, stearic, and arachidonic acid, SFA/UFA, and ω3/ ω6 ratios and also an increase in α-Linolenic acid and MUFA in non-athletes. We found positive and negative correlations between LVEF with ω3 and SFA/UFA ratio in both groups, respectively. In the non-athlete group, the ω3/ω6 ratio showed negative correlations with LVMI and LVEDDI.

Conclusions: The study indicated that the 12-week exercise by sedentary women could make their plasma FAs composition similar to athlete women. Moreover, the plasma FA levels were associated with cardiac hypertrophy indices, showing the importance of FAs in physiological hypertrophy.

Lipid Use and Misuse by the Heart

The heart utilizes large amounts of fatty acids as energy providing substrates. The physiological balance of lipid uptake and oxidation prevents accumulation of excess lipids. Several processes that affect cardiac function, including ischemia, obesity, diabetes mellitus, sepsis, and most forms of heart failure lead to altered fatty acid oxidation and often also to the accumulation of lipids. There is now mounting evidence associating certain species of these lipids with cardiac lipotoxicity and subsequent myocardial dysfunction. Experimental and clinical data are discussed and paths to reduction of toxic lipids as a means to improve cardiac function are suggested.

PKCβ: Expanding role in hepatic adaptation of cholesterol homeostasis to dietary fat/cholesterol

Cholesterol homeostasis relies on an intricate network of cellular processes whose deregulation in response to Western type high-fat/cholesterol diets can lead to several life-threatening pathologies. Significant advances have been made in resolving the molecular identity and regulatory function of transcription factors sensitive to fat, cholesterol, or bile acids, but whether body senses the presence of both fat and cholesterol simultaneously is not known. Assessing the impact of a high-fat/cholesterol load, rather than an individual component alone, on cholesterol homeostasis is more physiologically relevant because Western diets deliver both fat and cholesterol at the same time. Moreover, dietary fat and dietary cholesterol are reported to act synergistically to impair liver cholesterol homeostasis. A key insight into the role of protein kinase C-β (PKCβ) in hepatic adaptation to high-fat/cholesterol diets was gained recently through the use of knockout mice. The emerging evidence indicates that PKCβ is an important regulator of cholesterol homeostasis that ensures normal adaptation to high-fat/cholesterol intake. Consistent with this function, high-fat/cholesterol diets induce PKCβ expression and signaling in the intestine and liver, while systemic PKCβ deficiency promotes accumulation of cholesterol in the liver and bile. PKCβ disruption results in profound dysregulation of hepatic cholesterol and bile homeostasis and imparts sensitivity to cholesterol gallstone formation. The available results support involvement of a two-pronged mechanism by which intestine and liver PKCβ signaling converge on liver ERK1/2 to dictate diet-induced cholesterol and bile acid homeostasis. Collectively, PKCβ is an integrator of dietary fat/cholesterol signal and mediates changes to cholesterol homeostasis.

Cardiac lipotoxicity: molecular pathways and therapeutic implications

Diabetes and obesity are both associated with lipotoxic cardiomyopathy exclusive of coronary artery disease and hypertension. Lipotoxicities have become a public health concern and are responsible for a significant portion of clinical cardiac disease. These abnormalities may be the result of a toxic metabolic shift to more fatty acid and less glucose oxidation with concomitant accumulation of toxic lipids. Lipids can directly alter cellular structures and activate downstream pathways leading to toxicity. Recent data have implicated fatty acids and fatty acyl coenzyme A, diacylglycerol, and ceramide in cellular lipotoxicity, which may be caused by apoptosis, defective insulin signaling, endoplasmic reticulum stress, activation of protein kinase C, MAPK activation, or modulation of PPARs.

Altered heart and kidney phospholipid fatty acid composition are associated with cardiac hypertrophy in hypertensive rats

OBJECTIVE

We examined the association of cardiac hypertrophy or fibrosis with the phospholipid fatty acid (FA) composition of heart and kidney in hypertensive rats.

DESIGN AND METHODS

Eight-week-old spontaneously hypertensive rats (SHRs) (n=8) and Wistar Kyoto rats (WKYs, n=8) as a normotensive control, were fed ad libitum for 6 weeks with regular AIN-76 diet. Phospholipid FA compositions in the left ventricle and kidney were measured and histological analyses were performed.

RESULTS

Compared with WKYs, SHRs had lower proportions of γ-linolenic acid, α-linolenic acid, eicosadienoic acid, eicosatrienoic acid, dihomo-γ-linoleic acid, docosadienoic acid and nervonic acid in heart, and stearic acid (SA), γ-linolenic acid, and eicosapentaenoic acid (EPA) in kidney. After adjusting for food intake, SHRs still maintained higher proportions of SA, and total saturated FAs in the heart and a lower proportion of eicosapentaenoic acid in the kidney. Additionally, compared with WKYs, SHRs showed larger cardiomyocyte diameters in the left ventricles, indicating cardiac hypertrophy and interstitial fibrosis. Cardiomyocyte diameters also positively correlated with cardiac SA (r=0.550, p<0.05) and negatively with kidney EPA (r=-0.575, p<0.05).

CONCLUSION

Tissue FA compositions were associated with cardiac hypertrophy in a hypertensive setting, implicating the pathogenic role of tissue FAs in hypertension and related complications.

Docosahexaenoic acid supplementation does not improve Western diet-induced cardiomyopathy in rats

Obesity increases risk for cardiomyopathy in the absence of hypertension, diabetes or ischemia. The fatty acid milieu, modulated by diet, may modify myocardial structure and function, lending partial explanation for the array of cardiomyopathic phenotypy. We sought to identify gross, cellular and ultrastructural myocardial changes associated with Western diet intake, and subsequent modification with docosahexaenoic acid (DHA) supplementation. Wistar and Sprague-Dawley (SD) rats received 1 of 3 diets: control (CON); Western (WES); Western + DHA (WES+DHA). After 12 weeks of treatment, echocardiography was performed and myocardial adiponectin, fatty acids, collagen, area occupied by lipid and myocytes, and ultrastructure were determined. Strain effects included higher serum adiponectin in Wistar rats, and differences in myocardial fatty acid composition. Diet effects were evident in that both WES and WES+DHA feeding were associated with similarly increased left ventricular (LV) diastolic cranial wall thickness (LVW(cr/d)) and decreased diastolic internal diameter (LVID(d)), compared to CON. Unexpectedly, WES+DHA feeding was associated additionally with increased thickness of the LV cranial wall during systole (LVW(cr/s)) and the caudal wall during diastole (LVW(ca/d)) compared to CON; this was observed concomitantly with increased serum and myocardial adiponectin. Diastolic dysfunction was present in WES+DHA rats compared to both WES and CON. Myocyte cross sectional area (CSA) was greater in WES compared to CON rats. In both fat-fed groups, transmission electron microscopy (TEM) revealed myofibril degeneration, disorganized mitochondrial cristae, lipid inclusions and vacuolation. In the absence of hypertension and whole body insulin resistance, WES+DHA intake was associated with more global LV thickening and with diastolic dysfunction, compared to WES feeding alone. Myocyte hypertrophy, possibly related to subcellular injury, is an early change that may contribute to gross hypertrophy. Strain differences in adipokines and myocardial fatty acid accretion may underlie heterogeneous data from rodent studies.

The role of dietary fatty acids in predicting myocardial structure in fat-fed rats

Background

Obesity increases the risk for development of cardiomyopathy in the absence of hypertension, diabetes or myocardial ischemia. Not all obese individuals, however, progress to heart failure. Indeed, obesity may provide protection from cardiovascular mortality in some populations. The fatty acid milieu, modulated by diet, may modify obesity-induced myocardial structure and function, lending partial explanation for the array of cardiomyopathic phenotypy in obese individuals.

Methods

Adult male Sprague-Dawley rats were fed 1 of the following 4 diets for 32 weeks: control (CON); 50% saturated fat (SAT); 40% saturated fat + 10% linoleic acid (SAT+LA); 40% saturated fat + 10% α-linolenic acid (SAT+ALA). Serum leptin, insulin, glucose, free fatty acids and triglycerides were quantitated. In vivo cardiovascular outcomes included blood pressure, heart rate and echocardiographic measurements of structure and function. The rats were sacrificed and myocardium was processed for fatty acid analysis (TLC-GC), and evaluation of potential modifiers of myocardial structure including collagen (Masson's trichrome, hydroxyproline quantitation), lipid (Oil Red O, triglyceride quantitation) and myocyte cross sectional area.

Results

Rats fed SAT+LA and SAT+ALA diets had greater cranial LV wall thickness compared to rats fed CON and SAT diets, in the absence of hypertension or apparent insulin resistance. Treatment was not associated with changes in myocardial function. Myocardial collagen and triglycerides were similar among treatment groups; however, rats fed the high-fat diets, regardless of composition, demonstrated increased myocyte cross sectional area.

Conclusions

Under conditions of high-fat feeding, replacement of 10% saturated fat with either LA or ALA is associated with thickening of the cranial LV wall, but without concomitant functional changes. Increased myocyte size appears to be a more likely contributor to early LV thickening in response to high-fat feeding. These findings suggest that myocyte hypertrophy may be an early change leading to gross LV hypertrophy in the hearts of "healthy" obese rats, in the absence of hypertension, diabetes and myocardial ischemia.

Loss of protein kinase Cbeta function protects mice against diet-induced obesity and development of hepatic steatosis and insulin resistance

Obesity is an energy balance disorder in which intake is greater than expenditure, with most excess calories stored as triglyceride (TG). We previously reported that mice lacking the beta-isoform of protein kinase C (PKCbeta), a diacylglycerol- and phospholipid-dependent kinase, exhibit marked reduction in the whole body TG content, including white adipose tissue (WAT) mass. To investigate the role of this signaling kinase in metabolic adaptations to severe dietary stress, we studied the impact of a high-fat diet (HFD) on PKCbeta expression and the effect of PKCbeta deficiency on profound weight gain. We report herein that HFD selectively increased PKCbeta expression in obesity-prone C57BL/6J mice, specifically in WAT; the expression levels were little or unchanged in the liver, muscle, kidney, and heart. Basal PKCbeta expression was also found to be elevated in WAT of obese ob/ob mice. Remarkably, mice lacking PKCbeta were resistant to HFD-induced obesity, showing significantly reduced WAT and slightly higher core body temperatures. Unlike lean lipodystrophic mouse models, these mice did not have fatty livers, nor did they exhibit insulin resistance. Moreover, PKCbeta(-/-) mice exhibited changes in lipid metabolism gene expression, and such alterations were accompanied by significant changes in serum adipokines. These observations suggest that PKCbeta deficiency induced a unique metabolic state congruous with obesity resistance, thus raising the possibility that dysregulation of PKCbeta expression could contribute to dietary fat-induced obesity and related disorders.

RBCK1, a protein kinase CbetaI (PKCbetaI)-interacting protein, regulates PKCbeta-dependent function

RBCK1 (RBCC protein interacting with PKC 1) has originally been identified as a protein kinase CbetaI (PKCbetaI)-binding partner by a two-hybrid screen and as one of the gene transcripts that increases during adult cardiac hypertrophy. To address whether RBCK1 and PKCbetaI functions are interconnected, we used cultured neonatal myocytes where we previously found that the activity of PKCbetaI is required for an increase in cell size, also called hypertrophy. In this study, we showed that acute treatment of cardiac myocytes with phenylephrine, a prohypertrophic stimulant, transiently increased the association of RBCK1 with PKCbetaI within 1 min. A prolonged phenylephrine treatment also resulted in an increase of the interaction of the two proteins. Endogenous RBCK1 protein levels increased upon phenylephrine-induced hypertrophy. Further, adenovirus-based RBCK1 overexpression in the absence of phenylephrine increased cardiac cell size. This RBCK1-mediated hypertrophy required PKCbeta activity, since the increase in cell size was inhibited when the RBCK1-expressing cells were treated with PKCbeta-selective antagonists, supporting our previous observation that both PKCbetaI and PKCbetaII are required for hypertrophy. Unexpectedly, RBCK1-induced increased cell size was inhibited by phenylephrine. This effect correlated with a decrease in the level of both PKCbeta isoforms. Most importantly, RNA interference for RBCK1 significantly inhibited the increase in cell size of cardiac myocytes following phenylephrine treatment. Our results suggest that RBCK1 binds PKCbetaI and is a key regulator of PKCbetaI function in cells and that, together with PKCbetaII, the three proteins are essential for developmental hypertrophy of cardiac myocytes.

Distinct modulation of angiotensin II-induced early left ventricular hypertrophic gene programming by dietary fat type

Long-term dietary fatty acid intake alters the development of left ventricular hypertrophy, but the linking signaling pathways are unclear. We studied the role and underlying signaling mechanisms of dietary fat intake in the early phase of the hypertrophic process. Rats assigned for 4 weeks of high-oil, high-fat, or standard diet were subjected to angiotensin II (Ang II; 33 microg/kg/h, subcutaneous) or vehicle infusion for 24 h. The Ang II-induced increase in left ventricular mRNA levels of hypertrophy-associated genes was higher in rats fed the high-oil diet compared with the standard diet. Western blotting revealed that, in parallel with changes in gene expression, the high-oil diet increased c-Jun N-terminal kinase phosphorylation (P < 0.001). Ang II increased p38 mitogen-activated protein kinase (MAPK) phosphorylation in rats fed the high-fat diet (3-fold; P < 0.01). The increase in transcription factor activator protein-1 (AP-1) DNA binding activity in response to Ang II was higher in rats fed the high-oil diet compared with those fed the standard diet (P < 0.001). Ang II downregulated inducible nitric oxide synthase mRNA levels in fatty acid-supplemented groups compared with the standard diet group. These results show that dietary fat type modulates the early activation of hypertrophic genes in pressure-overloaded myocardium involving the distinct activation of AP-1 and MAPK signal transduction pathways.

High-fat diet prevents cardiac hypertrophy and improves contractile function in the hypertensive dahl salt-sensitive rat

1. The role that dietary lipid and plasma fatty acid concentration play in the development of cardiac hypertrophy in response to hypertension is not clear. 2. In the present study, we treated Dahl salt-sensitive rats with either normal chow (NC), normal chow with salt added (NC + salt) or a diet high in long-chain saturated fatty acids with added salt (HFD + salt). Cardiac function was assessed by echocardiography and left ventricular (LV) catheterization. 3. The HFD + salt group had significantly higher plasma free fatty acid concentrations and myocardial triglyceride content compared with the NC + salt group, but did not upregulate the activity of the fatty acid oxidation enzyme medium chain acyl-coenzyme A dehydrogenase. Systolic blood pressure was elevated to a similar extent in the NC + salt and HFD + salt groups compared with the NC group. Although LV mass was increased in the NC + salt group compared with the NC group, LV mass in the HFD + salt group did not differ from that of the NC group and was significantly lower than that in the NC + salt group. 4. There was no evidence of cardiac dysfunction in the NC + salt group compared with the NC group; however, high fat feeding significantly increased LV contractile performance (e.g. increased cardiac output and peak dP/dt). 5. In conclusion, the HFD + salt diet prevented the hypertrophic response to hypertension and improved the contractile performance of the heart. It remains to be determined whether preventing cardiac hypertrophic adaptations would be deleterious to the heart if the hypertensive stress is maintained long term.

Effects of excess salt and fat intake on myocardial function and infarct size in rat

Important risk factors for cardiovascular disease include excess dietary intake of saturated fat and (or) salt. This study tested the hypothesis that excess intakes of saturated fat (e.g., beef tallow) and salt cause greater myocardial cell death following ischemia-reperfusion injury than each risk factor alone. Male rats were divided into four groups: basal fat diet (4.5% as calories; control), high fat diet (40% as calories; FAT), basal fat diet and high salt (1% NaCl solution; SALT) and high fat diet and high salt (FATSALT). The gain in body weight was significantly higher for FAT and FATSALT groups than those of either the control or the SALT group. Five weeks of exposure to the dietary regimens did not significantly affect the coronary flow rate and except for the salt-fed group, had no effect on the rate-pressure-product of the isolated heart perfused in Langendorff mode. Although infarct size was not affected by the high fat diet, it was reduced by the high salt regimen relative to the high fat diet or the control groups. When rats were fed the FAT and SALT combination, the effect of salt feeding on infarct size was not observed. In addition, the FATSALT group displayed a more marked deterioration in contractile function following ischemia-reperfusion injury than the other groups. In conclusion, short-term intake of a high fat diet, which significantly increases body weight, does not worsen ischemia-reperfusion injury although the treatment prevents the reduction of infarct size associated with high salt feeding.