Sukhinder K. Cheema

Dietary fat: exogenous determination of membrane structure and cell function.

Evidence indicates that principal features of the membrane involve structural organization of lipids in the form of a bilayer with functional proteins either bound to the bilayer surface or inserted into the bilayer and interacting within specific domains in the lipid milieux. In homeotherms, intrinsic and extrinsic factors apparently form the basis for determination of membrane lipid composition and thus membrane physicochemical properties. Moreover, many intrinsic metabolic controls, such as fatty acid desaturation and phospholipid biosynthesis, may be attenuated by change in the nature of the extrinsic or dietary influence. This review will focus on the role of dietary fat as a determinant of subcellular structural constituents to illustrate that feeding nutritionally adequate diets differing in fatty acid composition can induce physiological transitions in membrane function involving the activity of enzymes responsible for synthesis of membrane constituents, hormone‐activated functions and expression of activity in the cell nucleus.—Clandinin, M. T.; Cheema, S.; Field, C. J., Garg, M. L., Venkatraman, J., Clandinin, T. R. Dietary fat: exogenous determination of membrane structure and cell function. FASEB J. 5: 2761‐2769; 1991.

Dietary Lipids Influence Insulin Action

Insulin binding and insulin responsiveness are altered by dietary fat-induced changes in the fatty acid composition of the adipocyte plasma membrane. Feeding a high P/S diet increased polyunsaturated fatty acid content of major membrane phospholipids of adipocyte plasma membrane in normal and diabetic animals, increased membrane linoleic acid content, and prevented a decrease in arachidonic acid level in diabetic animals. The high P/S diet increased insulin binding in control animals. Animals fed the high P/S diet had significantly higher rates of insulin-stimulated glucose transport and lipogenesis than did animals fed the low P/S diet. Feeding a high P/S diet significantly increased the amount of glucose transported when expressed as a function of the specific amount of insulin bound. To determine if dietary fat-induced alterations in the fatty acid composition of skeletal muscle lipid alter insulin-dependent and basal muscle metabolism, contralateral epitrochlearis and extensor digitorum longus muscles were isolated and incubated in vitro. High levels of dietary omega-3 fatty acids reduced PGE2 and PGF2 alpha synthesis in extensor digitorum longus and epitrochlearis muscle. Insulin increased glucose and amino acid transport; the increase in glucose transport by insulin was significantly greater after consumption of the high omega-3 fatty acid diet. Rats fed high levels of omega-3 fatty acids showed reduced net protein degradation in the presence and absence of insulin due to decreased rates of protein degradation and synthesis. These experiments indicate that high levels of dietary omega-3 fatty acids alter muscle membrane composition, glucose transport, and metabolism of muscle protein. To determine if dietary fatty acids alter the onset of diabetes and insulin binding to liver nuclei in spontaneously diabetic rats, weanling rats were fed chow or semipurified diets containing 20% (w/w) fat of either high or low P/S ratio. Feeding a high P/S diet increased insulin binding to liver nuclei of control and diabetic animals. Although diet did not alter the onset of diabetes, insulin binding to liver nuclei is higher in animals at the onset of diabetes than in highly diabetic animals. Eight-week-old female C57 B 6J lean and ob/ob mice were fed semipurified diets containing 20% (w/w) fat of either high or low P/S ratio to investigate the effect of diet on specific binding of insulin to liver nuclei. Insulin binding was highest in nuclei from lean mice fed a high P/S diet. Specific binding of insulin to nuclei from obese mice was also increased by the high P/S diet, but to a lesser extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-diabetic Activity of Swertiamarin is due to an Active Metabolite, Gentianine, that Upregulates PPAR-γ Gene Expression in 3T3-L1 cells

We have previously shown the anti‐diabetic effects of swertiamarin; however, pharmacokinetic analysis showed that swertiamarin had a plasma half‐life of 1.3 h. Gentianine is an active metabolite of swertiamarin that possesses a pharmacophoric moiety. The aim of this study was to explore the possibility whether the anti‐diabetic effect of swertiamarin is due to gentianine. Swertiamarin treatment had no significant effect on adipogenesis, or the mRNA expression of PPAR‐γ and GLUT‐4; however, there was a significant increase in the mRNA expression of adiponectin. On the other hand, treatment with gentianine significantly increased adipogenesis, which was associated with a significant increase in the mRNA expression of PPAR‐γ, GLUT‐4 and adiponectin. These findings suggest, for the first time, that the anti‐diabetic effect of swertiamarin is due to gentianine, an active metabolite of swertiamarin. Copyright

Developmental programming of lipid metabolism and Aortic Vascular Function in C57Bl/6 Mice: A novel study suggesting an involvement of LDL-receptor

We have previously shown that a maternal high-fat diet, rich in saturated fatty acids (SFA), alters the lipid metabolism of their adult offspring. The present study was designed to investigate 1) whether alterations in hepatic LDL-receptor (LDL-r) expression may serve as a potential mechanism of developmental programming behind the altered lipid metabolism of the offspring, 2) whether altered lipid metabolism leads to aortic vascular dysfunction in the offspring, 3) whether deleterious effects of SFA exposure preweaning are influenced by postweaning diet, and 4) whether gender-specific programming effects are observed. Female C57Bl/6 mice were fed a high-SFA diet or regular chow during gestation and lactation while their pups, both male and female, received either SFA or a chow diet after weaning. Male offspring obtained from mothers fed an SFA diet and those who continued on chow postweaning had higher plasma triglycerides and total cholesterol, whereas female offspring had higher plasma total and LDL cholesterol levels, lower hepatic LDL-r mRNA expression, and reduced aortic contractile responses compared with the offspring that were fed chow throughout the study. A comparison of the postweaning diet revealed significantly lower hepatic LDL-r expression along with significantly higher plasma LDL-cholesterol concentration in the female offspring that were obtained from mothers fed an SFA diet and who continued on an SFA diet postweaning, compared with the female offspring that were obtained from mothers fed an SFA diet but who continued on chow postweaning. In conclusion, we report a novel observation of hepatic LDL-r-mediated programming of altered lipid metabolism, along with aortic vascular dysfunction, in the female offspring of mothers fed a high-SFA diet. Male offspring only exhibited dyslipidemia, suggesting gender-mediated programming. This study further highlighted the role of postweaning diets in overriding the effects of maternal programming.

Diet fat alters expression of genes for enzymes of lipogenesis in lean and obese mice

The objective of this experiment was to determine the effect of polyunsaturated fatty acids on gene expression for fatty acid synthase, acetyl CoA-carboxylase, malic enzyme, pyruvate kinase, and phosphoenolpyruvate carboxykinase in obese mice. Eight-week-old female lean and obese mice were fed semi-purified diets containing 20% (w/w) fat of either high or low polyunsaturated to saturated (P/S) fatty acid ratio for four weeks. Total RNA was isolated from liver and was hybridized to cDNA probes for the above enzymes. Consumption of a high P/S diet decreased mRNA levels for all the lipogenic enzymes studied in both lean and obese mice. Compared to lean mice, obese mice exhibited a higher mRNA level for fatty acid synthase, acetyl CoA-carboxylase, malic enzyme, and pyruvate kinase in animals fed either a high or low P/S diet. Enzyme-specific activities followed the same profile as the mRNA levels in both lean and obese mice fed a high or low P/S diet. The decrease in liver fatty acid synthase mRNA level was more pronounced in lean mice compared to obese mice, suggesting that the obese mice may be more resistant to polyunsaturated fatty acid feedback control of gene expression.

Dietary rhubarb ( Rheum rhaponticum ) stalk fibre stimulates cholesterol 7α-hydroxylase gene expression and bile acid excretion in cholesterol-fed C57BL/6J mice

Both experimental and clinical studies have indicated that a novel source of dietary fibre, produced from rhubarb (Rheum rhaponticum) stalks, is potentially hypolipidaemic. The present study, using C57BL/6J mice, was undertaken to examine if this fibre source affects cholesterol degradation. Mice were maintained on semi-purified diets containing 50 g rhubarb fibre or cellulose/kg with or without 5 g cholesterol/kg for 4 weeks. In cholesterol-supplemented mice, rhubarb fibre caused significant lowering of plasma cholesterol (-13%) and the hepatic concentrations of total cholesterol (-34%) and cholesteryl esters (-34%). In parallel to the reduction of hepatic cholesteryl ester content, animals fed on rhubarb fibre had significantly lower activity of acyl CoA: cholesterol acyltransferase (EC 2.3.1.26) than the mice maintained on a diet containing cellulose and cholesterol. Rhubarb-fibre feeding accelerated the faecal bile-acid loss and diminished the gall-bladder bile-acid pool in both the normal and the cholesterol-fed mice. The increase in the bile-acid excretion was positively correlated with an increased activity as well as mRNA abundance of cholesterol 7 alpha-hydroxylase (EC 1.14.13.17). The increased excretion of bile acids and induction of cholesterol 7 alpha-hydroxylase activity may account for the hypocholesterolaemic effect of rhubarb fibre.

Dietary Omega-3 Polyunsaturated Fatty Acids Alter the Fatty Acid Composition of Hepatic and Plasma Bioactive Lipids in C57BL/6 Mice: A Lipidomic Approach

Background Omega (n)-3 polyunsaturated fatty acids (PUFA) are converted to bioactive lipid components that are important mediators in metabolic and physiological pathways; however, which bioactive compounds are metabolically active, and their mechanisms of action are still not clear. We investigated using lipidomic techniques, the effects of diets high in n-3 PUFA on the fatty acid composition of various bioactive lipids in plasma and liver. Methodology and Principal Findings Female C57BL/6 mice were fed semi-purified diets (20% w/w fat) containing varying amounts of n-3 PUFA before mating, during gestation and lactation, and until weaning. Male offspring were continued on their mothers’ diets for 16 weeks. Hepatic and plasma lipids were extracted in the presence of non-naturally occurring internal standards, and tandem electrospray ionization mass spectrometry methods were used to measure the fatty acyl compositions. There was no significant difference in total concentrations of phospholipids in both groups. However, there was a significantly higher concentration of eicosapentaenoic acid containing phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and cholesteryl esters (CE) (p < 0.01) in the high n-3 PUFA group compared to the low n-3 PUFA group in both liver and plasma. Plasma and liver from the high n-3 PUFA group also had a higher concentration of free n-3 PUFA (p < 0.05). There were no significant differences in plasma concentrations of different fatty acyl species of phosphatidylethanolamine, triglycerides, sphingomyelin and ceramides. Conclusions/Significance Our findings reveal for the first time that a diet high in n-3 PUFA caused enrichment of n-3 PUFA in PC, LPC, CE and free fatty acids in the plasma and liver of C57BL/6 mice. PC, LPC, and unesterified free n-3 PUFA are important bioactive lipids, thus altering their fatty acyl composition will have important metabolic and physiological roles.

Maternal dietary fat intake during gestation and lactation alters tissue fatty acid composition in the adult offspring of C57Bl/6 mice

We investigated the effects of maternal dietary fat intake during gestation and lactation on the tissue fatty acid composition of the adult offspring. Female C57Bl/6 mice were fed high fat diets enriched with lard or safflower oil or chow during mating, gestation and lactation. The offspring obtained from each group of mothers were continued on diets rich in lard, safflower oil or chow post-weaning until 11 weeks of age. Livers and hearts were collected for fatty acid analysis. A maternal diet rich in safflower oil was associated with enrichment of hepatic tissue with n-3 polyunsaturated fatty acids in the offspring fed chow post-weaning compared to the offspring fed chow throughout. However, a continuous exposure to a safflower oil- as well as lard-rich diet during the pre- and post-weaning time periods was associated with reduced content of docosahexaenoic acid in both liver and heart tissues compared to the offspring fed chow throughout. In conclusion, this study demonstrated lasting effects of maternal dietary fat intake, as well as an interaction between pre- and post-weaning diets, on the tissue fatty composition in adult offspring.

Hyperlipidaemic effect of fish oil in Bio F1B hamsters.

We investigated the dietary influence of low and high levels of fish oil, supplemented with or without dietary cholesterol, on the plasma lipoprotein profile in Bio F1B hamsters, a model susceptible to diet-induced hyperlipidaemia. The MIX diet, a diet supplemented with a mixture of lard and safflower-seed oil, was used as the control diet to maintain the saturated MUFA and PUFA levels similar to the fish-oil diet. The animals were fed the specific diets for 2 weeks and fasted for 14 h before killing. The plasma from the animals fed high levels of fish oil was milky and rich in chylomicron-like particles. The plasma total cholesterol, VLDL- and LDL-cholesterol and -triacylglycerol concentrations were significantly higher, whereas HDL-cholesterol was lower in hamsters fed fish oil compared with the MIX-diet-fed hamsters. Increasing the amount of fat in the diet increased plasma lipids in both the fish-oil- and the MIX-diet-fed hamsters; however, this hyperlipidaemic effect of dietary fat level was greater in the hamsters fed the fish-oil diet. The hepatic lipid concentrations were not dramatically different between the fish-oil-fed and the MIX-diet-fed hamsters. However, the hepatic LDL-receptor mRNA levels were significantly low in the fish-oil-fed hamsters compared with the MIX-diet-fed hamsters. Increasing the amount of fish oil in the diet further decreased the hepatic LDL-receptor mRNA expression. It is concluded that F1B hamsters are susceptible to fish-oil-induced hyperlipidaemia, especially at high fat levels, and this increase is partially explained by the inhibition of hepatic LDL-receptor mRNA expression.

Novel regulatory roles of omega-3 fatty acids in metabolic pathways: a proteomics approach

BackgroundOmega-3 polyunsaturated fatty acids (n-3 PUFA) have been shown to alleviate the symptoms of metabolic disorders, such as heart disease, diabetes, obesity and insulin resistance. Several putative mechanisms by which n-3 PUFA elicit beneficial health effects have been proposed; however, there is still a shortage of knowledge on the proteins and pathways that are regulated by n-3 PUFA.MethodsUsing two dimensional polyacrylamide gel electrophoresis (2D-PAGE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, we investigated the effects of diets high or low in n-3 PUFA on hepatic proteomic profile of C57BL/6 mice.ResultsThe findings show for the first time that high dietary n-3 PUFA reduced the expression of regucalcin, adenosine kinase and aldehyde dehydrogenase. On the other hand, diets high in n-3 PUFA increased the expression of apolipoprotein A-I, S-adenosylmethionine synthase, fructose-1, 6-bisphosphatase, ketohexokinase, malate dehydrogenase, GTP-specific succinyl CoA synthase, ornithine aminotransferase and protein disulfide isomerase-A3.ConclusionsOur findings revealed for the first time that n-3 PUFA causes alterations in several novel functional proteins involved in regulating lipid, carbohydrate, one-carbon, citric acid cycle and protein metabolism, suggesting integrated regulation of metabolic pathways. These novel proteins are potential targets to develop therapeutic strategies against metabolic disorders.