Improvement in the High-Fat Diet-Induced Dyslipidemia and Adiponectin Levels by Fish Oil Feeding Combined with Food Restriction in Obese KKAy Mice

Effects of dietary palmitoleic acid on vascular function in aorta of diabetic mice

BACKGROUND

Chronic hyperglycemia in diabetes causes atherosclerosis and progresses to diabetic macroangiopathy, and can lead to coronary heart disease, myocardial infarction and cerebrovascular disease. Palmitoleic acid (POA) is a product of endogenous lipogenesis and is present in fish and vegetable oil. In human and animal studies, POA is reported as a beneficial fatty acid related to insulin sensitivity and glucose tolerance. However, few studies have reported its effects on aortic function in diabetes. Here, we investigated the effects of POA administration on vascular function in KKAy mice, a model of type 2 diabetes.

METHODS

Male C57BL/6 J (control) and KKAy (experimental) mice at the age of 14 weeks were used in the present study. For each mouse strain, one group was fed with reference diet and a second group was fed POA-containing diet for 2 weeks. The vascular reactivities of prepared aortic rings were then measured in an organ bath to determine if POA administration changed vascular function in these mice.

RESULTS

KKAy mice treated with POA exhibited decreased plasma glucose levels compared with mice treated with reference diet. However, endothelium-dependent vasorelaxant responses to acetylcholine and protease-activated receptor 2 activating protein, which are attenuated in the aorta of KKAy mice compared to C57BL/6 J mice under a reference diet, were not affected by a 2-week POA treatment. In addition, assessment of vasoconstriction revealed that the phenylephrine-induced vasoconstrictive response was enhanced in KKAy mice compared to C57BL/6 J mice under a reference diet, but no effect was observed in KKAy mice fed a POA-containing diet. In contrast, there was an increase in vasoconstriction in C57BL/6 J mice fed the POA-containing diet compared to mice fed a reference diet. Furthermore, the vasoconstriction in aorta in both C57BL/6 J and KKAy mice fed a POA-containing diet were further enhanced under hyperglycemic conditions compared to normal glucose conditions in vitro. In the hyperinsulinemic, and hyperinsulinemic combined with hyperglycemic conditions, vasoconstriction was increased in KKAy mice fed with POA.

CONCLUSION

These results suggest that POA intake enhances vasoconstriction under hyperglycemic and hyperinsulinemic conditions, which are characteristics of type 2 diabetes, and may contribute to increased vascular complications in diabetes.

Ameliorating effects of Sporidiobolus pararoseus extract on dyslipidemia in mice with high fat diet induced obesity

The study investigated how an extract of Sporidiobolus pararoseus (S.p.) affects lipid metabolism in Kunming mice that were obese as a result of being fed a high-fat diet; the control group were administered Max EPA fish oil. Ten mice were randomly selected from a pool of 60 mice for the control group and the remaining 50 mice were fed with a high-fat diet to establish a dyslipidemia model. After 4 weeks, these 50 mice were randomly distributed among 5 groups: high-fat model group; Max EPA group; and 3 groups of mice fed different doses of S.p. extract (low dose, medium dose, and high dose). After 8 weeks, the mice were sacrificed and the relevant parameters were measured. Compared with the high-fat model group, the group administered the high dose of S.p. extract showed significantly decreased body mass and serum levels of total cholesterol, triglycerides, and low-density lipoprotein cholesterol, and increased levels of high-density lipoprotein cholesterol. The results from RT-PCR showed that the mRNA expression of sterol regulatory element-binding protein 1c, fatty acid synthesis enzyme, and acetyl-CoA carboxylase was lower in the groups supplemented with S.p. extract than in the high-fat model group, whereas the expression of carnitine palmitoyltransferase 1 was higher in the group supplemented with S.p. extract than in the high-fat model group. Our results suggest that taking S.p. extract could benefit patients with dyslipidemia. Therefore, S.p. extract should be developed as a dietary supplement to improve lipid metabolism in obese people.

Eicosapentaenoic acid ethyl ester improves endothelial dysfunction in type 2 diabetic mice

Background

Eicosapentaenoic acid (EPA) is thought to have many beneficial effects, such as anti-atherosclerogenic and anti-inflammatory properties. However, few studies have reported its effects of endothelial dysfunction in diabetes and its direct effects on the aorta. Here, we investigated the effects of EPA treatment on impaired endothelium-dependent relaxation of the aorta in KKAy mice, a model of type 2 diabetes.

Methods

Male KKAy mice were fed a high-fat (HF) diet for 8 weeks to induce diabetes, after which they were divided into two groups. One group was fed a HF diet, and the other group was fed a HF diet containing EPA ethyl ester (EPA-E, 10 mg/day) for 4 weeks. Then, the vascular reactivities of prepared aortic rings were measured in an organ bath to determine if EPA-E administration changed vascular function in these diabetic mice. In addition, we examined effect of EPA-E and its metabolites to vascular action using aorta separated from C57BL/6 J mice.

Results

Although EPA-E administration did not change the plasma glucose and insulin levels in diabetic mice, total cholesterol levels were significantly decreased. The aorta extracted from EPA-E untreated diabetic mice showed impaired endothelium-dependent relaxation in response to acetylcholine (ACh). However, EPA-E administration improved the relaxation response to ACh to the control levels observed in non-diabetic C57BL/6 J mice. On the other hand, endothelium-independent relaxation in response to sodium nitroprusside did not significantly differ among these three groups. The enhanced contractile response by phenylephrine in diabetic mice was not altered by the administration of EPA-E. In addition, the direct administration of EPA-E metabolites such as EPA, docosahexaenoic acid, and docosapentaenoic acid led to vasodilation in the aortic rings of C57BL/6 J mice.

Conclusion

These results showed that chronic EPA-E administration prevented the development of endothelial dysfunction in KKAy mice, partly via the direct action of EPA-E metabolites on the aorta.

Different Dietary Proportions of Fish Oil Regulate Inflammatory Factors but Do Not Change Intestinal Tight Junction ZO-1 Expression in Ethanol-Fed Rats

Sixty male Wistar rats were fed a control or an ethanol-containing diet in groups C or E. The fat compositions were adjusted with 25% or 57% fish oil substituted for olive oil in groups CF25, CF57, EF25, and EF57. Hepatic thiobarbituric acid-reactive substance (TBARS) levels, cytochrome P450 2E1 protein expression, and tumor necrosis factor- (TNF-) α, interleukin- (IL-) 1β, IL-6, and IL-10 levels, as well as intracellular adhesion molecule (ICAM)-1 levels were significantly elevated, whereas plasma adiponectin level was significantly reduced in group E (p < 0.05). Hepatic histopathological scores of fatty change and inflammation, in group E were significantly higher than those of group C (p < 0.05). Hepatic TBARS, plasma ICAM-1, and hepatic TNF-α, IL-1β, and IL-10 levels were significantly lower, and plasma adiponectin levels were significantly higher in groups EF25 and EF57 than those in group E (p < 0.05). The immunoreactive area of the intestinal tight junction protein, ZO-1, showed no change between groups C and E. Only group CF57 displayed a significantly higher ZO-1 immunoreactive area compared to group C (p = 0.0415). 25% or 57% fish oil substituted for dietary olive oil could prevent ethanol-induced liver damage in rats, but the mechanism might not be related to intestinal tight junction ZO-1 expression.

L-carnitine prevents metabolic steatohepatitis in obese diabetic KK-Ay mice

AIM

Pharmacological treatment for metabolic syndrome-related non-alcoholic steatohepatitis has not been established. We investigated the effect of L-carnitine, an essential substance for β-oxidation, on metabolic steatohepatitis in mice.

METHODS

Male KK-A^y mice were fed a high-fat diet (HFD) for 8 weeks, with supplementation of L-carnitine (1.25 mg/mL) in drinking water for the latter 4 weeks.

RESULTS

Serum total carnitine levels were decreased following HFD feeding, whereas the levels were reversed almost completely by L-carnitine supplementation. In mice given L-carnitine, exacerbation of hepatic steatosis and hepatocyte apoptosis was markedly prevented even though HFD feeding was continued. Body weight gain, as well as hyperlipidemia, hyperglycemia, and hyperinsulinemia, following HFD feeding were also significantly prevented in mice given L-carnitine. High-fat diet feeding elevated hepatic expression levels of carnitine palmitoyltransferase 1A mRNA; however, production of β-hydroxybutyrate in the liver was not affected by HFD alone. In contrast, L-carnitine treatment significantly increased hepatic β-hydroxybutyrate contents in HFD-fed mice. L-carnitine also blunted HFD induction in sterol regulatory element binding protein-1c mRNA in the liver. Furthermore, L-carnitine inhibited HFD-induced serine phosphorylation of insulin receptor substrate-1 in the liver. L-carnitine decreased hepatic free fatty acid content in 1 week, with morphological improvement of swollen mitochondria in hepatocytes, and increases in hepatic adenosine 5'-triphosphate content.

CONCLUSIONS

L-carnitine ameliorates steatohepatitis in KK-A^y mice fed an HFD, most likely through facilitating mitochondrial β-oxidation, normalizing insulin signals, and inhibiting de novo lipogenesis in the liver. It is therefore postulated that supplementation of L-carnitine is a promising approach for prevention and treatment of metabolic syndrome-related non-alcoholic steatohepatitis.

Does Fish Oil Have an Anti-Obesity Effect in Overweight/Obese Adults? A Meta-Analysis of Randomized Controlled Trials

Context

Accumulating evidence has suggested favorable effects of fish oil on weight loss in animal experiments; however, findings remain inconsistent in humans.

Objects

The meta-analysis was performed to investigate the influence of fish oil on some parameters of body composition in overweight/obese adults.

Design

Human randomized, placebo-controlled trials were identified by a systematic search of Embase, PubMed, the Cochrane Library, web of science and reference lists of related reviews and articles. The random-effects model was used to estimate the calculated results.

Results

In total, 21 studies with 30 study arms were included in this analysis. Calculated results of the meta-analysis demonstrated that fish oil had no effect on reducing body weight (overall SMD = -0.07, 95% CI -0.21 to 0.07, P = 0.31) and BMI (overall SMD = -0.09, 95% CI -0.22 to 0.03, P = 0.14) whether alone or combined with life modification intervention in overweight/obese subjects. However, waist circumference was significantly reduced (SMD = -0.23, 95% CI -0.40 to -0.06, P = 0.008) in those with fish oil supplementation combined with life modification intervention. Waist hip ratio (WHR) was significantly reduced (overall SMD = -0.52 95% CI -0.76 to -0.27, P < 0.0005) in fish oil supplemented individuals with or without combination life modification intervention.

Conclusion

Current evidence cannot support an exact anti-obesity role of n-3 polyunsaturated fatty acids (PUFAs) in overweight/obese subjects. However, these subjects may benefit from reducing abdominal fat with fish oil supplementation especially when combined with life modification intervention. Further large-scale and long-term clinical trials are needed to gain definite conclusions.