Exercise down-regulates hepatic fatty acid synthase in streptozotocin-treated rats

Physical activity to reduce PCSK9 levels

The amount of physical activity (PA) people practice everyday has been reducing in the last decades. Sedentary subjects tend to have an impaired lipid plasma profile with a higher risk of atherosclerosis and related cardio- and cerebrovascular events. Regular PA helps in both primary and secondary cardiovascular prevention because of its beneficial effect on the whole metabolism. Several studies reported lower levels of plasma lipids in trained subjects, but the precise mechanisms by which PA modulates lipoproteins remain only partially described. Thereupon, proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serin protease whose main function is to reduce the amount of low-density lipoprotein cholesterol (LDL-C) receptors, with the direct consequence of reducing LDL-C uptake by the liver and increasing its circulating pool. Accordingly, recently developed PCSK9 inhibitors improved cardiovascular prevention and are increasingly used to reach LDL-C goals in patients at high CV risk. Whether PA can modulate the levels of PCSK9 remains partially explored. Recent studies suggest PA as a negative modulator of such a deleterious CV mediator. Yet the level of evidence is limited. The aim of this review is to summarize the recent reports concerning the regulatory role of PA on PCSK9 plasma levels, highlighting the beneficial role of regular exercise on the prevention of atherosclerosis and overall CV health.

Electric pulse stimulation inhibited lipid accumulation on C2C12 myotubes incubated with oleic acid and palmitic acid

OBJECTIVE

To investigate the effect of electrical pulse stimulation (EPS) on lipid accumulation and alteration of fatty acid-related enzymes in C2C12 myotubes incubated with fatty acids.

METHODS

Mouse C2C12 myotubes were incubated with oleic acid and palmitic acid, and differentiated C2C12 myotubes were treated with EPS, oil-red O (ORO), BODIPY staining and triglyceride (TG) content were examined. Total RNA was isolated, and real-time polymerase chain reaction analysis was performed.

RESULTS

(1) EPS decreased TG content (p < .01). (2) EPS significantly induced the mRNA expression of FAD/CD36 (p < .05), FATP4 (p < .001), FABP1 (p < .01) and FABP5 (p < .01). (3) EPS significantly inhibited the mRNA expression of fatty acid synthase (p < .01). (4) Adipose triglyceride lipase and hormone-sensitive lipase expression were significantly elevated (p < .001), and induced the mRNA expression of CPT1 (p < .01), ACOX1 (p < .05), UCP3 (p < .05) and PPARα (p < .001) after EPS.

CONCLUSION

EPS reduced lipid droplet accumulation; enhanced CD36, FATP4, FABP1 and FABP5 expression; inhibited C2C12 myotube fatty acid re-esterification; and promoted fatty acid oxidation in C2C12 myotubes.

Fatty acid synthase polymorphisms, tumor expression, body mass index, prostate cancer risk, and survival

PURPOSE

Fatty acid synthase (FASN) regulates de novo lipogenesis, body weight, and tumor growth. We examined whether common germline single nucleotide polymorphisms (SNPs) in the FASN gene affect prostate cancer (PCa) risk or PCa-specific mortality and whether these effects vary by body mass index (BMI).

METHODS

In a prospective nested case-control study of 1,331 white patients with PCa and 1,267 age-matched controls, we examined associations of five common SNPs within FASN (and 5 kb upstream/downstream, R(2) > 0.8) with PCa incidence and, among patients, PCa-specific death and tested for an interaction with BMI. Survival analyses were repeated for tumor FASN expression (n = 909).

RESULTS

Four of the five SNPs were associated with lethal PCa. SNP rs1127678 was significantly related to higher BMI and interacted with BMI for both PCa risk (P(interaction) = .004) and PCa mortality (P(interaction) = .056). Among overweight men (BMI > or = 25 kg/m(2)), but not leaner men, the homozygous variant allele carried a relative risk of advanced PCa of 2.49 (95% CI, 1.00 to 6.23) compared with lean men with the wild type. Overweight patients carrying the variant allele had a 2.04 (95% CI, 1.31 to 3.17) times higher risk of PCa mortality. Similarly, overweight patients with elevated tumor FASN expression had a 2.73 (95% CI, 1.05 to 7.08) times higher risk of lethal PCa (P(interaction) = .02).

CONCLUSION

FASN germline polymorphisms were significantly associated with risk of lethal PCa. Significant interactions of BMI with FASN polymorphisms and FASN tumor expression suggest FASN as a potential link between obesity and poor PCa outcome and raise the possibility that FASN inhibition could reduce PCa-specific mortality, particularly in overweight men.

Activation of the mitogen-activated protein kinase (MAPK) signalling pathway in the liver of mice is related to plasma glucose levels after acute exercise

AIMS/HYPOTHESIS

We aimed to identify, in the liver of mice, signal transduction pathways that show a pronounced regulation by acute exercise. We also aimed to elucidate the role of metabolic stress in this response.

METHODS

C57Bl6 mice performed a 60 min run on a treadmill under non-exhaustive conditions. Hepatic RNA and protein lysates were prepared immediately after running and used for whole-genome-expression analysis, quantitative real-time PCR and immunoblotting. A subset of mice recovered for 3 h after the treadmill run. A further group of mice performed the treadmill run after having received a vitamin C- and vitamin E-enriched diet over 4 weeks.

RESULTS

The highest number of genes differentially regulated by exercise in the liver was found in the mitogen-activated protein kinase (MAPK) signalling pathway, with a pronounced and transient upregulation of the transcription factors encoded by c-Fos (also known as Fos), c-Jun (also known as Jun), FosB (also known as Fosb) and JunB (also known as Junb) and phosphorylation of hepatic MAPK. Acute exercise also activated the p53 signalling pathway. A major role for oxidative stress is unlikely since the antioxidant-enriched diet did not prevent the activation of the MAPK pathway. In contrast, lower plasma glucose levels after running were related to enhanced levels of MAPK signalling proteins, similar to the upregulation of Igfbp1 and Pgc-1alpha (also known as Ppargc1a). In the working muscle the activation of the MAPK pathway was weak and not related to plasma glucose concentrations.

CONCLUSIONS/INTERPRETATION

Metabolic stress evidenced as low plasma glucose levels appears to be an important determinant for the activation of the MAPK signalling pathway and the transcriptional response of the liver to acute exercise.

Daily exercise increases hepatic fatty acid oxidation and prevents steatosis in Otsuka Long-Evans Tokushima Fatty rats

Exercise training is commonly prescribed for treatment of nonalcoholic fatty liver disease (NAFLD). We sought to determine whether exercise training prevents the development of NAFLD in Otsuka Long-Evans Tokushima Fatty (OLETF) rats and to elucidate the molecular mechanisms underlying the effects of exercise on hepatic steatosis. Four-week-old OLETF rats were randomly assigned to either a sedentary control group (Sed) or a group given access to voluntary running wheels for 16 wk (Ex). Wheels were locked 2 days before euthanasia in the Ex animals, and both groups were euthanized at 20 wk old. Voluntary wheel running attenuated weight gain and reduced serum glucose, insulin, free fatty acids, and triglycerides in Ex animals compared with Sed (P < 0.001). Ex animals exhibited significantly reduced hepatic triglyceride levels and displayed fewer lipid droplets (Oil Red O staining) and reduced lipid droplet size compared with Sed. Wheel running increased by threefold the percent of palmitate oxidized completely to CO(2) in the Ex animals but did not alter AMP-activated protein kinase-alpha (AMPKalpha) or AMPK phosphorylation status. However, fatty acid synthase and acetyl-coenzyme A carboxylase (ACC) content were significantly reduced (approximately 70 and approximately 35%, respectively), and ACC phosphorylation and cytochrome c content were significantly elevated (approximately 35 and approximately 30%, respectively) in the Ex animals. These results unequivocally demonstrate that daily physical activity attenuates hepatic steatosis and NAFLD in an obese rodent model and suggest that this effect is likely mediated, in part, through enhancement of hepatic fatty acid oxidation and reductions in key protein intermediates of fatty acid synthesis.

Dietary fructose induces a wide range of genes with distinct shift in carbohydrate and lipid metabolism in fed and fasted rat liver

Dietary fructose has been suspected to contribute to development of metabolic syndrome. However, underlying mechanisms of fructose effects are not well characterized. We investigated metabolic outcomes and hepatic expression of key regulatory genes upon fructose feeding under well defined conditions. Rats were fed a 63% (w/w) glucose or fructose diet for 4 h/day for 2 weeks, and were killed after feeding or 24-hour fasting. Liver glycogen was higher in the fructose-fed rats, indicating robust conversion of fructose to glycogen through gluconeogenesis despite simultaneous induction of genes for de novo lipogenesis and increased liver triglycerides. Fructose feeding increased mRNA of previously unidentified genes involved in macronutrient metabolism including fructokinase, aldolase B, phosphofructokinase-1, fructose-1,6-bisphosphatase and carbohydrate response element binding protein (ChREBP). Activity of glucose-6-phosphate dehydrogenase, a key enzyme for ChREBP activation, remained elevated in both fed and fasted fructose groups. In the fasted liver, the fructose group showed lower non-esterified fatty acids, triglycerides and microsomal triglyceride transfer protein mRNA, suggesting low VLDL synthesis even though plasma VLDL triglycerides were higher. In conclusion, fructose feeding induced a broader range of genes than previously identified with simultaneous increase in glycogen and triglycerides in liver. The induction may be in part mediated by ChREBP.

Chronic ginseng consumption attenuates age-associated oxidative stress in rats

The antioxidant properties of North American ginseng (Panax quinquefolium) were investigated in young and old rats fed a ginseng-supplemented diet for 4 mo. Female Fischer 344 rats at 4 (Y, n = 38) or 22 (O, n = 25) mo of age were randomly divided into three groups and fed either a AIN-93G formula-based control diet (C) or a diet containing 0.5 g/kg (low dose, L) or 2.5 g/kg (high dose, H) dry ginseng power for 4 mo. Oxidant generation, measured with 2'7'-dichlorofluorescin (DCFH), was significantly lowered with ginseng feeding in the homogenates of heart, soleus, and the deep portion of vastus lateralis muscle (DVL) (P < 0.05) in both Y and O rats, and the effects were dose dependent. Superoxide dismutase activity was elevated in heart and DVL of H rats, and in soleus of L rats (P < 0.05). H rats showed higher glutathione peroxidase activity in DVL and soleus muscle (P < 0.05), and elevated citrate synthase activity in the heart of both age groups and DVL of Y rats (P < 0.05). Neither the H nor L diet affected age-dependent lipid peroxidation in the heart or muscle, but protein carbonyl content was attenuated with the H diet in the heart (P < 0.05) and with both the L and H diets in DVL (P < 0.01). We conclude that ginseng supplementation can prevent age-associated increase in oxidant production and oxidative protein damage in rats. These protective effects are explained in part by elevated antioxidant enzyme activities in the various tissues.

Lipid-Induced Insulin Resistance in the Liver

Hepatic lipid accumulation may be a result of one or several of the following factors: increased delivery of adipose tissue or dietary fatty acids to the liver, increased de novo synthesis of fatty acids in the liver, decreased rate of hepatic fatty-acid oxidation, or decreased rate in the exit of fatty acids from the liver in the form of triglycerides. Delivery of fatty acids to the liver appears to be the most potent mechanism for hepatic lipid accumulation. Hepatic lipid accumulation is linked to the development of hepatic insulin resistance, which is demonstrated by the impaired suppression of hepatic glucose output by insulin. Current evidence suggests that defects associated with the molecular mechanisms responsible for the propagation of the insulin signal in the liver cells are responsible for the impaired insulin effect and that these defects can develop secondary to lipid accumulation in the liver. Hepatic lipid accumulation appears to affect the activity of phosphatidylinositol 3-kinase, which has a central role in mediating the insulin action in hepatocytes. Generally, exercise has been shown to enhance the insulin action in the liver. Although an exercise-related mechanistic link between attenuation in hepatic lipid accumulation and enhancement in insulin action in the liver has not been described yet, the benefits of exercise on hepatic insulin action may relate to the potential effects of exercise on regulating/preventing hepatic lipid accumulation. However, direct effects of exercise on insulin action in the liver, independent of any effects on hepatic lipid metabolism, cannot currently be excluded. Further research is needed to evaluate the relative importance of exercise in the treatment of hepatic insulin resistance, specifically as it relates to lipid accumulation in the liver.