Camptothecin activates SIRT1 to promote lipid catabolism through AMPK/FoxO1/ATGL pathway in C2C12 myogenic cells.

Caloric restriction activates sirtuin 1 (SIRT1) and induces a variety of metabolic effects that are beneficial for preventing age-related disease. The present study screened a commercially available used drug library to develop small molecule activators of SIRT1 as therapeutics for treatment of metabolic disorders. Using an in vitro fluorescence assay, the cancer therapeutic camptothecin increased SIRT1 enzymatic activity by 5.5-fold, indicating it to be a potent SIRT1 activator. Camptothecin also elevated the nicotinamide adenine dinucleotide (NAD)+/NADH ratio and increased SIRT1 protein levels in differentiated C2C12 myogenic cells. Treatment of C2C12 myotubes with camptothecin increased phosphorylation of AMP-dependent kinase (AMPK) and acetyl-coenzyme A carboxylase, caused nuclear translocation and deacetylation of forkhead box O1 (FoxO1), increased transcription and protein expression of adipose triglyceride lipase (ATGL), decreased the amount of intracellular oil droplets, and significantly increased ß-oxidation of fatty acids. These in vitro data were confirmed in vivo as camptothecin treatment of C57BL/6J mice reduced fat and plasma triglyceride levels. All of the above camptothecin-induced alterations were attenuated by the SIRT1-specific inhibitor nicotinamide and/or 6-[4-(2-piperidin-1-ylethoxy) phenyl]-3-pyridin-4-ylpyrazolo [1,5-a]pyrimidin (compound C). Thus, camptothecin activation of SIRT1 promotes lipid catabolism through AMPK/FoxO1/ATGL signaling.

Ferrous glycinate regulates cell energy metabolism by restrictinghypoxia-induced factor-1α expression in human A549 cells.

Iron or oxygen regulates the stability of hypoxia inducible factor-1α (HIF-1α). We investigated whether ferrous glycinate would affect HIF-1α accumulation, aerobic glycolysis and mitochondrial energy metabolism in human A549 lung cancer cells. Incubation of A549 cells with ferrous glycinate decreased the protein levels of HIF-1α, which was abrogated by proteosome inhibitor, or prolyl hydroxylase inhibitor. The addition of ferrous glycinate decreased protein levels of glucose transporter-1, hexokinase-2, and lactate dehydrogenase A, and decreased pyruvate dehydrogenase kinase-1 (PDK-1) and pyruvate dehydrogenase (PDH) phosphorylation in A549 cells. Ferrous glycinate also increased the expression of the mitochondrial transcription factor A (TFAM), and the mitochondrial protein, cytochrome c oxidase (COX-IV). Silencing of HIF-1α expression mimicked the effects of ferrous glycinate on PDK-1, PDH, TFAM and COX-IV in A549 cells. Ferrous glycinate increased mitochondrial membrane potential and ATP production in A549 cells. These results suggest that ferrous glycinate may reverse Warburg effect through down regulating HIF-1α in A549 cells.

Monacolin K affects lipid metabolism through SIRT1/AMPK pathway in HepG2 cells.

Monacolin K is the secondary metabolite isolated from Monascus spp. It is the natural form of lovastatin, which is clinically used to reduce the synthesis of cholesterol by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A reductase. In the present study, monacolin K increased protein expression of SIRT1 and phosphorylation level of AMP-activated protein kinase (AMPK) in HepG2 cells. Through activation of SIRT1/AMPK pathway, monacolin K increased phosphorylation of acetyl CoA carboxylase and caused nuclear translocation of forkhead box O1. The western blotting results showed that monacolin K increased expression of adipose triglyceride lipase but decreased abundances of fatty acid synthase (FAS) and sterol regulatory element-binding protein 1 (SREBP1). Monacolin K also decreased the intracellular accumulation of lipids as demonstrated by Oil Red O staining. In addition, the immunostaining showed that monacolin K prevented the nuclear translocation of SREBP1, indicating the association with down-regulation of FAS. All the demonstrated effects of monacolin K were counteracted by nicotinamide or compound C, the inhibitors of SIRT1 or AMPK. In summary, monacolin K reduces the lipid content through SIRT1/AMPK pathway in HepG2 cells, which promotes catabolism and inhibits anabolism of lipid.

Alpha-lipoic acid induces adipose triglyceride lipase expression and decreases intracellular lipid accumulation in HepG2 cells.

Non-alcoholic fatty liver disease can be attributed to the imbalance between lipogenesis and lipolysis in the liver. Alpha-lipoic acid has been shown to activate the 5'-AMP-activated protein kinase (AMPK) signalling pathway and to effectively inhibit the lipogenesis pathway in liver. However, whether alpha-lipoic acid stimulates lipolysis remains unclear. Recently, adipose triglyceride lipase (ATGL) was shown to be responsible for triacylglycerol hydrolase activity in cells. In the present study, we established a fatty liver cell model by incubating HepG2 cells in a high glucose (30mM glucose) and high fat (0.1mM palmitate) medium. We found that the activation of the AMPK signalling pathway induced ATGL protein expression and enhanced lipid hydrolysis. Similarly, treatment of the fatty liver cell model with alpha-lipoic acid reduced intracellular lipid accumulation in HepG2 cells, increased AMPK phosphorylation, and induced ATGL expression. We showed that insulin phosphorylates the transcription factor forkhead box O1 (FOXO1), which regulates ATGL expression and inhibits FOXO1 translocation into the nucleus. In contrast, alpha-lipoic acid dephosphorylated FOXO1 and reversed the nuclear exclusion of FOXO1. These data suggest that alpha-lipoic acid can effectively ameliorate intracellular lipid accumulation and induce ATGL expression through the FOXO1/ATGL pathway in liver cells. Thus, alpha-lipoic acid may be a potential therapeutic agent for treating fatty liver disease.

Fenofibrate lowers lipid accumulation in myotubes by modulating the PPARα/AMPK/FoxO1/ATGL pathway.

Fenofibrate, a fibric acid derivative, is known to possess lipid-lowering effects. Although fenofibrate may activate peroxisome proliferator-activated receptor (PPAR)α and regulate the transcription of several genes, the underlying mechanisms are poorly understood. In this study, we demonstrated that incubation of C2C12 myotubes with fenofibrate increased adipose triglyceride lipase (ATGL) expression and suppressed fatty acid synthase (FAS) level, thereby decreasing intracellular triglyceride accumulation when cells were incubated at high-glucose condition. Fenofibrate increased the phosphorylation of AMP-activated protein kinase (AMPK), which subsequently increased fatty acid ß-oxidation. AMPK phosphorylation was reduced by pretreatment with GW9662 (a PPARα inhibitor), suggesting that AMPK may be a downstream effector of PPARα. Pretreatment with compound C (an AMPK inhibitor) or GW9662 blocked fenofibrate-induced ATGL expression and the lipid-lowering effect. Our results suggest that AMPK is as an upstream regulator of ATGL. With further exploration, we demonstrated that fenofibrate stimulated FoxO1 translocation from the cytosol to nuclei by immunefluorescence assay, chromatin immuneprecipitation assay, and reporter assay. Furthermore, oral administration of fenofibrate ameliorated the body weight, visceral fat and serum biochemical indexes in db/db mice. Taken together, our results suggest that the lipid-lowering effect of fenofibrate was achieved by activating PPARα and AMPK signaling pathway that resulted in increasing ATGL expression, lipolysis, and fatty acid ß-oxidation.

Metformin regulates hepatic lipid metabolism through activating AMP-activated protein kinase and inducing ATGL in laying hens.

Although many clinical trials have showed that metformin improves non-alcoholic fatty liver disease, which is a common liver disease associated with hepatic enzyme abnormalities, an animal model is required to investigate the effects of altered gene expression and post-translational processing (proteins) in mediating the observed responses. Laying hens appear to develop fatty livers, as in the case in human beings, when ingesting energy in excess of maintenance, and they can be used as an animal model for observing hepatic steatosis. The aim of this study was to investigate whether metformin could improve the non-alcoholic fatty liver of laying hens and to examine the possible mechanisms of lipid-lowering effects. Forty-eight Leghorn laying hens of Hy-Line variety W-36 - 44 weeks with 64.8% hen-day egg production - were randomly assigned into 4 treatments, each receiving 0, 10, 30, or 100mg of metformin with saline per kg body weight by daily wing vein injection. Results showed that, compared with the control, significant decreases existed in the laying rates; plasma triglyceride, cholesterol, and insulin levels; body weights; abdominal fat weights; hepatic lipid contents; and hepatic fatty acid synthase expression of layers receiving 30 or 100mg per kg body weight, whereas significant increases in their hepatic 5'adenosine monophosphate-activated protein kinase, acyl-CoA carboxylase phosphorylation, adipose triglyceride lipase, and carnitine palmitoyl transferase-1 expression were observed. These data suggest that metformin could reduce lipid deposits in the liver and that the laying hen is a valuable animal model for studying hepatic steatosis.