Go Woon Kim

Betulinic acid alleviates non-alcoholic fatty liver by inhibiting SREBP1 activity via the AMPK–mTOR–SREBP signaling pathway

Non-alcoholic fatty liver disease (NAFLD) is emerging as the most common liver disease in industrialized countries. The discovery of food components that can ameliorate NAFLD is therefore of interest. Betulinic acid (BA) is a triterpenoid with many pharmacological activities, but the effect of BA on fatty liver is as yet unknown. To explore the possible anti-fatty liver effects and their underlying mechanisms, we used insulin-resistant HepG2 cells, primary rat hepatocytes and liver tissue from ICR mice fed a high-fat diet (HFD). Oil Red O staining revealed that BA significantly suppressed excessive triglyceride accumulation in HepG2 cells and in the livers of mice fed a HFD. Ca(+2)-calmodulin dependent protein kinase kinase (CAMKK) and AMP-activated protein kinase (AMPK) were both activated by BA treatment. In contrast, the protein levels of sterol regulatory element-binding protein 1 (SREBP1), mammalian target of rapamycin (mTOR) and S6 kinase (S6K) were all reduced when hepatocytes were treated with BA for up to 24h. We found that BA activates AMPK via phosphorylation, suppresses SREBP1 mRNA expression, nuclear translocation and repressed SREBP1 target gene expression in HepG2 cells and primary hepatocytes, leading to reduced lipogenesis and lipid accumulation. These effects were completely abolished in the presence of STO-609 (a CAMKK inhibitor) or compound C (an AMPK inhibitor), indicating that the BA-induced reduction in hepatic steatosis was mediated via the CAMKK-AMPK-SREBP1 signaling pathway. Taken together, our results suggest that BA effectively ameliorates intracellular lipid accumulation in liver cells and thus is a potential therapeutic agent for the prevention of fatty liver disease.

IL-6 inhibitors for treatment of rheumatoid arthritis: past, present, and future.

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by polyarthritis. Numerous agents with varying mechanisms are used in the treatment of RA, including non-steroidal anti-inflammatory drugs, disease-modifying anti-rheumatic drugs, and some biological agents. Studies to uncover the cause of RA have recently ended up scrutinizing the importance of pro-inflammatory cytokine such as tumor necrosis factor α (TNF-α) and interleukin (IL)-6 in the pathogenesis of RA. TNF-α inhibitors are increasingly used to treat RA patients who are non-responsive to conventional anti-arthritis drugs. Despite its effectiveness in a large patient population, up to two thirds of RA patients are found to be partially responsive to anti-TNF therapy. Therefore, agents targeting IL-6 such as tocilizumab (TCZ) attracted significant attention as a promising agent in RA treatment. In this article, we review the mechanism of anti-IL-6 in the treatment of RA, provide the key efficacy and safety data from clinical trials of approved anti-IL-6, TCZ, as well as six candidate IL-6 blockers including sarilumab, ALX-0061, sirukumab, MEDI5117, clazakizumab, and olokizumab, and their future perspectives in the treatment of RA.

AMP-activated protein kinase: An emerging target for ginseng

The adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a key sensor of cellular energy. Once activated, it switches on catabolic pathways generating adenosine triphosphate (ATP), while switching off biosynthetic pathways consuming ATP. Pharmacological activation of AMPK by metformin holds a therapeutic potential to reverse metabolic abnormalities such as type 2 diabetes and nonalcoholic fatty liver disease. In addition, altered metabolism of tumor cells is widely recognized and AMPK is a potential target for cancer prevention and/or treatment. Panax ginseng is known to be useful for treatment and/or prevention of cancer and metabolic diseases including diabetes, hyperlipidemia, and obesity. In this review, we discuss the ginseng extracts and ginsenosides that activate AMPK, we clarify the various mechanisms by which they achieve this, and we discuss the evidence that shows that ginseng or ginsenosides might be useful in the treatment and/or prevention of metabolic diseases and cancer.

Beneficial Effect of Betulinic Acid on Hyperglycemia via Suppression of Hepatic Glucose Production

The inhibitory effect of betulinic acid (BA) on hepatic glucose production was examined in HepG2 cells and high fat diet (HFD)-fed ICR mice. BA significantly inhibited the hepatic glucose production (HGP) and gene expression levels of PGC-1α, PEPCK, and G6Pase. BA activated AMPK and suppressed the expression level of phosphorylated CREB. These effects were all abolished in the presence of compound C (an AMPK inhibitor). Moreover, inhibition of AMPK by overexpression of dominant negative AMPK prevented BA from suppression of HGP, indicating that the inhibitory effect of BA on HGP is AMPK-dependent. In addition, BA markedly phosphorylated CAMKK, and phosphorylation of AMPK and ACC, and suppression of HGP were all reversed in the presence of STO-609 (a CAMKK inhibitor), suggesting that CAMKK is an upstream kinase for AMPK. In an animal study, HFD-fed ICR mice were orally administered with 5 or 10 mg of BA per kg (B5 and B10) for three weeks. Plasma glucose, triglyceride, and the insulin resistance index of the B10 group were decreased by 34%, 59%, and 38%, respectively. In a pyruvate tolerance test, pyruvate-induced glucose excursion was decreased by 27% when mice were pretreated with 10 mg/kg of BA. In summary, BA effectively ameliorates hyperglycemia through inhibition of hepatic gluconeogenesis via modulating the CAMKK-AMPK-CREB signaling pathway.

Licochalcone A regulates hepatic lipid metabolism through activation of AMP-activated protein kinase.

Licochalcone A (LA) is a major phenolic ingredient of Glycyrrhiza plant. Although multiple pharmacological activities of LA have been reported, effect on hepatic lipid metabolism is unknown yet. The present study showed LA to suppress the hepatic triglyceride accumulation in HepG2 cells and ICR mice fed on a high fat diet (HFD). LA inhibited lipogenesis via suppression of sterol regulatory element-binding protein 1c (SREBP1c) and its target enzymes (stearoyl-CoA desaturase 1, fatty acid synthase and glycerol-3-phosphate acyltransferase) transcription. In addition, LA up-regulated gene expression of proteins such as peroxisome proliferator-activated receptor α (PPARα) and fatty acid transporter (FAT/CD36), which are responsible for lipolysis and fatty acid transport, respectively. These effects were mediated through activation of AMP-activated protein kinase (AMPK), and were abrogated when HepG2 cells were treated with an AMPK inhibitor, compound C. To explore how LA activates AMPK, oxygen consumption rate and ATP levels were measured in HepG2 cells. LA significantly inhibited the mitochondrial respiration and ATP levels, suggesting that LA activated AMPK indirectly. In animal study, LA (5 and 10mg/kg) was orally administered to six-week-old mice once a day for 3 weeks. In vitro results were likely to hold true in vivo experiment, as LA markedly lowered the triglyceride levels and activated AMPK signaling pathway in the liver of ICR mice fed on a HFD. In conclusion, the current study suggests that LA suppressed hepatic triglyceride accumulation through modulation of AMPK-SREBP signaling pathway and thus LA may be a potential therapeutic agent for treating fatty liver disease.

Effects of eugenol on hepatic glucose production and AMPK signaling pathway in hepatocytes and C57BL/6J mice.

Eugenol is a phenylpropanoid with many pharmacological activities, but its anti-hyperglycemic activity is not yet fully explored. For in vitro study, HepG2 cells and primary rat hepatocytes were used, and glucose production was induced by adding 100 nM of glucagon in the presence of gluconeogenic substrates. In animal study, hyperglycemia was induced by high fat diet (HFD) in male C57BL/6J mice, and eugenol was orally administered at 20 or 40 mg per kg (E20, E40) for 15 weeks. Eugenol significantly inhibited glucagon-induced glucose production and phosphorylated AMPK in the HepG2 and primary rat hepatocytes, and these effects were reversed in the presence of compound C (an AMPK inhibitor) or STO-609 (a CAMKK inhibitor). In addition, the protein and gene expression levels of CREB, CRTC2·CREB complex, PGC-1α, PEPCK and G6Pase were all significantly suppressed. Moreover, inhibition of AMPK by over-expression of dominant negative AMPK prevented eugenol from suppressions of gluconeogenic gene expression and hepatic glucose production. In animal study, plasma glucose and insulin levels of the E40 group were decreased by 31% and 63%, respectively, when compared to those of HFD control. In pyruvate tolerance tests, pyruvate-induced glucose excursions were decreased, indicating that the anti-hyperglycemic activity of eugenol is primarily due to the suppression of hepatic gluconeogenesis. In summary, eugenol effectively ameliorates hyperglycemia through inhibition of hepatic gluconeogenesis via modulating CAMKK-AMPK-CREB signaling pathway. Eugenol or eugenol-containing medicinal plants could represent a promising therapeutic agent to prevent type 2 diabetes.

Clinical implication of SGLT2 inhibitors in type 2 diabetes

Treatment of type 2 diabetes mellitus (T2DM) continues to present challenges, with many patients failing to achieve glycemic targets. Despite the availability of many oral and injectable anti-diabetic agents, therapeutic efficacy is often offset by undesirable side effects such as hypoglycemia, weight gain and cardiovascular complications. Therefore, the search for new therapeutic agents with an improved benefit–risk profile continues. Recent research has focused on the kidney as a potential therapeutic target, especially because maximal renal glucose reabsorption is increased in T2DM. Under normal physiological conditions, nearly all filtered glucose is reabsorbed in the proximal tubule of the nephron via the sodium/glucose co-transporter 2 (SGLT2). SGLT2-inhibitors are a new class of oral anti-diabetes, which reduce hyperglycemia by increasing urinary glucose excretion independently of insulin secretion or action. Canagliflozin and dapagliflozin in US market, and ipragliflozin and luseogliflozin in Japan market are now available for glycemic control in type 2 diabetics. There are several phase III clinical ongoing trials involving this new class of medications. This review examines some of the key efficacy and safety data from clinical trials of the SGLT2 inhibitors approved, and their future perspectives in the treatment of T2DM.

Nectandrin A Enhances the BMP-Induced Osteoblastic Differentiation and Mineralization by Activation of p38 MAPK-Smad Signaling Pathway

Osteoblastic activity of nectandrin A was examined in C2C12 cells. Nectandrin A enhances the BMP-induced osteoblastic differentiation and mineralization, manifested by the up-regulation of differentiation markers (alkaline phosphatase and osteogenic genes) and increased calcium contents. In C2C12 cells co-transfected with expression vector encoding Smad4 and Id1-Luc reporter, nectandrin A increased Id1 luciferase activity in a concentration-dependent manner, when compared to that in BMP-2 treated cells, indicating that Smad signaling pathway is associated with nectandrin A-enhanced osteoblastic differentiation in C2C12 cells. In addition, nectandrin A activated p38 mitogen-activated protein kinase (MAPK) in time- and concentration-dependent manners, and phosphorylated form of pSmad1/5/8 and alkaline phosphatase activity were both decreased when the cells were pretreated with SB203580, a p38 MAPK inhibitor, suggesting that p38 MAPK might be an upstream kinase for Smad signaling pathway. Taken together, nectandrin A enhances the BMP-induced osteoblastic differentiation and mineralization of C2C12 cells via activation of p38 MAPK-Smad signaling pathway, and it has a therapeutic potential for osteoporosis by promoting bone formation.

Ginseng seed oil ameliorates hepatic lipid accumulation in vitro and in vivo

Background Despite the large number of studies on ginseng, pharmacological activities of ginseng seed oil (GSO) have not been established. GSO is rich in unsaturated fatty acids, mostly oleic and linoleic acids. Unsaturated fatty acids are known to exert a therapeutic effect in nonalcoholic fatty liver disease (NAFLD). In this study, we investigated the protective effect and underlying mechanisms of GSO against NAFLD using in vitro and in vivo models. Methods In vitro lipid accumulation was induced by free fatty acid mixture in HepG2 cells and by 3 wk of high fat diet (HFD)-feeding in Sprague–Dawley rats prior to hepatocyte isolation. The effects of GSO against diet-induced hepatic steatosis were further examined in C57BL/6J mice fed a HFD for 12 wk. Results Oil Red O staining and intracellular triglyceride levels showed marked accumulation of lipid droplets in both HepG2 cells and rat hepatocytes, and these were attenuated by GSO treatment. In HFD-fed mice, GSO improved HFD-induced dyslipidemia and hepatic insulin resistance. Increased hepatic lipid contents were observed in HFD-fed mice and it was lowered in GSO (500 mg/kg)-treated mice by 26.4% which was evident in histological analysis. Pathway analysis of hepatic global gene expression indicated that GSO increased the expression of genes associated with β-oxidation (Ppara, Ppargc1a, Sirt1, and Cpt1a) and decreased the expression of lipogenic genes (Srebf1 and Mlxipl), and these were confirmed with reverse transcription and quantitative polymerase-chain reaction. Conclusion These findings suggest that GSO has a beneficial effect on NAFLD through the suppression of lipogenesis and stimulation of fatty acid degradation pathway.

Meta- and cross-species analyses of insulin resistance based on gene expression datasets in human white adipose tissues

Ample evidence indicates that insulin resistance (IR) is closely related to white adipose tissue (WAT), but the underlying mechanisms of IR pathogenesis are still unclear. Using 352 microarray datasets from seven independent studies, we identified a meta-signature which comprised of 1,413 genes. Our meta-signature was also enriched in overall WAT in in vitro and in vivo IR models. Only 12 core enrichment genes were consistently enriched across all IR models. Among the meta-signature, we identified a drug signature made up of 211 genes with expression levels that were co-regulated by thiazolidinediones and metformin using cross-species analysis. To confirm the clinical relevance of our drug signature, we found that the expression levels of 195 genes in the drug signature were significantly correlated with both homeostasis model assessment 2-IR score and body mass index. Finally, 18 genes from the drug signature were identified by protein-protein interaction network cluster. Four core enrichment genes were included in 18 genes and the expression levels of selected 8 genes were validated by quantitative PCR. These findings suggest that our signatures provide a robust set of genetic markers which can be used to provide a starting point for developing potential therapeutic targets in improving IR in WAT.