Piperidine alkaloids from Piper retrofractum Vahl. protect against high-fat diet-induced obesity by regulating lipid metabolism and activating AMP-activated protein kinase.

The fruits of Piper retrofractum Vahl. have been used for their anti-flatulent, expectorant, antitussive, antifungal, and appetizing properties in traditional medicine, and they are reported to possess gastroprotective and cholesterol-lowering properties. However, their anti-obesity activity remains unexplored. The present study was conducted to isolate the anti-obesity constituents from P. retrofractum Vahl. and evaluate their effects in high-fat diet (HFD)-induced obese mice. Piperidine alkaloids from P. retrofractum Vahl. (PRPAs), including piperine, pipernonaline, and dehydropipernonaline, were isolated as the anti-obesity constituents through a peroxisome proliferator-activated receptor δ (PPARδ) transactivation assay. The molecular mechanism was investigated in 3T3-L1 adipocytes and L6 myocytes. PRPA treatment activated AMP-activated protein kinase (AMPK) signaling and PPARδ protein and also regulated the expression of lipid metabolism-related proteins. In the animal model, oral PRPA administration (50, 100, or 300mg/kg/day for 8weeks) significantly reduced HFD-induced body weight gain without altering the amount of food intake. Fat pad mass was reduced in the PRPA treatment groups, as evidenced by reduced adipocyte size. In addition, elevated serum levels of total cholesterol, low-density lipoprotein cholesterol, total lipid, leptin, and lipase were suppressed by PRPA treatment. PRPA also protected against the development of nonalcoholic fatty liver by decreasing hepatic triglyceride accumulation. Consistent with the in vitro results, PRPA activated AMPK signaling and altered the expression of lipid metabolism-related proteins in liver and skeletal muscle. Taken together, these findings demonstrate that PRPAs attenuate HFD-induced obesity by activating AMPK and PPARδ, and regulate lipid metabolism, suggesting their potential anti-obesity effects.

meso-Dihydroguaiaretic acid inhibits hepatic lipid accumulation by activating AMP-activated protein kinase in human HepG2 cells.

Hepatic lipid accumulation is a major risk factor for dyslipidemia, nonalcoholic fatty liver disease, and insulin resistance. The present study was conducted to evaluate hypolipidemic effects of meso-dihydroguaiaretic acid (MDA), anti-oxidative and anti-inflammatory compound isolated from the Myristica fragrans HOUTT., by oil red O staining, reverse transcription-polymerase chain reaction (RT-PCR), and Western blot. MDA significantly inhibited insulin-induced hepatic lipid accumulation in a dose-dependent manner. The lipid-lowering effect of MDA was accompanied by increased expression of proteins involved in fatty acid oxidation and decreased expression of lipid synthetic proteins. In addition, MDA activated AMP-activated protein kinase (AMPK) as determined by phosphorylation of acetyl-CoA carboxylase (ACC), a downstream target of AMPK. The effects of MDA on lipogenic protein expression were suppressed by pretreatment with compound C, an AMPK inhibitor. Taken together, these findings show that MDA inhibits insulin-induced lipid accumulation in human HepG2 cells by suppressing expression of lipogenic proteins through AMPK signaling, suggesting a potent lipid-lowering agent.

Nordihydroguaiaretic acid protects against high-fat diet-induced fatty liver by activating AMP-activated protein kinase in obese mice.

Nonalcoholic fatty liver disease, one of the most common causes of chronic liver disease, is strongly associated with metabolic syndrome. Nordihydroguaiaretic acid (NDGA) has been reported to inhibit lipoprotein lipase; however, the effect of NDGA on hepatic lipid metabolism remains unclear. We evaluated body weight, adiposity, liver histology, and hepatic triglyceride content in high-fat diet (HFD)-fed C57BL/6J mice treated with NDGA. In addition, we characterized the underlying mechanism of NDGA's effects in HepG2 hepatocytes by Western blot and RT-PCR analysis. NDGA (100 or 200mg/kg/day) reduced weight gain, fat pad mass, and hepatic triglyceride accumulation, and improved serum lipid parameters in mice fed a HFD for 8 weeks. NDGA significantly increased AMP-activated protein kinase (AMPK) phosphorylation in the liver and in HepG2 hepatocytes. NDGA downregulated the level of mature SREBP-1 and its target genes (acetyl-CoA carboxylase and fatty acid synthase), but, it upregulated expression of genes involved in fatty acid oxidation, such as peroxisome proliferator-activated receptor (PPAR)α, PPARγ coactivator-1, carnitine palmitoyl transferase-1, and uncoupling protein-2. The specific AMPK inhibitor compound C attenuated the effects of NDGA on expression of lipid metabolism-related proteins in HepG2 hepatocytes. The beneficial effects of NDGA on HFD-induced hepatic triglyceride accumulation are mediated through AMPK signaling pathways, suggesting a potential target for preventing NAFLD.

Synergistic anticandidal activity of xanthorrhizol in combination with ketoconazole or amphotericin B.

Candida species are responsible for the fourth most common nosocominal bloodstream infection. Xanthorrhizol, a sesquiterpene compound isolated from Curcuma xanthorrhiza Roxb. has been reported to have anticandidal activity. The aim of this study is to investigate the synergistic anticandidal effect of xanthorrhizol in combination with ketoconazole or amphotericin B against Candida albicans, Candida glabrata, Candida guilliermondii, Candida krusei, Candida parapsilosis, and Candida tropicalis. Mostly, xanthorrhizol in combination with ketoconazole or amphotericin B exhibited the synergistic anticandidal effects against all species of Candida tested. In combination with xanthorrhizol, the concentration of ketoconazole or amphotericin B for inhibiting the growth of the tested Candida species could be reduced by >/=50%. Time-kill curves showed that 1/2 minimum inhibitory concentration (MIC) dose of xanthorrhizol, amphotericin B, or ketoconazole alone against each of the six Candida species did not inhibit the growth of all Candida species tested. However, 1/2 MIC dose of xanthorrhizol in combination with 1/2 MIC dose of ketoconazole or 1/2 MIC dose of amphotericin B exhibited growth inhibition of all Candida species tested and reduced viable cells by several logs within 4 h. These results support the potential use of xanthorrhizol as an anticandidal agent, and it can be used complementarily with other conventional antifungal agents.

Antiobesity effect of ginsenoside Rg3 involves the AMPK and PPAR-gamma signal pathways.

Ginsenosides, the active component of ginseng, exerts antidiabetic and anticancer effects. This study investigated the molecular basis of ginsenoside Rg3, a red ginseng rich constituent, focusing on its ability to inhibit adipocyte differentiation in 3T3-L1 cells. The data show that ginsenoside Rg3 was effective in the inhibition of adipocyte differentiation. This inhibitory effect of ginsenoside Rg3 on adipocyte differentiation was accompanied by PPAR-gamma inhibition in rosiglitazone-treated cells. The study also tested whether AMP-activated protein kinase (AMPK) activation was involved in the inhibitory effects of ginsenoside Rg3. AMPK plays a role in maintaining health in the context of diseases such as type 2 diabetes, obesity and cancer. AMPK was reported to control nutritional and hormonal signal modulating. Rg3 significantly and time-dependently activated AMPK. Taken together, these results suggest that the antiobesity effect of red ginseng rich constituent, ginsenoside Rg3, involves the AMPK signaling pathway and PPAR-gamma inhibition.

Vitisin A inhibits adipocyte differentiation through cell cycle arrest in 3T3-L1 cells.

Inhibition of adipocyte differentiation is one approach among the anti-obesity strategies. This study demonstrates that vitisin A, a resveratrol tetramer, inhibits adipocyte differentiation most effectively of 18 stilbenes tested. Fat accumulation and PPARgamma expression were decreased by vitisin A in a dose-dependent manner. Vitisin A significantly inhibited preadipocyte proliferation and consequent differentiation within the first 2 days of treatment, indicating that the anti-adipogenic effect of vitisin A was derived from anti-proliferation. Based on cell cycle analysis, vitisin A blocked the cell cycle at the G1-S phase transition, causing cells to remain in the preadipocyte state. Vitisin A increased p21 expression, while the Rb phosphorylation level was reduced. Therefore, vitisin A seems to induce G1 arrest through p21- and consequent Rb-dependent suppression of transcription. On the other hand, ERK and Akt signaling pathways were not involved in the anti-mitotic regulation by vitisin A. Taken together, these results suggest that vitisin A inhibits adipocyte differentiation through preadipocyte cell cycle arrest.

Anti-obesity effects of ginsenoside Rh2 are associated with the activation of AMPK signaling pathway in 3T3-L1 adipocyte.

Metabolic disorders such as obesity are major obstacles in improving the average life span. Therefore, a therapeutic approach using natural compounds has been proposed as a novel strategy for preventing metabolic disorders. Ginsenoside Rh2 is one of the ginsenosides that exert anti-diabetes, anti-inflammatory, and anti-cancer effects. However, the anti-obesity effects of Ginsenoside Rh2 remain unclear. Here, we investigated the anti-obesity ability of ginsenoside Rh2 using cell culture systems. Ginsenoside Rh2 effectively inhibited adipocyte differentiation via PPAR-gamma inhibition. Next, to find specific target molecules based on this result, we used cell culture systems to examine whether AMPK activation was involved in the anti-obesity ability of ginsenoside Rh2 since several published papers have indicated that AMPK signaling is involved in the regulation of metabolic disorders. Ginsenoside Rh2 significantly activated AMPK in 3T3-L1 adipocytes. In addition, we also examined the effect of AMPK on lipolysis molecules such as CPT-1 and UCP-2 by using an AMPK inhibitor. Ginsenoside Rh2 effectively induced CPT-1 and UCP-2 and this induction was abolished by AMPK inhibitor treatment. Moreover, we observed that ROS is an important upstream signal for AMPK activation during ginsenoside Rh2 treatment. Taken together, these results indicate that ginsenoside Rh2 is the most effective candidate for preventing metabolic disorders such as obesity and that it acts via the AMPK signaling pathway. Thus, AMPK signaling might contribute toward improving human health.

Ginsenoside Rc, an active component of Panax ginseng, stimulates glucose uptake in C2C12 myotubes through an AMPK-dependent mechanism.

ETHNOPHARMACOLOGICAL RELEVANCE: Panax ginseng and its major component, ginsenosides, are widely used for the prevention of various disorders in oriental medicine. AIM OF THE STUDY: To evaluate the effect of ginsenoside Rc (Rc), one of the active constituents in Panax ginseng, on glucose uptake in C2C12 myotubes. RESULTS: Treatment of the C2C12 myotubes with Rc significantly increased glucose uptake. To determine the mechanism of Rc-induced glucose uptake, either insulin-dependent signaling or insulin-independent signaling pathway activities were measured using western blot analysis. We showed that Rc significantly activated an insulin-independent AMPK signaling pathway. However, Rc had no effect on the components of the insulin-dependent signaling pathway, such as receptor substrates (IRS)-1 and protein kinase B or Akt (PKB/Akt). Moreover, we found that treatment with an AMPK inhibitor abolished both glucose uptake and p38 MAPK phosphorylation. This result implies that AMPK activity is critical for the Rc-induced glucose uptake and that AMPK is situated upstream of p38 MAPK. In addition, we also showed that the activation of AMPK and p38 induced by ginsenoside Rc is mediated by reactive oxygen species (ROS) production, suggesting that upstream regulators of AMPK- and p38 MAPK-mediated glucose uptake. CONCLUSION: Ginsenoside Rc significantly enhances glucose uptake by inducing ROS generation, which leads to AMPK and p38 MAPK activation. Consequently, ginsenoside Rc can be used as a potent natural anti-diabetic agent.