Melatonin ameliorates alcohol-induced bile acid synthesis by enhancing miR-497 expression.

Alcoholic liver disease is a major cause of chronic liver disease worldwide, and cannabinoid receptor type 1 (CB1R) is involved in a diverse metabolic diseases. B-cell translocation gene 2 (BTG2) and yin yang 1 (YY1) are a potent regulator of biological conditions. Melatonin plays a crucial role in regulating diverse physiological functions and metabolic homeostasis. MicroRNAs are key regulators of various biological processes. Herein, we demonstrate that melatonin improves bile acid synthesis in the liver of alcohol-fed mice by controlling miR-497 expression. The level of bile acid and the expression of Cb1r, Btg2, Yy1, and bile acid synthetic enzymes were significantly elevated in the livers of Lieber-DeCarli alcohol-fed mice. The overexpression of Btg2 enhanced Yy1 gene expression and bile acid production, whereas disrupting the CB1R-BTG2-YY1 cascade protected against the bile acid synthesis caused by alcohol challenge. We identified an alcohol-mediated YY1 binding site on the cholesterol 7α-hydroxylase (Cyp7a1) gene promoter using promoter deletion analysis and chromatin immunoprecipitation assays. Notably, melatonin attenuated the alcohol-stimulated induction of Btg2, Yy1 mRNA levels and bile acid production by promoting miR-497. Overexpression of a miR-497 mimic dramatically diminished the increase of Btg2 and Yy1 gene expression as well as bile acid production by alcohol, whereas this phenomenon was reversed by miR-497 inhibitor. These results demonstrate that the upregulation of miR-497 by melatonin represses alcohol-induced bile acid synthesis by attenuating the BTG2-YY1 signaling pathway. The melatonin-miR497 signaling network may provide novel therapeutic targets for the treatment of hepatic metabolic dysfunction caused by the alcohol-dependent pathway.

B-cell translocation gene 2 promotes hepatic hepcidin production via induction of Yin Yang 1.

Hepcidin is a peptide hormone secreted in the liver and plays a key role in maintaining iron homeostasis. Here, we demonstrate that B-cell translocation gene 2 (BTG2) is a key player in hepatic hepcidin regulation via induction of Yin Yang 1 (YY1). Hepatic hepcidin gene expression significantly enhanced by fasting states and glucagon exposure led to induction of gluconeogenic gene expression, and elevated serum hepcidin production in mice. Notably, overexpression of BTG2 using adenoviral system (Ad-BTG2) significantly elevated serum hepcidin levels via a significant induction of YY1 gene transcription. Immunoprecipitation studies demonstrated that BTG2 physically interacted with YY1 and recruited on the hepcidin gene promoter. Finally, ablation of hepatic BTG2 gene by gene silencing markedly attenuated the elevation of serum hepcidin production along with YY1 and hepcidin mRNA expression in fasting state. Likewise, forskolin (FSK)-stimulated hepcidin promoter activity was dramatically disrupted by endogenous BTG2 knockdown. Overall, our current study provides a novel molecular mechanism of BTG2-mediated induction of hepcidin gene expression, thereby contributing to a better understanding of the hepatic hepcidin production involved in iron homeostasis.

Pinusolide improves high glucose-induced insulin resistance via activation of AMP-activated protein kinase.

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) plays a crucial role in the maintenance of cellular energy homeostasis, and several natural compounds that activate AMPK possibly enhance glucose uptake by muscle cells. In this study, we found that pinusolide stimulated AMPK phosphorylation and glucose uptake and these effects were significantly reduced by siRNA LKB1 or compound C, suggesting that enhanced glucose uptake by pinusolide is predominantly accomplished via an LKB1-mediated AMPK activation pathway. An insulin resistance state was induced by exposing cells to 30mM glucose, as indicated by reduced insulin-stimulated tyrosine phosphorylation of IRS-1 and glucose uptake. Under these conditions, the phosphorylation of AMPK and ACC were decreased. Surprisingly, disrupted insulin signaling and decreased AMPK activity by high glucose concentrations were prevented by pinusolide. Moreover, this treatment increased insulin-stimulated glucose uptake via AMPK activation. Taken together, our findings suggest a link between high glucose and insulin resistance in muscle cells, and provide further evidence that pinusolide attenuates blockade of insulin signaling by enhancing IRS-1 tyrosine phosphorylation by the activating the AMPK pathway. In addition, this study indicates the targeting of AMPK represents a new therapeutic strategy for hyperglycemia-induced insulin resistance and type 2 diabetes.

Manassantin B isolated from Saururus chinensis inhibits cyclooxygenase-2-dependent prostaglandin D2 generation by blocking Fyn-mediated nuclear factor-kappaB and mitogen activated protein kinase pathways in bone marrow derived-mast cells.

The authors investigated the effect of manassantin B (Man B) isolated from Saururus chinensis (S. chinensis) on cyclooxygenase-2 (COX-2)-dependent prostaglandin D2 (PGD2) generation in mouse bone marrow derived-mast cells (BMMCs). Man B inhibited the generation of PGD2 dose-dependently by inhibiting COX-2 expression in immunoglobulin E (IgE)/Ag-stimulated BMMCs. To elucidate the mechanism responsible for the inhibition of COX-2 expression by Man B, the effects of Man B on the activation of nuclear factor-kappaB (NF-κB), a transcription factor essential and mitogen-activated protein kinases (MAPKs) for COX-2 induction, were examined. Man B attenuated the nuclear translocation of NF-κB p65 and its DNA-binding activity by inhibiting inhibitors of kappa Bα (IκBα) degradation and concomitantly suppressing IκB kinase (IKK) phosphorylation. In addition, Man B suppressed phosphorylation of MAPKs including extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH2-terminal kinase (JNK) and p38. It was also found that Man B suppressed Fyn kinase activation and consequent downstream signaling processes, including those involving Syk, Gab2, and Akt. Taken together, the present results suggest that Man B suppresses COX-2 dependent PGD2 generation by primarily inhibiting Fyn kinase in FcεRI-mediated mast cells.

Tanshinone IIA improves endoplasmic reticulum stress-induced insulin resistance through AMP-activated protein kinase.

The aim of the present study was to determine the effect of Tanshinone IIA (Tan IIA) on endoplasmic reticulum (ER) stress-induced insulin resistance in L6 myotubes and db/db mice. ER stress markers, RNA-activated protein kinase-like ER resident kinase (PERK), JNK, and AMPK activity were determined in tunicamycin-treated L6 myotubes. Insulin resistance was monitored using glucose uptake assays in vitro and blood glucose levels in vivo. Tan IIA clearly suppressed the phosphorylations of PERK and JNK and potentiated insulin-mediated Akt phosphorylation as well as glucose uptake via AMPK activation under ER stress. Furthermore, these effects are completely abrogated by siRNA-mediated knockdown of AMPK or LKB1. In addition, Tan IIA reduced blood glucose levels and body weights in db/db mice without altering food intake. These findings suggest that Tan IIA enhances insulin sensitivity and improves glucose metabolic disorders by increasing AMPK activity and attenuating ER stress-induced insulin resistance.

Effect of Curculigo orchioides on reflux esophagitis by suppressing proinflammatory cytokines.

This study was performed to investigate effects of Curculigo orchioides rhizome (curculiginis rhizome) on acute reflux esophigitis (RE) in rats that are induced by pylorus and forestomach ligation operation. Proinflammatory cytokine, as well as tumor necrosis factor (TNF)-α, interleukin (IL)-1ß and IL-6 were all assayed and the expression of TNF-α and COX2 analyzed by RT-PCR. The esophagic tissue damage of reflux esophagitis rat was increased compared to that of normal intact group. However, the esophagic damage percentage from the extract of curculiginis rhizoma (ECR) 600 mg/kg and ECR 300 mg/kg were significantly lower than that of the RE control group. Administration of α-tocopherol (30 mg/kg) and ECR (600 mg/kg, 300 mg/kg, and 150 mg/kg) had a significant effect on the gastric acid pH in rats with induced reflux esophagitis (p < 0.05). The treatment with ECR significantly reduced the production of cytokines TNF-α, IL-1ß and IL-6 levels compared to the model group (p < 0.05). The expression of TNF-α and COX2 in the intact esophageal mucosa was low while those of the RE control group were significantly higher due to an inflammatory reaction in the esophagus. Compare to the model group, treatment with α-tocopherol or ECR significantly inhibited the expression levels of COX2 and TNF-α in a dose-dependent manner. These results suggest that anti-inflammatory and protective effects of ECR could attenuate the severity of reflux esophagitis and prevent esophageal mucosal damage.

Heat-processed Gynostemma pentaphyllum extract improves obesity in ob/ob mice by activating AMP-activated protein kinase.

Gynostemma pentaphyllum is widely used in Asian countries as a herbal medicine to treat dyslipidemia, type 2 diabetes and inflammation. An ethanol extract of G. pentaphyllum lessened obesity by activating AMP-activated protein kinase (AMPK). The levels of damulins A and B, components responsible for AMPK activation in the extract, were increased by autoclaving in a time-dependent manner. Heat-processed G. pentaphyllum extract, actiponin containing damulins A (0.93 %, w/w) and B (0.68 %, w/w), significantly stimulated fat oxidation and glucose uptake via AMPK activation in L6 myotube cells. Oral administration of actiponin to ob/ob mice for 8 weeks decreased body weight gain, liver weight, and blood cholesterol levels with AMPK activation in the soleus muscle. Our results demonstrate the beneficial effect of G. pentaphyllum on improving obesity and have elucidated the underlying molecular mechanisms.