Fenretinide ameliorates insulin resistance and fatty liver in obese mice.

Fenretinide (FEN), a ligand of retinol binding protein 4 (RBP4), has been suggested as a measure to reduce insulin resistance and its associated disorders such as obesity, and fatty liver by reducing serum RBP4. We investigated whether there is another possible mechanism by which fenretinide reduces insulin resistance and fatty liver in genetically obese (ob/ob) mice. Male obese mice fed a high-fat diet (45% of calories from fat) were divided into two groups (n=13 each). One (FEN) received fenretinide (20 mg/kg body weight, intraperitoneally) and the other (O) received vehicle three times weekly for 24 d. C57BL/6J mice fed a normal-fat diet (16% of calories from fat) were used as a control (C; n=13). No changes in fat weight and serum leptin level could be observed in FEN mice. Lower plasma RBP4 was observed in FEN mice compared with O mice. Fenretinide improved whole-body insulin sensitivity based on glucose and insulin tolerance tests and the homeostasis model assessment of insulin resistance. Fenretinide decreased the plasma lipid (triglyceride, cholesterol, and free-fatty acid) levels, hepatic TG level, and histological steatosis score. The mechanism by which fenretinide prevents fatty liver may be explained by an increased plasma adiponectin level, increased activation of hepatic AMP-activated protein kinase, and the expression of peroxisome proliferator-activated protein-α and peroxisomal acyl-CoA oxidase, which promote fat oxidation. FEN alleviated insulin resistance and fatty liver in obese mice and thus may act as an anti-lipidemic and anti-diabetic drug.

High-fat diet stimulates IL-1 type I receptor-mediated inflammatory signaling in the skeletal muscle of mice.

Recently, substantial attention has been focused on the association between obesity and chronic inflammation. The aim of the present study was to investigate whether high-fat diet (HFD)-induced obesity induces the activation of the IL-1 type I receptor (IL-1RI)-mediated inflammatory signaling cascade in the skeletal muscle of mice. Male C57BL/6J mice were fed either an HFD or a normal diet (ND) for 12 wk. Compared with the results in mice receiving the ND, the HFD increased the expression of IL-1RI and downstream signaling proteins, such as myeloid differentiation primary response gene 88 (MyD88), IL-1R-associated kinase 4 and phospho-transforming growth factor-activated kinase 1 in the skeletal muscle. Additionally, activities of both inhibitor of kappaB kinase beta and inhibitor of kappaB degradation were significantly elevated in the skeletal muscle of mice fed with an HFD compared with mice receiving an ND. In contrast, the levels of other downstream transcription factors, such as activator protein-1 and INF regulatory factor 5, were not affected by the HFD. These results suggest that the IL-1RI-MyD88-nuclear factor kappaB signaling pathway might be involved in the induction of the inflammatory response in the skeletal muscle of mice fed with an HFD.

Inhibitory effect of capsaicin on B16-F10 melanoma cell migration via the phosphatidylinositol 3-kinase/Akt/Rac1 signal pathway.

Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide), the major pungent ingredient of red pepper, has been reported to possess anti-carcinogenic and anti-mutagenic activities. In this study, the anti-migration activity of capsaicin on highly metastatic B16-F10 melanoma cells was investigated. Capsaicin significantly inhibited the migration of melanoma cells without showing obvious cellular cytotoxicity at low doses. This effect correlated with the down-regulation of phosphatidylinositol 3-kinase (PI3-K) and its downstream target, Akt. Although B16-F10 cell migration was increased by the PI3-K activator through the activation of Akt, these PI3-K activator-induced phenomena were attenuated by capsaicin. Moreover, capsaicin was found to significantly inhibit Rac1 activity in a pull-down assay. These results demonstrate that capsaicin inhibits the migration of B16-F10 cells through the inhibition of the PI3-K/Akt/Rac1 signal pathway. The present investigation suggests that capsaicin targets PI3-K/Akt/ Rac1-mediated cellular events in B16-F10 melanoma cells. Consequently, capsaicin administration should be considered an effective approach for the suppression of invasion and metastasis in malignant melanoma chemotherapy.

High-fat diet alters PP2A, TC10, and CIP4 expression in visceral adipose tissue of rats.

OBJECTIVE: The aim of this study was to investigate a possible link between high-fat diet (HFD)-induced obesity and the expression of protein phosphatase 2A (PP2A) and Cdc42-interacting protein 4 (CIP4) proteins, potential downstream components of the IRS/PI3K/AKT and CAP/Cbl/TC10 pathway, respectively, in the visceral adipose tissue. METHODS AND PROCEDURES: Twenty male Sprague-Dawley rats were randomly divided into two groups and were given either HFD or the normal diet (ND) for 8 weeks. The HFD-induced changes in the expression of the epididymal adipose tissue genes involved in the insulin-signaling pathways were evaluated using real-time reverse-transcription PCR and western blot analysis. RESULTS: The exposure of rats to HFD for 8 weeks resulted in a significant increase in the expression of PP2A at both the transcriptional and translational levels, along with a marked reduction in the levels of phosphorylated AKT and insulin receptor substrate-1 (IRS-1) in the cytosol of visceral adipocytes, compared with the ND rats. Besides, there were significant HFD-induced decreases in the mRNA and protein levels of CIP4 and TC10 in the adipose tissue of rats. DISCUSSION: These data suggest that HFD might have a relevance to insulin resistance by increasing the expression of PP2A, an inhibitor of AKT activity in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway, and also by suppressing the expression of TC10 and CIP4, downstream effectors of the Cbl/CAP/TC10 insulin-signaling cascade in the visceral adipose tissue.

Capsaicin induced apoptosis of B16-F10 melanoma cells through down-regulation of Bcl-2.

Capsaicin (8-methyl-N-vanillyl-6-nonenamide), a pungent ingredient of hot chili peppers, has been reported to possess substantial anticarcinogenic and antimutagenic activities. In the present study, we investigated the effect of capsaicin on induction of apoptosis in highly metastatic B16-F10 murine melanoma cells. Capsaicin inhibited growth of B16-F10 cells in a concentration-dependent manner. Proapoptotic effect of capsaicin was evidenced by nuclear condensation, internucleosomal DNA fragmentation, in situ terminal nick-end labeling of fragmented DNA (TUNEL), and an increased sub G1 fraction. Treatment of B16-F10 cells with capsaicin caused release of mitochondrial cytochrome c, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase in a dose-dependent manner. Furthermore, Bcl-2 expression in the B16-F10 cells was slightly down-regulated by capsaicin treatment. In contrast, there were no alterations in the levels of Bax in capsaicin-treated cells. Collectively, these findings indicate that capsaicin-induces apoptosis of B16-F10 melanoma cells via down-regulation the Bcl-2.

Protective effect of soybean saponins and major antioxidants against aflatoxin B1-induced mutagenicity and DNA-adduct formation.

Saponins from various plant sources have been suggested as possible anticarcinogens. Major dietary sources of saponins include legumes such as soybeans. This study was performed to determine the effect of soybean saponins on aflatoxin B(1)(AFB(1))-induced mutagenicity and AFB(1)-DNA adduct formation using Salmonella typhimurium and human liver hepatoma (HepG2) cells, respectively. Major antioxidants including L-ascorbic acid, alpha-tocopherol, all-trans-retinol, and butylated hydroxytoluene (BHT), previously reported to possess antimutagenic activity, were used as test materials to evaluate the relative effectiveness of saponins. Results indicated antimutagenicity was in the order of BHT > saponins > alpha-tocopherol > L-ascorbic acid. Soybean saponins exerted a significant effect, inhibiting the mutagenicity of AFB(1) by 52%, 64%, and 81% at concentrations of 600, 900, and 1,200 microg per plate, respectively. The amount of tritiated AFB(1) metabolites-DNA adducts formed in HepG2 cells was significantly reduced when cells were preincubated with 10 or 30 microg/ml of test materials. Soybean saponins inhibited AFB(1)-DNA adduct formation by 50.1% at a concentration of 30 microg/ml, whereas L-ascorbic acid and BHT reduced adduct formation by 38.4% and 32.6%, respectively, at the same concentrations. These results indicate that soybean saponins possess not only a significant antimutagenic activity but a strong inhibitory action against carcinogen-induced DNA damages. Soybean saponins possibly block the initiation stage of carcinogenesis, and further studies are required to elucidate the mechanisms of action.