Yutaka Miura

Hypolipidemic action of dietary resveratrol, a phytoalexin in grapes and red wine, in hepatoma-bearing rats

Resveratrol is an antioxidant present in grapes and their related products. We investigated whether dietary resveratrol could inhibit the proliferation and metastasis of tumors and hyperlipidemia in Donryu rats subcutaneously implanted with an ascites hepatoma cell line of AH109A. By feeding 10 or 50 ppm resveratrol in the diet to hepatoma-bearing rats for 20 days, solid tumor growth and metastasis tended to be suppressed dose-dependently. Resveratrol (50 ppm) significantly suppressed the serum lipid peroxide level, indicating its antioxidative properties or those of its metabolite(s) in vivo. Resveratrol dose-dependently suppressed both the serum triglyceride and very-low-density lipoprotein + low-density lipoprotein (VLDL + LDL)-cholesterol levels. The hypocholesterolemic action of resveratrol is attributed, at least in part, to an increased excretion of neutral sterols and bile acids into feces. These results suggest that dietary resveratrol is hypolipidemic with a tendency for anti-tumor-growth and anti-metastasis effects in hepatoma-bearing rats.

Hypoglycemic effect of aspalathin, a rooibos tea component from Aspalathus linearis, in type 2 diabetic model db/db mice.

Effects of aspalathin, a green rooibos tea component, on glucose metabolism were studied in vitro and in vivo. We first examined the effect of aspalathin on glucose uptake by cultured L6 myotubes and on insulin secretion from cultured RIN-5F pancreatic beta-cells in vitro, and then investigated the effect of dietary aspalathin on fasting blood glucose level and conducted an intraperitoneal glucose tolerance test (IPGTT) using type 2 diabetes model mice in vivo. Aspalathin dose-dependently and significantly increased glucose uptake by L6 myotubes at concentrations 1-100 microM. It also significantly increased insulin secretion from cultured RIN-5F cells at 100 microM. Dietary aspalathin (0.1-0.2%) suppressed the increase in fasting blood glucose levels of db/db mice for 5 weeks. In IPGTT, aspalathin improved impaired glucose tolerance at 30, 60, 90, and 120 min in db/db mice. These results suggest that aspalathin has beneficial effects on glucose homeostasis in type 2 diabetes through stimulating glucose uptake in muscle tissues and insulin secretion from pancreatic beta-cells.

Leucine promotes glucose uptake in skeletal muscles of rats

Soleus muscles isolated from normal rats were incubated to evaluate whether or not leucine promotes glucose uptake under insulin-free conditions, using a labeled 2-deoxyglucose uptake assay. Glucose uptake was promoted by 2mM leucine. A metabolite of leucine, alpha-ketoisocaproic acid (alpha-KIC), also exhibited a similar stimulatory effect, although this was not as potent as leucine. Stimulation of glucose uptake by leucine was completely canceled by pre-treatment with either 10 microM LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3-kinase), or 6 microM GF109203X, a specific inhibitor of protein kinase C (PKC). No significant change was observed by pre-treatment with 1 microM rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR). These results suggest that leucine stimulates glucose transport in skeletal muscle via PI3-kinase and PKC pathways independently of the mammalian target of mTOR. They also suggest that leucine stimulates glucose transport by an insulin-independent mechanism.

Inhibitory effects of carotenoids on the invasion of rat ascites hepatoma cells in culture

The effects of carotenoids--alpha-carotene, beta-carotene, lycopene, beta-cryptoxanthin, zeaxanthin, lutein, canthaxanthin, astaxanthin--on the invasion of rat ascites hepatoma AH109A cells were investigated by co-culturing the hepatoma cells with rat mesentery-derived mesothelial cells (M-cells). All the carotenoids examined inhibited AH109A invasion in a dose-dependent manner up to 5 microM. Cancer cells previously cultured with hypoxanthine (HX) and xanthine oxidase (XO) showed a highly invasive activity. Carotenoids, 5 microM of beta-carotene and astaxanthin, suppressed this reactive oxygen species-potentiated invasive capacity by simultaneously treating AH109A cells with the carotenoids, HX and XO. These results suggest that the antioxidative property of these carotenoids may be involved in their anti-invasive action.

Resveratrol suppresses hepatoma cell invasion independently of its anti-proliferative action.

Resveratrol, found in grapes, is a phytoalexin with antioxidative activity. The compound (100 and 200 microM) inhibited the proliferation of hepatoma cells, although this phytoalexin exerted little influence up to 50 microM. Resveratrol, however, suppressed the invasion of the hepatoma cells even at a concentration of 25 microM. Sera from rats orally given resveratrol restrained only the invasion of AH109A cells. Resveratrol and resveratrol-loaded rat serum suppressed reactive oxygen species-potentiated invasive capacity. These results suggest that the anti-invasive activity of resveratrol is independent of the anti-proliferative activity, and that the antioxidative property of resveratrol may be involved in its anti-invasive action.

Inhibitory effects of chlorogenic acid and its related compounds on the invasion of hepatoma cells in culture

Actions of chlorogenic acid, a major component of coffee, andits constituents, caffeic and quinic acids, on theproliferation and invasion of AH109A, a rat ascites hepatomacell line, were investigated using in vitro assay systems. Allthree components suppressed the AH109A invasion atconcentrations of 5–40 μM without altering the cellproliferation. At the concentration of 10 μM, chlorogenic,caffeic and quinic acids significantly (P < 0.05) suppressedthe invasion by 68%, 36% and 31%, respectively, implying thatthe suppressive effect of chlorogenic acid on the AH109Ainvasion might result from the additive effects of itsconstituents, caffeic and quinic acids. At the concentrationof 10 μM, cinnamic acid and p-coumaric acid (4-hydroxycinnamicacid) exerted no or little influence on the invasion, whereascaffeic acid (3,4-dihydroxycinnamic acid) significantly (P <0.05) suppressed it, suggesting the possible involvement ofthe 3,4-dihydroxy group of caffeic acid in the suppression.Chlorogenic acid was thus demonstrated to be one of thechemical entities in coffee suppressing the hepatoma invasionin vitro, and both of its constituents, caffeic and quinicacids, to be responsible for the anti-invasive activity. Theseresults suggest the existence of nutritionally andpharmacologically important substances in coffee which controltumor cell invasion.

Suppression of hypercholesterolemia in hepatoma-bearing rats by cabbage extract and its component, S-methyl-L-cysteine sulfoxide.

The effect of cabbage extract on cholesterol metabolism was studied in Donryu rats subcutaneously implanted with an ascites hepatoma cell line (AH109A). The hepatoma-bearing rats exhibited hypercholesterolemia induced by increasing cholesterogenesis in the host liver and decreasing steroid excretion into feces. The cabbage extract intake or administration reduced serum cholesterol level and enhanced fecal bile acid excretion and cholesterol 7α-hydroxylase activity, the rate-limiting enzyme of bile acid biosynthesis, in the microsomal fraction of the liver. Furthermore, S-methyl-l-cysteine sulfoxide, a component of cabbage, could mimic the effect of cabbage extract when orally administered. These results suggest that cabbage suppresses hypercholesterolemia responding to hepatoma growth by upregulating cholesterol catabolism and that S-methyl-l-cysteine sulfoxide in cabbage is one of the factors suppressing hypercholesterolemia in the hepatoma-bearing rats.

Matrix assisted laser desorption/ionization‐time of flight‐mass spectrometry analysis of proteins detected by anti‐phosphotyrosine antibody on two‐dimensional‐gels of fibrolast cell lysates after tumor necrosis factor‐α stimulation

We describe efficient methods for using functional proteomics analysis to study signal transduction pathways in murine fibroblast L929 cells following stimulation with tumor necrosis factor (TNF)‐α. After stimulation with TNF‐α, cellular proteins of L929 cells were extracted with a lysis buffer containing 0.3% sodium dodecyl sulfate (SDS) for 10—30u2005min time intervals, and were separated by two‐dimensional (2‐D) electrophoresis followed by immunoblot analysis with anti‐phosphotyrosine antibody and alkaline phosphatase‐anti IgG antibody conjugate. To improve detection sensitivity by immunoblot analysis we used a chemifluorescent substrate for alkaline phosphatase. One hundred protein spots were detected in the TNF‐α stimulated L929 cell extract by immunoblot analysis. The use of chemifluorescence allowed us to quantitate immunoblotted spots with fluoroscanner so that we were able to detect time‐dependent changes of a number of immunoblotted spots. Protein spots on a silver‐stained 2‐D gel corresponding to those detected by immunoblot analysis were subjected to in‐gel trypsin digestion‐ matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF)‐mass spectrometry analysis, respectively. Twenty‐one proteins detected by immunoblot analysis were identified by MS‐Fit database search analysis. Among them, the proteins that show time‐dependent changes in staining intensity include vimentin, tubulin beta‐chain, eukaryotic translation initiation factor 1A, chromatin assembly factor 1 (P48 subunit), probable protein disulfide isomerase P5, and several other proteins. Vimentin and tubulin beta‐chain have been reported to be phosphorylated at tyrosine residues and involved in the signal transduction pathway induced by TNF‐α. However, the other proteins have no previously known function in the signal transduction pathway. Thus, the methods used in this study seem to be suitable for the identification of time‐dependent changes in many proteins that are involved in signal transduction. Usefulness of the method for comprehensive analysis of the proteins involved in signal transduction pathway and the limitations of the method are discussed.

Piceatannol, a resveratrol derivative, promotes glucose uptake through glucose transporter 4 translocation to plasma membrane in L6 myocytes and suppresses blood glucose levels in type 2 diabetic model db/db mice.

The skeletal muscle cells are one of the main sites of glucose uptake through glucose transporter 4 (GLUT4) in response to insulin. In muscle cells, 5 adenosine monophosphate-activated protein kinase (AMPK) is known as another GLUT4 translocation promoter. Natural compounds that activate AMPK have a possibility to overcome insulin resistance in the diabetic state. Piceatannol is a natural analog and a metabolite of resveratrol, a known AMPK activator. In this study, we investigate the in vitro effect of piceatannol on glucose uptake, AMPK phosphorylation and GLUT4 translocation to plasma membrane in L6 myocytes, and its in vivo effect on blood glucose levels in type 2 diabetic model db/db mice. Piceatannol was found to promote glucose uptake, AMPK phosphorylation and GLUT4 translocation by Western blotting analyses in L6 myotubes under a condition of insulin absence. Promotion by piceatannol of glucose uptake as well as GLUT4 translocation to plasma membrane by immunocytochemistry was also demonstrated in L6 myoblasts transfected with a glut4 cDNA-coding vector. Piceatannol suppressed the rises in blood glucose levels at early stages and improved the impaired glucose tolerance at late stages in db/db mice. These in vitro and in vivo findings suggest that piceatannol may be preventive and remedial for type 2 diabetes and become an antidiabetic phytochemical.

Suppression of adhesion and invasion of hepatoma cells in culture by tea compounds through antioxidative activity

To determine the actions of tea components on the invasion of a rat ascites hepatoma cell line of AH109A and to understand their modes of action, the cancer cells were co-cultured with a rat mesentery-derived mesothelial cell monolayer in the presence of tea components. The synergistic effects of (-)-epicatechin (EC) with (-)-epigallocatechin gallate (EGCG) on AH109A invasion were demonstrated. Further study showed that 10 microM of EGCG or theaflavins, or 2.5 microM of ethylenediaminetetra-acetic (EDTA) entirely abolished the increase in AH109A adhesion and invasion stimulated by reactive oxygen species (ROS) from the hypoxanthine-xanthine oxidase system. Our results suggest that (.)OH(-)- and other ROS-scavenging activity of EGCG and theaflavins may be responsible for the inhibition of (.)OH(-)- and related ROS-potentiated AH109A adhesion and invasion to the cultured rat mesothelial cell monolayer.