Shintaro Ishikawa

Progression of nephropathy in spontaneous diabetic rats is prevented by OPB-9195, a novel inhibitor of advanced glycation.

Levels of tissue advanced glycation end products (AGEs) that result from nonenzymatic reactions of glucose and proteins are high in both diabetic and aging people. Irreversible AGE formation is based on increases in AGE-derived protein-to-protein cross-linking and is considered to be a factor contributing to the complications of diabetes. A novel inhibitor of advanced glycation, OPB-9195, belongs to a group of thiazolidine derivatives, known as hypoglycemic drugs; however, they do not lower blood glucose levels. We did studies to determine if OPB-9195 would prevent the progression of nephropathy in spontaneous diabetic rats. In vitro inhibitory effects of OPB-9195 on AGE formation and AGE-derived cross-linking were examined by enzyme-linked immunosorbent assay (ELISA) and SDS-PAGE, respectively. Otsuka-Long-Evans-Tokushima-Fatty (OLETF) rats, a model of NIDDM, were used to evaluate the therapeutic effect of OPB-9195. Light microscopic findings by periodic acid-Schiff (PAS) staining, the extent of AGE accumulation detected by immunohistochemical staining in the kidneys, the levels of serum AGEs by AGE-specific ELISA, and urinary albumin excretion were examined. OPB-9195 effectively inhibited both AGE-derived cross-linking and the formation of AGEs, in a dose-dependent manner in vitro. In addition, the administration of OPB-9195 prevented the progression of glomerular sclerosis and AGE deposition in glomeruli. Elevation of circulating AGE levels and urinary albumin excretion were dramatically prevented in rats, even at 56 weeks of age and with persistent hyperglycemia. We concluded that a novel thiazolidine derivative, OPB-9195, prevented the progression of diabetic glomerular sclerosis in OLETF rats by lowering serum levels of AGEs and attenuating AGE deposition in the glomeruli.

Branched-Chain Amino Acids Enhance Premature Senescence through Mammalian Target of Rapamycin Complex I-Mediated Upregulation of p21 Protein

Branched-chain amino acids (BCAAs) have been applied as an oral supplementation to patients with liver cirrhosis. BCAAs not only improve nutritional status of patients but also decrease the incidence of liver cancer. Mammalian target of rapamycin (mTOR) links cellular metabolism with growth and proliferation in response to nutrients, energy, and growth factors. BCAAs, especially leucine, have been shown to regulate protein synthesis through mTOR activities. On the other hand, cellular senescence is suggested to function as tumor suppressor mechanisms, and induced by a variety of stimuli including DNA damage-inducing drugs. However, it is not clear how BCAA supplementation prevents the incidence of liver cancer in patients with cirrhosis. Here we showed that human cancer cells, HepG2 and U2OS, cultured in medium containing BCAAs with Fischers ratio about 3, which was shown to have highest activities to synthesize and secrete of albumin, had higher activities to induce premature senescence and elevate mTORC1 activities. Furthermore, BCAAs themselves enhanced the execution of premature senescence induced by DNA damage-inducing drugs, which was effectively prevented by rapamycin. These results strongly suggested the contribution of the mTORC1 pathway to the regulation of premature senescence. Interestingly, the protein levels of p21, a p53 target and well-known gene essential for the execution of cellular senescence, were upregulated in the presence of BCAAs. These results suggested that BCAAs possibly contribute to tumor suppression by enhancing cellular senescence mediated through the mTOR signalling pathway.