E.Y. Han

Comparative Nephrotoxicitiy Induced by Melamine, Cyanuric Acid, or a Mixture of Both Chemicals in Either Sprague-Dawley Rats or Renal Cell Lines

Acute nephrotoxicities of melamine (MEL), cyanuric acid (CA), and a mixture of both melamine and cyanuric acid (MC) were comparatively investigated in male Sprague-Dawley rats at 5 doses each with 10-fold dose interval as follows: MEL at 0.0315, 0.315, 3.15, 31.5, and 315 mg/kg; CA at 0.025, 0.25, 2.5, 25, and 250 mg/kg, and MC: [1×: (0.0315 + 0.025), 10×: (0.315 + 0.25), 100×: (3.15 + 2.5), 1000×: (31.5 + 25), and (315 + 250) mg/kg]. No marked adverse effects in renal function were observed in animals treated with MEL alone or CA alone, but evidence related to nephrotoxicity was noted in rats administered MC. Renal calculi and increased kidney weights were found in rats 7 d after daily oral administration of MC. Blood urea nitrogen (BUN) and creatinine were significantly elevated in the high dose MC groups at 100× or 1000×. In addition, elevated numbers of white blood cells (WBC), neutrophils, and lymphocytes in vivo and increased levels of prostaglandin E2 (PGE2) in vitro were found in the MC group. Based on these data, the NOAEL (no-observed-adverse-effect level) for nephrotoxicity for MC was estimated to be 3.15 mg/kg body weight (bw)/d (MEL) plus 2.5 mg/kg bw/d (CA). If a safety factor of 1000 or more were applied to NOAEL, tolerable daily intake (TDI) would be 0.00315 and 0.0025 mg/kg/d or less for MEL and CA, respectively, which is far below the TDI of 0.2 mg/kg/d set by World Health Organization (WHO). In addition, in vitro cytotoxicity assays showed that the ACHN human renal adenocarcinoma cell line was more sensitive to MEL, CA, and MC than the MDCK canine kidney epithelial cell line. The 24-h half maximal inhibitory concentration (IC50) values for MEL (4792, 2792 μg/ml) were less than those of CA (9890, 6725 μg/ml, respectively) in MDCK and ACHN cell lines, suggesting that MEL may be more cytotoxic than CA. Furthermore, the 24-h IC50 value for MC was found to be 208 μg/ml in ACHN cells. Data suggest that NOAELs based upon acute nephrotoxic parameters for MC were low, which might require further reassessment of the current TDI.

Chemopreventive mechanisms of methionine on inhibition of benzo(a)pyrene-DNA adducts formation in human hepatocellular carcinoma HepG2 cells.

This study was designed to investigate the molecular mechanism underlying the chemopreventive effects of methionine on benzo[a]pyrene (B[a]P)-DNA adducts formation in HepG2 cells. Methionine significantly inhibited B[a]P-DNA adduct formation in HepG2 cells. Methionine significantly decreased the cellular uptake of [(3)H] B[a]P, but increased the cellular discharge of [(3)H] B[a]P from HepG2 cells into the media. B[a]P significantly lowered total cellular glutathione (GSH) level, but co-cultured with B[a]P and methionine, gradually attenuated intracellular GSH levels in a concentration-dependent manner, which was markedly higher at 20-500μM methionine. The cellular proteins of treated cells were resolved by 2D-polyacrylamide gel electrophoresis. Proteomic profiles showed that phase II enzymes such as glutathione S-transferase (GST) omega-1, GSTM3, glyoxalase I (GLO1) and superoxide dismutase (SOD) were down-regulated by B[a]P treatment, whereas cathepsin B (CTSB), Rho GDP-dissociation inhibitor alpha (Rho-GDP-DIA), histamine N-methyltransferase (HNMT), spermidine synthase (SRM) and arginase-1 (ARG1) were up-regulated by B[a]P. B[a]P and methionine treatments, GST omega-1, GSTM3, GLO1 and SOD were significantly enhanced compared to B[a]P alone. Similarly, methionine was effective in diminishing the B[a]P-induced up-regulation of CTSB, Rho-GDP-DIA, HNMT, SRM and ARG1. Our data suggests that methionine might exert a chemoprotective effect on B[a]P-DNA adduct formation by attenuating intracellular GSH levels, blocking the uptake of B[a]P into cells, or by altering expression of proteins involved in DNA adduct formation.

Comparison of the Short Term Toxicity of Phthalate Diesters and Monoesters in Sprague-Dawley Male Rats

This study was carried out to investigate the short term toxicity of nine phthalate diesters including di-2 (ethylhexyl) phthalate (DEHP) , di (n-butyl) phthalate (DBP) , di-n-octyl phthalate (DnOP) , diethyl phthalate (DEP) , butylbenzyl phthalate (BBP) , dimethyl phthalate (DMP) , di-isodecyl phthalate (DIDP) , diundecyl phthalate (DUP) , and di-isononyl phthalate (DINP) and five phthalate monoesters including mono- (2-ethylhexyl) phthalate (MEHP) , monobutyl phthalate (MBuP) , monobenzyl phthalate (MBeP) , monoethyl phthalate (MEP) , monomethyl phthalate (MMP) and phthalic acid (PA) in Sprague-Dawley male rats. Animals were administered 250 mg/kg/day (monoesters and PA) or 500 mg/kg/day (diesters) of phthalate for two weeks. All animals were examined for body and organ weights, blood hematology, serum biochemistry, and urine analysis. The body weight gain was significantly lower in rats treated with BBP, DBP, DINP, MEHP, MBuP, and PA than that of control. Liver weights were significantly increased in the DEHP,DBP, DnOP, DIDP, and MEHP groups as compared to the control group. Testes weights were significantly decreased only in the DEHP-, DnOP-, and DIDP-treated groups as compared to the control. Significant differences in hematological changes were not observed in any treatment groups. Significant increases in blood glucose levels were observed in the DEHP, MEHP, and MBeP groups. Aspartate aminotransferase (AST) levels were significantly increased in the DBP, DUP, DINP, MBuP, and MBeP groups, whereas alanine aminotransferase (ALT) levels were significantly increased only in the DEHP and MEHP groups. Serum ALP levels were significantly higher in phthalate diester (500 mg/kg/day) -treated rats as compared to control. However, the total cholesterol level was significantly reduced in the DEHP- and DIDP-treated groups, whereas serum triglyceride (TG) levels were higher in the DINP-, MEHP-, and MBuP-treated groups. These results suggest that short term toxicity of phthalate monoesters produces adverse effects as similar to phthalate diesters in Sprague-Dawley rats.