Toxicity of glyphosate in feed for weanling piglets and the mechanism of glyphosate detoxification by the liver nuclear receptor CAR/PXR pathway

Glyphosate (GLP), the most widely used and productive pesticide worldwide, which safety and reliability gradually become a social concern. It is important to explore the toxic of GLP on the limitation level by governments on piglets and the potential role of hepatic CAR/PXR and Keap1-Nrf2 pathways in low levels of glyphosate detoxification. Compared with the control group, the production performance and organ index of GLP group showed no significant change. However, the liver GLP residue of 40 mg/kg group was significantly higher than the control group. We also found that the activity of ALP increased linearly and DBIL content increased quadratically. Furthermore, GLP could significantly increase SOD and GSH-Px and decrease T-AOC and CAT activities and significantly increase MDA and H2O2 contents (P < 0.05); however, the genes expression of Keap1/Nrf2 pathway was not affected. Gene expression of CAR/PXR pathway showed that GLP could significantly stimulate the expression of CAR, but it could not affect the expression of phase Ⅰ (CYP1A1, CYP1A2, CYP2E1, CYP2A19, CYP3A29), phase Ⅱ (UGT1A6, GSTA1, GSTA2) detoxification enzymes and transporters (MDR1, MRP2, P-gp). Our study showed that although 10-40 mg/kg GLP would inevitably cause some liver damage and dysfunction, it can self-alleviating the toxic effect of GLP.

Methyl isobutyl ketone-induced hepatocellular carcinogenesis in B6C3F1 mice: A constitutive androstane receptor (CAR)-mediated mode of action

In a National Toxicology Program (NTP) chronic inhalation study with methyl isobutyl ketone (MIBK), increases in hepatocellular adenomas and hepatocellular adenomas and carcinomas (combined) were observed in male and female B6C3F₁ mice at 1800 ppm. A DNA reactive Mode-of-Action (MOA) for this liver tumor response is not supported by the evidence as MIBK and its major metabolites lack genotoxicity in both in vitro and in vivo studies. Constitutive androstane receptor (CAR) nuclear receptor-mediated activation has been hypothesized as the MOA for MIBK-induced mouse liver tumorigenesis. To further investigate the MOA for MIBK-induced murine liver tumors, male and female B6C3F1, C57BL/6, and CAR/PXR Knockout (KO) mice were exposed to either 0 or 1800 ppm MIBK for 6 h/day, 5 days/week for a total of 10 days. On day 1, mice were implanted with osmotic mini-pumps containing 5-Bromo-2-deoxyuridine (BrdU) 1 h following exposure and humanely euthanized 1-3 h following the final exposure. B6C3F₁ and C57BL/6 mice had statistically significant increases in liver weights compared to controls that corresponded with hepatocellular hypertrophy and increased mitotic figures. Hepatocellular proliferation data indicated induction of S-phase DNA synthesis in B6C3F₁ and C57BL/6 mice exposed to 1800 ppm MIBK compared to control, and no increase was observed in MIBK exposed CAR/PXR KO mice. Liver gene expression changes indicated a maximally-induced Cyp2b10 (CAR-associated) transcript and a slight increase in Cyp3a11(PXR-associated) transcript in B6C3F₁ and C57BL/6 mice exposed to 1800 ppm MIBK compared to controls, but not in Cyp1a1 (AhR-associated) or Cyp4a10 (PPAR-α-associated) transcripts. CAR/PXR KO mice exposed to 1800 ppm MIBK showed no evidence of activation of AhR, CAR, PXR or PPAR-α nuclear receptors via their associated transcripts. MIBK induced hepatic effects are consistent with a phenobarbital-like MOA where the initiating events are activation of the CAR and PXR nuclear receptors and resultant hepatocellular proliferation leading to rodent liver tumors.