Effects of nicotine exposure on in vitro metabolism of chlorpyrifos in male Sprague-Dawley rats

Urinary Dialkylphosphate Metabolite Levels in US Adults-National Health and Nutrition Examination Survey 1999-2008

Background: Urinary dialkylphosphate metabolites are considered to be a proxy of the cumulative exposure to organophosphorus pesticides. We analyzed the urinary levels of six dialkylphosphate (DAP) metabolites in US adults, to assess the factors associated with levels of urinary metabolites, and observe the time trends. Methods: We analyzed the combined urinary levels of Dimethylphosphate (DMP), Diethylphosphate (DEP), Dimethylthiophosphate (DMTP), Diethylthiophosphate (DETP), Dimethyldithiophosphate (DMDTP), and Diethyldithiophosphate (DEDTP) in the National Health and Nutrition Examination Survey (NHANES) from 1999 and 2008. Results: Increased age and female gender were positively associated with combined levels of urinary DAP metabolites; BMI < 18.5 kg/m2, BMI > 25 kg/m2, current smoking, and later survey year were inversely associated with combined levels of DAP metabolites. Among those with at least one detectable DAP in their urine, the mean levels decreased starting in 2001, but stayed relatively stable through 2008. Although the maximum combined urinary DAP level was highest in 1999-2000, throughout all years, we observed extremely high levels of exposure for subgroups of individuals. Conclusion: Despite the fact that organophosphorus pesticides were banned for residential use in the US in 2006, there are still opportunities for exposure in the general population. The average urinary DAP levels have decreased over time; however, the decline appears to have plateaued in recent years, and there remains highly exposed individuals.

Subacute nicotine co-exposure has no effect on 2,2',3,5',6- pentachlorobiphenyl disposition but alters hepatic cytochrome P450 expression in the male rat

Polychlorinated biphenyls (PCBs) are metabolized by cytochrome P450 2B enzymes (CYP2B) and nicotine is reported to alter CYP2B activity in the brain and liver. To test the hypothesis that nicotine influences PCB disposition, 2,2',3,5',6-pentachlorobiphenyl (PCB 95) and its metabolites were quantified in tissues of adult male Wistar rats exposed to PCB 95 (6mg/kg/d, p.o.) in the absence or presence of nicotine (1.0mg/kg/d of the tartrate salt, s.c.) for 7 consecutive days. PCB 95 was enantioselectively metabolized to hydroxylated (OH-) PCB metabolites, resulting in a pronounced enrichment of E1-PCB 95 in all tissues investigated. OH-PCBs were detected in blood and liver tissue, but were below the detection limit in adipose, brain and muscle tissues. Co-exposure to nicotine did not change PCB 95 disposition. CYP2B1 mRNA and CYP2B protein were not detected in brain tissues but were detected in liver. Co-exposure to nicotine and PCB 95 increased hepatic CYP2B1 mRNA but did not change CYP2B protein levels relative to vehicle control animals. However, hepatic CYP2B protein in animals co-exposed to PCB 95 and nicotine were reduced compared to animals that received only nicotine. Quantification of CYP2B3, CYP3A2 and CYP1A2 mRNA identified significant effects of nicotine and PCB 95 co-exposure on hepatic CYP3A2 and hippocampal CYP1A2 transcripts. Our findings suggest that nicotine co-exposure does not significantly influence PCB 95 disposition in the rat. However, these studies suggest a novel influence of PCB 95 and nicotine co-exposure on hepatic cytochrome P450 (P450) expression that may warrant further attention due to the increasing use of e-cigarettes and related products.

Oxidative damage induced by chlorpyrifos in the hepatic and renal tissue of Kunming mice and the antioxidant role of vitamin E

Chlorpyrifos is a broad-spectrum, chlorinated organophosphate pesticide employed for pest control in various agricultural and animal husbandries. Acute and chronic exposure to CPF can elicit several adverse effects, including oxidative stress. We investigated neurotoxicity of CPF-treated mice, and evaluated the antioxidant effect of vitamin E against oxidative stress and histological changes in the livers and kidneys of CPF-treated mice. Kunming mice were divided randomly into five exposure groups of six: (A) peanut oil; (B) 3mg/kg CPF; (C) 6 mg/kg CPF; (D) 12 mg/kg CPF; (E) vitamin E (100 mg/kg), 3h after administration of CPF (12 mg/kg) and used as a post-treatment group. Oral administration of high-dose groups (12 mg/kg) CPF led to a significant increase in levels of reactive oxygen species, DNA-protein crosslinks, 8-hydroxy-2-deoxyguanosine and malondialdehyde, decreases in acetylcholinesterase activity and glutathione level, as well as causing hepatic and renal histopathological change. Except for AChE activity levels, administration of vitamin E to CPF-treated mice restored these biochemical parameters to within normal levels, and resulted in overall improvement in damage to livers and kidneys. These data suggest that oxidative stress is involved in CPF-induced toxicity and that vitamin E can protect against the tissue damage induced by CPF.

Impact of repeated nicotine and alcohol coexposure on in vitro and in vivo chlorpyrifos dosimetry and cholinesterase inhibition

Chlorpyrifos (CPF) is an organophosphorus insecticide, and neurotoxicity results from inhibition of acetylcholinesterase (AChE) by its metabolite, chlorpyrifos-oxon. Routine consumption of alcohol and tobacco modifies metabolic and physiological processes impacting the metabolism and pharmacokinetics of other xenobiotics, including pesticides. This study evaluated the influence of repeated ethanol and nicotine coexposure on in vivo CPF dosimetry and cholinesterase (ChE) response (ChE- includes AChE and/or butyrylcholinesterase (BuChE)). Hepatic microsomes were prepared from groups of naive, ethanol-only (1 g/kg/d, 7 d, po), and ethanol + nicotine (1 mg/kg/d 7 d, sc)-treated rats, and the in vitro metabolism of CPF was evaluated. For in vivo studies, rats were treated with saline or ethanol (1 g/kg/d, po) + nicotine (1 mg/kg/d, sc) in addition to CPF (1 or 5 mg/kg/d, po) for 7 d. The major CPF metabolite, 3,5,6-trichloro-2-pyridinol (TCPy), in blood and urine and the plasma ChE and brain acetylcholinesterase (AChE) activities were measured in rats. There were differences in pharmacokinetics, with higher TCPy peak concentrations and increased blood TCPy AUC in ethanol + nicotine groups compared to CPF only (approximately 1.8- and 3.8-fold at 1 and 5 mg CPF doses, respectively). Brain AChE activities after ethanol + nicotine treatments showed significantly less inhibition following repeated 5 mg CPF/kg dosing compared to CPF only (96 ± 13 and 66 ± 7% of naive at 4 h post last CPF dosing, respectively). Although brain AChE activity was minimal inhibited for the 1-mg CPF/kg/d groups, the ethanol + nicotine pretreatment resulted in a similar trend (i.e., slightly less inhibition). No marked differences were observed in plasma ChE activities due to the alcohol + nicotine treatments. In vitro, CPF metabolism was not markedly affected by repeated ethanol or both ethanol + nicotine exposures. Compared with a previous study of nicotine and CPF exposure, there were no apparent additional exacerbating effects due to ethanol coexposure.

Effect of in vivo nicotine exposure on chlorpyrifos pharmacokinetics and pharmacodynamics in rats

Routine use of tobacco products may modify physiological and metabolic functions, including drug metabolizing enzymes, which may impact the pharmacokinetics of environmental contaminants. Chlorpyrifos is an organophosphorus (OP) insecticide that is bioactivated to chlorpyrifos-oxon, and manifests its neurotoxicity by inhibiting acetylcholinesterase (AChE). The objective of this study was to evaluate the impact of repeated nicotine exposure on the pharmacokinetics of chlorpyrifos (CPF) and its major metabolite, 3,5,6-trichloro-2-pyridinol (TCPy) in blood and urine and also to determine the impact on cholinesterase (ChE) activity in plasma and brain. Animals were exposed to 7-daily doses of either 1mg nicotine/kg or saline, and to either a single oral dose of 35mg CPF/kg or a repeated dose of 5mg CPF/kg/day for 7 days. Groups of rats were then sacrificed at multiple time-points after receiving the last dose of CPF. Repeated nicotine and CPF exposures resulted in enhanced metabolism of CPF to TCPy, as evidenced by increases in the measured TCPy peak concentration and AUC in blood. However, there was no significant difference in the amount of TCPy (free or total) excreted in the urine within the first 24-h post last dose. The extent of brain acetylcholinesterase (AChE) inhibition was reduced due to nicotine co-exposure consistent with an increase in CYP450-mediated dearylation (detoxification) versus desulfuration. It was of interest to note that the impact of nicotine co-exposure was experimentally observed only after repeated CPF doses. A physiologically based pharmacokinetic model for CPF was used to simulate the effect of increasing the dearylation V(max) based upon previously conducted in vitro metabolism studies. Predicted CPF-oxon concentrations in blood and brain were lower following the expected V(max) increase in nicotine treated groups. These model results were consistent with the experimental data. The current study demonstrated that repeated nicotine exposure could alter CPF metabolism in vivo, resulting in altered brain AChE inhibition.