Inhibition of cholinergic and non-cholinergic targets following subacute exposure to chlorpyrifos in normal and high fat fed male C57BL/6J mice

Abstract

The effects of obesity on organophosphate pesticide-mediated toxicities, including both cholinergic and non-cholinergic targets, have not been fully elucidated. Therefore, the present study was designed to determine if high fat diet intake alters the effects of repeated exposure to chlorpyrifos (CPS) on the activities of both cholinergic and noncholinergic serine hydrolase targets. Male C57BL/6J mice were placed on either standard rodent chow or high fat diet for four weeks with CPS exposure (2.0 mg/kg) for the last 10 days of diet intake. Exposure to CPS did not alter acetylcholinesterase in the central nervous system, but it did significantly inhibit circulating cholinesterase activities in both diet groups. CPS significantly inhibited hepatic carboxylesterase and fatty acid amide hydrolase and this inhibition was significantly greater in high fat fed animals. Additionally, CPS exposure and high fat diet intake downregulated genes involved in hepatic de novo lipogenesis as well as cytochrome P450 enzymes involved in hepatic xenobiotic metabolism. In summary, the present study demonstrates that high fat diet intake potentiates CPS mediated inhibition of both carboxylesterase and fatty acid amide hydrolase in the liver of obese animals following subacute exposure and suggests obesity may be a risk factor for increased non-cholinergic hepatic CPS toxicity.

Keywords: Acetylcholinesterase; Carboxylesterase; Chlorpyrifos; Endocannabinoid; High fat diet; Organophosphate.

Fig. 1.

Effects of CPS exposure on CNS, RBC, and plasma ChE activities. Twelve hours following CPS exposure, AChE activities in brain (A.), RBCs (B.), or cholinesterase (ChE) activity in plasma (C.) were determined. Data are expressed as mean ± SEM of n = 8 animals/group. *P < 0.05 vs. vehicle-treated SD; #P < 0.05 vs. vehicle-treated high fat diet (HFD).

Fig. 2.

Hepatic CES activity was significantly inhibited by CPS in standard and high-fat diet fed animals. Hepatic (A.) and adipose (B.) CES activities were determined in tissue homogenates using para-nitrophenyl valerate as substrate. Data represent the mean ± SEM of n = 8 animals/group for liver and mean ± SEM of n = 6 animals/group for adipose. *P < 0.05 vs. vehicle-treated SD; #P < 0.05 vs. vehicle-treated HFD; &P ≤ 0.05 vs. CPS-treated SD.

Fig. 3.

Hepatic 2-AG and AEA hydrolysis was significantly inhibited following CPS exposure in high-fat fed animals. Following sacrifice, hepatic 2-AG (A.) and AEA (B.) hydrolysis and CNS 2-AG (C.) and AEA (D.) hydrolysis were determined as an index of MAGL and FAAH activities, respectively. Data represent the mean ± SEM of n = 5–6 animals/group. *P < 0.05 vs. vehicle-treated SD; #P < 0.05 vs. vehicle-treated HFD; &P ≤ 0.05 vs. CPS-treated SD.

Fig. 4.

CPS exposure and high fat diet intake decrease hepatic lipogenic gene expression. Expression of genes governing key processes in hepatic lipid metabolism was determined by real-time PCR following sacrifice. Data are expressed as the fold change from standard diet (SD), vehicle-treated controls and represent the mean ± SEM of n = 5–6 animals/group. *P < 0.05 vs. SD vehicle-treated animals.

Fig. 5.

High-fat diet intake decreases hepatic p450 expression. Expression of major hepatic p450 isoforms was determined by real-time PCR following sacrifice. Data are expressed as the fold change from SD vehicle-treated controls and represent the mean ± SEM of n = 5–6 animals/group. *P < 0.05 vs. vehicle-treated SD; &P ≤ 0.05 vs. CPS-treated SD.