Effect of organophosphate pesticides on the activities of lecithin-cholesterol acyltransferase and cholinesterase in rat serum

Relationships of human α/β hydrolase fold proteins and other organophosphate-interacting proteins

Organophosphates (OPs) are either found in nature or synthetized for use as pesticides, flame retardants, neurotoxic warfare agents or drugs (cholinergic enhancers in Alzheimer's disease and myasthenia gravis, or inhibitors of lipases in metabolic diseases). Because of the central role of acetylcholinesterase cholinergic neurotransmission in humans, one of the main purposes for using OPs is inactivation of the enzyme by phosphorylation of the nucleophilic serine residue in the active center. However, hundreds of serine hydrolases are expressed in the human proteome, and many of them are potential targets for OP adduction. In this review, we first situate the α/β hydrolase fold proteins among the distinctively folded proteins known to interact with OPs, in particular the different lipases, peptidases, and enzymes hydrolyzing OPs. Second, we compile the human α/β hydrolases and review those that have been experimentally shown to interact with OPs. Among the 120 human α/β hydrolase fold proteins, 102 have a serine in the consensus GXSXG pentapeptide compatible with an active site, 6 have an aspartate or a cysteine as the active site nucleophile residue, and 12 evidently lack an active site. 76 of the 120 have been experimentally shown to bind an OP.

Influence of exposure to pesticides on serum components and enzyme activities of cytotoxicity among intensive agriculture farmers

Although the effects of acute pesticide poisoning are well known for the pesticides most currently used, hardly any data exist on health effects after long-term low-dose exposures. Major unresolved issues include the effect of moderate exposure in the absence of poisoning. The increased utilization of pesticides other than organophosphates makes it even more difficult to find associations. In this study a cohort of 106 intensive agriculture workers were assessed twice during the course of a spraying season for changes in serum biochemistry, namely enzymes reflecting cytotoxicity (AST, ALT, LDH, CK, and amino-oxidase) and other biochemical parameters, such as markers of nephrotoxicity (urea, creatinine) and lipid profile (cholesterol and triglycerides). Several criteria for estimating pesticide exposure were used, the most important one being serum cholinesterase depression greater than 25% from baseline to peak exposure. Our results revealed an association of pesticide exposure with changes in AST (increased activity), LDH, and amino-oxidase (decreased activity) as well as with changes in serum creatinine and phosphorus (lower and higher levels, respectively). These results provide support for a very slight impairment of the liver function, but overall these findings are consistent with no clinically significant hepatotoxicity. Intriguingly, paraoxonase-1 R allele was found to be an independent predictor of higher rates of AST and lower rates of amino-oxidase, so that it may play a supporting role as an individual marker of susceptibility on pesticide-induced health effects. In conclusion, different biomarkers might be used to detect early biochemical effects of pesticides before adverse clinical health effects occur.

Some further data on the effects of two organophosphate pesticides on the oxidative metabolism in the liver

Sumithion is the most active cholinesterase inhibitor. The cholinesterase inhibiting action of the organophosphates (OPs) is better compensated by vitamin E in normal animals, but by vitamin A in vitamin A-deficient animals. The lipid peroxidation (LP) is enhanced by the antioxidant vitamins in the liver of normal rats; although they decrease it in the liver of vitamin A-deficient animals, in no case do they prevent the LP-enhancing effect of the OPs examined. The OPs examined inhibit protein synthesis in the liver of vitamin A-deficient animals.