Interaction between human serum esterases and environmental metal compounds

Paraoxonase-1 (PON1) and cholinesterase (BChE) are two of the major human serum esterases. Although most of variation in PON1 activity results from genetic factors, there is growing evidence that environmental chemicals also modulate its activity. The aim of this study was to investigate whether environmental exposure to metal compounds has any influence on those esterases. A cross-sectional study was conducted in a representative sample of the general population of Andalusia, South of Spain. PON1 activity against different substrates (paraoxon, phenylacetate, diazoxon and dihydrocoumarin) and BChE were measured in serum from 536 healthy subjects. Potential associations of these esterases with metal compounds, age, sex and body mass index as well as life-style habits (smoking, alcohol drinking and food habits) were explored. Multiple linear regression analysis showed that blood lead levels were significantly associated with increased PON1 in serum regardless of the substrate used for the assay. Mercury also showed a significant and direct association with PON1 towards paraoxon and phenylacetate. In turn, cadmium and zinc levels were significantly associated with a decreased PON1 activity (zinc was associated with all PON1 activities and cadmium with PON1 towards paraoxon and diazoxon). Arsenic, nickel and manganese failed to be significantly associated with any of the PON1 activities assayed. PON1 192R alloform predicted significantly higher levels of arsenic and lead. BChE, however, was inversely associated with serum levels of manganese and zinc. These results suggest that PON1 and BChE activities are modulated by background exposure to metal compounds, which may have implications in public health given the defensive role played by both enzyme proteins against environmental toxicants. The potential underlying mechanisms merit further investigation.