The haematological factors and their disruption by organophosphorus compounds
Abstract
Haematological parameters are typically monitored to detect changes in haemostasis due to illness or exposure to toxins. Of interest to the present study was the possibility that exposure to organophosphorous (OP) compounds might disrupt enzymes involved in the coagulation cascade includes (e.g. the plasma transglutaminase (TG) factor XIIIa and thrombin) and the proliferation and viability of white cells. Toxin-induced disruption of such enzyme activities or white cell number could interfere with the haemostatic balance. There have been limited studies on OP effects on coagulation enzymes and blood cells. The purpose of this study was to investigate the effects of the OPs phenyl saligenin phosphate (PSP), diazinon (DZ), chlorpyrifos (CPF), parathion (PTH), diazoxon (DZO), chlorpyrifos oxon (CPO), paraoxon (POX) on plasma and purified cholinesterases (AChE & BChE), FXIIIa and thrombin activities in plasma and pure enzyme preparations, and the growth and viability THP-1 leukemic monocyte cells.
The effects of OPs on enzyme activities were monitored using colorimetric activity assays of purified enzymes or whole plasma protein extracts, after samples had been pre-incubated with OPs. All OPs showed the expected patterns of toxicity against their recognised ChE targets. Most OPs demonstrated the ability to inhibit one or other of the transamidase activities in a concentration-dependent manner, being more effective against the pure enzyme. Thrombin inhibition was observed with some OPs but was more striking in whole plasma. All OPs reduced the levels of D-dimer detectable by ELISA. Covalent binding assays involving SDS-PAGE analysis of plasma proteins, rFXIIIa and purified thrombin incubated with rhodamine-labelled PSP, demonstrated covalent binding of PSP to both enzymes which could be competed out by non-labelled OPs. MS analysis revealed novel covalent adducts formed between pure FXIIIa and either unlabeled PSP or the 3 oxon OPs.
THP-1 cells proliferation and viability were decreased by most OPs in a concentration and time-dependent manner, although CPO promoted proliferation at an early time point prior a decline. In conclusion, the results obtained provide evidence that FXIIIa transamidase activities are inhibited by OPs and that FXIIIa could be a novel target of OP toxicity. Moreover, data suggest that OPs can disrupt the regulation of THP-1 proliferation. Future work is recommended to identify adduct forming sites on novel OP-binding proteins in plasma and THP-1 cells and to further examine the effects on THP-1 cells at a proteomic and genomic level.