Maturation-dependent effects of chlorpyrifos and parathion and their oxygen analogs on acetylcholinesterase and neuronal and glial markers in aggregating brain cell cultures

An in vitro model, the aggregating brain cell culture of fetal rat telencep halon, has been used to study the maturation-dependent sensitivity of brain cells to two organophosphorus pesticides (OPs), chlorpyrifos and parathion , and to their oxon derivatives. Immature (DIV 5-15) or differentiated (DIV 25-35) brain cells were treated continuously for 10 days. Acetylcholineste rase (AChE) inhibitory potency for the OPs was compared to that of eserine (physostigmine), a reversible AChE inhibitor. Oxon derivatives were more po tent AChE inhibitors than the parent compounds, and parathion was more pote nt than chlorpyrifos. No maturation-dependent differences for AChE inhibiti on were found for chlorpyrifos and eserine, whereas for parathion and parao xon there was a tendency to be more effective in immature cultures, while t he opposite was true for chlorpyrifos-oxon. Toxic effects, assessed by meas uring protein content as an index of general cytotoxicity, and various enzy me activities as cell-type-specific neuronal and glial markers (ChAT and GA D, for cholinergic and GABAergic neurons, respectively, and GS and CNP, for astrocytes and oligodendrocytes, respectively) were only found at more tha n 70% of AChE inhibition. Immature compared to differentiated cholinergic n eurons appeared to be more sensitive to OP treatments. The oxon derivates w ere found to be more toxic on neurons than the parent compounds, and chlorp yrifos was more toxic than parathion. Eserine was not neurotoxic. These res ults indicate that inhibition of AChE remains the most sensitive macromolec ular target of OP exposure, since toxic effects were found at concentration s in which AChE was inhibited. Furthermore, the compound-specific reactions , the differential pattern of toxicity of OPs compared to eserine, and the higher sensitivity of immature brain cells suggest that the toxic effects a nd inhibition of AChE are unrelated. (C) 2000 Academic Press.