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COMPARATIVE STUDY ON THE IMMUNOMODULATORY EFFECTS EXERTED IN VITRO BY LOW CONCENTRATIONS OF ORGANOPHOSPHORUS COMPOUNDS ON LYMPHOCYTE PROLIFERATION

DANIELA LUIZA BACONI¹, GINA MANDA^2*, IONELA NEAGOE², CAROLINA CONSTANTIN², CRISTIAN BĂLĂLĂU³, MARIA BÂRCĂ¹

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The aim of the study was the investigation of the immunotoxic potential of some organophosphorus compounds (OPH) on the proliferation capacity of normal human lymphocytes and K562 lymphoblastic cells. We studied the effects of chlorpyrifos (CPF), diazinon (DZN) and malathion (MLT) in the concentration range 1-1000 ng/mL. The proliferation of peripheral lymphocytes (resting and phytohemaglutinine (PHA)-activated) was measured by the tritium-labeled uridine incorporation method and of the lymphoblastic K562 cells was additionally measured by the MTS reduction test (MTS: [3-(4,5- dimethylthiazol-2yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium). In addition, the isolation, quantification and electrophoresis characterization of RNA from K562 cells were performed. The results indicate that the membrane integrity, evaluated by means of lactate dehydrogenase (LDH) release, is not altered by OPH, thus indicating that these compounds do not show rough cellular toxicity. At the concentration of 1μg/mL, DZN inhibits uridine incorporation by peripheral normal lymphocytes, resting or polyclonally stimulated ex vivo; at the same concentration, MLT exerts a slightly inhibitory action, but experimental activation of lymphocytes cancels these inhibitory signals. CPF has no statistically significant action on uridine incorporation. Distinct effects (both stimulatory and inhibitory) were noticed, independent of the experimental model used (isolated lymphocytes and whole blood). Surprisingly, OPH can sustain uridine incorporation by the neoplasic cells in a manner dependent on some critical concentrations, and tend to inhibit uridine incorporation by K562 cells at lower concentrations than 1μg/mL. The results suggest that CPF moderately inhibits RNA synthesis, while DZN and, at a lesser extent, MLT, have clear inhibitory effects. In all the investigated experimental models, cellular activation induced by OPH was also registered, mainly at low concentrations. The observed dose-dependent biphasic effects suggest potential receptor-dependent mechanisms of action. The study indicates that DZN, but not CPF, tends to restrain cell proliferation. MLT is only slightly more potent than CPF in inhibiting lymphocyte proliferation.