Effect of intrathecal pralidoxime administration upon survival of rats exposed to the organophosphate paraoxon

Effects of paraoxon on serum biochemical parameters and oxidative stress induction in various tissues of Wistar and Norway rats

This study investigates the effects of different doses of paroxon (POX), an active metabolite of the organophosphate pesticide parathion, on some serum biochemical parameters and induction of oxidative stress in various tissues of female Wistar and Norway rats. The rats were intraperitoneally treated with 0.3, 0.7, 1 and 1.5 mg/kg of POX. The parameters were evaluated after 24h. The results showed that the decreased glutathione level and catalase, glutathione-S-transferase and lactate dehydrogenase activities in tissues of Wistar rat were higher than Norway rat at higher doses of POX. At these concentrations, POX increased superoxide dismutase activity, malondialdehyde level and some serum biochemical indices. In conclusion, POX induces the production of free radicals and oxidative stress in a dose-dependent manner. Induction of oxidative stress in POX-treated rats is in the order of brain > liver > heart > kidney>spleen. Wistar rat is found to be more sensitive to the toxicity of POX compared to Norway rat.

Minireview: does in-vitro testing of oximes help predict their in-vivo action after paraoxon exposure?

K-oximes have recently been developed in the search for efficacious broad-band reactivators of acetylcholinesterase (AChE) inhibited by organophosphorus compounds (OPC). Before clinical use, their toxicity and efficacy need to be assessed, and there is clear demand for simple in vitro tests that can predict in vivo performance. This article summarizes our in vitro data obtained for conventional and experimental oximes in human and rat blood exposed to the OPC paraoxon and correlates them with our in vivo results. The intrinsic AChE inhibitory activity of oximes, as reflected by their in vitro IC(50), is strongly correlated with their LD(50) (rat): oximes with a high IC(50) (K-27, K-48, pralidoxime and obidoxime) also show a high LD(50) and are thus relatively non-toxic, whereas oximes K-105, K-108 and K-113 have a low IC(50), a low LD(50) and are far more toxic. The IC(50) is also correlated with the in vivo capacity to protect from paraoxon-induced mortality: oximes with a higher IC(50) reduce the relative risk of death more. In contrast, the protective ability as assessed in vitro by the slope of the IC(50) shift (tanalpha), is not correlated with in vivo protection from paraoxon-induced mortality: the best in vivo protectors (K-27 and K-48) show a much lower tanalpha value (around 2) than K-110 and K-113 (tanalpha around 10), which hardly reduce the relative risk of death after paraoxon exposure. The partition coefficient logP of the individual oximes is inversely correlated with their IC(50) and with their LD(50) and is therefore an indicator of toxicity: strongly hydrophilic oximes tend to be less toxic than less hydrophilic ones. These data highlight the good predictive value of in vitro IC(50) testing for in vivo toxicity and the limited practical significance of in vitro assessment of protective potency.

Effect of several new and currently available oxime cholinesterase reactivators on tabun-intoxicated rats

The therapeutical efficacies of eleven oxime-based acetylcholinesterase reactivators were compared in an in vivo (rat model) study of treatment of intoxication caused by tabun. In this group there were some currently available oximes (obidoxime, trimedoxime and HI-6) and the rest were newly synthesized compounds. The best reactivation efficacy for acetylcholinesterase in blood (expressed as percent of reactivation) among the currently available oximes was observed after administration of trimedoxime (16%) and of the newly synthesized K127 (22432) (25%). The reactivation of butyrylcholinesterase in plasma was also studied; the best reactivators were trimedoxime, K117 (22435), and K127 (22432), with overall reactivation efficacies of approximately 30%. Partial protection of brain ChE against tabun inhibition was observed after administration of trimedoxime (acetylcholinesterase 20%; butyrylcholinesterase 30%) and obidoxime (acetylcholinesterase 12%; butyrylcholinesterase 16%).