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Comparative evaluation of the toxicity profiles of HI-6 and K048 oximes in vivo using the enzyme assay and the alkaline comet assay

Organophosphorus (OP) compounds cause fatal intoxication based on inhibition of acetylcholinesterase (AChE), an essential enzyme in neurotransmission. There is an obvious need for appropriate therapeutic treatment against them due to their application in agriculture or their misuse in terrorist or war attack. Pyridinium oximes are causal antidotes employed for the protection/reactivation of AChE inhibited by OPs. Although their pharmacological profile is well known, possible cyto- and genotoxic effects have not been studied in detail so far. In present in vivo study we wanted to elucidate the toxicity profile of the standard oxime HI-6 and its modification - oxime K048 by simultaneous use of biochemical and genotoxicity assays. The catalytic activities of total cholinesterases (ChE) in plasma and of AChE in brain were determined 30 min, 60 min and 24 h after the rats were administered with single therapeutic dose of oximes (25% of their LD50). In addition, blood and brain tissue were sampled 24 h after treatment and used for the alkaline comet assay to study the levels of primary DNA damage in white blood cells (WBC) and brain cells. Experimental animals did not exhibit any clinical signs of poisoning following application of both oximes. Up to 25.3% decrease in plasma and up to 18.5% decrease in brain enzyme activities was observed in all experimental animals after application of HI-6. A decrease of enzyme activities after application of K048 was noticed only for time-point at 60 min in both plasma (11.9%) and brain (20%). These results indicate higher affinity of intact blood and tissue AChE for HI-6 but there were no significant differences compared to corresponding controls. Treatment with HI-6 and K048 did not induce a significant increase of DNA damage compared to the corresponding controls. Mean tail DNA% in the WBC of HI-6 treated rats was 0.27±0.03% (range: 0-3.90%), and in the brain cells 0.99±0.06% (range: 0-4.87%). Treatment with K048 induced slightly higher levels of primary DNA damage, compared to HI-6, both in the WBC (mean tail DNA% 0.56±0.07, range: 0-8.11%) and in the brain cells (mean tail DNA % 1.14±0.14, range 0-21.27%). Although both oximes had acceptable genotoxicity profiles, HI-6 induced lower level of DNA damage in the brain cells than K048 ; there were 6% of highly damaged comets with respect to the tail DNA% in HI-6 treated rats vs. 10% of highly damaged comets with respect to the tail DNA% in K048 treated rats. Taken together, results obtained by the enzyme assay and the alkaline comet assay, speak in favour of HI-6 as a promising molecule for therapeutic treatment against intoxication with OP compounds.

HI-6; K048; Acetylcholinesterase; DNA damage; Blood; Brain; Rats

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