Pre-clinical evidence of safety and protective effect of isatin and oxime derivatives against malathion-induced toxicity.

The inhibition of acetylcholinesterase (AChE) is a common outcome caused by organophosphorus (OPs) intoxication. Although inconsistent, the standard treatment consists of a muscarinic receptor antagonist (atropine) and AChE-reactivating molecules such as oximes. This study proposes to test unpublished compounds which contain the moieties of isatin and/or oxime have protective effects against the toxicity induced by malathion in two animal models: Artemia salina and Rattus norvegicus (Wistar rats). The lethality was assessed in A salina, and the calculated LD to (3Z)-5-chloro-3-(hydroxyimino) indolin-2-one oxime (Cℓ-HIN) and 2-(5-chloro-2-oxoindolin-3-ylidene)-hydrazinecarbothioamide (Cℓ-OXHS) was higher than 1000 µM while to 3-(phenylhydrazono) butan-2-one oxime (PHBO) was 38 µM. Our screening showed that Cℓ-HIN seems to be the most promising molecule, with low toxicity to A salina, protection against mortality (with or without atropine) and AChE inhibition induced by malathion. Similarly, the oral administration of 300 mg/kg of Cℓ-HIN induced low or no toxicity in rats. The plasma butyrylcholinesterase (BChE) and cortical AChE activities were reactivated by Cℓ-HIN (50 mg/kg, p.o.) in rats exposed to malathion (250 mg/kg, i.p). No difference was observed in paraoxonase-1 (PON-1) activity among groups treated. In conclusion, Cℓ-HIN restored the cholinesterase activities inhibited by malathion in A salina and rats with low toxicity in both. Thus, the data provide evidence that Cℓ-HIN, a compound that combines isatin and oxime functional groups, is safe and has important properties to reactivate the cholinesterases inhibited by malathion. In addition, we demonstrate the importance of a preliminary assessment in an alternative model in order to reduce the use of mammalians in drug discovery.