Efficacy of Novel Pyridinium Oximes against Two Organophosphates in Female Sprague Dawley Rats
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Anticholinesterase organophosphate (OP) compounds were developed as insecticides and are also used as nerve agents in chemical warfare. Treatment against acute OP toxicity includes oximes which reactivate phosphorylated acetylcholinesterase (AChE) restoring enzymatic activity. The oxime currently approved for use in the U.S., pralidoxime (2-PAM), has limited efficacy penetrating the blood-brain barrier. Our laboratory has developed novel substituted phenoxyalkyl pyridinium oximes (US Patent 9,227,937) designed to more effectively penetrate the central nervous system. This research investigated any differences in oxime reactivation among four age/sex groups and also survivability in adult female Sprague Dawley rats challenged with a lethal dose of OP. Initially in in vitro experiments, paraoxon (PXN) and a nerve agent (sarin) surrogate, 4-nitrophenyl isopropyl methylphosphonate (NIMP), were incubated with pooled rat brain homogenate from four sex/age groups: adult male or female, and 12-day old male or female rats. Reactivation was performed utilizing 2-PAM or one of three novel oximes (15, 20, or 55), alone or in combination, and AChE activity was measured in a spectrophotometric assay. Overall, the oximes were more effective reactivating inhibition from PXN than from NIMP. Out of all the oximes tested, 2-PAM showed the greatest reactivation percentages. Of the novel oximes, 15 and 20 displayed the highest reactivation against PXN and NIMP, respectively. No statistical difference was detected in reactivation for any oxime among the age/sex groups. For the in vivo study, female adult Sprague-Dawley rats were treated with LD99 dosages of NIMP or PXN. After development of seizure-like behavior, atropine and one of four oximes, 2-PAM, novel oxime 15, 20, or 55 or Multisol vehicle was administered. Animals were closely monitored for signs of cholinergic toxicity and 24-hour survivability. Against PXN, novel oximes 15 and 55 demonstrated an improved odds ratio of 6.5 and 3.1, respectively, over 2-PAM. The most effective oxime against NIMP was novel oxime 20 demonstrating an odds ratio of 3.2 over treatment with 2-PAM. These data indicate that the novel pyridinium oximes are equally efficacious reactivators in adult and juvenile rats of both sexes and enhance survivability against lethal-level OP toxicity as compared to 2-PAM in adult female rats.
Garcia, Jason Michael, "Efficacy of Novel Pyridinium Oximes against Two Organophosphates in Female Sprague Dawley Rats" (2019). Theses and Dissertations MSU. 1831.