Enhancing target tissue levels and diminishing plasma clearance of ionizing zwitterionic antidotes in organophosphate exposures

Yan Jye Shyong, Yadira Sepulveda, Arnold Garcia, Nathan M. Samskey, Zoran Radic, Rakesh K. Sit, K. Barry Sharpless, Jeremiah D. Momper, Palmer Taylor

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


Inhibition of acetylcholinesterase (AChE) by certain organophosphates (OPs) can be life-threatening and requires reactivating antidote accessibility to the peripheral and central nervous systems to reverse symptoms and enhance survival parameters. In considering dosing requirements for oxime antidotes in OP exposures that inactivate AChE, clearance of proton ionizable, zwitterionic antidotes is rapid and proceeds with largely the parent antidotal compound being cleared by renal transporters. Such transporters may also control disposition between target tissues and plasma as well as overall elimination from the body. An ideal small-molecule antidote should access and be retained in primary target tissues-central nervous system (brain), skeletal muscle, and peripheral autonomic sites- for sufficient periods to reactivate AChE and prevent acute toxicity. We show here that we can markedly prolong the antidotal activity of zwitterionic antidotes by inhibiting P-glycoprotein (Pgp) transporters in the brain capillary and renal systems. We employ the P-gp inhibitor tariquidar as a reference compound and show that tissue and plasma levels of RS194B, a hydroxylimino acetamido alkylamine reactivator, are elevated and that plasma clearances are reduced. To examine the mechanism, identify the transporter, and establish the actions of a transport inhibitor, we compare the pharmacokinetic parameters in a P-glycoprotein knockout mouse strain and see dramatic enhancements of short-term plasma and tissue levels. Hence, repurposed transport inhibitors that are candidate or Food and Drug Administration- approved drugs, should enhance target tissue concentrations of the zwitterionic antidote through inhibition of both renal elimination and brain capillary extrusion.

Original languageEnglish
Pages (from-to)315-321
Number of pages7
JournalJournal of Pharmacology and Experimental Therapeutics
Issue number3
Publication statusPublished - 2021 Sept 1

All Science Journal Classification (ASJC) codes

  • Molecular Medicine
  • Pharmacology


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