Metabolic Characterization of Sarin, Cyclosarin, and Novichoks (A-230, A-232) in Human Liver Microsomes

We have assessed the human liver microsomal (HLM) metabolism of the chemical warfare nerve agents' sarin (GB), cyclosarin (GF), and the Novichok agents A-230 and A-232. In HLM, GB showed drastically decreased stability (t_1/2 = 1.4 h). The addition of ethylenediaminetetraacetic acid (EDTA), which inhibits paraoxonase-1 (PON1), reduced the metabolism of GB in HLM suggesting at least a partial role in its metabolism (t_1/2 = 2.6 h). The absence of NADPH (a requirement for CYP activity) had a major impact on metabolism, suggesting a role of likely CYP-mediated metabolism, which was rescued with the later addition of NADPH at 4 h. GF was also metabolized readily in HLM (Control t_1/2 = 9.7 h; HLM t_1/2 = 0.5 h), and this metabolism was mitigated by the addition of EDTA (t_1/2 (fast) = 0.7 h, t_1/2 (slow) = 4.0 h), suggesting a PON1 role in the metabolism of GF. GF in HLMs also showed a reduced metabolism without NADPH, suggesting a CYP-mediated role. We have described for the first time the clearance of A-230 in HLM (t_1/2 (fast) = 0.9 h, t_1/2 (slow) = 26.5 h), with a significantly decreased stability from the control (t_1/2 = 48.3 h) and with the formation of the A-230 acid as the major metabolite. EDTA also reduced the metabolism of A-230 in HLMs (t_1/2 (fast) = 0.8 h, t_1/2 (slow) = 62 h). A-232 metabolism was also HLM-dependent (t_1/2 (fast) = 1.2 h, t_1/2 (slow) = 1190 h), although overall it was dramatically more stable in the control (t_1/2 = 2,300 h). The metabolism of A-232 in HLMs also showed some inhibition by EDTA (t_1/2 (fast) = 0.5 h, t_1/2 (slow) = 1480 h).