DENITROSATION OF 1,3-DIMETHYL-2-CYANO-1-NITROSOGUANIDINE IN RAT PRIMARY HEPATOCYTE CULTURES

N-Nitrosoguanidines are potential carcinogens. However, the toxicity o f these agents is attenuated significantly in laboratory rodents by pr ocesses that remove the nitroso group to generate the relatively innoc uous parent guanidinium compound. The denitrosation of 1,3-dimethyl-2- cyano-1-nitrosoguanidine (CyanoDMNG) mediated by rat hepatocytes in pr imary culture was investigated. At concentrations less than or equal t o 200 mu M, applied CyanoDMNG was converted efficiently to 1,3-dimethy l-2-cyanoguanidine (CyanoDMG). In trials using 50 mu M CyanoDMNG (5 mL dosing solutions), it was demonstrated that hepatocytes are capable o f denitrosating a 40 mu M concentration of the applied compound with l ittle change in the total or oxidized glutathione levels. The process was inhibited by coincidently applied ethacrynic acid, a glutathione t ransferase inhibitor. Reduction of hepatocyte glutathione to 20% of co ntrol levels by buthionine sulfoximine pretreatment had little effect on CyanoDMG production; total depletion of cytosolic glutathione by di ethyl maleate pretreatment arrested CyanoDMNG processing. Hepatocyte-m ediated CyanoDMNG denitrosation did not generate nitrite; nitrate yiel ds were 10% relative to the CyanoDMG produced. The mercuric chloride/a zo dye response of cultures lysed at times during 50 mu M CyanoDMNG pr ocessing indicated intact CyanoDMNG as the only dye-sensitive material present. At applied CyanoDMNG > 100 mu M, S-nitrosoglutathione (GSNO) yields were detectable; 4 mu M GSNO was generated (concentration in 5 mL lysates) and maintained during 60 min at the 200 mu M CyanoDMNG tr eatment level; this yield decayed if CyanoDMNG was withdrawn. Based on these and previous findings, it is hypothesized that CyanoDMNG is con verted to CyanoDMG and GSNO by glutathione trans ferases and that GSNO is catabolized to eventually regenerate reduced glutathione. The fate of most of the NO moiety released remains to be determined. (C) 1997 Elsevier Science Inc.