Arsenite is an important cancer chemotherapeutic. The liver is a major target tissue of arsenic toxicity and hepatotoxicity may limit its chemotherapeutic efficacy. O(2)-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO) is a liver-selective nitric oxide (NO)-producing prodrug metabolized by hepatic P450 enzymes to release NO locally. V-PYRRO/NO protects against various organic or inorganic hepatotoxicants but any role in arsenic hepatotoxicity is undefined. Thus, we studied the effects of V-PYRRO/NO (0-1000muM) pretreatment on inorganic arsenic-induced toxicity in cultured rat liver (TRL 1215) cells. These cells metabolized the prodrug to release NO, producing extracellular nitrite levels to 41.7-fold above control levels (7.50+/-0.38 microM) after 24h V-PYRRO/NO (1000 microM) exposure. The effect of pretreatment with V-PYRRO/NO (24h) on the cytolethality of arsenic (as NaAsO(2)) exposure (24h) was assessed. Arsenic was markedly less toxic in V-PYRRO/NO pretreated cells (LC(50)=30.3 microM) compared to control (LC(50)=20.1 microM) and the increases in LC(50) showed a direct relationship to the level of NO produced (measured as nitrite). Consistent with the cytolethality data, V-PYRRO/NO pretreatment markedly reduced arsenic-induced apoptosis as assessed by DNA fragmentation. Activation of the c-Jun N-terminal kinase (JNK) pathway can be critical to apoptosis and pretreatment with V-PYRRO/NO suppressed arsenic-induced JNK activation. V-PYRRO/NO pretreatment modestly increased metallothionein (MT), a metal-binding protein, but greatly enhanced arsenic induction of MT. Thus, V-PYRRO/NO pretreatment directly mitigates arsenic toxicity in cultured liver cells, reducing cytolethality, apoptosis and related JNK pathway activation, apparently through generation of NO. The role of NO in reducing the hepatotoxicity of arsenical chemotherapeutics in vivo deserves additional study.