Effects of nitric oxide on the eosinophil survival in vitro. A role for nitrosyl-heme

In a previous paper we showed that the nitric oxide (NO) donors azide and hydroxylamine inhibited eosinophil apoptosis. Azide and hydroxylamine generate a nitrosyl-heme complex - due to endogenous catalase activity - which activates soluble guanylate cyclase. In contrast, in the present paper, we show that NO donors (SNAP, SIN-1, S-nitroso-L-cysteine, NOC-18) which spontaneously release NO in physiological solutions did not support the survival of eosinophils and induced apoptosis or necrosis. However, the addition of hematin (the ferric form of heme) together with low doses of NO (SNAP 10 microM) promoted eosinophil survival. In conclusion, we propose that NO and heme (e.g. from heme-containing enzymes such as peroxidase or catalase), both released in inflammation sites, could form nitrosyl-heme and thus promote eosinophilic inflammation.