Electron spin resonance studies of nitrosyl haemoglobin in human liver, colon and stomach tumour tissues

Iron nitrosyl haemoglobin (HbFeNO) gives well defined ESR spectra, and can be detected at room temperature, in contrast with most transition metal complexes of biological importance. This is because the unpaired electron remains strongly localised on the NO ligand. It is of importance because it proves the formation of nitric oxide, which unfortunately cannot be detected directly by ESR spectroscopy. We have studied a range of tissues taken from human liver, colon and stomach tumours which have been directly frozen to 77K and studied at 77K. The results show that formation of HbFeNO is rare in tissue adjacent to tumour tissue ("peripheral tissue" but is always found in necrotic central regions, if present. However, in several cases, HbFeNO was also detected in tumour tissue which was not necrotic. Two factors contribute to the formation of this complex. One is the presence of "free" NO molecules in the cellular regions, and the other is the presence of deoxyferrohaemoglobin, since neither ferrihaemoglobin nor oxyhaemoglobin react to give this complex. [For systems containing myoglobin these comments include the possibility of the formation of nitrosylmyoglobin, which gives very similar ESR spectra.]