Temporospatial relationship between the expressions of superoxide dismutase and nitric oxide synthase in the developing human brain: immunohistochemical and immunoblotting analyses

To clarify a significant relationship between superoxide dismutase (SOD) and nitric oxide synthase (NOS) in the developing human brain temporospatially, we demonstrate immunohistochemical expression of Cu/Zn-binding SOD1 (SOD1), Mn-containing SOD2 (SOD2), neuronal NOS (nNOS), inducible NOS (iNOS), and nitrotyrosine in human brains from 13 weeks of gestation to 2 years after birth. The immunoreactivities of both SOD1 and SOD2 were detected in fetal neuroblasts at 13 weeks' gestation, as well as mature neurons at the age of 2 years. By contrast, nNOS neurons could be recognized only at 28 and 33 weeks of gestation in the cerebrum, and only at 15, 18, and 23 weeks of gestation in the brain stem. No significant immunoreactivity for iNOS or nitrotyrosine was detected in any type of cell in any region during any stage examined. Immunoblotting analysis using frontal tissue homogenates at 15, 28, 40 weeks of gestation and 18 months of age revealed single band corresponding to SOD1 molecular weight, observed at all stages examined; a single band compatible with the nNOS molecular mass was detected only at the 28th week of gestation. Together with the fact that nitric oxide (NO) plays a potential role in neuronal differentiation, and that large amounts of NO have cytotoxicity from the reaction of NO with superoxide anions, our data suggested that the expressions of both SOD1 and SOD2, as scavengers of superoxide anions, were maintained from an early developmental stage to prepare stage-specific nNOS expression for a potential differentiation role and to elude NO cytotoxicity.