Nitric oxide synthase expression of oligodendrogliomas

In the central nervous system, nitric oxide (NO) has a variety of biologica l functions including vasorelaxation and neurotransmission. The synthesis o f NO is catalyzed by NO synthases (NOS) existing in 3 isoforms, neuronal NO S (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS). NO synthase has implications in the pathophysiology of primary glial brain tumors with enha nced expression of nNOS and eNOS in high-grade astrocytic tumors, WHO grade s III and IV Only minor groups of pure oligodendrogliomas have been investi gated. The aim of the investigation was to study the expression of the 3 NO S isoforms in this genetically divergent group of primary gliomas and to co rrelate the findings with tumor grade and expression pattern for the major group of gliomas - the astrocytomas. We examined the NOS expression in 35 o ligodendrogliomas, WHO grade II, and 7 anaplastic oligodendrogliomas, WHO g rade III, by immunohistochemical methods using formalin-fixed paraffin-embe dded material. We observed only a minor expression of nNOS and sparse expre ssion of eNOS in the tumor cells, but a vivid expression of eNOS in the vas cular endothelial cells in both the tumor and the surrounding tissue. The r ich expression of eNOS in oligodendroglioma vessels independent of tumor gr ade may suggest that blood flow and angiogenesis in these richly vasculariz ed tumors are modified by NO. Interestingly, enhanced expression of inducib le NOS was observed in the oligodendroglial tumor cells in 19 of 35 oligode ndrogliomas (54%) and in 2 of 7 anaplastic oligodendrogliomas (29%). This i s diverging for iNOS expression in astroglial tumors and the data could be indicative of iNOS exerting anti-tumor activity which may protract the prog ression from low-grade oligodendrogliomas to more anaplastic types.