Aims--To study the expression of the endothelial and inducible isoforms of nitric oxide synthase (eNOS and iNOS, respectively) in human bladder carcinoma and schistosomal bladder disease, and to compare it with normal adult and fetal urothelium. Nitric oxide is thought to play a complex role in human carcinogenesis, but has only recently been investigated in bladder cancer.
Methods--Immunohistochemistry was performed on paraffin wax embedded sections of 33 human bladder carcinomas and five bladder carcinoma cell lines; in addition, seven schistosomal bladder cases and normal and fetal urothelium were investigated. In the cell lines enzymatic activity was examined by the NADPH diaphorase reaction.
Results--Immunoreactivity for eNOS was present in most cells of all 31 cases examined. Immunoreactivity for iNOS was less abundant and was seen in 23 of 25 cases. Similar findings were noted in schistosomal bladder cancer. In the normal bladder mucosa, eNOS immunoreactivity was found only in the superficial cell layer and iNOS was not expressed, whereas in the fetal urothelium immunoreactivity for both isoforms was seen in all cell layers. Enzymatic activity and immunoreactivity for eNOS and iNOS were evident in the five bladder carcinoma cell lines.
Conclusions--It is possible that NOS plays a role in the differentiation of the transitional epithelium in fetal life, has a biological function in the adult bladder mucosa, and is involved in bladder carcinogenesis. eNOS and iNOS immunoreactivity do not differ in schistosomal and non-schistosomal bladder carcinoma, but resemble the pattern of expression typical of fetal urothelium.
(J Clin Pathol: Mol Pathol 2001;54:248-252)
Keywords: bladder cancer; nitric oxide synthase; schistosoma
Nitric oxide (NO) is a small messenger molecule that was first discovered as a potent vasodilator, known as the endothelium derived relaxing factor, produced and released by vascular endothelial cells. [1,2] It is now well established that NO has several diverse biological functions, and is produced by many cell types other than endothelium. [3,4]
The NO radical is generated by the action of the enzyme NO synthase (NOS). There are three distinct isoforms of this enzyme, encoded by three different genes. Two of the NOS isoforms are constitutive and calcium/calmodulin dependent--the endothelial and neuronal types (eNOS and nNOS, respectively); the third is inducible (iNOS), and is not dependent upon calcium/calmodulin for its enzymatic action. [5,6]
Several reports on the possible role of NOS in neoplasia have been published recently. In colonic carcinomas and preneoplastic lesions a pronounced reduction in NOS activity, demonstrated by histochemistry, was found relative to normal colonic mucosa.  In human colon cancer cell lines a diverse pattern of NOS gene expression, not always followed by NO generation, was found.  In gynaecological cancer, constitutive NOS activity and immunoreactivity were inversely related to tumour differentiation.  In breast cancer, the inducible and constitutive isoforms of NOS were found to be expressed in cellular elements other than the epithelial tumour cells. [10,11] This expression was correlated with tumour grade and metastatic potential.
We have previously shown prominent immunoreactivity for eNOS in trophoblastic cells of the normal placenta, an organ...