Correlation between inducible nitric oxide synthase and cyclooxygenase-2 expression in human colorectal adenocarcinoma: a cross-sectional study

Abstract

Cyclooxygenase-2 (COX-2) enzyme is believed to play a role in tumor angiogenesis, differentiation, and apoptosis. The inducible isoform of nitric oxide synthase (iNOS) also has the potential ability to damage DNA and conceivably contribute to tumor formation by a rise in nitric oxide production. Seventeen patients diagnosed with colorectal adenocarcinoma, who underwent surgical resection of the tumor, were enrolled in the study. Two macroscopic tissue samples, one from the tumor and the other from the tumor free surgical margin were collected from every patient as formalin fixed paraffin embedded blocks. Samples were analyzed for iNOS and COX-2 expression by immunohistochemistry and Western blotting. Results were digitized and semi-quantitatively analyzed. Immunohistochemistry revealed a similar pattern of expression for both iNOS and COX-2, as both were detected in tumor and epithelial cells. The mean iNOS and COX-2 levels determined by Western blotting method were significantly higher in tumor than in the tumor-free tissues (Wilcoxon signed-rank test, p < 0.001 both for iNOS and COX-2). Patients with lymph node involvement had higher levels of both enzymes in tumors (Mann-Whitney U test, p < 0.05). There was correlation between iNOS and COX-2 expression of tumor determined by immunohistochemistry and also by Western blotting (Spearman's rho test, R = 0.53, p = 0.03 and R = 0.57, p = 0.02, respectively). In conclusion, our results point out a relationship between iNOS and COX-2 expression in human colorectal adenocarcinomas and may also suggest a possible link between advanced stages of the disease and higher expression of iNOS and COX-2.