Nitric oxide synthase activity in human renal cell carcinoma

Purpose: Nitric oxide (NO) is generated in mammalian tissue by the conversion of L-arginine to L-citrulline. The reaction is catalyzed by nitric oxide synthase (NOS). NO has been suggested to have a dual role in tumor biology with both antitumor and tumor promoter activity. Furthermore, it has been proposed that NO contributes to interleukin-2-induced antitumor activity. Since interleukin-2 is used in the treatment of renal cell carcinoma (RCC) it was of interest to study the NOS activity in the human kidney and in RCC and its correlation to tumor grade. Furthermore, the effect of cytokine treatment on NOS activity and the effect of NO donor application was studied in cultured cells. Materials and Methods: The effect of cytokine treatment on NOS activity and the effect of NO donor application on cell proliferation was studied in cultured human proximal tubular cells and in RCC cell lines HN4 and HN51. NOS activity was measured by the L-arginine to L-citrulline conversion assay. Results: Calcium-dependent NOS activity was found in all non-malignant kidney tissues (486 +/- 63 pmol. min(-1) g(-1) tissue). The activity was significantly lower in RCC (24 +/- 6 pmol. min-l g-l tissue) and correlated with tumor grade; thus high grade tumors showed lower activity than low grade tumors. Calcium-independent NOS activity was not detected in non-malignant kidney tissue or in RCC tissue. In cultured proximal tubular cells and RCC cell lines HN4 and HN51, cytokine treatment induced a marked increase in NOS activity and NO exerted cytostatic effects on these cell lines. Conclusions: The NOS activity was higher in non-malignant kidney tissue than in RCC tissue and was inversely correlated with tumor grade. Furthermore, cytokine treatment induced a marked increase in NOS activity and NO exerted cytostatic effects on cultured proximal tubular cells and RCC cell lines.