Renal cell carcinoma and oxidative stress: The lack of peroxisomes.

Oxidative stress plays an important role in carcinogenesis because of induction of DNA damage and its effects on intracellular signal transduction pathways. Here, we investigated the relationship between the defence against oxidative stress and human renal cell carcinoma that originates from proximal tubular epithelium. Oxygen insensitivity of the histochemical assay of glucose-6-phosphate dehydrogenase (G6PD) activity is a diagnostic tool for the detection of carcinomas. Its mechanism is based on high G6PD activity, reduced superoxide dismutase activity and reduced numbers of peroxisomes in the cancer cells. Five out of the 8 renal carcinomas studied here demonstrated oxygen insensitivity. These carcinomas showed high G6PD activity, whereas the other 3 carcinomas contained lower G6PD activity and were oxygen sensitive like non-cancer cells. Oxygen insensitivity did not correlate with tumour grade, staging or presence of metastases. Electron microscopy and immunofluorescence of catalase showed large numbers of peroxisomes in epithelial cells of proximal tubules of normal human kidney, whereas these organelles were completely absent in cancer cells of all carcinomas. As a consequence of the absence of peroxisomes in cancer cells, fatty acid metabolism is disturbed in addition to the altered glucose metabolism that is generally observed in cancer cells. Therefore, therapeutic approaches should focus on metabolism in addition to other strategies targeting signal transduction and angiogenesis.