Carbohydrate metabolism in human renal clear cell carcinomas

Abstract

Background: Renal cell carcinomas can be subclassified into clear cell carcinomas, chromophobe cell carcinomas, chromophilic cell carcinomas, and oncocytomas. Previous studies, in which no distinction among the different types of renal cell tumors and their grades of malignancy was performed, showed that these tumors had high glycolytic rates.

Experimental design: The carbohydrate metabolism of control human kidney samples and renal clear cell carcinomas with different degrees of cytologic malignancy (G I, G II, and G III) was studied by determining the glycogen and glucose-6-phosphate levels and the activities of key enzymes involved in glycolysis (hexokinase, glucokinase, pyruvate kinase), gluconeogenesis (glucose-6-phosphatase, fructose-1,6-diphosphatase), and the pentose phosphate pathway (glucose-6-phosphate dehydrogenase) in these tissues and compared with those of a limited number of chromophilic cell carcinomas, chromophobe cell carcinomas, and oncocytomas.

Results: The glycogen and glucose-6-phosphate levels were significantly higher in G I, G II, and G III clear cut carcinomas than in control kidneys; glucokinase, hexokinase, and glucose-6-phosphate dehydrogenase activities remained unchanged, pyruvate kinase activity was enhanced, and glucose-6-phosphatase as well as fructose-1,6-diphosphatase activities were strongly reduced when compared with control kidney values. In chromophilic cell carcinomas glycogen content, glucose-6-phosphate dehydrogenase, and pyruvate kinase activities were elevated, while fructose-1,6-diphosphatase activity was reduced. In chromophobe cell carcinomas glycogen content was elevated and gluconeogenesis was reduced, whereas glycolysis was not activated. In oncocytomas glycogen was not detected and glucose-6-phosphate dehydrogenase, pyruvate kinase, and fructose-1,6-diphosphatase activities remained unchanged.

Conclusions: It has been demonstrated that a series of characteristic changes occur in the carbohydrate metabolism of renal clear cell carcinomas: glycogen and glucose-6-phosphate levels increase, glycolysis is activated, and gluconeogenesis is reduced. Furthermore, the alterations of the carbohydrate metabolism within clear cell carcinomas are clearly distinct from those observed in chromophilic cell carcinomas, chromophobe cell carcinomas, and oncocytomas.