Hepatic glycerol metabolism in tumorous rats: a 13C nuclear magnetic resonance study

Cancer cachexia contributes to the demise of a significant number of cancer patients, and severe loss of adipose tissue is a prominent component of this syndrome. One of the products of fat catabolism is glycerol, and its turnover is elevated in the cancerous state. Since glycerol is also one of the most important gluconeogenic substrates, its role in the augmented and abnormal gluconeogenesis of cancer hosts needs to be defined. In the present study, we examined hepatic glycerol metabolism in livers of Fischer 344 rats bearing s.c. nonmetastatic adenocarcinoma R3230AC. Five weeks after tumor inoculation, the liver was removed and perfused with 5 mM [2-13C]glycerol while 13C nuclear magnetic resonance spectroscopy was performed. In the livers of tumorous rats, we found: (a) lipogenesis from glycerol was augmented; (b) the rate of hepatic glycerol uptake was unchanged; (c) glucose production from glycerol was not altered; and (d) conversion of glycerol 3-phosphate to dihydroxyacetone phosphate remains the rate-limiting step. Therefore, it appears that, in cancer hosts, diminished glycerol clearance is not due to reduction in hepatic glycerol uptake or metabolism, and the abnormal gluconeogenesis involves the pathway prior to the entry of glycerol. The exaggerated lipolysis is probably used for the pathological hepatomegaly, and the availability of the cytosolic hydrogen acceptor remains the rate-limiting factor for glycerol metabolism.