Rat serum lipoproteins during carcinogenesis of the liver in the preneoplastic and the neoplastic state

Abstract

AbstractThe serum lipoproteins of rats during carcinogenesis of the liver, induced by N‐2‐fluorenylacetamide, were investigated by disc electrophoresis, preparative ultracentrifugation and lipid and protein analyses. In the case of rats with preneoplastic livers, the very low‐density lipoproteins increased by about 100%, whereas both low‐density and high‐density lipoproteins increased by about 200% as compared with control rats. The serum lipoprotein concentrations were also determined in an additional control group of rats which were given a restricted amount of normal diet. The results established that the reduced intake of feed in carcinogen‐supplemented animals was not responsible for the elevation in serum high‐density lipoproteins. In rats bearing large, primary hepatomas, the total lipids and two lipid classes were significantly increased whereas the total serum proteins were unaffected as compared with control rats. At three different gel concentrations, no striking changes were observed in the total serum electrophoretic patterns of normal and tumor‐bearing animals. The lipoprotein concentrations obtained in this study provided the most conclusive proof to date that most of the serum lipoproteins, including HDL2(1.063 < d < 1.12.5), were significantly elevated in tumor‐bearing animals. On the basis of these and other observations, it was argued that the host serum high‐density lipoprotein concentrations were perhaps related to lipoprotein synthesis by liver tumors or the lack of it by non‐hepatic tumors such as Walker carcinosarcoma, mammary tumor or Ehrlich ascites tumor. In view of certain similarities between serum high‐density lipoproteins and cellular membraneous lipoproteins, it was proposed that these serum lipoproteins were perhaps utilized in the formation of cellular membranes.