Novel biochemical pathways for 5-Fluorouracil in managing experimental hepatocellular carcinoma in rats

Five fluorouracil (5-FU) is extensively used in the treatment of hepatocellular carcinoma (HCC). It is well documented that 5-FU and its metabolites inhibit DNA synthesis through inhibition of thymidylate synthetase. Little is known about additional pathways for 5-FU in managing HCC. The present experiment was mainly designed to study possible biochemical pathways that can be added to 5-FU's mechanisms of action. Four groups of rats constituted a control group (given saline only), a trichloroacetic acid group (TCA, 0.5 g/kg/day for 5 days, orally), a 5-FU-positive group (75 mg/kg body weight, intraperitoneally, once weekly for 3 weeks) and a TCA-treated with 5-FU group (24 h from last TCA dose). We executed both biochemical-serum alpha-fetoprotein (AFP), liver tissue contents of total glycosaminoglycan (TGAGs), collagen (represented as hydroxyproline), total sialic acid (TSA), free glucosamine (FGA) and proteolytic enzyme activity (as pepsin and free cathepsin-D-and histological examinations of the liver tissue. The results revealed histological changes such as central vein congestion and irregularly shaped, substantially enlarged, vesiculated and binucleated hepatocytes. The nuclei were mostly polymorphic and hyperchromatic, and several vacuolation was noticed in the cytoplasm encircling the nucleus with masses of acidophilic material. 5-FU greatly corrected these changes, except that some necrotic and cytotoxic effects of 5-FU were still shown. AFP was significantly elevated in TCA-intoxicated, but reversed in 5-FU-treated, groups. Increased proteolytic activity by TCA was reversed by 5-FU, which also restored TGAG contents to normal; but both TCA and 5-FU depleted collagen content. TCA significantly elevated FGA but depressed TSA; this action was reversed by 5-FU treatment. In conclusion, it is possible that proteolytic activity, expressed as upregulated pepsin and free cathepsin-D activities, is increased in HCC. This is accompanied by extracellular matrix macromolecular disturbance, manifested as decreased TGAGs, collagen and TSA, with marked increase in FGA liver tissue content. The elevated FGA with depressed TSA content of liver tissue may be attributed to a cancer-hampered N-acetylation of FGA into SA. 5-FU administration markedly depressed hepatic tissue proteolysis, possibly reactivated N-acetylation of FGA into SA and elevated TGAGs without stopping tissue fibrosis as collagen was not affected. This study explores additional pathways for the mechanism of action of 5-FU, through conservation of extracellular matrix composition in situ, inhibiting invasion and metastasis in addition to its DNA-disturbing pathway.