ACTIVITIES OF DNA TURN-OVER AND FREE RADICAL-METABOLIZING ENZYMES ANDLEVELS OF PEROXIDATION INDEXES IN HUMAN HEPATIC CANCER TISSUES

Activities of some DNA turn-over enzymes, namely adenosine deaminase ( ADA), 5'nucleotidase (5'NT), guanase (GUA), xanthine oxidase (XO), xan thine dehidrogenase (XD), and hypoxanthine-guanine phosphoribosyl tran sferase (HGPRT) and those of free radical defense enzymes, namely supe roxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase ( CAT) were measured in cancerous and non-cancerous human liver tissues. Levels of peroxidation indexes (PI), namely thiobarbituric acid-reage nt substances (TBARS) and conjugated diens (CD) were also measured in the liver tissues. Of the DNA turn-over enzymes, ADA, XO and HGPRT act ivities in cancerous tissues were found higher, 5'NT unchanged, GUA an d XD decreased compared with those of non-cancerous tissues. All of th e free radical defense enzymes were found inhibited or repressed in th e cancerous tissues. It has been found that the level of TEARS decreas ed but those of CD unchanged in the cancerous tissues. Correlation ana lysis results showed that enzymatic relations between enzyme activitie s were disordered in the cancerous tissues and mostly negative relatio ns existed between the activities of the DNA turn-over and free radica l defense enzymes. Results suggested that DNA turn-over was accelerate d and that the free radical defense system was depressed in human live r cancers. Although XO system, the main radical producing mechanism in most of the cells was activated and the enzymatic antioxidant defense system was suppressed, no peroxidation reactions happened in the canc erous tissues. This indicates that cancerous liver tissues have strong , non-enzymatic, antioxidant defense mechanisms capable of eliminating free radicals and preventing peroxidation reactions.