The mechanism of hepatoprotection by epsilon aminocaproic acid and putrescine.

Hepatic neutral serine proteases (including plasminogen activator) and ornithine decarboxylase (ODC) are induced by the hepatotoxin galactosamine (GALN). We examined the hepatoprotection conferred by epsilon-aminocaproic acid (EACA), a fibrinolytic inhibitor, putrescine (PUTR), the polyamine generated from ornithine by ODC, and alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. GALN, 450 mg/kg, was administered intraperitoneally to Wistar-Lewis rats (group I). Groups II, III, and IV were also given EACA (80 mg/kg), PUTR (0.3 mmol/kg), or DFMO (0.3 mmol/kg), respectively, 1 hour before and 3, 7, and 12 hours after GALN. Rats were killed 2 hours after an intraperitoneal dose of 3H-thymidine was administered, 30 or 45 hours after GALN. EACA and PUTR were effective protectants against necrosis as judged by enzymes and histologic findings. Neither increased thymidine incorporation above the levels seen with GALN only. DFMO offered no protection even though thymidine incorporation at 45 hours was increased. Both EACA and PUTR, which have similar chemical structures, possessed significant antiprotease activity in vitro, suggesting that they act by inhibiting toxin-induced neutral serine protease activity and not by accelerating regeneration.