Toxicity and pharmacokinetics of the nonprotein amino acid L-canavanine in the rat

Abstract

The toxicity of L-canavanine was investigated because of its demonstrated potential as an antitumor drug. This natural product was only slightly toxic to Sprague-Dawley rats following a single sc injection: the LD50 was 5.9 +/- 1 8 g/kg in adult rats and 5.0 +/- 1.0 g/kg in 10-day-old rats. Following a single dose of 2.0 g/kg, the systemic clearance value for canavanine in adult rats was 0.114 liter/hr, the volume of distribution at steady state was 0.154 liter, and the half-life was 1.56 hr. Forty-eight percent of the dose was excreted unaltered in the urine following an iv injection, and 16% of a sc dose was recovered in the urine. Bioavailability of a 2.0 g/kg sc dose was 72%. Single oral doses of canavanine were less toxic to adult rats than sc injections. Bioavailability of a 2.0 g/kg po dose was 43%, and only 1% of the administered canavanine was recovered in the urine. Twenty-one percent of the administered canavanine remained in the gastrointestinal tract 24 hr after an oral dose. Less than 1% of a 2.0 g/kg dose of L-[guanidinooxy-14C]canavanine was incorporated into the proteins of adult and neonatal rats 4 or 24 hr following administration. Repeated sc administration of canavanine resulted in more severe toxicity. Weight loss and alopecia were observed in rats given daily sc canavanine injections for 7 days. Food intake was decreased by 80% in adult rats subjected to this dosing regimen, but returned to normal after canavanine injections were terminated. Histological studies of tissues from adult rats treated with 3.0 g/kg canavanine daily for 6 days revealed pancreatic acinar cell atrophy and fibrosis. Serum amylase and lipase levels were elevated following one sc injection of 2.0 g/kg canavanine; after three daily injections both serum enzymes were depleted. Elevations in serum glucose and urea nitrogen, and depletion of cholesterol, were observed. The most significant changes were severe attenuations of serum aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activity.