Metabolic behavior and distribution of the synthetic nonapeptide fragment 163-171 of human IL-1 beta

The pharmacokinetic parameters and distribution of the adjuvant synthetic nonapeptide VQGEESNDK, corresponding to the fragment in position 163-171 in human IL-1, were analyzed after administration to rabbit through different routes. The radiolabeled peptide did not bind to plasma proteins and, when inoculated i.v., it disappeared very rapidly from the circulation, with a t1/2 alpha of 1 min and a t 1/2 beta of 166 min. Upon administration through i.m., s.c. and oral route, the Cmax was reached between 30 and 90 min after inoculum and ranged between 7 and 4% of the administered dose. Organ distribution showed that most of the radioactivity was concentrated in kidneys and excreted in urine. From Sephadex G-10 chromatography, about 60% of the peptide recovered in the urine 4h after i.v. inoculum was intact, whereas it was more than 85% degraded when administered by other routes. The amount of intact peptide recovered in the urine correlated with the biological effectiveness through different routes, suggesting that the adjuvant effect in vivo is exerted by the intact peptide, rather than by its metabolites.