ALTERATION OF THE PHARMACOKINETICS OF SMALL PROTEINS BY IODINATION

Autor: Susan L. Bernhard, Robert J. Bauer, Maria Fang, Scott D. Leigh, Ken Der, Nneka Ottah Ihejeto, Ada H. C. Kung, Stephen F. Carroll, Cynthia A. Birr
Rok vydání: 1996
Předmět:
Zdroj: Biopharmaceutics & Drug Disposition. 17:761-774
ISSN: 1099-081X
0142-2782
DOI: 10.1002/(sici)1099-081x(199612)17:9<761::aid-bdd992>3.0.co;2-z
Popis: The pharmacokinetics of several proteins were investigated using two different assays. A 23kDa recombinant protein fragment of bactericidal/permeability-increasing protein (rBPI 23 ) was radiolabeled with 125 I using Iodo-beads® and administered to rats. Plasma samples were collected and assayed for 125 I-rBPI 23 by radioactivity. In a separate experiment, rBPI 23 was administered to rats and plasma samples were assayed for rBPI 23 by ELISA. The clearance determined from plasma concentrations of 125 I-rBPI 23 measured by radioactivity was about 2.5-fold lower than that of rBPI 23 determined by ELISA. In addition, the steady state volumes of distribution and mean residence times of 125 I-rBPI 23 measured by radioactivity were four-fold and 10-fold greater, respectively, compared to those measured by the ELISA method. By studying several proteins with a range of molecular weights, we found that the pharmacokinetics of proteins below about 60kDa were different when assayed by radioactivity or ELISA, but those of proteins with molecular weights of at least 80kDA revealed only minor differences. To determine which assay method yielded the correct plasma pharmacokinetic profile, rBPI 23 was metabolically labeled with 35 S-methionine and administered to rats, and plasma samples were assayed by radioactivity. The concentration-time profile assessed by this method was very close to that determined by ELISA. Exposing rBPI 23 to chloramine-T (the oxidant used in the iodination process) and measuring its plasma concentration by ELISA revealed pharmacokinetics similar to those of the iodinated protein measured by radioactivity. In contrast, radiolabeling rBPI 23 using iodinated Bolton-Hunter reagent (which avoids exposing the protein to oxidant), and measuring 125 I-rBPI 23 by radioactivity, yielded pharmacokinetics that were similar, although not identical, to the pharmacokinetics of rBPI 23 measured by ELISA. Thus, our data suggest that directly iodinating low-molecular-weight proteins by oxidation procedures alters their clearance from the blood, preventing reliable determination of pharmacokinetic parameters.
Databáze: OpenAIRE
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