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ALTERATION OF THE PHARMACOKINETICS OF SMALL PROTEINS BY IODINATION
Author(s) -
Bauer Robert J.,
Leigh Scott D.,
Birr Cynthia A.,
Bernhard Susan L.,
Fang Maria,
Der Ken,
Ihejeto Nneka Ottah,
Carroll Stephen F.,
Kung Ada H. C.
Publication year - 1996
Publication title -
biopharmaceutics and drug disposition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.419
H-Index - 58
eISSN - 1099-081X
pISSN - 0142-2782
DOI - 10.1002/(sici)1099-081x(199612)17:9<761::aid-bdd992>3.0.co;2-z
Subject(s) - pharmacokinetics , chemistry , blood proteins , chromatography , chloramine t , pharmacology , biochemistry , biology , organic chemistry
The pharmacokinetics of several proteins were investigated using two different assays. A 23 kDa 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 60 kDa were different when assayed by radioactivity or ELISA, but those of proteins with molecular weights of at least 80 kDA 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.