PLASMA-PROTEINS AS EARLY BIOMARKERS OF EXPOSURE TO CARCINOGENIC AROMATIC-AMINES

Two-dimensional gel electrophoresis (2DG) has been used to study the c hanges induced in dog plasma polypeptides by the known urinary bladder carcinogens, 4-aminobiphenyl (4-ABP) and 2-naphthylamine (2-NA). Trea tment with 3-aminobiphenyl (3-ABP) and 1-naphthylamine (1-NA), both co nsidered to be non-carcinogenic, were used as controls. The purpose of this study was: (1) to determine whether or not changes that occurred in the plasma protein patterns were specific to 4-ABP and/or other re lated carcinogenic arylamines; (2) to measure the time course in the c hanges of the major polypeptides during dosing and their resynthesis d uring a recovery period; and (3) to determine, by microsequencing, the biochemical identity of the affected proteins. The results indicate t hat only the most potent carcinogen, CABP, had the effect of suppressi ng the expression of some proteins, while the other aromatic amines ca used no discernible change in the 2DG patterns during a 12-week dosing period. The 4-ABP caused dramatic suppression of two sets of proteins . One set of three spots had an apparent molecular weight of 32.5 kDa, and a pi of 5.8-6.0. The major component in this group was identified as the beta-chain of haptoglobin. Expression of this protein decrease d markedly during the first 2 weeks of treatment and recovered slowly after dosing stopped. Since haptoglobin functions to bind with free he moglobin and facilitates its elimination from the blood stream, these results can be rationalized as a consequence of 4-ABP binding to hemog lobin in the erythrocyte, resulting in cell death and hemolysis. The 4 -ABP modified hemoglobin then binds to haptoglobin and this tertiary c omplex is purged from the blood stream, resulting in the disappearance of free haptoglobin. A second set of spots (mel. wt., 65 kDa; pI, 6.5 -6.6) disappeared much faster than the haptoglobin, and recovered more quickly. The major protein is about one-fifth the intensity of haptog lobin and appeared to be N-terminally blocked. Internal microsequencin g of four fragments obtained from tryptic cleavage of the major spot o f this group showed significant similarity to the serum albumin sequen ce of several species. This spot group is not the major serum albumin spot, however, since the latter is readily identified as the most abun dant spot on the plasma map. During the course of this study, several other polypeptides in the 2DG map of dog plasma were identified and ar e presented here.