INCREASED EXPRESSION OF COMPLEMENT COMPONENT C3 IN THE PLASMA OF OBESE ZUCKER FA AND LA N FA(F) RATS COMPARED WITH THEIR LEAN COUNTERPARTS/

Objectives: The objectives of this study were to determine whether the re are differences in the electrophoretic profiles of plasma proteins from lean and obese rats and to identify a protein that was found to b e more abundant in the plasma of obese rats. Research Methods and Proc edures: plasma proteins from lean and obese Zucker fa and LA/N fa(f) r ats were separated by sodium dodecyl sulfate-polyacrylamide gel electr ophoresis. The identity of a band that was differentially expressed wa s determined by amino acid sequencing and Western blot analysis. Resul ts: A band migrating approximately the same distance as the 116 kDa mo lecular weight marker was more prominent in plasma from obese rats tha n in plasma of lean rats. Partial sequencing of the peptide revealed t hat 17 of the first 18 amino acids at the amino terminus were identica l with the; corresponding residues in the alpha-chain of complement co mponent C3. Western blot analysis confirmed the identity of the peptid e as complement component C3. Complement C3 activity was measured usin g a hemolytic assay to determine whether there was a corresponding inc rease in the biological activity of this component in the serum of obe se rats. Serum from obese rats was found to have 1.8 times as much com plement component C3 activity as serum from lean rats. Discussion: Ele vated levels of complement C3 in genetically obese rats may be relevan t because increased amounts of C3 could serve as a reservoir from whic h increased amounts of acylation stimulating protein, a cleavage produ ct of complement C3, could be produced.