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We analyzed the carbohydrate moiety of purified alpha-1-acid glycoprotein (AGP) from Lewis adult male rats that were healthy (AGPh) or had experimental polyarthritis (AGPi). Sodium dodecyl sulfate polyacrylamide gel electrophoresis before and after N-glycanase treatment showed that AGPi had a slightly lower molecular mass (43 kDa vs. 45 kDa for AGPh) due to a lesser carbohydrate content. Carbohydrate analysis of purified AGP showed a slight decrease in the sialyl and galactosyl molar ratio in polyarthritis. However, the same difference in AGPh and AGPi (i.e. 0.6 residue) between the sialyl and galactosyl molar ratio indicated more than one sialyl residue per complex-type branch. Affinity for concanavalin A (ConA) of the whole glycoprotein and released oligosaccharides showed a progression during polyarthritis towards more reactive glycoforms or more ConA-bound oligosaccharides. Anion-exchange HPLC of the ConA-fractionated oligosaccharides corroborated the decreased sialylation in polyarthritis. Taken together, these results suggest a fall in branched and sialylated oligosaccharides during experimental polyarthritis. These structural changes might be related to an increase in Gal beta 1-4GlcNAc alpha 2-6 sialyltransferase activity described elsewhere in inflammatory states.

When the two immunological methods, radial immunodiffusion (RID) and electroimmunodiffusion (EID), were used for the determination of alpha 1-acid glycoprotein, a significant discrepancy in the results was encountered depending on the degree of sialylation. It appeared that with desialylated alpha 1-acid glycoprotein, amounts estimated by EID were much lower than those actually present as assayed by the RID method. Determination of glycoprotein samples treated with neuraminidase for varying periods of time revealed an increasing underestimation by the EID method with decreasing sialic acid content. Partial resialylation of asialo-alpha 1-acid glycoprotein by bovine colostrum beta-galactoside alpha (2 leads to 6) sialyltransferase on the other hand resulted in less underestimation. Differential determination of alpha 1-acid glycoprotein by the two immunological methods thus offers a method for the estimation of the degree of sialylation of alpha 1-acid glycoprotein and other sialoglycoproteins in serum and body fluids.