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Inhibition of platelet aggregation by native and desialised alpha-1 acid glycoprotein


The alpha-1 acid glycoprotein (orosomucoid; AAG) is a normal constituent of human plasma (650±215 µg ml−1) which increases in concentration as much as fivefold in association with acute inflammation and cancer, and thus is recognised as an acute phase protein1,2. AAG consists of a single polypeptide chain, has a molecular weight of 44,100, and contains 45% carbohydrate including 12% sialic acid; it is the most negatively charged of the plasma proteins3. Certain of the biological properties of AAG are related to its sialic acid content1,3; thus, clearance and immunogenicity of AAG are markedly increased on desialisation4,5. The biological functions of AAG are largely unknown. AAG has the ability to inhibit certain lymphocyte reactivities including blastogenesis in response to concanavalin A, phytohaemagglutinin and allogeneic cells6, and these inhibitory effects are enhanced in association with desialisation7. In view of these observations, a report that unphysiologically large (5–15 mg ml−1) amounts of AAG inhibit the platelet aggregation induced by ADP and adrenaline8, and evidence that a sialic acid-deficient species of AAG appears elevated in several chronic disease states9,10, we compared the effects of AAG and its desialised counterpart (AAG-D) on platelet aggregation. We report that desialisation of AAG is associated with increased expression of activity inhibitory to the platelet aggregation otherwise observed on stimulation with ADP, collagen or thrombin.

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Costello, M., Fiedel, B. & Gewurz, H. Inhibition of platelet aggregation by native and desialised alpha-1 acid glycoprotein. Nature 281, 677–678 (1979).

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