Oxidative changes and desialylation of serum proteins in hyperthyroidism.

Background: Hyperthyroidism is associated with oxidative stress. Thyroid hormones are observed to influence the metabolism of plasma proteins. The present study was carried out to explore the level of sialic acid content and the oxidative changes of serum proteins in hyperthyroid subjects and matched healthy controls.

Methods: Blood was collected from 10 hyperthyroid patients and 10 age and sex matched healthy control subjects. The extent of carbonylation and desialylation of serum protein was estimated by dinitrophenylhydrazine and thiobarbituric acid methods, respectively. The protein cleavage and cross-linking were studied by separating serum protein in SDS-PAGE. The effects of in-vitro treatment of serum proteins with H(2)O(2) on the above-mentioned parameters were observed.

Results: The carbonylation was significantly higher and the sialic acid content was significantly lower in serum proteins of hyperthyroid cases in comparison to that of controls. Serum proteins were found to have increased levels of cleavage and cross-linking in hyperthyroid cases. The high molecular weight proteins were mostly cleaved. In-vitro treatment of serum proteins with H(2)O(2) led to similar changes.

Conclusions: The study indicated that in hyperthyroidism, serum proteins undergo increased levels of oxidative changes leading to high turnover rate of blood proteins. A significant negative correlation between carbonylation and sialic acid content of serum proteins in hyperthyroidism and enhanced desialylation and carbonylation of serum proteins by in-vitro H(2)O(2) treatment suggest that oxidative stress can cause desialylation of serum glycoproteins.