Ascorbic acid potentiates the formation of IgG-enriched protein aggregates in plasma in a Cu(II)-mediated manner

Abstract

Protein aggregates have been reported in disease but also in physiological contexts in tissues as well as circulating protein aggregates in the bloodstream. Free Cu(II) induces the aggregation of serum proteins and this metal yields highly oxidant species upon reaction with hydrogen peroxide and also reacts with ascorbic acid (AA). A broad population is exposed to high doses of AA as second line therapy for different pathologies or as nutritional supplementation. This study addresses the effect of AA on the formation of plasma protein aggregates, observed by optic density, protein quantification and electrophoresis (SDS-PAGE) that, contrary to hampering the Cu(II)-induced plasma protein aggregation, AA potentiates their formation. Free Cu(II) induces the formation of IgG-enriched plasma protein aggregates but the combination with AA potentiates the incorporation of gamma-globulin (IgG) whereas other proteins such as albumin become depleted. The potentiating effect of Cu(II) and AA was corroborated employing isolated IgG. This effect of AA on Cu(II)-induced protein aggregation is not reproduced with isolated albumin. Additionally, AA does not potentiate Fe(III)-mediated aggregation of IgG, albumin or human plasma. Finally, it was shown that in healthy subjects which were administered high doses of intravenous AA, the aggregates can be obtained from the centrifuged plasma after 30 min of the administration of the antioxidant. Aggregated IgG have been shown to activate Fc receptors, involved in oxidative burst and inflammatory processes observed in neutrophils. Thus, the effect of AA on the immune system could be linked to the accumulation of protein aggregates enriched in specific proteins.

Keywords: Ascorbate; Copper; IgG; Inflammation; Plasma; Protein aggregates.