Proteomic and redox-proteomic evaluation of homogentisic acid and ascorbic acid effects on human articular chondrocytes

Alkaptonuria (AKU) is a rare genetic disease associated with the accumulation of homogentisic acid (HGA) and its oxidized/polymerized products in connective tissues up to the deposition of melanin-like pigments (ochronosis). Since little is known on the effects of HGA and its metabolites on articular cells, we carried out a proteomic and redox-proteomic analysis to investigate how HGA and ascorbic acid (ASC) affect the human chondrocytic protein repertoire. We settled up an in vitro model using a human chondrocytic cell line to evaluate the effects of 0.33 mM HGA, alone or combined with ASC. We found that HGA and ASC significantly affect the levels of proteins with specific functions in protein folding, cell organization and, notably, stress response and cell defense. Increased protein carbonyls levels were found either in HGA or ASC treated cells, and evidences produced in this paper support the hypothesis that HGA-induced stress might be mediated by protein oxidation. Our finding can lay the basis towards the settling up of more sophisticated models to study AKU and ochronosis.