Conjugation of aspirin with vitamin C: uptake and stability studies

Aspirin and its prodrug obtained as conjugate with vitamin C (AA-Asp) were evaluated on human retinal pigment epithelium (HRPE) cells to investigate their ability to interact with the ascorbate transporter SVCT2 and their cellular uptake. Furthermore, stabilities in physiological fluids of these compounds were investigated. Transport and inhibition assays were performed adding [14C]AA and the unlabelled compounds to plated HRPE cells. Intracellular accumulation was measured incubating HRPE cells with the compounds, following by HPLC analysis. For kinetic experiments, aspirin and AA-Asp were incubated in phosphate buffer, human plasma and whole blood. Aspirin was uptaken into HRPE cells even if it was not able to interact with SVCT2; AA-Asp resulted as a competitive inhibitor of AA-transport weakly uptaken into HRPE cells. AA-Asp resulted a prodrug of aspirin when incubated in whole blood, but not when incubated in plasma: in this case the main metabolic product was salicylic acid.