The direct inhibitory effects of an antioxidant, N-acetylcysteine, against calcium oxalate crystal growth, aggregation and adhesion to MDCK renal cells

N-acetylcysteine (NAC), a potent antioxidant, can reduce nephrolithiatic pathogenesis by diminishing oxidative assault during crystalluria. However, its direct effects on calcium oxalate (CaOx) crystals that affect stone development were unknown. Herein, we examined the direct effects of NAC (at 1, 10 or 100 μM) on CaOx crystal formation, growth, aggregation, adhesion to MDCK renal cells, and internalization into the cells. The findings demonstrated that NAC at all these concentrations did not significantly affect size, number and mass of the newly generated CaOx crystals and their internalization into renal cells. However, NAC dose-dependently inhibited CaOx self-aggregation. Additionally, NAC at all concentrations significantly decreased the enlargement (growth) of the already-formed CaOx crystals and their adhesion to renal cells. Its dose-dependent inhibitory effects on crystal growth and adhesion were demonstrated at lower concentrations (0.01 and 0.1 μM). Measurement of adsorption energy (E_adsorption) between NAC molecule and Ca²⁺ ion revealed adsorption or affinity between NAC and Ca²⁺. Their affinity/binding was also confirmed by an ion-selective electrode (ISE)-based titration assay. These data have shown, for the first time, the direct inhibitory effects of NAC against CaOx crystal growth, aggregation and crystal adhesion to renal cells via Ca²⁺ binding that may impact the prevention of nephrolithiasis.