The effect of S-nitrosoglutathione and L-cysteine on chloride efflux from cystic fibrosis airway epithelial cells

The endogenous bronchodilator, S-nitrosoglutathione (GSNO), has been proposed as a possible pharmacological remedy that reverses the ΔF508-CFTR (cystic fibrosis transmembrane conductance regulator) maturation defect and increases CFTR-mediated chloride efflux in cultured cystic fibrosis airway epithelial cells (CFBE41o(-)). It has also been reported that L-cysteine enhanced S-nitrosothiol uptake and increased the intracellular S-nitrosothiol levels, likely through transnitrosation chemistry. The present study investigated whether L-cysteine augmented the effect of GSNO on chloride efflux from CF airway epithelial cells. Treatment with 10 μM GSNO combined with 20 μM L-cysteine resulted in increased chloride efflux from CFBE41o(-) cells after 5 minutes exposure compared to the control efflux rate and to the efflux rate in the presence of L-cysteine alone as measured using the fluorescent dye N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE). Chloride efflux rates from these cells after 4h exposure to GSNO and L-cysteine were not different from control. Treatment with 10 μM GSNO alone increased chloride efflux from CFBE41o(-) cells after 4h but not at shorter incubation times. GSNO with or without L-cysteine did not alter epithelial tight junction integrity. In conclusion, a combination of GSNO with L-cysteine led to significant increase in chloride efflux in CFBE41o(-) cells but the effect was transient and not sustained beyond minutes.