Comparison of N acetyl L cysteine and L cysteine in respect to their transmembrane fluxes

The objective of the present study was to compare cysteine and N-acetyl-L-cysteine in respect to their transmembrane fluxes and find out which one is a better available precursor for the cells and thus better supports the intracellular glutathione synthesis. Cysteine can directly participate in glutathione synthesis, whereas N-acetyl-L-cysteine must be first deacetylated before its incorporation to glutathione. In the present study we investigated and compared the efficiencies of cysteine and N-acetyl-L-cysteine influx and efflux through the erythrocyte membrane. Erythrocytes transported both cysteine and N-acetyl-L-cysteine in a concentration-dependent manner. However, our results demonstrated that cysteine crosses the erythrocyte membranes more efficiently as compared to N-acetyl-L-cysteine. Treatment of erythrocytes with 5 mM of cysteine or N-acetyl-L-cysteine for 1 hr raised the intracellular free sulfhydryl group (free-SH) levels to 3.37 ± 0.006 or 2.23 ± 0.08 μ mol/ml erythrocyte, respectively. Cysteine more effectively than N-acetyl-L-cysteine restored the intracellular free-SH level depleted beforehand. In erythrocytes previously depleted of free-SH, 5 mM cysteine raised the free-SH level to 1.45 ± 0.075 μ mol/ml within 1 hr, whereas N-acetyl-L-cysteine at the same concentration raised this level to 0.377 ± 0.034 μmol/ml only. The results of our study also revealed that both cysteine and N-acetyl-L-cysteine influx and efflux processes are temperature dependent indicating that their transport requires biological activity. Our results demonstrate that cysteine is a better thiol precursor for the erythrocytes. Availability of cysteine for the cells is higher than that of N-acetyl-L-cysteine