THE EFFECT OF L-CYSTEINE AND N-ACETYLCYSTEINE ON PORPHYRIN HEME BIOSYNTHETIC-PATHWAY IN CELLS TREATED WITH 5-AMINOLEVULINIC ACID AND EXPOSED TO RADIATION/

The effects of L-cysteine (LC) and N-acetylcysteine (NAC) on porphyrin accumulation in a human dermal microvascular endothelial cell line (H MEC-1) and a human epidermoid carcinoma cell line (A431) loaded with 5 -aminolevulinic acid (ALA) and exposed to ultraviolet A (UVA) and blue light radiation were determined. Porphyrin accumulation was decreased in the presence of 0.1-7.5 mM LC (24.8%-31.4% suppression in HMEC-1 c ell; 35.8%-48.9% suppression in A431 cells), and in the presence of 0. 1-10.0 mM NAC (30.9%-58.0% suppression in HMEC-1 cells; 8.5%-45.3% in A431 cells). The suppression occurred in a LC or NAC dose-dependent fa shion. The above was associated with partial reversal of suppression o f ferrochelatase (FeC) activity in HMEC-1 cells and in A431 cells. As compared to FeC activity in cells treated with ALA and irradiation, en zyme activity was higher (by 31.9%-62.1%) in the presence of LC (1.0 m M or 5.0 mM) and in the presence of NAC (1.0 mM or 5.0 mM). These data indicate that LC and NAC have protective effects on porphyrin- and ir radiation-induced diminution of FeC activity in HMEC-1 cells and A431 cells in vitro.