Effect of melanin on netilmicin-induced inhibition of collagen biosynthesis in human skin fibroblasts.

It is known that various drugs form complexes with melanins and that melanins are abundant constituents of the inner ear. In this study, we determined whether the aminoglycoside antibiotic, netilmicin, interacts with melanin and how this process affects collagen biosynthesis in cultured human skin fibroblasts. The obtained results indicate that netilmicin forms stable complexes with melanin characterized by the association constants K(1) approximately 10(6)M(-1) and K(2) approximately 10(3)M(-1). We have suggested that prolidase, an enzyme involved in collagen metabolism, may be one of the targets for aminoglycoside-induced inhibition of collagen biosynthesis. We found that netilmicin strongly induced inhibition of prolidase activity (IC(50)<5microM) and collagen biosynthesis (IC(50) approximately 10microM). At 10microM concentration of netilmicin, prolidase activity in human skin fibroblasts was inhibited by about 80% and DNA biosynthesis-only by about 25%. Melanin at 100microg/mL produced about 30% inhibition of collagen biosynthesis and about 30% inhibition of prolidase activity in cultured fibroblasts. However, the addition of melanin (100microg/mL) to netilmicin-treated cells (10microM) restored the prolidase activity in fibroblasts to almost 100% of control values and partially reversed the inhibitory action of the drug on collagen and DNA biosynthesis. The data suggest that the ability of netilmicin to form stable complexes with melanin may prevent its toxicity on prolidase activity and collagen biosynthesis.