L-Cysteinamide

Thiolate coordination to zinc(ii) ions occurs widely in such functional biomolecules as zinc enzymes or zinc finger proteins. Here, we introduce a simple method for determining the affinity of ligands toward the zinc-enzyme active-center model tetramethylrhodamine (TAMRA)-labeled 1,4,7,10-tetraazacyclododecane (cyclen)-zinc(ii) complex (TAMRA-ZnL). The 1 : 1 complexation of TAMRA-labeled cysteine (TAMRA-Cys) with TAMRA-ZnL (each at 2.5 μM), in which the TAMRA moieties approach one another closely, induces remarkable changes in the visible absorption and fluorescence spectra at pH 7.4 and 25 °C. The 1 : 1 complex formation constant (K = [thiolate-bound zinc(ii) complex]/[uncomplexed TAMRA-ZnL][uncomplexed TAMRA-Cys], M-1) was determined to be 106.7 M-1 from a Job's plot of the absorbances at 552 nm. By a ligand-competition method with the 1 : 1 complexation equilibrium, analogous K values for thiol-containing ligands, such as N-acetyl-l-cysteine, l-glutathione, and N-acetyl-l-cysteinamide, were evaluated to have similar values of about 104 M-1. As a result of the ligand affinities to TAMRA-ZnL, nonlabeled zinc(ii)-cyclen induced remarkable stabilization of the reduced form of l-glutathione and a cysteine-containing enolase peptide to aerial oxidation in aqueous solution at pH 7.4 and 25 °C.

The purpose of this study is to identify amino acid derivatives with potent anti-eumelanogenic activity. First, we compared the effects of twenty different amidated amino acids on tyrosinase (TYR)-mediated dopachrome formation in vitro and melanin content in dark-pigmented human melanoma MNT-1 cells. The results showed that only L-cysteinamide inhibited TYR-mediated dopachrome formation in vitro and reduced the melanin content of cells. Next, the antimelanogenic effect of L-cysteinamide was compared to those of other thiol compounds (L-cysteine, N-acetyl L-cysteine, glutathione, L-cysteine ethyl ester, N-acetyl L-cysteinamide, and cysteamine) and positive controls with known antimelanogenic effects (kojic acid and β-arbutin). The results showed the unique properties of L-cysteinamide, which effectively reduces melanin content without causing cytotoxicity. L-Cysteinamide did not affect the mRNA and protein levels of TYR, tyrosinase-related protein 1, and dopachrome tautomerase in MNT-1 cells. L-Cysteinamide exhibited similar properties in normal human epidermal melanocytes (HEMs). Experiments using mushroom TYR suggest that L-cysteinamide at certain concentrations can inhibit eumelanin synthesis through a dual mechanism by inhibiting TYR-catalyzed dopaquinone synthesis and by diverting the synthesized dopaquinone to the formation of DOPA-cysteinamide conjugates rather than dopachrome. Finally, L-cysteinamide was shown to increase pheomelanin content while decreasing eumelanin and total melanin contents in MNT-1 cells. This study suggests that L-cysteinamide has an optimal structure that can effectively and safely inhibit eumelanin synthesis in MNT-1 cells and HEMs, and will be useful in controlling skin hyperpigmentation.

To identify guidance molecules to promote long-distance growth of dopaminergic axons from transplanted embryonic ventral mesencephalon (VM) tissue, three pathways were created by expressing green fluorescent protein (GFP), glial cell line-derived neurotrophic factor (GDNF), or a combination of GDNF/GDNF receptor α1 (GFRα1) along the corpus callosum. To generate the guidance pathway, adenovirus encoding these transcripts was injected at four positions along the corpus callosum. In all groups, GDNF adenovirus was also injected on the right side 2.5 mm from the midline at the desired transplant site. Four days later, a piece of VM tissue from embryonic day 14 rats was injected at the transplant site. All rats also received daily subcutaneous injections of N-acetyl-L-cysteinamide (NACA; 100 μg per rat) as well as chondroitinase ABC at transplant site (10 U/ml, 2 μl). Two weeks after transplantation, the rats were perfused and the brains dissected out. Coronal sections were cut and immunostained with antibody to tyrosine hydroxylase (TH) to identify and count dopaminergic fibers in the corpus callosum. In GFP-expressing pathways, TH(+) fibers grew out of the transplants for a short distance in the corpus callosum. Very few TH(+) fibers grew across the midline. However, pathways expressing GDNF supported more TH(+) fiber growth across the midline into the contralateral hemisphere. Significantly greater numbers of TH(+) fibers grew across the midline in animals expressing a combination of GDNF and GFRα1 in the corpus callosum. These data suggest that expression of GDNF or a combination of GDNF and GFRα1 can support the long-distance dopaminergic fiber growth from a VM transplant, with the combination having a superior effect.