Melanin, formation

Skin lighteners, freckle and age spot removers, and other remedies for hyperpigmentation are not actually bleaches like the products listed so far. The active ingredient is hydroquinone, which inhibits melanin formation when applied to the skin. Since the effect is easily reversed by exposure to sunlight or ultraviolet light, a sunscreen is usually included in the formula. 

It is very difficult to treat melasma. Better results are obtained if between chemical peeling treatments, patients apply topical depigment-ing agents. The synergic action of the two treatments bleaches the skin and reduces melanin formation. 

Seiji, M.T., Yoshida, T., Itakura, H. and Irimajiri, T. (1969). Inhibition of melanin formation by sulfhydryl compounds. J. Invest. Dermatol. 52, 280-286. 

In the present paper we describe the catalytic mechanisms of synthetic polymer-Cu complexes a catalytic interaction between the metal ions which attached to a polymer chain at high concentration and an environmental effect of polymer surrounding Cu ions. In the latter half, the catalytic behavior is compared with the specific one of tyrosinase enzyme in the melanin-formation reaction which is a multi-step reaction. To the following polymers Cu ions are combined. 

Melanin formation rate constant Rate determining Catalyst pH 7 pH 4 (1/mol sec) step... 

Figure 5. The pH dependence of rate constant of dopachrome and melanin formation (Q) imidazole-Cu (O) PVIm-Cu (A) PIPo—Cu (9) tyrosinase 30°C, air, phosphate buffer... 

This acceleration by PIPo was restricted in the process of dopa oxidation to the quinone and was not observed in the melanin formation process. Thus the catalytic behavior of the PIPo-Cu... 

Skin depigmentation effect. Extract of the dried seed, administered externally to adults at a dose of 5%, was active. Skin-lightening cosmetics contained extract of Coffea arabica seeds (containing chlorogenic acid) as melanin-formation inhibitors. The extract has been incorporated into cosmetics for skin-aging prevention or into hair preparations for hair protection. Biological activity reported has been patented . 

At neutral pH adrenaline was oxidized first to adrenochrome and then to melanin different products were produced at alkaline pH and melanin formation was low. With noradrenaline similar processes took place at neutral pH, but at a slower rate in this case the alkaline oxidation was characterized by increased melanin formation.61... 

In his classical studies on melanin formation from DOPA (3), Raper proposed the following scheme for the formation of the red pigment now known to be the aminochrome dopachrome (4). The first stage involved the oxidation of the catechol nucleus of-3 to give the quinone dopa-quinone (16). The second stage was the non-oxidative intramolecular cyclization of 16 to leuco-dopachrome (17), which was in turn oxidized to dopachrome (4).72,73 Since... 

K.J. Kwon-Chung and J.C. Rhodes, Encapsulation and melanin formation as indicators of virulence in Cryptococcus neoformans, Infect. Immun., 51, 218, 1986. 

Organic acids are added to some foods in order to prevent sedimentation or darkening thus, citric, malic, phosphoric, and ascorbic acid are used to reduce or delay enzymatic browning. Melanin formation following production of a quinone is a pH-dependent process (the rate of the former process increases with increasing pH) (8). Polyhydroxyacids such as citric and malic acid... 

Copper is an essential component of numerous key metalloenzymes which are critical in melanin formation, myelin formation and crosslinking of collagen and elastin. Copper plays a vital role in hemopoiesis, maintenance of vascular and skeletal integrity, and structure and function of the nervous system. Thus a deficiency of copper can lead to a variety of adverse effects such as increased fragility in bones, aneurysm formation in arteries and a loss of lysyl oxidase activity in cartilage.54 57 Articles on copper also appear in Siget1, volumes 3 and 5, all of volumes 12 and 13, and volume 14,... 

Kinetically slow steps in the formation of melanin from DOPA are the formation of dopaquinone from DOPA (step 1, kD), the reaction of dopachrome to dihydroxyindole (step 2), and the polymerization to form melanin (step 3, kM). Step 1 and step 2 proceed with about the same rate in the oxidative coupling polymerization catalyzed by tyrosinase. However, step 1 becomes remarkably slow when a macromolecule-metal complex is used as a catalyst. The copper complex in poly(l-vinylimidazole-co-vinylpyrrolidone) has been found [38] to act as an excellent catalyst and to exhibit the highest activity for melanin formation. The ratio of the rate constants ( m/ d) is approximately 3 (tyrosinase... 

The following example describes the results of the dereplication of an HTP fraction library for inhibition of melanin formation in an in vitro assay with a B16 cell line [54]. Briefly, following the inhibition and cell viability assay, the active organic extract from the whole plant of Mallotus repandus was fractionated with HTP. All of the HTP fractions were tested for melanin inhibitory activities. As shown in Figure 8, there are three major peaks exhibiting > 50% inhibitions of melanin synthesis and seven minor peaks exhibiting weaker inhibitions. The sharp activity peaks indicate the quality of the separations, which distributed the active components in three to five cells. 

Since the melanin formation assay was run against a cell viability assay, the activity peak maximum at fraction Dll was most likely due to cytotoxicity. The dereplication of another active peak located from fractions D7 to D2 is illustrated in Figure 9. Every active fraction was analyzed by HPLC/PDA/MS. There was a peak located at Rt=16.33 min in the LC/MS total ion chromatogram of active fractions. This peak showed the same pattern of increasing to decreasing intensity as the trend exhibited by the melanin inhibition activities of those fractions. 

PABA is thought (0 play a role in melanin formation and to influence or catalyze tyro.sine activity. " It InhibiLs oxidative destruction of epinephrine and. stiibcstrol, counteracts the graying of fur attributable to hydroquinonc in cats and mice, exhibits an(i.sulfanilamidc activity, and counteracts the toxic cffccLs of corbarsonc and other pcntavalent phenylar-sonates. ... 

Mulberroside F (104) showed moderate inhibitory effects on tyrosinase activity and on the melanin formation of melan-a cells. It also exhibited superoxide scavenging activity that is involved in the protection against auto-oxidation [62]. The geranylated stilbenes 81 and chlorophorin from Chlorophora excelsa [51], prenylated ones 4-prenyloxyresveratrol and artocarbene (72) from Artocarpus incisus [528] all demonstrated tyrosinase inhibitory activity (ICso 96, 1.3, 0.66 and 2.45 //M, respectively). 

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