Synthesis and anti-melanogenic effects of lipoic acid-polyethylene glycol ester

Abstract

To develop a new potent anti-melanogenic agent, we have conjugated lipoic acid (LA) to poly (ethylene) glycol (PEG) of molecular weight 2000 and examined the effects on inhibition of tyrosinase activity and melanin synthesis in B16F10 melanoma cells. The water-soluble LA-PEG 2000 was synthesized from LA and methylated PEG by an esterification reaction in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. Synthetic LA-PEG 2000 was confirmed by IR and 1 H-NMR spectroscopy. The new conjugate is a highly water-soluble molecule, which has lower cell cytotoxicity than LA. Treatment with LA-PEG 2000 significantly suppressed the biosynthesis of melanin by up to 63% at 0.25 mM and reduced tyrosinase activity by up to 80% at 0.50 mM in B16F10 melanoma cells. Furthermore, Western blot and RT-PCR studies indicated that treatment with LA-PEG 2000 decreased the level of tyrosinase, which is a melanogenic enzyme. Taken together, these results suggest that LA-PEG 2000 may inhibit melanin biosynthesis by down-regulating levels and expression of tyrosinase activity. Therefore, LA-PEG 2000 can be used effectively as a new agent to inhibit melanogenesis, with lower cytotoxicity than LA (parent molecule) in B16F10 melanoma cells.Primarily synthesized within melanocytes, melanin contributes to the pigmentation of the skin, hair, brain and eyes. The complex regulatory control of the biosynthetic machinery involved in melanogenesis includes receptor-mediated pathways activated by hormones, neurotransmitters, cytokines and growth factors, as well as receptor-independent mechanisms activated or modified by nutrients, micromolecules, microelements, pH, cation and anion concentrations, and the oxidoreductive potential (Slominski et al 2004). Melanin production plays an important role in prevention of sun-induced skin injury (Hill et al 1997). However, abnormal hyperpigmentation such as freckles, chloasma, lentigines and other forms of melanin hyperpigmentation can be serious aesthetic problems (Gilchrest 1996). Melanin synthesis is mainly regulated by tyrosinase, which catalyses the rate-limiting reactions (tyrosine hydroxylation to L-3, 4-dihydroxyphenylalanine [L-DOPA], and oxidation of L-DOPA to DOPA-quinone) that are common to both eu-and pheomelanogenesis. The subsequent steps after the formation of DOPA-quinone are responsible for switching between these two types of melanin. The progression of these steps, including spontaneous chemical reactions, depends on the ratio of sulfhydryl compounds such as cysteine and/or glutathione (GSH) within melanocytes. In the absence of cysteine and/or GSH, DOPAquinone is oxidized to form DOPA-chrome as the intermediate product of eumelanin, which results in the advance of eumelanogenesis. In the presence of these compounds, DOPA-quinone is coupled with their SH groups to form cysteinyl DOPA as a precursor of sulfur-containing pigment known as pheomelanin, which corresponds to the progress of pheomelanogenesis.

Hair Dyes Resorcinol and Lawsone Reduce Production of Melanin in Melanoma Cells by Tyrosinase Activity Inhibition and Decreasing Tyrosinase and Microphthalmia-Associated Transcription Factor (MITF) Expression

“…Many compounds inhibit the production of melanin through their direct anti-tyrosinase activity, which include arbutin, deoxyArbutin, kojic acid and quercetin [ 19 , 20 ]. In contrast, several other compounds downregulate the expression of melanogenesis-related proteins to repress the melanin synthesis in melanocytes, such as lipoic acid, retinoic acid, fenofibrate and hispolon [ 21 , 22 , 23 , 24 ]. However, some hypopigmentation agents (such as resveratrol) can inhibit both the activity of cellular tyrosinase and the protein expressions of tyrosinase and MITF [ 25 ].…”

Selected South African plants with tyrosinase enzyme inhibition and their effect on gene expression

“…Lipoic acid contains both antioxidant and dopaquinone activity and has been proven to block the expression of the microphthalmia transcription factor (MITF) which subsequently inhibits the expression of tyrosinase (Lu et al, 2011). Although lipoic acid is very effective in depigmentation, it is unfeasible as a cosmetic since it is toxic to cells and might interrupt the expression of off-target genes, such as ribosomes or CPT2 (Kim et al, 2008).…”

Quantification of lipoic acid from skin samples by HPLC using ultraviolet, electrochemical and evaporative light scattering detectors

“…The drug concentration in the skin and its cutaneous bioavailability are fundamental to the performance studies of topical formulations because a considerable drug amount is necessary to produce local effect [10]. Although there are reports showing therapeutic applications of LA on the skin [11,12], there is no publication describing its extraction and quantification from the skin without labeling techniques. Indeed, the topical application of antioxidants could be more effective and practical for the treatment of skin pathologies [8].…”