Cysteine-dependent 5-S-cysteinyldopa formation and its regulation by glutathione in normal epidermal melanocytes

Clinical Efficacy of Cysteamine Application for Melasma: A Meta-Analysis

Background: Melasma is a challenging, acquired hyperpigmentary disorder. The gold standard treatment is Kligman's formulation, which contains hydroquinone, tretinoin, and dexamethasone, but its long-term use is limited by the risk of exogenous ochronosis. Cysteamine, a tyrosinase inhibitor, reduces melanocyte activity and melanin production, showing strong depigmenting effects in patients resistant to Kligman's formulation. Nonetheless, clinical studies have yielded inconsistent efficacy results. This meta-analysis aimed to assess the efficacy of cysteamine in treating melasma and to identify potential factors that may impact its therapeutic outcomes. Methods: A systematic search of PubMed, Embase, Web of Science, and CENTRAL, from the earliest record until August 2024, was conducted. Randomized controlled trials and quasi-randomized design studies related to topical cysteamine on melasma patients were included. The primary outcome was MASI or mMASI assessment after treatments. The current meta-analysis was conducted with a random-effects model. Subgroup analyses and meta-regressions were performed based on baseline MASI, disease duration of melasma, patient age, and sample size of the included studies. Funnel plots and Duval and Tweedie's trim and fill method were adopted to assess the publication bias. Results: Eight studies were included for quantitative analysis. The analysis of MASI after topical cysteamine demonstrated a significant decrease compared to the placebo (p = 0.002). Compared to other melasma treatments, cysteamine did not show superior efficacy in mMASI (p = 0.277). The treatment efficacy of hydroquinone, modified Kligman's formula, and tranexamic acid mesotherapy for melasma was not statistically different when compared to cysteamine (p = 0.434). Further analyses showed no benefit when allowing extended cysteamine application time (p < 0.0001). The meta-regression revealed the efficacy of cysteamine decreased as the duration of melasma increased (coefficient = 0.38, p = 0.0001, R2 = 0.99). The funnel plot displayed some asymmetry. The trim and fill method suggested the adjusted effect size was 0.607 (95% CI = -0.720 to 1.935). Conclusions: Cysteamine exhibited efficacy in treating melasma patients; however, its depigmentation effect was comparable to hydroquinone-based regimens, tranexamic acid mesotherapy, and modified Kligman's formula. Using cysteamine in patients with a short duration of melasma may result in better efficacy.

Glutathione-mediated redox regulation in Cryptococcus neoformans impacts virulence

The fungal pathogen Cryptococcus neoformans is well adapted to its host environment. It has several defence mechanisms to evade oxidative and nitrosative agents released by phagocytic host cells during infection. Among them, melanin production is linked to both fungal virulence and defence against harmful free radicals that facilitate host innate immunity. How C. neoformans manipulates its redox environment to facilitate melanin formation and virulence is unclear. Here we show that the antioxidant glutathione is inextricably linked to redox-active processes that facilitate melanin and titan cell production, as well as survival in macrophages and virulence in a murine model of cryptococcosis. Comparative metabolomics revealed that disruption of glutathione biosynthesis leads to accumulation of reducing and acidic compounds in the extracellular environment of mutant cells. Overall, these findings highlight the importance of redox homeostasis and metabolic compensation in pathogen adaptation to the host environment and suggest new avenues for antifungal drug development.

The Key Role of GSH in Keeping the Redox Balance in Mammalian Cells: Mechanisms and Significance of GSH in Detoxification via Formation of Conjugates

Glutathione (GSH) is a ubiquitous tripeptide that is biosynthesized in situ at high concentrations (1-5 mM) and involved in the regulation of cellular homeostasis via multiple mechanisms. The main known action of GSH is its antioxidant capacity, which aids in maintaining the redox cycle of cells. To this end, GSH peroxidases contribute to the scavenging of various forms of ROS and RNS. A generally underestimated mechanism of action of GSH is its direct nucleophilic interaction with electrophilic compounds yielding thioether GSH S-conjugates. Many compounds, including xenobiotics (such as NAPQI, simvastatin, cisplatin, and barbital) and intrinsic compounds (such as menadione, leukotrienes, prostaglandins, and dopamine), form covalent adducts with GSH leading mainly to their detoxification. In the present article, we wish to present the key role and significance of GSH in cellular redox biology. This includes an update on the formation of GSH-S conjugates or GSH adducts with emphasis given to the mechanism of reaction, the dependence on GST (GSH S-transferase), where this conjugation occurs in tissues, and its significance. The uncovering of the GSH adducts' formation enhances our knowledge of the human metabolome. GSH-hematin adducts were recently shown to have been formed spontaneously in multiples isomers at hemolysates, leading to structural destabilization of the endogenous toxin, hematin (free heme), which is derived from the released hemoglobin. Moreover, hemin (the form of oxidized heme) has been found to act through the Kelch-like ECH associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor-2 (Nrf2) signaling pathway as an epigenetic modulator of GSH metabolism. Last but not least, the implications of the genetic defects in GSH metabolism, recorded in hemolytic syndromes, cancer and other pathologies, are presented and discussed under the framework of conceptualizing that GSH S-conjugates could be regarded as signatures of the cellular metabolism in the diseased state.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

Efficacy of Cysteamine and Methimazole in Treating Melasma A Comparative Narrative Review

Melasma is a chronic and acquired pigmentary condition that primarily affects women and undermines patient satisfaction and confidence. Melasma mostly affects females, accounting for 90% of all cases. It affects people of all races, particularly those with skin types IV and V who live in areas with lots of UV radiation. According to the studies, Melasma lesions are seen throughout the face in centrofacial, malar, and mandibular patterns. Melasma lesions on the forehead, cheeks, nose, upper lip, and/or chin are the most prevalent centrofacial pattern. Melasma lesions can also be detected along the periorbital area, especially in Asian people. Melasma is notably resistant to treatment, with many patients experiencing only temporary relief and relapses. Combining therapies that target numerous pathologic components, including photodamage, inflammation, aberrant vascularity, and abnormal pigmentation, generally results in the most dramatic therapeutic improvements. Treatments for dark circles include topical depigmenting medicines like hydroquinone, kojic acid, azelaic acid, and topical retinoic acid, and physical treatments such as chemical peels, surgical adjustments, and laser therapy. The objective of therapy should be to figure out what's causing the hyperpigmentation and what's contributing to it. This article provides an overview of melasma therapies and the efficacy of methimazole and cysteamine for melasma therapy.

The pathogenesis of melasma and implications for treatment

BACKGROUND

Melasma is a complex and poorly understood disorder, with high rates of treatment failure and recurrences.

OBJECTIVES

We aimed to review the current knowledge of the pathogenesis of melasma and apply this knowledge to clinical implications on relevant therapeutic interventions.

METHODS

A systematic PubMed search was performed using the search term "((melasma[Text Word]) OR facial melanosis[Text Word]) AND (pathogenesis OR causality[MeSH Terms])" for articles published between 1990 and 2020. Included articles were then evaluated by two authors and assessed for relevant pathomechanistic pathways, after which they were divided into groups with minimal overlap. We then reviewed current treatment modalities for melasma and divided them according to the involved pathomechanistic pathway.

RESULTS

A total of 309 search results were retrieved among which 76 relevant articles were identified and reviewed. Five main pathomechanisms observed in melasma were identified: (1) melanocyte inappropriate activation; (2) aggregation of melanin and melanosomes in dermis and epidermis; (3a) increased mast cell count and (3b) solar elastosis; (4) altered basement membrane; and (5) increased vascularization. Treatment modalities were then divided based on these five pathways and detailed in 6 relevant tables.

CONCLUSION

The pathophysiology of melasma is multifactorial, resulting in treatment resistance and high recurrence rates. This wide variety of pathomechanisms should ideally be addressed separately in the treatment regimen in order to maximize results.

Chemical and biochemical control of skin pigmentation with special emphasis on mixed melanogenesis

Melanins are widely distributed in animals and plants; in vertebrates, most melanins are present on the body surface. The diversity of pigmentation in vertebrates is mainly attributed to the quantity and ratio of eumelanin and pheomelanin synthesis. Most natural melanin pigments in animals consist of both eumelanin and pheomelanin in varying ratios, and thus, their combined synthesis is called "mixed melanogenesis." Gene expression is an established mechanism for controlling melanin synthesis; however, there are multiple factors that affect melanin synthesis besides gene expression. Due to the differential sensitivity of the eumelanin and pheomelanin synthetic pathways to pH, melanosomal pH likely plays a major role in mixed melanogenesis. Here, we focused on various factors affecting mixed melanogenesis including (1) chemical regulation of melanin synthesis, (2) melanosomal pH regulation during normal melanogenesis and effect on mixed melanogenesis, and (3) mechanisms of melanosomal pH control (proton pumps, channels, transporters, and signaling pathways).

Effects of various doses of glutathione on the proliferation, viability, migration, and ultrastructure of cultured human melanocytes

Normal human cultured melanocytes were exposed to various glutathione concentrations (0.1, 0.5, 1.0, 5.0, and 10.0 mg/mL) for 72 hours. At the end of the experiment, proliferation, viability, migration, and ultrastructural changes were monitored. Glutathione at the doses of 0.5 to 10.0 mg/mL reduced the viability of melanocytes significantly as compared to the control (P < .05). Glutathione significantly reduced the proliferation of melanocytes at the doses of 0.5 to 10.0 mg/mL as compared to the control (P < .001). Glutathione at 0.5 to 10.0 mg/mL significantly reduced the migration of melanocytes as compared to the control (P < .001). The percentage of mature melanosomes was 53.43% in control and 50.58%, 41.83%, 33.4%, and 8.95% in 0.1, 0.5, 1.0, and 5.0 mg/mL glutathione exposed cells, respectively. This reduction in the number of mature melanosomes was statistically significant as compared to the control. However, no cytotoxic effects were recognized by electron micrographs. These results encourage the potential implementation of glutathione as a skin-lightening agent. However, this study is limited by cell culture and ultrastructural. It should therefore be expanded in the future to include patients with pigmentary disorders.

Skin-whitening and skin-condition-improving effects of topical oxidized glutathione: a double-blind and placebo-controlled clinical trial in healthy women

Purpose

Glutathione is a tripeptide consisting of cysteine, glycine, and glutamate and functions as a major antioxidant. It is synthesized endogenously in humans. Glutathione protects thiol protein groups from oxidation and is involved in cellular detoxification for maintenance of the cell environment. Reduced glutathione (GSH) has a skin-whitening effect in humans through its tyrosinase inhibitory activity, but in the case of oxidized glutathione (GSSG) this effect is unclear. We examined the skin-whitening and skin-condition effects of topical GSSG in healthy women.

Subjects and methods

The subjects were 30 healthy adult women aged 30 to 50 years. The study design was a randomized, double-blind, matched-pair, placebo-controlled clinical trial. Subjects applied GSSG 2% (weight/weight [w/w]) lotion to one side of the face and a placebo lotion to the other side twice daily for 10 weeks. We objectively measured changes in melanin index values, moisture content of the stratum corneum, smoothness, wrinkle formation, and elasticity of the skin. The principal investigator and each subject also used subjective scores to investigate skin whitening, wrinkle reduction, and smoothness. Analysis of variance was used to evaluate differences between groups.

Results

The skin melanin index was significantly lower with GSSG treatment than with placebo from the early weeks after the start of the trial through to the end of the study period (at 10 weeks, P<0.001). In addition, in the latter half of the study period GSSG-treated sites had significant increases in moisture content of the stratum corneum, suppression of wrinkle formation, and improvement in skin smoothness. There were no marked adverse effects from GSSG application.

Conclusion

Topical GSSG is safe and effectively whitens the skin and improves skin condition in healthy women.

Glutathione as an oral whitening agent: a randomized, double-blind, placebo-controlled study

OBJECTIVE

To determine whether orally administered glutathione, 500 mg per day for 4 weeks, affects the skin melanin index, when compared with placebo.

METHODS

This randomized, double-blind, two-arm, placebo-controlled study was set in the King Chulalongkorn Memorial Hospital, Bangkok, Thailand, a teaching hospital affiliated with a medical school. Sixty otherwise healthy medical students were randomized to receive either glutathione capsules, 500 mg/day in two divided doses, or placebo for 4 weeks. The main outcome was mean reduction of melanin indices measured at six different sites. Several secondary outcomes, including UV spots, were recorded by VISIA™. Efficacies of glutathione and placebo were compared by ANCOVA with baseline values as co-variates.

RESULTS

Sixty participants enrolled and completed the study. At 4 weeks, the melanin indices decreased consistently at all six sites in subjects who received glutathione. The reductions were statistically significantly greater than those receiving placebo at two sites, namely the right side of the face and the sun-exposed left forearm (p-values = 0.021 and 0.036, respectively). This was similarly reflected in the changes in the number of UV spots, as measured by VISIA. Both glutathione and placebo were very well tolerated.

CONCLUSION

Oral glutathione administration results in a lightening of skin color in a small number of subjects. However, long-term safety has not been established and warrants more extensive clinical trials.

L-DOPA treatment from the viewpoint of neuroprotection. Possible mechanism of specific and progressive dopaminergic neuronal death in Parkinson's disease

With regard to the mechanism of selective dopaminergic neuronal death, experimental results of studies on the neurotoxicity of MPTP and rotenone indicate that degeneration of dopamine neurons is closely related to mitochondrial dysfunction, inflammatory process and oxidative stress, particularly with regard to the generation of quinones as dopamine neuron-specific oxidative stress. Thus, it is now clear that the presence of high levels of discompartmentalized free dopamine in dopaminergic neurons may explain the specific vulnerability of dopaminergic neurons through the generation of highly toxic quinones.

The pheomelanin precursor 5-S-cysteinyldopa protects melanocytes from membrane damage induced by ultraviolet A radiation

Pheomelanin and pheomelanin precursors have been implicated as risk factors for induction of melanoma by ultraviolet radiation. The pheomelanin precursor, 5-S-cysteinyldopa, has been shown to sensitise DNA to oxidative damage by ultraviolet radiation. We here show that 5-S-cysteinyldopa significantly protects melanocytes from membrane damage (permeability) induced by ultraviolet A radiation. Thus, 5-S-cysteinyldopa, may at the same time sensitise DNA and protect membranes from damage induced by ultraviolet radiation.