Melanin and melanogenesis in adipose tissue: possible mechanisms for abating oxidative stress and inflammation?

Dose-effect of polystyrene microplastics on digestive toxicity in chickens (Gallus gallus): Multi-omics reveals critical role of gut-liver axis

INTRODUCTION

Microplastic pollution seriously threatens the health and safety of humans and wildlife. Avian is one of the main species endangered by microplastics. However, the damage mechanism of microplastics to the digestive system of avian is not clear.

OBJECTIVES

The gut-liver axis is a bidirectional channel that regulates the exchange of information between the gut and the liver and is also a key target for tissue damage caused by pollutants. This study aimed to elucidate the digestive toxicity of microplastics in avian and the key role of the gut-liver axis in it.

METHODS

We constructed an exposure model for microplastics in environmental concentrations and toxicological concentrations in chickens and reveal the digestive toxicity of polystyrene microplastics (PS-MPs) in avian by 16S rRNA, transcriptomics and metabolomics.

RESULTS

PS-MPs changed the death mode from apoptosis to necrosis and pyroptosis by upregulating Caspase 8, disrupting the intestinal vascular barrier, disturbing the intestinal flora and promoting the accumulation of lipopolysaccharide. Harmful flora and metabolites were translocated to the liver through the liver-gut axis, eliciting hepatic immune responses and promoting hepatic lipid metabolism disorders and apoptosis. Liver injury involves multiple molecular effects of mitochondrial dynamics disturbance, oxidative stress, endoplasmic reticulum stress, and cell cycle disturbance. Furthermore, metabolomics suggested that caffeine and melanin metabolites may be potential natural resistance substances for microplastics.

CONCLUSION

Taken together, our data demonstrate the digestive damage of PS-MPs in avian, revealing a critical role of the liver-gut axis in it. This will provide a reference for protecting the safety of avian populations.

Melanin: a unifying theory of disease as exemplified by Parkinson's, Alzheimer's, and Lewy body dementia

Melanin, a ubiquitous dark pigment, plays important roles in the immune system, including scavenging reactive oxygen species formed in response to ultraviolet radiation absorption, absorbing metals, thermal regulation, drug uptake, innate immune system functions, redox, and energy transduction. Many tissue types, including brain, heart, arteries, ovaries, and others, contain melanin. Almost all cells contain precursors to melanin. A growing number of diseases in which there is a loss of melanin and/or neuromelanin are increasingly thought to have infectious etiologies, for example, Alzheimer's disease (AD), Parkinson's disease (PD), Lewy Body Dementia (LBD), and vitiligo. AD, PD, LBD, and vitiligo have been linked with herpesvirus, which enters melanosomes and causes apoptosis, and with gut dysbiosis and inflammation. Herpesvirus is also linked with gut dysbiosis and inflammation. We theorize that under normal healthy states, melanin retains some of the energy it absorbs from electromagnetic radiation, which is then used to fuel cells, and energy from ATP is used to compliment that energy supply. We further theorize that loss of melanin reduces the energy supply of cells, which in the case of AD, PD, and LBD results in an inability to sustain immune system defenses and remove the plaques associated with the disease, which appear to be part of the immune system's attempt to eradicate the pathogens seen in these neurodegenerative diseases. In addition, in an attempt to explain why removing these plaques does not result in improvements in cognition and mood and why cognitions and moods in these individuals have ebbs and flows, we postulate that it is not the plaques that cause the cognitive symptoms but, rather, inflammation in the brain resulting from the immune system's response to pathogens. Our theory that energy retained in melanin fuels cells in an inverse relationship with ATP is supported by studies showing alterations in ATP production in relationship to melanin levels in melanomas, vitiligo, and healthy cells. Therefore, alteration of melanin levels may be at the core of many diseases. We propose regulating melanin levels may offer new avenues for treatment development.

A Notorious Trio! Inflammation, Metabolic Syndrome and Vitiligo

Background

There is evidence to support that vitiligo is linked to metabolic syndrome (MS), confirming its systemic nature. However, the underlying pathogenic mechanisms remain unknown.

Objectives

To reveal the possible association of MS with vitiligo. We also attempted to study the connection between some inflammatory markers and MS in vitiligo patients to evaluate their utility in predicting MS risk.

Materials and Methods

The study included 100 vitiligo patients with an age range between 18 to 60 years and 100 controls with matched age, gender, and body mass index. All subjects were tested for MS components. Serum visceral adipose tissue-derived serine protease inhibitor (vaspin), fatty acid binding protein 4 (FABP4), vascular adhesion protein 1 (VAP-1), chitinase-3-like protein 1 (YKL-40), and high-sensitivity C-reactive protein (hs-CRP) were also measured.

Results

Regarding MS, it was observed in 22.0% of vitiligo patients and 2.0% of control subjects (P < 0.001). Serum FABP4, VAP-1, YKL-40, and hs-CRP concentrations were higher in patients than in the control group (P < 0.05 each), and their levels showed high sensitivity and specificity to differentiate MS when using the receiver operating characteristic (ROC). Levels of these markers, except serum vaspin, were significantly positively correlated with lipid profile markers (except high-density lipoprotein cholesterol) and fasting blood glucose levels (P < 0.05 each).

Conclusion

MS was more common in vitiligo patients. The levels of the biomarkers studied were significantly higher in vitiligo patients. Furthermore, their levels accurately predicted MS in vitiligo patients. According to current research, these markers may be useful in assessing MS risk in vitiligo patients. Extensive research, however, is required.

S-adenosylmethionine blocks tumorigenesis and with immune checkpoint inhibitor enhances anti-cancer efficacy against BRAF mutant and wildtype melanomas

Despite marked success in treatment with immune checkpoint inhibitor (CPI), only a third of patients are responsive. Thus, melanoma still has one of the highest prevalence and mortality rates; which has led to a search for novel combination therapies that might complement CPI. Aberrant methylomes are one of the mechanisms of resistance to CPI therapy. S-adenosylmethionine (SAM), methyl donor of important epigenetic processes, has significant anti-cancer effects in several malignancies; however, SAM's effect has never been extensively investigated in melanoma. We demonstrate that SAM modulates phenotype switching of melanoma cells and directs the cells towards differentiation indicated by increased melanogenesis (melanin and melanosome synthesis), melanocyte-like morphology, elevated Mitf and Mitf activators' expression, increased antigen expression, reduced proliferation, and reduced stemness genes' expression. Consistently, providing SAM orally, reduced tumor growth and progression, and metastasis of syngeneic BRAF mutant and wild-type (WT) melanoma mouse models. Of note, SAM and anti-PD-1 antibody combination treatment had enhanced anti-cancer efficacy compared to monotherapies, showed significant reduction in tumor growth and progression, and increased survival. Furthermore, SAM and anti-PD-1 antibody combination triggered significantly higher immune cell infiltration, higher CD8+ T cells infiltration and effector functions, and polyfunctionality of CD8+ T cells in YUMMER1.7 tumors. Therefore, SAM combined with CPI provides a novel therapeutic strategy against BRAF mutant and WT melanomas and provides potential to be translated into clinic.

Melanin levels in relation to vitamin D among first-generation immigrants from different ethnic groups and origins: A comparative national Canadian cross-sectional study

Introduction

Immigrants to Western countries tend to have darker skin than native-born populations. We examined the relationship between skin melanin and serum vitamin D (vitD) [S-25(OH)D] levels and explored whether melanin levels explained S-25(OH)D variations between immigrants and native-born Canadians. This study offers novel findings as no such study has been conducted.

Methods

We used a national cross-sectional population-based design with data from the Canadian Health Measures Survey (CHMS). Skin melanin levels among first-generation immigrants based on their ethnicity and origin/country of birth were compared with white and native-born populations. We assessed the association between S-25(OH)D and melanin after adjusting for independent variables related to S-25(OH)D, melanin level, and immigration status.

Results

Of 11,579 participants, 21.9% were immigrants aged 3-79 years (mean age 39.23 years). Compared with non-immigrants, immigrants had lower S-25(OH)D levels (mean: 51.23 vs. 62.72; 95% CI: 8.37, 14.62; P < 0.001) but higher melanin levels (mean [SE]: 17.08 [0.25] vs. 16.29 [0.29]; 95% CI: -1.29, -0.281; P = 0.004). Melanin did not differ by length of stay in Canada but was weakly positively correlated (r = 0.088, P < 0.001) with S-25(OH)D. Sex (male), age (≥18 years), summer/fall seasons, sunlight exposure, sunscreen non-use, smoking, and alcohol consumption were associated with higher melanin levels, whereas indoor tanning use was not.

Conclusion

Skin melanin levels were associated with sociodemographic and behavioral characteristics. Immigrants had higher melanin levels, but melanin did not differ by length of stay in Canada. The weak positive correlation between melanin and S-25(OH)D suggested confounding factors may impact the relationship between melanin levels, S-25(OH)D, and immigration status.

Leptin deficiency in CD8+ T cells ameliorates non-segmental vitiligo by reducing interferon-γ and Granzyme B

Background

Vitiligo is an autoimmune skin disease mainly mediated by CD8⁺ T cells, which affects about 0.1%-2% population of the world. Leptin plays a critical role in regulating the activation of CD8⁺ T cells. However, the effect of Leptin on vitiligo remains unclear.

Objectives

To explore the effect of leptin on CD8⁺ T cells and its influence on vitiligo.

Methods

RNA sequencing and Quantitative Real-time PCR (RT-qPCR) were used to explore the differentially expressed genes. Immunofluorescence staining was performed on skin lesions. Leptin in serum was detected by enzyme linked immunosorbent assay (ELISA). The peripheral blood mononuclear cells were detected by flow cytometry after leptin stimulation for 72 hours. A vitiligo model was established by monobenzone on Leptin KO mice.

Results

557 differentially expressed genes were found, including 154 up-regulated and 403 down-regulated genes. Lipid metabolism pathways showed a close relationship to the pathogenesis of vitiligo, especially the PPAR signaling pathway. RT-qPCR (p = 0.013) and immunofluorescence staining (p = 0.0053) verified that LEPR expressed significantly higher in vitiligo. The serum leptin level of vitiligo patients was significantly lower than that of healthy controls (p = 0.0245). The interferon-γ subset of CD8⁺LEPR⁺ T cells from vitiligo patients was significantly higher (p = 0.0189). The protein level of interferon-γ was significantly increased after leptin stimulation in vitro (p = 0.0217). In mice, Leptin deficiency resulted in less severe hair depigmentation. Leptin deficiency also resulted in significantly lower expressed vitiligo-related genes, such as Cxcl9 (p = 0.0497), Gzmb (p < 0.001), Ifng (p = 0.0159), and Mx1 (p < 0.001) after modeling.

Conclusion

Leptin could promote the progression of vitiligo by enhancing the cytotoxic function of CD8⁺ T cells. Leptin may become a new target for vitiligo treatment.

Comorbidities in Patients with Vitiligo: A Systematic Review and Meta-Analysis

Vitiligo has been reported to be associated with a variety of diseases, but it has not been systematically reviewed. Therefore, we aimed to identify prevalent diseases in patients with vitiligo and quantify their associations compared with those in healthy controls. A comprehensive search of MEDLINE and EMBASE from the inception to June 2022 was conducted. Observational studies on prevalent diseases in patients with vitiligo compared with those in healthy controls were included, whereas studies limited to pediatrics or providing only laboratory results were excluded. A total of 78 studies were eligible for analyses. Patients with vitiligo showed higher risks of having comorbid autoimmune and connective tissue diseases, including alopecia areata (OR = 2.63, 95% confidence interval [CI] = 2.50‒2.78), discoid lupus erythematosus (OR = 2.54, 95% CI = 1.74‒3.72), Sjogren's syndrome (OR = 2.50, 95% CI = 1.98‒3.16), myasthenia gravis (OR = 2.30, 95% CI = 1.74‒3.02), systemic lupus erythematosus (OR = 1.96, 95% CI = 1.52‒2.52), and rheumatoid arthritis (OR = 1.82, 95% CI = 1.55‒2.15). Thyroid diseases, diabetes mellitus, metabolic syndrome, sensorineural hypoacusis, and ophthalmic abnormalities were also more prevalent in patients with vitiligo. In conclusion, vitiligo is associated with various systemic diseases. Physicians should evaluate and manage potential comorbid conditions in patients with vitiligo.

Recognition of Melanocytes in Immuno-Neuroendocrinology and Circadian Rhythms: Beyond the Conventional Melanin Synthesis

Melanocytes produce melanin to protect the skin from UV-B radiation. Notwithstanding, the spectrum of their functions extends far beyond their well-known role as melanin production factories. Melanocytes have been considered as sensory and computational cells. The neurotransmitters, neuropeptides, and other hormones produced by melanocytes make them part of the skin’s well-orchestrated and complex neuroendocrine network, counteracting environmental stressors. Melanocytes can also actively mediate the epidermal immune response. Melanocytes are equipped with ectopic sensory systems similar to the eye and nose and can sense light and odor. The ubiquitous inner circadian rhythm controls the body’s basic physiological processes. Light not only affects skin photoaging, but also regulates inner circadian rhythms and communicates with the local neuroendocrine system. Do melanocytes “see” light and play a unique role in photoentrainment of the local circadian clock system? Why, then, are melanocytes responsible for so many mysterious functions? Do these complex functional devices work to maintain homeostasis locally and throughout the body? In addition, melanocytes have also been shown to be localized in internal sites such as the inner ear, brain, and heart, locations not stimulated by sunlight. Thus, what can the observation of extracutaneous melanocytes tell us about the “secret identity” of melanocytes? While the answers to some of these intriguing questions remain to be discovered, here we summarize and weave a thread around available data to explore the established and potential roles of melanocytes in the biological communication of skin and systemic homeostasis, and elaborate on important open issues and propose ways forward.

Vitiligo and Metabolic Syndrome: Systematic Review and Meta-Analysis

BACKGROUND

Metabolic syndrome (MetS) has been associated with various skin conditions including vitiligo. However, the association between these 2 conditions has yet to be determined by quantitative meta-analysis.

OBJECTIVE

The aim of this paper was to determine the association between vitiligo and metabolic syndrome via systematic review and meta-analysis.

METHODS

A systematic literature search of Pubmed, Embase, Cochrane, and Web of Science was performed for all published literature prior to August 16, 2020. Case control and prospective cross-sectional studies analyzing the association between vitiligo and MetS were included in this review. The primary outcome measures include the type of vitiligo, diagnostic criteria for MetS, components of MetS (waist circumference, blood pressure, triglycerides, fasting glycemic index, and high-density lipoprotein cholesterol), low-density lipoprotein cholesterol levels, and BMI. A meta-analysis was performed to evaluate the prevalence and association of MetS in patients with vitiligo.

RESULTS

A total of 6 studies (n=734 participants) meeting eligibility criteria were included for systematic review and meta-analysis. The pooled prevalence of MetS in patients with vitiligo was (0.296, 95% CI 0.206, 0.386; P<.001). Patients with vitiligo were no more likely to develop MetS compared to control patients (odds ratio 1.66, 95% CI 0.83, 3.33; P=.01). A leave-one-out sensitivity analysis showed a significant association between MetS and vitiligo (P<.001). Significant elevations in fasting glycemic index (mean difference 5.35, 95% CI 2.77, 7.93; P<.001) and diastolic blood pressure (mean difference 1.97, 95% CI 0.02, 3.92; P=.05) were observed in patients with vitiligo compared to control patients.

CONCLUSIONS

The association between vitiligo and metabolic syndrome carries important clinical implications. Dermatologists and other multidisciplinary team members should remain vigilant when treating this patient population in order to prevent serious cardiovascular complications that may arise as a result of metabolic disease.

Skin optical properties in the obese and their relation to body mass index: a review

SIGNIFICANCE

Obesity is a worldwide epidemic contributing directly to several cardiovascular risk factors including hypertension and type 2 diabetes. Wearable devices are becoming better at quantifying biomarkers relevant for the management of health and fitness. Unfortunately, both anecdotal evidence and recent studies indicate that some wearables have higher levels of error when utilized by populations with darker skin tones and high body mass index (BMI). There is an urgent need for a better evaluation of the limits of wearable health technologies when used by obese individuals.

AIMS

(1) To review the current know-how on changes due to obesity in the skin epidermis, dermis, and subcutis that could affect the skin optical properties; (2) for the green wavelength range, to evaluate the difference in absorption and scattering coefficients from the abdominal skin between individuals with and without elevated BMI. The changes include alterations in layer thickness and cell size, as well as significant differences in chromophores and scatterer content, e.g., water, hemoglobin, collagen, and lipids.

APPROACH

We have summarized literature pertaining to changes in skin and its components in obesity and report the results of our search using articles published between years 1971 and 2020. A linear model was used to demonstrate the absorption and reduced scattering coefficient of the abdominal skin of individuals with and without elevated BMI in the green wavelength range (530 to 550 nm) that is typically found in most wearables.

RESULTS

The general trends indicate a decrease in absorption for both dermis and subcutis and an increase in reduced scattering for both epidermis and dermis. At 544-nm wavelength, a typical wavelength used for photoplethysmography (PPG), the absorption coefficient's relative percentage difference between high and low BMI skin, was 49% in the subcutis, 19% in the dermis, and negligible in the epidermis, whereas the reduced scattering coefficient relative difference was 21%, 29%, and 165% respectively.

CONCLUSIONS

These findings suggest that there could be significant errors in the output of optical devices used for monitoring health and fitness if changes due to obesity are not accounted for in their design.

Emerging Role of Dermal White Adipose Tissue in Modulating Hair Follicle Development During Aging

Hair follicle stem cells are extensively reprogrammed by the aging process, manifesting as diminished self-renewal and delayed responsiveness to activating cues, orchestrated by both intrinsic microenvironmental and extrinsic macroenvironmental regulators. Dermal white adipose tissue (dWAT) is one of the peripheral tissues directly adjacent to hair follicles (HFs) and acts as a critical macroenvironmental niche of HF. dWAT directly contributes to HF aging by paracrine signal secretion. However, the altered interrelationship between dWAT and HF with aging has not been thoroughly understood. Here, through microdissection, we separated dWAT from the skin of aged mice (18 months) and young mice (2 months) in telogen and depilation-induced anagen for transcriptome comparing. Notably, compared with young dWAT, aberrant inflammatory regulators were recapitulated in aging dWAT in telogen, including substantial overexpressed inflammatory cytokines, matrix metalloproteinases, and prostaglandin members. Nonetheless, with anagen initiation, inflammation programs were mostly abolished in aging dWAT, and instead of which, impaired collagen biosynthesis, angiogenesis, and melanin synthesis were identified. Furthermore, we confirmed the inhibitory effect on hair growth of CXCL1, one of the most significantly upregulated inflammation cytokines in aging dWAT. Besides this, we also identified the under-expressed genes related to Wnt signaling fibroblast growth factor family members and increased BMP signaling in aging dWAT, further unraveling the emerging role of dWAT in aging HFs malfunction. Finally, we proved that relieving inflammation of aging dWAT by injecting high-level veratric acid stimulated HF regenerative behavior in aged mice. Concomitantly, significantly decreased TNF-a, CCL2, IL-5, CSF2, and increased IL10 in dWAT was identified. Overall, the results elaborated on the complex physiological cycling changes of dWAT during aging, providing a basis for the potential regulatory effect of dWAT on aging HFs.

Possible enigmatic link between serum leptin and vitiligo with its metabolic derangements: A comparative controlled study

OBJECTIVE

Serum leptin, an adipocytokine of interleukin-6 family, has been linked to vitiligo-associated metabolic derangements. Additionally, it has been proposed as an inflammatory mediator with possible influence on vitiligo pathogenesis. This study aimed at assessing serum leptin in vitiligo patients compared to controls and whether different vitiligo characteristics have an influence on serum leptin levels.

METHODS

In this hospital-based, cross-sectional case-control study, 70 vitiligo (35 segmental vitiligo (SV) and 35 Non-segmental vitiligo (NSV)) and 70 age- and sex-matched controls were assessed for different anthropometric measurements including waist circumference (WC), index of central obesity (ICO), and body mass index (BMI) as well as serum leptin levels.

RESULTS

Central obesity as per ICO showed no significant difference between patients and controls. Additionally, patients of SV and NSV collectively showed significant higher incidence of +ve serum leptin than their controls (41.4% vs. 22.9%%, P: 0.019). Mere presence of vitiligo and ICO >0.5 were highlighted as independent predictors of +ve serum leptin (P: 0.009 and <0.001, respectively).

LIMITATION

Inability to determine a cause/effect relationship based on a cross-sectional study. Larger scale studies are needed to affirm our findings.

CONCLUSION

Mere presence of vitiligo being an independent predictor for high serum leptin could be either a contributor to pathogenesis of vitiligo or a sequel to accumulating evidence of metabolic nature of vitiligo. This is likely to influence the investigative panel and treatment protocol for vitiligo patients.

Adiponectin as a novel biomarker of disease severity in alopecia areata

The frequent coexistence of obesity and metabolic syndrome in patients with alopecia areata may indicate the common pathogenetic pathway in these conditions with an important role of adipokines. The aim of the study was to evaluate the serum level of adiponectin, resistin and leptin in patients with alopecia areata in comparison to healthy controls. The study included 65 patients with alopecia areata and 71 healthy controls. The concentration of adipokines was determined with the enzyme-linked immunosorbent assay. The mean concentrations of adiponectin and resistin were significantly lower in the sera of patients with alopecia areata when compared to healthy controls (7966 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 4087 vs 9947 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 5692 ng/ml; p = 0.0312 and 11.04 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 3.88 vs 14.11 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 8.69 ng/ml; p = 0.0176, respectively). A negative correlation between the serum level of adiponectin and severity of alopecia tool (SALT) score was observed (r = − 0.26; p < 0.05). The concentration of adiponectin was significantly lower in patients with alopecia universalis than in patients with patchy alopecia areata (4951 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 2499 vs 8525 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 4085 ng/ml; p = 0.0135). No significant difference in the serum concentration of leptin was observed between patients with alopecia areata and healthy controls. The negative correlation between the serum level of adiponectin and hair loss severity indicates that adiponectin may be considered a marker of hair loss severity in alopecia areata. Further studies are needed to evaluate the role of resistin in patients with alopecia areata and its decreased level irregardless of severity or activity of the disease.

Increased risk of subclinical atherosclerosis and metabolic syndrome in patients with vitiligo: a real association or a coincidence?

Inflammatory and autoimmune skin diseases such as vitiligo may be associated with systemic disorders, including endocrine and cardiovascular diseases, due to some similarities in the pathogenesis. It was aimed to evaluate metabolic syndrome and subclinical atherosclerosis in patients with vitiligo. Seventy patients with nonsegmental vitiligo and 70 age-matched and gender-matched healthy controls participated in the study. These participants were investigated for metabolic syndrome criteria. The mean intima-media thickness of the common carotid artery (MIMT-CCA) of the subjects was measured for assessment of subclinical atherosclerosis. Metabolic syndrome and subclinical atherosclerosis were significantly more frequent in vitiligo patients compared with the controls (P = .006 and P = .002, respectively). In addition, metabolic syndrome and subclinical atherosclerosis had positive, significant correlations with the severity and duration of vitiligo (P = .031 and r = .482; P < .01, respectively). Our study suggested that patients with vitiligo, especially those with more chronic and severe disease or concomitant metabolic syndrome, are at a higher risk of developing cardiovascular diseases. Therefore, early diagnosis and treatment of metabolic syndrome in patients with vitiligo to prevent cardiovascular complications were recommended.

Support for increased cardiovascular risk in non-segmental vitiligo among Egyptians: A hospital-based, case-control study

BACKGROUND

Data have been accumulating in the past few years that identify vitiligo as a disorder with systemic implications.

RESULTS AND METHODS

In this hospital-based, cross-sectional, case-control study, 50 patients with non-segmental vitiligo and 50 age- and sex-matched controls underwent analysis of serum lipid profile, oxidative stress biomarkers and carotid duplex. Hydrogen peroxide (H₂ O₂ ) and malondialdehyde (MDA) were significantly higher in patients than controls (p-value < .001, <.001, respectively); on the other hand, total antioxidant capacity (TAC) was significantly lower in patients than controls (p-value = .001). A significantly higher percentage of patients had hypercholesterolemia and borderline high, high or very high levels of LDL-C, compared to controls (p-value = .001 and .001, respectively). Atherosclerotic plaques and increased common carotid intima media thickness were significantly detected in patients versus controls.

DISCUSSION

Results of the present study suggest that a subset of patients with vitiligo are at a higher risk of developing dyslipidemia and atherosclerosis, which might increase their future risk for the development of cardiovascular disease. Confirmation of these findings would subsequently influence investigative and the treatment strategies in the management plan of vitiligo patients in the near future.

SIGNIFICANCE

Vitiligo patients might be at a higher risk of developing dyslipidemia and atherosclerosis, which might increase their risk for the development of cardiovascular disease necessitating prophylactic measures to improve prognosis. Our results might influence the investigative and treatment strategies in the management plan of vitiligo patients in the near future.

Vitiligo and Rise in Blood Pressure - a Case-Control Study in a Referral Dermatology Clinic in Southern Iran

Purpose

Vitiligo is an acquired hypopigmentation condition in which well-defined macules can develop virtually everywhere on the patients’ skin. This analytic case–control study was conducted in Faghihi Hospital outpatient dermatology clinic, affiliated to Shiraz University of Medical Sciences, southern Iran from June to September 2019. Furthermore, we studied the relationship of hypertension with activity, age of onset, duration, affected body surface area and type of vitiligo.

Patients and Methods

In the current case–control study, 166 individuals were enrolled in total (the case group was comprised of 83 vitiligo patients and 83 individuals actedas control group). The case group was made up of vitiligo patients (both segmental and non-segmental) between 20 and 50 years of age, no prior history of systemic disease and other hypopigmentation disorders, while individuals with any form of dermatologic findings were excluded from the control group. Individuals aged younger than 20 years old or older than 50, having a dermatologic disease other than vitiligo, being afflicted with the diseases which may lead to secondary hypertension, pregnancy, taking substances, and medication which can lead to hypertension were chosen as the exclusion criteria in this study.

Results

Data obtained from our study revealed that vitiligo patients had a higher prevalence of essential hypertension diagnosis than the control group (P=0.040). Also, no significant relationship was found between patients’ age at the first lesion appearance (P=0.856), duration of vitiligo involvement (P=0.497), and percentage of vitiligo involvement (P=0.681) with hypertension.

Conclusion

According to our results, vitiligo patients were more susceptible to hypertension while no association could be found between characteristics of the disease and rise in blood pressure.

Higher incidence of metabolic syndrome components in vitiligo patients: a prospective cross-sectional study

BACKGROUND/OBJECTIVES

To investigate the association between vitiligo and metabolic syndrome.

METHODS

A prospective cross-sectional study was conducted between 2014 and 2016. Study (n=155) and control groups (n=155) were evaluated for metabolic syndrome according to National Cholesterol Education Program Adult Treatment Panel III and the International Diabetes Federation criteria. Study group was divided into three groups according to their vitiligo area severity index and vitiligo disease activity score values (Group 1: 6.89 for VASI score, Group A: -1-0, Group B: 1-2 and Group C: 3-4 for vitiligo disease activity score respectively). MetS rates according to both criteria were compared between the vitiligo disease activity score and vitiligo area severity index groups.

RESULTS

Metabolic syndrome rates were 37.4% and 40% in the study group and 19.4% and 26.5% in the control group according to National CholesterolEducation Program Adult Treatment Panel III and International Diabetes Federation criteria, respectively (p<001 and p=0.011). Metabolic syndrome was more frequent in vitiligo area severity index Groups 2 and 3 compared to vitiligo area severity index Group 1, and in vitiligo disease activity score Group C compared to vitiligo disease activity score Groups A and B.

STUDY LIMITATIONS

Single center experience, absence of more specific oxidative-stress markers and lack of long-term follow-up of the patients.

CONCLUSIONS

Frequency of metabolic syndrome was higher in patients with non-segmental vitiligo and the rate was higher in active/severe form of the disease.

Functional polarization of macrophages of rats with progesterone-induced obesity treated with melanin from the Antarctic yeast Nadsoniella nigra

Progesterone-induced obesity develops in women who use this drug for contraception and the menopause treatment, though its mechanisms remain poorly understood. We studied functional M1 and M2 polarizations of the abdominal cavity macrophages of rats with progesterone induced obesity during 28 days of administration. The effect of melanin from the Antarctic yeast Nadsoniella nigra (Chaetothyriales, Herpotrichiellaceae, Nadsoniella Issatsch, 1914) was investigated. The NO level was determined by the accumulation of nitrites, ROS level was estimated by the NBT-test, arginase activity was assayed by the reaction of L-arginine hydrolysis. The body weights of rats administrated progesterone increased by 27% and continued to increase one month after withdrawal of progesterone (55% higher than control). Melanin prevents the weight gain when administered during one month after progesterone withdrawal. The NO production by peritoneal macrophages of obese animals intensified by 31% indicating their polarization towards pro-inflammatory M1 type. Production of ROS did not change. A 14% increase in arginase activity was observed, indicating the inhibition of M2 (anti-inflammatory) polarization. In the progesterone withdrawal group all these rates significantly decreased, indicating a reduction in the functional activity of peritoneal macrophages’. Melanin decreased the NO and ROS production by 60% and 18% respectively in comparison with the progesterone group and unexpectedly reduced arginase activity. Our data provide evidence of the spread of inflammation in response to progesterone-induced obesity. Peritoneal macrophages are involved in the inflammation in obesity, undergoing polarization towards the pro-inflammatory phenotype. The long-term consequences of such inflammation include the continuation of weight gain and likely the development of systemic inflammation associated with the exhaustion of the functional capacity of peritoneal cavity macrophages. Melanin has an anti-obesity effect and exhibits anti-inflammatory properties preventing progesterone-induced weight gain and macrophage M1 polarization. This requires detailed elucidation and can be valuable in designing countermeasures to prevent obesity outcomes.

The Effects of folic acid and topiramate on peripheral nerve regeneration

Peripheral nerve injury creates unusual sensitivity and pathological spontaneous activity in neurons that are described as ectopic discharge. Voltage dependent Na channels are responsible for ectopic discharge. Topiramate (TOP) inhibits voltage-gated sodium channels by blocking both the amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptor and folic acid (FA) activity in neurotransmitter synthesis reactions. FA and TOP are anti-apoptotic agents by both phosphorylated-Akt (p-Akt) signaling activation and anti-inflammatory effects at the injury site. We investigated the effects of FA and TOP in peripheral nerve injury. We used rats with a sciatic nerve injury (SNI) treated with FA or TOP once daily for 6 weeks. Histological and electrophysiological tests were used to evaluate the morphology, and motor and sensory functions. Numbers of axons, myelin sheath thickness and axon area were measured using stereological techniques; functionality also was evaluated. Although FA exhibited a positive effect on regeneration by increasing the number of axons, we found no difference in axonal outgrowth or myelin sheath formation between the TOP and FA groups.

Globular adiponectin acts as a melanogenic signal in human epidermal melanocytes

BACKGROUND

Adiponectin is an adipocyte-derived cytokine that circulates as a full-length protein and a fragment containing the globular domain of adiponectin (gAd). A recent study has reported the antimelanogenic effects of full-length adiponectin.

OBJECTIVES

To examine the involvement of gAd in melanogenesis and its mechanisms of action.

METHODS

The effects of gAd on melanogenesis and its mechanisms of action were investigated in human epidermal melanocytes and reconstructed epidermis, including melanin content, cellular tyrosinase activity, cyclic adenosine monophosphate (cAMP) production and protein kinase A (PKA) activity, expression and phosphorylation of signalling molecules.

RESULTS

Exogenous gAd increased melanin content, and the mRNA levels of microphthalmia-associated transcription factor (MITF) and its downstream genes TRP1, but not TRP2, were increased by gAd. However, cAMP production and PKA activity were not affected by gAd. Moreover, attempts to elucidate the underlying mechanism behind the gAd-mediated effect revealed that gAd could regulate melanogenesis by upregulating MITF through phosphorylation of the cAMP response element-binding protein (CREB). In addition, upregulation of MITF was mediated by activation of adenosine monophosphate-activated protein kinase (AMPK)-p38 mitogen-activated protein kinase (MAPK) signalling. Taken together, these findings indicate that promotion of melanogenesis by gAd occurs through increased expression of MITF, which is mediated by activation of the AMPK-p38 MAPK-CREB pathway.

CONCLUSIONS

These findings suggest that gAd contributes to epidermal homeostasis via its effect on melanocyte biology, and products of adipose tissue could affect epidermal biology.

TNFSF14 inhibits melanogenesis via NF-kB signaling in melanocytes

Melanin synthesis in melanocytes is affected by various cytokines. Here, we reported for the first time that tumor necrosis factor superfamily member 14 (TNFSF14) inhibits melanogenesis in the primary culture of human epidermal melanocytes. TNFSF14 is known to bind to its receptors herpes virus entry mediator (HVEM) and lymphotoxin β receptor (LTβR) for signal transduction, but TNFSF14-induced hypopigmentation was independent of HVEM and LTβR in melanocytes. To explore signaling in melanocytes treated with TNFSF14, we performed RNA-seq and found that nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) signaling is activated by TNFSF14. Further, we observed that inhibition of NF-kB effectively blocks the hypopigmentation induced by TNFSF14. We conclude that TNFSF14 inhibits melanogenesis in melanocytes via NF-κB signaling and could be applied in the treatment of cutaneous pigment disorders.

αMSH inhibits adipose inflammation via reducing FoxOs transcription and blocking Akt/JNK pathway in mice

Alpha melanocyte stimulating hormone (αMSH) abates inflammation in multiple tissues, while Forkhead box proteins O (FoxOs) stimulate inflammatory cascade. However, the relationship between αMSH and FoxOs in adipose inflammation remains unclear. In this study, we used LPS-induced inflammation model, attempted to interpret the function of αMSH in inflammation and the interactions with FoxOs. Results indicated that upon inflammatory situation, the secretion of αMSH and the expression of its receptor MC5R were greatly decreased, but FoxOs expressions were elevated. After the treatment with αMSH, LPS-induced adipose inflammation together with FoxOs expressions was significantly reduced. Conversely, when Foxo1, Foxo3a or Foxo4 overexpressed in αMSH treated inflammatory mouse model, all the anti-inflammatory impacts of αMSH were found disappeared. We further studied the mechanisms by which αMSH exerts its anti-inflammatory impacts and how FoxOs reverse αMSH's function. Foxo4 was found as a negative regulator for MC5R transcription in αMSH inhibited inflammation. Moreover, a negative role was found of αMSH in regulating both Akt and JNK signal pathways by observing the enhanced the anti-inflammatory impacts of pathway-specific inhibitors with αMSH treatment. Our findings demonstrate αMSH plays a key role in the prevention of adipose inflammation and inflammatory diseases by down-regulating Akt/JNK signal pathway and negatively interacting with FoxOs, which brings up αMSH as a novel candidate factor in the adipose anti-inflammation process in obesity.

Supplement comprising of laccase and citric acid as an alternative for antibiotics: In vitro triggers of melanin production

An indiscriminate use of antibiotics in humans and animals has led to the widespread selection of antibiotic-resistance, thus constricting the use of antibiotics. A possible solution to counter this problem could be to develop alternatives that can boost the host immunity, thus reducing the quantity and frequency of antibiotic use. In this work, for the first time, citric acid and laccase were used as extracellular inducers of melanin production in yeast cells and human cell lines. It is proposed that the formulation of laccase and citric acid together could further promote melatonin-stimulated, melanocyte-derived melanin production. Melanization as a probe of immunity described in this study, is an easy and a rapid test compared to other immunity tests and it allows performing statistical analyses. The results showed the synergistic effect of citric acid and laccase on melanin production by yeast cells, with significant statistical differences compared to all other tested conditions (p: 0.0005-0.005). Laccase and citric acid together boosted melanin production after 8 days of incubation. An increase in melanin production by two human colon cells lines (Cacao-2/15 and HT-29) was observed on supplementation with both laccase and citric acid in the cell growth medium. Produced melanin showed antimicrobial properties similar to antibiotics. Therefore, a formulation with citric acid and laccase may prove to be an excellent alternative to reduce the antibiotic use in human and animal subjects.

Metabolic syndrome in vitiligo patients among a semi-urban Maharashtrian population: A case control study

AIM

To assess the prevalence of metabolic syndrome and its correlation with the severity and duration of vitiligo.

METHODS

One hundred vitiligo patients and 100 age-and-sex matched controls were included, whose waist circumference and blood pressure were measured; fasting serum cholesterol, triglycerides and glucose levels quantified; disease severity assessed and metabolic syndrome defined by National Cholesterol Education Program (NCEP) criteria.

RESULTS

Metabolic syndrome (24%:12%), hypertriglyceridemia (41%:24%), impaired glucose tolerance (25%:16%) [P<0.05] and low HDL (P=0.044) were significantly more prevalent in cases as compared to controls as were the mean values of triglycerides and fasting blood sugar. Increased mean age of vitiligo patients correlated with the presence of metabolic syndrome.

CONCLUSION

Metabolic syndrome had significant presence in but remained unaffected by the severity of vitiligo in our study patients.

Neutrophil to lymphocyte ratio in patients with vitiligo

Introduction

There are a few studies showing an increased risk of insulin resistance, metabolic syndrome, and oxidative stress in patients with vitiligo.

Aim

To investigate whether systemic inflammation is increased in vitiligo patients in a case-control study design.

Material and methods

Nonsegmental vitiligo patients who had been followed at the outpatient dermatology clinic of a university-affiliated teaching hospital, and healthy controls were enrolled in the study. Patients who were receiving systemic treatments and having a systemic disease such as diabetes mellitus and thyroiditis were excluded. Demographic features were recorded and peripheral blood samples were taken from all participants to study serum whole blood count, creatinine, and C-reactive protein (CRP).

Results

Fifty patients with localized vitiligo, 43 patients with generalized vitiligo, and 50 healthy volunteers were enrolled in the study. Neutrophil to lymphocyte ratio and serum CRP levels were significantly higher in patients who have generalized vitiligo than those with localized vitiligo and healthy controls. However, there was no significant difference regarding neutrophil to lymphocyte ratio (NLR) and CRP between localized vitiligo and control groups.

Conclusions

Patients with generalized vitiligo seem to have increased systemic inflammation compared with localized vitiligo and control subjects in our cohort. To the best of our knowledge, this is the first study in the literature showing increased NLR values in generalized vitiligo patients. Further studies with cardiovascular disease markers are required to elicit this association better.

Autoimmune skin diseases and the metabolic syndrome

The metabolic syndrome represents an important association of cutaneous maladies with cardiovascular illnesses. Chronic inflammation, shared risk factors (ie, smoking and alcohol consumption), treatment (ie, immunosuppressive agents and drugs that alter the lipid profile), and shared genetic risk loci have been proposed to the cause metabolic syndrome and cardiovascular morbidity of autoimmune diseases. There are many possible inflammatory mediators that are suggested to play a role in insulin resistance pathogenesis, such as tumor necrosis factor-α, interleukin-6, leptin, and adiponectin. These mediators are also abnormal in autoimmune skin disorders. We discuss several autoimmune skin diseases, connective tissue diseases, bullous diseases, vitiligo, psoriasis, lichen planus, chronic urticaria, and atopic dermatitis.

Usefulness of ischemia-modified albumin in predicting oxidative stress in patients with vitiligo

Aim: To investigate the emphasis of oxidative stress in the pathogenesis of vitiligo through an evaluation of ischemia-modified albumin (IMA). Results/methodology: IMA was of higher statistical significance in patients than in the control group (IMA: 0.57 ± 0.2 vs 0.52 ± 0.2 ΔABSU; p < 0.0001). IMA (p < 0.0001; OR: 8.9; 95% CI = 3.1–26.1) was found as an independent predictor of oxidative stress. Increases in affected body surface area and age were found to be independent risk factors for IMA. The sensitivity, specificity and positive and negative predictive values and capacity of IMA were higher than other studied biomarkers. Discussion/conclusion: IMA can be detected in the condition of oxidative stress in vitiligo; it has great potential as a biomarker of said condition, when compared with other studied biomarkers.

Increased Risk of Metabolic Syndrome in Patients with Vitiligo

Background:

Inflammatory and immune processes can be triggered in vitiligo due to a decreased number of melanocytes and their anti-inflammatory effects. Because of the systemic nature of vitiligo, metabolic abnormalities such as insulin resistance and lipid profile disturbances as well as skin involvement may be observed in vitiligo.

Aims:

To investigate the association between metabolic syndrome and vitiligo.

Study Design:

Case-control study.

Methods:

The demographic, clinical and laboratory features in the subjects were compared according to presence of vitiligo and metabolic syndrome [patients (n=63) vs. gender-age matched controls (n=65) and metabolic syndrome positive (n=38) vs. negative (n=90)]. A logistic regression analysis was also used.

Results:

We identified metabolic syndrome in 24 (38.1%) subjects with vitiligo and 14 (21.5%) subjects without vitiligo (p=0.04). Active vitiligo, segmental vitiligo, an increased duration of vitiligo and an increased percentage in the affected body surface area were determined to be independent predictors of metabolic syndrome [activity of vitiligo: p=0.012, OR (95% CI)=64.4 (2.5-1672); type of vitiligo: p=0.007, OR (95% CI)=215.1 (4.3-10725.8); duration of vitiligo: p=0.03, OR (95% CI)=1.4 (1.1-2.0); percentage of affected body surface area: p=0.07, OR (95% CI)=1.2 (0.98-1.5)].

Conclusion:

The risk of developing metabolic syndrome is increased in patients with vitiligo. The poor clinical features of vitiligo, such as active, extended and segmental vitiligo with an increased duration of time, are independent predictors for developing metabolic syndrome.

Excessive consumption of fructose causes cardiometabolic dysfunctions through oxidative stress and inflammation

A rapid rise in obesity, as well as physical inactivity, in industrialized countries is associated with fructose-consumption-mediated metabolic syndrome having a strong association with cardiovascular disease. Although insulin resistance is thought to be at the core, visceral obesity, hypertension, and hypertriglyceridemia are also considered important components of this metabolic disorder. In addition, various other abnormalities such as inflammation, oxidative stress, and elevated levels of uric acid are also part of this syndrome. Lifestyle changes through improved physical activity, as well as nutrition, are important approaches to minimize metabolic syndrome and its deleterious effects.

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

This review presents a general view of all types of melanin in all types of organisms. Melanin is frequently considered just an animal cutaneous pigment and is treated separately from similar fungal or bacterial pigments. Similarities concerning the phenol precursors and common patterns in the formation routes are discussed. All melanins are formed in a first enzymatically-controlled phase, generally a phenolase, and a second phase characterized by an uncontrolled polymerization of the oxidized intermediates. In that second phase, quinones derived from phenol oxidation play a crucial role. Concerning functions, all melanins show a common feature, a protective role, but they are not merely photoprotective pigments against UV sunlight. In pathogenic microorganisms, melanization becomes a virulence factor since melanin protects microbial cells from defense mechanisms in the infected host. In turn, some melanins are formed in tissues where sunlight radiation is not a potential threat. Then, their redox, metal chelating, or free radical scavenging properties are more important than light absorption capacity. These pigments sometimes behave as a double-edged sword, and inhibition of melanogenesis is desirable in different cells. Melanin biochemistry is an active field of research from dermatological, biomedical, cosmetical, and microbiological points of view, as well as fruit technology.

Hair curvature: a natural dialectic and review

Although hair forms (straight, curly, wavy, etc.) are present in apparently infinite variations, each fibre can be reduced to a finite sequence of tandem segments of just three types: straight, bent/curly, or twisted. Hair forms can thus be regarded as resulting from genetic pathways that induce, reverse or modulate these basic curvature modes. However, physical interconversions between twists and curls demonstrate that strict one-to-one correspondences between them and their genetic causes do not exist. Current hair-curvature theories do not distinguish between bending and twisting mechanisms. We here introduce a multiple papillary centres (MPC) model which is particularly suitable to explain twisting. The model combines previously known features of hair cross-sectional morphology with partially/completely separated dermal papillae within single follicles, and requires such papillae to induce differential growth rates of hair cortical material in their immediate neighbourhoods. The MPC model can further help to explain other, poorly understood, aspects of hair growth and morphology. Separate bending and twisting mechanisms would be preferentially affected at the major or minor ellipsoidal sides of fibres, respectively, and together they exhaust the possibilities for influencing hair-form phenotypes. As such they suggest dialectic for hair-curvature development. We define a natural-dialectic (ND) which could take advantage of speculative aspects of dialectic, but would verify its input data and results by experimental methods. We use this as a top-down approach to first define routes by which hair bending or twisting may be brought about and then review evidence in support of such routes. In particular we consider the wingless (Wnt) and mammalian target of rapamycin (mTOR) pathways as paradigm pathways for molecular hair bending and twisting mechanisms, respectively. In addition to the Wnt canonical pathway, the Wnt/Ca(2+) and planar cell polarity (PCP) pathways, and others, can explain many alternatives and specific variations of hair bending phenotypes. Mechanisms for hair papilla budding or its division by bisection or fission can explain MPC formation. Epithelial-to-mesenchymal (EMT) and mesenchymal-to-epithelial (MET) transitions, acting in collaboration with epithelial-mesenchymal communications are also considered as mechanisms affecting hair growth and its bending and twisting. These may be treated as sub-mechanisms of an overall development from neural-crest stem cell (NCSC) lineages to differentiated hair follicle (HF) cell types, thus providing a unified framework for hair growth and development.

Parkinson's disease-associated melanin steal

Urinary dopamine fluctuations in the competitive inhibition state were first documented in 2009. At that time, it was noted that progressively higher daily dosing values of L-tyrosine decreased the magnitude of these fluctuations. While extensive statistical analysis has been performed by the authors since 2004, it was not until 2012 that a plausible explanation was formulated. In the process, correlations with L-tyrosine administration and the on/off effect of Parkinson's disease were defined. This paper documents the current knowledge with regard to the management of retrograde phase 1 dopamine fluctuations and investigates the hypothesis that they are caused by a melanin steal phenomenon.

Redox-inflammatory synergy in the metabolic syndrome

Metabolic syndrome (MetS) comprises interrelated disease states including obesity, insulin resistance and type 2 diabetes (T2DM), dyslipidemia, and hypertension. Essential to normal physiological function, and yet massively damaging in excess, oxidative stress and inflammation are pivotal common threads among the pathologies of MetS. Increasing evidence indicates that redox and inflammatory dysregulation parallels the syndrome's physiological, biochemical, and anthropometric features, leading many to consider the pro-oxidative, pro-inflammatory milieu an unofficial criterion in itself. Left unchecked, cross-promotion of oxidative stress and inflammation creates a feed-forward cycle that can initiate and advance disease progression. Such redox-inflammatory integration is evident in the pathogenesis of obesity, insulin resistance and T2DM, atherogenic dyslipidemia, and hypertension, and is thus hypothesized to be the "common soil" from which they develop. The present review highlights the synergistic contributions of redox-inflammatory processes to each of the components of the MetS.

The evaluation of depigmenting efficacy in the skin for the development of new whitening agents in Korea

In this review, the evaluation methods for the screening of depigmenting substrates were investigated. For this purpose, the evaluation method of tyrosinase, a key enzyme of melanin biosynthesis, is most frequently used, but evaluating methods based on the regulation of cellular signal transfer factors or the inhibition of melanosome transfer have also been developed. Evaluation of the depigmenting effect using melanocytes is complex. It has the advantage of being capable of analysing overall effects on melanin biosynthesis at cellular levels. Before the final clinical testing of depigmenting agents, in vitro testing should be conducted to confirm the depigmenting efficacy and safety. Clinical studies for depigmenting agents can be used to investigate the prevention of melanin biosynthesis and to determine whether melanin disappears from skin. Therefore, the most appropriate protocol has to be employed, depending on the mechanism of action of the depigmenting agent.