Melanin Concentration Research Articles

Indications of symbiotic state influencing melanin-synthesis immune response in the facultative coral Astrangia poculata.

Increased ocean warming is causing detrimental impacts to tropical corals worldwide. Compounding the effects of heat stress, incidences of tropical coral disease have risen concurrently. While tropical coral responses to these impacts are well studied, temperate coral responses remain largely unknown. The present study focused on the immune response of the temperate coral Astrangia poculata to increased temperature and disease. Symbiotic and aposymbiotic A. poculata were collected from Narragansett Bay, Rhode Island (USA) in summer and winter seasons and exposed to control (18°C) versus elevated temperatures (26°C) in the presence of an immune stimulant (i.e. lipopolysaccharide) for a 12 h period. Prophenoloxidase (PPO) and melanin concentrations from the melanin-synthesis pathway were assessed via spectrophotometry to examine immune responses. While PPO measurements were higher on average in symbiotic corals compared with aposymbiotic corals, temperature and season did not significantly affect this metric. Melanin was significantly higher in symbiotic compared to aposymbiotic corals, implying that symbiotic state may be important for melanin-synthesis response. Conversely, melanin as an immune response may be of less importance in aposymbiotic A. poculata due to the potential capacity of other immune responses in this species. In addition, differences in resource allocation to immune investment as a result of symbiosis is plausible given melanin production observed within the present study. However, thermal stressors may reduce the overall influence of symbiosis on melanin production. Future studies should build upon these results to further understand the entirety of innate immunity responses in temperate coral species.

Triple Wavelength and 810 nm Diode Lasers for Hair Removal: A Clinical and <i>in Silico</i> Comparative Study on Indian Skin

In laser hair removal treatments on dark skin, the high concentration of melanin in the skin competes with the melanin in the hair. During standard laser procedures, with wavelengths of 755 nm or 810 nm, a high level of laser light absorption by melanin in the skin is observed. Therefore, to avoid side effects, lower fluence values are used, which further reduces hair-removal efficacy. To improve results, 810 nm diode lasers operating in dynamic mode, with high frequency and multiple passes, are typically used. The aim of this study is to compare the efficacy and safety of triple-wavelength diode lasers (810 nm, 940 nm, 1060 nm) with that of 810 nm diode lasers on Indian patients. A side-by-side comparison was performed using a triple-wavelength diode laser in stamping mode on one side, and an 810 nm diode laser in dynamic mode on the other. Three subjects with skin type IV on the Fitzpatrick scale participated in the study. Efficacy was assessed through hair counting using clinical photographs, taken before and after the treatments, and the Global Aesthetic Improvement Scale (GAIS). Additionally, comparisons related to epidermal heating and thermal damage to the hair follicle were conducted through mathematical 3D simulations using COMSOL Multiphysics® software. Side effects were also evaluated. A superior end point was observed with triple wavelength compared to the 810 nm diode laser. Hair counting showed a 27% greater hair reduction with triple wavelength. No adverse effects were observed. Thermal simulations revealed 29% higher thermal damage with the triple-wavelength laser compared to the 810 nm diode laser. To conclude, on darker skin types, the triple-wavelength diode laser has been shown to be more effective at removing hair, compared to the 810 nm diode laser, while also being a safe procedure.

Экспериментальная оценка лечебных свойств мази на основе меланинов из природного сырья и глубинной культуры чаги

Introduction. Due to the acquisition of antibiotic resistance by pyogenic microbiota, the problem of topical (drug) treatment of wounds has worsened. Aim. Experimental evaluation of the antibiotic properties of melanin from natural raw material and a submerged culture of chaga (Inonotus obliquus) in vitro and the therapeutic properties of ointments prepared on the basis of these melanins in vivo. Materials and Methods. Melanins were obtained by alkaline hydrolysis. The antibiotic activity of melanins was determined by co-cultivation in a liquid medium of the studied samples with six cultures of test strains of gram-negative and gram-positive bacteria and two of yeast fungi. Ointments based on melanin from natural raw material and the submerged culture of chaga (Inonotus obliquus F-1244 strain) were obtained using two compositions of ointment base. The wound-healing efficacy of ointments was evaluated on three groups of mice. The control groups were mice untreated and treated with a comparison drug (Levomikon-TFF). The treatment of mice was continued until their incised skin wounds healed. Wound areas, motor activity, appetite, dynamics and character of wound healing were assessed daily in mice of all groups, as well as changes in their body weight every three days. Results. Melanins from natural raw materials and the submerged culture of chaga completely suppressed the growth of gram-positive spore-forming Bacillus cereus bacterium in a co-culture. Melanin from natural raw material of chaga on average suppressed the growth of the Staphylococcus aureus ATCC 6538 strain by an order of magnitude. Melanin from the submerged chaga culture completely suppressed the growth of a clinical isolate of the highly pathogenic Candida sp. Ft-5 strain from a deceased patient with generalized candida infection and, on average, inhibited the growth of the collection strain of yeast Candida albicans 620 by two orders of magnitude more intensively. It was found that ointments based on melanin from natural raw materials and the submerged culture of chaga, as well as ointment containing a fivefold increased concentration of melanin from natural chaga, do not have toxicity to experimental animals. Ointments containing 0.4 mg of melanin from natural raw material and the submerged chaga culture per 0.2 g of a single dose of ointment had the same wound healing efficacy, while not only were not inferior in this indicator to the combined antimicrobial comparison drug Levomikon-TFF, but also showed a tendency to more accelerated wound healing (on the 15–18th day of observation) compared with the process of wound regeneration in the group of animals treated with the drug of comparison. A more accelerated wound healing effect was demonstrated in experimental animals (already on the 12th day of observation) treated with a fivefold increased content of melanin from natural raw material of chaga, compared with mice treated with the comparison drug. Conclusion. Ointments containing melanin of chaga (Inonotus obliquus) have anti-inflammatory, regenerative properties and can be considered promising for topical treatment of wounds.

Development of voltammetric melanin sensor with 2,5-dimethylfuran modified platinum electrode

In this study, an electrochemical sensor was developed for the electrochemical determination of melanin. For this purpose, phosphate buffer salt (PBS, pH 7.00) solution was used as an electrolyte, 2,5-dimethylfuran (2,5-DMF) as a monomer, Pt wire as the auxilary electrode, Ag/AgCl electrode as the reference electrode and a platinum electrode as the working electrode. The modification of the electrode was performed by polymerization of 2,5-DMF at the bare Pt electrode surface using the cyclic voltammetry method. Parameters such as film thickness, scan rate and pulse amplitude with prepared 2,5-DMF modified platinum electrode (p(2,5-DMF)/PtE) were optimized by square wave voltammetry (SWV) in PBS buffer containing melanin. In optimum conditions, the anodic peak height showed a linear increase with the melanin concentration. The limit of detection (LOD) and limit of quantitation (LOQ) were calculated to be 0.088 mmol/l and 0.292 mmol/l, respectively, with melanin concentrations ranging from 0.10 to 2.20 mmol/l and the correlation coefficient (R2) was calculated as 0.9985. Stability of the prepared sensor was found to be 99.63% by using the reproducibility experiments (n = 15).

Triple combination therapy of narrowband ultraviolet B, fractional carbon dioxide laser and topical bimatoprost 0.01% for non-segmental vitiligo on non-facial areas: A randomized half-body, double-blind, placebo-controlled, comparative study.

Combination therapy shows superior outcomes over monotherapy in treating vitiligo. Topical bimatoprost is a melanogenic agent effectively used to induce repigmentation. However, topical bimatoprost 0.01% has never been explored in non-facial vitiligo, and triple therapy of phototherapy, fractional laser and topical bimatoprost has never been examined. This study aims to investigate the efficacy and safety of triple-modality treatment, combining narrowband ultraviolet B (NB-UVB), fractional carbon dioxide (CO2 ) laser and topical bimatoprost 0.01% for stable non-segmental vitiligo on non-facial areas. Fifteen vitiligo patients with at least two symmetrical, comparable-sized lesions on non-facial regions were included. The paired lesions were randomized to receive a treatment regimen of twice-daily application of either bimatoprost 0.01% solution or placebo in combination with once-monthly fractional CO2 laser and twice-weekly NB-UVB therapy for 12 weeks. There were no statistically significant differences in the vitiligo surface area (VSA) and melanin concentration (MC) at baseline between treatment sides. After 12 weeks of treatment, the percentage change from baseline of MC on the triple-therapy side was significantly higher than that on the dual-therapy side, 27.17 ± 13.62% versus 22.82 ± 10.10% (p= 0.028). The change from baseline of VSA was also greater on the triple-therapy side; however, a statistically significant difference was not reached. Improvement grades of repigmentation and adverse events were similar on both sides. Triple therapy with NB-UVB, fractional CO2 laser and topical bimatoprost 0.01% tends to be safe and more effective as compared to dual therapy of NB-UVB and fractional CO2 laser in non-facial vitiligo.

Quantification of soft tissue parameters from spatially resolved diffuse reflectance finite element models.

Spatially resolved diffuse reflectance spectroscopy (SRDRS) is a non-invasive optical technique that helps in clinical diagnosis of various tissue microcirculation and skin pigmentation disorders based on collected backscattered light from multi-layered tissue. The extraction of the optical properties from the reflectance spectrum using analytical solutions is laborious. Model-based light tissue interaction studies help in quantifying the optical properties. This work presents the use of finite element models of light tissue interaction for this purpose. A bilayer model mimicking human skin was considered and the diffused reflectance spectra at multiple detector points were generated using finite element modelling for varying melanin concentration, epidermal thickness, blood volume fraction, oxygen saturation and scattering components. The reflectance value based on varying optical parameters from multiple detection points lead to the generation of a look-up table (LUT), which is further used for finding the tissue parameters that contribute to the spatially resolved reflectance values. The tissue parameters estimated after inverse modelling showed a high degree of agreement with the expected tissue parameters for a test dataset different from the training dataset.

Natural Melanin Synthesized by Aureobasidium pullulans Using Food Wastes and its Characterization

Background and Objective: Food wastes cause economic losses and environmental problems. Hence, ability to transform food wastes into high-value added products is highly attractive. The aim of this study was to produce melanin pigments by fermentation that include wide potential uses in agriculture, cosmetics and pharmaceutical industries using domestic wastes such as melon peel, watermelon peel and carrot peel and industrial by-products such as whey and molasses. Material and Methods: Two Aureobasidium pullulans strains were assessed for melanin production. Fourier-transform infrared spectroscopy, scanning electron microscope, zeta potential, ultraviolet absorbance and solubility assays were carried out to characterize produced melanin nanoparticles. Results and Conclusion: The highest intracellular (0.19 g l-1) and extracellular (3.52 g l-1) melanin concentrations were produced by Aureobasidium pullulans NBRC 100716 using carrot peel extracts as fermentation media. Results of characterization were compared with those of synthetic melanin used as standard and the produced nanoparticles were validated. Particle sizes of the nanoparticles ranged 10-760 nm with negative charges, as suggested by previous literature. Results showed that carrot peel was a good candidate, which could be used for the production of high value-added melanin. When carrot peel extract was used as a fermentation medium, characteristics of the melanin produced by Aureobasidium pullulans NBRC 100716 strain were similar to those of synthetic melanin. Conflict of interest: The authors declare no conflict of interest

A Cost-Efficient Multiwavelength LED-Based System for Quantitative Photoacoustic Measurements.

The unique ability of photoacoustic (PA) sensing to provide optical absorption information of biomolecules deep inside turbid tissues with high sensitivity has recently enabled the development of various novel diagnostic systems for biomedical applications. In many cases, PA setups can be bulky, complex, and costly, as they typically require the integration of expensive Q-switched nanosecond lasers, and also presents limited wavelength availability. This article presents a compact, cost-efficient, multiwavelength PA sensing system for quantitative measurements, by utilizing two high-power LED sources emitting at central wavelengths of 444 and 628 nm, respectively, and a single-element ultrasonic transducer at 3.5 MHz for signal detection. We investigate the performance of LEDs in pulsed mode and explore the dependence of PA responses on absorber’s concentration and applied energy fluence using tissue-mimicking phantoms demonstrating both optical absorption and scattering properties. Finally, we apply the developed system on the spectral unmixing of two absorbers contained at various relative concentrations in the phantoms, to provide accurate estimations with absolute deviations ranging between 0.4 and 12.3%. An upgraded version of the PA system may provide valuable in-vivo multiparametric measurements of important biomarkers, such as hemoglobin oxygenation, melanin concentration, local lipid content, and glucose levels.

Large-Area Photoreceptor Degeneration Model in Rabbits by Photocoagulation and Oxidative Stress in the Retina.

Photocoagulation is used for the treatment of retinal ischemic disease. However, due to the invasive nature of photocoagulation and variety of melanin concentrations between individuals, it is challenging to avoid damaging the adjacent photoreceptors and inducing several side effects. Previous studies indicate the role of laser power, duration, and spot size on retinal lesions, but the effect of interspot distance of the laser pulses needs to be considered in panretinal photocoagulation. In this study, we examine different parameters of photocoagulation on lesions of the retina in rabbit, finding that the lesion level of the outer nuclear layer of the retina depended on the pulse duration and laser spot size, and decreasing interspot distance could completely abolish the photoreceptor layer. The degeneration of the photoreceptor by photocoagulation occurred in 24 h and was not restored afterward. We then conducted panretinal photocoagulation in rabbit and found that oxidative stress was decreased in the inner nuclear layer of the retina, and pupillary light reflex and ERG signals were impaired. Our study could provide a rabbit model to explore the mechanism of photoreceptor degeneration and therapies for the side effects after photocoagulation.

Two-layer spatial frequency domain imaging of compression-induced hemodynamic changes in breast tissue

.Significance: Longitudinal tracking of hemodynamic changes in the breast has shown potential for neoadjuvant chemotherapy (NAC) outcome prediction. Spatial frequency domain imaging (SFDI) could be suitable for frequent monitoring of shallow breast tumors, but strong sensitivity to superficial absorbers presents a challenge.Aim: We investigated the efficacy of a two-layer SFDI inverse model that accounts for varying melanin concentration in the skin to improve discrimination of optical properties of deep tissue of the breast.Approach: Hemodynamic changes in response to localized breast compression were measured in 13 healthy volunteers using a handheld SFDI device. Epidermis optical thickness was determined based on spectral fitting of the model output and used to calculate subcutaneous optical properties.Results: Optical properties from a homogeneous model yielded physiologically unreasonable absorption and scattering coefficients for highly pigmented volunteers. The two-layer model compensated for the effect of melanin and yielded properties in the expected range for healthy breast. Extracted epidermal optical thickness was higher for higher Fitzpatrick types. Compression induced a decrease in total hemoglobin consistent with tissue blanching.Conclusions: The handheld SFDI device and two-layer model show potential for imaging hemodynamic responses that potentially could help predict efficacy of NAC in patients of varying skin tones.

Correlation of Melanin Content with Collagen Density in Keloid Patients

BACKGROUND: Keloid is a form of wound healing that results from fibrous tissue activity. It can develop beyond the boundaries of the original wound, extends into the dermis layer, and disrupting the appearance. Previously, no studies have revealed a correlation between melanin pigment and keloid. AIM: This research aimed to describe the correlation between melanin concentration and collagen deposition in keloid tissue. MATERIALS AND METHODS: A prospective study conducted through the application of a cross-sectional analytic survey method. The color of the skin was measured using a chromameter, and a histopathologic examination was performed on the skin surrounding the keloid, as well as the keloid tissue. Data were analyzed using a t-test, correlation, and linear regression statistics. RESULTS: The results showed a significant difference between melanin concentration and collagen deposition in the skin surrounding the keloid tissue. No significant difference was observed between melanin concentration in the surrounding skin of keloid and those in the keloid tissue, as well as collagen deposition. Meanwhile, the melanin concentration in the surrounding skin of keloid and keloid tissue had a significant relationship with fibrocytes number. CONCLUSION: There is a significant correlation between melanin concentrations and collagen density in the keloid tissue.

Improving the Physical Properties of Polyvinyl Alcohol (PVA)-Melanin Doping

The Polyvinyl alcohol (PVA) is an artificial polymer that used in many medical applications but it has a few disadvantages that can overcome with the addition of chemical compounds. The present study aimed to investigate the efficacy of melanin to improvement the properties biopolymer PVA by doping with of melanin and reinforce the PVA electrical, optical and mechanical properties to prevent it from deformation with time or temperature. In the present work, dielectric relaxation and spectrophotometric techniques were used to characterize the biopolymer PVA doped melanin of different concentration. Reduction of dielectric constant of PVA accompanied with increased in conductivity with the doped melanin concentration. Moreover, relaxation times dropped with an increase of melanin content in PVA. A small shift in Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy of PVA due to increasing the concentration of melanin that caused to increase OH in PVA. A behavior can be used in electronic industries and medical applications.

Reciprocal Changes in miRNA Expression with Pigmentation and Decreased Proliferation Induced in Mouse B16F1 Melanoma Cells by L-Tyrosine and 5-Bromo-2'-Deoxyuridine.

Background: Many microRNAs have been identified as critical mediators in the progression of melanoma through its regulation of genes involved in different cellular processes such as melanogenesis, cell cycle control, and senescence. However, microRNAs’ concurrent participation in syngeneic mouse B16F1 melanoma cells simultaneously induced decreased proliferation and differential pigmentation by exposure to 5-Brd-2′-dU (5’Bromo-2-deoxyuridine) and L-Tyr (L-Tyrosine) respectively, is poorly understood. Aim: To evaluate changes in the expression of microRNAs and identify which miRNAs in-network may contribute to the functional bases of phenotypes of differential pigmentation and reduction of proliferation in B16F1 melanoma cells exposed to 5-Brd-2′-dU and L-Tyr. Methods: Small RNAseq evaluation of the expression profiles of miRNAs in B16F1 melanoma cells exposed to 5-Brd-2′-dU (2.5 μg/mL) and L-Tyr (5 mM), as well as the expression by qRT-PCR of some molecular targets related to melanogenesis, cell cycle, and senescence. By bioinformatic analysis, we constructed network models of regulation and co-expression of microRNAs. Results: We confirmed that stimulation or repression of melanogenesis with L-Tyr or 5-Brd-2′-dU, respectively, generated changes in melanin concentration, reduction in proliferation, and changes in expression of microRNAs 470-3p, 470-5p, 30d-5p, 129-5p, 148b-3p, 27b-3p, and 211-5p, which presented patterns of coordinated and reciprocal co-expression, related to changes in melanogenesis through their putative targets Mitf, Tyr and Tyrp1, and control of cell cycle and senescence: Cyclin D1, Cdk2, Cdk4, p21, and p27. Conclusions: These findings provide insights into the molecular biology of melanoma of the way miRNAs are coordinated and reciprocal expression that may operate in a network as molecular bases for understanding changes in pigmentation and decreased proliferation induced in B16F1 melanoma cells exposed to L-Tyr and 5-Brd-2′-dU.

In Vivo Transcutaneous Monitoring of Hemoglobin Derivatives Using a Red-Green-Blue Camera-Based Spectral Imaging Technique.

Cyanosis is a pathological condition that is characterized by a bluish discoloration of the skin or mucous membranes. It may result from a number of medical conditions, including disorders of the respiratory system and central nervous system, cardiovascular diseases, peripheral vascular diseases, deep vein thrombosis, and regional ischemia. Cyanosis can also be elicited from methemoglobin. Therefore, a simple, rapid, and simultaneous monitoring of changes in oxygenated hemoglobin and deoxygenated hemoglobin is useful for protective strategies against organ ischemic injury. We previously developed a red-green-blue camera-based spectral imaging method for the measurements of melanin concentration, oxygenated hemoglobin concentration (CHbO), deoxygenated hemoglobin concentration (CHbR), total hemoglobin concentration (CHbT) and tissue oxygen saturation (StO2) in skin tissues. We leveraged this approach in this study and extended it to the simultaneous quantifications of methemoglobin concentration (CmetHb), CHbO, CHbR, and StO2. The aim of the study was to confirm the feasibility of the method to monitor CmetHb, CHbO, CHbR, CHbT, and StO2. We performed in vivo experiments using rat dorsal skin during methemoglobinemia induced by the administration of sodium nitrite (NaNO2) and changing the fraction of inspired oxygen (FiO2), including normoxia, hypoxia, and anoxia. Spectral diffuse reflectance images were estimated from an RGB image by the Wiener estimation method. Multiple regression analysis based on Monte Carlo simulations of light transport was used to estimate CHbO, CHbR, CmetHb, CHbT, and StO2. CmetHb rapidly increased with a half-maximum time of less than 30 min and reached maximal values nearly 60 min after the administration of NaNO2, whereas StO2 dramatically dropped after the administration of NaNO2, indicating the temporary production of methemoglobin and severe hypoxemia during methemoglobinemia. Time courses of CHbT and StO2, while changing the FiO2, coincided with well-known physiological responses to hyperoxia, normoxia, and hypoxia. The results indicated the potential of this method to evaluate changes in skin hemodynamics due to loss of tissue viability and vitality.

Dark cyclobutane pyrimidine dimers are formed in the epidermis of Fitzpatrick skin types I/II and VI in vivo after exposure to solar-simulated radiation.

Unlike "light" cylobutane pyrimidine dimers (CPD) formed during ultraviolet radiation (UVR) exposure, dark CPD (dCPD) are formed afterwards. Studies have attributed this to delayed melanin sensitization. There are no data on the role of melanin in dCPD formation in human skin. Volunteers of Fitzpatrick skin types (FST I/II vs. VI) were exposed to erythemally equivalent doses of solar simulated radiation. CPD were assessed by semi-quantitative immunostaining in whole epidermis and in three epidermal zones, and quantitative HPLC-MS/MS (whole epidermis) at different times post-exposure up to 24hr. A CPD peak that appeared at 1-2hr post-exposure in whole epidermis measurements, in all skin types, demonstrated dCPD. However, both dCPD and light CPD were absent in the basal layer of FST VI with the greatest melanin concentration. Modelling the whole epidermis data showed no differences between the repair kinetics of FST I/II and VI. Melanin may be a sensitizer or "sunscreen" for dCPD depending on its location and concentration. Previous CPD repair studies in human skin have assumed peak CPD immediately after UVR exposure and so have overestimated total repair.

Dowling Degos Disease in a child: A rare case report from Northeast India

Dowling–Degos disease (DDD) is a rare genodermatosis with autosomal dominant inheritance. It is characterized by reticulate pigmentation of flexures, comedo-like follicular papules, and perioral pitted scars. Here, we report a 3-year-old female child presenting with hyperpigmentation of the external genitalia, intergluteal fold, and armpits with follicular keratotic papules over the neck. Histopathological examination showed hyperkeratosis, irregular acanthosis, papillomatosis, and basal layer pigmentation in the epidermis with elongated and branched rete pegs and relatively more melanin concentration in the tips of the rete pegs. The diagnosis of DDD was made. This case is reported due to the unusual early onset and involvement of external genitalia.

Distinct carbon fractions drive a generalisable two‐pool model of fungal necromass decomposition

Abstract Fungi represent a rapidly cycling pool of carbon (C) and nitrogen (N) in soils. Understanding of how this pool impacts soil nutrient availability and organic matter fluxes is hindered by uncertainty regarding the dynamics and drivers of fungal necromass decomposition. Here we assessed the generality of common models for predicting mass loss during fungal necromass decomposition and linked the resulting parameters to necromass substrate chemistry. We decomposed 28 different types of fungal necromass in laboratory microcosms over a 90‐day period, measuring mass loss on all types, and N release on a subset of types. We characterised the initial chemistry of each necromass type using: (a) fibre analysis methods commonly used for plant tissues, (b) initial melanin and nitrogen (N) concentrations and (c) Fourier transform infrared (FTIR) spectroscopy to assess the presence of bonds associated with common biomolecules. We found universal support for an asymptotic model of decomposition, which assumes that fungal necromass consists of an exponentially decomposing ‘fast’ pool, and a ‘slow’ pool that decomposes at a rate approaching zero. The strongest predictor of the fast pool decay rate (k) was the proportion of cell soluble components, though initial N concentration also predicted k, albeit more weakly. The size of the slow pool was best predicted by the acid non‐hydrolysable fraction, which was positively correlated with melanin‐associated aromatics. Nitrogen dynamics varied by necromass type, ranging from net N release to net immobilisation. The maximum quantity of N immobilised was inversely related to cell soluble contents and k, as positively related to FTIR spectra associated with cell wall polysaccharides. Collectively, our results indicate that the decomposition of fungal necromass in soils can be described as having two distinct stages that are driven by different components of substrate C chemistry, with implications for rates of N availability and organic matter accumulation in soils. A free Plain Language Summary can be found within the Supporting Information of this article.

Genetic deciphering of the antagonistic activities of the melanin-concentrating hormone and melanocortin pathways in skin pigmentation.

The genetic origin of human skin pigmentation remains an open question in biology. Several skin disorders and diseases originate from mutations in conserved pigmentation genes, including albinism, vitiligo, and melanoma. Teleosts possess the capacity to modify their pigmentation to adapt to their environmental background to avoid predators. This background adaptation occurs through melanosome aggregation (white background) or dispersion (black background) in melanocytes. These mechanisms are largely regulated by melanin-concentrating hormone (MCH) and α-melanocyte-stimulating hormone (α-MSH), two hypothalamic neuropeptides also involved in mammalian skin pigmentation. Despite evidence that the exogenous application of MCH peptides induces melanosome aggregation, it is not known if the MCH system is physiologically responsible for background adaptation. In zebrafish, we identify that MCH neurons target the pituitary gland-blood vessel portal and that endogenous MCH peptide expression regulates melanin concentration for background adaptation. We demonstrate that this effect is mediated by MCH receptor 2 (Mchr2) but not Mchr1a/b. mchr2 knock-out fish cannot adapt to a white background, providing the first genetic demonstration that MCH signaling is physiologically required to control skin pigmentation. mchr2 phenotype can be rescued in adult fish by knocking-out pomc, the gene coding for the precursor of α-MSH, demonstrating the relevance of the antagonistic activity between MCH and α-MSH in the control of melanosome organization. Interestingly, MCH receptor is also expressed in human melanocytes, thus a similar antagonistic activity regulating skin pigmentation may be conserved during evolution, and the dysregulation of these pathways is significant to our understanding of human skin disorders and cancers.

Melanin concentration and depolarization metrics measurement by polarization-sensitive optical coherence tomography

Imaging of melanin in the eye is important as the melanin is structurally associated with some ocular diseases, such as age-related macular degeneration. Although optical coherence tomography (OCT) cannot distinguish tissues containing the melanin from other tissues intrinsically, polarization-sensitive OCT (PS-OCT) can detect the melanin through spatial depolarization of the backscattered light from the melanin granules. Entropy is one of the depolarization metrics that can be used to detect malanin granules in PS-OCT and valuable quantitative information on ocular tissue abnormalities can be retrived by correlating entropy with the melanin concentration. In this study, we investigate a relationship between the melanin concentration and some depolarization metrics including the entropy, and show that the entropy is linearly proportional to the melanin concentration in double logarithmic scale when noise bias is corrected for the entropy. In addition, we also confirm that the entropy does not depend on the incident state of polarization using the experimental data, which is one of important attributes that depolarization metrics should have. The dependence on the incident state of polarization is also analyzed for other depolarization metrics.

Review on analysis of interesting whitening agents in cosmetics products

The skin whitening as known as skin lightening or skin bleaching is the most commonly used skincare treatment that helps to achieve a lighter and healthier skin complexion by reducing the melanin concentration in the skin in the practice of using chemical products. Several chemicals are effective in skin whitening, while some of them are toxic or have problematic safety profiles. The products requiring to contain either kind of whiting agents were seen to display labeling issues. Such an elevated number of differences suggested concerns of whether such differences between stated and revealed content of whiting agents. The Analytical chemical measurements of these objects look necessary, no reliable analytical methods have been recorded to determine most of these chemicals. Just the measurement of hydroquinone and some of its ethers is treated by a method registered by the European Commission.