Burn depth assessment by dual-wavelength light emitting diodes-excited photoacoustic imaging in rats

Accurate burn depth assessment is crucial to determine treatment plans for burn patients. We have previously proposed a method for performing burn depth assessments based on photoacoustic (PA) imaging, and we have demonstrated the validity of this method, which allows the successful detection of PA signals originating from the blood under the bloodless burned tissue, using rat burn models. Based on these findings, we started a clinical study in which we faced two technical issues: (1) When the burn depth was shallow, PA signals due to skin contamination and/or melanin in the epidermis (surface signals) could not be distinguished from PA signals originating from the blood in the dermis; (2) the size of the system was too large. To solve these issues, we propose a burn depth diagnosis based on dual-wavelength light emitting diodes (LEDs)-excited PA imaging. The use of LEDs rendered the system compact compared to the previous one that used a conventional solid-state laser. We replicated human burned skin by applying a titrated synthetic melanin solution onto the wound surface in albino rat burn models and measured their burn depths by PA excitation at 690 and 850 nm, where melanin and haemoglobin show greatly different absorption coefficients. As a result, the surface signals were eliminated by subtracting the PA signals at 690 nm from those at 850 nm. The resultant estimated burn depths were strongly correlated with the histological assessment results. The validity of the proposed method was also examined using a burn model of rats with real melanin.     

Hypopigmentation in Angelman syndrome

Chromosome region 15q is thought to contain one or more genes that are important for melanin pigment synthesis in the hair, skin, and eyes. Hypopigmentation has been identified in the Prader-Willi (PWS) and Angelman (AS) syndromes. We have examined 6 individuals with AS to further characterize the pigment pattern in this condition. The age of the 5 girls and one boy ranged from 2.4 to 7.0 years. None has obvious albinism. Hair color ranged from light blond to brown. Skin was type I in 3 and type II in 3. Eye changes included nystagmus in 2, strabismus in 4, and reduced retinal pigment in 5. The mean hairbulb tyrosinase activity was 0.37 ± 0.44 pmol/hb/120 min for the individuals with AS, with a range of 0.00 to 1.13 (normal brown control 1.49 ± 0.79, normal blond control 1.50 ± 0.85). Electron microscopic examination of hairbulb melanocytes showed normal melansome and melanocyte architecture and number, but reduced melanin formation, with many stage II and III premelanosomes but few stage IV fully melanized melanosomes. Hypopigmentation characterized by light skin, reduced retinal pigment, low hairbulb tyrosinase activity, and incomplete melanization of melanosomes is part of the phenotype of AS, and is similar to that found in PWS. © 1993 Wiley-Liss, Inc.     

Tyrosinase gene mutations in type I (tyrosinase-deficient) oculocutaneous albinism define two clusters of missense substitutions

Type I (tyrosinase-deficient) oculocutaneous albinism (OCA) results from mutations of the gene encoding tyrosinase, the enzyme that catalyzes the first 2 steps of melanin pigment biosynthesis. In type IA (tyrosinase-negative) OCA tyrosinase enzymatic activity is completely absent, and in type IB (“yellow”) OCA tyrosinase activity is greatly reduced. Here, we describe 11 novel mutations of the tyrosinase gene in Caucasian patients with these 2 forms of type I OCA. Type I OCA in Caucasians appears to result from a great variety of different uncommon alleles. More than 80% of the known missense substitutions associated with type I OCA cluster within 2 relatively small regions of the tyrosinase polypeptide, suggesting that these may correspond to functionally important sites within the enzyme. © 1992 Wiley-Liss, Inc.     

Melanin‐concentrating hormone‐1 receptor binding activity of pheophorbides isolated from morus alba leaves

The time‐resolved fluorescence technique based on melanin‐concentrating hormone (MCH) receptor subtype‐1 (MCH‐1 receptor) binding assay was adopted to carry out a bioassay‐guided fractionation of the methanol extract of Morus alba leaves. This fractionation and purification led to the isolation of two compounds identified as pheophorbide a methyl ester and 13²(S)‐hydroxypheophorbide a methyl ester. These active pheophorbides exhibited potent inhibitory activity in binding of europium‐labeled MCH to the human recombinant MCH‐1 receptor (IC₅₀ value; 4.03 and 0.33 ?M, respectively). Besides binding activity, the pheophorbides inhibited MCH‐mediated extracellular signal‐regulated kinase (ERK) phosphorylation in Chinese hamster ovary cells expressing human MCH‐1 receptor. These results suggest that pheophorbide a methyl ester and 13²(S)‐hydroxypheophorbide a methyl ester act as modulators of MCH‐1 receptor and MCH‐mediated ERK signaling. Copyright © 2009 John Wiley & Sons, Ltd.     

Amyloids,melanins and oxidative stress in melanomagenesis

Melanoma has traditionally been viewed as an ultraviolet (UV) radiation‐induced malignancy. While UV is a common inducing factor, other endogenous stresses such as metal ion accumulation or the melanin pigment itself may provide alternative pathways to melanoma progression. Eumelanosomes within melanoma often exhibit disrupted membranes and fragmented pigment which may be due to alterations in their amyloid‐based striated matrix. The melanosomal amyloid can itself be toxic, especially in combination with reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated by endogenous NADPH oxidase (NOX) and nitric oxide synthase (NOS) enzymes, a toxic mix that may initiate melanomagenesis. Further understanding of the loss of the melanosomal organization, the behaviour of the exposed melanin and the induction of ROS/RNS in melanomas may provide critical insights into this deadly disease.     

New insight in the treatment of refractory melasma: Laser Q‐switched Nd: YAG non‐ablative fractionated followed by intense pulsed light

The purpose of our study was to verify the results of the association of Q‐switched Nd: YAG non‐ablative fractionated with intense pulsed light, in order to treat patients with refractory melasma. The combination of these two devices seems to be the best treatment to combat hyperpigmentation produced by melasma, with low occurrence of side effects, which may be justified by the selective photothermolysis at subcellular level.     

Mechanism of tyrosinase inhibition by deoxyArbutin and its second-generation derivatives

Background Disorders, such as age spots, melasma and hyperpigmentation at sites of actinic damage, emanate from the augmentation of an increased amount of epidermal melanin. Objectives The ineptness of current therapies in treating these conditions, as well as high cytotoxicity, mutagenicity, poor skin penetration and low stability of skin‐depigmenting formulations led us to investigate new compounds that meet the medical requirements for depigmentation agents. We have shown previously that the tyrosinase inhibitor deoxyArbutin (dA) is a more effective and less toxic skin lightener than hydroquinone (HQ). Methods The efficacy and reversibility of dA and its derivatives on inhibiting tyrosine hydroxylase and DOPAoxidase was assessed using standard assays. Results dA and its second‐generation derivatives inhibit tyrosine hydroxylase and DOPAoxidase activities of tyrosinase dose dependently thereby inhibiting melanin synthesis in intact melanocytes, when used at concentrations that retain 95% cell viability in culture. This depigmenting effect was completely reversible when the compounds were removed. Tyrosinase inhibition was also observed in vitro when tested using human and purified mushroom tyrosinase, establishing that they are direct enzyme inhibitors. Lineweaver–Burk reciprocal plot analysis using mushroom tyrosinase illustrated that dA and its derivatives are more robust competitive inhibitors than HQ, when tyrosine is used as substrate. Conclusions Thus, dA and its second‐generation derivatives, which inhibit melanogenesis at safe concentrations by specifically acting on the tyrosinase enzyme at a post‐translational level, are promising agents to ameliorate hyperpigmented lesions or lighten skin.