Decreased phenylalanine uptake and turnover in patients with vitiligo

Insights into Molecular Structure of Pterins Suitable for Biomedical Applications

Pterins are an inseparable part of living organisms. Pterins participate in metabolic reactions mostly as tetrahydropterins. Dihydropterins are usually intermediates of these reactions, whereas oxidized pterins can be biomarkers of diseases. In this review, we analyze the available data on the quantum chemistry of unconjugated pterins as well as their photonics. This gives a comprehensive overview about the electronic structure of pterins and offers some benefits for biomedicine applications: (1) one can affect the enzymatic reactions of aromatic amino acid hydroxylases, NO synthases, and alkylglycerol monooxygenase through UV irradiation of H₄pterins since UV provokes electron donor reactions of H₄pterins; (2) the emission properties of H₂pterins and oxidized pterins can be used in fluorescence diagnostics; (3) two-photon absorption (TPA) should be used in such pterin-related infrared therapy because single-photon absorption in the UV range is inefficient and scatters in vivo; (4) one can affect pathogen organisms through TPA excitation of H₄pterin cofactors, such as the molybdenum cofactor, leading to its detachment from proteins and subsequent oxidation; (5) metal nanostructures can be used for the UV-vis, fluorescence, and Raman spectroscopy detection of pterin biomarkers. Therefore, we investigated both the biochemistry and physical chemistry of pterins and suggested some potential prospects for pterin-related biomedicine.

Autoxidation and photooxidation of tetrahydrobiopterin: a theoretical study

Pterins are naturally occurring pigments and enzyme cofactors widespread in living organisms. Tetrahydrobiopterin (H4Bip) is a coenzyme of aromatic amino acid hydroxylases, NO-synthases, and alkylglycerol monooxygenases. This coenzyme is prone to oxidation in the presence of molecular oxygen, a so-called autoxidation. The reactions participating in H4Bip autoxidation are well known. However, our study is an attempt to evaluate theoretically the feasibility of reactions participating in autoxidation. To do so, we have calculated the Gibbs free energy of elementary reactions between H4Bip, its derivatives, molecular oxygen, and reactive oxygen species (ROS). In the last few years, we have established the photosensitized oxidation of H4Bip experimentally. Thus, we have also evaluated the feasibility of H4Bip photooxidation reactions, which may occur according to both type-I and type-II photosensitized oxidation. We calculated Fukui indices for H4Bip and found particular atoms in the molecule that interact with nucleophiles (for example, singlet oxygen 1O2) and radicals (in particular, molecular oxygen 3O2). Therefore, we evaluated the probability of H4Bip autoxidation reactions, photooxidation reactions, and the reactivity of particular atoms in H4Bip molecule using the theoretical methods of quantum chemistry.

Correlation between gastrointestinal symptoms and adherence to traditional Persian medicine dietary recommendations in patients with vitiligo; a cross-sectional study

OBJECTIVES

Vitiligo is a chronic disease associated with the depigmentation of regions of the skin secondary to structural or functional damage to melanocytes. This damage results from interactions between the immune system and oxidative stress. In traditional Persian medicine (TPM), the concept of 'Barass' or 'Pissi' encompasses a group of skin diseases including vitiligo, for which there has been an emphasis on the preventive and therapeutic role of dietary modifications.

METHODS

In this cross-sectional study, 200 vitiligo patients and 200 controls were enrolled with a random sampling method. The participants included patients with vitiligo referred to the Dermatology Clinic of Shahid Faghihi Hospital (Shiraz, Iran), with the control group being comprised individuals who referred to this clinic for cosmetic purposes. Questionnaires comparing the severity of gastrointestinal symptoms and the rate of adherence to TPM dietary recommendations were filled by all participants. Data were analyzed using SPSS version 24.0.

RESULTS

The case group was significantly less adherent to TPM recommendations than the control group (8.25 ± 27.16 vs. 31.8 ± 10.47; p<0.001). However, there was no significant difference between both groups in the Gastrointestinal Symptom Rating Scale (GSRS) scores (14.09 ± 14.84 vs. 12.62 ± 11.71; p = 0.105). In the case group, the level of adherence to the recommendations of TPM was significantly lower among patients with lower education levels (R=-0.194; p=0.017). Furthermore, there was a significant negative relationship between the length of the disease and adherence to TPM dietary recommendations (R=-0.247; p=0.002).

CONCLUSIONS

In this study, the level of adherence to TPM recommendations was significantly lower among patients with vitiligo than the control group. Hence, further studies are suggested to identify the probable role of dietary habits in the pathogenesis of vitiligo.

A Systematic Review of Nutrition, Supplement, and Herbal-Based Adjunctive Therapies for Vitiligo

Background: Vitiligo is an autoimmune skin condition that affects people globally anywhere, from <0.1% to more than 8% of individuals. The disease destroys skin melanocytes, resulting in a patchy depigmentation of the skin. About 50% of all patients develop the disease before their 20s. Methods: We systematically searched the literature and reviewed the evidence for the use of nutritional supplements and diet in the management of vitiligo. Embase and Medline were searched for diet, herbal, and nutrition-based clinical studies. Additional filters were applied that looked for controlled trial or randomized controlled trial and article or article in press or letter and English and clinical study. We selected clinical studies in humans that showed how diet or natural supplements can improve the symptoms of vitiligo in all of our searches. Results: There were 62 manuscripts that resulted from the PubMed search and 259 from the Embase search. A final of 26 studies were reviewed, and other supplemental case and case-control studies were used to introduce diet components that may influence either exacerbation or amelioration of vitiligo. Possible mechanisms of action are introduced for natural and supplemental interventions. Conclusion: Some of the supplements reviewed include Gingko biloba, oral Polypodium leucotomos, alpha lipoic acid, vitamins B12, D, and E, folic acid, phenylalanine, canthaxanthin, Nigella sativa oil, and other combined herbal bio-actives. Overall, the growing evidence is promising, but more studies are needed in this area to further explore the impact that supplements and diet can have on vitiligo management. The most promising therapies included oral phenylalanine as adjuvant therapy with UVA therapy, oral G. biloba as monotherapy, both of which can be used with other traditional therapies, and oral P. leucotomos with phototherapy or photochemotherapy.

Solar light induces expression of acetylcholinesterase in skin keratinocytes: Signalling mediated by activator protein 1 transcription factor

Acetylcholinesterase (AChE) hydrolyses acetylcholine to choline and acetate, playing an important role in terminating the neurotransmission in brain and muscle. Recently, the non-neuronal functions of AChE have been proposed in different tissues, in which there are various factors to regulate the expression of AChE. In mammalian skin, AChE was identified in melanocytes and keratinocytes. Our previous study has indicated that AChE in keratinocyte affects the process of solar light-induced skin pigmentation; however, the expression of AChE in keratinocytes in responding to sunlight remains unknown. Here, we provided several lines of evidence to support a notion that AChE could be upregulated at transcriptional and translational levels in keratinocytes when exposed to solar light. The light-mediated AChE expression was triggered by Ca²⁺, supported by an induction of Ca²⁺ ionophore A23187 and a blockage by Ca²⁺ chelator BAPTA-AM. In addition, this increase on AChE transcriptional expression was eliminated by mutagenesis on the activating protein 1 (AP1) site in ACHE gene. Hence, the solar light-induced AChE expression is mediated by Ca²⁺ signalling through AP1 site. This finding supports the role of solar light in affecting the cholinergic system in skin cells, and which may further influence the dermatological function.

Alternative Systemic Treatments for Vitiligo: A Review

Vitiligo is a common, acquired disorder of skin pigmentation that can significantly impact quality of life. It often represents a therapeutic challenge, which has resulted in interest in alternative treatments such as herbal and vitamin supplements. In this review, we provide an overview of the most commonly studied complementary agents, describe proposed mechanisms of action, identify potential adverse effects, and discuss the primary evidence supporting their use. Our discussion focuses on L-phenylalanine, Polypodium leucotomos, khellin, Ginkgo biloba, and vitamins and minerals, including vitamins B12, C, and E, folic acid, and zinc used as monotherapy or in combination with other treatments for the management of vitiligo.

BmPAH catalyzes the initial melanin biosynthetic step in Bombyx mori

Pigmentation during insect development is a primal adaptive requirement. In the silkworm, melanin is the primary component of larval pigments. The rate limiting substrate in melanin synthesis is tyrosine, which is converted from phenylalanine by the rate-limiting enzyme phenylalanine hydroxylase (PAH). While the role of tyrosine, derived from phenylalanine, in the synthesis of fiber proteins has long been known, the role of PAH in melanin synthesis is still unknown in silkworm. To define the importance of PAH, we cloned the cDNA sequence of BmPAH and expressed its complete coding sequence using the Bac-to-Bac baculovirus expression system. Purified recombinant protein had high PAH activity, some tryptophan hydroxylase activity, but no tyrosine hydroxylase activity, which are typical properties of PAH in invertebrates. Because melanin synthesis is most robust during the embryonic stage and larval integument recoloring stage, we injected BmPAH dsRNA into silkworm eggs and observed that decreasing BmPAH mRNA reduced neonatal larval tyrosine and caused insect coloration to fail. In vitro cultures and injection of 4^th instar larval integuments with PAH inhibitor revealed that PAH activity was essential for larval marking coloration. These data show that BmPAH is necessary for melanin synthesis and we propose that conversion of phenylalanine to tyrosine by PAH is the first step in the melanin biosynthetic pathway in the silkworm.

Vitiligo: an update on current pharmacotherapy and future directions

INTRODUCTION

Vitiligo is a common pigmentary skin disorder, characterized by the appearance of white macules on the skin, mucosal or hair. Treatment is often a tough challenge and involves a wide range of therapies.

AREAS COVERED

This review focuses on available first- and second-line pharmacological treatments for vitiligo. In particular, the mechanisms of action, the main indications, the efficacy and the most important side effects are reviewed. Moreover, a brief discussion is provided, regarding other nonpharmacological treatments, such as phototherapy and surgical options, due to their importance and successful outcomes in vitiligo treatment. Finally, a concise overview regarding the future directions in vitiligo therapy is presented.

EXPERT OPINION

The promising outcomes reported here demonstrate that it is possible to achieve a satisfactory and often stable repigmentation of vitiligo lesions. Topical corticosteroids, calcineurin inhibitors, phototherapy and photochemotherapy represent the first-line therapeutic options, due to their safety and efficacy, whereas vitamin D analogues, targeted phototherapy, oral corticosteroids and surgery should be used as second-line therapies. Other therapies, such as antioxidants, can be used in association with other therapeutic options, whereas depigmenting agents should be used only in cases of extensive vitiligo, recalcitrant to other treatments.

Vitiligo: a comprehensive overview Part II: treatment options and approach to treatment

Vitiligo is a common skin disorder that results in depigmentation. With the appropriate management, many patients can minimize disease progression, attain repigmentation, and achieve cosmetically pleasing results. There are numerous medical and surgical treatments aimed at repigmentation; therapies for depigmentation are available for patients with recalcitrant or advanced disease. The use of cosmetics at all stages of treatment may be vital to the patient's quality of life. Understanding all the available options helps choose the appropriate treatment plan and tailor it to your patient. Part II of this two-part series on vitiligo discusses the indications for, evidence behind, and adverse effects associated with many of the therapies used for vitiligo. Both conventional medical and surgical options are discussed in addition to several alternative and promising new therapies.

Autoantibodies against tyrosine hydroxylase in patients with non-segmental (generalised) vitiligo

Vitiligo is an acquired idiopathic hypomelanotic skin disorder characterised by depigmented macules because of loss of cutaneous melanocytes. Although the exact cause of vitiligo remains obscure, evidence suggests that autoimmunity plays a role in the pathogenesis of the disease. Previously, tyrosine hydroxylase (TH) was identified as a putative autoantigen in vitiligo using phage-display technology. In this study, the prevalence of TH antibodies in patients with vitiligo was investigated. A radioimmunoassay (RIA) was used to detect TH antibodies in sera from patients with either non-segmental vitiligo (n=79), segmental vitiligo (n=8) or other autoimmune diseases without concomitant vitiligo (n=91). Sera from healthy individuals (n=28) were also tested. Patients with segmental vitiligo, healthy controls and patients with other autoimmune diseases without concomitant vitiligo were all negative for TH antibody reactivity. Of 79 patients with non-segmental vitiligo, 18 (23%) were positive for TH antibodies in the RIA, and a significant increase in the prevalence of TH antibodies in patients with non-segmental vitiligo was evident when compared with controls (P=0.003). TH antibody prevalence was also significantly elevated in patients with active vitiligo compared to those with stable disease (P=0.009). Overall, the results indicate that TH is an antibody target in non-segmental but not in segmental vitiligo and that TH antibodies appear to be more frequent in patients with active vitiligo.

Intraepidermal injection of dissociated epidermal cell suspension improves vitiligo

This study was initiated to evaluate the safety and effectiveness of intraepidermal injection of dissociated epidermal cells into the lesions of stable vitiligo patients. Autologous dissociated epidermal cell suspensions were injected intraepidermally into 10 stable vitiligo patients. None of the patients received adjuvant therapy. The response was evaluated as: marked (76-100%), moderate (51-75%), mild (26-50%) and minimal repigmentation (0-25%). Transmission electron microscopy was used to evaluate the transplanted cells and immunohistochemical staining with HMB-45 was performed to assess the repigmentation in vivo. In all cases, repigmentation started during the 4-week period after transplantation. Six months after transplantation, a marked repigmentation in four (40%), moderate repigmentation in two (20%) and mild repigmentation in two (20%) patients were observed. Two (20%) patients with white patches on their lids showed minimal repigmentation. No side effects were observed in any patients. Interestingly, repigmentation of gray hair in one patient, 4 months post transplantation was observed. Analysis of the ultrastructure of transplanted cells showed 1.5% of the cells had melanocyte morphology. HMB-45 positive cells were observed after cell transplantation. This method is an effective, simple and safe therapeutic option for stable vitiligo lesions.

Micronutrients and amino acids, main regulators of physiological processes

Human physiology is supposed to be a complex interaction of regulating processes, in which hormones, genes, their proteins and apoptosis are thought to play a dominant role. We hypothesize that regulation of physiological processes is mainly influenced by amino acids and micronutrients with hormones, proteins, apoptosis and gene modifications being their derivatives. Furthermore, we suppose that the cells power plant, the mitochondrion, is in fact an intracellular bacterium, living in absolute symbiosis. Because of its intracellular existence it depends on the host's micronutrients completely. Within the host these micronutrients regulate their own formation, degradation, uptake and excretion. Known deficiencies, such as iodine and vitamin D, affect billions of people. Many micronutrients neither have been investigated, nor have they been studied in relation to each other and solid data are not available. Optimal levels of many micronutrients and all amino acids are not known. Amino acids, vitamins and minerals are capable of altering gene expression, inducing apoptosis and regulating chemical processes. It makes them highly attractive for creating better health, against low cost, as we have already proven in the case of rickets, cretinism and scurvy in severe deficiencies. By creating optimal living conditions and study mitochondria from a symbiotic point of view we suppose that diseases not only can be prevented, but the course of diseases can be altered as well.

H(2)O(2) increases de novo synthesis of (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin via GTP cyclohydrolase I and its feedback regulatory protein in vitiligo

Patients with vitiligo accumulate up to 10(-3) mol/L concentrations of H(2)O(2) in their epidermis, which in turn affects many metabolic pathways in this compartment, including the synthesis and recycling of the cofactor (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (6BH(4)). De novo synthesis of 6BH(4) is dependent on the rate-limiting enzyme GTP cyclohydrolase I (GTPCHI) together with its feedback regulatory protein (GFRP). This step is controlled by 6BH(4) and the essential amino acid L-phenylalanine. In the study presented here we wanted to investigate whether H(2)O(2) affects the GTPCHI/GFRP cascade in these patients. Our results demonstrated concentration-dependent regulation of rhGTPCHI where 100 micromol/L H(2)O(2) was the optimum concentration for the activation of the enzyme and >300 micromol/L resulted in a decrease in activity. Oxidation of GFRP and GTPCHI does not affect feedback regulation via L-phenylalanine and 6BH(4). In vitiligo a constant upregulation of 6BH(4) de novo synthesis results from epidermal build up of L-phenylalanine that is not controlled by H(2)O(2). Taking the results together, 6BH(4) de novo synthesis is controlled by H(2)O(2) in a concentration-dependent manner, but H(2)O(2)-mediated oxidation does not affect the functionality of the GTPCHI/GFRP complex.

Anabolic function of phenylalanine hydroxylase in Caenorhabditis elegans

In humans, liver phenylalanine hydroxylase (PAH) has an established catabolic function, and mutations in PAH cause phenylketonuria, a genetic disease characterized by neurological damage, if not treated. To obtain novel evolutionary insights and information on molecular mechanisms operating in phenylketonuria, we investigated PAH in the nematode Caenorhabditis elegans (cePAH), where the enzyme is coded by the pah-1 gene, expressed in the hypodermis. CePAH presents similar molecular and kinetic properties to human PAH [S(0.5)(L-Phe) approximately 150 microM; K(m) for tetrahydrobiopterin (BH(4)) approximately 35 microM and comparable V(max)], but cePAH is devoid of positive cooperativity for L-Phe, an important regulatory mechanism of mammalian PAH that protects the nervous system from excess L-Phe. Pah-1 knockout worms show no obvious neurological defects, but in combination with a second cuticle synthesis mutation, they display serious cuticle abnormalities. We found that pah-1 knockouts lack a yellow-orange pigment in the cuticle, identified as melanin by spectroscopic techniques, and which is detected in C. elegans for the first time. Pah-1 mutants show stimulation of superoxide dismutase activity, suggesting that cuticle melanin functions as oxygen radical scavenger. Our results uncover both an important anabolic function of PAH and the change in regulation of the enzyme along evolution.

Regulation of melanogenesis--controversies and new concepts

Despite many efforts, regulation of skin and hair pigmentation is still not fully understood. This article focuses mainly on controversial aspects in pigment cell biology which have emerged over the last decade. The central role of tyrosinase as the key enzyme in initiation of melanogenesis has been closely associated with the 6BH4 dependent phenylalanine hydroxylase (PAH) and tyrosine hydroxylase isoform I (THI) providing evidence for an old concept of the three enzyme theory in the initiation of the pigmentation process. In this context, it is noteworthy that intracellular L-phenylalanine uptake and turnover to L-tyrosine via PAH is vital for substrate supply of THI and tyrosinase. While PAH acts in the cytosol of melanocytes, THI and tyrosinase are sitting side by side in the melanosomal membrane. THI at low pH provides L-3,4-hydroxyphenylalanine L-DOPA which in turn is required for activation of met-tyrosinase. After an intramelanosomal pH change, possibly by the p-protein, has taken place, tyrosinase is subject to control by 6/7BH4 and the proopiomelanocortin (POMC) peptides alpha-MSH melanocyte stimulating hormone and beta-MSH in a receptor independent manner. cAMP is required for the activation of microphthalmia-associated transcription factor to induce expression of tyrosinase, for transcription of THI and for activation of PAH. The redundancy of the cAMP signal is discussed. Finally, we propose a novel mechanism involving H2O2 in the regulation of tyrosinase via p53 through transcription of hepatocyte nuclear factor 1alpha which in turn can also affect the POMC response.

The Ca2+-binding capacity of epidermal furin is disrupted by H2O2-mediated oxidation in vitiligo

The Ca(2+)-dependent precursor convertase furin is abundantly expressed in epidermal keratinocytes and melanocytes. In this context, it is noteworthy that proopiomelanocortin (POMC) cleavage is also processed by furin, leading to ACTH, beta-lipotropin, and beta-endorphin. All prohormone convertases including furin are regulated by Ca(2+). Because numerous epidermal peptides and enzymes are affected by H(2)O(2)-mediated oxidation, including the POMC-derived peptides alpha-MSH and beta-endorphin as shown in the epidermis of patients with vitiligo, we here asked the question of whether furin could also be a possible target for this oxidation mechanism by using immunofluorescence, RT-PCR, Western blotting, Ca(2+)-binding studies, and computer modeling. Our results demonstrate significantly decreased in situ immunoreactivity of furin in the epidermis of patients with progressive vitiligo (n = 10), suggesting H(2)O(2)-mediated oxidation. This was confirmed by (45)Ca(2+)-binding studies with human recombinant furin identifying the loss of one Ca(2+)-binding site from the enzyme after oxidation with H(2)O(2). Computer simulation supported alteration of one of the two Ca(2+)-binding sites on furin. Taken together, our results implicate that the Ca(2+)-dependent proteolytic activity of this convertase is targeted by H(2)O(2), which in turn could contribute to the reduced epidermal expression of the POMC-derived peptides alpha-MSH and beta-endorphin as documented earlier in patients with vitiligo.

Autoimmunity as an aetiological factor in vitiligo

Vitiligo is a common dermatological disorder characterized by the presence on the skin of depigmented macules resulting from the destruction of cutaneous melanocytes. Autoimmunity is an important hypothesis with regard to vitiligo aetiology and the evidence for autoimmune responses being involved in the pathogenesis of this disorder will be discussed in the present review. All immune system compartments, including innate and adaptive immunity have been implicated in vitiligo development. Particularly relevant are autoantibodies and autoreactive T cells in vitiligo patients that have cytotoxic effects upon pigment cells. Furthermore, predisposition to vitiligo appears to be associated with certain alleles of the major histocompatibility complex class II antigens as well as with other autoimmune-susceptibility genes. Moreover, the association of vitiligo with autoimmune disorders, the animal models of the disease, and the positive response to immunosuppressive therapeutic agents emphasize the role of autoimmunity in the development of this disorder.

Structural and functional alterations in the ?2-adrenoceptor are caused by a point mutation in patients with atopic eczema

The density of beta2-adrenoceptors is significantly decreased in both keratinocytes and peripheral blood lymphocytes from patients with atopic eczema. Furthermore both cell types showed a sixfold increase in the K(D) for the specific binding of the non-specific antagonists (-)-[(3)H]CGP 12177 and [(125) I]CYP to keratinocytes and lymphocytes respectively compared with healthy controls. Based on these results polymorphism in the beta2-adrenoceptor gene was suspected. Consequently the entire intronless beta2-adrenoceptor gene was isolated from whole blood and by RT-PCR from keratinocyte extracts of nine patients with atopic eczema and four healthy controls. DNA sequence analysis of nine atopic eczema patients confirmed a substitution in codon (1618) GCC (Ala(119)) to GAC (Asp(119)). This point mutation is expressed on the third transmembrane helix only 13A away from the established agonist/antagonist binding site at Asp(113). Computer modelling of this third transmembrane helix revealed substantial structural changes in the mutant compared with the wild type. Epidermal keratinocytes were established from one patient with atopic eczema (homozygote), the mother (heterozygote) and one age-matched healthy control. Cells were grown in media containing different concentrations of l-phenylalanine and receptor densities were determined. The results showed that cells with atopic eczema showed an increased sensitivity to l-phenylalanine concentrations with a narrow homeostasis compared with healthy controls. The heterozygous mother was only 50% as sensitive as the child. In summary, the results indicate that atopic eczema is associated with a single point mutation in the beta2-adrenoceptor gene leading to an impaired adrenergic response in the epidermis of these patients.

Vitiligo: the historical curse of depigmentation

Vitiligo has been mentioned in the tomes of every major religion, with its first description dating back more than 3000 years, to the earliest Vedic and Egyptian texts. Despite this ancient recognition, confusion with disorders such as leprosy has been a problem throughout the ages. This has lead to the stigmatization of vitiligo sufferers. This is a social problem that is still widespread in some, but not all, parts of the world. The ancients also practiced phototherapy for vitiligo. This practice only became common in the Western world with development of psoralen plus ultraviolet A and later ultraviolet B phototherapy in the latter half of the 20th century. In this article, the history of vitiligo up until the end of the 20th century is outlined, covering medical, scientific, and social aspects.

Hydrogen peroxide-mediated oxidative stress disrupts calcium binding on calmodulin: More evidence for oxidative stress in vitiligo

Patients with acute vitiligo have low epidermal catalase expression/activities and accumulate 10(-3) M H(2)O(2). One consequence of this severe oxidative stress is an altered calcium homeostasis in epidermal keratinocytes and melanocytes. Here, we show decreased epidermal calmodulin expression in acute vitiligo. Since 10(-3)M H(2)O(2) oxidises methionine and tryptophan residues in proteins, we examined calcium binding to calmodulin in the presence and absence of H(2)O(2) utilising (45)calcium. The results showed that all four calcium atoms exchanged per molecule of calmodulin. Since oxidised calmodulin looses its ability to activate calcium ATPase, enzyme activities were followed in full skin biopsies from lesional skin of patients with acute vitiligo (n=6) and healthy controls (n=6). The results yielded a 4-fold decrease of ATPase activities in the patients. Computer simulation of native and oxidised calmodulin confirmed the loss of all four calcium ions from their specific EF-hand domains. Taken together H(2)O(2)-mediated oxidation affects calcium binding in calmodulin leading to perturbed calcium homeostasis and perturbed l-phenylalanine-uptake in the epidermis of acute vitiligo.

Advances in melanocyte basic science research

This article focuses on recent advances in melanocyte biology and physiology. The major function of this neural crest-derived cell is the production of melanins. A "three enzyme theory" in the initiation of pigmentation is put forward and backed up by recent findings. A receptor-independent role for alpha-MSH and the cofactor (6R)-l-erythro-5,6,7,8-terahydrobiopterin (6BH(4)) in the control of tyrosinase is described. The importance of intramelanosomal pH for melanogenesis is covered. Finally, the redundancy of the cAMP and IP3/DAG/calcium signal in melanocytes together with the downstream events are highlighted. The main message of this article is that the intracellular H(2)O(2)- redox-equilibrium controls melanocyte function in a concentration-dependent manner.

Specific interaction of the diastereomers 7(R)- and 7(S)-tetrahydrobiopterin with phenylalanine hydroxylase: implications for understanding primapterinuria and vitiligo

Pterin-4a-carbinolamine dehydratase (PCD) is an essential component of the phenylalanine hydroxylase (PAH) system, catalyzing the regeneration of the essential cofactor 6(R)-L-erythro-5,6,7,8-tetrahydrobiopterin [6(R)BH4]. Mutations in PCD or its deactivation by hydrogen peroxide result in the generation of 7(R,S)BH4, which is a potent inhibitor of PAH that has been implicated in primapterinuria, a variant form of phenylketonuria, and in the skin depigmentation disorder vitiligo. We have synthesized and separated the 7(R) and 7(S) diastereomers confirming their structure by NMR. Both 7(R)- and 7(S)BH4 function as poor cofactors for PAH, whereas only 7(S)BH4 acts as a potent competitive inhibitor vs. 6(R)BH4 (Ki=2.3-4.9 microM). Kinetic and binding studies, as well as characterization of the pterin-enzyme complexes by fluorescence spectroscopy, revealed that the inhibitory effects of 7(R,S)BH4 on PAH are in fact specifically based on 7(S)BH4 binding. The molecular dynamics simulated structures of the pterin-PAH complexes indicate that 7(S)BH4 inhibition is due to its interaction with the polar region at the pterin binding site close to Ser-251, whereas its low efficiency as cofactor is related to a suboptimal positioning toward the catalytic iron. 7(S)BH4 is not an inhibitor for tyrosine hydroxylase (TH) in the physiological range, presumably due to the replacement of Ser-251 by the corresponding Ala297. Taken together, our results identified structural determinants for the specific regulation of PAH and TH by 7(S)BH4, which in turn aid in the understanding of primapterinuria and acute vitiligo.

Analysis of allelic variants in the catalase gene in patients with the skin depigmenting disorder vitiligo

Vitiligo is an acquired hypomelanotic skin disorder characterised by circumscribed depigmented macules resulting from the loss of functional melanocytes from the cutaneous epidermis. Conditions that might result in epidermal oxidative stress and consequently damage to pigment cells have been reported in the skin of vitiligo patients, including low catalase activity and increases in hydrogen peroxide levels. However, the cause of the decrease in catalase activity has not been equivocally determined. Several allelic variants in the catalase gene, a number of which have deleterious effects upon the expression or function of the enzyme, have been described and the aim of the present work was to assess the relevance of catalase gene variants in patients with vitiligo. Associations between ten separate allelic variants in the catalase gene and a predisposition to vitiligo were investigated in case-control studies with 166 English patients and 169 ethnically-matched controls using DNA sequencing and restriction fragment length polymorphism-polymerase chain reaction methods. Of the ten allelic variants analysed, only a C/T single nucleotide polymorphism in exon 9 of the catalase gene was associated with vitiligo. The C/T genotype was significantly over-represented in the vitiligo patient group compared with the control cohort. Of 166 vitiligo genotypes, 66 (39.8%) had the C/T variant compared to 45/169 (26.6%) control genotypes (P = 0.030). No evidence for an association between other allelic variants in the catalase gene and vitiligo susceptibility was found. The low catalase activity in vitiligo patient epidermis is more likely to result from environmental conditions such as inhibitory levels of hydrogen peroxide rather than allelic variations in the catalase gene which affect either expression or function of the enzyme.