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.

[Vitiligo--loss of cutaneous pigmentation]

BACKGROUND

Vitiligo is an acquired pigmentary skin disorder that affects 0.5-2% of the population. Many patients contact their physician and alternative therapists for help. This review article presents an update of knowledge about vitiligo and is aimed at physicians that treat this patient group.

METHOD

The article is based on literature identified on PubMed, textbooks in Dermatology and supplemented by clinical experience.

RESULTS AND INTERPRETATION

Vitiligo is characterized by the absence of melanocytes in skin and hair follicles. The pathogenesis is complex with genetic, autoimmune and toxic contributors. Clinically well-defined milk-white maculae are seen in the skin, with a wide variety of spread and distribution. The debut of vitiligo is often in childhood and adolescence. Investigations indicate that vitiligo affects quality in life for both children and adults. Treatment of vitiligo is a challenge. Phototherapy with narrowband UVB or topical therapy with tacrolimus ointment or potent steroids may be indicated in some cases, but the effect is not well documented.

Vitiligo: a sign of systemic disease

Vitiligo reflects a systemic process that has important implications beyond the skin. These include other autoimmune diseases and ocular and neurological abnormalities. Alezzandrini syndrome and Vogt-Koyanagi-Harada syndrome particularly exemplify this relationship. In addition, vitiligo may be confused with other systemic disorders, including tuberous sclerosis, progressive systemic sclerosis (scleroderma), melanoma, and, in endemic regions, leprosy. We describe these associations and emphasize the importance of depigmenting disorders.

Skin diseases in consequence of endocrine alterations

The skin is a target organ of several hormones. Specific diseases appear in consequence of hypo- or hypersecretion of endocrine organs, particularly in the elderly patient. There, knowledge of skin alterations is important not only for dermatologists, but also for endocrinologists and other physicians, because a clinical diagnosis of the underlying disease is often possible. In this review, a number of representative skin diseases having an endocrinological basis are described. These include acanthosis nigricans, diseases due to alterations of androgen metabolism, carcinoid syndrome, diseases due to alterations of corticosteroid metabolism, diseases in association with diabetes mellitus, diseases due to alterations of estrogen metabolism, genetic syndromes including dermatological and endocrine symptoms, the glucagonoma syndrome, diseases due to dysfunctions of growth hormone secretion, diseases in association with Merkel cells of the skin, diseases due to dysfunctions of the thyroid gland, diseases to alteration of vitamin D metabolism, and vitiligo and disorders of pigmentation.

Disseminated vitiligo associated with AIDS

We report a case of vitiligo arising one year after human immunodeficiency virus (HIV) seropositivity but before clinical onset of acquired immunodeficiency syndrome (AIDS). To our knowledge, this specific time sequence has not been described. Generalization of such lesions began during a period of medical noncompliance, increasing viral load, rising CD8+ count, and markedly decreased CD4+ count. These findings suggest new mechanisms of autoimmune and infectious pathogenesis.

Cutaneous manifestations in celiac disease

Celiac disease (CD) is an autoimmune gluten-dependent enteropathy characterized by atrophy of intestinal villi that improves after gluten-free diet (GFD). CD is often associated with extra-intestinal manifestations; among them, several skin diseases are described in CD patients. The present review reports all CD-associated skin manifestations described in the literature and tries to analyze the possible mechanisms involved in this association. The opportunity to evaluate the possible presence of CD in patients affected by skin disorders is discussed.

Pseudovitiligo in Systemic Sclerosis

Progressive Systemic Sclerosis is a chronic connective tissue disease characterized by sclerosis of skin with involvement of the internal organs. The cause of PSS is unknown but autoimmune mechanisms and primary damage to blood vessels have been proposed to explain its pathogenesis. We report a case of PSS with widespread depigmentation resembling vitiligo.

Vitiligo

Vitiligo represents a selective destruction of the melanocytes. It is a relatively common, probably autoimmune disorder that affects people of all backgrounds and both genders. No particular group seems to be preferentially affected. Half of vitiligo patients have an onset before the age of 18 years. In regions where leprosy is endemic, individuals with vitiligo are often stigmatized due to similarities in appearance between the two diseases. We will review this important subject, emphasizing the latest therapeutic advances.

Immunogenicity, including vitiligo, and feasibility of vaccination with autologous GM-CSF-transduced tumor cells in metastatic melanoma patients

PURPOSE

To determine the feasibility, toxicity, and immunologic effects of vaccination with autologous tumor cells retrovirally transduced with the GM-CSF gene, we performed a phase I/II vaccination study in stage IV metastatic melanoma patients.

PATIENTS AND METHODS

Sixty-four patients were randomly assigned to receive three vaccinations of high-dose or low-dose tumor cells at 3-week intervals. Tumor cell vaccine preparation succeeded for 56 patients (88%), but because of progressive disease, the well-tolerated vaccination was completed in only 28 patients. We analyzed the priming of T cells against melanoma antigens, MART-1, tyrosinase, gp100, MAGE-A1, and MAGE-A3 using human leukocyte antigen/peptide tetramers and functional assays.

RESULTS

The high-dose vaccination induced the infiltration of T cells into the tumor tissue. Three of 14 patients receiving the high-dose vaccine showed an increase in MART-1- or gp100-specific T cells in the peripheral blood during vaccination. Six patients experienced disease-free survival for more than 5 years, and two of these patients developed vitiligo at multiple sites after vaccination. MART-1- and gp100-specific T cells were found infiltrating in vitiligo skin. Upon vaccination, the T cells acquired an effector phenotype and produced interferon-gamma on specific antigenic stimulation.

CONCLUSION

We conclude that vaccination with GM-CSF-transduced autologous tumor cells has limited toxicity and can enhance T-cell activation against melanocyte differentiation antigens, which can lead to vitiligo. Whether the induction of autoimmune vitiligo may prolong disease-free survival of metastatic melanoma patients who are surgically rendered as having no evidence of disease before vaccination is worthy of further investigation.

Vitiligo presentation in adults

The characteristics of vitiligo in 41 adults presenting to a university dermatology clinic in Sheffield, UK were studied in a case review. Of 41 patients, 29 women and 12 men, there were 37 European Caucasians, three Asian Caucasians and one black African. Symmetrical and acrofacial types of vitiligo predominated but there were no segmental cases. Age of onset was before 20 years in 17, with a mean of 28 years; the oldest onset was 74 years. The average duration of the disease was 16 years. Autoimmune thyroid disease was present in 14 cases (34%). Only seven (18%) gave a family history of vitiligo. A precipitating factor was identified in nine (22%), including pregnancy, sunburn and skin trauma. Topical steroid treatment was given in 33 and narrow-band ultraviolet B was prescribed in nine. This series is unusual in having no cases of segmental vitiligo, perhaps because no children are included, and in having a high prevalence of thyroid disease.

Different clinical and laboratory evolutions in ataxia-telangiectasia syndrome: report of four cases

We report four patients with ataxia-telangiectasia syndrome that presented varied neurologic evolution. Three patients initially presented neurologic alterations of slow progression, evolving to late immunocompromised conditions. The fourth patient presented, from symptom onset, immune and neurologic debilitation, that were both severe and of fast progression. The chronological sequence of the most commonly observed immunocompromised conditions were in our patients, in ascending order, IgA deficiency, IgG2 deficiency and the neutrophil phagocytosis stage and common variable immunodeficiency. The first two reports are of sisters in whom the diagnosis was done between the ages of three and six years, having ocular apraxia, cerebellar ataxia and telangiectasia. Slow progression of neurologic debilitation was observed, without presentation of intermittent infections. The patients began presenting accentuated immunocompromised conditions at the ages of 14 and 17 years, dying at the ages of 16 and 20 years, respectively, due to severe infections that were resistant to treatment. The diagnosis of the third case was established when the patient was two years old, presenting ataxia and telangiectasia. Syndrome progression was slow, presenting at the age of eight years more accentuated neurologic disorders and IgA deficiency. The fourth case presented significant neurologic compromise at the age of five, simultaneous to IgA and IgG2 deficiency, and repeating pneumonias and sinusitis. At this time, intravenous gammaglobulin reposition was done. The neurologic and immune disorders progressed rapidly, and at the age of eight presented the inability to walk. At this time inversion of the CD4/CD8 ration was verified through laboratory tests.

Halo dermatitis followed by the development of vitiligo associated with Sutton's nevi

Halo dermatitis (Meyerson's nevus) is an inflammatory, sometimes itchy, eczematous eruption usually encircling a preexisting melanocytic nevus that can be mistaken for malignant melanoma or Sutton's nevus. Unlike the latter, it mostly resolves spontaneously within weeks and never causes regression of the central lesion. Sutton's nevi, however, are frequently found in otherwise healthy individuals and patients suffering from vitiligo or malignant melanoma. The simultaneous appearance of Sutton's nevus and halo dermatitis has been reported before. However, the causes of both diseases remain unclear. We report a 16-year-old female who developed vitiligo and Sutton's nevi 6 months after a halo dermatitis lesion was excised. The coincidence of these disorders suggests common or similar immunological mechanisms induced by pigment cells and/or their components.

Vitiligo as a paraneoplastic syndrome preceding pituitary adenoma and subsequent acute lymphoblastic leukemia

We present an unusual case of rapid onset of vitiligo heralding blindness due to pituitary apoplexy secondary to a non-secreting pituitary adenoma in a 49-year-old man. Deterioration in vision and skin condition coincided with tumor progression over 3 years. He subsequently died of acute lymphoblastic leukemia after pituitary radiation. The possible pathological associations between the 2 malignancies and vitiligo are discussed.

Halo nevus, rather than vitiligo, is a typical dermatologic finding of Turner's syndrome: Clinical, genetic, and immunogenetic study in 72 patients

Turner's syndrome (TS) is a genetic disorder caused by numeric and/or structural abnormalities of the X chromosome; it is characterized by short stature, gonadal dysgenesis, and frequently by webbed neck, cubitus valgus, and lymphedema at birth. TS has been associated with several cutaneous abnormalities including an increased frequency of pigmented nevi, but few reports consider nevi in detail. Halo nevus (HN) is clinically defined as a melanocytic nevus surrounded by a halo of depigmentation. Vitiligo, a dermatologic disorder characterized by the presence of depigmented patches on the skin, has been described in the list of cutaneous findings associated with TS. The aim of this study was to determine the prevalence of HN and vitiligo in TS and to evaluate if a correlation between major histocompatibility complex genes, karyotype, autoimmunity, therapies, and the presence of HN exists. Of the 72 patients with TS examined, 13 had HN, a prevalence of 18.05%, which was significantly higher than in our control group (1%; P=.000001). On the contrary, only 2 patients with TS (2.77%, P=not significant) had vitiligo. By comparing the distribution of HLA class I alleles between patients with TS who did (13 of 72) and did not (59 of 72) have HN, we observed a significantly higher frequency of HLA-Cw6 in patients with TS and HN than in those without HN (26.92% vs 6.78%, respectively; P=.0067; odds ratio=5.06). The study of HLA class II genomic polymorphisms showed that the DRB1(*)0701 and DQB1*02 alleles for patients with TS and HN were overrepresented when compared with those without HN (34.61% vs 11.86%, respectively, P=.0078, odds ratio=3.93; and 34.61% vs 19.49%, respectively, P=.1386, odds ratio=2.19). In conclusion, this study is the first to demonstrate an increased prevalence of HN for patients with TS. Furthermore, the data suggest that a HN putative susceptibility gene in TS is located close to the HLA-C locus.

Association of angiotensin converting enzyme gene I/D polymorphism of vitiligo in Korean population

Vitiligo (leukoderma) is an acquired idiopathic hypomelanotic disorder characterized by the circumscribed depigmented patches. Vitiligo is a polygenic disease. The exact pathogenesis is not yet known. The angiotensin converting enzyme (ACE) gene was selected as a candidate gene as ACE plays an important role in the physiology of the vasculature, blood pressure and inflammation, and its relationship with various diseases, including autoimmune diseases, has been widely investigated. The I/D polymorphism of ACE gene in vitiligo patients has not been reported. In this study, we investigated ACE gene polymorphism in 120 vitiligo patients and in 429 healthy volunteers in Korea. The ACE gene genotype distribution (P = 0.032) and allele frequency (P = 0.012) were significantly different between vitiligo patients and healthy controls. This study suggests that the ACE gene polymorphism has a strong association with the development of vitiligo in Korean patients.

Trigger factors in childhood psoriasis and vitiligo

Psoriasis and vitiligo are very common skin disorders that may have a profound impact upon the affected individuals; the etiology of both diseases includes genetic factors and triggers, which could be endogenous or exogenous. Two groups of children population consisting of 153 patients suffering from skin disorder (65 with vitiligo and 88 with psoriasis) have been examined at the Department of Dermatovenerology, University Hospital Osijek, during three years period. Basic methods of data collection were: questionnaire, clinically examination and histological proven diagnosis. The aim of this investigation were to determine the most common triggers, which play a role at onset of disease among young patients with vitiligo and psoriasis, and to establish familial distribution among both groups of patients. The results of investigations showed that the onset of vitiligo was mostly connected with psychological factors (56.9%), but the most frequently trigger in childhood psoriasis was inflammatory focus (38.6%). According to morphologic patterns the authors separated two groups of patients among psoriatics: group I with plaque psoriasis, which pointed the inflammatory focus and physical trauma as trigger before onset of disease (each 25.0%) and group II with psoriasis guttata and inflammatory focus as trigger at even 62.5% cases. Familial distribution among psoriatic children was 55.6%, and among children with vitiligo only 16.9%. Ours children patients showed significantly disparity in structure of triggers according diagnosis and gender distributions and about familial occurrence. Also some difference has been established according to age of onset between psoriasis and vitiligo at early childhood.

Vaccination-induced autoimmune vitiligo is a consequence of secondary trauma to the skin

A major concern for cancer vaccines targeting self-tumor antigens is the risk of autoimmune sequelae. Although antitumor immunity correlates with autoimmune disease in some preclinical models, the mechanism(s) linking antitumor immunity and subsequent autoimmune pathology remain(s) to be determined. In the current study, we demonstrated that intradermal (i.d.) immunization with a recombinant adenovirus (Ad) expressing the murine melanoma antigen tyrosinase-related protein 2 (AdmTrp-2) results in a moderate level of tumor protection against the B16F10 murine melanoma without any vitiligo. Similar immunization with an Ad encoding human Trp-2 (AdhTrp-2) resulted in 50-fold greater protective immunity and produced vitiligo in all of the mice, suggesting that the development of autoimmunity may reflect the potency of the vaccine. Interestingly, delivery of AdhTrp-2 by i.m. injection generated protective immunity comparable with that seen in mice that received the vaccine by the i.d. route, but none of the recipients in the i.m. group developed vitiligo. The cellular and humoral responses in the i.m. immunized mice were greater than in the i.d. group; therefore, the lack of vitiligo was not caused by reduced efficacy of the vaccine. These results led us to hypothesize that vaccine-induced vitiligo was associated with local inflammatory responses. Mice immunized i.m. with AdhTrp-2 did develop vitiligo when they subsequently were injected i.d. with either a control Ad vector or complete Freund's adjuvant, suggesting that vitiligo is initiated by some form of trauma within the skin. Our data demonstrated that autoimmune pathology is not an unavoidable outcome of effective cancer vaccines directed against self-tumor antigens.