Vitiligo--a window in the darkness.
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Biopterins↗
Biomedical subjects
W Westerhof
Publications and source records attributed to W Westerhof.
Treatment of generalized bullous pemphigoid with topical corticosteroids.
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Administration, Cutaneous↗
Stromal cells from subcutaneous adipose tissue seeded in a native collagen/elastin dermal substitute reduce wound contraction in full thickness skin defects.
BACKGROUND: Dermal substitutes seeded with cultured fibroblasts have been developed to improve dermal regeneration in full thickness wounds. Because of cell cultivation, 3 weeks are required before patients can be treated with these autologous adipose tissue. This substitute is easily fabricated within hours, which allows immediate treatment of full thickness defects. EXPERIMENTAL DESIGN: Porcine full thickness wounds were substituted with native collagen/alpha-elastin hydrolysate matrices. One group of matrices was left unseeded as negative control. The second was seeded with cultured dermal fibroblasts as positive control. The third was seeded with a stromal-vascular-fraction of adipose tissue, and the fourth was seeded with a stromal fraction with few vascular fragments (SF). All substitutes were covered with split skin mesh grafts and were protected against dehydration and infection with a microporous polyether urethane membrane. For 8 weeks, weekly biopsies were taken, myofibroblasts and fibroblasts were counted, thickness of the granulation tissue band was measured, and wound contraction and histology were evaluated. RESULTS: Negative control and stromal-vascular-fraction substitutes were invaded by high numbers of myofibroblasts and fibroblasts. They did not reduce wound contraction, and scar tissue was formed. SF substitutes reduced the accumulation of myofibroblasts and fibroblasts and prevented the formation of granulation tissue. As a result, dermal regeneration improved, and wound contraction was less than by the other substitutes. CONCLUSIONS: Adipose tissue cell isolates included vascular fragments containing endothelial cells. Seeded in dermal substitutes, these vascular fragments induced hypergranulation tissue formation and caused wound contraction. SF substitutes contained few endothelial cells. As a result, the contraction arresting effect of the seeded stromal cell fraction was effective. Our concept of a cellular dermal substitute seeded with stromal cells from adipose tissue is feasible and allows immediate treatment of full thickness skin defects.
Adipose Tissue↗
Catechol-O-methyltransferase as a target for melanoma destruction?
Catechols may interfere in melanogenesis by causing increased levels of toxic quinones. Several catechols and known inhibitors of the enzyme catechol-O-methyltransferase (COMT) were therefore tested for their toxicity towards a pigmented melanoma cell line, UCLA-SO-(M14). The inhibition of thymidine incorporation as a result of exposure to the compounds was measured. All agents were compared to 4-hydroxyanisole (4HA), a depigmenting agent extensively studied as an antimelanoma drug. The compounds were also tested on the epithelial cell line, CNCM-I-(221) in the presence and absence of tyrosinase. All the compounds were more effective than 4HA towards the M14-cells at either 10(-4) M or 10(-5) M. The toxicity of 4HA towards the 221-cells was shown to be completely dependent on the presence of tyrosinase. Effects of the test agents on the 221-cells were also observed in the absence of tyrosinase. Although some of them were shown to be good substrates for tyrosinase only small changes in toxicity were observed as a result of the presence of the enzyme in comparison with 4HA. No direct correlation of the toxicity of the agents and COMT inhibition was observed. The possible mode of action of the compounds through inhibition of COMT and interference in melanogenesis is discussed together with other possibilities and factors involved.
Anisoles↗
Catechol-O-methyltransferase in vitiligo.
Catechol-O-methyltransferase (COMT) is involved in the metabolism of neurotransmitters such as epinephrine, norepinephrine and dopamine. For melanocytes, the enzyme is of particular importance in preventing the formation of toxic o-quinones during melanin synthesis. It has been suggested that COMT plays a regulatory role in melanin synthesis. Indeed, when the melanin precursor molecule DHI(2C) is methylated by COMT it is no longer available for incorporation into melanin. Auto-destruction by intermediates of melanin metabolism has been implicated in the aetiology of vitiligo. Therefore enzyme activities in vitiligo patients and in healthy controls were compared. Systemic COMT activities were measured using red blood cells (RBC) as starting material. However, as local alterations in COMT activity may be specifically involved in vitiligo, the enzyme activity was also measured in epidermal homogenates. Finally, to ascribe epidermal COMT activity to the responsible cell type(s), enzyme activity was measured in cultured vitiligo non-lesional melanocytes and melanocytes from healthy controls as well as in cultured keratinocytes from lesional skin and in purified keratinocytes from control skin. It was found that epidermal homogenates from vitiligo patients expressed higher levels of COMT activity than homogenates from healthy controls. Such differences were not found at the systemic level (i.e. in RBC) nor could they be explained by measurements on separately cultured epidermal cell types, indicating that the COMT activity was induced at the tissue level by extracellular factors.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Treatment of generalized bullous pemphigoid with oral tetracycline.
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Administration, Oral↗
Tissue repair: Where do we stand?
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Journal Article↗
Organotypic culture of human skin to study melanocyte migration.
An ex vivo model system was developed to investigate melanocyte migration. Within this model system, melanocytes migrate among other epidermal cells in the epibolic outgrowth of skin explants. This process is initiated by loss of contact inhibition of epidermal cells at the rim of the explants and by locally produced chemotactic factors. Punch biopsies provided explants of reproducible diameter. Optimal culture conditions include medium consisting of Dulbecco's Minimal Essential Medium containing 10% inactivated normal human serum and placement of explants epidermal side up at the air-liquid interphase. Within 7 days, epidermal cells completely surround the explant. Approximately 3 days after the onset of keratinocyte migration, melanocytes distribute themselves within the newly formed epidermis. Throughout the 7-day culture period, melanocytes and keratinocytes show maintenance of subcellular morphology, and the dermo-epidermal junction remains intact. Melanocyte migration was quantified using immunoperoxidase staining in combination with light microscopy and computer-aided image analysis. Preliminary results using the model system to compare migration in control and nonlesional vitiligo skin indicate that no inherent migration defect is responsible for impaired repigmentation of vitiligo lesions. The organotypic culture model system allows for investigations on melanocytes within their environment of autologous epidermal and dermal components, closely resembling in vivo circumstances in human skin.
Adult↗
O-methylation of L-dopa in melanin metabolism and the presence of catechol-O-methyltransferase in melanocytes.
O-Methylation of L-dopa was investigated as a possible regulatory mechanism in melanin metabolism. The methylation product of L-dopa, 3-O-methoxytyrosine was detected in extracts of cultured human melanocytes. The enzyme catechol-O-methyltransferase is responsible for this O-methylation and that of the dihydroxyindolic intermediates of melanogenesis. The enzyme is present in melanocytes in its soluble and membrane-bound isoforms. Immuno-electron microscopy suggests the presence of the membrane-bound enzyme in the endoplasmic reticulum. This localization may indicate a role of catechol-O-methyltransferase in protecting the melanocyte against reactive dihydroxyphenolic intermediates of melanogenesis leaking from the melanogenic compartments. On the other hand, the O-methylation of L-dopa may serve as a regulatory point in melanogenesis during early stage of tyrosinase processing in the endoplasmic reticulum.
1-Methyl-3-isobutylxanthine↗
L-phenylalanine and UVA irradiation in the treatment of vitiligo.
In order to evaluate the efficacy of L-phenylalanine (L-Phe) in combination with UVA therapy for vitiligo an open trial (149 patients, 18 months) and a small double-blind trial (32 patients, 6 months) were conducted. Oral L-Phe loading resulted in peak plasma levels of L-Phe after 30-60 min and a slight increase in the plasma tyrosine level. Response to L-Phe plus UVA irradiation was positive, and various grades of repigmentation not exceeding 77% in the open and 60% in the blind trial were observed. An increased L-Phe dose resulted in increased L-Phe plasma levels but not in improved clinical results. The optimal L-Phe dose appears to be lower than 50 mg/kg/day. Although it is difficult to draw firm conclusions from the present investigation, we think that L-Phe may have a place in the treatment of vitiligo and its role merits further investigation.
Administration, Oral↗
A novel, antigen-presenting function of melanocytes and its possible relationship to hypopigmentary disorders.
It is now well established that cultured human melanocytes are capable of expressing immunologically important cell surface molecules and that they can produce cytokines. Not all cells with the ability to express MHC class II molecules are capable of effective Ag presentation. However, the dendritic nature of melanocytes, their strategic position within the skin, and their phagocytic capacity seem to suggest a role for these cells in processing and presenting Ag. This study demonstrates that cultured normal human skin melanocytes can present peptide Ag, and process and present the mycobacterial HSP65 kDa protein and whole Mycobacterium leprae sonicate to CD4+ cytotoxic proliferative T cell clones in an Ag-specific and HLA-class II-restricted manner. T cell stimulation was dependent on costimulatory signals, i.e., LFA-3/CD2 and LFA-1/ICAM-1. Besides eliciting a T cell proliferative response, our studies further demonstrate that melanocytes can function as target cells for T cell-mediated cytotoxicity. The described Ag-processing and -presenting functions of melanocytes, taken together with in vivo behavior of melanocytes in hypopigmentation, provide new clues for the etiopathogenesis of melanin pigmentary disorders.
Antigen Presentation↗
[Turning white overnight, is it possible?].
A female aged 64 reported sudden whitening of the hair. Analysis proved it to be alopecia areata. Rarely, alopecia areata is of diffuse onset. If in such a case it is mostly the pigmented hairs that are lost the impression can be made of a person with grey hair turning white overnight. A review is given of some historical cases which may have been caused by this phenomenon.
Alopecia Areata↗
Phagocytosis by normal human melanocytes in vitro.
Phagocytosis is an important first step in processing of antigens ultimately to be presented in the context of MHC class II molecules on the cell surface. Degradation of internalized antigens can then proceed by fusion of the phagosome with organelles containing lysosomal enzymes. Evidence for the phagocytic capacity of cultured normal human skin melanocytes is provided, both by electron microscopy and by confocal laser scanning microscopy. The phagocytic capacity of melanocytes is approximately 5% of that found for cultured human dermal skin fibroblasts. However, in a mixed culture of keratinocytes and melanocytes, uptake of 1 micron latex beads in 72 h was found to be comparable for both epidermal cell types, implicating in vivo significance for phagocytosis by melanocytes. Furthermore, it is shown that phagosomes containing latex beads will fuse with melanosomes, indicating that melanosomes can function as specialized lysosomal organelles within normal human skin melanocytes. The present investigation indicates that melanocytes are equipped with the phagocytic machinery important for the processing of antigens and thus may function as accessory cells within the skin immune system.
Humans↗
Expression of different immunological markers by cultured human melanocytes.
The expression of different immunological markers by cultured human melanocytes (MC) in relation to immune phenomena, were investigated on ten different MC cell lines from early (1st) to late (22nd) passage. Four melanocyte lines (MC-a) which had undergone changes in growth behaviour during prolonged culture were included in the study, together with two melanoma lines. Cytospin preparations of the cells were stained for the presence of a set of different immunological markers and a melanoma-associated antigen (MAA). All MC lines, including the MC-a and the melanoma lines, showed expression of MHC class I, IL-1, IL-2, ICAM-1 and the MAA, NKI-Beteb, during all passages tested. Interestingly, four of the MC lines showed staining for the Fc receptor. A tendency towards a stronger expression of ICAM-1 on a higher percentage of cells was observed on MC with increasing passage number, the MC-a and the melanoma lines. Expression of the MAA was strongly reduced for the MC-a lines in comparison with the MC and the M14 melanoma lines. Positive staining for the HLA class II molecules was obtained on MC of intermediate and late passages, and on the MC-a and the melanoma lines in the decreasing order HLA-DR, DP and DQ. Additionally, we carried out a preliminary study showing that cultured MC also produce IL-1 and IL-6. However, we were not able to show the production of biologically active IL-2 testing several cultured MC lines. Nevertheless, the overall results taken together suggest that MC are immunologically important cells that are susceptible to changes during long-term culture.
Antibodies, Monoclonal↗
Dermal substitutes for full-thickness wounds in a one-stage grafting model.
We tested different biodegradable matrix materials as dermal substitutes in a porcine wound model. Matrixes were covered with a split-skin mesh graft and protected with a microporous, semipermeable membrane, which prevents blister formation, wound infection and provides ultimate healing conditions. Evaluation parameters were as follows: epithelization, dermal reconstitution, wound contraction, and cosmetic and functional aspect. A microfibrillar matrix of nondenatured collagen gave the best result, with immediate fibroblast ingrowth and epidermal outgrowth. Slight inflammatory reaction and minimal wound contraction were observed. Application of a split-skin mesh graft, in combination with this collagen matrix, generated a thicker dermal layer than did a split-skin mesh graft directly applied on a wound bed. However, the histologic dermal architecture was less optimal than one obtained with a full-thickness punch graft method. Other matrixes caused inflammatory reactions, interfering with epithelization and dermal reconstitution. We conclude that a nondenatured collagen matrix, in combination with a split-skin mesh graft, can provide a substitute dermis in a full-thickness wound. This combination is preferable to a split-skin mesh graft directly applied on the wound bed. With our microporous semipermeable membrane, the combined use of a dermal substitute and a split-skin mesh graft can be applied in a single-stage operation.
Journal Article↗
Presence or absence of melanocytes in vitiligo lesions: an immunohistochemical investigation.
There is a long-standing controversy over whether melanocytes in vitiligo lesions are actually lost or are still present but inactivated. Resolving this matter is essential for understanding the underlying pathology and for the development of treatment. Standard methods of detecting melanocytes are based on active melanin synthesis. However, it is possible that inactive melanocytes remain in the lesions. There are no methods presently available to detect such dormant melanocytes. Using a panel of one polyclonal and 17 monoclonal antibodies directed against melanocytic cells (largely selected by the European Organisation for Research and Treatment of Cancer Melanoma Group for diagnostic and therapeutic purposes), we investigated the absence or inactivation of melanocytes in vitiligo by immunohistochemistry. Results using this panel of antibodies on frozen skin sections suggest that melanocytes are indeed absent in the lesions. However, in epidermal split-skin preparations, residual staining was occasionally observed. To determine whether the staining obtained was due to degenerated melanocytes, confocal laser scanning microscopy was used. Immunofluorescent staining using the antibody NKI-beteb confirmed this to be the case. The results presented here strongly suggest that melanocytes are indeed lost in vitiligo lesions.
Adolescent↗
Review of the etiopathomechanism of vitiligo: a convergence theory.
Vitiligo is an acquired melanin pigmentary disorder manifesting itself by expanding depigmented lesions of the skin. To date, the etiopathomechanism of vitiligo has not been convincingly elucidated and a number of seemingly mutually opposed hypotheses with equal likelihood still coexist. Concurrent theories on vitiligo etiology, together with supportive evidence, are reviewed here. Due to the observed variation in clinical manifestations of the disease, it seems likely that the etiology of vitiligo may differ among patients. Therefore several theories on vitiligo etiopathogenesis have been combined to formulate a convergence theory for vitiligo, also presented in this article. This theory states that stress, accumulation of toxic compounds, infection, autoimmunity, mutations, altered cellular environment and impaired melanocyte migration and/or proliferation can all contribute to vitiligo etiopathogenesis in varying proportions.
Autoimmune Diseases↗