Biomedical subjects

I C Le Poole

Publications and source records attributed to I C Le Poole.

At least 19 recordsLinked to original sources

PubMed2001

A symbiotic concept of autoimmunity and tumour immunity: lessons from vitiligo.

Vitiligo is a skin disease in which melanocytes (MCs) are eradicated from lesional epidermis, resulting in disfiguring loss of pigment. MCs are destroyed by MC-reactive T cells, as well as other non-immune and immune components. Similarities exist between the autoimmunity observed in vitiligo and the tumour immunity observed in melanoma immuno-surveillance. An analysis of these mechanisms might lead to the development of new therapies for both vitiligo and melanoma.

Autoimmunity↗

PubMed2001

Inhibition of melanosome transfer from melanocytes to keratinocytes by lectins and neoglycoproteins in an in vitro model system.

We propose that some of the critical molecules involved in the transfer of melanosomes from melanocytes to keratinocytes include plasma membrane lectins and their glycoconjugates. To investigate this mechanism, co-cultures of human melanocytes and keratinocytes derived from neonatal foreskins were established. The process of melanosome transfer was assessed by two experimental procedures. The first involved labeling melanocyte cultures with the fluorochrome CFDA. Labeled melanocytes were subsequently co-cultured with keratinocytes, and the transfer of fluorochrome assessed visually by confocal microscopy and quantitatively by flow cytometry. The second investigative approach involved co-culturing melanocytes with keratinocytes, and processing the co-cultures after 3 days for electron microscopy to quantitate the numbers of melanosomes in keratinocytes. Results from these experimental approaches indicate significant transfer of dye or melanosomes from melanocytes to keratinocytes that increased with time of co-culturing. Using these model systems, we subsequently tested a battery of lectins and neoglycoproteins for their effect in melanosome transfer. Addition of these selected molecules to co-cultures inhibited transfer of fluorochrome by approximately 15-44% as assessed by flow cytometry, and of melanosomes by 67-93% as assessed by electron microscopy. Therefore, our results suggest the roles of selected lectins and glycoproteins in melanosome transfer to keratinocytes in the skin.

Cell Membrane↗

PubMed2001

'VIT1', a novel gene associated with vitiligo.

To define genes associated with the pigmentary disorder vitiligo, gene expression was compared in non-lesional melanocytes cultured from three vitiligo patients and from three control melanocyte cultures by differential display. A basic local alignment search tool search did not reveal homology of six differentially expressed cDNA fragments to previously identified expressed sequence tags; thus, one was used to screen a melanocyte cDNA library. The underlying VIT1 gene maps to chromosome 2p16. The 3' portion of the VIT1 message is complementary to the 3' end of hMSH6 mRNA, enabling the formation of RNA-RNA hybrids, which may interfere with G/T mismatch repair function. Moreover, the aligned cDNA sequence revealed an open reading frame identical to a hypothetical protein expressed in brain, with a similarity to Drosophila calmodulin, and containing a zinc-finger motif partially identical to N-recognin. Expression of ORF mRNA was confirmed for multiple skin cell types, suggesting its importance for skin physiology.

Adult↗

PubMed2001

Keratinocytes play a role in regulating distribution patterns of recipient melanosomes in vitro.

Melanosomes in keratinocytes of Black skin are larger and distributed individually whereas those within keratinocytes of Caucasian skin are smaller and distributed in clusters. This disparity contributes to differences in skin pigmentation and photoprotection, but the control of these innate distribution patterns is poorly understood. To investigate this process, cocultures were established using melanocytes and keratinocytes derived from different racial backgrounds and were examined by electron microscopy. Melanosomes transferred to keratinocytes were categorized as individual or in various clusters. Melanosome size was also determined for individual and clustered melanosomes. Results indicate that, in our model system, melanosomes in keratinocytes from different racial backgrounds show a combination of clustered and individual melanosomes. When keratinocytes from dark skin were cocultured with melanocytes from (i) dark skin or (ii) light skin, however, recipient melanosomes were individual versus clustered in (i) 77% vs 23% and (ii) 64% vs 36%, respectively. In contrast, when keratinocytes from light skin were cocultured with melanocytes from (iii) dark skin or (iv) light skin, recipient melanosomes were individual versus clustered in (iii) 34% vs 66% and (iv) 39% vs 61%, respectively. These results indicate that recipient melanosomes, regardless of origin, are predominantly distributed individually by keratinocytes from dark skin, and in membrane-bound clusters by those from light skin. There were also differences in melanosome size from dark or light donor melanocytes. Melanosome size was not related to whether the melanosomes were distributed individually or clustered, however, in cocultures. These results suggest that regulatory factor(s) within the keratinocyte determine recipient melanosome distribution patterns.

Black People↗

PubMed2000

Micro-anatomy related antigen expression in melanocytic lesions.

The in situ expression of antigens associated with melanosomes (gp-100), pigmentation (PAA), tyrosinase (TRP-1), melanoma (MAA-1/MAA-2), and HLA-DR was investigated immunohistochemically in frozen archival specimens of common acquired melanocytic naevi, in dysplastic melanocytic naevi, and in lymph node metastases of melanoma. Expression of these antigens was also studied in established cultured normal human melanocytes, naevus-derived melanocytes and melanoma cell lines of varying metastatic potential, by immunohistochemistry and flow cytometry. Compared with normal melanocytes, melanocytic naevi exhibited increased expression of gp-100, PAA, and TRP-1 in the lesional cells at or very near the dermo-epidermal junction, but with diminishing expression towards the intra-dermal base of the lesions. In contrast, expression of MAA-1 and MAA-2 was observed in melanocytes throughout the dermal part of the naevi. Melanocytes located at the basal layer of the epidermis were positive only for gp-100, PAA, and TRP-1 antigens. Dysplastic melanocytic naevi showed staining of gp-100, PAA, TRP-1, HLA-DR, MAA-1, and MAA-2 of junctional lesional melanocytes, but less intense than that of common acquired naevi. These antigens were not detectable in the dermal part of the dysplastic naevi. Expression of these antigens in lymph node metastases of melanoma was either positive or negative. Similar results regarding antigen expression were observed in all cultured melanocytic cells, both by immunohistochemistry and by flow cytometry. The present data suggest that analysis of these antigens may contribute to the discrimination of common acquired melanocytic naevi from their dysplastic counterparts. Furthermore, variations in the levels of expression in naevi may be consistently related to the micro-anatomy of the lesions, indicating that the micro-environment may have an influence on the expression levels of these antigens in different lesional melanocytes.

Antigens, Neoplasm↗

PubMed2000

The cytotoxicity and apoptosis induced by 4-tertiary butylphenol in human melanocytes are independent of tyrosinase activity.

It has been known for several decades that cutaneous depigmentation, i.e., contact/occupational vitiligo, can be caused by some phenolic derivatives that have a similar structure to tyrosine. Among these phenolic depigmenting agents, 4-tertiary butylphenol is the most potent. The cutaneous depigmentation induced by phenolic derivatives results from the loss of functional melanocytes. Tyrosinase is a melanocyte specific copper-containing enzyme that catalyzes the conversion of the amino acid tyrosine, through a complex series of intermediates, to melanin. In this study we tested the hypothesis that the cytotoxicity induced by 4-tertiary butylphenol is mediated by tyrosinase and occurs via an apoptotic process. Melanocyte cultures derived from African-American and Caucasian donors exhibiting a 3-fold difference in tyrosinase activity and 14-fold difference in melanin content demonstrate comparable concentration-dependent sensitivity to 4-tertiary butylphenol. In addition, cultures of dermal fibroblasts and epidermal keratinocytes exhibited similar and reduced sensitivity, respectively, to 4-tertiary butylphenol compared with autologous melanocytes. Two melanoma cell lines, one melanotic and one amelanotic lacking the expression of both tyrosinase protein and activity, when transfected with the tyrosinase cDNA, exhibited no alteration in its sensitivity to 4-tertiary butylphenol. These data suggest that 4-tertiary butylphenol cytotoxicity is not mediated via tyrosinase. Melanocytes treated with 4-tertiary butylphenol, however, did exhibit plasma membrane blebbing, DNA fragmentation, and phosphatidylserine relocalization indicating that 4-tertiary butylphenol induced melanocyte destruction occurs by an apoptotic process.

Apoptosis↗

PubMed2000

Expression and modulation of apoptosis regulatory molecules in human melanocytes: significance in vitiligo.

Although the aetiology of the hypopigmentary disorder vitiligo is ill understood, it is clear that pigment producing cells are absent from vitiliginous lesional skin. The present study was designed to investigate the possible role of melanocyte-expressed apoptosis regulatory molecules in melanocyte disappearance. Flow cytometric evaluation of p53, p21, Bcl-2 and Bax revealed no differences in in vitro expression levels between normal control and non-lesional melanocytes. Moreover, no in situ immunohistological differences were observed in melanocytes present in control, non-lesional and perilesional skin. However, an enhanced number of p53+ nuclei, in the absence of detectable p21 expression, was detected in involved areas. The observed p53 expression pattern did not involve melanocytes and could be the result of ultraviolet (UV) A irradiation. Further, we showed that UVB is capable of modulating melanocyte-expressed apoptosis regulatory molecules. Consequently, a lethal dose of UVB was given to two groups of cultured normal control and non-lesional melanocytes. No significant differences were found when comparing the percentages and kinetics of UVB-induced apoptosis in these groups. In conclusion, our results indicate that the relative apoptosis susceptibility of melanocytes in vitiligo is comparable with that of normal control cells. It is therefore unlikely that vitiligo is causally related to dysregulation of apoptosis regulatory molecules.

Apoptosis↗

PubMed2000

PIG3V, an immortalized human vitiligo melanocyte cell line, expresses dilated endoplasmic reticulum.

Vitiligo is an enigmatic pigmentary disorder of the skin. Factors potentially involved in the progressive loss of melanocytes from the basal layer of the epidermis include genetically determined aberrancies of the vitiligo melanocyte. It follows that analysis of melanocytes cultured from vitiligo donors can contribute to a further understanding of the etiopathomechanism. A setback for vitiligo research has been the limited availability of vitiligo-derived melanocytes. To overcome this limitation, we have generated a vitiligo melanocyte cell line according to a protocol established previously for the immortalization of normal human melanocytes. Vitiligo melanocytes Ma9308P4 were transfected with HPV16 E6 and E7 genes using the retroviral construct LXSN16E6E7. Successful transformants were selected using geneticin and subsequently cloned to ensure genetic homogeneity. The resulting cell line PIG3V has undergone more than 100 cell population doublings since its establishment as a confluent primary culture, whereas untransfected melanocytes derived from adult skin senesce after a maximum of 50 population doublings. Cells immortalized by this transfection procedure retain lineage-specific characteristics and proliferate significantly faster than parental cells. In this study, the phenotype of PIG3V resembled melanocytes rather than melanoma cells in culture. Tyrosinase was processed properly and melanosomes remained pigmented. Importantly, ultrastructural characterization of PIG3V cells revealed dilated endoplasmic reticulum profiles characteristic of vitiligo melanocytes. An explanation for this dilation may be found in the retention of proteins with molecular weight of 37.5. 47.5, and 56.5 kDa, as determined by gel electrophoresis of microsomal proteins isolated from radiolabeled cells.

Adult↗

PubMed1999

Keratinocytes suppress transforming growth factor-beta1 expression by fibroblasts in cultured skin substitutes.

Transforming growth factor (TGF)-beta1 is a multipotent growth factor with an important role in tissue homeostasis. This growth factor regulates cell proliferation, adhesion, migration and differentiation, as well as extracellular matrix deposition. The temporal secretion and activation of latent TGF-beta1 is thus of major importance to physiological and pathological processes and in wound healing and tumour formation. Cultured skin substitutes, as used to treat extensive acute or chronic skin wounds, offer an attractive model to investigate cellular interactions in cytokine and growth factor expression and response in vitro. In the present investigation, expression of TGF-beta1 was analysed in keratinocyte, fibroblast and melanocyte monolayer cultures, as well as in the dermal vs. epidermal components of reconstituted human skin. Immunohistology, enzyme-linked immunosorbent assay (ELISA) and Northern blotting were used to demonstrate expression at the RNA and protein level. In the monolayer cultures, levels of TGF-beta1 synthesized by melanocytes were observed to be considerably elevated when compared with keratinocytes. Most TGF-beta1, however, was secreted by fibroblasts. The relative contribution of the epidermal and dermal components of the skin substitutes to overall TGF-beta1 levels was determined by comparing results obtained for either component in the presence and absence of fibroblasts and keratinocytes. From results obtained by ELISA it was apparent that TGF-beta1 levels generated predominantly by fibroblasts within the skin substitutes were greatly reduced over time in the presence of keratinocytes. Suppression of fibroblast TGF-beta1 expression in the presence of keratinocytes was also demonstrable at the RNA level by Northern blotting. Results obtained by immunohistochemistry suggest that most, if not all, of the growth factor was present in the latent form. It is therefore most likely that the observed effect results from a factor secreted by keratinocytes, which is capable of suppressing TGF-beta1 synthesis by fibroblasts. These results suggest that expression of TGF-beta1 by fibroblasts is downregulated by paracrine actions of keratinocytes in healing skin.

Blotting, Northern↗

PubMed1999

Altered gene expression in melanocytes exposed to 4-tertiary butyl phenol (4-TBP): upregulation of the A2b adenosine receptor 1.

Exposure to phenolic agents contributes to the development of occupational vitiligo. Proposed as a causative factor for leukoderma in vivo, the para-substituted phenol 4-tertiary butyl phenol was chosen to investigate early cellular events responsible for selective disappearance of melanocytes from the epidermis of individuals sensitive to such agents. To this end, differential display of melanocyte mRNA isolated from three separate cultures was performed following a 12 h exposure of cells to 250 microM 4-tertiary butyl phenol or to vehicle alone. Fragments of cDNA representing differentially expressed messages were cloned and subsequently confirmed by reverse dot blotting. Alignment analysis revealed that the L30 ribosomal protein was upregulated by the treatment, potentially reflecting altered levels of protein synthesis in response to stress. In addition, a gene sequence upregulated following exposure to 4-tertiary butyl phenol was identified as the A2b receptor (a P1 receptor for adenosine). Differential expression of this gene was confirmed in an RNase protection assay. By reverse transcription-polymerase chain reaction, the gene was shown to be expressed in keratinocytes and fibroblasts as well. Flow cytometry confirmed differential expression in melanocytes and fibroblasts, but not in keratinocytes. Interestingly, it has been reported that P1 purinoceptor stimulation can induce apoptosis. This is in concordance with results reported elsewhere demonstrating induction of apoptosis by 4-tertiary butyl phenol in human melanocytes, as well as with morphologic changes observed in this study in cells exposed to 250 microM 4-tertiary butyl phenol for 72 h. In conclusion, differential display is useful to establish melanocyte components involved in the cellular response to phenolic agents.

Flow Cytometry↗

PubMed1997

Effect of nitric oxide on the adhesion of human melanocytes to extracellular matrix components.

The aim of the present study was to explore whether nitric oxide (NO) interferes with the attachment of human melanocytes to the extracellular matrix (ECM) components. Consequently, the effects have been investigated of the NO-releasing compounds 3-morpholino-sydnonimine (SIN-1) and S-nitroso-glutathione (GSNO) on the in vitro adhesion of human melanocytic cells to fibronectin. The NO donors induced a concentration-dependent reduction in the adhesion of both 51CrO4(2-)-labelled melanocytes and melanoma cells to fibronectin. Pigmented M14 melanoma cells were more susceptible to the effect of SIN-1 (half-maximal inhibiting effect at about 0.5 mM) than normal human melanocytes and also than the non-pigmented melanoma cells Mel57 (half-maximal inhibiting effects between 0.9 and 2 mM). This effect of SIN-1 also appeared to be related to the melanin content of normal melanocytes, whereas GSNO was significantly less active. Both flow cytometric analysis and immunocytochemical staining showed expression of neuronal NO synthase in all cell lines. The results of this study suggest that aberrant in vivo production of NO during infection and inflammation may contribute to loss of melanocytes in, for example, vitiligo, by reducing de novo attachment of melanocytes to the ECM. These findings could also be important for understanding the process of metastasis.

Cell Adhesion↗

PubMed1997

Generation of a human melanocyte cell line by introduction of HPV16 E6 and E7 genes.

Availability of a standard human melanocyte cell line with unlimited growth potential and otherwise normal melanocytic properties will greatly facilitate research in melanocyte biology and in vitro studies on the etiology of pigmentary disorders and melanoma. Using a retroviral vector, E6 and E7 open reading frames of human papilloma virus type 16 (HPV 16) have been introduced into cultured normal human melanocytes. Cells selected by increased resistance to geneticin conveyed by the vector and expressing E6E7 mRNA have been cloned to ensure genetic homogeneity. Since their establishment as primary cells, cloned PIG1 cells have undergone more than twice the amount of population doublings of senescent parental cells. Moreover, in passage numbers when parental cells had become senescent, proliferation of clonal cells was retained at levels exceeding those of normal human melanocytes in third passage by 100%. Further characterization has revealed that the cells remain dependent on tetradecanoyl phorbol 13-acetate (TPA) for growth and do not proliferate in soft agar nor form tumors in nude mice. The antigenic profile of the cells was slightly altered as compared to parental cells, but was incomparable to that of M14 melanoma cells. Importantly, PIG1 cells contain more melanin pigment than parental cells.

Animals↗

PubMed1997

In vitro tissue-digesting properties of krill enzymes compared with fibrinolysin/DNAse, papain and placebo.

Wound debridement, the removal of necrotic tissue, can be achieved with proteolytic enzymes. Recently, a new multi-enzyme preparation, krill enzyme, isolated from Antarctic shrimp-like organisms (Euphausia superba), was reported to possess powerful proteolytic activity towards protein substrates. In this paper, we study the in vitro digestive properties of krill enzymes towards whole tissue, compared with placebo, papain, and fibrinolysin/DNAse. Freshly obtained skin specimens were exposed for 3 days to krill enzymes (3; 0.6 and 0.06 U/ml), papain (120; 60; 6 and 0.6 U/ml), fibrinolysin/DNAse (2.5/1500 E and 1/600 E), and phosphate-buffered saline control solution. Tissue digestion was estimated by measuring wet wt, dry wt, and histological examination. After 72 hr of exposure to 3 U/ml krill enzymes, the dry wt of the specimens was reduced to 2.7% +/- 1.9 (SEM, n = 5), compared with 31.0% +/- 2.7 for placebo, 25.7% +/- 2.5 for 120 U/ml papain, and 24.5% +/- 3.3 for 2.5/1500 E/ml fibrinolysin/DNAse. The differences between krill enzymes and fibrinolysin/DNAse, papain, and control solution were statistically significant (p < 0.007). These data suggest that krill enzymes are more active than other commonly available proteolytic agents used for wound debridement.

Animals↗

PubMed1997

Tenascin is overexpressed in vitiligo lesional skin and inhibits melanocyte adhesion.

The aetiology of vitiligo remains obscure. In this study, the role of integrins in the observed inability of melanocytes to repopulate lesional skin was investigated. Antibodies directed to alpha 2, alpha 3, alpha 5, alpha v, alpha 6, beta 1 and beta 3 integrin subunits were used. Immunohistology revealed no marked differences in the overall levels of expression of integrins between control, non-lesional perilesional or lesional skin. Moreover, no differences were noted in the level of expression of integrins or the adhesive capacity between cultured control cells derived from three separate donors and vitiligo-derived melanocytes from two donors. Rather, it was clearly observed that towards the lesion, vitiligo skin contains increasing amounts of tenascin in the basal membrane and papillary dermis in five patients employing T2H5 antihuman tenascin antibody. The anti-adhesive effect observed in vitro for this extracellular matrix molecule using normal melanocytes may contribute to loss of pigment cells in vitiligo or to ineffective repopulation of the lesions.

Adult↗

PubMed1996

Foetal human melanocytes: in situ detection, in vitro culture and differentiation characteristics at 6-11 weeks EGA.

In vivo, melanocytes were detected in epidermis from human tissue of 6.5 weeks estimated gestinational age (EGA) and older. We have successfully established melanocyte monocultures from tissue of 9 to 10 weeks EGA. To our knowledge, this is the first report on physiology of human foetal melanocytes in monoculture. In culture, such melanocytes retained foetal characteristics. Proliferation rates noted were markedly higher (approximately 2.7-fold) when compared to those in cultures of neonatal melanocytes. Moreover, when analyzing cellular phenotypes by markers for cells of the melanocytic lineage, foetal cells isolated from tissue of 9 weeks EGA reproducibly showed expression of the high molecular weight (HMW) antigen and c-kit to an extent intermediate to that found in neonatal melanocytes and M14 melanoma cells. Such differential expression was not observed if cells were isolated from tissue of 10 weeks EGA, indicating that the foetal environment provides essential differentiation stimuli during the 10th week of gestation. Moreover, these results are supportive of the theory that malignant transformation involves a process of dedifferentiation. In all, human foetal melanocyte culture provides a useful model to investigate pigment cell differentiation.

Biomarkers, Tumor↗

PubMed1996

Presence of T cells and macrophages in inflammatory vitiligo skin parallels melanocyte disappearance.

Evidence for the involvement of cellular immunity in the etiopathogenesis of the hypopigmentary disorder vitiligo is provided by rare cases of inflammatory vitiligo. Nonlesional, perilesional, and lesional skin biopsies from three inflammatory vitiligo patients were immunohistochemically analyzed. The composition of inflammatory infiltrates present in perilesional skin was analyzed by antibodies to T cells (CD2, CD3, CD4, and CD8), Langerhans cells (CD1a), and macrophages (CD36 and CD68). The presence of activation markers on inflammatory cells was evaluated by analysis of HLA-DR, interleukin-2 receptor, and HECA452 expression. The presence or absence of melanocytes was determined by the antibody NKI-beteb. Moreover, the abundance of matrix molecule tenascin was semi-quantified using T2H5. Results indicate that within perilesional skin, epidermis-infiltrating T cells exhibit an increased CD8/CD4 ratio and increased cutaneous lymphocyte antigen and interleukin-2 receptor expression. These cells are frequently juxtapositionally apposed to remaining melanocytes. In perilesional dermis, CD68+OKM5- macrophages were more numerous than in lesional or nonlesional skin. Keratinocytes as well as melanocytes consistently express major histocompatibility complex class II antigens along stretches of basal and suprabasal layers in perilesional epidermis. Moreover, inflammation is accompanied by increased tenascin content. Although these observations do not permit differentiation between the immune infiltrates being a result as opposed to the cause of the disease process, results presented in this study are very suggestive of involvement of local immune reactivity in melanocyte destruction.

Adult↗

PubMed1995

Expression of CD44 splice variants in human cutaneous melanoma and melanoma cell lines is related to tumor progression and metastatic potential.

Expression of CD44, particularly of certain splice variants, has been linked to tumor progression and metastasis formation in a number of different animal and human cancers. Because human cutaneous melanoma is among the most aggressive human cancers, we explored expression of CD44 isoforms (CD44v) in lesions of melanocytic tumor progression. In addition, by RT-PCR and FACS analysis we assessed CD44v RNA species and cell surface expression of CD44v in cultured melanocytes isolated from human foreskin and in a panel of 2 non-, 2 sporadically and 2 highly metastatic human melanoma cell lines. We observed that all melanocytic lesions examined showed strong uniform expression of standard CD44 (CD44s) epitopes. We did not detect CD44v6 expression in the melanocytic lesions. However, CD44 isoforms containing v5 or v10 were differentially expressed. V5 was expressed in 16%, 0%, 20%, 67% and 58% of common nevi, atypical nevi, early primary melanomas (< or = 1.5 mm), advanced primary melanomas (> 1.5 mm) and metastases, respectively, and hence was related to tumor progression. In contrast, CD44v10 was expressed in all common nevi, whereas part of the atypical nevi and most primary melanomas and metastases lacked v10. CD44v RNA patterns were closely similar in cultured melanocytes and all melanoma cell lines. Melanocytes expressed high levels of CD44s but no CD44v, whereas all melanoma cell lines expressed CD44v at the surface. Interestingly, expression of v5 was strongly increased in the highly metastatic cell lines. Our results suggest a role for CD44 variant domains, particularly v5 and v10, in human melanocytic tumor progression.

Base Sequence↗

PubMed1994

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↗