Effect of the Alpha Melanocyte Stimulating Hormone of the Pituitary on Mammalian Epidermal Melanocytes

Roles of calcitonin gene-related peptide in the skin, and other physiological and pathophysiological functions

Skin immunity is regulated by many mediator molecules. One is the neuropeptide calcitonin gene-related peptide (CGRP). CGRP has roles in regulating the function of components of the immune system including T cells, B cells, dendritic cells (DCs), endothelial cells (ECs), and mast cells (MCs).

Herein we discuss actions of CGRP in mediating inflammatory and vascular effects in various cutaneous models and disorders.

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CGRP can help to recruit immune cells through endothelium-dependent vasodilation.

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CGRP plays an important role in the pathogenesis of neurogenic inflammation.

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Functions of many components in the immune system are influenced by CGRP.

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CGRP regulates various inflammatory processes in human skin by affecting different cell-types.

New Side Effects in Prolonged Chlorpromazine Therapy

Three new side effects of prolonged chlorpromazine therapy have been described. Their pathogenesis has been discussed, and increased melanin production was found to be the cause of these manifestations of chlorpromazine melanosis. Skin pigmentation has produced an appearance which is cosmetically undesirable. Ocular deposits have caused visual impairment. Diffuse melanosis of internal organs has been accompanied by functional disturbance of the involved organs. A preliminary report on the therapy of these side effects has been presented.

Melanin production through novel processing of proopiomelanocortin in the extracellular compartment of the auricular skin of C57BL/6 mice after UV-irradiation

The production of melanin is regulated by α-melanocyte-stimulating hormone (α-MSH), which is produced from proopiomelanocortin (POMC). Keratinocytes release POMC along with lower levels of α-MSH and ACTH. To clarify the mechanism of melanogenesis after ultraviolet (UV)-irradiation, this study focused on the expression of POMC and POMC-derived peptides after UV-irradiation. Western blot analysis and immunoassays indicated that both POMC and α-MSH-like immunoreactivity (α-MSH-LI) increased after UV-irradiation. However, other POMC-derived products were very low. In hypophysectomized mice, α-MSH-LI increased to the same level as in control mice after UV-irradiation. Structural analysis revealed that the major α-MSH-LI product was ACTH(1–8). Furthermore, ACTH(1–8) competed with [¹²⁵I]-α-MSH for receptor binding and increased melanin production via a melanocortin-1 receptor. These results suggested that melanin was produced through ACTH(1–8) after UV-irradiation. Trypsin-like enzymatic activity, which is responsible for POMC activation, increased after UV-irradiation and was identified as tryptase. In mast cell-deficient mice, which do not produce tryptase, α-MSH-LI levels were unchanged after UV-irradiation. The present study demonstrates the production of ACTH(1–8) from POMC by tryptase, which is a novel peptide-processing mechanism in the extracellular compartment of the skin.

The melanocortin-1 receptor and human pigmentation

alpha-Melanocyte stimulating hormone (alpha-MSH) is known to be the main physiologic regulator for integumental pigmentation of various vertebrate species. However, the role of alpha-MSH and related melanocortins in the regulation of human cutaneous pigmentation is only beginning to be understood. Cloning of the melanocortin-1 receptor (MC1R), and the feasibility of establishing normal human epidermal melanocyte cultures have made it possible to demonstrate direct and specific biological effects of alpha-MSH on these cells. It is now recognized that both alpha-MSH and ACTH have similar mitogenic and melanogenic effects on human epidermal melanocytes. These effects are mediated by binding of these hormones to the specific MC1R that recognizes them both with similar affinity. Human MC1R is homologous to its mouse counterpart in that its activation leads to stimulation of eumelanin synthesis. MC1R is also the binding site for agouti signaling protein (ASP), the product of the agouti locus. Human epidermal melanocytes respond to purified recombinant mouse or human ASP, with a reduction in basal tyrosinase activity, and complete abrogation of the mitogenic and melanogenic effects of alpha-MSH. These results suggest that ASP induces pheomelanin synthesis by competing with alpha-MSH for binding to the MC1R. This receptor seems to be subject to regulation by a variety of paracrine and/or autocrine factors that are synthesized in response to exposure of the skin to ultraviolet radiation (UVR). Activation of MC1R seems to be pivotal for UV-induced melanogenesis, since stimulation of the cAMP pathway plays a key role in the melanogenic response of human epidermal melanocytes. The melanogenic response to UVR might be influenced by the presence of allelic variants of the MC1R gene. Allelic variants have been identified and shown to be associated with red hair, poor tanning ability, and possibly melanoma. The possible influence of these variants on the function of the MC1R needs to be investigated, in order to understand the physiological consequence of these mutations. Also, the interaction of alpha-MSH with other factors that are known to affect pigmentation needs to be better understood in order to define the role possible of this hormone and its receptor in acquired human cutaneous hyper- or hypopigmentation.

Melanocyte stimulating hormone induces the differentiation of mouse epidermal melanocytes in serum-free culture

In serum-free primary culture of dissociated mouse epidermal cells, alpha-melanocyte stimulating hormone (alpha-MSH) and dibutyryl cyclic AMP (DBcAMP) induced the differentiation of melanocytes. Moreover, the proliferation of melanocytes was also induced in the dishes cultured with DBcAMP, but not with alpha-MSH. In order to clarify the role of keratinocytes in melanocyte proliferation and differentiation, pure cultures of keratinocytes were established in serum-free medium. Subconfluent primary keratinocytes were trypsinized and seeded into pure primary melanoblasts cultured with serum-free medium that did not contain alpha-MSH or DBcAMP. Melanoblasts were cultured with alpha-MSH or DBcAMP in the presence or absence of keratinocytes. alpha-MSH failed to induce melanocyte differentiation in the absence of keratinocytes. DBcAMP failed to induce melanocyte proliferation in the absence of keratinocytes, although it induced melanocyte differentiation even in the absence of keratinocytes. These results suggest that keratinocyte-derived factors are required not only for the induction of melanocyte differentiation by alpha-MSH but also for the induction of melanocyte proliferation by DBcAMP.

Plasma alpha-melanocyte-stimulating hormone, beta-endorphin, met-enkephalin, and natural killer cell activity in vitiligo

BACKGROUND

The immune system is important in the pathogenesis of vitiligo, and emotional stress has precipitated vitiligo in some patients. Opioid peptides, beta-endorphin, met-enkephalin, and alpha-melanocyte-stimulating hormone (MSH) act as immunomodulators, and their secretion increases during periods of stress.

OBJECTIVE

To see whether these three neuropeptides might be related to vitiligo itself or to some alterations of the immune system in patients with vitiligo, we compared circadian variations in their plasma concentrations and natural killer cell activity of peripheral blood lymphocytes in 14 patients with vitiligo with those of 12 healthy subjects.

METHODS

Plasma concentrations of neurohormones were evaluated by radioimmunoassay (immunoradiometric assay for beta-endorphin). Natural killer cell activity (NKCA) was assayed against K562 cells by 51Cr release technique. Data were compared by the Student t test and analyzed by cosinor analysis.

RESULTS

The NKCA in vitiligo patients was higher than in controls but had similar circadian rhythm. alpha-MSH had no circadian rhythm in controls or in patients; plasma alpha-MSH levels were the same. Daily met-enkephalin and beta-endorphin oscillations in patients were no longer circadian. beta-Endorphin plasma levels in stable vitiligo were higher than in controls. There were no differences between patients with active vitiligo and normal subjects. Met-enkephalin plasma levels were generally higher in vitiligo patients, especially in the one with active vitiligo, than in controls.

CONCLUSION

In vitiligo there are aberrations in neuropeptide, beta-endorphin, and met-enkephalin secretion. The plasma met-enkephalin level is positively correlated with the aggressiveness of the disease.

Effect of PUVA on plasma and skin immunoreactive alpha-melanocyte stimulating hormone concentrations

Plasma alpha-melanocyte stimulating hormone (alpha-MSH) concentrations were measured in patients receiving PUVA therapy as treatment for mycosis fungoides, and PUVA or UVB as treatment for psoriasis. Skin immunoreactive alpha-MSH was also measured in those patients who received PUVA. The mean plasma and skin alpha-MSH concentrations after 2-3 weeks of PUVA were not significantly different from pre-treatment values and showed no relationship either to skin type or to the degree of tanning that occurred in response to PUVA. Plasma alpha-MSH concentrations were also unchanged after UVB. There was also no short term change in plasma alpha-MSH concentrations in patients after receiving their first treatment with PUVA. It would appear that circulating and skin alpha-MSH levels are unaffected by UV and show no causal relationship to PUVA induced pigmentation.

Seasonal rhythm of the plasma level of alpha-melanocyte stimulating hormone

The present results indicate the presence of a seasonal rhythm of immunoreactive alpha-melanocyte stimulating hormone (alpha-MSH) in 20- to 40-year-old subjects of skin type I (light color of skin and eyes, red hair, no tanning after sun exposure) and skin type II (light color of skin, eyes, and hair, rare tanning) with raised levels of alpha-MSH in summer and low levels in winter. With increasing age of the investigated subjects, the seasonal rhythm seems to be lost. In subjects with skin type III (light skin, brown eyes and black hair, strong pigmentation after sun exposure) alpha-MSH shows only insignificant variations over the whole year. A seasonal rhythm of ACTH could not be demonstrated. A diurnal rhythm could be seen for ACTH, but not for alpha-MSH. To summarize, one can suppose that the seasonal rhythm of alpha-MSH is controlled by a varying UV exposure of the integument which is different over the whole year.

MSH peptides are present in mammalian skin

Immunoreactive alpha-MSH was found in human skin and the skin of numerous other mammals. After hypophysectomy the concentration of alpha-MSH in rat skin showed little change suggesting that the pituitary is not the source of this MSH. In human skin the highest concentration was found in the epidermis and HPLC revealed four peaks of immunoreactive alpha-MSH. Two of these co-eluted with mono- and des-acetyl alpha-MSH standards. An earlier peak probably represented an oxidized MSH and a later running peak, diacetylated alpha-MSH. Although no differences were found in alpha-MSH content of skin from albino and pigmented rats or between involved and non-involved epidermis of patients with vitiligo, its predominance in human epidermis could suggest a relationship with the melanocyte or its melanin. Whether alpha-MSH in the skin has any pigmentary significance or any other role has yet to be established.

The copper hypothesis of schizophrenia: a review

The hypothesis that excess tissue copper can cause schizophrenia is a relatively old theory that has never been compellingly demonstrated nor convincingly refuted. This article traces the development and abandonment of the copper hypothesis and examines the evidence for and against the etiological involvement of copper in schizophrenia. A plausible mechanism by which copper excesses could result in schizophrenia is presented and evaluated, and various attempts to reconcile the contradictory data are considered.

Melanotrophin-potentiating factor (MPF) potentiates MSH-induced melanogenesis in hair follicle melanocytes

Melanotrophin-potentiating factor (MPF) is a fragment of human beta-lipotrophin (LPH 88-91) which potentiates the action of alpha-MSH on Anolis skin. In the present study, we investigated the effect of MPF on MSH-induced melanogenesis. Pooled hair follicle scrapings from Siberian hamsters (Phodopus sungorus) were incubated for 48 hours with or without alpha-MSH and/or MPF. Melanogenesis was monitored by measuring tyrosinase activity and melanin accumulation. 10-8 M MPF potentiated the effect of no effect on melanogenesis, but 10-9 to 10-7 M alpha-MSH caused a dose-related increase. 10-8 M MPF potentiated the effect of each dose of alpha-MSH. Thus MPF potentiated MSH action on mammalian melanogenesis as well as on reptilian melanosome dispersion. Although each of these processes involve different intracellular responses the receptor mechanisms involved in each may therefore be the same.

The epidermal melanocyte system in individuals of Scandinavian origin, determined by DOPA-staining and TEM

The quantitative evaluation of DOPA-positive epidermal melanocytes in 16 patients of Scandinavian origin showed both individual and regional differences in the melanocyte count. Our data is in agreement with other published studies. The distribution in the number of melanocytes varies significantly in some specimens. This is due partly to the preparation procedure and partly to normal biological variations. We believe that we have demonstrated a cyclic function of the melanocyte in the epidermis. The varying density of cells in epidermal sheets as well as their varying morphology support the theory concerning the presence of the epidermal melanin unit.

Melanocyte-stimulating hormone--mimetic action of the phenothiazines

We have compared the melanophore-stimulating action of four phenothiazines, trifluoperazine, perphenazine, chlorpromazine, and prochlorperazine, with alpha-MSH on the skin of the lizard Anolis carolinensis, using a new rate method of bioassay. The dose-response curves for the phenothiazines were parallel to that of alpha-MSH, and when given together alpha-MSH and chlorpromazine were additive. The phenothiazines may therefore stimulate melanosome dispersion in the lizard skin by the same mechanism as alpha-MSH; a MSH-mimetic action of phenothiazines may similarly explain their pigmentary action in man. The pigmentary potency of the phenothiazines corresponded with their therapeutic potency in man; this is in keeping with a neuro-regulatory role for MSH peptides and suggests a possible therapeutic use for them.

The effect of MSH on thymidine incorporation by keratinocytes in the epidermal melanin unit

Epidermal melanocytes were observed in the black but not in the white skin of black-and-white spotted guinea pigs. In experiments designed to determine whether melanocyte-stimulating hormone (MSH) affects the incorporation of thymidine by kerationcyte nuclei of the epidermal melanin unit, the labeling index was the same in all skin before MSH administration. After MSH injections, the level of (3H)thymidine incorporation in keratinocytes increased significantly in black skin but not in white. We suggest that through the mediation of melanocytes MSH indirectly afffects keratinocytes in the epidermal melanin unit.

Increase of melanocytes around malignant melanoma

In split epidermal sheets with clinically normal appearance a quantitative study was carried out on dopa-positive cells in the vicinity of malignant melanomas. These data were then compared with the number of melanocytes found in the skin of the contralateral body side of the same patient. In the epidermis around superficial spreading melanoma and lentigo maligna melanoma, the number of dopa-positive cells was usually significantly higher than in the contralateral body side. On the other hand, no difference was generally found around nodular melanoma.

Sensitive method for the bioassay of melanocyte stimulating hormone in human saliva

A procedure for the biological assay of melanocyte stimulating hormone (MSH) or MSH-like peptide fractions in human saliva is described. Samples of whole saliva were collected from normal individuals. The amount of MSH-like activity was estimated to be between 0.3 and 1.0 international units per milliliter of saliva.

Calcium requirement for melanophore-stimulating hormone action on melanophores

The calcium ion is specifically required for the action of melanophorestimulating hormone on melanosome dispersion within lizard (Anolis carolinensis) melanophores in vitro. The response to this hormone is directly related to the concentration of the Ca(2+) ion. Lithium, choline, rubidium, and cesium will replace the sodium and potassium of Ringer solution if Ca(2+) is present. Calcium ions are not required for melanosome dispersion itself, since theophylline or dibutyryl cyclic adenosine monophosphate reversibly darkens lizard skins in the absence of calcium.