Histamine effect on melanocyte proliferation and vitiliginous keratinocyte survival

H2 antihistamines: May be useful for combination therapies in cancer?

Cancer morbimortality is still a great concern despite advances in research and therapies. Histamine and its receptors' ligands can modulate different biological responses according to the cell type and the receptor subtype involved. Besides the wide variety of histamine functions in normal tissues, diverse roles in the acquisition of hallmarks of cancer such as sustained proliferative signaling, resistance to cell death, angiogenesis, metastasis, altered immunity and modified microenvironment have been described. This review summarizes the present knowledge of the various roles of histamine H2 receptor (H2R) ligands in neoplasias. A bioinformatic analysis of human tumors showed dissimilar results in the expression of the H2R gene according to tumor type when comparing malignant versus normal tissues. As well, the relationship between patients' survival parameters and H2R gene expression levels also varied, signaling important divergences in the role of H2R in neoplastic progression in different cancer types. Revised experimental evidence showed multiple effects of H2R antihistamines on several of the cited hallmarks of cancer. Interventional and retrospective clinical studies evaluated different H2R antihistamines in cancer patients with two main adjuvant uses: improving antitumor efficacy (which includes regulation of immune response) and preventing toxic adverse effects produced by chemo or radiotherapy. While there is a long path to go, research on H2R antihistamines may provide new opportunities for developing more refined combination therapeutic strategies for certain cancer types to improve patients' survival and health-related quality of life.

Different therapeutic approaches in melasma: advances and limitations

Melasma is a chronic hyperpigmentation skin disorder that is more common in the female gender. Although melasma is a multifactorial skin disorder, however, sun-exposure and genetic predisposition are considered as the main etiologic factors in melasma occurrence. Although numerous topical and systemic therapeutic agents and also non-pharmacologic procedural treatments have been considered in melasma management, however, the commonly available therapeutic options have several limitations including the lack of sufficient clinical effectiveness, risk of relapse, and high rate of unwanted adverse drug reactions. Recruitment of nanotechnology for topical drug delivery in melasma management can lead to enhanced skin penetration, targeted drug delivery to the site of action, longer deposition at the targeted area, and limit systemic absorption and therefore systemic availability and adverse drug reactions. In the current review, first of all, the etiology, pathophysiology, and severity classification of melasma have been considered. Then, various pharmacologic and procedural therapeutic options in melasma treatment have been discussed. Afterward, the usage of various types of nanoparticles for the purpose of topical drug delivery for melasma management was considered. In the end, numerous clinical studies and controlled clinical trials on the assessment of the effectiveness of these novel topical formulations in melasma management are summarized.

Cosmetic Applications of Bee Venom

Bee venom (BV) is a typical toxin secreted by stingers of honeybee workers. BV and BV therapy have long been attractive to different cultures, with extensive studies during recent decades. Nowadays, BV is applied to combat several skin diseases, such as atopic dermatitis, acne vulgaris, alopecia, vitiligo, and psoriasis. BV is used extensively in topical preparations as cosmetics and used as dressing for wound healing, as well as in facemasks. Nevertheless, the safety of BV as a therapeutic choice has always been a concern due to the immune system reaction in some people due to BV use. The documented unfavorable impact is explained by the fact that the skin reactions to BV might expand to excessive immunological responses, including anaphylaxis, that typically resolve over numerous days. This review aims to address bee venom therapeutic uses in skin cosmetics.

Melanogenesis and Melasma Treatment

Melanocytes are highly specialised dendritic cells that transfer melanin to keratinocytes in subcellular lysosome-like organelles called melanosomes, where melanin is synthesised and stored. Melanin is a complex pigment that provides colour and photoprotection to the skin, hair, and eyes of mammals. The regulation of melanogenesis includes various mechanisms and factors including genetic, environmental, and endocrine factors. Knowledge of the pigmentation process is important not only to understand hyperpigmentation but also to design treatments and therapies to treat them. Whitening cosmetics with anti-melanogenesis activity are very popular. In the present manuscript, we review the mechanisms and the signalling pathways involved in skin pigmentation and we specifically focus on the alteration of melanogenesis that leads to melasma and results in hyperpigmentation. Finally, current therapies and treatments including topical, oral, and phototherapies are discussed and described, with a special emphasis on the cosmetics’ action.

The pathogenesis of melasma and implications for treatment

BACKGROUND

Melasma is a complex and poorly understood disorder, with high rates of treatment failure and recurrences.

OBJECTIVES

We aimed to review the current knowledge of the pathogenesis of melasma and apply this knowledge to clinical implications on relevant therapeutic interventions.

METHODS

A systematic PubMed search was performed using the search term "((melasma[Text Word]) OR facial melanosis[Text Word]) AND (pathogenesis OR causality[MeSH Terms])" for articles published between 1990 and 2020. Included articles were then evaluated by two authors and assessed for relevant pathomechanistic pathways, after which they were divided into groups with minimal overlap. We then reviewed current treatment modalities for melasma and divided them according to the involved pathomechanistic pathway.

RESULTS

A total of 309 search results were retrieved among which 76 relevant articles were identified and reviewed. Five main pathomechanisms observed in melasma were identified: (1) melanocyte inappropriate activation; (2) aggregation of melanin and melanosomes in dermis and epidermis; (3a) increased mast cell count and (3b) solar elastosis; (4) altered basement membrane; and (5) increased vascularization. Treatment modalities were then divided based on these five pathways and detailed in 6 relevant tables.

CONCLUSION

The pathophysiology of melasma is multifactorial, resulting in treatment resistance and high recurrence rates. This wide variety of pathomechanisms should ideally be addressed separately in the treatment regimen in order to maximize results.

Role of Amine Neurotransmitters and Their Receptors in Skin Pigmentation: Therapeutic Implication

Skin pigmentation can occur due to increased melanin, including melanocyte proliferation, melanin biosynthesis, or melanocyte migration. There are many factors that influence the melanin production process, but the role of neurotransmitters in this process is still unclear. We found that histamine and serotonin influence the different stages of melanogenesis and melanogenesis, which increase melanogenesis. Since then, several related papers have been published, and from these papers, it has been recognised that the role of neurotransmitters in skin-pigment-related diseases needs to be summarised. By introducing the role of neurotransmitters in the regulation of various pigment disorders, including vitiligo and melasma, through this review, many researchers can be expected to try to apply neurotransmitter-related agonists and antagonists as treatments for skin pigment disorders.

Loratadine, an H1 Antihistamine, Inhibits Melanogenesis in Human Melanocytes

It has long been believed that histamine is associated with cutaneous melanogenesis. Specifically, H2-receptor antagonists reportedly inhibit melanogenesis, but H1-receptor antagonists, which are some of the most commonly prescribed medicines in dermatology, have not been studied to determine whether and how they regulate melanogenesis. Therefore, we screened H1-receptor antagonists to determine whether they inhibit melanogenesis and found that loratadine was particularly effective, in this regard without compromising cellular viability. Loratadine downregulated microphthalmia-associated transcription factor (MITF) and tyrosinase in melanocytes. To determine the intracellular signaling pathways, Akt was consistently activated by loratadine. PI3K/Akt pathway inhibitor, LY294002, restored the reduced melanin content that was induced by loratadine. In addition, phospho-GSK-3β also was found to be increased following loratadine treatment. Loratadine reduced the amount of PKC-βII in the membrane fraction, thereby decreasing its activity. Taken together, our data indicate that loratadine regulates melanogenesis via Akt/MITF and PKC-βII signaling, thereby leading to the inhibition of melanogenic proteins. The antimelanogenic effects of loratadine have potentially significant and useful roles in dermatologic practice, although further clinical studies will be required to test this.

Melasma: Updates and perspectives

Management of melasma is highly challenging due to inconsistent treatment results and frequent relapses. However, recent studies revealed that melasma may not only be a disease of melanocytes, but also a photoaging skin disorder. Herein, we attempt to validate that melasma is indeed a photoaging disorder by presenting the histopathologic findings of melasma: solar elastosis, altered basement membrane, increased vascularization and increased mast cell count. We also provide some therapeutic implications based on these findings and a discussion on the latest updates and perspectives regarding treatment.

Topical Histamine Stimulates Repigmentation of Nonsegmental Vitiligo by a Receptor-Dependent Mechanism

BACKGROUND

Though vitiligo is a common depigmentary disorder, it still represents a substantial therapeutic challenge. Therapeutic options are limited in part due to its uncertain etiology.

OBJECTIVE

Because recent studies suggest that histamine stimulates melanogenesis in vitro, we determined here whether topical histamine stimulates repigmentation in patients with stable, nonsegmental vitiligo.

METHODS

A total of 23 otherwise normal volunteers with vitiligo, including 14 males and 9 females aged 6-59 years (mean age 29.2 ± 2.8), were enrolled in this study. 1% histamine in distilled water was applied to the lesions twice daily for 5 weeks, while comparable lesions, treated with distilled water alone, served as the controls. The melanin index was measured on the uninvolved and lesional skin sites before and after 5 weeks of treatments using the melanin/erythema probe connected to a Courage-Khazaka MPA5 (Cologne, Germany). Changes in epidermal permeability barrier were also assessed at the same time point. To determine whether histamine-induced repigmentation is receptor-dependent, both ears of C57BL/6J mice were treated topically with 5% cimetidine, a histamine type 2 receptor (H2r) antagonist, twice daily for 10 days. One hour after each cimetidine application, the right ear was treated topically with 10% histamine, while vehicle alone was applied to the left ear. Changes in melanin index were measured 24 h after the last application of histamine and vehicle as described in the human study.

RESULTS

In patients with vitiligo treated with vehicle alone for 5 weeks, the melanin index remained unchanged, while topical histamine treatment increased the melanin index by 38% (p < 0.001 vs. both vehicle and pretreatment), which was paralleled by a >60% reduction in lesion surface area. Moreover, topical histamine accelerated permeability barrier recovery. No adverse events were observed following histamine applications. In mice, topical histamine significantly increased the melanin index, while topical co-applications of the H2r antagonist (cimetidine) prevented the expected histamine-induced increase in melanin index.

CONCLUSIONS

These studies indicate that topical histamine or an H2r agonist could be useful for treating nonsegmental vitiligo, but further clinical studies in large populations will be required to validate the efficacy and safety of this approach.

PI3K pathway is involved in ERK signaling cascade activation by histamine H2R agonist in HEK293T cells

BACKGROUND

Histamine, through histamine H2 receptor (H2R), modulates different biological processes, involving the modulation of PI3K/AKT/mTOR and RAS/RAF/MEK/ERK pathways. Many evidences have demonstrated the existence and importance of the crossregulation between these two signaling pathways. The aim of the present work was to determine the molecular mechanisms leading to PI3K and ERK pathways modulation induced by the H2R agonist amthamine and to evaluate the possible interplay between them.

METHODS

Phosphorylation levels of ERK and Akt were examined by Western blot in HEK293T cells expressing the human H2R, in the presence of H2R agonist and dominant negative mutants or pharmacological inhibitors of different proteins/pathways. Transcriptional activity assays were assessed to determine SRE activity. Amthamine-mediated cellular proliferation was investigated in MA-10A cells in the presence of PI3K inhibitor.

RESULTS

H2R agonist inhibits PI3K/Akt/mTOR and stimulates Ras/MEK/ERK pathways. Moreover, PI3K/Akt/mTOR signaling inhibition is necessary to achieve H2R mediated ERK activation. In the presence of a constitutive active mutant of Akt, amthamine is not able to mediate ERK activation. This crosstalk affects classical ERK downstream targets such as Elk1 phosphorylation and the transcriptional activity of the SRE, classically associated to proliferation. We further demonstrate that amthamine-induced proliferation in Leydig MA-10 tumor cells, is enhanced by LY294002, a PI3K inhibitor.

CONCLUSIONS

These results describe a crosstalk between PI3K/AKT/mTOR and Ras/MEK/ERK pathways induced by H2R stimulation with implications in cell proliferation.

GENERAL SIGNIFICANCE

This work indicates that the modulation of PI3K/AKT/mTOR pathway by H2R in turn regulates Ras/MEK/ERK activation conditioning the proliferative capacity of the cells.

Heterogeneous Pathology of Melasma and Its Clinical Implications

Melasma is a commonly acquired hypermelanosis that affects sun-exposed areas of the skin, with frequent facial involvement. Its histologic manifestations are evident in the epidermis, extracellular matrix, and dermis. In addition to epidermal pigmentation, pathologic findings of melasma include extracellular matrix abnormality, especially solar elastosis. The disrupted basement membrane has been described in melasma with variable incidences. In the dermis, an increase in vascularity and an increase in the number of mast cells were observed, indicating that dermal factors have critical roles in the pathogenesis of melasma, despite the fact that melasma is characterized by epidermal hyperpigmentation. This review discusses such histologic characteristics of melasma, with consideration to their implications for melasma treatment.

In vivo time-sequential histological study focused on melanocytes: suggestion of golden time for intervention to prevent post-laser pigmentary changes

BACKGROUND

Post-inflammatory pigmentary changes after laser treatments are challenging adverse effect.

OBJECTIVE

To suggest an ideal time period with regard to intervention to prevent post-laser pigmentary changes, an in vivo time-sequential histological study focused on melanocytes was performed.

METHODS

The back skin of four volunteers was irradiated with Q-switched alexandrite laser (QSAL). In one subject (subject 4), topical corticosteroid was applied onto the irradiated skin from the time of irradiation to day 28. In all subjects, time-sequential skin biopsies were performed at baseline, an immediate time after irradiation, day 2, day 7, and day 28. Histological and immunohistochemical analyses were conducted.

RESULTS

Q-switched alexandrite laser led to the successful removal of pigments and most melanocytes from the epidermis in all subjects. At day 28, there was increased epidermal pigmentation in the skin of the subjects 1-3. It was noted that numerous activated melanocytes appeared on day 7, continued to be observed until day 28. However, in the subject 4, the melanocyte activation and post-laser pigmentary changes were not observed.

CONCLUSION

In regard to intervene melanocyte activation, at least 1 week after laser treatment is suggested as a 'golden' time period to prevent pigmentary changes.

The regulation of epidermal melanogenesis via cAMP and/or PKC signaling pathways: insights for the development of hypopigmenting agents

Abnormal pigmentation, particularly hyperpigmentation, is major issue of concern for people with colored skin. Several hypopigmenting agents, which exert their action by inhibiting tyrosinase activity and/or transcription, have been used for treatment. However, results have been discouraging. To manage abnormal pigmentation properly, the mechanisms of melanogenesis should be understood. Endogenous and exogenous factors affect melanogenesis via intracellular machineries. cAMP and PKC are critical factors of important transduction pathways and cross-talk between them could amplify the melanogenic effect. Here, factors involved in melanogenesis regulation via cAMP and/or PKC pathways are reviewed with their action mechanisms.

Proliferative effect of histamine on MA-10 Leydig tumor cells mediated through HRH2 activation, transient elevation in cAMP production, and increased extracellular signal-regulated kinase phosphorylation levels

Mast cells (MC) occur normally in the testis with a species-specific distribution, yet their precise role remains unclear. Testicular MC express histidine decarboxylase (HDC), the unique enzyme responsible for histamine (HA) generation. Evidence to date supports a role for HA as a local regulator of steroidogenesis via functional H₁ and H₂ receptor subtypes (HRH1 and HRH2, respectively) present in Leydig cells. Given that HA is a well-known modulator of physiological and pathological proliferation in many different cell types, we aimed in the present study to evaluate whether HA might contribute to the regulation of Leydig cell number as well as to the control of androgen production. Herein, we demonstrate, to our knowledge for the first time, that MA-10 Leydig tumor cells, but not normal immature Leydig cells (ILC), exhibit a proliferative response upon stimulation with HA that involves HRH2 activation, transient elevation of cAMP levels, and increased extracellular signal-regulated kinase (ERK) phosphorylation. Our results also reveal that MA-10 cells show significantly heightened HDC expression compared to normal ILC or whole-testicular lysate and that inhibition of HDC activity decreases MA-10 cell proliferation, suggesting a possible correlation between autocrine overproduction of HA and abnormally increased proliferation in Leydig cells. The facts that germ cells are also both source and target of HA and that multiple testicular cells are susceptible to HA action underline the importance of the present study, which we hope will serve as a first step for further research into regulation of non-MC-related HDC expression within the testis and its significance for testicular function.

Histamine receptor 2-mediated growth-differentiation factor-15 expression is involved in histamine-induced melanogenesis

Vitiligo is a progressive depigmenting disorder. Histamine has been shown to induce melanogenesis via histamine receptor 2, suggesting the possibility of histamine as a repigmenting agent for the treatment of vitiligo. However, the role and signaling mechanism of histamine are still unclear in melanogenesis, especially in relation to growth-differentiation factor-15, which is a protein belonging to transforming growth factor beta and found to be overexpressed in metastatic or malignant melanoma. We found that histamine induces growth-differentiation factor-15 in melanoma cell lines such as SK-MEL-2, B16F10, and melan-a cells. Therefore, in the present study, the role of growth-differentiation factor-15 in histamine-induced melanogenesis was investigated using gene silencing or overexpression of growth-differentiation factor-15 and histamine related compounds such as histamine, amthamine, and cimetidine. Gene silencing of growth-differentiation factor-15 suppressed histamine-induced proliferation, melanin production, tyrosinase activity, and chemotactic migration of SK-MEL-2 cells. Histamine-induced expression of tyrosinase, tyrosinase-related protein 1, and tyrosinase-related protein 2 was also suppressed by growth-differentiation factor-15 gene silencing. On the other hand, overexpression of growth-differentiation factor-15 using a plasmid containing growth-differentiation factor-15 in SK-MEL-2 cells increased melanin production and chemotactic migration. Amthamine induced expression of growth-differentiation factor-15 in a time and concentration dependent manner. Amthamine-induced expression of growth-differentiation factor-15 was suppressed by cimetidine. Our results suggest that growth-differentiation factor-15 is a new player in histamine-induced melanogenesis, which can help researchers to extend the knowledge of the role of the transforming growth factor beta family in melanogenesis and in skin pigment disorders such as vitiligo.

Towards a quantitative understanding of the MITF-PIAS3-STAT3 connection

Background

Expression of the two transcription factors microphthalmia-associated transcription factor (MITF) and signal transducer and activator of transcription 3 (STAT3) are tightly connected to cell proliferation and survival, and are important for melanocyte development. The co-regulation of MITF and STAT3 via their binding to a common inhibitor Protein Inhibitor of Activated STAT3 (PIAS3) is intriguing. A better quantitative understanding of this regulation is likely to be important for elucidation of the melanocyte biology.

Results

We present a mathematical model describing the MITF-PIAS3-STAT3 signalling network. A default parameter set was developed, partly informed by the literature and partly by constraining the model to mimic reported behavioural features of the system. In addition, a set of experiment-specific parameters was derived for each of 28 experiments reported in the literature. The model seems capable of accounting for most of these experiments in terms of observed temporal development of protein amounts and phosphorylation states. Further, the results also suggest that this system possesses some regulatory features yet to be elucidated.

Conclusions

We find that the experimentally observed crosstalk between MITF and STAT3 via PIAS3 in melanocytes is faithfully reproduced in our model, offering mechanistic explanations for this behaviour, as well as providing a scaffold for further studies of MITF signalling in melanoma.