Histamine receptors in the skin melanophores of Indian bullfrog Rana tigerina

Understanding the ultrastructural aspects of berberine-induced skin-darkening activity in the toad, Bufo melanostictus, melanophores

Berberine is an active compound of Berberis vulgaris (Daruhaldi) with known multiple pharmacological activities, including antimicrobial, antiviral, anti-inflammatory, cholesterol-lowering, and anticancer effects. The present work aimed to study the ultrastructural effects of berberine to determine its skin-darkening potential using Bufo melanostictus melanophores, which has not been done to date. Light and electron microscopic analysis of isolated dorsal skin melanophores of B. melanostictus has been done after treatment with various concentrations of berberine, along with specific antagonists and agonists of β-adrenoceptors in order to explore the mechanism of action of berberine-induced skin darkening. The results showed that the number of melanophores with melanin-loaded dendrites increased in the subepidermal layer significantly in berberine-treated skin pieces in a dose-dependent manner leading to skin darkening. Highly electron-dense melanosomes of Stage IV increased considerably due to the enhanced process of melanization. These effects were found to be antagonized by propranolol, and were also found to be highly potentiated by isoprenaline, which is a specific β-adrenoceptor agonist. The findings show that berberine possesses a skin-darkening potential and could be used as a safe melanogenic agent for the treatment of hypopigmentation disorders or vitiligo.

Rapid color change in fish and amphibians - function, regulation, and emerging applications

Physiological color change is important for background matching, thermoregulation as well as signaling and is in vertebrates mediated by synchronous intracellular transport of pigmented organelles in chromatophores. We describe functions of and animal situations where color change occurs. A summary of endogenous and external factors that regulate this color change in fish and amphibians is provided, with special emphasis on extracellular stimuli. We describe not only color change in skin, but also highlight studies on color change that occurs using chromatophores in other areas such as iris and on the inside of the body. In addition, we discuss the growing field that applies melanophores and skin color in toxicology and as biosensors, and point out research areas with future potential.

On the role of histamine receptors in regulating pigmentary responses in Oreochromis mossambicus melanophores

PURPOSE

The present work was carried out to reveal the involvement of histamine receptors at the neuro-melanophore junction of teleost, Oreochromis mossambicus.

METHODS

The isolated scale melanophores were assayed using the mean melanophore size index and their responses were recorded in presence of various concentrations of histamine along with H(1) and H(2) receptor specific agonists and antagonist and potentiator compound 48/80.

RESULTS

Melanophores showed high sensitivity to histamine and its specific agonists. Histamine caused a dose-dependent pigment aggregation, whereas 2-(2-Pyridyl) ethylamine (PEA), a specific H(1)R agonist also caused aggregation in a similar manner. Conversely, amthamine, a specific H(2)R agonist resulted in pigment dispersion. The effects were antagonized by mepyramine; specific H(1)R antagonist and ranitidine a specific H(2)R antagonist.

CONCLUSION

It is concluded that O. mossambicus melanophores have both H(1) and H(2) receptors which mediate melanophore aggregation and dispersion respectively. Compound 48/80 augmented the melanin-aggregating and dispersing effects of PEA and amthamine. It is suggested that the effect of histamine is directly mediated through H1 and H2 receptors, whereas H1Rs may be predominantly involved in the aggregatory responses.

Withania somnifera root extracts induce skin darkening in wall lizard melanophores via stimulation of cholinergic receptors

The effects of the root extract of Withania somnifera and its active ingredient Withaferin A on the isolated melanophores of the wall lizard H. flaviviridis were studied in order to establish the mechanism of skin darkening at the cellular level. Significant skin darkening activity of the extract of W. somnifera and Withaferin A was observed on the isolated melanophores of the wall lizard. The melanin dispersal effects leading to the darkening of the skin were antagonised by atropine and hyoscine, and were also found to be highly potentiated by neostigmine. These findings suggest that the extract of W. somnifera, as well as its active principle, mimic the action of acetylcholine in melanin dispersion, thus leading to skin darkening via stimulation of cholinergic receptors of muscarinic nature within the melanophores of the wall lizard.

5-HT receptors as novel targets for optimizing pigmentary responses in dorsal skin melanophores of frog, Hoplobatrachus tigerinus

BACKGROUND AND PURPOSE

Biochemical identification of 5-HT has revealed similar projection patterns across vertebrates. In CNS, 5-HT regulates major physiological functions but its peripheral functions are still emerging. The pharmacology of 5-HT is mediated by a diverse range of receptors that trigger different responses. Interestingly, 5-HT receptors have been detected in pigment cells indicating their role in skin pigmentation. Hence, we investigated the role of this monoaminergic system in amphibian pigment cells, melanophores, to further our understanding of its role in pigmentation biology together with its evolutionary significance.

EXPERIMENTAL APPROACH

Pharmacological profiling of 5-HT receptors was achieved using potent/selective agonists and antagonists. In vitro responses of melanophores were examined by Mean Melanophores Size Index assay. The melanophores of lower vertebrates are highly sensitive to external stimuli. The immediate cellular responses to drugs were defined in terms of pigment translocation within the cells.

KEY RESULTS

5-HT exerted strong concentration-dependent pigment dispersion at threshold dose of 1 × 10(-6) g·mL(-1). Specific 5-HT(1) and 5-HT(2) receptor agonists, sumatriptan and myristicin. also induced dose-dependent dispersion. Yohimbine and metergoline synergistically antagonized sumatriptan-mediated dispersion, whereas trazodone partially blocked myristicin-induced dispersion. Conversely, 5-HT(3) and 5-HT(4) receptor agonists, 1 (3 chlorophenyl) biguanide (1,3 CPB) and 5-methoxytryptamine (5-MT), caused a dose-dependent pigment aggregation. The aggregatory effect of 1,3 CPB was completely blocked by ondansetron, whereas L-lysine partially blocked the effect of 5-MT.

CONCLUSIONS AND IMPLICATIONS

The results suggest that 5-HT-induced physiological effects are mediated via distinct classes of receptors, which possibly participate in the modulation of pigmentary responses in amphibian.

On the action and mechanism of withaferin-A from Withania somnifera, a novel and potent melanin dispersing agent in frog melanophores

The present work was carried out to determine the effects of lyophilized root extracts of Withania somnifera along with pure withaferin-A, on the isolated skin melanophores of frog, Rana tigerina which are disguised type of smooth muscle cells and offer excellent in vitro opportunities for studying the effects of pharmacological and pharmaceutical agents. The lyophilized extract of W. somnifera and its active ingredient withaferin-A induced powerful dose-dependent physiologically significant melanin dispersal effects in the isolated skin melanophores of R. tigerina, which were completely blocked by atropine as well as hyoscine. The per se melanin dispersal effects of lyophilized extracts of W. somnifera and its active ingredient withaferin-A got highly potentiated by neostigmine. It appears that the melanin dispersal effects of the extracts of W. somnifera and withaferin-A is mediated by cholino-muscarinic like receptors having similar properties.

In vitro responses of fish melanophores to lyophilized extracts of Psoralea corylifolia seeds and pure psoralen

CONTEXT

Psoralens are naturally occurring furanocumarins used in photochemotherapy of several skin diseases. They are obtained from dried ripe fruits of Psoralea corylifolia Linn. (Fabaceae). However, little research has been done to study the melanogenic activity of P. corylifolia seeds and their active ingredients on the pigment cells, the melanophores taking account of their cholinergic activity.

OBJECTIVE

The present work was carried out to determine the effects of lyophilized seed extracts of P. corylifolia, along with pure psoralen on the isolated scale melanophores of Channa punctatus Bloch. (Channidae), which are a disguised type of smooth muscle cells and offer excellent in vitro opportunities for studying the effects of drugs.

MATERIALS AND METHODS

Effects of lyophilized extracts of P. corylifolia and pure psoralen were studied on the isolated scale melanophores of C. punctatus as per the modified method of Bhattacharya et al. (1976) .

RESULTS

The lyophilized extract of P. corylifolia and its active ingredient psoralen caused significant melanin dispersal responses leading to darkening of the fish scale melanophores, which were completely antagonized by atropine and hyoscine. These melanin dispersal effects were also found to be markedly potentiated by neostigmine, an anticholinesterase agent.

DISCUSSION

In the present study, the lyophilized extract of P. corylifolia seeds and standard psoralen in different dose ranges induced powerful melanin dispersal effects of the previously adrenaline-aggregated isolated scale melanophores of C. punctatus. Comparatively, psoralen caused a more sustained and powerful melanin dispersal within the isolated fish melanophores and interestingly the concentrations required to achieve maximal dispersion of melanophore were 10 times less than that of lyophilized seed extract of P. corylifolia. The physiologically significant dose-related melanin dispersion effects of lyophilized P. corylifolia seeds and synthetic psoralen per se were found to be completely abolished by atropine and hyoscine, which are specific cholino-muscarinic receptor blockers. These data strongly indicate that in the fish C. punctatus, the dispersion of melanin granules within the scale melanophores is mediated by choline receptors of muscarinic nature.

CONCLUSION

It appears that the melanin dispersal effects of the extracts of P. corylifolia and pure psoralen leading to skin darkening are mediated by cholino-muscarinic- or cholino-psoralen-like receptors having similar properties.

Nigella sativa seed extract and its bioactive compound thymoquinone: the new melanogens causing hyperpigmentation in the wall lizard melanophores

OBJECTIVE

The effects of the lyophilized seed extract of Nigella sativa and its active ingredient, thymoquinone, were studied on the isolated melanophores of the wall lizard to find the mechanism of skin darkening at the cellular level.

METHODS

The integumental melanophores of the wall lizard, Hemidactylus flaviviridis, were assayed using the mean melanophore size index and their responses were recorded in the presence of various concentrations of the plant extract, thymoquinone, specific antagonists and potentiator.

KEY FINDINGS

Significant skin darkening activity of the extract of N. sativa and thymoquinone was observed on the isolated melanophores of the wall lizard. The pigment cells responded by distinct dispersion leading to skin darkening. The effect was physiologically significant as re-immersion in physiological saline made the melanophores return to their normal intermediate state. These melanin dispersal effects were antagonized by atropine as well as hyoscine and were also found to be highly potentiated by neostigmine, an anticholinesterase agent.

CONCLUSIONS

These findings suggest that the extract of N. sativa, as well as its active principle, mimic the action of acetylcholine in melanin dispersion leading to skin darkening via stimulation of cholinergic receptors of muscarinic nature within the melanophores of wall lizard. This study opens new vistas for the use of N. sativa active ingredient, thymoquinone, as a novel melanogen for its clinical application in skin disorders such as hypopigmentation or vitiligo.

Vertebrate melanophores as potential model for drug discovery and development: a review

Drug discovery in skin pharmacotherapy is an enormous, continually expanding field. Researchers are developing novel and sensitive pharmaceutical products and drugs that target specific receptors to elicit concerted and appropriate responses. The pigment-bearing cells called melanophores have a significant contribution to make in this field. Melanophores, which contain the dark brown or black pigment melanin, constitute an important class of chromatophores. They are highly specialized in the bidirectional and coordinated translocation of pigment granules when given an appropriate stimulus. The pigment granules can be stimulated to undergo rapid dispersion throughout the melanophores, making the cell appear dark, or to aggregate at the center, making the cell appear light. The major signals involved in pigment transport within the melanophores are dependent on a special class of cell surface receptors called G-protein-coupled receptors (GPCRs). Many of these receptors of adrenaline, acetylcholine, histamine, serotonin, endothelin and melatonin have been found on melanophores. They are believed to have clinical relevance to skin-related ailments and therefore have become targets for high throughput screening projects. The selective screening of these receptors requires the recognition of particular ligands, agonists and antagonists and the characterization of their effects on pigment motility within the cells. The mechanism of skin pigmentation is incredibly intricate, but it would be a considerable step forward to unravel its underlying physiological mechanism. This would provide an experimental basis for new pharmacotherapies for dermatological anomalies. The discernible stimuli that can trigger a variety of intracellular signals affecting pigment granule movement primarily include neurotransmitters and hormones. This review focuses on the role of the hormone and neurotransmitter signals involved in pigment movement in terms of the pharmacology of the specific receptors.

Psoralea corylifolia extracts stimulate cholinergic-like psoralen receptors of tadpole-tail melanophores, leading to skin darkening

The present work was carried out to determine the effects of lyophilized seed extracts of Psoralea corylifolia along with pure psoralen, its active ingredient on the isolated tail-piece melanophores of Bufo melanostictus, a type of disguised smooth muscle cells, which offer excellent in vitro opportunities for studying the effects of pharmacological and pharmaceutical agents. In the present study, it was found that lyophilized extract of P. corylifolia and its active ingredient psoralen induced powerful, dose-dependent, physiologically significant melanin dispersal effects in the isolated tail melanophores of B. melanostictus, which were completely blocked by atropine as well as hyoscine. The per se melanin dispersal effects of lyophilized extracts of P. corylifolia and its active ingredient psoralen were highly potentiated by neostigmine. It appears that the melanin dispersal effects of the extracts of P. corylifolia and psoralen are mediated by cholino-muscarinic or cholino-psoralen like receptors having similar properties that need to be studied further.