The Vertebrate Pigmentary System: From Pigment Cells to Disorders

Skin color in vertebrates predominantly depends on the presence of specialized cells that produce pigment. These special cells absorb or reflect light in a specific way to impart color to the skin and are called as chromatophores. Chromatophores are grouped into melanophores, erythrophores, xanthophores, leucophores and iridophores which largely depend on the pigment they produce. Melanophores are the most important type of chromatophores responsible for dorsal pigmentation in many vertebrates including fishes, amphibians and reptiles. In birds and mammals, melanophores are called melanocytes. All melanophores or melanocytes store thousands of dark brown/black biopolymer pigment melanins, packaged into membrane bound intra-cytoplasmic vesicles called as melanosomes. Melanophores or melanocytes originated from the neural crest cells, induced by several extracellular signals. Melanoblasts, precursor of melanocytes migrate, proliferate, differentiate and spread to their final destination in the basal layer of epidermis and hair follicles, however, distribution of melanocytes varies among different species. The embryonic development of melanocytes offers an opportunity to better understand the concept of vertebrate pigmentation. Thus the present chapter provides siginificant knowledge on the vertebrate pigment cells from origin to different stages of their development.

Melanophores or melanocytes, originated from the neural crest cells, contain melanosomes which are membrane-bound vesicles. Melanosomes are filled with dark coloured pigment called melanin, which has a crucial function in the biological color adaptation of vertebrates. Melanophore control via melanosome trafficking with microfilaments produce a variety of striking color pattern. Melanosome relaxation and contraction during pigment transfer is similar to the relaxation and contraction of smooth muscle cells. Studies have revealed that melanophores of all vertebrates including fish, amphibians, reptiles, mammals are functionally modified smooth muscle cells. The present chapter highlights the experimental based studies that have shown the comparison of melanophores with smooth muscle cells.

Vertebrate skin pigmentation is the phenotypic trait which is determined by a pigment, melanin; a biopolymer produced within epidermal melanocytes, packaged in specialized organelles called melanosomes by a process called melanogenesis. Eumelanin and pheomelanin are the two types of melanin formed within the melanocytes. The process of melanin production and its transfer to keratinocytes defines visible skin pigmentation. Various intrinsic factors including several genes involved in many signalling pathways such as SCF/KIT, neuregulin, endothelin, WNT, glutamatergic, adrenergic signalling pathways are involved in the process of melanogenesis. Along with the internal factors, some external factors including ultraviolet radiations, environmental pollutants and hormonal impregnation are also responsible for the increase of melanin synthesis. In the present chapter, we have discussed the biochemistry of the process of melanogenesis with a focus on a mechanism of melanin synthesis and the internal and external factors affecting melanogenesis.

Skin pigmentation contributes predominantly to the health and quality of life of human beings. Melanin imparts color to the skin, which is produced during the process of melanogenesis by the specialized cells, melanocytes. Many endogenous and exogenous factors released from epidermal and dermal components regulate constitutive skin pigmentation. The dysregulation of these factors followed by irregular production and distribution of melanin leads to the onset of pigmentary disorders such as hyperpigmentation or hypopigmentation. Pigmentation disorders include the entities that are characterized by a pathological change in melanocytes to produce melanin. Excess production of melanin leads to hyperpigmentary disorders and less or lack of melanin leads to hypopigmentary disorders. The present chapter is dedicated to the introduction and discussion of various pigmentary disorders with an overview of their etiologies and pathogenesis.

Melasma, vitiligo, lentigos, post inflammatory hyperpigmentation are the most common pigmentary disorders, which are caused by the altered production and distribution of melanin in the skin. Various intrinsic and extrinsic factors including ultraviolet radiation, food, chemical, certain medications, hormones etc. are responsible for affecting pigment cell functions with an altered amount of melanin pigment. As a result, pigmentation disorders are caused, which may be either hyperpigmentation or hypopigmentation. These are commonly seen in dermatology practice and can have a negative psychosocial impact on human life. In spite being of cosmetic concern, these disorders are devastating and stigmatizing; hence, there is an urgent need for effective treatment of pigmentary disorders based on their prevalence and impact on the quality of life. Prevalence of pigmentary disorders has been assessed in many countries of the world. In the present chapter, we have discussed about the prevalence of pigmentary disorders with their impact on quality of life and social status of an individual.

Melanin is responsible for imparting color to the skin, hairs, eyes, and protecting the skin from harmful UV radiation. It is produced inside the specialized cells called melanocytes through a series of chemical and enzymatic reactions. However, due to the dysregulation of the factors responsible for melanin production, the irregular production and distribution of melanin occur, which lead to the onset of pigmentary disorders, such as hyperpigmentation or hypopigmentation. Pigmentary disorders are not always physically debilitating but have been associated with elevated psychosocial problems such as depression, frustration and anger. These psychosocial burdens in turn influence the quality of life and self-esteem. So, the treatment of pigmentation diseases appears as a growing concern to dermatologists today. Several treatment strategies including chemical peeling, stem cell transplant, topical treatment, laser therapy etc. have been unleashed in order to get rid of the problem. Hence, in the present chapter, we have discussed about the existing treatment options for pigmentation diseases practised by dermatologists all over the world.

Color of the human skin is primarily due to the presence of pigment melanin, which is produced by the specialized cells called melanocytes. Normal pigmentation is dependent on the normal structure and function of these cells. Irregular lightening of skin lead to hypopigmentary disorder of the skin in which cutaneous and ocular melanocytes are destroyed resulting in loss of pigmentation. Hypopigmentary disorders remained one of the enigmatic issues since the early days of human civilization. Several conventional treatment modalities are available for hypopigmentary disorders; however unsatisfactory results and the indefinite possibility of relapse generally make patients dissatisfied with the treatment. Consequently, the treatment with botanical extracts has better results with less or few side effects. Till date, various plants and their constituents have been tested for their repigmentation activity and results are highly acceptable. In the present chapter, we have emphasized the use of plants and their constituents for the treatment of skin hypopigmentation. Various studies in support of the plant based treatments have also been discussed.

Melanin is responsible to impart color to the skin as well as to provide protection from harmful UV radiation. But it’s excess production and distribution leads to hyperpigmentation and its related disorders. Several treatment strategies have been used to treat the problem of hyperpigmentation, including chemical peeling, dermabrasion, laser, topical treatment, etc. But skin burn, dyspigmentation, acne, swelling, pain etc. are some of the after effects found associated with these treatment options. To keep in view of the side effects of current treatment modalities and in order to get rid of the problem of hyperpigmentation, scientists were focussed on traditional system of treatment in which the skin treatment was done by natural products, which are without toxicological implications. Hence, various medicinal plants and their constituents having few or no risk of side effects have been tested for their efficacies to treat disorders of hyperpigmentation. In the present chapter, we have discussed some of those plants and their active ingredients which have been successfully used for the treatment of hyperpigmentation.

Melanin pigment has a photo defensive role in human skin, but its redundant production and distribution lead to the problem of hyperpigmentation. Biosynthesis of melanin initiated from tyrosine oxidation through the key enzyme tyrosinase. In addition to human and animal, tyrosinase is broadly distributed in plants also and is responsible for browning of fruits and vegetables. Quest for the search of tyrosinase inhibitors is significant to enable the development of therapies for the prevention and treatment of hyperpigmentation and the undesirable browning of fruits and vegetables. Various synthetic and natural compounds have been tested for their inhibitory activity but the mechanism of inhibition is not known so far, and there is a continuous hunt for information concerning intermolecular interaction between inhibitors and tyrosinase. Thus, computer aided methods are consequently used to overwhelmed such issues. In silico methods such as molecular docking simulation, make it possible to understand the intermolecular interaction between inhibitors and tyrosinase, and hence, help identify new and potent tyrosinase inhibitors. The present chapter has pointed out the role of computational tools for the elucidation of tyrosinase inhibitors, highlighting the examples of certain compounds whose antityrosinase activities have been evaluated using molecular docking algorithms.

A less or excess production and distribution of melanin pigment leads to pigmentary disorders in human beings. Reduced melanin production results in hypopigmentation, whereas its excess production results in hyperpigmentation. There are several intrinsic and extrinsic factors that are responsible for causing these disorders. Many proteins and enzymes are involved in the complex process of pigmentation called melanogenesis. Any defect in the proteins or enzymes and/or any pathway of melanogenesis due to any of the factors may cause pigmentary disorders. There are certain things that have to be taken care of in order to avoid the dysfunctioning of the components of melanogenesis. Such things include some drugs, chemical reagents, hair dyes, food allergens, prolonged use of antibiotics, use of certain natural allergens, excessive sun exposure etc. The present chapter is dedicated to the effects of these things on skin pigmentation and the preventive approach to overcome the problems of skin hypopigmentation and hyperpigmentation caused by them.