**Evaluation of Animal Models Suitable for Hair Research and Regeneration and Regeneration**

**Evaluation of Animal Models Suitable for Hair Research** 

DOI: 10.5772/intechopen.69698

Meda Sandra Orăsan and Andrei Coneac

Meda Sandra Orăsan and Andrei Coneac Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69698

#### **Abstract**

Hair loss and regeneration are the subjects of tremendous amount of research for multiple reasons: the well-known importance of hair in individual beauty, the fact that alopecia is a frequent dermatological disease, and that there are limited treatment options. The present work focuses on the evaluation of animal models used for hair research and regeneration. Besides mentioning the option of *in vitro* studies, the chapter analyzes the need of an animal model of alopecia, common used study designs, hair regrowth evaluation methods, and the limitations of the animal models in hair regrowth research. This chapter also discusses the structure of hair, its chemical composition, the properties and functions of hair, consequences of hair loss, the biology of hair loss, and regeneration and existing treatment options for alopecia. By using proper and well thought-out animal models, we aim to refine our knowledge on human hair diseases and hair regrowth. Hair research provides insights into the physiopathological pathways, genetic and cell biochemical mechanisms, and remains a field intensively explored and still inexhaustible.

**Keywords:** animal models, research *in vivo*, hair regrowth, hair regeneration, alopecia

#### **1. Introduction**

Hair loss and regeneration is the subject of tremendous amount of research for multiple reasons. First of all, as hair loss or alopecia is a frequent dermatological disease; second, the treatment options are limited and generate variable rates of success. Last but not least, hair is an important component of human outlook with a strong impact on the overall beauty and attraction of an individual. As several studies have shown, hair plays an interesting part in social and sexual communication.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

The chapter addresses several issues: the importance of hair from both personal and social perspective, the structure and chemical composition of hair, hair functions and properties, biology of hair loss and hair regrowth, and consequences of hair loss and treatment options. The authors aim to offer an overview of the hair regrowth *in vivo* and *in vitro* studies, focusing on the animal models, and describing the common study designs and their limitations.

Hair also contains inorganic substances (carbon 45.2%, oxygen 28%, hydrogen 6.6%, nitrogen 15%, and sulfur 5.2%) and water. Other mineral components of hair consist of iron, copper,

Evaluation of Animal Models Suitable for Hair Research and Regeneration

http://dx.doi.org/10.5772/intechopen.69698

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The color of hair depends on the type and quantity of melanin inside the cell. The hair follicle pigmentary unit provides the hair shaft color due to the melanin components (eumelanin and pheomelanin) and the interactions between follicular melanocytes, keratinocytes, and fibroblasts (also involved in wound healing) [11, 14]. In the case of the black hair, the pigment is

Hair is flexible and has elastic properties, being able to get longer by 20–50% under controlled traction. Under heat action, the elasticity decreases and hair can break easily. Hair is also hygroscopic, it can absorb water; a fact which decreases hair elasticity and resistance to a third

Hair resistance is mostly due to cysteine amino acid, a substance rich in sulphur, which plays an important role in hair cohesion. Hair resistance seems to be increased to physical and biological agents and decreased to chemicals. Excessive light with UV exposure, repetitive hair-dye, and hair perm generate the alteration of the hair elastic properties by the chemical and photochemical degradation of the amino acids from the keratin structure. Hair resistance equals to a force of 60 kg, but it is decreased in children and elderly people. Hair resistance

Human hair is different from hair grown by mammals due to unsynchronized growth cycles

Human hair exhibits a certain seasonal coordination, but the follicles work independently [15–17]. Latest research results sustain the idea that hair follicles act like neurons, being able to interconnect and generate hair loss and hair regrowth in a small region of the scalp. Human hair has a mosaic pattern as it consists of hair in different stages: the majority of the hair follicles (90%) being in growing phase (also known as anagen), 1–2% in regression (catagen phase), and 8–9% of the hair follicles are resting (in telogen phase) [18, 19]. The cyclic changes from anagen to telogen via catagen involve rapid remodeling of both the epithelial and der-

In both humans and animals, hair cycle is influenced by stimulatory and inhibitory factors, such as hormones, growth factors, cytokines, neuropeptides, and pharmaceutical products [18, 22, 23]. The dermal papilla supports an increased cell division and growth rate and induces the shift between anagen, catagen, and telogen [18, 19]. In telogen phase, the old hair is lost, but the follicle will be regenerated in early anagen, when new hair grows up

calcium, magnesium, zinc, potassium, and lead, all of them of external sources.

**5. Properties of hair**

of its normal value [4, 10].

also found in the extracellular compartment.

also depends on the hair diameter [4, 6].

and a sensitive response to androgen.

mal components of hair follicles [20, 21].

[24, 25].

**6. Biology of the hair loss and hair regrowth**

The main reason for hair research on animal models relies on the similarities between human and animal skin biology. New treatments for alopecia with different hair growth-promoting agents and various administration techniques have been tested on animal models to prove efficacy and to minimize possible adverse reactions.
