Hormone‐related hair disorders – from clinical needs to new therapeutic perspectives

Abstract

The hair follicle and its appendages are important target structures for hormones. Plasma levels, local hormone metabolism and differential receptor expression regulate hair growth and hair cycling as well as sebaceous gland function. Even minor imbalances in this system, e.g. abnormal expression of hair follicle‐associated isoenzymes, may cause clinical symptoms such as hair loss, seborrhoea or hirsutism.Conventional therapeutic strategies, which aim to control peripheral hyperandrogenism, include systemic administration of androgen inhibitors (e.g. oral contraceptives, GnRH analogues), peripheral androgen blockers (CPA, CMA, glutamide, finasteride) as well as topical application of estrogens. As our knowledge about hormone systems and their complex interactions increases, new molecules are gaining importance: rosiglitazone and metformin are compounds which increase the sensitivity to insulin, topical application of minoxidil has been shown to regulate perifollicular blood flow and vascularization, and anti‐inflammatory compounds can as well be beneficial in the treatment of androgenetic alopecia.Because such therapies are, still, rather unspecific, current research focuses on the development of individualized strategies which allow to specifically treat the various manifestations caused by hormone‐related disorders. From our perspective, the aims of future drug development are as follows.In the first place, the identification of new targets, possibly beyond sex steroids in the narrow sense is highly important. Components of the POMC‐system, for example, have been shown to regulate cell differentiation and also hair cycling.And secondly, to develop drug delivery systems, which allow to specifically directing active compounds to target structures. Such improved drug delivery may allow to reduce side‐effects and to increase the efficacy of current therapies. Studies by our group and others suggest that microparticles, due to their ability to aggregate in the hair follicle openings, are promising drug delivery systems. In fact, we recently reported that the penetration depths of transcutaneously applied microparticles into the follicular duct depends on the size of the particles and on the dimension of the hair follicle, suggesting that particle‐based drug delivery systems allow to selectively target hair follicle compartments such as the entry level of the sebaceous duct or the bulge region.