Limitations of human occipital scalp hair follicle organ culture for studying the effects of minoxidil as a hair growth enhancer

The Emergent Power of Human Cellular vs Mouse Models in Translational Hair Research

Different animal models have been used for hair research and regeneration studies based on the similarities between animal and human skins. Primary knowledge on hair follicle (HF) biology has arisen from research using mouse models baring spontaneous or genetically engineered mutations. These studies have been crucial for the discovery of genes underlying human hair cycle control and hair loss disorders. Yet, researchers have become increasingly aware that there are distinct architectural and cellular features between the mouse and human HFs, which might limit the translation of findings in the mouse models. Thus, it is enticing to reason that the spotlight on mouse models and the unwillingness to adapt to the human archetype have been hampering the emergence of the long-awaited human hair loss cure. Here, we provide an overview of the major limitations of the mainstream mouse models for human hair loss research, and we underpin a future course of action using human cell bioengineered models and the emergent artificial intelligence.

Dermal Adipose Tissue Secretes HGF to Promote Human Hair Growth and Pigmentation

Hair follicles (HFs) are immersed within dermal white adipose tissue (dWAT), yet human adipocyte‒HF communication remains unexplored. Therefore, we investigated how perifollicular adipocytes affect the physiology of human anagen scalp HFs. Quantitative immunohistomorphometry, X-ray microcomputed tomography, and transmission electron microscopy showed that the number and size of perifollicular adipocytes declined during anagen‒catagen transition, whereas fluorescence-lifetime imaging revealed increased lipid oxidation in adipocytes surrounding the bulge and/or sub-bulge region. Ex vivo, dWAT tendentially promoted hair shaft production, and significantly stimulated hair matrix keratinocyte proliferation and HF pigmentation. Both dWAT pericytes and PREF1/DLK1⁺ adipocyte progenitors secreted HGF during human HF‒dWAT co-culture, for which the c-Met receptor was expressed in the hair matrix and dermal papilla. These effects were reproduced using recombinant HGF and abrogated by an HGF-neutralizing antibody. Laser-capture microdissection‒based microarray analysis of the hair matrix showed that dWAT-derived HGF upregulated keratin (K) genes (K27, K73, K75, K84, K86) and TCHH. Mechanistically, HGF stimulated Wnt/β-catenin activity in the human hair matrix (increased AXIN2, LEF1) by upregulating WNT6 and WNT10B, and inhibiting SFRP1 in the dermal papilla. Our study demonstrates that dWAT regulates human hair growth and pigmentation through HGF secretion, and thus identifies dWAT and HGF as important novel molecular and cellular targets for therapeutic intervention in human hair growth and pigmentation disorders.

Cell Enriched Autologous Fat Grafts to Follicular Niche Improves Hair Regrowth in Early Androgenetic Alopecia

BACKGROUND

Adipose and adipose derived regenerative cells (ADRCs) play an increasing role in androgenetic alopecia.

OBJECTIVES

The authors sought to evaluate the safety and feasibility of fat grafts enriched with ADRCs in early androgenetic alopecia.

METHODS

Seventy-one patients were treated: 16 with Puregraft fat and 1.0 × 106 ADRCs/cm2 scalp; 22 with Puregraft fat and 0.5 × 106 ADRCs/cm2 scalp, 24 with Puregraft fat alone, and 9 with saline control. Treatments were delivered into the skin and subcutaneous layer of the scalp. A total of 40 cm2 of scalp was treated and macrophotography and global photography were obtained at baseline and at 6, 24, and 52 weeks.

RESULTS

A total of 71 patients tolerated the procedures well. No unanticipated associated adverse events were reported. When evaluating all patients at 24 weeks, there were no statistical differences between any of the treatment groups with respect to nonvellus (terminal) hair counts or width. There were increases (mean change from baseline) in terminal hair count for the low-dose ADRC group in the Norwood Hamilton 3 subgroup at week 6 (13.90 ± 16.68), week 12 (11.75 ± 19.42), week 24 (16.56 ± 14.68), and week 52 (2.78 ± 16.15). For this subgroup, the difference in hair count between the low-dose ADRC group and no-fat saline control was statistically significant (P = 0.0318) at week 24.

CONCLUSIONS

Puregraft fat and ADRCs are safe and well tolerated. In early male hair loss, this therapy demonstrated a statistically significant increase in terminal hair counts relative to the control population at 24 weeks and represents a promising approach for early androgenetic alopecia.

LEVEL OF EVIDENCE: 2

Methods to Study Human Hair Follicle Growth Ex Vivo: Human Microdissected Hair Follicle and Human Full Thickness Skin Organ Culture

The culture of microdissected hair follicles (HFs) and scalp skin enriched in terminal HFs are the best currently available preclinical assays for studying hair and skin biology/pathology in the human system. While microdissected HF organ culture only allows the testing of compounds added into the culture medium, mimicking a systemic application, the scalp skin organ culture also is suitable to test topical and intradermal applications. Here, we describe different methods for isolation of human scalp HFs, the procedures for culturing the scalp skin and microdissected HFs and we also outline different delivery techniques (e.g., topical, systemic) to test active and control substances.

Autologous adipose transplantation an effective method to treat alopecia after trauma: a case report

Finding new therapies for male and female pattern hair loss treatment remains as great interest. The autologous fat grafting technique is a new method, and clinical experience was increased over the past 10–15 years. Adipose tissue is a biologically active and important tissue and can help drive the complex hair growth cycle. Surgeons have previously reported that autologous fat not only have a positive affect for reconstructive volume and esthetics after transplant but can also have positive skin and hair changes post-transplantation. In this study, lipoaspiration of adipose was performed by cannula and scalp injection was done. In this case report, the authors report that scalp injection of adipose tissue has a positive effect on a patient with alopecia after trauma. The findings suggest adipose tissue can be a promising alternative method to treating men and women alopecia.

Culture of the human pilosebaceous unit, hair follicle and sebaceous gland

Terence Kealey first pioneered the isolation and organ maintenance of human eccrine and sebaceous glands in the early to mid-1980. This led to subsequent methods describing the isolation and culture of human hair follicles, the human pilosebaceous unit as well as the sebaceous duct. The importance of these models in the study of the biology of human skin glands and appendages has been demonstrated in numerous publications and their importance as models for animal replacement, refinement and reduction (3Rs) is increasingly important. In particular, in vitro (ex vivo) hair follicle culture has played a significant part in helping elucidate the role of signalling molecules in regulating hair growth and hair fibre formation and has been especially useful in understanding metabolic aspects of hair growth. However, obtaining sufficient numbers of hair follicles is becoming increasingly difficult as plastic surgery becomes less invasive and smaller skin samples provided. There is therefore an urgent requirement for the next generation of in vitro models using cell lines and tissue engineering, and this has led to the development of immortalised cell lines as well as attempts to model hair follicle embryogenesis in vitro and development of skin on a chip.

Hair follicle growth by stromal vascular fraction-enhanced adipose transplantation in baldness

Great interest remains in finding new and emerging therapies for the treatment of male and female pattern hair loss. The autologous fat grafting technique is >100 years old, with a recent and dramatic increase in clinical experience over the past 10-15 years. Recently, in 2001, Zuk et al published the presence of adipose-derived stem cells, and abundant research has shown that adipose is a complex, biological active, and important tissue. Festa et al, in 2011, reported that adipocyte lineage cells support the stem cell niche and help drive the complex hair growth cycle. Adipose-derived regenerative cells (also known as stromal vascular fraction [SVF]) is a heterogeneous group of noncultured cells that can be reliably extracted from adipose by using automated systems, and these cells work largely by paracrine mechanisms to support adipocyte viability. While, today, autologous fat is transplanted primarily for esthetic and reconstructive volume, surgeons have previously reported positive skin and hair changes posttransplantation. This follicular regenerative approach is intriguing and raises the possibility that one can drive or restore the hair cycle in male and female pattern baldness by stimulating the niche with autologous fat enriched with SVF. In this first of a kind patient series, the authors report on the safety, tolerability, and quantitative, as well as photographic changes, in a group of patients with early genetic alopecia treated with subcutaneous scalp injection of enriched adipose tissue. The findings suggest that scalp stem cell-enriched fat grafting may represent a promising alternative approach to treating baldness in men and women.

Minoxidil topical treatment may be more efficient if applied on damp scalp in comparison with dry scalp

There is yet no consensus among prescribers whether minoxidil (MXD) formulations should be applied on wet/damp or dry scalp and no clear FDA guidelines on the matter. We hypothesized that the use of MXD on damp scalp may lead to higher drug penetration. First, because the drug diffusion and consequent deposition into the hair follicle may be favored when follicle cast is humid. Second, because humidity may also prevent drug crystallization and, therefore, maintain a higher thermodynamic activity for longer periods, which leads to increased penetration. Following in vitro experiments on rat and porcine skin we confirmed the hypothesis, which could markedly improve treatment effectiveness.

Regenerative medicine and hair loss: how hair follicle culture has advanced our understanding of treatment options for androgenetic alopecia

Many of the current drug therapies for androgenetic alopecia were discovered serendipitously, with hair growth observed as an off-target effect when drugs were used to treat a different disorder. Subsequently, several studies using cultured cells have enabled identification of hair growth modulators with similar properties to the currently available drugs, which may also provide clinical benefit. In situations where the current therapeutics do not work, follicular unit transplantation is an alternative surgical option. More recently, the concept of follicular cell implantation, or hair follicle neogenesis, has been attempted, exploiting the inherent properties of cultured hair follicle cells to induce de novo hair growth in balding scalp. In this review, we discuss both the advances in cell culture techniques that have led to a wider range of potential therapeutics to promote hair growth, in addition to detailing current knowledge on follicular cell implantation, and the challenges in making this approach a reality.

Mimicking hair disorders by genetic manipulation of organ-cultured human hair follicles

Human hair follicles can be dissected out of scalp skin and cultured in vitro in defined growth medium. Hair follicle organ cultures have previously been used to investigate the molecular and cellular mechanisms through which various factors regulate the maintenance and cycling of adult hair follicles. In this issue, Samuelov et al. transfected organ-cultured human hair follicles with siRNA nucleotides and suppressed the expression of the endogenous P-cadherin gene in follicular keratinocytes. Knocking down the expression of P-cadherin in hair follicles in vitro recapitulated the hair follicle phenotype observed in patients with hypotrichosis with juvenile macular dystrophy (HJMD) and enabled the authors to establish a cause-effect relationship between loss of P-cadherin and suppression of the canonical Wnt signaling pathway and upregulation of TGFβ2 during development of the hair abnormalities observed in HJMD patients.

Techniques for the discovery and evaluation of drugs against alopecia

INTRODUCTION

Hair care, color and style play an important role in physical appearance and self-perception. Hair loss or alopecia is a common dermatological and affective disorder. Factors contributing to alopecia include genetic predisposition, hormonal factors, disease status, side effects of chemotherapeutic agents and stress. To keep pace with the demand for drugs for alopecia, attempts are being made to explore drugs with hair-growth-promotion activity. To explore and evaluate these, it is necessary to be familiar with the basics and the availability and suitability of techniques and experimental models of hair growth activity assessment.

AREAS COVERED

Basic and advanced techniques and models for assessing hair growth activity. A variety of pharmacological models of hair growth are reviewed. This review will help in selecting a suitable, relevant, inexpensive, easy and reliable model for hair growth assessment.

EXPERT OPINION

There is a need to identify the genes involved in hair follicle growth for the production of more effective animal models of the disorder. Standardization of pharmacological models will also be essential for better comparison and validation of results. Recently developed hair follicle organ culture models are a suitable, relevant and inexpensive alternative to traditional whole-animal pharmacological models and will, largely, replace whole-animal systems in the future.

Point scanning confocal microscopy facilitates 3D human hair follicle imaging in tissue sections

Efficiency is a key factor in determining whether a scientific method becomes widely accepted in practical applications. In dermatology, morphological characterisation of intact hair follicles by traditional methods can be rather inefficient. Samples are embedded, sliced, imaged and digitally reconstructed, which can be time-consuming. Confocal microscopy, on the other hand, is more efficient and readily applicable to study intact hair follicles. Modern confocal microscopes deliver and collect light very efficiently and thus allow high spatial resolution imaging of relatively thick samples. In this letter, we report that we successfully imaged entire intact human hair follicles using point scanning confocal microscopy. Light delivery and light-collection were further improved by preparing the samples in 2,2'-Thiodiethanol (TDE), thus reducing refractive index gradients. The relatively short total scan times and the high quality of the acquired 3D images make confocal microscopy a desirable method for studying intact hair follicles under normal and pathological conditions.

Intermediate hair follicles: a new more clinically relevant model for hair growth investigations

BACKGROUND

Alopecia causes widespread psychological distress, but is relatively poorly controlled. The development of new treatments is hampered by the lack of suitable human hair follicle models. Although intermediate and vellus hair follicles are the main clinical targets for pharmacological therapy, terminal hair follicles are more frequently studied as smaller hair follicles are more difficult to obtain.

OBJECTIVES

This investigation was designed to quantify in vivo morphological and in vitro behavioural differences in organ culture between matched intermediate and terminal hair follicles, in order to develop a new clinically relevant model system.

METHODS

Microdissected terminal and intermediate hair follicles, from the same individuals, were analysed morphometrically (250 follicles; five individuals), or observed and measured over 9 days of organ culture (210 follicles; six individuals).

RESULTS

Intermediate hair follicles were less pigmented and smaller, penetrating less below the skin surface (mean +/- SEM) (2.59 +/- 0.07 vs. 3.52 +/- 0.10 mm; P = 0.02), with smaller fibre (0.03 +/- 0.002 vs. 0.07 +/- 0.002 mm), connective tissue sheath (0.24 +/- 0.01 mm vs. 0.33 +/- 0.01 mm), bulb (0.19 +/- 0.01 vs. 0.31 +/- 0.01 mm) and dermal papilla (0.06 +/- 0.002 vs. 0.12 +/- 0.01 mm) diameters (P < 0.001). Intermediate hair follicle bulbs appeared 'tubular', unlike their 'bulbous' terminal follicle counterparts. In organ culture they also grew more slowly (0.044 +/- 0.002 vs. 0.067 +/- 0.003 mm per day; P < 0.001), remained in anagen longer (84 +/- 0.03% vs. 74 +/- 0.03% at day 9; P = 0.012) and produced less hair fibre (0.36 +/- 0.02 vs. 0.50 +/- 0.03 mm; P < 0.001) than terminal follicles.

CONCLUSIONS

Smaller intermediate hair follicles showed major morphological differences from terminal follicles in vivo and retained significant, biologically relevant differences in vitro in organ culture. Therefore, intermediate hair follicles offer a novel, exciting, more clinically relevant, albeit technically difficult, model for future investigations into hair growth. This should be particularly important for developing new therapies.

Biology of human hair: know your hair to control it

Hair can be engineered at different levels--its structure and surface--through modification of its constituent molecules, in particular proteins, but also the hair follicle (HF) can be genetically altered, in particular with the advent of siRNA-based applications. General aspects of hair biology are reviewed, as well as the most recent contributions to understanding hair pigmentation and the regulation of hair development. Focus will also be placed on the techniques developed specifically for delivering compounds of varying chemical nature to the HF, indicating methods for genetic/biochemical modulation of HF components for the treatment of hair diseases. Finally, hair fiber structure and chemical characteristics will be discussed as targets for keratin surface functionalization.

Human hair follicles contain two forms of ATP-sensitive potassium channels, only one of which is sensitive to minoxidil

Hair disorders cause psychological distress but are generally poorly controlled; more effective treatments are required. Despite the long-standing use of minoxidil for balding, its mechanism is unclear; suggestions include action on vasculature or follicle cells. Similar drugs also stimulate hair, implicating ATP-sensitive potassium (K(ATP)) channels. To investigate whether K(ATP) channels are present in human follicles, we used organ culture, molecular biological, and immunohistological approaches. Minoxidil and tolbutamide, a K(ATP) channel blocker, opposed each other's effects on the growing phase (anagen) of scalp follicles cultured in media with and without insulin. Reverse transcriptase-polymerase chain reaction identified K(ATP) channel component gene expression including regulatory sulfonylurea receptors (SUR) SUR1 and SUR2B but not SUR2A and pore-forming subunits (Kir) Kir6.1 and Kir6.2. When hair bulb tissues were examined separately, epithelial matrix expressed SUR1 and Kir6.2, whereas both dermal papilla and sheath exhibited SUR2B and Kir6.1. Immunohistochemistry demonstrated similar protein distributions. Thus, human follicles respond biologically to K(ATP) channel regulators in culture and express genes and proteins for two K(ATP) channels, Kir6.2/SUR1 and Kir6.1/SUR2B; minoxidil only stimulates SUR2 channels. These findings indicate that human follicular dermal papillae contain K(ATP) channels that can respond to minoxidil and that tolbutamide may suppress hair growth clinically; novel drugs designed specifically for these channels could treat hair disorders.

L-carnitine-L-tartrate promotes human hair growth in vitro

The trimethylated amino acid l-carnitine plays a key role in the intramitochondrial transport of fatty acids for beta-oxidation and thus serves important functions in energy metabolism. Here, we have tested the hypothesis that l-carnitine, a frequently employed dietary supplement, may also stimulate hair growth by increasing energy supply to the massively proliferating and energy-consuming anagen hair matrix. Hair follicles (HFs) in the anagen VI stage of the hair cycle were cultured in the presence of 0.5-50 microm of l-carnitine-l-tartrate (CT) for 9 days. At day 9, HFs treated with 5 microm or 0.5 microm of CT showed a moderate, but significant stimulation of hair shaft elongation compared with vehicle-treated controls (P < 0.05). Also, CT prolonged the duration of anagen VI, down regulated apoptosis (as measured by TUNEL assay) and up regulated proliferation (as measured by Ki67 immunohistology) of hair matrix keratinocytes (P < 0.5). By immunohistology, intrafollicular immunoreactivity for TGFbeta2, a key catagen-promoting growth factor, in the dermal papilla and TGF-beta II receptor protein in the outer root sheath and dermal papilla was down regulated. As shown by caspase activity assay, caspase 3 and 7, which are known to initiate apoptosis, are down regulated at day 2 and day 4 after treatment of HFs with CT compared with vehicle-treated control indicating that CT has an immediate protective effect on HFs to undergo programmed cell death. Our findings suggest that l-carnitine stimulates human scalp hair growth by up regulation of proliferation and down regulation of apoptosis in follicular keratinocytes in vitro. They further encourage one to explore topical and nutraceutical administration of l-carnitine as a well-tolerated, relatively safe adjuvant treatment in the management of androgenetic alopecia and other forms of hair loss.

The effect of tripeptide-copper complex on human hair growth in vitro

The tripeptide-copper complex, described as a growth factor for various kinds of differentiated cells, stimulates the proliferation of dermal fibroblasts and elevates the production of vascular endothelial growth factor, but decreased the secretion of transforming growth factor-beta1 by dermal fibroblasts. Dermal papilla cells (DPCs) are specialized fibroblasts, which are important in the morphogenesis and growth of hair follicles. In the present study, the effects of L-alanyl-L-histidyl-L-lysine-Cu2+ (AHK-Cu) on human hair growth ex vivo and cultured dermal papilla cells were evaluated. AHK-Cu (10(-12) - 10(-9) M) stimulated the elongation of human hair follicles ex vivo and the proliferation of DPCs in vitro. Annexin V-fluorescein isothiocyanate/propidium iodide labeling and flow cytometric analysis showed that 10(-9) M AHK-Cu reduced the number of apoptotic DPCs, but this decrease was not statistically significant. The ratio of Bcl-2/Bax was elevated, and the levels of the cleaved forms of caspase-3 and PARP were reduced by treatment with 10(-9) M AHK-Cu. The present study proposed that AHK-Cu promotes the growth of human hair follicles, and this stimulatory effect may occur due to stimulation of the proliferation and the preclusion of the apoptosis of DPCs.

Dissecting the impact of chemotherapy on the human hair follicle: a pragmatic in vitro assay for studying the pathogenesis and potential management of hair follicle dystrophy

Chemotherapy-induced alopecia represents one of the major unresolved problems of clinical oncology. The underlying molecular pathogenesis in humans is virtually unknown because of the lack of adequate research models. Therefore, we have explored whether microdissected, organ-cultured, human scalp hair follicles (HFs) in anagen VI can be exploited for dissecting and manipulating the impact of chemotherapy on human HFs. Here, we show that these organ-cultured HFs respond to a key cyclophosphamide metabolite, 4-hydroperoxycyclophosphamide (4-HC), in a manner that resembles chemotherapy-induced HF dystrophy as it occurs in vivo: namely, 4-HC induced melanin clumping and melanin incontinence, down-regulated keratinocyte proliferation, massively up-regulated apoptosis of hair matrix keratinocytes, prematurely induced catagen, and up-regulated p53. In addition, 4-HC induced DNA oxidation and the mitochondrial DNA common deletion. The organ culture system facilitated the identification of new molecular targets for chemotherapy-induced HF damage by microarray technology (eg, interleukin-8, fibroblast growth factor-18, and glypican 6). It was also used to explore candidate chemotherapy protectants, for which we used the cytoprotective cytokine keratinocyte growth factor as exemplary pilot agent. Thus, this novel system serves as a powerful yet pragmatic tool for dissecting and manipulating the impact of chemotherapy on the human HF.

Effect of caffeine and testosterone on the proliferation of human hair follicles in vitro

BACKGROUND

Androgenetic alopecia (AGA) is a common problem in men of all ages, affecting approximately 50% at 50 years of age. The underlying cause is an androgen-dependent miniaturization of genetically predetermined hair follicles. Here, the hair organ culture model was used to investigate the effects of testosterone and caffeine; the latter being a promising candidate for hair growth stimulation.

METHODS

Hair follicles from 14 biopsies, taken from the vertex areas from male AGA patients, were cultivated for 120-192 h in vitro with normal William's E medium (control) or William's E medium containing different concentrations of testosterone and/or caffeine. Hair shaft elongation was measured daily and at the end of cultivation, cryosections of follicles were stained with Ki-67 to evaluate the degree and localization of keratinocyte proliferation.

RESULTS

Significant growth suppression was found in hair follicles treated with 5 microg/ml testosterone. This was counteracted by caffeine in concentrations of 0.001% and 0.005%. Moreover, caffeine alone led to a significant stimulation of hair follicle growth. These results were confirmed immunohistochemically by Ki-67 staining.

CONCLUSIONS

Androgen-dependent growth inhibition of ex vivo hair follicles from patients suffering from AGA was present in the human hair organ culture model, a constellation which may serve for future studies to screen new substances against androgen-dependent hair loss. Caffeine was identified as a stimulator of human hair growth in vitro; a fact which may have important clinical impact in the management of AGA.

Keratinocyte growth factor protects epidermis and hair follicles from cell death induced by UV irradiation, chemotherapeutic or cytotoxic agents

Owing to its potent cytoprotective properties for epithelial cells, keratinocyte growth factor (KGF) is successfully used for the treatment of chemotherapy- and radiotherapy-induced oral mucositis in cancer patients. It is therefore of major interest to determine possible clinical applications of KGF in other organs and in different stress situations and to unravel common and organ-specific mechanisms of KGF action. Here we show that KGF protects human keratinocytes from the toxicity of xenobiotics with electrophilic and oxidative properties and reduces the cell death induced by UV irradiation. In contrast to other cell types, cytoprotection of keratinocytes by KGF is not a direct anti-apoptotic effect but requires de novo protein synthesis. The in vitro findings are clinically relevant because KGF protected keratinocytes in organ-cultured human scalp hair follicles from the toxicity of the xenobiotic menadione. Moreover, injection of KGF into murine back skin markedly reduced cell death in the epidermis after UVB irradiation. This activity is dependent on FGF receptor signaling because it was abrogated in transgenic mice expressing a dominant-negative FGF receptor mutant in keratinocytes. Taken together, our results encourage the use of KGF for skin protection from chemical and physical insults.

Human hair growth ex vivo is correlated with in vivo hair growth: selective categorization of hair follicles for more reliable hair follicle organ culture

Of the numerous assays used to assess hair growth, hair follicle organ culture model is one of the most popular and powerful in vitro systems. Changes in hair growth are commonly employed as a measurement of follicular activity. Hair cycle stage of mouse vibrissa follicles in vivo is known to determine subsequent hair growth and follicle behavior in vitro and it is recommended that follicles be taken at precisely the same cyclic stage. This study was performed to evaluate whether categorization of human hair follicles by the growth in vivo could be used to select follicles of the defined anagen stage for more consistent culture. Occipital scalp samples were obtained from three subjects, 2 weeks later after hair bleaching. Hair growth and follicle length of isolated anagen VI follicles were measured under a videomicroscope. Follicles were categorized into four groups according to hair growth and some were cultured ex vivo for 6 days. Follicles showed considerable variations with respect to hair growth and follicle length; however, these two variables were relatively well correlated. Hair growth in culture was closely related with hair growth rate in vivo. Moreover, minoxidil uniquely demonstrated a significant increase of hair growth in categorized hair follicles assumed at a similar early anagen VI stage of hair cycle. Selection of follicles at a defined stage based on hair-growth rate would permit a more reliable outcome in human hair follicle organ culture.

Zinc as an ambivalent but potent modulator of murine hair growth in vivo- preliminary observations

Oral zinc (Zn(2+)) is often employed for treating hair loss, even in the absence of zinc deficiency, although its mechanisms of action and efficacy are still obscure. In the current study, we explored the in vivo effects of oral zinc using the C57BL/6 mouse model for hair research. Specifically, we investigated whether continuous administration of high-dose ZnSO(4) x 7H(2)O (20 mg/ml) in drinking water affects hair follicle (HF) cycling, whether it retards or inhibits chemotherapy-induced alopecia (CIA) and whether it modulates the subsequent hair re-growth pattern. Here, we show that high doses of oral zinc significantly inhibit hair growth by retardation of anagen development. However, oral zinc also significantly retards and prolongs spontaneous, apoptosis-driven HF regression (catagen). Oral zinc can also retard, but not prevent, the onset of CIA in mice. Interestingly, Zn(2+) treatment of cyclophosphamide-damaged HFs also significantly accelerates the re-growth of normally pigmented hair shafts, which reflects a promotion of HF recovery. However, if given for a more extended time period, zinc actually retards hair re-growth. Thus, high-dose oral zinc is a powerful, yet ambivalent hair growth modulator in mice, whose ultimate effects on the HF greatly depend on the timing and duration of zinc administration. The current study also encourages one to explore whether oral zinc can mitigate chemotherapy-induced hair loss in humans and/or can stimulate hair re-growth.