The biology of hair diversity

The Trotter collection: A review of Mildred Trotter's hair research and an update for studies of human variation

OBJECTIVES

Mildred Trotter was an anatomist and physical anthropologist whose studies on hair morphology, growth, somatic distribution, and trait relationships to age and ethnogeographic population were foundational to the field of microscopical hair analysis. The collection of human hair samples she assembled for her research has been an underutilized resource for studies on human hair variation. We applied updated methods and reviewed Trotter's original data to reassess the relationship hair traits have to diverse population labels.

METHODS

Hair form and pigmentation patterns were measured from a subset of the hair samples accumulated by Trotter and we compared our data to Trotter's original results. Variability in hair traits were tested within individuals, within populations, and among ethnogeographic groups.

RESULTS

Measured hair cross-section dimensions and melanosome density and distribution revealed substantial variability within individuals and ethnogeographic populations. Hair traits were found to not be distinctly separable by ancestry but instead showed continuous variation across human populations. Trotter's measurements were precise and the dataset she compiled remains valid, though the conclusions should be reviewed in light of our current understanding of human variation.

DISCUSSION

Our findings support moving away from categorical ancestry classifications and eliminating the use of outdated racial typologies in favor of more descriptive trait analysis. Detailed analysis of trait pattern distributions are presented that may be useful for future research on human variation. We point to the need for additional research on human variation and hair trait relationships with reference to known population affinity.

The Role of BMP7 in the Proliferation of Hu Sheep Dermal Papilla Cells Is Influenced by DNA Methylation

Previous studies have shown that the BMP7 gene is differentially expressed in Hu sheep lamb skin of different pattern types, and its expression level is significantly correlated with hair follicle indices of different pattern types, but the molecular mechanism of the differential expression of the BMP7 gene remains unclear. This study investigated the effect of DNA methylation on the transcriptional expression of BMP7. Firstly, we found that the mRNA expression of the BMP7 gene and the activity of the core promoter of the BMP7 gene were upregulated after 5-Aza-Deoxycytidine-induced demethylation treatment using qRT-PCR and double luciferase reporter assay. Then, we found that the proliferation of Hu sheep DPCs in vitro was promoted after 5-Aza-Deoxycytidine-induced demethylation treatment through qRT-PCR, CCK-8, and EdU assay, and that the overexpression of DNMT1 in DPCs induced the opposite effect. In addition, the results of the cell cycle assay reveal that the percentage of cells in the S phase was increased after 5-Aza-Deoxycytidine-induced demethylation treatment, and that the percentage of cells in the S phase was decreased after overexpression of DNMT1 in DPCs. This study indicated that the differential expression of the BMP7 gene in different patterns of Hu sheep lamb skin may be regulated by DNA methylation modification. In addition, DNA methylation can regulate the proliferation and cell cycle of DPCs in Hu sheep.

Metabolomics reveals metabolites associated with hair follicle cycle in cashmere goats

BACKGROUND

The hair follicle is a skin accessory organ that regulates hair development, and its activity varies on a regular basis. However, the significance of metabolites in the hair follicle cycle has long been unknown.

RESULTS

Targeted metabolomics was used in this investigation to reveal the expression patterns of 1903 metabolites in cashmere goat skin during anagen to telogen. A statistical analysis was used to investigate the potential associations between metabolites and the hair follicle cycle. The findings revealed clear changes in the expression patterns of metabolites at various phases and in various feeding models. The majority of metabolites (primarily amino acids, nucleotides, their metabolites, and lipids) showed downregulated expression from anagen (An) to telogen (Tn), which was associated with gene expression, protein synthesis and transport, and cell structure, which reflected, to some extent, that the cells associated with hair follicle development are active in An and apoptotic in An-Tn. It is worth mentioning that the expression of vitamin D3 and 3,3',5-triiodo-L-thyronine decreased and then increased, which may be related to the shorter and longer duration of outdoor light, which may stimulate the hair follicle to transition from An to catagen (Cn). In the comparison of different hair follicle development stages (An, Cn, and Tn) or feeding modes (grazing and barn feeding), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that common differentially expressed metabolites (DEMs) (2'-deoxyadenosine, L-valine, 2'-deoxyuridine, riboflavin, cytidine, deoxyguanosine, L-tryptophan, and guanosine-5'-monophosphate) were enriched in ABC transporters. This finding suggested that this pathway may be involved in the hair follicle cycle. Among these DEMs, riboflavin is absorbed from food, and the expression of riboflavin and sugars (D-glucose and glycogen) in skin tissue under grazing was greater and lower than that during barn feeding, respectively, suggesting that eating patterns may also alter the hair follicle cycle.

CONCLUSIONS

The expression patterns of metabolites such as sugars, lipids, amino acids, and nucleotides in skin tissue affect hair follicle growth, in which 2'-deoxyadenosine, L-valine, 2'-deoxyuridine, riboflavin, cytidine, deoxyguanosine, L-tryptophan, and guanosine-5'-monophosphate may regulate the hair follicle cycle by participating in ABC transporters. Feeding practices may regulate hair follicle cycles by influencing the amount of hormones and vitamins expressed in the skin of cashmere goats.

Changing human hair fibre colour and shape from the follicle

INTRODUCTION

Natural hair curvature and colour are genetically determined human traits, that we intentionally change by applying thermal and chemical treatments to the fibre. Presently, those cosmetic methodologies act externally and their recurrent use is quite detrimental to hair fibre quality and even to our health.

OBJECTIVES

This work represents a disruptive concept to modify natural hair colour and curvature. We aim to model the fibre phenotype as it is actively produced in the follicle through the topical delivery of specific bioactive molecules to the scalp.

METHODS

Transcriptome differences between curly and straight hairs were identified by microarray. In scalp samples, the most variable transcripts were mapped by in situ hybridization. Then, by using appropriate cellular models, we screened a chemical library of 1200 generic drugs, searching for molecules that could lead to changes in either fibre colour or curvature. A pilot-scale, single-centre, investigator-initiated, prospective, blind, bilateral (split-scalp) placebo-controlled clinical study with the intervention of cosmetics was conducted to obtain a proof of concept (RNEC n.92938).

RESULTS

We found 85 genes transcribed significantly different between curly and straight hair, not previously associated with this human trait. Next, we mapped some of the most variable genes to the inner root sheath of follicles, reinforcing the role of this cell layer in fibre shape moulding. From the drug library screening, we selected 3 and 4 hits as modulators of melanin synthesis and gene transcription, respectively, to be further tested in 33 volunteers. The intentional specific hair change occurred: 8 of 14 volunteers exhibited colour changes, and 16 of 19 volunteers presented curvature modifications, by the end of the study.

CONCLUSION

The promising results obtained are the first step towards future cosmetics, complementary or alternative to current methodologies, taking hair styling to a new level: changing hair from the inside out.

Basic principles of hair follicle structure, morphogenesis, and regeneration

Diseases affecting the hair follicle are common in domestic animals, but despite the importance of an intact skin barrier and a fully functional hair coat, knowledge about the detailed morphological features and the diversity of these complex mini-organs are often limited, although mandatory to evaluate skin biopsies with a history of alopecia. The factors that regulate the innate hair follicle formation and the postnatal hair cycle are still not completely understood in rodents, only rudimentarily known in humans, and are poorly understood in our companion animals. This review aims to summarize the current knowledge about hair follicle and hair shaft anatomy, the arrangement of hair follicles, hair follicle morphogenesis in the embryo, and the lifelong regeneration during the postnatal hair cycle in domestic animals. The role of follicular stem cells and the need for a multitude of interacting signaling events during hair follicle morphogenesis and regeneration is unquestioned. Because of the lack of state of the art methods that can be applied in rodents but are not feasible in companion animals, most of the information in this review is based on rodent studies. However, the few data from domestic animals that are available will be discussed, and it can be assumed that at least the principal molecular mechanisms are similar in rodents and other species.

Morphological and chemical profiling for forensic hair examination: A review of quantitative methods

Within the past two decades, there have been many studies for quantitative analysis on human hair samples. Microscopical and chemical analysis techniques have been used to analyze various aspects of hair regarding biological, chemical, anthropological, cosmetic, and forensic applications. Studies have attempted to develop quantification methods to increase the evidentiary value of hair in forensic casework. The literature reviewed in this paper provides some of the current techniques used for forensic examinations and quantitative methods. Although microscopical analysis has been scrutinized in the past, using chemical and microscopical techniques can provide a myriad of information. The extraction of DNA from hair provides high-value evidence; however, it may not be readily available and may yield inconclusive results. Hair analysis can be used for many forensic applications such as comparison, toxicology, and exposure analysis. In this article, we will review published research material regarding chemical and microscopical techniques for human hair analysis. Aspects considered for this review were the sample size requirement for analysis and the destructive nature of the instrumental method. This review will focus on both macro and micro quantitative methods for human hair analysis.

How different is human hair? A critical appraisal of the reported differences in global hair fibre characteristics and properties towards defining a more relevant framework for hair type classification

This review critically appraises the reported differences in human hair fibre within three related domains of research: hair classification approaches, fibre characteristics and properties. The most common hair classification approach is based on geo-racial origin, defining three main groups: African, Asian and Caucasian hair. This classification does not account sufficiently for the worldwide hair diversity and intergroups variability in curl, shape, size and colour. A global classification into eight curl types has been proposed but may be too complex for reproducibility. Beyond that, hair cross-sectional shape and area have been found to have an inverse relation to curl: straighter fibres are circular with larger cross-sectional area, whilst the curlier fibres are elliptical with smaller cross-sectional area. These geometrical differences have been associated with bilateral vs homogenous distribution of cortical cell in curly vs straight hair respectively. However, there is no sufficient data demonstrating significant differences in hair amino composition, but proteomic studies are reporting associations of some proteins with curly hair. Eumelanin's relative abundance has been reported in all hair colours except for red hair which has a high pheomelanin content. Higher tensile and fatigue strength of straight hair are reported, however, curly hair fragility is attributed to knotting, and crack and flow formations rather than the structural variations. African hair has been found to have the highest level of lipids, whilst the water sorption of Caucasian hair is the highest, and that of Asian hair the lowest. Not all comparative studies clearly report their hair sampling approaches. Therefore, to strengthen the robustness of comparative studies and to facilitate cross-study data comparisons, it is recommended that the following hair defining characteristics are reported in studies: hair cross sectional diameter/area, curl type, hair assembly colour, as well as where possible donor data (age/gender) and sample pooling approach.

Assessment of the Genetic Spectrum of Uncombable Hair Syndrome in a Cohort of 107 Individuals

Importance

Uncombable hair syndrome (UHS) is a rare hair shaft anomaly that manifests during infancy and is characterized by dry, frizzy, and wiry hair that cannot be combed flat. Only about 100 known cases have been reported so far.

Objective

To elucidate the genetic spectrum of UHS.

Design, Setting, and Participants

This cohort study includes 107 unrelated index patients with a suspected diagnosis of UHS and family members who were recruited worldwide from January 2013 to December 2021. Participants of all ages, races, and ethnicities were recruited at referral centers or were enrolled on their own initiative following personal contact with the authors. Genetic analyses were conducted in Germany from January 2014 to December 2021.

Main Outcomes and Measures

Clinical photographs, Sanger or whole-exome sequencing and array-based genotyping of DNA extracted from blood or saliva samples, and 3-dimensional protein modeling. Descriptive statistics, such as frequency counts, were used to describe the distribution of identified pathogenic variants and genotypes.

Results

The genetic characteristics of patients with UHS were established in 80 of 107 (74.8%) index patients (82 [76.6%] female) who carried biallelic pathogenic variants in PADI3, TGM3, or TCHH (ie, genes that encode functionally related hair shaft proteins). Molecular genetic findings from 11 of these 80 individuals were previously published. In 76 (71.0%) individuals, the UHS phenotype were associated with pathogenic variants in PADI3. The 2 most commonly observed PADI3 variants account for 73 (48.0%) and 57 (37.5%) of the 152 variant PADI3 alleles in total, respectively. Two individuals carried pathogenic variants in TGM3, and 2 others carried pathogenic variants in TCHH. Haplotype analyses suggested a founder effect for the 4 most commonly observed pathogenic variants in the PADI3 gene.

Conclusions and Relevance

This cohort study extends and gives an overview of the genetic variant spectrum of UHS based on molecular genetic analyses of the largest worldwide collective of affected individuals, to our knowledge. Formerly, a diagnosis of UHS could only be made by physical examination of the patient and confirmed by microscopical examination of the hair shaft. The discovery of pathogenic variants in PADI3, TCHH, and TGM3 may open a new avenue for clinicians and affected individuals by introducing molecular diagnostics for UHS.

A Body-Neutral and Gender-Neutral Modified Ferriman-Gallwey Diagram

BACKGROUND

The modified Ferriman-Gallwey (mFG) diagram for scoring hirsutism uses images with traditionally Eurocentric feminine features. No reports have documented its utility in patients with other gender identities.

CASE

A 16-year-old nonbinary masculine patient, assigned female sex at birth, was seen for hyperandrogenism and irregular menses. They declined an exam, citing body dysphoria, and declined self-documenting on the mFG diagram, expressing anxiety with gendered images. We subsequently developed a novel, gender-inclusive mFG diagram, which the patient was then comfortable using to document their hair pattern.

SUMMARY AND CONCLUSION

This case documents how the binary gendered characteristics of the mFG diagram can impact the care of patients. As gender expression is highly individual, we created the first gender-inclusive version of the mFG diagram to enhance care for all patients.

A New Universal Follicular Unit Excision Classification System for Hair Transplantation Difficulty and Patient Outcome

Introduction

The difficulty of the follicular unit excision (FUE) hair transplantation procedure is currently attributed to hair curliness and subsurface angulation. Patients possessing the curliest hair shafts are considered the most challenging. Consequently, patients with these features are often denied FUE. However, this practice does not consider intrapatient variation in the graft attrition rate and the rates themselves, which are frequently low in very curly hair where the skin firmness/thickness is average. To better aid practitioners in predicting FUE performance, we have developed a new scoring system (the Sanusi FUE Score Scale [SFS Scale]) based on two major donor variables (hair and skin characteristics).

Material and Method

The scale assigns scores to each of three hair subtypes (straight-wavy, curly, and coily-kinky) and each of three skin subtypes (thick/firm, soft/thin, and medium thickness/firmness). The scores were weighted based on the assessment of 13 experienced FUE practitioners from around the globe, who were asked to score each of the three skin and hair characteristics for their contribution to FUE difficulty.

Results

On the contribution of skin characteristics to FUE difficulty, 12/13 (92%) practitioners assigned the highest (most difficult) score to thick/firm skin, with medium skin thickness/firmness being the least challenging. The same percentage of practitioners gave the highest difficulty score to coiled-kinky hair subtypes regarding the contribution of hair characteristics to FUE difficulty. All agreed that straight-wavy hair presents the least challenge to FUE performance. Tallying the scores of the skin and hair variables generates a final score range of 2–9, which is associated with five grades/classes of challenge in the FUE procedure, influencing the need for a specialized skill/nuanced approach or equipment.

Conclusion

We developed a universal FUE donor scoring scale that accounts for the diversity of human hair and skin types. Further evaluation to determine the validity of this new classification system in predicting and grading FUE difficulty and patient outcomes is warranted.

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Melatonin increases growth properties in human dermal papilla spheroids by activating AKT/GSK3β/β-Catenin signaling pathway

Background

Melatonin, a neurohormone, maybe involved in physiological processes, such as antioxidation, anti-inflammation, and hair growth. In the present study, we investigated the effects of melatonin on proliferation and intracellular signaling in DP cells using a three-dimensional (3D) spheroid culture system that mimics the in vivo hair follicle system.

Methods

DP cells were incubated in monolayer (2D) and 3D spheroid culture systems. The expression levels of melatonin receptors in DP cells were analyzed using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blotting. The effect of melatonin on the hair-inductive property of DP cells was analyzed using a WST-1-based proliferation assay, determination of DP spheroid size, expression analysis of DP signature genes, and determination of β-catenin stabilization in DP cells. The AKT/GSK3β/β-catenin signaling pathway associated with melatonin-induced β-catenin stabilization in DP cells was investigated by analyzing changes in upstream regulator proteins, including AKT, GSK3β, and their phosphorylated forms.

Results

The expression levels of the melatonin receptors were higher in human DP cells than in human epidermal keratinocytes and human dermal fibroblast cells. Comparing the expression level according to the human DP cell culture condition, melatonin receptor expression was upregulated in the 3D culture system compared to the traditional two-dimensional monolayer culture system. Cell viability analysis showed that melatonin concentrations up to 1 mM did not affect cell viability. Moreover, melatonin increased the diameter of DP cell 3D spheroids in a dose-dependent manner. Immunoblotting and qRT-PCR analysis revealed that melatonin upregulated the expression of hair growth-related genes, including alkaline phosphatase, bone morphogenetic protein 2, versican, and wingless-int 5A, in a melatonin receptor-dependent manner. Cell fractionation analysis showed that melatonin increased the nuclear localization of β-catenin. This result correlated with the increased transcriptional activation of T-cell factor/lymphoid enhancer factor-responsive luciferase induced by melatonin treatment. Interestingly, melatonin induced the phosphorylation of protein kinase B/AKT at serine 473 residue and GSK-3β at serine 9 residue. To determine whether AKT phosphorylation at serine 473 induced β-catenin nuclear translocation through GSK3β phosphorylation at serine 9, the PI3K/AKT inhibitor LY294002 was cotreated with melatonin. Immunoblotting showed that LY294002 inhibited melatonin-induced phosphorylation of GSK3β at serine 9 residue and β-catenin activation.

Conclusion

Collectively, this report suggests that melatonin promotes growth properties by activating the AKT/GSK3β/β-catenin signaling pathway through melatonin receptors.

Trichoscopic features of hair and scalp in noncomplaining individuals: A descriptive study

BACKGROUND

Trichoscopy is a simple noninvasive tool that is used in calculating different hair parameters and the diagnosis of different hair/scalp diseases at variable magnifications.

OBJECTIVE

The aim of this work is to describe the features and parameters of hair and scalp in a healthy sample of Egyptian population using videodermoscopy. This may help to provide standard range of measurements of normal hair in both males and females.

METHODS

A nonrandomized, observational study for features and parameters of hair structure, performed on 368 healthy Egyptian subjects with no hair/scalp complaint.

RESULTS

Each scalp area has its own vascular pattern. Male subjects showed different values regarding their hair parameters from the female subjects. No significant difference was seen after application of hair dye, except for few values. In both genders, there was a change in hair parameters with age. Smoking had a negative influence on hair parameters.

CONCLUSION

Hair features and parameters observed in our population are different from those reported by other populations. Smoking affects hair thickness and density. Dyed hair has greater thickness mostly due to the protective effect of hair conditioners.

The distinct morphological phenotypes of Southeast Asian aborigines are shaped by novel mechanisms for adaptation to tropical rainforests

Southeast Asian aborigines, the hunter-gatherer populations living in tropical rainforests, exhibit distinct morphological phenotypes, including short stature, dark skin, curly hair and a wide and snub nose. The underlying genetic architecture and evolutionary mechanism of these phenotypes remain a long-term mystery. We conducted whole genome deep sequencing of 81 Cambodian aborigines from eight ethnic groups. Through a genome-wide scan of selective sweeps, we discovered key genes harboring Cambodian-enriched mutations that may contribute to their phenotypes, including two hair morphogenesis genes (TCHH and TCHHL1), one nasal morphology gene (PAX3) and a set of genes (such as ENTPD1-AS1) associated with short stature. The identified new genes and novel mutations suggest an independent origin of the distinct phenotypes in Cambodian aborigines through parallel evolution, refuting the long-standing argument on the common ancestry of these phenotypes among the worldwide rainforest hunter-gatherers. Notably, our discovery reveals that various types of molecular mechanisms, including antisense transcription and epigenetic regulation, contribute to human morphogenesis, providing novel insights into the genetics of human environmental adaptation.

Brassica oleracea extract, glucosinlates, and sulforaphane promote hair growth in vitro and ex vivo

BACKGROUND

Androgenic alopecia (AGA) is the most common type of hair loss, in which dihyrotestosterone (DHT) plays a crucial role via modulating androgen receptors in hair follicles.

AIMS

The current objective is to search for new therapy of AGA.

METHODS

In the present study, we investigated the effects of sulforaphane, its precursor glucosinlates and glucosinlates-enriched Brassica oleracea L.var.italic Planch extract (BOE) on the growth of hair follicle and the related matrix cell viability, as well as the possible underlying mechanisms in vitro and ex vivo.

RESULTS

We observed that BOE, glucosinlates, and sulforaphane can prevent the testosterone-induced inhibition of dermal papilla (DP) cells viability. BOE and sulforaphane can even hinder the testosterone-induced inhibition of HaCaT cells viability. Moreover, BOE, glucosinlates, and sulforaphane can up-regulate the cytokeratin gene expression in HaCaT cells, prevent the increase in Bax gene levels induced by testosterone in DP, and promote the growth of hair follicle of mice. These effects can be linked to the enhancement of DP and HaCaT cells activities and the prevention of the testosterone-induced cell apoptosis of DP cells.

CONCLUSIONS

Taken together, BOE, glucosinlates, and sulforaphane can promote the growth of hair follicle of mice and can be used as potential treatment agents for androgenic alopecia.

Age-Related Changes in Female Scalp Dermal Sheath and Dermal Fibroblasts: How the Hair Follicle Environment Impacts Hair Aging

In women, aging leads to reduced hair density and thinner fibers and can result in female-pattern hair loss. However, the impact of the aging dermal environment on female scalp hair follicles remains unclear. In this study, we document in situ changes in 22 women (aged 19-81 years) and primary cultures of dermal fibroblast and dermal sheath cells. In situ, the papillary reticular boundary was indistinguishable in the young scalp but prominent in the scalp of those aged >40 years, accompanied by reduced podoplanin (PDPN) expression, increased versican expression, and changes in collagen organization. Hair follicles were shorter, not reaching the adipose layer. Hyaluronic acid synthase 2 was highly expressed, whereas matrix metalloproteinase 1 was elevated in the dermal papilla and dermal sheath in situ. Primary dermal fibroblast cultures confirmed that matrix metalloproteinase 1 mRNA, MMP1, increased with aging, whereas in dermal sheath cells, hyaluronic acid synthase 2, HAS2, and PDPN increased and α-smooth muscle actin αSMA mRNA decreased. Both exhibited increased cartilage oligomeric protein, COMP mRNA expression. Proteomics revealed an increase in dermal sheath proteins in the dermal fibroblast secretome with aging. In summary, aging female scalp shows striking structural and biological changes in the hair follicle environment that may impact hair growth.

Sustained release of dermal papilla-derived extracellular vesicles from injectable microgel promotes hair growth

Hair regeneration has long captured researchers' attention because alopecia is a common condition and current therapeutic approaches have significant limitations. Dermal papilla (DP) cells serve as a signaling center in hair follicles and regulate hair formation and cycling by paracrine secretion. Secreted EVs are important signaling mediators for intercellular communication, and DP-derived extracellular vesicles (DP-EVs) may play an important role in hair regeneration. However, the instability of EVs in vivo and their low long-term retention after transplantation hinder their use in clinical applications.

Methods: Human DP-EVs were encapsulated in partially oxidized sodium alginate (OSA) hydrogels, yielding OSA-encapsulated EVs (OSA-EVs), which act as a sustained-release system to increase the potential therapeutic effect of DP-EVs. The ability of the OSA-EVs to protect protein was assessed. The hair regeneration capacity of OSA-EVs, as well as the underlying mechanism, was explored in hair organ culture and a mouse model of depilation.

Results: The OSA-EVs were approximately 100 μm in diameter, and as the hydrogel degraded, DP-EVs were gradually released. In addition, the hydrogel markedly increased the stability of vesicular proteins and increased the retention of EVs in vitro and in vivo. The OSA-EVs significantly facilitated proliferation of hair matrix cells, prolonged anagen phase in cultured human hairs, and accelerated the regrowth of back hair in mice after depilation. These effects may be due to upregulation of hair growth-promoting signaling molecules such as Wnt3a and β-catenin, and downregulation of inhibitory molecule BMP2.

Conclusion: This study demonstrated that OSA hydrogels promote the therapeutic effects of DP-EVs, and indicate that our novel OSA-EVs could be used to treat alopecia.

Time course detection of dihydrocodeine in body hair after a single dose

BACKGROUND

When head hair is not suitable or not available, body hair, such as leg or beard hair might be the most suitable sample for drug hair analysis. Information about the time course of drugs in hair, from the different anatomical body sites, should still be well documented.

AIM

The aim of this study was to determine and compare (a) the detection window of dihydrocodeine in frequently shaved legs and beard, (b) in unshaved hair from head hair, chest hair, leg hair, and/or arm hair, and (c) the distribution concentrations over the scalp, after a single dihydrocodeine intake.

METHOD

Before a single intake of 12 mg dihydrocodeine by subject 1 (woman), both legs hair were shaved in the morning. The subject 2 (man) shaved his beard in the morning and 30 min later he had a dose of 10 mg of dihydrocodeine. The samples were washed with water and shampoo, dried and collected as follows: Subject 1: every 3-days shaved leg hair (n = 9) and 1-month-later head hair (n = 1). Subject 2: daily shaved beard hair (n = 15), 2 months later head hair (n = 145), and every 20 days unshaved arm, leg and chest hair (from different areas) (n = 4/area). The samples were analysed for dihydrocodeine using a validated liquid chromatography-tandem mass spectrometry method with a limit of quantification (LOQ) of 15.6 pg/mg for dihydrocodeine. About 20 mg of hair samples were weighted, washed with dichloromethane, centrifuged, dried, and pulverized in the same disposable tubes. Then the samples were incubated with methanol (under sonication at 45 °C) during 4 h. After centrifugation, the supernatant was evaporated and a cation exchange solid phase extraction followed by separation and quantification using ultra performance liquid chromatography-tandem mass spectrometry (ULC-MS/MS) was carried out. Chromatographic separation was achieved using a BEH phenyl column eluted with 0.1% formic acid: methanol (0.1% formic acid). The UPLC-MS/MS method was validated and used in routine for drug hair analysis for already several years.

RESULTS AND DISCUSSION

In the present study leg hair was collected every 3 days, as an average of frequent shaved hair in western woman population. Shaved leg hair was very limited and only one hair sample was available per analysis. Beard was collected daily and in a higher amount. Dihydrocodeine was detected in leg hair from the first sample (3 days after the intake). Maximum concentration at 68 pg/mg for the single intake was obtained after 15 days (±2 days), decreasing later to the LOQ from the 21th day. Beard hair was positive from the first day sample, and the maximum concentration was observed at 66 pg/mg, 6 days after the intake, decreasing later to the LOQ from day 13. This may be explained by growth rate and the amount of growing hairs, in anagen phase. In other body hair samples, dihydrocodeine was negative or detected from 1 month after the intake. No significant differences in dihydrocodeine concentrations over the scalp in the different regions were observed (p > 0.05).

CONCLUSION

Body hair presents different time course window detection due to the different growth rates. Frequently shaved leg and beard hair may be suitable samples for recent single dihydrocodeine dose detection from the first days up to 2-3 weeks after the intake, respectively, when a LOQ of 15.6 pg/mg is applied.

Raman spectroscopy and electronic microscopy structural studies of Caucasian and Afro human hair

Human hair fibre is subjected to various structural modifications due to the application of chemicals such as dyes, shampoos and bleaches and/or physical procedures such as heating, and often more than one procedure is performed on the same hair. The present work aims to analyze the changes incurred in hair samples of two ethnic groups, namely Caucasian and Afro, before and after different treatments such as thermal, bleaching and straightening. In addition to observing the damage caused by each treatment separately, the study of samples that received all three treatments was carried out. For molecular structural characterization, the Raman vibrational spectroscopic technique was used and scanning electron microscopy (SEM) was used for morphological analysis of the hair fibres. This investigation has shown, through vibrational spectroscopy, that several important bonds have been modified, such as the S-S, C-S, C-C and S-O bonds as well as the secondary structures of proteins that have indergone changes in their conformation as a result of the treatment. Hair from the two ethnic groups showed small differences in relation to each applied treatment. Excessive heat generated a higher rate of Raman spectral band intensity changes when compared to the other treatments and it was observed that the action of several treatments on the same hair fibres resulted in even more pronounced structural changes. Finally, scanning electron microscopy showed that each treatment caused a different morphological deformation pattern on the capillary surface of the human hair.

Hair Biology: Growth and Pigmentation

Healthy hair is vital to identity. Understanding the intricate anatomy and physiology of hair provides insight into the aging process and the eventual loss of either hair pigmentation or hair shafts. Several biologics are available that have enabled altering or slowing the aging process of hair, but, unfortunately, no agent exists that can reverse the natural course. The commonly used biologics are discussed.

The biology and genetics of curly hair

Hair fibres show wide diversity across and within all human populations, suggesting that hair fibre form and colour have been subject to much adaptive pressure over thousands of years. All human hair fibres typically have the same basic structure. However, the three-dimensional shape of the entire fibre varies considerably depending on ethnicity and geography, with examples from very straight hair with no rotational turn about the long axis, to the tightly sprung coils of African races. The creation of the highly complex biomaterials in hair follicle and how these confer mechanical functions on the fibre so formed is a topic that remains relatively unexplained thus far. We review the current understanding on how hair fibres are formed into a nonlinear coiled form and which genetic and biological factors are thought to be responsible for hair shape. We report on a new GWAS comparing low and high curl individuals in South Africa, revealing strong links to polymorphic variation in trichohyalin, a copper transporter protein CUTC and the inner root sheath component keratin 74. This builds onto the growing knowledge base describing the control of curly hair formation.

Titrated extract of Centella asiatica increases hair inductive property through inhibition of STAT signaling pathway in three-dimensional spheroid cultured human dermal papilla cells

Dermal papilla (DP) is a pivotal part of hair follicle, and the smaller size of the DP is related with the hair loss. In this study, we investigated the effect of titrated extract of Centella asiatica (TECA) on hair growth inductive property on 3D spheroid cultured human DP cells (HDP cells). Significantly increased effect of TECA on cell viability was only shown in 3D sphered HPD cells, not in 2D cultured HDP cells. Also, TECA treatment increased the sphere size of HDP cells. The luciferase activity of STAT reporter genes and the expression of STAT-targeted genes, SOCS1 and SOCS3, were significantly decreased. Also, TECA treatment increased the expression of the hair growth-related signature genes in 3D sphered HDP cells. Furthermore, TECA led to downregulation of the level of phosphorylated STAT proteins in 3D sphered HDP cells. Overall, TECA activates the potential of hair inductive capacity in HDP cells.

The colours of humanity: the evolution of pigmentation in the human lineage

Humans are a colourful species of primate, with human skin, hair and eye coloration having been influenced by a great variety of evolutionary forces throughout prehistory. Functionally naked skin has been the physical interface between the physical environment and the human body for most of the history of the genus Homo, and hence skin coloration has been under intense natural selection. From an original condition of protective, dark, eumelanin-enriched coloration in early tropical-dwelling Homo and Homo sapiens, loss of melanin pigmentation occurred under natural selection as Homo sapiens dispersed into non-tropical latitudes of Africa and Eurasia. Genes responsible for skin, hair and eye coloration appear to have been affected significantly by population bottlenecks in the course of Homo sapiens dispersals. Because specific skin colour phenotypes can be created by different combinations of skin colour-associated genetic markers, loss of genetic variability due to genetic drift appears to have had negligible effects on the highly redundant genetic 'palette' for the skin colour. This does not appear to have been the case for hair and eye coloration, however, and these traits appear to have been more strongly influenced by genetic drift and, possibly, sexual selection.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.

Mutations in Three Genes Encoding Proteins Involved in Hair Shaft Formation Cause Uncombable Hair Syndrome

Uncombable hair syndrome (UHS), also known as "spun glass hair syndrome," "pili trianguli et canaliculi," or "cheveux incoiffables" is a rare anomaly of the hair shaft that occurs in children and improves with age. UHS is characterized by dry, frizzy, spangly, and often fair hair that is resistant to being combed flat. Until now, both simplex and familial UHS-affected case subjects with autosomal-dominant as well as -recessive inheritance have been reported. However, none of these case subjects were linked to a molecular genetic cause. Here, we report the identification of UHS-causative mutations located in the three genes PADI3 (peptidylarginine deiminase 3), TGM3 (transglutaminase 3), and TCHH (trichohyalin) in a total of 11 children. All of these individuals carry homozygous or compound heterozygous mutations in one of these three genes, indicating an autosomal-recessive inheritance pattern in the majority of UHS case subjects. The two enzymes PADI3 and TGM3, responsible for posttranslational protein modifications, and their target structural protein TCHH are all involved in hair shaft formation. Elucidation of the molecular outcomes of the disease-causing mutations by cell culture experiments and tridimensional protein models demonstrated clear differences in the structural organization and activity of mutant and wild-type proteins. Scanning electron microscopy observations revealed morphological alterations in hair coat of Padi3 knockout mice. All together, these findings elucidate the molecular genetic causes of UHS and shed light on its pathophysiology and hair physiology in general.

The Hair Follicle: A Comparative Review of Canine Hair Follicle Anatomy and Physiology

The hair follicle (HF) has a wide range of functions including thermoregulation, physical and immunological protection against external insults, sensory perception, social interactions, and camouflage. One of the most characteristic features of HFs is that they self-renew during hair cycle (HC) throughout the entire life of an individual to continuously produce new hair. HC disturbances are common in humans and comparable to some alopecic disorders in dogs. A normal HC is maintained by follicular stem cells (SCs), which are predominately found in an area known as the bulge. Due to similar morphological characteristics of the human and canine bulge area, the particularity of compound HFs in humans and dogs as well as similarities in follicular biomarker expression, the dog might be a promising model to study human HC and SC disorders. In this review, we give an overview of normal follicular anatomy, the HC, and follicular SCs and discuss the possible pathogenetic mechanisms of noninflammatory alopecia.

A genome-wide association scan in admixed Latin Americans identifies loci influencing facial and scalp hair features

We report a genome-wide association scan in over 6,000 Latin Americans for features of scalp hair (shape, colour, greying, balding) and facial hair (beard thickness, monobrow, eyebrow thickness). We found 18 signals of association reaching genome-wide significance (P values 5 × 10(-8) to 3 × 10(-119)), including 10 novel associations. These include novel loci for scalp hair shape and balding, and the first reported loci for hair greying, monobrow, eyebrow and beard thickness. A newly identified locus influencing hair shape includes a Q30R substitution in the Protease Serine S1 family member 53 (PRSS53). We demonstrate that this enzyme is highly expressed in the hair follicle, especially the inner root sheath, and that the Q30R substitution affects enzyme processing and secretion. The genome regions associated with hair features are enriched for signals of selection, consistent with proposals regarding the evolution of human hair.

A primer on pigmentation

There is at least a temporary loss of skin pigmentation with all but first-degree burns. Commonly, pigment changes persist for months, and sometimes, permanent changes in skin color add to the ultimate change in appearance that commonly affects burn patients. There are many different treatment modalities for the treatment of pigment changes, but most of them have little scientific basis and often lead to disappointing results. The purpose of this review is to discuss the molecular and cellular mechanisms of skin pigmentation, mechanisms of repigmentation after burns, treatment options for dealing with pigmentation changes, and advice for dealing with the sun after burn injury.

Evaluation of the predictive capacity of DNA variants associated with straight hair in Europeans

DNA-based prediction of hair morphology, defined as straight, curly or wavy hair, could contribute to an improved description of an unknown offender and allow more accurate forensic reconstructions of physical appearance in the field of forensic DNA phenotyping. Differences in scalp hair morphology are significant at the worldwide scale and within Europe. The only genome-wide association study made to date revealed the Trichohyalin gene (TCHH) to be significantly associated with hair morphology in Europeans and reported weaker associations for WNT10A and FRAS1 genes. We conducted a study that centered on six SNPs located in these three genes with a sample of 528 individuals from Poland. The predictive capacity of the candidate DNA variants was evaluated using logistic regression; classification and regression trees; and neural networks, by applying a 10-fold cross validation procedure. Additionally, an independent test set of 142 males from six European populations was used to verify performance of the developed prediction models. Our study confirmed association of rs11803731 (TCHH), rs7349332 (WNT10A) and rs1268789 (FRAS1) SNPs with hair morphology. The combined genotype risk score for straight hair had an odds ratio of 2.7 and these predictors explained ∼ 8.2% of the total variance. The selected three SNPs were found to predict straight hair with a high sensitivity but low specificity when a 10-fold cross validation procedure was applied and the best results were obtained using the neural networks approach (AUC=0.688, sensitivity=91.2%, specificity=23.0%). Application of the neural networks model with 65% probability threshold on an additional test set gave high sensitivity (81.4%) and improved specificity (50.0%) with a total of 78.7% correct calls, but a high non-classification rate (66.9%). The combined TTGGGG SNP genotype for rs11803731, rs7349332, rs1268789 (European frequency=4.5%) of all six straight hair-associated alleles was identified as the best predictor, giving >80% probability of straight hair. Finally, association testing of 44 SNPs previously identified to be associated with male pattern baldness revealed a suggestive association with hair morphology for rs4679955 on 3q25.1. The study results reported provide the starting point for the development of a predictive test for hair morphology in Europeans. More studies are now needed to discover additional determinants of hair morphology to improve the predictive accuracy of this trait in forensic analysis.

Clinical and anthropological perspectives on chemical relaxing of afro-textured hair

The culturally engrained practice of 'relaxing' afro-textured hair has been linked with hair and scalp disorders. Herein, we discuss the evolution of human hair types, focusing in particular on afro-textured hair. We explore the biological features of this hair type, and discuss the different methods employed to straighten afro-textured hair, focusing in particular on chemical straightening. We also examine clinical, anthropological, and psychological issues associated with this latter practice. Examples of common scalp pathologies associated with chronic hair relaxing, such as alopecia, hair breakage, caustic burns and irritant contact dermatitis, are also highlighted. The data presented herein should enable clinicians to engage in culturally appropriate discussions with their patients about issues of appearance and conformity.

The evolution of skin pigmentation and hair texture in people of African ancestry

Our species, Homo sapiens, evolved in Africa, and humanity's highest levels of genetic diversity are maintained there today. Underlying genetic diversity combined with the great range of solar regimes and climatic conditions found in Africa has contributed to a wide range of human integumentary phenotypes within the continent. Millions of Africans have moved, voluntarily and involuntarily, to other continents in the past 2000 years, and the range of integumentary phenotypes among admixed African diaspora populations is enormous. In this contribution, we do not catalog this variation, but provide basic evolutionary background as to how it developed in the first place.