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PubMed1997

Autoantibodies to hair follicles in C3H/HeJ mice with alopecia areata-like hair loss.

We have previously described spontaneous but reversible hair loss that clinically and histologically resembles human alopecia areata in a colony of C3H/HeJ mice. Alopecia areata in humans is associated with antibodies to hair follicles. This study was conducted to determine whether C3H/HeJ mice with hair loss have a similar abnormal antibody response to hair follicles. Eighteen C3H/HeJ mice with alopecia, 12 unaffected littermates, and 15 control mice were examined for circulating antibodies to C3H/HeJ anagen hair follicles by indirect immunofluorescence and against extracts of isolated C3H/HeJ and human anagen hair follicles by immunoblotting. Using both procedures, antibodies to anagen hair follicles were present in all C3H/HeJ mice with alopecia but in none of the control mice. The antibodies were also present in some unaffected C3H/HeJ littermates but were absent in mice of an unrelated strain with inflammatory skin disease and alopecia, indicating that their appearance did not result from the hair loss. These antibodies reacted to hair follicle-specific antigens of 40-60 kDa present in murine and human anagen hair follicles. These antigens were also reactive with human alopecia areata antibodies. Some of the antibodies in both C3H/HeJ mice and humans with alopecia areata reacted to antigens of 44 and 46 kDa, which were identified as hair follicle-specific keratins. This study indicates that C3H/HeJ mice with hair loss have circulating antibodies to hair follicles similar to those present in humans with alopecia areata. These findings confirm that these mice are an appropriate model for human alopecia areata and support the hypothesis that alopecia areata results from an abnormal autoimmune response to hair follicles.

Alopecia Areata↗
PubMed2002

Hair pain (trichodynia): frequency and relationship to hair loss and patient gender.

BACKGROUND: Patients complaining of hair loss frequently claim that their hair has become painful. OBJECTIVE AND METHODS: The aim of the study was to evaluate the frequency of this phenomenon and its relationship to hair loss. Patients seeking advice for hair loss either spontaneously reported or were questioned about painful sensations of the scalp. Hair loss activity was quantified by a hair pull, daily count and wash test. Telogen percentage was obtained by a hair pluck. The scalp surface was examined by dermatoscopy. RESULTS: Of 403 examined patients, 20% of women and 9% of men reported hair pain, irrespective of the cause and activity of hair loss. A minority presented scalp telangiectasia. This strongly correlated with hair pain. CONCLUSIONS: Hair pain (trichodynia) affects a significant proportion of patients complaining of hair loss and may increase the anxiety. The symptom neither allows discrimination of the cause nor correlates with the activity of hair loss. A higher prevalence of female patients might be connected to gender-related differences in pain perception in relation to anxiety. The role of vasoactive neuropeptides in the interaction between the central nervous system and skin reactivity is discussed. In the absence of any correlation with quantitative parameters of hair loss or specific morphologic changes of the scalp, management remains empiric and tailored to the individual.

Adolescent↗
PubMedDate not supplied

Amphetamine and N-acetylamphetamine incorporation into hair: an investigation of the potential role of drug basicity in hair color bias.

To elucidate the role of drug basicity in the preferential incorporation of certain drugs into dark hair rather than light hair, Long-Evans rats were dosed with amphetamine or its non-basic analogue N-acetylamphetamine (N-AcAp) and their hair evaluated for drug content. Rats were shaved prior to dosing. On the 14th day after dosing, hair from the same area that was shaved prior to dosing was shaved and collected. After the addition of amphetamine-d3 or N-AcAp-d3 as an internal standard, hair samples (20 mg) were digested in 1M NaOH at 37 degrees C. Digested solutions were then extracted with n-butyl chloride/chloroform (4:1, v/v). After drying and reconstituting, samples were injected onto a ThermoQuest TSQ liquid chromatography-tandem mass spectrometry instrument for analysis. Black hair from rats dosed with amphetamine (n = 8) was found to contain 6.44 +/- 1.31 (SD) ng amphetamine/mg hair. White hair from the same rats contained 2.04 +/- 0.58 ng amphetamine/mg hair. In contrast, no difference in N-AcAp content was found between black hair (0.87 +/- 0.08 ng N-AcAp/mg hair) and white hair (0.83 +/- 0.15 ng N-AcAp/mg hair) from rats dosed with N-AcAp (n = 8).

Amphetamine↗
PubMed2006

Changes in the number of Merkel cells with the hair cycle in hair discs on rat back skin.

BACKGROUND: Hair discs are known to contain a large number of Merkel cells and are ideal for investigating Merkel cell biology. Hair follicles, which are important elements of hair discs, undergo unique cyclical morphological and biological changes. OBJECTIVES: To define the relationships between the number and the morphology of Merkel cells within the hair disc in association with the hair cycle on rat back skin. METHODS: Merkel cells in hair discs were observed three-dimensionally using immunohistochemistry. Epidermal sheets were incubated with monoclonal murine antibody to CK20. As a result, Merkel cells in hair discs were clearly demonstrated as whole shapes and were counted under a light microscope. RESULTS: Merkel cells in hair discs increased during the early to middle phase of anagen and decreased during the middle phase of anagen to catagen and telogen in perinatal and postnatal rat back skin. We observed the morphological variation of Merkel cells in hair discs of rat back skin, and consequently divided them into two subtypes at the light microscopic level: the oval type and the dendritic type. The number of oval-type Merkel cells was not markedly affected by the hair cycle. In contrast, the number of dendritic-type Merkel cells markedly changed with the hair cycle. CONCLUSIONS: This difference of the hair cycle dependency between oval and dendritic-type Merkel cells suggests some functional differences, such as a secretory function, related to the hair cycle.

Aging↗
PubMed1997

Hair analysis for drug abuse. XIV. Identification of substances causing acute poisoning using hair root. I. Methamphetamine.

A hair root was evaluated as a specimen for proving acute methamphetamine (MA) poisonings using an animal model and fatal cases of MA intoxicaton. First of all, male pigmented hairy rats (n = 5) were administered with acute poisonous doses (20, 40 and 60 mg/kg) of MA and the hair roots were plucked out with a hair nipper 5 min and 0.5, 1, 2, 6 and 24 h after i.p. injection. The hair root samples were, directly or after washing with detergent, extracted with methanol/5 N HCl (20:1) under vortex mixing at room temperature for 14 h. After evaporation, the residue was derivatized with pentafluoropropionic anhydride and analyzed with GC/MS. From all samples including a 5-min sample, MA was detected at high concentrations (approximately 150 ng/mg) with a small amount of amphetamine (AP). Many animals died within 120 min of administration, but the concentrations in the hair roots increased up to 120 min and then slowly decreased until 24 h. Although MA was definitely detected anytime in the hair roots, almost no MA was found in 24-h plasma. In comparison of the drug levels in hair roots between the washed group and the unwashed group, the levels of the washed group were as a whole 4-5-fold higher than those of the unwashed group. These differences show that most of the drug incorporated into hair root is still not immobilized in the early stage. The ratios of the MA remainder in the washed samples increased with the elapse of time in all cases. However, the slope of the curves definitely dropped after the death of rats, probably due to the stopping of the hair growth and the incorporation of drug into the hair shaft. The ratios of AP/MA after death became a plateau probably due to the stoppage of the activity of metabolism after death, while those before death had increased over time. We analyzed the specimens of hair root of four men who died mainly due to acute poisonings with MA. Consequently, MA in the hair roots was detected at high concentrations, 30.5-134.6 ng/mg, and its metabolic, AP, at the concentrations of 1.2-9.0 ng/mg. Our results suggested that hair root is a good specimen for probing acute MA poisoning.

Acute Disease↗
PubMed1985

Perpetual production of hair cells and maturational changes in hair cell ultrastructure accompany postembryonic growth in an amphibian ear.

Sensory hair cells are produced in the ears of birds and mammals only during early development, so that a programmed termination of hair cell proliferation leaves adult birds and mammals susceptible to irreversible deafness and balance disorders. This study reports that this is not an inherent feature of hair cells and is not shared through all the vertebrate classes. In toads (Bufo marinus) hair cells accumulate throughout life, increasing in the sacculus from approximately 400 cells at metamorphosis to more than 1600 in adulthood. In both embryonic and postembryonic ears new hair cells have been identified by scanning electron microscopy and through uptake of radioactively labeled thymidine. In the otic vesicle of postneurulation embryos there is a single primordial sensory epithelium that contains approximately 100 hair cells. Scanning electron microscopy has demonstrated that these newly formed hair cells all have stereocilia bundles that are shorter than 1.5 micron, whereas the majority of hair cells in postembryonic ears have stereocilia bundles that are at least 3 micron long. In the postembryonic sacculus the proliferation of hair cells never appears to cease, since newly produced hair cells identified by their short stereocilia have been found in a distinct peripheral growth zone at the edge of the sensory epithelium even in specimens from the oldest 1% of natural populations. This peripheral growth zone is also the site of the most frequent labeling of newly synthesized DNA in hair cells. It appears that the postembryonic enlargement of the toad sacculus occurs primarily through appositional addition of new hair cells at its edge, with few hair cells added within the existing structure of the epithelium.

Animals↗
PubMed1999

Active hair-bundle movements can amplify a hair cell's response to oscillatory mechanical stimuli.

To enhance their mechanical sensitivity and frequency selectivity, hair cells amplify the mechanical stimuli to which they respond. Although cell-body contractions of outer hair cells are thought to mediate the active process in the mammalian cochlea, vertebrates without outer hair cells display highly sensitive, sharply tuned hearing and spontaneous otoacoustic emissions. In these animals the amplifier must reside elsewhere. We report physiological evidence that amplification can stem from active movement of the hair bundle, the hair cell's mechanosensitive organelle. We performed experiments on hair cells from the sacculus of the bullfrog. Using a two-compartment recording chamber that permits exposure of the hair cell's apical and basolateral surfaces to different solutions, we examined active hair-bundle motion in circumstances similar to those in vivo. When the apical surface was bathed in artificial endolymph, many hair bundles exhibited spontaneous oscillations of amplitudes as great as 50 nm and frequencies in the range 5 to 40 Hz. We stimulated hair bundles with a flexible glass probe and recorded their mechanical responses with a photometric system. When the stimulus frequency lay within a band enclosing a hair cell's frequency of spontaneous oscillation, mechanical stimuli as small as +/-5 nm entrained the hair-bundle oscillations. For small stimuli, the bundle movement was larger than the stimulus. Because the energy dissipated by viscous drag exceeded the work provided by the stimulus probe, the hair bundles powered their motion and therefore amplified it.

Animals↗
PubMed1994

Effects of insulin and insulin-like growth factors on cultured human hair follicles: IGF-I at physiologic concentrations is an important regulator of hair follicle growth in vitro.

Insulin stimulated hair follicle growth in a dose-dependent manner over the range of 0.01 to 100 micrograms/ml. Maximum rates of hair follicle growth were observed when follicles were maintained in medium containing 10 micrograms/ml insulin, which is supraphysiologic. Hair follicles maintained in the absence of insulin or at physiologic levels showed premature entry into a catagen-like state. Insulin-like growth factor (IGF)-I and -II had no significant effect on hair follicle growth when maintained in the presence of 10 micrograms/ml insulin. However, in the absence of insulin, both IGF-I (0.01-100 ng/ml) and IGF-II (0.01-100 ng/ml) stimulated hair follicle growth in a dose-dependent manner. IGF-I was more potent than either insulin or IGF-II, stimulating maximum rates of hair follicle growth at 10 ng/ml, whereas IGF-II gave maximum stimulation at 100 ng/ml. The rates of hair follicle growth stimulated by 10 ng/ml IGF-I were identical to those stimulated by 10 micrograms/ml insulin. IGF-II (100 ng/ml), however, was unable to stimulate hair follicle growth to the same extent as insulin. Both IGF-I (10 ng/ml) and IGF-II (100 ng/ml) were more potent than insulin at preventing hair follicles from entering into a catagen-like state. Growth hormone had no effect on hair follicle growth or morphology in the absence of insulin. These data suggest that in vitro IGF-I may be an important physiologic regulator of hair growth and possibly the hair growth cycle. Moreover, the removal of insulin from tissue culture medium may be a useful method of generating large numbers of catagen hair follicles for further in vitro studies.

Cells, Cultured↗
PubMed2004

Comparative aspects of the inner root sheath in adult and developing hairs of mammals in relation to the evolution of hairs.

The inner root sheath (IRS) allows the exit of hairs through the epidermal surface. The fine structure of monotreme and marsupial IRS and trichohyalin is not known. Using electron microscopy and immunocytochemistry, the localization of trichohyalin and transglutaminase have been studied in monotreme and marsupial hairs, and compared with trichohyalin localization in placental hairs. Trichohyalin in all mammalian species studied here is recognized by a polyclonal antibody against sheep trichohyalin. This generalized immunoreactivity suggests that common epitopes are present in trichohyalin across mammals. In differentiating IRS cells, trichohyalin granules of variable dimensions are composed of an immunolabelled amorphous matrix associated with a network of 10-12-nm-thick keratin filaments. Transglutaminase labelling is present among keratin bundles and trichohyalin granules, and in condensed nuclei of terminally differentiating cells of the inner root sheath. The IRS in monotreme hairs is multistratified but lacks a distinguishable Henle layer. Cornification of IRS determines the sculpturing of the fibre cuticle and later shedding from the follicle for the exit of the hair fibre on the epidermal surface. It is hypothesized that the stratification of IRS in Henle, Huxley and IRS cuticle layers is derived from a simpler organization, like that present in the IRS of monotremes. The IRS is regarded as a localized shedding/sloughing layer needed for the exit of hairs without injury to the epidermis. The formation of the IRS during the evolution of mammalian epidermis allowed the physiological exit of hairs produced inside the skin. The peculiar morphogenesis of hairs in possible primitive skins, such as those of the monotremes (mammals with some reptilian characteristics) or the tails of some rodents (a scaled skin), may elucidate the evolution of hairs. In monotreme and rodent tail skin, the dermal papilla remains localized on the proximal side of the hair peg and forms a hair placode with bilateral symmetry. The papilla is progressively surrounded by the down-growing hair peg until a dermal papilla with radial symmetry is formed. It is speculated that the progressive reduction of the extended dermal papilla of reptilian scales into small and deep papillae of therapsid reptiles produced hairs in mammals.

Animals↗
PubMed2004

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

Minoxidil induces new hair growth in approximately one-third of patients with androgenetic alopecia after 1 year of treatment. With several conflicting reports in the literature based on small-scale studies, the current study aimed to clarify whether organ culture of human scalp anagen VI hair follicles is a suitable in vitro test system for reproducing, and experimentally dissecting, the recognized in vivo hair-growth-promoting capacity of minoxidil. Hair shaft elongation was studied in terminal anagen VI hair follicles microdissected from the occipital scalp of 36 healthy adults. A total of 2300 hair follicles, approximately 65 per individual, were tested using modifications of a basic organ culture protocol. It is shown here that minoxidil does not significantly increase hair shaft elongation or the duration of anagen VI in ex vivo culture despite several enhancements on the conventional methodology. This disparity to what is seen clinically in minoxidil responders may be explained by the following: (i) use of occipital (rather than frontotemporal or vertex) hair follicles; (ii) use of, already maximally growing, anagen VI hair follicles; (iii) a predominance of hair follicles from minoxidil unresponsive-donors; (iv) use of minoxidil rather than its sulfate metabolite; and/or (v) use of a suboptimal minoxidil dosage. This disparity questions the usefulness of standard human hair follicle organ culture in minoxidil research. Unexpectedly, minoxidil even inhibited hair shaft elongation in the absence of insulin, which may indicate that the actual hair-growth-modulatory effects of minoxidil depend on the concomitant local presence/absence of other growth modulators.

Adult↗
PubMed1994

Hair fibre production by human hair follicles in whole-organ culture.

We have used both pulse-chase radiolabelling and morphometric techniques to investigate the ability of whole-organ cultures of human hair follicles to synthesize hair fibre. Anagen hair follicles were obtained from human facial skin by microdissection. Follicles were pulse-labelled with 3H-leucine, and radioactivity in alkali-soluble protein (ASP) and alkali-insoluble hair fibre protein (HFP) fractions was determined by differential extraction. There was a slow decline in ASP radioactivity over 7 days of culture, with a half-life of 4 days. In contrast, leucine incorporation into HFP increased linearly from day 1 to day 5, following an initial delay of 17 h. Morphometric analysis revealed that hair follicles and hair fibres grew at the same rate (0.25 mm/day) for 4 days in culture, after which the rate of hair follicle growth declined progressively, whereas fibre growth continued at the initial rate for a further 3 days. Concurrent with the onset of the decline in follicle growth, the base of the hair fibre began to descend towards the follicle base, until hair fibre occupied almost the full length of the hair follicle at day 15. The decline in follicle growth was preceded by a decline in the rate of follicular 3H-thymidine incorporation, with a delay of approximately 1 day. Overall, these data demonstrate that human hair follicles in whole-organ culture are capable of the production of hair fibre, and suggest that cessation of hair growth in vitro results from depletion of the pool of differentiated follicular keratinocytes, secondary to a loss of matrix cell proliferative activity.

DNA↗
PubMed2026

Efficacy and Safety of Low-Molecular-Weight Collagen Peptide GT for Improving Hair Condition in Individuals with Damaged Hair: A Randomized, Double-Blind, Placebo-Controlled Trial.

Addressing hair damage is essential for maintaining overall hair and scalp health. Previous studies have suggested that low-molecular-weight collagen peptides may support hair follicle biology through regulation of extracellular matrix homeostasis and cellular signaling pathways. In addition, recent preclinical studies have demonstrated that low-molecular-weight fish collagen peptides promote hair regrowth through activation of proliferative signaling and suppression of inhibitory pathways. However, their clinical efficacy in improving hair damage has not been clearly established. In this study, the efficacy and safety of low-molecular-weight collagen peptide GT (LMWCP GT) were evaluated in Korean adults with damaged hair. In a randomized, placebo-controlled trial, individuals aged 19∼60 years without alopecia but with mild to moderate hair damage received LMWCP GT (3 g/day) for 24 weeks. Compared with placebo, the treatment group demonstrated significant improvements in hair gloss, as measured using a gloss meter (SAMBA) and scanning electron microscopy, as well as in hair elasticity, assessed by tensile strength and hair diameter. Subjective evaluations further indicated improvements in overall hair condition, including gloss, elasticity, thickness, texture, fullness, and appearance. In addition, scalp elasticity was significantly increased in the treatment group. No treatment-related adverse events were observed. These findings indicate that daily supplementation with LMWCP GT (3 g/day) for 24 weeks is safe and effective in improving overall hair condition in individuals with damaged hair without alopecia.

Antioxidants↗
PubMed2006

The critical roles of serum/glucocorticoid-regulated kinase 3 (SGK3) in the hair follicle morphogenesis and homeostasis: the allelic difference provides novel insights into hair follicle biology.

Mutation in the serum/glucocorticoid regulated kinase 3 (Sgk3, also known as Sgkl or Cisk) gene causes both defective hair follicle development and altered hair cycle in mice. We examined Sgk3-mutant YPC mice (YPC-Sgk3(ypc)/Sgk3(ypc)) and found expression of SGK3 protein with altered function. In the hair follicles of YPC mice, the aberrant differentiation and poor proliferation of hair matrix keratinocytes during the period of postnatal hair follicle development resulted in a complete lack of hair medulla and weak hair. Surprisingly, the length of postnatal hair follicle development and anagen term was shown to be dramatically shortened. Also, phosphorylation of GSK3beta at Ser9 and the nuclear accumulation of beta-catenin were reduced in the developing YPC hair follicle, suggesting that phosphorylation of GSK3beta and WNT-beta-catenin pathway takes part in the SGK3-dependent regulation of hair follicle development. Moreover, the above-mentioned features, especially the hair-cycling pattern, differ from those in other Sgk3-null mutant strains, suggesting that the various patterns of dysfunction in the SGK3 protein may result in phenotypic variation. Our results indicate that SGK3 is a very important and characteristic molecule that plays a critical role in both hair follicle morphogenesis and hair cycling.

Alleles↗
PubMed2004

[Hair follicle regeneration after implantation of hair follicle cells into subcutis of nude mice].

OBJECTIVE: To observe the hair follicle regeneration after implantation of hair follicle cells into the subcutis of nude mice. METHODS: The cultured hair papilla cells,dermal sheath cells and fibroblast of human scalp were mixed with the cells of hair follicle epithelium in different ratio, and then implanted into the subcutis of nude mice. The regeneration of hair follicle was observed. RESULT: The hair follicle-like structure was formed in cluster where the cultured hair follicle epithelium cells were mixed with hair papilla cells. But no hair follicles were formed where the hair follicle epithelium was implanted with dermal sheath cells or fibroblasts. CONCLUSION: The hair follicle-like structure is generated in vivo when the mixed cells of early passages cultured hair papilla cells with hair follicle epithelium are implanted into the subcutis of nude mice.

Animals↗
PubMed1993

IL-1 alpha inhibits human hair follicle growth and hair fiber production in whole-organ cultures.

In this study we have used a recently developed human hair follicle whole-organ culture system to investigate the effect of IL-1 alpha on hair follicle growth and hair fiber production. In the presence of 10 ng/ml IL-1 alpha, the growth of cultured human hair follicles ceased within 2-4 days, whereas control hair follicles grew for a period of 7-10 days. IL-1 alpha also inhibited hair fiber growth, but with an onset which occurred 3 days later than that of follicle growth inhibition. An IC50 value of approximately 30 pg/ml was obtained for IL-1 alpha inhibition of follicle growth. Incubation of hair follicles with IL-1 alpha resulted in a rapid, transient reduction in the rate of whole-follicle DNA synthesis. 1000-fold molar excess of IL-1 receptor antagonist prevented IL-1-induced follicle growth inhibition, while antagonist alone was without effect. The selective PKC inhibitor, Ro 31-7549, augmented IL-1-induced inhibition of hair follicle growth, but did not itself affect hair follicle growth. These findings indicate that IL-1 alpha exerts a rapid antiproliferative effect on hair follicles, and that inhibition of hair fiber growth is a secondary response. Thus, IL-1 may play a role in the pathophysiology of inflammatory hair loss conditions, such as alopecia areata, through a direct growth-inhibitory effect on hair follicles.

Cell Division↗
PubMed1996

Cuticle cell defects in lamellar ichthyosis hair and anomalous hair shaft syndromes visualized after detergent extraction.

BACKGROUND: The biochemical bases for fragility in most of the rare brittle hair shaft syndromes are unknown. The hypothesis being investigated in several syndromes is that the hair cuticle cells show defects in cross-linked protein features. Since transglutaminases stabilize protein structures by cross-linking them, hair from autosomal recessive lamellar ichthyosis patients lacking keratinocyte transglutaminase was examined to find whether this enzyme participates in hair shaft stabilization. METHODS: Hair shaft samples from patients afflicted with lamellar ichthyosis or several brittle hair syndromes were examined ultrastructurally by transmission electron microscopy after vigorous extraction with detergent and reducing agent to reveal cross-linked protein features. RESULTS: In hair cuticle cells from three patients with lamellar ichthyosis the marginal band (A layer) was present but nonuniform and subject to breakage, while in a fourth sample it was missing altogether. The exocuticle appeared less dense than in normal hair, consistent with extensive protein loss during detergent extraction. In cuticle cells from trichothiodystrophy hair, the exocuticle layer was essentially fully extractable in one sample, while in two others (from siblings) the exocuticle appeared less dense and the A layer was absent or greatly reduced in thickness. A sample of proximal trichorrhexis nodosa also displayed defects in cuticle cells, in which the endocuticle layer appeared subject to rupture. The outer cuticle cells in monilethrix hair displayed a thinning of the A layer and less dense exocuticle, while the cortex exhibited regions lacking remnant cell borders. Pili annulati hair displayed large gaps in the cortex, presumably reflecting the air-filled cavities characteristic of this syndrome, and wavy borders of some cuticle cells. CONCLUSIONS: Observations with autosomal recessive lamellar ichthyosis hair indicate that keratinocyte transglutaminase has a major role in maturation of the cuticle but appears unnecessary for stabilization of cell borders in the cortex. Defective cross-linking was also evident in cuticle cells of trichothiodystrophy and monilethrix.

Cross-Linking Reagents↗
PubMed2004

Fine structure and immunocytochemistry of monotreme hairs, with emphasis on the inner root sheath and trichohyalin-based cornification during hair evolution.

The fine structure of hairs in the most ancient extant mammals, the monotremes, is not known. The present study analyzes the ultrastructure and immunocytochemistry for keratins, trichohyalin, and transglutaminase in monotreme hairs and compares their distribution with that present in hairs of the other mammals. The overall ultrastructure of the hair and the distribution of keratins is similar to that of marsupial and placental hairs. Acidic and basic keratins mostly localize in the outer root sheath. The inner root sheath (IRS) comprises 4-8 cell layers in most hairs and forms a tile-like sheath around the hair shaft. No cytological distinction between the Henle and Huxley layers is seen as cells become cornified about at the same time. Externally to the last cornified IRS cells (homologous to the Henle layer), the companion layer contains numerous bundles of keratin. Occasionally, some granules in the companion layer show immunoreactivity for the trichohyalin antibody. This further suggests that the IRS in monotremes is ill-defined, as the companion layer of placental hairs studied so far does not express trichohyalin. A cross-reactivity with an antibody against sheep trichohyalin is present in the IRS of monotremes, suggesting conserved epitopes across mammalian trichohyalin. Trichohyalin granules in the IRS consist of a framework of immunolabeled coarse filaments of 10-12 nm. The latter assume a parallel orientation and lose the immunoreactivity in fully cornified cells. Transglutaminase immunolabeling is diffuse among trichohyalin granules and among the parallel 10-12 nm filaments of maturing inner root cells. Transglutaminase is present where its substrate, trichohyalin, is modified as matrix protein. Cornification of IRS is different from that of hair fiber cuticle and from that of the cornified layer of the epidermis above the follicle. The different consistency among cuticle, IRS, and corneous layer of the epidermis determines separation between hair fiber, IRS, and epidermis. This allows the hair to exit on the epidermal surface after shedding from the IRS and epidermis. Based on comparative studies of reptilian and mammalian skin, a speculative hypothesis on the evolution of the IRS and hairs from the skin of synapsid reptiles is presented.

Animals↗
PubMed1999

Ruby laser-assisted hair removal success in relation to anatomic factors and melanin content of hair follicles.

Ruby laser-assisted hair removal is thought to work via selective photothermolysis, which relies on light reaching the deeper layers of skin, and the absorption of light by the target chromophore, melanin. It is therefore possible that efficacy of treatment is affected by anatomic factors that determine the amount of light reaching the hair bulbs (i.e., skin color, depth of intracutaneous hair, epidermal thickness and dermal density) and the melanin content of hair. To examine this hypothesis, a prospective study was performed. Forty-eight volunteers were treated with the Chromos 694 Depilation Ruby Laser at a single standard fluence of 11 J/cm2. Treatment efficacy was determined by measuring hair density at 3 and 7 months after treatment. Epidermal depth and dermal density were measured from 2-mm biopsies taken before treatment, and the intracutaneous hair length was determined from plucked hair. Skin color was assessed using a spectrophotometer, and melanin content of dissolved hair was assessed using spectrophotometry. Efficacy of treatment for each patient was compared with the patient's age, intracutaneous hair length, epidermal depth, dermal density, skin color, and total melanin content and relative eumelanin content of hair. No correlation was found between the efficacy of treatment and age and the various anatomic factors. Patients with higher eumelanin content in their hair had better long-term results (Spearman rank test, p = 0.00219). The results suggested that the efficacy of treatment did not depend solely on the amount of laser light penetrating the skin but correlated well with the eumelanin content of hair. The clinical implication of this finding is discussed.

Adolescent↗