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Notes: To understand better the mechanisms by which thyroid hormone can exert its effects on the hair follicle, we looked for the expression of members of the thyroid hormone receptor (TR) family in human hair follicles. Immunoreactive TRs were detected in both dermal and epithelial compartments of the human pilosebaceous unit. Using reverse transcriptase–polymerase chain reaction, we established that TRβ1 was the predominant form of TR expressed in the human hair follicle. In addition, we investigated the effects of 3,3′,5-triiodo- l-thyronine (T3) on the survival of human hair follicles in vitro, to understand the role of this thyroid hormone on hair follicle homeostasis. A physiological level of free T3 significantly enhanced human hair survival in vitro.

Notes: Vitamin C (VitC) plays a critical role in the maintenance of a normal mature collagen network in humans (anti-scurvy properties) by preventing the auto-inactivation of lysyl and prolyl hyroxylase, two key enzymes in collagen biosynthesis. In this study two in vitro models were designed to evaluate the effects of VitC on collagen biosynthesis and cross-linking at cellular and tissue levels. It was shown that VitC induced a dose-dependent increase in collagen type I deposits by normal human fibroblasts (NHF) cultured in monolayer, and enhanced extracellular matrix contraction by NHF in a lattice model, in a non-cytotoxic range of concentrations (103m, 104m, 105m). Exogenous VitC supply could thus contribute to the maintenance of optimal collagenic density in the dermis and locally strengthen the collagen network. Vitamin C-phosphate (VitC-P) and vitamin C-glucoside (VitC-Glu) (two VitC derivatives presenting higher chemical stability in aqueous solution) were also tested in our two models, and showed similar biological properties, but with different potencies. These two compounds can be considered as pro-vitamins for skin, and could thus advantageously substitute for VitC in VitC-based anti-ageing products, as they allow the development of stable, easy-to-use formulations.〈section xml:id="abs1-2"〉〈title type="main"〉RésuméLa vitamine C (VitC) joue, chez l'homme, un rôle critique dans le maintein d'un réseau collagènique normal (propriété antiscorbutique) en empêchant l'autoinactivation de la lysyl- et de la prolyl-hydroxylase, deux enzymes clefs de la synthèse du collagène. Dans cet article, deux modèles in vitro ont été mis au point dans le but d'évaluer les effets de la VitC sur la biosynthèse du collagène et sa réticulation aux niveaux cellulaire et tissulaire. Nous montrons que la VitC favorise, de façon dose-dependante et dans un domaine de concentrations non cytotoxiques (10–5 M, 10–4 M, 10–3 M), la production de collagène de type I par des fibroblastes humains normaux (FHN) en culture. Dans les mêmes conditions, la VitC augmente, dans un modèle d'équivalent de derme, la contraction de la matrice extracellulaire par les FHNs. Un apport exogène de collagènique optimale et renforcer localement le réseau de collagène. Le phosphate de vitamine C (VitC-P) et le glucoside de vitamine C (VitC-Glu) (deux dérivés présentant une plus grande stabilité chimique en solution aqueuse) ont étéévalués dans ces deux modèles et ont présenté des propriétés biologiques comparables à celles de la VitC, mais avec des intensités variables. Ces deux composés peuvent être considérés comme des pro-vitamines pour la peau, et pourraient avantageusement remplacer la VitC dans les produits anti-âge à base de VitC, dans la mesure où ils devraient permettre le développement de formulations stables et simples d'usage. © Rapid Science Ltd. 1998

Notes: The transition from the growth phase (anagen) to the involution phase (catagen) involves profound morphological changes in the human hair follicle. Club hair and epithelial column formation, for example, are key features of the catagen phase, which result in the disruption of physical interaction between the bulb and the dermal papilla. However, the dynamics and tissue remodelling that occur during this involution process remain largely unknown. Using monoclonal antibodies directed against K14 keratin, trichohyalin, transglutaminase I, desmoglein and Ki67 antigen, we followed the movements of each of the main hair follicle compartments during the onset of catagen. Our results indicate that the inner root sheath is an early target in this process, suggesting a key role for this compartment in the maintenance of hair follicle homeostasis.

Notes: Drug metabolizing enzymes, particularly those involved in the metabolism of carcinogenic chemicals, were characterized in cultured human keratinocytes. Using immunoblotting experiments, we analysed the expression of phase I enzymes, cytochrome P4501A1 (CYP1A1) and NADPH reductase, and phase II enzymes, phenol UDP-glucuronosyltransferase (UGT) and glutathione S-transferase (GST) isoform pi, in the presence of either classical inducers (i.e. 3-methyicholanthrene, dimethylbenz[a]anthracene, phenobarbital. and clofibrate) or all-trans retinoic acid (RA). This study has shown that the expression of CYP1A1 and UGT is concomitantly induced by 3-methyIcholanthrene, dimethylbenz[a]anthracene, and RA, and that of NADPH reductase is only enhanced by phenobarbital and RA. In contrast, the expression of GST pi was not affected by the inducers. Using the reverse transcriptase-polymerase chain reaction, we have demonstrated that the effects of 3-methylcholanthrene, dimethylbenz[a]anthracene and RA on CYP1A1 expression correlate with an increase of CYP1A1 mRNA level. Our results indicate that, with the exception of clolibrate, xenobiotics and RA differentially modulate the expression of drug metabolizing enzymes.

Notes: Plasma from patients with active psoriasis has been shown to induce the formation of stellate fibrin-fibronectin microclots in vitro around cultured keratinocytes and fibroblasts. Such a stellate radiation of fibronectin and fibrin was also demonstrated around monocytes from patients with psoriasis. The phenomenon was not observed in healthy subjects but has been found in various disorders.

Notes: We compared the distribution in psoriatic skin of three different markers usually found in the stratum granulosum of normal skin. Using dansylcadaverine, we demonstrate that epidermal transglutaminase activity can be detected in most of the suprabasal layers of involved psoriatic skin and that the epidermal transglutaminase activity closely matches involucrin distribution. The glycoprotein GP37 was not detected in involved psoriatic skin of stable lesions. These results suggest that the integrated control of several independent pathways of terminal differentiation is lost in psoriasis, resulting in the classical feature of parakeratosis with absence of the stratum granulosum.

Notes: Following tape stripping of normal skin and uninvolved psoriatic skin, there was an early leakage of plasma proteins such as fibrinogen, fibronectin and immunoglobulins. This was accompanied by migration of mononuclear and polymorphonuclear cells into the epidermis. Both events appeared earlier, were more pronounced and lasted longer in psoriatic subjects than in controls.

Notes: Background  Although hair greying is a very common phenomenon characterized by loss of pigment in the hair shaft, the events that cause and control natural hair whitening with age in humans are still unclear.Objectives  To decipher the origin of natural hair whitening.Methods  Human hair melanocytes were immunohistochemically characterized at different stages of whitening.Results  Loss of hair shaft melanin was found to be associated with a decrease in both bulb melanin content and bulb melanocyte population. Although few melanocytes were present in the bulbs of grey hair, they still expressed tyrosinase and tyrosinase-related protein-1, synthesized and transferred melanins to cortical keratinocytes as seen by the presence of melanin granules. In white hair bulbs, no melanocytes could be detected either with pMel-17 or vimentin labelling. Pigmented hair follicles are known to contain inactive melanocytes in the outer root sheath (ORS), and grey and white hairs were also found to contain some of these quiescent melanocytes. However, their population was decreased compared with pigmented hair follicles, ranging from small to nil. This depletion of melanocytes in the different areas of white hairs was detected throughout the hair cycle, namely at telogen and early anagen stages. In contrast, the infundibulum and sebaceous gland of both pigmented and white hairs showed a similar distribution of melanocytes. Furthermore, other distinct cell populations located in the ORS, namely putative stem cells, Merkel cells and Langerhans cells were equivalently identified in pigmented and white hairs.Conclusions  Thus, hair greying appears to be a consequence of an overall and specific depletion of bulb and ORS melanocytes of human hair.

Notes: We compared the maturation pathway of normal and psoriatic epidermis using three different markers: (I) Involucrin, which is normally detected in the stratum granulosum in normal skin, was detected in all but the basal layer of involved psoriatic skin; (2) an antigen, recognized by the murine monoclonal antibody Ψ3, was present in all but the basal layer of involved psoriatic skin but was absent from uninvolved and normal skin; (3) fibronectin, which normally localizes in the dermis and the epidermal-dermal junction, was also detected intra- and extracellularly in the psoriatic epidermis. These results indicate that the alterations in keratinocyte maturation found in psoriasis do not arise from a truncation of the normal maturation pathway but rather reflect the onset of an abnormal pathway of differentiation characterized by the expression of Ψ3 antigen and fibronectin and the premature appearance of involucrin.