Programmed cell death of keratinocytes culminates in apoptotic secretion of a humectant upon secretagogue action of acetylcholine.

The programmed cell death of the stratified squamous epithelial cells comprising human epidermis culminates in abrupt transition of viable granular keratinocytes (KC) into dead corneocytes sloughed by the skin. The granular cell-corneocyte transition is associated with a loss in volume and dry cell weight but the mechanism for and biological significance of this form of keratinocyte apoptosis remain obscure. We show that terminally differentiated KC extrude into the intercellular spaces of living epidermis the cytoplasmic buds containing randomly congregated components of the cytosol as well as filaggrin, a precursor of the natural moisturizing factor. The discharge of secretory product is reminiscent of holocrine secretion, suggesting the term 'apoptotic secretion' for this novel, essential step in the process of cornification. The secretory product may become a part of the glycocalyx (a.k.a. 'intercellular cement substance' of epidermis) and serve as a humectant that counterbalances the osmotic pressure imposed by the natural moisturizing factor located in the stratum corneum comprised by corneocytes. The apoptotic secretion commences upon secretagouge action of acetylcholine which is synthesized and released by KC. A combination of a cholinergic nicotinic agonist and a muscarinic antagonist which increases intracellular calcium levels is required to trigger the apoptotic secretion. Analysis of the relative amounts of cholinergic enzymes and receptors expressed by KC capable of secretion and the pharmacological profiles of secretion regulation revealed an upward concentration gradient of free acetylcholine in epidermis which may provide for its unopposed secretagogue action via the m1 muscarinic and the alpha7, and alpha9 nicotinic receptor types expressed by KC at the latest stage of their development in the epidermis.

Methods for diagnosing onychomycosis: a comparative study and review of the literature.

OBJECTIVE: To identify the sensitivity of several readily available diagnostic tests for onychomycosis. DESIGN: Cross-sectional study. SETTING: Dermatology and podiatry departments at a teaching hospital. PATIENTS: Sixty-three adult men and women with a clinical examination highly suggestive of onychomycosis. MAIN OUTCOME MEASURES: Sensitivity of each test and of several test combinations. RESULTS: Nail samples underwent 6 diagnostic tests. Routine histopathologic examination with periodic acid-Schiff stain (PAS) (PATHPAS) was 85% sensitive. Sensitivities for potassium hydroxide dissolution and centrifugation combined with PAS, fluorescent brightener, or chlorazol black E were 57%, 53%, and 53%, respectively. Culture on Sabouraud agar withchloramphenicol and cycloheximide (Mycosel agar) was 32% sensitive; on Littman-oxgall agar, 23% sensitive. The most sensitive combination of tests, both culture methods plus PATHPAS, was 94% sensitive (not statistically different from the sensitivity of PATHPAS alone [P = .26]). CONCLUSIONS: When onychomycosis is suspected clinically, PATHPAS of the nail is the single most sensitive of the diagnostic tests we evaluated. Because it is quickly performed and relatively operator independent, PATHPAS is practical for clinical and research purposes. Further study is needed to determine if sensitivity may be enhanced by combining PATHPAS with cultures obtained by several collection methods (clipping, curettage, and shaving). Such combinations may serve as sensitive and efficient strategies for diagnosing onychomycosis.

Identification and mapping of keratinocyte muscarinic acetylcholine receptor subtypes in human epidermis.

Acetylcholine mediates cell-to-cell communications in the skin. Human epidermal keratinocytes respond to acetylcholine via two classes of cell-surface receptors, the nicotinic and the muscarinic cholinergic receptors. High affinity muscarinic acetylcholine receptors (mAChR) have been found on keratinocyte cell surfaces at high density. These receptors mediate effects of muscarinic drugs on keratinocyte viability, proliferation, adhesion, lateral migration, and differentiation. In this study, we investigated the molecular structure of keratinocyte mAChR and their location in human epidermis. Polymerase chain reaction amplification of cDNA sequences uniquely present within the third cytoplasmic loop of each subtype demonstrated the expression of the m1, m3, m4, and m5 mAChR subtypes. To visualize these mAChR, we raised rabbit anti-sera to synthetic peptide analogs of the carboxyl terminal regions of each subtype. The antibodies selectively bound to keratinocyte mAChR subtypes in immunoblotting membranes and epidermis, both of which could be abolished by preincubating the anti-serum with the peptide used for immunization. The immunofluorescent staining patterns produced by each antibody in the epidermis suggested that the profile of keratinocyte mAChR changes during epidermal turnover. The semiquantitative analysis of fluorescence revealed that basal cells predominantly expressed m3, prickle cells had equally high levels of m4 and m5, and granular cells mostly possessed m1. Thus, the results of this study demonstrate for the first time the presence of m1, m3, m4, and m5 mAChR in epidermal keratinocytes. Because keratinocytes express a unique combination of mAChR subtypes at each stage of their development in the epidermis, each receptor may regulate a specific cell function. Hence, a single cytotransmitter, acetylcholine, and muscarinic drugs may exert different biologic effects on keratinocytes at different stages of their maturation.

Glycolic acid peels for postinflammatory hyperpigmentation in black patients. A comparative study.

BACKGROUND: Treatment of postinflammatory hyperpigmentation in patients of Fitzpatrick skin types IV, V, and VI is difficult. Glycolic acid peels are useful for pigment dyschromias in caucasians; however, there are no controlled studies examining their safety and efficacy in dark-complexioned individuals. OBJECTIVE: To determine if serial glycolic acid peels provide additional improvement when compared with a topical regimen of hydroquinone and tretinoin. METHODS: Nineteen patients with Fitzpatrick skin type IV, V, or VI were randomized to a control or peel group. The control group applied 2% hydroquinone/10% glycolic acid gel twice daily and 0.05% tretinoin cream at night. The peel patients used the same topical regimen and, in addition, received six serial glycolic acid peels (68% maximum concentration). Patients were evaluated with photography, colorimetry, and subjectively. RESULTS: Sixteen patients completed the study. Both treatment groups demonstrated improvement, but the patients receiving the glycolic acid peels showed a trend toward more rapid and greater improvement. The peel group also experienced increased lightening of the normal skin. CONCLUSIONS: This pilot study demonstrates that serial glycolic acid peels provide an additional benefit, with minimal adverse effects, for the treatment of postinflammatory hyperpigmentation in dark-complexioned individuals.