Fetal epidermal differentiation and barrier development In vivo is accelerated by nuclear hormone receptor activators

Nuclear receptors which interact with the retinoid X receptor are involved in the regulation of epidermal differentiation and development. We have recently shown that activators of the peroxisome proliferator-activated receptor and of the farnesoid X-activated receptor accelerate epidermal barrier maturation in fetal rat skin in vitro. In this study we asked whether cutaneous development in utero was affected by peroxisome proliferator-activated receptor or farnesoid X-activated receptor activators, or by an activator of another retinoid X receptor partner, liver X receptor. Activators of the peroxisome proliferator-activated receptor (clofibrate or linoleic acid), farnesoid X-activated receptor (farnesol or juvenile hormone III), or liver X receptor (22R-hydroxycholesterol), were injected into the amniotic fluid of fetal rats on gestational day 17. Fetal epidermal barrier function and morphology was assessed on day 19. Whereas vehicle-treated fetal rats displayed no measurable barrier (transepidermal water loss > 10 mg per cm2 per h), a measurable barrier was induced by the intra-amniotic administration of all activators tested (transepidermal water loss range 4.0-8.5 mg per cm2 per h). By light microscopy, control pups lacked a well-defined stratum corneum, whereas a distinct stratum corneum and a thickened stratum granulosum were present in treated pups. By electron microscopy, the extracellular spaces of the stratum corneum in control pups revealed a paucity of mature lamellar unit structures, whereas these structures filled the stratum corneum interstices in treated pups. Additionally, protein and mRNA levels of loricrin and filaggrin, two structural proteins of stratum corneum, were increased in treated epidermis, as were the activities of two lipid catabolic enzymes critical to stratum corneum function, beta-glucocerebrosidase and steroid sulfatase. Finally, peroxisome proliferator-activated receptor-alpha and -delta and liver X receptor-alpha and -beta mRNAs were detected in fetal epidermis by reverse transcriptase-polymerase chain reaction and northern analyses. The presence of these receptors and the ability of their activators to stimulate epidermal barrier and stratum corneum development suggest a physiologic role for peroxisome proliferator-activated receptor and liver X receptor and their endogenous ligands in the regulation of cutaneous development.

The use of basic life support kits in general practice

Donegal is a predominantly rural area with many general practices situated considerable distances from a district hospital. Fifty Life Support Kits were supplied to General Practitioners by the Donegal Pre-Hospital Emergency Care Project in 1995 following appropriate training. This is a survey of the use of items in these kits. To determine the frequency of use of the equipment, the type and location of the incidents, the kit items utilised and patient outcome. Retrospective questionnaire survey of 49 participating GPs. 208 patient incidents were described by 46 doctors (average 4.5 per doctor) Most incidents were outside the surgery (88.24%). Road Traffic Accidents (36%) were the commonest reason for use, followed by cardiac emergencies (28%), other medical emergencies (14%) and other trauma (11%). All items except the burns sheet had been used. The most used items were cannulae, (64.7% of incidents) and fluids (50.9% incidents). Other useful items were emergency drugs, dressings, collars, airways, suction and torch. Regarding outcome, 162 patients required hospital transfer and 25 died. Eleven did not require hospital treatment. The participating doctors judged that the basic life support kits positively contributed to outcome in 79.4% of cases described. Basic Life Support kits contribute to the pre-hospital care of patients when used by GPs with immediate care training.

The role of automated external defibrillators in rural general practice

In a questionnaire survey (100% response rate) investigating the availability and use of automated external defibrillators (AEDs), it was found that the success rate (number discharged alive) compared favourably with pre-hospital defibrillation by other providers, and that AEDs aided the management of dysrhythmias not commonly seen in general practice. With appropriate training they are useful in rural general practice.

Induction of selected lipid metabolic enzymes and differentiation-linked structural proteins by air exposure in fetal rat skin explants

The epidermal permeability barrier of premature infants matures rapidly following birth. Previous studies suggest that air exposure could contribute to this acceleration, because: (i) development of a structurally and functionally mature barrier accelerates when fetal rat skin explants are incubated at an air-medium interface, and (ii) occlusion with a water-impermeable membrane prevents this acceleration. To investigate further the effects of air exposure on epidermal barrier ontogenesis, we compared the activities of several key enzymes of lipid metabolism and gene expression of protein markers of epidermal differentiation in fetal rat skin explants grown immersed versus air exposed. The rate-limiting enzymes of cholesterol (HMG CoA reductase) and ceramide (serine palmitoyl transferase) synthesis were not affected. In contrast, the normal developmental increases in activities of glucosylceramide synthase and cholesterol sulfotransferase, responsible for the synthesis of glucosylceramides and cholesterol sulfate, respectively, were accelerated further by air exposure. Additionally, two enzymes required for the final stages of barrier maturation and essential for normal stratum corneum function, beta-glucocerebrosidase, which converts glucosylceramide to ceramide, and steroid sulfatase, which desulfates cholesterol sulfate, also increased with air exposure. Furthermore, filaggrin and loricrin mRNA levels, and filaggrin, loricrin, and involucrin protein levels all increased with air exposure. Finally, occlusion with a water-impermeable membrane prevented both the air-exposure-induced increase in lipid enzyme activity, and the expression of loricrin, filaggrin, and involucrin. Thus, air exposure stimulates selected lipid metabolic enzymes and the gene expression of key structural proteins in fetal epidermis, providing a biochemical basis for air-induced acceleration of permeability barrier maturation in premature infants.

Rapid production of specific vaccines for lymphoma by expression of the tumor-derived single-chain Fv epitopes in tobacco plants

Rapid production of protein-based tumor-specific vaccines for the treatment of malignancies is possible with the plant-based transient expression system described here. We created a modified tobamoviral vector that encodes the idiotype-specific single-chain Fv fragment (scFv) of the immunoglobulin from the 38C13 mouse B cell lymphoma. Infected Nicotiana benthamiana plants contain high levels of secreted scFv protein in the extracellular compartment. This material reacts with an anti-idiotype antibody by Western blotting, ELISA, and affinity chromatography, suggesting that the plant-produced 38C13 scFv protein is properly folded in solution. Mice vaccinated with the affinity-purified 38C13 scFv generate >10 micrograms/ml anti-idiotype immunoglobulins. These mice were protected from challenge by a lethal dose of the syngeneic 38C13 tumor, similar to mice immunized with the native 38C13 IgM-keyhole limpet hemocyanin conjugate vaccine. This rapid production system for generating tumor-specific protein vaccines may provide a viable strategy for the treatment of non-Hodgkin's lymphoma.

Ligands and activators of nuclear hormone receptors regulate epidermal differentiation during fetal rat skin development

Because a protective barrier is essential for life, the development of the epidermis and stratum corneum must be completed prior to birth. The epidermal permeability barrier is comprised of corneocytes embedded in a lipid enriched matrix. Recent studies from our laboratory, using an explant model of fetal rat skin development that closely parallels in utero development, have shown that hormones and other activators of members of the nuclear receptor family regulate permeability barrier ontogenesis by stimulating lipid metabolism and the formation of the extracellular lipid lamellae. Using this model we sought to determine whether these hormones and nuclear activators also regulate keratinocyte differentiation during fetal development. Profilaggrin/filaggrin and loricrin expression, assessed by in situ hybridization and by immunohistochemistry, were progressively increased during epidermal ontogenesis. Whereas profilaggrin/filaggrin and loricrin were not expressed at day 17 of gestation, by day 19 both were present in the upper layers of the epidermis and both became still more abundant by day 21. These developmental changes also occurred in fetal skin explants cultured in vitro for 4 d, although the expression levels did not appear as robust as in utero. Whereas neither profilaggrin/filaggrin nor loricrin were expressed in control explants cultured for 2 d, they were seen in explants treated with either thyroid hormone, glucocorticoids, or estrogens. In contrast, dihydrotestosterone treatment delayed the expression of profilaggrin/filaggrin and loricrin. Moreover, both clofibrate, a peroxisome proliferator-activated receptor-alpha ligand, and juvenile hormone III, a farnesoid X-activated receptor activator, markedly accelerated fetal epidermal differentiation, stimulating both profilaggrin/filaggrin and loricrin expression. Our results demonstrate that several hormones and activators of nuclear hormone receptors regulate epidermal differentiation during fetal development, affecting key constituents of both keratohyalin granules and the cornified envelope. Thus, a variety of ligands/activators of nuclear receptors accelerate not only permeability barrier ontogenesis, but also the expression of structural proteins essential for stratum corneum formation.

Glucocorticoid deficiency delays stratum corneum maturation in the fetal mouse

The stratum corneum (SC) matures during late gestation in man and other mammals. Using the fetal rat as an experimental model, we have previously shown that glucocorticoids given in pharmacologic doses accelerate fetal SC maturation and barrier formation. To determine whether glucocorticoids are required for normal SC maturation, we examined the epidermal morphology of glucocorticoid-deficient (C-) murine pups, derived from matings of mice homozygous for null mutations of the corticotropin-releasing hormone alleles. In control pups on day 17.5 of gestation (term is 19.5 d), a multilayered SC was present and neutral lipid deposition in a membrane pattern was observed using Nile red fluorescence histochemistry. Ultrastructurally, mature lamellar unit structures predominate in the SC intercellular domains. In contrast, in C-pups only a single layer of SC was evident on day 17.5, and secreted lamellar material was not organized into mature lamellar structures. Furthermore, the expression of structural proteins necessary for cornified envelope formation, involucrin, loricrin, and filaggrin, and the activity of the lipid synthetic enzymes beta-glucocerebrosidase and steroid sulfatase, markers of barrier maturation, were reduced in day 17.5 C-pups. C-pups derived from pregnancies supplemented with physiologic amounts of cortisone, however, display normal SC ultrastructure on day 17.5 of gestation. Furthermore, at birth, both control and C-pups exhibit a multilayered SC replete with mature lamellar membrane structures. These data demonstrate that fetal glucocorticoid deficiency delays SC maturation, and suggests that normal levels of glucocorticoids are not absolutely required for SC development.

Ontogeny of the epidermal permeability barrier

A competent permeability barrier must be present by the end of gestation to allow for life in a terrestrial environment. Indeed, early preterm infants display serious complications of skin immaturity. Yet, regardless of their degree of prematurity, all infants quickly develop a competent barrier. To learn more about the mechanisms and regulation of barrier ontogeny, we have utilized late-gestation fetal rodents. In 19-21 d fetal rats, we showed that barrier competence is accompanied by both enhanced epidermal development and formation of extracellular lamellar membranes in the stratum corneum. The identical sequence and time-course occurs when fetal rat skin is cultured in a serum-free medium. Glucocorticoids, thyroid hormone (T3), and estrogen accelerate, while androgens delay barrier formation both in utero and in the in vitro system, explaining the poorer outcome of premature males versus females. But neither T3 nor glucocorticoids are absolutely required for barrier development. Lifting fetal skin cultures to an air-medium interface also accelerates barrier formation, explaining the rapid emergence of barrier competence in very premature infants. PPARalpha and FXR activators, which, like T3, heterodimerize with the nuclear receptor, RXR, also accelerate barrier development in vitro. Finally, not only the nuclear receptor family, but also Ca++ could regulate key events late in barrier development.

Keratinocyte differentiation is stimulated by activators of the nuclear hormone receptor PPARalpha

Peroxisome proliferator activated receptors (PPAR) belong to the superfamily of nuclear hormone receptors that heterodimerize with the retinoid X receptor and regulate transcription of several genes involved in lipid metabolism and adipocyte differentiation. Because of the role of 1,25-dihydroxyvitamin D3 and retinoic acid working through similar receptors (the vitamin D receptor and retinoic acid receptor, respectively) on keratinocyte differentiation, we have examined the effects of activators of PPARalpha on keratinocyte differentiation. The rate of cornified envelope formation was increased 3-fold in keratinocytes maintained in low calcium (0.03 mM) and incubated in the presence of clofibric acid, a potent PPARalpha activator. Involucrin, a cornified envelope precursor, and the cross-linking enzyme transglutaminase, were increased at both the message level (2-7-fold) and the protein level (4-12-fold) by clofibric acid. Furthermore, physiologic doses of the fatty acids oleic acid, linoleic acid, and eicosatetraynoic acid, which are also activators of PPARalpha, also induced involucrin and transglutaminase protein and mRNA. In contrast, the PPARgammaligand prostaglandin J2 had no effect on protein or mRNA levels of involucrin or transglutaminase. Levels of involucrin and transglutaminase mRNA and protein were induced by clofibric acid in keratinocytes incubated in 1.2 mM calcium, a concentration which by itself induces keratinocyte differentiation. Finally, PPARalpha activators inhibit DNA synthesis. This study demonstrates that PPARalpha activators, including putative endogenous ligands such as fatty acids, induce differentiation and inhibit proliferation in keratinocytes, and suggests a regulatory role for the PPARalpha in epidermal homeostasis.

The manufacturing process for recombinant factor IX

Advances in recombinant DNA manufacturing technology have now made possible the production of a highly purified and active recombinant factor IX (rFIX) product. Recombinant factor IX was developed by (1) stable insertion of the genes for both factor IX and PACE-SOL (a truncated, soluble serine protease needed to enhance the capacity of cells to remove the amino-terminal propeptide from rFIX) into Chinese hamster ovary cells; (2) selection of a cell line that was capable of expressing high amounts of active rFIX while growing in bioreactors containing a completely defined culture medium that does not contain blood or plasma products; and (3) inclusion of four independent chromatography steps, none of which require monoclonal antibodies. Furthermore, rFIX has been extensively tested to demonstrate similarity to plasma-derived factor IX and has been shown to be a consistent, high-purity product. For example, a high-specific-activity product (276+/-23 IU/mg) has been consistently produced throughout 65 consecutive batches from five consecutive manufacturing campaigns. Thus, rFIX offers a consistent and high-purity source of factor IX treatment for patients with hemophilia B.

Formation of the epidermal calcium gradient coincides with key milestones of barrier ontogenesis in the rodent

The epidermal permeability barrier forms late in gestation, coincident with decreased lipid synthesis, increased lipid processing, and development of a mature, multi-layered stratum corneum. Prior studies have shown that changes in the epidermal Ca++ gradient in vivo regulate lamellar body secretion and lipid synthesis, and modulations in extracellular Ca++ in vitro also regulate keratinocyte differentiation. We asked here whether a Ca++ gradient forms in fetal epidermis in utero, and whether its emergence correlates with key developmental milestones of barrier formation and stratum corneum development. Using either ion precipitation or proton induced X-ray emission analysis of fetal mouse and rat skin, we showed that a Ca++ gradient is not present at gestational days 16-18, prior to barrier formation, and that a gradient forms coincident with the emergence of barrier competence (day 19, mouse; day 20, rat) prior to birth. These results are consistent with a role for Ca++ in the regulation of key metabolic events leading to barrier formation. Whether the calcium gradient is formed actively or passively remains to be determined.

Hypothyroidism delays fetal stratum corneum development in mice

The epidermal permeability barrier, required for terrestrial life, is localized to lipid-enriched lamellar membranes in the extracellular spaces of the stratum corneum (SC). Immaturity of the SC is a significant contributor to morbidity and mortality in premature infants. Previous studies have shown that supraphysiologic concentrations of thyroid hormone accelerate epidermis/SC ontogenesis. Here we studied SC development in Hyt/Hyt mice who are genetically hypothyroid due to a mutation in the TSH receptor. In control mice on d 18 of gestation (term 19.5 d), only focal areas displayed a mature SC membrane pattern. By 19 d of gestation there was a mature multilayered SC with lamellar unit structures filling the extracellular spaces similar to that seen in mature mice. In Hyt/Hyt mice SC development was delayed at both 18 and 19 d of gestation. In both strains of mice, within the first day after birth there were no differences in epidermal or SC appearance, and the SC was fully mature. These findings indicate that thyroid hormone plays a physiologic role during normal intrauterine development of the SC. However, normal SC maturation ultimately occurs, indicating that thyroid hormone is not absolutely essential. Previous studies have shown that glucocorticoids accelerate SC development in euthyroid rats, and in the present study we demonstrate that glucocorticoids also accelerate SC ontogenesis in euthyroid mice. In contrast, in Hyt/Hyt mice glucocorticoids did not accelerate or normalize SC development, indicating that the glucocorticoid effect on SC maturation requires a euthyroid state or that glucocorticoids act via thyroid hormone. These studies demonstrate that thyroid hormone status is an important regulator of fetal SC development.

Activators of the nuclear hormone receptors PPARalpha and FXR accelerate the development of the fetal epidermal permeability barrier

Members of the superfamily of nuclear hormone receptors which are obligate heterodimeric partners of the retinoid X receptor may be important in epidermal development. Here, we examined the effects of activators of the receptors for vitamin D3 and retinoids, and of the peroxisome proliferator activated receptors (PPARs) and the farnesoid X-activated receptor (FXR), on the development of the fetal epidermal barrier in vitro. Skin explants from gestational day 17 rats (term is 22 d) are unstratified and lack a stratum corneum (SC). After incubation in hormone-free media for 3-4 d, a multilayered SC replete with mature lamellar membranes in the interstices and a functionally competent barrier appear. 9-cis or all-trans retinoic acid, 1,25 dihydroxyvitamin D3, or the PPARgamma ligands prostaglandin J2 or troglitazone did not affect the development of barrier function or epidermal morphology. In contrast, activators of the PPARalpha, oleic acid, linoleic acid, and clofibrate, accelerated epidermal development, resulting in mature lamellar membranes, a multilayered SC, and a competent barrier after 2 d of incubation. The FXR activators, all-trans farnesol and juvenile hormone III, also accelerated epidermal barrier development. Activities of beta-glucocerebrosidase and steroid sulfatase, enzymes previously linked to barrier maturation, also increased after treatment with PPARalpha and FXR activators. In contrast, isoprenoids, such as nerolidol, cis-farnesol, or geranylgeraniol, or metabolites in the cholesterol pathway, such as mevalonate, squalene, or 25-hydroxycholesterol, did not alter barrier development. Finally, additive effects were observed in explants incubated with clofibrate and farnesol together in suboptimal concentrations which alone did not affect barrier development. These data indicate a putative physiologic role for PPARalpha and FXR in epidermal barrier development.

Two discrete regions of deletion at 7q in uterine leiomyomas

This study further defines the region of consistent deletion of chromosome 7 in uterine leiomyomas. We have examined 74 leiomyomas for allelic loss of markers spanning the 7q22 region defined by markers D7S518 and D7S471. Forty tumors with cytogenetically defined 7q deletions, twenty-nine tumors without cytogenetically visible 7q deletions, and five tumors with no cytogenetic information were examined for allelic loss of D7S518, D7S666, D7S515, D7S658, D7S496, D7S692, and D7S471. Loss of heterozygosity for one or more of these loci was observed in twenty-eight leiomyomas with cytogenetically defined 7q deletions and in three leiomyomas with a normal karyotype. Allelic loss of D7S666 was common and was observed in all twenty-three informative tumors with 7q deletions and in two tumors with normal karyotypes. This study indicates the presence of a tumor suppressor gene in close proximity to the D7S666 locus. Eight tumors followed an unusual pattern of allelic loss. These tumors showed retention of heterozygosity for at least one locus flanked by deleted loci. These results suggest the possibility that two discrete regions of deletion at 7q22 are involved in the development of a subset of leiomyomas.

Epidermal steroid sulfatase and cholesterol sulfotransferase are regulated during late gestation in the fetal rat

Lipids in the stratum corneum (SC) are organized into lamellar membrane unit structures that provide the permeability barrier. Cholesterol sulfate, a SC membrane lipid, is synthesized by cholesterol sulfotransferase (CSTase) in the lower epidermis and hydrolyzed to cholesterol by steroid sulfatase (SSase) in the SC. To determine whether these enzymes are induced during barrier ontogenesis, we examined their activity in epidermis of fetal rats before (gestational day 17), during (day 19), and after (day 21) barrier formation. CSTase activity increased approximately 10-fold between day 17 and day 19, then declined between day 19 and day 21. In contrast, SSase activity reached its peak activity on day 21, increasing >5-fold. Fetal rat skin explants develop a SC and barrier over the same time course in vitro as in utero. Likewise, CSTase and SSase activities during in vitro ontogenesis precisely mirrored those obtained in utero. Moreover, hormones that accelerate barrier ontogenesis (e.g. glucocorticoids, thyroid hormone, and estrogen) accelerated the increase in CSTase and SSase activities during in vitro ontogenesis. mRNA levels of SSase increased in parallel with enzymatic activity, suggesting that these developmental changes are regulated at the genomic level. Finally, addition of exogenous cholesterol sulfate to explants in vitro did not accelerate either SC development or barrier formation. These studies suggest that induction of the cholesterol sulfate cycle enzymes during SC ontogenesis is a component of the fetal epidermal differentiation program and that the synthetic and degradative enzymes of this pathway are differentially regulated.

Keratinocyte K+ channels mediate Ca2+-induced differentiation

K+ channel activation has been associated with growth or differentiation in many cells. We have previously identified a 70-pS K+ channel that was found only in differentiated involucrin-positive cells. In this study we examined the role of K+ channels in Ca2+-induced keratinocyte differentiation. Consistent with our previous report, we found that a K+ conductance developed only in cells cultured in high extracellular Ca2+. Addition of charybdotoxin or verapamil blocked these K+ channels and inhibited Ca2+-induced differentiation, as assessed by cornified envelope formation or transglutaminase activity. These results suggest that K+ channel activation is necessary for Ca2+-induced differentiation. Finally, we used (125)I-labeled charybdotoxin to demonstrate the presence of K+ channels in intact human and mouse epidermis, hair follicles, and eccrine glands, indicating that these channels are found in keratinocytes both in vitro and in vivo. Thus K+ channels may moderate Ca2+ influx in more differentiated keratinocytes and may play a central role in keratinocyte differentiation.

Glucosylceramide metabolism is regulated during normal and hormonally stimulated epidermal barrier development in the rat

Glucosylceramides, delivered to the stratum corneum interstices by exocytosis of lamellar body contents, are enzymatically hydrolyzed to ceramides, which are major components of the lipid lamellar bilayers that mediate epidermal barrier function. Because this conversion is critical for permeability barrier homeostasis in the adult animal, in this study we measured the changes in activities of the enzymes responsible for the synthesis of glucosylceramide and its conversion to ceramide, UDP-glucose:ceramide glucosyltransferase (GC synthase) and beta-glucocerebrosidase (beta-GlcCer'ase), respectively, during fetal barrier formation. In epidermis from rats of gestational age 17-21 days, GC synthase activity peaked on day 19, prior to barrier competence, whereas beta-GlcCer'ase activity rose throughout barrier formation, exhibiting a 5-fold increase over this time period. beta-GlcCer'ase protein rose in parallel with activity, as did mRNA levels. Enzyme activities in skin explants from 17-day fetal rats, incubated up to 4 days in hormone- and serum-free media, paralleled those measured at corresponding time points in utero. Incubation with hormones that accelerate barrier development had minimal effects on GC synthase activity, whereas beta-GlcCer'ase activity was significantly increased after 1 or 2 days in culture. Finally, inhibition of beta-GlcCer'ase with conduritol B epoxide prevented barrier development in vitro and was accompanied by abnormalities in the lamellar bilayer ultrastructure of the stratum corneum. These data indicate that both synthesis and hydrolysis of glucosylceramide are regulated during fetal development. Furthermore, the enzymatic hydrolysis of glucosylceramide to ceramide is essential for fetal barrier ontogenesis.

Acceleration of barrier ontogenesis in vitro through air exposure

Immaturity of the epidermal barrier in the preterm infant may have serious clinical consequences. However, regardless of the degree of prematurity, the barrier rapidly matures such that by 2 wk all infants display a competent barrier. To determine whether the change from an aqueous (intrauterine) to a xeric environment might be the stimulus for this accelerated maturation, we examined the effects of air exposure on cutaneous barrier formation in vitro. Skin explants from d 17 fetal rats were incubated either submerged or at the air-medium interface. As previously reported, a competent barrier formed under submerged conditions after 3-4 d, precisely mirroring the time course of maturation in utero. In contrast, barrier maturation was accelerated in air-exposed explants, with functional, histologic, and structural markers of barrier formation observed after only 2 d of incubation. A water-impermeable membrane blocked the acceleration of barrier formation, resulting in a developmental time course comparable to that for submerged explants. In contrast a water vapor-permeable membrane did not block the acceleration. Glucocorticoids and thyroid hormone, which accelerate barrier formation in utero or in vitro under submerged conditions, did not further accelerate barrier formation in the air-exposed model. These data indicate that: 1) air exposure accelerates barrier ontogenesis, suggesting that water flux may be an important signal for the accelerated barrier formation that occurs in premature infants; and 2) factors which accelerate barrier formation in utero may not further accelerate barrier formation in neonates.

Hormonal basis for the gender difference in epidermal barrier formation in the fetal rat. Acceleration by estrogen and delay by testosterone

Previous studies have shown that ontogeny of the epidermal permeability barrier and lung occur in parallel in the fetal rat, and that pharmacologic agents, such as glucocorticoids and thyroid hormone, accelerate maturation at comparable developmental time points. Gender also influences lung maturation, i.e., males exhibit delayed development. Sex steroid hormones exert opposite effects on lung maturation, with estrogens accelerating and androgens inhibiting. In this study, we demonstrate that cutaneous barrier formation, measured as transepidermal water loss, is delayed in male fetal rats. Administration of estrogen to pregnant mothers accelerates fetal barrier development both morphologically and functionally. Competent barriers also form sooner in skin explants incubated in estrogen-supplemented media in vitro. In contrast, administration of dihydrotestosterone delays barrier formation both in vivo and in vitro. Finally, treatment of pregnant rats with the androgen antagonist flutamide eliminates the gender difference in barrier formation. These studies indicate that (a) estrogen accelerates and testosterone delays cutaneous barrier formation, (b) these hormones exert their effects directly on the skin, and (c) sex differences in rates of barrier development in vivo may be mediated by testosterone.

Decreased epidermal lipid synthesis accounts for altered barrier function in aged mice

The epidermis of aged mice displays decreased stratum corneum (SC) lipid content and decreased extracellular bilayers, which result in impaired barrier recovery following the solvent treatment or tape stripping. We assessed the role of altered lipid synthesis as the cause of the abnormal barrier and lipid content in aged epidermis, both under basal conditions and in response to acute barrier perturbations. In aged epidermis ( > or = 18 months), synthesis of one of the three key lipid classes (cholesterol) is decreased under basal conditions, and sterologenesis fails to attain the levels reached in young epidermis following comparable acute perturbations. In contrast, fatty acid and sphingolipid synthesis in aged epidermis increase sufficiently to approach the levels attained in stimulated young epidermis. The abnormalities in sterologenesis in aged epidermis are paralleled by a decrease in activity of its rate-limiting enzyme, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, under basal conditions, and enzyme activity also fails to increase as much as in young epidermis after barrier disruption. That defective lipid generation contributes to the barrier defect is shown directly by the ability of either a cholesterol-containing mixture of SC lipids or cholesterol alone to enhance barrier recovery. Finally, lipid-induced acceleration of barrier recovery in aged epidermis correlates with repletion of the extracellular spaces with normal lamellar structures. Thus, a deficiency in lipid synthesis, particularly in cholesterologenesis, accounts for the barrier abnormality in aged epidermis.

Epidermal barrier ontogenesis: maturation in serum-free media and acceleration by glucocorticoids and thyroid hormone but not selected growth factors

Because the cutaneous permeability barrier develops late in gestation, prematurity may result in increased morbidity and mortality due to barrier incompetence. The purpose of the present study was to develop an in vitro model of barrier ontogenesis in order to identify those factors critical for fetal barrier formation. Skin explants from gestational day 17 fetal rats (term is 22 days) were incubated in hormone- and serum-free media. After 4 d in culture, a multi-layered stratum corneum (SC) developed that demonstrated a membrane pattern of fluorescence using the hydrophobic probe, nile red, and the deposition of mature lamellar unit structures throughout the SC interstices, ultrastructurally. Transepidermal water loss rates declined during explant culture such that after 4 d a competent barrier was present. Similarly, lanthanum permeation studies showed tracer penetration into all cell layers in 2-d explants, whereas it did not penetrate above the stratum granulosum in 4-d explants. Thus, the chronology of epidermal development in the explants precisely mirrored that observed in utero. Treatment with either 10 nM dexamethasone or 10 nM triiodothyronine accelerated SC development and barrier formation by 2 d. These results indicate that (i) the late events of fetal epidermal development progress in vitro under serum- and growth factor-free conditions, culminating in the formation of a functional barrier, and (ii) both dexamethasone and triiodothyronine accelerate barrier development.

Amiloride blocks a keratinocyte nonspecific cation channel and inhibits Ca(++)-induced keratinocyte differentiation

Proliferation and differentiation in many cells are linked to specific changes in transmembrane ion fluxes. Previously, we have identified a nonspecific cation channel in keratinocytes, which is permeable to and activated by Ca++. To test whether this cation channel might serve as a pathway for Ca++ entry, we examined the effect of blocking this channel on membrane currents, markers of differentiation, and intracellular Ca++. In patch clamp studies, 10(-8) to 10(-6) M amiloride decreased the single-channel open probability. The same concentrations of amiloride inhibited the calcium-induced formation of cornified envelopes and activity of transglutaminase in a dose-dependent fashion. Amiloride inhibited the long-term rise of intracellular Ca++ induced by raised extracellular Ca++, without blocking the initial increase of intracellular Ca++. Amiloride at concentrations of 10(-7) to 10(-3) M did not change the resting intracellular pH of keratinocytes, although concentrations of 10(-6) M or greater inhibited the recovery from NH4(+)-induced acidification. To test whether the effect of amiloride was toxic, we measured DNA synthesis in the presence or absence of amiloride. DNA synthesis was unchanged, suggesting that amiloride's actions were not due to toxic effects. Although the exact mechanisms of amiloride's action remains to be determined, these experiments suggest that this compound may inhibit keratinocyte differentiation by blocking the nonspecific cation channel.

Chronic Losartan treatment blocks isoproterenol-induced dipsogenesis

Previous studies suggest that beta-adrenergic receptor agonists and other hypotensive agents stimulate water intake via the renin-angiotensin system (RAS). However, a recent study reported that acute peripheral administration of Losartan, an angiotensin II (AII) type I receptor antagonist, failed to inhibit isoproterenol-induced water intake. In the current study we assessed the role of chronic Losartan treatment on isoproterenol-induced water intake. Male Sprague-Dawley rats were divided into two groups (n = 10/group). The experimental group was chronically treated with Losartan in the drinking water (120 mg/kg/day). Rats in the control group were maintained on normal tap water. At the end of each week, water intake in response to isoproterenol was determined. On the days of the dipsogenic study, water intake was determined 1 h prior to and 2 h following SC injection of isoproterenol (25 micrograms/kg). Isoproterenol-induced water intake in the experimental group was significantly lower than the control rats by 71% and 88% at the end of weeks one and two respectively (p < 0.01). Following ten days of Losartan treatment, dipsogenic response to AII likewise demonstrated a complete blockage of AII receptors (75% decrease compared to the controls). These data strongly suggest that water intake in response to isoproterenol is mediated in part by the RAS.

Effects of streptozotocin-induced diabetes and insulin treatment on blood pressure in the male rat

Hyperinsulinemia may link diabetes to hypertension. We evaluated the effects of insulin on blood glucose and blood pressure in control and streptozotocin (STZ)-induced (60 mg/kg, i.v.) diabetes. Insulin was given daily for 10-14 weeks to both diabetic (0, 1, 2, and 3 U) and control (0, 2, and 3 U) male rats (n = 7-8/group). Indirect and direct blood pressures were measured as were blood glucose and several metabolic parameters. All treated rats became hyperinsulinemic. Untreated and 1 U insulin-treated diabetic rats were hyperglycemic. Higher doses of insulin significantly reduced blood glucoses in diabetic animals. Indirect blood pressure measurements were unchanged between groups. However, when measured directly, the untreated diabetic rats had significantly lower pressures that did untreated controls. Insulin treatment at dosages above 1 U normalized blood pressure in diabetic animals. These same doses of insulin also restored to normal all the metabolic parameters associated with diabetes. Insulin treatment did not affect any of the parameters evaluated in nondiabetic rats. Collectively, the results show that STZ-induced diabetes results in a decrease in blood pressure and that insulin treatment can restore blood pressure in diabetic rats. Although the results suggest that insulin may be involved in restoring blood pressure in animals with a carbohydrate imbalance, the precise mechanism for elevating blood pressure is not known with certainty.