What influences on their professional development do general practice trainees report from their hospital placements? A qualitative study

BACKGROUND

The clinical learning environment is important in GP specialty training and impacts professional development. Uniquely for GP trainees, about half of their training periods occur in a hospital environment, which is not their final workplace. There is still little understanding of how hospital-based training influences GP's professional development.

OBJECTIVES

To seek the views of GP trainees on how their hospital experience contributes to their professional development as a GP.

METHODS

This international and qualitative study seeks the views of GP trainees from Belgium, Ireland, Lithuania, and Slovenia. Semi-structured interviews were performed in the original languages. A joint thematic analysis in the English language resulted in key categories and themes.

RESULTS

From the four themes identified, GP trainees were found to experience additional challenges on top of the service provision/education tensions, which are common to all hospital trainees. Despite these, the hospital rotation component of GP training is valued by trainees. A strong finding of our study is the need to ensure that learning from the hospital placements is placed firmly in the context of general practice, e.g. GP placements prior or parallel with the hospital placements, educational activities resourced by GPs during their hospital experience, encouraging hospital teachers to have greater awareness of the educational needs of GPs, including an awareness of their training curriculum.

CONCLUSION

This novel study highlights how hospital placements for GP trainees could be enhanced. Further study could be broadened to recently qualified GPs, which may uncover new areas of interest.

Trainees' perceptions of course quality in postgraduate General Practice training in Ireland

BACKGROUND

Postgraduate General Practice (GP) training is structured around a formal curriculum set out by the training body. It also includes a "hidden curriculum" of experiential workplace learning in a heterogenous learning environment [1]. There is no formal national annual survey of GP trainees and their views in Ireland.

METHODS

The research aim was to evaluate what the trainee population think of their training environment, and to analyse the contributory factors. A mixed methods cross-sectional survey was distributed to all third- and fourth-year GP trainees (N = 404). The Manchester Clinical Placement Index was adapted for the study.

RESULTS

The response rate was 30.94% (N = 125). Questions 1 to 7 provided a description of the characteristics of the study population. The remainder of the questions focused on aspects which relate to constituents of the learning environment. The responses were broadly and convincingly positive and supportive of the good work being done in GP training and by trainers in Ireland today across both qualitative and quantitative findings. One notable exception was in the area of feedback where single handed fourth year practices were found to be underperforming.

CONCLUSIONS

The current research findings were broadly positive and supportive of the good work being done in GP training and by trainers in Ireland today. Further research will be needed to validate the study instrument and to further refine some aspects of its configuration. The implementation of such a survey on a regular basis may have merit as part of the quality assurance process in GP education alongside existing feedback structures [2].

Exploring the Irish general practice training community's perceptions on how an entrustable professional activities dashboard implementation could facilitate general practice training in Ireland

BACKGROUND

The Irish General Practitioner Training (GP) Programme is currently moving to Competency-Based Medical Education (CBME), facilitated by Programmatic Assessment (PA) and Entrustable Professional Activities (EPAs). These new assessment and feedback mechanisms may provide a rich and much sought-after dataset. However, given the possible number of feedback and assessment events, and the variety of modalities used, aggregating and interpreting these can be costly and difficult. Dashboard implementations (DI) have been purposed as a solution to bridge the gap between the large datasets and the training community at all levels.

AIMS

To explore the Irish GP training community's perceptions on how an EPAs DI could facilitate the delivery of GP training in Ireland.

METHODS

A qualitative approach was taken, using a focus group representative of different groups in the training community. Concurrently, an EPAs DI was developed. Focus group transcripts were analysed in an iterative fashion using Template Analysis to generate themes and subthemes.

RESULTS

Numerous advantages were seen in relation to the implementation of an EPAs DI around entrustment decisions, constructive alignment and summative decision-making. These advantages, however, need to be tempered with the realisation that the EPAs DI is not and should not be misinterpreted as being the learning analytic panacea for GP training.

CONCLUSION

This paper outlines the perceptions from a postgraduate medical education training community on an EPAs DI, which would be applicable to other training communities considering introducing similar mechanisms.

Covid-19 Epidemic Impact on Clinical Training in Irish GP Training

Aim To describe the effect of the Covid pandemic on the general practice workplace based learning of GP training in Ireland. Methods A prospective national survey of GP trainees who were in their GP practice placements on three separate occasions throughout the winter pandemic of 2020/2021 Results The average response rate to the three surveys was 19.4%. As the pandemic worsened, the number of face to face consultations dropped so that 51% (n=41) of trainees were seeing less than 5 patients face to face by the third survey. Conversely, the number of telephone/video consultations rose so that by the third survey 54% (n=44) of trainees were conducting more than 16 consultations per day remotely. Examinations and GP presentations expected to be daily occurrences diminished as the pandemic grew more severe, such that by the third survey 24-25% of trainees had not conducted a respiratory examination or dealt with new/unexpected hypertension in the previous month. Conclusion This study demonstrates abrupt change to the normal course of their training which was experienced by Irish GP trainees as a result of Covid, with examples from clinical practice. Adaptions of the training programme helped mitigate against the effects of the pandemic.

Warming conditions boost reproductive output for a northern gopher tortoise population

The effects of climate change on at-risk species will depend on how life history processes respond to climate and whether the seasonal timing of local climate changes overlaps with species-specific windows of climate sensitivity. For long-lived, iteroparous species like gopher tortoises Gopherus polyphemus, climate likely has a greater influence on reproduction than on adult survival. Our objective was to estimate the timing, magnitude, and direction of climate-driven effects on gopher tortoise reproductive output using a 25 yr dataset collected in southeastern Georgia, USA, near the northern edge of the species’ range. We assessed the timing of climate effects on reproductive output (both probability of reproduction and clutch size) by fitting models with climate covariates (maximum temperature, precipitation, and temperature range) summarized at all possible time intervals (in 1 mo increments) within the 24 mo period prior to the summer census date. We then fit a final model of reproductive output as a function of the identified climate variables and time windows using a Bayesian mixture model. Probability of reproduction was positively correlated with the prior year’s April-May maximum temperature, and clutch size was positively correlated with the prior year’s June maximum temperature. April-May and June maximum temperatures have increased over the past 3 decades at the study site, which likely led to an increase in clutch size of approximately 1 egg (15% increase over a mean of 6.5 eggs). However, the net effect of climate change on gopher tortoise population dynamics will depend on whether there are opposing or reinforcing climate responses for other demographic rates.

Performance in practice; exploring trainer and trainee experiences of user-designed formative assessment tools

INTRODUCTION

General Practice training in Ireland currently has various methods of formative assessment and feedback delivered to trainees. In 2018 the Irish College of General Practitioners commissioned the generation of two new user-designed formative feedback tools that would allow trainee feedback to drive learning. These tools became known as the Performance in Practice (PiP) tools.

AIMS

To explore the experiences of General Practice (GP) trainers and trainees having completed a pilot of using the PiP tools for 4 months.

METHODS

An explorative phenomenological approach was taken to understand the experiences of trainers and trainees. One to one interviews were conducted, and the transcripts analysed for themes and sub-theme via Template analysis.

RESULTS

User experiences focused on two main areas; educational value and acceptability. In relation to educational value, the PiP tools were seen as an improvement over established forms of formative feedback, as they were centred around the curriculum and therefore reflected the unique multifaceted requirements of an independently practising GP. Acceptability primarily focused around data governance and structures, as well as practical issues such as ease of software use.

CONCLUSIONS

Overall, the experience of using the PiP tools was positive for both trainers and trainees. Future plans to further explore implementation of the PiP tools have been significantly informed by this research.

Donegal Going against the Flow: National Differences in Long-Term Urinary Catheterisation Rates in Men (> 65 Years) With Benign Prostatic Hypertrophy

An analysis of Primary Care Reimbursement Service (PCRS, 2013) data demonstrated high rates of urinary catheter changes in Donegal compared to other regions of Ireland. There is a catheter change rate of 10.2% in Donegal men over 65 with medical cards (GMS) compared to rates of 2.7% and 0.17% in Waterford and South Dublin, respectively1. This 60-fold difference between an area with perceived good access to services (South Dublin) and Donegal an area that does not, prompted a survey of general practitioners in each of these areas to assess whether true male catheterisation rates were similarly disproportionate in Donegal. Based on this, data was collected from a population of 23,794 GMS patients in GP training practices in Donegal (Rural), Leinster (Urban) and Waterford (Suburban). The data sampled for Donegal demonstrated 19 long-term catheters (LTCs per 8603 GMS) compared to four LTCs (per 5,800 GMS) in Leinster and 3 LTCs (per 9,391 GMS) in Waterford (Table 1). This anomaly in LTC rates may be a proxy for lack of access to basic Urology services.

Clinical outcomes and the role of adjuvant therapy sequencing in Type II uterine cancer following definitive surgical treatment

PURPOSE OF INVESTIGATION

Because of rarity, consensus on adjuvant therapies for Type II endometrial cancers (BC) remains undefined. Reporting their institutional outcomes, the present authors assessed the impact of adjuvant therapies on recurrence and overall survival in women with 2009 FIGO Stage I-III Type II BC.

MATERIAL AND METHODS

The authors identified 108 women, treated with definitive surgery between 2000-2013, with pathologically-confirmed Type II EC (non-endometrioid [NEM, n=801 and high grade endometrioid [G3EEC, n=28]) Cox proportional hazard models were used to assess the effect of prognostic variables on disease-free (DFS) and overall survival (OS). Kaplan-Meier method was used to assess survival.

RESULTS

Of the 108 women, 83 (77%) were African American (AA). Fifty-nine (55%), 12 (11%), and 37 (34%) were Stage I, II, and III, respectively. Ninety-seven patients received adjuvant therapy: 52 (radiation only), four (chemotherapy only), and 40 (combined). During follow-up (median 41 months), 44 patients (41%) recurred. Five-year DFS was 53% overall (48% [NEM], 80% [G3EEC]). Five-year OS was 75% overall (68% [NEM], 95% [G3EEC]). On multivariate analysis, lower stage and adjuvant radiation improved DFS. Higher stage, NEM, and increasing age were poor prognostic indicators of OS.

CONCLUSION

Representing a large single institutional cohort for Type II BC, the present study's observed sur- vival rates are consistent with previous studies, despite the relatively high frequency of carcinosarcoma and Stage III/nodal disease. The protective effect on recurrence was not lost when radiation was delayed for chemotherapy. The present results support a multimodal adjuvant approach for treating all stages of invasive NEM EC.

Ecotoxicological characterization of biochars: role of feedstock and pyrolysis temperature

Seven contrasting feedstocks were subjected to slow pyrolysis at low (300 or 350°C) and high temperature (550 or 600°C), and both biochars and the corresponding feedstocks tested for short-term ecotoxicity using basal soil respiration and collembolan reproduction tests. After a 28-d incubation, soil basal respiration was not inhibited but stimulated by additions of feedstocks and biochars. However, variation in soil respiration was dependent on both feedstock and pyrolysis temperature. In the last case, respiration decreased with pyrolysis temperature (r=-0.78; p<0.0001, n=21) and increased with a higher volatile matter content (r=0.51; p<0.017), these two variables being correlated (r=-0.86, p<0.0001). Collembolan reproduction was generally unaffected by any of the additions, but when inhibited, it was mostly influenced by feedstock, and generally without any influence of charring itself and pyrolysis temperature. Strong inhibition was only observed in uncharred food waste and resulting biochars. Inhibition effects were probably linked to high soluble Na and NH4 concentrations when both feedstocks and biochars were considered, but mostly to soluble Na when only biochars were taken into account. The general lack of toxicity of the set of slow pyrolysis biochars in this study at typical field application rates (≤20 Mg ha(-1)) suggests a low short-term toxicity risk. At higher application rates (20-540 Mg ha(-1)), some biochars affected collembolan reproduction to some extent, but only strongly in the food waste biochars. Such negative impacts were not anticipated by the criteria set in currently available biochar quality standards, pointing out the need to consider ecotoxicological criteria either explicitly or implicitly in biochar characterization schemes or in management recommendations.

Who goes where? A prospective study of referral patterns within a newly established primary care team

BACKGROUND

Since the introduction of primary care teams, referral patterns of General Practitioners (GPs) in Ireland have not been studied.

AIMS

To study the referral patterns of GPs within a primary care team (PCT) to allied health care professionals in a PCT and to secondary care. To identify indirect referral pathways. To study variation in individual GP referral patterns.

METHOD

Questionnaire based survey. Statistical analysis was carried out using Epi Info version 3.5.1.

RESULTS

Of 3,166 consultations, 2,841 (89.7%) were dealt with by the GP and required no referral, 107 (3.4%) were referred within the PCT, and 218 (6.9%) were referred elsewhere. Therefore, 93.1% of consultations were managed in primary care alone. Ninety percent of GPs refer patients to the PCT. Indirect referrals constituted 17% of all outpatient referrals. Females have significantly higher referral rates than males. Referral rates of GPs in single-handed practices are higher than GPs in group practices.

CONCLUSIONS

GPs alone can manage the vast majority of presentations in general practice. Greater GP access to diagnostic and therapeutic interventions may reduce outpatient referrals. GPs in group practices may collectively have greater experience and expertise and therefore can manage more patients in primary care. There is a significant variation in referral rates between both genders.

Survival of adenovirus types 2 and 41 in surface and ground waters measured by a plaque assay

To manage artificial recharge systems, it is necessary to understand the inactivation process of microorganisms within aquifers so that requirements regarding storage times and treatment strategies for ground and surface waters can be developed and modeled to improve water management practices. This study was designed to investigate the survival of representative adenoviruses in surface- and groundwaters using a cell culture plaque assay with human lung carcinoma cells (A549) to enumerate surviving viruses. Adenovirus types 2 (Ad2) and 41 (Ad41) were seeded into 50 mL of three sterilized surface waters and groundwaters, and incubated at 10 and 19 °C for up to 301 days. Concentrations of Ad2 and Ad41 were relatively stable in all waters at 10 °C for at least 160 days and in some instances up to 301 days. At 19 °C, virus concentrations were reduced by 99.99% (4 log) after 301 days in surface water. There was approximately 90% (1 log) reduction of both viruses at 19 °C after 160 days of incubation in groundwater samples. There was no overall difference in survival kinetics in surface waters compared to groundwaters. The relatively high stability and long-term survival of adenoviruses in environmental waters at elevated temperatures should be considered in risk assessment models and drinking water management strategies.

Prescribing errors in general practice: a prospective study

Prescribing is one of the commonest tasks in daily general practice. Surprisingly there is little published research on errors that occur in this area. The aim of this study was to estimate the seriousness and level of prescribing errors that occurred in general practice. This prospective survey documented errors in prescriptions from 28 general practitioners as they occurred over a 3-day period in 12 community pharmacies. From a total of 3,948 prescriptions, 491 (12.4%) contained one or more errors. From a total of 8,686 drug items, 546 (6.2%) contained one or more errors. Of the errors the majority were minor (398, 72.9%), a smaller number (135, 24.7%) were major nuisance errors, and there were 13 (2.4%) potentially serious errors. The most common errors related to drug directions and dosage.

Extent of cervical involvement in endometrial cancer as a predictor of outcome

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Background: Endometrial cancer will affect 40,000 women this year. Extent of myometrial invasion and presence of cervical stromal disease are risk-factors for metastasis and recurrence. Uterine cervical involvement is often not known in advance of surgery, and superficial involvement may not be seen at frozen section. The objective of this study was to determine if the extent of cervical invasion is a predictor of outcome. Methods: The institutional cancer registry was searched for cases of stage II uterine cancer from 1996–2006. Inclusion criteria were endometrioid histology and clinical data and pathology available for evaluation. Demographics, extent of surgery, tumor grade, depth of myometrial invasion, presence of lymph-vascular space invasion (LVSI), and last follow up were collected. In addition, a gynecologic pathologist evaluated all slides to determine depth of cervical stromal invasion. Statistical analysis to compare predictors of outcome was performed. Results: There were 800 cases of endometrial cancer diagnosed from 1996–2006, 75 (9%) were stage II. Fifty two cases met all inclusion criteria. Mean age at diagnosis was 63.4 years. Mean BMI was 31.6. Ninety four percent were white, 4% black, and 2% Asian. All patients had a hysterectomy, 6 (11.5%) had a radical hysterectomy and 36 (69%) had lymphadenectomy performed. Eighteen (34.6%) were stage IIA and 32 (61.5%) were IIB. LVSI was seen in 15 (28.8%) cases. On pathologic review, 37.5% had no cervical stromal invasion, 42.5% had invasion of less than half and 20% had invasion of more than half of the cervical stroma. Forty patients (77%) received adjuvant radiation. There were 8 recurrences and 6 disease-related deaths. The mean follow up period was 30 months. Extent of cervical invasion did not correlate with recurrence or survival. Factors associated with increased risk of recurrence were: LVSI (p = 0.017), lack of lymph node sampling (p = 0.035), and age >55 years (p = 0.027). Women with and without recurrence were compared and did not significantly differ. Conclusions: In this study with pathologic review, extent of cervical involvement in stage II endometrial cancer was not associated with increased risk of recurrence or death. Age >55 years, lack of node sampling and presence of LVSI were predictors of recurrent disease.

No significant financial relationships to disclose.

Symptoms of vertigo in general practice: a prospective study of diagnosis

BACKGROUND

There is little published evidence of the general practice experience of the diagnostic outcomes when symptoms of vertigo present. What research there is has been dominated by specialist centres. This gives a skewed view of the prevalence of the causes of such symptoms.

AIM

To describe the likely diagnosis of symptoms of vertigo.

DESIGN OF STUDY

Prospective cohort study

METHODS

Thirteen GPs were recruited and trained to clinically assess and follow up all patients presenting with symptoms of vertigo over a six-month period Age-sex data were simultaneously gathered on those who consulted with non-vertiginous dizziness.

RESULTS

The main diagnoses assigned by the GPs in 70 patients were benign positional vertigo, acute vestibular neuronitis and Ménière's disease, which together accounted for 93% (95% confidence interval = 71% to 100%) of patients' symptoms. Ninety-one per cent of patients were managed in general practice and 60% received a prescription for a vestibular sedative.

CONCLUSION

This study suggests that presentations of symptoms of vertigo can be clinically diagnosed in most cases. The diagnoses recorded by GPs differ in proportion to those in specialist centres, with a larger number of patients suffering from benign positional vertigo and acute vestibular neuronitis in general practice, in contrast with specialist centres, which see more patients with Ménière's disease.

A measurement of the efficacy of anticoagulation monitoring in a general practice based setting

With increasing numbers of patients on anticoagulant therapy and a trend towards moving certain hospital services to a primary care setting, we looked at how GPs are managing Warfarin therapy in their patients. This prospective study measured the efficacy of INR monitoring in 325 patients who were being managed in a general practice setting. 41% (415 of 1016) of readings fell strictly within the target ranges recommended by the British Society for Haematology. There was a low rate of haemorrhagic events (3.7%) in patients on Warfarin. Possible methods of improving readings include the introduction of Decision Support Services and formal training.

A systematic review of vertigo in primary care

The symptom of vertigo is usually managed in primary care without further referral. This review examines the evidence on which general practitioners can base clinical diagnosis and management of this relatively common complaint. Research in this area has in the main been from secondary and tertiary centres and has been of variable quality. Indications are that the conditions that present in general practice are most likely to be benign positional vertigo, acute vestibular neuronitis, and Ménière's disease; however, vascular incidents and neurological causes, such as multiple sclerosis, must be kept in mind. An important practice point is that vestibular sedatives are not recommended on a prolonged basis for any type of vertigo. There is a need for basic epidemiological and clinical management research of vertigo in general practice.

Cholesterol sulfate stimulates involucrin transcription in keratinocytes by increasing Fra-1, Fra-2, and Jun D

Lipids that are synthesized de novo in the epidermis, including fatty acids, oxysterols, 1,25-dihydroxyvitamin D(3), and farnesol, can regulate the differentiation of normal human keratinocytes (NHK). Cholesterol sulfate (CS), an epidermal lipid that is produced in the upper nucleated layers of the epidermis coincident with terminal differentiation, has been shown to play a role in the regulation of the late stages of keratinocyte differentiation, including formation of the cornified envelope. In the present study, we determined i) whether CS regulates involucrin (INV), an early keratinocyte differentiation marker, and ii) the mechanism by which CS regulates differentiation. mRNA and protein levels of INV, a precursor protein of the cornified envelope, increased 2- to 3-fold in NHK incubated in the presence of CS. In contrast, cholesterol had no effect on INV protein or mRNA levels. Transcriptional regulation was assessed in NHK transfected with INV promoter-luciferase constructs. CS increased luciferase reporter activity approximately 2- to 3-fold in NHK transfected with a 3.7-kb INV promoter construct. Deletional analysis revealed a CS-responsive region of the INV promoter located between bp --2452 and --1880. A 5-base pair (bp) mutation of the AP-1 site (bp --2117 to --2111) within this responsive region abolished CS responsiveness, suggesting a role for the AP-1 complex in the regulation of INV transcription by CS. Electrophoretic mobility shift analysis demonstrated increased binding of nuclear extracts isolated from CS-treated NHK to AP-1 DNA as compared with vehicle-treated controls. Incubation of the nuclear extract with the appropriate antibodies showed that the AP-1 DNA-binding complex contained Fra-1, Fra-2, and Jun D. Western blots demonstrated that CS treatment increased the levels of Fra-1, Fra-2, and Jun D, and Northern analyses revealed that CS increased mRNA levels for these same AP-1 factors. These data indicate that CS, an endogenous lipid synthesized by keratinocytes, regulates the early stages of keratinocyte differentiation, and may do so through its ability to modulate levels of AP-1 proteins. -- Hanley, K., L. Wood, D. C. Ng, S. S. He, P. Lau, A. Moser, P. M. Elias, D. D. Bikle, M. L. Williams, and K. R. Feingold. Cholesterol sulfate stimulates involucrin transcription in keratinocytes by increasing Fra-1, Fra-2, and Jun D. J. Lipid Res. 2001. 42: 390--398.

Keratinocyte differentiation in hyperproliferative epidermis: topical application of PPARalpha activators restores tissue homeostasis

We recently showed that topically applied PPARalpha activators promote epidermal differentiation in intact adult mouse skin. In this study we determined the effect of clofibrate and Wy-14,643, activators of PPARalpha, on hyperproliferative epidermis in hairless mice, induced either by repeated barrier abrogation (subacute model) or by essential fatty acid deficiency (chronic model). The hyperproliferative epidermis was characterized by an increased number of proliferating cells expressing proliferating cell nuclear antigen. Topical treatment with PPARalpha activators resulted in a substantial decrease in epidermal hyperplasia in both the subacute and chronic models of hyperproliferation. Following topical treatment, proliferating cell nuclear antigen-expressing cells were restricted to the basal layer, similar to normal epidermis. In hyperproliferative epidermis there was decreased expression of involucrin, profilaggrin-filaggrin, and loricrin as assayed by in situ hybridization and immunohistochemistry. Following topical treatment with PPAR activators staining for these mRNAs and proteins increased towards normal levels. Finally, topically applied clofibrate also increased apoptosis. This study demonstrates that topical PPAR activators have profound effects on epidermal gene expression in hyperproliferative skin disorders. Treatment with PPARalpha activators normalizes cell proliferation and promotes epidermal differentiation, correcting the cutaneous pathology. This study identifies PPARalpha activators as potential skin therapeutic agents.

Stimulation of PPARalpha promotes epidermal keratinocyte differentiation in vivo

Our recent studies have demonstrated that PPARalpha activators stimulate differentiation and inhibit proliferation in cultured human keratinocytes and accelerate epidermal development and permeability barrier formation in fetal rat skin explants. As the role of PPARalpha activation in adult epidermis is not known, the aim of this study was to determine if topically applied PPARalpha ligands regulate keratinocyte differentiation in murine epidermis. Topical treatment with PPARalpha activators resulted in decreased epidermal thickness. Expression of structural proteins of the upper spinous/granular layers (involucrin, profilaggrin-filaggrin, loricrin) increased following topical treatment with PPARalpha activators. Furthermore, topically applied PPARalpha activators also increased apoptosis, decreased cell proliferation, and accelerated recovery of barrier function following acute barrier abrogation. Experiments with PPARalpha-/- knockout mice showed that these effects are specifically mediated via PPARalpha. Compared with the epidermis of PPARalpha+/+ mice, involucrin, profilaggrin-filaggrin, and loricrin expression were slightly decreased in PPARalpha-/- mice. Moreover, topical clofibrate treatment did not increase epidermal differentiation in PPARalpha-/- mice. Furthermore, in cultured human keratinocytes we have demonstrated that PPARalpha activators induce an increase in involucrin mRNA levels. We have also shown that this increase in gene expression requires an intact AP-1 response element at -2117 to -2111 bp. Thus, stimulation of PPARalpha stimulates keratinocyte/epidermal differentiation and inhibits proliferation.

Farnesol stimulates differentiation in epidermal keratinocytes via PPARalpha

The isoprenoids farnesol and juvenile hormone III (JH), metabolites of the cholesterol biosynthetic pathway, have been shown to stimulate fetal epidermal development in rodents. In this study we determined whether this effect might be attributed to a direct induction of keratinocytes differentiation and examined the mechanisms responsible for these effects. Rates of cornified envelope formation, a marker of keratinocyte terminal differentiation, as well as protein and mRNA levels of two proteins required for cornified envelope formation, involucrin (INV) and transglutaminase, increased 2- to 3-fold in normal human keratinocytes (NHK) treated with either farnesol or JH, even at low calcium concentrations (0.03 mM), which otherwise inhibit differentiation. In contrast, neither cholesterol nor mevalonate affected INV or transglutaminase mRNA levels. Effects of farnesol and JH on INV and transglutaminase mRNA levels were additive with high calcium concentrations (1.2 mM) that independently stimulate keratinocyte differentiation. In contrast, keratinocyte DNA synthesis was inhibited by these compounds. Both farnesol and JH stimulated INV and transglutaminase promoter activity, suggesting regulation at the transcriptional level. A series of truncation and deletion experiments revealed a farnesol-responsive region (-2452 to -1880 base pairs (bp)) in the INV gene. This region contained an AP-1 site. A single base pair mutation of the AP-1 site at -2116 to -2110 bp abolished farnesol responsiveness, identical to effects by peroxisome proliferator-activated receptor (PPARalpha) activators. Farnesoid X-activated receptor mRNA was not detected in NHK, but farnesol treatment increased activities of both a PPAR response element and PPARalpha mRNA levels in NHK. Furthermore, the increase in PPRE activity by farnesol was dependent upon PPARalpha in CV-1 cells. Finally, topical applications of farnesol increased mRNA and protein levels of the differentiation-specific genes, profilaggrin and loricrin, determined by immunohistochemistry and in situ hybridization, in wild-type but not in PPARalpha-/- murine epidermis. These findings suggest a novel role for selected isoprenoid cholesterol intermediates in the regulation of differentiation-specific gene transcription and a convergence of PPARalpha with the cholesterol synthetic pathway.

Oxysterols induce differentiation in human keratinocytes and increase Ap-1-dependent involucrin transcription

Ligands and activators of the nuclear hormone receptor superfamily are important in the regulation of epidermal development and differentiation. Previously, we showed that naturally occurring fatty acids, as well as synthetic ligands for the peroxisome proliferator-activated receptor, induce keratinocyte differentiation in vitro. Here we asked whether oxysterols, another class of lipids formed de novo in the epidermis and that activate liver X-activated receptor, regulate keratinocyte differentiation. mRNA and protein levels of involucrin and transglutaminase 1, markers of differentiation, increased 2- to 3-fold in normal human keratinocytes incubated in the presence of 25- or 22R-hydroxycholesterol in low calcium. In high calcium, which alone induces differentiation, mRNA levels were further increased by oxysterols. Rates of cornified envelope formation, an indicator of terminal differentiation, also increased 2-fold with oxysterol treatment. In contrast, the rate of DNA synthesis was inhibited approximately 50% by oxysterols. Transcriptional regulation was assessed in keratinocytes transfected with either transglutaminase 1 or involucrin promoter-luciferase constructs. 22R-hydroxycholesterol increased transglutaminase 1 and involucrin promoter activity 2- to 3-fold. Either deletion of the -2452 bp to -1880 bp region of the involucrin promoter, or mutation of the AP-1 site within this region, abolished oxysterol responsiveness. Moreover, increased AP-1 DNA binding was observed in oxysterol-treated keratinocytes by gel shift analyses. Finally, we demonstrated the presence of liver X-activated receptor alpha and beta mRNAs, and showed that oxysterols stimulate a liver X-activated receptor response element transfected into keratinocytes. These data suggest that oxysterols induce keratinocyte differentiation, in part through increased AP-1-dependent transcription of the involucrin gene, an effect that may be mediated by liver X-activated receptor.

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.