Automated Recognition of Visual Acuity Measurements in Ophthalmology Clinical Notes Using Deep Learning

Purpose

Visual acuity (VA) is a critical component of the eye examination but is often only documented in electronic health records (EHRs) as unstructured free-text notes, making it challenging to use in research. This study aimed to improve on existing rule-based algorithms by developing and evaluating deep learning models to perform named entity recognition of different types of VA measurements and their lateralities from free-text ophthalmology notes: VA for each of the right and left eyes, with and without glasses correction, and with and without pinhole.

Design

Cross-sectional study.

Subjects

A total of 319 756 clinical notes with documented VA measurements from approximately 90 000 patients were included.

Methods

The notes were split into train, validation, and test sets. Bidirectional Encoder Representations from Transformers (BERT) models were fine-tuned to identify VA measurements from the progress notes and included BERT models pretrained on biomedical literature (BioBERT), critical care EHR notes (ClinicalBERT), both (BlueBERT), and a lighter version of BERT with 40% fewer parameters (DistilBERT). A baseline rule-based algorithm was created to recognize the same VA entities to compare against BERT models.

Main Outcome Measures

Model performance was evaluated on a held-out test set using microaveraged precision, recall, and F1 score for all entities.

Results

On the human-annotated subset, BlueBERT achieved the best microaveraged F1 score (F1 = 0.92), followed by ClinicalBERT (F1 = 0.91), DistilBERT (F1 = 0.90), BioBERT (F1 = 0.84), and the baseline model (F1 = 0.83). Common errors included labeling VA in sections outside of the examination portion of the note, difficulties labeling current VA alongside a series of past VAs, and missing nonnumeric VAs.

Conclusions

This study demonstrates that deep learning models are capable of identifying VA measurements from free-text ophthalmology notes with high precision and recall, achieving significant performance improvements over a rule-based algorithm. The ability to recognize VA from free-text notes would enable a more detailed characterization of ophthalmology patient cohorts and enhance the development of models to predict ophthalmology outcomes.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

The Association Between Frailty and Visual Field Loss in US Adults

PURPOSE

To describe the association between visual field loss and frailty in a nationally representative cohort of US adults.

DESIGN

Retrospective cross-sectional study.

METHODS

The cohort included adults 40 years or older with complete eye examination data from the 2005-2006 and 2007-2008 National Health and Nutrition Examination Surveys (NHANES). Visual field loss (VFL) was determined by frequency doubling technology and a 2-2-1 algorithm. A 36-item deficit accumulation-based frailty index was used to divide subjects into 4 categories of increasing frailty severity.

RESULTS

Of the 4897 participants, 4402 (93.2%) had no VFL, 301 (4.1%) had unilateral VFL, and 194 (2.73%) had bilateral VFL. Within the sample, 2 subjects197 (53.1%) were categorized as non-frail, 1659 (31.3%) as vulnerable, 732 (11.3%) as mildly frail, and 312 (4.3%) as most frail. In multivariable models adjusted for demographics, visual acuity, and history of cataract surgery, subjects with unilateral VFL had higher adjusted odds of being in a more frail category (adjusted odds ratio [aOR], 2.07; 95% CI, 1.42-3.02) than subjects without VFL. Subjects with bilateral VFL also had higher odds of a more frail category compared to subjects without VFL (aOR, 1.74; 95% CI, 1.20-2.52).

CONCLUSIONS

In the 2005-2008 NHANES adult population, VFL is associated with higher odds of frailty, independent of central visual acuity loss. Frail individuals may be more susceptible to diseases that can cause VFL, and/or VFL may predispose to frailty. Additional studies are needed to determine the directionality of this relationship and to assess potential interventions.

Social Determinants of Health and Perceived Barriers to Care in Diabetic Retinopathy Screening

Importance

Regular screening for diabetic retinopathy often is crucial for the health of patients with diabetes. However, many factors may be barriers to regular screening and associated with disparities in screening rates.

Objective

To evaluate the associations between visiting an eye care practitioner for diabetic retinopathy screening and factors related to overall health and social determinants of health, including socioeconomic status and health care access and utilization.

Design, Setting, and Participants

This retrospective cross-sectional study included adults aged 18 years or older with type 2 diabetes who answered survey questions in the All of Us Research Program, a national multicenter cohort of patients contributing electronic health records and survey data, who were enrolled from May 1, 2018, to July 1, 2022.

Exposures

The associations between visiting an eye care practitioner and (1) demographic and socioeconomic factors and (2) responses to the Health Care Access and Utilization, Social Determinants of Health, and Overall Health surveys were investigated using univariable and multivariable logistic regressions.

Main Outcome and Measures

The primary outcome was whether patients self-reported visiting an eye care practitioner in the past 12 months. The associations between visiting an eye care practitioner and demographic and socioeconomic factors and responses to the Health Care Access and Utilization, Social Determinants of Health, and Overall Health surveys in All of Us were investigated using univariable and multivariable logistic regression.

Results

Of the 11 551 included participants (54.55% cisgender women; mean [SD] age, 64.71 [11.82] years), 7983 (69.11%) self-reported visiting an eye care practitioner in the past year. Individuals who thought practitioner concordance was somewhat or very important were less likely to have seen an eye care practitioner (somewhat important: adjusted odds ratio [AOR], 0.83 [95% CI, 0.74-0.93]; very important: AOR, 0.85 [95% CI, 0.76-0.95]). Compared with financially stable participants, individuals with food or housing insecurity were less likely to visit an eye care practitioner (food insecurity: AOR, 0.75 [95% CI, 0.61-0.91]; housing insecurity: AOR, 0.86 [95% CI, 0.75-0.98]). Individuals who reported fair mental health were less likely to visit an eye care practitioner than were those who reported good mental health (AOR, 0.84; 95% CI, 0.74-0.96).

Conclusions and Relevance

This study found that food insecurity, housing insecurity, mental health concerns, and the perceived importance of practitioner concordance were associated with a lower likelihood of receiving eye care. Such findings highlight the self-reported barriers to seeking care and the importance of taking steps to promote health equity.

Association between insurance status and hearing healthcare use in the United States

OBJECTIVE

Despite the high prevalence and morbidity of hearing loss, many individuals with hearing loss do not have access to hearing healthcare. This study aims to assess the relationship between insurance status and prior audiogram, and hearing aid use among subjects with hearing loss.

MATERIALS AND METHODS

This cross-sectional study of the 2009-10, 2011-12, and 2015-16 cycles of the U.S. National Health and Nutrition Examination Survey (NHANES) included 5270 adult subjects 18 years or older with subjective or audiometric hearing loss. Subjects were stratified by insurance: Medicare, Medicaid, private, uninsured, and 'other or unspecified'.

RESULTS

After adjusting for covariates, among subjects with audiometric hearing loss, prior audiogram was not associated with insurance type, including no insurance (OR 0.80, 95 % CI 0.45 to 1.42), Medicare (OR 1.34, 95 % CI 0.69 to 2.59), Medicaid (OR 1.27, 95 % CI 0.55 to 2.93), or 'other or unspecified' (OR 1.73, 95 % CI 0.67 to 4.47). Hearing aid use was not associated with insurance type, including no insurance (OR 0.20, 95 % CI 0.03 to 1.29), Medicare (OR 0.56, 95 % CI 0.27 to 1.14), Medicaid (OR 2.03, 95 % CI 0.47 to 8.71), or 'other or unspecified' (OR 1.76, 95 % CI 0.59 to 5.23).

CONCLUSIONS

Health insurance status was not associated with hearing healthcare use in our nationally-representative sample of individuals with hearing loss. Given variations in hearing coverage by Medicaid between states, future studies should compare the impact of Medicaid insurance on hearing aid use between states that cover hearing aids and those that do not.

Automated Radiomic Analysis of Vestibular Schwannomas and Inner Ears Using Contrast-Enhanced T1-Weighted and T2-Weighted Magnetic Resonance Imaging Sequences and Artificial Intelligence

OBJECTIVE

To objectively evaluate vestibular schwannomas (VSs) and their spatial relationships with the ipsilateral inner ear (IE) in magnetic resonance imaging (MRI) using deep learning.

STUDY DESIGN

Cross-sectional study.

PATIENTS

A total of 490 adults with VS, high-resolution MRI scans, and no previous neurotologic surgery.

INTERVENTIONS

MRI studies of VS patients were split into training (390 patients) and test (100 patients) sets. A three-dimensional convolutional neural network model was trained to segment VS and IE structures using contrast-enhanced T1-weighted and T2-weighted sequences, respectively. Manual segmentations were used as ground truths. Model performance was evaluated on the test set and on an external set of 100 VS patients from a public data set (Vestibular-Schwannoma-SEG).

MAIN OUTCOME MEASURES

Dice score, relative volume error, average symmetric surface distance, 95th-percentile Hausdorff distance, and centroid locations.

RESULTS

Dice scores for VS and IE volume segmentations were 0.91 and 0.90, respectively. On the public data set, the model segmented VS tumors with a Dice score of 0.89 ± 0.06 (mean ± standard deviation), relative volume error of 9.8 ± 9.6%, average symmetric surface distance of 0.31 ± 0.22 mm, and 95th-percentile Hausdorff distance of 1.26 ± 0.76 mm. Predicted VS segmentations overlapped with ground truth segmentations in all test subjects. Mean errors of predicted VS volume, VS centroid location, and IE centroid location were 0.05 cm 3 , 0.52 mm, and 0.85 mm, respectively.

CONCLUSIONS

A deep learning system can segment VS and IE structures in high-resolution MRI scans with excellent accuracy. This technology offers promise to improve the clinical workflow for assessing VS radiomics and enhance the management of VS patients.

Comparison of Ophthalmologist and Large Language Model Chatbot Responses to Online Patient Eye Care Questions

Importance

Large language models (LLMs) like ChatGPT appear capable of performing a variety of tasks, including answering patient eye care questions, but have not yet been evaluated in direct comparison with ophthalmologists. It remains unclear whether LLM-generated advice is accurate, appropriate, and safe for eye patients.

Objective

To evaluate the quality of ophthalmology advice generated by an LLM chatbot in comparison with ophthalmologist-written advice.

Design, Setting, and Participants

This cross-sectional study used deidentified data from an online medical forum, in which patient questions received responses written by American Academy of Ophthalmology (AAO)-affiliated ophthalmologists. A masked panel of 8 board-certified ophthalmologists were asked to distinguish between answers generated by the ChatGPT chatbot and human answers. Posts were dated between 2007 and 2016; data were accessed January 2023 and analysis was performed between March and May 2023.

Main Outcomes and Measures

Identification of chatbot and human answers on a 4-point scale (likely or definitely artificial intelligence [AI] vs likely or definitely human) and evaluation of responses for presence of incorrect information, alignment with perceived consensus in the medical community, likelihood to cause harm, and extent of harm.

Results

A total of 200 pairs of user questions and answers by AAO-affiliated ophthalmologists were evaluated. The mean (SD) accuracy for distinguishing between AI and human responses was 61.3% (9.7%). Of 800 evaluations of chatbot-written answers, 168 answers (21.0%) were marked as human-written, while 517 of 800 human-written answers (64.6%) were marked as AI-written. Compared with human answers, chatbot answers were more frequently rated as probably or definitely written by AI (prevalence ratio [PR], 1.72; 95% CI, 1.52-1.93). The likelihood of chatbot answers containing incorrect or inappropriate material was comparable with human answers (PR, 0.92; 95% CI, 0.77-1.10), and did not differ from human answers in terms of likelihood of harm (PR, 0.84; 95% CI, 0.67-1.07) nor extent of harm (PR, 0.99; 95% CI, 0.80-1.22).

Conclusions and Relevance

In this cross-sectional study of human-written and AI-generated responses to 200 eye care questions from an online advice forum, a chatbot appeared capable of responding to long user-written eye health posts and largely generated appropriate responses that did not differ significantly from ophthalmologist-written responses in terms of incorrect information, likelihood of harm, extent of harm, or deviation from ophthalmologist community standards. Additional research is needed to assess patient attitudes toward LLM-augmented ophthalmologists vs fully autonomous AI content generation, to evaluate clarity and acceptability of LLM-generated answers from the patient perspective, to test the performance of LLMs in a greater variety of clinical contexts, and to determine an optimal manner of utilizing LLMs that is ethical and minimizes harm.

The Association of Peripheral and Central Olfaction With Frailty in Older Adults

BACKGROUND

Olfactory impairment is increasingly recognized as a biomarker of frailty, but the relationship between olfactory subdomains that describe peripheral or central dysfunction and frailty remains unexplored.

METHODS

We examined 1 160 older adults from the National Social Life, Health, and Aging Project Wave 3. Olfactory identification (OI): the ability to identify an odorant; and olfactory sensitivity (OS): the ability to detect the presence of an odorant, were assessed using 5- and 6-point measures, respectively. Frailty was operationalized as both a 37-item frailty index (FI) and the 5-item Physical Frailty Phenotype (PFP). Mixed models were fit to examine the association between OI, OS, FI, and PFP, while adjusting for demographic and clinical covariates.

RESULTS

Participants in the most-frail PFP category had lower OI and OS scores (OI: 3.88 vs 4.19, p = .016; OS: 3.15 vs 3.47, p = .031), whereas participants in the most-frail FI category exhibited lower OI scores but not OS scores when compared to nonfrail participants (OI: 3.72 vs 4.27, p = .014; OS: 3.19 vs 3.43, p = .476). Adjusted mixed models showed that a point increase in OI was associated with a lower PFP score (β = -0.107, p = .006) and FI score (β = -0.009, p = .010). A point increase in OS was associated with a lower PFP score (β = -0.058, p = .016) but not FI score (β = -0.004, p = .064).

CONCLUSION

Both OS and OI, predominantly peripheral and central measures of olfaction, respectively, are associated with frailty implicating olfaction as a potential biomarker and risk factor for frailty.

Otolaryngic sensory loss as a measure of frailty among older US adults

BACKGROUND

Frailty is a syndrome characterized by reduced physiologic reserve and increased vulnerability to poor health outcomes. Disruption of sensorineural function appears to serve as a novel biomarker of frailty. Using population-level data, we sought to characterize the association between otolaryngic sensory dysfunction and frailty.

METHODS

A cross-sectional analysis of the 2011-2012 US National Health and Nutrition Examination Survey was performed on adults ≥40 years of age (n = 2138). Participants were grouped by subjective gustatory dysfunction (sGD), olfactory dysfunction (sOD), hearing loss (sHL), and measured hearing loss (mHL) with pure tone averages (PTAs). Frailty was operationalized using a continuous 36-item frailty index (FI) scored from 0 to 1, stratified in 4 categories ("non-frail," "vulnerable," "frail," or "most frail").

RESULTS

All sensory loss groups had significantly higher FI scores than those without sensory loss (sGD = 0.15; sOD = 0.14; sHL = 0.15; low-frequency mHL = 0.16; high-frequency mHL = 0.14 vs control = 0.11; p < 0.007 for all). "Vulnerable" individuals had increased odds of sOD (adjusted odds ratio [aOR], 1.45; 95% confidence interval [CI], 1.05-2.00), whereas "frail" individuals had increased odds of sOD (aOR, 1.85; 95% CI, 1.26-2.71) and low-frequency mHL (aOR, 4.01; 95% CI, 1.27-12.63). The "most frail" individuals had increased odds of sHL (aOR, 11.72; 95% CI, 2.88-47.66) and high-frequency mHL (aOR 5.10; 95% CI, 1.72-15.12). PTAs were linearly associated with FI (low: β = 10.15; 95% CI, 1.78-18.51; high: β = 19.85; 95% CI, 5.19-34.53).

CONCLUSION

Otolaryngic sensory loss is associated with increased frailty. Independent association of frailty with measures of olfaction and hearing suggests that olfactory and hearing assessments may help identify at-risk individuals with modifiable risk factors.

Predictors of academic career placement and scholarly impact in fellowship-trained rhinologists

BACKGROUND

As rhinology fellowship positions outpace the availability of academic rhinology jobs, it is increasingly important to identify characteristics that are associated with academic placement after fellowship completion. In this study, we evaluated the association of academic characteristics during training with current job placement and posttraining scholarly impact.

METHODS

Previous rhinology fellows were identified using publicly available data. Bibliometric indices, training institutions, graduate degrees, and job placement data were used in bivariate and multivariable regression analyses to assess for association with predictors and academic trajectory.

RESULTS

Data from 265 rhinologists, all graduating between 1991 and 2020, were included. Most surgeons (n = 185, 70%) held an academic position and 80 (30%) surgeons worked in a nonacademic setting; 93.2% had a Doctor of Medicine (MD) degree and 80.3% were male. Multivariable logistic regression indicated that a designation of MD, compared with Doctor of Osteopathic Medicine (DO; odds ratio [OR], 5.93; 95% confidence interval [CI], 1.97-21.9), number of publications during fellowship (OR, 1.19; 95% CI, 1.02-1.41), and h-index during training (OR, 1.25; 95% CI, 1.07-1.49]) were independently predictive of academic job placement. Meanwhile, number of primary authorships during fellowship (β = 1.47; 95% CI, 1.07-1.88]), h-index during training (β = 0.48; 95% CI, 0.25-0.71), and PhD (β = 4.16; 95% CI, 1.57-6.76) were associated with posttraining h-index. Medical school ranking; graduate degrees, including Master of Science (MS), Master of Business Administration (MBA), and Master of Public Health (MPH); and research metrics before residency were not associated with either academic placement or posttraining h-index.

CONCLUSION

The predictors of academic job placement in rhinology are unclear, but h-index during training, and research productivity during fellowship may serve as indicators of an academic career.

Association Between Chemosensory Dysfunction and Diet Quality in United States Adults

BACKGROUND

Evidence suggests chemosensory dysfunction (CSD) patients have altered diet, but population-level evidence assessing diet quality in CSD patients is lacking.

OBJECTIVE

We examined the association between CSD and diet quality in a representative sample of United States adults.

METHODS

This cross-sectional study included 2831 adults aged greater than 40 years from the 2013-2014 National Health and Nutrition Examination Survey who completed the taste/smell questionnaire and examination. Mean nutrient intake in subjects with self-reported olfactory/gustatory dysfunction (sOD/sGD) and measured olfactory/gustatory dysfunction (mOD/mGD) were compared to those without CSD using univariate Wilcoxon rank-sum tests. The Healthy Eating Index (HEI), a validated measure of diet quality, was calculated. The proportion of subjects with CSD with bottom-quartile HEI was compared to those without CSD using multivariate logistic regression, adjusting for demographic and socioeconomic covariates.

RESULTS

The population-weighted prevalence of sOD, sGD, mOD, and mGD was 20.1%, 14.4%, 15.9% and 25.6%, respectively. Subjects with mOD had lower mean intake of total calories, total fat, protein, sodium, and potassium compared to normal subjects (1873.4 ± 49.6 vs 2010.2 ± 24.2 kcal, 72.3 ± 2.7 vs 78.6 ± 1.0 gm, 74.0 ± 2.5 vs 80.4 ± 0.6 gm, 3122 ± 97.2 vs 3353.2 ± 37.0 mg, 2509.8 ± 69.8 vs 2684.7 ± 26.1 mg, P < 0.05 respectively). When controlling for sociodemographic factors and comorbidities, subjects with sOD were more likely to have bottom-quartile HEI compared to normal subjects (OR 1.33, 95% CI 1.04-1.70).

CONCLUSIONS

This population-level study suggests an association between poor diet quality and variation in dietary intake in patients with CSD, which warrants further investigation and suggests the possible need for nutritional counseling for CSD patients.

The association of frailty with olfactory and gustatory dysfunction in older adults: a nationally representative sample

BACKGROUND

Olfaction and gustation are associated with age-related decline. Deficits in these chemosenses have been associated with significant comorbidities. Meanwhile, frailty, defined as a reduced physiological reserve, is well correlated with mortality and worse health outcomes. We sought to analyze a nationally representative patient population to determine the association between chemosensory dysfunction and frailty.

METHODS

Cross-sectional analysis of U.S. National Health and Nutrition Examination Survey (NHANES) 2013-2014 was performed, using multivariate logistic regression to examine the association between chemosensory dysfunction and frailty in adults aged ≥40 years (n = 3547). Self-reported olfactory dysfunction (sOD) and gustatory dysfunction (sGD), and measured olfactory dysfunction (mOD) and gustatory dysfunction (mGD) were assessed for all participants. Frailty was operationalized using a 39-item frailty index (FI) and stratified into 4 groups using validated cutoffs.

RESULTS

Participants with sOD and mOD had significantly higher mean FI scores (sOD: 0.18 vs 0.13, p < 0.001; mOD: 0.20 vs 0.14, p < 0.001), whereas subjects with sGD, but not mGD, had higher mean FI scores (sGD: 0.21 vs 0.13, p < 0.001; mGD: 0.14 vs 0.14, p = 0.953). Multivariate logistic regression demonstrated frail participants had significantly greater odds of sGD (odds ratio [OR] 4.11; 95% confidence interval [CI], 3.46 to 4.88), sOD (OR 2.35; 95% CI, 1.98 to 2.78), and mOD (OR 1.58; 95% CI, 1.22 to 2.05), but not mGD (OR 1.21; 95% CI, 0.91 to 1.61). This association was strongest in the frailest group.

CONCLUSION

Self-reported chemosensory dysfunction and mOD are independently associated with measures of frailty, suggesting a novel method to assess or predict frailty.

Implications of Obesity on Endoscopic Sinus Surgery Postoperative Complications: An Analysis of the NSQIP Database

Objective

To evaluate the influence of body mass index on postoperative adverse events in adult patients undergoing endoscopic sinus surgery.

Study Design

Retrospective cohort study.

Setting

Database of the American College of Surgeons NSQIP (National Surgical Quality Improvement Program) from 2006 to 2018.

Methods

The NSQIP database was queried for adult patients undergoing endoscopic sinus surgery. The total sample (N = 1546) was stratified by nonobese (18.5 kg/m2≤ body mass index <30 kg/m2) and obese (≥30 kg/m2). Demographics, comorbidities, intraoperative variables, and postoperative adverse events were compared via chi-square analysis and multivariable logistic regression.

Results

Obese patients accounted for 49.7% (n = 768) of the cohort. Obese patients had a higher American Society of Anesthesiologists classification (class III, 45.1% vs 29.5%; P < .001), rate of diabetes (18.2% vs 7.2%, P < .001), and rate of hypertension requiring medication (43.1% vs 23.0%, P < .001). Nonobese patients were more likely to be >58 years of age (23.4% vs 29.0%, P = .02) and have disseminated cancer (<1% vs 3.2%, P < .001). The obese cohort had a lower frequency of surgical complications (3.0% vs 5.4%, P = .027), driven by frequency of perioperative bleeding (1.8% vs 3.7%, P = .022). There was no statistical difference in medical complications ( P = .775), unplanned readmissions ( P = .286), unplanned reoperations ( P = .053), or 30-day mortality ( P > .999). After multivariable adjustment, obese subjects had decreased odds of any surgical complication (adjusted odds ratio [aOR], 0.567; 95% CI, 0.329-0.979), perioperative bleeding (aOR, 0.474; 95% CI, 0.239-0.942), and any adverse postoperative event (aOR, 0.740; 95% CI, 0.566-0.968).

Conclusion

Obesity does not increase the risk of 30-day adverse outcomes following endoscopic sinus surgery and may even be protective against perioperative bleeding.

Multiple aspects of male germ cell development and interactions with Sertoli cells require inositol hexakisphosphate kinase-1

Inositol hexakisphosphate kinase-1 (IP6K1) is required for male fertility, but the underlying mechanisms have been elusive. Here, we report that IP6K1 is required for multiple aspects of male germ cell development. This development requires selective interactions between germ cells and Sertoli cells, namely apical ectoplasmic specialization. Spermiation (sperm release) requires tubulobulbar complexes. We found that the apical ectoplasmic specialization and tubulobulbar complexes were poorly formed or disrupted in IP6K1 KOs. Deletion of IP6K1 elicited several aberrations, including: 1, sloughing off of round germ cells; 2, disorientation and malformation of elongating/elongated spermatids; 3, degeneration of acrosomes; 4, defects in germ-Sertoli cell interactions and 5, failure of spermiation. Eventually the sperm cells were not released but phagocytosed by Sertoli cells leading to an absence of sperm in the epididymis.

Inositol Polyphosphate Multikinase Inhibits Angiogenesis via Inositol Pentakisphosphate-Induced HIF-1α Degradation

RATIONALE

Inositol polyphosphate multikinase (IPMK) and its major product inositol pentakisphosphate (IP5) regulate a variety of cellular functions, but their role in vascular biology remains unexplored.

OBJECTIVE

We have investigated the role of IPMK in regulating angiogenesis.

METHODS AND RESULTS

Deletion of IPMK in fibroblasts induces angiogenesis in both in vitro and in vivo models. IPMK deletion elicits a substantial increase of VEGF (vascular endothelial growth factor), which mediates the regulation of angiogenesis by IPMK. The regulation of VEGF by IPMK requires its catalytic activity. IPMK is predominantly nuclear and regulates gene transcription. However, IPMK does not apparently serve as a transcription factor for VEGF. HIF (hypoxia-inducible factor)-1α is a major determinant of angiogenesis and induces VEGF transcription. IPMK deletion elicits a major enrichment of HIF-1α protein and thus VEGF. HIF-1α is constitutively ubiquitinated by pVHL (von Hippel-Lindau protein) followed by proteasomal degradation under normal conditions. However, HIF-1α is not recognized and ubiquitinated by pVHL in IPMK KO (knockout) cells. IP5 reinstates the interaction of HIF-1α and pVHL. HIF-1α prolyl hydroxylation, which is prerequisite for pVHL recognition, is interrupted in IPMK-deleted cells. IP5 promotes HIF-1α prolyl hydroxylation and thus pVHL-dependent degradation of HIF-1α. Deletion of IPMK in mouse brain increases HIF-1α/VEGF levels and vascularization. The increased VEGF in IPMK KO disrupts blood-brain barrier and enhances brain blood vessel permeability.

CONCLUSIONS

IPMK, via its product IP5, negatively regulates angiogenesis by inhibiting VEGF expression. IP5 acts by enhancing HIF-1α hydroxylation and thus pVHL-dependent degradation of HIF-1α.

Molecular changes in the cell surface of differentiating epidermal keratinocytes

The specific binding of lectins to the cell surfaces in particular epidermal strata indicates that oligosaccharide moieties of the glycoconjugates on the cell membrane are altered as the keratinocyte differentiates. The disappearance of binding by the Bandeiraea simplicifolia isolectin I-B4 (BS I-B4) and the appearance of binding by the Ulex europeus agglutinin I (UEA), which occur as the basal cell moves up into the spinous layer of the cutaneous epidermis of the newborn rat, could result from (a) redistribution of existing glycoconjugates in the cell membrane, (b) hydrolysis of galactosyl residues exposing fucosyl binding sites, or (c) addition of fucosyl residues to pre-existing oligosaccharides with specificity for the galactoside. Isolation of glycoproteins from the cell membrane using lectin-affinity column chromatography on Sepharose-4B showed a decrease in the amount of protein which bound to the BS I-B4 and an increase in the protein with affinity for the UEA as the ratio of spinous to basal cells increased in the population of cells from which the glycoproteins were obtained. These data indicate the existence of two different classes of glycoproteins on the surfaces of cells in the lower epidermis and argue against a redistribution of glycoconjugates as the explanation for the selective binding of specific lectins observed in tissue sections. Exposure of sections of skin to alpha-galactosidase completely eliminated the binding of fluorescein isothiocyanate-labeled (FITC) BS I-B4 in the lower epidermis but did not result in additional binding of UEA. Exposure to fucosidase eliminated binding by UEA and increased the binding of BS I-B4 in the spinous layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular markers of differentiation in the epidermis of the newborn rat

Regulation in epidermal differentiation can best be studied if molecular mechanism can be associated with structural and functional changes. Such recognized associations include the cessation of mitosis through inhibition of DNA replication by a G1-inhibitor present in the suprabasal cells, the biosynthesis of a tonofilament-protein as an early event in keratinization, the biosynthesis of HRP0 (histidine-rich protein) and its polymerization to HRPI during the formation of keratohyalin, the conversion of HRPI to HRPII coincident with the loss of the nucleus from the granular cell, and the aggregation of the stratum corneum basic protein and keratin filaments to form fibers in the cornified cell. To this list can now be added changes in specificity for lectin-binding to the cell surface as the keratinocyte progresses toward the cutaneous surface. This report presents data on a) the conversion of HRPI to HRPII and b) the differential lectin-binding in the epidermis of the newborn rat. HRPI (Mol. Wgt. greater than or equal to 10(6)) and HRPII (Mol. Wgt. 6 X 10(4)) have similar unique amino acid compositions and exhibit extensive-but not complete-homology in primary structures as determined by peptide mapping after exposure to trypsin. When labeled by exposure in vivo to radioactivity histidine, about 75 of the labeled histidine from both HRPI and HRPII appeared in one peptide fraction in the map, HRPI appears to have on histidine-containing fragment which is not present in HRPII. This peptide appears to contain phosphate and to account for the organically-bound phosphate which was found in HRPI but not defected in HRPII. Changes which occur in the lectin-binding specificity of the cell during differentiation may result from either movement or chemical change in carbohydrates at the cell surface. Immunofluorescent studies have shown that an isolectin from Bandieraea simplicifolia with specificity for alpha-D-galactose binds to the surface of basal and lower spinous cells, a lectin from Ulex europaeus with specificity for alpha-L-focus labels spinous cells, and a second lectin from B. simplicifolia with specificity for N-acetyl-D-glucosamine labels cornified cells. The relationship fo these alterations in the carbohydrates of the cell surface in intracellular structural and/or functional changes in unknown.

An ergonomic comparison of rowing machine designs: possible implications for safety

OBJECTIVES

Ergometer training is a common cause of injuries in rowers. A randomised crossover study comparing two power head designs was carried out to examine ergonomic risk factors.

METHODS

Six elite male rowers undertook 20 minute fatiguing rowing pieces with both fixed and floating power heads. A CODA MPX infrared telemetric motion analysis detector and the ergometer's interface were used to measure displacement, force, work performed, and power output.

RESULTS

There was no significant difference in the total work performed, power per stroke, or metabolic load between the two ergometer designs. Fatigue was shown by a mean (SEM) fall of 9.7 (0.79) W/stroke (95% confidence interval (CI) 8.0 to 11.5) between minutes 8-10 and minutes 16-18 (p<0.001). The stroke length was 53 (13) mm (95% CI 18 to 89) longer with the fixed power head (p<0.02). With fatigue, the stroke with the fixed power head lengthened at the "catch" (beginning of the stroke) by 19.5 mm (p<0.01) and shortened at the finish of the stroke by 7.2 mm (p<0.05). No significant changes in stroke length were seen with the floating power head. The mean force per stroke was 12.1% (95% CI 3.0 to 21.2) (27.3 (8.0) N) higher with the power head fixed versus floating (p<0.02).

CONCLUSIONS

It is postulated that longer stroke lengths and greater forces are risk factors for soft tissue injuries. Further research into whether floating power head rowing ergometers are associated with lower injury rates than fixed power head designs is now needed.

DNA repair in primary human keratinocyte cultures after low level exposure to bis(2-chloroethyl)sulfide

The literature has reported the appearance and disappearance of single-strand breaks (SSBs) in the DNA of rat keratinocytes after exposure to low levels of bis(2-chloroethyl) sulfide (BCES). Since SSBs are a consequence of depurination or depyrimidination followed by excision of the apurinic or apyrimidinic site and deoxyguanosine (GdR) is the major alkylation site in DNA exposed to BCES, it was hypothesized that repair occurred by a GdR-specific base replacement and not by large section repair. To test this hypothesis, cultures of human keratinocytes (HK) were preincubated with 5-bromo-2'-deoxyuridine (BUdR), a heavy analog of thymidine (TdR) incorporated into replicating DNA, immediately before exposure to BCES. Cultures were incubated postexposure with BUdR, radiolabeled GdR, and/or deoxyadenosine (AdR), to measure base-specific repair, and/or radiolabeled TdR, to measure DNA replication and large section repair. A CsCl density gradient was used to remove any BUdR-containing postexposure DNA replication. Each gradient was assayed for radioactivity (cpm) and DNA content (absorbance at 260 nm). The peak A260 fractions were pooled and rebanded in another CsCl gradient. If DNA repair had occurred, the specific activity (cpm/A260) of the peak A260 fraction in the gradient would be greater than control. After exposure of the cultures to BCES, there was a concentration-dependent increase in the specific activity for [3H]GdR but not [4C]TdR over the concentration range used (20-50 microM BCES). A concentration-dependent increase in specific activity was also detected after [14C]AdR exposure. The literature has also reported that the removal of damaged DNA bases after alkylation is via glycosylases. In this series of experiments, we have demonstrated that cultures of HK exposed to the alkylating agent BCES repair their damaged DNA by the replacement of the damaged base only. In the case of BCES exposure, it is the GdR base and to a lesser extent the AdR base.

Cultured keratinocytes in in vitro dermatotoxicological investigation: a review

The keratinocyte is responsible for the architecture of the epidermis, that portion of the skin that forms the environmental barrier necessary for survival. It also interacts with other cell types in the epidermis in response to various environmental influences. This cell type is used frequently for in vitro cutaneous toxicological investigations as an alternative to whole-animal studies. Several areas of cutaneous research using cultured keratinocytes are germane as regards the scope of this journal. The following areas of biomedical research were reviewed: (1) dermatotoxicology, including environmental chemicals, antiseptics, drugs, metals, and pesticides; (2) immunotoxicology, including inflammation and allergic dermatitis; (3) radiation, including ultraviolet and x-irradiation; and (4) the development of assays as alternatives to whole-animal testing. Due to the abundance of such investigations reported in the last 30 years, this review is limited mainly to reviewing reports published in this decade.

Formation of interstrand DNA cross-links by bis-(2-chloroethyl)sulfide (BCES): a possible cytotoxic mechanism in rat keratinocytes

Interstrand cross-links in the DNA of epidermal basal keratinocytes may be responsible for cell death and consequent vesication in skin exposed to BCES. The formation of cross-links and cytotoxicity were compared when cells in primary monolayer cultures of rat epidermal keratinocytes, synchronized at the G1/S boundary or in the G1 phase of the cell cycle, were exposed to BCES. The dose-responsive formation of cross-links, measured with an ethidium bromide-fluorescence assay, was determined immediately after exposure of cells at either position of the cycle. At 24 hr post-exposure, the level of cross-links in cells exposed at the G1 phase showed had not decreased significantly and was still dose-dependent. However, cells exposed in the G1 phase showed a major decrease in cross-links. Formation of interstrand DNA cross-links appears to be related to the mustard's cytotoxicity.

Bis(2-chloroethyl)sulfide (BCES) disturbs the progression of rat keratinocytes through the cell cycle

Epidermal basal keratinocytes are the primary target in BCES-induced cutaneous injury. DNA synthesis is inhibited by exposure to BCES which could relate to the mustard's cytotoxic effect. The effects of BCES on the cell cycle in keratinocytes synchronized by aphidicolin were investigated. Primary keratinocytes synchronized at the G1/S boundary entered the S, G2, M, and G1 phases at successive times after release from the block. When cells were exposed to 1, 10, or 50 microM BCES in different phases of the cell cycle, cells in the S phase were more sensitive to BCES than cells in the other phases. Keratinocytes exposed to 1 microM BCES at the G1/S boundary exhibited a prolongation of the S phase and a block in the G2 phase. When these cells were exposed to 10 or 50 microM BCES, they did not enter the S phase for up to 12h and the incorporation of thymidine into DNA was inhibited. These results suggest that the blocks in the G2 and G1 phases relate to the cytotoxic effect of BCES on the germinative population of epidermal keratinocytes.

Appearance of interleukin 1 alpha relates DNA interstrand cross-links and cytotoxicity in cultured human keratinocytes exposed to bis-(2-chloroethyl) sulfide

The utility of an increase in the level of interleukin 1 alpha (IL-1 alpha) as an indicator of cytotoxicity from exposure to bis-(2-chloroethyl) sulfide (BCES) was evaluated in submerged monolayer cultures of human cutaneous keratinocytes. Four-day-old cultures were exposed to 1-100 microM BCES at 37 degrees for 30 min. The amounts of IL-1 alpha in the medium at and in cells 72 h after exposure were measured immunologically with an enzyme-linked immunosorbent assay using monoclonal antibody to human IL-1 alpha. The antibody was conjugated with peroxidase for visualization. Cell viability was measured concomitantly using the trypan blue exclusion technique. The degree of interstrand cross-linking as a measure of damage in the cellular DNA was determined by measuring the fluorescence resulting from the intercalation of ethidium bromide into double-stranded molecules that remained in heat-denatured DNA isolated from cells that had been exposed to BCES. A high correlation was observed between the dose-responsive increase in the level of IL-1 alpha in the medium and in the cells, and the dose-responsive decrease that took place in the fraction of viable cells in exposed cultures. The dose-responsive increase in the interstrand cross-linking found in the DNA of cells immediately after exposure to BCES also correlated with the increase in IL-1 alpha 72 h after exposure. These data suggest that the appearance of IL-1 alpha can be used to quantify the cytotoxicity resulting from BCES-medicated damage to cellular DNA and that degree of cross-linking in the DNA immediately after exposure to BCES is predictive of the level of cytotoxicity in an exposed culture 3 days later.

Growing a stratified, cornified primary culture of rat keratinocytes with epidermis-like water permeation barrier function

The culture of cutaneous keratinocytes grown on a Puropore nylon microporous membrane at the air-liquid interface has been shown to be similar to the epidermis in a number of molecular and morphologic characteristics but to exhibit a significantly greater degree of tritiated water permeation. Various culture conditions have been altered in an effort to improve the water barrier properties. A Kp value in the range of 5.5 +/- 1.6 x 10(3) has been obtained for 79% of the cultures a) by plating 0.9 x 10(6) viable basal cells on a piece (13-mm diameter) of membrane for 7 days of submerged growth, b) by placing two membranes on two stacked glass fiber filters (47-mm extra-thick) in a culture dish (60 mm) for 14 days of growth at the air-liquid interface, c) by replacing the growth medium, i.e., 1 ml of complete minimum essential medium (CMEM) every 24 h after lifting, d) by using 10% fetal bovine serum (FBS) in the CMEM during the submerged culture period and 15% FBS in the CMEM during the lifted culture period, and e) by adding a dialysis membrane on top and a Puropore nylon membrane below the culture when the cultures were inserted in the permeation cell for testing. The percentage of cultures with this value for Kp can be increased to 90% if only cultures with yellow, smooth, and shiny surfaces are tested. This system should be useful as a replacement for skin in testing the cutaneous permeation of some chemicals.

Use of human pseudo-epidermis to evaluate the toxicity of bis-(2-chloroethyl)sulfide (BCES) on water permeation barrier formation and function

Human pseudo-epidermis was used to investigate the effects of bis-(2-chloroethyl)sulfide (BCES) on the formation and function of the water permeation barrier. To generate the culture, 2 million viable basal cells derived from human skin were placed on a Puropore nylon microporous membrane pre-coated with calf skin collagen. Addition of bovine pituitary extract and epidermal growth factor to the medium favored the formation of homogeneous cultures and better barrier function. The water permeation constant (Kp) was shown to decrease significantly and reached 25 +/- 6 x 10(-3) when it was calculated from 71% of the cultures prepared. The effects of topically applied BCES on the incorporation of [14C]linoleic acid, as a marker for lipid synthesis, and Kp, as a measure of water permeation, were studied. Compared with untreated cultures, there was no difference in the Kp immediately after exposure to 1-10 nmol BCES/cm2 for 30 min. On the other hand, [14C]linoleic acid incorporation was dose-dependently decreased immediately after exposure and then returned to normal by 48 h later. These data suggest that BCES produces no direct damage to the water permeation barrier but may affect barrier formation by inhibiting lipid synthesis.

Failure to observe a relationship between bis-(beta-chloroethyl)sulfide-induced NAD depletion and cytotoxicity in the rat keratinocyte culture

It has been proposed that the activation of poly(ADP-ribose) polymerase (Papirmeister et al., 1985), which results from the presence of strand breaks in bis-(beta-chloroethyl)sulfide (BCES) damaged DNA, causes depletion in the level of nicotinamide adenine dinucleotide (NAD) leading to cell death. This hypothesis has now been evaluated in the primary submerged culture of rat keratinocytes. The DNA content, the viable cell number, and the proliferative capability (measured by thymidine incorporation) of the culture were all reduced 48 h after exposure to 10 microM BCES. However, the total NAD level, that is, NAD+ plus NADH, was not changed at a dose of BCES lower than 50 microM. This observation was the same in both proliferating and early differentiating cultures. To further test this hypothesis, the modifying effect of inhibiting poly(ADP-ribose) polymerase on cytotoxicity in BCES-exposed cells was investigated. After exposure to 250 microM BCES, the NAD level was reduced to approximately 26 pmol/micrograms DNA. This value was increased to 34-49 pmol/micrograms DNA at both 24 and 48 h postexposure when the cultures were incubated in medium supplemented with 1-10 mM nicotinamide. Nevertheless, the decrease in the DNA content of the culture was not reversed. These results suggest that in the rat keratinocyte culture exposed to BCES, depletion of NAD is not a prerequisite for cell death.

Differentiative changes in fucosyltransferase activity in newborn rat epidermal cells

An enzymatic activity catalyzing the transfer of L-fucose from GDP-L-fucose to a glycoprotein that is associated with the surfaces of the basal cells has been found in the membranous fraction of the cutaneous epidermis from the newborn rat. This fucosyltransferase which is located in the differentiated cells alters the acceptor glycoprotein's lectin-binding specificity from the Isolectin I-B4 of Griffonia simplicifolia (GS I-B4) to the Agglutinin I of Ulex europeus (UEA) and could be responsible for the same change in lectin-binding specificity that occurs as the epidermal basal cell differentiates. Another membraneous fucosyltransferase that can use asialofetuin--but not the GS I-B4-binding glycoprotein--as an acceptor, is also present in the membraneous fraction.

The effect of 2,2'-dichlorodiethyl sulfide on DNA synthesis of a murine stratified keratinocyte culture system

A primary stratified keratinocyte culture resembling the epidermis in situ was used as a model for studying the effects of exposure to 2,2'-dichlorodiethyl sulfide, or sulfur mustard (SM), on DNA synthesis. A method that distinguishes between semi-conservative (s.c.) DNA synthesis and repair synthesis was used to determine if the former was inhibited following treatment with SM. In this method the density of the newly synthesized DNA was increased by incorporation of 5-bromo-2-deoxyuridine. Density gradient centrifugation was then used to isolate the heavy DNA for quantification. It was demonstrated that topically applied SM in the dose range of 1-10 nmole/cm2 inhibited s.c. DNA synthesis (replication) in a dose and time related manner. Inhibition of DNA replication by SM would result in inhibition of cell division which must be preceded by s.c. DNA synthesis. This failure to replace damaged germinative cells may lead to the destruction of the basal layer which is observed in vivo and in our epidermal culture following exposure to SM. This may also be related to development of vesication observed in exposed intact human skin.

Assessment of the role of DNA damage and repair in the survival of primary cultures of rat cutaneous keratinocytes exposed to bis(2-chloroethyl)sulfide

Toxicity manifests itself as vesication in human skin exposed topically to bis(2-chloroethyl)sulfide (BCES). The destruction of the proliferating population of epidermal cells is a major component of the pathogenic process. Available data strongly suggest that damage to cellular DNA is a critical factor in the loss of these cells. However, the influence of DNA repair on this toxic response has not been adequately studied. Therefore, a study was undertaken to ascertain the influence of DNA repair on the survival of primary monolayer cultures of rat cutaneous keratinocytes exposed to BCES. The sensitive nucleoid sedimentation assay was employed for the determination of DNA damage in cultures exposed to very low levels of BCES. Initial experiments demonstrated that within 1 hr of exposure to as little as 0.1 microM BCES the structural integrity of cellular DNA was compromised, presumably resulting from the appearance of single-strand breaks in the nucleic acid. This same effect was demonstrated in basal cells derived from a stratified, cornified culture grown at the air-liquid interface and exposed topically to the vesicant. Further studies with the monolayer culture demonstrated that the gross structural integrity of the DNA in cells exposed to as much as 5 microM BCES was completely restored within the first 22 hr following the exposure. However, this repair process appeared to be inefficient since a depression of thymidine incorporation into DNA and a significant loss of DNA were exhibited in exposed cultures as long as 72 hr after the initial exposure.

Effect of bis(beta-chloroethyl)sulfide (BCES) on base mismatch repair of DNA in monkey kidney cells

Sulfur mustard, bis(beta-chloroethyl)sulfide (BCES), a bifunctional alkylating agent, is a vesicant whose mode of action involves interference with the integrity of cellular DNA. Alkylation of DNA is responsible for some of the biological effects of BCES in tissue. Another possible mechanism by which BCES could exert its toxic effect is interference with high fidelity repair of damaged DNA. This study evaluated the possible effects of BCES on the repair of specific errors, i.e., mismatched bases, in the DNA. Heteroduplex (ht) DNA, formed between two temperature-sensitive mutants of SV40 virus, tsA239 and tsA255, each having a different point mutation in the gene for large T antigen, was used to study the effect of BCES on mismatched base repair in African green monkey kidney (AGMK) cells. AGMK cells were exposed to dilute solutions of BCES in methylene chloride (MC) prior to cationic lipofection with ht DNA. In order for the cells to produce wild type (wt) SV40 DNA at a nonpermissive temperature (41 degrees C), repair of at least one of the two mismatches in the DNA had to occur. It was observed that (a) as the concentration of BCES was increased, a proportionally longer delay in the appearance of wt DNA at 41 degrees C was observed in treated cells transfected with ht DNA as compared with cultures exposed to MC alone and then transfected with ht DNA, (b) there was no such effect in exposed AGMK cells transfected with wt DNA, (c) wt and ht DNA were transfected at similar rates in unexposed cells, and (d) BCES did not affect the rate of transfection of wt cells. These observations are consistent with the hypothesis that BCES affects mismatched base repair.

Stratified cornified primary cultures of human keratinocytes grown on microporous membranes at the air-liquid interface

It was previously reported that rat keratinocytes grown at the air-liquid interface on collagen gels or on nylon membranes produce multilayered cultures of uniformly stratified cells, comparable to the epidermis in situ by morphological and biochemical criteria. A protocol has now been developed by which primary human keratinocytes grown for two weeks submerged on microporous nylon membranes and raised to the air-liquid interface for an additional three weeks, exhibit most of the comparable characteristics of the epidermal cells in vivo. Staining with fluorescein isothiocyanate-conjugated monoclonal antibodies indicated the presence of 56,5 and 65-67 kDa keratins as well as filaggrin-type proteins in the upper cellular layers. Desmosomes, lamellar granules and keratohyalin-like granules were observed. Cultures were covered with layers of cornified cells. This study differs from the majority of other investigations on human keratinocytes in that no feeder layers or other biological substrata were used. This system should be useful in toxicological studies of chemicals which are to be applied topically to the skin.

Levels of cytochrome P-450-mediated aryl hydrocarbon hydroxylase (AHH) are higher in differentiated than in germinative cutaneous keratinocytes

Induction of microsomal aryl hydrocarbon hydroxylase and cytochrome P-450 was observed in epidermal cells obtained from the skin of newborn rats exposed to benz(a)anthracene by topical exposure and in submerged cultures exposed to the procarcinogen in vitro. The level of aryl hydrocarbon hydroxylase activity was increased 2.5-fold in vivo and six- to sevenfold in vitro when the measurements were made on the entire epidermis or the entire culture, respectively. However, separate measurement on germinative (basal) and on differentiated cells revealed that AHH was sevenfold higher in differentiated cells as compared with basal cells in the skin of both unexposed animals and animals exposed in vivo. Similar results were obtained in cultured cells exposed in vitro. Immunocytochemical staining of sections of skin from animals exposed to benz(a)anthracene in vivo with a monoclonal antibody generated against cytochrome P-450c showed a higher binding of the antibody in lower spinous cells than in basal cells in the epidermis. Although more stained cells were observed in exposed cultures than in untreated cultures, the antibody, which inhibits at least 85% of the hydroxylase activity in the skin, inhibited only 6%-16% of the activity in culture. These observations support the interpretations that a) differentiated keratinocytes have a higher capacity in the metabolic activation of PAH than do germinative cells, although both types of cell are susceptible to induction of cytochrome P-450 by exposure to BA, and b) the cytochrome P-450 induced by exposure of epidermis to benz(a)anthracene in vivo exhibits some differences from the one induced upon exposure of keratinocytes to this procarcinogen in vitro.

Pseudoepidermis, constructed in vitro, for use in toxicological and pharmacological studies

The purpose of this study was to establish the validity of the stratified, cornified keratinocyte culture as a model for investigating cutaneous toxicities. This pseudoepidermis, grown on a nylon membrane at the air-liquid interface, responded to topical application of a known vesicant similarly to the response of the tissue in vivo. Alterations in the morphology of the in vitro model also resembled pathological changes seen in in vivo models after exposure to this agent. The effects of the skin irritants benzoate and salicylate on protein and DNA synthesis in the culture were also similar to those observed in vivo.

Characterization of a cDNA clone encoding human filaggrin and localization of the gene to chromosome region 1q21

Filaggrins are an important class of intermediate filament-associated proteins that interact with keratin intermediate filaments of terminally differentiating mammalian epidermis. They show wide species variations and their aberrant expression has been implicated in a number of keratinizing disorders. We have isolated a cDNA clone encoding human filaggrin and used this to demonstrate that the human gene encodes a polyprotein precursor containing numerous tandem filaggrin repeats. This structure is similar to that of mouse; however, the human filaggrin repeat is much longer (972 base pairs; 324 amino acids) and shows little sequence homology to the mouse protein. Also, data presented here reveal that the human filaggrin repeats show considerable sequence variations; such polymorphism is not found in the mouse. Furthermore, chromosomal mapping data revealed that the human gene is located at 1q21, indicating that the polymorphism is confined to a single locus. By peptide mapping, we define a short linker sequence within the human filaggrin repeat that is excised by proteolysis to yield functional molecules. Finally, we show by in situ hybridization that human filaggrin precursor gene expression is tightly regulated at the transcriptional level in terminally differentiating epidermis and that this represents a useful system in which to study intermediate filament-intermediate filament-associated protein interactions as well as disorders of keratinization.

Human lipoprotein influence on the partition of 2,2',4,4',5,5'-hexabromobiphenyl between 3T3L1 adipocytes and culture medium

A previous study established that 2,2',4,4',5,5'-hexabromobiphenyl (HBB) entered 3T3L1 adipocytes in culture by passive diffusion from the surrounding medium. The extent to which HBB accumulated within the cell was mediated by the level of triglyceride in the cell. The present study was concerned with the conditions that would facilitate HBB removal from adipocytes as part of a continuing effort to establish an effective and safe technology for reducing body burdens of lipophilic xenobiotics. Addition of human lipoprotein to the culture medium increased HBB removal from preloaded adipocytes 18 to 80 times more than did the addition of other blood proteins. Lipoproteins also decreased equilibrium deposition of HBB in the cells. The order of effect was low-density lipoprotein (LDL) much greater than high-density lipoproteins (HLD) greater than very-low-density lipoproteins (VLDL). These results are consistent with the hypothesis that lipoproteins act as a depot by binding HBB to immobilize the xenobiotic in the medium. The rate of removal of HBB was correlated with concentrations of lipoprotein cholesterol, cholesterol ester, and phospholipid in the culture medium (r greater than .95). Total lipoprotein fractions from individuals with high levels of serum cholesterol significantly increased HBB removal from preloaded adipocytes when compared with lipoproteins from normal human serum. Decreased removal was observed with lipoproteins from individuals with low serum cholesterol or triglyceride. These results suggest that cholesterol and/or cholesterol esters in the blood play an important role in both delivery and removal of HBB from the adipose tissue. Evidence has been presented that supports the hypothesis that HBB moves freely across the adipocyte membrane and is sequestered in either the cell or pseudoblood according to its relative solubility in these compartments.

bis-(beta-chloroethyl)sulfide (BCES)-induced changes in epidermal cell homeostasis in vitro

A rat cutaneous keratinocyte culture system was developed to study the effects of the vesicant bis-(beta-chloroethyl)sulfide (BCES) on the homeostasis of cell proliferation and differentiation. Lectins were used to reveal cell surface carbohydrate changes as the keratinocytes differentiate. In the newborn rat epidermis, the isolectin, Griffonia simplicifolia I-B4 (GS I-B4), binds to basal cell surfaces. Ulex europeus agglutinin I (UEA) binds to the surfaces of spinous and lower granular cells and is therefore considered an indicator of keratinocyte differentiation. A fluorometric assay was developed which determines the ratio of bound UEA to bound GS I-B4 (the UEA/B4 ratio) in primary monolayer cultures of rat cutaneous keratinocytes maintained in low Ca2+ medium. The UEA/B4 ratio was found to be a representation of the relative sizes of the differentiating and proliferating cell compartments in the monolayer cultures, respectively (W.W. Ku and I.A. Bernstein, 1988, Exp. Cell Res., 175, 298-316). Monolayer cultures exposed for 1 hr to BCES at Day 1 exhibited a dose-related increase in the UEA/B4 ratio at Day 7 when compared to solvent controls. The results from the analysis of lectin binding sites showed a decrease in GS I-B4 binding with little or no change in UEA binding as a result of BCES exposure, contributing to the increase in the UEA/B4 ratio. BCES-exposed monolayers also showed early perturbations in replicative DNA synthesis as revealed by autoradiography. Subsequent to the perturbations in replicative DNA synthesis was an inability of BCES-exposed cultures to produce cells into the monolayer through mitosis. In addition to an increase in the UEA/B4 ratio, BCES-exposed monolayers also showed a dose-related loss of DNA, with the appearance of enlarged cells at Day 7. These enlarged cells failed to show evidence of DNA synthesis, with groups of these cells showing intense UEA staining with only faint GS I-B4 staining. Overall, exposure to low concentrations of BCES appeared to disrupt the normal homeostasis of cell proliferation and differentiation in this monolayer culture system. This disruption was primarily through a reduction in the fraction of germinative (basal) cells with concomitant retention of some early differentiated cells, presumably early spinous or spinous cells.

Macromolecular metabolism of a differentiated rat keratinocyte culture system following exposure to sulfur mustard

A method for producing a stratified, squamous epithelium in vitro by cultivating rat keratinocytes on nylon membranes has been developed in this laboratory. This epidermal-like culture is being used to obtain a better understanding of the mechanism of skin vesication after topical exposure to the sulfur mustard bis(beta-chloroethyl) sulfide (BCES) dissolved in a selected solvent. Radiolabeled macromolecular precursors (thymidine, uridine, and leucine) have been used to study the effect of BCES on the synthesis of DNA, RNA, and protein, respectively, after topical exposure to the mustard at concentrations of 0.01-500 nmol/cm2 dissolved in 70% dimethyl sulfoxide (DMSO). From these and other studies it has been determined that exposure to even the low concentration of 0.01 nmol BCES/cm2 for 30 min results in significant inhibition of [3H]thymidine incorporation, although complete recovery occurs by 24 h. Significant inhibition of [3H]uridine and [14C]leucine incorporation is observed only after exposure to much higher concentrations of BCES (10-500 nmol/cm2). This suggests a very early lesion in macromolecular metabolism with DNA being the primary target.

Lectin binding as a probe of proliferative and differentiative phases in primary monolayer cultures of cutaneous keratinocytes

The surface of cells in the cutaneous epidermis of the newborn rat exhibits a discrete change in lectin-binding specificity from Griffonia simplicifolia I-B4 (GS I-B4), specific for alpha-D-galactosyl residues, to Ulex europeus agglutinin I (UEA), specific for alpha-L-fucose, as the cell leaves the basal layer and differentiates. Primary monolayer cultures of rat keratinocytes maintained in low Ca2+ medium (0.08 mM) exhibited a characteristic unimodal pattern in the ratio of bound UEA to bound GS I-B4 (UEA/B4 ratio) over a 7-day culture period as determined by a quantitative fluorometric assay. The UEA/B4 ratio was initially low between Days 1 and 2 (0.56 +/- 0.05), steadily increased to a maximum of 0.84 +/- 0.09 between Days 2 and 4, and then gradually decreased to 0.41 +/- 0.07 between Days 6 and 7. Estimation of DNA synthesis showed (a) a higher [3H]thymidine incorporation when the UEA/B4 ratio was low and (b) a steady but lower incorporation between Days 3 and 4, coincident with the higher UEA/B4 ratio. Autoradiographic results further showed that cells stained intensely with UEA failed to incorporate [3H]thymidine into their nuclei. Electrophoresis of [3H]fucose-labeled material isolated on UEA-Sepharose 4B revealed that the changes in labeling by [3H]fucose, bound UEA, and the UEA/B4 ratio in the monolayer were related in part to variable expression of "96K-associated UEA-bound" radioactivity corresponding to a major class of lectin-specific cell-surface glycoproteins (GP96 fraction) identified in situ. Overall, the results suggest that (a) the increase in the UEA/B4 ratio between Days 2 and 4 reflects the progression of a proportion of the cells in the monolayer to an early spinous cell stage, the ultimate fate of which is desquamation into the medium and (b) the decrease in the UEA/B4 ratio between Days 5 and 7 reflects a consequent proliferative response to this loss of cells. This system should be useful for studying environmental influences on the homeostasis of cell proliferation and differentiation in the cutaneous epidermis.

12-O-tetradecanoylphorbol-13-acetate induces an immediate, but transient increase in mitotic activity uncoupled from DNA synthesis in the monolayer cultures of rat keratinocyte

A single wave of mitotic activity was observed in a monolayer culture of rat keratinocytes immediately after exposure to 12-O-tetradecanoylphorbol-13-acetate. A peak for cells in prophase, observed at 10 min after the exposure, was followed by a peak for metaphase at 20 min, for anaphase at 25 min and telophase at 30 min after the exposure. Thereafter, the mitotic activity began to subside. This transient stimulation of mitotic activity resulted in an increase of population density in the monolayer culture. There was neither a stimulation of DNA synthesis during this period nor a change of the DNA content after the mitotic activity was completed. This single burst of synchronous mitotic activity which did not require a substantial stimulation of DNA synthesis suggests that the effect was on the initiation process of mitosis among a subpopulation of cells, presumably cells delayed in the G2 phase of the cell cycle.

Relationship between cell differentiation and binding of fluorescein isothiocyanate (FITC)-conjugated insulin of keratinocytes in culture

Basal-type keratinocytes, isolated from newborn rat skin and separated on Percoll density gradients, proliferate in low (0.1 mM) calcium medium and, after raising the calcium level to normal (1.96 mM), stratify. Cells in the low calcium culture do not have extensive cell-cell connections, as seen with fluorescein isothiocyanate (FITC)-conjugated insulin. Fluorescein isothiocyanate-conjugated concanavalin A and Griffonia simplicifolia isolectin B4, but not peanut agglutinin (PNA), fluorescently label these cells. In 3-day-old low calcium cultures, within 2 h after raising the calcium of the medium to the normal level, intense binding of PNA to cells appears and neighboring cells are connected through bundles of filaments that are fluorescently labeled by FITC-insulin. After 2 days in normal calcium medium, the cultures exhibit relatively smooth, straightlined, cell boundaries that are labeled by FITC-insulin and cell boundaries and intracellular granules that are stained by hematoxylin. One day later, similar cell boundaries are present, but they are not significantly decorated by FITC-insulin and, under phase contrast microscopy, are dark. Free FITC gives labeling patterns similar to those given by FITC-insulin, but the FITC labeling is blocked by mercaptoethanol and dithiothreitol in contrast to FITC-insulin binding. The present results suggest the insulin moiety is involved in the labeling by FITC-insulin and the labeling is chronologically related to the stage of cell differentiation.

Changes in lectin binding by differentiating cutaneous keratinocytes from the newborn rat

Surface glycoconjugates of cells from the basal layer of the skin of the newborn rat bind the isolectin I-B4 from Griffonia simplicifolia (GS I-B4) (alpha-D-galactosyl specificity). Surface glycoconjugates of the differentiated cells from the spinous and lower granular layers bind Ulex europeus agglutinin I (UEA) (alpha-L-fucosyl specificity). The change from GS I-B4 binding to UEA binding was studied in rat keratinocytes that were cultured as a monolayer in low-calcium medium until confluence, and then induced to stratify and terminally differentiate by raising the calcium concentration of the medium. The cells in the monolayer had basal cell morphology and exhibited surface binding of GS I-B4. However, at confluence, 30-40% of these cells also showed surface binding of UEA. There was an increase with time in the number of cells which bound both GS I-B4 and UEA. Raising the calcium concentration of the medium resulted in an increase in UEA binding. Cells of the upper layers of the stratifying cultures showed intense UEA binding but did not show any GS I-B4 binding. Double staining of frozen sections of newborn rat skin with fluorescein-conjugated GS I-B4 and rhodamine-conjugated UEA revealed that the surfaces of cells from the lower spinous layer bound both lectins. Thirty percent of the major glycoprotein fraction, that was isolated from the membranes of the epidermal cells of the newborn rat and was bound to an affinity column of UEA-Sepharose 4B, was also bound to an affinity column of GS I-B4-Sepharose 4B. These results indicate that surface glycoconjugates of rat keratinocytes differentiating in culture exhibit a change from GS I-B4 binding to UEA binding; the change in the cell surface glycoconjugates that results in the appearance of UEA binding, a feature of differentiated cells, occurs independently of stratification; and the change from GS I-B4 binding to UEA binding probably involves an "intermediate" glycoconjugate that binds both GS I-B4 and UEA and is found on the surface of cells from the lower spinous layer of the epidermis of the newborn rat.

Exposure to 12-O-tetradecanoylphorbol-13-acetate (TPA) induces the synthesis of histidine-rich protein (filaggrin) in monolayer cultures of rat keratinocytes

The effect of 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent tumor promoter, on epidermal differentiation has been studied by investigating the appearance of the epidermal differentiative marker protein, histidine-rich protein (HRP), in monolayer cultures of rat keratinocytes grown in low-calcium (0.1 mM) medium. Monoclonal antibody, 3F6-6, raised against the 60K HRP (HRPII) derived from the epidermis of the newborn rat was utilized to detect HRP in cultured keratinocytes. As a major component of keratohyalin in the cells of the granular layer in epidermis, HRP is not normally found in a monolayer culture of rat keratinocytes containing a high population of proliferating cells. However, when these cultures were exposed to 10 ng/ml of TPA, DNA and protein synthesis were decreased by up to 95% and 60%, respectively, and the cells in the monolayer culture became HRP-positive within 18-24 h. TPA has been shown to cause a withdrawal of the basal cells from the cell cycle and a commitment of these cells to an accelerated rate of terminal differentiation. Exposure to TPA at the same time that the calcium level of the monolayer cultures was raised to 2.0 mM in order to allow stratification resulted in positive immunostaining for HRP much earlier and much more intensively than in the absence of TPA. TPA also enhanced stratification of these cultures; however, the positive expression of HRP preceded the stratification. These observations support the view that the induction of terminal differentiation occurs independently of stratification and that the process of terminal differentiation (maturation) of basal cells precedes and triggers the movement of these cells to a suprabasal position (stratification).

Keratinocytes grown at the air-liquid interface

A procedure is described which allows primary cultures of rat keratinocytes grown at the liquid-air interface to develop and maintain multilayered strata and to produce highly keratinized sheets morphologically similar to those seen in epidermis in situ. Various substrata were tested and compared as to their ability to support growth and stratification of keratinocytes. It was found that when cultured on plastic surfaces, keratinocytes adhered tightly to the substratum and produced a confluent monolayer that later stratified to two to three layers. Cells plated on Vitrogen 100 collagen failed to reach confluence and, in addition, exhibited the "clustering" phenomenon and deterioration of collagen after 3 to 4 d of growth. Significantly better attachment and spreading were observed for cells grown on rat-tail collagen as compared with plastic and Vitrogen 100 collagen. The best results, including maximal and uniform stratification, were seen in cells grown on a mixture of rat-tail and Vitrogen 100 collagens. The system that was developed in the present study offers a model for use in the study of epidermal toxicity from topically applied environmental chemicals.

Influence of adipocyte triglyceride on the partition of 2,2',4,4',5,5'-hexabromobiphenyl between 3T3L1 adipocytes and surrounding pseudoblood

Removal from adipose tissue is an important first step in ultimate removal of many lipophilic xenobiotics from the body. This study concerned the elucidation of mechanisms by which hexabromobiphenyl (HBB) was deposited in and removed from adipocytes. Adipocytes derived from the 3T3L1 cell line of mouse fibroblasts were used to conduct studies in vitro. Results support the idea that HBB enters the 3T3L1 adipocyte via passive diffusion. A plot of the velocity of uptake versus concentration was linear, the uptake of HBB does not appear to be energy dependent, and structurally similar biphenyls did not cause an inhibition of uptake. A linear relationship between the quantities of triglyceride and HBB in the cells was found during both uptake of HBB in lipogenesis and removal of HBB in lipolysis (r greater than 0.98). This supports the contention that the quantity of triglyceride in the cells has a strong influence on the movement of HBB between adipocytes and surrounding pseudoblood. Evidence has been presented that is consistent with the hypothesis that HBB moves freely across the adipocyte membrane and is sequestered in either cells or medium according to its relative solubility in these compartments. Methods to increase the removal of HBB from adipocytes have been proposed.

Growth and differentiation of primary rat keratinocytes on synthetic membranes

The attachment, proliferation, and differentiation of primary cultures of keratinocytes isolated from murine epidermis were monitored after purified cell suspensions were seeded and incubated in vitro on various synthetic membranes. Concomitant studies of the effects of attachment factors added to synthetic membranes before use as substrata for keratinocytes were also done. The study demonstrated that a synthetic membrane composed of nylon was superior to other membranes and to plastic control culture vessels in supporting the growth of murine keratinocytes. Although laminin enhanced initial attachment and proliferation of cells on nylon membranes, the untreated substratum was more effective for extended incubation. Stratification and differentiation of these keratinocytes on the nylon substratum was enhanced by raising confluent cultures (7 d) to the air-medium interface so that they were in contact with medium only from the bottom. Cultures raised for 14 d produced many morphologic markers of the epidermis and closely resembled the architecture of this tissue in situ.

Preliminary characterization of cell surface glycoproteins associated with epidermal differentiation in the newborn rat

The cell surface of the newborn rat epidermis exhibits a discrete change in lectin-binding specificity from Griffonia simplicifolia I-B4 (GS I-B4), specific for alpha-D-galactosyl residues, to Ulex europeus agglutinin I (UEA), specific for alpha-L-fucose, as the cell leaves the basal layer and differentiates. It has been postulated that this change is a result of the addition of alpha-L-fucose to nonreducing terminal alpha-D-galactosyl residues on GS I-B4-binding cell surface glycoproteins. If this were the sole nature of the conversion, the physical properties of isolated GS I-B4- and UEA-bound glycoproteins should not differ greatly. UEA and GS I-B4-binding glycoproteins isolated from newborn rat epidermis have similar charge properties and are similar in the nature of their carbohydrate moieties, supporting the proposed hypothesis.

Radiometric assay for direct quantitation of rat liver cytochrome P-450b using monoclonal antibodies

A simple and sensitive assay has been developed that is capable of detecting as little as 0.2 ng of the major isozyme of cytochrome P-450 (P-450b) isolated from the livers of phenobarbital-induced rats. This assay employs monoclonal antibodies generated against cytochrome P-450b to directly quantify the levels of this enzyme in various tissues. Separation of bound from free labeled antibody is achieved by using 6,9-diaminoacridine lactate (Rivanol). The useful range of the assay is between 1 and 100 ng of P-450b.

Retinoids alter the direction of differentiation in primary cultures of cutaneous keratinocytes

The effects of vitamin A on the morphological expression of differentiation were studied in cell cultures of cutaneous keratinocytes from the newborn rat. The cells were first cultivated in a medium containing 0.11 mM calcium until a confluent monolayer had been formed. Stratification and terminal differentiation were then triggered by raising the calcium concentration of the medium to 1.96 mM ('normal' culture). The rise in the concentration of calcium was coupled with the addition of retinol (RL) of retinoic acid (RAC) to the medium to produce an excess of vitamin A (high-retinoid culture). Delipidized serum was used to produce a deficiency of vitamin A (low-retinoid culture). The tissue organization and the ultrastructure of the keratinocytes in the stratified culture were the same as those seen in conventional cultures and skin explants. These stratified cultures expressed the morphological features of the epidermis of intact skin. The addition of RL or RAC to the medium enhanced features characteristic of the secretory epithelium, such as the formation of an extensive endoplasmic reticulum, an enlargement of the Golgi zone, and an increase in the number of vacuoles. At the same time, the addition of retinoids diminished features characteristic of the terminal differentiation of the stratified squamous epithelium, such as stratification and keratinization. Deficiency of vitamin A in the medium resulted in a culture with many differentiated layers. The differentiated cells of the low-retinoid cultures contained densely packed tonofilaments and synthesized products that reacted with the monoclonal antibody AE2 that is specific for keratin peptides which are markers of epidermal differentiation. In the cell culture system that is presented here, an excess of retinoids redirected epithelial differentiation from a stratifying and keratinizing epithelium towards a secretory epithelium. This system is a useful tool for elucidating the mechanisms responsible for the effect of vitamin A on the differentiation of epithelial cells.

Epidermal fucosylation of cell surface glycoprotein

When Ulex europeus agglutinin I (UEA) conjugated with fluorescein isothiocyanate is applied to tissue sections from the cutaneous epidermis of the newborn rat, the lectin binds to the surfaces of cells in the layer immediately above the basal layer but not to the cells in the basal layer itself. The latter cells bind the isolectin I-B4, from Griffonia simplicifolia (GS I-B4). The addition of a fucosyl residue to the oligosaccharide of the glycoprotein found on the surface of the basal cell can account for the change in lectin-binding specificity which occurs as the basal cell moves toward the cutaneous surface and becomes a spinous cell. The epidermis of the newborn rat has the necessary transferase to convert a glycoprotein with binding-specificity for GS I-B4 to binding specificity for UEA by adding a fucosyl residue from GDP-L-fucose.

Modification of cell surface glycoprotein: addition of fucosyl residues during epidermal differentiation

When cutaneous sections from the newborn rat were treated with alpha-fucosidase, Ulex europeus agglutinin I (UEA) binding to the cell surface of the differentiated cells in the epidermis was diminished and there was an appearance in these cell layers of binding by Bandeiraea simplicifolia I-B4 lectin (BS I-B4), which normally is specific for the basal cells. A similar treatment with alpha-galactosidase resulted in a loss of BS I-B4 binding, but had no effect on UEA binding. Glycoproteins isolated from the membranes of epidermal cells showed a threefold increase in the ratio of binding to UEA versus BS I-B4 affinity columns as the proteins were derived from the more differentiated cell populations. These data suggest that alpha-fucosyl residues are added to the glycoproteins on the cell surfaces of differentiated cells, thus blocking alpha-galactosyl residues and changing the lectin binding specificity as epidermal cells move out of the basal cell layer.