The short-term impact of the 2020 pandemic lockdown on employment in Greece

This paper analyzes the short-term employment impact of the COVID-19 lockdown in Greece during the first few months following the pandemic onset. During the initial lockdown period, aggregate employment was lower by almost 9 percentage points than it would have been expected based on pre-pandemic employment trends. However, due to a government intervention that prohibited layoffs, this was not due to higher separation rates. The overall short-term employment impact was due to lower hiring rates. To uncover the mechanism behind this, we use a difference-in-differences framework, and show that tourism-related activities, which are exposed to seasonal variation, had significantly lower employment entry rates in the months following the pandemic onset compared to non-tourism activities. Our results highlight the relevance of the timing of unanticipated shocks in economies with strong seasonal patterns, and the relative effectiveness of policy interventions to partly absorb the consequences of such shocks.

Heterogeneity of management practices surrounding operable gallbladder cancer - results of the OMEGA-S international HPB surgical survey

BACKGROUND

Gallbladder cancer (GBC) is an aggressive, uncommon malignancy, with variation in operative approaches adopted across centres and few large-scale studies to guide practice. We aimed to identify the extent of heterogeneity in GBC internationally to better inform the need for future multicentre studies.

METHODS

A 34-question online survey was disseminated to members of the European-African Hepatopancreatobiliary Association (EAHPBA), American Hepatopancreatobiliary Association (AHPBA) and Asia-Pacific Hepatopancreatobiliary Association (A-PHPBA) regarding practices around diagnostic workup, operative approach, utilization of neoadjuvant and adjuvant therapies and surveillance strategies.

RESULTS

Two hundred and three surgeons responded from 51 countries. High liver resection volume units (>50 resections/year) organised HPB multidisciplinary team discussion of GBCs more commonly than those with low volumes (p < 0.0001). Management practices exhibited areas of heterogeneity, particularly around operative extent. Contrary to consensus guidelines, anatomical liver resections were favoured over non-anatomical resections for T3 tumours and above, lymphadenectomy extent was lower than recommended, and a minority of respondents still routinely excised the common bile duct or port sites.

CONCLUSION

Our findings suggest some similarities in the management of GBC internationally, but also specific areas of practice which differed from published guidelines. Transcontinental collaborative studies on GBC are necessary to establish evidence-based practice to minimise variation and optimise outcomes.

ACTH vs steroids for the treatment of acute gout in hospitalized patients: a randomized, open label, comparative study

The management of acute gout in the hospital setting may be challenging since most patients are elderly with multiple unstable comorbidities. However, there are no prospective clinical trials for hospitalized patients with gout to guide optimal management. Evidence indicates that steroids or adrenocorticotropic hormone (ACTH) may be effective and safe therapeutic options for these patients. This study aimed at directly comparing the efficacy and safety of ACTH vs betamethasone for the treatment of gout in hospitalized patients. This is the first prospective clinical trial for hospitalized patients with gout. We designed a randomized, open label study to assess the efficacy and safety of a single intramuscular injection of either ACTH or betamethasone in hospitalized patients with acute gout. Primary efficacy endpoints were the change in intensity of pain as recorded using a Visual Analogue Scale (VAS) at baseline compared to 24 h (ΔVAS24h), and 48 h. Moreover, we assessed safety and effects on the hypothalamic-pituitary-adrenal (HPA) axis, glucose and lipid homeostasis, bone metabolism, electrolytes and renal function. 38 patients were recruited. Both treatments were highly effective. The mean ± SE ΔVAS24h and ΔVAS48h for ACTH was 4.48 ± 0.29 and 5.58 ± 0.26, respectively. The mean ± SE ΔVAS24h and ΔVAS48h for betamethasone was 4.67 ± 0.32 and 5.67 ± 0.28, respectively. Direct comparison between the two groups at 24 h and 48 h did not show statistically significant differences. Both treatments were well tolerated and safe. The effects on all metabolic parameters were mostly minimal and transient for both treatments. However, ACTH may affect less the HPA axis and bone metabolism compared to betamethasone, thus leading to the conclusion that. ACTH and betamethasone are effective and safe for the management of acute gout in hospitalized patients but that ACTH may associate with less disturbance of the HPA axis and bone metabolism. Our data support the use of both drugs as first line treatments for hospitalized patients with gout.Clinical trial registration: ClinicalTrials.gov NCT04306653.

P788Discharge echocardiographic parameters of RV and LV function but not of changes in cardiac unloading are related to 12-month prognosis during hospitalization for acute decompensated heart failure

Introduction

Acute decompensated heart failure (ADHF) is associated with a high mortality and rehospitalization rate. The aim of this study was to assess whether echocardiographic markers of systolic and diastolic function, and their changes under treatment during hospitalization for ADHF, would predict 12-months mortality.

Methods

Adult patients admitted to our emergency department for ADHF between June 2015 and January 2018 were included if a complete transthoracic echocardiography (TTE) could be obtained within 12 hours of admission. TTE was repeated upon discharge. Baseline clinical and echocardiographic characteristics were collected on admission and at discharge, and outcome at 12 months was obtained by telephone interview. All parameters are given as median [interquartile range].

Results

A total of 221 patients were identified but 45 excluded because of in-hospital death (n=8), early transfer to another hospital (n=31) or refusal to perform discharge TTE (n=6), leaving 176 patients for final analysis. Age was 83 [74–87] years, 95 (54%) were men and 89 (51%) were in sinus rhythm. Baseline TTE was performed within 6.6h [4.1–11.9] of admission and median duration of hospital stay was 13 days [9–19]. Admission ejection fraction (EF) was 45% [37–54] (29% HFrEF, 37% HFmrEF, 34% HFpEF). Between admission and discharge, significant changes were observed for global longitudinal LV strain (−10.3 [−7.2 to 15.1] to −11.8% [−8.1 to 15.0], p=0.017), mitral E velocity (100 [80–124] to 96 cm/s [74–117], p=0.001), E/e' ratio (16 [12–20] to 15 [11–19], p=0.003, RV basal diameter (41 [36–45] to 41mm [34–44], p=0.007), tricuspid regurgitation gradient (41 [34–52] to 35 mmHg [28–44], p=0.0001 and vena cava diameter (22 [19–26] to 19 mm [15–23],. Deaths occurred in 35 (20%) at 12 months follow-up. In our multivariable model, none of the changes in TTE parameters was predictive of mortality. Age (OR 1.09, p0.01), LVEF (OR 0.95, p0.02) and TAPSE (OR 0.86, p0.01) measured at discharge, but not LV or RV strain, were identified as independent predictors of 12-months mortality (see figure).

Survival according to LVEF and TAPSE

Conclusion

Several changes in TTE parameters were observed during hospitalization for ADHF, reflecting effective cardiac unloading with diuretic treatment. However, none of these changes appears to have prognostic significance. LVEF and TAPSE at discharge were identified as the only independent echocardiographic predictors of 12-months mortality, in addition to age.

Acknowledgement/Funding

Swiss Heart Foundation

Expanded national database collection and data coverage in the FINDbase worldwide database for clinically relevant genomic variation allele frequencies

FINDbase (http://www.findbase.org) is a comprehensive data repository that records the prevalence of clinically relevant genomic variants in various populations worldwide, such as pathogenic variants leading mostly to monogenic disorders and pharmacogenomics biomarkers. The database also records the incidence of rare genetic diseases in various populations, all in well-distinct data modules. Here, we report extensive data content updates in all data modules, with direct implications to clinical pharmacogenomics. Also, we report significant new developments in FINDbase, namely (i) the release of a new version of the ETHNOS software that catalyzes development curation of national/ethnic genetic databases, (ii) the migration of all FINDbase data content into 90 distinct national/ethnic mutation databases, all built around Microsoft's PivotViewer (http://www.getpivot.com) software (iii) new data visualization tools and (iv) the interrelation of FINDbase with DruGeVar database with direct implications in clinical pharmacogenomics. The abovementioned updates further enhance the impact of FINDbase, as a key resource for Genomic Medicine applications.

Exploiting expert systems in cardiology: a comparative study

An improved Adaptive Neuro-Fuzzy Inference System (ANFIS) in the field of critical cardiovascular diseases is presented. The system stems from an earlier application based only on a Sugeno-type Fuzzy Expert System (FES) with the addition of an Artificial Neural Network (ANN) computational structure. Thus, inherent characteristics of ANNs, along with the human-like knowledge representation of fuzzy systems are integrated. The ANFIS has been utilized into building five different sub-systems, distinctly covering Coronary Disease, Hypertension, Atrial Fibrillation, Heart Failure, and Diabetes, hence aiding doctors of medicine (MDs), guide trainees, and encourage medical experts in their diagnoses centering a wide range of Cardiology. The Fuzzy Rules have been trimmed down and the ANNs have been optimized in order to focus into each particular disease and produce results ready-to-be applied to real-world patients.

DruGeVar: an online resource triangulating drugs with genes and genomic biomarkers for clinical pharmacogenomics

BACKGROUND/AIMS

Pharmacogenomics aims to rationalize drug use by minimizing drug toxicity and/or by increasing drug efficacy. A large number of genomic markers have been correlated with variable drug responses and severity of adverse drug reactions. Although a number of these drugs bear pharmacogenomic information in their labels--approved by regulatory agencies--and comprehensive drug/gene lists exist online, information related to the respective pharmacogenomic biomarkers is currently missing from such lists.

METHODS

We extracted information from the published literature and online resources and developed DruGeVar (http://drugevar.genomicmedicinealliance.org), an online resource triangulating drugs with genes and pharmacogenomic biomarkers in an effort to build a comprehensive database that could serve clinical pharmacogenomics.

RESULTS AND CONCLUSIONS

A user-friendly data querying and visualization interface allows users to formulate simple and complex queries. Such a database would be readily applicable as a stand-alone resource or a plug-in module for other databases.

Developments in FINDbase worldwide database for clinically relevant genomic variation allele frequencies

FINDbase (http://www.findbase.org) aims to document frequencies of clinically relevant genomic variations, namely causative mutations and pharmacogenomic markers, worldwide. Each database record includes the population, ethnic group or geographical region, the disorder name and the related gene, accompanied by links to any related databases and the genetic variation together with its frequency in that population. Here, we report, in addition to the regular data content updates, significant developments in FINDbase, related to data visualization and querying, data submission, interrelation with other resources and a new module for genetic disease summaries. In particular, (i) we have developed new data visualization tools that facilitate data querying and comparison among different populations, (ii) we have generated a new FINDbase module, built around Microsoft’s PivotViewer (http://www.getpivot.com) software, based on Microsoft Silverlight technology (http://www.silverlight.net), that includes 259 genetic disease summaries from five populations, systematically collected from the literature representing the documented genetic makeup of these populations and (iii) the implementation of a generic data submission tool for every module currently available in FINDbase.

Updates of the HbVar database of human hemoglobin variants and thalassemia mutations

HbVar (http://globin.bx.psu.edu/hbvar) is one of the oldest and most appreciated locus-specific databases launched in 2001 by a multi-center academic effort to provide timely information on the genomic alterations leading to hemoglobin variants and all types of thalassemia and hemoglobinopathies. Database records include extensive phenotypic descriptions, biochemical and hematological effects, associated pathology and ethnic occurrence, accompanied by mutation frequencies and references. Here, we report updates to >600 HbVar entries, inclusion of population-specific data for 28 populations and 27 ethnic groups for α-, and β-thalassemias and additional querying options in the HbVar query page. HbVar content was also inter-connected with two other established genetic databases, namely FINDbase (http://www.findbase.org) and Leiden Open-Access Variation database (http://www.lovd.nl), which allows comparative data querying and analysis. HbVar data content has contributed to the realization of two collaborative projects to identify genomic variants that lie on different globin paralogs. Most importantly, HbVar data content has contributed to demonstrate the microattribution concept in practice. These updates significantly enriched the database content and querying potential, enhanced the database profile and data quality and broadened the inter-relation of HbVar with other databases, which should increase the already high impact of this resource to the globin and genetic database community.

Institutional Profile: Golden Helix Institute of Biomedical Research: interdisciplinary research and educational activities in pharmacogenomics and personalized medicine

The Golden Helix Institute of Biomedical Research is an international nonprofit scientific organization with interdisciplinary research and educational activities in the field of genome medicine in Europe, Asia and Latin America. These activities are supervised by an international scientific advisory council, consisting of world leaders in the field of genomics and translational medicine. Research activities include the regional coordination of the Pharmacogenomics for Every Nation Initiative in Europe, in an effort to integrate pharmacogenomics in developing countries, the development of several national/ethnic genetic databases and related web services and the critical assessment of the impact of genetics and genomic medicine on society in various countries. Educational activities also include the organization of the Golden Helix Symposia(®), which are high-profile scientific research symposia in the field of personalized medicine and the Golden Helix Pharmacogenomics Days, an international educational activity focused on pharmacogenomics, as part of its international pharmacogenomics education and outreach efforts.

Microattribution and nanopublication as means to incentivize the placement of human genome variation data into the public domain

The advances in bioinformatics required to annotate human genomic variants and to place them in public data repositories have not kept pace with their discovery. Moreover, a law of diminishing returns has begun to operate both in terms of data publication and submission. Although the continued deposition of such data in the public domain is essential to maximize both their scientific and clinical utility, rewards for data sharing are few, representing a serious practical impediment to data submission. To date, two main strategies have been adopted as a means to encourage the submission of human genomic variant data: (1) database journal linkups involving the affiliation of a scientific journal with a publicly available database and (2) microattribution, involving the unambiguous linkage of data to their contributors via a unique identifier. The latter could in principle lead to the establishment of a microcitation-tracking system that acknowledges individual endeavor and achievement. Both approaches could incentivize potential data contributors, thereby encouraging them to share their data with the scientific community. Here, we summarize and critically evaluate approaches that have been proposed to address current deficiencies in data attribution and discuss ways in which they could become more widely adopted as novel scientific publication modalities.

Population-ethnic group specific genome variation allele frequency data: a querying and visualization journey

National/ethnic mutation databases aim to document the genetic heterogeneity in various populations and ethnic groups worldwide. We have previously reported the development and upgrade of FINDbase (www.findbase.org), a database recording causative mutations and pharmacogenomic marker allele frequencies in various populations around the globe. Although this database has recently been upgraded, we continuously try to enhance its functionality by providing more advanced visualization tools that would further assist effective data querying and comparisons. We are currently experimenting in various visualization techniques on the existing FINDbase causative mutation data collection aiming to provide a dynamic research tool for the worldwide scientific community. We have developed an interactive web-based application for population-based mutation data retrieval. It supports sophisticated data exploration allowing users to apply advanced filtering criteria upon a set of multiple views of the underlying data collection and enables browsing the relationships between individual datasets in a novel and meaningful way.

Population-specific documentation of pharmacogenomic markers and their allelic frequencies in FINDbase

Aims: Population and ethnic group-specific allele frequencies of pharmacogenomic markers are poorly documented and not systematically collected in structured data repositories. We developed the Frequency of Inherited Disorders Pharmacogenomics database (FINDbase-PGx), a separate module of the FINDbase, aiming to systematically document pharmacogenomic allele frequencies in various populations and ethnic groups worldwide. Materials & methods: We critically collected and curated 214 scientific articles reporting pharmacogenomic markers allele frequencies in various populations and ethnic groups worldwide. Subsequently, in order to host the curated data, support data visualization and data mining, we developed a website application, utilizing Microsoft™ PivotViewer software. Results: Curated allelic frequency data pertaining to 144 pharmacogenomic markers across 14 genes, representing approximately 87,000 individuals from 150 populations worldwide, are currently included in FINDbase-PGx. A user-friendly query interface allows for easy data querying, based on numerous content criteria, such as population, ethnic group, geographical region, gene, drug and rare allele frequency. Conclusion: FINDbase-PGx is a comprehensive database, which, unlike other pharmacogenomic knowledgebases, fulfills the much needed requirement to systematically document pharmacogenomic allelic frequencies in various populations and ethnic groups worldwide.

FINDbase: a worldwide database for genetic variation allele frequencies updated

Frequency of INherited Disorders database (FIND base; http://www.findbase.org) records frequencies of causative genetic variations worldwide. Database records include the population and ethnic group or geographical region, the disorder name and the related gene, accompanied by links to any related external resources and the genetic variation together with its frequency in that population. In addition to the regular data content updates, we report the following significant advances: (i) the systematic collection and thorough documentation of population/ethnic group-specific pharmacogenomic markers allele frequencies for 144 markers in 14 genes of pharmacogenomic interest from different classes of drug-metabolizing enzymes and transporters, representing 150 populations and ethnic groups worldwide; (ii) the development of new data querying and visualization tools in the expanded FINDbase data collection, built around Microsoft's PivotViewer software (http://www.getpivot.com), based on Microsoft Silverlight technology (http://www.silverlight.net) that facilitates querying of large data sets and visualizing the results; and (iii) the establishment of the first database journal, by affiliating FINDbase with Human Genomics and Proteomics, a new open-access scientific journal, which would serve as a prime example of a non-profit model for sustainable database funding.

Intestinal neurofibromatosis and small-bowel adenocarcinoma: a single case study

OBJECTIVE

Patients with Von Recklinghausen's disease (neurofibromatosis type 1) are at increased risk of developing various tumours. However, the coexistence of neurofibromatosis with small-bowel adenocarcinoma is exceedingly rare. We present an uncommon case of neurofibromatosis type 1, involving the small bowel in a 73-year-old man, who was admitted to our department with signs of acute abdomen. At laparotomy, multiple mesenteric and intramural nodules were seen in the distal ileum. These nodules obstructed ileal lumen, while the intestine wall was perforated in one point. A wide resection of the affected ileum together with all visible nodules in the adjacent mesentery was performed. Histology revealed neurofibromatosis type 1 with malignant transformation to small-bowel adenocarcinoma. The patient had no additional therapy. In a follow-up of 2 years, the patient is very well and there was no recurrence of the disease. We suggest that adenocarcinoma of small bowel should be considered in the evaluation of acute abdominal pain in neurofibromatosis patients.

The MAP kinase phosphatase-1 MKP-1/DUSP1 is a regulator of human liver response to transplantation

Orthotopic liver transplantation (OLT) continues to be the only remedy for end-stage liver disease. In an attempt to decrease the ever-widening gap between organ donor and recipient numbers, and ultimately make more livers amenable to transplantation, we characterized the healthy human liver's response to ischemia and reperfusion-induced injury during transplantation. This was carried out by transcriptional profiling using cDNA microarray to identify genes whose expression was modulated at the 1-h postreperfusion time point. We observed that the map kinase phosphatase-1/dual-specificity phosphatase-1 (MKP-1/DUSP1) mRNA was strongly and significantly upregulated. Validation of this observation was carried out using reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblotting and immunohistochemistry. In addition, we characterized the signaling pathways regulating MKP-1 expression using the human hepatoma cell line HepG2. Finally, by combining MKP-1 silencing with reperfusion-associated stresses, we reveal the preferential role of this protein in attenuating the activity of the JNK and p38(MAPK) pathways, and the resulting apoptosis, making MKP-1 a potential target for therapeutic intervention.

The role of metabolism and toxicokinetics in retinoid teratogenesis

Retinoids (vitamin A and its analogs) exert profound effects on a wide variety of life processes, including morphogenesis and embryonic development. Several retinoids are also effective drugs for therapy of skin diseases and some types of cancer. However, the applicability of this class of compounds is limited by their teratogenic activity. A major question in retinoid toxicology has been the marked interspecies differences in the lowest teratogenic doses of 13-cis-retinoic acid and retinol. In addition, great attention has been drawn to the risk assessment of embryotoxicity resulting from excessive intake of vitamin A by pregnant women. The present review first gives an overview of the biochemistry, metabolism and mode of action of retinoids as well as their role in embryonic development. It then summarizes the results of recent studies on retinoid metabolism, toxicokinetics, and embryonic exposure and discusses how the available information provides explanation of the aforementioned interspecies variations. Finally, it presents some approaches for risk assessment of high vitamin A intake by humans based on various animal models and epidemiological studies.

Paronychia with pyogenic granuloma in a child treated with indinavir: the retinoid-mediated side effect theory revisited

BACKGROUND

The introduction of HIV-1 protease inhibitors into the treatment of patients infected with HIV-1 has had a major influence on clinical practice. However, the use of protease inhibitors is frequently associated with the development of resistance and several side effects and interactions with other drugs have been reported.

OBSERVATIONS

We present the first pediatric patient with paronychia with pyogenic granuloma associated with the administration of the protease inhibitor indinavir. Clinical findings are discussed in view of a possible interference of indinavir with endogenous retinoid metabolism.

CONCLUSION

Considerable evidence advocates the mediation of indinavir side effects by impaired oxidative metabolism of retinoic acid through the inhibition of cytochromes P450 3A by indinavir rather than by impaired formation of 9-cis-retinoic acid.

Human uterine leiomyomata express higher levels of peroxisome proliferator-activated receptor gamma, retinoid X receptor alpha, and all-trans retinoic acid than myometrium

Uterine leiomyomata are the main indication for a hysterectomy in the United States and occur in 25% of women >35 years. Because uterine leiomyomata can form when ovariectomized guinea pigs are exposed to estradiol and retinoic acids, we tested whether human leiomyomata had high levels of retinoic acids and related nuclear receptors. Compared with normal human myometrium, leiomyomata had 3- to 5-fold higher levels of peroxisome proliferator-activated receptor gamma (PPARgamma), retinoid X receptor alpha proteins, and all-trans retinoic acid, but only during the follicular phase of the menstrual cycle. 9-cis Retinoic acid was undetectable in either leiomyomata or myometrium. PPARgamma mRNA levels were lower in leiomyomata than myometrium, but only during the luteal phase of the cycle. A PPARgamma agonist, troglitazone, was given to guinea pigs along with estradiol and all-trans retinoic acid and produced the largest leiomyomata seen to date in this model. By contrast, no tumors formed when troglitazone was given alone or with estradiol or when troglitazone was given with estradiol and 9-cis retinoic acid. New therapies for human leiomyomata may emerge by combining antagonists for PPARgamma and retinoid X receptor alpha with selective estrogen receptor modulators.

Metabolism of retinaldehyde isomers in pregnant rats: 13-cis- and all-trans-retinaldehyde, but not 9-cis-retinaldehyde, yield very similar patterns of retinoid metabolites

Retinaldehyde (RAL), a key intermediate in retinoid metabolism, acts as a retinoic acid (RA) precursor, but is also reduced to retinol (ROH), which can subsequently be esterified to retinyl esters, the storage form of vitamin A. Limited information is available on the metabolism of geometric isomers of RAL as well as on the transplacental distribution of their metabolites, including RA isomers. Such information would be very helpful for the assessment of the teratogenic potency of RAL isomers, as teratogenesis represents a major side effect of retinoid use in pharmacotherapy. In the present study we examined concentrations of retinoids in plasma, maternal tissues, and embryos of pregnant rats 2 h after a single oral dose (100 mg/kg body weight) of all-trans-, 13-cis-, or 9-cis-RAL on gestational day 13. The main findings of this study were the very similar patterns of retinoid metabolites (consisting of retinoids with mainly the all-trans-configuration) after administration of all-trans- and 13-cis-RAL, and the high concentrations of 9-cis-RA, 9,13-dicis-RA, and 9-cis-retinoyl-beta-D-glucuronide after dosing with 9-cis-RAL. In addition, all-trans-RA as a RAL metabolite reached the embryos to a much greater extent than any of its cis-isomers. The results are discussed in view of in vitro data on enzymes involved in the biotransformation of RAL isomers.

Retinoid teratogenicity in the macaque: verification of dosing regimen

To further define teratogenicity associated with 13-cis-retinoic acid (13-cis-RA) in the cynomolgus monkey, the drug was orally administered on three different treatment regimens. Experiment (Exp.) 1 (2.5 mg/kg/day, gestational day [GD] 12-27, n = 11) investigated the teratogenicity of a single daily dose of 13-cis-RA administered shortly after embryo implantation. Pharmacokinetic sampling was done to determine retinoid profiles on the first (GD12) and last (GD27) days of treatment. Exposure to 13-cis-RA during early organogenesis in Exp. 2 (2.5 mg/kg/day, GD20-27, and 2 x 2.5 mg/kg/day, GD28-30, n = 5) investigated the potential adverse effects of 13-cis-RA on the developing limb. The use of multiple doses of 13-cis-RA in Exp. 3 (2 x 2.5 mg/kg/day, GD26-27, n = 5) investigated the necessity of double dosing on the induction of retinoid embryopathy in the macaque. Malformations of retinoid target organs as well as embryolethality were most prevalent when single daily doses of 13-cis-RA were administered during pre- and early organogenesis in Exp. 1. Moreover, multiple doses on GD26-27 failed to induce any manifestation of abnormal development in Exp. 3. These results confirm that the lowest observed adverse effect level (LOAEL) in macaques is 2.5 rather than 5.0 times greater than that observed in human pregnancies. Exposure during forelimb development (GD20-30) in Exp. 2 was unsuccessful in inducing defects of this skeletal region, although defects in several retinoid target organs (i.e., cerebellum and internal ear) were present, indicating that a teratogenic threshold was achieved. Pharmacokinetic analysis of 13-cis-RA and its metabolites on GD12 and 27 in Exp. 1 showed considerable exposure to the administered drug and its 4-oxo-metabolite. In contrast, the exposure to all-trans-RA was negligible. The results support the use of a specific treatment schedule in early gestation in the macaque as the most appropriate model for characterizing the teratogenic potential of retinoids in humans.

The area under the concentration-time curve of all-trans-retinoic acid is the most suitable pharmacokinetic correlate to the embryotoxicity of this retinoid in the rat

Earlier studies with etretinate and its metabolite acitretin suggested that area under the concentration-time curve (AUC) is the most suitable pharmacokinetic correlate to etretinate-induced teratogenesis. In an attempt to test this hypothesis with respect to the embryotoxic effects of all-trans-retinoic acid (all-trans-RA), we determined the embryotoxicity and plasma pharmacokinetics of all-trans-RA and its metabolites following administration of all-trans-RA to Wistar rats on Gestational Day (GD) 9, either subcutaneously (sc; dose levels 1, 3, or 5 mg/kg body mass) or orally (po; 5 mg/kg body mass). The 5 mg/kg dose of all-trans-RA was not embryotoxic when administered orally but led to high rates of embryolethality and skeletal defects following sc treatment. Determination of retinoids by HPLC showed that all-trans-RA reached similar maximum plasma concentrations (C(max)) after both dosing regimens, but its plasma AUC was ca. threefold higher after sc injection than po administration due to the slower uptake rate of the drug and its limited detoxification via beta-glucuronidation following sc injection. Furthermore, retinoid analysis in rat tissues (liver, kidney, duodenum, and jejunum), collected 1 hr after sc or po administration of 5 mg all-trans-RA/kg body mass on GD 9, confirmed that formation of all-trans-retinoyl-beta-glucuronide was much more extensive after po than after sc administration. Finally, linear regression analysis of either C(max). or AUC values of all-trans-RA in rat plasma and fetal abnormality rates showed that AUC values are better correlated with the embryotoxic outcome than C(max) [AUC-based correlation coefficient (r) > 0.90; C(max)-based r < 0.43]. Our findings establish the relevance of the AUC of all-trans-RA, and not its C(max), as the most appropriate pharmacokinetic marker of embryonic exposure and embryotoxic potency of all-trans-RA and stress the importance of the duration of exposure as a major determinant of embryotoxic outcome for retinoids.

The percutaneous absorption of topically applied tretinoin and its effect on endogenous concentrations of tretinoin and its metabolites after single doses or long-term use

BACKGROUND

The percutaneous absorption of topically applied tretinoin cream and emollient cream formulations has not been comprehensively studied.

OBJECTIVE

To assess tretinoin absorption and plasma levels of tretinoin and its metabolites after single and repeated topical tretinoin doses.

METHODS

In study 1, 28 subjects were equally divided into four treatment groups that received a single dose of tritiated tretinoin in a 0.05% formulation of emollient cream (Renova, Retinova) or cream (Retin-A) alone or after 28 days of repeated nonradioactive doses. In study 2, subjects received single topical doses of tritiated tretinoin cream alone (n = 5) or after 1 year of nonradioactive applications (n = 4). Plasma, urine, and fecal samples were analyzed to determine absorption; plasma samples in study 1 were also analyzed for concentrations of tretinoin and its metabolites.

RESULTS

Percutaneous absorption of tretinoin was approximately 2% after a single dose and after 28 days of daily application. In patients receiving long-term therapy (i.e., > 1 year), absorption averaged 1.1%. Mean plasma concentrations of tretinoin after 28 days of treatment with either tretinoin emollient cream or tretinoin cream were not significantly changed when compared with the corresponding endogenous concentrations before treatment.

CONCLUSION

Minimal percutaneous absorption of tretinoin was obtained after its topical application in cream formulations. Neither single-dose nor long-term treatment with topical tretinoin formulations appeared to affect the endogenous levels of tretinoin or its metabolites.

Retinoid metabolism and transplacental pharmacokinetics in the cynomolgus monkey following a nonteratogenic dosing regimen with all-trans-retinoic acid

Retinoids often exhibit a complex metabolic pattern and differential transplacental kinetics, which make it difficult to pinpoint the proximate compound responsible for the observed teratogenic effect. We have therefore studied the pharmacokinetics and metabolism of all-trans-retinoic acid (all-trans-RA) in cynomolgus monkeys following application of a nonteratogenic dosing regimen and compared the results with corresponding data from a previous study with a teratogenic dosing regimen with 13-cis-RA [Hummler et al. (1994) Teratology 50:184-193]. All-trans-RA was administered to pregnant cynomolgus monkeys (Macaca fascicularis) by nasogastric intubation at a dose of 5 mg/kg body wt once daily from gestational day (GD) 16 to 26 and twice daily at 8-h intervals from GD 27 to 31. Examination of the fetuses of four dams on GD 100 +/- 2 showed no embryotoxic or teratogenic effects of the applied dosing regimen (Experiment 1). Maternal plasma retinoid pharmacokinetics on GD 16, 26, and 31 as well as embryonic retinoid profiles after the last drug administration on GD 31 were determined in thirteen further dams (Experiment 2). All-trans-RA reached much lower plasma concentrations after the last two treatments on GD 31 than after the first one on GD 16 and the eleventh one on GD 26 (0-24-h area-under-the-concentration-time-curve (AUC) values: 104 +/- 59 ng x h/ml (after the last treatment on GD 31), 189 +/- 110 (GD 16) and 393 +/- 305 ng x h/ml (GD 26). The predominant plasma metabolites of all-trans-RA were its beta-glucuronide and the beta-glucuronide of all-trans-4-oxo-RA. Both of these retinoids accumulated in the plasma during the period of treatment and displayed AUC values 5- to 30-fold higher than those of all-trans-RA. Embryonic concentrations of all-trans-RA were not increased over endogenous levels after the last administration on GD 31 when plasma concentrations were low. To evaluate the placental transport of all-trans-RA in the presence of high plasma concentrations, a further experiment was performed, in which a single dose of all-trans-RA (10 mg/kg body wt) was given to four pregnant monkeys on GD 31, and plasma pharmacokinetics as well as embryonic concentrations of retinoids at 4 h post-treatment were determined (Experiment 3). This dosing schedule yielded high plasma concentrations of all-trans-RA, while embryonic concentrations were about 40% of plasma levels. Based on the plasma AUC values on GDs 16 and 26 obtained in Experiment 2 and the degree of placental transfer, as determined on GD 31 in the presence of high plasma levels in Experiment 3, we estimated embryonic AUC values for the 24-h period following the nonteratogenic doses on GDs 16 and 26 in Experiment 2. These AUC values were similarly high to the embryonic AUC value of all-trans-RA obtained after application of the teratogenic dosing regimen with 13-cis-RA [Hummler et al. (1994) Teratology 50:184-193]. In addition, plasma AUC values of all-trans-RA were 2- to 7-fold higher after all-trans-RA administration (present study) than after dosing with the teratogenic dose of 13-cis-RA. These results strengthen our recent suggestion that the teratogenic effects induced in cynomolgus monkeys by 13-cis-RA treatment cannot solely result from the action of all-trans-RA, but may involve 13-cis-RA and 13-cis-4-oxo-RA, which could act directly or function as transport vehicle.

Embryotoxic doses of vitamin A to rabbits result in low plasma but high embryonic concentrations of all-trans-retinoic acid: risk of vitamin A exposure in humans

Retinoid pharmacokinetics were examined in plasma, placenta and embryos of gestational d 12 rabbits following application of an embryotoxic dosing regimen (10 mg retinyl palmitate/kg body wt per day from gestational d 7 to 12). Vehicle-treated or untreated rabbits served as controls. Physiological concentrations of all-trans-retinoic acid (all-trans-RA) and 13-cis-RA in rabbit plasma (5-8.33 nmol/L) were very close to the endogenous levels in human plasma. In addition, we identified endogenous all-trans-RA, 3,4-didehydroretinol and 3,4-didehydroretinoic acid in rabbit embryo. Following the last retinyl palmitate administration, apparent steady-state concentrations of all retinoids were reached in the examined compartments of rabbits. The major polar retinoid in plasma was 9, 13-di-cis-RA, but its embryonic concentrations were only about 6% of those in plasma. In the embryo, retinol and its esters were found at high concentrations; lower amounts of all-trans-4-oxo-RA and the newly identified 14-hydroxy-4, 14-retro-retinol could also be measured. Embryonic concentrations of all-trans-RA were about 100% higher than endogenous levels. The overall exposure of the embryo to this retinoid was, however, substantial. Embryonic area under the concentration time curve values strongly suggest that the embryotoxicity of the applied dosing regimen is mainly due to the action of all-trans-RA. A very remarkable finding of this study is the marginal increase of plasma concentrations of all-trans-RA over their endogenous levels, which is comparable to the human situation after vitamin A intake. This analogy indicates that high vitamin A intake may be associated with a higher risk for teratogenic effects in humans even in the absence of high elevation of plasma all-trans-RA levels.

Identification of 9-cis-retinoic acid, 9,13-di-cis-retinoic acid, and 14-hydroxy-4,14-retro-retinol in human plasma after liver consumption

Vitamin A is a well-established teratogen in several animal species. Case reports as well as a recent epidemiological study suggest that vitamin A intake in excess of 25,000 or 10,000 IU respectively, can result in retinoid-specific defects in the offspring. A single meal of liver contains, on the average, a 10- to 20-fold higher amount of vitamin A than what is already suspected to be teratogenic. To evaluate the risk of liver consumption during pregnancy, we have studied levels of vitamin A and a number of potentially active retinoid metabolites in plasma of ten healthy male volunteers following consumption of fried turkey liver (2 g raw weight/kg body weight). HPLC, UV spectroscopy and mass spectrometry were used for identification and quantitation of retinoids in plasma. As shown previously, vitamin A intake via liver consumption resulted in greatly increased plasma levels of 13-cis-retinoic acid (13-cis-RA) and 13-cis-4-oxo-RA, and low levels of all-trans-RA and all-trans-4-oxo-RA. In our present investigation 9-cis-RA, 9,13-di-cis-RA, and 14-hydroxy-4,14-retro-retinol (14-HRR) were identified for the first time in humans as physiological metabolites of vitamin A. 9-cis-RA is a potent teratogen as well as a high affinity ligand of retinoid receptors, and 14-HRR was previously shown to promote lymphocyte activation in vitro. The present study bears on the issue of a possible teratogenic risk of liver consumption, as active retinoids were identified in human plasma, and their levels could be related to previous human studies as well as to experimental studies in sensitive animal species.

Identification of 14-hydroxy-4,14-retro-retinol as an in vivo metabolite of vitamin A

Retinol (vitamin A alcohol) undergoes extensive metabolism in vertebrates. We report here (i) the identification of a yet undescribed in vivo metabolite of retinol as 14-hydroxy-4,14-retro-retinol in pregnant mice, rats and rabbits following dosing with vitamin A, and (ii) the preferential accumulation of 14-hydroxy-4,14-retro-retinol in maternal and embryonic tissues, rather than in material plasma.

Developmental stage-associated differences in the transplacental distribution of 13-cis- and all-trans-retinoic acid as well as their glucuronides in rats and mice

In mice and rats, 13-cis-retinoic acid (13-cis-RA) has a much lower teratogenic potency than all-trans-retinoic acid (all-trans-RA). Previous studies on Gestational Day (GD) 11 or 12 (in mice or rats, respectively) showed a limited transfer of 13-cis-RA to the embryo, in contrast to the efficient transplacental passage of all-trans-RA. In the present study we examined if the distribution between maternal circulation and embryo of 13-cis- and all-trans-RA as well as their metabolites is different at gestational times when the placenta is developing from a choriovitelline to a chorioallantoic type. In the first experiment, 13-cis-RA was administered orally to pregnant rats (75 mg/kg/day) daily, from either GD 7 to 12 or 11 to 16. In the second experiment, 13-cis-RA or all-trans-RA was given orally to pregnant mice once on either GD 11 or 14, at two dose levels (10 and 100 mg/kg). HPLC analysis of plasma and embryo samples collected at various time points post-treatment showed that 13-cis-RA was predominantly metabolized to its beta-glucuronide (13-cis-RAG) while all-trans-RA was primarily biotransformed to all-trans-4-oxo-RA and to a lesser extent to all-trans-RAG. 13-cis-RA showed a more efficient transplacental passage to the rat embryo on GD 16 than on GD 12, as indicated by higher ratios of embryonic to maternal plasma concentrations (E/M concentration ratio) on GD 16 vs. GD 12 and its E/M ratio of area-under-the-concentration-time-curve values (E/M AUC ratio; twofold higher on GD 16 vs. GD 12). In the mouse, the E/M concentration ratio of 13-cis-RA was significantly higher on GD 14 than on GD 11 only at the low dose. On the other hand, all-trans-RA and all-trans-4-oxo-RA showed an efficient transfer to the mouse embryo at both gestational times. In both species, 13-cis- and all-trans-RAG embryonic concentrations on the later gestational days exceeded significantly the corresponding ones on the earlier gestational days which resulted in far higher E/M concentration and AUC ratios for each of these metabolites on the later vs earlier gestational days. This may result from a more efficient placental transfer of the RAGs during later gestational stages and/or higher capacity of the late embryo or other conceptal tissues to biotransform RAs in situ to their glucuronides.(ABSTRACT TRUNCATED AT 400 WORDS)

Antiepileptic drugs alter endogenous retinoid concentrations: a possible mechanism of teratogenesis of anticonvulsant therapy

The major antiepileptic drugs used for the control of seizures can induce developmental toxicity when administered during pregnancy. Vitamin A and retinoids are thought to control many processes of embryonic development including growth, differentiation and morphogenesis. We have therefore studied if the teratogenic action of antiepileptic agents could be mediated via alteration of the endogenous vitamin A--retinoid metabolism. Retinol and its oxidative metabolites all-trans-, 13-cis- and 13-cis-4-oxo-retinoic acid were measured in the plasma of 75 infants and children treated with various antiepileptic drugs for the control of seizures, and in 29 untreated controls of comparable age. Retinol levels increased with age, while the concentrations of retinoic acid compounds did not exhibit age-dependency. Valproic acid monotherapy increased retinol levels in the young age group and a trend toward increased retinol concentrations was also observed in all other patient groups. The plasma levels of the oxidative metabolites 13-cis- and 13-cis-4-oxo-retinoic acids were strongly decreased in all patient groups treated with phenytoin, phenobarbital, carbamazepine and ethosuximide, in combination with valproic acid, to levels which were below 1/3rd and 1/10th of corresponding control values, respectively. Little changes were observed with all-trans-retinoic acid except in one patient group treated with valproic acid/ethosuximide cotherapy where increased levels of this retinoid were found. Our study indicates that therapy with antiepileptic agents can have a profound effect on the endogenous retinoid metabolism. Because of the importance of retinoids for the signaling of crucial biological events during embryonic development, such altered retinoid metabolism may be highly significant in regard to antiepileptic drug teratogenesis.

Single versus multiple dose administration of all-trans-retinoic acid during organogenesis: differential metabolism and transplacental kinetics in rat and rabbit

Standard teratogenicity testing is usually performed by administration of a test compound daily throughout an extended period of organogenesis (e.g., between Days 6 and 15 in rat and 6 and 18 in rabbit). On the other hand, single dose experiments during a specific period were often demonstrated to be more effective in unveiling a particular teratogenic effect. We have assessed here if toxicokinetics is an important factor for the interpretation of the differences between two administration regimens of all-trans-retinoic acid (all-trans-RA) in two species. The transplacental pharmacokinetics of a low teratogenic dose of all-trans-RA administered orally were compared in a single versus multiple dose regimen in both the Wistar rat and the Swiss hare rabbit. In both species, the single dose animals were treated on Gestational Day 12, while the multiple dose animals received daily doses from Gestational Days 7 through 12. Pharmacokinetic profiles were determined for maternal plasma and embryo after dosing on Gestational Day 12 (for both the single and multiple dose regimens) and analyzed by reverse-phase HPLC. The dose used for both species was 6 mg/kg body wt/day which has recently been reported to be a marginal to low teratogenic dose when administered daily throughout organogenesis. In both rat and rabbit, the AUC of all-trans-retinoic acid in maternal plasma was much reduced (factor of 9 in the rat, factor of 2 in the rabbit) after multiple application as compared to the single administration, presumably due to enzyme induction. A similar, but not as pronounced effect was also observed in the embryo of both species. This diminished effect in the embryo indicates a relative increase of placental transfer at the lower maternal plasma concentration observed after multiple dosing, which may possibly be due to an increased availability of binding sites such as cytosolic retinoic acid binding protein and nuclear receptors in the embryo. In the rat, also the metabolite levels were reduced, while in the rabbit, the metabolites of the 13-cis-configuration were concomitantly increased. Our results suggest that multiple administration of a drug such as retinoic acid, which induces its own elimination pathways, results in substantially lowered drug levels in maternal plasma and embryo.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of 9,13-dicis-retinoic acid as a major plasma metabolite of 9-cis-retinoic acid and limited transfer of 9-cis-retinoic acid and 9,13-dicis-retinoic acid to the mouse and rat embryos

9-Cis-retinoic acid (9-cis-RA) has been proposed to be the endogenous ligand of retinoid X receptors. We examined the plasma pharmacokinetics of 9-cis-RA and its metabolites in nonpregnant female NMRI mice after oral dosing with 50 mg 9-cis-RA/kg body weight. Furthermore, we studied the metabolism of 9-cis-RA and its transfer to the embryo following oral administration of the precursor 9-cis-retinaldehyde (9-cis-RAL; 100 mg/kg body weight) to pregnant mice and rats on gestational days 11 and 13, respectively. Following 9-cis-RA administration, plasma levels of 9-cis-RA reached their maximum within 40-60 min and then declined in a monoexponential manner with an apparent half-life of 64 +/- 32 min. A great variety of polar metabolites of 9-cis-RA was found; among them, the beta-glucuronides of 9-cis-RA (9-cis-RAG) and of 9-cis-4-oxo-RA (9-cis-4-oxo-RAG) could be identified. A further prominent polar metabolite of 9-cis-RA in mouse plasma was shown to be an additional RA isomer (distinct from 13-cis-RA and all-trans-RA) whose concentrations weeesimilarly high as those of 9-cis-RA.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous status of retinoids and their cytosolic binding proteins in limb buds of chick vs mouse embryos

The morphogenetic role of all-trans-retinoic acid (RA) during limb development, especially its activity in directing anterior/posterior pattern formation remains controversial. We have measured retinoids and cytosolic binding proteins in anterior and posterior pieces of limb buds from comparably aged chick and mouse embryos expecting that localization patterns of morphological significance will be evident across species. Many species differences were found including: (1) nondetectable 3,4-didehydroretinoic acid (ddRA) in mouse limb buds, the predominant morphogenetically active retinoid in chick limbs; the precursor of ddRA, 3,4-didehydroretinol (ddROH), was also not present in mouse limb buds but found in high concentration in chick limb buds; (2) a higher concentration of morphogenetically active retinoid (RA + ddRA) in chick compared to mouse limb buds; (3) a high level of retinyl esters (1.5 microM) in chick limb bud, but undetectable concentration in mouse limb buds; and (4) a higher level of cytosolic retinoic acid binding proteins (CRABPs) in chick limb buds, especially CRABP II, which is 10X greater than in mouse limb buds. An interesting finding seen in mouse and chick limb buds was a disparity between the concentration of ligand and cytosolic binding protein. Retinol (ROH) and ddROH were present in much higher concentrations than cytosolic retinol binding protein (CRBP). Conversely, RA and ddRA were in far lower concentration than CRABPs. Any morphological significance of these disparities is unknown. A putative gradient of RA, high posteriorly, was found in chick limb buds as in earlier studies (Thaller and Eichele, 1987), but the magnitude of this gradient was less than previously reported. We also found ddRA in equal concentration in the anterior and posterior pieces of chick limb bud studied here, further weakening the idea of an RA gradient as the direct force in anterior/posterior pattern formation. The "free" concentration of retinoic acid, calculated from ligand and binding protein concentration and affinity, was slightly higher in posterior chick limb tissue (2.0X) and in mouse limb buds at a concentration similar to the Kd of murine nuclear retinoic acid receptors.

Comparative teratology and transplacental pharmacokinetics of all-trans-retinoic acid, 13-cis-retinoic acid, and retinyl palmitate following daily administrations in rats

The retinoids are teratogenic in a wide variety of species. In the rat, 13-cis-retinoic acid and retinyl palmitate are significantly less potent teratogens than all-trans-retinoic acid. This investigation questioned whether differing teratogenic potencies of these moieties can be correlated with the concentrations of these drugs and/or metabolites in the embryonic compartment. Approximately equipotent teratogenic doses of these three retinoids were administered and the pharmacokinetics in maternal plasma and embryo of the most prevalent vitamin A metabolites were measured. The glucuronides of the respective retinoids were the predominant metabolites in the maternal plasma, but were not detected in the embryo. Also, the transport of 13-cis-retinoic acid across the placenta occurred to a much lesser extent than the transport of all-trans-retinoic acid. Administration of either all-trans- or 13-cis-retinoic acid causes a depression in the endogenous retinol concentration. This depression is more pronounced in the maternal plasma than in the embryo. The depression of the retinol level in both plasma and embryo after 13-cis-retinoic acid administration (75 mg/kg/day) was greater than the depression after all-trans-retinoic acid (6 mg/kg/day), corroborating the inferential teratological data that the 13-cis-retinoic acid dose was more embryotoxic than the all-trans-retinoic acid dose. Although the dose of all-trans-retinoic acid was less embryotoxic than that of either 13-cis-retinoic acid or retinyl palmitate, the embryonic exposure to all-trans-retinoic acid was considerably larger, as determined by maximum concentration or area under the concentration-versus-time curve, after administration of all-trans-retinoic acid than after either retinyl palmitate or 13-cis-retinoic acid application. These results suggest that embryonic retinoids other than all-trans-retinoic acid--including the administered substances themselves--are important in the teratogenic process induced by 13-cis-retinoic acid and retinyl palmitate.

The high sensitivity of the rabbit to the teratogenic effects of 13-cis-retinoic acid (isotretinoin) is a consequence of prolonged exposure of the embryo to 13-cis-retinoic acid and 13-cis-4-oxo-retinoic acid, and not of isomerization to all-trans-retinoic acid

Previous studies suggested that the rabbit is much more susceptible to the teratogenic action of 13-cis-retinoic acid (13-cis-RA) than the mouse or the rat, while the teratogenicity of all-trans-RA was comparable in these species. In the present study we investigated if pharmacokinetics can explain these species- and structure-related differences. The embryotoxic and teratogenic potential of all-trans-retinoic acid (all-trans-RA) and 13-cis-RA were evaluated in the Swiss hare rabbit after oral administration of daily doses of the two drugs throughout organogenesis, from gestation day (GD) 6 to 18 (plug day = GD 0). All-trans-RA was given at dose levels of 0.7, 2 or 6 mg/kg body weight per day and 13-cis-RA at 3, 7.5 or 10 mg/kg per day. The doses needed to elicit a minimum teratogenic response were found to be 6 mg/kg per day for all-trans-RA and 10 mg/kg per day for 13-cis-RA. Using these doses, transplacental pharmacokinetics of all-trans- and 13-cis-RA were performed. Pregnant rabbits were treated once daily from GD 7 to 12 and plasma and embryo samples were collected for HPLC analysis at various time intervals after the final dose. The main plasma metabolites of all-trans- and 13-cis-RA were all-trans-beta-glucuronide (all-trans-RAG) and 13-cis-4-oxo-RA, respectively. The elimination of 13-cis-RA and its metabolites from maternal plasma were much slower than of all-trans-RA resulting in accumulation of the 13-cis-isomers in plasma. Marked differences in the placental transfer of the two drugs and their metabolites were observed. All-trans-RA and all-trans-4-oxo-RA were efficiently transferred to the rabbit embryo, reaching concentrations similar to the plasma levels. On the contrary, the 13-cis-isomers reached the embryo to a lesser extent. Despite its limited placental transfer, a considerable embryonic exposure to 13-cis-RA and 13-cis-4-oxo-RA was noticed after treatment with isotretinoin, as indicated by their area-under-the-concentration-time-curve (AUC) values in the embryo, which were in the same range as the corresponding AUC value of all-trans-RA after treatment with the all-trans-isomer.(ABSTRACT TRUNCATED AT 400 WORDS)

9-cis-retinoyl-beta-D-glucuronide is a major metabolite of 9-cis-retinoic acid

The in vivo metabolism of 9-cis-retinoic acid (9-c-RA), an endogenous ligand of retinoid X receptors (RXRs), which can also bind to retinoic acid receptors (RARs), was examined in pregnant mice and rats following a single oral dose of 100 mg 9-cis-retinaldehyde (9-c-RAL)/kg body weight. 9-Cis-retinoyl-beta-D-glucuronide (9-c-RAG), a metabolite not found in vivo before, was a major metabolite of 9-c-RA in mouse plasma and was also present in all mouse tissues examined as well as in rat plasma. In both species putative oxidation products of retinoic acids and high levels of retinyl esters were found. Concentrations of retinoic acid isomers and retinoyl-beta-D-glucuronides in the mouse plasma greatly exceeded those of the rat plasma. The finding of high levels of 9-c-RAG underlines the importance of glucuronidation in the metabolism of retinoids.

Modulation of myb gene expression in sponges by retinoic acid

We demonstrate that the cells of the sponge Geodia cydonium are equipped with the basic elements required for a retinoic acid (RA)-dependent response pathway; RA was identified and quantitated, the cellular RA-binding protein (CRABP) was detected and the nuclear RA receptor (RAR) was found. In the isolated cell system the level of CRABP, but not of RAR, is strongly induced after incubating the cells for 10h with the homologous aggregation factor. In induced cells incubation with 0.3 microM RA results in a strong down-regulation of the c-myb (or c-myb-related) proto-oncogene (M(r) 63,000; mRNA 3.3 kb). We postulate that this pathway is also functionally active and that RA acts as a natural morphogen.