Expression, purification, and binding properties of human cellular retinoic acid-binding protein type I and type II

Acne Transcriptomics: Fundamentals of Acne Pathogenesis and Isotretinoin Treatment

This review on acne transcriptomics allows for deeper insights into the pathogenesis of acne and isotretinoin's mode of action. Puberty-induced insulin-like growth factor 1 (IGF-1), insulin and androgen signaling activate the kinase AKT and mechanistic target of rapamycin complex 1 (mTORC1). A Western diet (hyperglycemic carbohydrates and milk/dairy products) also co-stimulates AKT/mTORC1 signaling. The AKT-mediated phosphorylation of nuclear FoxO1 and FoxO3 results in their extrusion into the cytoplasm, a critical switch which enhances the transactivation of lipogenic and proinflammatory transcription factors, including androgen receptor (AR), sterol regulatory element-binding transcription factor 1 (SREBF1), peroxisome proliferator-activated receptor γ (PPARγ) and signal transducer and activator of transcription 3 (STAT3), but reduces the FoxO1-dependent expression of GATA binding protein 6 (GATA6), the key transcription factor for infundibular keratinocyte homeostasis. The AKT-mediated phosphorylation of the p53-binding protein MDM2 promotes the degradation of p53. In contrast, isotretinoin enhances the expression of p53, FoxO1 and FoxO3 in the sebaceous glands of acne patients. The overexpression of these proapoptotic transcription factors explains isotretinoin's desirable sebum-suppressive effect via the induction of sebocyte apoptosis and the depletion of BLIMP1(+) sebocyte progenitor cells; it also explains its adverse effects, including teratogenicity (neural crest cell apoptosis), a reduced ovarian reserve (granulosa cell apoptosis), the risk of depression (the apoptosis of hypothalamic neurons), VLDL hyperlipidemia, intracranial hypertension and dry skin.

The Effects of Isotretinoin on The Menstrual Cycle: A Cross-Sectional Study

Menstrual irregularities during isotretinoin therapy, including amenorrhea, can cause a great deal of health-status uncertainty such as the possibility of pregnancy. This study aimed to evaluate the effects of isotretinoin treatment on the menstrual cycle. This cross-sectional study was conducted among females aged between 15−45 years taking isotretinoin for acne. Descriptive statistics were used in the form of frequencies and percentages to represent categorical variables. Pearson’s chi-squared test was performed to assess the relationship between some of the variables with menstrual irregularities. A logistic regression model was performed to assess the risk factors for developing menstrual irregularities during isotretinoin therapy. Of participants with a known regular menstrual cycle, 10.4% were found to have irregularity in their cycle after starting the drug (p < 0.001). Amenorrhea was the most commonly reported menstrual irregularity in isotretinoin-treated females. Our results showed that single females, those who took isotretinoin for 10−12 months and who were concurrently taking hormonal contraceptives all have a statistically significant higher risk of developing menstrual irregularities than others. In conclusion, we found that a statistically significant number of participants with a regular menstrual cycle pre-isotretinoin intake developed irregularity in their cycle after starting the drug. The mechanism of how isotretinoin influences female hormonal imbalances, thereby affecting menstrual irregularities is still poorly understood and needs to be clarified in further clinical studies.

CRABPs Alter all-trans-Retinoic Acid Metabolism by CYP26A1 via Protein-Protein Interactions

Cellular retinoic acid binding proteins (CRABP1 and CRABP2) bind all-trans-retinoic acid (atRA), the active metabolite of vitamin A, with high affinity. CRABP1 and CRABP2 have been shown to interact with the atRA-clearing cytochrome P450 enzymes CYP26B1 and CYP26C1 and with nuclear retinoic acid receptors (RARs). We hypothesized that CRABP1 and CRABP2 also alter atRA metabolism and clearance by CYP26A1, the third key atRA-metabolizing enzyme in the CYP26 family. Based on stopped-flow experiments, atRA bound CRABP1 and CRABP2 with K_d values of 4.7 nM and 7.6 nM, respectively. The unbound atRA K_m values for 4-OH-atRA formation by CYP26A1 were 4.7 ± 0.8 nM with atRA, 6.8 ± 1.7 nM with holo-CRABP1 and 6.1 ± 2.7 nM with holo-CRABP2 as a substrate. In comparison, the apparent k_cat value was about 30% lower (0.71 ± 0.07 min⁻¹ for holo-CRABP1 and 0.75 ± 0.09 min⁻¹ for holo-CRABP2) in the presence of CRABPs than with free atRA (1.07 ± 0.08 min⁻¹). In addition, increasing concentrations in apo-CRABPs decreased the 4-OH-atRA formation rates by CYP26A1. Kinetic analyses suggest that apo-CRABP1 and apo-CRABP2 inhibit CYP26A1 (K_i = 0.39 nM and 0.53 nM, respectively) and holo-CRABPs channel atRA for metabolism by CYP26A1. These data suggest that CRABPs play a critical role in modulating atRA metabolism and cellular atRA concentrations.

Isotretinoin Induced Hyperlipidemia and Impact of Leptin Gene rs 7799039 Polymorphism in Safety of Acne Patients

Background

Acne vulgaris (AV) is a chronic inflammatory disease that affects the pilosebaceous unit. Leptin (LEP) gene polymorphisms is associated with higher risk of multiple disorders. Insulin-like growth factor-1 (IGF-1) exerts comedogenic effect by stimulating the sebaceous glands. Isotretinoin is an effective oral therapy for AV with many side effects including hyperlipidemia and increased serum levels of liver enzymes.

Purpose

To evaluate the impact of LEP gene rs7799039 polymorphism in acne patients' clinical response lipid profile and liver enzymes following 6 months oral isotretinoin therapy in Egyptian AV patients.

Methods

One hundred eligible AV patients received 0.5 mg/kg oral isotretinoin for 6 months. Patients' demographics and clinical data were obtained. Body mass index (BMI), lipid profile, liver enzymes and IGF-1 were measured at baseline and after 6 months of therapy. Genotyping was done for LEP gene rs 7799039.

Results

Six month administration of oral isotretinoin in Egyptian AV patients is associated with significantly elevated aspartate transaminase (AST) in CC and AC genotypes (P<0.001). Significant alanine aminotransferase (ALT) elevation was observed in CC, AC and AA genotypes (P <0.001, 0.004, 0.002, respectively). Total cholesterol (TC), triglycerides (TG) and low density lipoprotein (LDL) were elevated significantly P<0.001) in the three genotypes. IGF-1 was decreased significantly in CC and AC genotypes (P<0.001). CC genotype is associated with highest response (P<0.001).

Conclusion

LEP rs7799039 gene had an impact on the clinical response, lipid profile and liver enzymes in AV patients treated with oral isotretinoin. LEP rs7799039 CC genotype is predicted to be the treatment candidate for 6 month oral isotretinoin.

Specific non-genetic IAP-based protein erasers (SNIPERs) as a potential therapeutic strategy

As a newly emerged technology, PROTAC (proteolysis targeting chimera) is a promising therapeutic strategy for varieties of diseases. Unlike small molecule inhibitors, PROTACs catalytically induce target proteins degradation, including currently "undruggable" target proteins. In addition, PROTACs can be a potentially successful strategy to overcome drug resistance. IAPs can inhibit apoptosis by inhibiting caspase, and also exhibits the activity of E3 ubiquitin ligase. Specific and nongenetic IAP-based protein erasers (SNIPERs) are hybrid molecules that designed based on IAPs, and used to degrade the target proteins closely associated with diseases. Their structures consist of three parts, including target protein ligand, E3 ligase ligand and the linker between them. SNIPERs (PROTACs) degrade diseases-associated proteins through human inherent ubiquitin-proteasome system. So far, many SNIPERs have been developed to treat diseases that difficult to handle by traditional methods, such as radiotherapy, chemotherapy and small molecule inhibitors, and showed promising prospects in application. In this paper, the recent advances of SNIPERs were summarized, and the chances and challenges associated with this area were also highlighted.

Evaluation of oral isotretinoin effects on hearing system in patients with acne vulgaris: Reversible or not?

Systemic isotretinoin is commonly used for severe acne treatment. It has many side effects, one of these is about hearing system, which has rarely been reported, also previous studies reported contradictory results about systemic isotretinoin and its association with hearing system. In this study, we aimed to investigate whether systemic isotretinoin affected on the hearing system or not. The study included 32 acne vulgaris patients (64 ears) who treated with oral isotretinoin 0.5 mg/kg body weight for at least 4 months and audiometric tests including pure-tone, speech, bilateral acoustic reflexes, and tympanometric measurements were performed at baseline, in the first week, in the first month, and third month of treatment, and sixth month after treatment. Audiometric tests were performed for right and left ears separately. A significant difference was found in the pure-tone thresholds (before treatment, first week, first month, third month of treatment, and sixth month after treatment) for the both ears at 8000 Hz (P < .001) and a significant decrease in the sixth month post-treatment pure-tone thresholds compared to pre-treatment thresholds at 8000 Hz. Additionally, a statistically significant increase was observed in serum LDL and triglyceride levels in the third month of treatment and a significant decrease at the sixth month after treatment (P < .001). Systemic isotretinoin caused bilateral hearing threshold changes in acne patients during the therapy but the changes improved after discontinuation. Therefore, our findings may provide safety using for dermatologists about hearing effects of isotretinoin, which is quite effective on severe acne.

Washout Period for Pregnancy Post Isotretinoin Therapy

Introduction and Background:

Isotretinoin is an oral medication used for the treatment of severe acne unresponsive to other medications. This drug is teratogenic and should be prescribed with appropriate caution in selected group of patients. The washout period for pregnancy post isotrenoin therapy has always been a topic of controversy. Several guidelines have recommended a wash out period of one month if pregnancy is planned in a patient being administered with the drug.

Objective:

This article discusses the available evidence for different recommended wash out periods and addresses important clinical questions that arise.

Methods:

Pubmed research was carried out to collect relevant data using the keywords isotretinoin, pregnancy, contraception, pharmacokinetics and guidelines.

Conclusion:

Our research based on the published data concludes that a wash out period of 35 days post isotretinoin therapy is adequate in routine clinical practice.

The Safe Management of Acne Vulgaris in Lupus Erythematosus: A Systematic Review with Evidence-Based Treatment Recommendations

BACKGROUND

To date, there have been no studies that have specifically investigated which medications can and cannot be safely used to treat acne vulgaris in patients who have lupus erythematosus (LE). These patients require a highly individualized treatment approach, as the use of certain acne medications may exacerbate LE symptomology, such as photosensitivity and hypercoagulability.

OBJECTIVE

In this systematic review, we examine safety outcomes associated with commonly prescribed oral acne medications, specifically in the context of LE.

METHODS

A literature search, conducted on PubMed/MEDLINE, revealed 146 studies, of which 13 met the criteria. We assigned a level of evidence to each study and sought to determine evidence-based recommendations for each class of drug; each recommendation was then assigned a corresponding grade.

RESULTS

There were very few high-quality studies available on this topic. Although we determined recommendations based on the existing literature, the grading was occasionally unfavorable due to the low-quality nature of the evidence supporting the recommendation. However, our recommendation against the use of combined oral contraceptive pills and in favor of spironolactone for the treatment of acne, in the setting of LE, received a satisfactory grading (grade A).

CONCLUSION

While no definitive recommendations for the treatment of acne in LE can be made based on the existing quality and quantity of studies available, this article aims to provide a comprehensive overview and analysis of oral acne medication safety in patients with LE, while emphasizing the immense need for higher quality studies and distinct acne treatment guidelines for this vulnerable patient population.

The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates

Vitamin A is an essential nutrient necessary for numerous basic physiological functions, including reproduction and development, immune cell differentiation and communication, as well as the perception of light. To evade the dire consequences of vitamin A deficiency, vertebrates have evolved specialized metabolic pathways that enable the absorption, transport, and storage of vitamin A acquired from dietary sources as preformed retinoids or provitamin A carotenoids. This evolutionary advantage requires a complex interplay between numerous specialized retinoid-transport proteins, receptors, and enzymes. Recent advances in molecular and structural biology resulted in a rapid expansion of our understanding of these processes at the molecular level. This progress opened new avenues for the therapeutic manipulation of retinoid homeostasis. In this review, we summarize current research related to the biochemistry of carotenoid and retinoid-processing proteins with special emphasis on the structural aspects of their physiological actions. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Epidermolytic hyperkeratosis: clinical update

Epidermolytic hyperkeratosis (EHK), earlier termed as bullous congenital ichthyosiform erythroderma is a skin disorder characterized as an autosomal dominant and rare disorder which has been observed to affect 1 in over 200,000 infants as a consequence of a significant mutation in the genes responsible for the keratin proteins, mostly keratin 1 and 10. The features present at birth include erythema and blistering. In adults, the hallmarks include hyperkeratosis, erosions, and blisters. The major symptoms including xerosis, pruritus, and painful fissuring lead not only to cosmetic problems but also stress, inferiority complex and other psychological conditions. While clinical inspection followed by confirmatory tests including histopathology and electron microscopic assessment is used for diagnosis, treatment modalities can be further improved for better diagnosis. This article reviews subtypes of ichthyosis, with a focus on EHK, genetics behind the disease, recently reported mutations, the existing diagnostics and treatments for the same and potential of new modalities in diagnosis/treatment.

Regulation of Hepatitis C Virus Infection by Cellular Retinoic Acid Binding Proteins through the Modulation of Lipid Droplet Abundance

Retinoid (vitamin A) is an essential diet constituent that governs a broad range of biological processes. Its biologically active metabolite, all-trans retinoic acid (ATRA), exhibits a potent antiviral property by enhancing both innate and adaptive antiviral immunity against a variety of viral pathogens, such as, but not limited to, HIV, respiratory syncytial virus (RSV), herpes simplex virus (HSV), and measles. Even though the hepatocyte is highly enriched with retinoid and its metabolite ATRA, it supports the establishment of efficient hepatitis C virus (HCV) replication. Here, we demonstrate the hepatocyte-specific cell-intrinsic mechanism by which ATRA exerts either a proviral or antiviral effect, depending on how it engages cellular retinoic acid binding proteins (CRABPs). We found that the engagement of CRABP1 by ATRA potently supported viral infection by promoting the accumulation of lipid droplets (LDs), which robustly enhanced the formation of a replication complex on the LD-associated endoplasmic reticulum (ER) membrane. In contrast, ATRA binding to CRABP2 potently inhibited HCV via suppression of LD accumulation. However, this antiviral effect of CRABP2 was abrogated due to the functional and quantitative predominance of CRABP1 in the hepatocytes. In summary, our study demonstrates that CRABPs serve as an on-off switch that modulates the efficiency of the HCV life cycle and elucidates how HCV evades the antiviral properties of ATRA via the exploitation of CRABP1 functionality.IMPORTANCE ATRA, a biologically active metabolite of vitamin A, exerts pleiotropic biological effects, including the activation of both innate and adaptive immunity, thereby serving as a potent antimicrobial compound against numerous viral pathogens. Despite the enrichment of hepatocytes with vitamin A, HCV still establishes an efficient viral life cycle. Here, we discovered that the hepatocellular response to ATRA creates either a proviral or an antiviral environment depending on its engagement with CRABP1 or -2, respectively. CRABP1 supports the robust replication of HCV, while CRABP2 potently inhibits the efficiency of viral replication. Our biochemical, genetic, and microscopic analyses reveal that the pro- and antiviral effects of CRABPs are mediated by modulation of LD abundance, where HCV establishes the platform for viral replication and assembly on the LD-associated ER membrane. This study uncovered a cell-intrinsic mechanism by which HCV exploits the proviral function of CRABP1 to establish an efficient viral life cycle.

Chemical Protein Degradation Approach and its Application to Epigenetic Targets

In addition to traditional drugs, such as enzyme inhibitors, receptor agonists/antagonists, and protein-protein interaction inhibitors as well as genetic technology, such as RNA interference and the CRISPR/Cas9 system, protein knockdown approaches using proteolysis-targeting chimeras (PROTACs) have attracted much attention. PROTACs, which induce selective degradation of their target protein via the ubiquitin-proteasome system, are useful for the down-regulation of various proteins, including disease-related proteins and epigenetic proteins. Recent reports have shown that chemical protein knockdown is possible not only in cells, but also in vivo and this approach is expected to be used as the therapeutic strategy for several diseases. Thus, this approach may be a significant technique to complement traditional drugs and genetic ablation and will be more widely used for drug discovery and chemical biology studies in the future. In this personal account, a history of chemical protein knockdown is introduced, and its features, recent progress in the epigenetics field, and future outlooks are discussed.

Identification of Apolipoprotein A-I as a Retinoic Acid-binding Protein in the Eye

All-trans-retinoic acid may be an important molecular signal in the postnatal control of eye size. The goal of this study was to identify retinoic acid-binding proteins secreted by the choroid and sclera during visually guided ocular growth. Following photoaffinity labeling with all-trans-[11,12-(3)H]retinoic acid, the most abundant labeled protein detected in the conditioned medium of choroid or sclera had an apparent Mr of 27,000 Da. Following purification and mass spectrometry, the Mr 27,000 band was identified as apolipoprotein A-I. Affinity capture of the radioactive Mr 27,000 band by anti-chick apolipoprotein A-I antibodies confirmed its identity as apolipoprotein A-I. Photoaffinity labeling and fluorescence quenching experiments demonstrated that binding of retinoic acid to apolipoprotein A-I is 1) concentration-dependent, 2) selective for all-trans-retinoic acid, and 3) requires the presence of apolipoprotein A-I-associated lipids for retinoid binding. Expression of apolipoprotein A-I mRNA and protein synthesis were markedly up-regulated in choroids of chick eyes during the recovery from induced myopia, and apolipoprotein A-I mRNA was significantly increased in choroids following retinoic acid treatment. Together, these data suggest that apolipoprotein A-I may participate in a regulatory feedback mechanism with retinoic acid to control the action of retinoic acid on ocular targets during postnatal ocular growth.

Cellular Retinoic Acid Binding Proteins: Genomic and Non-genomic Functions and their Regulation

Cellular retinoic acid binding proteins (CRABPs) are high-affinity retinoic acid (RA) binding proteins that mainly reside in the cytoplasm. In mammals, this family has two members, CRABPI and II, both highly conserved during evolution. The two proteins share a very similar structure that is characteristic of a "β-clam" motif built up from10-strands. The proteins are encoded by two different genes that share a very similar genomic structure. CRABPI is widely distributed and CRABPII has restricted expression in only certain tissues. The CrabpI gene is driven by a housekeeping promoter, but can be regulated by numerous factors, including thyroid hormones and RA, which engage a specific chromatin-remodeling complex containing either TRAP220 or RIP140 as coactivator and corepressor, respectively. The chromatin-remodeling complex binds the DR4 element in the CrabpI gene promoter to activate or repress this gene in different cellular backgrounds. The CrabpII gene promoter contains a TATA-box and is rapidly activated by RA through an RA response element. Biochemical and cell culture studies carried out in vitro show the two proteins have distinct biological functions. CRABPII mainly functions to deliver RA to the nuclear RA receptors for gene regulation, although recent studies suggest that CRABPII may also be involved in other cellular events, such as RNA stability. In contrast, biochemical and cell culture studies suggest that CRABPI functions mainly in the cytoplasm to modulate intracellular RA availability/concentration and to engage other signaling components such as ERK activity. However, these functional studies remain inconclusive because knocking out one or both genes in mice does not produce definitive phenotypes. Further studies are needed to unambiguously decipher the exact physiological activities of these two proteins.

Enzymology of retinoic acid biosynthesis and degradation

All-trans-retinoic acid is a biologically active derivative of vitamin A that regulates numerous physiological processes. The concentration of retinoic acid in the cells is tightly regulated, but the exact mechanisms responsible for this regulation are not completely understood, largely because the enzymes involved in the biosynthesis of retinoic acid have not been fully defined. Recent studies using in vitro and in vivo models suggest that several members of the short-chain dehydrogenase/reductase superfamily of proteins are essential for retinoic acid biosynthesis and the maintenance of retinoic acid homeostasis. However, the exact roles of some of these recently identified enzymes are yet to be characterized. The properties of the known contributors to retinoid metabolism have now been better defined and allow for more detailed understanding of their interactions with retinoid-binding proteins and other retinoid enzymes. At the same time, further studies are needed to clarify the interactions between the cytoplasmic and membrane-bound proteins involved in the processing of hydrophobic retinoid metabolites. This review summarizes current knowledge about the roles of various biosynthetic and catabolic enzymes in the regulation of retinoic acid homeostasis and outlines the remaining questions in the field.

Duplicated crabp1 and crabp2 genes in medaka (Oryzias latipes): gene structure, phylogenetic relationship and tissue-specific distribution of transcripts

Here we report the genomic organization of duplicated cellular retinoic acid-binding protein genes, crabp1 and crabp2, in medaka (Japanese ricefish; Oryzias latipes), the phylogenetic relationship of medaka Crabp1a, Crabp1b, Crabp2a and Crabp2b with other Crabp/CRABP sequences from teleosts/tetrapods, and the tissue-specific distribution of crabp1a, crabp1b, crabp2a, and crabp2b transcripts in adult medaka. The duplicated medaka crabp1 and crabp2 genes contain four exons separated by three introns, which encode polypeptides of 137 and 142 amino acids, respectively. Sequence alignment revealed that medaka Crabp sequences share highest sequence identity and similarity with their orthologs from vertebrates. Phylogenetic analysis confirmed the orthology of the medaka Crabps as they form a distinct clade with their orthologous polypeptides from vertebrates. Conserved gene synteny was evident between the duplicated crabp1 and crabp2 genes from medaka, and CRABP1 and CRABP2 genes from human, which provides compelling evidence that the identified duplicated crabp1 and crabp2 genes from medaka most likely arose owing to teleost-specific whole-genome duplication. The tissue-specific distribution of zebrafish (Danio rerio) and medaka crabp1a, crabp1b, crabp2a, and crabp2b gene transcripts suggests acquisition of new function by these genes in medaka, which may explain potential evolutionary processes that led to the retention of sister duplicates of crabp1 and crabp2 genes in the medaka genome.

Cellular retinoic acid binding protein I mediates rapid non-canonical activation of ERK1/2 by all-trans retinoic acid

All-trans retinoic acid (atRA), one of the active ingredients of vitamin A, exerts canonical activities to regulate gene expression mediated by nuclear RA receptors (RARs). AtRA could also elicit certain non-canonical activities including, mostly, rapid activation of extracellular signal regulated kinase 1/2 (ERK1/2); but the mechanism was unclear. In this study, we have found that cellular retinoic acid binding protein I (CRABPI) mediates the non-canonical, RAR- and membrane signal-independent activation of ERK1/2 by atRA in various cellular backgrounds. In the context of embryonic stem cells (ESCs), atRA/CRABPI-dependent ERK1/2 activation rapidly affects ESC cell cycle, specifically to expand the G1 phase. This is mediated by ERK stimulation resulting in dephosphorylation of nuclear p27, which elevates nuclear p27 protein levels to block G1 progression to S phase. This is the first study to identify CRABPI as the mediator for non-canonical activation of ERK1/2 by atRA, and demonstrate a new functional role for CRABPI in modulating ESC cell cycle progression.

Double protein knockdown of cIAP1 and CRABP-II using a hybrid molecule consisting of ATRA and IAPs antagonist

Protein knockdown can be achieved by the use of a small molecule that possesses affinity for both the target protein and ubiquitin ligase. We have designed such a degradation-inducing molecule targeting cIAP1 and CRABP-II, which are involved in proliferation of several cancer cell lines and in neuroblastoma growth, respectively. As a CRABP-II-recognizing moiety, all-trans retinoic acid (ATRA, 3), a physiological ligand of CRABP, was chosen. As a cIAP1-recognizing moiety, MV1 (5), which is a cIAP1/cIAP2/XIAP pan-ligand, was chosen. Although cIAP1 itself possesses ubiquitin ligase activity, we expected that its decomposition would be efficiently mediated by related molecules, including cIAP2 and XIAP, which also possess ubiquitin ligase activity. The designed degradation inducer 6, in which ATRA (3) and MV1 (5) moieties are connected via a linker, was synthesized and confirmed to induce efficient degradation of both cIAP1 and CRABP-II. It showed potently inhibited the proliferation of IMR32 cells.

Design, synthesis and biological evaluation of nuclear receptor-degradation inducers

Compounds that regulate the function(s) of nuclear receptors (NRs) are useful for biological studies and as candidate therapeutic agents. Most such compounds are agonists or antagonists. On the other hand, we have developed specific protein degradation inducers, which we designated as SNIPERs (Specific and Nongenetic IAPs-dependent Protein ERasers), for selective degradation of target proteins. SNIPERs are hybrid molecules consisting of an appropriate ligand for the protein of interest, coupled to a ligand for inhibitor of apoptosis proteins (IAPs), which target the bound protein for polyubiquitination and proteasomal degradation. We considered that protein knockdown with SNIPERs would be a promising alternative approach for modulating NR function. In this study, we designed and synthesized degradation inducers targeting retinoic acid receptor (RAR), estrogen receptor (ER), and androgen receptor (AR). These newly synthesized RAR, ER, and AR SNIPERs, 9, 11, and 13, respectively, were confirmed to significantly reduce the levels of the corresponding NRs in live cells.

Development of target protein-selective degradation inducer for protein knockdown

Our previous technique for inducing selective degradation of target proteins with ester-type SNIPER (Specific and Nongenetic Inhibitor-of-apoptosis-proteins (IAPs)-dependent Protein ERaser) degrades both the target proteins and IAPs. Here, we designed a small-molecular amide-type SNIPER to overcome this issue. As proof of concept, we synthesized and biologically evaluated an amide-type SNIPER which induces selective degradation of cellular retinoic acid binding protein II (CRABP-II), but not IAPs. Such small-molecular, amide-type SNIPERs that induce target protein-selective degradation without affecting IAPs should be effective tools to study the biological roles of target proteins in living cells.

The use of isotretinoin in acne

Systemic isotretinoin remains the most efficacious treatment for severe acne as well as many cases of more moderate disease that are unresponsive to other treatment modalities. The current chapter outlines the mechanisms behind the excellent efficacy, describes how to optimize treatment, reviews the recommended guidelines for monitoring and summarizes adverse effects.

LIF removal increases CRABPI and CRABPII transcripts in embryonic stem cells cultured in retinol or 4-oxoretinol

Murine embryonic stem (ES) cells cultured without leukemia inhibitory factor (LIF) or with retinoids differentiate and concomitantly metabolize retinol (vitamin A) to 4-oxoretinol. Our objective was to examine the effects of retinol or 4-oxoretinol on cellular retinoic acid binding protein (CRABP) I and II mRNA levels and retinol metabolism. ES cells were cultured with or without LIF, and with various doses of all-trans-retinol, all-trans-4-oxoretinol, or all-trans-retinoic acid (RA). In ES cells treated with retinol or 4-oxoretinol in the absence of LIF the CRABP-I (Crabp1, NM_013496; GI:7304974) and CRABP-II (Crabp2, NM_007759; GI:33469074) mRNA levels at 72h were 66+/-4 and 413+/-6 fold higher, respectively, than the levels in control ES cells cultured without retinoids and in the presence of LIF. The increase in CRABPI mRNA occurred through an increase in CRABPI gene transcription. CRABPI protein was also increased by >50-fold in cells treated with retinol in the absence of LIF. However [(3)H]4-oxoretinol does not bind to murine CRABPI or CRABPII. CYP26A1 mRNA levels and [(3)H]4-oxoretinol production from [(3)H]retinol increased in cells cultured without LIF and with exogenous retinoids. The enormous increases in CRABPI and II transcripts ( approximately 60 and 400-fold, respectively) in the absence of LIF may regulate aspects of the ES cell differentiation program in response to retinol.

Transporter-to-trap conversion: a disulfide bond formation in cellular retinoic acid binding protein I mutant triggered by retinoic acid binding irreversibly locks the ligand inside the protein

Transport proteins must bind their ligands reversibly to enable release at the point of delivery, while irreversible binding is usually associated with the extreme cases of ligand sequestration. Protein conformational dynamics is an important modulator of binding kinetics, as increased flexibility in the regions adjacent to the binding site may facilitate both association and dissociation processes. Ligand entry to, and exit from, the internal binding site of the cellular retinoic acid binding protein I (CRABP I) occurs via a flexible portal region, which functions as a dynamic aperture. We designed and expressed a CRABP I mutant (A35C/T57C), in which a small-scale conformational switch caused by the ligand binding event triggers formation of a disulfide bond in the portal region, thereby arresting structural fluctuations and effectively locking the ligand inside the binding cavity. At the same time, no formation of the disulfide bond is observed in the apo form of the mutant, and most characteristics of the mutant, including protein stability, are very similar to those of the wild-type protein in the absence of retinoic acid. The mutation does not alter the kinetics of retinoic acid binding to the protein, although the disulfide formation makes the binding effectively irreversible, as suggested by the absence of retinoic acid transfer from the holo form of the mutant to lipid vesicles in the absence of a reducing agent. Taken together, these data suggest that the disulfide bond formation in the portal region arrests large-scale structural fluctuations, which are required for retinoic acid release from the protein. The unique properties of the CRABP I mutant described in this work can be used to inspire and guide a design of nanodevices for multiple tasks ranging from sequestering small-molecule toxins in both tissue and circulation to nutrient deprivation of pathogens.

Retinoic acid metabolism blocking agents (RAMBAs): a new paradigm in the treatment of hyperkeratotic disorders

Synthetic vitamin A derivatives, retinoids,have long been the mainstay of treatment for several disorders of keratinization, notably the ichthyoses and severe acne. Some forms of psoriasis also respond well. Their considerable power comes at a price. They have dose-limiting side effects and can be highly teratogenic, limiting their use in women of childbearing age.Thus, retinoids are used less often than their potential would warrant. However, the recent development of compounds that block the catabolism of endogenous vitamin A, called Retinioic Acid Metabolism Blocking Agents or RAMBAs, offers new possibilities. With these drugs, retinoid effects with less side effects and a reduction of the post-treatment teratogenicity period due to their favourable pharmacokinetic profile might be expected. In this review, we discuss how retinoids work, how they are metabolized and how RAMBAs influence this process. We also review the presently available data from clinical trials with RAMBAs.

[Retinoid metabolism and cancer]

Retinoids play important roles in cell differentiation and apoptosis, notably in epithelial tissues. Their utility in cancer therapy has been demonstrated in specific cancer types. Use of retinoic acid (RA) in the treatment of acute promyelocytic leukemia was the first successful example of retinoid-based differentiation therapy. RA has since been evaluated for treatment of other cancers, revealing variable effectiveness. The observation that expression of enzymes involved in RA biosynthesis is suppressed during tumorigenesis suggests that intra-tumor depletion in RA levels may contribute to tumor development and argues for the use of retinoids in cancer treatment. However, the induction of RA-inactivating enzymes is one of the mechanisms that may limit the efficacy of retinoid therapy and contribute to acquired resistance to RA treatment, suggesting that retinoic acid metabolism blocking agents may be effective agents in differentiation therapy.

Pharmacologic Modulation of Sebaceous Gland Activity: Mechanisms and Clinical Applications

Acne vulgaris is a common skin condition seen by physicians. It primarily affects adolescents, but can continue into adulthood. A key factor in the pathogenesis of acne is sebum production. Typical therapy includes combinations of topical retinoids and antimicrobials for mild acne, with the addition of oral antibiotics for moderate to severe disease. In the most recalcitrant cases or for nodulocystic acne, oral retinoids are indicated. In women who fail to respond to conventional treatment, hormonal therapy is often used adjunctively. Only isotretinoin and hormonal therapy improve acne via their action on the sebaceous glands. This article focuses on the mechanisms by which these treatment modalities act on the sebaceous glands and their clinical use in the practice of medicine.

13-cis Retinoic acid induces apoptosis and cell cycle arrest in human SEB-1 sebocytes

Isotretinoin (13-cis retinoic acid (13-cis RA)) is the most potent inhibitor of sebum production, a key component in the pathophysiology of acne, yet its mechanism of action remains largely unknown. The effects of 13-cis RA, 9-cis retinoic acid (9-cis RA), and all-trans retinoic acid (ATRA) on cell proliferation, apoptosis, and cell cycle proteins were examined in SEB-1 sebocytes and keratinocytes. 13-cis RA causes significant dose-dependent and time-dependent decreases in viable SEB-1 sebocytes. A portion of this decrease can be attributed to cell cycle arrest as evidenced by decreased DNA synthesis, increased p21 protein expression, and decreased cyclin D1. Although not previously demonstrated in sebocytes, we report that 13-cis RA induces apoptosis in SEB-1 sebocytes as shown by increased Annexin V-FITC staining, increased TUNEL staining, and increased cleaved caspase 3 protein. Furthermore, the ability of 13-cis RA to induce apoptosis cannot be recapitulated by 9-cis RA or ATRA, and it is not inhibited by the presence of a retinoid acid receptor (RAR) pan-antagonist AGN 193109. Taken together these data indicate that 13-cis RA causes cell cycle arrest and induces apoptosis in SEB-1 sebocytes by a RAR-independent mechanism, which contributes to its sebosuppressive effect and the resolution of acne.

13-cis retinoic acid and isomerisation in paediatric oncology--is changing shape the key to success?

Retinoic acid isomers have been used with some success as chemotherapeutic agents, most recently with 13-cis retinoic acid showing impressive clinical efficacy in the paediatric malignancy neuroblastoma. The aim of this commentary is to review the evidence that 13-cis retinoic acid is a pro-drug, and consider the implications of retinoid metabolism and isomerisation for the further development of retinoic acid for cancer therapy. The low binding affinity of 13-cis retinoic acid for retinoic acid receptors, low activity in gene expression assays and the accumulation of the all-trans isomer in cells treated with 13-cis retinoic acid, coupled with the more-favourable pharmacokinetic profile of 13-cis retinoic acid compared to other isomers, suggest that intracellular isomerisation to all-trans retinoic acid is the key process underlying the biological activity of 13-cis retinoic acid. Intracellular metabolism of all-trans retinoic acid by a positive auto-regulatory loop may result in clinical resistance to retinoic acid. Agents that block or reduce the metabolism of all-trans retinoic acid are therefore attractive targets for drug development. Devising strategies to deliver 13-cis retinoic acid to tumour cells and facilitate the intracellular isomerisation of 13-cis retinoic acid, while limiting metabolism of all-trans retinoic acid, may have a major impact on the efficacy of 13-cis retinoic acid in paediatric oncology.

Increasing the intracellular availability of all-trans retinoic acid in neuroblastoma cells

Recent data indicate that isomerisation to all-trans retinoic acid (ATRA) is the key mechanism underlying the favourable clinical properties of 13-cis retinoic acid (13cisRA) in the treatment of neuroblastoma. Retinoic acid (RA) metabolism is thought to contribute to resistance, and strategies to modulate this may increase the clinical efficacy of 13cisRA. The aim of this study was to test the hypothesis that retinoids, such as acitretin, which bind preferentially to cellular retinoic acid binding proteins (CRABPs), or specific inhibitors of the RA hydroxylase CYP26, such as R116010, can increase the intracellular availability of ATRA. Incubation of SH-SY5Y cells with acitretin (50 μM) or R116010 (1 or 10 μM) in combination with either 10 μM ATRA or 13cisRA induced a selective increase in intracellular levels of ATRA, while 13cisRA levels were unaffected. CRABP was induced in SH-SY5Y cells in response to RA. In contrast, acitretin had no significant effect on intracellular retinoid concentrations in those neuroblastoma cell lines that showed little or no induction of CRABP after RA treatment. Both ATRA and 13cisRA dramatically induced the expression of CYP26A1 in SH-SY5Y cells, and treatment with R116010, but not acitretin, potentiated the RA-induced expression of a reporter gene and CYP26A1. The response of neuroblastoma cells to R116010 was consistent with inhibition of CYP26, indicating that inhibition of RA metabolism may further optimise retinoid treatment in neuroblastoma.

Differential regulation of Cu, Zn- and Mn-superoxide dismutases by retinoic acid in normal and psoriatic human fibroblasts

Superoxide dismutases' (SODs) expression is altered in several diseases including Alzheimer, atherosclerosis, cancer and psoriasis. Previously, we reported a marked increase in Mn-SOD and Cu,Zn-SOD functional activity in human dermal psoriatic fibroblasts. As retinoic acid (RA) has been used in the treatment of psoriasis and a mechanism for its beneficial effects is not understood, we investigated the effects of RA on SOD mRNA and protein expression levels in human normal and psoriatic fibroblasts. Prior to RA exposure, Cu,Zn-SOD protein and mRNA levels were similar in normal compared to psoriatic fibroblasts while Mn-SOD protein and mRNA levels were increased in psoriatic cells. However, in contrast to normal fibroblasts, exposure of psoriatic fibroblasts to 1 microM RA down-regulated Mn-SOD mRNA, and also decreased Mn-SOD activity by approximately 80% with no change in Mn-SOD protein levels. In contrast, Cu,Zn-SOD protein and enzymatic activity were modestly reduced by RA treatment in both normal and psoriatic fibroblasts. Furthermore, RA treatment of psoriatic fibroblasts also caused a decrease in Cu,Zn-SOD steady-state mRNA levels. These results indicate that RA can serve as a regulatory agent to down-regulate the steady-state levels of both Mn-SOD and Cu,Zn-SOD in psoriatic cells. These findings offer a new model for the antiinflammatory activity of RA when used in the treatment of psoriasis.

A cellular retinoic acid-binding protein from zebrafish (Danio rerio): cDNA sequence, phylogenetic analysis, mRNA expression, and gene linkage mapping

We report the sequence of a cDNA clone coding for a cellular retinoic acid-binding protein (CRABP) in zebrafish. The encoded polypeptide is 142 amino acids in length with an estimated molecular mass of 15.8 kDa and a calculated isoelectric point of 5.2. The zebrafish CRABP exhibits highest sequence identity to the pufferfish CRABPIIa (83%) and CRABPIIb (79%), and human CRABPII (74%) than to any other member of the intracellular lipid-binding protein (ILBP) family. A phylogenetic tree for different members of the ILBP multigene family including fatty acid-binding proteins (FABPs), cellular retinol-binding proteins (CRBPs) and CRABPs shows that the cloned zebrafish cDNA encodes a protein that clusters with CRABPs from other species and not with CRBPs and FABPs. Reverse-transcription polymerase chain reactions (RT-PCR), using oligonucleotide primers specific to the zebrafish CRABP cDNA made from total RNA of embryos collected at various developmental stages, did not detect the CRABP mRNA until 12 h post-fertilization. In adult zebrafish, CRABP mRNA was detected by RT-PCR in total RNA extracted from muscle, testes and skin, barely detectable in heart, ovary and brain and undetectable in liver, kidney and intestine. Quantitative RT-PCR (qRT-PCR) revealed a similar tissue-specific distribution for zebrafish CRABP mRNA with highest levels of CRABP mRNA in muscle followed by testes, skin, ovary and much lower levels in heart. Radiation hybrid mapping assigned the CRABP gene to linkage group 16 in the zebrafish genome. Comparison of the mapped zebrafish CRABP and human CRABPII genes revealed that zebrafish linkage group 16 has a syntenic relationship with human chromosome 1. Based on phylogenetic analysis and the syntenic relationship to the CRABPII gene in human, the zebrafish cDNA clone appears to code for a type II CRABP.

Homozygous deletion of the CRABPI gene in AB1 embryonic stem cells results in increased CRABPII gene expression and decreased intracellular retinoic acid concentration

The cellular retinoic acid (RA) binding proteins I and II (CRABPI and CRABPII), intracellular proteins which bind retinoic acid with high affinity, are involved in the actions of RA, though their exact roles are not fully understood. We have generated several genetically engineered AB1 cell lines in which both alleles of the CRABPI gene have been deleted by homologous recombination. We have used these CRABPI knockout cell lines to examine the consequences of functional loss of CRABPI on RA-induced gene expression and RA metabolism in the murine embryonic stem cell line, AB1, which undergoes differentiation in response to RA. Complete lack of CRABPI results in decreased intracellular [3H]RA concentrations under conditions in which external concentrations of [3H]RA are low (1-10nM) and in an altered distribution of [3H] polar metabolites of [3H]RA in the cell and in the medium. Fewer [3H] polar metabolites are retained within the CRABPI(-/-) cells compared to the wild-type cells. These data suggest that CRABPI functions to regulate the intracellular concentrations of retinoic acid and to maintain high levels of oxidized retinoic acid metabolites such as 4-oxoretinoic acid within cells.

Intracellular lipid binding proteins and nuclear receptors involved in branched-chain fatty acid signaling

Branched-chain fatty acids are potent regulators of gene expression. Among them are the vitamin A-derived retinoic acids, which are involved in cell growth and differentiation, and the chlorophyll-derived phytol metabolites such as phytanic and pristanic acids, which affect catabolic lipid metabolism. Gene expression regulated by these signaling molecules is mediated by two protein families. These are, on the one hand, the intracellular lipid binding proteins, i.e. cellular retinoic acid binding protein and liver-type fatty acid binding protein, which are responsible for ligand-transport to the nucleus. On the other hand are the ligand-activated nuclear receptors, i.e. the retinoic acid receptors for retinoic acids and the peroxisome proliferator-activated receptors for the phytol metabolites. In this review, we discuss the cross-talk between the two protein families and how this cross-talk contributes to targeted signaling with branched-chain fatty acids.

Development of a retinoic acid receptor-binding assay with rainbow trout tissue: characterization of retinoic acid binding, receptor tissue distribution, and developmental changes

Retinoic acid (RA) regulates the transcription of various genes required for several essential functions in vertebrates through binding to two classes of nuclear receptors, the retinoic acid receptors (RAR) and retinoid X receptors (RXR). We investigated nuclear RA binding in tissues from rainbow trout using the radiolabeled all-trans and 9-cis isomers of RA. Specific binding (indicative of receptor binding) of both all-trans- and 9-cis-RA was found in all tissues tested, including the adult trout ovary, testis, gill, liver, kidney, blood, white muscle, and heart. The kinetics and absolute amount of RA binding were dependent on both the tissue and the isomer of RA used. All-trans-RA bound with high affinity (K(d) approximately 1.0-3.9 nM), and low capacity (B(max) approximately 75-484 fmol RA/mg protein), while 9-cis-RA bound with lower affinity (K(d) approximately 7-56 nM), but with a greater capacity (B(max) approximately 214-1076 fmol RA/mg protein). The B(max) results were used to estimate RAR and RXR levels and revealed that the gill possesses primarily RARs while the liver possesses primarily RXRs. The RAR-specific competitor TTNPB was able to effectively displace all-trans-[3H]RA in most tissues, and the RXR-specific competitor AGN 194204 was able to effectively displace 9-cis-[3H]RA. However, TTNPB and AGN 194204 could not displace all of the RA in the kidney and testis, suggesting the existence of another nuclear RA binding protein. Binding of all-trans- and 9-cis-RA was also found in developing trout embryos and fry. Kinetic analysis revealed that RAR levels predominated at the eyed-embryo stage, but decreased 87% by the swim-up fry stage, while RXR levels remained relatively constant over the same time period. These findings suggest that RA and its receptors may play a key role in early trout development. This study has provided a simple and rapid radioligand binding assay that can identify RAR and RXRs in trout tissues.

Physical and functional interactions between cellular retinoic acid binding protein II and the retinoic acid-dependent nuclear complex

Two sorts of proteins bind to, and mediate the developmental and homeostatic effects of, retinoic acid (RA): the RAR and RXR nuclear receptors, which act as ligand-dependent transcriptional regulators, and the cellular RA binding proteins (CRABPI and CRABPII). CRABPs are generally known to be implicated in the synthesis, degradation, and control of steady-state levels of RA, yet previous and recent data have indicated that they could play a role in the control of gene expression. Here we show for the first time that, both in vitro and in vivo, CRABPII is associated with RARalpha and RXRalpha in a ligand-independent manner in mammalian cells (HL-60, NB-4, and MCF-7). In the nucleus, this protein complex binds the RXR-RAR-specific response element of an RA target gene (RARE-DR5). Moreover, in the presence of retinoids that bind both the nuclear receptors and CRABPII, enhancement of transactivation by RXRalpha-RARalpha heterodimers is observed in the presence of CRABPII. Thus, CRABPII appears to be a novel transcriptional regulator involved in RA signaling.

Leukemia cell differentiation: cellular and molecular interactions of retinoids and vitamin D

1. The conventional approach to treatment of acute myeloid leukemia has been the use of chemotherapy, which although being cytotoxic to malignant clones, is also cytodestructive to normal cells. In addition, some leukemia cells develop resistance to chemotherapy and are therefore difficult to eradicate. 2. Differentiation therapy, whereby immature cells are induced to attain a mature phenotype by differentiation agents, has provided an alternative strategy in the treatment of hyperproliferative disorders. This has been highlighted by the use of all-trans retinoic acid (ATRA) in the treatment of acute promyelocytic leukemia (APL). 3. Another differentiation agent, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), directs monocytic maturation of normal and leukemic cells. Cellular studies have revealed that combinations of vitamin D derivatives and retinoids such as ATRA and 9-cis retinoic acid (9-cis RA) exhibit cooperative effects on differentiation in established leukemia cell lines such as HL-60, U937, and NB4. Furthermore, vitamin D compounds, although not able to induce apoptosis when used alone, potentiate apoptosis induced by 9-cis RA in HL-60 cells and differentially regulate the expression of the apoptosis-related gene products bcl-2 and bax. The molecular mechanisms involved in regulating differentiation and apoptosis by these agents are mediated through the interactions of the nuclear receptors for vitamin D (VDR), ATRA (RAR), and 9-cis RA (RXR), which are able to form homo- or heterodimeric complexes and transcriptionally activate or repress target gene expression. 4. There is evidence to suggest that nitric oxide may also play a role in leukemic cell differentiation and that 1,25(OH)2D3 may influence endogenous nitric oxide production either by directly increasing tumor necrosis factor-alpha (TNF-alpha) or through a secondary mediator such as the C-type lectin CD23.

Retinoids and their receptors in skeletal development

The embryonic vertebrate limb serves as an excellent experimental model system in which to study mechanisms that regulate morphogenesis of the skeleton. The appendicular skeleton arises through the process of endochondral ossification, whereby a cartilage template is initially formed and subsequently replaced by bone. One molecule that has a dramatic effect on these processes is the vitamin-A metabolite, retinoic acid (RA). RA functions through a class of nuclear hormone receptors, the retinoic acid receptors (RARs) and retinoid-X-receptors (RXRs), to regulate gene transcription. Experimental evidence from RA teratogenesis suggests that the presence of ligand-activated RARs and/or inappropriate expression of RARs inhibits chondrogenesis. Conversely, genetic analysis has shown that the absence of the receptors can lead to deficiencies in cartilage formation while also promoting chondrogenesis at ectopic sites. Taken together, these studies suggest that the RARs play a fundamental role in the early stages of skeletal development, specifically those involved in the formation of prechondrogenic condensations and their subsequent differentiation into chondroblasts.

Nuclear detection of cellular retinoic acid binding proteins I and II with new antibodies

Apart from the retinoic acid nuclear receptor family, there are two low molecular weight (15 kD) cellular retinoic acid binding proteins, named CRABPI and II. Mouse monoclonal and rabbit polyclonal antibodies were raised against these proteins by using as antigens either synthetic peptides corresponding to amino acid sequences unique to CRABPI or CRABPII, or purified CRABP proteins expressed in E. coli. Antibodies specific for mouse and/or human CRABPI and CRABPII were obtained and characterized by immunocytochemistry and immunoblotting. They allowed the detection not only of CRABPI but also of CRABPII in both nuclear and cytosolic extracts from transfected COS-1 cells, mouse embryos, and various cell lines.

Clinical efficacy and safety comparison of adapalene gel and tretinoin gel in the treatment of acne vulgaris: Europe and U.S. multicenter trials

BACKGROUND

Adapalene is a new chemical entity that exhibits tretinoin-like activities in the terminal differentiation process.

OBJECTIVE

We evaluated a dose range effect of two concentrations of adapalene gel as acne treatment and compared adapalene 0.1% gel with tretinoin 0.025% gel in the treatment of acne patients in two large multicenter studies.

METHODS

Multicenter, investigator-masked, parallel group studies including 89 acne patients in the dose range study and 591 patients in the concurrent controlled studies were conducted.

RESULTS

Adapalene gel 0.1% was significantly more effective in treating acne lesions than 0.03% adapalene gel. Adapalene gel 0.1% was significantly more effective than 0.025% or tretinoin gel in one study and of the same effectiveness in the other study. Adapalene gel was always better tolerated than tretinoin gel.

CONCLUSION

Adapalene 0.1% gel is a safe and effective treatment of acne vulgaris.

Multiple factors contribute to the toxicity of the aromatic retinoid, TTNPB (Ro 13-7410): binding affinities and disposition

The aromatic retinoid (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthylenyl)-1 -propenyl] benzoic acid (TTNPB) is 1000-fold more potent as a teratogen than all trans-retinoic acid (tRA) in several species and in the inhibition of chondrogenesis in the mouse limb bud cell culture. Factors responsible for the potency of TTNPB were investigated including binding to nuclear retinoic acid receptors (RARs and RXRs), cytosolic binding proteins (CRABPs), and metabolic disposition of TTNPB. For competitive binding assays and saturation kinetics, nucleosol or cytosol fractions were obtained from COS-1 cells transfected with cDNAs encoding the appropriate nuclear receptor or binding protein. TTNPB binds to RAR alpha, beta, and gamma with Kds in the nanomolar range; however, these binding affinities are 10-fold less than those of tRA. Although the affinities are high for TTNPB, it is unlikely that the binding affinities to nuclear receptors alone account for the potency of TTNPB. The binding affinities of TTNPB for the CRABPs are significantly lower than those of tRA. TTNPB did not compete with [3H]9-cis RA for binding to RXR alpha, beta, or gamma. Mouse limb bud cell cultures, a well characterized model for retinoid teratogenesis, were used to compare the metabolic disposition of TTNPB and tRA. In the media of limb bud cell cultures treated with either retinoid, the disappearance of TTNPB was significantly slower than that of tRA over 72 hr. Both retinoids reached approximately equal concentrations in cell uptake experiments; however, TTNPB disappeared from the limb bud cell at a significantly slower rate than did tRA. Collectively, these results indicate that high affinity binding to RARs, lower affinity to CRABPs, and resistance to metabolism contribute to the potency of TTNPB.

Structure-function relationships of cellular retinoic acid-binding proteins. Quantitative analysis of the ligand binding properties of the wild-type proteins and site-directed mutants

It has been suggested that electrostatic interactions are critical for binding of retinoic acid by cellular retinoic acid-binding proteins (CRABP-I and CRABP-II). However, the roles of two conserved arginine residues (Arg-111 and Arg-131 in CRABP-I; Arg-111 and Arg-132 in CRABP-II) that interact with the carboxyl group of retinoic acid have not been evaluated. A novel competitive binding assay has been developed for measuring the relative dissociation constants of the site-directed mutants of CRABPs. Arg-111 and Arg-132 of CRABP-II were replaced with methionine by site-directed mutagenesis. The relative dissociation constants of R111M and R132M (Kd (R111M)/Kd (CRABP-II) and Kd (R132M)/Kd(CRABP-II)) were determined to be 40-45 and 6-8, respectively. The ring protons of the aromatic residues of the wild-type CRABP-II and the two mutants were sequentially assigned by two-dimensional homonuclear NMR in conjunction with three-dimensional heteronuclear NMR. Detailed analysis of the nuclear Overhauser effect spectroscopy spectra of the proteins indicated that the conformations of the two mutants are highly similar to that of the wild-type CRABP-II. These results taken together showed that Arg-111 and Arg-132 are important for binding retinoic acid but contribute to the binding energy only by approximately 2.2 and 1.2 kcal/mol, respectively. In addition, the relative dissociation constant of CRABP-II and CRABP-I (Kd (CRABP-II)/Kd (CRABP-I)) was determined to be 2-3, in close agreement with that calculated using the apparent Kd values determined under the same conditions by fluorometric titrations.

9-cis retinoic acid--a better retinoid for the modulation of differentiation, proliferation and gene expression in human neuroblastoma

To date, the clinical success of 13-cis or all-trans retinoic acid in the treatment of neuroblastoma has been disappointing. In vivo, 13-cis will isomerise to both all-trans and 9-cis retinoic acid, believed to be the main biologically-active isomers. In vitro studies with an N-type neuroblastoma cell line, SH SY 5Y, show that 9-cis is better than other isomers at both inducing morphological differentiation and inhibiting proliferation. RAR-beta, a gene which may mediate retinoic acid responsiveness and be of prognostic significance, is also more-effectively induced by 9-cis retinoic acid. 9-cis and all-trans retinoic acid do not have synergistic effects on SH SY 5Y cell proliferation and gene expression. A retinoid X receptor (RXR)-specific analogue of 9-cis retinoic acid had similar effects on gene expression to 9-cis retinoic acid alone. In view of these results, 9-cis retinoic acid or stable analogues of this retinoid may have potential for the treatment of neuroblastoma.

Increased concentrations of 3,4-didehydroretinol and retinoic acid-binding protein (CRABPII) in human squamous cell carcinoma and keratoacanthoma but not in basal cell carcinoma of the skin

Retinoids are biologic response modifiers that are present in normal skin and may possibly be perturbed in carcinogenesis. To examine this possibility in human skin, we analyzed vitamin A and cytosolic retinoid binding proteins (cellular retinol binding protein and cellular retinoic acid binding protein [CRABP]) in a total of 38 non-melanoma skin tumors and 25 healthy skin samples using high performance liquid chromatography, radioligand electrophoresis, and reverse transcriptase-polymerase chain reaction. The mean +/- SEM retinol concentration was normal in basal cell carcinoma (0.60 +/- 0.10 microM) and seborrheic keratosis (0.47 +/- 0.07 microM), but increased in keratoacanthoma (1.60 +/- 0.41 microM) and squamous cell carcinoma (1.17 +/- 0.28 microM) (p < 0.05 for both). Also, the concentrations of 3,4-didehydroretinol, a major vitamin A metabolite produced in human skin, were markedly elevated (6-7 times normal) in keratoacanthoma and squamous cell cancer. All types of tumors showed moderately increased levels of cellular retinol binding protein. In addition, keratoacanthoma and squamous cell cancer showed markedly increased levels (6-7 times normal) of CRABPII protein. Transcriptional activity of the CRABPII gene was demonstrated in both normal and neoplastic epidermis, but clear CRABPI mRNA expression was found only in basal cell carcinoma. The data indicate that characteristic perturbations of the vitamin A and retinoid binding protein levels occur in squamous cell-derived skin tumors, but whether these reflect intrinsic errors in retinoid metabolism or are secondary to abnormal cellular differentiation is unknown.

A comparison of the efficacy and safety of adapalene gel 0.1% and tretinoin gel 0.025% in the treatment of acne vulgaris: a multicenter trial

BACKGROUND

Adapalene is a new synthetic retinoid analogue developed for the topical treatment of acne vulgaris.

OBJECTIVE

The study was designed to compare the efficacy and safety and adapalene gel 0.1% with tretinoin gel 0.025% in the treatment of grade II to II facial acne vulgaris.

METHODS

Three hundred twenty-three patients were enrolled in this investigator-masked, randomized, parallel group, multicenter trial. Patients applied the test materials to the entire facial area daily, for a period of 12 weeks. Efficacy and cutaneous tolerance were assessed at baseline and weeks 2,4,8, and 12. Efficacy was determined by investigator counts of noninflammatory open and closed comedones, and inflammatory papules and pustules, as well as global improvement. Cutaneous tolerance was evaluated by erythema, scaling, and dryness, along with burning and pruritus.

RESULTS

Staring at weeks 2 and 4, adapalene gel produced numerically greater lesion reductions than did tretinoin gel for all lesion types. At week 12, the mean percent reduction in the different lesion counts was as follow: 49% versus 37% for total lesions (p<0.01); 46% versus 33% for noninflammatory lesions (p=0.02); 48% versus 38% for inflammatory lesions (p=0.06) in adapalene and tretinoin gel treatment groups, respectively. Cutaneous side effects were limited to a mild "retinoid dermatitis" occurring in both treatment groups; however, patients treated with adapalene gel tolerated this therapy significantly better than those treated with tretinoin gel. Laboratory test evaluations (hematology, blood chemistries, urinalysis) were performed in 54 patients before and after 3 months of treatment. No clinically significant changes were observed.

CONCLUSION

Adapalene gel 0.1% applied once daily was significantly more effective in reducing acne lesions and was better tolerated than tretinoin gel 0.025% in the treatment of acne vulgaris.