Localization of cellular retinoid-binding proteins suggests specific roles for retinoids in the adult central nervous system

Isotretinoin and neuropsychiatric side effects: Continued vigilance is needed

Background

Isotretinoin (13-cis-retinoic acid, marketed under the names Accutane, Roaccutane, and others) is an effective treatment for acne that has been on the market for over 30 years, although reports of neuropsychiatric side effects continue to be reported. Isotretinoin is an isomer of the active form of Vitamin A, 13-trans-retinoic acid, which has known psychiatric side effects when given in excessive doses, and is part of the family of compounds called retinoids, which have multiple functions in the central nervous system.

Methods

The literature was reviewed in pubmed and psychinfo for research related to isotretinoin and neuropsychiatric side effects including depression, suicidal thoughts, suicide, mania, anxiety, impulsivity, emotional lability, violence, aggression, and psychosis.

Results

Multiple case series have shown that successful treatment of acne with isotretinoin results in improvements in measures of quality of life and self esteem However, studies show individual cases of clinically significant depression and other neuropsychiatric events that, although not common, are persistent in the literature. Since the original cases of depression were reported to the United States Food and Drug Administration, numerous cases have been reported to regulatory agencies in the United Kingdom, France, Ireland, Denmark, Australia, Canada, and other countries, making isotretinoin one of the top five medications in the world associated with depression and other neuropsychiatric side effects. Clinicians are advised to warn patients of the risks of neuropsychiatric side effects with isotretinoin which may arise from the medication itself, and not just as a side effect of acne or youth.

Vitamin A and Retinoic Acid in Cognition and Cognitive Disease

The history of vitamin A goes back over one hundred years, but our realization of its importance for the brain and cognition is much more recent. The brain is more efficient than other target tissues at converting vitamin A to retinoic acid (RA), which activates retinoic acid receptors (RARs). RARs regulate transcription, but their function in the cytoplasm to control nongenomic actions is also crucial. Controlled synthesis of RA is essential for regulating synaptic plasticity in regions of the brain involved in learning and memory, such as the hippocampus. Vitamin A deficiency results in a deterioration of these functions, and failure of RA signaling is perhaps associated with normal cognitive decline with age as well as with Alzheimer's disease. Further, several psychiatric and developmental disorders that disrupt cognition are also linked with vitamin A and point to their possible treatment with vitamin A or RA.

Ultrasensitive Vibrational Imaging of Retinoids by Visible Preresonance Stimulated Raman Scattering Microscopy

High-sensitivity chemical imaging offers a window to decipher the molecular orchestra inside a living system. Based on vibrational fingerprint signatures, coherent Raman scattering microscopy provides a label-free approach to map biomolecules and drug molecules inside a cell. Yet, by near-infrared (NIR) pulse excitation, the sensitivity is limited to millimolar concentration for endogenous biomolecules. Here, the imaging sensitivity of stimulated Raman scattering (SRS) is significantly boosted for retinoid molecules to 34 micromolar via electronic preresonance in the visible wavelength regime. Retinoids play critical roles in development, immunity, stem cell differentiation, and lipid metabolism. By visible preresonance SRS (VP-SRS) imaging, retinoid distribution in single embryonic neurons and mouse brain tissues is mapped, retinoid storage in chemoresistant pancreatic and ovarian cancers is revealed, and retinoids stored in protein network and lipid droplets of Caenorahbditis elegans are identified. These results demonstrate VP-SRS microscopy as an ultrasensitive label-free chemical imaging tool and collectively open new opportunities of understanding the function of retinoids in biological systems.

Retinoic acid receptor alpha activation is necessary and sufficient for plasticity induced by recurrent central apnea

Reductions in respiratory-related synaptic inputs to inspiratory motor neurons initiate a form of plasticity that proportionally enhances inspiratory motor output, even in the absence of changing blood gases. This form of plasticity is known as inactivity-induced inspiratory motor facilitation (iMF). iMF triggered by brief, recurrent reductions in respiratory neural activity requires local retinoic acid (RA) synthesis, but receptor subtypes activated by RA are unknown. To test the hypothesis that retinoic acid receptor alpha (RARα) is necessary for iMF, RAR subtype-specific inhibitors were delivered intrathecally above the phrenic motor pool in urethane-anesthetized, ventilated rats before 5, ∼1 min central apneas (without hypoxia; separated by 5 min) while monitoring phrenic inspiratory output. Pretreatment with a spinal RARα inhibitor impaired the capacity for recurrent central apnea to trigger long-lasting increases in phrenic inspiratory output, but plasticity was expressed in rats pretreated with an RARβ/γ inhibitor. Intrathecal RA application in the absence of reduced respiratory neural activity elicited an increase in phrenic inspiratory output, which was prevented by pretreatment with an RARα inhibitor. These data indicate that spinal RARα activation is necessary for iMF triggered by recurrent reductions in respiratory neural activity, and that RARα activation in/near the phrenic motor pool in the absence of respiratory neural activity deprivation is sufficient to elicit phrenic inspiratory motor facilitation. Understanding cellular cascades underlying plasticity induced by reductions in respiratory neural activity may define avenues for pharmacological intervention in disorders in which endogenous compensatory mechanisms that defend ongoing inspiratory motor output are impaired.NEW & NOTEWORTHY Local mechanisms near phrenic motor neurons respond to reductions in respiratory-related synaptic inputs by triggering a chemoreflex-independent, proportional enhancement in inspiratory output, a form of plasticity called inactivity-induced inspiratory motor facilitation (iMF). Here, we show that activation of spinal retinoic acid receptor alpha (RARα) is necessary to trigger phrenic iMF, and that spinal RARα activation in the absence of respiratory neural activity deprivation is sufficient to elicit phrenic inspiratory facilitation.

Retinoic Acid and the Gut Microbiota in Alzheimer's Disease: Fighting Back-to-Back?

BACKGROUND

There is growing evidence that the gut microbiota may play an important role in neurodegenerative diseases such as Alzheimer's disease. However, how these commensals influence disease risk and progression still has to be deciphered.

OBJECTIVE

The objective of this review was to summarize current knowledge on the interplay between gut microbiota and retinoic acid. The latter one represents one of the important micronutrients, which have been correlated to Alzheimer's disease and are used in initial therapeutic intervention studies.

METHODS

A selective overview of the literature is given with the focus on the function of retinoic acid in the healthy and diseased brain, its metabolism in the gut, and the potential influence that the bioactive ligand may have on microbiota, gut physiology and, Alzheimer's disease.

RESULTS

Retinoic acid can influence neuronal functionality by means of plasticity but also by neurogenesis and modulating proteostasis. Impaired retinoid-signaling, therefore, might contribute to the development of diseases in the brain. Despite its rather direct impact, retinoic acid also influences other organ systems such as gut by regulating the residing immune cells but also factors such as permeability or commensal microbiota. These in turn can also interfere with retinoid-metabolism and via the gutbrain- axis furthermore with Alzheimer's disease pathology within the brain.

CONCLUSION

Potentially, it is yet too early to conclude from the few reports on changed microbiota in Alzheimer's disease to a dysfunctional role in retinoid-signaling. However, there are several routes how microbial commensals might affect and might be affected by vitamin A and its derivatives.

Association of ADH7 Gene Polymorphism with Schizophrenia in the Han Population of Northern China: a Case-Control Study

Schizophrenia is a serious neurodevelopmental disorder. Genetics is an important factor leading to schizophrenia, but its exact role is still unclear. Many studies have focused on neurotransmitters and regulators that participate in the processes mediated by these neurotransmitters. Alcohol dehydrogenase may not only catalyze the oxidation of retinol and ethanol but also be involved in a variety of neurotransmitter metabolic pathways. Therefore, our study investigated whether ADH7 gene variations in the Chinese Han population were associated with schizophrenia. Genomic DNA was extracted from a cohort of 275 schizophrenic patients (136 men and 139 women) and 313 healthy controls (160 men and 153 women) from the Northern Han Chinese population. The Hardy-Weinberg equilibrium test and linkage disequilibrium analysis were performed. Differences in genotypes, alleles, and haplotypes between the schizophrenic and control groups were determined using the chi-square test and correlation analysis. The distribution of the CC + TT genotype of rs284787 was statistically different between the case and control groups (p = 0.026, OR = 1.448); however, the difference disappeared after Bonferroni correction. Linkage analysis indicated that rs739147, rs284787, rs3805329, rs894369, rs3805331, and rs284786 were closely linked in one block. The haplotype analysis found no association between the composed haplotypes and the occurrence of schizophrenia. Our study showed that the ADH7 gene was not associated with the risk of schizophrenia. Additional studies with larger cohorts of different ethnicities are needed to validate our findings.

Identification of molecular markers distinguishing adult neural stem cells in the subventricular and subcallosal zones

Neural stem cells (NSCs) in the adult subventricular zone (SVZ) are regionally specified and have distinct molecular gene expression signatures. Recently, we identified the subcallosal zone (SCZ) as a novel brain region where adult NSCs maintain and spontaneously produce neuroblasts. In an attempt to isolate genes specifically expressed in the SCZ or SVZ, microarray analyses of their differentially expressing transcripts were done. The comparison between neurospheres generated from SVZ and SCZ revealed differential expression >1.5-fold in two groups in only 83 genes, representing <0.03% of the genes examined, suggesting that these two populations are largely similar. The differential expression patterns SCZ and SVZ genes were confirmed by RT-PCR and Western blots. The selective expressions of two genes (CRBP1, HMGA1) in SVZ-NSCs were further confirmed by immunohistochemistry. These molecular markers could be useful for further molecular and cellular characterization of NSCs.

Genome-wide Analysis of RARβ Transcriptional Targets in Mouse Striatum Links Retinoic Acid Signaling with Huntington's Disease and Other Neurodegenerative Disorders

Retinoic acid (RA) signaling through retinoic acid receptors (RARs), known for its multiple developmental functions, emerged more recently as an important regulator of adult brain physiology. How RAR-mediated regulation is achieved is poorly known, partly due to the paucity of information on critical target genes in the brain. Also, it is not clear how reduced RA signaling may contribute to pathophysiology of diverse neuropsychiatric disorders. We report the first genome-wide analysis of RAR transcriptional targets in the brain. Using chromatin immunoprecipitation followed by high-throughput sequencing and transcriptomic analysis of RARβ-null mutant mice, we identified genomic targets of RARβ in the striatum. Characterization of RARβ transcriptional targets in the mouse striatum points to mechanisms through which RAR may control brain functions and display neuroprotective activity. Namely, our data indicate with statistical significance (FDR 0.1) a strong contribution of RARβ in controlling neurotransmission, energy metabolism, and transcription, with a particular involvement of G-protein coupled receptor (p = 5.0e^-5), cAMP (p = 4.5e^-4), and calcium signaling (p = 3.4e^-3). Many identified RARβ target genes related to these pathways have been implicated in Alzheimer's, Parkinson's, and Huntington's disease (HD), raising the possibility that compromised RA signaling in the striatum may be a mechanistic link explaining the similar affective and cognitive symptoms in these diseases. The RARβ transcriptional targets were particularly enriched for transcripts affected in HD. Using the R6/2 transgenic mouse model of HD, we show that partial sequestration of RARβ in huntingtin protein aggregates may account for reduced RA signaling reported in HD.

Vitamin A and Retinoids as Mitochondrial Toxicants

Vitamin A and its derivatives, the retinoids, are micronutrient necessary for the human diet in order to maintain several cellular functions from human development to adulthood and also through aging. Furthermore, vitamin A and retinoids are utilized pharmacologically in the treatment of some diseases, as, for instance, dermatological disturbances and some types of cancer. In spite of being an essential micronutrient with clinical application, vitamin A exerts several toxic effects regarding redox environment and mitochondrial function. Moreover, decreased life quality and increased mortality rates among vitamin A supplements users have been reported. However, the exact mechanism by which vitamin A elicits its deleterious effects is not clear yet. In this review, the role of mitochondrial dysfunction in the mechanism of vitamin A-induced toxicity is discussed.

Intracellular transport of fat-soluble vitamins A and E

Vitamins are compounds that are essential for the normal growth, reproduction and functioning of the human body. Of the 13 known vitamins, vitamins A, D, E and K are lipophilic compounds and are therefore called fat-soluble vitamins. Because of their lipophilicity, fat-soluble vitamins are solubilized and transported by intracellular carrier proteins to exert their actions and to be metabolized properly. Vitamin A and its derivatives, collectively called retinoids, are solubilized by intracellular retinoid-binding proteins such as cellular retinol-binding protein (CRBP), cellular retinoic acid-binding protein (CRABP) and cellular retinal-binding protein (CRALBP). These proteins act as chaperones that regulate the metabolism, signaling and transport of retinoids. CRALBP-mediated intracellular retinoid transport is essential for vision in human. α-Tocopherol, the main form of vitamin E found in the body, is transported by α-tocopherol transfer protein (α-TTP) in hepatic cells. Defects of α-TTP cause vitamin E deficiency and neurological disorders in humans. Recently, it has been shown that the interaction of α-TTP with phosphoinositides plays a critical role in the intracellular transport of α-tocopherol and is associated with familial vitamin E deficiency. In this review, we summarize the mechanisms and biological significance of the intracellular transport of vitamins A and E.

Effect of Oral Isotretinoin Treatment on Retinal Nerve Fiber Layer Thickness

Background:

Oral isotretinoin treatment can cause ocular side effects.

Objective:

This study was performed to detect possible toxic effects of oral isotretinoin treatment on the retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL).

Methods:

The study population consisted of 54 eyes of 27 patients with nodulocystic acne who used oral isotretinoin (Roaccutane) treatment. Macular GCL and peripapillary RNFL thickness measurements were performed using spectral domain optical coherence tomography (OCT) before and after therapy.

Results:

Before and after treatment, a complete ophthalmologic examination was normal in all eyes. However, posttreatment lower temporal (TL) values were significantly lower (76.80 ± 16.31) than pretreatment TL values (84.96 ± 24.83) ( p = .02). There was no statistically significant difference in the other OCT values, upper temporal, superotemporal, superonasal, upper nasal, lower nasal, inferonasal, and inferotemporal ( p = .35, p = .40, p = .56, p = .95, p = .94, p = .93, p = .61, respectively). Also, there was no statistically significant difference between the right and left eyes and between genders for all parameters ( p > .05).

Conclusion:

The use of oral isotretinoin treatment has increased in recent years. In addition, oral isotretinoin treatment has a broad adverse effect potential on the ocular system. The measurement of RNFL thickness, especially TL thickness, by OCT may be useful for detecting the possible toxic effect of oral isotretinoin therapy on RNFL.

Retinoid signaling is necessary for, and promotes long-term memory formation following operant conditioning

Retinoic acid, a metabolite of vitamin A, is proposed to play an important role in vertebrate learning and memory, as well as hippocampal-dependent synaptic plasticity. However, it has not yet been determined whether retinoic acid plays a similar role in learning and memory in invertebrates. In this study, we report that retinoid signaling in the mollusc Lymnaea stagnalis, is required for long-term memory formation following operant conditioning of its aerial respiratory behaviour. Animals were exposed to inhibitors of the RALDH enzyme (which synthesizes retinoic acid), or various retinoid receptor antagonists. Following exposure to these inhibitors, neither learning nor intermediate-term memory (lasting 2 h) was affected, but long-term memory formation (tested at either 24 or 72 h) was inhibited. We next demonstrated that various retinoid receptor agonists promoted long-term memory formation. Using a training paradigm shown only to produce intermediate-term memory (lasting 2 h, but not 24 h) we found that exposure of animals to synthetic retinoids promoted memory formation that lasted up to 30 h. These findings suggest that the role of retinoids in memory formation is ancient in origin, and that retinoid signaling is also important for the formation of implicit memories, in addition to its previously demonstrated role in hippocampal-dependent memories.

Characterization of the expression profile of CRBP1 and CRBP3 gene in chicken

In this study, we quantified the expression of CRBP1 and CRBP3 in Roman layer (R) and Erlang mountainous chickens (SD02 and SD03), to discern the tissue, breed and age-related expression patterns in order to discover potential involvement in egg production and other related reproduction traits. Real-time quantitative PCR assays were developed for accurate measurement of CRBP1 and CRBP3 mRNA levels in different tissues from chickens at four ages (12, 20, 32 and 45 weeks). We found that the CRBP1 and CRBP3 were expressed in all six tissues examined in all three breeds of chicken at 32 weeks. CRBP1 mRNA levels in SD02 kidneys were slightly higher than those in SD03 and R at 12 weeks, whereas, at the other three time points, the expression levels of CRBP1 in SD03 were higher than those in SD02 and R. In addition, there was higher hepatic expression of CRBP3 mRNA in layers (R) compared to broilers (SD02 and SD03) at 20 and 32 weeks. An age-related expression pattern of CRBP1 gene was evident in liver (P < 0.01), but not in pituitary (P > 0.05). Overall, the expression level of CRBP1 gene in kidney, ovary and oviduct at the different ages had a "decline-rise-decline" trend in all three breeds. In contrast, in pituitary, hypothalamus, liver and kidney CRBP3 mRNA expression levels were significantly different at various ages (P < 0.05) and exhibited a "rise-decline-rise" pattern in all three breeds. Our results show that the expression of CRBP1 and CRBP3 in chicken tissues exhibit specific developmental changes and age-related patterns.

Amygdala nuclei critical for emotional learning exhibit unique gene expression patterns

The amygdala is a heterogeneous, medial temporal lobe structure that has been implicated in the formation, expression and extinction of emotional memories. This structure is composed of numerous nuclei that vary in cytoarchitectonics and neural connections. In particular the lateral nucleus of the amygdala (LA), central nucleus of the amygdala (CeA), and the basal (B) nucleus contribute an essential role to emotional learning. However, to date it is still unclear to what extent these nuclei differ at the molecular level. Therefore we have performed whole genome gene expression analysis on these nuclei to gain a better understanding of the molecular differences and similarities among these nuclei. Specifically the LA, CeA and B nuclei were laser microdissected from the rat brain, and total RNA was isolated from these nuclei and subjected to RNA amplification. Amplified RNA was analyzed by whole genome microarray analysis which revealed that 129 genes are differentially expressed among these nuclei. Notably gene expression patterns differed between the CeA nucleus and the LA and B nuclei. However gene expression differences were not considerably different between the LA and B nuclei. Secondary confirmation of numerous genes was performed by in situ hybridization to validate the microarray findings, which also revealed that for many genes, expression differences among these nuclei were consistent with the embryological origins of these nuclei. Knowing the stable gene expression differences among these nuclei will provide novel avenues of investigation into how these nuclei contribute to emotional arousal and emotional learning, and potentially offer new genetic targets to manipulate emotional learning and memory.

Characterization of the Expression Profile and Genetic Polymorphism of the Cellular Retinol-Binding Protein (CRBP IV) Gene in Erlang Mountainous Chickens

In this study, we cloned the coding sequence of chicken CRBP IV, quantified the mRNA expression in Erlang Mountainous Chickens, and investigated a polymorphism in this gene and its association with egg production traits among 349 individuals. The cloned fragment contained a 384 bp open reading frame, which encoded a predicted protein of 127 amino acids and was highly conserved among species. Expression of CRBP IV mRNA was detected in all eight tissues (small intestine, heart, liver, kidney, oviduct, ovary, pituitary, and hypothalamus) at different ages (12, 24, 32 and 45 w). High expression was found in small intestine, pituitary, kidney and liver, whereas it was low in the heart (p < 0.05). The CRBP IV mRNA levels changed with age in the various tissues, and were highly expressed in all tissues at 32 w, except for the heart. We identified one nucleotide substitution (c. 826T>C) in the second exon, which caused an amino acid change (p. S49L). Genotypes (TT, TC and CC) had significant effects on the age at first egg (AFE), total eggs for 300 days (TE300) and highest continuous laying days (HCLD). The CC genotype would be genetically advantageous to improve egg production traits due to earlier AFE, more TE300, and longer HCLD.

Identification of retinol binding protein 1 promoter hypermethylation in isocitrate dehydrogenase 1 and 2 mutant gliomas

BACKGROUND

Mutations in isocitrate dehydrogenase 1 (IDH1) and associated CpG island hypermethylation represent early events in the development of low-grade gliomas and secondary glioblastomas. To identify candidate tumor suppressor genes whose promoter methylation may contribute to gliomagenesis, we compared methylation profiles of IDH1 mutant (MUT) and IDH1 wild-type (WT) tumors using massively parallel reduced representation bisulfite sequencing.

METHODS

Reduced representation bisulfite sequencing was performed on ten pathologically matched WT and MUT glioma samples and compared with data from a methylation-sensitive restriction enzyme technique and data from The Cancer Genome Atlas (TCGA). Methylation in the gene retinol-binding protein 1 (RBP1) was identified in IDH1 mutant tumors and further analyzed with primer-based bisulfite sequencing. Correlation between IDH1/IDH2 mutation status and RBP1 methylation was evaluated with Spearman correlation. Survival data were collected retrospectively and analyzed with Kaplan-Meier and Cox proportional hazards analysis. All statistical tests were two-sided.

RESULTS

Methylome analysis identified coordinated CpG island hypermethylation in IDH1 MUT gliomas, consistent with previous reports. RBP1, important in retinoic acid metabolism, was found to be hypermethylated in 76 of 79 IDH1 MUT, 3 of 3 IDH2 MUT, and 0 of 116 IDH1/IDH2 WT tumors. IDH1/IDH2 mutation was highly correlated with RBP1 hypermethylation (n = 198; Spearman R = 0.94, 95% confidence interval = 0.92 to 0.95, P < .001). The Cancer Genome Atlas showed IDH1 MUT tumors (n = 23) to be RBP1-hypermethylated with decreased RBP1 expression compared with WT tumors (n = 124). Among patients with primary glioblastoma, patients with RBP1-unmethylated tumors (n = 102) had decreased median overall survival compared with patients with RBP1-methylated tumors (n = 22) (20.3 months vs 36.8 months, respectively; hazard ratio of death = 2.48, 95% confidence interval = 1.30 to 4.75, P = .006).

CONCLUSION

RBP1 promoter hypermethylation is found in nearly all IDH1 and IDH2 mutant gliomas and is associated with improved patient survival. Because RBP1 is involved in retinoic acid synthesis, our results suggest that dysregulation of retinoic acid metabolism may contribute to glioma formation along the IDH1/IDH2-mutant pathway.

Photoperiodic expression of two RALDH enzymes and the regulation of cell proliferation by retinoic acid in the rat hypothalamus

Retinoic acid (RA) has been found to regulate hypothalamic function, but precisely where it acts is unknown. This study shows expression of retinaldehyde dehydrogenase (RALDH) enzymes in tanycytes that line the third ventricle in an area overlapping with the site of hypothalamic neural stem cells. The influence of RA was examined on the proliferation of progenitors lining the third ventricle using organotypic slice cultures. As has been shown in other regions of neurogenesis, RA was found to inhibit proliferation. Investigations of the dynamics of RALDH1 expression in the rat hypothalamus have shown that this enzyme is in tanycytes under photoperiodic control with highest levels during long versus short days. In parallel to this shift in RA synthesis, cell proliferation in the third ventricle was found to be lowest during long days when RA was highest, implying that RALDH1 synthesized RA may regulate neural stem cell proliferation. A second RA synthesizing enzyme, RALDH2 was also present in tanycytes lining the third ventricle. In contrast to RALDH1, RALDH2 showed little change with photoperiodicity, but surprisingly the protein was present in the apparent absence of mRNA transcript and it is hypothesized that the endocytic tanycytes may take this enzyme up from the cerebrospinal fluid (CSF).

Daily patterns of clock and cognition-related factors are modified in the hippocampus of vitamin A-deficient rats

The circadian expression of clock and clock-controlled cognition-related genes in the hippocampus would be essential to achieve an optimal daily cognitive performance. There is some evidence that retinoid nuclear receptors (RARs and RXRs) can regulate circadian gene expression in different tissues. In this study, Holtzman male rats from control and vitamin A-deficient groups were sacrificed throughout a 24-h period and hippocampus samples were isolated every 4 or 5 h. RARα and RXRβ expression level was quantified and daily expression patterns of clock BMAL1, PER1, RORα, and REVERB genes, RORα and REVERB proteins, as well as temporal expression of cognition-related RC3 and BDNF genes were determined in the hippocampus of the two groups of rats. Our results show significant daily variations of BMAL1, PER1, RORα, and REVERB genes, RORα and REVERB proteins and, consequently, daily oscillating expression of RC3 and BDNF genes in the rat hippocampus. Vitamin A deficiency reduced RXRβ mRNA level as well as the amplitude of PER1, REVERB gene, and REVERB protein rhythms, and phase-shifted the daily peaks of BMAL1 and RORα mRNA, RORα protein, and RC3 and BDNF mRNA levels. Thus, nutritional factors, such as vitamin A and its derivatives the retinoids, might modulate daily patterns of BDNF and RC3 expression in the hippocampus, and they could be essential to maintain an optimal daily performance at molecular level in this learning-and-memory-related brain area.

Transient expression of cellular retinol-binding protein-1 during cardiac repair after myocardial infarction

Retinoic acid (RA) is a vitamin A derivative that exerts pleiotropic biological effects. Intracellular transport and metabolism of RA are regulated by cellular retinol-binding proteins (CRBP). CRBP-1 is transiently expressed in granulation tissue fibroblasts during wound healing; however, its role in cardiac remodeling remains unknown. A rat myocardial infarction (MI) model was established by ligation of the left coronary artery, and hearts were obtained at 3, 6, 15, 30 and 45 days after operation. Heart sections were examined immunohistochemically using anti-vimentin, anti-α-smooth muscle actin (α-SMA), anti-matrix metalloproteinase (MMP)-2, anti-MMP-9 and anti-CRBP-1 antibodies. Infarction involved 48.8 ± 3.6% of the left ventricle and was followed by an important cardiac remodeling. Vimentin-positive fibroblastic cells including α-SMA-positive myofibroblasts expressed CRBP-1 at 3-, 6-, and 15-days after MI. Expression of CRBP-1 reached a maximum at 6-days after infarction. Thereafter, CRBP-1 expression was dramatically decreased, showing a similar tendency to MMP expression. Human heart specimens of individuals with a recent myocardial infarction demonstrated presence of CRBP-1-positive fibroblasts by immunohistochemistry. We have demonstrated that CRBP-1 is transiently expressed by fibroblasts during cardiac remodeling. Our results suggest that CRBP-1 plays a role in ventricular remodeling after MI allegedly through its RA binding activity.

High expression of retinoic acid receptors and synthetic enzymes in the human hippocampus

Retinoic acid, the active form of the nutrient vitamin A, regulates several facets of neuronal plasticity in the hippocampus, including neurogenesis and synaptic strength, acting via specific retinoic acid receptors (RARs). Essential for conversion of vitamin A to retinoic acid is the enzyme retinaldehyde dehydrogenase (RALDH) and in the rodent hippocampus this is only present in the adjacent meninges where it must act as a locally released paracrine hormone. Little is known though about the expression of RALDHs and RARs in the human hippocampus. This study confirms that RALDH levels are very low in mouse neurons but, surprisingly, strong expression of RALDH protein is detected by immunohistochemistry in hippocampal neurons. The receptors RARα, β and γ were also detected, each receptor exhibiting differing subcellular locations implying their potential regulation of both transcription and non-genomic actions. These results imply an essential function of retinoic acid in the human hippocampus likely to include regulation of neuronal plasticity.

Molecular regulation of both dietary vitamin A and fatty acid absorption and metabolism associated with larval morphogenesis of Senegalese sole (Solea senegalensis)

The present study aimed to deepen the understanding of molecular mechanisms governing the absorption and metabolism of some nutrients, growth and development in larvae of Senegalese sole (Solea senegalensis) fed with Artemia enriched with Easy Selco (ES, INVE) or Aquagrow Gold (AGG, ABN), which mainly differed in their vitamin A (VA) content and fatty acid composition. The expression profile of genes involved in VA metabolism (crbp2, rbp, crabp1), lipid transport (i-fabp, l-fabp), nuclear receptors for VA and fatty acids (rarα1, rxrα, pparβ), growth (igf1, igf2 and their receptor igf1r) and development (bgp) was analyzed at 22, 30 and 38 days post hatching. The main results suggested that the amount of VA absorbed by larvae is controlled at the intestinal level by crbp2 in both groups, preventing excessive accumulation of this vitamin in the target tissues. The stable expression of i-fabp in the ES group with age could cause an excessive fat accumulation in the intestine inducing, in turn, the steatosis found in the liver and vascular system of these specimens. In liver, the regulation of rbp and fabp expression reflected the status of the physiological functions demanding VA and lipids. The findings revealed that dietary composition induced different strategies for VA and lipid absorption and metabolism affecting, in turn, larval development, growth and health.

Modeling Parkinson's disease genetics: altered function of the dopamine system in Adh4 knockout mice

Class IV alcohol dehydrogenase (ADH4) efficiently reduces aldehydes produced during lipid peroxidation, and may thus serve to protect from toxic effects of aldehydes e.g. on neurons. We hypothesized that ADH4 dysfunction may increase risk for Parkinson's disease (PD) and previously reported association of an ADH4 allele with PD. We found that a promoter polymorphism in this allele induced a 25-30% reduction of transcriptional activity. Based on these findings, we have now investigated whether Adh4 homo- (Adh4-/-) or heterozygous (Adh4+/-) knockout mice display any dopamine system-related changes in behavior, biochemical parameters or olfaction compared to wild-type mice. The spontaneous locomotor activity was found to be similar in the three groups, whereas administration of d-amphetamine or apomorphine induced a significant increase in horizontal activity in the Adh4-/- mice compared to wild-type mice. We measured levels of monoamines and their metabolites in striatum, frontal cortex and substantia nigra and found increased levels of dopamine and DOPAC in substantia nigra of Adh4-/- mice. Investigation of olfactory function revealed a reduced sense of smell in Adh4-/- mice accompanied by alterations in dopamine metabolite levels in the olfactory bulb. Taken together, our results suggest that lack of Adh4 gene activity induces changes in the function of the dopamine system, findings which are compatible with a role of loss-of-function mutations in ADH4 as possible risk factors for PD.

Vitamin A supplementation at clinical doses induces a dysfunction in the redox and bioenergetics states, but did change neither caspases activities nor TNF-alpha levels in the frontal cortex of adult Wistar rats

Vitamin A and its derivatives, the retinoids, exert modulatory roles on central nervous system (CNS) function. However, the clinical use of vitamin A at moderate to high doses induces serious side effects, including dysfunctional brain metabolism and mood disorders. Then, we have investigated in this work the effects of vitamin A supplementation at 1000, 2500, 4500, or 9000IU/kg/day for 28 days on redox and bioenergetics parameters in adult rat frontal cortex. Additionally, we have measured caspase-3 and caspase-8 activities to analyze whether vitamin A supplementation as retinol palmitate induces neuronal death in such brain area. The levels of the pro-inflammatory cytokine TNF-alpha were also quantified. We have found increased rates of O(2)(-) production and increased levels of markers of oxidative insult in frontal cortex and also in mitochondrial membranes. Superoxide dismutase (SOD) enzyme activity was increased, and catalase (CAT) enzyme activity did not change in this experimental model. Surprisingly, we observed increased mitochondrial electron transfer chain (METC) activity. Caspase-3 and caspase-8 activities and TNF-alpha levels did not change in this experimental model. Finally, vitamin A supplementation did not induce depression in adult rats after 28 days of treatment. However, exploration in the center of an open field was decreased and time spent in freezing behavior was increased in vitamin A treated rats.

Identification of differentially expressed genes in the zebrafish hypothalamic-pituitary axis

The vertebrate hypothalamic-pituitary axis (HP) is the main link between the central nervous system and endocrine system. Although several signal pathways and regulatory genes have been implicated in adenohypophysis ontogenesis, little is known about hypothalamic-neurohypophysial development or when the HP matures and becomes functional. To identify markers of the HP, we constructed subtractive cDNA libraries between adult zebrafish hypothalamus and pituitary. We identified previously published genes, ESTs and novel zebrafish genes, some of which were predicted by genomic database analysis. We also analyzed expression patterns of these genes and found that several are expressed in the embryonic and larval hypothalamus, neurohypophysis, and/or adenohypophysis. Expression at these stages makes these genes useful markers to study HP maturation and function.

Retinoic acid and environmental enrichment alter subventricular zone and striatal neurogenesis after stroke

Neurogenesis increases in the adult rodent forebrain subventricular zone (SVZ) after experimental stroke. Newborn neurons migrate to the injured striatum, but few survive long-term and little evidence exists to suggest that they integrate or contribute to functional recovery. One potential strategy to improve stroke recovery is to stimulate neurogenesis and integration of adult-born neurons by using treatments that enhance neurogenesis. We examined the influence of retinoic acid (RA), which stimulates neonatal SVZ and adult hippocampal neurogenesis, and environmental enrichment (EE), which enhances survival of adult-born hippocampal neurons. We hypothesized that the combination of RA and EE would promote survival of adult-generated SVZ-derived neurons and improve functional recovery after stroke. Adult rats underwent middle cerebral artery occlusion, received BrdU on days 5-11 after stroke and were treated with RA/EE, RA alone, EE/vehicle or vehicle alone and were killed 61 days after stroke. Rats underwent repeated MRI and behavioral testing. We found that RA/EE treatment preserved striatal and hemisphere tissue and increased SVZ neurogenesis as demonstrated by Ki67 and doublecortin (DCx) immunolabeling. All treatments influenced the location of BrdU- and DCx-positive cells in the post-stroke striatum. RA/EE increased the number of BrdU/NeuN-positive cells in the injured striatum but did not lead to improvements in behavioral function. These results demonstrate that combined pharmacotherapy and behavioral manipulation enhances post-stroke striatal neurogenesis and decreases infarct volume without promoting detectable functional recovery. Further study of the integration of adult-born neurons in the ischemic striatum is necessary to determine their restorative potential.

Phosphatidylinositide 3-kinase and protein kinase C zeta mediate retinoic acid induction of DARPP-32 in medium size spiny neurons in vitro

Mature striatal medium size spiny neurons express the dopamine and cAMP-regulated phosphoprotein, 32 kDa (DARPP-32), but little is known about the mechanisms regulating its levels, or the specification of fully differentiated neuronal subtypes. Cell extrinsic molecules that increase DARPP-32 mRNA and/or protein levels include retinoic acid (RA), brain-derived neurotrophic factor, and estrogen (E(2)). We now demonstrate that RA regulates DARPP-32 mRNA and protein in primary striatal neuronal cultures. Furthermore, DARPP-32 induction by RA in vitro requires phosphatidylinositide 3-kinase, but is independent of tropomyosin-related kinase B, cyclin-dependent kinase 5, and protein kinase B. Using pharmacologic inhibitors of various isoforms of protein kinase C (PKC), we also demonstrate that DARPP-32 induction by RA in vitro is dependent on PKC zeta (PKCzeta). Thus, the signal transduction pathways mediated by RA are very different than those mediating DARPP-32 induction by brain-derived neurotrophic factor. These data support the presence of multiple signal transduction pathways mediating expression of DARPP-32 in vitro, including a novel, important pathway via which phosphatidylinositide 3-kinase regulates the contribution of PKCzeta.

ADH7 variation modulates extraversion and conscientiousness in substance-dependent subjects

Human personality traits have been closely linked to substance dependence (SD), and are partially genetically determined. Recently, associations between alcohol dehydrogenase 7 (ADH7) and SD have been reported, which led us to investigate the relationship between ADH7 variation and personality traits. We assessed dimensions of the five-factor model of personality and genotyped 4 ADH7 markers and 38 unlinked ancestry-informative markers in 244 subjects with SD [178 European-Americans (EAs) and 66 African-Americans (AAs)] and 293 healthy subjects (253 EAs and 40 AAs). The relationships between ADH7 markers and personality traits were comprehensively examined using multivariate analysis of covariance (MANCOVA), and then decomposed by Roy Bargmann Stepdown analysis of covariance (ANCOVA). Generally, older individuals, AAs, and males had significantly lower personality scores (4.7 x 10(-5) < or = P < or = 0.032), as reported previously. In SD subjects, Extraversion was most significantly associated with ADH7 haplotypes (3.7 x 10(-4) < or = P < or = 0.001), diplotypes (0.007 < or = P < or = 0.012), and genotypes (P = 0.001), followed by Conscientiousness (0.005 < or = P < or = 0.033). The contributory haplotype and diplotypes contained the alleles and genotypes of rs284786 (SNP1) and rs1154470 (SNP4). In healthy subjects, other personality factors (except Extraversion) were associated with ADH7 diplotypes (0.005 < or = P < or = 0.016) and genotypes (0.002 < or = P < or = 0.052). Some of the gene effects on personality factors were modified by sex. The present study demonstrated that the ADH7 variation may contribute to the genetic component of variation in personality traits, with the risk for SD and personality traits being partially shared.

The neurobiology of retinoic acid in affective disorders

Current models of affective disorders implicate alterations in norepinephrine, serotonin, dopamine, and CRF/cortisol; however treatments targeted at these neurotransmitters or hormones have led to imperfect resolution of symptoms, suggesting that the neurobiology of affective disorders is incompletely understood. Until now retinoids have not been considered as possible contributors to affective disorders. Retinoids represent a family of compounds derived from vitamin A that perform a large number of functions, many via the vitamin A product, retinoic acid. This signaling molecule binds to specific retinoic acid receptors in the brain which, like the glucocorticoid and thyroid hormone receptors, are part of the nuclear receptor superfamily and regulate gene transcription. Research in the field of retinoic acid in the CNS has focused on the developing brain, in part stimulated by the observation that isotretinoin (13-cis retinoic acid), an isomer of retinoic acid used in the treatment of acne, is highly teratogenic for the CNS. More recent work has suggested that retinoic acid may influence the adult brain; animal studies indicated that the administration of isotretinoin is associated with alterations in behavior as well as inhibition of neurogenesis in the hippocampus. Clinical evidence for an association between retinoids and depression includes case reports in the literature, studies of health care databases, and other sources. A preliminary PET study in human subjects showed that isotretinoin was associated with a decrease in orbitofrontal metabolism. Several studies have shown that the molecular components required for retinoic acid signaling are expressed in the adult brain; the overlap of brain areas implicated in retinoic acid function and stress and depression suggest that retinoids could play a role in affective disorders. This report reviews the evidence in this area and describes several systems that may be targets of retinoic acid and which contribute to the pathophysiology of depression.

Is the modulation of retinoid and retinoid-associated signaling a future therapeutic strategy in neurological trauma and neurodegeneration?

The complex molecular pathways that mediate the effects of vitamin A and its derivatives, are increasingly recognized as a component of the repair capacity that could be activated to induce protection and regeneration in the mature nervous tissue. Retinoid and retinoid-associated signaling plays an essential role in normal neurodevelopment and appears to remain active in the adult CNS. In this paper, we review evidence which supports the hypothesis of an activation of retinoid-associated signaling molecular pathways in the mature nervous tissue and its significance in the context of neurodegenerative, trauma-induced and psychiatric disorders, at spinal and supra-spinal levels. Finally, we summarize the potential therapeutic avenues based on the modulation of retinoid targets undergoing reactivation under conditions of acute injury and chronic degeneration in the central nervous system, and discuss some of the unresolved issues linked to this treatment strategy.

Expression of cellular retinoic acid-binding protein I is specific to neurons in adult transgenic mouse brain

Cellular retinoic acid binding protein I (CRABP-I) plays a role in retinoic acid (RA) metabolism or transport. This report shows specific neuronal expression of CRABP-I in adult transgenic mouse brain using CRABP-I promotor-driven lac-Z and neuron- and astrocyte-markers. Double staining indicates that CRABP-I is expressed in neurons and large cells (>12 microm) but to much lesser degree the astrocytes. CRABP-I-lac-Z(+) neurons were distributed throughout the brain, but in a very discreet pattern in each brain region. CRABP-I expression in specific populations of brain neurons suggests that RA is extensively metabolized in mature brains, mostly in neurons. Additionally, the genetic basis of its specific expression in these brain areas is located in the 5' regulatory region of this gene.

All-trans retinoic acid induces COX-2 and prostaglandin E2 synthesis in SH-SY5Y human neuroblastoma cells: involvement of retinoic acid receptors and extracellular-regulated kinase 1/2

BACKGROUND

Our recent results show that all-trans retinoic acid (ATRA), an active metabolite of vitamin A, induces COX-dependent hyperalgesia and allodynia in rats. This effect was mediated by retinoic acid receptors (RARs) and was associated with increased COX-2 expression in the spinal cord. Since ATRA also up-regulated COX-2 expression in SH-SY5Y human neuroblastoma cells, the current study was undertaken to analyze in these cells the mechanism through which ATRA increases COX activity.

METHODS

Cultured SH-SY5Y neuroblastoma cells were treated with ATRA. COX expression and kinase activity were analyzed by western blot. Transcriptional mechanisms were analyzed by RT-PCR and promoter assays. Pharmacological inhibitors of kinase activity and pan-antagonists of RAR or RXR were used to assess the relevance of these signaling pathways. Production of prostaglandin E2 (PGE2) was quantified by enzyme immunoabsorbent assay. Statistical significance between individual groups was tested using the non-parametric unpaired Mann-Whitney U test.

RESULTS

ATRA induced a significant increase of COX-2 expression in a dose- and time-dependent manner in SH-SY5Y human neuroblastoma cells, while COX-1 expression remained unchanged. Morphological features of differentiation were not observed in ATRA-treated cells. Up-regulation of COX-2 protein expression was followed by increased production of PGE2. ATRA also up-regulated COX-2 mRNA expression and increased the activity of a human COX-2 promoter construct. We next explored the participation of RARs and mitogen-activated peptide kinases (MAPK). Pre-incubation of SH-SY5Y human neuroblastoma cells with either RAR-pan-antagonist LE540 or MAP kinase kinase 1 (MEK-1) inhibitor PD98059 resulted in the abolition of ATRA-induced COX-2 promoter activity, COX-2 protein expression and PGE2 production whereas the retinoid X receptor pan-antagonist HX531, the p38 MAPK inhibitor SB203580 or the c-Jun kinase inhibitor SP600125 did not have any effect. The increase in RAR-beta expression and extracellular-regulated kinase 1/2(ERK1/2) phosphorylation in ATRA-incubated cells suggested that RARs and ERK1/2 were in fact activated by ATRA in SH-SY5Y human neuroblastoma cells.

CONCLUSION

These results highlight the importance of RAR-dependent and kinase-dependent mechanisms for ATRA-induced COX-2 expression and activity.

Genetic patterning of the mammalian telencephalon by morphogenetic molecules and transcription factors

Patterning centers that produce gradients of morphogenetic molecules, including fibroblast growth factor (FGF), bone morphogenetic proteins (BMP), Wnt, Sonic hedgehog (Shh), and retinoic acid (RA), are located in telencephalic anlage during early stages of development. Genetic evidence based on loss-of-function and gain-of-function studies indicate that they are involved in regional specification of the dorsal, ventral, and lateral telencephalon. For patterning of the dorsal telencephalon, FGF8 controls the anteroposterior patterning, while BMP and Wnt molecules regulate the mediolateral patterning. Shh and retinoic acid regulate patterning of the ventral and the lateral telencephalon. The regionalization of telencephalon is accompanied by expression of region-specific codes of transcription factors, which in turn regulate different phases of neuronal development to generate different cell types in each brain region. Therefore, bioactive signals of morphogenetic molecules are translated into transcription factor codes for regional specification, which subsequently leads to neurogenesis of the diversity of cell types in different regions of the telencephalon.

Nur77 and retinoid X receptors: crucial factors in dopamine-related neuroadaptation

Dopaminergic systems in the brain adapt in response to various stimuli from the internal and external world, but the mechanisms underlying this process are incompletely understood. Here, we review recent evidence that certain types of transcription factor of the nuclear receptor family, specifically Nur77 and retinoid X receptors, have important roles in adaptation and homeostatic regulation of dopaminergic systems. These findings call for a reassessment of our fundamental understanding of the molecular and cellular basis of dopamine-mediated transmission. Given that diseases such as Parkinson's disease and schizophrenia are thought to involve adaptation of dopamine signalling, these findings might provide new insight into these pathologies and offer new avenues for drug development.

Lentiviral vector expressing retinoic acid receptor beta2 promotes recovery of function after corticospinal tract injury in the adult rat spinal cord

Spinal cord injury often results in permanent and devastating neurological deficits and disability. This is due to the limited regenerative capacity of neurones in the central nervous system (CNS). We recently demonstrated that a transcription factor retinoic acid receptor beta2 (RARbeta2) promoted axonal regeneration in adult sensory neurones located peripherally. However, it is not known if RARbeta2 can promote axonal regeneration in cortical neurones of the CNS. Here, we demonstrate that delivery of RARbeta2 via a lentiviral vector to adult dissociated cortical neurones significantly enhances neurite outgrowth on adult cortical cryosections, which normally provide an unfavourable substrate for growth. We also show that lentiviral-mediated transduction of corticospinal neurones resulted in robust transgene expression in layer V corticospinal neurones and their axonal projections in the corticospinal tract (CST) of the spinal cord. Expression of RARbeta2 in these neurones enhanced regeneration of the descending CST fibres after injury to these axons in the mid-cervical spinal cord. Furthermore, we observed functional recovery in sensory and locomotor behavioural tests in RARbeta2-treated animals. These results suggest that a direct and selective delivery of RARbeta2 to the corticospinal neurones promotes long-distance functional regeneration of axons in the spinal cord and may thus offer new therapeutic gene strategy for the treatment of human spinal cord injuries.

Chronic administration of 13-cis-retinoic acid increases depression-related behavior in mice

Retinoid signaling plays a well-established role in neuronal differentiation, neurite outgrowth, and the patterning of the anteroposterior axis of the developing neural tube. However, there is increasing evidence that nutritional vitamin A status and retinoid signaling play an important role in the function of the adult brain. 13-Cis-retinoic acid (13-cis-RA) (isotretinoin or Accutane), a synthetic retinoid that is an effective oral treatment for severe nodular acne, has been linked with depression and suicide in patients. The purpose of this study was to test the hypothesis that chronic administration of 13-cis-RA would lead to depression-related behaviors in mice. Young, adult male mice received 13-cis-RA (1 mg/kg) by daily intraperitoneal injection for 6 weeks. This treatment paradigm produced plasma levels of 13-cis-RA that are comparable to those reported in human patients taking Accutane. In both the forced swim test and the tail suspension test, we found that 13-cis-RA-treated mice spent significantly more time immobile compared to vehicle-treated controls. In the open field test, there was no change in anxiety-related behavior in 13-cis-RA-treated mice. Furthermore, chronic administration of 13-cis-RA did not impair locomotion in either the open field or the rotarod test. Taken together, these results suggest that administration of 13-cis-RA increases depression-related behaviors in mice.

Vitamin A active metabolite, all-trans retinoic acid, induces spinal cord sensitization. I. Effects after oral administration

BACKGROUND AND PURPOSE

Retinoic acid is an active metabolite of vitamin A involved in the modulation of the inflammatory and nociceptive responses. The aim of the present study was to analyze the properties of spinal cord neuronal responses of male Wistar rats treated with all-trans retinoic acid (ATRA) p.o. in the normal situation and under carrageenan-induced inflammation. We also studied the expression and distribution of cyclooxygenases (COX) in the spinal cord.

EXPERIMENTAL APPROACH

Properties of spinal cord neurons were studied by means of the single motor unit technique. The expression of COX enzymes in the spinal cord was assessed by Western blot analysis and immunohistochemistry.

KEY RESULTS

Intensity thresholds for mechanical and electrical stimulation (C-fibers) were significantly lower in animals treated with ATRA than vehicle, either in normal rats or in rats with inflammation. The size of cutaneous receptive fields was also larger in animals treated with ATRA in the normal and inflammatory conditions. The expression of COX-2 enzyme, but not COX-1, was significantly higher in animals treated with ATRA. COX-2 labeling was observed in dorsal horn cells and in ventral horn motoneurons.

CONCLUSIONS AND IMPLICATIONS

In conclusion, the oral treatment with ATRA in rats induces a sensitization-like effect on spinal cord neuronal responses similar to that observed in animals with inflammation and might explain the enhancement of allodynia and hyperalgesia observed in previously published behavioral experiments. The mechanism of action involves an over-expression of COX-2, but not COX-1, in dorsal and ventral horn areas of the lumbar spinal cord.

Characterisation of transthyretin and retinol-binding protein in plasma and cerebrospinal fluid of dogs

The aim of this study was to investigate differences in concentrations of vitamin A, transthyretin (TTR) and retinol-binding protein (RBP) between plasma and cerebrospinal fluid (CSF) in dogs. RBP was detected using ELISA, and both RBP and TTR by Western blot analysis after separation on SDS-PAGE. Vitamin A was determined by high performance liquid chromatography. RBP and TTR as well as vitamin A were detected in all samples but at substantially lower concentrations in CSF compared to plasma. RBP in dog plasma showed a similar molecular mass to that of humans, whereas canine TTR had a lower molecular mass. Comparison between plasma and CSF showed that both RBP and TTR were of lower molecular mass in CSF. In CSF, RBP and retinol were present at 10-100-fold lower concentrations compared to plasma. Retinyl esters were present only in minute amounts in 5/17 samples. In conclusion, the CSF of dogs compared to humans is significantly different in terms of both quality and quantity of transport proteins for vitamin A.

Short-term oral isotretinoin therapy does not cause clinical or subclinical peripheral neuropathy

BACKGROUND

Subclinical neurophysiologic abnormalities mainly suggestive of sensory fibers dysfunction were observed in some patients after 1 and 3 months of treatment with oral acitretin. Moreover, two cases of peripheral sensory neuropathy and one of sensorimotor polyneuropathy were observed after short-term oral administration of this compound.

OBJECTIVE

The objective of this prospective study was to investigate whether short-term treatment with oral isotretinoin can also affect peripheral nerve function.

METHODS

Serial neurologic and neurophysiologic examinations were performed on 18 young patients with severe nodulocystic acne prior to and 1 and 3 months after the onset of oral isotretinoin treatment (1 mg/kg per day).

RESULTS

Clinical neurologic examination before and under treatment disclosed no abnormalities in any of the patients. There were no significant differences between the pre- and post-treatment neurophysiologic parameters. Furthermore, evaluation of the serial neurophysiologic measurements in each patient separately under oral isotretinoin treatment revealed no changes fulfilling the criteria of abnormality.

CONCLUSIONS

Short-term administration of oral isotretinoin in young patients does not cause clinical or subclinical neuropathy.

Once and again: Retinoic acid signaling in the developing and regenerating olfactory pathway

Retinoic acid (RA), a member of the steroid/thyroid superfamily of signaling molecules, is an essential regulator of morphogenesis, differentiation, and regeneration in the mammalian olfactory pathway. RA-mediated teratogenesis dramatically alters olfactory pathway development, presumably by disrupting retinoid-mediated inductive signaling that influences initial olfactory epithelium (OE) and bulb (OB) morphogenesis. Subsequently, RA modulates the genesis, growth, or stability of subsets of OE cells and OB interneurons. RA receptors, cofactors, and synthetic enzymes are expressed in the OE, OB, and anterior subventricular zone (SVZ), the site of neural precursors that generate new OB interneurons throughout adulthood. Their expression apparently accommodates RA signaling in OE cells, OB interneurons, and slowly dividing SVZ neural precursors. Deficiency of vitamin A, the dietary metabolic RA precursor, leads to cytological changes in the OE, as well as olfactory sensory deficits. Vitamin A therapy in animals with olfactory system damage can accelerate functional recovery. RA-related pathology as well as its potential therapeutic activity may reflect endogenous retinoid regulation of neuronal differentiation, stability, or regeneration in the olfactory pathway from embryogenesis through adulthood. These influences may be in register with retinoid effects on immune responses, metabolism, and modulation of food intake.

Retinoic acid signaling and function in the adult hippocampus

Retinoic acid (RA) is an essential growth factor, derived from vitamin A, which controls growth by activating specific receptors that are members of the nuclear receptor family of transcriptional regulators. Its function in control of growth and differentiation in the embryonic CNS has been extensively investigated, but a role for RA in the mature brain has only recently become apparent. Although the adult CNS has much less capacity for change compared to the embryonic CNS, a limited amount of flexibility, referred to as neural plasticity, still exists. It is these processes that RA influences in the adult brain, including long-term potentiation and neurogenesis. The hippocampus is a brain region dependent upon neural plasticity for its function in learning and memory, and this review focuses on the roles that RA may play in regulating these processes in the adult.

A vitamin A-free diet results in impairment of the rat hippocampal somatostatinergic system

Previous studies have revealed the presence of retinoid specific receptors in the hippocampus and have demonstrated that vitamin A deficiency produces a severe deficit in spatial learning and memory which are linked to a proper hippocampal functioning. It is also well known that the tetradecapeptide somatostatin binds to specific receptors in the hippocampus and, when injected into this brain area, facilitates the acquisition of spatial tasks. In addition, depletion of somatostatin by cysteamine impairs acquisition of these tasks. Taken together, these studies support the idea that the hippocampal somatostatinergic system might be regulated by vitamin A. Hence, we evaluated the effects of vitamin A deprivation and subsequent administration of vitamin A on the rat hippocampal somatostatinergic system. Rats fed a vitamin A-free diet exhibited a significant reduction of somatostatin-like immunoreactivity content in the hippocampus whereas the somatostatin mRNA levels were unaltered. Vitamin A deficiency increased the somatostatin receptor density and its dissociation constant. Functional Gi activity as well as the capacity of somatostatin to inhibit basal and forskolin-stimulated adenylyl cyclase activity was decreased in vitamin A deficiency rats as compared with the control animals. All these parameters were fully restored when vitamin A was replaced in the diet. Furthermore, we found that the Gialpha1, Gialpha2 and Gialpha3 protein levels were unaltered in hippocampal membranes from rats fed a vitamin A-free diet whereas subsequent vitamin A administration to these rats caused a significant increase in the levels of Gialpha1 and Gialpha2. Altogether, the present findings suggest that dietary vitamin A levels modulate the somatostatinergic system in the rat hippocampus.

Regulation of multiple dopamine signal transduction molecules by retinoids in the developing striatum

Increasing evidence based on pharmacological and genetic studies suggests that retinoid signaling plays an important role in developmental control of striatal neurons. In the present report, we screened for genes that might be regulated by retinoids in the developing striatum. We cultured tissue explants from the lateral ganglionic eminence (striatal primordium), and for regional comparison, its adjacent structures of the cerebral cortex and the medial ganglionic eminence in embryonic day 15 rat telencephalon. Using the ribonuclease protection assay, we found that both all-trans retinoic acid and 9-cis retinoic acid significantly up-regulated dopamine D1 receptor, heterotrimeric G protein olfactory, adenylyl cyclase type V and dopamine- and cyclic adenosine 3':5'-monophosphate-regulated phosphoprotein mRNAs in the lateral ganglionic eminence culture. By contrast, neither all-trans retinoic acid nor 9-cis retinoic acid significantly altered D1 receptor, heterotrimeric G protein olfactory, adenylyl cyclase type V and dopamine- and cyclic adenosine 3':5'-monophosphate-regulated phosphoprotein mRNAs in the cortical and the medial ganglionic eminence cultures except that D1 receptor mRNA was dramatically induced in the medial ganglionic eminence by retinoic acid treatments. To test whether the induction of multiple dopamine signaling molecules in the lateral ganglionic eminence was due to a general enhancement of neuronal differentiation by retinoic acid, we assayed the effects of retinoic acid on other differentiation markers, including glutamate decarboxylase 65, NR1 subunit of glutamate NMDA receptor and microtubule-associated protein-2. None of these genes were significantly altered by retinoic acid treatments in the lateral ganglionic eminence culture, indicating the specificity of gene regulation by retinoic acid signaling. As D1 receptor, heterotrimeric G protein olfactory, adenylyl cyclase type V and dopamine- and cyclic adenosine 3':5'-monophosphate-regulated phosphoprotein are important molecules involved in propagation of striatal dopamine neurotransmission, our study raises the hypothesis that retinoid signaling may coordinately activate the transcriptional program that is associated with the dopamine signaling pathway in developing striatal neurons. Such coordinate regulation by retinoids may be part of the mechanisms by which the complex yet highly organized neurochemical constituents of the striatum are established during development.

Tumorigenicity issues of embryonic carcinoma-derived stem cells: relevance to surgical trials using NT2 and hNT neural cells

Cell therapy is a rapidly moving field with new cells, cell lines, and tissue-engineered constructs being developed globally. As these novel cells are further developed for transplantation studies, it is important to understand their safety profiles both prior to and posttransplantation in animals and humans. Embryonic carcinoma-derived cells are considered an important alternative to stem cells. The NTera2/D1 teratocarcinoma cell-line (or NT2-N cells) gives rise to neuron-like cells called hNT neurons after exposure to retinoic acid. NT2 cells form tumors upon transplantation into the rodent. However, when the NT2 cells are treated with retinoic acid to produce hNT cells, they terminally differentiate into post-mitotic neurons with no sign of tumorigenicity. Preliminary human transplantation studies in the brain of stroke patients also demonstrated a lack of tumorigenicity of these cells. This review focuses on the use of hNT neurons in cell transplantation for the treatment in central nervous system (CNS) diseases, disorders, or injuries and on the mechanism involved in retinoic acid exposure, final differentiation state, and subsequent tumorigenicity issues that must be considered prior to widespread clinical use.