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

Therapeutic insights elaborating the potential of retinoids in Alzheimer’s disease

Alzheimer’s disease (AD) is perceived with various pathophysiological characteristics such oxidative stress, senile plaques, neuroinflammation, altered neurotransmission immunological changes, neurodegenerative pathways, and age-linked alterations. A great deal of studies even now are carried out for comprehensive understanding of pathological processes of AD, though many agents are in clinical trials for the treatment of AD. Retinoids and retinoic acid receptors (RARs) are pertinent to such attributes of the disease. Retinoids support the proper functioning of the immunological pathways, and are very potent immunomodulators. The nervous system relies heavily on retinoic acid signaling. The disruption of retinoid signaling relates to several pathogenic mechanisms in the normal brain. Retinoids play critical functions in the neuronal organization, differentiation, and axonal growth in the normal functioning of the brain. Disturbed retinoic acid signaling causes inflammatory responses, mitochondrial impairment, oxidative stress, and neurodegeneration, leading to Alzheimer’s disease (AD) progression. Retinoids interfere with the production and release of neuroinflammatory chemokines and cytokines which are located to be activated in the pathogenesis of AD. Also, stimulating nuclear retinoid receptors reduces amyloid aggregation, lowers neurodegeneration, and thus restricts Alzheimer’s disease progression in preclinical studies. We outlined the physiology of retinoids in this review, focusing on their possible neuroprotective actions, which will aid in elucidating the critical function of such receptors in AD pathogenesis.

Decreased levels of serum retinoic acid in chinese children with autism spectrum disorder

Previous studies framed a possible link of retinoic acid (RA) regulation in brain to autism spectrum disorders (ASD) etiology. The aim of this study was to measure serum levels of RA in relation to the degree of the severity of autism. Serum RA levels were measured by enzyme-linked immunosorbent assay (ELISA) colorimetric detection Kit in 81 children with autism and 81 age-sex matched typical development children. The severity of autistic symptomatology was measured by the Childhood Autism Rating Scale (CARS) score using the Chinese version. The serum levels of RA in the children with ASD (1.68 ± 0.52 ng/ml) were significantly lower than those of control subjects (2.13 ± 0.71 ng/ml) (P < 0.001). At admission, 57 children (70.4%) had a severe autism. In those children, the mean serum RA levels were lower than in those children with mild to moderate autism (1.57 ± 0.47 ng/ml VS. 1.95 ± 0.55 ng/ml; P = 0.003). Furthermore, in multivariate model, low RA level was associated with having/the presence of ASD (adjusted odd ratio[OR] 0.516; P = 0.003) and severe ASD (OR 0.415; P = 0.015) after adjusted for confounding factors. The data suggested that serum RA levels were reduced in the group with ASD, and the levels negative correlated significantly with the severity of autism.

Systematic review of the literature on vitamin A and memory

Background

Over the last 30 years, a variety of studies reporting the effects of vitamin A on memory have been published.

Objective

To perform a rigorous systematic review of the literature on vitamin A and memory in order to organize evidence-based data on the subject.

Methods

Four authors carried out the systematic review in accordance with strict guidelines. The terms "vitamin A" OR "retinol" OR "retinoic acid" AND "memory" OR "cognition" OR "Alzheimer" were searched in virtually all medical research databases.

Results

From 236 studies containing the key words, 44 were selected for this review, numbering 10 reviews and 34 original articles. Most studies used animal models for studying vitamin A and cognition. Birds, mice and rats were more frequently employed whereas human studies accounted for only two reports on brain tissue from autopsies and one on the role of isotretinoin in cognition among individuals taking this medication to treat acne.

Conclusion

Vitamin A may be an important and viable complement in the treatment and prevention of Alzheimer's disease. Clinical trials are imperative and, at present, there is no evidence-based data to recommend vitamin A supplementation for the prevention or treatment of Alzheimer's disease.

Effect of marginal vitamin A deficiency during pregnancy on retinoic acid receptors and N-methyl-D-aspartate receptor expression in the offspring of rats

This study examined whether pregnancy-related marginal vitamin A deficiency (MVAD) influences postnatal development of retinoic acid receptors (RARs) and N-methyl-D-aspartate (NMDA) receptor subunit 1 (NR1) in hippocampus of rat pups. Sixteen female rats were randomized equally into control and MVAD groups. Dams and pups were fed with either a normal control diet or one deficient in vitamin A. Eight female pups in each group were killed at 1 day, 2 weeks, 4 weeks and 8 weeks after birth, respectively. Serum retinol levels were monitored. The messenger RNA (mRNA) and protein expressions and subcellular localization of RARα, RARβ and NR1 in postnatal hippocampus were detected. At 1 day, 2 weeks and 8 weeks after birth, serum retinol levels in the MVAD group were significantly lower than those in the control group. Results of Morris water maze test at 7 weeks of age showed that spatial learning and memory in the MVAD group were affected. Vitamin A deficiency resulted in decreased mRNA levels of RARα, RARβ and NR1 (P<.05). The protein level of RARα and NR1 in the MVAD group was lower than that of the control group (P<.05). There was no significant difference in RARβ between the groups (P>.05). A mass of RARα and NR1 colocalized in hippocampal cell cytoplasm on postnatal day 1. Our data suggested that vitamin A deficiency in pregnancy may affect the postnatal expression of RARα and NR1, affecting learning and memory function in the hippocampus and synaptic plasticity of the calcium signaling pathway.

Effect of vitamin A deficiency on retinol and retinyl esters contents in rat brain

In the present study, the pattern of vitamin A (retinol and retinyl esters) contents in discrete brain areas was investigated in Wistar rats (both sexes of 10-12 weeks old) fed on vitamin A deficient diet. The animals were placed on standard laboratory diet for the control animals and a vitamin A deficient diet for the experimental animals for 20 weeks. At the end of this period, brain retinol and retinyl esters contents from control and vitamin A deficient diet animals were measured by HPLC. Retinol was the predominant form of retinoids in male rat brains (77 to 92% of total retinol) and retinyl esters were the predominant form in female brain rats (4 to 44% of total retinol). The abundant ester in both sexes was the retinyl linoleate. Olfactory bulb and the midbrain contained the highest quantities of retinol and retinyl esters in both sexes. On the other hand, the vitamin A deficient diet significantly decreased the retinoid contents in male brain, in olfactory bulb (-30.7%), hindbrain (-46.2%) and increased it in forebrain (84.3%) and midbrain (2.2%). Total retinol was decreased in olfactory bulb (-38.7%), forebrain (-44.5%) and midbrain (-30.7%) and increased in hindbrain (23.4%) of vitamin A deficient female rats. In conclusion, retinol and retinyl esters were the brain compounds heterogeneously distributed throughout the brain areas in both the sexes and were significantly affected by vitamin A deficiency status as well.

Vitamin A deficiency in rats induces anatomic and metabolic changes comparable with those of neurodegenerative disorders

Anatomic and metabolic changes in central nervous system induced by 14 wk of vitamin A deprivation (VAD) were monitored and quantified in rats. In vivo brain magnetic resonance imaging (4.7T) was performed at 5, 7, 9, 11, and 14 wk of each diet after weaning in the following: 1) VAD group; 2) control pair-fed group; and 3) control group that consumed the diet ad libitum (1.15 microg retinol/g diet). After 14 wk, high-resolution magic angle spinning proton NMR spectroscopy (11.7T) was performed on small samples of cortex, hippocampus, and striatum. Serum retinol concentrations remained stable and cerebral volume (CV) increased as a linear function of body weight in the ad libitum group (R(2) = 0.78; P = 0.047) and pair-fed controls (R(2) = 0.78; P = 0.046). In VAD rats, retinol decreased from the onset of deprivation (2.2 +/- 0.14 micromol/L) to reach 0.3 +/- 0.13 micromol/L at wk 5, followed by a stopping of body weight gain from wk 7. In VAD rats, the CV decreased from wk 5 and reached a value 11% lower than that of the control group (P < 0.001) at wk 14 and was correlated with retinol status (R(2) = 0.99; P = 0.002). The VAD hippocampal volume decreased beginning at wk 9 and was 22% lower than that of the control group at wk 14 (P < 0.001). Compared with the control, VAD led to lower N acetyl aspartate:creatine+phosphocreatine (Cr) in cortex (-36%), striatum (-22%), and hippocampus (-19%) and higher myoinositol:Cr in cortex (+127%) and striatum (+150%). VAD induced anatomic and metabolic changes comparable to those associated with neurodegenerative disorders. By wk 7 of deprivation, the slowing in cerebral growth that correlated with the retinol level could be considered as a predictive marker of brain disorders, confirmed by metabolic data from VAD rats after 14 wk.

Applied shared log-normal frailty Cox-proportional hazard model to evaluating the effect of vitamin A on the rat passive avoidance memory

In this research, the Cox-proportional hazard model is used to investigate the effect of various values of vitamin A (3000, 4500 and 6000 IU kg(-1)) and sesame oil on the passive avoidance memory of rats by shuttle box. Present results confirm that various values of vitamin A do not improve the passive avoidance memory of rats (p < 0.05). We found that the animals are clustered (p < 0.001) and applying shared log-normal frailty for clustering improves present results (p < 0.05) such that sesame oil improves the passive avoidance memory task (p < 0.05). Therefore we should consider clustering in the analysis of biological data or we should use cloned animals.

Retinoic acid in the development, regeneration and maintenance of the nervous system

Retinoic acid (RA) is involved in the induction of neural differentiation, motor axon outgrowth and neural patterning. Like other developmental molecules, RA continues to play a role after development has been completed. Elevated RA signalling in the adult triggers axon outgrowth and, consequently, nerve regeneration. RA is also involved in the maintenance of the differentiated state of adult neurons, and disruption of RA signalling in the adult leads to the degeneration of motor neurons (motor neuron disease), the development of Alzheimer's disease and, possibly, the development of Parkinson's disease. The data described here strongly suggest that RA could be used as a therapeutic molecule for the induction of axon regeneration and the treatment of neurodegeneration.