Evaluation of the effects of vitamin A supplementation on adult rat substantia nigra and striatum redox and bioenergetic states: mitochondrial impairment, increased 3-nitrotyrosine and alpha-synuclein, but decreased D2 receptor contents

Preventive Vitamin A Supplementation Improves Striatal Function in 6-Hydroxydopamine Hemiparkinsonian Rats

Background

The mechanisms leading to a loss of dopaminergic (DA) neurons from the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) have multifactorial origins. In this context, nutrition is currently investigated as a modifiable environmental factor for the prevention of PD. In particular, initial studies revealed the deleterious consequences of vitamin A signaling failure on dopamine-related motor behaviors. However, the potential of vitamin A supplementation itself to prevent neurodegeneration has not been established yet.

Objective

The hypothesis tested in this study is that preventive vitamin A supplementation can protect DA neurons in a rat model of PD.

Methods

The impact of a 5-week preventive supplementation with vitamin A (20 IU/g of diet) was measured on motor and neurobiological alterations induced by 6-hydroxydopamine (6-OHDA) unilateral injections in the striatum of rats. Rotarod, step test and cylinder tests were performed up to 3 weeks after the lesion. Post-mortem analyses (retinol and monoamines dosages, western blots, immunofluorescence) were performed to investigate neurobiological processes.

Results

Vitamin A supplementation improved voluntary movements in the cylinder test. In 6-OHDA lesioned rats, a marked decrease of dopamine levels in striatum homogenates was measured. Tyrosine hydroxylase labeling in the SNc and in the striatum was significantly decreased by 6-OHDA injection, without effect of vitamin A. By contrast, vitamin A supplementation increased striatal expression of D2 and RXR receptors in the striatum of 6-OHDA lesioned rats.

Conclusions

Vitamin A supplementation partially alleviates motor alterations and improved striatal function, revealing a possible beneficial preventive approach for PD.

Role and Mechanism of Vitamin A Metabolism in the Pathophysiology of Parkinson's Disease

Evidence shows that altered retinoic acid signaling may contribute to the pathogenesis and pathophysiology of Parkinson's disease (PD). Retinoic acid is the bioactive derivative of the lipophilic vitamin A. Vitamin A is involved in several important homeostatic processes, such as cell differentiation, antioxidant activity, inflammation and neuronal plasticity. The role of vitamin A and its derivatives in the pathogenesis and pathophysiology of neurodegenerative diseases, and their potential as therapeutics, has drawn attention for more than 10 years. However, the literature sits in disparate fields. Vitamin A could act at the crossroad of multiple environmental and genetic factors of PD. The purpose of this review is to outline what is known about the role of vitamin A metabolism in the pathogenesis and pathophysiology of PD. We examine key biological systems and mechanisms that are under the control of vitamin A and its derivatives, which are (or could be) exploited for therapeutic potential in PD: the survival of dopaminergic neurons, oxidative stress, neuroinflammation, circadian rhythms, homeostasis of the enteric nervous system, and hormonal systems. We focus on the pivotal role of ALDH1A1, an enzyme expressed by dopaminergic neurons for the detoxification of these neurons, which is under the control of retinoic acid. By providing an integrated summary, this review will guide future studies on the potential role of vitamin A in the management of symptoms, health and wellbeing for PD patients.

Mitochondrial Agents for Bipolar Disorder

Background

Bipolar disorder is a chronic and often debilitating illness. Current treatment options (both pharmaco- and psychotherapy) have shown efficacy, but for many leave a shortfall in recovery. Advances in the understanding of the pathophysiology of bipolar disorder suggest that interventions that target mitochondrial dysfunction may provide a therapeutic benefit.

Methods

This review explores the current and growing theoretical rationale as well as existing preclinical and clinical data for those therapies aiming to target the mitochondrion in bipolar disorder. A Clinicaltrials.gov and ANZCTR search was conducted for complete and ongoing trials on mitochondrial agents used in psychiatric disorders. A PubMed search was also conducted for literature published between January 1981 and July 2017. Systematic reviews, randomized controlled trials, observational studies, case series, and animal studies with an emphasis on agents affecting mitochondrial function and its role in bipolar disorder were included. The search was augmented by manually searching the references of key papers and related literature. The results were presented as a narrative review.

Results

Mitochondrial agents offer new horizons in mood disorder treatment. While some negative effects have been reported, most compounds are overall well tolerated and have generally benign side-effect profiles.

Conclusions

The study of neuroinflammation, neurodegeneration, and mitochondrial function has contributed the understanding of bipolar disorder's pathophysiology. Agents targeting these pathways could be a potential therapeutic strategy. Future directions include identification of novel candidate mitochondrial modulators as well as rigorous and well-powered clinical trials.

Biocompatible Gold Nanoparticles Ameliorate Retinoic Acid-Induced Cell Death and Induce Differentiation in F9 Teratocarcinoma Stem Cells

The unique properties of gold nanoparticles (AuNPs) have attracted much interest for a range of applications, including biomedical applications in the cosmetic industry. The current study assessed the anti-oxidative effect of AuNPs against retinoic acid (RA)-induced loss of cell viability; cell proliferation; expression of oxidative and anti-oxidative stress markers, pro- and anti-apoptotic genes, and differentiation markers; and mitochondrial dysfunction in F9 teratocarcinoma stem cells. AuNPs were prepared by reduction of gold salts using luteolin as a reducing and stabilizing agent. The prepared AuNPs were spherical in shape with an average diameter of 18 nm. F9 cells exposed to various concentrations of these AuNPs were not harmed, whereas cells exposed to RA exhibited a dose-dependent change in cell viability and cell proliferation. The RA-mediated toxicity was associated with increased leakage of lactate dehydrogenase, reactive oxygen species, increased levels of malondialdehyde and nitric oxide, loss of mitochondrial membrane potential, and a reduced level of ATP. Finally, RA increased the level of pro-apoptotic gene expression and decreased the expression of anti-apoptotic genes. Interestingly, the toxic effect of RA appeared to be decreased in cells treated with RA in the presence of AuNPs, which was coincident with the increased levels of anti-oxidant markers including thioredoxin, glutathione peroxidases, glutathione, glutathione disulfide, catalase, and superoxide dismutase. Concomitantly, AuNPs ameliorated the apoptotic response by decreasing the mRNA expression of p53, p21, Bax, Bak, caspase-3, caspase-9, and increasing the expressions of Bcl-2 and Bcl-Xl. Interestingly, AuNPs not only ameliorated oxidative stress but also induced differentiation in F9 cells by increasing the expression of differentiation markers including retinoic acid binding protein, laminin 1, collagen type IV, and Gata 6 and decreasing the expressions of markers of stem cell pluripotency including Nanog, Rex1, octamer-binding transcription factor 4, and Sox-2. These consistent cellular and biochemical data suggest that AuNPs could ameliorate RA-induced cell death and facilitate F9 cell differentiation. AuNPs could be suitable therapeutic agents for the treatment of oxidative stress-related diseases such as atherosclerosis, cancer, diabetes, rheumatoid arthritis, and neurodegenerative diseases.

Astragaloside IV improves the isoproterenol-induced vascular dysfunction via attenuating eNOS uncoupling-mediated oxidative stress and inhibiting ROS-NF-κB pathways

OBJECTIVE

Oxidative stress and inflammation are regarded as two important triggers of endothelial dysfunction and play pivotal role in progression of vascular damage associated with cardiac hypertrophy. Our previous studies demonstrated that astragaloside IV (AsIV) could protect against cardiac hypertrophy in rats induced by isoproterenol (Iso), but its effects on the aorta are not known. In present study, we aimed to assess the effects of AsIV on Isoinduced vascular dysfunction.

METHODS

Sprague-Dawley (SD) rats were treated with Iso (10mg/kg/d) alone or in combination with AsIV (50mg/kg/d).

RESULTS

Compared with Isotreated alone, AsIV significantly reduced the ratios of heart weight/body weight and left ventricular weight/body weight. AsIV ameliorated the increased vasoconstriction response to phenylephrine induced by Iso and suppressed superoxide anion generation in rat aorta, increased endothelial nitric oxide synthase (eNOS) dimer/monomer ratio and its critical cofactor tetrahydrobiopterin (BH4) content in aorta as well as the NO production in the serum, reduced the plasmatic peroxynitrite (ONOO-). Moreover, in contrast with Isotreatment alone, AsIV decreased the ratio of nuclear-to-cytosolic protein expression of the NF-κB p65 subunit while enhanced its inhibited protein expression of IκB-α, down-regulated mRNA expression of IL-1β, IL-6 and TNF-α of the aorta.

CONCLUSIONS

The present study suggested that AsIV protects against Isoinduced vascular dysfunction probably via attenuating eNOS uncoupling-mediated oxidative stress and inhibiting ROS-NF-κB pathways.

The neurotoxic effects of vitamin A and retinoids

Vitamin A (retinol) and its congeners - the retinoids - participate in a panoply of biological events, as for instance cell differentiation, proliferation, survival, and death, necessary to maintain tissue homeostasis. Furthermore, such molecules may be applied as therapeutic agents in the case of some diseases, including dermatological disturbances, immunodeficiency, and cancer (mainly leukemia). In spite of this, there is a growing body of evidences showing that vitamin A doses exceeding the nutritional requirements may lead to negative consequences, including bioenergetics state dysfunction, redox impairment, altered cellular signaling, and cell death or proliferation, depending on the cell type. Neurotoxicity has long been demonstrated as a possible side effect of inadvertent consumption, or even under medical recommendation of vitamin A and retinoids at moderate to high doses. However, the exact mechanism by which such molecules exert a neurotoxic role is not clear yet. In this review, recent data are discussed regarding the molecular findings associated with the vitamin A-related neurotoxicity.

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.

Increased cerebral oxidative damage and decreased antioxidant defenses in ovariectomized and sham-operated rats supplemented with vitamin A

Previous studies have linked oxidative stress with aging and aging-related processes, including menopause. Abnormalities in the redox state similar to those observed in menopausal women can be modeled experimentally with rat ovariectomy. The aim of the present study was to investigate the effects of vitamin A (retinol palmitate) supplementation (500 or 1,500 IU kg(-1) day(-1) for 30 days) on behavioral parameters and brain redox profile in ovariectomized (OVX) and sham-operated rats. Ovariectomy caused pronounced uterine atrophy and decreased locomotor/exploratory activity. Moreover, we found increased hypothalamic and frontal cortex superoxide dismutase/catalase (SOD/CAT) ratio and decreased hippocampal thiol content, accompanied by increased frontal cortex lipid oxidative damage (TBARS) in OVX rats. Vitamin A at 1,500 IUkg(-1) day(-1) decreased exploratory behavior and decreased total hippocampal thiol content in sham-operated rats, increased hippocampal SOD/CAT ratio and decreased total antioxidant potential in the hippocampus of both sham and OVX groups, and increased cortical TBARS levels in OVX rats. Thus, vitamin A may induce a pro-oxidant state in discrete brain regions of sham-operated and OVX rats. These results suggest some caution regarding the use of high doses of vitamin A supplementation during menopause.

Increased susceptibility of mitochondria isolated from frontal cortex and hippocampus of vitamin A-treated rats to non-aggregated amyloid-β peptides 1-40 and 1-42

OBJECTIVE

Vitamin A is a redox-active molecule and its inadvertent utilisation as a preventive therapy against ageing or neurodegeneration has become a harmful habit among humans at different ages. Mitochondrial dysfunction and redox impairment may be induced by vitamin A supplementation experimentally. Nonetheless, it is still not clear by which mechanisms vitamin A elicits such effects. Then, we performed this investigation to analyse whether mitochondria isolated from frontal cortex and hippocampus of vitamin A-treated rats are more sensitive to a challenge with amyloid-β (Aβ) peptides 1-40 or 1-42.

METHODS

Adult Wistar rats received vitamin A at 1000-9000 IU/kg/day orally for 28 days. Then, mitochondria were isolated and the challenge with Aβ peptides 1-40 or 1-42 (at 0.2 or 0.1 μM, respectively) for 10 min was carried out before mitochondrial electron transfer chain enzyme activity, superoxide anion radical (O2 -•) production and 3-nitrotyrosine content quantification.

RESULTS

Mitochondria obtained from vitamin A-treated rats are more sensitive to Aβ peptides 1-40 or 1-42 than mitochondria isolated from the control group, as decreased mitochondrial complex enzyme activity and increased O2 -• production and 3-nitrotyrosine content were observed in incubated mitochondria isolated from vitamin A-treated rats.

CONCLUSION

These data suggest that oral intake of vitamin A at clinical doses increases the susceptibility of mitochondria to a neurotoxic agent even at low concentrations.

The effects of vitamin A supplementation for 3 months on adult rat nigrostriatal axis: increased monoamine oxidase enzyme activity, mitochondrial redox dysfunction, increased β-amyloid(1-40) peptide and TNF-α contents, and susceptibility of mitochondria to an in vitro H2O2 challenge

Even though vitamin A has been viewed as an antioxidant molecule, recent findings demonstrate that such vitamin elicits pro-oxidant effects in vivo. Moreover, vitamin A supplements utilization may increase mortality rates among healthy subjects. However, the mechanism by which vitamin A elicits such effects remains to be better analyzed. In this regard, we investigated here the consequences of vitamin A supplementation at 500, 1000, or 2500 IU/kg day(-1) for 3 months on adult rat substantia nigra and striatum total and mitochondrial redox state (both oxidative and nitrosative stress markers), electron transfer chain activity, monoamine oxidase (MAO) enzyme activity, endoplasmic reticulum stress marker (BiP), α- and β-synucleins, β-amyloid peptide (1-40), dopamine D2 receptor (D2R), receptor for advanced glycation end products (RAGE), caspase-3 and caspase-8 enzyme activity and tumor necrosis factor-α (TNF-α) levels. Also, nigrostriatal mitochondria were isolated and challenged with 50 μM H2O2 in vitro after vitamin A supplementation and complexes I-III, II-III, and IV enzyme activity was recorded. We observed both total and mitochondrial oxidative and nitrosative stress, increased MAO enzyme activity, and increased levels of α-synuclein, β-amyloid peptide, RAGE, and TNF-α, but decreased D2R in both rat brain areas. Furthermore, vitamin A supplementation induced a decrease in nigral, but not striatal, β-synuclein levels in this work. Moreover, mitochondria isolated from both substantia nigra and striatum of vitamin A-treated rats were more sensitive to H2O2 than control mitochondria as assessed through the in vitro assay. Overall, these data may be useful to explain how vitamin A elicits neurotoxic effects chronically.

Increased 3-nitrotyrosine levels in mitochondrial membranes and impaired respiratory chain activity in brain regions of adult female rats submitted to daily vitamin A supplementation for 2 months

Vitamin A supplementation among women is a common habit worldwide in an attempt to slow aging progression due to the antioxidant potential attributed to retinoids. Nonetheless, vitamin A elicits a myriad of side effects that result from either therapeutic or inadvertent intake at varying doses for different periods. The mechanism behind such effects remains to be elucidated. In this regard, we performed the present work aiming to investigate the effects of vitamin A supplementation at 100, 200, or 500IU/kgday(-1) for 2 months on female rat brain, analyzing tissue lipid peroxidation levels, antioxidant enzyme activities (both Cu/Zn-superoxide dismutase - SOD - and Mn-SOD); glutathione S-transferase (GST) and monoamine oxidase (MAO) enzyme activity; mitochondrial respiratory chain activity and redox parameters in mitochondrial membranes, as well as quantifying α- and β-synucleins, β-amyloid peptide(1-40), immunoglobulin heavy-chain binding protein/78kDa glucose-regulated protein (BiP/GRP78), receptor for advanced glycation end products (RAGE), D2 receptor, and tumor necrosis factor-α (TNF-α) contents in rat frontal cortex, hippocampus, striatum, and cerebellum. We observed increased lipid peroxidation marker levels, altered Cu/Zn-SOD and Mn-SOD enzyme activities, mitochondrial nitrosative stress, and impaired respiratory chain activity in such brain regions. On the other hand, we did not find any change in MAO and GST enzyme activities, and on α- and β-synucleins, β-amyloid peptide(1-40), GRP78/BiP, RAGE, D2 receptor, and TNF-α contents. Importantly, we did not observed any evidence regarding an antioxidant effect of such vitamin at low doses in this experimental model. The use of vitamin A as an antioxidant therapy among women needs to be reexamined.

The effects of vitamin A supplementation to rats during gestation and lactation upon redox parameters: increased oxidative stress and redox modulation in mothers and their offspring

Vitamin A is an essential nutrient required in adequate amounts for reproduction and development. Subtle variations in the status of maternal nutrition may affect physiological and metabolic parameters in the fetus. Evidence suggests a key role for oxidative stress in these events. Literature is controversial about the effects of vitamin A supplementation. Here, we studied the effects of vitamin A supplementation on female Wistar rats during gestation and lactation on oxidative stress parameters of maternal and offspring tissues. Rats received daily doses of vitamin A at 2500, 12,500 and 25,000IU/kg. We observed an increase of oxidative damage markers in the reproductive tissues and plasma of dams. The activity of glutathione-S-transferase was modulated by vitamin A supplementation. It was found to be increased in the liver of dams and decreased in the kidneys of mothers and offspring. In pups, supplementation decreased the total antioxidant potential of the liver along with decreased superoxide dismutase/catalase activity ratio in the kidney. The levels of lipoperoxidation were increased in male offspring, but decreased in female pups. Collectively, the results suggest that excessive vitamin A intake during gestation and lactation might be toxic for mothers with adverse effects for the developing offspring.

Reactive oxygen species in the regulation of synaptic plasticity and memory

The brain is a metabolically active organ exhibiting high oxygen consumption and robust production of reactive oxygen species (ROS). The large amounts of ROS are kept in check by an elaborate network of antioxidants, which sometimes fail and lead to neuronal oxidative stress. Thus, ROS are typically categorized as neurotoxic molecules and typically exert their detrimental effects via oxidation of essential macromolecules such as enzymes and cytoskeletal proteins. Most importantly, excessive ROS are associated with decreased performance in cognitive function. However, at physiological concentrations, ROS are involved in functional changes necessary for synaptic plasticity and hence, for normal cognitive function. The fine line of role reversal of ROS from good molecules to bad molecules is far from being fully understood. This review focuses on identifying the multiple sources of ROS in the mammalian nervous system and on presenting evidence for the critical and essential role of ROS in synaptic plasticity and memory. The review also shows that the inability to restrain either age- or pathology-related increases in ROS levels leads to opposite, detrimental effects that are involved in impairments in synaptic plasticity and memory function.

Increased blood oxidative stress in experimental menopause rat model: the effects of vitamin A low-dose supplementation upon antioxidant status in bilateral ovariectomized rats

Menopause has been reported to be associated with increased oxidative stress and metabolic disorders among women worldwide. Disarrangements in the redox state similar to those observed in women during the decline of ovarian hormonal activity can be obtained experimentally through rat bilateral ovariectomy. The search for alternative treatments to improve life quality in postmenopausal woman is really important. The aim of this study was to evaluate biochemical and oxidative stress parameters that distinguish sham-operated female rats from Wistar rats bilaterally ovariectomized (OVX). Additionally, we have also investigated the effects of retinol palmitate (a vitamin A supplement) low-dose supplementation (500 or 1500 IU/kg/day, during 30 days) upon blood and plasma antioxidant status in OVX rats. Ovariectomy caused an increase in body weight gain, pronounced uterine atrophy, decreased plasma triglycerides and increased total cholesterol levels, and reduced acid uric content. Moreover, we found increased blood peroxidase activities (catalase and glutathione peroxidase), decreased plasma non-enzymatic antioxidant defenses total reactive antioxidant potential and total antioxidant reactivity, decreased protein and non-protein SH levels, accompanied by increased protein oxidative damage (carbonyl). In addition, vitamin A low-dose supplementation was capable to ameliorate antioxidant status in OVX rats, restoring both enzymatic and non-enzymatic defenses, promoting reduction in plasma SH content, and decreasing protein oxidative damage levels. This is the first work in the literature showing that vitamin A at low dose may be beneficial in the treatment of menopause symptoms. Further studies will be made to better understand the effects of vitamin A supplementation in menopause rat model.

Total and mitochondrial nitrosative stress, decreased brain-derived neurotrophic factor (BDNF) levels and glutamate uptake, and evidence of endoplasmic reticulum stress in the hippocampus of vitamin A-treated rats

Vitamin A supplementation has caused concern among public health researchers due to its ability in decreasing life quality from acute toxicological effects to increasing mortality rates among vitamin supplement users. For example, it was described cognitive decline (i.e. irritability, anxiety, and depression) in patients subjected to long-term vitamin A therapy, as occurs in cancer treatment. However, the mechanism by which vitamin A affects mammalian cognition is not completely understood. Then, we performed the present work to investigate the effects of vitamin A supplementation at clinical doses (1,000-9,000 IU/kg day(-1)) for 28 days on rat hippocampal nitrosative stress levels (both total and mitochondrial), bioenergetics states, brain-derived neurotrophic factor (BDNF), alpha- and beta-synucleins, BiP and dopamine receptor 2 (D2 receptor) contents, and glutamate uptake. We observed mitochondrial impairment regarding respiratory chain function: increased complex I-III, but decreased complex IV enzyme activity. Also, decreased BDNF levels were observed in vitamin A-treated rats. The present data demonstrates, at least in part, that mitochondrial dysfunction and decreased BDNF and D2 receptors levels, as well as decreased glutamate uptake may take an important role in the mechanism behind the previously reported cognitive disturbances associated to vitamin A supplementation.

Nitrated alpha-synuclein induces the loss of dopaminergic neurons in the substantia nigra of rats

Background

The pathology of Parkinson's disease (PD) is characterized by the degeneration of the nigrostriatal dopaminergic pathway, as well as the formation of intraneuronal inclusions known as Lewy bodies and Lewy neurites in the substantia nigra. Accumulations of nitrated α-synuclein are demonstrated in the signature inclusions of Parkinson's disease. However, whether the nitration of α-synuclein is relevant to the pathogenesis of PD is unknown.

Methodology/Principal Findings

In this study, effect of nitrated α-synuclein to dopaminergic (DA) neurons was determined by delivering nitrated recombinant TAT-α-synuclein intracellular. We provide evidence to show that the nitrated α-synuclein was toxic to cultured dopaminergic SHSY-5Y neurons and primary mesencephalic DA neurons to a much greater degree than unnitrated α-synuclein. Moreover, we show that administration of nitrated α-synuclein to the substantia nigra pars compacta of rats caused severe reductions in the number of DA neurons therein, and led to the down-regulation of D₂R in the striatum in vivo. Furthermore, when administered to the substantia nigra of rats, nitrated α-synuclein caused PD-like motor dysfunctions, such as reduced locomotion and motor asymmetry, however unmodified α-synuclein had significantly less severe behavioral effects.

Conclusions/Significance

Our results provide evidence that α-synuclein, principally in its nitrated form, induce DA neuron death and may be a major factor in the etiology of PD.