Vitamin A (retinol) up-regulates the receptor for advanced glycation endproducts (RAGE) through p38 and Akt oxidant-dependent activation

Modulatory effects of rutin and vitamin A on hyperglycemia induced glycation, oxidative stress and inflammation in high-fat-fructose diet animal model

In the current study we investigated the impact of combination of rutin and vitamin A on glycated products, the glyoxalase system, oxidative markers, and inflammation in animals fed a high-fat high-fructose (HFFD) diet. Thirty rats were randomly divided into six groups (n = 5). The treatments, metformin (120 mg/kg), rutin (100 mg/kg), vitamin A (43 IU/kg), and a combination of rutin (100 mg/kg) and vitamin A (43 IU/kg) were given to relevant groups of rats along with high-fructose high-fat diet for 42 days. HbA1c, D-lactate, Glyoxylase-1, Hexokinase 2, malondialdehyde (MDA), glutathione peroxidase (GPx), catalase (CAT), nuclear transcription factor-B (NF-κB), interleukin-6 (IL-6), interleukin-8 (IL-8) and histological examinations were performed after 42 days. The docking simulations were conducted using Auto Dock package. The combined effects of rutin and vitamin A in treated rats significantly (p < 0.001) reduced HbA1c, hexokinase 2, and D-lactate levels while preventing cellular damage. The combination dramatically (p < 0.001) decreased MDA, CAT, and GPx in treated rats and decreased the expression of inflammatory cytokines such as IL-6 andIL-8, as well as the transcription factor NF-κB. The molecular docking investigations revealed that rutin had a strong affinity for several important biomolecules, including as NF-κB, Catalase, MDA, IL-6, hexokinase 2, and GPx. The results propose beneficial impact of rutin and vitamin A as a convincing treatment strategy to treat AGE-related disorders, such as diabetes, autism, alzheimer's, atherosclerosis.

Could Vitamins Have a Positive Impact on the Treatment of Parkinson's Disease?

Parkinson's disease (PD) is the second most common progressive neurodegenerative disorder after Alzheimer's disease. Pathophysiologically, it is characterized by intracytoplasmic aggregates of α-synuclein protein in the Lewy body and loss of dopaminergic neurons from substantia nigra pars compacta and striatum regions of the brain. Although the exact mechanism of neurodegeneration is not fully elucidated, it has been reported that environmental toxins such as MPTP, rotenone, paraquat, and MPP⁺ induce oxidative stress, which is one of the causative factors for it. To date, there is no complete cure. However, the indispensable role of oxidative stress in mediating PD indicates that antioxidant therapy could be a possible therapeutic strategy against the disease. The deficiency of vitamins has been extensively co-related to PD. Dietary supplementation of vitamins with antioxidant, anti-inflammatory, anti-apoptotic, and free radical scavenging properties could be the potential neuroprotective therapeutic strategy. This review summarizes the studies that evaluated the role of vitamins (A, B, C, D, E, and K) in PD. It will guide future studies in understanding the potential therapeutic role of vitamins in disease pathophysiology and may provide a framework for designing treatment strategies against the disease.

RAGE against the Machine: Can Increasing Our Understanding of RAGE Help Us to Battle SARS-CoV-2 Infection in Pregnancy?

The receptor of advanced glycation end products (RAGE) is a receptor that is thought to be a key driver of inflammation in pregnancy, SARS-CoV-2, and also in the comorbidities that are known to aggravate these afflictions. In addition to this, vulnerable populations are particularly susceptible to the negative health outcomes when these afflictions are experienced in concert. RAGE binds a number of ligands produced by tissue damage and cellular stress, and its activation triggers the proinflammatory transcription factor Nuclear Factor Kappa B (NF-κB), with the subsequent generation of key proinflammatory cytokines. While this is important for fetal membrane weakening, RAGE is also activated at the end of pregnancy in the uterus, placenta, and cervix. The comorbidities of hypertension, cardiovascular disease, diabetes, and obesity are known to lead to poor pregnancy outcomes, and particularly in populations such as Native Hawaiians and Pacific Islanders. They have also been linked to RAGE activation when individuals are infected with SARS-CoV-2. Therefore, we propose that increasing our understanding of this receptor system will help us to understand how these various afflictions converge, how forms of RAGE could be used as a biomarker, and if its manipulation could be used to develop future therapeutic targets to help those at risk.

Novel advances in inhibiting advanced glycation end product formation using natural compounds

Advanced glycation end products (AGEs) are a group of complex compounds generated by nonenzymatic interactions between proteins and reducing sugars or lipids. AGEs accumulate in vivo and activate various signaling pathways closely related to the occurrence of various chronic metabolic diseases. In this paper, we describe the process through which AGEs are formed, the classification of AGEs, and biological effects of AGEs on human health. Most importantly, we review recent progress in natural compound-based AGE formation inhibitors. Major classes of natural inhibitors, including polyphenols, polysaccharides, terpenoids, vitamins and alkaloids, have been described. Their mechanisms of action have been summarized as scavenging free radicals, chelating metal ions, capturing active carbonyl compounds, protecting protein glycation sites, and lowering blood glucose levels. Although these natural compounds have good antiglycation activity, to date, they are not widely used in the clinic, likely because of their low content levels. However, these natural compounds and their molecular frameworks will play a valuable role in inspiring drug discovery.

Effects of IC50 dose of retinol on metabolomics of RAW264.7 cells

Vitamin A is one of the most multifunctional vitamins in normal human physiology and is involved in several basic physiological processes from embryonic development to adulthood, such as embryogenesis, vision, immunity, cell differentiation, and proliferation. In this study, we conducted ¹ H- NMR to evaluate the metabolomic changes in RAW264.7 cells after treatment with retinol at an IC₅₀ dose to identify its effects on the differential metabolites and main metabolic pathways. Our results showed that the IC₅₀ dose (140 μM) of retinol affected the metabolism of RAW264.7 cells, with a total of 22 differential metabolites identified via ¹ H-NMR, including amino acids, sugars, organic acids, glutathione, glycerin, and creatine. Additionally, multiple metabolic pathways were affected by retinol treatment, including downregulation of amino acid biosynthesis, protein synthesis, and pyruvate metabolism. We speculate that the cytotoxicity of retinol at the IC₅₀ dose is attributed to mitochondrial dysfunction as a result of oxidative stress or lipid peroxidation. PRACTICAL APPLICATIONS: With the general improvement of people's living standards, people use dietary supplements to improve the level of retinol to prevent non-specific diseases. But there are more and more cases of acute or chronic poisoning caused by excessive intake of vitamin A. Therefore, it is necessary to study the toxicity of vitamin A, and more attention should be paid to the excessive intake of vitamin A. From the perspective of metabolomics, this experiment studies the adverse effects of high dose retinol through the changes of metabolites and metabolic pathways at the cellular level. This study will assist further analyses of the toxic mechanism of excessive retinol as fortified foods and nutrient supplementation.

Changes in Cell Cycle and Up-Regulation of Neuronal Markers During SH-SY5Y Neurodifferentiation by Retinoic Acid are Mediated by Reactive Species Production and Oxidative Stress

Human neuroblastoma SH-SY5Y cells have been used as an in vitro model for neurodegenerative disorders such as Parkinson's disease and can be induced to a mature neuronal phenotype through retinoic acid (RA) differentiation. However, mechanisms of RA-induced differentiation remain unclear. Here, we investigate the role of reactive species (RS) on SH-SY5Y neuroblastoma cells under RA differentiation, using the antioxidant Trolox® as co-treatment. We found that RA treatment for 7 days reduced the cell number and proliferative capacity and induced the expression of adult catecholaminergic/neuronal markers such as tyrosine hydroxylase (TH), β-III tubulin, and enolase-2. Evaluation of intracellular RS production by DCFH oxidation assay and quantification of cell non-enzymatic antioxidant activity by TRAP demonstrated that RA increases RS production. Furthermore, mitochondrial NADH oxidation showed to be inhibited under differentiation with RA. Cells subjected to co-treatment with antioxidant Trolox® demonstrated a remaining proliferative capacity and a decrease in the pro-oxidant state and RS production. Besides, antioxidant treatment restores the mitochondrial NADH oxidation. Importantly, Trolox® co-treatment inhibited the appearance of morphological characteristics such as neurite extension and branching, and decreased the expression of TH, β-III tubulin, and enolase-2 after a seven-day differentiation with RA, indicating that RS production is a necessary step in this process. Trolox® also inhibited the phosphorylation of Akt and ERK1/2, which are involved in differentiation and survival, respectively, of these cells. Altogether, these data indicate the presence of a redox-dependent mechanism in SH-SY5Y RA-differentiation process and can be a useful insight to improve understanding of neuronal differentiation signaling.

Supplementation with vitamin A enhances oxidative stress in the lungs of rats submitted to aerobic exercise

Exercise training induces reactive oxygen species production and low levels of oxidative damage, which are required for induction of antioxidant defenses and tissue adaptation. This process is physiological and essential to improve physical conditioning and performance. During exercise, endogenous antioxidants are recruited to prevent excessive oxidative stress, demanding appropriate intake of antioxidants from diet or supplements; in this context, the search for vitamin supplements that enhance the antioxidant defenses and improve exercise performance has been continuously increasing. On the other hand, excess of antioxidants may hinder the pro-oxidant signals necessary for this process of adaptation. The aim of this study was to investigate the effects of vitamin A supplementation (2000 IU/kg, oral) upon oxidative stress and parameters of pro-inflammatory signaling in lungs of rats submitted to aerobic exercise (swimming protocol). When combined with exercise, vitamin A inhibited biochemical parameters of adaptation/conditioning by attenuating exercise-induced antioxidant enzymes (superoxide dismutase and glutathione peroxidase) and decreasing the content of the receptor for advanced glycation end-products. Increased oxidative damage to proteins (carbonylation) and lipids (lipoperoxidation) was also observed in these animals. In sedentary animals, vitamin A decreased superoxide dismutase and increased lipoperoxidation. Vitamin A also enhanced the levels of tumor necrosis factor alpha and decreased interleukin-10, effects partially reversed by aerobic training. Taken together, the results presented herein point to negative effects associated with vitamin A supplementation at the specific dose here used upon oxidative stress and pro-inflammatory cytokines in lung tissues of rats submitted to aerobic exercise.

Choline and Cystine Deficient Diets in Animal Models with Hepatocellular Injury: Evaluation of Oxidative Stress and Expression of RAGE, TNF-α, and IL-1β

This study aims to evaluate the effects of diets deficient in choline and/or cystine on hepatocellular injury in animal models (young male Wistar rats, aged 21 days), by monitoring some of the oxidative stress biomarkers and the expression of RAGE, TNF-α, and IL-1β. The animals were divided into 6 groups (n = 10) and submitted to different diets over 30 days: AIN-93 diet (standard, St), AIN-93 choline deficient (CD) diet and AIN-93 choline and cystine deficient (CCD) diet, in the pellet (pl) and powder (pw) diet forms. Independently of the diet form, AIN-93 diet already led to hepatic steatosis and CD/CCD diets provoked hepatic damage. The increase of lipid peroxidation, represented by the evaluation of thiobarbituric acid reactive species, associated with the decrease of levels of antioxidant enzymes, were the parameters with higher significance toward redox profile in this model of hepatic injury. Regarding inflammation, in relation to TNF-α, higher levels were evidenced in CD_(pl), while, for IL-1β, no significant alteration was detected. RAGE expression was practically the same in all groups, with exception of CCD_(pw) versus CCD_(pl). These results together confirm that AIN-93 causes hepatic steatosis and choline and/or cysteine deficiencies produce important hepatic injury associated with oxidative stress and inflammatory profiles.

Preventive supplementation with fresh and preserved peach attenuates CCl4-induced oxidative stress, inflammation and tissue damage

The present study was elaborated to comparatively evaluate the preventive effect of different peach-derived products obtained from preserved fruits (Syrup and Preserve Pulp Peach [PPP]) and from fresh peels and pulps (Peel and Fresh Pulp Peach [FPP]) in a model of liver/renal toxicity and inflammation induced by carbon tetrachloride (CCl4) in rats. Tissue damage (carbonyl, thiobarbituric acid reactive species and sulfhydril), antioxidant enzymes activity (catalase and superoxide dismutase) and inflammatory parameters [tumor necrosis factor (TNF)-α and interleukin (IL)-1β levels, and receptor for advanced glycation end-products (RAGE) and nuclear factor (NF)κB-p65 immunocontent] were investigated. Our findings demonstrated that Peel, PPP and FPP (200 or 400 mg/kg) daily administration by oral gavage for 30 days conferred a significant protection against CCl4-induced antioxidant enzymes activation and, most importantly, oxidative damage to lipids and proteins as well as blocked induction of inflammatory mediators such as TNF-α, IL-1β, RAGE and NFκB. This antioxidant/anti-inflammatory effect seems to be associated with the abundance of carotenoids and polyphenols present in peach-derived products, which are enriched in fresh-fruit-derived preparations (Peel and FPP) but are also present in PPP. The Syrup - which was the least enriched in antioxidants - displayed no protective effect in our experiments. These effects cumulated in decreased levels of transaminases and lactate dehydrogenase leakage into serum and maintenance of organ architecture. Therefore, the herein presented results show evidence that supplementation with peach products may be protective against organ damage caused by oxidative stress, being interesting candidates for production of antioxidant-enriched functional foods.

Development of nonalcoholic hepatopathy: contributions of oxidative stress and advanced glycation end products

Advanced glycation end products (AGEs) are generated spontaneously in cells; however, under conditions of hyperglycemia and lipid peroxidation, their levels are higher than usual, which contribute to the development of diseases such as the nonalcoholic fatty liver disease (NAFLD). NAFLD is associated with oxidative stress (OS), which is linked to the transition of steatosis to steatohepatitis due to lipid peroxidation. The AGE-receptor interaction in hepatic stellate cells leads to an increase in reactive oxygen species and enhances the proliferation and activation of these cells, worsening liver fibrosis and disease progression. In this vicious cycle, there is production of (carboxymethyl)lysine, a biomarker for products of advanced glycation and lipid peroxidation, being a shared component between the two pathways. In this review, we aim to compile evidence to support the basic molecular mechanisms of AGEs and OS generation and their influence, independently or combined, on the evolution of NAFLD. The deeper understanding of the interrelations of AGEs + OS may help to elucidate the pathogenic pathways of NAFLD and to devise rational therapeutic interventions for this disease, with an expected positive impact on quality of life of patients.

Coal and tire burning mixtures containing ultrafine and nanoparticulate materials induce oxidative stress and inflammatory activation in macrophages

Ultra-fine and nano-particulate materials resulting from mixtures of coal and non-coal fuels combustion for power generation release to the air components with toxic potential. We evaluated toxicological and inflammatory effects at cellular level that could be induced by ultrafine/nanoparticles-containing ashes from burning mixtures of coal and tires from an American power plant. Coal fly ashes (CFA) samples from the combustion of high-S coal and tire-derived fuel, the latter about 2-3% of the total fuel feed, in a 100-MW cyclone utility boiler, were suspended in the cell culture medium of RAW 264.7 macrophages. Cell viability, assessed by MTT reduction, SRB incorporation and contrast-phase microscopy analysis demonstrated that CFA did not induce acute toxicity. However, CFA at 1mg/mL induced an increase of approximately 338% in intracellular TNF-α, while release of this proinflammatory cytokine was increased by 1.6-fold. The expression of the inflammatory mediator CD40 receptor was enhanced by 2-fold, the receptor for advanced glycation endproducts (RAGE) had a 5.7-fold increase and the stress response protein HSP70 was increased nearly 12-fold by CFA at 1mg/mL. Although CFA did not induce cell death, parameters of oxidative stress and reactive species production were found to be altered at several degrees, such as nitrite accumulation (22% increase), DCFH oxidation (3.5-fold increase), catalase (5-fold increase) and superoxide dismutase (35% inhibition) activities, lipoperoxidation (4.2 fold-increase) and sulfhydryl oxidation (40% decrease in free SH groups). The present results suggest that CFA containing ultra-fine and nano-particulate materials from coal and tire combustion may induce sub-chronic cell damage, as they alter inflammatory and oxidative stress parameters at the molecular and cellular levels, but do not induce acute cell death.

Antiproliferative effect of catechin in GRX cells

The phenolic compounds present in cocoa seeds have been studied regarding health benefits, such as antioxidant and anti-inflammatory activities. Fibrosis is a wound healing response that occurs in almost all patients with chronic liver injury. A large number of cytokines and soluble intercellular mediators are related to changes in the behavior and phenotype of the hepatic stellate cell (HSC) that develop a fibrogenic and contractile phenotype leading to the development of fibrosis. The objective of this study was to assess the catechin effect in GRX liver cells in activities such as cell growth and inflammation. The GRX cells treatment with catechin induced a significant decrease in cell growth. This mechanism does not occur by apoptosis or even by autophagy because there were no alterations in expression of caspase 3 and PARP (apoptosis), and LC3 (autophagy). The expression of p27 and p53 proteins, regulators of the cell cycle, showed increased expression, while COX-2 and IL-6 mRNA showed a significant decrease in expression. This study shows that catechin decreases cell growth in GRX cells and, probably, this decrease does not occur by apoptosis or autophagy but through an anti-inflammatory effect and cell cycle arrest. Catechin also significantly decreased the production of TGF-β by GRX cells, showing a significant antifibrotic effect.

Retinol induces morphological alterations and proliferative focus formation through free radical-mediated activation of multiple signaling pathways

AIM

Toxicity of retinol (vitamin A) has been previously associated with apoptosis and/or cell malignant transformation. Thus, we investigated the pathways involved in the induction of proliferation, deformation and proliferative focus formation by retinol in cultured Sertoli cells of rats.

METHODS

Sertoli cells were isolated from immature rats and cultured. The cells were subjected to a 24-h treatment with different concentrations of retinol. Parameters of oxidative stress and cytotoxicity were analyzed. The effects of the p38 inhibitor SB203580 (10 μmol/L), the JNK inhibitor SP600125 (10 μmol/L), the Akt inhibitor LY294002 (10 μmol/L), the ERK inhibitor U0126 (10 μmol/L) the pan-PKC inhibitor Gö6983 (10 μmol/L) and the PKA inhibitor H89 (1 μmol/L) on morphological and proliferative/transformation-associated modifications were studied.

RESULTS

Retinol (7 and 14 μmol/L) significantly increases the reactive species production in Sertoli cells. Inhibition of p38, JNK, ERK1/2, Akt, and PKA suppressed retinol-induced [(3)H]dT incorporation into the cells, while PKC inhibition had no effect. ERK1/2 and p38 inhibition also blocked retinol-induced proliferative focus formation in the cells, while Akt and JNK inhibition partially decreased focus formation. ERK1/2 and p38 inhibition hindered transformation-associated deformation in retinol-treated cells, while other treatments had no effect.

CONCLUSION

Our results suggest that activation of multiple kinases is responsible for morphological and proliferative changes associated to malignancy development in Sertoli cells by retinol at the concentrations higher than physiological level.

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.