Oral vitamin A and retinoic acid supplementation stimulates antibody production and splenic Stra6 expression in tetanus toxoid-immunized mice

Dietary Intervention Impacts Immune Cell Functions and Dynamics by Inducing Metabolic Rewiring

Accumulating evidence has shown that nutrient metabolism is closely associated with the differentiation and functions of various immune cells. Cellular metabolism, including aerobic glycolysis, fatty acid oxidation, and oxidative phosphorylation, plays a key role in germinal center (GC) reaction, B-cell trafficking, and T-cell-fate decision. Furthermore, a quiescent metabolic status consolidates T-cell-dependent immunological memory. Therefore, dietary interventions such as calorie restriction, time-restricted feeding, and fasting potentially manipulate immune cell functions. For instance, intermittent fasting prevents the development of experimental autoimmune encephalomyelitis. Meanwhile, the fasting response diminishes the lymphocyte pool in gut-associated lymphoid tissue to minimize energy expenditure, leading to the attenuation of Immunoglobulin A (IgA) response. The nutritional status also influences the dynamics of several immune cell subsets. Here, we describe the current understanding of the significance of immunometabolism in the differentiation and functionality of lymphocytes and macrophages. The underlying molecular mechanisms also are discussed. These experimental observations could offer new therapeutic strategies for immunological disorders like autoimmunity.

Multiple Vaccinations and the Enigma of Vaccine Injury

A growing number of vaccines are administered at the same time or in close succession, increasing the complexity of assessing vaccine safety. Individual vaccines are assumed to have no other effect than protection against the targeted pathogen, but vaccines also have nonspecific and interactive effects, the outcomes of which can be beneficial or harmful. To date, no controlled trials and very few observational studies have determined the impact of vaccination schedules on overall health. The balance of the risks and benefits from mass vaccination therefore remains uncertain. Recent studies worryingly suggest links between multiple vaccinations and increased risks of diverse multisystem health problems, including allergies, infections, and neuropsychiatric or neurodevelopmental disorders. Here, we propose that, in susceptible persons, multiple vaccinations activate the retinoid cascade and trigger apoptotic hepatitis, leading to cholestatic liver dysfunction, in which stored vitamin A compounds (retinyl esters and retinoic acid) enter the circulation in toxic concentrations; this induces endogenous forms of hypervitaminosis A, with the severity of adverse outcomes being directly proportional to the concentration of circulating retinoids. In very low concentrations, vitamin A and its major metabolite retinoic acid contribute to immune function and to the process of immunization, whereas excess vitamin A increases the risk of adverse events, including common "side-effects" as well as chronic adverse outcomes. The increasing rates of allergy, ear infections, and neurodevelopmental disorders (NDDs) in countries with high rates of vaccination could be related to mass vaccination and to its impact on liver function and vitamin A metabolism, collectively representing endogenous manifestations of hypervitaminosis A. Further studies of health outcomes in vaccinated and unvaccinated groups are urgently needed, to increase understanding of the pathophysiology and treatment of vaccine injury, to identify the risk factors and screen for vaccine injury, to inform public health policy on potential hazards related to vaccination schedules, and to optimize the safety and benefits of vaccines.

Retinoic Acid Exerts Disease Stage-Dependent Effects on Pristane-Induced Lupus

We previously showed that all-trans-retinoic acid (tRA), an active metabolite of vitamin A, exacerbated pre-existing autoimmunity in lupus; however, its effects before the development of autoimmunity are unknown. Here, using a pristane-induced model, we show that tRA exerts differential effects when given at the initiation vs. continuation phase of lupus. Unlike tRA treatment during active disease, pre-pristane treatment with tRA aggravated glomerulonephritis through increasing renal expression of pro-fibrotic protein laminin β1, activating bone marrow conventional dendritic cells (cDCs), and upregulating the interaction of ICAM-1 and LFA-1 in the spleen, indicating an active process of leukocyte activation and trafficking. Transcriptomic analysis revealed that prior to lupus induction, tRA significantly upregulated the expression of genes associated with cDC activation and migration. Post-pristane tRA treatment, on the other hand, did not significantly alter the severity of glomerulonephritis; rather, it exerted immunosuppressive functions of decreasing circulatory and renal deposition of autoantibodies as well as suppressing the renal expression of proinflammatory cytokines and chemokines. Together, these findings suggest that tRA differentially modulate lupus-associated kidney inflammation depending on the time of administration. Interestingly, both pre- and post-pristane treatments with tRA reversed pristane-induced leaky gut and modulated the gut microbiota in a similar fashion, suggesting a gut microbiota-independent mechanism by which tRA affects the initiation vs. continuation phase of lupus.

Effects of vitamin A supplementation in the diet of breeding geese on offspring intestinal tissue morphology and immune performance

Objective

The effects of maternal and offspring dietary vitamin A (VA) supplementation on early body weight, digestive tract function and immune function in goslings were studied.

Methods

Yangzhou geese (180 d old) were randomly divided into 5 experimental groups of 15 females and 3 males (the males were kept until slaughter). Eggs were collected for hatching during the peak laying period. A total of 96 goslings were selected from each treatment group (each fed a basic diet supplemented with 0, 4,000, 8,000, 12,000 or 16,000 IU/kg VA) and randomly divided into 2 groups, with 6 replicates in each group and 8 goslings in each replicate. The gosling diet was supplemented with 0 or 9,000 IU/kg VA.

Results

i) Villus length, villus width and the muscle thickness of the duodenum, jejunum and ileum were increased and the crypt depth was reduced after adding 12,000 IU/kg VA to the goslings’ diet (p<0.05). Adding 9,000 IU/kg VA to the offspring diet increased the length of the duodenal villi and width of the ileum and decreased the crypt depth of the ileum (p<0.05). ii) Supplementing the maternal diet with 12,000 IU/kg VA increased immune organ weight, the immune organ index and immunoglobulin content in goslings (p<0.05). The bursa weight and immunoglobulin G content of offspring were higher in the 9,000 IU/kg VA supplementation group than in the group with no supplementation (p<0.05).

Conclusion

Offspring growth and development were affected by the amount of VA added into maternal diet. The negative effect of maternal VA deficiency on offspring can be compensated by adding VA to the offspring diet. Continued VA supplementation in the offspring diet after excessive VA supplementation in the maternal diet is unfavorable for gosling growth and development.

Vitamins as influenza vaccine adjuvant components

A number of adjuvant formulations were assayed in mice immunized with 3.75 µg of A/California/7/2009 (H1N1) pdm09 influenza vaccine with vitamins A, D and/or E in emulsions or B2 and/or B9 combined with Bordetella pertussis MPLA and/or alum as adjuvants. Squalene was used as positive control, as well as MPLA with alum. The immune response was evaluated by a panel of tests, including a hemagglutination inhibition (HAI) test, ELISA for IgG, IgG1, and IgG2a and IFN-γ, IL-2, IL-6 and IL-10 quantification in splenocyte culture supernatant after stimulus with influenza antigen. Immunological memory was evaluated using a 1/10 dose booster 60 days after the first immunization followed by assessment of the response by HAI, IgG ELISA, and determination of the antibody affinity index. The highest increases in HAI, IgG1 and IgG2a titers were obtained with the adjuvant combinations containing vitamin E, or the hydrophilic combinations containing MPLA and alum or B2 and alum. The IgG1/IgG2a ratio indicates that the response to the combination of B2 with alum would have more Th2 character than the combination of MPLA with alum. In an assay to investigate the memory response, a significant increase in HAI titer was observed with a booster vaccine dose at 60 days after immunization with vaccines containing MPLA with alum or B2 with alum. Overall, of the 27 adjuvant combinations, MPLA with alum and B2 with alum were the most promising adjuvants to be evaluated in humans.

Vitamin A Transport Mechanism of the Multitransmembrane Cell-Surface Receptor STRA6

Vitamin A has biological functions as diverse as sensing light for vision, regulating stem cell differentiation, maintaining epithelial integrity, promoting immune competency, regulating learning and memory, and acting as a key developmental morphogen. Vitamin A derivatives have also been used in treating human diseases. If vitamin A is considered a drug that everyone needs to take to survive, evolution has come up with a natural drug delivery system that combines sustained release with precise and controlled delivery to the cells or tissues that depend on it. This "drug delivery system" is mediated by plasma retinol binding protein (RBP), the principle and specific vitamin A carrier protein in the blood, and STRA6, the cell-surface receptor for RBP that mediates cellular vitamin A uptake. The mechanism by which the RBP receptor absorbs vitamin A from the blood is distinct from other known cellular uptake mechanisms. This review summarizes recent progress in elucidating the fundamental molecular mechanism mediated by the RBP receptor and multiple newly discovered catalytic activities of this receptor, and compares this transport system with retinoid transport independent of RBP/STRA6. How to target this new type of transmembrane receptor using small molecules in treating diseases is also discussed.

Compartmental modeling of whole-body vitamin A kinetics in unsupplemented and vitamin A-retinoic acid-supplemented neonatal rats

Little is known about the contribution of different tissues to whole-body vitamin A (VA) kinetics in neonates. Here, we have used model-based compartmental analysis of tissue tracer kinetic data from unsupplemented (control) and VA-retinoic acid (VARA)-supplemented neonatal rats to determine VA kinetics in specific tissues under control and supplemented conditions. First, compartmental models for retinol kinetics were developed for individual tissues, and then an integrated compartmental model incorporating all tissues was developed for both groups. The models predicted that 52% of chylomicron (CM) retinyl ester was cleared by liver in control pups versus 22% in VARA-treated pups, whereas about 51% of VA was predicted to be extrahepatic in 4- to 6-day-old unsupplemented neonatal rats. VARA increased CM retinyl ester uptake by lung, carcass, and intestine; decreased the release into plasma of retinol that had been cleared by liver and lung as CM retinyl esters; stimulated the uptake of retinol from plasma holo-retinol binding protein into carcass; and decreased the retinol turnover out of the liver. Overall, neonatal VA trafficking differed from that previously described for adult animals, with a larger contribution of extrahepatic tissues to CM clearance, especially after VA supplementation, and a significant amount of VA distributed in extrahepatic tissues.

Differential and isomer-specific modulation of vitamin A transport and the catalytic activities of the RBP receptor by retinoids

Retinoids are vitamin A derivatives with diverse biological functions. Both natural and artificial retinoids have been used as therapeutic reagents to treat human diseases, but not all retinoid actions are understood mechanistically. Plasma retinol binding protein (RBP) is the principal and specific carrier of vitamin A in the blood. STRA6 is the membrane receptor for RBP that mediates cellular vitamin A uptake. The effects of retinoids or related compounds on the receptor's vitamin A uptake activity and its catalytic activities are not well understood. In this study, we dissected the membrane receptor-mediated vitamin A uptake mechanism using various retinoids. We show that a subset of retinoids strongly stimulates STRA6-mediated vitamin A release from holo-RBP. STRA6 also catalyzes the exchange of retinol in RBP with certain retinoids. The effect of retinoids on STRA6 is highly isomer-specific. This study provides unique insights into the RBP receptor's mechanism and reveals that the vitamin A transport machinery can be a target of retinoid-based drugs.

Stra6, a retinoic acid-responsive gene, participates in p53-induced apoptosis after DNA damage

Stra6 is the retinoic acid (RA)-inducible gene encoding the cellular receptor for holo-retinol binding protein. This transmembrane protein mediates the internalization of retinol, which then upregulates RA-responsive genes in target cells. Here, we show that Stra6 can be upregulated by DNA damage in a p53-dependent manner, and it has an important role in cell death responses. Stra6 expression induced significant amounts of apoptosis in normal and cancer cells, and it was also able to influence p53-mediated cell fate decisions by turning an initial arrest response into cell death. Moreover, inhibition of Stra6 severely compromised p53-induced apoptosis. We also found that Stra6 induced mitochondria depolarization and accumulation of reactive oxygen species, and that it was present not only at the cellular membrane but also in the cytosol. Finally, we show that these novel functions of Stra6 did not require downstream activation of RA signalling. Our results present a previously unknown link between the RA and p53 pathways and provide a rationale to use retinoids to upregulate Stra6, and thus enhance the tumour suppressor functions of p53. This may have implications for the role of vitamin A metabolites in cancer prevention and treatment.