Vitamin A and immune regulation: role of retinoic acid in gut-associated dendritic cell education, immune protection and tolerance

Retinoic Acid (RA): A Critical Immunoregulatory Molecule in Asthma and Allergies

INTRODUCTION

Asthma and allergies are chronic inflammatory disorders that are triggered owing to aberrant responses of the immune system against typically innocent environmental substances. Retinoic acid (RA) represents a biologically active metabolite of vitamin A (VA) and high-affinity ligand for RA receptor (RAR) that is implicated in a wide variety of biological processes, including cell proliferation, differentiation, apoptosis, organogenesis, reproduction, and immune responses. In the immune system, RA contributes to the induction of regulatory T (Treg) cells, adhesion molecules required for homing of B and T cells in the gut, and tolerance. Noteworthy, RA has a pivotal role in maintaining the balance of Th17-Treg cells and is also indispensable for appropriate responses of T helper (Th) cells.

AIMS

This mini-review article intends to expose the immune functions of RA, with an emphasis on the enzymatic pathways converting VA into RA and its receptor-dependent actions in asthma and allergies.

CONCLUSIONS

Recent findings have depicted that RA levels are reduced in asthma and allergies and that treatment with RA alleviates allergy symptoms and airway inflammation. RA also modulates allergic airway disorders by inhibiting Th2/Th17 response and increasing Treg cells. Therefore, RA could be considered a novel and promising therapeutic agent to be studied and used for treating these diseases.

Identification of diagnostic signature and immune infiltration for ischemic cardiomyopathy based on cuproptosis-related genes through bioinformatics analysis and experimental validation

BACKGROUND

Ischemic cardiomyopathy (IC) is primarily due to long-term ischemia/hypoxia of the coronary arteries, leading to impaired cardiac contractile or diastolic function. A new form of cell death induced by copper, called "cuproptosis" is related to the development and progression of multiple diseases. The cuproptosis-related gene (CuGs) plays an important role in acute myocardial infarction, while the specific mechanisms of CuGs in ischemic cardiomyopathy remain unclear.

METHODS

The expressions of CuGs and their immune characteristics were analyzed with the IC datasets obtained from the Gene Expression Omnibus, namely GSE5406 and GSE57338, identifying core genes associated with IC development. By comparing RF, SVM, GLM and XGB models, the optimal machine learning model was selected. The expression of marker genes was validated based on the GSE57345, GSE48166 and GSE42955 datasets. Construct a CeRNA network based on core genes. Therapeutic chemiacals targeting core genes were acquired using the CTD database, and molecular docking was performed using Autodock vina software. By ligating the left anterior descending (LAD) coronary artery, an IC mouse model is established, and core genes were experimentally validated using Western blot (WB) and immunohistochemistry (IHC) methods.

RESULTS

We identified 14 CuGs closely associated with the onset of IC. The SVM model exhibited superior discriminative power (AUC = 0.914), with core genes being DLST, ATP7B, FDX1, SLC31A1 and DLAT. Core genes were validated on the GSE42955, GSE48166 and GSE57345 datasets, showing excellent performance (AUC = 0.943, AUC = 0.800, and AUC = 0.932). The CeRNA network consists of 218 nodes and 264 lines, including 5 core diagnostic genes, 52 miRNAs, and 161 lncRNAs. Chemicals predictions indicated 8 chemicals have therapeutic effects on the core diagnostic genes, with benzo(a)pyrene molecular docking showing the highest affinity (-11.3 kcal/mol). Compared to the normal group, the IC group,which was established by LAD ligation, showed a significant decrease in LVEF as indicated by cardiac ultrasound, and increased fibrosis as shown by MASSON staining, WB results suggest increased expression of DLST and ATP7B, and decreased expression of FDX1, SLC31A1 and DLAT in the myocardial ischemic area (p < 0.05), which was also confirmed by IHC in tissue sections.

CONCLUSION

In summary, this study comprehensively revealed that DLST, ATP7B, FDX1, SLC31A1 and DLAT could be identified as potential immunological biomarkers in IC, and validated through an IC mouse model, providing valuable insights for future research into the mechanisms of CuGs and its diagnostic value to IC.

Systemic Factors Effecting Human Beta-Defensins in Oral Cavity

Human beta-defensins are host defense peptides with broad antimicrobial and inflammatory functions. In the oral cavity, these peptides are produced mainly by the keratinocytes of the epithelium; however, fibroblasts, monocytes, and macrophages also contribute to oral human beta-defensin expressions. The resident and immune cells of the oral cavity come into contact with various microbe-associated molecular patterns continuously and simultaneously. The overall antimicrobial cellular response is highly influenced by local and environmental factors. Recent studies have produced evidence showing that not only systemic chronic diseases but also systemic factors like hyperglycemia, pregnancy, the long-term use of certain vitamins, and aging can modulate oral cellular antimicrobial responses against microbial challenges. Therefore, the aim of this narrative review is to discuss the role of systemic factors on oral human beta-defensin expressions.

Adjunct Therapy With All-trans-Retinoic Acid Improves Therapeutic Efficacy Through Immunomodulation While Treating Tuberculosis With Antibiotics in Mice

Tuberculosis is the second leading infectious killer after coronavirus disease 2019 (COVID-19). Standard antitubercular drugs exhibit various limitations like toxicity, long treatment regimens, and lack of effect against dormant and drug-resistant organisms. Here, we report that all-trans-retinoic acid (ATRA) improves Mycobacterium tuberculosis clearance in mice during treatment with the antitubercular drug isoniazid. Interestingly, ATRA promoted activities of lysosomes and mitochondria, and production of various inflammatory mediators in macrophages. Furthermore, ATRA upregulated the expression of genes of lipid metabolism pathways in macrophages. We demonstrated that ATRA activated the MEK/ERK pathway in macrophages in vitro and MEK/ERK and p38 MAPK pathways in mice. Finally, ATRA induced both Th1 and Th17 responses in lungs and spleens of M. tuberculosis-infected mice. Together, these data indicate that ATRA provides beneficial adjunct therapeutic value by modulating MEK/ERK and p38 MAPK pathways and thus warrants further testing for human use.

Maternal immunization and vitamin A sufficiency impact sow primary adaptive immunity and passive protection to nursing piglets against porcine epidemic diarrhea virus infection

Porcine epidemic diarrhea virus (PEDV) causes a highly contagious enteric disease with major economic losses to swine production worldwide. Due to the immaturity of the neonatal piglet immune system and given the high virulence of PEDV, improving passive lactogenic immunity is the best approach to protect suckling piglets against the lethal infection. We tested whether oral vitamin A (VA) supplementation and PEDV exposure of gestating and lactating VA-deficient (VAD) sows would enhance their primary immune responses and boost passive lactogenic protection against the PEDV challenge of their piglets. We demonstrated that PEDV inoculation of pregnant VAD sows in the third trimester provided higher levels of lactogenic protection of piglets as demonstrated by >87% survival rates of their litters compared with <10% in mock litters and that VA supplementation to VAD sows further improved the piglets' survival rates to >98%. We observed significantly elevated PEDV IgA and IgG antibody (Ab) titers and Ab-secreting cells (ASCs) in VA-sufficient (VAS)+PEDV and VAD+VA+PEDV sows, with the latter maintaining higher Ab titers in blood prior to parturition and in blood and milk throughout lactation. The litters of VAD+VA+PEDV sows also had the highest serum PEDV-neutralizing Ab titers at piglet post-challenge days (PCD) 0 and 7, coinciding with higher PEDV IgA ASCs and Ab titers in the blood and milk of their sows, suggesting an immunomodulatory role of VA in sows. Thus, sows that delivered sufficient lactogenic immunity to their piglets provided the highest passive protection against the PEDV challenge. Maternal immunization during pregnancy (± VA) and VA sufficiency enhanced the sow primary immune responses, expression of gut-mammary gland trafficking molecules, and passive protection of their offspring. Our findings are relevant to understanding the role of VA in the Ab responses to oral attenuated vaccines that are critical for successful maternal vaccination programs against enteric infections in infants and young animals.

A Lacticaseibacillus rhamnosus secretome induces immunoregulatory transcriptional, functional and immunometabolic signatures in human THP-1 monocytes

Macrophage responses to activation are fluid and dynamic in their ability to respond appropriately to challenges, a role integral to host defence. While bacteria can influence macrophage differentiation and polarization into pro-inflammatory and alternatively activated phenotypes through direct interactions, many questions surround indirect communication mechanisms mediated through secretomes derived from gut bacteria, such as lactobacilli. We examined effects of secretome-mediated conditioning on THP-1 human monocytes, focusing on the ability of the Lacticaseibacillus rhamnosus R0011 secretome (LrS) to drive macrophage differentiation and polarization and prime immune responses to subsequent challenge with lipopolysaccharide (LPS). Genome-wide transcriptional profiling revealed increased M2-associated gene transcription in response to LrS conditioning in THP-1 cells. Cytokine and chemokine profiling confirmed these results, indicating increased M2-associated chemokine and cytokine production (IL-1Ra, IL-10). These cells had increased cell-surface marker expression of CD11b, CD86, and CX3CR1, coupled with reduced expression of the M1 macrophage-associated marker CD64. Mitochondrial substrate utilization assays indicated diminished reliance on glycolytic substrates, coupled with increased utilization of citric acid cycle intermediates, characteristics of functional M2 activity. LPS challenge of LrS-conditioned THP-1s revealed heightened responsiveness, indicative of innate immune priming. Resting stage THP-1 macrophages co-conditioned with LrS and retinoic acid also displayed an immunoregulatory phenotype with expression of CD83, CD11c and CD103 and production of regulatory cytokines. Secretome-mediated conditioning of macrophages into an immunoregulatory phenotype is an uncharacterized and potentially important route through which lactic acid bacteria and the gut microbiota may train and shape innate immunity at the gut-mucosal interface.

Fecal microbiota transplantation stimulates type 2 and tolerogenic immune responses in a mouse model

OBJECTIVES

Clostridioides difficile infection (CDI) is the leading hospital-acquired infection in North America. While previous work on fecal microbiota transplantation (FMT), a highly effective treatment for CDI, has focused on colonization resistance mounted against C. difficile by FMT-delivered commensals, the effects of FMT on host gene expression are relatively unexplored. This study aims to identify transcriptional changes associated with FMT, particularly changes associated with protective immune responses.

METHODS

Gene expression was assessed on day 2 and day 7 after FMT in mice after antibiotic-induced dysbiosis. Flow cytometry was also performed on colon and mesenteric lymph nodes at day 7 to investigate changes in immune cell populations.

RESULTS

FMT administration after antibiotic-induced dysbiosis successfully restored microbial alpha diversity to levels of donor mice by day 7 post-FMT. Bulk RNA sequencing of cecal tissue at day 2 identified immune genes, including both pro-inflammatory and Type 2 immune pathways as upregulated after FMT. RNA sequencing was repeated on day 7 post-FMT, and expression of these immune genes was decreased along with upregulation of genes associated with restoration of intestinal homeostasis. Immunoprofiling on day 7 identified increased colonic CD45+ immune cells that exhibited dampened Type 1 and heightened regulatory and Type 2 responses. These include an increased abundance of eosinophils, alternatively activated macrophages, Th2, and T regulatory cell populations.

CONCLUSION

These results highlight the impact of FMT on host gene expression, providing evidence that FMT restores intestinal homeostasis after antibiotic treatment and facilitates tolerogenic and Type 2 immune responses.

A randomized phase 2 trial of oral vitamin A for graft-versus-host disease in children and young adults

ABSTRACT

Vitamin A plays a key role in the maintenance of gastrointestinal homeostasis and promotes a tolerogenic phenotype in tissue resident macrophages. We conducted a prospective randomized double-blinded placebo-controlled clinical trial in which 80 recipients of hematopoietic stem cell transplantation (HSCT) were randomized 1:1 to receive pretransplant high-dose vitamin A or placebo. A single oral dose of vitamin A of 4000 IU/kg, maximum 250 000 IU was given before conditioning. The primary end point was incidence of acute graft-versus-host disease (GVHD) at day +100. In an intent-to-treat analysis, incidence of acute GVHD was 12.5% in the vitamin A arm and 20% in the placebo arm (P = .5). Incidence of acute gastrointestinal (GI) GVHD was 2.5% in the vitamin A arm (P = .09) and 12.5% in the placebo arm at day +180. Incidence of chronic GVHD was 5% in the vitamin A arm and 15% in the placebo arm (P = .02) at 1 year. In an "as treated" analysis, cumulative incidence of acute GI GVHD at day +180 was 0% and 12.5% in recipients of vitamin A and placebo, respectively (P = .02), and cumulative incidence of chronic GVHD was 2.7% and 15% in recipients of vitamin A and placebo, respectively (P = .01). The only possibly attributable toxicity was asymptomatic grade 3 hyperbilirubinemia in 1 recipient of vitamin A at day +30, which self-resolved. Absolute CCR9+ CD8+ effector memory T cells, reflecting gut T-cell trafficking, were lower in the vitamin A arm at day +30 after HSCT (P = .01). Levels of serum amyloid A-1, a vitamin A transport protein with proinflammatory effects, were lower in the vitamin A arm. The vitamin A arm had lower interleukin-6 (IL-6), IL-8, and suppressor of tumorigenicity 2 levels and likely a more favorable gut microbiome and short chain fatty acids. Pre-HSCT oral vitamin A is inexpensive, has low toxicity, and reduces GVHD. This trial was registered at www.ClinicalTrials.gov as NCT03202849.

Immunomodulatory and Anti-Inflammatory Effects of Vitamin A and Tryptophan on Monocyte-Derived Dendritic Cells Stimulated with Gliadin in Celiac Disease Patients

Celiac Disease (CeD) is an autoimmune disorder with various symptoms upon gluten exposure. Dendritic cells (DCs) play a crucial role in gliadin-induced inflammation. Vitamin A (retinol; Ret) and its metabolite, retinoic acid (RA), along with tryptophan (Trp) and its metabolite, kynurenic acid (KYNA), are known to influence the immune function of DCs and enhance their tolerogenicity. This research aims to assess the impact of gliadin on DC maturation and the potential of vitamin A and tryptophan to induce immune tolerance in DCs. The monocyte cells obtained from peripheral blood mononuclear cells (PBMCs) of celiac disease patients were differentiated into DCs in the absence or presence of Ret, RA, Trp, KYNA, and then stimulated with peptic and tryptic (PT) digested of gliadin. We used flow cytometry to analyze CD11c, CD14, HLA-DR, CD83, CD86, and CD103 expression. ELISA was carried out to measure TGF-β, IL-10, IL-12, and TNF-α levels. qRT-PCR was used to assess the mRNA expression of retinaldehyde dehydrogenase 2 (RALDH2) and integrin αE (CD103). The mRNA and protein levels of Indoleamine 2, 3-dioxygenase (IDO) was analyzed by qRT-PCR and Western blot assays, respectively. Our findings demonstrate that PT-gliadin enhances the expression of maturation markers, i.e. CD83, CD86 and HLA-DR and promote the secretion of TNF-α and IL-12 in DCs. Interestingly, vitamin A, tryptophan, and their metabolites increase the expression of CD103, while limiting the expression of HLA-DR, CD83, and CD86. They also enhance RALDH2 and IDO expression and promote the secretion of TGF-β and IL-10, while limiting IL-12 and TNF-α secretion. These findings suggest that vitamin A and tryptophan have beneficial effects on PT-gliadin-stimulated DCs, highlighting their potential as therapeutic agents for celiac disease. However, further research is needed to fully understand their underlying mechanisms of action in these cells.

Dietary composition of adult eosinophilic esophagitis patients is related to disease severity

BACKGROUND

In addition to the elimination diet, dietary composition may influence disease severity in patients with eosinophilic esophagitis (EoE) through modulation of the immune response.

AIM

To explore the immunomodulatory role of nutrition before and during elimination diet in adult EoE patients.

METHODS

Nutritional intake was assessed in 39 Dutch adult EoE patients participating in the Supplemental Elemental Trial (Dutch trial registry NL6014, NTR6778) using 3-day food diaries. In this randomized controlled trial, diagnosed patients received either a four-food elimination diet alone (FFED) or FFED with addition of an amino acid-based formula for 6 weeks. Multiple linear regression analyses were performed to assess associations between the intake of nutrients and food groups per 1000 kCal and peak eosinophil count/high power field (PEC), both at baseline and after 6 weeks.

RESULTS

At baseline, we found a statistically significant negative (thus favorable) relationship between the intake of protein, total fat, phosphorus, zinc, vitamin B12, folate, and milk products and PEC (p < .05), while calcium (p = .058) and full-fat cheese/curd (p = .056) were borderline (favorably) significant. In contrast, total carbohydrates, prepacked fruit juice, and white bread were significantly positively (unfavorable) related to PEC (p < .05), while ultra-processed meals (p = .059) were borderline (unfavorably) significant. After dietary intervention, coffee/tea were significantly negatively (favorably) related to PEC, hummus/legumes were significantly positively (unfavorably) related with PEC, while peanuts were borderline significantly positively related (p = .058).

CONCLUSION

Dietary composition may be related to inflammation in adult EoE patients. High-quality and anti-inflammatory diets may be a promising adjuvant therapy in the dietary management of EoE.

Effects of supplemental vitamin A on reproduction and antioxidative status of aged laying hens, and growth, blood indices and immunity of their offspring

The purpose of this investigation was to evaluate the impacts of vitamin A (VA) supplementation in feed at levels of 0 (control), 2,000, 4,000, 6,000, and 8,000 IU VA/kg diet on the reproductive efficiency and antioxidative properties of aged Sinai laying hens at 52 wk of age (n = 300 females and 30 males) in 6 replicates (10 females + 1 male/replicate). As well as blood biochemical indicators, carcass characteristics, growth performance, immunity, and the antioxidative status of their chicks. Results showed that diets supplemented with 2,000 or 6,000 IU/kg of VA increased fertility rate and decreased early embryonic mortality (P < 0.05). Increasing VA from 4,000 to 6,000 IU/kg significantly boosted hatchability rates. All VA levels significantly enhanced glutathione peroxidase (GPx) and reduced malondialdehyde (MDA) and late embryonic mortality. In the shell gland, dietary supplementation of 6,000 or 8,000 IU/kg of VA enhanced actions of GPx actions, catalase (CAT), and superoxide dismutase (SOD). In hatched chicks, all VA levels boosted (P < 0.05) hemoglobin, red blood cell count, and serum concentration of total proteins and IgA while decreasing eosinophils percentage and aspartate aminotransferase activity (AST) concentration. Dietary VA supplementations from 4,000 to 8,000 IU/kg improved lymphocytes, serum total antioxidant capacity (TAC), SOD, and IgM, while decreasing heterophils, heterophils/lymphocytes ratio, and creatinine in hatched chicks. Serum triglyceride concentration was reduced by adding 6,000 or 8,000 IU/kg of VA, while globulin and high-density lipoprotein concentrations were heightened only by 8,000 IU/kg of VA. It could be concluded that the dietary supplementation of VA (6,000 IU/kg) improved reproductive efficiency and antioxidative status in the liver and the shell gland of aged laying hens and improved hemato-biochemicals parameters, antioxidative status, and immunity of their offspring.

Mucin Expression Profiles in Ulcerative Colitis: New Insights on the Histological Mucosal Healing

A structural weakness of the mucus barrier (MB) is thought to be a cause of ulcerative colitis (UC). This study aims to investigate the mucin (MUC) composition of MB in normal mucosa and UC. Ileocolonic biopsies were taken at disease onset and after treatment in 40 patients, including 20 with relapsing and 20 with remitting UC. Ileocolonic biopsies from 10 non-IBD patients were included as controls. Gut-specific MUC1, MUC2, MUC4, MUC5B, MUC12, MUC13, MUC15, and MUC17 were evaluated immunohistochemically. The promoters of mucin genes were also examined. Normal mucosa showed MUC2, MUC5B, and MUC13 in terminal ileum and colon, MUC17 in ileum, and MUC1, MUC4, MUC12, and MUC15 in colon. Membranous, cytoplasmic and vacuolar expressions were highlighted. Overall, the mucin expression was abnormal in UC. Derangements in MUC1, MUC4, and MUC5B were detected both at onset and after treatment. MUC2 and MUC13 were unaffected. Sequence analysis revealed glucocorticoid-responsive elements in the MUC1 promoter, retinoic-acid-responsive elements in the MUC4 promoter, and butyrate-responsive elements in the MUC5B promoter. In conclusion, MUCs exhibited distinct expression patterns in the gut. Their expression was disrupted in UC, regardless of the treatment protocols. Abnormal MUC1, MUC4, and MUC5B expression marked the barrier dysfunction in UC.

Synergistic Effect of Retinoic Acid and Lactoferrin in the Maintenance of Gut Homeostasis

Lactoferrin (LF) is a glycoprotein that binds to iron ions (Fe2+) and other metallic ions, such as Mg2+, Zn2+, and Cu2+, and has antibacterial and immunomodulatory properties. The antibacterial properties of LF are due to its ability to sequester iron. The immunomodulatory capability of LF promotes homeostasis in the enteric environment, acting directly on the beneficial microbiota. LF can modulate antigen-presenting cell (APC) biology, including migration and cell activation. Nonetheless, some gut microbiota strains produce toxic metabolites, and APCs are responsible for initiating the process that inhibits the inflammatory response against them. Thus, eliminating harmful strains lowers the risk of inducing chronic inflammation, and consequently, metabolic disease, which can progress to type 2 diabetes mellitus (T2DM). LF and retinoic acid (RA) exhibit immunomodulatory properties such as decreasing cytokine production, thus modifying the inflammatory response. Their activities have been observed both in vitro and in vivo. The combined, simultaneous effect of these molecules has not been studied; however, the synergistic effect of LF and RA may be employed for enhancing the secretion of humoral factors, such as IgA. We speculate that the combination of LF and RA could be a potential prophylactic alternative for the treatment of metabolic dysregulations such as T2DM. The present review focuses on the importance of a healthy diet for a balanced gut and describes how probiotics and prebiotics with immunomodulatory activity as well as inductors of differentiation and cell proliferation could be acquired directly from the diet or indirectly through the oral administration of formulations aimed to maintain gut health or restore a eubiotic state in an intestinal environment that has been dysregulated by external factors such as stress and a high-fat diet.

Investigating the Impact of Vitamin A and Amino Acids on Immune Responses in Celiac Disease Patients

Amino acids (AAs) and vitamin imbalances are observed in celiac disease (CD). This study evaluated the plasma profile of vitamin A and AAs and the expression level of IL-2, IL-4, IL-10, IL-12 and TGFβ in CD patients. A total of 60 children and adults with CD and 40 healthy controls (HCs) were included. The plasma profile of Vitamin A and AAs and the mRNA expression levels of target genes were assessed. Active adult patients exhibited a decrease in Vitamin A levels (p = 0.04) and an increase in IL-2 (p = 0.008) and IL-12 (p = 0.007) mRNA expression compared to the HCs. The treated adult patients showed elevated Serine (p = 0.003) and Glycine (p = 0.04) levels, as well as increased IL-12 (p < 0.0001) mRNA expression, and a decrease in Tryptophan (p = 0.04) levels relative to the controls. Additionally, the treated adult patients had higher plasma levels of Threonine compared to both the active (p = 0.04) and control (p = 0.02) subjects, and the increased mRNA expression of IL-4 (p = 0.01) in comparison to the active patients. In active children with CD, the IL-2 mRNA level was found to be higher than in the controls (p < 0.0001) and in the treated children (p = 0.005). The treated children with CD exhibited decreased plasma levels of Tryptophan (p = 0.01) and Isoleucine (p = 0.01) relative to the controls, and the increased mRNA expression of TGFβ (p = 0.04) relative to the active patients. Elevated levels of specific AAs (Serine, Glycine, Threonine) in the treated CD patients suggested their potential to improve intestinal damage and inflammation, while decreased levels of Tryptophan and Isoleucine highlighted the need for dietary intervention.

Circulating vitamin levels mediate the causal relationship between gut microbiota and cholecystitis: a two-step bidirectional Mendelian randomization study

Background

The relationship between gut microbiota and the occurrence of cholecystitis remains unclear. Existing research lacks a clear understanding of how circulating vitamin levels modulate this relationship. Therefore, our study aims to investigate whether circulating vitamin levels mediate the causal relationship between gut microbiota and cholecystitis using a two-step bidirectional Mendelian randomization approach.

Methods

In this study, we initially employed Linkage Disequilibrium Score Regression (LDSC) analysis to assess the genetic correlation of five circulating vitamin level genome-wide association study (GWAS) summary datasets, thereby avoiding potential sample overlap. Subsequently, we conducted a two-step analysis to investigate the causal effects between gut microbiota and cholecystitis. In the second step, we explored the causal relationship between circulating vitamin levels and cholecystitis and identified the mediating role of vitamin D. The primary method used for causal analysis was the inverse variance-weighted approach. We performed additional sensitivity analyses to ensure result robustness, including the cML-MA method and reverse Mendelian randomization (MR) analysis.

Results

An increment of one standard deviation in RuminococcaceaeUCG003 was associated with a 25% increased risk of cholecystitis (OR = 1.25, 95%CI = 1.01-1.54, p = 0.04), along with a 3% decrease in 25-hydroxyvitamin D levels (OR = 0.97, 95%CI = 0.944-0.998, p = 0.04). However, following the rigorous Bonferroni correction, every one standard deviation decrease in circulating vitamin D levels was associated with a 33% increased risk of cholecystitis (OR = 0.67, 95%CI = 0.49-0.90, p = 0.008, Padjust = 0.04). Thus, the potential link between gut microbiota and cholecystitis risk might be mediated by circulating vitamin D levels (proportion mediated = 5.5%). Sensitivity analyses provided no evidence of pleiotropy.

Conclusion

Our study results suggest that an elevated abundance of specific gut microbiota is associated with an increased susceptibility to cholecystitis, with the causal relationship being mediated by circulating vitamin D levels. Further large-scale randomized controlled trials are necessary to validate the causal effects of gut microbiota on cholecystitis risk. This study provides novel insights into cholecystitis prevention through the regulation of gut microbiota.

PFAS Exposures and the Human Metabolome: A Systematic Review of Epidemiological Studies

Purpose of Review

There is a growing interest in understanding the health effects of exposure to per- and polyfluoroalkyl substances (PFAS) through the study of the human metabolome. In this systematic review, we aimed to identify consistent findings between PFAS and metabolomic signatures. We conducted a search matching specific keywords that was independently reviewed by two authors on two databases (EMBASE and PubMed) from their inception through July 19, 2022 following PRISMA guidelines.

Recent Findings

We identified a total of 28 eligible observational studies that evaluated the associations between 31 different PFAS exposures and metabolomics in humans. The most common exposure evaluated was legacy long-chain PFAS. Population sample sizes ranged from 40 to 1,105 participants at different stages across the lifespan. A total of 19 studies used a non-targeted metabolomics approach, 7 used targeted approaches, and 2 included both. The majority of studies were cross-sectional (n = 25), including four with prospective analyses of PFAS measured prior to metabolomics.

Summary

Most frequently reported associations across studies were observed between PFAS and amino acids, fatty acids, glycerophospholipids, glycerolipids, phosphosphingolipids, bile acids, ceramides, purines, and acylcarnitines. Corresponding metabolic pathways were also altered, including lipid, amino acid, carbohydrate, nucleotide, energy metabolism, glycan biosynthesis and metabolism, and metabolism of cofactors and vitamins. We found consistent evidence across studies indicating PFAS-induced alterations in lipid and amino acid metabolites, which may be involved in energy and cell membrane disruption.

The Transcription Factor RXRα in CD11c+ APCs Regulates Intestinal Immune Homeostasis and Inflammation

APCs such as dendritic cells and macrophages play a pivotal role in mediating immune tolerance and restoring intestinal immune homeostasis by limiting inflammatory responses against commensal bacteria. However, cell-intrinsic molecular regulators critical for programming intestinal APCs to a regulatory state rather than an inflammatory state are unknown. In this study, we report that the transcription factor retinoid X receptor α (RXRα) signaling in CD11c+ APCs is essential for suppressing intestinal inflammation by imparting an anti-inflammatory phenotype. Using a mouse model of ulcerative colitis, we demonstrated that targeted deletion of RXRα in CD11c+ APCs in mice resulted in the loss of T cell homeostasis with enhanced intestinal inflammation and increased histopathological severity of colonic tissue. This was due to the increased production of proinflammatory cytokines that drive Th1/Th17 responses and decreased expression of immune-regulatory factors that promote regulatory T cell differentiation in the colon. Consistent with these findings, pharmacological activation of the RXRα pathway alleviated colitis severity in mice by suppressing the expression of inflammatory cytokines and limiting Th1/Th17 cell differentiation. These findings identify an essential role for RXRα in APCs in regulating intestinal immune homeostasis and inflammation. Thus, manipulating the RXRα pathway could provide novel opportunities for enhancing regulatory responses and dampening colonic inflammation.

Recruitment and Residence of Intestinal T Cells - Lessons for Therapy in Inflammatory Bowel Disease

Targeting leukocyte trafficking in the management of inflammatory bowel disease [IBD] has been a significant therapeutic advance over the past 15 years. However, as with other advanced therapies, phase III clinical trials report response to trafficking inhibitors in only a proportion of patients, with fewer achieving clinical remission or mucosal healing. Additionally, there have been significant side effects, most notably progressive multifocal leukoencephalopathy in association with the α4 inhibitor natalizumab. This article reviews the mechanisms underpinning T cell recruitment and residence, to provide a background from which the strength and limitations of agents that disrupt leukocyte trafficking can be further explored. The therapeutic impact of trafficking inhibitors is underpinned by the complexity and plasticity of the intestinal immune response. Pathways essential for gut homing in health may be bypassed in the inflamed gut, thus providing alternative routes of entry when conventional homing molecules are targeted. Furthermore, there is conservation of trafficking architecture between proinflammatory and regulatory T cells. The persistence of resident memory cells within the gut gives rise to local established pro-inflammatory populations, uninfluenced by inhibition of trafficking. Finally, trafficking inhibitors may give rise to effects beyond the intended response, such as the impact of vedolizumab on innate immunity, as well as on target side effects. With significant research efforts into predictive biomarkers already underway, it is ultimately hoped that a better understanding of trafficking and residence will help us predict which patients are most likely to respond to inhibition of leukocyte trafficking, and how best to combine therapies.

Retinoic Acid Signaling Is Required for Dendritic Cell Maturation and the Induction of T Cell Immunity

Vitamin A and its biologically active metabolites, all-trans and 9-cis retinoic acid (RA), are thought to be important in generating and modulating immune function. However, RA modulates the function of many types of immune cells, and its specific role in dendritic cell (DC) activation, Ag presentation, and T cell effector function has not been fully characterized. Because RA works primarily through RA receptor (RAR)α, we examined mice with a myeloid cell-specific defect in RA signaling. These transgenic mice have a CD11c-cre-driven expression of a truncated form of RARα that specifically blocks the signaling of all forms of RARs in myeloid cells. This defect results in abnormal DC function, with impaired DC maturation and activation, and reduced Ag uptake and processing. These DC abnormalities were associated with a reduced ability to mount Ag-specific T cell responses to immunization despite having normally functioning T cells. In contrast, the loss of DC-specific RA signaling did not significantly alter levels of Ag-specific Abs postimmunization and resulted in an increase in bronchial IgA. Our findings indicate that RA signaling in DCs is crucial for immune activation, and its absence impairs the development of Ag-specific effector functions of T cell immunity.

Cuproptosis-related gene identification and immune infiltration analysis in systemic lupus erythematosus

Background

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by loss of tolerance to self-antigen, autoantibody production, and abnormal immune response. Cuproptosis is a recently reported cell death form correlated with the initiation and development of multiple diseases. This study intended to probe cuproptosis-related molecular clusters in SLE and constructed a predictive model.

Methods

We analyzed the expression profile and immune features of cuproptosis-related genes (CRGs) in SLE based on GSE61635 and GSE50772 datasets and identified core module genes associated with SLE occurrence using the weighted correlation network analysis (WGCNA). We selected the optimal machine-learning model by comparing the random forest (RF) model, support vector machine (SVM) model, generalized linear model (GLM), and the extreme gradient boosting (XGB) model. The predictive performance of the model was validated by nomogram, calibration curve, decision curve analysis (DCA), and external dataset GSE72326. Subsequently, a CeRNA network based on 5 core diagnostic markers was established. Drugs targeting core diagnostic markers were acquired using the CTD database, and Autodock vina software was employed to perform molecular docking.

Results

Blue module genes identified using WGCNA were highly related to SLE initiation. Among the four machine-learning models, the SVM model presented the best discriminative performance with relatively low residual and root-mean-square error (RMSE) and high area under the curve (AUC = 0.998). An SVM model was constructed based on 5 genes and performed favorably in the GSE72326 dataset for validation (AUC = 0.943). The nomogram, calibration curve, and DCA validated the predictive accuracy of the model for SLE as well. The CeRNA regulatory network includes 166 nodes (5 core diagnostic markers, 61 miRNAs, and 100 lncRNAs) and 175 lines. Drug detection showed that D00156 (Benzo (a) pyrene), D016604 (Aflatoxin B1), D014212 (Tretinoin), and D009532 (Nickel) could simultaneously act on the 5 core diagnostic markers.

Conclusion

We revealed the correlation between CRGs and immune cell infiltration in SLE patients. The SVM model using 5 genes was selected as the optimal machine learning model to accurately evaluate SLE patients. A CeRNA network based on 5 core diagnostic markers was constructed. Drugs targeting core diagnostic markers were retrieved with molecular docking performed.

Vitamin A deficiency and vitamin A supplementation affect innate and T cell immune responses to rotavirus A infection in a conventional sow model

Rotavirus A (RVA) causes ~200,000 diarrheal deaths annually in children <5yrs, mostly in low- and middle-income countries. Risk factors include nutritional status, social factors, breastfeeding status, and immunodeficiency. We evaluated the effects of vitamin A (VA) deficiency/VA supplementation and RVA exposure (anamnestic) on innate and T cell immune responses in RVA seropositive pregnant and lactating sows and passive protection of their piglets post-RVA challenge. Sows were fed VA deficient (VAD) or sufficient (VAS) diets starting at gestation day (GD)30. A subset of VAD sows received VA supplementation from GD|76 (30,000IU/day, VAD+VA). Sows (6 groups) were inoculated with porcine RVA G5P[7] (OSU strain) or Minimal Essential Medium (mock) at GD~90: VAD+RVA; VAS+RVA; VAD+VA+RVA; VAD-mock; VAS-mock; and VAD+VA-mock. Blood, milk, and gut-associated tissues were collected from sows at several time points to examine innate [natural killer (NK), dendritic (DC) cells], T cell responses and changes in genes involved in the gut-mammary gland (MG)-immunological axis trafficking. Clinical signs of RVA were evaluated post inoculation of sows and post-challenge of piglets. We observed decreased frequencies of NK cells, total and MHCII+ plasmacytoid DCs, conventional DCs, CD103+ DCs and CD4+/CD8+ and T regulatory cells (Tregs) and NK cell activity in VAD+RVA sows. Polymeric Ig receptor and retinoic acid receptor alpha (RARα) genes were downregulated in mesenteric lymph nodes and ileum of VAD+RVA sows. Interestingly, RVA-specific IFN-γ producing CD4+/CD8+ T cells were increased in VAD-Mock sows, coinciding with increased IL-22 suggesting inflammation in these sows. VA supplementation to VAD+RVA sows restored frequencies of NK cells and pDCs, and NK activity, but not tissue cDCs and blood Tregs. In conclusion, similar to our recent observations of decreased B cell responses in VAD sows that led to decreased passive immune protection of their piglets, VAD impaired innate and T cell responses in sows, while VA supplementation to VAD sows restored some, but not all responses. Our data reiterate the importance of maintaining adequate VA levels and RVA immunization in pregnant and lactating mothers to achieve optimal immune responses, efficient function of the gut-MG-immune cell-axis and to improve passive protection of their piglets.

Metabolite Profiling of the Gut–Renal–Cerebral Axis Reveals a Particular Pattern in Early Diabetic Kidney Disease in T2DM Patients

Type 2 diabetes mellitus (T2DM) represents an important microvascular disease concerning the kidney and the brain. Gut dysbiosis and microbiota-derived metabolites may be in relation with early pathophysiological changes in diabetic kidney disease (DKD). The aim of the study was to find new potential gut-derived biomarkers involved in the pathogenesis of early DKD, with a focus on the complex interconnection of these biomarkers with podocyte injury, proximal tubule dysfunction, renal and cerebrovascular endothelial dysfunction. The study design consisted of metabolite profiling of serum and urine of 90 T2DM patients (subgroups P1-normoalbuminuria, P2-microalbuminuria, P3-macroalbuminuria) and 20 healthy controls (group C), based on ultra-high-performance liquid chromatography coupled with electrospray ionization-quadrupole-time of flight-mass spectrometry analysis (UHPLC-QTOF-ESI+-MS). By multivariate and univariate analyses of serum and urine, which included Partial Least Squares Discriminant Analysis (PLSDA), Variable Importance Plots (VIP), Random Forest scores, One Way ANOVA and Biomarker analysis, there were discovered metabolites belonging to nitrogen metabolic pathway and retinoic acid signaling pathway which differentiate P1 group from P2, P3, C groups. Tyrosine, phenylalanine, indoxyl sulfate, serotonin sulfate, and all-trans retinoic acid express the metabolic fingerprint of P1 group vs. P2, P3, C groups, revealing a particular pattern in early DKD in T2DM patients.

Nano-Encapsulated Antioxidant: Retinoic Acid as a Natural Mucosal Adjuvant for Intranasal Immunization against Chronic Experimental Toxoplasmosis

The tight relationship between immunity and retinoid levels provides evidence on the critical role of retinoic acid (RA) in regulating immune activity, especially the mucosal one. Mucosal immune response is the key for determination of the outcome of infection, particularly against intracellular mucosal pathogens such as Toxoplasma gondii, where it plays a crucial role as a sentinel against parasite invasion. Herein, the immunomodulatory adjuvant role of RA was evaluated for prophylactic vaccination against chronic Toxoplasma infection. A quantity of 15 µg of RA pre-encapsulated with lipid-based nanoparticles (SLNs) was intranasally used in three doses, two weeks apart, as an adjuvant to the Toxoplasma lysate antigen (TLA). Afterward, mice were infected with 20 cysts of T. gondii (ME49 strain) and were sacrificed at the 4th week post-infection. Parasitological, immunological, biochemical, and histopathological studies were applied as vaccine efficacy measures. The protective role of the tested vaccine was noted using the statistically marked reduction in brain cyst count, accompanied by remarkable levels of protective IFN-γ and antibodies, with amelioration of infection-induced oxidative stress and brain pathology. Ultimately, this experiment outlined the prospective role of a novel, natural, nano-encapsulated and mucosal vaccine adjuvant RA-SLNs as a propitious candidate against chronic toxoplasmosis.

The immunomodulatory effects of all-trans retinoic acid and docosahexaenoic acid combination treatment on the expression of IL-2, IL-4, T-bet, and GATA3 genes in PBMCs of multiple sclerosis patients

OBJECTIVES

Multiple sclerosis (MS) is a potentially disabling autoimmune disease of the central nervous system. Neither the pathogenesis nor the effectiveness of treatment of MS has been fully understood. This in vitro trial evaluated the beneficial immunomodulatory effects of single and combined treatments of all-trans retinoic acid (ATRA) and docosahexaenoic acid (DHA) on the peripheral blood mononuclear cells (PBMCs) of relapsing-remitting MS (RRMS) patients who were receiving interferon beta (IFN-β).

METHODS

The PBMCs of 15 RRMS patients were isolated, cultured, and treated with single and combined treatments of ATRA and DHA. The expressions of IL-2, IL-4, T-bet, and GATA3 genes were evaluated using real-time PCR.

RESULTS

The results showed that a single treatment of ATRA could significantly suppress the gene expression of the pro-inflammatory cytokine, IL-2 (P < 0.05), and related transcription factor, T-bet (P < 0.001). The gene expression level of the anti-inflammatory cytokine, IL-4, and its transcription factor, GATA3, were not significantly changed. The expression of IL-2 and T-bet genes was significantly decreased in combination treatments of ATRA and DHA (P < 0.001). Significant suppression of IL-2 and T-bet (P < 0.001) was observed in ATRA and DHA combination therapy with half doses of their single treatment, which suggested a synergistic effect of these components.

DISCUSSION

Co-administration of vitamin A and DHA, an omega-3 fatty acid derivative, may exert a synergistic effect in modulating the immune system in MS patients; however, more studies are needed to evaluate the exact effects and mechanism of their actions on the immune cells.

Limosilactobacillus reuteri FN041 prevents atopic dermatitis in pup mice by remodeling the ileal microbiota and regulating gene expression in Peyer’s patches after vertical transmission

Objectives

Limosilactobacillus reuteri FN041 is a potential probiotic bacterium isolated from breast milk in traditional farming and pastoral areas of China. The purpose of this study was to investigate the optimal intervention mode and potential mechanism of FN041 to prevent atopic dermatitis (AD) in mice.

Methods

In intervention mode I, FN041 was supplemented to dams during the late trimester and lactation and pups after weaning; in intervention mode II, FN041 was supplemented after pups were weaned. AD was induced in pups with MC903 plus ovalbumin on the ear after weaning.

Results

The effect of intervention mode I in preventing AD was significantly better than that of intervention mode II. Compared with the model group, the inflammatory response of the pup’s ears, the proportion of spleen regulatory T cells and the plasma IgE were significantly decreased in mice in intervention mode I. Furthermore, the intestinal mucosal barrier was enhanced, and the Shannon index of the ileal microbiota was significantly increased. The microbiota structure deviated from the AD controls and shifted toward the healthy controls according to the PCoA of unweighted UniFrac. The relative abundances of Limosilactobacillus, Faecalibacterium, Bifidobacterium, and Akkermansia in the ileum were significantly increased compared to the AD group. Based on RNA-seq analysis of pups’ Peyer’s patches (PPs), FN041 inhibits autoimmune pathways such as asthma and systemic lupus erythematosus and activates retinol metabolism and PPAR signaling pathways to reduce inflammatory responses. Intervention mode II also significantly reduced AD severity score, but the reduction was approximately 67% of that of intervention mode I. This may be related to its ineffective remodeling of the ileal microbiota.

Conclusion

Prenatal and postnatal administration of FN041 is an effective way to prevent AD in offspring, and its mechanism is related to remodeling of ileal microbiota and PPs immune response.

Probiotic supplementation and systemic inflammation in relapsing-remitting multiple sclerosis: A randomized, double-blind, placebo-controlled trial

Background

Multiple sclerosis (MS) is a complex inflammatory disease in which demyelination occurs in the central nervous system affecting approximately 2.5 million people worldwide. Intestinal microbiome changes play an important role in the etiology of chronic diseases.

Objective

This study aimed to investigate the effect of probiotic supplementation on systemic inflammation in patients with MS.

Methods

A 12-week double-blind clinical trial study was designed and seventy patients with MS were randomly divided into two groups receiving probiotics and placebo. Patients in the intervention group received two capsules containing multi-strain probiotics daily and patients in the control group received the same amount of placebo. Factors associated with systemic inflammation were assessed at the beginning and end of the study.

Results

Sixty-five patients were included in the final analysis. There was no significant difference between the two groups in terms of baseline variables except for the duration of the disease (P > 0.05). At the end of the study, probiotic supplementation compared to the placebo caused a significant reduction in the serum levels of CRP (-0.93 ± 1.62 vs. 0.05 ± 1.74, P = 0.03), TNF-α (-2.09 ± 1.88 vs. 0.48 ± 2.53, P = 0.015) and IFN-γ (-13.18 ± 7.33 vs. -1.93 ± 5.99, P < 0.001). Also, we found a significant increase in the FOXP3 and TGF-β levels in the intervention group (P < 0.05).

Conclusion

The results of our study showed that supplementation with probiotics can have beneficial effects on serum levels of some factors associated with systemic inflammation.

Clinical trial registration

[http://www.irct.ir], identifier [IRCT20181210041 918N1].

Effect of amino acid-based formula added to four-food elimination in adult eosinophilic esophagitis patients: A randomized clinical trial

BACKGROUND

Elimination of key foods restricts dietary options in eosinophilic esophagitis (EoE) patients. Addition of amino acid-based formula (AAF) to an elimination diet might facilitate adherence and, therefore, enhance efficacy of dietary management.

AIM

To evaluate whether addition of AAF to a four-food elimination diet (FFED) is more effective than FFED alone in decreasing eosinophilia, endoscopic signs, and clinical outcomes.

METHODS

This randomized controlled trial enrolled 41 adult patients with active EoE (≥15 eosinophils (eos) per high power field (hpf)) at baseline biopsy. Subjects were randomized (1:1 ratio) to groups given a FFED or FFED with addition of AAF providing 30% of their daily energy needs (FFED + AAF). Histological disease activity, endoscopic signs, symptoms, and disease-related quality of life (EoEQoL) were measured at baseline and after 6 weeks of intervention.

RESULTS

Patients (60% male, age 34.5 (interquartile range (IQR) 29-42.8 years)) were randomized to FFED (n = 20) or FFED + AAF (n = 21); 40 participants completed the diet. Complete histological remission (<15 eos/hpf) was achieved in 48% of FFED + AAF subjects (n = 21) vs. 25% of FFED subjects (n = 20), respectively (p = 0.204). Peak eosinophil counts (PEC) decreased significantly in both groups between baseline and week 6, but the change in PEC between groups was not different (p = 0.130). A significant but similar endoscopic and symptomatic reduction was observed in both groups (all; p<0.05). Total EoEQoL scores significantly improved in the FFED + AAF group between baseline and week 6 (p = 0.007), and not in the FFED group.

CONCLUSION

The addition of AAF to a FFED did not lead to a larger decrease in PEC between baseline and 6 weeks, but may result in a significant improvement of QoL in adult EoE patients NL6014 (NTR6778).

Retinol Depletion in COVID-19

Background and aims

COVID-19 has been a devastating pandemic. There are indications that vitamin A is depleted during infections. Vitamin A is important in development and immune homeostasis. It has been used successfully in measles, RSV and AIDS infections. In this study, we aimed to measure the serum retinol levels in severe COVID-19 patients to assess the importance of vitamin A in the COVID-19 pathogenesis.

Methods

The serum retinol level was measured in two groups of patients: the COVID-19 group, which consisted of 27 severe COVID-19 patients hospitalized in the intensive care unit with respiratory failure, and the control group, which consisted of 23 patients without COVID-19 symptoms.

Results

The mean serum retinol levels were 0.37 mg/L in the COVID-19 group and 0.52 mg/L in the control group. The difference between the serum retinol levels in the two groups was statistically significant. There was no significant difference in retinol levels between different ages and genders within the COVID-19 group. Comorbidity did not affect serum retinol levels.

Conclusion

The serum retinol level was significantly lower in patients with severe COVID-19, and this difference was independent of age or underlying comorbidity. Our data show that retinol and retinoic acid signaling might be important in immunopathogenesis of COVID-19.

Actions of Retinoic Acid in the Pathophysiology of HIV Infection

The vitamin A metabolite all-trans retinoic acid (RA) plays a key role in tissue homeostasis and mucosal immunity. RA is produced by gut-associated dendritic cells, which are among the first cells encountered by HIV. Acute HIV infection results in rapid reduction of RA levels and dysregulation of immune cell populations whose identities and function are largely controlled by RA. Here, we discuss the potential link between the roles played by RA in shaping intestinal immune responses and the manifestations and pathogenesis of HIV-associated enteropathy and similar conditions observed in SIV-infected non-human primate models. We also present data demonstrating the ability of RA to enhance the activation of replication-competent viral reservoirs from subjects on suppressive anti-retroviral therapy. The data suggest that retinoid supplementation may be a useful adjuvant for countering the pathologic condition of the gastro-intestinal tract associated with HIV infection and as part of a strategy for reactivating viral reservoirs as a means of depleting latent viral infection.

"Molding" immunity-modulation of mucosal and systemic immunity by the intestinal mycobiome in health and disease

Fungi are important yet understudied contributors to the microbial communities of the gastrointestinal tract. Starting at birth, the intestinal mycobiome undergoes a period of dynamic maturation under the influence of microbial, host, and extrinsic influences, with profound functional implications for immune development in early life, and regulation of immune homeostasis throughout life. Candida albicans serves as a model organism for understanding the cross-talk between fungal colonization dynamics and immunity, and exemplifies unique mechanisms of fungal-immune interactions, including fungal dimorphism, though our understanding of other intestinal fungi is growing. Given the prominent role of the gut mycobiome in promoting immune homeostasis, emerging evidence points to fungal dysbiosis as an influential contributor to immune dysregulation in a variety of inflammatory and infectious diseases. Here we review current knowledge on the factors that govern host-fungi interactions in the intestinal tract and immunological outcomes in both mucosal and systemic compartments.

Diet and Hygiene in Modulating Autoimmunity During the Pandemic Era

The immune system is an efficiently toned machinery that discriminates between friends and foes for achieving both host defense and homeostasis. Deviation of immune recognition from foreign to self and/or long-lasting inflammatory responses results in the breakdown of tolerance. Meanwhile, educating the immune system and developing immunological memory are crucial for mounting defensive immune responses while protecting against autoimmunity. Still to elucidate is how diverse environmental factors could shape autoimmunity. The emergence of a world pandemic such as SARS-CoV-2 (COVID-19) not only threatens the more vulnerable individuals including those with autoimmune conditions but also promotes an unprecedented shift in people's dietary approaches while urging for extraordinary hygiene measures that likely contribute to the development or exacerbation of autoimmunity. Thus, there is an urgent need to understand how environmental factors modulate systemic autoimmunity to better mitigate the incidence and or severity of COVID-19 among the more vulnerable populations. Here, we discuss the effects of diet (macronutrients and micronutrients) and hygiene (the use of disinfectants) on autoimmunity with a focus on systemic lupus erythematosus.

Research Progress in Vitamin A and Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder. Over the past few decades, many studies have investigated the effects of VA supplementation in ASD patients and the relationship between vitamin A (VA) levels and ASD. VA is an essential micronutrient that plays an important role in various systems and biological processes in the form of retinoic acid (RA). Recent studies have shown that serum VA concentration is negatively correlated with the severity of ASD. The lack of VA during pregnancy or early fetal development can affect brain development and lead to long-term or even permanent impairment in the learning process, memory formation, and cognitive function. In addition, VA deficiency has been reported to have a major impact on the gastrointestinal function of children with ASD, while VA supplementation has been shown to improve the symptoms of ASD to a certain extent. This paper provides a comprehensive review of the relationship between VA and ASD.

Retinoic acid signaling drives differentiation toward the absorptive lineage in colorectal cancer

Retinoic acid (RA) signaling is an important and conserved pathway that regulates cellular proliferation and differentiation. Furthermore, perturbed RA signaling is implicated in cancer initiation and progression. However, the mechanisms by which RA signaling contributes to homeostasis, malignant transformation, and disease progression in the intestine remain incompletely understood. Here, we report, in agreement with previous findings, that activation of the Retinoic Acid Receptor and the Retinoid X Receptor results in enhanced transcription of enterocyte-specific genes in mouse small intestinal organoids. Conversely, inhibition of this pathway results in reduced expression of genes associated with the absorptive lineage. Strikingly, this latter effect is conserved in a human organoid model for colorectal cancer (CRC) progression. We further show that RXR motif accessibility depends on progression state of CRC organoids. Finally, we show that reduced RXR target gene expression correlates with worse CRC prognosis, implying RA signaling as a putative therapeutic target in CRC.

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RA signaling contributes to enterocyte differentiation in murine intestinal organoids

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Inhibition of RXR decreases enterocyte gene expression in colon cancer organoids

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Accessibility of RXR motifs correlates with RXRi susceptibility

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High expression of RA signaling targets correlates with higher CRC patient survival

A novel hypothesis for COVID-19 pathogenesis: Retinol depletion and retinoid signaling disorder

The SARS-CoV-2 virus has caused a worldwide COVID-19 pandemic. In less than a year and a half, more than 200 million people have been infected and more than four million have died. Despite some improvement in the treatment strategies, no definitive treatment protocol has been developed. The pathogenesis of the disease has not been clearly elucidated yet. A clear understanding of its pathogenesis will help develop effective vaccines and drugs. The immunopathogenesis of COVID-19 is characteristic with acute respiratory distress syndrome and multiorgan involvement with impaired Type I interferon response and hyperinflammation. The destructive systemic effects of COVID-19 cannot be explained simply by the viral tropism through the ACE2 and TMPRSS2 receptors. In addition, the recently identified mutations cannot fully explain the defect in all cases of Type I interferon synthesis. We hypothesize that retinol depletion and resulting impaired retinoid signaling play a central role in the COVID-19 pathogenesis that is characteristic for dysregulated immune system, defect in Type I interferon synthesis, severe inflammatory process, and destructive systemic multiorgan involvement. Viral RNA recognition mechanism through RIG-I receptors can quickly consume a large amount of the body's retinoid reserve, which causes the retinol levels to fall below the normal serum levels. This causes retinoid insufficiency and impaired retinoid signaling, which leads to interruption in Type I interferon synthesis and an excessive inflammation. Therefore, reconstitution of the retinoid signaling may prove to be a valid strategy for management of COVID-19 as well for some other chronic, degenerative, inflammatory, and autoimmune diseases.

Effect of Radiation on the Essential Nutrient Homeostasis and Signaling of Retinoids in a Non-human Primate Model with Minimal Bone Marrow Sparing

ABSTRACT

High-dose radiation exposure results in hematopoietic (H) and gastrointestinal (GI) acute radiation syndromes (ARS) followed by delayed effects of acute radiation exposure (DEARE), which include damage to lung, heart, and GI. Whereas DEARE includes inflammation and fibrosis in multiple tissues, the molecular mechanisms contributing to inflammation and to the development of fibrosis remain incompletely understood. Reports that radiation dysregulates retinoids and proteins within the retinoid pathway indicate that radiation disrupts essential nutrient homeostasis. An active metabolite of vitamin A, retinoic acid (RA), is a master regulator of cell proliferation, differentiation, and apoptosis roles in inflammatory signaling and the development of fibrosis. As facets of inflammation and fibrosis are regulated by RA, we surveyed radiation-induced changes in retinoids as well as proteins related to and targets of the retinoid pathway in the non-human primate after high dose radiation with minimal bone marrow sparing (12 Gy PBI/BM2.5). Retinoic acid was decreased in plasma as well as in lung, heart, and jejunum over time, indicating a global disruption of RA homeostasis after IR. A number of proteins associated with fibrosis and with RA were significantly altered after radiation. Together these data indicate that a local deficiency of endogenous RA presents a permissive environment for fibrotic transformation.

Tolerogenic Dendritic Cells Shape a Transmissible Gut Microbiota That Protects From Metabolic Diseases

Excess chronic contact between microbial motifs and intestinal immune cells is known to trigger a low-grade inflammation involved in many pathologies such as obesity and diabetes. The important skewing of intestinal adaptive immunity in the context of diet-induced obesity (DIO) is well described, but how dendritic cells (DCs) participate in these changes is still poorly documented. To address this question, we challenged transgenic mice with enhanced DC life span and immunogenicity (DC^hBcl-2 mice) with a high-fat diet. Those mice display resistance to DIO and metabolic alterations. The DIO-resistant phenotype is associated with healthier parameters of intestinal barrier function and lower intestinal inflammation. DC^hBcl-2 DIO-resistant mice demonstrate a particular increase in tolerogenic DC numbers and function, which is associated with strong intestinal IgA, T helper 17, and regulatory T-cell immune responses. Microbiota composition and function analyses reveal that the DC^hBcl-2 mice microbiota is characterized by lower immunogenicity and an enhanced butyrate production. Cohousing experiments and fecal microbial transplantations are sufficient to transfer the DIO resistance status to wild-type mice, demonstrating that maintenance of DCs' tolerogenic ability sustains a microbiota able to drive DIO resistance. The tolerogenic function of DCs is revealed as a new potent target in metabolic disease management.

Oral Delivery of Encapsulated All-Trans Retinoic Acid Ameliorates Disease in Rodent Models of Colitis

BACKGROUND

All-trans retinoic acid (ATRA) is a biologically active isomer of retinoic acid (RA). Topical ATRA (retin-a, retin-a micro, atralin, renova, and avita) is the active pharmaceutical ingredient for FDA-approved treatments for acne and skin wrinkles. Oral formulations (Vesanoid) treat acute promyelocytic leukemia, but oral dosing can induce severe side effects. Despite benefits in various rodent models of inflammatory bowel disease (IBD), toxicity and controversial clinical observations have diminished enthusiasm for ATRA IBD clinical trials. To circumvent these issues and to use ATRA's key role in maintaining gut tolerance, we developed a poly(lactic-co-glycolic acid) (PLGA) microsphere (MS) encapsulated ATRA formulation aimed at directing ATRA delivery to immune structures of the gut, limiting systemic exposure. Initially, ATRA MS was developed as a component of a combinatorial product (TreXTAM) that also contained encapsulated transforming growth factor (TGF)-β and ATRA in a 1:2 w/w ratio. Although the combination was optimal, benefit was also observed when ATRA MS was given alone in the CD4+ CD25-T-cell adoptive transfer (ACT) colitis model.

METHODS

We used the ACT and DSS-induced murine models of colitis to expand on the dose-dependent effects of oral ATRA MS when given alone. The DSS model was also used to compare the efficacy of ATRA MS and soluble ATRA, while healthy animals were used to compare the pharmacokinetics of the two drugs.

RESULTS

In both the ACT and DSS-induced murine models of colitis, ATRA MS was observed to be effective in ameliorating disease. ATRA MS was also observed to be more effective than soluble ATRA in these models and displayed more favorable pharmacokinetics.

CONCLUSIONS

We suggest ATRA MS, as a standalone product, may attenuate IBD and perhaps limit fibrosis, while limiting systemic side effects.

Nutraceuticals in Viral Infections: An Overview of the Immunomodulating Properties

Nutraceuticals, including vitamin D, vitamin A, zinc, lactoferrin, polyphenols coenzyme Q, magnesium, and selenium, are implicated in the modulation of the complex molecular pathways involved in the immune response against viral pathogens. A common element of the activity of nutraceuticals is their ability to enhance the innate immune response against pathogens by acting on the major cellular subsets and inducing the release of pro-inflammatory cytokines and antimicrobial peptides. In some cases, this action is accompanied by a direct antimicrobial effect, as evidenced in the specific case of lactoferrin. Furthermore, nutraceuticals act through complex molecular mechanisms to minimize the damage caused by the activation of the immune system against pathogens, reducing the oxidative damage, influencing the antigen presentation, enhancing the differentiation and proliferation of regulatory T cells, driving the differentiation of lymphocyte subsets, and modulating the production of pro-inflammatory cytokines. In this paper, we review the main molecular mechanisms responsible for the immunomodulatory function of nutraceuticals, focusing on the most relevant aspects for the prevention and treatment of viral infections.

Effects of therapeutic vaccination on the control of SIV in rhesus macaques with variable responsiveness to antiretroviral drugs

A therapeutic vaccine that induces lasting control of HIV infection could eliminate the need for lifelong adherence to antiretroviral therapy. This study investigated a therapeutic DNA vaccine delivered with a single adjuvant or a novel combination of adjuvants to augment T cell immunity in the blood and gut-associated lymphoid tissue in SIV-infected rhesus macaques. Animals that received DNA vaccines expressing SIV proteins, combined with plasmids expressing adjuvants designed to increase peripheral and mucosal T cell responses, including the catalytic subunit of the E. coli heat-labile enterotoxin, IL-12, IL-33, retinaldehyde dehydrogenase 2, soluble PD-1 and soluble CD80, were compared to mock-vaccinated controls. Following treatment interruption, macaques exhibited variable levels of viral rebound, with four animals from the vaccinated groups and one animal from the control group controlling virus at median levels of 10³ RNA copies/ml or lower (controllers) and nine animals, among all groups, exhibiting immediate viral rebound and median viral loads greater than 10³ RNA copies/ml (non-controllers). Although there was no significant difference between the vaccinated and control groups in protection from viral rebound, the variable virological outcomes during treatment interruption enabled an examination of immune correlates of viral replication in controllers versus non-controllers regardless of vaccination status. Lower viral burden in controllers correlated with increased polyfunctional SIV-specific CD8⁺ T cells in mesenteric lymph nodes and blood prior to and during treatment interruption. Notably, higher frequencies of colonic CD4⁺ T cells and lower Th17/Treg ratios prior to infection in controllers correlated with improved responses to ART and control of viral rebound. These results indicate that mucosal immune responses, present prior to infection, can influence efficacy of antiretroviral therapy and the outcome of immunotherapeutic vaccination, suggesting that therapies capable of modulating host mucosal responses may be needed to achieve HIV cure.

Self-Assembled Biodegradable Core-Shell Nanocomposites of Amphiphilic Retinoic Acid-LMW bPEI Conjugates Exhibit Enhanced Transgene Expression in Hepatocellular Carcinoma Cells With Inherent Anticancer Properties

Low molecular weight branched polyethylenimines (LMW bPEIs) are almost nontoxic but display poor transfection efficiency due to lack of adequate complexation ability with nucleic acids followed by transportation across the cell membrane. Here, a series of amphiphilic retinoyl-bPEI conjugates (RP-1, RP-2 and RP-3) has been synthesized by allowing the reaction between bPEI (1.8 kDa) and a bioactive and hydrophobic vitamin A metabolite, all-trans-retinoic acid (ATRA), in varying amounts. In aqueous medium, these conjugates self-assembled into core-shell RP nanocomposites with size ranging from ~113-178 nm and zeta potential from ~ +15-35 mV. Evaluation of pDNA complexes of RP nanocomposites revealed that all the complexes exhibited significantly enhanced transfection efficiency without compromising on the cytocompatibility. RP-3/pDNA complex, with the highest content of retinoic acid, exhibited the best transfection efficiency. Further, due to anticancer properties of ATRA, these nanocomposites significantly reduced the viability of cancer cells (HepG2 and MCF-7 cells) without affecting the viability of non-cancerous cells (HEK 293 cells) demonstrating the cell-selective nature of the formulated nanocomposites. The intracellular trafficking and co-localization studies involving RP-3 nanocomposites also showed their higher uptake with intracellular and nuclear accumulation properties. Altogether, the results demonstrate the promising potential of the RP conjugates that can be used in future hepatocellular carcinoma targeted gene delivery applications.

TLR2 Deficiency Exacerbates Imiquimod-Induced Psoriasis-Like Skin Inflammation through Decrease in Regulatory T Cells and Impaired IL-10 Production

Emerging evidence has demonstrated that Toll-like receptors (TLRs) are associated with autoimmune diseases. In this study, we investigated the role of TLR2 in psoriasis using imiquimod-induced psoriasis-like dermatitis. Although TLR2 signaling is known to play a critical role in the induction of proinflammatory cytokines by immune cells, such as dendritic cells (DCs), macrophages, and monocytes, TLR2 deficiency unexpectedly exacerbated psoriasiform skin inflammation. Importantly, messenger RNA (mRNA) levels of Foxp-3 and IL-10 in the lesional skin were significantly decreased in TLR2 KO mice compared with wild-type mice. Furthermore, flow cytometric analysis of the lymph nodes revealed that the frequency of regulatory T cells (Tregs) among CD4-positive cells was decreased. Notably, stimulation with Pam3CSK4 (TLR2/1 ligand) or Pam2CSK4 (TLR2/6 ligand) increased IL-10 production from Tregs and DCs and the proliferation of Tregs. Finally, adoptive transfer of Tregs from wild-type mice reduced imiquimod-induced skin inflammation in TLR2 KO mice. Taken together, our results suggest that TLR2 signaling directly enhances Treg proliferation and IL-10 production by Tregs and DCs, suppressing imiquimod-induced psoriasis-like skin inflammation. Enhancement of TLR2 signaling may be a new therapeutic strategy for psoriasis.

Carotenoid metabolism at the intestinal barrier

Carotenoids exert a rich variety of physiological functions in mammals and are beneficial for human health. These lipids are acquired from the diet and metabolized to apocarotenoids, including retinoids (vitamin A and its metabolites). The small intestine is a major site for their absorption and bioconversion. From here, carotenoids and their metabolites are distributed within the body in triacylglycerol-rich lipoproteins to support retinoid signaling in peripheral tissues and photoreceptor function in the eyes. In recent years, much progress has been made in identifying carotenoid metabolizing enzymes, transporters, and binding proteins. A diet-responsive regulatory network controls the activity of these components and adapts carotenoid absorption and bioconversion to the bodily requirements of these lipids. Genetic variability in the genes encoding these components alters carotenoid homeostasis and is associated with pathologies. We here summarize the advanced state of knowledge about intestinal carotenoid metabolism and its impact on carotenoid and retinoid homeostasis of other organ systems, including the eyes, liver, and immune system. The implication of the findings for science-based intake recommendations for these essential dietary lipids is discussed. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

COVID-19: Endogenous Retinoic Acid Theory and Retinoic Acid Depletion Syndrome

This study presents two new concepts and definitions to the medical literature. One of those is "endogenous retinoic acid theory" and the other "retinoic acid depletion syndrome". A new classification will be provided for the immune system: "retinoic acid-dependent component" and "retinoic acid non-dependent component". If this theory is verified, all the diseases where the retinoic acid metabolism is defective and retinoic acid levels are low will be identified and new approaches will be developed fortreating such diseases. When the need for retinoic acids increases, such as acute infection, high fever, severe catabolic process, or chronic antigenic stimulation, cytochrome oxidase enzymes are inhibited by drugs or internal mechanisms. Metabolism and excretion of retinoic acids stored in the liver are prevented. In this way, retinoic acid levels in the blood are raised to therapeutic levels. This is called "Endogenous Retinoic Acid Theory". Retinoic acids also manage their metabolism through feedback mechanisms. Despite compensatory mechanisms, causes such as high fever, serious catabolic process and excessively large viral genome (SARS-CoV-2), excessive use of RIG-I and Type I interferon synthesis pathway using retinoic acid causes emptying of retinoic acid stores. As a result, the RIG-I pathway becomes ineffective, Type I IFN synthesis stops, and the congenital immune system collapses. Then the immune mechanism passes to TLR3, TLR7, TLR8, TLR9, MDA5 and UPS pathways in the monocyte, macrophage, neutrophil and dendritic cells of the adaptive immune defense system that do not require retinoic acid. This leads to excessive TNFα and cytokine discharge from the pathway. With the depletion of retinoic acid stores as a result of this overuse, the immune defense mechanism switches from the congenital immune system to the adaptive immune system, where retinoic acids cannot be used. As a result of this depletion of retinoic acids, the shift of the immune system to the NFκB arm, which causes excessive cytokine release, is called "retinoic acid depletion syndrome". COVID-19 and previously defined sepsis, SIRS and ARDS are each retinoic acid depletion syndrome. We claim that retinoic acid metabolism is defective in most inflammatory diseases, particularly COVID-19 (cytokine storm) sepsis, SIRS and ARDS. Finding a solution to this mechanism will bring a new perspective and treatment approach to such diseases.

CELL THERAPY IN INFLAMMATORY BOWEL DISEASE

In recent years, cell-based therapies have been explored in various immune-mediated inflammatory diseases, including inflammatory bowel disease (IBD). Cell therapy is the process of introducing new cells into an organism or tissue in order to treat a disease. The most studied cellular treatment in IBD was "stem cells-based therapy", which was explored according to different protocols in terms of type of donors, stem cells sources, study design and clinical endpoints. More recently, preliminary studies have also described the clinical use of "regulatory cells", which include T-reg and Tr1 cells, and "tolerogenic" dendritic cells. Finally, induced pluripotent stem cells are the subject of an intensive preclinical research program on animal models, including those related to colitis.

Phenotypic landscape of intestinal organoid regeneration

The development of intestinal organoids from single adult intestinal stem cells in vitro recapitulates the regenerative capacity of the intestinal epithelium^1,2. Here we unravel the mechanisms that orchestrate both organoid formation and the regeneration of intestinal tissue, using an image-based screen to assay an annotated library of compounds. We generate multivariate feature profiles for hundreds of thousands of organoids to quantitatively describe their phenotypic landscape. We then use these phenotypic fingerprints to infer regulatory genetic interactions, establishing a new approach to the mapping of genetic interactions in an emergent system. This allows us to identify genes that regulate cell-fate transitions and maintain the balance between regeneration and homeostasis, unravelling previously unknown roles for several pathways, among them retinoic acid signalling. We then characterize a crucial role for retinoic acid nuclear receptors in controlling exit from the regenerative state and driving enterocyte differentiation. By combining quantitative imaging with RNA sequencing, we show the role of endogenous retinoic acid metabolism in initiating transcriptional programs that guide the cell-fate transitions of intestinal epithelium, and we identify an inhibitor of the retinoid X receptor that improves intestinal regeneration in vivo.

The Need to Consider Context in the Evaluation of Anti-infectious and Immunomodulatory Effects of Vitamin A and its Derivatives

Vitamin A and its derivatives (retinoids) act as potent regulators in many aspects of mammalian reproduction, development, repair, and maintenance of differentiated tissue functioning. Unlike other vitamins, Vitamin A and retinoids, which have hormonal actions, present significant toxicity, which plays roles in clinically relevant situations, such as hypervitaminosis A and retinoic acid ("differentiation") syndrome. Although clinical presentation is conspicuous in states of insufficient or excessive Vitamin A and retinoid concentration, equally relevant effects on host resistance to specific infectious agents, and in the general maintenance of immune homeostasis, may go unnoticed, because their expression requires either pathogen exposure or the presence of inflammatory co-morbidities. There is a vast literature on the roles played by retinoids in the maintenance of a tolerogenic, noninflammatory environment in the gut mucosa, which is considered by many investigators representative of a general role played by retinoids as anti-inflammatory hormones elsewhere. However, in the gut mucosa itself, as well as in the bone marrow and inflammatory sites, context determines whether one observes an anti-inflammatory or proinflammatory action of retinoids. Both interactions between specialized cell populations, and interactions between retinoids and other classes of mediators/regulators, such as cytokines and glucocorticoid hormones, must be considered as important factors contributing to this overall context. We review evidence from recent studies on mucosal immunity, granulocyte biology and respiratory allergy models, highlighting the relevance of these variables as well as their possible contributions to the observed outcomes.

The correlation between vitamin a status and refractory Mycoplasma Pneumoniae pneumonia (RMPP) incidence in children

Background

Vitamin A plays a pivotal role in respiratory infection, accurate estimation of vitamin A status was recommended in planning and implementing interventions. As infections affect serum vitamin A productions, the real status need to be adjusted by acute phase protein (APP). Mycoplasma pneumoniae is an important cause of respiratory infection in children, the association between vitamin A concentrations and refractory Mycoplasma pneumoniae pneumonia (RMPP) remains unclear.

Methods

181 MPP patients were enrolled in this retrospective study, adjusted vitamin A concentrations and other parameters were compared between RMPP and general-MPP (GMPP) patients. Multivariate logistic regression test was performed to evaluate the association between vitamin A levels and RMPP incidence, linear correlation tests were applied to evaluate correlation between vitamin A concentrations and fever duration, length of stay (LOS).

Results

Vitamin A concentrations in RMPP group were significantly lower than those in GMPP patients (P < 0.05), vitamin A (OR = 0.795, 95% C. I 0.669–0.946) and CRP (OR = 1.050, 95% C. I 1.014–1.087) were independently associated with RMPP incidence. Linear correlation tests found vitamin A concentrations were negatively correlated with fever duration and LOS (P < 0.001).

Conclusions

Serum vitamin A concentrations were independently associated with RMPP incidence, which may correlate with reduced incidence of RMPP.