1,25-Dihydroxyvitamin D3 prevents toluene diisocyanate-induced airway epithelial barrier disruption

Spatial modeling connecting childhood atopic dermatitis prevalence with household exposure to pollutants

BACKGROUND

Atopic dermatitis (AD) is a chronic, inflammatory disease characterized by dry, pruritic skin. In the U.S., the prevalence of AD has increased over three-fold since the 1970s. We previously reported a geographic association between isocyanate-containing air pollution and AD as well as mechanistic data demonstrating that isocyanates induce skin dysbiosis and activate the host itch receptor TRPA1. However, non-spatial models are susceptible to spatial confounding and may overlook other meaningful associations.

METHODS

We added spatial analysis to our prior model, contrasting pollution data with clinical visits. In addition, we conducted a retrospective case-control survey of childhood exposure to BTEX-related products. Finally, we assessed implicated compounds, in pure form and as part of synthetic fabric, for their effect on the growth and metabolism of skin commensal bacteria.

RESULTS

Spatial analysis implicate benzene, toluene, ethylbenzene, and, most significantly, xylene (BTEX) compounds. Survey odds ratios for AD were significant for xylene-derived polyester bed sheets (OR = 9.5; CI 2.2-40.1) and diisocyanate-containing wallpaper adhesive (OR = 6.5; CI 1.5-27.8). Staphylococcus aureus lives longer on synthetic textiles compared to natural textiles. Meanwhile, synthetic fabric exposure shifts the lipid metabolism of health-associated commensals (Roseomonas mucosa and S. epidermidis) away from therapeutic pathways.

CONCLUSIONS

We propose that BTEX chemicals in their raw forms and in synthetic products represent a unifying hypothesis for environmentally induced AD flares through their ability to create dysbiosis in the skin microbiota and directly activate TRPA1. Unequal distribution of these pollutants may also influence racial disparities in AD rates.

Vitamin D3 protects against respiratory syncytial virus-induced barrier dysfunction in airway epithelial cells via PKA signaling pathway

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infection in infants and young children globally and is responsible for hospitalization and mortality in the elderly population. Virus-induced airway epithelial barrier damage is a critical step during RSV infection, and emerging studies suggest that RSV disrupts the tight junctions (TJs) and adherens junctions (AJs) between epithelial cells, increasing the permeability of the airway epithelial barrier. The lack of commercially available vaccines and effective antiviral drugs for RSV emphasizes the need for new management strategies. Vitamin D3 is a promising intervention for viral infection due to its critical role in modulating innate immune responses. However, there is limited evidence on the effect of vitamin D3 on RSV pathogenies. Here, we investigated the impact of vitamin D3 on RSV-induced epithelial barrier dysfunction and the underlying mechanisms. We found that pre-incubation with 1,25(OH)2D3, the active form of vitamin D3, alleviated RSV-induced epithelial barrier disruption in a dose-dependent manner without affecting viability in 16HBE cells. 1,25(OH)2D3 induced minor changes in the protein expression level of TJ/AJ proteins in RSV-infected cells. We observed increased CREB phosphorylation at Ser133 during 1,25(OH)2D3 exposure, indicating that vitamin D3 triggered protein kinase A (PKA) activity in 16HBE. PKA inhibitors modified the restoration of barrier function by 1,25(OH)2D3 in RSV-infected cells, implying that PKA signaling is responsible for the protective effects of vitamin D3 against RSV-induced barrier dysfunction in airway epithelial cells. Our findings suggest vitamin D3 as a prophylactic intervention to protect the respiratory epithelium during RSV infections.

Protective effects of inhaled antioxidants against air pollution-induced pathological responses

As the public health burden of air pollution continues to increase, new strategies to mitigate harmful health effects are needed. Dietary antioxidants have previously been explored to protect against air pollution-induced lung injury producing inconclusive results. Inhaled (pulmonary or nasal) administration of antioxidants presents a more promising approach as it could directly increase antioxidant levels in the airway surface liquid (ASL), providing protection against oxidative damage from air pollution. Several antioxidants have been shown to exhibit antioxidant, anti-inflammatory, and anti-microbial properties in in vitro and in vivo models of air pollution exposure; however, little work has been done to translate these basic research findings into practice. This narrative review summarizes these findings and data from human studies using inhaled antioxidants in response to air pollution, which have produced positive results, indicating further investigation is warranted. In addition to human studies, cell and murine studies should be conducted using more relevant models of exposure such as air-liquid interface (ALI) cultures of primary cells and non-aqueous apical delivery of antioxidants and pollutants. Inhalation of antioxidants shows promise as a protective intervention to prevent air pollution-induced lung injury and exacerbation of existing lung disease.

Diisocyanates influence models of atopic dermatitis through direct activation of TRPA1

We recently used EPA databases to identify that isocyanates, most notably toluene diisocyanate (TDI), were the pollutant class with the strongest spatiotemporal and epidemiologic association with atopic dermatitis (AD). Our findings demonstrated that isocyanates like TDI disrupted lipid homeostasis and modeled benefit in commensal bacteria like Roseomonas mucosa through disrupting nitrogen fixation. However, TDI has also been established to activate transient receptor potential ankyrin 1 (TRPA1) in mice and thus could directly contribute to AD through induction of itch, rash, and psychological stress. Using cell culture and mouse models, we now demonstrate that TDI induced skin inflammation in mice as well as calcium influx in human neurons; each of these findings were dependent on TRPA1. Furthermore, TRPA1 blockade synergized with R. mucosa treatment in mice to improve TDI-independent models of AD. Finally, we show that the cellular effects of TRPA1 are related to shifting the balance of the tyrosine metabolites epinephrine and dopamine. This work provides added insight into the potential role, and therapeutic potential, or TRPA1 in the pathogenesis of AD.

Vitamin D Receptor Influences Intestinal Barriers in Health and Disease

Vitamin D receptor (VDR) executes most of the biological functions of vitamin D. Beyond this, VDR is a transcriptional factor regulating the expression levels of many target genes, such as genes for tight junction proteins claudin-2, -5, -12, and -15. In this review, we discuss the progress of research on VDR that influences intestinal barriers in health and disease. We searched PubMed and Google Scholar using key words vitamin D, VDR, tight junctions, cancer, inflammation, and infection. We summarize the literature and progress reports on VDR regulation of tight junction distribution, cellular functions, and mechanisms (directly or indirectly). We review the impacts of VDR on barriers in various diseases, e.g., colon cancer, infection, inflammatory bowel disease, and chronic inflammatory lung diseases. We also discuss the limits of current studies and future directions. Deeper understanding of the mechanisms by which the VDR signaling regulates intestinal barrier functions allow us to develop efficient and effective therapeutic strategies based on levels of tight junction proteins and vitamin D/VDR statuses for human diseases.

Micronutrient Improvement of Epithelial Barrier Function in Various Disease States: A Case for Adjuvant Therapy

The published literature makes a very strong case that a wide range of disease morbidity associates with and may in part be due to epithelial barrier leak. An equally large body of published literature substantiates that a diverse group of micronutrients can reduce barrier leak across a wide array of epithelial tissue types, stemming from both cell culture as well as animal and human tissue models. Conversely, micronutrient deficiencies can exacerbate both barrier leak and morbidity. Focusing on zinc, Vitamin A and Vitamin D, this review shows that at concentrations above RDA levels but well below toxicity limits, these micronutrients can induce cell- and tissue-specific molecular-level changes in tight junctional complexes (and by other mechanisms) that reduce barrier leak. An opportunity now exists in critical care—but also medical prophylactic and therapeutic care in general—to consider implementation of select micronutrients at elevated dosages as adjuvant therapeutics in a variety of disease management. This consideration is particularly pointed amidst the COVID-19 pandemic.

Oral Supplementation of the Vitamin D Metabolite 25(OH)D3 Against Influenza Virus Infection in Mice

Vitamin D is a fat-soluble vitamin that is metabolized by the liver into 25-hydroxyvitamin D [25(OH)D] and then by the kidney into 1,25-dihydroxyvitamin D [1,25(OH)2D], which activates the vitamin D receptor expressed in various cells, including immune cells, for an overall immunostimulatory effect. Here, to investigate whether oral supplementation of 25-hydroxyvitamin D3 [25(OH)D3], a major form of vitamin D metabolite 25(OH)D, has a prophylactic effect on influenza A virus infection, mice were fed a diet containing a high dose of 25(OH)D3 and were challenged with the influenza virus. In the lungs of 25(OH)D3-fed mice, the viral titers were significantly lower than in the lungs of standardly fed mice. Additionally, the proinflammatory cytokines IL-5 and IFN-γ were significantly downregulated after viral infection in 25(OH)D3-fed mice, while anti-inflammatory cytokines were not significantly upregulated. These results indicate that 25(OH)D3 suppresses the production of inflammatory cytokines and reduces virus replication and clinical manifestations of influenza virus infection in a mouse model.

Protective effects of vitamin D against injury in intestinal epithelium

BACKGROUND

Vitamin D deficiency is associated with intestinal barrier dysfunction, which contributes to pathogenesis of acute intestinal injury in children. We aim to investigate the effects of vitamin D on intestinal injury in intestinal epithelial cells and organoids.

METHODS

Lipopolysaccharide (LPS) was used to induce injury in intestinal epithelial cells (IEC-18) and organoids, and the effect of vitamin D was assessed. Cell viability was measured and inflammation cytokines TNFα and IL-8 were quantified. FITC-dextran 4 kDa (FD4) permeability was measured using Transwell while tight junction markers were assessed by immunofluorescence staining in IEC-18 and intestinal organoids. Data were compared using one-way ANOVA with Bonferroni post-test.

RESULTS

IEC-18 viability was decreased by LPS treatment, but was prevented by vitamin D. The upregulation of inflammation was inhibited by vitamin D, which also decreased epithelium permeability. Vitamin D restored tight junction ZO-1 and claudin 2. In addition, vitamin D decreased TNFα expression and prevented the disruption of ZO-1 in injured organoids.

CONCLUSIONS

Vitamin D rescued epithelial barrier function by improving permeability and restoring tight junctions, leading to decrease inflammation. This study confirms the protective effects of vitamin D, which could be used as a treatment strategy for infants at risk of developing intestinal injury.

Andrographolide prevented toluene diisocyanate-induced occupational asthma and aberrant airway E-cadherin distribution via p38 MAPK-dependent Nrf2 induction

Toluene diisocyanate (TDI) is a major cause of chemical-induced occupational asthma, which contributes about 15% of global asthma burden. Resistance and compounded side effects associated with the use of corticosteroid in asthma necessitate the search for alternative drugs. Andrographolide (AGP), a naturally occurring diterpene lactone is known to exhibit various bioactivities. Its ability to ameliorate cardinal features of allergic asthma was previously suggested in an eosinophilic asthma endotype. However, its potential antiasthma activity and mechanism of action in a neutrophilic occupational asthma model, as well as its effect on epithelial dysfunction remain unknown. BALB/c mice were dermally sensitised with 0.3% TDI or acetone olive oil (AOO) vehicle on day 1 and 8, followed by 0.1% TDI intranasal challenge on days 15, 18 and 21. Endpoints were evaluated via bronchoalveolar lavage fluid (BALF) cell analysis, 2',7'-dichlorofluorescein diacetate (DCFDA) assays, immunoblotting, immunohistochemistry and methacholine challenge test. Decreases in total and differential leukocyte counts of BALF were recorded in AGP-treated animals. The compound dose-dependently reduced intracellular de-esterification of DCFDA, thus suggesting AGP's potential to inhibit intracellular reactive oxygen species (ROS). Mechanistically, the treatment prevented TDI-induced aberrant E-cadherin distribution and restored airway epithelial β-catenin at cell to cell contact site. Furthermore, AGP ameliorated TDI induced pulmonary collagen deposition. In addition, the treatment significantly upregulated pulmonary HO-1, Nrf2 and phospho-p38 levels. Airway hyperresponsiveness was markedly suppressed among AGP-treated animals. Collectively, these findings suggest AGP's protective function against TDI-induced airway epithelial barrier dysfunction and oxidative lung damage possibly through the upregulation of adherence junction proteins and the activation of p38/Nrf2 signalling. This study elucidates the therapeutic potential of AGP in the control and management of chemical-induced allergic asthma. To the best of our knowledge, the potential anti-asthma activity of AGP in TDI-induced occupational asthma has not been reported previously.

Vitamin D supplementation of initially vitamin D-deficient mice diminishes lung inflammation with limited effects on pulmonary epithelial integrity

In disease settings, vitamin D may be important for maintaining optimal lung epithelial integrity and suppressing inflammation, but less is known of its effects prior to disease onset. Female BALB/c dams were fed a vitamin D₃‐supplemented (2280 IU/kg, VitD⁺) or nonsupplemented (0 IU/kg, VitD⁻) diet from 3 weeks of age, and mated at 8 weeks of age. Male offspring were fed the same diet as their mother. Some offspring initially fed the VitD⁻ diet were switched to a VitD⁺ diet from 8 weeks of age (VitD^−/+). At 12 weeks of age, signs of low‐level inflammation were observed in the bronchoalveolar lavage fluid (BALF) of VitD⁻ mice (more macrophages and neutrophils), which were suppressed by subsequent supplementation with vitamin D₃. There was no difference in the level of expression of the tight junction proteins occludin or claudin‐1 in lung epithelial cells of VitD⁺ mice compared to VitD⁻ mice; however, claudin‐1 levels were reduced when initially vitamin D‐deficient mice were fed the vitamin D₃‐containing diet (VitD^−/+). Reduced total IgM levels were detected in BALF and serum of VitD^−/+ mice compared to VitD⁺ mice. Lung mRNA levels of the vitamin D receptor (VDR) were greatest in VitD^−/+ mice. Total IgG levels in BALF were greater in mice fed the vitamin D₃‐containing diet, which may be explained by increased activation of B cells in airway‐draining lymph nodes. These findings suggest that supplementation of initially vitamin D‐deficient mice with vitamin D₃ suppresses signs of lung inflammation but has limited effects on the epithelial integrity of the lungs.

Modulation of inflammatory and immune responses by vitamin D

Vitamin D (VitD) is a prohormone most noted for the regulation of calcium and phosphate levels in circulation, and thus of bone metabolism. Inflammatory and immune cells not only convert inactive VitD metabolites into calcitriol, the active form of VitD, but also express the nuclear receptor of VitD that modulates differentiation, activation and proliferation of these cells. In vitro, calcitriol upregulates different anti-inflammatory pathways and downregulates molecules that activate immune and inflammatory cells. Administration of VitD has beneficial effects in a number of experimental models of autoimmune disease. Epidemiologic studies have indicated that VitD insufficiency is frequently associated with immune disorders and infectious diseases, exacerbated by increasing evidence of suboptimal VitD status in populations worldwide. To date, however, most interventional studies in human inflammatory and immune diseases with VitD supplementation have proven to be inconclusive. One of the reasons could be that the main VitD metabolite measured in these studies was the 25-hydroxyVitD (25OHD) rather than its active form calcitriol. Although our knowledge of calcitriol as modulator of immune and inflammatory reactions has dramatically increased in the past decades, further in vivo and clinical studies are needed to confirm the potential benefits of VitD in the control of immune and inflammatory conditions.

Vitamin D treatment modulates immune activation in cystic fibrosis

Persistent inflammatory response in cystic fibrosis (CF) airways is believed to play a central role in the progression of lung damage. Anti-inflammatory treatment may slow lung disease progression, but adverse side effects have limited its use. Vitamin D has immunoregulatory properties. We randomized 16 CF patients to receive vitamin D2, vitamin D3 or to serve as controls, and investigated the effect of vitamin D supplementation on soluble immunological parameters, myeloid dendritic cells (mDCs) and T cell activation. Three months of vitamin D treatment were followed by two washout months. Vitamin D status at baseline was correlated negatively with haptoglobin, erythrocyte sedimentation rate and immunoglobulin A concentration. Total vitamin D dose per kg bodyweight correlated with the down-modulation of the co-stimulatory receptor CD86 on mDCs. Vitamin D treatment was associated with reduced CD279 (PD-1) expression on CD4⁺ and CD8⁺ T cells, as well as decreased frequency of CD8⁺ T cells co-expressing the activation markers CD38 and human leucocyte antigen D-related (HLA-DR) in a dose-dependent manner. There was a trend towards decreased mucosal-associated invariant T cells (MAIT) cell frequency in patients receiving vitamin D and free serum 25-hydroxyvitamin D (free-s25OHD) correlated positively with CD38 expression by these cells. At the end of intervention, the change in free-s25OHD was correlated negatively with the change in CD279 (PD-1) expression on MAIT cells. Collectively, these data indicate that vitamin D has robust pleiotropic immunomodulatory effects in CF. Larger studies are needed to explore the immunomodulatory treatment potential of vitamin D in CF in more detail.

Vitamin D and Bronchial Asthma: An Overview of Data From the Past 5 Years

PURPOSE

Vitamin D is a potent immunomodulator capable of dampening inflammatory signals in several cell types involved in the asthmatic response. Its deficiency has been associated with increased inflammation, exacerbations, and overall poor outcomes in patients with asthma. Given the increase in the prevalence of asthma over the past few decades, there has been enormous interest in the use of vitamin D supplementation as a potential therapeutic option. Here, we critically reviewed the most recent findings from in vitro studies, animal models, and clinical trials regarding the role of vitamin D in treating bronchial asthma.

METHODS

Using the key terms [Vitamin D, asthma, clinical trials, in vivo and in vitro studies], the [PubMed, Google Scholar] databases were searched for [clinical trials, original research articles, meta-analyses, and reviews], English-language articles published from [2012] to the present. Articles that were [Articles that did not meet these criteria were excluded] excluded from the analysis.

FINDINGS

Several studies have found that low serum levels of vitamin D (< 20 ng/mL) are associated with increased exacerbations, increased airway inflammation, decreased lung function, and poor prognosis in asthmatic patients. Results from in vitro and in vivo studies in animals and humans have suggested that supplementation with vitamin D may ameliorate several hallmark features of asthma. However, the findings obtained from clinical trials are controversial and do not unequivocally support a beneficial role of vitamin D in asthma. Largely, interventional studies in children, pregnant women, and adults have primarily found little to no effect of vitamin D supplementation on improved asthma symptoms, onset, or progression of the disease. This could be related to the severity of the disease process and other confounding factors.

IMPLICATIONS

Despite the conflicting data obtained from clinical trials, vitamin D deficiency may influence the inflammatory response in the airways. Further studies are needed to determine the exact mechanisms by which vitamin D supplementation may induce antiinflammatory effects.

Distinct roles of short and long thymic stromal lymphopoietin isoforms in house dust mite-induced asthmatic airway epithelial barrier disruption

Loss of airway epithelial integrity contributes significantly to asthma pathogenesis. Thymic stromal lymphopoietin (TSLP) may have dual immunoregulatory roles. In inflammatory disorders of the bowel, the long isoform of TSLP (lfTSLP) promotes inflammation while the short isoform (sfTSLP) inhibits inflammation. We hypothesize that lfTSLP contributes to house dust mite (HDM)-induced airway epithelial barrier dysfunction and that synthetic sfTSLP can prevent these effects. In vitro, airway epithelial barrier function was assessed by monitoring transepithelial electrical resistance, fluorescent-dextran permeability, and distribution of E-cadherin and β-catenin. In vivo, BALB/c mice were exposed to HDM by nasal inhalation for 5 consecutive days per week to establish an asthma model. sfTSLP and 1α,25-Dihydroxyvitamin D3 (1,25D3) were administered 1 h before HDM exposure. After 8 weeks, animal lung function tests and pathological staining were performed to evaluate asthma progression. We found that HDM and lfTSLP impaired barrier function. Treatment with sfTSLP and 1,25D3 prevented HDM-induced airway epithelial barrier disruption. Moreover, sfTSLP and 1,25D3 treatment ameliorated HDM-induced asthma in mice. Our data emphasize the importance of the different expression patterns and biological properties of sfTSLP and lfTSLP. Moreover, our results indicate that sfTSLP and 1,25D3 may serve as novel therapeutic agents for individualized treatment of asthma.

1,25-Dihydroxyvitamin D3 targeting VEGF pathway alleviates house dust mite (HDM)-induced airway epithelial barrier dysfunction

BACKGROUND

In our previous studies, we have indentified that 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) can alleviate toluene diisocyanate-induced airway epithelial barrier disruption and we also found that vascular endothelial growth factor (VEGF) derived from airway epithelials cells could disrupt epithelial barrier.

OBJECTIVE

The study aimed to investigate whether 1,25(OH)₂D₃ can inhibit house dust mite (HDM) induced airway epithelial barrier dysfunction by regulating the VEGF pathway.

METHOD

The 16HBE and BEAS-2B cells were cultured and treated according to the experiment requirement. Trans Epithelial Electric Resistance (TEER), permeability of epithelial layer, and distribution and expression of junction proteins were used to evaluate the cell layer barrier function, Western Blot was used to evaluate the expression of junction proteins and phosphorylated Akt in the cells, RT-PCR and ELISA were used to evaluate the VEGF gene expression and protein release in the cells. Recombinant VEGF165 was used to determine the role of the VEGF pathway in the epithelial barrier function.

RESULTS

HDM resulted in a decline in TEER and increase of cell permeability, following abnormal distribution and expression of junction proteins (E-Cadherin and zona occludens (ZO)-1), accompanied by a significant upregulation of VEGF and phosphorylated Akt, which were all partly recovered by treatment with either 1,25(OH)₂D₃ or PI3K inhibitor LY294002. VEGF165-induced barrier dysfunction was accompanied by disruption of the epithelial E-cadherin and β-catenin, pretreatment of 1,25(OH)₂D₃ and LY294002 markedly attenuated VEGF-induced airway barrier disruption in 16HBE cells.

CONCLUSION

1,25(OH)₂D₃ can alleviate HDM-induced airway epithelial barrier dysfunction by inhibiting PI3K pathway-dependent VEGF release.