Vitamin Levels in Lung Tissue of Rats with Bleomycin Induced Pulmonary Fibrosis

GPRC5A reduction contributes to pollutant benzo[a]pyrene injury via aggravating murine fibrosis, leading to poor prognosis of IIP patients

Air pollution exposure is recently reported to be one of the drivers of exacerbation in idiopathic pulmonary fibrosis (IPF). But there was a lack of direct evidence between pollution and lung fibrosis. Here, our data show effects of pollutant benzo[a]pyrene (BaP) and protein G-protein-coupled receptor family C group 5 type A (GPRC5A) on pulmonary fibrosis, which might help limit potential pollutant injury and disease progression. We cross-referenced epithelial differentially-expressed-genes (DEGs) from pollutant injury and published experimental fibrosis and IPF patients' data, top common-DEG (CO-DEG) GPRC5A was identified as a potential link between exposure-damage and fibrogenesis. The role of GPRC5A was evaluated under BaP exposure, in idiopathic interstitial pneumonia (IIP) tissue-array and via CRISPR/Cas9 knockout mice (Gprc5a^-/-). BaP exposure enhanced bleomycin (BLM)-induced murine pulmonary fibrosis with increased Fibronectin and α-SMA expression in primary fibroblasts, thickened respiratory membrane and damaged alveolar type II cell, combined with Gprc5a decline in fibrotic mass. GPRC5A mRNA reduced after 10-14 days' BaP exposure in human epithelial cell A549. GPRC5A protein was further found to decrease in IIP epithelium, especially hyperplastic regions. A high epithelial GPRC5A expression score was positively associated with long survival time (R = 0.34) while negatively with high age (R = -0.4) and IIP type IPF (R = -0.5). Low GPRC5A expression predicts poor prognosis (HR = 4.5). Gprc5a depletion aggravated mortality rate (50%) with increased collagen deposition and myofibroblast activation under BLM treatment and exacerbated BaP injury in lung remodeling. Vitamin metabolic imbalance and Mitofusion2 (Mfn2) or Opa1-regulated mitochondrial dynamics were deduced to contribute to Gprc5a depletion and fibrogenesis. Pollutant BaP exposure worsens murine fibrosis and myofibroblast activation via GPRC5A reduction in the damaged epithelium. GPRC5A deficiency was first confirmed to contribute to both poor prognosis of IIP patients and fibrogenesis in murine model; thus, GPRC5A could serve as a novel therapeutic target in pollutant injury and pulmonary fibrosis.

1,25-Dihydroxyvitamin D Enhances Alveolar Fluid Clearance by Upregulating the Expression of Epithelial Sodium Channels

Vitamin D is implicated in the pathogenesis of asthma, acute lung injury, and other respiratory diseases. 1,25-Dihydroxyvitamin D (1,25(OH)2D3), the hormonal form of vitamin D, has been shown to reduce vascular permeability and ameliorate lung edema. Therefore, we speculate that 1,25(OH)2D3 may regulate alveolar Na(+) transport via targeting epithelial Na(+) channels (ENaC), a crucial pathway for alveolar fluid clearance. In vivo total alveolar fluid clearance was 39.4 ± 3.8% in 1,25(OH)2D3-treated mice, significantly greater than vehicle-treated controls (24.7 ± 1.9 %, n = 10, p < 0.05). 1,25(OH)2D3 increased amiloride-sensitive short-circuit currents in H441 monolayers, and whole-cell patch-clamp data confirmed that ENaC currents in single H441 cell were enhanced in 1,25(OH)2D3-treated cells. Western blot showed that the expression of α-ENaC was significantly elevated in 1,25(OH)2D3-treated mouse lungs and 1,25(OH)2D3-treated H441 cells. These observations suggest that vitamin D augments transalveolar fluid clearance, and vitamin D therapy may potentially be used to ameliorate pulmonary edema.

Preventive effects of vitamin D treatment on bleomycin-induced pulmonary fibrosis

Patients with pulmonary fibrosis often have low vitamin D levels, the effects of which are largely unknown. We here report that early vitamin D supplementation significantly reduced the severity of pulmonary fibrosis and inflammatory cell accumulationin in the bleomycin-induced pulmonary fibrosis mouse model on supplementary days 14, 21 and 28 (P < 0.001). Vitamin D supplementation also prevented some ultrastructural changes in response to bleomycin administration, including basement membrane thickening, interstitial fibrin deposition and microvilli flattening or disappearance on days 14, 21 and 28, and lamellar body swelling or vacuolation on days 21 and 28. The bleomycin group had rising hydroxyproline level on days 14, 21 and 28, whereas the vitamin D treatment group showed consistently lower hydroxyproline level but still higher than that of the control group (P < 0.001). Our immunohistochemistry and densitometry analyses showed less staining for α-smooth muscle actin, a myofibroblast marker, in the vitamin D group compared to the bleomycin group (P < 0.001). Thus, vitamin D treatment could prevent bleomycin-induced pulmonary fibrosis by delaying or suppressing ultrastructural changes, as well as attenuating hydroxyproline accumulation and inhibiting myofibroblastic proliferation. These data further our understanding of the roles of vitamin D in pulmonary fibrogenesis and in the treatment of pulmonary fibrosis.

Tocopherol supplementation reduces NO production and pulmonary inflammatory response to bleomycin

Bleomycin causes acute lung injury through production of reactive species and initiation of inflammation. Previous work has shown alteration to the production of reactive oxygen species results in attenuation of injury. Vitamin E, in particular, γ-tocopherol, isoform, has the potential to scavenge reactive oxygen and nitrogen species. This study examines the utility of dietary supplementation with tocopherols in reducing bleomycin-mediated acute lung injury. Male C57BL6/J mice were intratracheally instilled with PBS or 2 units/kg bleomycin. Animals were analyzed 3 and 8 days post instillation at the cellular, tissue, and organ levels. Results showed successful delivery of tocopherols to the lung via dietary supplementation. Also, increases in reactive oxygen and nitrogen species due to bleomycin are normalized in those mice fed tocopherol diet. Injury was not prevented but inflammation progression was altered, in particular macrophage activation and function. Inflammatory scores based on histology demonstrate limited progression of inflammation in those mice treated with bleomycin and fed tocopherol diet compared to control diet. Upregulation of enzymes and cytokines involved in pro-inflammation were limited by tocopherol supplementation. Day 3 functional changes in elastance in response to bleomycin are prevented, however, 8 days post injury the effect of the tocopherol diet is lost. The effect of tocopherol supplementation upon the inflammatory process is demonstrated by a shift in the phenotype of macrophage activation. The effect of these changes on resolution and the progression of pulmonary fibrosis has yet to be elucidated.

Vitamin D deficiency and reduced lung function in connective tissue-associated interstitial lung diseases

BACKGROUND

Vitamin D is a steroid hormone with pleiotropic effects including immune system modulation, lung tissue remodeling, and bone health. Vitamin D deficiency has been implicated in the development of autoimmune diseases. We sought to evaluate the prevalence of vitamin D deficiency in a cohort of patients with interstitial lung disease (ILD) and hypothesized that vitamin D deficiency would be associated with an underlying connective tissue disease (CTD) and reduced lung function.

METHODS

Patients in the University of Cincinnati ILD Center database were evaluated for serum 25-hydroxyvitamin D levels as part of a standardized protocol. Regression analysis evaluated associations between 25-hydroxyvitamin D levels and other variables.

RESULTS

One hundred eighteen subjects were included (67 with CTD-ILD, 51 with other forms of ILD). The overall prevalence of vitamin D deficiency and insufficiency in the study population was 38% and 59%, respectively. Those with CTD-ILD were more likely to have vitamin D deficiency (52% vs 20%, P < .0001) and insufficiency (79% vs 31%, P < .0001) than other forms of ILD. Diminished FVC was associated with lower 25-hydroxyvitamin D(3) levels (P = .01). The association between vitamin D insufficiency and CTD-ILD persisted (OR, 11.8; P < .0001) after adjustment for potential confounders. Among subjects with CTD-ILD, reduced 25-hydroxyvitamin D(3) levels were strongly associated with reduced lung function (FVC, P = .015; diffusing capacity for carbon monoxide, P = .004).

CONCLUSIONS

There is a high prevalence of vitamin D deficiency in patients with ILD, particularly those with CTD-ILD, and it is associated with reduced lung function. Vitamin D may have a role in the pathogenesis of CTD-ILD.