Protein S-palmitoylation enhances profibrotic signaling in response to cadmium.

Cadmium (Cd) is a naturally occurring, toxic environmental metal found in foods. Humans do not have an efficient mechanism for Cd elimination; thus, Cd burden in humans increases with age. Cell and mouse studies show that Cd burden from low environmental levels of exposure impacts lung cell metabolism, proliferation signaling and cell growth as part of disease-promoting profibrotic responses in the lungs. Prior integrative analysis of metabolomics and transcriptomics identified the zDHHC11 transcript as a central functional hub in response to Cd dose. zDHHC11 encodes a protein S-palmitoyltransferase, but no evidence is available for effects of Cd on protein S-palmitoylation. In the present research, we studied palmitoylation changes in response to Cd and found increased protein S-palmitoylation in human lung fibroblasts that was inhibited by 2-bromopalmitate (2-BP), an irreversible palmitoyltransferase inhibitor. Mass spectrometry-based proteomics showed palmitoylation of proteins involved in divalent metal transport and in fibrotic signaling. Mechanistic studies showed that 2-BP inhibited palmitoylation of divalent metal ion transporter ZIP14 and also inhibited cellular Cd uptake. Transcription analyses showed that Cd stimulated transforming growth factor (TGF)-ß1 and ß3 expression within 8 h and lung fibrotic markers α-smooth muscle actin, matrix metalloproteinase-2, and collagen 1α1 gene expression and that these effects were blocked by 2-BP. Because 2-BP also blocked palmitoylation of proteins controlled by TGFß1, these results show that palmitoylation impacts Cd-dependent fibrotic signaling both by enhancing cellular Cd accumulation and by supporting post-translational processing of TGFß1-dependent proteins.

Low-dose vanadium pentoxide perturbed lung metabolism associated with inflammation and fibrosis signaling in male animal and in vitro models.

Vanadium is available as a dietary supplement and also is known to be toxic if inhaled, yet little information is available concerning the effects of vanadium on mammalian metabolism when concentrations found in food and water. Vanadium pentoxide (V+5) is representative of the most common dietary and environmental exposures, and prior research shows that low-dose V+5 exposure causes oxidative stress measured by glutathione oxidation and protein S-glutathionylation. We examined the metabolic impact of V+5 at relevant dietary and environmental doses (0.01, 0.1, and 1 ppm for 24 h) in human lung fibroblasts (HLFs) and male C57BL/6J mice (0.02, 0.2, and 2 ppm in drinking water for 7 mo). Untargeted metabolomics using liquid chromatography-high-resolution mass spectrometry (LC-HRMS) showed that V+5 induced significant metabolic perturbations in both HLF cells and mouse lungs. We noted 30% of the significantly altered pathways in HLF cells, including pyrimidines and aminosugars, fatty acids, mitochondrial and redox pathways, showed similar dose-dependent patterns in mouse lung tissues. Alterations in lipid metabolism included leukotrienes and prostaglandins involved in inflammatory signaling, which have been associated with the pathogenesis of idiopathic pulmonary fibrosis (IPF) and other disease processes. Elevated hydroxyproline levels and excessive collagen deposition were also present in lungs from V+5-treated mice. Taken together, these results show that oxidative stress from environmental V+5, ingested at low levels, could alter metabolism to contribute to common human lung diseases.NEW & NOTEWORTHY We used relevant dietary and environmental doses of Vanadium pentoxide (V+5) to examine its metabolic impact in vitro and in vivo. Using liquid chromatography-high-resolution mass spectrometry (LC-HRMS), we found significant metabolic perturbations, with similar dose-dependent patterns observed in human lung fibroblasts and male mouse lungs. Alterations in lipid metabolism included inflammatory signaling, elevated hydroxyproline levels, and excessive collagen deposition were present in V+5-treated lungs. Our findings suggest that low levels of V+5 could trigger pulmonary fibrotic signaling.

Metabolomics of V2O5 nanoparticles and V2O5 nanofibers in human airway epithelial BEAS-2B cells.

Vanadium is a toxic metal listed by the IARC as possibly carcinogenic to humans. Manufactured nanosize vanadium pentoxide (V2O5) materials are used in a wide range of industrial sectors and recently have been developed as nanomedicine for cancer therapeutics, yet limited information is available to evaluate relevant nanotoxicity. In this study we used high-resolution metabolomics to assess effects of two V2O5 nanomaterials, nanoparticles and nanofibers, at exposure levels (0.01, 0.1, and 1 ppm) that did not cause cell death (i.e., non-cytotoxic) in a human airway epithelial cell line, BEAS-2B. As prepared, V2O5 nanofiber exhibited a fibrous morphology, with a width approximately 63 ± 12 nm and length in average 420 ± 70 nm; whereas, V2O5 nanoparticles showed a typical particle morphology with a size 36 ± 2 nm. Both V2O5 nanoparticles and nanofibers had dose-response effects on aminosugar, amino acid, fatty acid, carnitine, niacin and nucleotide metabolism. Differential effects of the particles and fibers included dibasic acid, glycosphingolipid and glycerophospholipid pathway associations with V2O5 nanoparticles, and cholesterol and sialic acid metabolism associations with V2O5 nanofibers. Examination by transmission electron microscopy provided evidence for mitochondrial stress and increased lysosome fusion by both nanomaterials, and these data were supported by effects on mitochondrial membrane potential and lysosomal activity. The results showed that non-cytotoxic exposures to V2O5 nanomaterials impact major metabolic pathways previously associated with human lung diseases and suggest that toxico-metabolomics may be useful to evaluate health risks from V2O5 nanomaterials.

A pilot metabolomics study across the continuum of interstitial lung disease fibrosis severity.

Interstitial lung diseases (ILDs) include a variety of inflammatory and fibrotic pulmonary conditions. This study employs high-resolution metabolomics (HRM) to explore plasma metabolites and pathways across ILD phenotypes, including non-fibrotic ILD, idiopathic pulmonary fibrosis (IPF), and non-IPF fibrotic ILD. The study used 80 plasma samples for HRM, and involved linear trend and group-wise analyses of metabolites altered in ILD phenotypes. We utilized limma one-way ANOVA and mummichog algorithms to identify differences in metabolites and pathways across ILD groups. Then, we focused on metabolites within critical pathways, indicated by high pathway overlap sizes and low p-values, for further analysis. Targeted HRM identified putrescine, hydroxyproline, prolyl-hydroxyproline, aspartate, and glutamate with significant linear increases in more fibrotic ILD phenotypes, suggesting their role in ILD fibrogenesis. Untargeted HRM highlighted pathway alterations in lysine, vitamin D3, tyrosine, and urea cycle metabolism, all associated with pulmonary fibrosis. In addition, methylparaben level had a significantly increasing linear trend and was higher in the IPF than fibrotic and non-ILD groups. This study highlights the importance of specific amino acids, metabolic pathways, and xenobiotics in the progression of pulmonary fibrosis.

Validation of a screening panel for pediatric metabolic dysfunction-associated steatotic liver disease using metabolomics.

BACKGROUND: Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as NAFLD, is the most common liver disease in children. Liver biopsy remains the gold standard for diagnosis, although more efficient screening methods are needed. We previously developed a novel NAFLD screening panel in youth using machine learning applied to high-resolution metabolomics and clinical phenotype data. Our objective was to validate this panel in a separate cohort, which consisted of a combined cross-sectional sample of 161 children with stored frozen samples (75% male, 12.8±2.6 years of age, body mass index 31.0±7.0 kg/m2, 81% with MASLD, 58% Hispanic race/ethnicity). METHODS: Clinical data were collected from all children, and high-resolution metabolomics was performed using their fasting serum samples. MASLD was assessed by MRI-proton density fat fraction or liver biopsy and cardiometabolic factors. Our previously developed panel included waist circumference, triglycerides, whole-body insulin sensitivity index, 3 amino acids, 2 phospholipids, dihydrothymine, and 2 unknowns. To improve feasibility, a simplified version without the unknowns was utilized in the present study. Since the panel was modified, the data were split into training (67%) and test (33%) sets to assess the validity of the panel. RESULTS: Our present highest-performing modified model, with 4 clinical variables and 8 metabolomics features, achieved an AUROC of 0.92, 95% sensitivity, and 80% specificity for detecting MASLD in the test set. CONCLUSIONS: Therefore, this panel has promising potential for use as a screening tool for MASLD in youth.

Metabolic alterations and mitochondrial dysfunction in human airway BEAS-2B cells exposed to vanadium pentoxide.

Vanadium pentoxide (V+5) is a hazardous material that has drawn considerable attention due to its wide use in industrial sectors and increased release into environment from human activities. It poses potential adverse effects on animals and human health, with pronounced impact on lung physiology and functions. In this study, we investigated the metabolic response of human bronchial epithelial BEAS-2B cells to low-level V+5 exposure (0.01, 0.1, and 1 ppm) using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Exposure to V+5 caused extensive changes to cellular metabolism in BEAS-2B cells, including TCA cycle, glycolysis, fatty acids, amino acids, amino sugars, nucleotide sugar, sialic acid, vitamin D3, and drug metabolism, without causing cell death. Altered mitochondrial structure and function were observed with as low as 0.01 ppm (0.2 µM) V+5 exposure. In addition, decreased level of E-cadherin, the prototypical epithelial marker of epithelial-mesenchymal transition (EMT), was observed following V+5 treatment, supporting potential toxicity of V+5 at low levels. Taken together, the present study shows that V+5 has adverse effects on mitochondria and the metabolome which may result in EMT activation in the absence of cell death. Furthermore, results suggest that high-resolution metabolomics could serve as a powerful tool to investigate metal toxicity at levels which do not cause cell death.

Lipidome Changes Associated with a Diet-Induced Reduction in Hepatic Fat among Adolescent Boys with Metabolic Dysfunction-Associated Steatotic Liver Disease.

Little is known about lipid changes that occur in the setting of metabolic-dysfunction-associated steatotic liver disease (MASLD) regression. We previously reported improvements in hepatic steatosis, de novo lipogenesis (DNL), and metabolomic profiles associated with oxidative stress, inflammation, and selected lipid metabolism in 40 adolescent boys (11-16 y) with hepatic steatosis ≥5% (98% meeting the definition of MASLD). Participants were randomized to a low-free-sugar diet (LFSD) (n = 20) or usual diet (n = 20) for 8 weeks. Here, we employed untargeted/targeted lipidomics to examine lipid adaptations associated with the LFSD and improvement of hepatic steatosis. Our LC-MS/MS analysis revealed decreased triglycerides (TGs), diacylglycerols (DGs), cholesteryl esters (ChE), lysophosphatidylcholine (LPC), and phosphatidylcholine (PC) species with the diet intervention (p < 0.05). Network analysis demonstrated significantly lower levels of palmitate-enriched TG species post-intervention, mirroring the previously shown reduction in DNL in response to the LFSD. Targeted oxylipins analysis revealed a decrease in the abundance of 8-isoprostane and 14,15-DiHET and an increase in 8,9-DiHET (p < 0.05). Overall, we observed reductions in TGs, DGs, ChE, PC, and LPC species among participants in the LFSD group. These same lipids have been associated with MASLD progression; therefore, our findings may indicate normalization of key biological processes, including lipid metabolism, insulin resistance, and lipotoxicity. Additionally, our targeted oxylipins assay revealed novel changes in eicosanoids, suggesting improvements in oxidative stress. Future studies are needed to elucidate the mechanisms of these findings and prospects of these lipids as biomarkers of MASLD regression.

Discovery of phytochelatins in human urine: Evidence for function in selenium disposition and protection against cadmium.

This report identifies, for the first time, a phytochelatin compound, phytochelatin 2 [γ-E-C-γ-E-C-G], and related metabolites in human urine. Phytochelatins are metal-binding peptides produced by plants. They are present in nearly all human diets, due to their ubiquity in plants. The urinary concentration of phytochelatin 2 among 143 adults was in the low micromolar range, and phytochelatin 2 and its metabolites had differential correlations with urinary selenium and toxic metals. Activities of ingested phytochelatins are largely undescribed. Observed urinary metal interactions were investigated further in cell and animal models. Selenite reacted with phytochelatin to form a phytochelatin selenotrisulfide, and the preformed selenotrisulfide showed increased selenium uptake by renal proximal tubule cells. In vivo studies further showed that oral phytochelatin increased renal selenium content and decreased lung cadmium in mice. Presence of phytochelatin in human urine combined with its function in selenium and heavy metal distribution present a new route by which diet may influence metal disposition and bioavailability.

Third Trimester Serum Amino Acid Metabolism is Associated with Maternal Breast Cancer Diagnosed within 15 years of Pregnancy.

A prospective metabolome-wide association study revealed widespread amino acid limitation in late pregnancy is associated with early onset breast cancer. Archival third trimester pregnancy serum samples from 172 women who subsequently were diagnosed with breast cancer within 38 years after pregnancy were compared to 351 women without breast cancer. No individual metabolite differed after false discovery rate adjustment, indicating that individual metabolites are unlikely to be useful for classification or prediction. Despite this, pathway enrichment analysis showed that amino acid pathways, including lysine, arginine, proline, aspartate, asparagine, alanine, tyrosine, tryptophan, histidine, branched-chain amino acid and urea cycle, were enriched among metabolites that differed at raw p < 0.05. Several of these pathways previously were linked to breast carcinogen exposures, including dichlorodiphenyltrichloroethane and perfluorinated alkyl substances. Network analyses showed that amino acids correlated with parity and the ratio of estriol to estrone and estradiol known risk factors for breast cancer in this cohort. Overall, amino acid associations were stronger for early onset breast cancer, defined here as occurring within the first 15 years following pregnancy. Although results must be interpreted cautiously, lower amino acid concentrations for histidine, threonine and proline, and stronger associations for tryptophan, histidine, and lysine pathways with breast cancer within 15 years, suggests that amino acid limitations during late pregnancy contribute to metabolic reprogramming that is causally related to early onset breast cancer. Environmental chemical effects on nutrient sensing could account for these effects through known oncogenic mechanisms linked to nutrient stress.

Study on the relationship between selenium and cadmium in diseased human lungs.

Cadmium (Cd) is a toxic environmental metal that interacts with selenium (Se) and contributes to many lung diseases. Humans have widespread exposures to Cd through diet and cigarette smoking, and studies in rodent models show that Se can protect against Cd toxicities. We sought to identify whether an antagonistic relationship existed between Se and Cd burdens and determine whether this relationship may associate with metabolic variation within human lungs. We performed metabolomics of 31 human lungs, including 25 with end-stage lung disease due to idiopathic pulmonary fibrosis, cystic fibrosis, chronic obstructive lung disease (COPD)/emphysema and other causes, and 6 non-diseased lungs. Results showed pathway associations with Cd including amino acid, lipid and energy-related pathways. Metabolic pathways varying with Se had considerable overlap with these pathways. Hierarchical cluster analysis (HCA) of individuals according to metabolites associated with Cd showed partial separation of disease types, with COPD/emphysema in the cluster with highest Cd, and non-diseased lungs in the cluster with the lowest Cd. When compared to HCA of metabolites associated with Se, the results showed that the cluster containing COPD/emphysema had the lowest Se, and the non-diseased lungs had the highest Se. A greater number of pathway associations occurred for Cd to Se ratio than either Cd or Se alone, indicating that metabolic patterns were more dependent on Cd to Se ratio than on either alone. Network analysis of interactions of Cd and Se showed network centrality was associated with pathways linked to polyunsaturated fatty acids involved in inflammatory signaling. Overall, the data show that metabolic pathway responses in human lung vary with Cd and Se in a pattern suggesting that Se is antagonistic to Cd toxicity in humans.

Metabolic reprograming and increased inflammation by cadmium exposure following early-life respiratory syncytial virus infection-the involvement of protein S-palmitoylation.

Early-life respiratory syncytial virus (RSV) infection (eRSV) is one of the leading causes of serious pulmonary disease in children. eRSV is associated with higher risk of developing asthma and compromised lung function later in life. Cadmium (Cd) is a toxic metal, widely present in the environment and in food. We recently showed that eRSV re-programs metabolism and potentiates Cd toxicity in the lung, and our transcriptome-metabolome-wide study showed strong associations between S-palmitoyl transferase expression and Cd-stimulated lung inflammation and fibrosis signaling. Limited information is available on the mechanism by which eRSV re-programs metabolism and potentiates Cd toxicity in the lung. In the current study, we used a mouse model to examine the role of protein S-palmitoylation (Pr-S-Pal) in low dose Cd-elevated lung metabolic disruption and inflammation following eRSV. Mice exposed to eRSV were later treated with Cd (3.3 mg CdCl2/L) in drinking water for 6 weeks (RSV+Cd). The role of Pr-S-Pal was studied using a palmitoyl transferase inhibitor, 2-bromopalmitate (BP, 10 µM). Inflammatory marker analysis showed that cytokines, chemokines and inflammatory cells were highest in the RSV+Cd group, and BP decreased inflammatory markers. Lung metabolomics analysis showed that pathways including phenylalanine, tyrosine and tryptophan, phosphatidylinositol and sphingolipid were altered across treatments. BP antagonized metabolic disruption of sphingolipid and glycosaminoglycan metabolism by RSV+Cd, consistent with BP effect on inflammatory markers. This study shows that Cd exposure following eRSV has a significant impact on subsequent inflammatory response and lung metabolism, which is mediated by Pr-S-Pal, and warrants future research for a therapeutic target.

Vanadium pentoxide induced oxidative stress and cellular senescence in human lung fibroblasts.

Both environmental exposure to vanadium pentoxide (V2O5, V+5 for its ionic counterparts) and fibroblast senescence are associated with pulmonary fibrosis, but whether V+5 causes fibroblast senescence remains unknown. We found in a dose-response study that 2-40 µM V+5 caused human lung fibroblasts (HLF) senescence with increased senescence-associated ß-galactosidase activity and p16 expression, while cell death occurred at higher concentration (LC50, 82 µM V+5). Notably, measures of reactive oxygen species (ROS) production with fluorescence probes showed no association of ROS with V+5-dependent senescence. Preloading catalase (polyethylene-conjugated), a H2O2 scavenger, did not alleviate the cellular senescence induced by V+5. Analyses of the cellular glutathione (GSH) system showed that V+5 oxidized GSH, increased GSH biosynthesis, stimulated cellular GSH efflux and increased protein S-glutathionylation, and addition of N-acetyl cysteine inhibited V+5-elevated p16 expression, suggesting that thiol oxidation mediates V+5-caused senescence. Moreover, strong correlations between GSSG/GSH redox potential (Eh), protein S-glutathionylation, and cellular senescence (R2 > 0.99, p < 0.05) were present in V+5-treated cells. Studies with cell-free and enzyme-free solutions showed that V+5 directly oxidized GSH with formation of V+4 and GSSG in the absence of O2. Analyses of V+5 and V+4 in HLF and culture media showed that V+5 was reduced to V+4 in cells and that a stable V+4/V+5 ratio was rapidly achieved in extracellular media, indicating ongoing release of V+4 and reoxidation to V+5. Together, the results show that V+5-dependent fibroblast senescence is associated with a cellular/extracellular redox cycling mechanism involving the GSH system and occurring under conditions that do not cause cell death. These results establish a mechanism by which environmental vanadium from food, dietary supplements or drinking water, can cause or contribute to lung fibrosis in the absence of high-level occupational exposures and cytotoxic cell death.

Low-Dose Cadmium Potentiates Metabolic Reprogramming Following Early-Life Respiratory Syncytial Virus Infection.

Respiratory syncytial virus (RSV) infection causes serious pulmonary disease and death in high-risk infants and elderly. Cadmium (Cd) is a toxic environmental metal contaminant and constantly exposed to humans. Limited information is available on Cd toxicity after early-life respiratory virus infection. In this study, we examined the effects of low-dose Cd exposure following early-life RSV infection on lung metabolism and inflammation using mouse and fibroblast culture models. C57BL/6J mice at 8 days old were exposed to RSV 2 times with a 4-week interval. A subset of RSV-infected mice was subsequently treated with Cd at a low dose in drinking water (RSV infection at infant age [RSVinf]+Cd) for 16 weeks. The results of inflammatory marker analysis showed that the levels of cytokines and chemokines were substantially higher in RSVinf+Cd group than other groups, implying that low-dose Cd following early-life RSV infection enhanced lung inflammation. Moreover, histopathology data showed that inflammatory cells and thickening of the alveolar walls as a profibrotic signature were evident in RSVinf+Cd. The metabolomics data revealed that RSVinf+Cd-caused metabolic disruption in histamine and histidine, vitamin D and urea cycle, and pyrimidine pathway accompanying with mechanistic target of rapamycin complex-1 activation. Taken together, our study demonstrates for the first time that cumulative Cd exposure following early-life RSV infection has a significant impact on subsequent inflammation and lung metabolism. Thus, early-life respiratory infection may reprogram metabolism and potentiate Cd toxicity, enhance inflammation, and cause fibrosis later in life.

Firsthand and Secondhand Exposure Levels of Maltol-Flavored Electronic Nicotine Delivery System Vapors Disrupt Amino Acid Metabolism.

Electronic nicotine delivery system (ENDS) use has become a popular, generally regarded as safe, alternative to tobacco use. The e-liquids used for ENDS vapor generation commonly contain flavoring agents, such as maltol, which have been subjected to little investigation of their effects on lung health from ENDS usage. In the present study, we examined the impacts of firsthand (3.9 mM) and secondhand (3.9 µM) exposure levels to maltol-flavored ENDS vapors on lung metabolism. Human lung bronchial epithelial cells were exposed to ENDS vapors using a robotic system for controlled generation and delivery of exposures, and the effects on metabolism were evaluated using high-resolution metabolomics. The results show that maltol in e-liquids impacts lung airway epithelial cell metabolism at both firsthand and secondhand exposure levels. The effects of maltol were most notably seen in amino acid metabolism while oxidative stress was observed with exposure to all ENDS vapors including e-liquids alone and maltol-contained e-liquids. Many effects of firsthand exposure were also observed with secondhand exposure, suggesting need for systematic investigation of both firsthand and secondhand effects of flavored ENDS vapors on lung metabolism and risk of lung disease.

Metabolome-wide association study of flavorant vanillin exposure in bronchial epithelial cells reveals disease-related perturbations in metabolism.

Electronic cigarettes (e-cig) are an increasingly popular alternative to traditional smoking but have been in use for too short of a period of time to fully understand health risks. Furthermore, associated health risks are difficult to evaluate because of a large range of flavoring agents and their combinations for use with e-cig. Many flavoring agents are generally regarded as safe but have limited studies for effects on lung. Vanillin, an aromatic aldehyde, is one of the most commonly used flavoring agents in e-cig. Vanillin is electrophilic and can be redox active, with chemical properties expected to interact within biologic systems. Because accumulating lung metabolomics studies have identified metabolic disruptions associated with idiopathic pulmonary fibrosis, asthma and acute respiratory distress syndrome, we used human bronchial epithelial cells (BEAS-2B) with high-resolution metabolomics analysis to determine whether these disease-associated pathways are impacted by vanillin over the range used in e-cig. A metabolome-wide association study showed that vanillin perturbed specific energy, amino acid, antioxidant and sphingolipid pathways previously associated with human disease. Analysis of a small publicly available human dataset showed associations with several of the same pathways. Because vanillin is a common and high-abundance flavorant in e-cig, these results show that vanillin has potential to be mechanistically important in lung diseases and warrants in vivo toxicity testing in the context of e-cig use.

Plasma acylcarnitine levels increase with healthy aging.

Acylcarnitines transport fatty acids into mitochondria and are essential for ß-oxidation and energy metabolism. Decreased mitochondrial activity results in increased plasma acylcarnitines, and increased acylcarnitines activate proinflammatory signaling and associate with age-related disease. Changes in acylcarnitines associated with healthy aging, however, are not well characterized. In the present study, we examined the associations of plasma acylcarnitines with age (range: 20-90) in 163 healthy, non-diseased individuals from the predictive medicine research cohort (NCT00336570) and tested for gender-specific differences. The results show that long-chain and very long-chain acylcarnitines increased with age, while many odd-chain acylcarnitines decreased with age. Gender-specific differences were observed for several acylcarnitines, e.g., eicosadienoylcarnitine varied with age in males, and hydroxystearoylcarnitine varied in females. Metabolome-wide association study (MWAS) of age-associated acylcarnitines with all untargeted metabolic features showed little overlap between genders. These results show that plasma concentrations of acylcarnitines vary with age and gender in individuals selected for criteria of health. Whether these variations reflect mitochondrial dysfunction with aging, mitochondrial reprogramming in response to chronic environmental exposures, early pre-disease change, or an adaptive response to healthy aging, is unclear. The results highlight a potential utility for untargeted metabolomics research to elucidate gender-specific mechanisms of aging and age-related disease.