Metabolomics of airways disease in cystic fibrosis

Sodium-Coupled Monocarboxylate Absorption in the Airway Epithelium Is Facilitated by the SLC5A8 Co-Transporter

AIM

Amino acids, sugars, short-chain fatty acids (SCFA), vitamins, and other small molecules compose the extracellular metabolome on the airway lumen surface, but how the airway epithelium deals with these molecules has not been deeply studied. Due to the broad spectrum of metabolites transported by SLC5A8 and SLC5A12, we aim to determine if they are functionally expressed and participate in the absorption of Na+, short-chain fatty acids, and monocarboxylates in mouse and human airway epithelium.

METHODS

Tracheas isolated from male or female mice and human bronchial epithelial cells (HBECs) were used for electrophysiological studies in the Ussing chamber and to detect members of the SLC16 family by RT-PCR and bulk RNAseq. Additionally, cell lines expressing the human and murine SLC5A8 transporter were employed for uptake studies using a fluorescent lactate probe.

RESULTS

We showed for the first time that human and murine airway epithelium express a functional SLC5A8 transporter, facilitating the absorption of glucose metabolites and SCFAs. The Na+-coupled monocarboxylate transport was not additive with ENaC-mediated Na+ absorption in mouse trachea. We observed that valproate acts as an inhibitor of the murine but not of the human SLC5A8 transporter.

CONCLUSIONS

Our results demonstrate that several metabolites derived from bacterial and cellular metabolism can be transported from the airway lumen into the epithelial cells, participating in a homeostatic relation of the tissue with its environment.

The impact of cystic fibrosis transmembrane conductance regulator (CFTR) modulators on the pulmonary microbiota

Cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy has significantly changed the course of the disease in people with cystic fibrosis (CF) (pwCF). The approved triple therapy of elexacaftor, tezacaftor and ivacaftor (ETI), commercially known as Trikafta, increases CFTR channel function, leading to improvements in sweat chloride concentration, exercise capacity, body mass index, lung function and chronic respiratory symptoms. Because of this, the majority of pwCF are living longer and having fewer CF exacerbations. However, colonization with the common CF respiratory pathogens persists and remains a major cause of morbidity and mortality. Here, we review the current literature on the effect of ETI on the respiratory microbiota and discuss the challenges in addressing CF lung infections in the era of these new life-extending therapies.

Nutrient conditions affect antimicrobial pharmacodynamics in Pseudomonas aeruginosa

The infectious microenvironment in chronic respiratory tract infections is characterized by substantial variability in nutrient conditions, which may impact colonization and treatment response of pathogens. Metabolic adaptation of the cystic fibrosis (CF)-associated pathogen Pseudomonas aeruginosa has been shown to lead to changes in antibiotic sensitivity. The impact of specific nutrients on the response to antibiotics is, however, poorly characterized. Here, we investigated how different carbon sources impact the antimicrobial pharmacodynamic responses in P. aeruginosa. We evaluated the effect of six antibiotics (aztreonam, ceftazidime, ciprofloxacin, colistin, imipenem, and tobramycin) on P. aeruginosa cultured in a basal medium enriched for seven different carbon sources (alanine, arginine, aspartate, glucose, glutamate, lactate, and proline). Pharmacodynamic responses were characterized by measuring time-kill profiles for a bioluminescent P. aeruginosa PAO1 Xen41 strain. We show that single-nutrient modifications minimally affected bacterial growth rate. For specific nutrient-antibiotic combinations, we find relevant alterations in antibiotic sensitivity (i.e., EC50) and the maximum drug effect (Emax), in particular for ciprofloxacin, colistin, imipenem, and tobramycin. The most pronounced effect was observed for tobramycin, where glucose was found to reduce the EC50 (0.5-fold), whereas lactate-enriched conditions led to a 4.3-fold increase in EC50. Using pharmacokinetic-pharmacodynamic simulations, we illustrate that the magnitude of the nutrient-driven pharmacodynamic changes impact treatment for clinical dosing strategies of tobramycin. In summary, this study underscores the impact of nutrient composition on antimicrobial pharmacodynamics, which could potentially contribute to observed variability of antimicrobial treatment responses in CF patients.IMPORTANCEChronic respiratory tract infections in cystic fibrosis patients present significant challenges for antibiotic treatment due to the complexity of the respiratory environment. This study investigated how variations in nutrient levels, altered during chronic infections, affect pathogen response to antibiotics in an experimental setting. By simulating different nutrient conditions, we aimed to uncover interactions between nutrient availability and antibiotic sensitivity. Our findings provide critical insights that could lead to more effective treatment strategies for managing chronic respiratory tract infections in cystic fibrosis patients while also guiding future research in improving treatment methodologies.

Metabolomic profiling of saliva from cystic fibrosis patients

The development of targeted therapies that correct the effect of mutations in patients with cystic fibrosis (CF) and the relevant heterogeneity of the clinical expression of the disease require biomarkers correlated to the severity of the disease useful for monitoring the therapeutic effects. We applied a targeted metabolomic approach by LC-MS/MS on saliva samples from 70 adult CF patients and 63 age/sex-matched controls to investigate alterations in metabolic pathways related to pancreatic insufficiency (PI), Pseudomonas aeruginosa (PA) colonization, CF liver disease (CFLD), and CF related diabetes (CFRD). Sixty salivary metabolites were differentially expressed, with 11 being less abundant and 49 more abundant in CF patients. Among these, the most relevant alterations involved salivary ADMA, N-acetylornithine, methionine and methionine sulfoxide levels. Furthermore, methionine was significantly lower in CF patients with PI and salivary histamine levels were significantly lower in patients colonized by PA. Moreover, ADMA as well as N-acetylornithine and methionine were significantly lower in CF patients with CFRD than in patients without CFRD. Finally, the levels of DOPA resulted significantly lower in saliva from patients with liver disease. Our study revealed an imbalance in arginine methylation and tryptophan pathway related to CFRD and PI as well as alterations in dopaminergic pathway and Krebs cycle related to CFLD. This study also highlights different salivary metabolites as new potential biomarkers in a non-invasive sample that could represent a useful tool for the stratification and management of CF patients.

Redox remodeling of central metabolism as a driving force for cellular protection, proliferation, differentiation, and dysfunction

The production of reactive oxygen species (ROS) is elevated via metabolic hyperactivation in response to a variety of stimuli such as growth factors and inflammation. Tolerable amounts of ROS moderately inactivate enzymes via oxidative modification, which can be reversed back to the native form in a redox-dependent manner. The excessive production of ROS, however, causes cell dysfunction and death. Redox-reactive enzymes are present in primary metabolic pathways such as glycolysis and the tricarboxylic acid cycle, and these act as floodgates for carbon flux. Oxidation of a specific form of cysteine inhibits glyceraldehyde-3-phosphate dehydrogenase, which is reversible, and causes an accumulation of upstream intermediary compounds that increases the flux of glucose-6-phosphate to the pentose phosphate pathway. These reactions increase the NADPH and ribose-5-phosphate that are available for reductive reactions and nucleotide synthesis, respectively. On the other hand, oxidative inactivation of mitochondrial aconitase increases citrate, which is then recruited to synthesize fatty acids in the cytoplasm. Decreases in the use of carbohydrate for ATP production can be compensated via amino acid catabolism, and this metabolic change makes nitrogen available for nucleic acid synthesis. Coupling of the urea cycle also converts nitrogen to urea and polyamine, the latter of which supports cell growth. This metabolic remodeling stimulates the proliferation of tumor cells and fibrosis in oxidatively damaged tissues. Oxidative modification of these enzymes is generally reversible in the early stages of oxidizing reactions, which suggests that early treatment with appropriate antioxidants promotes the maintenance of natural metabolism.

Substrate-dependent metabolomic signatures of myeloperoxidase activity in airway epithelial cells: Implications for early cystic fibrosis lung disease

Myeloperoxidase (MPO) is released by neutrophils in inflamed tissues. MPO oxidizes chloride, bromide, and thiocyanate to produce hypochlorous acid (HOCl), hypobromous acid (HOBr), and hypothiocyanous acid (HOSCN), respectively. These oxidants are toxic to pathogens, but may also react with host cells to elicit biological activity and potential toxicity. In cystic fibrosis (CF) and related diseases, increased neutrophil inflammation leads to increased airway MPO and airway epithelial cell (AEC) exposure to its oxidants. In this study, we investigated how equal dose-rate exposures of MPO-derived oxidants differentially impact the metabolome of human AECs (BEAS-2B cells). We utilized enzymatic oxidant production with rate-limiting glucose oxidase (GOX) coupled to MPO, and chloride, bromide (Br-), or thiocyanate (SCN-) as substrates. AECs exposed to GOX/MPO/SCN- (favoring HOSCN) were viable after 24 h, while exposure to GOX/MPO (favoring HOCl) or GOX/MPO/Br- (favoring HOBr) developed cytotoxicity after 6 h. Cell glutathione and peroxiredoxin-3 oxidation were insufficient to explain these differences. However, untargeted metabolomics revealed GOX/MPO and GOX/MPO/Br- diverged significantly from GOX/MPO/SCN- for dozens of metabolites. We noted methionine sulfoxide and dehydromethionine were significantly increased in GOX/MPO- or GOX/MPO/Br--treated cells, and analyzed them as potential biomarkers of lung damage in bronchoalveolar lavage fluid from 5-year-olds with CF (n = 27). Both metabolites were associated with increasing bronchiectasis, neutrophils, and MPO activity. This suggests MPO production of HOCl and/or HOBr may contribute to inflammatory lung damage in early CF. In summary, our in vitro model enabled unbiased identification of exposure-specific metabolite products which may serve as biomarkers of lung damage in vivo. Continued research with this exposure model may yield additional oxidant-specific biomarkers and reveal explicit mechanisms of oxidant byproduct formation and cellular redox signaling.