Endogenous airway acidification. Implications for asthma pathophysiology

Acid-sensitive prodrugs; a promising approach for site-specific and targeted drug release

Drugs administered through conventional formulations are devoid of targeting and often spread to various undesired sites, leading to sub-lethal concentrations at the site of action and the emergence of undesired effects. Hence, therapeutic agents should be delivered in a controlled manner at target sites. Currently, stimuli-based drug delivery systems have demonstrated a remarkable potential for the site-specific delivery of therapeutic moieties. pH is one of the widely exploited stimuli for drug delivery as several pathogenic conditions such as tumor cells, infectious and inflammatory sites are characterized by a low pH environment. This review article aims to demonstrate various strategies employed in the design of acid-sensitive prodrugs, providing an overview of commercially available acid-sensitive prodrugs. Furthermore, we have compiled the progress made for the development of new acid-sensitive prodrugs currently undergoing clinical trials. These prodrugs include albumin-binding prodrugs (Aldoxorubicin and DK049), polymeric micelle (NC-6300), polymer conjugates (ProLindac™), and an immunoconjugate (IMMU-110). The article encompasses a broad spectrum of studies focused on the development of acid-sensitive prodrugs for anticancer, antibacterial, and anti-inflammatory agents. Finally, the challenges associated with the acid-sensitive prodrug strategy are discussed, along with future directions.

The Roles of Proton-Sensing G-Protein-Coupled Receptors in Inflammation and Cancer

The precise regulation of pH homeostasis is crucial for normal physiology. However, in tissue microenvironments, it can be impacted by pathological conditions such as inflammation and cancer. Due to the overproduction and accumulation of acids (protons), the extracellular pH is characteristically more acidic in inflamed tissues and tumors in comparison to normal tissues. A family of proton-sensing G-protein-coupled receptors (GPCRs) has been identified as molecular sensors for cells responding to acidic tissue microenvironments. Herein, we review the current research progress pertaining to these proton-sensing GPCRs, including GPR4, GPR65 (TDAG8), and GPR68 (OGR1), in inflammation and cancer. Growing evidence suggests that GPR4 and GPR68 are mainly pro-inflammatory, whereas GPR65 is primarily anti-inflammatory, in various inflammatory disorders. Both anti- and pro-tumorigenic effects have been reported for this family of receptors. Moreover, antagonists and agonists targeting proton-sensing GPCRs have been developed and evaluated in preclinical models. Further research is warranted to better understand the roles of these proton-sensing GPCRs in pathophysiology and is required in order to exploit them as potential therapeutic targets for disease treatment.

Breath and Sputum Analyses in Asthmatic Patients: An Overview

Recent advancements in asthma management include non-invasive methodologies such as sputum analysis, exhaled breath condensate (EBC), and fractional exhaled nitric oxide (FeNO). These techniques offer a means to assess airway inflammation, a critical feature of asthma, without invasive procedures. Sputum analysis provides detailed insights into airway inflammation patterns and cellular composition, guiding personalized treatment strategies. EBC collection, reflecting bronchoalveolar lining fluid composition, provides a non-invasive window into airway physiology. FeNO emerges as a pivotal biomarker, offering insights into eosinophilic airway inflammation and aiding in asthma diagnosis, treatment monitoring, and the prediction of exacerbation risks. Despite inherent limitations, each method offers valuable tools for a more comprehensive assessment of asthma. Combining these techniques with traditional methods like spirometry may lead to more personalized treatment plans and improved patient outcomes. Future research is crucial to refine protocols, validate biomarkers, and establish comprehensive guidelines in order to enhance asthma management with tailored therapeutic strategies and improved patient outcomes.

Fractional exhaled nitric oxide distribution and its relevant factors in the general adult population and its healthy subpopulation

Background

Measurement of fractional exhaled nitric oxide (Feno) has been used in the diagnosis and management of asthma. Understanding the distribution of Feno in a larger resident population and its "healthy" subpopulation would contribute to the interpretation of Feno in clinical practice.

Objective

This study aimed to investigate the distribution and its associated factors in the adult population and its healthy subpopulations.

Methods

We conducted a cross-sectional study of 8,638 men and 17,288 women aged 20 years or older living in Miyagi prefecture, Japan. We investigated the distribution of Feno and its associated factors in all subjects, a subpopulation with no history of upper and lower airway diseases (healthy subpopulation 1), and a subpopulation with no history of upper and lower airway diseases, normal lung function, and no positivity for other biomarkers of type 2 inflammation (healthy subpopulation 2).

Results

The distribution of Feno in healthy subpopulations, especially in healthy subpopulation 2 (median [interquartile range], 17 [12-23] with 95th percentile of 36 ppb) was lower than in all subjects (19 [13-26] ppb with 95th percentile of 47 ppb). In healthy subpopulation 1, 10.3% had elevated Feno (≥35 ppb), and elevated Feno was positively associated with factors including obstructive ventilatory defect, blood eosinophilia, house dust mite-specific IgE positivity, and history of hypertension. Male sex was associated with elevated Feno in all subjects and healthy subpopulations.

Conclusion

The distribution of Feno in the healthy subpopulation supports the validity of the criteria (≥35 ppb) currently used in Japan for the diagnosis of asthma.

The Role of Exhaled Breath Condensate in Chronic Inflammatory and Neoplastic Diseases of the Respiratory Tract

Asthma and chronic obstructive pulmonary disease (COPD) are among the most common chronic respiratory diseases. Chronic inflammation of the airways leads to an increased production of inflammatory markers by the effector cells of the respiratory tract and lung tissue. These biomarkers allow the assessment of physiological and pathological processes and responses to therapeutic interventions. Lung cancer, which is characterized by high mortality, is one of the most frequently diagnosed cancers worldwide. Current screening methods and tissue biopsies have limitations that highlight the need for rapid diagnosis, patient differentiation, and effective management and monitoring. One promising non-invasive diagnostic method for respiratory diseases is the assessment of exhaled breath condensate (EBC). EBC contains a mixture of volatile and non-volatile biomarkers such as cytokines, leukotrienes, oxidative stress markers, and molecular biomarkers, providing significant information about inflammatory and neoplastic states in the lungs. This article summarizes the research on the application and development of EBC assessment in diagnosing and monitoring respiratory diseases, focusing on asthma, COPD, and lung cancer. The process of collecting condensate, potential issues, and selected groups of markers for detailed disease assessment in the future are discussed. Further research may contribute to the development of more precise and personalized diagnostic and treatment methods.

Extracellular acidification attenuates bronchial contraction via an autocrine activation of EP2 receptor: Its diminishment in murine experimental asthma

PURPOSE

Extracellular acidification is a major component of tissue inflammation, including airway inflammation in asthmatics. However, its physiological/pathophysiological significance in bronchial function is not fully understood. Currently, the functional role of extracellular acidification on bronchial contraction was explored.

METHODS

Left main bronchi were isolated from male BALB/c mice. Epithelium-removed tissues were exposed to acidic pH under submaximal contraction induced by 10-5 M acetylcholine in the presence or absence of a COX inhibitor indomethacin (10-6 M). Effects of AH6809 (10-6 M, an EP2 receptor antagonist), BW A868C (10-7 M, a DP receptor antagonist) and CAY10441 (3×10-6 M, an IP receptor antagonist) on the acidification-induced change in tension were determined. The release of prostaglandin E2 (PGE2) from epithelium-denuded tissues in response to acidic pH was assessed using an ELISA.

RESULTS

In the bronchi stimulated with acetylcholine, change in the extracellular pH from 7.4 to 6.8 caused a transient augmentation of contraction followed by a sustained relaxing response. The latter inhibitory response was abolished by indomethacin and AH6809 but not by BW A868C or CAY10441. Both indomethacin and AH6809 significantly increased potency and efficacy of acetylcholine at pH 6.8. Stimulation with low pH caused an increase in PGE2 release from epithelium-denuded bronchi. Interestingly, the acidic pH-induced bronchial relaxation was significantly reduced in a murine asthma model that had a bronchial hyperresponsiveness to acetylcholine.

CONCLUSION

Taken together, extracellular acidification could inhibit the bronchial contraction via autocrine activation of EP2 receptors. The diminished acidic pH-mediated inhibition of bronchial tone may contribute to excessive bronchoconstriction in inflamed airways such as asthma.

Crosstalk with renal proximal tubule cells drives acidosis-induced inflammatory response and dedifferentiation of fibroblasts via p38-singaling

BACKGROUND

Tubulointerstitial kidney disease associated microenvironmental dysregulation, like acidification, inflammation and fibrosis, affects tubule cells and fibroblasts. Micromilieu homeostasis influences intracellular signaling and intercellular crosstalk. Cell-cell communication in turn modulates the interstitial microenvironment. We assessed the impact of acidosis on inflammatory and fibrotic responses in proximal tubule cells and fibroblasts as a function of cellular crosstalk. Furthermore, cellular signaling pathways involved were identified.

METHODS

HK-2 (human proximal tubule) and CCD-1092Sk (human fibroblasts), in mono and coculture, were exposed to acidic or control media for 3 or 48 h. Protein expression of inflammation markers (TNF, TGF-ß and COX-2), dedifferentiation markers (N-cadherin, vinculin, ß-catenin and vimentin), fibrosis markers (collagen III and fibronectin) and phospho- as well as total MAPK levels were determined by western blot. Secreted collagen III and fibronectin were measured by ELISA. The impact of MAPK activation was assessed by pharmacological intervention. In addition, necrosis, apoptosis and epithelial permeability were determined.

RESULTS

Independent of culture conditions, acidosis caused a decrease of COX-2, vimentin and fibronectin expression in proximal tubule cells. Only in monoculture, ß-Catenin expression decreased and collagen III expression increased in tubule cells during acidosis. By contrast, in coculture collagen III protein expression of tubule cells was reduced. In fibroblasts acidosis led to an increase of TNF, COX-2, vimentin, vinculin, N-cadherin protein expression and a decrease of TGF-ß expression exclusively in coculture. In monoculture, expression of COX-2 and fibronectin was reduced. Collagen III expression of fibroblasts was reduced by acidosis independent of culture conditions. In coculture, acidosis enhanced phosphorylation of ERK1/2, JNK1/2 and p38 transiently in proximal tubule cells. In fibroblasts, acidosis enhanced phosphorylation of p38 in a sustained and very strong manner. ERK1/2 and JNK1/2 were not affected in fibroblasts. Inhibition of JNK1/2 and p38 under coculture conditions reduced acidosis-induced changes in fibroblasts significantly.

CONCLUSIONS

Our data show that the crosstalk between proximal tubule cells and fibroblasts is crucial for acidosis-induced dedifferentiation of fibroblasts into an inflammatory phenotype. This dedifferentiation is at least in part mediated by p38 and JNK1/2. Thus, cell-cell communication is essential for the pathophysiological impact of tubulointerstitial acidosis.

pH-dependent modulation of TRPV1 by modality-selective antagonists

BACKGROUND AND PURPOSE

Antagonists of TRPV1 that inhibit all activation modes cause hyperthermia, hampering their medical use as novel analgesics. TRPV1 antagonists that do not (fully) inhibit responses to low pH do not cause hyperthermia, but it remains incompletely understood how such antagonists affect channel gating. We tested the hypothesis that pH-sparing antagonists act in a modality-selective manner on TRPV1, differentially affecting channel activation by protons and capsaicin.

EXPERIMENTAL APPROACH

Using whole-cell patch-clamp and calcium imaging to measure channel activity in cells expressing wild type human TRPV1 or the pH-insensitive mutant F660A. Responses to protons and capsaicin were measured at different pH values in the presence of antagonists that reportedly partially spare (A-1165442) or potentiate (AMG7905) acid-evoked channel activation.

KEY RESULTS

At pH 5.5, A-1165442 was equipotent at blocking acid- and capsaicin-evoked responses of wild type TRPV1. Its potency to inhibit acid-evoked responses was attenuated at pH ≤ 5.0. AMG7905, at a concentration (1 μM) that fully inhibits capsaicin-evoked responses, potentiated proton-evoked (pH 5.5) responses of wild type TRPV1. In the F660A mutant, the inhibitory efficacy of A-1165442 and AMG7905 towards capsaicin-evoked responses was reduced at lower pH values and AMG7905 acted as a partial agonist.

CONCLUSION AND IMPLICATIONS

Our findings show that A-1165442 and AMG7905 interact in a pH-dependent manner with TRPV1, but this pH dependence is not strictly modality-selective. Reduced TRPV1 antagonism at acidic pH may limit analgesic efficacy in injured tissue and needs to be considered in models explaining the effects of antagonists on core body temperature.

Hidden chronic metabolic acidosis of diabetes type 2 (CMAD): Clues, causes and consequences

Interpretation of existing data revealed that chronic metabolic acidosis is a pathognomic feature for type 2 diabetes (T2D), which is described here as "chronic metabolic acidosis of T2D (CMAD)" for the first time. The biochemical clues for the CMAD are summarised in the following; low blood bicarbonate (high anionic gap), low pH of interstitial fluid and urine, and response to acid neutralization, while the causes of extra protons are worked out to be; mitochondrial dysfunction, systemic inflammation, gut microbiota (GM), and diabetic lung. Although, the intracellular pH is largely preserved by the buffer system and ion transporters, a persistent systemic mild acidosis leaves molecular signature in cellular metabolism in diabetics. Reciprocally, there are evidences that CMAD contributes to the initiation and progression of T2D by; reducing insulin production, triggering insulin resistance directly or via altered GM, and inclined oxidative stress. The details about the above clues, causes and consequences of CMAD are obtained by searching literature spanning between 1955 and 2022. Finally, the molecular bases of CMAD are discussed in details by interpretation of an up-to-date data and aid of well constructed diagrams, with a conclusion unravelling that CMAD is a major player in T2D pathophysiology. To this end, the CMAD disclosure offers several therapeutic potentials for prevention, delay or attenuation of T2D and its complications.

Stability and structure-activity relationship of the SPA4 peptide under ambient and stressed conditions of lung injury

Lung inflammation and injuries are major health problems. The SPA4 peptide (amino acid sequence GDFRYSDGTPVNYTNWYRGE) binds to Toll-like receptor-4 and exerts anti-inflammatory activity. In this study, we have determined the stability of the structure and structure-activity relationship of the SPA4 peptide under ambient and stressed conditions of lung injury. The SPA4 peptide was maintained at different pH and temperatures, in solutions of different ionic strengths, and simulated lung fluids. The primary and secondary structure of the SPA4 peptide was determined by ultraviolet-visible (UV-VIS) and circular dichroism (CD) spectroscopy. The activity of the SPA4 peptide was determined by measurement of secreted levels of chemokine C-X-C motif ligand 1/keratinocyte-derived chemokine (CXCL1/KC) and lactate by primary mouse lung epithelial cells against lipopolysaccharide (LPS) stimuli. Our results demonstrate the stability of the structure of the SPA4 peptide at room temperature and 4 °C over 10 days. The original UV-VIS spectra of the SPA4 peptide followed a typical pattern when incubated in solutions of pH 5.7, 7.0, and 8.0 at different temperatures, simulated lung fluids, and most of the chemical components. Slight shifts in the absorbance peaks, derivative values, and vibrational fine structures were noted in the fourth-derivative spectra of the SPA4 peptide under some conditions. An increased level of lactate is the hallmark of lung injury. The SPA4 peptide on its own and in the presence of lactate exerts anti-inflammatory activity. The primary and secondary structure and the activity of the SPA4 peptide remain intact when pre-incubated in 2 mM sodium lactate solution. The results provide important insights about the stability and structure-activity relationship of the SPA4 peptide.

Differences in airborne stability of SARS-CoV-2 variants of concern is impacted by alkalinity of surrogates of respiratory aerosol

The mechanistic factors hypothesized to be key drivers for the loss of infectivity of viruses in the aerosol phase often remain speculative. Using a next-generation bioaerosol technology, we report measurements of the aero-stability of several SARS-CoV-2 variants of concern in aerosol droplets of well-defined size and composition at high (90%) and low (40%) relative humidity (RH) upwards of 40 min. When compared with the ancestral virus, the infectivity of the Delta variant displayed different decay profiles. At low RH, a loss of viral infectivity of approximately 55% was observed over the initial 5 s for both variants. Regardless of RH and variant, greater than 95% of the viral infectivity was lost after 40 min of being aerosolized. Aero-stability of the variants correlate with their sensitivities to alkaline pH. Removal of all acidic vapours dramatically increased the rate of infectivity decay, with 90% loss after 2 min, while the addition of nitric acid vapour improved aero-stability. Similar aero-stability in droplets of artificial saliva and growth medium was observed. A model to predict loss of viral infectivity is proposed: at high RH, the high pH of exhaled aerosol drives viral infectivity loss; at low RH, high salt content limits the loss of viral infectivity.

Mucus Penetration of Surface-Engineered Nanoparticles in Various pH Microenvironments

The penetration behavior of nanoparticles in mucous depends on physicochemical properties of the nanoparticles and the mucus microenvironment, due to particle-mucin interactions and the presence of the mucin mesh space filtration effect. To date, it is still unclear how the surface properties of nanoparticles influence their mucus penetration behaviors in various physiological and pathophysiological conditions. In this study, we have prepared a comprehensive library of amine-, carboxyl-, and PEG-modified silica nanoparticles (SNPs) with controlled surface ligand densities. Using multiple particle tracking, we have studied the mechanism responsible for the mucus penetration behaviors of these SNPs. It was found that PEG- and amine-modified SNPs exhibited pH-independent immobilization under iso-density conditions, while carboxyl-modified SNPs exhibited enhanced movement only in weakly alkaline mucus. Biophysical characterizations demonstrated that amine- and carboxyl-modified SNPs were trapped in mucus due to electrostatic interactions and hydrogen bonding with mucin. In contrast, high-density PEGylated surface formed a brush conformation that shields particle-mucin interactions. We have further investigated the surface property-dependent mucus penetration behavior using a murine airway distribution model. This study provides insights for designing efficient transmucosal nanocarriers for prevention and treatment of pulmonary diseases.

Infectious and Inflammatory Pathways to Cough

Coughing is a dynamic physiological process resulting from input of vagal sensory neurons innervating the airways and perceived airway irritation. Although cough serves to protect and clear the airways, it can also be exploited by respiratory pathogens to facilitate disease transmission. Microbial components or infection-induced inflammatory mediators can directly interact with sensory nerve receptors to induce a cough response. Analysis of cough-generated aerosols and transmission studies have further demonstrated how infectious disease is spread through coughing. This review summarizes the neurophysiology of cough, cough induction by respiratory pathogens and inflammation, and cough-mediated disease transmission.

Diet Quality and Exhaled Breath Condensate Markers in a Sample of School-Aged Children

Exhaled breath condensate (EBC) analysis is a recently developed, non-invasive method used to identify and quantify biomarkers, mainly those coming from the lower respiratory tract. It seems that diet can influence the airway's inflammation and change the exhaled breath composition. This study aimed to assess the association between diet quality intake and markers in EBC among school-aged children. A cross-sectional analysis included 150 children (48.3% females, aged 7-12 years, mean age: 8.7 ± 0.8 years) from 20 schools across Porto, Portugal. We assessed diet quality through the Healthy Eating Index (HEI)-2015, which was estimated based on a single 24 h food recall questionnaire. EBC samples were collected, and we assessed their ionic content (Na⁺, K⁺) and conductivity. The association between diet quality and Na⁺, K⁺, Na⁺/K⁺ ratio and conductivity was estimated using logistic regression models adjusted for potential confounders. After adjustment, a higher quality diet score increases the odds of higher conductivity values of the EBC (aOR = 1.04, 95%CI 1.00; 1.08). Our findings suggest that a higher diet quality in school-aged children is associated with higher conductivity levels of the EBC.

Mendelian Randomization Analysis Reveals a Complex Genetic Interplay among Atopic Dermatitis, Asthma, and Gastroesophageal Reflux Disease

Rationale: Gastroesophageal reflux disease (GERD) is commonly associated with atopic disorders, but cause-effect relationships remain unclear. Objectives: We applied Mendelian randomization analysis to explore whether GERD is causally related to atopic disorders of the lung (asthma) and/or skin (atopic dermatitis [AD]). Methods: We conducted two-sample bidirectional Mendelian randomization to infer the magnitude and direction of causality between asthma and GERD, using summary statistics from the largest genome-wide association studies conducted on asthma (Ncases = 56,167) and GERD (Ncases = 71,522). In addition, we generated instrumental variables for AD from the latest population-level genome-wide association study meta-analysis (Ncases = 22,474) and assessed their fidelity and confidence of predicting the likely causal pathway(s) leading to asthma and/or GERD. Measurements and Main Results: Applying three different methods, each method revealed similar magnitude of causal estimates that were directionally consistent across the sensitivity analyses. Using an inverse variance-weighted method, the largest effect size was detected for asthma predisposition to AD (odds ratio [OR], 1.46; 95% confidence interval [CI], 1.34-1.59), followed by AD to asthma (OR, 1.34; 95% CI, 1.24-1.45). A significant association was detected for genetically determined asthma on risk of GERD (OR, 1.06; 95% CI, 1.03-1.09) but not genetically determined AD on GERD. In contrast, GERD equally increased risks of asthma (OR, 1.21; 95% CI, 1.09-1.35) and AD (OR, 1.21; 95% CI, 1.07-1.37). Conclusions: This study uncovers previously unrecognized causal pathways that have clinical implications in European-ancestry populations: 1) asthma is a causal risk for AD, and 2) the predisposition to AD, including asthma, can arise from specific pathogenic mechanisms manifested by GERD.

Antifungal and Anti-Inflammatory Activities of PS1-2 Peptide against Fluconazole-Resistant Candida albicans

Clinically, fungal pneumonia rarely occurs in adults, and invasive fungal infections can cause substantial morbidity, and mortality due to sepsis and septic shock. In the present study, we have designed peptides that exhibit potent antifungal activities against fluconazole-resistant Candida albicans in physiological monovalent, and divalent ionic buffers, with minimal fungicidal concentrations ranging from 16 to 32 µM. None of these tested peptides resulted in the development of drug resistance similar to fluconazole. Among them, the PS1-2 peptide did not induce stimulation of macrophages by C. albicans, and it exerted antifungal and anti-inflammatory effects against C. albicans-induced intratracheal infection, in an acute lung injury mouse model. PS1-2 is likely a novel therapeutic agent for the control, and prevention of drug-resistant C. albicans infection, and our findings may be useful for designing antimicrobial peptides to combat fungal infection.

Contact-dependent, polarized acidification response during neutrophil-epithelial interactions

Neutrophil (PMN) infiltration during active inflammation imprints changes in the local tissue environment. Such responses are often accompanied by significant extracellular acidosis that result in predictable transcriptional responses. In this study, we explore the mechanisms involved in inflammatory acidification as a result of PMN-intestinal epithelial cell (IEC) interactions. Using recently developed tools, we revealed that PMN transepithelial migration (TEM)-associated inflammatory acidosis is dependent on the total number of PMNs present during TEM and is polarized toward the apical surface. Extending these studies, we demonstrate that physical separation of the PMNs and IECs prevented acidification, whereas inhibition of PMN TEM using neutralizing antibodies enhanced extracellular acidification. Utilizing pharmaceutical inhibitors, we demonstrate that the acidification response is independent of myeloperoxidase and dependent on reactive oxygen species generated during PMN TEM. In conclusion, inflammatory acidosis represents a polarized PMN-IEC-dependent response by an as yet to be fully determined mechanism.

Hyperresponsiveness to Extracellular Acidification-Mediated Contraction in Isolated Bronchial Smooth Muscles of Murine Experimental Asthma

PURPOSE

Extracellular acidification is a major component of tissue inflammation, including airway inflammation. The extracellular proton-sensing mechanisms are inherent in various cells including airway structural cells, although their physiological and pathophysiological roles in bronchial smooth muscles (BSMs) are not fully understood. In the present study, to explore the functional role of extracellular acidification on the BSM contraction, the isolated mouse BSMs were exposed to acidic pH under contractile stimulation.

METHODS AND RESULTS

The RT-PCR analyses revealed that the proton-sensing G protein-coupled receptors were expressed both in mouse BSMs and cultured human BSM cells. In the mouse BSMs, change in the extracellular pH from 8.0 to 6.8 caused an augmentation of contraction induced by acetylcholine. Interestingly, the acidic pH-induced BSM hyper-contraction was further augmented in the mice that were sensitized and repeatedly challenged with ovalbumin antigen. In this animal model of asthma, upregulations of G protein-coupled receptor 68 (GPR68) and GPR65, that were believed to be coupled with Gq and Gs proteins respectively, were observed, indicating that the acidic pH could cause hyper-contraction probably via an activation of GPR68. However, psychosine, a putative antagonist for GPR68, failed to block the acidic pH-induced responses.

CONCLUSION

These findings suggest that extracellular acidification contributes to the airway hyperresponsiveness, a characteristic feature of bronchial asthma. Further studies are required to identify the receptor(s) responsible for sensing extracellular protons in BSM cells.

Kidney metabolism and acid-base control: back to the basics

Kidneys are central in the regulation of multiple physiological functions, such as removal of metabolic wastes and toxins, maintenance of electrolyte and fluid balance, and control of pH homeostasis. In addition, kidneys participate in systemic gluconeogenesis and in the production or activation of hormones. Acid-base conditions influence all these functions concomitantly. Healthy kidneys properly coordinate a series of physiological responses in the face of acute and chronic acid-base disorders. However, injured kidneys have a reduced capacity to adapt to such challenges. Chronic kidney disease patients are an example of individuals typically exposed to chronic and progressive metabolic acidosis. Their organisms undergo a series of alterations that brake large detrimental changes in the homeostasis of several parameters, but these alterations may also operate as further drivers of kidney damage. Acid-base disorders lead not only to changes in mechanisms involved in acid-base balance maintenance, but they also affect multiple other mechanisms tightly wired to it. In this review article, we explore the basic renal activities involved in the maintenance of acid-base balance and show how they are interconnected to cell energy metabolism and other important intracellular activities. These intertwined relationships have been investigated for more than a century, but a modern conceptual organization of these events is lacking. We propose that pH homeostasis indissociably interacts with central pathways that drive progression of chronic kidney disease, such as inflammation and metabolism, independent of etiology.

Virus blocking textile for SARS-CoV-2 using human body triboelectric energy harvesting

Effective mitigation technology to prevent the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is required before achieving population immunity through vaccines. Here we demonstrate a virus-blocking textile (VBT) that repulses SARS-CoV-2 by applying repulsive Coulomb force to respiratory particles, powered by human body triboelectric energy harvesting. We show that SARS-CoV-2 has negative charges, and a human body generates high output current of which peak-to-peak value reaches 259.6 μA at most, based on triboelectric effect. Thereby, the human body can sustainably power a VBT to have negative electrical potential, and the VBT highly blocks SARS-CoV-2 by repulsion. In an acrylic chamber study, we found that the VBT blocks SARS-CoV-2 by 99.95%, and SARS-CoV-2 in the VBT is 13-fold reduced. Our work provides technology that may prevent the spread of virus based on repulsive Coulomb force and triboelectric energy harvesting.

Transient receptor potential cation channel subfamily V (TRPV) and its importance in asthma

Transient receptor potential (TRP) ion channels play critical roles in physiological and pathological conditions. Increasing evidence has unveiled the contribution of TRP vanilloid (TRPV) family in the development of asthma. The TRPV family is a group (TRPV1-TRPV6) of polymodal channels capable of sensing thermal, acidic, mechanical stress, and osmotic stimuli. TRPVs can be activated by endogenous ligands including, arachidonic acid derivatives or endocannabinoids. While TRPV1-TRPV4 are non-selective cation channels showing a predominance for Ca2+ over Na + influx, TRPV5 and TRPV6 are only Ca2+ permeable selective channels. Asthma is a chronic inflammatory bronchopulmonary disorder involving airway hyperresponsiveness (AHR) and airway remodeling. Patients suffering from allergic asthma display an inflammatory pattern driven by cytokines produced in type-2 helper T cells (Th2) and type 2 innate lymphoid cells (ILC2s). Ion channels are essential regulators in airway smooth muscle (ASM) and immune cells physiology. In this review, we summarize the contribution of TRPV1, TRPV2, and TRPV4 to the pathogenesis of asthma. TRPV1 is associated with hypersensitivity to environmental pollutants and chronic cough, inflammation, AHR, and remodeling. TRPV2 is increased in peripheral lymphocytes of asthmatic patients. TRPV4 contributes to ASM cells proliferation, and its blockade leads to a reduced eosinophilia, neutrophilia, as well as an abolished AHR. In conclusion, TRPV2 may represent a novel biomarker for asthma in children; meanwhile, TRPV1 and TRPV4 seem to be essential contributors to the development and exacerbations of asthma. Moreover, these channels may serve as novel therapeutic targets for this ailment.

Therapeutic potential of targeting cathepsin S in pulmonary fibrosis

Cathepsin S (CTSS), a lysosomal protease, belongs to a family of cysteine cathepsin proteases that promote degradation of damaged proteins in the endolysosomal pathway. Aberrant CTSS expression and regulation are associated with the pathogenesis of several diseases, including lung diseases. CTSS overexpression causes a variety of pathological processes, including pulmonary fibrosis, with increased CTSS secretion and accelerated extracellular matrix remodeling. Compared to many other cysteine cathepsin family members, CTSS has unique features that it presents limited tissue expression and retains its enzymatic activity at a neutral pH, suggesting its decisive involvement in disease microenvironments. In this review, we investigated the role of CTSS in lung disease, exploring recent studies that have indicated that CTSS mediates fibrosis in unique ways, along with its structure, substrates, and distinct regulation. We also outlined examples of CTSS inhibitors in clinical and preclinical development and proposed CTSS as a potential therapeutic target for pulmonary fibrosis.

Hydroxyl Radical Production by Air Pollutants in Epithelial Lining Fluid Governed by Interconversion and Scavenging of Reactive Oxygen Species

Air pollution is a major risk factor for human health. Chemical reactions in the epithelial lining fluid (ELF) of the human respiratory tract result in the formation of reactive oxygen species (ROS), which can lead to oxidative stress and adverse health effects. We use kinetic modeling to quantify the effects of fine particulate matter (PM2.5), ozone (O₃), and nitrogen dioxide (NO₂) on ROS formation, interconversion, and reactivity, and discuss different chemical metrics for oxidative stress, such as cumulative production of ROS and hydrogen peroxide (H₂O₂) to hydroxyl radical (OH) conversion. All three air pollutants produce ROS that accumulate in the ELF as H₂O₂, which serves as reservoir for radical species. At low PM2.5 concentrations (<10 μg m^-3), we find that less than 4% of all produced H₂O₂ is converted into highly reactive OH, while the rest is intercepted by antioxidants and enzymes that serve as ROS buffering agents. At elevated PM2.5 concentrations (>10 μg m^-3), however, Fenton chemistry overwhelms the ROS buffering effect and leads to a tipping point in H₂O₂ fate, causing a strong nonlinear increase in OH production. This shift in ROS chemistry and the enhanced OH production provide a tentative mechanistic explanation for how the inhalation of PM2.5 induces oxidative stress and adverse health effects.

Uncovering the interplay between pH receptors and immune cells: Potential drug targets (Review)

Extracellular acidosis is associated with various immunopathological states. The microenvironment of numerous solid tumours and inflammatory responses during acute or chronic infection are all related to a pH range of 5.5‑7.0. The relationship between inflammation and immune escape, cancer metabolism, and immunologic suppression drives researchers to focus on the effects of low pH on diverse components of disease immune monitoring. The potential effect of low extracellular pH on the immune function reveals the importance of pH in inflammatory and immunoreactive processes. In this review, the mechanism of how pH receptors, including monocarboxylate transporters (MCTs), Na⁺/H⁺ exchanger 1, carbonic anhydrases (CAs), vacuolar‑ATPase, and proton‑sensing G‑protein coupled receptors (GPCRs), modulate the immune system in disease, especially in cancer, were studied. Their role in immunocyte growth and signal transduction as part of the immune response, as well as cytokine production, have been documented in great detail. Currently, immunotherapy strategies have positive therapeutic effects for patients. However, the acidic microenvironment may block the effect of immunotherapy through compensatory feedback mechanisms, leading to drug resistance. Therefore, we highlight promising therapeutic developments regarding pH manipulation and provide a framework for future research.

Deficiency of voltage-gated proton channel Hv1 aggravates ovalbumin-induced allergic lung asthma in mice

Asthma is a chronic airway inflammation that caused by many factors. The voltage-gated proton channel Hv1 has been proposed to extrude excessive protons produced by NADPH oxidase (NOX) from cytosol to maintain its activity during respiratory bursts. Here, we showed that loss of Hv1 aggravates ovalbumin (OVA)-induced allergic lung asthma in mice. The numbers of total cells, eosinophils and neutrophils in bronchoalveolar lavage fluid (BALF) of Hv1-deficiency (KO) mice are obviously increased after OVA challenge compared with that of wild-type (WT) mice. Histopathological staining reveals that Hv1-deficiency aggravates OVA-induced inflammatory cell infiltration and goblet cell hyperplasia in lung tissues. The expression of IL-4, IL-5 and IL-13 are markedly increased in lung tissues of OVA-challenged KO mice compared with that of WT mice. Furthermore, the expression levels of NOX2, NOX4 and DUOX1 are dramatically increased, while the expression levels of SOD2 and catalase are significantly reduced in lung tissues of OVA-challenged KO mice compared with that of WT mice. The production of ROS in lung tissues of KO mice is significantly higher than that of WT mice after OVA challenge. Our data suggest that Hv1-deficiency might aggravate the development of allergic asthma through increasing ROS production.

Exhaled Breath Condensate-A Non-Invasive Approach for Diagnostic Methods in Asthma

The pathophysiology of asthma has been intensively studied, but its underlying mechanisms such as airway inflammation, control of airway tone, and bronchial reactivity are still not completely explained. There is an urgent need to implement novel, non-invasive diagnostic tools that can help to investigate local airway inflammation and connect the molecular pathways with the broad spectrum of clinical manifestations of asthma. The new biomarkers of different asthma endotypes could be used to confirm diagnosis, predict asthma exacerbations, or evaluate treatment response. In this paper, we briefly describe the characteristics of exhaled breath condensate (EBC) that is considered to be an interesting source of biomarkers of lung disorders. We look at the composition of EBC, some aspects of the collection procedure, the proposed biomarkers for asthma, and its clinical implications. We also indicate the limitations of the method and potential strategies to standardize the procedure of EBC collection and analytical methods.

Attachment of human adenovirus onto household paints

Attachment of human adenovirus 40 (HAdV40) onto surfaces coated with three compositionally different household paints was evaluated experimentally and interpreted based on measured physicochemical properties of the paints. Polar, dispersive and electrostatic interactions between HAdV40 and the paints were predicted using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) model. Quartz crystal microbalance (QCM-D) was used to quantify virus attachment to paints from 1 mM and 150 mM NaCl solutions, with the latter having the ionic strength of a typical respiratory fluid. Acrylic latex water-based, alkyd water-based, and alkyd oil-based paints were all determined to be highly hydrophobic (ΔG_sws < - 48 mJ/m²). XDLVO modeling and preliminary QCM-D tests evaluated virus-paint interactions within and outside pH windows of favorable virus-paint electrostatic interactions. Hydrophobic and electrostatic interactions governed virus attachment while van der Waals interactions played a relatively minor role. In higher ionic strength solutions, the extent of virus attachment correlated with the free energy of virus-paint interfacial interaction, [Formula: see text] : more negative energies corresponded to higher values of the areal mass density of attached viruses. Hydrophobicity was the dominant factor in determining virus adhesion from high ionic strength solutions where electrostatic interactions were screened out. The hydrophobicity of paints, while desirable for minimizing moisture intrusion, also facilitates attachment of colloids such as viruses. The results call for new approaches to the materials design of indoor paints with enhanced resistance to virus adhesion. Paints so formulated should help reduce human exposure to viruses.

Xanthene-based Fluorescence Turn-on Probe for Highly Acidic pH Range in Aqueous Solution

A xanthene-based probe, Xanth-NPr, is developed as a molecular system that exhibits sensitivity for the highly acidic environments with fluorescence turn-on behavior. Xanth-NPr is designed on the principle of photoinduced electron transfer (PET), which controls the fluorescence profile of the probe. The structure of Xanth-NPr contains the dipropylaniline group as a PET promoting unit. Xanth-NPr exhibited quenched fluorescence as long as it is present in neutral or moderately acidic conditions. However, in the highly acidic pH range, it displayed a strong red-colored fluorescence at 592 nm as the protonation of dipropylaniline moiety inhibits the PET process. A model probe Xanth-M without any PET promoting unit was also synthesized. The model probe along with theoretical calculations was employed to explain the role of the PET process in regulating the fluorescence behavior of Xanth-NPr. Xanth-NPr showed linear fluorescence response as a function of pH in the range of 1 to 4.1 with the pKa value of 2.72. Likewise, its fluorescence profile is not altered by the presence of biologically relevant cations.

Airway Surface Liquid pH Regulation in Airway Epithelium Current Understandings and Gaps in Knowledge

Knowledge on the mechanisms of acid and base secretion in airways has progressed recently. The aim of this review is to summarize the known mechanisms of airway surface liquid (ASL) pH regulation and their implication in lung diseases. Normal ASL is slightly acidic relative to the interstitium, and defects in ASL pH regulation are associated with various respiratory diseases, such as cystic fibrosis. Basolateral bicarbonate (HCO3-) entry occurs via the electrogenic, coupled transport of sodium (Na+) and HCO3-, and, together with carbonic anhydrase enzymatic activity, provides HCO3- for apical secretion. The latter mainly involves CFTR, the apical chloride/bicarbonate exchanger pendrin and paracellular transport. Proton (H+) secretion into ASL is crucial to maintain its relative acidity compared to the blood. This is enabled by H+ apical secretion, mainly involving H+/K+ ATPase and vacuolar H+-ATPase that carry H+ against the electrochemical potential gradient. Paracellular HCO3- transport, the direction of which depends on the ASL pH value, acts as an ASL protective buffering mechanism. How the transepithelial transport of H+ and HCO3- is coordinated to tightly regulate ASL pH remains poorly understood, and should be the focus of new studies.

Human Inhalation Study with Zinc Oxide: Analysis of Zinc Levels and Biomarkers in Exhaled Breath Condensate

Workers in the zinc processing, for example, welding or hot-dip galvanizing, are exposed to aerosols consisting of particles and gases, including zinc oxide (ZnO), which can affect human health. In this study, we addressed the effects of short-term controlled exposure to nano-sized ZnO on the airway inflammatory markers in healthy volunteers. To this end, we determined the influence of ZnO inhalation on the content of zinc and biomarkers (leukotriene B₄ (LTB₄), peptide leukotrienes (LTC₄/D₄/E₄), 8-iso-PGF_2α, pH, and prostaglandin E₂ (PGE₂)) in exhaled breath condensate (EBC). Sixteen non-smoking subjects (8 females, 8 men) were exposed to filtered air (sham) or ZnO nanoparticles (0.5, 1.0, and 2.0 mg/m³) for 4 h. EBC samples were collected according to specific study design. We found that the peptide leukotrienes were below the limit of quantification (LOQ) in all the EBC samples. ZnO exposure showed no detectable effect on any other parameters investigated when comparing the two groups. The content of Zn in EBC was unaffected by ZnO inhalation at any concentration used. Therefore, we conclude that the evaluation of Zn and biomarker content in EBC would not be a suitable way to assess the exposure to inhaled ZnO.

TRP channels in airway sensory nerves

Transient Receptor Potential (TRP) channels expressed in specific subsets of airway sensory nerves function as transducers and integrators of a diverse range of sensory inputs including chemical, mechanical and thermal signals. These TRP sensors can detect inhaled irritants as well as endogenously released chemical substances. They play an important role in generating the afferent activity carried by these sensory nerves and regulating the centrally mediated pulmonary defense reflexes. Increasing evidence reported in recent investigations has revealed important involvements of several TRP channels (TRPA1, TRPV1, TRPV4 and TRPM8) in the manifestation of various symptoms and pathogenesis of certain acute and chronic airway diseases. This mini-review focuses primarily on these recent findings of the responses of these TRP sensors to the biological stresses emerging under the pathophysiological conditions of the lung and airways.

Relative humidity in droplet and airborne transmission of disease

A large number of infectious diseases are transmitted by respiratory droplets. How long these droplets persist in the air, how far they can travel, and how long the pathogens they might carry survive are all decisive factors for the spread of droplet-borne diseases. The subject is extremely multifaceted and its aspects range across different disciplines, yet most of them have only seldom been considered in the physics community. In this review, we discuss the physical principles that govern the fate of respiratory droplets and any viruses trapped inside them, with a focus on the role of relative humidity. Importantly, low relative humidity-as encountered, for instance, indoors during winter and inside aircraft-facilitates evaporation and keeps even initially large droplets suspended in air as aerosol for extended periods of time. What is more, relative humidity affects the stability of viruses in aerosol through several physical mechanisms such as efflorescence and inactivation at the air-water interface, whose role in virus inactivation nonetheless remains poorly understood. Elucidating the role of relative humidity in the droplet spread of disease would permit us to design preventive measures that could aid in reducing the chance of transmission, particularly in indoor environment.

A Treatment to Eliminate SARS-CoV-2 Replication in Human Airway Epithelial Cells Is Safe for Inhalation as an Aerosol in Healthy Human Subjects

BACKGROUND

Low airway surface pH is associated with many airway diseases, impairs antimicrobial host defense, and worsens airway inflammation. Inhaled Optate is designed to safely raise airway surface pH and is well tolerated in humans. Raising intracellular pH partially prevents activation of SARS-CoV-2 in primary normal human airway epithelial (NHAE) cells, decreasing viral replication by several mechanisms.

METHODS

We grew primary NHAE cells from healthy subjects, infected them with SARS-CoV-2 (isolate USA-WA1/2020), and used clinical Optate at concentrations used in humans in vivo to determine whether Optate would prevent viral infection and replication. Cells were pretreated with Optate or placebo prior to infection (multiplicity of infection = 1), and viral replication was determined with plaque assay and nucleocapsid (N) protein levels. Healthy human subjects also inhaled Optate as part of a Phase 2a safety trial.

RESULTS

Optate almost completely prevented viral replication at each time point between 24 h and 120 h, relative to placebo, on both plaque assay and N protein expression (P < .001). Mechanistically, Optate inhibited expression of major endosomal trafficking genes and raised NHAE intracellular pH. Optate had no effect on NHAE cell viability at any time point. Inhaled Optate was well tolerated in 10 normal subjects, with no change in lung function, vital signs, or oxygenation.

CONCLUSIONS

Inhaled Optate may be well suited for a clinical trial in patients with pulmonary SARS-CoV-2 infection. However, it is vitally important for patient safety that formulations designed for inhalation with regard to pH, isotonicity, and osmolality be used. An inhalational treatment that safely prevents SARS-CoV-2 viral replication could be helpful for treating patients with pulmonary SARS-CoV-2 infection.

Mucosal pathogenesis in gastro-esophageal reflux disease

BACKGROUND

Despite gastro-esophageal reflux disease affecting up to 20% of Western populations, relatively little is known about the molecular mechanisms underlying its most troublesome symptom: heartburn. Recent findings have unveiled the role of components of the esophageal mucosa in the pathogenesis of GERD including sensory nociceptive nerves and inflammatory mediators. Erosive esophagitis was long believed to develop as a result of acid injury at the esophageal lumen, but novel concepts suggest the generation of reflux-induced esophageal injury as a result of cytokine-mediated inflammation. Moreover, the localization and characterization of mucosal afferent nerves vary between GERD phenotypes and could explain the heterogeneity of symptom perception between patients who experience similar levels of acid reflux.

PURPOSE

The purpose of this review is to consider the crosstalk of different factors of the esophageal mucosa in the pathogenesis of GERD, with a particular focus on mucosal innervation and molecular basis of acid-induced cytokine response. We discuss the current understanding of the mucosal response to acid injury, the nociceptive role of acid-sensitive receptors expressed in the esophageal mucosa, and the role of esophageal epithelial cells in initiating the onset of erosive esophagitis.

Reduced Exhaled Breath Condensate pH and Severity of Allergic Sensitization Predict School Age Asthma

BACKGROUND

We previously reported that deaerated breath condensate pH (dEBC pH) can identify preschool children with recurrent wheezing at high asthma risk.

OBJECTIVE

To assess the ability of preschool dEBC pH to predict asthma risk at school age.

METHODS

Children of the baseline cohort were recontacted for follow-up. Asthma diagnosis at school age was evaluated according to Global Initiative for Asthma recommendations in 135 children who at baseline had been classified into the following groups: (asymptomatic) atopic wheezers (n = 30), (asymptomatic) nonatopic wheezers (n = 57), allergic rhinitis only (n = 14), and healthy controls (n = 34).

RESULTS

All (100%) former atopic wheezers, 12 (21%) of nonatopic wheezers, 2 (14%) of allergic rhinitis group, and 1 (3%) of healthy controls had developed asthma at follow-up. Among all children with baseline wheezing, baseline dEBC pH predicted asthma at follow-up with an area under the receiver operating characteristic curve (AUC) of 0.72 (sensitivity, 0.67; specificity, 0.76; at pH 7.83). Combining pH and Capacity class (CAP) led to substantial gain in sensitivity (0.96) and negative predictive value (NPV, 0.94). Additional clinical information (Asthma Predictive Index, family atopy, family asthma, and inhaled corticosteroids) further increased the potential to predict asthma (AUC, 0.94) and raised sensitivity (0.98) and NPV (0.97) to nearly perfect values.

CONCLUSION

Our findings suggest (1) that dEBC pH combined with CAP class may serve as highly sensitive, noninvasive marker for the early detection of young asymptomatic preschool children with increased asthma risk, and (2) the need for additional biomarkers with high specificity to optimize early risk stratification in this clinically challenging scenario.

Bioresponsive drug delivery systems for the treatment of inflammatory diseases

Inflammation is intimately related to the pathogenesis of numerous acute and chronic diseases like cardiovascular disease, inflammatory bowel disease, rheumatoid arthritis, and neurodegenerative diseases. Therefore anti-inflammatory therapy is a very promising strategy for the prevention and treatment of these inflammatory diseases. To overcome the shortcomings of existing anti-inflammatory agents and their traditional formulations, such as nonspecific tissue distribution and uncontrolled drug release, bioresponsive drug delivery systems have received much attention in recent years. In this review, we first provide a brief introduction of the pathogenesis of inflammation, with an emphasis on representative inflammatory cells and mediators in inflammatory microenvironments that serve as pathological fundamentals for rational design of bioresponsive carriers. Then we discuss different materials and delivery systems responsive to inflammation-associated biochemical signals, such as pH, reactive oxygen species, and specific enzymes. Also, applications of various bioresponsive drug delivery systems in the treatment of typical acute and chronic inflammatory diseases are described. Finally, crucial challenges in the future development and clinical translation of bioresponsive anti-inflammatory drug delivery systems are highlighted.

Outdoor air pollutants exposure associated with pulmonary function and EBC pH value in atopic asthmatic and non-asthmatic children

OBJECTIVE

Air pollution is associated with the prevalence of respiratory diseases. This study aimed to evaluate the impacts of outdoor air pollutants and indoor Dermatophagoides pteronyssinus 1 (Der p 1) exposure on levels of fractional exhaled nitric oxide (FeNO), exhaled breath condensate (EBC) pH, and pulmonary function in atopic children.

METHODS

This study recruited 59 atopic mild-to-moderate asthmatic children and 23 atopic non-asthmatic children. Data on personal characteristics, FeNO, EBC pH, and pulmonary function were collected. Group 1 allergens of Der p 1 were measured on the tops of mattresses and on bedroom floors in the children's homes, and outdoor air pollutant concentrations were estimated from air quality monitoring stations, using the ordinary kriging method.

RESULTS

Exposure levels of outdoor air pollutants, except for particulate matter (PM)_2.5, for the recruited children met outdoor air quality standards set by the Taiwan Environmental Protection Agency. The lag effect of outdoor PM₁₀ exposure was negatively associated with the forced expiratory volume in one second (FEV₁) [(Lag 1: β=-0.771, p = 0.028), and O₃ (Lag 1-7: β=-2.02, p = 0.04, Lag 1-28: β=-3.213, p = 0.029)]. Median pulmonary function parameters differed significantly in forced vital capacity (FVC) (p = 0.004) and FEV₁ (p = 0.024) values between atopic asthmatic and non-asthmatic children. No association was found between the FeNO/EBC pH level and exposure to Der p 1 allergen and air pollutants in the recruited children.

CONCLUSIONS

Outdoor PM₁₀ and O₃ exposure was associated with reduction in FEV₁ in atopic asthmatic and non-asthmatic children.

Environmental and Endogenous Acids Can Trigger Allergic-Type Airway Reactions

Inflammatory allergic and nonallergic respiratory disorders are spreading worldwide and often coexist. The root cause is not clear. This review demonstrates that, from a biochemical point of view, it is ascribable to protons (H+) released into cells by exogenous and endogenous acids. The hypothesis of acids as the common cause stems from two considerations: (a) it has long been known that exogenous acids present in air pollutants can induce the irritation of epithelial surfaces, particularly the airways, inflammation, and bronchospasm; (b) according to recent articles, endogenous acids, generated in cells by phospholipases, play a key role in the biochemical mechanisms of initiation and progression of allergic-type reactions. Therefore, the intracellular acidification and consequent Ca2+ increase, induced by protons generated by either acid pollutants or endogenous phospholipases, may constitute the basic mechanism of the multimorbidity of these disorders, and environmental acidity may contribute to their spread.

Safety, Tolerability, and Effects of Sodium Bicarbonate Inhalation in Cystic Fibrosis

BACKGROUND

Among the many consequences of loss of CFTR protein function, a significant reduction of the secretion of bicarbonate (HCO₃^-) in cystic fibrosis (CF) is a major pathogenic feature. Loss of HCO₃^- leads to abnormally low pH and impaired mucus clearance in airways and other exocrine organs, which suggests that NaHCO₃ inhalation may be a low-cost, easily accessible therapy for CF.

OBJECTIVE

To evaluate the safety, tolerability, and effects of inhaled aerosols of NaHCO₃ solutions (4.2% and 8.4%).

METHODS

An experimental, prospective, open-label, pilot, clinical study was conducted with 12 CF volunteer participants over 18 years of age with bronchiectasis and pulmonary functions classified as mildly to severely depressed. Sputum rheology, pH, and microbiology were examined as well as spirometry, exercise performance, quality-of-life assessments, dyspnea, blood count, and venous blood gas levels.

RESULTS

Sputum pH increased immediately after inhalation of NaHCO₃ at each clinical visit and was inversely correlated with rheology when all parameters were evaluated: [G' (elasticity of the mucus) = - 0.241; G″ (viscosity of the mucus) = - 0.287; G* (viscoelasticity of the mucus) = - 0.275]. G* and G' were slightly correlated with peak flow, forced expiratory volume in 1 s (FEV₁), and quality of life; G″ was correlated with quality of life; sputum pH was correlated with oxygen consumption (VO₂) and vitality score in quality of life. No changes were observed in blood count, venous blood gas, respiratory rate, heart rate, peripheral oxygen saturation of hemoglobin (SpO₂), body temperature, or incidence of dyspnea. No adverse events associated with the study were observed.

CONCLUSION

Nebulized NaHCO₃ inhalation appears to be a safe and well tolerated potential therapeutic agent in the management of CF. Nebulized NaHCO₃ inhalation temporarily elevates airway liquid pH and reduces sputum viscosity and viscoelasticity.

TNFα and IL-17 alkalinize airway surface liquid through CFTR and pendrin

The pH of airway surface liquid (ASL) is a key factor that determines respiratory host defense; ASL acidification impairs and alkalinization enhances key defense mechanisms. Under healthy conditions, airway epithelia secrete base ([Formula: see text]) and acid (H⁺) to control ASL pH (pH_ASL). Neutrophil-predominant inflammation is a hallmark of several airway diseases, and TNFα and IL-17 are key drivers. However, how these cytokines perturb pH_ASL regulation is uncertain. In primary cultures of differentiated human airway epithelia, TNFα decreased and IL-17 did not change pH_ASL. However, the combination (TNFα+IL-17) markedly increased pH_ASL by increasing [Formula: see text] secretion. TNFα+IL-17 increased expression and function of two apical [Formula: see text] transporters, CFTR anion channels and pendrin Cl^-/[Formula: see text] exchangers. Both were required for maximal alkalinization. TNFα+IL-17 induced pendrin expression primarily in secretory cells where it was coexpressed with CFTR. Interestingly, significant pendrin expression was not detected in CFTR-rich ionocytes. These results indicate that TNFα+IL-17 stimulate [Formula: see text] secretion via CFTR and pendrin to alkalinize ASL, which may represent an important defense mechanism in inflamed airways.

Cathepsin S: investigating an old player in lung disease pathogenesis, comorbidities, and potential therapeutics

Dysregulated expression and activity of cathepsin S (CTSS), a lysosomal protease and a member of the cysteine cathepsin protease family, is linked to the pathogenesis of multiple diseases, including a number of conditions affecting the lungs. Extracellular CTSS has potent elastase activity and by processing cytokines and host defense proteins, it also plays a role in the regulation of inflammation. CTSS has also been linked to G-coupled protein receptor activation and possesses an important intracellular role in major histocompatibility complex class II antigen presentation. Modulated CTSS activity is also associated with pulmonary disease comorbidities, such as cancer, cardiovascular disease, and diabetes. CTSS is expressed in a wide variety of immune cells and is biologically active at neutral pH. Herein, we review the significance of CTSS signaling in pulmonary diseases and associated comorbidities. We also discuss CTSS as a plausible therapeutic target and describe recent and current clinical trials examining CTSS inhibition as a means for treatment.

The proton-sensing receptor ovarian cancer G-protein coupled receptor 1 (OGR1) in airway physiology and disease

Numerous G protein-coupled receptors (GPCRs) regulate multiple airway functions and play fundamental roles in normal and aberrant airway and lung physiology. Thus, GPCRs are prime candidates of targeting by disease therapeutics. The intriguing proton-sensing GPCR Ovarian cancer G-protein coupled receptor 1 (OGR1; aka GPR68) has recently been shown capable of regulating airway smooth muscle (ASM) contraction and proliferation. Although the study of OGR1 has been confounded by the fact that the proton is the presumed cognate ligand of OGR1, recent studies have begun to identify novel ligands and modulators capable of regulating the diverse signaling, and functional role of OGR1. Such studies offer hope for OGR1-targeting drugs as therapeutics for obstructive lung diseases such as asthma. Herein, we review the literature to date detailing the receptor biology and pharmacology of OGR1, receptor function in the airway, and describe the potential clinical utility of OGR1-modulating drugs.

Chitinases and Chitinase-Like Proteins in Obstructive Lung Diseases - Current Concepts and Potential Applications

Chitinases, enzymes that cleave chitin’s chain to low molecular weight chitooligomers, are widely distributed in nature. Mammalian chitinases belong to the 18-glycosyl-hydrolase family and can be divided into two groups: true chitinases with enzymatic activity (AMCase and chitotriosidase) and chitinase-like proteins (CLPs) molecules which can bind to chitin or chitooligosaccharides but lack enzymatic activity (eg, YKL-40). Chitinases are thought to be part of an innate immunity against chitin-containing parasites and fungal infections. Both groups of these hydrolases are lately evaluated also as chemical mediators or biomarkers involved in airway inflammation and fibrosis. The aim of this article is to present the current knowledge on the potential role of human chitinases and CLPs in the pathogenesis, diagnosis, and course of obstructive lung diseases. We also assessed the potential role of chitinase and CLPs inhibitors as therapeutic targets in chronic obstructive pulmonary disease and asthma.

Activation of pH-Sensing Receptor OGR1 (GPR68) Induces ER Stress Via the IRE1α/JNK Pathway in an Intestinal Epithelial Cell Model

Proton-sensing ovarian cancer G-protein coupled receptor (OGR1) plays an important role in pH homeostasis. Acidosis occurs at sites of intestinal inflammation and can induce endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), an evolutionary mechanism that enables cells to cope with stressful conditions. ER stress activates autophagy, and both play important roles in gut homeostasis and contribute to the pathogenesis of inflammatory bowel disease (IBD). Using a human intestinal epithelial cell model, we investigated whether our previously observed protective effects of OGR1 deficiency in experimental colitis are associated with a differential regulation of ER stress, the UPR and autophagy. Caco-2 cells stably overexpressing OGR1 were subjected to an acidic pH shift. pH-dependent OGR1-mediated signalling led to a significant upregulation in the ER stress markers, binding immunoglobulin protein (BiP) and phospho-inositol required 1α (IRE1α), which was reversed by a novel OGR1 inhibitor and a c-Jun N-terminal kinase (JNK) inhibitor. Proton-activated OGR1-mediated signalling failed to induce apoptosis, but triggered accumulation of total microtubule-associated protein 1 A/1B-light chain 3, suggesting blockage of late stage autophagy. Our results show novel functions for OGR1 in the regulation of ER stress through the IRE1α-JNK signalling pathway, as well as blockage of autophagosomal degradation. OGR1 inhibition might represent a novel therapeutic approach in IBD.

An aggregation-induced emission active vitamin B6 cofactor derivative: application in pH sensing and detection of latent fingerprints

Aggregation-induced emission (AIE) properties of an easy-to-prepare and structurally planar Schiff base derivative of the vitamin B₆ cofactor pyridoxal (L) were investigated in DMSO–H₂O mixed solvents.

Predictive Value of Combining Inflammatory Biomarkers and Rapid Decline of FEV1 for COPD in Chinese Population: A Prospective Cohort Study

Background

In China, the high prevalence and mortality rate of Chronic Obstructive Pulmonary Disease (COPD) and the poor intervention effect makes it into a heavy social burden. The main reason is that the current diagnosis of COPD mainly based on the static lung function, which is difficult for early intervention. Through matching a predictive model for high-risk groups of COPD that rewards FEV₁ rapid decline as the core, we will establish the early warning model and prove its validity and socio-economic value.

Methods

This is a multi-center, prospective, cohort study. A total of 10,000 people aged 40∼75 without lung disease will be recruited and followed for 3 years. Some questionnaires such as St George’s Respiratory Questionnaire (SGRQ), income class, educational level, comorbidity, smoking habit, and biomass smoke exposure history will be collected. The baseline level of Interleukin 6 (IL-6), high-sensitivity C-reactive Protein (hs-CRP), microRNAs-23a (miR-23a) in peripheral blood and pH value in exhaled breath condensate (EBC) will be measured, lung spirometry will be tested in the first, second, and fourth years. Primary outcome is the incidence of COPD, multivariate regression analysis will be used to establish the predictive model for COPD in China.

Discussion

With the rapid decline of lung function as the core and the baseline inflammatory biomarkers in peripheral blood and pH of the exhaled breath condensate as affecting factors, a predictive model to achieve early detection of high-risk COPD groups will be established and promoted.

Trial registration

This study has been registered at www.ClinicalTrials.gov (registration identifier: NCT03532893) on 21 May 2018, https://register.clinicaltrials.gov.