Urinary desmosine excretion as a marker of lung injury in the adult respiratory distress syndrome

Effects of mechanical ventilation on the interstitial extracellular matrix in healthy lungs and lungs affected by acute respiratory distress syndrome: a narrative review

BACKGROUND

Mechanical ventilation, a lifesaving intervention in critical care, can lead to damage in the extracellular matrix (ECM), triggering inflammation and ventilator-induced lung injury (VILI), particularly in conditions such as acute respiratory distress syndrome (ARDS). This review discusses the detailed structure of the ECM in healthy and ARDS-affected lungs under mechanical ventilation, aiming to bridge the gap between experimental insights and clinical practice by offering a thorough understanding of lung ECM organization and the dynamics of its alteration during mechanical ventilation.

MAIN TEXT

Focusing on the clinical implications, we explore the potential of precise interventions targeting the ECM and cellular signaling pathways to mitigate lung damage, reduce inflammation, and ultimately improve outcomes for critically ill patients. By analyzing a range of experimental studies and clinical papers, particular attention is paid to the roles of matrix metalloproteinases (MMPs), integrins, and other molecules in ECM damage and VILI. This synthesis not only sheds light on the structural changes induced by mechanical stress but also underscores the importance of cellular responses such as inflammation, fibrosis, and excessive activation of MMPs.

CONCLUSIONS

This review emphasizes the significance of mechanical cues transduced by integrins and their impact on cellular behavior during ventilation, offering insights into the complex interactions between mechanical ventilation, ECM damage, and cellular signaling. By understanding these mechanisms, healthcare professionals in critical care can anticipate the consequences of mechanical ventilation and use targeted strategies to prevent or minimize ECM damage, ultimately leading to better patient management and outcomes in critical care settings.

Early Changes and Indicators Characterizing Lung Aging in Neonatal Chronic Lung Disease

Infants suffering from neonatal chronic lung disease, i.e., bronchopulmonary dysplasia, are facing long-term consequences determined by individual genetic background, presence of infections, and postnatal treatment strategies such as mechanical ventilation and oxygen toxicity. The adverse effects provoked by these measures include inflammatory processes, oxidative stress, altered growth factor signaling, and remodeling of the extracellular matrix. Both, acute and long-term consequences are determined by the capacity of the immature lung to respond to the challenges outlined above. The subsequent impairment of lung growth translates into an altered trajectory of lung function later in life. Here, knowledge about second and third hit events provoked through environmental insults are of specific importance when advocating lifestyle recommendations to this patient population. A profound exchange between the different health care professionals involved is urgently needed and needs to consider disease origin while future monitoring and treatment strategies are developed.

Proteomic study of acute respiratory distress syndrome: current knowledge and implications for drug development

The acute respiratory distress syndrome (ARDS) is a common cause of acute respiratory failure, and is associated with substantial mortality and morbidity. Dozens of clinical trials targeting ARDS have failed, with no drug specifically targeting lung injury in widespread clinical use. Thus, the need for drug development in ARDS is great. Targeted proteomic studies in ARDS have identified many key pathways in the disease, including inflammation, epithelial injury, endothelial injury or activation, and disordered coagulation and repair. Recent studies reveal the potential for proteomic changes to identify novel subphenotypes of ARDS patients who may be most likely to respond to therapy and could thus be targeted for enrollment in clinical trials. Nontargeted studies of proteomics in ARDS are just beginning and have the potential to identify novel drug targets and key pathways in the disease. Proteomics will play an important role in phenotyping of patients and developing novel therapies for ARDS in the future.

Synthesis and LC-MS/MS analysis of desmosine-CH2, a potential internal standard for the degraded elastin biomarker desmosine

Desmosine-CH2, an analog of the elastic tissue degradation biomarker desmosine, can be regarded as a potential internal standard for precise quantification of desmosines by LC-MS/MS. In this study, the chemical synthesis of desmosine-CH2 was completed in 22% overall yield in five steps. The LC-MS/MS analysis of desmosine-CH2 was also achieved.

[(13)C3,(15)N1]-labeled isodesmosine: A potential internal standard for LC-MS/MS analysis of desmosines in elastin degradation

Isodesmosine and desmosine are crosslinking amino acids that are present only in elastin. They are useful biomarkers for the degradation of elastin, which occurs during the progression of chronic obstructive pulmonary disease (COPD) and related diseases. This Letter describes the synthesis of [(13)C3,(15)N1]-labeled isodesmosine, using Chichibabin pyridine synthesis as a key reaction. The labeled isodesmosine is a potential internal standard for the quantitative LC-MS/MS analysis of desmosines in elastin degradation.

ADAM9 is a novel product of polymorphonuclear neutrophils: regulation of expression and contributions to extracellular matrix protein degradation during acute lung injury

A disintegrin and a metalloproteinase domain (ADAM) 9 is known to be expressed by monocytes and macrophages. In this study, we report that ADAM9 is also a product of human and murine polymorphonuclear neutrophils (PMNs). ADAM9 is not synthesized de novo by circulating PMNs. Rather, ADAM9 protein is stored in the gelatinase and specific granules and the secretory vesicles of human PMNs. Unstimulated PMNs express minimal quantities of surface ADAM9, but activation of PMNs with degranulating agonists rapidly (within 15 min) increases PMN surface ADAM9 levels. Human PMNs produce small quantities of soluble forms of ADAM9. Surprisingly, ADAM9 degrades several extracellular matrix (ECM) proteins, including fibronectin, entactin, laminin, and insoluble elastin, as potently as matrix metalloproteinase-9. However, ADAM9 does not degrade types I, III, or IV collagen or denatured collagens in vitro. To determine whether Adam9 regulates PMN recruitment or ECM protein turnover during inflammatory responses, we compared wild-type and Adam9(-/-) mice in bacterial LPS- and bleomycin-mediated acute lung injury (ALI). Adam9 lung levels increase 10-fold during LPS-mediated ALI in wild-type mice (due to increases in leukocyte-derived Adam9), but Adam9 does not regulate lung PMN (or macrophage) counts during ALI. Adam9 increases mortality, promotes lung injury, reduces lung compliance, and increases degradation of lung elastin during LPS- and/or bleomycin-mediated ALI. Adam9 does not regulate collagen accumulation in the bleomycin-treated lung. Thus, ADAM9 is expressed in an inducible fashion on PMN surfaces where it degrades some ECM proteins, and it promotes alveolar-capillary barrier injury during ALI in mice.

Stable deuterium internal standard for the isotope-dilution LC-MS/MS analysis of elastin degradation

Chemical synthesis of the deuterium isotope desmosine-d4 has been achieved. This isotopic compound possesses all four deuterium atoms at the alkanyl carbons of the alkyl amino acid substitution in the desmosine molecule and is stable toward acid hydrolysis; this is required in the measurement of two crosslinking molecules, desmosine and isodesmosine, as biomarkers of elastic tissue degradation. The degradation of elastin occurs in several widely prevalent diseases. The synthesized desmosine-d₄ is used as the internal standard to develop an accurate and sensitive isotope-dilution liquid chromatography-tandem mass spectrometry analysis, which can serve as a generalized method for an accurate analysis of desmosine and isodesmosine as biomarkers in many types of biological tissues involving elastin degradation.

Cytochrome b5 and cytokeratin 17 are biomarkers in bronchoalveolar fluid signifying onset of acute lung injury

Acute lung injury (ALI) is characterized by pulmonary edema and acute inflammation leading to pulmonary dysfunction and potentially death. Early medical intervention may ameliorate the severity of ALI, but unfortunately, there are no reliable biomarkers for early diagnosis. We screened for biomarkers in a mouse model of ALI. In this model, inhalation of S. aureus enterotoxin A causes increased capillary permeability, cell damage, and increase protein and cytokine concentration in the lungs. We set out to find predictive biomarkers of ALI in bronchoalveolar lavage (BAL) fluid before the onset of clinical manifestations. A cutting edge proteomic approach was used to compare BAL fluid harvested 16 h post S. aureus enterotoxin A inhalation versus BAL fluid from vehicle alone treated mice. The proteomic PF 2D platform permitted comparative analysis of proteomic maps and mass spectrometry identified cytochrome b5 and cytokeratin 17 in BAL fluid of mice challenged with S. aureus enterotoxin A. Validation of cytochrome b5 showed tropic expression in epithelial cells of the bronchioles. Importantly, S. aureus enterotoxin A inhalation significantly decreased cytochrome b5 during the onset of lung injury. Validation of cytokeratin 17 showed ubiquitous expression in lung tissue and increased presence in BAL fluid after S. aureus enterotoxin A inhalation. Therefore, these new biomarkers may be predictive of ALI onset in patients and could provide insight regarding the basis of lung injury and inflammation.

Cough and sputum production as risk factors for poor outcomes in patients with COPD

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality in developed countries, and its prevalence is projected to increase over the coming decades. According to the World Health Organization, COPD will become the third leading cause of death worldwide by 2020. COPD has a chronic and progressive course, and is often aggravated by exacerbations, which typically arise as a result of bronchial infection. Exacerbations are characterised by periods of increasing acute symptoms, particularly cough, dyspnoea and production of sputum, which worsen airflow obstruction, further impair quality of life and generally require a change in regular medication. Exacerbations are the most common cause of medical visits, hospital admissions and death in patients with COPD, and frequent exacerbations worsen health status and may cause a permanent decline in lung function. Chronic cough and sputum production are common in the general population, but significantly more prevalent in patients with respiratory disorders; these symptoms have been suggested as a risk factor for exacerbations of COPD. This article will review the consequences of chronic cough and sputum production in patients with COPD and analyse whether these risk factors may be useful for identifying a specific phenotype of patient that requires different management to reduce the occurrence of exacerbations.

The pathogenetic and prognostic value of biologic markers in acute lung injury

Over the past 2 decades, measurement of biomarkers in both the airspaces and plasma early in the course of acute lung injury has provided new insights into the mechanisms of lung injury. In addition, biologic markers of cell-specific injury, acute inflammation, and altered coagulation correlate with mortality from acute lung injury in several single center studies as well as in multicenter clinical trials. To date, biomarkers have been measured largely for research purposes. However, with improved understanding of their role in the pathogenesis of acute lung injury, biomarkers may play an important role in early detection of lung injury, risk stratification for clinical trials, and, ultimately, tailoring specific therapies to individual patients. This article provides a review of biologic markers in acute lung injury, with an emphasis on recent analysis of results from multicenter clinical trials.

Progress in the methodological strategies for the detection in real samples of desmosine and isodesmosine, two biological markers of elastin degradation

Desmosines are crosslinking amino acids unique to mature elastin in humans. Owing to this unicity, they have been discussed as potentially attractive indicators of connective tissue disorders whose clinical manifestations are mostly the result of elastin degradation. This review covers advances in immunochemical, chromatographic, and electrophoretic procedures applied in the last 25 years to detect and quantitate these crosslinksin a variety of biological samples. Recent applications of CE with LIF detection (CE-LIF) for investigating the content of desmosines in different fluids will also be discussed.

Urinary desmosine as a biomarker in acute lung injury

Acute lung injury (ALI) is a complex disorder associated with an acute inflammatory response thought to contribute to tissue injury. Desmosine, a cross-linking amino acid present in elastin, is released during matrix degradation and cleared by the kidney. Results from animal models and human disease studies have suggested that ALI is associated with the release of desmosine, resulting in increased urinary desmosine. A radioimmunoassay was used to monitor urinary desmosine levels over 10 days in ten patients with ALI. The concentration of desmosine was measured with and without acid hydrolysis. Baseline urinary desmosine was increased in two of ten patients. The concentration of desmosine at baseline did not appear to be related to age, gender, neutrophil elastase (NE)/alpha(1)-antiprotease complex concentration or P(a)O(2)/F(i)O(2) ratio. No meaningful changes in desmosine levels were noted after removal from mechanical ventilation. Baseline desmosine concentrations did not appear to correlate with the risk of death. The limited sensitivity, predictive correlations and dynamic modulation would suggest that urine desmosine has a limited role as a biomarker for ALI. Hydrolysis of urine samples appears necessary for optimal measurement of urine desmosine.

Higher urine desmosine levels are associated with mortality in patients with acute lung injury

Desmosine is a stable breakdown product of elastin that can be reliably measured in urine samples. We tested the hypothesis that higher baseline urine desmosine would be associated with higher mortality in 579 of 861 patients included in the recent Acute Respiratory Distress Syndrome Network trial of lower tidal volume ventilation (1). We also correlated urine desmosine levels with indexes of disease severity. Finally, we assessed whether urine desmosine was lower in patients who received lower tidal volumes. Desmosine was measured by radioimmunoassay in urine samples from days 0, 1, and 3 of the study. The data were expressed as a ratio of urine desmosine to urine creatinine to control for renal dilution. The results show that higher baseline (day 0) urine desmosine-to-creatinine concentration was associated with a higher risk of death on adjusted analysis (odds ratio 1.36, 95% confidence interval 1.02-1.82, P=0.03). Urine desmosine increased in both ventilator groups from day 0 to day 3, but the average rise was higher in the 12-ml/kg predicted body weight group compared with the 6-ml/kg predicted body weight group (P=0.053, repeated-measures model). In conclusion, patients with acute lung injury ventilated with lower tidal volumes have lower urine desmosine levels, a finding that may reflect reduced extracellular matrix breakdown. These results illustrate the value of evaluating urinary biological markers that may have prognostic and pathogenetic significance in acute lung injury.

The detection and quantitation of free desmosine and isodesmosine in human urine and their peptide-bound forms in sputum

Desmosine (D) and isodesmosine (I), the intramolecular crosslinking amino acids that occur in chains of elastin, have now been found in free form in human urine. Until now, these amino acids (M(r) = 526) were found to occur in urine only as higher molecular weight (M (r) = 1,000-1,500) peptides. Thus, the previously used analytical methods required, as the first step, acid hydrolysis of the urine at elevated temperature to liberate D and I from their peptides. The analytical method described here uses HPLC followed by electrospray ionization MS for the detection and quantitation of free D and I in unhydrolyzed urine. Identities of both D and I were established by their retention times on LC and by their mass ion at 526 atomic mass units, characteristic of each compound. The sensitivity of the method is 0.10 ng. The average values of free D and I in the urine of seven healthy subjects were 1.42 +/- 1.16 and 1.39 +/- 1.04 microg/g of creatinine, respectively. After acid hydrolysis of the urine, the amounts of D and I were 8.67 +/- 3.75 and 6.28+/-2.87 microg/g of creatinine, respectively. The method was also successfully used to measure peptide-bound D and I levels in the sputum of patients with chronic obstructive pulmonary disease.

Comparison of urinary desmosine excretion in patients with chronic obstructive pulmonary disease or cystic fibrosis

Neutrophil elastase is involved in the pathogenesis of several pulmonary diseases; a strategy for monitoring in vivo elastase activity is to measure changes in biochemical markers. The objective of this study was to determine whether differences in the urinary excretion of the elastin crosslinks, desmosine and isodesmosine (which are unique amino acid products of elastase activity), could be discerned between groups of patients with chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF), and non-diseased, age-matched controls. Twenty-four-hour urine collections were analysed to eliminate variations in excretion throughout the day, and urine was collected on four separate days in 29-31 subjects/group to investigate the variability in desmosines excretion among the groups. Both sets of patient populations had significantly more variable desmosines readings (higher standard deviations) relative to their respective age-matched control group. The means for three adult groups (COPD, controls and a COPD-smoker subset) ranged from 28.4 to 35.5 pmol desmosines/mg creatinine and there were no differences among the groups. Values in children were higher: 55 pmol desmosines/mg creatinine in the non-CF children and 77 pmol desmosines/mg creatinine for the CF group (P<0.01 vs. age-matched controls). The results of this study show that urinary desmosines, as a surrogate marker for enhanced elastase activity, are more highly variant in both patient populations relative to age-matched controls, and an overall increase in the mean value is further observed in patients with cystic fibrosis.

Acute respiratory distress syndrome. Potential pharmacologic interventions

Remarkable progress has been made in the past 10 years with regard to understanding the interplay of potent physiologic mediators in patients with acute lung injury. Because there are so many mediators and the interaction of these agents is complex, true insight into the process has been slow in coming. Clinical studies in ARDS, as well as sepsis, the leading cause of ARDS, have increased in number, size, and quality over this same period. Although none of these studies has produced an accepted new therapy for ARDS, each has laid the groundwork for more efficient and more elegant studies of the problem. The stage is now set for the real advances to be brought forward and put to rigorous, efficient clinical testing.

Enrichment and analysis of desmosine and isodesmosine in biological fluids

A method has been developed for the enrichment and analysis of the elastin crosslinks, desmosine and isodesmosine, in biological fluids and tissues. It is adapted from published methods, offering improved recovery, sensitivity, resolution, and speed of analysis. Samples were hydrolyzed in 6 M HCl, after which the desmosines were enriched by CF1 cellulose chromatography and analyzed by HPLC with a C18 column. Isodesmosine and desmosine were quantitated based on absorbance at 275 nm, with a limit of detection of approximately 30 pmol and recovery of approximately 66% in urine. Their tR values on our HPLC system were approximately 9 and 12 min, respectively. This method was used to evaluate the daily and weekly variation in the concentrations of desmosine and isodesmosine in human urine. The results suggest that this method can be used to process large numbers of biological samples for analysis of desmosine and isodesmosine.