Long-term variability of desmosine/isodesmosine as biomarker in alpha-1-antritrypsin deficiency-related COPD

Desmosine as a biomarker for the emergent properties of pulmonary emphysema

Developing an effective treatment for pulmonary emphysema will require a better understanding of the molecular changes responsible for distention and rupture of alveolar walls. A potentially useful approach to studying this process involves the concept of emergence in which interactions at different levels of scale induce a phase transition comprising a spontaneous reorganization of chemical and physical systems. Recent studies in our laboratory provide evidence of this phenomenon in pulmonary emphysema by relating the emergence of airspace enlargement to the release of elastin-specific desmosine and isodesmosine (DID) crosslinks from damaged elastic fibers. When the mean alveolar diameter exceeded 400 μm, the level of peptide-free DID in human lungs was greatly increased, reflecting rapid acceleration of elastin breakdown, alveolar wall rupture, and a phase transition to an active disease state that is less responsive to treatment. Based on this finding, it is hypothesized that free DID in urine and other body fluids may serve as a biomarker for early detection of airspace enlargement, thereby facilitating timely therapeutic intervention and reducing the risk of respiratory failure.

The relationship between elastin cross linking and alveolar wall rupture in human pulmonary emphysema

To better define the role of mechanical forces in pulmonary emphysema, we employed methods recently developed in our laboratory to identify microscopic level relationships between airspace size and elastin-specific desmosine and isodesmosine (DID) cross links in normal and emphysematous human lungs. Free DID in wet tissue (a biomarker for elastin degradation) and total DID in formalin-fixed, paraffin-embedded (FFPE) tissue sections were measured using liquid chromatography-tandem mass spectrometry and correlated with alveolar diameter, as determined by the mean linear intercept (MLI) method. There was a positive correlation between free lung DID and MLI (P < 0.0001) in formalin-fixed lungs, and elastin breakdown was greatly accelerated when airspace diameter exceeded 400 µm. In FFPE tissue, DID density was markedly increased beyond 300 µm (P < 0.0001) and leveled off around 400 µm. Elastic fiber surface area similarly peaked at around 400 µm, but to a much lesser extent than DID density, indicating that elastin cross linking is markedly increased in response to early changes in airspace size. These findings support the hypothesis that airspace enlargement is an emergent phenomenon in which initial proliferation of DID cross links to counteract alveolar wall distention is followed by a phase transition involving rapid acceleration of elastin breakdown, alveolar wall rupture, and progression to an active disease state that is less amenable to therapeutic intervention.NEW & NOTEWORTHY The current findings support the hypothesis that airspace enlargement is an emergent phenomenon in which initial proliferation of DID cross links to counteract alveolar wall distention is followed by a phase transition involving rapid acceleration of elastin breakdown, alveolar wall rupture, and progression to an active disease state that is less amenable to therapeutic intervention.

A 28-day clinical trial of aerosolized hyaluronan in alpha-1 antiprotease deficiency COPD using desmosine as a surrogate marker for drug efficacy

INTRODUCTION

A previous 2-week clinical trial of aerosolized hyaluronan (HA) in COPD showed a rapid reduction in lung elastic fiber breakdown, as measured by sputum levels of the unique elastin crosslinks, desmosine and isodesmosine (DID). To further assess the therapeutic efficacy of HA and the utility of DID as surrogate markers for the development of pulmonary emphysema, we have conducted a 28-day randomized, double-blind, placebo-controlled, phase 2 trial of HA involving 27 subjects with alpha-1 antiprotease deficiency COPD.

METHODS

The study drug consisted of a 3 ml inhalation solution containing 0.03% HA with an average molecular weight of 150 kDa that was self-administered twice daily. DID levels were measured in urine, sputum, and plasma using tandem mass spectrometry.

RESULTS

Free urine DID in the HA group showed a significant negative correlation with time between days 14 and 35 (r = -1.0, p = 0.023) and was statistically significantly decreased from baseline at day 35 (15.4 vs 14.2 ng/mg creatinine, p = 0.035). A marked decrease in sputum DID was also seen in the HA group between days 1 and 28 (0.96 vs 0.18 ng/mg protein), but the difference was not significant, possibly due to the small number of adequate specimens. Plasma DID remained unchanged following HA treatment and no significant reductions in urine, sputum, or plasma DID were seen in the placebo group.

CONCLUSIONS

The results support additional clinical trials to further evaluate the therapeutic effect of HA and the use of DID as a real-time marker of drug efficacy.

Obstacles to Early Diagnosis and Treatment of Alpha-1 Antitrypsin Deficiency: Current Perspectives

This review summarizes the current research and outlooks regarding the obstacles to diagnosing and treating early alpha-1-antitrypsin deficiency (AATD). It draws on prior systematic reviews and expert surveys to discover precisely what difficulties exist in early diagnosis and treatment of AATD and elucidate potential solutions to ease these difficulties. The perceived rarity of AATD may translate to a condition poorly understood by primary care physicians, and even many respiratory physicians, which results in opportunities for diagnosis being missed, especially in mild or asymptomatic patients. There are diagnostic techniques involving biomarkers and home testing methods which could improve the rate of early diagnosis. With respect to treatment, AATD involves treating two separate pathologies, lung disease and liver disease. The only specific AATD treatment, augmentation therapy, has proven ability in treating lung disease but not liver disease. Alpha-1-antitrypsin (AAT) synthesized in the liver can form damaging polymers that also result in reduced circulating AAT levels and, whilst liver transplantation is used to effectively treat AATD, it is inappropriate in early disease. Novel therapeutic areas such as gene editing and increasing autophagy are therefore being researched as future treatments. Ultimately, diagnosis and treatment are intrinsically linked in AATD, with earlier diagnosis leading to better treatment options and thus better patient outcomes.

The Proinflammatory Activity of Structurally Altered Elastic Fibers

The mechanisms responsible for the increased loss of pulmonary function following acute lung inflammation in chronic obstructive pulmonary disease remain poorly understood. To investigate this process, our laboratory developed a hamster model that uses a single intratracheal instillation of LPS to superimpose an inflammatory response on lungs treated with intratracheal elastase 1 week earlier. Parameters measured at 2 days after LPS included total leukocyte content and percent neutrophils in BAL fluid (BALF), and BALF levels of both total and peptide-free elastin-specific crosslinks, desmosine and isodesmosine (DID). Airspace enlargement, measured by the mean linear intercept method, and relative interstitial elastic fiber surface area were determined at 1 week after LPS. Compared with animals only treated with elastase, those receiving elastase/LPS showed statistically significant increases in mean linear intercept (156.2 vs. 85.5 μm), BALF leukocytes (187 vs. 37.3 × 10⁴ cells), neutrophils (39% vs. 3.4%), and free DID (182% vs. 97% of controls), which exceeded the sum of the individual effects of the two agents. Despite increased elastin breakdown, the elastase/LPS group had significantly greater elastic fiber surface area than controls (49% vs. 26%) owing to fragmentation and splaying of the fibers. Additional experiments showed that the combination of elastin peptides and LPS significantly enhanced their separate effects on BALF neutrophils and BALF DID in vivo and leukocyte chemotaxis in vitro. The results suggest that structural changes in elastic fibers have proinflammatory activity and may contribute to the decline in pulmonary function related to chronic obstructive pulmonary disease exacerbations.

Enzymatic and non-enzymatic crosslinks found in collagen and elastin and their chemical synthesis

This review summarized the enzymatic and non-enzymatic crosslinks found in collagen and elastin and their organic synthesis.

Copper-Heparin Inhalation Therapy To Repair Emphysema: A Scientific Rationale

Current pharmacotherapy of chronic obstructive pulmonary disease (COPD) aims at reducing respiratory symptoms and exacerbation frequency. Effective therapies to reduce disease progression, however, are still lacking. Furthermore, COPD medications showed less favorable effects in emphysema than in other COPD phenotypes. Elastin fibers are reduced and disrupted, whereas collagen levels are increased in emphysematous lungs. Protease/antiprotease imbalance has historically been regarded as the sole cause of emphysema. However, it is nowadays appreciated that emphysema may also be provoked by perturbations in the sequential repair steps following elastolysis. Essentiality of fibulin-5 and lysyl oxidase-like 1 in the elastin restoration process is discussed, and it is argued that copper deficiency is a plausible reason for failing elastin repair in emphysema patients. Since copper-dependent lysyl oxidases crosslink elastin as well as collagen fibers, copper supplementation stimulates accumulation of both proteins in the extracellular matrix. Restoration of abnormal elastin fibers in emphysematous lungs is favorable, whereas stimulating pulmonary fibrosis formation by further increasing collagen concentrations and organization is detrimental. Heparin inhibits collagen crosslinking while stimulating elastin repair and might therefore be the ideal companion of copper for emphysema patients. Efficacy and safety considerations may lead to a preference of pulmonary administration of copper-heparin over systemic administration.

COPD Pathogenesis: Finding the Common in the Complex

Developing an effective treatment for COPD, and especially pulmonary emphysema, will require an understanding of how fundamental changes at the molecular level affect the macroscopic structure of the lung. Currently, there is no accepted model that encompasses the biochemical and mechanical processes responsible for pulmonary airspace enlargement. We propose that pulmonary emphysematous changes may be more accurately described as an emergent phenomenon, involving alterations at the molecular level that eventually reach a critical structural threshold where uneven mechanical forces produce alveolar wall rupture, accompanied by advanced clinical signs of COPD. The coupling of emergent morphologic changes with biomarkers to detect the process, and counteract it therapeutically, represents a practical approach to the disease.

Biomarkers in Alpha-1 Antitrypsin Deficiency Chronic Obstructive Pulmonary Disease

Biomarkers of pathogenesis in chronic obstructive pulmonary disease (COPD) can significantly accelerate drug development. In COPD related to alpha-1 antitrypsin deficiency, the role of neutrophil elastase and its inhibition by alpha-1 antitrypsin protein focused interest on elastin degradation and the development of pulmonary emphysema. Amino acids desmosine and isodesmosine are unique cross-links in mature elastin fibers and can serve as biomarkers of elastin degradation when measured in body fluids. This review gives a perspective on what has been learned by the earliest measurements of desmosine and isodesmosine followed by later studies using methods of increased sensitivity and specificity and the meaning for developing new therapies. Also included are brief statements on the biomarkers fibrinogen, CC-16, and Aa-Val-360 in COPD.

Therapeutics: Alpha-1 Antitrypsin Augmentation Therapy

Subjects with alpha-1 antitrypsin deficiency who develop pulmonary disease are managed following general treatment guidelines, including disease management interventions. In addition, administration of intravenous infusions of alpha-1 proteinase inhibitor (augmentation therapy) at regular schedules is a specific therapy for individuals with AATD with pulmonary involvement.This chapter summarizes the manufacturing differences of commercially available formulations and the available evidence of the effects of augmentation therapy. Biologically, there is clear evidence of in vivo local antiprotease effects in the lung and systemic immunomodulatory effects. Clinically, there is cumulative evidence of slowing lung function decline and emphysema progression. The optimal dose of augmentation therapy is being revised as well as more individualized assessment of who needs this therapy.

The Effect of Alpha-1 Proteinase Inhibitor on Biomarkers of Elastin Degradation in Alpha-1 Antitrypsin Deficiency: An Analysis of the RAPID/RAPID Extension Trials

The RAPID (NCT00261833; N=180) and RAPID Extension (NCT00670007; N=140) trials demonstrated significantly reduced lung density decline in patients with alpha-1 antitrypsin deficiency (AATD) receiving alpha-1 proteinase inhibitor (A1PI) versus placebo. Desmosine and isodesmosine (DES/IDES) are unique crosslinkers of mature elastin fibers and are utilized as measures of elastin degradation. The aim of this post-hoc study was to determine the effect of A1PI therapy on DES/IDES levels in patients from RAPID/RAPID Extension. Plasma levels of DES/IDES were measured using high-performance liquid chromatography and tandem mass spectrometry. Correlation between changes in DES/IDES levels and computed tomography (CT) lung density decline was assessed. Analysis showed that DES/IDES levels were significantly reduced versus baseline in patients receiving A1PI at all time points, from month 3 through month 48. A significant increase from baseline in DES/IDES was observed with placebo at month 24 (n=54; 0.016; p=0.018). DES/IDES change from baseline was significantly different with A1PI versus placebo at months 3 (-0.021; 95% confidence interval [CI] -0.037, 0.004; p=0.026), 12 (-0.040; 95% CI -0.055, 0.025; p<0.001), and 24 (-0.052; 95% CI -0.070, 0.034; p<0.001). Placebo patients started A1PI therapy at month 24 and showed significant reductions in plasma DES/IDES at months 36 (p<0.001) and 48 (p<0.001). Reduced elastin degradation was associated with slower lung density decline (p=0.005), correlating a chemical index of therapy with an anatomical index by CT. In conclusion, A1PI therapy reduced elastin degradation, including pulmonary elastin, in patients with AATD. These data support using DES/IDES levels as biomarkers to monitor emphysema progression and treatment response.

The Pattern of Elastic Fiber Breakdown in Bleomycin-Induced Pulmonary Fibrosis May Reflect Microarchitectural Changes

INTRODUCTION

Desmosine and isodesmosine (DID) are unique elastin crosslinks that may serve as biomarkers for elastic fiber degradation in chronic obstructive pulmonary disease. Previously, our laboratory found that the ratio of free to peptide-bound DID in bronchoalveolar lavage fluid (BALF) showed a significant positive correlation with the extent of airspace enlargement in an elastase model of pulmonary emphysema. To further evaluate this hypothesis, our laboratory measured this ratio in a bleomycin (BLM) model of pulmonary fibrosis, which involved different microarchitectural changes than those associated with pulmonary emphysema.

METHODS

Syrian hamsters were instilled intratracheally with 1.0 unit BLM in 0.2 ml of normal saline (controls received the vehicle alone), and BALF was analyzed for both free and total DID, using a combination of liquid chromatography and tandem mass spectrometry.

RESULTS

Total BALF DID was significantly increased in hamsters receiving BLM at 1 week post-treatment (92 vs 13 pg/ml; p < 0.001), consistent with elastic fiber degradation. However, in contrast to elastase-induced emphysema, free/bound DID was lower in BLM-treated animals compared to controls at both 1 week (0.76 vs 0.84) and 2 weeks post-treatment (0.69 vs 0.86), though the differences were not statistically significant.

CONCLUSIONS

These results indicate that it may be possible to identify specific pulmonary microarchitecture changes, based on the ratio of free to peptide-bound DID. It is speculated that the proportionate decrease in free DID in BLM-induced fibrosis may be due to preservation of intact elastic fibers as the lung injury progresses.

Augmentation therapy of alpha-1 antitrypsin deficiency associated emphysema

INTRODUCTION

Alpha-1 antitrypsin, secreted by the liver, inhibits neutrophil elastase. Its deficiency favours the development of emphysema. Restoring a "protective" serum level in deficient patients should make it possible to inhibit the development of emphysema.

STATE OF THE ART

Human plasma-derived alpha-1 antitrypsin is a blood-derived drug sold in France under the name Alfalastin(®). The recommended posology is an I.V. administration of 60 mg/kg once a week. Human plasma-derived alpha-1 antitrypsin restores anti-elastase protection in the lower lung and prevents experimental emphysema induced by the elastasis of human neutrophils in hamster. The low number of patients with alpha-1 antitrypsin deficiency is one of the difficulties to perform sufficiently powerful randomised studies. However, randomised studies have reported the efficacy of human plasma-derived alpha-1 antitrypsin perfusions on mortality, FEV1 decline and the frequency of exacerbations. Randomised control trials have demonstrated the efficacy of human plasma-derived alpha-1 antitrypsin perfusions on the loss of lung density assessed by CT scan.

CONCLUSION

Augmentation therapy is simple in its conception and implementation, but it is expensive. However, there are currently no other solutions.

The Ratio of Free to Bound Desmosine and Isodesmosine May Reflect Emphysematous Changes in COPD

BACKGROUND

The unique elastin crosslinks, desmosine and isodesmosine (DID) are significantly elevated in blood, urine, and sputum from patients with COPD, and may decline following treatment of the disease. However, the large degree of variance in this biomarker among COPD patients with similar levels of disease suggests that it has limited prognostic value with regard to the degree of lung disease in a given individual. As an alternative to measuring the total amount of DID, we propose using the ratio of free to peptide-bound DID, which may provide a better indication of overall lung disease.

METHODS

To test this hypothesis, the free/bound DID ratio was measured in bronchoalveolar lavage fluid (BALF) from both hamsters with elastase-induced emphysema and controls not given the enzyme, using a combination of liquid chromatography and tandem mass spectroscopy. This ratio was then correlated with airspace enlargement, as measured by the mean percentage of lung surface area at ×100 microscopic magnification.

RESULTS

There was a significant negative correlation between the free/bound DID ratio in BALF and lung surface area. However, there was no correlation between this ratio and total BALF DID, suggesting that free/bound DID is unrelated to the immediate rate of breakdown of elastic fibers, and may instead measure the cumulative effect of elastase injury in the lung.

CONCLUSIONS

The free/bound DID ratio may be a useful measure of emphysematous changes in the lung and might also serve as a screening procedure for healthy smokers and other individuals at risk for developing COPD.

α1 Antitrypsin deficiency: current best practice in testing and augmentation therapy

α1 Antitrypsin deficiency (AATD) increases the risk of chronic obstructive pulmonary disease (COPD), liver disease and other conditions. Although it is not a rare disease, it is a condition rarely diagnosed because of unawareness by most healthcare providers who manage subjects at risk. Testing recommendations have been published and strongly suggest testing all subjects with confirmed COPD, cryptogenic liver cirrhosis, subjects with incompletely reversible airflow obstruction and siblings of affected individuals. Testing strategies usually imply a combination of measures of α1 antitrypsin (AAT) levels, phenotyping and genotyping, techniques that have been facilitated for in-office use by development of testing kits using dried blood spots. Early detection of subjects is crucial to apply effective preventive measures and early institution of therapy. The only specific Food and Drug Administration - approved therapy for this condition is lifelong weekly intravenous AAT replacement (augmentation therapy). Observational studies strongly suggest a beneficial effect of augmentation therapy in slowing lung function decline and randomized trials suggest a beneficial effect in slowing the progression of emphysema over time as measured by computed tomography. In addition, augmentation therapy has been shown to modulate systemic inflammatory responses and affect markers of elastin degradation. As new markers of disease progression are discovered, new doses of AAT replacement are tested and sub-phenotypes of disease are described, treatment recommendations are likely to change towards a more individualized therapeutic approach.

Biomarkers in chronic obstructive pulmonary disease: confusing or useful?

The field of biomarker research has almost reached unmanageable proportions in chronic obstructive pulmonary disease (COPD). The developments of new technology platforms have generated a huge information data base, both cross sectionally and increasingly, longitudinally. The knowledge emerging provides an enormous potential for understanding the disease pathophysiology, for developing markers specific for long-term outcomes, and for developing new therapeutic strategies. However, the excitement must be tempered with an understanding of the limitations of the data collection techniques, and of the variations in disease state, activity, impact, and progression. Nevertheless, the most crucial aspect in interpreting the current literature is the recognition of the relatively superficial characterization of what is a complex group of pathological processes with a common end point of airflow limitation. The current review explores some of these issues together with those areas where real progress appears to have been made, and provides caution on interpretation.

The role of desmosines as biomarkers for chronic obstructive pulmonary disease

Since chronic obstructive pulmonary disease (COPD) has a progressive and major impact on health management, many aspects of this disorder, including development of effective and reliable biomarkers to monitor disease progression, are under intensive investigation. A huge amount of data, accumulated over the years, have provided solid evidence that two pyridinium-ring-containing amino acid isoforms, desmosine and isodesmosine (usually referred to as desmosines), unique to mature elastin in humans, are representative of the elastin breakdown occurring in chronic destructive disorders, such as COPD. This paper is aimed at providing a critical review of the methodological steps that have marked the progress in the detection of desmosines in biological fluids in health and disease, as well as the progress in the authors knowledge of desmosines' role in the pathophysiology of COPD. The authors have tried to emphasize that the suitability of desmosine as a biomarker for COPD increased over the years, as the techniques developed for its detection became progressively more sophisticated and precise. The authors conclude that desmosines, although not yet definitely proven, have nevertheless all the requisites to become a critical COPD biomarker.

Augmentation therapy for alpha-1 antitrypsin deficiency: towards a personalised approach

Background

Intravenous augmentation therapy is the only specific treatment available for emphysema associated with alpha-1 antitrypsin deficiency. Despite large observational studies and limited interventional studies there remains controversy about the efficacy of this treatment due to the impracticality of conducting adequately powered studies to evaluate the rate of decline in lung function, due to the low prevalence and the slow progression of the disease. However, measurement of lung density by computed tomography is a more specific and sensitive marker of the evolution of emphysema and two small placebo-controlled clinical trials have provided evidence supporting a reduction in the rate of decline in lung density with augmentation therapy.

The problem

Where augmentation therapy has become available there has been little consideration of a structured approach to therapy which is often introduced on the basis of functional impairment at diagnosis. Data from registries have shown a great variability in the evolution of lung disease according to patient acquisition and the presence of recognised risk factors. Avoidance of risk factors may, in many cases, stabilise the disease. Since augmentation therapy itself will at best preserve the presenting level of lung damage yet require intravenous administration for life with associated costs, identification of patients at risk of continued rapid or long term progression is essential to select those for whom this treatment can be most appropriate and hence generally more cost-effective. This represents a major reconsideration of the current practice in order to develop a consistent approach to management world wide.

Purpose of this review

The current review assesses the evidence for efficacy of augmentation therapy and considers how the combination of age, physiological impairment, exacerbation history and rate of decline in spirometry and other measures of emphysema may be used to improve therapeutic decision making, until a reliable predictive biomarker of the evolution of lung impairment can be identified. In addition, individual pharmacokinetic studies may permit the selection of the best regimen of administration for those who need it.

Summary

The rarity and variable characteristics of the disease imply the need for an individualised approach to therapy in specialised centres with sufficient experience to apply a systematic approach to monitoring and management.

What percolation theory can tell us about COPD

Damage to the lung elastic fiber network is largely responsible for the distention and rupture of alveolar walls in chronic obstructive pulmonary disease (COPD). It has therefore been suggested that blood or urine levels of the unique elastic fiber crosslinks, desmosine and isodesmosine (DID), may serve as a biomarker for the progression of the disease. The prognostic value of DID may be limited, however, by the large degree of variance associated with their measurement in patients with COPD. To overcome this problem, we propose that specific patterns of DID release from damaged elastic fibers, rather than their absolute quantity, may provide a better indication of morphological changes in the lungs of patients with COPD. Using percolation theory to model the elastic fiber network in the lung, it will be shown that the relative amounts of damaged and intact elastic fibers may be reflected at the molecular level by urinary levels of free and peptide-bound DID, respectively. The self-similar nature of percolation networks further suggests that detachment of crosslinks from elastic fibers may be analogous to the rupture of alveolar walls in COPD. Consequently, the ratio of free to bound DID may be a measure of emphysematous changes in this disease.