Background Prolonged past exposure to secondhand tobacco smoke (SHS) in never-smokers is associated with abnormal lung function and reduced diffusing capacity suggestive of an associated lung tissue injury and damage. The mechanisms by which past SHS exposure may contribute to lung tissue damage are unknown. Elastin is a major constituent of extracellular matrix in lung parenchyma. Objective To determine whether past exposure to SHS is associated with ongoing lung tissue damage as indicated by elevated elastin degradation products that are linked to lung function. Methods We measured the plasma levels of elastin degradation markers (EDM) from 193 never-smoking flight attendants with history of remote SHS exposure in aircraft cabin and 103 nonsmoking flight attendants or sea-level control participants without such history of cabin SHS exposure, and examined those levels versus their lung function with adjustment for covariates. The cabin SHS exposure was estimated based on airline employment history and years of smoking ban enactment. Results The median [interquartile range] plasma EDM level for all participants was 0.30 [0.24-0.36] ng/mL with a total range of 0.16-0.65 ng/mL. Plasma EDM levels were elevated in those with history of exposure to cabin SHS compared to those not exposed (0.33±0.08 vs. 0.26±0.06 ng/mL; age- and sex-adjusted P<0.001). In those with history of cabin SHS-exposure, higher EDM levels were associated with lower diffusing capacity (parameter estimate (PE) [95%CI]=4.2 [0.4-8.0] %predicted decrease per 0.1 ng/mL increase in EDM; P=0.030). Furthermore, EDM levels were inversely associated with FEV1, FEV1/FVC, and FEF25-75 (PE [95%CI]=5.8 [2.1-9.4], 4.0 [2.2-5.7], and 12.5 [5.8-19.2] %predicted decrease per 0.1 ng/mL increase in EDM, respectively; P<0.001). Plasma EDM mediated a substantial fraction of the association of SHS with FEV1, FVC, and FEF25-75 (P<0.05). Conclusions Long after past exposure to SHS, there is ongoing elastin degradation beyond what is expected from the aging process, which likely contributes to lower lung function and reduced pulmonary capillary bed as seen in COPD.

ABSTRACTBackgroundProlonged past exposure to secondhand tobacco smoke (SHS) in never-smokers is associated with occult obstructive lung disease and abnormal lung function, in particular reduced diffusing capacity. Previous studies have shown ongoing SHS exposure to be associated with increased elastin degradation markers (EDM) desmosine and isodesmosine.Research QuestionAre EDM levels elevated in persons with remote history of SHS exposure, and are those levels associated with reduced lung function?Study Design and MethodsWe measured the plasma levels of EDM from 193 never-smoking flight attendants with history of remote but prolonged SHS exposure in aircraft cabin and 103 nonsmoking flight attendants or sea-level control participants without history of cabin SHS exposure, and examined those levels versus their lung function with adjustment for covariates. The cabin SHS exposure was estimated based on airline employment history and dates of smoking ban enactment. EDM plasma levels were quantified by high-performance liquid chromatography and tandem mass spectrometry.ResultsThe median [interquartile range; IQR] plasma EDM level for all participants was 0.30 [0.24 to 0.36] ng/mL with a total range of 0.16 to 0.65 ng/mL. Plasma EDM levels were elevated in those with history of exposure to cabin SHS compared to those not exposed (0.33±0.08 vs. 0.26±0.06 ng/mL; age- and sex-adjusted P<0.001). In those with history of cabin SHS-exposure, higher EDM levels were associated with lower diffusing capacity (parameter estimate (PE) [95%CI]=4.2 [0.4 to 8.0] %predicted decrease per 0.1 ng/mL increase in EDM; P=0.030). Furthermore, EDM levels were inversely associated with FEV1, FEV1/FVC, and FEF25-75 (PE [95%CI]=5.8 [2.1 to 9.4], 4.0 [2.2 to 5.7], and 12.5 [5.8 to 19.2]% predicted decrease per 0.1 ng/mL increase in EDM, respectively) (P<0.001).InterpretationProlonged past exposure to SHS, even when remote, is associated with higher systemic elastin degradation markers that in turn is associated with lower lung function and in particular reduced diffusing capacity.

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.

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.

Rationale: Augmentation therapy with intravenous AAT (alpha-1 antitrypsin) is the only specific therapy for individuals with pulmonary disease from AAT deficiency (AATD). The recommended standard dose (SD; 60 mg/kg/wk) elevates AAT trough serum levels to around 50% of normal; however, outside of slowing emphysema progression, its effects in other clinical outcomes have not been rigorously proven.Objectives: To evaluate the biological effects of normalizing AAT trough levels with double-dose (DD) therapy (120 mg/kg/wk) in subjects with AATD already receiving SD therapy.Methods: Clinically stable subjects were evaluated after 4 weeks of SD therapy, followed by 4 weeks of DD therapy, and 4 weeks after return to SD therapy. At the end of each phase, BAL fluid (BALF) and plasma samples were obtained.Measurements and Main Results: DD therapy increased trough AAT levels to normal and, compared with SD therapy, reduced serine protease activity in BALF (elastase and cathepsin G), plasma elastase footprint (Aα-Val360), and markers of elastin degradation (desmosine/isodesmosine) in BALF. DD therapy also further downregulated BALF ILs and cytokines including Jak-STAT (Janus kinases-signal transducer and activator of transcription proteins), TNFα (tumor necrosis factor-α), and T-cell receptor signaling pathways, cytokines involved in macrophage migration, eosinophil recruitment, humoral and adaptive immunity, neutrophil activation, and cachexia. On restarting SD after DD treatment, a possible carryover effect was seen for several biological markers.Conclusions: Subjects with AATD on SD augmentation therapy still exhibit inflammation, protease activity, and elastin degradation that can be further improved by normalizing AAT levels. Higher AAT dosing than currently recommended may lead to enhanced clinical benefits and should be explored further.Clinical trial registered with www.clinicaltrials.gov (NCT01669421).

Purpose While the elastin-specific crosslinks, desmosine and isodesmosine (DID), are increased in blood, urine, and sputum of patients with clinically documented pulmonary emphysema, the usefulness of DID in detecting early lung injury remains untested. To this end, our laboratory has measured DID in a hamster model of smoke-induced emphysema, involving only minimal alveolar wall damage. Methods Animals were either treated with cigarette smoke for 2 h/day, 5 days/week, or exposed only to room air (controls) for a period of 3 months. DID levels in bronchoalveolar lavage fluid (BALF) and whole lungs were determined at monthly intervals, using liquid chromatography and tandem mass spectrometry. Lung surface area was also determined, as a measure of airspace enlargement. Results The portion of BALF DID not bound to peptides (free DID) was significantly higher in smoke-exposed animals at 2 months (9.2 vs 4.4 pg/mg protein; p < 0.05), whereas total BALF DID showed no significant increases over the course of the study, and total lung DID remained unchanged. There was a mild, but significant, loss of lung surface area in the smoke-exposed group at 2 months (28.8% vs 25.2%, p < 0.05), which showed no further progression, consistent with the return of free DID to control levels at 3 months. Conclusions These findings support the hypothesis that free DID are sensitive indicators of smoke-induced lung injury. Measurement of free DID in smokers with minimally decreased lung mass may help determine the utility of this parameter as a test for incipient pulmonary emphysema.

Background: Increased serum desmosine (DES) and isodesmosine (IDES) levels occur in individuals with alpha-1 antitrypsin deficiency (AATD). Small series have confirmed the association with emphysema in moderate COPD. Methods: The QUANTitative lung CT UnMasking emphysema progression in AATD (QUANTUM-1) study was a multicenter, prospective 3-year study of 49 PiZZ individuals with normal lung function. All received serial chest computed tomography (CT), spirometry and serum collection. VIDA analysis software defined the baseline 15th percentile density (PD15). Least squares regression of FEV1 values defined FEV1 slope. We analyzed correlations between demographics, FEV1 decline (n = 49), and PD15 slope (n = 31). Results: The 49 participants had six study visits during which DES/IDES was measured. Despite normal FEV1% predicted, mild emphysema was present on visual analysis. Baseline serum DES/IDES did not correlate with baseline PD15 (r2 = 0.02, p = 0.32). Baseline and average DES/IDES were highly correlated with patient age (r2 = 0.29 and 0.42, p < 0.0001 for both). The mean DES/IDES averaged per patient over 3 years was 0.30 ng/ml, higher than historical controls from the normal population (0.19 ng/ml). The mean DES/IDES over 3 years trended in the same direction as PD15 slope (r2 = 0.06, p = 0.16). Conclusions: Mean DES/IDES was higher than normal in PiZZ individuals with FEV1 ≥ 80%. DES/IDES failed to correlate with baseline PD15, PD15 decline, or FEV1 slope. The consistency of the 6 DES/IDES measurements in each patient adds knowledge about test to test variability of DES/IDES despite study limitations that include small size and lack of concurrent PiMM controls. Despite the presence of near normal pulmonary function in alpha-1 antitrypsin deficient patient’s elevations of DES/IDES indicate increased elastin degradation which can progress and warrants preventive therapies. *Correspondence to: Tatsiana Beiko, Division of Pulmonary and Critical Care Medicine, Medical University of South Carolina, 96 Jonathan Lucas St CSB 816, MSC 630, Charleston, SC, 29407, USA, Tel: +1 (843) 792 6833; E-mail: beiko@ musc.edu

Insights into the clinical course of COPD indicate the need for new therapies for this condition. The discovery of alpha-1 antitrypsin deficiency (AATD) led to the protease-antiprotease imbalance hypothesis, which was applied to COPD related to AATD as well as COPD not related to AATD. The discovery of AATD brought recognition to the importance of elastin fibers in maintaining lung matrix structure. Two cross-linking amino acids, desmosine and isodesmosine (DI), are unique to mature elastin and can serve as biomarkers of the degradation of elastin. The intravenous augmentation treatment and lung density in severe alpha-1 antitrypsin deficiency (RAPID) study shows a correlation of an anatomic index of COPD (on CT imaging) correlating with a chemical indicator of matrix injury in COPD, DI. The results suggest that preservation of lung elastin structure may slow the progression of COPD. Hyaluronan aerosol decreases the severity of elastase-induced emphysema in animals and has induced reductions in DI levels in preliminary human studies. Hyaluronan deserves further development as a therapy for COPD.

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.

Delayed diagnosis is common in patients with pulmonary arterial hypertension (PAH). Right-sided heart catheterization, the gold standard for diagnosis, is invasive and cannot be applied for routine screening. Some biomarkers have been looked into; however, due to the lack of a clear pathological mechanism linking the marker to PAH, the search for an ideal one is still ongoing. Elastin is a significant structural constituent of blood vessels. Its synthesis involves cross-linking of monomers by 2 amino acids, desmosine and isodesmosine (D&I). Being extremely stable, elastin undergoes little metabolic turnover in healthy individuals resulting in very low levels of D&I amino acids in the human plasma, urine, or sputum. We hypothesized that in PAH patients, the elastin turnover is high; which in turn should result in elevated levels of D&I in plasma and urine. Using mass spectrometry, plasma and urine levels of D&I were measured in 20 consecutive patients with PAH confirmed by cardiac catheterization. The levels were compared with 13 healthy controls. The mean level of total plasma D&I in patients with PAH was 0.47 ng/mL and in controls was 0.19 ng/mL (P = 0.001). The mean levels of total D&I in the urine of PAH patients was 20.55 mg/g creatinine and in controls was 12.78 mg/g creatinine (P = 0.005). The mean level of free D&I in the urine of PAH patients was 10.34 mg/g creatinine and in controls was 2.52 mg/g creatinine (P < 0.001). This is the first study highlighting that the serum and urine D&I has a potential to be a novel screening biomarker for patients with PAH. It paves the way for larger studies to analyze its role in assessing for disease severity and response to treatment.

A novel therapy for COPD involving the use of aerosolized hyaluronan (HA) was tested on a small cohort of COPD patients to determine both its safety and efficacy in reducing levels of desmosine and isodesmosine (DID), biomarkers for elastin degradation. In a 2-week, randomized, double-blind trial, 8 patients receiving 150 kDa HA (mean molecular weight) and 3 others given placebo did not show significant adverse effects with regard to spirometry, electrocardiograms, and hematological indices. Furthermore, measurements of DID in plasma from HA-treated patients indicated a progressive decrease over a 3-week period following initiation of treatment (r = -0.98; p = 0.02), whereas patients receiving placebo showed no reduction in DID (r = -0.70; p = 0.30). Measurements of sputum in the HA-treated group also revealed a progressive decrease in DID (r = -0.97; p = 0.03), but this finding was limited by the absence of similar measurements in the placebo group. Nevertheless, the results of this small, pilot study support a longer-term trial of HA in a larger population of COPD patients.

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.

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.

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.

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.

BACKGROUND:Intravenous alpha-1 antitrypsin protein (AAT) augmentation is a prescribed therapy for severe, genetically determined, alpha-1 antitrypsin deficiency (AATD), a genetic basis for pulmonary emphysema. AAT, a predominant systemic inhibitor of neutrophil elastase thus far has not been shown to decrease elastin degradation in a significant number of patients on this therapy. The objective of this study was to compare levels of biomarkers of elastin degradation in plasma, bronchoalveolar lavage (BALF) fluid and urine before and after beginning AAT augmentation therapy in patients with AATD.METHODS:Desmosine and isodesmosine (DI), which occur only in elastin, are amino acid cross-links in mature elastin. Levels of DI in body fluids measure degradation of elastin and can be measured more specifically by mass spectrometry. This method was used to measure DI levels in plasma, bronchoalveolar lavage fluid and urine in cohorts of severe AATD patients on augmentation, not on augmentation and before and after the initiation of augmentation therapy.RESULTS:Statistically significant reductions in plasma DI and in BALF DI were demonstrated in AATD patients receiving intravenous (IV) augmentation therapy as compared with those not receiving it. Administration by aerosol also produced statistically significant reductions in levels of DI in BALF.CONCLUSIONS:Results indicate that the currently prescribed doses of AAT augmentation inhibit neutrophil elastase adequately to reduce elastin degradation, both systemically and in the lung per se. The currently prescribed doses did not reduce elastin degradation to control levels, which may be possible with higher doses.

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.

BACKGROUND:Tobacco smoke is a major risk factor in the development of COPD. Secondhand smoke (SHS) exposure is a known risk factor in asthma, bronchitis, and coronary artery disease. Elastin is a recognized target for injury in COPD, and the amino acids desmosine and isodesmosine (D/I), which are specific for elastin degradation, are elevated in COPD. This study determined whether exposure to SHS affects elastin degradation in asymptomatic individuals.METHODS:Two cohorts of asymptomatic individuals without evidence of respiratory or circulatory disease, exposed to SHS, were studied. Both cohorts comprised normal nonsmokers, active smokers, and those exposed to SHS. D/I were measured in plasma and quantified by high-performance liquid chromatography and tandem mass spectrometry by published methods. Plasma cotinine, a metabolite of nicotine, was also measured.RESULTS:In each cohort, the levels of D/I in plasma were statistically significantly higher in secondhand-smoke-exposed subjects than in the normal nonexposed subjects. Smokers had the highest levels of D/I but their levels were not statistically significantly higher than those of the secondhand-smoke-exposed. Cotinine levels were elevated in secondhand-smoke-exposed subjects and active smokers but not in most nonsmoking control subjects.CONCLUSIONS:Results indicate a tissue matrix effect of degradation of body elastin from SHS exposure and possible lung structure injury, which may result in COPD. Long-term studies of individuals exposed to SHS for the development of COPD are warranted.