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.
Keywords: COPD; Desmosine; Elastin; Emphysema; Lung.