Accumulation of hyaluronan (hyaluronic acid) in the lung in adult respiratory distress syndrome.

The concentrations of hyaluronan (HA) were measured in bronchoalveolar lavage (BAL) fluid and serum from 12 patients with adult respiratory distress syndrome (ARDS). The median BAL fluid HA concentration was 353 micrograms/L, about six times higher than that seen in control patients (p less than 0.001). The median serum HA value was 619 micrograms/L, which was a 30-fold increase compared with that in the control patients (p less than 0.001). Another connective tissue component, type III procollagen peptide, was not recovered in significant amounts during lavage in patients with ARDS, but it appeared in the bloodstream in increased concentrations (p less than 0.001). Obtained recovery of HA during lavage of patients with ARDS cannot be explained by an enhanced passive leakage from the bloodstream because of increased alveolar-capillary permeability, but rather could reflect a mobilization of HA from lung interstitial tissue because of hydrostatic mechanisms. Alternatively, the appearance of HA in the alveolar space in ARDS might reflect an enhanced lung synthesis of HA. An increased HA production can possibly be mediated, directly or indirectly, by activated complement components, since a significant relationship was seen between increased plasma concentrations of C3a des Arg and BAL fluid HA (r = 0.61; p less than 0.05). The observed accumulation of HA in the small airways in ARDS may be expected to immobilize water and thereby contribute to the interstitial and alveolar edema. The inverse correlation (r = 0.71; p less than 0.01) seen between BAL fluid HA and pulmonary oxygenation index (PaO2/inspired oxygen fraction) supports such a hypothesis.