Decreased lung hyaluronan in a model of ARDS in the rat: effect of an inhibitor of leukocyte elastase

Abstract

Background: Hyaluronan (HA) is a component of the extracellular matrix in lung tissue and is normally present at low concentrations in blood. HA is rapidly cleared from blood by the liver. Increased concentrations of plasma HA have been found in patients with acute respiratory distress syndrome (ARDS). We investigated changes in HA levels in plasma, bronchoalveolar lavage fluid (BALF), and lung, and their relationship to pretreatment with a leukocyte elastase inhibitor in a rat model of ARDS.

Methods: Rats were randomly assigned to three groups: control, thrombin, and thrombin plus elastase inhibitor. By use of a radiometric assay, HA was measured in lungs, BALF, and plasma. Tissue samples from the lungs were stained for HA and examined microscopically. Liver circulation and cardiac output were monitored using radiolabeled microspheres.

Results: Infusion of thrombin produced a pronounced increase in wet weight to dry weight ratio, and relative lung water content. This increase was blunted by a leukocyte elastase inhibitor. A decrease in lung HA and increases in both BALF and plasma HA were found. The leukocyte elastase inhibitor counteracted not only the decrease in lung tissue HA, but also the increase in plasma HA. Histologically, there was decreased HA-staining of peribronchial and perivascular areas in the injured rat lung. Decreased liver perfusion was observed after infusion of thrombin.

Conclusions: The decrease in lung HA may be involved in the development of pulmonary edema in this ARDS model, and leukocyte elastase may be one cause of this decrease. In addition, an elevated plasma HA level may be an indicator of lung injury.

Figure 1.

Experimental protocol.

Figure 2.

A: Staining of lung sections with biotin-avidin-hyaluronan-binding protein in a control rat. The red area represents hyaluronan-specific staining. The arrow indicates the intense staining of the perivascular and peribronchiolar space. The section was counterstained with hematoxylin (×140). B: Staining of lung sections with biotin-avidin-hyaluronan-binding protein in a representative rat with thrombin-induced pulmonary injury. The red area represents hyaluronan-specific staining. The arrow indicates the weaker staining of hyaluronan in the perivascular and peribronchiolar space. The section was counterstained with hematoxylin (×140). (PA = pulmonary artery; Br = bronchus.)

Figure 3.

A: Cardiac output (CO; mL/min/kg B.W.) before (0) and 10, 30, 60, and 90 min after the end of thrombin (Thr) infusion in six rats with thrombin-induced pulmonary injury. Data are expressed as mean ± SEM. Baseline (0 min) represents steady-state values before thrombin infusion. ** P < 0.01 compared to the baseline values in CO. *** P < 0.001 compared to the baseline values in CO. † P < 0.05 compared to CO measured at 60 min after thrombin infusion. B: Liver blood flow (LBF; mL/min/kg liver) before (0) and 10, 30, 60, and 90 min after the end of thrombin (Thr) infusion in eight rats with thrombin-induced pulmonary injury. Data are expressed as mean ± SEM. Baseline (0 min) represents steady-state values before thrombin infusion. ** P < 0.01 compared to the baseline values in LBF. † P < 0.05 compared to LBF measured at 60 min after thrombin infusion.