The purpose of this study was to determine whether
26S proteasome is detectable in human bronchoalveolar lavage fluid (BALF) and whether
burn and inhalation injury is accompanied by changes in BALF
proteasome content or activity. BALF was obtained on hospital admission from 28 patients with
burn and inhalation injury (controls: 10 healthy volunteers).
Proteasome concentrations were quantified by
enzyme-linked
immunosorbent assay, and their native molecular mass was assessed by gel filtration.
Proteasome peptidase activity was measured using a chymotryptic-like
peptide substrate in combination with
epoxomicin (specific
proteasome inhibitor). BALF
protein was increased in patients (P<.001) and correlated positively with the degree of inhalation injury. The 20S/26S proteasomes were detectable in all BALF by
enzyme-linked
immunosorbent assay. Gel filtration confirmed the presence of intact 20S and
26S proteasome that was stable without soluble
ATP/Mg. In all BALF chymotryptic-like activity was detectable and could be inhibited with
epoxomicin by 60 to 70% (P<.01). Absolute amounts of 20S/26S proteasomes and
proteasome activity were increased in patients (P<.001 for all). The relative BALF composition after injury was characterized by increased concentrations of
20S proteasome/mg
protein (P=.0034 vs volunteers), decreased concentrations of
26S proteasome/mg
protein (P=.041 vs volunteers), and reduced specific
proteasome activity (P=.044 vs volunteers). The
26S proteasome per milligram and specific
proteasome activity were even further reduced in patients who developed
ventilator-associated pneumonia (P=.045 and P=.03 vs patients without
ventilator-associated pneumonia). This study supports the novel concept that extracellular proteasomes could play a pathophysiological role in the injured lung and suggests that insufficient
proteasome function may increase susceptibility for pulmonary complications.