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Carboxypeptidase M activity is increased in bronchoalveolar lavage in human lung disease
T Dragović1, D E Schraufnagel, R P Becker
1Department of Pharmacology, University of Illinois College of Medicine, Chicago, USA.
Abstract:
Carboxypeptidase M (CPM) cleaves the C-terminal arginine and lysine of peptides; it is expressed in the lung, especially on the plasma membrane of alveolar type I cells. Here, we report on CPM in human bronchoalveolar lavage (BAL) collected from 69 patients and analyzed for activity, cell number and type, and protein level. Seventy-six percent of CPM activity, measured at pH 7.5 with 5-dimethylamino-naphthalene-1-sulfonyl-alanyl-arginine (Dansyl-Ala-Arg) substrate, was immunoprecipitated with polyclonal antibody to purified human enzyme. In patients without active lung disease, CPM activity in BAL was 7.69 (+/- 2.12) nmol/h/mg protein, but in patients with acute pneumonia, it was 29.25 (+/- 4.06) (p < 0.01). In patients with Pneumocystis carinii pneumonia, CPM activity was elevated to 26.00 (+/- 4.85) (p < 0.01) and in patients with lung cancer, to 30.95 (+/- 4.12) (p < 0.01). The activity was not associated with the cellular elements of BAL. The highest specific activity was in the large aggregate fraction of surfactant, which also contained the highest concentration of phosphorus. Transmission electron microscopy of this fraction revealed the presence of typical lamellar bodies and tubular myelin structures. The high CPM activity may stem from its induction and release in acute lung disease. In addition, CPM may be a marker of infection with certain pathogens and an indicator of type I cell injury in parenchymal lung diseases.
Insights
Carboxypeptidase M (CPM) levels significantly increase in bronchoalveolar lavage fluid during acute lung diseases like pneumonia and lung cancer. This enzyme may serve as a biomarker for lung injury and infection.
Area of Science:
- Biochemistry
- Pulmonary Medicine
- Cell Biology
Background:
- Carboxypeptidase M (CPM) is an enzyme that cleaves specific amino acids from peptides.
- CPM is notably expressed in the lung, particularly on alveolar type I cells.
Purpose of the Study:
- To investigate the presence and activity of CPM in human bronchoalveolar lavage (BAL) fluid.
- To determine if CPM levels correlate with different lung conditions and cellular components in BAL.
Main Methods:
- Analysis of CPM activity, cell counts, cell types, and protein levels in BAL from 69 patients.
- Measurement of CPM activity using a specific substrate (Dansyl-Ala-Arg) at pH 7.5.
- Immunoprecipitation to confirm antibody specificity for human CPM.
- Transmission electron microscopy of surfactant fractions.
Main Results:
- Seventy-six percent of CPM activity was confirmed by immunoprecipitation.
- CPM activity was significantly elevated in patients with acute pneumonia, Pneumocystis carinii pneumonia, and lung cancer compared to healthy individuals.
- CPM activity did not correlate with cellular elements in BAL.
- Highest specific CPM activity was found in the surfactant large aggregate fraction, containing lamellar bodies and tubular myelin.
Conclusions:
- Elevated CPM activity in BAL suggests its induction and release during acute lung diseases.
- CPM may function as a biomarker for certain lung infections and indicate type I cell injury in parenchymal lung diseases.