Thrombin contributes to bronchoalveolar lavage fluid mitogenicity in lung disease of the premature infant
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Willem A Dik1, Luc J I Zimmermann, Brigitta A Naber
1Department of Immunology, Erasmus MC, Rotterdam, The Netherlands. dik@immu.fgg.eur.nl
Insights
Thrombin is a key factor in lung fibroblast proliferation in premature infants with chronic lung disease (CLD) and respiratory distress syndrome (RDS). Early lung injury involves thrombin, suggesting potential therapeutic targets for CLD prevention.
Area of Science:
- Neonatology
- Pulmonology
- Cell Biology
Background:
- Chronic lung disease of prematurity (CLD) involves pulmonary fibrosis, potentially linked to increased thrombin activity.
- Thrombin in bronchoalveolar lavage (BAL) fluid may stimulate fibroblast proliferation, a key process in fibrosis.
Purpose of the Study:
- To investigate if BAL fluid from infants developing CLD has higher mitogenic activity for lung fibroblasts than from infants with resolving respiratory distress syndrome (RDS).
- To determine the contribution of thrombin to this mitogenic activity.
Main Methods:
- Sequential BAL fluid collection from 37 premature infants with RDS (26 developing CLD, 11 resolving).
- Assessing BAL fluid mitogenic activity using human fetal lung fibroblast proliferation assays.
- Evaluating thrombin's role with the inhibitor PPACK and measuring thrombin activity and thrombin-antithrombin III complex (TATIII) levels.
Main Results:
- BAL fluid mitogenic activity was similar between CLD and resolving RDS groups.
- Thrombin inhibition significantly reduced mitogenic activity in early BAL samples (days 2-4).
- Thrombin activity and TATIII levels were unexpectedly lower in CLD infants on days 2 and 4.
Conclusions:
- BAL fluid from premature infants, with or without CLD development, exhibits significant mitogenic activity for lung fibroblasts.
- Thrombin is a major contributor to this early mitogenic activity, suggesting its role in fibroproliferation in both CLD and RDS.
- Other mitogenic factors also contribute to CLD development beyond early stages.
Abstract:
Chronic lung disease of prematurity (CLD) is a common consequence of neonatal respiratory distress syndrome (RDS) and is characterized by pulmonary fibrosis. Increased thrombin activity in the alveolar compartment is associated with pulmonary fibrosis in adults and animals, and contributes to bronchoalveolar lavage (BAL) fluid mitogenicity for fibroblasts. We hypothesized that BAL fluid from infants who develop CLD contains increased mitogenic activity for lung fibroblasts compared to BAL fluid from resolving RDS, and that increased thrombin levels contribute to this activity. Sequential BAL (postnatal days 2-14) was obtained from 37 premature infants who were ventilated for RDS. Twenty-six infants developed CLD, whereas 11 resolved. BAL fluid mitogenic activity was determined in a proliferation assay, using human fetal lung fibroblasts. The contribution of thrombin to mitogenic activity was determined using the thrombin inhibitor PPACK. Furthermore, thrombin levels in BAL fluid were measured using a specific substrate to detect thrombin activity and by measuring thrombin-antithrombin III complex (TATIII). BAL fluid mitogenic activity was comparable between CLD and RDS (CLD, 33% proliferation on day 2 to 41% on day 14; RDS, 21% on day 2 to 54% on day 7). Thrombin inactivation by PPACK completely inhibited mitogenic activity in BAL samples obtained on days 2 and 4 (CLD, P < 0.001 on days 2 and 4; RDS, P < 0.05 on day 4). From day 7 onwards, inhibition of thrombin only partly reduced (P < 0.05) CLD BAL fluid mitogenic activity, indicating that other mitogenic factors contribute as well. Surprisingly, thrombin activity and TATIII were decreased in BAL fluid from CLD compared with RDS patients on days 2 and 4. In conclusion, our study shows that BAL fluid from infants with and without CLD development is equally mitogenic for lung fibroblasts, and that thrombin is a major mitogen in these samples. This suggests that fibroproliferation may occur early in the lungs from infants with both CLD and RDS, and that thrombin contributes to this.
