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Background: Bronchiolitis obliterans syndrome (BOS), the major cause of death on lung transplantation, is characterized by bronchiolar inflammation and tissue remodeling. Matrix metalloproteinases (MMPs) have been implicated in these processes, although it is still unclear whether MMP activity and binding to their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMPs), is abnormal in BOS., Methods: We studied total MMP-1,-2,-3,-7,-8,-9,-12,-13 levels, their activity state using activity-based extraction and their binding to TIMP-1, -2, -3, and -4 in bronchoalveolar lavage (BAL) of lung transplant recipients with good outcome and BOS using a multiplex immunoassay., Results: The BAL levels of TIMP-1 and -2 and MMP-2, -3, -7, -8, and -9 were significantly increased in BOS compared to good outcome recipients. Interestingly, activity of MMP-7, but none of the other MMPs, was detected in good outcome recipients, whereas no active MMPs were observed in BOS recipients. However, BAL levels of TIMP-bound MMP-8 and -9 were higher in BOS than in good outcome recipients, suggesting activity of these MMPs in an earlier stage., Conclusions: We demonstrate that development of BOS is associated with increased levels of TIMP-1 and -2 and total MMP-2, -3, -7, -8, and -9. Although active MMP-7 was only observed in good outcome recipients, levels of TIMP-bound MMP-8 and -9 were higher in BOS. By enabling profiling of active and TIMP-bound MMPs, our novel method may open opportunities for the screening of early predictors for BOS.

Obliterative bronchiolitis after lung transplantation is a chronic inflammatory and fibrotic condition of small airways. The fibrosis associated with obliterative bronchiolitis might be reversible. Matrix metalloproteinases (MMPs) participate in inflammation and tissue remodeling. MMP-2 localized to myofibroblasts in post-transplant human obliterative bronchiolitis lesions and to allograft fibrosis in a rat intrapulmonary tracheal transplant model. Small numbers of infiltrating T cells were also observed within the fibrosis. To modulate inflammation and tissue remodeling, the broad-spectrum MMP inhibitor SC080 was administered after the allograft was obliterated, starting at post-transplant day 21. The allograft lumen remained obliterated after treatment. Only low-dose (2.5 mg/kg per day) SC080 significantly reduced collagen deposition, reduced the number of myofibroblasts and the infiltration of T cells in association with increased collagenolytic activity, increased MMP-2 gene expression, and decreased MMP-8, MMP-9, and MMP-13 gene expression. In in vitro experiments using cultured myofibroblasts, a relatively low concentration of SC080 increased MMP-2 activity and degradation of type I collagen. Moreover, coculture with T cells facilitated persistence of myofibroblasts, suggesting a role for T-cell infiltration in myofibroblast persistence in fibrosis. By combining low-dose SC080 with cyclosporine in vivo at post-transplant day 28, partial reversal of obliterative fibrosis was observed at day 42. Thus, modulating MMP activity might reverse established allograft airway fibrosis by regulating inflammation and tissue remodeling., (Copyright © 2011 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Obliterative bronchiolitis (OB) is thought to be a form of chronic allograft rejection. However, immunosuppressive therapy is not effective once fibrosis has developed. We hypothesize that disordered tissue remodeling is a mechanism for the pathogenesis of OB. We examined allograft airway fibrosis in an intrapulmonary tracheal transplant model of OB. Allograft airways were completely obliterated at day 21 by fibrotic tissue; however, tissue remodeling continued thereafter, as demonstrated by the change of collagen deposition density, shift from type I to type III collagen, shift from fibroblasts to myofibroblasts and shift of expression profiles and activities of matrix metalloproteinases (MMPs). We then used a broad-spectrum MMP inhibitor, SC080, to attempt to manipulate tissue remodeling. Administration of the MMP inhibitor from day 0 to day 28 reduced airway obliteration, without inhibiting T-cell activation. MMP inhibition from day 14 to day 28 showed similar effects on airway obliteration. MMP inhibition from day 21 to day 35 did not reverse the airway obliteration, but significantly reduced the collagen deposition, type III collagen and myofibroblasts in the lumen. We conclude that tissue remodeling plays a critical role in the development and maintenance of fibrosis after transplantation.

Bronchiolitis obliterans (BO) is a survival-limiting factor in lung transplantation. There are no common BO markers in use. Since BO is associated with extracellular matrix remodeling, we asked whether matrix metalloproteases (MMPs) and their tissue inhibitors (TIMPs) could serve as BO markers. In 72 lung transplant patients (34 BO syndrome (BOS) 0, 15 BOS 0-p, and 23 BOS 1) serum and broncho-alveolar lavage (BAL) MMP and TIMP levels were examined by ELISA. The BAL cell counts were additionally analyzed. The serum MMP-2, MMP-8, MMP-9 and TIMP-2 levels were not different in all groups. In contrast, the BAL MMP-8, -9 and TIMP-1 levels were significantly elevated in BOS 0-p (p = 0.003; p = 0.007; p = 0.0003, respectively) and BOS 1 (p = 0.003; p = 0.001; p = 0.0004, respectively) as compared to BOS 0 patients. The BAL MMP-8, -9 and TIMP-1 levels were significant predictors of BOS 0-p (p = 0.01; p = 0.01; p = 0.01, respectively) and BOS-1 (p = 0.007; p = 0.01; p = 0.006, respectively) in receiver operating characteristic analysis. Except for BAL macrophages that were significantly decreased in BOS 0-p versus BOS 0 patients; other cell counts were not different between the groups. BAL MMP-8, -9 and TIMP-1 might be useful markers to detect BO in lung transplant patients.