Tuberculous pericarditis, a form of extra-pulmonary tuberculosis (TB) leads to a life threatening form of fibrosis, constrictive pericarditis, in 30-60% of patients despite therapy. There are currently no effective predictors and prophylactics for the condition. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), an antifibrotic peptide, made by prolyl oligopeptidase (POP) and degraded by angiotensin converting enzyme (ACE), and the pro-fibrotic Galectin-3 have been detected in pericardial fluid.
We investigated the role of Ac-SDKP, ACE and Galectin-3 in the pathophysiology of TB pericarditis and the in vitro effects of Ac-SDKP, its peptide sequences and ACE inhibitors lisinopril and RXP407 on the prevention of fibrosis.
Ac-SDKP and Galectin-3 levels in pericardial fluid from TB pericarditis cases were compared to control samples by ELISA whilst the enzymatic activities of ACE and POP in TB pericardial fluid were measured by fluorogenic assays. The effects of Ac-SDKP, fragment peptides (Ac-SDK, Ac-DKP, SDK and DKP), and ACE inhibitors, on the prevention of fibrosis in a CT-1 cell line, were quantified by a hydroxyproline assay. HPLC analysis was used for assessing the cleavage of Ac-SDKP peptides by ACE.
Levels of Ac-SDKP in participants with TB pericarditis were significantly lower (p=0.04) than in controls without pericardial disease. Further a mild upregulation in Galectin-3 levels and ACE activities could be measured in tuberculous pericardial fluid. Further, Ac-SDKP alone and in combination with the ACE inhibitors reversed the effect of AngII on collagen formation in the fibroblasts. The Ac-DKP sequence was cleaved by ACE whilst the SDK, DKP and Ac-DKP fragments resisted ACE degradation.
We show here decreased levels of Ac-SDKP in TB pericarditis, possibly from an upregulation of ACE in pericardial fluid. A definite implication of altered Ac-SDKP homeostasis in TB pericarditis would constitute a strong rationale for the implementation of ACE inhibitors, specifically of N-domain selective inhibitors, in the management of the disease.