Effects of Blockade of the Renin–Angiotensin and Endothelin Systems on Experimental Bronchiolitis Obliterans

Angiotensin receptors as sensitive markers of acute bronchiole injury after lung transplantation

BACKGROUND

Although lung transplantation is the only means of survival for patients with end-stage pulmonary disease, outcomes from this intervention are inferior to other solid organ transplants. The reason for the poor outcomes may be linked to an early reaction, such as primary graft dysfunction, and associated with marked inflammatory response, bronchiole injury, and later fibrotic responses. Mediators regulating these effects include angiotensin II and matrix metalloproteinases (MMPs).

METHODS

We investigated changes to these mediators over the course of cardiopulmonary bypass (CPB) and up to 72 h after lung transplantation, using immunohistochemistry, Western blot, and ELISA techniques.

RESULTS

We found 4- and 16-fold increases in plasma angiotensin II and MMP-9, respectively, from pre-CPB to post-CPB. MMP-9 levels remained elevated 1 h after transplantation. MMP-2 levels were elevated 6-24 h after lung transplantation. Type 2 angiotensin II receptor (ATR2) expression was 3.5-fold higher in bronchoalveolar cells 1-6 h after transplantation than in controls.

CONCLUSIONS

The study suggests that the combination of cardiopulmonary bypass and lung transplantation is associated with early changes in the angiotensin II receptor system and in MMPs, and that altered expression of these mediators may be a useful marker to examine pathological changes that occur in lungs during transplant surgery.

The pathophysiology of endothelin in complications after solid organ transplantation: a potential novel therapeutic role for endothelin receptor antagonists

Although short-term allograft survival after solid organ transplantation has improved during the past two decades, improvement in long-term graft survival has been less pronounced. Common complications after transplantation include chronic allograft rejection, nephrotoxicity from calcineurin inhibitors (CNIs), and systemic hypertension, which all impact posttransplantation morbidity and mortality. Endothelin (ET)-1, a potent endogenous vasoconstrictor, inducer of fibrosis, and vascular smooth muscle cell proliferation, may play a key role in both the development of CNI-induced nephrotoxicity and endothelial vasculopathy in chronic allograft rejection. ET-1 levels increase after isograft implantation, and ET-1 plays a key role in CNI-induced renal vasoconstriction, sodium retention, and hypertension. Preclinical studies have demonstrated that endothelin receptor antagonists (ERAs) can reduce or prevent CNI-induced hypertension after renal transplantation. In addition, ERAs can ameliorate CNI-induced renal vasoconstriction and improve proteinuria and preserve renal function in animal models of renal transplantation. ET-1 may also play a significant role in cardiac allograft vasculopathy, and in animal models, ERAs improve pulmonary function and ischemic-reperfusion injury in lung transplantation and hepatic function and structure in liver transplantation. Emerging pharmacokinetic data suggest that the selective ERA ambrisentan may be used safely in conjunction with the most commonly used immunosuppressive agents tacrolimus and mycophenolate, albeit with appropriate dose adjustment. The weight of available evidence pointing toward a potential beneficial role of ERAs in ameliorating common complications after solid organ transplantation must be balanced with potential toxicities of ERAs but suggests that a randomized clinical trial of ERAs in transplant patients is warranted.

Pulmonary hypertension before first and second lung transplantation

BACKGROUND

Pulmonary hypertension (PH) is frequently encountered in patients with advanced lung disease before the first and second lung transplantation. We sought to determine whether there is any relationship between pulmonary hemodynamics obtained before first and second lung transplantation. We also assessed whether PH has prognostic implications in lung transplant patients going for second transplantation.

METHODS

We included consecutive adult (16-yr-old or older) patients who underwent lung re-transplantation, between 1997 and 2009, and had right heart catheterization before their first and second lung transplantation.

RESULTS

Eighteen patients were included in the study. Age at first transplantation was 50.4 (SD 10.4) yr, and bronchiolitis obliterans syndrome (BOS) in the transplanted lung was the only indication for re-transplantation. PH was observed in 39% of the patients before the first lung transplant and in 56% of the subjects before re-transplantation (p = 0.91). Pre-capillary PH was present in 28% (n = 5) and 33% (n = 6) of the patients before first and second lung transplantation, respectively. None of the hemodynamic variables obtained before the first transplant predicted the development of PH before re-transplantation. PH before re-transplantation did not predict survival or development of BOS after re-transplantation.

CONCLUSIONS

PH before initial lung transplantation did not predict the development of PH before the second transplantation. In our cohort, PH before second lung transplantation did not predict outcomes after re-transplantation.

Endothelin-1 is a useful biomarker for early detection of bronchiolitis obliterans in lung transplant recipients

OBJECTIVES

Bronchiolitis obliterans (BO) is a severe complication limiting long-term survival after lung transplantation. To date, no cure exists for BO, and the mechanisms leading to BO are not well understood. Endothelin-1 (ET-1) is a potent mitogenic and profibrotic peptide produced by pulmonary vascular endothelial cells that play a role in the pathophysiology of lung allograft dysfunction. Whether ET-1 could predict BO syndrome (BOS) development is unknown.

METHODS

Transbronchial biopsy specimens and serum and bronchoalveolar lavage were obtained from 30 lung transplantation patients with and 30 without BOS at 3 points. The serum and bronchoalveolar lavage ET-1 concentrations were measured by enzyme-linked immunosorbent assay, and the ET-1 mRNA expression in the transbronchial biopsy specimens was examined using real-time polymerase chain reaction.

RESULTS

The pretransplant ET-1 serum concentrations were greater in the patients with BOS (P = .02); and ET-1 mRNA was significantly upregulated in the lung grafts of those with versus those without BOS at 3 and 12 months after transplant (P = .01). At 3 and 12 months after transplantation, the ET-1 concentrations were significantly elevated in the serum (P < .01 and P < .0001, respectively) and bronchoalveolar lavage (P < .01 and P = .02, respectively) of patients with compared with those without BOS. On logistic regression analysis, the pretransplant and 3-month post-transplant serum ET-1 level predicted for BOS (odds ratio, 1.01; 95% confidence interval, 1.004-1.025; P < .007; odds ratio, 2.9; 95% confidence interval, 1.01-8.52; P < .001). The serum ET-1 level at 12 months was diagnostic for BOS (odds ratio, 3.9; 95% confidence interval, 1.42-10.80; P = .008).

CONCLUSIONS

Elevated serum ET-1 concentrations were predictive of BOS, and the assessment of circulating ET-1 might be beneficial in diagnosing and monitoring BO.

Endothelin receptor antagonist and airway dysfunction in pulmonary arterial hypertension

BACKGROUND

In idiopathic pulmonary arterial hypertension (IPAH), peripheral airway obstruction is frequent. This is partially attributed to the mediator dysbalance, particularly an excess of endothelin-1 (ET-1), to increased pulmonary vascular and airway tonus and to local inflammation. Bosentan (ET-1 receptor antagonist) improves pulmonary hemodynamics, exercise limitation, and disease severity in IPAH. We hypothesized that bosentan might affect airway obstruction.

METHODS

In 32 IPAH-patients (19 female, WHO functional class II (n = 10), III (n = 22); (data presented as mean +/- standard deviation) pulmonary vascular resistance (11 +/- 5 Wood units), lung function, 6 minute walk test (6-MWT; 364 +/- 363.7 (range 179.0-627.0) m), systolic pulmonary artery pressure, sPAP, 79 +/- 19 mmHg), and NT-proBNP serum levels (1427 +/- 2162.7 (range 59.3-10342.0) ng/L) were measured at baseline, after 3 and 12 months of oral bosentan (125 mg twice per day).

RESULTS AND DISCUSSION

At baseline, maximal expiratory flow at 50 and 25% vital capacity were reduced to 65 +/- 25 and 45 +/- 24% predicted. Total lung capacity was 95.6 +/- 12.5% predicted and residual volume was 109 +/- 21.4% predicted. During 3 and 12 months of treatment, 6-MWT increased by 32 +/- 19 and 53 +/- 69 m, respectively; p < 0.01; whereas sPAP decreased by 7 +/- 14 and 10 +/- 19 mmHg, respectively; p < 0.05. NT-proBNP serum levels tended to be reduced by 123 +/- 327 and by 529 +/- 1942 ng/L; p = 0.11). There was no difference in expiratory flows or lung volumes during 3 and 12 months.

CONCLUSION

This study gives first evidence in IPAH, that during long-term bosentan, improvement of hemodynamics, functional parameters or serum biomarker occur independently from persisting peripheral airway obstruction.

Late treatment with angiotensin-converting enzyme inhibitors plus endothelin receptor antagonists ameliorates rat tracheal allograft rejection

Inhibition of the renin-angiotensin and endothelin (ET) systems prevents the development of obliterative airway disease (OAD) in rat tracheal allografts. In this study, we assessed whether these therapeutic approaches are effective even when the same were started after signs of OAD were already manifest. Rat tracheas were heterotopically transplanted from Brown-Norway donors into Brown-Norway or Lewis recipients. Allograft recipients received bosentan, ramipril, bosentan plus ramipril or vehicle from day 10 to 24. Untreated allografts and isografts were harvested at day 10 or 24. In tracheal grafts, morphometric studies together with molecular analysis by real-time PCR were performed. Fibroproliferative process in untreated tracheal allografts but not in isografts started already at day 10. Neither bosentan nor ramipril treatment alone as monotherapy could modify the development of OAD when administered only between day 10 and day 24. By contrast, the combination treatment of bosentan and ramipril ameliorated airway obstruction by day 24, which was accompanied by reduced mRNA expression of intragraft transforming growth factor-beta1 and platelet-derived growth factor-A and -B chains. Only the combined blockade with angiotensin-converting enzyme inhibitors and ET receptor antagonists can reduce the progression of OAD in this model if the treatment is initiated late in the disease course.