Role of endogenous endothelin-1 in transplant obliterative airway disease in the rat

Therapeutic benefits of nitric oxide in lung transplantation

Lung transplantation is an evolutionary procedure from its experimental origin in the twentieth century and is now recognized as an established and routine life-saving intervention for a variety of end-stage pulmonary diseases refractory to medical management. Despite the success and continuous refinement in lung transplantation techniques, the widespread application of this important life-saving intervention is severely hampered by poor allograft quality offered from donors-after-brain-death. This has necessitated the use of lung allografts from donors-after-cardiac-death (DCD) as an additional source to expand the pool of donor lungs. Remarkably, the lung exhibits unique properties that may make it ideally suitable for DCD lung transplantation. However, primary graft dysfunction (PGD), allograft rejection and other post-transplant complications arising from unavoidable ischemia-reperfusion injury (IRI) of transplanted lungs, increase morbidity and mortality of lung transplant recipients annually. In the light of this, nitric oxide (NO), a selective pulmonary vasodilator, has been identified as a suitable agent that attenuates lung IRI and prevents PGD when administered directly to lung donors prior to donor lung procurement, or to recipients during and after transplantation, or administered indirectly by supplementing lung preservation solutions. This review presents a historical account of clinical lung transplantation and discusses the lung as an ideal organ for DCD. Next, the author highlights IRI and its clinical effects in lung transplantation. Finally, the author discusses preservation solutions suitable for lung transplantation, and the protective effects and mechanisms of NO in experimental and clinical lung transplantation.

Biological pathways and potential targets for prevention and therapy of chronic allograft nephropathy

Renal transplantation (RT) is the best option for patients with end-stage renal disease, but the half-life is limited to a decade due to progressive deterioration of renal function and transplant failure from chronic allograft nephropathy (CAN), which is the leading cause of transplant loss. Extensive research has been done to understand the pathogenesis, the biological pathways of fibrogenesis, and potential therapeutic targets for the prevention and treatment of CAN. Despite the advancements in the immunosuppressive agents and patient care, CAN continues to remain an unresolved problem in renal transplantation. The aim of this paper is to undertake a comprehensive review of the literature on the pathogenesis, biological pathways of RT fibrogenesis, and potential therapeutic targets for the prevention and therapy of CAN.

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 governs proliferation and migration of bronchoalveolar lavage-derived lung mesenchymal stem cells in bronchiolitis obliterans syndrome

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) has an incidence of 57% at 5 years after lung transplantation, accounts for 30% of all deaths 3 years posttransplant and because treatment options are extremely limited, it constitutes a significant health care problem. Adult mesenchymal stem cells (MSCs) play a role in lung turnover; however, their role in BOS remains unknown.

METHODS

MSCs were isolated from bronchoalveolar lavage (BAL) in 101 lung allograft recipients. BAL was screened by protein array and MSCs were analyzed by real-time polymerase chain reaction, proliferation, migration, and enzyme linked immunosorbent assays.

RESULTS

Multipotent MSCs were isolated from BAL of lung recipients independent of BOS presence. However, MSCs from BOS patients proliferated at higher rates (P<0.001) and were associated with higher α-smooth muscle actin (P = 0.03) but lower surfactant protein B (P = 0.02) compared with those from no-BOS patients. Histological analysis revealed that MSCs are abundant in lung tissue of BOS patients. MSCs from BOS patients produced higher endothelin-1 (ET-1) amounts (P<0.001) compared with those from no-BOS; and ET-1 stimulated whereas ET-1 blockade suppressed MSC proliferation, migration, and differentiation.

CONCLUSIONS

These results indicate that MSCs are associated with BOS and are governed by ET-1. Targeting MSCs by ET-1 blockade might be useful in BOS treatment.

Innate and adaptive immune responses in obliterative airway disease in rat tracheal allografts

BACKGROUND

We assessed cellular innate and adaptive immune responses in a rat heterotopic tracheal allograft model during the development of obliterative airway disease.

METHODS

Syngeneic tracheal grafts were transplanted heterotopically from DA to DA rats and fully MHC-mismatched allografts from DA to WF rats. The recipients received either no immunosuppression or two different doses of cyclosporine and were euthanized at 3, 10 and 30 days. Non-transplanted DA tracheas served as controls. Histologic, immunohistochemical and real-time RT-PCR analyses were performed.

RESULTS

The syngrafts had normal epithelium at 10 days and no tracheal occlusion was seen at 30 days. In non-immunosuppressed allografts, almost total loss of epithelium was observed at 10 days, culminating in tracheal occlusion at 30 days. The activation of innate immune response was observed during the ischemic period at 3 days in both groups. Influx of the infiltrating inflammatory cells was more prominent in the allografts. In syngrafts, mRNA expression of pro-inflammatory, but also tolerogenic, cytokines was significantly upregulated, whereas Th1 and Th17 priming factors were significantly downregulated. In allografts, prominent mRNA expression of pro-inflammatory cytokines was seen and adaptive Th1 and Th17 alloresponses were increased. Cyclosporine treatment reduced tracheal occlusion and inhibited both tolerogenic and pro-inflammatory T-cell responses in allografts.

CONCLUSIONS

Ischemia induced a self-limiting, alloantigen-independent innate immune response in syngrafts. In allografts, the predominant pro-inflammatory milieu and alloantigen-dependent Th1 and Th17 responses were linked to the development of obliterative airway disease and were inhibited by cyclosporine treatment.

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.

Concomitant endothelin-1 overexpression in lung transplant donors and recipients predicts primary graft dysfunction

Primary graft dysfunction (PGD) causes significant morbidity following lung transplantation (LTX). Mortality is high in PGD and therapeutic strategies are limited. To investigate whether endothelin-1 (ET-1) that mediates increased vascular permeability and edema formation in lung grafts can predict PGD, ET-1 mRNA expression was examined in lung tissue biopsies of 105 donors and recipients obtained shortly before LTX. Serum ET-1 concentration was assessed by ELISA. PGD grade was diagnosed and scored by oxygenation and radiological characteristics according to ISHLT guidelines. PGD grade 3 developed in 11% of patients. ET-1 mRNA expression was significantly increased in both donor (p < 0.0001) and recipient (p = 0.01) developing PGD as compared to no PGD group. Pretransplant ET-1 serum concentrations were elevated in recipients with PGD as compared to no PGD group (p < 0.0001), although serum ET-1 was not different between donors whose grafts developed PGD grades 0-3. In regression analysis, concomitant elevated donor tissue ET-1 and recipient serum ET-1 predicted PGD grade 3. This study indicates that pretransplant ET-1 mRNA overexpression in donors associated with elevated pretransplant serum ET-1 in recipients contribute to PGD development and that their assessment might be beneficial to predict PGD and to identify recipients who could benefit from a targeted ET-1 blockade.

Endothelin receptor antagonism by tezosentan attenuates lung injury induced by aortic ischemia-reperfusion

Tezosentan is a novel dual endothelin receptor antagonist. The purpose of this study was to examine the effect of tezosentan on lung injury induced by abdominal aortic ischemia-reperfusion (IR) in rats. Thirty-two Wistar-albino rats were randomized into four groups (eight per group) as follows: control group (sham laparotomy), aortic IR group (120 min ischemia and 120 min reperfusion), aortic IR + tezosentan group (a bolus intravenous injection of 10 mg/kg tezosentan before ischemia plus continuous intravenous infusion of 1 mg/kg/hr tezosentan during 120 min ischemia and 120 min reperfusion), and control + tezosentan. Blood and lung tissue samples were obtained for biochemical analysis. Protein concentrations in bronchoalveolar lavage fluid and lung wet/dry weight ratios were measured. A histological evaluation was also done. Aortic IR significantly increased (p < 0.05 vs. control group) and tezosentan significantly decreased (p < 0.05 vs. aortic IR group) the plasma level of tumor necrosis factor-alpha; lung tissue levels of malondialdehyde, catalase, and myleperoxidase; and protein concentration in bronchoalveolar lavage fluid and lung wet/dry weight ratio. Histological evaluation showed that tezosentan attenuated the morphological changes associated with lung injury. The results of this study indicate that tezosentan attenuates lung injury induced by aortic IR in rats. We propose that this protective effect of tezosentan is due to (1) reduced systemic inflammatory response, (2) reduced oxidative stress and lipid peroxidation in lung tissue, (3) reduced pulmonary microvascular leakage, and (4) inhibition of leukocyte infiltration into lung tissue.

Ganciclovir for cytomegalovirus: a call for indefinite prophylaxis in lung transplantation

BACKGROUND

Universal ganciclovir (GCV) prophylaxis is a strategy aimed at reducing cytomegalovirus (CMV) infection and delaying the development of bronchiolitis obliterans syndrome (BOS). However, the optimal duration of GCV prophylaxis remains unclear. We report our experience with GCV prophylaxis administered indefinitely and its effect on CMV pneumonitis, BOS and survival after lung transplantation (LT).

METHODS

One hundred fifty-one patients surviving >100 days after LT were analyzed. GCV was given to 130 CMV donor- or recipient-seropositive patients. Data from 90 patients who received indefinite GCV prophylaxis (IND) and 40 patients who discontinued their GCV prophylaxis (STOP) were compared.

RESULTS

CMV pneumonitis occurred in 16%, 8%, 17% and 19% of patients in the D+R+, D-R+, D+R- and D-R- groups, respectively. In the STOP cohort, 15 of 40 patients developed CMV pneumonitis (median time 79 days) after GCV was stopped. Ten of these 15 patients developed BOS (median time 116 days) after discontinuing GCV. The risk of CMV pneumonitis in the STOP cohort was significantly higher when GCV prophylaxis was discontinued within the first year. Cumulative incidence of CMV pneumonitis in the IND and STOP groups at 5 years was 2% and 57%, respectively (p < 0.001). BOS-free survival and survival were similar across both groups.

CONCLUSIONS

Indefinite GCV prophylaxis prevents CMV pneumonitis in 98% of LT recipients. Thirty-eight percent of patients discontinuing prophylaxis developed CMV pneumonitis, 50% of whom progressed to BOS within 1 year. Continuing ganciclovir prophylaxis indefinitely after lung transplantation should be considered.

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.

Late kidney allograft loss: what we know about it, and what we can do about it

Despite dramatic improvements in immunosuppression, late graft loss after kidney transplantation remains a common and difficult problem. Histologic evaluation may reveal changes related to BK polyomavirus infection, hypertension, or calcineurin inhibitor toxicity, which can help to guide therapy. The designation chronic allograft nephropathy should thus be reserved for biopsies with tubular atrophy and interstitial fibrosis without an apparent cause. Although the cause clearly includes both antigen-dependent and antigen-independent events, the approach remains largely to exclude immune mechanisms. Although this review discusses the potential contribution of antibody to chronic injury, it focuses on the basic elements of kidney injury, the role of parenchymal cells in promoting injury, and the proliferative and inflammatory responses that accompanying injury. Strategies to manage these recipients include close attention to accompanying hypertension, diabetes, and hyperlipidemia, as well as consideration for altering immunosuppression; however, therapies that limit epithelial-to-mesenchymal transition or directly block fibrosis pathways may reduce chronic allograft fibrosis and may prove to be useful. Understanding the basic pathogenesis sufficiently to allow early intervention may finally benefit patients who are at high risk for tubular atrophy and interstitial fibrosis and promote their long-term graft function.

Therapeutic targets in the treatment of allograft fibrosis

The dramatic improvements in short-term graft survival and acute rejection rates could only have been dreamed of 20 years ago. Late graft loss following kidney transplantation is now the critical issue of this decade. Frequently, graft loss is associated with the development of tubular atrophy and interstitial fibrosis within the kidney (i.e. chronic allograft nephropathy; CAN). Major treatment strategies in this disorder are non-specific and the focus of intervention has been on limiting injurious events. Following graft injury is a fibrogenesis phase featuring both proliferative and infiltrative responses mediated by chemokines, cytokines and growth factors. In particular, TGFbeta has been strongly implicated in the pathogenesis of chronic injury and epithelial-mesenchymal transformation (EMT) may be part of this process. The cascade of events results in matrix accumulation, due to either increased production and/or reduced degradation of matrix. Recent investigations into the pathogenesis of tissue fibrosis have suggested a number of new strategies to ameliorate matrix synthesis. While the majority of therapies have focused on TGFbeta, this may not be an ideal maneuver in transplant settings and alternative targets identified in other fibrotic diseases will be discussed. Attacking graft fibrosis should be a new focus in organ transplantation.

Effects of olmesartan medoxomil as an angiotensin II-receptor blocker in chronic hypoxic rats

We established a rat chronic alveolar hypoxia in vivo model to evaluate the efficacy against hypoxic pulmonary hypertension of a new angiotensin II-receptor I blocker, olmesartan medoxomil. Three groups of rats were established: rats exposed for 2-6 weeks to 10% oxygen atmosphere in a normobaric chamber; hypoxic rats treated with olmesartan medoxomil oral administration (5 mg/day) every day; and control rats fed in a normoxic condition. After hypoxia treatment, the presence, etiology and severity of pulmonary hypertension, was echocardiographically evaluated, and expressions of brain natriuretic peptide (BNP), transforming growth factor (TGF-beta) and endothelin-1 genes measured by both immunohistochemical assay and real-time polymerase chain reaction. Olmesartan medoxomil significantly reduced the induction of hypoxic cor pulmonale not only on echocardiographical observations but also in BNP, TGF-beta and endothelin gene expressions in molecular studies. However, systolic blood pressure was independent of olmesartan medoxomil. The present study clearly indicates that the angiotensin II-type I-receptor blocker olmesartan medoxomil has significant efficacy for hypoxic cor pulmonale.