Gabriel T. Schnickel

A prospective, randomized, crossover pilot study of inhaled nitric oxide versus inhaled prostacyclin in heart transplant and lung transplant recipients

OBJECTIVE Inhaled nitric oxide has been shown to reduce pulmonary vascular resistance in patients undergoing cardiothoracic surgery, but it is limited by toxicity, the need for special monitoring, and cost. Inhaled prostacyclin also decreases pulmonary artery pressure, is relatively free of toxicity, requires no specific monitoring, and is less expensive. The objective of this study was to compare nitric oxide and prostacyclin in the treatment of pulmonary hypertension, refractory hypoxemia, and right ventricular dysfunction in thoracic transplant recipients in a prospective, randomized, crossover pilot trial. METHODS Heart transplant and lung transplant recipients were randomized to nitric oxide or prostacyclin as initial treatment, followed by a crossover to the other agent after 6 hours. Pulmonary vasodilators were initiated in the operating room for pulmonary hypertension, refractory hypoxemia, or right ventricular dysfunction. Nitric oxide was administered at 20 ppm, and prostacyclin was administered at 20,000 ng/mL. Hemodynamic and oxygenation parameters were recorded before and after initiation of pulmonary vasodilator therapy. At 6 hours, the hemodynamic and oxygenation parameters were recorded again, just before discontinuing the initial agent. Crossover baseline parameters were measured 30 minutes after the initial agent had been stopped. The crossover agent was then started, and the hemodynamic and oxygenation parameters were measured again 30 minutes later. RESULTS Heart transplant and lung transplant recipients (n = 25) were randomized by initial treatment (nitric oxide, n = 14; prostacyclin, n = 11). Nitric oxide and prostacyclin both reduced pulmonary artery pressure and central venous pressure, and improved cardiac index and mixed venous oxygen saturation on initiation of therapy. More importantly, at the 6-hour crossover trial, there were no significant differences between nitric oxide and prostacyclin in the reduction of pulmonary artery pressures or central venous pressure, or in improvement in cardiac index or mixed venous oxygen saturation. Nitric oxide and prostacyclin did not affect the oxygenation index or systemic blood pressure. There were no complications associated with nitric oxide or prostacyclin. CONCLUSION In heart transplant and lung transplant recipients, nitric oxide and prostacyclin similarly reduce pulmonary artery pressures and central venous pressure, and improve cardiac index and mixed venous oxygen saturation. Inhaled prostacyclin may offer an alternative to nitric oxide in the treatment of pulmonary hypertension in thoracic transplantation.

Combined CXCR3/CCR5 blockade attenuates acute and chronic rejection.

Chemokine-chemokine receptor interactions orchestrate mononuclear cells recruitment to the allograft, leading to acute and chronic rejection. Despite biologic redundancy, several experimental studies have demonstrated the importance of CXCR3 and CCR5 in acute rejection of allografts. In these studies, deficiency or blockade of CXCR3 or CCR5 led to prolongation of allograft survival, yet allografts were ultimately lost to acute rejection. Given the above findings and the specificity of mononuclear cells bearing CXCR3 and CCR5, we hypothesized that combined blockade of CXCR3 and CCR5 will lead to indefinite (>100 days) graft survival in a full MHC-mismatched murine cardiac allograft model. The donor hearts in the control group were rejected in 6 ± 1 days after transplantation. Combined blockade of CXCR3 and CCR5 prolonged allograft survival >15-fold vs the control group; all allografts survived for >100 days. More importantly, the donor hearts did not display any intimal lesions characteristic of chronic rejection. Further analysis of the donor hearts in the CXCR3/CCR5 blockade group demonstrated graft infiltration with CD4+CD25+ T cells expressing the Foxp3 gene. Depletion of CD25+ cells in the combined CXCR3 and CCR5 blockade group resulted in acute rejection of the allografts in 22 ± 2 days. Combined CXCR3 and CCR5 blockade also reduced alloantigen-specific T lymphocyte proliferation. Combined CXCR3 and CCR5 blockade is effective in preventing acute and chronic rejection in a robust murine model. This effect is mediated, in part, by CD25+ regulatory T cell recruitment and control of T lymphocyte proliferation.

Assessment of hepatic steatosis by transplant surgeon and expert pathologist: A prospective, double‐blind evaluation of 201 donor livers

An accurate clinical assessment of hepatic steatosis before transplantation is critical for successful outcomes after liver transplantation, especially if a pathologist is not available at the time of procurement. This prospective study investigated the surgeons accuracy in predicting hepatic steatosis and organ quality in 201 adult donor livers. A steatosis assessment by a blinded expert pathologist served as the reference gold standard. The surgeons steatosis estimate correlated more strongly with large‐droplet macrovesicular steatosis [ld‐MaS; nonparametric Spearman correlation coefficient (rS) = 0.504] versus small‐droplet macrovesicular steatosis (sd‐MaS; rS = 0.398). True microvesicular steatosis was present in only 2 donors (1%). Liver texture criteria (yellowness, absence of scratch marks, and round edges) were mainly associated with ld‐MaS (variance = 0.619) and were less associated with sd‐MaS (variance = 0.264). The prediction of ≥30% ld‐MaS versus <30% ld‐MaS was excellent when liver texture criteria were used (accuracy = 86.2%), but it was less accurate when the surgeons direct estimation of the steatosis percentage was used (accuracy = 75.5%). The surgeons quality grading correlated with the degree of ld‐MaS and the surgeons steatosis estimate as well as the incidence of poor initial function and primary nonfunction. In conclusion, the precise estimation of steatosis remains challenging even in experienced hands. Liver texture characteristics are more helpful in identifying macrosteatotic organs than the surgeons actual perception of steatosis. These findings are especially important when histological assessment is not available at the donors hospital. Liver Transpl 19:437–449, 2013.

Inflammation/oxidation in chronic rejection: apolipoprotein a-i mimetic peptide reduces chronic rejection of transplanted hearts.

Background. Chronic rejection in transplanted hearts or cardiac allograft vasculopathy (CAV) is the leading cause of late death among heart transplant recipients. Strategies to control CAV traditionally have focused on lymphocyte functions. We hypothesized that D-4F, an apoA-I mimetic peptide with potent anti-inflammatory/antioxidant properties, will attenuate CAV. Methods. We used a previously characterized murine model of CAV. B6.C-H2bm12 hearts were heterotopically transplanted into C57BL/6 mice. Recipient mice were treated with either 20 &mgr;g of D-4F or carrier daily. Donor hearts were harvested on day 24 after transplantation. Results. Treatment of recipients with D-4F reduced the severity of intimal lesions (62.5±3.4% vs. 31.1±8.7%, P<0.009). Treatment also resulted in a decrease in the number of graft-infiltrating CD4 and CD8 lymphocytes and CXCR3+ T-lymphocyte subsets. Heme oxygenase-1 (HO-1) gene transcript in the donor hearts was up-regulated with D-4F treatment, and HO-1 blockade partially reversed the beneficial effects of D-4F. In vitro studies showed that D-4F reduced allogeneic T-lymphocyte proliferation and effector cytokine production. These processes were HO-1 independent. Conclusion. This study suggests that D-4F, a prototypical apoA-I mimetic peptide, is effective in controlling CAV via induction of HO-1 in the graft and a direct effect on T-lymphocyte function. This class of peptides with anti-inflammatory/antioxidant properties provides a novel strategy in the treatment of CAV.

CD8 lymphocytes are sufficient for the development of chronic rejection

Background. The role of CD8 lymphocytes, in chronic rejection or cardiac allograft vasculopathy (CAV), is incompletely understood. The purposes of this study were to determine whether CD8 lymphocytes, in the absence of CD4 lymphocytes, are capable of causing the intimal lesions of CAV; and if so, to define the effector mechanism(s) of CD8 lymphocytes. Methods. We modified a previously characterized major histocompatibility complex class II mismatched murine model of CAV. Wild-type CD8 lymphocytes were transferred to nude mice followed by heterotopic heart transplantation. Recipient mice were then treated with a CD40 activating antibody, which is known to provide help for CD8 lymphocyte activation, in the absence of CD4 lymphocytes. Donor hearts were harvested on day 40 posttransplantation and analyzed for cellular infiltrates and intimal thickening. In separate experiments, isolated perforin −/−, Fas ligand (FasL) −/−, and interferon (IFN)-&ggr; −/− CD8 lymphocytes were transferred to nude mice followed by identical experimented protocol. Results. With adaptive transfer of wild-type CD8 lymphocytes, the donor hearts were infiltrated with activated CD8 lymphocytes and displayed significant intimal lesions. Adoptive transfer of perforin −/− and FasL −/− CD8 lymphocytes to nude mice resulted in similar patterns of CD8 lymphocyte infiltration and similar severity of intimal lesions. The donor hearts from IFN-&ggr; −/− CD8 lymphocyte reconstituted recipients displayed minimal intimal lesions, although CD8 lymphocytes were present in the allografts. Conclusions. Unprimed CD8 lymphocytes in the absence of CD4 lymphocytes can cause intimal lesions of CAV. CD8 lymphocytes production of IFN-&ggr;, but not the perforin or the FasL-mediated cytotoxicity, is the critical step in the development of intimal lesions.

Chemokine Receptor Blockade With a Synthetic Nonpeptide Compound Attenuates Cardiac Allograft Vasculopathy

Background. Recruitment of recipient mononuclear cells to the donor heart is a central event in the development of cardiac allograft vasculopathy (CAV). The role of individual chemokine receptors in this process is incompletely defined. TAK-779 (N,N-dimethyl-N-[4-[[[2-(4-methylphenyl)-6,7-dihydro-5H-benzocyclohepten-8-yl]carbonyl]amino]benzyl]tetra-hydro-2H-pyran-4-aminium chloride) is a synthetic nonpeptide antagonist of CCR5 and CXCR3. The purpose of this study is to determine if combined CCR5 and CXCR3 blockade by TAK-779 would attenuate CAV in an experimental model. Methods. We used a previously characterized murine model of CAV. Recipient mice were treated with TAK-779 or vehicle control. Donor hearts were harvested on day 24 posttransplantation and analyzed for intimal thickening and cellular infiltration. Recipient splenocytes were analyzed for proliferative response and interferon (IFN)-γ production by enzyme-linked immunosorbent spot assay. The donor hearts were also examined for heme oxygenase-1 (HO-1) gene induction. Results. CCR5 and CXCR3 blockade by TAK-779 reduced the severity of intimal lesions (53±10% vs. 16±2%; P<0.05) and decreased the number of graft infiltrating CCR5+ and CXCR3+ CD4 and CD8 lymphocytes. Moreover, treatment with TAK-779 (a) decreased alloantigen-specific T-lymphocyte proliferation and number of IFN-γ producing cells and (b) increased HO-1 gene transcript level in the allografts. Conclusions. Antagonism of CCR5 and CXCR3 by TAK-779 is effective in controlling CAV. The beneficial effects of TAK-779 may be because of (a) reduction in CCR5+ and CXCR3+ T-lymphocyte subset infiltration into the graft, (b) attenuation of alloantigen-specific T-lymphocyte proliferative response and IFN-γ production, and (c) induction of HO-1 gene. This compound may offer a novel approach in clinical management of CAV.

Liberalization of donor criteria for lung transplantation

Purpose of reviewThe greatest factor limiting the number of lung transplants performed each year is the availability of acceptable donors. Liberalization of currently accepted donor criteria would allow for an increase in the number of donor lungs procurable. This would help treat those patients on the ever-expanding transplant waiting list. Recent findingsThe generally accepted criteria for an acceptable donor are: age less than 55 years, clear chest radiograph, PaO2/FiO2 ratio greater than 300, and a clear bronchoscopy. Historically these parameters have little evidence-based support. Numerous recent studies of patients transplanted with nonstandard lungs show no difference in outcomes when compared with those transplanted with lungs that met all criteria. However, a few studies have noted that certain donor criteria could predict short-term adverse outcome. The specific criteria implicated as risk factors are donor age and prolonged graft ischemic time in conjunction with advanced donor age. Studies assessing outcomes beyond the first posttransplant year have found no difference between recipients of standard and nonstandard donor lungs. SummaryIncreased waiting time and recent advances in transplant procurement, preservation, and operative technique warrant the expansion of current standard donor criteria. Most contemporary evidence demonstrates no difference in outcome when nonstandard donors are used. Although caution is justified when transplanting nonstandard lungs with multiple risk factors into high-risk patients, liberalization of the criteria now is well supported.