Manuel Maglione

Intracellular signaling pathways control mitochondrial events associated with the development of ischemia/ reperfusion-associated damage.

Ischemia (I) and reperfusion (R) trigger a series of events, which culminate in severe injury to the transplanted organ. Cell death resulting from the formation of mitochondrial reactive oxygen species (ROS) coupled with the perturbation of mitochondrial Ca2+ homeostasis is central to the development of IR‐associated tissue damage. We and others have shown recently that intracellular signaling pathways critically control these mitochondrial changes, making them potential targets for therapeutic intervention. Using a heterotopic murine heart transplant model as well as primary and immortalized cardiomyocyte cells we established the activity patterns of mitogen‐activated protein kinases (MAPKs) ERK, JNK, and p38 during IR, and probed into their role in the perturbation of mitochondrial ROS and Ca2+ homeostasis, which are necessary for cardiomyocyte death. Our results showed a strong activation of all three MAPKs as well as a rise in mitochondrial ROS and Ca2+ during early reoxygenation. Inhibiting p38 kinase most efficiently prevented ROS production, Ca2+ overload and cell death, suggesting that targeting this signaling molecule may provide a possible strategy to limit the effects of IR.

Tetrahydrobiopterin compounds prolong allograft survival independently of their effect on nitric oxide synthase activity

Background. In previous work, the four-amino analogue of tetrahydrobiopterin, a novel, selective inhibitor of inducible nitric oxide synthase, has been shown to prolong survival of murine cardiac allografts. Methods. To further elucidate the underlying molecular immunosuppressive mechanism, we compared the effect of four-amino tetrahydrobiopterin with that of the unsubstituted parent compound tetrahydrobiopterin and of N6-(iminoethyl)-L-lysine (L-NIL), a nonpterin inhibitor of inducible nitric oxide synthase using a murine cardiac transplant model. We analyzed allograft survival, intragraft gene expression in grafts by microarray and real-time polymerase chain reaction, graft nitrotyrosine staining by immunohistochemistry and plasma nitrite plus nitrate levels by high-performance liquid chromatography. Results. Allograft survival was significantly prolonged by tetrahydrobiopterin and cyclosporin A, but not by L-NIL although decreased plasma nitrite plus nitrate levels confirmed nitric oxide synthase inhibition in vivo. As compared to allogeneic untreated controls, intragraft peroxynitrite formation and hence nitrotyrosine staining was lowered in all groups except in cyclosporine A-treated animals. Gene expression profiles obtained by microarray analysis demonstrated that cyclosporine A was able to counteract the expression changes of more than half of the genes differently expressed in syngeneic grafts versus allografts, whereas tetrahydrobiopterin compounds and L-NIL showed only smaller influences on gene expression profiles. Conclusions. These results demonstrate that the four-amino substitution, which is essential for inhibition of nitric oxide synthase, is not required for the immunosuppressive effect of tetrahydrobiopterin compounds. We describe a novel immunosuppressive role of pharmacologically applied tetrahydrobiopterin.

Proteomic profiling of acute cardiac allograft rejection.

Background. Proteome analysis has emerged as a valuable tool for the study of large-scale protein expression profiles. Here, we applied this novel technology to identify specific biomarkers for acute cardiac allograft rejection. Methods. Hearts of C57BL/10 mice were placed in fully major histocompatibility complex-mismatched C3H/He recipients. Syngeneic transplants served as controls. Intragraft protein expression analysis was performed using fluorescence two-dimensional difference gel electrophoresis on day 6 posttransplant. Spots of interest were subsequently subjected to nanospray ionization tandem mass spectrometry (MS/MS) for protein identification. In addition, expression of selected proteins was confirmed by Western blot analysis and by immunohistochemistry. Results. Two-dimensional difference gel electrophoresis enabled detection of 1541 protein spots. For 95 protein spots, the expression level during acute rejection differed by more than 1.5-fold from that observed in syngeneic grafts. Spots with significant differential regulation identified by tandem mass spectrometry were derived from peroxiredoxin 6, pyruvate kinase isozyme M2, coronin 1A, protein disulfide isomerase A3 precursor, and aconitate hydratase. Conclusion. These identified proteins may constitute novel biomarkers of acute cardiac allograft rejection and might hold great potential as surrogate markers for monitoring in vivo alloimmune response.

Tetrahydrobiopterin Attenuates Microvascular Reperfusion Injury Following Murine Pancreas Transplantation

In this study we investigated the effect of tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide synthases, on ischemia‐reperfusion injury (IRI) following murine pancreas transplantation. Pancreatic grafts were exposed to prolonged cold ischemia times (CIT) and different treatment regimens: normal saline (S), S + 16 h CIT, BH4 50 mg/kg + 16 h CIT. Nontransplanted animals served as controls. Graft microcirculation was analyzed by means of functional capillary density (FCD) and capillary diameters (CD) after 2 h reperfusion using intravital microscopy. Quantification of inflammatory responses (mononuclear infiltration) and endothelial disintegration (edema formation) was done by histology (hematoxylin and eosin), and peroxynitrite formation assessed by nitrotyrosine immunostaining. FCD was significantly reduced after prolonged CIT, paralleled by increased peroxynitrite formation as compared with controls (all p < 0.05). Microcirculatory changes correlated significantly with intragraft peroxynitrite generation (Spearman: r=−0.56; p < 0.01). Pancreatic grafts treated with BH4 displayed markedly higher FCD values (p < 0.01) and abrogated nitrotyrosine staining (p = 0.03). CD were not significantly different in any group. Histology showed increased inflammation, interstitial edema, hemorrhage, acinar vacuolization and focal areas of necrosis after 16 h CIT, which was diminished by BH4 administration (p < 0.01). BH4 treatment significantly reduces post‐ischemic deterioration of microcirculation as well as histologic damage and might be a promising novel strategy in attenuating IRI following pancreas transplantation.

Identification of Molecular Markers of Delayed Graft Function Based on the Regulation of Biological Ageing

Introduction Delayed graft function is a prevalent clinical problem in renal transplantation for which there is no objective system to predict occurrence in advance. It can result in a significant increase in the necessity for hospitalisation post-transplant and is a significant risk factor for other post-transplant complications. Methodology The importance of microRNAs (miRNAs), a specific subclass of small RNA, have been clearly demonstrated to influence many pathways in health and disease. To investigate the influence of miRNAs on renal allograft performance post-transplant, the expression of a panel of miRNAs in pre-transplant renal biopsies was measured using qPCR. Expression was then related to clinical parameters and outcomes in two independent renal transplant cohorts. Results Here we demonstrate, in two independent cohorts of pre-implantation human renal allograft biopsies, that a novel pre-transplant renal performance scoring system (GRPSS), can determine the occurrence of DGF with a high sensitivity (>90%) and specificity (>60%) for donor allografts pre-transplant, using just three senescence associated microRNAs combined with donor age and type of organ donation. Conclusion These results demonstrate a relationship between pre-transplant microRNA expression levels, cellular biological ageing pathways and clinical outcomes for renal transplantation. They provide for a simple, rapid quantitative molecular pre-transplant assay to determine post-transplant allograft function and scope for future intervention. Furthermore, these results demonstrate the involvement of senescence pathways in ischaemic injury during the organ transplantation process and an indication of accelerated bio-ageing as a consequence of both warm and cold ischaemia.

Excellent post-transplant survival in patients with intermediate stage hepatocellular carcinoma responding to neoadjuvant therapy.

Current treatment guidelines preclude liver transplantation for patients with BCLC B (intermediate stage) HCC, and expanding transplantation criteria for selected patients beyond early stage HCC remains controversial. The aim of this study was to determine stage‐dependent HCC recurrence and overall survival rates in transplant recipients and the impact of response to neoadjuvant treatment on outcome.

Single-center experience with third and fourth kidney transplants

Kidney retransplantation is often associated with a higher immunological risk than is primary renal transplantation. Faced with increasing organ shortage and growing waiting lists, results of kidney retransplantation are of particular interest. Fifty‐six third and fourth kidney transplants were analyzed retrospectively. Parameters included patient and donor demographics, operative details, incidence of surgical, immunological and infectious complications and patient and graft survival. Patients receiving third kidney grafts had 1‐ and 5‐year patient/graft survival rates of 97.4%/72.9% and 88.9%/53.6%, respectively. Episodes of acute rejection and delayed graft function were observed in 44% and 49% of these patients. Fourth kidney transplantation was associated with 1‐ and 2‐year patient/graft survival rates of 84.8%/68.5% and 63.6%/47%, respectively. Acute rejection and delayed graft function occurred in 33% and in 60% of cases. Acceptable patient and graft survival may be achieved after third and fourth kidney transplantation. Graft losses in this sensitized population are mainly because of rejection. Profound immunosuppression may lead to major infectious problems.

Donor Pretreatment with Tetrahydrobiopterin Saves Pancreatic Isografts from Ischemia Reperfusion Injury in a Mouse Model

Depletion of the nitric oxide synthase cofactor tetrahydrobiopterin (H4B) during ischemia and reperfusion is associated with severe graft pancreatitis. Since clinically feasible approaches to prevent ischemia reperfusion injury (IRI) by H4B‐substitution are missing we investigated its therapeutic potential in a murine pancreas transplantation model using different treatment regimens. Grafts were subjected to 16 h cold ischemia time (CIT) and different treatment regimens: no treatment, 160 μM H4B to perfusion solution, H4B 50 mg/kg prior to reperfusion and H4B 50 mg/kg before recovery of organs. Nontransplanted animals served as controls. Recipient survival and endocrine graft function were assessed. Graft microcirculation was analyzed 2 h after reperfusion by intravital fluorescence microscopy. Parenchymal damage was assessed by histology and nitrotyrosine immunohistochemistry, H4B tissue levels by high pressure liquid chromatography (HPLC). Compared to nontransplanted controls prolonged CIT resulted in significant microcirculatory deterioration. Different efficacy according to route and timing of administration could be observed. Only donor pretreatment with H4B resulted in almost completely abrogated IRI‐related damage showing graft microcirculation comparable to nontransplanted controls and restored intragraft H4B levels, resulting in significant reduction of parenchymal damage (p < 0.002) and improved survival and endocrine function (p = 0.0002 each). H4B donor pretreatment abrogates ischemia‐induced parenchymal damage and represents a promising strategy to prevent IRI following pancreas transplantation.

Functional capillary density in ischemic conditioning : implications for esophageal resection with the gastric conduit

BACKGROUND Ischemia may lead to leakage at the esophagogastric anastomosis after esophagectomy. The aim of this study was to investigate time dependent changes of gastric microcirculation after ischemic conditioning. METHODS Twenty male Lewis rats were used and analyzed in 3 study groups and 1 control group. Group 1 (n = 5) underwent ligation of the left gastric artery and intravital fluorescence microscopy (IVM) on day 0; group 2 (n = 5) underwent IVM at 28 days after ligation of the LGA; and group 3 (n = 5) underwent IVM at 56 days after ligation of the LGA. The controls (n = 5) underwent sham surgery and IVM at 28 days thereafter. IVM was used to analyze gastric microcirculation by means of functional capillary density. RESULTS Ligation of the LGA immediately led to significant reduction of perfusion at the lesser (100.5 +/- 3.1 microm/mm(2) vs 220.4 +/- 7.4 microm/mm(2); P <.001) and greater curvatures (195.1 +/- 7.9 microm/mm(2) vs 234.1 +/- 9.4 microm/mm(2); P = .013). During 28 days, microcirculation at the lesser curve ameliorated (164.9 +/- 12.8 microm/mm(2)) and reached normal values after 56 days (215.8 +/- 7.4 microm/mm(2)). At the greater curve, microcirculation was improved during 4 (261.3 +/- 8 microm/mm(2)P = .039) and 8 weeks (317.9 +/- 10.3 microm/mm(2); P <.001 vs control). CONCLUSIONS Gastric microperfusion continuously improves after partial devascularization. The results support further clinical studies to optimize gastric ischemic conditioning in patients undergoing esophagectomy.

Cytoplasmic signaling in the control of mitochondrial uproar

The concept of a pre-emptive strike as a good means to prevent greater harm may be frequently over-stressed in daily life. However, biological systems in a homeostatic balance are prepared to withstand a certain degree of hostile fire by rather passive means. This also applies to the maintenance of cell survival, where a plethora of protective proteins provide safeguard against erroneous activation of death pathways. Apart from these mechanisms active processes are also essential for the maintenance of cellular homeostasis, commonly referred to as survival signaling. Frequently their targets may be mitochondrial, assuring organelle integrity, which is essential for continued energy production and survival. Transient or permanent failures in these cellular defense strategies result in pathophysiological conditions, which manifest themselves e.g. as cancer or ischemia/reperfusion-associated organ damage.