Heterotopic Heart Transplantation Model Research Articles

The natural killer cell activating receptor, NKG2D, is critical to antibody-dependent chronic rejection in heart transplantation

Chronic rejection is among the most pressing clinical challenges in solid organ transplantation. Interestingly, in a mouse model of heterotopic heart transplantation, antibody-dependent, natural killer (NK) cell-mediated chronic cardiac allograft vasculopathy occurs in some donor-recipient strain combinations, but not others. In this study, we sought to identify the mechanism underlying this unexplained phenomenon. Cardiac allografts from major histocompatibility complex (MHC) mismatched donors were transplanted into immune-deficient C57Bl/6.rag-/- recipients, followed by administration of a monoclonal antibody against the donor MHC class I antigen. We found marked allograft vasculopathy in hearts from C3H donors, but near-complete protection of BALB/c allografts from injury. We found no difference in recipient NK cell phenotype or intrinsic responsiveness to activating signals between recipients of C3H versus BALB/c allografts. However, cardiac endothelial cells from C3H allografts showed an approximately twofold higher expression of Rae-1, an activating ligand of the NK cell receptor natural killer group 2D (NKG2D). Importantly, the administration of a neutralizing antibody against NKG2D abrogated the development of allograft vasculopathy in recipients of C3H allografts, even in the presence of donor-specific antibodies. Therefore, the activating NK cell receptor NKG2D is necessary in this model of chronic cardiac allograft vasculopathy, and strain-dependent expression of NK activating ligands correlates with the development of this disease.

68Ga]DOTA-TATE PET for the detection of early transplant rejection in a heterotopic allograft heart transplantation model of the rat: a pilot study.

The most important cause of heart transplant loss is early acute allograft rejection, caused by the infiltration of lymphocytes, development of edema and myocardial necrosis. It has been propagated that [68Ga]DOTA-TATE PET might be suitable to quantify the presence of SSTR over-expressing lymphocytes. With heterotopic allogenic heart transplant models in the rat readily available, we aimed to investigate, if monitoring and quantification of acute allograft rejection after heterotopic allogenic heart transplantation was feasible by non-invasive serial [68Ga]DOTA-TATE PET. Seventeen Lewis rats (9 for serial PET imaging, 8 for histological correlation) received allogenic heterotopic heart transplants from 17 Brown-Norway rats. On days 4, 6 and 7 a [68Ga]DOTA-TATE PET scan was performed. Imaging of acute transplant rejection until 7 days after allogenic heart transplantation in the rat is feasible. Heterotopic allografts showed significantly increased tracer uptake on day 4 until day 7 after transplantation, reflecting the process of histologically detected myocardial lymphocytic infiltration. Both the area of infarction and the amount of necrosis increased over the course of 7 days, with necrosis reaching statistical significance. We purport that the detected PET signal is primarily a specific marker of lymphocyte infiltration and only to a lesser extent an unspecific marker of infarction and necrosis. Thus, [68Ga]DOTA-TATE PET might be a suitable tool for serial imaging and quantification of lymphocyte infiltration as a direct mediator of acute allograft rejection at an early stage after heart transplantation.

Overexpression of miR-223 Promotes Tolerogenic Properties of Dendritic Cells Involved in Heart Transplantation Tolerance by Targeting Irak1.

Dendritic cells (DCs) are key mediators of transplant rejection. Numerous factors have been identified that regulate transplant immunopathology by modulating the function of DCs. Among these, microRNAs (miRNAs), small non-coding RNA molecules, have received much attention. The miRNA miR-223 is very highly expressed and tightly regulated in hematopoietic cells. It plays an important role in modulating the immune response by regulating neutrophils and macrophages, and its dysregulation contributes to multiple types of immune diseases. However, the role of miR-223 in immune rejection is unclear. Here, we observed expression of miR-223 in patients and mice who had undergone heart transplantation and found that it increased in the serum of both, and also in DCs from the spleens of recipient mice, although it was unchanged in splenic T cells. We also found that miR-223 expression decreased in lipopolysaccharide-stimulated DCs. Increasing the level of miR-223 in DCs promoted polarization of DCs toward a tolerogenic phenotype, which indicates that miR-223 can attenuate activation and maturation of DCs. MiR-223 effectively induced regulatory T cells (Tregs) by inhibiting the function of antigen-presenting DCs. In addition, we identified Irak1 as a miR-223 target gene and an essential regulator of DC maturation. In mouse allogeneic heterotopic heart transplantation models, grafts survived longer and suffered less immune cell infiltration in mice with miR-223-overexpressing immature (im)DCs. In the miR-223-overexpressing imDC recipients, T cells from spleen differentiated into Tregs, and the level of IL-10 in heart grafts was markedly higher than that in the control group. In conclusion, miR-223 regulates the function of DCs via Irak1, differentiation of T cells into Tregs, and secretion of IL-10, thereby suppressing allogeneic heart graft rejection.

Refining murine heterotopic heart transplantation: A model to study ischemia and reperfusion injury in donation after circulatory death hearts.

Heart transplantation is a lifesaving procedure, which is limited by the availability of donor hearts. Using hearts from donors after circulatory death, which have sustained global ischemia, requires thorough studies on reliable and reproducible models that developing researchers may not have mastered. By combining the most recent literature and our recommendations based on observations and trials and errors, the methods here detail a sound in vivo heterotopic heart transplantation model for rats in which protective interventions on the ischemic heart can be studied, and thus allowing the scientific community to advance organ preservation research. Knowledge gathered from reproducible animal models allow for successful translation to clinical studies.

Blood Circuit Reconstruction in an Abdominal Mouse Heart Transplantation Model.

The surgical technique of heterotopic abdominal heart transplantation in mice is a standard model for research in transplantation immunology. Here, the established technique for a modified blood circuit reconstruction in a heterotopic abdominal heart transplantation model is presented. This method uses the intrathoracic inferior vena cava (IIVC) instead of the pulmonary artery of the donor heart for the anastomosis to the inferior vena cava of the recipient. It is facilitating and improving success rates for abdominal heart transplantation in mice.

Immutol regulates CD4+Tregs, CD8+Tregs and pDCs via IDO signaling pathway to induce immune tolerance in rat heart allograft transplant

Indoleamine 2,3-dioxygenase (IDO) can promote tryptophan metabolism to kynurenine and modulate regulatory T cells (Tregs), thereby maintains lower efficiency to induce tolerance. Our aim is to investigate the mechanism of tolerance induction by a IDO metabolite named Immutol. MethodsWe established rat heterotopic heart transplantation models and treated them with Immutol, cyclosporine A (CsA) and 1-methyl-DL-tryptophan (1-MT) in vivo. The drugs were administered via gavage to all but the control group one day before surgery. CsA was gavaged continually for 20 days and Immutol for 60 days; after withdrawal of the drugs, the recipients were observed for at least 10 months. Immune cells were analyzed by flow cytometry. The IDO signaling pathway was evaluated by Western blotting, RT-PCR and immunochemical staining. Enzyme-linked immunosorbent assays (ELISAs) were used to detect changes in cytokines. ResultsCsA or Immutol alone prolonged survival but did not induce tolerance after withdrawal. Immutol+CsA inhibited acute rejection, and the grafts survived more than 400 d, with tolerance detected in most rats (13/15). Increased protein IDO and kynurenine could regulate the accumulation of CD4+Tregs, CD8+Tregs and pDC to induce immune tolerance. I-MT specifically blocked IDO, weakened the expression of IDO and kynurenine, and produced grafts rejection. Additionally, Tregs could down-regulate immune responses through production of the immunosuppressive cytokines IL-10 and TGF-beta, thus induce immune tolerance. CD8+ Tregs produce IFN-γ, and tolerance is dependent on both IFN-γ and IDO. ConclusionImmutol combined with CsA can control acute rejection and induce tolerance in rats with cardiac allografts after withdrawal. Immutol may become a novel drug for future clinical use.

Effect of Inhibition of the JAK2/STAT3 Signaling Pathway on the Th17/IL-17 Axis in Acute Cellular Rejection After Heart Transplantation in Mice.

Acute immune rejection is one of the most serious complications of heart transplantation, and its mechanism has always been a hot spot. Th17 cells and cytokine interleukin-17 (IL-17) have been proved to be involved in acute immune rejection, and the signaling pathway mechanism has attracted our interest. It has been confirmed that the Janus kinase 2-signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway is involved in the differentiation of CD4+ T cells, so we focus on whether the JAK2/STAT3 signaling pathway is involved in the occurrence of acute immune rejection by regulating the Th17/IL-17 axis. In this study, we used Bagg's Albino c mice and C57BL/6 mice to construct heterotopic heart transplantation models, which were divided into the acute rejection group and AG490-treated group (n = 5), and donor tissue and serum were collected in 3 experimental days from the recipient mice for H&E staining analysis of paraffin sections and ELISA, Western blot, flow cytometry, and real time-polymerase chain reaction. The results showed that the acute rejection rating of the heart decreased, and the expression of related factors decreased significantly after using the inhibitor AG490, suggesting that the JAK2/STAT3 signaling pathway regulates expression of the Th17/IL-17 axis in cardiac allograft rejection.

Prolyl endopeptidase contributes to early neutrophilic inflammation in acute myocardial transplant rejection.

Altered inflammation and tissue remodeling are cardinal features of cardiovascular disease and cardiac transplant rejection. Neutrophils have increasingly been understood to play a critical role in acute rejection and early allograft failure; however, discrete mechanisms that drive this damage remain poorly understood. Herein, we demonstrate that early acute cardiac rejection increases allograft prolyl endopeptidase (PE) in association with de novo production of the neutrophil proinflammatory matrikine proline-glycine-proline (PGP). In a heterotopic murine heart transplant model, PGP production and PE activity were associated with early neutrophil allograft invasion and allograft failure. Pharmacologic inhibition of PE with Z-Pro-prolinal reduced PGP, attenuated early neutrophil graft invasion, and reduced proinflammatory cytokine expression. Importantly, these changes helped preserve allograft rejection-free survival and function. Notably, within 2 independent patient cohorts, both PGP and PE activity were increased among patients with biopsy-proven rejection. The observed induction of PE and matrikine generation provide a link between neutrophilic inflammation and cardiovascular injury, represent a potential target to reduce allogenic immune responses, and uncover a mechanism of cardiovascular disease that has been previously unrecognized to our knowledge.

Effects of carvedilol and metoprolol on the myocardium during mechanical unloading in a rat heterotopic heart transplantation model.

Left ventricular assist devices enable recovery from severe heart failure and serve as a bridge to heart transplantation. However, chronic mechanical unloading can impair myocardial recovery. We aimed to assess myocyte size, fibrosis, apoptosis, and β-adrenoreceptor levels after rats with left ventricle unloading induced by heterotopic heart transplantation were administered carvedilol and metoprolol. Thirty rats with heart transplants were divided randomly into control, carvedilol treatment, and metoprolol treatment groups. Follow-up was conducted after 2 and 4 weeks of unloading. Carvedilol and metoprolol treatments did not prevent the decrease in myocyte diameter in unloaded left ventricles. Metoprolol significantly decreased the ratio of the fibrotic area in the unloaded heart, measured using Masson's trichrome staining after 2 weeks. However, carvedilol and metoprolol did not reduce apoptosis, based on measurements of terminal deoxynucleotidyl-transferase-mediated dUTP nick end-labelling positive cells and the expression of caspase-3 in unloaded hearts after 2 and 4 weeks. Metoprolol treatment did not significantly decrease the mRNA expression of myocardial SERCA2a in the unloaded heart after 2 weeks. Compared to carvedilol treatment, metoprolol treatment improved myocardial fibrosis and SERCA2a expression to a greater extent; however, neither drug prevented myocardial apoptosis.

Rat model of heterotopic heart transplantation to investigate relevant donor heart harvesting method

Rat model of heterotopic heart transplantation to investigate relevant donor heart harvesting method

Fingolimod (FTY720) Preserves High Energy Phosphates and Improves Cardiac Function in Heterotopic Heart Transplantation Model.

During heart transplantation, donor heart leads to reduced oxygen supply resulting in low level of high energy phosphate (HEP) reserves in cardiomyocyte. Lower HEP is one of the underlying reasons of cell death due to ischemia. In this study we investigated the role of Fingolimod (FTY720) in heart transplantation ischemia. Eight groups of Sprague-Dawley rats (n = 5 for each subgroup) were made, A1 and C1 were given FTY720 1 mg/kg while B1 and D1 were given normal saline. The hearts were implanted into another set of similar rats after preservation period of 1 h at 4–8 °C. Significantly higher Left ventricular systolic pressure (LVSP), dP/dT maximum (p < 0.05), dP/dT minimum (p < 0.05) were recorded in the FTY720 treated group after 24 h of reperfusion while after 1 h of reperfusion, there were no significant differences in LVSP, maximum and negative dP/dT, and Left ventricular end diastolic pressure (LVEDP) between the control and the FTY720-treated transplant groups. Coronary blood flow (CBF) was enhanced (p < 0.05) in the FTY720 treated group after 1 and 24 h. ATP p < 0.001, p < 0.05 at 1 and 24 h, ADP p < 0.001, p > 0.05 at 1 and 24 h, and phosphocreatine p < 0.05, p > 0.05 at 1 and 24 h were better preserved by FTY720 treatment as compared to control group. The study concluded that pretreatment of grafted hearts with FTY720 improved hemodynamics, CBF, high energy phosphate reserves, reduces the peroxynitrite level and poly (ADP ribose) polymerase (PARP) inhibition that prevents ischemia-reperfusion injury.

Role of syndecan-1 in the interaction between dendritic cells and T cells.

Syndecan-1 (Sdc-1) is a heparan sulfate proteoglycan that can bind cytokines and chemokines via its heparan sulfate side chains, and has immunomodulatory properties in experimental models. Sdc-1 expression has been reported on dendritic cells (DC) and T cells. The potential role of Sdc-1 in DC-T cell interaction has not been investigated yet. We postulate that Sdc-1 is involved in DC-T cell interaction and may influence graft survival in an allogeneic transplant model. Sdc-1 expression on bone marrow-derived DC and T cells was analyzed by flow cytometry. Unstimulated and LPS stimulated Sdc-1 deficient DC were evaluated in vitro for phenotype and stimulatory capacity in mixed lymphocyte reaction. Sdc-1 deficient T cells were evaluated for proliferative capacity and differentiation in a mixed lymphocyte reaction and a proliferation assay. Allograft survival was evaluated in a fully MHC mismatched heterotopic heart transplant model, with either Sdc-1 deficient donors or recipients. Sdc-1 was expressed on the cell surface of unstimulated and LPS matured DC. Sdc-1 deficiency had no effect on expression of co-stimulatory molecules, cytokine production or T cell stimulatory capacity as compared to WT DC. Sdc-1 expression was not detectable on WT T cells, although intracellular Sdc-1 expression could be demonstrated after ConA activation. Sdc-1 deficient T cells showed reduced proliferation upon DC or ConA stimulation and reduced IL-17 production upon ConA stimulation, compared to WT T cells. Sdc-1 deficiency of either allograft or recipient did not prolong allograft survival. In conclusion, Sdc-1 is expressed on the cell surface of DC, where its absence does not affect DC phenotype or T cell stimulatory capacity. Sdc-1 is intracellularly expressed in ConA activated T cells. Sdc-1 deficiency in T cells results in a reduced proliferative response in vitro, as induced by DC and ConA. Sdc-1 deficiency in donor or recipient does not affect allograft survival.

Use of peroxiredoxin for preconditioning of heterotopic heart transplantation in a rat

Peroxiredoxin 6 (Prdx6) is an antioxidant enzyme in the human body that performs a number of important functions in the cell. Prdx6 restores a wide range of peroxide substrates, thus playing a leading role in maintaining redox homeostasis in mammalian cells. In addition to peroxidase activity, Prdx6 has an activity of phospholipase A2, thus taking part in membrane phospholipid metabolism. Due to its peroxidase and phospholipase activity, Prdx6 participates in intracellular and intercellular signal transmission, thereby facilitating the initiation of regenerative processes in the cell, suppression of apoptosis and activation of cell proliferation. Given the functions performed, Prdx6 can effectively deal with oxidative stress caused by various factors, including ischemia-reperfusion injury. On an animal model of rat heterotopic heart transplantation, we showed the cardioprotective potential of exogenous recombinant Prdx6, introduced before transplantation and subsequent reperfusion injury of the heart. It has been demonstrated that exogenous Prdx6 effectively alleviates the severity of ischemia-reperfusion injury of the heart by 2–3 times, providing normalization of its structural and functional state during heterotopic transplantation. The use of recombinant Prdx6 can be an effective approach in preventing/alleviating ischemia-reperfusion injury of the heart, as well as in maintaining an isolated heart during transplantation.

Novel delivery of cellular therapy to reduce ischemia reperfusion injury in kidney transplantation.

Ex vivo normothermic machine perfusion (NMP) of donor kidneys prior to transplantation provides a platform for direct delivery of cellular therapeutics to optimize organ quality prior to transplantation. Multipotent Adult Progenitor Cells (MAPC® ) possess potent immunomodulatory properties that could minimize ischemia reperfusion injury. We investigated the potential capability of MAPC cells in kidney NMP. Pairs (5) of human kidneys, from the same donor, were simultaneously perfused for 7 hours. Kidneys were randomly allocated to receive MAPC treatment or control. Serial samples of perfusate, urine, and tissue biopsies were taken for comparison. MAPC-treated kidneys demonstrated improved urine output (P=.009), decreased expression of injury biomarker NGAL (P=.012), improved microvascular perfusion on contrast-enhanced ultrasound (cortex P=.019, medulla P=.001), downregulation of interleukin (IL)-1β (P=.050), and upregulation of IL-10 (P<.047) and Indolamine-2, 3-dioxygenase (P=.050). A chemotaxis model demonstrated decreased neutrophil recruitment when stimulated with perfusate from MAPC-treated kidneys (P<.001). Immunofluorescence revealed prelabeled MAPC cells in the perivascular space of kidneys during NMP. We report the first successful delivery of cellular therapy to a human kidney during NMP. Kidneys treated with MAPC cells demonstrate improvement in clinically relevant parameters and injury biomarkers. This novel method of cell therapy delivery provides an exciting opportunity to recondition organs prior to transplantation.

Combined abdominal heterotopic heart and aorta transplant model in mice.

Allograft vasculopathy (AV) remains a major obstacle to long-term allograft survival. While the mouse aortic transplantation model has been proven as a useful tool for study of the pathogenesis of AV, simultaneous transplantation of the aorta alongside the transplantation of another organ may reveal more clinically relevant mechanisms that contribute to the pathogenesis of chronic allograft rejection. Therefore, we developed a combined abdominal heart and aorta transplantation model in mice which benefits from reducing animal and drug utilization, while providing an improved model to study the progressive nature of AV. The middle of the infrarenal aorta of the recipient mouse was ligatured between the renal artery and its bifurcation. Proximal and distal aortotomies were performed at this site above and below the ligature, respectively, for the subsequent anastomoses of the donor aorta and heart grafts to the recipient infrarenal aorta in an end-to-side fashion. The distal anastomotic site of the recipient infrarenal aorta was connected with the outlet of the donor aorta. Uniquely, the proximal anastomotic site on the recipient infrarenal aorta was shared to connect with both the inlet of the donor aorta and the inflow tract to the donor heart. The outflow tract from the donor heart was connected to the recipient inferior vena cava (IVC). The median times for harvesting the heart graft, aorta graft, recipient preparation and anastomosis were 11.5, 8.0, 9.0 and 40.5 min, respectively, resulting in a total median ischemic time of 70 min. The surgery survival rate was more than 96% (29/30). Both the syngeneic C57Bl/6 aorta and heart grafts survived more than 90 days in 29 C57Bl/6 recipients. Further, Balb/c to C57Bl/6 allografts treated with anti-CD40L and CTLA4.Ig survived more than 90 days with a 100% (3/3) survival rate. (3/3). This model is presented as a new tool for researchers to investigate transplant immunology and assess immunosuppressive strategies. It is possible to share a common anastomotic stoma on the recipient abdominal aorta to reconstruct both the aorta graft entrance and heart graft inflow tract. This allows for the study of allogeneic effects on both the aorta and heart from the same animal in a single survival surgery.

Methane-Enriched Custodiol Preservation Solution Improves Graft Function in Experimental Model of Heterotopic Heart Transplantation

The key goal of cold storage is to maintain cell viability for a prolonged time during solid organ transplantation. Methane (CH4) has been recognized as novel therapeutic gas exerting anti-inflammatory effects in ischemia-reperfusion (IR) injuries. We aimed to investigate whether cold storage of donor hearts in CH4-enriched Custodiol preservation solution could protect against IR and preserve myocardial function in a rat model of heterotopic heart transplantation (HTX). The hearts of donor Lewis rats were explanted and stored for 1 h in cold Custodiol (CS group, n=12) or in CH4-saturated (0.054 mg/100 ml) Custodiol (CS-CH4 group, n=12). 60 min after HTX left ventricular (LV) pressure-volume relations and coronary blood flow (CBF) were assessed to evaluate early post-transplant graft function. At the end of haemodynamic measurements, samples were taken for qPCR of endoplasmic reticulum (ER) stress and mitochondria-related apoptosis markers (CHOP, GRP78, GSK3β, VLDR, Caspase 3 and 9, Bcl2, Bax), biochemical parameters and mitochondrial functional analysis with high-resolution respirometry (Oxygraph2K, Austria). LV contractility (LV systolic pressure at 120µl of LV volume: 86±6 vs. 57±7mmHg, p=0.01; dP/dtmax: 2326±167 vs. 1583±139mmHg, p=0.007) and active relaxation (dP/dtmin at 120µl of LV volume: -1660±185 vs. -1043±169mmHg, p=0.04) improved significantly after an hour of reperfusion, while alteration of CBF standardized to heart weight (2.11±0.35 vs. 1.13±0.2ml/min/g, p=0.04) was also significantly improved following pretreatment. CS-CH4 storage significantly reduced the transcription of pro-apoptotic proteins and Bcl2/Bax ratios as compared to CS grafts. Increased mitochondrial oxidative phosphorylation, reduced leak respiration and cytochrome c release were demonstrated in response to CS-CH4 preservation. These results might provide reliable evidence for the benefit of CH4-enriched preservation solution during HTX, through a mechanism which involves the inhibition of pro-apoptotic signals. Hence CH4-enriched preservation solution could be a potential cardioprotective agent in the inventory of heart transplantation surgery and other cardiac surgical procedures requiring prolonged cardioplegia.

Successful Gene Delivery to Cardiac Allograft with Adeno-Associated Viral Vector Using Ex Vivo Storage Perfusion Platform

Cardiac gene therapy remains limited by inefficient transgene delivery with currently available methods (intravenous infusion, transcatheter coronary artery infusion, direct myocardial injection). We previously demonstrated in a porcine heterotopic heart transplant model that cardiac allograft gene transfer can be achieved using ex vivo perfusion with adenovirus (Ad). Adeno-associated viral (AAV) vectors generally achieve lower transgene expression compared to Ad. However, AAV vectors also achieve a significantly longer duration of expression, and thus are more suitable for therapies with genes that are effective even at lower levels but require prolonged expression. The purpose of this study is to evaluate whether ex vivo perfusion can also be used as a platform for cardiac allograft gene therapy using AAV. Heart transplantation was performed using blood type-matched and swine leukocyte antigen-matched Yucatan mini pigs (n=2 transplants). Donor hearts received ex vivo perfusion for two hours with a perfusate including AAV vector bearing the firefly luciferase gene (dosed at 2 × 10^13 and 1 × 10^14 genome-containing vectors for transplants 1 and 2, respectively). The allograft was implanted heterotopically into the recipient abdomen. Recipients were survived for 30 days on oral immunosuppression and then euthanized. Transgene expression in allograft and native recipient tissues was assessed using a luciferase enzymatic assay, and transgene detection was performed using qPCR on DNA extracted using a modified Hirt protocol. Luciferase activity was detected in the allograft in both experiments. While luciferase activity was undetectable in the right and left atria and coronary arteries from the allograft exposed to the lower dose, the higher dose of AAV resulted in detectable luciferase activity throughout the entire heart and at high levels. Luciferase activity was undetectable in all recipient tissues (heart, lung, liver, spleen, and psoas muscle). Additionally, luciferase DNA was detectable on qPCR in allograft specimens (1.5-1.9 × 10^3 transgene copies per 100 ng of DNA). Ex vivo perfusion can be used as a platform for cardiac allograft gene therapy using AAV vectors, with robust transgene expression detectable 30 days following transplant.

Stimulation of soluble guanylate cyclase improves donor organ function in rat heart transplantation

Heart transplantation remains the definitive therapy of end-stage heart failure. Ischemia-reperfusion injury occurring during transplantation is a primary determinant of long-term outcome of heart transplantation and primary graft insufficiency. Modification of the nitric oxide/soluble guanylate cyclase/cyclic guanosine monophosphate signaling pathway appears to be one of the most promising among the pharmacological interventional options. We aimed at characterizing the cardio-protective effects of the soluble guanylate cyclase stimulator riociguat in a rat model of heterotopic heart transplantation. Donor Lewis rats were treated orally with either riociguat or placebo for two days (n = 9) in each transplanted group and (n = 7) in donor groups. Following explantation, hearts were heterotopically transplanted. After one hour reperfusion, left ventricular pressure-volume relations and coronary blood flow were recorded. Molecular biological measurements and histological examination were also completed. Left ventricular contractility (systolic pressure: 117 ± 13 vs. 48 ± 5 mmHg, p < 0.001; dP/dtmax: 2963 ± 221 vs. 1653 ± 159 mmHg/s, p < 0.001), active relaxation (dP/dtmin: −2014 ± 305 vs. −1063 ± 177 mmHg/s, p = 0.02; all at 120 µl of left ventricular volume), and alteration of coronary blood flow standardized to heart weight (2.55 ± 0.32 vs. 1.67 ± 0.22 ml/min/g, p = 0.03) were markedly increased following preconditioning with riociguat. Myocardial apoptosis markers were also significantly reduced in the riociguat pretreated group as well as the antioxidant markers were elevated. Pharmacological preconditioning with riociguat decreases ischemia-reperfusion injury and improves donor organ function in our animal model of heart transplantation. Therefore, riociguat might be a potential cardioprotective agent.

Indoleamine 2,3-dioxgenase-transfected mesenchymal stem cells suppress heart allograft rejection by increasing the production and activity of dendritic cells and regulatory T cells

Expression of indoleamine 2,3-dioxygenase (IDO) in mesenchymal stem cells (MSC) is thought to contribute to MSC-mediated immunosuppression. A lentiviral-based transgenic system was used to generate bone marrow stem cells (BMSC)...

Delivery of FK506-loaded PLGA nanoparticles prolongs cardiac allograft survival.

In this study, FK506-loaded poly(lactide-co-glycolide) nanoparticles (PLGA-FK506-NPs) were developed using an O/W emulsion solvent evaporation method. The PLGA-FK506-NPs were observed to be monodispersed and spherical by transmission and scanning electron microscopy. The mean size and zeta potential measured by dynamic light scattering were 110±1.3nm and -20.56±3.65mV, respectively. The FK506 entrapment and loading efficiency were 94.46±1.88% and 5.38±0.24%, respectively. Moreover, a pharmacokinetics study revealed that the PLGA-FK506-NPs behaved significantly different than free FK506 by exhibiting a higher area under curve (1.69-fold), higher mean residence time (1.29-fold), slower clearance and longer elimination half-life. Notably, the concentrations of FK506 in the spleen and mesenteric lymph nodes of the PLGA-FK506-NP group were 3.1-fold and 2.9-fold higher than those of the free FK506 group. Furthermore, the immunosuppressive efficacy was evaluated in a rat heterotopic heart transplantation model, and the results showed that PLGA-FK506-NP treatment could successfully alleviate acute rejection and prolong allograft survival compared with the free FK506 treatment (mean survival time, 17.1±2.0 versus 13.3±1.7days). In conclusion, PLGA-FK506-NPs are a promising formulation for spleen and lymph node delivery and have potential use in the treatment of cardiac allograft acute rejection.