Early graft failure after heart transplantation: prevention and treatment

[Histological and ultrastructural analysis of biopsy specimens of donor heart under conditions of extended period of pharmaco-cold ischaemia]

OBJECTIVE

At the histological and ultramicroscopic level, compare biopsy specimens of donor heart under standard (up to 240 min) and extended (more than 240 min) periods of pharmaco-cold preservation.

MATERIAL AND METHODS

Biopsy specimens of the left atrium of donor hearts: group 1 - 8 samples after transportation with pharmaco-cold preservation of the graft in Bretschneider solution (Dr. Franz Köhler Chemie GmbH, Germany) up to 240 min, (Me 140), and group 2 - 5 samples after an extended pharmaco-cold period (more than 240 min; Me 375) were examined using light microscopy of semi-thin sections and transmission electron microscopy, followed by stereological and statistical analysis.

RESULTS

A comparative study of the myocardium of donor hearts revealed stereotypical dystrophic changes in cardiomyocytes. Semi-thin sections demonstrated a mosaic pattern of myocardial parenchyma in both groups, caused by contracture and less pronounced lytic changes in myocytes, which were accompanied by stromal edema without statistically significant differences according to stereological studies. Ultrathin sections of the perinuclear zones of cardiomyocytes visualized reduction and focal damage to myofibrils and mitochondria in combination with pronounced autophagy; at the same time, with a shorter duration of the pharmaco-cold period, the stereological indicators of cardiomyocyte organelles indicated a relatively better supply of myofibrils with mitochondria.

CONCLUSION

The results obtained suggest a sufficiently high degree of preservation of the tissue and ultrastructural organization of donor hearts with prolonged (more than 240 min) pharmaco-cold ischemia to restore adequate cardiac activity after heart transplantation.

TFNR2 in Ischemia-Reperfusion Injury, Rejection, and Tolerance in Transplantation

Tumor necrosis factor receptor 2 (TNFR2) has been shown to play a crucial role in CD4+ T regulatory cells (CD4+Tregs) expansion and suppressive function. Increasing evidence has also demonstrated its role in a variety of immune regulatory cell subtypes such as CD8+ T regulatory cells (CD8+ Tregs), B regulatory cells (Bregs), and myeloid-derived suppressor cells (MDSCs). In solid organ transplantation, regulatory immune cells have been associated with decreased ischemia-reperfusion injury (IRI), improved graft survival, and improved overall outcomes. However, despite TNFR2 being studied in the context of autoimmune diseases, cancer, and hematopoietic stem cell transplantation, there remains paucity of data in the context of solid organ transplantation and islet cell transplantation. Interestingly, TNFR2 signaling has found a clinical application in islet transplantation which could guide its wider use. This article reviews the current literature on TNFR2 expression in immune modulatory cells as well as IRI, cell, and solid organ transplantation. Our results highlighted the positive impact of TNFR2 signaling especially in kidney and islet transplantation. However, further investigation of TNFR2 in all types of solid organ transplantation are required as well as dedicated studies on its therapeutic use during induction therapy or treatment of rejection.

Mitochondrial transplantation prolongs cold ischemia time in murine heart transplantation

BACKGROUND

Cold ischemia time (CIT) causes ischemia‒reperfusion injury to the mitochondria and detrimentally effects myocardial function and tissue viability. Mitochondrial transplantation replaces damaged mitochondria and enhances myocardial function and tissue viability. Herein we investigated the efficacy of mitochondrial transplantation in enhancing graft function and viability after prolonged CIT.

METHODS

Heterotopic heart transplantation was performed in C57BL/6J mice. Upon heart harvesting from C57BL/6J donors, 0.5 ml of either mitochondria (1 × 10⁸ in respiration buffer; mitochondria group) or respiration buffer (vehicle group) was delivered antegrade to the coronary arteries via injection to the coronary ostium. The hearts were excised and preserved for 29 ± 0.3 hours in cold saline (4°C). The hearts were then heterotopically transplanted. A second injection of either mitochondria (1 × 10⁸) or respiration buffer (vehicle) was delivered antegrade to the coronary arteries 5 minutes after transplantation. Grafts were analyzed for 24 hours. Beating score, graft function, and tissue injury were measured.

RESULTS

Beating score, calculated ejection fraction, and shortening fraction were significantly enhanced (p < 0.05), whereas necrosis and neutrophil infiltration were significantly decreased (p < 0.05) in the mitochondria group as compared with the vehicle group at 24 hours of reperfusion. Transmission electron microscopy showed the presence of contraction bands in vehicle but not in mitochondria grafts.

CONCLUSIONS

Mitochondrial transplantation prolongs CIT to 29 hours in the murine heart transplantation model, significantly enhances graft function, and decreases graft tissue injury. Mitochondrial transplantation may provide a means to reduce graft failure and improve transplantation outcomes after prolonged CIT.

Perioperative myocardial injury after adult heart transplant: determinants and prognostic value

Background and Aim of the Study

Implications of Cardiac troponin (cTnI) release after cardiac transplantation are still unclear. This study disclosed risk factors and prognostic implication of cTnI early levels in a single centre cohort operated on between January 1999 and December 2010.

Methods

Data on 362 consecutive recipients (mean age: 47.8±13.7, 20.2% female, 18.2% diabetics, 22.1% with previous cardiac operations, 27.6% hospitalized, 84.9±29.4 ml/min preoperative glomerular filtration rate) were analyzed using multivariable logistic regression modeling. Target outcomes were determinants of troponin release, early graft failure (EGF), acute kidney injury (AKI) and operative death.

Results

Mean cTnI release measured 24 hours after transplant was 10.9±11.6 μg/L. Overall hospital mortality was 10.8%, EGF 10.5%, and AKI was 12.2%. cTnI release>10 μg/L proved an independent predictor of EGF (OR 2.2; 95% CI, 1.06–4.6) and AKI (OR 1.031; 95% CI, 1.001-1.064). EGF, in turn, proved a determinant of hospital mortality. Risk factors for cTnI>10 μg/L release were: status 2B (OR 0.35; 95% CI, 0.18-0.69, protective), duration of the ischemic period (OR 1.006; 95% CI, 1.001-1.011), previous cardiac operation (OR 2.9; 95% CI, 1.67-5.0), and left ventricular hypertrophy (OR 3.3; 95% CI, 1.9-5.6).

Conclusions

Myocardial enzyme leakage clearly emerged as an epiphenomenon of more complicated clinical course. The complex interplay between surgical procedure features, graft characteristics and recipient end-organ function highlights cTnI release as a risk marker of graft failure and acute kidney injury. The search for optimal myocardial preservation is still an issue.

Correlation of serum- and glucocorticoid-regulated kinase 1 expression with ischemia-reperfusion injury after heart transplantation

IRI of a transplanted heart may result in serious early and late disadvantageous effects such as increased allograft immunogenicity, primary graft dysfunction, and initiation of fibroproliferative cascades that compromise the survival of the recipient. Sgk-1 has recently been linked to cell growth and survival. It has been reported that through a renal transplantation model, Dexa increases Sgk-1 expression and therefore protects from renal IRI. In our current study, we aim to assess the expression of Sgk-1 and its protective effects on cardiomyocyte IRI after heart transplantation. Heart allograft model was performed from Wistar into Lewis, and isograft model was from Lewis into Lewis. Grafts were then harvested at one, six, 12, or 24 h post-transplantation for Sgk-1 expression analyses. In some groups, part donors were treated with Dexa 2 h prior at doses of 0.05, 0.5 and 2 mg/BWkg, respectively. Sgk-1 expression was markedly increased in grafted heart 6-12 h post-transplantation in both the allogenic and isogenic models. Immunostaining experiments confirmed that Sgk-1 was expressed in cardiomyocytes rather than infiltrated immune cells. Furthermore, Dexa treatment significantly increased Sgk-1 expression and the donor cardiomyocyte injury was greatly minimized by Dexa treatment. These results suggest that induction of Sgk-1 might explain some of the beneficial impact of corticosteroids in IRI and hence might have therapeutic implications.

MicroRNA and mRNA signatures in ischemia reperfusion injury in heart transplantation

Ischemia reperfusion (I/R) injury is an unavoidable event occurring during heart transplantation, leading to graft failures and lower long-term survival rate of the recipient. Several studies have demonstrated that microRNAs (miRNAs) are vital regulators of signalling pathways involved in I/R injury. The present study aims to quantify the altered expression levels of miRNA and mRNA upon I/R injury in a mouse heart transplantation model, and to investigate whether these miRNA can regulate genes involved in I/R injury. We performed heterotopic heart transplantation on mouse models to generate heart tissue samples with I/R and non-I/R (control). The expression levels of miRNAs as well as genes were measured in heart grafts by microarray and real time RT-PCR. miRNA alteration in cardiomyocytes exposed to hypoxia was also detected by qRT-PCR. We observed significant alterations in miRNA and gene expression profile after I/R injury. There were 39 miRNAs significantly downregulated and 20 upregulated up to 1.5 fold in heart grafts with I/R injury compared with the grafts without I/R. 48 genes were observed with 3 fold change and p<0.05 and 18 signalling pathways were enriched using Keggs pathway library. Additionally, hypoxia/reperfusion induced primary cardiomyocyte apoptosis and altered miRNA expression profiles. In conclusion, this is the first report on miRNA expression profile for heart transplantation associated with I/R injury. These findings provide us with an insight into the role of miRNA in I/R injury in heart transplantation.