A Modified Technique for Heterotopic Heart Transplantation in Rats

Animal Models in Allogenic Solid Organ Transplantation

Animal models provide the link between in vitro research and the first in-man application during clinical trials. They provide substantial information in preclinical studies for the assessment of new therapeutic interventions in advance of human clinical trials. However, each model has its advantages and limitations in the ability to imitate specific pathomechanisms. Therefore, the selection of an animal model for the evaluation of a specific research question or evaluation of a novel therapeutic strategy requires a precise analysis. Transplantation research is a discipline that largely benefits from the use of animal models with mouse and pig models being the most frequently used models in organ transplantation research. A suitable animal model should reflect best the situation in humans, and the researcher should be aware of the similarities as well as the limitations of the chosen model. Small animal models with rats and mice are contributing to the majority of animal experiments with the obvious advantages of these models being easy handling, low costs, and high reproductive rates. However, unfortunately, they often do not translate to clinical use. Large animal models, especially in transplantation medicine, are an important element for establishing preclinical models that do often translate to the clinic. Nevertheless, they can be costly, present increased regulatory requirements, and often are of high ethical concern. Therefore, it is crucial to select the right animal model from which extrapolations and valid conclusions can be obtained and translated into the human situation. This review provides an overview in the models frequently used in organ transplantation research.

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.

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.

METHODS

We 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.

RESULTS

CsA 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.

CONCLUSION

Immutol 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.

Improving acute cardiac transplantation rejection therapy using ultrasound-targeted FK506-loaded microbubbles in rats

FK506-MBs combined with the UTMD technique increased drug concentrations in transplanted hearts and enhanced the therapeutic effect.

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.

Pyruvate kinase isoenzyme M2 expression correlates with survival of cardiomyocytes after allogeneic rat heterotopic heart transplantation

The aim of our study was to assess correlations between PKM2 and the survival of cardiomyocytes after heart transplantation in rat. The PKM2, Bcl-xl, active caspase-3 proteins were detected by western blot, and PKM2 was testified by immunohistochemistry and immunofluorescence. At the same time, active caspase-3, α-actinin, VCAM-1, and CD4 were detected by immunofluorescence. Compared with rare expression in syngeneic Lewis rat hearts, the PKM2 protein level in allogeneic hearts was detected at various survival times after transplantation, which prominently expressed on day five postoperatively. In addition, we examined the expression of Bcl-xl and active caspase-3 in allogeneic hearts, which has a similar expression pattern with PKM2. Immunohistochemical and immunofluorescent methods displayed that PKM2 was widely expressed in cardiac tissue, and active caspase-3 was also expressed in cardiomyocytes. However, the PKM2 was not expressed in T cells and other immune response cells. These results suggested that PKM2 may regulate the survival of cardiomyocytes in acute rejection after heart transplantation in rat.

A simple technique for a new working heterotopic heart transplantation model in rats

OBJECTIVE

A new working model of heterotopic heart transplantation in rats was established using a simplified technique.

MATERIALS AND METHODS

Sprague-Dawley rats were used as donors and recipients. The donor left common carotid artery and left pulmonary artery were anastomosed to the recipient left renal artery and vein by a "sleeve and cuff" method, respectively. The donor left ventricle was blood volume loaded by anastomosing the left atrium to the recipient's abdominal aorta in end-to-side fashion. The characteristics of the donor heart were evaluated by palpating the abdominal wall of the rats. We examined the surgical success rate, changes in heart weight, and histology at 1 month after transplantation.

RESULTS

The model was attempted in 32 rats with the success rate of 93.7% (30/32); the 2 failed cases died due to postoperative bleeding. There was no significant difference in mean weight changes between the donor and native hearts at 1 month after transplantation (1.13 ± 0.13 g vs 1.09 ± 0.12 g, P = .244). The donor heart myocardium showed regularly shaped, unidirectional, healthy muscle similar to the native heart.

CONCLUSIONS

The technique was easily learned, allowing less recipient surgical stress. The hemodynamic performance appeared to be similar to the normal cardiac physiological situation, and thus may be more suitable for pre-clinical studies.

Establishment of a novel volume-loaded heterotopic heart transplantation model in rats

BACKGROUND

Non-volume-loaded (NL) donor hearts in the heterotopic heart transplantation model in rats undergo atrophy and thrombus formation in graft cavities after transplantation. The present study aimed to establish a novel model with volume-loaded donor hearts.

METHODS

We used Sprague-Dawley rats as donors and recipients. We established an NL model by anastomosing the donor ascending aorta and pulmonary artery end-to-side to the recipient abdominal aorta and inferior vena cava, respectively, and ligating the superior and inferior vena cava on the donor right atrium. The method of the volume-loaded (VL) model was the same as described above, except we performed an anastomosis of the donor left atrium to the recipient abdominal aorta to allow volume loading of the donor's left ventricle. We assessed the characteristics of the grafts by the surgical success rate, echocardiography, and histologic evaluation between the two models.

RESULTS

Echocardiography showed that donor left ventricle in VL models was volume loaded and had normal systolic and diastolic function compared with the NL models. The mean weight of NL hearts was significantly less than that of VL hearts. Morphologic observation revealed that thrombus formation in donor heart cavities in NL model was significantly higher than that in the VL model. The area of cardiomyocytes per high-power field in the NL model was significantly lower than that in the VL model.

CONCLUSIONS

We provide a novel VL heterotopic heart transplantation model in rats, in which hemodynamic performance of grafts is close to the normal cardiac physiologic situation; thus, the novel model will be more suitable for clinical research.

Peripheral blood T regulatory cell counts may not predict transplant rejection

Background

Recent evidence shows that allograft survival rates show a positive correlation with the number of circulating T regulatory cells (Tregs). This study investigated both the number and the cytokine profiles exhibited by Foxp3⁺ Tregs in blood, spleen and lymph nodes of Lewis rat recipients of BN rat cardiac allografts after a single-dose of Rapamycin (RAPA).

Results

Rats were divided into three groups: control group (containing healthy control and acute rejection group), and recipients treated with a single dose of RAPA on either Day 1 (1D group)or Day 3 (3D group) post-transplant. We analyzed the number of Foxp3+Tregs and the expression of Foxp3 and cytokines in the peripheral blood and the peripheral lymphoid tissues. No difference was found in the numbers of circulating Foxp3+ Tregs between these three groups. RAPA administration significantly increased Foxp3 expression in peripheral lymphoid tissues after a single dose of RAPA on Day 3 post-transplant. Foxp3+Tregs inhibited the activity of effector T cells (T_eff) via the secretion of TGF-β1.

Conclusion

The number of Tregs in the recipient's blood may not be a good predictor of transplant rejection. Foxp3+Tregs inhibit the activity of T_eff cells mainly in the peripheral lymphoid tissues.