The orthotopic left lung transplantation in rats: a valuable experimental model without using cuff technique

A modified orthotopic left lung transplantation model in rats

To enhance the operability of the rat orthotopic left lung transplantation model, we implemented several improvements and meticulously detailed the procedure. One hundred and thirty-one healthy male Sprague Dawley rats, weighing between 250 and 300 g, were utilized, with 64 serving as donors, 64 as recipients, and 3 as sham controls. We employed a modified three-cuff technique for the orthotopic left lung transplantation. Notably, our modified perfusion method could prevent donor lung edema, while waist-shaped cuffs minimized suture slippage during anastomosis. Additionally, positioning the recipient rat in a slightly left-elevated supine position during anastomosis reduced tension on the lung hilum, thus mitigating the risk of vascular laceration. The introduction of a unique two-person anastomosis technique significantly reduced operation time and substantially improved success rates. Furthermore, maximizing inflation of donor lungs both during preservation and surgery minimized the occurrence of postoperative atelectasis. Various other procedural refinements contributed to the enhanced operability of our model. Sixty-four rat orthotopic left lung transplantations were performed with only one surgical failure observed. The acquisition time for donor lungs averaged (19 ± 4) minutes, while (11 ± 1) minutes were allocated for donor lung hilum anatomy and cuff installation. Recipient thoracotomy and left lung hilar anatomy before anastomosis required (24 ± 8) minutes, with anastomosis itself taking (31 ± 6) minutes. Remarkably, the survival rate at the 4-h postoperative mark stood at 96.7 %. Even six months post-operation, transplanted left rat lungs continued to exhibit proper inflation and contraction rhythms, displaying signs of chronic pathological changes. In summary, our modified rat model of orthotopic left lung transplantation demonstrates robust operability, significantly reducing surgical duration, improving operation success rates, and enhancing postoperative survival rates. Furthermore, its long-term survival capacity enables the simulation of acute and chronic disease processes following lung transplantation.

Establishment of rat allogenic vein replacement model and pathological characteristics of the replaced vessels

Background

With the advancement of vascular anastomosis techniques in recent years, radical surgery for tumors combined with venous vascular resection and reconstruction has been widely used. This study intends to establish two different rat vein replacement models, and further analyze the pathological changes of blood vessels after replacement.

Methods

Brown-Norway (BN) rats were selected as donors and recipients, randomly divided into control group, cuff group (1-week group, 2-week group, and 4-week group), and suture group (1-week group, 2-week group, and 4-week group), with 6 rats in each group. The perioperative conditions, inner diameter, flow velocity and histopathological changes of the replaced vessels at different time points were analyzed.

Results

Both cuff group and suture group can safely establish the rat vein replacement model. From the surgical operation, the operation time and venous cross-clamp time in the cuff group were shorter than those in the suture group (P < 0.05). At 2 and 4 weeks after operation, the diameter of suture group was wider than that of cuff group, and the flow rate was faster (P < 0.05). With prolonged postoperative survival, the wall of the replaced vessels underwent infiltration of CD4+ and CD8+ lymphocytes and high TGF-β1 gene expression. This leads to the proliferation of blood vessels and intimal layer. The results of vascular pathological staining showed that the infiltration degree of CD4+ lymphocytes at 2 weeks after operation and CD8+ lymphocytes at 4 weeks after operation in the suture group was lighter than that in the cuff group (P < 0.05). Meanwhile, TGF-β1 gene content at 4 weeks after operation in suture group was significantly lower than that in cuff group (P < 0.05).

Conclusion

Compared with cuff method, suture method is more suitable for the study of long-term pathological changes after vein replacement in rats. The main pathological changes in the long term after venous replacement in syngeneic background may be vascular fibrosis caused by inflammatory cell infiltration.

Vein Suturing Results in Worse Lung Graft Outcomes Compared to the Cuff Method

BACKGROUND

The rat orthotopic lung transplant model is not widely used yet because of the complexity of the procedure, in particular, venous anastomosis. Here, we performed a rat orthotopic lung transplantation using either the suture (ST) or cuff (CT) method for vein anastomosis.

OBJECTIVES

To compare the vein ST and CT techniques in terms of operative time, success, recipient survival, and early histological outcomes was the objective of this study.

METHODS

A total of 24 left lung transplants in rats were performed. Twelve syngeneic (Lewis to Lewis) and 12 allogeneic (Brown-Norway to Lewis) lung transplants were performed using either the vein ST or the CT procedure. Arterial and bronchial anastomoses were performed with the CT technique. Graft histological damage was evaluated 3-7 days post-transplant in all rat lungs.

RESULTS

The surgical success rate was 75% in both the ST and CT groups. Failures related mainly to vein bleeding (n = 2 in the ST group) and thrombosis (n = 1 in the ST group; n = 2 in the CT group). Total ischemia time was longer in the ST group (122 ± 25 min in ST group vs. 83 ± 10 min in CT group, mean ± SD), due to prolonged warm ischemia time (60 ± 12 min in the ST group vs. 21 ± 5 min in the CT group, mean ± SD), reflecting the time required to complete the vein ST procedure. The prolonged warm ischemia time resulted in significantly higher vascular inflammation in syngeneic grafts (2.3 ± 1.2 ST group vs. 0 in the CT group, mean ± SD) and in increased severity of ischemia/reperfusion injury and acute graft rejection (3.6 ± 0.4 in the ST group vs. 2.6 ± 0.4 in the CT group, mean ± SD) in allogeneic lung transplants.

CONCLUSIONS

The vein ST technique is a more time-consuming procedure than the CT method and the prolonged anastomosis time has a deleterious impact on transplant outcomes. These findings suggest that warm ischemia time - one of the modifiable transplant factors - should be considered a major risk factor in lung transplantation, particularly in the setting of donation after cardiac death.

Anastomotic techniques for rat lung transplantation

The first lung transplantation in the rat was achieved by Asimacopoulos et al using sutured anastomoses in 1971. Subsequent development of a cuffed technique to construct the anastomoses by Mizuta and colleagues in 1989 represented a breakthrough that resulted in simplification of the procedure and shorter warm ischemic times. Since then, a number of further variations on the technique of rat lung transplantation have been described. In spite of this, the procedure remains technically demanding and involves a long learning curve. This minireview describes the following new technical safeguards to further evolve the technique for cuffed anastomoses in rat lung transplantation: the use of anatomical landmarks to avoid twisting of the everted donor pulmonary vein and bronchus in the cuff, the use of the cuff tie as a landmark to avoid twisting of the anastomotic cuffs relative to the recipient vessels, distal ties on the recipient vessels to achieve a bloodless field and triangulation of the venotomy to avoid pulmonary vein tearing.

Revascularization of the graft in obliterative bronchiolitis after heterotopic tracheal transplantation

Obliterative bronchiolitis is the principal long-term problem for lung transplant patients. One of the simplest and most reproducible animal models of obliterative bronchiolitis is heterotopic tracheal transplantation in subcutaneous tissue, where the graft is not primarily vascularized. We demonstrate here the rapid graft revascularization and the kinetics of expression of its angiogenic and lymphatic factors. We performed iso- and allotracheal transplantations harvested on day 0-21. The number of functional blood vessels, quantified after intravenous biotinylated dextran administration, increased from D0 (0 for both iso- and allografts) to D21 (44 ± 8 vessels/mm(2) in isografts and 22 ± 3 in allografts, P < 0.001 for both vs. D0). VEGF mRNA expression assessed by qPCR peaked on D1 (4.3-fold increase in isografts and 4.0-fold in allografts, P < 0.0001 for both vs. D0), but receded thereafter. Angiopoietin-1, involved in the maturation of the neoformed vessels, increased later on, by 6.2-fold (P < 0.05) in isografts and 11.5-fold in allografts (P < 0.001) by D21, and angiopoietin-2 by 7.8-fold in isografts (P < 0.05) and 13.8-fold in allografts (P < 0.01). Although always present in the iso- and allografts, there were significantly more and larger LYVE1(+) lymphatic vessels at D21 in allografts than in isografts. Thus, we demonstrate that tracheal grafts are rapidly revascularized by functional blood and lymphatic vessels, due to early VEGF and subsequent angiopoietins expression, which is a new advantage of this model, in addition to its ease of use, reproducibility, and viability in the absence of immunosuppressive treatment.

Improvements of the surgical technique on the established mouse model of orthotopic single lung transplantation

BACKGROUND

A wide range of knockout and transgenic murine models for the study of nonimmune and immune mechanisms in lung transplants are available nowadays, but the microsurgical techniques are difficult to learn. We describe methods to simplify techniques and facilitate learning.

METHODS

Traditional procedures were implemented to perform lung transplants in 30 cases (group 1). Improved techniques which included cuff without tail, broadening of the cuff diameter for bronchus, establishment of one tunnel between three structures, innovative technology of the vascular anastomosis and placement of the chest tube post-operation were used to perform lung transplants in 30 cases (group 2).

RESULTS

The improved techniques considerably shorten operative times (96.75 ± 6.16 min and 85.32 ± 6.98 min in groups 1 and 2, respectively). The survival rates in the recipient animals were 86.7% and 96.7% in groups 1 and 2, respectively. Chest X-rays and macroscopic changes of transplanted recipients showed that grafts were well inflated on postoperative day 30. There was no significant difference of the arterial oxygen tension (PaO2) between two groups (115.9 ± 7.11 mm Hg and 116.3 ± 6.87 mm Hg in groups 1 and 2, respectively). Histologically, no lung injury was seen in grafts.

CONCLUSIONS

We described the modified procedures of orthotopic left lung transplants in mice, which could shorten operative time and increase survival rate.