Review of significant microvascular surgical breakthroughs involving the heart and lungs in rats

Techniques for experimental heterotopic and orthotopic tracheal transplantations — When to use which model?

BACKGROUND

Different animal models have been developed to study the pathogenesis and treatment of obliterative airway disease (OAD). Here we describe the techniques of heterotopic and orthotopic tracheal transplantations in the rat, comparing the kinetics of systemic host immune response and of histopathologic OAD development.

METHODS

Heterotopic and orthotopic tracheal transplantations were performed in both allogeneic (Brown Norway-to-Lewis) and syngeneic (Lewis-to-Lewis) models. Grafts were harvested after 7, 30, and 60 days post-transplant for histologic evaluation and analysis of host cellular and humoral response.

RESULTS

Syngeneic tracheal grafts did not develop luminal obliteration and were morphologically indistinguishable from native tracheas. In heterotopic allografts, airway epithelium was rapidly destroyed and OAD progressed with complete luminal occlusion by 30 days. Orthotopic allografts showed enhanced early infiltration (1298+/-45 vs. 674+/-75 cells/high power field, p<0.001) with concomitant greater day 7 luminal narrowing (45+/-6% vs. 14+/-3%, p<0.001). In this model, donor-type BN epithelium (62+/-17%, 21+/-19%, and 1+/-1% on days 7, 30, and 60) was gradually replaced by recipient-type epithelial cells (2+/-4%, 70+/-22%, and 98+/-2%). OAD developed with circular orientation of cells and connective tissue fibers to 45+/-6% obliteration by day 60. Cellular host response, as determined by IFN-gamma-ELISPOT assay (548+/-132 vs. 402+/-197 spots, p=0.046) and anti-donor alloreactive IgM antibody production (2827+/-148 vs. 1565+/-393 mean channel fluorescence, p<0.001) were significantly stronger in rats bearing orthotopic vs. heterotopic allografts.

CONCLUSIONS

The orthotopic tracheal transplantation model may be more representative of OAD found in human lung transplant recipients and we therefore encourage the wider use of this model.

Sirolimus and FK778: a comparison of two anti-proliferative immunosuppressants for prevention of experimental obliterative airway disease

This study examined the efficacies of sirolimus and the novel immunosuppressive agent FK778 to prevent obliterative airway disease (OAD). Tracheae from Brown-Norway donors were heterotopically transplanted in the greater omentum of Lewis rats. Recipients were treated for 28 days with sirolimus (0.5 or 2 mg/kg), FK778 (5 or 20 mg/kg), or combination regimens (0.5 + 5 mg/kg, 2 + 20 mg/kg). Tracheal segments were evaluated for degree of luminal obliteration, percentage of luminal epithelial cell coverage, and peritracheal infiltration. In vitro smooth muscle cell (SMC) proliferation and migration assays were performed to assess direct nonimmune-related effects of the drugs. Sirolimus 2 mg/kg and FK778 20 mg/kg effectively reduced graft infiltration and prevented airway obliteration, whereas FK778 5 mg/kg was insufficient. Sirolimus 0.5 mg/kg at least showed moderate inhibitory effects on luminal obliteration and graft infiltration. Combination regimens revealed no significant beneficial effects. Both sirolimus and FK778 barely showed preserved epithelial coverage. Within the range of relevant concentrations, FK778 showed more potent anti-proliferative and anti-migratory effects on SMC in vitro than sirolimus. Both agents proved effective to prevent OAD development without preserving relevant amounts of epithelium. The anti-proliferative potency on SMCs seems to be an especially important mechanism for FK778. De novo combination regimens revealed no beneficial interaction and thus remain doubtful.