Diabetes mellitus (DM) is associated with increased risk for the development of in-stent restenosis (ISR) [15
]. Underlying pathogenetic mechanisms are as yet unknown, and adequate treatment modalities are lacking. In order to increase our insights into the molecular and cellular mechanism(s) underlying type 1 DM-enhanced development of ISR a clinically relevant rodent model might be of great value. Yet a model as such is not available. We therefore tested the hypothesis that long-term spontaneously diabetic hyperglycaemic BBDP rats develop enhanced ISR and may be used as a suitable model to study the molecular and cellular mechanism(s) involved in DM-enhanced development of ISR.
The hyperglycemic syndrome in BBDP rats develops spontaneously due to a disturbed balance in autoreactive and regulatory T cells [26
]. The BBDP rat has been suggested to represent the best rodent model for human type 1 DM as in this model diabetes manifests during adolescence and involves an autoimmune disorder without the need of exogenous intervention.
To achieve suboptimally controlled DM with manifest hyperglycaemia and elevated HbA1c
levels, recent onset diabetic BBDP rats were treated with insulin using slow release insulin implants. By doing so, we were able to maintain DM BBDP rats in a rather permanent hyperglycaemic state for at least 8 months. The hyperglycaemic state was associated with increased HbA1c
levels as well as polyuria, polydipsia, proteinuria, and glomerular hyperfiltration. Severity of proteinuria was within the range reported by Cohen et al. who also determined protein excretion in long-term DM BBDP rats that were treated with daily insulin injections [35
]. As older age is associated with increased restenosis rates independent of DM [17
], for our study it was important to include age-matched non-diabetic controls rather than prediabetic young BBDP rats. In order to prevent diabetes development in BBDP rats thymectomy was performed at the age of 21 days as we described previously [30
]. DM and non-DM BBDP rats were followed for 7 months after which they received a bare metal stent implanted in the abdominal aorta. Our results clearly demonstrated that long-term DM significantly enhanced the development of ISR by 32% compared with non-DM age-matched thymectomized BBDP rats. This enhanced development of ISR in diabetic BBDP rats was not associated with increased vascular injury, that is, increased penetration of the stent struts through the internal elastic lamina into the medial layer. The severity of ISR was previously shown to be positively correlated with the mean injury score [29
]. However, in the same study we demonstrated differences in severity of ISR between bare metal and sirolimus-eluting stents, which was independent of the mean injury score. Our data suggest that T1DM enhances the development of ISR by factors other than direct vascular injury.
The current study was performed as a proof of concept to demonstrate that long-term T1DM in BBDP rats indeed enhances the development of ISR following stenting in the abdominal aorta. Although we did not study the underlying mechanism(s) of enhanced ISR in diabetic BBDP rats yet, we suggest that long-term diabetes increases the proliferative and migratory capacity of medial and neointimal smooth muscle cells, thereby facilitating neointima formation [36
]. In addition, reduced endothelial repair capacity in diabetic BBDP rats might have contributed to enhanced ISR [38
], but this needs to be determined.
The major advantage of the BBDP model to study the development of ISR over other T1DM rodent models is the fact that diabetes develops due to autoimmune-mediated destruction of pancreatic islets without having the toxic side effects of the use of streptozotocin or alloxan. By using slow release insulin implants we showed that long-term studies are feasible without the need of daily insulin injections. A possible weakness of the model is that BBDP rats are T cell lymphopenic and are, in that respect, not fully immunocompetent. However, despite T cell lymphopenia BBDP rats do develop autoimmune diabetes which is mediated by autoreactive T cells indicating that functional T cells are present in BBDP rats. Whether T cells are pivotal in the development of ISR is however unclear. Percutaneous transluminal coronary angioplasty has been shown to induce T cell activation in a small cohort of 10 patients with stable angina. Patients that developed restenosis had higher T cell activation levels than patients that did not develop restenosis [39
]. However, treatment with the calcineurin inhibitor cyclosporine to prevent T cell activation did not reduce the development of restenosis in rabbits [40
]. We therefore assume that the presence of T cell lymphopenia in BBDP rats has not been of major influence on the development of ISR.