A novel model of accelerated intimal hyperplasia in the pig iliac artery

Abstract

There is no good animal model of large artery injury-induced intimal hyperplasia (IH). Those available are reproducible, providing only a few layers of proliferating cells or have the disadvantage of the presence of a metallic stent that complicates histology evaluation. This study was designed to develop a new, simple model of accelerated IH based on balloon injury in conjunction with disruption of the Internal Elastic Lamina (IEL) in pig external iliac arteries. Iliac artery injury (n = 24) was performed in 12 Yorkshire pigs divided in two groups: Group I (n = 10), overdistention injury induced by an oversized non-compliant balloon; Group II (n = 14), arterial wall disruption by pulling back an isometric cutting balloon (CB) followed by stretching with a compliant Fogarty Balloon (FB). At two weeks, arteries were processed for morphometric analysis and immunohistochemistry (IHC) for smooth muscle cells (SMC) and proliferating cell nuclear antigen (PCNA). When comparing the two groups, at 2 weeks, arteries of group II had a higher incidence of IH (100%vs. 50%, P = 0.0059), increased intimal areas (2.54 ± 0.33 mm(2) vs. 0.93 ± 0.36 mm(2) , P = 0.004), increased intimal area/Media area ratios (0.95 ± 0.1 vs. 0.28 ± 0.05; P < 0.0001) and decreased lumen areas (6.24 ± 0.44 vs. 9.48 ± 1.56, P = 0.026). No thrombosis was noticed in Group II. Neointima was composed by proliferating SMC located with the highest concentration in the area of IEL disruption (IHC). Arterial injury by pulling back CB and FB induces significant IH in pig iliac arteries by two weeks without thrombosis. This model is superior to the classical overdistention non-compliant model and should be useful and cost-effective for preclinical testing of procedures designed to inhibit IH in large peripheral arteries.

Figure 1

(a) Lawson's elastic van Gieson stain; Non-injured external iliac artery (EIA); magnification ×100. (b) Injured EIA from Group II, Lawson's elastic van Gieson stain, (magnification ×25). (c) Injured EIA from Group II, IHC using anti-smooth muscle α-actin antibody (1:100), Smooth muscle cells are brown stained (magnification ×200), and Hematoxylin counterstaining was used. Black arrow: Internal Elastic Lamina (IEL); Single star: Media; Double star: NeoIntima; White arrow: disrupted IEL. Note the abundant presence of SMC in the neointima.

Figure 2

Intimal area/medial area ratio 14 days after injury. Mean (±standard error of the mean) of Group I (n = 10, oversized Cutting Balloon and non-compliant balloon), and Group II (n = 14, pull-back of Cutting Balloon and Fogarty Balloon). Group II > Group I (Student's t-test, P<0.0001).

Figure 3

Immuno-histo-chemistry using anti-proliferating cell nuclear antigen (PCNA) antibody. Proliferative cells are brown coloured stained. (a) Non-injured external iliac artery (EIA) (magnification ×100), non-PCNA detected. (b) Injured EIA from Group II (magnification ×200), note the presence in the neointima and the media of proliferative cells, proliferative cells are abundant where the Internal Elastic Lamina (IEL) is disrupted. Black arrow: IEL; single star: Media; double star: NeoIntima; white arrow: disrupted IEL.