Increased angiogenic response but deficient arteriolization and abnormal microvessel ultrastructure in critical leg ischaemia

Abstract

Ischaemia is known to induce angiogenesis, but the effects of critical leg ischaemia (CLI) on angiogenesis remain unclear. The aim of this study was to examine the physiological angiogenic response in CLI by investigating the extent of neovascularization, characterizing microvessel subtypes and determining the microvessel ultrastructure. Gastrocnemius muscles were biopsied from 12 patients with CLI and 12 without leg ischaemia. Microvessels were evaluated immunohistochemically using three endothelial markers (anti-CD31, anti-CD34 and PAL-E) and anti-alpha smooth muscle actin (SMA) as a mural cell marker to label arterioles. Ki67 was used to demonstrate active cell proliferation. Further microvessel ultrastructural characteristics were determined by transmission electron microscopy. The CLI group had significantly higher microvessel density and microvessel : muscle fibre ratio for all endothelial subtypes examined (P < 0.001). PAL-E staining demonstrated the highest increase: 4.7 times higher in CLI muscle. There was no significant difference in alphaSMA-positive microvessel density (P = 0.118) or microvessel: muscle fibre ratio (P = 0.214). Ki67 staining showed no active cell proliferation. Transmission electron microscopy showed CLI microvessels had abnormal morphology, mainly a thick basement membrane. A physiological angiogenic response was found in CLI, but the microvessels had an abnormal ultrastructure. A lack of active cell proliferation suggests that the angiogenic response may have been exhausted.