Acquired microvascular dysfunction in inflammatory bowel disease: Loss of nitric oxide-mediated vasodilation

Background & Aims: Inflammatory bowel disease (IBD; i.e., Crohn's disease, ulcerative colitis) is characterized by refractory inflammatory ulceration and damage to the intestine. Mechanisms underlying impaired healing are not defined. Because microvascular dysfunction resulting in diminished vasodilatory capacity and tissue hypoperfusion is associated with impaired wound healing, we hypothesized that microvascular dysfunction may also occur in chronic IBD. Methods: Intact submucosal arterioles from control, involved, and uninvolved IBD specimens were assessed using in vitro videomicroscopy to assess endothelium-dependent vasodilation in response to acetylcholine (Ach) and fluorescence microscopy to detect oxyradicals. Results: Normal microvessels dilated in a dose-dependent and endothelium-dependent manner to Ach (maximum, 82% ± 2%; n = 34). Inhibition of nitric oxide synthase with N^G-nitro-L-arginine methyl ester (L-NAME) reduced maximal dilation to 54% ± 6% (P < 0.05, n = 7), and further reduction was observed after inhibiting cyclooxygenase (indomethacin; 23% < 10%, n = 6). Chronically inflamed IBD microvessels showed significantly reduced Ach-induced vasodilation (maximum, 15% ± 2%; n = 33), with no effect of L-NAME. Indomethacin eliminated the remaining Ach-induced vasodilation, resulting in frank vasoconstriction (-54% ± 9%, n = 6). Uninvolved IBD gut vessels and non-IBD inflammatory controls responded in a fashion similar to normal vessels. IBD-involved microvessels generated significantly higher levels of reactive oxygen species compared with control and uninvolved IBD vessels (P < 0.01). Conclusions: Human intestinal microvessels from chronically inflamed IBD show microvascular endothelial dysfunction, characterized by loss of NO-dependent dilation that may contribute to reduced perfusion, poor wound healing, and maintenance of chronic inflammation.