Ocular dysfunction in a mouse model of chronic gut inflammation

Recovery of Ischemic Limb and Femoral Artery Endothelial Function Are Preserved in Mice with Dextran Sodium Sulfate-Induced Chronic Colitis

Simple Summary

The present study examines the effect of experimental inflammatory bowel disease on femoral artery endothelial function and limb ischemia recovery in female mice using a chronic colitis model induced by dextran sodium sulfate exposure. As expected, plasma levels of proinflammatory cytokines, including interleukin-6, interleukin-17, tumor necrosis factor alpha, and chemokine ligand 1, were significantly increased in the chronic colitis model. However, ROS levels in the ischemic muscle tissues were not significantly increased in mice with colitis as compared to controls. There were no significant changes in endothelium-dependent or -independent vasodilation of femoral artery between the colitis model and the control. Recovery of function and blood flow of the ischemic limb and capillary density in the ischemic muscle were preserved in the colitis model as compared with the control.

Abstract

Inflammatory bowel disease (IBD) produces significant systemic inflammation and increases the risk of endothelial dysfunction and peripheral artery disease. Our recent study demonstrated that abdominal aortic endothelial cell function was impaired selectively in female mice with chronic colitis. This study aimed to test the hypothesis that experimental colitis leads to femoral artery endothelial cell dysfunction and impairs limb ischemia recovery in female mice. An experimental chronic colitis model was created in female C57BL/6 mice with dextran sodium sulfate (DSS) treatment. Unilateral hind limb ischemia was produced by femoral artery ligation. Limb blood perfusion, vascular density, tissue ROS levels, and plasma levels of proinflammatory cytokines were assessed. Femoral artery endothelium-dependent and -independent vasodilation of the contralateral limb were evaluated ex vivo using acetylcholine and nitroglycerin, respectively. As expected, the plasma levels of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, and IL-17, were significantly increased in the DSS-induced colitis model. However, ROS levels in the ischemic muscle tissues were not significantly increased in colitis model as compared to the controls. There were no significant changes in endothelium-dependent or -independent vasodilation of the femoral artery between colitis model and the control. Recovery of function and blood flow in the ischemic limb and capillary density in the ischemic gastrocnemius muscle were preserved in the colitis model as compared with the control. The data demonstrated that DSS-induced chronic colitis had no significant impact on femoral artery endothelial function or ischemic limb recovery in female mice.

Abdominal Aortic Endothelial Dysfunction Occurs in Female Mice With Dextran Sodium Sulfate-Induced Chronic Colitis Independently of Reactive Oxygen Species Formation

Background and Objective

Inflammatory bowel disease (IBD) produces significant local and systemic inflammation with increased reactive oxygen species (ROS) formation. IBD Patients are at an increased risk for developing endothelial dysfunction and cardiovascular diseases. The present study tested the hypothesis that IBD impairs aortic endothelial function via ROS formation and investigate potential sex-related differences.

Methods and Results

Acute and chronic colitis models were induced in male and female C57BL/6 mice with dextran sodium sulfate (DSS) treatment. Aortic wall stiffness, endothelial function, and ROS levels, as well as serum levels of pro-inflammatory cytokines were evaluated. Acetylcholine (Ach)-induced endothelium-dependent relaxation of abdominal aorta without perivascular adipose tissue (PVAT) was significantly reduced in female mice, not males, with chronic colitis without a change in nitroglycerin-induced endothelium-independent relaxation. PVAT effectively preserved Ach-induced relaxation in abdominal aorta of female mice with chronic colitis. Aortic peak velocity, maximal intraluminal diameters, pulse wave velocity, distensibility and radial strain were preserved in mice with both acute and chronic colitis. Although pro-inflammatory cytokines levels were increased in mice with acute and chronic colitis, aortic ROS levels were not increased.

Conclusion

The data demonstrate that abdominal aortic endothelial function was attenuated selectively in female mice with chronic colitis independent of ROS formation. Further, PVAT played an important role in preserving endothelial function in female mice with chronic colitis.

MAdCAM-1 mediates retinal neuron degeneration in experimental colitis through recruiting gut-homing CD4+ T cells

Extra-intestinal manifestations (EIMs) of the eyes are found in IBD patients, but the underlying pathogenesis remains unknown. To investigate the pathogenesis of IBD-associated retinal dysfunction, chronic colitis was induced in mice by oral administration of dextran sodium sulfate (DSS). Electroretinography (ERG) was performed to evaluate retinal function. Retinal neuron degeneration was analyzed by immunohistochemistry. Colitic mice displayed aberrant amplitudes of ERG a-, b-wave and oscillatory potentials (OP). Importantly, we observed severe degeneration of bipolar and ganglion cells. In contrast, outer retinal neurons (mainly photoreceptor cells) are mildly affected by colitis. Moreover, retinal inflammatory responses were significantly upregulated during colitis, including microglia activation, lymphocyte infiltration and cytokine/chemokine production. Notably, mucosal addressin cell adhesion molecule 1 (MAdCAM-1) was upregulated in retinal microvessels, especially the superficial and deep plexuses, and recruited gut-homing CD4⁺ T cells to be co-localized with bipolar and ganglion cells during colitis. Expectedly, in vivo depletion of CD4⁺ T cells or blockade of MAdCAM-1 greatly alleviated colitis-induced retinal inflammatory responses and neuron degeneration. Therefore, our data provide novel insight into the pathogenesis of IBD-associated retinal dysfunction, and targeted immune therapy directly against MAdCAM-1 might provide a novel approach in the management of eye EIM of IBD.

Anemia and retinal function in a mouse model of acute colitis

Individuals with inflammatory bowel diseases (IBD) have an elevated risk of ocular inflammation. Both the anterior and posterior eye can be affected by IBD, although posterior eye dysfunction is more likely to go undetected. Little investigative attention has been directed toward the mechanisms of ocular dysfunction with IBD; however, given the prevalence of anemia in IBD and the effects of anemia on the retina, we examined the association between retinal function (electroretinography, ERG) and the anemia induced by experimental IBD, and we tested for a potential retinal benefit of acutely attenuating anemia (via red blood cell (RBC) infusion). Colitis was induced in mice in a model involving drinking water ingestion of dextran sodium sulfate (DSS), with untreated drinking water administered to controls. A subset of the DSS mice was infused with RBCs to attenuate the severity of the anemia induced by DSS. ERG signals (a-waves, b-waves, and oscillatory potential amplitudes and implicit times) were compared between the three groups of mice to evaluate retinal function. ERG amplitudes were significantly decreased in DSS mice compared to controls, with the amplitudes demonstrating a positive correlation with hematocrit, that is, the lowest ERG amplitudes were found with the most severe cases of anemia. An acute infusion of RBCs into DSS mice provided an improvement in the oscillatory potential implicit times, but no significant improvements in other ERG parameters. Despite the association between anemia and ERG signals in DSS-induced colitis, acute RBC infusion may only partially attenuate the associated retinal dysfunction.

Decreased retinal blood flow in experimental colitis; improvement by eye drop administration of losartan

Patients with inflammatory bowel disease suffer not only from gut inflammation, but also from extraintestinal manifestations of the disease, including ocular pathology. The mechanisms causing ocular inflammation in these patients are unknown. The purpose of the current study was to investigate the possible vascular changes occurring in the retina using a mouse model of acute colitis, that is, ingestion of dextran sodium sulfate (DSS). Intravital microscopy of anesthetized mice revealed that DSS caused a significant 30-40% decrease in retinal red blood cell velocities, and a 45% decrease in total retinal blood flow, but no changes in intraocular pressure. To determine whether the decreases in retinal perfusion could be inhibited by an angiotensin II receptor antagonist, losartan was administered by eye drops in a subset of the mice prior to the intravital microscopy measurements. Topical losartan was able to largely attenuate the altered hemodynamics induced by DSS. We conclude that angiotensin II might be a possible target for reducing the vascular changes occurring distantly in the eye during colitis.