Modified labeling technique for in vivo visualization of platelets in the cerebral microcirculation of Mongolian gerbils

Shedding-induced gap formation contributes to gut barrier dysfunction in endotoxemia

BACKGROUND

The intestinal mucosa exhibits high turnover rates with a balance of shedding and the migration of epithelial cells to maintain gut barrier function. Systemic diseases such as sepsis and major thermal injury accelerate the rate of cell shedding, subsequent gap formation, and gut barrier dysfunction. However, the detailed changes of intestinal villi in barrier dysfunction have not been well described.

METHODS

In this study, intestinal barrier dysfunctions were induced through the injection of lipopolysaccharide (LPS) in C57BL/6 mice. Intravital images of the small intestine were observed with multiphoton microscopy for cellular dynamics analysis. The changes of epithelial cells shedding, gap formation, goblet cells, and intestinal leaks were observed, calculated, and analyzed.

RESULTS

Endotoxemia enhanced chromatin condensation, accelerated migration, and increased the shedding of intestinal epithelial cells compared with the control group. Furthermore, LPS-induced shedding resulted in gap formation and subsequent intestinal leaks. In total, 40% of intestinal leaks were through gaps, and 60% were through paracellular spaces. Although LPS injection significantly increased the leaks in gaps and paracellular spaces, it did not change the percentage of leaks in gaps and paracellular spaces compared with the control group.

CONCLUSION

We conclude that endotoxemia causes gut barrier dysfunction by increasing epithelium shedding, gaps, and intestinal leaks. However, the effect of the impairment of local barrier maintenance on the distribution of intestinal leaks in gaps and paracellular spaces is minimal.

Bradykinin-induced leukocyte- and platelet-endothelium interactions in the cerebral microcirculation

Bradykinin is known for its pathophysiological role as mediator of inflammation. Following cerebral ischemia, bradykinin promotes the secondary brain damage through an increase of vascular permeability and brain edema formation, again hallmarks of inflammation. It is not clear, whether bradykinin also activates inflammatory cells and regulates microcirculatory blood flow in the brain. The purpose of the study is to investigate the reaction of bradykinin upon cerebral leukocyte- and thrombocyte-endothelium interactions as well as microvascular perfusion. Intravital fluorescence microscopy of pial blood vessels was performed in gerbils. Intracarotid injection of bradykinin resulted in increased numbers of rolling and adherent leukocytes as well as rolling platelets at the venular endothelium. This was reversed by administration of a bradykinin B2 receptor antagonist. In contrast, after additional administration of a B1 receptor antagonist, microvascular blood-flow and capillary density was decreased. We conclude that bradykinin initiates leukocyte- and platelet-endothelium interactions in the cerebral microcirculation via activation of B2 receptors. Activation of B1 receptors ensures regular cerebral perfusion. Thus, to attenuate secondary brain damage, inhibition of B2 but not B1 receptors might be of therapeutical benefit.