Attenuation of endotoxin-induced intestinal microcirculatory damage by eicosapentanoic acid

Deoxycholic acid enhancement of lymphocyte migration through direct interaction with the intestinal vascular endothelium

BACKGROUND AND AIM

The small intestine plays a central role in gut immunity, and enhanced lymphocyte migration is involved in the pathophysiology of various enteropathy. Bile acid (BA) is closely related to lipid metabolism and gut microbiota and essential for gut homeostasis. However, the effects of BA on gut immunity have not been studied in detail, especially on the small intestine and lymphocyte migration. Therefore, we aimed to investigate the effect of BA on small intestinal lymphocyte microcirculation.

METHODS

The effect of deoxycholic acid (DCA), taurocholic acid (tCA), or cholic acid (CA) on the indomethacin (IND)-induced small intestinal enteropathy in mice was investigated. Lymphocyte movements were evaluated after exposure to BA using intravital microscopy. The effects of BA on surface expression of adhesion molecules on the vascular endothelium and lymphocytes through BA receptors were examined in vitro.

RESULTS

IND-induced small intestinal enteropathy was histologically aggravated by DCA treatment alone. The expression of adhesion molecules ICAM-1 and VCAM-1 was significantly enhanced by DCA. Exposure to DCA increased lymphocyte adhesion in the microvessels of the ileum, which was partially blocked by anti-α4β1 integrin antibody in vivo. The expression of ICAM-1 and VCAM-1 was significantly enhanced by DCA in vitro, which was partially suppressed by the sphingosine-1-phosphate receptor 2 (S1PR2) antagonist. The S1PR2 antagonist significantly ameliorated IND-induced and DCA-exaggerated small intestinal injury.

CONCLUSION

DCA exacerbated IND-induced small intestinal enteropathy. DCA directly acts on the vascular endothelium and enhances the expression levels of adhesion molecules partially via S1PR2, leading to enhanced small intestinal lymphocyte migration.

Regional intestinal blood flow and nitric oxide synthase inhibition during sepsis in the rat

OBJECTIVE

Regional circulatory changes in intestinal mucosa were evaluated after the onset of septic shock and the effect of nitric oxide (NO) inhibition on mucosal blood flow was investigated at different locations along the intestine.

SUMMARY BACKGROUND DATA

The response of intestinal blood flow to different physiologic and pharmacologic stimuli is known to vary along the intestine, but limited data are available on regional alterations in intestinal blood flow during septic shock. These regional variations in intestinal blood flow could become important because NO inhibition might restore the circulation of one segment of the gut or exacerbate ischemia that may be occurring concomitantly in another segment of the intestine.

METHODS

Mucosal blood flow was studied with fluorescent microspheres in conscious unrestrained rats before and 2, 4, and 6 hours after lipopolysaccharide (LPS, 20 mg/kg intraperitoneally) induced sepsis in the presence and absence of the nitric oxide synthase inhibitor N(G)-nitro-L-argininemethylester (L-NAME, 5 mg/kg subcutaneously).

RESULTS

Control mucosal blood flow was significantly higher in the ileum than in the duodenum, jejunum, or colon. During LPS-induced sepsis, mucosal blood flow to the ileum decreased and perfusion to the remaining gut was preserved. This was accompanied by hypotension throughout the experiment. L-NAME administration during sepsis prevented hypotension and decreased mucosal blood flow to all segments of small intestine at 2 hours. In this group, mucosal blood flow to the proximal small intestine but not to the ileum returned to baseline levels at 4 and 6 hours. L-NAME alone decreased mucosal blood flow to the small intestine throughout the experiment.

CONCLUSIONS

This study indicates that mucosal blood flow alterations during septic shock vary along the intestine, with a significant change only in the ileum, suggesting that perfusion in the small intestine is dependent on physiologic NO production.

Retinal leukocyte behavior in experimental autoimmune uveoretinitis of rats

In vivo retinal leukocyte behavior in the experimental autoimmune uveoretinitis (EAU) of rats was investigated using acridine orange digital fluorography. The technique employed high resolution images obtained from a scanning laser ophthalmoscope (SLO) subsequent to staining with the fluorescent nuclear dye, acridine orange. Two weeks after immunization with synthetic peptides of retinal soluble antigen (S-Ag), acridine orange was intravenously injected, and fundus images were generated by SLO. Many rolling leukocytes were observed along the venous walls as slowly moving fluorescent dots; moreover, leukocytes infiltrating into the vitreous cavity were also noted especially over the retinal veins, but not over the retinal arteries. In addition, major retinal vessels were significantly dilated. The diameters of the retinal veins at a distance of 1 disc diameter away from the center of the optic disc were 49.8+/-4.5 micron for the normal rats and 88.2+/-3.6 micron for the EAU rats, respectively (P<0.001). Similarly, the diameters of retinal arteries were 32.6+/-3.7 micron for the normal rats, 53.8+/-1.5 micron for the EAU rats, respectively (P<0.01). The dilation was more prominent in the veins than in the arteries. These results suggest that it is possible to visualize the retinal involvement of EAU in vivo. The results also suggest that leukocyte-endothelial interaction and extravascular infiltration in the retinal venous vasculature may play significant roles in the early stages of posterior segment inflammation in EAU.

Induction mechanism of small intestinal lesions caused by intravenous injection of endotoxin in rats

The pathogenesis of intestinal damage caused by bolus intravenous injection of endotoxin (ETX; 3 mg/kg) was investigated. Administration of ETX to rats induced reddish discoloration suggestive of bleeding, increased hemoglobin amounts, and leakage of plasma protein in the intestine. However, light microscopic examination of the intestine demonstrated blood congestion of the microvessels. Plasma accumulation was partially inhibited by combined pretreatment with a histamine H1 antagonist and a serotonin (5-HT) antagonist. Neither a 5-lipoxygenase inhibitor, a soybean trypsin inhibitor, nor atropine was observed to inhibit plasma accumulation. Both the intestinal leakage of plasma and the accumulation of hemoglobin were completely inhibited by indomethacin, a selective thromboxane A synthetase inhibitor (OKY 1581), and a stable PGI2 analogue (beraprost). Intravital microscopic observation of the microvessels of the small intestinal villi demonstrated microthrombus formation within several minutes after the injection of ETX, and pretreatment with OKY 1581 attenuated the formation of microthrombus. Platelet counts decreased significantly 10 min after ETX administration, and the decrease was not inhibited by pretreatment with either OKY 1581 or beraprost. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were not prolonged. These observations thus suggest that microcirculatory disturbances by platelet thrombus, which are mediated by thromboxane A2 at least in part, play an important role in ETX-induced intestinal damage.