Deficient iNOS in inflammatory bowel disease intestinal microvascular endothelial cells results in increased leukocyte adhesion

Microvascular endothelial cells play a key role in inflammation by undergoi ng activation and recruiting circulating immune cells into tissues and foci of inflammation, an early and rate-limiting step in the inflammatory proce ss. We have previously [Binion er al., Gastroenterology 112:1898-1907, 1997 ] shown that human intestinal microvascular endothelial cells (HIMEC) isola ted from surgically resected inflammatory bowel disease (IBD) patient tissu e demonstrate significantly increased leukocyte binding in vitro compared t o normal HIMEC. Our studies [Binion et al., Am. J. Physiol. 275 (Gastrointe st. Liver Physiol. 38):G592-G603, 1998] have also demonstrated that nitric oxide (NO) production by inducible nitric oxide synthase (iNOS) normally pl ays a key role in downregulating HIMEC activation and leukocyte adhesion. U sing primary cultures of HIMEC derived from normal and IBD patient tissues, we sought to determine whether alterations in iNOS-derived NO production u nderlies leukocyte hyperadhesion in IBD. Both nonselective (N-G-monomethyl- L-arginine) and specific (N-Iminoethyl-L-lysine) inhibitors of iNOS signifi cantly increased leukocyte binding by normal HIMEC activated with cytokines and lipopolysaccharide (LPS), but had no effect on leukocyte adhesion by s imilarly activated IBD HIMEC. When compared to normal HIMEC, IBD endothelia l cells had significantly decreased levels of iNOS mRNA, protein, and NO pr oduction following activation. Addition of exogenous NO by co-culture with normal HIMEC or by pharmacologic delivery with the long-acting NO donor det aNONOate restored a normal leukocyte binding pattern in the LED HIMEC. Thes e data suggest that loss of iNOS expression is a feature of chronically inf lamed microvascular endothelial cells, which leads to enhanced leukocyte bi nding, potentially contributing to chronic, destructive inflammation in LED . (C) 2000 Elsevier Science Inc.