The physiological expression of inducible nitric oxide synthase (iNOS) in the human colon.
BACKGROUND
Inducible nitric oxide synthase (iNOS) is expressed in the colonic epithelium in both inflammatory bowel disease and colorectal cancer. Nitric oxide (NO), the product of this enzyme, has been implicated in the pathogenesis of both conditions. However, there are conflicting data on whether iNOS is expressed in the normal, uninflamed human colon.


OBJECTIVE
To evaluate the expression of iNOS in histologically normal, non-inflamed human colonic mucosa.


METHODS
Reverse transcription polymerase chain reaction (RT-PCR), immunoblotting, and immunohistochemistry were used to investigate the expression of iNOS in 17 histologically normal specimens obtained at colectomy performed for colorectal neoplasia. In addition, 16 endoscopic mucosal biopsies, taken from normal individuals, were also evaluated. Eleven surgical specimens and 16 endoscopic biopsies from patients with refractory ulcerative colitis were used as inflammatory controls.


RESULTS
All types of specimens expressed iNOS mRNA. Immunoblotting revealed a protein of approximately 130 kDa consistent with iNOS in mucosal extracts of 77% of normal individuals, and 85% of diseased controls. Immunolabelling localised this protein to the surface epithelium in most of the normal specimens and also to the crypt epithelium and inflammatory cells in the diseased controls.


CONCLUSIONS
These findings provide evidence that iNOS is often expressed in the surface epithelium of non-inflamed human colon, suggesting that it is induced by local luminal factors, such as bacterial lipopolysaccharide (endotoxin). The resultant NO produced at this site might act as an oxidative barrier, reducing bacterial translocation and providing a means of defence against pathogenic microorganisms.
Roberts
P J
PJ
Department of Gastroenterology, Addenbrookes Hospital, CB2 2QQ Cambridge, UK.
Riley
G P
GP
Morgan
K
K
Miller
R
R
Hunter
J O
JO
Middleton
S J
SJ
D000328:Adult; D000368:Aged; D003093:Colitis, Ulcerative / Q000201:enzymology; D003106:Colon / Q000201:enzymology*; D003110:Colonic Neoplasms / Q000201:enzymology; D004848:Epithelium / Q000201:enzymology; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D019001:Nitric Oxide Synthase / Q000032:analysis*; D052247:Nitric Oxide Synthase Type II; D020133:Reverse Transcriptase Polymerase Chain Reaction
C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II