Nitric oxide-mediated intestinal injury is required for alcohol-induced gut leakiness and liver damage.
BACKGROUND
Alcoholic liver disease (ALD) requires endotoxemia and is commonly associated with intestinal barrier leakiness. Using monolayers of intestinal epithelial cells as an in vitro barrier model, we showed that ethanol-induced intestinal barrier disruption is mediated by inducible nitric oxide synthase (iNOS) upregulation, nitric oxide (NO) overproduction, and oxidation/nitration of cytoskeletal proteins. We hypothesized that iNOS inhibitors [NG-nitro-l-arginine methyl ester (l-NAME), l-N(6)-(1-iminoethyl)-lysine (l-NIL)] in vivo will inhibit the above cascade and liver injury in an animal model of alcoholic steatohepatitis (ASH).


METHODS
Male Sprague-Dawley rats were gavaged daily with alcohol (6 g/kg/d) or dextrose for 10 weeks +/- l-NAME, l-NIL, or vehicle. Systemic and intestinal NO levels were measured by nitrites and nitrates in urine and tissue samples, oxidative damage to the intestinal mucosa by protein carbonyl and nitrotyrosine, intestinal permeability by urinary sugar tests, and liver injury by histological inflammation scores, liver fat, and myeloperoxidase activity.


RESULTS
Alcohol caused tissue oxidation, gut leakiness, endotoxemia, and ASH. l-NIL and l-NAME, but not the d-enantiomers, attenuated all steps in the alcohol-induced cascade including NO overproduction, oxidative tissue damage, gut leakiness, endotoxemia, hepatic inflammation, and liver injury.


CONCLUSIONS
The mechanism we reported for alcohol-induced intestinal barrier disruption in vitro - NO overproduction, oxidative tissue damage, leaky gut, endotoxemia, and liver injury - appears to be relevant in vivo in an animal model of alcohol-induced liver injury. That iNOS inhibitors attenuated all steps of this cascade suggests that prevention of this cascade in alcoholics will protect the liver against the injurious effects of chronic alcohol and that iNOS may be a useful target for prevention of ALD.
Tang
Yueming
Y
Department of Internal Medicine, Division of Digestive Diseases and Nutrition, Rush University, Chicago, Illinois, USA.
Forsyth
Christopher B
CB
Farhadi
Ashkan
A
Rangan
Jayanthi
J
Jakate
Shriram
S
Shaikh
Maliha
M
Banan
Ali
A
Fields
Jeremy Z
JZ
Keshavarzian
Ali
A
D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D000431:Ethanol / Q000008:administration & dosage / Q000633:toxicity*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000293:injuries* / Q000378:metabolism*; D008108:Liver Diseases, Alcoholic / Q000378:metabolism* / Q000517:prevention & control; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D000431:Ethanol; D052247:Nitric Oxide Synthase Type II