Nitric oxide plays a crucial role in the development/progression of nonalcoholic steatohepatitis in the choline-deficient, l-amino acid-defined diet-fed rat model.
BACKGROUND
The pathogenesis of nonalcoholic steatohepatitis (NASH) is still unclear. Recently, the 2-hit hypothesis was proposed, in which nitric oxide production, representing oxidative stress, was proposed as a very important candidate for the second hit.


METHODS
The total study period was 10 weeks. A total of 20 rats were randomly divided into 2 groups. Group 1 was administered the Choline-Deficient, l-Amino Acid-Defined diet to produce a NASH model, and Group 2 as control received the Choline-Sufficient, l-Amino Acid-defined diet. The blood and tissue concentrations of nitrate + nitrite were measured using the Griess reagent and the expression levels of inducible nitric oxide synthase (iNOS) proteins and mRNA was determined by Western blotting.


RESULTS
In regard to nitric oxide (NO) and NO metabolites, there were significant differences in the blood (especially portal venous blood) as well as tissue (liver and visceral fat) concentrations between the 2 animal groups; the amounts of NO metabolites in the tissues were much higher in the NASH models. The level of nitrotyrosine was much markedly higher in the NASH models than in the controls. In regard to the tissue expression of iNOS a significant difference between the 2 groups was found in the visceral fat, especially in the mesenterium.


CONCLUSIONS
Based on these results, we hypothesize that the iNOS expression and NO levels in the visceral fat increase, with increased diffusion of NO and its metabolites into the liver, resulting in increased nitrotyrosine formation in the liver; this, in turn, induces inflammation, apoptosis, and fibrosis in the liver, which are one of the characteristic features of NASH.
Fujita
Koji
K
From the Division of Gastroenterology, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
Nozaki
Yuichi
Y
Yoneda
Masato
M
Wada
Koichiro
K
Takahashi
Hirokazu
H
Kirikoshi
Hiroyuki
H
Inamori
Masahiko
M
Saito
Satoru
S
Iwasaki
Tomoyuki
T
Terauchi
Yasuo
Y
Maeyama
Shiro
S
Nakajima
Atsushi
A
D000596:Amino Acids / Q000008:administration & dosage*; D000818:Animals; D015153:Blotting, Western; D002794:Choline / Q000008:administration & dosage; D002796:Choline Deficiency; D004032:Diet; D004195:Disease Models, Animal; D005234:Fatty Liver / Q000209:etiology* / Q000378:metabolism; D050152:Intra-Abdominal Fat / Q000737:chemistry / Q000201:enzymology; D008099:Liver / Q000737:chemistry / Q000201:enzymology; D008297:Male; D009566:Nitrates / Q000032:analysis / Q000097:blood; D009569:Nitric Oxide / Q000032:analysis / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000235:genetics; D009573:Nitrites / Q000032:analysis / Q000097:blood; D018384:Oxidative Stress; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011916:Rats, Inbred F344; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism
D000596:Amino Acids; D009566:Nitrates; D009573:Nitrites; D012333:RNA, Messenger; D009569:Nitric Oxide; C002744:3-nitrotyrosine; D014443:Tyrosine; D052247:Nitric Oxide Synthase Type II; D002794:Choline