Increased lipopolysaccharide sensitivity in alcoholic fatty livers is independent of leptin deficiency and toll-like receptor 4 (TLR4) or TLR2 mRNA expression.
BACKGROUND
Both alcoholic (AFL) and nonalcoholic (NAFL) fatty livers show increased sensitivity to endotoxin-induced injury. Lipopolysaccharide (LPS) is recognized by toll-like receptor 4 (TLR4), whereas lipopeptide triggers TLR2 to induce common downstream activation of nuclear factor (NF)-kappaB and pro-inflammatory pathways that are activated in AFL and NAFL.


METHODS
Serum alanine aminotransferase (ALT), tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 levels; hepatic NF-kappaB activity; and expression of TLR2, TLR4, inducible nitric oxide synthase (iNOS), and heme oxygenase (HO)-1 mRNAs were investigated in lean and leptin-deficient ob/ob mice after LPS challenge in combination with acute or chronic alcohol feeding.


RESULTS
Increased LPS sensitivity in AFL and NAFL was characterized by elevated serum TNF-alpha and IL-6 induction. However, there was no difference in TLR2 and TLR4 mRNA levels between lean and ob/ob livers at baseline and after acute or chronic alcohol treatment. LPS increased TLR2, but not TLR4, mRNA levels in all groups. Chronic alcohol feeding and LPS increased serum ALT and TNF-alpha levels in lean but not in ob/ob mice compared with pair-fed controls. Hepatic NF-kappaB activation was increased in both ob/ob and lean mice after chronic alcohol feeding compared with pair-fed controls. Expression of iNOS, an inducer of oxidative stress, and HO-1, a cytoprotective protein, were higher in ob/ob compared with lean mice after chronic alcohol feeding. However, LPS-induced HO-1, but not iNOS, expression was attenuated in ob/ob compared with lean mice.


CONCLUSIONS
These results imply that the increased sensitivity of AFL to LPS occurs without up-regulation of TLR2 or TLR4 genes and may be related to an imbalance of pro-inflammatory/oxidative and cytoprotective mechanisms.
Liver Center, Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01606, USA.
Laszlo
L
Romics
Pranoti
P
Mandrekar
Karen
K
Kodys
Arumugam
A
Velayudham
Yvonne
Y
Drechsler
Angela
A
Dolganiuc
Gyongyi
G
Szabo
D000818:Animals; D004195:Disease Models, Animal; D005234:Fatty Liver / Q000378:metabolism / Q000473:pathology; D005235:Fatty Liver, Alcoholic / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D020738:Leptin / Q000172:deficiency*; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008820:Mice, Obese; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D054411:Receptors, Leptin; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D015850:Interleukin-6; D020738:Leptin; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; C515447:leptin receptor, mouse; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D006419:Heme Oxygenase (Decyclizing)