alpha-lipoic acid prevents the induction of iNOS gene expression through destabilization of its mRNA in proinflammatory cytokine-stimulated hepatocytes.
OBJECTIVE
α-Lipoic acid (α-LA) has been reported to reduce ischemia-reperfusion injury (IRI). Proinflammatory cytokines stimulate the induction of inducible nitric oxide synthase (iNOS) gene expression, leading to excess production of NO and resulting in liver injury including IRI. We hypothesized that inhibition of iNOS induction underlies the protective effects of α-LA on the liver. The objective was to investigate whether α-LA directly influences iNOS induction in cultured hepatocytes, which is used as a simple in vitro injury model, and the mechanism involved.


METHODS
Primary cultured rat hepatocytes were treated with interleukin (IL)-1β in the presence or absence of α-LA. The induction of iNOS and NO production  and its signal were analyzed.


RESULTS
α-LA inhibited the expression of iNOS mRNA and protein dose- and time-dependently, resulting in decreases in NO production. α-LA had no effects on the degradation of IκB proteins and activation of NF-κB. In contrast, α-LA inhibited the upregulation of type I IL-1 receptor stimulated by IL-1β, although α-LA had no effect on Akt activation. Transfection experiments with iNOS promoter-luciferase constructs revealed that α-LA had no effect on the transactivation of the iNOS promoter, but decreased the stabilization of iNOS mRNA. Further, α-LA inhibited the expression of an iNOS gene antisense-transcript, which is involved in iNOS mRNA stability.


CONCLUSIONS
Results indicate that α-LA inhibits the induction of iNOS gene expression at a posttranscriptional step via iNOS mRNA stabilization, rather than promoter activation. It may provide useful therapeutic effects through the suppression of iNOS induction involved in liver injury.
Department of Surgery, Kansai Medical University, 10-15 Fumizonocho, Moriguchi, Osaka 570-8506, Japan.
Masanori
M
Yamada
Masaki
M
Kaibori
Hironori
H
Tanaka
Kozo
K
Habara
Takeshi
T
Hijikawa
Yoshito
Y
Tanaka
Masaharu
M
Oishi
Tadayoshi
T
Okumura
Mikio
M
Nishizawa
A-Hon
AH
Kwon
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002478:Cells, Cultured; D015870:Gene Expression / Q000187:drug effects*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D053583:Interleukin-1beta / Q000494:pharmacology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D020871:RNA Stability / Q000187:drug effects*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017472:Receptors, Interleukin-1 / Q000378:metabolism; D008063:Thioctic Acid / Q000494:pharmacology*; D015533:Transcriptional Activation / Q000187:drug effects
D000975:Antioxidants; D053583:Interleukin-1beta; D016328:NF-kappa B; D012333:RNA, Messenger; D017472:Receptors, Interleukin-1; D008063:Thioctic Acid; D007770:L-Lactate Dehydrogenase; D052247:Nitric Oxide Synthase Type II