Inhibition of LPS‐induced nitric oxide and TNF‐α production by α‐lipoic acid in rat Kupffer cells and in RAW 264.7 murine macrophages

Abstract

The activation of Kupffer cells represents a central mechanism of inflammatory liver injury involving the production of two important inflammatory mediators, nitric oxide and TNF-α. The aim of this study was to investigate the effect of the hepatoprotective compound α-lipoic acid (thioctic acid) on the production of nitric oxide and TNF-α in isolated rat Kupffer cells and RAW 264.7 macrophages. Isolated rat Kupffer cells or RAW 264.7 were either untreated, treated with α-lipoic acid (500 µg/mL), or activated with 1 µg/mL of lipopolysaccharide in the presence or absence of α-lipoic acid (0.2−500 µg/mL). After 20 h the accumulation of nitrite was measured by the Griess assay. Tumour necrosis factor-α secretion was quantified after 4 h by L929 bioassay. Cell viability was determined by mitochondrial reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test, nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) DNA binding activity by gelshift assays. Treatment of Kupffer cells and RAW 264.7 with α-lipoic acid alone had no effect on basal nitric oxide production. However, α-lipoic acid significantly inhibited lipopolysaccharide-induced nitrite accumulation. α-Lipoic acid did not alter basal TNF-α secretion in Kupffer cells, whereas it significantly inhibited lipopolysaccharide-induced TNF-α production. α-Lipoic acid attenuated the activation of nuclear factor-κB and AP-1, two transcription factors pivotal in induction of inducible nitric oxide synthase and TNF-α. α-Lipoic acid significantly inhibits lipopolysaccharide-induced macrophage production of nitric oxide and TNF-α via an attenuated activation of NF-κB and activator protein-1. The reduced production of nitric oxide and TNF-α in Kupffer cells may be involved in the hepatoprotective action conveyed by α-lipoic acid.