Thyroid hormone-induced cytosol-to-nuclear translocation of rat liver Nrf2 is dependent on Kupffer cell functioning.

L-3,3',5-triiodothyronine (T(3)) administration upregulates nuclear factor-E2-related factor 2 (Nrf2) in rat liver, which is redox-sensitive transcription factor mediating cytoprotection. In this work, we studied the role of Kupffer cell respiratory burst activity, a process related to reactive oxygen species generation and liver homeostasis, in Nrf2 activation using the macrophage inactivator gadolinium chloride (GdCl(3); 10 mg/kg i.v. 72 h before T(3) [0.1 mg/kg i.p.]) or NADPH oxidase inhibitor apocynin (1.5 mmol/L added to the drinking water for 7 days before T(3)), and determinations were performed 2 h after T(3). T(3) increased nuclear/cytosolic Nrf2 content ratio and levels of heme oxygenase 1 (HO-1), catalytic subunit of glutamate cysteine ligase, and thioredoxin (Western blot) over control values, proteins whose gene transcription is induced by Nrf2. These changes were suppressed by GdCl(3) treatment prior to T(3), an agent-eliciting Kupffer-cell depletion, inhibition of colloidal carbon phagocytosis, and the associated respiratory burst activity, with enhancement in nuclear inhibitor of Nrf2 kelch-like ECH-associated protein 1 (Keap1)/Nrf2 content ratios suggesting Nrf2 degradation. Under these conditions, T(3)-induced tumor necrosis factor-α (TNF-α) response was eliminated by previous GdCl(3) administration. Similar to GdCl(3), apocynin given before T(3) significantly reduced liver Nrf2 activation and HO-1 expression, a NADPH oxidase inhibitor eliciting abolishment of colloidal carbon-induced respiratory burst activity without altering carbon phagocytosis. It is concluded that Kupffer cell functioning is essential for upregulation of liver Nrf2-signaling pathway by T(3). This contention is supported by suppression of the respiratory burst activity of Kupffer cells and the associated reactive oxygen species production by GdCl(3) or apocynin given prior to T(3), thus hindering Nrf2 activation.

Liver NF-kappaB and AP-1 DNA binding in obese patients.

Oxidative stress and insulin resistance (IR) are major contributors in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and in the progression from steatosis to nonalcoholic steatohepatitis (NASH). Our aim was to assess nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) activation and Toll-like receptor 4 (TLR4) expression as signaling mechanisms related to liver injury in obese NAFLD patients, and examined potential correlations among them, oxidative stress, and IR. Liver NF-kappaB and AP-1 (electromobility shift assay (EMSA)), TLR4 expression (western blot), ferric reducing ability of plasma (FRAP), and IR evolution (HOMA) were evaluated in 17 obese patients who underwent subtotal gastrectomy with gastro-jejunal anastomosis in Roux-en-Y and 10 nonobese subjects who underwent laparoscopic cholecystectomy (controls). Liver NF-kappaB and AP-1 DNA binding were markedly increased in NASH patients (n = 9; P < 0.05) compared to controls, without significant changes in NAFLD patients with steatosis (n = 8), whereas TLR4 expression was comparable between groups. Hepatic NF-kappaB activation was positively correlated with that of AP-1 (r = 0.79; P < 0.0001); both liver NF-kappaB and AP-1 DNA binding were inversely associated with FRAP (r = -0.43 and r = -0.40, respectively; P < 0.05) and directly correlated with HOMA (r = 0.66 and r = 0.62, respectively, P < 0.001). Data presented show enhanced liver activation of the proinflammatory transcription factors NF-kappaB and AP-1 in obese patients with NASH, parameters that are significantly associated to oxidative stress and IR.