Identification of a novel class of dithiolethiones that prevent hepatic insulin resistance via the adenosine monophosphate–activated protein kinase–p70 ribosomal S6 kinase-1 pathway

Abstract

Several established liver diseases of various causes are highly associated with hepatic insulin resistance, which is characterized by the desensitization of target cells to insulin. Peripheral insulin resistance is observed in most patients who have cirrhosis. Conversely, insulin-resistant diabetic patients are at increased risk for developing liver disease. Current therapeutic interventions in insulin resistance are limited and therefore likely to be advanced by new tailor-made drugs. Oltipraz, a prototype dithiolthione, inhibits transforming growth factor ␤1 and has the ability to regenerate cirrhotic liver. We investigated the effects of oltipraz and synthetic dithiolthiones on hepatic insulin resistance and the molecular basis of action. Oltipraz and other dithiolethione compounds were tested on tumor necrosis factor ␣ (TNF-␣)-induced insulin resistance and glucose homeostasis in vitro and in vivo via immunoblotting, plasmid transfection, kinase analysis, and functional assays. Oltipraz treatment inhibited the ability of TNF-␣ to activate p70 ribosomal S6 kinase-1 (S6K1) downstream of mammalian target of rapamycin, thus preventing insulin receptor substrate-1 serine phosphorylation and protecting insulin signals. Moreover, oltipraz activated AMP-activated protein kinase (AMPK), whose inhibition by a dominant negative mutant abolished S6K1 inhibition and protected insulin signaling, indicating that AMPK activation leads to S6K1 inhibition. In hepatocyte-derived cell lines, oltipraz inhibited glucose production. Oltipraz prevented hepatic insulin resistance in C57BL/6 mice challenged with endotoxin (or TNF-␣), leptin-deficient mice, and mice fed a high-fat diet. Synthetic dithiolethiones comparably inhibited insulin resistance. Conclusion: Our findings led to the identification of dithiolethione compounds that prevent insulin resistance through a mechanism involving AMPK-mediated S6K1 inhibition and thereby sensitize hepatic insulin response. (HEPATOLOGY 2007;46:730-739.)

Oxidized Metabolites of Oltipraz Exert Cytoprotective Effects against Arachidonic Acid through AMP-Activated Protein Kinase-Dependent Cellular Antioxidant Effect and Mitochondrial Protection

“…The lysates were centrifuged at 10,000g for 10 min to obtain supernatants and stored at Ϫ70°C until use. Immunoblot analysis was performed according to previously published procedures (Bae et al, 2007). Protein bands of interest were developed using the enhanced chemiluminescence system (GE Healthcare, Chalfont St. Giles, Buckinghamshire, UK).…”

“…The plasmid encoding a dominant-negative mutant of AMPK␣ (D157A; DN-AMPK␣) was kindly provided by Dr. J. Ha (Kyung Hee University, Seoul, Korea) (Bae et al, 2007). To generate recombinant adenovirus that expresses DN-AMPK␣, the construct was subcloned into an attL-containing shuttle plasmid, pENTR-BHRNX (Newgex, Seoul, Korea).…”

“…Moreover, oltipraz has a therapeutic effect on the cirrhotic liver (Kang et al, 2002;Cho et al, 2006). More recently, we also found that oltipraz prevents insulin resistance induced by tumor necrosis factor-␣, a cytokine known to promote production of reactive oxygen species (ROS), as a consequence of AMP-activated protein kinase (AMPK) activation (Bae et al, 2007). In addition, oltipraz exerts a cytoprotective effect against arachidonic acid (AA) and/or iron via AMPK (Shin and Kim, 2009).…”

Abrogation of Hyperosmotic Impairment of Insulin Signaling by a Novel Class of 1,2-Dithiole-3-thiones through the Inhibition of S6K1 Activation

“…Antibodies directed against IRS1, IR␤, S6K1, and inhibitor of nuclear factor-B (IB) ␣ were obtained from Santa Cruz Biotechnology (Santa Cruz, CA). Anti-phosphotyrosine (4G10) and anti-p-Ser Chemical Synthesis of 1,2-Dithiol-3-thione Analogs 1,2-Dithiol-3-thione analogs were synthesized at CJ Central Laboratories (Ichon City, Korea) according to the methods described by Curphey (2002), as described previously (Bae et al, 2007).…”

“…In our previous study, we found that oltipraz and novel dithiolethiones prevent TNF␣-induced hepatic insulin resistance through AMP-activated protein kinase (AMPK)-dependent S6K1 inhibition (Bae et al, 2007). Hyperosmotic stress has been shown to activate the mTOR pathway (Gual et al, 2003a), which causes insulin resistance.…”