Cyclic AMP, Cytokine Modulation and Alcoholic Liver Disease

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DESCRIPTION (provided by applicant): Alcoholic Liver Disease (ALD) remains a leading cause of liver-related deaths in the U.S., and there is still no FDA-approved therapy. Abnormal cytokine metabolism is a major feature of ALD. Elevated serum concentrations of tumor necrosis factor (TNF) and TNF-inducible proinflammatory cytokines/chemokines, such as IL-8 and IL-18 have been reported in patients with alcoholic hepatitis and/or cirrhosis, and levels correlated with markers of the acute phase response, liver function, and clinical outcome. Similarly, there are depressed levels of the critical anti-inflammatory cytokine IL-10. Studies in animal models support an etiologic role for cytokines in the liver injury of ALD. The major problem to be investigated in this proposal is the mechanism(s) for this dysregulated cytokine metabolism, and our overall goal is the development of novel therapeutic interventions. ALD is associated with an increase in oxidative stress with a concomitant decrease in cellular antioxidants, such as glutathione (GSH) and importantly, S-adenosyl-L-methionine (SAM), due to subnormal synthesis. Clinical studies have suggested that SAM has beneficial effects in many hepatic disorders including ALD, and numerous animal studies have clearly demonstrated the protective effects of SAM against a variety of hepatotoxins. Previous studies from our group evaluated the role of SAM in positively modulating endotoxin (LPS)-stimulated TNF and IL-10 production related to ALD. We showed that SAM decreased LPS stimulated TNF production and increased LPS stimulated IL-10 production, and that SAM increased cellular levels of cyclic AMP (cAMP), which is known to positively modulate cytokine production. We therefore began an evaluation of the role of cAMP in dysregulated cytokine production in ALD, which is the research focus of this current proposal. We present compelling preliminary data that cAMP is decreased in a macrophage cell line chronically cultured in alcohol, and in Kupffer cells from mice chronically fed ethanol intragastrically. Our working hypothesis is that altered phosphodiesterase 4B (PDE4B) and cAMP metabolism cause abnormal TNF and IL-10 metabolism, which play a critical role in the development and perpetuation of ALD. Specific Objectives for this proposal are to: 1. Document increased PDE4B expression/activity and decreased cAMP in peripheral blood monocytes from patients with alcoholic hepatitis (AH) and alcoholic cirrhosis, and evaluate whether in vitro incubation of monocytes with specific phosphodiesterase inhibitors corrects dysregulated cAMP and cytokine metabolism; 2. Determine whether PDE4 (and specifically, PDE4B) inhibition blocks the development of alcohol-induced liver injury in a murine intra-gastric ethanol-feeding model of chronic ALD and in a murine model of AH; 3. Evaluate potential molecular and epigenetic mechanisms whereby cAMP metabolism is altered in alcoholic liver disease; and 4. Evaluate the effects of combined consumption of a commercially- available adenyl cyclase agonist (Misoprostol - increases cAMP production) and a phosphodiesterase inhibitor (Pentoxyfilline - decreases cAMP breakdown) in normal volunteers and in patients with stable alcoholic cirrhosis. PUBLIC HEALTH RELEVANCE: Alcoholic Liver Disease (ALD) remains a leading cause of death from liver disease in the U.S. and there is still no FDA-approved therapy. Abnormal cytokine metabolism is a major feature of ALD. Elevated serum concentration levels of tumor necrosis factor (TNF) and TNF-inducible proinflammatory cytokines/chemokines, such as IL-8 and IL-18 have been reported in patients with alcoholic hepatitis and/or cirrhosis, and levels correlated with markers of the acute phase response, liver function, and clinical outcome. Similarly, there are depressed levels of the critical anti-inflammatory cytokine IL-10. Studies in animal models support an etiologic role for cytokines in the liver injury of ALD. The major problem to be investigated in this proposal is the mechanism(s) for this dysregulated cytokine metabolism, and our overall goal is the development of novel therapeutic interventions.