Enhanced PDE4B expression augments LPS-inducible TNF expression in ethanol-primed monocytes: Relevance to alcoholic liver disease

Dept. of Internal Medicine, Univ. of Louisville Medical Ctr., 550 S. Jackson St., ACB 3rd Floor, Louisville, KY 40292, USA.
AJP Gastrointestinal and Liver Physiology (Impact Factor: 3.8). 09/2008; 295(4):G718-24. DOI: 10.1152/ajpgi.90232.2008
Source: PubMed


Increased plasma and hepatic TNF-alpha expression is well documented in patients with alcoholic hepatitis and is implicated in the pathogenesis of alcoholic liver disease. We have previously shown that monocytes from patients with alcoholic hepatitis show increased constitutive and LPS-induced NF-kappaB activation and TNF-alpha production. Our recent studies showed that chronic ethanol exposure significantly decreased cellular cAMP levels in both LPS-stimulated and unstimulated monocytes and Kupffer cells, leading to an increase in LPS-inducible TNF-alpha production by affecting NF-kappaB activation and induction of TNF mRNA expression. Accordingly, the mechanisms underlying this ethanol-induced decrease in cellular cAMP leading to an increase in TNF expression were examined in monocytes/macrophages. In this study, chronic ethanol exposure was observed to significantly increase LPS-inducible expression of cAMP-specific phosphodiesterase (PDE)4B that degrades cellular cAMP. Increased PDE4B expression was associated with enhanced NF-kappaB activation and transcriptional activity and subsequent priming of monocytes/macrophages leading to enhanced LPS-inducible TNF-alpha production. Selective inhibition of PDE4 by rolipram abrogated LPS-mediated TNF-alpha expression at both protein and mRNA levels in control and ethanol-treated cells. Notably, PDE4 inhibition did not affect LPS-inducible NF-kappaB activation but significantly decreased NF-kappaB transcriptional activity. These findings strongly support the pathogenic role of PDE4B in the ethanol-mediated priming of monocytes/macrophages and increased LPS-inducible TNF production and the subsequent development of alcoholic liver disease (ALD). Since enhanced TNF expression plays a significant role in the evolution of clinical and experimental ALD, its downregulation via selective PDE4B inhibitors could constitute a novel therapeutic approach in the treatment of ALD.

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    • "Evidence suggests that PDE4B may be a target of interest for addiction research, due to its high expression levels in brain regions associated with reward and reinforcement (e.g., NAc and central nucleus of the amygdala [CeA]; Cherry and Davis 1999; Perez-Torres et al. 2000). PDE4B expression is upregulated following chronic alcohol exposure in vitro (Gobejishvili et al. 2008) and is heavily involved in inflammatory processes (cf. Jin et al. 2012) which are implicated in alcohol and drug dependence (Crews et al. 2011). "
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    ABSTRACT: Phosphodiesterase-4 (PDE4) and neuroimmune signaling have been posited to regulate alcohol drinking. This study evaluated the involvement of PDE4 and Il22ra2 on ethanol (EtOH) intake by alcohol-preferring (P) and high-alcohol-drinking (HAD1) rats. Exp 1 determined the dose-response effects of PDE4 inhibitors, rolipram, and Ro 20-1724, on 2 h/day free-choice EtOH intake by adult P and HAD1 rats. Exps 2-3 examined the effects of repeated administration with the PDE4 inhibitors on EtOH or sucrose intake and locomotor behavior. Exp 4 determined Pde4-associated gene expression differences in subregions of the extended amygdala, between high- and low-alcohol-consuming rat lines. Exp 5 evaluated the effects of infusing short hairpin RNA to knock down Il22ra2 in the nucleus accumbens (NAc) shell on a 24-h free-choice EtOH drinking by P rats. Administration of rolipram or Ro 20-1724 reduced EtOH intake by P rats; Ro 20-1724 reduced EtOH intake by HAD1 rats. Repeated rolipram or Ro 20-1724 exposure reduced EtOH intake by P and HAD1 rats. PDE4 inhibition induced motor impairment during the first hour of EtOH intake by P rats. Higher gene expression levels for PDE4A were found in the NAc shell of P vs NP rats. ShRNAs targeting Il22ra2 in the NAc shell significantly reduced chronic EtOH intake. PDE4 and neuroinflammatory/immune signaling pathways could represent molecular targets for the treatment of alcohol use disorders in genetically predisposed subjects. This study underscores the importance of testing compounds over multiple days and rat lines when determining efficacy to disrupt excessive alcohol intake.
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    • "Nevertheless, our results, in which LGG supplementation normalized alcohol-induced decrease in Nrf2, indicate that LGG has the potential to suppress alcohol-induced oxidative stress in the liver. Initial studies in our laboratory showed that increased priming of human monocytes and Kupffer cells by alcohol led to exaggerated LPS-induced expression of TNFα [39]. Notably, the current study demonstrated that ethanol pretreatment sensitized both LPS-and flagellin-induced TNFα production in macrophages. "
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    ABSTRACT: The therapeutic effects of probiotic treatment in alcoholic liver disease (ALD) have been studied in both patients and experimental animal models. Although the precise mechanisms of the pathogenesis of ALD are not fully understood, gut-derived endotoxin has been postulated to play a crucial role in hepatic inflammation. Previous studies have demonstrated that probiotic therapy reduces circulating endotoxin derived from intestinal gram-negative bacteria in ALD. In this study, we investigated the effects of probiotics on hepatic tumor necrosis factor-α (TNFα) production and inflammation in response to chronic alcohol ingestion. Mice were fed Lieber DeCarli liquid diet containing 5% alcohol for 8weeks, and Lactobacillus rhamnosus GG (LGG) was supplemented in the last 2 weeks. Eight-week alcohol feeding caused a significant increase in hepatic inflammation as shown by histological assessment and hepatic tissue myeloperoxidase activity assay. Two weeks of LGG supplementation reduced hepatic inflammation and liver injury and markedly reduced TNFα expression. Alcohol feeding increased hepatic mRNA expression of Toll-like receptors (TLRs) and CYP2E1 and decreased nuclear factor erythroid 2-related factor 2 expression. LGG supplementation attenuated these changes. Using human peripheral blood monocytes-derived macrophages, we also demonstrated that incubation with ethanol primes both lipopolysaccharide- and flagellin-induced TNFα production, and LGG culture supernatant reduced this induction in a dose-dependent manner. In addition, LGG treatment also significantly decreased alcohol-induced phosphorylation of p38 MAP kinase. In conclusion, probiotic LGG treatment reduced alcohol-induced hepatic inflammation by attenuation of TNFα production via inhibition of TLR4- and TLR5-mediated endotoxin activation.
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    • "Specific inhibition of PDE4 in human peripheral monocytes by a number of agents causes decreased production of LPS-induced TNFα.35 Monocytes and macrophages chronically treated with ethanol showed increased expression of PDE4B, reduced expression of cAMP, and increased nuclear factor kappa beta (NFκB) signaling, ultimately leading to an increase in lipopolysaccharide-stimulated TNFα production. This effect was abolished by the addition of the classical PDE4 inhibitor, rolipram, highlighting the potential of this class of drug to control NFκB-mediated immune processes.36 Intriguingly, such effects are not restricted to the control of proinflammatory mediators. "
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