PDE4 Inhibition by Rolipram Protects against Alcohol‐induced ER Stress and Hepatocyte Death in An Alcoholic Liver Injury Model
Authors: Wahlang Banrida , Rodriguez Walter , Wang Yali , Zhang Jingwen , Barve Shirish , McClain Craig , Gobejishvili Leila 
Published: June 2021

Purpose

Alcoholic liver disease (ALD) is a major cause of liver‐related mortality in the US. However, there is still no FDA‐approved therapy for ALD, and therefore identifying therapeutic targets is needed. Previously, our group demonstrated that chronic ethanol exposure to monocytes/macrophages and hepatocytes decreased levels of the second messenger, cAMP, by upregulating the cAMP‐degrading enzyme, phosphodiesterase 4 (PDE4), leading to inflammation and steatosis. The objective of the current study was to investigate if the PDE4‐specific inhibitor, rolipram, could protect against alcohol‐induced hepatic injury and to identify the underlying protective mechanisms both in vivo and in vitro.

Methods

Rat hepatoma cells (H4IIEC3) were sensitized to ethanol (24 h) and pretreated with either rolipram or dibutyryl‐cAMP (cAMP analog) before exposure to TNFa. For in vivo studies, C57Bl/6 and Pde4b−/− knockout male mice were pair‐fed the Lieber‐DeCarli liquid diet containing isocaloric maltose dextrin (pair‐fed, PF) or 5% (w/v) ethanol (alcohol‐fed, AF) for 10 days. On day 11, AF mice were gavaged with ethanol (5 g/kg body weight) and rolipram was administered 12 h prior to gavage. Mice were euthanized 9 hours after gavage and samples were taken for analysis.

Results

Ethanol exposure in H4IIEC3 cells exacerbated TNFa‐induced ER stress as seen with increased gene expression and protein levels of C/EBP homologous protein (CHOP), a transcription factor that directs ER stress‐induced apoptosis, as well as key genes of the ER stress induction pathway (ATF3 and ATF4). This effect was attenuated with both rolipram and dibutyryl‐cAMP. Importantly, along with ER Stress, hepatocytes exposed to TNFa showed higher levels of Pde4b. Mice demonstrated notable steatosis (Oil Red O staining), liver injury (ALT and AST) and apoptosis (TUNEL staining) in alcohol‐fed group, which was attenuated with rolipram. Alcohol also induced hepatic ER stress (increased mRNA levels of CHOP, ATF3, and ATF4) in mice, which receded with rolipram administration. Rolipram‐mediated protection was also associated with increased levels of survival protein Bcl‐xl. Pde4b−/− knockout mice exhibited protection against alcohol‐induced ER stress further confirming the role of PDE4B as a negative mediator in ALD.

Conclusions

The current findings demonstrated that rolipram attenuated pathological features of ALD such as steatosis and hepatocyte injury in vivo. Furthermore, in vitro results indicated that cAMP activation plays a protective role against etiologic factors that trigger disease progression such as ER stress. Taken together, the results suggest that targeting enzymes that influence intracellular cAMP signaling, namely PDE4s, using PDE4 inhibitors, may be an excellent targeted therapy for ALD.

Support or Funding Information

This work was supported by R44AA021331, P50AA024337, 5R01AA023681, 5P20GM113226

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.