cAMP Signaling in Pathobiology of Alcohol Associated Liver Disease

Discovery of 7-alkoxybenzofurans as PDE4 inhibitors with hepatoprotective activity in D-GalN/LPS-induced hepatic sepsis

Sepsis can quickly result in fatality for critically ill individuals, while liver damage can expedite the progression of sepsis, necessitating the exploration of new strategies for treating hepatic sepsis. PDE4 has been identified as a potential target for the treatment of liver damage. The scaffold hopping of lead compounds FCPR16 and Z19153 led to the discovery of a novel 7-methoxybenzofuran PDE4 inhibitor 4e, demonstrating better PDE4B (IC50 = 10.0 nM) and PDE4D (IC50 = 15.2 nM) inhibitor activity as a potential anti-hepatic sepsis drug in this study. Compared with FCPR16 and Z19153, 4e displayed improved oral bioavailability (F = 66 %) and longer half-life (t1/2 = 2.0 h) in SD rats, which means it can be more easily administered and has a longer-lasting effect. In the D-GalN/LPS-induced liver injury model, 4e exhibited excellent hepatoprotective activity against hepatic sepsis by decreasing ALT and AST levels and inflammatory infiltrating areas.

Regulatory pathways and therapeutic potential of PDE4 in liver pathophysiology

Phosphodiesterase 4 (PDE4), crucial in regulating the cyclic adenosine monophosphate (cAMP) signaling pathway, significantly impacts liver pathophysiology. This article highlights the comprehensive effects of PDE4 on liver health and disease, and its potential as a therapeutic agent. PDE4's role in degrading cAMP disrupts intracellular signaling, increasing pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). This contributes to liver inflammation in conditions such as hepatitis and non-alcoholic steatohepatitis (NASH). Additionally, PDE4 is a key factor in liver fibrosis, characterized by excessive extracellular matrix deposition. Inhibiting PDE4 shows promise in reducing liver fibrosis by decreasing the activation of hepatic stellate cells, which is pivotal in fibrogenesis. PDE4 also influences hepatocyte apoptosis a common feature of liver diseases. PDE4 inhibitors protect against hepatocyte apoptosis by raising intracellular cAMP levels, thus activating anti-apoptotic pathways. This suggests potential in targeting PDE4 to prevent hepatocyte loss. Moreover, PDE4 regulates hepatic glucose production and lipid metabolism, essential for liver function. Altering cAMP levels through PDE4 affects enzymes in these metabolic pathways, making PDE4 a target for metabolic disorders like type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). Since PDE4 plays a multifaceted role in liver pathophysiology, influencing PDE4's mechanisms in liver diseases could lead to novel therapeutic strategies. Still, extensive research is required to explore the molecular mechanisms and clinical potential of targeting PDE4 in liver pathologies.

Elucidating the role of intrinsic adenosine A1 receptors in acute alcoholism using human-induced pluripotent stem cell-derived hepatocytes

Acute alcoholic hepatitis (AAH) from binge drinking is a serious disease. It is associated with a high mortality rate, especially among young adults. Apoptosis is known to be a primary cause of liver damage, and it can be induced by either intrinsic signaling pathways or by reactive oxygen species (ROS). Adenosine A1 receptors (ADORA1) are known to be involved in ethanol metabolism; however, underlying mechanism is not well understood. For investigating how the intrinsic ADORA1 function in ethanol metabolism in normal human hepatocytes without interference by extrinsic molecules, primary hepatocytes pose a challenge, due to unavoidable contamination by other kinds of cells in the liver. Also, they are difficult to culture stably. As a novel alternative, hepatocytes derived from human-induced pluripotent stem cells were employed because they display similar function to primary hepatocytes and they can be stably cultured. The dynamics and integrity of signal transduction mechanisms were investigated by following chronological changes in gene expression. This shed light on how and when the ADORA1 function and on causal relationships between the pathways and clinical symptoms. The findings of the present study shows that ADORA1 are most activated soon after exposure to ethanol, and transfection of small interfering RNA targeting ADORA1-messenger-RNA (ADORA1-siRNA) into the hepatocytes significantly suppresses production of actin protein and ROS. It suggests that ADORA1 in the liver contribute to apoptosis in acute alcoholism through both intrinsic pathway and ROS activity. Also, actin that is abundant in the cells could be an appropriate biomarker evaluating hepatic function status.

Increased expression of phosphodiesterase 4 in activated hepatic stellate cells promotes cytoskeleton remodeling and cell migration

Activation and transdifferentiation of hepatic stellate cells (HSC) into migratory myofibroblasts is a key process in liver fibrogenesis. Cell migration requires an active remodeling of the cytoskeleton, which is a tightly regulated process coordinated by Rho-specific guanine nucleotide exchange factors (GEFs) and the Rho family of small GTPases. Rho-associated kinase (ROCK) promotes assembly of focal adhesions and actin stress fibers by regulating cytoskeleton organization. GEF exchange protein directly activated by cAMP 1 (EPAC1) has been implicated in modulating TGFβ1 and Rho signaling; however, its role in HSC migration has never been examined. The aim of this study was to evaluate the role of cAMP-degrading phosphodiesterase 4 (PDE4) enzymes in regulating EPAC1 signaling, HSC migration, and fibrogenesis. We show that PDE4 protein expression is increased in activated HSCs expressing alpha smooth muscle actin and active myosin light chain (MLC) in fibrotic tissues of human nonalcoholic steatohepatitis cirrhosis livers and mouse livers exposed to carbon tetrachloride. In human livers, TGFβ1 levels were highly correlated with PDE4 expression. TGFβ1 treatment of LX2 HSCs decreased levels of cAMP and EPAC1 and increased PDE4D expression. PDE4 specific inhibitor, rolipram, and an EPAC-specific agonist decreased TGFβ1-mediated cell migration in vitro. In vivo, targeted delivery of rolipram to the liver prevented fibrogenesis and collagen deposition and decreased the expression of several fibrosis-related genes, and HSC activation. Proteomic analysis of mouse liver tissues identified the regulation of actin cytoskeleton by the kinase effectors of Rho GTPases as a major pathway impacted by rolipram. Western blot analyses confirmed that PDE4 inhibition decreased active MLC and endothelin 1 levels, key proteins involved in cytoskeleton remodeling and contractility. The current study, for the first time, demonstrates that PDE4 enzymes are expressed in hepatic myofibroblasts and promote cytoskeleton remodeling and HSC migration. © 2023 The Pathological Society of Great Britain and Ireland.

Dysregulated Cyclic Nucleotide Metabolism in Alcohol-Associated Steatohepatitis: Implications for Novel Targeted Therapies

BACKGROUND

Cyclic nucleotides are second messengers, which play significant roles in numerous biological processes. Previous work has shown that cAMP and cGMP signaling regulates various pathways in liver cells, including Kupffer cells, hepatocytes, hepatic stellate cells, and cellular components of hepatic sinusoids. Importantly, it has been shown that cAMP levels and enzymes involved in cAMP homeostasis are affected by alcohol. Although the role of cyclic nucleotide signaling is strongly implicated in several pathological pathways in liver diseases, studies describing the changes in genes regulating cyclic nucleotide metabolism in ALD are lacking.

METHODS

Male C57B/6 mice were used in an intragastric model of alcohol-associated steatohepatitis (ASH). Liver injury, inflammation, and fibrogenesis were evaluated by measuring plasma levels of injury markers, liver tissue cytokines, and gene expression analyses. Liver transcriptome analysis was performed to examine the effects of alcohol on regulators of cyclic AMP and GMP levels and signaling. cAMP and cGMP levels were measured in mouse livers as well as in livers from healthy human donors and patients with alcohol-associated hepatitis (AH).

RESULTS

Our results show significant changes in several phosphodiesterases (PDEs) with specificity to degrade cAMP (Pde4a, Pde4d, and Pde8a) and cGMP (Pde5a, Pde6d, and Pde9a), as well as dual-specificity PDEs (Pde1a and Pde10a) in ASH mouse livers. Adenylyl cyclases (ACs) 7 and 9, which are responsible for cAMP generation, were also affected by alcohol. Importantly, adenosine receptor 1, which has been implicated in the pathogenesis of liver diseases, was significantly increased by alcohol. Adrenoceptors 1 and 3 (Adrb), which couple with stimulatory G protein to regulate cAMP and cGMP signaling, were significantly decreased. Additionally, beta arrestin 2, which interacts with cAMP-specific PDE4D to desensitize G-protein-coupled receptor to generate cAMP, was significantly increased by alcohol. Notably, we observed that cAMP levels are much higher than cGMP levels in the livers of humans and mice; however, alcohol affected them differently. Specifically, cGMP levels were higher in patients with AH and ASH mice livers compared with controls. As expected, these changes in liver cyclic nucleotide signaling were associated with increased inflammation, steatosis, apoptosis, and fibrogenesis.

CONCLUSIONS

These data strongly implicate dysregulated cAMP and cGMP signaling in the pathogenesis of ASH. Future studies to identify changes in these regulators in a cell-specific manner could lead to the development of novel targeted therapies for ASH.

Exacerbating effects of single-dose acute ethanol exposure on neuroinflammation and amelioration by GPR110 (ADGRF1) activation

BACKGROUND

Neuroinflammation is a widely studied phenomenon underlying various neurodegenerative diseases. Earlier study demonstrated that pharmacological activation of GPR110 in both central and peripheral immune cells cooperatively ameliorates neuroinflammation caused by systemic lipopolysaccharide (LPS) administration. Ethanol consumption has been associated with exacerbation of neurodegenerative and systemic inflammatory conditions. The goal of this study is to determine the effects of single-dose acute ethanol exposure and GPR110 activation on the neuro-inflammation mechanisms.

METHODS

For in vivo studies, GPR110 wild type (WT) and knockout (KO) mice at 10-12 weeks of age were given an oral gavage of ethanol (3 g/kg) or maltose (5.4 g/kg) at 1-4 h prior to the injection of LPS (1 mg/kg, i.p.) followed by the GPR110 ligand, synaptamide (5 mg/kg). After 2-24 h, brains were collected for the analysis of gene expression by RT-PCR or protein expression by western blotting and enzyme-linked immunosorbent assay (ELISA). Microglial activation was assessed by western blotting and immunohistochemistry. For in vitro studies, microglia and peritoneal macrophages were isolated from adult WT mice and treated with 25 mM ethanol for 4 h and then with LPS (100 ng/ml) followed by 10 nM synaptamide for 2 h for gene expression and 12 h for protein analysis.

RESULTS

Single-dose exposure to ethanol by gavage before LPS injection upregulated pro-inflammatory cytokine expression in the brain and plasma. The LPS-induced Iba-1 expression in the brain was significantly higher after ethanol pretreatment in both WT and GPR110KO mice. GPR110 ligand decreased the mRNA and/or protein expression of these cytokines and Iba-1 in the WT but not in GPR110KO mice. In the isolated microglia and peritoneal macrophages, ethanol also exacerbated the LPS-induced expression of pro-inflammatory cytokines which was mitigated at least partially by synaptamide. The expression of an inflammasome marker NLRP3 upregulated by LPS was further elevated with prior exposure to ethanol, especially in the brains of GPR110KO mice. Both ethanol and LPS reduced adenylate cyclase 8 mRNA expression which was reversed by the activation of GPR110. PDE4B expression at both mRNA and protein level in the brain increased after ethanol and LPS treatment while synaptamide suppressed its expression in a GPR110-dependent manner.

CONCLUSION

Single-dose ethanol exposure exacerbated LPS-induced inflammatory responses. The GPR110 ligand synaptamide ameliorated this effect of ethanol by counteracting on the cAMP system, the common target for synaptamide and ethanol, and by regulating NLRP3 inflammasome.

Combined carvacrol and cilostazol ameliorate ethanol-induced liver fibrosis in rats: Possible role of SIRT1/Nrf2/HO-1 pathway

Carvacrol is a natural phenolic monoterpenoid, and cilostazol is a selective phosphodiesterase-3 inhibitor with antioxidant, anti-inflammatory and antiapoptotic effects. This experiment aimed to explore the hepatoprotective effects of carvacrol and cilostazol alone and in combination against alcoholic liver fibrosis (ALF), and the underlying mechanisms, using silymarin as a reference anti-fibrotic product. ALF was induced by oral administration of ethanol (1 ml/100 g/day) thrice per week. Silymarin (100 mg/kg), carvacrol (70 mg/kg), cilostazol (50 mg/kg), or carvacrol + cilostazol combination were administered daily and concurrently with ethanol for six weeks. Hepatic changes were evaluated by quantifying serum biomarkers of liver injury, hepatic MDA, GSH and NOx as oxidative stress markers, interleukin (IL)-10 as an anti-inflammatory cytokine, 4-hydroxyproline (4-HYP) as a collagen synthesis indicator, transforming growth factor (TGF)-β1 as a profibrogenic cytokine, α-smooth muscle actin (α-SMA) as a marker of hepatic stellate cells (HSCs) activation, histopathological (necroinflammation and fibrosis) scores and hepatic sirtuin-1 (SIRT1), nuclear factor-erythroid 2-related factor 2 (Nrf2), and hemeoxygenase-1 (HO-1) mRNA levels. Our results showed that carvacrol, cilostazol, and their combination significantly ameliorated ethanol-induced hepatic fibrosis manifested as improving hepatic functions and histopathological features, attenuating α-SMA immunostaining, reducing TGF-β1 and 4-HYP levels, suppressing oxidativeinjury and elevating IL-10 contents. Such effects were accompanied by upregulating SIRT1, Nrf2 and HO-1 genes. This work disclosed for the first time the hepatoprotective effect of carvacrol against ALF and, to a greater extent, with carvacrol + cilostazol combination that could be partially accredited to SIRT1/Nrf2/HO-1 pathway with consequent antioxidant, anti-inflammatory, and anti-fibrotic features.

Laminarin ameliorates alcohol-induced liver damage and its molecular mechanism in mice

Alcoholic liver disease (ALD) has become a health issue globally. Laminarin, a low molecular weight marine-derived β-glucan, has been identified with multiple biological activities. In this study, the ameliorative effect on ALD of laminarin isolated from brown algae was investigated. Phenotypic, pathological alterations and biochemical characteristics indicated that laminarin administration (100 mg/kg/day) significantly alleviated liver injury and improved liver function in the alcohol-induced mice. Gene chip results indicated that laminarin treatment caused 52 up-regulated and 13 down-regulated genes in the hepatic tissues of alcohol-induced damage mice, and most of these genes are associated with regulation of oxidative stress (such as CYP450/glutathione-dependent antioxidation), Wnt signaling pathway, retinol metabolism, and cAMP pathway based on GO and KEGG analysis. PPI network analysis indicated that the downstream target genes lied in the hub of the net. Our experiments also confirmed the changed expressions of some target genes. Taken together, these results suggest that laminarin can ameliorate alcohol-induced damage in mice and its molecular mechanism lies in modulating anti-oxidation pathway, WNT pathway, and cAMP pathway, which regulate the expressions of downstream target genes and alleviate alcohol-induced damage. Our study provides new clue to prevent alcohol-induced damage and will be benefit to develop functional foods. PRACTICAL APPLICATIONS: This study verified the positive effect on alcoholic liver disease (ALD) of laminarin, a water-soluble brown algae-derived β-glucan, linked by β-(1,3) glycosidic bonds with β-(1,6) branches. Laminarin significantly alleviated liver injury and improved liver function of ALD mice. Moreover, transcriptomics and bioinformatics analysis further revealed the gene expression patterns, hub targets, and signalings including CYP450/glutathione, Wnt, retinol metabolism, cAMP pathways regulated by laminarin. This research is the first evidence for hepatoprotective effect of laminarin against ALD and its molecular mechanism, which will be advantage to develop functional foods or adjuvant therapy of ALD.

Gαs-Coupled CGRP Receptor Signaling Axis from the Trigeminal Ganglion Neuron to Odontoblast Negatively Regulates Dentin Mineralization

An inflammatory response following dental pulp injury and/or infection often leads to neurogenic inflammation via the axon reflex. However, the detailed mechanism underlying the occurrence of the axon reflex in the dental pulp remains unclear. We sought to examine the intracellular cyclic adenosine monophosphate (cAMP) signaling pathway in odontoblasts via the activation of G_s protein-coupled receptors and intercellular trigeminal ganglion (TG) neuron-odontoblast communication following direct mechanical stimulation of TG neurons. Odontoblasts express heterotrimeric G-protein α-subunit Gα_s and calcitonin receptor-like receptors. The application of an adenylyl cyclase (AC) activator and a calcitonin gene-related peptide (CGRP) receptor agonist increased the intracellular cAMP levels ([cAMP]_i) in odontoblasts, which were significantly inhibited by the selective CGRP receptor antagonist and AC inhibitor. Mechanical stimulation of the small-sized CGRP-positive but neurofilament heavy chain-negative TG neurons increased [cAMP]_i in odontoblasts localized near the stimulated neuron. This increase was inhibited by the CGRP receptor antagonist. In the mineralization assay, CGRP impaired the mineralization ability of the odontoblasts, which was reversed by treatment with a CGRP receptor antagonist and AC inhibitor. CGRP establishes an axon reflex in the dental pulp via intercellular communication between TG neurons and odontoblasts. Overall, CGRP and cAMP signaling negatively regulate dentinogenesis as defensive mechanisms.

Nanoparticle Delivery of Novel PDE4B Inhibitor for the Treatment of Alcoholic Liver Disease

The incidence of alcoholic liver disease (ALD) is increasing worldwide while no effective treatment has been approved. The progression of ALD has proven to be related to the upregulation of phosphodiesterase 4 (PDE4) expression, and PDE4 inhibitors showed potential to improve ALD. However, the application of PDE4 inhibitors is limited by the gastrointestinal side effects due to PDE4D inhibition. Therefore, we used a novel PDE4B inhibitor KVA-D88 as the therapeutic for ALD treatment. KVA-D88 inhibited inflammatory response, promoted β-oxidation, increased the level of antioxidants in the hepatocytes, and suppressed hepatic stellate cell (HSC) activation in vitro. To improve the solubility and availability in vivo, KVA-D88 was encapsulated into mPEG-b-P(CB-co-LA) nanoparticles (NPs) by solvent evaporation, with a mean particle size of 135 nm and drug loading of 4.2%. We fed the male C57BL/6 mice with a Lieber–DeCarli liquid diet containing 5% (v/v) ethanol for 6 weeks to induce ALD. Systemic administration of KVA-D88 free drug and KVA-D88-loaded NPs at 5 mg/kg significantly improved the ALD in mice. KVA-D88 significantly ameliorated alcohol-induced hepatic injury and inflammation. KVA-D88 also markedly reduced steatosis by promoting fatty acid β-oxidation. Liver fibrosis and reactive oxygen species (ROS)-caused cellular damage was observed to be alleviated by KVA-D88. KVA-D88-loaded NPs proved better efficacy than free drug in the animal study. In conclusion, the novel PDE4B inhibitor KVA-D88-loaded NPs have the potential to treat ALD in mice

cAMP Signalling Pathway in Biocontrol Fungi

Biocontrol is a complex process, in which a variety of physiological and biochemical characteristics are altered. The cAMP signalling pathway is an important signal transduction pathway in biocontrol fungi and consists of several key components. The G-protein system contains G-protein coupled receptors (GPCRs), heterotrimeric G-proteins, adenylate cyclase (AC), cAMP-dependent protein kinase (PKA), and downstream transcription factors (TFs). The cAMP signalling pathway can regulate fungal growth, development, differentiation, sporulation, morphology, secondary metabolite production, environmental stress tolerance, and the biocontrol of pathogens. However, few reviews of the cAMP signalling pathway in comprehensive biocontrol processes have been reported. This work reviews and discusses the functions and applications of genes encoding each component in the cAMP signalling pathway from biocontrol fungi, including the G-protein system components, AC, PKA, and TFs, in biocontrol behaviour. Finally, future suggestions are provided for constructing a complete cAMP signalling pathway in biocontrol fungi containing all the components and downstream effectors involved in biocontrol behavior. This review provides useful information for the understanding the biocontrol mechanism of biocontrol fungi by utilising the cAMP signalling pathway.

D-Carvone Attenuates CCl4-Induced Liver Fibrosis in Rats by Inhibiting Oxidative Stress and TGF-ß 1/SMAD3 Signaling Pathway

D-carvone is a natural monoterpene found in abundance in the essential oil of aromatic medicinal plants with a wide range of pharmacological values. However, the impact of D-carvone on liver fibrosis remains unclear. This study aimed to evaluate the anti-fibrotic potential of D-carvone in a rat model of liver fibrosis and to clarify the possible underlying mechanisms. Liver fibrosis was induced in rats by carbon tetrachloride, CCl₄ (2.5 mL/kg, interperitoneally every 72 h for 8 weeks). Oral treatment of rats with D-carvone (50 mg/kg, daily) started on the 3rd week of CCl₄ administration. D-carvone significantly enhanced liver functions (ALT, AST), oxidant/antioxidant status (MDA, SOD, GSH, total antioxidant capacity; TAC), as well as histopathological changes. Moreover, D-carvone effectively attenuated the progression of liver fibrosis, evident by the decreased collagen deposition and fibrosis score by Masson trichrome staining (MT) and α-SMA protein expression. Moreover, D-carvone administration resulted in a significant downregulation of the pro-fibrogenic markers TGF-β1 and SMAD3 and upregulation of MMP9. These findings reveal the anti-fibrotic effect of D-carvone and suggest regulation of the TGF-β1/SMAD3 pathway, together with the antioxidant activity as a mechanistic cassette, underlines this effect. Therefore, D-carvone could be a viable candidate for inhibiting liver fibrosis and other oxidative stress-related hepatic diseases. Clinical studies to support our hypothesis are warranted.

Novel Liposomal Rolipram Formulation for Clinical Application to Reduce Emesis

Introduction

The phosphodiesterase 4 (PDE4) inhibitor, rolipram, has beneficial effects on tissue inflammation, injury and fibrosis, including in the liver. Since rolipram elicits significant CNS side-effects in humans (ie, nausea and emesis), our group developed a fusogenic lipid vesicle (FLV) drug delivery system that targets the liver to avoid adverse events. We evaluated whether this novel liposomal rolipram formulation reduces emesis.

Methods

C57Bl/6J male mice were used to compare the effect of three doses of free and FLV-delivered (FLVs-Rol) rolipram in a behavioral correlate model of rolipram-induced emesis. Tissue rolipram and rolipram metabolite levels were measured using LC-MS/MS. The effect of FLVs-Rol on brain and liver PDE4 activities was evaluated.

Results

Low and moderate doses of free rolipram significantly reduced anesthesia duration, while the same doses of FLVs-Rol had no effect. However, the onset and duration of adverse effects (shortening of anesthesia period) elicited by a high dose of rolipram was not ameliorated by FLVs-Rol. Post-mortem analysis of brain and liver tissues demonstrated that FLVs affected the rate of rolipram uptake by liver and brain. Lastly, administration of a moderate dose of FLVs-Rol attenuated endotoxin induced PDE4 activity in the liver with negligible effect on the brain.

Discussion

The findings that the low and moderate doses of FLVs-Rol did not shorten the anesthesia duration time suggest that FLV delivery prevented critical levels of drug from crossing the blood-brain barrier (BBB) to elicit CNS side-effects. However, the inability of high dose FLVs-Rol to prevent CNS side-effects indicates that there was sufficient unencapsulated rolipram to cross the BBB and shorten anesthesia duration. Notably, a moderate dose of FLVs-Rol was able to decrease PDE4 activity in the liver without affecting the brain. Taken together, FLVs-Rol has a strong potential for clinical application for the treatment of liver disease without side effects.

Production of Bioactive Substances to Alleviates Hangover and Ethanol-Induced Liver Damage through Fermentation of Oenanthe javanica Using Lactiplantibacillus plantarum

The purpose of this study is to evaluate the effect of the bioconversion products of Oenanthe javanica extract fermented by Lactiplantibacillus plantarum (OEFL) on relieving hangovers and improving liver function. In addition, the bioactive substance of the OEFL, which alleviates hangover and ethanol-induced liver damage, was identified and its bioactive property was verified through in vivo experiments. In major substances analysis using high-performance liquid chromatography, OEFL produced 9.5-fold higher p-coumaric acid than the O. Javanica extract (OE). In addition, considering that quinic acid, which is not present in the OE, was produced in the OEFL it was confirmed that chlorogenic acid was decomposed into quinic acid by bioconversion. In the in vivo experiment using Sprague-Dawley rats, the OEFL and p-coumaric acid diets reduced blood ethanol, acetaldehyde, GPT, and ALP concentrations, increasing blood albumin concentrations compared to ethanol-administered groups, demonstrating that OEFL and p-coumaric acid, the main substance in the OEFL, improved ethanol-induced liver damage. Furthermore, the OEFL and its main bioactive substance, p-coumaric acid, alleviated liver fibrosis by downregulating TGF-β, SMAD-2, SMAD-4, α-SMA, and upregulating MMP-1. Therefore, OEFL is expected to be used as a functional food or pharmaceutical material as it has been confirmed to effectively relieve hangovers, prevent liver damage, and delay liver fibrosis in ethanol-induced liver damages.

Role of Mitochondrial Cytochrome P450 2E1 in Healthy and Diseased Liver

Cytochrome P450 2E1 (CYP2E1) is pivotal in hepatotoxicity induced by alcohol abuse and different xenobiotics. In this setting, CYP2E1 generates reactive metabolites inducing oxidative stress, mitochondrial dysfunction and cell death. In addition, this enzyme appears to play a role in the progression of obesity-related fatty liver to nonalcoholic steatohepatitis. Indeed, increased CYP2E1 activity in nonalcoholic fatty liver disease (NAFLD) is deemed to induce reactive oxygen species overproduction, which in turn triggers oxidative stress, necroinflammation and fibrosis. In 1997, Avadhani’s group reported for the first time the presence of CYP2E1 in rat liver mitochondria, and subsequent investigations by other groups confirmed that mitochondrial CYP2E1 (mtCYP2E1) could be found in different experimental models. In this review, we first recall the main features of CYP2E1 including its role in the biotransformation of endogenous and exogenous molecules, the regulation of its expression and activity and its involvement in different liver diseases. Then, we present the current knowledge on the physiological role of mtCYP2E1, its contribution to xenobiotic biotransformation as well as the mechanism and regulation of CYP2E1 targeting to mitochondria. Finally, we discuss experimental investigations suggesting that mtCYP2E1 could have a role in alcohol-associated liver disease, xenobiotic-induced hepatotoxicity and NAFLD.

Toxic responses of liver in Lateolabrax maculatus during hypoxia and re-oxygenation

Estuarine environmental have been reported to undergo significant fluctuations in oxygen concentrations with hypoxic conditions and subsequent re-oxygenation events being of significant concern for resident fish populations. In this study we assessed the toxicological effects of hypoxia and re-oxygenation on the liver of hypoxia-sensitive spotted sea bass (Lateolabrax maculatus) that were exposed to hypoxia (1.17 mg/L dissolved oxygen) for 12 h and then re-oxygenated for 12 h. The activities of glutamic-pyruvic transaminase and glutamic-oxalacetic transaminase in serum significantly increased under hypoxia (p < 0.05) and continued to increase during re-oxygenation (p < 0.05), indicating that normal liver function might be disrupted by hypoxia and might become worse during re-oxygenation for 12h. Total protein, albumin, and globulin levels in serum decreased under hypoxia but began to return to normal during re-oxygenation, showing that protein synthesis in the liver decreased during hypoxia but could be restored by re-oxygenation. We also used RNA-Seq technology to identify changes in gene expression in the liver during hypoxia and re-oxygenation. Transcriptome sequencing revealed that the hypoxia-inducible factor (HIF-1) signaling pathway, apoptosis, and purine metabolism transcripts were significantly enriched under hypoxia and re-oxygenation conditions. A total of 15 and 16 apoptosis-related genes were induced by hypoxia and re-oxygenation stress, respectively. The apoptosis index increased from the normal to the hypoxic condition and was highest under re-oxygenation. Additionally, 19 and 29 genes, that are involved in purine metabolism in the liver of L. maculatus during hypoxia and re-oxygenation, respectively, were dysregulated. Unexpectedly, the serum uric acid level significantly increased during hypoxia and significantly decreased under re-oxygenation, indicating the presence of purine metabolic disorder in the liver of L. maculatus. These results illustrate that hypoxia poses a pronounced threat to hepatocyte function in L. maculatus and that liver damage is difficult to reverse with 12 h of re-oxygenation, and it may actually become worse when re-oxygenation is established.

Selective Inhibition of PDE4B Reduces Binge Drinking in Two C57BL/6 Substrains

Cyclic AMP (cAMP)-dependent signaling is highly implicated in the pathophysiology of alcohol use disorder (AUD), with evidence supporting the efficacy of inhibiting the cAMP hydrolyzing enzyme phosphodiesterase 4 (PDE4) as a therapeutic strategy for drinking reduction. Off-target emetic effects associated with non-selective PDE4 inhibitors has prompted the development of selective PDE4 isozyme inhibitors for treating neuropsychiatric conditions. Herein, we examined the effect of a selective PDE4B inhibitor A33 (0–1.0 mg/kg) on alcohol drinking in both female and male mice from two genetically distinct C57BL/6 substrains. Under two different binge-drinking procedures, A33 pretreatment reduced alcohol intake in male and female mice of both substrains. In both drinking studies, there was no evidence for carry-over effects the next day; however, we did observe some sign of tolerance to A33’s effect on alcohol intake upon repeated, intermittent, treatment (5 injections of 1.0 mg/kg, every other day). Pretreatment with 1.0 mg/kg of A33 augmented sucrose intake by C57BL/6NJ, but not C57BL/6J, mice. In mice with a prior history of A33 pretreatment during alcohol-drinking, A33 (1.0 mg/kg) did not alter spontaneous locomotor activity or basal motor coordination, nor did it alter alcohol’s effects on motor activity, coordination or sedation. In a distinct cohort of alcohol-naïve mice, acute pretreatment with 1.0 mg/kg of A33 did not alter motor performance on a rotarod and reduced sensitivity to the acute intoxicating effects of alcohol. These data provide the first evidence that selective PDE4B inhibition is an effective strategy for reducing excessive alcohol intake in murine models of binge drinking, with minimal off-target effects. Despite reducing sensitivity to acute alcohol intoxication, PDE4B inhibition reduces binge alcohol drinking, without influencing behavioral sensitivity to alcohol in alcohol-experienced mice. Furthermore, A33 is equally effective in males and females and exerts a quantitatively similar reduction in alcohol intake in mice with a genetic predisposition for high versus moderate alcohol preference. Such findings further support the safety and potential clinical utility of targeting PDE4 for treating AUD.