Elevated cAMP Protects against Diclofenac-Induced Toxicity in Primary Rat Hepatocytes: A Protective Effect Mediated by the Exchange Protein Directly Activated by cAMP/cAMP-Regulated Guanine Nucleotide Exchange Factors

The role of exosomal lncRNAs in acetaminophen-induced induced liver injury in SD rats

Background

Drug-induced liver injury (DILI) is a leading cause of drug development failures during clinical trials and post-market introduction. Current biomarkers, such as ALT and AST, lack the necessary specificity and sensitivity needed for accurate detection. Exosomes, which protect LncRNAs from RNase degradation, could provide reliable and easily accessible options for biomarkers.

Materials and methods

RNA-sequencing was used to identify differentially expressed LncRNAs (DE-LncRNAs), followed by isolation of LncRNAs from plasma exosomes in this study. Exosome characterization was conducted by transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and Western blot (WB). Bioinformatics analysis included functional enrichment and co-expression network analysis. Five rat models were established, and quantitative real-time PCR was used to verify the specificity and sensitivity of two candidate exosomal LncRNAs.

Results

The APAP-induced hepatocellular injury model was successfully established for RNA-sequencing, leading to the identification of several differentially expressed exosomal LncRNAs. Eight upregulated exosomal DE-LncRNAs were selected for validation. Among them, NONRATT018001.2 (p < 0.05) and MSTRG.73954.4 (p < 0.05) exhibited a more than 2-fold increase in expression levels. In hepatocellular injury and intrahepatic cholestasis models, both NONRATT018001.2 and MSTRG.73954.4 showed earlier increases compared to serum biomarkers ALT and AST. However, no histological changes were observed until the final time point. In the fatty liver model, NONRATT018001.2 and MSTRG.73954.4 increased earlier than ALT and AST at 21 days. By the 7th day, minor steatosis was evident in liver tissue, while the expression levels of the two candidate exosomal LncRNAs exceeded 2 and 4 times, respectively. In the hepatic fibrosis model, NONRATT018001.2 and MSTRG.73954.4 showed increases at every time point. By the 49th day, hepatocellular necrosis and fibrosis were observed in the liver tissue, with NONRATT018001.2 showing an increase of more than 8 times. The specificity of the identified exosomal DE-LncRNAs was verified using a myocardial injury model and they showed no significant differences between the case and control groups.

Conclusion

NONRATT018001.2 and MSTRG.73954.4 hold potential as biomarkers for distinguishing different types of organ injury induced by drugs, particularly enabling early prediction of liver injury. Further experiments, such as siRNA interference or gene knockout, are warranted to explore the underlying mechanisms of these LncRNAs.

Targeting the PDE3B-cAMP-autophagy axis prevents liver injury in long-term supercooling liver preservation

In liver transplantation, donor livers are typically stored in a preservation solution at 4°C for up to 12 hours. However, this short preservation duration can lead to various issues, such as suboptimal donor-recipient matching and limited opportunities for organ sharing. Previous studies have developed a long-term preservation method called supercooling liver preservation (SLP) to address these issues. However, in this study using a rat model, we observed that long-term SLP led to more severe liver damage compared with clinically prevalent traditional static cold storage (SCS) for durations less than 8 hours. To understand the potential mechanism of SLP-induced liver injury, we conducted an integrative metabolomic, transcriptomic, and proteomic analysis. We identified the PDE3B-cAMP-autophagy pathway as a key determinant of SLP-induced liver injury. Specifically, we found that PDE3B was elevated during SLP, which promoted a reduction of cAMP metabolites, triggering an AMPK-dependent autophagy process that led to liver injury in rats. We found that blocking the reduction in cAMP using the PDE3B inhibitor cilostamide inhibited autophagy and substantially ameliorated liver injury during 48-hour SLP in rat livers. Furthermore, we validated the effectiveness of cilostamide treatment in preventing liver injury in pig and human liver 48-hour SLP models. In summary, our results reveal that metabolic reprogramming involving the PDE3B-cAMP-autophagy axis is the key determinant of liver injury in long-term SLP and provide an early therapeutic strategy to prevent liver injury in this setting.

Protective effects of caffeine against palmitate-induced lipid toxicity in primary rat hepatocytes is associated with modulation of adenosine receptor A1 signaling

BACKGROUND

Epidemiological evidence has shown an association between coffee consumption and reduced risk for chronic liver diseases, including metabolic-dysfunction-associated liver disease (MALFD). Lipotoxicity is a key cause of hepatocyte injury during MAFLD. The coffee component caffeine is known to modulate adenosine receptor signaling via the antagonism of adenosine receptors. The involvement of these receptors in the prevention of hepatic lipotoxicity has not yet been explored. The aim of this study was to explore whether caffeine protects against palmitate-induced lipotoxicity by modulating adenosine receptor signaling.

METHODS

Primary hepatocytes were isolated from male rats. Hepatocytes were treated with palmitate with or without caffeine or 1,7DMX. Lipotoxicity was verified using Sytox viability staining and mitochondrial JC-10 staining. PKA activation was verified by Western blotting. Selective (ant)agonists of A1AR (DPCPX and CPA, respectively) and A2AR (istradefyline and regadenoson, respectively), the AMPK inhibitor compound C, and the Protein Kinase A (PKA) inhibitor Rp8CTP were used. Lipid accumulation was verified by ORO and BODIPY 453/50 staining.

RESULTS

Caffeine and its metabolite 1,7DMX prevented palmitate-induced toxicity in hepatocytes. The A1AR antagonist DPCPX also prevented lipotoxicity, whereas both the inhibition of PKA and the A1AR agonist CPA (partially) abolished the protective effect. Caffeine and DPCPX increased lipid droplet formation only in palmitate-treated hepatocytes and decreased mitochondrial ROS production.

CONCLUSIONS

The protective effect of caffeine against palmitate lipotoxicity was shown to be dependent on A1AR receptor and PKA activation. Antagonism of A1AR also protects against lipotoxicity. Targeting A1AR receptor may be a potential therapeutic intervention with which to treat MAFLD.

Roflumilast escalates α-synuclein aggregate degradation in rotenone-induced Parkinson's disease in rats: Modulation of the ubiquitin-proteasome system and endoplasmic reticulum stress

Perturbation of the protein homeostasis circuit is one of the principal attributes associated with many neurodegenerative disorders, such as Parkinson's disease (PD). This study aimed to explore the neuroprotective effect of roflumilast (ROF), a phosphodiesterase-4 inhibitor, in a rotenone-induced rat model of PD and investigate the potential underlying mechanisms. Interestingly, ROF (1 mg/kg, p.o.) attenuated motor impairment, prevented brain lesions, and rescued the dopaminergic neurons in rotenone-treated rats. Furthermore, it reduced misfolded α-synuclein burden. ROF also promoted the midbrain cyclic adenosine monophosphate level, which subsequently enhanced the 26S proteasome activity and the expression of the 20S proteasome. ROF counteracted rotenone-induced endoplasmic reticulum stress, which was demonstrated by its impact on activating transcription factor 6, glucose-regulated protein 78, and C/EBP homologous protein levels. Moreover, ROF averted rotenone-induced oxidative stress, as evidenced by its effects on the levels of nuclear factor erythroid 2-related factor 2, heme oxygenase-1, reduced glutathione, and lipid peroxides with a significant anti-apoptotic activity. Collectively, this study implies repurposing of ROF as a novel neuroprotective drug owning to its ability to restore normal protein homeostasis.

CREB is a potential marker associated with drug-induced liver injury: Identification and validation through transcriptome database analysis

Drug-induced liver injury (DILI) is the main cause of failure in drug development and postapproval withdrawal. Although toxicogenomic techniques provide an unprecedented opportunity for mechanistic assessment and biomarker discovery, they are not suitable for the screening of large numbers of exploratory compounds in early drug discovery. Using a comprehensive analysis of toxicogenomics (TGx) data, we aimed to find DILI-relevant transcription factors (TFs) that could be incorporated into a reporter gene assay system. Gene set enrichment analysis (GSEA) of the Open TG-GATEs dataset highlighted 4 DILI-relevant TFs, including CREB, NRF2, ELK-1, and E2F. Using ten drugs with already assigned idiosyncratic toxicity (IDT) risks, reporter gene assays were conducted in HepG2 cells in the presence of the S9 mix. There were weak correlations between NRF2 activity and IDT risk, whereas strong correlations were observed between CREB activity and IDT risk. In addition, CREB activation associated with 3 Withdrawn/Black box Warning drugs was reversed by pretreatment with a PKA inhibitor. Collectively, we suggest that CREB might be a sensitive biomarker for DILI prediction, and its response to stress induced by high-risk drugs might be primarily regulated by the PKA/CREB signaling pathway.

Repercussion of cAMP and EPAC in Memory and Signaling

It is well recognized that cyclic adenosine monophosphate (cAMP) signaling within neurons plays a key role in the foundation of long-term memories. Memory storage is the process that demands the movement of signals, neural plasticity, and the molecules which can transfer the signals from the sensory neuron to the dorsal root ganglion (DRG) neurons and later into the temporal region of the brain. The discovery of cAMP in 1958 as the second messenger also had a role in memory formation and other neural aspects. Further, in 1998 the scientists found that cAMP does not just activate protein kinase A (PKA) but also exchange protein directly activated by cAMP (Epac) which has an active role to play in hyperalgesia, memory, and signaling. The cAMP has three targets, hyperpolarization-activated cyclic nucleotide modulated (HCN) channels, protein kinase A (PKA), and exchange protein activated by cAMP (Epac). Different research has exposed that both PKA and HCN channels are significant for long-term memory creation. Epac is a cAMP-dependent guanine nucleotide exchange factor for the small G proteins including Rap1. However, slight information is there about the role of Epac in this process. The effects of cAMP are predominantly imparted by activating protein kinase A (PKA) and the more newly discovered exchange proteins are directly activated by cAMP 1 and 2 (EPAC1 and EPAC2). This review provides an insight regarding the function and role of both of these secondary messengers in memory and nerve signaling.

Metformin protects against diclofenac-induced toxicity in primary rat hepatocytes by preserving mitochondrial integrity via a pathway involving EPAC

BACKGROUND AND PURPOSE

It has been shown that the antidiabetic drug metformin protects hepatocytes against toxicity by various stressors. Chronic or excessive consumption of diclofenac (DF) - a pain-relieving drug, leads to drug-induced liver injury via a mechanism involving mitochondrial damage and ultimately apoptotic death of hepatocytes. However, whether metformin protects against DF-induced toxicity is unknown. Recently, it was also shown that cAMP elevation is protective against DF-induced apoptotic death in hepatocytes, a protective effect primarily involving the downstream cAMP effector EPAC and preservation of mitochondrial function. This study therefore aimed at investigating whether metformin protects against DF-induced toxicity via cAMP-EPACs.

EXPERIMENTAL APPROACH

Primary rat hepatocytes were exposed to 400 µmol/L DF. CE3F4 or ESI-O5 were used as EPAC-1 or 2 inhibitors respectively. Apoptosis was measured by caspase-3 activity and necrosis by Sytox green staining. Seahorse X96 assay was used to determine mitochondrial function. Mitochondrial reactive oxygen species (ROS) production was measured using MitoSox, mitochondrial MnSOD expression was determined by immunostaining and mitochondrial morphology (fusion and fission ratio) by 3D refractive index imaging.

KEY RESULTS

Metformin (1 mmol/L) was protective against DF-induced apoptosis in hepatocytes. This protective effect was EPAC-dependent (mainly EPAC-2). Metformin restored mitochondrial morphology in an EPAC-independent manner. DF-induced mitochondrial dysfunction which was demonstrated by decreased oxygen consumption rate, an increased ROS production and a reduced MnSOD level, were all reversed by metformin in an EPAC-dependent manner.

CONCLUSION AND IMPLICATIONS

Metformin protects hepatocytes against DF-induced toxicity via cAMP-dependent EPAC-2.