The role of acetaldehyde dehydrogenase 2 in the pathogenesis of liver diseases

Acetaldehyde dehydrogenase 2 attenuates lipopolysaccharide -induced endothelial barrier damage by inhibiting mitochondrial fission in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common neurological complication of sepsis, and acetaldehyde dehydrogenase 2 (ALDH2) has been identified as a protective factor for endothelial cells against oxidative stress. In this study, we aimed to investigate the therapeutic potential of ALDH2 and its impact on mitochondrial dynamics using both mouse and brain microvascular endothelial cells (BMECs) injury models induced by lipopolysaccharide (LPS). Our findings demonstrated that ALDH2 attenuated LPS-induced brain endothelial barrier damage, as evidenced by reduced brain water content and Evans blue dye in mice, decreased transepithelial electrical resistance (TEER), and increased fluorescein isothiocyanate-dextran (FITC-Dextran) leakage in bEnd.3 cells. Furthermore, ALDH2 reduced the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), while enhancing the activities of superoxide dismutase (SOD) and catalase (CAT). ALDH2 also decreased 4-HNE content and restored mitochondrial membrane potential and ATP production, promoting a balanced mitochondrial fission and fusion. Notably, our use of the mitochondrial fission inhibitor Mdivi-1 confirmed that ALDH2 alleviated mitochondrial damage by inhibiting dynamin-related protein 1 (Drp1). Consequently, our findings suggest that the effects of ALDH2 on LPS-induced blood-brain barrier (BBB) damage and oxidative stress may alleviate SAE by inhibiting Drp1 to maintain mitochondrial homeostasis.

The role of ALDHs in lipid peroxidation-related diseases

Lipid peroxidation presents the oxidative degradation of polyunsaturated fatty acids lincited by reactive species. Excessive accumulation of lipid peroxidation byproducts, including 4-hydroxy-2-nonenal (4-HNE) and malondialdehyde (MDA), causes protein dysfunction and various illnesses. Aldehyde dehydrogenases (ALDHs) catalyze the metabolism of both endogenous and exogenous aldehydes. These enzymes participate in detoxification and intermediary metabolism. Contemporary research has affirmed the involvement of both enzymatic and non-enzymatic pathways of ALDHs in modulating the evolution of diseases associated with lipid peroxidation. This review provides an overview of the biological functions and clinical implications concerning the enzymatic and non-enzymatic pathways of ALDHs in diseases related to lipid peroxidation, such as, non-alcoholic fatty liver disease (NAFLD), atherosclerosis, and type 2 diabetes (T2DM). Furthermore, the activators or inhibitors of ALDHs represent a promising therapeutic strategy for lipid peroxidation-related diseases.

Expression pattern and prognostic significance of aldehyde dehydrogenase 2 in lung adenocarcinoma as a potential predictor of immunotherapy efficacy

Background

The incidence of alcohol-associated cancers is higher within Asian populations having an increased prevalence of an inactivating mutation in aldehyde dehydrogenase 2 (ALDH2), a mitochondrial enzyme required for the clearance of acetaldehyde, a cytotoxic metabolite of ethanol. The role of alcohol consumption in promoting lung cancer is controversial, and little attention has been paid to the association between alcohol drinking and pulmonary ALDH2 expression.

Methods

We performed a comprehensive bioinformatic analysis of multi-omics data available in public databases to elucidate the role of ALDH2 in lung adenocarcinoma (LUAD).

Results

Transcriptional and proteomic data indicate a substantial pulmonary expression of ALDH2, which is functional for the metabolism of alcohol diffused from the bronchial circulation. ALDH2 expression is higher in healthy lung tissue than in LUAD and inhibits cell cycle, apoptosis, and epithelial-mesenchymal transition pathways. Moreover, low ALDH2 mRNA levels predict poor prognosis and low overall survival in LUAD patients. Interestingly, ALDH2 expression correlates with immune infiltration in LUAD.

Conclusions

A better understanding of the role of ALDH2 in lung tumor progression and immune infiltration might support its potential use as a prognostic marker and therapeutic target for improving immunotherapeutic response.

ALDH2 attenuates radiation-induced lung injury by inhibiting ROS and epithelial-mesenchymal transition mediated by the TGF-β1/Smad pathway

Radiation-induced lung injury is a significant complication of thoracic malignant tumor radiotherapy, yet effective treatments remain scarce. Aldehyde dehydrogenase 2 (ALDH2) possesses antioxidant and anti-inflammatory properties, but its specific role in radiation-induced lung injury is not well understood. This study aimed to investigate the impact of ALDH2 on radiation-induced lung injury and elucidate the underlying mechanisms. Through analysis of radiation-induced lung injury datasets, intervention with ALDH2 agonists and inhibitors in an in vivo radiation-induced lung injury model, and establishment of an in vitro radiation-induced lung injury model using A549 stable cells with varying ALDH2 expressions, we discovered that ALDH2 expression is reduced in radiation-induced lung injury. Enrichment analysis suggested that ALDH2 may mitigate radiation-induced lung injury by modulating oxidative stress and inflammation levels. Additionally, single-cell data analysis reveals that ALDH2 is primarily localized in myeloid macrophages within the lungs, with its expression also being reduced in lung cancer patients. Subsequent examination of mouse pathological sections, reactive oxygen species (ROS), and inflammatory factor levels confirmed that ALDH2 can lessen radiation-induced lung injury by suppressing ROS and inflammatory factors. Both in vivo and in vitro Western blot analysis further validated that ALDH2 can attenuate epithelial-mesenchymal transition and inhibit the TGF-β1/Smad pathway. Therefore, ALDH2 shows promise in reducing radiation-induced lung injury by inhibiting ROS and TGF-mediated epithelial-mesenchymal transition, making it a potential target for the treatment of radiation-induced lung injury.

Alcohol-related liver disease (ALD): current perspectives on pathogenesis, therapeutic strategies, and animal models

Alcohol-related liver disease (ALD) is a major cause of morbidity and mortality worldwide. It encompasses conditions such as fatty liver, alcoholic hepatitis, chronic hepatitis with liver fibrosis or cirrhosis, and hepatocellular carcinoma. Numerous recent studies have demonstrated the critical role of oxidative stress, abnormal lipid metabolism, endoplasmic reticulum stress, various forms of cell death (including apoptosis, necroptosis, and ferroptosis), intestinal microbiota dysbiosis, liver immune response, cell autophagy, and epigenetic abnormalities in the pathogenesis of ALD. Currently, abstinence, corticosteroids, and nutritional therapy are the traditional therapeutic interventions for ALD. Emerging therapies for ALD mainly include the blockade of inflammatory pathways, the promotion of liver regeneration, and the restoration of normal microbiota. Summarizing the advances in animal models of ALD will facilitate a more systematic investigation of the pathogenesis of ALD and the exploration of therapeutic targets. This review summarizes the latest insight into the pathogenesis and molecular mechanisms of ALD, as well as the pros and cons of ALD rodent models, providing a basis for further research on therapeutic strategies for ALD.

Network pharmacology combined with metabolomics to reveal the anti-fibrotic mechanism of Polygoni Orientalis Fructus in CCl4-induced hepatic fibrosis rats

Polygoni Orientalis Fructus (POF), a dried ripe fruit of Polygonum orientale L., is commonly used in China for liver disease treatment. However, its therapeutic mechanism remains unclear. The aim of this study was to elucidate the effects of POF on the regulation of endogenous metabolites and identify its key therapeutic targets in hepatic fibrosis (HF) rats by integrating network pharmacology and metabolomics approaches. First, serum liver indices and histopathological analyses were used to evaluate the therapeutic effects of POF on carbon tetrachloride (CCl4)-induced HF. Subsequently, differential metabolites and potential therapeutic targets of POF were screened using plasma metabolomics and network pharmacology, respectively. The key targets of POF were identified by overlapping differential metabolite-associated targets with the potential targets and validated by molecular docking and ELISA experiments. The results showed that POF effectively alleviated HF in rats. A total of 51 metabolites related to HF were screened, and 24 were associated with POF. 232 potential therapeutic targets were identified by network pharmacology analysis. Finally, six key targets were identified through a combined analysis. Furthermore, molecular docking and ELISA validation revealed that AGXT, PAH, and NOS3 are targets of POF action, while CBS, ALDH2, and ARG1 were identified as potential targets. SIGNIFICANCE: POF is now commonly used in the treatment of liver disease, but its mechanism of action remains unclear. Current studies on metabolomics of liver disease primarily focuse on the interpretation of differential metabolites and related metabolic pathways. This research delves into the intricate details of metabolomics findings via network pharmacology to uncover the targets and pathways of drug action.

Aldehyde Dehydrogenase 2 (ALDH2): A novel sorafenib target in hepatocellular carcinoma unraveled by the proteome-wide cellular thermal shift assay

Sorafenib is a multikinase inhibitor indicated for first-line treatment of unresectable hepatocellular carcinoma. Despite its widespread use in the clinic, the existing knowledge of sorafenib mode-of-action remains incomplete. To build upon the current understanding, we used the Cellular Thermal Shift Assay (CETSA) coupled to Mass Spectrometry (CETSA-MS) to monitor compound binding to its target proteins in the cellular context on a proteome-wide scale. Among the potential sorafenib targets, we identified aldehyde dehydrogenase 2 (ALDH2), an enzyme that plays a major role in alcohol metabolism. We validated the interaction of sorafenib with ALDH2 by orthogonal methods using pure recombinant protein, proving that this interaction is not mediated by other cellular components. Moreover, we showed that sorafenib inhibits ALDH2 activity, supporting a functional role for this interaction. Finally, we were able to demonstrate that both ALDH2 protein expression and activity were reduced in sorafenib-resistant cells compared to the parental cell line. Overall, our study allowed the identification of ALDH2 as a novel sorafenib target and sheds light on its potential role in both hepatocellular carcinoma and sorafenib resistance condition.

ALDH2 deficiency exacerbates MCD-diet induced MASLD by modulating bile acid metabolism

Aldehyde dehydrogenase 2 (ALDH2), an acetaldehyde dehydrogenase in mitochondria, is primarily responsible for metabolizing alcohol-derived acetaldehyde and other endogenous aldehydes. Inactivating ALDH2 rs671 polymorphism is found in up to 8 % of the global population and 40 % of the East Asian population. Recent studies have shown that rs671 SNP mutation in the human ALDH2 gene is associated with an increased risk of metabolic dysfunction-associated steatotic liver diseases (MASLD), but the mechanism remains unclear. Here, we identify the role of ALDH2 in MASLD. Firstly, ALDH2 activity was lower in MASLD patients and the methionine-choline deficiency (MCD) diet induced MASLD model. Secondly, activation of ALDH2 activity with Alda-1 (ALDH2 agonist) attenuated MCD-diet induced hepatic triglyceride (TG) accumulation and steatosis, whereas the opposite result was observed with cyanamide (CYA, ALDH2 inhibitor). Furthermore, ALDH2 deficiency exacerbated hepatic steatosis, inflammation, and fibrosis in the MCD-diet induced mice. RNA sequencing (RNA-seq) revealed that oxysterol 7-α hydroxylase (Cyp7b1) and the related metabolic pathway significantly changed in the MCD-diet challenged ALDH2-/- mice. In ALDH2-/- mice, the expression of Cyp7b1 was downregulated and FXR/SHP signaling was inhibited, reducing the alternative bile acid (BA) synthetic pathway. In our in vitro experiments, knockdown of ALDH2 exacerbated TG accumulation in hepatocytes, whereas the opposite result was observed with overexpression of ALDH2. Moreover, chenodeoxycholic acid (CDCA) rescued ALDH2 downregulation induced TG accumulation in hepatocytes. Our study reveals that ALDH2 attenuates hepatocyte steatosis by regulating the alternative BA synthesis pathway, and ALDH2 may serve as a potential target for the treatment of MASLD.

Role of Immunological Cells in Hepatocellular Carcinoma Disease and Associated Pathways

Hepatocellular carcinoma (HCC) remains one of the predominant causes of cancer-related mortality across the globe. It is attributed to obesity, excessive alcohol consumption, smoking, and infection by the hepatitis virus. Early diagnosis of HCC is essential, and local treatments such as surgical excision and percutaneous ablation are effective. Palliative systemic therapy, primarily with the tyrosine kinase inhibitor Sorafenib, is used in advanced cases. However, the prognosis for advanced HCC remains poor. This Review additionally describes the pathophysiological mechanisms of HCC, which include aberrant molecular signaling, genomic instability, persistent inflammation, and the paradoxical position of the immune system in promoting and suppressing HCC. The paper concludes by discussing the growing body of research on the relationship between mitochondria and HCC, suggesting that mitochondrial dysfunction may contribute to the progression of HCC. This Review focuses on immunological interactions between different mechanisms of HCC progression, including obesity, viral infection, and alcohol consumption.

SLC3A2, as an indirect target gene of ALDH2, exacerbates alcohol-associated liver cancer via the sphingolipid biosynthesis pathway

Excessive drinking is one of the main causes of liver cancer. In the process of alcohol metabolism, aldehyde dehydrogenase 2 (ALDH2) is the key enzyme of acetaldehyde metabolism. ALDH2 gene deficiency is positively associated with the risk of hepatocellular carcinoma (HCC). However, no studies have shown a connection between ALDH2 and another metabolic regulatory gene, SLC3A2. In this study, we analyzed the expression levels of ALDH2 and SLC3A2 in liver cancer tissues based on the TCGA database. Subsequently, we constructed ALDH2 knockout and SLC3A2 knock-in transgenic mice to check the roles of ALDH2 and SLC3A2 in tumorigenesis in vivo. In addition, we examined the mechanisms of ALDH2 and SLC3A2 in HCC cells using small RNA interference technology. Consistent with previous studies, we also confirmed the functions of ALDH2 in inhibiting hepatocarcinogenesis, while SLC3A2 had the opposite effect. The main finding of this study is that ALDH2 inhibited BSG expression through the TGF-β1 pathway, which indirectly inhibited SLC3A2 expression; subsequently, the sphingolipid metabolism pathway was also inhibited in HCC cells. Therefore, SLC3A2 is a novel target for HCC treatment.