Novel Fluorescence-Based Method To Characterize the Antioxidative Effects of Food Metabolites on Lipid Droplets in Cultured Hepatocytes

Inhibition of Accumulation of Neutral Lipids and Their Hydroperoxide Species in Hepatocytes by Bioactive Allium sativum Extract

Our ongoing research suggests that extracts from plant-based foods inhibit the accumulation of lipid droplets (LDs) and oxidized lipid droplets (oxLDs) in liver cells. These findings suggest their potential use in the alleviation of metabolic dysfunction-associated fatty liver disease (MAFLD) and its most severe manifestation, metabolic dysfunction-associated steatohepatitis (MASH). Allium extracts (ALs: AL1-AL9) were used to assess their ability to reduce lipid droplet accumulation (LDA) and oxidized lipid droplet accumulation (oxLDA) by inhibiting neutral lipid accumulation and oxidation in LD. Among the tested Allium extracts, AL1, AL3, and AL6 demonstrated substantial inhibitory effects on the LDA. Furthermore, AL1 extract showed real-time inhibition of LDA in HepG2 cells in DMEM supplemented with oleic acid (OA) within 12 h of treatment. Our lipidomic approach was used to quantify the accumulation and inhibition of intracellular triacylglycerol (TAG) and oxidized TAG hydroperoxide [TG (OOH) n = 3] species in hepatocytes under OA and linoleic acid loading conditions. These results suggest that Allium-based foods inhibit LD accumulation by decreasing intracellular lipids and lipid hydroperoxides in the hepatocytes. The metabolomic analysis of AL1-the bioactive LDAI extract-using both LC-MS/MS and 1D-NMR [1H, 13C, and Dept (135 and 90)] approaches revealed that AL1 contains mainly carbohydrates and glucoside metabolites, including iridoid glucosides, as well as minor amino acids, organosulfur compounds, and organic acids such as the antioxidant ascorbic acid (KA2 = S13), and their derivatives, suggesting that AL1 could be a potential resource for the development of functional foods and in drug discovery targeting MAFLD/MASH and other related diseases.

Inhibition of Lipid Accumulation and Oxidation in Hepatocytes by Bioactive Bean Extracts

During our search for natural resources that can inhibit lipid droplet accumulation (LDA) and potentially prevent metabolic dysfunction-associated fatty liver disease (MAFLD) and its progressive stages, such as metabolic dysfunction-associated steatohepatitis (MASH), eight bean extracts (BE1-BE8) were tested for their ability to inhibit lipid accumulation and oxidation in hepatocytes. Substantial inhibitory effects on LDA with bean extracts (BEs) BE2, BE4, BE5, and BE8 were demonstrated. An advanced lipidomic approach was used to quantify the accumulation and inhibition of intracellular triacylglycerol (TAG) and its oxidized species, TAG hydroperoxide (TGOOH), in hepatocytes under fatty acid-loading conditions. The results show that the antioxidants BE2 and BE8 are potential candidates for regulating TAG and TGOOH accumulation in fatty acid-induced lipid droplets (LDs). This study suggests that bean-based foods inhibit LDs formation by decreasing intracellular lipids and lipid hydroperoxides in the hepatocytes. The metabolic profiling of BEs revealed that BE2 and BE8 contained polyphenolic compounds. These may be potential resources for the development of functional foods and drug discovery targeting MAFLD/MASH.

Chlorogenic Acid: A Systematic Review on the Biological Functions, Mechanistic Actions, and Therapeutic Potentials

Chlorogenic acid (CGA) is a type of polyphenol compound found in rich concentrations in many plants such as green coffee beans. As an active natural substance, CGA exerts diverse therapeutic effects in response to a variety of pathological challenges, particularly conditions associated with chronic metabolic diseases and age-related disorders. It shows multidimensional functions, including neuroprotection for neurodegenerative disorders and diabetic peripheral neuropathy, anti-inflammation, anti-oxidation, anti-pathogens, mitigation of cardiovascular disorders, skin diseases, diabetes mellitus, liver and kidney injuries, and anti-tumor activities. Mechanistically, its integrative functions act through the modulation of anti-inflammation/oxidation and metabolic homeostasis. It can thwart inflammatory constituents at multiple levels such as curtailing NF-kB pathways to neutralize primitive inflammatory factors, hindering inflammatory propagation, and alleviating inflammation-related tissue injury. It concurrently raises pivotal antioxidants by activating the Nrf2 pathway, thus scavenging excessive cellular free radicals. It elevates AMPK pathways for the maintenance and restoration of metabolic homeostasis of glucose and lipids. Additionally, CGA shows functions of neuromodulation by targeting neuroreceptors and ion channels. In this review, we systematically recapitulate CGA's pharmacological activities, medicinal properties, and mechanistic actions as a potential therapeutic agent. Further studies for defining its specific targeting molecules, improving its bioavailability, and validating its clinical efficacy are required to corroborate the therapeutic effects of CGA.

The role of ferroptosis in cell-to-cell propagation of cell death initiated from focal injury in cardiomyocytes

AIMS

Ferroptosis has grown in importance as a key factor in ischemia-reperfusion (I/R) injury. This study explores the mechanism underlying fibrotic scarring extending along myofibers in cardiac ischemic injury and demonstrates the integral role of ferroptosis in causing a unique cell death pattern linked to I/R injury.

MAIN METHODS

Cadaveric hearts from individuals who had ischemic injury were examined by histological assays. We created a novel model of inducing cell death in H9c2 cells, and used it to demonstrate ferroptotic cell death extending in a cell-to-cell manner. Ex vivo Langendorff-perfused hearts were used alongside the model to replicate cell death extension along myofibers while also demonstrating protective effects of a ferroptosis inhibitor, ferrostatin-1 (Fer-1).

KEY FINDINGS

Human hearts from individuals who had I/R injury demonstrated scarring along myofibers that was consistent with mouse models, suggesting that cell death extended from cell-to-cell. Treatment with Ras-selective lethal 3 (RSL3), a ferroptosis inducer, and exposure to excess iron exacerbated cell death propagation in in vitro models, and inhibition of ferroptosis by Fer-1 blunted this effect in both settings. In ex vivo models, Fer-1 was sufficient to reduce cell death along the myofibers caused by external injury.

SIGNIFICANCE

The unique I/R injury-induced pattern of cell death along myofibers requires novel injury models that mimic this phenomenon, thus we established new methods to replicate it. Ferroptosis is important in propagating injury between cells and better understanding this mechanism may lead to therapeutic responses that limit I/R injury.

Global Proteomics for Identifying the Alteration Pathway of Niemann-Pick Disease Type C Using Hepatic Cell Models

Niemann-Pick disease type C (NPC) is an autosomal recessive disorder with progressive neurodegeneration. Although the causative genes were previously identified, NPC has unclear pathophysiological aspects, and patients with NPC present various symptoms and onset ages. However, various novel biomarkers and metabolic alterations have been investigated; at present, few comprehensive proteomic alterations have been reported in relation to NPC. In this study, we aimed to elucidate proteomic alterations in NPC and perform a global proteomics analysis for NPC model cells. First, we developed two NPC cell models by knocking out NPC1 using CRISPR/Cas9 (KO1 and KO2). Second, we performed a label-free (LF) global proteomics analysis. Using the LF approach, more than 300 proteins, defined as differentially expressed proteins (DEPs), changed in the KO1 and/or KO2 cells, while the two models shared 35 DEPs. As a bioinformatics analysis, the construction of a protein-protein interaction (PPI) network and an enrichment analysis showed that common characteristic pathways such as ferroptosis and mitophagy were identified in the two model cells. There are few reports of the involvement of NPC in ferroptosis, and this study presents ferroptosis as an altered pathway in NPC. On the other hand, many other pathways and DEPs were previously suggested to be associated with NPC, supporting the link between the proteome analyzed here and NPC. Therapeutic research based on these results is expected in the future.

Chlorogenic acids: A pharmacological systematic review on their hepatoprotective effects

BACKGROUND

Liver diseases have a negative impact on global health and are a leading cause of death worldwide. Chlorogenic acids (CGAs), a family of esters formed between certain trans-cinnamic acids and quinic acid, are natural polyphenols abundant in coffee, tea, and a variety of traditional Chinese medicines (TCMs). They are reported to have good hepatoprotective effects against various liver diseases.

PURPOSE

This review aims to analyze the available literature on the hepatoprotective effect of CGAs, with particular emphasis on their mechanisms.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. PubMed and Web of Science databases were adopted to retrieve all relevant literature on CGAs for liver disease from 2013 to March 2023.

RESULTS

Research has indicated that CGAs play a crucial role in improving different types of liver diseases, including drug-induced liver injury (DILI), alcoholic liver disease (ALD), metabolic (dysfunction)-associated fatty liver disease (MAFLD), cholestatic liver disease (CLD), liver fibrosis, and liver cancer. CGAs display remarkable antioxidant and anti-inflammatory effects by activating erythroid 2-related factor 2 (Nrf2) and inhibiting toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) signaling pathways. Some important molecules such as AMP-activated protein kinase (AMPK) and extracellular signal-regulated kinases 1 and 2 (ERK1/2), and other key physiological processes like intestinal barrier and gut microbiota have also been discovered to participate in CGAs-provided amelioration on various liver diseases.

CONCLUSION

In this review, different studies indicate that CGAs have an excellent protective effect against various liver diseases associated with various signaling pathways.

Oxidized Low-Density Lipoproteins Trigger Hepatocellular Oxidative Stress with the Formation of Cholesteryl Ester Hydroperoxide-Enriched Lipid Droplets

Oxidized low-density lipoproteins (oxLDLs) induce oxidative stress in the liver tissue, leading to hepatic steatosis, inflammation, and fibrosis. Precise information on the role of oxLDL in this process is needed to establish strategies for the prevention and management of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Here, we report the effects of native LDL (nLDL) and oxLDL on lipid metabolism, lipid droplet formation, and gene expression in a human liver-derived C3A cell line. The results showed that nLDL induced lipid droplets enriched with cholesteryl ester (CE) and promoted triglyceride hydrolysis and inhibited oxidative degeneration of CE in association with the altered expression of LIPE, FASN, SCD1, ATGL, and CAT genes. In contrast, oxLDL showed a striking increase in lipid droplets enriched with CE hydroperoxides (CE-OOH) in association with the altered expression of SREBP1, FASN, and DGAT1. Phosphatidylcholine (PC)-OOH/PC was increased in oxLDL-supplemented cells as compared with other groups, suggesting that oxidative stress increased hepatocellular damage. Thus, intracellular lipid droplets enriched with CE-OOH appear to play a crucial role in NAFLD and NASH, triggered by oxLDL. We propose oxLDL as a novel therapeutic target and candidate biomarker for NAFLD and NASH.

Arsenic-Loaded Biomimetic Iron Oxide Nanoparticles for Enhanced Ferroptosis-Inducing Therapy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) has a poor response to most available systemic therapies due to intrinsic or acquired resistance to apoptosis. Ferroptosis-based therapy is expected to circumvent those limitations. Therefore, the rational design of ferroptosis-based therapies with targeted delivery of ferroptosis inducers for HCC is in need. In this study, we found that arsenic trioxide (ATO) can efficiently induce ferroptosis in HCC cells, and this effect could be reversed by the iron chelator deferoxamine. On this basis, a drug delivery system was constructed to enhance the therapeutic efficacy of ATO by camouflaging ATO-loaded magnetic nanoparticles (Fe3O4) with HCC cell membranes, termed AFN@CM. After AFN@CM treatment, glutathione peroxidase 4 was strongly inhibited and intracellular lipid peroxide species were significantly increased in HCC cells. In addition, enhanced ferroptosis and tumor suppression were observed both in vitro and in vivo. The bio-safety of AFN@CM was also demonstrated by the in vivo toxicity evaluation. In addition, benefiting from the cell membrane coating, AFN@CM showed enhanced accumulation at tumor sites and achieved continuous tumor elimination in the mouse model. In conclusion, AFN@CM exhibited satisfactory therapeutic efficacy in the treatment of HCC and provided a desirable ferroptosis-based strategy for safe and reliable HCC therapeutics.

Food-Derived β-Carboline Alkaloids Ameliorate Lipid Droplet Accumulation in Human Hepatocytes

Lipid droplet accumulation (LDA) in hepatocytes is the initial stage of nonalcoholic fatty liver disease (NAFLD). In the search for natural compounds for the prevention of NAFLD, a series of β-carboline alkaloid derivatives, inspired by flazin and its derivative, newly identified in Crassostrea gigas Thunberg. extracts, were examined for LDA inhibition (LDAI) activity in oleic acid–loaded hepatocytes (HepG2). Eight compounds with a piperidine or pyridine C-ring were chemically synthesized (1–8). Among them, compounds 2 and 4 (flazin) with a carboxy group at C-3 and furfuryl alcohol moiety at C-1 showed low cytotoxicity and they exhibited significant LDAI activity. Compound 2 with piperidine C-ring was identified for the first time in C. gigas extract, and ameliorated the lipid accumulation with the LDAI value of 25.4%. Active compounds 2 and 4 significantly inhibited triacylglycerol species accumulation in cells. These compounds upregulated ATGL and downregulated SREBP1, FASN, and SCD1 genes, suggesting that they activated lipolysis and suppressed lipogenesis, respectively. These results suggest that β-carboline alkaloids, especially compounds 2 and 4, might be potentially useful for preventing NAFLD.

Determination of trans-fatty acids in food samples based on the pre-column fluorescence derivatization by high performance liquid chromatography

Trans-fatty acids are unsaturated fatty acids that are considered to have health risks. 1,3,5,7-Tetramethyl-8-butyrethylenediamine-difluoroboradiaza-s-indacene is a highly-sensitive fluorescent labeling reagent for carboxylic acids developed by our lab. In this study, using this pre-column fluorescent derivatization reagent, a rapid and accurate high-performance liquid chromatography-fluorescence detection method was developed for the determination of two trans-fatty acids in food samples. Under the optimized derivative conditions, two trans-fatty acids were tagged with the fluorescent labeling reagent in the presence of 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide at 25 °C for 30 min. Then, the baseline separation of trans- and cis-fatty acids and their saturated fatty acid with similar structures was achieved with less interference using a reversed-phased C₁₈ column with isocratic elution in 14 min. With fluorescence detection at λ_ex /λ_em = 490 nm/510 nm, the linear range of the trans-fatty acids was 1.0-200 nM with low detection limits in the range of 0.1-0.2 nM (signal-to-noise ratio = 3). In addition, the proposed approach was successfully applied for the detection of trans-fatty acids in food samples, and the recoveries using this method ranged from 96.02% to 109.22% with low relative standard deviations of 1.2-4.3% (n = 6). This article is protected by copyright. All rights reserved.

Lysophosphatidylethanolamine Affects Lipid Accumulation and Metabolism in a Human Liver-Derived Cell Line

The physiological functions of lysophosphatidylethanolamine (lysoPE) have not been fully elucidated. In this study, the effects of lysoPE on lipogenesis and lipolysis were investigated in a cultured human liver-derived cell line. The intracellular lipid profile was investigated in detail using liquid chromatography–tandem mass spectrometry (LC-MS/MS) to better understand the underlying mechanism. The expression of genes related to lipid metabolism and catabolism was analyzed using real-time PCR. LysoPE supplementation induced cellular lipid droplet formation and altered triacylglycerol (TAG) profiles. Furthermore, lysoPE downregulated expression of the TAG hydrolyzation regulation factor ATGL, and reduced the expression of fatty acid biosynthesis-related genes SREBP1 and SCD1. LC-MS/MS-based lipidomic profiling revealed that the addition of lysoPE 18:2 increased the PE species containing linoleic acyl, as well as the CE 18:2 species, likely due to the incorporation of linoleic acyl from lysoPE 18:2. Collectively, these findings suggest that lysoPE 18:2 is involved in lipid droplet formation by suppressing lipolysis and fatty acid biosynthesis. Thus, lysoPE might play a pathological role in the induction of fatty liver disease.

Docosahexaenoic Acid Esters of Hydroxy Fatty Acid Is a Novel Activator of NRF2

Fatty acid esters of hydroxy fatty acids (FAHFAs) are a new class of endogenous lipids with interesting physiological functions in mammals. Despite their structural diversity and links with nuclear factor erythroid 2-related factor 2 (NRF2) biosynthesis, FAHFAs are less explored as NRF2 activators. Herein, we examined for the first time the synthetic docosahexaenoic acid esters of 12-hydroxy stearic acid (12-DHAHSA) or oleic acid (12-DHAHOA) against NRF2 activation in cultured human hepatoma-derived cells (C3A). The effect of DHA-derived FAHFAs on lipid metabolism was explored by the nontargeted lipidomic analysis using liquid chromatography-mass spectrometry. Furthermore, their action on lipid droplet (LD) oxidation was investigated by the fluorescence imaging technique. The DHA-derived FAHFAs showed less cytotoxicity compared to their native fatty acids and activated the NRF2 in a dose-dependent pattern. Treatment of 12-DHAHOA with C3A cells upregulated the cellular triacylglycerol levels by 17-fold compared to the untreated group. Fluorescence imaging analysis also revealed the suppression of the degree of LDs oxidation upon treatment with 12-DHAHSA. Overall, these results suggest that DHA-derived FAHFAs as novel and potent activators of NRF2 with plausible antioxidant function.

High-fat diet impairs ferroptosis and promotes cancer invasiveness via downregulating tumor suppressor ACSL4 in lung adenocarcinoma

BACKGROUND

Long-chain acyl-CoA synthetase-4 (ACSL4) is involved in fatty acid metabolism, and aberrant ACSL4 expression could be either tumorigenic or tumor-suppressive in different tumor types. However, the function and clinical significance of ACSL4 in lung adenocarcinoma remain elusive.

RESULTS

ACSL4 was frequently downregulated in lung adenocarcinoma when analyzing both the TCGA database and the validation samples, and the lower ACSL4 expression was correlated with a worse prognosis. Using gene set enrichment analysis, we found that high ACSL4 expression was frequently associated with the oxidative stress pathway, especially ferroptosis-related proteins. In vitro functional studies showed that knockdown of ACSL4 increased tumor survival/invasiveness and inhibited ferroptosis, while ACSL4 overexpression exhibited the opposite effects. Moreover, high-fat treatment could also inhibit erastin-induced ferroptosis by affecting ACSL4 expression. The anti-tumor effects of ferroptosis inducers and the anti-ferroptosis effects of the high-fat diet were further validated using the mouse xenograft model.

CONCLUSIONS

ACSL4 plays a tumor-suppressive role in lung adenocarcinoma by suppressing tumor survival/invasiveness and promoting ferroptosis. Our study provided a theoretical reference for the application of ferroptotic inducers and dietary guidance for lung adenocarcinoma patients.

Comprehensive lipidomic profiling in serum and multiple tissues from a mouse model of diabetes

INTRODUCTION

Diabetes mellitus is a serious metabolic disorder causing multiple organ damage in human. However, the lipidomic profiles in different organs and their associations are rarely studied in either diabetic patients or animals.

OBJECTIVES

To evaluate and compare the characteristics of lipid species in serum and multiple tissues in a diabetic mouse model.

METHODS

Semi-quantitative profiling analyses of intact and oxidized lipids were performed in serum and multiple tissues from a diabetic mouse model fed a high fat diet and treated with streptozotocin by using LC/HRMS and MS/MS. The total content of each lipid class, and the tissue-specific lipid species in all tissue samples were determined and compared by multivariate analyses.

RESULTS

The diabetic mouse model displayed characteristic differences in serum and multiple organs: the brain and heart showed the largest reduction in cardiolipin, while the kidney had more alterations in triacylglycerol. Interestingly, the lipidomic differences also existed between different regions of the same organ: cardiolipin species with highly polyunsaturated fatty acyls decreased only in atrium but not in ventricle, while renal cortex showed longer fatty acyl chains for both increased and decreased triacylglycerol species than renal medulla. Importantly, diabetes caused an accumulation of lipid hydroperoxides, suggesting that oxidative stress was induced in all organs except for the brain during the development of diabetes.

CONCLUSIONS

These findings provided novel insight into the organ-specific relationship between diabetes and lipid metabolism, which might be useful for evaluating not only diabetic tissue injury but also the effectiveness of diabetic treatments.

Discovery of Eicosapentaenoic Acid Esters of Hydroxy Fatty Acids as Potent Nrf2 Activators

Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are a recently discovered class of biologically active lipids with anti-inflammatory and anti-diabetic properties. Despite the possible link between endogenous FAHFA levels and nuclear factor erythroid 2-related factor 2 (Nrf2), their possible function as antioxidants and the mechanisms involved in this are unknown. Here, we investigate FAHFAs’ plausible antioxidant potential with reference to their effect on the Nrf2 levels, oxidative stress, and lipid droplet oxidation in human hepatocytes (C3A). Six authentic FAHFAs were chemically synthesized and performed activity-based screening by reporter gene assay. Among them, eicosapentaenoic acid (EPA) esterified 12-hydroxy stearic acid (12-HSA) and 12-hydroxy oleic acid (12-HOA) FAHFAs showed less cytotoxicity compared to their free fatty acids and potent activators of Nrf2. To define their mode of action, relative levels of nuclear Nrf2 were determined, which found a higher amount of Nrf2 in nucleus of cells treated with 12-EPAHSA compared to the control. Furthermore, 12-EPAHSA increased the expression of Nrf2-dependent antioxidant enzyme genes (NQO1, GCLM, GCLC, SOD-1, and HO-1). Fluorescence imaging analysis of linoleic-acid-induced lipid droplets (LDs) in C3A cells treated with 12-EPAHSA revealed the strong inhibition of small-size LD oxidation. These results suggest that EPA-derived FAHFAs as a new class of lipids with less cytotoxicity, and strong Nrf2 activators with plausible antioxidant effects via the induction of cytoprotective proteins against oxidative stress, induced cellular damage.