Sodium 4-phenylbutyrate prevents murine dietary steatohepatitis caused by trans-fatty acid plus fructose

Elaidic acid induced hepatocyte pyroptosis via autophagy-CTSB-NLRP3 pathway

Elaidic acid (EA, C18:1 trans) is a kind of principal Trans fatty acid (TFA) and is widely found in processed food. Pyroptosis is a form of programmed cell death, distinct from apoptosis and traditional necrosis. Excessive pyroptosis could induce body injury and serious inflammation. However, the effect of EA on pyroptosis has not been reported. In the study, we found that EA exposure caused liver damage and hepatocyte pyroptosis by testing GSDMD-N, Caspase 1, IL-18, and IL-1β in mice and HepG2 cells. Further exploring the mechanisms, we found that EA-induced pyroptosis depended on Cathepsin B (CTSB)-mediated NLRP3 inflammasome activation. Cell autophagy was closely related to lysosomes. Our study revealed that EA promoted hepatocyte autophagy, and activated autophagy induced lysosomal membrane permeabilization (LMP) and CTSB leakage. Inhibition of autophagy by 3-MA mitigated the CTSB leak, reduced the activation of the NLRP3 inflammasome, and then attenuated the EA-induced pyroptosis. In summary, these results indicated that EA induced hepatocyte pyroptosis via autophagy-CTSB-NLRP3 inflammasome pathway. The study revealed new insights into the toxicity mechanism of EA.

Trans-unsaturated fatty acid activates NLRP3 inflammasome in macrophages and exacerbates intestinal inflammation in mice

Higher consumption of trans fatty acid (TFA) is a risk factor for several inflammatory diseases including inflammatory bowel disease (IBD). However, the detailed mechanisms by which TFA intake affects IBD pathology remain unclear. We demonstrate here that elaidate, a trans-isomer of oleate, enhances interleukin (IL)-1β production through the activation of NLRP3 inflammasome in mouse bone marrow-derived macrophages (BMDMs). Oleate has no effect on IL-1β production. Elaidate also induces oxidative stress and activates endoplasmic reticulum stress in BMDMs. The elaidate-induced IL-1β production is suppressed by co-treatments with antioxidants and a chemical chaperone. Furthermore, we analyze the effects of elaidate administration on intestinal inflammation using 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis model in mice. Increased colonic damage and myeloperoxidase activity after TNBS treatment are elevated by elaidate administration. Also, TNBS treatment induces IL-1β production in colonic mucosa; elaidate administration enhances the induction. We believe that these data reveal some mechanisms by which the TFA intake is associated with increased risk for IBD.

Towards a standard diet-induced and biopsy-confirmed mouse model of non-alcoholic steatohepatitis: Impact of dietary fat source

BACKGROUND

The trans-fat containing AMLN (amylin liver non-alcoholic steatohepatitis, NASH) diet has been extensively validated in C57BL/6J mice with or without the Lep^ob/Lep^ob (ob/ob) mutation in the leptin gene for reliably inducing metabolic and liver histopathological changes recapitulating hallmarks of NASH. Due to a recent ban on trans-fats as food additive, there is a marked need for developing a new diet capable of promoting a compatible level of disease in ob/ob and C57BL/6J mice.

AIM

To develop a biopsy-confirmed mouse model of NASH based on an obesogenic diet with trans-fat substituted by saturated fat.

METHODS

Male ob/ob mice were fed AMLN diet or a modified AMLN diet with trans-fat (Primex shortening) substituted by equivalent amounts of palm oil [Gubra amylin NASH, (GAN) diet] for 8, 12 and 16 wk. C57BL/6J mice were fed the same diets for 28 wk. AMLN and GAN diets had similar caloric content (40% fat kcal), fructose (22%) and cholesterol (2%) level.

RESULTS

The GAN diet was more obesogenic compared to the AMLN diet and impaired glucose tolerance. Biopsy-confirmed steatosis, lobular inflammation, hepatocyte ballooning, fibrotic liver lesions and hepatic transcriptome changes were similar in ob/ob mice fed the GAN or AMLN diet. C57BL/6J mice developed a mild to moderate fibrotic NASH phenotype when fed the same diets.

CONCLUSION

Substitution of Primex with palm oil promotes a similar phenotype of biopsy-confirmed NASH in ob/ob and C57BL/6J mice, making GAN diet-induced obese mouse models suitable for characterizing novel NASH treatments.

Targeting Oxidative Stress for the Treatment of Liver Fibrosis

Oxidative stress is a reflection of the imbalance between the production of reactive oxygen species (ROS) and the scavenging capacity of the antioxidant system. Excessive ROS, generated from various endogenous oxidative biochemical enzymes, interferes with the normal function of liver-specific cells and presumably plays a role in the pathogenesis of liver fibrosis. Once exposed to harmful stimuli, Kupffer cells (KC) are the main effectors responsible for the generation of ROS, which consequently affect hepatic stellate cells (HSC) and hepatocytes. ROS-activated HSC undergo a phenotypic switch and deposit an excessive amount of extracellular matrix that alters the normal liver architecture and negatively affects liver function. Additionally, ROS stimulate necrosis and apoptosis of hepatocytes, which causes liver injury and leads to the progression of end-stage liver disease. In this review, we overview the role of ROS in liver fibrosis and discuss the promising therapeutic interventions related to oxidative stress. Most importantly, novel drugs that directly target the molecular pathways responsible for ROS generation, namely, mitochondrial dysfunction inhibitors, endoplasmic reticulum stress inhibitors, NADPH oxidase (NOX) inhibitors, and Toll-like receptor (TLR)-affecting agents, are reviewed in detail. In addition, challenges for targeting oxidative stress in the management of liver fibrosis are discussed.

Lipid-regulating properties of butyric acid and 4-phenylbutyric acid: Molecular mechanisms and therapeutic applications

In the past two decades, significant advances have been made in the etiology of lipid disorders. Concomitantly, the discovery of liporegulatory functions of certain short-chain fatty acids has generated interest in their clinical applications. In particular, butyric acid (BA) and its derivative, 4-phenylbutyric acid (PBA), which afford health benefits against lipid disorders while being generally well tolerated by animals and humans have been assessed clinically. This review examines the evidence from cell, animal and human studies pertaining to the lipid-regulating effects of BA and PBA, their molecular mechanisms and therapeutic potential. Collectively, the evidence supports the view that intakes of BA and PBA benefit lipid homeostasis across biological systems. We reviewed the evidence that BA and PBA downregulate de novo lipogenesis, ameliorate lipotoxicity, slow down atherosclerosis progression, and stimulate fatty acid β-oxidation. Central to their mode of action, BA appears to function as a histone deacetylase (HDAC) inhibitor while PBA acts as a chemical chaperone and/or a HDAC inhibitor. Areas of further inquiry include the effects of BA and PBA on adipogenesis, lipolysis and apolipoprotein metabolism.

The Chemical Chaperone 4-Phenylbutyric Acid Prevents Alcohol-Induced Liver Injury in Obese KK-Ay Mice

BACKGROUND

Co-occurrence of metabolic syndrome and chronic alcohol consumption is increasing worldwide. The present study investigated the effect of the chemical chaperone 4-phenylbutyric acid (PBA)-which has been shown to alleviate dietary steatohepatitis caused by endoplasmic reticulum (ER) stress-on chronic-plus-binge ethanol (EtOH)-induced liver injury in a mouse model of obesity.

METHODS

Male KK-A^y mice (8 weeks old) were fed a Lieber-DeCarli diet (5% EtOH) for 10 days. Some mice were given PBA intraperitoneally (120 mg/kg body weight, daily) during the experimental period. On day 11, mice were gavaged with a single dose of EtOH (4 g/kg body weight). Control mice were given a dextrin gavage after being pair-fed a control diet. All mice were then serially euthanized before or at 9 hours after gavage.

RESULTS

Chronic-plus-binge EtOH intake induced massive hepatic steatosis along with hepatocyte apoptosis and inflammation, which was reversed by PBA treatment. Administration of PBA also suppressed chronic-plus-binge EtOH-induced up-regulation of ER stress-related genes including binding immunoglobulin protein (Bip), unspliced and spliced forms of X-box-binding protein-1 (uXBP1 and sXBP1, respectively), inositol trisphosphate receptor (IP3R), and C/EBP homologous protein (CHOP). Further, it blocked chronic-plus-binge EtOH-induced expression of the oxidative stress marker heme oxygenase-1 (HO-1) and 4-hydroxynonenal. Chronic EtOH alone (without binge) increased Bip and uXBP1, but it did not affect those of sXBP1, IP3R, CHOP, or HO-1. PBA reversed the prebinge expression of these genes to control levels, but it did not affect chronic EtOH-induced hepatic activity of cytochrome P450 2E1.

CONCLUSIONS

Binge EtOH intake after chronic consumption induces massive ER stress-related oxidative stress and liver injury in a mouse model of obesity through dysregulation of the unfolded protein response. PBA ameliorated chronic-plus-binge EtOH-induced liver injury by reducing ER and oxidative stress after an EtOH binge.

Elaidic acid induces cell apoptosis through induction of ROS accumulation and endoplasmic reticulum stress in SH‑SY5Y cells

Elaidic acid, which is a major trans fatty acid, has been reported to be involved in neurotoxicity; however, the underlying molecular mechanisms underlying its neurotoxic effects remain largely unknown. Therefore, the present study aimed to investigate the potential mechanisms underlying elaidic acid‑induced neuronal damage in vitro. The SH‑SY5Y neuroblastoma cell line was used as a model in the present study. Following treatment of cells with various concentrations of elaidic acid or with vehicle for 24 h, cell viability was measured using the MTT assay. Mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) release were measured using flow cytometry. Cell apoptosis was measured by Annexin V‑fluorescein isothiocyanate/propidium iodide double staining, and cellular redox status was determined using ELISA analysis. Furthermore, western blotting was used to detect the protein expression levels of factors associated with oxidative damage and components of the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) signaling pathways. The results demonstrated that elaidic acid treatment inhibited cell viability, elevated cell apoptosis and resulted in a loss of MMP. In addition, elaidic acid induced marked alterations in cellular redox status. Treatment with high doses of elaidic acid treatment also enhanced the release of ROS, and upregulated lipid peroxide and malondialdehyde levels; however, it reduced superoxide dismutase and glutathione peroxidase activities. Furthermore, elaidic acid resulted in upregulation of nuclear factor erythroid 2‑related factor 2 and downregulation of heme oxygenase 1, which are two key antioxidative factors. Elaidic acid treatment also induced or inhibited the expression of numerous ER stress/UPR‑associated molecules. It induced glucose‑regulated protein 78 (GRP78) expression, whereas the expression levels of activating transcription factor 4 (ATF4) and CCAAT/enhancer‑binding protein homologous protein (CHOP) were upregulated and then downregulated following treatment with various doses of elaidic acid. These results indicated that elaidic acid inhibited SH‑SY5Y cell growth and induced apoptosis by enhancing oxidative stress and activating the ER stress/UPR signaling pathway and the GRP78/ATF4/CHOP pathway.

Orally administered sodium 4-phenylbutyrate suppresses the development of dextran sulfate sodium-induced colitis in mice

Sodium 4-phenylbutyrate (PBA) exerts therapeutic effects in a wide range of pathologies. A previous study by the present authors revealed that intraperitoneal administration of PBA suppresses the onset of dextran sulfate sodium (DSS)-induced colitis in mice. In the present study, the effects of orally administered PBA are investigated, as this route of administration is more clinically relevant. The therapeutic efficacy of PBA (10 mg/12 h) in mice with experimental colitis was assessed based on the disease activity index, production of inflammatory cytokines, colon length and histopathological investigations. The results of the present study demonstrated a significantly higher survival rate in the PBA-treated group compared with the PBA-untreated (DSS control) group (P=0.0156). PBA treatment improved pathological indices of experimental colitis (P<0.05). Furthermore, the oral administration of PBA significantly inhibited the DSS-induced shortening of the colon (P<0.05) and overproduction of interleukin (IL)-1β and IL-6 (both P<0.05) as measured in colonic lavage fluids. A marked attenuation of the DSS-induced overproduction of tumor necrosis factor was also observed. For histopathological analysis, a marked decrease in mature goblet cells and increase in enlarged nuclei of the absorptive cells was observed in colon lesions of DSS control mice as compared with normal untreated mice. However, in the PBA-treated mice, no such lesions were observed and the mucosa resembled that of DSS-untreated mice. The results of the present study, combined with those results of a previous study, suggest that oral and intraperitoneal administration of PBA have similar preventative effects on DSS-induced colitis, achieved by suppressing its pathogenesis.

Sodium 4-phenylbutyric acid prevents murine acetaminophen hepatotoxicity by minimizing endoplasmic reticulum stress

BACKGROUND

Acetaminophen (APAP) overdose induces severe oxidative stress followed by hepatocyte apoptosis/necrosis. Previous studies have indicated that endoplasmic reticulum (ER) stress is involved in the cell death process. Therefore, we investigated the effect of the chemical chaperone 4-phenyl butyric acid (PBA) on APAP-induced liver injury in mice.

METHODS

Eight-week-old male C57Bl6/J mice were given a single intraperitoneal (i.p.) injection of APAP (450 mg/kg body weight), following which some were repeatedly injected with PBA (120 mg/kg body weight, i.p.) every 3 h starting at 0.5 h after the APAP challenge. All mice were then serially euthanized up to 12 h later.

RESULTS

PBA treatment dramatically ameliorated the massive hepatocyte apoptosis/necrosis that was observed 6 h after APAP administration. PBA also significantly prevented the APAP-induced increases in cleaved activating transcription factor 6 and phosphorylation of c-Jun N-terminal protein kinase and significantly blunted the increases in mRNA levels for binding immunoglobulin protein, spliced X-box binding protein-1, and C/EBP homologous protein. Moreover, PBA significantly prevented APAP-induced Bax translocation to the mitochondria, and the expression of heme oxygenase-1 mRNA and 4-hydroxynonenal. By contrast, PBA did not affect hepatic glutathione depletion following APAP administration, reflecting APAP metabolism.

CONCLUSIONS

PBA prevents APAP-induced liver injury even when an APAP challenge precedes its administration. The underlying mechanism of action most likely involves the prevention of ER stress-induced apoptosis/necrosis in the hepatocytes during APAP intoxication.

L-carnitine prevents metabolic steatohepatitis in obese diabetic KK-Ay mice

AIM

Pharmacological treatment for metabolic syndrome-related non-alcoholic steatohepatitis has not been established. We investigated the effect of L-carnitine, an essential substance for β-oxidation, on metabolic steatohepatitis in mice.

METHODS

Male KK-A^y mice were fed a high-fat diet (HFD) for 8 weeks, with supplementation of L-carnitine (1.25 mg/mL) in drinking water for the latter 4 weeks.

RESULTS

Serum total carnitine levels were decreased following HFD feeding, whereas the levels were reversed almost completely by L-carnitine supplementation. In mice given L-carnitine, exacerbation of hepatic steatosis and hepatocyte apoptosis was markedly prevented even though HFD feeding was continued. Body weight gain, as well as hyperlipidemia, hyperglycemia, and hyperinsulinemia, following HFD feeding were also significantly prevented in mice given L-carnitine. High-fat diet feeding elevated hepatic expression levels of carnitine palmitoyltransferase 1A mRNA; however, production of β-hydroxybutyrate in the liver was not affected by HFD alone. In contrast, L-carnitine treatment significantly increased hepatic β-hydroxybutyrate contents in HFD-fed mice. L-carnitine also blunted HFD induction in sterol regulatory element binding protein-1c mRNA in the liver. Furthermore, L-carnitine inhibited HFD-induced serine phosphorylation of insulin receptor substrate-1 in the liver. L-carnitine decreased hepatic free fatty acid content in 1 week, with morphological improvement of swollen mitochondria in hepatocytes, and increases in hepatic adenosine 5'-triphosphate content.

CONCLUSIONS

L-carnitine ameliorates steatohepatitis in KK-A^y mice fed an HFD, most likely through facilitating mitochondrial β-oxidation, normalizing insulin signals, and inhibiting de novo lipogenesis in the liver. It is therefore postulated that supplementation of L-carnitine is a promising approach for prevention and treatment of metabolic syndrome-related non-alcoholic steatohepatitis.