Immunohistochemical expression of autophagosome markers LC3 and p62 in preneoplastic liver foci in high fat diet-fed rats

Peroxisome Proliferator Activator α Agonist Clofibrate Induces Pexophagy in Coconut Oil-Based High-Fat Diet-Fed Rats

Peroxisomes are crucial for fatty acid β-oxidation in steatosis, but the role of pexophagy-the selective autophagy of peroxisomes-remains unclear. This study investigated the effects of the peroxisome proliferator-activated receptor-α (PPARα) agonist clofibrate on pexophagy in a coconut oil-based high-fat diet (HFD)-induced hepatocarcinogenesis model. Rats were divided into four groups: control, clofibrate, HFD, and HFD with clofibrate. The HFD induced steatosis, along with a 2.4-fold increase in pexophagy receptor NBR1-positive granules in hepatocytes. Clofibrate significantly inhibited HFD-induced steatosis, increasing p62-, LAMP2-, and Pex5-positive granules by 7.5-, 7.2-, and 71.4-fold, respectively, while decreasing NBR1 expression. The effects were associated with peroxisome proliferation and pexophagy in ultrastructural observations and increased levels of Lc3, p62, Pex2, Pex14, Acox1, and Scd1 in gene expression analysis. The results suggested that clofibrate effectively reduced steatosis through combined peroxisome proliferation and pexophagy, though it had a marginal impact on hepatocarcinogenesis in coconut oil-based HFD-fed rats. These findings highlight the utility of PPARα agonists in studying mammalian pexophagy.

High-Fat Diet Delays Liver Fibrosis Recovery and Promotes Hepatocarcinogenesis in Rat Liver Cirrhosis Model

More effective treatments for hepatitis viral infections have led to a reduction in the incidence of liver cirrhosis. A high-fat diet can lead to chronic hepatitis and liver fibrosis, but the effects of lipid intake on liver disease status, including hepatitis C virus and alcohol, after elimination of the cause are unclear. To investigate the effects, we used a rat cirrhosis model and a high-fat diet in this study. Male Wistar rats were administered carbon tetrachloride for 5 weeks. At 12 weeks of age, one group was sacrificed. The remaining rats were divided into four groups according to whether or not they were administered carbon tetrachloride for 5 weeks, and whether they were fed a high-fat diet or control diet. At 12 weeks of age, liver fibrosis became apparent and then improved in the groups where carbon tetrachloride was discontinued, while it worsened in the groups where carbon tetrachloride was continued. Liver fibrosis was notable in both the carbon tetrachloride discontinuation and continuation groups due to the administration of a high-fat diet. In addition, liver precancerous lesions were observed in all groups, and tumor size and multiplicity were higher in the high-fat diet-fed groups. The expression of genes related to inflammation and lipogenesis were upregulated in rats fed a high-fat diet compared to their controls. The results suggest that a high-fat diet worsens liver fibrosis and promotes liver carcinogenesis, presumably through enhanced inflammation and lipogenesis, even after eliminating the underlying cause of liver cirrhosis.

Phenobarbital, a hepatic metabolic enzyme inducer, inhibits preneoplastic hepatic lesions with expression of selective autophagy receptor p62 and ER-phagy receptor FAM134B in high-fat diet-fed rats through the inhibition of ER stress

We investigated the role of endoplasmic reticulum (ER)-phagy in NAFLD-related hepatocarcinogenesis in high-fat diet (HFD)-fed and/or phenobarbital (PB)-treated rats by clustering the expression levels of the selective autophagy receptor p62 and the ER-phagy-specific receptor FAM134B in preneoplastic hepatic lesions. We obtained four clusters with variable expression levels of p62 and FAM134B in preneoplastic lesions, and a variable population of clusters in each group. PB administration increased the clusters with high expression levels of p62 while HFD feeding increased the clusters with high expression levels of both p62 and FAM134B. The areas of preneoplastic lesions of these clusters were significantly increased than those of other clusters with low expression levels of p62 and FAM134B. The combination of HFD feeding with PB counteracted the effects of each other, and the cluster composition was similar to that in the control group. The results were associated with decreased gene expression of ER stress, inflammatory cytokine, autophagy, and increased expression of antioxidant enzyme. The present study demonstrated that clustering analysis is useful for understanding the role of autophagy in each preneoplastic lesion, and that HFD feeding increased preneoplastic lesions through the inhibition of ER-phagy, which was cancelled with PB administration through the induction of ER-phagy.

Inhibition of autophagy with expression of NADPH oxidase subunit p22phox in preneoplastic lesions in a high-fat diet and streptozotocin-related hepatocarcinogenesis rat model

To study the effects of autophagy inducer carbamazepine (CBZ) in a high-fat diet (HFD)/streptozotocin (STZ)-related early hepatocarcinogenesis model, we determined autophagic flux by immunohistochemical analysis of autophagy marker expression in preneoplastic liver foci and compared that with the expression of the NADPH oxidase subunit. Male F344 rats were fed a basal diet or HFD and subjected to two-stage hepatocarcinogenesis; diabetes mellitus was induced via STZ administration. Several STZ-treated, HFD-fed rats were administered CBZ (a total of five doses every one or two days) at week 7 and 8. STZ-treated, HFD-fed rats decreased β cells in the islet of Langerhans and increased adipophilin-positive lipid droplets in the liver; moreover, they had a larger area of glutathione S-transferase placental form-immunopositive preneoplastic liver foci, which was associated with inhibition of autophagy and induction of the NADPH oxidase subunit, as demonstrated by increased immunohistochemical expression of an autophagosome receptor marker microtubule-associated protein light chain 3 (LC3)-binding protein p62, and of an NADPH oxidase subunit p22phox in the preneoplastic foci. An increased trend of an autophagy phagophore marker LC3 in preneoplastic foci was also detected. CBZ administration could induce autophagy and impair p22phox expression, as shown by altered expression of autophagy regulators (Atg5, Atg6, Lamp1, Lamp2, and Lc3), NADPH oxidase subunits (P22phox and P67phox), and antioxidant enzymes Gpx1 and Gpx2. These results suggest that inhibition of autophagy and induction of p22phox might contribute to HFD/STZ-related early hepatocarcinogenesis in rats; however, the effects of CBZ administration on the STZ/HFD-increased preneoplastic foci were marginal in this study.

Metronidazole enhances steatosis-related early-stage hepatocarcinogenesis in high fat diet-fed rats through DNA double-strand breaks and modulation of autophagy

Nonalcoholic fatty liver disease is a hepatic disorder with deposition of fat droplets and has a high risk of progression to steatosis-related hepatitis and irreversible hepatic cancer. Metronidazole (MNZ) is an antiprotozoal and antimicrobial agent widely used to treat patients infected with anaerobic bacteria and intestinal parasites; however, MNZ has also been shown to induce liver tumors in rodents. To investigate the effects of MNZ on steatosis-related early-stage hepatocarcinogenesis, male rats treated with N-nitrosodiethylamine following 2/3 hepatectomy at week 3 were received a control basal diet, high fat diet (HFD), or HFD containing 0.5% MNZ. The HFD induced obesity and steatosis in the liver, accompanied by altered expression of Pparg and Fasn, genes related to lipid metabolism. MNZ increased nuclear translocation of lipid metabolism-related transcription factor peroxisome proliferator-activated receptor gamma in hepatocytes, together with altered liver expression of lipid metabolism genes (Srebf1, Srebf2, Pnpla2). Furthermore, MNZ significantly increased the number of preneoplastic liver foci, accompanied by DNA double-strand breaks and late-stage autophagy inhibition, as reflected by increased levels of γ-H2AX, LC3, and p62. Therefore, MNZ could induce steatosis-related hepatocarcinogenesis by inducing DNA double-strand breaks and modulating autophagy in HFD-fed rats.

Hydroxysafflor yellow A induces autophagy in human liver cancer cells by regulating Beclin 1 and ERK expression

Hydroxysafflor yellow A (HSYA) is a water-soluble component of the safflower (Carthamus tinctorius), and research has revealed that HSYA exhibits antitumor effects. In the present study, the effects of HSYA on the autophagy of a Hep-G2 liver cancer cell line, as well as the underlying mechanisms, were investigated. Hep-G2 cells were treated with HSYA and the viability of cells was measured using an MTT assay. Western blotting and immunofluorescence assays were performed to determine the expression of light chain 3 II (LC3-II) and p62, as well as the autophagy regulators Beclin 1 and ERK1/2. Transmission electron microscopy was performed to observe the formation of autophagosomes. The combined effects of HSYA and the autophagy inhibitor chloroquine (CQ) were also determined. The results revealed that the viability of Hep-G2 cells decreased with increasing concentrations of HSYA. Furthermore, LC3-II expression increased significantly and the level of p62 decreased significantly in the HYSA group compared with the control group. Additionally, an increase in Beclin 1 expression and a decrease in phosphorylated-ERK1/2 expression was observed in Hep-G2 cells treated with HYSA. Following treatment with CQ and HSYA, a significant increase in the viability of Hep-G2 cells was observed compared with the HSYA group. Collectively, the results indicated that HSYA induced autophagy by promoting the expression of Beclin 1 and inhibiting the phosphorylation of ERK in liver cancer cells. Therefore, HSYA may serve as a potential therapeutic agent for liver cancer.