Sustained feeding of a diet high in fat resulted in a decline in the liver's insulin-degrading enzyme levels in association with the induction of oxidative and endoplasmic reticulum stress in adult male rats: Evaluation of 4-phenylbutyric acid

Abstract

The current study explored the impact of high fat diet (HFD) on hepatic oxidative and endoplasmic reticulum (ER) stress and its insulin degrading enzyme (IDE) content with the injection of 4-phenyl butyric acid (4-PBA) in adult male rats. Following the weaning period, male offspring were distributed among six distinct groups. The corresponding diet was used for 20 weeks, subsequently 4-PBA was administered for three consecutive days. Plasma glucose and insulin levels, HOMA-β (homeostasis model assessment of β-cell), hepatic ER and oxidative stress biomarkers and IDE protein content were assessed. Long-term ingestion of HFD (31 % cow butter) induced oxidative and ER stress in the liver tissue. Accordingly, a rise in the malondialdehyde (MDA) content and catalase enzyme activity and a decrease in the glutathione (GSH) content were detected within the liver of the HFD and HFD + DMSO groups. Consumption of this diet elevated the liver expression of binding immunoglobulin protein (BIP) and C/enhancer-binding protein homologous protein (CHOP) levels while reduced its IDE content. The HOMA-β decreased significantly. The injection of the 4-PBA moderated all the induced changes. Findings from this study indicated that prolonged HFD consumption led to a reduction in plasma insulin levels, likely attributed to pancreatic β cell malfunction, as evidenced by a decline in the HOMA-β index. Also, the HFD appears to have triggered oxidative and ER stress in the liver, along with a decrease in its IDE content.

Keywords: 4-Phenylbutyric acid; Endoplasmic reticulum and oxidative stress; High fat diet; Insulin degrading enzyme.

Fig. 1

The impact of high fat diet and/or 4-PBA on body weight changes (A), body weight AUC (B), amount of food intake alterations (C), and food intake AUC (D) during the experimental period. The column/point demonstrates Mean ± SEM for 6 animals. ****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05 substantial distinction with control group consuming normal diet, ^$$$$P < 0.0001, ^$$$P < 0.001, ^$$P < 0.01 substantial distinction with ND + DMSO group, ⁺⁺⁺⁺ P<0.000, ⁺⁺⁺ P<0.001, ⁺⁺ P<0.01,+P<0.05 substantial distinction with ND+4-PBA group. Crl: Control, ND: Normal Diet, HFD: High-Fat Diet, 4-PBA: 4-Phenyl Butyric Acid and DMSO: Dimethyl Sulfoxide.

Fig. 2

Impact of high-fat diet and/or 4-PBA on intra-abdominal fat (A) and liver (B) weight. The column demonstrates Mean ± SEM for 6 animals. ****P < 0.0001 substantial distinction with control group consuming normal diet, ^$$$$P < 0.0001 substantial distinction with ND + DMSO group, and ⁺⁺⁺⁺P<0.0001 substantial distinction with ND+4-PBA group. Crl: Control, ND: Normal Diet, HFD: High-Fat Diet, 4-PBA: 4-Phenyl Butyric Acid and DMSO: Dimethyl Sulfoxide.

Fig. 3

The impact of HFD and/or 4-PBA on fasting plasma concentrations of glucose (A), insulin (B) and HOMA-β index (C). The column demonstrates Mean ± SEM for 6 animals. ****P < 0.0001 substantial distinction with the normal diet consuming group, ^$$$$P < 0.0001 substantial distinction with the ND + DMSO group, and ⁺⁺⁺⁺P<0.0001 substantial distinction with HFD and HFD + DMSO groups. Crl: Control, ND: Normal Diet, HFD: High-Fat Diet, 4-PBA: 4-Phenyl Butyric Acid, DMSO: Dimethyl Sulfoxide and HOMA-β: Homeostasis Model Assessment of β-cell.

Fig. 4

The impact of HFD and/or 4-PBA on the content of liver MDA level (A), catalase activity (B) and GSH level (C) . The column demonstrates Mean ± SEM for 6 animals. ****P < 0.0001 substantial distinction with the control group consuming normal diet, ^$$$$P < 0.0001 substantial distinction with the ND + DMSO group, and ⁺⁺⁺⁺P<0.0001 substantial distinction with HFD and HFD + DMSO groups. Crl: Control, ND: Normal Diet, HFD: High-Fat Diet, 4-PBA: 4-Phenyl Butyric Acid, DMSO: Dimethyl Sulfoxide, MDA: Malondialdehyde and GSH: reduced Glutathione.

Fig. 5

The impact of HFD and/or 4-PBA on BIP (A, B) and CHOP (A, C) protein expression in the liver tissue. The column demonstrates Mean ± SEM for 4 animals. ****P < 0.0001 substantial distinction with the control group consuming a normal diet, ^$$$$P < 0.0001 substantial distinction with the ND + DMSO group, and ⁺⁺⁺⁺P<0.0001 substantial distinction with HFD and HFD + DMSO groups. The original non-adjusted images of Western blot are presented as supplementary file named “full images of Western blot”. Crl: Control, ND: Normal Diet, HFD: High-Fat Diet, 4-PBA: 4-Phenyl Butyric Acid, DMSO: Dimethyl Sulfoxide, BIP: Binding Immunoglobulin Protein, CHOP: C/enhancer-binding protein Homologous Protein.

Fig. 6

The impact of HFD and/or 4-PBA on liver IDE content. The column demonstrates Mean ± SEM for 6 animals. ****P < 0.0001 substantial distinction with the normal diet received rats, ^$$$$P < 0.0001 substantial distinction with the ND + DMSO group, and ⁺⁺⁺⁺P<0.0001 substantial distinction with HFD and HFD + DMSO groups. Crl: Control, ND: Normal Diet, HFD: High-Fat Diet, 4-PBA: 4-Phenyl Butyric Acid, DMSO: Dimethyl Sulfoxide and IDE: Insulin-Degrading Enzyme.