Partial Replacement of Dietary Fat with Polyunsaturated Fatty Acids Attenuates the Lipopolysaccharide-Induced Hepatic Inflammation in Sprague-Dawley Rats Fed a High-Fat Diet

Abstract

In this study, we investigated whether the partial replacement of dietary fat with polyunsaturated fatty acids (PUFAs) ameliorated the lipopolysaccharide (LPS)-induced hepatic inflammation in rats fed a high-fat diet. Male Sprague-Dawley rats were divided into three groups and provided each of the following diets: (1) high-fat diet (HFD), (2) HFD with perilla oil (PO), and (3) HFD with corn oil (CO). After 12 weeks of dietary intervention, the rats were intraperitoneally injected with LPS (5 mg/kg) from Escherichia coli O55:B5 or phosphate-buffered saline (PBS). Following LPS stimulation, serum insulin levels were increased, while PO and CO lowered the serum levels of glucose and insulin. In the liver, LPS increased the triglyceride levels, while PO and CO alleviated the LPS-induced hepatic triglyceride accumulation. In the LPS injected rats, the mRNA expression of genes related to inflammation and endoplasmic reticulum (ER) stress was attenuated by PO and CO in the liver. Furthermore, hepatic levels of proteins involved in the nuclear factor kappa-light-chain-enhancer of activated B cells/mitogen-activated protein kinase pathways, antioxidant response, and ER stress were lowered by PO- and CO-replacement. Therefore, the partial replacement of dietary fat with PUFAs alleviates LPS-induced hepatic inflammation during HFD consumption, which may decrease metabolic abnormalities.

Keywords: corn oil; high-fat diet; inflammation; lipopolysaccharide; perilla oil; polyunsaturated fatty acids.

Figure 1

Effects of partial replacement of dietary fat with PO or CO on the body weight and food intake of rats. Five-week-old male Sprague-Dawley rats were fed either a high-fat diet (HFD), HFD supplemented with perilla oil (HFD + PO), or corn oil (HFD + CO) for 12 weeks (n = 16 per group). (a) Body weight changes; (b) daily body weight gain; (c) daily food intake; (d) food efficiency ratio (FER). Values are presented as the mean ± standard deviation. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’s multiple comparisons post hoc test for multiple comparisons. ‘ns’ indicates p ≥ 0.05.

Figure 2

Effects of partial replacement of dietary fat with PO or CO on oral glucose tolerance test (OGTT). Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks (n = 16 per group). (a,c,e) OGTT at weeks 3, 7, and 11; (b,d,f) area under the curve (AUC) at weeks 3, 7, and 11 following OGTT. Values are represented by the line or as the mean ± standard deviation. Data were analyzed using one-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. ‘ns’ indicates p ≥ 0.05.

Figure 3

Effects of partial replacement of dietary fat with PO or CO and LPS stimulation on serum glucose, insulin, and leptin levels. Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks and then treated with PBS or LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Glucose level; (b) insulin level; (c) homeostasis model assessment-estimated insulin resistance (HOMA-IR); (d) leptin level. Data were analyzed using two-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. Asterisk indicates a significant main effect for LPS (**** p < 0.0001). LPS, lipopolysaccharide; PBS, phosphate-buffered saline.

Figure 4

Effects of partial replacement of dietary fat with PO or CO and LPS stimulation on the serum lipid profile. Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks and then treated with PBS or LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Serum triglyceride (TG) level; (b) serum total cholesterol (TC) level; (c) high-density lipoprotein (HDL)-cholesterol level; (d) non-HDL-cholesterol level; (e) atherogenic coefficient; (f) cardiac risk factor. Data were analyzed using two-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. Asterisk indicates a significant main effect for LPS (**** p < 0.0001). LPS, lipopolysaccharide; PBS, phosphate-buffered saline.

Figure 5

Effects of partial replacement of dietary fat with PO or CO and LPS stimulation on liver function parameters in serum. Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks and then treated with PBS or LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Aspartate aminotransferase (AST) activity; (b) alanine aminotransferase (ALT) activity; (c) alkaline phosphatase (ALP) activity. Data were analyzed using two-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. LPS, lipopolysaccharide; PBS, phosphate-buffered saline.

Figure 6

Effects of partial replacement of dietary fat with PO or CO and LPS stimulation on the relative weights of liver and white adipose tissue (WAT). Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks, followed by treatment with PBS or LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Liver weight; (b) WAT weight; (c) epididymal adipose tissue (EAT) weight; (d) mesenteric adipose tissue (MAT) weight; (e) retroperitoneal adipose tissue (RAT) weight; (f) perirenal adipose tissue (PAT) weight. Data were analyzed using two-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. Hash indicates a significant main effect for diet (^## p < 0.01). LPS, lipopolysaccharide; PBS, phosphate-buffered saline; BW, body weight.

Figure 7

Effects of partial replacement of dietary fat with perilla oil or corn oil and LPS stimulation on lipid contents in liver and epididymal adipose tissue (EAT). Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks and then treated with PBS or LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Hepatic TG level; (b) hepatic TC level; (c) TG level in EAT; (d) TC level in EAT. Data were analyzed using two-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. LPS, lipopolysaccharide; PBS, phosphate-buffered saline.

Figure 8

Effects of partial replacement of dietary fat with PO or CO and LPS stimulation on the mRNA expression of genes related to inflammation and endoplasmic reticulum (ER) stress in the liver. Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks and were then treated with LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Interleukin (IL)-1β level; (b) chemokine (C-X-C motif) ligand 1 (CXCL1) level; (c) binding immunoglobulin protein (BiP) level; (d) C/EBP homologous protein (CHOP) level. Relative expression of each gene was quantified by using the 2^−ΔΔCT method. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was used as the reference gene for normalization. Values are presented as the mean ± standard deviation. Data were analyzed using one-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. LPS, lipopolysaccharide.

Figure 9

Effects of partial replacement of dietary fat with PO or CO and LPS stimulation on the levels of proteins related to the nuclear factor-kappa B (NF-kB) and mitogen-activated protein kinase (MAPK) pathways, oxidative stress, and ER stress in the liver. Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks and then treated with LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Representative Western blot images; (b) phospho-nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (p-IkBα) level; (c) phospho-nuclear factor kappa-light-chain-enhancer of activated B cells (p-NF-κB) level; (d) phospho-c-Jun N-terminal kinases (p-JNK) level; (e) phospho-extracellular signal-regulated kinases (p-ERK) level; (f) phospho-p38 (p-p38) level; (g) nuclear factor erythroid 2-related factor 2 (Nrf2) level; (h) heme oxygenase 1 (HO-1); (i) binding immunoglobulin protein (BiP) level; (j) C/EBP homologous protein (CHOP) level. The expression of each protein was normalized to a value for β-actin, the internal control of protein content. Values are presented as the mean ± standard deviation. Data were analyzed using one-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. LPS, lipopolysaccharide.

Figure 9

Effects of partial replacement of dietary fat with PO or CO and LPS stimulation on the levels of proteins related to the nuclear factor-kappa B (NF-kB) and mitogen-activated protein kinase (MAPK) pathways, oxidative stress, and ER stress in the liver. Five-week-old male Sprague-Dawley rats were fed either the HFD, HFD + PO, or HFD + CO for 12 weeks and then treated with LPS (5 mg/kg) for 24 h (n = 8 per group). (a) Representative Western blot images; (b) phospho-nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (p-IkBα) level; (c) phospho-nuclear factor kappa-light-chain-enhancer of activated B cells (p-NF-κB) level; (d) phospho-c-Jun N-terminal kinases (p-JNK) level; (e) phospho-extracellular signal-regulated kinases (p-ERK) level; (f) phospho-p38 (p-p38) level; (g) nuclear factor erythroid 2-related factor 2 (Nrf2) level; (h) heme oxygenase 1 (HO-1); (i) binding immunoglobulin protein (BiP) level; (j) C/EBP homologous protein (CHOP) level. The expression of each protein was normalized to a value for β-actin, the internal control of protein content. Values are presented as the mean ± standard deviation. Data were analyzed using one-way ANOVA and Tukey’s multiple comparisons post hoc test for multiple comparisons. Means with different letters indicate significant differences at p < 0.05. LPS, lipopolysaccharide.