The effects of diet-induced obesity on hepatocyte insulin signaling pathways and induction of non-alcoholic liver damage

Figures & data

Table 1 Physiological and metabolic characteristics of the four experimental groups

	Chow-fed	Untreated	Fenofibrate treated	Diet-to-chow
Body weight (g)
• Initial	195 ± 3	196 ± 3	–	–
• Mid study	500 ± 7	570 ± 12a	568 ± 12a	569 ± 14a
• Terminal	569 ± 7	699 ± 22a	589 ± 14bc	606 ± 16bc
% total fat mass	16.5 ± 1.1	23.6 ± 1.3a	19.9 ± 1.2bc	18.7 ± 1.2bc
% total lean mass	83.5 ± 1.0	76.4 ± 1.4a	80.1 ± 1.3bc	81.3 ± 1.5b
Epididymal fat-pad mass (g)	5.9 ± 0.4	11.9 ± 1.1a	6.4 ± 0.7b	6.8 ± 0.6b
Perirenal fat-pad mass (g)	5.5 ± 0.2	11.3 ± 1.2a	6.3 ± 0.5b	6.7 ± 0.5b
Gastrocnemius muscle mass (g)	3.1 ± 0.1	3.2 ± 0.1	3.1 ± 0.1	3.2 ± 0.1
Plasma glucose (mM)	11.7 ± 0.5	13.8 ± 0.3	10.5 ± 0.3	12.7 ± 0.4
Plasma insulin (μg/L)	1.4 ± 0.1	3.7 ± 0.6a	1.2 ± 0.1b	1.4 ± 0.1b
Plasma triglyceride (mM)	0.76 ± 0.03	1.57 ± 0.16a	0.60 ± 0.03b	0.88 ± 0.04b
Plasma NEFA (mM)	0.40 ± 0.02	0.51 ± 0.02a	0.31 ± 0.02b	0.45 ± 0.03b
Plasma TNFα (pg/mL)	608 ± 56	1047 ± 167a	532 ± 91b	660 ± 102b

Notes: Data are mean ± SEM for n = 10 in each group.

a P < 0.001 vs lean control;

b P < 0.001 vs untreated;

c P < 0.05 vs lean control.

Abbrevoations: NEFA, ; TNFα, .

Figure 1 Liver weight of the animals at the end of the experiment in four groups: chow-fed (C), vehicle (V), diet-to-chow (DC), and fenofibrate treated (F).

Notes: Data represents means ± SEM for each group. There were significant increases in both vehicle and fenofibrate treated liver weights compared with chow-fed groups. *P < 0.01, **P < 0.0001.

Figure 2 Content of hepatic triglycerides (TG) in four experimental groups: chow-fed (C), vehicle (V), diet-to-chow (DC), and fenofibrate treated (F).

Notes: Data represents means ± SEM for each group. There was a significant increase in the vehicle group’s liver triglyceride levels which was reversed by fenofibrate treatment. *P < 0.01, **P < 0.000.

Figure 3 Protein expression of A) IR-β, and B) IRS-1 in rat liver. Equal amounts (50 μg/well) of protein were separated by SDS-PAGE and immunoblotted with IR-β or IRS-1 antibodies, respectively. The animal groups are: C) chow-fed lean control, V) vehicle group (untreated dietary obese), DC (diet-to-chow group), and F) fenofibrate treated group.

Notes: Data (mean ± SEM) are normalized to that of the control group and expressed as a percentage of chow fed (control) rats. *P < 0.001 versus chow-fed.

Figure 4 Protein expression of A) IRS-2 and B) PI 3-kinase in rat liver. Equal amounts (50 μg/well) of protein were separated by SDS-PAGE and immunoblotted with IRS-2 and PI 3-kinase antibodies, respectively. The animal groups are: C) chow-fed lean control, V) vehicle group (untreated dietary obese), DC) diet-to-chow group, of the control group and expressed as a percentage of chow fed (control) rats.

Notes: *P < 0.05; **P < 0.0005 versus chow-fed.

Figure 5 Protein expression of AKt in rat liver. Equal amounts (50 μg/well) of protein were separated by SDS-PAGE and immunoblotted with AKt antibody. The animal groups are: C) chow-fed lean control, V) vehicle group (untreated dietary obese), DC) diet-to-chow group, and F) fenofibrate treated group.

Notes: Data (mean ± SEM) are normalized to that of the control group and expressed as a percentage of chow fed (control) rats. *P < 0.05, **P < 0.000005 versus chow-fed.

Figure 6 Protein expression of eNOS in rat liver. Equal amounts (50 μg/well) of protein were separated by SDS-PAGE and immunoblotted with eNOS antibody. The animal groups are: C) chow-fed lean control, V) vehicle group (untreated dietary obese), DC) diet-to-chow group, and F) fenofibrate treated group.

Notes: Data (mean ± SEM) are normalized to that of the control group and expressed as a percentage of chow fed (control) rats. No significant differences were seen between the four groups.

Figure 7 Protein expression of A) Shc and B) ERK1/2 in rat liver. Equal amounts (50 μg/well) of protein were separated by SDS-PAGE and immunoblotted with Shc or ERK 1/2 antibodies, respectively. The animal groups are: C) chow-fed lean control, V) vehicle group (untreated dietary obese), DC) diet-to-chow group, and F) fenofibrate treated group.

Notes: Data (mean ± SEM) are normalized to that of the control group and expressed as a percentage of the chow-fed (control) rats. *P < 0.01 versus chow-fed.

Figure 8 Histologic sectioning for the liver: A) normal liver, B) steatosis fatty liver grade one, C) steatosis fatty liver grade two and D) steatohepatitis grade one. Note: The arrows indicate the presence of adipocytes in each section.

Table 2 Total percentage of hepatic change (steatosis) in stage 1 of non-alcoholic fatty liver disease in the four experimental groups

	Grade	Chow-fed	Vehicle	Diet-to-chow	Fenofibrate
Steatosis (fatty change in the liver)	0 (negative samples)	50%	20%	50%	90%
	1	50%	40%	40%	–
	2	–	30%	10%	10%
	3	–	10%	–	–
Total % of fatty change in each group		50%	80%	50%	10%

Table 3 Percentage of hepatic inflammation in stage II of non-alcoholic fatty liver disease in the four experimental groups

	Grade	Chow-fed	Vehicle	Diet-to-chow	Fenofibrate
Hepatic inflammation	0 (negative samples)	60%	30%	70%	90%
	1	40%	70%	30%	10%
	2	–	–	–	–
	3	–	–	–	–
Total % of inflammation in each group		40%	70%	30%	10%