Type of supplemented simple sugar, not merely calorie intake, determines adverse effects on metabolism and aortic function in female rats

Abstract

High consumption of simple sugars causes adverse cardiometabolic effects. We investigated the mechanisms underlying the metabolic and vascular effects of glucose or fructose intake and determined whether these effects are exclusively related to increased calorie consumption. Female Sprague-Dawley rats were supplemented with 20% wt/vol glucose or fructose for 2 mo, and plasma analytes and aortic response to vasodilator and vasoconstrictor agents were determined. Expression of molecules associated with lipid metabolism, insulin signaling, and vascular response were evaluated in hepatic and/or aortic tissues. Caloric intake was increased in both sugar-supplemented groups vs. control and in glucose- vs. fructose-supplemented rats. Hepatic lipogenesis was induced in both groups. Plasma triglycerides were increased only in the fructose group, together with decreased expression of carnitine palmitoyltransferase-1A and increased microsomal triglyceride transfer protein expression in the liver. Plasma adiponectin and peroxisome proliferator-activated receptor (PPAR)-α expression was increased only by glucose supplementation. Insulin signaling in liver and aorta was impaired in both sugar-supplemented groups, but the effect was more pronounced in the fructose group. Fructose supplementation attenuated aortic relaxation response to a nitric oxide (NO) donor, whereas glucose potentiated it. Phenylephrine-induced maximal contractions were reduced in the glucose group, which could be related to increased endothelial NO synthase (eNOS) phosphorylation and subsequent elevated basal NO in the glucose group. In conclusion, despite higher caloric intake in glucose-supplemented rats, fructose caused worse metabolic and vascular responses. This may be because of the elevated adiponectin level and the subsequent enhancement of PPARα and eNOS phosphorylation in glucose-supplemented rats.

New & noteworthy: This is the first study comparing the effects of glucose and fructose consumption on metabolic factors and aortic function in female rats. Our results show that, although total caloric consumption was higher in glucose-supplemented rats, fructose ingestion had a greater impact in inducing metabolic and aortic dysfunction.

Keywords: adiponectin; fructose; glucose; insulin resistance; liver.

Fig. 1.

Supplementation with glucose and fructose induces hepatic lipogenesis. mRNA levels of stearoyl-CoA desaturase-1 (scd1, A) and fatty acid synthase (fas, C) in the liver from control, glucose-, and fructose-supplemented rats. Bars represent means ± SE of values obtained from n = 8 animals. Protein levels of SCD1 (B), FAS (D), phosphorylated (p)-acetyl-CoA carboxylase (ACC, E), total ACC (F), carbohydrate response element-binding protein (ChREBP, G), and mature sterol response element-binding protein-1c (SREBP-1, H) in liver samples from control, glucose-, and fructose-supplemented rats. Each bar represents the mean ± SE of values obtained from n = 5 animals. To show representative bands corresponding to 3 different rats/treatment group, images from different parts of the same gel have been juxtaposed, which is indicated by white dividing lines in the figure. *P < 0.05, **P < 0.01, and ***P < 0.001 vs. control. One-way ANOVA followed by Bonferroni’s post hoc test.

Fig. 2.

Differential effects of glucose and fructose on peroxisome proliferator-activated receptor-α (PPARα), PPARα target genes, and microsomal triglyceride transfer protein (MTP). Protein levels of PPARα (A), liver carnitine palmitoyl-CoA transferase-I (L-CPT-1A, D), and MTP (E) in hepatic samples from control, glucose-, and fructose-supplemented rats. Each bar represents the mean ± SE of values obtained from n = 5 animals. To show representative bands corresponding to 3 different rats/treatment group, images from different parts of the same gel have been juxtaposed, which is indicated by white dividing lines. mRNA levels of l-cpt-1a (B) and acyl-CoA oxidase (aco, C) in hepatic samples from control, glucose-, and fructose-supplemented rats. Each bar represents the mean ± SE of values obtained from n = 8 animals. *P < 0.05 and **P < 0.01 vs. control; ^##P < 0.01 vs. glucose. One-way ANOVA followed by Bonferroni’s post hoc test.

Fig. 3.

Effects of glucose and fructose supplementation on the expression of proteins involved in insulin signaling in liver and aortic tissues. Protein levels of hepatic insulin receptor substrate (IRS)-1 (A) and IRS-2 (B), aortic IRS-1 (C) and IRS-2 (D), and hepatic (E) and aortic (F) phosphorylated and total V-akt murine thymoma viral oncogene homolog-2 (Akt) in samples from control, glucose-, and fructose-supplemented rats. Each bar represents the mean ± SE of values obtained from n = 5 animals. To show representative bands corresponding to 3 different rats/treatment group, images from different parts of the same gel have been juxtaposed, which is indicated by white dividing lines. *P < 0.05, **P < 0.01, and ***P < 0.001 vs. control. One-way ANOVA followed by Bonferroni’s post hoc test.

Fig. 4.

Effects of supplementation with glucose and fructose on the responses of aortic rings to relaxation agents. Relaxation responses to cumulative concentrations of acetylcholine (ACh, A), bradykinin (BK, B), and sodium nitroprusside (SNP, C) in intact aortic rings from female rats after 2 mo of supplementation with 20% wt/vol liquid fructose or glucose. Aortic rings were precontracted with phenylephrine (2 µM) (A and B) or U-46619 (100 nM) (C). Data are expressed as means ± SE of values obtained from n = 5–8 animals. *P < 0.05 and ***P < 0.001 vs. control, analyzed using two-way ANOVA followed by Bonferroni’s post hoc test.

Fig. 5.

Supplementation with glucose reduces the contractile responses of aortic rings. A: contractile responses to cumulative concentrations of phenylephrine (PE) in intact aortic rings from female rats after 2 mo of supplementation with 20% wt/vol liquid fructose or glucose. B-D: contraction to PE was measured in aortae from control, glucose-, and fructose-supplemented rats before and after incubation with N^ω-nitro-l-arginine methyl ester (l-NAME, 200 μM). Responses were performed in the presence of indomethacin (10 μM). Data are expressed as means ± SE of values obtained from n = 7–8 animals. *P < 0.05 and ***P < 0.001 vs. control condition (control rats in A, before l-NAME in B-D), analyzed using two-way ANOVA followed by Bonferroni’s post hoc test.

Fig. 6.

Supplementation with glucose enhances endothelial NO synthase (eNOS) phosphorylation, and supplementation with fructose increases inducible NO synthase (iNOS) expression in aortic tissue. Western blots of phosphorylated and total eNOS (A) and iNOS (B) in aortic samples from control, glucose-, and fructose-supplemented rats. Each bar represents the mean ± SE of values obtained from n = 5 animals. To show representative bands corresponding to 3 different rats/treatment group, images from different parts of the same gel have been juxtaposed, which is indicated by white dividing lines. *P < 0.05 vs. control; ^##P < 0.01 vs. glucose. One-way ANOVA followed by Bonferroni’s post hoc test.

Fig. 7.

In vitro adiponectin (but not glucose or fructose) increases NO level in EA.hy926 cells. Levels of nitrate and nitrite in EA.hy926 medium after incubation with vehicle (CT), adiponectin (APN, 5 and 15 μg/ml), 25 mM glucose, 25 mM fructose, 25 mM mannitol (MAN), and the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 100 µM). Each bar represents the mean ± SE of 5–6 different assays performed in duplicate. ***P < 0.001 and ****P < 0.0001 vs. control. One-way ANOVA followed by Bonferroni’s post hoc test.

Fig. 8.

Differential effects of fructose and glucose supplementation on intracellular pathways related to aortic relaxation. A: mRNA levels of adenylyl cyclase (ac6), soluble guanylate cyclase (gcsa1), phosphodiesterase 4 (pde4d), and phosphodiesterase 4 (pde5) in aortic tissue samples from control, glucose-, and fructose-supplemented rats. Each bar represents the mean ± SE of values obtained from n = 8 animals. Protein levels of cGMP-dependent protein kinase (PKG, B), vasodilator-stimulated phosphoprotein (VASP) phosphorylated in Ser²³⁹ (C), total VASP (D), VASP phosphorylated in Ser¹⁵⁷ (E), phosphorylated protein kinase A (PKAc, F), and PDE4 (G) in aortic samples from control, glucose-, and fructose-supplemented rats. Each bar represents the mean ± SE of values obtained from n = 5 animals. To show representative bands corresponding to 3 different rats/treatment group, images from different parts of the same gel have been juxtaposed, which is indicated by white dividing lines. *P < 0.05, **P < 0.01, and ***P < 0.001 vs. control; ^#P < 0.05 and ^##P < 0.01 vs. glucose. One-way ANOVA followed by Bonferroni’s post hoc test.