High-Fat Diet-Induced Obesity Model Does Not Promote Endothelial Dysfunction via Increasing Leptin/Akt/eNOS Signaling

Abstract

Experimental studies show that the unsaturated high-fat diet-induced obesity promotes vascular alterations characterized by improving the endothelial L-arginine/Nitric Oxide (NO) pathway. Leptin seems to be involved in this process, promoting vasodilation via increasing NO bioavailability. The aim of this study was to test the hypothesis that unsaturated high-fat diet-induced obesity does not generate endothelial dysfunction via increasing the vascular leptin/Akt/eNOS signaling. Thirty-day-old male Wistar rats were randomized into two groups: control (C) and obese (Ob). Group C was fed a standard diet, while group Ob was fed an unsaturated high-fat diet for 27 weeks. Adiposity, hormonal and biochemical parameters, and systolic blood pressure were observed. Concentration response curves were performed for leptin or acetylcholine in the presence or absence of Akt and NOS inhibitor. Our results showed that an unsaturated high-fat diet promoted a greater feed efficiency (FE), elevation of body weight and body fat (BF), and an adiposity index, characterizing a model of obesity. However, comorbidities frequently associated with experimental obesity were not visualized, such as glucose intolerance, dyslipidemia and hypertension. The evaluation of the endothelium-dependent relaxation with acetylcholine showed no differences between the C and Ob rats. After NOS inhibition, the response was completely abolished in the Ob group, but not in the C group. Furthermore, Akt inhibition completely blunted vascular relaxation in the C group, but not in the Ob group, which was more sensitive to leptin-induced vascular relaxation. L-NAME incubation abolished the relaxation in both groups at the same level. Although Akt inhibitor pre-incubation reduced the leptin response, group C was more sensitive to its effect. In conclusion, the high-unsaturated fat diet-induced obesity improved the vascular reactivity to leptin and does not generate endothelial dysfunction, possibly by the increase in the vascular sensitivity to leptin and increasing NO bioavailability. Moreover, our results suggest that the increase in NO production occurs through the increase in NOS activation by leptin and is partially mediated by the Akt pathway.

Keywords: Akt; high-fat diet; leptin; obesity; vascular reactivity.

FIGURE 1

Evolution of body weight at 27 week of experimental protocol of obesity. C, control; Ob, obese; BW, body weight. Data are reported as the means ± SEM. Two-way ANOVA repeated measures for independent samples followed by Tukey post hoc test. ^∗p < 0.05 Ob vs. C.

FIGURE 2

Glucose tolerance profile at 27 week of experimental protocol of obesity. Glucose tolerance test (A), area under the curve for glucose – AUC (B), insulin serum level (C) and (D) homeostatic model assessment index (HOMA-IR) from control (C; n = 9) and obese (Ob; n = 7) groups. Data are reported as the means ± SEM. Two-way ANOVA repeated measures for independent samples followed by Tukey post hoc test. ^∗p < 0.05 Ob vs. C.

FIGURE 3

Concentration-response curve to phenylephrine obtained from control and obese (Ob) groups rings before (A) and after nitric oxide synthase inhibition with L-NAME (100 μM – B–D). Parentheses indicates the number of rings and rats, respectively. Data are presented as the mean ± SEM. Two-way ANOVA followed by the Fisher′s post hoc test for multiple comparisons. ^∗p < 0.05.

FIGURE 4

Concentration-response curve to acetylcholine in the thoracic aorta obtained from C and Ob groups in the presence or absence of L-NAME (100 μM – A) or Akt inhibitor (5 μM – B). Parentheses indicates the number of rings and rats, respectively. Data are presented as mean ± SEM. Two-way ANOVA followed by the Fisher′s post hoc test for multiple comparisons. ^∗p < 0.05.

FIGURE 5

Concentration-response curve to leptin in the thoracic aorta from C and Ob groups in the presence or absence of L-NAME (100 μM – A) or Akt inhibitor (5 μM – B). Parentheses indicates the number of rings and rats, respectively. Data are presented as mean ± SEM. Two-way ANOVA was used followed by the Fisher′s post hoc test for multiple comparisons. ^∗p < 0.05 Ob vs. C.