Prevention of Elevation in Plasma Triacylglycerol with High-Dose Bezafibrate Treatment Abolishes Insulin Resistance and Attenuates Glucose Intolerance Induced by Short-Term Treatment with Dexamethasone in Rats

Abstract

Objective: Fibrates are used as lipid-lowering drugs and are well tolerated as cotreatments when glucose metabolism disturbances are also present. Synthetic glucocorticoids (GCs) are diabetogenic drugs that cause dyslipidemia, dysglycemia, glucose intolerance, and insulin resistance when in excess. Thus, we aimed to describe the potential of bezafibrate in preventing or attenuating the adverse effects of GCs on glucose and lipid homeostasis.

Methods: Male Wistar rats were treated with high-dose bezafibrate (300 mg/kg, body mass (b.m.)) daily for 28 consecutive days. In the last five days, the rats were also treated with dexamethasone (1 mg/kg, b.m.).

Results: Dexamethasone treatment reduced the body mass gain and food intake, and bezafibrate treatment exerted no impact on these parameters. GC treatment caused an augmentation in fasting and fed glycemia, plasma triacylglycerol and nonesterified fatty acids, and insulinemia, and bezafibrate treatment completely prevented the elevation in plasma triacylglycerol and attenuated all other parameters. Insulin resistance and glucose intolerance induced by GC treatment were abolished and attenuated, respectively, by bezafibrate treatment.

Conclusion: High-dose bezafibrate treatment prevents the increase in plasma triacylglycerol and the development of insulin resistance and attenuates glucose intolerance in rats caused by GC treatment, indicating the involvement of dyslipidemia in the GC-induced insulin resistance.

Figure 1

Experimental design. At 3 months old, rats ingested bezafibrate ((300 mg/kg of body mass (b.m.)) once a day via oral gastric gavage administration between 0700 and 0800 h, diluted in 5% gum Arabic, for 28 consecutive days, while control group received a daily gavage administration of vehicle alone (equivalent to 1 ml/kg of b.m.). In the last 5 days of bezafibrate treatment, half of rats under bezafibrate treatment received daily intraperitoneal (i.p.) injection of dexamethasone phosphate (equivalent to 1 mg/kg of dexamethasone, b.m., diluted in saline solution), between 0700 and 0800 h, while half of rats from the control group received daily i.p. injection of vehicle (0.9% NaCl, at 1 ml/kg of b.m.). A day after the last dexamethasone or vehicle administration, separate groups of rats were submitted to ipGTT, ipITT, and euthanasia for biochemical data analyses and ex vivo experiments. ipGTT: intraperitoneal glucose tolerance test; ipITT: intraperitoneal insulin tolerance test.

Figure 2

Body mass and relative food intake. (a) The average body mass values during the treatments with bezafibrate and dexamethasone. (b) The estimated growth rate (based on 1st and 23rd days) where no differences were observed between the groups. (c) The average body mass values during the treatment with dexamethasone. Observe the reduction in body mass by an effect of dexamethasone treatment. (d) Relative food intake during glucocorticoid treatment and (e) the percentage of reduction in the food intake from the end to the initial treatment with glucocorticoid. We can observe a reduction of relative food intake by an effect of dexamethasone. Results are expressed as mean ± SEM in (a, c, and d) and mean ± SD in (b) and (e). In (a, c, and d), the variances were expressed as standard error of the mean (SEM) for esthetic reasons. ^∗Significantly different vs. the respective control group (dexamethasone effect) using two-way ANOVA with Tukey's post hoc test. n = 8–10, p < 0.05.

Figure 3

Biochemical data. Fasting plasma (a) triacylglycerol, (b) NEFA, (c) T-Chol, (d) blood glucose, and (e) plasma insulin values. Observe the marked effect of bezafibrate treatment on prevention of elevation of triacylglycerolemia and insulinemia caused by dexamethasone treatment. Fed plasma (f) triacylglycerol, (g) NEFA, (h) T-Chol, (i) blood glucose, and (j) plasma insulin values. We can note the marked effect of bezafibrate treatment on prevention of elevation of plasma triacylglycerol and NEFA and blood glucose. Results are expressed as mean ± SD. ^∗Significantly different vs. the respective control group (dexamethasone effect) and ^#significantly different vs. the respective control group (bezafibrate effect) using two-way ANOVA with Tukey's post hoc test. n = 7–12, p < 0.05. NEFA: nonesterified fatty acid; T-Chol: total cholesterol; ns: not significant.

Figure 4

Glucose tolerance and insulin sensitivity. (a) The average blood glucose values during an intraperitoneal glucose tolerance test (ipGTT) (2 g/kg, body mass), (b) the average values of area under curve (AUC), and (c) the plasma insulin in response to glucose load. Bezafibrate treatment attenuated the glucose intolerance caused by the dexamethasone treatment in the BezaDexa group. (d) The average of normalized blood glucose values (as % from min 0) during an intraperitoneal insulin tolerance test (ipITT) (2 IU/kg, body mass) and (e) the respective constant for glucose disappearance (K_ITT). Bezafibrate treatment prevented the insulin resistance caused by the dexamethasone treatment in the BezaDexa group. Results are expressed as mean ± SEM in (a, c, and d) and as mean ± SD in (b) and (e). In (a, c, and d), the variances were expressed as standard error of the mean (SEM) for esthetic reasons. ^∗Significantly different vs. the respective control group (dexamethasone effect) and ^#significantly different vs. the respective control group (bezafibrate effect) using two-way ANOVA with Tukey's post hoc test. n = 6–8, p < 0.05.

Figure 5

Glucose-stimulated insulin secretion. Insulin response to (a) 2.8 mM and (b) 16.7 mM of glucose in freshly isolated islets. (c) Insulin secretion ratio between 16.7 mM and 2.8 mM glucose. Rats from Beza group also had higher insulin response to high glucose concentration. Results are expressed as mean ± SD. ^∗Significantly different vs. the respective control group (dexamethasone effect) and ^#significantly different vs. the respective control group (bezafibrate effect) using two-way ANOVA with Tukey's post hoc test. n = 10–12 wells from 2 independent experiments, p < 0.05.