Altered bioavailability of epoxyeicosatrienoic acids is associated with conduit artery endothelial dysfunction in type 2 diabetic patients

Abstract

Background: This pathophysiological study addressed the hypothesis that soluble epoxide hydrolase (sEH), which metabolizes the vasodilator and anti-inflammatory epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs), contributes to conduit artery endothelial dysfunction in type 2 diabetes.

Methods and results: Radial artery endothelium-dependent flow-mediated dilatation in response to hand skin heating was reduced in essential hypertensive patients (n = 9) and type 2 diabetic subjects with (n = 19) or without hypertension (n = 10) compared to healthy subjects (n = 36), taking into consideration cardiovascular risk factors, flow stimulus and endothelium-independent dilatation to glyceryl trinitrate. Diabetic patients but not non-diabetic hypertensive subjects displayed elevated whole blood reactive oxygen species levels and loss of NO release during heating, assessed by measuring local plasma nitrite variation. Moreover, plasma levels of EET regioisomers increased during heating in healthy subjects, did not change in hypertensive patients and decreased in diabetic patients. Correlation analysis showed in the overall population that the less NO and EETs bioavailability increases during heating, the more flow-mediated dilatation is reduced. The expression and activity of sEH, measured in isolated peripheral blood mononuclear cells, was elevated in diabetic but not hypertensive patients, leading to increased EETs conversion to DHETs. Finally, hyperglycemic and hyperinsulinemic euglycemic clamps induced a decrease in flow-mediated dilatation in healthy subjects and this was associated with an altered EETs release during heating.

Conclusions: These results demonstrate that an increased EETs degradation by sEH and altered NO bioavailability are associated with conduit artery endothelial dysfunction in type 2 diabetic patients independently from their hypertensive status. The hyperinsulinemic and hyperglycemic state in these patients may contribute to these alterations. Trial registration NCT02311075. Registered December 8, 2014.

Keywords: Endothelial dysfunction; Epoxyeicosatrienoic acids; Soluble epoxide hydrolase; Type 2 diabetes.

Fig. 1

Presence of conduit artery endothelial dysfunction in type 2 diabetes and essential hypertension. Variations in radial artery diameter (a) and mean wall shear stress (b) in response to hand skin heating, and variation in radial artery diameter in response to glyceryl trinitrate (c) in healthy, hypertensive (HT), type 2 diabetic (T2D) and hypertensive type 2 diabetic (HT + T2D) subjects. Mean values ± SEM are shown. *P < 0.05, **P < 0.01

Fig. 2

Altered NO bioavailability in type 2 diabetes. Plasma levels of the NO metabolite nitrite (a) before (34 °C) and at the end of hand skin heating (44 °C) in healthy (n = 23), hypertensive (HT; n = 6), type 2 diabetic (T2D; n = 8) and hypertensive type 2 diabetic (HT + T2D; n = 18) subjects. Whole blood levels of reactive oxygen species (ROS) (b) in healthy, hypertensive (HT), type 2 diabetic (T2D) and hypertensive type 2 diabetic (HT + T2D) subjects. Mean values ± SEM are shown. *P < 0.05, **P < 0.01. Linear relationships between the magnitude of radial artery flow-mediated dilatation with the variations in plasma nitrite levels during heating (c) and with ROS levels (d). The dashed lines represent the 95% confidence interval for the regression

Fig. 3

Type 2 diabetes profoundly impaired EETs bioavailability during endothelial stimulation. Plasma levels of epoxyeicosatrienoic acids (EETs) (a), dihydroxyeicosatrienoic acids (DHETs) (b) regioisomers and total EETs + DHETs levels (c) before (34 °C) and at the end of hand skin heating (44 °C), in healthy (n = 28), hypertensive (HT; n = 8), type 2 diabetic (T2D; n = 9) and hypertensive type 2 diabetic (HT + T2D; n = 19) subjects. Mean values ± SEM are shown. *P < 0.05, **P < 0.01. Linear relationships between the magnitude of radial artery flow-mediated dilatation with the variations in plasma EETs + DHETs during heating (d). The dashed lines represent 95% confidence interval for the regression

Fig. 4

Increased EETs degradation by sEH in type 2 diabetes. Ratio of plasma 14,15-dihydroxyeicosatrienoic acid-to-14,15-epoxyeicosatrienoic acid (14,15-DHET/14,15-EET) (a), sEH activity (b), mRNA (c) and protein expression (d) in peripheral blood mononuclear cells in healthy, hypertensive (HT), type 2 diabetic (T2D) and hypertensive type 2 diabetic (HT + T2D) subjects. β2M: beta2-microglobulin. Mean values ± SEM are shown. *P < 0.05, **P < 0.01

Fig. 5

Acute hyperglycemia and hyperinsulinemia altered conduit artery endothelial function in healthy subjects. Variations in radial artery diameter (a) and mean wall shear stress (b) in response to hand skin heating and variation in radial artery diameter in response to glyceryl trinitrate (c) during saline infusion an during the hyperglycemic (HyperGly) and hyperinsulinemic euglycemic (HyperInsu) clamps in 8 healthy subjects. Plasma levels of nitrite (d) and total epoxyeicosatrienoic acids + dihydroxyeicosatrienoic acids (EETs + DHETs) (e) at baseline at 34 °C, at steady-state and at the end of hand skin heating at 44 °C during saline infusion and during the hyperglycemic and hyperinsulinemic euglycemic clamps in 8 healthy subjects. Mean values ± SEM are shown. *P < 0.05, **P < 0.01