Pemafibrate, A Novel Selective Peroxisome Proliferator-Activated Receptor α Modulator, Reduces Plasma Eicosanoid Levels and Ameliorates Endothelial Dysfunction in Diabetic Mice

Abstract

Aims: Various pathological processes related to diabetes cause endothelial dysfunction. Eicosanoids derived from arachidonic acid (AA) have roles in vascular regulation. Fibrates have recently been shown to attenuate vascular complications in diabetics. Here we examined the effects of pemafibrate, a selective peroxisome proliferator-activated receptor α modulator, on plasma eicosanoid levels and endothelial function in diabetic mice.

Methods: Diabetes was induced in 7-week-old male wild-type mice by a single injection of streptozotocin (150 mg/kg). Pemafibrate (0.3 mg/kg/day) was administered orally for 3 weeks. Untreated mice received vehicle. Circulating levels of eicosanoids and free fatty acids were measured using both gas and liquid chromatography-mass spectrometry. Endothelium-dependent and endothelium-independent vascular responses to acetylcholine and sodium nitroprusside, respectively, were analyzed.

Results: Pemafibrate reduced both triglyceride and non-high-density lipoprotein-cholesterol levels (P＜0.01), without affecting body weight. It also decreased circulating levels of AA (P＜0.001), thromboxane B₂ (P＜0.001), prostaglandin E₂, leukotriene B₄ (P＜0.05), and 5-hydroxyeicosatetraenoic acid (P＜0.001), all of which were elevated by the induction of diabetes. In contrast, the plasma levels of 15-deoxy-Δ^12,14-prostaglandin J₂, which declined following diabetes induction, remained unaffected by pemafibrate treatment. In diabetic mice, pemafibrate decreased palmitic acid (PA) and stearic acid concentrations (P＜0.05). Diabetes induction impaired endothelial function, whereas pemafibrate ameliorated it (P＜0.001). The results of ex vivo experiments indicated that eicosanoids or PA impaired endothelial function.

Conclusion: Pemafibrate diminished the levels of vasoconstrictive eicosanoids and free fatty acids accompanied by a reduction of triglyceride. These effects may be associated with the improvement of endothelial function by pemafibrate in diabetic mice.

Keywords: Diabetes; Eicosanoid; Endothelial function; Pemafibrate.

Fig.1. Effect of pemafibrate on lipid profile

Induction of diabetes with STZ significantly elevated plasma lipid concentrations, whereas pemafibrate reduced the levels of triglycerides and non-HDL-cholesterol in diabetic mice. Pemafibrate did not affect the levels of HDL-cholesterol, total cholesterol, and blood glucose ( n =16–18 per group). ^＊＊ P ＜0.01 and ^＊＊＊ P ＜0.001. All values are mean±SEM.

Fig.2. Pemafibrate reduced eicosanoids produced by the COX2 pathway

Induction of diabetes elevated the levels of AA, TXB ₂ , and PGE ₂ , whereas pemafibrate decreased their expression levels. Induction of diabetes reduced 15d-PGJ ₂ levels, which remained unaffected by pemafibrate treatment ( n =5 per group). ^＊ P ＜0.05 and ^＊＊＊ P ＜0.001. All values are mean±SEM.

Fig.3. Pemafibrate reduced the expression of PGE synthase and thromboxane synthase

Induction of diabetes by STZ significantly promoted the levels of thromboxane synthase, which tended to decline after treatment with pemafibrate. Furthermore, STZ-induced diabetes tended to increase PGE synthase levels, which were significantly lowered by pemafibrate ( n =8 per group). All values are mean±SEM. ^＊ P ＜0.05.

Fig.4. Pemafibrate reduced eicosanoids produced by the LOX pathway

Induction of diabetes elevated LTB ₄ and 5-HETE levels, whereas pemafibrate reduced their expressions ( n =5 per group). ^＊ P ＜0.05, ^＊＊ P ＜0.01, and ^＊＊＊ P ＜0.001. All values are mean±SEM.

Fig.5. Eicosanoid levels positively correlated with triglyceride levels

The levels of AA and AA-derived eicosanoids positively correlated with triglyceride levels ( n =5 per group).

Fig.6. Pemafibrate reduced saturated free fatty acids

Pemafibrate reduced palmitic acid and stearic acid in diabetic mice ( n =5 per group). ^＊ P ＜0.05. All values are mean±SEM.

Fig.7. Pemafibrate attenuated endothelial dysfunction in diabetic mice

Vascular reactivity to Ach or SNP was determined using aortic rings obtained from our mice. (A) Induction of diabetes impaired endothelium-dependent vasodilation in response to Ach. Pemafibrate ameliorated endothelial dysfunction, as compared with vehicle. (B) Endothelium-independent vascular response did not differ among the three groups ( n =13–18 per group). ^＊＊ P ＜0.01 vs. control, ^† P ＜0.05 vs. STZ. All values are mean±SEM.

Fig.8. Eicosanoids impaired endothelial function in non-diabetic mice

(A) Incubation with PGE ₂ significantly impaired endothelium-dependent vasodilation, as determined by the response to Ach. (B) TXB ₂ tended to impair endothelial function although it did not reach statistical significance. (C) PA significantly impaired endothelial function. Endothelium-independent vascular function, as measured in response to SNP, did not differ across these groups ( n =8–9 per group). ^＊ P ＜0.05 vs. NT (non-treatment). All values are mean±SEM.