Differential anti-atherosclerotic effects in the innominate artery and aortic sinus by the liver X receptor agonist T0901317

Abstract

Activation of liver X receptors (LXRs) has been reported to reduce atherosclerosis in mouse models. However, this can be associated with enhanced liver de novo lipogenesis and elevation of plasma triglyceride-rich VLDL, which may limit its clinical use. In this study, we administered orally the LXR agonist T0901317 to male LDLR-/- mice fed a Western diet. This induced a persistent enhanced hypertriglyceridemia by largely increasing plasma triglyceride-rich VLDL. T0901317 treatment decreased atherosclerosis with a much more pronounced response and dose dependence in the innominate artery than in the aortic sinus. Lesions in the innominate artery were less complex containing mostly macrophage foam cells in T0901317-treated mice. However, in the aortic root, a significant reduction of atherosclerosis was seen only in the right coronary-related aortic sinus (RC) of T0901317-treated mice. Increasing the dose of T0901317 did not extend atheroprotection to the other sinuses of the aortic root. Lesions in the RC were less complex both in T0901317 and vehicle-treated mice with macrophage foam cells predominating. On the other hand, in T0901317-treated mice, the left coronary-related sinus (LC) lesions while not reduced in size, were more complex with a large fibrous cap and necrotic core, more collagen-positive areas, and variable macrophage foam cell content compared to vehicle-treated mice. These data suggest that activation of LXR by T0901317 had differential anti-atherosclerotic effects in two arterial regions in mice with hypertriglyceridemia.

Fig. 1

Plasma lipid levels in male LDLR−/− mice after 12 weeks of treatment with vehicle (control, n=10), or 0.2 (n=8), 0.5 (n=11), 1 (n=12), and 2 mg/kg/day (n=8) of T0901317. Significant differences between vehicle and T0901317-treated groups are indicated as * P<0.05, and ** P<0.001.

Fig. 2

LXR target gene expression in mouse intestine (A) and peritoneal macrophages (B). Male LDLR−/− mice were treated for two weeks with 0.5 mg/kg/day of T0901317 (n=7) or vehicle (n=8). Specific mRNA levels were measured by quantitative RT-PCR and presented relative to controls. Significant differences between control and T0901317-treated groups are indicated as * P<0.05, and ** P<0.001.

Fig. 3

Atherosclerosis in the innominate artery (A), aortic sinus (B) and three parts of the aortic sinus (C) named RC (D), LC (E), and NC (F). Male LDLR−/− mice on a Western diet were gavaged daily for 12 weeks with vehicle (control, n=10), 0.2 (n=8), 0.5 (n=11), 1 (n=12), or 2 mg/kg/day (n=8) of T0901317. Atherosclerotic lesions were measured as described in Methods. Significant differences between vehicle and compound treated groups are indicated as * P<0.05, and ** P<0.001.

Fig. 4

Analysis of atherosclerotic lesion composition. Lesions of the innominate artery (A–C) and aortic sinus (D, E) from mice treated with vehicle (A, D), or 0.5 (B), 1 (C, E) mg/kg/day of T0901317 were immunostained with MoMa-2 antibody to detect macrophages. (F) The percentage of macrophage foam cell area in the innominate artery lesions from vehicle (n=8) and 1 mg/kg/day of T0901317 (n=10) treated mice. H & E staining was also performed on LC (G, H), RC (J, K) and NC (L, M) lesions from vehicle (G, J, L) or 1 mg/kg/day of T0901317 (H, K, M)-treated mice. (I) Quantitative analysis of necrotic core area in LC lesions (n=8 in vehicle and n=10 in 1 mg/kg/day of T0901317 treated mice). Original magnification: 100 × (A–C), 40 × (D, E) and 200 × (G, H, J–M). Significant difference between vehicle and compound treated group is indicated as * P<0.05, and ** P<0.001.

Fig. 5

Collagen staining of LC lesions from vehicle (A, C, E) or 1 mg/kg/day of T0901317 (B, D, F)-treated mice. (A, B) Representative photomicrographs from trichrome staining (Masson). (C, D) Representative photomicrographs from sirius red staining. (E, F) Representative polarized photomicrographs from sirius red staining. Arrows indicate the fibrous cap. Original magnification: 200 ×.