Hypercholesterolemia forms the background of several cardiovascular pathologies. LDL receptor-knockout (LDLR-KO) mice kept on a high-fat diet (HFD) develop high cholesterol levels and atherosclerosis (AS). Cannabinoid type 1 receptors (CB₁Rs) induce vasodilation, although their role in cardiovascular pathologies is still controversial. We aimed to reveal the effects of CB₁Rs on vascular function and remodeling in hypercholesterolemic AS-prone LDLR-KO mice. Experiments were performed on a newly established LDLR and CB₁R double-knockout (KO) mouse model, in which KO and wild-type (WT) mice were kept on an HFD or a control diet (CD) for 5 months. The vascular functions of abdominal aorta rings were tested with wire myography. The vasorelaxation effects of acetylcholine (Ach, 1 nM–1 µM) were obtained after phenylephrine precontraction, which was repeated with inhibitors of nitric oxide synthase (NOS) and cyclooxygenase (COX), Nω-nitro-L-arginine (LNA), and indomethacin (INDO), respectively. Blood pressure was measured with the tail-cuff method. Immunostaining of endothelial NOS (eNOS) was carried out. An HFD significantly elevated the cholesterol levels in the LDLR-KO mice more than in the corresponding WT mice (mean values: 1039 ± 162 mg/dL vs. 91 ± 18 mg/dL), and they were not influenced by the presence of the CB₁R gene. However, with the defect of the CB₁R gene, damage to the Ach relaxation ability was moderated. The blood pressure was higher in the LDLR-KO mice compared to their WT counterparts (systolic/diastolic values: 110/84 ± 5.8/6.8 vs. 102/80 ± 3.3/2.5 mmHg), which was significantly elevated with an HFD (118/96 ± 1.9/2 vs. 100/77 ± 3.4/3.1 mmHg, p < 0.05) but attenuated in the CB₁R-KO HFD mice. The expression of eNOS was depressed in the HFD WT mice compared to those on the CD, but it was augmented if CB₁R was knocked out. This newly established double-knockout mouse model provides a tool for studying the involvement of CB₁Rs in the development of hypercholesterolemia and atherosclerosis. Our results indicate that knocking out the CB₁R gene significantly attenuates vascular damage in hypercholesterolemic mice.

Background: Atherosclerosis forms the background of several cardiovascular pathologies. LDL receptor knockout (LDLR-KO) mice kept on a high-fat diet (HFD) develop high cholesterol levels. Previously we found that vasodilation responses in HFD LDLR-KO mice were improved in the absence of type 1 cannabinoid receptors (CB₁Rs). We aimed to reveal the effects of HFD and CB₁Rs on vascular contractile and structural properties. Methods: Experiments were performed on LDLR-CB₁R double knockout and wild type (WT) mice, kept on an HFD or control diet (CD) for 5 months. Thoracic aortas were isolated for Oil Red plaque staining and abdominal aorta segments for myography to obtain phenylephrine (Phe)-induced (100 nM–10 µM) contractile responses. Aorta samples were subjected to histology stainings with hematoxylin–eosin and resorcin–fuchsin (elastin density) and for smooth muscle actin (SMA) immunohistochemistry. Results: Phe-induced contractions significantly increased in HFD groups (p < 0.05) similarly in all genotypes. However, contractions were stronger with CD in CB₁R-KO compared to WT. Plaque areas were increased in LDLR-KO mice compared to WT, significant in HFD groups (p < 0.05). SMA increased to HFD, while elastin density remained similar, with the highest value in double KO-HFD. Intima/media ratio significantly decreased in double KO-HFD vs. CD. Conclusions: Our results indicate that HFD-treated LDLR-KO mice develop atherosclerosis with functional contractile and structural alterations modulated by CB₁Rs: absence of CB₁Rs elicited higher contraction properties with some modification in vascular remodeling indicating contribution of the CB₁R to cellular signalization controlling wall thickness and elasticity in pathological conditions.