Effects of beetroot juice supplementation on vascular functional and structural changes in aged mice

This study investigated whether beetroot juice (BRJ) ingestion ameliorates aging-induced functional and structural changes in vasculature. Aged mice (98-100 weeks old) were supplemented with BRJ (nitrate: 3.5 mmol/L) or drinking water for 4 weeks and compared with young mice (12-15 weeks old). The vasorelaxant response of isolated aortas to acetylcholine was markedly weaker in aged mice than in young mice, but the attenuated relaxation was significantly improved in BRJ-supplemented aged mice. The acetylcholine-induced relaxation was completely abolished by N^ω -nitro-l-arginine methyl ester in all groups. Additionally, the response to sodium nitroprusside was comparable among the three groups. The aortic medial thickness was significantly greater in aged mice than in young mice, and BRJ supplementation did not suppress this thickening. Plasma nitrate levels were significantly higher in BRJ-supplemented aged mice than in non-supplemented aged mice. Conversely, non-supplemented aged mice had high plasma levels of thiobarbituric acid-reactive substances, but the levels were suppressed in BRJ-supplemented aged mice. These findings suggest that BRJ ingestion improves vascular endothelial dysfunction associated with aging, at least in part, by enhancing nitric oxide bioavailability and reducing oxidative stress. Therefore, beetroot ingestion may be a highly useful self-medication option to prevent vascular aging.

3D in vitro Model of Vascular Medial Thickening in Pulmonary Arterial Hypertension

In pulmonary arterial hypertension (PAH), excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) causes vascular medial thickening. Medial thickening is a histopathological hallmark of pulmonary vascular remodeling, the central disease process driving PAH progression. Pulmonary vascular remodeling causes stenosis and/or obstruction of small pulmonary arteries. This leads to increased pulmonary vascular resistance, elevated pulmonary arterial pressure, and ultimately right heart failure. To improve the survival of PAH patients, which remains at approximately 60% at 3 years after diagnosis, the development of novel PAH-targeted drugs is desired. To this end, a detailed understanding of the mechanisms underlying excessive PASMC proliferation and the medial thickening that ensues is necessary. However, a lack of in vitro models that recapitulate medial thickening impedes our deeper understanding of the pathogenetic mechanisms involved. In the present study, we applied 3-dimensional (3D) cell culture technology to develop a novel in vitro model of the pulmonary artery medial layer using human PAH patient-derived PASMCs. The addition of platelet-derived growth factor (PDGF)-BB, a mitogen known to promote excessive PASMC proliferation in PAH, resulted in increased thickness of the 3D-PAH media tissues. Conversely, administration of the PDGF receptor inhibitor imatinib or other clinical PAH drugs inhibited this medial thickening-inducing effect of PDGF-BB. Altogether, by using 3D cell culture technology, we report the generation of an in vitro model of medial thickening in PAH, which had hitherto not been successfully modeled in vitro. This model is potentially useful for assessing the ability of candidate PAH drugs to suppress medial thickening.

Fibroblast Angiotensin II Type 1a Receptors Contribute to Angiotensin II-Induced Medial Hyperplasia in the Ascending Aorta

OBJECTIVE

Angiotensin II (Ang II) infusion causes aortic medial thickening via stimulation of angiotensin II type 1a (AT1a) receptors. The purpose of this study was to determine the cellular loci of AT1a receptors that mediate this Ang II-induced aortic pathology.

APPROACH AND RESULTS

Saline or Ang II was infused into AT1a receptor floxed mice expressing Cre under control of cell-specific promoters. Initially, AT1a receptors were depleted in aortic smooth muscle cell and endothelium by expressing Cre under control of SM22 and Tie2 promoters, respectively. Deletion of AT1a receptors in either cell type had no effect on Ang II-induced medial thickening. To determine whether this effect was related to neural stimulation, AT1a receptors were depleted using an enolase 2-driven Cre. Depletion of AT1a receptors in neural cells attenuated Ang II-induced medial thickening of the ascending, but not descending aorta. Lineage tracking studies, using ROSA26-LacZ, demonstrated that enolase 2 was also expressed in adventitial cells adjacent to the region of attenuated thickening. To determine whether adventitial fibroblasts contributed to this attenuation, AT1a receptors in fibroblasts were depleted using S100A4 driven Cre. Similar to enolase 2-Cre, Ang II-induced medial thickening was attenuated in the ascending, but not the descending aorta. Lineage tracking demonstrated an increase of S100A4-LacZ positive cells in the media of the ascending region during Ang II infusion.

CONCLUSIONS

AT1a receptor depletion in fibroblasts attenuates Ang II-induced medial hyperplasia in the ascending aorta.