Ginsenoside Rb1 inhibits vascular calcification as a selective androgen receptor modulator.

Ginsenoside Rb1 (Rb1), a major component of ginseng, has a steroidal chemical structure, implying that it exerts sex hormone-like actions. Recent studies have been suggested cardioprotective actions of Rb1. However, the actions of Rb1 in vascular calcification, one of the significant pathological features associated with aging and atherosclerosis, have not been examined. In the present study, we examined the effects of Rb1 on vascular calcification, focusing on its androgen-like actions. Using inorganic phosphate (Pi)-induced calcification of vascular smooth muscle cells (VSMC), we found that Rb1, like testosterone, significantly inhibited calcium deposition in a concentration-dependent manner. Further, this inhibition of Rb1 was abolished by bicalutamide, an androgen receptor antagonist, but not by MPP or PHTPP, estrogen receptor α or ß antagonists. Rb1 significantly inhibited apoptosis, one of the regulatory mechanisms of calcification, and restored growth arrest-specific gene 6 (Gas6) expression that was suppressed by Pi. Moreover, Rb1 transactivated Gas6, and proximal androgen-responsive element (ARE) of the promoter region was found to be crucial for Gas6 transactivation. In contrast, in a human prostate cancer cell line, testosterone-induced ARE activity was abrogated by Rb1. This antagonistic effect was also confirmed by the transrepression and downregulation of prostate-specific antigen in the presence of testosterone and Rb1 together. Thus, these findings provide a novel mechanistic insight into the vasculoprotective actions of Rb1 as a selective androgen receptor modulator, i.e., inhibitory effects on VSMC calcification through androgen receptor-mediated Gas6 transactivation and antagonistic effects in prostate cancer cells.

Establishment of Novel Murine Model showing Vascular Inflammation-derived Cognitive Dysfunction.

Inflammation is a critical feature of aging and its related diseases, including cardiovascular diseases. Recent epidemiological studies demonstrated that abdominal aortic aneurysm (AAA), an aging-related vascular pathological condition, is associated with cognitive decline. However, the underlying mechanism, especially the role of vascular inflammation, is largely unknown because of lack of an available animal model. In this study, we examined whether vascular inflammation affects synaptic and cognitive dysfunction, using an AAA mouse model. In young (3 months) and middle-aged (12 months) C57BL/6J mice, AAA was induced by angiotensin II infusion with calcium chloride application. After 4 weeks of induction, aortic diameter was significantly increased and excessive Mac3-positive inflammatory cells infiltrated the destroyed aorta in middle-aged mice. AAA-induced middle-aged mice further exhibited cognitive impairment. Neuronal loss was observed in the CA3 region of the hippocampus. IBA1/MHCII-double-positive microglia activation was also seen in the hippocampus, suggesting that vascular inflammation drives neuroinflammation and subsequent cognitive dysfunction. Furthermore, we found that senescence-accelerated mice prone 8 exhibited robust AAA formation and a marked decrease of cognitive and synaptic function in the hippocampus mediated by inflammation. In conclusion, this novel murine model convincingly suggested the occurrence of vascular inflammation-derived cognitive dysfunction.

Protective effects of estrogen against vascular calcification via estrogen receptor α-dependent growth arrest-specific gene 6 transactivation.

Vascular calcification is one of the major complications of cardiovascular disease and is an independent risk factor for myocardial infarction and cardiac death. Postmenopausal women have a higher prevalence of vascular calcification compared with premenopausal women, suggesting protective effects of estrogen (E2). However, the underlying mechanisms of its beneficial effects remain unclear. In the present study, we examined the inhibitory effects of E2 on vascular smooth muscle cell (VSMC) calcification, and found that growth arrest-specific gene 6 (Gas6), a crucial molecule in vascular calcification, is transactivated by estrogen receptor α (ERα) in response to E2. In human aortic smooth muscle cells, physiological levels of E2 inhibited inorganic phosphate (Pi)-induced calcification in a concentration-dependent manner. This inhibitory effect was significantly abolished by MPP, an ERα-selective antagonist, and ERα siRNA, but not by PHTPP, an ERß-selective antagonist, and ERß siRNA, implicating an ERα-dependent action. Apoptosis, an essential process for Pi-induced VSMC calcification, was inhibited by E2 in a concentration-dependent manner and further, MPP abolished this inhibition. Mechanistically, E2 restored the inhibited expression of Gas6 and phospho-Akt in Pi-induced apoptosis through ERα. Furthermore, E2 significantly activated Gas6 transcription, and MPP abrogated this E2-dependent Gas6 transactivation. E2-BSA failed to activate Gas6 transcription and to inhibit Ca deposition in VSMC, suggesting beneficial actions of genomic signaling by E2/nuclear ERα. Taken together, these results indicate that E2 exerts inhibitory effects on VSMC apoptosis and calcification through ERα-mediated Gas6 transactivation. These findings indicate a potential therapeutic strategy for the prevention of vascular calcification, especially in postmenopausal women.