ABSTRACT
Amyloid beta-peptides (Aβ) are known to undergo active transport across the blood-brain barrier, and cerebral amyloid angiopathy has been shown to be a prominent feature in the majority of Alzheimer׳s disease. Quercetin is a natural flavonoid molecule and has been demonstrated to have potent neuroprotective effects, but its protective effect on endothelial cells under Aβ-damaged condition is unclear. In the present study, the protective effects of quercetin on brain microvascular endothelial cells injured by fibrillar Aβ 1-40 (fAβ 1-40) were observed. The results show that fAβ 1-40-induced cytotoxicity in human brain microvascular endothelial cells (hBMECs) can be relieved by quercetin treatment. Quercetin increases cell viability, reduces the release of lactate dehydrogenase, and relieves nuclear condensation. Quercetin also alleviates intracellular reactive oxygen species generation and increases superoxide dismutase activity. Moreover, it strengthens the barrier integrity through the preservation of the transendothelial electrical resistance value, the relief of aggravated permeability, and the increase of characteristic enzyme levels after being exposed to fAβ 1-40. In conclusion, quercetin protects hBMECs from fAβ 1-40-induced toxicity.
ABSTRACT
CONTEXT: The buds of Coreopsis tinctoria Nutt (Compositae) are used in the treatment of hypertension in the Uyghur folk medicine in China. OBJECTIVE: To investigate vasorelaxant properties of extracts and some flavonoids from C. tinctoria (CT) and their underlying mechanisms in isolated rat thoracic aortic rings. MATERIALS AND METHODS: Vasorelaxant effects of ethanol extracts of CT (CTA) and its flavonoids as well as water-ethanol eluates from CTA by AB-8 resins (CTAAâ¼CTAF) were evaluated on rat aortic rings pre-contracted with phenylephrine (PE, 1 µM) or high KCl (60 µM). We evaluated the effect of CTA, CTAD and CTAE on PE-induced contraction in a Ca²âº-free medium and a dose-effect curve of Ca²âº in pre-contracted ring with high KCl. RESULTS: Endothelial removal did not modify the effect of CTAD and CTAE (3.00 g/L) neither on PE-pre-contracted rings (164.78 ± 21.44 and 191.47 ± 16.75%) nor on KCl-pre-contracted rings (75.68 ± 10.76 and 125.14 ± 17.41%) compared with intact-endothelium rings pre-contracted with high KCl (100.49 ± 17.30 and 110.81 ± 16.33%). CTAD and CTAE (3.00 g/L) down-regulated the dose-effect curve of Ca²âº in pre-contraction with high KCl, and inhibited the pre-contraction with PE in a Ca²âº-free medium (p < 0.05). Seven flavonoids were obtained from CTAD, of which luteolin (5) and quercetin (6) were found to be the most effective relaxation in rings precontracted with PE (EC50: 0.006 and 0.039 g/L, p < 0.05) or high KCl (EC50: 0.023 and 0.045 g/L, p < 0.05). DISCUSSION AND CONCLUSION: These data demonstrated the vasorelaxant effect of CT, and its mechanism is likely due to an inhibitory effect on calcium movements through cell membranes.
