Increased acute blood flow induced by the aqueous extract of Euterpe oleracea Mart. fruit pulp in rats in vivo is not related to the direct activation of endothelial cells

Ethnopharmacological relevance: Scientific evidence supports the antioxidant, anti-inflammatory and anti-lipidemic properties of Euterpe oleracea Mart. (açaí), which all converge to reduce cardiovascular risks. Macerating the pulp of açaí fruit produces a viscous aqueous extract (AE) rich in flavonoids that is commonly used in food production. In addition to nutritional aspects, cardiovascular benefits are attributed to AE by traditional medicine.

Aim of the study: Evaluation of AE impact on blood flow in vivo in rats and investigation of the mechanism underlying this response in vitro in rat endothelial cells (RECs).

Materials and methods: For the measurement of acute blood flow, a perivascular ultrasound probe was used in Wistar rats. The in vitro assays employed REC to evaluate: concentration (1-1000 μg/mL) and time response (2-180 min) of AE in MTT cell viability assays; nitric oxide (NO) levels measurement and intracellular calcium handling using DAF-2DA and Fluo-4-AM, respectively; cellular biopterin content by HPLC; activation of Akt pathway using western blot analysis. For the chemical analyses of AE, stock solutions of the standards (+)catechin and quercetin were used for obtaining linear calibration curves. Identification and quantification of flavonoids in AE were based on comparisons with the retention times, increase in peak area determine by co-injection of AE with standards, UV-Vis scan and standard curves of known spectra. Results were expressed as mean ± standard deviation and data were analyzed using ANOVA followed by Tukey's post-test (p < 0.05).

Results: Although in vivo data have revealed the participation of NO in increasing of acute blood flow on abdominal aorta, in vitro analysis demonstrated that vasodilatation AE-induced is not related to its direct action on endothelial cells inducing eNOS activation. Besides, we demonstrated in isolated endothelial cells that highest concentrations of AE caused a reduction in NO levels, effect that could be partly justified by inhibition of Akt phosphorylation which, in turn, could decrease NOS activation. The involvement of cell transduction pathways involving variations in intracellular calcium and biopterins concentration were discarded. The participation of catechin and quercetin, identified in AE, was postulated to induce the responses of AE in REC.

Conclusions: Despite the responses in vitro, vasodilation prevailed in vivo, probably by activating intermediate pathways, validating a potential beneficial effect of AE in reducing cardiovascular risks.