A dose-response study of the bioavailability of grape seed proanthocyanidin in rat and lipid-lowering effects of generated metabolites in HepG2 cells.

Hyperlipidemia is one of the principal causes of cardiovascular disease and proanthocyanidins (PAs) regulate lipid homeostasis. This study aims to evaluate the concentration of PAs in rat serum after the administration of different doses of PAs and to determine the capacity of these metabolites to reduce de novolipid synthesis in HepG2 cells. Two hours after oral administration of different doses of a grape seed proanthocyanidin extract (GSPE) (1000, 375, 250 and 125mg/kg), serum was semi-purified and characterised by HPLC-ESI-MS/MS before analysing the synthesis and secretion of lipids in HepG2 cells. Results showed a dose-dependent appearance of metabolised PAs in serum at doses up to 375mg/kg and saturation at 1000mg/kg of GSPE. A reduction in cholesterol esters (CE), free cholesterol (FC) and triglycerides (TG) synthesis was observed without dose-dependence when the cells were treated with PAs metabolites. Moreover, a low dose of metabolites (125mg/kg) was sufficient to reduce FC and TG synthesis. In conclusion, the study demonstrated that PAs metabolise in a dose-dependent manner up to 370mg/kg but not dose-dependent effect was shown in reducing the de novosynthesis of lipids.

Serum metabolites of proanthocyanidin-administered rats decrease lipid synthesis in HepG2 cells.

The regular consumption of flavonoids has been associated with reduced mortality and a decreased risk of cardiovascular diseases. The proanthocyanidins found in plasma are very different from the original flavonoids in food sources. The use of physiologically appropriate conjugates of proanthocyanidins is essential for the in vitro analysis of flavonoid bioactivity. In this study, the effect of different proanthocyanidin-rich extracts, which were obtained from cocoa (CCX), French maritime pine bark (Pycnogenol extract, PYC) and grape seed (GSPE), on lipid homeostasis was evaluated. Hepatic human cells (HepG2 cells) were treated with 25 mg/L of CCX, PYC or GSPE. We also performed in vitro experiments to assess the effect on lipid synthesis that is induced by the bioactive GSPE proanthocyanidins using the physiological metabolites that are present in the serum of GSPE-administered rats. For this, Wistar rats were administered 1 g/kg of GSPE, and serum was collected after 2 h. The semipurified serum of GSPE-administered rats was fully characterized by liquid chromatography tandem triple quadrupole mass spectrometry (LC-QqQ/MS(2)). The lipids studied in the analyses were free cholesterol (FC), cholesterol ester (CE) and triglycerides (TG). All three proanthocyanidin-rich extracts induced a remarkable decrease in the de novo lipid synthesis in HepG2 cells. Moreover, GSPE rat serum metabolites reduced the total percentage of CE, FC and particularly TG; this reduction was significantly higher than that observed in the cells directly treated with GSPE. In conclusion, the bioactivity of the physiological metabolites that are present in the serum of rats after their ingestion of a proanthocyanidin-rich extract was demonstrated in Hep G2 cells.

Inhibition of angiotensin-converting enzyme activity by flavonoids: structure-activity relationship studies.

Previous studies have demonstrated that certain flavonoids can have an inhibitory effect on angiotensin-converting enzyme (ACE) activity, which plays a key role in the regulation of arterial blood pressure. In the present study, 17 flavonoids belonging to five structural subtypes were evaluated in vitro for their ability to inhibit ACE in order to establish the structural basis of their bioactivity. The ACE inhibitory (ACEI) activity of these 17 flavonoids was determined by fluorimetric method at two concentrations (500 µM and 100 µM). Their inhibitory potencies ranged from 17 to 95% at 500 µM and from 0 to 57% at 100 µM. In both cases, the highest ACEI activity was obtained for luteolin. Following the determination of ACEI activity, the flavonoids with higher ACEI activity (i.e., ACEI >60% at 500 µM) were selected for further IC(50) determination. The IC(50) values for luteolin, quercetin, rutin, kaempferol, rhoifolin and apigenin K were 23, 43, 64, 178, 183 and 196 µM, respectively. Our results suggest that flavonoids are an excellent source of functional antihypertensive products. Furthermore, our structure-activity relationship studies show that the combination of sub-structures on the flavonoid skeleton that increase ACEI activity is made up of the following elements: (a) the catechol group in the B-ring, (b) the double bond between C2 and C3 at the C-ring, and (c) the cetone group in C4 at the C-ring. Protein-ligand docking studies are used to understand the molecular basis for these results.