Bioavailability of gallic acid and catechins from grape seed polyphenol extract is improved by repeated dosing in rats: implications for treatment in Alzheimer's disease

Abstract

The present study explored the bioavailability and brain deposition of a grape seed polyphenolic extract (GSPE) previously found to attenuate cognitive deterioration in a mouse model of Alzheimer's disease (AD). Plasma pharmacokinetic response of major GSPE phenolic components was measured following intragastric gavage of 50, 100, and 150 mg GSPE per kg body weight. Liquid chromatography-mass spectrometry (LC-MS) analysis identified gallic acid (GA), catechin (C), and epicatechin (EC) in plasma of rats gavaged acutely with GSPE. Additionally, 4-methylgallic acid (4-OMeGA), 3'-methylcatechin (3'-OMeC), and 3'-methylepicatechin (3'-OMeEC) were identified as circulating metabolites of GSPE phenolic constituents. Cmax for individual GSPE constituents and their metabolites increased in a dose-dependent fashion (with increasing GSPE oral dose). Repeated daily exposure to GSPE was found to significantly increase bioavailability (defined as plasma AUC0-8h) of GA, C, and EC by 198, 253, and 282% relative to animals receiving only a single acute GSPE dose. EC and C were not detectable in brain tissues of rats receiving a single GSPE dose but reached levels of 290.7 +/-45.9 and 576.7 +/- 227.7 pg/g in brain tissues from rats administered GSPE for 10 days. This study suggests that brain deposition of GA, C, and EC is affected by repeated dosing of GSPE.

Figure 1

Chemical structure of gallic acid (GA), catechin (C), epicatechin (EC) and a basic proanthocyanidin (PAC) dimer (P2) and PAC trimer (P3). GSPE PAC’s are composed of individual units including C and EC linked to each other by either C4–C8 or C4–C6 linkages. Gallate is generally substituted to position 3 in the monmeric units but most have been hydrolyzed in the GSPE extract (MegaNatural-AZ) used in this study.

Figure 2

LC-UV separation of major GSPE PAC’s demonstrates the presence of gallic acid (GA), monomeric PAC’s (C and EC) along with dimer (P₂), trimer (P₃) and oligomeric PAC’s. Compounds were identified based on in line MS spectra as described by Wu et al. [24]. UV signal at 280nm is shown.

Figure 3

LC-MS separation of major GSPE phenolic constituents from an extract of rat plasma. LC-MS conditions can be seen in Material and Methods. Extracted ion chromatograms at169, 183, 289, and 303 m/z are shown. Peak identifications can be seen in Table 1.

Figure 4

Collected in-line MS spectrum of (A) peak 3 identified as EC and (B) peak 5 tentatively identified as 3′-OMeEC.

Figure 5

Plasma pharmacokinetic response of GA, C, EC and their corresponding methylated metabolites following intragastric gavage of () 50, () 100 and 150 mg GSPE per kg BW (●) before and (○) after pre-treatment with dose-escalation of GSPE. Data represents mean ± SEM n=8 rats per group.

Figure 6

LC-MS separation of major C and EC from extracts rat brain tissue collected after 10 day GSPE treatment in dose-escalation. LC-MS conditions can be seen in Material and Methods. Extracted ion chromatograms at 289 m/z is shown. Peak identifications can be seen in Table 1. Collected in-line MS spectrum of (A) peak 2 identified as C and (B) peak 3 identified EC is shown.

Figure 7

Concentration (pg/g) of C and EC in brain tissue of following intragastric gavage of 150 mg GSPE per kg BW before and after pre-treatment with dose-escalation of GSPE. No detectable (ND) catechins or metabolites were found in brain tissues of rats receiving a single acute dose of GSPE. Data represents mean ± SEM n=8 rats per group.