Colonic metabolism of dietary grape seed extract: Analytical method development, effect on tight-junction proteins, tissue accumulation, and pan-colonic pharmacokinetics

Procyanidins (PCs) have been extensively investigated for their potential health protective activities, but the prospective bioactivities are limited by their poor bioavailability. The majority of the ingested dose remains unabsorbed and reaches the colon where extensive microbial metabolism occurs. The objectives of these studies are to better understand the roles and activities of PCs in the lower gastrointestinal tract. First, a new high-throughput Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry method was developed to efficiently analyze PCs and an extensive profile of their microbial metabolites. This method is sufficiently sensitive and effective in simultaneously extracting and measuring native PCs and their microbial metabolites in biological samples. Furthermore, administration of grape seed extract increased the expression of gut junction protein occludin and reduced levels of fecal calprotectin, which suggests an improvement of gut barrier integrity and a potential modulation of endotoxemia. Additionally, chronic supplementation of the diet with flavanols did not increase colonic tissue accumulation of PCs or their microbial metabolites over a 12 week feeding study. This was the first long-term study of its kind, and the results indicate that we still do not fully understand the outcome of ingested flavanols in the colon during chronic exposure rather than acute doses. Lastly, new understanding of the microbial metabolism of PCs in the colon has been reached by studying the colon as 4 segments, rather than as a complete unit as previous studies have done. Data show that a gradient is established along the length of the colon for both PCs and their metabolites, with PCs reaching highest concentrations within 3 h after ingestion, while metabolites reach maximum concentrations anywhere form 3-18 h after ingestion. Moreover, data indicate the progressive, step-wise degradation of PCs into small metabolites throughout the length of the colon. Overall, there is greater understanding of the colonic metabolism of dietary PCs derived from GSE and cocoa, the accumulation of these compounds, and their effect on gut permeability. Future work will build off of these novel studies, and will continue to advance the understanding of the health benefits of dietary PCs.