Bioavailability of blueberry-derived phenolic acid metabolites and their activity in endothelial cells

Abstract

Intake of blueberry polyphenols is believed to promote good cardiovascular health by preventing endothelial dysfunction. However, ingested polyphenols have limited bioavailability and their phenolic metabolites may be the active components in modulating their vascular bioactivity. Phenolic acids are recognised as an abundant class of metabolites established in the circulation following intake of berry polyphenols, but relatively little is known on how they affect vascular health at physiologically-relevant concentrations. Cell culture studies exploring the effects of bioavailable blueberry-derived phenolic acids on vascular function in endothelial cells are required to advance understanding of their potential vascular bioactivity. It was the aim of this thesis to identify bioavailable phenolic acid metabolites in human plasma following consumption of blueberry juice, and to determine their plasma concentration-time profiles for the design of phenolic acid mixtures that model circulating in vivo concentrations available to interact with the endothelium at different time segments. Oxidative stress and inflammation are important contributing factors of endothelial dysfunction. Therefore, the ability of each mixture to induce cellular antioxidant response proteins regulated by nuclear factor erythroid 2-related factor 2 (Nrf2) or to reduce endothelial cell monocyte adhesion under pro-inflammatory challenge with tumour necrosis factor alpha (TNFα), was investigated in cultured human umbilical vein endothelial cells (HUVECs). Nrf2 is a transcription factor that regulates the expression of cellular antioxidant response proteins important for vascular protection such as heme oxygenase-1 (HO-1) which removes heme released as a product of protein catabolism and glutamate-cysteine ligase modifier subunit (GCLM) which is important for glutathione synthesis. Blueberry-derived phenolic acid aglycones were able to significantly induce the expression of Nrf2-regulated HO-1 and GCLM proteins in HUVECs in the presence of a sub-lethal oxidative challenge presented by 2.5 μM H₂O₂. Furthermore, these metabolites were also found to significantly reduce adhesion of monocytes to HUVECs challenged with the pro-inflammatory cytokine, TNFα. Altogether, these findings suggest that at physiologically-observed concentrations achievable from a single serving of blueberry juice, phenolic acid metabolites could contribute to the prevention of endothelial dysfunction.