Biological activity of anthocyanins and their phenolic degradation products and metabolites in human vascular endothelial cells
Human, animal, and in vitro data indicate significant vasoprotective activity of anthocyanins. However, few studies have investigated the activity of anthocyanin degradation products and metabolites which are likely to mediate bioactivity in vivo. The present thesis therefore examined the vascular bioactivity in vitro of anthocyanins, their phenolic degradants, and the potential for interactions between dietary bioactive compounds. Seven treatment compounds (cyanidin-, peonidin-, petunidin- & malvidin-3-glucoside, and protocatechuic, vanillic, and syringic acid) and two treatment combinations (cyanidin-3-glucoside or protocatechuic acid with epicatechin, quercetin, and ascorbic acid) were screened in a human endothelial cell model for effects on endothelial nitric oxide synthase (eNOS) activity (via ELISA & colourimetric assay), and NADPH oxidase (NOX)-mediated superoxide production (by cytochrome c reduction assay, optimised in-house). A bioactive treatment was then chosen to explore possible mechanisms of NOX inhibition, namely gene expression of NOX2, NOX4, p47phox, p67phox, p22phox, & haem oxygenase-1 (HO-1), and activation/expression of p47phox and HO-1 protein; using RT-qPCR and immunoblotting (optimised for cell stimulation conditions and qPCR reference genes). Differential bioactivity of parent anthocyanins and their phenolic degradants was observed at physiologically relevant concentrations, as only anthocyanins upregulated eNOS expression (by 4- to 7-fold; p < 0.01), whereas both anthocyanins and degradants appeared to reduce endothelial superoxide levels (by 1- to 8-fold; p < 0.05). The phenolic degradant vanillic acid significantly reduced (p < 0.05) superoxide by 2-fold at 1μM, and has been reported at low micromolar levels in human serum; therefore vanillic acid was selected to elucidate pathways potentially underlying observed bioactivity. Vanillic acid did not significantly modulate expression of NOX isoforms/subunits, but an apparent induction of the cytoprotective enzyme HO-1 by vanillic acid (2-fold increase) was observed in human umbilical vein and coronary artery endothelial cells, although changes were non-significant (p ≥ 0.3). In conclusion, anthocyanin phenolic degradants could enhance vascular function in vivo by decreasing superoxide production, and thus scavenging of the key mediator nitric oxide (NO). Vanillic acid might inhibit endothelial superoxide production through modulation of HO-1, thereby preserving NO bioavailability and vascular homoeostasis, and this pathway should be the focus of future research.
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