| dc.description.abstract | Phenolic compounds circulate to their sites of action bound to human serum albumin (HSA), whether injected into the bloodstream or absorbed from the human GI tract, and consequently, molecular interactions with albumin may influence phenolic biological activity. HSA associates with a variety of ligands, endogenous and exogenous, and serves as the conveyor to their sites of action, metabolism or elimination, though this physiological aspect is often neglected in literature reviews and experimentation. Thus, the objective of the following studies was to investigate the role of the albumin-phenolic interaction in preclinical and clinical models. To address the variability commonly associated with food and nutrition studies, gallotannins from Rhus coriaria (sumac) were used because gallotannin bonds are hydrolyzable by commercial enzymes and sumac is a rich source of hydrolyzable tannins, thereby making the product of sumac gallotannin hydrolysis, gallic acid (GA) and its metabolite methyl gallate (MG), more easily targeted and enriched in sumac tea study treatments. Three hypotheses were tested: (1) the biophysical interaction between GA, MG and albumin in a fluorescence quenching assay, (2) the effect of albumin-phenolic interaction on GA, MG antiproliferative activity in a HepG2 cancer cell model, and (3) the effect of albumin-phenolic interaction on the evaluation of a food processing technique in a pilot human clinical trial. The results of the biophysical study showed that MG associated with albumin significantly more than GA (MG, KSV= 9.97E+03 ± 7.01E+01; GA, KSV= 1.35E+03 ± 1.55E+01, p<0.05) and this result was attributed to the greater hydrophobic character of MG provided by the methyl group substitution about the phenolic ring. The results of the in vitro antiproliferative activity assay (MTT) in HepG2 cells showed that MG was significantly more potent (p<0.05) when assayed alone (MG IC₅₀ = 310 ± 52 µM, GA IC₅₀ = 436 ± 25 µM, but significantly less potent (p<0.05) when combined with HSA (MG+HSA IC₅₀ = 5167 ± 289 µM, GA+HSA IC₅₀ = 2466 ± 340 µM). Accordingly, the human clinical trial LC-MS method performance analyses revealed that the albumin-rich, human plasma matrix suppressed the signal of the internal standard (IS) ethyl gallate (EG) significantly more (p<0.05) than in mobile phase. However, a significant increase in GA absorption was still observed between tea treatments hydrolyzed with tannase (Pre-Treated and Co-Consumed treatments) and the unhydrolyzed control. In summary, these results suggest that phenolic bioactivity and bioavailability are dependent upon albumin-binding. | |
