Abstract
While dietary or supplementary antioxidants are thought to inhibit or delay oxidation of biological molecules, their utility in vivo has been marred by equivocal evidence. Consumption of polyphenol rich foods has been thought to alleviate postprandial oxidative stress and/or improve endothelial function. Although, previous studies suggested the utility of allantoin as a biomarker of oxidative stress, controlled dose response studies with dietary antioxidants to test this in humans have been limited. We therefore investigated the effects of 2 doses of polyphenol rich curry consumption on postprandial plasma concentrations of allantoin, allantoin to uric acid ratio, F2-isoprostanes using liquid chromatography-tandem mass spectrometry (LCMS-MS) and measured endothelial function using peripheral arterial tonometry (endoPAT). In a randomized controlled crossover trial in 17 non-smoking, healthy, Chinese men, aged 23.7 ± 2.4 years and BMI 23.1 ± 2.3 kg/m2, the volunteers consumed 3 test meals in a random order, consisting of either non-curry Dose 0 Control (D0C, 0 g spices), or Dose 1 Curry (D1C, 6 g spices) or Dose 2 Curry (D2C, 12 g spices), after overnight fast. There were significant reductions in postprandial allantoin concentrations (p < 0.001) and allantoin to uric acid ratio (p < 0.001) at 2 h and 3 h following test meal consumption, indicating improvements in postprandial redox balance with increasing curry doses, although there were no differences between treatments on F2-isoprostane concentrations or on RHI (measured at 2 h only). Allantoin may have a utility as a biomarker of redox balance, in an acute setting. The study was registered at www.clinicaltrials.gov (Identifier No. NCT02599272).
Highlights
A number of recent studies have shown that the consumption of polyphenol-rich foods can simultaneously improve markers of postprandial oxidative stress (Umeno et al, 2016), markers of inflammatory response (Cerletti et al, 2015) as well as vascular function (Storniolo et al, 2014)
The test meals contained same total amounts of vegetables (180 g per portion), with Dose 0 Control (D0C) consisting of 130 g peeled eggplant and 50 g tomato puree, Dose 1 Curry (D1C) made of 90 g peeled eggplant and 90 g “curry base vegetables” and Dose 2 Curry (D2C) made of 180 g curry base vegetables, in the same ratio as D1C
Similar but independent, singledose trials using the same mixed herbs and spices mix added to hamburgers previously found significant reductions in other markers of postprandial oxidative stress such as plasma malondialdehyde (MDA) concentration in healthy volunteers (Li et al, 2013) as well as improvements in endothelial function, and decreases in urinary MDA excretion in type 2 diabetics, we did not observe any effects using our curry preparations on either plasma F2-isoprostanes or on endothelial function
Summary
A number of recent studies have shown that the consumption of polyphenol-rich foods can simultaneously improve markers of postprandial oxidative stress (Umeno et al, 2016), markers of inflammatory response (Cerletti et al, 2015) as well as vascular function (Storniolo et al, 2014). Markers of oxidative stress/redox balance used in the different studies have been rather variable and given the large inter-individual variability in polyphenol metabolism and the small numbers of participants involved, some of these studies could well have been underpowered All of these have led to several controversies regarding the roles and utilities of dietary (exogenous) antioxidants, defined as “substances in foods that significantly decreases the adverse effects of reactive oxygen species, reactive nitrogen species, or both on normal physiological function in humans” (Institute of Medicine Standing Committee on the Scientific Evaluation of Dietary Reference Institut, 1998), including polyphenols, in improving redox balance in healthy participants (Touyz, 2004). Recent reviews and commentaries have argued against the direct antioxidant role of dietary polyphenols in vivo, suggesting instead, alternative mechanisms through which dietary polyphenol intake appears to benefit metabolic functions which include modulation of gene expression, cell signaling, inflammation, mitochondrial function, insulin resistance, glucose, and lipid metabolism (Hollman et al, 2011; Kerimi and Williamson, 2016)
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