Effect of honey and sugars on the metabolism and disposition of naringin in rabbits

Effects of glucose, fructose and 5-hydroxymethyl-2-furaldehyde on the presystemic metabolism and absorption of glycyrrhizin in rabbits

Our previous study reported that co-administration of honey significantly increased the serum levels of glycyrrhetic acid (GA) after oral administration of glycyrrhizin (GZ) in rabbits. The components of honey are sucrose, glucose, fructose and 5-hydroxymethyl-furaldehyde (HMF). To clarify the causative component(s) in honey that altered the metabolic pharmacokinetics of GZ, rabbits were given GZ (150 mg kg(-1)) with and without glucose (5 g/rabbit), fructose (5 g/rabbit) and HMF (1 mg kg(-1)), respectively, in crossover designs. An HPLC method was used to determine concentrations of GZ and GA in serum as well as GA and 3-dehydroglycyrrhetic acid (3-dehydroGA) in faeces suspension. A noncompartment model was used to calculate the pharmacokinetic parameters and analysis of variance was used for statistical comparison. Our results indicated that the area under curve (AUC) of GA was significantly increased by 29% when HMF was coadministered, whereas the pharmacokinetics of GZ and GA were not significantly altered by coadministration of glucose or fructose. An in-vitro study, using faeces to incubate GZ and GA individually, indicated that HMF significantly inhibited the oxidation of GA to 3-dehydroGA and this may explain the enhanced GA absorption in-vivo. It was concluded that HMF is the causative component in honey that affects the presystemic metabolism and pharmacokinetics of GZ in-vivo.

Dietary polyphenols decrease glucose uptake by human intestinal Caco-2 cells

The effect of different classes of dietary polyphenols on intestinal glucose uptake was investigated using polarised Caco-2 intestinal cells. Glucose uptake into cells under sodium-dependent conditions was inhibited by flavonoid glycosides and non-glycosylated polyphenols whereas aglycones and phenolic acids were without effect. Under sodium-free conditions, aglycones and non-glycosylated polyphenols inhibited glucose uptake whereas glycosides and phenolic acids were ineffective. These data suggest that aglycones inhibit facilitated glucose uptake whereas glycosides inhibit the active transport of glucose. The non-glycosylated dietary polyphenols appear to exert their effects via steric hindrance, and (-)-epigallochatechingallate, (-)-epichatechingallate and (-)-epigallochatechin are effective against both transporters.

Influence of honey on the gastrointestinal metabolism and disposition of glycyrrhizin and glycyrrhetic acid in rabbits

To investigate the effects of honey on the pharmacokinetics of glycyrrhizin and glycyrrhetic acid, administration of glycyrrhizin or glycyrrhetic acid with and without honey was carried out in rabbits in a randomized crossover design. An in vitro study using rabbit fecal flora was employed to elucidate the mechanism of the interaction. HPLC methods were used for the determination of glycyrrhizin, glycyrrhetic acid and 3-dehydroglycyrrhetic acid concentrations in serum and feces. Paired and unpaired Student's t-tests were used for statistical comparisons for in vivo and in vitro studies, respectively. Our study indicated that the area under the curve (AUC0-t) of glycyrrhetic acid was significantly enhanced by 53% when honey was concomitantly given with glycyrrhizin, whereas that of glycyrrhizin was not significantly altered. Nevertheless, lack of effect was observed when honey was concurrently given with glycyrrhetic acid. Fecal study indicated that both the hydrolysis of glycyrrhizin to glycyrrhetic acid and subsequent oxidation of glycyrrhetic acid to 3-dehydroglycyrrhetic acid were significantly affected in the presence of honey to result in more glycyrrhetic acid available for absorption. It could be concluded that honey significantly affected the gastrointestinal metabolism of glycyrrhizin and resulted in the increased glycyrrhetic acid exposure. Therefore, honey might enhance the efficacy and adverse effects of glycyrrhizin.