The fate of olive oil polyphenols in the gastrointestinal tract: Implications of gastric and colonic microflora-dependent biotransformation

Abstract

We have conducted a detailed investigation into the absorption, metabolism and microflora-dependent transformation of hydroxytyrosol (HT), tyrosol (TYR) and their conjugated forms, such as oleuropein (OL). Conjugated forms underwent rapid hydrolysis under gastric conditions, resulting in significant increases in the amount of free HT and TYR entering the small intestine. Both HT and TYR transferred across human Caco-2 cell monolayers and rat segments of jejunum and ileum and were subject to classic phase I/II biotransformation. The major metabolites identified were an O-methylated derivative of HT, glucuronides of HT and TYR and a novel glutathionylated conjugate of HT. In contrast, there was no absorption of OL in either model. However, OL was rapidly degraded by the colonic microflora resulting in the formation of HT. Our study provides additional information regarding the breakdown of complex olive oil polyphenols in the GI tract, in particular the stomach and the large intestine.

Metabolism and Bioavailability of Olive Oil Polyphenols

“…Corona et al (2006) demonstrated that secoiridoids, which appear not to be absorbed in the small intestine, suffer bacterial catabolism in the large intestine with Ol undergoing rapid degradation by the colonic microflora producing Hyty as the major end product.…”

“…The effect of such environment on aglycone secoiridoids has been examined in vitro by incubating the compounds at 37 ºC in simulated gastric pH conditions and during normal physiological time frames (Corona et al, 2006;Pinto et al, 2011). Although hydrolysis takes place releasing free phenolic alcohols, a significant amount remains intact and thus, enters the small intestine unmodified.…”

Phenolic Content, Antioxidant and Antimicrobial Activities of “Chemlali” Olive Leaf (<i>Olea europaea </i>L.) Extracts

“…Oleuropein, the major phytochemical in olive leaf, is a complex phenol present in large quantities in olive leaves but in lower quantities in olive oil [6]. Oleuropein can be hydrolyzed to hydroxytyrosol, elenolic acid, oleuropein aglycone, and glucose [7,8].…”

Obtention and Characterization of Rosemary and Ash Tree Seed Extracts and Study of Their Preventive Effects on Metabolic Disorders

“…For example, an in vitro study showed that part of oleuropein, the main secoiridoid glycoside found in olives, is hydrolyzed in gastric conditions and another portion is degraded by the colonic microflora (Corona et al, 2006). The authors reported paracellular absorption and/or an active transport mechanism via SGLT1 (Edgecombe et al, 2000).…”

“…Resulting metabolites could then be subjected to classic Phase I/II biotransformation before reaching general circulation (Corona et al, 2006). As there is no information on bioavailability of nuzhenide or GI3, we can suppose that their mechanism of absorption is close to the absorption of oleuropein.…”