Effect of luteolin and apigenin on rosmarinic acid bioavailability in Caco-2 cell monolayers Pedro L. Fal´ e, ab Lia Ascens~ ao b and Maria L. M. Serralheiro * a Herbal teas are usually complex mixtures of therapeutically active compounds. The present study is focused on the interference of flavonoids on the bioavailability of rosmarinic acid, as these types of compounds are often present together in decoctions of medicinal plants, namely Lamiaceae species. The bioavailability of rosmarinic acid was analysed in the decoction of P. barbatus and in mixtures with apigenin and luteolin. Rosmarinic acid in the herbal tea showed a 43% bioavailability through the Caco-2 cells when luteolin and apigenin were approximately 30 mM each. In the artificial mixtures the bioavailability could be increased to 90% when the concentration of flavonoids was increased to 90 mM. The co-administration of substrates of known intestinal transport systems, Pgp, Oatp and MCT, showed that the extract components not only modulated the activity of these transporters but also their own bioavailability was dependent on them. Our results demonstrate that plant extracts with a high diversity of polyphenol compounds may have higher bioavailability than that predicted by the isolated compounds. 1 Introduction Herbal teas are among the oldest and most common drinks in human culture and are consumed for their pleasant avour and/or for their health improving properties. These plant aqueous extracts are oen composed of polyphenolic compounds such as phenolic acids and avonoids. These types of compounds have been reported for the composition of several taxonomically unrelated medicinal plants, 1 which proved to be therapeutically active. Previous studies demonstrated that the herbal tea from leaves of Plectranthus barbatus (Lamiaceae) has relevant in vitro antioxidant and anti-acetylcholinesterase activities, which are due to its main components: rosmarinic acid, avonoid glucu- ronides (apigenin, luteolin and acacetin glucuronides), and abietane diterpenoids. 2,3 Rosmarinic acid and the avonoid components remained aer in vitro digestion of the P. barbatus aqueous extract with gastric and pancreatic juices, but avonoid glucuronides were hydrolysed into their aglycones by b-glucuronidase of the microorganisms in the gut ora. 3 The abietane diterpenoids were transformed by the pancreatic juice and become non-active. 3 When the P. barbatus extract was intragastrically administered to rats its components were found in the plasma and a decrease in brain acetylcholinesterase activity was observed. 4 The signicant activities of the plant extract, mainly due to its main component rosmarinic acid, increase the importance of studies on the interaction of other compounds in the bioavailability of rosmarinic acid. Rosmarinic acid, apigenin and luteolin, the main constitu- ents of P. barbatus herbal tea, are very commonly found together in many other herbal teas and foodstuffs containing Lamiaceae species such as marjoram, melissa, oregano, peppermint, rosemary, sage, spearmint and thyme. 5 However, little is known about the way that these compounds affect the bioavailability of each other. Nevertheless, it is known that phenolic acids and avonoids interact with transport systems in intestinal cells, such as the monocarboxylic acid transporters (MCT), 6 the ABC transporters P-glycoprotein (Pgp) and multidrug resistance proteins (MRP), which actively transport or inhibit them. 7 The MCT4, MCT5, MRP1, MRP3 and MRP5 transporters, located in the basolateral membrane of the intestinal cells, promote the transport of their substrates to the bloodstream, while Pgp and MRP2, located in the apical membrane, promote the transport of their substrates from the intracellular compartment to the intestinal lumen. 6,8,9 The MCT1 transporter is located in the apical as well as in the basolateral membrane of the intestinal membrane. 9,10 The aim of this study was to evaluate the permeation through intestinal Caco-2 cell monolayers of mixtures of phenolic compounds usually present in herbal teas (rosmarinic acid, luteolin and apigenin) in a proportion similar to that found in these aqueous extracts, taking as a model the decoc- tion extract of P. barbatus leaves. This study focused on the differences in the bioavailability of mixtures of puried compounds versus the bioavailability of mixtures of compounds, as usually they occur in herbal teas. The effect of a Centro Qu´ ımica e Bioqu´ ımica da Faculdade de Ciˆ encias da Universidade de Lisboa, Edif´ ıcio C8, Campo Grande, 1749-016 Lisboa, Portugal. E-mail: mlserralheiro@fc. ul.pt; Fax: +351 217500088; Tel: +351 217500925 b Centro de Biotecnologia Vegetal (IBB), Faculdade de Ciˆ encias da Universidade de Lisboa, Edif´ ıcio C2, Campo Grande, 1749-016 Lisboa, Portugal Cite this: Food Funct., 2013, 4, 426 Received 9th October 2012 Accepted 20th November 2012 DOI: 10.1039/c2fo30318c www.rsc.org/foodfunction 426 | Food Funct., 2013, 4, 426–431 This journal is ª The Royal Society of Chemistry 2013 Food & Function PAPER