Mutual interactions between flavonoids and enzymatic and transporter elements responsible for flavonoid disposition via phase II metabolic pathways

Transmembrane transport of steviol glucuronide and its potential interaction with selected drugs and natural compounds

Steviol glucuronide (SVG) is the major metabolite derived from steviol, the aglycone of stevioside and rebaudioside A. After the ingestion of stevioside and rebaudioside A, SVG is formed and excreted into the urine in humans. In the present study, transporter mediated efflux and uptake of SVG was investigated in order to understand molecular mechanisms underlying its renal clearance. Results showed that SVG was not a substrate of efflux transporters BCRP, MRP2, MATE1 or P-gp. In contrast, OAT3 played a predominant role in the uptake of SVG in comparison to OATP1B1, OATP1B3, or OATP2B1. Quercetin, telmisartan, diclofenac, and mulberrin displayed a relatively strong inhibition against OAT3 mediated uptake of SVG with IC50 values of 1.8, 2.9, 8.0, and 10.0 μM, respectively. Because OAT3 is a major uptake transporter in the kidney, inhibition of OAT3 activity may alter SVG's renal clearance by drugs and natural compounds that are used concomitantly with stevia leaf extracts.

Pennyroyal and gastrointestinal cells: multi-target protection of phenolic compounds against t-BHP-induced toxicity

Pennyroyal infusion maintains gastrointestinal cells antioxidant balance.

Membrane transport of nobilin conjugation products and use of the extract of Chamomillae romanae flos influence absorption of nobilin in the Caco-2 model

The purpose of this work was to investigate the role of bioconjugation and carrier mediated efflux of conjugation products in the absorption mechanism of the sesquiterpene lactone nobilin in the Caco-2 model in vitro and to elucidate the impact of the extract of Chamomillae romanae flos and its ingredients on absorption. Transport experiments with inhibitors of P-gp, BCRP, and MRPs were performed to detect efflux and its connection to bioconversion and the effect of different ingredients of the plant extract on absorption processes was determined. Permeability, transport and bioconversion parameter values were deduced by kinetic multi-compartment modeling. Nobilin exhibited high permeability, low relative absorption and fast bioconversion producing glucuronide, cysteine conjugate, and glutathione conjugate that were transported by P-gp (the first two), apical MRP2 and basal MRP3 and possibly MRP1 out of the cell. Inhibition of efflux resulted in diminished bioconjugation and improved absorption. The extract increased the relative fraction absorbed primarily by directly inhibiting bioconversion, and by reducing efflux. Individual extract ingredients could only partly explain this effect. Extensive bioconversion, hence, limited absorption of nobilin in the Caco-2 model and the interplay between conjugation and efflux was shown to provide a possible mechanism for absorption increase. Plant extract increased absorption by this mechanism in addition to metabolic enzyme inhibition.

Dietary supplementation with cocoa flavanols does not alter colon tissue profiles of native flavanols and their microbial metabolites established during habitual dietary exposure in C57BL/6J mice

Metabolism of flavanols (catechins, procyanidins) by gut microbiota has been extensively characterized. Comparatively little is known about accumulation of flavanols and their metabolites in the colon tissues, particularly during chronic exposure to low doses. Mice were fed low doses of cocoa flavanols for 12 weeks. Supplementation of the control diet with flavanols did not increase colonic tissue accumulation of flavanols nor microbial metabolites versus control. The type of cocoa flavanols did not affect colonic tissue accumulation of native flavanols or metabolites. Total phenolic content of the diets indicated that these results are not explained by background levels of undetected phenolics in the control diet. This is the longest known chronic flavanol feeding study to examine colonic tissue accumulation. Vast differences appear to exist between acute high doses and chronic low doses, to which gut microbiota and epithelium adapt. These results indicate that the fate of flavanols in the colon during chronic exposure is not fully understood.

Quercetin-3-O-β-D-glucopyranosyl-(4→1)-α-L-rhamnoside metabolites in the rat using UPLC-Q-TOF/MS

Ultraperformance liquid chromatography/quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF/MS) and the Metabolynx™ software, combined with mass defect filtering, were applied to identity the metabolites of quercetin-3-O-β-D-gluco-pyranosyl-(4→1)-α-L-rhamnoside (QGR) in rats after intravenous administration. MS(E) was used for simultaneous acquisition of precursor ion information and fragment ion data at high and low collision energy in one analytical run, which facilitated the rapid structural characterization of eight metabolites in rat plasma, urine and bile. The results indicated that methylation and glucuronidation were the major metabolic pathways of QGR in vivo. The present study provided important information about the metabolism of QGR which will be useful for fully understanding the mechanism of action of this compound. Furthermore, this work demonstrated the potential of the UPLC-Q-TOF/MS approach using Metabolynx for rapid and automated research of the metabolites of natural products.

The gut microbiota ellagic acid-derived metabolite urolithin A and its sulfate conjugate are substrates for the drug efflux transporter breast cancer resistance protein (ABCG2/BCRP)

The breast cancer resistance protein (BCRP/ABCG2) is a drug efflux transporter that can affect the pharmacological and toxicological properties of many molecules. Urolithins, metabolites produced by the gut microbiota from ellagic acid (EA) and ellagitannins, have been acknowledged with in vivo anti-inflammatory and cancer chemopreventive properties. This study evaluated whether urolithins (Uro-A, -B, -C, and -D) and their main phase II metabolites Uro-A sulfate, Uro-A glucuronide, and Uro-B glucuronide as well as their precursor EA were substrates for ABCG2/BCRP. Parental and Bcrp1-transduced MDCKII cells were used for active transport assays. Uro-A and, to a lesser extent, Uro-A sulfate showed a significant increase in apically directed translocation in Bcrp1-transduced cells. Bcrp1 did not show affinity for the rest of the tested compounds. Data were confirmed for murine, human, bovine, and ovine BCRP-transduced subclones as well as with the use of the selective BCRP inhibitor Ko143. The transport inhibition by Uro-A was analyzed by flow cytometry compared to Ko143 using the antineoplastic agent mitoxantrone as a model substrate. Results showed that Uro-A was able to inhibit mitoxantrone transport in a dose-dependent manner. This study reports for the first time that Uro-A and its sulfate conjugate are ABCG2/BCRP substrates. The results suggest that physiologically relevant concentrations of these gut microbiota-derived metabolites could modulate ABCG2/BCRP-mediated transport processes and mechanisms of cancer drug resistance. Further in vivo investigations are warranted.