In Vitro Interaction of the HIV Protease Inhibitor Ritonavir with Herbal Constituents: Changes in P-gp and CYP3A4 Activity

Abstract

The purpose of this study was to evaluate in vitro interactions of commercially obtained pure herbal constituents with p-glycoprotein P-gp and cytochrome P-450 3A4 (CYP3A4) activities, which can further modulate the transcellular transport and metabolism kinetics of orally administered drugs. Caco-2 cells grown in the presence of 0.25 micromol/L 1alpha,25-dihydroxy vitamin D3 and multidrug-resistant 1 (MDR1) transfected MDCK cells were used as models to evaluate the effect of purified herbal constituents (quercetin, hypericin, hyperforin from St. John's wort, kaempferol from ginseng, silibinin from milk thistle, and allicin from garlic) on P-gp-mediated efflux of the human immunodeficiency virus (HIV) protease inhibitor ritonavir. In addition, the inhibitory effect of these constituents on CYP3A4-mediated metabolism was determined by using cortisol as a model compound. Silibinin and hyperforin did not significantly alter cellular uptake of H-ritonavir in Caco-2 cells. A similar result was also observed for silibinin when tested in MDR1-MDCK cells. Quercetin, hypericin, and kaempferol exhibited a remarkable inhibition of P-gp-mediated efflux of ritonavir by increasing its cellular uptake in these models. These values were also comparable with the inhibitory effect of quinidine in Caco-2 cells, a well-known inhibitor of P-gp, on ritonavir efflux from Caco-2 cells. Allicin exhibited a concentration-dependent inhibition of ritonavir efflux when tested on MDR1-MDCK cells. There was a significant decrease in the Apical to Basal/Basal to Apical (AP-BL/BL-AP) transport ratio of ritonavir in presence of hypericin, kaempferol, and quercetin. These herbal constituents inhibited the CYP3A4 activity when tested with the Vivid CYP3A4 assay kit, whereas silibinin did not alter cortisol metabolism. Hypericin showed a significant inhibition in reduced nicotinamide adenine dinucleotide phosphate (NADPH)-dependent metabolism of cortisol with 64.6% of intact drug at the end of a 1-hour study. Similarly, kaempferol and quercetin also caused substantial inhibition of cortisol metabolism with 89.7% and 90.1% of intact cortisol, respectively, compared with 45.9% in the control. Prolonged exposure of quercetin resulted in significant increase of mRNA expression of both MDR1 and CYP3A4 levels in Caco-2 cells. However, hyperforin caused upregulation of CYP3A4 and downregulation of MDR1, whereas the effect of silibinin and kaempferol remained inconclusive on these gene expressions. Hypericin, kaempferol, quercetin, and allicin inhibit the efflux and CYP3A4-mediated metabolism of xenobiotics in vitro. Hence, this study warns against the use of herbal constituents along with prescribed HIV protease inhibitors that are substrates for P-gp and/or CYP3A4.

Improving the oral bioavailability of beneficial polyphenols through designed synergies

“…Recent work by Molnar et al [49] has shown that a wide range of naturally occurring lipophilic phytochemicals (diterpenes, triterpines and carotenoids) were able to inhibit human Pgp in vitro at the low lg/ml range, whereas other combinations had positive synergistic activity. Using purified polyphenols on Pgp overexpressing cells in vitro, Patel et al [59] showed that quercetin, hypericin and kaempferol were able to increase the cellular uptake of ritonavir by five-to eightfold. It is also interesting to note that in vitro assays or short-term exposure to these polyphenols in vivo appears to inhibit the action of efflux pumps and increase substrate bioavailability, whilst chronic exposure in healthy volunteers actually increases the expression of Pgp and, hence, reduces the bioavailability of efflux pump substrate drugs [14,27].…”

Hyperforin, a new lead compound against the progression of cancer and leukemia?

“…However, contradictory results have been published concerning the regulation of MDR-1/P-gp by HF. Patel et al 58 observed that HF caused a downregulation of MDR1 in human Caco-2 epithelial cells. In contrast, Tian et al 59 reported that SJW extracts and HF increased in a reversible way the expression and function of P-gp in the intestinal LS 180 cell line.…”

Influence of the flavonoids apigenin, kaempferol, and quercetin on the function of organic anion transporting polypeptides 1A2 and 2B1

“…A study with Caco-2 cells provided some in vitro evidence that OATP2B1 may be involved in the translocation of quercetin from the apical to the basal compartment [29]. Quercetin seems to be a potent inhibitor of the OATP1A2-and OATP2B1-mediated transport represented by the determined K i values in this study.Interestingly, quercetin is also a potent inhibitor of CYP3A4 and P-glycoprotein [30].Considering that quercetin is also one of the most abundant flavonoids, foods and herbal preparations containing quercetin may be therefore associated with a high risk for food-drug or drug-drug interactions by influencing the intestinal drug uptake, metabolism, and excretion. Furthermore, the potency of inhibition of OATP1A2 and OATP2B1 by apigenin and quercetin was different for the investigated substrates BSP, fexofenadine and atorvastatin.…”