St. John's Wort constituents modulate P-glycoprotein transport activity at the blood-brain barrier.
OBJECTIVE
The purpose of this study was to investigate the short-term signaling effects of St. John's Wort (SJW) extract and selected SJW constituents on the blood-brain barrier transporter P-glycoprotein and to describe the role of PKC in the signaling.


METHODS
Cultured porcine brain capillary endothelial cells (PBCEC) and freshly isolated brain capillaries from pig were used as in vitro/ex vivo blood-brain barrier model. SJW modulation of P-glycoprotein function was studied in PBCEC using a calcein-AM uptake assay and in isolated pig brain capillaries using the fluorescent cyclosporine A derivative NBD-CSA and confocal microscopy.


RESULTS
SJW extract and the constituents hyperforin, hypericin, and quercetin decreased P-glycoprotein transport activity in a dose- and time-dependent manner. SJW extract and hyperforin directly inhibited P-glycoprotein activity, whereas hypericin and quercetin modulated transporter function through a mechanism involving protein kinase C. Quercetin at high concentrations decreased P-glycoprotein transport activity, but increased transporter function at low concentrations. This increase in P-glycoprotein activity was likely due to trafficking and membrane insertion of vesicles containing transporter protein.


CONCLUSIONS
Our findings provide new insights into the short-term interaction of SJW with P-glycoprotein at the blood-brain barrier. They are of potential relevance given the wide use of SJW as OTC medication and the importance P-glycoprotein has for CNS therapy.
Institute of Pharmacy and Molecular Biotechnology, Ruprecht-Karls-University Heidelberg, INF 366, 69120, Heidelberg, Germany.
Melanie
M
Ott
Miriam
M
Huls
Michael G
MG
Cornelius
Gert
G
Fricker
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects*; D001812:Blood-Brain Barrier / Q000187:drug effects*; D015153:Blotting, Western; D002196:Capillaries / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D016572:Cyclosporine; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes; D020902:Hypericum / Q000737:chemistry*; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D011493:Protein Kinase C / Q000378:metabolism; D011794:Quercetin / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013552:Swine
C091682:(N-5-(4-nitrobenzofurazan-7-yl)lysyl(8))cyclosporine; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D005452:Fluoresceins; D005456:Fluorescent Dyes; C085925:calcein AM; D016572:Cyclosporine; D011794:Quercetin; D011493:Protein Kinase C