Acetaminophen Modulates P-Glycoprotein Functional Expression at the Blood-Brain Barrier by a Constitutive Androstane Receptor–Dependent Mechanism

Abstract

Effective pharmacologic treatment of pain with opioids requires that these drugs attain efficacious concentrations in the central nervous system (CNS). A primary determinant of CNS drug permeation is P-glycoprotein (P-gp), an endogenous blood-brain barrier (BBB) efflux transporter that is involved in brain-to-blood transport of opioid analgesics (i.e., morphine). Recently, the nuclear receptor constitutive androstane receptor (CAR) has been identified as a regulator of P-gp functional expression at the BBB. This is critical to pharmacotherapy of pain/inflammation, as patients are often administered acetaminophen (APAP), a CAR-activating ligand, in conjunction with an opioid. Our objective was to investigate, in vivo, the role of CAR in regulation of P-gp at the BBB. Following APAP treatment, P-gp protein expression was increased up to 1.4-1.6-fold in a concentration-dependent manner.Additionally, APAP increased P-gp transport of BODIPY-verapamil in freshly isolated rat brain capillaries. This APAP-induced increase in P-gp expression and activity was attenuated in the presence of CAR pathway inhibitor okadaic acid or transcriptional inhibitor actinomycin D, suggesting P-gp regulation is CAR-dependent. Furthermore, morphine brain accumulation was enhanced by P-gp inhibitors in APAP-treated animals, suggesting P-gp-mediated transport. A warm-water (50°C) tail-flick assay revealed a significant decrease in morphine analgesia in animals treated with morphine 3 or 6 hours after APAP treatment, as compared with animals treated concurrently. Taken together, our data imply that inclusion of APAP in a pain treatment regimen activates CAR at the BBB and increases P-gp functional expression, a clinically significant drugdrug interaction that modulates opioid analgesic efficacy.

Deciphering the roles of the constitutive androstane receptor in energy metabolism

“…Accumulating evidence shows that CAR is necessary for normal function in tissues in which the expression of CAR is relatively low. The human CAR agonist CITCO induces the expression of drug transporters at the blood-brain barrier, indicating that the expression of CAR in endothelial cells is important for drug resistance [107][108][109] . The association of CAR single-nucleotide polymorphisms with bone mineral density was also reported, and loss of CAR increased bone mass, suggesting that CAR is essential for osteoblast/osteoclast homeostasis [110,111] .…”

Hypoxia/Reoxygenation Stress Signals an Increase in Organic Anion Transporting polypeptide 1a4 (Oatp1a4) at the Blood–Brain Barrier: Relevance to CNS Drug Delivery

“…At this time, the supernatant was aspirated and the pellet was collected for use in western blot analyses or for preparation of plasma membrane isolates as described by our group. 24 Plasma membrane preparations were obtained by resuspending the pellet in a modified radioimmunoprecipitation buffer consisting of 50 mmol/L Tris-HCl, pH 7. cocktail (Sigma-Aldrich). Samples were gently rocked for 15 minutes at 41C to allow lysis to occur.…”

Interaction of PER2 with the Constitutive Androstane Receptor Possibly Links Circadian Rhythms to Metabolism

“…44,45 If this is the case, such findings should be considered in the pharmacoki-netics of drug active ingredients, especially as CAR regulates the expression of several CYPs. 18,21,46 This work may therefore provide an important new link in understanding the connection between internal clock machinery, metabolism and pharmacokinetics.…”

“…barbiturates, paracetamol and some compounds with a steroid-like structure, it would also be interesting to see if such activation has any physiological effect on transcription of genes involved in circadian rhythms. 13,16,19,46 It would be possible that high levels of CAR could affect the molecular clock in the periphery, but CAR also binds other co-activators. We cannot exclude that the robust molecular clock could be affected, which would mean that different CAR activators (eg.…”