Acute Regulation of P-glycoprotein at the Blood-Brain Barrier by Peripheral Inflammatory Pain

Abstract

P-glycoprotein (Pgp; ABCB1) is a well known transporter involved in energy-dependent-drug efflux activity. At the brain capillary endothelium, its luminal membrane location is ideal for its ascribed role in the physiological efflux of a wide array of structurally and functionally diverse compounds from the brain. This is a critical issue in regards to the delivery of central nervous system (CNS)-acting therapeutics. Moreover, a dysregulation of Pgp has been implicated in specific CNS disease states, including Alzheimer's disease, epilepsy, and brain cancer where an upregulation of Pgp has been well established as a mediator of multi-drug resistance. Inflammation is a common component in all of these conditions. Previously our laboratory has reported changes in BBB molecular and functional properties during inflammatory pain (Huber et al. 2001). This has led us to investigate the effects of peripheral inflammatory pain on Pgp efflux transport properties at the BBB, in vivo. In the present study we examined the effects of lambda-carrageenan-induced inflammatory pain (i.e. hyperalgesia; CIP) on the molecular and functional properties of Pgp at the BBB. Western blots using enriched fractions of isolated rat brain microvessels revealed that Pgp expression at the BBB was increased by CIP and that this increase occurred predominantly within the membrane region of the cell. Additionally, both in situ brain perfusions and whole body antinociceptive profiling of the Pgp substrate and opioid analgesic, [3H] morphine, indicate that changes in Pgp at the BBB, mediated by peripheral inflammation, can impact brain uptake of morphine. To further elucidate the mechanism(s) behind the rapid upregulation (3 h) of Pgp at this region, we explored regulation of Pgp at the plasma membrane. Our findings show that CIP induces a movement of Pgp within these domains and that Pgp co-localizes with caveolin-1 and clathrin, key structural proteins associated with caveolae and clathrin-pit lipid rafts, respectively. Our data indicate for the first time that peripheral inflammatory pain induces functional and molecular changes in Pgp, a critical efflux transporter, at the BBB in vivo and that these alterations may be mediated in part via a proteolipidic re-organization mechanism.