Targeting uptake transporters such as organic anion transporting polypeptide 1a4 (Oatp1a4) at the blood-brain barrier (BBB) can facilitate central nervous system (CNS) drug delivery. Effective blood-to-brain drug transport via this strategy requires characterization of mechanisms that modulate BBB transporter expression and/or activity. Here, we show that activation of activin receptor-like kinase (ALK)-1 using bone morphogenetic protein (BMP)-9 increases Oatp1a4 protein expression in rat brain microvessels in vivo. These data indicate that targeting ALK1 signaling with BMP-9 modulates BBB Oatp1a4 expression, presenting a unique opportunity to optimize drug delivery and improve pharmacotherapy for CNS diseases.
The microenvironment of the brain requires tight regulation for proper neuronal function. Protecting the central nervous system (CNS) from the varying concentrations of ions, proteins, and toxins in the periphery is the dynamically regulated blood-brain barrier (BBB). Recent studies have demonstrated significant modulation of the BBB in a number of diseases and physiological states, including pain. This study expands on previous explorations of acute and chronic pain-induced effects on the function and molecular cytoarchitecture of the barrier. It describes the role of cyclooxygenase (COX) up-regulation by blocking with diclofenac (30 mg/kg, i.p.), and it examines the variation in BBB regulation through various brain regions. Edema and hyperalgesia were induced by lambda-carrageenan and attenuated by the additional administration of diclofenac. Examination of unidirectional [14C]sucrose permeability with multitime in situ perfusion studies demonstrated that lambda-carrageenan significantly increased cerebral permeability and decreased brainstem permeability. There were no significant changes in any of the other brain regions examined. These permeability changes correlated with up- and down-regulation of the tight junction (TJ) protein claudin-5 in the cerebrum and brainstem, respectively. Diclofenac administration attenuated the cerebral permeability uptake as well as the claudin-5 up-regulation. In addition, diclofenac reversed the lowered permeability in the brainstem, but it did not attenuate TJ protein expression. These studies demonstrate the complex regulation of the BBB occurring during inflammatory pain and the role of COX in this process. An understanding of BBB regulation during pain states is critically important for pharmacotherapy, and it holds great promise for new therapies to treat central nervous system pathologies.
Hypertension is involved in the exacerbation of stroke. It is unclear how blood-brain barrier (BBB) tight-junction (TJ) and ion transporter proteins critical for maintaining brain homeostasis contribute to cerebral infarction during hypertension development. In the present study, we investigated cerebral infarct volume following permanent 4-h middle cerebral artery occlusion (MCAO) and characterized the expression of BBB TJ and ion transporter proteins in brain microvessels of spontaneously hypertensive rats (SHR) compared with age-matched Wistar-Kyoto (WKY) rats at 5 wk (prehypertension), 10 wk (early-stage hypertension), and 15 wk (later-stage hypertension) of age. Hypertensive SHR show increased infarct volume following MCAO compared with WKY control rats. BBB TJ and ion transporter proteins, known to contribute to edema and fluid volume changes in the brain, show differential protein expression patterns during hypertension development. Western blot analysis of TJ protein zonula occludens-2 (ZO-2) showed decreased expression, while ion transporter, Na(+)/H(+) exchanger 1 (NHE-1), was markedly increased in hypertensive SHR. Expression of TJ proteins ZO-1, occludin, actin, claudin-5, and Na(+)-K(+)-2Cl(-) cotransporter remain unaffected in SHR compared with control. Selective inhibition of NHE-1 using dimethylamiloride significantly attenuated ischemia-induced infarct volume in hypertensive SHR following MCAO, suggesting a novel role for NHE-1 in the brain in the regulation of ischemia-induced infarct volume in SHR.
P-glycoprotein (Pgp, ABCB1) is a critical efflux transporter at the blood-brain barrier (BBB) where its luminal location and substrate promiscuity limit the brain distribution of numerous therapeutics. Moreover, Pgp is known to confer multi-drug resistance in cancer chemotherapy and brain diseases, such as epilepsy, and is highly regulated by inflammatory mediators. The involvement of inflammatory processes in neuropathological states has led us to investigate the effects of peripheral inflammatory hyperalgesia on transport properties at the BBB. In the present study, we examined the effects of lambda-carrageenan-induced inflammatory pain (CIP) on brain endothelium regulation of Pgp. Western blot analysis of enriched brain microvessel fractions showed increased Pgp expression 3 h post-CIP. In situ brain perfusion studies paralleled these findings with decreased brain uptake of the Pgp substrate and opiate analgesic, [(3)H] morphine. Cyclosporin A-mediated inhibition of Pgp enhanced the uptake of morphine in lambda-carrageenan and control animals. This indicates that the CIP induced decrease in morphine transport was the result of an increase in Pgp activity at the BBB. Furthermore, antinociception studies showed decreased morphine analgesia following CIP. The observation that CIP modulates Pgp at the BBB in vivo is critical to understanding BBB regulation during inflammatory disease states.
