The blood-brain barrier (BBB) provides a vast interface for cytokines to affect CNS function. The BBB is a target for therapeutic intervention. It is essential, therefore, to understand how cytokines interact with each other at the level of the BBB and how secondary signals modulate CNS functions beyond the BBB. The interactions between cytokines and lipids, however, have not been fully addressed at the level of the BBB. Here, we summarize current understanding of the localization of cytokine receptors and transporters in specific membrane microdomains, particularly lipid rafts, on the luminal (apical) surface of the microvascular endothelial cells composing the BBB. We then illustrate the clinical context of cytokine effects on the BBB by neuroendocrine regulation and amplification of inflammatory signals. Two unusual aspects discussed are signaling crosstalk by different classes of cytokines and genetic regulation of drug efflux transporters. We also introduce a novel area of focus on how cytokines may act through nuclear hormone receptors to modulate efflux transporters and other targets. A specific example discussed is the ATP-binding cassette transporter-1 (ABCA-1) that regulates lipid metabolism. Overall, cytokine signaling at the level of the BBB is a crucial feature of the dynamic regulation that can rapidly change BBB function and affect brain health and disease.

Mitragyna speciosa (kratom) is a popular herb in Southeast Asia, which is traditionally used to treat withdrawal symptoms associated with opiate addiction. Mitragynine, 7-hydroxymitragynine, and mitraphylline are reported to be the central nervous system active alkaloids which bind to the opiate receptors. Mitraphylline is also present in the bark of Uncaria tomentosa (cat's claw). Several therapeutic properties have been reported for these compounds but limited information is available on the absorption and distribution properties. This study focuses on evaluating the absorption, distribution, metabolism, and excretion (ADME) properties of these compounds and their effect on major efflux transporter P-glycoprotein, using in vitro methods. Quantitative analysis was performed by the Q-TOF LC-MS system. Mitragynine was unstable in simulated gastric fluid with 26 % degradation but stable in simulated intestinal fluid. 7-Hydroxymitragynine degraded up to 27 % in simulated gastric fluid, which could account for its conversion to mitragynine (23 %), while only 6 % degradation was seen in simulated intestinal fluid. Mitraphylline was stable in simulated gastric fluid but unstable in simulated intestinal fluid (13.6 % degradation). Mitragynine and 7-hydroxymitragynine showed moderate permeability across Caco-2 and MDR-MDCK monolayers with no significant efflux. However, mitraphylline was subjected to efflux mediated by P-glycoprotein in both Caco-2 and MDR-MDCK monolayers. Mitragynine was found to be metabolically stable in both human liver microsomes and S9 fractions. In contrast, both 7-hydroxymitragynine and mitraphylline were metabolized by human liver microsomes with half-lives of 24 and 50 min, respectively. All three compounds exhibited high plasma protein binding (> 90 %) determined by equilibrium dialysis. Mitragynine and 7-hydroxymitragynine inhibited P-glycoprotein with EC50 values of 18.2 ± 3.6 µM and 32.4 ± 1.9 µM, respectively, determined by the calcein-AM fluorescent assay, while no inhibition was seen with mitraphylline. These data indicate the possibility of a drug interaction if mitragynine and 7-hydroxymitragynine are coadministered with drugs that are P-glycoprotein substrates.

The current study evaluated a new series of N, analogs with C 6 -C 12 methylene linkers as nicotinic acetylcholine receptor (nAChR) antagonists, for nicotine-evoked [ 3 H]dopamine (DA) overflow, for blood-brain barrier choline transporter affinity, and for attenuation of discriminative stimulus and locomotor stimulant effects of nicotine. bAPi analogs exhibited little affinity for ␣4␤2* (* indicates putative nAChR subtype assignment) and ␣7* high-affinity ligand binding sites and exhibited no inhibition of DA transporter function. With the exception of C 6 , all analogs inhibited nicotine-evoked [ 3 H]DA overflow (IC 50 ϭ 2 nM-6 M; I max ϭ 54 -64%), with N, C 12 ) being most potent. bPiDDB did not inhibit electrically evoked [ 3 H]DA overflow, suggesting specific nAChR inhibitory effects and a lack of toxicity to DA neurons. Schild analysis suggested that bPiDDB interacts in an orthosteric manner at nAChRs mediating nicotine-evoked [ 3 H]DA overflow.To determine whether bPiDDB interacts with ␣-conotoxin MIIsensitive ␣6␤2-containing nAChRs, slices were exposed concomitantly to maximally effective concentrations of bPiDDB (10 nM) and ␣-conotoxin MII (1 nM). Inhibition of nicotine-evoked [ 3 H]DA overflow was not different with the combination compared with either antagonist alone, suggesting that bPiDDB interacts with ␣6␤2-containing nAChRs. C 7 , C 8 , C 10 , and C 12 analogs exhibited high affinity for the blood-brain barrier choline transporter in vivo, suggesting brain bioavailability. Although none of the analogs altered the discriminative stimulus effect of nicotine, C 8 , C 9 , C 10 , and C 12 analogs decreased nicotine-induced hyperactivity in nicotine-sensitized rats, without reducing spontaneous activity. Further development of nAChR antagonists that inhibit nicotine-evoked DA release and penetrate brain to antagonize DA-mediated locomotor stimulant effects of nicotine as novel treatments for nicotine addiction is warranted.Nicotine, the principal tobacco alkaloid, is an agonist at neuronal nicotinic acetylcholine receptor (nAChR) subtypes modulating dopamine (DA) release. Habitual tobacco smoking is maintained via rapid nicotine delivery to brain (Le Foll and Goldberg, 2006) and results from the intrinsic rewarding properties of nicotine, believed to be due to increased DA release. Classical nAChR antagonists mecamylamine and dihydro-␤-erythroidine (DH␤E) inhibit nicotine-evoked DA release and decrease the locomotor stimulant and reinforcing effects of nicotine in rats Watkins et al., 1999;Rahman et al., 2004), suggesting a role for nAChRmediated DA release in these abuse-related behavioral efThis research was supported by National Institutes of Health Grants K02 DA00399, T32 DA007304, and U19 DA017548.Potential royalty payments to L.P.D., P.A.C., and J.T.A. may occur consistent with the University of Kentucky policy.Article, publication date, and citation information can be found at

The blood–brain barrier (BBB) is a specialized vascular interface that restricts the entry of many compounds into brain. This is accomplished through the sealing of vascular endothelial cells together with tight junction proteins to prevent paracellular diffusion. In addition, the BBB has a high degree of expression of numerous efflux transporters which actively extrude compounds back into blood. However, when a metastatic lesion develops in brain the vasculature is typically compromised with increases in passive permeability (blood-tumor barrier; BTB). What is not well documented is to what degree active efflux retains function at the BTB despite the changes observed in passive permeability. In addition, there have been previous reports documenting both increased and decreased expression of P-glycoprotein (P-gp) in lesion vasculature. Herein, we simultaneously administer a passive diffusion marker (14C-AIB) and a tracer subject to P-gp efflux (rhodamine 123) into a murine preclinical model of brain metastases of breast cancer. We observed that the metastatic lesions had similar expression (p > 0.05; n = 756–1214 vessels evaluated) at the BBB and the BTB. Moreover, tissue distribution of R123 was not significantly (p > 0.05) different between normal brain and the metastatic lesion. It is possible that the similar expression of P-gp on the BBB and the BTB contribute to this phenomenon. Additionally we observed P-gp expression at the metastatic cancer cells adjacent to the vasculature which may also contribute to reduced R123 uptake into the lesion. The data suggest that despite the disrupted integrity of the BTB, efflux mechanisms appear to be intact, and may be functionally comparable to the normal BBB. The BTB is a significant hurdle to delivering drugs to brain metastasis.