Role of anti-inflammatory compounds in human immunodeficiency virus-1 glycoprotein120-mediated brain inflammation.

BACKGROUND: Neuroinflammation is a common immune response associated with brain human immunodeficiency virus-1 (HIV-1) infection. Identifying therapeutic compounds that exhibit better brain permeability and can target signaling pathways involved in inflammation may benefit treatment of HIV-associated neurological complications. The objective of this study was to implement an in vivo model of brain inflammation by intracerebroventricular administration of the HIV-1 viral coat protein gp120 in rats and to examine anti-inflammatory properties of HIV adjuvant therapies such as minocycline, chloroquine and simvastatin. METHODS: Male Wistar rats were administered a single dose of gp120ADA (500 ng) daily for seven consecutive days, intracerebroventricularly, with or without prior intraperitoneal administration of minocycline, chloroquine or simvastatin. Maraviroc, a CCR5 antagonist, was administered intracerebroventricularly prior to gp120 administration for seven days as control. Real-time qPCR was used to assess gene expression of inflammatory markers in the frontal cortex, hippocampus and striatum. Interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) secretion in cerebrospinal fluid (CSF) was measured applying ELISA. Protein expression of mitogen-activated protein kinases (MAPKs) (extracellular signal-related kinase 1/2 (ERK1/2), c-Jun N-terminal kinases (JNKs) and P38 kinases (P38Ks)) was detected using immunoblot analysis. Student's t-test and ANOVA were applied to determine statistical significance. RESULTS: In gp120ADA-injected rats, mRNA transcripts of interleukin-1ß (IL-1ß) and inducible nitric oxide synthase (iNOS) were significantly elevated in the frontal cortex, striatum and hippocampus compared to saline or heat-inactivated gp120-injected controls. In CSF, a significant increase in TNF-α and IL-1ß was detected. Maraviroc reduced upregulation of these markers suggesting that the interaction of R5-tropic gp120 to CCR5 chemokine receptor is critical for induction of an inflammatory response. Minocycline, chloroquine or simvastatin attenuated upregulation of IL-1ß and iNOS transcripts in different brain regions. In CSF, minocycline suppressed TNF-α and IL-1ß secretion, whereas chloroquine attenuated IL-1ß secretion. In gp120-injected animals, activation of ERK1/2 and JNKs was observed in the hippocampus and ERK1/2 activation was significantly reduced by the anti-inflammatory agents. CONCLUSIONS: Our data demonstrate that anti-inflammatory compounds can completely or partially reverse gp120-associated brain inflammation through an interaction with MAPK signaling pathways and suggest their potential role in contributing towards the prevention and treatment of HIV-associated neurological complications.

Drug transporters at brain barriers: expression and regulation by neurological disorders.

Drug transport in the central nervous system can be highly regulated by the expression of numerous influx and efflux transport proteins not only at the blood-brain barrier and blood-cerebrospinal fluid barrier but also in brain parenchymal cellular compartments (i.e., astrocytes, microglia, neurons). In particular, members of the ATP-Binding Cassette membrane-associated transporter superfamily and Solute Carrier family are known to be involved in the traffic of several endobiotics and xenobiotics (including drugs) into and out ofthe brain. These transport proteins have also been implicated in a number of neurological disorders including HIV-encephalitis, Alzheimer's disease, Parkinson's disease and neoplasia. This chapter summarizes recent knowledge on the role of drug transporters in the brain.

Regulation of P-glycoprotein by human immunodeficiency virus-1 in primary cultures of human fetal astrocytes.

P-glycoprotein (P-gp), a drug efflux pump, is known to alter the bioavailability of antiretroviral drugs at several sites, including the brain. We have previously shown that human immunodeficiency virus-1 (HIV-1) glycoprotein 120 (gp120) induces proinflammatory cytokine secretion and decreases P-gp functional expression in rat astrocytes, a cellular reservoir of HIV-1. However, whether P-gp is regulated in a similar way in human astrocytes is unknown. This study investigates the regulation of P-gp in an in vitro model of gp120-triggered human fetal astrocytes (HFAs). In this system, elevated levels of interleukin-6 (IL-6), IL-1ß, and tumor necrosis factor-α were detected in culture supernatants. Pretreatment with CCR5 neutralizing antibody attenuated cytokine secretion, suggesting that gp120-CCR5 interaction mediated cytokine production. Treatment with gp120 (R5-tropic) resulted in reduced P-gp expression (64%) and function as determined by increased (1.6-fold) cellular accumulation of [(3) H]digoxin, a P-gp substrate. Exposure to R5 or R5/X4-tropic viral isolates led to a downregulation in P-gp expression (75% or 90%, respectively), and treatment with IL-6 also showed lower P-gp expression (50%). Moreover, IL-6 neutralizing antibody blocked gp120-mediated P-gp downregulation, suggesting that IL-6 is a key modulator of P-gp. Gp120- or IL-6-mediated downregulation of P-gp was attenuated by SN50 (a nuclear factor-κB [NF-κB] inhibitor), suggesting involvement of NF-κB signaling in P-gp regulation. Our results suggest that, similarly to the case with rodent astrocytes, pathophysiological stressors associated with brain HIV-1 infection have a downregulatory effect on P-gp functional expression in human astrocytes, which may ultimately result in altered antiretroviral drug accumulation within brain parenchyma.

Regulation of multidrug resistance protein 1 by tumor necrosis factor alpha in cultured glial cells: involvement of nuclear factor-kappaB and c-Jun N-terminal kinase signaling pathways.

Pharmacotherapy of brain HIV-1 infection may be limited by ABC transporters [i.e., P-glycoprotein (P-gp), multidrug resistance protein 1 (Mrp1)] that export antiretroviral drugs from HIV-1 brain cellular targets (i.e., astrocytes, microglia). Using an in vitro astrocyte model of an HIV-1 associated inflammatory response, our laboratory has shown that cytokines [i.e., tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1 beta, IL-6], which are secreted in response to HIV-1 envelope glycoprotein gp120 exposure, can decrease P-gp functional expression; however, it is unknown whether these same cytokines can alter expression and/or activity of other ABC transporters (i.e., Mrp1). In primary cultures of rat astrocytes, Mrp1 expression was increased by TNF-alpha (2.7-fold) but was not altered by IL-1 beta or IL-6. Cellular retention of 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, an Mrp substrate, was reduced in TNF-alpha-treated astrocytes, suggesting increased Mrp-mediated transport. Pharmacologic inhibition of nuclear factor-kappaB (NF-kappaB) signaling with SN50 prevented both TNF-alpha release and Mrp1 expression changes in astrocytes triggered with gp120; however, SN50 did not attenuate Mrp1 expression in cells triggered with TNF-alpha. In contrast, Mrp1 functional expression was not altered in the presence of gp120 or TNF-alpha when astrocyte cultures were pretreated with 1,9-pyrazoloanthrone (SP600125), an established c-Jun N-terminal kinase (JNK) inhibitor. SP600125 did not affect TNF-alpha release from cultured astrocytes triggered with gp120. Mrp1 mRNA expression was increased after treatment with gp120 (1.6-fold) or TNF-alpha (1.7-fold), suggesting altered Mrp1 gene transcription. These data suggest that gp120 and TNF-alpha can up-regulate Mrp1 expression in cultured astrocytes. Furthermore, our results imply that both NF-kappaB and JNK signaling are involved in Mrp1 regulation during an HIV-1 associated inflammatory response.

Functional expression of drug transporters in glial cells: potential role on drug delivery to the CNS.

Drug permeability in the central nervous system (CNS) across blood-brain and blood-cerebrospinal fluid barriers is an important determinant of neurological disorders therapeutic efficacy and is highly regulated by the expression of membrane-associated transporters belonging to the ATP-binding cassette (ABC) and solute carrier (SLC) superfamilies. Functional expression of ABC efflux transporters exists not only at the brain barriers (primary biochemical barrier) but also in astrocytes, microglia, neurons, and oligodendrocytes can significantly restrict drug penetration into these cells, thus creating a secondary biochemical barrier to permeability in brain parenchyma. In contrast, SLC members primarily contribute to the uptake of endogenous substrates (i.e., hormones, neurotransmitters) and pharmacological agents and can play a critical role in maintaining CNS homeostasis and drug response. In this chapter, we review the functional expression and localization of drug transporters in the brain, their role in CNS drug delivery, and their regulation in neuropathological conditions.

Role of CNS transporters in the pharmacotherapy of HIV-1 associated neurological disorders.

Membrane-associated drug transporters are important determinants of antiretroviral drug disposition in the central nervous system during HIV-1 infection. A number of influx and efflux transport proteins expressed at the blood-brain barrier, blood-cerebrospinal fluid barrier and in brain parenchyma cellular compartments (i.e., astrocytes, microglia) have been implicated in the traffic of many antiretroviral drugs into and out of the brain. In particular, members of the ATP-binding cassette membrane associated transporter superfamily and Solute Carrier family are known to be involved in the efflux and/or influx of drugs, respectively. As a result, changes in the functional expression of these transporters can alter the disposition and distribution of drugs in the brain. Moreover, antiretroviral therapy itself and/or pathological events (i.e., inflammation, oxidative stress) associated with viral infection may affect the functional expression of these transporters. This review summarizes recent knowledge on the role of drug transporters in regulating brain antiretroviral drug transport in the context of HIV-1 infection.