The antiretroviral protease inhibitors indinavir and nelfinavir stimulate Mrp1-mediated GSH export from cultured brain astrocytes

Glutathione in HIV-Associated Neurocognitive Disorders

A large portion of patients with Human Immunodeficiency Virus (HIV) have neurologic sequelae. Those with better-controlled HIV via antiretroviral therapies generally have less severe neurologic symptoms. However, for many patients, antiretrovirals do not adequately resolve symptoms. Since much of the pathogenesis of HIV/AIDS (Autoimmune Deficiency Syndrome) involves oxidative stress either directly, through viral interaction, or indirectly, through inflammatory mechanisms, we have reviewed relevant trials of glutathione supplementation in each of the HIV-associated neurocognitive diseases and have found disease-specific results. For diseases for which trials have not been completed, predicted responses to glutathione supplementation are made based on relevant mechanisms seen in the literature. It is not sufficient to conclude that all HIV-associated neurocognitive disorders (HAND) will benefit from the antioxidant effects of glutathione supplementation. The potential effects of glutathione supplementation in patients with HAND are likely to differ based on the specific HIV-associated neurocognitive disease.

Role of Dysregulated Autophagy in HIV Tat, Cocaine, and cART Mediated NLRP3 Activation in Microglia

Despite the ability of combination antiretroviral therapy (cART) to suppress viremia, there is persistence low levels of HIV proteins such as Transactivator of transcription (Tat) in the central nervous system (CNS), contributing to glial activation and neuroinflammation. Accumulating evidence also implicates the role of drugs of abuse in exacerbating neurological complications associated with HIV-1. The combined effects of HIV Tat, drugs of abuse, and cART can thus create a toxic milieu in the CNS. The present study investigated the combinatorial effects of HIV-Tat, cocaine, and cART on autophagy and NLRP3 inflammasome activation. We selected a combination of three commonly used cART regimens: tenofovir, emtricitabine, and dolutegravir. Our results demonstrated that exposure of mouse primary microglia (MPMs) to these agents-HIV Tat (25 ng/ml), cocaine (1 μM), and cART (1 μM each) resulted in upregulation of autophagy markers: Beclin1, LC3B-II, and SQSTM1 with impaired lysosomal functioning involving increased lysosomal pH, decreased LAMP2 and cathepsin D, ultimately leading to dysregulated autophagy. Our findings also demonstrated activation of the NLRP3 signaling in microglia exposed to these agents. We further demonstrated that gene silencing of key autophagy protein BECN1 significantly blocked NLRP3-mediated activation of microglia. Silencing of NLRP3, however, failed to block HIV Tat, cocaine, and cART-mediated dysregulation of the autophagy-lysosomal axis; these in vitro phenomena were also validated in vivo using iTat mice administered cocaine and cART. This study thus underscores the cooperative effects of HIV Tat, cocaine, and cART in exacerbating microglial activation involving dysregulated autophagy and activation of the NLRP3 inflammasome signaling.

The far-reaching HAND of cART: cART effects on astrocytes

Following the introduction of combination antiretroviral therapy (cART), the morbidity and mortality from human immunodeficiency virus (HIV) infection has been drastically curtailed and HIV has now become a chronic manageable disease. Persons living with HIV (PLWH) are living longer and experiencing significant co-morbidities and conditions of aging. NeuroHIV, clinically defined as HIV-Associated Neurocognitive Disorders (HAND) and pathologically manifested by persistent inflammation in the CNS despite cART, is a significant co-morbid condition for PLWH. In the pre-cART era, HIV mediated much of the pathogenesis in the Central Nervous System (CNS); in the cART era, with low to undetectable viremia, other mechanisms may be contributing to persistent neuroinflammation. Emerging data point to the adverse effects at the cellular level of cART, independent of HIV. Astrocytes are the most abundant cells in the CNS, playing vital roles in maintaining CNS homeostasis (e.g. metabolic support to neurons, clearance of neurotransmitters, ion balance, modulation of synaptic functions and maintaining the structural integrity of the blood brain barrier (BBB). Therefore, any disruption of their function will have wide repercussions in the CNS. In this review, we will address current knowledge and gaps on the impact of antiretrovirals (ARVs) on astrocytes and physiologic consequences in the CNS. Understanding the status of this field, will provide a practical framework to elucidate the potential role of cART-mediated dysregulation of astrocytes in neuroHIV pathogenesis and inform therapeutic strategies that are "neuro-friendly". Graphical abstract CNS-penetrating cART have the potential to cause resting astrocytes to become activated into an A1 or neurotoxic phenotype. These cells can in turn secrete inflammatory cytokines that affect surrounding microglia macrophages, as well as neurotoxic factors that impact nearby neurons. In addition, impairment in the physiologic functions of astrocytes will result in altered BBB permeability and disrupted metabolic homeostasis. CNS=Central Nervous System; cART=combined antiretroviral therapy; BBB=blood brain barrier.

Protease Inhibitors, Saquinavir and Darunavir, Inhibit Oligodendrocyte Maturation: Implications for Lysosomal Stress

Despite the introduction of antiretroviral (ARV) therapy (ART), approximately 30-50% of people living with human immunodeficiency virus-1 (HIV-1) will develop a spectrum of measurable neurocognitive dysfunction, collectively called HIV-associated neurocognitive disorder (HAND). While the clinical manifestations of HAND have changed with the advent of ART, certain pathological features have endured, including white matter alterations and dysfunction. The persistence of white matter alterations in the post-ART era suggests that ARV drugs themselves may contribute to HAND pathology. Our group has previously demonstrated that two ARV compounds from the protease inhibitor (PI) class, ritonavir and lopinavir, inhibit oligodendrocyte maturation and myelin protein production. We hypothesized that other members of the PI class, saquinavir and darunavir, could also negatively impact oligodendrocyte differentiation. Here we demonstrate that treating primary rat oligodendrocyte precursor cells with therapeutically relevant concentrations of either ARV drug results in a concentration-dependent inhibition of oligodendrocyte maturation in vitro. Furthermore, we show that acidifying endolysosomal pH via a mucolipin transient receptor potential channel 1 (TRPML1) agonist provides protection against saquinavir- and darunavir-induced inhibition of oligodendrocyte maturation. Moreover, our findings suggest, for the first time, an imperative role of proper endolysosomal pH in regulating OL differentation, and that therapeutic targeting of endolysosomes may provide protection against ARV-induced oligodendrocyte dysregulation. Graphical Abstract Treatment of primary rat oligodendrocyte precursor cells with therapeutically relevant concentrations of either antiretroviral compound of the protease inhibitor class, darunavir or saquinavir, results in a concentration-dependent inhibition of oligodendrocyte maturation in vitro. Additionally, in darunavir or saquinavir-treated cultures we observed a concentration-dependent decrease in the number of acidic lysosomes, via immunostaining with LysoTracker Red, compared with vehicle-treated cultures. Finally, we showed that acidifying endolysosomal pH via a mucolipin transient receptor potential channel 1 (TRPML1) agonist provides protection against saquinavir- or darunavir-induced inhibition of oligodendrocyte maturation. Our findings suggest, for the first time, a critical role of proper endolysosomal pH in regulating OL differentation, and that therapeutic targeting of endolysosomes may provide protection against antiretroviral-induced oligodendrocyte dysregulation.

White matter loss and oligodendrocyte dysfunction in HIV: A consequence of the infection, the antiretroviral therapy or both?

While the severe cognitive effects of HIV-associated dementia have been reduced by combined antiretroviral therapy (cART), nearly half of HIV-positive (HIV+) patients still suffer from some form of HIV-Associated Neurocognitive Disorders (HAND). While frank neuronal loss has been dramatically reduced in HAND patients, white matter loss, including dramatic thinning of the corpus callosum, and loss of volume and structural integrity of myelin persists despite viral control by cART. It remains unclear whether changes in white matter underlie the clinical manifestation seen in patients or whether they are the result of persistent viral reservoirs, remnant damage from the acute infection, the antiretroviral compounds used to treat HIV, secondary effects due to peripheral toxicities or other associated comorbid conditions. Both HIV infection itself and its treatment with antiretroviral drugs can induce metabolic syndrome, lipodystrophy, atherosclerosis and peripheral neuropathies by increased oxidative stress, induction of the unfolded protein response and dysregulation of lipid metabolism. These virally and/or cART-induced processes can also cause myelin loss in the CNS. This review aims to highlight existing data on the contribution of white matter damage to HAND and explore the mechanisms by which HIV infection and its treatment contribute to persistence of white matter changes in people living with HIV currently on cART.

Ligand-displacement-based two-photon fluorogenic probe for visualizing mercapto biomolecules in live cells, Drosophila brains and zebrafish

Investigating the change in expression level of mercapto biomolecules (GSH/Cys/Hcy) necessitates a rapid detection method for a series of physiological and pathological processes. Herein, we present a ligand-displacement-based two-photon fluorogenic probe based on an Fe(iii) complex, TPFeS, which is a GSH/Cys/Hcy rapid detection fluorogenic probe for in vitro analysis and live cell/tissue/in vivo imaging. The "in situ" probe is non-fluorescent and was prepared from a 1 : 2 ratio of Fe(iii) and TPS, a novel two-photon (TP) fluorophore with excellent one-photon (OP) and TP properties under physiological conditions, as a fluorescent ligand. This probe shows a rapid and remarkable fluorescence restoration (OFF-ON) property due to the ligand-displacement reaction of mercapto biomolecules in a recyclable manner in vitro. A significant two-photon action cross-section, good selectivity for biothiols, low cytotoxicity, and insensitivity to pH over the biologically relevant pH range allowed the direct visualization of mercapto biomolecules at different levels between normal/drug-treated live cells, as well as in Drosophila brain tissues/zebrafish based on the use of two-photon fluorescence microscopy.

Dicoumarol Inhibits Multidrug Resistance Protein 1-Mediated Export Processes in Cultured Primary Rat Astrocytes

Dicoumarol is frequently used as inhibitor of the detoxifying enzyme NAD(P)H:quinone acceptor oxidoreductase 1 (NQO1). In order to test whether dicoumarol may also affect the cellular glutathione (GSH) metabolism, we have exposed cultured primary astrocytes to dicoumarol and investigated potential effects of this compound on the cell viability as well as on the cellular and extracellular contents of GSH and its metabolites. Incubation of astrocytes with dicoumarol in concentrations of up to 100 µM did not acutely compromise cell viability nor was any GSH consumption or GSH oxidation to glutathione disulfide (GSSG) observed. However, unexpectedly dicoumarol inhibited the cellular multidrug resistance protein (Mrp) 1-dependent export of GSH in a time- and concentration-dependent manner with half-maximal effects observed at low micromolar concentrations of dicoumarol. Inhibition of GSH export by dicoumarol was not additive to that observed for the known Mrp1 inhibitor MK571. In addition, dicoumarol inhibited also the Mrp1-mediated export of GSSG during menadione-induced oxidative stress and the export of the GSH-bimane-conjugate (GS-B) that had been generated in the cells after exposure to monochlorobimane. Half-maximal inhibition of the export of Mrp1 substrates was observed at dicoumarol concentrations of around 4 µM (GSH and GSSG) and 30 µM (GS-B). These data demonstrate that dicoumarol strongly affects the GSH metabolism of viable cultured astrocytes by inhibiting Mrp1-mediated export processes and identifies for the first time Mrp1 as additional cellular target of dicoumarol.

Astrocytes synthesize primary and cyclopentenone prostaglandins that are negative regulators of their proliferation

Recently, the modulation of cellular inflammatory responses via endogenous regulators became a major focus of medically relevant investigations. Prostaglandins (PGs) are attractive regulatory molecules, but their synthesis and mechanisms of action in brain cells are still unclear. Astrocytes are involved in manifestation of neuropathology and their proliferation is an important part of astrogliosis, a cellular neuroinflammatory response. The aims of our study were to measure synthesis of PGs by astrocytes, and evaluate their influence on proliferation in combination with addition of inflammatory pathway inhibitors. With UPLC-MS/MS analysis we detected primary PGs (1410 ± 36 pg/mg PGE₂, 344 ± 24 PGD₂) and cyclopentenone PGs (cyPGs) (87 ± 17 15d-PGJ₂, 308 ± 23 PGA₂) in the extracellular medium after 24-h lipopolysaccharide (LPS) stimulation of astrocytes. PGs reduced astrocytic proliferation with the following order of potencies (measured as inhibition at 20 μM): most potent 15d-PGJ₂ (90%) and PGA₂ (80%), > PGD₂ (40%) > 15d-PGA₂ (20%) > PGE₂ (5%), the least potent. However, PGF_2α and 2-cyclopenten-1-one, and ciglitazone and rosiglitazone (synthetic agonists of PPARγ) had no effect. Combinations of cyPGs with SC-560 or NS-398 (specific anti-inflammatory inhibitors of cyclooxygenase-1 and -2, respectively) were not effective; while GW9662 (PPARγ antagonist) or MK-741 (inhibitor of multidrug resistance protein-1, MRP1, and CysLT1 receptors) amplified the inhibitory effect of PGA₂ and 15d-PGJ₂. Although concentrations of individual PGs and cyPGs are low, all of them, as well as primary PGs suppress proliferation. Thus, the effects are potentially additive, and activated PGs synthesis suppresses proliferation in astrocytes.

Efavirenz: What is known about the cellular mechanisms responsible for its adverse effects

The HIV infection remains an important health problem worldwide. However, due to the efficacy of combined antiretroviral therapy (cART), it has ceased to be a mortal condition, becoming a chronic disease instead. Efavirenz, the most prescribed non-nucleoside analogue reverse transcriptase inhibitor (NNRTI), has been a key component of cART since its commercialization in 1998. Though still a drug of choice in many countries, its primacy has been challenged by the arrival of newer antiretroviral agents with better toxicity profiles and treatment adherence. The major side effects related to EFV have been widely described in clinical studies, however the mechanisms that participate in their pathogenesis remain largely ununderstood. This review provides an insight into the cellular and molecular mechanisms responsible for the development of the most significant undesired effects induced by efavirenz, both short- and long-term, revealed by in vitro and in vivo experimental pharmacological research. Growing evidence implicates the drug in energy metabolism, mitochondrial function, and other cellular processes involved in stress responses including oxidative stress, inflammation and autophagy.

Pyrrolopyrimidine derivatives and purine analogs as novel activators of Multidrug Resistance-associated Protein 1 (MRP1, ABCC1)

Multidrug resistance (MDR) is the main cause of diminished success in cancer chemotherapy. ABC transport proteins are considered to be one important factor of MDR. Besides P-glycoprotein (P-gp, ABCB1) and Breast Cancer Resistance Protein (BCRP, ABCG2), Multidrug Resistance-associated Protein 1 (MRP1, ABCC1) is associated with non-response to chemotherapy in different cancers. While considerable effort was spent in overcoming MDR during the last two decades, almost nothing is known with respect to activators of transport proteins. In this work we present certain pyrrolo[3,2-d]pyrimidine derivatives with variations at positions 4 and 5 and purine analogs with variations at position 6 as novel activators of MRP1-mediated transport of the MRP1 substrate calcein AM and the anticancer drug daunorubicin in low nanomolar concentration range. Two different MRP1 overexpressing cell lines were used, the doxorubicin-selected human lung cancer cell line H69 AR and the transfected Madin-Darby Canine Kidney cell line MDCK II MRP1. No effect was observed in the sensitive counterparts H69 and MDCK II wild type (wt). Derivatives with higher molecular weight possessed also inhibitory properties at low micromolar concentrations, although most compounds were rather poor MRP1 inhibitors. Purine analogs derived from potent MRP1 inhibitors of the pyrrolopyrimidine class showed equal activating, but no inhibiting effects at all. All tested compounds were non-toxic and had only minor impact on P-gp or BCRP, showing no inhibition or activation.

MRP1 and its role in anticancer drug resistance

The phenomenon of multidrug resistance (MDR) in cancer is associated with the overexpression of the ATP-binding cassette (ABC) transporter proteins, including multidrug resistance-associated protein 1 (MRP1) and P-glycoprotein. MRP1 plays an active role in protecting cells by its ability to efflux a vast array of drugs to sub-lethal levels. There has been much effort in elucidating the mechanisms of action, structure and substrates and substrate binding sites of MRP1 in the last decade. In this review, we detail our current understanding of MRP1, its clinical relevance and highlight the current environment in the search for MRP1 inhibitors. We also look at the capacity for the rapid intercellular transfer of MRP1 phenotype from spontaneously shed membrane vesicles known as microparticles and discuss the clinical and therapeutic significance of this in the context of cancer MDR.

Altered Oligodendrocyte Maturation and Myelin Maintenance: The Role of Antiretrovirals in HIV-Associated Neurocognitive Disorders

Despite effective viral suppression through combined antiretroviral therapy (cART), approximately half of HIV-positive individuals have HIV-associated neurocognitive disorders (HAND). Studies of antiretroviral-treated patients have revealed persistent white matter abnormalities including diffuse myelin pallor, diminished white matter tracts, and decreased myelin protein mRNAs. Loss of myelin can contribute to neurocognitive dysfunction because the myelin membrane generated by oligodendrocytes is essential for rapid signal transduction and axonal maintenance. We hypothesized that myelin changes in HAND are partly due to effects of antiretroviral drugs on oligodendrocyte survival and/or maturation. We showed that primary mouse oligodendrocyte precursor cell cultures treated with therapeutic concentrations of HIV protease inhibitors ritonavir or lopinavir displayed dose-dependent decreases in oligodendrocyte maturation; however, this effect was rapidly reversed after drug removal. Conversely, nucleoside reverse transcriptase inhibitor zidovudine had no effect. Furthermore, in vivo ritonavir administration to adult mice reduced frontal cortex myelin protein levels. Finally, prefrontal cortex tissue from HIV-positive individuals with HAND on cART showed a significant decrease in myelin basic protein compared with untreated HIV-positive individuals with HAND or HIV-negative controls. These findings demonstrate that antiretrovirals can impact myelin integrity and have implications for myelination in juvenile HIV patients and myelin maintenance in adults on lifelong therapy.

HIV-1, methamphetamine and astrocytes at neuroinflammatory Crossroads

As a popular psychostimulant, methamphetamine (METH) use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10 and 15% of human immunodeficiency virus-1 (HIV-1) patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND) through direct and indirect mechanisms. Repetitive METH use impedes adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression toward AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte numbers and activity, cytokine signaling, phagocytic function and infiltration through the blood brain barrier. Further, METH triggers the dopamine reward pathway and leads to impaired neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation, which modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress, and excitotoxicity. Pathologically, reactive gliosis is a hallmark of both HIV-1- and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus, this review highlights alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, with special emphasis on HAND-associated neuroinflammation. Importantly, this review carefully evaluates interventions targeting astrocytes in HAND and METH as potential novel therapeutic approaches. This comprehensive overview indicates, without a doubt, that during HIV-1 infection and METH abuse, a complex dialog between all neural cells is orchestrated through astrocyte regulated neuroinflammation.

Efavirenz and the CNS: what we already know and questions that need to be answered

The NNRTI efavirenz has long been one of the most frequently employed antiretroviral drugs in the multidrug regimens used to treat HIV infection, in accordance with its well-demonstrated antiretroviral efficacy and favourable pharmacokinetics. However, growing concern about its adverse effects has sometimes led to efavirenz being replaced by other drugs in the initial treatment selection or to switching of therapy to efavirenz-free regimens in experienced patients. Neurological and neuropsychiatric reactions are the manifestations most frequently experienced by efavirenz-treated patients and range from transitory effects, such as nightmares, dizziness, insomnia, nervousness and lack of concentration, to more severe symptoms including depression, suicidal ideation or even psychosis. In addition, efavirenz has recently been associated with mild/moderate neurocognitive impairment, which is of specific relevance given that half of the patients receiving ART eventually suffer some form of HIV-associated neurocognitive disorder. The mechanisms responsible for efavirenz-induced neurotoxicity are unclear, although growing evidence points to disturbances in brain mitochondrial function and bioenergetics. This review offers a comprehensive overview of the current evidence on the interaction that efavirenz displays with the CNS, including the penetration and concentration of the drug in the brain. We discuss the prevalence, types and specificities of its side effects and recently uncovered cellular mechanisms that may be involved in their development.

Efavirenz alters mitochondrial respiratory function in cultured neuron and glial cell lines

BACKGROUND

The NNRTI efavirenz is among the most widely employed antiretroviral drugs. Although it is considered safe, efavirenz has been linked with several adverse effects including neurological manifestations, which appear in the majority of the patients on efavirenz-containing regimens. The molecular mechanisms responsible for these manifestations are not understood, but mounting evidence points to altered brain bioenergetics.

METHODS

We evaluated the effect of short-term efavirenz treatment on the mitochondrial respiratory function of cultured glioblastoma and differentiated neuroblastoma cell lines using a Seahorse Extracellular Flux Analyzer.

RESULTS

Incubation with efavirenz provoked a significant and concentration-dependent decrease in basal respiration and specifically in ATP production-coupled O2 consumption in both SH-SY5Y and U-251MG cells, with the effect being more pronounced in the latter. In contrast, efavirenz did not alter mitochondrial proton leakage in either of the cell types. Efavirenz led to a decrease in the respiratory control ratio as well as to a reduction in the maximal respiration rate and spare respiratory capacity in both U-251MG and SH-SY5Y cells, the former cells being more susceptible.

CONCLUSIONS

These findings reveal that efavirenz specifically alters mitochondrial respiration, which is of relevance for a better understanding of the molecular mechanisms responsible for the efavirenz-associated neurological effects that have been recorded in clinical situations.

Glutathione-Dependent Detoxification Processes in Astrocytes

Astrocytes have a pivotal role in brain as partners of neurons in homeostatic and metabolic processes. Astrocytes also protect other types of brain cells against the toxicity of reactive oxygen species and are considered as first line of defence against the toxic potential of xenobiotics. A key component in many of the astrocytic detoxification processes is the tripeptide glutathione (GSH) which serves as electron donor in the GSH peroxidase-catalyzed reduction of peroxides. In addition, GSH is substrate in the detoxification of xenobiotics and endogenous compounds by GSH-S-transferases which generate GSH conjugates that are efficiently exported from the cells by multidrug resistance proteins. Moreover, GSH reacts with the reactive endogenous carbonyls methylglyoxal and formaldehyde to intermediates which are substrates of detoxifying enzymes. In this article we will review the current knowledge on the GSH metabolism of astrocytes with a special emphasis on GSH-dependent detoxification processes.

Arsenite stimulates glutathione export and glycolytic flux in viable primary rat brain astrocytes

Intoxication with inorganic arsenicals leads to neuropathies and impaired cognitive functions. However, little is known so far on the cellular targets that are involved in the adverse effects of arsenite to brain cells. To test whether arsenite may affect neural glucose and glutathione (GSH) metabolism, primary astrocyte cultures from rat brain were used as a model system. Exposure of cultured astrocytes to arsenite in concentrations of up to 0.3mM did not compromise cell viability during incubations for up to 6h, while 1mM arsenite damaged the cells already within 2h after application. Determination of cellular arsenic contents of astrocytes that had been incubated for 2h with arsenite revealed an almost linear concentration-dependent increase in the specific cellular arsenic content. Exposure of astrocytes to arsenite stimulated the export of GSH and accelerated the cellular glucose consumption and lactate production in a time- and concentration-dependent manner. Half-maximal stimulation of GSH export and glycolytic flux were observed for arsenite in concentrations of 0.1mM and 0.3mM, respectively. The arsenite-induced stimulation of both processes was abolished upon removal of extracellular arsenite. The strong stimulation of GSH export by arsenite was prevented by MK571, an inhibitor of the multidrug resistance protein 1, suggesting that this transporter mediates the accelerated GSH export. In addition, presence of MK571 significantly increased the specific cellular arsenic content, suggesting that Mrp1 may also be involved in arsenic export from astrocytes. The data observed suggest that alterations in glucose and GSH metabolism may contribute to the reported adverse neural consequences of intoxication with arsenite.

Neuronal bioenergetics and acute mitochondrial dysfunction: a clue to understanding the central nervous system side effects of efavirenz

BACKGROUND

Neurological pathogenesis is associated with mitochondrial dysfunction and differences in neuronal/glial handling of oxygen and glucose. The main side effects attributed to efavirenz involve the CNS, but the underlying mechanisms are unclear.

METHODS

Human cell lines and rat primary cultures of neurons and astrocytes were treated with clinically relevant efavirenz concentration.

RESULTS

Efavirenz alters mitochondrial respiration, enhances reactive oxygen species generation, undermines mitochondrial membrane potential, and reduces adenosine triphosphate (ATP) levels in a concentration-dependent fashion in both neurons and glial cells. However, it activates adenosine monophosphate-activated protein kinase only in glial cells, upregulating glycolysis and increasing intracellular ATP levels, which do not occur in neurons. To reproduce the conditions that often exist in human immunodeficiency virus-related neuroinflammatory disorders, the effects of efavirenz were evaluated in the presence of exogenous nitric oxide, an inflammatory mediator and mitochondrial inhibitor. The combination potentiated the effects on mitochondrial parameters in both neurons and glial cells, but ATP generation and lactate production were enhanced only in glial cells.

CONCLUSIONS

Efavirenz affects the bioenergetics of neurons through a mechanism involving acute mitochondrial inhibition, an action exacerbated in neuroinflammatory conditions. A similar scenario of glial cells survival and degeneration of neurons with signs of mitochondrial dysfunction and oxidative stress has been associated with neurocognitive disorders.

Short time exposure to hydrogen peroxide induces sustained glutathione export from cultured neurons

Hydrogen peroxide is a normal by-product of cellular metabolism that in higher concentrations can cause oxidative stress. Cultured cerebellar granule neurons efficiently disposed of micromolar concentrations of hydrogen peroxide with half-times in the minute range in a process that predominately involved catalase. Application of up to 100 µM hydrogen peroxide did not affect the cell viability for up to 4h, but caused a time- and concentration-dependent increase in the extracellular glutathione (GSH) content that was accompanied by a matching decrease in the cellular GSH content. Hydrogen peroxide at 100 µM stimulated maximally the GSH export from viable neurons, but did not affect GSH export from cultured astrocytes. The peroxide-induced extracellular GSH accumulation from neurons was lowered by 70% in the presence of MK571, an inhibitor of multidrug resistance protein (Mrp) 1. The extracellular GSH content determined after 4h of incubation was already significantly increased after a 5-min exposure of neurons to hydrogen peroxide and became maximal after 15 min of peroxide application. These data demonstrate that just a short exposure of viable cerebellar granule neurons to micromolar concentrations of hydrogen peroxide stimulates a prolonged Mrp1-mediated export of cellular GSH. This process may compromise the antioxidative potential of neurons and increase their sensitivity toward drugs and toxins.

Importance of ABCC1 for cancer therapy and prognosis

Multidrug resistance presents one of the most important causes of cancer treatment failure. Numerous in vitro and in vivo data have made it clear that multidrug resistance is frequently caused by enhanced expression of ATP-binding cassette (ABC) transporters. ABC transporters are membrane-bound proteins involved in cellular defense mechanisms, namely, in outward transport of xenobiotics and physiological substrates. Their function thus prevents toxicity as carcinogenesis on one hand but may contribute to the resistance of tumor cells to a number of drugs including chemotherapeutics on the other. Within 48 members of the human ABC superfamily there are several multidrug resistance-associated transporters. Due to the well documented susceptibility of numerous drugs to efflux via ABC transporters it is highly desirable to assess the status of ABC transporters for individualization of treatment by their substrates. The multidrug resistance associated protein 1 (MRP1) encoded by ABCC1 gene is one of the most studied ABC transporters. Despite the fact that its structure and functions have already been explored in detail, there are significant gaps in knowledge which preclude clinical applications. Tissue-specific patterns of expression and broad genetic variability make ABCC1/MRP1 an optimal candidate for use as a marker or member of multi-marker panel for prediction of chemotherapy resistance. The purpose of this review was to summarize investigations about associations of gene and protein expression and genetic variability with prognosis and therapy outcome of major cancers. Major advances in the knowledge have been identified and future research directions are highlighted.

8-Hydroxy-efavirenz, the primary metabolite of the antiretroviral drug Efavirenz, stimulates the glycolytic flux in cultured rat astrocytes

In active antiretroviral therapy antiretroviral drugs are employed for the restoration of a functional immune system in patients suffering from the acquired immunodeficiency syndrome. However, potential adverse effects of such compounds to brain cells are discussed in connection with the development of neurocognitive impairments in patients. To investigate potential effects of antiretroviral drugs on cell viability and the glycolytic flux of brain cells, astrocyte-rich primary cultures were exposed to various antiretroviral compounds, including the non-nucleoside reverse transcriptase inhibitor efavirenz. In a concentration of 10 μM, neither efavirenz nor any of the other investigated antiretroviral compounds acutely compromised the cell viability nor altered glucose consumption or lactate production. In contrast, the primary metabolite of efavirenz, 8-hydroxy-efavirenz, stimulated the glycolytic flux in viable astrocytes in a time- and concentration-dependent manner with half-maximal and maximal effects at concentrations of 5 and 10 μM, respectively. The stimulation of glycolytic flux by 8-hydroxy-efavirenz was not additive to that obtained for astrocytes that were treated with the respiratory chain inhibitor rotenone and was abolished by removal of extracellular 8-hydroxy-efavirenz. In a concentration of 10 μM, 8-hydroxy-efavirenz and efavirenz did not affect mitochondrial respiration, while both compounds lowered in a concentration of 60 μM significantly the oxygen consumption by mitochondria that had been isolated form cultured astrocytes, suggesting that the stimulation of glycolytic flux by 8-hydroxy-efavrienz is not caused by direct inhibition of respiration. The observed alteration of astrocytic glucose metabolism by 8-hydroxy-efavirenz could contribute to the adverse neurological side effects reported for patients that are chronically treated with efavirenz-containing medications.

Specific increase in MDR1 mediated drug-efflux in human brain endothelial cells following co-exposure to HIV-1 and saquinavir

Persistence of HIV-1 reservoirs within the Central Nervous System (CNS) remains a significant challenge to the efficacy of potent anti-HIV-1 drugs. The primary human Brain Microvascular Endothelial Cells (HBMVEC) constitutes the Blood Brain Barrier (BBB) which interferes with anti-HIV drug delivery into the CNS. The ATP binding cassette (ABC) transporters expressed on HBMVEC can efflux HIV-1 protease inhibitors (HPI), enabling the persistence of HIV-1 in CNS. Constitutive low level expression of several ABC-transporters, such as MDR1 (a.k.a. P-gp) and MRPs are documented in HBMVEC. Although it is recognized that inflammatory cytokines and exposure to xenobiotic drug substrates (e.g HPI) can augment the expression of these transporters, it is not known whether concomitant exposure to virus and anti-retroviral drugs can increase drug-efflux functions in HBMVEC. Our in vitro studies showed that exposure of HBMVEC to HIV-1 significantly up-regulates both MDR1 gene expression and protein levels; however, no significant increases in either MRP-1 or MRP-2 were observed. Furthermore, calcein-AM dye-efflux assays using HBMVEC showed that, compared to virus exposure alone, the MDR1 mediated drug-efflux function was significantly induced following concomitant exposure to both HIV-1 and saquinavir (SQV). This increase in MDR1 mediated drug-efflux was further substantiated via increased intracellular retention of radiolabeled [(3)H-] SQV. The crucial role of MDR1 in (3)H-SQV efflux from HBMVEC was further confirmed by using both a MDR1 specific blocker (PSC-833) and MDR1 specific siRNAs. Therefore, MDR1 specific drug-efflux function increases in HBMVEC following co-exposure to HIV-1 and SQV which can reduce the penetration of HPIs into the infected brain reservoirs of HIV-1. A targeted suppression of MDR1 in the BBB may thus provide a novel strategy to suppress residual viral replication in the CNS, by augmenting the therapeutic efficacy of HAART drugs.

Targeting multidrug resistance protein 1 (MRP1, ABCC1): past, present, and future

The human ATP-binding cassette transporter multidrug resistance protein 1 (MRP1), encoded by ABCC1, was initially identified because of its ability to confer multidrug resistance in lung cancer cells. It is now established that MRP1 plays a role in protecting certain tissues from xenobiotic insults and that it mediates the cellular efflux of the proinflammatory cysteinyl leukotriene C4 as well as a vast array of other endo- and xenobiotic organic anions. Many of these are glutathione (GSH) or glucuronide conjugates, the products of Phase II drug metabolism. MRP1 also plays a role in the cellular efflux of the reduced and oxidized forms of GSH and thus contributes to the many physiological and pathophysiological processes influenced by these small peptides, including oxidative stress. In this review, the pharmacological and physiological aspects of MRP1 are considered in the context of the current status and future prospects of pharmacological and genetic modulation of MRP1 activity.