HIV-1 reverse transcriptase sequence in plasma and cerebrospinal fluid of patients with AIDS dementia complex treated with Abacavir

Crucial Role of Central Nervous System as a Viral Anatomical Compartment for HIV-1 Infection

The chronic infection established by the human immunodeficiency virus 1 (HIV-1) produces serious CD4+ T cell immunodeficiency despite the decrease in HIV-1 ribonucleic acid (RNA) levels and the raised life expectancy of people living with HIV-1 (PLWH) through treatment with combined antiretroviral therapies (cART). HIV-1 enters the central nervous system (CNS), where perivascular macrophages and microglia are infected. Serious neurodegenerative symptoms related to HIV-associated neurocognitive disorders (HAND) are produced by infection of the CNS. Despite advances in the treatment of this infection, HAND significantly contribute to morbidity and mortality globally. The pathogenesis and the role of inflammation in HAND are still incompletely understood. Principally, growing evidence shows that the CNS is an anatomical reservoir for viral infection and replication, and that its compartmentalization can trigger the evolution of neurological damage and thus make virus eradication more difficult. In this review, important concepts for understanding HAND and neuropathogenesis as well as the viral proteins involved in the CNS as an anatomical reservoir for HIV infection are discussed. In addition, an overview of the recent advancements towards therapeutic strategies for the treatment of HAND is presented. Further neurological research is needed to address neurodegenerative difficulties in people living with HIV, specifically regarding CNS viral reservoirs and their effects on eradication.

The impact of HIV central nervous system persistence on pathogenesis

: The persistence of HIV in the central nervous system is somewhat controversial particularly in the context of HIV viral suppression from combined antiretroviral therapy. Further, its significance in relation to HIV pathogenesis in the context of HIV-associated neurocognitive disorders, systemic HIV pathogenesis, and eradication in general, but especially from the brain, are even more contentious. This review will discuss each of these aspects in detail, highlighting new data, particularly from recent conference presentations.

Early Antiretroviral Therapy Is Associated with Lower HIV DNA Molecular Diversity and Lower Inflammation in Cerebrospinal Fluid but Does Not Prevent the Establishment of Compartmentalized HIV DNA Populations

Even when antiretroviral therapy (ART) is started early after infection, HIV DNA might persist in the central nervous system (CNS), possibly contributing to inflammation, brain damage and neurocognitive impairment. Paired blood and cerebrospinal fluid (CSF) were collected from 16 HIV-infected individuals on suppressive ART: 9 participants started ART <4 months of the estimated date of infection (EDI) ("early ART"), and 7 participants started ART >14 months after EDI ("late ART"). For each participant, neurocognitive functioning was measured by Global Deficit Score (GDS). HIV DNA levels were measured in peripheral blood mononuclear cells (PBMCs) and CSF cell pellets by droplet digital (dd)PCR. Soluble markers of inflammation (sCD163, IL-6, MCP-1, TNF-α) and neuronal damage (neurofilament light [NFL]) were measured in blood and CSF supernatant by immunoassays. HIV-1 partial C2V3 env deep sequencing data (Roche 454) were obtained for 8 paired PBMC and CSF specimens and used for phylogenetic and compartmentalization analysis. Median exposure to ART at the time of sampling was 2.6 years (IQR: 2.2-3.7) and did not differ between groups. We observed that early ART was significantly associated with lower molecular diversity of HIV DNA in CSF (p<0.05), and lower IL-6 levels in CSF (p = 0.02), but no difference for GDS, NFL, or HIV DNA detectability compared to late ART. Compartmentalization of HIV DNA populations between CSF and blood was detected in 6 out of 8 participants with available paired HIV DNA sequences (2 from early and 4 from late ART group). Phylogenetic analysis confirmed the presence of monophyletic HIV DNA populations within the CSF in 7 participants, and the same population was repeatedly sampled over a 5 months period in one participant with longitudinal sampling. Such compartmentalized provirus in the CNS needs to be considered for the design of future eradication strategies and might contribute to the neuropathogenesis of HIV.

Clinical Trials in Neurovirology: Successes, Challenges, and Pitfalls

Clinical trials in neurovirology illustrate the special challenges confronting investigators planning to study these conditions, as well as the contributions of successful trials in establishing appropriate management for these devastating diseases. This article reviews key examples of progress in neurovirology that have been spurred by clinical trials, emphasizing human herpes virus encephalitis, HIV, and JC virus. Clinical trials in the setting of neurovirological diseases are characterized by specific challenges, which may include small sample sizes, clinical presentations from life-threatening conditions to chronic courses of disease, regional and temporally restricted outbreaks scenarios, and the unavailability of validated diagnostic tests that can be rapidly deployed at the bedside. This review aims to highlight these methodological challenges and pitfalls in designing and executing clinical neurovirology trials, as well as to outline innovative trial designs, which could be useful in addressing common challenges.

Compartmentalization, Viral Evolution, and Viral Latency of HIV in the CNS

Human immunodeficiency virus type 1 (HIV-1) infection occurs throughout the body and can have dramatic physical effects, such as neurocognitive impairment in the central nervous system (CNS). Furthermore, examining the virus that resides in the CNS is challenging due to its location and can only be done using samples collected either at autopsy, indirectly form the cerebral spinal fluid (CSF), or through the use of animal models. The unique milieu of the CNS fosters viral compartmentalization as well as evolution of viral sequences, allowing for new cell types, such as macrophages and microglia, to be infected. Treatment must also cross the blood-brain barrier adding additional obstacles in eliminating viral populations in the CNS. These long-lived infected cell types and treatment barriers may affect functional cure strategies in people on highly active antiretroviral therapy (HAART).

Cerebrospinal fluid HIV escape associated with progressive neurologic dysfunction in patients on antiretroviral therapy with well controlled plasma viral load

OBJECTIVE

To characterize HIV-infected patients with neurosymptomatic cerebrospinal fluid (CSF) 'escape', defined as detectable CSF HIV RNA in the setting of treatment-suppressed plasma levels or CSF RNA more than 1-log higher than plasma RNA.

DESIGN

Retrospective case series.

SETTING

Four urban medical centers in the United States and Europe.

PARTICIPANTS

Virologically controlled HIV-infected patients on antiretroviral therapy (ART) with progressive neurologic abnormalities who were determined to have CSF 'escape'. INTERVENTION Optimization of ART based upon drug susceptibility and presumed central nervous system exposure.

MAIN OUTCOME MEASURES

Levels of CSF HIV RNA and inflammatory markers, clinical signs and symptoms, and MRI findings.

RESULTS

Ten patients presented with new neurologic abnormalities, which included sensory, motor, and cognitive manifestations. Median CSF HIV RNA was 3900 copies/ml (range 134-9056), whereas median plasma HIV RNA was 62 copies/ml (range <50 to 380). Median CD4 T-cell count was 482 cells/μl (range 290-660). All patients had been controlled to less than 500 copies/ml for median 27.5 months (range 2-96) and five of 10 had been suppressed to less than 50 copies/ml for median 19.5 months (range 2-96). Patients had documentation of a stable ART regimen for median 21 months (range 9-60). All had CSF pleocytosis or elevated CSF protein; seven of eight had abnormalities on MRI; and six of seven harbored CSF resistance mutations. Following optimization of ART, eight of nine patients improved clinically.

CONCLUSION

The development of neurologic symptoms in patients on ART with low or undetectable plasma HIV levels may be an indication of CSF 'escape'. This study adds to a growing body of literature regarding this rare condition in well controlled HIV infection.

HIV genetic diversity between plasma and cerebrospinal fluid in patients with HIV encephalitis

In patients with HIV encephalitis, a low viral diversity between the plasma and cerebrospinal fluid (CSF) HIV-1 viruses was associated with detectable HIV RNA in plasma and a higher level of central nervous system penetration effectiveness (CPE) score, taking into account the genotypic susceptibility score of the current treatment (named balanced score). This result suggests that the CSF viruses were probably originating from the plasma. Conversely, a high viral genetic diversity was associated with an undetectable HIV RNA in plasma and low-balanced CPE, which is in favour of an autonomous replication in the central nervous system.

Could differential virological characteristics account for ongoing viral replication and insidious damage of the brain during HIV 1 infection of the central nervous system?

Neurocognitive disorders due to human immunodeficiency virus type 1 (HIV-1) infection have been reported in 25-60% of cases,(1-3) despite a sustained viral response in peripheral blood while on highly active anti-retroviral therapy (HAART). A possible reason may be that the central nervous system (CNS) is less accessible for anti-retroviral agents, therefore this sanctuary site can provide a reservoir for ongoing HIV-1 replication. Mutations conferring resistance to anti-retroviral drugs may predominate in compartments where drug levels are suboptimal. This review provides an overview on the literature regarding the development of resistance mutations and the sensitivity for co-receptors in CNS. Mutations caused by the anti-retroviral drugs with the lowest intracerebral penetration would be expected to be found in higher percentages in the CNS than in the periphery of the human body. However, few studies have been performed that can confirm or reject this claim. Zidovudine, the anti-retroviral drug with the best intracerebral penetration, has been studied to some extent. This drug indeed induces resistance mutations in blood as well as the CNS. HAART induces a switch from HIV that uses co-receptor CRR5 to HIV that uses co-receptor CXCR4. This switch may appear later in the CNS compartment compared to the periphery. However, current literature shows conflicting evidence. In conclusion, the current understanding of HIV-strain evolution under drug pressure in sanctuary sites like CNS is incomplete. Therefore, more research is needed in order to establish the role of these sites in the development of drug resistant mutants under adequate HAART.

Cross-sectional characterization of HIV-1 env compartmentalization in cerebrospinal fluid over the full disease course

OBJECTIVES

To characterize HIV-1 env compartmentalization between cerebrospinal fluid (CSF) and peripheral blood plasma over all stages of the HIV-1 disease course, and to determine the relationship between the extent of CSF HIV-1 env compartmentalization and clinical neurologic disease status.

DESIGN

Paired blood plasma and CSF specimens were collected from 66 HIV-infected patients cross-sectionally representing all major clinical stages relating to HIV-associated neurologic disease, including primary infection, asymptomatic chronic infection, chronic infection with minor global impairment, and immune deficiency with HIV-associated dementia.

METHODS

Heteroduplex tracking assays and bulk sequence analysis targeting the V1/V2, C2-V3, and V4/V5 regions of env were performed to characterize the genetic makeup of complex HIV-1 populations in the cross-sectional blood plasma and CSF specimens. The levels of blood plasma/CSF env compartmentalization were quantified and compared across the different clinical stages of HIV-1 neurologic disease.

RESULTS

Blood plasma/CSF env compartmentalization levels varied considerably by disease stage and were generally consistent across all three regions of env characterized. Little or no compartmentalization was observed in non-impaired individuals with primary HIV-1 infection. Compartmentalization levels were elevated in chronically infected patients, but were not significantly different between mildly impaired and non-impaired patients. Patients with HIV-associated dementia showed significantly greater blood plasma/CSF env compartmentalization relative to other groups.

CONCLUSION

: Increased CSF compartmentalization of the HIV-1 env gene, which may reflect independent HIV-1 replication and evolution within the central nervous system, is specifically associated with HIV-associated dementia and not the less severe forms of HIV-1 neurologic disease.

Antiretroviral therapy and central nervous system HIV type 1 infection

Central nervous system (CNS) human immunodeficiency virus type 1 (HIV-1) infection begins during primary viremia and continues throughout the course of untreated systemic infection. Although frequently accompanied by local inflammatory reactions detectable in cerebrospinal fluid (CSF), CNS HIV-1 infection usually is not clinically apparent. In a minority of patients, CNS HIV-1 infection evolves into encephalitis during the late stages of systemic infection, which compromises brain function and presents clinically as acquired immunodeficiency syndrome dementia complex (ADC). Combination antiretroviral therapy (ART) has had a major impact on all aspects of CNS HIV-1 infection and disease. In those with asymptomatic infection, ART usually effectively suppresses HIV-1 in CSF and markedly reduces the incidence of symptomatic ADC. In those presenting with ADC, ART characteristically prevents neurological progression and leads to variable, and at times substantial, recovery. Similarly, treatment has reduced CNS opportunistic infections. With better control of these severe disorders, attention has turned to the possible consequences of chronic silent infection and the issue of whether indolent, low-grade brain injury might require earlier treatment intervention.

Neurologic and neurodevelopmental manifestations of pediatric HIV/AIDS: a global perspective

Neurodevelopmental abnormalities associated with HIV infection have been described since the first reports of pediatric AIDS in the 1980s. Before antiretroviral therapy (ART) became widely available, progressive HIV-1 encephalopathy (PHE) was reported in the US in 13-35% of children with HIV-1 infection and in 35-50% of children with AIDS. Introduction of ART can prevent PHE and reverse PHE present at ART initiation, but a high prevalence of residual problems has been described. Even though 90% of HIV-infected children live in the developing world, few children have access to ART and little is known regarding the neurological manifestations of perinatal HIV infection in those regions. Mechanisms of pediatric HIV-1 neuropathogenesis and factors associated with neurodevelopmental abnormalities in perinatally infected children are not yet fully understood. Studies have demonstrated that HIV-1 enters the CNS soon after infection and may persist in this compartment over the entire course of HIV-1 infection. The CNS is a distinct viral reservoir, differing from peripheral compartments in target cells and antiretroviral penetration. Neurotropic HIV-1 likely develops distinct genotypic characteristics in response to this unique environment. We reviewed the literature on pediatric neuroAIDS and identified gaps in the current knowledge.

Salvage therapy with abacavir and other reverse transcriptase inhibitors for human immunodeficiency-associated encephalopathy

BACKGROUND

HIV-associated encephalopathy (HIV-AE) is a severe neurologic condition that affects HIV-infected children. The potential benefit of antiretroviral (ARV) agents with good cerebrospinal fluid (CSF) penetration remains to be defined. Abacavir (ABC) achieves good CSF concentrations and studies of high-dose ABC showed benefit in adults with HIV dementia. The present study evaluated the safety and virologic, immunologic and neuropsychological responses of an ARV regimen including high-dose ABC in children with HIV-AE.

METHODS

Children between 3 months and 18 years old and abacavir-naive with HIV-AE and virologic failure were eligible.

RESULTS

: Seventeen children (16 ARV-experienced) were enrolled and 14 children completed 48 weeks of therapy. The overall tolerability was good; 2 children had a possible hypersensitivity reaction. At week 48, 53% and 59% of the children achieved HIV RNA levels below the limit of quantitation in plasma and CSF, respectively. The median (25%-75% range) change of HIV RNA from baseline to week 48 was -2.29 (-0.81 to -2.47) log10 copies/mL in plasma and -0.94 (0 to -1.13) log10 copies/mL in CSF. The mean increases in CD4 (+/-standard error of mean) cell count and CD4% were 427 (+/-169) cells/mm and 8% (+/-2), respectively. Concentrations of soluble tumor necrosis factor receptor II were reduced in plasma and CSF. Children less than 6 years of age demonstrated significant neuropsychological improvement at week 48.

CONCLUSIONS

In the present study with a limited number of children, highly active ARV therapy including high-dose ABC showed a safety profile similar to standard dose ABC and provided clinical, immunologic and virologic response in children with HIV-AE at week 48. Children less than 6 years of age also demonstrated significant neuropsychological improvement.

Defining and evaluating HIV-related neurodegenerative disease and its treatment targets: a combinatorial approach to use of cerebrospinal fluid molecular biomarkers

There are a number of reasons that the accomplishments of clinical trials related to HIV-related neurodegenerative disease (HRND) and the AIDS dementia complex (ADC) have had such limited impact on clinical practice. These include: rapid evolution and progress in the treatment of systemic HIV infection that has quickly outpaced neurological efforts and has markedly reduced disease incidence; ethical constraints that (rightly) demand neurologically compromised patients receive the best available treatment before experimental therapeutics; complicated backgrounds and comorbidities of patients now most susceptible to HRND; and reluctance of general AIDS clinicians and drug companies to look beyond systemic or pivotal outcomes. However, the field has also been slow to adopt methods that better exploit advances in understanding of the pathogenesis of central nervous system (CNS) infection and brain injury, and that might circumvent some of these constraints. Using a simple model of pathogenesis, we propose an approach to characterizing patients, selecting treatment targets, and evaluating outcomes that emphasize a combination of cerebrospinal fluid (CSF) markers. This model begins by using three markers related to cardinal components of HRND: CNS HIV infection (measurement of CSF HIV RNA), intrathecal immunoactivation (CSF neopterin), and brain injury [CSF light chain neurofilament (NFL)]. Careful analysis of this and other marker combinations promises more rational trial design and more rapid progress in managing CNS HIV infection and HRND using both antiviral and adjuvant treatment approaches.

Changing patterns in the neuropathogenesis of HIV during the HAART era

Rapid progress in the development of highly active antiretroviral therapy has changed the observed patterns in HIV encephalitis and AIDS-related CNS opportunistic infections. Early in the AIDS epidemic, autopsy studies pointed to a high prevalence of these conditions. With the advent of nucleoside reverse transcriptase inhibitors, the prevalence at autopsy of opportunistic infections, such as toxoplasmosis and progressive multifocal leukoencephalopathy, declined while that of HIV encephalitis increased. After the introduction of protease inhibitors, a decline in both HIV encephalitis and CNS opportunistic infections was observed. However, with the increasing resistance of HIV strains to antiretrovirals, there has been a resurgence in the frequency of HIV encephalitis and HIV leukoencephalopathy. HIV leukoencephalopathy in AIDS patients failing highly active antiretroviral therapy is characterized by massive infiltration of HIV infected monocytes/macrophages into the brain and extensive white matter destruction. This condition may be attributable to interactions of anti-retrovirals with cerebrovascular endothelium, astroglial cells and white matter of the brain. These interactions may lead to cerebral ischemia, increased blood-brain barrier permeability and demyelination. Potential mechanisms of such interactions include alterations in host cell signaling that may result in trophic factor dysregulation and mitochondrial injury. We conclude that despite the initial success of combined anti-retroviral therapy, more severe forms of HIV encephalitis appear to be emerging as the epidemic matures. Factors that may contribute to this worsening include the prolonged survival of HIV-infected patients, thereby prolonging the brain's exposure to HIV virions and proteins, the use of increasingly toxic combinations of poorly penetrating drugs in highly antiretroviral-experienced AIDS patients, and selection of more virulent HIV strains with higher replication rates and greater virulence in neural tissues.

Cerebrospinal fluid HIV infection and pleocytosis: relation to systemic infection and antiretroviral treatment

BACKGROUND

Central nervous system (CNS) exposure to HIV is a universal facet of systemic infection. Because of its proximity to and shared barriers with the brain, cerebrospinal fluid (CSF) provides a useful window into and model of human CNS HIV infection.

METHODS

Prospective study of the relationships of CSF to plasma HIV RNA, and the effects of: 1) progression of systemic infection, 2) CSF white blood cell (WBC) count, 3) antiretroviral therapy (ART), and 4) neurological performance. One hundred HIV-infected subjects were cross-sectionally studied, and 28 were followed longitudinally after initiating or changing ART.

RESULTS

In cross-sectional analysis, HIV RNA levels were lower in CSF than plasma (median difference 1.30 log10 copies/mL). CSF HIV viral loads (VLs) correlated strongly with plasma VLs and CSF WBC counts. Higher CSF WBC counts associated with smaller differences between plasma and CSF HIV VL. CSF VL did not correlate with blood CD4 count, but CD4 counts <50 cells/microL associated with a low prevalence of CSF pleocytosis and large differences between plasma and CSF VL. CSF HIV RNA correlated neither with the severity of the AIDS dementia complex (ADC) nor abnormal quantitative neurological performance, although these measures were associated with depression of CD4 counts. In subjects starting ART, those with lower CD4 counts had slower initial viral decay in CSF than in plasma. In all subjects, including five with persistent plasma viremia and four with new-onset ADC, CSF HIV eventually approached or reached the limit of viral detection and CSF pleocytosis resolved.

CONCLUSION

CSF HIV infection is common across the spectrum of infection and is directly related to CSF pleocytosis, though whether the latter is a response to or a contributing cause of CSF infection remains uncertain. Slowing in the rate of CSF response to ART compared to plasma as CD4 counts decline indicates a changing character of CSF infection with systemic immunological progression. Longer-term responses indicate that CSF infection generally responds well to ART, even in the face of systemic virological failure due to drug resistance. We present simple models to explain the differing relationships of CSF to plasma HIV in these settings.

Neurological complications of HIV infection

Cognitive disorders, vacuolar myelopathy, and sensory neuropathies associated with HIV are the most common disorders in patients with HIV AIDS, and are the focus of this review. These disorders are treatable and of those associated with HIV AIDS the pathogenic mechanisms are the most understood. Although triggered by productive HIV macrophage infections, aberrant immune activation plays a major role in inducing the CNS disorders. Novel therapies aimed at these inflammatory mechanisms can be effective. The sensory neuropathies associated with HIV infection are a major cause of morbidity; incidence may be increased by the toxic effects of specific antiretroviral drugs within the peripheral nervous system.

Limited development and progression of resistance of HIV-1 to the nucleoside analogue reverse transcriptase inhibitor lamivudine in human primary macrophages

OBJECTIVES

The aim of this study was to investigate the development and progression of phenotypic resistance to the HIV-1-reverse transcriptase (RT) inhibitor lamivudine, and genotypic variations of HIV-1-RT occurring under lamivudine treatment in HIV-1-infected human primary monocytes-macrophages (M/M).

METHODS

Cellular passages in the presence of lamivudine were performed every 2 weeks by transferring supernatants of infected M/M to fresh M/M. A fitness assay using wild-type virus and a lamivudine-resistant HIV-1 virus (harbouring the M184V RT mutation) was performed in peripheral blood mononuclear cells. Culture supernatants were tested for p24 antigen production and RT activity. The M184V RT mutant virus was obtained by site-directed mutagenesis on a CCR5-using HIV-1 backbone.

RESULTS

The mutagenized M184V RT virus showed full resistance to lamivudine in M/M. However, no detectable phenotypic and genotypic resistance (neither virus breakthrough, nor RT resistance-related mutations) developed in M/M infected by HIV-1 and cultured for up to seven passages in vitro (i.e. 105 days). This inefficiency of M/M to develop M184V RT mutated virus is tightly related to the low 2'-deoxynucleotide (dNTP) pool in such cells, which in turn decreases the kinetics of HIV-1-RT. Despite this, the M184V RT mutant virus replicates in M/M, although with a 30% decreased efficiency compared with the wild-type.

CONCLUSIONS

Our results show that the chances of development of resistance are far lower in M/M than in lymphocytes. This underlines the importance and the peculiar role of M/M as reservoirs of either wild-type or resistant strains in human organs.

Human immunodeficiency virus type 1 genetic diversity in the nervous system: evolutionary epiphenomenon or disease determinant?

Over the past decade there has been a revolution in the understanding and care of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS)-associated disease. Much of this progress stems from a broader recognition of the importance of differences in viral types, including receptor preference(s), replication properties, and reservoirs, as contributing factors to immunosuppresion and disease progression. In contrast, there is limited conceptualizatin of viral diversity and turnover in the brain and circulation in relation to neurocognitive impairments. Herein, the authors review current concepts regarding viral molecular diversity and phenotypes together with features of HIV-1 neuroinvasion, neurotropism, neurovirulence and neurosusceptiblity. Viral genetic and antigenic diversity is reduced within the brain compared to blood or other systemic organs within individuals. Conversely, viral molecular heterogeneity is greater in patients with HIV-associated dementia compared to nondemented patients, depending on the viral gene examined. Individual viral proteins exert multiple neuropathogenic effects, although the neurological consequences of different viral polymorphisms remain uncertain. Nonetheless, host genetic polymorphisms clearly influence neurological disease outcomes and likely dictate both acquired and innate immune responses, which in turn shape viral evolution within the host. Emerging issues include widespread antiretroviral therapy resistance and increasing awareness of viral superinfections together with viral recombination, all of which are likely to impact on both HIV genetic variation and neuropathogenesis. With the persisting prevalence of HIV-induced neurocognitive disabilities, despite marked improvements in managing immunosuppression, it remains imperative to fully define and understand the mechanisms by which viral dynamics and diversity contribute to neurological disease, permitting the development of new therapeutic strategies.

Altered P-glycoprotein expression in AIDS patients with HIV encephalitis

Penetrance of anti-retroviral drugs into the CNS depends partly on the activity of P-glycoprotein (P-gp), an ATP-dependent efflux pump involved in restricting entry of lipophilic drugs into the brain. The present study characterizes the patterns of P-gp expression in the brains of AIDS patients and examines its relationship with clinical and neuropathological indicators of HIV encephalitis (HIVE). For this purpose, brain tissue collected at autopsy from 26 subjects with a history of HIV (9 without HIVE; 17 with HIVE) was analyzed. Immunocytochemical staining and Western blot analyses for regional P-gp expression were performed and levels were correlated with neuropathological indicators and with HIV RNA. Double labeling experiments were performed with antibodies against astroglial (GFAP), endothelial (CD31), microglial (CD45) and neuronal (MAP2) cell markers. In the HIVE-negative cases, P-gp immunoreactivity was associated primarily with endothelial cells. HIVE-positive cases showed extensive immunolabeling of astroglial and microglial cells, but relatively less endothelial cell immunolabeling. No neuronal P-gp immunostaining was detected in brain tissue from any cases in the study. In the HIVE-positive cases with extensive astroglial labeling, the most intense immunoreactivity was detected in white matter. A subset of HIVE-positive cases displayed intense P-gp immunostaining of astrocytes closely associated with blood vessels in the cortex. Both the immunocytochemical and Western blot analyses showed a significant correlation between P-gp expression and HIV RNA levels. In conclusion, P-gp immunoreactivity was detected largely in glial cells in tissue from HIVE-positive patients. Furthermore, in HIVE-positive patients, brain viral burden and P-gp levels were significantly higher than those in HIVE-negative patients. Taken together, our data suggest that P-gp may be part of a central pathway mediating viral compartmentalization in the brains of HIV-infected individuals and may play a significant part in HIV disease progression in the brain.

Membrane permeation characteristics of abacavir in human erythrocytes and human T-lymphoblastoid CD4+ CEM cells: comparison with (-)-carbovir

Abacavir, (-)-(1S,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene-1-methanol, is a novel purine carbocyclic nucleoside analogue that has been approved by the FDA for the treatment of HIV (as Ziagen trade mark [abacavir sulfate]). Chemically, abacavir and (-)-carbovir (CBV) differ only at the 6-position of the purine ring; abacavir contains a cyclopropylamino moiety in place of the 6-lactam functionality of CBV. Intracellularly both are ultimately metabolized to CBV triphosphate. We compared the membrane permeation characteristics of these two compounds at 20 degrees C in human erythrocytes and in human T-lymphoblastoid CD4+ CEM cells, using a "papaverine-stop" assay. In erythrocytes, abacavir influx was rapid, nonsaturable (rate constant=200 pmol/s/mM/microl cell water), and unaffected by inhibitors of nucleoside or nucleobase transport. CBV influx was slow, saturable, strongly inhibited by adenine or hypoxanthine, and occurred via both the nucleobase carrier (Vmax=0.67 pmol/s/microl cell water; Km=50 microM) and the nucleoside carrier (Vmax=0.47 pmol/s/microl cell water; Km=440 microM). Similar qualitative results were obtained with CD4+ CEM cells, although CBV influx rates were somewhat higher and abacavir influx rates lower, compared to the corresponding rates in erythrocytes. Equilibrium studies further revealed that both compounds are concentrated intracellularly, but nonmetabolically, in both cell types, apparently due to cytosolic protein binding (absent in erythrocyte ghosts). We conclude that, in both cell types, while CBV influx is slow and carrier-dependent, abacavir influx occurs rapidly by nonfacilitated diffusion. The membrane permeation characteristics of abacavir are consistent with its superior oral bioavailability and its impressive ability to penetrate the central nervous system.

Clinical implications of HIV-1 drug resistance in the neurological compartment

The tropism of human immunodeficiency virus type 1 (HIV-1) for the central nervous system (CNS) develops early during the course of the infection. Potent antiretroviral therapy has been demonstrated to be effective in controlling the replication of HIV-1 in cerebrospinal fluid (CSF), even though a variable response in this compartment compared with that in plasma has been observed. Different concentrations of antiretroviral drugs are found in CSF and the use of antiretroviral drugs penetrating across the blood-brain barrier is considered to be required for controlling CNS infection in advanced patients, particularly in those with neurological disorders. The compartmentalization of HIV-1 infection in the CNS may affect the treatment response, which may cause a different evolution of viral drug resistance in the 2 compartments. Although HIV-1 resistance testing in CSF is not recommended for the routine management of patients with virological failure, treatment decisions in patients with neurological disorders may require knowledge of the resistance profile of the virus in the CSF.

Choroid plexus controls brain availability of anti-HIV nucleoside analogs via pharmacologically inhibitable organic anion transporters

OBJECTIVE

In AIDS, early suppression of the viral load in the central nervous system is critical for the efficacy of antiretroviral therapy, in order to prevent the emergence of a reservoir of resistant strains of virus, and brain impairment in late stages of the infection. The blood-cerebrospinal fluid (CSF) interface (i.e. the choroidal epithelium) constitutes the most direct route to reach the ventricular meningeal and perivascular infected macrophages, and may modulate the cerebral biodisposition of antiretroviral drugs through various transport systems. Our aim was to address nucleoside drug transfer specifically across the blood-CSF interface, and identify the possible mechanisms involved in their transport.

METHODS

Drug influx and efflux were measured using an in vitro cellular model that reproduces the barrier and transport properties of the blood-CSF interface in vivo. Transport mechanisms were investigated by competition studies.

RESULTS

The CSF influx rate of zidovudine was the highest, although moderate, followed by that of stavudine. The permeability coefficients of the other drugs tested were low. Zidovudine influx into the CSF is independent of thymidine transport systems, and more importantly is limited by an efflux mechanism. This efflux involves an apical (CSF-facing) carrier belonging to the solute carrier (Slc) 22 family of organic anion transporters, and can be inhibited by a therapeutic concentration of benzbromarone.

CONCLUSIONS

The demonstration and characterization of this efflux mechanism is the basis for the development of specific inhibitory agents in view to increase the delivery of antiretroviral nucleoside analogs to the brain.

Phenotypic and genotypic HIV-1 drug resistance assays provide complementary information

To determine the extent to which genotype (GT) or phenotype (PT) methods provide HIV-1 drug resistance information that is overlapping or complementary, both tests were performed on 1378 patient plasma samples. Discordance, defined as determination of reduced susceptibility measured by PT but sensitivity by GT (PT-R/GT-S), or vice versa (PT-S/GT-R), was common: 83, 62, 43, and 28% of samples with evidence of drug resistance had at least 1, 2, 3, or 4 drugs discordant, respectively. Three types of discordance were observed: PT-R/GT-S, and PT-S/GT-R with or without the presence of mixtures at resistance-associated positions (25%, 34%, and 41% of all discordance, respectively). After accounting for mixtures, results for didanosine (30%), zalcitabine (18%), tenofovir (17%), abacavir (14%), lamivudine (12%), and amprenavir (11%) were discordant in >or= 10% of samples. PT-S/GT-R results were most common for didanosine and zalcitabine, whereas PT-R/GT-S results were most common for lamivudine and amprenavir. PT provided quantitative assessment of the degree of reduced susceptibility and identified reduced susceptibility (PT-R/GT-S) or normal susceptibility (PT-S/GT-R) that was not recognized by the GT interpretation algorithm. GT provided valuable information when mixtures were present and minor populations of drug resistant virus were not detected by phenotyping (PT-S/GT-R results). This demonstrates the complementary nature of information provided by PT and GT tests and suggests that their combined use can provide additional clinically-relevant information.

Effect of combination antiretroviral therapy on cerebrospinal fluid HIV RNA, HIV resistance, and clinical manifestations of encephalopathy

OBJECTIVES

This study evaluated the effect of treatment with abacavir/lamivudine/zidovudine versus lamivudine/zidovudine on cerebrospinal fluid (CSF) human immunodeficiency virus (HIV) RNA and clinical manifestations of HIV encephalopathy in children.

STUDY DESIGN

HIV-infected children 7 months to 10 years of age (n = 23) were studied. CSF and plasma were obtained at baseline and weeks 8, 16, and 48. Genotype analysis of HIV was attempted at baseline and week 48. Neurologic evaluations were performed at baseline and weeks 16, 32, and 48.

RESULTS

At baseline, 83% of children had >2.00 log(10) copies/mL HIV RNA in CSF, but only 10% had HIV RNA measurable at week 48. Among children in whom paired genotyping of HIV was possible, 8 of 11 had identical patterns in both CSF and plasma at baseline, whereas at week 48, only 1 of 9 children had similar patterns. Neurologic abnormalities were observed in 83% of children at baseline but only 35% of children at week 48 (P =.004), suggesting a benefit of treatment.

CONCLUSIONS

Antiretroviral therapy was associated with a decline in CSF HIV RNA and an improvement in neurologic status. The development of genotypic mutations was different in CSF and plasma, suggesting discordant viral evolution. These results suggest that antiretroviral treatment in children should include agents with activity in the CNS.

AIDS dementia

AIDS dementia complex is a relatively recently discovered source of cognitive and motor decline, clearly linked to CNS infection by HIV. While this condition is generally subacutely progressive, and leads to death in a short time-span in untreated patients, improvement in function and prognosis may be achieved by application of highly active antiretroviral therapy. Although this therapy is essential, it may also be necessary in the long term to provide additional neuroprotection, blocking secondary mechanisms of neurotoxicity. With current therapy, infection is never completely eradicated, and significant portions of toxicity seem mediated by indirect mechanisms that may continue even during antiretroviral therapy.