Neuroscience research in AIDS

Approaches for CNS delivery of drugs - nose to brain targeting of antiretroviral agents as a potential attempt for complete elimination of major reservoir site of HIV to aid AIDS treatment

INTRODUCTION

Human immune-deficiency virus (HIV) infection causing acquired immune-deficiency syndrome (AIDS) is one of the most life-threatening infections. The central nervous system (CNS) is reported to be the most important HIV reservoir site where the antiretroviral drugs are unable to reach.

AREAS COVERED

This article includes the review about HIV infections, its pathogenesis, HIV infections in CNS, its consequences, current therapies, challenges associated with the existing therapies, approaches to overcome them, CNS delivery of drugs - barriers, transport routes, approaches for transporting drugs across the blood-brain barrier, nasal route of drug delivery, and nose to brain targeting of antiretroviral agents as a potential approach for complete cure of AIDS.

EXPERT OPINION

Various approaches are exploited to enhance the drug delivery to the brain for various categories of drugs. However, very few have investigated on the delivery of antiretrovirals to the brain. Targeting antiretrovirals to CNS through oral/nasal routes along with oral/parenteral delivery of drug to the plasma can be a promising approach for an attempt to completely eradicate HIV reservoir and cure AIDS, after clinical trials. Further research is required to identify the exact location of the HIV reservoir in CNS and developing good animal models for evaluation of different newly developed formulations.

An Update of the Review of Neuropsychological Consequences of HIV and Substance Abuse: A Literature Review and Implications for Treatment and Future Research

Neuropyschological dysfunction, ranging from mild cerebral indicators to dementia has been a consistent part of the medical picture of HIV/AIDS. However, advances in medical supervision, particularly as a result of antiretroviral (ARV) treatment, have resulted in some mitigation of the neuropsychological effects of HIV and necessitate re-evaluation of the pattern and nature of HIV-related cognitive or mental deficits. The associated enhancements in morbidity and mortality that have occurred as a result of ARV medication have led to a need for interventions and programs that maintain behaviors that are healthy and stop the resurgence of the risk of HIV transmission. Risk factors such as mental illness and substance use that may have contributed to the initial infection with HIV still need consideration. These risk factors may also increase neuropsychological dysfunction and impact observance of prevention for treatment and recommendations. Explicitly, a better comprehension of the role of substance use on the progression of HIV-related mental decline can enlighten management and evaluation of persons living with HIV with concurrent disorders of substance use. This review provides a summary of the neurophyschology of substance use and HIV and the existing research that has looked at the effects of both substance use and HIV disease on neurophyscological function and suggestions for future research and treatment.

Brain uptake of a Zidovudine prodrug after nasal administration of solid lipid microparticles

Our previous results demonstrated that a prodrug obtained by the conjugation of the antiretroviral drug zidovudine (AZT) with ursodeoxycholic acid (UDCA) represents a potential carrier for AZT in the central nervous system, thus possibly increasing AZT efficiency as an anti-HIV drug. Based on these results and in order to enhance AZT brain targeting, the present study focuses on solid lipid microparticles (SLMs) as a carrier system for the nasal administration of UDCA-AZT prodrug. SLMs were produced by the hot emulsion technique, using tristearin and stearic acid as lipidic carriers, whose mean diameters were 16 and 7 μm, respectively. SLMs were of spherical shape, and their prodrug loading was 0.57 ± 0.03% (w/w, tristearin based) and 1.84 ± 0.02% (w/w, stearic acid based). The tristearin SLMs were able to control the prodrug release, whereas the stearic acid SLMs induced a significant increase of the dissolution rate of the free prodrug. The free prodrug was rapidly hydrolyzed in rat liver homogenates with a half-life of 2.7 ± 0.14 min (process completed within 30 min). The tristearin SLMs markedly enhanced the stability of the prodrug (75% of the prodrug still present after 30 min), whereas the stabilization effect of the stearic acid SLMs was lower (14% of the prodrug still present after 30 min). No AZT and UDCA-AZT were detected in the rat cerebrospinal fluid (CSF) after an intravenous prodrug administration (200 μg). Conversely, the nasal administration of stearic acid based SLMs induced the uptake of the prodrug in the CSF, demonstrating the existence of a direct nose-CNS pathway. In the presence of chitosan, the CSF prodrug uptake increased six times, up to 1.5 μg/mL within 150 min after nasal administration. The loaded SLMs appear therefore as a promising nasal formulation for selective zidovudine brain uptake.

Contributors to neuropsychological impairment in HIV-infected and HIV-uninfected opiate-dependent patients

Neuropsychological (NP) impairment is multiply determined among HIV-infected and HIV-uninfected individuals who are also dually diagnosed with depression and who use illicit substances. The purpose of the present study was to assess the impact of HIV status, depression, and problematic substance use on NP performance. A total of 160 opiate-dependent outpatients undergoing methadone maintenance (80 HIV-infected, 80 HIV-uninfected) completed diagnostic and NP evaluations. Raw scores from individual NP tests were converted to Z scores relative to standard norms and were averaged to form a composite score. HIV-infected participants had significantly lower overall NP performance--as well as lower performance on tests of attention, motor speed, and verbal memory--than HIV-uninfected participants. In multiple regression analyses considering the role of depression and substance use, only HIV status emerged as a significant predictor of NP impairment. These findings confirm NP impairment in HIV-infected substance abusing patients independent of comorbid depression and severity of substance use.

The impact of neuropsychological functioning on adherence to HAART in HIV-infected substance abuse patients

This study assessed the frequency of neuropsychological impairment and its relationship to adherence in a sample of HIV-infected injection drug users (IDUs) in treatment. One hundred eight participants recruited between September 2006 and October 2008 completed psychodiagnostic and neuropsychological assessments and monitored HAART adherence over a 2-week period via the use of Medication Event Monitoring System (MEMS) electronic pill caps and self-report. Assessment of concurrent functioning included clinician-rated scales of depression and substance use severity, and a battery of neuropsychological tests. Findings from individual neuropsychological tests were converted to Z scores relative to standard norms and averaged to form a composite score (NPZ). NPZ was generally poor (mean = -1.505, standard deviation = 1.120), with 76.9% of the sample being classified as highly impaired. Self-reported adherence was significantly higher than MEMS cap adherence. In contrast with previous studies, overall neuropsychological functioning was not a significant predictor of electronically monitored or self-reported adherence. However, examiner-rated current global severity of substance use and delayed word list recall emerged as significant predictors of self-reported adherence. Additionally, estimated premorbid verbal intelligence emerged as a significant predictor of the discrepancy between electronically monitored and self-reported adherence. Given the extent of neuropsychological impairment in this sample, future studies should examine the degree to which the impact of neuropsychological impairment may moderate interventions for this population, and the extent to which skills to cope with neuropsychological problems may boost the potential efficacy of such interventions.

Adherence to antiretroviral medication in older adults living with HIV/AIDS: a comparison of alternative models

The CDC estimates that by 2015, half of all persons living with HIV/AIDS in the USA will be over the age of 50. Despite increasing HIV seroprevalence rates in older adults, most research examining adherence to antiretroviral therapy (ART) has focused on young HIV-infected persons and, in general, has been atheoretical in nature. This study examined two ART adherence conceptual frameworks to determine whether these models generalize to HIV-seropositive older adults. Two hundred and forty-four HIV-positive adults 50-plus years of age were recruited through AIDS service organizations in Ohio and New York. Participants completed a neuropsychological battery and an audio computer-assisted self-interview. FIML SEM analyses revealed that neuropsychological functioning was not associated with adherence. Fit indices supported a stress and coping model, with negative affect mediating the effects of social support and maladaptive coping on ART adherence. Results were consistent with stress and coping models and suggest that interventions intending to increase adherence to ART in HIV-infected older adults may be more effective if they address negative affect and enhance adaptive coping and social support.

Neuropsychological consequences of HIV and substance abuse: a literature review and implications for treatment and future research

Neuropsychological dysfunction, ranging from mild cognitive symptoms to dementia has been a consistent part of the clinical picture of HIV/AIDS. However, advances in clinical management, particularly antiretroviral (ARV) treatment, have mitigated the neuropsychological effects of HIV and revised the pattern and nature of cognitive deficits, which are observed in HIV-infected individuals. The attendant improvements in mortality and morbidity have led to a need for programs and interventions that sustain healthy behavior and prevent a resurgence of HIV transmission risk. Psychiatric risk factors, particularly substance use, which often contribute to initial acquisition of HIV, still require attention. These risk factors may also exacerbate neuropsychological dysfunction and compromise adherence to prevention recommendations and treatment. Specifically, a more complete understanding of the effects of substance abuse on the progression of HIV related cognitive decline can inform evaluation and management of HIV seropositives with concurrent substance use disorders. This review provides an overview of the neuropsychology of HIV and substance abuse and the extant research that has examined the effects of both HIV disease and substance use on neuropsychological functioning and implications for treatment and future research.

The impact of environmental risk factors on HIV-associated cognitive decline in children

Both the human immunodeficiency virus (HIV) and environmental stress have been independently associated with decreased cognitive functioning in children. Given that they are also known to have a strong relationship with each other, the present study sought to test the hypothesis that children in conditions of high environmental risk would be at greater risk for the cognitive complications related to immunosuppression. A retrospective review was conducted to examine the records of 141 children treated at a large pediatric AIDS clinic from 1993 to 2000. CD4+ lymphocyte levels were recorded from laboratory results and IQ scores were recorded from routine psychological evaluations. Key indicators of environmental risk were collected and combined into one measure of overall environmental risk. Pearson product moment correlations were conducted to examine the relationship between environmental risk, age-adjusted CD4 and IQ. Results indicated a significant correlation between CD4 and IQ, with higher levels of immunocompetence predicting higher IQ scores. When subjects were dichotomized based on their environmental risk score, there was no relationship between CD4 count and IQ in the low environmental risk group. In contrast, CD4 was positively associated with IQ in the high environmental risk group. It is proposed that this may be due to gp120 levels in immunocompromised children being particularly toxic to the hippocampus and cortex under conditions of high stress but not so under conditions of low stress.

Dominican Children with HIV not Receiving Antiretrovirals: Massage Therapy Influences their Behavior and Development

Forty-eight children (M age = 4.8 years) infected with HIV/AIDS and living in the Dominican Republic were randomly assigned to a massage therapy or a play session control group. The children in the massage therapy group received two weekly 20-min massages for 12 weeks; the children in the control group participated in a play session (coloring, playing with blocks) for the same duration and length as the massage therapy group. Overall, the children in the massage therapy group improved in self-help abilities and communication, suggesting that massage therapy may enhance daily functioning for children with HIV/AIDS. Moreover, the HIV infected children who were six or older also showed a decrease in internalizing behaviors; specifically depressive/anxious behaviors and negative thoughts were reduced. Additionally, baseline assessments revealed IQ equivalence below normal functioning for 70% of the HIV infected children and very high incidences of mood problems (depression, withdrawn) for 40% of the children and anxiety problems for 20% of the children, suggesting the need for better monitoring and alternative interventions in countries with limited resources to improve cognition and the mental health status of children infected with HIV/AIDS.

Neurocognitive function profile in HIV-infected school-age children

OBJECTIVES

Evaluation of neurocognitive function of school-age children with HIV.

DESIGN

Cross-sectional observational study.

METHODS

Twenty-two children (median age 9.46 years) with perinatally acquired HIV infection were administered a global intelligence test and tests from the Amsterdam Neuropsychological Tasks (ANT) program. The relationship between various patient-, disease- and treatment factors and neurocognitive outcome variables was examined.

RESULTS

Compared with age-appropriate norms, mean IQ of the HIV-infected children was in the average range. However, the HIV-infected children performed poorer on several neuropsychological tests compared with age-appropriate norms. Executive function (attentional flexibility, visuospatial working memory) and processing speed emerged as the most sensitive cognitive measures in relation to HIV disease. The correlational analyses resulted in only two significant outcomes, showing that higher CD4% at initiation of highly active antiretroviral therapy (HAART) and longer treatment duration were associated with better working memory function and attentional control, respectively.

CONCLUSIONS

These exploratory data suggest that subtle neurocognitive impairments may exist in HIV-infected school-age children, in particular characterized by compromised executive function and slowed information processing. Further research with larger sample sizes is needed to confirm these findings.

Psychiatric disorders, HIV infection and HIV/hepatitis co-infection in the correctional setting

Psychiatric disorders such as bipolar disorder, schizophrenia and depression have long been associated with risk behaviors for HIV, hepatitis C virus (HCV) and hepatitis B virus (HBV). The US prison population is reported to have elevated rates of HIV, hepatitis and most psychiatric disorders. This study examined the association of six major psychiatric disorders with HIV mono-infection, HIV/HCV co-infection and HIV/HBV co-infection in one of the nation's largest prison populations. The study population consisted of 370,511 Texas Department of Criminal Justice inmates who were incarcerated for any duration between January 1, 2003 and July 1, 2006. Information on medical conditions and sociodemographic factors was obtained from an institution-wide electronic medical information system. Offenders diagnosed with HIV mono-infection, HIV/HCV, HIV/HBV and all HIV combined exhibited elevated rates of major depression, bipolar disorder, schizophrenia, schizoaffective disorder, non-schizophrenic psychotic disorder and any psychiatric disorder. In comparison to offenders with HIV mono-infection, those with HIV/HCV co-infection had an elevated prevalence of any psychiatric disorder. This cross-sectional study's finding of positive associations between psychiatric disease and both HIV infection and hepatitis co-infection among Texas prison inmates holds both clinical and public health relevance. It will be important for future investigations to examine the extent to which psychiatric disorders serve as a barrier to medical care, communication with clinicians and adherence to prescribed medical regimens among both HIV-mono-infected and HIV/hepatitis-co-infected inmates.

Paediatric HIV and neurodevelopment in sub-Saharan Africa: a systematic review

OBJECTIVE

To determine the degree of motor, cognitive, language and social-emotional impairment related to HIV infection in children living in sub-Saharan Africa (SSA).

METHODS

Literature searches using MEDLINE and PsycINFO. Additionally, the reference lists of previous reviews were checked to ensure that all eligible studies were identified. Cohen's d, a measure of effect size, was computed to estimate the level of impairment.

RESULTS

Six reports met the inclusion criteria. In infancy a consistent delay in motor development was observed with a median value of Cohen's d = 0.97 at 18 months, indicating a severe degree of impairment. Mental development showed a moderate delay at 18 months, with a median value d = 0.67. Language delay did not appear until 24 months of age, d = 0.91. Less clear findings occurred in older subjects.

CONCLUSION

Although HIV has been shown to affect all domains of child functioning, motor development is the most apparent in terms of severity, early onset, and persistence across age groups. However, motor development has been the most widely assessed domain while language development has been less vigorously evaluated in SSA, hence an accurate quantitative estimate of the effect cannot yet be made.

Motor based assessment of neurocognitive functioning in resource-limited international settings

This study compared variance accounted for by neuropsychological tests in both a brief motor battery and in a comprehensive neuropsychological battery. 327 HIV+ subjects received a comprehensive cognitive battery and a shorter battery (Timed Gait, Grooved Pegboard, and Fingertapping). A significant correlation existed between the motor component tests and the more comprehensive battery (52% of variance). Adding Digit symbol and Trailmaking increased the amount of variance accounted for (73%). Motor battery sensitivity to impairment diagnosis was 0.79 and specificity was 0.76. A motor battery may have broader utility to diagnose and monitor HIV related neurocognitive disorders in international settings.

Psychotropic medication use in human immunodeficiency virus-infected youth receiving treatment at a single institution

A cross-sectional study designed to document the use of psychotropic medication in a population of human immunodeficiency virus (HIV)-infected children and adolescents (n = 64) found 45% of the sample had been prescribed at least one psychotropic medication over a 4-year period. The most common medication category prescribed was antidepressants (30%), followed by stimulant-type medications (25%). This study suggests that psychotropic medications are commonly prescribed to HIV-infected children and adolescents. Close partnership with mental health professionals to develop treatment approaches for psychiatric disorders in youth living with HIV is recommended.

Critical implication of the (70-96) domain of human immunodeficiency virus type 1 Vpr protein in apoptosis of primary rat cortical and striatal neurons

The human immunodeficiency virus (HIV)-1 regulatory protein Vpr has been detected in the serum of HIV-seropositive individuals and in the cerebrospinal fluid of acquired immunodeficiency syndrome (AIDS) patients suffering from neurological disorders. Therefore, Vpr could play a critical role in the neuronal apoptosis observed postmortem in the brain of patients, often connected to a severe AIDS-related disease termed HIV-associated dementia (HAD). This suggests that the Vpr neurotoxicity already observed in vitro on hippocampal neurons could also occur in other brain structures. In this study the authors have investigated the ability of synthetic Vpr to induce apoptosis in primary cultures of rat cortical and striatal neurons. Moreover, the authors have explored the Vpr minimal proapoptotic region using synthetic Vpr fragments and mutants of the protein. Treatments of both neuronal types with Vpr, its C-terminal domain, Vpr(52-96), or a shorter fragment, Vpr(70-96), led to dose- and time-dependent cell death as determined by flow cytometry after propidium iodide labeling, phase-contrast microscopy, and TUNEL labeling. Taken together, these results support an apoptosis-induced death of these neurons. The (71-82) Vpr peptide, previously shown toxic to isolated mitochondria, was inactive on neurons. Vpr-induced neuronal apoptosis was associated with activation of caspase-3 beginning 3 h after Vpr extracellular addition and peaking 3 h later. Moreover, an hyperproduction of reactive oxygen species was observed. In addition to hippocampal neurons, the extension of the apoptotic property of Vpr to cortical and striatal neurons could account for several signs observed in HAD and is thus consistent with a possible involvement of Vpr in this syndrome.

Health, neurologic, and cognitive status of HIV-infected, long-surviving, and antiretroviral-naive Ugandan children

OBJECTIVE

The purpose of this study was to assess the health status and school-age neurodevelopmental progress of antiretroviral treatment (ARVT)-naive, HIV-infected Ugandan children who had been followed as part of cohorts of children born to HIV-infected and -noninfected mothers between 1989 and 1993.

METHODS

Twenty-eight children, aged 6 to 12 years, vertically infected with HIV-1 and never treated with ARVT were evaluated in terms of health status, neurologic, and psychometric testing. A randomly selected group of 42 seroreverters and 37 HIV-1 negative children who were age- and gender-matched and who had been followed in the same cohorts were evaluated also. The families studied were homogenous in their socioeconomic status. None of the mothers or children had received ARVT or been exposed to illicit drugs.

RESULTS

The HIV-infected children showed significantly more evidence of acute malnutrition. They also had more illness, especially parotitis, otitis media, upper respiratory infections, and lymphadenopathy. However, they did not differ significantly in neurologic and cognitive assessments when compared with age- and gender-matched seroreverter and HIV-negative children. They were in the normal range with respect to neurologic and psychometric development measures.

CONCLUSIONS

These children seem to represent a significant subgroup of HIV-infected child survivors for whom the progress of the disease is less aggressive throughout early life. Given the fact that many infants, especially in developing countries, continue to be born without the benefit of perinatal ARVT, there will likely continue to be many older HIV-infected children in the same situation as those described in this follow-up study. They will not have been recognized as being HIV-infected. It is important that such children be identified and offered access to ARVT and other appropriate support services.

HIV-assoziierte tuberkul�se Meningoenzephalitis als Ursache abnormen Verhaltens in Haft

Little is known about the type and frequency of psycho-organic syndromes among prisoners. We report the case of a 20-year-old African HIV-I-positive male asylum seeker who developed increasingly bizarre behaviour in prison. The observation of complex behavioural disturbances with a hallucinatory-delusional state led to the diagnosis of delirium caused by AIDS-defining tuberculous meningoencephalitis. The patient improved with specific, symptomatic treatment. This case illustrates the difficulties in diagnosis when communication is impeded. Scrupulous differential diagnosis is necessary for all prisoners manifesting behavioural disturbances. We discuss the pathogenesis and diagnostic procedures of tuberculous meningoencephalitis.

Methamphetamine dependence increases risk of neuropsychological impairment in HIV infected persons

Both HIV infection and methamphetamine dependence can be associated with brain dysfunction. Little is known, however, about the cognitive effects of concurrent HIV infection and methamphetamine dependence. The present study included 200 participants in 4 groups: HIV infected/methamphetamine dependent (HIV+/METH+), HIV negative/methamphetamine dependent (HIV-/METH+), HIV infected/methamphetamine nondependent (HIV+/METH-), and HIV negative/methamphetamine nondependent (HIV-/METH-). Study groups were comparable for age, education, and ethnicity, although the HIV-/METH- group had significantly more females. A comprehensive, demographically corrected neuropsychological battery was administered yielding a global performance score and scores for seven neurobehavioral domains. Rates of neuropsychological impairment were determined by cutoff scores derived from performances of a separate control group and validated with larger samples of HIV+ and HIV- participants from an independent cohort. Rates of global neuropsychological impairment were higher in the HIV+/METH+ (58%), HIV-/METH+ (40%) and HIV+/METH- (38%) groups compared to the HIV-/METH- (18%) group. Nonparametric analyses revealed a significant monotonic trend for global cognitive status across groups, with least impairment in the control group and highest prevalence of impairment in the group with concurrent HIV infection and methamphetamine dependence. The results indicate that HIV infection and methamphetamine dependence are each associated with neuropsychological deficits, and suggest that these factors in combination are associated with additive deleterious cognitive effects. This additivity may reflect common pathways to neural injury involving both cytotoxic and apoptotic mechanisms.

The association of psychiatric disorders and HIV infection in the correctional setting

PURPOSE

Psychiatric disorders, such as bipolar disorder, schizophrenia, and depression, have been associated with both HIV-associated risk behaviors and HIV infection. While the US prison population is reported to exhibit elevated rates of HIV/AIDS and most psychiatric disorders, scarce information currently exists on the association of these conditions in the prison setting. The present study examined the association of six major psychiatric disorders with HIV infection in one of the nation's largest prison populations.

METHODS

The study population consisted of 336,668 Texas Department of Criminal Justice inmates who were incarcerated for any duration between January 1, 1999 and December 31, 2001. Information on medical conditions and sociodemographic factors was obtained from an institution-wide medical information system.

RESULTS

Inmates diagnosed with HIV infection exhibited elevated rates of major depression, dysthymia, bipolar disorder, schizophrenia, schizoaffective disorder, and non-schizophrenic psychotic disorder. These rates persisted in stratified analyses and in a multivariate analysis that statistically adjusted for gender, race, and age category.

CONCLUSION

The present cross-sectional study's finding of a positive association between HIV infection and psychiatric diagnoses among inmates holds both clinical and public health relevance. It will be important for future investigations to prospectively assess the underlying mechanisms of these associations in the correctional setting.

Expression of stromal cell-derived factor 1alpha protein in HIV encephalitis

Analysis of the patterns of stromal cell-derived factor 1alpha (SDF-1alpha) expression in the brains from HIV-positive patients suggests that in neuronal cells, SDF-1alpha might play a role in neuroprotection and neurite extension in response to HIV infection. In all cases analyzed, SDF-1alpha immunoreactivity was primarily present in astroglial cells. Patients with HIV encephalitis (HIVE) showed intense somato-dendritic neuronal SDF-1alpha immunoreactivity, while HIVE negative patients with neurodegeneration had a significant decrease in neuronal SDF-1alpha immunoreactivity. Neuronal cells treated with SDF-1alpha displayed increased neurite outgrowth. Similarly, neurons treated with HIV-Tat, which induced SDF-1alpha expression, also showed neurite outgrowth. Tat-mediated neurite outgrowth was blocked by anti-SDF-1alpha antibody. These results suggest that SDF-1alpha may play a role in the neuronal response to HIV in the brains of AIDS patients.

Effects of a P-glycoprotein inhibitor on brain and plasma concentrations of anti-human immunodeficiency virus drugs administered in combination in rats

Most of the existing anti-human immunodeficiency virus agents enter the central nervous system (CNS) inefficiently and thus may allow slow viral replication in the brain. This may provide a sanctuary for the virus in the CNS and contribute to the development of acquired immunodeficiency syndrome dementia complex. This study evaluates a prodrug approach to improve the CNS delivery of the reverse transcriptase inhibitor 2',3'-dideoxyinosine (ddI) in combination with inhibition of P-glycoprotein-mediated efflux to increase the CNS delivery of the protease inhibitor nelfinavir and to determine whether any unanticipated drug interactions occur in this combination therapy. Three rats received either 6-chloro-2'3'-dideoxypurine (6-Cl-ddP), a prodrug of ddI activated by adenosine deaminase, nelfinavir, nelfinavir and 6-Cl-ddP, nelfinavir and N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) (a P-glycoprotein inhibitor), 6-Cl-ddP and GF120918, or 6-Cl-ddP, nelfinavir, and GF120918. Both 6-Cl-ddP and nelfinavir were administered as i.v. infusions, whereas GF120918 was given as an i.v. bolus 2 h before sampling. Plasma and brain tissue concentrations of 6-Cl-ddP, ddI, and nelfinavir were determined. Neither nelfinavir nor GF120918 was shown to alter the brain/plasma ratios of 6-Cl-ddP or ddI. GF120918, however, increased the plasma concentrations of 6-Cl-ddP and ddI, resulting in increased brain concentrations. GF120918 increased the brain/plasma ratio of nelfinavir significantly (approximately 100-fold). The brain/plasma ratios of nelfinavir were reduced nearly 2-fold in rats treated with nelfinavir, 6-Cl-ddP, and GF120918 compared with rats receiving only nelfinavir and GF120918, suggesting a modest inhibition of nelfinavir uptake by 6-Cl-ddP. Overall, combined 6-Cl-ddP, nelfinavir, and GF120918 administration enhances the brain/plasma ratios of both ddI and nelfinavir.