Apsara Kandanearatchi

Assessing the efficacy of highly active antiretroviral therapy in the brain.

The devastating effects of HIV infection have been documented for the last 2 decades. Since the 1980s over 60 million people have been infected and at present 40 million people globally are living with HIV (72). HIV infects the central nervous system (CNS) early in the disease process. Indeed, numerous studies document the presence of HIV within the cerebrospinal fluid (CSF) (14,15). Direct infection of the brain by HIV ultimately results in HIV associated dementia (HAD), which (prior to the advent of antiretroviral therapy) affected 20% of patients (48, 55). An increasing number of drugs have been developed to treat this infection and delay the development of AIDS. Current treatment is aimed at inhibiting viral replication, and thus, lowering the viral load. However a subsequent increase in viral load can occur as patients become resistant to drug therapy. In the era of HAART, the incidence of HAD has been reduced, whereas the prevalence rate is increasing as people with HIV survive longer. However, in a study of initial AIDS defining illnesses, the proportion with HIV related dementia did not decline following introduction of HAART (19). In a separate study, no decrease was found in the incidence of dementia per se, although there was a decrease in the incidence of all AIDS‐defining illnesses during this time period (50). It is evident from most studies that since the introduction of HAART, its effect on HAD is not entirely clear, although the majority of findings indicate that it is beneficial. Here we will outline the issues relevant to preventing HAD by HAART.

The kynurenine pathway and quinolinic acid: pivotal roles in HIV associated neurocognitive disorders

This brief review will first consider HIV associated neurocognitive disorder followed by the current understanding of its neuropathogenesis. Against this background the role of the kynurenine pathway will be detailed. Evidence both direct and indirect will be discussed for involvement of the kynurenine pathway at each step in the neuropathogenesis of HIV associated neurocognitive disorder.

Calprotectin in microglia from frontal cortex is up-regulated in schizophrenia: evidence for an inflammatory process?

Schizophrenia is associated with a number of pathological changes, including alterations in levels of specific proteins. Calprotectin is a novel 36 kDa calcium‐binding protein of the S100 family and appears to be a nonspecific marker of inflammation. Calprotectin has not previously been investigated in brain tissue. Samples of post‐mortem brain tissue from Brodmann area 9 were obtained from prefrontal cortex from subjects with schizophrenia, bipolar affective disorder, major depression, and from controls. Calprotectin levels were determined by ELISA. To determine cellular localization, immunocytochemical and fluorescent double‐labelling analyses were performed. Exogenous calprotectin was added to retinoic acid‐differentiated human SH‐SY5Y neuroblastoma cell cultures in order to investigate mechanisms of action of calprotectin. Calprotectin was detectable in all samples, and mean levels were noted to be highest in schizophrenic brains (P < 0.05) and lowest in controls. Levels were intermediate in bipolar affective disorder and major depression. Exogenous calprotectin appeared to induce dendritic extension in SH‐SY5Y cell culture in a dose‐dependent manner. Calprotectin was found to be localized to microglia. These findings suggest that increased levels of calprotecitn in the brain may reflect inflammatory processes, which play a role in the pathogenesis of major psychiatric disorders. Furthermore, calprotectin may influence dendritic plasticity.

Granulocyte-macrophage colony-stimulating factor enhances viral load in human brain tissue: Amelioration with stavudine

Background Granulocyte-macrophage colony-stimulating factor (GM-CSF) is elevated in cerebrospinal fluid in HIV- associated dementia; in addition, therapeutic GM-CSF elevates plasma viral load. Objective To assess the effect of GM-CSF on viral replication and the potential ameliorative effect of antiretroviral therapy. Design A primary human brain aggregate system is used as a model of the in vivo situation. Method Cultured aggregates were infected with the macrophage tropic strain HIV-1SF162 and then exposed to varying GM-CSF concentrations and 0.3 μmol/l stavudine. Viral replication was assessed by p24 expression in the supernatant and aggregates. Immunohistochemistry identified neurons, astrocytes, microglia and oligodendrocytes. Results A GM-CSF concentration of 1 ng/ml resulted in a fivefold increase in microglial cells, the main HIV cellular reservoir (P = 0.0001). Prior GM-CSF exposure before infection of the aggregates resulted in sixfold increase in p24 levels compared with non-GM-CSF-exposed infected aggregates. Infected aggregates with or without GM-CSF had significant neuronal loss of 50% and 45%, respectively, and astrocytosis. Addition of stavudine to the infected aggregates, even in the presence of GM-CSF, reduced p24 levels to zero and prevented neuronal loss and astrocytosis. Conclusions This study demonstrates that GM-CSF enhances viral replication while addition of stavudine prevents this potentially detrimental process.

Infection of stationary human brain aggregates with HIV-1 SF162 and IIIB results in transient neuronal damage and neurotoxicity

The cellular basis of HIV associated dementia has been correlated with microglial activation and neuronal dysfunction in symptomatic HIV‐1 disease. As a cellular model of HIV‐1 infection of brain tissue in vitro, we established a stationary human brain aggregate (SHBA) system to compare infection of HIV‐1 SF162 (R5 virus) to that of IIIB (X4 virus). Aggregates were analysed by immunohistochemistry, morphometry, flow cytometry and p24 ELISA. SHBAs had a 1 mm3 size with a mixed cellular composition of 36% neurones, 27% astrocytes, 2% macrophages/microglia and 14% oligodendrocytes. Infection of SHBAs with the R5 HIV‐1 SF162 virus led to the expression of HIV‐1 p24 antigen in 6% of cells. Infection with this R5 using virus culminated in transient neuronal damage and a decrease in mitotically active progenitor cells within aggregates. Infection with X4 using HIV‐1 IIIB was associated with astrocytosis and neurotoxicity. We propose that: (1) the pattern of cellular damage elicited by HIV‐1 infection of brain tissue in vitro depends on virus subtype as determined by its preferential use of R5 or X4 chemokine receptors for entry into cells; (2) SHBAs are a reliable and readily established model of the cellular complexity of human brain tissue in vitro.

Suppression of human immunodeficiency virus replication in human brain tissue by nucleoside reverse transcriptase inhibitors

Human immunodeficiency virus (HIV) infection of the brain is associated pathologically with neuronal damage and loss. Clinically cognitive impairments can develop, which in some can be improved by highly active antiretroviral therapy (HAART), whereas in others, the infection persists despite treatment. The efficacy of antiretrovirals to treat cognitive impairments may be related to their ability to suppress viral replication in the brain and also to prevent neurodegeneration. To investigate this question, the authors assessed the ability of stavudine (300 nM), zidovudine (2 nM), and abacavir (300 nM) to suppress viral replication in human brain tissue aggregates infected with HIV-1 SF162. Aggregates were cultured for 4 weeks and exposed to nucleoside reverse transcriptase inhibitors (NRTIs) either 24 h prior, simultaneously, or 24 h post infection. Viral replication was assessed by p24 enzyme-linked immunosorbent assay (ELISA) in culture medium. The authors observed a statistically significant reduction in the rate of viral replication for stavudine added 24 h prior to infection univariate analysis of variance ([UANOVA], t = 2.55, df = 17, P =.021). Decreased viral replication observed with zidovudine and abacavir was not statistically significant.

Expression of the Rap1 Guanine Nucleotide Exchange Factor, MR-GEF, Is Altered in Individuals with Bipolar Disorder

In the rodent forebrain GABAergic neurons are generated from progenitor cells that express the transcription factors Dlx1 and Dlx2. The Rap-1 guanine nucleotide exchange factor, MR-GEF, is turned on by many of these developing GABAergic neurons. Expression of both Dlx1/2 and MR-GEF is retained in both adult mouse and human forebrain where, in human, decreased Dlx1 expression has been associated with psychosis. Using in situ hybridization studies we show that MR-GEF expression is significantly down-regulated in the forebrain of Dlx1/2 double mutant mice suggesting that MR-GEF and Dlx1/2 form part of a common signalling pathway during GABAergic neuronal development. We therefore compared MR-GEF expression by in situ hybridization in individuals with major psychiatric disorders (schizophrenia, bipolar disorder, major depression) and control individuals. We observed a significant positive correlation between layers II and IV of the dorso-lateral prefrontal cortex (DLPFC) in the percentage of MR-GEF expressing neurons in individuals with bipolar disorder, but not in individuals with schizophrenia, major depressive disorder or in controls. Since MR-GEF encodes a Rap1 GEF able to activate G-protein signalling, we suggest that changes in MR-GEF expression could potentially influence neurotransmission.