Memantine protects hippocampal neuronal function in murine human immunodeficiency virus type 1 encephalitis

Regulation of neural cell survival by HIV-1 infection

Infection by the lentivirus, human immunodeficiency virus type 1 (HIV-1), results in a variety of syndromes involving both the central (CNS) and the peripheral (PNS) nervous systems. Productive HIV-1 infection of the CNS is chiefly detectable in perivascular macrophages and microglia. HIV-1 encoded transcripts and proteins have also been detected in the PNS; however, productive viral replication appears to be sparse and restricted to the macrophage cell population. Despite the absence of productive infection of neurons, HIV-1 infection has been associated with neuronal loss in distinct regions of the brain. Neuronal cell loss may occur through both necrosis and apoptosis, although neuronal apoptosis appears to be a feature of AIDS, as only rare apoptotic neurons have been demonstrated in a few pre-AIDS cases. Although there is no clear consensus as to the underlying mechanism of HIV-induced neuropathogenesis, two complementary concepts predominate. Firstly, HIV-1 encoded proteins injure neurons directly without requiring the intermediary functions of nonneuronal cells. Alternatively, neuronal apoptosis may result indirectly from the secretion of neurotoxic host molecules by resident brain macrophages or microglia in response to HIV-1 infection, stimulation by viral proteins or immune activation. Herein, we review the neurological disorders and their underlying mechanisms associated with HIV infection, focusing on HIV-associated dementia (HAD) and HIV sensory neuropathy (HIV-SN). The evidence that neuronal loss in HIV-1-infected individuals may be due to neuronal apoptosis is then discussed. This review also summarizes the current data supporting both the direct and indirect mechanisms by which neuronal death may occur during infection with HIV-1 or the closely related lentiviruses SIV and FIV. Lastly, strategies are examined for treating or preventing HAD by targeting specific neurotoxic mechanisms.

Molecular mechanisms of HIV-1 associated neurodegeneration

Since identification of the human immunodeficiency virus-1 (HIV-1), numerous studies suggest a link between neurological impairments, in particular dementia, with acquired immunodeficiency syndrome (AIDS) with alarming occurrence worldwide. Approximately, 60% of HIV-infected people show some form of neurological impairment, and neuropathological changes are found in 90% of autopsied cases. Approximately 30% of untreated HIV-infected persons may develop dementia. The mechanisms behind these pathological changes are still not understood. Mounting data obtained by in vivo and in vitro experiments suggest that neuronal apoptosis is a major feature of HIV associated dementia (HAD), which can occur in the absence of direct infection of neurons. The major pathway of neuronal apoptosis occurs indirectly through release of neurotoxins by activated cells in the central nervous system (CNS) involving the induction of excitotoxicity and oxidative stress. In addition a direct mechanism induced by viral proteins in the pathogenesis of HAD may also play a role. This review focuses on the molecular mechanisms of HIV-associated dementia and possible therapeutic strategies.

Experimental and potential future therapeutic approaches for HIV-1 associated dementia targeting receptors for chemokines, glutamate and erythropoietin

Severe and debilitating neurological problems that include behavioral abnormalities, motor dysfunction and frank dementia can occur after infection with the human immunodeficiency virus-1 (HIV-1). Infected peripheral immune-competent cells, in particular macrophages, infiltrate the central nervous system (CNS) and provoke a neuropathological response involving all cell types in the brain. HIV-1 infection results in activation of chemokine receptors, inflammatory mediators, extracellular matrix-degrading enzymes and glutamate receptor-mediated excitotoxicity, all of which can trigger numerous downstream signaling pathways that result in disruption of neuronal and glial function. Despite many major improvements in the control of viral infection in the periphery, a truly effective therapy for HIV-1 associated dementia is currently not available. This review will discuss experimental and potentially future therapeutic strategies based on recently uncovered pathologic mechanisms contributing to neuronal damage induced by HIV-1.

The AIDS dementia complex: clinical and basic neuroscience with implications for novel molecular therapies

The AIDS dementia complex (ADC, also referred to as HIV-associated cognitive impairment) is a common disorder among HIV-infected patients associated with both inflammatory and neurodegenerative processes. This review describes recent advances in the clinical and basic neurosciences of HIV infection and discusses the multivariable nature of what has become a chronic disorder in the context of highly active antiretroviral therapies (HAART). Since its initial description twenty years ago, advances in cell and molecular biology along with those in neuroimaging have furthered our understanding of the underlying pathogenic mechanisms. The clinical and neuropsychological profile of ADC is generally consistent with a "frontal-subcortical" pattern of injury. Neuropathogenesis is largely driven by indirect mechanisms mediated by infected, or more commonly, immune activated macrophages, which secrete viral and host-derived factors. Magnetic resonance spectroscopy (MRS) provides a robust in vivo method to measure the inflammatory and neurotoxic events triggered by these factors and their associated signals. Although the use of combined or highly active antiretroviral therapies (HAART) has significantly improved survival rates, cerebral injury and cognitive impairment remain common events. Factors such as aging and chronic infection will likely impact the course of this disease, its pathogenesis, and treatment. The combined observations presented in this review suggest a number of critical areas for future inquiry.

Coregistration of quantitative proton magnetic resonance spectroscopic imaging with neuropathological and neurophysiological analyses defines the extent of neuronal impairments in murine human immunodeficiency virus type-1 encephalitis

Relatively few immune-activated and virus-infected mononuclear phagocytes (MP; perivascular macrophages and microglia) may affect widespread neuronal dysfunction during human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD). Indeed, histopathological evidence of neuronal dropout often belies the extent of cognitive impairment. To define relationships between neuronal function and histopathology, proton magnetic resonance spectroscopic imaging (1H MRSI) and hippocampal long-term potentiation (LTP) were compared with neuronal and glial immunohistology in a murine model of HIV-1 encephalitis (HIVE). HIV-1(ADA)-infected human monocyte-derived macrophages (MDM) were stereotactically injected into the subcortex of severe combined immunodeficient (SCID) mice. Sham-operated and unmanipulated mice served as controls. Seven days after cell injection, brain histological analyses revealed a focal giant cell encephalitis, with reactive astrocytes, microgliosis, and neuronal dropout. Strikingly, significant reductions in N-acetyl aspartate concentration ([NAA]) and LTP levels in HIVE mice were in both injected and contralateral hemispheres and in brain subregions, including the hippocampus, where neuropathology was limited or absent. The data support the importance of 1H MRSI as a tool for assessing neuronal function for HAD. The data also demonstrate that a highly focal encephalitis can produce global deficits for neuronal function and metabolism.

Neuroprotective strategies for HIV-1 associated dementia

The human immunodeficiency virus-1 (HIV-1) commonly affects cognitive, behavioral and motor functions during the disease course. The neuropathogenesis of viral infection revolves around neurotoxins produced from infected and immune-activated mononuclear phagocytes (MP; perivascular macrophages and microglia). Direct infection of neurons occurs rarely, if at all. Neurologic disease arises in part as a consequence of MP metabolic dysfunction. Although the advent of highly active antiretroviral therapy (HAART) has attenuated the incidence and severity of neurologic disease, it, nonetheless, remains a common and disabling problem for those living with HIV-1 infection. Adjunctive therapies are currently designed to ameliorate clinical outcomes and are included in the therapeutic armamentarium. Anti-inflammatory drugs that inhibit cytokines, chemokines and interferons linked to neurodegenerative processes can significantly ameliorate neuronal function. HIV-1 neurotoxins have the unique ability to up-regulate glycogen synthase kinase-3beta (GSK-3beta) activity that in turn elicits neuronal apoptosis. GSK-3beta inhibitors are neuroprotective in animal models of Neuro AIDS. They are also currently in Phase 1 clinical trials designed for safety and tolerability in patients with HIV-1 infection. Neurotrophins are only beginning to be realized for their therapeutic potential in HIV-1 associated neurologic disease. This review article provides a broad overview of neuroprotective strategies for HIV-1 infection and details how such strategies act and may be implemented for treatment of human disease.