The neuropathology of HIV infection in the era of Highly Active AntiRetroviral Therapy (HAART)

HIV and COVID-19: two pandemics with significant (but different) central nervous system complications

Human immunodeficiency virus (HIV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cause significant neurologic disease. Central nervous system (CNS) involvement of HIV has been extensively studied, with well-documented invasion of HIV into the brain in the initial stage of infection, while the acute effects of SARS-CoV-2 in the brain are unclear. Neuropathologic features of active HIV infection in the brain are well characterized whereas neuropathologic findings in acute COVID-19 are largely non-specific. On the other hand, neuropathologic substrates of chronic dysfunction in both infections, as HIV-associated neurocognitive disorders (HAND) and post-COVID conditions (PCC)/long COVID are unknown. Thus far, neuropathologic studies on patients with HAND in the era of combined antiretroviral therapy have been inconclusive, and autopsy studies on patients diagnosed with PCC have yet to be published. Further longitudinal, multidisciplinary studies on patients with HAND and PCC and neuropathologic studies in comparison to controls are warranted to help elucidate the mechanisms of CNS dysfunction in both conditions.

Cerebral vasculitis associated with drug abuse

PURPOSE OF REVIEW

To review understand the epidemiology, background, neuropharmacology, and histopathology of literature verified cases, and likely etiopathogenic mechanisms.

RECENT FINDINGS

There are only a handful of histologically confirmed patients in the literature with cerebral vasculitis because of drug abuse.

SUMMARY

There is little justification for invasive laboratory investigation given the ready availability of highly accurate vascular neuroimaging techniques to dictate management, which usually rests upon avoidance of further exposure and minimizing the secondary neurotoxic effects of the abused substances and polypharmacy use.

Central Nervous System Vasculitis Due to Substance Abuse

Illicit drug abuse is a common differential diagnosis of acquired central nervous system vasculitis even though there are only a handful of histopathologically confirmed patients in the literature from among the many potential classes of abused drugs traditionally implicated in this disease. This article considers the major classes of illicit drugs in those with and without human immunodeficiency virus type-1 infection and acquired immune deficiency syndrome.

The role of tau protein in HIV-associated neurocognitive disorders

Given the increased life expectancy of human immunodeficiency virus (HIV) infected individuals treated with combination antiretroviral therapy (cART) and the ongoing inflammation observed in the brains of these patients, it is likely that premature neurodegeneration as measured by phospho-tau (p-tau) or increased total tau (t-tau) protein may become an increasing problem. This review examines the seven human studies that have occurred over the past 14 years measuring p-tau and/or t-tau in cerebrospinal fluid (CSF) or via post-mortem brain immunohistochemistry. Although not all studies are in agreement as to the changes in p-and t-tau in HIV infected patients, HIV persists in the brain despite cART. Thus is it is suggested that those maintained on long-term cART may develop tau pathology beyond the extent seen in the studies reviewed herein and overtime may then reach the threshold for clinical manifestation.

Neuropathology of AIDS: An Autopsy Review of 284 Cases from Brazil Comparing the Findings Pre- and Post-HAART (Highly Active Antiretroviral Therapy) and Pre- and Postmortem Correlation

A retrospective study of central nervous system (CNS) in 284 autopsy AIDS cases in Brazil (1989–2008) divided into 3 groups: A (without antiretroviral treatment: 163 cases); B (other antiretroviral therapies: 76 cases); C (HAART for 3 months or more: 45 cases). In 165 (58.1%) cases, relevant lesions were found, predominantly infections (54.2%); the most frequent was toxoplasmosis (29.9%) followed by cryptococcosis (15.8%), purulent bacterial infections (3.9%), and HIV encephalitis (2.8%); non-Hodgkin lymphomas occurred in 1.4% and vascular lesions in 1.1%. There was no difference when compared the frequency of lesion among the groups; however, toxoplasmosis was less common while HIV encephalitis was more frequent in group C related to A. CNS lesions remain a frequent cause of death in AIDS; however, the mean survival time was four times greater in group C than in A. In 91 (55.1%) of 165 cases with relevant brain lesions (or 32% of the total 284 cases), there was discordance between pre- and postmortem diagnosis; disagreement type 1 (important disease that if diagnosed in life could change the patient prognosis) occurred in 49 (53.8%) of 91 discordant cases (17.6% of the total 284) indicating the autopsy importance, even with HAART and advanced diagnostics technologies.

The Neuropathology of HIV/AIDS

The introduction of Highly Active Anti-retroviral Therapy (HAART) has resulted in significant decreases in morbidity and mortality for subjects infected with HIV. The brain is a major target organ for HIV resulting in significant neuropathological changes in most HIV infected subjects and a wide range of clinical neurological symptoms including HIV associated dementia. In the pre-HAART era HIV associated dementia was a common complication of AIDS. However, since the introduction of HAART the incidence of HIV associated dementia has fallen, but the prevelance has actually risen due to the increasing number of infected subjects and increased life expectancy. HIV associated dementia correlates most closely with neuroinflammation rather than directly with viral load or HIV encephalitis. HIV related clinical and neuropathological disorders are more prevalent in drug abusers than in other risk groups. This review focuses on the shifting pathology observed in HIV infected subjects since the introduction of HAART, discussing the clinical manifestations of these and the influence of confounding factors such as drug abuse and Hepatitis C co-infection.

The high affinity peripheral benzodiazepine receptor ligand DAA1106 binds to activated and infected brain macrophages in areas of synaptic degeneration: implications for PET imaging of neuroinflammation in lentiviral encephalitis

HIV encephalitis (HIVE) is characterized by neurodegeneration mediated by toxins derived from infected and activated brain macrophages. Since the peripheral benzodiazepine receptor (PBR) is abundant on brain macrophages, we hypothesized that [(3)H]DAA1106, a new PBR ligand, can label infected and activated brain macrophages in HIVE. Using cell culture and postmortem brain tissues from HIVE and a macaque model of HIVE, we show that [(3)H]DAA1106 binds with high affinity to activated and infected macrophages in regions of synaptic damage. Further, binding affinity reflected by lower K(D) (dissociation constant) values and the B(max) (total number of binding sites) to K(D) ratios reflective of ligand-binding potential was significantly higher with [(3)H]DAA1106 compared to the extensively characterized PBR ligand [(3)H](R)-PK11195. These data suggest that DAA1106 binds with high affinity to activated and infected brain macrophages and possesses binding characteristics beneficial for in vivo use in the detection and clinical monitoring of HIVE using positron emission tomography.

Accelerated Tau deposition in the brains of individuals infected with human immunodeficiency virus-1 before and after the advent of highly active anti-retroviral therapy

This study aims to investigate the influence of human immunodeficiency virus (HIV) infection on the neurodegenerative processes normally associated with ageing. We have looked for evidence of beta amyloid and hyperphosphorylated Tau deposition in HIV-infected subjects before and after the advent of highly active anti-retroviral therapy (HAART). In addition we have looked for evidence of axonal damage. We have compared these HIV-positive cases with age-matched controls and with older non-demented controls. We find no evidence of significant premature beta amyloid deposition in HIV-infected cases; however, we do observe elevated levels of hyperphosphorylated Tau in the hippocampus of many HIV-infected subjects, compared with age-matched controls. The greatest levels of hyperphosphorylated Tau are noted in HAART-treated subjects. Axonal damage marked by expression of beta amyloid pre-cursor protein (BAPP) was highly variable in all groups including control subjects. We surmise that HIV infection and/or the use of anti-retroviral therapy may predispose to accelerated neuroageing in the form of hyperphosphorylated Tau deposition in the hippocampus. Within the age groups studied these significant neuropathological changes remained subclinical and were not yet associated with cognitive impairment.

Neurobiology of multiple insults: HIV-1-associated brain disorders in those who use illicit drugs

Despite two decades of research, certain aspects of HIV-related central nervous system (CNS) disease remain poorly understood. HIV targets microglia and macrophages within the CNS and enters the brain compartment early. However, HIV is there held in check apparently until the onset of significant immune compromise, when viral replication, microglial activation, neuronal damage, and cognitive impairment are likely to ensue. Illicit drug abuse continues to be a significant risk factor for HIV transmission worldwide. Whether HIV-related CNS disease is more prevalent or more severe in this risk group has long been debated. Drugs of abuse can of themselves cause immune suppression, blood-brain barrier breakdown, microglial activation, and neuronal injury. This review presents evidence that HIV associated CNS disorders are indeed accentuated in drug abusers. However, the advent of effective therapy has added a new dimension, which must be taken into consideration. Treated individuals are surviving much longer and HIV encephalitis and HIV-associated dementia have become much less common. However, more subtle forms of CNS damage are emerging. Examination of the brains of individuals who have been treated long term with highly active antiretroviral therapy (HAART) reveals a surprising degree of microglial activation, comparable at times to that seen formerly in milder cases of HIV encephalitis. In addition, these individuals show evidence of increased deposition of neurodegenerative proteins, particularly hyperphosphorylated tau. Similar observations have been made in young opiate abusers who are HIV negative. Taken together, these results suggest that neuroinflammation and neurodegeneration, which are clinically silent at present, may cause problems in the future in HAART-treated subjects.

Influence of HAART on HIV-related CNS disease and neuroinflammation

Neuroinflammation has an established link with AIDS-related dementia but has not been investigated in the post-highly active anti-retroviral therapy (HAART) era. In this autopsy study we examined post-HAART cases in Edinburgh for the presence of HIV-related pathology and in well-treated cases for evidence of neuroinflammation. We focused on basal ganglia and the hippocampus, 2 key areas of the brain for cognitive functioning and compared pre- and post-HAART cases for neuroinflammatory status. We find evidence, post-HAART, that there is a high level of microglial/macrophage activation that is comparable with the levels seen, pre-HAART, in HIV encephalitis (HIVE) and AIDS cases. This result was maximal in the hippocampus where microglial/macrophage upregulation in the HAART-treated group exceeded that seen in HIVE. In the basal ganglia, HAART-treated cases showed significantly higher levels of CD68-positive microglia/macrophages than in control brains (p = 0.004), and in the hippocampus levels were significantly higher than those seen in control cases, pre-HAART AIDS, and presymptomatic brains (p = 0.01). However, lymphocyte levels in the areas examined were low in HAART-treated cases. We conclude that there is a surprising degree of ongoing neuroinflammation in HAART-treated patients, particularly in the hippocampus. This may pose a threat for the future health of individuals maintained long-term on HAART therapy.

Viral diseases of the central nervous system

Viral diseases of the central nervous system encompass a wide range of different processes, mainly inflammation affecting the brain (encephalitis), the meninges (meningitis), or a combined meningoencephalitis. The spinal cord can be affected as well (myelitis). Another group of viral-related disorders, sometimes without a clear pathophysiological mechanism disclosed, include post-viral illnesses. All of these groups of diseases are discussed in this article, with an emphasis on their imaging presentation, using magnetic resonance imaging.

Neurotoxicité et neuroprotection, les deux facettes de l’activation microgliale au cours de l’infection par le virus de l’immunodéficience humaine (VIH)

Microglial cells and macrophages are the only cells within the central nervous system, in which productive HIV infection has been unquestionably demonstrated. Those cells play a key role in the origin of the neuronal dysfunction underlying HIV-related cognitive disorders. The neurotoxicity of the cells is both direct, related to HIV proteins, and indirect, through the release by activated macrophages and microglial cells (AMM) of multiple neurotoxic factors. The mechanisms of neuronal damage, the final irreversible stage of which is neuronal apoptosis, are only partly understood but appear to involve oxidative stress and glutamate-receptor mediated toxicity. On the other hand, recent experimental in vitro and in vivo studies, and neuropathological studies in HIV infected patients at different stages of the disease, tend to show that AMM express excitatory amino acid transporters (EAAT) suggesting that in addition to their neurotoxic properties, they also have a neuroprotective role by clearing extra-cellular glutamate and producing antioxidant glutathione. This neuroprotective role could counteract, at least in the early stages of the disease, the neurotoxicity of AMM explaining the discrepancy between the conspicuous microglial activation at that stage and the absence of cognitive disorder, neuronal loss and neuronal apoptosis. It could also explain the regression of the cognitive disorders in some patients who received highly active antiretroviral treatment.