Could cholinesterase inhibitors and memantine alleviate HIV dementia?

Mechanisms of Cognitive Aging in the HIV-Positive Adult

PURPOSE OF REVIEW

As of the year 2016, an estimated 50% of the United States' HIV-Positive population is aged 50 years or older. Due to a combination of increased rates of infection in older adults, and successful anti-retroviral (ART) regimens allowing HIV-positive adults to survive for decades with the disease, we are now faced with a steadily graying HIV-positive population, with only limited knowledge of how the cognitive and physiological effects of aging intersect with those of chronic HIV-infection.

RECENT FINDINGS

Age-related changes to mood, cognition, and neurological health may be experienced differently in those living with HIV, and research concerning quality of life, mental health, and cognitive aging needs to account for and explore these factors more carefully in the coming years.

SUMMARY

This review will explore the topic of cognitive aging with HIV: 1. Central nervous system (CNS) infection of HIV and how the virus affects brain integrity and function; 2. Cognitive and behavioral symptoms of HIV-Associated Neurocognitive Disorders (HAND); 3. Neurobiological theories of Cognitive Aging and how these processes may be exacerbated by HIV-infection; 4: Clinical implications and complications of aging with HIV and factors that may result in poorer cognitive outcomes.

HIV-associated dementia in older adults: clinical and tomographic aspects

BACKGROUND

Elderly adults with human immunodeficiency virus (HIV) are at greater risk of developing cognitive impairment. The purpose of this study was to describe clinical and tomographic characteristics of HIV-1 associated dementia (HIVD) in older adults.

METHODS

A descriptive study was carried out involving eight HIVD patients. Seven tests were employed for cognitive assessment and transformed to whole number z-scores using appropriate normative sets.

RESULTS

The average age of the patients was 71 years; seven cases described the route of HIV infection as being heterosexual; and mean schooling was 6.5 years. Six subjects were using highly active anti-retroviral therapy (HAART), with an average CD4 count of 407.8 cells/mm3. Mild dementia was detected in most cases (87.5%). Deficits on neuropsychological tests showed results similar to multi-center transversal studies on HIVD. The classic HIVD triad observed in younger adults was also seen in this population: i.e. cognitive changes, psychiatric changes and motor impairment. Cortical injury shown by dyscalculia, visual-spatial change and language deficits were frequent. Brain images showed cortical atrophy in all patients but was restricted to frontal lobes in five cases.

CONCLUSION

The findings on brain imaging were non-specific, revealing images similar to those of the elderly brain and to HIVD in younger adults. HIVD in the elderly is a challenge and become an increasingly significant differential diagnosis for cognitive loss in old age. This dementia must be clinically suspected and image exams are useful in excluding other central disorders. Prospective studies of HIV-positive elderly people are warranted to better understand HIVD.

HIV-associated neurocognitive disorders: a changing pattern

Combination antiretroviral therapy has dramatically decreased the incidence of HIV-related mortality and serious opportunistic diseases, among which is HIV-associated dementia. However, minor forms of cognitive dysfunction have not disappeared and may even have increased in frequency. Aging of HIV+ patients, insufficient penetration of antiretroviral drugs into the brain with continuous low-grade viral production and inflammation may play a role. A putative neurotoxicity of combination antiretroviral therapy is controversial. In this article, we will discuss these aspects, as well as clinical and pathophysiological features shared by HIV-associated neurocognitive disorders and other neurodegenerative diseases, especially Alzheimer’s disease. This article will briefly summarize the current clinical trials on neuroprotective agents, and the management of patients with neurocognitive disorders will be discussed.

Molecular pathology of neuro-AIDS (CNS-HIV)

The cognitive deficits in patients with HIV profoundly affect the quality of life of people living with this disease and have often been linked to the neuro-inflammatory condition known as HIV encephalitis (HIVE). With the advent of more effective anti-retroviral therapies, HIVE has shifted from a sub-acute to a chronic condition. The neurodegenerative process in patients with HIVE is characterized by synaptic and dendritic damage to pyramidal neurons, loss of calbindin-immunoreactive interneurons and myelin loss. The mechanisms leading to neurodegeneration in HIVE might involve a variety of pathways, and several lines of investigation have found that interference with signaling factors mediating neuroprotection might play an important role. These signaling pathways include, among others, the GSK3beta, CDK5, ERK, Pyk2, p38 and JNK cascades. Of these, GSK3beta has been a primary focus of many previous studies showing that in infected patients, HIV proteins and neurotoxins secreted by immune-activated cells in the brain abnormally activate this pathway, which is otherwise regulated by growth factors such as FGF. Interestingly, modulation of the GSK3beta signaling pathway by FGF1 or GSK3beta inhibitors (lithium, valproic acid) is protective against HIV neurotoxicity, and several pilot clinical trials have demonstrated cognitive improvements in HIV patients treated with GSK3beta inhibitors. In addition to the GSK3beta pathway, the CDK5 pathway has recently been implicated as a mediator of neurotoxicity in HIV, and HIV proteins might activate this pathway and subsequently disrupt the diverse processes that CDK5 regulates, including synapse formation and plasticity and neurogenesis. Taken together, the GSK3beta and CDK5 signaling pathways are important regulators of neurotoxicity in HIV, and modulation of these factors might have therapeutic potential in the treatment of patients suffering from HIVE. In this context, the subsequent sections will focus on reviewing the involvement of the GSK3beta and CDK5 pathways in neurodegeneration in HIV.

Psychopharmacology in HIV-infected patients

Neuropsychiatric disorders and syndromes may be underdiagnosed and inadequately treated in individuals infected with HIV. Depression in particular is among the most prevalent diagnoses, and data from controlled clinical studies have shown that antidepressant medications are efficacious and safe for treating depression in HIV-infected persons. A significant shortcoming of this literature is that most of the available data are from studies conducted before the advent of highly active antiretroviral therapy. In addition, apart from antidepressant medications, controlled studies systematically assessing efficacy and safety issues for other classes of psychotropic drugs (e.g., antipsychotic and anxiolytic medications) in HIV-infected persons are lacking. This review summarizes essential findings pertaining to the use of psychotropic medications to treat depression and other neuropsychiatric disorders in the context of HIV. It includes a discussion of clinically relevant treatment considerations (e.g., side effects, drug-drug interactions) derived from the existing literature as well as judgments that clinicians face in the absence of research data. Despite some shortcomings of the existing literature, overall there is compelling evidence that the appropriate use of psychotropic medications (coupled with behavioral therapy) can improve the quality of life of mentally ill HIV-infected individuals.

Addressing risk factors of cognitive impairment in adults aging with HIV: a social work model

With advances in life-extending medications and later- life infections, the number of older adults with HIV is increasing. Unfortunately, the synergistic effects of aging with HIV may place many people at risk of developing cognitive impairments which can disrupt everyday functioning. Fortunately, cognitive reserve may be maintained, or in some cases improved, by taking action to prevent or mitigate such loss. Preventative and treatment strategies that support biopsychosocial aspects of cognition include reducing alcohol and substance use; improving nutrition; diminishing the effects of comorbidities; increasing social contact; reducing depression and stress levels; engaging in cognitively stimulating activities; applying cognitive remediation therapies; and incorporating psychopharmacological interventions. Such strategies can improve the physiological integrity and health of the brain, thus supporting neuroplasticity and increasing cognitive reserve. Social workers are in a favorable position to recognize cognitive decline in clients and recommend or administer solutions to address such problems. A model for social workers advocating for older clients with HIV who have cognitive problems is provided.