The ART of HIV therapies: dopaminergic deficits and future treatments for HIV pediatric encephalopathy

Bioenergetic adaptations to HIV infection. Could modulation of energy substrate utilization improve brain health in people living with HIV-1?

The human brain consumes more energy than any other organ in the body and it relies on an uninterrupted supply of energy in the form of adenosine triphosphate (ATP) to maintain normal cognitive function. This constant supply of energy is made available through an interdependent system of metabolic pathways in neurons, glia and endothelial cells that each have specialized roles in the delivery and metabolism of multiple energetic substrates. Perturbations in brain energy metabolism is associated with a number of different neurodegenerative conditions including impairments in cognition associated with infection by the Human Immunodeficiency Type 1 Virus (HIV-1). Adaptive changes in brain energy metabolism are apparent early following infection, do not fully normalize with the initiation of antiretroviral therapy (ART), and often worsen with length of infection and duration of anti-retroviral therapeutic use. There is now a considerable amount of cumulative evidence that suggests mild forms of cognitive impairments in people living with HIV-1 (PLWH) may be reversible and are associated with specific modifications in brain energy metabolism. In this review we discuss brain energy metabolism with an emphasis on adaptations that occur in response to HIV-1 infection. The potential for interventions that target brain energy metabolism to preserve or restore cognition in PLWH are also discussed.

Dopamine increases HIV entry into macrophages by increasing calcium release via an alternative signaling pathway

Dopaminergic dysfunction has long been connected to the development of HIV infection in the CNS. Our previous data showed that dopamine increases HIV infection in human macrophages by increasing the susceptibility of primary human macrophages to HIV entry through stimulation of both D1-like and D2-like receptors. These data suggest that, in macrophages, both dopamine receptor subtypes may act through a common signaling mechanism. To define better the mechanism(s) underlying this effect, this study examines the specific signaling processes activated by dopamine in primary human monocyte-derived macrophages (hMDM). In addition to confirming that the increase in entry is unique to dopamine, these studies show that dopamine increases HIV entry through a PKA insensitive, Ca²⁺ dependent pathway. Further examination demonstrated that dopamine can signal through a previously defined, non-canonical pathway in human macrophages. This pathway involves both Ca²⁺ release and PKC phosphorylation, and these data show that dopamine mediates both of these effects and that both were partially inhibited by the G_q/11 specific inhibitor YM-254890. Studies have shown that G_q/11 preferentially couples to the D1-like receptor D5, indicating an important role of the D1-like receptors in mediating these effects. These data indicate a role for Ca²⁺ flux in the HIV entry process, and suggest a distinct signaling mechanism mediating some of the effects of dopamine in macrophages. Together, the data indicate that targeting this alternative dopamine signaling pathway might provide new therapeutic options for individuals with elevated CNS dopamine suffering from NeuroHIV.

Novel use of levodopa in human immunodeficiency virus encephalopathy-mediated parkinsonism in an adult

We report a case of a 36-year-old man with a medical history of human immunodeficiency virus (HIV) infection who presented with hypomimia, hypophonia, bradykinesia, rigidity, and freezing of gait. His clinical presentation and magnetic resonance imaging were consistent with HIV encephalopathy with involvement of the bilateral basal ganglia and diffuse leukoencephalopathy. We initiated a trial of carbidopa-levodopa. The dose was escalated to 1050 mg levodopa daily. Amantadine was also started. The patient was closely monitored for behavioral, neurological, or systemic side effects. He tolerated therapy well without adverse effects. The patient's neurological status significantly improved with levodopa, including hypomimia, hypophonia, bradykinesia, and fluidity of gait. This case demonstrates that carbidopa-levodopa can be safely utilized to manage parkinsonism in an adult patient with HIV encephalopathy.

Dose-dependent neurocognitive deficits following postnatal day 10 HIV-1 viral protein exposure: Relationship to hippocampal anatomy parameters

Despite the availability of antiretroviral prophylactic treatment, pediatric human immunodeficiency virus type 1 (HIV-1) continues to be a significant risk factor in the post-cART era. The time of infection (i.e., during pregnancy, delivery or breastfeeding) may play a role in the development of neurocognitive deficits in pediatric HIV-1. HIV-1 viral protein exposure on postnatal day (P)1, preceding the postnatal brain growth spurt in rats, had deleterious effects on neurocognitive development and anatomical parameters of the hippocampus (Fitting et al., 2008a,b). In the present study, rats were stereotaxically injected with HIV-1 viral proteins, including Tat1-86 and gp120, on P10 to further examine the role of timing on neurocognitive development and anatomical parameters of the hippocampus (Fitting et al., 2010). The dose-dependent virotoxin effects observed across development following P10 Tat1-86 exposure were specific to spatial learning and absent from prepulse inhibition and locomotor activity. A relationship between alterations in spatial learning and/or memory and hippocampal anatomical parameters was noted. Specifically, the estimated number of neurons and astrocytes in the hilus of the dentate gyrus explained 70% of the variance of search behavior in Morris water maze acquisition training for adolescents and 65% of the variance for adults; a brain-behavior relationship consistent with observations following P1 viral protein exposure. Collectively, late viral protein exposure (P10) results in selective alterations in neurocognitive development without modifying measures of somatic growth, preattentive processing, or locomotor activity, as characterized by early viral protein exposure (P1). Thus, timing may be a critical factor in disease progression, with children infected with HIV earlier in life being more vulnerable to CNS disease.

Global developments in HIV neurology

Neurologic conditions associated with HIV remain major contributors to morbidity and mortality, and are increasingly recognized in the aging population on long-standing combination antiretroviral therapy (cART). Importantly, growing evidence suggests that the central nervous system (CNS) serves as a reservoir for viral replication with major implications for human immunodeficiency virus (HIV) eradication strategies. Though there has been major progress in the last decade in our understanding of the pathogenesis, burden, and impact of HIV-associated neurologic conditions, significant scientific gaps remain. In many low-income settings, second- and third-line cART regimens that carry substantial neurotoxicity remain treatment mainstays. Further, patients continue to present severely immunosuppressed with CNS opportunistic infections. Public health efforts should emphasize improvements in access and optimizing treatment of HIV-positive patients, specifically in resource-limited settings, to reduce the risk of neurologic sequelae.

Cognitive Function in Young Persons With and Without Perinatal HIV in the AALPHI Cohort in England: Role of Non-HIV-Related Factors

BACKGROUND

 There is limited evidence about the cognitive performance of older adolescents with perinatally acquired human immunodeficiency virus (HIV) compared with HIV-negative (HIV-) adolescents.

METHODS

 A total of 296 perinatally HIV-infected (PHIV+) and 97 HIV- adolescents (aged 12-21 and 13-23 years, respectively) completed 12 tests covering 6 cognitive domains. The HIV- participants had PHIV+ siblings and/or an HIV-infected mother. Domain-specific and overall (NPZ-6) z scores were calculated for PHIV+ participants, with or without Centers for Disease Control and Prevention (CDC) stage C disease, and HIV- participants. Linear regression was performed to explore predictors of NPZ-6.

RESULTS

 One hundred twenty-five (42%) of the PHIV+ and 31 (32%) of the HIV- participants were male; 251 (85%) and 69 (71%), respectively, were black African; and their median ages (interquartile range) were 16 (15-18) and 16 (14-18) years, respectively. In PHIV+ participants, 247 (86%) were receiving antiretroviral therapy, and 76 (26%) had a previous CDC C diagnosis. The mean (standard deviation) NPZ-6 score was -0.81 (0.99) in PHIV+ participants with a CDC C diagnosis (PHIV+/C), -0.45 (0.80) in those without a CDC C diagnosis (PHIV+/no C), and -0.32 (0.76) in HIV- participants (P < .001). After adjustment, there was no difference in NPZ-6 scores between PHIV+/no C and HIV- participants (adjusted coefficient, -0.01; 95% confidence interval, -.22 to .20). PHIV+/C participants scored below the HIV- group (adjusted coefficient, -0.44; -.70 to -.19). Older age predicted higher NPZ-6 scores, and black African ethnicity and worse depression predicted lower NPZ-6 scores. In a sensitivity analysis including PHIV+ participants only, no HIV-related factors apart from a CDC C diagnosis were associated with NPZ-6 scores.

CONCLUSIONS

 Cognitive performance was similar between PHIV+/no C and HIV- participants and indicated relatively mild impairment compared with normative data. The true impact on day-to-day functioning needs further investigation.

HIV-1 proteins, Tat and gp120, target the developing dopamine system

In 2014, 3.2 million children (< 15 years of age) were estimated to be living with HIV and AIDS worldwide, with the 240,000 newly infected children in the past year, i.e., another child infected approximately every two minutes [1]. The primary mode of HIV infection is through mother-to-child transmission (MTCT), occurring either in utero, intrapartum, or during breastfeeding. The effects of HIV-1 on the central nervous system (CNS) are putatively accepted to be mediated, in part, via viral proteins, such as Tat and gp120. The current review focuses on the targets of HIV-1 proteins during the development of the dopamine (DA) system, which appears to be specifically susceptible in HIV-1-infected children. Collectively, the data suggest that the DA system is a clinically relevant target in chronic HIV-1 infection, is one of the major targets in pediatric HIV-1 CNS infection, and may be specifically susceptible during development. The present review discusses the development of the DA system, follows the possible targets of the HIV-1 proteins during the development of the DA system, and suggests potential therapeutic approaches. By coupling our growing understanding of the development of the CNS with the pronounced age-related differences in disease progression, new light may be shed on the neurological and neurocognitive deficits that follow HIV-1 infection.

Evidence for developmental dopaminergic alterations in the human immunodeficiency virus-1 transgenic rat

Neurologic impairments associated with human immunodeficiency virus (HIV) infection in pediatric patients may affect quality of life, and can develop despite antiretroviral therapy (ART). Behavioral changes observed in clinical studies of HIV-infected children suggest alterations in dopaminergic neurotransmission. Findings from our model of choice, the HIV-1 transgenic rat, reveal a significant increase in phosphorylated tyrosine hydroxylase protein expression and a decrease in dopamine transporter mRNA, without changes in tyrosine hydroxylase (TH) or dopamine transporter (DAT) protein or in more general markers of protein and gene expression levels in the HIV-1 transgenic rat midbrain. Thus these findings suggest selective vulnerability of the dopamine system in developing brains to HIV-1 infection.