There is good evidence that the kynurenine pathway (KP) and one of its products, quinolinic acid (QUIN), play a role in the pathogenesis of neurological diseases, in particular AIDS dementia complex. Although QUIN has been shown to be produced in neurotoxic concentrations by macrophages and microglia, the role of astrocytes in QUIN production is controversial. Using cytokine‐stimulated cultures of human astrocytes, we assayed key enzymes and products of the KP. We found that human astrocytes lack kynurenine hydroxylase so that large amounts of kynurenine and the QUIN antagonist kynurenic acid were produced. However, the amounts of QUIN that were synthesized were subsequently completely degraded. We then showed that kynurenine in concentrations comparable with those produced by astrocytes led to significant production of QUIN by macrophages. These results suggest that astrocytes alone are neuroprotective by minimizing QUIN production and maximizing synthesis of kynurenic acid. However, it is likely that, in the presence of macrophages and/or microglia, astrocytes become indirectly neurotoxic by the production of large concentrations of kynurenine that can be secondarily metabolized by neighbouring or infiltrating monocytic cells to form the neurotoxin QUIN.

Background: We previously reported similar AIDS-free survival at 3 years in children who were >1 year old initiating antiretroviral therapy (ART) and randomized to early versus deferred ART in the Pediatric Randomized to Early versus Deferred Initiation in Cambodia and Thailand (PREDICT) study. We now report neurodevelopmental outcomes. Methods: Two hundred eighty-four HIV-infected Thai and Cambodian children aged 1–12 years with CD4 counts between 15% and 24% and no AIDS-defining illness were randomized to initiate ART at enrollment (“early,” n = 139) or when CD4 count became <15% or a Centers for Disease Control (CDC) category C event developed (“deferred,” n = 145). All underwent age-appropriate neurodevelopment testing including Beery Visual Motor Integration, Purdue Pegboard, Color Trails and Child Behavioral Checklist. Thai children (n = 170) also completed Wechsler Intelligence Scale (intelligence quotient) and Stanford Binet Memory test. We compared week 144 measures by randomized group and to HIV-uninfected children (n = 319). Results: At week 144, the median age was 9 years and 69 (48%) of the deferred arm children had initiated ART. The early arm had a higher CD4 (33% versus 24%, P < 0.001) and a greater percentage of children with viral suppression (91% versus 40%, P < 0.001). Neurodevelopmental scores did not differ by arm, and there were no differences in changes between arms across repeated assessments in time-varying multivariate models. HIV-infected children performed worse than uninfected children on intelligence quotient, Beery Visual Motor Integration, Binet memory and Child Behavioral Checklist. Conclusions: In HIV-infected children surviving beyond 1 year of age without ART, neurodevelopmental outcomes were similar with ART initiation at CD4 15%–24% versus <15%, but both groups performed worse than HIV-uninfected children. The window of opportunity for a positive effect of ART initiation on neurodevelopment may remain in infancy.

Objective: Understanding the extent to which early antiretroviral therapy (ART) can limit the establishment and persistence of the HIV reservoir is an important step to designing interventions aimed at achieving HIV cure. We measured the markers of HIV persistence and HIV-specific immunity in early treated children. Design: This is a cross-sectional study that enrolled 15 children older than 2 years of age who initiated ART before 6 months of age and had sustained viral suppression. Total and integrated HIV DNA, and 2-LTR circles in CD4⁺ T cells, HIV antibody response by fourth generation HIV enzyme immunoassay, and CD4⁺ and CD8⁺ T-cell responses to gag/env peptides by intracellular cytokine staining of CD4⁺ and CD8⁺ T cells were measured. Results: The median current age was 6.3 years and age at ART initiation was 17 weeks. The median duration of viral suppression was 6 years, and all had HIV RNA less than 50 copies/ml. The median CD4⁺ T cells was 44%. The median total HIV DNA was 132 copies/10⁶ CD4⁺ T cells (range 11–1804) and integrated HIV DNA was 17 copies/10⁶ CD4⁺ T cells (range 0–516), and no one had detectable 2-LTR circles. Nine of the 15 children (60%) had undetectable or extremely low integrated HIV DNA (<20 copies/10⁶ CD4⁺ T cells). All except one (93%) had undetectable HIV-specific CD4⁺/CD8⁺ cell responses and seven (47%) had nonreactive enzyme immunoassay. Conclusion: Early ART resulted in very low levels of markers of HIV persistence and undetectable HIV-specific immune responses in the majority of HIV-infected children who started ART before 6 months of age.

Quinolinic acid (QUIN) has been associated with several inflammatory neurologic disorders, including AIDS dementia complex (ADC). Recent studies suggest that activation of macrophages with either HIV-1 or interferone (IFN-γ) can lead to QUIN production. However, the importance of other cytokines, especially those related to the macrophage and that are especially important in ADC pathogenesis, remains unclear. We, therefore, sought to determine the role of tumor necrosis factor-α (TNF-α) and IFN-α in the production of QUIN. Primary human macrophages were stimulated with two different concentrations of these cytokines alone, in combination with each other, and with IFN-γ. QUIN concentrations in the supernatants were then measured by mass spectrometry at 24, 48, and 72 hs. Results at 72 h showed significant increases in QUIN production in the cells stimulated with IFN-γ (10297 ± 170 nmol/L) and also in those stimulated with IFN-α (3600 ± 113 nmol/L), whereas TNF-α-stimuIated macrophages produced low levels of QUIN (1108 ±23 nmol/L). Macrophages stimulated with the cytokine combinations TNF-α and IFN-γ, IFN-α, and IFN-γ, and TNF-α and IFN-α also resulted in increases in QUIN production (11471 ± 77.6 nmol/L, 16656 ± 184 nmol/L, and 3369 ± 120.5 nmol/L, respectively). The increases in QUIN production in all of the cytokine treatments approached or exceeded in vivo concentrations of QUIN that have been shown to be neurotoxic. These data further support a role for QUIN in cytokine-mediated neuronal death in inflammatory disorders of the brain, especially ADC.