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Regional brain volumetric changes despite 2 years of treatment initiated during acute HIV infection
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Participants enrolled during AHI exhibited progressive brain atrophy 2 years after infection, despite very early initiation of cART.
"Our results are bolstered by data from separate cohorts indicating early brain damage and preferential susceptibility of the putamen during PHI [11,56]. Impaired cognition seen in a subset of SEARCH010/RV254 participants after 6 months of treatment [57] suggests that brain injury may be incompletely ameliorated. Moreover, consistent with our findings, the cognitive deficits were manifested in domains in which basal ganglia play crucial roles (psychomotor speed, fine motor skills, and executive functioning [57-59]). Reduced putamen volume in PHI has been correlated with psychomotor slowing [56], and basal ganglia reductions in chronic HIV disease are associated with motor [60] and executive [61] dysfunction......
......The decreases of about 3% in putamen and caudate volumes over 2 years, or annual atrophy rates of 1.5% which we note are greater than the 0.63%/year rate reported even in untreated PHI [30], should be compared with normal age-related loss.
........The decreases we observed in putamen and caudate volumes most likely reflect atrophy due to HIV (or to neurotoxic effects of cART), although this remains speculative in the absence of an HIV-uninfected Thai comparison group. Caudate and putamen atrophy was lowest in participants who achieved plasma HIV RNA below 50 copies/ml by week 4. The trend association observed between mega-cART and rapidity of viral suppression is supported by previous observations of the SEARCH 010/RV254 cohort [67] and by neurocognitive improvement linked to maraviroc-intensified cART [68]. Taken together, these findings indicate that cART intensification by raltegravir and maraviroc should be further examined for its ability to preserve brain integrity in HIV-infected individuals.
HIV invasion of the central nervous system (CNS) occurs early. The virus has been isolated in the brain 15 days after iatrogenic HIV infection, only 1 day after it was first found in blood [27]. Computational modeling of clinical data has identified the first 3 weeks postinfection as a window of opportunity in which cART initiation may optimally control HIV replication and prevent immune activation, and the establishment of viral reservoirs [28]. Whether HIV-induced brain injury can be arrested or slowed by immediate treatment remains unknown. SEARCH010/RV254 - a longitudinal cohort study of AHI - enrolls and evaluates participants 2-3 weeks following history of exposure. Thereafter, cART is commenced at once. Matched samples at baseline and 2-year follow-up are a strength of this study.....The present work evaluated SEARCH010/RV254 participants for changes in volumes of nine a priori brain regions of interest after 24 months of cART. Although HIV-infected individuals over age 60 have exhibited progressive brain atrophy despite more than 3 years of viral suppression [29], previous longitudinal studies suggest that early cART may prevent such injury....Brain volume deficits have been associated with disrupted levels of cerebral metabolites [33] and plasma cytokines [34] in chronic HIV infection.
Data on illicit substance use were unavailable for three individuals, but the majority of our cohort (n = 21, or 68%) denied use within the 4 months prior to baseline. Ten participants reported using illicit substances during that time: poppers (n = 4); methamphetamine (n = 3); poppers and methamphetamine (n = 2); and no specific substance information (n = 1; only 'illicit drug use' was noted)......likely confounding factors such as substance use and sexually transmitted diseases (STDs) did not appear to influence our results. STD prevalence was below 6% and had no effect. The relatively low rate of illicit substance use in the SEARCH010/RV254 cohort [57] distinguishes it from other HIV studies that may have been confounded by drug or alcohol consumption (reviewed by Zahr [87]). Recreational substance use data were self-reported, available only at M0, and during the period of our study, not systematically collected, which limited their usefulness. However, individuals recruited into the cohort reported no history of substance use judged severe enough to compromise patient care (as evidenced by viral suppression by week 36 in 100% of the sample). Sensitivity analyses confirmed that illicit substance use in the 4 months prior to baseline did not affect atrophy of the caudate or putamen."
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Regional brain volumetric changes despite 2 years of treatment initiated during acute HIV infection
AIDS March 1 2020 - Kalpana J. Kallianpura, Neda Jahanshadb, Napapon Sailasutaa, Khunthalee Benjapornpongc, Phillip Chanc, Mantana Pothisrid, Netsiri Dumrongpisutikuld, Elizabeth Lawsa, Lishomwa C. Ndhlovua, Katherine M. Clifforde, Robert Paulf, Linda Jagodzinskig, Shelly Krebsg,h, Jintanat Ananworanicha,g,h, Serena Spudichi,
Victor Valcoure, on behalf of the SEARCH010/RV254 Study Group
Abstract
Objective:
To assess changes in regional brain volumes after 24 months among individuals who initiated combination antiretroviral therapy (cART) within weeks of HIV exposure.
Design:
Prospective cohort study of Thai participants in the earliest stages of HIV-1infection.
Methods:
Thirty-four acutely HIV-infected individuals (AHI; Fiebig I-V) underwent brain magnetic resonance (MR) imaging and MR spectroscopy at 1.5 T and immediately initiated cART. Imaging was repeated at 24 months. Regional brain volumes were quantified using FreeSurfer's longitudinal pipeline. Voxel-wise analyses using tensor-based morphometry (TBM) were conducted to verify regional assessments. Baseline brain metabolite levels, blood and cerebrospinal fluid biomarkers assessed by ELISA, and peripheral blood monocyte phenotypes measured by flow cytometry were examined as predictors of significant volumetric change.
Results:
Participants were 31 ± 8 years old. The estimated mean duration of infection at cART initiation was 15 days. Longitudinal analyses revealed reductions in volumes of putamen (P < 0.001) and caudate (P = 0.006). TBM confirmed significant atrophy in the putamen and caudate, and also in thalamic and hippocampal regions. In exploratory post-hoc analyses, higher baseline frequency of P-selectin glycoprotein ligand-1 (PSGL-1)-expressing total monocytes correlated with greater caudate volumetric decrease (ρ = 0.67, P = 0.017), whereas the baseline density of PSGL-1-expressing inflammatory (CD14+CD16+) monocytes correlated with putamen atrophy (ρ = 0.65, P = 0.022).
Conclusion:
Suppressive cART initiated during AHI may not prevent brain atrophy. Volumetric decrease appears greater than expected age-related decline, although examination of longitudinal change in demographically similar HIV-uninfected Thai individuals is needed. Mechanisms underlying progressive HIV-related atrophy may include early activation and enhanced adhesive and migratory capacity of circulating monocyte populations.
Discussion
Contrary to expectations, AHI participants demonstrated decreased volumes of caudate and putamen after 2 years of cART. The finding that brain injury may occur despite very early implementation of therapy is somewhat surprising, given the anticipated neuroprotective effects of acutely administered cART. However, HIV invasion of the CNS within 8 days of exposure [41] and CNS inflammation during AHI [41] constitute indirect evidence that the impact of HIV on the brain is almost immediate and may compete with mitigating effects of concomitant cART initiation. Our results are bolstered by data from separate cohorts indicating early brain damage and preferential susceptibility of the putamen during PHI [11,56]. Impaired cognition seen in a subset of SEARCH010/RV254 participants after 6 months of treatment [57] suggests that brain injury may be incompletely ameliorated. Moreover, consistent with our findings, the cognitive deficits were manifested in domains in which basal ganglia play crucial roles (psychomotor speed, fine motor skills, and executive functioning [57-59]). Reduced putamen volume in PHI has been correlated with psychomotor slowing [56], and basal ganglia reductions in chronic HIV disease are associated with motor [60] and executive [61] dysfunction.
The decreases of about 3% in putamen and caudate volumes over 2 years, or annual atrophy rates of 1.5% which we note are greater than the 0.63%/year rate reported even in untreated PHI [30], should be compared with normal age-related loss. Published rates of brain atrophy in healthy individuals are inconsistent [62]. Cross-sectional studies may not accurately characterize normal change [63,64], and many longitudinal studies, in addressing brain development or aging, overlook younger adults. Research on older adults typically focuses on global and medial temporal lobe atrophy in the context of aging-related dementia, with consequent neglect of other regions [63]. A 5-year study of healthy individuals (baseline age 20-77 years) measured respective annual atrophy rates of 0.83 and 0.73% for the caudate and putamen, independently of age [65]. In a different, similarly aged cohort, caudate and putamen shrinkage over 2 years was 0.44 and 0.47% (i.e. negligible) [66]. The decreases we observed in putamen and caudate volumes most likely reflect atrophy due to HIV (or to neurotoxic effects of cART), although this remains speculative in the absence of an HIV-uninfected Thai comparison group. Caudate and putamen atrophy was lowest in participants who achieved plasma HIV RNA below 50 copies/ml by week 4. The trend association observed between mega-cART and rapidity of viral suppression is supported by previous observations of the SEARCH 010/RV254 cohort [67] and by neurocognitive improvement linked to maraviroc-intensified cART [68]. Taken together, these findings indicate that cART intensification by raltegravir and maraviroc should be further examined for its ability to preserve brain integrity in HIV-infected individuals.
A potential limitation of morphometric MRI studies is the reliability of regional brain volume estimates. Longitudinal investigations of atrophy are facilitated by automated segmentation software, but confounded by multiple factors including variability due to data processing techniques. Gunter et al.[69] conducted a careful examination of sources of error in a study of semiautomated methods for computing brain volume loss. Volunteers aged 23-45 years were scanned every 6 weeks over a 5-month period to gauge errors inherent in the measurement process. With atrophy assumed to be imperceptible, image processing accounted for only 1/5 to 1/2 of test-retest variability [69]. Other variations reflected MRI acquisition differences (head position, motion, etc.) or real changes (e.g. from hydration effects [69,70]), which, together with variability due to quantification methods, make 'true' rates of atrophy elusive [69]. Recent versions of FreeSurfer are competitive with gold standard manual measurements in cognitively normal and impaired individuals [71], and FreeSurfer was validated for subcortical volumetry in HIV [72]. Importantly, for healthy young volunteers (aged 26-31 years) scanned repeatedly over 31 days (20 sessions; 2 scans per session), FreeSurfer's intersession volumetric variability did not exceed intrasession variability for the caudate, putamen, or any structure, except lateral ventricles [73] (intrasession variability is presumably unaffected by biological change). The reliability and consistency of FreeSurfer volume estimates in health and disease [72,74-79] impart confidence in our findings, which were confirmed by TBM analyses.
Decreased astrocytic uptake and glutamate metabolism is a major contributing factor in excitotoxic neuronal death linked to cognitive impairment in HIV [80,81]. We observed relationships between putamen atrophy and lower baseline Cho/creatine and Glx/creatine in frontal gray matter, which did not, however, overcome correction for multiple comparisons. Our ability to identify such associations may have been constrained by the modest sample size. The analyses of monocyte inflammatory markers also were exploratory and not corrected for multiple comparisons. However, the link between baseline monocyte expression of PSGL-1 and basal ganglia shrinkage suggests that increased trafficking of HIV-infected monocytes into the brain in AHI may play a causative role in subsequent atrophy. PSGL-1 promotes leukocyte trafficking across the blood-brain barrier (BBB) during inflammation by tethering the leukocytes to endothelial surfaces of blood vessels [82,83]. The intermediate/inflammatory CD14+CD16+ monocyte subset, in particular, appears to be involved in putamen atrophy. CD16-expressing monocytes are highly susceptible to HIV infection [84], selectively transmigrate across the BBB [84], and preferentially harbor the virus in cART-treated individuals [85]. New findings indicate that PSGL-1 promotes T-cell immune exhaustion, and it has also become evident that migration-independent functions of PSGL-1 in myeloid cells lead to immune activation and increased MCP-1 secretion through a mammalian target of rapamycin (mTOR) pathway [86]. Collectively, these findings provide clues to mechanisms associated with brain atrophy that warrant further investigation.
As CSF S100B and monocyte data were available only for participant subsets, our analyses of brain volumetric change in relation to baseline S100B and monocyte subsets had limited power. The sample size did not allow statistical adjustments for several known modifiers of brain aging, either adverse (e.g. vascular risk factors and stress) or beneficial (educational level, aerobic fitness) [62], which could affect brain volumes in this cohort. Comparison with normal brain alterations was hampered by the lack of an HIV-uninfected Thai comparison group. Nevertheless, likely confounding factors such as substance use and sexually transmitted diseases (STDs) did not appear to influence our results. STD prevalence was below 6% and had no effect. The relatively low rate of illicit substance use in the SEARCH010/RV254 cohort [57] distinguishes it from other HIV studies that may have been confounded by drug or alcohol consumption (reviewed by Zahr [87]). Recreational substance use data were self-reported, available only at M0, and during the period of our study, not systematically collected, which limited their usefulness. However, individuals recruited into the cohort reported no history of substance use judged severe enough to compromise patient care (as evidenced by viral suppression by week 36 in 100% of the sample). Sensitivity analyses confirmed that illicit substance use in the 4 months prior to baseline did not affect atrophy of the caudate or putamen.
A unique strength of the SEARCH010/RV254 study is its well characterized cohort, a significant proportion of which initiates cART during Fiebig I/II, permitting assessment of the earliest phase of the disease and the impact of immediate treatment. This eliminates what usually is a major source of uncertainty, the duration of infection, and minimizes the occurrence of pre-cART damage - a critical obstacle in determining whether cART is protective.
Conclusions
Participants enrolled during AHI exhibited progressive brain atrophy 2 years after infection, despite very early initiation of cART. Longitudinal assessment of HIV-uninfected Thai individuals is required to determine whether the volumetric decline is steeper than in healthy controls. Intensification of cART by maraviroc and raltegravir may inhibit brain atrophy by promoting faster viral suppression. Caudate and putamen volume loss is supported by a plausible link to early expansion of PSGL-1-expressing monocytes, particularly the intermediate/inflammatory subpopulation. Therapeutic strategies targeting viral production in PSGL-1 monocytes may reduce HIV-CNS invasion and eventual brain injury.
Regional brain volumetric changes after 24 months of combination antiretroviral therapy
Volumetric reductions were observed in the putamen (P < 0.001) and caudate (P = 0.006) over the first 24 months of cART (Table 2). As computed by the median percentage change, caudate and putamen volumes decreased by approximately 3%. The changes were significant after Holm-Bonferroni correction and were subsequently examined for relationships with baseline brain metabolites, plasma and CSF biomarkers, and monocyte subsets.
The TBM results can be visualized in Fig. 1. Briefly, TBM showed that the most significant change from baseline occurred bilaterally in the putamen (up to 5.2% atrophy in 24 months, P < 5 x 10-6, corrected), confirming FreeSurfer findings. Atrophy of the caudate was significant, although less striking at 2.5% (P < 1.4 x 10-4, corrected). In the thalamus, atrophy of approximately 4% was detected over 24 months (P < 2 x 10-4, corrected). Thalamic atrophy appears to be in regions representing the ventral posterior nucleus, pulvinar, lateral geniculate nucleus, and/or medial geniculate nucleus (individual nuclei cannot be distinguished without higher field strength and spatial resolution, so their identities were inferred from the observed locations of atrophy). The head of the hippocampus exhibited nearly 3% atrophy in 24 months (P < 2 x 10-4, corrected). Significant volumetric loss was also noted outside subcortical regions; for example, in the orbitofrontal cortex and the cingulate gyrus. Large portions of temporal white matter were observed to undergo atrophy of up to 3% (P < 2 x 10-6, corrected), along with the isthmus of the corpus callosum (2.5% atrophy; P < 1 x 10-4, corrected). In addition, CSF expansion was detected in sulcal regions.
Baseline clinical variables and regional brain volumetric change
Changes in caudate and putamen volumes did not correlate with age, years of education, baseline CD4+ cell count, plasma viral load, CSF viral load, or mega-cART status. Suppression of plasma viral load below 50 copies/ml by week 4 (n = 8) was associated with a smaller decrease from M0 to M24 in caudate volume (median 0.66 vs. 3.1%; P = 0.009), and a trend toward lower putamen volume loss (1.9 vs. 3.5%; P = 0.07).
Baseline brain metabolites as predictors of regional brain volumetric change
Greater change (decrease) in putamen volume correlated with lower baseline Cho/creatine (ρ = -0.43, P = 0.015) and lower Glx/creatine (ρ = -0.39, P = 0.027) in frontal GM (Fig. 2). The results do not survive Holm-Bonferroni correction for comparisons involving four metabolite ratios, four MRS voxel locations, and two regional volumes. Brain metabolite ratios at baseline did not relate to reduced caudate volume.
Substance use, co-infections, and regional brain volumetric change
To examine the possible confounding effects of substance use on our results, we compared percentage volume changes of caudate and putamen between participants who had used illicit substances during the 4 months preceding enrollment (n = 10) and those who had not (n = 21). The groups did not differ in either putamen (Mann-Whitney P = 0.72) or caudate (P = 0.35) volume loss. Additionally, we assessed caudate and putamen atrophy from M0 to M24 separately in the users and nonusers. For the putamen, P values of 0.013 and 0.012 for users and nonusers, respectively, revealed volumetric changes in both groups (less significant than in the combined sample because of reduced power). Similarly, caudate volume loss was comparable between users (P = 0.059) and nonusers (P = 0.063).
Volumetric loss in the putamen and caudate remained essentially unaltered when the three cases of co-infection with syphilis, gonorrhoea, or hepatitis C at baseline were excluded from analyses.
Plasma and cerebrospinal fluid biomarkers and monocyte subsets
Exploratory analyses examined baseline values of plasma and CSF biomarkers as predictors of percentage volume changes of the caudate and putamen. No significant correlations were found. Associations were also assessed between the volumetric changes and baseline blood monocyte subpopulations, including those expressing CCR2, CCR5, CX3CR1, PSGL-1, and CD163. Greater decrease in caudate volume correlated with higher total frequency and density [mean fluorescence intensity (MFI)] of PSGL-1-expressing monocytes at baseline (ρ = 0.67, P = 0.017; and ρ = 0.60, P = 0.038, respectively). Putamen volume decrease correlated positively with the baseline frequency (ρ = 0.61, P = 0.037) and density (ρ = 0.65, P = 0.022) of PSGL-1-expressing inflammatory monocytes. Volumetric associations with PSGL-1-expressing monocytes are plotted in Fig. 3.
Introduction
The neuroimaging signature of chronic HIV infection includes gray and white matter atrophy [1-3], disrupted frontostriatal functional connectivity [4,5], and abnormal white matter structural connectivity patterns [6]. Many neuroHIV studies have included participants with advanced disease or severe immune compromise prior to treatment [7-10]. However, reductions in total and cortical gray matter (GM) volumes have been identified even during primary HIV infection (PHI, <1 year post-transmission) [11], and decreased brain parenchymal volume was observed within the first 100 days [12]. Initial brain alterations may be determined by the severity of immunosuppression [13].
Early initiation of combination antiretroviral therapy (cART) is associated with greater probability of restoring normal CD4+ cell counts [14,15] and appears protective.
Neurofilament light protein - a marker of ongoing HIV-related neurodegeneration [16] - is elevated in cerebrospinal fluid (CSF) during untreated PHI [17], but is normal after 6 months of cART initiated during acute HIV infection (AHI) [18]. Treatment that is implemented within 6 months of infection greatly decreases CD4+ T-cell activation, and HIV DNA and RNA reservoir size [19,20]. The HIV DNA reservoir in peripheral blood mononuclear cells (PBMCs), established early in infection [21], predicts HIV disease progression and the time to viremic rebound following cessation of cART [22,23]. We and others have shown that peripheral monocytes harboring HIV in the setting of chronic HIV infection, and monocyte phenotypic changes associated with migration and activation, are linked to a range of brain abnormalities that persist, despite therapy [24]. Plasma elevations of soluble CD163 (sCD163) in PHI correlate with the proportion of CD14+CD16+ monocytes and decrease with effective cART [25]. Similar changes have been observed in AHI [26].
HIV invasion of the central nervous system (CNS) occurs early. The virus has been isolated in the brain 15 days after iatrogenic HIV infection, only 1 day after it was first found in blood [27]. Computational modeling of clinical data has identified the first 3 weeks postinfection as a window of opportunity in which cART initiation may optimally control HIV replication and prevent immune activation, and the establishment of viral reservoirs [28]. Whether HIV-induced brain injury can be arrested or slowed by immediate treatment remains unknown. SEARCH010/RV254 - a longitudinal cohort study of AHI - enrolls and evaluates participants 2-3 weeks following history of exposure. Thereafter, cART is commenced at once. Matched samples at baseline and 2-year follow-up are a strength of this study.
The present work evaluated SEARCH010/RV254 participants for changes in volumes of nine a priori brain regions of interest after 24 months of cART. Although HIV-infected individuals over age 60 have exhibited progressive brain atrophy despite more than 3 years of viral suppression [29], previous longitudinal studies suggest that early cART may prevent such injury. In a PHI cohort (infected for ∼3.7 months and followed for up to 6 years), duration of untreated infection correlated with brain volume loss prior to cART initiation; however, after cART, no further atrophy was observed [30]. Two-year changes in subcortical volumes of aviremic chronically HIV-infected individuals on cART were comparable to those of HIV-negative controls, although the HIV+ group had smaller volumes [31,32]. We therefore hypothesized the absence of HIV-related brain atrophy; namely, volumetric loss beyond that attributable to normal aging, which in the SEARCH010/RV254 cohort would be small. The link between brain atrophy in chronic, stable HIV disease and a history of immunosuppression supports our conjecture that very early antiretroviral intervention may prevent brain damage [33].
Brain volume deficits have been associated with disrupted levels of cerebral metabolites [33] and plasma cytokines [34] in chronic HIV infection. Plasma neopterin - a marker of immune activation - correlates with peripheral blood HIV DNA burden [35], which, in turn, relates to HIV-associated brain injury [36] and cognitive disorders [35]. Soluble CD14 (sCD14) is a marker of monocyte activation [37]; high plasma sCD14 levels predict morbidity and mortality in HIV [38]. CSF concentrations of the neuronal injury marker S100B may be elevated in HIV-infected individuals [39] and, in Alzheimer's disease, correlate with brain atrophy [40]. Brain inflammation at baseline in the SEARCH010/RV254 cohort has been identified by magnetic resonance spectroscopy (MRS) and by elevated CSF levels of inflammatory markers such as neopterin [41,42]. The present work investigated baseline brain metabolites as predictors of volumetric changes found to be significant. Exploratory analyses examined plasma and CSF biomarkers, and monocyte phenotypes potentially implicated in HIV neuropathogenesis, for their predictive value.
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