A prospective longitudinal in vivo 1H MR spectroscopy study of the SIV/macaque model of neuroAIDS

Longitudinal trajectories of brain volume in combined antiretroviral therapy treated and untreated simian immunodeficiency virus-infected rhesus macaques

OBJECTIVES

We used simian immunodeficiency virus (SIV)-infected nonhuman primates to investigate longitudinal changes of brain volume caused by SIV and the effect of combined antiretroviral therapy (cART). In addition, the relation between viral load, immune status, and brain volume were explored.

DESIGN

A longitudinal study of two healthy controls, five SIVmac239-infected macaques received cART (SIV+cART+) at 40 days postinnoculation, and five SIVmac239-infected macaques received no therapy (SIV+cART-).

METHODS

Structural T1-weighted MRI, blood and cerebrospinal fluid testing were acquired at multiple time points for 48 weeks postinfection (wpi). Brain volume was estimated using region of interest (ROI)-based analysis. Volume differences were compared among three groups. Linear regression models tested the associations between brain volumes and biomarkers (viral load, CD4+ T-cell count, CD4+/CD8+ ratio).

RESULTS

In our model, brain volume alteration in SIV-infected macaques can be detected at 12 wpi in several brain regions. As the infection progresses, the SIV+cART- macaques displayed generalized gray matter atrophy at the endpoint. Though initiate cART right after acute infection, SIV+cART+ macaques still displayed brain atrophy but showed signs of reversibility. Plasma viral load is mainly associated with subcortical nucleus volume whereas CD4+ T-cell count and CD4+/CD8+ ratio in plasma were associated with widespread cortical volume.

CONCLUSION

The SIVmac239-infected Chinese origin macaque is a valid model for neuroHIV. Brain atrophy caused by SIV infection can be relieved, even reversed, by cART. Our model also provides new insights into understanding the pathogenesis of brain injury in people with HIV (PWH).

Alterations of Brain Metabolites in Adults With HIV: A Systematic Meta-analysis of Magnetic Resonance Spectroscopy Studies

OBJECTIVE

A meta-analysis of proton magnetic resonance spectroscopy studies to investigate alterations in brain metabolites in people with HIV (PWH), the relationship between metabolite alterations and combination antiretroviral therapy (cART), and the relationship between metabolite alterations and cognitive impairment.

METHODS

The PubMed database was searched for studies published from 1997 to 2020. Twenty-seven studies were identified, which included 1255 PWH and 633 controls. Four metabolites (N-acetyl aspartate [NAA], myo-inositol [mI], choline [Cho], and glutamatergic metabolites [Glx]) from 5 brain regions (basal ganglia [BG], frontal gray and white matter [FGM and FWM], and parietal gray and white matter [PGM and PWM]) were pooled separately using random-effects meta-analysis.

RESULTS

During early HIV infection, metabolite alterations were largely limited to the BG, including Cho elevation, a marker of inflammation. cART led to global mI and Cho normalization (i.e., less elevations), but improvement in NAA was negligible. In chronic PWH on cART, there were consistent NAA reductions across brain regions, along with Cho and mI elevations in the FWM and BG, and Glx elevations in the FWM. Cognitive impairment was associated with NAA reduction and to a lesser degree mI elevation.

CONCLUSIONS

The BG are the primary region affected during early infection. cART is successful in partially controlling neuroinflammation (global mI and Cho normalization). However, neuronal dysfunction (NAA reductions) and neuroinflammation (mI and Cho elevations) persist and contribute to cognitive impairment in chronic PWH. Novel compounds targeting NAA signal pathways, along with better neuroinflammation control, may help to reduce cognitive impairment in PWH.

Advances in SIV/SHIV Non-Human Primate Models of NeuroAIDS

Non-human primates (NHPs) are the most relevant model of Acquired Immunodeficiency Syndrome (AIDS) and neuroAIDS, being of great importance in explaining the pathogenesis of HIV-induced nervous system damage. Simian Immunodeficiency Virus (SIV)/ Simian-Human Immunodeficiency Virus (SHIV)-infected monkeys have provided evidence of complex interactions between the virus and host that include host immune response, viral genetic diversity, and genetic susceptibility, which may explain virus-associated central nervous system (CNS) pathology and HIV-associated neurocognitive disorders (HAND). In this article, we review the recent progress contributions obtained using monkey models of HIV infection of the CNS, neuropathogenesis and SIV encephalitis (SIVE), with an emphasis on pharmacologic therapies and dependable markers that predict development of CNS AIDS.

Dimethyl Fumarate, an Approved Multiple Sclerosis Treatment, Reduces Brain Oxidative Stress in SIV-Infected Rhesus Macaques: Potential Therapeutic Repurposing for HIV Neuroprotection

Dimethyl fumarate (DMF), an antioxidant/anti-inflammatory drug approved for the treatment of multiple sclerosis, induces antioxidant enzymes, in part through transcriptional upregulation. We hypothesized that DMF administration to simian immunodeficiency virus (SIV)-infected rhesus macaques would induce antioxidant enzyme expression and reduce oxidative injury and inflammation throughout the brain. Nine SIV-infected, CD8⁺-T-lymphocyte-depleted rhesus macaques were studied. Five received oral DMF prior to the SIV infection and through to the necropsy day. Protein expression was analyzed in 11 brain regions, as well as the thymus, liver, and spleen, using Western blot and immunohistochemistry for antioxidant, inflammatory, and neuronal proteins. Additionally, oxidative stress was determined in brain sections using immunohistochemistry (8-OHdG, 3NT) and optical redox imaging of oxidized flavoproteins containing flavin adenine dinucleotide (Fp) and reduced nicotinamide adenine dinucleotide (NADH). The DMF treatment was associated with no changes in virus replication; higher expressions of the antioxidant enzymes NQO1, GPX1, and HO-1 in the brain and PRDX1 and HO-2 in the spleen; lower levels of 8-OHdG and 3NT; a lower optical redox ratio. The DMF treatment was also associated with increased expressions of cell-adhesion molecules (VCAM-1, ICAM-1) and no changes in HLA-DR, CD68, GFAP, NFL, or synaptic proteins. The concordantly increased brain antioxidant enzyme expressions and reduced oxidative stress in DMF-treated SIV-infected macaques suggest that DMF could limit oxidative stress throughout the brain through effective induction of the endogenous antioxidant response. We propose that DMF could potentially induce neuroprotective brain responses in persons living with HIV.

Regional Brain Recovery from Acute Synaptic Injury in Simian Immunodeficiency Virus-Infected Rhesus Macaques Associates with Heme Oxygenase Isoform Expression

Brain injury induced by acute simian (or human) immunodeficiency virus infection may persist or spontaneously resolve in different brain regions. Identifying the host factor(s) that promotes spontaneous recovery from such injury may reveal targets for therapeutic drug strategies for promoting recovery from acute neuronal injury. The gradual recovery from such injury observed in many, but not all, brain regions in the rhesus macaque model is consistent with the possible existence of a therapeutic window of opportunity for intervening to promote recovery, even in those regions not showing spontaneous recovery. In persons living with human immunodeficiency virus infection, such neuroprotective treatments could ultimately be considered as adjuncts to the initiation of antiretroviral drug therapy.

Brain injury occurs within days in simian immunodeficiency virus (SIV) or human immunodeficiency virus (HIV) infection, and some recovery may occur within weeks. Inflammation and oxidative stress associate with such injury, but what drives recovery is unknown. Chronic HIV infection associates with reduced brain frontal cortex expression of the antioxidant/anti-inflammatory enzyme heme oxygenase-1 (HO-1) and increased neuroinflammation in individuals with cognitive impairment. We hypothesized that acute regional brain injury and recovery associate with differences in regional brain HO-1 expression. Using SIV-infected rhesus macaques, we analyzed multiple brain regions through acute and chronic infection (90 days postinfection [dpi]) and quantified viral (SIV gag RNA), synaptic (PSD-95; synaptophysin), axonal (neurofilament/neurofilament light chain [NFL]), inflammatory, and antioxidant (enzymes, including heme oxygenase isoforms [HO-1, HO-2]) markers. PSD-95 was reduced in the brainstem, basal ganglia, neocortex, and cerebellum within 13 dpi, indicating acute synaptic injury throughout the brain. All areas except the brainstem recovered. Unchanged NFL was consistent with no acute axonal injury. SIV RNA expression was highest in the brainstem throughout infection, and it associated with neuroinflammation. Surprisingly, during the synaptic injury and recovery phases, HO-2, and not HO-1, progressively decreased in the brainstem. Thus, acute SIV synaptic injury occurs throughout the brain, with spontaneous recovery in regions other than the brainstem. Within the brainstem, the high SIV load and inflammation, along with reduction of HO-2, may impair recovery. In other brain regions, stable HO-2 expression, with or without increasing HO-1, may promote recovery. Our data support roles for heme oxygenase isoforms in modulating recovery from synaptic injury in SIV infection and suggest their therapeutic targeting for promoting neuronal recovery.

IMPORTANCE Brain injury induced by acute simian (or human) immunodeficiency virus infection may persist or spontaneously resolve in different brain regions. Identifying the host factor(s) that promotes spontaneous recovery from such injury may reveal targets for therapeutic drug strategies for promoting recovery from acute neuronal injury. The gradual recovery from such injury observed in many, but not all, brain regions in the rhesus macaque model is consistent with the possible existence of a therapeutic window of opportunity for intervening to promote recovery, even in those regions not showing spontaneous recovery. In persons living with human immunodeficiency virus infection, such neuroprotective treatments could ultimately be considered as adjuncts to the initiation of antiretroviral drug therapy.

A subtype of cerebrovascular pericytes is associated with blood-brain barrier disruption that develops during normal aging and simian immunodeficiency virus infection

Lax phenotypic characterization of these morphologically distinct pericytes has delayed our understanding of their role in neurological disorders. We herein establish markers which uniquely distinguish different subpopulations of human brain microvascular pericytes and characterize them independently from cerebrovascular smooth muscle cells. Furthermore, we begin to elucidate the roles of these subsets in blood-brain barrier (BBB) breakdown by studying natural aging and simian immunodeficiency virus (SIV) infection in rhesus macaques. We demonstrate that the main type-1 pericyte subpopulation in the brain of young uninfected adults is positive for platelet-derived growth factor receptor-β (PDGFRB) and negative for α-smooth muscle actin (SMA) and myosin heavy chain 11 (MYH11), whereas PDGFRB+/SMA+/MYH11- (type-2) pericytes are found more frequently in older adults and are associated with SIV infection and progression. Interestingly, we find a strong positive correlation between the degree of BBB breakdown and the percentage of type-2 pericytes regardless of age or SIV status. Taken together, our findings suggest that type-2 pericytes may be a cellular biomarker related to BBB disruption independent of disease status.

Simian immunodeficiency virus transiently increases brain temperature in rhesus monkeys: detection with magnetic resonance spectroscopy thermometry

PURPOSE

To evaluate brain temperature effects of early simian immunodeficiency virus (SIV) infection in rhesus macaques using proton magnetic resonance spectroscopy (MRS) thermometry (MRSt) and to determine whether temperature correlates with brain choline or myo-inositol levels.

METHODS

Brain temperature was retrospectively determined in serial MRS scans that had been acquired at baseline and at 2 and 4 weeks post-SIV infection (wpi) in 16 monkeys by calculating the chemical shift difference between N-acetylaspartate (NAA) and water peaks in sequentially acquired water-suppressed and unsuppressed point-resolved spectroscopy (PRESS) spectra. Frontal and parietal cortex, basal ganglia, and white matter spectra were analyzed.

RESULTS

At 2 wpi, brain and rectal temperatures increased relative to baseline and normalized at 4 wpi. Brain temperatures correlated with choline levels in several brain areas, but not with myo-inositol levels.

CONCLUSION

These data indicate that SIV transiently increases brain temperature soon after infection and that temperature is correlated with transient changes in choline levels. Given that choline levels are associated with brain inflammation in SIV-infected monkeys, our findings suggest that the SIV-induced temperature increase reflects brain inflammation. We conclude that MRSt may be informative in human immunodeficiency virus models and may be useful for assessing effects of treatments that reduce inflammation. This study also illustrates that existing MRS data sets containing unsuppressed water spectra can be used to measure tissue temperature, an important physiological parameter.

The Aging Brain With HIV Infection: Effects of Alcoholism or Hepatitis C Comorbidity

As successfully treated individuals with Human Immunodeficiency Virus (HIV)-infected age, cognitive and health challenges of normal aging ensue, burdened by HIV, treatment side effects, and high prevalence comorbidities, notably, Alcohol Use Disorders (AUD) and Hepatitis C virus (HCV) infection. In 2013, people over 55 years old accounted for 26% of the estimated number of people living with HIV (~1.2 million). The aging brain is increasingly vulnerable to endogenous and exogenous insult which, coupled with HIV infection and comorbid risk factors, can lead to additive or synergistic effects on cognitive and motor function. This paper reviews the literature on neuropsychological and in vivo Magnetic Resonance Imaging (MRI) evaluation of the aging HIV brain, while also considering the effects of comorbidity for AUD and HCV.

Sonic Hedgehog mimetic prevents leukocyte infiltration into the CNS during acute HIV infection

Infiltration of infected leukocytes culminates in establishment of a brain niche for Human Immunodeficiency Virus (HIV) during acute phase of infection, initiating an ongoing cascade of persistent viral replication and inflammation, that causes irreversible neuronal injury and HIV associated neurocognitive disease (HAND). In this study, humanized mice were treated with Smoothened Agonist (SAG), a Sonic Hedgehog (Shh) mimetic in order to fortify blood brain barrier (BBB) and dampen leukocyte extravasation into CNS during AHI. Results indicate that SAG treatment reduced viral burden in the CNS immediately after HIV transmission, but also conferred extended neuroprotection via increased BBB integrity (elevated levels of tight-junction protein, Claudin 5, and reduced S100B levels in periphery). These mice also showed healthier neurons with thick, uniform dendrites and reduced numbers of activated astrocytes. Additional in vitro experiments suggested SAG treatment was not associated with the establishment or reversal of latency in the target cells. Altogether, these findings validate neuroprotective role of Shh signaling and highlight the therapeutic potential of Shh mimetics against CNS complications associated with HIV infection. Further our results strongly demonstrate that pharmacological interventions to reduce leukocyte mobilization during early HIV infection, can provide prolonged neuroprotection, which might significantly delay the onset of HAND.

Neuronal-Glia Markers by Magnetic Resonance Spectroscopy in HIV Before and After Combination Antiretroviral Therapy

OBJECTIVE

Combination antiretroviral therapy (cART) can suppress plasma HIV RNA to undetectable levels; yet reports indicate persistent HIV-associated neurocognitive disorders (HAND) among treated individuals. We sought to investigate imaging correlates of incomplete cognitive recovery among individuals with chronic HIV.

METHODS

We used single voxel proton magnetic resonance spectroscopy in 4 regions of the brain to measure changes in neuronal and glia biomarkers in cART-naive subjects before (n = 59, 27 with HAND) and after 12 months of cART.

RESULTS

At baseline, we observed elevated total choline (CHO) in the basal ganglia (BG, P = 0.002) and in the posterior cingulate gyrus (PCG, P = 0.022) associated with HIV infection. Myo-inositol (MI) was elevated in the frontal white matter (FWM, P = 0.040). N-acetylaspartate was elevated in the BG (P = 0.047). Using a mixed model approach among all HIV-infected individuals, at 6 months, we observed decreased n- acetylaspartate in FWM (P = 0.031), decreased creatine in PCG (P = 0.026) and increased MI in frontal gray matter (FGM, P = 0.023). At 12 months, we observed an increase in BG MI (P = 0.038) and in FGM (P = 0.021). Compared to those with normal cognition, HAND cases had higher FGM MI (P = 0.014) at baseline. At 12 months, individuals that remained cognitively impaired compared with those without HAND exhibited elevated CHO in the PCG (P = 0.018) and decreased glutamate in both FWM (P = 0.027) and BG (P = 0.013).

CONCLUSIONS

cART started during chronic HIV is associated with reduced neuronal-glia and inflammatory markers. Alterations in CHO are noted among individuals who remain impaired after 12 months of cART.

Anti-α4 antibody treatment blocks virus traffic to the brain and gut early, and stabilizes CNS injury late in infection

Four SIV-infected monkeys with high plasma virus and CNS injury were treated with an anti-α4 blocking antibody (natalizumab) once a week for three weeks beginning on 28 days post-infection (late). Infection in the brain and gut were quantified, and neuronal injury in the CNS was assessed by MR spectroscopy, and compared to controls with AIDS and SIV encephalitis. Treatment resulted in stabilization of ongoing neuronal injury (NAA/Cr by 1H MRS), and decreased numbers of monocytes/macrophages and productive infection (SIV p28⁺, RNA⁺) in brain and gut. Antibody treatment of six SIV infected monkeys at the time of infection (early) for 3 weeks blocked monocyte/macrophage traffic and infection in the CNS, and significantly decreased leukocyte traffic and infection in the gut. SIV – RNA and p28 was absent in the CNS and the gut. SIV DNA was undetectable in brains of five of six early treated macaques, but proviral DNA in guts of treated and control animals was equivalent. Early treated animals had low-to-no plasma LPS and sCD163. These results support the notion that monocyte/macrophage traffic late in infection drives neuronal injury and maintains CNS viral reservoirs and lesions. Leukocyte traffic early in infection seeds the CNS with virus and contributes to productive infection in the gut. Leukocyte traffic early contributes to gut pathology, bacterial translocation, and activation of innate immunity.

To determine whether ongoing cell traffic is required for SIV-associated tissue damage, we blocked monocyte and T lymphocyte traffic to the brain and gut during a) ongoing infection or, b) at the time of infection. When animals were treated at four weeks post infection (late), once significant neuronal injury and accumulation of infected macrophages had already occurred, neuronal injury was stabilized, and CNS infection and the number of CNS lesions decreased. In the gut, there were significantly fewer productively infected cells and decreased inflammatory macrophages post treatment. Treatment at the time of infection (early) blocked infection of the CNS (SIV –DNA, RNA, or protein) and macrophage accumulation. In the gut, treatment at the time of infection blocked productive infection (SIV –RNA and protein) but not SIV –DNA. Interestingly, with treatment at the time of infection, there was no evidence of microbial translocation or elevated sCD163 in plasma, demonstrating that leukocyte traffic early plays a role in damage to gut tissues. Overall, these data point to the role of monocyte traffic and possibly lymphocytes to the CNS and leukocyte traffic to the gut to establish and maintain viral reservoirs. They underscore the role of monocyte/macrophage traffic and accumulation in the CNS for neuronal injury and maintenance of CNS lesions.

Longitudinal cerebral metabolic changes in pig-tailed macaques infected with the neurovirulent virus SIVsmmFGb

Longitudinal cerebral metabolite changes in pig-tailed macaques inoculated with the simian immunodeficiency virus SIVsmmFGb were evaluated with in vivo proton MRS at 3 T. Blood sample collection, and MRS were carried out before and 2, 4, 8, 12, 16, 20, and 24 weeks after SIV inoculation. Significant reduction of N-acetylaspartate (NAA)/creatine (Cr) and choline (Cho)/Cr ratios in prefrontal gray matter (PGM) and glutamate/glutamine(Glx)/Cr ratio in striatum, and increase of myo-inositol (mI)/Cr in striatum were observed during acute SIV infection. The metabolite alterations during the SIVsmmFGb infection are largely in agreement with previous findings in other non-human primate models and HIV patients. Also, NAA/Cr in PGM and striatum and Glx/Cr in striatum are negatively correlated with the percentage of CD8+ T cells after the SIV infection, suggesting the interaction between brain metabolite and immune dysfunction. The present study complements previous studies by describing the time course of alterations of brain metabolites during SIVsmmFGb infection. The findings further demonstrate the efficacy of the SIVsmmFGb-infected macaque as a model to characterize central nervous system infection using novel neuroimaging approaches and also as a tool for exploration of novel and advanced neuroimaging techniques in HIV/AIDS studies.

Imaging neuroinflammation? A perspective from MR spectroscopy

Neuroinflammatory mechanisms contribute to the brain pathology resulting from human immunodeficiency virus (HIV) infection. Magnetic resonance spectroscopy (MRS) has been touted as a suitable method for discriminating in vivo markers of neuroinflammation. The present MRS study was conducted in four groups: alcohol dependent (A, n = 37), HIV-infected (H, n = 33), alcohol dependent + HIV infected (HA, n = 38) and healthy control (C, n = 62) individuals to determine whether metabolites would change in a pattern reflecting neuroinflammation. Significant four-group comparisons were evident only for striatal choline-containing compounds (Cho) and myo-inositol (mI), which follow-up analysis demonstrated were due to higher levels in HA compared with C individuals. To explore the potential relevance of elevated Cho and mI, correlations between blood markers, medication status and alcohol consumption were evaluated in H + HA subjects. Having an acquired immune deficiency syndrome (AIDS)-defining event or hepatitis C was associated with higher Cho; lower Cho levels, however, were associated with low thiamine levels and with highly active antiretroviral HIV treatment (HAART). Higher levels of mI were related to greater lifetime alcohol consumed, whereas HAART was associated with lower mI levels. The current results suggest that competing mechanisms can influence in vivo Cho and mI levels, and that elevations in these metabolites cannot necessarily be interpreted as reflecting a single underlying mechanism, including neuroinflammation.

Cerebral metabolite changes prior to and after antiretroviral therapy in primary HIV infection

OBJECTIVE

We examined the longitudinal effects of primary HIV infection (PHI) and responses to early antiretroviral therapy (ART) on the brain using high-field magnetic resonance spectroscopy (MRS).

METHODS

Cerebral metabolites were measured longitudinally with 4T proton MRS and assessed for ART effects in participants with PHI. Levels of glutamate (Glu), N-acetylaspartate (NAA), myo-inositol (MI), and choline-containing metabolites (Cho) were measured relative to creatine + phosphocreatine (Cr) in anterior cingulate, basal ganglia, frontal white matter, and parietal gray matter.

RESULTS

Fifty-three participants recruited at median 3.7 months post HIV transmission were followed a median 6.0 months. A total of 23 participants initiated ART during follow-up. Prior to ART, increases per month were observed in Cho/Cr (slope = 0.0012, p = 0.005) and MI/Cr (slope = 0.0041, p = 0.005) in frontal white matter as well as increases in MI/Cr (slope = 0.0041, p < 0.001) and NAA/Cr (slope = 0.0024, p = 0.030) in parietal gray matter. After initiation of ART, prior positive slopes were no longer significantly different from zero, while Glu/Cr in basal ganglia decreased (slope = -0.0038, p = 0.031).

CONCLUSIONS

Early in HIV infection, increases of Cho/Cr and MI/Cr in treatment-naive participants suggest progressive inflammation and gliosis in the frontal white matter and parietal gray matter, which is attenuated after initiation of ART. Elevated baseline Glu/Cr in basal ganglia may signal excitotoxicity; its subsequent stabilization and downward trajectory with ART may lend further support for early ART initiation.

Structure-specific glial response in a macaque model of neuroAIDS: multivoxel proton magnetic resonance spectroscopic imaging at 3 Tesla

OBJECTIVE

As ~40% of persons with HIV also suffer neurocognitive decline, we sought to assess metabolic dysfunction in the brains of simian immunodeficiency virus (SIV)-infected rhesus macaques, an advanced animal model, in structures involved in cognitive function. We test the hypothesis that SIV-infection produces proton-magnetic resonance spectroscopic imaging (H-MRSI)-observed decline in the neuronal marker, N-acetylaspartate (NAA), and elevations in the glial marker, myo-inositol (mI), and associated creatine (Cr) and choline (Cho) in these structures.

DESIGN

Pre- and 4-6 weeks post-SIV infection (with CD8 T-lymphocyte depletion) was monitored with T2-weighted quantitative MRI and 16×16×4 multivoxel H-MRSI (TE/TR = 33/1400 ms) in the brains of five rhesus macaques.

METHODS

Exploiting the high-resolution H-MRSI grid, we obtained absolute, cerebrospinal fluid partial volume-corrected NAA, Cr, Cho and mI concentrations from centrum semiovale, caudate nucleus, putamen, thalamus and hippocampus regions.

RESULTS

Pre- to post-infection mean Cr increased in the thalamus: 7.2±0.4 to 8.0±0.8 mmol/l (+11%, P<0.05); mI increased in the centrum semiovale: 5.1±0.8 to 6.6±0.8 mmol/l, caudate: 5.7±0.7 to 7.3±0.5 mmol/l, thalamus: 6.8±0.8 to 8.5±0.8 mmol/l and hippocampus: 7.7±1.2 to 9.9±0.4 mmol/l (+29%, +27%, +24% and +29%, all P<0.05). NAA and Cho changes were not significant.

CONCLUSION

SIV-infection appears to cause brain injury indirectly, through glial activation, while the deep gray matter structures' neuronal cell bodies are relatively spared. Treatment regimens to reduce gliosis may, therefore, prevent neuronal damage and its associated neurocognitive impairment.

Global gray and white matter metabolic changes after simian immunodeficiency virus infection in CD8-depleted rhesus macaques: proton MRS imaging at 3 T

To test the hypotheses that global decreased neuro-axonal integrity reflected by decreased N-acetylaspartate (NAA) and increased glial activation reflected by an elevation in its marker, the myo-inositol (mI), present in a CD8-depleted rhesus macaque model of HIV-associated neurocognitive disorders. To this end, we performed quantitative MRI and 16 × 16 × 4 multivoxel proton MRS imaging (TE/TR = 33/1400 ms) in five macaques pre- and 4-6 weeks post-simian immunodeficiency virus infection. Absolute NAA, creatine, choline (Cho), and mI concentrations, gray and white matter (GM and WM) and cerebrospinal fluid fractions were obtained. Global GM and WM concentrations were estimated from 224 voxels (at 0.125 cm(3) spatial resolution over ~35% of the brain) using linear regression. Pre- to post-infection global WM NAA declined 8%: 6.6 ± 0.4 to 6.0 ± 0.5 mM (p = 0.05); GM Cho declined 20%: 1.3 ± 0.2 to 1.0 ± 0.1 mM (p < 0.003); global mI increased 11%: 5.7 ± 0.4 to 6.5 ± 0.5 mM (p < 0.03). Global GM and WM brain volume fraction changes were statistically insignificant. These metabolic changes are consistent with global WM (axonal) injury and glial activation, and suggest a possible GM host immune response.

Quantitative MRI Measures in SIV-Infected Macaque Brains

Multiple MRI modalities including Diffusion Tensor Imaging (DTI), perfusion MRI, in vivo MR Spectroscopy (MRS), volumetric MRI, contrast-enhanced MRI, and functional MRI have demonstrated abnormalities of the structural and functional integrity as well as neurochemical alterations of the HIV-infected central nervous system (CNS). MRI has been proposed as a robust imaging approach for the characterization of the stage of progression in HIV infection. However, the interpretation of the MRI findings of HIV patients is complicated by the fact that these clinical studies cannot readily be controlled. Simian immunodeficiency virus (SIV) infected macaques exhibit neuropathological symptoms similar to those of HIV patients, and are an important model for studying the course of CNS infection, cognitive impairment, and neuropathology of HIV disease as well as treatment efficacy. MRI of non-human primates (NHPs) is of limited benefit on most clinical scanners operating at or below 1.5 Tesla because this low field strength does not produce high-quality images of the relatively small NHP brain. Contemporary high field MRI (3T or more) for clinical use provides impressive sensitivity for magnetic resonance signal detection and is now accessible in many imaging centers and hospitals, facilitating the use of various MRI techniques in NHP studies. In this article, several high field MRI techniques and applications in macaque models of neuroAIDS are reviewed and the relation between quantitative MRI measures and blood T-cell alterations is discussed.

Central nervous system viral invasion and inflammation during acute HIV infection

BACKGROUND

Understanding the earliest central nervous system (CNS) events during human immunodeficiency virus (HIV) infection is crucial to knowledge of neuropathogenesis, but these have not previously been described in humans.

METHODS

Twenty individuals who had acute HIV infection (Fiebig stages I-IV), with average 15 days after exposure, underwent clinical neurological, cerebrospinal fluid (CSF), magnetic resonance imaging, and magnetic resonance spectroscopy (MRS) characterization.

RESULTS

HIV RNA was detected in the CSF from 15 of 18 subjects as early as 8 days after estimated HIV transmission. Undetectable CSF levels of HIV (in 3 of 18) was noted during Fiebig stages I, II, and III, with plasma HIV RNA levels of 285651, 2321, and 81978 copies/mL, respectively. On average, the CSF HIV RNA level was 2.42 log(10) copies/mL lower than that in plasma. There were no cases in which the CSF HIV RNA level exceeded that in plasma. Headache was common during the acute retroviral syndrome (in 11 of 20 subjects), but no other neurological signs or symptoms were seen. Intrathecal immune activation was identified in some subjects with elevated CSF neopterin, monocyte chemotactic protein/CCL2, and interferon γ-induced protein 10/CXCL-10 levels. Brain inflammation was suggested by MRS.

CONCLUSIONS

CSF HIV RNA was detectable in humans as early as 8 days after exposure. CNS inflammation was apparent by CSF analysis and MRS in some individuals during acute HIV infection.

Early detection of neuropathophysiology using diffusion-weighted magnetic resonance imaging in asymptomatic cats with feline immunodeficiency viral infection

HIV infection results in a highly prevalent syndrome of cognitive and motor disorders designated as HIV-associated dementia (HAD). Neurologic dysfunction resembling HAD has been documented in cats infected with strain PPR of the feline immunodeficiency virus (FIV), whereas another highly pathogenic strain (C36) has not been known to cause neurologic signs. Animals experimentally infected with equivalent doses of FIV-C36 or FIV-PPR, and uninfected controls were evaluated by magnetic resonance diffusion-weighted imaging (DW-MRI) and spectroscopy (MRS) at 17.5-18 weeks post-infection, as part of a study of viral clade pathogenesis in FIV-infected cats. The goals of the MR imaging portion of the project were to determine whether this methodology was capable of detecting early neuropathophysiology in the absence of outward manifestation of neurological signs and to compare the MR imaging results for the two viral strains expected to have differing degrees of neurologic effects. We hypothesized that there would be increased diffusion, evidenced by the apparent diffusion coefficient as measured by DW-MRI, and altered metabolite ratios measured by MRS, in the brains of FIV-PPR-infected cats relative to C36-infected cats and uninfected controls. Increased apparent diffusion coefficients were seen in the white matter, gray matter, and basal ganglia of both the PPR and C36-infected (asymptomatic) cats. Thalamic MRS metabolite ratios did not differ between groups. The equivalently increased diffusion by DW-MRI suggests similar indirect neurotoxicity mechanisms for the two viral genotypes. DW-MRI is a sensitive tool to detect neuropathophysiological changes in vivo that could be useful during longitudinal studies of FIV.

CD8+ lymphocyte depletion without SIV infection does not produce metabolic changes or pathological abnormalities in the rhesus macaque brain

BACKGROUND

Simian immunodeficiency virus (SIV) infection and persistent CD8(+) lymphocyte depletion rapidly leads to encephalitis and neuronal injury. The objective of this study is to confirm that CD8 depletion alone does not induce brain lesions in the absence of SIV infection.

METHODS

Four rhesus macaques were monitored by proton magnetic resonance spectroscopy ((1) H-MRS) before and biweekly after anti-CD8 antibody treatment for 8 weeks and compared with four SIV-infected animals. Post-mortem immunohistochemistry was performed on these eight animals and compared with six uninfected, non-CD8-depleted controls.

RESULTS

CD8-depleted animals showed stable metabolite levels and revealed no neuronal injury, astrogliosis or microglial activation in contrast to SIV-infected animals.

CONCLUSIONS

Alterations observed in MRS and lesions in this accelerated model of neuroAIDS result from unrestricted viral expansion in the setting of immunodeficiency rather than from CD8(+) lymphocyte depletion alone.

Brain creatine elevation and N-Acetylaspartate reduction indicates neuronal dysfunction in the setting of enhanced glial energy metabolism in a macaque model of neuroAIDS

Proton magnetic resonance spectroscopy has emerged as one of the most informative neuroimaging modalities for studying the effect of HIV infection in the brain, providing surrogate markers by which to assess disease progression and monitor treatment. Reductions in the level of N-Acetylaspartate and N-Acetylaspartate/creatine are established markers of neuronal injury or loss. However, the biochemical basis of altered creatine levels in neuroAIDS is not well understood. This study used a rapid progression macaque model of neuroAIDS to elucidate the changes in creatine. As the disease progressed, proton magnetic resonance spectroscopy revealed a decrease in N-Acetylaspartate, indicative of neuronal injury, and an increase in creatine yet to be elucidated. Subsequently, immunohistochemistry and stereology measures of decreased synaptophysin, microtubule-associated protein 2, and neuronal density confirmed neuronal injury. Furthermore, increases in ionized calcium binding adaptor molecule 1 and glial fibrillary acidic protein indicated microglial and astroglial activation, respectively. Given these data, elevated creatine may reflect enhanced high-energy phosphate turnover in highly metabolizing activated astrocytes and microglia.

PP2A1 binding, cell transducing and apoptotic properties of Vpr(77-92): a new functional domain of HIV-1 Vpr proteins

Background

The hallmark of HIV-1 pathogenesis is the progressive CD4⁺ T cell depletion and high propensity of CD4⁺ T cells to apoptosis. HIV-1 viral protein R (Vpr) is a major pro-apoptotic gene product. A first Vpr-mediated apoptotic mechanism that requires a physical interaction of HIV-1 Vpr_71-82 mitochondriotoxic domain containing the conserved sequence _71-HFRIGCRHSRIG_-82 with the Adenine Nucleotide Translocator (ANT) has been characterized. The family of Ser/Thr protein phosphatase PP2A interacts with several viral proteins to regulate cell growth and apoptotic pathways. Previous studies based on yeast two hybrid assays and mutational experiments indicated that PP2A₁ is involved in the induction of G2 arrest by HIV-1 Vpr.

Principal Findings

Experiments combining pull-down, cell penetration and apoptosis analyses in distinct human cells indicate that the PP2A₁ binding sequence from Vpr_77–92 is a new cell penetrating apoptotic sequence. We also found that the I84P mutation or the IIQ/VTR_83–85 and T89A substitutions in the Vpr_77–92 sequence prevent PP2A₁ binding, cell penetration and apoptosis. In addition the double R77A and R80A mutation known to inactivate the mitochondriotoxic Vpr_71–82 domain, has no effect on the biological properties of the Vpr_77–92 domain.

Conclusion

Together our data provide evidence for the first time that the Vpr_77–92 sequence delineates a biological active domain of Vpr with PP2A₁ binding and pro-apopototic capacities and, it is conceivable that this cell penetrating sequence may account for the Vpr internalization in uninfected cells. Finally, our data also implicate the existence of two partially overlapping pro-apoptotic domains in the Vpr C-terminal part, a redundancy that represents a new approach to address the question of biological relevance of HIV-1 Vpr. In this context, future studies will be required to determine the functional relevance of the Vpr_77–92 domain in full length Vpr protein and also in entire HIV provirus.

Neurometabolite abnormalities in simian immunodeficiency virus-infected macaques with chronic morphine administration

Opiate abuse increases the risk for human immunodeficiency virus (HIV) infection, while both opiates and HIV may impact the immune and nervous systems. To model potential interactions between opiate drugs and HIV on the brain, neurometabolite levels were evaluated in simian immunodeficiency virus (SIV)-infected macaques with or without chronic morphine administration. Over the course of the study, 58% of these SIV-infected animals progressed to acquired immune deficiency syndrome (AIDS). Brain extracts from four brain regions were evaluated with proton magnetic resonance spectroscopy. Animals with AIDS had lower N-acetyl-aspartate in all four brain regions (p ≤ 0.05) as well as lower frontal gray matter total creatine (p= 0.03), lower frontal white matter (p= 0.003) and caudate (p = 0.002) glutamate, and higher frontal white matter myo-inositol (p= 0.05) than the healthier non-AIDS macaques. Morphine-dependent animals had higher levels of myo-inositol in the putamen (p = 0.003), especially those with AIDS. In the animals with AIDS, those with morphine dependence had higher total creatine in the frontal white matter (p= 0.04) than those treated with saline, which in turn had lower creatine than saline-injected animals without AIDS (p = 0.04), leading to an interaction between the effects of morphine and AIDS on total creatine in this brain region (ANOVA p = 0.02). The majority of these brain metabolites correlated with viral counts indicating more severe metabolite abnormalities in animals with higher viral loads or set points. Collectively, these findings suggest that chronic morphine may protect against the neurotoxic effect of AIDS and reinforce the importance of maintaining a low viral load in AIDS.

Changes in MRS neuronal markers and T cell phenotypes observed during early HIV infection

OBJECTIVE

To determine if changes in brain metabolites are observed during early HIV infection and correlate these changes with immunologic alterations.

METHODS

Eight subjects with early HIV infection, 9 HIV-seronegative controls, and 10 chronically HIV-infected subjects without neurologic impairment underwent 1H magnetic resonance spectroscopy. Subjects with early stage infection were identified near the time of HIV seroconversion and imaged within 60 days of an evolving Western blot, while still having detectable plasma virus. Subjects had blood drawn for viral RNA and T cell quantification.

RESULTS

Both N-acetylaspartate (NAA) and Glx (glutamate + glutamine) were decreased in the frontal cortical gray matter of seropositive subjects. NAA levels were found to be decreased in the centrum semiovale white matter of chronically HIV-infected subjects, but not in those with early infection. Both HIV-infected cohorts demonstrated a lower number of CD4+ T lymphocytes and a higher number of CD8+ T lymphocytes in their blood. Lower NAA levels in the frontal cortex of subjects with early infection were associated with an expansion of CD8+ T cells, especially effector CD8+ T cells.

CONCLUSIONS

These results verify metabolism changes occurring in the brain early during HIV infection. Lower NAA and Glx levels in the cortical gray matter suggests that HIV causes neuronal dysfunction soon after infection, which correlates to the expansion of CD8+ T cells, specifically to an activated phenotype. Utilizing magnetic resonance spectroscopy to track NAA levels may provide important information on brain metabolic health while allowing better understanding of the virus-host interactions involved in CNS functional deficits.

In vivo proton magnetic resonance spectroscopy reveals region specific metabolic responses to SIV infection in the macaque brain

BACKGROUND

In vivo proton magnetic resonance spectroscopy (1H-MRS) studies of HIV-infected humans have demonstrated significant metabolic abnormalities that vary by brain region, but the causes are poorly understood. Metabolic changes in the frontal cortex, basal ganglia and white matter in 18 SIV-infected macaques were investigated using MRS during the first month of infection.

RESULTS

Changes in the N-acetylaspartate (NAA), choline (Cho), myo-inositol (MI), creatine (Cr) and glutamine/glutamate (Glx) resonances were quantified both in absolute terms and relative to the creatine resonance. Most abnormalities were observed at the time of peak viremia, 2 weeks post infection (wpi). At that time point, significant decreases in NAA and NAA/Cr, reflecting neuronal injury, were observed only in the frontal cortex. Cr was significantly elevated only in the white matter. Changes in Cho and Cho/Cr were similar across the brain regions, increasing at 2 wpi, and falling below baseline levels at 4 wpi. MI and MI/Cr levels were increased across all brain regions.

CONCLUSION

These data best support the hypothesis that different brain regions have variable intrinsic vulnerabilities to neuronal injury caused by the AIDS virus.

Metabolic markers of neuronal injury correlate with SIV CNS disease severity and inoculum in the macaque model of neuroAIDS

In vivo MR spectroscopy (MRS) studies have shown reductions in NAA/Cr levels in patients with severe neurocognitive deficits due to AIDS dementia complex (ADC), also known as neuroAIDS. The relationship between the cellular changes within the brain during neuroAIDS and the role of NAA/Cr as a metabolic marker remains unclear. In order to clarify the relationship between NAA/Cr and disease severity we utilized the simian immunodeficiency virus (SIV)/macaque model of encephalitis. High-field proton MRS was performed on extracted metabolites from frontal cortex tissue samples of 29 rhesus macaques (6 healthy, 23 moribund with AIDS). Neuropathologic determination of encephalitis severity for each animal was completed and was found to correlate with NAA/Cr levels. Decreases in Glu/Cr and GABA/Cr may indicate that both excitatory and inhibitory neurons are affected. Highly significant correlations between NAA/Cr, Glu/Cr, and GABA/Cr were observed. These neuronal metabolites were also decreased in the absence of classical SIV encephalitis (SIVE). At any disease classification, animals inoculated with SIVmac251 were found to have lower levels of NAA/Cr than animals inoculated with SIVmac239. In considering therapy for neuroAIDS the findings here support prevention of the encephalitic process, but suggest that suppressing the formation of multinucleated giant cells alone would be insufficient to prevent neuronal injury.

Contributions of non-human primates to neuroscience research

Non-human primates have a small but important role in basic and translational biomedical research, owing to similarities with human beings in physiology, cognitive capabilities, neuroanatomy, social complexity, reproduction, and development. Although non-human primates have contributed to many areas of biomedical research, we review here their unique contributions to work in neuroscience, and focus on four domains: Alzheimer's disease, neuroAIDS, Parkinson's disease, and stress. Our discussion includes, for example, the role of non-human primates in development of new treatments (eg, stem cells, gene transfer) before phase I clinical trials in patients; basic research on disease pathogenesis; and understanding neurobehavioural outcomes resulting from genotype-environment interactions.

In vitro (1)H NMR studies of RD human cell infection with echovirus 11

The effects of echovirus 11 infection on RD human cell line (derived from rhabdomyosarcoma) were studied using (1)H NMR spectroscopy and optical microscopy. Both uninfected and infected cells consumed glucose and produced lactate, acetate and formate as extracellular metabolites. In infected whole cells, phosphocholine and uridine-sugar were observed in addition to the metabolites observed in uninfected cells. Water-soluble intracellular metabolites of infected cells showed glutamine, phosphocholine and glycine which were not observed in uninfected cells. Cellular metabolites except lipid components gradually decreased and disappeared during 24-48 h of viral infection. The quantity of lipid components in infected cells was comparable with that in uninfected cells, indicating that echovirus 11 does not utilize cell lipid molecules. Unlike optical microscopy, (1)H NMR spectroscopy identified early stages of infection through metabolic changes. These results may have potential implications in probing virus-cell interactions using NMR-based metabolomics.

HIV-1 Vpr causes neuronal apoptosis and in vivo neurodegeneration

Despite the introduction of highly active antiretroviral therapy, dementia caused by human immunodeficiency virus-1 (HIV-1) infection remains a devastating and common neurological disorder. Although the mechanisms governing neurodegeneration during HIV-1 infection remain uncertain, the HIV-1 accessory protein, viral protein R (Vpr), has been proposed as a neurotoxic protein. Herein, we report that Vpr protein and transcript were present in the brains of HIV-infected persons. Moreover, soluble Vpr caused neuronal apoptosis, involving cytochrome c extravasation, p53 induction, and activation of caspase-9 while exerting a depressive effect on whole-cell currents in neurons (p < 0.05), which was inhibited by iberiotoxin. Vpr-activated glial cells secreted neurotoxins in a concentration-dependent manner (p < 0.001). Transgenic (Tg) mice expressing Vpr in brain monocytoid cells displayed the transgene principally in the basal ganglia (p < 0.05) and cerebral cortex (p < 0.01) compared with hindbrain expression. Vpr was released from cultured transgenic macrophages, which was cytotoxic to neurons and was blocked by anti-Vpr antibody (p < 0.05). Neuronal injury was observed in Tg animals compared with wild-type littermates, chiefly affecting GAD65 (p < 0.01) and vesicular acetylcholine transferase (p < 0.001) immunopositive neuronal populations in the basal ganglia. There was also a loss of subcortical synaptophysin (p < 0.001) immunoreactivity as well as an increase in activated caspase-3, which was accompanied by a hyperexcitable neurobehavioral phenotype (p < 0.05). Thus, HIV-1 Vpr caused neuronal death through convergent pathogenic mechanisms with ensuing in vivo neurodegeneration, yielding new insights into the mechanisms by which HIV-1 injures the nervous system.

Enteric ganglionitis in rhesus macaques infected with simian immunodeficiency virus

Gastrointestinal (GI) disease is a debilitating feature of human immunodeficiency virus (HIV) infection that can occur in the absence of histopathological abnormalities or identifiable enteropathogens. However, the mechanisms of GI dysfunction are poorly understood. The present study was undertaken to characterize changes in resident and inflammatory cells in the enteric nervous system (ENS) of macaques during the acute stage of simian immunodeficiency virus (SIV) infection to gain insight into potential pathogenic mechanisms of GI disease. Ganglia from duodenum, ileum, and colon were examined in healthy and acutely infected macaques by using a combination of routine histology, double-label immunofluorescence and in situ hybridization. Evaluation of tissues from infected macaques showed progressive infiltration of myenteric ganglia by CD3+ T cells and IBA1+ macrophages beginning as early as 8 days postinfection. Quantitative image analysis revealed that the severity of myenteric ganglionitis increased with time after SIV infection and, in general, was more severe in ganglia from the small intestine than in ganglia from the colon. Despite an abundance of inflammatory cells in myenteric ganglia during acute infection, the ENS was not a target for virus infection. This study provides evidence that the ENS may be playing a role in the pathogenesis of GI disease and enteropathy in HIV-infected people.

New insights into the neuroimmunity of SIV infection by magnetic resonance spectroscopy

(1)H magnetic resonance spectroscopy (MRS) was employed to noninvasively monitor neuronal injury in eight rhesus macaques infected with simian immunodeficiency virus (SIV), whose immune system was compromised by CD8 T lymphocyte depletion and treated with highly active antiretroviral therapy (HAART). SIV infection and CD8 depletion resulted in a rapid decline in cerebral N-acetylaspartate (NAA) levels, a sensitive marker of neuronal health. Within 3 months of SIV infection and CD8 depletion, four animals developed AIDS and severe SIV encephalitis. The other four macaques underwent daily doses of HAART beginning 4 weeks after infection/CD8 depletion. HAART involved drugs that do not penetrate the central nervous system (CNS) including 9-[2(R)-(phosphonomethoxy)propyl]adenine and a racemic mixture of D: -L: -enantiomers of 2',3'-dideoxy-5-fluoro-3'thiacytidine. HAART resulted in reversal of NAA/Cr decline after 4 weeks of therapy, and no virus or encephalitis was found in brain samples analyzed. These results indicate that the CNS injury in AIDS is entirely dependent on events involving the peripheral immune system mediated by trafficking of SIV-infected monocytes into the brain. The rapid decline in NAA/Cr with SIV infection/CD8 depletion and its rapid recovery with HAART suggest that: (1) infected monocyte turnover in the CNS is rapid, occurring in days to weeks; (2) there are endogenous mechanisms that reverse neuronal injury; and (3) a threshold level of infected monocytes/macrophages in the CNS is required to overcome the neuronal recovery processes. These observations explain the clinical success of antiretroviral therapy in reducing the incidence of HIV-associated dementia and minor cognitive/motor disorder and suggest novel targets for drug development.

Atteintes du système nerveux central et infection par le VIH-1

Central nervous system complications are common in HIV-1 infected patients and occur either as a result of concomitant immunosuppression (opportunistic infections, lymphoma and tumors), as a primary manifestation of HIV infection, or as an adverse effect of therapy (immune restoration and toxicity). These complications contribute largely to patient morbidity and mortality. In the era of highly active antiretroviral therapy (HAART) these disease states have changed in presentation, outcome and incidence. We review in detail the epidemiology, pathogenesis, clinical features, diagnosis, and management of these disorders.

Imaging in CNS lupus

The diagnosis of neuropsychiatric systemic lupus erythematosus (NPSLE) is complex not only on account of the heterogeneous nature of neurological presentation but also because of the difficulty of differentiating lupus-related pathology from other neuropsychiatric diseases. Magnetic resonance imaging (MRI) remains the gold standard for the non-invasive assessment of NPSLE but there are problems, both with sensitivity and specificity. Both T(2) quantitation and the use of gadolinium have shown promise in differentiating acute from chronic lesions. Nonetheless, the lack of sensitivity of conventional MRI has led to the exploration of other MR-based techniques. Magnetic resonance spectroscopy (MRS) allows the measurement of brain metabolites, whereas diffusion weighted imaging and diffusion tensor imaging allow assessment of white matter structure and integrity. MRS studies in NPSLE have consistently shown a reduction in N-acetyl aspartate (a neuronal marker). Diffusion weighted imaging has had only limited application in lupus and the results to date have shown abnormal diffusivity in lupus patients consistent with inflammation and loss of white matter structure. These techniques remain research tools at this early stage. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) have also been explored as functional imaging tools in lupus and both appear to be more sensitive in detecting subtle brain changes in NPSLE but there are issues with specificity which deter their use in the clinical setting.

Cortical NAA deficits in HIV infection without dementia: influence of alcoholism comorbidity

Alcoholism comorbidity is highly prevalent in individuals infected with human immunodeficiency virus (HIV). Each condition is known to affect brain structure, function, and metabolism, but the combined effects on the brain have only recently been considered. Single-voxel, proton MR spectroscopy (MRS) has yielded sensitive measures of early brain deterioration in the progression of HIV, but has limited coverage of neocortex, whereas MRS imaging (MRSI) can simultaneously interrogate large regions of cortex. Included were 15 men with HIV+alcoholism, nine men with HIV alone, eight men with alcoholism alone (abstinent for 3-17 months), and 23 controls. The two HIV groups were matched in T-cell count and were not demented; the two alcoholism groups were relatively matched in lifetime alcohol consumption. We used MRSI with a variable-density spiral sequence to quantify major proton metabolites--N-acetylaspartate (NAA), creatine (Cr), and choline (Cho)-in the superior parietal-occipital cortex. Metabolites were expressed in absolute units and as the NAA/Cr ratio. Significant group effects were present for NAA and Cr. Only the HIV+alcoholism group was significantly affected, exhibiting a 0.8 SD deficit in NAA and a 1.0 SD deficit in Cr. The deficits were not related to highly active antiretroviral therapy (HAART) status. Neither HIV infection nor alcoholism independently resulted in parietal-occipital cortical metabolite abnormalities, yet each disease carried a liability that put affected individuals at a heightened risk of neuronal compromise when the diseases were compounded. Further, the use of absolute measures revealed deficits in NAA and Cr that would have gone undetected if these metabolites were expressed as a ratio.

Relationships between astrogliosis and 1H MR spectroscopic measures of brain choline/creatine and myo-inositol/creatine in a primate model

BACKGROUND AND PURPOSE

In vivo 1H MR spectroscopy demonstrates elevated choline (Cho)/creatine (Cr) and myo-inositol (MI)/Cr in many neurologic diseases that has been ascribed to gliosis. We tested the hypotheses that in vivo Cho/Cr and/or MI/Cr levels are correlated with glial fibrillary acidic protein (GFAP) immunostains and that the changes are water-soluble metabolites.

METHODS

We performed postmortem 1H MR spectroscopy and GFAP immunohistochemistry in brains from seven rhesus macaques acutely infected with simian immunodeficiency virus (SIV) and in four controls and compared the findings with previous in vivo MR spectroscopic results. Changes in neuropathologic and MR spectroscopic markers after infection and relationships among plasma viral load, GFAP immunostaining results, and ex vivo and in vivo MR spectroscopic measures were statistically evaluated.

RESULTS

On GFAP immunostaining and in vivo MR spectroscopy, GFAP, Cho/Cr and MI/Cr were highest near the time of peak plasma viral load at 11 days postinfection (dpi). Immunostains returned to baseline by 14 dpi, whereas Cho/Cr and MI/Cr had different time courses, with the former dropping below baseline and the latter remaining elevated. Viral load and immunostains were significantly correlated. No correlation was found between ex vivo Cho/Cr or MI/Cr and viral load or between metabolite ratios from in vivo and ex vivo MR spectroscopy.

CONCLUSION

In acute SIV infection, plasma viral load was significantly correlated with brain GFAP immunostains and in vivo 1H MR spectroscopic Cho/Cr. In vivo changes in Cho/Cr and MI/Cr were principally due to contributions other than those of low-molecular-weight water-soluble metabolites.

High-field localized 1H NMR spectroscopy in the anesthetized and in the awake monkey

Localized cerebral in vivo 1H NMR spectroscopy (MRS) was performed in the anesthetized as well as the awake monkey using a novel vertical 7 T/60 cm MR system. The increased sensitivity and spectral dispersion gained at high field enabled the quantification of up to 16 metabolites in 0.1- to 1-ml volumes. Quantification was accomplished by using simulations of 18 metabolite spectra and a macromolecule (MM) background spectrum consisting of 12 components. Major cerebral metabolites (concentrations >3 mM) such as glutamate (Glu), N-acetylaspartate (NAA), creatine (Cr)/phosphocreatine (PCr) and myo-inositol (Ins) were identified with an error below 3%; most other metabolites were quantified with errors in the order of 10%. Metabolite ratios were 1.39:1 for total NAA, 1.38:1 for glutamate (Glu)/glutamine (Gln) and 0.09:1 for cholines (Cho) relative to total Cr. Taurine (Tau) was detectable at concentrations lower than 1 mM, while lactate (Lac) remained below the detection limit. The spectral dispersion was sufficient to separate metabolites of similar spectral patterns, such as Gln and Glu, N-acetylaspartylglutamate (NAAG) and NAA, and PCr-Cr. MRS in the awake monkey required the development and refinement of acquisition and correction strategies to minimize magnetic susceptibility artifacts induced by respiration and movement of the mouth or body. Periods with major motion artifacts were rejected, while a frequency/phase correction was performed on the remaining single spectra before averaging. In resting periods, both spectral amplitude and line width, that is, the voxel shim, were unaffected permitting reliable measurements. The corrected spectra obtained from the awake monkey afforded the reliable detection of 6-10 cerebral metabolites of 1-ml volumes.