A multicenter proton magnetic resonance spectroscopy study of neurological complications of AIDS

MR spectroscopy in HIV associated neurocognitive disorder in the era of cART: a review

Neuroimaging has been a critical tool for understanding the neuropathological underpinnings observed in HIV. The pathophysiology of HAND is chiefly driven by neuroinflammation. Despite adhering to cART, low levels of viraemia probably persist in the brain in some patients leading to chronic immune activation with resultant neuroinflammation and consequent neuronal injury. MR spectroscopy has been widely used as a biomarker for the presence and severity of HAND in several studies. By studying the MRS signatures, it is possible to characterise the presence of neuroinflammation and neural injury. Furthermore, metabolite concentrations measured by MRS could be used as a quantitative indicator of HIV cerebral involvement, thereby affording the opportunity to assess the efficacy of cART in HAND. However, currently there are three significant limitations in the MRS HIV research literature: the relative paucity of prospective studies, the small number of regions of interrogation due to current methodology (single voxel MRS), and the evolving understanding of the impact of co-morbidities (e.g. ageing, mood disorders, alcoholism etc.) on MRS measurements. This review critically addresses the current literature of MRS studies in people living with HIV (PWH) with HAND to determine its value, especially in the context of the current cART era. In addition, we discuss technical considerations related to the disease and the future direction in HAND using MRS.

Brain Metabolite, N-Acetylaspartate Is a Potent Protein Aggregation Inhibitor

Deposition of toxic protein inclusions is a common hallmark of many neurodegenerative disorders including Alzheimer's disease, Parkinson disease etc. N-acetylaspartate (NAA) is an important brain metabolite whose levels got altered under various neurodegenerative conditions. Indeed, NAA has been a widely accepted biological marker for various neurological disorders. We have also reported that NAA is a protein stabilizer. In the present communication, we investigated the role of NAA in modulating the aggregation propensity on two model proteins (carbonic anhydrase and catalase). We discovered that NAA suppresses protein aggregation and could solubilize preformed aggregates.

Distinguishing Brain Impact of Aging and HIV Severity in Chronic HIV Using Multiparametric MR Imaging and MR Spectroscopy

Background

Combination antiretroviral therapy (cART) has transformed HIV into a manageable but complex chronic disease, in which it is uncertain which brain insults may relate to age vs initial disease severity. We evaluate N-acetyl-aspartate/creatine (NAA/Cr), white matter hyperintensities (WMH), and mean cortical thickness to identify which subclinical markers of brain insult best relate to CD4 nadir and aging. This is a prospective study of the association between brain markers with age and initial infection severity, based on CD4 nadir, in chronic HIV patients.

Methods

Thirty-seven chronic HIV patients (age 25–77 years) with successful viral suppression were scanned on a GE 3T magnetic resonance imaging scanner to obtain NAA/Cr (standardized and averaged over 5 brain regions), log-transformed WMH volume, and mean cortical thickness. The brain measures were fitted with both CD4 nadir and age to evaluate the significance of their relationship.

Results

NAA/Cr, WMH, and cortical thickness were all correlated with age and CD4 nadir in unadjusted associations. Stepwise regression models showed that NAA/Cr alone best predicted CD4 nadir (β = 40.1 ± 13.3; P = .005), whereas WMH (β = 2.3 ± .9; P = .02) and mean cortical thickness (β = –2.7 ± 6.6; P < .0001) together produced the best model fit with age. NAA/Cr was higher for HIV stage 1 (CD4 nadir ≥ 500 cells/ µL; n = 15) compared with stage 2 (200 ≥ CD4 nadir < 500; n = 13) and stage 3 (CD4 nadir < 200; n = 9; P < .01 for both).

Conclusions

In patients with effectively suppressed HIV, NAA reflects the subclinical brain impact of initial disease severity related to development of even mild immune compromise, whereas cortical thickness and WMH volume are useful to evaluate age-related changes.

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.

Reproducibility of brain metabolite concentration measurements in lesion free white matter at 1.5 T

Background

Post processing for brain spectra has a great influence on the fit quality of individual spectra, as well as on the reproducibility of results from comparable spectra. This investigation used pairs of spectra, identical in system parameters, position and time assumed to differ only in noise. The metabolite amplitudes of fitted time domain spectroscopic data were tested on reproducibility for the main brain metabolites.

Methods

Proton spectra of white matter brain tissue were acquired with a short spin echo time of 30 ms and a moderate repetition time of 1500 ms at 1.5 T. The pairs were investigated with one time domain post-processing algorithm using different parameters. The number of metabolites, the use of prior knowledge, base line parameters and common or individual damping were varied to evaluate the best reproducibility.

Results

The protocols with most reproducible amplitudes for N-acetylaspartate, creatine, choline, myo-inositol and the combined Glx line of glutamate and glutamine in lesion free white matter have the following common features: common damping of the main metabolites, a baseline using only the points of the first 10 ms, no additional lipid/macromolecule lines and Glx is taken as the sum of separately fitted glutamate and glutamine. This parameter set is different to the one delivering the best individual fit results.

Discussion

All spectra were acquired in “lesion free” (no lesion signs found in MR imaging) white matter. Spectra of brain lesions, for example tumors, can be drastically different. Thus the results are limited to lesion free brain tissue. Nevertheless the application to studies is broad, because small alterations in brain biochemistry of lesion free areas had been detected nearby tumors, in patients with multiple sclerosis, drug abuse or psychiatric disorders.

Conclusion

Main metabolite amplitudes inside healthy brain can be quantified with a normalized root mean square deviation around 5 % using CH₃ of creatine as reference. Only the reproducibility of myo-inositol is roughly twice as bad. The reproducibility should be similar using other references like internal or external water for an absolute concentration evaluation and are not influenced by relaxation corrections with literature values.

Disrupted cerebral metabolite levels and lower nadir CD4 + counts are linked to brain volume deficits in 210 HIV-infected patients on stable treatment

Cognitive impairment and brain injury are common in people with HIV/AIDS, even when viral replication is effectively suppressed with combined antiretroviral therapies (cART). Metabolic and structural abnormalities may promote cognitive decline, but we know little about how these measures relate in people on stable cART. Here we used tensor-based morphometry (TBM) to reveal the 3D profile of regional brain volume variations in 210 HIV + patients scanned with whole-brain MRI at 1.5 T (mean age: 48.6 ± 8.4 years; all receiving cART). We identified brain regions where the degree of atrophy was related to HIV clinical measures and cerebral metabolite levels assessed with magnetic resonance spectroscopy (MRS). Regional brain volume reduction was linked to lower nadir CD4 + count, with a 1–2% white matter volume reduction for each 25-point reduction in nadir CD4 +. Even so, brain volume measured by TBM showed no detectable association with current CD4 + count, AIDS Dementia Complex (ADC) stage, HIV RNA load in plasma or cerebrospinal fluid (CSF), duration of HIV infection, antiretroviral CNS penetration-effectiveness (CPE) scores, or years on cART, after controlling for demographic factors, and for multiple comparisons. Elevated glutamate and glutamine (Glx) and lower N-acetylaspartate (NAA) in the frontal white matter, basal ganglia, and mid frontal cortex — were associated with lower white matter, putamen and thalamus volumes, and ventricular and CSF space expansion. Reductions in brain volumes in the setting of chronic and stable disease are strongly linked to a history of immunosuppression, suggesting that delays in initiating cART may result in imminent and irreversible brain damage.

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We mapped the 3D pattern of brain abnormalities in 210 HIV patients on stable cART.

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Brain atrophy was linked to MRS metabolite disturbances reflecting neuronal injury.

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Lower nadir CD4 + count was associated with greater white matter atrophy.

Change in brain magnetic resonance spectroscopy after treatment during acute HIV infection

Objective

Single voxel proton magnetic resonance spectroscopy (MRS) can be used to monitor changes in brain inflammation and neuronal integrity associated with HIV infection and its treatments. We used MRS to measure brain changes during the first weeks following HIV infection and in response to antiretroviral therapy (ART).

Methods

Brain metabolite levels of N-acetyl aspartate (NAA), choline (tCHO), creatine (CR), myoinositol (MI), and glutamate and glutamine (GLX) were measured in acute HIV subjects (n = 31) and compared to chronic HIV+individuals (n = 26) and HIV negative control subjects (n = 10) from Bangkok, Thailand. Metabolites were measured in frontal gray matter (FGM), frontal white matter (FWM), occipital gray matter (OGM), and basal ganglia (BG). Repeat measures were obtained in 17 acute subjects 1, 3 and 6 months following initiation of ART.

Results

After adjustment for age we identified elevated BG tCHO/CR in acute HIV cases at baseline (median 14 days after HIV infection) compared to control (p = 0.0014), as well as chronic subjects (p = 0.0023). A similar tCHO/CR elevation was noted in OGM; no other metabolite abnormalities were seen between acute and control subjects. Mixed longitudinal models revealed resolution of BG tCHO/CR elevation after ART (p = 0.022) with tCHO/CR similar to control subjects at 6 months.

Interpretation

We detected cellular inflammation in the absence of measurable neuronal injury within the first month of HIV infection, and normalization of this inflammation following acutely administered ART. Our findings suggest that early ART may be neuroprotective in HIV infection by mitigating processes leading to CNS injury.

Persistence of HIV-associated cognitive impairment, inflammation, and neuronal injury in era of highly active antiretroviral treatment

OBJECTIVE

To determine whether cognitive impairment and brain injury as measured by proton magnetic resonance spectroscopy (MRS) persist in the setting of HAART.

DESIGN

This study is an observational cohort study.

METHODS

MRS was performed in 268 patients: HIV-negative controls (N = 28), HIV-positive neuroasymptomatic individuals (N = 124), and individuals with AIDS dementia complex (ADC; N = 50) on stable antiretroviral therapy (ART) with a mean duration of infection of 12 years and CD4 cell count of 309 cells/μl. Four metabolites were measured over creatine: N-acetyl aspartate (NAA), marker of neuronal integrity; choline (Cho), myoinositol, markers of inflammation, and glutamate and glutamine (Glx) in the basal ganglia, frontal white matter (FWM), and mid-frontal cortex. Analyses included analysis of variance, analysis of covariance, linear, and nonparametric regression models.

RESULTS

Cognitive impairment was found in 48% of HIV-infected individuals. Both HIV-positive groups showed significant increases in myoinositol/creatine or Cho/creatine in all brain regions when compared to controls; a significant decrease in Glx/creatine in the FWM was observed in the neuroasymptomatic group; and only individuals with ADC showed a significant reduction in NAA/creatine, although a significant trend for decreasing NAA/creatine in the basal ganglia was found across the groups. Effects related to aging and duration of infection, but not central nervous system penetration effectiveness were observed.

CONCLUSION

Brain inflammatory changes remain ubiquitous among HIV-infected individuals, whereas neuronal injury occurs predominantly in those with cognitive impairment. Together these findings indicate that despite the widespread use of HAART, HIV-associated cognitive impairment and brain injury persist in the setting of chronic and stable disease.

Evidence of reduced glutamate in the frontal lobe of HIV-seropositive patients

Neurological complications associated with the acquired immunodeficiency syndrome, in particular, HIV-associated dementia, continue to plague those infected. We report our finding that the concentration of brain Glu is reduced in the frontal white matter region in this condition. In addition, our data appear to absolve highly active retroviral therapy (HAART) from blame, as drug-naïve patients were equally affected. Our findings suggest that Glu neurotransmission is abnormal and may be a key target for early interventions to reduce the later incidence of neurocognitive impairment and dementia among HIV-seropositive patients.

Two-dimensional 1H MR spectroscopy of the brain in human immunodeficiency virus (HIV)-infected children

PURPOSE

To measure cerebral metabolites in brains of human immunodeficiency virus (HIV)-infected patients using two-dimensional (2D) proton ((1)H) magnetic resonance spectroscopy (MRS), which enables more sensitive detection of metabolites at lower concentrations and delineation of the components of the different choline (Ch) groups in the frequency domain when compared to one dimensional (1D) (1)H-MRS.

MATERIALS AND METHODS

We examined metabolite/creatine (Cr) and metabolite/Ch ratios in the left frontal brain of 10 HIV-infected (mean age 13.7 +/- 4.7 years) and 11 control (mean age 15.3 +/- 4.6 years) adolescents and children using 2D localized chemical shift correlated spectroscopy (L-COSY). The integrated volume under each 2D metabolite peak was calculated with reference to the diagonal creatine methyl peak (Cr_d) or the diagonal choline trimethylamine peak (Ch_d).

RESULTS

In the HIV-infected patients, myoinositol (mI)/Cr_d (P = 0.009) and mI/Ch_d (P = 0.006) were elevated. The ratios of the following metabolites were also significantly elevated (P < 0.05): mI-Ch/Cr_d, gamma-aminobutyrate (GABA)/ Cr_d, GABA/Ch_d, threonine-lactate (Thr-Lac)/Cr_d, Thr-Lac/Ch_d, and N-acetyl aspartate (NAA)/Cr_d.

CONCLUSION

We have demonstrated for the first time the feasibility of 2D-MRS in HIV-infected children and adolescents to assess cerebral metabolites and found elevated mI and elevated GABA, in the left frontal brain of clinically stable HIV-infected patients. A larger study population is needed to confirm these pilot GABA findings.

Effects of human immunodeficiency virus and methamphetamine on cerebral metabolites measured with magnetic resonance spectroscopy

Human immunodeficiency virus (HIV) and methamphetamine (METH) use disorders are associated with cerebral dysfunction. To determine whether these effects were evident on in vivo neuroimaging, quantitative, single voxel magnetic resonance (MR) spectroscopy was used to assess frontal white matter, frontal gray matter, and basal ganglia in 40 HIV+/METH+, 66 HIV+/METH-, 48 HIV-/METH+, and 51 HIV-/METH- participants. HIV was associated with lower N-acetylaspartate (NAA) in frontal white and frontal gray matter but METH was not associated with cerebral metabolite differences in any region. Among HIV+ individuals, lower CD4 counts and higher plasma HIV viral loads were associated with lower NAA in frontal gray matter and basal ganglia. The relationship between detectable plasma HIV viral load and NAA in frontal white matter was significantly stronger in the HIV+/METH+ group, compared to HIV+/METH-. Higher detectable plasma HIV viral load was significantly associated with higher myo-inositol (MI) in frontal white and gray matter for HIV+/METH+, but not HIV+/METH-. For the HIV-/METH+ group, lifetime duration of METH use was associated with higher choline levels in frontal gray matter and higher MI levels in basal ganglia. Our findings are consistent with significant disruption of neuronal integrity in the frontal lobes of HIV-infected individuals. Although METH was not associated with cerebral metabolite levels, other findings suggested that METH use did affect the brain. For example, the relationship between detectable plasma HIV viral load and NAA levels was limited to HIV+/METH+ individuals. This evidence indicates when HIV is poorly suppressed, METH may modify the effects of the virus on neuronal integrity.

N-Acetylaspartate in the CNS: from neurodiagnostics to neurobiology

The brain is unique among organs in many respects, including its mechanisms of lipid synthesis and energy production. The nervous system-specific metabolite N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A in neurons, appears to be a key link in these distinct biochemical features of CNS metabolism. During early postnatal central nervous system (CNS) development, the expression of lipogenic enzymes in oligodendrocytes, including the NAA-degrading enzyme aspartoacylase (ASPA), is increased along with increased NAA production in neurons. NAA is transported from neurons to the cytoplasm of oligodendrocytes, where ASPA cleaves the acetate moiety for use in fatty acid and steroid synthesis. The fatty acids and steroids produced then go on to be used as building blocks for myelin lipid synthesis. Mutations in the gene for ASPA result in the fatal leukodystrophy Canavan disease, for which there is currently no effective treatment. Once postnatal myelination is completed, NAA may continue to be involved in myelin lipid turnover in adults, but it also appears to adopt other roles, including a bioenergetic role in neuronal mitochondria. NAA and ATP metabolism appear to be linked indirectly, whereby acetylation of aspartate may facilitate its removal from neuronal mitochondria, thus favoring conversion of glutamate to alpha ketoglutarate which can enter the tricarboxylic acid cycle for energy production. In its role as a mechanism for enhancing mitochondrial energy production from glutamate, NAA is in a key position to act as a magnetic resonance spectroscopy marker for neuronal health, viability and number. Evidence suggests that NAA is a direct precursor for the enzymatic synthesis of the neuron specific dipeptide N-acetylaspartylglutamate, the most concentrated neuropeptide in the human brain. Other proposed roles for NAA include neuronal osmoregulation and axon-glial signaling. We propose that NAA may also be involved in brain nitrogen balance. Further research will be required to more fully understand the biochemical functions served by NAA in CNS development and activity, and additional functions are likely to be discovered.

Reducing inter-scanner variability of activation in a multicenter fMRI study: Role of smoothness equalization

Scanner-to-scanner variability of activation in multicenter fMRI studies is often considered undesirable. The purpose of this investigation was to evaluate the effect of a new procedure, "smoothness equalization", on reducing scanner differences in activation effect size as part of a multicenter fMRI project (FIRST BIRN). Five subjects were sent to 9 centers (10 scanners) and scanned on 2 consecutive days using a sensorimotor fMRI protocol. High-field (4 T and 3 T) and low-field (1.5 T) scanners from three vendors (GE, Siemens, and Picker) were included. The activation effect size of the scanners for the detection of neural activation during a sensorimotor task was evaluated as the percent of temporal variance accounted for by our model (percent of variance accounted for or PVAF). Marked scanner effects were noted for both PVAF as well as the degree of smoothness of the raw and processed images. After smoothness equalization, there was a dramatic (low field) or consistent (high-field) reduction in scanner-to-scanner variation of activation. It was shown that the likely basis of the scanner differences in smoothness was differences in k-space filtering algorithms. This work highlights the need to account for differences in smoothness when comparing scanners on activation effect size in multicenter fMRI studies.

Short echo-time proton magnetic resonance spectroscopy in regions of severe HIV-related diffuse white matter abnormality on MRI

The purpose of this study was to determine whether short echo-time proton magnetic resonance spectroscopy (H-MRS) could detect mobile lipid resonances attributable to myelin breakdown products in the deep cerebral white matter of patients with AIDS who have severe diffuse/patchy white matter hyperintensity on T2-weighted magnetic resonance imaging (MRI). Seven patients with AIDS and clinical HIV-associated dementia complex (HADC) and 12 male controls were studied at 1.5T using a single 8 ml voxel, gradient localised, stimulated echo acquisition mode (STEAM) spectroscopy sequence. Spectra were acquired at an echo time of 20 ms with a repetition time of 5000 ms. No spectroscopic peaks were identified at 0.9 ppm and 1.3 ppm (corresponding to lipid resonances) in 6 of the 7 patients with AIDS or in any of the controls. Lipid resonances were identified in 1 patient who had been taking anti-retroviral therapy for 8 weeks. Follow up MRI/H-MRS, performed after a further 14 weeks of anti-retroviral therapy, showed partial resolution of white matter hyperintensity and lipid resonances were not detectable. These data suggest that mobile lipids are only rarely detected by H-MRS in patients with HADC and abnormalities on MRI and that their presence may be transitory.

A multicenter reproducibility study of single-voxel 1H-MRS of the medial temporal lobe

Proton magnetic resonance spectroscopy ((1)H-MRS) has provided evidence for a reduction of N-acetyl-aspartate (NAA) in the medial temporal lobe (MTL) in cerebral disorders such as Alzheimer's Disease. Within the (1)H-MRS study of the German Research Network on Dementia, we determined the multicenter reproducibility of single-voxel (1)H-MRS of the MTL. At five sites with 1.5T MR systems, single-voxel (1)H spectra from the MTL of an identical healthy subject were measured. The same subject was also examined at one of the sites five times to assess intracenter stability. The protocol included water-suppressed spectra with TE 272 ms and TE 30 ms and unsuppressed spectra for absolute quantification of metabolite concentrations. The intracenter reproducibility of absolute NAA concentration, expressed as coefficient of variation (CV), was 1.8%. CV for the concentrations of creatine (Cr), choline (Cho), and myoinositol (MI) and for the ratios NAA/Cr, NAA/Cho, and MI/NAA varied by 11-16%. Intercenter CV was 3.9% for NAA and were below 10% for all other metabolites and metabolic ratios. Our study demonstrates that quantitative assessment of NAA with single-voxel MRS can be performed with high intercenter reproducibility. This is the basis for applying (1)H-MRS in large-scale early recognition and treatment studies in MTL affecting disorders.

HIV-producing T cells in cerebrospinal fluid

In HIV-1-infected subjects, the magnitude of HIV-1 viral load in cerebrospinal fluid (CSF) correlates with the CSF white cell count. To determine whether HIV-1-producing T cells appear in CSF and whether their percentage and number correlate with viral load in CSF, we developed a flow cytometric assay that detects HIV-1-producing T cells by identifying intracellular p24 HIV-1 antigen. We found that most CSF T cells were not HIV-1 producing, even when cell-free viral load in CSF was high. Most activated T cells in CSF were also not HIV-1 producing, but the activated CD38+ CD4 T-cell fraction in CSF was independently associated with the fraction of HIV-1-producing T cells in CSF. We conclude that HIV-1-producing T cells appear in CSF and that their percentage and number correlate with cell-free viral load in CSF, even though the CSF total white cell count remains the best predictor for CSF viral load. In HIV-1 infection, CSF white cell counts seem to contain a large number of uninfected cells. White cell counts and viral load in CSF may result from systemic inflammation and immune activation.

Brain mitochondrial injury in human immunodeficiency virus-seropositive (HIV+) individuals taking nucleoside reverse transcriptase inhibitors

Nucleoside reverse transcriptase inhibitors (NRTIs) suppress human immunodeficiency virus (HIV) replication, but are often associated with mitochondrial toxicity. Although well studied outside of the central nervous system, no investigation has examined the effects of these drugs on brain mitochondria of individuals living with HIV. The authors used proton magnetic resonance spectroscopy to evaluate NRTI-related changes in brain mitochondria. N-acetylaspartate (NAA; sensitive to alterations in mitochondrial integrity) was measured in frontal lobe white and gray matter of 18 HIV+ individuals taking didanosine and/or stavudine (two NRTIs likely to cause mitochondrial toxicity), 14 HIV+ individuals taking zidovudine and lamivudine, 16 HIV+ individuals not currently taking antiretrovirals, and 17 HIV- controls. The HIV+ groups were comparable on demographic measures, estimates of illness severity, and estimated length of HIV infection. Those taking didanosine and/or stavudine had a significant 11.4% decrease in concentrations of frontal white matter NAA compared to HIV- controls, whereas NAA levels of the other HIV+ groups were intermediate. Group differences in metabolites were not found in frontal gray matter. Lower levels of frontal white matter NAA were associated with longer periods of didanosine and/or stavudine treatment (r = -.41, P = .06). Levels of NAA were not related to length of zidovudine/lamivudine treatment (r = -.04, P = .44). Furthermore, taking more than one of stavudine, didanosine, and abacavir increased the likelihood of having reduced NAA. The results are consistent with previous studies finding HIV-related changes in neuronal integrity. However, because NRTIs can injure mitochondria, we propose that the observed reductions in NAA in individuals taking didanosine and/or stavudine may be the result of depleted brain mitochondria and/or alterations in cellular respiration. Measurement of brain metabolites sensitive to impairments in energy metabolism, including NAA, may aid in early detection of subclinical NRTI-mediated mitochondrial toxicity.

A multicenter study of two magnetic resonance spectroscopy techniques in individuals with HIV dementia

PURPOSE

To evaluate single-voxel proton magnetic resonance spectroscopy (SV-MRS) and magnetic resonance spectroscopic imaging (MRSI) metabolite results in individuals with HIV dementia.

MATERIALS AND METHODS

Twenty HIV-positive (HIV+) individuals underwent SV-MRS (TE 35 msec) and MRSI (TE 280 msec). Results were stratified according to serostatus, dementia severity, psychomotor speed performance, and functional impairment.

RESULTS

HIV+ individuals with psychomotor slowing had an increased myoinositol/creatine (mI/Cr) ratio (0.63 vs. 0.45) in the frontal white matter using SV-MRS and an increased choline (Cho)/Cr ratio (1.88 vs. 1.41) in the mesial frontal gray matter using MRSI compared to HIV+ individuals without psychomotor slowing. Using MRSI, subjects with HIV dementia also had a decreased N-acetyl aspartate (NAA)/Cho ratio (1.55 vs. 2.53) compared to HIV+ individuals without cognitive impairment in the mesial frontal gray matter. Both techniques detected metabolite ratio abnormalities associated with abnormal functional performance.

CONCLUSION

SV-MRS and MRSI offer complementary roles in evaluating individuals with HIV dementia. Short TE SV-MRS measures mI, which may be elevated in early HIV dementia, whereas MRSI provides wider spatial coverage to examine specific regional changes.

A multicenter in vivo proton-MRS study of HIV-associated dementia and its relationship to age

OBJECTIVE

Differences in diagnostic criteria and methods have led to mixed results regarding the metabolite pattern of HIV-associated brain injury in relation to neurocognitive impairment. Therefore, a multicenter MRS consortium was formed to evaluate the neurometabolites in HIV patients with or without cognitive impairment.

METHODS

Proton magnetic resonance spectroscopy (MRS) at short-echo time (30 ms) was assessed in the frontal white matter, basal ganglia, and parietal cortex of 100 HIV patients [61 with AIDS dementia complex (ADC) and 39 neuroasymptomatic (NAS)] and 37 seronegative (SN) controls.

RESULTS

Compared to SN, NAS had higher glial marker myoinositol-to-creatine ratio (MI/Cr) in the white matter (multivariate analyses, adjusted P=0.001), while ADC showed further increased MI/Cr in the white matter and basal ganglia (both P<0.001), and increased choline compounds (Cho)/Cr in white matter (P=0.04) and basal ganglia (P<0.001). Compared to NAS, ADC showed a reduction in the neuronal marker N-acetyl compound (NA)/Cr in the frontal white matter (P=0.007). CSF, but not plasma, viral load correlated with MI/Cr and Cho/Cr in white matter and NAA/Cr in parietal cortex. HIV infection and aging had additive effects on Cho/Cr and MI/Cr in the basal ganglia and white matter.

CONCLUSIONS

The results suggest that glial activation occurs during the NAS stages of HIV infection, whereas further inflammatory activity in the basal ganglia and neuronal injury in the white matter is associated with the development of cognitive impairment. Aging may further exacerbate brain metabolites associated with inflammation in HIV patient and thereby increase the risk for cognitive impairment.

Neuroimaging in human immunodeficiency virus infection

Human immunodeficiency virus (HIV) is associated with central nervous system (CNS) changes that may affect cerebral blood flow (CBF), metabolism, structure, and diffusion. Each of the available neuroimaging techniques offers unique insight into the neural mechanisms underlying HIV, as well as a potential means of monitoring disease progression and treatment response. The purpose of the article is to provide a review of experimental studies evaluating changes related to HIV with imaging techniques, including single-photon emission computed tomography (SPECT), positron emission tomography (PET), volumetric magnetic resonance imaging (MRI), functional MRI (fMRI), magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), and perfusion MRI (pMRI).

Antiretroviral Treatment Alters Relationship between Mcp-1 and Neurometabolites in HIV Patients

Objective

The relationships between neurometabolites and macrophage chemoattractant protein (MCP-1) in serum and cerebrospinal fluid (CSF) were evaluated in HIV patients before and after antiretroviral treatment. Design: Prior studies found higher CSF MCP-1 levels in patients with HIV-associated dementia compared to those in neuroasymptomatic. We hypothesized that CSF MCP-1 levels would correlate inversely to neuronal metabolites [including N-acetyl compounds, gluta-mate+glutamine, as assessed by principal component analyses (PCA)] and positively to glial metabolites (including myo-inositol and choline compounds).

Methods

Thirty-nine antiretroviral-naive HIV patients were evaluated prospectively with proton magnetic resonance spectroscopy (1H MRS), and serum and CSF MCP-1 measurements prior to highly active antiretroviral therapy (HAART); 31 of these patients completed follow-up studies after 3 months of HAART but only 24 had follow-up CSF studies.

Results

After HAART, brain metabolites and clinical signs showed no change despite improvements in systemic (CD4 counts, plasma viral load, MCP-1) and CSF (viral load and MCP-1) variables. CSF, but not serum, MCP-1 levels correlated inversely with the neuronal component (from PCA) prior to treatment ( r=-0.59, P=0.0008). Conversely, after 3 months of HAART, the glial component (from PCA) correlated positively with CSF MCP-1 levels ( r=0.70, P=0.0002; ANCOVA interaction for treatment status, P=0.003).

Conclusions

These findings suggest that higher CSF MCP-1 levels are associated with neuronal dysfunction in untreated patients. After 3 months of HAART, the decreased systemic factors (viral burden, systemically derived MCP-1) no longer associate with neuronal dysfunction, but subjects with the strongest glial response in the brain continue to produce the highest levels of MCP-1.

A multi-center 1H MRS study of the AIDS dementia complex: validation and preliminary analysis

PURPOSE

To demonstrate the technical feasibility and reliability of a multi-center study characterizing regional levels of the brain metabolite ratios choline (Cho)/creatine (Cr) and myoinositol (MI)/Cr, markers of glial cell activity, and N-acetyl aspartate (NAA)/Cr, a marker of mature neurons, in subjects with AIDS dementia complex (ADC).

MATERIALS AND METHODS

Using an automated protocol (GE PROBE-P), short echo time spectra (TE = 35 msec) were obtained at eight sites from uniformly prepared phantoms and from three brain regions (frontal white matter, basal ganglia, and parietal cortex) of normal volunteers and ADC and HIV-negative subjects.

RESULTS

A random-effects model of the phantom and volunteer data showed no significant inter-site differences. Feasibility of a multi-center study was further validated by detection of significant differences between the metabolite ratios of ADC subjects and HIV-negative controls. ADC subjects exhibited significantly higher Cho/Cr and MI/Cr in the basal ganglia and significantly reduced NAA/Cr and significantly higher MI/Cr in the frontal white matter. These results are consistent with the predominantly subcortical distribution of the pathologic abnormalities associated with ADC.

CONCLUSION

This is the first study to ascertain and validate the reliability and reproducibility of a short echo time (1)H-MRS acquisition sequence from multiple brain regions in a multi-center setting. It should now be possible to examine the regional effects of HIV infection in the brain in a large number of subjects and to study the metabolic effects of new therapies for the treatment of ADC in a clinical trial setting.

Cerebral MR spectroscopy in neurologically asymptomatic HIV-infected patients

PURPOSE

To detect early metabolic changes in the brain of neurologically asymptomatic HIV-infected patients with normal MR imaging and to find the correlation between 1H MR results and immune status.

MATERIAL AND METHODS

Twenty neurologically asymptomatic HIV seropositive patients underwent MR imaging and single-voxel 1H MR spectroscopy (MRS) using a PRESS sequence. For all patients, the signals from N-acetyl-aspartate (NAA), choline-containing compounds (Cho), creatine-phosphocreatine (Cr) and myoinositol (mI) were compared with 32 healthy volunteers as metabolite ratios and metabolite areas to non-suppressed water area ratios.

RESULTS

In HIV patients, the NAA/Cho ratio was significantly lower ( p < 0.01), but there were no changes in NAA/Cr ratio. A statistically significant reduction in NAA/H2O and Cr/H2O (both p < 0.05) was observed. For the immune status there was a statistically significant correlation (r=0.47, p<0.05) between CD4 counts and NAA/H2O ratio. A significant increase in Cho/Cr ( p<0.001) and mI/Cr ( p<0.01) ratios in HIV patients was found, but Cho/H2O and mI/H2O concentrations were non-significantly increased.

CONCLUSION

These results indicate that neuronal loss and gliosis in HIV-infected patients may be associated with impairment of energy metabolism. The spectral changes found suggest that 1H MRS can be used for early detection of brain damage induced by HIV.

Relationships among brain metabolites, cognitive function, and viral loads in antiretroviral-naïve HIV patients

This study aims to determine the relationship among cerebral metabolite concentrations (on proton magnetic resonance spectroscopy or (1)H MRS), cognitive function, and clinical variables (CD4, plasma and CSF viral loads, and lipids) in antiretroviral medication-nai;ve HIV patients. We hypothesized that the probable glial markers myo-inositol [MI] and choline compounds [CHO] would correlate with cognitive function, CD4 count, and viral loads, but not with serum lipids. Forty-five antiretroviral-drug-nai;ve HIV patients and 25 control subjects were evaluated. Frontal lobe [MI], [CHO], and total creatine [CR] were elevated, while basal ganglia [CR] were decreased, with increasing dementia severity. As a group, HIV patients showed slowing on fine motor (Grooved Pegboard) and psychomotor function (Trails A & B), and deficits on executive function (Stroop tasks). Lower CD4 counts and elevated plasma viral loads were associated with elevated frontal white matter [MI], which in turn correlated with the Stroop tasks. These findings suggest that systemic factors (resulting from suppressed immune function and higher plasma viral load) may lead to glial proliferation (elevated [MI], [CHO], and [CR]) in the frontal white matter, which in turn may contribute to deficits on executive function in HIV. Studying antiretroviral-nai;ve patients minimized the confounding effects of antiretroviral treatment on the clinical, MRS, and neuropsychological variables, and allowed for a more accurate assessment of the relationships among these measurements. Metabolite concentrations, rather than metabolite ratios, should be measured since [CR], a commonly used reference for metabolite ratios, varies with disease severity in both frontal lobe and basal ganglia.

Understanding pathogenesis and treatment of HIV dementia: a role for magnetic resonance?

HIV dementia (HIVD) is among the most common and most feared neurological complications of AIDS. In vitro studies have identified a constellation of potentially neurotoxic inflammatory and non-inflammatory pathways, one or more of which could underlie HIVD. Magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) studies can distinguish between inflammatory and non-inflammatory pathways in vivo and suggest that either or both might be active in different patients or at different times in the same patient. This could perhaps explain the variability in HIVD development, progression and response to therapy. These findings also suggest that MRI and MRS can identify patients at risk for HIVD and predict response to therapy.

Magnetic resonance spectroscopy: an in vivo tool for monitoring cerebral injury in SIV-infected macaques

The purpose of our study was to demonstrate the feasibility of using in vivo proton Magnetic Resonance Spectroscopy (MRS) to monitor the brain manifestations of SIV infection in the macaque model of AIDS. Previous spectroscopy work on macaque brain tissue and in vivo work in humans is reviewed to provide the motivation and context for this study. We collected 34 MRS data sets on 14 uninfected rhesus macaques. From this data, we demonstrate that we are capable of detecting changes similar to those observed in human MRS studies for most metabolites using less than 10 animals. The juvenile macaques utilized in this study demonstrate age-related changes in the levels of N-acetyl aspartate (NAA), a neuronal marker. The quantity and distribution of neurochemicals in the macaque are found to be slightly, but significantly, different than in the human.

Magnetic resonance spectroscopy of the brain in neurologically asymptomatic HIV-infected patients

The CNS involvement is frequently found in human immunodeficiency virus (HIV) infection. The purpose of our study was to determine whether proton magnetic resonance spectroscopy (MRS) could detect early brain involvement in neurologically asymptomatic HIV-infected patients with normal MR imagings and to find the correlation between MRS and the immune status. We performed MRS in 30 HIV seropositive neurologically asymptomatic patients with normal MRI and compared the MRS findings with 13 controls. A statistically significant reduction in N-acetylaspartate (NAA)/creatine (Cr) and N-acetylaspartate (NAA)/choline (Cho) in both centrum semiovale (p < 0.005) and thalamic areas (p < 0.05) was found. There is no statistically significant difference as to choline (Cho)/creatine (Cr) and myoinositol (mI)/creatine (Cr) ratios in both regions. The difference of NAA/Cr was more pronounced in the white matter than in the gray matter. As for the immune status, there was a trend towards correlation between CD4 counts and NAA/Cr but devoid of statistical significance. Our results suggest that MRS is more sensitive than conventional MR imaging in detecting CNS involvement in neurologically asymptomatic HIV patients and may, therefore, be used for early detection of brain damage induced by HIV.

Frontal lobe neuronal injury correlates to altered function in FIV-infected cats

Six cats infected intravenously at 8 weeks of age with feline immunodeficiency virus Maryland isolate (FIV-MD), were evaluated at 8 and 14 months of age (6 months and 12 months postinfection, respectively) with high spatial resolution proton magnetic resonance spectroscopy (MRS) of the frontal cortex. Two separate control cat groups were evaluated at 8 months and 16 months of age. Single voxel two-dimensional high-resolution proton magnetic resonance imaging was performed using the PRESS sequence by selecting a 0.125 ml volume of interest in the medial frontal cortex. A significant reduction in both N-acetylaspartate (NAA) and NAA: choline ratio was found in the FIV 14-month-old group compared with FIV 8-month-old cats, and to the respective age-matched control 16-month-old cats. A negative correlation between NAA and CD4 lymphocyte count was seen in the FIV-14 group only. This group of FIV cats also exhibited a higher proportion of quantitative electroencephalographic relative slow wave activity (RSWA) that correlated to lower NAA content in the frontal cortical voxel. Although peripheral blood proviral load increased over time of infection, no correlation was found between proviral blood or lymph node load and NAA values, CD4 lymphocyte counts, or frontal cortical RSWA. Thus, this study demonstrated that neurologic functional disruption of the frontal cortex correlated strongly with neuronal injury and/or loss in FIV-MD-infected cats independent of peripheral proviral load. The ability to define in vivo neurodegeneration further in this animal model helps in understanding the neuropathogenesis of lentivirus infection, and possibly, a means to follow progression and reversibility during the initial stages of brain infection as therapeutic agents are identified.

Metabolic characterization of AIDS dementia complex by spectroscopic imaging

Prospective proton chemical shift imaging (CSI) of the brain was performed in 30 HIV- 1-seropositive patients and 11 healthy controls. Significant (P < 0.05) reductions in the N-acetyl-L-aspartate (NAA)/total creatine (Cr), and NAA/total choline (Cho) ratios and significant increases in Cho/Cr occurred in patients with 1) AIDS-defining diagnoses; 2) <200 CD4 lymphocyte counts/microl; 3) neurological evidence for an AIDS dementia complex (ADC); 4) magnetic resonance imaging (MRI) signs of cerebral atrophy. The basal ganglia and the insula were affected to approximately the same extent and without indications of spatial variations within these areas. Reduced NAA seems to indicate progressive neuronal injury or loss due to productive HIV infection in the brain and its clinical picture ADC. Spectroscopic abnormalities were, however, also observed in neurologically normal HIV patients or those with normal MRI results. Proton CSI may therefore serve as an early quantitative marker of central nervous system involvement in AIDS.

Localized proton magnetic resonance spectroscopy of the brain in children infected with human immunodeficiency virus with and without encephalopathy

Twenty children older than 2 y infected with human immunodeficiency virus (HIV) were examined by in vivo proton magnetic resonance spectroscopy (1H MRS) to study their cerebral metabolism and to identify metabolic profiles in relation with different stages of the disease. Patients were rated regarding their clinical and immunologic status according to the Centers for Disease Control classification and were divided into two groups: without encephalopathy (E-, n = 15) and with progressive encephalopathy (E+, n = 5). The acquisition was performed in the centrum semiovale using the short echo stimulated echo acquisition mode 20-ms sequence. The MRS profile was abnormal in all HIV-infected children compared with healthy age-matched controls (n = 7), even when magnetic resonance images were normal. A significant increase of the proportion of the lipid signals (ANOVA, p < 0.05) was found in all HIV-infected children. In addition, a significant decrease of the proportion of the N-acetylaspartate signal and a significant increase of the proportion of the myo-inositol signal (ANOVA, p < 0.05) characterized the E+ group. The principal component analysis performed on eight variables on 30 spectra confirms that the spectra of HIV-infected children differ from control spectra. The E+ group and the E- group are clearly separated on the map of subjects on the principal plane. The E- group lies in an intermediate position between the E+ group and the control group. The evolution of metabolic alterations in the brain of HIV-infected children can clearly be monitored by 1H MRS and associated with the occurrence of an encephalopathy.

Isolation and characterization of a neuropathogenic simian immunodeficiency virus derived from a sooty mangabey

Transfusion of blood from a simian immunodeficiency virus (SIV)- and simian T-cell lymphotropic virus-infected sooty mangabey (designated FGb) to rhesus and pig-tailed macaques resulted in the development of neurologic disease in addition to AIDS. To investigate the role of SIV in neurologic disease, virus was isolated from a lymph node of a pig-tailed macaque (designated PGm) and the cerebrospinal fluid of a rhesus macaque (designated ROn2) and passaged to additional macaques. SIV-related neuropathogenic effects were observed in 100% of the pig-tailed macaques inoculated with either virus. Lesions in these animals included extensive formation of SIV RNA-positive giant cells in the brain parenchyma and meninges. Based upon morphology, the majority of infected cells in both lymphoid and brain tissue appeared to be of macrophage lineage. The virus isolates replicated very well in pig-tailed and rhesus macaque peripheral blood mononuclear cells (PBMC) with rapid kinetics. Differential replicative abilities were observed in both PBMC and macrophage populations, with viruses growing to higher titers in pig-tailed macaque cells than in rhesus macaque cells. An infectious molecular clone of virus derived from the isolate from macaque PGm (PGm5.3) was generated and was shown to have in vitro replication characteristics similar to those of the uncloned virus stock. While molecular analyses of this virus revealed its similarity to SIV isolates from sooty mangabeys, significant amino acid differences in Env and Nef were observed. This virus should provide an excellent system for investigating the mechanism of lentivirus-induced neurologic disease.

Human immunodeficiency virus type 1 and its coat protein gp120 induce apoptosis and activate JNK and ERK mitogen-activated protein kinases in human neurons

Detection of apoptotic neurons and microglial cells in the brains of human immunodeficiency virus type 1 (HIV-1)-infected patients has suggested that programmed cell death may be implicated in the physiopathology of HIV-1 encephalopathy. To analyze in vitro the intracellular signals induced by HIV-1 in human neurons and the associated neuronal death, we tested cultured human central nervous system (CNS) cells for apoptosis induced by HIV-1 and gp120 and for signaling pathways activated by gp120. HIV-1 and gp120 induced apoptosis of neurons and microglial cells but not of astrocytes or transformed microglial cells. Gp120 activated c-Jun N-terminal kinase (JNK) and p42 extracellular-regulated kinase (ERK) in primary CNS cells, with an early peak of activation at 2 to 5 minutes that was not present when pure microglial or astrocyte cultures were tested, followed by a late and sustained activation (10 and 60 minutes) in primary and enriched glial cell cultures as well as in transformed microglial cells. This demonstrates that gp120 could be an effector of HIV-1-induced apoptosis in the CNS and act directly on neuronal and glial cells.

Brain proton magnetic resonance spectroscopy in HIV-related encephalopathy: identification of evolving metabolic patterns in relation to dementia and therapy

Proton MRS has proved useful in the early diagnosis of HIV-related encephalopathy. The modifications of brain metabolism in HIV-related encephalopathy can be classified according to different metabolic patterns (Vion-Dury J et al. CR Acad Sci 1994;317:833-840). The present study describes the relative occurrence of these patterns and evaluates their evolution under zidovudine treatment. We have examined 112 HIV patients--35 neuroasymptomatic patients and 77 patients with ADC (AIDS dementia complex)--with localized proton MRS, using the PRESS 135-msec sequence. We have found the same metabolic modifications in N-acetylaspartate and choline-containing compounds as described in the literature. In addition, 14% of HIV patients with normal MRI displayed abnormal MRS, whatever their neurological status. The MRS-added diagnostic value in neuroasymptomatic patients reaches 30 %. The occurrence of undifferentiated (modification of NAA/Cho ratio only) and Cho (mainly an increase in choline signal) patterns is not significantly different in neuroasymptomatic and ADC patients. The NAA pattern (mainly a significant loss of NAA) is more frequent in ADC patients. Only ADC patients display the double pattern (with a significant increase in choline signal and a significant loss of NAA). Quantitated cerebral atrophy (bifrontal ratio) is related to the occurrence of NAA loss (in NAA and double patterns). An MRS follow-up study of 11 HIV patients showed that the clinical outcome was favorable after a 1000-mg/day zidovudine treatment in patients displaying an NAA pattern whereas this treatment had no effect on the patients displaying the Cho pattern. Consequently, MRS appears to be of great interest in predicting responsiveness to antiretroviral drugs and detecting early any resistance to treatment.

Cerebral metabolic alterations in human immunodeficiency virus-related encephalopathy detected by proton magnetic resonance spectroscopy. Comparison between sequences using short and long echo times

RATIONALE AND OBJECTIVES

The aim of this study is to evaluate comparatively the metabolic information afforded by proton magnetic resonance (MR) spectroscopy with stimulated-echo acquisition mode (STEAM) (echo time [TE], 20 mseconds) and point-resolved spectroscopy sequence (PRESS) (TE, 135 mseconds) spectra in HIV-related encephalopathy.

METHODS

Sixty-three human immunodeficiency virus (HIV) patients and 8 controls were examined by single-voxel proton MR spectroscopy at 1.5 tesla, using both PRESS (TE, 135 mseconds) and STEAM (TE, 20 mseconds) sequences performed during the same MR examination, in the same volume of interest. Cerebral atrophy was quantitated using bicaudate ratio (BCR) and bifrontal ratio (BFR).

RESULTS

With the STEAM (TE, 20 mseconds) spectra, mean N-acetylaspartate (NAA)/choline (Cho) and NAA/creatine and phosphocreatine (Cr-PCr) ratios are reduced in acquired immunodeficiency syndrome (AIDS) dementia complex (ADC) patients but not in neuroasymptomatics. The proportion of inositol signal is increased, that of NAA decreased in ADC patients. NAA/Cho and NAA/ Cr-PCr mean values measured with PRESS (TE, 135 mseconds) spectra are significantly reduced in ADC and neuroasymptomatic patients. Bifrontal ratio only correlates with NAA/Cr-PCr and NAA/Cho measured on the PRESS spectrum. PRESS (TE, 135 mseconds) spectra allow a definition of different metabolic patterns in HIV-related encephalopathy. At last, no correlation has been found between the NAA raw signals measured on the PRESS (TE, 135 mseconds) and STEAM (TE, 20 mseconds) spectra obtained in the same MR examination.

CONCLUSIONS

STEAM (TE, 20 mseconds) spectra provide more metabolic information-namely an evaluation of glial-neuronal status-than PRESS (TE, 135 mseconds) spectra, which afford a metabolic classification of the HIV-related encephalopathy. Because both sequences afford a similar diagnostic gain, MR spectroscopy examination probably requires spectrum acquisition with both sequences.

Cerebral proton magnetic resonance spectroscopy in asymptomatic HIV infection

OBJECTIVE

To determine whether proton magnetic resonance spectroscopy (MRS) demonstrates central nervous system abnormalities in asymptomatic HIV-1-infected individuals.

DESIGN

Both prospective and retrospective cross-sectional analyses of MRS in asymptomatic HIV-infected individuals.

SETTING

Two specialists HIV/AIDS outpatient facilities in London.

PARTICIPANTS

Eighty-four HIV-1 seropositive asymptomatic men; 29 HIV-1 antibody-negative homosexual men at high-risk for HIV infection and 48 HIV-1 antibody-negative men at low-risk for HIV infection as controls.

MAIN OUTCOME MEASURES

Single voxel, gradient-localized proton MRS performed at 1.5 T with 135 msec echo-time and 1,600 msec repeat-time in an 8 ml volume of interest positioned in the parieto-occipital white matter. Spectroscopic results were expressed as ratios between the areas under the N-acetyl (NA), creatine (Cr) and choline (Cho) resonance peaks.

RESULTS

There were no differences between those controls at high and those at low-risk for HIV infection. Comparing the combined control groups with the asymptomatic seropositive patients there were statistically significant differences in NA/Cho, NA/Cr (both P < 0.05) and NA/(NA + Cho + Cr) (P < 0.01).

CONCLUSION

Abnormalities in cerebral biochemistry may be demonstrated by proton MRS during asymptomatic HIV-1 infection.

Cerebral volumes and spectroscopic proton metabolites on MR: is sex important?

One of the factors that may influence the selection of appropriate controls for MR studies of the brain is gender. This study compared calculated intracranial volumes and proton spectroscopic metabolite ratios obtained from male and female volunteers. Thirty-two males (mean age = 36; range = 30-53 yr) and 19 females (mean age = 39; range = 26-53 yr) underwent investigation at 1.5T. Brain, cerebrospinal fluid (CSF), and intracranial (ICV = brain + CSF) volumes were measured by the CLASS technique on data acquired using an axial dual spin-echo imaging sequence (TE = 20/90 ms, TR = 3500 ms). Proton spectra (TE = 135 ms, TR = 1600 ms) were acquired from an 8 ml cubic region placed in parieto-occipital white matter. The mean male and female brain, CSF and ICV were significantly different (p < .005). However, the mean CSF/ICV ratios of the two groups were not significantly different. The N-acetyl/choline and choline/creatine metabolite ratios of the two groups were significantly different (p < .05). When comparing proton metabolite ratios and absolute brain volumes between groups, gender is an important factor. CSF/ ICV ratios do not appear to depend on gender.