1H MR spectroscopy of the brain in HIV-1-seropositive subjects: evidence for diffuse metabolic abnormalities

Depression and Cognitive Dysfunction in Patients with Chronic Hepatitis C: Correlation with Viral Replication in the Peripheral Blood Mononuclear Cells and Cytokines in Serum

Chronic hepatitis C virus (HCV) infection is commonly associated with depression and cognitive dysfunction, the cause of which could be related to the HCV neuroinvasion and/or state of chronic inflammation. Viral sequences and proteins were previously detected in the brain and since blood leukocytes can cross the blood-brain barrier, they could provide viral access to the CNS. Eighty chronic hepatitis C patients were tested for viral replication in PBMCs (detection of the HCV RNA-negative strand) and serum cytokines. Depression was assessed by the Beck Depression Inventory (BDI), neuroticism by the Eysenck Personality Inventory (N/EPO-R), and anxiety by the State-Trait Anxiety Inventory (STAI) while neurocognitive testing included the Wisconsin Card Sorting Test (WCST), Ruff Figural Fluency Test (RFFT), California Verbal Learning Test (CVLT), and Grooved Pegboard Test (GPT). The HCV RNA-negative strand was detected in PBMCs from 24 (30%) patients and these patients had significantly higher BDI scores (median 12.5 [IQR] 6.3-20.5 vs. median 8.00 [IQR] 3-12; p = 0.013). Both depression and anxiety correlated positively with IL-8 while cognitive flexibility, executive function, problem-solving skills, memory, and motor functioning correlated negatively with some proinflammatory cytokines. Our findings suggest that due to chronic HCV infection, the brain function is negatively affected by both viral replication in PBMCs and by the immune activation state.

HIV-associated neurodegeneration and neuroimmunity: multivoxel MR spectroscopy study in drug-naïve and treated patients

OBJECTIVES

The aim of this study was to test neurobiochemical changes in normal appearing brain tissue in HIV+ patients receiving and not receiving combined antiretroviral therapy (cART) and healthy controls, using multivoxel MR spectroscopy (mvMRS).

METHODS

We performed long- and short-echo 3D mvMRS in 110 neuroasymptomatic subjects (32 HIV+ subjects on cART, 28 HIV+ therapy-naïve subjects and 50 healthy controls) on a 3T MR scanner, targeting frontal and parietal supracallosal subcortical and deep white matter and cingulate gyrus (NAA/Cr, Cho/Cr and mI/Cr ratios were analysed). The statistical value was set at p < 0.05.

RESULTS

Considering differences between HIV-infected and healthy subjects, there was a significant decrease in the NAA/Cr ratio in HIV+ subjects in all observed locations, an increase in mI/Cr levels in the anterior cingulate gyrus (ACG), and no significant differences in Cho/Cr ratios, except in ACG, where the increase showed trending towards significance in HIV+ patients. There were no significant differences between HIV+ patients on and without cART in all three ratios.

CONCLUSION

Neuronal loss and dysfunction affects the whole brain volume in HIV-infected patients. Unfortunately, cART appears to be ineffective in halting accelerated neurodegenerative process induced by HIV but is partially effective in preventing glial proliferation.

KEY POINTS

• This is the first multivoxel human brain 3T MRS study in HIV. • All observed areas of the brain are affected by neurodegenerative process. • Cingulate gyrus and subcortical white matter are most vulnerable to HIV-induced neurodegeneration. • cART is effective in control of inflammation but ineffective in preventing neurodegeneration.

Hepatitis C virus infection, and neurological and psychiatric disorders - A review

An association between hepatitis C virus infection and neuropsychiatric symptoms has been proposed for some years. A variety of studies have been undertaken to assess the nature and severity of these symptoms, which range from fatigue and depression to defects in attention and verbal reasoning. There is evidence of mild neurocognitive impairment in some patients with HCV infection, which is not fully attributable to liver dysfunction or psychosocial factors. Further evidence of a biological cerebral effect has arisen from studies using magnetic resonance spectroscopy; metabolic abnormalities correlate with cognitive dysfunction and resemble the patterns of neuroinflammation that have been described in HIV infection. Recent research has suggested that, in common with HIV infection, HCV may cross the blood brain barrier leading to neuroinflammation. Brain microvascular endothelial cells, astrocytes and microglia may be minor replication sites for HCV. Importantly, patient reported outcomes improve following successful antiviral therapy. Further research is required to elucidate the molecular basis for HCV entry and replication in the brain, and to clarify implications and recommendations for treatment.

Association of Hippocampal Magnetic Resonance Imaging With Learning and Memory Deficits in HIV-1-Seropositive Patients

OBJECTIVE

To investigate the relationship between cognitive impairment and hippocampal morphological and functional changes in HIV-seropositive patients.

METHODS

Thirty HIV+ patients who complain of memory decrease and 15 healthy volunteers were recruited. Performances of learning and memory were assessed using Hopkins Verbal Learning Test-Revised (HVLT-R) and Brief Visuospatial Memory Test-Revised (BVMT-R). Bilateral hippocampal volume, apparent diffusion coefficient (ADC) value, fractional anisotropy value, and magnetic resonance spectroscopy variables of bilateral hippocampus and parahippocampal gyrus were detected by 3.0 T magnetic resonance scanner.

RESULTS

We found significant differences in all cognitive outcomes but one between HIV+ and HIV- patients. There was a difference in the ADC value of left parahippocampal gyrus between mild-impairment group and severe-impairment group (P = 0.018). We found differences in the choline (Cho), Cho/creatinine (Cr), and N-acetylaspartate/Cr of left hippocampus (P = 0.002, P = 0.008, P = 0.002) and the Cho/Cr of right parahippocampal gyrus (P = 0.023) between HIV+ and HIV- patients and in the myoinositol of left hippocampus (P = 0.003) and the glutamate and glutamine of right hippocampus (P < 0.001) between mild-impairment group and severe-impairment group. We found significant positive correlations between N-acetylaspartate/Cr of left hippocampus and outcomes of HVLT-R and BVMT-R. There were significant negative correlations between ADC values of hippocampus and parahippocampal gyrus and outcomes of HVLT-R and BVMT-R and between Cho and Cho/Cr of hippocampus and parahippocampal gyrus and outcomes of HVLT-R and BVMT-R.

CONCLUSIONS

The performance of verbal learning and visual memory was significantly decreased in HIV-1-seropositive patients. The cognitive impairment of HIV infection was associated with conductive function and metabolic changes of hippocampus and parahippocampal gyrus in this study.

Role of neurotrophic factor alterations in the neurodegenerative process in HIV associated neurocognitive disorders

Migration of HIV infected cells into the CNS is associated with a spectrum of neurological disorders, ranging from milder forms of HIV-associated neurocognitive disorders (HAND) to HIV-associated dementia (HAD). These neuro-psychiatric syndromes are related to the neurodegenerative pathology triggered by the release of HIV proteins and cytokine/chemokines from monocytes/macrophages into the CNS -a condition known as HIV encephalitis (HIVE). As a result of more effective combined anti-retroviral therapy patients with HIV are living longer and thus the frequency of HAND has increased considerably, resulting in an overlap between the neurodegenerative pathology associated with HIV and that related to aging. In fact, HIV infection is believed to hasten the aging process. The mechanisms through which HIV and aging lead to neurodegeneration include: abnormal calcium flux, excitotoxicity, signaling abnormalities, oxidative stress and autophagy defects. Moreover, recent studies have shown that defects in the processing and transport of neurotrophic factors such as fibroblast growth factors (FGFs), neural growth factor (NGF) and brain-derived growth factor (BDNF) might also play a role. Recent evidence implicates alterations in neurotrophins in the pathogenesis of neurodegeneration associated with HAND in the context of aging. Here, we report FGF overexpression curtails gp120-induced neurotoxicity in a double transgenic mouse model. Furthermore, our data show disparities in brain neurotrophic factor levels may be exacerbated in HIV patients over 50 years of age. In this review, we discuss the most recent findings on neurotrophins and HAND in the context of developing new therapies to combat HIV infection in the aging population.

Human immunodeficiency virus-1 uses the mannose-6-phosphate receptor to cross the blood-brain barrier

HIV-1 circulates both as free virus and within immune cells, with the level of free virus being predictive of clinical course. Both forms of HIV-1 cross the blood-brain barrier (BBB) and much progress has been made in understanding the mechanisms by which infected immune cells cross the blood-brain barrier BBB. How HIV-1 as free virus crosses the BBB is less clear as brain endothelial cells are CD4 and galactosylceramide negative. Here, we found that HIV-1 can use the mannose-6 phosphate receptor (M6PR) to cross the BBB. Brain perfusion studies showed that HIV-1 crossed the BBB of all brain regions consistent with the uniform distribution of M6PR. Ultrastructural studies showed HIV-1 crossed by a transcytotic pathway consistent with transport by M6PR. An in vitro model of the BBB was used to show that transport of HIV-1 was inhibited by mannose, mannan, and mannose-6 phosphate and that enzymatic removal of high mannose oligosaccharide residues from HIV-1 reduced transport. Wheatgerm agglutinin and protamine sulfate, substances known to greatly increase transcytosis of HIV-1 across the BBB in vivo, were shown to be active in the in vitro model and to act through a mannose-dependent mechanism. Transport was also cAMP and calcium-dependent, the latter suggesting that the cation-dependent member of the M6PR family mediates HIV-1 transport across the BBB. We conclude that M6PR is an important receptor used by HIV-1 to cross the BBB.

The liver-cytokine-brain circuit in interferon-based treatment of patients with chronic viral hepatitis

Psychiatric symptoms are commonly identified in patients with viral hepatitis. They may have been present prior to the onset of disease and may include symptoms related to addiction issues. Furthermore, the virus and antiviral therapy, in particular interferon, may induce or modify psychiatric symptoms. Recent data support chronic hepatitis C replication in the brain and subsequent changes of cerebral metabolite spectra and magnetic resonance alterations. In chronic viral hepatitis and in other chronic inflammatory diseases, an alteration of the neuro-endocrine-immune system response has been observed. Catecholamines and glucocorticoids modulate this immune/inflammatory reaction. Psychiatric assessment and monitoring before, during and after antiviral therapy can identify patients whose psychiatric symptoms preclude therapy, and those who may benefit from psychopharmacological therapy and counselling, thereby improving therapeutic results. This review will discuss current insights into the complex interplay between cytokines, liver and brain in chronic viral hepatitis closely associated with psychiatric issues, especially in the case of antiviral therapy, with the aim of indicating future research and possible treatments.

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.

Loss of neuronal integrity during progressive HIV-1 infection of humanized mice

Neuronal damage induced by ongoing human immunodeficiency virus type 1 (HIV-1) infection was investigated in humanized NOD/scid-IL-2Rγ(c)(null) mice transplanted at birth with human CD34-positive hematopoietic stem cells. Mice infected at 5 months of age and followed for up to 15 weeks maintained significant plasma viral loads and showed reduced numbers of CD4(+) T-cells. Prospective serial proton magnetic resonance spectroscopy tests showed selective reductions in cortical N-acetyl aspartate in infected animals. Diffusion tensor imaging revealed structural changes in cortical gray matter. Postmortem immunofluorescence brain tissue examinations for neuronal and glial markers, captured by multispectral imaging microscopy and quantified by morphometric and fluorescence emission, showed regional reduction of neuronal soma and synaptic architectures. This was evidenced by loss of microtubule-associated protein 2, synaptophysin, and neurofilament antigens. This study is the first, to our knowledge, demonstrating lost neuronal integrity after HIV-1 infection in humanized mice. As such, the model permits studies of the relationships between ongoing viral replication and virus-associated neurodegeneration.

Factors affecting brain structure in men with HIV disease in the post-HAART era

INTRODUCTION

The purpose of this study was to characterize brain volumetric differences in HIV seropositive and seronegative men and to determine effects of age, cardiovascular risk, and HIV infection on structural integrity.

METHODS

Magnetic resonance imaging was used to acquire high-resolution neuroanatomic data in 160 men aged 50 years and over, including 84 HIV seropositive and 76 seronegative controls. Voxel-based morphometry was used to derive volumetric measurements at the level of the individual voxel. Data from a detailed neuropsychological test battery were recombined into four summary scores representing psychomotor speed, visual memory, verbal memory, and verbal fluency.

RESULTS

Both age and HIV status had a significant effect on both gray matter (GM) and white matter (WM) volume. The age-related GM atrophy was primarily in the superior temporal and inferior frontal regions; the HIV-related GM loss included the posterior and inferior temporal lobes, the parietal lobes, and the cerebellum. Among all subjects, the performance on neuropsychological tests, as indexed by a summary variable, was related to the volume of both the GM and WM. Contrary to our predictions, the CVD variables were not linked to brain volume in statistically adjusted models.

CONCLUSION

In the post-HAART era, having HIV infection is still linked to atrophy in both GM and WM. Secondly, advancing age, even in this relatively young cohort, is also linked to changes in GM and WM volume. Thirdly, CNS structural integrity is associated with overall cognitive functions, regardless of the HIV infection status of the study volunteers.

Lower brain glutamate is associated with cognitive deficits in HIV patients: a new mechanism for HIV-associated neurocognitive disorder

PURPOSE

To determine whether subjects with human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND) show altered concentrations of brain glutamate (GLU), and whether lower GLU levels correlate with cognitive deficits.

MATERIALS AND METHODS

GLU concentrations were measured in the basal ganglia, frontal gray and white matter, and parietal gray matter of 45 HIV-positive and 46 age-and-education-matched HIV-negative subjects using echo-time averaged proton magnetic resonance spectroscopy ((1)H MRS).

RESULTS

Compared to controls, HIV subjects with cognitive deficits had lower GLU in the parietal gray matter, while those without cognitive deficits tended to show higher basal ganglia GLU. Lower parietal and frontal gray matter GLU were associated with a greater number of nucleoside reverse transcriptase inhibitors, and were predictive of poorer cognitive performance. Correlations between GLU and cognitive performance, but not the other findings, remained significant after correction for multiple comparisons.

CONCLUSION

Parietal gray matter GLU is lower in HIV subjects with cognitive deficits. This reduction might result from reduced astrocytic reuptake of GLU, secondary excitotoxicity, and mitochondrial toxicity from antiretroviral treatments. The glutamatergic system may play an important role in the pathophysiology of HAND, and brain GLU on (1)H MRS may provide an early surrogate marker for monitoring disease severity and treatment effects.

Proton magnetic resonance spectroscopy reveals neuroprotection by oral minocycline in a nonhuman primate model of accelerated NeuroAIDS

BACKGROUND

Despite the advent of highly active anti-retroviral therapy (HAART), HIV-associated neurocognitive disorders continue to be a significant problem. In efforts to understand and alleviate neurocognitive deficits associated with HIV, we used an accelerated simian immunodeficiency virus (SIV) macaque model of NeuroAIDS to test whether minocycline is neuroprotective against lentiviral-induced neuronal injury.

METHODOLOGY/PRINCIPAL FINDINGS

Eleven rhesus macaques were infected with SIV, depleted of CD8+ lymphocytes, and studied until eight weeks post inoculation (wpi). Seven animals received daily minocycline orally beginning at 4 wpi. Neuronal integrity was monitored in vivo by proton magnetic resonance spectroscopy and post-mortem by immunohistochemistry for synaptophysin (SYN), microtubule-associated protein 2 (MAP2), and neuronal counts. Astrogliosis and microglial activation were quantified by measuring glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1 (IBA-1), respectively. SIV infection followed by CD8+ cell depletion induced a progressive decline in neuronal integrity evidenced by declining N-acetylaspartate/creatine (NAA/Cr), which was arrested with minocycline treatment. The recovery of this ratio was due to increases in NAA, indicating neuronal recovery, and decreases in Cr, likely reflecting downregulation of glial cell activation. SYN, MAP2, and neuronal counts were found to be higher in minocycline-treated animals compared to untreated animals while GFAP and IBA-1 expression were decreased compared to controls. CSF and plasma viral loads were lower in MN-treated animals.

CONCLUSIONS/SIGNIFICANCE

In conclusion, oral minocycline alleviates neuronal damage induced by the AIDS virus.

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.

Neuronal injury in simian immunodeficiency virus and other animal models of neuroAIDS

The success of antiretroviral therapy has reduced the incidence of severe neurological complication resulting from human immunodeficiency virus (HIV) infection. However, increased patient survival has been associated with an increased prevalence of protracted forms of HIV encephalitis leading to moderate cognitive impairment. NeuroAIDS remains a great challenge to patients, their families, and our society. Thus development of preclinical models that will be suitable for testing promising new compounds with neurotrophic and neuroprotective capabilities is of critical importance. The simian immunodeficiency virus (SIV)-infected macaque is the premiere model to study HIV neuropathogenesis. This model was central to the seminal work of Dr. Opendra "Bill" Narayan. Similar to patients with HIV encephalitis, in the SIV model there is injury to the synaptodendritic structure of excitatory pyramidal neurons and inhibitory calbindin-immunoreactive interneurons. This article, which is part of a special issue of the Journal of NeuroVirology in honor of Dr. Bill Narayan, discusses the most important neurodegenerative features in preclinical models of neuroAIDS and their potential for treatment development.

Hepatitis C virus neuroinvasion: identification of infected cells

Hepatitis C virus (HCV) infection often is associated with cognitive dysfunction and depression. HCV sequences and replicative forms were detected in autopsy brain tissue and cerebrospinal fluid from infected patients, suggesting direct neuroinvasion. However, the phenotype of cells harboring HCV in brain remains unclear. We studied autopsy brain tissue from 12 HCV-infected patients, 6 of whom were coinfected with human immunodeficiency virus. Cryostat sections of frontal cortex and subcortical white matter were stained with monoclonal antibodies specific for microglia/macrophages (CD68), oligodendrocytes (2',3'-cyclic nucleotide 3'-phosphodiesterase), astrocytes (glial fibrillary acidic protein [GFAP]), and neurons (neuronal-specific nuclear protein); separated by laser capture microscopy (LCM); and tested for the presence of positive- and negative-strand HCV RNA. Sections also were stained with antibodies to viral nonstructural protein 3 (NS3), separated by LCM, and phenotyped by real-time PCR. Finally, sections were double stained with antibodies specific for the cell phenotype and HCV NS3. HCV RNA was detected in CD68-positive cells in eight patients, and negative-strand HCV RNA, which is a viral replicative form, was found in three of these patients. HCV RNA also was found in astrocytes from three patients, but negative-strand RNA was not detected in these cells. In double immunostaining, 83 to 95% of cells positive for HCV NS3 also were CD68 positive, while 4 to 29% were GFAP positive. NS3-positive cells were negative for neuron and oligodendrocyte phenotypic markers. In conclusion, HCV infects brain microglia/macrophages and, to a lesser extent, astrocytes. Our findings could explain the biological basis of neurocognitive abnormalities in HCV infection.

Factor analysis reveals differences in brain metabolism in macaques with SIV/AIDS and those with SIV-induced encephalitis

MRS has often been used to study metabolic processes in the HIV-infected brain. However, it remains unclear how changes in individual metabolites are related to one another in this context of virus-induced central nervous system dysfunction. We used factor analysis (FA) to identify patterns of metabolite distributions from an MRS study of healthy macaques and those infected with simian immunodeficiency virus (SIV) which were moribund with AIDS. FA summarized the correlations from nine metabolites into three main factors. Factor 3 identified patterns that discern healthy animals from those with SIV/AIDS. Factor 2 was able to differentiate between animals that had encephalitis and those moribund with AIDS but lacking encephalitis. Specifically, Factor 2 was able to distinguish animals with moderate to severe encephalitis from animals with mild or no encephalitis as well as uninfected controls. FA not only confirmed the involvement of neuronal metabolites (N-acetylaspartate and glutamate) in disease severity, but also detected changes in creatine and myo-inositol that have not been observed in the SIV macaque model previously. These results suggest that the divergent pathways of N-acetylaspartate and creatine in this disease may enable the commonly reported ratio N-acetylaspartate/creatine to be a more sensitive marker of disease severity.

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.

Central nervous system changes in hepatitis C virus infection

Patients with chronic hepatitis C virus (HCV) infection frequently describe neuropsychological symptoms. Although hepatic encephalopathy is the best established neurological association of HCV infection, there is a growing body of literature on cerebral dysfunction, occurring at an early stage of chronic HCV infection, well before the development of cirrhosis. In this review we describe recent studies that have documented mild, but significant neurocognitive impairment in HCV infection. These deficits in patients with minimal or absent liver disease do not appear to be attributable to a history of substance abuse, coexistent depression or hepatic encephalopathy. Recent studies employing in-vivo magnetic resonance spectroscopy have suggested that a biological mechanism associated with the virus may be responsible. The hypothesis that HCV infection of the central nervous system may be related to the reported neuropsychological symptoms and cognitive impairment is supported by molecular virological studies of post-mortem brain tissue.

Emerging evidence of hepatitis C virus neuroinvasion

It has been reported that hepatitis C virus (HCV) infection is associated with cognitive dysfunction, fatigue and depression, which do not correlate with the severity of liver disease and cannot be accounted for by hepatic encephalopathy or drug abuse. There is also emerging evidence that HCV infection can have negative neurocognitive effects in HIV-infected cohorts. Magnetic resonance spectroscopy has suggested the likely existence of a biological basis for these effects. HCV replicative forms have recently been detected in autopsy brain tissue and the infected cells have been identified as CD68-positive (macrophages/microglia). These findings raise the possibility that HCV infection of the brain could be directly related to the reported neuropsychological and cognitive changes. HCV is not strictly hepatotropic, as it can also replicate in leukocytes, including monocytes/macrophages. The latter cells could provide access of HCV into the central nervous system ('Trojan horse' mechanism) in a process similar to that postulated for HIV-1. In support of this hypothetical mechanism come reports showing a close relationship between HCV sequences present in the brain and cerebrospinal fluid and sequences found in lymph nodes and peripheral blood mononuclear cells. However, despite some similarities there is a fundamental difference between HIV-1 and HCV infection as the latter does not progress into AIDS-type dementia.

The shifting patterns of HIV encephalitis neuropathology

HIV infected macrophages infiltrate the nervous system early in the progression of HIV infection, leading to a complex set of neuropathological alterations including HIV encephalitis (HIVE), leukoencephalopathy and vacuolar myelopathy that in turn result in neurodegeneration of selective cellular populations and pathways involved in regulating cognitive and motor functioning. Rapid progress in the development of highly active antiretroviral therapy (HAART) has changed the patterns of HIV related neuropathology and neurological manifestations in the past 10 years. The prevalence of opportunistic infections and central nervous system (CNS) neoplasms has decreased, and some groups have proposed that the frequency of chronic forms of HIVE have been rising as the HAART-treated HIV population ages. Accordingly, clinical manifestations have shifted from severe dementia forms to more subtle minor cognitive impairment, leading to the suggestion of a classification of HIV associated neurological conditions into an inactive form, a chronic variety, and a 'transformed' variant. From a neuropathological point of view these variants might correspond to: a) aggressive forms with severe HIVE and white matter injury, b) extensive perivascular lymphocytic infiltration, c) 'burnt-out' forms of HIVE and d) aging-associated amyloid accumulation with Alzheimer's-like neuropathology. Factors contributing to the emergence of these variants of HIVE include the development of viral resistance, immune reconstitution, anti-retroviral drug toxicity and co-morbid factors (e.g., methamphetamine, HCV). More detailed characterization of these proposed variants of HIVE is important in order to better understand the pathogenesis of HIV-associated neurological damage and to design more effective treatments to protect the nervous system.

A review of cognitive impairment and cerebral metabolite abnormalities in patients with hepatitis C infection

Numerous studies have reported associations between chronic hepatitis C virus (HCV) infection and fatigue, depression and impairments in health-related quality of life, which are independent of the severity of liver disease. Although there are a large number of potential explanations for these symptoms, including a history of substance abuse and associated personality types, or the effect of the diagnosis of HCV infection itself, there has been recent interest in the possibility of a biological effect of HCV infection on cerebral function. There is emerging evidence of mild, but significant neurocognitive impairment in HCV infection, which cannot be wholly attributed to substance abuse, co-existent depression or hepatic encephalopathy. Impairments are predominantly in the domains of attention, concentration and information processing speed. Furthermore, in-vivo cerebral magnetic resonance spectroscopy studies in patients with hepatitis C and normal liver function have reported elevations in cerebral choline-containing compounds and reductions in N-acetyl aspartate, suggesting that a biological mechanism may underlie the cognitive findings. The recent detection of HCV genetic sequences in post-mortem brain tissue raises the intriguing possibility that HCV infection of the central nervous system may be related to the reported neuropsychological symptoms and cognitive impairment.

Coregistration of quantitative proton magnetic resonance spectroscopic imaging with neuropathological and neurophysiological analyses defines the extent of neuronal impairments in murine human immunodeficiency virus type-1 encephalitis

Relatively few immune-activated and virus-infected mononuclear phagocytes (MP; perivascular macrophages and microglia) may affect widespread neuronal dysfunction during human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD). Indeed, histopathological evidence of neuronal dropout often belies the extent of cognitive impairment. To define relationships between neuronal function and histopathology, proton magnetic resonance spectroscopic imaging (1H MRSI) and hippocampal long-term potentiation (LTP) were compared with neuronal and glial immunohistology in a murine model of HIV-1 encephalitis (HIVE). HIV-1(ADA)-infected human monocyte-derived macrophages (MDM) were stereotactically injected into the subcortex of severe combined immunodeficient (SCID) mice. Sham-operated and unmanipulated mice served as controls. Seven days after cell injection, brain histological analyses revealed a focal giant cell encephalitis, with reactive astrocytes, microgliosis, and neuronal dropout. Strikingly, significant reductions in N-acetyl aspartate concentration ([NAA]) and LTP levels in HIVE mice were in both injected and contralateral hemispheres and in brain subregions, including the hippocampus, where neuropathology was limited or absent. The data support the importance of 1H MRSI as a tool for assessing neuronal function for HAD. The data also demonstrate that a highly focal encephalitis can produce global deficits for neuronal function and metabolism.

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.

In Vitro Methods in the Study of Viral and Prion Permeability Across the Blood–Brain Barrier

(1) Infectious agents capable of entering the central nervous system (CNS) produce some of the most dreaded diseases known to man. The infectious agent within the CNS is often protected by the blood-brain barrier (BBB), shielded from endogenous and exogenous anti-infectious agents. (2) The use of in vitro methods offers many advantages to the study of how infectious agents interact with the BBB. Two such agents which negotiate the BBB early in the course of disease before damage to the BBB are the autoimmune deficiency syndrome virus, or human immunodeficiency virus 1, and scrapie prion. Our laboratories have used in vitro methods to study these agents. (3) Here, we review some of the results form our laboratories and those of others.

Hepatitis C virus infection affects the brain-evidence from psychometric studies and magnetic resonance spectroscopy

BACKGROUND/AIMS

Up to 50% of patients infected with the hepatitis C virus (HCV) complain of chronic fatigue and difficulties in concentration and memory. The aim of the present study was to seek evidence for the presence of central nervous system involvement in HCV infected patients with only mild liver disease.

METHODS

Thirty HCV infected patients with normal liver function, 15 of whom were identified as having mild and 15 moderate to severe fatigue using the fatigue impact scale, underwent neurological and neuropsychological examination, electroencephalography (EEG) and cerebral proton magnetic resonance imaging (MRI) and spectroscopy (MRS). Fifteen healthy volunteers, matched for age and educational attainment, served as controls.

RESULTS

In comparison to the healthy controls the patients with HCV infection showed evidence of cognitive impairment, primarily attention and higher executive functions, higher levels of anxiety and depression and impairment of quality of life. In addition they showed a significant decrease of the N-acetyl-aspartate/creatine ratio in the cerebral cortex on 1H MRS while the EEG was slowed in 25%. In general the deficits were more marked in the patients with moderate rather than mild fatigue.

CONCLUSIONS

The data provide evidence of central nervous system involvement in patients with HCV infection.

MR spectroscopy of brain tumors

MR Spectroscopy provides a means to characterize the metabolite profiles of tumoral and non-tumoral lesions in the brain. This article aims to provide tools to increase our sensitivity and specificity of neurodiagnosis, particularly in combination with other advanced MRI techniques such as perfusion MR imaging.

Human immunodeficiency virus 1-associated minor motor disorders: perfusion-weighted MR imaging and H MR spectroscopy

PURPOSE

To investigate whether advanced magnetic resonance (MR) imaging techniques such as diffusion-weighted (DW) and perfusion-weighted (PW) MR imaging and hydrogen 1 (1H) MR spectroscopy can depict functional and pathophysiologic mechanisms in patients who have minor motor deficits (MMDs) associated with human immunodeficiency virus 1 (HIV-1).

MATERIALS AND METHODS

Thirty-two patients with results seropositive for HIV-1 and different degrees of HIV-1-related MMD underwent conventional brain MR imaging, as well as DW and PW MR imaging and 1H MR spectroscopy of the basal ganglia. PW MR imaging data were computed pixel by pixel for creation of time-to-peak, relative regional cerebral blood volume, and bolus amplitude parameter maps. In addition, quantitative regional cerebral blood flow (rCBF) maps were calculated with respect to the arterial input function by using the singular value decomposition algorithm. For 1H MR spectroscopy, a stimulated echo acquisition mode 20, or STEAM 20, sequence was used. Spectra were fit for determination of the signal intensities of the different metabolites. According to psychomotor testing results, patients were divided into three groups: group 1, 10 patients with normal motor function; group 2, eight patients with psychomotor slowing for the first time; and group 3, 14 patients who had had sustained pathologic psychomotor slowing for at least 6 months before the MR imaging examination.

RESULTS

No patients had an abnormality at either conventional or DW MR imaging. PW MR imaging depicted significantly elevated rCBF in group 2 patients (P =.039, analysis of variance [ANOVA]) and significantly elevated myo-inositol-to-creatine ratio levels in group 3 patients (P =.020, ANOVA).

CONCLUSION

Quantitative PW MR imaging and 1H MR spectroscopy can depict pathologic changes in patients who have HIV-1-related MMD but normal clinical examination and conventional MR imaging findings.

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.

Cerebral dysfunction in chronic hepatitis C infection

A number of studies have reported an association between chronic hepatitis C (HCV) infection and significant impairments in health-related quality of life (QOL), which are independent of the severity of liver disease. There are numerous reports documenting the prevalence of symptoms such as fatigue and depression in chronic HCV infection, which may in part account for the reductions in quality of life. Although there are a large number of potential explanations for these symptoms, including depression and anxiety associated with the diagnosis of HCV infection or substance abuse, there has been recent interest in the possibility of a biological effect of HCV infection on cerebral function. There is emerging evidence of mild, but significant neurocognitive impairment in HCV infection, which cannot be attributed to substance abuse, coexistent depression or hepatic encephalopathy. In vivo magnetic resonance spectroscopy and neurophysiological studies have suggested that a biological mechanism may underlie these cognitive findings. The recent detection of HCV genetic sequences in post mortem brain tissue raises the intriguing possibility that HCV infection of the central nervous system may be related to the reported neuropsychological symptoms and cognitive impairment.

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.

Impaired spatial cognition and synaptic potentiation in a murine model of human immunodeficiency virus type 1 encephalitis

Injection of human immunodeficiency virus type 1 (HIV-1)-infected human monocyte-derived macrophages (MDMs) into the basal ganglia of severe combined immunodeficient mice recapitulates histopathologic features of HIV-1 encephalitis (HIVE). Here, we show that the neural damage in HIVE mice extends beyond the basal ganglia and is associated with cognitive impairment. Morris water maze tests showed impaired spatial learning 8 d after MDM injection. Moreover, impaired synaptic potentiation in the hippocampal CA1 subregion was demonstrated at 8 and 15 d. By day 15, post-tetanic, short-term, and long-term potentiation were reduced by 14.1, 29.5, and 45.3% in HIVE mice compared with sham-injected or control animals. Neurofilament (NF) and synaptophysin (SP) antigens were decreased significantly in the CA2 hippocampal subregion of HIVE mice with limited neuronal apoptosis. By day 15, the CA2 region of HIVE mice expressed 3.8- and 2.6-fold less NF and SP than shams. These findings support the notion that HIV-1-infected and immune-competent brain macrophages can cause neuronal damage at distant anatomic sites. Importantly, the findings demonstrate the value of the model in exploring the physiological basis and therapeutic potential for HIV-1-associated dementia.

Hepatitis C and cognitive impairment in a cohort of patients with mild liver disease

Patients with chronic hepatitis C virus (HCV) infection frequently report fatigue, lassitude, depression, and a perceived inability to function effectively. Several studies have shown that patients exhibit low quality-of-life scores that are independent of disease severity. We therefore considered whether HCV infection has a direct effect on the central nervous system, resulting in cognitive and cerebral metabolite abnormalities. Twenty-seven viremic patients with biopsy-proven mild hepatitis due to HCV and 16 patients with cleared HCV were tested with a computer-based cognitive assessment battery and also completed depression, fatigue, and quality-of-life questionnaires. The HCV-infected patients were impaired on more cognitive tasks than the HCV-cleared group (mean [SD]: HCV-infected, 2.15 [1.56]; HCV-cleared, 1.06 [1.24]; P =.02). A factor analysis showed impairments in power of concentration and speed of working memory, independent of a history of intravenous drug usage (IVDU), depression, fatigue, or symptom severity. A subgroup of 17 HCV-infected patients also underwent cerebral proton magnetic resonance spectroscopy (1H MRS). The choline/creatine ratio was elevated in the basal ganglia and white matter in this group. Patients who were impaired on 2 or more tasks in the battery had a higher mean choline/creatine ratio compared with the unimpaired patients. In conclusion, these preliminary results demonstrate cognitive impairment that is unaccounted for by depression, fatigue, or a history of IVDU in patients with histologically mild HCV infection. The findings on MRS suggest that a biological cause underlies this abnormality.

MR spectroscopy: a powerful tool for investigating brain function and neurological diseases

Magnetic resonance spectroscopy (MRS) has attracted much attention in recent years and has become an important tool to study in vivo particular biochemical aspects of brain disorders. Since the proton is the most sensitive stable nucleus for MRS, and since almost all metabolites contain hydrogen atoms, investigation by in vivo 1H MRS provides chemical information on tissue metabolites, thus enabling a non-invasive assessment of changes in brain metabolism underlying several brain diseases. In this review a brief description of the basic principles of MRS is given. Moreover, we provide some explanations on the techniques and technical problems related to the use of 1H MRS in vivo including water suppression, localization, editing, quantitation and interpretation of 1H spectra. Finally, we discuss the more recent advancement in three major areas of neurological diseases: brain tumors, multiple sclerosis, and inborn errors of metabolism.

Optimal voxel size for measuring global gray and white matter proton metabolite concentrations using chemical shift imaging

Quantification of gray and white matter levels of spectroscopically visible metabolites can provide important insights into brain development and pathological conditions. Chemical shift imaging offers a gain in efficiency for estimation of global gray and white matter metabolite concentrations compared to single voxel methods. In the present study, the optimal voxel size is calculated from segmented human brain data and accompanying field maps. The optimal voxel size is found to be approximately 8 cc, but a wide range of values, 4-64 cc, can be chosen with little increase in estimated concentration error (<15%). Magn Reson Med 44:10-18, 2000.

Possible mechanisms of action and reasons for failure of antiviral therapy in chronic hepatitis C

The known mechanisms of hepatitis C virus (HCV) clearance and their failure in persistent infection are discussed. Interferon-alpha is the main treatment in chronic HCV but has shown poor sustained virological response rates when used as a monotherapy. The effects of interferon-a may include inhibition of HCV virion production by an effect on viral RNA and protein synthesis, enhancement of immune lysis of HCV infected cells, inhibition of hepatic fibrosis by an effect on TGFbeta, and an effect on HCV induced carcinogenesis. Mathematical modelling studies have provided insights into the mechanisms of action of interferon-alpha in chronic HCV. The two-phase plasma HCV RNA disappearance curve may reflect the presence of an interferon-resistant second site of HCV replication either within or outside the liver. Clinical observations and cerebral magnetic resonance scans provide evidence of functional cerebral impairment in HCV infected patients, raising the issue of the central nervous system (CNS) as a site for HCV replication. Recent studies using ribavirin in combination with interferon suggest that this approach doubles the sustained response rates obtained without having a major effect on the initial rate of HCV clearance (see Zeuzem paper). The potential mechanisms of action of ribavirin, although not yet fully understood, include inhibition of synthesis of GTP by an effect on inosine monophosphate dehydrogenase thereby limiting viral RNA synthesis, and enhancement of TH1 responses, which may assist viral clearance. There is no significant effect on HCV RNA polymerase activity. It is possible that ribavirin may have activity at extrahepatic sites of HCV infection, thus explaining the marked reduction in relapse rates with combination therapy, without an appreciable effect on initial antiviral response.

Reversible alterations in brain metabolites during therapy for disseminated nocardiosis using proton magnetic resonance spectroscopy

We report reversible abnormalities in magnetic resonance spectra acquired from a patient with AIDS undergoing antibiotic and corticosteroid therapy for disseminated nocardiosis, a rare opportunistic infection of immunosuppressed patients which can cause cerebral abscess formation. There was no clinical, CT or MRI evidence of HIV-1 encephalitis. MR spectra were acquired before and after treatment using a two-dimensional chemical shift imaging technique (TR 1500ms, TE 130ms). Prior to treatment, a rise in the choline to creatine ratio and a reduction in the N-acetylaspartate to creatine ratio were observed in MR spectra localized to areas of the left anteromedial centrum semiovale that appeared normal on MR imaging. After 16 weeks, the patient had recovered with complete resolution of the cerebral abscesses on MRI. The MR spectral abnormalities also returned to normal. Two months later, the patient had a relapse with focal neurological signs and further abscesses were demonstrated on MRI of the brain. The patient subsequently died and histopathological and microbiological findings at autopsy confirmed the clinical picture of a recurrence of cerebral nocardiosis with no evidence of HIV-1 encephalitis. This case illustrates reversible MR-measurable metabolite changes in the brain of an HIV-seropositive patient without HIV-1 encephalitis who underwent treatment for cerebral nocardiosis.