Predictors of CNS injury as measured by proton magnetic resonance spectroscopy in the setting of chronic HIV infection and CART

The reasons for persistent brain dysfunction in chronically HIV-infected persons on stable combined antiretroviral therapies (CART) remain unclear. Host and viral factors along with their interactions were examined in 260 HIV-infected subjects who underwent magnetic resonance spectroscopy (MRS). Metabolite concentrations (NAA/Cr, Cho/Cr, MI/Cr, and Glx/Cr) were measured in the basal ganglia, the frontal white matter, and gray matter, and the best predictive models were selected using a bootstrap-enhanced Akaike information criterion (AIC). Depending on the metabolite and brain region, age, race, HIV RNA concentration, ADC stage, duration of HIV infection, nadir CD4, and/or their interactions were predictive of metabolite concentrations, particularly the basal ganglia NAA/Cr and the mid-frontal NAA/Cr and Glx/Cr, whereas current CD4 and the CPE index rarely or did not predict these changes. These results show for the first time that host and viral factors related to both current and past HIV status contribute to persisting cerebral metabolite abnormalities and provide a framework for further understanding neurological injury in the setting of chronic and stable disease.

Altered neurometabolites and motor integration in children exposed to methamphetamine in utero

Methamphetamine (METH) is a neurotoxic drug. This study aimed to evaluate brain metabolite levels and cognitive function in young children with prenatal METH exposure. 101 children ages 3-4 years were evaluated with neuropsychological tests and underwent proton magnetic resonance spectroscopy ((1)H-MRS) without sedation. Complete datasets from 49 METH-exposed and 49 controls who completed the neuropsychological test battery, and 38 METH-exposed and 37 controls with high-quality MR spectra are reported here. Despite similar physical characteristics (including head circumference), global cognitive function (on Stanford-Binet), parental education, intelligence, mood, and socioeconomic status, METH-exposed children had higher total creatine (tCr: +7%, p=0.003), N-acetyl compounds (NA: +4.3%, p=0.004) and glutamate+glutamine (GLX: +9.6%, p=0.02) concentrations in the frontal white matter, but lower myoinositol (MI: -7%, p=0.01) and MI/tCr (-7.5%, p=0.03) in the thalamus, than control children. The higher frontal white matter NA in the METH-exposed children was due to the higher NA in the METH-exposed girls (+10.2%, p=0.003), but not the boys (+0.8%) compared to sex-matched controls. Furthermore, the METH-exposed children had poorer performance on a visual motor integration (VMI) task, which correlated with lower MI in the thalamus (r=0.26, p=0.03). The higher NA, tCr and GLX concentrations suggest higher neuronal density or cellular compactness in the white matter, especially in the girls, whereas the lower MI suggests lower glial content in the thalamus of these METH-expose children. These findings combined with their poorer performance on VMI also suggest accelerated but aberrant neuronal and glial development in these brain regions.

Brain lesions in patients with AIDS: H-1 MR spectroscopy

PURPOSE

To evaluate the role of proton (hydrogen-1) magnetic resonance (MR) spectroscopy in the differential diagnosis of focal brain lesions in patients with acquired immunodeficiency syndrome (AIDS).

MATERIALS AND METHODS

Twenty-six men with 35 AIDS-related brain lesions underwent MR imaging and localized H-1 MR spectroscopy. Lesions consisted of 11 toxoplasmic abscesses, 12 progressive multifocal leukoencephalopathic lesions, eight lymphomas, and four cryptococcomas. Metabolite peak areas in the lesions were compared with those in the contralateral hemisphere in each patient.

RESULTS

H-1 MR spectroscopic findings showed significantly different biochemical profiles for each diagnostic group (P = .0001) with regard to N-acetyl compounds, total creatine pool, choline-containing compounds, myoinositol, and lactate. H-1 MR spectroscopy alone helped correctly diagnose 94% (84% with jackknifed classification) of the brain lesions, without overlap between toxoplasmosis and lymphoma.

CONCLUSION

H-1 MR spectroscopy is a sensitive and potentially specific noninvasive adjunctive method for differential diagnosis of focal brain lesions in AIDS.

Analysis of brain tumors using 1H magnetic resonance spectroscopy

BACKGROUND

Magnetic resonance imaging (MRI) is superior in delineating anatomic and pathologic information and has subsequently been married to the ability of magnetic resonance spectroscopy (MRS) to provide insight into the biochemical changes underlying pathology. Proton magnetic resonance spectroscopy (1H MRS) allows the non-invasive in vivo collection and measurement of chemical information from a selected volume of tissue (voxel).

METHODS

We conducted a prospective trial in 23 patients with brain mass lesions and 16 normal subjects using proton magnetic resonance spectroscopy (1H MRS). The spectra were analyzed for N-acetyl-aspartate (NAA), choline compounds (Cho), creatine (Cr), and lactate (Lac). The ratios of the compounds in tumors were compared to normals.

RESULTS

The tumors showed significant decreases in the mean peak height ratios of NAA/Cho, NAA/Cr, and significant increases in Cho/Cr when compared to tissue from normal subjects. Cho was elevated in all of the meningiomas and gliomas. In benign tumors, Cho was usually elevated while in metastases Cho was often normal or decreased. The four metastatic tumors showed NAA/Cho, NAA/Cr, and Cho/Cr that were similar to controls. Lac varied with tumor type and was elevated in many malignant primary brain tumors.

CONCLUSIONS

1H MRS is a powerful tool for safe, noninvasive analysis of tissue chemistry in vivo. Analysis of intracranial tumors reveals significant trends that might eventually be used in the classification of tumor histology and evaluation of the efficacy of tumor treatment.

Muscle energetics and pulmonary oxygen uptake kinetics during moderate exercise

The present study tested whether, during moderate exercise, 1) the dynamic responses of ADP and changes in free energy of ATP hydrolysis (delta GATP) were similar to those of phosphocreatine [PCr; as would be expected for a simple controller of muscle respiration (QO2)] and 2) the rise in pulmonary O2 uptake (VO2) during cycle exercise would reflect the rise in muscle QO2 indicated by the calf PCr kinetics. The responses of PCr, Pi, ADP, and delta GATP were measured from the calf in five subjects during supine treadle exercise using 31P-magnetic resonance spectroscopy and compared with those for VO2, measured breath by breath during upright cycle exercise. The time constants for delta GATP [24.2 +/- 14.2 (SE) s] were not significantly different from those for PCr (26.3 +/- 17.3 s) and Pi (30.7 +/- 22.5 s) (P > 0.05). The time constants for phase 2 VO2 (29.9 +/- 16.8 s) were also similar to those of PCr. In contrast, the dynamics of ADP were distorted from those of PCr due to dynamic changes in pH. These results are consistent with mechanisms of respiratory control that feature substrate control by PCr or thermodynamic control through changes in delta GATP. However, these results are not consistent with substrate control by ADP in a simple fashion. Furthermore, the similarity of time constants for phase 2 VO2 and muscle PCr suggests that phase 2 VO2 kinetics reflect those of muscle QO2 in healthy subjects during moderate exercise.

31P-magnetic resonance spectroscopy of leg muscle metabolism during exercise in children and adults

Gas exchange response to high-intensity exercise differs in children and adults. We hypothesized that these findings are related to a lower anaerobic ATP supply in children. We predicted therefore a maturation of muscle high-energy phosphate metabolism during exercise. To test this hypothesis, we measured calf muscle Pi, phosphocreatine (PCr), and pH with 31P-nuclear magnetic resonance spectroscopy during rest and progressive exercise in 10 children and 8 adults. No differences were found at rest in pH and Pi/PCr between children and adults. Exercise resulted in a greater increase in Pi/PCr (P < 0.001) and decrease in pH (P < 0.0001) in adults than in children. Six adults and five children exhibited a transition from a slow to a faster rate of Pi/PCr increase and pH decrease during exercise. No significant differences were found between the two groups in the initial slow-phase slopes of Pi/PCr and pH as a function of work rate. In contrast, during the fast phase, Pi/PCr increased (slope: adults 23.6 +/- 9.8, children 10.7 +/- 2.5; P < 0.05) and pH decreased (slope: adults -6.0 +/- 1.9, children -3.7 +/- 1.2; P < 0.05) more rapidly in adults than in children. In conclusion, high-intensity exercise results in different kinetics of Pi/PCr and pH between children and adults. These results suggest that children are less able than adults to affect ATP rephosphorylation by anaerobic metabolic pathways during high-intensity exercise.

Hepatic D-galactosamine toxicity studied with localized in vivo 31P magnetic resonance spectroscopy in intact rats

Spatially resolved 31P magnetic resonance spectroscopy (MRS) at 4.7 T was applied to noninvasively assess liver phosphorus metabolites in a biochemically well-characterized model of hepatotoxicity induced by injection of a sublethal dose of D-galactosamine (galN). A newly developed hybrid method based on spectral localization with B0 and B1 gradients was employed to obtain multivoxel spectra in intact anesthesized rats. Spatially localized in vivo spectra were recorded 0 to 26 h after galN injection of female rats. In response to galN exposure, diphosphodiester peaks ascribed to UDP-hexosamines became detectable by 4 h and persisted up to 26 h. A metabolite coresonating with inorganic phosphate increased rapidly in intensity by 2 h after galN and returned to baseline by 18 h; this resonance was shown not to be Pi and was assigned to galN-1-phosphate by subsequent high resolution MRS experiments on extracts prepared from these livers. These results confirmed in vivo the metabolic perturbations described previously for this model of hepatotoxicity following biochemical studies based on classical extraction methods. Unlike the in vitro studies, however, these noninvasive experiments provided additional information on the time course of metabolic alterations on the same animal.