Diana M. Lindquist

Altered myelination and axonal integrity in adults with childhood lead exposure: A diffusion tensor imaging study

Childhood lead exposure is associated with adverse cognitive, neurobehavioral and motor outcomes, suggesting altered brain structure and function. The purpose of this work was to assess the long-term impact of childhood lead exposure on white matter integrity in young adults. We hypothesized that childhood lead exposure would alter adult white matter architecture via deficits in axonal integrity and myelin organization. Adults (22.9+/-1.5 years, range 20.0-26.1 years) from the Cincinnati Lead Study were recruited to undergo a study employing diffusion tensor imaging (DTI). The anatomic regions of association between water diffusion characteristics in white matter and mean childhood blood lead level were determined for 91 participants (52 female). Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were measured on an exploratory voxel-wise basis. In adjusted analyses, mean childhood blood lead levels were associated with decreased FA throughout white matter. Regions of the corona radiata demonstrated highly significant lead-associated decreases in FA and AD and increases in MD and RD. The genu, body, and splenium of the corpus callosum demonstrated highly significant lead-associated decreases in RD, smaller and less significant decreases in MD, and small areas with increases in AD. The results of this analysis suggest multiple insults appear as distinct patterns of white matter diffusion abnormalities in the adult brain. Neurotoxic insults from the significant lead burden the participants experienced throughout childhood affect neural elements differently and may be related to the developmental stage of myelination at periods of exposure. This study indicates that childhood lead exposure is associated with a significant and persistent impact on white matter microstructure as quantified with diffusivity changes suggestive of altered myelination and axonal integrity.

Proton Magnetic Resonance Spectroscopy in Adults with Childhood Lead Exposure

Background Childhood lead exposure adversely affects neurodevelopment. However, few studies have examined changes in human brain metabolism that may underlie known adverse cognitive and behavioral outcomes. Objective We examined the association between mean childhood blood lead levels and in vivo brain metabolite concentrations as adults, determined by proton magnetic resonance spectroscopy (MRS) in a birth cohort with documented low-to-moderate lead exposure. Methods Adult participants from the Cincinnati Lead Study [n = 159; mean age (± SD), 20.8 ± 0.9 years] completed a quantitative, short-echo proton MRS protocol evaluating seven regions to determine brain concentrations of N-acetyl aspartate (NAA), creatine and phosphocreatine (Cr), cholines (Cho), myo-inositol, and a composite of glutamate and glutamine (GLX). Correlation and multiple linear regression analyses were conducted. Results Mean childhood blood lead levels were associated with regionally specific brain metabolite concentrations adjusted for age at imaging and Full-Scale intelligence quotient. Adjusted analyses estimated for a unit (micrograms per deciliter) increase in mean childhood blood lead concentrations, a decrease of NAA and Cr concentration levels in the basal ganglia, a decrease of NAA and a decrease of Cho concentration levels in the cerebellar hemisphere, a decrease of GLX concentration levels in vermis, a decrease of Cho and a decrease of GLX concentration levels in parietal white matter, and a decrease of Cho concentration levels in frontal white matter. Conclusions Gray-matter NAA reductions associated with increasing childhood blood lead levels suggest that sustained childhood lead exposure produces an irreversible pattern of neuronal dysfunction, whereas associated white-matter choline declines indicate a permanent alteration to myelin architecture.

Cyclocreatine treatment improves cognition in mice with creatine transporter deficiency

The second-largest cause of X-linked mental retardation is a deficiency in creatine transporter (CRT; encoded by SLC6A8), which leads to speech and language disorders with severe cognitive impairment. This syndrome, caused by the absence of creatine in the brain, is currently untreatable because CRT is required for creatine entry into brain cells. Here, we developed a brain-specific Slc6a8 knockout mouse (Slc6a8-/y) as an animal model of human CRT deficiency in order to explore potential therapies for this syndrome. The phenotype of the Slc6a8-/y mouse was comparable to that of human patients. We successfully treated the Slc6a8-/y mice with the creatine analog cyclocreatine. Brain cyclocreatine and cyclocreatine phosphate were detected after 9 weeks of cyclocreatine treatment in Slc6a8-/y mice, in contrast to the same mice treated with creatine or placebo. Cyclocreatine-treated Slc6a8-/y mice also exhibited a profound improvement in cognitive abilities, as seen with novel object recognition as well as spatial learning and memory tests. Thus, cyclocreatine appears promising as a potential therapy for CRT deficiency.

Ex Vivo Diffusion Tensor Imaging and Neuropathological Correlation in a Murine Model of Hypoxia–Ischemia-Induced Thrombotic Stroke

Diffusion tensor imaging (DTI) is a powerful method to visualize white matter, but its use in patients with acute stroke remains limited because of the lack of corresponding histologic information. In this study, we addressed this issue using a hypoxia–ischemia (HI)-induced thrombotic model of stroke in adult mice. At 6, 15, and 24 hours after injury, animals were divided into three groups for (1) in vivo T2- and diffusion-weighted magnetic resonance imaging, followed by histochemistry, (2) ex vivo DTI and electron microscopy, and (3) additional biochemical or immunochemical assays. The temporal changes of diffusion anisotropy and histopathology were compared in the fimbria, internal capsule, and external capsule. We found that HI caused a rapid reduction of axial and radial diffusivities in all three axonal bundles. A large decrease in fractional anisotropy, but not in axial diffusivity per se, was associated with structural breakdown of axons. Furthermore, the decrease in radial diffusivity correlated with swelling of myelin sheaths and compression of the axoplasma. The gray matter of the hippocampus also exhibited a high level of diffusion anisotropy, and its reduction signified dendritic degeneration. Taken together, these results suggest that cross-evaluation of multiple DTI parameters may provide a fuller picture of axonal and dendritic injury in acute ischemic stroke.

Preclincial testing of sorafenib and RAD001 in the Nf(flox/flox) ;DhhCre mouse model of plexiform neurofibroma using magnetic resonance imaging.

Neurofibromatosis type 1 (NF1) is an inherited disease predisposing affected patients to variable numbers of benign neurofibromas. To date there are no effective chemotherapeutic drugs available for this slow growing tumor. Molecularly targeted agents that aim to slow neurofibroma growth are being tested in clinical trials. So preclinical models for testing potential therapies are urgently needed to prioritize drugs for clinical trials of neurofibromas.

Evidence of resilience: Neuroimaging in former prisoners of war

In this study, single voxel proton magnetic resonance spectroscopic imaging ((1)H-MRS) and volumetric analysis of hippocampal magnetic resonance imaging (MRI) images were used to determine if any differences in hippocampal biochemistry or volume were present between former prisoners of war (POWs) with and without posttraumatic stress disorder (PTSD) and control subjects matched for age and education. This study did not find lower hippocampal concentrations of N-acetylaspartate (NAA), smaller hippocampal volumes, or more impaired memory function in older veterans with PTSD compared with a group matched for traumatic experience or a nontraumatized control group.

The AMPK β2 Subunit Is Required for Energy Homeostasis during Metabolic Stress

ABSTRACT AMP activated protein kinase (AMPK) plays a key role in the regulatory network responsible for maintaining systemic energy homeostasis during exercise or nutrient deprivation. To understand the function of the regulatory β2 subunit of AMPK in systemic energy metabolism, we characterized β2 subunit-deficient mice. Using these mutant mice, we demonstrated that the β2 subunit plays an important role in regulating glucose, glycogen, and lipid metabolism during metabolic stress. The β2 mutant animals failed to maintain euglycemia and muscle ATP levels during fasting. In addition, β2-deficient animals showed classic symptoms of metabolic syndrome, including hyperglycemia, glucose intolerance, and insulin resistance when maintained on a high-fat diet (HFD), and were unable to maintain muscle ATP levels during exercise. Cell surface-associated glucose transporter levels were reduced in skeletal muscle from β2 mutant animals on an HFD. In addition, they displayed poor exercise performance and impaired muscle glycogen metabolism. These mutant mice had decreased activation of AMPK and deficits in PGC1α-mediated transcription in skeletal muscle. Our results highlight specific roles of AMPK complexes containing the β2 subunit and suggest the potential utility of AMPK isoform-specific pharmacological modulators for treatment of metabolic, cardiac, and neurological disorders.

Therapeutic Administration of Plasminogen Activator Inhibitor-1 Prevents Hypoxic–Ischemic Brain Injury in Newborns

Disruption of the integrity of the blood–brain barrier (BBB) is an important mechanism of cerebrovascular diseases, including neonatal cerebral hypoxia–ischemia (HI). Although both tissue-type plasminogen activator (tPA) and matrix metalloproteinase-9 (MMP-9) can produce BBB damage, their relationship in neonatal cerebral HI is unclear. Here we use a rodent model to test whether the plasminogen activator (PA) system is critical for MMP-9 activation and HI-induced brain injury in newborns. To test this hypothesis, we examined the therapeutic effect of intracerebroventricular injection of plasminogen activator inhibitor-1 (PAI-1) in rat pups subjected to unilateral carotid artery occlusion and systemic hypoxia. We found that the injection of PAI-1 greatly reduced the activity of both tPA and urokinase-type plasminogen activator after HI. It also blocked HI-induced MMP-9 activation and BBB permeability at 24 h of recovery. Furthermore, magnetic resonance imaging and histological analysis showed the PAI-1 treatment reduced brain edema, axonal degeneration, and cortical cell death at 24–48 h of recovery. Finally, the PAI-1 therapy provided a dose-dependent decrease of brain tissue loss at 7 d of recovery, with the therapeutic window at 4 h after the HI insult. Together, these results suggest that the brain PA system plays a pivotal role in neonatal cerebral HI and may be a promising therapeutic target in infants suffering hypoxic–ischemic encephalopathy.

Blocking Lymphocyte Trafficking with FTY720 Prevents Inflammation-Sensitized Hypoxic–Ischemic Brain Injury in Newborns

Intrauterine infection (chorioamnionitis) aggravates neonatal hypoxic–ischemic (HI) brain injury, but the mechanisms linking systemic inflammation to the CNS damage remain uncertain. Here we report evidence for brain influx of T-helper 17 (TH17)-like lymphocytes to coordinate neuroinflammatory responses in lipopolysaccharide (LPS)-sensitized HI injury in neonates. We found that both infants with histological chorioamnionitis and rat pups challenged by LPS/HI have elevated expression of the interleukin-23 (IL-23) receptor, a marker of early TH17 lymphocytes, in the peripheral blood mononuclear cells. Post-LPS/HI administration of FTY720 (fingolimod), a sphingosine-1-phosphate receptor agonist that blocks lymphocyte trafficking, mitigated the influx of leukocytes through the choroid plexus and acute induction of nuclear factor-κB signaling in the brain. Subsequently, the FTY720 treatment led to attenuated blood–brain barrier damage, fewer cluster of differentiation 4-positive, IL-17A-positive T-cells in the brain, less proinflammatory cytokine, and better preservation of growth and white matter functions. The FTY720 treatment also provided dose-dependent reduction of brain atrophy, rescuing >90% of LPS/HI-induced brain tissue loss. Interestingly, FTY720 neither opposed pure-HI brain injury nor directly inhibited microglia in both in vivo and in vitro models, highlighting its unique mechanism against inflammation-sensitized HI injury. Together, these results suggest that the dual hit of systemic inflammation and neonatal HI injury triggers early onset of the TH17/IL-17-mediated immunity, which causes severe brain destruction but responds remarkably to the therapeutic blockade of lymphocyte trafficking.

Effects of antipsychotic drugs on metabolite ratios in rat brain in vivo

Localized in vivo proton magnetic resonance spectroscopy at 4.7 T was used to examine the brains of rats that were given the antipsychotic drugs haloperidol, clozapine, or olanzapine for 1 week. Spectra were collected before and during treatment. The ratios of N‐acetylaspartate (NAA) to creatine (Cr) and choline to Cr were determined from the spectra. No significant differences in these ratios were seen among the rats given the various antipsychotic medications or between the control rats and the treated rats. No significant time‐dependent changes were seen in most cases, except for a small reduction of NAA/Cr after 7 days of olanzapine administration. These results suggest that differences in brain metabolite ratios in vivo in schizophrenics relative to controls, at least for short‐term treatment, arise from the disease, and not as a metabolic effect of the medication. Magn Reson Med 43:355–358, 2000.