Adeno-associated virus-mediated gene transfer to the brain: duration and modulation of expression.

Adeno-associated virus (AAV) is a promising vector for central nervous system (CNS) gene transfer, but a number of issues must be addressed if AAV is to be used for widespread delivery throughout the CNS. Our aim was to test the effect of dose, route of delivery, and hydroxyurea treatment on brain expression of beta-galactosidase activity after cerebral inoculation with an rAAV-lacZ vector (rAAV-beta-gal). We also wished to test whether an immune response appeared against the vector and the transgene product. We found in BALB/c mice that beta-Gal expression increased during the first 2 months after inoculation, then decreased slightly by 4 months, and continued out to 6, 12, and 15 months in single animals. Cerebral injection produced localized beta-Gal expression that did not diffuse to other regions despite a fivefold increase in injection volume. Intraventricular injection resulted in negligible transduction. Antibodies to AAV capsid protein and beta-Gal appeared at low levels at 2 and 4 months, but correlated poorly with beta-Gal expression and did not prevent readministration of rAAV-beta-gal. Hydroxyurea treatment did not result in increased transduction in vivo. We conclude that our study confirms rAAV vectors as having considerable potential for CNS gene transfer; however, several important problems must be addressed if this vector system is to be used for long-term transduction of the entire brain. Sustained, regulatable expression will be needed if rAAV is to be used in the treatment of chronic CNS disease. The difficulty in delivering AAV to diverse regions of the brain is an important problem that must be overcome if these vectors are to be used for anything beyond localized transduction.

Recombinant adeno-associated virus-mediated correction of lysosomal storage within the central nervous system of the adult mucopolysaccharidosis type VII mouse.

The central nervous system (CNS) is a predominant site of involvement in several lysosomal storage diseases (LSDs); and for many patients, these diseases are diagnosed only after the onset of symptoms related to the progressive accumulation of macromolecules within lysosomes. The mucopolysaccharidosis type VII (MPS VII) mice are deficient for the lysosomal enzyme beta-glucuronidase and, by early adulthood, develop a significant degree of glycosaminoglycan storage within neuronal, glial, and leptomeningeal cells. Using this animal model, we investigated whether gene transfer mediated by a recombinant adeno-associated virus (rAAV) vector is capable of reversing the progression of storage lesions within the CNS. Adult MPS VII mice received intracerebral injections of 4 X 10(7) infectious units of a rAAV vector carrying the murine beta-glucuronidase (gus-s(a)) cDNA under the transcriptional direction of the cytomegalovirus immediate-early promoter and enhancer. By 1 month after vector administration, transgene-derived beta-glucuronidase was present surrounding the injection site. Enzyme levels were between 50 and 240% of that found in wild-type mice. This level of beta-glucuronidase activity was sufficient to reduce the degree of lysosomal storage. Moreover, the reduction in storage was maintained for at least 3 months post-rAAV administration. These data demonstrate that rAAV vectors can transduce the diseased CNS of MPS VII mice and mediate levels of transgene expression necessary for a therapeutic response. Thus, rAAV vectors are potential tools in the treatment of the mucopolysaccharidoses and other lysosomal storage diseases.

Centronuclear myopathy and type-1 hypotrophy without central nuclei. Distinct nosologic entities?

Four infants presented with severe hypotonia, weakness, and hypoventilation or apnea at birth. Their clinical presentations and courses resembled those of the x-linked recessive form of centronuclear myopathy. Histologic examination of their muscle biopsy specimens showed patterns ranging between centronuclear myopathy and type-1 hypotrophy without central nuclei. Regardless of their gender or the appearance of their biopsy specimens, the children all had a poor outcome. The clinical and biopsy findings in these infants suggest that centronuclear myopathy and type-1 hypotrophy without central nuclei do not represent distinct nosologic entities. It seems more likely that the histologic changes represent abnormalities in fiber size distribution and development, which are nonspecific and which reflect a primary defect at one or more sites in the neuraxis.

Suppression of experimental autoimmune encephalomyelitis by restraint stress: sex differences.

We have recently reported that female Lewis rats exhibit significantly higher basal circadian levels of corticosterone (Cort) than male Lewis rats. The studies reported here were designed to explore whether male and female Lewis rats demonstrate a differential suppression of experimental autoimmune encephalomyelitis (EAE) following exposure to an identical regimen of repetitive restraint stress. Rats were restrained for 1 or 9 h/day beginning 5 days before myelin basic protein (MBP) challenge and extending through the recovery period (18 days post challenge). Both clinical signs and histopathological changes of EAE were more significantly suppressed in 9-h-stressed females relative to male Lewis rats. Investigation of the mechanism underlying the stress-induced suppression of EAE revealed that restraint stress did not alter the clinical course of EAE in rats challenged with MBP 68-88 encephalitogenic peptide, suggesting that restraint stress may affect processing and/or presentation of the MBP molecule. Stressed rats exhibited decreased interleukin-2 and interferon gamma production, and the frequency of MBP-reactive lymphocytes was reduced in comparison to non-stressed rats. Finally, repetitive restraint stress had no effect on blood-spinal cord permeability during EAE. The results presented here underscore the importance of such experimental variables as sex, strain, time of day, and the kinetics of immune response development.

Effect of neutrophil depletion in acute cerebritis.

Inhibition of the host's neutrophil response has been proposed as one means to reduce tissue damage in acute inflammation. If this approach can be applied in acute central nervous system (CNS) infection, the long-term morbidity, which occurs in CNS infection, might be reduced. Previous studies in models of CNS infection yielded conflicting results whether neutrophil depletion might be protective. To determine whether neutrophil depletion reduces tissue necrosis and cerebrovascular injury in experimental bacterial cerebritis, we depleted circulating neutrophils with an IgM monoclonal antibody, RP3, given after the start of the infection. RP3 treatment successfully depleted circulating neutrophils and reduced the extent of neutrophil influx into the cerebritis region. The extent of tissue necrosis, measured histologically, and the regional increase of blood-brain barrier (BBB) permeability were not inhibited by neutrophil depletion, and in animals treated with RP3 alone, the extent of tissue necrosis and BBB permeability tended to be larger than in S. aureus inoculated controls. We conclude that host neutrophils do not add to the tissue and cerebrovascular damage created by the intracerebral inoculation of a pathogenic bacteria, and the neutrophils serve to diminish local damage in the setting of a cerebritis.

Blood-brain barrier permeability and the brain extracellular space in acute cerebral inflammation.

The diffusion properties of the brain cortical extracellular space have never been examined in models of inflammation, even though inflammation can cause increased blood-brain barrier permeability. Uptake of intravascular 125I-labelled albumin and the diffusion of the tetramethylammonium ion within the brain extracellular space was measured in an experimental brain abscess to determine the effect of acute inflammation upon blood-brain barrier permeability and diffusion properties of the cortical extracellular space. The blood-brain transfer constant for albumin was increased in the abscess region, indicating that an increase in blood-brain barrier permeability occurred in animals inoculated with a weakly pathogenic strain of Staphylococcus aureus. The volume fraction of the extracellular space, as measured by the diffusion of tetramethylammonium ion, ranged from 0.19 to 0.23 in bacteria inoculated subjects and from 0.21 to 0.22 in controls. The tortuosity of the extracellular space ranged from 1.40 to 1.42 in bacteria inoculated subjects and was 1.39 in controls. These results showed that the volume fraction and tortuosity of the cortical extracellular space were not affected by inflammation even though vascular permeability was increased. This result was supported by the finding that brain water content, measured in the same animals, was increased to a non-significant extent in the bacteria inoculated subjects. These findings lead to the conclusion that acute inflammation induced by a weak pathogen can cause increased blood-brain barrier permeability without a significant change in the diffusion properties of the brain cortical space.

Blood-brain barrier permeability in an experimental model of bacterial cerebritis.

The mechanisms affecting blood-brain barrier (BBB) permeability in a brain abscess are not well defined. We sought to determine whether one bacterial species, Staphylococcus aureus, when inoculated into the brain, can cause the BBB to become abnormally permeable before leukocytes begin migrating into the brain. Cerebritis was induced by inoculating a suspension of S. aureus into the brain of the rat. The extent of leukocyte migration into the brain was assessed from histological sections at sequential times after the injection. BBB permeability was assessed by 1) detecting the presence of serum albumin leakage into the brain with a fluorescein-labeled antibody to rat albumin, and 2) detecting evidence of staining of the brain parenchyma with Evans blue dye. The fluorescein labelled anti-rat albumin antibody studies showed that the BBB was immediately damaged in experimental and control animals by the process of inoculation, but remained open to a greater extent in subjects inoculated with bacteria. Within 6 hours after inoculation, neutrophils began migrating into bacteria-inoculated brains. Evans blue dye, however, did not become detectable in the surrounding parenchyma until 72 hours later, long after leukocyte migration had occurred. The findings indicate that an acute disruption of the BBB in the needle track precedes leukocyte influx, but a more widespread increase in regional BBB permeability does not occur until 3 days after the bacterial inoculation. The time course for the development of increased vascular permeability suggests that a delayed product of the inoculation caused impairment of the regional BBB.

Blood-brain barrier permeability in staphylococcal cerebritis and early brain abscess.

The pattern of radiographic enhancement in cases of brain abscess has been extensively studied, but the magnitude of blood-brain barrier (BBB) damage that accompanies enhancement has not. The question of whether BBB permeability increases continuously as a cerebritis evolves into an abscess was studied. The tracers 3H-labeled aminoisobutyric acid and 14C-labeled butanol were used in a rat Staphylococcus aureus cerebritis model to measure simultaneously BBB permeability and blood flow. The rats were examined at 1, 2, 3, 5, or 7 days after inoculation, and tissue samples were collected from the cerebritis site and uninoculated regions. Permeability of the BBB in the cerebritis region increased to five times the normal values by 72 hours after inoculation, then reached a plateau. The plasma volume in the cerebritis region increased to six times greater than the normal value at 72 hours, then remained unchanged. Uninoculated brain in both ipsilateral and contralateral hemispheres showed no significant changes. Cerebral blood flow was not substantially altered at the inoculated or uninoculated sites. In this model, incidence of BBB damage rises rapidly, reaches a plateau, and does not continue to increase despite the ongoing evolution of a cerebritis into an abscess. The BBB damage is accompanied by an increase in the regional plasma volume, a novel finding that has not been previously reported in central nervous system inflammation. These results suggest that the vascular events contributing to brain edema formation become established early in the cerebritis phase and imply that control of the host's inflammatory response is important in the management of cerebritis-associated brain edema.

Asymmetric hypsarrhythmia and infantile spasms in west syndrome.

The video encephalograms (EEGs) of 77 consecutive infantile spasms patients were evaluated for the presence of focal or asymmetric hypsarrhythmia and infantile spasms, to determine whether these findings were useful in predicting the presence of focal structural brain disease and were of any additional diagnostic or prognostic significance. Of the 77 patients with infantile spasms, 38% had focal or lateralized features present on video-EEG studies. Unilateral hypsarrhythmia and asymmetric ictal EEG changes during infantile spasms often occurred together: each always indicated the side of a focal or asymmetric structural cerebral lesion that was visible on computed tomographic or magnetic resonance imaging brain scan and was usually large. Clinically asymmetric infantile spasms were less common, always occurred in the presence of asymmetric ictal EEG changes, and did not appear to have additional localizing value. Lateralized hypsarrhythmia, with or without asymmetric infantile spasms, occurred in the presence of bilateral structural lesions that were more abnormal in the area of the greater EEG abnormality. Partial seizures also indicated symptomatic etiologies but were less localizing to visible focal lesions. Patients with symmetric hypsarrhythmia and infantile spasms rarely had focal/lateralized lesions visible on imaging studies. Although the majority of the symmetric group had structural brain disease, these brain lesions were diffuse, not lateralized. This group also included all patients who had cryptogenic etiology and normal development.

Familial adrenal insufficiency, achalasia, alacrima, peripheral neuropathy, microcephaly, normal plasma very long chain fatty acids, and normal muscle mitochondrial respiratory chain enzymes.

Adrenal insufficiency has been associated with adrenoleukodystrophy and adrenomyeloneuropathy. In these diseases, plasma very long chain fatty acids are elevated. Peripheral neuropathy is frequently seen in adults with adrenomyeloneuropathy. We encountered two first cousins with adrenal insufficiency, who also developed peripheral neuropathy, achalasia, alacrima, and microcephaly. However, plasma very long chain fatty acids, pipecolic acid, phytanic acid, and cranial computed tomographic scan were normal. Muscle mitochondrial respiratory chain enzymes were also normal. This syndrome of adrenal insufficiency, achalasia, alacrima, microcephaly, and peripheral neuropathy is different from either adrenomyeloneuropathy or adrenoleukodystrophy.

Myasthenia gravis and associated autoimmune diseases in children.

Myasthenia gravis has been associated with other autoimmune disorders. We report two children with myasthenia gravis and another autoimmune disease: an 18-month-old boy with ocular myasthenia gravis and Hashimoto's disease and a 14-year-old girl presenting with autoimmune polymyositis, then generalized myasthenia gravis 2 years later. The rare combinations of myasthenia gravis and Hashimoto's disease or polymyositis in children are discussed, and we also briefly review myasthenia gravis and other associated autoimmune diseases in children.

Mitochondrial respiratory-chain defects presenting as nonspecific features in children.

Patients with mitochondrial respiratory-chain defects frequently exhibit lactic acidosis, ragged red fibers in skeletal muscle samples, and abnormal enzyme assays for the respiratory-chain complex. However, ragged red fibers and lactic acidosis are not always seen in all patients with mitochondrial respiratory-chain defects. We have encountered six children with biochemically proven respiratory chain defects, but typical ragged red fibers were not found in all six patients, and only five patients had increased serum lactate levels. Initially, they present with nonspecific features. However, persistent or progressive clinical features or multiple organ involvement eventually led to the diagnosis of respiratory-chain defects in these patients. Mitochondrial respiratory-chain defects should be considered in the differential diagnosis when persistent, progressive features and especially multiple organ involvement occur.

Congestive heart failure and cardiac thrombus as first presentations of Friedreich ataxia.

The majority of patients with Friedreich ataxia present with gait ataxia. Congestive heart failure usually is a terminal event. We report a 9-year-old boy who developed congestive heart failure and thrombus formation in the left ventricle at age 5 years and then progressive ataxia as well as other features of Friedreich ataxia; therefore, congestive heart failure and thrombus formation may rarely be the initial findings in Friedreich ataxia.

Variability of serial CT scans in subacute necrotizing encephalomyelopathy (Leigh disease).

Computed tomographic (CT) brain scans of patients with subacute necrotizing encephalomyelopathy (SNE) may reveal focal lesions that correspond to sites of anatomic involvement of the disease. Three patients with SNE were followed with serial CT brain scans. In two patients radiographic abnormalities appeared well after the onset of clinical symptoms. In all three patients the radiographic lesions changed with time. This variability seen with serial scanning is an important feature of SNE.

Oxygen free-radical reduction of brain capillary rubidium uptake.

Free radicals are proposed to play a role in the injury following cerebral ischemia in which cerebral edema is a prominent feature. To determine whether free radicals might alter the movement of ions and water across the blood-brain barrier, we examined their effect on brain capillary transport. Rat brain capillaries were isolated, incubated with a system that generates free radicals, and various capillary transport systems were studied. Rubidium uptake was reduced 74% whereas rubidium efflux, glucose transport, and capillary water space were unchanged. The results following the addition of radical scavengers indicated that hydrogen peroxide or a related free radical was the toxic species. These data suggest that free radicals can impair capillary endothelial cell mechanisms that help maintain homeostasis of electrolytes and water in brain.

Similarity of brain CT appearance in spongy degeneration to that of subacute necrotizing encephalomyelopathy.

Reports of brain computed tomography (CT) findings in spongy degeneration describe radiolucent changes of the cerebral white matter, but have not described changes in the posterior fossa. We describe an infant with spongy degeneration in whom CT scans detected brainstem, cerebellar, and cerebral white matter radiolucencies before the diagnosis was established. The posterior fossa CT findings resembled the periventricular changes described in subacute necrotizing encephalomyelopathy (SNE). As the patient's initial clinical findings were consistent with SNE, the similarity of the posterior fossa radiolucencies was misleading. Without basal ganglia or thalamic involvement, or without variability in their appearance over time, posterior fossa periventricular radiolucencies are not diagnostic of a specific degenerative disorder.