Mark A. Edgar

Intraneuronal Aβ42 accumulation in human brain

Alzheimers disease (AD) is characterized by the deposition of senile plaques (SPs) and neurofibrillary tangles (NFTs) in vulnerable brain regions. SPs are composed of aggregated β-amyloid (Aβ) 40/42(43) peptides. Evidence implicates a central role for Aβ in the pathophysiology of AD. Mutations in βAPP and presenilin 1 (PS1) lead to elevated secretion of Aβ, especially the more amyloidogenic Aβ42. Immunohistochemical studies have also emphasized the importance of Aβ42 in initiating plaque pathology. Cell biological studies have demonstrated that Aβ is generated intracellularly. Recently, endogenous Aβ42 staining was demonstrated within cultured neurons by confocal immunofluorescence microscopy and within neurons of PS1 mutant transgenic mice. A central question about the role of Aβ in disease concerns whether extracellular Aβ deposition or intracellular Aβ accumulation initiates the disease process. Here we report that human neurons in AD-vulnerable brain regions specifically accumulate γ-cleaved Aβ42 and suggest that this intraneuronal Aβ42 immunoreactivity appears to precede both NFT and Aβ plaque deposition. This study suggests that intracellular Aβ42 accumulation is an early event in neuronal dysfunction and that preventing intraneuronal Aβ42 aggregation may be an important therapeutic direction for the treatment of AD.

Intraneuronal Alzheimer Aβ42 Accumulates in Multivesicular Bodies and Is Associated with Synaptic Pathology

A central question in Alzheimers disease concerns the mechanism by which beta-amyloid contributes to neuropathology, and in particular whether intracellular versus extracellular beta-amyloid plays a critical role. Alzheimer transgenic mouse studies demonstrate brain dysfunction, as beta-amyloid levels rise, months before the appearance of beta-amyloid plaques. We have now used immunoelectron microscopy to determine the subcellular site of neuronal beta-amyloid in normal and Alzheimer brains, and in brains from Alzheimer transgenic mice. We report that beta-amyloid 42 localized predominantly to multivesicular bodies of neurons in normal mouse, rat, and human brain. In transgenic mice and human Alzheimer brain, intraneuronal beta-amyloid 42 increased with aging and beta-amyloid 42 accumulated in multivesicular bodies within presynaptic and especially postsynaptic compartments. This accumulation was associated with abnormal synaptic morphology, before beta-amyloid plaque pathology, suggesting that intracellular accumulation of beta-amyloid plays a crucial role in Alzheimers disease.

Prolonged convection-enhanced delivery into the rat brainstem.

OBJECTIVEProlonged convection-enhanced delivery was used in an attempt to achieve large volumes of distribution (Vd) in the rat brainstem. Clinical assessment and histological analysis were performed to establish the safety of this approach. METHODSFor evaluation of Vd,, 10 rats underwent stereotactic cannula placement into the brainstem. Five rats underwent a 24-hour infusion (volume of infusion [Vi], 200 &mgr;l), and 5 rats underwent a 7-day infusion (Vi, 2 ml) of fluorescein isothiocyanate-dextran. Serial brainstem sections were imaged with ultraviolet illumination, and Vd was assessed. For assessment of clinical tolerance, 30 additional rats underwent chronic infusions of an isotonic saline solution into the brainstem. Serial neurological examinations were performed, followed by histological analysis after the animals’ death. RESULTSNo animal demonstrated clinically recognized neurological deficits. Foci of organizing necrosis were limited to the site of infusion and cannula tract. Vd increased linearly with increasing Vi (range, 24.8–130.6 mm3). Maximal cross sectional area of fluorescence and craniocaudal extent of fluorescence increased with increasing Vi. Fluorescence was detected throughout the entire brainstem beyond the compact area of highly concentrated tracer. CONCLUSIONProlonged convection-enhanced delivery can be applied safely in the rat brainstem with no recognized limitations of Vd and minimal histological changes beyond the site of infusion. Chronic brainstem infusions may enhance the potential application of convection-enhanced delivery for therapeutic purposes in treating diffuse pontine gliomas.

MIB-1 staining index of pediatric meningiomas

OBJECTIVEFor adult meningiomas, the staining index (SI) for the anti-Ki-67 monoclonal antibody MIB-1 is well correlated with histological atypia and tumor recurrence. MIB-1 SIs for meningiomas in the pediatric population have not been previously reported. Meningiomas tend to be more histologically aggressive and to recur more frequently in children, compared with adults. The objectives of this study were to determine whether MIB-1 SIs are correlated with pathological atypia and recurrence among pediatric meningiomas and to compare the MIB-1 SIs of pediatric meningiomas with those of adult meningiomas. METHODSMIB-1 SIs were assessed on paraffin-embedded sections of 14 pediatric meningiomas (patient age, 2–17 yr), 5 of which contained atypical or malignant features. For comparison with benign pediatric meningiomas, MIB-1 SIs were also assessed on paraffin-embedded sections of 14 adult meningiomas (patient age, 38–90 yr), none of which displayed atypical or malignant features or recurred within a 5-month median follow-up period. RESULTSMIB-1 SIs of pediatric meningiomas ranged from 1.2 to 31.6% (median, 9.1%). Significant differences were observed between the MIB-1 SIs for tumors with atypical or malignant features (median, 12.3%; range, 7.0–31.6%) and those for tumors without atypia (median, 7.0%; range, 1.2–12.6%;P = 0.045). There were six recurrences after gross total resection, during a 36.5-month median follow-up period. All five of the tumors with pathological atypia recurred; one tumor without atypia recurred. Significant differences were observed between MIB-1 SIs for nonrecurrent tumors (median, 6.6%; range, 1.2–12.2%) and those for recurrent tumors (median, 12.5%; range, 7.0–31.6%;P = 0.012). The median MIB-1 SI for adult control specimens was 8.8% (range, 1.2–19.3%), which did not differ significantly from that for pediatric meningiomas without atypia (P = 0.68). CONCLUSIONFor this cohort of pediatric meningiomas, pathological atypia and the tendency to recur were correlated with elevated MIB-1 SIs. The median MIB-1 SI for pediatric meningiomas without histological atypia did not differ significantly from that for adult meningiomas without atypia, suggesting that the more aggressive clinical features of meningiomas in children may be attributable to factors other than the rate of cellular proliferation.

Proton magnetic resonance spectroscopy of choroid plexus tumors in children.

A variety of lesions may present as intraventricular masses in children. We report quantitative proton magnetic resonance spectroscopy (MRS) of two intraventricular tumors of the choroid plexus: choroid plexus carcinoma (CPC) and choroid plexus papilloma (CPP). Both lesions were characterized by high levels of choline‐containing compounds and a complete absence of creatine and the neuronal/axonal marker N‐acetyl aspartate. The CPC showed higher levels of choline compared to the CPP, and it also had elevated lactate. These preliminary results, if confirmed in a larger cohort of patients, indicate that proton MRS may have a role in the presurgical diagnosis of choroid plexus tumors in children, which may also have important implications for therapy and prognosis. J. Magn. Reson. Imaging 2001;14:78–82.

A lack of dimorphism of sex or sexual orientation in the human anterior commissure

Four studies have examined the cross-sectional area of the anterior commissure (AC) for variation with sex, with conflicting results. One also reported the AC to be larger in homosexual as opposed to heterosexual men. We examined the cross-sectional area of the AC in postmortem material from 120 individuals, and found no variation in the size of the AC with age, HIV status, sex, or sexual orientation.

Prostate-Specific Membrane Antigen as a Potential Novel Vascular Target for Treatment of Glioblastoma Multiforme

CONTEXT Prostate-specific membrane antigen (PSMA) is expressed in endothelium of vessels in malignant solid tumors but not in normal vessels. OBJECTIVE To examine whether neovasculature of glioblastoma multiforme (GBM) expresses PSMA. Design.-After institutional review board approval at Memorial Sloan-Kettering Cancer Center, formalin-fixed paraffin-embedded tissue from 32 patients who underwent a maximally safe neurologic resection during 2004 to 2005 for GBM (World Health Organization criteria) was obtained. We performed immunohistochemical staining on the vessels of the GBM specimens for PSMA expression in tumor endothelium. The tissue samples were also stained for CD31 to verify that the PSMA was staining tumor vessels. The PSMA percent staining was scored: less than 5%, 6% to 25%, 26% to 50%, 51% to 75%, and 76% to 100%. Staining intensity was ranked as follows: 0 (none), 1+ (faint), 2+ (moderately-intense), and 3+ (maximum-intensity). RESULTS Immunohistochemical staining on the vessels of 32 paraffin-embedded GBM specimens revealed that all 32 (100%) specimens exhibited staining for PSMA to a variable extent. Of these, 22 of 32 specimens (69%) had more than 51% vascular staining for PSMA. The intensity of staining was 2+ to 3+ in most of the specimens (29 of 32; 91%). CONCLUSIONS Prostate-specific membrane antigen is expressed in the vasculature of GBM vessels, thus rendering a potential novel therapeutic vascular target. A clinical trial with a cytotoxin-conjugated antibody to PSMA is planned.

Interstitial Infusion of Glioma-Targeted Recombinant Immunotoxin 8H9scFv-PE38

Monoclonal antibodies have the potential to target therapy for high-grade gliomas. Monoclonal antibody 8H9 is specific for membrane protein B7H3 and is reactive with most human high-grade gliomas. We tested the 8H9scFv-PE38 recombinant Pseudomonas immunotoxin in a preclinical model of high-grade glioma. The half maximal inhibitory concentration (IC50) of 8H9scFv-PE38 in vitro was determined using glioblastoma cell lines U87 and U251. Maximum tolerated infusion dose of 8H9scFv-PE38 following interstitial infusion to the striatum and pons was defined using athymic rats. Maximum tolerated infusion dose of 8H9scFv-PE38 or PBS control were interstitially delivered to athymic rats xenografted with U87 in the striatum or brain stem. Radiographic response and survivals were measured and compared between treatment groups. The in vitro IC50 of 8H9scFv-PE38 for U87 was 1,265 ng/mL and, for U251, 91 ng/mL. The maximum tolerated infusion doses of interstitially infused 8H9scFv-PE38 to the striatum and brain stem were 0.75 and 1.8 μg, respectively. For rats harboring intracranial U87 xenografts, infusion of 8H9scFv-PE38 increased mean survival (striatum, 43.4 versus 24.6 days; brain stem, 80.6 versus 45.5 days; n = 28 total) and produced three long-term survivors past 120 days. None of the 14 placebo-treated animals survived >54 days. Tumors also showed volumetric response to infusion of 8H9scFv-PE38 by magnetic resonance imaging. Interstitial infusion of 8H9scFv-PE38 shows potential for the treatment of hemispherical and brain stem glioma. Mol Cancer Ther; 9(4); 1039–46. ©2010 AACR.

Interstitial Infusion of IL13-PE38QQR in the Rat Brain Stem

Interstitial infusion of IL13-PE38QQR, a tumor specific, chimeric cytotoxin, into the rat brain stem was performed in an effort to assess safety. Six rats underwent stereotaxic cannula placement into the pontine segment of the brain stem followed by a 24-h infusion of IL13-PE38QQR (volume of infusion (Vi) 200 ul) at a concentration of 10 ug/ml. The animals were assessed neurologically and then sacrificed either immediately or after 2 weeks. All animals tolerated the infusions without exhibiting any neurological changes. Postmortem examination of the brains revealed no significant histological changes beyond the site of the cannula tract. These findings indicate that supratherapeutic concentrations of IL13-PE38QQR administered by interstitial infusion into the rat brain stem is well tolerated and may serve as a potential therapeutic strategy for children with diffuse pontine gliomas.

Effect of Hyperosmolar Mannitol on Convection-enhanced Delivery into the Rat Brain Stem

AbstractIntroduction: Convection-enhanced delivery (CED) can safely achieve high local infusate concentrations within the rat brain stem with predictable distribution volumes. The authors investigated the effects of co-infusion or systemic administration of hyperosmolar mannitol on distribution parameters for infusions into the rat brain stem. Methods: Fifteen rats underwent stereotactic cannula placement into the pontine nucleus oralis (PnO) followed by infusions at a constant rate to a total volume of 1 ul. Five rats underwent infusion of fluorescein isothiocyanate (FITC)-dextran diluted in 20% mannitol. Five rats received an intraperitoneal injection of 20% mannitol 10 min prior to infusion of FITC-dextran diluted in isotonic saline. As a control group, 5 rats underwent infusion of FITC-dextran diluted in isotonic saline without mannitol administration. Serial brain sections were imaged using confocal microscopy with ultraviolet illumination, and distribution volume (Vd) was calculated by computer image analysis. Histologic analysis was performed on adjacent sections. Results: Volumes of distribution were not significantly increased by co-infusion of mannitol directly into the brain stem or by systemic mannitol administration compared to infusion without mannitol. Similarly, mannitol administration by either means failed to significantly alter maximal cross-sectional area or cranio-caudal extent of fluorescence. No animal demonstrated a postoperative neurological deficit or histologic evidence of tissue disruption. Conclusions: Neither systemic administration nor co-infusion of hyperosmolar mannitol significantly affects distribution parameters for CED infusions into the rat brain stem.