MR-Less Surface-Based Amyloid Assessment Based on 11C PiB PET

Background

β-amyloid (Aβ) plaques in brain''s grey matter (GM) are one of the pathological hallmarks of Alzheimer''s disease (AD), and can be imaged in vivo using Positron Emission Tomography (PET) with ¹¹C or ¹⁸F radiotracers. Estimating Aβ burden in cortical GM has been shown to improve diagnosis and monitoring of AD. However, lacking structural information in PET images requires such assessments to be performed with anatomical MRI scans, which may not be available at different clinical settings or being contraindicated for particular reasons. This study aimed to develop an MR-less Aβ imaging quantification method that requires only PET images for reliable Aβ burden estimations.

Materials and Methods

The proposed method has been developed using a multi-atlas based approach on ¹¹C-PiB scans from 143 subjects (75 PiB+ and 68 PiB- subjects) in AIBL study. A subset of 20 subjects (PET and MRI) were used as atlases: 1) MRI images were co-registered with tissue segmentation; 2) 3D surface at the GM-WM interfacing was extracted and registered to a canonical space; 3) Mean PiB retention within GM was estimated and mapped to the surface. For other participants, each atlas PET image (and surface) was registered to the subject''s PET image for PiB estimation within GM. The results are combined by subject-specific atlas selection and Bayesian fusion to generate estimated surface values.

Results

All PiB+ subjects (N = 75) were highly correlated between the MR-dependent and the PET-only methods with Intraclass Correlation (ICC) of 0.94, and an average relative difference error of 13% (or 0.23 SUVR) per surface vertex. All PiB- subjects (N = 68) revealed visually akin patterns with a relative difference error of 16% (or 0.19 SUVR) per surface vertex.

Conclusion

The demonstrated accuracy suggests that the proposed method could be an effective clinical inspection tool for Aβ imaging scans when MRI images are unavailable.     

The promise and the potential consequences of the global transport of mycorrhizal fungal inoculum

Advances in ecology during the past decade have led to a much more detailed understanding of the potential negative consequences of species' introductions. Moreover, recent studies of mycorrhizal symbionts have led to an increased knowledge of the potential utility of fungal inoculations in agricultural, horticultural and ecological management. The intentional movement of mycorrhizal fungal species is growing, but the concomitant potential for negative ecological consequences of invasions by mycorrhizal fungi is poorly understood. We assess the degree to which introductions of mycorrhizal fungi may lead to unintended negative, and potentially costly, consequences. Our purpose is to make recommendations regarding appropriate management guidelines and highlight top priority research needs. Given the difficulty in discerning invasive species problems associated with mycorrhizal inoculations, we recommend the following. First, careful assessment documenting the need for inoculation, and the likelihood of success, should be conducted prior to inoculation because inoculations are not universally beneficial. Second, invasive species problems are costly and often impossible to control by the time they are recognized. We recommend using local inoculum sources whenever possible. Third, non-sterile cultures of inoculum can result in the movement of saprobes and pathogens as well as mutualists. We recommend using material that has been produced through sterile culture when local inoculum is not available. Finally, life-history characteristics of inoculated fungi may provide general guidelines relative to the likelihood of establishment and spread. We recommend that, when using non-local fungi, managers choose fungal taxa that carry life-history traits that may minimize the likelihood of deleterious invasive species problems. Additional research is needed on the potential of mycorrhizal fungi to spread to non-target areas and cause ecological damage.     

A composite molecular phylogeny of living lemuroid primates

Lemuroid phylogeny is a source of lively debate among primatologists. Reconstructions based on morphological, physiological, behavioural and molecular data have yielded a diverse array of tree topologies with few nodes in common. In the last decade, molecular phylogenetic studies have grown in popularity, and a wide range of sequences has been brought to bear on the problem, but consensus has remained elusive. We present an analysis based on a composite molecular data set of approx. 6,400 bp assembled from the National Center for Biotechnology Information (NCBI) database, including both mitochondrial and nuclear genes, and diverse analytical methods. Our analysis consolidates some of the nodes that were insecure in previous reconstructions, but is still equivocal on the placement of some taxa. We conducted a similar analysis of a composite data set of approx. 3,600 bp to investigate the controversial relationships within the family Lemuridae. Here our analysis was more successful; only the position of Eulemur coronatus remained uncertain.     

Reconciling the origins of Africa, India and Madagascar with vertebrate dispersal scenarios

Africa, India and Madagascar were once part of the supercontinent of Gondwana. This land mass began to fragment approx. 170 million years ago, and by 83 million years, all of the major components we recognize today were separated by tracts of water. Madagascar's fossil record and estimates of the timing of the extant vertebrate radiations in Madagascar are not easily reconciled with this history of fragmentation. Fossil faunas that lived prior to approx. 65 million years had a cosmopolitan flavour, but this was lost after the Cretaceous-Tertiary boundary. Phylogenetic reconstructions of most extant Malagasy vertebrate radiations indicate divergence times that postdate the End-Cretaceous (lemurs, tenrecs, cichlid fish) and even the Early Miocene (chameleons, carnivores, rodents). Most biogeographic explanations of these groups rely, therefore, on Simpson's model of sweepstakes dispersal (see also cover figure), but there are significant problems in applying the model to migrations from Africa to Madagascar, although its application is not so intractable between India and Madagascar. Alternative migration routes for consideration lie: (1) along the suite of fracture zones between Antarctica and Africa/Madagascar (known as the Antarctic-Africa Corridor), which may have been exposed episodically above sea level; (2) along a series of submerged basaltic ridges/plateaus with known or suspected continental crust between Antarctica and Africa/Madagascar/India flanking the Antarctic-Africa Corridor (e.g. the Madagascar Ridge, Mozambique Ridge, Conrad Plateau, Gunnerus Ridge); (3) between Africa and Madagascar along the Davie Ridge (parts of which are known to have been exposed episodically above sea level); (4) along the Deccan hotspot corridor between India and greater Africa.     

Lack of torpor in free-ranging southern lesser galagos, Galago moholi: ecological and physiological considerations

Studies investigating heterothermy under natural conditions are particularly scarce for tropical species. However, heterothermy patterns in tropical and subtropical environments often differ markedly from those observed in arctic and temperate species. The investigation of heterothermy in strepsirhine primates has focussed largely on the Malagasy cheirogaleids. In addition, a physiological verification of torpor occurrence in mainland strepsirhines is important with regard to arguments pertaining to the colonization of Madagascar by strepsirhine primates. We measured body temperatures of 11 free-ranging Galago moholi, between February 2002 and September 2003, for 3 consecutive months for each animal. No incidents of heterothermy were recorded throughout the study period. We considered how physiological and ecological aspects of G. moholi biology might have obviated the use of torpor. It was suggested that the breeding pattern observed in G. moholi prevented torpor use whilst increasing fecundity, and that the ecological costs of torpor far outweighed the energetic costs. This study highlights the need for more studies on free-ranging animals to elucidate the physiological, ecological and phylogenetic constraints and determinants of torpor use. Furthermore, if convincing arguments are to be made regarding the possible role of heterothermy in species dispersal, more data from free-ranging animals are needed.     

Nutrition and health at contact in late prehistoric central Gulf Coast Florida

This paper presents an analysis of human remains from Tatham Mound, a dual-component mortuary site from central Gulf Coast Florida. The human remains from Tatham are significant because they come from a limited time period during the initial contact with Europeans at AD 1525-1550. Dietary reconstruction demonstrates that at the time of European contact, maize was not a predominant dietary item. Low frequencies for several dental and skeletal pathological indicators are consistent with relatively good health as compared to other Southeastern late prehistoric and protohistoric populations. Despite the limited time period represented by the mound population, critical interactions occurred between Native Americans and Spaniards, as indicated by skeletal elements severed by metal weapons. The Tatham population is significant because it is one of the earliest studied populations contacted by Europeans in North America, and the only one with well-documented sharp-force trauma that represents intergroup hostility.     

Copper-mediated amyloid-beta toxicity is associated with an intermolecular histidine bridge

Amyloid-beta peptide (Abeta) is pivotal to the pathogenesis of Alzheimer disease. Here we report the formation of a toxic Abeta-Cu2+ complex formed via a histidine-bridged dimer, as observed at Cu2+/peptide ratios of >0.6:1 by EPR spectroscopy. The toxicity of the Abeta-Cu2+ complex to cultured primary cortical neurons was attenuated when either the pi -or tau-nitrogen of the imidazole side chains of His were methylated, thereby inhibiting formation of the His bridge. Toxicity did not correlate with the ability to form amyloid or perturb the acyl-chain region of a lipid membrane as measured by diphenyl-1,3,5-hexatriene anisotropy, but did correlate with lipid peroxidation and dityrosine formation. 31P magic angle spinning solid-state NMR showed that Abeta and Abeta-Cu2+ complexes interacted at the surface of a lipid membrane. These findings indicate that the generation of the Abeta toxic species is modulated by the Cu2+ concentration and the ability to form an intermolecular His bridge.     

Diminished FAD binding in the Y459H and V492E Antley-Bixler syndrome mutants of human cytochrome P450 reductase

Numerous mutations/polymorphisms of the POR gene, encoding NADPH:cytochrome P450 oxidoreductase (CYPOR), have been described in patients with Antley-Bixler syndrome (ABS), presenting with craniofacial dysmorphogenesis, and/or disordered steroidogenesis, exhibiting ambiguous genitalia. CYPOR is the obligate electron donor to 51 microsomal cytochromes P450 that catalyze critical steroidogenic and xenobiotic reactions, and to two heme oxygenase isoforms, among other redox partners. To address the molecular basis of CYPOR dysfunction in ABS patients, the soluble catalytic domain of human CYPOR was bacterially expressed. WT enzyme was green, due to air-stable FMN semiquinone (blue) and oxidized FAD (yellow). The ABS mutant V492E was blue-gray. Flavin analysis indicated that WT had a protein:FAD:FMN ratio of approximately 1:1:1, whereas approximately 1:0.1:0.9 was observed for V492E, which retained 9% of the WT k(cat)/K(m) in NADPH:cytochrome c reductase assays. V492E was reconstituted upon addition of FAD, post-purification, as shown by flavin analysis, activity assay, and near UV-visible CD. Both Y459H and V492E were expressed as membrane anchor-containing proteins, which also exhibited FAD deficiency. CYP4A4-catalyzed omega-hydroxylation of prostaglandin E1 was supported by WT CYPOR but not by either of the ABS mutants. Hydroxylation activity was rescued for both Y459H and V492E upon addition of FAD to the reaction. Based on these findings, decreased FAD-binding affinity is proposed as the basis of the observed loss of CYPOR function in the Y459H and V492E POR mutations in ABS.     

Molecular dissection of the interaction between amyloid precursor protein and its neuronal trafficking receptor SorLA/LR11

SorLA/LR11 is a sorting receptor that regulates the intracellular transport and processing of the amyloid precursor protein (APP) in neurons. SorLA/LR11-mediated binding results in sequestration of APP in the Golgi and in protection from processing into the amyloid-beta peptide (Abeta), the principal component of senile plaques in Alzheimer's disease (AD). To gain insight into the molecular mechanisms governing sorLA and APP interaction, we have dissected the respective protein interacting domains. Using a fluorescence resonance energy transfer (FRET) based assay of protein proximity, we identified binding sites in the extracellular regions of both proteins. Fine mapping by surface plasmon resonance analysis and analytical ultracentrifugation of recombinant APP and sorLA fragments further narrowed down the binding domains to the cluster of complement-type repeats in sorLA that forms a 1:1 stoichiometric complex with the carbohydrate-linked domain of APP. These data shed new light on the molecular determinants of neuronal APP trafficking and processing and on possible targets for intervention with senile plaque formation in patients with AD.     

Overexpression of Abeta is associated with acceleration of onset of motor impairment and superoxide dismutase 1 aggregation in an amyotrophic lateral sclerosis mouse model

Transgenic mice carrying mutant Cu/Zn superoxide dismutase (SOD1) recapitulate the motor impairment of human amyotrophic lateral sclerosis (ALS). The amyloid-beta (Abeta) peptide associated with Alzheimer's disease is neurotoxic. To investigate the potential role of Abeta in ALS development, we generated a double transgenic mouse line that overexpresses SOD1(G93A) and amyloid precursor protein (APP)-C100. The transgenic mouse C100.SOD1(G93A) overexpresses Abeta and shows earlier onset of motor impairment but has the same lifespan as the single transgenic SOD1(G93A) mouse. To determine the mechanism associated with this early-onset phenotype, we measured copper and zinc levels in brain and spinal cord and found both significantly elevated in the single and double transgenic mice compared with their littermate control mice. Increased glial fibrillary acidic protein and decreased APP levels in the spinal cord of C100.SOD1(G93A) mice compared with the SOD1(G93A) mice agree with the neuronal damage observed by immunohistochemical analysis. In the spinal cords of C100.SOD1(G93A) double transgenic mice, soluble Abeta was elevated in mice at end-stage disease compared with the pre-symptomatic stage. Buffer-insoluble SOD1 aggregates were significantly elevated in the pre-symptomatic mice of C100.SOD1(G93A) compared with the age-matched SOD1(G93A) mice, correlating with the earlier onset of motor impairment in the C100.SOD1(G93A) mice. This study supports abnormal SOD1 protein aggregation as the pathogenic mechanism in ALS, and implicates a potential role for Abeta in the development of ALS by exacerbating SOD1(G93A) aggregation.