Illustrating the effect of viscoelastic additives on cavitation and turbulence with X-ray imaging

The effect of viscoelastic additives on the topology and dynamics of the two-phase flow arising within an axisymmetric orifice with a flow path constriction along its main axis has been investigated employing high-flux synchrotron radiation. X-ray Phase Contrast Imaging (XPCI) has been conducted to visualise the cavitating flow of different types of diesel fuel within the orifice. An additised blend containing Quaternary Ammonium Salt (QAS) additives with a concentration of 500 ppm has been comparatively examined against a pure (base) diesel compound. A high-flux, 12 keV X-ray beam has been utilised to obtain time resolved radiographs depicting the vapour extent within the orifice from two views (side and top) with reference to its main axis. Different test cases have been examined for both fuel types and for a range of flow conditions characterised by Reynolds number of 35500 and cavitation numbers (CN) lying in the range 3.0-7.7. It has been established that the behaviour of viscoelastic micelles in the regions of shear flow is not consistent depending on the cavitation regimes encountered. Namely, viscoelastic effects enhance vortical (string) cavitation, whereas hinder cloud cavitation. Furthermore, the use of additised fuel has been demonstrated to suppress the level of turbulence within the orifice.

Did postglacial sea-level changes initiate the evolutionary divergence of a Tasmanian endemic raptor from its mainland relative?

Populations on continental islands are often distinguishable from mainland conspecifics with respect to body size, appearance, behaviour or life history, and this is often congruent with genetic patterns. It is commonly assumed that such differences developed following the complete isolation of populations by sea-level rise following the Last Glacial Maximum (LGM). However, population divergence may predate the LGM, or marine dispersal and colonization of islands may have occurred more recently; in both cases, populations may have also diverged despite ongoing gene flow. Here, we test these alternative hypotheses for the divergence between wedge-tailed eagles from mainland Australia (Aquila audax audax) and the threatened Tasmanian subspecies (Aquila audax fleayi), based on variation at 20 microsatellite loci and mtDNA. Coalescent analyses indicate that population divergence appreciably postdates the severance of terrestrial habitat continuity and occurred without any subsequent gene flow. We infer a recent colonization of Tasmania by marine dispersal and cannot discount founder effects as the cause of differences in body size and life history. We call into question the general assumption of post-LGM marine transgression as the initiator of divergence of terrestrial lineages on continental islands and adjacent mainland, and highlight the range of alternative scenarios that should be considered.

Three-dimensional optical tomography of hemodynamics in the human head

We report on the first three-dimensional, volumetric, tomographic localization of vascular reactivity in the brain. To this end we developed a model-based iterative image reconstruction scheme that employs adjoint differentiation methods to minimize the difference between measured and predicted data. The necessary human-head geometry and optode locations were determined with a photogrammetric method. To illustrate the performance of the technique, the three-dimensional distribution of changes in the concentration of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin during a Valsalva maneuver were visualized. The observed results are consistent with previously reported effects concerning optical responses to hemodynamic perturbations.

Encapsulation in biodegradable microparticles enhances serum antibody response to parenterally-delivered beta-amyloid in mice

Poly(lactide-co-glycolide) (PLG) microspheres were tested as a parenteral delivery system for human beta-amyloid (1-42) (Abeta), a potential immunotherapeutic undergoing assessment in Phase 1 studies for Alzheimer's disease (AD). Abeta was successfully encapsulated in PLG microspheres of average sizes of 3 or 15 microm diameter. Swiss Webster (SW) mice were injected by the sub-cutaneous (s.c.) or intra-peritoneal (i.p.) routes with 3-33 microg Abeta. Abeta-PLG microparticles (3 microm) induced dose-dependent antibody responses, which were maximal at 33 microg Abeta, while Abeta in phosphate-buffered saline (PBS) produced weak antibody responses at the same doses by both routes. Significantly increased antibody responses were seen for both small and large particle formulations given by the i.p. route in comparison to the s.c route. It was previously reported that passive immunisation with Abeta-specific antibodies cleared amyloid plaques in a mouse model of AD (Bard F, Cannon C, Barbour R, et al. Peripherally administered antibodies against amyloid beta-peptide enter the nervous system and reduce pathology in a mouse model of Alzheimer disease. Nature Med 2000;6:916-19), an indication that induction of serum antibody is a prerequisite for efficacy.

Normalized-constraint algorithm for minimizing inter-parameter crosstalk in DC optical tomography

In this report, we present a method for reducing the inter-coefficient crosstalk problem in optical tomography. The method described is an extension of a previously reported normalized difference method that evaluates relative detector values, and employs a weight matrix scaling technique together with a constrained CGD method for image reconstruction. Results from numerical and experimental studies using DC measurement data demonstrate that the approach can effectively isolate absorption and scattering heterogeneities, even for complex combinations of perturbations in optical properties. The significance of these results in light of recent theoretical findings is discussed.

Retention of the Alzheimer's amyloid precursor fragment C99 in the endoplasmic reticulum prevents formation of amyloid beta-peptide

gamma-Secretase is a membrane-associated endoprotease that catalyzes the final step in the processing of Alzheimer's beta-amyloid precursor protein (APP), resulting in the release of amyloid beta-peptide (Abeta). The molecular identity of gamma-secretase remains in question, although recent studies have implicated the presenilins, which are membrane-spanning proteins localized predominantly in the endoplasmic reticulum (ER). Based on these observations, we have tested the hypothesis that gamma-secretase cleavage of the membrane-anchored C-terminal stump of APP (i.e. C99) occurs in the ER compartment. When recombinant C99 was expressed in 293 cells, it was localized mainly in the Golgi apparatus and gave rise to abundant amounts of Abeta. Co-expression of C99 with mutant forms of presenilin-1 (PS1) found in familial Alzheimer's disease resulted in a characteristic elevation of the Abeta(42)/Abeta(40) ratio, indicating that the N-terminal exodomain of APP is not required for mutant PS1 to influence the site of gamma-secretase cleavage. Biogenesis of both Abeta(40) and Abeta(42) was almost completely eliminated when C99 was prevented from leaving the ER by addition of a di-lysine retention motif (KKQN) or by co-expression with a dominant-negative mutant of the Rab1B GTPase. These findings indicate that the ER is not a major intracellular site for gamma-secretase cleavage of C99. Thus, by inference, PS1 localized in this compartment does not appear to be active as gamma-secretase. The results suggest that presenilins may acquire the characteristics of gamma-secretase after leaving the ER, possibly by assembling with other proteins in peripheral membranes.

Peripherally administered antibodies against amyloid beta-peptide enter the central nervous system and reduce pathology in a mouse model of Alzheimer disease

One hallmark of Alzheimer disease is the accumulation of amyloid beta-peptide in the brain and its deposition as plaques. Mice transgenic for an amyloid beta precursor protein (APP) mini-gene driven by a platelet-derived (PD) growth factor promoter (PDAPP mice), which overexpress one of the disease-linked mutant forms of the human amyloid precursor protein, show many of the pathological features of Alzheimer disease, including extensive deposition of extracellular amyloid plaques, astrocytosis and neuritic dystrophy. Active immunization of PDAPP mice with human amyloid beta-peptide reduces plaque burden and its associated pathologies. Several hypotheses have been proposed regarding the mechanism of this response. Here we report that peripheral administration of antibodies against amyloid beta-peptide, was sufficient to reduce amyloid burden. Despite their relatively modest serum levels, the passively administered antibodies were able to enter the central nervous system, decorate plaques and induce clearance of preexisting amyloid. When examined in an ex vivo assay with sections of PDAPP or Alzheimer disease brain tissue, antibodies against amyloid beta-peptide triggered microglial cells to clear plaques through Fc receptor-mediated phagocytosis and subsequent peptide degradation. These results indicate that antibodies can cross the blood-brain barrier to act directly in the central nervous system and should be considered as a therapeutic approach for the treatment of Alzheimer disease and other neurological disorders.

Purification and cloning of amyloid precursor protein beta-secretase from human brain

Proteolytic processing of the amyloid precursor protein (APP) generates amyloid beta (Abeta) peptide, which is thought to be causal for the pathology and subsequent cognitive decline in Alzheimer's disease. Cleavage by beta-secretase at the amino terminus of the Abeta peptide sequence, between residues 671 and 672 of APP, leads to the generation and extracellular release of beta-cleaved soluble APP, and a corresponding cell-associated carboxy-terminal fragment. Cleavage of the C-terminal fragment by gamma-secretase(s) leads to the formation of Abeta. The pathogenic mutation K670M671-->N670L671 at the beta-secretase cleavage site in APP, which was discovered in a Swedish family with familial Alzheimer's disease, leads to increased beta-secretase cleavage of the mutant substrate. Here we describe a membrane-bound enzyme activity that cleaves full-length APP at the beta-secretase cleavage site, and find it to be the predominant beta-cleavage activity in human brain. We have purified this enzyme activity to homogeneity from human brain using a new substrate analogue inhibitor of the enzyme activity, and show that the purified enzyme has all the properties predicted for beta-secretase. Cloning and expression of the enzyme reveals that human brain beta-secretase is a new membrane-bound aspartic proteinase.

Modeling of sensitivity and resolution to an included object in homogeneous scattering media and in MRI-derived breast maps

We have examined the measured sensitivity and edge resolution to an included tumor in MR-derived maps of the breast exposed to NIR illumination. A large parameter space was explored, enabling a systematic examination of the influence that measurement parameters (e.g., view angle, source position, wavelength) and target medium parameters (e.g., breast and tumor size, background tissue properties, and tumor contrast) have on the computed responses. The significance of these finding on data collection schemes for imaging studies is discussed.

Immunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse

Amyloid-beta peptide (Abeta) seems to have a central role in the neuropathology of Alzheimer's disease (AD). Familial forms of the disease have been linked to mutations in the amyloid precursor protein (APP) and the presenilin genes. Disease-linked mutations in these genes result in increased production of the 42-amino-acid form of the peptide (Abeta42), which is the predominant form found in the amyloid plaques of Alzheimer's disease. The PDAPP transgenic mouse, which overexpresses mutant human APP (in which the amino acid at position 717 is phenylalanine instead of the normal valine), progressively develops many of the neuropathological hallmarks of Alzheimer's disease in an age- and brain-region-dependent manner. In the present study, transgenic animals were immunized with Abeta42, either before the onset of AD-type neuropathologies (at 6 weeks of age) or at an older age (11 months), when amyloid-beta deposition and several of the subsequent neuropathological changes were well established. We report that immunization of the young animals essentially prevented the development of beta-amyloid-plaque formation, neuritic dystrophy and astrogliosis. Treatment of the older animals also markedly reduced the extent and progression of these AD-like neuropathologies. Our results raise the possibility that immunization with amyloid-beta may be effective in preventing and treating Alzheimer's disease.

Amyloid precursor protein processing and A beta42 deposition in a transgenic mouse model of Alzheimer disease

The PDAPP transgenic mouse, which overexpresses human amyloid precursor protein (APP717V-->F), has been shown to develop much of the pathology associated with Alzheimer disease. In this report, levels of APP and its amyloidogenic metabolites were measured in brain regions of transgenic mice between 4 and 18 months of age. While absolute levels of APP expression likely contribute to the rate of amyloid beta-peptide (Abeta) deposition, regionally specific factors also seem important, as homozygotic mice express APP levels in pathologically unaffected regions in excess of that measured in certain amyloid plaque-prone regions of heterozygotic mice. Regional levels of APP and APP-beta were nearly constant at all ages, while A beta levels dramatically and predictably increased in brain regions undergoing histochemically confirmed amyloidosis, most notably in the cortex and hippocampus. In hippocampus, A beta concentrations increase 17-fold between the ages of 4 and 8 months, and by 18 months of age are over 500-fold that at 4 months, reaching an average level in excess of 20 nmol of A beta per g of tissue. A beta1-42 constitutes the vast majority of the depositing A beta species. The similarities observed between the PDAPP mouse and human Alzheimer disease with regard to A beta42 deposition occurring in a temporally and regionally specific fashion further validate the use of the model in understanding processes related to the disease.

Reduction of beta-amyloid peptide42 in the cerebrospinal fluid of patients with Alzheimer's disease

In this clinical study the cerebrospinal fluid (CSF) level of a novel form of the beta-amyloid peptide (A beta) extending to position 42 (A beta 42) was determined in patients with Alzheimer's disease (AD) as well as controls. In addition to measurement of CSF A beta 42 levels, total A beta peptides, microtubule-associated protein tau, and apolipoprotein E (ApoE) genotype were also assessed. It is interesting that CSF A beta 42 levels were found to be significantly lower in AD patients relative to controls, whereas total A beta levels were not. A beta 42 has recently been shown to preferentially deposit in the brain tissue of patients with AD, suggesting that diminished clearance may account for its reduction in CSF. As previously reported, tau levels were increased in AD patients; however, neither A beta 42 nor tau levels were apparently influenced by the ApoE genotype.

Detection of phosphorylated Ser262 in fetal tau, adult tau, and paired helical filament tau

Paired helical filaments (PHFs) are the major structural elements of Alzheimer's disease neurofibrillary lesions, and these filaments are formed from hyperphosphorylated brain tau known as PHF-tau. Recent studies showed that many previously identified phosphorylated residues in PHF-tau also are phosphate acceptor sites in fetal and rapidly processed adult brain tau. However, Ser262 has been suggested to be uniquely phosphorylated in PHF-tau and a key regulator of the binding of tau to microtubules. For these reasons, we generated a monoclonal antibody (12E8) specific for phosphorylated Ser262 and showed that 12E8 binds to PHF-tau, rat and human fetal brain tau, as well as to rapidly processed adult rat and biopsy-derived human brain tau. Further, phosphorylation Ser262 was developmentally regulated, and endogenous brain phosphatases rapidly dephosphorylated Ser262 in biopsy-derived brain tau isolates. Finally, the phosphorylation of Ser262 did not eliminate the binding of tau to microtubules. Thus, we speculate that the binding of tau to microtubules is regulated by phosphorylation at multiple sites and that the generation of PHF-tau in Alzheimer's disease results from the reduced efficiency of phosphatases leading to the incremental accumulation of hyperphosphorylated tau.

Elevation of microtubule-associated protein tau in the cerebrospinal fluid of patients with Alzheimer's disease

Currently, there is no biochemical marker clinically available to test for the presence of Alzheimer's disease (AD). Recent studies suggest that the core component of AD-associated neurofibrillary tangles (NFTs), the microtubule-associated protein tau, might be present in CSF. This study focuses on establishing both the presence of tau in CSF and its potential utility in the diagnosis of AD. We obtained CSF from 181 individuals; 71 of these were diagnosed as having probable AD by NINCDS-ADRDA criteria. The remaining 110 individuals were divided into three groups: (1) age-matched demented non-AD patients (n = 25), (2) neurologic controls (n = 59), and (3) other controls (n = 26). We developed a sensitive enzyme-linked immunosorbent tau assay using monoclonal antibodies prepared against recombinant human tau. We confirmed specificity of the antibodies by a combination of immunoprecipitation and immunoblot results. By this assay we measured that the AD population has a mean level of tau 50% greater than the non-AD dementia patients. Comparing AD patients with all other groups, the difference in tau levels as analyzed by one-way ANOVA is highly statistically significant (p < 0.001). Postmortem analysis of two AD patients with high levels of CSF tau revealed a high density of NFTs in the hippocampus. There was no significant correlation between tau and age in the non-AD groups. This study suggests that CSF tau is elevated in AD and might be a useful aid in antemortem diagnosis.

Alzheimer-type neuropathology in transgenic mice overexpressing V717F beta-amyloid precursor protein

Alzheimer's disease (AD) is the most common cause of progressive intellectual failure in aged humans. AD brains contain numerous amyloid plaques surrounded by dystrophic neurites, and show profound synaptic loss, neurofibrillary tangle formation and gliosis. The amyloid plaques are composed of amyloid beta-peptide (A beta), a 40-42-amino-acid fragment of the beta-amyloid precursor protein (APP). A primary pathogenic role for APP/A beta is suggested by missense mutations in APP that are tightly linked to autosomal dominant forms of AD. A major obstacle to elucidating and treating AD has been the lack of an animal model. Animals transgenic for APP have previously failed to show extensive AD-type neuropathology, but we now report the production of transgenic mice that express high levels of human mutant APP (with valine at residue 717 substituted by phenylalanine) and which progressively develop many of the pathological hallmarks of AD, including numerous extracellular thioflavin S-positive A beta deposits, neuritic plaques, synaptic loss, astrocytosis and microgliosis. These mice support a primary role for APP/A beta in the genesis of AD and could provide a preclinical model for testing therapeutic drugs.

Secretion of beta-amyloid precursor protein cleaved at the amino terminus of the beta-amyloid peptide

The accumulation in brain of senile plaques containing beta-amyloid protein (A beta) is a defining feature of Alzheimer's disease. The amyloid precursor protein (APP)4 from which A beta is derived is subject to several genetic mutations which segregate with rare familial forms of the disease, resulting in early onset of dementia and plaque formation, suggesting that APP metabolism plays a causal role in the disease. Various cell types have been shown to release a soluble form of A beta, thus allowing for the in vitro study of A beta generation. We report here evidence that a substantial portion of the APP secreted by human mixed brain cell cultures, as well as that present in cerebrospinal fluid, is of a novel form cleaved precisely at the amino terminus of A beta, suggesting that a secretory pathway is involved in A beta genesis.

Kunitz protease inhibitor-containing amyloid beta protein precursor immunoreactivity in Alzheimer's disease

The amyloid beta protein (beta/A4) that is deposited in senile plaques and in cerebral vessels in Alzheimer's disease (AD) is derived from a larger membrane-associated glycoprotein, the amyloid beta protein precursor (APP). The gene encoding APP produces at least four major transcripts. Three of the four transcripts contain an alternatively-spliced exon encoding a Kunitz protease inhibitor domain (KPI). We now report the results of a series of experiments using novel immunohistochemical reagents to anatomically localize beta/A4, APP, and KPI-containing forms of APP (APP-KPI) in the hippocampal formation and temporal neocortex. A new monoclonal antibody against beta/A4 recognized senile plaques and vascular amyloid, but no cellular elements. Anti-APP and anti-KPI monoclonal antibodies stained neurons, including proximal axons and dendrites. The neuritic component of some plaques in patients with AD and in elderly control individuals were also immunoreactive for both APP and APP-KPI. Quantitative assessment of senile plaques in temporal neocortex showed that, on average, about one-third of beta/A4 immunoreactive plaques stained with either anti-APP or anti-KPI. Amyloid beta protein precursor and APP-KPI immunoreactivity were also found in the white and grey matter vessels of both AD patients and control individuals. These results suggest that KPI-containing forms of APP are present in dystrophic neurites of senile plaques, and normally in neurons, neuronal processes, and in the vascular compartment in the brain. Thus, APP-KPI is in a position to be intimately associated with beta/A4 deposition in the neuropil, in plaques and in amyloid angiopathy.

Human liver cell transplantation. Prolonged function in athymic-Gunn and athymic-analbuminemic hybrid rats

Isolated cryopreserved human liver cells, attached to collagen-coated microcarriers, were injected intraperitoneally into mutant rat recipients genetically deficient in either bilirubin uridine diphosphoglucuronosyltransferase activity (Gunn rats) or albumin synthesis (Nagase analbuminemic rats). One group of the recipient Gunn and analbuminemic rats were made genetically immunodeficient by interbreeding with athymic rats with inherited T-cell deficiency. Injected microcarriers and cells formed aggregates on the surface of the pancreas. There was no morphologic evidence of rejection in athymic recipients, whereas immunocompetent recipients demonstrated rejection within 5 days of transplantation. Athymic-Gunn rat recipients demonstrated excretion of bilirubin glucuronides in bile for 30 days and reduction in their serum bilirubin levels. In recipient athymic-analbuminemic rats, plasma albumin levels increased from pretransplantation levels of 0.025-0.05 mg/ml to 3.9-4.8 mg/ml 8 days posttransplantation and remained nearly at that level throughout the 30 days of the study. A method of harvesting, attaching to microcarriers, cryopreserving, and in vivo testing of human hepatocytes with prolonged survival and function in athymic-Gunn and athymic-analbuminemic hybrid rats is reported. These rats are excellent animal models for testing xenograft function.

Recombinant basic fibroblast growth factor accelerates wound healing

Basic fibroblast growth factor (bFGF) stimulates extracellular matrix metabolism, growth, and movement of mesodermally derived cells. We have previously shown that collagen content in polyvinyl alcohol sponges increased after bFGF treatment. We hypothesized that bFGF-treated incisional wounds would heal more rapidly. After intraperitoneal pentobarbital anesthesia, male, 200- to 250-g, Sprague-Dawley rats (n = 27) each underwent two sets of paired, transverse, dorsal incisions closed with steel sutures. On Day 3 postwounding, 0.4 ml of bFGF (recombinant, 400 ng. Synergen) or normal saline was injected into one of each paired incisions. Animals were killed with ether on postwounding Days 5, 6, and 7 and their dorsal pelts were excised. Fresh or formalin-fixed wound strips were subjected to tensile strength measurements using a tensiometer. Breaking energy was calculated. Wound collagen content (hydroxyproline) was measured in wound-edge samples following hydrolysis using high-performance liquid chromatography. There was an overall significant increase in fresh wound tensile strength (13.7 +/- 1.06 vs 19.1 +/- 1.99 g/mm, P less than 0.01) and wound breaking energy (476 +/- 47 vs 747 +/- 76 mm2, P less than 0.001) in bFGF-treated incisions. There was an increase in wound collagen content which was not statistically significant and there was no difference in fixed incisional tensile strength. Histologic examination showed better organization and maturation in bFGF wounds. Recombinant bFGF accelerates normal rat wound healing. This may be due to earlier accumulation of collagen and fibroblasts and/or to greater collagen crosslinking in bFGF-treated wounds.

Taurine and osmoregulation: taurine is a cerebral osmoprotective molecule in chronic hypernatremic dehydration

We studied the effect of 8-wk dietary taurine depletion on the vulnerability to hypernatremic dehydration in postweanling kittens. While experimental taurine depletion was not associated with increased susceptibility to acute hypernatremia (1.5 M NaCl/NaHCO3, 35 ml/kg body weight, single injection), there was an increase in mortality (five of seven versus one of seven, p = 0.05) and seizure activity (three of seven versus none of seven, p = 0.08) in taurine-depleted compared to taurine-replete kittens rendered chronically hypernatremic over 96 h. Furthermore, there was a significant decrease in brain cell water (517.4 +/- 21.7 versus 671.6 +/- 32.3 ml/100 g fat-free dry weight, p less than 0.05), derived almost exclusively from the intracellular compartment (352.5 +/- 12.3 versus 483.8 +/- 34.6 ml/100 g fat-free dry weight, p less than 0.05) that correlated with the reduction in the cerebral taurine content in the taurine-depleted versus control kittens during chronic hypernatremic dehydration. These results suggest that taurine is an important cerebral osmoprotective molecule. This aminoacid constitutes nearly 50% of the adaptable intracellular osmolal pool whose concentration varies in the course of osmoregulating in response to perturbations in the extracellular fluid tonicity.