Microstructural and Metabolic Changes in Normal Aging Human Brain Studied with Combined Whole-Brain MR Spectroscopic Imaging and Quantitative MR Imaging.

PURPOSE: This study aimed to detect age-related brain metabolic and microstructural changes in healthy human brains by the use of whole-brain proton magnetic resonance spectroscopic imaging (1H­MRSI) and quantitative MR imaging (qMRI). METHODS: In this study, 60 healthy participants with evenly distributed ages (between 21 and 69 years) and sex underwent MRI examinations at 3T including whole-brain 1H­MRSI. The concentrations of the metabolites N­acetylaspartate (NAA), choline-containing compounds (Cho), total creatine and phosphocreatine (tCr), glutamine and glutamate (Glx), and myo-inositol (mI), as well as the brain relaxation times T2, T2' and T1 were measured in 12 regions of interest (ROI) in each hemisphere. Correlations between measured parameters and age were estimated with linear regression analysis and Pearson's correlation test. RESULTS: Significant age-related changes of brain regional metabolite concentrations and tissue relaxation times were found: NAA decreased in eight of twelve ROIs, Cho increased in three ROIs, tCr in four ROIs, and mI in three ROIs. Glx displayed a significant decrease in one ROI and an increase in another ROI. T1 increased in four ROIs and T2 in one ROI, while T2' decreased in two ROIs. A negative correlation of tCr concentrations with T2' relaxation time was found in one ROI as well as the positive correlations of age-related T1 relaxation time with concentrations of tCr, mI, Glx and Cho in another ROI. CONCLUSION: Normal aging in human brain is associated with coexistent brain regional metabolic alterations and microstructural changes, which may be related to age-related decline in cognitive, affective and psychomotor domains of life in the older population.

Comparative uptake, translocation, and plant mediated transport of Tc-99, Cs-133, Np-237, and U-238 in Savannah River Site soil columns for the grass species Andropogon virginicus.

This study examines the ability of the grass species Andropogon virginicus to alter the subsurface transport and redistribution of a suite of radionuclides (99Tc, 133Cs (stable analog for 135Cs and 137Cs), 237Np, 238U) with varying chemical behaviors in a Savannah River Site soil via the use of vegetated and unvegetated soil columns. After an acclimation period, a small volume of solution containing all radionuclides was introduced into the columns via Rhizon© pore water sampling tubes. Plants were grown for an additional 4 weeks before shoots were harvested, and columns were prepared for sampling. Plant presence led to decreased radionuclide release from the columns, mainly due to radionuclide specific combinations of system hydrology differences resulting from plant transpiration as well as plant uptake. For the most mobile radionuclides, 99Tc followed by 237Np, plant presence resulted in significantly different soil concentration profiles between vegetated and unvegetated columns, including notable upward migration for 237Np in columns with plants. Additionally, plant uptake of 99Tc was the greatest of all the radionuclides, with plant tissues containing an average of 44 % of the 99Tc, while plant uptake only accounted for <2 % of 237Np and <0.5 % of 133Cs and 238U in the system. Although overall plant uptake of 133Cs and 238U were similar, the majority of 133Cs taken up by plants was associated with 133Cs already available in the aqueous phase while 238U uptake was mainly associated with the solid phase, meaning that plant activity resulted in a fraction of the native 238U being mobilized and thus, made available for plant uptake. Overall, this study quantified the influence of several plant-mediated physical and biogeochemical factors that have significant influence on radionuclide mobility and transport in this complex system which can be further utilized in future system or site-specific environmental transport and risk assessment models.

Comparison of spectral fitting methods for overlapping J-coupled metabolite resonances.

There is increasing interest in the use of two-dimensional J-resolved spectroscopic acquisition (multiecho) methods for in vivo proton magnetic resonance spectroscopy due to the improved discrimination of overlapping J-coupled multiplet resonances that is provided. Of particular interest is the potential for discrimination of the overlapping resonances of glutamate and glutamine. In this study, a new time-domain parametric spectral model that makes use of all available data is described for fitting the complete two-dimensional multiecho data, and the performance of this method was compared with fitting of one-dimensional spectra obtained following averaging multiecho data (echo time-averaged) and single-echo time PRESS (Point Resolved Spectroscopy) acquired spectra. These methods were compared using data obtained from a phantom containing typical brain metabolites and a human brain. Results indicate that improved performance and accuracy is obtained for the two-dimensional acquisition and spectral fitting model.

Reproducibility of serial whole-brain MR spectroscopic imaging.

The reproducibility of serial measurements using a volumetric proton MR Spectroscopic Imaging (MRSI) acquisition implemented at 3 Tesla and with lipid suppression by inversion-recovery has been evaluated. Data were acquired from two subjects at five time points, and processed using fully-automated procedures that included rigid registration between studies. These data were analyzed to determine coefficients of variance (COV) for each metabolite and for metabolite ratio images based on an individual voxel analysis, as well as for average and grey-matter and white-matter values from atlas-defined brain regions. The volumetric MRSI acquisition was found to obtain data of sufficient quality for analysis over 70 +/- 6% of the total brain volume, and spatial distributions of the resultant COV values were found to reflect the known distributions of susceptibility-induced magnetic field inhomogeneity. Median values of the resultant voxel-based COVs were 6.2%, 7.2%, and 9.7% for N-acetylaspartate, creatine, and choline respectively. The corresponding mean values obtained following averaging over lobar-scale brain regions within the cerebrum were 3.5%, 3.7%, and 5.2%. These results indicate that longitudinal volumetric MRSI studies with post-acquisition registration can provide an intra-subject reproducibility for voxel-based analyses that is comparable to previously-reported single-voxel MRS measurements, while additionally enabling increased sensitivity by averaging over larger tissue volumes.

Testing the accuracy of Bedek et al's new models based on 1-to-7 mandibular teeth for age estimation in 7-15 year old south Indian children.

The goal of long term research on age assessment is to focus on the strengths and weaknesses of existing reliable methods of age estimation. In cases of age estimation when all teeth are present, maximum accuracy can be obtained using a 7 tooth model. Demirjian's system and Willems models require all seven mandibular teeth in the lower left quadrant for age assessment. Unfortunately, these methods cannot be applied in children with hypodontia. In 2019, Bedek et al., from Croatia, developed new models of age estimation based on a combination of one to seven mandibular teeth. In the present study, we tested the accuracy of the newly developed models for age estimation in South Indian children. Tested in parallel with Willems models, the accuracy of the new models was tested in terms of mean difference, mean absolute error (MAE) and percentage of correct estimations within intervals of +0.5 and +1 years. In terms of mean difference between chronological age (CA) and estimated dental age (DA), all models along with Willems models have underestimated the CA except Bedek et al's 6 tooth model where overestimation of CA was seen in boys. For MAE and percentage of correct estimations, the new models performed better than Willems models. With regards to our results, it can be concluded that the new models for dental age calculation are accurate and suitable. Therefore, we may encourage their use for age estimation in South Indian children, particularly in individuals with hypodontia or when multiple teeth are missing.

COVID-19 in sub-Saharan Africa: impacts on vulnerable populations and sustaining home-grown solutions.

This commentary draws on sub-Saharan African health researchers' accounts of their countries' responses to control the spread of COVID-19, including social and health impacts, home-grown solutions, and gaps in knowledge. Limited human and material resources for infection control and lack of understanding or appreciation by the government of the realities of vulnerable populations have contributed to failed interventions to curb transmission, and further deepened inequalities. Some governments have adapted or limited lockdowns due to the negative impacts on livelihoods and taken specific measures to minimize the impact on the most vulnerable citizens. However, these measures may not reach the majority of the poor. Yet, African countries' responses to COVID-19 have also included a range of innovations, including diversification of local businesses to produce personal protective equipment, disinfectants, test kits, etc., which may expand domestic manufacturing capabilities and deepen self-reliance. African and high-income governments, donors, non-governmental organizations, and businesses should work to strengthen existing health system capacity and back African-led business. Social scientific understandings of public perceptions, their interactions with COVID-19 control measures, and studies on promising clinical interventions are needed. However, a decolonizing response to COVID-19 must include explicit and meaningful commitments to sharing the power-the authority and resources-to study and endorse solutions.

The collectins in innate immunity.

The collectins are proteins with collagen tails and globular lectin domains that appear to play an important role in mammalian first line host defense. Recent insights have clarified the structural basis of ligand recognition, the interactions of collectins with complement cascades, and the association with disease susceptibility.

Aging associated changes in amygdalar corticotropin-releasing hormone (CRH) and CRH-binding protein in Fischer 344 rats.

Behavioral adaptation in aging may become impaired from abnormal expression of amygdalar corticotropin-releasing hormone (CRH) and/or CRH-binding protein (CRH-BP). In this study, we serially sectioned the amygdala in 4-, 12-, and 24-month-old Fischer 344 rats following perfusion with 4% paraformaldehyde. We determined the amount of CRH and CRH-BP containing cells as well as the density of fibers expressing CRH or CRH-BP utilizing densitometric methods. Images were digitized using Zeiss Axiovision software and densitometrically analyzed using Scion Image. Both sides were analyzed in sections cut at 30 mum thickness. Cell counts of CRH-BP containing cells in the basolateral and lateral nucleus of the amygdala were lower in 24-month-old rats vs. 4-month-old rats, respectively (mean cells/section +/- SE): 31 +/- 6 vs. 72 +/- 10 (n = 3; P < 0.05 via ANOVA and Fisher's PLSD). There was a trend for cell counts of CRH containing cells in the central nucleus of the amygdala to be lower in 24-month-old rats vs. 4-month-old rats, respectively 28 +/- 7 vs. 47 +/- 9 (n = 3; P = 0.07 via ANOVA). Densitometric analysis of the number of CRH-BP positive fibers revealed no age differences in CeA; however, with regards to CRH-positive fibers, both 4- and 12-month rats had greater CeA CRH immunoreactivity relative to 24-month-old rats (Ps < 0.05 via ANOVA and Fisher's PLSD). These changes may contribute to impaired adaptations to stress, cognitive decline, and other pathophysiological processes during aging.

Amylin inhibits insulin-stimulated glucose uptake in C2C12 muscle cell line through a cholera-toxin-sensitive mechanism.

Rat amylin inhibits insulin-stimulated glucose uptake with an IC50 of 12.1 +/- 4.1 pM in C2C12 myotubes. The maximal inhibition is 64 +/- 5.4% observed at a 100-pM dose of the peptide. Consistently, presence of 100 pM amylin shifted the dose-response curve of insulin to the right, increasing the ED50 from 0.71 to 16 nM. No effect of amylin is observed on basal glucose uptake in these cells. Cholera-toxin treatment of the cells did not affect the insulin-stimulated glucose uptake, while the inhibitory effect is completely lost in toxin-treated cells. These findings strongly suggest that rat amylin is active at a physiological concentration and the amylin inhibition of glucose uptake is mediated through a cholera-toxin-sensitive mechanism.

Structure of myohemerythrin in the azidomet state at 1.7/1.3 A resolution.

The molecular model of myohemerythrin, an oxygen-carrying protein from sipunculan worms, has been refined by stereochemically restrained least-squares minimization at 1.7/1.3 A resolution to a conventional R-value of 0.158. The estimated positional standard deviation is better than 0.15 A for most of the 979 protein atoms. The average isotropic displacement parameter, B, for the protein atoms is 23.1 A2. This high average B parameter appears to be due to the overall motion of the molecule, which correlates with the observed anisotropic diffraction. The side-chains of seven residues were modeled in two conformations, i.e. the side-chains were discretely disordered, and B parameters for several lysine and glutamate side-chains indicate that they are poorly localized. Of the residues in myohemerythrin, 66% are helical, with 62% occurring in four long alpha-helices with mean values for the backbone torsion angles of phi = -65 degrees, psi = -42 degrees, and for the hydrogen bonds distances of N ... O, 3.0 A and H ... O, 2.1 A, and angles of N ... O = C, 153 degrees, N-H ... O, 157 degrees, and H ... O = C, 147 degrees. For two-thirds of the alpha-helical residues, the torsional rotation of the C alpha-C beta bond, chi 1, is approximately -60 degrees, and for one-third chi 1 is approximately 180 degrees. Although most turns in myohemerythrin are well-categorized by previous classification, two do not fit in established patterns. Also included in the refined model are three sulfate ions, all partially occupied, and 157 water molecules, 40% of which are modeled fully occupied. Only one water molecule is internal to the protein, the remainder occur on the surface and are observed principally between symmetry-related molecules contributing, along with van der Waals' contacts, most of the interactions between molecules. There are eight intermolecular protein-protein hydrogen bonds, of which only four are between well-located atoms.

Comparison of CH1 domains in different classes of murine antibodies.

The CH1 domains of antibodies belonging to the following five murine immunoglobulin (Ig) classes IgG1, IgG2a, IgG2b, IgG3 and IgA have been compared. The IgG CH1 domain structures are, as would be expected, similar overall, but show local conformational variations. When compared with IgG CH1 domain structures, the IgA CH1 domain displays several significant structural differences, which are a consequence of insertions/ deletions and specific structural constraints. In regions of structural differences in the IgG CH1 domains, the spatial correspondence of residues is not reflected by conventional (Kabat) sequence number. Thus the sequence alignment and numbering for CH1 domains has been revised to be consistent with the three-dimensional alignments.

X-ray structure of the uncomplexed anti-tumor antibody BR96 and comparison with its antigen-bound form.

The X-ray structure of the uncomplexed human chimeric Fab' of the anti-tumor antibody BR96 has been determined at 2.6 A resolution. The structure has been compared with Lewis Y antigen-complexed structures of BR96 which were determined previously. The comparison reveals segmental motions and/or conformational rearrangements of three CDR loops (L1, L3, and H2), whereas CDR H3 does not undergo changes upon complexation despite its significant main-chain contacts to the carbohydrate antigen. In light of the uncomplexed chimeric Fab' structure reported here, the previously observed high mobility of the CL:CH1 domains of the complexed chimeric BR96 Fab is rationalized as a "swinging" motion approximately about the axis of the elbow bend.

Crystallization and preliminary X-ray analysis of an anti-staphylococcal nuclease-staphylococcal nuclease complex and of a second anti-staphylococcal nuclease antibody.

The Fab fragments of several monoclonal antibodies that bind Staphylococcal nuclease have been screened for crystallization conditions. Two of these, N10 and N25, have been crystallized in forms suitable for X-ray structural analysis. The anti-Staphylococcal nuclease antibody complex N10 Fab-nuclease crystallizes with symmetry consistent with space group C2 and cell parameters of a = 234.7 A; b = 43.5 A; c = 74.4 A; beta = 106.4 degrees. A second anti-Staphylococcal nuclease antibody, N25, although crystallized starting with the Fab-nuclease complex, apparently crystallizes as uncomplexed N25 Fab with symmetry consistent with space group P3(1)21 (or its enantiomorph P3(2)21) and cell parameters of a = b = 80.9 A; c = 138.4 A.

Structure and specificity of the anti-digoxin antibody 40-50.

We determined the sequence, specificity for structurally related cardenolides, and three-dimensional structure of the anti-digoxin antibody 40-50 Fab in complex with ouabain. The 40-50 antibody does not share close sequence homology with other high-affinity anti-digoxin antibodies. Measurement of the binding constants of structurally distinct digoxin analogs indicated a well-defined specificity pattern also distinct from other anti-digoxin antibodies. The 40-50-ouabain Fab complex crystallizes in space group C2 with cell dimensions of a = 93.7 A, b = 84.8 A, c = 70.1 A, beta = 128.0 degrees. The structure of the complex was determined by X-ray crystallography and refined at a resolution of 2.7 A. The hapten is bound in a pocket extending as a groove from the center of the combining site across the light chain variable domain, with five of the six complementarity-determining regions involved in interactions with the hapten. Approximately three-quarters of the hapten surface area is buried in the complex; two hydrogen bonds are formed between the antibody and hapten. The surface area of the antibody combining site buried by ouabain is contributed equally by the light and heavy chain variable domains. Over half of the surface area buried on the Fab consists of the aromatic side-chains. The surface complementarity between hapten and antibody is sufficient to make the complex specific for only one lactone ring conformation in the hapten. The crystal structure of the 40-50-ouabain complex allows qualitative explanation of the observed fine specificities of 40-50, including that for the binding of haptens substituted at the 16 and 12 positions. Comparison of the crystal structures of 40-50 complexed with ouabain and the previously determined 26-10 anti-digoxin Fab complexed with digoxin, demonstrates that the antibodies bind these structurally related haptens in different orientations, consistent with their different fine specificities. These results demonstrate that the immune system can generate antibodies that provide diverse structural solutions to the binding of even small molecules.

The crystal structure of the antibody N10-staphylococcal nuclease complex at 2.9 A resolution.

The three-dimensional structure of the antibody N10 Fab fragment complexed with staphylococcal nuclease (SNase) has been determined to 2.9 A resolution. Eighteen residues from six complementarity-determining regions (CDR) recognize an epitope of five distinct SNase segments with a total of 17 residues. The overall shape of the antibody-antigen interface is U-shaped rather than the more or less rectangular interface seen in other antibody-protein antigen interfaces. Despite the U-shaped interface, the amount of surface buried in the complex, 828 A2 for SNase and 793 A2 for N10, is typical of antibody-protein antigen complexes. Contributing to the shape of the interface is the shortest antibody heavy chain-CDR3 loop reported to date, which probably allows access of bulk solvent in the center of the "U" interface. Another unusual feature of the N10 antibody is the 15 residue antibody light chain-CDR1, a length seen in only three other reported antibodies. Antibody light chain-CDR1 displays a previously unobserved conformation in its distal portion. Finally, although some of the movement observed in the antibody-bound SNase may be due to crystal contacts, it is clear that some side-chain rearrangements are the result of antigen-antibody interaction.

Crystallization and preliminary X-ray analysis of the monoclonal anti-tumor antibody BR96 and its complex with the Lewis Y determinant.

The monoclonal anti-tumor antibody BR96 binds a tetrasaccharide, Lewis y (Le(y)), in vitro and recognizes a Le(y)-bearing or Le(y)-related tumor-associated antigen in vivo. The Fab of the murine monoclonal antibody, mBR96 (IgG3, kappa), and the Fab' of its human chimera, cBR96 (IgG1, kappa), and their complexes with Le(y) have been screened for crystallization conditions. Crystals suitable for X-ray diffraction have been obtained for uncomplexed cBR96 Fab', cBR96 Fab' in complex with Le(y) and mBR96 Fab in complex with Le(y). The symmetry of the cBR96 Fab' crystals is consistent with space group P2(1)2(1)2, a = 61.1 A; b = 174.3 A; c = 45.6 A; the symmetry of the cBR96 Fab'-Le(y) complex crystals with space group P4(3)2(1)2 (or its enantiomorph), a = b = 82.2 A; c = 167.1 A and the symmetry of the mBR96 Fab-Le(y) complex crystals with space group P2(1)2(1)2(1), a = 69.4 A; b = 84.9 A; c = 86.8 A.

Crystallization and preliminary X-ray analysis of a trimeric form of human mannose binding protein.

A trimeric form of the carbohydrate recognition domain of human mannose binding protein has been crystallized in two different forms. The first form crystallizes with symmetry consistent with space group P2(1)2(1)2(1) and a = 61 A; b = 144 A; c = 107 A with presumably two trimers in the asymmetric unit. The second form crystallizes with symmetry consistent with space group P321 and a = b = 77 A; c = 58 A and one monomer per asymmetric unit. The molecular and crystallographic 3-folds must be coincident in this crystal form.

Structure and refinement at 1.8 A resolution of the aspartic proteinase from Rhizopus chinensis.

The structure of rhizopuspepsin (EC 3.4.23.6), the aspartic proteinase from Rhizopus chinensis, has been refined to a crystallographic R-factor of 0.143 at 1.8 A resolution. The positions of 2417 protein atoms have been determined with a root-mean-square (r.m.s.) error of 0.12 A. In the final model, the r.m.s. deviation from ideality for bond distances is 0.010 A, and for angle distances it is 0.034 A. During the course of the refinement, a calcium ion and 373 water molecules, of which 17 are internal, have been located. The active aspartate residues, Asp35 and Asp218, are involved in similar hydrogen-bonding interactions with neighboring residues and with several water molecules. One water molecule is located between the two carboxyl groups of the catalytic aspartate residues in a tightly hydrogen-bonded position. The refinement resulted in an unambiguous interpretation of the highly mobile "flap", a beta-hairpin loop region that projects over the binding pocket. Large solvent channels are formed when the molecules pack in the crystal, exposing the binding pocket and making it easily accessible. Intermolecular contacts involve mainly solvent molecules and a few protein atoms. The three-dimensional structure of rhizopuspepsin closely resembles other aspartic proteinase structures. A detailed comparison with the structure of penicillopepsin showed striking similarities as well as subtle differences in the active site geometry and molecular packing.

Internalization of cloned pancreatic polypeptide receptors is accelerated by all types of Y4 agonists.

Internalization of cloned rat or human Y4 receptors expressed in Chinese hamster ovary (CHO) cells increased with concentration of all types of Y4 agonists, including human and rat pancreatic polypeptides, the Y1 receptor group co-agonists possessing C-terminal TRPRY.NH2 pentapeptide, and a C-terminally amidated dimeric nonapeptide related to neuropeptide Y, GR231118. These peptides also inhibited forskolin-stimulated adenylyl cyclase activity in Y4 receptor-expressing cells, and stimulated the binding of 35S-labeled GTP-gamma-S to pertussis toxin-sensitive G-proteins in particulates from these cells. Peptide VD-11 (differing from GR231118 only by C-terminal oxymethylation) acted as a competitive antagonist in all of the above processes. Agonist-induced stimulation of the Y4 receptor internalization persisted in the presence of allosteric inhibitors of hPP binding, N5-substituted amilorides, which also were relatively little active in G-protein stimulation and cyclase inhibition by Y4 agonists. Acceleration of Y4 receptor internalization by agonists apparently is related to relaxation of allosteric constraints to ligand attachment and sequestration of the receptor-ligand complex.

Modulation of antibody affinity by a non-contact residue.

Antibody LB4, produced by a spontaneous variant of the murine anti-digoxin monoclonal antibody 26-10, has an affinity for digoxin two orders of magnitude lower than that of the parent antibody due to replacement of serine with phenylalanine at position 52 of the heavy chain variable region (Schildbach, J.F., Panka, D.J., Parks, D.R., et al., 1991, J. Biol. Chem. 266, 4640-4647). To examine the basis for the decreased affinity, a panel of engineered antibodies with substitutions at position 52 was created, and their affinities for digoxin were measured. The antibody affinities decreased concomitantly with increasing size of the substituted side chains, although the shape of the side chains also influenced affinity. The crystal structure of the 26-10 Fab complexed with digoxin (P.D.J., R.K. Strong, L.C. Sieker, C. Chang, R.L. Campbell, G.A. Petsko, E.H., M.N.M., & S.S., submitted for publication) shows that the serine at heavy chain position 52 is not in contact with hapten, but is adjacent to a tyrosine at heavy chain position 33 that is a contact residue. The mutant antibodies were modeled by applying a conformational search procedure to position side chains, using the 26-10 Fab crystal structure as a starting point. The results suggest that each of the substituted side chains may be accommodated within the antibody without substantial structural rearrangement, and that none of these substituted side chains are able to contact hapten. These modeling results are consistent with the substituents at position 52 having only an indirect influence upon antibody affinity.(ABSTRACT TRUNCATED AT 250 WORDS)