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Biomedical subjects

D G Davis

Publications and source records attributed to D G Davis.

At least 19 recordsLinked to original sources
PubMed1999

Alzheimer neuropathologic alterations in aged cognitively normal subjects.

The histopathologic changes distinguishing early Alzheimer disease (AD) from normal or pathologic aging are not clearly defined. This report describes the autopsy findings of 59 elderly, well-educated, volunteers. They were examined longitudinally with mental status testing, some for up to 8 years, as part of our normal aging study. This study reveals that (1) the brains of many subjects who did not show cognitive impairment on neuropsychologic testing contain abundant senile plaques (SP) and/or neurofibrillary tangles (NFT); (2) 29 subjects met Khachaturian criteria for AD, 15 met CERAD and 7 met National Institute on Aging-Reagan Institute guidelines; (3) Braak and Braak staging method included 9 in stage IV subjects, 4 in stage V, and 1 in stage VI; (4) there was a progression of NFT from entorhinal cortex to hippocampus and amygdala as a function of age; (5) 2 subjects met criteria for a diagnosis of dementia with Lewy bodies but were not demented; (6) cerebral amyloid angiopathy was present in leptomeningeal vessels in 75% of subjects and in parenchymal vessels in 62% of subjects; (7) only 10 of 59 subjects (17%) had no or few degenerative brain changes. Our study demonstrates that the brains of a large percentage of cognitively normal, relatively well-educated individuals contain numerous degenerative changes and only a small percentage are relatively free of these changes.

Aged↗
PubMed1997

A phase I trial of neutron brachytherapy for the treatment of malignant gliomas.

We performed a phase I trial to test the feasibility of neutron brachytherapy using californium-252 (252Cf) as the sole source of radiation, and to determine the maximum tolerable dose (MTD), for the treatment of malignant gliomas. Previous studies using external beam neutron radiation have shown that neutrons are capable of totally eradicating malignant gliomas. However, in most cases, fatal widespread radiation necrosis resulted. Radioactive implants are a logical method of increasing the dose to the tumour and decreasing the dose to normal brain. 252Cf is a relatively stable neutron-emitting isotope suitable for implant therapy. The study was an open ended dose-escalation study. All radiation was delivered by using only 252Cf implants, without external beam therapy of any type. The first dose step was 900 neutron cGy (ncGy); each subsequent step was increased by 100 ncGy. Three patients with newly diagnosed malignant gliomas were entered at each dose step, and the number was increased to six patients in dose steps at which necrosis of brain occurred. The study ended when two patients at any dose step developed radiation necrosis of brain outside the prescribed radiation field. 33 patients were entered into the study. 10 patients developed scalp necrosis associated with scalp doses above 900 ncGy. The study ended when two patients at the 1300 ncGy dose step developed radiation necrosis of brain. We conclude: (1) neutron brachytherapy using 252Cf as the sole source of radiation is a feasible treatment for malignant gliomas; (2) the scalp tolerates less neutron radiation than the brain; (3) the MTD (and the recommended dose for a phase II trial) of interstitial neutron brachytherapy is 1200 ncGy.

Adult↗
PubMed1996

Increased ALZ-50 immunoreactivity in sudden infant death syndrome.

Neuronal expression of the ALZ-50 epitope was investigated in hippocampus and medulla from infants dying of sudden infant death syndrome or known causes (controls). Hippocampal studies include data from 31 infants dying of known causes between 32 weeks' gestation and 16 months postpartum and 46 infants who died of sudden infant death syndrome. The medulla at the level of the mid olivary protuberance was investigated in 22 infants with sudden infant death syndrome and 11 controls matched for age and postmortem interval. Medullary sections were also examined using immunohistochemical methods to demonstrate reactivity to glial fibrillary acidic protein antibody. The density of ALZ-50-immunodecorated neurons in control hippocampus rises from the level observable in utero to a maximum between 1 and 4 months of age and declines thereafter. The density of ALZ-50-immunoreactive neurons in hippocampus is significantly increased in infants with sudden infant death syndrome at all ages. Significant regionally specific increases in the number of ALZ-50-immunoreactive neurons, and glial fibrillary acidic protein-reactive cells were found in sudden infant death syndrome medulla; coincidental increases were observed in only the solitary nucleus. Neurons exhibiting the ALZ-50 epitope may reflect apoptotic neuron death of normal development, and increased numbers of immunoreactive neurons may suggest enhanced neurodegeneration in sudden infant death syndrome.

Antibodies↗
PubMed1995

Catalytic activity of the SH2 domain of human pp60c-src; evidence from NMR, mass spectrometry, site-directed mutagenesis and kinetic studies for an inherent phosphatase activity.

During solution structural studies it was apparent that the human recombinant pp60c-src SH2 domain (srcSH2, residues 144-249) possessed an inherent phosphatase (Pase) activity. Complexes of U[13C,15N]srcSH2 with unlabeled Ac-pYEEIE (I) were examined using 31P and 1H-detected isotope filtered NMR methods. The presence of a high-affinity complex in equimolar solutions of I and U[13C, 15N]-srcSH2 was demonstrated by chemical shift perturbations, line broadening, and the observation of intermolecular nuclear Overhauser effects from the pY and Ile side-chain protons of I to protons on amino acid residues present in the binding pocket of srcSH2. Solutions containing excess I relative to srcSH2 revealed a slow hydrolysis of I to produce Ac-YEEIE and inorganic phosphate. The hydrolysis rate determined from NMR and HPLC-electrospray ionization mass spectrometry data at 30 degrees C for solutions containing excess I was 0.002-0.003 h-1. srcSH2 also catalyzed the hydrolysis of p-nitrophenyl phosphate (pNPP). Isoelectric focusing gels of a number of mutant srcSH2s demonstrated that this activity comigrated with srcSH2. Km, kcat, and kcat/Km were 3.7 +/- 0.4 mM, 3.1 +/- 0.2 x 10(-2) min-1, and 8.4 +/- 0.4 M-1 min-1, respectively, toward pNPP. The C188A mutant of the srcSH2 domain displayed 15% of the activity displayed by wild-type srcSH2, demonstrating that this residue is not absolutely required for activity. Two additional mutations in the known pY binding site, R178K and R158K, also resulted in decreased pNPPase activity, suggesting that the activity resides in or near this site. The inhibitor profile and pH dependence suggest that this is a novel protein Pase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Solution structure of the human pp60c-src SH2 domain complexed with a phosphorylated tyrosine pentapeptide.

Human pp60c-src is a cellular nonreceptor tyrosine kinase that participates in cytosolic signal transduction and has been implicated in the development of malignant tumors in the human breast and colon. Signal transduction is mediated by highly specific interactions between the SH2 domain and receptor phosphorylated tyrosine binding motifs. To elucidate the molecular conformation and interactions in solution, a family of highly resolved nuclear magnetic resonance (NMR) structures was determined for the src SH2 domain complexed with a high-affinity phosphorylated pentapeptide, acetyl-p YEEIE-OH. The 23 structures, generated with a distance geometry (DG) and a dynamical simulated annealing (SA) procedure, satisfied 2072 experimental restraints derived from a variety of multifrequency/multidimensional and isotope-filtered NMR data. Superimposition of residues 143-245 upon the mean coordinate set yielded an atomic rmsd of 0.58 +/- 0.09 A for the N, C alpha, C' atoms and 1.04 +/- 0.08 for all the non-hydrogen atoms. Residues in the ordered secondary structure regions superimpose to 0.29 +/- 0.04 A for the N, C alpha, C' and 0.73 +/- 0.08 A for all the non-hydrogen atoms. The angular order parameter calculated for the phi, psi angles was > 0.9 for 81 of the 106 protein residues. The main protein conformational features are three antiparallel beta-strands that traverse a compact core with an alpha-helix on each side of the core near the N- and C-termini. The observed intermolecular nuclear Overhauser effects (NOE) from the pY, +1E, and +3I residues positioned the ligand in an extended conformation across the SH2 domain surface with the pY and +3I side chains inserted into the protein binding pockets. In general, the protein conformation is consistent with previously reported structures of different SH2 domain complexes determined by X-ray crystallography. However, inter- or intramolecular interactions involving the guanidinium side chains of the solvated R alpha A2 or the buried R beta B5 were not observed at pH = 5.5 or 7.0. If such interactions exist in solution, the absence of any confirming data probably arises from rapid exchange with solvent and/or undetermined dynamic components. Thus, the unrestrained R alpha A2 side chain did not show an amino-aromatic interaction or a hydrogen bond to the -1 carbonyl oxygen as observed in the crystal structures. This result is consistent with the solution structure of a different SH2 domain complex. A more detailed comparison between the crystal structure and the NMR-derived solution structures of the same src SH2 domain complex is presented.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1995

Multiple steroid-binding orientations: alteration of regiospecificity of dehydroepiandrosterone 2- and 7-hydroxylase activities of cytochrome P-450 2a-5 by mutation of residue 209.

The mutation of Ala-117 to Val conferred dehydroepiandrosterone (DHEA) hydroxylase activity on cytochrome P-450 2a-4, with the production of both 2 alpha- and 7 alpha-hydroxyDHEA at similar rates. P-450 2a-5 which has Val at position 117, acquired high DHEA hydroxylase activity by mutation of Phe-209. Mutant F209L of P-450 2a-5 exhibited strong regiospecificity at the 2-position of the DHEA molecule with the production of 2 alpha-hydroxy DHEA as the major metabolite. On the other hand, mutant F209V of P-450 2a-5 showed the 7-position to be the major hydroxylation site, 7 beta-hydroxyDHEA and 7 alpha-OHDHEA being produced. Therefore the regiospecificity of DHEA hydroxylase activity of P-450 2a-5 is altered between the 2- and 7-position depending on the amino acid at position 209. Modelling of the DHEA molecule in the pocket of bacterial P-450cam showed that the steroid can be accommodated in at least two orientations for which the 2- or 7- position is near the sixth axial position of the haem. Moreover, these two orientations, which are of similar energy, can be interconverted by a 180 degrees rotation of the steroid molecule around its long axis. These results support the hypothesis that the steroid molecule in the pocket is in dynamic equilibrium with multiple binding orientations and that the equilibrium is apparently determined by a few critical residues including those at positions 117 and 209.

Aryl Hydrocarbon Hydroxylases↗
PubMed1995

Dopaminergic and serotonergic neurotransmitters in bone marrow transplant patients.

Depigmentation of neurons in the substantia nigra (SN) is found in patients dying after bone marrow transplantation (BMT). This study examined neurochemical striatal changes related to BMT. Caudate nucleus and putamen of 6 BMT subjects and 10 age-matched controls were analyzed for levels of dopamine (DA), homovanillic acid (HVA), 5-hydroxyindoleamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA), by high pressure liquid chromatography-electron capture detection (HPLC-ECD). In addition, assays of the enzymatic activities of monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B), choline acetyltransferase (ChAT), and acetylcholinesterase (AChE) were performed. Cholinergic markers, ChAT and AChE, were reduced in BMT caudate (p < 0.05) but not in the putamen. A recovery toward normal cholinergic enzymatic activity was identified with increased post-transplant survival time. The level of DA was reduced 50% in BMT caudate and putamen while HVA was increased 30%, however, neither reduction achieved statistical significance. Increasing post-transplant survival time correlated with decreased levels of DA in caudate nucleus and putamen in the early post-transplant period, while HVA was increased over the same interval but tended to return to normal levels with increasing survival time. Two-fold increases of BMT caudate 5-HT (p < 0.003) and 5-HIAA were found; similar changes were noted in putamen 5-HT and 5-HIAA (p < 0.0008). Significant increases in MAO-A and B were found in BMT caudate (p < 0.0001 and p < 0.06, respectively) and putamen (p < 0.0005 and p < 0.006, respectively). No statistically significant changes were noted in the 5-HT, 5-HIAA, or MAO A or MAO B with increasing post-transplant survival. Whether these changes are the result of physiologic or toxic effects is unknown.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1994

NMR solution structure of a peptide nucleic acid complexed with RNA.

Peptide nucleic acids (PNA) incorporating nucleic acid bases into an achiral polyamide backbone bind to DNA in a sequence-dependent manner. The structure of a PNA-ribonucleic acid (RNA) complex was determined with nuclear magnetic resonance methods. A hexameric PNA formed a 1:1 complex with a complementary RNA that is an antiparallel, right-handed double helix with Watson-Crick base pairing similar to the "A" form structure of RNA duplexes. The achiral PNA backbone assumed a distinct conformation upon binding that differed from previously proposed models and provides a basis for further structure-based design of antisense agents.

Magnetic Resonance Spectroscopy↗
PubMed1994

Studies of inhibitor binding to Escherichia coli purine nucleoside phosphorylase using the transferred nuclear Overhauser effect and rotating-frame nuclear Overhauser enhancement.

NMR studies of the adenosine analog tubercidin have been carried out in the presence of Escherichia coli purine nucleoside phosphorylase (PNP) in order to characterize the conformation of the enzyme-complexed nucleoside. Although analysis of transferred NOE data at various enzyme/inhibitor ratios indicated a predominantly syn nucleoside conformation in the enzyme-complexed state, the results, particularly the 8(1') and 8(3') NOE interactions, were not quantitatively consistent with any single bound conformation. Dissociation rate constants for the tubercidin-PNP complex were determined based on analysis of chemical shift and line width data as a function of enzyme/inhibitor ratio, Carr-Purcell-Meiboom-Gill measurements of the transverse relaxation rate as a function of pulse rate, and T1 rho experiments as a function of the spin-lock field strength. Dissociation rate constants of 2100 s-1 at 20 degrees C and 1400 s-1 at 10 degrees C were determined using the latter two methods. These rates are sufficiently high to justify the validity of the transferred NOE method for an enzyme as large as PNP. The possible significance of spin diffusion was investigated by the use of the deuterated analog [2'-2H]tubercidin, for which many of the intraligand spin diffusion pathways are eliminated, and by performing a series of transferred ROE experiments. A comparison of data obtained using transferred NOE and ROE measurements provides a basis for separating direct and indirect relaxation pathways. Both approaches indicated that the relatively significant 8(3') NOE interaction was not dominated by spin diffusion. Furthermore, analysis of chemical shift and transverse relaxation data for the tubercidin H-2 resonance gave inconsistent results for the chemical shift of the bound species and was inconsistent with the assumption of a single, bound conformation. These results were interpreted in terms of a 2:1 ratio of a syn, 3'-exo:anti, 3'-endo geometry for bound tubercidin. Ligand competition experiments using 9-deazainosine show that all of the tubercidin TRNOE effects are reversed by addition of the second nucleoside, suggesting that the TRNOE data for tubercidin arise due to interactions at the active sites of PNP rather than as a consequence of nonspecific binding to the enzyme.

Binding Sites↗
PubMed1994

Direct measurements of the dissociation-rate constant for inhibitor-enzyme complexes via the T1 rho and T2 (CPMG) methods.

The unimolecular dissociation rate constant, k-1, for the inhibitor-enzyme complex tubercidin-Escherichia coli purine nucleoside phosphorylase (PNPase) has been determined directly via two related 1H NMR methods for studying exchange-mediated transverse relaxation. One method involves measurements of the decay rate, 1/T1 rho, of spin-locked magnetization in the rotating frame as a function of the strength of the spin-locking field, omega SL. The second method involves measurements of the Carr-Purcell-Meiboom-Gill (CPMG) spin-echo decay rate, 1/TCPMG2, as a function of the repetition rate, 1/tcp, of the refocusing pulses. Expressions describing the dependence of TCPMG2 as a function of 1/tcp and k-1 have been previously derived with sufficient generality to include the two-site inhibitor-enzyme exchange case. Existing expressions for T1 rho as a function of kex and omega SL, however, had to be reformulated to take into account differences between Tb2 and Tb1 for the bound form of the inhibitor as well as offset corrections important at low values of omega SL. A new expression for exchange-mediated T1 rho has been derived to take these factors into account and is shown to provide a more accurate description of observed T1 rho data than previous models. Numerical analysis of relaxation rates, measured independently by either the rotating-frame or the spin-echo method for the H1' and H2 protons of tubercidin at different inhibitor:enzyme ratios, yields comparable values for k-1 of 2400 (+/- 350) and 900 (+/- 80) s-1 at 20 and 10 degrees C, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic Resonance Spectroscopy↗
PubMed1994

Cumulative effects model: a response to Williams (1994)

The cumulative effects (CE) model explains free-operant choice by the ratio of total numbers of responses and reinforcements, a probability-like variable. Williams (1994) argues that the model is vulnerable to experiments that disprove melioration, a local probability model. The authors note critical differences between the nonlocal CE model and local probability models that allow the CE model to handle some data with which they are incompatible. All models are simplifications of reality; hence, a model's failures are as revealing as its successes. Williams suggests that simple models may need to be abandoned in favor of a "representational" account. The authors point out that representations must be both acquired and acted on. Acquisition requires processing of responses and reinforcers; action requires decision rules. Models are simply testable suggestions for what these rules and processes might be.

Behavior Therapy↗
PubMed1994

Neurochemical and histopathologic alterations characteristic of Pick's disease in a non-demented individual.

In the course of investigating a large number of non-demented subjects, a 68 year old female dying of coronary artery disease was found to have Pick bodies in her grossly normal brain. Although only mild subcortical gliosis and no neuron loss were observed. Pick bodies were found throughout the brain and occasional balloon cells were noted. Pick bodies and numerous neurons were also ALZ-50 and Tau-1 immunoreactive. Retrospective studies indicated a lack of overt intellectual decline or depression in this individual. Frontal, temporal and occipital poles, amygdala, hypothalamus and nucleus basalis of Meynert (nbM) were analyzed for ChAT, AChE and MAO-A and -B enzymatic activities and for the binding of 5HT and imipramine. Cholinergic decreases were found only in subcortical structures. Serotonin binding decreases were widespread, excluding the nbM. Altered MAO-B activity was regionally variable, and no differences in MAO-A activity or imipramine binding were observed. Few differences in neurochemical alterations were observed in the current non-demented subject with abundant Pick bodies compared to previous studies of demented Pick's patients. This case strongly suggests that chemical dysfunction and neuropathological features of Pick's disease occur in advance of overt clinical manifestations of the disorder.

Acetylcholinesterase↗
PubMed1993

Engineering mouse P450coh to a novel corticosterone 15 alpha-hydroxylase and modeling steroid-binding orientation in the substrate pocket.

The F209L mutation alters specificity of P450coh from coumarin 7-hydroxylation to 15 alpha-hydroxylation of 11-deoxysteroids such as testosterone and 11-deoxycorticosterone. Neither the wild-type nor F209L exhibits activity toward 11 beta-hydroxysteroids including corticosterone. Mutation of Phe-209 to Asn, however, confers on mutant F209N a high corticosterone 15 alpha-hydroxylase activity. F209V also exhibits low corticosterone 15 alpha-hydroxylase activity; Km and Vmax are 10-fold higher and lower, respectively, than for F209N. The results are consistent with the hypothesis that direct interaction of Asn-209 with 11OH is responsible for high corticosterone 15 alpha-hydroxylase activity. To support this hypothesis, a possible steroid-binding orientation is modeled in the substrate pocket of P450cam. Our weighted homology and constrained alignments map residue 209 of P450coh to Met-184 and Met-191 of P450cam. Energy minimization of corticosterone in the substrate pocket results in the 11OH of the steroid directed toward Met-184 (7 A) and Met-191 (16 A), and in C15 located near the sixth axial position of the heme. The steroid-binding model suggests that the P450cam's substrate pocket may be conserved in the mammalian P450 and can accommodate a steroid molecule, and that residue 209 appears to be located at the critical site that determines the steroid-substrate specificity of a P450 depending on the type of group at the 11-position of steroid molecule.

Amino Acid Sequence↗
PubMed1993

Lipidized medulloblastoma in adults.

We describe the clinical, imaging, histologic, immunohistochemical, and ultrastructural features as well as the DNA ploidy analysis of two primitive neuroectodermal neoplasms demonstrating prominent cytoplasmic lipid accumulation originating in the posterior fossa of adults. These two tumors most likely exemplify a variant of medulloblastoma with heavily lipidized cells and support the postulated pluripotentiality of primitive neuroectodermal neoplasms. Recognition of this entity as a phenotypic variant of medulloblastoma will militate against diagnostic confusion with other entities that may contain cells with lipoblastic or adipocytic differentiation.

Cerebellar Neoplasms↗