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D G Walker

Publications and source records attributed to D G Walker.

174 records · Page 10Linked to original sources
PubMedDate not supplied

Expression and regulation of complement C1q by human THP-1-derived macrophages.

The regulation of C1q expression was examined in the human monocytic cell line THP-1. Since these cells can be differentiated into cells with macrophage properties and induced to express C1q, they were used as models for mature human monocyte/macrophages and indirectly microglia. Interferon-gamma (IFN-gamma) and the anti-inflammatory steroid agents dexamethasone and prednisone were powerful stimulators of C1q production, alone or in combination. Interleukin-6 (IL-6) and lipopolysaccharide (LPS) also had significant stimulatory activity. Phorbol myristate acetate, a protein kinase C activator, reduced C1q expression. Four additional classes of pharmacological agents were tested for their effect on C1q secretion. Tacrine, but not indomethacin, cimetidine, or propentofylline, showed activity in inhibiting C1q secretion by IFN-gamma treated THP-1-derived macrophages.

Brain↗
PubMedDate not supplied

Characterization of glial cultures from rapid autopsies of Alzheimer's and control patients.

We have developed isolated and mixed cultures of microglia, astrocytes, and oligodendrocytes from rapid (mean of 2 h 55 min) autopsies of nondemented elderly patients and patients with Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Cultures were derived from both the corpus callosum (CC) and superior frontal gyrus (SFG). Cultured microglia phagocytosed latex beads, were reactive for Dil-acetylated low density lipoprotein, were immunoreactive for CD68 and major histocompatibility complex II markers, and were not immunoreactive for fibroblast, astrocyte, or oligodendrocyte markers. Cultured astrocytes included fibrous and protoplasmic types, were immunoreactive for GFAP, and were not immunoreactive for fibroblast, microglia, or oligodendrocyte markers. Cultured oligodendrocytes were poorly adherent, were slow to develop, were immunoreactive for galactocerebroside, and were not immunoreactive for fibroblast, microglia, or astrocyte markers. Because they are readily manipulated under controlled experimental conditions, and because they permit immediate access to individual cells and sets of cells from patients who have actually suffered the disease, these cultures may provide an important new tool for unravelling the etiology and pathogenesis of human CNS disorders.

Aged↗
PubMedDate not supplied

Gene expression profiling of amyloid beta peptide-stimulated human post-mortem brain microglia.

Activation of microglia is a central part of the chronic inflammatory processes in Alzheimer's disease (AD). In the brains of AD patients, activated microglia are associated with amyloid beta (Abeta) peptide plaques. A number of previous studies have shown that aggregated synthetic Abeta peptide activates cultured microglia to produce a range inflammatory products. The full extent of the inflammatory response still remains to be determined. In this study, gene array technology was employed to investigate in a more extensive manner the consequences of microglial activation by Abeta peptide. RNA was prepared from pooled samples of cortical human microglia isolated from post-mortem cases and incubated with a low dose (2.5 microM) of Abeta1-42 (or peptide solvent) for 24 h. This material was used to prepare cDNA probes, which were used to detect the differential pattern of expressed genes on a 1,176 Clontech membrane gene array. Results obtained showed that 104 genes were either upregulated or downregulated by 1.67 fold or greater. The most highly induced genes belonged to the chemokine family with interleukin-8 (IL-8) expression being increased by 11.7 fold. Interestingly, many of the highly induced genes had been identified as being responsive to activation by the transcription factor NF-kappaB. A number of genes were downregulated. Thymosin beta, prothymosin alpha and parathymosin, all belonging to the same gene family, were downregulated. To validate these semi-quantitative results, the expression of intercellular adhesion molecule-1 (ICAM-1) and rhoB were measured by RT-PCR in samples of cDNA derived from Abeta and control stimulated human cortical microglia. These results confirm the usefulness of the gene array approach for studying Abeta-mediated inflammatory processes.

Alzheimer Disease↗
PubMedDate not supplied

Modeling microglial activation in Alzheimer's disease with human postmortem microglial cultures.

Alzheimer's disease (AD) is a uniquely human disorder. Despite intense research, the lack of availability of model systems has hindered AD studies though in recent years transgenic mouse models have been produced, which develop AD-like amyloid beta peptide (Abeta) plaques. For the study of inflammatory changes in AD brains, these transgenic mice may have limitations due to differences in the innate immune system of humans and rodents. Many studies of inflammatory processes in AD have focused on the role of activated microglia. Over the last 8 years, our research has focused on the properties of human microglia cultured from brain tissues of AD and non-demented (ND) individuals. As these are the cells observed to be activated in AD tissues, they represent a useful system for modeling the inflammatory components of AD. In this review, we summarize data by our group and others on the use of microglia for AD-related inflammatory research, with emphasis on results using human postmortem brain microglia. A range of products have been shown to be produced by human postmortem microglia, both constitutively and in response to treatment with Abeta, including proinflammatory cytokines such as interleukin (IL)-1beta, IL-6, tumor necrosis factor (TNF) alpha, and macrophage colony stimulating factor (M-CSF), along with complement proteins, especially C1q, superoxide radicals and neurotoxic factors. In our studies, we have demonstrated that there was a significant difference between AD and ND microglia in terms of their secretion of M-CSF and C1q. We also discuss the role of putative Abeta microglial receptors, particular recent data showing a role for the receptor for advanced glycation endproducts (RAGE) in mediating the responses of human microglia to Abeta. Finally, our studies on the use of an Abeta spot paradigm to model microglia interactions with plaques demonstrated that many of the features of AD inflammation can be modeled with postmortem brain derived microglia.

Alzheimer Disease↗
PubMedDate not supplied

Molecular and cellular characterization of the membrane attack complex, C5b-9, in Alzheimer's disease.

The membrane attack complex, C5b-9, is of considerable importance in many inflammatory reactions. It is the terminal, cytolytic component of both classical and alternative pathway activation, and its presence presupposes other potentially destructive complement constituents, including anaphylotoxins and opsonins. We have characterized C5b-9 and its C9 constituent in the Alzheimer's disease (AD) and nondemented elderly (ND) brain using immunohistochemistry at the light and electron microscopic levels, Western blot analysis, and the reverse transcriptase polymerase chain reaction. We have also conducted in vitro ELISA assays of amyloid beta-peptide-stimulated SC5b-9 production. C5b-9 is abundantly present in Alzheimer's disease cortex, associated with neurofibrillary tangle containing neurons, dystrophic neurites within neuritic plaques, and neuropil threads, but is weakly detected, if at all, in nondemented elderly cortex under the same conditions. Staining of Alzheimer's disease sections is abolished both by deletion of primary antibody or preabsorption with purified SC5b-9.

Alzheimer Disease↗
PubMedDate not supplied

Correlation of the expression level of C1q mRNA and the number of C1q-positive plaques in the Alzheimer Disease temporal cortex. analysis of C1q mrna and its protein using adjacent or nearby sections.

We compared the expression level of C1q mRNA and the number of C1q-positive plaques in adjacent or nearby brain sections from Alzheimer disease (AD) and control cases. Small blocks of temporal cortex were fixed with 4% paraformaldehyde for 2 days at 4 degrees C. After cryoprotection with solutions containing 10-20% glycerol and 2% dimethylsulfoxide, 40-microm sections were cut from the tissue blocks. A section from each case was stained by immunohistochemistry using a C1q antibody, while RNA was purified from adjacent or nearby sections using a combination of proteinase K pretreatment followed by extraction using Trizol reagent. The expression of C1q B chain mRNA was analyzed in these samples by the reverse-transcription polymerase chain reaction (RT-PCR). The intensities of the PCR products were measured by an image analyzer. The expression of C1q B chain mRNA was significantly more abundant in AD than in control cases (p < 0.05). Immunohistochemical analysis showed that C1q protein was localized in senile plaques in the AD brain. The number of C1q-positive plaques correlated with the expression level of C1q gene (p < 0.05). The present results suggest that C1q protein in senile plaques originates is endogenously produced in the AD brain.

Aged↗
PubMedDate not supplied

Survival after severe envenomation by the blue-ringed octopus (Hapalochlaena maculosa).

I report two cases of life-endangering respiratory failure after envenomation by a blue-ringed octopus (Hapalochlaena maculosa). Early and efficient support of respiratory function is vital in such cases. Cardiac asystole occurred in one patient. Both patients recovered completely after the vigorous application of routine resuscitation techniques.

Adolescent↗
PubMedDate not supplied

Snorkelling deaths in Australia, 1987-1996.

OBJECTIVE: To examine the causes and circumstances of snorkelling deaths in Australia from 1987 to 1996. DESIGN: Retrospective case extraction. CASES AND DATA SOURCES: 60 snorkelling deaths extracted from an ongoing diving fatality survey and from coroners' reports. Further details were obtained from police reports, diving industry (incorporating commercial operators, relevant government departments and instructors' organisations) inquiries and coronal inquests. MAIN OUTCOME MEASURES: Cause of death (determined by the authors from information obtained and from detailed autopsy findings) and the circumstances surrounding death. RESULTS: 15 of the 60 snorkellers who died were female. The three major causes of death were drowning (27 cases), cardiac events (18) and hypoxia with breath-holding after hyperventilation and/or during ascent producing unconsciousness then drowning (12). Overseas tourists were notable among those who drowned, while middle-aged men dominated the group who died of cardiac events (mostly on the surface). Those who died of breath-holding hypoxia were all young, Australian and male. The use of "buddy" diving was infrequent overall, and many of those who drowned or suffered cardiac events were not wearing flippers to aid propulsion. Adverse environmental conditions were implicated in 14 deaths. CONCLUSIONS: Hyperventilation to increase breath-hold time is a dangerous practice which should be discouraged. Safety measures, such as the use of flippers for propulsion and employment of the "buddy" system, should be encouraged, and made mandatory in commercial diving operations.

Adult↗
PubMedDate not supplied

The disposition of 2-cyano-1-methyl 3-(4-(4-methyl-6-oxo-1,4,5,6-tetrahydro-pyridazin-3-yl)phenyl)guanidine in animals.

2-Cyano-1-methyl 3-(4-(4-methyl-6-oxo-1,4,5,6-tetrahydro-pyridazin-3-yl)phenyl)guan idine (SK&F 94836), a new positive inotrope/vasodilator, is being evaluated for the treatment of congestive heart failure. The absorption, metabolism, and disposition of the compound have been investigated in the rat, mouse, and dog. SK&F 94836 was rapidly absorbed, widely distributed, and rapidly and completely excreted primarily via the urine. There was no evidence of metabolism of the compound in any of the species studied. The compound showed minimal interaction with cytochrome P-450. The compound contains a chiral center. The enantiomers have been shown not to interconvert in either rat or dog. The serum protein binding was low in all species, including humans, and exhibited no stereoselectivity. Studies conducted in rat and dog using constant rate co-infusion of racemic SK&F 94836 and radiolabeled inulin have demonstrated that SK&F 94836 is eliminated by active tubular secretion.

Animals↗