On the possible role of iron-induced free radical peroxidation in neural degeneration in Alzheimer's disease.
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Alzheimer Disease↗
Biomedical subjects
J S Richardson
Publications and source records attributed to J S Richardson.
The kinemage: a tool for scientific communication.
A "kinemage" (kinetic image) is a scientific illustration presented as an interactive computer display. Operations on the displayed kinemage respond within a fraction of a second: the entire image can be rotated in real time, parts of the display can be turned on or off, points can be identified by selecting them, and the change between different forms can be animated. A kinemage is prepared and specified by the author(s) of a journal article, in order to better communicate ideas that depend on three-dimensional information. The kinemages are distributed as plain text files of commented display lists and accompanying explanations. They are viewed and explored in an open-ended way by the reader using a simple graphics program, such as the one described here (called MAGE), which presently runs on Macintosh computers. A utility (called PREKIN) helps authors prepare the kinemages. Kinemages are being implemented under the auspices of the Innovative Technology Fund.
Communication↗
Looking at proteins: representations, folding, packing, and design. Biophysical Society National Lecture, 1992.
Looking at proteins is an active process of interpretation and selection, emphasizing some features and deleting others. Multiple representations are needed, for such purposes as showing motions or conveying both the chain connectivity and the three-dimensional shape simultaneously. In studying and comparing protein structures, ideas are suggested about the determinants of tertiary structure and of folding (e.g., that Greek key beta barrels may fold up two strands at a time). The design and synthesis of new proteins "from scratch" provides a route toward the experimental testing of such ideas. It has also been a fruitful new perspective from which to look at structures, requiring such things as statistics on very narrowly defined structural categories and explicit attention to "negative design" criteria that actively block unwanted alternatives (e.g., reverse topology of a helix bundle, or edge-to-edge aggregation of beta sheets). Recently, the field of protein design has produced a rather unexpected general result: apparently we do indeed know enough to successfully design proteins that fold into approximately correct structures, but not enough to design unique, native-like structures. The degree of order varies considerably, but even the best designed material shows multiple conformations by NMR, more similar to a "molten globule" folding intermediate than to a well ordered native tertiary structure. In response to this conclusion, we are now working on systems that test useful questions with approximate structures (such as determining which factors most influence the choice of helix-bundle topology) and also analyzing how natural proteins achieve unique core conformations (e.g., for side chains on the interior side of a beta sheet, illustrated in the kinemages).
Amino Acid Sequence↗
Animal models of depression reflect changing views on the essence and etiology of depressive disorders in humans.
1. Since it is ethically unacceptable to use human subjects to conduct manipulative experimental hypothesis-testing research on major depression, investigators interested in the development, the substrates or the mechanisms of treatment of depressive disorders have turned to observational models with humans or to interactive models with animals. 2. One of the earliest animal models of depression, the infant/mother separation in monkeys, is based on the Freudian notion of the loss-inward directed anger-depression connection. 3. The hypothesis that depression is caused by stress led to the development of numerous animal models of depression based on the behavioral abnormalities induced in animals, usually rats but occasionally other species, by exposure to prolonged or intense stress. 4. The selective therapeutic efficacy of antidepressant drugs suggested the hypothesis that depression is caused by a neurochemical abnormality that is alleviated by chronic exposure to antidepressants. This hypothesis has been refined to state that depressive disorders are caused by genetically based neurochemical dysregulation of neural activity in the limbic system. 5. Models based on the limbic dysfunction hypothesis could be used to explore the specific neural substrates of depression. At present, the rat with limbic dysfunction induced by olfactory bulbectomy appears to fulfill best the requirements for a model of depression. The future development or discovery of a genetic strain of animals that shows comparable behavioral and neurovegetative deficits and similar selective drug responses to those seen in patients with depressive disorder, would make tremendous contributions to the understanding not only of depression but also of the neurobiology of the limbic system.
Animals↗
Using appropriate nomenclature.
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Carrier Proteins↗
Oxygen free radicals and brain dysfunction.
Oxygen free radicals, any chemical moiety containing an oxygen atom with an unpaired electron in the outer orbital shell, are generated during many normal biochemical reactions in living tissue. The unpaired electron makes these compounds highly reactive and they can initiate disruptive peroxidation reactions with various substrates important to the survival of cells such as proteins, lipids and nucleic acids. A fairly complex defense system has evolved to protect living tissue from free radicals and to minimize the damage they might cause. Neurons are especially vulnerable to free radical attack and impaired defenses or exposure to excess free radicals can lead to neuronal death. Free radicals contribute to neuronal loss in cerebral ischemia and hemorrhage and may be involved in the degeneration of neurons in epilepsy, schizophrenia, tardive dyskinesia, normal aging, Parkinson's Disease and Alzheimer's Disease. The development of drugs that limit or prevent the attack of free radicals on neurons would be an important advance in the treatment of these conditions.
Animals↗
Differential effects of olfactory bulbectomy on beta-adrenoceptors in rat amygdala, hippocampus and cerebral cortex.
Rats were bilaterally olfactory bulbectomized. At 15 days post-lesion, olfactory bulbectomized (OB) rats exhibited significant deficits in the acquisition of passive avoidance learning compared to sham lesioned rats. beta-Adrenoceptor binding in the amygdala, hippocampus and cerebral cortex was assayed with (-)-[125I]iodocyanopindolol (ICYP). Scatchard analyses revealed no difference between OB and sham rats in maximal binding density (Bmax) in any of the three tissues. However, in the OB rats, the affinity of the beta-adrenoceptor for the ligand was significantly increased in the amygdala and hippocampus but not in the cortex. Bulbectomy did not affect the ratio of beta 1- to beta 2-adrenoceptor subtypes in the three brain tissues. In amygdala and hippocampus but not cerebral cortex, bulbectomy resulted in an increase in the proportion and the affinity of the high-affinity beta-adrenoceptor binding sites for isoproterenol. The affinity of the low-affinity sites in the hippocampus was also increased in the OB rats. The results suggest that olfactory bulbectomy causes supersensitivity of the amygdaloid and hippocampal beta-adrenoceptor by increasing the degree of coupling of the receptor with the stimulatory guanine nucleotide binding protein (Gs protein).
Amygdala↗
De novo design, expression, and characterization of Felix: a four-helix bundle protein of native-like sequence.
The protein Felix was designed de novo to fold into an antiparallel four-helix bundle of specific topology. Its sequence of 79 amino acid residues is not homologous to any known protein sequence, but is "native-like" in that it is nonrepetitive and contains 19 of the 20 naturally occurring amino acids. Felix has been expressed from a synthetic gene cloned in Escherichia coli, and the protein has been purified to homogeneity. Physical characterization of the purified protein indicates that Felix (i) is monomeric in solution, (ii) is predominantly alpha-helical, (iii) contains a designed intramolecular disulfide bond linking the first and fourth helices, and (iv) buries its single tryptophan in an apolar environment and probably in close proximity with the disulfide bond. These physical properties rule out several alternative structures and indicate that Felix indeed folds into approximately the designed three-dimensional structure.
Amino Acid Sequence↗
Beta-adrenoceptor and post-receptor components show different rates of desensitization to desipramine.
Both 3-day and 15-day desipramine treatments (10 mg/kg, once daily) significantly reduced beta 1- but not beta 2-adrenoceptor and isoproterenol-stimulated adenylyl cyclase activities in rat cortical, hippocampal and amygdaloid membrane preparations. In contrast, 15-day but not 3-day desipramine treatment resulted in a significant reduction in NaF-, GppNHp- and forskolin-stimulated adenylyl cyclase activity. The results suggest that post-beta-adrenoceptor component desensitization occurs more slowly than receptor downregulation in response to desipramine.
Adenylyl Cyclases↗
Iron-dependent peroxidation of rat brain: a regional study.
Iron has been shown to initiate a variety of free radical reactions in biological systems. The present study examined the in vitro susceptibility of homogenates prepared from different regions of rat brain to iron-induced peroxidation. Among the regions studied, basal thiobarbituric acid-reactive product (TBAR) formation is highest in the cerebellum and amygdala, intermediate in the cortex, hippocampus, and neostratium, and lowest in the hypothalamus, midbrain, and brainstem. In the presence of 200 microM FeCl3, there is a 20-25-fold increase in the net TBAR formation in all regions, with TBAR formation in the cerebellum and amygdala being significantly higher than in the midbrain and brainstem. Time-course and dose-response studies of iron-induced peroxidation showed that the cerebellum and amygdala are the most susceptible regions with respect to concentration of iron and duration of the incubation time, whereas the midbrain and brainstem are the least affected areas. Following low-speed (1,000 g) centrifugation of brain part homogenates, TBAR formation in the supernatant fractions is quite uniform across regions, while the pellet fractions give the same regional variations as the whole homogenates. TBAR formation in both fractions is increased 20-30-fold in the presence of 200 microM iron. Brain tissue TBAR formation induced by 200 microM iron is inhibited by the iron chelator desferrioxamine (IC50 = 600 microM), by Tris buffer pH = 8.0 (2.5 mM Tris gives 50% inhibition by trapping hydroxyl radicals), and by high concentrations of the cyclooxygenase inhibitor indomethacin (IC50 = 1.2 mM).
Animals↗
Autopsy samples of Alzheimer's cortex show increased peroxidation in vitro.
The formation of thiobarbituric acid-reactive products was measured as an index of peroxidation by oxygen free radicals in homogenates of frontal cortex and cerebellum from brains taken at autopsy and verified histologically as being Alzheimer's (n = 6) or normal (n = 6). Compared with controls, basal peroxidation is significantly higher in Alzheimer's cortex, and this difference is also evident in the presence of exogenous iron. Peroxidation in cerebellum and levels of total glutathione, RNA, and DNA in cortex and cerebellum do not differ significantly between Alzheimer's brain and controls. Iron-induced peroxidation in cortex is reduced by the lazaroid U-74500A, with calculated IC50 values that are significantly higher in Alzheimer's samples (10 microM) than in controls (2.5 microM). These observations suggest that cerebral cortex from Alzheimer's patients differs from controls with respect to in vitro peroxidation.
Aged↗
The characterization of beta adrenoceptor subtypes in the rat amygdala and hippocampus.
(-)-[125I]Iodocyanopindolol [-]ICYP), is a ligand with high specific activity and nearly equal affinity for beta 1 and beta 2 adrenoceptors in a variety of tissues. Unfortunately, (-)ICYP also has affinity for 5HT1B serotonin receptors. To get an accurate estimate of beta adrenoceptors in the rat amygdala and hippocampus, (-)ICYP binding studies were done with membranes from these limbic structures in the presence of 10 microM serotonin to prevent the binding of (-)ICYP to serotonin receptors. Under these conditions. (-)ICYP binding to amygdaloid and hippocampus membrane preparations is saturable and reversible. Scatchard analyses revealed in both regions a single class of binding sites with an equilibrium dissociation constant (KD) of 18.5 pM for the amygdala and 19.6 pM for the hippocampus. The hippocampus has a significantly lower density of binding sites (Bmax) than amygdala (51.6 vs 62.3 fmol/mg membrane protein, p less than .05). The two brain regions do not differ with respect to kinetic reactions in that both show comparable slow association and dissociation rates. However, the dissociation reactions do reveal two affinity states for the binding sites in both areas. Detailed competition analyses with beta adrenoceptor subtype selective drugs (ICI-89406 and ICI-118551) show that in both regions about 70% of the beta adrenoceptor population is of the beta 1 subtype with the remainder being beta 2 subtype.
Adenylyl Cyclases↗
Alzheimer's disease: clinical and pathological characteristics.
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Alzheimer Disease↗
Prostacyclin, thromboxane A2, and hypertension.
Prostacyclin and thromboxane A2, products of separate branches of the arachidonic acid cascade, can have opposing effects on kidney function and on the vascular musculature. Prostacyclin acts as a vasodilator while thromboxane A2 has a vasoconstrictor effect and the balance between these two compounds appears to contribute to the homeostatic regulation of normal blood pressure. In the hypertensive state, this balance is disrupted and, at least in animal models of hypertension, there is excessive production of both. The increase in prostacyclin formation may be a reaction to the elevated blood pressure, possibly due to mechanical stimulation of the vascular smooth muscle cells in the blood vessel wall. However, the increase in thromboxane A2 may be more directly involved in the development and maintenance of hypertension. Not only is thromboxane A2 a vasoconstrictor but it can also stimulate the growth and proliferation of vascular smooth muscle cells which may account for the vascular hypertrophy seen in hypertension. Both of these actions would increase total peripheral resistance and contribute to hypertension. Whether prostacyclin and thromboxane A2 are in fact involved as causative agents in essential hypertension must await future research.
Animals↗
Brain benzodiazepine receptors in fathead minnows and the behavioral response to alarm pheromone.
Fathead minnows (Pimephales promelas) exposed to 1 or 10 mg/l chlordiazepoxide showed normal alarm behavior during the presentation of alarm pheromone. Fish exposed to 20 mg/l drug, however, showed little or no behavioral alarm and did not appear sedated. A food extract stimulus presented after alarm pheromone led to a large foraging response by fish exposed to 20 mg/l chlordiazepoxide. Control fish or fish exposed to 1 to 10 mg/l drug showed less tendency to begin foraging. Exposure to 1, 10, or 20 mg/l chlordiazepoxide for 3 hr did not affect whole-brain concentrations of tryptophan, 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, tyrosine, or dopamine. The binding of [3H]diazepam to specific brain receptor sites (KD = 10 nM, estimated Bmax = 3.3 fmol/mg wet weight) could be displaced by chlordiazepoxide (IC50 = 1.6 microM). These results suggest that benzodiazepine receptors in the central nervous system of lower vertebrates may function in ways similar to those in mammals, i.e., in the modulation of behavior in anxiety-like states.
Animals↗
The de novo design of protein structures.
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Drug Design↗
On the use of fibroblasts in tissue culture to study the neurochemistry of brain mechanisms controlling blood pressure.
Fibroblasts grown in tissue culture from skin biopsies taken from the genetic model of spontaneously hypertensive rats (SHR), show a reduction in the accumulation of choline when compared to fibroblasts grown from skin biopsies taken from normotensive Wistar Kyoto rats. Choline uptake by fibroblasts from both strains of rats is sodium dependent but there is no difference between the strains in the effects of sodium depletion. These results suggest that fibroblasts in tissue culture may be a useful source of tissue for analyzing differences between hypertensive and normotensive individuals that are genetically determined rather than due to prolonged exposure to elevated blood pressure. In addition, the fibroblast shares several biochemical characteristics with the neuron and, at least as far as these common characteristics are concerned, appears to be a good model for neurochemical study.
Animals↗
On the neurobiology of depression: research based on heterogeneous diagnostic groups produces heterogeneous biological data.
An improvement in the accuracy and specificity of the criteria for identifying people with major depressive disorder would be of great benefit not only in the diagnosis and treatment of patients with depression, but also in research concerning the biological substrates of the emotions. Unfortunately, attempts at developing a biological diagnostic test for depression based on the analysis of major depressive disorder patients identified on the basis of existing diagnostic criteria have not been successful. Undoubtedly, this is due in part to the complexity of the neurochemistry and neuroanatomy of the emotions. But more importantly, it is due to the broad global nature of the criteria used to identify depressed patients. This results in the biological study of patients who are similar in general terms but who differ in specific behavioral symptoms and underlying neurobiology. A detailed analysis of the behavior of depressed people might reveal subtle differences that could be used to separate patients with depression into more homogeneous subgroups for biological study. This would increase the probability of developing biological tests that would lead to further refinement in the diagnosis of depression and in the selection of the most appropriate therapeutic intervention for a particular patient.
Animals↗