Biomedical subjects

R A Harris

Publications and source records attributed to R A Harris.

At least 163 records · Page 9Linked to original sources

PubMed1997

GABA and the GABAA receptor.

The neurotransmitter gamma-aminobutyric acid (GABA) inhibits the activity of signal-receiving neurons by interacting with the GABAA receptor on these cells. The GABAA receptor is a channel-forming protein that allows the passage of chloride ions into the cells. Excessive GABAA activation may play a role in mediating the sedative effects of alcohol and other sedating and anesthetic agents. For example, alcohol enhances the GABAA-mediated chloride flow into cells and may thereby enhance neuronal inhibition. Alcohol's effects on the GABAA-receptor function likely involve other molecules (e.g., other neurotransmitters and proteins that add phosphate groups to the receptor [i.e., protein kinases]). Several experimental approaches also have suggested that changes in GABAA-receptor function contribute to the tolerance to and dependence on alcohol. Finally, individual differences in the GABA system may play a role in determining a person's susceptibility to developing alcohol dependence.

Alcoholism↗

PubMed1997

Inhibition of 5-hydroxytryptamine type 2A receptor-induced currents by n-alcohols and anesthetics.

5-Hydroxytryptamine type 2A receptors (5-HT2A) are G protein-coupled receptors that increase intracellular Ca2+ concentrations via activation of phospholipase C-beta and elevation of myo-inositol-1,4,5-triphosphate levels. In the central nervous system, these receptors are involved in regulating sleep and alertness. We now report that ethanol inhibited (IC50 = 41 mM) 5-HT2A receptor-induced Ca2+-dependent Cl- currents in Xenopus laevis oocytes. Pharmacologically relevant concentrations of other n-alcohols (propanol to octanol) also inhibited 5-HT responses; however, longer-chain alcohols (decanol, undecanol and dodecanol) had little or no effect. The protein kinase C inhibitor GF109203X and the nonspecific protein kinase inhibitor staurosporine abolished the inhibitory effects of ethanol and octanol on 5-HT2A receptors. GF109203X enhanced 5-HT2A receptor function when administered alone. In addition, the volatile anesthetics halothane and 1-chloro-1,2,2-trifluorocyclobutane decreased 5-HT2A responses in a concentration-dependent manner. The inhibitory effects of the volatile anesthetics were also attenuated in oocytes treated with GF109203X. The intravenous anesthetics propofol, ketamine, pentobarbital and etomidate did not affect 5-HT2A receptor function. The modulation of 5-HT2A receptor-dependent current was also investigated using two novel halogenated compounds that do not produce anesthesia. The nonanesthetic compound 2,3-chloro-octafluorobutane had no effects on 5-HT-induced currents; however, the nonanesthetic compound 1,2-dichlorohexafluorocyclobutane had an inhibitory effect at lower concentrations than the predicted anesthetic concentration. Thus, 5-HT2A receptors are inhibited by alcohols and volatile anesthetics, and these actions are dependent on protein kinase C.

Anesthetics↗

PubMed1997

Mitochondrial alpha-ketoacid dehydrogenase kinases: a new family of protein kinases.

Four mitochondrial protein kinases have been cloned. These proteins represent a new family of protein kinases, related by sequence to the bacterial protein kinases but by function to the eukaryotic serine protein kinases. Arg288 is required for recognition by BCKDK of the phosphorylation site on the E1alpha subunit of the BCKDH complex. BCKDK inhibits the dehydrogenase activity of the BCKDH complex by introducing a negative charge into the active-site pocket of the E1 component. Protein starvation of rats induces an increase in the amount of BCKDK bound to the BCKDH complex. This causes inactivation of the BCKDH complex and conserves branched-chain amino acids for protein synthesis in the protein-starved state. Expression of the different PDK isoenzymes is tissue specific, and the different PDK isoenzymes are unique with respect to kinetic parameters for ATP and ADP and sensitivity to allosteric effectors (NADH, NAD+, coenzyme A, acetyl-CoA, pyruvate, and dichloroacetate). Preliminary experiments indicate that an increased amount of PDK2 protein partly explains the increase in PDK activity that occurs in rat liver in response to chemically induced diabetes.

Amino Acid Sequence↗

PubMed1997

Proton pump inhibitors or histamine-2 receptor antagonists for the prevention of recurrences of erosive reflux esophagitis: a cost-effectiveness analysis.

OBJECTIVES: Erosive esophagitis is a recurring condition for which many patients require preventive therapy. If maintenance therapy must be provided, the most cost-effective treatment strategy should be established. We evaluated the costs and benefits associated with three treatment strategies: 1) maintenance therapy with a proton pump inhibitor (PPI) strategy, 2) maintenance therapy with a high-dose histamine-2 receptor antagonist (H2RA) strategy, and 3) maintenance therapy with a standard-dose H2RA. If patients experience a symptomatic recurrence on the H2RA strategies, they then receive PPI maintenance. METHODS: We used a cost-effectiveness model with a 1-yr time frame; data were obtained from randomized trials of lansoprazole and ranitidine, from case series, and expert opinion. RESULTS: In most situations, the high-dose H2RA strategy is the most costly, yet it is less effective than the PPI strategy. Among the remaining two options, the PPI strategy is more costly and more effective than the standard-dose H2RA strategy, requiring an additional $52-688 per recurrence prevented, depending on drug acquisition costs. The greater the degree to which esophagitis decreases quality of life, the more cost effective is the PPI strategy. For example, with a $50,000 per quality-adjusted life year cost-effectiveness threshold and a market-weighted average of drug costs, the PPI strategy appears cost effective for those patients who report that symptoms of esophagitis cause greater than a 9% decrement in quality of life. CONCLUSIONS: The high-dose H2RA strategy is not preferred in terms of either costs or benefits. The PPI strategy appears cost effective relative to the standard-dose H2RA strategy in the following situations: when patients are significantly bothered by esophagitis and in institutional settings where the difference in drug costs between PPIs and H2RAs is small.

2-Pyridinylmethylsulfinylbenzimidazoles↗

PubMed1996

Primary structure and tissue-specific expression of human beta-hydroxyisobutyryl-coenzyme A hydrolase.

beta-Hydroxyisobutyryl-CoA (HIBYL-CoA) hydrolase is responsible for the specific hydrolysis of HIBYL-CoA, a saline catabolite, as well as the hydrolysis of beta-hydroxypropionyl-CoA, an intermediate in a minor pathway of propionate metabolism. We have obtained the amino acid sequences of several tryptic peptides derived from purified rat liver HIBYL-CoA hydrolase, and the NH2-terminal peptize sequence was matched to the translated sequence of a human expressed sequence tag present in the data base of the IMAGE Consortium (Lawrence Livermore National Laboratory, Livermore, CA). The complete nucleotide sequence and the deduced amino acid sequence showed no similarity to the sequences of well known thioesterases but showed significant homology to the enoyl-CoA hydratase/isomerase enzyme family. The cDNA fragment corresponding to the mature (processed) protein was expressed in Escherichia coli. The purified recombinant enzyme displayed substrate specificity very similar to that of the rat enzyme and was specifically bound by polyclonal antibodies raised against purified rat liver HIBYL-CoA hydrolase. Northern and Western blot analyses with various human tissues indicated predominant expression in liver, heart, and kidney, with discrepancies occurring in the amounts of HIBYL-CoA hydrolase mRNA compared to stably expressed protein in several tissues.

Amino Acid Sequence↗

PubMed1996

Cloning and characterization of PDK4 on 7q21.3 encoding a fourth pyruvate dehydrogenase kinase isoenzyme in human.

Different isoenzymes of pyruvate dehydrogenase kinase (PDK) inhibit the mitochondrial pyruvate dehydrogenase complex by phosphorylation of the E1alpha subunit, thus contributing to the regulation of glucose metabolism. By positional cloning in the 7q21.3-q22.1 region linked with insulin resistance and non-insulin-dependent diabetes mellitus in the Pima Indians, we identified a gene encoding an additional human PDK isoform, as evidenced by its amino acid sequence identity (>65%) with other mammalian PDKs, and confirmed by biochemical analyses of the recombinant protein. We performed detailed comparative analyses of the gene, termed PDK4, in insulin-resistant and insulin-sensitive Pima Indians, and detected five DNA variants with comparable frequencies in both subject groups. Using quantitative reverse transcription polymerase chain reaction, we found that the variants identified in the promoter and 5'-untranslated region did not correlate with differences in mRNA level in skeletal muscle and adipose tissue. We conclude that alterations in PDK4 are unlikely to be the molecular basis underlying the observed linkage at 7q21.3-q22.1 in the Pima Indians. Information about the genomic organization and promoter sequences of PDK4 will be useful in studies of other members of this family of mitochondrial protein kinases that are important for the regulation of glucose metabolism.

Adipose Tissue↗

PubMed1996

Brain lipids that induce sleep are novel modulators of 5-hydroxytrypamine receptors.

Amide derivatives of fatty acids were recently isolated from cerebrospinal fluid of sleep-deprived animals and found to induce sleep in rats. To determine which brain receptors might be sensitive to these novel neuromodulators, we tested them on a range of receptors expressed in Xenopus oocytes. cis-9,10-Octadecenamide (ODA) markedly potentiated the action of 5-hydroxytryptamine (5-HT) on 5-HT2A and 5-HT2C receptors, but this action was not shared by related compounds such as oleic acid and trans-9,10-octacenamide. ODA was active at concentrations as low as 1 nM. The saturated analog, octadecanamide, inhibited rather than potentiated 5-HT2C responses. ODA had either no effect or only weak effects on other receptors, including muscarinic cholinergic, metabotropic glutamate, GABA(A), N-methyl-D-asparate, or alpha-amino-3-hydroxy-5-methyl-4-isoxozolepropionic acid receptors. Modulation of 5-HT2 receptors by ODA and related lipids may represent a novel mechanism for regulation of receptors that activate G proteins and thereby play a role in alertness, sleep, and mood as well as disturbances of these states.

Amides↗

PubMed1996

Modelling cost-effectiveness of Helicobacter pylori screening to prevent gastric cancer: a mandate for clinical trials.

BACKGROUND: It is unknown whether eradication of Helicobacter pylori infection prevents development of gastric adenocarcinoma. To determine whether screening and treatment trials are warranted, we conducted a cost-effectiveness analysis to estimate the costs and benefits associated with screening for H pylori at age 50 and treating those individuals infected with antibiotics. METHODS: We compared two interventions: (1) screen for H pylori and treat those with a positive test, and (2) do not screen and do not treat. Estimates of risks and costs were obtained by review of published reports. Since the efficacy of H pylori therapy in cancer prevention is unknown, we did sensitivity analyses, varying this estimate widely. In our base-case analysis, we assumed that H pylori treatment prevented 30% of attributable gastric cancers. FINDINGS: In the base-case analysis, 11,646,000 persons in the US would be screened and 4,658,400 treated, at a cost of $996 million. Cost-effectiveness was $25,000 per year of life saved. Cost-effectiveness was sensitive to the efficacy of the cancer prevention strategy. At low efficacy rates (< 10%), the screening programme was more expensive (> $75,000 per year of life saved). In a high-risk group such as Japanese-Americans, however, screening and treatment required less than $50,000 per year of life saved, even at 5% treatment efficacy. INTERPRETATION: Screening and treatment for H pylori infection is potentially cost-effective in the prevention of gastric cancer, particularly in high-risk populations. Cancer prevention trials are strongly recommended.

Adenocarcinoma↗

PubMed1996

Structural and mechanistic similarities of 6-phosphogluconate and 3-hydroxyisobutyrate dehydrogenases reveal a new enzyme family, the 3-hydroxyacid dehydrogenases.

Rat 3-hydroxyisobutyrate dehydrogenase exhibits significant amino acid sequence homology with 6-phosphogluconate dehydrogenase, D-phenylserine dehydrogenase from Pseudomonas syringae, and a number of hypothetical proteins encoded by genes of microbial origin. Key residues previously proposed to have roles in substrate binding and catalysis in sheep 6-phosphogluconate dehydrogenase are highly conserved in this entire family of enzymes. Site-directed mutagenesis, chemical modification, and substrate specificity studies were used to compare possible mechanistic similarities of 3-hydroxyisobutyrate dehydrogenase with 6-phosphogluconate dehydrogenase. The data suggest that 3-hydroxyisobutyrate and 6-phosphogluconate dehydrogenases may comprise, in part, a previously unrecognized family of 3-hydroxyacid dehydrogenases.

Alcohol Oxidoreductases↗

PubMed1996

Platelet-derived growth factor induces a long-term inhibition of N-methyl-D-aspartate receptor function.

Platelet-derived growth factor (PDGF) is a multifunctional protein that plays important roles in many tissues, including the mammalian central nervous system. PDGF and PDGF receptors (PDGFRs) are expressed in virtually every region of the central nervous system where they are involved in the development, survival, growth, and differentiation of both neuronal and glial cells. We now report that a brief activation of PDGFRs produced a long-lasting inhibition of N-methyl-D-aspartate (NMDA)-dependent excitatory postsynaptic currents in CA1 pyramidal neurons in rat hippocampal slices. PDGF also inhibited NMDA receptors (NMDA-Rs) in cultured hippocampal neurons by a mechanism that involves a decrease in single channel open probability. Non-NMDA receptor function was not affected by PDGF in hippocampal neurons. Experiments with mutant PDGFRs and chelation of intracellular Ca2+ in Xenopus oocytes indicate that this inhibition depends on a phospholipase C-gamma-induced elevation of intracellular Ca2+ levels. The PDGF-induced inhibition of NMDA-Rs is produced by a mechanism different than the well characterized phenomenon of Ca2+-dependent NMDA-R run down because the effect of PDGF was blocked by the phosphatase inhibitor, calyculin A, and was not affected by the microtubule polymerizing agent, phalloidin. Because elevations of PDGF levels are associated with neurological trauma or disease, we propose that PDGF can exert neuroprotective effects by inhibiting NMDA-R-dependent excitotoxicity.

Analysis of Variance↗

PubMed1996

C-reactive protein binds to a novel ligand on Leishmania donovani and increases uptake into human macrophages.

C-reactive protein (CRP) is a major acute phase protein of man, with serum concentrations increasing dramatically following stimulation of hepatocytes by inflammatory cytokines. However, the role of CRP in inflammation and resistance to infection is still poorly understood. Here, the specificity of CRP binding to the surface of Leishmania donovani, an obligate intracellular parasite of mononuclear phagocytes, is described. CRP is shown to bind to promastigotes at the infectious metacyclic stage of development, at concentrations found in normal human serum. The presence of CRP on the surface of promastigotes substantially increases uptake into human monocyte-derived macrophages. Unusually, CRP does not bind via its characteristic ligand, phosphorylcholine. We show that CRP binds to the lipophosphoglycan (LPG) component of the promastigote cell surface, a molecule implicated in both uptake and survival of these parasites within the macrophage, and also to the major secreted protein of promastigotes, secreted acid phosphatase. Using mAb to LPG with known ligand specificities, we define a novel ligand for CRP as the repeating phosphorylated disaccharide units that form the backbone of LPG.

Acid Phosphatase↗

PubMed1996

Catabolism of isobutyrate by colonocytes.

Isolated colonocytes have more capacity for the oxidation of isobutyrate and alpha-ketoisovalerate than isolated enterocytes. Both enterocytes and colonocytes express high levels of 3-hydroxyisobutyryl-CoA hydrolase, an enzyme activity important in maintaining low intracellular concentrations of methacrylyl-CoA, a common, potentially toxic intermediate in the catabolic pathways of these compounds. In spite of comparable 3-hydroxyisobutyryl-CoA hydrolase activities in both cell types, and much greater amounts of 3-hydroxyisobutyrate dehydrogenase in colonocytes than in enterocytes, only the colonocytes produced 3-hydroxyisobutyrate as an endproduct of alpha-ketoisovalerate and isobutyrate catabolism. Butyrate very effectively inhibits isobutyrate catabolism by colonocytes, most likely by competitively inhibiting activation of isobutyrate to its CoA ester. Oleate also inhibits isobutyrate catabolism, but at a site more distal than butyrate. Starvation of rats for 72 h decreased the capacity of colonocytes for butyrate but not isobutyrate catabolism. We conclude that isobutyrate could function as a carbon source for energy and anapleurosis in colonocytes under conditions of defective butyrate oxidation or low butyrate availability.

Animals↗

PubMed1996

Cost-effectiveness of HIV screening in acute care settings.

BACKGROUND: Although screening inpatients for human immunodeficiency virus (HIV) in acute care hospital settings has been recommended, the cost-effectiveness of screening is not known. OBJECTIVE: To estimate the cost-effectiveness of a voluntary screening program in acute care hospitals and associated clinics. RESULTS: During the first year, an HIV screening program implemented in acute care hospital settings in which the seroprevalence of HIV infection is 1% or more would result in the identification of approximately 110,000 undetected cases of HIV infection. The program would result in expenditures of approximately $171 million for testing and counseling, and expenditures of approximately $2 billion for incremental medical care for the patients identified as having HIV infection during the first year of screening. When the seroprevalence of HIV is 1%, the cost-effectiveness of screening is $47,200 per year of life saved. When the effect of early identification of HIV infection on the patient's quality of life also is considered, screening is less cost-effective. Screening-induced reductions in risk behavior improve the cost-effectiveness of screening by preventing the transmission of HIV.

Acute Disease↗

PubMed1996

Use of excluded volume to increase the heterogeneity of pore size in agarose gels.

When testing theoretical models that quantitatively describe the sieving of macromolecules during gel electrophoresis, investigators have been limited by absence of control of the heterogeneity of the size of pores in the gel. In a recent study performed by electron microscopy of thin sections (G. A. Griess et al., J. Struct. Biol. 1993, III, 39-47), pore size heterogeneity has been increased for agarose gels by a combination of both derivatization and molecular weight reduction of the polysaccharide chains of agarose. In the present study, pore size heterogeneity is increased by a mechanism that appears to have an origin different from the origin of this previously observed increase in heterogeneity: Pore size heterogeneity is increased by addition of a polyethylene glycol (PEG) of high molecular weight (18,500) to molten agarose before gelation. In contrast, the use of a lower molecular weight PEG (either 4,000 or 7,500) causes the formation of micron-sized precipitates within a gelled network of agarose fibers. Thus far, the PEG-induced heterogeneity of pore size occurs primarily in 100-1,000 microns scale zones separated from each other by interzone regions of decreased agarose fiber density. More uniform gels are needed for the study of sieving.

Dose-Response Relationship, Drug↗

PubMed1996

The valine catabolic pathway in human liver: effect of cirrhosis on enzyme activities.

The activities of key enzymes in the valine catabolic pathway--branched-chain aminotransferase, branched-chain alpha-keto acid dehydrogenase complex, methacrylyl (MC)-coenzyme A (CoA) hydratase (crotonase), and 3-hydroxyisobutyryl-CoA (HIB-CoA) hydrolase--were measured in normal and cirrhotic human livers. Unlike rat liver, which does not contain branched-chain aminotransferase, the aminotransferase activity in the normal liver was measurable and is increased somewhat in cirrhosis of the human liver. The total activity of branched-chain alpha-keto acid dehydrogenase complex in the normal human liver was approximately 1% of that in rat liver, and 20% to 30% of the complex was in the active form in both normal and cirrhotic livers. Only the actual activity of the enzyme was significantly decreased by cirrhosis. These results suggest that human liver is less active than rat liver in the catabolism of branched-chain amino and alpha-keto acids. Activities of MC-CoA hydratase and HIB-CoA hydrolase in human liver were very high compared with that of branched-chain alpha-keto acid dehydrogenase complex, suggesting an important role for these enzymes in catabolism of a potentially toxic compound, MC-CoA, formed as an intermediate in the catabolism of valine and isobutyrate. Cirrhosis resulted in a significant decrease in HIB-CoA hydrolase activity but had no effect on the citrate synthase activity, suggesting that the decrease in HIB-CoA hydrolase activity does not reflect a general decrease in mitochondria but that it may contribute to cellular damage that culminates in liver failure.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗

PubMed1996

Repair of transversely incised abdominal wall fascia in a rabbit model.

OBJECTIVE: To compare several commonly used methods of closing transversely incised anterior abdominal wall in order to determine which technique results in the strongest incisional tensile strength. METHODS: Thirty-six rabbits were randomized to receive either interrupted or continuous closure with 0-Vicryl. Within these groups, each animal was randomized to one of three different bite and interval techniques: 1-cm bites/0.5-cm intervals, 1-cm bites/1-cm intervals, and 2-cm bites/1-cm intervals. Each rabbit received three to four transverse abdominal wall incisions of approximately 3-8 cm in length. The incisions were excised en bloc and stored at -70C at postoperative week 1, 2, or 4 in a random fashion. Representative 1-cm strips were harvested from each incision after thawing. The Instron tensiometer was used to determine the maximum intrinsic tensile strength required to disrupt each tissue strip at the incision. Statistical analysis was performed using analysis of variance, two-sample t test, Scheffé multiple comparison, and Kruskal-Wallis test. RESULTS: Two hundred thirty-seven strips were analyzed. The mean maximum tensile strength of all of the interrupted and continuous suture repairs was 48 and 38 lb, respectively (P < .001). The maximum tensile strength for interrupted closures was achieved at week 1 and was similar at week 4. The continuous closure was weakest at week 1 and increased to a maximum value during week 4. There was no difference in maximum tensile strength between the interrupted and continuous closure groups at week 4. There was no significant difference in the maximum tensile strength of the three repair techniques. The mean maximum tensile strength of all specimens was significantly less among those harvested during weeks 1 and 2 compared with week 4 (P = .001). CONCLUSION: In this randomized study, the interrupted closure had a greater maximum tensile strength than the continuous closure in repair of transverse incisions during the first 2 postoperative weeks. Both repair methods were associated with a similar maximum tensile strength at 4 postoperative weeks. Repair techniques using different bite sizes and intervals resulted in similar maximum tensile strengths.

Abdominal Muscles↗

PubMed1996

Measurement of glycine receptor function by radioactive chloride uptake.

The glycine receptor is an important inhibitory receptor for both spinal and supraspinal functions, and mutations in receptor subunits are responsible for neurological disorders in several species, including humans. However, functional measurements of glycine receptors have generally been restricted to electrophysiological analysis of immature, cultured neurons. We developed a 36Cl- flux assay to measure glycine receptor function using membrane vesicles from spinal cord and brainstem of adult mice. The uptake of 36Cl- stimulated by glycine was characterized by a glycine EC50 of 22 microM for the major component and an EC50 of 0.5 microM for a minor component. Strychnine inhibited the glycine-stimulated uptake with an IC50 of 0.4 microM. The uptake was not affected by picrotoxin, bicuculline, or pentobarbital. Glycine-stimulated uptake reached a maximum by 10 s. This technique should prove useful for genetic and pharmacological analysis of the function of glycine receptors.

Animals↗

PubMed1996

Different trypanozoan species possess CD8 dependent lymphocyte triggering factor-like activity.

Trypanosoma brucei brucei (T. b. brucei) release a molecule, trypanosome derived lymphocyte triggering factor (TLTF), which stimulates CD8+ cells to produce cytokines and to proliferate. We now report that T. evansi, T.b. gambiense and T.b. rhodesiense also contain factor(s) with similar activity. Thus, homogenates from these parasite taxa triggered mouse or rat lymphoid tissue of mononuclear cells (MNC) to produce interferon gamma (IFN-gamma) and to proliferate. These responses were dependent on CD8 since the activity was blocked by (a) anti CD8 antibodies, (b) occurred in CD8+ but not in CD8- mice and (c) was recorded in human CD8+ but not in CD4+ enriched peripheral blood mononuclear cells (PBL). The presence of TLTF or TLTF-like molecules in the trypanozoan species was also examined by T.b. brucei directed anti-TLTF Mabs using two Mabs with inhibitory activity and one with stimulatory activity. The lymphocyte triggering activity of T.b. gambiense and T.b. rhodesiense, but not T. evansi, was affected by the anti-TLTF Mabs. We conclude that T. evansi, T.b. rhodesiense and T.b. gambiense similar to T.b. brucei, all possess molecule(s) which CD8 dependently trigger lymphocytes. The latter three, related parasite taxa, share TLTF antibody binding epitopes.

Animals↗