Biomedical subjects

H D Brown

Publications and source records attributed to H D Brown.

At least 19 recordsLinked to original sources

PubMed1992

Mixed function oxidase demethylase and dealkylase activity in an electromagnetic field.

In contrast to the increase in reaction rate of microsomal NADPH-cytochrome-P450 reductase activity resulting from low-level microwave perturbation (reported earlier) transformations involving the entire MFO-pathway were inhibited by a microwave field. Dealkylation of 7-ethoxycoumarin was inhibited 25% and demethylation of p-nitroanisole was inhibited 40% when the reaction was carried forward in a 9.14 GHz CW field. Microsomal preparations from the liver of mature chickens had enzymic characteristics (kinetic constants, inhibitor-response spectrum) for these substrates similar to those reported for rodent and human MFO complex.

7-Alkoxycoumarin O-Dealkylase↗

PubMed1991

Ouabain inhibition of kidney ATPase is altered by 9.14 GHz radiation.

At each of several stabilized temperatures between 7.0 and 43.8 degrees C, increases in dog-kidney, Na(+)-, K(+)-ATPase catalytic activity were usually observed in association with exposure for 5 min to 9.14 GHz CW microwave radiation in a thin tubular reactor. However, at 24.9 degrees C, a 23% decrease occurred. Comparisons of activity of ouabain-inhibited reactions revealed that the efficacy of the cardiac glycoside as an inhibitor of ATPase activity was severely diminished by the microwave field. The ouabain-site control mechanism may be a specific microwave target at this exposure frequency. Experimental results can be interpreted in terms of molecular structural changes or direct energy input. The estimated SAR of energy that was incident on preparations is 20 W/kg.

Animals↗

PubMed1991

EM-field effect upon properties of NADPH-cytochrome P-450 reductase with model substrates.

Artificial substrates, including ferricyanide and dichlorophenol indophenol (IP), are frequently used to model the activity of NADPH-cytochrome P-450 reductase, in the xenobiotic-metabolic pathway catalyzed by the P-450 complex. Here, the two oxidants were compared in a microsomal preparation from chicken liver. Low-energy 9.14 GHz perturbation affected both reactions similarly, though the IP reaction may be more sensitive to extremely low energy levels. The reactions of the two oxidants differed from each other in their response to the prior incubation of the microsomes with carbon monoxide and to the presence of superoxide dismutase. The mechanics of the reduction of ferricyanide and the reduction of IP are not identical and the electron-flow paths may be dissimilar. Microwave effect cannot be attributed a temperature change in the reaction medium; it appears to occur at the level of the electron-flow path across the dual-flavin reductase.

Animals↗

PubMed1990

Use of plasmid analysis to determine the source of bacterial invasion of the urinary tract.

Gram negative colonisation and infection of the urinary tract is a well recognised complication of the neuropathic bladder caused by spinal cord injury (SCI). K. pneumoniae accounts for one third of all urinary tract infections in hospitalised SCI patients. Plasmid analysis has been shown to reliably fingerprint bacterial strains, particularly K. pneumoniae, so that growth from two separate locations in or on the body can be accurately analysed as to migration from a reservoir to a target location. Eighty seven hospitalised SCI patients on intermittent catheterisation for a total of 586 patient-weeks were studied. Twice weekly catheterised urine specimens and once weekly rectal swab cultures were taken from each patient. Thirty seven patients experienced at least one clinically significant (colony count greater than 10,000/mL) urinary tract colonisation caused by K. pneumoniae, representing 66 total colonisations. Further analysis of 31 of these 37 patients revealed: K. pneumoniae in all of their stool cultures (p less than 0.05) and the identical strain of K. pneumoniae in the urine as well as the stool in 72% of the 66 colonisations (p less than 0.05). Analysis of 14 patients without K. pneumoniae urinary colonisations showed absence of faecal K. pneumoniae in 3, and predominant growth in only 4. In 22 of the 37 patients, multiple K. pneumoniae urinary colonisations were noted, representing 27 pairs of colonisation. Fifteen of the pairs were found to be relapsing (caused by two identical bacterial strains), and 12 were recurrent (caused by two different bacterial strains). Thirteen of the 15 relapsing pairs also had identical urine and stool K. pneumonia strains (p less than 0.05). All colonisations were treated with appropriate antibiotics based on culture and sensitivity reports. Fourteen of the 15 relapsing colonisation pairs have identical antibiograms (p less than 0.05), while all 12 of the recurrent colonisation pairs had different antibiograms (p less than 0.05). The differences noted on sensitivity patterns (antibiograms) correlated with differences among strains of K. pneumoniae based upon plasmid analysis. Treatment of bacteriuria did not affect the nature of repeated colonisations regardless of the antibiotic chosen, the route of administration or the duration of treatment.

Adolescent↗

PubMed1990

Gram staining apparatus for space station applications.

A self-contained, portable Gram staining apparatus (GSA) has been developed for use in the microgravity environment on board the Space Station Freedom. Accuracy and reproducibility of this apparatus compared with the conventional Gram staining method were evaluated by using gram-negative and gram-positive controls and different species of bacteria grown in pure cultures. A subsequent study was designed to assess the performance of the GSA with actual specimens. A set of 60 human and environmental specimens was evaluated with the GSA and the conventional Gram staining procedure. Data obtained from these studies indicated that the GSA will provide the Gram staining capability needed for the microgravity environment of space.

Aerospace Medicine↗

PubMed1990

Microwave effect upon chlorpromazine-inhibited kidney ATPase.

Presence of chlorpromazine, a non-active-site inhibitor of Na(+)-K(+)-ATPase catalytic activity, in a reaction system exposed to 9.14 GHz CW radiation, resulted in approximately 23% inhibition. This effect was temperature-independent within the normal range for this protein. A low-level microwave field also inhibited the enzyme catalytic rate. Loci of chlorpromazine inhibition and of low-level microwave inhibition appear to be distinct and non-interactive under the conditions of this study. Use of enzyme reaction systems as models for microwave causation of leukemia and the possible involvement of pharmacological agents, such as ouabain and chlorpromazine, in this process has been considered.

Adenosine Triphosphatases↗

PubMed1988

Bacterial challenge study of a porous carbon percutaneous implant.

Numerous percutaneous devices for power transmission and control to electrically powered, intracorporeal blood pumps have been used for periods ranging from 12 months to 4 yrs; however, consistent and reliable performance has not been achieved, due most frequently to the development of infection and sinus tracts at the percutaneous lead exit site. The present study showed that percutaneous devices fabricated from porous vitreous carbon can function satisfactorily in vivo over extended periods. The implant sites successfully resisted infection by normal flora bacteria for as long as 48 months, although superficial surface colonization and infection did occur after deliberate application of pathogens.

Animals↗

PubMed1988

Electromagnetic-field exposure and cancer.

Electromagnetic fields are a ubiquitous part of man's environment. Natural sources of energy have been present, and possibly have contributed to the processes of the evolution of living forms. In very recent time, however, exploitation of the properties of the electromagnetic spectrum, has added variables in intensity, frequency, modulation frequency, and alterations in contributions of electrical and magnetic components. Biological impact has been little studied and poorly defined. Animal carcinogenesis studies and human epidemiological data indicate that exposure to nonionizing radiation can play a role in cancer causation. Numerous effects at the physiological and biochemical level have been reported; many are of such a nature that a relationship to the causation of neoplastic transformation can rationally be hypothesized. Many bioeffects of electromagnetic fields can be adequately and economically explained in terms of heat effects alone. However, observations of frequency-, pulse form or modulation-, and intensity-specificity as well as effects opposite to that known for temperature-rise, imply direct interaction of radiant energy with biomolecules. The possibility of such direct interaction has been shown in quantum mechanical models.

Animals↗

PubMed1987

Energetics of ligand and inhibitor interactions with acetylcholinesterase.

Acetylcholinesterase (AChE, EC 3.1.1.7) from Electrophorus electricus, purified by affinity chromatography to a specific activity of 7000-10,000 U/mg protein, was studied at 27 degrees C in conduction-type microcalorimeters for the heats of reaction, with the subsite-specific cationic ligands edrophonium and propidium and with the irreversible inhibitor diisopropylfluorophosphate (DFP), in an ion-free aqueous medium. Edrophonium and propidium, each at 0.5 x 10(-5) M, yielded reaction heats of +3.2 and -1.5 kcal/mol (1 kcal = 4.184 J) respectively, with 1.3 x 10(-5) M AChE active sites. DFP (1.3 x 10(-5) M) reacted exothermically yielding -0.5 kcal/mol at stoichiometric level with AchE active sites. Circular dichroic spectra showed that a ternary complex of AChE (6.5 x 10(-7) M active sites) and the two ligands (each at 1 x 10(-3) M) in 1 mM Tris-HCl buffer (pH 8.0) had a positive Cotton effect at 235 nm. Neither DFP nor phosphoric acid 2,2-dichloroethenyl dimethyl ester (DDVP) caused any appreciable change. DFP-AChE, however, behaved like a normal enzyme in showing a positive Cotton effect in association with the two ligands. DDVP-AChE showed an increase in negative ellipticity at 287 nm in the presence of the two ligands. Another cationic ligand, d-tubocurarine, when present together with edrophonium, increased negative ellipticity at 302 nm and blue-shifted a 265-nm peak of the normal AChE. DFP interactions with AChE appear to be energetically different from those of edrophonium, the latter of which is believed to associate with the acetylcholine-binding subsite.

Acetylcholinesterase↗

PubMed1986

Substrate-ligand interactions with acetylcholinesterase and energetics of binding.

Ester hydrolysis by acetylcholinesterase (from electric eel, Electrophorus electricus) increased in the presence of low concentrations (ca 10(-7) M) of edrophonium, propidium, d-tubocurarine, gallamine, decamethonium or bis-N-methylacridinium, and decreased at higher concentrations. The overall sensitivity of the substrates to inhibition by the ligands was acetylcholine (Ach) greater than phenylacetate (PA) greater than indophenylacetate (IPA). Complete (saturable) inhibition was unattainable with edrophonium or gallamine for IPA and, to a lesser degree, with propidium for PA. Reaction heats between the enzyme and the ligands (edrophonium, propidium and decamethonium) measured directly in a microcalorimeter revealed binding sites that are different from each other in their interaction energetics.

Acetylcholinesterase↗

PubMed1985

Enthalpy of acetylcholine hydrolysis by acetylcholinesterase.

Direct microcalorimetric measurements were made of the reaction between acetylcholine chloride and acetylcholinesterase (EC 3.1.1.7) that was extracted from electric eel (Electrophorus electricus) and purified by affinity chromatography. Tris-HCl, sodium phosphate and potassium phosphate were used as buffers and sources of ions for the reaction. At pH 7.2 and in 0.1-0.2 M phosphate buffer, the delta H for acetylcholine hydrolysis was found to be -0.107 kcal/mol (under buffered conditions) and -0.931 kcal/mol under unbuffered conditions (water). At pH 8.0 in 0.1 M Tris-HCl buffer, values greater than -2.5 kcal/mol were obtained, with the highest value of -9.2 kcal/mol being seen with bovine erythrocyte acetylcholinesterase. Tris-HCl buffer at 4 X 10(-2) M enhanced the reaction velocity by 51.2% over that of 4 X 10(-3) M buffer. Enzyme purity, pH and ionic milieu of reaction mixture, and substrate concentration affected the measured delta H value.

Acetylcholine↗

PubMed1985

Clinical and biochemical effects of aflatoxin in feed ration of chicks.

Aflatoxin carcinogenesis appears to relate to multiple factors. This includes bulky adduct formation at DNA guanine N-7. The process also requires more extensive physiological degradation, possibly by the toxin alone as the active principle, but in instances also involving other assaults (e.g., hepatitis B virus). Since aflatoxin carcinogenesis involves complex effects, we have undertaken to define the range of influence of this common food contaminant upon a susceptible model, the broiler-type chick. Aflatoxicosis in two treated groups was indicated by jaundice, coagulopathy, dehydration of combs and shanks, retardation of body weight, and decrease in bursa weight. Blood clotting time, hemoglobin content, erythrocyte and packed-cell volume were affected. Hepatocytes were swollen and had undergone fatty degeneration. Bile duct hyperplasia was evident. Total serum protein, alkaline phosphatase, creatine, lactate dehydrogenase, serum glutamic oxalacetic transaminase and glutamyl transpeptidase were similarly abnormal in birds receiving the contaminated (0.5 and 2.5 micrograms/g aflatoxin B1) feed rations. The aflatoxin B1 and its metabolites were isolated by HPLC from chick serum, liver and muscle.

Aflatoxin B1↗

PubMed1984

Information requirements for chemists in the pharmaceutical industry.

The principal information needs of chemists in the pharmaceutical industry center around a substance, methods used for its characterization, its reactions, its physicochemical and biomedical properties, and its metabolic fate in biological media. Novelty searches for a specific chemical are critical because of the need for patent protection for product candidates. Chemical relatives are important, necessitating substructure searching. Therapeutic neighbors may give insight into its biological mode of action. The phases of drug discovery and development are used to indicate the diversity of the information needs of chemists and to emphasize the dual process of generation and use of information.

Animals↗

PubMed1983

Microcalorimetric determination of binding sites of acetylcholinesterase.

Acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7), phosphorylated with dichlorvos, showed relatively more reactivity toward the substrate indophenyl acetate than the enzyme that was carbamylated with carbaryl. When the anionic subsite of the phosphorylated or carbamylated enzyme was alkylated with an aziridinium ion, the reaction velocity toward indophenyl acetate increased in the phosphorylated enzyme but not in the carbamylated enzyme. The organophosphate binding site--which appears to be different from that of carbamate or indophenyl acetate, but probably the same as that of acetylcholine -- is apparently alkylated in such a way that the modified (phosphorylated) enzyme is better-fit for the binding (and hydrolysis) of indophenyl acetate. The modified conformation presumably results in the release of the phosphoryl group from the esteratic subsite.

Acetylcholinesterase↗

PubMed1983

Exposure of professional pest control operator to dichlorvos (DDVP) and residue on house structures.

Each of the 13 human volunteers carried out a 1-day urban pest control work in 4 homes using 10-14 aerosol cans (230-330 g dichlorvos (DDVP] and 18-22 pints of 0.5% emulsion spray (40-50 g DDVP). Average residue levels of 75.85 micrograms/ft2, 40.9 micrograms/ft2 were found on the applicator's back, chest and respirator filter, respectively. Residue on the house structure was 219.7 micrograms/ft2 on the first day, which fell to 50.9 micrograms/ft2 by the end of 5 days. Blood and urine analyses revealed no changes in various clinical parameters, including serum cholinesterase levels.

Acetylcholinesterase↗

PubMed1983

A pharmaceutical information manager's viewpoint on R & D information resource management.

An overview of the environment (from my perspective) related to information resource management in pharmaceutical R & D has been presented. Some notions of organizational preference (functional), employee selection (chemist turned information scientist), automation (user friendly, cost effective), and the value of project teams (information transfer) have been noted. Difficulties associated with keeping our innovative tools sharp were observed. Finally, we noted that our bottom line--productivity--should first consider what is useful (effectiveness) and then learn how to do it well--efficiency. Success in the management of information resources depends on the proactive delivery of information packets which find their way into problem solving and decision support for scientists or line managers.

Chemistry, Pharmaceutical↗

PubMed1983

Energetics of the oxidase activity of NADPH-cytochrome P-450 reductase.

Oxidase activity of rat liver microsomes has been evaluated microcalorimetrically. delta H for the oxidation of reduced nicotine adenine dinucleotide phosphate was measured to be -39.33 (uncertainty 2.18) kcal/mol. The contribution of peroxide reduction and NADPH ring opening heats to this value have been considered. Calorimetric assay of the hydroxylase activity of the P-450-reductase-hydroxylase enzymatic complex has been demonstrated using the organocarbamate, Isolan (1-isopropyl-3-methyl-5-pyrazolyl dimethylcarbamate), as substrate.

Animals↗

PubMed1978

Cholesterol oxidase: thermochemical studies and the influence of hydroorganic solvents on enzyme activity.

Thermal and binary cosolvent studies of the cholesterol oxidase (cholesterol: oxygen oxidoreductase, EC 1.1.3.6) reaction have been carried out using batch microcalorimetry and ultraviolet spectrophotometry respectively. Heat conduction measurements are shown to provide the basis for a serum cholesterol assay yielding results comparable to conventional automated clinical assay. The enthalpy of the reaction for cholesterol oxidation, measured with different sources of the enzyme in the presence and absence of catalase is -113 +/- 7.2 mJ/mumol. The value is agreement with calculated estimates based on bond energies, enthalpies of formation and trigonal additivity contribution calculations. From this heat of reaction the deltaHf0 of cholestenone (c) is calculated to be -490 kJ . mol-1. No evidence for the reverse reaction could be adduced. Enzyme activation with detergent (Surfal) is attributed to the formation of mixed micelles of cholesterol with detergent molecules. The detergent concentration at which the enzyme is half activated corresponds to the critical micelle concentration of Surfal. The enhanced enzyme activity found when ethanol, acetonitrile and dioxane were examined as binary cosolvents with water is ascribed to a conformational change in the enzyme mediated through the altered structuredness of water. This cosolvent effect is abolished in the presence of 0.18% Surfal due to the formation of inverted mixed micelles of detergent with cholesterol.

3-Hydroxysteroid Dehydrogenases↗