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Biomedical subjects

J B Johnson

Publications and source records attributed to J B Johnson.

At least 19 recordsLinked to original sources
PubMed1992

The effect of food on the absorption of methotrexate sodium tablets in healthy volunteers.

OBJECTIVE: To examine the effect of food on the absorption and bioavailability of low-dose orally administered methotrexate sodium tablets. METHODS: In this randomized, 2-way crossover study, a 7.5-mg dose of methotrexate (three 2.5-mg tablets) was administered to 12 healthy male volunteers after an overnight fast or within 10 minutes of consuming a high fat-content breakfast. Serum methotrexate concentrations over the next 24 hours were used to determine the area under the concentration-time curve (AUC), the maximum concentration, the time to maximum concentration (tmax), and the serum half-life for each phase. RESULTS: Food delayed the tmax by approximately 30 minutes, but the extent of absorption, as measured by the AUC, for both phases was similar. CONCLUSION: These results demonstrate that the bioavailability of low-dose orally administered methotrexate sodium tablets is not influenced by food.

Administration, Oral↗
PubMed1992

Stomatal patterning in Tradescantia: an evaluation of the cell lineage theory.

The cell lineage theory, which explains stomatal patterning in monocot leaves as a consequence of orderly divisions, was studied in Tradescantia. Data were collected to test the theory at three levels of organization: the individual stoma; stomata distributed in one dimension, in linear fashion along cell files; and stomata apportioned in two dimensions, across the length and breadth of the leaf. In an attempt to watch the patterning process through regeneration, stomata in all visible stages of development were laser ablated. The results showed that the formation of stomatal initials was highly regular, and measurements of stomatal frequency and spacing showed that pattern was determined near the basal meristem when the stomatal initials arose. Following the origin of initials, the pattern was not readjusted by division of epidermal cells. Stomatal initials were not committed when first present and a small percentage of them arrested. The arrested cells, unlike stomata, were consistently positioned in cell files midway between a developed pair of stomata. At the one-dimensional level of pattern, stomata in longitudinal files were separated by a variable number of epidermal cells and the frequency of these separations was not random. The sequential spacing of stomata also was not random, and stomata separated by single epidermal cells were grouped into more short and long series than expected by chance. The stomatal pattern across the width of the leaf resulted from cell files free of stomata which alternated with cell files containing stomata, but not with a recurring periodicity. Files lacking stomata were found only over longitudinal vascular bundles. Laser ablations of developing stomata did not disrupt the pattern in nearby cells or result in stomatal regeneration. We conclude that the cell lineage theory explains pattern as an individual stomatal initial arises from its immediate precursor and satisfactorily accounts for the minimum spacing of stomata in a cell file, i.e., stoma-epidermal cell-stoma. However, the theory does not explain the collective stomatal pattern along the cell files, at the one-dimensional level of patterning. Nor does the theory account for the for the two-dimensional distribution of stomata in which regions devoid of stomata alternate with regions enriched with stomata, but not in a highly regular nor haphazard manner. We suggest that the grouping of epidermal cells and stomata separated by single epidermal cells in cell files may result from cell lineages at a specific position in the cell cycle as they traverse the zone where stomatal initials form.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Division↗
PubMed1992

The determination and prevention of cytotoxic effects induced in human lymphocytes by the alkylating agent 2,2'-dichlorodiethyl sulfide (sulfur mustard, HD).

2,2'-Dichlorodiethyl sulfide (sulfur mustard, HD, 1,1'-thio-bis[2-chloroethane]) is a potent vesicant which can cause severe lesions to skin, lung, and eyes. There is no convenient in vitro or in vivo method(s) to objectively measure the damage induced by HD; therefore, a simple in vitro method was developed using human peripheral lymphocytes to study HD-induced cytotoxicity. The cytotoxicity of HD was measured using dye exclusion as an indicator of human lymphocyte viability. Exposure to HD resulted in both a time- and a concentration-dependent cytotoxic effect on human lymphocytes. Using this in vitro assay, the effectiveness of various therapeutics (niacin, niacinamide, and 3-aminobenzamide) in preventing HD-induced cytotoxicity was studied. Niacinamide and 3-aminobenzamide prevented the cytotoxic effects of HD for up to 2 days.

Benzamides↗
PubMed1992

Determination of rate distributions from kinetic experiments.

Rate processes in proteins are often not adequately described by simple exponential kinetics. Instead of modeling the kinetics in the time domain, it can be advantageous to perform a numerical inversion leading to a rate distribution function f(lambda). The features observed in f(lambda) (number, positions, and shapes of peaks) can then be interpreted. We discuss different numerical techniques for obtaining rate distribution functions, with special emphasis on the maximum entropy method. Examples are given for the application of these techniques to flash photolysis data of heme proteins.

Carbon Monoxide↗
PubMed1992

Bioequivalence of verapamil hydrochloride extended-release pellet-filled capsules when opened and sprinkled on food and when swallowed intact.

A study was performed to determine whether verapamil hydrochloride administered in extended-release pellet-filled capsules is bioequivalent to the same formulation administered by sprinkling the contents of the capsules onto food. Thirty-two healthy subjects participated in the randomized, two-way crossover study. In treatment A, the subjects swallowed the contents of a verapamil hydrochloride extended-release pellet-filled capsule, 240 mg, that had been sprinkled on applesauce. In treatment B, the subjects swallowed the same type of capsule intact. Blood samples were drawn at baseline, every hour for 10 hours, and at 12, 15, 24, 30, 36, and 48 hours after each dose administration. The plasma was analyzed for verapamil and norverapamil by high-performance liquid chromatography. The following calculations were performed: AUC0-48, AUC0-infinity, Cmax, tmax, and k. Results for the two treatments were compared by analysis of variance. There were no significant differences between the AUC0-48, AUC0-infinity, Cmax, tmax, and k for the two methods of dose administration. For verapamil the differences for all variables were less than 5%, and for norverapamil the differences were less than 4% for all variables except tmax (9.5%). The 90% confidence intervals were within acceptable limits for all variables except the norverapamil tmax comparison. Sprinkling the contents of extended-release pellet-filled capsules onto food provides verapamil hydrochloride that is bioequivalent to that obtained from the intact capsules.

Administration, Oral↗
PubMed1991

Ligand binding to heme proteins: connection between dynamics and function.

Ligand binding to heme proteins is studied by using flash photolysis over wide ranges in time (100 ns-1 ks) and temperature (10-320 K). Below about 200 K in 75% glycerol/water solvent, ligand rebinding occurs from the heme pocket and is nonexponential in time. The kinetics is explained by a distribution, g(H), of the enthalpic barrier of height H between the pocket and the bound state. Above 170 K rebinding slows markedly. Previously we interpreted the slowing as a "matrix process" resulting from the ligand entering the protein matrix before rebinding. Experiments on band III, an inhomogeneously broadened charge-transfer band near 760 nm (approximately 13,000 cm-1) in the photolyzed state (Mb*) of (carbonmonoxy)myoglobin (MbCO), force us to reinterpret the data. Kinetic hole-burning measurements on band III in Mb* establish a relation between the position of a homogeneous component of band III and the barrier H. Since band III is red-shifted by 116 cm-1 in Mb* compared with Mb, the relation implies that the barrier in relaxed Mb is 12 kJ/mol higher than in Mb*. The slowing of the rebinding kinetics above 170 K hence is caused by the relaxation Mb*----Mb, as suggested by Agmon and Hopfield [(1983) J. Chem. Phys. 79, 2042-2053]. This conclusion is supported by a fit to the rebinding data between 160 and 290 K which indicates that the entire distribution g(H) shifts. Above about 200 K, equilibrium fluctuations among conformational substates open pathways for the ligands through the protein matrix and also narrow the rate distribution. The protein relaxations and fluctuations are nonexponential in time and non-Arrhenius in temperature, suggesting a collective nature for these protein motions. The relaxation Mb*----Mb is essentially independent of the solvent viscosity, implying that this motion involves internal parts of the protein. The protein fluctuations responsible for the opening of the pathways, however, depend strongly on the solvent viscosity, suggesting that a large part of the protein participates. While the detailed studies concern MbCO, similar data have been obtained for MbO2 and CO binding to the beta chains of human hemoglobin and hemoglobin Zürich. The results show that protein dynamics is essential for protein function and that the association coefficient for binding from the solvent at physiological temperatures in all these heme proteins is governed by the barrier at the heme.

Binding Sites↗
PubMed1990

Methods for predicting migration to packaged pharmaceuticals.

The compatibility of the pharmaceutical product with packaging materials is an important parameter which must be evaluated during the product development process. This paper discusses the possibility that pertinent FDA methodology can be modified in a more efficient way using currently available analytical techniques. Several studies on potential migrants from packaging materials, such as heat-seal adhesives, amber polyethylene terephthalate (PET) containers, and rubber gaskets of aerosol valves, are presented to show that commonly encountered questions with regard to packaging materials used during product stability studies can also be answered in the same way.

Chemical Phenomena↗
PubMed1990

Determination of potential migrants from commercial amber polyethylene terephthalate bottle wall.

Potential migrants were isolated from commercial polyethylene terephthalate (PET) bottles using Soxhlet extraction. The concentrated extract was then subjected to GC/MS analysis. A total of 19 migrants has been identified. The majority of compounds appeared to be intermediate reaction products or residual monomers of their dehydration and transesterification products. Several processing aids such as fatty acids and commonly used plasticizers were also identified. The amount of seven compounds present in the major portion of exhaustive extract of the PET bottle wall ranged from 800 micrograms/g polymer to as low as 0.6 microgram/g.

Drug Packaging↗
PubMed1987

Rebinding and relaxation in the myoglobin pocket.

The infrared stretching bands of carboxymyoglobin (MbCO) and the rebinding of CO to Mb after photodissociation have been studied in the temperature range 10-300 K in a variety of solvents. Four stretching bands imply that MbCO can exist in four substates, A0-A3. The temperature dependences of the intensities of the four bands yield the relative binding enthalpies and and entropies. The integrated absorbances and pH dependences of the bands permit identification of the substates with the conformations observed in the X-ray data (Kuriyan et al., J. Mol. Biol. 192 (1986) 133). At low pH, A0 is hydrogen-bonded to His E7. The substates A0-A3 interconvert above about 180 K in a 75% glycerol/water solvent and above 270 K in buffered water. No major interconversion is seen at any temperature if MbCO is embedded in a solid polyvinyl alcohol matrix. The dependence of the transition on solvent characteristics is explained as a slaved glass transition. After photodissociation at low temperature the CO is in the heme pocket B. The resulting CO stretching bands which are identified as B substates are blue-shifted from those of the A substates. At 40 K, rebinding after flash photolysis has been studied in the Soret, the near-infrared, and the integrated A and B substates. All data lie on the same rebinding curve and demonstrate that rebinding is nonexponential in time from at least 100 ns to 100 ks. No evidence for discrete exponentials is found. Flash photolysis with monitoring in the infrared region shows four different pathways within the pocket B to the bound substates Ai. Rebinding in each of the four pathways B----A is nonexponential in time to at least 10 ks and the four pathways have different kinetics below 180 K. From the time and temperature dependence of the rebinding, activation enthalpy distributions g(HBA) and preexponentials ABA are extracted. No pumping from one A substate to another, or one B substate to another, is observed below the transition temperature of about 180 K. If MbCO is exposed to intense white light for 10-10(3) s before being fully photolyzed by a laser flash, the amplitude of the long-lived states increases. The effect is explained in terms of a hierarchy of substates and substate symmetry breaking. The characteristics of the CO stretching bands and of the rebinding processes in the heme pocket depend strongly on the external parameters of solvent, pH and pressure. This sensitivity suggests possible control mechanisms for protein reactions.

Carbon Monoxide↗
PubMed1985

Sulfur mustard lowers nicotinamide adenine dinucleotide concentrations in human skin grafted to athymic nude mice.

Human skin grafted to athymic nude mice shows a decrease in nicotinamide adenine dinucleotide (NAD+) concentrations when exposed to sulfur mustard (HD). The lowering of NAD+ is dependent on both dose of HD and time after exposure. When HD is applied to grafted skin at 127 micrograms/cm2, the decrease in NAD+ begins immediately after exposure, approaches minimal values by 4 hr. NAD+ returned to normal within 18 hr. With higher concentrations of HD, NAD+ concentrations fall precipitously within 4 hr, reach a minimum value at 18 hr, and seem to remain at this depressed value for at least 72 hr. NAD+ loss appears to precede and be proportional to tissue injury. Pretreatment of mice with 3-aminobenzamide, a specific inhibitor of poly(ADP-ribose) polymerase, seems to lessen the effect of HD. At higher concentrations of HD, human grafts from mice pretreated with 3-aminobenzamide show significant protection from loss of NAD+ levels after 4 hr.

Animals↗
PubMed1985

Molecular basis for mustard-induced vesication.

A biochemical hypothesis explaining the generation of pathology in human skin by mustard gas (HD) is presented which links the initiation of DNA damages to local alterations of metabolism and subsequent development of blisters. The proposed sequence involves HD alkylation of purines in DNA which are processed to form apurinic sites. Apurinic endonucleases act at these sites to produce backbone breaks in DNA which cause activation of the chromosomal enzyme poly(ADP-ribose)polymerase. This enzyme utilizes NAD+ as a substrate and, at vesicating doses of HD, would deplete the cells of their NAD+ content. The depletion in NAD+ would cause inhibition of glycolysis, and the resulting accumulation of common intermediates would stimulate the NADP+-dependent hexosemonophosphate shunt (HMS). Such stimulation of the HMS has been associated with DNA damage and enhancement of protease synthesis and release. These proteases could be responsible for development of subepidermal blisters which result from fluid accumulation in the cavity created by separation of the moribund basal cell layer from the basement membrane--a characteristic feature of HD-exposed human skin. Partial validation of this biochemical hypothesis has been achieved. DNA alkylated with either monofunctional or bifunctional sulfur mustards, followed by spontaneous or enzymatic depurination, was shown to be sensitized to degradation by apurinic endonuclease. Studies on the effect of HD on human skin grafted to athymic nude mice demonstrated dose- and time-related decreases in NAD+ levels. These decreases in NAD+ levels preceded and correlated to the predicted severity of pathology. The participation of poly(ADP-ribose)polymerase activity in the HD-induced NAD+ loss was substantiated by prevention of this loss in the presence of inhibitors of the enzyme. Additional supporting evidence for the proposed mechanism was obtained at the cellular level by studies which utilized human leukocytes. The subsequent involvement of the HMS and proteases in HD-induced vesication is discussed.

Animals↗