Biomedical subjects

Richard E Sweeney

Publications and source records attributed to Richard E Sweeney.

5 recordsLinked to original sources

PubMed2006

Stoichiometric and catalytic scavengers as protection against nerve agent toxicity: a mini review.

Currently fielded treatments for nerve agent intoxication promote survival, but do not afford complete protection against either nerve agent-induced motor and cognitive deficits or neuronal pathology. The use of human plasma-derived butyrylcholinesterase (HuBuChE) to neutralize the toxic effects of nerve agents in vivo has been shown to both aid survival and protect against decreased cognitive function after nerve agent exposure. Recently, a commercially produced recombinant form of human butyrylcholinesterase (r-HuBuChE; PharmAthene Inc.) expressed in the milk of transgenic goats has become available. This material is biochemically similar to plasma-derived HuBuChE in in vitro assays. The pharmacokinetic characteristics of a polyethylene glycol coated (pegylated) form of r-HuBuChE were determined in guinea pigs; the enzyme was rapidly bioavailable with a half-life (t(1/2)) and pharmacokinetic profile that resembled that of plasma-derived huBuChE. Guinea pigs were injected with 140mg/kg (i.m.) of pegylated r-HuBuChE 18h prior to exposure (sc) to 5.5xLD(50) VX or soman. VX and soman were administered in a series of three injections of 1.5xLD(50), 2.0xLD(50), and 2.0xLD(50), respectively, with injections separated by 2h. Pretreatment with pegylated r-HuBuChE provided 100% survival against multiple lethal doses of VX and soman. Guinea pigs displayed no signs of nerve agent toxicity following exposure. Assessments of motor activity, coordination, and acquisition of spatial memory were performed for 2 weeks following nerve agent exposure. There were no measurable decreases in motor or cognitive function during this period. In contrast, animals receiving 1.5xLD(50) challenges of soman or VX and treated with standard atropine, 2-PAM, and diazepam therapy showed 50 and 100% survival, respectively, but exhibited marked decrements in motor function and, in the case of GD, impaired spatial memory acquisition. The advances in this field have resulted in the decision to select both the plasma-derived and the recombinant form of BuChE for advanced development and transition to clinical trials. Efforts have now been expanded to identify a catalytic protein capable of not only binding, but also rapidly hydrolyzing the standard threat nerve agents. Recent work has focused on paraoxonase-1 (PON1), a naturally occurring human serum enzyme with the capacity to catalyze the hydrolysis of nerve agents, albeit too slowly to afford dramatic protection. Using rational design, several amino acids involved in substrate binding have been identified and site-directed mutations have revealed that residue H115 plays an important role in binding. In addition, the stereospecificity of PON1 for the catalytic hydrolysis of soman has been examined. The enzyme exhibits a slight stereospecificity for the C+P+ isomer of soman, which is due more to preferential binding than to selective hydrolysis of this isomer. The results suggest that it may be possible to engineer a mutant form of PON1 with enhanced activity and stereospecificity for the most toxic nerve agent isoforms.

Animals↗

PubMed2006

Acetylcholinesterase inhibition: does it explain the toxicity of organophosphorus compounds?

The hypothesis that acetylcholinesterase (AChE) inhibition is the mechanism of toxicity of organophosphorus (OP) compounds was examined by mathematically modeling the in vivo lethal effects of OP compounds and determining the amount of variation in OP toxicity that is explained by AChE inhibition. Mortality dose-response curves for several OP compounds (i.e., VX, soman, cyclosarin, sarin, tabun, diisopropylfluorophosphate and paraoxon) exhibited steep probit slopes (> 9.6) in guinea pigs. Steep probit slopes were also observed when the mortality dose-response curves for soman were examined in mice, rats, rabbits and non-human primates. The consistently steep probit slopes of the dose-response curves for highly toxic OP compounds suggested that these compounds have a single specific mechanism of toxicity regardless of the OP compound or the species in which it was tested. Regression analysis indicated that 93% of the 3,280-fold variation in the median lethal doses (i.e., LD(50)) of OP compounds in rats was explained by the variation in their in vitro rate constants for inhibition of AChE. Conversely, 91% of the 23-fold variation in the ability of the oximes pralidoxime and obidoxime to protect against the toxicity of OP compounds in guinea pigs was explained by the variation in the in vitro ability of oximes to reactivate OP-inhibited AChE. The best explanation for this variety of observations was that the primary mechanism of in vivo toxicity for highly toxic OP compounds is the inhibition of AChE, and the residual unexplained variation in OP toxicity that might be explained by other mechanisms represents < 10% of the total variation in OP toxicity.

Animals↗

PubMed2006

A physiologically based pharmacokinetic (PB/PK) model for multiple exposure routes of soman in multiple species.

A physiologically based pharmacokinetic (PB/PK) model has been developed in advanced computer simulation language (ACSL) to describe blood and tissue concentration-time profiles of the C(+/-)P(-) stereoisomers of soman after inhalation, subcutaneous and intravenous exposures at low (0.8-1.0 x LD(50)), medium (2-3 x LD(50)) and high (6 x LD(50)) levels of soman challenge in three species (rat, guinea pig, marmoset). Allometric formulae were used to compute the compartment volumes, blood flow rates, tidal volume and respiratory rate based upon total animal weight. Blood/tissue partition coefficients for soman, initial carboxylesterase and acetylcholinesterase levels and the rate constants for interactions between soman and these enzymes were species-dependent and were obtained from in vitro measurements reported in the literature. The model incorporated arterial and venous blood, lung, kidney, liver, richly perfused, poorly perfused and fat tissue compartments as well as subcutaneous and nasal exposure site compartments. First-order absorption from linearly filled soman deposits into metabolizing exposure site compartments was employed to model subcutaneous and inhalation exposures. The model was validated by comparing the predicted and observed values for C(+/-)P(-)-soman in arterial blood at various times following exposure and by regression analysis. Sensitivity analysis was used to determine the effects of perturbations in the model parameters on the time-course of arterial C(-)P(-)-soman concentrations for different exposure routes. In our evaluation of 28 datasets, predicted values were generally within 95% confidence limits of the observed values, and regression coefficients comparing predicted and observed data were greater than 0.85 for 95% of the intravenous and subcutaneous datasets and 25% of the inhalation datasets. We conclude that the model predicts the soman toxicokinetics for doses >or=1 x LD(50) for intravenous and subcutaneous exposures and inhalation exposures of 8 min or less sufficiently well to allow its use in the modeling of bioscavenger protection.

Administration, Inhalation↗

PubMed2003

Behavioral data management using Visual Basics for Applications to automate data capture and analysis.

Many researchers are familiar with the spreadsheet capabilities of Microsoft Excel, but have never explored using customized VISUAL BASIC FOR APPLICATIONS (VBA) macros embedded in the program. At the United States Army Medical Research Institute of Chemical Defense (USAMRICD), the implementation of VBA program code to carry out repetitive operations has resulted in a tremendous savings in both the time and manpower required to reliably capture, analyze, and plot data from research protocols. A set of "template" workbooks was developed and is used to organize data from different types of studies. At the heart of the concept is a "setup information" worksheet onto which the user enters information about the study (i.e. the number of subjects, groups, graphs). Clicking a control button on this worksheet launches the VBA code that creates worksheets for each subject, group and chart specified. A "pairmatch" function allows the user to create groups either randomly or by pair matching based on user-specified variables. Controls are provided that run VBA program code to parse subject data files into the proper worksheets and perform group averages. Charts are updated automatically whenever group averages change so that the researcher always has an up-to-date plot available. The ability to reformat the captured data onto a "statistical output" worksheet allows data to be imported easily to statistical software packages. The concept is being used for several different types of studies at USAMRICD and has significantly reduced not only amount of time spent on data management, but also the number of data entry errors. Readers interested in acquiring an electronic copy of the startle workbook example, which contains the complete VBA code, should send the request to the authors at reseco@erols.com or maurice.sipos@us.army.mil.

Acoustic Stimulation↗

PubMed2003

A theoretical expression for the protection associated with stoichiometric and catalytic scavengers in a single compartment model of organophosphorus poisoning.

The ability of certain organophosphorus (OP) compounds to inhibit acetylcholinesterase (AChE) has made them useful for industrial (insecticides) and military (nerve agents) purposes. We have previously published a single compartment mathematical model of the interactions between OP nerve agents and the enzymes affected by these agents. That model, which could be used to predict the LD50 of seven nerve agents in rats, has been extended to include the protective actions of stoichiometric and catalytic OP-scavenger enzymes (delivered as pretreatments) so that protective ratios attributable to the scavengers may be predicted. Prediction of expected human protection from in vitro rate constant and initial enzyme level measurements is the ultimate goal for this work. The enhanced model predicts the LD50 from rate constants of the OP agent's binding reactions with AChE, carboxylesterase (CaE) and a stoichiometric scavenger (S); a first-order OP elimination rate (including a contribution due to a catalytic scavenger); and whole body estimates of AChE, CaE and S. The ratio of the scavenger-treated LD50 estimate to the scavenger-free LD50 estimate provided a theoretical expression describing the scavenger's contributions to the protective ratio. Published in vivo protective ratios for two stoichiometric scavengers (fetal bovine serum AChE and human utyrylcholinesterase) against challenge by several OP agents in mice were compared with ratios predicted by the model. A linear regression analysis of in vivo protective ratios in mice versus the ratios predicted by the model from the in vitro measurements resulted in an R(2) value of 0.902. The catalytic scavenger portion of the theory could not be validated due to a lack of published data. We conclude that the one-compartment model can be used to make reasonable estimates of the protective ratio attributable to stoichiometric scavengers, but can make no conclusions regarding the ability of the model to predict catalytic scavenger protection ratios.

Animals↗