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G S Wilson

Publications and source records attributed to G S Wilson.

At least 19 recordsLinked to original sources
PubMed1992

Studies of the low dose 'hook' effect in a competitive homogeneous immunoassay.

The interactions of two monoclonal antibodies with human growth hormone (hGH) have been investigated. The individual antibodies showed normal behavior in a competitive binding assay, but mixtures of the antibodies demonstrated a 'hook' attributable to cooperative interactions. Cooperativity was observed in titrations which preceded the competitive binding assay. Size exclusion chromatographic data suggest that the cooperativity is explained by the formation of higher molecular weight complexes (up to 700 kDa). The major complex is probably linear, consisting of three antibody molecules. Circular and linear complexes with four antibody molecules (octameric complexes) are also possible. Theoretical models also support the formation of cyclic complexes in a competitive binding assay.

Allosteric Regulation↗
PubMed1992

Studies of the 'hook' effect in the one-step sandwich immunoassay.

The one-step sandwich immunoassay is increasingly replacing the traditional two-step immunoassay due to obvious advantages such as assay speed. However, the one-step sandwich immunoassay suffers from the 'hook' effect irrespective of the analyte characteristics. The 'hook' effect is dependent primarily on the analyte concentration. Three different model analytes, human growth hormone (hGH), the dimeric form of hGH (D-hGH, having a discrete number of repeating epitopes) and ferritin (multiple epitopes) having different immunological properties have been employed in studies of the one-step sandwich immunoassay. The characteristics of each of the model analytes offer new insights into general guidelines for assay procedures. These guidelines permit rapid optimization of assay conditions for an immunoassay without a priori knowledge of the immunological characteristics of the antibody or antigen. Both experimental and theoretical data show several instances where high capacity solid-phase antibodies can effectively shift the 'hook' to relatively higher analyte concentrations. The effect of the concentration of labeled antibody on assay response was examined theoretically.

Antigen-Antibody Reactions↗
PubMed1992

Multiple epitope interactions in the two-step sandwich immunoassay.

The 'hook' effect as related to the two-step sandwich immunoassay has been investigated experimentally and theoretically. The multiple epitope interactions between the analyte and the labeled antibody cause a 'hook' in the two-step sandwich immunoassay. Three different analytes and monoclonal antibodies were chosen to carefully demonstrate the effect of the analyte characteristics on this immunoassay. Two monoclonal antibodies against two different epitopes of biosynthetic human growth hormone (hGH) was the simplest model for this study. The sandwich immunoassay for hGH shows no 'hook' effect. The non-covalent dimeric form of hGH (D-hGH) possesses two repeating epitopes which is the simplest model for an analyte having a discrete number of repeating epitopes. The D-hGH assay demonstrated a 'hook' effect in the two-step sandwich immunoassay if the labeled antibody was allowed to interact with more than one epitope. In a third system multiple epitope interactions with the labeled antibody were observed using ferritin. The effect of the analyte concentration and the liquid-phase antibody have been examined to elucidate the nature of these various interactions. The cause of the 'hook' effect in the two-step sandwich immunoassay is attributed to the desorption of the bound analyte due to a conformational change after the labeled antibody interacts with several epitopes of the adsorbed analyte.

Antibodies, Monoclonal↗
PubMed1992

Can continuous glucose monitoring be used for the treatment of diabetes.

In the case of the glucose sensor, clinicians and chemists must cooperate in interdisciplinary research to carefully define the analytical problem. Although not specifically discussed in this article, another group that must participate in this effort is engineers. Their expertise is needed to design the monitoring and control unit that contains the alarm and pump systems. The glucose sensor must operate reliably in an in vivo environment, provide the clinical information needed, and be easy to operate and manufacture.

Animals↗
PubMed1992

Towards continuous glucose monitoring: in vivo evaluation of a miniaturized glucose sensor implanted for several days in rat subcutaneous tissue.

A miniaturized amperometric, enzymatic, glucose sensor (outer diameter 0.45 mm) was evaluated after implantation in the subcutaneous tissue of normal rats. A simple experimental procedure was designed for the long-term assessment of the sensor's function which was performed by recording the current during an intraperitoneal glucose load. The sensor was calibrated by accounting for the increase in the current during the concomitant increase in plasma glucose concentration, determined in blood sampled at the tail vein. This made it possible to estimate the glucose concentration in subcutaneous tissue. During the glucose load, the change in subcutaneous glucose concentration followed that in blood with a lag time consistently shorter than 5 min. The estimations of subcutaneous glucose concentration during these tests were compared to the concomitant plasma glucose concentrations by using a grid analysis. Three days after implantation (n = 6 experiments), 79 estimations were considered accurate, except for five which were in the acceptable zone. Ten days after implantation (n = 5 experiments), 101 estimations were accurate, except for one value, which was still acceptable. The sensitivity was around 0.5 nA.mmol-1.l-1 on day 3 and day 10. A longitudinal study on seven sensors tested on different days demonstrated a relative stability of the sensor's sensitivity. Finally, histological examination of the zone around the implantation site revealed a fibrotic reaction containing neocapillaries, which could explain the fast response of the sensor to glucose observed in vivo, even on day 10. We conclude that this miniaturized glucose sensor, whose size makes it easily implanted, works for at least ten days after implantation into rat subcutaneous tissue.

Animals↗
PubMed1992

Progress toward the development of an implantable sensor for glucose.

The development of an electrochemically based implantable sensor for glucose is described. The sensor is needle-shaped, about the size of a 28-gauge needle. It is flexible and must be implanted subcutaneously by using a 21-gauge catheter, which is then removed. When combined with a monitoring unit, this device, based on the glucose oxidase-catalyzed oxidation of glucose, reliably monitors glucose concentrations for as long as 10 days in rats. Various design considerations, including the decision to monitor the hydrogen peroxide produced in the enzymatic reaction, are discussed. Glucose constitutes the most important future target analyte for continuous monitoring, but the basic methodology developed for glucose could be applied to several other analytes such as lactate or ascorbate. The success in implementation of such a device depends on a reaction of the tissue surrounding the implant so as not to interfere with the proper functioning of the sensor. Histochemical evidence indicates that the tissue response leads to enhanced sensor performance.

Biocompatible Materials↗
PubMed1991

Factors affecting the specific activity of immobilized antibodies and their biologically active fragments.

Factors affecting the specific activity of immobilized antibodies and their biologically active fragments were studied with goat anti-mouse and goat anti-human immunoglobulin G. Antibodies were immobilized on HW 65 polymeric support matrix activated with carbonyldiimidazole, hydrazide and iodoacetic acid. The most significant factors influencing the specific activity of stochastic coupling of antibodies are multi-site attachment, multiple orientations and steric hindrance imposed by crowding of antibody and the size of the antigen. In oriented immobilization the specific activity is affected only by steric hindrance. The specific activity of immunosorbents prepared by immobilization of F(ab') fragments can be improved to almost 100% by limiting the amount of protein immobilization and the size of the antigen. The present study shows the protocols for optimizing immobilized antibody performance.

Adipates↗
PubMed1991

Design and in vitro studies of a needle-type glucose sensor for subcutaneous monitoring.

A new miniaturized glucose oxidase based needle-type glucose microsensor has been developed for subcutaneous glucose monitoring. The sensor is equivalent in shape and size to a 26-guage needle (0.45-mm o.d.) and can be implanted with ease without any incision. The novel configuration greatly facilitates the deposition of enzyme and polymer films so that sensors with characteristics suitable for in vivo use (upper limit of linear range greater than 15 mM, response time less than 5 min, and sensitivity yielding a 5:1 signal-to-background ratio at normal basal glucose levels) can be prepared in high yield (greater than 60%). The sensor response is largely independent of oxygen tension in the normal physiological range. It also exhibits good selectivity against common interferences except for the exogenous drug acetaminophen.

Animals↗
PubMed1991

Application of cell culture toxicity tests to the development of implantable biosensors.

Cell culture toxicity testing methods were modified and applied to the development of implantable glucose microsensors, and positive and negative control materials suitable for the microsensor assessment were established. The location, source and degree of the toxic effect in a multi-component biosensor was spatially visualized with cell monolayers. A freshly prepared sensor showed moderate toxicity, mainly as a result of the presence of glutaraldehyde and the residual solvents in the polymer layers. However, it was possible to reduce the toxicity by removing the leachable toxic substances through extraction in phosphate buffer, and a non-toxic sensor was readily obtained.

Agar↗
PubMed1991

Children of battered women: developmental and learning profiles.

Children in battered women's shelters have been shown to have more behavior problems than their peers but limited information is available about their development. A pilot survey was undertaken to determine the prevalence of developmental or academic problems in children of residents of a battered women's shelter. Demographic data, medical and school histories and responses to standardized developmental or behavioral surveys were obtained from 39 mothers of 76 children. Two-thirds of the children were victims of abuse. On the Minnesota Child Development Inventory, the mean General Developmental Quotient (DQ) of 28 preschool children was 98; however, 39% had developmental delays by test criteria. Of 46 school-aged children, 21 (46%) had evidence of academic problems, including grade repetition, failing grades and need for special educational services. On the Louisville Behavior Checklist, 75% of 48 children had behavior problems. Children in a battered women's shelter are likely to experience academic and behavioral problems; however, further study is needed to elucidate etiological factors.

Adolescent↗
PubMed1991

Patterns of growth and development in narcotic-exposed children.

The results of the studies reviewed indicate that intrauterine growth is adversely affected by drug use during pregnancy. Whether the impairment is a direct effect of narcotic exposure or is the result of the interaction of deleterious health, environmental, and socioeconomic factors closely associated with the lifestyle of the woman who abuses drugs cannot be determined at present. Reports on the long-term effects of drug use on growth and intellectual functioning in the offspring of women who abuse drugs are not consistent. While some studies indicate that most of the exposed infants exhibit catchup growth by 6 months of age (Lifschitz et al. 1983, 1985), one methodologically strong study suggests that methadone may have a small direct teratogenic effect reflected in reduced head size at 2 years of age (Hans 1989). Unexplained is the pattern of growth deceleration observed in some narcotic-exposed children (Lifschitz et al. 1983, 1985). The few available reports on long-term outcome concur that narcotic-exposed children have a high incidence of behavioral and learning problems (Strauss et al. 1979; Rosen and Johnson 1985; Wilson 1989), but population studies have been too small to demonstrate that they differ significantly from controls. There is a suggestion that narcotic use during pregnancy promotes a biological vulnerability to adverse environments, manifested in the neurobehavioral and intellectual areas.

Child↗
PubMed1990

Optimization of multienzyme flow reactors for determination of acetylcholine.

Immobilized enzyme reactors have been used with high-performance liquid chromatography (HPLC) and electrochemical detection to detect acetylcholine and choline in brain tissue samples. Acetylcholine and choline eluting from the LC column are introduced into a reactor containing immobilized acetylcholinesterase, which hydrolyzes acetylcholine to choline. The product is converted by a second enzyme, choline oxidase, to hydrogen peroxide, which is determined amperometrically. Several novel immobilization techniques including immobilization through enzyme-specific antibodies were used to immobilize these enzymes to retain maximum activity. Improved detection limits were observed when the enzymes were immobilized through the avidin-biotin linkage. Better sensitivity and detection limit were obtained when both enzymes were immobilized together on the same support through the avidin-biotin linkage than when they were separately immobilized and used in two columns. The postcolumn system was applied to brain tissue extracts.

Acetylcholine↗
PubMed1990

Improved methods for separation of human cytokeratins.

The cytokeratins from human bladder and esophageal epithelia were separated using chromatographic techniques. The cytokeratins were first extracted from fresh autopsy tissue using high and low salt buffers. Urea, 8.0-9.5 M, was used to solubilize the resulting cytokeratin pellet. Imidazole was found to increase the solubility of the pellet but reducing agents such as 2-mercaptoethanol were not beneficial. DEAE ion exchange chromatography produced three fractions which were analyzed by using one and two-dimensional electrophoresis. The third fraction was shown to contain the acidic cytokeratins and was further fractionated on a moderately polar reverse phase HPLC column using an acetonitrile elution gradient. Tetramethylammonium tetrafluoroborate was added to the mobile phase to react with any unreacted silanol groups on the stationary phase, and trifluoroacetic acid was added to ion pair with the protein. HPLC fractions of the acidic proteins from human esophagus revealed seven reproducible peaks. All seven peaks were shown by Western blotting to contain an epitope found on cytokeratin 13. The results suggest that the isolation and separation procedures have produced a series of peptide products which all retain a similar epitope but which vary significantly in their hydrophobic characteristics.

Chromatography, High Pressure Liquid↗
PubMed1990

Effect of H2O2 concentration and exposure time on stromal swelling: an epithelial perfusion model.

The corneal epithelium can be affected adversely by some preservatives used in contact lens solutions. To test the effect of H2O2 at the epithelial surface, the rabbit cornea was perfused with various concentrations of H2O2, and the effect on stromal and Anterior Bright Band (ABB) thickness measured for 150 min. The study compares stromal swelling and ABB swelling for a single 10-min pulse with that for a 150-min sustained dose. With the 10-min pulse dose there was no significant swelling up to 235 ppm H2O2, the highest dose tested. With the sustained dose, significant stromal swelling began between 72 and 153 ppm H2O2. These results indicate that residual H2O2 present at the epithelial surface after neutralization in current contact lens disinfection systems does not have a high enough concentration to affect corneal function adversely.

Animals↗
PubMed1990

An exploratory study of the structure and validity of pediatric examination of educational readiness (PEER) factors.

The Pediatric Examination of Educational Readiness (PEER) is an assessment instrument specifically designed for use by pediatricians in assessing the development of preschool children. The present study investigated the psychometric properties of the PEER. Specifically, factor analyses of items from the Developmental Attainment and Associated Observation components of the test were performed. The PEER was administered to 69 preschool children. Three major factors were identified as making up the Developmental Attainment portion of the test: perceptual-motor, verbal-cognitive, and gross motor. The Associated Observations component was found to be composed of only one factor, attention. Children's performance on only two of these four factors was associated with their performance on the McCarthy Scales, the Woodcock-Johnson skills cluster, and the Minnesota Child Development Inventory. Discussion focused on the validity and utility of the PEER.

Attention↗
PubMed1990

Nonhandicapped very-low-birth-weight infants at one year of age: developmental profile.

The developmental profile of 61 very-low-birth-weight infants without major cognitive, motor, or sensory deficits was compared with that of 28 term infants at 1 year chronologic age. The groups significantly differed in two ways on the Revised Gesell Developmental Schedules. First, very-low-birth-weight infants were more likely than term infants to have significant discrepancies between either their fine motor or language abilities and their early problem-solving skills as measured by the Adaptive scale of the Gesell. Second, across all fields of behavior (adaptive, gross motor, fine motor, language, and personal/social), very-low-birth-weight infants scored significantly below term infants. The very-low-birth-weight infant's motor performance significantly correlated with bronchopulmonary dysplasia, intracranial hemorrhage, and number of days spent in the hospital. Language performance significantly correlated with intracranial hemorrhage, birth weight, and sex. These findings underscore the limitations of global developmental scores to describe adequately the developmental performance of very-low-birth-weight infants. Instead, a comprehensive assessment of all fields of behavior is necessary to provide an accurate profile of this high-risk group.

Bronchopulmonary Dysplasia↗
PubMed1989

Pulsed amperometric detection of glucose in biological fluids at a surface-modified gold electrode.

A nonenzymatic glucose sensor that utilizes permselective membranes to achieve the selectivity required for screening glucose in biological fluids has been described. Interference from endogenous oxidizable substances such as amino acids, urea, ascorbic acid, and uric acid, as well as the effect of chloride and proteins on glucose response, is studied by using flow injection analysis. A set of membranes made of Naflin perfluorinated membrane and collagen, when arranged in front of the working electrode (gold), result in significant improvement in the system selectivity. Even at physiological pH, which is far from being the optimum pH for pulsed amperometric detection of carbohydrates, the sensor shows a good limit of detection (4-5 micrograms of glucose injected).

Acetaminophen↗