Biomedical subjects

K McLellan

Publications and source records attributed to K McLellan.

4 recordsLinked to original sources

PubMed1999

Age, testing at preferred or nonpreferred times (testing optimality), and false memory.

Two experiments investigated whether age and testing at preferred (optimal) times of day or nonpreferred (nonoptimal) times affected the ability to select relevant from irrelevant but thematically related alternatives in a verbal false memory paradigm. A 3rd experiment pursued the same issues with a visual false memory paradigm. In all 3 experiments, younger adults (n = 195) correctly recalled studied items more often than older adults (n = 121), whereas the 2 age groups correctly recognized about the same numbers of previously studied items. In all 3 experiments, nonoptimally tested older adults had more difficulty excluding nonstudied but thematically related items than the other groups; thus, they showed the greatest evidence of false memory, although all groups did so to a significant extent. The results suggest that optimality and its circadian determinants need to be considered with some tasks for the elderly. Various models and mechanisms are discussed.

Adolescent↗

PubMed1996

Estimation of antigenic tetanus toxoid extracted from biodegradable microspheres.

Microspheres made from poly (lactic/glycolic acid) polymers have been considered as a new delivery system for single-dose tetanus toxoid (TT) vaccines. One of the most critical properties of the proposed vaccines is the loading and distribution of TT as this will have a profound effect on immunogenicity. As the concentration of TT in microspheres is very low sensitive assay methods are required. An assay incorporating monoclonal antibody (MAb) recognizing a neutralizing epitope and cross-reacting with TT was developed (MAp capture ELISA) which provided a sensitivity of 0.001 Lf/ml. An extraction procedure was devised which did not destroy the antigenicity and gave a recovery of 90.6 +/- 3.39% when applied to different preparations. The extracted TT was then quantified by MAb capture ELISA which was estimated to be 250-fold more sensitive than single-site ELISA for toxoid. The loading of 20 microspheres preparations (12 filled and 8 placebo) was determined by both protein micro-BCA assay and the developed assay for TT. The TT content obtained for the 12 filled microspheres preparations from different sources varied up to 400-fold (range 0.01-4.0 Lf/mg microspheres). The utility of the MAb capture ELISA for detection of total antigenic content in microspheres was confirmed by the observation that the determine TT loading correlated with the theoretical loading predicted from the protein content for the best preparations. Preparations with high loading gave the greatest peak response. There was no relationship between dose and the in vivo immunogenic response, suggesting that encapsulated vaccines with differential loading, release properties and presence of excipients will have different response curves in vivo. Hence, the present assay, when combined with information on toxoid release rate and presence and effect of excipients may be of value in predicting in vivo response.

Animals↗

PubMed1996

Refinement and validation of an alternative bioassay for potency testing of therapeutic botulinum type A toxin.

The type A neurotoxin produced by Clostridium botulinum is a potent neuromuscular blocking agent which causes paralysis by preventing the release of neurotransmitter from motor neurones. This property has led to the use of the toxin in the treatment of a number of neuromuscular diseases involving muscle spasms. At present, the only recognised assay with the specificity and sensitivity to estimate accurately the potency of botulinum toxin in clinical preparations is bioassay, in which lethality is used as the end point. Refinement of this assay, with respect to the end point, was explored on the basis of the development of flaccid paralysis of muscles following subcutaneous injection of the toxin at the inguinocrural region. Potency estimates, relative to in house reference preparations, for different therapeutic preparations obtained using flaccid paralysis as a scored response gave excellent agreement with estimates obtained in independent assay using the currently required control method. This study demonstrates that an alternative, more humane bioassay for potency testing of clostridia neurotoxins gives valid estimates equivalent to those currently in use.

Animals↗

PubMed1995

Immunological detection of Clostridium botulinum toxin type A in therapeutic preparations.

The potent neurotoxins produced by strains of Clostridium botulinum act by blocking the release of acetylcholine from peripheral nerve junctions. This specific action of the botulinum neurotoxins is now being exploited therapeutically to treat a variety of conditions involving involuntary muscle spasms. We aimed to develop a sensitive and specific enzyme-linked immunosorbent assay (ELISA) which may be used in parallel with the currently accepted mouse bioassay test for the determination of botulinum neurotoxin type A in therapeutic preparations. High titre polyclonal antitoxins and their biotin derivatives, highly labelled horseradish peroxidase (HRP)-antibody conjugates, and streptavidin-biotin-HRP complexes were prepared and used in a sandwich ELISA for the detection of pure neurotoxin and neurotoxin in therapeutic material. The ELISA utilized either a monoclonal or polyclonal antibody as capture agent and HRP-labelled IgG or F(ab')2 fragment as second antibody. The limit of detection was 4-8 pg of purified toxin/ml (gcv < 13%), equivalent to 1-2 mouse bioassay units/ml. The assay was used to evaluate therapeutic preparations and the results compared with the mouse bioassay. The lower limit of detection for a therapeutic preparation of BoTxA was 2-5 mouse bioassay units/ml. Although across different manufacturers and bulk products there was no correlation between immunologically detected neurotoxin and its biological activity in different therapeutic preparations (r = -0.44, p = 0.34, n = 8), the assay could be used to quantify neurotoxin in therapeutic preparations derived from the same bulk concentrate and manufacturer. The assay is relatively simple, and may be readily adapted to routine monitoring of BoTxA content in therapeutic preparations.

Antibodies↗