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Biomedical subjects

R Ekins

Publications and source records attributed to R Ekins.

At least 19 recordsLinked to original sources
PubMed2000

Thyroid hormone receptor gene expression in first trimester human fetal brain.

Maternal thyroid hormone is transferred to the fetus early in pregnancy and is postulated to regulate brain development. Thyroid hormone nuclear receptor (TR) proteins are present in fetal brain, but their isoformal composition is unknown. We therefore investigated the ontogeny of TR isoforms and related splice variants in first trimester human fetal brain (n = 9) by semi-quantitative reverse transcriptase-polymerase chain reaction analysis. Expression of the TRbeta1, TRalpha1 and c-erbAalpha2 isoforms was detected from 8.1 weeks gestation (wg). An additional truncated species was detected with the c-erbAalpha2 primer set, consistent with the c-erbAalpha3 splice variant previously described in the rat. All c-erbAalpha-derived transcripts were co-ordinately expressed and increased (ca. 8-fold) between 8.1 and 13.9 wg. A more complex ontogenic pattern was observed for TRbeta1, suggestive of a nadir between 8.4 and 12.0 wg. These findings point to an important role for the TRalpha1 isoform in mediating maternal thyroid hormone action during first trimester human fetal brain development.

Adult↗
PubMed1999

The role of the dental nurse in general practice.

Dental nurses have reported dissatisfaction with their work which is associated with feelings of lack of control and being undervalued. This paper examines some of the possible reasons behind job dissatisfaction with illustrations from a pilot study conducted in general dental practice.

Attitude of Health Personnel↗
PubMed1997

Immunoassay and other ligand assays: present status and future trends.

Immunoassay and other ligand assays have made a major impact on medical research and diagnosis since the first modern (radioisotopically-based) methods emerged. These ubiquitous microanalytic techniques are broadly classifiable as first generation (generally of "competitive" design, e.g., radioimmunoassay), and second generation (generally "noncompetitive," and relying on nonisotopic labels) these (often described as "ultrasensitive") being distinguished by dramatic improvements in sensitivity and performance time. A third generation is now in prospect (based on microarrays of antibody microspots) capable of ultrasensitive determination of hundreds of analytes in a drop of blood. Analogous technology (based on oligonucleotide arrays) is under intensive development for DNA analysis. Array technologies are likely to transform diagnostic medicine in the next decade.

Animals↗
PubMed1997

On the meaning of "sensitivity".

The term "sensitivity" (as applied to an analytical method's performance) has again become a subject of controversy. Certain authorities (e.g., IUPAC) define a system's sensitivity as the response curve slope (or response/dose), others (e.g., IFCC) in terms of the detection limit. Many investigators have failed to perceive the contradiction between these concepts, wrongly assuming that maximizing "sensitivity" in the first sense maximizes it in the second (i.e., that they are inversely related). The existence of different meanings for this term (when used in the present context) is a source of confusion that has, among other things, led to erroneous ideas relating to immunoassay design. Such confusion should be terminated by adoption of one or the other of the definitions. However, the definitions are not of equal merit. We advance arguments against retention of the "slope" definition, which conflicts with the word's common meaning and is meaningless as an indicator of the performance of a measuring system.

Clinical Chemistry Tests↗
PubMed1994

Immunoassay: recent developments and future directions.

All analytical techniques employed in the biological sciences rely on recognition of the shape and structure of molecules of the substance of interest (the analyte). Such molecular recognition and sensing usually relies on the use other molecules possessing a complementary structure, implying a specific lock and key relationship between the two. Antibodies comprise a class of recognition molecules evolved by nature for the purpose of bodily defence, and are clearly of particular utility in this context. However techniques of increasing sophistication (including the techniques of molecular biology) are currently being developed which enable the artificial construction of antibody-like molecules possessing improved molecular recognition properties which can be harnessed for microanalytical purposes. Oligonucleotide probes likewise exhibit the property of binding to complementary nucleotide sequences, and the techniques of, for example, in situ hybridisation therefore share many features with immunoassay techniques. Microanalytical techniques relying on binding reactions between substances possessing complementary lock and key molecular structures are unlikely to be superseded within the foreseeable future, only the labels used to monitor such reactions, and the means of production of "recognition molecules", being subject to further development. Such techniques already enter into all areas of life, including medicine, agriculture, etc, and are likely to increase further in importance with increasing concern regarding chemically complex contaminants in food, the environment, etc. Developments in this field are clearly directed to slightly differing objectives as indicated in this presentation. These include methodological simplification (making the techniques cheaper and more widely available), improvements in sensitivity (to enable the detection and measurement of substances beyond the reach of current methods) and the construction of transducer-based sensor methods (permitting, inter alia, the monitoring of changing analyte concentrations). However the combination of the "ultrasensitivity" of current single analyte assay methods with the ability simultaneously to determine multiple analytes in the same sample represents, in my view, the next major methodological challenge in this field, and--if successfully addressed--will constitute a quantum advance on present analytical methods. Indeed the development of miniaturised multianalyte binding assay techniques may ultimately comes to be seen as analagous to, for example, the introduction of the word processor, and other similar major technological advances of the past decade.

Antigen-Antibody Reactions↗
PubMed1993

Free hormone assays.

The specific binding by serum proteins of circulating thyroid and steroid hormones is a phenomenon whose physiological significance is still not fully understood. Recent controversy on these proteins' role in hormone transport reveals that disagreement persists regarding the basic physicochemical implications of their presence within the microcirculation. Theoretical analysis of the effects of intracapillary protein binding reactions on target-tissue hormone uptake is of considerable complexity and has not, as yet, been successfully accomplished. A fuller analysis of the physicochemical consequences of hormone binding in body compartments under the 'dynamic' conditions which obtain in vivo is a necessary prerequisite to the demonstration of the validity (or otherwise) of the free hormone hypothesis, and the elucidation of the physiological role, if any, of serum binding proteins. Similar misunderstanding of physicochemical concepts has also emerged in the field of free hormone measurement. The advent of relatively simple immunoassay techniques and kits has made 'free hormone assay' more widely available than hitherto, resulting in a near exponential increase in the number of publications in this area. However, close examination of some of the modern technologies reveals that the ideas on which they are based contradict elementary physicochemical laws, and are demonstrably incorrect. Indeed many such kits--though claimed as conforming to legitimate physicochemical principles--comprise nothing more than increasingly complex reagent 'cocktails' (often of undisclosed chemical nature) empirically adjusted to yield clinically acceptable results in certain patient categories. Not only has the publication of numerous reports based on the use of such kits created considerable confusion in the endocrinological and physiological literature, but, in attempting to justify their claims, commercial kit manufacturers have introduced numerous false concepts into the free hormone measurement field.

Blood Proteins↗
PubMed1993

Analytic measurements of free thyroxine.

This article has attempted to clarify two main areas of uncertainty relating to the clinical use of free TH determinations. The first centers on the validity of the free hormone hypothesis. This has been the subject of contentious debate for more than a decade, and final agreement among endocrinologists on this issue has yet to be reached. It is thus important that diagnosticians should not assume the validity of the hypothesis when assessing the analytic validity of free TH assay kits. In short, the reliability of the kits should be judged by analytic criteria (such as their theoretic basis and the results yielded on diluted samples) and not merely on the claim that they yield correct results in certain patient categories. Indeed, the finding that fT4 decreases in pregnancy (albeit to a limited extent) illustrates the danger of assuming the validity of the hypothesis when judging the reliability of fT4 assay kits. The second area of uncertainty relates to the true serum fT4 concentrations present in various clinical conditions, in consequence of doubts regarding the analytical validity of currently available methods. An attempt has been made in this presentation to clarify the physicochemical concepts underlying the more widely-used kits, and some of the reasons for their unreliability, although this also constitutes a contentious area. Errors generated in analogue-based free TH assay kits arise in part in consequence of the use of analogues that fail to conform to the physicochemical theory underlying "unbound analogue" assay, compounding errors resulting from the inclusion in assay reagents of various additives (e.g., albumin) that, inter alia, disturb the equilibrium between free and bound hormone moieties, and which also distort the effects of binding competitors. Regrettably different manufacturers have, in practice, relied on different analogues and/or reagent additives, buffers, blockers, and so forth, and different operating temperatures. Indeed different kits from the same manufacturer frequently differ in their formulation (see, for example, footnote on page 618), and yield widely differing results in certain sera. Also manufacturers may modify kit components from time to time without disclosure. Thus, though many analogue-based kits may arguably be diagnostically useful in well-defined clinical situations, total reliance cannot be placed in the results they yield in more complicated circumstances (such as those characterizing NTI), which may be diagnostically misleading.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Proteins↗
PubMed1992

Multianalyte microspot immunoassay. The microanalytical 'compact disk' of the future.

Throughout the 1970s, controversy centered both on immunoassay 'sensitivity' per se and on the relative sensitivities of labelled antibody and labelled analyte methods. Our own theoretical studies in this period revealed that radioimmunoassay (RIA) sensitivities could be surpassed only by the use of very high specific activity non-isotopic labels in 'non-competitive' designs, preferably based on the use of monoclonal antibodies. The time-resolved fluorescence methodology known as Delfia - developed in collaboration with the instrument manufacturer LKB/Wallac - represented the first commercial 'ultra-sensitive' non-isotopic technique based on these theoretical insights, the same concepts being subsequently adopted in comparable methodologies relying on the use of chemiluminescent and enzyme labels. However, a second advantage of high specific activity labels is that they permit the development of 'multi-analyte' immunoassay systems combining ultra-sensitivity with the simultaneous measurement of tens, hundreds or thousands of analytes in a small biological sample. This possibility relies on simple, albeit hitherto unexploited, physicochemical concepts. The first is that all immunoassays rely on measurement of Ab occupancy by analyte. The second is that, provided the Ab concentration used is 'vanishingly small', fractional Ab occupancy is independent of both Ab concentration and sample volume. This leads to the notion of 'ratiometric' immunoassay, involving measurement of the ratio of signals (eg fluorescent signals) emitted by two labelled Ab's, the first ('sensor' Ab) deposited as a microspot on a solid support, the second a 'developing' Ab directed against either occupied or unoccupied sensor Ab binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding, Competitive↗
PubMed1991

Immunoassay standardization.

Assays employed in the biological sciences fall into two categories, which may be respectively termed "comparative" (or "functionally-specific") and "analytical" (or "structurally-specific"). The former are intended to compare the relative effects of substances, or mixtures of substances--not necessarily of identical chemical structure--on a biological system (e.g. whole animal, tissue, cell, etc). Results are represented by units of effect (i.e. they are not units of "amount" of the substance(s) measured), and differ depending on the biological system used. Such assays cannot be "standardised" by the use of a calibrant. In contrast, analytical assays are intended to measure the number of molecules (or mass) of a single substance of unique chemical structure in a test sample, and cannot legitimately be employed to measure mixtures of substances of different structure. Results are represented by units of molecular number or mass, and should be identical for any test sample irrespective of the assay system used. Immunoassays generally fall into this category. Insofar as the antigenic substances present in standards or test samples are dissimilar and/or molecularly heterogeneous, an immunoassay is invalid, and the results it yields have no universal significance. Attempts to standardize "analytically-invalid" immunoassays inevitably fail. Many substances of biological interest (e.g. TSH)--initially defined in terms of their biological function--have subsequently been shown to be molecularly heterogenous. Problems thus arise in the standardization of immunoassays used for their measurement, reflecting the fact that the measurement of a mixture of substances of differing molecular structure (and function) is a meaningless concept. It is thus impossible to "measure TSH"; it is only possible to measure the effect TSH exerts in a particularly assay system. The only long-term solution to this problem is the development of assay systems measuring individual components of such heterogenous mixtures.

Animals↗