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Biomedical subjects

P Froguel

Publications and source records attributed to P Froguel.

186 records · Page 11Linked to original sources
PubMed1989

In vitro and in vivo stability of electrode potentials in needle-type glucose sensors. Influence of needle material.

Enzymatic glucose sensors are based on the amperometric detection of an oxidable species generated during the oxidation of glucose by glucose oxidase. This measurement usually requires a working electrode (anode), an auxiliary electrode (cathode), and a reference electrode, the function of the latter being to keep constant the working potential of the anode, which is responsible for current generation. However, in the needle-type glucose sensors proposed so far, the reference electrode is missing, and its function is performed by the auxiliary electrode. We investigated, in vitro and in vivo in rats, the ability of several cathode-needle materials to behave as a reference electrode in two-electrode glucose sensors, i.e., to present a stable auxiliary electrode potential. In vitro, when glucose concentration was raised from 0 to 30 mM, the auxiliary potential of both gold- and silver-coated sensors presented a cathodic drift, whereas that of silver/silver chloride-coated sensors remained stable. In vivo, during insulin-induced hypoglycemia (5.9-2.4 mM), the auxiliary potentials of all sensors remained stable, whereas during glucose infusion (mean blood glucose concentration 11.2 mM), the auxiliary potentials of both gold- and silver-coated sensors presented an anodic drift, whereas those of silver/silver chloride-coated sensors remained stable. We also indirectly quantified the changes in sensor response induced by variations in the working potential in vitro and in vivo, simulating those that might be produced by a drift in the auxiliary potential. Such changes in the working potential could bring about a 30% unspecific variation in sensor response. We conclude that improvements in sensor analytical characteristics should be obtained with silver/silver-chloride-coated cathodes.

Animals↗
PubMed1989

Strategies for calibrating a subcutaneous glucose sensor.

The calibration of the glucose sensor is a critical issue for the subcutaneous implantation of such devices, since it allows from the sensor output the estimation of the prevailing subcutaneous glucose concentration. This study has compared estimations of subcutaneous glucose concentration in rats, calculated from the sensor's signal by using calibration parameters (sensitivity coefficient and background current) determined either under in vitro or in vivo conditions. The in vitro calibration was performed in phosphate buffer at 37 degrees C. The in vivo parameters were calculated by comparing changes in the sensor output current to concomitant changes in blood glucose concentration, induced by intravenous insulin injection and glucose infusion. The apparent subcutaneous glucose concentration, calculated with in vitro parameters, remained much lower than the concomitant blood glucose levels throughout the experiments. By contrast, when it was calculated with the calibration parameters determined in vivo, either in the hypoglycemia or hyperglycemia range, the apparent subcutaneous glucose concentration well reflected blood glucose levels with a five min time lag. We conclude that it is the two-point in vivo calibration procedure which allows the calculation of an apparent subcutaneous glucose concentration best reflecting blood glucose levels.

Biosensing Techniques↗
PubMedDate not supplied

[Diabetes and heredity].

Genetic factors are essential to the occurrence of insulin-dependent diabetes (IDD) and non-insulin-dependent diabetes (NIDD), and all that environmental factors do is facilitate the development of diabetes in genetically predisposed subjects. Recent advances in molecular biology have improved our understanding of diabetic heredity. IDD is closely linked to the HLA region of chromosome 6. Ninety percent of IDD belong to the DR3 or DR4 group. The occurrence of IDD is facilitated by a peculiar conformation of the HLA DQ molecule which permits the presentation of antigens to the T-cells. Other genes still have to be discovered since IDD seems to be of polygenic origin. NIDD is even more "hereditary" than IDD, but owing to the lack of an unquestionable marker the responsible genes cannot be located with certainty. Several possible genes such as those of insulin, insulin receptor and glucose transporter, are suspected, at least in some forms of NIDD--a clinically and biologically highly heterogeneous disease. Widespread family studies should, in a not too distant future, locate the responsible gene thereby leading to early detection or even prevention of NIDD.

Animals↗
PubMedDate not supplied

Effect of insulin immunization on glucose tolerance in normal rats.

Normal rats were immunized with insulin and Freund's adjuvant and submitted to an intravenous glucose tolerance test. Plasma glucose and free and total IRI levels were determined and compared to those observed in untreated rats, and in animals injected with the Freund's adjuvant used for the immunization procedure. In six of the 15 insulin injected animals, a significant amount of IRI (more than 100 mU/l) was found to circulate in bound form. In these animals, the fasting plasma glucose concentrations, and glucose disappearance rates were not different from those observed in all the other groups. However, the rise in their free IRI level was delayed, as was the return to basal level: 45 min after glucose injection, the free IRI concentration was still 98 +/- 29 mU/l in the six immunized rats vs 14 +/- 6 mU/l in those treated with Freund's adjuvant (p less than 0.01). Furthermore, the secondary nadir in the plasma glucose concentration observed at 60 min after glucose injection, was lower in the immunized rats (5.4 +/- 0.5 vs 6.8 +/- 0.3 mmol/l, p less than 0.05). It is concluded that in normal animals, IRI binding in proportions similar to those commonly observed in insulin-treated diabetic patients does not alter glucose tolerance but might lead to abnormal insulin kinetics and secondary hypoglycemia. These results might have implications for the use of closed-loop insulin delivery systems in type 1 (insulin-dependent) diabetic patients with insulin antibodies.

Animals↗
PubMedDate not supplied

Genetic determinants of type 2 diabetes mellitus: lessons learned from family studies.

Non insulin dependent diabetes mellitus (Type 2) is a multifactorial disease, with a polygenic inheritance and environmental factors contributing to its clinical expression. The search for the genetic determinants of Type 2 diabetes began when several genes involved in the mechanisms of insulin secretion or action were cloned, localized in the human genome, and when informative polymorphisms were described within or in the vicinity of these genes. It then became possible to compare, in groups of patients and normoglycaemic controls from various populations, the frequency of the different alleles of polymorphic markers of various candidate genes (e.g. insulin, insulin receptor, glucose transporters). The conflicting results observed in these studies can be ascribed to the small size of the population samples, to the genetic heterogeneity of Type 2 diabetes mellitus, but also to the methodology used therein. Indeed, these studies searched for a correlation between the frequency of certain alleles or genotypes and the phenotype of diabetes (studies of associations in affected populations compared to healthy controls). However in order to attribute to a gene the responsibility for a disease it is necessary to demonstrate the cotransmission in affected kindreds of a morbid allele of the gene along with the disease (familial or linkage analysis). The aim of this review is to summarize the results of family studies of Type 2 diabetes and Maturity Onset Diabetes of the Young (MODY), particularly with concern to the mutations described in candidate genes, and the implication of glucokinase in these disorders.

Amyloid↗