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Biomedical subjects

G Velho

Publications and source records attributed to G Velho.

87 records · Page 5Linked to original sources
PubMed1992

Close linkage of glucokinase locus on chromosome 7p to early-onset non-insulin-dependent diabetes mellitus.

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem, affecting 5% of the world population. Genetic factors are important in NIDDM, but the mechanisms leading to glucose intolerance are unknown. Genetic linkage has been investigated in multigeneration families to localize, and ultimately identify, the gene(s) predisposing to NIDDM. Here we report linkage between the glucokinase locus on chromosome 7p and diabetes in 16 French families with maturity-onset diabetes of the young, a form of NIDDM characterized by monogenic autosomal dominant transmission and early age of onset. Statistical evidence of genetic heterogeneity was significant, with an estimated 45-95% of the 16 families showing linkage to glucokinase. Because glucokinase is a key enzyme of blood glucose homeostasis, these results are evidence that a gene involved in glucose metabolism could be implicated in the pathogenesis of NIDDM.

Adenosine Deaminase↗
PubMed1992

Evaluating in vitro and in vivo the interference of ascorbate and acetaminophen on glucose detection by a needle-type glucose sensor.

The aim of this work was to assess, in vitro and in vivo, the interference of ascorbate and acetaminophen on glucose measurements by a needle-type glucose sensor detecting hydrogen peroxide generated during the enzymatic oxidation of glucose, and to ascertain whether the protection against interference by the membranes used in the construction of the electrode is feasible. The oxidation of ascorbate and acetaminophen on a platinum electrode set at a 650 mV potential yielded a current representing 75 +/- 5% and 25 +/- 6% of that generated by the oxidation of an equimolar concentration of hydrogen peroxide, respectively. The bias introduced by the presence of 100 mumol l-1 ascorbate on the reading of 5 mmol l-1 glucose by the complete sensor (electrode + membranes) would be minimal (approximately 0.4 mmol l-1). By contrast, the bias introduced by 200 mumol l-1 of acetaminophen (a plasma concentration easily reached in clinical practice) was about 7 mmol l-1. The sensor was implanted subcutaneously in anaesthetized rats (n = 3). Using the current generated in the presence of a plasma acetaminophen concentration of about 200 mumol l-1 for glucose monitoring would lead to a major underestimation (approx. 6 mmol l-1) of subcutaneous glucose concentrations.

Acetaminophen↗
PubMed1989

Determination of peritoneal glucose kinetics in rats: implications for the peritoneal implantation of closed-loop insulin delivery systems.

Peritoneal glucose kinetics were evaluated in the anaesthetized rat, to assess whether the peritoneal cavity would be a suitable site for the implantation of membrane-protected islets of Langerhans (bioartificial pancreas) or the glucose sensor of an artificial B cell. Glucose was measured in peritoneal fluid samples aspirated by needle puncture. Basal peritoneal and blood glucose concentrations were identical in 16 h fasted (n = 4) and non fasted (n = 3) animals. After 10 min of an i.v. glucose infusion (n = 15) the increment in peritoneal glucose concentration was 63 +/- 3% of the increment in blood glucose concentration and both values were significantly correlated (r = 0.92; p less than 0.001). After 10 min of glucose clamping (12.6 +/- 0.8 mmol/l), the increment in peritoneal glucose concentration was 69 +/- 3% (n = 5; p less than 0.05) of the increment in blood glucose concentration. In three additional experiments it was 93 +/- 3% of the increment in blood glucose concentration (NS), after 30 min of glucose clamping (8.0 +/- 0.5 mmol/l). Peritoneal glucose concentration monitored by a glucose sensor: (a) followed blood glucose sluggishly during a glucose clamp (n = 5), confirming the data shown above, (b) followed blood glucose with a 5 min delay and reached the same plateau after the intravenous injection of 1U insulin (n = 3; NS). We conclude that peritoneal glucose reflects blood glucose at basal state and during variations of glycaemia, nevertheless, presenting heterogeneous kinetics. These kinetics might be appropriate for a bioartificial pancreas but not for an in vivo calibration procedure, of a peritoneally implanted glucose sensor.

Animals↗
PubMed1989

Study and development of multilayer needle-type enzyme-based glucose microsensors.

Glucose oxidase (GOD) was covalently coupled to a cellulose acetate (CA) layer, using bovine serum albumin (BSA) and parabenzoquinone (PBQ) linkages. Prior to GOD coupling this CA layer was deposited on the platinum tip of a needle-type sensor and covered with an outer layer of polyurethane (PU). Such microsensors were found to be active, their GOD load reaching 1.6 to 3.0 micrograms mm-2 and their glucose response reaching 1 to 3 microA M-1 mm-2, even when the upper limit of their linear range reached 10-30 mM. Due to the multilayer structure and composition of these microsensors, small anions such as ascorbate were partially discriminated from neutral molecules such as hydrogen peroxide. When implanted subcutaneously in anaesthetized rats, sensor responses correlated correctly with blood glucose concentration but presented sensitivity coefficients significantly different to those determined in vitro: a 2 point calibration procedure was found necessary for in vivo experiments.

Animals↗
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↗
PubMed1989

Monitoring the kinetics of glucose transfer across a bioreactor membrane with a glucose sensor.

Bioreactors for cell culture, in which hollow fibers are sealed into a protective jacket, cells are seeded in the fibers' outer surface and a culture medium circulates through the fibers, have been proposed as a bioartificial pancreas. We used a needle-type glucose sensor to study the kinetics of glucose transfer across the membrane of one such device. The glucose transfer was found to be dependent on the flow rate of the circulating medium, which suggests the involvement of an ultrafiltration flux across the membrane. The glucose concentration was heterogeneous within the cell compartment. This heterogeneity, and the delay in transmission of changes in glucose concentration from the circulating medium to the cell compartment, can be ascribed to the large volume of the compartment. The design of these bioreactors should therefore be modified, in order to meet the requirements of glucose transfer kinetics of a bioartificial pancreas.

Equipment Design↗
PubMed1988

Absence of effect of heparin on insulin secretion.

Bioartificial pancreatic devices containing isolated islets of Langerhans have been designed, in which the blood of the recipient circulates in contact with an artificial membrane, protecting the islets against immune rejection. This system assumes that heparin, required to prevent blood clotting, does not alter insulin secretion. However, heparin has been reported to inhibit in vitro insulin secretion by rat islets and to suppress in vivo insulin secretion in dogs. Therefore, the following evaluation was made on the effect of different heparin preparations on insulin secretion. (a) Isolated rat islets of Langerhans were perfused or incubated in the absence or presence of 20 micrograms/ml heparin; insulin secretion in response to a stimulation by glucose 20 mM was not altered by the presence of heparin. (b) Insulin secretion by an insulin-secreting cell line (RINm5F) in response to leucine and theophylline was not suppressed by heparin up to 100 micrograms/ml concentration. However, an inhibitory effect was observed at 200 micrograms/ml, which is 100 times higher than the heparin concentration commonly used for therapeutic use. (c) Neither in normal rats nor in dogs did heparin alter portal plasma insulin levels and the increase in plasma insulin following an intravenous injection of glucose. In conclusion, these data do not confirm the formerly observed inhibitory effect of heparin, which can therefore be used for the in vivo evaluation of a bioartificial pancreas.

Animals↗
PubMedDate not supplied

Two recent cases of tertiary syphilis.

Tertiary syphilis is now a rare disease in Europe, mainly as a result of occasional antibiotherapy for concomitant infections. However early syphilis is rising in USA and Germany, and it is necessary to maintain an high level of knowledge and suspicion to achieve a diagnosis in the tertiary stage of the disease. In this report two patients with benign tertiary syphilis are described. The first one is a 55-year-old female with erythemato-violaceous annular scaling plaques on the right buttock and scapula and on both thighs, which had a negative and then a low VDRL titer. The second case is a 33-year-old mentally handicapped female with erythematous plaques, with psoriasiform scaling in the trunk and well defined crusted ulcers on the face, which also had negative VDRL. Biopsy of the skin lesions revealed plasmocytic infiltrate with endothelial swelling without granulomas and with negative silver stains in both patients. The investigation for cardiovascular and neurological involvement was negative in both patients. Diagnosis of tertiary syphilis can be difficult as clinical pictures can be misleading, similar to other granulomatous diseases, and serological titers can be low or negative. We recall the necessity of ruling out neurological and cardiac involvement in this stage of syphilis. These cases are reported as a reminder of the possibility of syphilis, so that new cases are not misdiagnosed and mistreated as other diseases.

Adult↗
PubMedDate not supplied

[Prevalence of cutaneous lesions in Freixo de Espada à Cinta].

Incidence or prevalence studies on cutaneous lesions in general populations are not available. The community observed by the authors (Freixo de Espada à Cinta, North-Eastern Portugal) is relatively closed. A pre-tested questionnaire for socio-demographic and clinical information was used and a physical observation was conducted in January and February 1994 by the Dermatology Team of Santo António General Hospital, Oporto. The analysis was supported by independent tests (Pearson and Fisher chi 2, Student-t, Mann-Whitney and Kruskall-Wallis). The Spearman correlation coefficient was also used. The results indicated that 51.9% of 1000 subjects analysed were in phototype III. Concerning specific pathologies, the following percentages were observed: melanocytic nevi 81.2; hemangiomas 26.5; androgenetic alopecia 20.5; deshydrotic eczema 12.7; seborrheic keratosis 11; solar keratosis 9.6; acne vulgaris 9.5; seborrheic dermatitis 6.9; superficial mycosis 6.4; other dermatitis 5.5; vascular spiders 4.4; vulgar psoriasis 1.9; vulgar warts 1.5; pediculosis and scabiosis 1.2.; herpes simplex 0.9; impetigo 0.7; tumours (neoplasias) 0.7; dysplastic nevi 0.6; urticaria 0.3. More than nine nevi were counted in 50% of the subjects observed. A difference was observed (p < 0.05) concerning the presence of nevi, mycosis, hemangiomas, non-specific dermatitis, vascular spider and solar keratosis according to sex. The females had more nevi in number than males (Mann-Whitney, p = 0.03). According to age there was a difference concerning the presence of nevi, superficial mycosis, deshydrotic eczema, seborrheic dermatitis, acne, psoriasis, tumours, hemangiomas, non-specific dermatitis, vascular spider, solar keratosis (with linear augmentation by age) and seborrheic keratosis. Nevi increased with ageing (Rs = 0.10 p < 0.001) and a greater number were observed in age groups 0-9 and 60 or more years. Acne was observed in 9.4% of the females and 9.7% of the males, 46.2% in the 15-29 year-old age group. This study indicated that the population had a mean of nine nevi. Psoriasis was similar to that mentioned in other studies: about 1% in the United States of America. Atopic dermatitis (5.5%) is below the values for the northern population (> = 15%), but above that indicated for the English and American population. Nevertheless, the values of the present study were higher than those in the latter populations, when children until seven years old were considered. The Freixo de Espada à Cinta population above 60 years had solar keratosis in 30.6%, a value three times higher than the previous decade (10.9%); reference values were not found. Contrary to the literature, an association was not established between phototype and solar keratosis. Cutaneous tumours were observed in 0.7% of the cases.

Adolescent↗
PubMedDate not supplied

In vitro and in vivo evaluation in dogs of a miniaturized glucose sensor.

A miniaturized glucose sensor was developed, consisting of a platinum wire entirely coated with teflon, except for a 1 mm section near its extremity where glucose oxidase is immobilized. The in vitro sensitivity to glucose of the sensors was 2.3 +/- 0.4 nA/mM, mean +/- SEM (n = 23). These sensors were implanted in the subcutaneous tissue of normal beagles. Two consecutive glucose infusions (15-30 mg/kg/min) were performed. The current generated by the sensor was used for calculation of the sensitivity coefficient (SC) (nA/mM), and the background current in the absence of glucose (lo) (nA). These parameters were used for determination of the apparent subcutaneous glucose concentration. The in vivo sensitivity was less than the in vitro sensitivity (0.5 +/- 0.1 vs. 2.2 +/- 0.2; n = 12 comparisons; p less than 0.01). Stability of sensor function was demonstrated by the absence in variation of SC and lo, calculated from the different plateaus obtained during the glucose infusions. This study provides a simple method for evaluating in vivo the function of a miniaturized sensor implanted in subcutaneous tissue.

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↗