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M Acosta

Publications and source records attributed to M Acosta.

At least 19 recordsLinked to original sources
PubMed1992

Catalytic oxidation of 2,4,5-trihydroxyphenylalanine by tyrosinase: identification and evolution of intermediates.

The oxidation of 3,4-dihydroxyphenylalanine (dopa) by O2 catalyzed by tyrosinase yields 4-(2-carboxy-2-aminoethyl)-1,2-benzoquinone, with its amino group protonated (o-dopaquinone-H+). This evolves non-enzymatically through two branches (cyclization and/or hydroxylation), whose respective operations are determined by pH. The hydroxylation branch of o-dopaquinone-H+ only operates significantly at pH < or = 5.0 and involves the accumulation of 2,4,5-trihydroxyphenylalanine (topa), which has been detected by high-performance liquid chromatography (HPLC). This last compound is also a substrate of tyrosinase. The oxidation of topa by both tyrosinase and periodate yields 5-(2-carboxy-2-aminoethyl)-4-hydroxy-1,2-benzoquinone, with its amino group protonated (o-topaquinone-H+), which is red (RTQH) (lambda max 272-485 nm) at pH 7.0 and yellow (TTQH) (lambda max 265-390 nm) at pH 3.0. This is based on pKa 4.5 of the 2-OH group of the benzene ring of o-topaquinone-H+, as derived from spectrophotometric and HPLC assays. At physiological pH, RTQH undergoes deprotonation of the ammonium group of the side chain to yields RTQ, which cyclize into 2-carboxy-2,3-dihydroxyindolen-5,6-quinone (dopachrome), with a 1:1 stoichiometry and first-order kinetics. The evolution of RTQH has been analyzed by spectrophotometry, HPLC, cyclic voltammetry and constant potential electrolytic assays. From HPLC assays, the value of the first-order constant for the evolution of RTQH at pH 7.0 (kRTQHapp 4.83 x 10(-5) s-1), as well as of the rate constant for the cyclization step of RTQ (kRTQc 2.53 x 10(-3) s-1) were determined.

Animals↗
PubMed1992

The use of low glycaemic index foods improves metabolic control of diabetic patients over five weeks.

The aim of the present study was to determine whether any benefit might occur from lowering the glycaemic index of diet in the medium term in diabetic patients. Eighteen well-controlled diabetic patients (12 Type 1 and 6 Type 2 non-insulin-treated), were assigned to either a high mean glycaemic index or low mean glycaemic index diet for 5 weeks each in a random order using a cross-over design. The two diets were equivalent in terms of nutrient content and total and soluble fibre content. The glycaemic indices were 64 +/- 2 (mean +/- SD) % and 38 +/- 5% for the two diets. The high glycaemic index diet was enriched in bread and potato and the low glycaemic index diet in pasta, rice, and legumes. At the end of the study periods, the following variables were improved on the low compared to the high glycaemic index diet: fructosamine (3.9 +/- 0.9 vs 3.4 +/- 0.4 mmol l-1, p less than 0.05); fasting blood glucose (10.8 +/- 2.8 vs 9.6 +/- 2.7 mmol l-1, p less than 0.02); 2-h postprandial blood glucose (11.6 +/- 2.9 vs 10.3 +/- 2.5 mmol l-1, p less than 0.02); mean daily blood glucose (12.0 +/- 2.5 vs 10.4 +/- 2.7 mmol l-1, p less than 0.02); serum triglycerides (1.5 +/- 0.9 vs 1.2 +/- 0.6 mmol l-1, p less than 0.05). No significant differences were found in body weight, HbA1C, insulin binding to erythrocytes, insulin and drug requirements, and other circulating lipids (cholesterol, HDL-cholesterol, phospholipids, Apolipoprotein A1, Apolipoprotein B). Thus the inclusion of low glycaemic index foods in the diet of diabetic patients may be an additional measure which slightly but favourably influences carbohydrate and lipid metabolism, requires only small changes in nutritional habits and has no known deleterious effects.

Adult↗
PubMed1991

1-Aminocyclopropane-1-carboxylic acid as a substrate of peroxidase: conditions for oxygen consumption, hydroperoxide generation and ethylene production.

Conditions in which 1-aminocyclopropane-1-carboxylic acid (ACC) functions as a substrate of peroxidase have been investigated by measuring oxygen consumption in the reaction medium and the production of ethylene. In both cases, the presence of Mn2+ and either H2O2 or the activated form of peroxidase, namely compound I of peroxidase, was found to be essential. Both oxygen consumption and ethylene production were dependent on enzyme concentration, the optimum ACC/Mn2+ ratio being 1:1. Oxygen consumption in a system with ACC, Mn2+ and compound I showed an enzyme-dependent lag phase and then proceeded to total depletion, suggesting that the system itself generates hydroperoxides that completed the catalytic cycle of the enzyme. The presence of these hydroperoxides in the reaction medium was detected by a colorimetric method. High H2O2 concentration progressively decreased oxygen consumption, the same effect being produced by catalase. Ethylene production was oxygen dependent, mediated by ACC-free radicals and gave a poor yield. The results suggest that the fate of these ACC-free radicals determines the yield in ethylene. These radicals must be oxidized immediately, otherwise their stabilization to hydroperoxides would prevent ethylene production.

Amino Acids↗
PubMed1991

Delayed sternal closure for life-threatening complications in cardiac operations: an update.

Over a 7-year-period, 25 patients had delayed sternal closure after open heart operations out of 34 patients whose sternum was not closed. The indications were extreme cardiac dilatation and uncontrollable mediastinal hemorrhage. This represented a 1.79% incidence in the overall open heart surgical experience at our unit. Sternal closure was performed at a mean of 2.64 days after the initial operation. Eighteen patients (52.9%) left the hospital alive and well, representing a 72% survival rate among patients undergoing delayed sternal closure. No mediastinal or fatal infection developed and only 1 patient had late superficial wound infection after delayed sternal closure. We conclude that delayed sternal closure is an effective method to treat severe complications after cardiac operations.

Adult↗
PubMed1991

[Replacement of the aortic root and ascending aorta with a fresh antibiotic-sterilized homograft].

The case of a 53-year-old male suffering from aortic stenosis and aneurysm of the ascending aorta treated by aortic root replacement with a fresh antibiotic-sterilized aortic homograft is presented. The technique and indications are commented on, focusing attention in the scanty results available in the literature with regard to this technique. We support the use of homografts in aortic root replacement in selected cases.

Anti-Bacterial Agents↗
PubMed1990

A kinetic study on the suicide inactivation of peroxidase by hydrogen peroxide.

In the absence of reductant substrates, and with excess H2O2, peroxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) shows the kinetic behaviour of a suicide inactivation, H2O2 being the suicide substrate. From the complex (compound I-H2O2), a competition is established between two catalytic pathways (the catalase pathway and the compound III-forming pathway), and the suicide inactivation pathway (formation of inactive enzyme). A kinetic analysis of this system allows us to obtain a value for the inactivation constant, ki = (3.92 +/- 0.06) x 10(-3) x s-1. Two partition ratios (r), defined as the number of turnovers given by one mol of enzyme before its inactivation, can be calculated: (a) one for the catalase pathway, rc = 449 +/- 47; (b) the other for the compound III-forming pathway, rCoIII = 2.00 +/- 0.07. Thus, the catalase activity of the enzyme and, also, the protective role of compound III against an H2O2-dependent peroxidase inactivation are both shown to be important.

Horseradish Peroxidase↗
PubMed1990

Inactivation of peroxidase by hydrogen peroxide and its protection by a reductant agent.

Hydrogen peroxide, the oxidant substrate of peroxidase, is also an inactivating agent of this enzyme. The reductant substrates protect the enzyme from the inactivating process. A reaction mechanism is proposed, in which two competitive routes exist for Compound I of peroxidase; one catalytic and one inactivating. The analytical solution produced at the end of the reaction supports the proposed mechanism and shows the dependence between the number of turnovers of the enzyme (r) and the ratio of both substrates.

Benzothiazoles↗
PubMed1990

An enzymatic colorimetric method for measuring naringin using 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid)(ABTS) in the presence of peroxidase.

A sensitive colorimetric method for naringin estimation using 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) as peroxidase substrate is described. The method is based on the coupling reaction of an ABTS radical cation with an oxidation product of naringin formed by peroxidase. This coupling reaction leads to the formation of a purple-colored compound with a maximum absorption at 560 nm. A molar absorption coefficient at this wavelength was calculated to be 13,286 +/- 200 M-1 cm-1. The lowest amount of naringin that can be detected is 1 nmol. The application of this method to the quantification of naringin in grapefruit tissues is presented.

Benzothiazoles↗
PubMed1990

Is the copper T 380A device associated with an increased risk of removal due to bleeding and/or pain? An analysis.

Previous studies have consistently shown that the family of the Copper T 380 devices is more effective in preventing accidental pregnancies than the inert, as well as most other, if not all, copper devices. However, a number of these studies also reported a higher removal rate due to bleeding and/or pain for the TCu 380A than for other devices. The programmatical importance of these findings prompted us to analyze the international multi-center randomized clinical trial datasets to examine this question on the new TCu 380A (ParaGard) recently marketed in the U.S. Our results, while confirming the inherent superior efficacy of the TCu 380A, did not reveal a significantly higher removal rate because of bleeding and/or pain among TCu 380A users than among users of the comparative devices, which included the Lippes Loop D, the TCu 200, the TCu 220 and the Multiload Cu 250 devices.

Adolescent↗
PubMed1990

A new technical alternative in the surgery for retroperitoneal fibrosis: the Gore-Tex surgical membrane.

The case of a male patient with retroperitoneal fibrosis secondary to an abdominal aortic aneurysm which was surgically treated with success, is presented herein. What is considered technically new is the management of the ureters after surgical lysis. An expanded polytetrafluoroethylene Gore-Tex surgical membrane, initially developed for pericardial closure after open-heart surgery, was used to isolate the bifurcated aortofemoral graft from the duodenum and the ureters from the vascular prosthesis and surrounding retroperitoneal tissues. This is considered to be a simple and safe technique and a technical alternative when dealing with this complex situation. To date, there has been no other description of such a technique using this material. The potential value of this material to prevent reencasement in retroperitoneal fibrosis from other origins should be kept in mind.

Aorta, Abdominal↗
PubMed1985

Oxygen consumption during the indole-3-acetic acid oxidation catalyzed by peroxidase. Effect of the enzyme/substrate ratio.

Oxygen consumption during the oxidation of indole-3-acetic acid (IAA) by peroxidase has been studied, in conditions of no limitation by oxygen. For different enzyme/substrate ratios the quotient O2 consumed/IAA oxidized shows rather small differences and it is always less than unity. During the reaction, however, the quotient undergoes important variations because oxygen uptake ceases long before the decarboxylation of IAA. The results are discussed in the light of previous proposed mechanisms.

Free Radicals↗
PubMed1975

Hormonal pattern of relapse in hyperthyroidism.

22 patients with Grave's disease were followed up for up to a year after antithyroid drug therapy was discontinued. Clinical assessment and serum T3, T4, and thyroid-stimulating-hormone (T.S.H.) estimations were done serially and simultaneously. Serum T3 or T4 concentrations may be elevated briefly in the first few weeks after antithyroid drugs are stopped, as a rebound effect not necessarily indicative of subsequent relapsf. Clinical relapse of hyperthyroidism with subsequent improvement on antithyroid drugs occurred in 13 patients. Of these 13, serum T3 concentrations became elevated before serum T4 concentrations in 5, thus predicting the subsequent development of clinical hyperthyroidism. In the remaining 8 patients who relapsed, serum T4 was elevated a month before the serum T3. Hyperthyroidism was diagnosed clinically after elevated serum T3 concentrations in 11 patients and at the same time in 2 patients. The mean period of "biochemical hyperthyroidism" in these 11 patients was 12 weeks, with a range of 1 to 56 weeks. During this period 9 of the 11 had minor clinical changes attributable to hyperthyroidism. It is concluded that serial estimations of serum T3 provide the most reliable method of monitoring relapse in hyperthyroidism.

Carbimazole↗
PubMed1975

Ecologic studies of Venezuelan encephalitis virus in Peru during 1970-1971.

Venezuelan encephalitis (VE) virus has intermittently produced epidemics and equine epizootics on the dry Pacific coastal plain of Peru since at least the 1930's. However, evidence that the virus exists in the Amazon region of Peru to the east of the Andes mountains was not obtained until antibodies were found in human sera collected in 1965, and 10 strains of the virus were isolated in a forest near the city of Iquitos, Peru during February and March 1971. Eight strains came from mosquitoes and two from dead sentinel hamsters. Three hamsters exposed in forests near Iquitos developed VE virus antibodies suggesting that hamster-benign strains also exist there. Antibody tests of equine sera revealed no evidence that VE virus was actively cycling during the late 1950's or 1960's in southern coastal Peru, where equine epizootics had occurred in the 1930's and 1940's. In northern coastal Peru bordering Ecuador, antibodies were present in equine sera, presumably residual from the 1969 outbreak caused by subtype I virus, since neutralizing antibody titers were higher to subtype I virus than to subtypes III or IV. No VE virus was detected in this northern region during the dry season of 1970 by use of sentinel hamsters. The possibility is considered that VE epidemics and equine epizootics on the Pacific coast of Peru are caused by movements of virus in infected vertebrates traversing Andean passes or in infected vertebrates or mosquitoes carried in airplanes from the Amazon region.

Animals↗
PubMed1975

Serum triiodothyronine in solitary autonomous nodules of the thyroid.

Seventeen patients with solitary autonomous nodules of the thyroid were studied. Eight had clinical features of hyperthyroidism though in some the clinical manifestations were mild. The serum T3 concentration was elevated in all patients with hyperthyroidism but the serum T4 and free thyroxine index were within the normal range in five. All patients with hyperthyroidism subsequently responded to treatment. These findings suggest a high incidence of preferential T3 hypersecretion in hyperthyoidism associated with solitary autonomous thyroid nodule. A further nine patients with single autonomous nodules were clinically euthyroid with normal serum T3 and T4 concentrations and remained euthyroid from 6 to 24 months on serial review.

Chromatography, Gel↗