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Biomedical subjects

E Silva

Publications and source records attributed to E Silva.

13 recordsLinked to original sources
PubMed1992

Riboflavin-photosensitized anaerobic modification of rat lens proteins. A correlation with age-related changes.

When rat lens homogenate or its soluble protein fractions are irradiated in the presence of riboflavin, a photo-adduct is obtained between this vitamin and the lens proteins. Irradiation of these proteins in the presence of riboflavin also leads to a modification in the chromatographic elution pattern with an increase in the high-molecular-weight fraction. In an aging study with rats, it was shown that the proportion of the high-molecular-weight protein fraction significantly increased with age, whereas the proportion of the low-molecular-weight protein fraction concomitantly decreased. It is postulated that aging produces an increase in the accessibility of the tryptophan residues of the lens proteins, as established by iodide fluorescence quenching experiments.

Aging↗
PubMed1992

Uterine papillary serous carcinoma (UPSC) treated with cisplatin, doxorubicin, and cyclophosphamide (PAC).

Uterine papillary serous carcinoma (UPSC) is an aggressive malignancy that accounts for a disproportionate number of intraabdominal failures among endometrial carcinoma patients. The histologic appearance and tendency toward intraabdominal spread resemble those of papillary serous adenocarcinoma of the ovary. Because approximately 70% of untreated ovarian carcinoma patients respond to platinum-based chemotherapy, it has been suggested that UPSC patients might respond to similar treatment regimens. Twenty patients with UPSC were treated with cisplatin, doxorubicin (Adriamycin), cyclophosphamide (PAC) chemotherapy between January 1982 and December 1989. They included 9 patients with advanced primary disease, 5 with recurrence, and 6 who received PAC as adjuvant therapy. Patients received a mean of five cycles of PAC. Only 2 of 11 patients with measurable disease greater than 2 cm achieved complete clinical responses of 12 and 31 months duration; there were no partial responses. Actuarial 5-year survival for all patients was 23%. The mean progression-free interval was 9 months. Patients with clinical stages I or II disease had a higher survival rate than those with stage III or IV disease (P = 0.003). Survival did not correlate with depth of myometrial invasion (P = 0.81) or size of residual tumor following initial surgery (P = 0.16). Estrogen or progesterone receptors were detected in 10 of 11 tumors tested. Seven of 9 patients tested had elevated serum levels of CA-125 (greater than 35 U/ml). Correlation between CA-125 value and clinical course was demonstrated in 3 of 5 patients who had serial measurements. Of all patients, 3 are currently alive; 1 has documented disease. Moderate to severe toxicity was seen in 14 patients (70%). There was one possible treatment-related death from cardiomyopathy. UPSC, despite its histologic and clinical similarities to ovarian carcinoma, was relatively resistant to PAC chemotherapy in this mixed group of patients.

Adult↗
PubMed1992

Clinical features and treatment of Elapidae bites: report of three cases.

This report describes two accidents, involving snakes of the Micrurus corallinus species, where compromising respiratory function was not observed and the specific anti-elapidic serum was the single therapy used, and a third incident, probably involving Micrurus frontalis, where neostigmine was used to remedy respiratory failure.

Adult↗
PubMed1992

Competitive parabolic inhibition of bovine trypsin by bis-benzamidines.

1. Competitive parabolic inhibition, a rare type of inhibition of one-substrate enzymes, is described for alpha- and beta-trypsin. The enzymes were so inhibited by two bis-benzamidines, 4-4'-diazoamino-bis-benzamidine, Berenil (DABB) and its platinum complex, DABB-PtCl2, acting on acyl-amino acid and -peptidyl nitroanilides (Nan) substrates, when inhibitor concentrations exceed 10 mM and approach the millimolar range. 2. The type of nonlinear inhibition observed requires ternary complex formation between one enzyme molecule and two inhibitor molecules (M.E.M), and also permits the formation of the mixed ternary complex (M.E.S). Binding of the first DABB molecule to the active center of trypsin takes place with Ki values of ca. 1.50 microM for both alpha- and beta-trypsin. The secondary binding site binds the inhibitor with dissociation constants Ki2 close to 0.25 mM for both forms of the enzyme, as determined with different substrates. 3. The dissociation constants of the ternary mixed complexes (Ksi and Kis), however, depend on the structural features of the substrates, which are of negligible importance for Bz-Arg-Nan, but significant for Ac-Phe-Arg-Nan and D-Val-Leu-Arg-Nan, reflecting subsite interactions between S1-S3 and S'2. 4. Pentamidine, a diamidino-4,4'-diphenoxy-alkane with a flexible chain, behaved as a strict competitive inhibitor. This implies that the triazene moiety of DABB is involved in the interaction between the inhibitor and the secondary binding site of the enzyme.

Animals↗
PubMed1979

Rate constants studies of the dye-sensitized photoinactivation of lysozyme.

The rate constants for the photodynamic inactivation of hen egg-white lysozyme at different temperatures were studied. Arrhenius plots of the methylene blue sensitized photo-inactivation of lysozyme gave an experimental activation energy of 7.5 kcal/mol. The rate constants for the photodynamic inactivation of lysozyme in the presence of riboflavin decreased almost linearly in the temperature range 4-38 degrees C. The photosensitized oxidation of lysozyme at -20 degrees C in freezing and non-freezing solvents was possible only in the presence of riboflavin. The effect of dye concentration on the quantum yield and rate constant for the photodynamic inactivation of lysozyme was examined. The quantum yields were lower when the concentrations of methylene blue used were low, and increased on increasing dye concentration, getting to a maximum and then declined at higher dye concentrations. It was found that in the case of riboflavin sensitized photo-inactivation of lysozyme both the rate constant and the quantum yield increased as the dye concentration increased. No maximum was observed over the range of dye concentrations studied. A new mechanism is postulated for the photodynamic action of lysozyme in the presence of riboflavin.

Chemical Phenomena↗
PubMed1977

Light-induced binding of riboflavin to lysozyme.

The photodynamic inactivation of lysozyme in air saturated H2O and D2O (phosphate buffer 0.05 M, pH 7.0) in the presence of methylene blue and riboflavin has been studied. When H2O was replaced by D2O a great increase in the rate of photoinactivation of lysozyme was observed. This finding, together with the fact that photooxidation is inhibited by singlet oxygen quenchers like NaN3, suggests that these reactions occur via a singlet oxygen mechanism. During the course of the studies of the riboflavin sensitized photoinactivation of lysozyme, it was found that riboflavin is strongly bound to the enzyme as a result of illumination. This finding would explain the higher quantum yield observed when riboflavin is used, although this dye is bleached during irradiation.

Chemical Phenomena↗
PubMed1977

Stimulation of hepatic mitochondrial alpha-glycerophosphate dehydrogenase and malic enzyme by L-triiodothyronine. Characteristics of the response with specific nuclear thyroid hormone binding sites fully saturated.

Experiments were designed to analyze the relationship of a single i.v. dose of triiodothyronine (T3), the level of plasma and hepatic nuclear T3 attained, and the tissue response as reflected in increased activity of hepatic mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytosol "malic enzyme" (ME). These studied were carried out in euthyroid rats by varying the dose of T3 injected and the time at which the animals were killed and the enzyme levels measured. The plasma T3 concentration was determined and the fraction of nuclear sites occupied at any time t was calculated from the known plasma:nuclear relationship. As a first step, the analysis was confined to the limiting situation in which all nuclear sites were effectively saturated. The following additional information was required and obtained: A proportional relationship between the half-neutralizing volume of a specific antiserum to malic enzyme and the activity of malic enzyme was established, thus confirming previous reports that the increase in enzyme activity induced by T3 is due to increased enzyme mass. The absolute refractory period immediately after i.v. injection of T3, during which no enzyme response could be detected, was determined. This was shown to be 13.4 h for alpha-GPD and 8.2 h for ME. Lastly, the t1/2 of the enzyme decay after pulse injection of T3 was measured. This was similar for both enzymes, 2.8+/-0.6 (SD) days for alpha-GPD and 2.7+/-0.6 (SD) days for ME. The results of these studies indicated that the extent of hepatic response appears limited by full occupancy of a set of intracellular receptor sites by T3 which is in rapid equilibrium with the plasma hormone pool. The kinetic properties of the receptors, as functionally defined in these studies, resemble those associated with the recently described specific nuclear T3 sites. These data per se are thus compatible with but do not prove a nuclear site of initiation of hormone effect. Thye do allow the development of an internally consistent mathematical model which permits prediction of enzyme response when the receptor sites are fully occupied for a given length of time after the i.v. injection of hormone. A separate series of studies was carried out in thyroidectomized rats. The response characteristics of alpha-GPD were similar to those observed in euthyroid animals. In contrast, however, the early response of ME to pulse injections of T3 was very much reduced in hypothyroid animals as compared to euthryoid animals in which nuclear sites were saturated for comparable periods. These findings raise the possibility that a factor required for the induction of malic enzyme but not alpha-GPD is deficient in the hypothyroid state.

Animals↗
PubMed1977

Alpha-amanitin administration results in a temporary inhibition of hepatic enzyme induction by triiodothyronine: further evidence favoring a long-lived mediator of thyroid hormone action.

Alpha-amanitin was shown to inhibit triiodothyronine (T3)-induced increases in mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytoplasmic malic enzyme activity in the livers of male Sprague-Dawley rats. A 3-fold increase in alpha-GPD observed 24 h after the iv injection of 3 microngT3/100 g BW was completely inhibited by administration of alpha-amanitin at 0 and 8 h. Similarly, alpha-amanitin blocked a two- to four-fold increase in malic enzyme 24 h following iv injection of 3 mg T3/100 g BW into euthyroid rats. After the initial inhibition of enzyme induction by alpha-amanitin was dissipated, however, a delayed but striking increase in enzyme activity occurred. In hypothyroid animals, alpha-GPD activity rose after the initial 24 h inhibition and reached levels at 72 h equal to those observed in hypothyroid rats treated with T3 only. In euthyroid animals treated with T3 and alpha-amanitin, a delayed increase in malic enzyme activity was observed at 72 h and attained values at 96 h similar to those in euthyroid animals injected with T3 only. The delayed rise in enzyme response is most easily explained by the formation of a long-lived intermediate during the exposure of the nuclear sites to T3.

Amanitins↗
PubMed1977

Studies of a thyroid hormone and androgen dependent protein in rat liver cytosol.

Sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis of the liver cytosol of euthyroid male rats revealed a prominent band (molecular weight, 26 000 daltons), designated Protein II, which was virtually absent in the cytosol of hypothyroid animals. Injection of 500 mug triiodothyronine (T3) per 100 g body weight resulted in a maximal increase in the level of Protein II, reaching 90% of the euthyroidal level 3 days after hormone administration. Concomitant studies with the liver mitochondrial enzyme alpha-glycerophosphate dehydrogenase (alpha-GPD) indicated that this T3 dose also resulted in a maximal enzyme response in this time period. Since we have estimated that 500 mug of T3 will saturate nearly all nuclear T3 binding sites, these results support the concept that the synthesis of both proteins is limited by nuclear binding. Protein II was absent in the liver cytosol of female rats but could be induced in ovariectomized female rats by androgens. Treatment of male rats with oestradiol resulted in disappearance of Protein II. Since administration of testosterone to hypothyroid male rats caused only a minimal increase in the amount of Protein II, the absence of the protein in hypothyroid animals was not due to androgen deficiency. Similarities in the molecular weight and the response to hormonal manipulation of Protein II and of the urinary alpha2uglobulin, previously reported by Roy (1973) raise the possibility that these proteins are the same. The high concentration of Protein II in male rat cytosol and the relative ease in its identification by SDS polyacrylamide gel electrophoresis make it a potentially useful model protein for the study of thyroid hormone action at the cellular level.

Animals↗