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Biomedical subjects

G A Silva

Publications and source records attributed to G A Silva.

At least 19 recordsLinked to original sources
PubMed2005

Entrapment ability and release profile of corticosteroids from starch-based microparticles.

We previously described the synthesis of starch-based microparticles that were shown to be bioactive (when combined with Bioactive Glass 45S5) and noncytotoxic. To further assess their potential for biomedical applications such as controlled release, three corticosteroids with a similar basic structure-dexamethasone (DEX), 16alpha-methylprednisonole (MP), and 16alpha-methylprednisolone acetate (MPA)-were used as models for the entrapment and release of bioactive agents. DEX, MP, and MPA were entrapped into starch-based microparticles at 10% wt/wt of the starch-based polymer and the loading efficiencies, as well as the release profiles, were evaluated. Differences were found for the loading efficiencies of the three corticosteroids, with DEX and MPA being the most successfully loaded (82 and 84%, respectively), followed by MP (51%). These differences might be explained based on the differential distribution of the molecules within the matrix of the microparticles. Furthermore, a differential burst release was observed in the first 24 h for all corticosteroids with DEX and MP being more pronounced (around 25%), whereas only 12% of MPA was released during the same time period. Whereas the water uptake profile can account for this first stage burst release, the subsequent slower release stage was mainly attributed to degradation of the microparticle network. Differences in the release profiles can be explained based on the structure of the molecule, because MPA, a more bulky and hydrophobic molecule, is released at a slower rate compared with DEX and MP. In this work, it is shown that these carriers were able to sustain a controlled release of the entrapped corticosteroids over 30 days, which confirms the potential of these systems to be used as carriers for the delivery of bioactive agents.

Dexamethasone↗
PubMed2004

Synthesis and evaluation of novel bioactive composite starch/bioactive glass microparticles.

The aim of the development of composite materials is to combine the most desired properties of two or more materials. In this work, the biodegradable character, good controlled-release properties, and natural origin of starch-based biomaterials are combined with the bioactive and bone-bonding properties of bioactive glass (BG). Novel, bioactive composite starch-BG microparticles were synthesized starting from a blend of starch and polylactic acid (50%/50% wt) with BG 45S5 powder using a simple emulsion method. Morphological and chemical characterization showed that these particles exhibited a spherical morphology with sizes up to 350 microm and that BG 45S5 was incorporated successfully into the composite particles. Upon immersion in a solution simulating body fluids, for periods up to 3 weeks, their bioactive nature was confirmed, as a calcium-phosphate layer resembling biological apatite was formed onto their surface. The short-term cytotoxicity of these materials was also tested by placing 24-h leachables of the materials extracted in culture medium in contact with a fibroblastic cell line (L929) up to 72 h. At this time period, two biochemical tests--MTT and total protein quantification--were performed. The results showed that these materials are not cytotoxic. These results constitute the basis of future encapsulation studies using bone-acting therapeutic agents such as bone morphogenetic proteins or other bone-relevant factors. The particles developed here may be very useful for applications in which controlled release, degradability, and bone-bonding ability are the main requirements.

Animals↗
PubMed2004

Preparation and characterisation in simulated body conditions of glutaraldehyde crosslinked chitosan membranes.

Chitosan membranes, aimed at biomedical applications, were prepared by a solvent casting methodology. Crosslinking was previously performed in acetic acid solution with glutaraldehyde, in order to obtain different degrees of crosslinking. Some membranes were neutralised in a NaOH solution. Mechanical tensile tests comprised quasi-static experiments at constant stress rate and temperature sweep dynamic mechanical analysis tests. This included measurements with the samples immersed in isotonic saline solution at 37 degrees C, in order to simulate physiological conditions, that were performed using a specific liquid container. It was observed that for higher crosslinking levels the membranes become stiffer but their strength decreases; these results are in agreement with swelling tests, also performed at body temperature. All the membranes exhibited similar and significant damping properties in wet conditions, which were stable in a broad temperature range. Weight loss measurements showed that the developed membranes degrade slowly up to 60 days. Cytotoxicity screening, using cell culture tests, showed that eventually such materials could be adequate for use in biomedical applications.

Acetic Acid↗
PubMed2003

Effect of hypocaloric meals with different macronutrient compositions on energy metabolism and lung function in obese women.

OBJECTIVE: We investigated the effect of hypocaloric mixed diets with different proportions of carbohydrate, protein, and fat on resting metabolic rate and the thermic effect of food in obese women. METHODS: Three mixed hypocaloric diets were consumed in random order during separate periods lasting 7 d each. Between each dietary period there was a washout period of 10 d. Diet 1 had a higher proportion of energy from carbohydrate (72%), diet 2 had a higher proportion of energy from protein (43%), and diet 3 had a higher proportion of energy from fat (68%). Indirect calorimetry and lung function tests were done after the completion of each 7-d diet. Seven obese women, ages 22 to 45 y and with body mass indexes of 32 to 59 kg/m(2), participated in the study. Oxygen consumption, carbon dioxide production, resting metabolic rate, and the thermic effect of food by indirect calorimetry were measured. Lung function tests included spirometry in the seated and upright positions, arterial blood gas analysis, and maximal inspiratory and expiratory pressures. RESULTS: There were no statistically significant differences in the resting metabolic rate and the thermic effect of food resulting from the three diets. The mean resting metabolic rates (kJ/d) were 7453 +/- 1446 for diet 1, 7461 +/- 1965 for diet 2, and 7076 +/- 2048 for diet 3. The mean thermic effects of food (kcal/min) were -0.02 +/- 0.07 for diet 1, -0.01 +/- 0.25 for diet 2, and 0.05 +/- 0.13 for diet 3. Lung function tests were normal before and after the hypocaloic diets: partial pressure of oxygen (mmHg) values were 81 +/- 13, 77 +/- 8, and 78 +/- 11 for diets 1 to 3, respectively; and partial pressure of carbon dioxide (mmHg) were 37 +/- 4, 37 +/- 3, and 37 +/- 4 for diets 1 to 3, respectively. CONCLUSIONS: Obese women with normal lung function tests and consuming mixed hypocaloric diets showed no alteration in resting metabolic rate and a reduced or absent thermic effect of food independently of the macronutrient composition.

Adult↗
PubMed2003

In vitro degradation and cytocompatibility evaluation of novel soy and sodium caseinate-based membrane biomaterials.

Soy- and casein-based membranes are newly proposed materials disclosing a combination of properties that might allow for their use in a range of biomedical applications. Two of the most promising applications are drug delivery carrier systems and wound dressing membranes. As for all newly proposed biomaterials, a cytotoxic scanning must be performed as a preliminary step in the process of the determination of the compatibility with biological systems (biocompatibility). In this study, the cytotoxicity of both soy- and casein-based protein biomaterials has been evaluated and correlated with the materials degradation behavior. It was possible to show, through morphological and biochemical tests that these natural origin materials do not exert any cytotoxic effect over cells, and in some cases can in fact enhance cell proliferation. The different treatments to which the membranes were subjected during their processing (that include crosslinking with glyoxal and tannic acid, and physical modification by thermal treatment) seemed to have a clear effect both on the materials mechanical properties and on their in vitro biological behavior.

Journal Article↗
PubMed2002

Do steroids interfere in dyspnoea sensation?

Dyspnoea remains a remarkable clinical problem and a therapeutic challenge, mainly in chronic respiratory conditions. This study investigated the potential effects of steroids on dyspnoea sensation regardless of their pulmonary anti-inflammatory actions. Sixteen healthy men (mean age +/- SD = 22.5 +/- 1.6 years) developed uncomfortable breathing by the use of inspiratory resistors (loads of 0, 7, 14 and 21 cm H2O/l/s) and breathholding 6 h after taking 40 mg of prednisone (Pred) or placebo (Plac). Respiratory discomfort during breathing with loads was evaluated with a 100 mm visual analog scale. The maximum voluntary apnoea time did not differ between the prednisone and placebo days (Plac = 96 +/- 11.8 s x Pred = 105 +/- 12.2 s) and prednisone did not influence the dyspnoea sensation induced by different inspiratory loads (0 cm H2O/l/s: Pred = 2.8 mm x Plac = 1.9 mm; 7 cm H2O/l/s: Pred = 18.3 mm x Plac = 18.6 mm; 14 cm H2O/l/s; Pred = 33.0 mm x Plac = 34.1 mm; 21 cm H2O/l/s: Pred = 48.1 mm x Plac = 49.6 mm). Prednisone intake was associated with a significant increase in minute ventilation during breathing with no inspiratory loads (Pred = 11.91 +/- 1.28 l/min- x Plac = 9.95 +/- 0.86 l/min). Although steroids certainly may improve respiratory conditions due to anti-inflammatory actions, available evidence does not support any specific beneficial effect of these drugs on these perception of dyspnoea itself.

Administration, Oral↗
PubMed2001

Dynamic and steady-state light adaptation of mouse rod photoreceptors in vivo.

1. Electroretinographic (ERG) methods were used to investigate the effects of background illumination on the responses of mouse rod photoreceptors in vivo. A paired-flash procedure, involving the recording and analysis of the ERG a-wave response to a bright probe flash presented after a brief test flash, was used to derive the rod response to the test flash in steady background light. A related, step-plus-probe procedure was used to derive the step response of the rods to backgrounds of defined strength. 2. Steady background light produced a maintained derived response that was graded with background strength. Determinations of the full time course of the derived weak-flash response in steady background light, and of the effect of background strength on the flash response at fixed post-test-flash times, showed that moderate backgrounds reduce the peak amplitude and duration of the flash response. 3. The response to stepped onset of an approximately half-saturating background (1.2 sc cd m(-2)) exhibited a gradual rise over the first 200-300 ms, and an apparent subsequent relaxation to plateau amplitude within 1 s after background onset. Determinations of normalized amplitudes of the derived response to a test flash presented at 50 or 700 ms after background onset indicated substantial development of background-induced shortening of the test flash response within this 1 s period. These findings indicate a time scale of approximately 1 s or less for the near-completion of light adaptation at this background strength. 4. Properties of the derived response to a stepped background and to test flashes presented in steady background light are in general agreement with photocurrent data obtained from mammalian rods in vitro and suggest that the present results describe, to good approximation, the in vivo desensitization of mouse rods by background light.

Adaptation, Ocular↗
PubMed2000

Histological and histoquantitative study of the rat parotid gland after Trypanosoma cruzi infection.

The present study deals with the morphology of the rat parotid gland and its changes after Trypanosoma cruzi infection. The glands of control and infected animals were analyzed by histologic and histoquantitative methods. After 18 days of infection with T. cruzi, a significant reduction of the density of the volume of the acini and duct system, as well as a significant increase in the amount of connective tissue was noted. In addition, these animals displayed an increase in the number of cells undergoing mitosis. In the 45 day infected rats, there was return to the normal pattern. It is suggested that in the infected animals the decrease in body weight could be responsible for retarded sexual maturity, leading to the lower level of testosterone. It can be assumed that decreased levels of epidermal growth factor (EGF) and neural growth factor (NGF) caused by the lack of testosterone in infected animals also contribute to the atrophy of the parotid gland and to the proliferation of the connective tissue.

Acute Disease↗
PubMed2000

Dyspnea scales in the assessment of illiterate patients with chronic obstructive pulmonary disease.

BACKGROUND: Multiple physiological, psychological, social and environmental factors may affect the perception of dyspnea. Although different scales have been used to record the severity of dyspnea in subjects with chronic obstructive pulmonary disease (COPD), none has reported evaluating the properties of such tools in illiterate patients. The objective of this study was to evaluate the reliability and features of concurrent validity of 4 dyspnea scales in illiterate (IL) subjects with COPD. METHODS: One hundred COPD patients submitted to spirometry and were asked to score their breathlessness using a visual analogue scale (VAS), a numerical rating scale (NRS), the Borg scale (BS), and the basal dyspnea index (BDI). Each scale was presented to the patients before and after they had performed spirometry and measurement of residual volume. The obtained scores were analyzed according to the literacy status of the patients. RESULTS: Thirty-three patients were classified as IL and 67 as literate (L). Both groups showed similar respiratory impairment and median scores of dyspnea (VAS, L = 45.0, IL = 49.0; NRS, L = 5.0, IL = 5.0; BS, L = 3.0, IL = 3.0; BDI, L = 5.0, IL = 4.0). No significant differences were found between the dyspnea scores obtained before and after spirometry for all scales in both groups. The degree of correlation between forced expiratory volume in 1 second (FEV1) and usual dyspnea evaluated by BDI did not show a statistical difference between the two groups (L, r = 0.37; IL, r = 0.51). CONCLUSION: The employed dyspnea scales showed comparable reliability in both L and IL COPD subjects.

Adult↗
PubMed1999

Group I and II metabotropic glutamate receptor expression in cultured rat spinal cord astrocytes.

We have examined the development of expression of group I and II metabotropic glutamate receptors (mGluRs) in pure rat spinal cord astrocyte cultures, using immunocytological and calcium imaging techniques. mGluR1alpha and mGluR2/3 antibodies were found to label roughly 10% of the total astrocyte population at all time points examined, whereas mGluR5 was poorly expressed in our culture system. Results from intracellular Ca2+ imaging experiments, measured using fura-2 ratio imaging, suggest that 20% of these cultured astrocytes express functional group I mGluRs (mGluR1 and/or 5). Our results contrast with previously published work in cultured cortical astrocytes where mGluR5 and not mGluR1 is expressed, suggesting that cultured astrocytes from different parts of the CNS exhibit different patterns of mGluR expression.

2-Amino-5-phosphonovalerate↗
PubMed1998

A novel and rapid method for culturing pure rat spinal cord astrocytes on untreated glass.

Astrocytes are the major population of glial cells, and are key players in the development, maintenance, and functioning of the central nervous system (CNS). Their potential as targets of therapeutic intervention following CNS injury makes the elucidation of their cellular and subcellular physiology a primary research goal. Well defined and pure cell culture systems are required to examine astrocytic physiology, biochemical pathways and underlying responses to pathophysiologically altered conditions. Previously published protocols for establishing primary astrocyte cultures are time- and resource-consuming or suffer high contamination from other undesired cell types. Here we describe a new and simple procedure for producing highly pure ( > 99%) rat primary astrocyte cultures. The method involves a simple mechanical dissociation of harvested spinal cord tissue through a porous membrane and the subsequent plating of the cells on plain, untreated glass coverslips. Astrocytes adhere very well to the untreated glass while other cell types require a substrate such as poly-L-lysine. The method described here is, therefore, ideal for experiments which require highly pure astrocyte cultures.

Animals↗
PubMed1995

Cystatin S in secretory granules fractions isolated from submandibular gland of infected rats by Trypanosoma cruzi.

We have measured the relative concentrations of cysteine proteinase in the granular fractions of submandibular glands of control and Trypanosoma cruzi infected rats by using a sensitive solid phase ELISA. Gland samples were homogenized in 0.34 M sucrose and 0.5 mM EDTA in 10 mM HEPES buffer at a pH of 7.4. The extract was centrifuged and filtered through Millipore filters to prepare a purer granular fraction. Immunochemical studies using antibody against cystatin S and electrophoretic analysis showed higher cystatin S levels in infected rats than in control. The role of this inhibitor during acute phase of Chagas disease is discussed.

Acute Disease↗
PubMed1994

Isolation and partial characterization of an endopeptidase from Enterolobium contortisiliquum seeds.

1. Aqueous extracts of Enterolobium contortisiliquum seeds contain an endopeptidase of M(r) 60,000 with specificity for basic amino acid residues. The enzyme was purified by chromatography on DEAE Sephadex, followed by gel filtration on Sephadex G-75 and affinity chromatography on Zinc-Sepharose. The overall purification was 300-fold and the yield about 46%. 2. The endopeptidase hydrolyzes benzoyl-arginine-p-nitroanilide (Bz-Arg-pNan) and acetyl-phenylalanine-arginine-p-nitroanilide (Ac-Phe-Arg-pNan) with Km 14.4 mM and 0.062 mM, respectively. Succinyl-phenylalanine-p-nitroanilide (Suc-Phe-pNan) and tosyl-arginine methyl ester (TAME) were not hydrolyzed. E. contortisiliquum endopeptidase also cleaves a seed protein of low molecular weight from the same E. contortisiliquum seeds, and converts Met-Lys-bradykinin into bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg). 3. Metals (1.0 mM) such as Cr3+, Fe3+ and Zn2+ ions inactivate the enzyme when Bz-Arg-pNan was the substrate. Enzyme activity is abolished by EDTA but is partially restored by Cu2+, Al3+, Ba2+, Mn2+, Mg2+, Fe2+, Ca2+ and Co2+ ions. The endopeptidase is not inhibited by the previously purified E. contortisiliquum inhibitors of trypsin and cysteine proteinases, or by soybean trypsin inhibitor (Oliva et al. (1987). Brazilian Journal of Medical and Biological Research, 20:767-770).

Amino Acid Sequence↗
PubMed1991

Screening of plants used in south Brazilian folk medicine.

Thirty-seven species of medicinal plants used in folk phytotherapy were chemically screened for alkaloids, coumarins, flavonoids, anthraquinones, saponins, sterols and/or triterpenes and tannins. Seven of these were also screened for the presence of mutagenic activity using the Ames test (Salmonella/microsome).

Brazil↗