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J C Silva

Publications and source records attributed to J C Silva.

At least 37 records · Page 2Linked to original sources
PubMed1997

Testing transposable elements as genetic drive mechanisms using Drosophila P element constructs as a model system.

The use of transposable elements (TEs) as genetic drive mechanisms was explored using Drosophila melanogaster as a model system. Alternative strategies, employing autonomous and nonautonomous P element constructs were compared for their efficiency in driving the ry+ allele into populations homozygous for a ry- allele at the genomic rosy locus. Transformed flies were introduced at 1%, 5%, and 10% starting frequencies to establish a series of populations that were monitored over the course of 40 generations, using both phenotypic and molecular assays. The transposon-borne ry+ marker allele spread rapidly in almost all populations when introduced at 5% and 10% seed frequencies, but 1% introductions frequently failed to become established. A similar initial rapid increase in frequency of the ry+ transposon occurred in several control populations lacking a source of transposase. Constructs carrying ry+ markers also increased to moderate frequencies in the absence of selection on the marker. The results of Southern and in situ hybridization studies indicated a strong inverse relationship between the degree of conservation of construct integrity and transposition frequency. These finding have relevance to possible future applications of transposons as genetic drive mechanisms.

Animals↗
PubMed1997

Plasma cortisol levels in captive wild felines after chemical restraint.

Eight Panthera onca (Po), 13 Felis concolor (Fc), 7 Felis yagouaroundi (Fy), 7 Felis tigrina (Ft) and 5 Felis pardalis (Fp) specimens from São Paulo State zoos were used. All animals were restrained with darts containing 10 mg/kg ketamine and 1 mg/kg xylazine. Venous blood samples were collected as soon as possible (within 15-20 min) and serum was frozen until the time for cortisol quantification. Cortisol was determined using a solid phase radioimmunoassay with an intra-assay coefficient of 8.51%. Data were analyzed statistically by the Kruskal-Wallis test, followed by Dunn's multiple comparisons test, and the one-sample t-test, with the level of significance set at P < 0.05. Data are reported as means +/- SEM. Cortisol levels differed among the captive felines: Po = 166 +/- 33a, Fc = 670 +/- 118b, Fy = 480 +/- 83b, Ft = 237 +/- 42ab, Fp = 97 +/- 12a nmol/l (values followed by different superscript letters were significantly different (P < 0.001)). Since most of the veterinary procedures on these species involve chemical restraint, these results show the necessity of preventive measures in order to minimize the effect of restraint stress on more susceptible species.

Animals↗
PubMed1996

Purification and characterization of versicolorin B synthase from Aspergillus parasiticus. Catalysis of the stereodifferentiating cyclization in aflatoxin biosynthesis essential to DNA interaction.

The absolute configuration of the dihydrobisfuran ring system characteristic of aflatoxin B1 is essential to the covalent reaction of its metabolically activated form with double-stranded DNA. The biosynthesis of this potent mycotoxin proceeds through three configurationally labile intermediates to racemic versiconal hemiacetal. Subsequent enzymatic cyclization establishes the stereochemistry of this, critical ring fusion in (-)-versicolorin B and is catalyzed by versicolorin B synthase (VBS). The isolation and purification of VBS from Aspergillus parasiticus (SU-1, ATCC 56775) and its kinetic characterization and attempted inactivation are described. Initial purification trials were plagued both by a chromophoric impurity which was difficult to remove and by low recoveries of active protein. The discovery of a remarkably broad pH range of enzyme stability and catalytic activity led to an efficient procedure involving preparative isoelectric focusing and ion exchange FPLC chromatography. The enzyme behaved as a dimer upon gel filtration and migrated with M(r) 78000 Da during denaturing gel electrophoresis. The UV spectrum of pure VBS gave no evidence of a bound chromophore. Detailed kinetic analysis of VBS revealed that this protein selects from two equilibrating enantiomers of versiconal hemiacetal to cyclize the appropriate antipode to optically pure versicolorin B. By varying the amount of enzyme to a fixed concentration of substrate, the rate of enzymic cyclization could be limited by the intrinsic rate of enantiomerization of the substrate under the conditions of reaction. It was possible to quantitate the dynamics of this substrate enantiomerization/cyclization process, to establish the role played by VBS, and to evaluate the significance of each to the overall biosynthesis of aflatoxin. The potential role of an acidic residue of the enzyme in catalysis was supported by analysis of the pH-rate profile of VBS and chemical labeling studies. Successful demonstration of competitive inhibition of VBS by a simple substrate analogue led to the design and synthesis of a potential mechanism-based inactivator of the protein.

Aflatoxin B1↗
PubMed1996

Isolation and characterization of the versicolorin B synthase gene from Aspergillus parasiticus. Expansion of the aflatoxin b1 biosynthetic gene cluster.

Versicolorin B synthase catalyzes the side chain cyclization of racemic versiconal hemiacetal to the bisfuran ring system of(-)-versicolorin B, an essential transformation in the aflatoxin biosynthetic pathway of Aspergillus parasiticus. The dihydrobisfuran is key to the mutagenic nature of aflatoxin B1. The protein, which shows 58% similarity and 38% identity with glucose oxidase from Aspergillus niger, possesses an amino-terminal sequence homologous to the ADP-binding region of other flavoenzymes. However, this enzyme does not require flavin or nicotinamide cofactors for its cyclase activity. The 643-amino acid native enzyme contains three potential sites for N-linked glycosylation, Asn-Xaa-Thr or Asn-Xaa-Ser. The cDNA and genomic clones of versicolorin B synthase were isolated by screening the respective libraries with random-primed DNA probes generated from an exact copy of an internal vbs sequence. This probe was created through polymerase chain reaction by using nondegenerate polymerase chain reaction primers derived from the amino acid sequences of peptide fragments of the enzyme. The 1985-base genomic vbs DNA sequence is interrupted by one intron of 53 nucleotides. Southern blotting, nucleotide sequencing, and detailed restriction mapping of the vbs-containing genomic clones revealed the presence of omtA, a methyltransferase active in the biosynthesis, 3.3 kilobases upstream of vbs and oriented in the opposite direction from vbs. The presence of omtA in close proximity to vbs supports the theory that the genes encoding the aflatoxin biosynthetic enzymes in A. parasiticus are clustered.

Aflatoxin B1↗
PubMed1995

Findings of coronary angioscopy in angiographically normal coronary segments of patients with coronary artery disease.

Compared with pathologic studies coronary angiography is a relatively insensitive technique to detect early atherosclerosis. Coronary angioscopy is a new technique providing direct information on luminal vessel surface. To determine whether coronary angioscopy may detect the presence of atherosclerotic disease on angiographically normal coronary segments, 52 patients underwent a study with coronary angioscopy before coronary angioplasty. The mean age was 59 +/- 10 years; 46 patients were men and 6 were women. The reason for coronary angioplasty was unstable angina in 36 patients, stable angina in 8 patients, and silent ischemia in 8 patients. In seven patients angiography revealed luminal irregularities on the coronary segment proximal to the culprit lesion, and all these patients also had proximal disease as demonstrated by coronary angioscopy. In the remaining 45 (87%) patients angiography revealed a smooth-vessel contour proximal to the target lesion. On quantitative angiography these "normal" coronary segments measured 2.8 +/- 0.4 mm in luminal diameter. In 30 (67%) of these patients angioscopy revealed proximal disease on the vessel wall, but in 15 (33%) patients the luminal surface of these segments also appeared normal on angioscopy. Disease as detected by angioscopy in angiographically normal segments included yellow plaque in 19 patients, mural thrombus in 5, mixed plaques in 4, and small flaps in 2 patients. In eight patients coronary angioscopy detected that atherosclerotic disease extended proximally from the target lesion, but in the remaining 22 patients the angioscopic findings appeared to be discrete and well separated from the angiographic lesion. All these plaques were relatively small and did not protrude into the coronary lumen.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Higher incidence of Gastrospirillum sp. in swine with gastric ulcer of the pars oesophagea.

Gastric ulcer in swine is characterized by an area of acid-peptic digestion, occurs usually in the pars oesophagea of the stomach, and has unknown etiopathogenesis. The present work was carried out to investigate the prevalence of the newly described spiral-shaped microorganism Gastrospirillum sp. ("Gastrospirillum suis") in stomachs of abattoir pigs with and without gastric ulcer. Stomachs were removed from 32 consecutive pigs presenting apparently normal mucosa and from 32 additional consecutive pigs presenting frank, chronic gastric ulcer of the pars oesophagea. Fragments of antral, oxyntic, cardiac and pars oesophagea regions were taken from each stomach and processed for histology and for identification of Gastrospirillum sp. in tissue sections. The microorganisms were identified mainly in the mucous layer and in gastric foveolas of the antral and oxyntic mucosa. Forty pigs (62.5%) were positive for Gastrospirillum sp.; among them, 27 (67.5%) had gastric ulcer, and 13 (32.5%) had no ulcer. Twenty-four pigs (37.5%) were negative for Gastrospirillum sp.; among them, five (20.8%) presented with gastric ulcer, and 19 (79.2%) had no ulcer. There was a significant difference between pigs with and without gastric ulcer in regard to the presence of Gastrospirillum sp. (P < 0.01). The spiral-shaped microorganism Gastrospirillum sp. that inhabits the stomach of pigs should be considered a possible factor connected with the etiopathogenesis of swine gastric ulcer.

Animals↗
PubMed1995

Diltiazem effects on left ventricular function preliminary results of 12 patients evaluated by calibrated apexcardiogram.

Diltiazem is a calcium channel blocker whose effects on left ventricular function (LVF) are controversial. We studied 12 patients with ischemic heart disease (IHD) before starting and 15 and 30 days after having initiated Diltiazem 60 mg t.i.d. LVF was accessed by means of the normalized indexes of the calibrated apexcardiogram: nS for systolic LVF evaluation and nA for diastolic LVF evaluation. Recent works have shown that these indexes have a good correlation with invasive parameters of LVF. We verified that nS did not change and nA decreased significantly (p < 0.05) after Diltiazem. We preliminary concluded that Diltiazem has no deleterious effect on LV systolic function and improves LV diastolic function, by decreasing nA, a parameter which correlates well with LV end diastolic pressure.

Depression, Chemical↗
PubMed1995

Quantitative genetic variation photoinduced by 8-methoxypsoralen in yeast.

The variation in cell mass production within cultured populations of Saccharomyces cerevisiae derived from untreated cells and from cells treated with 8-methoxypsoralen plus near-UV light (8MOP-NUV) was determined. Spontaneous mutation was not significant source of variation, since no genetic component of variance was detected in the untreated population. Following mutagenesis significant levels of genetic variation were found, showing that 8MOP-NUV was effective in inducing quantitative genetic variation among clonal populations of the yeast. The magnitudes of the estimates of the heritability and of the genetic coefficient of variation, indicate that, in phenotypic selection, greater genetic progress can be expected after mutagenic treatment than with untreated populations. The highest estimate of genetic gain was obtained at the intermediate survival level.

Analysis of Variance↗
PubMed1994

Epidemic optic neuropathy in Cuba. Eye findings.

OBJECTIVE: To characterize and establish a clinical definition of the optic neuropathy that appeared in epidemic form in Cuba in 1992 and 1993. METHODS: At the invitation of the Cuban Ministry of Health, Havana, members of ORBIS International and the Pan American Health Organization, assembled teams that traveled to Cuba in May 1993. We were initially briefed by Cuban national experts in the areas of virology, nutrition, toxicology, ophthalmology, neurology, and public health. We then examined 20 patients on our own. Thirteen of these patients underwent a comprehensive neuro-ophthalmologic examination, including neurologic examination, ophthalmologic examination, visual fields, optic nerve function studies, contrast sensitivity studies, and funduscopy. We returned 4 months later to perform an additional 12 comprehensive neuro-ophthalmologic and follow-up examinations. RESULTS: Only seven of the 13 patients who were alleged to have the optic form of the epidemic and who were rigorously and systematically examined on the first visit demonstrated a bilateral optic neuropathy. These seven patients had several features that included decreased visual acuity, poor color vision, central scotomas, decreased contrast sensitivity, saccadic eye movements, and most prominent and distinctive of all, nerve fiber layer wedge defects of the papillomacular bundle. Our clinical definition was then implemented by the Cuban ophthalmologists and epidemiologists. On returning 4 months later, we found that all newly presented patients were correctly diagnosed to have the epidemic disease. With the new case definition and the application of a few simple psychophysical tests, the false-positive rate of diagnosis became much lower. After vitamin therapy, we reexamined the patients seen on our initial visit, and all showed marked improvement. CONCLUSIONS: The Cuban epidemic was characterized by an optic neuropathy with features that were similar to those of tobacco/alcohol amblyopia and Leber's optic atrophy. Recent political, economic, and social changes in Cuba may have contributed to the nutritional and/or toxic compromise of mitochondrial function of an acquired nature, which led to selective retinal ganglion cell damage. We have termed this condition Cuban epidemic optic neuropathy.

Adult↗
PubMed1994

Validation of the cumulative or replicate NAA method for the determination of trace elements in biological materials.

To make the best use of time and facilities, a neutron activation system, fully automatic, including spectrum and data processing, to be used with short-lived nuclides, has been recently developed at the Portuguese Research Reactor (in Portuguese "Reactor Portugês de Investigação," RPI). Using this system, the cumulative neutron activation analysis method is now being implemented. This article summarizes the experimental procedures used to validate the cumulative NAA method for the determination of selenium in biological samples, emphasizing the determination of the essential characteristics of precision, accuracy, and limits of detection and of quantification of the method. The article also examines how detection limits and precision are improved when the samples are analyzed by this method compared to the cyclic activation measurements in use at RPI for the determination of selenium. The improvement is demonstrated for the measurement of selenium in several reference materials when the result obtained by adding up seven spectra of separate aliquots of the same sample is compared to the result from a cumulative spectrum of seven (whenever possible) consecutive cycles of a single sample.

Animals↗
PubMed1994

Coronary stenting for acute coronary dissection after coronary angioplasty: implications of residual dissection.

OBJECTIVES: The aim of this study was to assess the implications of residual coronary dissections after stenting. BACKGROUND: Coronary stenting is currently used in selected patients with coronary dissection after angioplasty. However, in some patients the total length of the dissection may not be completely covered with the device. METHODS: Forty-two consecutive patients (mean [+/- SD] age 58 +/- 11 years; 39 men, 3 women) undergoing stenting for a major coronary dissection after angioplasty were studied. RESULTS: Thirty (67%) coronary dissections were small (< or = 15 mm), and 29 (64%) were occlusive (Thrombolysis in Myocardial Infarction [TIMI] flow grade < or = 2). In 3 patients, coronary stenting was unable to open large occlusive dissections, but a good angiographic result was obtained in 39 patients (93%). After stenting, 22 of these patients (56%) had no visible residual dissections, and 13 (33%) had small and 4 (10%) had large residual dissections. These residual dissections were stable and did not compromise coronary flow. In a repeat angiogram (24 h later) the stent was patent in all 39 patients. However, two patients experienced a subacute stent occlusion. Of the remaining 37 patients, 36 (97%) had a late angiogram after stenting. Quantitative angiography revealed a reduction in minimal lumen diameter at the stent site (2.6 +/- 0.4 vs. 2 +/- 0.7 mm, p < 0.05) and a trend toward improvement in vessel diameter at the site of the previous residual dissection (1.7 +/- 0.6 vs. 1.9 +/- 0.5 mm, p < 0.1). The angiographic image of residual dissection disappeared in all patients. These factors provided a rather smooth angiographic appearance at follow-up. The four patients with large residual dissections after stenting did not have restenosis and were asymptomatic at last visit. CONCLUSIONS: Coronary stenting is effective in the management of acute coronary dissections after angioplasty. In this setting, small residual dissections are frequently seen but have a good outcome and disappear at follow-up. Large residual dissections may have a good outcome if coronary flow is not impaired and no residual stenosis is visualized.

Acute Disease↗
PubMed1994

Clinicopathologic correlation of drusen and retinal pigment epithelial abnormalities in age-related macular degeneration.

BACKGROUND: Clinicopathologic studies of eyes lead to a better understanding of the nature of the ophthalmoscopic and fluorescein angiographic features of drusen. A study was conducted to provide clinicopathologic correlation of drusen and present a classification of drusen based on clinical and histopathologic features. METHODS: The macular areas of three eyes from two patients were serially sectioned and studied, and features were depicted in a two-dimensional map and compared with clinical findings. RESULTS: All three tyes had large drusen (> 63 microns) with soft morphologic characteristics (poorly demarcated borders) documented on fundus photographs. In both eyes from one patient, these large drusen corresponded to areas of focal retinal pigment epithelium hypopigmentation overlying Bruch's membrane, which was diffusely thickened throughout the macula. Similar findings were noted in another eye from a second patient, and additionally, where there was relatively marked fluorescein staining of large drusen on the late phase of an angiogram, the pathologic correlation demonstrated detachment of the thickened inner aspect of Bruch's membrane from the remainder of Bruch's membrane. Focal hyperpigmentation corresponded to areas of hypertrophy of the retinal pigment epithelium and to clusters of pigmented cells in the subretinal space and outer nuclear area. CONCLUSION: Diffuse thickening of the inner aspect of Bruch's membrane is associated with retinal pigment epithelial hypopigmentation, focal atrophy, and soft (large) drusen formation.

Aged↗
PubMed1994

[Perforation of the mitral valve: transesophageal echocardiographic diagnosis in 3 cases].

We submit 3 cases of perforation of the mitral valve leaflet as a consequence of infectious endocarditis. In the first of this cases, perforation was the result of the impact of the regurgitant jet of an aortic insufficiency affected by bacterial endocarditis of the anterior mitral leaflet in a young female presenting various congenital malformations. Both the transthoracic and transesophageal echocardiography showed that the regurgitant jet affected the area where the lesions were later detected. In the other 2 cases the perforation appeared in valves previously affected by endocarditis. In these cases, only the transesophageal echocardiography showed the lesions. Surgery was performed in all 3 cases with satisfactory results, confirming the echocardiographical findings. We wish to emphasize the role of transesophageal echocardiography in the diagnosis of this rare process that may be the primary effect of the destructive action of the endocarditis, or a secondary effect, on dissemination by means of affected valves, on previously unaffected valvular leaflets.

Adult↗
PubMed1992

Ocular histopathologic characteristics of cobalamin C type vitamin B12 defect with methylmalonic aciduria and homocystinuria.

The eyes of a 22-month-old girl with the cobalamin C complementation type of combined methylmalonic aciduria and homocystinuria were studied with light and electron microscopy. We observed vacuolization of the iris pigment epithelium, loss of photoreceptors in the central 3.3 mm of the macula, partial loss of the nerve fiber and ganglion cell layers between the fovea and optic disk, and partial optic atrophy. The sclera in the posterior pole was thickened with deposition of mucopolysaccharide. Electron microscopy showed inclusions containing fine granular material in conjunctival fibrocytes; corneal epithelium, keratocytes, and endothelial cells; iris pigment epithelium; ganglion cells; retinal pigment epithelium; and choroid and scleral fibrocytes. Enlarged mitochondria and clear vacuoles distended the corneal endothelial cells. We found evidence of possible lysosomal dysfunction and mucopolysaccharide storage, as well as a clinicopathologic correlation of the macular degeneration in this disease.

Eye↗
PubMed1992

Clinicopathologic correlation of occult choroidal neovascularization in age-related macular degeneration.

We report the clinicopathologic features of an eye with occult choroidal neovascularization associated with age-related macular degeneration. Ophthalmoscopic findings at presentation included subretinal fluid and lipid. We noted angiographic staining of irregularly elevated areas of retinal pigment epithelium. In the late phase of the angiogram, fluorescein leakage at the level of the outer retina was observed that did not correspond to well-demarcated areas of hyperfluorescence in earlier phases. The patient was randomized to treatment in a pilot trial comparing the effects of grid laser treatment with the effects of no treatment for occult choroidal neovascularization. Three weeks after treatment, some of the subretinal fluid had cleared and vision improved. The patient died 6 weeks after laser treatment. Histopathologic study disclosed a subretinal pigment epithelial fibrovascular membrane. Neovascularization originated from the choroid.

Aged↗
PubMed1992

Cytogenetics study on coke oven workers with abnormal blood counts.

Thirty steelworkers with abnormal blood counts and 22 controls were studied cytogenetically. Fifty percent of the workers had a combination of leukopenia, neutropenia and lymphocytosis, and the remaining 50% showed different combinations or even a single type of alteration. The frequency of chromosome and chromatid gaps and chromosome deletions was significantly higher among workers than among controls, and the same was true for the number of individuals with some type of chromosome alteration. We also noted that the major factor related to the production of chromosome breaks is not the total time of work in the steel mill, but specifically the time of work at the coke oven.

Adult↗