Biomedical subjects
Publications and source records attributed to A Rassi.
We studied secreted-excreted immunogens in human patients infected with Trypanosoma cruzi. A pair of 45- to 55-kDa antigens and a family of shed acute-phase antigens characterized the acute phase, while antibodies against a 160- to 170-kDa immunogen appeared at the chronic phase of the disease.
Here we describe the characterization of a Trypanosoma cruzi DNA sequence (clone A13) that codes for a polypeptide recognized by IgM and IgG antibodies from sera of acute and congenital chagasic patients. Antibodies to A13 antigen are also detected in the sera of chronic patients with different clinical forms of Chagas' disease, but not in sera of patients with leishmaniasis or other parasitic diseases. The antigenic determinants encoded by clone A13 are found in amastigotes and trypomastigotes of several T. cruzi strains, but not in the noninfective epimastigotes. The DNA sequence of the recombinant clone reveals one open reading frame encoding 251 amino acids without tandemly repeated sequences. Our data suggest that the A13 antigen may be useful for the development of serodiagnostic procedures.
A genomic clone expressing a Trypanosoma cruzi antigen in Escherichia coli was identified using human chagasic sera. Chagasic antibodies affinity purified on extracts of this clone recognized a high-molecular-weight protein expressed in all developmental stages of the parasite life cycle, as well as in various T. cruzi strains. The antigen is associated with the cytoskeleton of the parasite and localizes along the attachment region between the flagellum and the cell body. Antibodies to the recombinant antigen were detected in the sera of 115 chagasic patients from different endemic regions, but not in sera of patients with leishmaniasis, T. rangeli infection, or other parasitic diseases. Our data suggest that the presence of antibodies to this antigen may be specifically associated with Chagas' disease.
A Trypanosoma cruzi antigen which is shed into the culture medium by the trypomastigote stage of the parasite and detected in blood of acutely infected mice was cloned and characterized. We designate this antigen shed acute phase antigen (SAPA). Five protein bands with apparent molecular masses ranging from 160 to 200 kDa were detected by immunoblotting of plasma from infected mice and in supernatants of cultured trypomastigotes upon reaction with antibodies against SAPA. A serum obtained from a patient acutely infected with Chagas' disease revealed a similar set of polypeptides in supernatants of cultured trypomastigotes when tested by immunoblotting. SAPA seems thus to be a major shed protein during the acute period of the disease. Twenty-six of 28 sera from human acute cases of Chagas' disease tested reacted with SAPA. Conversely, only 8-10% of sera from chronic cases of the disease contained detectable levels of antibody against SAPA. Sera from rabbits infected with six different parasite strains all contained antibodies against SAPA. Antibodies against SAPA are detectable 15 days after the manifestation of acute Chagas' disease symptoms in humans and 15 days post-infection in sera from mice and rabbits. The nucleotide sequence of a genomic clone encoding the 3' end of the SAPA gene revealed the presence of 14 tandemly arranged 12-amino acid-long repeats. A 39-amino acid-long region that is very hydrophobic precedes the stop codon. Due to its early appearance it might be possible to design diagnostic assays which are based on SAPA for identification of recently infected cases of Chagas' disease.
To determine the mechanisms by which blood flow increases across the mitral and aortic valves during exercise, 18 normal men were studied during graded supine and upright bicycle exercise at matched workloads. Mitral valve orifice and ascending aortic blood velocities were recorded by Doppler echocardiography during steady states at each stage of exercise. Parasternal two-dimensional echocardiographic imaging of the ascending aorta adjacent to the aortic valve orifice and the mitral valve orifice at the tips of the valve leaflets was used to calculate changes in cross-sectional area during exercise. Heart rate increased from rest to exercise from 67 to 150 beats/min (124%) during supine exercise and from 72 to 147 beats/min (104%) during upright exercise. Stroke volume increased 20% during supine and 46% during upright exercise; the increase in stroke volume was statistically significant when rest and exercise were compared and when the magnitude of change was compared vs position (p less than .05). The increase in stroke volume measured at the ascending aorta was accomplished by an increase in the velocity-time integral (+15% supine and +48% upright, p less than .05), with little change in aortic cross-sectional area (5% supine and 0% upright, p = NS). By contrast, the increase in flow rate measured at the mitral valve was predominantly due to an increase in mean diastolic cross-sectional area (+29% supine and 34% upright, p less than .05); the velocity-time integral did not increase significantly (-10% supine and 4% upright; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)
EMG examination was performed in 41 patients with Chagas' disease, belonging to the several clinical forms of the disease. Constant and direct relationship between the amount of muscle skeletal denervation and the clinical forms has been shown. In addition light peripheral axonal neuropathy was seen. Both muscular and sensory denervation was intense in the group with cardio-digestive form, moderate in the groups with either cardiac or digestive form and light in the group with the indeterminate form. The severity of the clinical symptoms was not related with the amount of peripheral denervation.
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Because catecholamines and digitalis have different effects on the time course of myocardial intracellular calcium concentration, their effects on the time course of left ventricular contraction and relaxation may also be different. To study this question, dogs were instrumented to measure left ventricular pressure and determine left ventricular volume from three ultrasonic dimensions. After full recovery from the instrumentation, the effects of dobutamine (2-10 micrograms/kg), ouabain (0.5 mg i.v.) alone, and ouabain given after propranolol (2 mg/kg i.v.), or phentolamine (5 mg i.v.) and incremental doses of ouabain (0.25-0.75 mg i.v.) were assessed on different days. Left ventricular pressure and volume were varied by caval occlusions. Dobutamine significantly increased the slope of the left ventricular end-systolic pressure-volume relation (Emax) and the slope of the dP/dtmax-end-diastolic volume relation (dE/dtmax), while significantly decreasing the time from end-diastole to end-systole (tmax) and the time constant (T) of the isovolumic fall in left ventricular pressure. Ouabain also increased Emax and dE/dtmax but did not alter tmax or T. Dobutamine produced a greater increase in dE/dtmax than in Emax, whereas ouabain produced similar increases in both. These effects of ouabain were not altered by pretreatment with propranolol or phentolamine. We conclude that although dobutamine and ouabain are both positive inotropes that increase Emax, dobutamine speeds the rate of left ventricular contraction (tmax) and relaxation (T), whereas ouabain does not. These effects of ouabain and dobutamine on global parameters of left ventricular chamber performance mirror their influence on intracellular calcium availability. Furthermore, these observations are consistent with the predictions of the time-varying elastance model of the left ventricle and support its usefulness as a conceptual framework to understand and link events occurring during isovolumic contraction, end-systole, and isovolumic relaxation.
The clinical characteristics of acute and chronic Chagas' disease in central Brazil are described (29 acute cases and 111 chronic cases). The geographical distribution of Trypanosoma cruzi zymodemes in this region was mapped. Zymodeme (Z) 1 was identified in 12 acute cases, Z2 in 13 and repeated xenodiagnosis gave the same zymodeme identification. The clinical pictures of the Z1 and Z2 acute phases were similar. Resistance to benznidazole treatment occurred after either Z1 or Z2 acute infections. Only 14 positive xenodiagnosis were obtained from the 111 chronic phase patients examined. For 12 of these 14 patients the zymodeme was identified. All 12 carried Z2, 10 of whom had mega involvement. There were several possible explanations for the failure to detect T. cruzi Z1 in chronic Chagas' disease with mega syndromes: suggestions were made for follow-up investigations.
Neurophysiological examination before and after the administration of benzonidazole, has shown peripheral polyneuropathy induced by this drug in most of the patients treated for chronic Chagas' disease. The polyneuropathy was mostly axonal and it was dose dependent being more severe in patients who had denervation of skeletal muscles before receiving the drug.
Sera from 143 patients considered to be infected with Trypanosoma cruzi on the basis of epidemiological, clinical and standard serological evidence gave positive results in the enzyme-linked immunosorbent assay (ELISA) using a lectin affinity purified 90,000 molecular weight glycoprotein (GP90) antigen preparation. Levels of antibody did not discriminate between clinically classified groups of patients in the chronic phase of infection. The GP90 preparation was found to be heterogeneous.
Development of a highly specific test system for the diagnosis of Chagas' disease (CD) was sought using Gp25, a surface glycoprotein recently isolated from Trypanosoma cruzi culture forms. Radioimmunoprecipitation assays were performed to screen 567 sera for IgG antibodies to Gp25. Correct diagnosis was attained in 97.8% of the 321 sera collected from chagasic patients in several endemic areas of South America. Sera from patients with various clinical forms of chronic disease displayed similar levels of antibodies (Abs) to Gp25. Moreover, there was little cross-reactivity when assayed against 246 sera from non-chagasic individuals, including 105 samples from individuals infected with unrelated trypanosomatids. Cross-reactivity was found in two such sera; these were used to identify a minor protein contaminant as the nonspecific antigen. Residual cross-reactive molecules were eliminated from Gp25 by affinity purification on Concanavalin A (Con A) columns. We recommend this antigen-antibody system for use in routine screening of blood donors.
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Normal subjects and cardiac chagasic patients without previous history of congestive failure or actual evidences of cardiac decompensation were exercised on a treadmill or a bicycle ergometer. Patients with less than the expected increase in heart rate during exercise were found to exhibit also an abnormal heart rate response to pharmacologic blockade and acute alterations in systemic vascular resistance. These results are in agreement with previous observations showing neuronal degeneration and autonomic impairment in chronic Chagas' heart disease.
Studies of heart rate and blood pressure responses to 70 degrees head-up tilt and 30 degrees head-down tilt were conducted in normal subjects and in chronic cardiac chagasic patients without past or present cardiac decompensation. During steady state of tilt, heart rate alterations were less marked in the chagasic than in the control group. Vasodepressor syncope supervened in three cardiac chagasic patients, two of whom showed the distinctive feature of hypotension without reflex bradycardia. In these patients, vagal control of cardiac rate could not be demonstrated either following a full blocking dose of atropine or during sudden elevation of systemic arterial blood pressure. These results are interpreted in the context of the pathologic and functional derangements of autonomic control which occur in Chagas' heart disease.
Eleven strains of Trypanosoma cruzi were isolated from patients with Chagas disease in central Brazil by xenodiagnosis and inoculation into newborn mice. Biological characterization and isoenzyme analysis showed that 6 strains were type II (zymodeme 2) and 5 were type III (zymodeme 1). Patients were treated with benznidazole or benznidazole plus nifurtimox. Mice infected with each isolated strain were treated for comparison with the results obtained in the respective patient. Evaluation of cure of the patients was based on the indirect immunofluorescence test, complement fixation reaction and xenodiagnosis. For the mice, haemoculture, indirect immunofluorescence testing, xenodiagnosis and inoculation of blood into newborn mice were used. Tests were performed 3-6 months after the end of treatment. The cure rate was 66-100% in mice infected with type II strains and 0-9% in those infected with type III strains. The correlation between treatment results in patients and mice was 81.8% (9 of 11 cases). Type II strains were more susceptible to treatment, in contrast to type III strains which yielded the majority of therapeutic failures.