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M A Contreras

Publications and source records attributed to M A Contreras.

At least 37 records · Page 2Linked to original sources
PubMed1998

Solution conformation of an immunogenic peptide from HRV2: comparison with the conformation found in a complex with a Fab fragment of an anti-HRV2 neutralizing antibody.

The conformation of a [15]-peptide (H-VKAETRLNPDLQPTE-NH2) from VP2 of rhinovirus HRV2 complexed with a Fab fragment was previously shown by X-ray crystallographic studies to be similar to the one found in the corresponding region of HRV1A. Antibodies raised against this peptide bind to and neutralize HRV2. In order to identify structural features preserved in solution that may explain the ability of this short peptide to mimic the structure of the protein surface, the peptide has been studied by NMR in aqueous solution as well as under denaturing conditions. The peptide is shown to be a random coil in solution. However, the sequence forming a 3(10)helix in the complex is biased into a helical conformation according to NOE intensity data as well as from urea and pH titrations. This sequence adopts the same conformation in an unrelated protein. NOE data suggest that a beta-turn found in the complex may be sampled in solution. Also, Glu4, interacting with Arg6 in the crystal, has a reduced pKa value in solution. It is concluded that the local structure present in the random coil state of VP2(156-170) contains enough information to direct the production of antibodies that bind to and neutralize HRV2.

Amino Acid Sequence↗
PubMed1998

Identification of multiple genes with altered expression at the distal anastomosis of healing polytetrafluoroethylene grafts.

PURPOSE: Anastomotic intimal hyperplasia remains a significant cause of delayed prosthetic arterial graft failure. Prior studies have identified several genes with altered expression within the hyperplastic region at the downstream polytetrafluoroethylene arterial anastomosis as compared with normal arteries. The purpose of the current study was to determine the sequence of early gene-related events at the distal anastomosis of an in vivo prosthetic arterial graft model. Messenger RNA (mRNA) differential display was used to screen for alterations in gene expression between anastomotic sites and control arterial segments. METHODS: Six carotid interposition 6-mm expanded polytetrafluoroethylene grafts were placed in mongrel dogs, with the intervening carotid artery segment serving as the baseline control. Five days after graft implantation, the distal anastomotic artery segments were harvested and total RNA was isolated from both the intervening normal arteries and anastomotic segments. Differential mRNA display was used to identify candidate complementary DNA (cDNA) clones with expression that differed in anastomotic segments as compared with normal intervening arteries. Northern blot analysis confirmed alteration of gene expression. The cDNA clones were sequenced, and gene databases were searched. Novel sequences were used as probes for screening human cDNA libraries. RESULTS: Approximately 7000 mRNA species were screened, and 26 candidate clones were obtained. Northern blot analysis showed altered gene expression in 10 (38%) of the clones, undetectable signals in 13 (50%), and nonregulation in 3 (12%). Seven clones with 92% homology at the nucleotide level to human alpha1 (III) procollagen gene and novel sequence were expressed only at the distal anastomosis. A clone representing apolipoprotein J and a novel sequence had increased expression at the distal anastomosis of 364% +/- 236% and 156% +/- 47%, respectively (mean percentage, control +/- standard deviation). CONCLUSIONS: These studies identified genes with expressions that increased or were exclusive to the distal anastomosis of healing prosthetic arterial grafts in an in vivo prosthetic arterial graft model. Type III collagen may contribute significantly to the composition of the extracellular matrix associated with intimal hyperplasia by increasing lesion volume. Apolipoprotein J, through its association with proteases, may modulate some of the matrix changes seen early after grafting.

Anastomosis, Surgical↗
PubMed1997

Vascular endothelial growth factor expression in canine peripheral vein bypass grafts.

PURPOSE: Autologous veins used as arterial bypass grafts undergo initial loss of the endothelial cell (EC) lining, which is followed by reendothelialization. We characterized the expression of the EC-specific angiogenic mitogen, vascular endothelial growth factor (VEGF), in vascular grafts to help elucidate the molecular and cellular events after bypass procedures. METHODS: Cephalic vein-femoral artery interposition grafts were placed in mongrel dogs. Vein grafts and arteries were harvested at either 48 hours or 4 weeks after bypass, the total RNA was isolated, and the VEGF mRNA expression was evaluated by Northern blot analysis. Tissue segments from each time period were evaluated by immunohistochemical analysis using anti-VEGF antibodies. RESULTS: VEGF mRNA expression in vein grafts as compared with control veins was increased 2.5-fold 48 hours after bypass grafting (p = 0.02) but returned to initial control levels in grafts removed at 4 weeks. Distal arterial segments, which included the anastomotic site without attached vein graft, had a 21.4-fold increase in VEGF expression at 48 hours (p = 0.02) and a 6.6-fold increase at 4 weeks (p < 0.01) as compared with control arterial segments. Vessels subjected to arteriotomy or ischemia alone also demonstrated increased VEGF expression. Immunohistochemical analysis revealed VEGF protein within ECs and smooth muscle cells of the venous bypass graft, with maximal levels observed within intimal hyperplasia at the arterial anastomosis. CONCLUSIONS: After arterial reconstruction procedures using venous conduits, VEGF is significantly increased at 48 hours in the vein graft and arterial anastomosis. VEGF expression in the vein graft normalizes within 4 weeks but remains significantly elevated in the adjacent arterial segment. Increased VEGF production after arterial grafting may facilitate reendothelialization, thus partially accounting for optimal patency rates achieved with autologous vein grafts.

Animals↗
PubMed1996

Results of a policy with arm veins used as the first alternative to an unavailable ipsilateral greater saphenous vein for infrainguinal bypass.

PURPOSE: Aggressive policies for distal bypass and coronary revascularization increase the need to identify alternatives to autologous saphenous vein grafts. We examined the performance of arm vein as the primary alternative to contralateral saphenous vein when the ipsilateral saphenous vein was not available. METHODS: A total of 250 arm vein grafts were studied retrospectively in 224 patients (143 men, 81 women, 82.6% with diabetes, mean age 68.3 years) from February 1989 to April 1994. Intraoperative angioscopy was carried out to observe valve lysis, remove abnormalities, and select optimal vein segments. RESULTS: A total of 85 primary, 103 repeat, and 62 graft revision procedures were done for limb salvage in 99.2% of the patients. A total of 41 femoropopliteal, 114 femorotibial-pedal, 33 popliteodistal, and 62 jump or interposition grafts were constructed. A total of 199 grafts were single vein, and 51 were composite vein. The source was cephalic vein alone in 50.4%, cephalic and basilic vein in 35.6%, and basilic vein only in 14%. The contralateral saphenous vein as an alternative conduit was available in 97 (38.8%) instances. Interventions guided by angioscopy to "upgrade" the graft were necessary in 51.6%. Overall early patency (< or = 30 days) was 94.8% (n = 13 occlusions). The cumulative primary patency rate at 1 year was 70.6%, the secondary patency rate was 76.9%, and the limb salvage rate was 88.2%. The 3-year patency rate (limb salvage) was 51.9% (92.4%) for primary grafts, 56.7% (67.1%) in revision grafts, and 42.4% (79.9%) in repeat grafts. In 22.7% (22 of 97) the available contralateral saphenous vein was used for distal revascularization within the follow-up period. CONCLUSIONS: Arm veins are an easily accessible autologous conduit of sufficient length to reach the midtibial level. Excellent patency rates allow durable limb salvage in otherwise difficult circumstances. Vein configuration and splicing do not affect patency rates, but vein quality and repeat operations do. Angioscopy is a valuable adjunct to upgrade graft quality. The contralateral saphenous should be saved for subsequent contralateral revascularization or coronary artery bypass grafting.

Adult↗
PubMed1995

Isolation of genes differentially expressed at the downstream anastomosis of prosthetic arterial grafts with use of mRNA differential display.

PURPOSE: Downstream anastomotic intimal hyperplasia in prosthetic arterial grafts remains a major cause of delayed graft failure. The new method of messenger RNA (mRNA) differential display was used to screen numerous genes to gain insight into the molecular mechanisms of intimal hyperplasia. METHODS: Fifty-centimeter-long 8 mm expanded polytetrafluoroethylene grafts were placed in four mongrel dogs from the carotid artery to the distal abdominal aorta. At 3 months the distal anastomoses and adjacent normal aortas were harvested; a portion was taken for histologic examination, and total RNA was isolated from the remainder. Differential mRNA display was used to identify candidate cDNA clones whose expression differed in anastomotic intimal hyperplasia as compared with adjacent unaffected aorta. The clones were sequenced, and national gene databases were searched. Northern blot analysis confirmed alteration of gene expression. RESULTS: Approximately 5000 mRNA species were screened, and 11 candidate clones were obtained. DNA sequence revealed homology of five clones to known gene sequences. Homologous genes included an interferon-gamma-induced human gene, (IGUP I-5111), alpha-1 protease inhibitor gene, human retinoblastoma susceptibility gene, and human creatine kinase gene (two clones). Northern blot analysis revealed altered gene expression in 4 of 11, nonregulation in 1 of 11, and undetectable signals in 6 of 11. Expression of the clone representing IGUP I-5111 in the segment of intimal hyperplasia was found to be decreased over threefold to only 31% +/- 16.4% SE of the level seen in normal aorta. CONCLUSIONS: The technique of mRNA differential display has identified differences in gene expression in an in vivo model of anastomotic intimal hyperplasia. Expression of RNA with homology to an interferon-gamma-induced human gene was consistently decreased within the hyperplastic region at the downstream polytetrafluoroethylene arterial anastomosis.

Anastomosis, Surgical↗
PubMed1994

Role of angioscopy in reoperation for the failing or failed infrainguinal vein bypass graft.

The purpose of this retrospective study is to review our ongoing experience with the use of angioscopy during reoperation for failed or failing infrainguinal vein bypass grafts and define the role of angioscopy in the management of this clinically demanding patient group. All hospital records, arteriograms, and intraoperative angioscopic video recordings of 79 consecutive failed or failing grafts (76 patients) examined with angioscopy during reoperation between 1987 and 1993 were reviewed. Clinical and intraoperative data, comparison of the preoperative arteriogram and intraoperative angioscopic findings, and surgical decisions or interventions resulting from the additional angioscopic findings were collated and analyzed according to a predetermined protocol. Sixty-six additional angioscopic findings were noted during the 79 reoperations and resulted in 61 additional interventions and surgical decisions with salvage of all or part of the graft in 90.9% in the early (< 30 day) failed (group 1), 84.6% in the late (> 30 day) failed (group 2), and 90.3% in the late (> 30 day) failing grafts (group 3). The amount of residual thrombus within the graft, as assessed by angioscopy after all interventions, was the critical determinant for overall early graft patency (p < 0.001) and long-term patency for all the subgroups after reoperation (group 1, p < 0.001; group 2, p = 0.0016; and group 3, p = 0.0194). Intraoperative angioscopy has an important role in these challenging procedures. It provides additional and useful information that not only influences the conduct and extent of the reoperative surgery but may provide insights into the pathogenesis of graft failure.

Adult↗
PubMed1991

Persistent platelet activation by passivated grafts.

Vascular grafts in canines exhibit similar healing patterns to humans in that the graft surface forms a pseudointima over time but endothelializes only near the anastomotic sites. Thus the pseudointima at the midportion of the graft may represent a nidus for persistent platelet activation. The purpose of this investigation was to examine the effect of the maturing graft surface on platelet activation. Long Dacron subcutaneous carotid to aorta grafts (50 cm x 8 mm) were placed in nine dogs. Blood samples were obtained by direct graft puncture, at the proximal and distal ends of the graft, at 1, 24, 48, 72 hours, 1, 2, 3, 4 weeks, and monthly thereafter for 8 months. Seven sham dogs had subcutaneous grafts implanted without arterial anastomoses, and blood samples were drawn from the femoral artery. Platelet counts were determined with a platelet counter. Platelet aggregation and release of adenosine triphosphate was determined with a whole blood aggregometer by use of arachidonic acid, collagen, and adenosine diphosphate as agonists. No difference was found in platelet aggregation to collagen or adenosine diphosphate stimulation across the graft, but platelets released significantly less adenosine triphosphate to collagen and adenosine diphosphate stimulation distally versus proximally. In the graft dogs a decrease in systemic platelet counts of 50% occurred from the preoperative level which persisted over 8 months (p less than 0.01). Also less response occurred to collagen and ADP stimulated platelet aggregation in the graft animals than the sham animals during the first month of study. These data suggest that significant platelet-graft interactions occur even after the graft has formed a mature pseudointima.

Adenosine Triphosphate↗
PubMed1989

Correlates of arterial oxygenation during exercise in severe chronic obstructive pulmonary disease.

In the present study, we have undertaken a detailed analysis of the respiratory physiologic correlates of SaO2 during mild constant-load exercise in 38 patients with severe but stable COPD. Several respiratory physiologic variables that would be expected to influence exercise SaO2 were entered into a stepwise multiple linear regression analysis with mean exercise SaO2 as the dependent variable. Two variables (Dco and resting SaO2) were found to correlate strongly with mean exercise SaO2 (multiple r = 0.80; p less than 0.00001) and accounted for 65 percent of the variability among patients. The PaCO2 influenced resting SaO2 but had no independent influence on exercise SaO2. Subsequently, the model of mean exercise SaO2 derived in the present analysis was found to accurately predict mean exercise SaO2 in a group of 19 similar patients (r = 0.85; p less than 0.0001). While these findings do not establish a cause-and-effect relationship, they may provide clinicians with further insight as to which patients are likely to desaturate during exercise.

Aged↗
PubMed1989

Approaches to rehabilitation of patients with ventilatory insufficiency.

Multi-disciplinary rehabilitation programmes are popular in Europe and North America in the management of patients with chronic respiratory disease. Patients experience an increase in exercise tolerance, a decrease in dyspnoea and spend fewer days in hospital after completing the programme. Criteria for admission often include a well motivated nonsmoking patient with severe but stable disease of the ventilatory system. Although most patients have chronic airflow limitation, we have received a number of referrals concerning patients with non-obstructive ventilatory insufficiency, particularly thoracic restrictive disease and neuromuscular disease. Such patients frequently have hypercapnic respiratory failure, easily aggravated by increased activity or respiratory tract infection. Therefore, they cannot engage in a supervised exercise training programme unless we can stabilize their clinical state. We consider elective mechanical ventilatory support a valuable tool in their rehabilitation. Such support is often required only at night. By preventing the sleep-related alterations in arterial blood gases the clinical course of the disease is stabilized, functional level is increased and patients are then protected from episodes of acute respiratory failure which may be life-threatening.

Aged↗
PubMed1988

Pulmonary infection with nontuberculous mycobacteria.

Nontuberculous mycobacterial infections (NTM) are being increasingly recognized as a cause of chronic pulmonary disease. We recently reviewed the clinical, radiologic, and bacteriologic presentation of 89 adult patients ill enough to have been hospitalized between 1981 and 1985 with the diagnosis of NTM. Preexisting lung disease was present in 82% and alcohol abuse in 40%. Although M. avium complex was identified in 51% of the patients, M. xenopi, which is usually reported to occur infrequently, accounted for 38% of our cases and M. kansasii for only 9%. Treatment was limited by a high incidence of associated disease, in vitro drug resistance, drug toxicity, and a mortality rate of 32% within 18 months of admission. Nevertheless, bacteriologic conversion occurred in 29% of those treated. M. xenopi appears to be an important pathogen in southern Ontario. It differs from the other NTM by having a different pattern of in vitro drug resistance but not by its clinical or radiologic presentation.

Adult↗
PubMed1980

Factors influencing localization of labeled antibodies in tumors.

Recent success with antibody to carcinoembryonic antigen makes it desirable to survey the practicality of producing other tumor-localizing antibodies for diagnosis and therapy. General procedures for reaching these goals are outlined. Experimental animal studies show some progress; detecting moderate-sized tumors by scanning appears a reasonable goal, but there is a basic lack of knowledge regarding the extent to which tumors express tumor-specific or associated antigens in vivo. This makes it difficult to evaluate the probability for success of different therapeutic proposals now under study. For organs not vital for the life and well-being of the patient, organ-specific antigens expressed on tumor may offer a target for immunological attack. Techniques for cloning antibody-producing cells promise more uniform and specific antibody preparations.

Animals↗