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2.
Health Educ Res ; 38(2): 139-149, 2023 03 23.
Artigo em Inglês | MEDLINE | ID: mdl-36539329

RESUMO

This study examined whether knowledge of sexual consent buffers the relationship between risk factors for sexual violence (SV) and SV perpetration among first-year college men. The study data were drawn from a longitudinal study with 1144 first-year college men. A series of generalized linear models were conducted to examine whether knowledge of sexual consent moderated the relationship between SV risk factors and SV perpetration. Knowledge of sexual consent moderated the effect of hypermasculinity (P < 0.001), binge drinking (P < 0.001), rape-supportive social norms (P = 0.007) and peer support for SV (P < 0.001) such that there was a positive association between risk factors and SV perpetration among those with lower, but not higher, knowledge of sexual consent. Knowledge of sexual consent did not significantly moderate the relationship between SV perpetration and outcome expectancies for non-consensual sex (P = 0.387) and pornography use (P = 0.494). Knowledge of sexual consent may counteract risk factors for SV perpetration among young college men. The findings highlight the need for consent education to be incorporated in youth comprehensive sexual education to increase knowledge of sexual consent prior to college and campus-based SV prevention programming delivered to college students.


Assuntos
Delitos Sexuais , Masculino , Adolescente , Humanos , Fatores de Proteção , Estudos Longitudinais , Delitos Sexuais/prevenção & controle , Comportamento Sexual , Universidades
3.
Eur Rev Med Pharmacol Sci ; 26(9): 3386-3398, 2022 05.
Artigo em Inglês | MEDLINE | ID: mdl-35587093

RESUMO

OBJECTIVE: SARS-CoV-2 is a new Coronavirus identified as the cause of Coronavirus disease in 2019 (COVID-19). The epidemic spread in China and beyond its borders, involving 114 countries with more than 5 million dead. On March 11, the WHO declared the spread of SARS-CoV-2 to be a pandemic and encouraged nations to adopt harsh restrictive measures. Therefore, patients more and more often turn to dental offices only for emergencies. Healthcare professionals, including dentists, are at high infectious risk. In fact, the closeness to the oral cavity and nasopharynx and the use of drills or ultrasonic devices that cause aerosol release, make dental professions at high risk of bacterial and viral infections. The way patients are treated has changed. In fact, it should be mandatory to carry out a pre-treatment telephone triage and the use of mouthwashes to reduce bacterial load. In the current pandemic, it is necessary to adopt specific safety protocols that can protect dental operators as well as limit the spread of the virus. The purpose of this review is to present an overview on ways to reduce the risk of SARS-CoV-2 contagion in dentistry by focusing on the immediate situation as well as by looking towards the future. MATERIALS AND METHODS: To reach the review purpose, we selected a series of studies using keywords "COVID-19" OR "SARS-CoV-2" in association with "dentistry" AND "safety protocols" AND "healthcare procedures" AND "individual protection dispositive" AND "air transmission" AND "droplet". We selected papers exclusively in English language, up to 1st January 2022. RESULTS: During future phases of the pandemic, everywhere in the World, it is necessary to impose all dentistry team both a serological screening and the vaccination, as already established for all health staff in Italy. CONCLUSIONS: For own safety, it is an important for the whole dentistry category constantly update the devices and the protocols adopted, as well as monitoring the real infectious threats, which may occur.


Assuntos
COVID-19 , SARS-CoV-2 , Aerossóis , Odontologia , Humanos , Pandemias/prevenção & controle
4.
Eur J Radiol ; 143: 109945, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34492625

RESUMO

OBJECTIVE: To investigate the role of quantitative muscle biomarkers assessed with skeletal muscle index at the third lumbar vertebra (L3-SMI) and temporal muscle thickness (TMT) in predicting progression-free and overall survival in patients with primary central nervous system lymphoma (PCNSL) undergoing first-line high-dose methotrexate-based chemotherapy. METHODS: L3-SMI and TMT were calculated on abdominal CT and brain high-resolution 3D-T1-weighted MR images, respectively, using predefined validated methods. Standardized sex-specific cut-off values were used to divide patients in different risk categories. Kaplan-Meier plots were calculated, and survival analysis was performed using log-rank tests, univariate, and multivariable Cox-regression models, calculating hazard ratios (HR) and 95% confidence intervals (CI), also adjusting for potential confounders (age, sex, and performance status). RESULTS: Forty-three patients were included in this study. Median follow-up was 23 months (interquartile range 12-40); at median follow-up, rates of progression-free and overall survival for the cohort were 46% and 57%, respectively. Thirteen (30%) and 11 (26%) patients showed L3-SMI or TMT values below the predefined cut-offs. In Cox-regression multivariable analysis patients with low L3-SMI or TMT showed significantly worse progression-free (HR 4.40, 95% CI 1.66-11.61, p = 0.003; HR 4.40, 95% CI 1.68-11.49, p = 0.003, respectively) and overall survival (HR 3.16, 95% CI 1.09-9.11, p = 0.034; HR 4.93, 95% CI 1.78-13.65, p = 0.002, respectively) compared to patients with high L3-SMI or TMT. CONCLUSIONS: Quantitative muscle mass evaluation assessed by both L3-SMI and TMT is a promising tool to identify PCNSL patients at high risk of negative outcome. Confirmatory studies on larger independent series are warranted.


Assuntos
Linfoma não Hodgkin , Sarcopenia , Biomarcadores , Sistema Nervoso Central , Feminino , Humanos , Linfoma não Hodgkin/patologia , Masculino , Músculo Esquelético/patologia , Prognóstico , Estudos Retrospectivos , Sarcopenia/patologia , Músculo Temporal , Tomografia Computadorizada por Raios X
5.
Dent Mater ; 34(6): 879-890, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29598882

RESUMO

OBJECTIVES: The dental market moves towards high-translucency monolithic zirconia dental crowns, which are usually placed either with - or without - a thin glaze layer. The microstructural features and the mechanical performances of these materials are still controversial, as well as their susceptibility to aging. This paper aims at studying these aspects in the current generation of zirconia dental crowns showing different degrees of translucency. METHODS: Four different commercial zirconia materials were investigated, including one standard 'full-strength' 3Y-TZP and three grades with improved translucency. The microstructural features (phase composition and assemblage, grain size) were carefully studied, as well as mechanical properties (biaxial bending strength and indentation toughness), translucency and aging behavior (in autoclave at 134°C). Aging was conducted on crowns with and without glaze to better represent clinical uses. RESULTS: Important differences are found in terms of microstructures among the materials in terms of cubic phase content and yttria in the tetragonal phase, leading to different optical, mechanical and aging resistance properties. We show that higher cubic phase content leads to better translucency and stability in water steam, but at the expense of strength and toughness. A compromise is always inevitable between translucency and aging resistance on one side and mechanical properties on the other side.


Assuntos
Cerâmica/química , Coroas , Materiais Dentários/química , Ítrio/química , Zircônio/química , Fenômenos Biomecânicos , Desenho Assistido por Computador , Dureza , Teste de Materiais , Propriedades de Superfície
6.
Med Hypotheses ; 100: 59-63, 2017 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-28236850

RESUMO

Physical inactivity and a low maximal aerobic capacity (VO2max) strongly predict morbidity and mortality in patients with type 2 diabetes (T2D). Patients with T2D have a reduced VO2max when compared with healthy individuals of similar age, weight, and physical activity levels, and this lower aerobic capacity is usually attributed to a reduced oxygen delivery to the working muscles. The oxygen carrying capacity of the blood, as well as increases in cardiac output and blood flow, contribute to the delivery of oxygen to the active muscles during exercise. Hemoglobin mass (Hb mass), a key determinant of oxygen carrying capacity, is suggested to be reduced in patients with T2D following the observation of a lower blood volume (BV) in combination with normal hematocrit levels in this population. Therefore, a lower Hb mass, in addition to a reported lower BV and impaired cardiovascular response to exercise, likely contributes to the reduced oxygen delivery and VO2max in patients with T2D. While exercise training increases Hb mass, BV, and consequently VO2max, the majority of patients with T2D are not physically active, highlighting the need for alternative methods to improve VO2max in this population. Exposure to hypoxia triggers the release of erythropoietin, the hormone regulating red blood cell production, which increases Hb mass and consequently BV. Exposure to mild intermittent hypoxia (IH), characterized by few and short episodes of hypoxia at a fraction of inspired oxygen ranging between 10 and 14% interspersed with cycles of normoxia, increased red blood cell volume, Hb mass, and plasma volume in patients with coronary artery disease or chronic obstructive pulmonary disease, which resulted in an improved VO2max in both populations. We hypothesize that 12 exposures to mild IH over a period of 4weeks will increase Hb mass, BV, cardiac function, and VO2max in patients with T2D. Therefore, exposures to mild IH may increase oxygen delivery and VO2max without the need to perform exercise in patients with T2D.


Assuntos
Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/terapia , Hemoglobinas/metabolismo , Hipóxia , Consumo de Oxigênio/fisiologia , Volume Sanguíneo , Débito Cardíaco , Doenças Cardiovasculares , Eritrócitos/metabolismo , Eritropoetina/sangue , Exercício Físico/fisiologia , Hematócrito , Humanos , Músculo Esquelético/fisiologia , Oxigênio/metabolismo
7.
Expert Opin Drug Saf ; 15(sup2): 61-67, 2016 12.
Artigo em Inglês | MEDLINE | ID: mdl-27875919

RESUMO

OBJECTIVE: This study aims to evaluate the frequency of off-label use of ketorolac in Italy and the related suspected adverse drug reactions (ADRs) reported. METHODS: All the suspected cases associated with ketorolac recorded in the Italian Pharmacovigilance database were retrieved. Case evaluations were carried out in order to identify the off-label use of ketorolac. Moreover, an analysis of the inappropriate use of ketorolac was conducted using the 'Arianna' database of Caserta local health unit. RESULTS: Up to December 2014, 822 reports of suspected ADRs related to ketorolac were retrieved in the database. The use of ketorolac was classified as off-label for 553 reports and on-label for 269. Among the off-label cases, 58.6% were serious compared to 39.0% of on-label cases. Gastrointestinal events were more frequently reported with off-label use. The analysis of Arianna database showed that 37,729 out of 61,910 patients, were treated off-label. CONCLUSIONS: The off-label use of ketorolac is widespread in Italy. This use increases the risk of serious ADR, especially in in case of prolonged duration of treatment and in elderly patients. The Italian Medicine Agency has decided to accurately monitor the appropriate use of the drug in Italy and, if necessary, take measures in order to minimize the risks.


Assuntos
Sistemas de Notificação de Reações Adversas a Medicamentos , Cetorolaco/efeitos adversos , Uso Off-Label , Farmacovigilância , Adolescente , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Anti-Inflamatórios não Esteroides/efeitos adversos , Anti-Inflamatórios não Esteroides/uso terapêutico , Criança , Bases de Dados Factuais , Feminino , Humanos , Itália/epidemiologia , Cetorolaco/uso terapêutico , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Fatores de Tempo , Adulto Jovem
8.
Int J Immunopathol Pharmacol ; 28(4): 532-8, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25990828

RESUMO

Although several therapeutic approaches are available at present for the treatment of chronic pharyngitis, new therapeutic strategies acting on pharyngeal mucous function should be investigated in order to improve symptoms and quality of life. High-molecular weight hyaluronate performs important functions on mucociliary clearance, tissues hydration, defense against micro-organisms, and on tissue repair as well, but at present there is no clinical evidence of its exogenous use in patients with chronic pharyngitis. Our open, randomized controlled study was carried out to investigate efficacy, and tolerability of exogenous high molecular weight sodium hyaluronate (SH) at the dosage of 9 mg three times a day for a period of 30 days, in patients with chronic pharyngitis. Results show significant improvements of symptoms and cytology in active group (A, n = 10) vs. control group (B, n = 10). Good compliance and no adverse events were reported in group A. In conclusion, SH was effective and safe in patients with chronic pharyngitis.


Assuntos
Ácido Hialurônico/uso terapêutico , Faringite/tratamento farmacológico , Adulto , Doença Crônica , Humanos , Ácido Hialurônico/efeitos adversos , Pessoa de Meia-Idade , Peso Molecular , Projetos Piloto , Estudos Prospectivos
9.
Int J Pediatr Otorhinolaryngol ; 78(2): 377-80, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24332666

RESUMO

Laryngotracheal cleft (LTC) is a rare congenital anomaly. Severe forms of LTC are usually treated surgically using extracorporeal circulation. Despite tremendous improvement of surgical techniques, postoperative complications are still frequent. We report a comprehensive description of an endoscopic approach to diagnosis, surgical repair and endoscopic treatment of complications after correction in a type IV LTC.


Assuntos
Anormalidades Congênitas/cirurgia , Laringoscopia/métodos , Laringe/anormalidades , Complicações Pós-Operatórias , Traqueia/anormalidades , Doenças da Traqueia/cirurgia , Anormalidades Congênitas/etiologia , Feminino , Humanos , Lactente , Laringe/cirurgia , Traqueia/cirurgia
10.
BMC Infect Dis ; 12 Suppl 2: S9, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-23173812

RESUMO

The SINERGIE (South Italian Network for Rational Guidelines and International Epidemiology) project is intended to set up a collaborative network comprising virologists, clinicians and public health officials dealing with patients affected by HCV disease in the Calabria Region. A prospective observational data-base of HCV infection will be developed and used for studies on HCV natural history, response to treatment, pharmaco-economics, disease complications, and HCV epidemiology (including phylogenetic analysis). With this approach, we aim at improving the identification and care of patients, focusing on upcoming research questions. The final objective is to assist in improving care delivery and inform Public Health Authorities on how to optimize resource allocation in this area.


Assuntos
Hepatite C/epidemiologia , Hepatite C/prevenção & controle , Bases de Dados Factuais , Diretrizes para o Planejamento em Saúde , Hepatite C/tratamento farmacológico , Humanos , Itália/epidemiologia , Saúde Pública
11.
Phys Rev Lett ; 100(11): 117001, 2008 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-18517813

RESUMO

A new charge quantization in a phase-polarized Cooper-pair pump is proposed, based on the topological properties of its Hamiltonian ground state over a three-dimensional parameter space P. The charge is quantized using a set of paths in P covering the surface of a torus, and is a multiple of the integer Chern index c1 of this surface. This quantization is asymptotic but the pumped charge converges rapidly to the quantized value with the increase in the path frequency. The topological nature of the current makes this Cooper-pair pump implementation an excellent candidate for a metrological current standard.

12.
Eur J Clin Pharmacol ; 64(3): 303-9, 2008 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-17992523

RESUMO

OBJECTIVE: To analyze prescriptions in a general-practitioner database over 1 year to determine the frequency, the characteristics, and the monitoring of the severe potential drug-drug interactions (DDIs). METHODS: We retrospectively analyzed the clinical records from 16 general practitioners in the Veneto region, an area in northern Italy. The study covered the period from January 1 to December 31, 2004. We selected all severe and well-documented interactions according to the book Drug Interaction Facts by David S. Tatro (Facts and Comparisons, St. Louis, MO, 2006). We grouped severe potential DDIs according to their specific potential risk, and for the most frequently interacting drug pairs, we investigated whether some specific tests had been prescribed by physicians for safety monitoring. RESULTS: During the study period, 16,037 patients (55% female) with at least one drug prescription were recorded, and a total of 185,704 prescriptions relating to 1,020 different drugs were analyzed. Ramipril was the most frequently prescribed drug followed by acetylsalicylic acid and atorvastatin. The final number of different types of severe potential DDIs was 119, which occurred 1,037 times in 758 patients (4.7% of the total number of patients). More than 80% of drugs involved in severe potential DDIs were cardiovascular drugs. Digoxin was the most frequently involved drug. Electrolyte disturbances, increase in serum digoxin levels, risk of hemorrhage, severe myopathy or rhabdomyolysis, and cardiac arrhythmias were the most commonly implicated potential risks. When considering patients using digoxin with loop or thiazide diuretics for more than 5 months, 72% had at least one test to monitor potential digoxin toxicity, whereas 28% had no tests. Sixty-four percent of patients using digoxin with amiodarone, verapamil, or propafenone had an ECG and/or digoxin monitoring, and 36% of them did not have any tests. CONCLUSIONS: The present study revealed that, in a group of Italian general practitioners, the risks of severe potential drug interactions are relatively low and the drugs concerned are few. Analyses of specific tests showed that physicians are generally aware of the potential risks caused by digoxin drug associations. However not all patients were closely monitored and this should be improved.


Assuntos
Sistemas de Notificação de Reações Adversas a Medicamentos/estatística & dados numéricos , Interações Medicamentosas , Monitoramento de Medicamentos/estatística & dados numéricos , Padrões de Prática Médica/estatística & dados numéricos , Adolescente , Adulto , Idoso , Criança , Pré-Escolar , Bases de Dados Factuais , Monitoramento de Medicamentos/normas , Feminino , Humanos , Lactente , Itália , Masculino , Pessoa de Meia-Idade , Médicos de Família/normas , Médicos de Família/estatística & dados numéricos , Padrões de Prática Médica/normas , Estudos Retrospectivos , Fatores de Risco
13.
Med Chem ; 2(3): 227-37, 2006 May.
Artigo em Inglês | MEDLINE | ID: mdl-16948468

RESUMO

The aim of this study was to investigate cellular response to several ruthenium(III), chromium(III) and rhodium(III) compounds carrying bidentate beta-diketonato ligands: [(acac)--acetylacetonate ligand, (tfac)--trifluoroacetylacetonate ligand]. Cell sensitivity studies were performed on several cell lines (A2780, cisplatin-sensitive and -resistant U2-OS and U2-OS/Pt, HeLa, B16) using growth-inhibition assay. Effect of intracellular GSH depletion on cell sensitivity to the agents was analyzed in A2780 cells. Flow cytometry was used to assess apoptosis by Annexin-V-FITC/PI staining, and to analyze induction of caspase-3 activity. Possible DNA binding/damaging affinity was investigated, by inductively coupled mass spectrometry, and by 14C-thymidine / 3H-uridine incorporation assay. Cell sensitivity studies showed that the pattern of sensitivity to Ru(tfac)3 complex of the two cisplatin-sensitive/-resistant osteosarcoma cell lines, U2-OS and U2-OS/Pt, was similar to that of A2780 cells (72 h exposure), with the IC50 being around 40 microM. The growth-inhibitory effect of Ru(acac)3 ranged over 100 microM, while Cr(III) and Rh(III) complexes were completely devoid of antitumor action in vitro. Ru(tfac)3 exhibited strong potential for apoptosis induction on A2780 cells (up to 40%) and caused cell cycle arrest in the S phase as well as decrease of the percent of G1 and G2 cells. Ru(acac)3-induced apoptosis was slightly higher than 10%, whereas activation of caspase-3 in HeLa cells was moderate. DNA binding study revealed that only Cr(acac)3 was capable of binding DNA, while Cr(III) and Ru(III) compounds possess potential to inhibit DNA/RNA synthesis. In conclusion, only Ru(III) complexes showed potential for antitumor action.


Assuntos
Apoptose/efeitos dos fármacos , Ciclo Celular/efeitos dos fármacos , Cromo/farmacologia , Ródio/farmacologia , Rutênio/farmacologia , Caspase 3 , Caspases/metabolismo , Linhagem Celular Tumoral , DNA de Neoplasias/biossíntese , DNA de Neoplasias/efeitos dos fármacos , Citometria de Fluxo , Humanos , RNA Neoplásico/biossíntese , RNA Neoplásico/efeitos dos fármacos
14.
Transplant Proc ; 38(5): 1638-40, 2006 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-16797373

RESUMO

INTRODUCTION: While acute models of orthotopic lung transplantation have been described in dogs, the technical considerations of developing a survival model in this species have not been elaborated. Herein, we describe optimization of a canine survival model of orthotopic lung transplantation. METHODS: Protocols of orthotopic left lung transplantation and single lung ventilation were established in acute experiments (n=9). Four dogs, serving as controls, received autologous, orthotopic lung transplants. Allogeneic transplants were performed in 16 DLA-identical and 16 DLA-mismatched unrelated recipient dogs. Selective right lung ventilation was utilized in all animals. A Malecot tube was left in the pleural space connected to a Heimlich valve for up to 24 hours. To date, animals have been followed up to 24 months by chest radiography, pulmonary function tests, bronchoscopy with lavage, and open biopsies. RESULTS: Long-term survival was achieved in 34/36 animals. Two recipients died intraoperatively secondary to cardiac arrest. All animals were extubated on the operating table, and in all cases the chest tube was removed within 24 hours. Major complications included thrombosis of the pulmonary artery and subcritical stenosis of bronchial anastamosis. One recipient underwent successful treatment of a small bowel intussusception. CONCLUSIONS: We report our experience in developing a survival canine model of orthotopic single lung transplantation. While short-term survival following canine lung transplantation is achievable, we report particular considerations that facilitate animal comfort, early extubation, and lung reexpansion in the immediate postoperative period, further optimizing use of this species for experimental modeling of long-term complications after lung transplantation.


Assuntos
Sobrevivência de Enxerto/fisiologia , Transplante de Pulmão/fisiologia , Animais , Cães , Sobrevivência de Enxerto/imunologia , Transplante de Pulmão/imunologia , Transplante de Pulmão/veterinária , Modelos Animais , Fatores de Tempo , Coleta de Tecidos e Órgãos/métodos , Coleta de Tecidos e Órgãos/veterinária , Obtenção de Tecidos e Órgãos/métodos , Transplante Autólogo , Transplante Homólogo
15.
Arch Dis Child Fetal Neonatal Ed ; 90(6): F514-9, 2005 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-16244211

RESUMO

AIMS: To determine in a case-control study possible associations between the development of acute renal failure in preterm newborns and therapeutic interventions, particularly drug treatments. METHODS: The study population was 172 preterm infants of <38 weeks gestation; 71 had acute renal failure and 101 were controls closely matched for gestational age and birth weight. Maternal and neonatal information was collected for both groups through questionnaires and interviews. Routine data on renal variables were also collected. Univariate and multivariate logistic regression analyses were performed. RESULTS: Very low birthweight infants were at high risk of acute renal failure (79% of cases were <1500 g). However, the acute renal failure was transient. Mothers of infants with acute renal failure received more drugs during pregnancy and delivery (mainly antibiotics and non-steroidal anti-inflammatory drugs). Of the possible therapeutic interventions, intubation, catheterisation, and phototherapy were mainly applied to case subjects. A low Apgar score and patent ductus arteriosus were diagnosed in a greater percentage of neonates with acute renal failure. Moreover, in the first few days of life and before diagnosis of acute renal failure, case subjects received more drugs (antibiotics, non-steroidal anti-inflammatory drugs, and diuretics) and for a longer time. In the multivariate logistic analysis, medullary hyperechogenicity (odds ratio (OR) 4.491; 95% confidence interval (CI) 1.879 to 10.731) and ceftazidime administration (OR 5.082; 95% CI 1.493 to 17.297) were associated with a greater risk of acute renal failure. CONCLUSIONS: The results suggest the need for careful monitoring of very low birthweight infants and attention to drug treatments, as it is difficult to differentiate between normality and renal failure in the first few days of life.


Assuntos
Injúria Renal Aguda/etiologia , Doenças do Prematuro/etiologia , Antibacterianos/efeitos adversos , Anti-Inflamatórios não Esteroides/efeitos adversos , Índice de Apgar , Peso ao Nascer , Estudos de Casos e Controles , Feminino , Idade Gestacional , Humanos , Recém-Nascido , Recém-Nascido Prematuro , Doenças do Prematuro/terapia , Recém-Nascido de muito Baixo Peso , Modelos Logísticos , Masculino , Troca Materno-Fetal , Gravidez , Efeitos Tardios da Exposição Pré-Natal , Fatores de Risco
16.
J Chem Phys ; 121(11): 5468-81, 2004 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-15352842

RESUMO

Colloidal aggregation processes arising at different electrolyte concentrations were studied by means of experiments and confronted with theoretical predictions of different kinetic aggregation models. For this purpose, aqueous dispersions of relatively large polystyrene microspheres were chosen as experimental systems. Aggregation was induced by adding KBr electrolyte to the initially stable particle dispersions. During the aggregation processes, the cluster-size distribution was monitored by means of single cluster light scattering. Analyzing the time evolution of the monomer concentration, we found that the processes arising even at moderate electrolyte concentrations cannot be described by pure time-independent irreversible aggregation models. Hence, alternative models such as time-dependent irreversible aggregation and several reversible aggregation models were also tested. The model that considers a time-dependent sticking probability was found to fit the data quite satisfactorily. Nevertheless, the fitted was so slow that it seems not very likely to find such a behavior in real systems. The aggregation-fragmentation models reported in the literature were unable to reproduce the experimental observations. Hence, a more realistic reversible aggregation model was developed. This model accounts also for reenforced or double bonds between the constituent particles. The corresponding fit improved significantly and reached the same quality as the time-dependent model. Moreover, the obtained fitting parameters were in qualitative agreement with the DLVO predictions and so, reversible aggregation seems to be a more reasonable explanation for the experimental data than time-dependent irreversible aggregation. However, no definite statement on the possible secondary bond fragmentation mechanism may be made since both the applied shear stress in the measuring cell and thermal fluctuations can cause weaker bonds to break.

17.
Eur Phys J E Soft Matter ; 13(2): 165-78, 2004 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-15052426

RESUMO

The results of computer models for colloidal aggregation, that consider both Brownian motion and gravitational drift experienced by the colloidal particles and clusters, are extended to include concentrations spanning three orders of magnitude. In previous publications and for a high colloidal concentration, it was obtained that the aggregation crosses over from diffusion-limited colloidal aggregation (DLCA) to another regime with a higher cluster fractal dimension and a speeding up followed by a slowing down of the aggregation rate. In the present work we show, as the concentration is decreased, that we can still cross over to a similar regime during the course of the aggregation, as long as the height of the sample is increased accordingly. Among the differences between the mentioned new regimes for a high and a low colloidal concentration, the cluster fractal dimension is higher for the high concentration case and lowers its value as the concentration is decreased, presumably reaching for low enough concentrations a fixed value above the DLCA value. It is also obtained the fractal dimension of the sediments, arising from the settling clusters that reach the bottom and continue a 2D-like diffusive motion and aggregation, on the floor of the container. For these clusters we now see two and sometimes three regimes, depending on concentration and sedimentation strength, with their corresponding fractal dimensions. The first two coming from the crossover already mentioned, that took place in the bulk of the sample before the cluster deposition, while the third arises from the two-dimensional aggregation on the floor of the container. For these bottom clusters we also obtain their dynamical behavior and aggregation rate.


Assuntos
Coloides/química , Algoritmos , Anisotropia , Análise por Conglomerados , Relação Dose-Resposta a Droga , Fractais , Método de Monte Carlo , Movimento , Ligação Proteica
18.
Phys Rev E Stat Nonlin Soft Matter Phys ; 67(3 Pt 1): 031401, 2003 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-12689061

RESUMO

The influence of the sticking probability P and the drift velocity on kinetics and structure formation arising in coupled aggregation and sedimentation processes was studied by means of simulations. For this purpose, a large prism with no periodical conditions for the sedimentation direction was considered allowing for sediment formation at the prism base. The time evolution of the cluster size distribution (CSD) and weight-average cluster size (n(w)) were determined in three different regions of the prism. The cluster morphology and the sediment structure were also analyzed. We found that the coupled aggregation and sedimentation processes in the bulk are governed by P for short times, and controlled by the Péclet number Pe for long times. In the lower part of the reaction volume, where the sediment grows, the local n(w) grows at sufficiently large times analytically with an exponent of four. This behavior seems to be independent of Pe and P. The obtained results are in good agreement with the experimental data reported by C. Allain, M. Cloitre, and M. Wafra [Phys. Rev. Lett. 74, 1478 (1995)] and support the idea of a possible internal cluster rearrangement for the experiments. Finally, we discuss how the scale dependent fractal character of the sediment is related to the different stages of the aggregation process.

19.
Eur J Cancer ; 39(7): 996-1003, 2003 May.
Artigo em Inglês | MEDLINE | ID: mdl-12706370

RESUMO

Nephrotoxicity is a side-effect and the main factor limiting the clinical use of cisplatin. In vivo, the administration of the cysteine-containing tripeptide glutathione (GSH) has been found to reduce nephrotoxicity, but the biochemical mechanism of this protective action is not fully understood. The present study was designed to gain insights into the mechanism by which GSH prevents cisplatin nephrotoxicity. We also wanted to verify the hypothesis of whether the protective action of GSH is mediated by products of the extracellular breakdown of GSH catalysed by gamma-glutamyl transpeptidase (GGT), an enzyme that is highly expressed in kidney tubular cells. The study was performed in HK-2 cells, derived from the immortalisation of human kidney proximal tubule cells. We investigated the influence of modulators of GGT activity and/or thiols on the antiproliferative activity of cisplatin and on the intracellular GSH content. We determined the antiproliferative activity of cisplatin, platinum cellular accumulation and DNA platination following precomplexing of the drug with thiols. The antiproliferative effect of cisplatin was minimally affected by the addition of GSH. However, when the antiproliferative assay was performed in the presence of glycyl-glycine (GlyGly), to serve as a transpeptidation acceptor and thus to stimulate GGT-mediated GSH catabolism, cisplatin-induced growth inhibition was largely prevented. This effect was not mediated through an increase of intracellular GSH levels, which were not affected by the GlyGly supplementation. The thiol dipeptide cysteinyl-glycine, i.e. the GSH catabolite generated by GGT activity, showed a higher reactivity against cisplatin in vitro than GSH, as was shown by the more rapid oxidation of its -SH groups. The cisplatin/GSH or cisplatin/cysteinyl-glycine adducts did not display an antiproliferative effect. However, 2 h precomplexing with GSH in the presence of GGT, or directly with the GSH catabolite cysteinyl-glycine, decreased the antiproliferative effect of cisplatin and drug-induced DNA platination to a greater extent than precomplexing with GSH alone. The results of the present study show that, in HK-2 cells, extracellular GSH decreases the antiproliferative effects of cisplatin only upon its hydrolysis by GGT, thereby supporting the hypothesis that the extracellular metabolism of GSH by GGT plays a role in modulating cisplatin nephrotoxicity. A primary role in the protection of HK-2 cells appears to be played by cysteinyl-glycine, the proximal product of the GGT-mediated hydrolysis of GSH, which shows a high reactivity against CDDP resulting in the rapid inactivation of the drug.


Assuntos
Antineoplásicos/farmacocinética , Cisplatino/farmacocinética , Túbulos Renais Proximais/metabolismo , gama-Glutamiltransferase/farmacologia , Antineoplásicos/efeitos adversos , Linhagem Celular , Cisplatino/efeitos adversos , Glutationa/farmacologia , Humanos , Inativação Metabólica , Nefropatias/induzido quimicamente , Nefropatias/prevenção & controle , Compostos de Sulfidrila/metabolismo
20.
Phys Rev E Stat Nonlin Soft Matter Phys ; 65(3 Pt 1): 031405, 2002 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-11909055

RESUMO

Reversible aggregation processes were simulated for systems of freely diffusing sticky particles. Reversibility was introduced by allowing that all bonds in the system may break with a given probability per time interval. In order to describe the kinetics of such aggregation-fragmentation processes, a fragmentation kernel was developed and then used together with the Brownian aggregation kernel for solving the corresponding kinetic master equation. The deduced fragmentation kernel considers a single characteristic lifetime for all bonds and accounts for the cluster morphology by averaging over all possible configurations for clusters of a given size. It became evident that the simulated cluster-size distributions could be described only when an additional fragmentation effectiveness was considered. Doing so, the stochastic solutions were in good agreement with the simulated data.

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