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Biomedical subjects

A Guimaraes

Publications and source records attributed to A Guimaraes.

15 recordsLinked to original sources
PubMed2006

Optimisation and validation of a solid-phase microextraction method for simultaneous determination of different types of pesticides in water by gas chromatography-mass spectrometry.

A solid-phase microextraction (SPME) method for the simultaneous determination of a large number of pesticides (46) with a wide range of polarities and chemical structures (organochlorine, organophosphorous, triazines, pyrethroids and others) in water samples by GC-MS has been developed. Three different fibres and parameters that influence the extraction and desorption efficiency were studied. The selected conditions were: a 60 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibre, 45 min of extraction time, sample agitation and temperature control at 60 degrees C; neither pH adjustment nor ionic strength correction were applied. Good detection limits, linearity and repeatability were obtained with this method for the 46 pesticides studied. The method was validated for 29 pesticides following the recommendations of the international norm ISO/IEC 17025 including the calculation of the uncertainties. The detection limits ranged from 4 to 17 ng l(-1). Furthermore, repeatability (6.9-20.5%) and intermediate precision (4.5-19.7%) were shown to be satisfactory. To validate matrix effects for drinking and surface water analytical recoveries were calculated for these matrices. The accuracy of the method was also evaluated by participating in a proficiency inter-laboratory test.

Gas Chromatography-Mass Spectrometry↗
PubMed2005

Tau suppression in a neurodegenerative mouse model improves memory function.

Neurofibrillary tangles (NFTs) are the most common intraneuronal inclusion in the brains of patients with neurodegenerative diseases and have been implicated in mediating neuronal death and cognitive deficits. Here, we found that mice expressing a repressible human tau variant developed progressive age-related NFTs, neuronal loss, and behavioral impairments. After the suppression of transgenic tau, memory function recovered, and neuron numbers stabilized, but to our surprise, NFTs continued to accumulate. Thus, NFTs are not sufficient to cause cognitive decline or neuronal death in this model of tauopathy.

Aging↗
PubMed2001

Familial amyloid polyneuropathy: receptor for advanced glycation end products-dependent triggering of neuronal inflammatory and apoptotic pathways.

Familial amyloid polyneuropathy (FAP) is a neurodegenerative disorder associated with extracellular deposition of mutant transthyretin (TTR) amyloid fibrils, particularly in the peripheral nervous system. We have hypothesized that binding of TTR fibrils to the receptor for advanced glycation end products (RAGE) on critical cellular targets is associated with a destructive stress response underlying peripheral nerve dysfunction. Analysis of nerve biopsy samples from patients with FAP (n = 16) at different stages of disease (0-3), compared with age-matched controls (n = 4), by semiquantitative immunohistology and in situ hybridization showed increased levels of RAGE, beginning at the earliest stages of the disease (FAP 0; p < 0.02) and especially localized in axons. Upregulation of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-1beta) (approximately threefold; p < 0.02) and the inducible form of nitric oxide synthase (iNOS) ( approximately 2.5-fold; p < 0.04) was also observed in a distribution overlapping RAGE expression. Tyrosine nitration and increased activated caspase-3 in axons from FAP patients (p < 0.03) were apparent. Although these data suggest the presence of ongoing neuronal stress, there was no upregulation of neurotrophins (nerve growth factor and neurotrophin-3) in FAP nerves. Studies on cultured neuronal-like, Schwann, and endothelial cells incubated with TTR fibrils displayed RAGE-dependent expression of cytokines and iNOS at early times (6 and 12 hr, respectively), followed by later (24 hr) activation of caspase-3 and DNA fragmentation. We propose that the interaction of TTR fibrils with RAGE may contribute to cellular stress and toxicity in FAP. Furthermore, there is an apparent lack of responsiveness of Schwann cells in FAP nerve to provide neurotrophic factors.

Adolescent↗
PubMed1998

High-dose therapy including carboplatin adjusted for renal function in patients with relapsed or refractory germ cell tumour: outcome and prognostic factors.

Thirty-one consecutive patients with relapsed or refractory GCT received an HDT schedule including carboplatin, the dose of which was adjusted to measured glomerular filtration rate. There was one HDT-associated death (3%), due to acute renal failure. The 3-year probability of overall and disease-free survival for 21 patients with primary refractory disease or responsive relapse was 60% and 42%, respectively, while none of ten patients with refractory relapse have survived disease free.

Carboplatin↗
PubMed1998

Cocaine decreases cortical cerebral blood flow but does not obscure regional activation in functional magnetic resonance imaging in human subjects.

The authors used functional magnetic resonance imaging (fMRI) to determine whether acute intravenous (i.v.) cocaine use would change global cerebral blood flow (CBF) or visual stimulation-induced functional activation. They used flow-sensitive alternating inversion recovery (FAIR) scan sequences to measure CBF and blood oxygen level-dependent (BOLD) sensitive T2* scan sequences during visual stimulation to measure neuronal activation before and after cocaine and saline infusions. Cocaine (0.6 mg/kg i.v. over 30 seconds) increased heart rate and mean blood pressure and decreased end tidal carbon dioxide (CO2). All measures returned to baseline by 2 hours, the interinfusion interval, and were unchanged by saline. Flow-sensitive alternating inversion recovery imaging demonstrated that cortical gray matter CBF was unchanged after saline infusion (-2.4 +/- 6.5%) but decreased (-14.1 +/- 8.5%) after cocaine infusion (n = 8, P < 0.01). No decreases were detected in white matter, nor were changes found comparing BOLD signal intensity in cortical gray matter immediately before cocaine infusion with that measured 10 minutes after infusion. Visual stimulation resulted in comparable BOLD signal increases in visual cortex in all conditions (before and after cocaine and saline infusion). Despite a small (14%) but significant decrease in global cortical gray matter CBF after acute cocaine infusion, specific regional increases in BOLD imaging, mediated by neurons, can be measured reliably.

Adult↗
PubMed1996

Helper and cytotoxic lymphocyte responses to chronic myeloid leukaemia: implications for adoptive immunotherapy with T cells.

We studied 19 patients with chronic myeloid leukaemia (CML) to characterize T-cell autologous responses to leukaemia. Third party stimulated alloresponses in mixed lymphocyte reactions were normal in all patients. Using the helper T-lymphocyte precursor frequency (HTLPf) assay we demonstrated a low frequency of T helper cells recognizing autologous leukaemia cells from CML blood (1/850 000) and marrow (1/965 000). However, similar frequencies to autologous bone marrow and lymphoid cells were also found in normal individuals. In 11 patients studied, HLA-matched siblings had a higher HTLPf to leukaemia than the patient's autologous response (P < 0.004). Alloresponse in mixed lymphocyte reactions (MLR), and autologous HTLPf to leukaemia, were comparable at all stages of disease progression and time from diagnosis, and independent of treatment given. In order to generate autologous cytotoxic lymphocyte responses to CML, lymphocytes were stimulated with CML cells. Cultures were fed again with CML cells and examined for cytotoxicity after 21 d. Strong lymphokine-activated killer (LAK) cytotoxicity was found against K562 and Daudi cell lines, and to Epstein-Barr virus-transformed allogeneic and autologous lymphoblastoid cell lines. Autologous leukaemia cells were lysed to a lesser extent in only 3/13 patients tested. The findings indicate that immune reactivity in CML is normal but suggest that CML cells are relatively resistant to lysis by cytotoxic T cells. The results do not support the existence of a leukaemia-specific T-cell response in CML.

Adult↗
PubMed1995

Syngeneic bone marrow transplantation eliminates V beta 8.2 T lymphocytes from the spinal cord of Lewis rats with experimental allergic encephalomyelitis.

Experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis (MS), is a paralytic disease of the central nervous system (CNS) mediated by T-lymphocytes reactive to myelin basic protein (MBP). Lewis rats actively immunized with fragment 68 to 82 of guinea pig MBP develop a monophasic disease with spontaneous recovery. Lymphocyte recognition of the primary encephalitogenic sequence of MBP (fragment 68 to 82) is V beta 8.2 T cell receptor (TCR) skewed [1-3]. Lewis rats in clinical remission at 1 month and 3 months after spontaneous resolution of EAE retain V beta 8.2 T-lymphocytes in the CNS when analyzed by reverse transcriptase polymerase chain reaction or in situ hybridization. In contrast, 1 and 3 months after clinical remission from syngeneic bone marrow transplantation, V beta 8.2 T lymphocytes are absent from the CNS. During clinically active EAE and inflammatory breakdown of the blood-brain barrier, immune ablation and reconstitution with syngeneic bone marrow results in clinical tolerance of the new immune system to myelin.

Animals↗
PubMed1994

Distributed random electrical neuromuscular stimulation: effects of the inter-stimulus interval statistics on the EMG spectrum and frequency parameters.

An electrophysiological approach was used to study a distributed random electrical neuromuscular stimulation (ENMS) scheme in which a probability density is assigned to the inter-stimulus intervals (ISI) of the stimuli. One of the objectives of using ENMS techniques in the study of skeletal muscles is to obtain information about the electrical, physiological, and mechanical properties of muscles in a near-physiological situation under a well-controlled experimental design in which problems related to the uncertainty of firing patterns of the central nervous system and physiological interference are avoided. In particular, ISI with a Gaussian density were varied in mean rate, standard deviation (SD), and coefficient of variation. The influence of varying ISI, and the interaction of the ISI statistics with compound motor unit action potentials (CMUAP) on EMG power spectra and their frequency parameters, was assessed theoretically using a mathematical model which is similar to that of EMG signal generation in the electrophysiological case. In order to quantify the effects of ISI statistics on the EMG spectrum, the median frequency was calculated as a function of stimulation rate using analytical expressions for various values of the coefficients of a Gaussian ISI variation. The results obtained suggest that 1) the interaction between ISI statistics and the shape of the CMUAP plays a major role in determining the EMG spectrum; 2) the median frequencies (MF) determined from EMG spectra tend to increase with increasing mean rates of stimulation for a given CMUAP. The rate of increase of the MF depends on the coefficient of the ISI variation; 3) the EMG spectra of random electrically stimulated muscle show peaks at the mean rate of stimulation, and multiples of it, when the coefficient of variation of ISI is small. These peaks decrease in magnitude with increasing coefficients of variation of ISI; and, 4) a variation in the ISI should be introduced in the ENMS, when a reproduction of 'normal' EMG spectra is needed. These results are consistent with those reported for voluntary contraction of skeletal muscles.

Electric Stimulation↗
PubMed1993

Immunological characterization of the tumor-specific bcr/abl junction of Philadelphia chromosome positive chronic myeloid leukemia.

Recent developments in the understanding of the process of antigen presentation by major histocompatibility complex (MHC) molecules and their recognition by T-lymphocytes has led investigators to speculate that the hybrid bcr/abl fusion protein P210 present in chronic myeloid leukemia (CML) cells may generate leukemia-specific antigens recognized by T-cells. We used synthetic peptides representing the fusion region of P210 to study MHC class I and class II pathways of antigen recognition in normal subjects and patients with CML. We found that most normal individuals have a low proliferative response to 18mer fusion peptides representing the two alternative splicing variants b2a2 and b3a2, and a T-lymphocyte precursor frequency (HTLPf) characteristic of unprimed responders. No increase in HTLPf was found in CML patients after bone marrow transplantation (BMT), suggesting that peptide recognition does not form part of the graft-versus-leukemia process. In contrast, untransplanted patients with CML had very high HTLPf, suggesting an autologous but immunologically ineffective recognition of leukemia-specific peptides through HLA class II. Preliminary studies using the T2 cell line (which expresses HLA class I only in the presence of peptides binding to HLA-A2) indicate that nonapeptides spanning the breakpoint of the b2a2 and b3a2 variants of P210 do not bind to this particular class I molecule and are therefore unlikely to initiate class I mediated lymphocyte responses.

Antigen-Presenting Cells↗
PubMed1989

Characterization of an activity-dependent, neuronal surface proteoglycan identified with monoclonal antibody Cat-301.

Monoclonal antibody Cat-301 was previously shown to recognize a surface-associated antigen on subsets of mammalian CNS neurons whose expression is regulated by neuronal activity early in an animal's postnatal life. We now present the partial purification and characterization of the Cat-301 antigen and demonstrate that it is a chondroitin sulfate proteoglycan. Extracellular localization of the Cat-301 epitope is demonstrated by staining live, intact neurons in situ. Extraction of the antigen from membranes in the absence of detergent indicates that it is either a peripheral membrane protein or a component of an extracellular matrix. The Cat-301 antigen migrates on Western blots of SDS gels with a molecular weight of integral of 680,000 dalton and is purified by DEAE chromatography and Sepharose gel filtration in 8 M urea (pH 4.9) buffer. The antigen is sensitive to chondroitinase ABC, indicating that it is a chondroitin sulfate proteoglycan. Furthermore, we provide strong evidence that the biochemically characterized antigen is indeed the histologically detected species by using a second antibody, Cat-304, that produces immunohistological staining patterns identical to those of Cat-301 and reacts with the purified antigen, but at a distinct epitope. Our earlier developmental findings and the present localization and biochemical results suggest that the antigen may play a role in the maturation of functional connections between neurons, perhaps through stabilization of axosomatic and axodendritic synapses.

Animals↗
PubMed1979

[Quantitative and electron microscope study of the nerve in seven cases of sporadic idiopathic sensory neuropathy (author's transl)].

An electron microscope study and quantitation of myelinated and unmyelinated fibers of seven nerve biopsies performed in sporadic cases of idiopathic sensory neuropathy is reported. The number of myelinated fibers is markedly decreased or absent in every case. On the contrary, the unmyelinated fiber numbers are normal or increased. In most cases, the small diameter myelinated and unmyelinated fibers proportions are higher than those of control biopsies. The electron microscope study discloses evidence of degeneration of Wallerian tye and regeneration is also indicated by quantitative studies. Regenerative phenomena seen more obvious in sporadic cases than in previously reported studies of familial cases.

Biopsy↗