PubMed Health⌕ Search

Biomedical subjects

R Floris

Publications and source records attributed to R Floris.

At least 37 records · Page 2Linked to original sources
PubMed1999

Thermodynamic analysis of halide binding to haloalkane dehalogenase suggests the occurrence of large conformational changes.

Haloalkane dehalogenase (DhlA) hydrolyzes short-chain haloalkanes to produce the corresponding alcohols and halide ions. Release of the halide ion from the active-site cavity can proceed via a two-step and a three-step route, which both contain slow enzyme isomerization steps. Thermodynamic analysis of bromide binding and release showed that the slow unimolecular isomerization steps in the three-step bromide export route have considerably larger transition state enthalpies and entropies than those in the other route. This suggests that the three-step route involves different and perhaps larger conformational changes than the two-step export route. We propose that the three-step halide export route starts with conformational changes that result in a more open configuration of the active site from which the halide ion can readily escape. In addition, we suggest that the two-step route for halide release involves the transfer of the halide ion from the halide-binding site in the cavity to a binding site somewhere at the protein surface, where a so-called collision complex is formed in which the halide ion is only weakly bound. No large structural rearrangements are necessary for this latter process.

Bromides↗
PubMed1999

[The clinical efficacy of magnetic resonance with diffusion-weighted sequences in the assessment of acute cerebral ischemia].

PURPOSE: To evaluate the efficacy of diffusion weighted Magnetic Resonance Imaging in the diagnosis of acute ischemic infarction and correlate the signal changes observed in the acute phase with final brain damage. MATERIAL AND METHODS: Fifteen patients (six women and nine men: mean age 68 years) with acute ischemic stroke (within 12 hours) underwent diffusion MRI. All the patients were selected on the basis of sudden focal neurologic symptoms and CT findings excluding other conditions than ischemia. MRI was performed with a 1.5 T magnet with echo-planar gradients. All the patients underwent follow-up CT and/or MRI. RESULTS: Diffusion MRI, performed in the acute phase, showed signal changes in all the patients whose infarction was later confirmed by CT or MRI. In 10 of 12 patients with positive diffusion imaging, CT was normal. FLAIR sequences showed the lesions in 4 of 12 cases. In the 2 patients with transient ischemic attack diffusion MRI was normal as well as follow-up examinations. Apparent Diffusion Coefficients values in the infarcted area were almost half those of the contralateral normal brain. Final damage (as assessed by CT or MRI) was larger than observed in acute diffusion images in all cases but one. CONCLUSION: Because of its high sensitivity and specificity, diffusion MRI is going to play a more important role in the management of acute ischemic stroke patients.

Acute Disease↗
PubMed1998

Trans-sphenoidal treatment of postsurgical cerebrospinal fluid fistula: CT-guided closure.

Cerebrospinal fluid (CSF) leakage after trans-sphenoidal surgery is a troublesome complication with a risk of meningitis and pneumocephalus. We suggest CT-guided intrasphenoidal injection of fibrin sealant through a 12-gauge needle as a simple alternative to surgical management of CSF fistulae. We treated eight patients, operated via the trans-sphenoidal route (five pituitary adenomas, three craniopharyngiomas), for a postoperative CSF leak by CT-guided intrasphenoidal injection of fibrin sealant alone in three cases and fibrin sealant and autologous blood in 5. CT was obtained 10 days after the procedure in all cases. In four patients, the CSF leak was closed successfully at the first attempt. The procedure was repeated on the four remaining patients because only a reduction in leakage was obtained at the first attempt. This procedure preserves olfaction and avoids the risk of frontal lobe damage. It could therefore represent the treatment of choice in many cases of anterior cranial fossa postsurgical CSF leaks.

Adult↗
PubMed1998

Non-invasive assessment of neck-vessel pathology.

Clinical trials (NASCET, ECTS) have shown that carotid endarterectomy is protective against stroke in patients with symptomatic severe carotid stenosis. To decrease costs and risks, new diagnostic tools have been developed, such as duplex ultrasound (DUS), magnetic resonance angiography (MRA), and more recently computed tomography angiography (CTA). CTA and MRA provide excellent 3D angiography images of the extracranial vessels, using a volume-rendering technique. Digitally subtracted MRA (DSA-MRA) obtained with high-speed acquisitions during gadolinium injection has also recently become available. These techniques are changing the role of non-invasive assessment of carotid stenosis. Although it is probably too early to assess a definite diagnostic algorithm, the use of DSA as a pre-surgical tool for defining carotid stenosis is rapidly decreasing.

Angiography, Digital Subtraction↗
PubMed1998

[An evaluation of the carotid bifurcation and of the intracranial circle by angio-spiral computed tomography].

INTRODUCTION: Some clinical trials (NASCET, ECTS) have assessed that carotid endarterectomy is protective against stroke in patients with asymptomatic severe carotid stenosis. In order to decrease costs and risks, new diagnostic tools have been developed, such as Magnetic Resonance Angiography (MRA), duplex Ultrasound (US) and more recently Spiral Computed Tomography Angiography (CTA). CTA provides excellent 3D angiography images of the extracranial vessels using a volume rendering technique. This study was aimed at prospectively evaluating the accuracy of CTA in the diagnosis of carotid bifurcation. The circle of Willis was also studied during the same bolus injection. DSA was used as the gold standard technique. Surgery was also used for comparison. MATERIAL AND METHODS: Spiral CTA and DSA were performed in 106 carotid bifurcations. DSA was performed in all patients within 48-72 hours of CTA. The degree of internal carotid stenosis was evaluated according to NASCET criteria. Degree of stenosis, presence of calcifications, ulcerations and tandem lesions were reviewed by two different neuroradiologists blinded to each other and to the results of the other technique. In 19 cases the size of residual lumen of the ICA was surgically evaluated and correlated with CTA. RESULTS: There was an overall correlation between CTA and DSA in 94% of cases. Our data are in agreement with the results of the current literature. CT angiograms overrated by one category 6 cases (25%) of mild and one of moderate stenosis (7.14%). Calcifications were seen on spiral CT angiography in 69 (65.09%) carotid bifurcations while DSA detected the presence in 31 (29.24%). Ulcerations were missed by CTA in 3 cases. Five (4.71%) tandem lesions were visualized by DSA distal to bifurcation: 2 (1.88%) were also diagnosed by CTA. The patency of the circle of Willis was assessed in all cases. In 19 cases, the size of ICA stenosis evaluated at surgery was comparable with CTA findings. CONCLUSIONS: In conclusion CTA offers an outstanding alternative to catheter angiography in the evaluation of stenosis-occlusion of the carotid bifurcation. The intracranial circulation can be easily assessed by CTA as well, which allows the study of tandem lesions and of the circle of Willis.

Aged↗
PubMed1997

Early postoperative MRI findings following surgery for herniated lumbar disc. Part II: A gadolinium-enhanced study.

The aim of our study was to evaluate the contrast-enhanced MR imaging (MRI) findings, in the early postoperative period, in unselected patients undergoing lumbar microdiscectomy (15/16 had total resolution of their symptoms). Contrast-enhanced imaging studies were performed, in all 16 patients of our series, before surgery, and at the third postoperative day and, two months after surgery. Postoperative paraspinal muscles enhancement was present in all patients. In the postoperative period, nerve root enhancement was present in 5/16 patients at the early survey and persisted in one after two months. A pseudohernia depicted as epidural intermediate signal intensity tissue, was seen in 13 patients at the third day MRI, and only in eight after two months. This pseudohernia enhanced peripherally in 8/13 patients and enhanced homogeneously in the remaining five at the first postsurgical examination; in the late MRI the peripheral enhancement was appreciable in only two patients while a homogeneous enhancement was observed in six. Clinical symptoms resolved completely in 14/16 patients on clinical evaluation at the third postoperative day, while the remaining two patients showed residual symptoms and signs of radicular compression. At the early MRI these two patients showed intradural nerve root enhancement. Two months later, one patient did not show the previously described nerve root enhancement and improved clinically, while the other had a positive Straight Leg Raising Sign with persistent intradural nerve root enhancement. In conclusion, no correlation between clinical course and contrast-enhancement of pseudohernia and extradural nerve root was appreciable, although intradural nerve root enhancement seems to represent a clinically relevant finding.

Adult↗
PubMed1997

Early postoperative MRI findings following surgery for herniated lumbar disc.

MRI is routinely used in the evaluation and management of patients with failed back surgery syndrome (FBSS). However, its value is unclear in the early detection of signs that can negatively affect that later course of surgical cases. The purpose of the present study is to describe the MR images of early postoperative MRI at 3 days in 30 unselected patients who underwent lumbar microdiscectomy, and to correlate the findings with follow up MRI at 8 weeks and with final outcome. The findings are correlated with literature data. Early postoperative MRI findings were consisting of pseudohernia in 24 patients (80%), annular rent in 23 patients (80%), and other non-specific postoperative findings. On the late MRI the pseudohernia persisted in 12 patients (50%), the annular rent in 4 patients (15%) and asymptomatic pseudo-spondylodiscitis was apparent in 3 patients (10%) as was a case of true spondylodiscitis. Therefore, early postoperative findings have limited value in the management of patients after surgery for lumbar disc herniation, since the images were not correlated with the immediate clinical course after surgery nor with the late radiological and clinical outcome. The evident imaging changes in the early postoperative period after lumbar disc surgery limit the accuracy of the interpretation of MRI examinations.

Discitis↗
PubMed1997

Computed tomography-guided transsphenoidal closure of postsurgical cerebrospinal fluid fistula: a transmucosal needle technique.

BACKGROUND: Cerebrospinal fluid (CSF) fistula represents a fearful complication of transsphenoidal surgery and, despite careful intraoperative repair and prolonged postoperative lumbar CSF drainage, need for a new surgical intrasphenoidal plasty is not uncommon. METHODS: These cases prompted us to develop a simple, minimally invasive, harmless repeatable technique consisting of a computed tomography (CT)-guided intrasphenoidal injection of fibrin glue through a 12-gauge spinal needle. RESULTS: Five patients presenting with rhinoliquorrhea following a transsphenoidal approach for the excision of pituitary adenomas (three cases) and craniopharyngiomas (two cases) were treated successfully with the presented technique. In two cases the first attempt attained only partial success and therefore the procedure was repeated. In the last two cases, the injection of fibrin glue was preceded by 2 cc of fresh autologous blood, with the aim of enhancing the mechanisms of healing, possibly inducing adhesions and fibrosis. CONCLUSIONS: The proposed method of treatment for CSF leakage following transsphenoidal surgery may represent a valid alternative to the surgical option.

Adult↗
PubMed1997

Case report: subependymal diffuse heterotopia. Clinical, EEG, and neuroimaging findings.

We report the case of a 41 year-old woman with a slight mental retardation and epilepsy. MRI showed a diffuse subependymal heterotopia. The cognitive level supports the view that the ectopic cells are probably not important for the normal cortical functions but that they are likely able to maintain some of the electric properties of normal neurons, even if with altered discharge modalities. The genetic etiology of subependymal neuronal migration disorders is discussed. This is the second reported case of diffuse subependymal heterotopia in a female patient.

Adult↗
PubMed1997

[Magnetic resonance features in cerebral primary lymphomas in non-immunocompromised subjects].

In the past few years, non-Hodgkin's lymphomas have been paid increasing attention to because of their recently increasing frequency. We reviewed the MR images of 17 patients with histologically proved primary CNS lymphoma, all of them immunocompetent at diagnosis. We studied the site, number and shape of the lesions, the presence and grade of edema and possible periventricular spread. The exams were performed with 0.5 T and 1.5 T MR units, using SE sequences on the sagittal, axial and coronal planes, before and after Gd-DTPA administration. The most typical neuroradiologic signs which may suggest the diagnosis of CNS lymphoma are deep or periventricular lesion site, diffuse and marked contrast enhancement, poorly defined borders, moderate edema surrounding the mass and a tendency to periventricular spread. MRI demonstrated 35 lesions in 17 patients. The lymphoma was unifocal in 9 cases (53%) and 7 lesions were localized in subtentorial site. Lesion size did not exceed 2 cm in 49% of cases, ranged 2-4 cm in 40% and exceeded 4 cm in 11% of cases only. These lesions and hypo- to isointense on T1-weighted images (97%) and their signal intensity varies on T2-weighted images, with mainly iso-/hypointense patterns (79%). All lesions enhanced after Gd-DTPA administration, 74% of them markedly and 26% moderately; enhancement was mostly homogeneous (80% of cases). Perilesional edema was observed in 74% of cases. In conclusion, MRI yields some useful information for the diagnosis of primary CNS lymphoma, but the clinical and radiologic signs of this lesion may exhibit aspecific signal features, meaning that no correct diagnosis can be made even in immuno-competent patients.

Adult↗
PubMed1996

MRI appearances consistent with haemorrhagic infarction as an early manifestation of carbon monoxide poisoning.

High signal in the globus pallidus on T1-weighted images was observed in two patients who underwent early MRI, after exposure to carbon monoxide (CO). We compare these MRI abnormalities with those previously reported, and with CT findings which suggested that the damage to the globi pallidi is of vascular origin. We discuss also the hypothesis that haemorrhagic infarction is an early manifestation of CO poisoning.

Adult↗
PubMed1996

Phase II study of recombinant human granulocyte colony-stimulating factor in children undergoing bone marrow transplantation.

Twenty-three children with congenital or acquired hematological disorders and 8 children with solid tumors received filgrastim at a dose of 5 micrograms/Kg by a daily 2-hour infusion following allogeneic (18 cases) or autologous (13 cases) bone marrow transplantation (group I). The results were compared with those of a disease, age and type of transplant matched cohort of 31 children treated in the same institution who did not receive the growth factor (group II). Filgrastim treatment was started within 24 hours of completion of the marrow infusion and lasted for 21 consecutive days or until the absolute neutrophil count reached 10 x 10(9)/l for 3 consecutive days. Twelve variables were evaluated prospectively in Group I and retrospectively in Group II. Myeloid reconstitution with peripheral granulocyte counts > 0.5 x 10(9)/L was achieved at a median time of 13 days in group I and of 14 days in group II (p = ns). Platelet recovery to > 50 x 10(9)/L was slower in group I (43 vs 30 days: p < .05). Median time to last platelet and red blood cell infusion was higher in group I (33 vs 18 days for platelets, p < .05; 45 vs 25 for red blood cells, p < .005). Filgrastim-treated children undergoing autologous BMT had fewer days of fever (6 vs 10 days, p < .05). There was no significant toxicity ascribable to filgrastim. Clinically and microbiologically documented infections, days of antibiotic therapy, duration of total parenteral nutrition and median time in hospital were similar in both groups. We conclude that in children undergoing autologous BMT for malignancies, filgrastim significantly reduced the number of febrile days. Similar benefits were not observed in children undergoing allogeneic BMT. Children receiving filgrastim experienced a delay in erythrocyte and platelet recovery. A prospective randomized study is required to better define the cost-benefit of filgrastim in children undergoing autologous or allogeneic BMT.

Adolescent↗
PubMed1995

Venous angiomas: plain and contrast-enhanced MRI and MR angiography.

We studied 17 patients with venous angiomas, 4 of whom had associated cavernous angiomas. All underwent MRI with spin-echo T1- and T2-weighted images and T1-weighted images after Gd-DTPA; MR angiography (MRA) was also performed with 3D and 2D time-of-flight technique; 5 patients underwent conventional angiography. Contrast-enhanced MRI demonstrated all the lesions, showing the peripheral medullary veins, the collector and the type of drainage. Both 3D and 2D MRA provided diagnostic information identical to that obtained after infusion of Gd-DTPA. Contrast-enhanced were T1-weighted images and MRA superior in all the cases to images without gadolinium. The possible association with cavernous angiomas (24% in our study) indicates T2-weighted imaging.

Adolescent↗
PubMed1994

Optical spectrum of myeloperoxidase. Origin of the red shift.

The optical spectrum of reduced myeloperoxidase (EC 1.11.1.7) displays an unusual red shift of the Soret band which is at 472 nm and the alpha-band which is at 636 nm. The spectral properties of myeloperoxidase can be modified by means of acid treatment. Upon short exposure to acid (pH 1.7) the red-shifted optical absorption spectrum of the reduced enzyme (lambda max at 472 nm) was blue-shifted (lambda max at 448 nm) but the spectrum of the reduced state could be restored by increasing the pH. By contrast, the resonance Raman spectra of both the oxidized and reduced enzyme are essentially the same at both pH 1.7 and pH 7.0. This shows that the optical spectrum and the resonance Raman spectrum are not directly correlated, which we interpret to indicate that the reversible effects of lower pH primarily affect the excited-state energy levels of the macrocycle. The EPR spectrum of the oxidized enzyme showed a reversible conversion from a high-spin rhombic spectrum (gx = 6.7, gy = 5.2) at neutral pH into a more axial high-spin spectrum (gx = gy = 5.8) at low pH. Upon prolonged exposure to acid (20 min) optical absorbance spectra, EPR spectra, resonance Raman spectra and the chlorinating activity were irreversibly affected. We propose that a negatively charged protonatable residue in the proximity of a pyrrole nucleus of the haem group is present that imposes the red shift in the optical absorption spectrum. This is consistent with the available X-ray structure data.

Electron Spin Resonance Spectroscopy↗
PubMed1994

Do carbohydrates play a role in the lignin peroxidase cycle? Redox catalysis in the endergonic region of the driving force.

The redox cycle of lignin peroxidase (LiP) is discussed in terms of the Marcus theory of electron transfer. The difference in kinetic behaviour of the two redox couples LiP-Compound I/LiP-Compound II (LiPI/LiPII), respectively LiPII/LiP, in the oxidation of veratryl alcohol is attributed to an estimated increase in reorganization energy of about 0.5 eV for the conversion of LiPII to native enzyme compared to the reduction of LiPI to LiPII. Whereas LiPI/LiPII involves a transition from a low-spin oxyferryl prophyrin radical cation to a low-spin oxyferryl porphyrin system, the conversion of LiPII to native enzyme involves a change in spin-state to high-spin ferric, accompanied by a conformational change of the protein. In addition, a molecule of water is formed after protonation of the oxyferryl porphyrin system by the distal His-47 and Arg-43. Furthermore, the reduction of LiPI to LiPII is observed as an irreversible process. Since the oxidation of veratryl alcohol by oxidized LiP will occur in the endergonic region of the driving force, it is postulated that the thermodynamic unfavourable formation of veratryl alcohol radical cation is facilitated by reaction of a nucleophile with the incipient radical cation. It is further postulated that the ordered carbohydrate residues found near the entrance to the active site channel in the LiP crystal structure play a role in this process.

Aspartic Acid↗
PubMed1994

Resonance Raman microspectroscopic characterization of eosinophil peroxidase in human eosinophilic granulocytes.

A resonance Raman microspectroscopic study is presented of eosinophil peroxidase (EPO) in human eosinophilic granulocytes. Experiments were carried out at the single cell level with laser excitation in Soret-, Qv-, and charge transfer absorption bands of the active site heme of the enzyme. The Raman signal obtained from the cells was almost exclusively due to EPO. Methods were developed to determine depolarization ratios and excitation profiles of Raman bands of EPO in situ. A number of Raman band assignments based on earlier experiments with isolated EPO have been revised. The results show that in agreement with literature on isolated eosinophil peroxidase, the prosthetic group of the enzyme in the (unactivated) cells is a high spin, 6-coordinated, ferric protoporphyrin IX. The core size of the heme is about 2.04 A. The proximal and distal axial ligands are most likely a histidine with the strong imidazolate character typical for peroxidases, and a weakly bound water molecule, respectively. The data furthermore indicate that the central iron is displaced from the plane of the heme ring. The unusual low wavenumber Raman spectrum of EPO, strongly resembling that of lactoperoxidase, intestinal peroxidase and myeloperoxidase, suggests that these mammalian peroxidases are closely related, and characterized by, as yet unspecified, interactions between the peripheral substituents and the protein, different from those found in other protoheme proteins.

Binding Sites↗
PubMed1994

Ophthalmoplegic migraine-like syndrome due to pituitary apoplexy.

A patient with a history of migraine without aura developed a complete left III nerve palsy a day after the onset of bilateral throbbing headache associated with vegetative symptoms. Magnetic resonance imaging showed a hemorrhagic pituitary adenoma as the probable cause of the symptoms, presumably by a compressive mechanism. This case suggests a further possible cause of ophthalmoplegia associated with migraine and confirms the clinical utility of magnetic resonance imaging in the differential diagnosis of ophthalmoplegic migraine and other conditions in which the symptomatology is secondary to intracranial lesions.

Adult↗