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Biomedical subjects

R Floris

Publications and source records attributed to R Floris.

At least 19 recordsLinked to original sources
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↗
PubMed1994

T stages of tumors of the tongue and floor of the mouth: correlation between MR with gadopentetate dimeglumine and pathologic data.

PURPOSE: To define MR accuracy in the evaluation of the T stages of tumors of the tongue and floor of the mouth. METHODS: Fifty-two patients affected by squamous cell carcinoma were studied with a superconductive system at 1.5 T. The study was performed with spin-echo T1- and T2-weighted images before contrast and short spin-echo T1-weighted and gradient-echo sequences after gadopentetate dimeglumine administration. The results obtained with MR were compared with pathologic data. RESULTS: Good correlation of T stages (TNM system) was obtained in 45 of 52 cases. MR did not show four superficial lesions. In one case, infiltration of the cortical bone of the mandible was not demonstrated (MR, T2; pathologic, T4), and in another the lesion was classified as T2 instead of T3, as it was pathologically. One lesion was classified as T4 on MR because of infiltration of the alveolar ridge but was classified as T2 at surgery. In 46 patients who underwent surgery, the accuracy of MR was excellent for predicting the relationship of tumor to midline and oral floor musculature. The results obtained with gadopentetate dimeglumine were better than those obtained in noncontrast studies in 32 (62%) of 53 cases. CONCLUSION: MR showed high accuracy in the study of tumors of the tongue and floor of the mouth.

Adolescent↗
PubMed1994

[Magnetic resonance imaging in denervated muscle. A preliminary study].

Ten patients with various forms of peripheral neuropathy and spinal radiculopathy were examined with MRI using a low-field permanent magnet (0.2 T) and spin echo (SE)/inversion recovery (IR) sequences, with an adequate inversion time to suppress healthy muscle signal. In acute denervation MR sensitivity was low on both sequences; in subacute denervation the damaged muscle was more intense than the healthy muscle only on IR sequences. MRI adequately depicted fatty infiltration in chronic denervation. In conclusion, MRI is a promising tool for mapping and noninvasively monitoring denervated motor units in skeletal muscles, whose role is currently complementary to that of electromyography.

Acute Disease↗
PubMed1994

[An introduction to fast and ultrafast sequences in magnetic resonance].

The main limitations of magnetic resonance imaging (MRI) are due to the long acquisition time needed for data sampling. Fast and ultrafast sequences, thanks to progress in hardware and software technology, allow the acquisition times to be dramatically reduced. Such improvements will definitely increase MR capabilities and make MRI a fast and dynamic technique no longer depending on patients' cooperation and limited by patients' conditions--e.g., trauma, pediatric, or claustrophobic patients--or even by the anatomic features of the region of interest. The latest experimental studies are aimed at increasing the clinical applications and the perspectives of clinical MRI and at such ambitious goals as MR-fluoroscopy, interventional MRI, total body examination in less than one minute and functional MRI. In this paper the technical principles and the main indications of this new kind of sequences are reported, with a special emphasis on Gradient-Echo (GE), Turbo Spin-Echo (turbo SE) or Fast Spin-Echo (fast SE), Turbo FLASH and Echo Planar (EP) sequence. A smaller flip angle (FA) and the substitution of the 180 degrees RF pulse with a gradient reversal are the main differences of GE from SE sequences. From GE sequences, several fast sequences are derived, such as angiographic and turbo FLASH sequences. The latter, thanks to 180 degrees preinversion RF pulse, using idoneous inversion times (IT), provide flexible contrast. Turbo SE sequences, which are directly derived from conventional SE sequence, allow the acquisition time to be markedly shortened, by acquiring several Fourier lines of K-space for each TR. The repetition of several 180 degrees pulses following the excitatory 90 degrees RF pulse does the trick through the creation of multiple echoes for a single TR. EP sequences are the fastest ones currently available: with them, an image can be acquired in 30-100 ms. However, the limited availability of the relative hardware and the need of both quality implementation and the definition of clinical indications are major obstacles to the widespread use of these sequences. The SE T2-weighted sequence, the main responsible for the long examination time, will be replaced soon. Further implementation of these sequences will make MRI a fast, flexible and adaptable method to any exam and patient disability.

Echo-Planar Imaging↗
PubMed1993

Interaction of myeloperoxidase with peroxynitrite. A comparison with lactoperoxidase, horseradish peroxidase and catalase.

Polymorphonuclear neutrophils generate both nitric oxide and superoxide and these molecules can combine to form peroxynitrite. Neutrophils also contain myeloperoxidase which reacts with peroxynitrous acid (HOONO). On mixing myeloperoxidase with HOONO compound II was formed. Compound I could not be detected as an intermediate. The apparent second-order rate constant of formation of compound II was strongly pH-dependent (2.5 x 10(5) M-1 x s-1 at pH 8.9 and 6.2 x 10(6) M-1 x s-1 at pH 7.2). The pKa of this effect is 6.9 and it was concluded that the enzyme reacts with the protonated form of the peroxide, that is peroxynitrous acid, with a pH-independent second-order rate constant of 2.0 x 10(7) M-1 x s-1 at 12 degrees C. The interaction of HOONO with lactoperoxidase was studied for comparison. As was observed for myeloperoxidase, compound I could not be detected as an intermediate. The apparent second-order rate constant of compound II formation is pH-dependent and is 3.3 x 10(5) M-1 x s-1 at pH 7.4 and 8.4 x 10(4) M-1 x s-1 at pH 9.0. In contrast, horseradish peroxidase reacts with HOONO to form compound I, which is subsequently followed by the formation of compound II. The second-order rate constant for the formation of compound I is 3.2 x 10(6) M-1 x s-1 and is pH-dependent, the pKa for this effect is 6.8. Catalase (up to 3 microM) does not affect the rate of decomposition of peroxynitrite and no compound I formation is observed. Since nitrite may be present in the peroxynitrite preparation and to discriminate between the reaction of the enzyme with nitrite or peroxynitrite, the effect of nitrite on myeloperoxidase was studied. The dissociation constant for the myeloperoxidase-nitrite complex is pH-dependent and has values of 580 microM at pH 6.0 and 55 mM at pH 8.5.

Catalase↗
PubMed1993

Lignin peroxidase L3 from Phlebia radiata. Pre-steady-state and steady-state studies with veratryl alcohol and a non-phenolic lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol.

The catalytic cycle of lignin peroxidase (LiP, ligninase) isozyme L3 from the white-rot fungus Phlebia radiata was investigated using stopped-flow techniques. Veratryl (3,4-dimethoxybenzyl) alcohol and a lignin model compound, non-phenolic beta-O-4 dimer 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol, were used as electron donors. This is the first report on the detailed kinetic analysis of a LiP-catalysed C alpha-C beta bond cleavage of the dimer, representing the major depolymerisation reaction in the lignin polymer. The native enzyme showed a typical heme peroxidase absorbance spectrum with a Soret maximum at 407 nm. Following the reaction with H2O2, the Soret band decreased in absorbance, shifted to 403 nm and then to 421 nm, demonstrating the formation of compound I followed by the formation of compound II, respectively. Similar results have been reported for the LiP from Phanerochaete chrysosporium upon reaction with H2O2. However, compound I of L3 was more stable in the absence of additional electron donors. The second-order rate constant of compound I formation by H2O2 was determined to be 6 x 10(5) M-1 s-1 and was the same at pH 3.0 and 6.0. Compound I was rapidly reduced to compound II and further to native enzyme when either veratryl alcohol or the beta-O-4 dimer was supplied as electron donor and in both cases veratraldehyde appeared as the major product. At pH 6.0, the second-order rate constant for compound II formation was similar with either veratryl alcohol or the beta-O-4 dimer (6.7 x 10(3) and 6.5 x 10(3) M-1 s-1, respectively). At pH 3.0 formation of compound II with either reductant proceeded so rapidly that determination of the respective rate constants was not possible. The results point to identical catalytic cycles of L3 with veratryl alcohol or the beta-O-4 dimer involving both compounds I and II as intermediates and participation of the same veratryl alcohol radical as the most appropriate reductant for compound II. Chemical evidence of such a radical, formed after the initial LiP-catalysed one-electron oxidation of beta-O-4 dimeric lignin models, is presented in a separate article [Lundell, T., Schoemaker, H., Hatakka, A. & Brunow, G. (1993) Holzforschung, in the press]. The catalytic redox-cycle and the oxidation mechanism presented here reconcile seemingly contradictory results obtained in previous studies on LiP kinetics during the last decade.

Benzyl Alcohols↗
PubMed1993

The role of early postoperative CT scan following surgery for herniated lumbar disc.

40 patients underwent lumbosacral microdiscectomy in a 12 months period covering the years 1988-1989 in our center. For the purpose of the present study, we considered the 30 cases who underwent CT control of the operated interspaces and of the adjacent vertebral endplates. This was routinely carried out on the 3rd post-operative day. The present study failed to show correlations between early post-operative CT data and subsequent clinical results in this unselected series of patients. In fact an image suggesting persistent disc herniation was as a rule observed in spite of satisfactory clinical results, and other CT findings that have been considered of clinical significance, such as intraspinal air and low attenuation of disc space, were commonly observed in patients with an uncomplicated post-operative course. The present study suggests that early post-operative CT appears to be of no value in the management of potential early complications of low-back surgery. The introduction of MRI appears to offer other possibilities in the evaluation and management of failed back surgery syndrome (FBSS).

Adult↗
PubMed1993

Serial determinations of leukocyte aggregation in patients with ischemic stroke.

The pattern of leukocyte aggregation and its possible relationship with the clinical outcome were evaluated in 35 untreated patients with acute cerebrovascular disease during each of the first three days of hospitalization. Although statistically significant differences were found when comparing patients and age and sex matched controls during any of the 3 days, a large overlapping of values was noted in each comparison. The overlapping was strongly reduced when the average 3-day value was compared. Similarly, when comparing subgroups of patients classified on the basis of their clinical status, the overlap of values observed during any of the 3 days dropped from 70% to 30% when considering the average 3-day levels of leukocyte aggregation. Furthermore, the level of correlation between leukocyte aggregation and size of cerebral infarction was better when considering the average 3-day value (p = .005) than the best single-day correlation (p = .01). These data suggest that the association between acute cerebrovascular ischemia and leukocyte rheology is better discovered when repeated evaluation of the latter are performed.

Age Factors↗
PubMed1992

Reaction of myeloperoxidase with its product HOCl.

The reaction of human myeloperoxidase with its product, hypochlorous acid was investigated using both rapid-scan spectrophotometry and the stopped-flow technique. In the reaction of myeloperoxidase with hypochlorous acid a primary compound is found with properties similar to that of compound I and which is converted into compound II. The primary reaction is strongly pH-dependent. At pH 7.2 the reaction is too fast to be measured but at higher pH values it is possible to determine the apparent second-order rate constant. Its value decreases to about 2 x 10(7) M-1.s-1 at pH 8.3 and to 2.3 (+/- 0.4) x 10(6) M-1.s-1 at pH 9.2, respectively. The dissociation constant for the formation of the primary compound is 25.7 (+/- 15.3) microM at pH 9.2 and about 2.5 microM at pH 8.3. The apparent second-order rate constant for the formation of compound II is hardly affected by pH and varies between 2 to 5 x 10(4) M-1.s-1 at pH 10.2 and pH 8.3, respectively. Reaction of myeloperoxidase with hypochlorous acid also resulted in irreversible partial bleaching of the chromophore. Chloride, which is a substrate of the enzyme not only protects myeloperoxidase against bleaching by hypochlorous acid but also competitively inhibits the binding of hypochlorous acid to myeloperoxidase, a process which also has been observed in the reaction with hydrogen peroxide. It is concluded that hypochlorous acid binds at the heme iron to form compound I.

Humans↗
PubMed1992

Catalytic mechanisms and regulation of lignin peroxidase.

Lignin peroxidase (LiP) is a fungal haemoprotein similar to the lignin-synthesizing plant peroxidases, but it has a higher oxidation potential and oxidizes dimethoxylated aromatic compounds to radical cations. It catalyses the degradation of lignin models but in vitro the outcome is net lignin polymerization. LiP oxidizes veratryl alcohol to radical cations which are proposed to act by charge transfer to mediate in the oxidation of lignin. Phenolic compounds are, however, preferentially oxidized, but transiently inactivate the enzyme. Analysis of the catalytic cycle of LiP shows that in the presence of veratryl alcohol the steady-state turnover intermediate is Compound II. We propose that veratryl alcohol is oxidized by the enzyme intermediate Compound I to a radical cation which now participates in charge-transfer reactions with either veratryl alcohol or another reductant, when present. Reduction of Compound II to native state may involve a radical product of veratryl alcohol or radical product of charge transfer. Phenoxy radicals, by contrast, cannot engage in charge-transfer reactions and reaction of Compound II with H2O2 ensues to form the peroxidatically inactive intermediate, Compound III. Regulation of LiP activity by phenolic compounds suggests feedback control, since many of the products of lignin degradation are phenolic. Such control would lower the concentration of phenolics relative to oxygen and favour degradative ring-opening reactions.

Benzyl Alcohols↗