Search PubMed⌕ Search

Biomedical subjects

M Fisher

Publications and source records attributed to M Fisher.

At least 109 records · Page 6Linked to original sources
PubMed2000

The X-ray structure of Brassica napus beta-keto acyl carrier protein reductase and its implications for substrate binding and catalysis.

BACKGROUND: beta-Keto acyl carrier protein reductase (BKR) catalyzes the pyridine-nucleotide-dependent reduction of a 3-oxoacyl form of acyl carrier protein (ACP), the first reductive step in de novo fatty acid biosynthesis and a reaction often performed in polyketide biosynthesis. The Brassica napus BKR enzyme is NADPH-dependent and forms part of a dissociable type II fatty acid synthetase (FAS). Significant sequence similarity is observed with enoyl acyl carrier protein reductase (ENR), the other reductase of FAS, and the short-chain alcohol dehydrogenase (SDR) family. RESULTS: The first crystal structure of BKR has been determined at 2.3 A resolution in a binary complex with an NADP(+) cofactor. The structure reveals a homotetramer in which each subunit has a classical dinucleotide-binding fold. A triad of Ser154, Tyr167 and Lys171 residues is found at the active site, characteristic of the SDR family. Overall BKR has a very similar structure to ENR with good superimposition of catalytically important groups. Modelling of the substrate into the active site of BKR indicates the need for conformational changes in the enzyme. CONCLUSIONS: A catalytic mechanism can be proposed involving the conserved triad. Helix alpha6 must shift its position to permit substrate binding to BKR and might act as a flexible lid on the active site. The similarities in fold, mechanism and substrate binding between BKR, which catalyzes a carbon-oxygen double-bond reduction, and ENR, the carbon-carbon double-bond oxidoreductase in FAS, suggest a close evolutionary link during the development of the fatty acid biosynthetic pathway.

3-Oxoacyl-(Acyl-Carrier-Protein) Reductase↗
PubMed2000

Characterization of ricin heterogeneity by electrospray mass spectrometry, capillary electrophoresis, and resonant mirror.

Electrospray mass spectrometry (ES/MS), capillary-zone electrophoresis (CZE), capillary isoelectric focusing (CIEF), and multianalyte resonant mirror are used to evaluate the heterogeneity of samples of ricin toxins extracted from five horticultural varieties of Ricinus communis seeds: R. communis zanzibariensis, carmencita, impala, sanguineus, and gibsonii. The investigation is also extended to the geographical provenance of the beans. Combining mass spectrometry, CE techniques, and resonant mirror results in a powerful analytical tool capable to characterize and differentiate between different varieties of ricin toxins. Each technique complements the others, adding another level of information. This study reveals a large extent of heterogeneity for each cultivar, demonstrating that ricin toxins consist of a series of glycosylated proteins most likely originating from a multigene family. By combining these techniques, it is possible to differentiate between zanzibariensis and the other four varieties, and that variations in the functional characteristics may be observed between the different cultivars. This study demonstrates that knowledge of the variety of R. communis beans used and their geographical provenance is essential before any type of investigation of ricin toxins is carried out. Consequently, any unusual behavior observed can only be attributed to that particular cultivar studied and not automatically extended to include all R. communis varieties.

Biosensing Techniques↗
PubMed2000

Temporal evolution of ischemic injury evaluated with diffusion-, perfusion-, and T2-weighted MRI.

OBJECTIVE: Ischemic lesions seen on diffusion-weighted imaging (DWI) are reversible if reperfusion is performed within minutes after the onset of ischemia. This study was designed to determine whether acute reversibility of DWI abnormalities is transient following brief temporary focal brain ischemia and to characterize the temporal evolution of in vivo ischemic lesions. METHODS: Eight rats were subjected to 30 minutes of temporary middle cerebral artery occlusion and underwent diffusion-, perfusion-, and T2-weighted MRI during occlusion; immediately after reperfusion; 30, 60, and 90 minutes after reperfusion; and 12, 24, 48, and 72 hours after reperfusion. Average apparent diffusion coefficient (ADCav) values and the cerebral blood flow index (CBFi) ratio were calculated in both the lateral caudoputamen and overlying cortex at each time point. The size of the in vivo ischemic abnormalities was calculated from the ADCav and the T2 maps. Postmortem triphenyltetrazolium chloride (TTC) staining was used to verify ischemic injury. RESULTS: Both the CBFi ratio and ADCav values declined significantly in the two regions during occlusion. The CBFi ratio recovered immediately after reperfusion and remained unchanged over 72 hours. However, ADCav values returned to normal at 60 to 90 minutes and secondarily decreased at 12 hours after reperfusion as compared with those in the contralateral hemisphere. The extent of the in vivo ischemic lesions maximized at 48 hours and was highly correlated with TTC-derived lesion size. CONCLUSIONS: Acute recovery of initial ADCav-defined lesions after reperfusion is transient, and secondary ADCav-defined lesions develop in a slow and delayed fashion.

Animals↗
PubMed2000

Hypophosphatemia secondary to oral refeeding in anorexia nervosa.

OBJECTIVE: Hypophosphatemia is a well-known complication of the refeeding syndrome in severe cases of anorexia nervosa, described mostly as a result of refeeding with total parenteral nutrition. Few cases have been reported secondary to either nasogastric or oral refeeding. METHOD: The authors present three cases in which hypophosphatemia developed secondary to oral refeeding in severe anorexia nervosa. RESULTS: All 3 patients developed significant hypophosphatemia, to a low of 0.9 mg/dl in two cases and a low of 1. 7 mg/dl in the third. The first patient received close to 3,000 calories per day, along with intravenous fluids, in the hospital; the other 2 patients ate large amounts for several days at home. Caloric restriction and replenishment with phosphorous resulted in a rapid return of phosphorous values to normal levels. DISCUSSION: Those who treat severely malnourished patients with eating disorders, whether as inpatients or outpatients, need to be vigilant for the development of the refeeding syndrome, even in patients receiving oral refeeding alone.

Adolescent↗
PubMed2000

Multispectral analysis of the temporal evolution of cerebral ischemia in the rat brain.

A major difficulty in staging and predicting ischemic brain injury by magnetic resonance (MR) imaging is the time-varying nature of the MR parameters within the ischemic lesion. A new multispectral (MS) approach is described to characterize cerebral ischemia in a time-independent fashion. MS analysis of five MR parameters (mean diffusivity, diffusion anisotropy, T2, proton density, and perfusion) was employed to characterize the progression of ischemic lesion in the rat brain following 60 minutes of transient focal ischemia. k-Means (KM) and fuzzy c-means (FCM) classification methods were employed to define the acute and subacute ischemic lesion. KM produced an estimate of lesion volume that was highly correlated with postmortem infarct volume, independent of the age of the lesion. Overall classification rates for KM exceeded FCM at acute and subacute time points as follows: KM, 90.5%, 94.4%, and 95. 9%; FCM, 82.4%, 90.6%, and 82.6% (for 45 minutes, 180 minutes, and 24-120 hours post MCAO groups). MS analysis also offers a formal method of combining diffusion and perfusion parameters to provide an estimate of the ischemic penumbra (KM classification rate = 70.3%). J. Magn. Reson. Imaging 2000;12:842-858.

Acute Disease↗
PubMed2000

Broad-spectrum cation channel inhibition by LOE 908 MS reduces infarct volume in vivo and postmortem in focal cerebral ischemia in the rat.

Cation channels conduct calcium, sodium, and potassium, cations that are likely deleterious in the evolution of focal ischemic injury. Diffusion-weighted magnetic resonance imaging (DWI) is a powerful tool for evaluation of acute cerebral ischemia. We studied the effects of a novel, broad-spectrum inhibitor of several cation channels, LOE 908 MS, on acute ischemic lesion development with DWI and on cerebral infarct size using 2,3,5-triphenyltetrazolium chloride (TTC) staining postmortem. Eighteen male Sprague-Dawley rats underwent middle cerebral artery occlusion (MCAO) and were randomly and blindly assigned to either LOE 908 MS (1 mg/kg bolus 30 min after MCAO and continuous i.v. infusion of 10 mg/kg for 4 h thereafter) or vehicle. Whole-brain DWI was done before initiation of treatment and repeated every 30 min for the next 3.5 h. The animals were reperfused in the magnetic resonance imaging (MRI) scanner 90 min after MCAO. At 24 h, the animals were killed, and the brains were cut into six 2-mm-thick slices and stained with 2% TTC. Percent hemispheric lesion volume (%HLV) was calculated for each animal. Physiological parameters, body weight, and premature mortality (3 in the placebo group and 1 in the treated group) did not differ between the groups. No hypotension, abnormal behavior, or other adverse effects were seen. Pretreatment, the DWI-derived %HLV did not differ between the groups (19.8 +/- 6.2 in the control group and 17.9 +/- 7.9 in the treated group), whereas at 4 h after MCAO, it was significantly smaller in the treated group (21.8 +/- 15.4 vs 40.4 +/- 15.5, p = 0.03). Postmortem, TTC-derived %HLV was significantly attenuated in the LOE 908 MS group (21.3 +/- 11.9 vs 50.1 +/- 10.7, p = 0.0001) and the neurological scores at 24 h were significantly better among the treated rats (2.1 +/- 1.5 vs 4.0 +/- 1.0, p < 0.02). LOE 908 MS significantly improved neurological outcome and reduced infarct size without observable effects in rats as demonstrated in vivo by DWI and confirmed postmortem by TTC staining. Blocking several distinct cation channels by LOE 908 MS showed significant neuroprotection.

Acetamides↗
PubMed2000

A glycine site antagonist ZD9379 reduces number of spreading depressions and infarct size in rats with permanent middle cerebral artery occlusion.

Spreading depressions (SDs) occur in experimental focal ischemia and contribute to lesion evolution. N-methyl-D-aspartate (NMDA) antagonists inhibit SDs and reduce infarct size. The glycine site on the NMDA receptor complex offers a therapeutic target for acute focal ischemia, potentially devoid of many side effects associated with competitive and non-competitive NMDA antagonists. We evaluated the effect of the glycine antagonist, ZD9379, on SDs and brain infarction. Male Sprague-Dawley rats (n = 18) weighing 290 to 340 g undergoing permanent middle cerebral artery occlusion (MCAO) were randomly and blindly assigned to receive drug or placebo: Group 1 (pre-MCAO treatment group, n = 5) a 5 mg/kg bolus of ZD9379 over 5 minutes followed by 5 mg/kg/hour drug infusion for 4 hours beginning 30 minutes before MCAO; Group 2 (post-MCAO treatment group, n = 7) a 5 mg/kg bolus of ZD9379 30 minutes after MCAO followed by 5 mg/kg/hour drug infusion for 4 hours; and Group 3 (control group, n = 6) vehicle for 5 hours beginning 30 minutes before MCAO. SDs were monitored electrophysiologically for 4.5 hours following MCAO by continuous recording of cortical direct current (DC) potentials and electrocorticogram (ECoG). Infarct volume was measured 24 hours after MCAO by 2,3,5 triphenyltetrazolium chloride (TTC) staining. Corrected infarct volume was 90 +/- 72 mm3 (mean +/- standard deviation) in Group 1, 105 +/- 46 mm3 in Group 2, and 226 +/- 41 mm3 in Group 3 (P < .001). The corresponding numbers of SDs in the 3 groups were 8.2 +/- 5.8, 8.1 +/- 2.5, and 16.0 +/- 5.1, respectively (P < .01). When all animals (n = 18) were analyzed, infarct volumes and the number of SDs were significantly correlated (r = .68, P = .002). This study demonstrated that ZD9379 initiated before or after MCAO significantly reduced the number of SDs and infarct volume in a permanent focal ischemia model, implying that ZD9379 is neuroprotective and its neuroprotective effect may be related to inhibiting ischemia-related SDs.

Animals↗
PubMed2000

Patients with acute stroke: recent developments in neuroimaging.

The authors discuss recent developments in neuroimaging and their role in the evaluation of patients with acute stroke from diagnostic, therapeutic, and prognostic points of view. New techniques permit a more detailed evaluation of the pathophysiology of stroke and therefore may lead to better management. This improvement is due to the increased sensitivity of the diagnostic tests in the acute phase of stroke to detect ischemic lesions and the ability to estimate tissue perfusion to determine vascular status.

Cerebrovascular Circulation↗
PubMed2000

The reliability of measuring nursing clinical performance using a competency based assessment tool: a pilot study.

The clinical performance of the novice nurse has been identified as problematic in the areas of medication administration, time management, and comfort and safety. In order to assess new graduate nurses' clinical competence in these areas, a forty four (44) item assessment tool was developed which was drawn from the Australian Nursing Council Inc. (ANCI) (1991) competency statements. A correlation descriptive design was used to determine the inter-rater reliability between assessors using this competency based tool. A pilot study utilising a convenience sample of 30 new graduate nurses were each assessed by two observers for a mean period of 127.5 minutes. Kappa coefficients were calculated to determine the level of agreement between the two observers. Very little rating agreement was found for individual items, however, there was no significant difference in the total competency scores between the two observers. The competency assessment tool has face validity and is internally consistent. However, inter-rater reliability for individual competency items was found to be poor.

Attitude of Health Personnel↗
PubMed2000

Depression is common and precludes accurate assessment of functional status in elderly patients with congestive heart failure.

BACKGROUND: Congestive heart failure (CHF) and depression are independently known to result in physical decline and diminished functional capacity in the general population. The prevalence and relationship of depressive symptoms in CHF to physical limitations has not been objectively examined. METHODS AND RESULTS: The Center for Epidemiological Studies Depression Scale (CES-D) was used to ascertain depressive symptoms in 33 elderly ambulatory individuals with CHF. Self-report assessment of functional status, cardiopulmonary exercise testing (CPX), and measurement of energy expenditure by doubly labeled water and Caltrac Accelerometer (Muscle Dynamics, Torrance, CA) were performed. Depressed and nondepressed groups were compared. Forty-two percent of the patients scored in the depressed range (CES-D score of 16 or greater). There were no differences in demographic variables or severity of illness between the depressed and nondepressed patients. Energy expenditure was comparable across groups. Although obtaining similar maximal heart rate and maximal oxygen consumption (VO2max) on CPX, the depressed group showed less exertion on exercise testing with a significantly lower respiratory quotient (P = .017). CONCLUSION: Depressive symptoms were common and unrelated to the severity of CHF. Although depressed individuals tended to report worse physical functioning than nondepressed individuals, objective assessment of energy expenditure was comparable. Depressed patients appear to underestimate their functional ability. Subsequently, inaccurate assessment of functional status may occur.

Activities of Daily Living↗
PubMed2000

Characteristics of patients referred for cardiac transplantation: implications for the donor organ shortage.

BACKGROUND: When the decision is made to proceed with cardiac transplantation, the risk/benefit ratio for continued medical therapy in that particular patient must be weighed against the risk/benefit ratio associated with cardiac transplantation. This can only be accomplished while the patient is on maximal medical therapy. METHODS: To better define the appropriateness of patients being referred for consideration of transplant, we examined the records of 100 consecutive adult patients referred to a cardiac transplant program. RESULTS: Two of five patients referred for transplantation had at least one contraindication for transplantation. Twenty percent of the patients were not treated with angiotensin-converting enzyme inhibitors and did not have any documented reason for undertreatment. Of those deemed too well for cardiac transplantation, 84% were alive and either class I or II (mean follow-up 21 months). CONCLUSIONS: We found the majority to be undertreated or with an absolute contraindication to transplantation. Of those deemed too well for transplantation after appropriate treatment, 84% were alive and well.

Adolescent↗
PubMed2000

Crystallization of the NADP-dependent beta-keto acyl-carrier protein reductase from Brassica napus.

The NADP-dependent beta-keto acyl-carrier protein reductase (BKR) from Brassica napus has been crystallized by the hanging-drop vapour-diffusion method using polyethylene glycol of average molecular weight 1500 as the precipitant. The crystals belong to the hexagonal space group P6(4)22, with unit-cell parameters a = b = 129. 9, c = 93.1 A, alpha = beta = 90, gamma = 120 degrees. Calculated values for V(m), the use of rotation and translation functions and consideration of the packing suggest that the asymmetric unit contains a monomer. The crystals diffract to beyond 2.8 A resolution and are more amenable to X-ray diffraction analysis than those reported previously for the Escherichia coli enzyme. The structure determination of B. napus BKR will provide important insights into the catalytic mechanism of the enzyme and into the evolution of the fatty-acid elongation cycle by comparisons with the other oxidoreductase of the pathway, enoyl acyl-carrier protein reductase (ENR).

3-Oxoacyl-(Acyl-Carrier-Protein) Reductase↗
PubMed2000

Attenuated nontoxinogenic and nonencapsulated recombinant Bacillus anthracis spore vaccines protect against anthrax.

Several highly attenuated spore-forming nontoxinogenic and nonencapsulated Bacillus anthracis vaccines differing in levels of expression of recombinant protective antigen (rPA) were constructed. Biochemical analyses (including electrospray mass spectroscopy and N terminus amino acid sequencing) as well as biological and immunological tests demonstrated that the rPA retains the characteristics of native PA. A single immunization of guinea pigs with 5 x 10(7) spores of one of these recombinant strains, MASC-10, expressing high levels of rPA (>/=100 microgram/ml) from a constitutive heterologous promoter induced high titers of neutralizing anti-PA antibodies. This immune response was long lasting (at least 12 months) and provided protection against a lethal challenge of virulent (Vollum) anthrax spores. The recombinant B. anthracis spore vaccine appears to be more efficacious than the vegetative cell vaccine. Furthermore, while results clearly suggest a direct correlation between the level of expression of PA and the potency of the vaccine, they also suggest that some B. anthracis spore-associated antigen(s) may contribute in a significant manner to protective immunity.

Animals↗
PubMed2000

Screening for CMV retinitis using chromatic discrimination thresholds and achromatic contrast sensitivity.

BACKGROUND: Many patients with cytomegalovirus retinitis (CMVR) are unaware of visual disturbance so screening is advocated for patients with HIV and low CD4 counts. Many tests of retinal function have been recommended but few are effective at detecting CMVR. We assess the potential of chromatic discrimination thresholds and achromatic contrast sensitivity as screening tests for patients with CMVR. METHOD: 11 HIV+ patients with CMVR, 16 age matched HIV+ patients, and 29 age matched controls were recruited. Visual acuity, chromatic discrimination thresholds, and achromatic contrast sensitivity were measured. Fundal examination was performed by slit lamp biomicroscopy for HIV+ patients. Those with CMVR were photographed and the CMVR graded from the photographs. RESULTS: Loss of chromatic discrimination was found in patients with CMVR (tritan p<0.0005, red/green p<0.05). The same group had deterioration in achromatic contrast sensitivity at 2.2, 3.4, and 10 cpd (p<0.05). There was correlation between the zone of CMVR with chromatic gratings (tritan r=0.83, p<0.005). No statistically significant difference was found between the HIV+ patients and the controls for all tests (p>0.1). CONCLUSIONS: HIV+ patients with CMVR have a loss of chromatic discrimination and achromatic contrast sensitivity and this may be used to screen HIV+ patients for CMVR.

AIDS-Related Opportunistic Infections↗
PubMed2000

Inapparent hemodynamic insufficiency exacerbates ischemic damage in a rat microembolic stroke model.

BACKGROUND AND PURPOSE: Patients with severe carotid artery stenosis may have more severe ischemic damage after embolic stroke than patients without this abnormality. Unilateral proximal carotid occlusion (UCO) alone typically does not induce infarction in normotensive rats. The aim of this study was to investigate whether UCO increases infarct size after microembolic, experimental stroke. METHODS: Microembolic infarction was induced in 2 groups of Sprague-Dawley rats by injecting 2000 microspheres (50-micrometer diameter) intracranially from the external carotid artery. The common carotid artery (CCA) was either ligated just after the injection (CCA occlusion group, n=8) or left intact (CCA open group, n=8). In the control group (n=4), vehicle without microspheres was injected and the CCA was ligated. Twenty-four hours later, the brains were removed and infarct volumes measured. Perfusion-weighted imaging was used to evaluate the cerebral circulation before and after CCA occlusion with and without microsphere injection in a separate group of animals (n=16). RESULTS: All animals in the microemboli groups survived and had only a slight hemiparesis 24 hours after occlusion. No neurological deficits were observed in the control group. Infarct volumes were 145+/-57 mm(3) in the CCA occlusion group and 45+/-26 mm(3) in the CCA open group (P <0.01). There were no infarctions detected in the control group. Perfusion-weighted imaging showed that cerebral blood flow decreased after the CCA occlusion in both experiments with and without the microsphere injection. CONCLUSIONS: UCO alone does not induce ischemic damage, but it worsens ischemic lesion size after multiple microemboli. This is probably due to the slight cerebral perfusion insufficiency caused by UCO. These results suggest that patients with cerebral hemodynamic insufficiency, such as those with severe carotid stenosis, may have increased ischemic damage after microembolic events.

Animals↗
PubMed2000

Transient and permanent resolution of ischemic lesions on diffusion-weighted imaging after brief periods of focal ischemia in rats : correlation with histopathology.

BACKGROUND AND PURPOSE: The early ischemic lesions demonstrated by diffusion-weighted imaging (DWI) are potentially reversible. The purposes of this study were to determine whether resolution of initial DWI lesions is transient or permanent after different brief periods of focal brain ischemia and to evaluate histological outcomes. METHODS: Sixteen rats were subjected to 10 minutes (n=7) or 30 minutes (n=7) of temporary middle cerebral artery occlusion or sham operation (n=2). DWI, perfusion-weighted imaging (PWI), and T(2)-weighted imaging (T(2)WI) were performed during occlusion; immediately after reperfusion; and at 0.5, 1.0, 1.5, 12, 24, 48, and 72 hours after reperfusion. After the last MRI study, the brains were fixed, sectioned, stained with hematoxylin and eosin, and evaluated for neuronal necrosis. RESULTS: No MRI or histological abnormalities were observed in the sham-operated rats. In both the 10-minute and 30-minute groups, the perfusion deficits and DWI hyperintensities that occurred during occlusion disappeared shortly after reperfusion. The DWI, PWI, and T(2)WI results remained normal thereafter in the 10-minute group, whereas secondary DWI hyperintensity and T(2)WI abnormalities developed at the 12-hour observation point in the 30-minute group. Histological examinations demonstrated neuronal necrosis in both groups, but the number of necrotic neurons was significantly higher in the 30-minute group (95+/-4%) than in the 10-minute group (17+/-10%, P<0.0001). CONCLUSIONS: Transient or permanent resolution of initial DWI lesions depends on the duration of ischemia. Transient resolution of DWI lesions is associated with widespread neuronal necrosis; moreover, permanent resolution of DWI lesions does not necessarily indicate complete salvage of brain tissue from ischemic injury.

Animals↗