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Biomedical subjects

R Green

Publications and source records attributed to R Green.

At least 235 records · Page 13Linked to original sources
PubMed1993

Inhibition of sickling after reduction of intracellular hemoglobin concentration with an osmotic pulse: characterization of the density and hemoglobin concentration distributions.

Hemoglobin S polymerization is markedly dependent on intracellular hemoglobin concentration. In the studies presented here, sickle RBC were subjected to a transient osmotic stress, which induced a short period of increased membrane permeability and allowed partial efflux of Hb S. Morphological sickling of the resulting hypochromic RBC was inhibited. The response of RBC to this osmotic pulse is influenced by the presence of a polyanion, which in these experiments was either inositol hexaphosphate (IHP, 27 mM or 46 mM) or pyrophosphate (69 mM or 95 mM). The decrease in MCHC, measured manually, ranged from 3.1 +/- 1.7 (1 SD) to 6.3 +/- 2.8 g/dl, depending on the conditions used during modification. Parallel electronic analysis of RBC indices demonstrated a comparable decrease in MCHC which was due to both an increased MCV and a decreased MCH. Since the modified cell population is quite heterogeneous, cells were analyzed using discontinuous stractan gradients and/or a laser-based instrument which measures the hemoglobin concentration (HC) of individual cells. For most treatment conditions, the modified cells have a bimodal HC distribution with one peak centered at about 20 g/dL and the other peak corresponding to the unmodified cells. With the higher concentration of IHP, however, many cells had an intermediate HC. For modified RBC with a bimodal HC distribution (27 mM IHP, 69 mM PP, 95 mM PP), inhibition of morphological sickling was proportional to the change in HC and there were no subpopulations with an increased tendency to undergo sickling. However, the intermediate density cells present when RBCs were treated with the higher concentration of IHP underwent sickling at a higher oxygen partial pressure than control cells.

Anemia, Sickle Cell↗
PubMed1992

Selection of a ribozyme that functions as a superior template in a self-copying reaction.

The sunY ribozyme is derived from a self-splicing RNA group I intron. This ribozyme was chosen as a starting point for the design of a self-replicating RNA because of its small size. As a means of facilitating the self-replication process, the size of this ribozyme was decreased by the deletion of nonconserved structural domains; however, when such deletions were made, there were severe losses of enzymatic activity. In vitro genetic selection was used to identify mutations that reactivate a virtually inactive sunY deletion mutant. A selected mutant with five substitution mutations scattered throughout the primary sequence showed greater catalytic activity than the original ribozyme under the selection conditions. The sunY ribozyme and its small selected variant can both catalyze template-directed oligonucleotide assembly. The small size and reduced secondary structure of the selected variant results in an enhancement, relative to that of the original ribozyme, of its rate of self-copying. This engineered ribozyme is able to function effectively both as a catalyst and as a template in self-copying reactions.

Bacteriophage T4↗
PubMed1992

Crystallization and preliminary crystallographic data of a Streptomyces scabies extracellular esterase.

X-ray quality single crystals of an extracellular esterase from pathogenic Streptomyces scabies were obtained by the hanging drop method. The crystals are monoclinic (space group C2, a = 161.1 A, b = 51.2 A, c = 124.2 A, beta = 100.6 degrees) with two molecules related by a noncrystallographic dyad in the asymmetric unit, with a solvent content of approximately 64%. The diffraction pattern from fresh crystals extends beyond 2 A resolution using sealed tube CuK alpha radiation. The study has been initiated in order to elucidate the mechanism of this unusual non-serine-dependent esterase, and to gain better understanding of the molecular basis of the pathogenesis of the scab disease.

Crystallization↗
PubMed1992

Expression, purification and crystallization of the Vibrio harveyi acyltransferase.

We have obtained X-ray quality single crystals of Vibrio harveyi acyltransferase. The protein was obtained from V. harveyi by a gene mobilization expression system. The crystals are monoclinic (space group P2(1), a = 89.9 A, b = 83.6 A, c = 47.1 A, beta = 97.3 degrees) with two molecules related by a pronounced non-crystallographic dyad in the asymmetric unit, with a solvent content of approximately 50%. The diffraction pattern from fresh crystals extends beyond 2 A resolution using sealed tube CuK alpha radiation. The elucidation of the three-dimensional structure of this enzyme, believed to contain a proteinase-like catalytic triad, which resembles in many ways other eukaryotic fatty acid chain terminating enzymes, may have important consequences for our understanding of the molecular basis of the final stages of the synthesis of fatty acids.

Acyltransferases↗
PubMed1992

Glial cells as a model for the role of cobalamin in the nervous system: impaired synthesis of cobalamin coenzymes in cultured human astrocytes following short-term cobalamin-deprivation.

The conversion of cyanocobalamin to adenosyl- and methylcobalamin is impaired in cobalamin-deficient cultured human glial cells. In contrast cultured human skin fibroblasts retained their ability to synthesize coenzyme forms when grown in cobalamin-deficient medium. Cells were pre-conditioned by growing in cobalamin-deficient media for six weeks and then subcultured in medium containing either free or transcobalamin II-bound 57Co-cyanocobalamin. Although both coenzyme levels were low in cobalamin-deficient glial cells, the decrease in methylcobalamin was more marked than that of adenosylcobalamin. Methionine synthase and Cb1 reductase activities were markedly decreased in cobalamin-deficient glial cells but were unchanged in fibroblasts cultured in cobalamin-deficient medium. Our data suggest that in glial cells, cobalamin coenzyme synthesis and function is exquisitely sensitive to short-term cobalamin deprivation. Glial cells apparently synthesize and secrete transcobalamin II since antibodies directed against the transport protein inhibit the uptake of free cobalamin.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1992

Sickle cells modified by an osmotic pulse in the presence of inositol hexaphosphate have decreased intracellular hemoglobin concentration and decreased in vitro sickling without prolonged in vivo survival.

An osmotic pulse was used to modify red blood cells (RBC) from two patients with sickle cell disease, resulting in an increased volume and decreased hemoglobin content. This treatment yielded cells which were divided into two populations, one in which RBC had markedly decreased hemoglobin concentration and another in which the cells appeared to be unmodified. Morphological sickling at low oxygen partial pressure was markedly decreased. However, there was no evidence for increased RBC lifespan when the 51Cr-labeled, modified cells were reinfused.

Anemia, Sickle Cell↗
PubMed1992

Cerebral blood flow and metabolism in hypothermic circulatory arrest.

Although hypothermic circulatory arrest has been accepted for use in cardiovascular operations, the potential for cerebral injury exists. The mechanism of the cerebral injury remains unclear. To address these questions we studied cerebral blood flow and metabolism. Sixteen puppies were randomly assigned to undergo either 45 or 90 minutes of hypothermic circulatory arrest after perfusion/surface cooling to 13 degrees C. Cerebral blood flow, cerebral oxygen and glucose metabolism, and cerebral vascular resistance measurements were obtained at 37 degrees C, 13 degrees C, 10 minutes after reperfusion, 30 degrees C and 2 and 4 hours after hypothermic circulatory arrest. No neurologic or behavioral changes were observed in any of the long-term survivors (11/16). Metabolic and cerebral blood flow data did not differ between groups. Cerebral blood flow was significantly lower in the late postarrest measurements, whereas oxygen and glucose consumption had returned to baseline values. In the presence of low cerebral blood flow and high cerebral vascular resistance it is notable that control levels of oxygen consumption were attained by abnormally high oxygen extraction. These data strongly suggest a vulnerable interval after hypothermic circulatory arrest in which cerebral metabolism is limited by cerebral blood flow.

Animals↗
PubMed1992

Episcleral plaque thermoradiotherapy in patients with choroidal melanoma.

From 1988 to 1991, 21 patients with uveal melanoma were treated in a Phase I study with episcleral plaque radiotherapy (EPRT). This irradiation was combined with localized current field episcleral hyperthermia (LCFHT). Tumor stage was: T3 = 15 (71%) and T2 = 6 (29%). Follow-up ranged from 2 to 42 months (mean 9.2 months). EPRT was given using custom built I-125 gold plaques. Radiation doses to the tumor apex ranged from 13 to 123 Gy (mean dose 70.0 Gy) given at a mean dose rate of 55 cGy/hr. LCFHT was given with 500 KHz frequency for 45 min immediately before EPRT. The temperature was controlled on the scleral surface using four thermocouples. T mean ranged from 42.5 degrees C to 45 degrees C +/- 0.5 degrees C (mean 43.4 degrees C). The study patients showed rapid tumor necrosis. A 25% mean decrease of apical tumor dimension was noted, p = 0.0007. At least ambulatory vision (greater than 5/200) was maintained by 17/21 (81%) patients. Visual acuity was seen to improve greater than 6 months post-plaque therapy in 10 (48%) study patients. This was following an intermediate decrease in visual acuity. Severe complications, including large hemorrhagic retinal detachment and large vitreous hemorrhage, were seen in two (9.5%) of the early study patients. A mean scleral temperature reduction to less than or equal to 44 degrees C +/- 0.5 degrees C resulted in good treatment tolerance and a lack of serious complications in subsequently treated patients. A Phase II prospective randomized trial comparing LCFHT with 60 versus 80 Gy EPRT dose to the tumor apex is currently being activated for patients with choroidal melanoma.

Adolescent↗
PubMed1992

The use of risk-adjusted complication rates to compare hospitals performing coronary artery bypass surgery or angioplasty.

A hospital's quality of care is generally assessed by a review of individual records. This study used unadjusted and risk-adjusted complication rates to measure the quality of care for hospitals that perform coronary artery bypass surgery or angioplasty. Hospitals differed greatly in their complication rates. Only a small percentage of this difference was due to differences in the risks that patients faced.

Aged↗
PubMed1992

Acute stroke outcome: effects of stroke type and risk factors.

We studied 925 consecutive patients hospitalised with acute stroke to determine how stroke type, age, gender and risk factors influence acute, in-hospital outcome. Stroke types included carotid territory cortical or large subcortical infarction (52%), vertebrobasilar infarction (12%), lacunar infarction (11%), intracerebral haemorrhage (16%), and subarachnoid haemorrhage (9%). Mean age (mean +/- 1 SD) was 66 +/- 15 years, but patients with cerebral infarction were older than those with cerebral haemorrhage. The prevalence of hypertension, diabetes mellitus and cardiac disease increased with age across all stroke types, while the prevalence of smoking decreased with age. Mortality was 19% overall, but varied significantly between stroke types, highest in intracerebral haemorrhage (34%), and lowest in lacunar infarction (1%). Age had a marked adverse effect on mortality, independent of stroke type, the probability of death increasing by 3 +/- 0.5% per year from 20-92 years, whereas gender had no effect. Cardiac disease and diabetes were independent adverse prognostic factors (Odds Ratios 1.6 and 1.5 respectively). Cerebral haemorrhage, age, cardiac disease and diabetes all independently worsen acute stroke outcome.

Acute Disease↗
PubMed1992

Assessing providers of coronary revascularization: a method for peer review organizations.

OBJECTIVES: Current methods to evaluate quality of care are usually limited to reviews of individual cases or comparisons of hospital mortality rates. We present an alternative method that compares complication rates adjusted for patient characteristics. METHODS: Detailed clinical data that were specifically designed for quality comparisons of providers of revascularization procedures were abstracted from the medical records of 1998 Medicare patients, in 16 hospitals, who had coronary artery bypass surgery and 2091 patients, in 16 hospitals, who had angioplasty. Providers were ranked on the basis of an unadjusted risk, a risk adjusted for detailed clinical information, and a risk adjusted only for patient comorbidities. RESULTS: Complication rates differed significantly and substantially among the hospitals. Clinical adjustment changed the hospital rankings for the bypass surgery hospitals, but not for the angioplasty hospitals. Adjustment for comorbidities did not affect hospital rankings for either procedure. CONCLUSIONS: When sample sizes are limited, adverse outcome rates may be a more sensitive measure of quality of care than mortality rates. Rates that are unadjusted or adjusted only for comorbidities may be inadequate for evaluating some providers of bypass surgery.

Aged↗