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Biomedical subjects

M Newman

Publications and source records attributed to M Newman.

At least 19 recordsLinked to original sources
PubMed1992

X-ray analyses of peptide-inhibitor complexes define the structural basis of specificity for human and mouse renins.

X-ray analyses have defined the three-dimensional structures of crystals of mouse and human renins complexed with peptide inhibitors at resolutions of 1.9 and 2.8 A, respectively. The exquisite specificity of renin arises partly from ordered loop regions at the periphery of the binding cleft. Although the pattern of main-chain hydrogen bonding in other aspartic proteinase inhibitor complexes is conserved in renins, differences in the positions of secondary structure elements (particularly helices) also lead to improved specificity in renins for angiotensinogen substrates.

Amino Acid Sequence↗
PubMed1992

Effect of clomipramine and lithium on fenfluramine-induced hormone release in major depression.

Prolactin (PRL) and cortisol responses to oral administration of d-1 fenfluramine hydrochloride (60 mg) and placebo were examined in patients with endogenous major depressive disorder on three separate occasions: prior to treatment with clomipramine (CMI), after 4 weeks of CMI administration (175-250) mg/day), and 3 weeks after addition of lithium (Li) carbonate (serum level 0.5-0.9 mmol) to the treatment regimen. CMI significantly increased baseline PRL levels which were further elevated following Li supplementation. PRL response to fenfluramine (minus elevated baseline PRL levels) but not to placebo, was significantly increased by CMI administration, reflected over the 6-hr time course examined and in peak minus baseline values. Following addition of Li, the degree of enhancement was diminished although the peak minus baseline value remained significant relative to the pretreatment response. Cortisol levels were not increased by fenfluramine and were not altered by CMI or CMI + Li administration. The effect of CMI extends previous observations regarding the action of antidepressant treatment on serotenergically mediated hormone release. Methodological considerations relevant to the effect of CMI + Li are discussed.

Adult↗
PubMed1992

Multidisciplinary cycles for protein engineering: site-directed mutagenesis and X-ray structural studies of aspartic proteinases.

The specificity and pH profile of aspartic proteinases have evolved to include not only pepsin with a broad specificity and an optimal activity in acid media, but also renin, with high specificity for angiotensinogen and activity close to neutral pH. Comparisons of the structures and catalytic activities of aspartic proteinases provide helpful clues for engineering new activity profiles. We illustrate an approach that involves recombinant DNA techniques, biochemistry, structure determination and biocomputing. We use the 3-D structures of inhibitor complexes of several aspartic proteinases to define likely intermediates and specificity sub-sites. The multidisciplinary research is organised as cycles, in which each cycle tests a design hypothesis proposed in the previous cycle. We use one member of the aspartic proteinase family, chymosin, to illustrate these ideas in engineering enzymes with altered pH optima and specificities.

Amino Acid Sequence↗
PubMed1992

The effect of temperature on cerebral metabolism and blood flow in adults during cardiopulmonary bypass.

The effect of temperature on cerebral blood flow and metabolism was studied in 41 adult patients scheduled for operations requiring cardiopulmonary bypass. Plasma levels of midazolam and fentanyl were kept constant by a pharmacokinetic model-driven infusion system. Cerebral blood flow was measured by xenon 133 clearance (initial slope index) methods. Cerebral blood flow determinations were made at 27 degrees C (hypothermia) and 37 degrees C (normothermia) at constant cardiopulmonary bypass pump flows of 2 L/min/m2. Blood gas management was conducted to maintain arterial carbon dioxide tension (not corrected for temperature) 35 to 40 mm Hg and arterial oxygen tension of 150 to 250 mm Hg. Blood gas samples were taken from the radial artery and the jugular bulb. With decreased temperature there was a significant (p less than 0.0001) decrease in the arterial venous-oxygen content difference, suggesting brain flow in excess of metabolic need. For each patient, the cerebral metabolic rate of oxygen consumption at 37 degrees C and 27 degrees C was calculated from the two measured points at normothermia and hypothermia with the use of a linear relationship between the logarithm of cerebral metabolic rate of oxygen consumption and temperature. The temperature coefficient was then computed as the ratio of cerebral metabolic rate of oxygen consumption at 37 degrees C to that at 27 degrees C. The median temperature coefficient for man on nonpulsatile cardiopulmonary bypass is 2.8. Thus reducing the temperature from 37 degrees to 27 degrees C reduces cerebral metabolic rate of oxygen consumption by 64%.

Aged↗
PubMed1991

X-ray analyses of aspartic proteinases. IV. Structure and refinement at 2.2 A resolution of bovine chymosin.

The structure of calf chymosin (EC 3.4.23.3), the aspartic proteinase from the gastric mucosa, was solved using the technique of molecular replacement. We describe the use of different search models based on distantly related fungal aspartic proteinases and investigate the effect of using only structurally conserved regions. The structure has been refined to a crystallographic R-factor of 17% at 2.2 A resolution with an estimated co-ordinate error of 0.21 A. In all, 136 water molecules have been located of which eight are internal. The structure of chymosin resembles that of pepsin and other aspartic proteinases. However, there is a considerable rearrangement of the active-site "flap" and, in particular, Tyr75 (pepsin numbering), which forms part of the specificity pockets S1 and S1'. This is probably a consequence of crystal packing. Electrostatic interactions on the edge of the substrate binding cleft appear to account for the restricted proteolysis of the natural substrate kappa-casein by chymosin. The local environment of invariant residues is examined, showing that structural constraints and side-chain hydrogen bonding can play an important role in the conservation of particular amino acids.

Amino Acid Sequence↗
PubMed1991

Adverse effects of low-pressure reperfusion after hypothermic cardioplegia in normal and hypertrophic hearts.

The aim of this study was to determine the effect of low-pressure and high-pressure reperfusion, with and without ventricular fibrillation, on the recovery of hypertrophic and normal hearts after hypothermic cardioplegia. Fourteen hearts rendered hypertrophic by valvular aortic stenosis and 18 normal canine hearts were subjected to 1 hour of cardioplegic arrest at 28 degrees C during cardiopulmonary bypass. Each heart was then reperfused at a coronary pressure of either 40 mm Hg (low) or 80 mm Hg (high), initially in the empty beating state and then during ventricular fibrillation. Low-pressure reperfusion produced left ventricular subendocardial ischemia in hypertrophic and in normal hearts, shown by marked depression of subendocardial blood flow, myocardial pH, and myocardial oxygen consumption. In hypertrophic hearts the ischemia was more severe and resulted in a persistent depression of left ventricular function and myocardial oxygen consumption even when coronary pressure was returned to normal levels. High-pressure reperfusion was associated with rapid and complete recovery of myocardial metabolism and function in hypertrophic and in normal hearts. During low-pressure reperfusion, ventricular fibrillation exacerbated ischemia in hypertrophic and in normal hearts. During high-pressure reperfusion, a short period of ventricular fibrillation produced no adverse effects either in hypertrophic or in normal hearts. We conclude that low-pressure reperfusion produces subendocardial ischemia in normal and in hypertrophic hearts even in the empty beating state; in hypertrophic hearts it also impairs recovery of myocardial metabolism and function. The adverse effects of low-pressure reperfusion are exacerbated by ventricular fibrillation.

Animals↗
PubMed1991

Nurse case management. The coming together of theory and practice.

Newman proves that theory can be a practical approach to nursing care delivery by applying a theory to the new nursing role of the case manager. The illustration applies Newman's theory of health and nursing and looks at its implications for various aspects of provider interface.

Continuity of Patient Care↗
PubMed1991

Absence of particle-induced coronary vasoconstriction during cardioplegic infusion: is it desirable to use a microfilter in the infusion line?

Many cardiac surgical units now use a microfilter in the infusion line for delivery of crystalloid cardioplegic solution to protect against the potential hazards of particulate contamination of cardioplegic solution. The aim of this group of studies was to determine the effects of particulate contamination of cardioplegic solutions, in order to establish whether a microfilter is needed in the infusion line. Total particle counts performed on two commercial cardioplegic solutions were low, but there were sufficient particles greater than 10 microns in diameter to cause coronary vasoconstriction. In isolated rat hearts a 20-minute infusion of St. Thomas' Hospital cardioplegic solution produced a progressive reduction in coronary flow, which was not prevented by the inclusion of a 0.8 micron filter in the infusion line. Two studies were performed on canine hearts to determine the effects of unfiltered cardioplegic solution on coronary vascular resistance. In the first, cardioplegic solution at 20 degrees C was infused for 20 minutes at a constant pressure of 50 mm Hg and flow rate was measured. In the second, the same solution at 4 degrees C was infused at a constant flow rate for 2 1/2 minutes and the infusion pressure was measured. In neither study did coronary vascular resistance rise. A final clinical study involving patients undergoing coronary bypass surgery compared the effects on coronary resistance of infusion at a constant flow of filtered versus unfiltered cardioplegic solution (n = 10 in each group). There was a similar rise in coronary perfusion pressure in both groups during the infusion. We conclude that there is insufficient evidence of particle-induced coronary vasoconstriction to justify the expense of a microfilter in the cardioplegic infusion line.

Animals↗
PubMed1990

Engineering enzyme subsite specificity: preparation, kinetic characterization, and X-ray analysis at 2.0-A resolution of Val111Phe site-mutated calf chymosin.

Comparison of the three-dimensional structure of bovine chymosin with the structures of homologous aspartic proteinases complexed with peptide inhibitors shows that Val111 in chymosin occupies a position between the specificity subsites S1 and S3. A mutation corresponding to Val111 to Phe has been introduced in an intermediary plasmid construct of prochymosin by bridging its unique restriction sites by a synthetic mutant oligonucleotide duplex. A prochymosin fusion product was expressed in Escherichia coli in such a way that the extension and substitution of the propart does not interfere with the activation of the zymogen. After activation of the crude prochymosin, the enzyme was purified by affinity chromatography on Sepharose with V-dL-P-F-F-V-dL as ligand. This procedure provided large amounts of pure protein as judged by FPLC, the activity/protein ratio, and SDS-PAGE. The enzymatic properties were determined by using a variety of peptide substrates and inhibitors; KM values for the mutant enzyme were approximately twice those of the wild type, but the kcat values were little changed. The mutant enzyme was crystallized, X-ray data were collected to 2.0-A resolution by using a FAST area detector, and the structure was solved by using difference Fourier methods and refined to an R factor of 19.5%. The mutation leads to only local changes in conformation, with the phenylalanine side chain occupying part of the S1 and S3 pockets. This accounts for the increased KM of this mutant for a substrate with a large phenylalanine side chain at P1. It is also consistent with the higher affinity of the mutant for an inhibitor with small side chains at P1 and P3 when compared with the wild-type enzyme.

Amino Acid Sequence↗
PubMed1990

Inhibition by antibiotic tetracyclines of rat cortical noradrenergic adenylate cyclase and amphetamine-induced hyperactivity.

Two antibiotic tetracyclines, demeclocycline (DMC) and minocycline, share several biochemical and behavioral properties with lithium (Li). DMC inhibited both noradrenaline- and chloradenosine-sensitive cyclic AMP accumulation in rat cerebral cortical slices both in vitro and ex vivo following two weeks of chronic dietary treatment. Minocycline, a lipophilic tetracycline, produced similar results in vitro. Both DMC and minocycline reduced open-field activity levels in rats following acute treatment, four hours prior to testing. Moreover, both drugs inhibited amphetamine-induced hyperactivity in the open field. Chronic treatment with 0.4% and 0.8% dietary DMC for two weeks attenuated amphetamine hyperactivity without affecting baseline activity levels in the open field. Neither DMC nor minocycline attenuated apomorphine-induced stereotypy at doses that attenuated amphetamine hyperactivity, a profile which is similar to that of lithium. Unlike lithium, however, DMC did not reverse reserpine-induced hypoactivity.

2-Chloroadenosine↗
PubMed1990

Anorexia and bulimia.

Anorexia nervosa and bulimia nervosa are eating disorders with distinct clinical presentations. Reduced caloric intake, a hallmark of both disorders, is manifested by self-induced starvation in anorexia and by binge eating and gastrointestinal purging in bulimia. Treatment includes nutritional intervention, psychotherapy and pharmacotherapy in either the ambulatory or the hospital setting.

Adolescent↗
PubMed1990

Diabetic patients have abnormal cerebral autoregulation during cardiopulmonary bypass.

We tested the hypothesis that insulin-dependent diabetic patients with coronary artery bypass graft surgery experience altered coupling of cerebral blood flow and oxygen consumption. In a study of 23 patients (11 diabetics and 12 age-matched controls), cerebral blood flow was measured using 133Xe clearance during nonpulsatile, alpha-stat blood gas managed cardiopulmonary bypass at the conditions of hypothermia and normothermia. In diabetic patients, the cerebral blood flow at 26.6 +/- 2.42 degrees C was 25.3 +/- 14.34 ml/100 g/min and at 36.9 +/- 0.58 degrees C it was 27.3 +/- 7.40 ml/100 g/min (p = NS). The control patients increased cerebral blood flow from 20.7 +/- 6.78 ml/100 g/min at 28.4 +/- 2.81 degrees C to 37.6 +/- 8.81 ml/100 g/min at 36.5 +/- 0.45 degrees C (p less than or equal to 0.005). The oxygen consumption was calculated from jugular bulb effluent and increased from hypothermic values of 0.52 +/- 0.20 ml/100 g/min in diabetics to 1.26 +/- 0.28 ml/100 g/min (p = 0.001) at normothermia and rose from 0.60 +/- 0.27 to 1.49 +/- 0.35 ml/100 g/min (p = 0.0005) in the controls. Thus, despite temperature-mediated changes in oxygen consumption, diabetic patients did not increase cerebral blood flow as metabolism increased. Arteriovenous oxygen saturation gradients and oxygen extraction across the brain were calculated from arterial and jugular bulb blood samples. The increase in arteriovenous oxygen difference between temperature conditions in diabetic patients and controls was significantly different (p = 0.01). These data reveal that diabetic patients lose cerebral autoregulation during cardiopulmonary bypass and compensate for an imbalance in adequate oxygen delivery by increasing oxygen extraction.

Brain↗
PubMed1989

Chromosome assignment of the murine Hox-4.1 gene.

The murine homebox gene 4.1 was assigned to chromosome 2 by Southern analysis of somatic cell hybrids and by in situ hybridization. This assignment and the report of Featherstone et al. (M. S. Featherstone, A. Baron, S. J. Gaunt, M. G. Mattei, and D. Duboule, 1988, Proc. Natl. Acad. Sci. USA, 85, 4760-4764) indicate that a fourth group of homeobox genes is located on chromosome 2 in the mouse (in addition to the homeobox gene clusters on chromosomes 6, 11, and 15).

Animals↗
PubMed1989

A comparison of heat exchangers for blood cardioplegia.

During open heart surgery, myocardial protection provided by oxygenated blood-based cardioplegia is superior to that provided by non-oxygenated crystalloid cardioplegia. However, the widespread use of blood cardioplegia has been limited by the cost and complexity of the associated cooling and delivery systems. The performance of a simple system--a polyethylene coil immersed in ice--has been compared with three systems incorporating specialized, water-jacketed heat exchangers: Buckberg Shiley, Shiley BCD and Bentley HE-100. Blood was diluted to a haematocrit of 22% and delivered to each cooling system at flow rates of 200-500 mL/min and temperatures of 25 degrees C and 30 degrees C. Cooling water at 0-1 degree C was supplied to the heat exchangers at flow rates of 2, 4, and 6 L/min. Performance was measured by comparing the blood outflow temperatures at the same inflow temperature under a variety of test conditions which simulated those occurring in clinical practice. All cooling systems, except the Buckberg Shiley, were able consistently to cool blood cardioplegia adequately (below 10 degrees C), but the ice coil was the most effective. The heat exchanger systems are 3-4 times more expensive than the ice coil and require an external source of cold water. Thus the ice coil system has the advantages of simplicity, efficiency, and economy.

Heart Arrest, Induced↗