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Biomedical subjects

A Fisher

Publications and source records attributed to A Fisher.

At least 145 records · Page 8Linked to original sources
PubMed1993

R2 C-terminal peptide inhibition of mammalian and yeast ribonucleotide reductase.

Eucaryotic ribonucleotide reductases (RR) catalyze the reduction of ribonucleoside diphosphates to 2'-deoxyribonucleoside diphosphates. Each has an R1(2)R2(2) quaternary structure with each subunit playing a critical role in catalysis. Separation of the subunits results in loss of activity. Previous studies have demonstrated that peptides corresponding to the C-terminus of R2 disrupt subunit association by competion with R2 and have potential usefulness as therapeutics. Extensive structure-function studies have been carried out on peptide inhibition of herpes simplex RR in an effort to develop antiviral agents based on the observation that the herpes simplex R2 C-terminus, YAGAVVNDL, is quite different from the corresponding mammalian sequence. In this work we report a detailed structure-function analysis of peptide inhibition of mammalian and, to a more limited extent, Saccharomyces cerevisiae RRs. Our results for mammalian RR support the following conclusions with regard to the effect of substitution on inhibitory potency: (a) the N-acetylated R2 C-terminal heptapeptide N-AcPhe384Thr385Leu386Asp387Ala388Asp389Phe390 (N-AcF7TLDADF1) is the minimal core peptide length required; deletion of the N-terminus or of middle positions (resulting in penta- and hexapeptides) results in large losses in inhibitory potency; (b) a free carboxylate is required on the C-terminal Phe; (c) Phe is strongly preferred to Leu in positions 1 and 7 and a bulky aliphatic group is preferred in position 5; (d) neither negative charge in positions 2 or 4 nor a polar side chain in position 6 are required for peptide binding, contrary to what evolutionary patterns in the R2 C-terminus of RR would suggest. S. cerevisiae RR displays a similar length dependence on the corresponding N-acetylated R2 C-terminal heptapeptide, N-AcFTFNEDF. This peptide has a 4-fold higher inhibitory potency toward S. cerevisiae RR than toward mammalian RR. Such selectivity raises the possibility that peptide analogs related to R2 C-termini can be developed as therapeutic agents even against organisms having R2 C-terminal sequences similar to that of mammalian RR.

Acetylation↗
PubMed1993

Cloning, sequence determination, and regulation of the ribonucleotide reductase subunits from Plasmodium falciparum: a target for antimalarial therapy.

Malaria remains a leading cause of morbidity and mortality worldwide, accounting for more than one million deaths annually. We have focused on the reduction of ribonucleotides to 2'-deoxyribonucleotides, catalyzed by ribonucleotide reductase, which represents the rate-determining step in DNA replication as a target for antimalarial agents. We report the full-length DNA sequence corresponding to the large (PfR1) and small (PfR2) subunits of Plasmodium falciparum ribonucleotide reductase. The small subunit (PfR2) contains the major catalytic motif consisting of a tyrosyl radical and a dinuclear Fe site. Whereas PfR2 shares 59% amino acid identity with human R2, a striking sequence divergence between human R2 and PfR2 at the C terminus may provide a selective target for inhibition of the malarial enzyme. A synthetic oligopeptide corresponding to the C-terminal 7 residues of PfR2 inhibits mammalian ribonucleotide reductase at concentrations approximately 10-fold higher than that predicted to inhibit malarial R2. The gene encoding the large subunit (PfR1) contains a single intron. The cysteines thought to be involved in the reduction mechanism are conserved. In contrast to mammalian ribonucleotide reductase, the genes for PfR1 and PfR2 are located on the same chromosome and the accumulation of mRNAs for the two subunits follow different temporal patterns during the cell cycle.

Amino Acid Sequence↗
PubMed1993

Selective signaling via unique M1 muscarinic agonists.

Rigid analogs of acetylcholine (ACh) were designed for selective actions at muscarinic receptor (mAChR) subtypes and distinct second messenger systems. AF102B, AF150, and AF151 are such rigid analogs of ACh. AF102B, AF150 and AF151 are centrally active M1 agonists. AF102B has a unique agonistic profile showing, inter alia: only part of the M1 electrophysiology of ACh and unusual binding parameters to mAChRs. AF150 and AF151 are more efficacious agonists than AF102B for M1 AChRS in rat cortex and in CHO cells stably transfected with the m1 AChR subtype. Notably, the selectivity of the new m1 agonists is reflected also by activation of select second messenger systems via distinct G-proteins. These compounds reflect a new pharmacological concept, tentatively defined as ligand-selective signaling. Thus, agonist/m1AChR complexes may activate different combinations of signaling pathways, depending on the ligand used. Rigid agonists may activate a limited repertoire of signaling systems. In various animal models for Alzheimer's disease (AD) the agonists AF102B, AF150 and AF151, exhibited positive effects on mnemomic processes and a wide safety margin. Such agonists, and especially AF102B, can be considered as a rational treatment strategy for AD.

Acetylcholine↗
PubMed1993

Effects of muscarinic receptor agonists and anticholinesterase drugs on high voltage spindles and slow waves.

The effects of muscarinic agonists (AF102B, pilocarpine, oxotremorine) and anticholinesterases (physostigmine, tetrahydroaminoacridine) were investigated on the incidence of thalamically generated rhythmic high voltage spindles and on scopolamine (0.2 mg/kg)-induced neocortical slow wave activity (i.e. increased sum amplitude value of the 1-20 Hz band in a quantitative electroencephalography (qEEG) analysis). AF102B and pilocarpine decreased high voltage spindles and scopolamine increased sum amplitude values at 3 and 9 mg/kg, but not at 1 mg/kg. Oxotremorine was less potent than AF102B or pilocarpine in suppressing high voltage spindles. Oxotremorine had no effect on the scopolamine-induced qEEG changes. Tetrahydroaminoacridine decreased high voltage spindles at 1, 3 and 9 mg/kg and slow waves at 9 mg/kg. Physostigmine decreased high voltage spindles and slow waves at 0.12 and 0.36 mg/kg. Based on the present results we propose that agonists possessing muscarinic M1 receptor activity are effective in decreasing high voltage spindles and scopolamine-induced slow wave activity, but agonists showing predominant muscarinic M2 receptor activity may be less effective in decreasing high voltage spindles and slow waves. Furthermore, tetrahydroaminoacridine decreased high voltage spindles at doses lower than those required to decrease scopolamine-induced slow waves. Physostigmine decreased high voltage spindles and slow waves over the same dose range. This result may indicate that non-cholinergic mechanisms are involved in the tetrahydroaminoacridine-induced decrease in high voltage spindles.

Alzheimer Disease↗
PubMed1993

Fundholding.

Explore the source record for details and available documents.

Capital Financing↗
PubMed1993

Comparative trial of clomiphene citrate/human menopausal gonadotropin and the contraceptive pill, followed by clomiphene citrate/human menopausal gonadotropin, in a gamete intrafallopian transfer program.

PURPOSE: It may sometimes be necessary to regulate cycles in assisted reproduction. Cycles can be regulated with gonadotropin releasing hormone (GnRHa) agonist but other methods can also be used. The aim of this study was to compare the pregnancy rate in a gamete intrafallopian transfer (GIFT) program in patients receiving a contraceptive pill/Clomid/human menopausal gonadotropin (hMG) regimen (study group), with the standard Clomid/hMG regime (control group). Fifty one patients in the study group were carefully matched for patient age, infertility diagnosis (female), semen parameters, number of follicles, and number of oocytes transferred into consideration with a control group. RESULTS: The overall pregnancy rate was 21.6% (11/51) in the study group and 47% (24/51) in the control group (P = 0.01). However, the ongoing pregnancy rate in the two groups did not differ significantly, 11.8% (6/51) vs 27.5% (14/51) (P = 0.08). In the study group, 7.8% of patients had to be seen over a weekend, compared to 13.7% in the control group (not significant). CONCLUSION: From the findings we conclude that, although this method of controlling cycles can be useful in selected patients, it is not the ultimate method.

Adult↗
PubMed1993

Does modern cardiac surgery require conventional intensive care?

We considered that, with modern perfusion equipment and mildly hypothermic cardiopulmonary bypass, protracted post-operative ventilation in an intensive care unit (ITU) is no longer required after most cardiac operations. We used a three-bedded cardiac recovery area (CRA) within the operating suite for 1,000 patients between January 1990 and June 1991. Forty-five patients with special needs were managed in the ITU. The time to extubation (T50%; range) for coronary bypass, aortic valve, mitral valve, and double-valve patients was 2.0 (0-42), 2.5 (0-12), 3.0 (0-15), and 3.0 (1-36) hours, respectively. Recovery beds were re-used allowing 5-6 operations daily. The difference in nursing staff complement for a CRA versus ITU bed was 4.5/7.8. Patient management was by nurse specialists supported by cardiac surgeons. Intervention by cardiac anaesthetists or intensivists was limited to specific ventilatory problems or renal failure. The early extubation policy failed in ten patients (five coronary, three aortic, one mitral and one double-valve patient) through poor pre-operative respiratory function, left ventricular failure or intra-operative events. The overall mortality in CRA was 1.4%. The mean duration of post-operative stay was 7 days (range 5-12). We conclude that a CRA staffed by nurse practitioners provides a safe and effective alternative to the anaesthetist-managed ITU. A rapid turnover of CRA beds removes the constraints of ITU bed availability.

Adolescent↗
PubMed1993

The effect of a cardiac surgical recovery area on the timing of extubation.

The anesthetic and postoperative management of cardiac surgical patients was modified to achieve an early return to spontaneous ventilation. A total of 278 patients were studied to determine the effect of this change. Patients in group I (n = 198) were managed in a cardiac surgical recovery area according to the new policy. Group II (n = 80) was a comparable group of patients operated upon before this change. The median duration of postoperative ventilation was reduced from 5 hours in group II to 1 hour in group I, and the time to extubation was reduced from 7 hours to 2 hours, respectively. There were no major postoperative complications resulting from this change. The factors that influence the duration of postoperative ventilation are discussed.

Adult↗
PubMed1993

Comparison of the promoter region of the human and porcine choline acetyltransferase genes: localization of an important enhancer region.

Genomic clones of human and porcine choline acetyltransferase were obtained by screening genomic libraries with synthetic oligonucleotides. The human and porcine genes exhibit significant conservation of both their intron/exon structure and the nucleotide sequence in their 5' flanking regions. However, the two genes differ in several respects, including the absence of a "TATA" box in the human gene and differences in the position of the methionine start codon. Analysis of the promoter region of the two genes has led to the localization of an enhancer element that appears necessary for efficient transcription of the gene.

Animals↗
PubMed1993

Activity and distribution of tissue transglutaminase in association with nerve-muscle synapses.

We have measured, characterized, and localized calcium-dependent protein cross-linking activity in rat skeletal muscle, and in myotubes cultured independently or in coculture with spinal neurones, catalyzed by the enzyme tissue transglutaminase (tTG). The enzyme activity was present in both motor endplate and endplate-free zones of rat diaphragm muscle. tTG in the endplate zone was more tightly associated with the tissue. This form of association was absent in extracts of peripheral nerve. Cross-linking of endogenous proteins, as measured by the content of epsilon-(gamma-glutamyl)lysine isopeptide, was higher in the endplate than in the nonendplate zone. Cytosolic (C) and particulate (B) forms of tTG were separated by ion-exchange chromatography from both regions of the muscle. In the motor endplate zone, a higher proportion of tightly bound tTG was recovered as a separate (B1) particulate form. Km values for calcium activation of the three forms of tTG were in the range of 5-15 microM. Immunocytochemistry with polyclonal and monoclonal antibodies revealed the enzyme at motor endplates and at contacts between neurites of rat embryo spinal neurones and myotubes in primary cocultures. Appearance of the B1 transglutaminase could be induced by coculturing myotubes of the mouse C2C12 cell line with neurones. The results suggest that tTG is most concentrated and active at the motor endplate.

Animals↗
PubMed1993

Postoperative pain: the effect of low-dose ketamine in addition to general anesthesia.

In a randomized, double-blind study, postoperative pain was assessed in 22 patients undergoing elective open cholecystectomy with two types of anesthesia: standardized general anesthesia (control group), and low-dose ketamine as an addition to the same method of general anesthesia, before surgical incision (ketamine group). After the operation we found that the time from the end of surgery to the first request for analgesic was longer in the ketamine group. Postoperatively, patients in both groups were treated with patient-controlled analgesia (PCA) in exactly the same way. The major difference in the study was the reduced dose requirement of morphine in the ketamine group compared with the control group after the operation. The mean dose of morphine given in patients of the control group during the first 24 h was 48.7 mg vs 29.5 mg in the ketamine group. Mean visual analog scale (VAS) and verbal rating scale (VRS) were higher in patients in the control group during the first 5 h after surgery (P < 0.02), but between 5 and 24 h after surgery VAS and VRS were not significantly different (P > 0.05). Our results indicate that postoperative pain can be decreased when ketamine in low doses is added to general anesthesia before surgical stimulation.

Adult↗
PubMed1993

Progress in medicinal chemistry of novel selective muscarinic agonists.

Rigid analogs of acetylcholine (ACh) were designed for selective actions at muscarinic receptor subtypes. AF102B, AF125, AF150 and AF151 are such rigid analogs of ACh. Whilst AF125 is an M2 > M1 agonist, AF102B, AF150 and AF151 are centrally active M1 agonists. AF102B has a unique agonistic profile showing, inter alia, only part of the M1 electrophysiology of ACh and unusual binding parameters to mAChRs. AF150 and AF151 are more efficacious agonists than AF102B for M1 AChRs in rat cortex and in CHO cells stably transfected with the m1 AChR subtype. In various animal models for Alzheimer's disease (AD) all three agonists (AF102B, AF150 and AF151), and in particular AF102B, exhibited positive effects on mnemonic processes and a wide safety margin. Such agonists, and especially AF102B, can be considered as a rational treatment strategy in AD. Here we review some current features of these compounds, which may be relevant to a rational treatment strategy in AD. Comparison is made, whenever possible, with some new and old muscarinic agonists.

Acetylcholine↗
PubMed1992

AF102B, a muscarinic M1 receptor agonist, mimics some effects of acetylcholine on neurons of rat hippocampus slices.

The putative muscarinic M1 receptor agonist, AF102B, was applied to rat hippocampal slices and the responses of intracellularly recorded pyramidal cells were examined. AF102B mimicked some effects of acetylcholine on these cells as follows: at low concentration, AF102B attenuated a slow after-hyperpolarization in response to a long depolarizing current pulse. This effect was blocked by the M1 antagonist, pirenzepine. At higher concentrations, AF102B also depolarized the cells and caused an increase in their input resistance. AF102B did not affect local excitatory postsynaptic potentials or reactivity to topically applied excitatory amino acid substances. These experiments indicate that AF102B acts as an agonist at some muscarinic M1 receptor subtypes in mammalian brain.

Acetylcholine↗
PubMed1992

Differential long-term effect of AF64A on [3H]ACh synthesis and release in rat hippocampal synaptosomes.

The activities of various presynaptic cholinergic parameters were determined in hippocampal synaptosomes of rats 29 weeks after intracerebroventricular injection of ethylcholine aziridinium (AF64A) (3 nmol/2 microliters/side) or vehicle (saline). Synaptosomes were preloaded with [3H]choline ([3H]Ch), treated with diisopropyl fluorophosphate to inhibit cholinesterase activity and then were assayed for their content of [3H]Ch and [3H]acetylcholine ([3H]ACh) and for their ability to synthesize and release [3H]ACh. In synaptosomes from AF64A-treated rats compared with synaptosomes from vehicle-treated rats we observed that: (i) specific uptake of [3H]Ch was reduced to 60% of control; (ii) residing [3H]ACh levels were 43% of control while residing [3H]Ch levels were 72% of control; (iii) basal and K(+)-induced [3H]ACh release were 77% and 73% of control, respectively; (iv) high K(+)-induced synthesis of [3H]ACh was only 9% of control; (v) but, choline acetyltransferase activity remained relatively high, being 80% of control. These results suggest that AF64A-induced cholinergic hypofunction is expressed by both loss of some cholinergic neurons and impairment in the functioning of the spared neurons.

Acetylcholine↗
PubMed1992

Causes of death in persons with human immunodeficiency virus infection.

PURPOSE: Pneumocystis carinii pneumonia (PCP) was reported to be the predominant cause of human immunodeficiency virus (HIV)-related deaths prior to 1988, the year that effective prophylaxis against PCP entered routine use. Our study was performed to study the causes of HIV-related death since January 1988 in a region where patient tracking is virtually complete. PATIENTS AND METHODS: We surveyed physicians associated with the Brown University Acquired Immunodeficiency Syndrome (AIDS) Program who cared for greater than 95% of known HIV-positive patients in Rhode Island. These physicians identified all those HIV-infected persons who had died under their care between January 1988 and July 1990, and determined these patients' causes of death by chart review. For comparison, death certificates of identified persons were also reviewed at the Rhode Island Department of Vital Statistics. RESULTS: Among 126 deaths since January 1988, bacterial infections were the most common cause of death (30%), whereas PCP was responsible for only 16% of deaths. Persons not receiving any form of PCP prophylaxis were more likely to die from PCP than were those who received prophylaxis (26% versus 11% [p = 0.04]). Cause of death as recorded on actual death certificates was imprecise, although bacterial infections were again the most common cause indicated. Only one death occurred in a patient with a CD4 count greater than 200/mL, and this was not HIV-related. CONCLUSION: PCP has not been the leading cause of death in our region since January 1988. Bacterial infections contribute substantially to mortality, and this may influence future prophylactic regimens. HIV-related deaths in patients with CD4 counts greater than 200/mL are unusual.

AIDS-Related Opportunistic Infections↗
PubMed1992

A study of core domains, and the core domain-domain interaction of cytochrome c fragment complex.

To gain insight into the folding mechanism of the cytochrome c complex, we prepared a complete set of homologous and hybrid two-fragment ferric complexes of four different types and related complexes from horse, tuna, yeast iso-l, and Candida cytochromes c. The complexes were characterized for structural properties. Apparent equilibrium constants of the complexes were determined to calculate delta G0 for binding. The results have allowed us to assign four core domains of the complex. A core domain is a structural region containing a hydrophobic core and the surrounding shell which folds and unfolds as a unit. Core domain 1 folds by itself and consists essentially of the right channel structure, found by R. E. Dickerson and colleagues, and a part of the heme. Core domains 2, 3, and 4, respectively, are assigned based on the cores located on the left (the Fe-S bond) and right sides and at the bottom of heme. Evidence of the core domain-domain interaction to stabilize the Fe-S bond, combined with the kinetic studies by G. R. Parr and H. Taniuchi, has led to a model of two alternative folding orders of the core domains for the horse type I complex: domain 1----3----2----4 or 1----2----3----4. Furthermore, delta G0 variation between the complexes has shown non-additive behavior, indicating the existence of a residue-residue interaction between the heme- and apofragments in the complex. Evidence suggests that this interaction in most cases occurs within or through the core groups of the ordered interface between the heme- and the apo-fragments formed by folding of core domains 1, 2, and 3. Evidence also suggests that such core group interaction manifests itself in the interaction to stabilize the Fe-S bond and may be manifested in the core domain-domain interaction.

Amino Acid Sequence↗