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Biomedical subjects

M Afshar

Publications and source records attributed to M Afshar.

At least 19 recordsLinked to original sources
PubMed1999

Structure-based and combinatorial search for new RNA-binding drugs.

The discovery by structure-based and combinatorial methods of new RNA-binding drugs presents great opportunities for pharmacological development against drug-resistant bacterial and viral pathogens. A handful of recent RNA structures and more numerous studies of the interaction of combinatorial libraries and oligomeric RNA-binding compounds are providing the foundation for effective RNA-targeted drug discovery programs.

Chemistry, Pharmaceutical↗
PubMed1999

Dose of compound A, not sevoflurane, determines changes in the biochemical markers of renal injury in healthy volunteers.

UNLABELLED: Administration of sevoflurane in a circle absorption system generates Compound A, a nephrotoxin in rats. Reports examining the potential of Compound A to produce renal injury in humans have provided conflicting results. We tested the possibility that there is a threshold to Compound A-induced renal injury in humans and that, above this threshold, renal injury increases with increasing doses of Compound A. Eleven volunteers received 3% sevoflurane for 8 h at 2 L/min, and three volunteers received 3% sevoflurane for 8 h at 4-6 L/min. We measured inspired and expired concentrations of Compound A and urinary excretion of albumin, alpha-glutathione-S-transferase (GST), and glucose. The median urinary excretion of albumin, glucose, and alpha-GST for the first 3 days after anesthesia increased significantly from preanesthetic values in the 2-L/min group. Compound A doses < 240 ppm-h resulted in normal urinary excretion of albumin, glucose, and alpha-GST. Five of seven subjects who received doses > 240 ppm-h had abnormal excretion of albumin, and six of seven had abnormal alpha-GST urinary excretion (P < 0.05). Urinary excretion of albumin, alpha-GST, and glucose was normal by 14 days after exposure. We conclude that sevoflurane administration for 8 h at 2 L/min results in albuminuria and enzymuria when the dose of Compound A exceeds 240 ppm-h. That is, a Compound A concentration of 30 ppm breathed for > or = 8 h may produce transient renal injury. IMPLICATIONS: We examined the dose-response relationship of sevoflurane/Compound A and urinary excretion of albumin, glucose, and alpha-GST. Sevoflurane exposure for 8 h at a 2-L/min inflow rate produces transient albuminuria and enzymuria in healthy volunteers when the dose of Compound A exceeds 240 ppm-h (30 ppm for 8 h).

Adolescent↗
PubMed1998

Towards structural models of molecular recognition in olfactory receptors.

The G protein coupled receptors (GPCR) are an important class of proteins that act as signal transducers through the cytoplasmic membrane. Understanding the structure and activation mechanism of these proteins is crucial for understanding many different aspects of cellular signalling. The olfactory receptors correspond to the largest family of GPCRs. Very little is known about how the structures of the receptors govern the specificity of interaction which enables identification of particular odorant molecules. In this paper, we review recent developments in two areas of molecular modelling: methods for modelling the configuration of trans-membrane helices and methods for automatic docking of ligands into receptor structures. We then show how a subset of these methods can be combined to construct a model of a rat odorant receptor interacting with lyral for which experimental data are available. This modelling can help us make progress towards elucidating the specificity of interactions between receptors and odorant molecules.

Aldehydes↗
PubMed1997

The role of phenylalanine 31 in maintaining the conformational stability of ribonuclease P2 from Sulfolobus solfataricus under extreme conditions of temperature and pressure.

Ribonuclease P2 from the thermophilic archaebacterium Sulfolobus solfataricus is a small protein (7 kDa) with a known three-dimensional structure. Inspection of the structure and molecular dynamics simulation reveal that three aromatic residues (Phe5, Phe31, and Tyr33) from the hydrophobic core have a strong van der Waals interaction energy. We studied the thermodynamics of the heat, cold, and pressure-induced protein conformational changes of the wild type and of the F31A and F31Y mutants by analyzing the protein UV absorbance in the fourth derivative mode. The wild-type protein was extremely stable under all conditions of temperature and pressure. Heat and cold denaturation of both mutants, as well as denaturation by pressure of the F31A mutant, led to significant blue shifts of the derivative spectrum, indicating increased solvent exposure of Tyr33. For the F31Y mutant, high pressure (400 MPa) protected the protein against thermal denaturation. This study, probing the properties of the hydrophobic aromatic core, complements a thermal unfolding study which probes the overall structural changes [Knapp, S., Karshikoff, A., Berndt, K. D., Christova, P., Atanasov, B., & Ladenstein, R. (1996) J. Mol. Biol. 264,1132-1144]. The differences observed in response to extremes of temperature, pressure, and pH may be rationalized by an unfolding mechanism involving larger parts of the peripheral protein while the integrity of the hydrophobic core is maintained.

Enzyme Stability↗
PubMed1997

Dual phosphorylation of the T-loop in cdk7: its role in controlling cyclin H binding and CAK activity.

A cyclin-dependent kinase (cdk)-activating kinase (CAK) has been shown previously to catalyze T-loop phosphorylation of cdks in most eukaryotic cells. This enzyme exists in either of two forms: the major one contains cdk7, cyclin H and an assembly factor called MAT-1, whilst the minor one lacks MAT-1. Cdk7 is unusual among cdks because it contains not one but two residues (S170 and T176 in Xenopus cdk7) in its T-loop that are phosphorylated in vivo. We have investigated the role of S170 and T176 phosphorylation in the assembly and activity of cyclin H-cdk7 dimers. In the absence of MAT-1, phosphorylation of the T-loop appears to be required for cdk7 to bind cyclin H. Phosphorylation of both residues does not require cyclin H binding in vitro. Phosphorylation of S170 is sufficient for cdk7 to bind cyclin H with low affinity, but high affinity binding requires T176 phosphorylation. By mutational analysis, we demonstrate that in addition to its role in promotion of cyclin H binding, S170 phosphorylation plays a direct role in the control of CAK activity. Finally, we show that dual phosphorylation of S170 and T176, or substitution of both phosphorylatable residues by aspartic residues, is sufficient to generate CAK activity to one-third of its maximal value in vitro, even in the absence of cyclin H and MAT-1, and may thus provide further clues as to how cyclins activate cdk subunits.

Animals↗
PubMed1997

Double-blind comparison of two doses of rocuronium and succinylcholine for rapid-sequence intubation.

STUDY OBJECTIVE: To compare the pharmacodynamics of two commonly recommended doses of rocuronium bromide (0.7 mg/kg and 0.9 mg/kg) and succinylcholine (1.5 mg/kg) when used for rapid-sequence intubation. DESIGN: Prospective, double-blind, randomized study. SETTING: Operating rooms at a university hospital. PATIENTS: 45 ASA physical status I and II adult patients scheduled for elective surgeries under general anesthesia. INTERVENTIONS: Nonpremedicated patients were anesthetized with fentanyl 2 mcg/kg followed by thiopental sodium 4 to 5 mg/kg and muscle relaxant using rapid-sequence technique. Group 1 (n = 15) received rocuronium bromide 0.7 mg/kg. Group 2 (n = 16) received rocuronium bromide 0.9 mg/kg, and Group 3 (n = 14) received succinylcholine 1.5 mg/kg. Intubation was performed 60 seconds after the administration of muscle relaxant. MEASUREMENTS AND MAIN RESULTS: The case of intubation was scored using a scale of 1 to 4. Blood pressure and heart rate were measured beginning one minute before induction of anesthesia up to 5 minutes after intubation. Intubation scores were similar in groups 2 and 3 and were noted as good or excellent in all patients. Group 1 displayed a significantly lower intubation score than the other two groups; 60% were rated as poor. No significant differences in hemodynamic data were seen among the three groups. CONCLUSIONS: Rocuronium bromide at a dose of 0.9 mg/kg provides intubating conditions similar to succinylcholine 1.5 mg/kg at 1 minute. Intubating conditions at 1 minute following a 0.7 mg/kg dose of rocuronium are not as good as those following a 0.9 mg/kg dose of rocuronium or a 1.5 mg/kg dose of succinylcholine.

Adolescent↗
PubMed1997

Modeling of the three-dimensional structure of the human melanocortin 1 receptor, using an automated method and docking of a rigid cyclic melanocyte-stimulating hormone core peptide.

A model is presented of the melanocortin 1 receptor (MC1R), constructed by use of an unbiased, objective method. The model is created directly from data derived from multiple sequence analysis, a low-resolution EM-projection map of rhodopsin, and the approximate membrane thickness. The model agrees well with available data concerning natural mutations of MC1Rs occurring in different species. A model is also presented of the most rigid ligand for this receptor, the cyclic pentapeptide cHFRWG, shown docked in the receptor model. The receptor-ligand complex model agrees well with available experimental data. The ligand is located between transmembrane region 1 (TM1), TM2, TM3, TM6, and TM7 of the receptor. Multiple interactions occur between ligand and receptor, including interactions with Leu-48 (TM1), Ser-52 (TM1), Glu-55 (TM1), Asn-91 (TM2), Glu-94 (TM2), Thr-95 (TM2) Ile-98 (TM2), Asp-121 (TM3), Thr-124 (TM3), Phe-257 (TM6), Phe-283 (TM7), Asn-290 (TM7), and Asp-294 (TM7) of the receptor.

Amino Acid Sequence↗
PubMed1997

The effects of general anesthesia and surgery on basal and interferon stimulated natural killer cell activity of humans.

UNLABELLED: Natural killer (NK) cells can lyse certain tumor cells as well as virally infected cells without prior sensitization. Animal studies have shown that general anesthesia (GA) alone or GA followed by surgery decreases both basal NK cytotoxicity and enhancement of NK activity by interferon (IFN). The purpose of this study was to determine whether similar inhibition of NK activity by anesthesia and surgery occurs in humans. Venous blood was drawn 1 h before and 20-24 h after surgery under isoflurane/N2O anesthesia. Peripheral blood mononuclear cells (PBMC) were assayed for basal and IFN-alpha-stimulated NK cytotoxicity using a chromium release assay with K562 cells as targets. Flow cytometry was used to enumerate NK, T-helper, and T-cytotoxic/suppressor cell populations in each sample. Basal NK activity was significantly depressed after GA and GA and surgery. Although the postoperative IFN treatment increased NK activity to the preoperative basal level, the level achieved was significantly lower than the level observed after IFN stimulation of PBMC as evaluated preoperatively. This decreased activity does not seem to be the result of a decrease in the percentage of circulating NK cells. The decrease in NK activity after anesthesia and surgery may lead to increased susceptibility to infection and/or tumor dissemination and thus needs to be explored. IMPLICATIONS: Natural killer cells can kill cancer cells and virally infected cells. This study shows that surgery with general anesthesia leads to decreased natural killer cell activity as assessed int he laboratory. This decreased natural killer cell activity may lead to infection or tumor dissemination. NK activity can be restored to presurgery levels by treating isolated NK cells with interferon-alpha.

Adolescent↗
PubMed1996

Mutagenicity of cosmetic products containing Kathon.

A variety of shampoos, conditioners, skin-care lotions, and other cosmetic products contain the biocide Kathon CG, which is a mixture of two heterocyclic isothiazolinones: methylisothiazolinone and methylchloroisothiazolinone. This mixture and the related biocide, Kathon 886, have been shown to be potent sensitizers and bacterial mutagens. Five cosmetic products that list the components of Kathon on their labels and two that do not were screened for mutagenicity with Salmonella typhimurium TA100 without S-9. Five of these products and Kathon 886 were further evaluated in TA100 without and with S-9. Kathon 886, a cosmetic product that contained Kathon, and thin layer chromatography-separated components of Kathon 886 were identified by GC/MS analysis. Three of the five products that listed Kathon were direct acting mutagens with TA100. The remaining two products were considerably more toxic than the other products and could not be evaluated for mutagenicity. The addition of S-9 reduced toxicity but did not eliminate mutagenicity. The mutagenic evaluation of Kathon 886 resulted in a dose response similar to that seen with some cosmetic products but at a 1,000-fold lower concentration, and activity was also reduced by the addition of S-9 mix. S-9 reduced activity both with and without cofactors present. Thin layer chromatography separation of the components and subsequent identification by GC/MS indicated that methylisothiazolinone was nonmutagenic while methylchloroisothiazolinone was mutagenic. Additionally, a dichlorinated compound was identified which was also mutagenic. In light of these findings and the reported skin sensitization by Kathon CG in various cosmetics, we recommend that additional testing be done to assure the safety of products containing Kathon CG.

Chromatography, Thin Layer↗
PubMed1996

The effects of the menstrual cycle on the incidence of emesis and efficacy of ondansetron.

Postoperative nausea and vomiting after general anesthesia remains a complex and perturbing phenomenon associated with several factors. In women, the phase of the menstrual cycle as a factor in postoperative nausea and emesis is controversial. This retrospective study was performed to assess the effects of the menstrual cycle and efficacy of the antiemetic ondansetron on postoperative emesis. A total of 1169 ASA grade I-II patients from two double-blind, placebo-controlled studies were enrolled in 18 centers. Patients with irregular cycles or taking estrogens or progesterones were excluded from the analysis, leaving 873 patients eligible for this study. The patients were stratified on the basis of their last menses into four groups: 1) 1-8, 2) 9-16, 3) 17-28, and 4) 29-35 days. All patients received a general anesthetic with endotracheal intubation. Patients received either 1, 4, or 8 mg ondansetron or placebo given intravenously before induction of anesthesia. All patients were studied for a 24-h period. Emesis rates were compared with respect to the phase of the menstrual cycle and between menstruating and nonmenstruating patients. There was no relationship (P = 0.100) between the incidence of emesis and the phase of the menstrual cycle in the group receiving the placebo. There was, however, a significant reduction (P < 0.001) in emesis for the ondansetron-treated patients regardless of the phase of the menstrual cycle. In addition, ondansetron had a similar dose-response curve in both menstruating and nonmenstruating women.

Adult↗
PubMed1994

Investigating the high affinity and low sequence specificity of calmodulin binding to its targets.

Calmodulin (CaM) is a calcium binding protein that regulates a wide range of enzymes. Recently the structures of a number of complexes between CaM and synthetic target peptides have been determined. The peptides correspond to the CaM-binding domain of skeletal and smooth muscle myosin light-chain kinase (MLCK) and calmodulin-dependent protein kinase II alpha. Comparison of the peptide-free and peptide-bound structures reveals that CaM undergoes a large conformational change when forming a complex, resulting in the formation of a binding surface that provides for an optimal interaction with its target. In this work, the available co-ordinates of the NMR solution structure of CaM-skeletal MLCK peptide are used as a basis upon which several molecular models of binding are built. The detailed features of the protein's peptide binding surface are revealed through two-dimensional topographical projections. Negatively charged margins at the binding surface extremities interact strongly with basic peptide residues separated by nine or ten positions. The binding surface core is hydrophobic and displays a groove with four deep pockets, which can accommodate bulky peptide residues at relative positions 4 and 8 (pocket A), 11 (pocket B), 13 (pocket C), 14 and 17 (pocket D). Therefore, both electrostatic and van der Waals' features contribute to the high affinity binding. A search for alternative peptide placements in the binding tunnel reveals the dominant role of specific electrostatic interactions in the binding energy. Apolar interactions are more permissive, such that the hydrophobic side-chains that line the binding tunnel adapt in order to maintain favourable van der Waals' contacts. The model suggests that the structure can accommodate large peptide translations (up to 5 A) and a reversed peptide binding mode, with a little loss in binding interaction energy. These calculations are compared with available experimental data, providing a structural rationale for the low sequence specificity of the CaM target recognition.

Amino Acid Sequence↗
PubMed1994

A protein/peptide assay using peptide-resin adduct: application to the calmodulin/RS20 complex.

To obtain equilibrium and kinetic constants of a protein/peptide complex, we have developed a rapid procedure which uses peptides specifically linked to a resin. With this peptide-resin adduct, bound and free 125I-labeled protein could be easily separated by simple centrifugation. The feasibility of the method was demonstrated with the calmodulin/RS20 complex, where RS20 is the putative calmodulin binding peptide of the smooth muscle myosin light chain kinase (smMLCK). In addition to the wild-type calmodulin (SYNCAM) expressed in Escherichia coli, we also examined calmodulin mutants with charge reversals called SYNCAM12A (DEE 118-120-->KKK) and SYNCAM18A (EEE 82-84-->KKK and DEE 118-120-->KKK). The kinetic analysis of the interaction between SYNCAM and RS20 associated with titration experiments allowed us to measure dissociation constants (KD) in the range of 10(-9) M, in good agreement with previously published data. Moreover, the binding assays showed that SYN-CAM18A did not interact with RS20, whereas SYN-CAM12A did with a KD around 10(-8) M. The lack of binding of SYNCAM18A to RS20 provides an explanation for the lack of smMLCK activation by SYNCAM18A. Altogether, these results demonstrate that peptide-resin can be used as a tool for separating bound from free protein, thus enabling a rapid and reliable quantification of the protein/peptide interaction.

Amino Acid Sequence↗
PubMed1994

Doppler-guided cannulation of the internal jugular vein: a prospective, randomized trial.

OBJECTIVES: The internal jugular vein (IJ) is commonly used as an access to the central venous system. Despite the high success rate for cannulation of the IJ, the incidence of complications (1% to 16%) has remained essentially the same, with most complications resulting from unintentional punctures of surrounding structures. In an attempt to reduce the complication rate of this technique, we evaluated the use of a Doppler-guided needle device to cannulate the IJ. METHODS: The study was performed on 41 patients scheduled for cardiothoracic or major vascular surgery requiring central vein cannulation as part of their anesthetic management. RESULTS: The number of needle advances in the Doppler group was 1.35 (SD 0.88) compared with 2.8 (SD 2.78) in the control group (p = 0.037). A significantly greater percentage of cannulations were successful on the first attempt in the Doppler group (85%), compared with the control group (55%) (95% CI for proportion = 0.3 to 0.57). CONCLUSION: The Doppler-guided cannulation technique can reduce the number of attempts required for successful IJ cannulation.

Catheterization, Central Venous↗
PubMed1994

Postoperative nystagmus and nausea.

OBJECTIVE: To evaluate the presence and the relationship between postoperative nystagmus and nausea. DESIGN: Open-label study. SETTING: University hospital. PATIENTS: Sixty-six patients recovering from general anesthesia following elective ambulatory surgeries. INTERVENTIONS: Patients were tested postoperatively for nystagmus using an electronystagmography, and were monitored for nausea and vomiting for the first postoperative day. MAIN OUTCOME MEASURES: A comparison of the incidence of nausea was made among patients with and without postoperative nystagmus. RESULTS: Twenty-four patients (36 percent) experienced postoperative nausea and 28 patients (42 percent) had nystagmus. There were no significant differences in age, weight, height, dosage of fentanyl, or postoperative use of narcotics between those who experienced postoperative nausea or had nystagmus than those who did not. A significantly greater percentage of female patients compared with male patients had nausea during the first postoperative day. Sixty percent of patients with nystagmus experienced nausea in the hospital compared with 18 percent of the patients without nystagmus (p < 0.01, 95 percent confidence interval [CI] of the difference = 11.3 to 61.3 percent). Twenty-two patients (78 percent) with nystagmus experienced nausea during the first postoperative day compared with 14 patients (36 percent) with no nystagmus (p < 0.01, 95 percent CI of the difference = 20.1 to 63.3 percent). Eighty-three percent of the nauseated patients experienced vomiting during the first postoperative day. CONCLUSIONS: The presence of nystagmus in the early part of recovery from general anesthesia is associated with a higher incidence of nausea and vomiting during the first postoperative day.

Adolescent↗
PubMed1992

Comparative evaluation of the neuromuscular and cardiovascular effects of pipecuronium, pancuronium, atracurium, and vecuronium under isoflurane anesthesia.

The neuromuscular and cardiovascular effects of intubating doses of pipecuronium 80 micrograms/kg, pancuronium 100 micrograms/kg, atracurium 500 micrograms/kg, and vecuronium 100 micrograms/kg were compared in 62 patients under isoflurane (end-tidal concentration = 0.5-1%) anesthesia. Pipecuronium, pancuronium, and vecuronium had no significant effect on systolic or diastolic blood pressure. In one patient the administration of atracurium resulted in significant hypotension. Heart rate was significantly increased only after the administration of pancuronium. The neuromuscular-blocking effect of pipecuronium and pancuronium appears to be twice as long as that of vecuronium and atracurium. Administration of neostigmine resulted in significantly faster recovery of muscle function in patients receiving vecuronium or atracurium. Although pipecuronium's neuromuscular-blocking effect is similar to that of pancuronium, its lack of cardiovascular effects more closely resembles that of vecuronium.

Adolescent↗
PubMed1992

The effect of desmopressin acetate on postoperative hemorrhage in patients receiving aspirin therapy before coronary artery bypass operations.

It has been suggested that desmopressin acetate has been effective in reducing hemorrhage after coronary artery bypass grafting in patients receiving aspirin before operation. We conducted a prospective, randomized, placebo-controlled, double-blind trial to determine the effectiveness and safety of desmopressin in these patients. Sixty-five patients pretreated with aspirin within 7 days before their scheduled elective coronary artery bypass grafting were randomized to receive desmopressin (0.3 micrograms/kg) or placebo after cessation of bypass and reversal of heparin with protamine. The demographic characteristics and last dose of aspirin were similar in both groups. There was a significant reduction in postoperative blood loss noted between groups for both chest tube blood loss (833 +/- 311 ml for the 1-desamino-8-D-arginine vasopressin [desmopressin] group versus 1176 +/- 674 ml for the placebo group; p = 0.016) and total blood loss (1215 +/- 381 ml for the desmopressin group versus 1637 +/- 761 ml for the placebo group; p = 0.0097). Despite the differences in blood loss between the two groups, the red cell transfusions were not significantly different, but the use of platelets was less in the desmopressin group and almost achieved statistical significance (p = 0.053). Neither was there a difference in the occurrence of thrombotic complications between groups. It appears that desmopressin in this specific subgroup of patients receiving preoperative aspirin is effective as a prophylactic agent for reduction of postsurgical hemorrhage.

Aged↗