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Biomedical subjects

M Gilbert

Publications and source records attributed to M Gilbert.

At least 55 records · Page 3Linked to original sources
PubMed2000

Displaced scaphoid fractures treated with open reduction and internal fixation with a cannulated screw.

BACKGROUND: This study was performed to determine if the accuracy of screw placement was improved with use of the Herbert-Whipple cannulated screw compared with use of the AO/ASIF cannulated screw and also to evaluate the functional results in patients with an acute displaced fracture of the waist of the scaphoid treated with open reduction and internal fixation with a cannulated screw. METHODS: We retrospectively reviewed the results for thirty-five patients in whom an acute displaced fracture of the waist of the scaphoid had been treated with internal fixation with use of a cannulated screw. The patients were divided into two groups; Group 1 consisted of nineteen patients managed with a 3.5-millimeter cannulated AO/ASIF screw from 1990 through 1997, and Group 2 consisted of sixteen patients managed with a Herbert-Whipple screw from 1993 through 1997. RESULTS: There were no clinical or radiographic differences between the two groups. The average time to union (and standard deviation), confirmed with tomography, was 4.2 +/- 1.2 months for Group 1 and 4.0 +/- 1.2 months for Group 2. Both screws significantly improved the alignment of the scaphoid and decreased carpal collapse (p < 0.01). Importantly, the use of either cannulated screw improved the height-to-length ratio and the lateral intrascaphoid angle, which were correlated with an increase in the range of motion of the wrist (r = 0.584 and 0.625). In addition, both screws allowed for accurate placement in the central portion of the proximal pole. Regardless of the type of screw used, the time to union increased with increasing age of the patient (r = 0.665) and with increasing initial displacement of the fracture (r = 0.541). Within both groups, the time to union was longer for the patients who smoked (p < 0.01). CONCLUSIONS: Within both groups, cannulated screw fixation maintained the corrected fracture alignment and promoted healing and return of function. Our study shows cannulated screws to be a safe and effective method of treatment.

Adult↗
PubMed2000

The distinct HERG missense mutation L564P causes long QT syndrome in one French Canadian family.

BACKGROUND: Long QT syndrome is a congenital abnormality of cardiac repolarization causing syncope and sudden death from ventricular tachyarrhythmias known as torsades de pointes. This hereditary cardiac disorder often shows an increase of the value of the QT interval corrected for heart rate over 0.45 s in a 12-lead electrocardiogram. OBJECTIVE: To find and identify pertinent mutations occurring in French Canadians by extracting genomic DNA from blood samples and performing a combination of polymerase chain reaction (PCR), single-strand conformational polymorphism and DNA sequencing. RESULTS: A novel mutation was identified in the S5 region of the HERG potassium channel. In codon 564 CTA, T was replaced by C, resulting in a leucine to proline substitution. Two family members had the mutation in two distinct generations. A new restriction site was created at this position and therefore enabled the development of a rapid diagnostic test using PCR. HERG wild type and mutant potassium channel mRNAs were then expressed in Xenopus laevis oocytes. CONCLUSION: This electrophysiological study suggests that coexpression of HERG wild type and mutant L564P results in a dominant negative effect of the mutation.

Adult↗
PubMed2000

Issues in assessing and interpreting quality of life in patients with malignant glioma.

Although primary brain tumors are relatively uncommon types of adult cancer, their location and resistance to treatment can significantly affect the patient's physical and cognitive function. Consequently, quality of life (QOL) issues are extremely important in the design and evaluation of clinical trials of high-grade glioma treatment. Although a number of studies have examined QOL in patients with primary brain tumors, very little is known about QOL in these patients. These studies often use either poorly validated instruments or tools, such as the Karnofsky performance scale, that do not fully evaluate the effects of the tumor on QOL. Recent attempts to better evaluate QOL in brain tumor patients have led to the development of brain tumor-specific QOL instruments, such as the European Organization for Research and Treatment of Cancer's Quality of Life Questionnaire-Brain Cancer Module and the Functional Assessment of Cancer Therapy-Brain, which offer more insight into the QOL aspects of cancer and its treatment. Instruments such as quality time without symptoms or toxicity (Q-TWiST) provide a means of integrating both quality of time of survival and absence of symptoms or toxicity.

Adult↗
PubMed1999

Synthesis of a disialylated hexasaccharide of type VIII group B Streptococcus capsular polysaccharide.

As part of our program to design, develop and prepare protective vaccines against the bacterial pathogens Group B Streptococcus, we report the synthesis of a disialylated hexasaccharide. This hexasaccharide represents a portion of the serotype-specific capsular polysaccharide of Type VIII that has the tetrasaccharide repeat unit [beta-L-Rhap-(1-->4)-beta-D-Glcp-(1-->4)-[alpha-Neu5Ac-(2--> 3)]-beta-D- Galp-(1-->4)]n. A tetrasaccharide corresponding to this repeat unit has been synthesized by us [E. Eichler, H.J. Jennings, D.M. Whitfield, J. Carbohydr. Chem., 16 (1997) 385-411]. Since the protective epitopes are believed to involve several repeat units, methods to extend this tetrasaccharide were examined. This objective requires a glycosylation of the unreactive OH-4 of the beta-L-Rhap, which was accomplished by coupling a D-Galp glycosyl trichloroacetimidate donor with a beta-L-Rhap-(1-->4)-D-Glcp acceptor. Subsequent coupling of this trisaccharide as a donor to an alpha-Neu5Ac-(2-->3)-D-Galp disaccharide acceptor gave a pentasaccharide. The pentasaccharide was deprotected and enzymatically sialylated using an alpha-(2-->3)-sialyltransferase from Campylobacter jejuni to give the title hexasaccahride alpha-Neu5Ac-(2-->3)- beta-D-Galp-(1-->4)-beta-L-Rhap-(1-->4)-beta-D-Glcp-(1-->4)-[alpha -Neu5Ac- (2-->3)]-beta-D-Galp-(1-->O)-(CH2)3N3.

Bacterial Capsules↗
PubMed1999

Fluorescein monophosphates as fluorogenic substrates for protein tyrosine phosphatases.

A series of novel fluorescein monophosphates aimed as substrates for protein tyrosine phosphatases (PTPs) were synthesized and evaluated against fluorescein diphosphate (FDP), the currently used fluorescent substrate for PTPs. In contrast to FDP, which is dephosphorylated to monophosphate and then to fluorescein in a sequential reaction, these monophosphates are dephosphorylated in a single step. This eliminates the complication in assaying PTPs due to the cleavage of the second phosphate group. The kinetic studies of these substrates with PTPs were performed and Michaelis-Menten parameters were obtained. These designed substrates have Km 0.03-0. 35 mM, kcat/Km of 3-100 mM-1 s-1 with CD45 and PTP1B. The results showed that the substrates with negative charge groups on the fluorescein have higher affinities for PTP1B, which are consistent with other observations. In this series, fluorescein monosulfate monophosphate (FMSP) was the best substrate observed. Since FMSP showed large increases in both absorption and fluorescence upon dephosphorylation by PTPs at pH>6.0, it is one of the most sensitive, stable and high affinity substrates reported for PTPs.

Fluoresceins↗
PubMed1999

Comparison of IgE and IgG antibody-dependent cytotoxicity in vitro and in a SCID mouse xenograft model of ovarian carcinoma.

Allergic reactions are mediated by IgE antibodies bound to high-affinity receptors on mast cells in peripheral tissues and are characterized by their immediacy and hypersensitivity. These properties could also be advantageous in immunotherapy against cancer growth in peripheral tissues. We have constructed chimeric IgE and IgG1 antibodies with murine V regions and human C regions corresponding to the MOv18 monoclonal antibody against the human ovarian tumor-associated antigen, folate binding protein. The antibodies exhibited the expected binding affinities for antigen and Fc receptors, and effector activities with human basophils and platelets in vitro. The protective activities of MOv18-IgE and MOv18-IgG1 were compared in a SCID mouse xenograft model of ovarian carcinoma. The beneficial effects of MOv18-IgE were greater and of longer duration than those of MOv18-IgG1. Our results suggest that the allergic reaction could be harnessed for the suppression of ovarian tumors.

Animals↗
PubMed1999

Expression and characterization of human salivary statherin from Escherichia coli using two different fusion constructs.

Saliva is a supersaturated solution with respect to hydroxyapatite, the main inorganic component of tooth enamel. Several acidic phosphoproteins are present in saliva which allow the supersaturated state to be maintained without random crystallization occurring. Statherin is the only salivary protein currently known to inhibit both the primary and secondary precipitation of hydroxyapatite in the supersaturated environment of saliva. To identify the residues of statherin that are necessary to control biomineralization, a recombinant form of human statherin was produced from Escherichia coli using a yeast intein fusion construct. The primary structure of the recombinant statherin was characterized by SDS-PAGE, N-terminus sequencing, MALDI mass spectrometry, and amino acid analysis and found to have the expected values relative to human-derived statherin. The secondary structure of the recombinant statherin was investigated by circular dichroism spectroscopy, which revealed the predominant presence of random coil in phosphate-buffered saline solution, with a higher propensity toward alpha helicity in 100% TFE. This increase in helicity in 100% TFE was also found in statherin that was synthesized by solid-phase synthesis. These results demonstrate that human statherin can be produced in a recombinant form which behaves comparably to the natural form.

Amino Acid Sequence↗
PubMed1999

The priming effect of 12(S)-hydroxyeicosatetraenoic acid on lymphocyte phospholipase D involves specific binding sites.

We have previously shown that 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE)-enrichment primed human peripheral blood mononuclear cells for phospholipase D activation by mitogens. Given that 12(S)-HETE-enriched cells stimulated with concanavalin A released free 12(S)-HETE in the extracellular medium, and that the priming effect of 12(S)-HETE on phospholipase D was suppressed by the non-permeant drug, suramin, we hypothesized an extracellular mechanism for 12(S)-HETE-induced PLD activation. Using [3H]12(S)-HETE as a ligand and a rapid filtration technique, we have pointed out the presence of specific low-affinity 12(S)-HETE binding sites on intact human mononuclear cells and lymphocytes. [3H]12(S)-HETE binding was efficiently displaced by other monohydroxylated and n-3 fatty acids but not by oleate and arachidonate, and was also significantly inhibited by suramin and pertussis toxin. Furthermore, 12(S)-HETE-induced PLD activation was strongly inhibited by pertussis toxin and genistein, but was not PKC-dependent. In addition, 12(S)-HETE also potentiated the ConA-induced tyrosine phosphorylation of a 46-50 kDa protein, which was inhibited by genistein. Collectively, these results suggest that 12(S)-HETE binding sites on human lymphocytes may be coupled to phospholipase D through pertussis toxin sensitive G-proteins and tyrosine kinases.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1999

Synthesis of cholesterol modified cationic lipids for liposomal drug delivery of antisense oligonucleotides.

The paper describes a novel synthesis of cholest-5-en-3 beta-yl-6-aminohexyl ether (AH-Chol). AH-Chol was used to prepare positively charged liposomes. The liposomes consisted of phospholipon 90H and the cationic cholesterol derivative in an equimolar ratio. Liposome preparation was achieved by membrane homogenization after rehydration of a dry lipid film. Oligonucleotides (ODN) were adsorbed to the cationic liposomes very efficiently. At an ODN/liposome ratio of 1:5 (10:50 micrograms/ml) 84.2 +/- 5.4% of the ODNs were bound to the liposomal membrane. Within the range of 1:40 and 1:100 charge neutralization occurred and the liposome dispersion showed an increase in particle size due to aggregation. Below or above this range of charge neutralization the ODN loaded liposome preparation was physically stable, no sedimentation, increase of vesicle size or vesicle aggregation occurred.

Cholesterol↗
PubMed1999

Evaluation of aminoalkylmethacrylate nanoparticles as colloidal drug carrier systems. Part I: Synthesis of monomers, dependence of the physical properties on the polymerization methods.

Conventional nanoparticles based on acrylic compounds are lipophilic and possess a negative surface charge. This is due to their manufacturing process and to the chemical structure of the polymer. Hence, these particles are not suitable for the adsorption of hydrophilic anionic drugs. In the present investigation, positively charged copolymer nanoparticles prepared from aminoalkyl- and methylmethacrylates were evaluated, with regard to their physical properties. This report provides a detailed description of the synthesis of the non-commercially available monomers and their polymerization procedure. Various parameters were investigated, such as comonomer content, total amount of monomer, concentration of the radical initiator, and the composition of the polymerization medium. The resulting particle diameter and the surface charge were found to be strongly dependent on the polymerization conditions and on the pH. Optimization of the polymerization procedure yielded nanoparticles of about 200 nm exhibiting a positive surface charge. The charges of the different copolymer particles were then compared at different pH values. N-trimethylaminoethylmethacrylate (TMAEMC) nanoparticles with quaternary ammonium groups located at their surfaces, possessed a nearly constant positive zeta potential at various pH values and, consequently, pH-independent particle diameters. The physical characteristics of the other aminoalkyl copolymers correlated with the basicity of the monomers employed and were found to be strongly dependent on the pH of the dispersion medium. Aminoethylmethacrylate (AEMC), methylaminoethylmethacrylate (MMAEMC), and aminohexylmethacrylate (AHMC) as well as aminoethylmethacrylamide (AHMAC) copolymer nanoparticles exhibited a strong positively charged surface even at physiological pH and, therefore, are useful candidates for the adsorption of anionic drugs.

Biocompatible Materials↗
PubMed1999

Evaluation of aminoalkylmethacrylate nanoparticles as colloidal drug carrier systems. Part II: characterization of antisense oligonucleotides loaded copolymer nanoparticles.

Aminoalkylmethacrylate methylmethacrylate copolymer nanoparticles were evaluated for their use as potential drug carrier systems. Their cytotoxicity, as well as the loading of antisense oligonucleotides that were employed as anionic model drugs depended on the substitution of the basic aminoalkyl copolymer. Toxic influences on the integrity of cell membranes depended on aminoalkyl groups located on the particle surfaces. Toxicity was observed either by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays using African green monkey kidney (AGMK) cells or by a hemolysis test, where the efflux of haemoglobin from disrupted erythrocytes was measured. The cytotoxic effects were increased by the elongation of the N-alkyl chain by four additional methylene groups. Lipophilic polymethylmethacrylate (PMMA) homopolymer nanoparticles showed a negative surface charge and, therefore, were not suitable for the adsorption of anionic drugs. The surface charge was changed to positive values by the incorporation of basic monomers. Consequently, the loading efficacy was increased by raising the basic copolymer portion. Additionally, a pH-dependent loading behaviour of oligonucleotides was observed. Substitution of the amino nitrogen protons by methyl groups led to a decreased oligonucleotide loading and to a reduced cytotoxicity. Nanoparticles with permanent positively charged quarternary ammonium groups showed a high pH-independent loading efficacy, but also possessed a high cytotoxic potential. In this study, cationic copolymer nanoparticles containing 30% (w/w) methylaminoethyl-methacrylate (MMAEMC) were found to be optimal with regard to biocompatibility and carrier properties for hydrophilic anionic antisense oligonucleotides. A significant portion of adsorbed oligonucleotides were protected from enzymatic degradation. The cellular uptake of oligonucleotides into Vero cells was significantly enhanced by this methylaminoethyl-methacrylate derivative.

Animals↗
PubMed1999

Allylmalonamide as a bivalent linker: synthesis of biantennary GM3-saccharide--keyhole limpet hemocyanin glycoconjugate and the immune response in mice.

A biantennary GM3-saccharide (sialyllactoside) derivative (4) was constructed using allylmalonic acid as a bivalent linker, both carboxylic acids of which were condensed with 3-aminopropyl lactoside (2) prior to enzymatic sialylation with a fusion enzyme. While ozonolysis of its allyl group generated a saccharide having a terminal aldehyde (6), we were unable to couple 6 directly to protein by reductive amination. However, extension of the spacer by means of introducing a maleimide group to 6 through its aldehyde group to give 7 enabled the latter to be successfully coupled to thiolated proteins. The average ratios of saccharide to protein were observed to be 35 in KLH conjugate (13) and 9-12 in HSA conjugates (14 and 15). The antisera obtained by immunizing mice with the biantennary sialyllactoside-KLH conjugate (13) together with MPL adjuvant were analyzed by ELISA. Using several structurally related saccharide-HSA conjugates as screening antigens, it was concluded that anti-sialyllactoside antibodies, both IgG and IgM, were effectively raised. This was further supported by competitive inhibition experiments using lactoside (1), sialyllactoside (8) and biantennary sialyllactoside (4) as inhibitors.

Adjuvants, Immunologic↗
PubMed1999

Planned change to implement a restraint reduction program.

Physical restraints have been the standard of practice to manage certain types of patient behavior, such as unstable mobility, wandering, agitation, and interference with medical treatment. However, this intervention is not without serious negative consequences. Patients with neurological disorders or injuries are often at high risk for being restrained. The need to change to a more positive, patient-focused, restraint-free model was the goal of this project. A convenience sample of adult patients who were admitted to a neurological unit were studied. Outcome data that were assessed included (1) staff nurses' perception of restraints, (2) fall rate, (3) fall rate with injury, and (4) tube/line loss rate. Staff perceptions of restraints were assessed by administering the Perception of Restraints Use Questionnaire (PRUQ) before and after implementation of the restraint-reduced environment. The results of the outcome data support the change to a more restraint-reduced environment, as indicated by fall rate, fall rate with injury, and tube/line loss. Additionally, nurses' perceptions of restraints, as measured by the PRUQ, indicated a trend toward less emphasis on the use of restraints to control specific unsafe or undesirable patient behaviors.

Accidental Falls↗
PubMed1999

Stereoselective disposition of the antiarrhythmic agent mexiletine during the concomitant administration of caffeine.

Caffeine consumption is extensive in industrialized countries and its role in drug-drug interactions is often overlooked. CYP1A2, the major cytochrome P450 isoform involved in the metabolism of caffeine, has also been implicated in the formation of N-hydroxymexiletine, the major metabolite of mexiletine. Therefore, the objective of this study was to assess the effects of a clinically relevant dosage of caffeine on the stereoselective disposition of mexiletine. Fourteen healthy volunteers--10 extensive metabolizers (EMs) and 4 poor metabolizers (PMs) of CYP2D6--received a single 200 mg oral dose of racemic mexiletine hydrochloride on two occasions (1 week apart): once by itself and once during administration of caffeine (100 mg four times daily). Serial blood and urine samples were collected and pharmacokinetic parameters were estimated. Although the total clearance of mexiletine was not significantly altered by the coadministration of caffeine in EMs and PMs, a stereoselective decrease (16% in EMs and 14% in PMs) in the urinary recovery of N-hydroxymexiletine from the R-(-)-enantiomer was observed. Also, the partial metabolic clearance of R-(-)-mexiletine to N-hydroxymexiletine glucuronide was reduced from 126 +/- 48 mL/min to 106 +/- 32 mL/min and 152.6 (73.4-196.2) mL/min to 109 (77-127) mL/min by the coadministration of caffeine in EMs and PMs, respectively. Consequently, the R/S ratio for urinary recovery and the partial metabolic clearance of mexiletine to N-hydroxymexiletine were 28% lower during the coadministration of caffeine. In conclusion, data obtained in this study indicate that coadministration of caffeine does not lead to clinically significant changes in mexiletine plasma concentrations. However, results obtained suggest that CYP1A2 is involved in the formation of N-hydroxymexiletine.

Adult↗
PubMed1999

Lipid infusion lowers sympathetic nervous activity and leads to increased beta-cell responsiveness to glucose.

We investigated the possible involvement of the autonomic nervous system in the effect of a long-term elevation of plasma free fatty acid (FFA) concentration on glucose-induced insulin secretion (GIIS) in rats. Rats were infused with an emulsion of triglycerides (Intralipid) for 48 hours (IL rats). This resulted in a twofold increase in plasma FFA concentration. At the end of infusion, GIIS as reflected in the insulinogenic index (DeltaI/DeltaG) was 2.5-fold greater in IL rats compared with control saline-infused rats. The ratio of sympathetic to parasympathetic nervous activities was sharply decreased in IL rats relative to controls. GIIS was studied in the presence of increasing amounts of alpha- and beta-adrenoreceptor agonists and antagonists. The lowest concentrations of the alpha2A-adrenoreceptor agonist oxymetazoline, which were ineffective in control rats, reduced GIIS in IL rats. At the dose of 0.3 pmol/kg, GIIS became similar in IL and control rats. The use of beta-adrenoreceptor agonist (isoproterenol) or antagonist (propranolol) did not result in a significant alteration in GIIS in both groups. GIIS remained as high in IL vagotomized rats as in intact IL rats, indicating that changes in parasympathetic tone were of minor importance. Altogether, the data show that lipid infusion provokes beta-cell hyperresponsiveness in vivo, at least in part through changes in alpha2-adrenergic innervation.

Animals↗