PubMed Health⌕ Search

Biomedical subjects

M Gilbert

Publications and source records attributed to M Gilbert.

At least 91 records · Page 5Linked to original sources
PubMed1999

Block of potassium currents in guinea pig ventricular myocytes and lengthening of cardiac repolarization in man by the histamine H1 receptor antagonist diphenhydramine.

Treatment with second generation histamine H1 receptor antagonists has been associated with lengthening of the Q-T interval and proarrhythmia. Similarly, lengthening of the Q-T interval has been reported in patients after overdosing with diphenhydramine (DPH), a first generation agent. Therefore, our study was designed 1) to assess effects of DPH on cardiac repolarization and 2) to characterize effects of the drug on major voltage-dependent cardiac K+ currents. First, we noticed that oral administration of DPH at usual dosages to healthy volunteers or to patients (prior to angioplasty) was associated with prolongation of the Q-Tc interval. Although this effect was modest in most individuals, Q-Tc was increased more than 20 ms in 7 of 20 patients. Second, we noticed that exposure of isolated guinea pig hearts to DPH 10(-5) M caused a lengthening of monophasic action potential duration. This effect was potentiated by the combined perfusion of other K+ channel blockers such as indapamide. Finally, experiments performed with the patch-clamp technique demonstrated unequivocal block of the rapid component of the delayed rectifier (IKr) by DPH; however, IC50 determined for block of IKr (3 x 10(-5) M) is approximately 40-fold greater than plasma concentrations of the drug measured at usual dosages (7 x 10(-7) M). Consequently, in agreement with the long-term clinical use of the drug, prolongation of cardiac repolarization should be minimal in most patients at usual dosages but may be observed with overdosing. Nevertheless, caution remains since excessive lengthening of cardiac repolarization may occur after administration of DPH with other drugs due to 1) concomitant block of other ionic currents or 2) pharmacokinetic interactions leading to toxic concentrations of DPH.

Action Potentials↗
PubMed1998

Repertoire analysis of CD8+ T cell responses to minor histocompatibility antigens involved in graft-versus-host disease.

Graft-vs-host disease (GVHD) is a major complication of allogeneic bone marrow transplantation. Experimentally, lethal GVHD can be induced in MHC-matched strain combinations differing in expression of multiple minor histocompatibility Ags (miHA). Recently, the GVHD potential of C57BL/6By (B6) T cells in irradiated BALB.B (both H2b) and related CXB recombinant inbred strains of mice has been studied to determine the scope of the response to miHA in vivo and how it compared with CTL responses to immunodominant miHA in vitro. The GVHD response in these strain combinations appeared to be limited to a few Ags, yet there was no correlation of these miHA with that of in vitro CTL responses. To further investigate the role of CD8+ T cells in GVHD, we analyzed positively selected miHA-specific donor CD8+ thoracic duct lymphocytes (TDL) collected from irradiated BALB.B and CXBE mice, 5 to 6 days after transplantation of B6 T cells. Flow cytometric analysis of B6-->BALB.B TDL did not indicate expansion of any particular TCR Vbeta family, whereas Vbeta10 and Vbeta14 families were significantly expanded in the B6-->CXBE TDL. However, PCR-based complementarity-determining region 3 size spectratyping revealed overlapping involvement of donor Vbeta1, 6, 8, 9, 10, and 14 families in both BALB.B and CXBE recipients and unique utilization of the Vbeta4 family in BALB.B mice, suggesting oligoclonal T cell responses to a limited number of miHA. In addition, the injection of CD8+ Vbeta14+ B6 T cells into irradiated BALB.B and CXBE mice induced lethal GVHD, confirming the involvement of miHA-specific T cells within an individual Vbeta family.

Animals↗
PubMed1998

Structure of an alpha-2,6-sialylated lipooligosaccharide from Neisseria meningitidis immunotype L1.

The recent cloning of the lipooligosaccharide (LOS) a-2,3-sialyltransferase from Neisseria meningitidis immunotype L3 permitted us to examine other immunotypes for this structural gene. We identified the gene and measured the enzyme activity in the L1 immunotype strain which had previously been reported to lack sialic acid in its LOS because it contains a terminal alpha-linked galactose which was thought not to be an acceptor for the sialyltransferase. This finding prompted us to re-examine the structure of the LOS from the L1 immunotype, which revealed the presence of sialic acid on the terminal alpha-linked galactose. Oligosaccharides derived from the LOS were shown to be sialylated by composition and methylation analysis, mass spectrometry and nuclear magnetic resonance. The detailed structural analysis showed the sialic acid to occur only at 06 of the terminal a-D-galactopyranose residue of the alpha-D-Gal-1,4-beta-D-Gal-1,4-beta-D-glc trisaccharide (Pk epitope) chain of the LOS, in the alpha-D configuration. These data are the first report of a alpha-2,6-linked sialic acid in a bacterial LOS or lipopolysaccharide, and also the first report of a sialylated Pk epitope.

Carbohydrate Conformation↗
PubMed1998

Intrafocal (Kapandji) pinning of distal radius fractures with and without external fixation.

Seventy-three patients were treated with either intrafocal pinning (Kapandji technique) alone or in combination with external fixation between 1988 and 1993 for extra-articular fractures of the distal radius (with or without a nondisplaced extension into the radiocarpal articular surface) with inadequate alignment after initial closed reduction. Sixty-one patients were available for follow-up examination at an average of 34 months (range, 24-71 months). The average age was 52 years (range, 16-84 years). Thirty-three of the patients were female. The patients all had dorsally displaced extra-articular fractures, although 56% had a nondisplaced extension of the fracture into the radiocarpal joint and 46% had a nondisplaced fracture extending into the distal radioulnar joint. The patients were separated into groups based on age, degree of comminution, and whether external fixation was also used. In the older patients, range of motion, grip strength, and pain relief were significantly better when external fixation was used, even when only 1 cortex of the radius demonstrated comminution. In the younger patients, good results in terms of range of motion, grip strength, and pain relief were obtained when percutaneous intrafocal pins were used alone in patients with comminution of only 1 surface of the radius (<50% of the metaphyseal diameter). When > or = 2 sides of the radial metaphysis were comminuted, the patients with external fixation had better results than those without external fixation. Although the correction of palmar tilt and radial tilt did result in better functional results, the restoration of radial length had the most significant effect on range of motion and grip strength.

Adolescent↗
PubMed1998

In situ osteotomy for extra-articular malunion of the proximal phalanx.

Eleven patients had correction of extra-articular malunions of the proximal phalanx by in situ osteotomy stabilized with a dorsal plate, which healed within 7 weeks. The patients' average age was 27 years; 8 of the patients were male. After an average follow-up period of 35 months (range, 25-54 months), all the patients had correction of the overlapping or scissoring of the digits during flexion. The rotation deformity improved from 17 degrees to 2 degrees and the angular deformity present in 6 patients improved from 14 degrees to 0 degrees. None of the patients lost motion. On average, the patients improved from 85 degrees to 100 degrees flexion for the proximal interphalangeal joint and from 45 degrees to 55 degrees for the distal interphalangeal joint.

Adolescent↗
PubMed1998

The synthesis of sialylated oligosaccharides using a CMP-Neu5Ac synthetase/sialyltransferase fusion.

Large-scale enzymatic synthesis of oligosaccharides, which contain terminal N-acetyl-neuraminic acid residues requires large amounts of the sialyltransferase and the corresponding sugar-nucleotide synthetase, which is required for the synthesis of the sugar-nucleotide donor, CMP-Neu5Ac. Using genes cloned from Neisseria meningitidis, we constructed a fusion protein that has both CMP-Neu5Ac synthetase and alpha-2,3-sialyltransferase activities. The fusion protein was produced in high yields (over 1200 U/L, measured using an alpha-2,3-sialyltransferase assay) in Escherichia coli and functionally pure enzyme could be obtained using a simple protocol. In small-scale enzymatic syntheses, the fusion protein could sialylate various oligosaccharide acceptors (branched and linear) with N-acetyl-neuraminic acid as well as N-glycolyl- and N-propionyl-neuraminic acid in high conversion yield. The fusion protein was also used to produce alpha-2,3-sialyllactose at the 100 g scale using a sugar nucleotide cycle reaction, starting from lactose, sialic acid, phosphoenolpyruvate, and catalytic amounts of ATP and CMP.

Catalysis↗
PubMed1998

Effect of amino acid substitutions in the heavy chain CDR3 of an autoantibody on its reactivity.

In this study, we applied site-directed mutagenesis to the Fab fragment of a mouse IgM (IE12) that was previously shown to inhibit the binding of IgG to autoantigens by interacting with their variable regions. Its native structure was very similar to that of a polyreactive natural IgM (ppc15-30). Indeed, they both use the same light chain and the same VH, D and JH segments. However, the N regions differ and the D is translated in two different reading frames, giving different amino acid compositions of the heavy chain CDR3 (HCDR3). Site-directed mutagenesis modified the HCDR3 of IE12 compared to that of the natural antibody and the resulting effects on its reactivity were analyzed. Because the HCDR3 of IE12 is very rich in aliphatic residues, which are hydrophobic, we replaced them with the more hydrophilic residues of the HCDR3 of the polyreactive IgM. In addition, we evaluated the impact of the proline residues in the HCDR3 of IE12 on its activity, because they are known to restrict backbone flexibility. We found that a more hydrophilic HCDR3 conferred to the IE12 Fab a polyreactive profile. Prolines seem to play an important role in this context, because when they were replaced by glycines, the resulting Fab fragments were highly polyreactive. Our results suggest that, for polyreactivity, hydrophilicity and a certain plasticity of the HCDR3 seem to be necessary. Greater flexibility of the CDR, particularly the HCDR3, might be an important characteristic for polyreactive antibodies.

Animals↗
PubMed1998

Phase I study of paclitaxel in patients with recurrent malignant glioma: a North American Brain Tumor Consortium report.

PURPOSE: To determine the maximum-tolerated dose (MTD) of paclitaxel administered as a 3-hour infusion in patients with recurrent malignant glioma. PATIENTS AND METHODS: Patients were stratified by starting dose of paclitaxel and concurrent anticonvulsant (AC) use and were treated in cohorts of three patients. The starting dose was 240 mg/m2 administered intravenously with escalations of 30 mg/m2 until the MTD was established. Pharmacokinetic data were obtained for each patient for the first infusion. Tumor response was assessed at 6-week intervals and treatment was continued until documented tumor progression, unacceptable toxicity, or a total of 12 paclitaxel infusions. RESULTS: From April 1995 to December 1996, 34 patients were treated; 27 patients in the AC group and seven patients in the non-AC group. The MTD for patients who received ACs was established at 360 mg/m2 and the dose-limiting toxicity (DLT) was central neurotoxicity, characterized as transient encephalopathy and seizures. In contrast, the MTD for patients who did not receive ACs was 240 mg/m2, and myelosuppression, gastrointestinal toxicity, and fatigue were the DLTs. Pharmacokinetic data confirmed that the plasma drug levels and clearance rates were similar for patients in both groups at the respective dose levels that produced DLTs. CONCLUSION: The pharmacokinetics of paclitaxel are altered by ACs, and significantly larger doses of the drug can be administered to patients with brain tumors on AC therapy. The toxicity profile is different for patients on AC therapy treated at these higher doses. A phase II study has been initiated that uses a dose of 330 mg/m2 for patients on AC therapy and 210 mg/m2 for patients not on AC therapy.

Adult↗
PubMed1998

Insulin, but not glucose lowering corrects the hyperglucagonemia and increased proglucagon messenger ribonucleic acid levels observed in insulinopenic diabetes.

The factors that regulate glucagon biosynthesis and proglucagon gene expression are poorly defined. We previously reported that insulin inhibits proglucagon gene expression in vitro. In vivo, however, the effects of insulin on the regulation of the proglucagon gene have been controversial. Furthermore, whether glucose plays any role alone or in conjunction with insulin on proglucagon gene expression is unknown. We investigated the consequences of insulinopenic diabetes on glucagon gene expression in the endocrine pancreas and intestine and whether insulin and/or glucose could correct the observed abnormalities. We show here that in the first 3 days after induction of hyperglycemia by streptozotocin, rats have levels of plasma glucagon and proglucagon messenger RNA comparable to those of normoglycemic controls despite hyperglycemia. With more prolonged diabetes, plasma glucagon and proglucagon messenger RNA levels increase; this increase is corrected by insulin treatment, but not by phloridzin despite normalization of the glycemia by both treatments. Proglucagon gene expression exhibits the same regulatory response to glucose and insulin in both pancreas and ileum. We conclude that insulin tonically inhibits proglucagon gene expression in the pancreas and ileum and that glucose plays a minor, if any, role in this regulation.

Animals↗
PubMed1998

Hormonal counterregulation failure in rats is related to previous hyperglycaemia-hyperinsulinaemia.

Hyperglycaemia and hyperinsulinaemia were induced in rats by a continuous 48-h infusion with glucose. Discontinuation of glucose infusion resulted in marked, persistent hypoglycaemia. To further delineate the mechanism underlying this condition, we measured counterregulatory hormone levels, in vivo glucose kinetics (glucose production = rate of appearance = Ra; glucose utilization = rate of disappearance = Rd), and in vitro gluconeogenesis during the 48-h postinfusion period. Prior to cessation of glucose infusion, Rd was increased 6-fold when compared to control rats, whereas Ra was totally abolished. During the first hour after the end of glucose infusion, Ra increased and Rd decreased (but was still higher than Ra), inducing hypoglycaemia which stabilized after 1 h at ¿¿126¿¿3.5 mmol/l when both Ra and Rd became equal. Despite hypoglycaemia, plasma glucagon and catecholamine levels did not increase during the 3-to 36-h time interval. The increase in Ra during the first hour post-infusion was not related to changes in counterregulatory hormone response. The increase in glucose production was accounted for by glycogenolysis, as shown by total depletion in liver glycogen within 6 h and thereafter by gluconeogenesis. In vitro experiments using isolated hepatocytes suggested that gluconeogenesis was supported during the first 24 h by substrates entering the pathway beyond the step catalysed by the PEPCK enzyme. Thereafter, lactate became the major substrate, and this condition was associated with a progressive rise in glucagon concentration. It is concluded that 48 h of hyperglycaemia/hyperinsulinaemia resulted in a failure of counterregulatory hormonal response to hypoglycaemia. Yet, despite this lack of counterregulatory response, hepatic gluconeogenesis was stimulated in response to hypoglycaemia.

Animals↗
PubMed1997

Eicosapentaenoic and docosahexaenoic acids reduce PGH synthase 1 expression in bovine aortic endothelial cells.

To enlighten the mechanism of inhibition of prostacyclin (PGI2) production by n-3 fatty acids, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, cultured endothelial cells were incubated with albumin bound-EPA or -DHA for 22 h. Under these conditions, PGI2 formation in response to bradykinin, calcium ionophore or exogenous arachidonic acid was equally inhibited by 50%, suggesting that the inhibition might occur downstream the phospholipase step, likely at the level of PGH synthase and/or PGI2 synthase activities. Western blot analysis indicated that the mass of the constitutive isoform of PGH synthase (PGH synthase 1), but not PGI2 synthase, was significantly reduced in n-3 fatty acid-enriched cells. In subsequent experiments, PGH synthase 1 mRNA level, measured by northern blotting, was also decreased in n-3 supplemented cells. This reduction was not due to mRNA destabilization. None of these parameters were altered by similar enrichment with oleic acid (OA). These results suggest that EPA and DHA may affect PGH synthase 1 expression, presumably at the transcriptional level.

Animals↗
PubMed1997

Characterization of a recombinant Neisseria meningitidis alpha-2,3-sialyltransferase and its acceptor specificity.

The structure and specificity of the recombinant alpha-2,3-sialyltransferase from Neisseria meninigitidis are reported. This enzyme showed an unusual acceptor specificity in that it could use alpha-terminal and beta-terminal Gal residues as acceptors. In addition (beta1-->4)-linked and (beta1-->3)-linked terminal Gal served as acceptors. These properties distinguish the bacterial enzyme from the more widely investigated mammalian equivalents. The protein was expressed as a membrane-associated protein in Escherichia coli at a level of 750 U/l (approximately 250 mg/l). The protein could be extracted with buffers containing 0.2% Triton X-100 and purified to homogeneity using immobilized-metal-affinity chromatography. Electrospray-ionization mass spectrometry of peptides obtained by cleavage with cyanogen bromide and trypsin confirmed over 95% of the deduced amino acid sequence. When used for enzymatic synthesis in coupled reactions with recombinant CMP-Neu5Ac synthetase, the alpha-2,3-sialyltransferase could sialylate fluorescent derivatives of N-acetyllactosamine with N-acetylneuraminic acid, N-propionylneuraminic acid and N-glycoloylneuraminic acid.

Amino Acid Sequence↗
PubMed1997

Influence of Bcl-2 overexpression on Na+/K(+)-ATPase pump activity: correlation with radiation-induced programmed cell death.

Bcl-2 overexpression in transfected PW cells is associated with inhibition of radiation-induced programmed cell death (PCD). We have previously reported that there is a relationship between inhibition of radiation-induced PCD and membrane hyperpolarization in these cells. In this article, we report that Na+/ K(+)-ATPase pump activity, as measured by the uptake of Rubidium-86 (86Rb+), is significantly higher in Bcl-2 overexpressing PW cells than in control PW cells, and that pump activity following irradiation with doses > or = 500 cGy was reduced to a lesser extent in the Bcl-2 transfectants than in the control cells. When PW-Bcl-2 cells were incubated with a dose of ouabain (1 microM) that decreased pump activity significantly, but did not induce PCD, the previously reported protection from radiation-induced PCD associated with overexpression of Bcl-2 no longer existed. In order to demonstrate that reactive oxygen species (ROS) affected Na+/ K(+)-ATPase pump activity, cells were incubated with N-acetyl cysteine (NAC) prior to irradiation, or treated with the ROS generating drug buthionine sulphoxamine (BSO). 86Rb+ uptake was significantly higher in irradiated cells incubated with NAC compared to cells irradiated in the absence of NAC, while BSO resulted in lower levels of 86Rb+ uptake, suggesting that the effects of radiation on the Na+/K(+)-ATPase pump were due to ROS. Furthermore, the resting cell membrane potential of cells exposed to NAC were slightly hyperpolarized compared to control PW cells, whereas cells exposed to BSO were depolarized in comparison to control PW cells. In summary, this data suggests that Bcl-2 affects Na+/K(+)-ATPase pump activity, which is associated with the resting membrane potential and the level of susceptibility to radiation-induced PCD.

Apoptosis↗
PubMed1997

Isolated tears of the triangular fibrocartilage: management by early arthroscopic repair.

To evaluate the efficacy of arthroscopic repair of the triangular fibrocartilage complex (TFCC) tears treated within 4 months after injury, functional outcome after repair was determined following arthroscopic repair in 24 patients. The patients' average age was 31 years (range, 22-38 years); the average follow-up period was 34 months (range, 26-48 months). All patients had wrist pain limiting their participation in work prior to surgery. Patients with central attrition tears identified by arthroscopy were excluded from the study. Twenty-three patients had a preoperative arthrogram. Twelve of the patients with positive arthrogram findings had an avulsion of the TFCC from the sigmoid notch (Palmer type 1D tears). Of the eleven patients with negative arthrograms, 10 had ulnar tears in capsular attachments of the TFCC. The ulna variance averaged 0.2 mm +/- 0.6 mm. Separate arthroscopic techniques were developed for reattaching the TFCC to the radius (nine patients) versus to the peripheral capsule on the volar or ulnar side of the wrist (eight patients). Postoperatively, there was a significant relief of pain (p < .01). Postoperative range of motion averaged 89% +/- 9% SD of the contralateral side, and grip strength averaged 85% +/- 20% SD of the contralateral side. Thirteen of the 19 patients returning to work did so in their original jobs.

Adult↗
PubMed1997

Failure of cast immobilization for thumb ulnar collateral ligament avulsion fractures.

To determine if small avulsion fractures of the thumb ulnar collateral ligament (UCL) with minimal (< or = 2.0 mm) displacement can successfully be treated by cast immobilization, the authors reviewed 9 patients with minimally displaced fractures initially treated by casting. Despite immobilization within an average of 2 days of the initial injury (range, 0-6 days), a minimum of 6 weeks of immobilization in a cast, and adequate rehabilitation, all 9 patients had persistent thumb pain, especially with activities requiring strong pinch. After undergoing open reduction and internal fixation, the patients had relief of thumb pain and pinch strength improved from 36% of the contralateral side to 89% (p < .01). Grip strength increased from 77% to 93% (p < .05), but the ranges of motion of the thumb metacarpophalangeal and interphalangeal joints were not significantly altered. Minimally displaced UCL avulsion fractures frequently have significant rotation that prevents successful fracture healing even with prompt cast immobilization.

Adolescent↗