Search PubMed⌕ Search

Biomedical subjects

L T Nguyen

Publications and source records attributed to L T Nguyen.

At least 73 records · Page 4Linked to original sources
PubMed1998

Time course of the regenerative response in bupivacaine injured orbicularis oculi muscle.

Local anesthetics, particularly bupivacaine, are known to be myotoxic to skeletal muscle. Injury is followed by satellite cell mediated regeneration. The eyelid is a common site for the injection of local anesthetics. Due to the complex anatomy of this region and the unique properties of facial musculature compared to limb skeletal muscle, the response of the orbicularis oculi to local injection of bupivacaine was examined to determine the time course of maximum satellite cell activation and division. The lower eyelids of rabbits were injected with two doses of a combination of bupivacaine and hyaluronidase, spaced 18 h apart. To assess the time course of satellite cell division, bromodeoxyuridine (BrdU) was injected immediately or, 1, 2, 3, 6 or 13 days after the second bupivacaine injury. The rabbits were sacrificed 24 h later. The eyelids were prepared for immunohistological examination and morphometric analysis of the presence of CD11-positive monocytes, neutrophils and macrophages, MyoD expression in satellite cells and/or myoblasts, and co-expression of BrdU and the developmental myosin heavy chain isoform. One day after bupivacaine injury of the orbicularis oculi, there was a large influx of CD11-positive cells which gradually decreased over time. Maximum activation of satellite cells, as defined by MyoD expression, occurred 2 and 3 days after the injury. Using double labeling techniques, the peak of BrdU incorporation occurred on day 3 and was identified in developmental myosin co-labeled cells 4 days after injury. The peak of satellite cell activation and division occurred 3 days after bupivacaine induced injury, as demonstrated by both MyoD expression and after pulse labeling with BrdU as identified in double labeled cells positive for BrdU and the developmental myosin heavy chain isoform. The process of regeneration in this muscle extended beyond the duration of this study. Muscle fibers remained small in cross-sectional area and positive for developmental myosin 2 weeks after injury, at a time when the fiber number had reached control, uninjured levels.

Animals↗
PubMed1998

Mechanism-based inactivation of human cytochrome P450 3A4 by grapefruit juice and red wine.

Grapefruit juice is well documented to cause clinically significant increases in the plasma concentrations of many therapeutic agents. These interactions are believed to be mediated via inhibition of intestinal cytochrome P-450 3A4 (CYP3A4) by flavonoids and/or other chemicals in grapefruit juice, although the mechanism of that inhibition has not been fully characterized. Like grapefruit juice, red wine contains large amounts of flavonoids and other xenobiotics which could also mediate CYP3A4 inhibition. In this study, we investigated the mechanism of inhibition of CYP3A4 by grapefruit juice and also examined the ability of red wine to inhibit this enzyme. Both red wine and grapefruit juice potently inhibited CYP3A4 activity in a concentration-dependent manner. At 8% of natural strength, enzyme activity was inhibited almost 90 and 84%, respectively, by grapefruit juice and red wine. In contrast, white wine did not appreciably inhibit CYP3A4 activity. Grapefruit juice irreversibly inactivated CYP3A4 in a time- and NADPH-dependent manner. The rate of inactivation mediated by grapefruit juice was similar to that mediated by troleandomycin, a potent mechanism-based inhibitor of CYP3A4. Red wine also inactivated CYP3A4 but at a rate approximately 16% that of grapefruit juice. Inhibition of CYP3A4 by red wine is primarily reversible in nature. The clinical implications of this research are discussed.

Beverages↗
PubMed1998

Aquagenic urticaria: report of a case and review of the literature.

OBJECTIVE: To present a case of aquagenic urticaria and to review the literature regarding this very rare physical urticaria. METHOD: We described the clinical history of a patient with aquagenic urticaria. A water challenge test was performed, with plasma histamine levels measured before and after the challenge. RESULT: Our patient presented with a history of severe itching and wheals within five minutes of contact with water, regardless of its temperature or source (sea or tap water). A water challenge produced hives but serum histamine levels did not change. Prophylaxis with antihistamine or anticholinergic medications was not effective. CONCLUSION: Exposure to water can cause urticaria in susceptible patients and antihistamine and anticholinergic medication may not prevent the reaction. The mechanism of this phenomenon remains poorly understood.

Adult↗
PubMed1998

Microfluorometric analyses of glycogen in freshly dissected, single skeletal muscle fibres of the cane toad using a mechanically skinned fibre preparation.

The main objective of this study was to analyse glycogen in single muscle fibres, using a recently developed microfluorometric method which detects subpicomol amounts of NADPH, glucose and glycogen (as glucosyl units) (detection limit 0.16-0.17 pmol in a 25 nl sample) without fluorochrome amplification. The fibres were freshly dissected from the twitch region of the iliofibularis muscle of the cane toad (Bufo marinus), and were mechanically skinned under paraffin oil to gain access to the intracellular compartments. The results show that (1) glycogen concentrations in toad skeletal muscle fibres range between 25.8 and 369 mmol glucosyl units/litre fibre volume; (2) there is a large variation in glycogen content between individual fibres from the iliofibularis muscle of one animal; (3) there are seasonal differences in the glycogen content of toad single muscle fibres; (4) the total amount of glycogen in single muscle fibres of the toad does not decrease significantly when storing the tissue, under paraffin oil, at 20-25 degree C for up to 6 h or at 4 degree C for up to 24 h; and (5) 15-26% of fibre glycogen can be washed in an aqueous solution at pH 5-7, within 5 min, while 74-85% of fibre glycogen remains associated with the washed skinned fibre, even after 40 min exposure of the skinned fibre preparation to the aqueous environment. The retention of most glycogen in the fibre preparation after mechanical removal of the plasma membrane and extensive washing indicates that in toad skeletal muscle fibres the largest proportion of glycogen is tightly bound to intracellular structures. The results also show that the skinned muscle fibre preparation is well suited for microfluorometric glycogen determination, since low molecular weight non-glycogen contributors to the fluorescence signal can be removed from the myoplasmic space prior to the glycogen hydrolysis step.

Animals↗
PubMed1998

Doxorubicin chemomyectomy is enhanced when performed two days following bupivacaine injections: the effect coincides with the peak of muscle satellite cell division.

PURPOSE: Doxorubicin is effective in permanently removing muscle after direct injection into the eyelid for treatment of blepharospasm and hemifacial spasm. However, patients often require two or more injection series before full abatement of their spasms is achieved. Local anesthetics cause muscle necrosis, followed by regeneration, a process that requires activation and division of muscle satellite cells. This study examined whether the muscle toxicity of doxorubicin could be amplified by injection of doxorubicin into the eyelid of rabbits 2 days after a local anesthetic injury, perhaps exploiting the toxic effects of doxoribicin on satellite cells at the peak time of their division after injury. METHODS: Rabbit eyelids received two series of injections of bupivacaine and hyaluronidase spaced 18 hours apart. Two days later, the eyelids were injected with either 0.5 or 1 mg doxorubicin. Animals were monitored daily for onset and duration of skin injury. After 1 month, the eyelids were assessed for muscle loss using histologic and morphometric techniques. RESULTS: Injection of doxorubicin during the peak of satellite cell activation and division 2 days after injury significantly increased muscle loss over doxorubicin alone. This treatment did not result in increased skin injury compared with doxorubicin alone. CONCLUSIONS: Permanent muscle loss was increased when doxorubicin was injected at the peak of satellite cell division 2 days after injury of the muscle with bupivacaine in rabbit eyelid, taking advantage of the antimitotic effects of doxorubicin on satellite cell division during the period of active regeneration. When local anesthetic injection immediately preceded the doxorubicin injection, increased myotoxicity was not seen. The injection of doxorubicin into muscle 2 days after a previous injury maximizes muscle loss. The increased muscle loss provided by this double treatment may decrease the number of injection visits required by blepharospasm and hemifacial spasm patients during their course of treatment, thus reducing the number of patients with side effects, which increases with repeated exposures of the eyelid to doxorubicin.

Anesthetics, Local↗
PubMed1998

Interferon-gamma-inhibitory oligodeoxynucleotides alter the conformation of interferon-gamma.

The aptamer mechanism of action involves the direct interaction of oligonucleotide with protein and is responsible for the biological effects of many pharmacologically active oligodeoxynucleotides. In the work reported here, we have determined the effects of aptamers on the secondary, tertiary, and quaternary structures of the proteins with which they interact using interferon-gamma and the interferon-gamma-inhibitory aptamer oligonucleotide, 5'-GGG GTT GGT TGT GTT GGG TGT TGT GT, as a model system. CD, fluorescence spectroscopy studies, and antibody binding studies in this system demonstrate that the interferon-gamma-inhibitory aptamer oligonucleotide causes significant changes in secondary and tertiary structures of interferon-gamma. These structural changes do not result in, or resemble, protein denaturation or aggregation, and the results suggest that aptamer oligodeoxynucleotides can significantly alter the structure of the proteins they interact with.

Circular Dichroism↗
PubMed1997

Empyema thoracis in children: a 26-year review of the Montreal Children's Hospital experience.

The appropriate management of pediatric empyema thoracis remains controversial. The authors reviewed 47 cases of empyema thoracis over a 26-year period. The management of empyema included initial diagnostic thoracentesis and classification as acute, fibropurulent, or chronic. If the empyema was "acute," therapeutic tap, tube thoracostomy, or no surgical intervention was performed. "Fibropurulent" empyemas were uniformly treated with tube thoracostomy. The lung was decorticated when the empyema was encased by a thick peel, had recurred and was multiloculated, was refractory and the patient remained clinically unwell, or had occurred as a complication of previous thoracotomy. All patients with acute empyemas responded to antibiotics irrespective of drainage (average duration of fever, 17 days; average stay in hospital, 27 days). Of the fibropurulent empyemas in our review, complete drainage was attained in seven of 39 (18%), and decortication was not required in any empyema that was completely drained. Loculations persisted in 25 of 39 (64%) after tube thoracostomy but nonetheless resolved. The remaining seven of 39 (18%) with persistent loculations required formal decortication. Of the patients with fibropurulent empyemas that responded to tube thoracostomy, the average duration of fever was 13 days and hospitalization, 23 days. Of those requiring decortication the average duration of fever was 24 days and hospitalization, 40 days. These results will allow a baseline for comparison of new strategies (fibrinolytics and early thoracoscopy) that may reduce days of fever, hospitalization, and risk of formal decortication.

Adolescent↗
PubMed1997

Site-specific thrombin receptor antibodies inhibit Ca2+ signaling and increased endothelial permeability.

Thrombin receptor is activated by thrombin-mediated cleavage of the receptor's NH2 terminus between Arg-41 and Ser-42, generating a new NH2 terminus that functions as a "tethered ligand" by binding to sites on the receptor. We prepared antibodies (Abs) directed against specific receptor domains to study the tethered ligand-receptor interactions required for signaling the increase in endothelial permeability to albumin. We used polyclonal Abs directed against the peptide sequences corresponding to the extracellular NH2 terminus [residues 70-99 (AbDD) and 1-160 (AbEE)] and extracellular loops 1 and 2 [residues 161-178 (AbL1) and 244-265 (AbL2)] of the seven-transmembrane thrombin receptor. Receptor activation was determined by measuring changes in cytosolic Ca2+ concentration ([Ca2+]i) in human dermal microvascular endothelial cells (HMEC) loaded with Ca(2+)-sensitive fura 2-acetoxymethyl ester dye. The transendothelial 125I-labeled albumin clearance rate (a measure of endothelial permeability) was determined across the confluent HMEC monolayers. AbEE (300 micrograms/ml), directed against the entire extracellular NH2-terminal extension, inhibited the thrombin-induced increases in [Ca2+]i and the endothelial 125I-albumin clearance rate (> 90% reduction in both responses). AbDD (300 micrograms/ml), directed against a sequence within the NH2-terminal extension, inhibited 70% of the thrombin-induced increase in [Ca2+]i and 60% of the increased 125I-albumin clearance rate. AbL2 (300 micrograms/ml) inhibited these responses by 70 and 80%, respectively. However, AbL1 (300 micrograms/ml) had no effect on either response. We conclude that NH2-terminal extension and loop 2 are critical sites for thrombin receptor activation in endothelial cells and thus lead to increased [Ca2+]i and transendothelial permeability to albumin.

Antibodies↗
PubMed1996

Recurrent intussusception: safe use of hydrostatic enema.

Recurrent intussusception (RI) occurs in 5% to 8% of patients with intussusception. The authors reviewed their 15-year experience to better define the management of RI. Among 258 patients, 28 (10.8%) had episodes of RI (37 episodes altogether). Twenty-two patients had a single recurrence, four had double recurrence, one had triple recurrence, and one had quadruple recurrence. RI and non-RI patients were compared with respect to symptoms. The incidence of vomiting and bloody stools was significantly lower in the RI group. Ten percent of RI patients had lead points. Thirty percent of RI episodes occurred within 24 hours, and 74% occurred within 6 months. The success rate of hydrostatic enema reduction for recurrent episodes was 62.8%, which is comparable to that for the initial episode (68.9%). Among patients with previous surgery, 36.3% of enemas were successful; after previous enema reduction, 75% were successful. There was no complication related to the enema. Enema reduction is safe and has a good success rate in cases of RI, even after previous surgical reduction.

Chi-Square Distribution↗
PubMed1996

Radiation inactivation and in situ renaturation of protein tyrosine kinases reveal a major 50-kDa enzyme as part of a membrane complex present in dividing but not in resting prostatic epithelial cells.

Because protein tyrosine kinases play a crucial role in the regulation of cell division and carcinogenesis, we have herein measured such enzyme activities (specific activity and subcellular distribution) and compared their characteristics with respect to hydrodynamic properties and radiation inactivation sizes as well as renaturation after electrophoresis in denaturing conditions in canine prostatic epithelial cells either in a resting (freshly isolated) or in a dividing (cultured cells) state. In quiescent cells, most protein tyrosine kinase activity was expressed by soluble proteins with a Stokes' radius (Rs) of 3.05 nm, a sedimentation coefficient (S20,w) of 4.0 S, and a molecular mass of 50 kDa. By contrast, in dividing cells (three days in primary culture), the specific activity was higher and the enzyme was mainly membrane bound. The use of a detergent (Triton X-100) allowed the extraction of most of that enzyme; its partial specific volume, S20,w and Rs were then 0.883 cm3/g, 4.0 S, and 5.6 nm, respectively, hence yielding a molecular mass of 215 kDa, which decreased to 125-145 kDa when corrected for detergent binding. Probing these chromatography-peak fractions, 50 kDa from cytosol of resting cells and 215 kDa from membrane extracts of dividing cells, with a phosphotyrosine antibody following their incubation with ATP and electrophoresis in denaturing conditions revealed the presence of a common 50-kDa phosphotyrosylated protein along with three other bands (130, 75, and 40 kDa) in the high-Mr peak of enzyme. However, the radiation inactivation size for protein tyrosine kinases expressed in both resting and dividing cells were similar, 47.2 +/- 8.7 and 44.5 +/- 6.1 kDa, respectively. Furthermore, by renaturation after electrophoresis in denaturing conditions, major protein tyrosine kinase polypeptides of 50 kDa were identified in both cell populations. Taken together, these results indicate that, in dividing prostatic epithelial cells, membrane-bound protein tyrosine kinases of low molecular weight with properties similar to those of monomeric soluble forms present in quiescent cells are part of high-molecular weight complexes. This activation process may be critical for hormone-independent proliferation of prostatic epithelial cells.

Animals↗
PubMed1996

Regulation and activation of focal adhesion kinase and paxillin during the adhesion, proliferation, and differentiation of prostatic epithelial cells in vitro and in vivo.

Focal adhesion kinase (pp125FAK) is a nonreceptor protein tyrosine kinase transducing signals initiated through integrin activation triggered by cell/extracellular matrix (ECM) interactions. To examine its role in epithelial cell adhesion, proliferation, and differentiation, we have studied pp125FAK expression, activity, and association with paxillin in two canine prostate models in which these functions can be selectively regulated: in vitro by vitronectin (VN) and serum factors, and in vivo by sex steroids. Kinetic studies revealed that the adhesion and spreading of prostatic epithelial cells in primary culture was regulated by serum VN and a natural ECM containing VN produced by prostate cells. While barely detectable in freshly isolated prostate cells, proliferating cells, after 72 h in culture, expressed higher levels of FAK mRNA (8-fold), pp125FAK (50-fold), and paxillin (50-fold). In prostate cells with a reduced growth rate after 2 weeks in culture, we observed a decrease in pp125FAK (4-fold) and its transcript (3-fold), but no change in paxillin. In vivo, both proteins were undetectable in normal and hyperplastic glands composed of a well differentiated epithelium, and in prostates restored by androgen supplementation. In contrast, pp125FAK and paxillin were up-regulated by androgen deprivation (castration) and further increased by estrogen treatment, which yielded metaplastic prostates mostly composed of proliferating basal epithelial cells. Moreover, both proteins were constitutively phosphorylated on tyrosine in the metaplastic prostate, as well as in proliferating cultured cells. Together, these results demonstrate that pp125FAK expression is regulated at the protein and mRNA levels and forms active signaling complexes with paxillin when epithelial cells in contact with ECM proteins are induced to proliferate in vivo and in vitro.

Amino Acid Sequence↗
PubMed1995

Purification and characterization of a novel valine dehydrogenase from Streptomyces aureofaciens.

The first valine dehydrogenase of S. aureofaciens had been described (Vancurová, I., Vancura, A., Volc, J., Neuzil, J., Flieger, M., Basarová, G. and Bĕhal, V. (1988) J. Bacteriol. 170, 5192-5196). In the present work, a second valine dehydrogenase was detected and purified by hydrophobic and fast protein liquid chromatographies. The enzyme has a relative molecular mass (M(r)) of 240,000 and is composed of 6 identical subunits, each of M(r) 41,000. In the presence of NAD, the enzyme catalyzes the reversible deamination of several branched- and straight-chain amino acids. The enzyme activities with L-2-aminobutyrate and deamino-NAD+ are markedly higher than those with L-valine and NAD+, respectively. The enzyme synthesis is significantly induced by L-valine but severely repressed by ammonia. Molecular and catalytic properties of the enzyme distinguish it from the other described valine dehydrogenases. The results directly demonstrate the presence of two valine dehydrogenases in a single Streptomyces species.

Amino Acid Oxidoreductases↗
PubMed1995

Diaphragmatic pacing in children with congenital central alveolar hypoventilation syndrome.

BACKGROUND: The purposes of this study were to study congenital central alveolar hypoventilation syndrome (CCAHS), to report the experience at our institution with this disorder, and to describe the surgical technique of diaphragmatic pacing. Three patients are in our diaphragmatic pacing program. They all have CCAHS, documented by means of lack of respiratory drive to hypercapnia and normal peripheral nerve and muscle studies. Two patients have associated Hirschsprung's disease. METHODS: The ages of patients at insertion of bilateral phrenic nerve pacemakers were 1, 2, and 5 years. A bilateral axillary thoracotomy in the third interspace was used in two patients, and anterior thoracotomy was used in one for insertion of electrodes on the phrenic nerves. Counterincisions in both flanks were used in all patients for insertion of the receivers in subcutaneous pockets. RESULTS: In all patients pacing was commenced within 1 week of the surgical procedure, because no primary pacemaker failures occurred. One patient has experienced no failure of the equipment and no infectious complications at 4 years. A second patient has had the pacemakers for 6 months without complications. The third patient underwent placement of bilateral pacemakers in 1984. In this patient a 10-year experience has resulted in subcutaneous implant failure on two separate occasions; also the presence of a staphylococcal empyema necessitated the temporary removal of one phrenic nerve electrode for 6 months, with successful reinsertion. All patients now receive mechanical assisted ventilation when sleeping and phrenic nerve pacing when awake. CONCLUSIONS: Pediatric surgeons should be aware of CCAHS because it may be treated with surgically implanted electrodes that allow for pacing of the diaphragm. The technique has an acceptable complication rate, and it can greatly decrease the impact of the disease on the lifestyle and activity of the patient. CCAHS also may be associated with Hirschsprung's disease.

Artificial Organs↗
PubMed1995

Cement burn.

People working with cement should be aware of the potential for cement burn. The alkalinity of cement is due to the exothermic reaction of calcium oxide with water, which forms calcium hydroxide. Prolonged exposure of the skin to wet cement may result in a caustic burn.

Adult↗
PubMed1995

Reoperation for cysts of the thyroglossal duct.

OBJECTIVE: To determine the causes of recurrence of thyroglossal duct cysts (TDCs). DESIGN: A case series. SETTING: A university-affiliated children's hospital. PATIENTS: Between 1974 and 1990, 121 children were treated for TDCs. They ranged in age from 1 month to 18 years. Of these 121 children, 23 had recurrent TDC. INTERVENTIONS: Simple aspiration of the cyst, incision and drainage, cystectomy without hyoidectomy and the Sistrunk operation. MAIN OUTCOME MEASURES: Initial procedures that led to recurrence and procedures that resulted in cure. RESULTS: Six children had recurrence of TDCs after simple cystectomy without hyoidectomy; all were cured by the Sistrunk operation. Fourteen children with infected cysts initially underwent a variety of procedures with recurrence and were eventually managed by the Sistrunk operation. TDCs recurred in eight of these. Three children without infected cysts had recurrence after the Sistrunk operation. Of 34 TDCs infected initially, 40% recurred, whereas of 87 TDCs that were not infected initially, only 8% recurred. CONCLUSION: Simple cystectomy without hyoidectomy and pre-existing infection are the main causes of recurrence of TDCs.

Adolescent↗