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Biomedical subjects

Q Nguyen

Publications and source records attributed to Q Nguyen.

At least 37 records · Page 2Linked to original sources
PubMed1998

Yeast adaptation on softwood prehydrolysate.

Several strains and genera of yeast, including Saccharomyces cerevisiae D5A, Pachysolen tannophilus, S. cerevisiae K-1, Brettanomyces custersii, Candida shehatae, and Candida acidothermophilum, are screened for growth on dilute acid-pretreated softwood prehydrolysate. Selected softwood species found in forest underbrush of the western United States, which contain predominantly hexosan hemicellulose, were studied. This phase of the work emphasized debarked Douglas fir. The two best initial isolates were gradually selected for improved growth by adaptation to increasing prehydrolysate concentrations in batch culture, with due consideration of nutrient requirements. Microaerophilic conditions were evaluated to encourage tolerance of pretreatment hydrolysate, as well as ethanol product. Adaptation and simultaneous saccharification and fermentation (SSF) results are used to illustrate improved performance with an adapted strain, compared to the wild type.

Adaptation, Physiological↗
PubMed1998

A time-motion study of the emergency medical services turnaround interval.

STUDY OBJECTIVE: Because overall EMS system response depends on ambulance availability, we conducted a prospective study of the EMS turnaround interval. This interval represents the time elapsed from ambulance arrival at the hospital until the ambulance reports back in service. METHODS: An on-site observer, while monitoring EMS radio traffic, recorded the delivery and recovery activities of personnel from a large urban EMS system at a university hospital emergency department. System policy permitted a maximum turnaround interval of 30 minutes. Prospectively defined subintervals were analyzed. RESULTS: A convenience sample of 122 patient deliveries was collected. Observed and radio-reported times of arrival at the hospital differed by -1'24" to +11'08". In 18.9% of cases, arrival was reported on radio more than 5 minutes after the observed arrival. Time from arrival to removal of the patient from the ambulance averaged 59" (range, 13" to 2'53"), and time from patient removal to emergency department entry averaged 42" (range, 10" to 5'22"). Time from ED entry to placement of the patient on an ED bed averaged 2'11" (range, 33" to 9'35"). Although the mean interval for the verbal report to ED staff was 33" (range, 13" to 2'53"). it was 15" or less in 36% of cases. Writing the ambulance call report took an average of 17'12" (range, 5'20" to 52'11"). The mean time off radio was 29'51" (range, 11'43" to 53'37"), and the mean time the ambulance was actually at the ED was 30'01" (range, 11'25" to 1 degree 17'53"). Observed and radio-reported ambulance departure times differed by -4'31" to +23'32". In 22% of cases, departure times differed by -4'31" to +23'32". In 22% of cases, departure was reported by radio more than 5' after actual departure. CONCLUSION: In this system, ambulance call report documentation required the greatest subinterval of turnaround interval. The turnaround interval and its subintervals varied widely, and radio contact times correlated poorly with observed times at the ED. Attempts at improvement of overall system response through active management of the turnaround interval may be frustrated by reliance on radio-reported availability.

Ambulances↗
PubMed1997

c-myc-Dependent hepatoma cell apoptosis results from oxidative stress and not a deficiency of growth factors.

Expression of c-myc regulates apoptotic cell death in the human hepatoma cell line HuH-7 during culture in serum-free medium (SFM) plus zinc. To understand the mechanism of this c-myc effect, the ability of various serum-contained factors to prevent apoptosis was determined. Apoptosis was not inhibited by growth factors and was even accelerated by supplementation with insulin-like growth factor I or insulin. Cell death was prevented by SFM supplementation with the amino acid glutamine but not serine or asparagine. Improved cell survival with glutamine was associated with increased levels of glutathione (GSH). In HuH-7 cells cultured in SFM plus zinc, c-myc expression led to decreased levels of GSH, and elevated intracellular levels of hydrogen peroxide (H2O2). Cell death induced by c-myc expression was inhibited by the addition of catalase or dimethyl sulfoxide, a hydroxyl radical scavenger, or by increased intracellular expression of catalase. In contrast to findings in fibroblasts, c-myc-dependent apoptosis during serum deprivation in HuH-7 hepatoma cells was unrelated to a loss of growth factors. Apoptosis resulted from H2O2-mediated oxidative stress with associated glutamine dependent intracellular GSH depletion.

Apoptosis↗
PubMed1996

Effects of combining propofol and alfentanil on ventilation, analgesia, sedation, and emesis in human volunteers.

BACKGROUND: Propofol and alfentanil frequently are administered together for intravenous sedation. This study investigated pharmacokinetic and pharmacodynamic interactions between propofol and alfentanil, at sedative concentrations, with specific regard to effects on ventilation, analgesia, sedation, and nausea. METHODS: Ten male volunteers underwent steady-state infusions on 3 separate days consisting of propofol alone, alfentanil alone, or a combination of the two. Target plasma concentrations for propofol were 150, 300, and 600 ng/ml for 1 h at each concentration; for alfentanil it was 40 ng/ml for 3 h. Assessment included serial measurements of (1) ventilatory function (minute ventilation, carbon dioxide production, end-tidal carbon dioxide, ventilatory response to rebreathing 7% CO2); (2) analgesia (subjective pain report in response to graded finger shock and evoked potential amplitude); (3) sedation (subjective rating, observer scores, and digit symbol substitution test); (4) nausea (visual analog scale, 0-100 mm). RESULTS: During combination treatment, propofol plasma concentration was 22% greater than during propofol alone using replicate infusion schemes (P < 0.009). End-tidal carbon dioxide was unchanged by propofol, and increased equally by alfentanil and alfentanil/propofol combined (delta end-tidal carbon dioxide 7.5 and 6.2 mmHg, respectively). Analgesia with propofol/alfentanil combined was greater than with alfentanil alone. (Pain report decreased 50% by PA vs. 28% for alfentanil, P < 0.05). Sedation was greater with propofol/alfentanil combined than with alfentanil or propofol alone (digit symbol substitution test 30 for propofol/alfentanil combined vs. 57 for alfentanil, and 46 for propofol, P < 0.05). Nausea occurred in 50% of subjects during alfentanil, but in none during propofol/alfentanil combination treatment. CONCLUSIONS: The combination of propofol and alfentanil produced greater sedation and analgesia than that with either drug alone. Propofol offset the emetic effects of alfentanil. Equivalent depression of the carbon dioxide response curve, and elevation of end-tidal carbon dioxide occurred with propofol/alfentanil combined and alfentanil.

Adult↗
PubMed1996

Cervical thymic cyst: case reports and review of the literature.

Due to its rarity, cervical thymic cyst is seldom included in the differential diagnosis of a neck mass. Approximately 80 cases have been reported thus far, and most of these cases have occurred asymptomatically in children and adults. Only 5 cases have involved patients younger than 1 year of age. The authors report four new patients with thymic cyst in the neck. Two of the patients were newborns in whom the cyst caused airway obstruction and dysphagia. All four patients underwent successful resection of the lesions, with complete resolution of symptoms. The embryology, histopathology, and differential diagnosis of cervical thymic cysts are also reviewed. The authors recommend that despite its infrequent occurrence cervical thymic cyst should be considered in the evaluation of neck masses in children.

Child, Preschool↗
PubMed1996

Decision rules of listeners in spectral-shape discrimination with or without signal-frequency uncertainty.

A correlation technique was used to assess the decision rules of three listeners in two cases of spectral-shape discrimination tasks. In one case the signal frequency was fixed, and in the other it was randomly varied within each block of trials. In order to estimate the decision rule of the listeners, the experimenter superimposed random level perturbations on each frequency component upon each stimulus presentation. Over many trials, correlation coefficients were computed between the random perturbations and the binary responses of the listeners, and were expressed as a function of signal level. For both the fixed- and random-signal cases, the measured correlation functions were in reasonably good agreement with those predicted based on the likelihood-ratio decision rules. Thus the listeners appeared to use information nearly optimally in discriminating spectral shapes. This investigation demonstrated that the correlation technique can be used to reveal the decision rules for cases where the decision statistics are nonlinear functions of the observations.

Auditory Perception↗
PubMed1996

Phase independence of pitch produced by narrow-band sounds.

Three listeners matched the pitch of a simple tone to that of narrow-band complex signals having different phases. The pitch matches were independent of the phases; the frequency of the simple tone approximately equaled the center of gravity of the power spectrum of each complex signal. This result is inconsistent with a model that calculates the pitch of a waveform as the average of instantaneous frequency weighted by the envelope of the waveform.

Humans↗
PubMed1996

Induction of hepatoma cell apoptosis by c-myc requires zinc and occurs in the absence of DNA fragmentation.

Since c-myc expression is increased during apoptosis in toxin-induced liver injury in vivo, the role of c-myc in liver cell apoptosis was investigated. The human hepatoma cell line HuH-7, which constitutively expresses c-myc, was stably transfected with sense and antisense c-myc expression vectors under the control of the zinc-inducible metallothionein promoter. None of the three cell types (wild-type, sense c-myc, or antisense c-myc) underwent apoptosis when cultured in serum-free medium (SFM). With the addition of SFM plus 37.5 microM zinc, wild-type and sense c-myc-expressing cells underwent rapid cell death, whereas antisense c-myc-expressing cells exhibited increased survival. This cell death had the light, fluorescent, and electron microscopic appearance of apoptosis, but did not result in DNA fragmentation. This apoptosis could be terminated by the addition of medium containing 2% fetal calf serum or the overexpression of bcl-2 but not by supplementation with specific growth factors. Altering c-myc expression did not affect cellular metallothionein mRNA levels or the rate of cell death from copper or cadmium. The requirement for zinc and absence of DNA fragmentation in c-myc-induced hepatoma cell apoptosis under serum-free conditions provides further evidence of the complex regulation of apoptosis in different cell types.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Imaging and quantitation of chemiluminescence using photoexcitable storage phosphor screen.

A novel storage phosphor (SrS:Ce,Sm) imaging screen optimized for the detection of luminescence has been developed. When coupled with an appropriate scanning system, this screen exhibits the following characteristics: (i) a range of visible light detection between 400 and 500 nm with a peak response at 450 nm; (ii) sensitivity comparable to X-ray film; (iii) 200-microns resolution; (iv) linear dynamic range greater than four orders of magnitude; and (v) a uniformity of response of +/- 1.32% coefficient of variation. These features facilitate the detection and accurate quantitation of light radiation produced from the enzymatic catalysis of chemiluminescent substrates such as 1,2-dioxetanes and luminol. Its suitability for chemiluminescent applications is demonstrated by the analysis of cosmid hybridization and enzyme-linked immunosorbent assay samples.

Alkaline Phosphatase↗
PubMed1995

Modulation of GABAA receptor binding in human brain by neuroactive steroids: species and brain regional differences.

Allosteric modulation by neuroactive steroids of radioligand binding sites on the GABAA receptor complex was demonstrated by autoradiography in vitro in several regions of human brain and the effects compared to those in rat brain. Comparing human and rat, two steroids known to be active in enhancing GABA-mediated postsynaptic inhibition, 5 alpha-pregnane-3 alpha,21-diol-20-one (tetrahydro-deoxycorticosterone, THDOC) and alphaxalone (5 alpha-pregnane-3 alpha-hydroxy-11,20-dione), allosterically inhibited [35S]T-BPS binding to the picrotoxin/convulsant site in both species in several regions including the hippocampus. Unlike rat, human brain binding of [3H]flunitrazepam to the benzodiazepine site was not enhanced by alphaxalone (at any concentration), but was unaffected in many regions and inhibited in others. Binding of [3H]muscimol to high and low affinity GABA sites were enhanced by both steroids in all tested regions of rat brain, although to varying degrees. However, several lobes of human cortex showed no modulation of muscimol binding by either steroid, and THDOC, but not alphaxalone, inhibited in some areas. Comparing regions, THDOC at high concentrations (10 microM) enhanced in human frontal lobe and primary sensory and motor cortex, with greater effect in deep layers than superficial. This steroid had no effect in other parts of parietal lobe and inhibited muscimol binding in temporal lobe, primary visual cortex, and other parts of occipital lobe. Concentration-dependence curves for THDOC showed regional variation, e.g., in the hippocampal formation and surrounding neocortex. These regional and species differences are consistent with the existence of multiple GABAA receptor subtypes that differ in pharmacology. This heterogeneity provides both the opportunity and the difficulty of targeting clinically useful medications such as antiepileptic drugs to the appropriate human brain regions, and the species differences in regional subtype expression suggest caution in use of animal models.

Autoradiography↗
PubMed1995

Laser resurfacing in pigmented skin.

BACKGROUND: Laser skin resurfacing is a very promising new treatment for solar elastosis and acne scars. The Ultrapulse carbon dioxide (CO2) laser and the SilkTouch flashscanner allow precise depth control and char-free ablation. Earlier studies have been done mainly on Caucasian skin types I and II, but very little data were available on pigmented skin. OBJECTIVE: The purpose of this study is to assess the efficacy and safety of laser skin resurfacing in skin types III and IV. METHODS: Thirty Asian and Hispanic patients were treated for facial rhytides and acne scars. All patients were instructed to use tretinoin cream 0.05%, hydroquinone 5%, and desonide 0.1% cream nightly for 2-4 weeks prior to the laser treatment. The Ultrapulse 5000C CO2 laser with the Truespot 3-mm collimated handpiece at the setting of 250-450 mJ per pulse, or the Silk-Touch flashscanner at the setting of 5-7 W, 0.2-second pulse duration, and 4-mm (M) spot size, was used. Patients were evaluated clinically, and global response was assessed by both clinicians and patients. RESULTS: The facial rhytides and acne scars improved 25-50% in all patients after one laser treatment. The most common side effects were persistent erythema that resolved on the average of 6 weeks. Hyperpigmentation occurred, but was reduced with regular use of tretinoin, hydroquinone, and desonide cream both pre- and postoperatively along with use of broad spectrum sunscreen after treatments. CONCLUSION: Laser skin resurfacing can be used to treat facial rhytides and acne scars in skin phototypes III and IV. When proper pre- and postoperative management is implemented, the risk of dyspigmentation can be reduced.

Acne Vulgaris↗
PubMed1995

Mini-slit graft hair transplantation using the Ultrapulse carbon dioxide laser handpiece.

BACKGROUND: The new Ultrapulse carbon dioxide (CO2) laser technology has added a new dimension to many cosmetic surgery procedures including hair transplantation. Early reports by Unger and David (Laser Hair Transplantation. J Dermatol Surg Oncol 1994;20:515-21) have been encouraging with the potential of minimal bleeding, ease of placing transplanted grafts, and an overall shortened operative time. A 2-mm slit handpiece has been recently created to expedite this procedure. OBJECTIVE: The purpose of this study is to further investigate the use and efficiency of the new Ultrapulse CO2 laser slit handpiece in hair transplants. METHOD: Mini-slit graft hair transplants using the new Ultrapulse CO2 laser slit handpiece were done on 25 patients in 30 transplant sessions. Donor minigrafts were obtained by the strip harvesting technique using a triple-blade scalpel. Approximately 200-400 recipient slits were made with the 2-mm slit handpiece at the laser setting of 350 mJ, 12 W, 0.8 seconds per pulse. RESULTS: All grafts were easily placed into recipient sites with minimal bleeding and charring. The procedure was done in half the time of the conventional non-laser technique. Postoperatively, patients were quite satisfied with little pain and swelling. Histologic exams of the laser-treated slits showed minimal adjacent tissue necrosis. Long-term follow-up visits showed good regrowth of hair in these grafts. CONCLUSION: The new Ultrapulse CO2 laser slit handpiece proved to be an effective tool for mini-slit graft hair transplantation.

Adult↗
PubMed1994

Assessment of the role of the fibronectin-like domain of gelatinase A by analysis of a deletion mutant.

The properties of a deletion mutant delta V191-Q364 of gelatinase A, which represents the removal of the fibronectin-like type II repeats defined by exons 5-7, were compared with those of full-length gelatinase A. Both enzymes underwent self-activation over a similar time course in the presence of 4-aminophenylmercuric acetate. The fully active enzymes had similar kcat/Km values for the cleavage of an octapeptide substrate, but the deletion mutant had 50% of the activity of wild type gelatinase A against beta-casein and 10% of the activity against gelatin. The cleavage pattern for gelatin was similar for both enzymes but differed for type IV collagen. Comparison of the rates of association of the tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2 and their N-terminal domains to both forms of gelatinase indicated that the fibronectin-like domain plays little role in TIMP binding. The deletion mutant failed to bind to collagen, while the wild type gelatinase bound tightly, indicating that the fibronectin-like domain is the sole site of collagen binding. Both gelatinases could be activated by concanavalin A-activated fibroblasts, suggesting that the fibronectin-like domain is not required for the membrane-mediated activation process.

Animals↗
PubMed1994

Different domain interactions are involved in the binding of tissue inhibitors of metalloproteinases to stromelysin-1 and gelatinase A.

The matrix metalloproteinases gelatinase A and stromelysin-1 have definable N-terminal (catalytic) and C-terminal domains. In order to analyze their interactions with the N- and C-terminal domains of the tissue inhibitors of metalloproteinases TIMP-1 and -2, mutants of both the enzymes and the inhibitors were prepared in which the C-terminal domains had been deleted. Since the Ki values for TIMP inhibition of the matrix metalloproteinases are in the picomolar range, it was not possible to measure these accurately within the sensitivity of available activity assays. Rate constants for the association of the wild-type proteins were therefore determined and systematically compared with those for the deletion mutants. It was found that TIMP-1 binds more rapidly than TIMP-2 to stromelysin-1 and that the C-terminal domain of the enzyme does not affect the rate of association of enzyme and inhibitor. This is in contrast to gelatinase A, where the C-terminal domain has been shown to play an important role in increasing the rate of complex formation with the TIMPs (Willenbrock et al., 1993). The TIMPs are also comprised of an N- and C-terminal domain. By deletion mutagenesis, we found that the C-terminal domain of both TIMPs contributed less to the rate of complex formation with stromelysin-1 than to that with gelatinase A. Hybrids of the N- and C-terminal domains of gelatinase A and stromelysin-1 were prepared and used to analyze further the differences in domain interactions with the TIMPs. They demonstrated that the interactions between the C-terminal domains of enzyme and inhibitor can occur irrespective of the nature of the N-terminal domain. We can conclude that the TIMPs have two major binding regions which associate in different ways with the domains of the enzymes gelatinase A and stromelysin-1. The N-terminal domains of the TIMPs bind to the enzyme catalytic domains to inhibit activity. The TIMP C-terminal domain acts to increase the association rate constant by binding to the N-terminal domain of stromelysin or the C-terminal domain of gelatinase A.

Amino Acid Sequence↗
PubMed1994

Purification and characterization of insecticidal toxins from venom glands of the parasitic wasp, Bracon hebetor.

The potency of venom from Bracon hebetor against lepidopterous larvae has been known for over 40 years, but previous attempts to purify and characterize individual protein toxins have been largely unsuccessful. Three protein toxins were purified from venom of this small parasitic wasp and the amino acid sequences of 22-31 consecutive residues at the amino-terminus were determined. These relatively large toxins (apparent molecular mass 73 kDa) were labile under many isolation techniques, but anion-exchange chromatography allowed purification with retention of biological activity. Two purified toxins were quite insecticidal (LD50 < 0.3 microgram/g) when injected into six species of lepidopterous larvae. On a molar basis, one toxin (Brh-I) has the highest known biocidal activity against Heliothis virescens (LD50 = 2 pmol/g).

Amino Acid Sequence↗
PubMed1993

Matrix metalloproteinases cleave at two distinct sites on human cartilage link protein.

The actions of human recombinant stromelysins-1 and -2, collagenase, gelatinases A and B and matrilysin on neonatal human proteoglycan aggregates were examined. With the exception of gelatinase B, aggrecan was degraded extensively by most metalloproteinases studied, whereas link protein showed only limited proteolysis. Sequencing studies of modified link protein components revealed that stromelysins-1 and -2, gelatinases A and B and collagenase cleaved specifically between His16 and Ile17, and matrilysin, stromelysin-2 and gelatinase A cleaved between Leu25 and Leu26. Cleavage at the former bond generated a link protein component with the same N-terminus as that isolated from newborn human cartilage. Based on previously determined in situ cleavage sites it is evident that matrix metalloproteinases are not solely responsible for the accumulation of link protein degradation products in adult human cartilage, indicating that additional proteolytic agents are involved in the normal catabolism of human cartilage matrix.

Aggrecans↗