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Biomedical subjects

H Ngo

Publications and source records attributed to H Ngo.

At least 19 recordsLinked to original sources
PubMed2005

Polyethyleneimine as a transmembrane carrier of fluorescently labeled proteins and antibodies.

Polyethyleneimine (PEI) has been used previously as a nonviral DNA transfer vector. In this article, we demonstrate its use as a vehicle for transmembrane delivery of proteins in cell culture conditions. Linking proteins to PEI required no other treatment beyond mixing them with PEI. The bond between PEI and protein combined at optimal ratios was maintained in electrophoresis, even in the presence of 2.5% sodium dodecyl sulfate (SDS). The optimal time for delivery of proteins was determined to be 24 h. We have successfully delivered an Alexa 488-labeled avidin protein into human glioblastoma cells. A functional antibody against the nuclear protein lamin was delivered into human fibroblasts and reacted with lamin inside live cells. PEI-based delivery of antibodies and fluorescently labeled proteins can be used for fluorescent detection, tracking, and evaluation of cellular protein function in vivo.

Avidin↗
PubMed2004

Diagnostic comparison of three groups of examiners using visual and laser fluorescence methods to detect occlusal caries in vitro.

BACKGROUND: To evaluate the accuracy of the DIAGNOdent laser device (DD) for detecting occlusal fissure caries when used by three groups of examiners. METHODS: Three final-year dental students (S), three General Dental Practitioners (G), and three Academic Clinicians (A) individually examined the non-cavitated occlusal surfaces of 25 extracted permanent molars using visual inspection (VI) then DD assessments. The presence of caries was confirmed following tooth sectioning. A cut-off limit of 30 was used for the DD to avoid over-treatment in a low caries-risk situation. RESULTS: For VI, individual examiner sensitivity (caries correctly diagnosed) ranged from 53 to 86 per cent, and specificity (sound teeth correctly diagnosed) ranged from 76 to 95 per cent, with low Kappa agreements. Group S achieved the highest sensitivity (80 per cent) and Groups G and A achieved the highest specificities (88 per cent). For DD, individual examiner sensitivity ranged from 19DD, individual examiner sensificity ranged from 19 to 77 per cent, and specificity from 71 to 97 per cent, with generally moderate Kappa agreements. Group A achieved the highest (67 per cent) and Group G the lowest (44 per cent) sensitivities, and Group G achieved the highest specificity (94 per cent). CONCLUSIONS: There were similar widely varying results for the two diagnostic methods and for the three groups of examiners. However, the relatively high sensitivities found with VI and specificities found with DD should avoid over-treatment in low caries-risk populations.

Chi-Square Distribution↗
PubMed2001

Effect of different conditioning protocols on adhesion of a GIC to dentin.

PURPOSE: This study examined the ultrastructure and microtensile bond strength (microTBS) of a restorative glass-ionomer cement (GIC; Dentsply) to sound dentin that was conditioned with various techniques. MATERIALS AND METHODS: Dentin surfaces from extracted human third molars were abraded with 180-grit SiC paper. Five groups of three teeth each were prepared: C - no acid pretreatment (control); P - 10% polyacrylic acid (PAA) for 10 s, no rinsing; R - 10% PAA for 20 s, rinsed; K - 25% PAA for 25 s, rinsed; and H -32% phosphoric acid for 15 s, rinsed. TEM was performed on a bonded specimen from each group, using unstained, undemineralized sections. GIC buildups were made on the remaining teeth, and after storage at 100% humidity for 24 h, the teeth were sectioned for microTBS and SEM evaluation. RESULTS: TEM revealed the presence of a structure known as the intermediate layer in all groups. This layer contains metallic salts contributed by both the GIC and dentin. In group C, this layer was restricted to the smear layer. In groups P and R, intermediate layers could be found above partially demineralized zones within the intertubular dentin. In groups conditioned with more aggressive protocols (K and H), the intermediate layers shifted downward to reside within the superficial portions of completely demineralized collagen. Group C had statistically lower microTBS (p < 0.05), while the other groups were not significantly different from each other. SEM revealed adhesive failures along the dentin surface in group C and mixed failures in the other groups. CONCLUSION: The lower microTBS observed in the control group reflects the weakness of the smear layer attachment to dentin. The higher microTBS in the other groups probably represent the cohesive strength of GIC under tension, rather than its true adhesive strength to dentin. Acid pretreatment dissolves the smear layer, creates a zone of partially demineralized dentin, and allows the PAA to interact with dentin via the intermediate layer. Overly aggressive conditioning renders the dentinal tubules patent, and leaves deeper demineralized dentin that does not form part of the intermediate layer.

Acid Etching, Dental↗
PubMed2000

Erythroid Kruppel-like factor is recruited to the CACCC box in the beta-globin promoter but not to the CACCC box in the gamma-globin promoter: the role of the neighboring promoter elements.

The programmed expression of the five beta-like globin genes (epsilon, (A)gamma, (G)gamma, delta, and beta) is characterized by a series of switches that are developmentally regulated. The (A)gamma- and (G)gamma- (fetus) to beta-globin (adult) switch depends on transcription factor erythroid Krüppel-like factor (EKLF), which, like Sp1, binds to CACCC boxes. EKLF is essential for the expression of the beta-globin but not the gamma-globin gene. Because both gamma-globin and beta-globin promoters contain the CACCC box, and their promoter elements are similar, it is not known why the two promoters behave so differently. In this report, we searched for the functional differences between the two promoters by studying their ability to recruit EKLF. We used the in vivo PIN*POINT assay to show that EKLF is recruited to the beta-globin promoter but not to the gamma-globin promoter. We show that this selectivity is a result of differences in surrounding promoter elements and not CACCC box alone. One of the differences between the two promoters with a functional consequence is the CCTTG repeat that is present in the gamma-globin promoter but not in the beta-globin promoter. The repeat, when inserted in the beta-globin promoter, decreases EKLF recruitment to and activity of the beta-globin promoter, suggesting that the repeat functions as a suppressor element. The CCTTG repeat can also suppress the SV40 promoter in cis, and the suppressor factor binding to the repeat can be squelched with a plasmid containing a high copy number of the repeat. These findings may have implications in designing drug targets for treatment of beta-globin disorders.

Animals↗
PubMed2000

Impaired transactivation of the glucocorticoid receptor cloned from the Guyanese squirrel monkey.

Squirrel monkeys are among a diverse group of New World primates that demonstrate unusually high levels of circulating corticosteroids and glucocorticoid receptor (GR) insensitivity. Recent evidence suggests that overexpression of an immunophilin impairs dexamethasone binding to GR in the Bolivian squirrel monkey (Saimiri boliviensis). Here we describe the cloning, expression, and functional characterization of GR from the closely related Guyanese squirrel monkey (S. sciureus). The cloned Guyanese squirrel monkey GR (gsmGR) cDNA closely resembles human GR (hGR) cDNA, and yields a high affinity dexamethasone binding receptor when expressed in COS-1 cells. Transactivation analysis of hGR and gsmGR expressed in CV-1 cells and cultured squirrel monkey kidney (SMK) cells indicates that: (1) SMK cells elaborate a functional high activity GR from human GR cDNA; (2) gsmGR is an order of magnitude less efficient than hGR at transactivation in CV-1 and SMK cells; and (3) maximal transactivation by gsmGR is attenuated in both cell lines. Glucocorticoid resistance in S. sciureus is at least partly attributable to a naturally occurring mutation in the GR gene that results in impaired GR transactivation.

Animals↗
PubMed2000

Minimal intervention: a new concept for operative dentistry.

The term minimal intervention is relatively new in dentistry and has been introduced to suggest to the profession that it is time for change in the principles of operative dentistry. The disease should be treated first; the surgical approach should be undertaken only as a last resort and then with the removal of as little natural tooth structure as possible. This article discusses the advances in techniques and materials that have led to change and attempts to put them into perspective. Treatment should begin with identification and elimination of the disease. There will then be a need for limited restoration of actual cavitation arising from demineralization of the tooth crown. Restorations, per se, will not prevent or eliminate disease. Caries is a bacterial infection and, until the microflora is controlled, all restorations are at risk of further demineralization in remaining tooth structure. This leads to the continuum of replacement dentistry that keeps the profession occupied for much of its productive time. If this cycle is to be broken, the profession must first acknowledge the primacy of prevention.

Bacterial Infections↗
PubMed2000

Minimal intervention: early lesions.

The use of modified cavity designs for the treatment of initial carious lesions can be justified on the grounds that, because no restorative material can adequately replace natural tooth structure for the long term, preservation of natural tooth structure is important. It is apparent that it is possible to remineralize and heal demineralized tooth structure to some degree. Therefore, neither enamel nor dentin should be removed simply because it has lost calcium and phosphate ions as a result of acid attack. The older surgical approach to cavity design was adopted in the absence of adhesive techniques and on the basis of Black's principle of "extension for prevention," but this theory is no longer tenable. The current availability of adhesive bioactive restorative materials makes it possible to maintain areas of tooth structure even though they appear to be undermined and weakened. Thus, the concept of geometric designs for prescribed cavities is no longer valid. The purpose of this article is to describe a series of simplified, modified cavity designs for small initial lesions; preservation of natural tooth structure is the principle objective of these designs.

Dental Caries↗
PubMed2000

Minimal intervention: advanced lesions.

Minimal intervention techniques are generally considered in relation to initial carious lesions. However, it appears logical to apply the same principles to extensive cavities as well as to the replacement of failed existing restorations. As the cavity becomes larger, there is an increasing need to consider protection of remaining cusps because they become seriously weakened by loss of the central core of the crown and therefore become subject to the development of splits at the base. However, it is possible to develop a protective cavity design without undue sacrifice of remaining tooth structure, at the same time that maintenance of occlusal anatomy and correct contact with the opposing arch are ensured. For larger cavities, special consideration needs to be given to the strength of the restorative material. Glass ionomer is relatively brittle and should not be exposed to undue occlusal load. Resin composites cannot be regarded as universal in their physical properties, and placement is time-consuming. A lamination technique is often useful, combining the advantages of both glass ionomer and resin composite. Amalgam should not be entirely discarded as an option because it has greater strength than both glass ionomer and resin composite and is still useful for the restoration of extensive cavities and for protection and retention of weakened cusps. Minimal intervention principles, designed to limit the loss of natural tooth structure, should be applied to all restorative dentistry. None of the available restorative materials is entirely satisfactory in the long term.

Bite Force↗
PubMed2000

Focused ion beam in dental research.

Focused ion beam (FIB) has been available for over 10 yrs but until recently its usage has been confined to the semiconductor industry. It has been developed as an important tool in defect analysis, circuit modification and recently transmission electron microscope sample preparation. This paper introduces FIB and demonstrates its application in dental research. Its ion and electron imaging modes complement the SEM while its ability to prepare TEM samples from a wide range of material will allow the study of new types of adhesive interface. As an example, its use is described in the characterization of the interface of resin to a tribochemically treated surface of an experimental fiber-reinforced resin-based composite. As with all new techniques, the initial learning curve was difficult to manage. This new instrument offers opportunities to expand research in dental materials to areas not possible before.

Aluminum Oxide↗
PubMed1999

Gastrostomy for enteral access. A comparison among placement by laparotomy, laparoscopy, and endoscopy.

BACKGROUND: Access to the stomach for long-term enteral feeding can be achieved via laparotomy (open GT), laparoscopy (lap GT) or endoscopy (PEG). We compared the three methods of gastrostomy to determine whether any one has an advantage over the others. METHODS: A retrospective analysis was done of 356 gastrostomies performed between January 1990 and June 1995. RESULTS: Of these 356 gastrostomies, 214 were open GT, 60 were lap GT, and 82 were PEG. The completion rate was high, 98.1% to 100%. The perioperative mortality rates were low and similar among the 3 methods; 4.2% for open GT, 5.3% for lap GT, and 4.9% for PEG (p = 0.87, Chi square test). Cardiac arrest was the predominant immediate cause of all perioperative deaths (68.8%). Overall, none of the deaths was directly related to the gastrostomy procedure. Major complications occurred in 24.9% of patients receiving open GT, in 18.3% of patients with lap GT, and in 17.1% of patients with PEG. Long-term complications developed in 25.9% of open GT, 25.6% of lap GT, and 30. 4% of PEG. The revision rates were similar for all 3 methods, 6.7% for open GT, 10% for lap GT, and 6.1% for PEG. CONCLUSIONS: Gastrostomy can be performed safely by all three techniques, with similar outcomes. PEG is our method of choice. Lap GT is preferred in patients with head and neck carcinoma, patients with obstructing esophageal carcinoma, and patients who have problems with overlying liver or colon. Open GT is reserved for cases with extensive intraabdominal adhesions or those where the procedure is done during an ongoing laparotomy.

Adult↗
PubMed1998

Studies on the genotoxicity of molybdenum salts in human cells in vitro and in mice in vivo.

Molybdenum is an essential element in plants and animals as a cofactor for enzymes. Molybdenum trioxide is used in metallurgical processes, in cosmetics as a pigment, and in contact lens solution, yet limited information is available on molybdenum genotoxicity. In the present study the micronucleus (MN) assay in human lymphocytes and mouse bone marrow and the dominant lethal assay in mice were used to assess the genotoxic effects of molybdenum salts in vitro and in vivo. Two salts of molybdenum were tested in whole blood cultures. Ammonium molybdate was more potent than sodium molybdate in causing a dose-dependent decrease in viability and replicative index and an increase in MN formation in binucleated lymphocytes (P < 0.001). A dose-response in both kinetochore-positive MN (caused by chromosome lagging) and kinetochore-negative MN (associated with chromosome breakage) was observed. Based on the results of a toxicity study of sodium molybdate, two doses, 200 and 400 mg/kg, were assessed in the bone marrow MN assay in mice (two i.p. injections 24 and 48 hr prior to euthanasia). A modest but statistically significant increase in MN frequency in polychromatic erythrocytes was observed (P < 0.05). The same treatment protocol was used to analyze dominant lethality. A dose-dependent increase in postimplantation loss represented mostly by early resorptions was observed the first week after treatment (P = 0.003). These preliminary data suggest that sodium molybdate induces dominant lethality at the postmeiotic stage of spermatogenesis. Overall, molybdenum salts produced moderately positive results both in vitro in human cells and in vivo in mice.

Adult↗
PubMed1997

Electron probe microanalysis and transverse microradiography studies of artificial lesions in enamel and dentin: a comparative study.

In cardiology and research involving the interactions between restorative materials and dental hard tissues, it is important for small changes in tooth mineral content to be measurable. Currently, transverse microradiography (TMR) is the most accepted tool for the above purpose. Electron Probe Microanalysis (EPMA) can yield both qualitative identification of elements and quantitative compositional information. The purpose of this study was to compare the mineral distribution in well-defined artificial lesions, in dentin and enamel, by the use of both TMR and EPMA on the same sample. The good correlation between the two sets of data validates EPMA as a technique and helps in the interpretation of its results. The data from TMR analysis are expressed as vol% of mineral, while EPMA gives the levels of Ca and phosphate in wt%. The conversion between the two sets of data is complicated by the fact that local density is, as yet, unknown.

Analysis of Variance↗
PubMed1997

A study of glass-ionomer cement and its interface with enamel and dentin using a low-temperature, high-resolution scanning electron microscopic technique.

This report describes a method of immobilizing the water contained in glass-ionomer cement and dental hard tissues and stabilizing the delicate organic component of dentin. With this method, the intact interface between glass-ionomer and dental hard tissues can be observed under scanning electron microscope with few of the artifacts that are caused by the desiccation associated with conventional scanning electron microscopic studies. There was a distinct zone of interaction between the glass-ionomer cement and enamel and dentin. Under severe thermal stress, glass-ionomer cement failed cohesively, leaving an intact interface with enamel and dentin. Machine-mixed glass-ionomer cements displayed a high level of porosity. Some glass particles were separated from the matrix, and there was evidence that some are dislodged from the matrix during specimen preparation.

Dental Enamel↗
PubMed1995

Endothelin during cardiovascular surgery: the effect of diltiazem and nitroglycerin.

To investigate whether the vasoconstrictor peptide endothelin (ET) is elevated during cardiovascular surgery and might predispose to perioperative vasoconstriction and ischemia, we compared the effect of the calcium channel blocker diltiazem with that of the nitric oxide (NO) donor nitroglycerin on ET and hemodynamics in 32 patients undergoing coronary artery bypass grafting (CABG). Following a double-blind protocol, 16 patients (3 women, 13 men; ages 63 +/- 10 years) received 1 microgram/kg/min nitroglycerin and 16 patients (5 women, 11 men; ages 64 +/- 8 years) received 3 micrograms/kg/min diltiazem intravenously 30 min before until 12 h after CABG. ET was measured in the superior vena cava before, during, and 1 h after CABG. Compared with ET levels before CABG, ET was significantly elevated during CABG and further increased after CABG (p < 0.05). During and after surgery, ET levels were lower in patients receiving diltiazem than in those receiving nitroglycerin (both p < 0.01). Mean arterial blood pressure and heart rate were lower in patients receiving diltiazem compared with those receiving nitroglycerin (both p < 0.05). These data demonstrate that diltiazem is more effective than nitroglycerin in preventing ET increase during cardiovascular surgery. Studies using ET receptor antagonists may be useful in assessing the clinical relevance of ET levels with respect to the risk for perioperative vasoconstriction and ischemia.

Aged↗
PubMed1995

Facilitation of olfactory learning by a modulator of AMPA receptors.

The effects of a benzoyl-piperidine drug (BDP) that facilitates AMPA receptor-mediated synaptic responses were tested on the acquisition and retention of long-term memory at dosages that had no detectable effects on a variety of performance measures. BDP-12 produced a dose-dependent suppression of exploratory activity in rats with statistically reliable effects occurring at 50 mg/kg (i.p.). The drug had no effects on balance beam performance at 30 mg/kg but at 45 mg/kg reduced the number of crossings made within a session; it did not, however, affect the time required to perform a traversal. The performance of well-trained rats presented with a familiar pair of odors (correct and incorrect) was not not detectably altered by BDP-12 at 30 mg/kg; however, the number of correct responses made in a five-trial test was reduced at 45 mg/kg. These results indicate that the AMPA receptor modulator at 30 mg/kg has little influence on arousal, motivation, sensori-motor processing, and attention; higher dosages cause a depression of learned and unlearned prepotent responses. The effects of the lower concentration were tested on two-odor discrimination learning in rats that had extensive training on the task. The animals (n = 20) were given three or five acquisition trials with novel odor pairs immediately after an injection of drug or vehicle and then tested 1-3 d later for retention in five unrewarded probe trials. Retention performance was not significantly better than chance 52.6 +/- 4.5% correct) for odors learned on vehicle injection days but was well above chance for odors learned on drug injection days (70.6 +/- 4.2% correct). Within-subject comparisons confirmed the memory enhancing effect of BDP-12 (p < 0.01). Analyses of performance during five training trials indicated that the rats made more correct responses on days on which they were given the drug than on days on which they were injected with vehicle (p < 0.02). Within-subject differences in acquisition were correlated with differences in retention (r = 0.70). There were no evident effects of the drug on response latencies during acquisition. These results suggest that AMPA receptor modulators reduce the amount of training needed for the formation of long-term memory and do so at dosages which have little effect on variables that secondarily influence acquisition. Possible reasons for this selectivity are discussed.

Animals↗
PubMed1987

Inverted papillomas of the nose and paranasal sinuses in children.

Inverted papillomas are uncommon lesions in the nose and paranasal sinuses, especially in the pediatric age group. We report the occurrence of one case in a 13-year-old Chinese female. Review of the literature and conclusions about management of these lesions in children are provided.

Adolescent↗
PubMed1987

[ORL localizations of Rosai-Dorfman disease. Apropos of 4 cases].

Four cases of Rosai and Dorfman's disease are presented. This adenomegalic sinusal histiocytosis is usually a benign affection even though the appearance and degree of glandular enlargement can suggest malignant disease. A literature review showed 215 cases reported up to the present.

Adolescent↗