Biomedical subjects

L J Hahn

Publications and source records attributed to L J Hahn.

At least 37 records · Page 2Linked to original sources

PubMed1999

Long-term survival of patients with mandibular osteosarcoma.

Osteosarcoma generally has a poor prognosis. Osteosarcoma of the mandible is rare and may have a less aggressive course. Three patients with osteosarcoma of the mandible were treated during the past 19 years at National Taiwan University Hospital. All were women, with an average age of 49 years. The patients were treated with radical excision of the tumor, with either pre- or postoperative radiotherapy. None of the patients received chemotherapy. Reconstruction with iliac osteocutaneous free flap, fibular osteoseptocutaneous free flap, or Leibinger reconstruction plate was performed to repair the facial defects resulting from tumor resection or radiation-induced necrosis. The three patients were alive and without evidence of recurrence at the time of writing, with follow-up periods ranging from 7 to 18 years. All had acceptable facial contour and satisfactory oromandibular function after reconstruction. These results support the effectiveness of wide resection with radiotherapy for treatment of mandibular osteosarcoma. With the availability of microsurgical reconstruction and biocompatible reconstruction plates, we advocate extensive ablation of this tumor. Long-term survival, good functional recovery, and acceptable facial contour can be expected.

Adult↗

PubMed1998

Cytotoxicity of sodium fluoride on human oral mucosal fibroblasts and its mechanisms.

Because sodium fluoride (NaF) is widely used for prevention of dental caries, pathobiological effects of NaF were investigated on human oral mucosal fibroblasts. The results showed that NaF was cytotoxic to oral mucosal fibroblasts at concentrations of 4 mmol/L or higher. Exposure of cells to NaF for 2 h also inhibited protein synthesis, cellular ATP level and functional mitochondrial activities in a dose-dependent manner. However, incubation of cells with NaF up to 12 mmol/L for 2 h depleted only 13% of cellular glutathione level. The IC50 of NaF on cellular ATP level was about 5.75 mmol/L. Preincubation of the cells with pyruvate and succinate did not protect cells from NaF-induced ATP depletion. At concentrations of 4 mmol/L, 8 mmol/L and 12 mmol/L, NaF inhibited 31%, 56% and 57% of mitochondrial functions, respectively, after 2 h incubation. No significant inhibition for NaF was found at concentrations lower than 2 mmol/L (40 ppm). These results indicate that NaF can be toxic to oral mucosal fibroblasts in vitro by its inhibition of protein synthesis, mitochondrial function and depletion of cellular ATP. Because of repeated and long-term usage of NaF, more detailed studies should be undertaken to understand its toxic effects in vitro and in vivo.

Adenosine Triphosphate↗

PubMed1998

X-ray CT monitoring of iceball growth and thermal distribution during cryosurgery.

X-ray CT is able to image the internal architecture of frozen tissue. Phantoms of distilled water, a saline-gelatin mixture, lard and a calf liver-gelatin suspension cooled by a plastic tube acting as a long liquid nitrogen cryoprobe were used to study the relationship between Hounsfield unit (HU) values and temperature. There is a signature change in HU value from unfrozen to completely frozen tissue. No discernible relation exists between temperature in a completely frozen tissue and its HU value for the temperature range achieved with commercial cryoprobes. However, such a relation does exist in the typically narrow region of phase change and it is this change in HU value that is the parameter of concern for quantitative monitoring of the freezing process. Calibration of temperature against change in HU value allows a limited set of isotherms to be generated in the phase change region for direct monitoring of iceball growth. The phase change temperature range, mid-phase change temperature and the absolute value of HU change from completely frozen to unfrozen tissue are shown to be sensitive to the medium. Modelling of the temperature distribution within the region of completely frozen phantom using the infinite cylinder solution to the Fourier heat equation allows the temperature history of the phantom to be predicted. A set of isotherms, generated using a combination of thermal modelling and calibrated HU values demonstrates the feasibility of routine x-ray CT assisted cryotherapy. Isotherm overlay will be a major aid to the cryosurgeon who adopts a fixed target temperature as the temperature below which there is a certainty of ablation of the diseased tissue.

Animals↗

PubMed1998

A model for the time-dependent thermal distribution within an iceball surrounding a cryoprobe.

The optimal cooling parameters to maximize cell necrosis in different types of tissue have yet to be determined. However, a critical isotherm is commonly adopted by cryosurgeons as a boundary of lethality for tissue. Locating this isotherm within an iceball is problematic due to the limitations of MRI, ultrasound and CT imaging modalities. This paper describes a time-dependent two-dimensional axisymmetric model of iceball formation about a single cryoprobe and extensively compares it with experimental data. Thermal histories for several points around a CRYOprobe are predicted to high accuracy (5 degrees C maximum discrepancy). A realistic three-dimensional probe geometry is specified and cryoprobe temperature may be arbitrarily set as a function of time in the model. Three-dimensional temperature distributions within the iceball, predicted by the model at different times, are presented. Isotherm locations, as calculated with the infinite cylinder approximation, are compared with those of the model in the most appropriate region of the iceball. Infinite cylinder approximations are shown to be inaccurate when applied to this commercial probe. Adopting the infinite cylinder approximation to locate the critical isotherm is shown to lead the user to an overestimate of the volume of target tissue enclosed by this isotherm which may lead to incomplete tumour ablation.

Computer Simulation↗

PubMed1998

Comparison of ordered subsets expectation maximization and Chang's attenuation correction method in quantitative cardiac SPET: a phantom study.

Photon attenuation is one of the primary causes of artifacts in cardiac single photon emission tomography (SPET). Several attenuation correction algorithms have been proposed. The aim of this study was to compare the effect of using the ordered subsets expectation maximization (OSEM) reconstruction algorithm and Chang's non-uniform attenuation correction method on quantitative cardiac SPET. We performed SPET scans of an anthropomorphic phantom simulating normal and abnormal myocardial studies. Attenuation maps of the phantom were obtained from computed tomographic images. The SPET projection data were corrected for attenuation using OSEM reconstruction, as well as Chang's method. For each defect scan and attenuation correction method, we calculated three quantitative parameters: average radial maximum (ARM) ratio of the defect-to-normal area, maximum defect contrast (MDC) and defect volume, using automated three-dimensional quantitation. The differences between the two methods were less than 4% for defect-to-normal ARM ratio, 19% for MDC and 13% for defect volume. These differences are within the range of estimated statistical variation of SPET. The calculation times of the two methods were comparable. For all SPET studies, OSEM attenuation correction gave a more correct activity distribution, with respect to both the homogeneity of the radiotracer and the shape of the cardiac insert. The difference in uniformity between OSEM and Chang's method was quantified by segmental analysis and found to be less than 8% for the normal study. In conclusion, OSEM and Chang's attenuation correction are quantitatively equivalent, with comparable calculation times. OSEM reconstruction gives a more correct activity distribution and is therefore preferred.

Algorithms↗

PubMed1998

Expression of CD44s, CD44v5, CD44v6 and CD44v7-8 in betel quid chewing-associated oral premalignant lesions and squamous cell carcinomas in Taiwan.

Aberrant expression of the cell surface adhesion molecule CD44 and its variant forms has been shown to be associated with the invasive and metastatic potential of cancer cells, and with poor prognosis in several types of cancers. Expression of CD44 standard (CD44s) and variant (CD44v) forms in oral squamous cell carcinoma (SCC), epithelial dysplasia (ED), epithelial hyperkeratosis (EH) and normal buccal mucosa (NBM) have been examined using antibodies to CD44s, CD44v5, CD44v6 and CD44v7-8. Positive CD44s, CD44v5, CD44v6 and CD44v7-8 staining was detected in all the specimens from NBM, EH and ED. Positive staining of CD44s, CD44v5, CD44v6 or CD44v7-8 was detected in 55 (88.7%), 48 (77.4%), 59 (95.2%) and 22 (35.5%) of the 62 SCC specimens, respectively. The positive staining of CD44v7-8 in oral SCC was significantly less than that in NBM (P<0.01). No significant correlation was found between CD44v7-8 expression and daily or total consumption of betel quids or cigarettes by the SCC patients. The 5-year survival rate for patients with CD44v7-8-positive tumours was significantly higher than that for the CD44v7-8-negative group (P<0.03). These results indicate that loss of CD44v7-8 expression may be a valuable factor for determining prognosis in oral SCC patients.

Adult↗

PubMed1998

Areca nut extract inhibits the growth, attachment, and matrix protein synthesis of cultured human gingival fibroblasts.

Betel quid chewing is a popular oral habit in India, South Africa, and many Southeast Asian countries. The effects of areca nut (AN) extract on the growth, attachment, and protein synthesis of healthy human gingival fibroblasts (GF) were investigated to determine why betel quid (BQ) chewers have higher prevalence of periodontal disease than non-chewers. Twenty-four hour exposure of human GF to AN extract (> 200 microg/ml) in culture led to the formation of numerous intracellular vacuoles. As analyzed by modified MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide] assay, AN extract significantly suppressed the growth of GF over 5 days of incubation in a dose-dependent manner. At concentrations of 50 and 300 microg/ml, AN extract suppressed the growth of GF with 30% and 57% (P < 0.05), respectively. AN extract also significantly suppressed the synthesis of [3H]proline incorporation into trichloroacetic acid (TCA) precipitated proteins. At concentrations of 200, 400, and 600 microg/ml, AN extract suppressed the protein synthesis with 33%, 58%, and 63% of inhibition (P < 0.05), respectively. Preincubation of cells in a medium containing AN extract for 2 hours inhibits the subsequent attachment of cultured GF to type I collagen at the 50% inhibitory concentration (IC50) which is about 720 to 798 microg/ml. Considering the frequent consumption of BQ throughout the day, impairment of sequential fibroblast functions by BQ ingredients is a potential mechanism through which BQ chewing exert a deleterious effect to the gingival tissues.

Areca↗

PubMed1997

Use of a moratorium to achieve consistent liquid nitrogen cryoprobe performance.

BACKGROUND AND OBJECTIVES: During liver cryosurgical procedures, the authors observed seriously inconsistent rates of iceball growth implying inconsistent probe cooling rates. This inconsistency can lead to several problems, most importantly, loss of precision and reliability in freezing the chosen volume of tissue. The observation led to investigation of the performance of the cryosurgery machine. METHODS: The performance of the Cryotech LCS 3000 with different moratorium periods was investigated. Freezing was performed in a gelatin phantom with thermocouple monitoring at the probe tip. RESULTS: It was determined that a moratorium period between unit filling and clinical use essentially eliminates the uncertainty in probe performance. The need for this arises from the design of the system. A full liquid nitrogen tank does not have the necessary pressure required to induce effective freezing. A partially filled tank increases vapor pressure in the storage dewar driving more liquid nitrogen through the probes, thus allowing a more reliable and faster freeze. CONCLUSION: The simple measure of introducing a moratorium period between filling the dewar with liquid nitrogen and its use in surgery allows partial evaporation of the nitrogen and enhances cryoprobe performance. This protocol modification may reduce the chance of inconsistent probe performance thus making liver cryosurgery more reliable.

Cryosurgery↗

PubMed1997

Cytotoxic and cytostatic effects of arecoline on oral mucosal fibroblasts.

Betel quid (BQ) chewing shows strong correlation to the incidence of oral submucous fibrosis and oral cancer in Taiwan. Arecoline, the main areca alkaloid, is considered to be one of the etiologic factors in BQ. To elucidate the role(s) of arecoline in the pathogenesis of BQ chewing related oral mucosal lesions, we used oral mucosal fibroblasts to study the effects of serum concentration, cell density, and incubation time on the cytotoxic response to arecoline. At a concentration less than 0.2 mM, arecoline was not cytotoxic to oral mucosal cells after 1, 3, and 6 days of incubation. After 3 days of incubation, the cytotoxic and cytostatic effects of arecoline became evident when the cells were exposed to higher concentrations of arecoline (0.2 mM) and serum (10% FCS). Exposure of cells (1 x 10(4) cells/well) to 0.2 mM of arecoline in 0.5% FCS for 3 and 6 days led to a 20% and 23% decrease, respectively, in the cell number, whereas exposure of cells (1 x 10(4) cells/well) to 0.2 mM arecoline in 10% FCS led to a 38% and 53% decrease, respectively, in cell number. At a higher cell density (5 x 10(4) and 1 x 10(5) cells/well), 0.2 mM arecoline led to less cytotoxicity (38% and 21% of decreasing in cell number, respectively) after 6 days of incubation. Our results indicated that arecoline was not mitogenic to oral mucosal fibroblasts, and that the cytotoxic and cytostatic effects of arecoline on oral mucosal fibroblasts could be modulated by the changes in the cell density, serum concentrations, and incubation time.

Arecoline↗

PubMed1996

Inhibition of the migration, attachment, spreading, growth and collagen synthesis of human gingival fibroblasts by arecoline, a major areca alkaloid, in vitro.

Because betel quid (BQ) chewing has been linked to a higher prevalence of periodontal diseases, the pathobiological effects of arecoline, a main alkaloid found in areca nut, were investigated in cultured human gingival fibroblasts. At concentrations higher than 0.4 mM, arecoline inhibits cell attachment, cell spreading and cell migration in a dose-dependent manner. These inhibitory effects were associated with intracellular depletion of glutathione (GSH). At concentrations of 0.4 mM and 1 mM, arecoline depleted about 26% and 45% of GSH after 2 h incubation. Exposure of cells to arecoline at concentrations lower than 0.4 mM for 2 h showed no significant decrease in either cell viability or intracellular GSH. However, incubation of cells for 24 h in 1 mM are colined decreased the cell numbers to only 35% of those in the untreated control. Arecoline also decreased cell growth and collagen synthesis in a dose-dependent manner. Because of repeated and long-term exposure to arecoline, BQ chewers could be more susceptible to periodontal damage and less responsive to new attachment procedures.

Arecoline↗

PubMed1995

Elevated ras p21 expression in oral premalignant lesions and squamous cell carcinoma in Taiwan.

Expression of ras p21 oncoproteins was examined in histological sections of oral squamous cell carcinoma (SCC), epithelial dysplasia, epithelial hyperkeratosis and normal oral mucosa using antibodies to ras p21 with an immunoperoxidase technique. Ras p21-positive staining was found in 47 of 51 (92.2%) cases of oral SCC, 4 of 4 (100%) cases of epithelial dysplasia, 7 of 7 (100%) cases of epithelial hyperkeratosis, and 1 of 6 (16.7%) cases of normal oral mucosa. The positive staining rate of ras p21 in oral SCC, epithelial dysplasia or epithelial hyperkeratosis was significantly higher than that in normal oral mucosa (P < 0.05). No correlation was found between ras p21 expression and patient age, tumour location, tumour size, clinical staging or histological differentiation of SCC. However, a significant positive correlation was found between ras p21 expression and patients' sex (P < 0.05) or regional lymph node status (P < 0.05). A significant positive correlation was also discovered between ras p21 expression and patients' smoking habits (P < 0.01), as well as daily or total betel quid (BQ) consumption (P < 0.05). Of the 47 immunostain-positive SCC patients, specimens from 6 patients were also obtained after chemotherapy, when ras p21 expression was found to be reduced. These results indicate that ras p21 overexpression may play an important role in the initiation and progression of oral SCCs in patients who are smokers and BQ chewers.

Adult↗

PubMed1995

Collagen biosynthesis in human oral submucous fibrosis fibroblast cultures.

To investigate the mechanism of collagen accumulation in oral submucous fibrosis (OSF) tissues, we examined the biosynthesis of collagen in fibroblast cultures established from OSF lesions. Fibroblasts obtained from four of ten OSF specimens showed more than a 1.5-fold increase in the production of collagens compared with fibroblasts from age-, sex-, and passage-matched normal controls (p < 0.05). When the relative amounts of collagen synthesis were estimated by SDS polyacrylamide gel electrophoresis, it was found that both OSF and control cells produced about 85% type I collagen and 15% type III collagen. The ratio of alpha 1(I) to alpha 2(I) chains was about 3:1 in OSF cells instead of the 2:1 expected for type I collagen. The excess alpha 1(I) chains could mean that collagen type I trimer was synthesized by the fibroblasts. These findings suggest that collagen overproduction and a reduced degradation of the structure-stable collagen type I trimer synthesized by OSF fibroblasts might contribute to the accumulation of collagen in OSF lesions in vivo. The mechanism(s) of increased procollagen production were analyzed by Northern blot, slot blot, and Southern blot. The OSF fibroblast strains with elevated collagen production also contained higher-than-normal levels of procollagen mRNA, and the ratios of alpha 1(I), alpha 2(I), and alpha 1(III) procollagen mRNAs were compatible with the results of corresponding procollagen alpha chains. The gene copy number of pro alpha 2(I) collagen gene in OSF fibroblasts was about 1.05. No gene amplification was found. These results indicate that expression of these procollagen genes in cultured fibroblasts is regulated at the transcriptional level.

Case-Control Studies↗

PubMed1994

Mutations of Ki-ras oncogene codon 12 in betel quid chewing-related human oral squamous cell carcinoma in Taiwan.

In Taiwan, there are two million people who have a betel quid chewing habit, and approximately 80% of all oral cancer deaths are associated with this habit. To investigate the incidence and types of Ki-ras codon 12 mutations in oral cancer associated with betel quid chewing, we used a sensitive mutation-specific two-stage polymerase chain reaction (PCR) technique to examine human oral squamous cell carcinomas from formalin-fixed, paraffin-embedded tissues. DNA sequence analysis of PCR products revealed that 6 of 33 (18%) tumour specimens contained Ki-ras codon 12 mutations. Four of the tumours contained more than one mutation. Three different base changes were detected, resulting from a substitution of wild type glycine (GGT) to either serine (AGT), aspartic acid (GAT) or cysteine (TAT). These results indicate that Ki-ras oncogene activation may play a role in the oncogenesis of betel quid chewing-related human oral squamous cell carcinomas.

Adult↗

PubMed1994

Genotoxic and non-genotoxic effects of betel quid ingredients on oral mucosal fibroblasts in vitro.

To understand the role of betel quid (BQ) in the pathogenesis of oral submucous fibrosis (OSF) and oral cancer, we used DNA damage, cytotoxicity, and cell proliferation assays to study the pathobiological effects of aqueous extracts of three BQ constituents [betel nut (Areca catechu, BN), inflorescence of Piper betle (IPB), and lime], one BN alkaloid (arecoline), and one BN polyphenol [(+)-catechin] on cultured oral mucosal fibroblasts. Extracts of BN and IPB induced DNA strand break formation in a dose-dependent manner. Extracts of BN and IPB, (+)-catechin, and arecoline decreased cell survival and proliferation in a dose-dependent manner. However, aqueous extract of lime (50-800 micrograms/mL) increased cell proliferation by 20-40%. These results indicate that BQ contains not only genotoxic and cytotoxic agents, but also compounds which stimulate cell proliferation. These compounds may act synergistically in the pathogenesis of OSF and oral cancer in BQ chewers. In addition, five anti-oxidants [glutathione (GSH), cysteine, mannitol, catalase, and superoxide dismutase (SOD)] were tested for their protective effects against the cytotoxicity of BQ constituents. GSH (1.95 and 2.6 mmol/L) and cysteine (4 and 8 mmol/L) prevented the arecoline-induced cytotoxicity. In contrast, mannitol, catalase, and SOD did not decrease the arecoline-induced cytotoxicity. These results indicate that thiol depletion, but not the attack of oxygen free radicals, could be the mechanism for arecoline cytotoxicity. GSH could also protect cells from the cytotoxicity of IPB extract. Increasing dietary intake of GSH-rich foods or dietary supplements of GSH may have chemopreventive potential to reduce BQ-associated oral lesions.

Antimutagenic Agents↗

PubMed1994

Eugenol triggers different pathobiological effects on human oral mucosal fibroblasts.

Pathobiological effects of eugenol (4-allyl-2-methoxyphenol), a major constituent of betel quid (BQ), were studied on oral mucosal fibroblasts. At a concentration higher than 3 mmol/L, eugenol was cytotoxic to oral mucosal fibroblasts in a concentration- and time-dependent manner. Cell death was associated with intracellular depletion of glutathione (GSH). Most of the GSH was depleted prior to the onset of cell death. At concentrations of 3 mmol/L and 4 mmol/L, eugenol depleted about 45% and 77% of GSH after one-hour incubation. In addition, eugenol decreased cellular ATP level in a concentration- and time-dependent manner. Eugenol also inhibited lipid peroxidation. Inhibition of lipid peroxidation was partially explained by its dose-dependent inhibition of xanthine oxidase activity. The IC50 of eugenol on xanthine oxidase activity was about 0.3 mmol/L. No DNA strand break activity for eugenol was found at concentrations between 0.5 and 3 mmol/L. Taken together, frequent exposure of oral mucosa to a high concentration of eugenol during the chewing of BQ might be involved in the pathogenesis of oral submucous fibrosis and oral cancer via its cytotoxicity. In contrast, eugenol at a concentration less than 1 mmol/L might protect cells from the genetic attack of reactive oxygen species via inhibition of xanthine oxidase activity and lipid peroxidation.

Adenosine Triphosphate↗

PubMed1993

Low prevalence of hepatitis C virus infection among dentists in Taiwan.

To evaluate whether hepatitis C virus (HCV) infection is an occupational hazard in the dental environment, serum samples collected in 1990-1991 from 461 dentists were tested for the antibody to HCV (anti-HCV) with first- and second-generation HCV enzyme-linked immunoassays (EIAs). Five of the 363 (1.38%) serum samples were reactive by the first-generation (C100-3) HCV EIA. Of the same 363 samples and the other 98 samples, 3 (0.65%) were reactive by the second-generation test. Of the 5 first-generation EIA reactive samples, only the 2 samples showing an absorbance of greater than 2.0 were also reactive to the second-generation EIA. The other 3 low-absorbance samples became negative and were regarded as false positives. Among the 358 samples negative by the first-generation EIA, 1 was reacted by the second-generation EIA. Those samples positive by the first- and/or second-generation HCV EIA were analyzed further by cDNA/polymerase chain reaction (PCR) to detect the presence of HCV RNA. Only 1 of the 5 first-generation EIA reactive samples was positive by PCR, but 2 of the 3 second-generation EIA reactive samples were PCR positive. These results are comparable to the anti-HCV prevalence of healthy blood donors (0.95% by C100-3 assay) and pregnant women (0.63% by recombinant immunoblot assay). We conclude that the prevalence of HCV infection among dentists in Taiwan is low, and there is no increased risk of HCV infection through the practice of dentistry, at least in our area.

Adult↗

PubMed1992

Collagen gene expression in human dental pulp cell cultures.

Pulp cells from human permanent molars were isolated and established in culture; 40% showed positive alkaline phosphatase staining. When incubated with 50 micrograms/ml of ascorbic acid and 10 mM of beta-glycerophosphate, the cells formed a mineralized extracellular matrix; they could thus have the potential to differentiate into odontoblast-like cells in vitro. Collagen synthesis was analysed by SDS interrupted gel electrophoresis, Northern blot and slot blot: the cells produced predominantly (approximately 99%) type I collagen and only trace amount of type III collagen. The ratio of alpha 1 (I) to alpha 2(I) procollagen chains was about 68:32, indicating that no significant amount of collagen type I trimer was synthesized in this system. The ratios of alpha 1(I), alpha 2(I) and alpha 1(III) procollagen mRNAs were about 61:25:1; these were compatible with the ratios of corresponding procollagen alpha chains. In addition, a novel 5.8 kb pro alpha 1(III) mRNA was detected. These observations indicate that collagen synthesis in these cultured pulp cells was regulated at the transcriptional level.

Adolescent↗

PubMed1991

Glucosyltransferase gene polymorphism among Streptococcus mutans strains.

Genetic polymorphisms in genes coding for the glucosyltransferases were detected among Streptococcus mutans serotype c strains by Southern blot analysis with DNA probes located within the gtfB gene (H. Aoki, T. Shiroza, M. Hayakawa, S. Sato, and H. K. Kuramitsu, Infect. Immun. 53:587-594, 1986). Restriction endonucleases were used to examine genomic DNAs isolated from serotype a to h strains. The variations were readily detected among 33 strains of serotype c by EcoRI and PstI restriction enzyme digestions. Serotypes e and f, which are genetically similar to serotype c, also had comparable polymorphism; however, serotypes a, b, d, g, and h did not hybridize to the same DNA probes in parallel experiments. Further analysis of enzymatic activities for glucan synthesis and sucrose-dependent adherence revealed no significant differences among the serotype c strains. Our results suggested that genetic polymorphisms existing in S. mutans serotype c strains may reflect a complexity in genes coding for the glucosyltransferases, which are produced ubiquitously in members of the S. mutans group.

Bacterial Adhesion↗