Biomedical subjects

A J Cheng

Publications and source records attributed to A J Cheng.

17 recordsLinked to original sources

PubMed2001

High prevalence of coeliac disease in a population-based study from Western Australia: a case for screening?

OBJECTIVES: To determine the prevalence of coeliac disease in an Australian rural community. DESIGN: Retrospective analysis of stored serum samples from 3,011 random subjects from the Busselton Health Study. IgA antiendomysial antibodies (AEA) were detected by indirect immunofluorescence, and subjects testing positive were contacted and offered small-bowel biopsy. MAIN OUTCOME MEASURES: Prevalence of AEA positivity and biopsy-proven coeliac disease in the community with reference to the proportion of symptomatic to asymptomatic patients. RESULTS: 10 of 3,011 subjects were AEA positive. One subject had died, one subject could not be traced and one refused small-bowel biopsy. All subjects with detectable AEA who consented to biopsy had pathological changes consistent with coeliac disease. The prevalence of newly diagnosed biopsyproven coeliac disease is 7 in 3,011 (1 in 430). Two further subjects had a diagnosis of coeliac disease before this study. When all AEA-positive patients and those previously diagnosed are included, the prevalence is 12/3,011 (1 in 251). There was a significant clustering of cases in the 30-50-years age range, with 10/12 (83%; 95% CI, 52%-98%) aged between 30 and 50 years, compared with 1,092/3,011 (36%; 95% CI, 35%-38%) of the total population (P<0.03). Of the eight AEA-positive subjects who could be contacted, four had symptoms consistent with coeliac disease and four were asymptomatic. Three subjects were iron-deficient, four subjects had first-degree relatives with coeliac disease and one subject had type 1 diabetes mellitus. CONCLUSIONS: The prevalence of coeliac disease is high in a rural Australian community. Most patients are undiagnosed, and asymptomatic.

Adult↗

PubMed2001

Antisense-induced exon skipping and synthesis of dystrophin in the mdx mouse.

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disease arising from defects in the dystrophin gene, typically nonsense or frameshift mutations, that preclude the synthesis of a functional protein. A milder, allelic version of the disease, Becker muscular dystrophy, generally arises from in-frame deletions that allow synthesis of a shorter but still semifunctional protein. Therapies to introduce functional dystrophin into dystrophic tissue through either cell or gene replacement have not been successful to date. We report an alternative approach where 2'-O-methyl antisense oligoribonucleotides have been used to modify processing of the dystrophin pre-mRNA in the mdx mouse model of DMD. By targeting 2'-O-methyl antisense oligoribonucleotides to block motifs involved in normal dystrophin pre-mRNA splicing, we induced excision of exon 23, and the mdx nonsense mutation, without disrupting the reading frame. Exon 23 skipping was first optimized in vitro in transfected H-2K(b)-tsA58 mdx myoblasts and then induced in vivo. Immunohistochemical staining demonstrated the synthesis and correct subsarcolemmal localization of dystrophin and gamma-sarcoglycan in the mdx mouse after intramuscular delivery of antisense oligoribonucleotide:liposome complexes. This approach should reduce the severity of DMD by allowing a dystrophic gene transcript to be modified, such that it can be translated into a Becker-dystrophin-like protein.

Animals↗

PubMed2001

Characteristics of mutations in the p53 gene in oral squamous cell carcinoma associated with betel quid chewing and cigarette smoking in Taiwanese.

p53 mutations are etiologically associated with the development of oral squamous cell carcinomas (OSCCs) or are associated with exposure to specific carcinogens. In this study, we used PCR-single strand conformation polymorphism and DNA sequencing to analyze the conserved regions of the p53 gene (exons 5-9) in OSCC tumor specimens from 187 patients with varied histories of betel quid, tobacco and alcohol use. Ninety-one of the 187 OSCCs (48.66%) showed p53 gene mutations at exons 5-9. The incidence of p53 mutations was not associated with age, sex, TNM stage, status of cigarette smoking or betel quid chewing. However, alcohol drinkers exhibited a significantly higher incidence (57/101, 56.44%) of p53 mutations than non-users (39.53%, 34/86) (P = 0.02). The effect of alcohol on the incidence of p53 mutations was still statistically significant (RR = 2.24; 95% CI, 1.21-4.15) after adjustment for cigarette smoking and betel quid (BQ) chewing. G:C to A:T transitions were the predominant mutations observed and associated with BQ and tobacco use. Alcohol drinking could enhance these transitions. After adjustment for cigarette smoking and BQ chewing, alcohol drinking still showed an independent effect on G:C to A:T transitions (RR = 2.41; 95% CI, 1.01-5.74). These findings strongly suggest an important contributive role of tobacco carcinogens to p53 mutation in this series of Taiwanese OSCCs and alcohol might enhance these mutagenic effects. As safrole-DNA adducts have been detected in 77% (23/30) of the OSCC tissues from Taiwanese oral cancer patients with a BQ chewing history, we cannot rule out the possibility that safrole or other carcinogens present in the BQ may cause a similar pattern of mutagenesis. Determination of the role of safrole and other carcinogens present in BQ on the pattern of p53 gene mutation in OSCC will require further study.

Adult↗

PubMed2001

Poor prognosis in nasopharyngeal cancer patients with low glucose-6-phosphate-dehydrogenase activity.

Nasopharyngeal carcinoma (NPC) is endemic among well-defined ethnic groups in several world regions, such as Southeastern China and Taiwan. Glucose-6-phosphate-dehydrogenase (G6PD)- deficiency, a sex-linked disorder, is one of the most common enzymopathies in Taiwan. The major role of G6PD is to generate NADPH to protect cells from oxidative damage, which is a major contributing factor to certain degenerative diseases, such as aging and cancer. In view of the coincidence of epidemic distribution of NPC and G6PD deficiency, as well as the house-keeping function of G6PD in cellular oxidative defense, we investigated the correlation of G6PD activity with NPC. The stage of NPC was classified by AJCC (1997) criteria. G6PD levels were determined in 108 NPC male patients and 75 healthy male individuals. The mean G6PD level of NPC patients was 218.9 U/10(12) RBC or 7.53 U/g hemoglobin (Hb), being much lower than in normal individuals (260.6 U/10(12) erythrocytes (RBC) or 8.92 U / gHb). The level of G6PD activity had no correlation with tumor stage or lymph node or distant metastasis, but was significantly correlated with tumor recurrence (P = 0.004 when using G6PD = 130 U/10(12) RBC as cutoff value). These results indicated that low G6PD activity in patients with NPC is associated with poor prognosis.

Adult↗

PubMed2000

Telomerase activity is frequently found in metaplastic and malignant human nasopharyngeal tissues.

Telomerase is a specialized ribonucleoprotein polymerase that directs the synthesis of telomere repeats at chromosome ends. Accumulating evidence has indicated that telomerase is stringently repressed in normal human somatic tissues but reactivated in cancers and immortal cells, suggesting that reactivation of telomerase plays an important role in carcinogenesis. In this study, the status of telomerase activity in diseased human nasopharyngeal lesions was determined by the telomeric repeat amplification protocol (TRAP). Fifty-four patients participated including 17 inflammation or hyperplasia, eight with squamous metaplasia, and 29 with different stages of carcinomas. Telomerase activity was detected in 1 of 17 (5.9%) inflammatory or lymphoid hyperplastic tissues, 3 of 8 (37.5%) squamous metaplastic, and 25 of 29 (86.2%) carcinoma tissues. The differences in telomerase expression in these groups is statistically significant (P < 0.001). Levels of telomerase activity correlated with tumour stage (P = 0.024). These results suggest that telomerase reactivation plays a role in the carcinogenesis of nasopharyngeal cancer. Since telomerase activity is found in the majority of nasopharyngeal cancers and a subset of metaplasia, this enzyme may be served as a reference to monitoring the status of abnormal nasopharyngeal tissues.

Biopsy↗

PubMed1999

Telomerase activity is a useful marker to distinguish malignant pancreatic cystic tumors from benign neoplasms and pseudocysts.

BACKGROUND: Pancreatic serous cystadenoma, mucinous cystic neoplasms, ductal adenocarcinoma with cystic change, and pseudocysts are a spectrum of pancreatic cystic lesions. Their management strategy and prognosis are extremely diverse. Imaging study, cytology, and analysis of the tumor markers of cyst fluid are not always reliable in differentiation of these disease entities. MATERIALS AND METHODS: Fifteen patients with pancreatic cystic neoplasms (including six mucinous cystadenocarcinomas, two mucinous cystic neoplasms with borderline malignancy, two mucinous cystadenomas, and five serous cystadenomas), 4 patients with pancreatic ductal adenocarcinomas with cystic change, and 10 patients with pseudocysts were studied. Echo-guided or computed tomography-guided biopsies of pancreatic cystic lesions and their normal counterparts were conducted on all patients prior to operation or other management. The specimens were assayed for telomerase activity by using TRAP (telomere repeat amplification protocol). The level of telomerase activity in each specimen was semiquantitated as strong, moderate, weak, and none. The final diagnoses were made from histopathological examination of surgically resected or biopsied specimens. The efficacy of telomerase activity as a tumor marker to predict malignancy of pancreatic cystic lesions was evaluated. RESULTS: Three of the four pancreatic ductal adenocarcinomas with cystic change had strong or moderate telomerase activity; four of the six mucinous cystadenocarcinomas had moderate or weak telomerase activity; one of the two mucinous cystadenomas with borderline malignancy had weak telomerase activity; and none of their normal counterparts had detectable telomerase activity. In contrast, none of the two mucinous cystadenomas, five serous cystadenomas, and 10 pseudocysts had detectable telomerase activity. Based on these results, the sensitivity of telomerase activity for prediction of malignancy or premalignancy of pancreatic cystic lesions was 67%, the specificity was 100%, and the positive and negative predictive values were 1.0 and 0.81, respectively. The overall accuracy was 86%. CONCLUSIONS: The differential expressions of telomerase activity have been detected specifically in malignant and premalignant pancreatic cystic tumors, but not in benign cystic neoplasms or pseudocysts. The implications of these results are that telomerase activation takes part in the malignant transformation of pancreatic cystic neoplasms and that telomerase activity is a useful marker to distinguish malignant pancreatic cystic tumors from benign neoplasms and pseudocysts.

Adult↗

PubMed1999

Polymerase chain reaction-based enzyme immunoassay for quantitation of telomerase activity: application to colorectal cancers.

Telomerase is a specialized reverse transcriptase that synthesizes telomeric sequences onto human chromosomal ends. It appears to be present in the majority of primary human cancer tissues, and may have potential as a universal tumor marker. In this report, we describe a sensitive, non-radioactive, polymerase chain reaction (PCR)-based enzyme immunoassay (EIA) for the quantitation of telomerase activity in human cells. This PCR-EIA is convenient and can be easily completed within 3 h. The correlation coefficient between the results of PCR-EIA and the conventional telomeric repeat amplification protocol (TRAP) method, as measured on 4 different cell lines, was over 0.98. Evaluation of this method for clinical application was conducted with tissues obtained from patients with colorectal cancers and the results were compared with those of the conventional TRAP method. Our data indicate that telomerase activities measured by conventional TRAP and PCR-EIA are highly correlated, and we suggest that the PCR-EIA method can substitute for conventional TRAP.

Autoradiography↗

PubMed1998

Close correlation between telomerase expression and adenomatous polyp progression in multistep colorectal carcinogenesis.

To investigate the role of telomerase in the multistep colorectal carcinogenesis, we examined telomerase activity in 31 adenomatous polyps and 22 paired cancer-normal mucosa specimens from non-hereditary nonpolyposis colorectal cancer patients. Telomerase activity was detected in 18% of normal mucosa, 16% of small (<1.0 cm) polyps, 20% of intermediate polyps, 71% of large (>2.0 cm) polyps, and 96% of adenocarcinoma samples (P for trend, <0.0001). High-level enzyme activities were seen in none of the normal mucosa, 5% of small polyps, 20% of intermediate polyps, 43% of large polyps, and 73% of adenocarcinoma samples (P for trend, <0.0001). These data indicate telomerase reactivation occurs with adenomatous polyp progression in multistep colorectal carcinogenesis.

Adenomatous Polyposis Coli↗

PubMed1998

Possible role of telomerase activation in the cancer predisposition of patients with hereditary nonpolyposis colorectal cancers.

BACKGROUND: Hereditary nonpolyposis colorectal cancer syndrome (HNPCC syndrome; also called Lynch syndrome) is one of the most common cancer predisposition syndromes. Most cases of cancer associated with this syndrome are due to the inheritance of germline mutations in genes that encode proteins required for DNA mismatch repair; defects in these proteins allow mutations to accumulate more rapidly in the DNA and influence the rate of cancer development. Recent studies indicate that the reactivation of the activity of telomerase, an enzyme involved in the synthesis of chromosomal ends, in somatic cells may play a role in carcinogenesis. In this study, we evaluated the expression of telomerase in normal and cancerous colorectal tissue specimens from HNPCC and non-HNPCC patients. METHODS: The polymerase chain reaction-based telomeric repeat amplification protocol was used to assay telomerase activity in colorectal tissue specimens from 33 non-HNPCC patients (23 normal, 26 polyps, and 37 cancer specimens) and from 24 HNPCC patients (24 normal, 0 polyps, and 28 cancer specimens). RESULTS: Thirty-one of 37 carcinoma samples from 18 non-HNPCC patients and 27 of 28 carcinoma samples from 24 HNPCC patients were found to be positive for telomerase activity. Whereas only one of 23 normal mucosa samples from 23 non-HNPCC patients was found to have (weak) telomerase activity, eight of 24 normal mucosa samples from 24 HNPCC patients were positive for telomerase; the difference between the two groups was statistically significant (two-sided P = .0226). IMPLICATION: This study generates the hypothesis that genetic defects in individuals with HNPCC syndrome facilitate the reactivation of telomerase activity, a process which may be associated with their predisposition to develop cancer.

Adult↗

PubMed1998

Telomerase activity in benign and malignant human thyroid tissues.

Telomerase is a specialized ribonucleoprotein polymerase that directs the synthesis of telomerase repeats at chromosome ends. Accumulating evidence has indicated that telomerase is stringently repressed in normal human somatic tissues but reactivated in cancers and immortal cells, suggesting that activation of telomerase activity plays a role in carcinogenesis and immortalization. In this work, the status of telomerase activity during the development of human thyroid cancer was determined using telomeric repeat amplification protocol (TRAP) in 14 nodular hyperplasia, 14 adenomas, 23 papillary carcinomas and 11 follicular carcinomas. Positive telomerase activity was detected in 2 of 14 nodular hyperplasias (14%), 4 of 14 adenomas (29%), 12 of 23 papillary carcinomas (52%) and 10 of 11 follicular carcinomas (91%). The cancers that are negative for telomerase activity are mostly in early stage (stage I or II). These results suggest that telomerase reactivation plays a role during the development of thyroid cancer.

Adenocarcinoma, Follicular↗

PubMed1998

Self-association of G-rich oligodeoxyribonucleotides under conditions promoting purine-motif triplex formation.

Efficient purine-motif triple-helix formation with guanosine/thymidine-rich oligodeoxyribonucleotides requires the presence of divalent cations (e.g., Mg2+) or polyamines at physiologic concentrations. However, under such conditions, we found that G-rich oligonucleotides were capable of self-association. Mixing experiments indicated a stoichiometry of two G-rich oligonucleotide strands in each complex. Dimerization was proportional to the oligonucleotide length, facilitated by increasing concentrations of multivalent cations, and inhibited by monovalent cations that promote G-quartet formation (e.g., K+, Rb+ NH4+). Although dimer formation was relatively slow (t(1/2) approximately 20 minutes), these species were quite stable, with dissociation rates on the order of days. Methylation protection experiments indicated that these dimers exhibited protected N7 position on most all guanines consistent with Hoogsteen base pairing, although this pattern differed from that observed under conditions favoring intramolecular quadruplex formation. Most important, G-rich oligonucleotide dimers were less capable of purine-motif triplex formation than were their denatured counterparts. Thus, these data indicated that G-rich oligodeoxyribonucleotides can form alternate self-associated structures under conditions that do not favor standard quadruplex formation and that these species can have altered properties with regard to their recognition of biologic targets.

Base Composition↗

PubMed1998

Involvement of recF, recO, and recR genes in UV-radiation mutagenesis of Escherichia coli.

The recF, recO, and recR genes were originally identified as those affecting the RecF pathway of recombination in Escherichia coli cells. Several lines of evidence suggest that the recF, recO, and recR genes function at the same step of recombination and postreplication repair. In this work, we report that null mutations in recF, recO, or recR greatly reduce UV-radiation mutagenesis (UVM) in an assay for reversion from a Trp- (trpE65) to a Trp+ phenotypes. Introduction of the defective lexA51 mutation [lexA51(Def)] and/or UmuD' into recF, recO, and recR mutants failed to restore normal UVM in the mutants. On the other hand, the presence of recA2020, a suppressor mutation for recF, recO, and recR mutations, restored normal UVM in recF, recO, and recR mutants. These results indicate an involvement of the recF, recO, and recR genes and their products in UVM, possibly by affecting the third role of RecA in UVM.

Bacterial Proteins↗

PubMed1997

Inhibition of telomerase activity by PKC inhibitors in human nasopharyngeal cancer cells in culture.

Telomerase is a specialized ribonucleoprotein polymerase that adds hexanucleotides (TTAGGG) onto human chromosomal ends. The expression of telomerase activity has been associated with cell immortalization and the malignant phenotype in most cancers. How the telomerase activity is regulated in cancer cells is presently not known. In this work, the effects of cell cycle blockers, DNA damaging agents, TopII inhibitors and proteins kinase inhibitors on the telomerase activity were examined in cultured nasopharyngeal carcinoma cells NPC-076. Agents which interfere with tubulin assembly (Taxol and vinblastine) and agents which arrest cells at S phase (methotrexate and 5-fluorouracil) did not inhibit telomerase activity of treated cells. Agents which damage DNA (cisplatin, methyl methanesulfonate, and UV radiation) and TopII inhibitors (etoposide and daunorubicin) also did not inhibit telomerase activity of treated cells. Among the protein kinase inhibitors examined, no significant inhibition of telomerase activity was observed with cells treated with quercetin, H-89, or herbimycin A. On the other hand, two protein kinase C (PKC) inhibitors (bisindolylmaleimide I and H-7) were found to produce a big inhibition of telomerase activity in treated cells. Staurosporine produced a moderate inhibition, and sphingosine had a small inhibitory effect. The inhibition of telomerase activity by PKC inhibitors appears to be specific since the treated cells were mostly viable (i.e., greater than 75%) and still retained significant levels of protein synthesis capability. These results implicate that protein kinase C is involved in the regulation of telomerase activity in vivo.

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

PubMed1997

Oligodeoxyribonucleotide length and sequence effects on intramolecular and intermolecular G-quartet formation.

The potential of guanine-rich oligodeoxyribonucleotides (oligos) as nucleic acid drugs is increasingly being investigated, for example, as aptamers against heparin-binding proteins and as purine-motif triplex-forming oligos. However, G-rich oligos can be very polymorphic under physiological conditions, often with the resulting structures possessing vastly different functional capabilities. To better understand the intrinsic oligo parameters that affect their structure, we used nondenaturing gel electrophoresis to investigate a series of G-rich oligos derived from the sequence 5'-TGGGTGGGGTGGGGTGGGT for their abilities to self-associate through G-quartet formation. From these studies the following observations could be made: (1) oligos containing four clusters of three or more contiguous Gs readily associated intramolecularly but did not associate intermolecularly; (2) intermolecular dimerization was the preferred mode of interaction when one of the oligos contained only two G clusters; and (3) T-rich extensions promoted multimerization of oligos into still higher-order species.

Base Sequence↗

PubMed1997

Differential inhibition of telomerase activity during induction of differentiation in hematopoietic, melanoma, and glioma cells in culture.

Accumulating evidence indicates that telomerase activity is stringently repressed in normal human somatic cells but reactivated in cancers and immortal cells, suggesting that activation of telomerase activity may play a role in carcinogenesis and immortalization. Recently, down-regulation of telomerase activity by induction of differentiation has been reported for cells of pre-myelocytic and myelocytic leukemia as well as embryonic carcinoma. To gain further insight about the regulation of telomerase activity following induction of differentiation, telomerase activity was examined in a human hematopoietic progenitor cell line (D2), a melanoma cell line (CM73-36) and a glioma cell line (Ast812) before and after addition of differentiation inducing agents. The state of differentiation was assessed by growth inhibition and cell morphological maturation. Telomerase activity was assayed by a PCR-based telomeric repeat amplification protocol (TRAP). Our data show that telomerase activity was inhibited only in differentiation-induced D2 cells but not in differentiation-induced melanoma and glioma cells. A model for the differential inhibition of telomerase activity following induction of differentiation in different cancer cells will be presented.

Brain Neoplasms↗

PubMed1994

Oligodeoxyribonucleotide length and sequence effects on intermolecular purine-purine-pyrimidine triple-helix formation.

The binding of guanosine/thymidine-rich oligodeoxyribonucleotides containing various deletions, extensions, and point mutations to polypurine DNA targets was investigated by DNase I footprinting. Intermolecular purine-purine-pyrimidine triple-helical DNA formation was best achieved using oligonucleotides 12 nucleotides in length. Longer oligonucleotides were slightly weaker in binding affinity, whereas shorter oligonucleotides were considerably weaker. Oligonucleotide extensions had a slight effect on triplex formation, while single point mutations located near the oligonucleotide ends had a greater effect. In the cases of extensions and point mutations, changes to the 3' end of the oligonucleotide had a consistently greater effect on triplex formation than changes to the 5' end. Such differences in triplex-forming ability were not caused by an intrinsic property of these oligonucleotides, since the same point mutated oligonucleotides could bind with high affinity to duplex DNAs containing complementary sites. Taken together, our data suggest that there may be an asymmetry involved in the process of purine-motif triplex formation, with interactions between the 3' end of the oligonucleotide and complementary sequences on the target duplex DNA being dominant.

Base Sequence↗

PubMed1993

Monovalent cation effects on intermolecular purine-purine-pyrimidine triple-helix formation.

The binding of a 19-mer guanosine-rich oligodeoxyribonucleotide, TG3TG4TG4TG3T (ODN 1), to a complementary polypurine DNA target was investigated by DNase I footprinting and restriction endonuclease protection assays. Monovalent cations inhibited intermolecular purine-purine-pyrimidine triple-helical DNA formation, with K+ and Rb+ being most effective, followed by NH4+ and Na+. Li+ and Cs+ had little to no effect. Similar results were observed with the G/A-rich oligonucleotide AG3AG4AG4AG3AGCT. Kinetic studies indicated that monovalent cations interfered with oligonucleotide-duplex DNA association but did not significantly promote triplex dissociation. The observed order of monovalent cation inhibition of triplex formation is reminiscent of their effect on tetraplex formation with G/T-rich oligonucleotides. However, using electrophoretic mobility shift assays we found that the oligonucleotide ODN 1 did not appear to form a four-stranded species under conditions promoting tetraplex formation. Taken together, our data suggest that processes other than the self-association of oligonucleotides into tetraplexes might be involved in the inhibitory effect of monovalent cations on purine-pyrimidine-purine triplex formation.

Base Sequence↗