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Chi Pui Pang

Publications and source records attributed to Chi Pui Pang.

At least 37 records · Page 2Linked to original sources
PubMed2004

Absence of myocilin and optineurin mutations in a large Philippine family with juvenile onset primary open angle glaucoma.

PURPOSE: To analyze the role of the two primary open angle glaucoma (POAG) genes, myocilin (MYOC) and optineurin (OPTN), in a large Philippine family segregating autosomal dominant juvenile onset open angle glaucoma (JOAG). METHODS: The coding sequences of the MYOC and OPTN genes were screened in 27 family members by polymerase chain reaction and direct sequencing. The specific MYOC promoter polymorphism (MYOC.mtl) was identified by restriction endonuclease assay. All of the ABI MD-10 microsatellite markers on chromosomes 1, 2, 3, 7, 8, and 10, which harbor the six known POAG loci, were analyzed for linkage with POAG. RESULTS: No mutation was identified in this large kindred. Instead, three polymorphisms (-80G->A, -1000G->C, R76K) in MYOC and four polymorphisms (T34T, M98K, R545Q, IVS7+24G->A) in OPTN were found. All markers flanking the six known POAG loci gave LOD scores not more than 1.1. Non-parametric linkage analysis for all these markers resulted in p values more than 0.05. CONCLUSIONS: Both mutation testing and linkage analysis provide strong evidence against MYOC and OPTN being the causative gene in this large family. It indicates that unidentified genes will underlie the occurrence of glaucoma in this family.

Adult↗
PubMed2004

Determination of catechins and catechin gallates in tissues by liquid chromatography with coulometric array detection and selective solid phase extraction.

Catechins levels in organ tissues, particularly liver, determined by published methods are unexpectedly low, probably due to the release of oxidative enzymes, metal ions and reactive metabolites from tissue cells during homogenization and to the pro-oxidant effects of ascorbic acid during sample processing in the presence of metal ions. We describe a new method for simultaneous analysis of eight catechins in tissue: (+)-catechin (C), (-)-epicatechin (EC), (-)-gallocatechin (GC), (-)-epigallocatechin (EGC), (-)-catechin gallate (CG), (-)-epicatechin gallate (ECG), (-)-gallocatechin gallate (GCG) and (-)-epigallocatechin gallate (EGCG) (Fig. 1). The new extraction procedure utilized a methanol/ethylacetate/dithionite (2:1:3) mixture during homogenization for simultaneous enzyme precipitation and antioxidant protection. Selective solid phase extraction was used to remove most interfering bio-matrices. Reversed phase HPLC with CoulArray detection was used to determine the eight catechins simultaneously within 25 min. Good linearity (>0.9922) was obtained in the range 20-4000 ng/g. The coefficients of variance (CV) were less than 5%. Absolute recovery ranged from 62 to 96%, accuracy 92.5 +/- 4.5 to 104.9 +/- 6%. The detection limit was 5 ng/g. This method is capable for determining catechins in rat tissues of liver, brain, spleen, and kidney. The method is robust, reproducible, with high recovery, and has been validated for both in vitro and in vivo sample analysis.

Animals↗
PubMed2004

Two cases of X-linked juvenile retinoschisis with different optical coherence tomography findings and RS1 gene mutations.

The optical coherence tomography (OCT) findings, clinical features, and mutations in the RS1 gene of two unrelated patients with X-linked retinoschisis (XLRS) are reported herein. Two Chinese patients with early onset XLRS were given a comprehensive ophthalmologic examination and OCT investigation. The RS1 gene was screened for sequence alterations in all exons and splice regions. The two patients presented with different phenotypic features and OCT findings. One patient with more severe clinical presentation had a RS1 exon 1 deletion and a P193S mutation was found in the other patient with mild macular involvement. OCT demonstrates the markedly different features of XLRS patients with different RS1 mutations. This study strengthens the role of OCT in the diagnosis and monitoring of XLRS.

Adolescent↗
PubMed2004

Microsatellite instability and MLH1 promoter methylation in human retinoblastoma.

PURPOSE: To investigate the link between microsatellite instability and epigenetic silencing of the MLH1 gene in the human retinoblastoma genome. METHODS: Methylation at the 5' region of MLH1 was studied, along with its protein expression level by using immunohistochemical staining in 51 retinoblastoma tumors and 2 retinoblastoma cell lines. Also assessed was the genomic stability of 26 retinoblastoma DNAs from microdissected tumor tissue and matched normal retina tissue obtained from the same patient by microsatellite instability (MSI) analysis. The National Cancer Institute-designed reference panel, and 85 markers on chromosomes 1, 6, 9, and 13 were used. RESULTS: Hypermethylation of the MLH1 promoter was detected in the WERI-Rb1 cell line and in 34 (67%) of the 51 tumors, but not in cell line Y79 and the other 17 tumors. MLH1 hypermethylation was associated with null MLH1 protein expression (P < 0.0005) and with well-differentiated histology (P < 0.05). MSI at three markers (D2S123, D6S470, and D13S265) was frequently identified among 26 retinoblastoma specimens with matched normal DNA. Among these 26 retinoblastomas, high-frequency MSI (MSI-H) tumors were detected in 19% (5/26) and low-frequency MSI (MSI-L) in another 19% (5/26). The remaining 62% (15/26) were genetically stable (MSS). MSI status (MSS, MSI-L, and MSI-H) was not associated with MLH1 promoter hypermethylation (P = 0.088; Kruskal-Wallis test). CONCLUSIONS: Epigenetic silencing of the DNA repair gene MLH1 by promoter hypermethylation is a frequent event in retinoblastoma. The results showed that somatic genetic changes involving MSI occur in a subset of retinoblastoma and implicated the presence of a defective DNA mismatch repair pathway resulting in MSI in retinoblastoma.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Genetic alterations on chromosome 19, 20, 21, 22, and X detected by loss of heterozygosity analysis in retinoblastoma.

PURPOSE: To explore the presence of common genetic alterations in retinoblastoma and to localize the altered genomic regions. METHODS: Genetic analysis included determinations of the loss of heterozygosity (LOH) and microsatellite instability (MSI) on chromosomes 19, 20, 21, 22, and X. Investigations were carried out among 15 microdissected retinoblastoma tumors and corresponding genomic DNA specimens. RESULTS: Among the 15 retinoblastoma cases, 73% (11/15) showed genome instability (LOH and/or MSI) at one or more loci on the 5 chromosomes, although loci with recurrent LOH was infrequent. The loss of a single allele was more frequent in chromosomes 19 (33%) and 20 (27%) than the other 3 chromosomes. Five loci with recurrent allelic loss were identified, among them the most frequent allelic losses were between D19S902 and D19S571 on 19q13 and were identified in 3 out of the 15 tumor specimens. The results suggested that gene loci in the 19q13 region may be associated with tumor development in retina. In addition, 3 specimens showed moderate frequency of LOH and/or MSI in more than 6 microsatellite markers, indicating genomic instability to occur at least in a subset of retinoblastoma. CONCLUSIONS: Our results provide the first evidence of LOH in chromosomes 19 and 20 in retinoblastoma. They also support the proposition that presence of genome instability in retinoblastoma may play a role in the tumorigenesis or progression of retinoblastoma.

Child, Preschool↗
PubMed2003

The dual role of dexamethasone on anti-inflammation and outflow resistance demonstrated in cultured human trabecular meshwork cells.

PURPOSE: Dexamethasone (DEX) is a glucocorticoid commonly used in topical eyedrops to treat eye inflammation. It has an undesirable effect of inducing glaucoma in certain patients. In human Trabecular Meshwork (TM) cells DEX regulates a number of genes but its global influence on TM gene expression is still elusive. In the present work, DEX effects on global gene expressions of an established human TM cell line were studied by microarray. METHODS: The whole experiment of microarray was repeated three times. Differentially expressed genes were identified by an empirical Bayes approach and confirmed by Reverse Transcription Polymerase Chain Reaction. RESULTS: Eight genes (GAS1, CDH4, MT1L, CST3, ATF4, ASNS/TS11, CHOP, HSPA5) were identified that are at least a thousand times more likely to be differentially expressed due to DEX treatment and six genes (TSC22, LDHA, IGFBP2, TAGLN, SCG2, WARS) were identified that are at least a hundred times more likely to be differentially expressed due to DEX treatment. Except for MT1L, ASNS/TS11, IGFBP2, SCG2, and WARS, all the other genes are first reported here to be regulated by DEX in TM. Intriguingly, several of them have overlapping roles in anti-inflammatory response and outflow resistance. CONCLUSIONS: The results of our experiments on cultured human TM cells indicate that the increase in outflow resistance and ultimate ocular hypertension may be byproducts of the favorable anti-inflammatory response triggered by DEX.

Anti-Inflammatory Agents↗
PubMed2003

Quantifying F2-isoprostanes in umbilical cord blood of newborn by gas chromatography-mass spectrometry.

We attempted to improve the extraction procedures to determine the F(2)-isoprostanes in plasma of umbilical cord arterial and venous blood by gas chromatography mass spectrometry. Plasma samples were deproteinized and hydrolyzed; free and esterified F(2)-isoprostanes were extracted by solid-phase extraction columns with citric acid/methanol/cyclohexane and ammonia solution/methanol and then derivatized by PFBBr and BSTFA. Concentrations of total plasma F(2)-isoprostanes eluted at the retention time of an internal standard of 8-iso-prostaglandin F(2alpha)-D(4) were quantified. The absolute recovery was 83+/-1.9% (95% confidence). Intraassay precision and interassay precision were lower than 1.0%. Analytical accuracy was 99.0+/-0.4% (95% confidence). Linearity, r(2), over the concentration range of 10 to 5000 pg/ml of spiked 8-iso-prostaglandin F(2alpha) in plasma was 0.9985. The method detection limit was 21 pg/ml (99% confidence) and the limit of quantitation was approximately 4 pg/ml. Analysis of 200 neonatal cord blood samples revealed few overlapping peaks causing interference in the elution of the F(2)-isoprostanes. With the use of an autosampler and one technician, 48 samples can be completed within 24h with 6h of actual hands-on work. This method could be potentially employed for routine analysis of plasma F(2)-isoprostanes in clinical laboratories.

F2-Isoprostanes↗
PubMed2003

Ocular-hypertensive and anti-inflammatory response to rimexolone therapy in children.

OBJECTIVE: To compare the ocular-hypertensive and anti-inflammatory response to rimexolone (116-hydroxy-16alphafluoro-6alphamethylpresdnisolone) and fluorometholone (21-deoxy-9alphafluoro-6alphamethylprednisolone) therapy in children's eyes. METHODS: With parental consent, children who underwent surgical procedures for bilateral symmetric strabismus from January 18, 2000, through November 16, 2001, were recruited. One eye was randomized to receive topical 1% rimexolone while the contralateral eye received topical 0.1% fluorometholone, 4 times daily for 4 weeks. MAIN OUTCOME MEASURES: Intraocular pressures and anti-inflammatory responses were the main outcome measures and were serially measured postoperatively for 8 weeks. RESULTS: Fifty-four children, aged from 4 to 8 years (mean [SD] age, 5.33 [1.26] years), participated in the study. Intraocular pressure increased significantly in both treatment groups compared with the preoperative values (P<.001). The mean (SD) peak intraocular pressure was significantly higher in the rimexolone-treated group, 19.7 (6.1) vs 17.6 (4.6) mm Hg (P<.001). Similarly, the mean (SD) net increase in intraocular pressure (P<.001), was also higher in the rimexolone-treated eyes, 5.9 (4.4) vs 3.9 (4.1) mm Hg (P<.001). In addition, a greater percentage of the rimexolone-treated patients had no conjunctival erythema on days 13 (11.1% vs 0.0%) and 20 (88.9% vs 55.6%) (P =.03). CONCLUSIONS: Rimexolone seems to be a more effective anti-inflammatory agent than fluorometholone. However, unlike adults, the ocular-hypertensive effect in children treated with rimexolone was higher. It would be desirable to monitor the intraocular pressure regularly when rimexolone therapy is used in children.

Anti-Inflammatory Agents↗
PubMed2003

Effect of indocyanine green and illumination on gene expression in human retinal pigment epithelial cells.

PURPOSE: To investigate the biological effects of indocyanine green (ICG) and acute illumination on human retinal pigment epithelial (RPE) cells. METHODS: Three concentrations (0, 0.25, and 2.5 mg/mL) of ICG were applied to ARPE19 cells for 1 minute. After isotonic rinsing, the cells were irradiated with a light beam with a wavelength spectrum from 400 to 800 nm and an output of 1850 lumens for 15 minutes. The cells were collected at timed intervals for the investigation of cell death and expression of stress-response genes by reverse transcription-polymerase chain reaction, immunofluorescence, and Western blot analysis. RESULTS: After ICG incubation, photoreactive changes were observed in the RPE cells. A reduction in cellular viability and considerable shrinkage of the cells were observed. The expressions of the apoptosis-related genes p53 and bax and the cell cycle arrest protein p21 were upregulated in cells treated with both ICG and light. Of the early-response genes, the expression of c-fos was specifically enhanced by light, with additive effects from the presence of ICG. Such stimulatory effects on these gene expressions were greater at 2.5 mg/mL than at 0.25 mg/mL ICG. CONCLUSIONS: ICG in the presence of acute illumination can elicit cell-cycle arrest and even apoptosis in RPE cells. The establishment of a safety level in the application of ICG in the region of 0.25 mg/mL is recommended.

Apoptosis↗
PubMed2003

TGFbeta-induced factor: a candidate gene for high myopia.

PURPOSE: To investigate the coding exons of transforming growth factor (TGF)-beta-induced factor (TGIF) for mutations in Chinese patients with high myopia. METHODS: Seventy-one individuals with high myopia of -6.00 D or less and 105 control subjects were screened by DNA sequencing for sequence alterations. Univariate analysis and logistic regression were performed to identify single-nucleotide polymorphisms (SNPs) and their interactions in TGIF that may be associated with myopia. RESULTS: Six SNPs showed a significant difference (P < 0.05) between patient and control subject in univariate analysis. Four of them cause codon changes: G223R, G231S, P241T, and A262G. Among all the SNPs that entered multivariate analysis, only 657(T-->G) showed statistical significance in the logistic regression model (odds ratio 0.133; 95% confidence interval 0.037-0.488; P = 0.002). CONCLUSIONS: TGIF is a probable candidate gene for high myopia. Further studies are needed to identify the underlying mechanism.

Adult↗
PubMed2003

Different optineurin mutation pattern in primary open-angle glaucoma.

PURPOSE: The optineurin gene (OPTN) is the second gene besides MYOC in which mutations have been identified to be associated with primary open-angle glaucoma (POAG). In this study, sequence alterations in the OPTN gene associated with POAG in Chinese subjects were investigated. METHODS: All the coding exons of OPTN were screened, including the intron-exon boundaries, for sequence alterations in a Chinese sample of 119 sporadic patients with POAG and 126 unrelated control subjects by polymerase chain reaction-conformation-sensitive gel electrophoresis and DNA sequencing. RESULTS: Sixteen sequence changes were identified: 3 had been reported (T34T, M98K, and R545Q) and 13 were novel (T49T, E103D, V148V, P199P, T202T, H486R, IVS6-5T-->C, IVS6-10G-->A, IVS7+24G-->A, IVS8+20G-->A, IVS13+21C-->G, IVS15+10G-->A, and IVS15-48C-->A). Among them, only E103D, H486R, V148V, and IVS13+21C-->G were found exclusively in patients with POAG, whereas P199P, T202T, and IVS8+20G-->A were present only in control subjects. The genotype of IVS7+24G-->A showed a significant association with POAG (P = 0.02, Fisher two-tailed exact test) and with and increased cup-to-disc ratio in these patients (P = 0.005, Mann-Whitney test). CONCLUSIONS: The findings in the current study enrich the evidence on the OPTN gene as a causative gene for POAG and suggest a different mutation pattern of OPTN in Chinese than in whites. The wide spectrum of putative mutations detected in this study suggests that both structural and functional disruptions in OPTN may contribute to the pathogenesis of glaucoma.

Adolescent↗
PubMed2003

The toxic and stress responses of cultured human retinal pigment epithelium (ARPE19) and human glial cells (SVG) in the presence of triamcinolone.

PURPOSE: To compare the cytotoxic effect of TA on human retinal pigment epithelium (ARPE19) and human glial (SVG) cells over a range of concentrations and durations of exposure. METHODS: TA (0.01-1 mg/mL) or vehicle (benzyl alcohol, 0.025%) was added to the ARPE19 and SVG cultures on day 0 and then subsequently for 1, 3, or 5 days. The amount of cell proliferations with or without TA treatment was performed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. All samples were read in triplicate (n = 4 in all cases). c-Fos, c-jun, caspase-3, c-myc, and p53 expression was determined after TA treatments after 0, 10, 20, 30, 40, 50, 60, and 90 minutes. All results were analyzed with ANOVA. RESULTS: TA (0.01-1 mg/mL) caused a significant reduction in ARPE19 cells that had been exposed to it for more than 1 day. Significant reductions in the number of SVG cells were observed as early as day 1 at 0.1 and 1 mg/mL TA. In general, the level of remaining SVG cells was less than that of the APRE19 cells over the 5 days. SVG cells appeared more susceptible to TA. Caspase-3 was elevated in both ARPE19 and SVG cells after TA treatment. c-Fos and c-jun expression was also increased in ARPE19 cells but not in SVG. The vehicle of TA had no effect, and there was no change in p53 or c-myc expression. CONCLUSIONS: TA was cytotoxic to both SVG and ARPE19 cells, with higher efficacy on SVG. TA caused the activation of the caspase-3 pathway more readily than the cell-protective c-fos and c-jun pathways in SVG cells, making those cells more vulnerable than the ARPE19 cells. The results suggest that TA toxicity in one cell type may not reliably indicate its toxicity in other cells. Different cells within the retina may react to TA differently, or TA may cause changes in the gene expressions differentially with different concentrations of the same stimulus.

Anti-Inflammatory Agents↗
PubMed2002

Differential occurrence of mutations causative of eye diseases in the Chinese population.

Ethnic differences and geographic variations affect the frequencies and nature of human mutations. In the literature, descriptions of causative mutations of eye diseases in the Chinese population are few. In this paper we attempt to reveal molecular information on genetic eye diseases involving Chinese patients from published and unpublished works by us and other groups. Our studies on candidate genes of eye diseases in the Chinese population in Hong Kong include MYOC and TISR for primary open angle glaucoma, RHO and RP1 for retinitis pigmentosa, ABCA4 and APOE for age-related macular degeneration, RB1 for retinoblastoma, APC for familial adenomatous polyposis with congenital hypertrophy of retinal pigment epithelium, BIGH3/TGFBI for corneal dystrophies, PAX6 for aniridia and Reiger syndrome, CRYAA and CRYBB2 for cataracts, and mtDNA for Leber hereditary optic neuropathy. We have revealed novel mutations in most of these genes, and in RHO, RP1, RB1, BIGH3, and PAX6 we have reported mutations that contribute to better understanding of the functions and properties of the respective gene products. We showed absence of MYOC does not necessarily cause glaucoma. No disease causative mutations have been identified in MYOC or ABCA4. There are similarities in the patterns of sequence alterations and phenotype-genotype associations in comparison with other ethnic groups, while the MYOC, RB1, APC, and PAX6 genes have more Chinese-specific sequence alterations. Establishment of a mutation database specific for the Chinese is essential for identification of genetic markers with diagnostic, prognostic, or pharmacological values.

Asian People↗
PubMed2002

Loss of heterozygosity and mutations are the major mechanisms of RB1 gene inactivation in Chinese with sporadic retinoblastoma.

We investigated sequence alternation, promoter methylation, and loss of heterozygosity (LOH) of the RB1 gene as possible mechanisms of its inactivation in retinoblastoma. In 42 Chinese patients with sporadic retinoblastoma, the promoter and entire coding region of RB1 were examined for sequence changes. Status of methylation of the CpG-rich island at the 5'end was determined by methylation specific PCR assay. We detected 15 RB1 mutations in 38% (16/42) of the retinoblastoma patients, among them 19% (8/42) were germ-line mutations. A total of nine novel mutations were identified: E54X, S114X, I126S, g73779insG, D718N, IVS2+1G>C, IVS14+1G>C, IVS21+1G>C, and a complex alteration g78177G>T/g78176insTT leading to 543X. Most of them are likely to affect the RB1large pocket domain through the production of truncated gene products. None of the DNA samples showed methylation at the RB1promoter. In 15 cases where both normal and cancerous retinoblastoma tissue specimens were available, allelic loss according to microsatellite markers within or distal to the RB1 locus was analyzed and immunohistological staining for RB1 expression performed. Among them, frequency of LOH at 13q14 was found to be high at 60% (9/15) with no segregation with unilateral tumors. All these nine tumors did not express RB1 protein, showing an association of LOH at the RB1 locus with its loss of expression in retinoblastoma. Our results indicate that the RB1 gene in sporadic retinoblastoma is commonly inactivated because of loss-of-function mutations and loss of heterozygosity but not by the epigenetic phenomenon of promoter hypermethylation.

Child, Preschool↗
PubMed2002

An in vitro study of ceftazidime and vancomycin concentrations in various fluid media: implications for use in treating endophthalmitis.

PURPOSE: To investigate the precipitation process of a mixture of vancomycin and ceftazidime by equilibrium dialysis and determine its subsequent effect on the level of free antibiotics for treatment of endophthalmitis. METHODS: Concentrations of vancomycin and ceftazidime in an equilibrium dialysis chamber were measured during the equilibrium process by high-performance liquid chromatography. Normal saline (NS), balanced salt solution (BSS), and vitreous were used separately as the medium of dialysis. RESULTS: Precipitation of ceftazidime occurred at 37 degrees C but not at room temperature and did not affect the pH of the medium. It formed precipitate on its own or when mixed with vancomycin in all the three media of NS, BSS, and vitreous. More precipitation was formed if ceftazidime was initially prepared in BSS than in NS. After 168 hours in the dialysis chambers, ceftazidime prepared in NS precipitated to 54% of that in vitreous, compared with 88% if prepared in BSS. At 48 hours, ceftazidime prepared in NS decreased from an initial concentration of 137.5 to 73.4 microg/mL in vitreous medium and to 6.3 microg/mL if prepared in BSS. Precipitation of vancomycin was negligible. CONCLUSIONS: Based on this in vitro investigation, ceftazidime precipitates in vitreous at body temperature, regardless of the presence of vancomycin. NS is preferred to BSS as a preparation medium for antibiotics for intravitreal injection, because the extent of ceftazidime precipitation is less. However, due to precipitation, the concentration of free ceftazidime in vitreous may not be sufficiently high for antibacterial activity against most common organisms.

Anti-Bacterial Agents↗
PubMed2002

Impaired expression and promotor hypermethylation of O6-methylguanine-DNA methyltransferase in retinoblastoma tissues.

PURPOSE: To investigate the role of epigenetic changes in the promoter region of tumor-suppressor genes in the retinoblastoma genome and to study the disruption of expression of O6-methylguanine-DNA Methyltransferase (MGMT) due to aberrant methylation and its association with retinoblastoma. METHODS: A series of 23 retinoblastoma tissue specimens and 2 retinoblastoma cell lines (Y79 and WERI-Rb1) were subjected to methylation-specific PCR (MSP) analysis of hypermethylated genes identified in human cancers, including p14(ARF), p15(INK4b), p16(INK4a), VHL, and MGMT. Further, the expression of MGMT was studied by immunohistochemistry and, when fresh tissue was available, by Western blot analysis and RT-PCR. RESULTS: Aberrant methylation of at least one MGMT locus was detected in 8 of the 23 tumors (35%), all of which (100%) had impaired or absent expression of MGMT. The remaining 15 tumor specimens were nonmethylated, and, among them, 7 (43%) showed defective expression. No methylation of tumor DNA was found on the p14(ARF), p15(INK4b), p16(INK4a), and VHL genes. Hypermethylation in the MGMT promoter was found to be prominently present in retinoblastoma with poor tissue differentiation, and was more frequently detected among patients with bilateral disease. Production of MGMT was consistent with expression of mRNA. No methylation of MGMT promoter was detected in the two retinoblastoma cell lines (Y79, WERI-Rb1). CONCLUSIONS: The data show a clear association between impaired production of MGMT and hypermethylation of the MGMT promoter, which appeared to relate to early onset and poor differentiation, suggesting that epigenetic silencing of MGMT by methylation of the promoter and reduced expression of MGMT may play an important role in the development and progression of retinoblastoma.

Blotting, Western↗