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Biomedical subjects

B H Woo

Publications and source records attributed to B H Woo.

At least 19 recordsLinked to original sources
PubMed2002

Birth prevalence of Down syndrome in Singapore from 1993 to 1998.

OBJECTIVE: To examine the livebirth prevalence rate of Down Syndrome in Singapore from 1993 to 1998. DESIGN: Index cases for the National Birth Defects Register were obtained from all neonatal nurseries in Singapore, all hospital discharge summaries, cytogenetic and pathology reports from all pathology laboratories in Singapore and from the compulsory reporting of all termination of pregnancy cases and stillbirths delivered. SETTING: Information for the Register was obtained from case notes retrieved from the medical record offices, antenatal clinics, cytogenetic laboratories, pathology departments and the Registry of Births and Deaths. SUBJECTS: All foetuses with Trisomy 21 diagnosed prenatally together with livebirths and stillbirths with Down Syndrome diagnosed at or after birth were identified from the Registry database. MAIN OUTCOME MEASURES: Prevalence of Down Syndrome RESULTS: From 1993 to 1998, there were 295 Down Syndrome livebirths, four stillbirths and 197 Down Syndrome foetuses aborted. There has been an increasing number of Down Syndrome foetuses diagnosed antenatally ending in termination and this is accompanied by a falling trend in the Down Syndrome livebirth rate in the same years from 1.17 to 0.89 per 1000 total live births. This is despite an expected increase in Down Syndrome livebirth rate obtained by modelling maternal Down Syndrome age-related risks on the maternal age distribution over the years. CONCLUSIONS: The livebirth prevalence of Down Syndrome in Singapore has fallen over the years from 1.17/1000 livebirths in 1993 to 0.89/1000 livebirths in 1998 due to antenatal diagnosis and selective termination.

Abortion, Induced↗
PubMed2001

Preparation, characterization and in vivo evaluation of 120-day poly(D,L-lactide) leuprolide microspheres.

A 120-day poly(D,L-lactide) (PLA) microsphere delivery system for a luteinizing hormone-releasing hormone (LHRH) analogue, leuprolide, was prepared and evaluated. Leuprolide microspheres were prepared with PLA (m.w. 11000 Da) by a dispersion/solvent extraction-evaporation method and characterized for drug load by HPLC, particle size by laser diffractometry and surface morphology by scanning electron microscopy. In vitro peptide release and polymer degradation were studied using a modified dialysis method. Serum peptide and testosterone levels were analyzed after subcutaneous administration using a rat model. Spherical microspheres with a mean diameter of 52 microm containing 13.4% peptide released 10% of the peptide within 24 h, followed by a linear release for 150 days. Serum leuprolide levels increased immediately after administration of the microspheres to 45.6 ng/ml, but then fell to 4.3 ng/ml at 15 days and approximately 2.0 ng/ml at 30 days where they remained for 120 days. The testosterone levels increased initially to 15 ng/ml and then decreased to below 0.5 ng/ml by day 4 where they remained for 120 days. In conclusion, a 120-day microsphere formulation of leuprolide was developed with excellent controlled peptide release characteristics and in vivo efficacy.

Animals↗
PubMed2001

Sepharose-unbinding ricin E as a source for ricin A chain immunotoxin.

To evaluate the Sepharose-unbinding ricin E as a preference source material for ricin A chain (RTA) in immunotoxin studies, RTA of ricin E (RTA(E)) was characterized and compared with RTA of the Sepharose-binding ricin D (RTA(D)). RTA(E) and RTA(D) were separated into two subunits of A(1) and A(2) by capillary electrophoresis. The isoelectric points of A(1) and A(2) subunits were determined to be 7.6 and 7.4, respectively, for RTA(E), while they were 7.4 and 7.3, respectively, for RTA(D). The molecular masses of A(1) and A(2) isomers determined by the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry were 31059 and 32266 Da, respectively, for RTA(E), while they were 30892 and 32179 Da, respectively, for RTA(D). There were no significant differences in the cell surface affinity and cytotoxicity between RTA(E) and RTA(D). Anti-CD4-RTA(E) immunotoxin was prepared by conjugating RTA(E) with anti-CD4 monoclonal antibody using a heterobifunctional crosslinker, 4-succinimidyl-oxycarbonyl-alpha-methyl-alpha-(2-pyridyldithio) toluene. Anti-CD4-RTA(E) immunotoxin showed comparable cytotoxic effects to anti-CD4-RTA(D) immunotoxin to antigen-positive CEM cells in vitro. It is concluded that RTA(E) from ricin E is one of different variants of RTA(D) and may be used as a preference source material of RTA in immunotoxin studies.

Animals↗
PubMed2001

Matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-3 mRNA expression in ectopic and eutopic endometrium in women with endometriosis: a rationale for endometriotic invasiveness.

OBJECTIVE: To investigate mRNA expression of metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-3 (TIMP-3) in ectopic endometriosis tissue and uterine endometrium from women with and without endometriosis throughout the menstrual cycle. DESIGN: Molecular studies in human tissue. SETTING: Department of Gynecology and Obstetrics, Reproductive Immunology Laboratory, Stanford University Medical Center. PATIENT(S): Fifty-three premenopausal woman (23 women with endometriosis and 30 women without endometriosis undergoing laparoscopic surgery). Endometrium and ectopic endometriosis tissue were obtained at the time of surgery. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): mRNA expression from eutopic and ectopic endometrium was analyzed by quantitative, competitive PCR. RESULT(S): Both uterine endometrium and ectopic endometriotic tissue from women with endometriosis expressed significantly (P<.05) lower levels of TIMP-3 than endometrium from normal women. Also, ectopic endometrium expressed higher levels of MMP-9 and a higher ratio of MMP-9/TIMP-3 than eutopic endometrium from normal and endometriosis patients. CONCLUSION(S): These results suggest that ectopic and eutopic endometrium from endometriosis patients may be more invasive and prone to peritoneal implantation because of greater MMP and less TIMP-3 mRNA expression than endometrium from women without endometriosis. Thus, increased proteolytic activity may be one of the reasons for the invasive properties of the endometrium, resulting in the development of endometriosis.

Actins↗
PubMed2001

Preparation and characterization of a composite PLGA and poly(acryloyl hydroxyethyl starch) microsphere system for protein delivery.

PURPOSE: To prepare and characterize a novel composite microsphere system based on poly(D,L-lactide-co-glycolide) (PLGA) and poly(acryloyl hydroxyethyl starch) (acHES) hydrogel for controlled protein delivery. METHODS: Model proteins, bovine serum albumin, and horseradish peroxidase were encapsulated in the acHES hydrogel, and then the protein-containing acHES hydrogel particles were fabricated in the PLGA matrix by a solvent extraction or evaporation method. The protein-loaded PLGA-acHES composite microspheres were characterized for protein loading efficiency, particle size, and in vitro protein release. Protein stability was examined by size-exclusion chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and monitoring the enzymatic activity. RESULTS: Scanning electron microscopy showed discrete PLGA microspheres containing many acHES particles. The composite microspheres were spherical and smooth in size range of 39-93 microm. The drug loading efficiency ranged from 51 to 101%. The composite microspheres showed more favorable in vitro release than conventional PLGA microspheres. The composite microspheres showed 20% less initial with a gradual sustained release compared to high burst (approximately 60%) followed by a very slow release with the conventional PLGA microspheres. The composite microspheres also stabilized encapsulated proteins from the loss of activity during the microsphere preparation and release. Proteins extracted from the composite microspheres showed good stability without protein degradation products and structural integrity changes in the size-exclusion chromatography and SDS-PAGE analyses. Horseradish peroxidase extracted from microspheres retained more than 81% enzymatic activity. CONCLUSION: The PLGA-acHES composite microsphere system could be useful for the controlled delivery of protein drugs.

Acrylic Resins↗
PubMed2001

Enhancement of bone growth by sustained delivery of recombinant human bone morphogenetic protein-2 in a polymeric matrix.

PURPOSE: The purpose of this study was to develop a polymeric sustained delivery system for recombinant human bone morphogenetic protein-2 (BMP-2) and to evaluate local bone growth induced by the sustained release of BMP-2 in an animal model. METHODS: BMP-2 was incorporated in biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microspheres to obtain different release rates. Two sustained and an immediate release implants were produced by suspending the BMP-2 loaded PLGA microspheres in aqueous sodium carboxymethylcellulose (CMC), lyophilizing, and cutting the dried materials to the size of the animal bone defects. The local in vivo release at the implantation site in rat calvarial defects was determined by gamma scintigraphy using radiolabeled BMP-2. The local bone induction in the critical size of rabbit calvarial defects was evaluated six weeks post implantation. RESULTS: The immediate release implant showed about 65% initial drug release within 24 h and the remaining BMP-2 quickly exhausted from the implantation site within 7 days. The sustained release implants, showing 45-55% initial release followed by a prolonged release for 21 days, released a greater amount of BMP-2 at the implantation site and maintained higher serum BMP-2 for the longer period of time compared to the immediate release implant. Significant bone growth was observed in all BMP-2 treated defects while the defects without treatment or with BMP-2-free implant showed minimal bone healing. 75-79% of rabbit calvarial defect area was healed with newly induced bone matrix by the sustained release implants in 6 weeks as compared to 45% recovery from the immediate release implant. CONCLUSION: The sustained delivery of BMP-2 based on the biodegradable PLGA microsphere system resulted in faster and more complete bone healing in the animal model.

Animals↗
PubMed2001

Is air pollution a risk factor for low birth weight in Seoul?

Environmental factors contributing to reduced birth weight are of great concern because of the well-known relation of birth weight to infant mortality and adverse effects in later life. We examined the associations between air pollution exposures during pregnancy and low birth weight among all full-term births (gestational age 37-44 weeks) for a 2-year period (January 1996 through December 1997) in Seoul, South Korea. We evaluated these associations with a generalized additive logistic regression adjusting for gestational age, maternal age, parental educational level, parity, and infant sex. We used smoothing plots with generalized additive models to analyze the exposure-response relation for each air pollutant. The adjusted relative risk of low birth weight was 1.08 [95% confidence interval (CI) = 1.04-1.12] for each interquartile increase for carbon monoxide concentrations during the first trimester of pregnancy. The relative risks were 1.07 (95% CI = 1.03-1.11) for nitrogen dioxide, 1.06 (95% CI = 1.02-1.10) for sulfur dioxide, and 1.04 (95% CI = 1.00-1.08) for total suspended particles also for interquartile increase in exposure. Carbon monoxide, nitrogen dioxide, sulfur dioxide, and total suspended particle concentrations in the first trimester of pregnancy period are risk factors for low birth weight.

Adult↗
PubMed2000

Formulation and in vitro transfection efficiency of poly (D, L-lactide-co-glycolide) microspheres containing plasmid DNA for gene delivery.

The stability, in vitro release, and in vitro cell transfection efficiency of plasmid DNA (pDNA) poly (D,L-lactide-co-glycolide) (PLGA) microsphere formulations were investigated. PLGA microspheres containing free and polylysine (PLL)-complexed pDNA were prepared by a water-oil-water solvent extraction/evaporation technique. Encapsulation enhanced the retention of the supercoiled structure of pDNA as determined by gel electrophoresis. PLL complexation of pDNA prior to encapsulation increased both the stability of the supercoiled form and the encapsulation efficiency. Free pDNA was completely degraded after exposure to DNase, while encapsulation protected the pDNA from enzymatic degradation. Rapid initial in vitro release of pDNA was obtained from microspheres containing free pDNA, while the release from microspheres containing PLL-complexed pDNA was sustained for more than 42 days. Bioactivity of encapsulated pDNA determined by in vitro cell transfection using Chinese hamster ovary cells (CHO) showed that the bioactivity of encapsulated pDNA was retained in both formulations but to a greater extent with PLL-complexed pDNA microspheres. These results demonstrated that PLGA microspheres could be used to formulate a controlled-release delivery system for pDNA that can protect the pDNA from DNase degradation without loss of functional activity.

Animals↗
PubMed1999

Influence of formulation parameters on the characteristics of poly(D, L-lactide-co-glycolide) microspheres containing poly(L-lysine) complexed plasmid DNA.

This study describes the influence of polymer type, surfactant type/concentration, and target drug loading on the particle size, plasmid DNA (pDNA) structure, drug loading efficiency, in vitro release, and protection from DNase I degradation of poly(D, L-lactide-co-glycolide) (PLGA) microspheres containing poly(L-lysine) (PLL) complexed pDNA. PLGA microspheres containing pDNA-PLL were prepared using the water-in-oil-in-water (w-o-w) technique with poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) as surfactants in the external aqueous phase. A complex ratio of 1:0.33 (pDNA-PLL, w/w) enhanced the stability of pDNA during microsphere preparation. Higher pDNA-PLL loading efficiency (46.2%) and supercoiled structure (64.9%) of pDNA were obtained from hydrophobic PLGA (M(w) 31000) microspheres compared with hydrophilic PLGA or low-molecular-weight PLGA microspheres. The particle size decreased from 6.6 to 2.2 microm when the concentration of PVA was increased from 1 to 7%. At the same concentration of surfactant, PVA stabilized microspheres showed higher pDNA-PLL loading efficiency (46.2%) than PVP stabilized microspheres (24.1%). Encapsulated pDNA in PLGA microspheres was protected from enzymatic degradation and maintained in the supercoiled form. The pDNA-PLL microspheres showed in vitro release of 95.9 and 84.9% within 38 days from the low-molecular-weight PLGA and hydrophilic PLGA microspheres, respectively, compared to 54.2% release from the hydrophobic, higher-molecular-weight PLGA microspheres. The results suggest loading and release of pDNA-PLL complex can be influenced by surfactant concentration and polymer type.

DNA Adducts↗
PubMed1999

Stability and cytotoxicity of Fab-ricin A immunotoxins prepared with water soluble long chain heterobifunctional crosslinking agents.

The effects of the hindered and non-hindered water soluble long-chain disulfide bonds on the stability and cytotoxicity of the ricin A chain (RTA) immunotoxin were examined. The RTA immunotoxins were prepared with the Fab fragments of anti-common acute lymphoblastic leukemia antigen (CALLA) monoclonal antibody (Fab-RTA) using sulfosuccinimidyl-6-[(-methyl-(-(2-pyridyldithio)toluamido]hexanoate (S-LC-SMPT) and sulfosuccinimidyl-6-[3-(2-pyridyldithio)-propionamido]hexanoate (S-LC-SPDP). The prepared Fab-RTA immunotoxins were evaluated for their conjugation yield, immunoreactivity, thermal and disulfide bond stability and cytotoxicity. The conjugation yield of the Fab-RTA immunotoxin from the water soluble long chain crosslinking agents, S-LC-SMPT and S-LC-SPDP, were comparable. Both Fab-RTA immunotoxins exhibited a similar immunoreactivity and thermal stability in aqueous solution. However, S-LC-SMPT -mediated Fab-RTA, sterically hindered, showed an enhanced disulfide bond stability in vitro over S-LC-SPDP mediated one. In the cytotoxicity against antigenic cell Daudi, the S-LC-SMPT -mediated RTA immunotoxin maintained a comparable cytotoxicity, compared with S-LC-SPDP mediated Fab-RTA immunotoxin.

Animals↗
PubMed1999

Isolation and characterization of biologically active lectin from Korean mistletoe, Viscum album var. Coloratum.

A mistletoe lectin was isolated from water extracts of Korean mistletoe, a subspecies of Viscum album, grown on Quercus mongolica using CM-Sepharose chromatography followed by an affinity chromatography on a concanavalin A-Sepharose column. The compound proved to be a mistletoe lectin II with D-galactose and N-acetyl-D-galactosamine specificity. Matrix-assisted laser desorption time-of-flight mass spectroscopy showed it to have an average molecular mass of 62.7 kDa and to consist of two subunits of 30.6 kDa and 32.5 kDa. It was a basic protein with isoelectric points of 9.4 and 9.6 by capillary isoelectric focusing and was cytotoxic to Molt4 cell.

Humans↗
PubMed1999

Preparation and characterization of poly (D,L-lactide-co-glycolide) microspheres for controlled release of poly(L-lysine) complexed plasmid DNA.

PURPOSE: To produce and characterize controlled release formulations of plasmid DNA (pDNA) loaded in poly (D,L-lactide-co-glycolide) (PLGA) microspheres both in free form and as a complex with poly (L-lysine). METHODS: Poly (L-lysine) (PLL) was used to form pDNA/PLL complexes with complexation ratio of 1:0.125 and 1:0.333 w/w to enhance the stability of pDNA during microsphere preparation and protect pDNA from nuclease attack. pDNA structure, particle size, zeta potential, drug loading, in vitro release properties, and protection from DNase I were studied. RESULTS: The microspheres were found to be spherical with average particle size of 3.1-3.5 microm. Drug loading of 0.6% was targeted. Incorporation efficiencies of 35.1% and 29.4-30.6% were obtained for pDNA and pDNA/PLL loaded microspheres respectively. Overall, pDNA release kinetics following the initial burst did not correlate with blank microsphere polymer degradation profile suggesting that pDNA release is convective diffusion controlled. The percentage of supercoiled pDNA in the pDNA and pDNA/PLL loaded microspheres was 16.6 % and 76.7-85.6% respectively. Unencapsulated pDNA and pDNA/PLL degraded completely within 30 minutes upon the addition of DNase I. Encapsulation of DNA/PLL in PLGA microspheres protected pDNA from enzymatic degradation. CONCLUSIONS: The results show that using a novel process, pDNA can be stabilized and encapsulated in PLGA microspheres to protect pDNA from enzymatic degradation.

Biocompatible Materials↗
PubMed1999

Preparation and characterization of polyethylene-glycol-modified salmon calcitonins.

The conjugation of salmon calcitonin (sCT) by covalent linkage of polyethylene glycol (PEG) was attempted to overcome several disadvantages of sCT as a therapeutic drug, namely its rapid clearance from blood circulation and enzymatic degradation. The polymer employed was succinimidyl carbonate monomethoxypolyethylene glycol (12 kDa). Superose HR size-exclusion chromatography was applied to separate the PEGylated sCTs (mono-PEG-sCT and di-PEG-sCT) from the unmodified sCT. The PEGylation of sCT was verified by an electrophoresis gel stained with iodine and by MALDI-TOF mass spectrometry. The molecular weights of mono-PEG-sCT and di-PEG-sCT were determined to be 16,094 and 29,077 Da, respectively. PEGylated sCTs showed a substantially improved stability in rat liver homogenates as compared to the intact sCT, indicating that PEG molecules protected sCT from various degrading enzymes. These PEGylated sCTs exhibited similar biological activity to the intact sCT by adenosine cyclic 3',5'-phosphate (cAMP) assay. In clearance studies in the rat, PEGylated sCTs had significantly longer circulating half-lives than the intact sCT (11.2 min for mono-PEG-sCT and 54.0 min for di-PEG-sCT versus 4.7 min for intact sCT).

Amino Acid Sequence↗
PubMed1999

Stability of poly(L-lysine)-complexed plasmid DNA during mechanical stress and DNase I treatment.

The aim of this study was to investigate the formation and stability of complexes between plasmid DNA (pDNA) and poly(L-lysine) (PLL). Formation of pDNA/PLL complexes with various ratios was determined by a fluorescence spectrophotometric method using fluorescamine. The effects of sonication, vortexing, and exposure to DNase I on the stability of free pDNA and pDNA/PLL complexes are discussed. A linear correlation between PLL added and PLL bound was obtained with overall reaction efficiency of 84.2-92.6%. Sonication degraded both free and PLL-complexed pDNA within 15 sec of vortexing. However, vortexing did not alter the stability of free and complexed pDNA. Dramatic increase in the protection of pDNA in pDNA/PLL complexes was observed in the DNase I digestion experiment; 68.1-89.0% of total pDNA in the pDNA/PLL complexes was protected from DNase I digestion compared to only 19.2% of total pDNA that remained undegraded after DNase I treatment of free pDNA. An increase in the PLL/pDNA ratio led to an increase in the protection of supercoiled pDNA; 15.5-38.2% of supercoiled pDNA pin PLL/pDNA complexes was protected after DNase I treatment. The results show that complexation of pDNA with PLL can stabilize the supercoiled structure of pDNA for the development of biodegradable microspheres as a delivery system for pDNA. Stability of pDNA/PLL complex can be monitored by PicoGreen dye and fluorescence densitometric assay methods.

DNA↗