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Biomedical subjects

K K Yeung

Publications and source records attributed to K K Yeung.

At least 19 recordsLinked to original sources
PubMed2001

Capillary electrophoresis using a surfactant-treated capillary coupled with offline matrix-assisted laser desorption ionization mass spectrometry for high efficiency and sensitivity detection of proteins.

A method of combining capillary electrophoresis (CE) using a surfactant-modified capillary with matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is described for protein analysis. The CE-MALDI-MS coupling is based on CE fraction collection of nanoliter volume samples in less than 5 microl of dilute acid. This offline coupling does not require any special instrumentation and can be readily performed with commercial instruments. Protein adsorption during CE separation is prevented by coating the capillary with the surfactant didodecyldimethylammonium bromide. This surfactant binds strongly with the capillary wall, hence it does not desorb significantly to interfere with subsequent MALDI-MS analysis. It is shown that the use of a dilute acid for CE fraction collection is advantageous in lowering the detection limit of MALDI-MS compared to using an electrophoretic buffer. The detection limit for proteins such as cytochrome c is 23 fmol injected for CE, or 1.2 fmol spotted for MALDI-MS. This sensitivity is comparable to alternative CE-MALDI-MS coupling techniques using direct CE sample deposition on the MALDI target. In addition, the fraction collection approach has the advantage of allowing multiple reactions to be carried out on the fractioned sample. These reactions are very important in protein identification and structure analysis.

Cytochrome c Group↗
PubMed2001

Improved patency of infrainguinal polytetrafluoroethylene bypass grafts using a distal Taylor vein patch.

OBJECTIVE: The purpose of this study was to evaluate graft patency and limb salvage rates for infrainguinal polytetrafluoroethylene (PTFE) bypass grafts using distal anastomotic Taylor vein patch in patients lacking suitable vein conduit. METHODS: We reviewed 44 patients who underwent infrainguinal bypass between January 1996 and August 2000 using 6-mm PTFE and a distal Taylor vein patch. Postoperative oral anticoagulation was administered to 80% of patients. Graft patency was confirmed during follow-up with serial graft duplex scanning. RESULTS: Operative indications were rest pain, nonhealing ulcer, or gangrene in 76% of patients, 43% of whom had undergone previous ipsilateral leg bypass. Distal anastomotic sites were the below-knee popliteal (29%) and tibial-peroneal arteries (67%). At 1 month, 1 year, and 2 years, respectively, the primary patencies (SE <10%) were 86%, 71%, and 71%; limb salvage rates were 95%, 75%, and 66%; and mortality rates were 5%, 20%, and 20%. CONCLUSIONS: These early results with PTFE and distal Taylor vein patch are promising, and markedly superior to previous reports of PTFE without anastomotic modification. Further long-term follow-up will be necessary to determine the 3- to 5-year durability of such reconstructions.

Aged↗
PubMed2001

Aphakic hydrogel contact lens fitting on a monocular canine: a case report.

BACKGROUND: Though plano bandage contact lenses used for therapeutic purposes are not uncommon for dogs, no literature regarding contact lenses to correct aphakic canines currently exists. CASE REPORT: Oliver, a 7-year-old terrier mix, was aphakic in his left eye and essentially blind in his right eye as the result of a large retinal detachment. Surgical complications and endothelium damage contraindicated an intraocular lens implant in his left eye. While co-managed with his veterinary ophthalmologist, Oliver was prescribed an aphakic hydrogel contact lens to improve his monocular vision. CONCLUSION: Oliver was successful (by clinical criteria) with his contact lens. Although it is difficult to quantify his vision without a visual evoked potential, Oliver appeared more attentive and confident with the contact lens. This case report demonstrates a successful canine aphakic contact lens fit through the efforts of his owners, co-managing veterinary ophthalmologist, and optometrist.

Animals↗
PubMed2000

A comparison of Fluoracaine and Fluorox on corneal epithelial cell desquamation after Goldmann Applanation Tonometry.

BACKGROUND: The purpose of this study was to quality the frequency and amount of corneal desquamation from a sodium fluorescein/proparacaine combination (Fluoracaine) as compared with sodium fluorescein/benoxinate combination ophthalmic solution (Fluorox) after Goldmann Applanation Tonometry. METHODS: One drop of Fluoracaine was randomly instilled into one eye and one drop of Fluorox was instilled into the opposite eye of the same patient. Intraocular pressures (IOPs) by GAT and tear break-up times (TBUTs) were taken. Corneal stinging was compared. Corneal integrity by Cornea and Contact Lens Research Unit (CCLRU) standards was evaluated at 0, 3, 7, 10, 15, and 20 minutes after instillation of the ophthalmic solutions. RESULTS: Sixty eyes of 30 patients were observed Forty-seven percent of the patients reported Fluorox to string more than Fluoracaine; 23% of the patients reported that Fluoracaine stings more than Fluorox; and 30% the patients reported no difference. Average TBUTs were 6.87 and 7.17 seconds with Fluoracaine and Fluorox, respectively. Fluoracaine produced micro- and macropunctate keratitis of the superficial epithelium in 31% to 45% of the cornea. Fluorox caused superficial micropunctate keratitis in about 16% to 30% of the cornea. At 20 minutes, all eyes with Fluoracaine and all eyes but one with Fluorox had corneal desquamation. CONCLUSIONS: Fluoracaine causes marginally less stinging--however, clinically and statistically more corneal desquamation--than Fluorox after GAT. Corneal integrity after use of Fluoracaine should be evaluated even 20 minutes after GAT procedures for corneal disruption.

Adolescent↗
PubMed2000

Complexed prostate specific antigen provides significant enhancement of specificity compared with total prostate specific antigen for detecting prostate cancer.

PURPOSE: Determining serum total prostate specific antigen (PSA) has proved to be a valuable diagnostic aid for detecting prostatic carcinoma, although the lack of specificity has limited its usefulness. Studies indicate that the use of percent free PSA would improve specificity while maintaining sensitivity. Since complexed PSA represents the major proportion of measurable PSA in serum, we determined whether it represents a single test alternative to the use of percent free PSA for the early detection of prostate cancer. MATERIALS AND METHODS: Archival serum was obtained from 385 men with no evidence of malignancy on biopsy and 272 with biopsy confirmed prostate cancer. We determined the concentration and proportion of total, complexed and free PSA. RESULTS: Receiver operating characteristics analysis using total PSA results from all samples (range 0.32 to 117 ng./ml.) indicated that the areas under the curve for complexed PSA alone as well as the free-to-total and complexed-to-total PSA ratios were similar and significantly greater than those for total PSA alone. Within the range of 85% to 95% sensitivity receiver operating characteristics analysis revealed that the specificity of complexed PSA was higher than that of total PSA and equivalent to that of the free-to-total PSA ratio. We noted a similar improvement in specificity in the 4 to 10 ng./ml. total PSA range. Using published cutoff values for complexed, total and percent free PSA when total PSA was in the 4 to 10 ng./ml. range the sensitivity and specificity of complexed and percent free PSA were similar. Within the 4 to 10 ng./ml. total PSA range the population of patients with no evidence of malignancy and complexed PSA below the upper limit was different with respect to total PSA from that with no evidence of malignancy and free PSA greater than 25%. CONCLUSIONS: The measurement of complexed PSA represents an alternative to the use of percent free PSA, although the patient populations identified by the 2 tests are different.

Humans↗
PubMed1999

Ultrahigh-resolution capillary electrophoretic separation with indirect ultraviolet detection: isotopic separation of [14N]- and [15N]ammonium.

Separation of isotopically labeled [14N]/[15N] ammonium was performed with capillary electrophoresis. This ultrahigh-resolution separation was based on mobility counterbalance with precise control of the anodic electroosmotic flow. Mixtures of zwitterionic surfactant (Rewoteric AM CAS U) and cationic surfactant (cetyltrimethylammonium bromide) were used as buffer additives to modify the electroosmotic mobility. Indirect ultraviolet detection was used with benzyltributylammonium as the buffer coion. Baseline-resolved peaks of [14N]- and [15N]ammonium were obtained within 11 min. The detection limit was 0.01 mM for both [14N]-and [15N]ammonium. Linear calibration in concentration was observed up to 1.0 mM for [15N]ammonium and 2.0 mM for [14N]ammonium. Calibration of the isotopic ratio, [15N]ammonium concentration to total ([14N] and [15N])ammonium, was valid from 5 to 95%.

Betaine↗
PubMed1999

Analysis of monoclonal antibodies to prostate-specific antigen: reactivity with native and recombinant prostate-specific antigen.

Epitope mapping analysis was performed on 53 antibodies submitted to the ISOBM TD-3 PSA Workshop. Western blotting and N-terminal amino acid sequencing, using both native and recombinant human prostate-specific antigen (rPSA), identified four different epitope groups for native PSA. Under reducing conditions native PSA was not recognized by 18/53 antibodies suggesting they reacted with conformation-dependent epitopes. Nine other antibodies reacted with a rPSA polypeptide doublet of 34-35 kD corresponding to different rPSA glycoforms. From sequence mapping studies 22/53 antibodies bound epitopes within amino acid residues 25-85, 3/53 antibodies bound to epitopes within residues 86-220, while 10/53 antibodies bound epitopes within residues 221-261. These results indicate that there are multiple immunogenic epitopes localized on the PSA molecule.

Antibodies, Monoclonal↗
PubMed1999

Measurement of four tumor marker antigens in the sera of pregnant women.

We sought to determine the maternal serum levels of four tumor-associated antigens during the three trimesters of pregnancy in healthy women. CEA, CA 228, CA 15-3, and Her2/neu oncogene product p105 assay values were determined for 90 healthy pregnant women during the three trimesters of pregnancy at five participating evaluation sites. Results were compared to means and cut-off values determined for healthy nonpregnant women. Differences in assay values in the 1st and 3rd trimester were analyzed for statistical significance (Student's t-test). CEA, CA 228 and CA 15-3 assay values in general were found to be within the normal range. CA 15-3 and Her2/neu p105 serum assay values were above the cut-off (3.3% and 8.2%, respectively) and were significantly elevated in the 3rd trimester as compared to the 1st trimester of pregnancy (P < 0.05 and P < 0.001, respectively). CEA and CA 228 may be of potential value in monitoring pregnant women with malignant disease. Normal elevations in 3rd trimester serum Her2/neu p105 and CA 15-3 assay values should be considered when monitoring a pregnant patient with malignant disease.

Adolescent↗
PubMed1998

Equivalent recognition of free and ACT-complexed PSA in a monoclonal-polyclonal sandwich assay is conferred by binding specificity of the monoclonal antibody.

The Bayer Immuno 1 PSA Assay measures free and ACT-complexed PSA on an equimolar basis, although it uses a monoclonal antibody (MM1) for capture and polyclonal antibodies for detection. Competitive inhibition studies using antibodies directed at various epitopes on PSA and PSA-ACT demonstrated that the capture antibody, MM1, does not bind to free PSA simultaneously with antibodies against Epitope E which is exposed only in free PSA. Affinity studies showed that the affinity constants of MM1 for both free PSA and PSA-ACT are similar. One explanation for the properties of MM1 is that it precludes the binding of antibodies to Epitope E due to steric hindrance. Alternatively, the binding of MM1 causes a conformation change within the free PSA molecule, so that Epitope E is altered in a way that causes a loss of binding affinity. The unusual properties of MM1 are responsible for the equimolar response of this monoclonal-polyclonal sandwich assay for free and ACT-complexed PSA.

Alkaline Phosphatase↗
PubMed1998

Measurement of complexed PSA improves specificity for early detection of prostate cancer.

OBJECTIVES: Prostate-specific antigen (PSA) is the most useful of all tumor markers. Although the sensitivity is impressive, low specificity results in a lack of cancer detection in a significant proportion of patients undergoing prostate biopsy. Several recent studies have addressed the need for improved specificity. Of all these approaches, the free/total PSA ratio appears to be the most promising. Given that most circulating PSA is complexed to alpha1-antichymotrypsin, and that this moiety represents a greater proportion of the total PSA in those men with carcinoma, we set out to determine whether complexed PSA would improve specificity in the detection of men with prostate cancer. METHODS: Archival sera were obtained from 300 men, 75 of whom had biopsy-proved prostate cancer. All sera had been previously stored at -70 degrees C for variable periods. An investigative assay for complexed PSA (Bayer) was used. The Tandem-R free and total PSA assays (Hybritech) were used according to the manufacturer's recommendations. RESULTS: Among all patients, specificities for the total PSA, free/total PSA, and complexed PSA alone were 21.8%, 15.6%, and 26.7%, respectively, at cutoffs yielding 95% sensitivity. Similar equivalence or superior performance, in terms of specificity relative to the free/total PSA ratio, was seen at other sensitivity thresholds and other total PSA ranges. CONCLUSIONS: Complexed PSA alone performs better than total PSA or the free/total PSA ratio and obviates the need for a second analyte determination. We believe this marker may offer significant enhancement in PSA testing with significant economic advantages.

Aged↗
PubMed1998

Summary report on the ISOBM TD-6 workshop: analysis of 20 monoclonal antibodies against Sialyl Lewisa and related antigens. Montreux, Switzerland, September 19-24, 1997.

The ISOBM TD-6 Workshop is the first international workshop on monoclonal antibodies against the Sialyl Lewisa (SLea) antigen. Eight research groups participated in a blind study to characterize the epitope binding, relative affinity and performance in immunoradiometric assays, of a panel of 20 monoclonal antibodies. The antibodies were tested against a diverse panel of neoglycoconjugates, purified antigens and human serum pools from gastrointestinal malignancies. Epitope specificities were determined for the majority of antibodies in the panel. Cross-reactivity with related saccharide structures was noted in several antibodies. Overall, the results of the TD-6 Workshop show further development of SLea immunoassays may yield yet more specific assays for the detection and management of gastrointestinal and other malignancies.

Antibodies, Monoclonal↗
PubMed1998

Effect of desialylation on binding, affinity, and specificity of 56 monoclonal antibodies against MUC1 mucin.

We evaluated 56 monoclonal antibodies (MAbs), submitted to the ISOBM TD-4 Workshop, for changes in binding following desialylation of the MUC1 molecule and for epitope specificity. Antibody binding of MAbs was assayed by an ELISA method using microtiter plates coated with the MUC1 mucin obtained from supernatants of the ZR75-1 cell line. The MUC1 mucin was desialylated directly on the plate by treatment with neuraminidase. For each MAb, binding to untreated mucin was compared over a range of antibody concentrations. The concentration at which binding was half-maximal (K50) was determined for all antibodies whose binding reached saturation in the assay. Results showed that K50 values for MAb binding to untreated MUC1 mucin varied from 10(-10) to 10(-6) M. These data suggest that MAbs to MUC1 mucin bind with a broad range of intrinsic affinities. Desialylation was found to have variable effects on antibody binding, in that binding was either increased, decreased, or unchanged. No relationship was found between the apparent affinities for untreated mucin and changes in binding following desialylation. Among the 56 Workshop MAbs, 33 were found reactive with synthetic peptides which mimic the MUC1 tandem repeat. We determined the epitope specificity of the 33 MAbs by competitive binding using 10 amino acid peptides corresponding to various regions of the 20-amino acid tandem repeat domain of MUC1. All antibodies which recognized epitopes in the 1-10 amino acid region of the tandem repeat showed increased binding to desialylated mucin. Antibodies to other peptide epitopes showed no consistent pattern of change in binding following desialylation. Our results suggest that sialic acid residues on the MUC1 mucin may contribute either positively or negatively to antibody binding. In addition, our results suggest that improved antibody selection methods could provide MAbs with improved selectivity for cancer-derived mucin compared with mucin from normal tissues. This could form the basis of improved biomarker assays for breast cancer.

Amino Acid Sequence↗
PubMed1998

Bayer Immuno 1 PSA Assay: an automated, ultrasensitive method to quantitate total PSA in serum.

The Bayer Immuno 1 PSA Assay measures total PSA in human serum and demonstrates excellent performance with an interassay CV < or = 3.4% and a biological detection limit of 0.03 microgram/L. No significant interference from common hormonal and chemotherapeutic drugs, kallikrein, prostatic acid phosphatase, and trypsin, or elevated levels of total bilirubin, hemoglobin, triglycerides, and IgG was observed. The 95th percentile values for healthy individuals increased with age from 3.0 micrograms/L for males 50-59 years and 3.3 micrograms/L for males 60-69 years, to 4.6 micrograms/L for males > or = 70 years. Clinical studies with retrospective samples demonstrated correspondence between serial measurements of PSA and clinical outcome for 98% of 159 prostate cancer patients. Clinical sensitivity for patients with clinical evidence of disease, untreated at the time of specimen draw, increased with increasing stage from 77.5-100%. Specificity of 60-70% for BPH and other benign urogenital diseases was consistent with previous findings. Bayer Immuno 1 PSA Assay values for 2131 specimens from healthy subjects and patients with prostate cancer, BPH, and other malignant and nonmalignant diseases correlated well with the Abbott IMx PSA Assay over the range 0.0-6,238 micrograms/L (Y = 1.10 x + 0.02). The Bayer Immuno 1 PSA Assay provides automated ultrasensitive, precise, and equimolar measurement of total PSA in human serum.

Aged↗
PubMed1998

Multicenter evaluation of the Bayer Immuno I CA 15-3 assay.

We conducted a multicenter evaluation of the analytical and clinical features of the automated Bayer Immuno 1 CA 15-3 assay and compared assay performance to two manual tests. Results of the 10-day imprecision study of the Bayer Immuno 1 assay pooled across four evaluation sites and three lots of reagent produced total CV < or = 4%. Lot-to-lot reproducibility for 26 different lots of reagents and calibrators manufactured over a 2-year period was demonstrated (CV, 1.1%). Results for the Bayer Immuno 1 assay correlated well with the Biomira TRUQUANT BR 27.29 and Centocor CA 15-3 RIAs (r > or = 0.94). The upper limit of the reference interval for the Bayer Immuno 1 assay was 35.9 kilounits/L (35.9 units/mL); values were similar for all methods. Longitudinal monitoring of healthy women yielded assay values with an average CV of 11% and 21% for the Bayer Immuno 1 and Biomira assays, respectively. The Bayer Immuno 1 assay demonstrated the analytical features, intermethod correlation, and long-term performance characteristics that are essential for longitudinal monitoring of breast cancer patients.

Adolescent↗
PubMed1998

Novel immunoassay for the measurement of complexed prostate-specific antigen in serum.

Serum prostate-specific antigen (PSA) is an effective diagnostic tool for detection of prostate cancer (CaP) at an early and potentially curable stage, but specificity is low. Studies have shown that the proportion of serum PSA complexed with alpha-1-antichymotrypsin (ACT) is higher in men with CaP than in men with benign prostate disease. We developed a novel immunoassay for complexed PSA based on the unique binding properties of a monoclonal antibody that fails to bind free PSA in the presence of antibodies specific for free PSA. The assay measured mixtures of free and complexed PSA accurately, and the measured values of free + complexed PSA in artificial mixtures and in patient sera were equivalent to the measured value of total PSA. Both the serum concentration and the proportion of complexed PSA was substantially higher in patients with CaP compared with patients with benign prostate disease. The cPSA assay may have utility in improving specificity in screening for prostate cancer.

Antibodies, Monoclonal↗
PubMed1997

Contact lens correction of patients with Marfan syndrome.

BACKGROUND: Marfan syndrome, a genetic connective tissue disorder, manifests many problems: high myopia, astigmatism, crystalline lens subluxation, and cataracts. No published studies have described the contact lens corrections that can be used with Marfan syndrome patients. This report describes the variety of contact lens modalities used for a subpopulation of patients with Marfan syndrome. METHODS: The clinical records of eight patients with Marfan syndrome (16 eyes) from two hospital-based contact lens practices were retrospectively reviewed. Seven different contact lens modalities were used for this subpopulation. RESULTS: Mean unaided visual acuities were 20/296, while mean best-corrected optimal spectacle refraction visual acuities were 20/33. Contact lenses improved the mean visual acuity to 20/27. Patients wore the contact lenses for an average of 12 hours per day. Complications of contact lens wear occurred in approximately 70% of eyes and included neovascularization, giant papillary conjunctivitis, 3 and 9 o'clock staining, and central superficial punctate staining. Additionally, ocular non-contact lens-related complications occurred in 50% of patients. CONCLUSIONS: A variety of contact lens designs may be used during the care of patients with Marfan syndrome. However, patients may experience an increased rate of complications associated with contact lens wear or unrelated to lens wear, and thus they deserve more intensive follow-up care than non-Marfan syndrome patients.

Adolescent↗
PubMed1996

Technicon Immuno 1 PSA assay measures both free and alpha-1-antichymotrypsin-complexed prostate-specific antigen on an equimolar basis.

In this study, we investigated the immunoreactivity of the Technicon Immuno 1 PSA assay, a monoclonal-polyclonal sandwich immunoassay, with free and ACT-complexed PSA. Assay calibrators prepared with free PSA (standard Immuno 1 calibrators) and calibrators consisting of 90% ACT-complexed and 10% free PSA (90:10 calibrators) yielded virtually identical PSA recoveries at all concentrations tested. Concentrations of total PSA at approximately 4 and 10 ng/mL, prepared in varying ratios of free PSA to PSA-ACT complex, recovered from 92-104% at 4 ng/mL and from 98-102% at 10 ng/mL. Additionally, an excellent correlation of serum total PSA values from a panel of 40 prostatic cancer patient samples was obtained using calibration curves generated with the standard Immuno 1 calibrators or the 90:10 calibrators. These results demonstrate that the Technicon Immuno 1 PSA assay measures free and ACT-complexed PSA on an equal molar basis.

Automation↗