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Biomedical subjects

R Cheung

Publications and source records attributed to R Cheung.

At least 19 recordsLinked to original sources
PubMed2005

Effect of zoledronate on bone quality in the treatment of aseptic loosening of hip arthroplasty in the dog.

Periprosthetic bone loss, which is a direct cause of aseptic loosening in total hip arthroplasty (THA), can be suppressed by bisphosphonates. It is unknown how the quality of this bone is affected in the presence of both wear debris (from implant) and bisphosphonates. The objective of this study was to evaluate the effect of zoledronate (ZLN) on bone quality in the presence of wear debris [polyethylene (PE) particles] in a canine model of uncemented THA. Thirty dogs underwent THA, and aseptic loosening was induced via implantation of PE particles packed into the femoral component. For 26 weeks until sacrifice, two groups (each n = 10) received weekly injections of ZLN (low dose 2 mug/kg, high dose 10 mug/kg) and the third group (control) received saline. Histological and radiographic examinations were performed to evaluate the degree of implant reaction. Histomorphometry (static/dynamic) was performed to evaluate bone turnover. Back-scattered electron imaging was used to quantify the newly formed bone and to evaluate the mineralization distribution. Density fractionation and X-ray diffraction were used to evaluate mineral properties, while four-point bending was used to determine mechanical properties. A dose-dependent presence of newly formed subperiosteal bone was found, which appeared to be less mineralized than the adjacent cortical bone. The high-dose ZLN group showed decreased cortical porosity and turnover and increased mineralization profile, failure strength, and modulus. We conclude that ZLN affects some of the material properties of cortical bone and allows the newly formed subperiosteal bone to remain and therefore affect the overall quality of the bone.

Animals↗
PubMed2001

A study of doxorubicin loading onto and release from sulfopropyl dextran ion-exchange microspheres.

The objective of this study was to investigate various factors that influence doxorubicin (Dox) loading onto and release from sulfopropyl dextran ion-exchange microspheres (MS), and to evaluate the anticancer activity of the released drug in vitro. Dox was incorporated into the MS by incubating the MS with aqueous solutions of Dox at room temperature. The drug release was carried out at 37 degrees C in aqueous solutions containing NaCl with or without CaCl2. The kinetics of drug absorption and release, the amount of Dox released, and the stability of Dox after loading, freeze-drying, and release were determined by spectrophotometry. The cytotoxicity of Dox (the original drug or that released from MS) against murine EMT6 breast cancer cells was assessed using a clonogenic assay. An increase in the MS to drug ratio resulted in a higher absorption rate and a higher fraction of the drug extracted from the solution. The release rate and the equilibrium fraction of Dox released increased with a decrease in the initial amount of Dox loaded or an increase in the salt concentration. The addition of divalent ions (Ca2+) promoted drug release compared to NaCl alone. The percent loss of colony forming ability of the cells, a measure of cytotoxicity of the released Dox, was the same as parent Dox solutions, indicating that the drug bioactivity was fully preserved after the drug loading and release cycle. This work demonstrated that various drug release rates were achieved by varying the drug loading and that the MS-delivered Dox was effective against the cancer cells in vitro.

Animals↗
PubMed2001

Quantitative analysis of hepatitis C virus in peripheral blood and liver: replication detected only in liver.

Prior studies seeking evidence of viral replication in peripheral lymphocytes of hepatitis C virus (HCV)-infected patients have yielded conflicting results. This study sought to quantitatively determine whether a permissive HCV cell interaction could be detected in leukocytes from infected patients. Peripheral leukocytes from chronically infected patients were purified and were tested for HCV RNA. The results show that virus load is highest in B cells. Other subsets of peripheral leukocytes consistently had very low levels of viral RNA or were negative. Negative-strand HCV was found only in hepatocytes. To determine whether HCV replication could be induced by activation, B cells from HCV-infected patients were stimulated in vitro. No HCV replicating in peripheral leukocytes was detected by a highly sensitive assay. If HCV replication occurs in the leukocyte subsets analyzed here, it is at extremely low levels or occurs under alternate physiological conditions.

Adult↗
PubMed2001

Type I diabetes and multiple sclerosis patients target islet plus central nervous system autoantigens; nonimmunized nonobese diabetic mice can develop autoimmune encephalitis.

Type I diabetes and multiple sclerosis (MS) are distinct autoimmune diseases where T cells target either islet or CNS self-proteins. Unexpectedly, we found that autoreactive T cells in diabetic patients, relatives with high diabetes risk, nonobese diabetic (NOD) mice, and MS patients routinely target classical islet as well as CNS autoantigens. The pathogenic potential of CNS autoreactivity was testable in NOD mice. Pertussis holotoxin, without additional Ags or adjuvants, allowed development of an NOD mouse-specific, autoimmune encephalitis with variable primary-progressive, monophasic, and relapsing-remitting courses. T cells from diabetic donors transferred CNS disease to pertussis toxin-pretreated NOD.scid mice, with accumulation of CD3/IFN-gamma transcripts in the brain. Diabetes and MS appear more closely related than previously perceived. NOD mouse-specific, autoimmune encephalitis provides a new MS model to identify factors that determine alternative disease outcomes in hosts with similar autoreactive T cell repertoires.

Acute Disease↗
PubMed2001

ROC optimization may improve risk stratification of prostate cancer patients.

OBJECTIVES: Rational treatment decision requires accurate projection of the clinical course of a patient. Current methods in clinical outcome analysis mostly focus on population data. We investigated the applicability and optimization of the widely used actuarial method to project individual clinical outcomes. METHODS: We designed and implemented a Clinical Outcome Prediction Expert (COPE) that performs, assesses, and optimizes actuarial prediction on individual cases. We analyzed a post-prostatectomy database, consisting of 1043 patients. Sixty percent of the database was used for training and 40% for validation. Stratified actuarial curves are used to project individual outcomes. The prostate-specific antigen (PSA) level, the Gleason score, and the clinical American Joint Commission on Cancer Staging T-stage before treatment were used as predictors. The area under the receiver operator characteristic (ROC) curve was used to measure predictive performance. RESULTS: We obtained simple optimized stratification of pretreatment PSA level of 10 ng/mL or less, or more than 10 ng/mL; Gleason score of 6 or lower, or higher than 6; and clinical AJCC T-stage of T2a or lower, or higher. The optimized univariate risk scores were used to generate a multivariate score. After optimization, we found the higher risk group consisted of patients with PSA more than 10 ng/mL, or with PSA of 10 ng/mL or less and Gleason score higher than 6 and clinical AJCC T-stage higher than T2a. The optimized multivariate risk score has the highest ROC area of 0.77 among all predictors. CONCLUSIONS: The best conditions to perform actuarial prediction on individual cases are not known a priori and require optimization. This study shows that ROC optimization simplifies risk stratification and may improve the accuracy of clinical outcome prediction.

Data Interpretation, Statistical↗
PubMed2001

Using the receiver operating characteristic curve to select pretreatment and pathologic predictors for early and late postprostatectomy PSA failure.

OBJECTIVES: Pretreatment prostate-specific antigen (PSA), prostatectomy Gleason score, margin status, and pathologic T stage are known explanatory variables for the postprostatectomy PSA outcome. We used the receiver operating characteristic (ROC) curve to select those factors that were optimal for predicting early and late postoperative PSA failure. METHODS: We designed and implemented a clinical outcome prediction expert that performs, assesses, and optimizes the actuarial prediction on individual cases. A postprostatectomy database of 1022 patients was divided into 60% for training and 40% for validation. The ROC areas of the predictors were calculated over a range of cutoff time from 24 to 60 months. RESULTS: Multivariate pathologic T stage/prostatectomy Gleason score/margin status had the highest ROC area of 0.900. Patients with Stage T disease less than T3, negative surgical margins, and Gleason score of 6 or less had a 90% probability to be PSA failure free at 4 years versus 36% otherwise. The pathologic T stage/margin status accurately predicted PSA failure at 24 months or less after prostatectomy with an ROC area of 0.800. Lower risk patients (less than Stage T3, negative surgical margins) had a 94% probability to be PSA failure free at 2 years versus 46% otherwise. CONCLUSIONS: A combination of actuarial analysis and ROC optimization accurately identified the individual patients at high risk of early and late postprostatectomy PSA failure.

Actuarial Analysis↗
PubMed2001

Manganese intake and cholestatic jaundice in neonates receiving parenteral nutrition: a randomized controlled study.

UNLABELLED: Infants requiring parenteral nutrition (n = 244) were randomized to receive either 1 (group 1, n = 121) or 0.0182 micromol/kg/d (group 2, n = 123) of manganese supplementation. The whole-blood manganese and serum direct bilirubin concentrations of the infants were monitored, as was the development of cholestasis (peak serum direct bilirubin concentration >50 micromol/L). Subgroup analysis was carried out on the data of 78 infants in group 1 and 82 in group 2 who had received manganese supplementation and more than three-quarters of their total daily fluid as parenteral nutrition for >14 d. Of all the infants randomized, the high manganese group (group 1) showed a trend towards developing higher peak whole-blood manganese concentration [group 1 versus group 2: median (interquartile range): 606.0 (421.0; 1005.0) vs 566.0 (336.0: 858.0); p=0.061] and higher peak serum direct bilirubin concentration [37.0 (10.5; 122.5) vs 19.0 (8.0; 112.5); p=0.153], but the differences between the 2 groups did not reach statistical significance. The 2 groups did not differ in terms of the occurrence of cholestasis during parenteral nutrition (63/121 vs 57/123; p=0.444). Subgroup analysis of infants who had received more than three-quarters of their total daily fluid as parenteral nutrition showed, however, that the high manganese group developed significantly higher whole-blood manganese concentration [743.5 (498.0; 1211.0) vs 587.0 (438.0; 982.0); p=0.037] and serum direct bilirubin concentration [84.0 (28.0; 170.0) vs 25.5 (9.0; 117.0): p < 0.001]. Although there was no significant difference in the occurrence of cholestasis (58/78 vs 49/82; p = 0.073), more infants in the high manganese group developed a more severe degree of direct hyperbilirubinaemia, with peak serum direct bilirubin >100 micromol/L (32/78 vs 20/82; p = 0.038). CONCLUSION: We conclude that the pathogenesis of parenteral nutrition-related cholestasis is probably multifactorial, and that high manganese intake is a significant contributory factor.

Cholestasis↗
PubMed2001

Comparison of craniofacial skeletal characteristics of infants with bilateral choanal atresia and an age-matched normative population: computed tomography analysis.

Choanal atresia (CA) results from the developmental failure of the posterior nasal cavity to communicate with the nasopharynx. Computed tomographic (CT) scanning is often used as a diagnostic tool for CA as it is able to provide information regarding the extent and type of atresia. Studies have used CT measurements to analyze the skeletal deformities of children with CA. Computed tomographic analysis of the complete craniofacial skeletal characteristics of children with CA has not been previously reported. This study analyzed the craniofacial skeletal characteristics of infants with bilateral choanal atresia (BCA) and compared them with age-matched standards. Eight patients with BCA under the age of 3 months were evaluated. Fourteen cranio-orbitozygomatic variables were used to represent the craniofacial skeletal configuration. The measurements from the control group were compared with the available values of age-matched normal controls. Statistically significant differences between the means of the sample group and control group were demonstrated in 10 of 14 variables. The sample group means were consistently smaller than the control group mean. Detailed knowledge of the underlying anatomy of infants with BCA will help in the development of treatment strategies and will provide data for evaluation of operative intervention on craniofacial growth.

Age Factors↗
PubMed2000

Dissociation of G-protein alpha from rhabdomeric membranes decreases its interaction with rhodopsin and increases its degradation by calpain.

Photoactivation of invertebrate rhodopsin activates a GTP-binding protein, Gq, which in turn activates a phospholipase C (PLC) enzyme. Gqalpha is a membrane-associated protein that is progressively released from the membrane by washing with buffers containing increasing concentrations of beta-mercaptoethanol (beta-ME). Isolated, soluble Gqalpha showed a decreased ability to be activated by rhodopsin but was more active in stimulating PLC when compared with the membrane-associated form of Gqalpha. The calcium-activated protease, calpain, selectively cleaved the soluble but not the membrane-bound form of Gqalpha. Calpain cleaved a small peptide from the amino-terminus of Gqalpha reducing the ability of the G-protein to bind GTP. The uncoupling of Gqalpha from rhodopsin and subsequent calcium-dependent proteolysis to further inactivate the G-protein may therefore be a regulatory mechanism of light adaptation in rhabdomeric photoreceptors.

Animals↗
PubMed2000

Intracellular mechanisms regulating apoB-containing lipoprotein assembly and secretion in primary hamster hepatocytes.

We studied the biogenesis of apolipoprotein B (apoB) in primary hepatocytes isolated from hamster liver, an animal model with striking resemblance to humans in lipoprotein metabolism. Hamster hepatocytes were found to assemble and secrete apoB-containing lipoproteins at a density of VLDL. Intracellular mechanisms of apoB biogenesis were investigated in both intact and permeabilized hamster hepatocytes. Translocational status of hamster apoB-100 was examined using trypsin protection assays in permeabilized cells as well as isolated microsomes which revealed that 27-42% of newly synthesized apoB was trypsin accessible as opposed to a control protein, transferrin, which was found to be essentially insensitive to exogenous trypsin. Subcellular fractionation of membrane and lumenal apoB pools indicated, however, that only a minor fraction of hamster apoB was associated with the microsomal membrane. Approximately 40% of newly synthesized apoB was found to be degraded post-translationally in a process sensitive to MG132. Immunoblotting analysis of apoB immunoprecipitates revealed ubiquitination of hamster apoB suggesting the involvement of the proteasome in its intracellular turnover. In addition to MG132, o-phenanthroline, a metalloprotease inhibitor, was also effective in stabilizing hamster apoB. Experiments in permeabilized hamster hepatocytes further confirmed post-translational instability of hamster apoB which was degraded over a 3-h chase generating proteolytic fragments including 167, 70, 57, and 46 kDa intermediates. Of these only the 70 kDa fragment was ALLN sensitive. Oleate treatment of hamster hepatocytes provided protection against intracellular apoB degradation, but did not stimulate its extracellular secretion. ApoB was assembled in the microsomal lumen into lipoprotein particles with densities of LDL and VLDL which were subsequently secreted as VLDL with a minor fraction forming HDL-like particles. In summary, hamster hepatocytes appear to efficiently assemble and secrete apoB-containing VLDL, although a significant pool of newly synthesized apoB is retained intracellularly and becomes sensitive to proteasome-mediated degradation as well as other proteases in the secretory pathway, generating specific degradative intermediates.

Animals↗
PubMed1999

Quantitative analysis of hepatitis C virus-specific CD8(+) T cells in peripheral blood and liver using peptide-MHC tetramers.

It is believed that the hepatitis C virus (HCV)-specific CD8(+) cytotoxic T lymphocytes (CTLs) play a role in the development of liver cell injury and in the clearance of the virus. To develop a direct binding assay for HCV-specific CTLs, we generated two peptide-MHC tetramers by using the recombinant HLA A2.1 molecule and A2-restricted T cell epitopes of the HCV NS3 protein. With these reagents we are able to detect specific CD8(+) cells in the blood of 15 of 20 HLA-A2(+), HCV-infected patients, at a frequency ranging from 0.01% to 1.2% of peripheral CD8(+) T cells. Phenotypic analysis of these specific cells indicated that there is a significant variation in the expression of the CD45 isoforms and CD27 in different patients. A 6-hour incubation of one patient's blood with NS3 peptides resulted in the activation of the epitope-specific CD8(+) cells, as indicated by their expression of CD69 and IFN-gamma. We also detected NS3-specific CD8(+) T cells in the intrahepatic lymphocyte population isolated from liver biopsies of two HCV-infected patients. The frequency of these specific CD8(+) cells in the liver was 1-2%, at least 30-fold higher than in the peripheral blood. All of the intrahepatic NS3-specific CD8(+) T cells were CD69(+), suggesting that they were activated CTLs. Direct quantitation and characterization of HCV-specific CTLs should extend our understanding of the immunopathogenesis and the mechanism of clearance or persistence of HCV.

Antigens, CD↗
PubMed1999

Atorvastatin increases ecNOS levels in human platelets of hyperlipidemic subjects.

BACKGROUND: The purpose of this study was to probe the pleiotrophic effects of Atorvastatin on intraplatelet-nitric oxide metabolism. METHODS AND RESULTS: Hyperlipidemic subjects (n = 19) were treated for 1 month (following a 3-week washout) with either Atorvastatin or placebo in a double-blinded randomized (n = 2, crossover), placebo-controlled study. Changes in the levels of intraplatelet nitric oxide synthase, nitrotyrosine were correlated with cholesterol, LDL-C, HDL-C and triglyceride levels. These studies indicate that with atrovastatin ecNOS levels increased on average by approximately approximately 1.7-fold (paired t-test p = 0.009). Interestingly, levels of nitrotyrosylated platelet proteins, an indication of peroxynitrite damage, decreased as ecNOS levels increased in presence of the drug (paired t-test p = 0.33). Atorvastatin, at 10 mg per day, lowered cholesterol and LDL-C levels in all patients with the average lowering of approximately 21% and approximately 17% respectively. The effect on HDL was not significant whilst triglyceride levels were lowered by an average of approximately 18%. CONCLUSIONS: This study adds to the volume of evidence that statins have beneficial effects other than lipid lowering. Here, Atorvastatin is shown to significantly elevate intraplatelet ecNOS levels in hyperlipidemic subjects without affecting iNOS expression. The net result of this would be the elevation of NO production which would promote platelet deaggregation and vasodilation.

Adult↗
PubMed1999

The effect of valsartan and captopril on lipid parameters in patients with type II diabetes mellitus and nephropathy.

The study compared valsartan 80 mg or 160 mg o.d. with captopril 25 mg t.i.d. or placebo on plasma lipids in normotensive and treated hypertensive patients with type II diabetes and microalbuminuria. One hundred and twenty-two adult outpatients were randomised to receive either valsartan 80 mg or 160 mg, captopril 25 mg or placebo for 360 days. Changes from baseline to endpoint in plasma lipid parameters were measured. The primary criterion for tolerability was the incidence of adverse events. All treatment groups showed minor changes in lipid parameters. Triglyceride increased by 2.7% (valsartan 160 mg) to 9.1% (placebo). Total cholesterol decreased under valsartan 80 mg, while other groups showed increases of up to 0.031 mmol/l. Decreases in total cholesterol (p = 0.018), apolipoprotein B (p = 0.042) and apolipoprotein A1 (p = 0.025), were significant for the comparison of 80 mg valsartan and captopril. Valsartan 80 mg or 160 mg o.d. does not cause deleterious changes in the diabetic lipid profile and, unlike captopril, is not associated with dry cough.

Adult↗
PubMed1998

Replacements of single basic amino acids in the pleckstrin homology domain of phospholipase C-delta1 alter the ligand binding, phospholipase activity, and interaction with the plasma membrane.

The pleckstrin homology (PH) domain of phosphatidylinositol-specific phospholipase C-delta1 (PLC-delta1) binds to both D-myo-inositol 1,4, 5-trisphosphate (Ins(1,4,5)P3) and phosphatidylinositol 4, 5-bisphosphate (PtdIns(4,5)P2) with high affinities. We have previously identified a region rich in basic amino acids within the PH domain critical for ligand binding (Yagisawa, H., Hirata, M., Kanematsu, T., Watanabe, Y., Ozaki, S., Sakuma, K., Tanaka, H., Yabuta, N., Kamata, H., Hirata, H., and Nojima, H. (1994) J. Biol. Chem. 269, 20179-20188; Hirata, M., Kanematsu, T., Sakuma, K., Koga, T., Watanabe, Y., Ozaki, S., and Yagisawa, H. (1994) Biochem. Biophys. Res. Commun. 205, 1563-1571). To investigate the role of these basic residues, we have performed site-directed mutagenesis replacing each of the basic amino acid in the N-terminal 60 residues of PLC-delta1 (Lys24, Lys30, Lys32, Arg37, Arg38, Arg40, Lys43, Lys49, Arg56, Lys57, and Arg60) with a neutral or an acidic amino acid. The effects of these mutations on the PH domain ligand binding properties and their consequence for substrate hydrolysis and membrane interactions of PLC-delta1 were analyzed using several assay systems. Analysis of [3H]-Ins(1,4,5)P3 binding, measurement of the binding affinities, and measurements of phospholipase activity using PtdIns(4,5)P2-containing phospholipid vesicles, demonstrated that residues Lys30, Lys32, Arg37, Arg38, Arg40, and Lys57 were required for these PLC-delta1 functions; in comparison, other mutations resulted in a moderate reduction. A subset of selected mutations was further analyzed for the enzyme activity toward substrate present in cellular membranes of permeabilized cells and for interaction with the plasma membrane after microinjection. These experiments demonstrated that mutations affecting ligand binding and PtdIns(4,5)P2 hydrolysis in phospholipid vesicles also resulted in reduction in the hydrolysis of cellular polyphosphoinositides and loss of membrane attachment. All residues (with the exception of the K43E substitution) found to be critical for the analyzed PLC-delta1 functions are present at the surface of the PH domain shown to contain the Ins(1,4,5)P3 binding pocket.

Amino Acid Sequence↗
PubMed1997

Regulation of inositol lipid-specific phospholipase cdelta by changes in Ca2+ ion concentrations.

Studies of inositol lipid-specific phospholipase C (PLC) have elucidated the main regulatory pathways for PLCbeta and PLCgamma but the regulation of PLCdelta isoenzymes still remains obscure. Here we demonstrate that an increase in Ca2+ ion concentration within the physiological range (0.1-10 microM) is sufficient to stimulate PLCdelta1, but not PLCgamma1 and PLCbeta1, to hydrolyse cellular inositol lipids present in permeabilized cells. The activity of PLCdelta1 is further enhanced in the presence of phosphatidylinositol transfer protein (PI-TP). Both full activation by Ca2+ ions and stimulation in the presence of PI-TP require an intact PH domain involved in the membrane attachment of PLCdelta1. The physiological implication of this study is that PLCdelta1 could correspond to a previously uncharacterized PLC responsible for Ca2+ ion-stimulated inositol lipid hydrolysis observed in many cellular systems.

Animals↗