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Biomedical subjects

X Q Chen

Publications and source records attributed to X Q Chen.

At least 55 records · Page 3Linked to original sources
PubMed1997

Survival of Blastocystis hominis clones after exposure to a cytotoxic monoclonal antibody.

Our previous studies have shown that monoclonal antibodies (MAbs) to Blastocystis hominis react mainly with carbohydrate epitopes, while 1 MAb (1D5) reacts specifically with a protein of 30.5 kDa. In the present study, 3 monoclonal antibodies (1D5, 1E7 and 4F7) were used in immunogold localization. 1E7 and 4F7 were found to react primarily with the surface coat, while 1D5 was plasma membrane-specific. In the presence of complement, only 1D5 exhibited a cytotoxic effect on B. hominis whereas 1E7 and 4F7 did not, suggesting that the surface coat of B. hominis could serve as an immunological barrier against host antibodies. Using a recently described agar plating method, only 1D5 exhibited significant (P < 0.01) complement-independent cytotoxicity to B. hominis, inhibiting colony growth at low concentrations. Parasites that had been exposed to 1D5 were morphologically smaller than those that were not exposed to this MAb. Colonies that grew in the presence of 1D5 were isolated and grown in liquid medium containing increasing amounts of the cytotoxic MAb. Two clones that grew well in liquid medium containing 1D5 were also able to develop into colonies in soft agar. This study has shown that the 30.5 kDa protein found on the plasma membrane of B. hominis is a functionally important protein and that not all cells within a certain population would be susceptible to the cytotoxic effects of 1D5. These findings suggest that a heterogenous population exists in continuously maintained cultures of B. hominis.

Animals↗
PubMed1997

Immunogenicity of two versus three injections of inactivated hepatitis A vaccine in adults.

AIM: To investigate the immunogenicity of two versus three injections of inactivated strain CR326F-derived hepatitis A vaccine in healthy adults. METHODS: Healthy adult volunteers (n = 105) at Utrecht University Hospital, The Netherlands, were randomly assigned to receive intramuscular injections (deltoid muscle) of 25 Units (U) at 0 and 6 months (group A, n = 53), or at 0, 2 and 6 months (group B, n = 52). Blood was drawn before and at various time points after vaccination for determination of serum antibody to hepatitis A (anti-HAV). RESULTS: One month after the first injection, the seroconversion rates (> or = 10 mIU/ml, international units) were 88% for group A and 90% for group B. Only 2/ 103 (one in each group) showed IgM anti-HAV. One month after the second injection, seroconversion rates were 100% in both groups. At months 3, 6 and 7, anti-HAV geometric mean titers were significantly different because of the different vaccination schedules, but they were similar at months 1, 2 and 12. The anti-HAV geometric mean titer increase after the second injection was higher when the interval between the two doses was of longer duration. Anti-HAV titers of females were significantly higher than those of males and vaccinees < or = 30 years had higher titers than those > 30 years. CONCLUSIONS: Two 25 U doses of the vaccine investigated given at 0 and 6 months, induce adequate anti-HAV titers in all adult healthy vaccinees and are as immunogenic as three doses given at 0, 2 and 6 months.

Adolescent↗
PubMed1997

Expression of constitutively active alpha-PAK reveals effects of the kinase on actin and focal complexes.

The family of p21-activated protein kinases (PAKs) appear to be present in all organisms that have Cdc42-like GTPases. In mammalian cells, PAKs have been implicated in the activation of mitogen-activated protein kinase cascades, but there are no reported effects of these kinases on the cytoskeleton. Recently we have shown that a Drosophila PAK is enriched in the leading edge of embryonic epithelial cells undergoing dorsal closure (N. Harden, J. Lee, H.-Y. Loh, Y.-M. Ong, I. Tan, T. Leung, E. Manser, and L. Lim, Mol. Cell. Biol. 16:1896-1908, 1996), where it colocalizes with structures resembling focal complexes. We show here by transfection that in epithelial HeLa cells alpha-PAK is recruited from the cytoplasm to distinct focal complexes by both Cdc42(G12V) and Rac1(G12V), which themselves colocalize to these sites. By deletion analysis, the N terminus of PAK is shown to contain targeting sequences for focal adhesions which indicate that these complexes are the site of kinase function in vivo. Cdc42 and Rac1 cause alpha-PAK autophosphorylation and kinase activation. Mapping alpha-PAK autophosphorylation sites has allowed generation of a constitutively active kinase mutant. By fusing regions of Cdc42 to the C terminus of PAK, activated chimeras were also obtained. Plasmids encoding these different constitutively active alpha-PAKs caused loss of stress fibers when introduced into both HeLa cells and fibroblasts, which was similar to the effect of introducing Cdc42(G12V) or Rac1(G12V). Significantly dramatic losses of focal adhesions were also observed. These combined effects resulted in retraction of the cell periphery after plasmid microinjection. These data support our previous suggestions of a role for PAK downstream of both Cdc42 and Rac1 and indicate that PAK functions include the dissolution of stress fibers and reorganization of focal complexes.

Actins↗
PubMed1996

Observations on the ultrastructure and viability of the cystic stage of Blastocystis hominis from human feces.

This report describes the ultrastructure and viability of cysts of Blastocystis hominis from feces of infected patients. The cysts were round to ovoid, measured 2-5 microns in size, and contained a condensed cytoplasm that had vacuoles of varying sizes, four nuclei, and as many as six cristate mitochondria. The cell wall was rather electron-lucent. Surprisingly, chromatoid-like structures were found in the cytoplasm and nucleus of some of the cysts. These have not previously been reported in Blastocystis. The cysts can survive in water for up to 19 days at normal temperatures but are fragile at extreme temperatures and in common disinfectants.

Animals↗
PubMed1996

Clonal growth of Blastocystis hominis in soft agar with sodium thioglycollate.

The present report describes a method for establishment of colonies of Blastocystis hominis from single cells in soft agar. The percentage of colony-forming efficiency (% CFE = number of colonies grown/number of cells inoculated x 100) for the cultures was greatly improved by the addition of sodium thioglycollate. Five human Blastocystis isolates chosen for this study showed no apparent variation in colonial morphology. Isolated colonies were also successfully grown in liquid medium, providing a means of obtaining large numbers of B. hominis cells that had arisen from a single clone.

Animals↗
PubMed1996

Production and characterization of murine monoclonal antibodies to Blastocystis hominis.

Several hybridomas producing antibodies detected by enzyme-linked immunosorbent assay (ELISA) were established by fusions of mouse myeloma P3.X63.Ag8.U1 with spleen cells from BALB/c mice immunized against an isolate of Blastocystis hominis. Five strongly positive hybrids (6B6, 1D5, 1E7, 4F7 and 4G11) were cloned and all were found to secrete IgM monoclonal antibodies. Four MAbs (6B6, 1E7, 4F7 and 4G11) reacted in immunoblots with a number of B. hominis antigens (mol. wt ranging from 25,000 to 220,000) which were likely to be repeating oligosaccharide epitopes located on glycoproteins, as indicated by pronase and periodate treatment. Another MAb (1D5) reacted with a single antigenic band (mol. wt 30,5000). Similar results were obtained in immunoblots using 4 other B. hominis isolates. Indirect fluorescent-antibody assay (IFA) using MAbs showed 3 patterns of reactivity. 1D5 showed patchy fluorescence, 4F7 showed peripheral fluorescence and 6B6, 1E7 and 4G11 showed bright diffuse fluorescence. These patterns were observed for all 5 human Blastocystis isolates. The MAbs exhibited some cross-reactivity with 2 reptilian Blastocystis isolates but not with Giardia intestinalis, Trichomonas vaginalis or Entamoeba histolytica.

Animals↗
PubMed1996

Microsatellite alterations in plasma DNA of small cell lung cancer patients.

Microsatellite instability is an important characteristic of many tumor types especially those associated with hereditary non-polyposis colorectal carcinoma (HNPCC) syndrome. Microsatellite alterations in 50% of primary small cell lung carcinoma (SCLC) have been found. These alterations were also found in the sputum. Because neoplastic characteristics such as decreased strand stability9 and ras mutations have been found in the plasma DNA of cancer patients, we looked for microsatellite alterations in the plasma of SCLC patients. A microsatellite alteration was present in 16 out of 21 (76%) SCLC tumors and in 15 out of 21 (71%) plasma samples. In one case, the alteration was present only in the plasma DNA. If confirmed in larger studies, microsatellite analysis of plasma DNA might constitute a new tool for tumor staging, management and, possibly, detection.

Adult↗
PubMed1996

The p160 RhoA-binding kinase ROK alpha is a member of a kinase family and is involved in the reorganization of the cytoskeleton.

The GTPase RhoA has been implicated in various cellular activities, including the formation of stress fibers, motility, and cytokinesis. We recently reported on a p150 serine/threonine kinase (termed ROK alpha) binding RhoA only in its active GTP-bound state and on its cDNA; introduction of RhoA into HeLa cells resulted in translocation of the cytoplasmic kinase to plasma membranes, consistent with ROK alpha being a target for RhoA (T. Leung, E. Manser, L. Tan, and L. Lim, J. Biol. Chem. 256:29051-29054, 1995). Reanalysis of the cDNA revealed that ROK alpha contains an additional N-terminal region. We also isolated another cDNA which encoded a protein (ROK beta) with 90% identity to ROK alpha in the kinase domain. Both ROK alpha and ROK beta, which had a molecular mass of 160 kDa, contained a highly conserved cysteine/histidine-rich domain located within a putative pleckstrin homology domain. The kinases bound RhoA, RhoB, and RhoC but not Rac1 and Cdc42. The Rho-binding domain comprises about 30 amino acids. Mutations within this domain caused partial or complete loss of Rho binding. The morphological effects of ROK alpha were investigated by microinjecting HeLa cells with DNA constructs encoding various forms of ROK alpha. Full-length ROK alpha promoted formation of stress fibers and focal adhesion complexes, consistent with its being an effector of RhoA. ROK alpha truncated at the C terminus promoted this formation and also extensive condensation of actin microfilaments and nuclear disruption. The proteins exhibited protein kinase activity which was required for stress fiber formation; the kinase-dead ROK alpha K112A and N-terminally truncated mutants showed no such promotion. The latter mutant instead induced disassembly of stress fibers and focal adhesion complexes, accompanied by cell spreading. These effects were mediated by the C-terminal region containing Rho-binding, cysteine/histidine-rich, and pleckstrin homology domains. Thus, the multidomained ROK alpha appears to be involved in reorganization of the cytoskeleton, with the N and C termini acting as positive and negative regulators, respectively, of the kinase domain whose activity is crucial for formation of stress fibers and focal adhesion complexes.

Amino Acid Sequence↗
PubMed1996

A follow-up study of first trimester induced abortions at hospitals and family planning clinics in Sichuan province, China.

Four-thousand women aged 18-40 underwent an early induced abortion at hospitals and family planning clinics in six counties in Sichuan province, China, between 1 July 1990 and 30 June 1991. The subjects were followed-up three times, on days 15, 90 and 180 after the operation. Information was obtained about their age, parity, contraceptive use, social behaviors, and gynecological and psychological characteristics before and after the abortion. The results indicate that induced abortion is safe when provided by medically trained personnel in health facilities such as hospitals or clinics. Depressive symptomatology was assessed by the CES-D and SCL-90 scales. The depressive symptoms declined over time. A substantial proportion of the abortions were to unmarried women or resulted from non-use of contraception or contraceptive failure, implying that the incidence of unintended pregnancies and induced abortions could be reduced by more effective and accessible contraception.

Abortion, Induced↗
PubMed1995

"Balanced" karyotypes in six abnormal offspring of balanced reciprocal translocation normal carrier parents.

Among 6800 consecutive blood samples studied for clinical cytogenetic diagnosis, we identified 30 families in which one parent of the proband had a balanced reciprocal autosomal translocation (excluding Robertsonian rearrangements). Twenty-eight of the 30 families had a malformed and/or mentally retarded proband: 19 with an unbalanced derived chromosome, 3 with abnormalities involving chromosomes other than those in the translocation, 5 with a "balanced" reciprocal translocation, and 1 with a normal karyotype. We hypothesize that the latter 6 affected probands with "balanced" karyotypes could be abnormal due to submicroscopic deletions and duplications as was originally suggested by Jacobs [1984]. Particularly in these 6 families, 83% of translocation breakpoints were associated with fragile sites, more than expected by chance (P < 0.025). This supports the report of an association between fragile sites and constitutional chromosome breakpoints by Hecht and Hecht [1984]. To explain these findings, we propose that autosomal fragile sites are unstable areas which predispose to breaks and unequal crossing over near the fragile site breakpoints creating minute duplications and deletions. Consequently, newborn infants inheriting a seemingly "balanced" karyotype from a normal parent with a balanced reciprocal translocation may still be at an increased risk of being malformed and/or developmentally delayed because of submicroscopic chromosomal imbalances.

Abnormalities, Multiple↗
PubMed1995

Induced abortion among unmarried women in Sichuan province, China.

This report describes the social and demographic characteristics of 457 unmarried women who underwent a first trimester induced abortion at hospitals and family planning clinics in Sichuan province, China. The data show a very low level of medical complications. However, improved access to contraception for unmarried women is needed in order to reduce the incidence of unintended pregnancies and induced abortion.

Abortion, Induced↗
PubMed1995

Calcium phosphate supplementation results in lower rat fecal bile acid concentrations and a more quiescent colonic cell proliferation pattern than does calcium lactate.

Although there is general agreement that dietary calcium is protective against colon carcinogenesis, considerable controversy exists on the relative efficacy of the counterion in calcium supplements. We therefore conducted a comparative study in rats of four forms of calcium supplementation (calcium phosphate, casein, lactate, and a 50:50 phosphate-carbonate combination). The relative effects of these supplements on measurements of colon physiology, in vivo pH, fecal fat, individual bile acids, and in vivo cell proliferation were measured in the same animals. In contrast to results when amounts of calcium are varied, there was no effect of form of supplement on total fecal output or output of fecal fat. Calcium phosphate resulted in the most acidified cecal contents. Calcium phosphate and calcium casein resulted in lower fecal concentrations of lithocholate and lower amounts of total fecal bile acids than supplementation with the calcium lactate or combination diets. In addition, rats fed calcium phosphate had lower concentrations of fecal beta-muricholate than rats provided with the calcium combination supplement. In the proximal colon, calcium phosphate resulted in a significantly lower number of cells per crypt column and a lower labeling index than the calcium lactate diet. The position of the highest labeled cell was lower with calcium phosphate supplementation than with supplementation from the calcium combination or the calcium lactate diet. There was a highly significant correlation between the pH of cecal contents and labeling index in the proximal colon (r = 0.98, p = 0.003). The results suggest that calcium phosphate may inhibit colon tumor incidence more effectively than calcium lactate, because the calcium phosphate group had a lower colonic proliferative status than the calcium lactate group. Changes in the proliferative status of colonocytes are known to precede and accompany neoplasia.

Animals↗
PubMed1995

Structure of artificial enamel lesions after topical applications of high-concentration sodium fluoride solution in vitro.

A three-layer structure, including a columnar layer (CL), a buffer layer, and unaffected intact enamel, was successively formed from the outer to the inner part of artificial enamel lesions (AEL) by topical applications of a high-concentration acidic sodium fluoride solution (10,000 ppm, pH 5.6) in vitro. The AEL was produced in bovine enamel that was decalcified for 5 days in a lactic acid gel system. The morphological observations by using scanning electron microscopy showed that the CL was made of columnar deposits of small globules about 0.5 microns in diameter. It was observed for the first time that small globules filled the demineralized interprismatic regions in the buffer layer. The unaffected intact enamel was protected from further demineralization under the acidic condition. Structure and composition of the CL were investigated by using X-ray diffraction and X-ray photoelectron spectroscopy. In the CL the atomic ratio was Ca:P = 12.6 and Ca:F = 0.75, and the small globules were mainly a mixture of polycrystalline calcium fluoride and hydroxyapatite. For comparison, the sound enamel and the AEL attained by applications of 0 and 100 ppm acidic sodium fluoride solutions (pH 5.6) were also investigated. The formation mechanism of the three-layer structure and the related cariostatic effects are discussed.

Animals↗
PubMed1994

A very low intake of fat is required to decrease fecal bile acid concentrations in rats.

The purpose of this study was to determine the effect of different amounts of dietary fat on colonic cell proliferation and fecal bile acid concentrations. Thirty-nine male Sprague-Dawley rats were randomly assigned to three diets (13 rats per diet) containing 5, 10 and 20 g butter/100 g diet. Diets were fed for 3 wk. As fat intake increased, total fecal fat excretion remained constant. When dietary fat was decreased from 20 to 10 g/100 g diet, total fecal bile acid concentrations tended to increase 14.5%. However, a further reduction to 5 g butter/100 g diet significantly decreased fecal total bile acid concentration by 48% from the concentration in feces of rats fed 10 g butter/100 g diet. The concentration of deoxycholate (considered a highly promotive bile acid) was not reduced unless the amount of fat in the diet was reduced to 5 g/100 g. Labeling index was used as an intermediate marker for colon carcinogenesis. For deoxycholate, a decrease of fat intake to 5 g/100 g diet decreased the cecal labeling index relative to those of rats fed 10 or 20 g butter/100 g diet. These data indicate that decreasing the dietary fat from 20 to 10 g/100 g does not decrease fecal bile acid concentration or colonic cell proliferation, but some effects are seen in rats fed 5 g butter/100 g diet.

Animals↗
PubMed1994

Rats fed high fat diets with increased calcium levels have fecal bile acid concentrations similar to those of rats fed a low fat diet.

The mechanism by which calcium may protect against colon carcinogenesis was studied in rats fed three levels of calcium (0.5, 1.0 and 1.5 g/100 g diet) and a high butter diet (20 g/100 g). Results were compared with values obtained using a low butter diet (5 g/100 g) supplemented with 0.5 g Ca/100 g diet. Concentration and relative proportions of individual fecal bile acids were determined by gas chromatography, and in vivo colonic cell proliferation was assessed using [3H]thymidine. Total fecal output and total fecal lipids increased as dietary calcium increased. When calcium supplementation remained at 0.5%, raising the level of fat in the diet increased the fecal concentrations of deoxycholate, omega-muricholate and total bile acids. However, when the level of fat supplementation remained constant at 20 g/100 g diet, but dietary calcium was 1.0 or 1.5 g/100 g, the concentration of these bile acids returned to the level found in feces of rats fed the low fat diet. Despite the significant decrease in the concentrations of certain fecal bile acids with increasing calcium supplementation, these differences were not reflected in substantive changes in epithelial cytokinetics. These data show that in rats fed high butter diets, 1.0% calcium is sufficient to lower total bile acid concentration and the concentrations of certain individual bile acids to those found in feces of rats fed low fat diets. Despite the significant effects of calcium on bile acid concentrations, minimal effects were observed on indices of colonic cell proliferation.

Animals↗
PubMed1994

[Localization of apoptosis-antagonizing bcl-2 translated product in Hodgkin's disease].

We applied more sensitive immunohistochemical method, i.e. multilayered PAP, to investigate the expression and distribution of apoptosis-antagonizing gene bcl-2 in Hodgkin's disease (HD), bcl-2-positive Reed-Sternberg (RS) cells were found in 7 of 21 (33%) of HD, and 2 of 7 (mixed cellularity) accompanied by a lot of reactive lymphoid follicles, the germinal centers of which were also positive for bcl-2. In contrast, in 4 cases of inflammatory lymphoid follicular hyperplasia as positive controls, the mantle zones rich in long-lived B cells were strongly positive stained with bcl-2 antibody, whereas germinal centers were negative. Thus, our data indicate that overexpressed bcl-2 gene-mediated apoptosis impairment is strongly associated with pathogenesis of HD.

Apoptosis↗