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Biomedical subjects

J Chen

Publications and source records attributed to J Chen.

At least 1,171 records · Page 65Linked to original sources
PubMed1999

Human DNA repair systems: an overview.

DNA repair systems act to maintain genome integrity in the face of replication errors, environmental insults, and the cumulative effects of age. More than 70 human genes directly involved in the five major pathways of DNA repair have been described, including chromosomal location and cDNA sequence. However, a great deal of information as to the precise functions of these genes and their role in human health is still lacking. Hence, we summarize what is known about these genes and their contra part in bacterial, yeast, and rodent systems and discuss their involvement in human disease. While some associations are already well understood, it is clear that additional diseases will be found which are linked to DNA repair defects or deficiencies.

Animals↗
PubMed1999

Association of antibiotic treatment-resistant Lyme arthritis with T cell responses to dominant epitopes of outer surface protein A of Borrelia burgdorferi.

OBJECTIVE: To explore further the association of antibiotic treatment-resistant Lyme arthritis and T cell reactivity with outer surface protein A (OspA) of Borrelia burgdorferi, including the identification of T cell epitopes associated with this treatment-resistant course. METHODS: The responses of peripheral blood and, if available, synovial fluid lymphocytes to B burgdorferi proteins, fragments, and synthetic peptides, as determined by proliferation assay and interferon-gamma production, were compared in 16 patients with treatment-responsive and 16 with treatment-resistant Lyme arthritis. RESULTS: The maximum severity of joint swelling correlated directly with the response to OspA. Moreover, the only significant difference between patients with treatment-resistant and treatment-responsive arthritis was in reactivity with N-terminal and C-terminal fragments of OspA, OspA1 (amino acids [aa] 16-106), and OspA3 (aa 168-273). Epitope mapping showed that 14 of the 16 patients with treatment-resistant arthritis had responses to OspA peptides (usually 4 or 5 epitopes), whereas only 5 of the 16 patients with treatment-responsive arthritis had reactivity with these peptides (usually 1 or 2 epitopes) (P = 0.003). Patients with HLA-DRB1 alleles associated with treatment-resistant arthritis were more likely to react with peptide 15 (aa 154-173) and, to a lesser degree, with peptide 21 (aa 214-233) than patients with other alleles, whereas the responses to other epitopes were similar in both groups. CONCLUSION: The maximum severity of joint swelling and the duration of Lyme arthritis after antibiotic treatment are associated with T cell responses to specific epitopes of OspA.

Adolescent↗
PubMed1999

Formation of 4-hydroxynonenal adducts with cytochrome c oxidase in rats following short-term ethanol intake.

This study addresses the role of the lipid peroxidation product, 4-hydroxynonenal (HNE), in ethanol-related damage of cytochrome c oxidase (COX) in vivo. It utilizes an animal model with acute ethanol exposure in which HNE levels in liver mitochondria are strikingly increased. Pregnant female Sprague-Dawley rats were administered 5 doses of ethanol (4 gm/kg, po at 12-hour intervals) beginning on day 17 of gestation and were sacrificed on day 19. Controls were pair-fed and received dextrose isocaloric to ethanol. Mitochondria were isolated from maternal and fetal livers and COX activities were measured spectrophotometrically. Compared with the pair-fed controls, COX activity was decreased with exposure to ethanol by 25% in maternal rats and 43% in fetal rats (P<.05). Western Blot with an HNE-Histidine antibody showed enhanced formation of HNE adducts with COX from ethanol-exposed rats, which was more pronounced in fetal than in adult livers. The HNE adducts were mainly with subunit IV of COX. The cause and effect relationship between HNE adduct formation and COX inhibition was examined in vitro by incubating purified COX with HNE. COX inhibition was accompanied by concentration-dependent HNE adduct formation that was consistent with those found in in vivo ethanol-exposed samples. These results suggest that the ethanol-related decreases in COX activity found in liver mitochondria could be attributable to HNE adduct formation with the enzyme complex. This could be an important mechanism by which modification of proteins occur in in vivo oxidative stress.

Alcoholic Intoxication↗
PubMed1999

Mechanisms of regulation of the MacMARCKS gene in macrophages by bacterial lipopolysaccharide.

Bacterial lipopolysaccharide (LPS) stably induced the protein kinase C substrate, MacMARCKS, in murine resident peritoneal macrophages; initial induction of MacMARCKS mRNA was detected within 15 min and was protein synthesis-independent. This response was observed in the macrophage cell line RAW264, and occurred also in response to plasmid DNA, a partial mimetic of other responses to LPS. In murine bone marrow-derived macrophages, MacMARCKS was expressed constitutively due to induction by macrophage colony-stimulating factor. Nuclear run-on transcription revealed that, like tumor necrosis factor alpha (TNF-alpha), MacMARCKS was transcribed constitutively in RAW264 cells. The MacMARCKS promoter was sequenced to -1.7 kb and the transcription start site determined. Transient transfections of RAW264 cells revealed that the 113-bp GC-rich proximal promoter contained all the elements required for both high basal activity and 15- to 20-fold activation by LPS.

Animals↗
PubMed1999

A physiologically relevant hyperthermia selectively activates constitutive hsp70 in H9c2 cardiac myoblasts and confers oxidative protection.

Whole body hyperthermia (42-43 degrees C for 15-20 min) elicits the formation of heat shock proteins (hsps) and improves cardiac recovery from subsequent ischemia/reperfusion. However, the beneficial effects of this response are compromised by initial tissue injury, which limits its clinical applicability. Using a simplified myocardial model (rat heart-derived H9c2 myoblasts) a hypothesis was tested that chronic, mild hyperthermia is as effective as acute heat shock in inducing the heat shock response. Our results indicate that 39 degrees C pre-conditioning evoked thermotolerance and oxidative resistance, but caused no detectable adverse effects. An improved survival after hydrogen peroxide (H2O2) exposure (40-54 microm for 3 h) was first observed in cells pre-conditioned at 39 degrees C for 24 h. As the duration of thermal pre-incubation increased, cells became more resistant than the control (37 degrees C) to a greater toxicity of H2O2(68 microm). An optimal oxidative protection developed by;4 days at 39 degrees C and this persisted for as long as the cells were incubated at this temperature. Three hsps are known to modulate cellular antioxidant defenses: the constitutive-hsp70 (hsc70), its inducible counterpart (hsp70), and hsp27. The authors found that mild hyperthermia selectively induced only hsc70, which demonstrates a lower temperature threshold for activation of hsc70. The initial protection against the milder H2O2challenge correlated with a homogenous distribution of pre-existing hsc70. The subsequent optimal protection was associated with an identical distribution pattern and a moderate increase of hsc70. These observations suggest that mild hyperthermia induces a beneficial adaptive response, in which hsc70 plays a critical role.

Adaptation, Physiological↗
PubMed1999

High-level expression and single-step purification of leucyl-tRNA synthetase from Escherichia coli.

A T7 promoter-based His6-tagging vector has been constructed that directs the synthesis in Escherichia coli of fusion proteins containing a stretch of six histidine residues at the N terminus. The vector allows overproduction and single-step purification of His6-fusion protein by immobilized metal (Ni2+) chelate affinity chromatography. The gene encoding leucyl-tRNA synthetase (leuS) was cloned into this vector and expressed in high level. The specific activity of the synthetase in the crude extract of E. coli JM109(DE3) transformant containing the His6-tagging vector with the gene leuS was approximately 110 times that of JM109(DE3) (the host strain without the vector). The overproduced His6-fusion leucyl-tRNA synthetase can be purified to homogeneity under native conditions within 2 h by one-step affinity chromatography with an overall yield of 55%. The His6-tag at the N terminus of leucyl-tRNA synthetase did not affect its aminoacylation activity or the secondary structure.

Chromatography, Affinity↗
PubMed1999

Stresses in the normal and diabetic human penis following implantation of an inflatable prosthesis.

The prevalence of impotence in diabetes mellitus ranges as high as 75%. The implantation of an inflatable penile prosthesis (IPP) is frequently carried out to restore erectile function. However, clinical studies have demonstrated that severe post-implantation penile pain during erection is a common complication in diabetic men. A biomechanical model of the penis/prosthesis complex is developed, based on cross-sectional anatomy, to simulate the internal stress distribution due to interaction of the prosthesis with both normal and diabetic penile tissues. The material properties of the model components are adopted from experimental data. The model is solved by using commercial finite-element software for a characteristic inflation loading of the penile prosthesis. Elevated structural stresses during erection are found in the dorsal aspect of the tunica albuginea (normal 5.1-31.5 kPa, diabetic 5.1-70 kPa post-implantation). Following IPP implantation, stresses in the diabetic penis are almost as twice as high as those in the normal one and can cause a painful sensation owing to nerve stimulation or to ischaemia in regions of compressed vascular tissue.

Diabetic Angiopathies↗
PubMed1999

A rapid screening and diagnosis on fragile X syndrome by PCR.

Polymerase chain reaction (PCR) technique combined with direct detection by silver staining on denaturing DNA sequencing gel was used to analyze the (CGG)n repeats within the FMR1 gene on 169 suspected patients with mental retardation and 33 kindreds of 6 fragile X families. The results showed that: (1) No PCR products were detected in 3 males in the suspected group. (2) In the fragile X family studies, the 5 male probands failed to show any PCR products. (3) Diplex PCR with the primers flanking the FRAXE locus was used to serve as an internal control for the 8 above-mentioned males and only normal products of the FRAXE locus were detected, indicating that the possibility of false negative results of the FRAXA locus could be eliminated. These findings suggested that analysis of (CGG)n repeat within the FMR1 gene by PCR technique could efficiently detect premutation carriers and that negative PCR products in mentally retarded males might highly imply the diagnosis of fragile X syndrome after the false negative results have been excluded by diplex PCR. This PCR assay is suitable for the screening and diagnosis of fragile X syndrome in a large number of populations due to its rapidity, simplicity, stability and reliability.

Alleles↗
PubMed1999

Preparation of adriamycin magnetic albumin microspheres and their experimental antitumor effects in vitro and in vivo.

The adriamycin magnetic microspheres (ADM-MAMs) were prepared by the heat-stabilized protein methods. Their physico-chemical properties were examined; their cytotoxicities against tumor cells in vitro were assayed by a modified MTT method, and their effects were observed on the implanted gastric tumor in Wistar rats given ADM-MAMs via alimentary canal at the presence of the external magnetic fields. The results showed that the ADM-MAMs were successfully prepared and had cytotoxic effect on tumor cells in vitro similar to the free ADM (P > 0.05). The inhibitory effects of ADM-MAMs on the implanted gastric tumor in vivo were significantly increased as compared with the controls (P < 0.01). Our results suggested that ADM-MAMs were a new type of adriamycin (ADM) preparation and its form alteration did not affect its anticancer effects.

Animals↗
PubMed1999

The effect of locally implanted complexes of adriamycin-hydroxyapatite complexes on tumor--study of a new alternative treatment for hepatic cancer.

A new targeting anticancer system was prepared by using hydroxyapatite particles (2 mm in diameter) as carrier material and adriamycin as anticancer agent. The adsorption and release properties of the complexes were assayed by fluorometry in vivo and in vitro and the curative effect on W-256 sarcoma of rat was observed. The results showed that one particle of hydroxyapatite could adsorb approximately 0.08 mg adriamycin and they can maintain a steady and slow release of adriamycin from hydroxyapatite for one month. When hydroxyapatite-adriamycin complexes were implanted into the liver of rat, liver adriamycin concentration at the implanted region was obviously higher than that achieved by injection of adriamycin solution. The locally implanted complexes obviously inhibited the growth of subcutaneous implanted tumor of rat, and increased the survival rate of rat with implanted liver tumor.

Animals↗
PubMed1999

Behavior of pythium Torulosum zoospores during their interaction with tobacco roots and Bacillus cereus.

Bacillus cereus UW85 suppresses seedling damping-off diseases caused by Oomycetes and produces antibiotics that inhibit development of Oomycetes in culture. The goal of this study was to determine how UW85 and its antibiotics affected the behavior of an Oomycete, Pythium torulosum, in its interaction with plant roots. We studied tobacco seedlings inoculated with zoospores of P. torulosum and UW85 culture, culture filtrate, washed cells, antibiotics (zwittermicin A or kanosamine), purified from cultures of UW85, and UW030, a mutant of UW85 that does not suppress disease and does not produce the antibiotics. Microscopic observation revealed that all of the treatments inhibited zoospore activity around roots and encystment on roots. Treatment with UW85 culture, culture filtrate, zwittermicin A, or kanosamine delayed cyst germination and the elongation rate of germ tubes, whereas treatment with UW030 or washed UW85 cells did not. In an in vitro seedling bioassay of disease suppression, the antibiotics, zwittermicin A and kanosamine, suppressed disease singly or together, although UW85 culture suppressed disease more effectively than did the antibiotics. The results show that B. cereus cultures affect zoospore behavior in the presence of roots, and B. cereus-produced antibiotics, zwittermicin A and kanosamine, contribute to disease suppression and inhibition of germ tube elongation in the presence of the plant root.

Anti-Bacterial Agents↗
PubMed1999

Effects of SCH 59228, an orally bioavailable farnesyl protein transferase inhibitor, on the growth of oncogene-transformed fibroblasts and a human colon carcinoma xenograft in nude mice.

The products of the Ha-, Ki-, and N-ras proto-oncogenes comprise a family of 21 kDa guanine nucleotide-binding proteins which play a crucial role in growth factor signal transduction and in the control of cellular proliferation and differentiation. Activating mutations in the ras oncogenes occur in a wide variety of human tumors. Ras proteins undergo a series of posttranslational processing events. The first modification is addition of the 15-carbon isoprene, farnesyl, to a Cys residue near the carboxy-terminus of Ras. Prenylation allows the Ras oncoprotein to localize to the plasma membrane where it can initiate downstream signalling events leading to cellular transformation. Inhibitors of the enzyme which catalyzes this step, farnesyl protein transferase (FPT), are a potential class of novel anticancer drugs which interfere with Ras function. SCH 59228 is a tricyclic FPT inhibitor which inhibits the farnesylation of purified Ha-Ras with an IC50 of 95 nM and blocks the processing of Ha-Ras in Cos cells with an IC50 of 0.6 microM. SCH 59228 has favorable pharmacokinetic properties upon oral dosing in nude mice. The in vivo efficacy of SCH 59228 was evaluated using a panel of tumor models grown in nude mice. These included several rodent fibroblast lines expressing mutationally-activated (val12) forms of the Ha-Ras oncogene. In some cases, these proteins contain their native C-terminal sequence (CVLS) which directs farnesylation. In one model, the C-terminal sequence was altered to CVLL, making the expressed protein a substrate for a distinct prenyl transferase, geranylgeranyl protein transferase-1. When dosed orally at 10 and 50 mg/kg (four times a day, 7 days a week) SCH 59228 significantly inhibited tumor growth of cells expressing farnesylated Ha-Ras in a dose-dependent manner; over 90% growth inhibition was observed at the 50 mg/kg dose. Tumor growth of cells expressing the geranylgeranylated form of Ha-Ras was less potently inhibited. Growth of tumors derived from a rodent fibroblast line expressing activated Ki-Ras containing its native C-terminal sequence (CVIM), which preferentially directs farnesylation, was also inhibited by SCH 59228. Inhibition in the Ki-Ras model was less than that observed in the Ha-Ras model. In contrast, tumors derived from cells transformed with the mos oncogene were not significantly inhibited even at the highest dose level. SCH 59228 also significantly and dose-dependently inhibited the growth of human colon adenocarcinoma DLD-1 xenografts (which express activated Ki-ras). These results indicate that SCH 59228 possesses in vivo antitumor activity upon oral dosing in tumor models expressing activated ras oncogenes. This is the first report of oral antitumor activity with an FPT inhibitor. These results are discussed in light of recent observations on alternative prenylation of some Ras isoforms.

Alkyl and Aryl Transferases↗
PubMed1999

Specific detection of Xylella fastidiosa Pierce's disease strains.

Pierce's disease (PD, Xylella fastidiosa) of grapevine is the primary pathogen limiting vinifera grape production in Florida and other regions of the southeastern United States. Quick and accurate detection of PD strains is essential for PD studies and control. A unique random amplified polymorphic DNA (PD1-1-2) was isolated from a PD strain from Florida. Fragment PD1-1-2 was cloned, sequenced, and found to be 1005 bp in length. PCR primers were designed to utilize these sequence data for PD strain detection. One primer set (XF176f-XF954r) amplified a 779-bp DNA fragment from 34 PD strains including seven pathotypes of X. fastidiosa, but not from strains of Xanthomonas campestris pv. campestris, Xan. vesicatoria or Escherichia coli. A second primer set (XF176f and XF686r) amplified a 511-bp fragment specific to 98 PD strains, but not from strains of citrus variegated chlorosis, mulberry leaf scorch, oak leaf scorch, periwinkle wilt, phony peach, or plum leaf scald. Sequence analysis indicated that RAPD fragment PD1-1-2 contains a Ser-tRNA gene. The PD-specific region includes a TaqI restriction site (TCGA) and is 150 bp downstream of the Ser-tRNA gene.

Base Sequence↗
PubMed1999

Invasion and metastasis of liver cancer: expression of intercellular adhesion molecule 1.

PURPOSE: To study the relationship between intercellular adhesion molecule 1 (ICAM-1) and liver cancer metastasis and to find predicting factors that could indicate the growth and metastasis of liver cancer. METHODS: ICAM-1 expression in fresh tissue of normal liver and hepatocellular cancer (HCC) was examined by immunoperoxidase staining. Serum soluble intercellular adhesion molecule 1 (sICAM-1) from patients with a benign HCC tumor, and the expression of ICAM-1 in the orthotopically transplanted LCI-D20 tumor of a nude mouse liver cancer metastasis model, and in human hepatoma, the tumor surrounding tissue and normal liver, was analyzed semiquantitatively by the immuno-dot blot method. Tissue ICAM-1 expression (mRNA level) was detected by Northern blotting. RESULTS: ICAM-1 expression in LD1-20 D metastatic liver cancer had a positive correlation with tumor size and the time after implantation. It increased suddenly as metastasis occurred being 3.03+/-0.51 before metastasis and 8.24+/-0.95 after metastasis, P < 0.01, then remained high, appending on the number of sites involved (monosite metastasis 5.48+/-0.49, multisite metastasis 10.05+/-1.17, P < 0.05). All six cases of normal liver samples were negative in anti-ICAM-1 immunohistochemical staining, 80.0% (36/45) of the HCC showed some ICAM-1 expression. The rate of positive cells was a little higher in large tumors, tumors with an intact capsule and tumors with metastasis, but there was no significant difference. It was noticed that two cancer emboli also had high ICAM-1 expression. The ICAM-1 concentration in HCC (13.43+/-0.09) was higher than that in tumor surrounding the liver (5.89+/-0.17, P < 0.01) and that in normal liver (4.27+/-0.21, P < 0.01). sICAM-1, like tissue ICAM-1, was higher in HCC patients than in patients (with benign liver tumor and normal controls. Both tissue ICAM-1 and sICAM-1 were higher in the metastasis group than in the group without metastasis (tissue ICAM-1 20.24+/-0.30 vs 10.23+/-0.12 P < 0.05; sICAM-1 12.18+/-0.25 vs 9.77+/-0.54 P < 0.05). Northern blot analysis revealed that ICAM-1 expression, as indicated by mRNA level, was also higher in HCC and in cancer emboli than in tumor surrounding liver and normal liver. CONCLUSIONS: Tissue ICAM-1 and serum sICAM-1 could indicate the stage of HCC, and the potential of hepatoma cells for invasion and metastasis. They may play an important role in the metastasis cascade.

Animals↗
PubMed1999

Interaction of baboon anti-alpha-galactosyl antibody with pig tissues.

As barriers to xenotransplantation are surmounted, such as suppression of hyperacute rejection allowing improved graft survival, it becomes important to define longer-term host-xenograft interactions. To this end we have prepared in baboons high titer anti-alpha-Galactosyl (alphaGal) and anti-porcine aortic endothelial cell antibodies, similar to human natural xenoantibodies and reactive with epitopes of thyroglobulin, laminin, and heparan sulfate proteoglycans. When injected into pigs with a protocol similar to that used in the rat to show the nephritogenic potential of heterologous anti-laminin and anti-heparan sulfate proteoglycan antibodies, baboon immunoglobulins bound first to renal vascular endothelium, and later to interstitial cells, especially fibroblasts and macrophages, and to antigens in basement membranes and extracellular matrix, where they colocalized with laminin- and heparan sulfate proteoglycan-antibodies, and with bound Griffonia simplicifolia B4. A similar binding was observed in other organs. The pigs did not develop an acute complement-dependent inflammation, but rather chronic lesions of the basement membranes and the extracellular matrix. Incubation of renal fibroblasts with baboon anti-alpha-Galactosyl antibodies resulted in increased synthesis of transforming growth factor-beta and collagen, suggesting a possible basis for the fibrotic response. The results demonstrate that in this experimental model a consequence of alphaGal antibody interaction with porcine tissues, is immunoreactivity with alphaGal on matrix molecules and interstitial cells, priming mechanisms leading to fibrosis resembling that in chronic allograft rejection. The possibility that similar lesions may develop in long-surviving pig xenografts is discussed.

Animals↗
PubMed1999

Characterization of dental follicle cells in developing mouse molar.

Dental follicle has been implicated as the origin of alveolar bone, cementum and periodontal ligament, but there is no direct evidence of their cellular lineage. The present pilot study was designed to characterize the phenotype of cultured cells obtained from the dental follicle of neonatal mouse molars. Developing mandibular molars from 6-day-old CD-1 mice were subjected to 1% trypsin in Hank's balanced salt solution. After trypsinization, the dental follicle was enucleated from the tooth germ and separated from the associated epithelial root sheath. Pure dental follicle tissue was cultured in alpha-minimal essential medium containing 10% fetal bovine serum and antibiotics. The nature of the cultured follicle cells was determined in situ by immunocytochemical staining for type I and III collagen, fibronectin, and alkaline phosphatase expression. Earlier phenotypic markers for mineralization such as bone sialoprotein and osteopontin were also examined by in situ hybridization of matched molar tissues. The extracellular matrix proteins (such as type I collagen and fibronectin) were moderately expressed cytochemically. However, type III collagen was strongly stained. Gene expression of bone sialoprotein and osteopontin was detected in sections of mouse molars of similar age. The ALPase activity showed moderate to strong intensity in these primary cultured cells and responded to 1,25(OH)2 vitamin D3 treatment. Cytokeratin stains were not noted in these cells. In conclusion, the 6-day-old dental follicle cells exhibit partial characteristics of a mineralized tissue-forming phenotype even though the expression of osteopontin, type I collagen and fibronectin was low at this stage.

Alkaline Phosphatase↗
PubMed1999

Contraceptive status and sexual function of climacteric Chinese women.

The objective of the present survey was to assess the contraceptive status and sexual function of climacteric Chinese women. One cross-sectional study randomly recruited 742 premenopausal, perimenopausal, and naturally menopausal women aged 45-55 years from Beijing. Contraceptive methods were used by 75.6% of premenopausal and 54.2% of perimenopausal women. The primary methods were the IUD and barrier method. The women's choices of methods were related to parity and frequency of sexual activities. Sexual activity was related to the satisfaction of contraceptive methods. Perimenopausal and postmenopausal women were about half as likely to enjoy sexual activity and to experience orgasms than premenopausal women. Women of higher socioeconomic status had a lower risk for decreased sexual functioning. The IUD was the most popular and the most appropriate contraceptive method for perimenopausal women. Sexual function was associated with the women's satisfaction with the contraceptive method used, their menopausal status, and their socioeconomic class.

China↗