Search PubMed⌕ Search

Biomedical subjects

W Chen

Publications and source records attributed to W Chen.

At least 703 records · Page 39Linked to original sources
PubMed1997

Inhibition of cyclobutane pyrimidine dimer formation in epidermal p53 gene of UV-irradiated mice by alpha-tocopherol.

Mutations or alterations in the p53 gene have been observed in 50-100% of ultraviolet light (UV)-induced squamous cell carcinoma in humans and animals. Most of the mutations occurred at dipyrimidine sequences, suggesting that pyrimidine dimers in the p53 gene play a role in the pathogenesis of cutaneous squamous cell carcinoma. We previously showed that topical alpha-tocopherol prevents UV-induced skin carcinogenesis in the mouse. In the present study we asked whether topical alpha-tocopherol reduces the level of UV-induced cyclobutane pyrimidine dimers in the murine epidermal p53 gene. Mice received six dorsal applications of 25 mg each of alpha-tocopherol, on alternate days, before exposure to 500 J/m2 of UV-B irradiation. Mice were killed at selected times after irradiation. The level of dimers in the epidermal p53 gene was measured using the T4 endonuclease V assay with quantitative Southern hybridization. Topical alpha-tocopherol caused a 55% reduction in the formation of cyclobutane pyrimidine dimers in the epidermal p53 gene. The rate of reduction of pyrimidine dimers between 1 and 10 hours after irradiation was similar in UV-irradiated mice, regardless of alpha-tocopherol treatment. Therefore, the lower level of cyclobutane pyrimidine dimers in UV-irradiated mice treated with alpha-tocopherol than in control UV-irradiated mice resulted from the prevention of formation of the dimers, and not from enhanced repair of these lesions. Our results indicate that alpha-tocopherol acts as an effective sunscreen in vivo, preventing the formation of premutagenic DNA lesions in a gene known to be important in skin carcinogenesis.

Administration, Cutaneous↗
PubMed1997

Food restriction reduces aflatoxin B1 (AFB1)-DNA adduct formation, AFB1-glutathione conjugation, and DNA damage in AFB1-treated male F344 rats and B6C3F1 mice.

The objective of this study was to examine effects of food restriction (FR) on the metabolic activation of aflatoxin B1 (AFB1) in rats and mice, which are AFB1-sensitive and -resistant rodent species, respectively. Forty percent FR [60% of ad libitum (AL) food consumption] reduced the metabolic activation of AFB1 in both rats and mice, causing formation of hepatic AFB1-DNA adducts to be 43% and 31% lower, respectively. The AFB1-DNA adduct 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 (AFB1-N7-Gua) was predominantly formed in rat liver DNA; the formation of the ring-open analogue of AFB1-N7-Gua, AFB1-formamidopyrimidine (AFB1-FAP), was predominantly found in mouse liver DNA. In contrast to the in vivo results, the in vitro AFB1-DNA adduct formation mediated by the microsomes of liver, kidney or lung from FR-mice was greater than the formation of AFB1-DNA adducts mediated by the tissue microsomes from the AL-mice. Food restriction induced hepatic glutathione S-transferase (GST) activity, as measured by the formation of AFB1-glutathione conjugates (AFB1-SG), in both rats and mice; AFB1-SG was also formed in mouse kidney. Food restriction-induced GST activity assayed in an in vitro system, using [3H]AFB1-8,9-epoxide and glutathione (GSH) as substrates, was also found when mouse kidney and lung cytosolic fractions were used. Food restriction inhibited the AFB1-induced DNA double strand breaks in mouse kidney. The reduction of levels of AFB1-DNA adduct formation in mouse kidney was comparable to the degree of AFB1-induced DNA strand breakages. The results of this study indicate that the metabolic activation of AFB1 can be modulated by FR through the alteration of the formation of AFB1-DNA adducts and AFB1-SG conjugation. However, species and tissue specificities exist regarding the metabolic activation of AFB1.

Aflatoxin B1↗
PubMed1997

Correlation of serum immunoglobulin G Helicobacter pylori antibody titers with histologic and endoscopic findings in patients with dyspepsia.

Serum immunoglobulin G (IgG) antibody tests are used extensively. We attempted to find out whether the titers of anti-Helicobacter pylori IgG antibody correlated with the degree of macroscopic gastrointestinal damage, the severity of antral gastritis, and the density of antral H. pylori colonization in symptomatic patients. Peripyloric antral biopsy specimens were obtained from 50 consecutive patients with dyspepsia undergoing upper gastrointestinal endoscopy. The macroscopic gastrointestinal damage and the histologic grades of antral gastritis were scored by a modified Lanza scale and Sydney system, respectively. In addition, the densities of antral H. pylori colonization were graded semiquantitatively. Serum IgG antibodies to H. pylori were measured by enzyme-linked immunosorbent assay. Thirty-six (M/F = 29/7) of the 50 patients had H. pylori infection documented by histologic examination or rapid urease test or both. Among the subjects, the IgG antibody titers to H. pylori correlated significantly with the grades of antral polymorphonuclear cell infiltration (p = 0.002) and antral bacterial density (p = 0.01) but not with endoscopic scores, the grades of mononuclear cell infiltration, mucosal atrophy, or intestinal metaplasia (p > 0.05). In addition, endoscopic scores also were found to be significantly correlated with antral bacterial density (p = 0.049) and the grade of polymorphonuclear cell infiltration (p = 0.012). We therefore conclude that high titers of IgG antibody to H. pylori in patients with dyspepsia indicate dense H. pylori colonization and severe antral polymorphonuclear cell infiltration. However, it cannot replace endoscopic examination to evaluate the degree of macroscopic gastrointestinal damage.

Aged↗
PubMed1997

Environmental health response clinics. A survey of program options.

Environmental Health Response Clinics are established in response to concerns about community exposures to hazardous situations (chemical, biological, radiological). They are developed in response to a demand for "clinical services" and operate outside the usual health care financing and delivery mechanisms. Prompted by their experience in California, the authors formed a focus group to identify possible goals and services. A mail survey of occupational-environmental health professionals was then conducted to evaluate the feasibility and priority of representative goals. The analysis suggests that services should focus on the specific hazard of concern and that communication and education are essential components. The tendency to "do a general physical examination" should be eschewed. Ratings for priority and feasibility were disparate for several possible goals. In some instances, a "hands-on examination" may not be the best use of resources. Environmental health professionals may serve by direct clinical service or by advising community-based practitioners. Providing routine clinical services alone cannot meet the expectations for an environmental health response clinic.

California↗
PubMed1997

Insecticidal activity of a recombinant baculovirus containing an antisense c-myc fragment.

Attempts to develop baculovirus-based insecticides by insertion of genes encoding enzyme inhibitors, neuropeptides or toxins have met with some success. However, it is often difficult to ensure correct processing or secretion of the encoded peptides. Here we tested a simpler strategy by insertion of an antisense fragment of a host gene to block translation of a protein essential for larval growth and development. We selected the c-myc gene for two main reasons: (i) its protein is known to be well conserved in evolution and to have multiple essential functions during development; and (ii) c-myc family genes have yet to be characterized in insects, thus blockage of essential genes by anti-sense transcripts from a strong virus promoter could provide a sensitive test for the existence of myc-like gene products. An appropriate fragment of the human c-myc gene was inserted downstream from the polyhedrin promoter of Autographa californica nucleopolyhedrovirus and tested in bioassays on Spodoptera frugiperda larvae. Western blot analysis with a human c-myc antibody revealed an endogenous protein band which bound specifically to these antibodies. This band disappeared more rapidly from cells infected with the antisense c-myc recombinant virus than from those infected with c-myc-negative virus. Results of bioassays showed that the antisense construct stopped feeding as soon as the polyhedrin promoter-driven transcripts accumulated, followed shortly by death of the larvae. These results suggest that c-myc-like protein(s) exist in insects and that the antisense strategy is an effective approach to virus insecticide productions.

Animals↗
PubMed1997

Purification and characterization of the NS3 serine protease domain of hepatitis C virus expressed in Saccharomyces cerevisiae.

cDNA encoding the putative core of the hepatitis C virus NS3 serine protease domain (residues 1-181 of NS3; NS3 (181)) was expressed as an N-terminally (His)6-tagged fusion protein in Saccharomyces cerevisiae. NS3 (181) protease activity was found in soluble cell lysates, and the N-terminal metal-chelating domain facilitated the efficient purification of active enzyme, using immobilized metal affinity chromatography. The purified NS3(181), protease activity was characterized by assaying the trans-cleavage of in vitro transcription-translation generated substrates, and subsequently a previously unobserved cleavage site within the NS5A region was identified. The inhibitory effect of known protease inhibitors was also examined. It is hoped that availability of this method for the expression and purification of the NS3(181) protease will facilitate the development of anti-hepatitis C therapies.

Amino Acid Sequence↗
PubMed1997

Therapy with cultured T cells: principles revisited.

In animals and in humans, T-cell therapy can cure advanced disseminated leukemia that would otherwise be fatal. The therapeutic effect of immune T cells is quantitative. As the dose of effector T cells is increased, survival is proportionately increased. Therefore, effective T-cell therapy is predicated on the ability to procure large numbers of immune effector T cells. By using cultured T cells, the number of immune T cells can be increased in vivo substantially above the level achievable by vaccination. The survival of cultured T cells in vivo is dependent upon both the culture conditions used and the therapeutic regimens employed. Under appropriate conditions, cultured T cells can proliferate in vivo in response to stimulation by antigen, distribute widely and survive long term to provide effector function and immunologic memory. Given that T cells recognize peptides, the need for immunization with tumor can be circumvented by immunization with peptide. Peptide-specific T cells and the progeny of single T-cell clones can provide the necessary cellular functions to eradicate disseminated murine leukemia. The ability of cloned T cells to similarly provide substantial measurable immunity in humans has been validated in clinical trials. By priming with peptides and by using established culture conditions, T-cell therapy can now be directed against virtually any antigen within the host T-cell repertoire. The major remaining question to be answered is which proteins and which peptides are the most suitable targets for T-cell therapy trials.

Animals↗
PubMed1997

Episodic evolution mediates interspecies transfer of a murine coronavirus.

Molecular mechanisms permitting the establishment and dissemination of a virus within a newly adopted host species are poorly understood. Mouse hepatitis virus (MHV) strains (MHV-A59, MHV-JHM, and MHV-A59/MHV-JHM) were passaged in mixed cultures containing progressively increasing concentrations of nonpermissive Syrian baby hamster kidney (BHK) cells and decreasing concentrations of permissive murine DBT cells. From MHV-A59/MHV-JHM mixed infection, variant viruses (MHV-H1 and MHV-H2) which replicated efficiently in BHK cells were isolated. Under identical treatment conditions, the parental MHV-A59 or MHV-JHM strains failed to produce infectious virus or transcribe detectable levels of viral RNA or protein. The MHV-H isolates were polytrophic, replicating efficiently in normally nonpermissive Syrian hamster smooth muscle (DDT-1), Chinese hamster ovary (CHO), human adenocarcinoma (HRT), primate kidney (Vero), and murine 17Cl-1 cell lines. Little if any virus replication was detected in feline kidney (CRFK) and porcine testicular (ST) cell lines. The variant virus, MHV-H2, transcribed seven mRNAs equivalent in relative abundance and size to those synthesized by the parental virus strains. MHV-H2 was an RNA recombinant virus containing a crossover site in the S glycoprotein gene. At the molecular level, episodic evolution and positive Darwinian natural selection were apparent within the MHV-H2 S and HE glycoprotein genes. These findings differ from the hypothesis that neutral changes are the predominant feature of molecular evolution and argue that changing ecologies actuate episodic evolution in the MHV spike glycoprotein genes that govern interspecies transfer and spread into alternative hosts.

Animals↗
PubMed1997

Genetic evidence for interaction between Cbp1 and specific nucleotides in the 5' untranslated region of mitochondrial cytochrome b mRNA in Saccharomyces cerevisiae.

The cytochrome b (COB) gene is encoded by the mitochondrial genome; however, its expression requires the participation of several nuclearly encoded protein factors. The yeast Cbp1 protein, which is encoded by the nuclear CBP1 gene, is required for the stabilization of COB mRNA. A previous deletion analysis identified an 11-nucleotide-long sequence within the 5' untranslated region of COB mRNA that is important for Cbp1-dependent COB mRNA stability. In the present study, site-directed mutagenesis experiments were carried out to define further the features of this cis element. The CCG sequence within this region was shown to be necessary for stability. A change in residue 533 of Cbp1 from aspartate to tyrosine suppresses the effects of a single-base change in the CCG element. This is strong genetic evidence that the nuclearly encoded Cbp1 protein recognizes and binds directly to the sequence containing CCG and thus protects COB mRNA from degradation.

Basic Helix-Loop-Helix Leucine Zipper Transcriptio↗
PubMed1997

Abnormal regulation of HGP by hyperglycemia in mice with a disrupted glucokinase allele.

Glucokinase (GK) catalyzes the phosphorylation of glucose in beta-cells and hepatocytes, and mutations in the GK gene have been implicated in a form of human diabetes. To investigate the relative role of partial deficiencies in the hepatic vs. pancreatic GK activity, we examined insulin secretion, glucose disposal, and hepatic glucose production (HGP) in response to hyperglycemia in transgenic mice 1) with one disrupted GK allele, which manifest decreased GK activity in both liver and beta-cells (GK+/-), and 2) with decreased GK activity selectively in beta-cells (RIP-GKRZ). Liver GK activity was decreased by 35-50% in the GK+/- but not in the RIP-GKRZ compared with wild type (WT) mice. Hyperglycemic clamp studies were performed in conscious mice with or without concomitant pancreatic clamp. In all studies [3-(3)H]glucose was infused to measure the rate of appearance of glucose and HGP during 80 min of euglycemia (Glc approximately 5 mM) followed by 90 min of hyperglycemia (Glc approximately 17 mM). During hyperglycemic clamp studies, steady-state plasma insulin concentration, rate of glucose infusion, and rate of glucose disappearance (Rd) were decreased in both GK+/- and RIP-GKRZ compared with WT mice. However, whereas the basal HGP (at euglycemia) averaged approximately 22 mg x kg(-1) x min(-1) in all groups, during hyperglycemia HGP was suppressed by only 48% in GK+/- compared with approximately 70 and 65% in the WT and RIP-GKRZ mice, respectively. During the pancreatic clamp studies, the ability of hyperglycemia per se to increase Rd was similar in all groups. However, hyperglycemia inhibited HGP by only 12% in GK+/-, vs. 42 and 45%, respectively, in the WT and RIP-GKRZ mice. We conclude that, although impaired glucose-induced insulin secretion is common to both models of decreased pancreatic GK activity, the marked impairment in the ability of hyperglycemia to inhibit HGP is due to the specific decrease in hepatic GK activity.

Alleles↗
PubMed1997

L-glutamine stimulates intestinal cell proliferation and activates mitogen-activated protein kinases.

We studied the mechanisms by which L-glutamine (Gln), a major fuel for enterocytes, signals proliferation in intestinal epithelial cell lines. Gln was additive to epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) in stimulating DNA synthesis, as assessed by [3H]thymidine incorporation. Extracellular signal-regulated kinases (ERKs) p42mapk and p44mapk and Jun nuclear kinases (JNKs) phosphorylate and activate nuclear transcription factors. Proteins of the c-Jun, ATF-2, and c-Fos families aggregate to form DNA-binding homodimers or heterodimers called activating protein 1 (AP-1). In vitro assays and functional assays of phosphorylation demonstrated that Gln activates both ERKs and JNKs, resulting in a fourfold increase in AP-1-dependent gene transcription. Gln was required for EGF signaling through ERKs. Maximal stimulation of proliferation required approximately 2.5 mM Gln. c-Jun mRNA levels responded to Gln in "Gln-starved" porcine IPEC-J2 cells and in rat IEC-6 cells. Although Gln metabolism is required for the proliferative response, several Gln by-products did not stimulate [3H]thymidine incorporation, with the exception of arginine. Gln may be a unique nutrient for enterocytes, capable of dual signaling and augmenting the effects of growth factors that govern cellular proliferation and repair.

Animals↗
PubMed1997

Fat accretion and the regulation of insulin-mediated glycogen synthesis after puberty in rats.

Peripheral insulin sensitivity decreases after puberty in both humans and rodents and can be explained mostly by a reduction in insulin-mediated glycogen synthesis. We tested the hypothesis that the increase in postpubertal fat mass (FM), reflecting an alternative energy store, regulates a decrease in the capacity to store muscle glycogen. We studied Sprague-Dawley rats (n = 21) before puberty (Pre) or after puberty (at 4 mo of age) in groups that were either ad libitum fed (Post) or moderately caloric restricted (CR). FM (by 3H2O isotope dilution technique) was decreased by >40% in CR compared with Post. Glucose uptake (Rd, by 18 mU x kg(-1) x min(-1) hyperinsulinemic clamp) was 63 +/- 8 mg x kg(-1) x min(-1) in Pre and decreased to 39 +/- 2 mg x kg(-1) x min(-1) in Post (P < 0.001). However, it increased in CR to 53 +/- 2 mg x kg(-1) x min(-1) (P < 0.001 vs. Post). This increase in Rd was mainly accounted for by an increase in glycogen synthesis (Rd glycolysis determined by the rate of conversion of 3H-labeled glucose to 3H2O) from 23 +/- 2 in Post to 33 +/- 2 mg x kg(-1) x min(-1) in CR (P < 0.001; 38 +/- 7 mg x kg(-1) x min(-1) in Pre). Correction of glycogen synthesis in CR to near-prepubertal levels was further supported by directly assayed muscle glycogen content after insulin stimulation that was 45% higher and by a 35% enhanced accumulation of [3H]glucose into glycogen. No changes in the enzyme kinetics of glycogen synthase or phosphorylase were observed. An additional group of 2-mo-old postpubertal ad libitum-fed rats was matched with CR for lean body mass but had more FM. This group demonstrated 25% lower rates of insulin-mediated glycogen synthesis compared with CR, further supporting the notion that a moderate reduction of FM prevents the decline in insulin responsiveness and glycogen synthesis occurring after puberty. These data suggest a cause-effect relationship between the increased deposition of fat and the reduced ability to store glucose in skeletal muscle after puberty.

Adipose Tissue↗
PubMed1997

The Caenorhabditis elegans NK-2 homeobox gene ceh-22 activates pharyngeal muscle gene expression in combination with pha-1 and is required for normal pharyngeal development.

Pharyngeal muscle development in the nematode Caenorhabditis elegans appears to share similarities with cardiac muscle development in other species. We have previously described CEH-22, an NK-2 class homeodomain transcription factor similar to Drosophila tinman and vertebrate Nkx2-5, which is expressed exclusively in the pharyngeal muscles. In vitro, CEH-22 binds the enhancer from myo-2, a pharyngeal muscle-specific myosin heavy chain gene. In this paper, we examine the role CEH-22 plays in pharyngeal muscle development and gene activation by (a) ectopically expressing ceh-22 in transgenic C. elegans and (b) examining the phenotype of a ceh-22 loss-of-function mutant. These experiments indicate that CEH-22 is an activator of myo-2 expression and that it is required for normal pharyngeal muscle development. However, ceh-22 is necessary for neither formation of the pharyngeal muscles, nor for myo-2 expression. Our data suggest parallel and potentially compensating pathways contribute to pharyngeal muscle differentiation. We also examine the relationship between ceh-22 and the pharyngeal organ-specific differentiation gene pha-1. Mutations in ceh-22 and pha-1 have strongly synergistic effects on pharyngeal muscle gene expression; in addition, a pha-1 mutation enhances the lethal phenotype caused by a mutation in ceh-22. Wild-type pha-1 is not required for the onset of ceh-22 expression but it appears necessary for maintained expression of ceh-22.

Animals↗
PubMed1997

The impact of maternal cocaine use on neonates in socioeconomic disadvantaged population.

Maternal cocaine use has emerged as a major public health concern because the number of users has markedly increased in 1990s and the impact on neonates is severe. The problem of maternal cocaine use is especially important in socioeconomic disadvantaged population since they are more likely to be victims of this drug use. Social support programs including drug education are utmost important and should be offered to all socioeconomic disadvantage pregnant women to prevent and control maternal cocaine use.

Cocaine↗
PubMed1997

[Expression of human papillomavirus 16, 18 E6 protein of cervical squamous cell carcinoma].

OBJECTIVE: To investigate the expression of human papillomavirus (HPV) 16, 18 E6 protein of cervical squamous cell carcinoma and to assess the practical value of HPV 16, 18 E6 antibody. METHODS: Immunohistochemistry SP method was used to examine HPV 16, 18 E6 protein expression in 40 cases of squamous cell carcinoma of uterine cerivx, 30 cases of chronic cervicitis and 30 cases of normal cervical epidermal tissue. RESULTS: 27/40 carcinoma cases and 1/30 chronic cervicitis showed positive staining. None of the normal epithelium specimens gave positive results. The difference between malignant and benign groups was significant. CONCLUSION: A close relation between high risk HPV 16, 18 E6 antibody could be a good indicator for HPV 16, 18 infection and early diagnosis of cervical carcinoma.

Carcinoma, Squamous Cell↗
PubMed1997

[Comparison of plasma thyroxin and insulin concentrations between 10-day old layer and broiler chickens].

In this study both sexes of 10 day old layer and broiler chickens were used to investigate plasma circulating concentrations of 3,3'-5-triiodothyronine (T3), thyroxine (T4) and insulin by using the radioimmunoassay (RIA) methods. The results were as follows: serum T3 concentration was higher in broilers than that in layers (P < 0.01), especially a significant difference between male strains was seen in this experiment (P < 0.001), and the levels of plasma insulin was significantly higher in male broilers than that in male layers (P < 0.001), however, no clear differences in plasma T4 was seen between strains and sexes (P > 0.05). In addition, there were sex differences in T3 and insulin levels in layers, that is to say, those in the female layers was higher than those in the male layers, but no clear deifference was seen between sexes in broilers. A significant positive correlation between T3, insulin and their weight gained (P < 0.05). The results suggest that the levels of serum T3 and Insulin may influence the various growth rate during early posthatch development in layers and broilers.

Animals↗
PubMed1997

[Cloning and sequencing of the gene for premature beta nerve growth factor].

The entire coding sequence of premature nerve growth factor (NGF) beta subunit was amplified from Genomic DNA extracted from peripheral white blood cells of Chinese by polymerase chain reaction (PCR). The PCR products were cloned into a premade T-vector (linearized plasmid pBluescript II SK (+) with a T base at 3' terminal), followed by automatic sequencing with double strand plasmids. The nucleotide sequence coding for the mature NGF is the same as that reported by Europeans, but there is a base difference within the proper region, resulting in an amino acid replacement in premature NGF.

Amino Acid Sequence↗