Biomedical subjects

Z Chen

Publications and source records attributed to Z Chen.

1,672 records · Page 93Linked to original sources

PubMedDate not supplied

Extraction of pesticide residues in tea by water during the infusion process.

The extraction rate of pesticide residues in water during the infusion process is dependent on the water solubility. The extraction of pesticide residues by boiling water can be regarded as a reversible equilibrium between adsorption and dissolution. The influence of chemical degradation is not important. When the water solubility is lower than 5 mg/kg, the extraction rate is 1-4%. Within the water solubility range of 10-150 mg/kg the extraction rate (Ri) is very sensitive to the water solubility (S); the relationship can be described as Ri = 59.8log S-42.5. When water solubility is higher than 170 mg/kg, the extraction rate is 90-100%.

Pesticide Residues↗

PubMedDate not supplied

All other things being equal: acquisition and transfer of the control of variables strategy.

The ability to design unconfounded experiments and make valid inferences from their outcomes is an essential skill in scientific reasoning. The present study addressed an important issue in scientific reasoning and cognitive development: how children acquire a domain-general processing strategy (Control of Variables Strategy or CVS) and generalize it across various contexts. Seven- to 10-year-olds (N = 87) designed and evaluated experiments and made inferences from the experimental outcomes. When provided with explicit training within domains, combined with probe questions, children were able to learn and transfer the basic strategy for designing unconfounded experiments. Providing probes without direct instruction, however, did not improve children's ability to design unconfounded experiments and make valid inferences. Direct instruction on CVS not only improved the use of CVS, but also facilitated conceptual change in the domain because the application of CVS led to unconfounded, informative tests of domain-specific concepts. With age, children increasingly improved their ability to transfer learned strategies to remote situations. A trial-by-trial assessment of children's strategy use also allowed the examination of the source, rate, path, and breadth of strategy change.

Awareness↗

PubMedDate not supplied

Rapid isolation of tissue-specific genes from rat kidney.

A systematic effort to isolate kidney-specific genes was performed using recently described PCR-select methodology. Using this technique, a kidney-specific mini-gene library was generated and a number of kidney-specific genes that share significant homology to previously characterized kidney genes from rats and other species were isolated. These included three renal-specific transporters (an ADH water channel, the anion transporters RST and ROAT1), a cell adhesion molecule (K-cadherin) and a kidney-specific protein upregulated in renal carcinoma (DD96). In addition, we isolated two novel genes from a rat kidney. One of the genes shares limited homology to rat profilin-1 while the other did not share any similarity to genes in the Genbank. Northern blot analysis revealed that the mRNA for each of these genes is expressed in a highly kidney-restricted fashion. Our results suggested that tissue-specific genes can be rapidly isolated and characterized using PCR-select techniques and this methodology may be generally applicable to isolate specific genes from a variety of tissues.

Animals↗

PubMedDate not supplied

Mechanoenergetic alterations during the transition from cardiac hypertrophy to failure in Dahl salt-sensitive rats.

BACKGROUND: The time course and mechanisms of altered mechanoenergetics and depressed cross-bridge cycling in hypertrophied and failing myocardium are uncertain. METHODS AND RESULTS: We studied mechanoenergetics in Dahl salt-sensitive (DS) rats fed high-salt diet (HS) for 6 (HS-6) and 12 (HS-12) weeks to produce compensated hypertrophy and failure. The slope of the end-systolic pressure-volume relation (E'max) was similar in HS-6 and low-salt controls (LS-6), but reduced in HS-12 compared with controls (LS-12). Efficiency [1/slope of oxygen consumption (&f1;O2)-pressure-volume area (PVA) relation] was similar in HS-6 and LS-6 but higher in HS-12 versus LS-12 (59+/-16% versus 44+/-7%, P<0.05). Economy [1/slope of the force-time integral (FTI)-&f1;O2 relation] was similar in HS-6 and LS-6 but higher in HS-12 versus LS-12 (218+/-123 versus 74+/-39x10(3) g. s. mL O2-1. g; P<0.05). Compared with controls, myofibrillar ATPase activity was reduced by 24% in HS-6 and 44% in HS-12. V3 Isomyosin was increased in HS-6 (40+/-12% versus 9+/-8%; P<0.05) and further increased in HS-12 (76+/-10% versus 22+/-18%; P<0.05). Hypothyroid LS-12 rats had 100% V3 isomyosin, yet efficiency, economy, and ATPase values were intermediate between LS-12 and HS-12. HS-12 rats demonstrated increased troponin T3 isoform (17+/-2 versus 23+/-2%, P<0.05). There were no changes in troponin I or tropomyosin isoforms. However, the proportion of phosphorylated troponin T was reduced in HS-12 versus LS-12 hearts (P<.001). CONCLUSIONS: In DS rats, the transition to failure is associated with depressed E'max and increased efficiency and economy. These findings are linked to myofibrillar ATPase activity and suggest that mechanisms other than isomyosin switching are important determinants of ventricular energetics. A troponin T isoform switch is one potential mechanism.

Adenosine Triphosphatases↗

PubMedDate not supplied

Estrogen mustard induces cell cycle arrest of human epithelial ovarian cancer cell lines.

OBJECTIVE: Pharmacologic disruption of microtubule function may provide effective therapy for advanced epithelial ovarian cancer, as has been observed in clinical trials using taxol. However, the limited availability of taxol and taxol's side effects emphasize a need to develop alternative antimicrotubule agents. Estramustine (EM) inhibits binding of microtubule-associated proteins (MAPs) to microtubules, promotes microtubule disassembly, disrupts spindle formation, and induces metaphase arrest in human prostate carcinoma and glioma cells in culture. We studied the effect of EM on DNA synthesis and on the cell cycle in four human ovarian carcinoma cell lines and examined the cell lines for evidence of MAP-like immunoreactivity. METHODS: The effect of EM on DNA synthesis and on the cell cycle was determined using [3H]thymidine incorporation assays and flow cytometry, respectively. Microtubule-associated protein-like immunoreactivity was determined using monoclonal antibodies directed against MAP 1A, MAP 1B, and MAP 2(2A + 2B) for Western analysis after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. RESULTS: We demonstrated a dose-dependent inhibitory response to EM in BIXLER, DK2NMA, and SKOV3. BIX3 showed a dose-dependent inhibitory response to EM concentrations from 25 micrograms/mL to 100 micrograms/mL, but a stimulatory response at 10 micrograms/mL. Estramustine inhibited exponentially growing cells by causing mitotic arrest with subsequent accumulation of cells in G2/M phase of the cell cycle in all four cell lines. We found MAP 1A, MAP 1B, and MAP 2-like immunoreactivity in all four cells lines studied. CONCLUSIONS: These results are consistent with a MAP-microtubule mechanism of action for EM in ovarian carcinoma cells and provide reason to conduct further study of EM for potential use in the treatment of human epithelial ovarian cancer.

Antineoplastic Agents, Hormonal↗

PubMedDate not supplied

The association of conjunctival snake-like chromatin with keratoconjunctivitis SICCA.

PURPOSE: This work describes the snake-like chromatin cells in the conjunctiva of patients with keratoconjunctivitis sicca (KCS), assessing the relationship between tear function parameters and the severity of the disease, and searching for any differential pattern that could lead to early and diagnosis help clarify the etiology of KCS. METHODS: The conjunctiva of 366 eyes from 187 patients with KCS, and 30 eyes from 15 controls, were classified according to the results of the Schirmer I test, break-up time, rose Bengal staining, osmolarity, ferning tests and electrophoresis; they were then studied by impression cytology and electron microscopy. RESULTS: Snake-like chromatin cells, other nuclear changes, and a decreased number of goblet cells were found by impression cytology in different areas of the KCS conjunctiva. The presence of snake-like chromatin was significantly correlated with the severity of the disease. No nuclear changes were found in the control group. CONCLUSIONS: We assume these findings can be attributed to a natural regeneration of conjunctival cells and to resistance to a pathological reaction to KCS.

Adult↗

PubMedDate not supplied

Treatment of acute promyelocytic leukemia with arsenic trioxide: clinical and basic studies.

Arsenic trioxide (As2O3) has recently been identified as an effective drug in the treatment of newly diagnosed and relapsed acute promyelocytic leukemia (APL) without cross-resistance to all-trans retinoic acid and achieved complete remission rates of 80-90% according to most reports. With intravenous infusion at a dose of 0.08-0.16 mg/kg daily, a course of 28-42 days is required to induce remission. As2O3 in combination with chemotherapy as postremission therapy results in longer survival than arsenic alone. In vitro, As2O3 exerts dose-dependent dual effect; triggering apoptosis at relatively high concentration (0.5-2.0 micromol/l), which is associated with the disruption of mitochondrial transmembrane potentials, while inducing partial differentiation at low concentration (0.1-0.5 micromol/l), which might be related to retinoic acid signaling pathway. Importantly, at both concentrations, As2O3 can degrade PML (promyelocytic leukemia) -RAR alpha (retinoic acid receptor), an oncoprotein that has a central role in leukemogenesis.

Apoptosis↗

PubMedDate not supplied

Local inflammation may influence oral tumor cell differentiation.

The mRNA levels of keratin K13, involucrin, protein kinase C alpha and epsilon, and interferon-gamma and its receptors were examined in biopsies from human oral squamous cell carcinomas. Expression of all the genes was elevated in the histologically more differentiated tumors, but it was at or below normal (perilesional control) levels in the poorly differentiated ones. For the same set of biopsies, we had previously shown that the well differentiated tumors expressed higher levels of T cell markers. As interferon-gamma stimulates differentiation, its secretion by inflammatory cells at the tumor site may influence the differentiation status of the tumor.

Cell Differentiation↗

PubMedDate not supplied

Differential sensitivity to mitomycin C between human RSa cell line and its derivative UVr-1.

To study cellular signaling factors responsible for the susceptibility of human cells to cell proliferation inhibition by anticancer drugs, human RSa cell line and its ultraviolet-resistant derivative UVr-1 were compared with respect to their sensitivity to the anti-proliferative effects of mitomycin C (MMC), 5-fluorouracil, nimustine (ACNU), cisplatin, pirarubicin (THP), bleomycin, methotrexate and ifosfamide. RSa cells were found to be highly sensitive to MMC by MTT assay compared to UVr-1 cells. The half maximum inhibition concentration of MMC against proliferation of RSa cells was approximately 100 ng/ml while that of UVr-1 cells was greater than 1 microgram/ml. There was no significant difference observed between RSa and UVr-1 cells in the sensitivity to other seven drugs examined. Analysis by flow cytometry revealed that the cell cycle of RSa was completely blocked at the G2/M phase 40 h after treatment with MMC at a concentration of 100 ng/ml whereas a substantial proportion of UVr-1 cells was not arrested at that phase even in the presence of MMC. Further immunoblot analysis on MMC-induced signal transduction showed that the amounts of phosphorylated ERK MAP kinases were increased in UVr-1 cells to a greater extent than those in RSa cells after treatment with MMC for longer than 2 h. However, the increase in p21Cip1 was observed in RSa cells 1 h after addition of MMC but was not observed in UVr-1 cells. These distinct signaling pathways might account for the differences in sensitivity to MMC between RSa and UVr-1 cells.

Antibiotics, Antineoplastic↗

PubMedDate not supplied

Differentiation-dependent expression of growth regulatory cytokines and their receptors in squamous cell carcinomas of the head and neck.

Cytokines, such as IFN-alpha and TNF-alpha are capable of affecting keratinocyte proliferation in the microenvironment of the tumor. Their elevated expression along with high levels of their receptor mRNAs was determined by a semiquantitative reverse transcription- polymerase chain reaction (RT-PCR) method in biopsies of head and neck squamous cell carcinomas that were established as histologically well or moderately differentiated. In contrast, tumors with poor differentiation exhibited low levels of these growth suppressive factors, although levels of their receptors were elevated. In fact, expression of these growth suppressive cytokines highly correlated with the histological status of tumors suggesting a role of these agents in growth regulation of those tumors. Apparently, growth signaling in these tumors differs in the availability of either the ligand or the receptor.

Antigens, CD↗

PubMedDate not supplied

Correlation of cisplatin sensitivity with differential alteration of EGFR expression in head and neck cancer cells.

Overexpression of human epidermal growth factor (EGFR) has been associated with a variety of human malignancies. The exact role of EGFR in human malignancies and its correlation with chemotherapeutiveness response has not been determined. Using a quantitative RT-PCR method, we previously studied the effects of cisplatin treatment on levels of EGFR mRNA in human papillomavirus (HPV)-positive head and neck cancer cell lines. In this report we extended these studies to HPV-negative head and neck cancer cells. We also compared the growth inhibition and 50% inhibitory concentration (IC50) of cisplatin between these cells. We found that three of four HPV-negative cell lines had 3 to 5 times higher cisplatin IC50 values as compared to two HPV-positive cell lines. EGFR mRNA levels were increased after exposure to cisplatin in the cell lines with the higher IC50 values, while EGFR levels were reduced after cisplatin exposure in the cell lines with the lower IC50 values. These results suggest that the cisplatin sensitivity of head and neck cancer cells corresponds to subsequent alteration of EGFR levels following cisplatin treatment.

Cell Division↗

PubMedDate not supplied

Serological survey of a captive macaque colony in China for antibodies to simian type D retroviruses.

Sera from 510 macaques consisting of Macaca mulatta, Macaca assamensis, Macaca fascicularis, Macaca nemestrina, and Macaca arctoides were investigated for antibodies to simian AIDS type D retrovirus (SRV) by ELISA and Western blot with viral antigens purified from supernatants of SRV-1 infected cell cultures. Of these monkeys, 104 were seropositive by ELISA; only 23 were confirmed by Western blot. The true positive reaction to SRV was found in 15 of 463 (3.2%) M. mulatta and eight of eleven (72.7%) M. assamensis.

Animals↗

PubMedDate not supplied

Cancer cytogenetics and molecular genetics: detection and therapeutic strategy.

It has become increasingly evident that cancers are "genetic diseases" resulting from an accumulation of inherited and environmentally-induced changes or mutations in the genome, i.e., the modification, activation, or inactivation of various genes, including oncogenes, tumor-suppressor genes, and genes related to cell death. Cancer genetics has, therefore, become a burgeoning area of both cytogenetic/molecular genetic research and practical clinical application in human cancer. This article summarizes the specific types of chromosomal and associated molecular genetic alterations in leukemia and cancer. The emphasis is on the application of cytogenetics and molecular cytogenetics as diagnostic, prognostic and therapeutic indices, as approaches to the evaluation of minimal residual disease and as guides for differentiation therapy and the molecular localization of oncogenes/tumor suppressor genes related to gene therapy in leukemias and cancers. This review is intended to update physicians of various disciplines on the rapid advances that have been made in the understanding of the chromosomal and molecular basis of cancer and in approaches for improving the management of cancer patients through knowledge of genetics.

Acute Disease↗

PubMedDate not supplied

Murine Pam 212 cutaneous squamous cell carcinoma is nonimmunogenic in normal syngeneic hosts and resistant to immune effector mechanisms.

We established a mouse model of cutaneous squamous cell carcinoma (SCC) using the Pam 212 cell line to study antitumor immunity in normal syngeneic hosts. In vitro, Pam 212 cells expressed very low levels of class I major histocompatibility complex (MHC) antigen; interferon-gamma (IFN-gamma) significantly increased the expression of this antigen. In vivo, Pam 212 tumors grew progressively in normal BALB/c hosts and resembled poorly differentiated human cutaneous SCC. Immunization of normal syngeneic hosts with irradiated, class I-negative or -positive Pam 212 cells failed to prevent tumor growth or induce specific cytotoxic T lymphocytes (CTL). However, Pam 212 tumor cells were rejected by C3H allogeneic mice, indicating adequate and functional class I antigen expression in vivo. Rejection of Pam 212 tumors by C3H hosts was in part dependent on CD8+ CTL lysis, as alloreactive anti-H-2d CTL lysed class I-positive Pam 212 cells, demonstrating that Pam 212 cells express functional class I MHC antigens. Both class I-positive and -negative Pam 212 cells were resistant to natural killer cell lysis. We hypothesize that ineffective syngeneic immune responses against Pam 212 cells may involve multiple mechanisms: inability of Pam 212 cells to elicit a primary immune response, as well as resistance to cell-mediated lysis.

Animals↗

PubMedDate not supplied

Effects on tumor cells of ribozymes that cleave the RNA transcripts of human papillomavirus type 18.

Many human cervical and oral carcinomas express RNA of human papillomaviruses, and the RNA transcript provides a potential target for gene therapy of these carcinomas. Three hammerhead ribozymes that were targeted to RNA of human papillomavirus type 18 (HPV-18) were cloned into a plasmid expression vector. Each plasmid was then transfected into the HPV-18-expressing cell line. HeLa, or the non-HPV-expressing oral cancer cell line, Tu167. None of the ribozymes had any effect on the phenotype of Tu167 cells. In contrast, each ribozyme affected the phenotype of HeLa cells, causing reduced growth rates, increased serum dependency, and reduced focus formation in soft agar. A molecule that had the same antisense sequences as a ribozyme but lacked the catalytic sequences affected the HeLa cell phenotype to a much lesser extent. The effects of two of the ribozymes could be attributed in part to an increased intracellular concentration of the tumor suppressor protein p53. The most effective ribozyme was targeted to nucleotide 309 in the HPV-18 transcript, but each of the three ribozymes appears to have potential for gene therapy of cancers that express HPV-18.

Base Sequence↗

PubMedDate not supplied

Differentiation markers in oral carcinoma cell lines and tumors.

Cell lines are useful as models if they retain the relevant characteristics of the tissue of origin. We compared two human squamous carcinoma cell lines derived from tumors of the tongue that vary in their extent of differentiation, with human biopsies of carcinomas of the tongue that were either poorly or well-differentiated. The mRNA levels of suprabasal cell proteins (keratin K13, involucrin, transglutaminase) and of protein kinase C (PKC) isozymes were measured by RT-PCR. Apart from PKC beta and PKC delta (mostly expressed by Langerhans cells and missing in culture), qualitatively similar patterns were found in vitro and in vivo. The more differentiated cells had expression levels moderately lower to higher than the normal controls. The poorly differentiated cells generally had substantially lower levels.

Biomarkers↗