Biomedical subjects

Lei Shen

Publications and source records attributed to Lei Shen.

49 records · Page 3Linked to original sources

PubMed2004

A season-dependent variation of genotoxicity of surface water samples from Taihu Lake, Yangzte delta.

The present study is to assess a year round change of genotoxicity of surface water in Taihu Lake, Yangtze delta. The water samples were collected in spring, summer, autumn and winter of 2001, respectively. The bacterial L-arabinose resistance forward mutation test (ara test), along with the Ames test, was performed for the evaluation of time profile of mutagenicity of the surface water samples. The strong genotoxic potentials were detected in the near-shore area, especially in the vicinity to the major city. All the samples collected from the lake center and areas distant from dense human activity showed genotoxicity-free in year round time. Intensified human activity along the lake may play an important role for the genotoxic pollution. By comparison of the samples from year round, the winter samples showed the strongest mutagenic potential of all seasons, which indicates that meteorological and hydrological factors also affect the water quality. The impact of dense human activity, improper management and season change should be put into consideration for designing an effective remediation project in the lake basin area.

Arabinose↗

PubMed2004

Cancer-specific activation of the survivin promoter and its potential use in gene therapy.

Survivin is expressed in many cancers but not in normal adult tissues and is transcriptionally regulated. To test the feasibility of using the survivin promoter to induce cancer-specific transgene expression in lung cancer gene therapy, a vector expressing a luciferase gene driven by the survivin promoter was constructed and evaluated in vitro and in vivo. We found that the survivin promoter was generally more highly activated in cancer cell lines than in normal and immortalized normal cell lines. When delivered intravenously by DNA:liposome complexes, the survivin promoter was more than 200 times more cancer specific than the cytomegalovirus promoter in vivo. To identify lung cancer patients who may benefit from gene therapy with the survivin promoter, we measured survivin protein expression in surgical specimens of 75 non-small-cell lung cancers and 10 normal lung tissues by immunohistochemical staining and found that survivin is expressed in most of the non-small-cell lung cancers tested (81%, 61 of 75) but none of the normal lung tissues. The survivin promoter also induced transgene expression of a mutant Bik in cancer cells, which suppressed the growth of cancer cells in vitro and in vivo. These results indicate that the survivin promoter is a cancer-specific promoter for various cancers and that it may be useful in cancer gene therapy.

Base Sequence↗

PubMed2003

c-CBL is not required for leukemia induction by Bcr-Abl in mice.

Bcr-Abl tyrosine kinase activity is essential for the pathogenesis of chronic myeloid leukemia (CML). A number of Bcr-Abl substrates have been identified, but it is not clear which of these substrates are required for Bcr-Abl to transform cells. The multifunctional protein c-Cbl is one of the most prominently tyrosine-phosphorylated proteins in Bcr-Abl-expressing cells. Using cell lines and mice with homozygous disruption of the c-CBL locus, we investigated the role of this protein for Bcr-Abl-driven transformation. We find that although c-Cbl(-/-) fibroblast cell lines show a deficit in Bcr-Abl transformation compared to wild-type (Wt) cells, this deficit was less pronounced in c-Cbl(-/-) B cells derived from murine bone marrow. Most importantly, in a transplantation model of CML, Bcr-Abl was capable of inducing fatal leukemia in mice in the absence of c-Cbl protein. Our results indicate that c-Cbl is dispensable for Bcr-Abl-induced leukemogenesis in mice.

Animals↗

PubMed2003

Identification of a MHC class-II restricted epitope in carcinoembryonic antigen.

PURPOSE: The carcinoembryonic antigen (CEA) is extensively expressed on the vast majority of colorectal, gastric, and pancreatic carcinomas, and, therefore, is a good target for tumor immunotherapy. CD4+ T-helper (Th) cells play a critical role in initiation, regulation, and maintenance of immune responses. In this study, we sought to identify Th epitopes derived from CEA which can induce CEA-specific Th responses. The combined application with cytotoxic T lymphocyte (CTL) epitopes would be more potent than tumor vaccines that primarily activate CTL alone. METHODS: We utilized a combined approach of using a computer-based algorithm analysis TEPITOPE and in vitro biological analysis to identify Th epitopes in CEA. RESULTS: Initial screening of healthy donors showed that all five predicted peptides derived from CEA could induce peptide-specific T-cell proliferation in vitro. We characterized these CEA epitopes by establishing and analyzing peptide-specific T-cell clones. It was shown that CD4+ T-cells specific for the CEA(116 )epitope can recognize and respond to naturally processed CEA protein and CEA(116 )epitope can be promiscuously presented by commonly found major histocompatibility complex (MHC) alleles. Furthermore, it was demonstrated that immunization of human leukocyte antigen (HLA)-DR4 transgenic mice with CEA(116) peptide elicited antigen-specific Th responses which can recognize the antigenic peptides derived from CEA protein and CEA-positive tumors. CONCLUSION: The MHC class II-restricted epitope CEA(116) could be used in the design of peptide-based tumor vaccine against several common cancers expressing CEA.

Algorithms↗

PubMed2003

A broadly applicable, personalized heat shock protein-mediated oncolytic tumor vaccine.

Each tumor harbors unique repertoire of mutated antigenic peptides that are immunogenic and potentially can induce tumor-specific immune responses. Because heat shock proteins (HSPs) have the promiscuous ability to chaperone and present a broad repertoire of tumor antigens to antigen presenting cells, HSP tumor vaccine has been tested in clinical trials. However, this vaccine has many limitations, including individual preparation of HSP vaccines from each tumor ex vivo, and quantity of HSPs for therapy strictly limited by the size of the resected tumor mass. Hence, we developed a novel HSP-mediated oncolytic tumor vaccine, referred to as HOT vaccine, by combining the versatile ability of overexpressed HSPs to chaperone antigenic peptides and induce immune responses against a broad array of mutated tumor antigens, with the oncolytic activity of viruses. The results of this study demonstrate that intratumor vaccination with a recombinant oncolytic adenovirus overexpressing the HSP70 protein can eradicate primary tumors, as well as inhibit the growth of established metastatic tumor in mice. Because of its capacity to induce individual tumor-specific immune responses, this HSP-mediated oncolytic tumor vaccine might become a universally applicable, personalized vaccine against any type of solid tumor.

Adenoviruses, Human↗

PubMed2003

Human telomerase reverse transcriptase-specific T-helper responses induced by promiscuous major histocompatibility complex class II-restricted epitopes.

An effective tumor vaccine may require the induction of both CTL and T-helper (Th) cell responses against tumor-associated antigens. Human telomerase reverse transcriptase (hTERT) is highly expressed in >85% of cancer cells and thus is a potential target for tumor vaccines. We therefore sought to identify promiscuous Th epitopes in hTERT, which can be presented by more than one MHC class II allele. Each of 10 peptides derived from hTERT that were predicted to bind to MHC class II molecules was found to be able to induce primary human T-cell responses in vitro. We then established CD4(+) T-cell clones specific for these peptides and found that only hTERT(766) (LTDLQPYMRQFVAHL)-specific CD4(+) Th cells were effective in recognizing naturally processed hTERT antigen. We further found that the naturally processed epitopes hTERT(766) and hTERT(672) (which was identified previously) were promiscuous and capable of inducing CD4(+) T-cell responses in the context of several commonly found HLA-DR alleles, including DR1, DR7, and DR15 for hTERT(672), and DR4, DR11, and DR15 for hTERT(766). We further demonstrated that immunization of humanized HLA-DR4 transgenic mice with hTERT(766) peptide elicited antigen-specific Th responses that can recognize the antigenic peptides derived from hTERT protein and various hTERT-positive tumors, such as breast cancer, melanoma, and leukemia. It was also shown that T-cell precursors specific for the naturally processed epitopes are part of the T-cell repertoires in healthy donors and prostate cancer patients. Thus, these promiscuous, naturally processed Th epitopes in hTERT could be used to develop improved cancer vaccines through the simultaneous stimulation of CTL and Th cells against a broad spectrum of hTERT-positive tumors.

Alleles↗

PubMed2003

Identification of MHC class II-restricted T-cell epitopes in prostate-specific membrane antigen.

An effective tumor vaccine may be required to induce both CTLs and T-helper (Th) responses against tumor-associated antigens. CD4+ Th cells that recognize MHC class II-restricted epitopes play a central role in the initiation and maintenance of antitumor immune responses. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and thus is a potential target for prostate cancer immunotherapy. In this study, we attempted to identify Th epitopes derived from PSMA for enhancing prostate cancer vaccine by eliciting PSMA-specific Th responses. We first screened a panel of six epitope peptide candidates selected with the TEPITOPE program and found that all six peptides induced peptide-specific T-cell proliferation from one or more donors with estimated T-cell precursor frequencies of 0-4.17 x 10(-6). We then established peptide-specific T-cell clones for five of these six peptides and demonstrated that the T-cell clone specific for the PSMA(459) epitope (NYTLRVDCTPLMYSL) can recognize processed antigens from recombinant PSMA proteins. The PSMA(459) peptide was found to induce CD4+ T-cell responses in healthy individuals and prostate cancer patients with different HLA-DR alleles. To test the potential clinical application, human HLA-DR4 transgenic mice were immunized with PSMA(459) peptide and we found that PSMA(459) peptide immunization activated T cells that specifically responded to antigenic peptides derived from PSMA proteins and PSMA-positive tumor. Thus, the naturally processed Th epitope PSMA(459) could be included in prostate tumor vaccines to enhance PSMA-specific CTL responses.

Alleles↗

PubMed2003

The mutagenic potentials of tap water samples in Shanghai.

The tap water samples were collected from the users' ends in several areas of Shanghai, which is located in Taihu Lake basin, Eastern China. Source water samples were also collected from two municipal source water facilities at the same time. Samples were assayed by three different short-term mutagenicity test systems: Salmonella/microsome assay (Ames test), the Arabinose resistance test (Ara test) and the SOS/umu test. The data showed that two source water samples did not display direct mutagenic potentials. Two tap water samples from city north, which were directly from Yangtze River, were also not mutagenic. Water samples from city south and middle which used source water originating from Taihu Lake were proved to be contaminated with mutagenic potentials by three different assay techniques. The boiled water displayed an even stronger mutagenic potential compared to its original tap water. The molecular mechanism of mutagenicity was associated with a reading frame-shifting potential. GC-MS analysis of tap water extracts from city middle and corresponding source water was compared. Qualitatively similar spectra were observed except for the peaks of three chlorinated aromatic hydrocarbon compounds, which existed only in the tap water. Since the water source has been polluted, raw water was heavily chlorinated in order to sterilize. More toxic compounds, including mutagens, might form during the multi-chlorination. Caution about the possibility of elevated cancer risks in the population that consumes heavily chlorinated water should be kept in mind. A cohort study in the residents of Shanghai is required.

Arabinose↗

PubMed2003

No correlation between the proliferative status of Bcr-Abl positive cell lines and the proapoptotic activity of imatinib mesylate (Gleevec/Glivec).

Imatinib mesylate (Gleevec, formerly STI571) has been shown to be a safe and effective treatment for chronic myelogenous leukemia (CML). However, despite high rates of hematologic and cytogenetic remissions, molecular remissions are rare. Recent work has revealed the existence of a population of Bcr-Abl-positive, quiescent hematopoietic CML stem cells that are insensitive to induction of apoptosis by imatinib ex vivo. Thus, quiescence is postulated as a mechanism of molecular resistance to imatinib. To model a cell population with reduced cell cycle activity in vitro, we applied three different established approaches to block the cell cycle at the G1/S boundary using Bcr-Abl-positive cell lines. Subsequently, the cells were exposed to imatinib and apoptosis after 48 h of treatment was determined by analysis of activated caspase-3 and apoptotic DNA strand breaks. In these models, reduced cell cycle activity did not have a significant impact on the ability of imatinib to induce apoptosis. These data suggest that the proapoptotic activity of imatinib in vitro is not dependent on cell cycle transit. We conclude that resistance of primary CML cells that are insensitive to imatinib may be the result of molecular properties causing drug resistance rather than a consequence of quiescence itself.

Antineoplastic Agents↗

PubMed2003

Prevalence of nonalcoholic fatty liver among administrative officers in Shanghai: an epidemiological survey.

AIM: To determine the prevalence of nonalcoholic fatty liver in a specific population in Shanghai by an epidemiological survey, and to analyze risk factors of fatty liver. METHODS: Total 4009 administrative officers who denied regular alcohol drinking participated in the survey, and underwent physical examination and laboratory tests. The important parameters were body mass index (BMI), waist hip circumferences ratio (WHR) and levels of serum lipids. Diagnosis of fatty liver was based on established real-time ultrasonographic criteria, the presence of an ultrasonographic pattern consistent with "bright liver", with evident ultrasonographic contrast between hepatic and renal parenchyma, vessel blurring, and narrowing of the lumen of the hepatic veins. Analysis of data was performed through SPSS for Windows statistical package. RESULTS: The overall prevalence of fatty liver was 12.9 %, 15.8 % in males and 7.5 % in females, and the prevalence of fatty liver in males younger than 50 years old, was significantly higher (13.3 %) than that of in females (2.7 %). But the difference between the sexes became less significant in people older than 50 years (19.1 % vs 18.1 %). The prevalence of fatty liver was increased with age; this was markedly presented in females younger than 50 years. Multiple variant regression analysis demonstrated that the prevalence of fatty liver was positively correlated to several risk factors, including male, aging (>50yr), hyperlipidemia, impaired glucose tolerance/diabetes mellitus, hypertension and overweight/obesity. CONCLUSION: There is a high prevalence of nonalcoholic fatty liver among certain population in Shanghai, to which overweight and hyperlipidemia are closely relevant.

Adult↗

PubMed2002

Gla domain-mutated human protein C exhibiting enhanced anticoagulant activity and increased phospholipid binding.

Protein C is a member of the vitamin K- dependent protein family. Proteins in this family have similar gamma-carboxyglutamic acid (Gla)-rich domains, but their affinities for negatively charged phospholipid membranes vary more than 1000-fold. We have shown that it is possible to enhance anticoagulant activity and membrane affinity of protein C by selective mutagenesis of the Gla domain. In this study, 3 new mutants, Q10G11N12 (QGN), S23E32D33Y44 (SEDY), and Q10G11N12S23E32D33Y44 (QGNSEDY), were created. In plasma-based coagulation assays, the activated form of QGNSEDY (QGNSEDY-APC) demonstrated approximately 20-fold higher anticoagulant activity than wild-type activated protein C (WT APC), while QGN-APC and SEDY-APC did not. Both normal activated factor V (FVa) and FVa Leiden (Arg506Gln) were degraded much more efficiently by QGNSEDY-APC than by WT APC in the presence as well as in the absence of protein S. Binding of protein C variants to negatively charged phospholipid membranes was investigated using light scattering and the BIAcore technique. QGNSEDY demonstrated 3- to 7-fold enhanced binding as compared with WT protein C, suggesting the membrane affinity to be influenced by several residues located at different parts of the Gla domain. The anticoagulant activity as well as phospholipid binding ability was only enhanced when multiple regions of the Gla domain were modified. The results provide insights into the molecular mechanisms that are involved in determining the binding affinity of the interaction between Gla domains and phospholipid membranes. The unique properties of QGNSEDY-APC suggest this APC variant possibly to have greater therapeutic potential than WT APC.

1-Carboxyglutamic Acid↗

PubMed2002

Bias adjustment in analysing longitudinal data with informative missingness.

The recent biostatistical literature contains a number of methods for handling the bias caused by 'informative censoring', which refers to drop-out from a longitudinal study after a number of visits scheduled at predetermined intervals. The same or related methods can be extended to situations where the missing pattern is intermittent. The pattern of missingness is often assumed to be related to the outcome through random effects which represent unmeasured individual characteristics such as health awareness. To date there is only limited experience with applying the methods for informative censoring in practice, mostly because of complicated modelling and difficult computations. In this paper, we propose an estimation method based on grouping the data. The proposed estimator is asymptotically unbiased in various situations under informative missingness. Several existing methods are reviewed and compared in simulation studies. We apply the methods to data from the Wisconsin Diabetes Registry Project, a longitudinal study tracking glycaemic control and acute and chronic complications from the diagnosis of type I diabetes.

Bias↗

PubMedDate not supplied

Pre- and post-operative plasma big endothelin-1 levels in patients with gastric carcinoma undergoing radical gastrectomy.

BACKGROUND: Big Endothelin-1 levels increase significantly in patients with various tumors, and raised plasma concentrations are associated with worse outcome. The aim of this study was to investigate plasma Big Endothelin-1 levels in patients with gastric carcinoma before and after radical gastrectomy and to explore its clinical significance. MATERIALS AND METHODS: One hundred and six patients with gastric carcinoma and 20 controls were studied. Big Endothelin-1 plasma levels in patients with advanced gastric cancer were examined by enzyme-linked immunosorbent assay before and on days 1, 3 and 10 after curative surgery and were then tested every 3 months. RESULTS: All patients, except those with stage I gastric cancer, had significantly higher mean plasma Big Endothelin-1 levels compared with the normal controls (p = 0.000). The plasma Big Endothelin-1 levels were markedly increased on the first post-operative day (1st POD) in all patients but decreased on the 3rd POD with no significant difference compared to the pre-operative levels. On the 10th POD, patients with stages I and II gastric cancer showed a marked reduction in the plasma Big Endothelin-1 levels (p=0.010 and p=0.000, respectively), whereas no significant difference was observed in stage III and IVpatients. During the follow-up, plasma Big Endothelin-1 levels immediately before recurrences occurred in stage II patients were significantly higher compared with the levels on the 10th POD (p=0.011). CONCLUSION: Plasma Big Endothelin-1 levels might be a reliable marker to determine the severity of gastric carcinoma. Monitoring plasma Big Endothelin-I levels after curative resection in stage II gastric cancer patients was valuable in predicting recurrences.

Adult↗