Biomedical subjects

Dong Xie

Publications and source records attributed to Dong Xie.

30 records · Page 2Linked to original sources

PubMed2004

Synthesis and evaluation of HEMA-free glass-ionomer cements for dental applications.

OBJECTIVE: The objective of this study was to synthesize and characterize amino acid acrylate and methacrylate derivatives, use them to formulate light-cured glass-ionomer cements (LCGICs), and evaluate their mechanical strengths. MATERIALS AND METHODS: Acrylate and methacrylate derivatives of six amino acids were synthesized and characterized using FT-IR and 1HNMR spectroscopy. The LCGICs were formulated using a newly synthesized polymer having pendant methacrylate groups (in other words, a methacryloyl derived polymer or MDP), amino acid derivatives, water, and Fuji II LC glass. Compressive strength of the cements and viscosities of the resin liquids were used as screening tools in order to determine the optimal formulation. The specimens were conditioned in distilled water at 37 degrees C for 24 h prior to testing. RESULTS: The measured compressive strengths (MPa) of the cements were found to depend on the amino acid derivative used: acryloyl aspartic acid (268.5) > methacryloyl beta-alanine (259.1) = methacryloyl glutamic acid (254.5) = acryloyl beta-alanine (251.9) > acryloyl glutamic acid (238.8) > methacryloyl aspartic acid (210.9). Methacryloyl beta-alanine (MBA) was selected for further formulations due to its relatively low solution viscosity and high compressive strength. Effects of MDP content and power/liquid (P/L) ratio were significant. The formulation with a liquid composition of 50/25/25 (MDP/MBA/water) and P/L ratio of 2.7/1 was found to give optimal properties and handling of all the formulations studied. CONCLUSIONS: A novel HEMA-free LCGIC system based on amino acid derivatives has been developed. This system may eliminate potential cytotoxicity in current LCGICs caused by leached 2-hydroxyethyl methacrylate (HEMA). The optimal MBA-modified cements were 20% higher in compressive strength, 70% higher in diametral tensile strength (DTS) and 93% higher in flexure strength (FS), as compared to Fuji II LC cement.

Amino Acids↗

PubMed2004

A novel approach to xenotransplantation combining surface engineering and genetic modification of isolated adult porcine islets.

BACKGROUND: Effective cytoprotection to xenoislets would circumvent the major tissue limitation for pancreatic islet transplantation (PIT). Cell-surface engineering with poly[ethylene glycol] (PEG) derivatives can successfully prevent antibody binding to the surface antigens. Gene transfer of the antiapoptotic Bcl-2 gene has been shown to decrease cytotoxicity mediated by xenoreactive natural antibodies and complement. In this study, we assessed survival and function of surface-engineered porcine islets genetically modified to overexpress Bcl-2. METHODS: Incorporation of PEG derivatives into the islet surface and adenovirus-mediated gene transfer of Bcl-2 (AdBcl-2) was accomplished within 24 hours post-isolation. Cytotoxicity induced by human xenoreactive natural antibodies was evaluated by islet intracellular lactate dehydrogenase release and microscopic analysis using membrane-integrity staining. Islet functionality was assessed by static incubation and after intraportal infusion (5000 IEQ) into diabetic NOD-SCID mice reconstituted with human lymphocytes (5 x 10 8 /intraperitoneally/15 days before PIT). RESULTS: No significant change in islet viability, morphology, and functionality was demonstrated after the incorporation of PEG-mono-succimidyl-succinate (MSPEG), or PEG-di-succimidyl-succinate "end"-capped with albumin (DSPEG) with or without gene transfer of Bcl-2. Islets treated with MSPEG presented a significant reduction in lactate dehydrogenase release compared with controls (41.2 +/- 3 vs 72.1 +/- 7, respectively, P <.05). Further protection was accomplished by DSPEG or AdBcl-2. The maximal cytoprotection was achieved by DSPEG +AdBcl-2 (15.5 +/- 4.9%, P <.001). Nonfasting glucose >200 mg/dL was found in 100% of the animals given control islets (n = 6) within 48 hours post-transplant. In contrast, euglycemia was achieved in 100% of the animals given islets modified with DSPEG + AdBcl-2 during the observation time. CONCLUSIONS: Surface-engineering with functionalized PEG derivatives in combination with genetic modification with Bcl-2 significantly reduced islet loss after PIT. Application of this novel technology may improve results in xenoislet transplantation.

Animals↗

PubMed2004

Imprinting status of DLK1 gene in brain tumors and lymphomas.

DLK1 and GTL2 are reciprocally imprinted genes on human chromosome 14q32. DLK1 encodes a transmembrane protein that is a paternally expressed gene. The maternally expressed GTL2 allele encodes a non-translated RNA. Many of features of DLK1/GTL2 are remarkably similar to those of the prototypical IGF2/H19 reciprocally imprinted gene pair. Imprinting status of IGF2 has been studied in many types of tumors, and loss of imprinting (LOI) leads to biallelic expression of IGF2 in most of these tumors. The imprinting status of DLK1 has seldom been investigated in clinical tumor samples. We examined whether DLK1 was imprinted in brain tumors and lymphomas by analyzing a single nucleotide polymorphism (SNP), rs1802710. Analysis of 47 brain tumors and 55 lymphomas found that 23 and 29 of them were heterozygous for rs1802710, respectively. Monoallelic expression of DLK1 was detected in the heterozygous samples. These data show that imprinting of DLK1 is maintained in brain tumors and lymphomas, even though the DLK1 gene is very analogous to the IGF2 gene in its DNA structure and regulation. Also, the high frequency of heterozygosity (about 50%) showed that the polymorphic site that we chose is a good genomic marker for imprinting studies of the DLK1 gene in additional tumor types.

Alleles↗

PubMed2003

TMEFF1 and brain tumors.

TMEFF1 is a novel transmembrane protein, containing two follisatin domains and an epidermal growth factor-like region. These structural domains suggest a role for TMEFF1 in growth factor signaling. TMEFF1 fused to enhanced green fluorescent protein revealed that TMEFF1 is expressed on the cell membrane. Northern analysis of normal human tissue showed that TMEFF1 is predominantly expressed in the brain. Study of cancer cell lines from different tissues including the brain, demonstrated moderate to low levels of TMEFF1 in most of these transformed cell lines. Furthermore, quantitative real-time RT-PCR analysis of 54 brain tumors showed that most of these tumors (96%) had lower levels of TMEFF1 expression than normal brain tissue. Interestingly, ectopic expression of TMEFF1 in brain cancer cells resulted in their growth inhibition. These data suggest that TMEFF1 may behave as a tumor suppressor gene in brain cancers.

Brain↗

PubMed2003

DNA repair gene O6-methylguanine-DNA methyltransferase: promoter hypermethylation associated with decreased expression and G:C to A:T mutations of p53 in brain tumors.

The DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT) removes alkylating adducts from the O(6) position of guanine and protects cells from cytotoxic and mutagenic effects. Expression of MGMT is decreased in some cancers, which may be the result of methylation of CpG islands of both the promoter and coding regions of the gene. We studied the methylation status of the MGMT promoter in a very large collection of brain tumors (85) using methylation-specific polymerase chain reaction (PCR). Aberrant methylation occurred in 48% of 85 human brain tumor samples. Quantitative real-time PCR showed that expression of MGMT mRNA levels was significantly decreased (P < 0.001) in those brain tumors that had methylation of the promoter region of their MGMT gene. MGMT can prevent G to A mutations by removing alkyl groups from the O(6) position of guanine. We found a significantly increased frequency of G:C to A:T mutations of the p53 gene in brain tumors having a methylated MGMT promoter compared with those having an unmethylated MGMT promoter (P < 0.05), and all the non-CpG dinucleotide G:C to A:T mutations of p53 were in samples with a methylated MGMT promoter.

Base Sequence↗

PubMed2003

A hybrid zinc-calcium-silicate polyalkenoate bone cement.

A novel bone cement composed of sintered zinc-calcium-silicate phosphate and hybrid polyalkenoates has been developed. Synthesis and formulation of glass fillers, monomers and polymers as well as formulation of the cement were described. The effects of sintering, polymer content, glass powder/polymer liquid (P/L) ratio and comonomer on compressive strength (CS) and curing time (CT) were investigated. The effects of P/L ratio and comonomers on shrinkage as well as exotherm were also studied. Results show that the experimental cement was 61% higher in CS, 10% lower in diametral tensile strength, 35% lower in flexural strength, 62% less in exotherm, and 68% less in shrinkage, compared to conventional polymethylmethacrylate cement. With increasing polymer content and P/L ratio in the cement formulation CS of the cement increased but CT decreased. Curing time, shrinkage and exotherm of the cement decreased with increasing P/L ratio. It appears that this novel cement may be a potential candidate for orthopedic restoration if its biological performance is good and formulation is optimized.

Biocompatible Materials↗

PubMed2003

NADE (p75NTR-associated cell death executor) suppresses cellular growth in vivo.

NADE, a p75NTR (low-affinity neurotrophin receptor p75) -associated cell death executor, was initially cloned from a human ovarian granulosa cell cDNA library, as an unknown protein with the name, pHGR74. It was reported to mediate nerve growth factor-induced apoptosis. We independently isolated human NADE (pHGR74) from breast cancer cell lines. Expression of NADE in various human cancer cell lines, and human and murine tissues was examined. NADE was highly expressed in human endocrine-related organs and embryotic murine tissues. Forced expression of NADE in CHO (Chinese hamster ovary) cells and MDA-MB-231 human breast cancer cells had little effect on the growth of the cells in vitro, while it dramatically suppressed cellular growth in vivo. We used the yeast two-hybrid system to search for NADE binding protein. Dynactin was identified as a candidate. The p75NTR was not found in this assay and did not co-immunoprecipitate with human NADE. Furthermore, the cells stably transfected with NADE did not respond to NGF or TNF. Thus, human and murine NADE appear to have different functions.

Animals↗

PubMed2002

Methylation, expression, and mutation analysis of the cell cycle control genes in human brain tumors.

Methylation status of the p15(INK4B), p16(INK4A), p14(ARF) and retinoblastoma (RB) genes was studied using methylation specific polymerase chain reaction (MSP) in 85 human brain tumors of various subtypes and four normal brain samples. These genes play an important role in the control of the cell cycle. Twenty-four out of 85 cases (28%) had at least one of these genes methylated. The frequency of p14(ARF) methylation was 15 out of 85 (18%) cases, and the expression of p14(ARF) in methylated gliomas was significantly lower than in unmethylated gliomas. The incidence of methylation of p15(INK4B), p16(INK4A) and RB gene was 4%, 7%, and 4%, respectively. Samples with p14(ARF) methylation did not have p16(INK4A) methylation even though both genes physically overlap. None of the target genes was methylated in the normal brain samples. In addition, the p53 gene was mutated in 19 out of 85 (22%) samples as determined by single strand conformation polymorphism (SSCP) analysis and DNA sequencing. Thirty out of 85 (35%) brain tumors had either a p53 mutation or methylation of p14(ARF). Also, the p14(ARF) expression in p53 wild-type gliomas was lower than levels in p53 mutated gliomas. This finding is consistent with wild-type p53 being able to autoregulate its levels by down-regulating expression of p14(ARF). In summary, inactivation of the apoptosis pathway that included the p14(ARF) and p53 genes by hypermethylation and mutation, respectively, occurred frequently in human brain tumors. Down-regulation of p14(ARF) in gliomas was associated with hypermethylation of its promoter and the presence of a wild-type p53 in these samples.

Base Sequence↗

PubMed2002

Distal and proximal cis-linked sequences are needed for the total expression phenotype of the mouse alcohol dehydrogenase 1 (Adh1) gene.

Mouse alcohol dehydrogenase 1 (Adh1) gene expression occurs at high levels in liver and adrenal, moderate levels in kidney and intestine, low levels in a number of other tissues, and is undetectable in thymus, spleen and brain by Northern analysis. In transgenic mice, a minigene construct containing 10 kb of upstream and 1.5 kb of downstream flanking sequence directs expression in kidney, adrenal, lung, epididymis, ovary and skin but promotes ectopic expression in thymus and spleen while failing to control expression in liver, eye, intestine and seminal vesicle. Cosmids containing either 7 kb of upstream and 21 kb of downstream or 12 kb of upstream and 23 kb of downstream sequence flanking genetically marked Adh1 additionally promotes seminal vesicle expression suggesting downstream or intragenic sequence controls expression in this tissue. However, expression in liver, adrenal, or intestine is not promoted. The Adh1(a) allele on the cosmid expresses an enzyme electrophoretically distinct from that of the endogenous Adh1(b) allele, and presence of the heterodimeric enzyme in expressing tissues confirms that transgene activity occurs in the same cell-type as the endogenous gene. Transgene expression levels promoted by cosmids were at physiologically relevant amounts and exhibited greater copy-number dependence than observed with minigenes. Transgene mRNA expression correlated with expression measured at the enzyme level. A bacterial artificial chromosome containing 110 kb of 5'- and 104 kb of 3'-flanking sequence surrounding the Adh1 gene promoted expression in tissues at levels comparable to the endogenous gene most importantly including liver, adrenal and intestinal tissue where high level Adh1 expression occurs. Transgene expression in liver was in the same cell types as promoted by the endogenous gene. Although proximal elements extending 12 kb upstream and 23 kb downstream of the Adh1 gene promote expression at physiologically relevant levels in most tissues, more distal elements are additionally required to promote normal expression levels in liver, adrenal and intestinal tissue where Adh1 is most highly expressed.

5' Flanking Region↗

PubMed2002

Overcoming drug resistance in HIV-1 chemotherapy: the binding thermodynamics of Amprenavir and TMC-126 to wild-type and drug-resistant mutants of the HIV-1 protease.

Amprenavir is one of six protease inhibitors presently approved for clinical use in the therapeutic treatment of AIDS. Biochemical and clinical studies have shown that, unlike other inhibitors, Amprenavir is severely affected by the protease mutation I50V, located in the flap region of the enzyme. TMC-126 is a second-generation inhibitor, chemically related to Amprenavir, with a reported extremely low susceptibility to existing resistant mutations including I50V. In this paper, we have studied the thermodynamic and molecular origin of the response of these two inhibitors to the I50V mutation and the double active-site mutation V82F/I84V that affects all existing clinical inhibitors. Amprenavir binds to the wild-type HIV-1 protease with high affinity (5.0 x 10(9) M(-1) or 200 pM) in a process equally favored by enthalpic and entropic contributions. The mutations I50V and V82F/I84V lower the binding affinity of Amprenavir by a factor of 147 and 104, respectively. TMC-126, on the other hand, binds to the wild-type protease with extremely high binding affinity (2.6 x 10(11) M(-1) or 3.9 pM) in a process in which enthalpic contributions overpower entropic contributions by almost a factor of 4. The mutations I50V and V82F/I84V lower the binding affinity of TMC-126 by only a factor of 16 and 11, respectively, indicating that the binding affinity of TMC-126 to the drug-resistant mutants is still higher than the affinity of Amprenavir to the wild-type protease. Analysis of the data for TMC-126 and KNI-764, another second-generation inhibitor, indicates that their low susceptibility to mutations is caused by their ability to compensate for the loss of interactions with the mutated target by a more favorable entropy of binding.

Binding Sites↗

PubMed2002

Discovery of over-expressed genes and genetic alterations in breast cancer cells using a combination of suppression subtractive hybridization, multiplex FISH and comparative genomic hybridization.

To identify genes that are involved in breast cancer, suppression subtractive hybridization (SSH) was utilized to construct a breast cancer subtracted library. Differential screening of the library isolated 28 genes which by Northern analysis were highly expressed in the breast cancer cell line MDA-MB-231 compared to the normal breast cell line MCF12A. Sequence analysis revealed that 15 clones coded for previously described genes such as SNAP43, Cyr61, Thymosin beta4, tra1, elongation factor 1alpha, BSF-2/IL6, BiP, and GDP/GTP exchange protein. The remaining 13 clones did not match sequences in GenBank/EMBL database, indicating that they may be novel genes. SNAP43, a subunit of the TBP-TAF complex, was expressed 20-fold higher in MDA-MB-231 compared to MCF12A and several breast cancer cell lines, implying that SNAP43 may be involved in tumorigenesis of a specific subset of breast cancers. Amplification of SNAP43 was not found by Southern analysis. However, genetic alterations of MDA-MB-231 included a deletion of chromosome 14 with a reciprocal translocation t(6;14) and two additional translocations [t(12;14) and t(14;15)] as determined by fluorescent in situ hybridization (FISH) with YAC 823G8 located at chromosome 14q23 which contained SNAP43. Because of the numerous alterations observed by FISH in MDA-MB-231, we further explored the genetic abnormalities in this breast cancer cell line using multiplex FISH (M-FISH) and comparative genomic hybridization (CGH). These cells were replete with numerous complex structural rearrangements and had DNA copy-number imbalances involving multiple chromosomes including gains on chromosomes 2p, 2q31-q32, 3p14-pter, 5q, 6p, 7q36-qter, 11, 14q21-q24, 17p11.2-pter, 17q21-qter, 19, 20, Xp11-q13 and losses on chromosomes 4pter-q32, 8p, 9p21-p24, 10q26-qter, 16p13-pter, 18q12-qter, 22, Xp11.3-p22.1, Xq13-qter. In summary, SSH revealed a number of genes that were either novel or previously not associated with breast cancer. In addition, we found that breast cancer cells abounded with abnormalities as observed by M-FISH and CGH. Together, these results may facilitate defining the genetic alterations associated with breast cancer progression.

Breast Neoplasms↗

PubMedDate not supplied

AIM-2: a novel tumor antigen is expressed and presented by human glioma cells.

Antigen isolated from Immunoselected Melanoma-2 (AIM-2) was recently identified using melanoma-reactive CD8 T cells. AIM-2 antigen is expressed in a wide variety of tumor types, including neuroectodermal tumors, as well as breast, ovarian and colon carcinomas. In this study, we analyzed AIM-2 expression in glioblastoma multiforme (GBM) in primary cultured cells and established GBM cell lines. We found that the primary GBM cell lines expressed 88.4% and 93.0% of non-spliced and spliced AIM-2, respectively. Five out of seven of the established GBM cell lines expressed both non-spliced and spliced AIM-2. Furthermore, the C9 CTL clone, which is specific for AIM-2 peptide (RSDSGQQARY), efficiently recognized GBM tumor cells in an antigen-specific and HLA-A1 restricted manner. IFN-gamma treatment of the GBM tumor cells dramatically increased HLA-A1 expression levels and, consequently, increased CTL recognition of the treated tumor cells. More importantly, seven out of 12 HLA-A1 and AIM-2 positive patients from our dendritic cell clinical trial generated AIM-2 specific CTL activity in their PBMC after vaccinations. These data indicate that AIM-2 could be used as a tumor antigen target for monitoring vaccine trials or to develop antigen specific active immunotherapy for glioma patients.

Antigens, Neoplasm↗