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Wei M, Junzhu C, Hui Y, Liangrong Z, Qianmin T, Yiming N. e0356 The research on calcium homeostasis expression and gene transcription of atrial myocytes in patients with atrial fibrillation. BRITISH HEART JOURNAL 2010. [DOI: 10.1136/hrt.2010.208967.356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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127
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Zhuo W, Chen B, Wei M. Estimation of indoor (220)Rn progeny concentrations with (220)Rn measurements. RADIATION PROTECTION DOSIMETRY 2010; 141:408-411. [PMID: 20833675 DOI: 10.1093/rpd/ncq256] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
For estimating indoor thoron ((220)Rn) progeny concentrations with (220)Rn measurements, both theoretical studies and field measurements were carried out in this work. Based on the theoretical study, it was found that the exhalation rate of (220)Rn (E(Tn)) could be optimally assessed with the (220)Rn concentration measured at a point of 50 cm far from the source wall, and the equilibrium equivalent thoron concentration (EETC) could be further estimated with the E(Tn) and the area of wall surface as well as the room volume. Field measurements testified that the estimated EETCs were in general agreement with the directly measured results with an average ratio of 0.87 ± 0.12. The new method developed in this study is thought to be preferable for long-term and large-scale surveys of indoor EETC.
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Wei M, Zhang X, Li S, Shao C, Wang C, She Z, Lin Y. A new dihydroisocoumarin with an isoprenyl group from the endophytic fungus Cephalosporium sp. Chem Nat Compd 2010. [DOI: 10.1007/s10600-010-9612-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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129
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Yuefeng M, Weili F, Wenxiang T, Ligang X, Guiling L, Hongwei G, Wencai L, Xiaoguang W, Wei M, Zhongyi F. Long-term outcome of patients with lamivudine after early cessation of hepatitis B immunoglobulin for prevention of recurrent hepatitis B following liver transplantation. Clin Transplant 2010; 25:517-22. [PMID: 20560989 DOI: 10.1111/j.1399-0012.2010.01290.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
BACKGROUND The aim of this study is to examine the efficacy of long-term prophylaxis with lamivudine (LAM) after a course of post-operative hepatitis B immunoglobulin (HBIG) in patients who underwent liver transplantation (LT) for hepatitis B virus (HBV)-related disease. RESULT The medical records of HBV-infected patients who underwent a LT in our institution between July 2001 and May 2005 were reviewed. There were 15 liver transplant recipients who were administered HBIG for <18 months and used LAM as a maintenance prophylaxis regime enrolled in this study. At enrollment, all patients were hepatitis B surface antigen (HBsAg) positive and three patients were HBeAg positive. There were 13 patients who were HBV DNA positive with a mean viral load of 5.4 log copies/mL, and among them, 12 recipients were on antiviral therapy with LAM (100 mg/d orally) for 12-168 d, resulting in HBV DNA negative levels in nine patients prior to their transplant. HBV recurrence post-LT was noted in two patients who had very high-HBV DNA levels pre-LT. Both of these patients showed LAM-resistant mutation at the time of recurrence. The 11 patients who were HBV DNA negative before LT (low-risk patients) had no HBV recurrence during a follow-up at a median of 58 months post-LT. This included five patients who had intermittent low-level HBV DNA post-LT (HBsAg negative), of whom two had YMDD mutation and these two were given adefovir in addition to LAM. CONCLUSION Our retrospective study demonstrated excellent long-term outcomes in the low-risk patients treated with LAM after a short course of HBIG.
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Charles LF, Shaw MT, Olson JR, Wei M. Fabrication and mechanical properties of PLLA/PCL/HA composites via a biomimetic, dip coating, and hot compression procedure. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2010; 21:1845-1854. [PMID: 20238147 DOI: 10.1007/s10856-010-4051-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2009] [Accepted: 03/01/2010] [Indexed: 05/28/2023]
Abstract
Currently, the bone-repair biomaterials market is dominated by high modulus metals and their alloys. The problem of stress-shielding, which results from elastic modulus mismatch between these metallic materials and natural bone, has stimulated increasing research into the development of polymer-ceramic composite materials that can more closely match the modulus of bone. In this study, we prepared poly(L: -lactic acid)/hydroxyapatite/poly(epsilon-caprolactone) (PLLA/HA/PCL) composites via a four-step process, which includes surface etching of the fiber, the deposition of the HA coating onto the PLLA fibers through immersion in simulated body fluid (SBF), PCL coating through a dip-coating process, and hot compression molding. The initial HA-coated PLLA fiber had a homogeneous and continuous coating with a gradient structure. The effects of HA: PCL ratio and molding temperature on flexural mechanical properties were studied and both were shown to be important to mechanical properties. Mechanical results showed that at low molding temperatures and up to an HA: PCL volume ratio of 1, the flexural strain decreased while the flexural modulus and strength increased. At higher mold temperatures with a lower viscosity of the PCL a HA: PCL ratio of 1.6 gave similar properties. The process successfully produced composites with flexural moduli near the lower range of bone. Such composites may have clinical use for load bearing bone fixation.
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DeAngelis GC, Wei M, Angelaki DE. Does the oculomotor system make use of high-level visual cues to viewing distance? J Vis 2010. [DOI: 10.1167/3.9.148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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132
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Shao C, Wang C, Wei M, Jia Z, She Z, Lin Y. Two new benzaldehyde derivatives from mangrove endophytic fungus (No. ZZF 32). Chem Nat Compd 2010. [DOI: 10.1007/s10600-010-9509-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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133
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Jin L, Ni X, Liu X, Wei M. Selective Adsorption of Adenosine and Guanosine by a β-Cyclodextrin/Layered Double Hydroxide Intercalation Compound. Chem Eng Technol 2010. [DOI: 10.1002/ceat.200900264] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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134
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Yu R, Wei M. False Positive test Results for Pheochromocytoma from 2000 to 2008. Exp Clin Endocrinol Diabetes 2009; 118:577-85. [DOI: 10.1055/s-0029-1237699] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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135
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Ma J, Yang W, Fang N, Zhu W, Wei M. The association between intensive glycemic control and vascular complications in type 2 diabetes mellitus: a meta-analysis. Nutr Metab Cardiovasc Dis 2009; 19:596-603. [PMID: 19819121 DOI: 10.1016/j.numecd.2009.07.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2009] [Revised: 06/01/2009] [Accepted: 07/09/2009] [Indexed: 12/15/2022]
Abstract
BACKGROUND AND AIM In patients with type 2 diabetes mellitus, the relationship between lowering glycated hemoglobin (HbA(1c)) and macrovascular complications is not clear and therefore lowering the level of HbA(1c) is controversial. METHODS AND RESULTS We searched for all randomized controlled trials comparing the effects of intensive and standard glycemic control on vascular events in patients with type 2 diabetes mellitus. The primary endpoint was combined macrovascular complications, including cardiac events, stroke and peripheral vascular disease. Fixed and random effect models were used to analyze the results. Eight studies were included according to selection criteria. The results showed no benefits of intensive glycemic control on macrovascular and microvascular complications (P>0.1), but a higher rate of severe hypoglycemia (P<0.00001) in the intensive control group when the target HbA(1c) level was <7.0%. When the target HbA(1c) level was lowered to 7.0-7.9%, intensive glycemic control showed benefits on the reduction of microvascular events (P<0.05) without increasing the risk of severe hypoglycemia (P=0.74), but no influence on macrovascular complications (P>0.1). CONCLUSION The results of this analysis suggest that a target HbA(1c) level of 7.0-7.9% may be a better glycemic control target than that of <7.0% in patients with established type 2 diabetes mellitus.
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Wei M, Fu J, Li X, Wang Y, Li Y. Influence of dent corn genetic backgrounds on QTL detection for plant-height traits and their relationships in high-oil maize. J Appl Genet 2009; 50:225-34. [DOI: 10.1007/bf03195676] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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137
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Wei M, Kuukasjärvi P, Laurikka J, Pehkonen E, Kaukinen S, Laine S, Tarkka M. Pump Prime Aprotinin Fails to Limit Proinflammatory Cytokine Release After Coronary Artery Bypass Surgery. SCAND CARDIOVASC J 2009; 35:50-4. [PMID: 11354573 DOI: 10.1080/140174301750101528] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
BACKGROUND The purpose of this study was to establish whether pump prime aprotinin could limit the cytokine responses in patients undergoing elective coronary artery bypass surgery. METHODS Twenty-one patients admitted for first-time elective coronary artery bypass surgery were randomized into control or aprotinin groups. Patients in the aprotinin group received 280 mg aprotinin in the pump prime. Leukocyte count, creatine kinase cardiac isoenzyme (CK-MB), cytokine production and postoperative blood loss were analyzed perioperatively and compared with preoperative values. RESULTS The peak level of leukocyte count was lower in the aprotinin group than in controls (9.3 +/- 0.58 vs 11.2 +/- 0.68 x 10(9)/L, p = 0.01). Interleukin (IL)-6 and IL-8 did not differ significantly between the groups throughout the study period. Plasma IL-10 levels were higher in the controls than in the aprotinin group at 5 min (49.6 +/- 24.9 vs 8.13 +/- 2.8 pg/ml, p = 0.01) after reperfusion. CONCLUSION Pump prime aprotinin fails to limit proinflammatory cytokine response in circulating blood.
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138
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Peng F, Olson J, Shaw M, Wei M. Influence of pretreatment on the surface characteristics of PLLA fibers and subsequent hydroxyapatite coating. J Biomed Mater Res B Appl Biomater 2009; 88:220-9. [DOI: 10.1002/jbm.b.31172] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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139
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Wang D, Wu Q, Yao L, Wei M, Kou X, Zhang J. New target tissue for food-borne virus detection in oysters. Lett Appl Microbiol 2008; 47:405-9. [DOI: 10.1111/j.1472-765x.2008.02445.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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140
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Shao C, Wang C, Wei M, Gu Y, Xia X, She Z, Lin Y. Structure elucidation of two new xanthone derivatives from the marine fungus Penicillium sp. (ZZF 32#) from the South China Sea. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2008; 46:1066-1069. [PMID: 18759333 DOI: 10.1002/mrc.2293] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Two new xanthones, 8-(methoxycarbonyl)-1-hydroxy-9-oxo-9H-xanthene-3-carboxylic acid (1) and dimethyl 8-methoxy-9-oxo-9H-xanthene-1,6-dicarboxylate (2) and one known xanthone methyl 8-hydroxy-6-methyl-9-oxo-9H-xanthene-1-carboxylate (3) were isolated from the culture broth of the mangrove fungus Penicillium sp. (ZZF 32#) collected from the South China Sea. Their structures were established by comprehensive analysis of one-dimensional (1D) and two-dimensional (2D) NMR data. The structure of compound 3 was confirmed by X-ray crystallography, which led to the suggestion that janthinone (4) might have the same structure as 3. Compounds 1-3 were inactive against KB or KBv200 cells during cytotoxicity evaluations.
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141
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Shao C, Wang C, Wei M, Li S, She Z, Gu Y, Lin Y. Structural and spectral assignments of six anthraquinone derivatives from the mangrove fungus (ZSUH-36). MAGNETIC RESONANCE IN CHEMISTRY : MRC 2008; 46:886-889. [PMID: 18615624 DOI: 10.1002/mrc.2266] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A new natural product named 6,8,1'-tri-O-methyl averantin (1) has been isolated together with five known anthraquinones 1'-O-methyl averantin (2), 6,8-di-O-methyl averufin (3) averufin (4), versicolorin C (5) and 6,8-di-O-methyl averufanin (6) from a mangrove endophytic fungus ZSUH-36 collected from the South China Sea. NMR techniques including COSY, HMQC, and HMBC were used to elucidate the structures of these compounds. We report the unambiguous assignments of the (1)H and (13)C NMR spectra of the new compound 6,8,1'-tri-O-methyl averantin(1).
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Shi Q, Wang X, Wei M. NITRIC OXIDE MODULATES THE METABOLISM OF PLASMA MEMBRANE AND TONOPLAST IN CUCUMBER ROOTS. ACTA ACUST UNITED AC 2007. [DOI: 10.17660/actahortic.2007.761.37] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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143
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Hao H, Xin T, Nancai Y, Yanxia W, Qian L, Wei M, Yandong Y, Hanju H. Short-interfering RNA-mediated silencing of proliferating cell nuclear antigen inhibit proliferation and induce apoptosis in HeLa cells. Int J Gynecol Cancer 2007; 18:36-42. [PMID: 17466038 DOI: 10.1111/j.1525-1438.2007.00955.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Proliferating cell nuclear antigen (PCNA) is an important protein for DNA polymerase delta in the nucleus, and shown to have a fundamental role in cellular proliferation. It is overexpressed to support cell growth in cervical carcinoma. To study its role in stress response, we design and use short hairpin RNA (shRNA) to inhibit PCNA expression in HeLa cells and validate its effect on cell proliferation. In this study, three PCNA-shRNA expression vectors are constructed and introduced into HeLa cells, and the cell cycle is analyzed by flow cytometry. Apoptotic cell is detected by single cell gel electrophoresis assay (comet assay), and caspase cleavage is studied also. Expression of PCNA is assessed by real-time reverse transcription-polymerase chain reaction and Western blot analysis. Upon transient transfection with plasmid encoding shRNA, it is found that expression of PCNA decreased in shRNA-transfected cells, downregulation of PCNA inhibit cell growth and induce apoptosis in HeLa cells. PCNA downregulation also increase cell population in the G0-G1 phase. In conclusion, our findings demonstrate that shRNA can inhibit the DNA replication and induce apoptosis in HeLa cells effectively and, therefore, could be used as a new potential anticancer tool for therapy of human cervical carcinoma.
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Chao LT, Wei M, MacManus-Driscoll JL. Synthesis and characterisation of nanocrystalline iron oxides via ultrasonic spray assisted chemical vapour deposition. ACTA ACUST UNITED AC 2006. [DOI: 10.1088/1742-6596/26/1/073] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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145
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McMinn J, Wei M, Sadovsky Y, Thaker HM, Tycko B. Imprinting of PEG1/MEST Isoform 2 in Human Placenta. Placenta 2006; 27:119-26. [PMID: 16338457 DOI: 10.1016/j.placenta.2004.12.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2004] [Revised: 11/30/2004] [Accepted: 12/02/2004] [Indexed: 10/25/2022]
Abstract
The PEG1 gene (a.k.a. MEST) is expressed in human placental trophoblast and endothelium, and data from knockout mice show that this gene regulates placental and fetal growth. Isoform 1 of PEG1 mRNA initiates from exon 1c and produces the long form of the MEST protein. This isoform is imprinted, with expression only from the paternal allele in many human and mouse organs, including placenta. In contrast, PEG1 isoform 2, initiating from exon 1a and producing the short form of MEST protein, is biallelically expressed (non-imprinted) in several non-placental organs. Here we show that PEG1 isoform 2 is in fact imprinted in a large subset of human placentae. A CpG island overlapping PEG1 exon 1a is unmethylated in various fetal and adult non-placental tissues, but is often substantially methylated in the placenta, with the extent of methylation in a large series approximating a normal distribution. Bisulfite conversion/sequencing indicates that the inter-individual differences reflect the relative representation of heavily methylated vs. unmethylated alleles, and RT-PCR/RFLP analysis shows strongly biased allelic expression of PEG1 isoform 2 mRNA in a majority of placentae with a high proportion of methylated alleles. These data highlight PEG1 isoform 2 as a marker for future studies of inter-individual epigenetic variation and its relation to placental and fetal growth in humans.
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Johnson (F) EB, McMinn J, Wei M, Schupf N, Cusmai J, Smith A, Weksberg R, Thaker H, Tycko B. Potential serum markers for IUGR identified through microarray-based expression profiling. Am J Obstet Gynecol 2005. [DOI: 10.1016/j.ajog.2005.10.497] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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147
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McMinn J, Wei M, Schupf N, Cusmai J, Johnson EB, Smith AC, Weksberg R, Thaker HM, Tycko B. Unbalanced placental expression of imprinted genes in human intrauterine growth restriction. Placenta 2005; 27:540-9. [PMID: 16125225 DOI: 10.1016/j.placenta.2005.07.004] [Citation(s) in RCA: 211] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2005] [Revised: 07/08/2005] [Accepted: 07/11/2005] [Indexed: 10/25/2022]
Abstract
Imprinted genes control fetal and placental growth in mice and in rare human syndromes, but the role of these genes in sporadic intrauterine growth restriction (IUGR) is less well-studied. We measured the ratio of mRNA from a maternally expressed imprinted gene, PHLDA2, to that from a paternally expressed imprinted gene, MEST, by Northern blotting in 38 IUGR-associated placentae and 75 non-IUGR placentae and found an increase in the PHLDA2/MEST mRNA ratio in IUGR (p=0.0001). Altered expression of PHLDA2 and MEST was not accompanied by changes in DNA methylation within their imprinting centers, and immunohistochemistry showed PHLDA2 protein appropriately restricted to villous and intermediate cytotrophoblast in the IUGR placentae. We next did a genome-wide survey of mRNA expression in 14 IUGR placentae with maternal vascular under-perfusion compared to 15 non-IUGR placentae using Affymetrix U133A microarrays. In this series six imprinted genes were differentially expressed by ANOVA with a Benjamini-Hochberg false discovery rate of 0.05, with increased expression of PHLDA2 and decreased expression of MEST, MEG3, GATM, GNAS and PLAGL1 in IUGR placentae. At lower significance, we found IGF2 mRNA decreased and CDKN1C mRNA increased in the IUGR cases. We confirmed the significant reduction in MEG3 non-translated RNA in IUGR placentae by Northern blotting. In addition to imprinted genes, the microarray data highlighted non-imprinted genes acting in endocrine signaling (LEP, CRH, HPGD, INHBA), tissue growth (IGF1), immune modulation (INDO, PSG-family genes), oxidative metabolism (GLRX), vascular function (AGTR1, DSCR1) and metabolite transport (SLC-family solute carriers) as differentially expressed in IUGR vs. non-IUGR placentae.
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148
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Qu H, Vasiliev AL, Aindow M, Wei M. Incorporation of fluorine ions into hydroxyapatite by a pH cycling method. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2005; 16:447-53. [PMID: 15875255 DOI: 10.1007/s10856-005-6985-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Accepted: 11/01/2004] [Indexed: 05/02/2023]
Abstract
Fluorine ions were incorporated into hydroxyapatite (HA) using a pH cycling method and the resulting materials were studied using transmission electron microscopy (TEM), X-ray diffraction (XRD), and electrochemical analysis. TEM observations showed that fluoridated hydroxyapatite (FHA) nanoparticles with a narrow particle size distribution were obtained at several different levels of fluorine incorporation. Significant particle growth was observed following calcining at 1200 degrees C. The TEM data revealed that, instead of forming laminated structures, a mixture of HA and FA was obtained, and that this mixture transformed into a single homogeneous FHA phase upon heating. It was found that the efficiency of fluorine incorporation did not vary significantly with the initial HA particle size, but increased as the fluorine content of the initial solution was increased. A relatively low fluorine incorporation efficiency, approximately 60%, was attained for most of the FHA samples and this was attributed to the short holding time at each pH cycle and the limited number of pH cycles employed in the current study.
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Kothapalli CR, Wei M, Legeros RZ, Shaw MT. Influence of temperature and aging time on HA synthesized by the hydrothermal method. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2005; 16:441-6. [PMID: 15875254 DOI: 10.1007/s10856-005-6984-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Accepted: 11/01/2004] [Indexed: 05/02/2023]
Abstract
The influence of temperature and aging time on the morphology and mechanical properties of nano-sized hydroxyapatite (HA) synthesized by a hydrothermal method is reported here. The pre-mixed reactants were poured into a stirred autoclave and reacted at temperatures between 25-250 degrees C for 2-10 h. HA powders thus obtained were examined using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FESEM) and a particle size analyzer. It was found that the aspect ratio of the particles increased with the reaction temperature. The length of the HA particles increased with the reaction temperature below 170 degrees C, but it decreased when the temperature was raised above 170 degrees C. The agglomerates of HA particles were formed during synthesis, and their sizes were strongly dependent on reaction temperatures. As the reaction temperature increased, the agglomerate size decreased (p = 0.008). The density of the discs pressed from these samples reached 85-90% of the theoretical density after sintering at 1200 degrees C for 1 h. No decomposition to other calcium phosphates was detected at this sintering temperature. A correlation existed (p = 0.05) between the agglomerate sizes of HA particles synthesized at various conditions and their sintered densities. With the increase of the agglomerate size, the sintered density of the HA compact decreased. It was found that both the sintered density and flexural strength increased with increasing aging time and reaction temperature. A maximum flexural strength of 78 MPa was observed for the samples synthesized at 170 degrees C for 5 h with the predicted average at these conditions being 65 MPa. These samples attained an average sintered density of 88%.
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Wei M, Ruys AJ, Milthorpe BK, Sorrell CC. Precipitation of hydroxyapatite nanoparticles: effects of precipitation method on electrophoretic deposition. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2005; 16:319-324. [PMID: 15803276 DOI: 10.1007/s10856-005-0630-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2004] [Accepted: 11/17/2004] [Indexed: 05/24/2023]
Abstract
Electrophoretic deposition is a low-cost, simple, and flexible coating method for producing hydroxyapatite (HA) coatings on metal implants with a broad range of thicknesses, from < 1 microm to > 500 microm. As for many other HA coating techniques, densification of electrophoretically deposited coatings involves heating the coated metal to temperatures above 1000 degrees C. Metal substrates tend to react with HA coatings at such temperatures inducing decomposition at temperatures below 1050 degrees C (decomposition for pure HA normally occurs above 1300 degrees C). Therefore, densification of these coatings needs to be conducted at temperatures lower than 1050 degrees C, and this necessitates the use of high-surface-area HA nano-precipitates, rather than commercially available pre-calcined powders, which densify at temperatures typically higher than 1200 degrees C. HA nano-precipitates were prepared by three methods and deposited on metal substrates by electrophoresis: (1) the acid base method, which produced plate-like nano-particles with a 2.5:1 aspect ratio, and severely cracked coatings; (2) the calcium acetate method, which produced needle-like nano-particles with a 10:1 aspect ratio, and slightly cracked coatings; (3) the metathesis method, which produced rounded nano-particles with a 2:1 aspect ratio, and high-quality crack-free coatings. The results suggested that the less equiaxed the nano-particles, the more cracked the coatings obtained by the electrophoretic deposition technique.
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