Biomedical subjects

G Xu

Publications and source records attributed to G Xu.

At least 145 records · Page 8Linked to original sources

PubMed2000

Internal atomic distortion and layer roughness of epitaxial SiC thin films studied by short wavelength X-Ray diffraction

Epitaxial silicon carbide thin films grown on a silicon substrate were examined by short wavelength ( 0.71 A from a molybdenum anode) x-ray diffraction to study their atomic distortion and internal layer roughness. Up to 5 order Bragg peaks along (100) were measured and crystallographic structure factors were obtained. Electron density distributions along the surface normal were reconstructed via Fourier transform. In comparing to the ideal situation, it was found that, due to the lattice mismatch, the silicon atoms are no longer fixed on the same atomic plane, thus the corresponding electron distribution maxima were broadened. Also, the maxima for carbon atoms are flattened, indicating the randomized locations.

Journal Article↗

PubMed2000

Manumycin enhances the cytotoxic effect of paclitaxel on anaplastic thyroid carcinoma cells.

Despite the current multimodal approach to treatment of anaplastic thyroid cancer (ATC), the prognosis for patients with the disease is poor. New effective therapy for ATC is desperately needed. Thus, we investigated the effects of manumycin (a farnesyl:protein transferase inhibitor), alone and in combination with other drugs frequently used to treat ATC, in six human ATC cell lines: ARO, C643, DRO, Hth-74, KAT-4, and KAT-18. By means of a formazan dye-based spectrophotometric assay of cell viability and light microscopy, manumycin was shown to decrease the number of viable cells in all six of the cell lines though to a lesser degree in DRO and C643 cells than in ARO, Hth-74, KAT-4, and KAT-18 cells. In combination, manumycin enhanced the effect of paclitaxel in all six of the cell lines. The mechanism of cell death was investigated by measuring caspase-3 activity, immunoblotting with anti-poly-(ADP-ribose)polymerase (PARP) antibody and electrophoresis of DNA. After an 18-h incubation, manumycin plus paclitaxel caused enhanced activation of caspase-3 activity, cleavage of PARP into Mr 89,000 and 28,000 fragments, and internucleosomal fragmentation of DNA (all of which are characteristic of apoptotic cell death). In contrast, neither manumycin alone, paclitaxel alone, doxorubicin alone, nor doxorubicin plus manumycin produced significant specific cleavage of PARP and internucleosomal DNA fragmentation after 18 h of incubation. The in vivo effect and toxicity of combined manumycin and paclitaxel treatments were evaluated in a nude mouse xenograft model using ARO and KAT-4 cells. Drugs were injected i.p. on days 1 and 3 of a 7-day cycle for three cycles. Both manumycin (7.5 mg/kg/dose) and paclitaxel (20 mg/kg/dose) had significant inhibitory effects on tumor growth. Combined manumycin and paclitaxel treatments seemed as effective as manumycin against ARO cells and more effective than either manumycin or paclitaxel alone against KAT-4 cells. No significant morbidity or mortality was caused by the treatments. In conclusion, manumycin can inhibit the growth of ATC both in vitro and in vivo. Manumycin plus paclitaxel has enhanced cytotoxic effects and increased apoptotic cell death in ATC cells in vitro compared with either drug by itself. The combination of manumycin and paclitaxel is also effective in vivo with no significant toxicity observed. The lack of synergy observed in this in vivo experiment may be due to a ceiling effect, and further experimentation is warranted to ascertain the optimal way to combine these two agents for maximal therapeutic effects.

Alkyl and Aryl Transferases↗

PubMed2000

8-Aminocyclazocine analogues: synthesis and structure-activity relationships.

Opioid binding affinities were assessed for a series of cyclazocine analogues where the prototypic 8-OH substituent of cyclazocine was replaced by amino and substituted-amino groups. For mu and kappa opioid receptors, secondary amine derivatives having the (2R,6R,11R)-configuration had the highest affinity. Most targets were efficiently synthesized from the triflate of cyclazocine or its enantiomers using Pd-catalyzed amination procedures.

Analgesics↗

PubMed2000

Modular retro-vectors for transgenic and therapeutic use.

Retroviruses have been used for many years as vectors for human gene therapy as well as for making transgenic animals. However, the efficient insertion of genes by retroviruses is often complicated by transcriptional inactivation of the retroviral long terminal repeats (LTRs) and by the production of replication-competent retroviruses (RCR). Solutions to these and other difficulties are being found in modular vectors, in which the desirable features of different vector systems are combined. Examples of synergistic vectors include virosomes (liposome/virus delivery), adeno-retro vectors, and MLV/VL30 chimeras. As gene delivery systems become increasingly complex, methodology is also needed for precise assembly of modular vectors. Gene self-assembly (GENSA) technology permits seamless vector construction and simultaneous, multifragment assembly.

Animals↗

PubMed2000

Model peptide studies of sequence repeats derived from the intracrystalline biomineralization protein, SM50. II. Pro,Asn-rich tandem repeats.

In the biomineralization process, a number of Pro-rich proteins participate in the formation of three-dimensional supramolecular structures. One such protein superfamily, the Pro,Gly-rich sea urchin intracrystalline spicule matrix proteins, form protein-protein supramolecular assemblies that modify the microstructure of the inorganic mineral phase (calcite) within embryonic sea urchin spicules and adult sea urchin spines. These proteins represent a useful model for understanding Pro sequence usage and the resulting generation of extended or "open" structures for protein-protein and/or protein-crystal recognition. In the sea urchin spicule matrix protein, SM50 (Strongylocentrotus purpuratus), there exists an unusual 20-residue Pro,Asn-containing repeat, &bond;PNNPNNPNPNNPNNPNNPNPbond which links the upstream 15-residue C-terminal domain and the downstream 211-residue beta-spiral repeat domain. To define the structural preferences of this 20-residue repeat, we created a 20-residue N- and C-terminal "capped" peptidomimetic of this sequence. Using far-uv CD dichroism, CH(alpha) and alpha-(15)N conformational shifts, (3)J(NH-CHalpha) coupling constants, sequential d(NN(i, i + 1)) rotating frame nuclear Overhauser effect connectivities, d(alphaN(i, i + 1))/d(NN(i, i + 1)) intensity ratios, amide temperature shift coefficients, amide solvent exchange, and simulated annealing refinement protocols, we have determined that this 20-residue repeat motif adopts an extended "twist" structure consisting of turn- and coil-like regions. These findings are consistent with previous studies, which have shown that Pro-rich tandem repeats adopt extended, flexible structures in solution. We hypothesize that this 20-residue repeat may fulfill the role of a mineral-binding domain, a protein-protein docking domain, or as an internal "molecular spacer" for the SM50 protein during spicule biocomposite formation.

Amino Acid Motifs↗

PubMed2000

Excretion pattern investigation of urinary normal and modified nucleosides of breast cancer patients by RP-HPLC and factor analysis method.

Modified nucleosides, formed post-transcriptionally in RNA by a number of modification enzymes, are excreted in abnormal levels in the urine of patients with malignant tumors. To test their usefulness as tumor markers, and to compare them with the conventional tumor markers, a reversed-phase high-performance liquid chromatographic (RP-HPLC) method and a factor analysis method have been used to study the excretion pattern of nucleosides of breast cancer patients. A clear cut differentiation of the breast cancer group and the healthy individuals in two clusters without overlapping was obtained.

Adult↗

PubMed2000

Effects of diabetes and hypoxia on gene markers of angiogenesis (HGF, cMET, uPA and uPAR, TGF-alpha, TGF-beta, bFGF and Vimentin) in cultured and transplanted rat islets.

AIMS/HYPOTHESIS: The vascularisation of newly transplanted islets originates from the recipients. Because islets transplanted into a diabetic do less well than those transplanted into a euglycaemic environment, we examined the hypothesis that gene expression of angiogenic factors in grafts is delayed in diabetes. These factors include hepatocyte growth factor (HGF) and its receptor c-MET, and urokinase plasminogen activator (uPA) and its receptor uPAR, basic fibroblast growth factor (bFGF), TGF-alpha and TGF beta-1. METHODS: Isolated rat islets were studied in vitro under normoxic and hypoxic culture conditions and gene expression was determined with semi-quantitative multiplex RT-PCR. We found that HGF but not c-MET expression was induced by hypoxia in vitro. Using syngeneic Lewis rats, gene expression was also studied in grafts on days 1, 3, 5, 7 and 14 after transplantation. RESULTS: In grafts of normoglycaemic rats, HGF expression was enhanced on day 3 and maintained whereas expression of c-MET fell and remained down until day 14. Expression of uPA was up at day 3 and remained high; expression of uPAR was also up at day 3 but then fell to control levels at day 14. Expression of bFGF, TGF-alpha and TGF beta-1 persisted throughout. Vimentin, a marker of fibroblasts, had increased expression at day 1 which was further enhanced in subsequent days. In the grafts of diabetic recipients the expression of HGF, uPA and uPAR were delayed, being clearly expressed at day 5 rather than day 3. Vimentin expression was similarly delayed. CONCLUSION/INTERPRETATION: This apparent delay in angiogenesis provides a potential mechanism for the less favourable outcomes of islets transplanted into diabetic recipients.

Animals↗

PubMed2000

A comparison of diabetic polyneuropathy in type II diabetic BBZDR/Wor rats and in type I diabetic BB/Wor rats.

AIMS/HYPOTHESIS: To examine the functional, metabolic and structural abnormalities in peripheral nerve in the spontaneously Type II (non-insulin-dependent) diabetic BBZDR/Wor rat and compare these data with those in the Type I (insulin-dependent) diabetic BB/Wor rat. METHODS: Animals were examined at 6 and 14 months of diabetes. Nerve conduction velocity was measured longitudinally. Nerve polyols were analysed using gas liquid chromatography and Na/K(+)-ATPase activity was measured enzymatically. Light and electron microscopic techniques were used for nerve morphometry. RESULTS: Diabetic BBZDR/Wor rats showed a slowly progressive nerve conduction defect that reached 17% (p < 0.01) at 14 months. There was a decrease in Na+/K(+)-ATPase of 35% (p < 0.05). Structurally, there were mild myelinated fibre atrophy (p < 0.05), mild or absent changes of the node of Ranvier, but significant (p < 0.001) segmental demyelination and Wallerian degeneration. These findings point to a more severe nerve conduction defect, severe myelinated fibre atrophy and profound nodal changes in Type I spontaneously diabetic BB/Wor rats maintained at the same hyperglycaemic concentrations. CONCLUSION/INTERPRETATION: We conclude that other factors, beside hyperglycaemia, are involved in the pathogenesis of the more severe Type I diabetic neuropathy which possibly involve insulin and C-peptide deficiencies.

Animals↗

PubMed2000

Immunohistochemical localization of mitogen-activated protein kinase (MAPK) family and morphological changes in rat heart after ischemia-reperfusion injury.

The mitogen-activated protein kinase (MAPK) family is considered to be activated by stress, but the role of the MAPK family is still unknown in cardiac pathology. In the present study, not only the localization of MAPKs such as the extracellular responsive kinase (ERK), c-jun N-terminal kinase (JNK), and p38 MAPK (p38), but also ultrastructural changes were investigated in the ischemia-reperfusion model of Wistar rats. At 5, 10, 30, 60, and 180 min reperfusion after 30 min ischemia by occluding the coronary artery, the expression of these MAPKs was increased in blood vessels and cardiomyocytes by Western blotting and immunohistochemical methods. In addition, after ischemia reperfusion, various ultrastructural changes such as decreased glycogen granules, mitochondrial swelling, and myolysis were observed in the blood vessels and cardiomyocytes. These results suggest that protein kinases may regulate numerous biological processes, including the regulation of contraction and ion transport.

Animals↗

PubMed2000

Gender comparisons of income expectations in the USA at the beginning of medical school during the past 28 years.

This study was designed to investigate gender differences in the USA, in anticipated professional income. Participants were 5314 medical students (3880 men, 1434 women) who entered Jefferson Medical College between 1970 and 1997. The annual peak professional income estimated at the beginning of medical school was the dependent variable and gender within selected time periods was the independent variable. Results showed significant differences between men and women on their anticipated future incomes in different time periods. Women generally expected 23% less income than men. The effect size estimates of the differences were moderately high. The gender gap in income expectations was more pronounced for those who planned to pursue surgery than their counterparts who planned to practice family medicine or pediatrics. A unique feature of this study is that its outcomes could not be confounded by active factors such as experience, working hours, age and productivity. Findings suggest that social learning may contribute to gender gap in anticipated income.

Economics, Medical↗

PubMed2000

Polyclonal antibodies to a fluorescent 4-hydroxy-2-nonenal (HNE)-derived lysine-lysine cross-link: characterization and application to HNE-treated protein and in vitro oxidized low-density lipoprotein.

Oxidative modification of low-density lipoprotein (LDL) is thought to play a key role in the etiology of atherosclerosis. Oxidized LDL that accumulates in atherosclerotic plaques is known to exhibit a characteristic fluorescence with excitation and emission near 360 and 430 nm, respectively. (E)-4-Hydroxy-2-nonenal (HNE), formed during LDL oxidation, is capable of modifying LDL to generate the same fluorescent signature. The HNE-derived fluorophore was shown by us to possess a 2-hydroxy-2-pentyl-1,2-dihydropyrrol-3-one iminium (HPDPI) structure. We herein report the synthesis of the HPDPI-derived lysine-lysine cross-link needed as a standard reference for HPLC quantitation of the cross-link in protein hydrolysates. The main focus of the current work, however, is the design and development of two polyclonal antibodies against the HPDPI epitope. Utilizing these antibodies, levels of the HPDPI epitope were estimated in HNE-treated bovine serum albumin and in copper-oxidized LDL by an enzyme-linked immunosorbent assay. Our results are consistent with the premise that the fluorescent HPDPI cross-link is a key contributor to the fluorescence exhibited by atherosclerotic lesions.

Aldehydes↗

PubMed2000

The frequency and proliferative potential of megakaryocytic colony-forming cells (Meg-CFC) in cord blood, cytokine-mobilized peripheral blood and bone marrow, and their correlation with total CFC numbers: implications for the quantitation of Meg-CFC to predict platelet engraftment following cord blood transplantation.

CFC numbers have shown to correlate with success of engraftment and speed of neutrophil recovery following cord blood (CB) transplantation. To investigate whether the number of Meg-CFC in a CB stem cell preparation might correlate with time to platelet engraftment, we evaluated the frequency of Meg-CFC among all CFC types in 134 CB, 21 adult bone marrow (BM) and 52 cytokine-mobilized peripheral blood (PB) stem cell preparations. The correlation of Meg-CFC with the total number of CFC and mixed cell-CFC was also assessed. The frequency of Meg-CFC was highest in CB and correlated significantly with total CFC numbers (mean 20.8%, correlation coefficient (r) 0.84, P = 0.0001) compared with Meg-CFC from mobilized PB (mean 13.1%, r = 0.29, P = 0.07) and BM (mean 4%, r = 0. 39, P = 0.13). In addition, mixed-cell CFC numbers in CB were highly correlated with the total number of Meg-CFC (r = 0.7, P = 0.0001). No such correlations were found with mobilized PB or BM. We conclude that, based on the high degree of correlation between Meg-CFC and non-Meg-CFC numbers in CB, no additional information concerning time to platelet engraftment would be gained by routinely performing Meg-CFC assays in addition to non-Meg-CFC assays. The fact that CB Meg-CFC and mixed-cell CFC are strongly correlated suggests that CB Meg-CFC are more primitive than their counterparts in BM and PB and may reflect the number of stem cells in CB. Bone Marrow Transplantation (2000).

Adult↗

PubMed2000

Fusogenic effects of murine retroviruses and cationic enhancers of transduction.

The maturation of retrovirus particles involves proteolytic cleavage of the envelope glycoprotein transmembrane component, resulting in conversion of the virus particle to a fusogenic or infectious state. Susceptible murine cells exposed to virus-containing supernatants from ecotropic retroviral helper cells occasionally fused to neighboring cells, resulting in syncytia (giant cells with multiple nuclei). Polycationic molecules dramatically enhanced the effect, leading to widespread cell death. The degree of cell fusion was dependent upon the retroviral envelope subtype (ecotropic-->amphotropic, gibbon ape leukemia virus was negative) as well as on the polycationic reagent used (G9 dendrimer-->Lipofectamine-->polybrene). Cell fusion effects were not mediated by the retroviral vector backbone, because virus-containing supernatants from helper cells (without vector) and vector producer cells had a similar effect. Human target cells were not fused by any type of murine retrovirus; in addition, amphotropic virus from human helper cells was not fusogenic toward murine cells. Thus, fusogenic effects were important during the propagation of vectors using murine helper cells but were not a significant factor during the transduction of human cells.

3T3 Cells↗

PubMed2000

The cationic C-terminus of rat Muc2 facilitates dimer formation post translationally and is subsequently removed by furin.

Earlier immunolocalization experiments showed that the extreme cationic C-terminus of the rat intestinal mucin Muc2 (RMC) was present at the base of intestinal goblet cells in the vicinity of ER and golgi compartments, but was not found with the rest of the mucin in apical storage granules. This prompted us to investigate the possibility that an early proteolytic cleavage reaction occurs post-translationally. A plasmid pRMC, encoding the C-terminal 534 amino acids of the mucin, was expressed in COS-7 cells and was shown to undergo cleavage at an R-T-R-R sequence located within the C-terminal 14 amino acids. Cleavage did not occur with the construct RMCfH, a furin site-mutated (A-T-A-A) counterpart of pRMCH (poly His6 tagged RMC). Addition of a furin inhibitor to COS-7 cell incubations also prevented cleavage of RMC and RMCH products. 35S pulse-chase kinetic experiments revealed that a truncated mutant lacking the C-terminal 14 amino acids (pRMCDeltaCT) forms faulty (doublet) dimers in the ER. These were not secreted as efficiently as the normal dimer of wild-type (pRMC) constructs. Thus the cationic C-terminus of rMuc2 apppears to facilitate the correct formation of normal Muc2 domain dimers.

Animals↗

PubMed2000

Levels and repair of cyclobutane pyrimidine dimers and 6-4 photoproducts in skin of sporadic basal cell carcinoma patients.

The 32P-postlabeling method was applied to measure directly the levels and repair rates of specific cyclobutane pyrimidine dimers and 6-4 photoproducts in 10 basal cell carcinoma patients and 10 controls matched on age, skin type, and gender after exposure to 400 J per m2 of solar simulating radiation on previously unexposed buttock skin. The results showed an identical level of photoproducts at 0 h after solar simulating radiation in the basal cell carcinoma group and the control group. Erythemal response correlated with the repair of cyclobutane pyrimidine dimers within 24 h in both groups, i.e., repair was faster in those with a strong erythemal reaction. The basal cell carcinoma patients showed a somewhat slower repair of photoproducts in skin compared with the controls, but the result was not significant. Photoproducts formed at the TTC sites were repaired faster than those at the TTT sites for both cyclobutane pyrimidine dimers and 6-4 photoproducts in the basal cell carcinoma group and in the controls.

Aged↗

PubMed2000

Cutaneous melanoma patients have normal repair kinetics of ultraviolet-induced DNA repair in skin in situ.

The DNA lesions induced by ultraviolet radiation include cyclobutane pyrimidine dimers and 6-4 photoproducts. We investigated whether cutaneous melanoma patients have an impaired ability to repair their ultraviolet-induced photolesions. Seventeen patients with melanoma and 13 healthy controls took part in this study. Both groups received a dose of 40 mJ per cm2 Commission Internationale de l'Eclairage of solar simulating radiation on previously unexposed buttock skin. Skin biopsies were taken at 0 h, 24 h, and 48 h after ultraviolet exposure. A 32P-postlabeling method was used to measure both cyclobutane pyrimidine dimers and 6-4 photoproducts in skin. Cyclobutane pyrimidine dimers and 6-4 photoproduct levels did not differ in the melanoma patients from those in the control group at any time point post-ultraviolet radiation. The repair rate of cyclobutane dimer TT=C was faster than that for TT=T both at 24 h and 48 h postirradiation in both groups, providing evidence of site-specific repair (p < 0.05). We conclude that patients with melanoma have a normal ultraviolet-induced DNA repair capacity in skin in situ.

Adult↗

PubMed2000

3-Hydroxy-3-methylglutaryl-coenzyme A reductase activity is inhibited by cholesterol and up-regulated by sitosterol in sitosterolemic fibroblasts.

Sitosterolemia is an inherited recessive disease characterized by abnormally increased plasma and tissue plant sterol concentrations. Patients hyperabsorb sitosterol. In addition, hepatic, ileal, and mononuclear leukocyte 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-controlling enzyme in the cholesterol biosynthetic pathway, is markedly suppressed in this disease. It is still controversial whether the down-regulation is due to accumulated sitosterol, but the effect of sitosterol on HMG-CoA reductase activity has not been studied in sitosterolemic tissues. To investigate whether sitosterol inhibits HMG-CoA reductase activity in sitosterolemia, we measured the enzyme activities in liver and cultured skin flbroblasts from patients. Hepatic HMG-CoA reductase activities in patients were decreased 76% (P < .05) as compared with results in control subjects. In contrast, HMG-CoA reductase activities in sitosterolemic fibroblasts were not decreased as compared with results in control fibroblasts, and the activities in all cells were up-regulated similarly when they were exposed to delipidated medium. Because the cultured sitosterolemic fibroblasts contained only trace amounts of plant sterols, we added 20 microg/mL sitosterol directly to the cell medium. Raising the intracellular sitosterol concentration to 7% of cellular cholesterol level increased HMG-CoA reductase activity 23% (P < .05), while the addition of the same amount of cholesterol to the cells reduced the activity 46% (P < .05). Thus, when sitosterolemic skin fibroblasts were used, it was possible to distinguish between the effects of cholesterol and those of sitosterol on the activity of HMG-CoA reductase. These results suggest that reduced HMG-CoA reductase activity in this disease is caused by secondary effects of unknown regulator(s) other than sitosterol.

Adolescent↗

PubMed2000

Two C-terminal variants of NBC4, a new member of the sodium bicarbonate cotransporter family: cloning, characterization, and localization.

We report the cloning, characterization, and chromosomal assignment of a new member of the sodium bicarbonate cotransporter (NBC) family, NBC4. The NBC4 gene was mapped to chromosome 2p13 and is a new candidate gene for Alstrom syndrome. Two variants of the transporter have been isolated from human testis and heart, which differ in their C termini. NBC4a encodes a 1137-residue polypeptide and is widely expressed in various tissues, including liver, testis, and spleen. NBC4b is identical to NBC4a except that it has a 16-nucleotide insert, creating a C-terminal frame shift. NBC4b encodes a 1074-residue polypeptide and is highly expressed in heart. Amino acids 1-1046 are common to both NBC4 variants. NBC4a has two protein-interacting domains that are lacking in NBC4b: a proline-rich sequence, PPPSVIKIP (amino acids 1102-1110), and a consensus PDZ-interacting domain, SYSL (1134-1137). NBC4b lacks the stretch of charged residues present in the C terminus of NBC4a and other members of the NBC family. Unlike other members of the NBC family, both NBC4a and NBC4b have a unique glycine-rich region (amino acids 440-469). In comparison with other members of the bicarbonate transport superfamily, NBC4a and NBC4b are most similar structurally to the electrogenic sodium bicarbonate cotransporters (NBC1).

Amino Acid Sequence↗