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Biomedical subjects

X D Zhang

Publications and source records attributed to X D Zhang.

At least 19 recordsLinked to original sources
PubMed2006

Preparation of bioactive nanotitania ceramics with biomechanical compatibility.

In this article, bioactive nanotitania ceramics with biomechanical compatibility was prepared by using an additive of hydroxyapatite or MgO as particle growth inhibitor. After sintering at 1000 degrees C, the particle size of nanotitania ceramics prepared by using HA as additive (HT) was much smaller than that prepared by using MgO as additive (MT). In simulated body fluid (SBF), HT could induce apatite formation in 4 days, while no apatite could be found on MT even after it was soaked in SBF for 14 days. After Ros17/28 osteoblasts were cultured on the materials for 1, 4, and 6 days, MTT results showed that the osteoblasts on the HT differentiated faster than that on the MT. Mechanical tests results showed that the bending and compressive strength of HT were 160 and 200 MPa, while those of MT were 70 and 88 MPa, respectively. These results demonstrated that it is suitable to prepare bioactive nanotitania ceramics, with biomechanical compatibility, by using HA as particle growth inhibitor.

Animals↗
PubMed2006

Current strategies in overcoming resistance of cancer cells to apoptosis melanoma as a model.

Most anticancer agents mediate their effects through common pathways which induce apoptosis or in some cases necrosis of cancer cells. The apoptotic pathways are regulated by Bcl-2 family proteins, which include both pro- and anti-apoptotic members. Much is known about the interactions of these proteins involved in apoptosis and this information is being utilized in the development of new reagents that may be used to treat patients with cancers. The inhibitor of apoptosis family of proteins constitute a second group of proteins which inhibit the effector caspases. Reagents that inhibit their activity are also under development. Resistance of cancer cells to treatment can in many instances be attributed to activation of intracellular signal pathways involved in survival, such as the Ras-Raf-MEK-ERK1/2 or the P13K-Akt pathway. Again, much has been learned about the control of these pathways and their activation of resistance mechanisms. Inhibitors of such pathways are being evaluated in preclinical and clinical studies and are showing promise as a new class of anticancer agents. Much of the progress in future studies will likely depend on the ability to target these new treatments to particular subgroups of patients with tumor characteristics that make them responsive to the agents in question.

Antineoplastic Agents↗
PubMed2006

The influence of surface bioactivated modification on titanium percutaneous implants anchored in bone.

In order to achieve biological sealing and resist mechanical damage of load-bearing percutaneous devices, Ti with excellent mechanical properties was anodic-oxidized to be endowed with bioactivity, with plasma-sprayed hydroxyapatite coated Ti as control. Similar to previous works, hydroxyapatite coating could bond tightly with living tissues, resulting in implant stability for whole implantation periods. Meanwhile, when anodic-oxidized bioactivated Ti was implanted percutaneously in vivo, it could induce a layer of calcium phosphate at the interface of tissues/implant. This layer of Ca-P not only induced the fibrous tissue or collagen ingrowth in its structure, but also improved the osteointegration between the bone and the implant. There was no significant biological response difference for the anodic-oxidized Ti and HA coated Ti at different implantation period with histological statistical analysis (p>0.05). Accordingly, suitable bioactivated modified surface of Ti by anodic-oxidized method could not only obtain the same results as the HA coating, but also might avoid some drawbacks of plasma-sprayed HA coatings to achieve biological sealing for a long period in vivo.

Animals↗
PubMed2005

Dynamic study of calcium phosphate formation on porous HA/TCP ceramics.

Bone-like apatite formation on porous calcium phosphate ceramics was investigated in static simulated body fluid (SBF) and dynamic SBF at different flowing rates. The results of a 14-day immersion in static SBF showed that the formation of bone-like apatite occurred both on the surface and in the pores of the samples. When SBF flowed at the physiological flow rate in muscle (2 ml/100 ml.min), bone-like apatite could be detected only in internal surface of the pores of samples. The result that bone-like apatite formation could only be found in the pores when SBF flowed at physiological flow rate was consistent with that of porous calcium phosphate ceramics implanted in vivo: osteoinduction was only detected inside the pores of the porous calcium phosphate ceramics. This result implicates that the bone-like apatite may play an important role in the osteoinduction of Ca-P materials. The dynamic model used in this study may be better than usually used static immersion model in imitating the physiological condition of bone-like apatite formation. Dynamic SBF method is very useful to understand bone-like apatite formation in vivo and the mechanism of ectopic bone formation in calcium phosphate ceramics.

Apatites↗
PubMed2005

Sildenafil citrate treatment for erectile dysfunction after kidney transplantation.

OBJECTIVE: Our goal was to analyze the morbidity of organic erectile dysfunction (ED) in kidney-transplant patients and to evaluate the efficacy and reliability of sildenafil citrate treatment. METHOD: Sixty-five ED patients with normal graft function for 3 to 12 months after kidney transplantation were involved in our study. Erectile dysfunction was diagnosed in all the patients by the International Index of Erectile Dysfunction (IIEF). Among them, 10 patients were in light degree; 32 patients in moderate degree, and 23 patients in severe degree according to IIEF score. All of the patients underwent medical history, physical and chemical examinations. In each patient, the IIEF score, blood urea nitrogen, creatinine, and trough concentrations of cyclosporine were compared before and after taking sildenafil citrate at an initial dose of 50 mg every night. RESULTS: Twenty-six patients without ED before transplantation suffered ED after the operation, and 32 patients with ED before transplantation noticed worsening. Taking sildenafil citrate was effective in 53 patients (81.54%). There were no statistical differences in blood urea nitrogen, creatinine, or trough concentrations of cyclosporine in patients before and after sildenafil treatment. CONCLUSIONS: The morbidity of organic erectile dysfunction increased after transplantation. Sildenafil citrate treatment for ED in kidney-transplant patients was effective and safe. Graft function and trough concentrations of cyclosporine were not affected by sildenafil citrate.

Blood Urea Nitrogen↗
PubMed2005

Activation of the extracellular signal regulated kinase (ERK) pathway in human melanoma.

BACKGROUND: Several studies suggest that melanoma may be resistant to treatment because of resistance to apoptosis and that this may be the result of activation of the extracellular signal regulated kinase (ERK1/2) pathway. AIMS: To test this hypothesis by examining the expression of ERK1/2 and its activated form in histological sections of melanoma and its relation to known prognostic features of the disease. MATERIALS/METHODS: Immunohistochemistry with antibodies to ERK1/2 and phosphorylated ERK (p-ERK) was performed on formalin fixed sections from 42 primary melanomas, 38 metastases, and 20 naevi. Fourteen of the primary melanomas were in the radial and 28 in the vertical growth phase. RESULTS: ERK1/2 was widely expressed (100%) in all the (pigmented) lesions studied. p-ERK1/2 expression was much lower in compound (32.4%) and dysplastic (54.5%) naevi than in primary melanoma (nodular 78.8%, superficial spreading 67%) and subcutaneous metastases (76.3%). p-ERK expression was much lower in lymph node metastases (48.5%), suggesting that the microenvironment may influence the activation of ERK. There was a (non-significant) trend for p-ERK expression to be higher in thick (>1.0 mm) versus thin (< or =1.0 mm) melanoma (p = 0.23). There was a trend for overall survival to be related to p-ERK expression in patients with melanoma over 1 mm in thickness. CONCLUSIONS: Expression of activated ERK1/2 in melanocytic lesions appears to be related to malignant potential so that activation of ERK1/2 may be important in melanoma progression. These results provide important histological support for the proposal that inhibition of this signalling pathway may be useful in treatment of melanoma.

Adolescent↗
PubMed2004

Dynamic study of calcium phosphate formation on porous HA/TCP ceramics.

Bone-like apatite formation on porous calcium phosphate ceramics was investigated in static simulated body fluid (SBF) and dynamic SBF at different flowing rates. The results of a 14-day immersion in static SBF showed that the formation of bone-like apatite occurred both on the surface and in the pores of the samples. When SBF flow at the physiological flow rate in muscle (2 ml/100 ml min1), bone-like apatite could be detected only in internal surface of the pores of samples. The result that bone-like apatite formation could only be found in the pores when SBF flown at physiological flow rate was consistent with that of porous calcium phosphate ceramics implanted in vivo: osteoinduction was only detected inside the pores of the porous calcium phosphate ceramics. This result implicates that the bone-like apatite may play an important role in the osteoinduction of Ca-P materials. The dynamic model used in this study may be better than usually used static immersion model in imitating the physiological condition of bone-like apatite formation. Dynamic SBF method is very useful to understand bone-like apatite formation in vivo and the mechanism of ectopic bone formation in calcium phosphate ceramics.

Biomimetic Materials↗
PubMed2004

Characterization of titanium surfaces with calcium and phosphate and osteoblast adhesion.

The titanium surfaces containing calcium, phosphate ions and the carbonate apatite were characterized. The effect of surface chemistry on the initial rabbit osteoblast response on these surfaces was investigated. The cell count and alkaline phosphatase (ALP) specific activity assay were used for biochemical analyses. Scanning electron microscopy was used for morphology observation and in particular X-ray photoelectron spectroscopy (XPS) for surface chemistry characterization. The number of cells adhering to the apatite coating surface was the maximum, the number of cells on the surface containing calcium without phosphate ions was higher than that containing phosphate without calcium, and the number on the unmodified titanium surface was the least. The osteoblasts cultured on the apatite surface exhibited the highest ALP specific activity, next were the ones on the surface containing solely calcium, the lowest were on the unmodified titanium surface. On the substrate surfaces removed of adhered cells, the order of nitrogen amounts detected by XPS was consistent with ones of ALP specific activity and cell number, except for the unmodified titanium surface. For the substrate surfaces removed of adhered osteoblasts, XPS analysis showed that calcium and phosphorous amounts decreased during cell adhesion. After cell culture the Ca2p binding energy (BE) values for apatite coating and the surface containing solely calcium were similar to those of the two surfaces adsorbed bovine serum albumin (BSA). The P2p BE values for the surfaces containing phosphate ions, including the apatite coating and the surface containing solely phosphate ions, showed the same change. But after cell culture the decrease of the P2p BE value for the coating surface was larger than the one for the surface containing solely phosphate ions. Considering the bovine serum albumin adsorption on the same samples, these results indicated that calcium ions on titanium surfaces play a more important role than phosphate ions in initial interactions among culture medium, osteoblasts and titanium surfaces. On the apatite coating surface, calcium ions are active sites for osteoblast adhesion, while calcium and phosphate ions co-exist on titanium surfaces, the former promotes the osteoblast adhesion onto the phosphate sites on titanium surfaces. The cell adhesion was a complicated biological and chemical process relating to surface several elements similar to protein adsorption.

Animals↗
PubMed2004

Evaluation of the expression of collagen type I in porous calcium phosphate ceramics implanted in an extra-osseous site.

The aim of the present study is to demonstrate the newly formed tissue in calcium phosphate (Ca/P) ceramics after extra-osseous implantation by histological and immunohistochemistry (IHC) methods. Synthesis porous Ca/P ceramics without adding any growth factor and living cell were implanted in the dorsal muscle of dogs for 1 and 2 months. Undecalcified and decalcified sections were stained by hematoxylin and eosin (H&E), and IHC, respectively. The histological results showed the beginning of osteogenesis and angiogenesis after being implanted for 1 month and the obvious new bone formation after being implanted for 2 months. IHC were conducted via the avidin-biotin peroxidase complex (ABC) method and the primary antibody was collagen type I. IHC results indicated that collagen type I was expressed within osteoblast-like cells and newly formed bone-like tissue in Ca/P ceramics after 1 month, and in the mineralized matrix of newly formed bone and osteoblasts, some osteocytes and some lacunae after 2 months. No cartilage and chondrocytes were observed in the histological and IHC-stained sections. Evidence of intramembranous osteogenesis was confirmed.

Animals↗
PubMed2003

Effect of spinal cord injury on urinary bladder spinal neural pathway: a retrograde transneuronal tracing study with pseudorabies virus.

OBJECTIVES: To determinate the effect of acute and chronic spinal cord injury (SCI) resulting from thoracic cord transection on the urinary bladder spinal neural pathway. METHODS: Seventy-six adult Sprague-Dawley rats were randomly divided into four groups, non-SCI (normal rats undergoing no surgical procedure except pseudorabies virus [PRV] injection), SCI(b) (SCI and PRV injected immediately after SCI), SCI(c) (SCI and PRV injected at 3 weeks after SCI), and SCI(d) (SCI and PRV injected at 3 months after SCI). Transcardiac perfusion fixation was done at appropriate survival periods after PRV injection into the bladder wall tissue. Sections of the dorsal root ganglion, spinal cord, and brain were processed for visualization of the virus by the streptavidin-peroxidase immunohistochemical procedure. RESULTS: The bladder weight of the non-SCI, SCI(b), SCI(c), SCI(d) rats was 144 +/- 9 mg, 142 +/- 8 mg, 486 +/- 51 mg, and 656 +/- 69 mg, respectively. The time-ordered flow charts of PRV tracing were similar in the non-SCI and SCI rats. The cross-sectional area of the labeled dorsal root ganglion cell profiles increased significantly after SCI (P <0.001): 593 +/- 40 microm2, 588 +/- 39 microm2, 815 +/- 53 microm2, and 902 +/- 57 microm2 in the non-SCI, SCI(b), SCI(c), SCI(d) rats, respectively. The number of labeled cells in the dorsal horn in the L6 and S1 segments 3 days after PRV injection markedly increased in chronic SCI rats, as did the number of labeled motor neurons 4 days after injection. CONCLUSIONS: Acute and chronic SCI have no effect on the process of virus transneuronal transport below the level of the lesion. Subsequent to chronic SCI, reorganization of the micturition reflex pathways may occur.

Acute Disease↗
PubMed2003

Characterization of surface oxide films on titanium and adhesion of osteoblast.

The relationship between surface characteristics of titanium and initial interactions of titanium-osteoblasts was investigated. Titanium plates were heat-treated in different oxidation atmospheres. The third passage rabbit osteoblasts were cultured on the titanium plates for 24h. After the heat-treatment, the crystal structure of the surface oxide films on titanium was identified using X-ray diffractometer and X-ray photoelectron spectroscopy (XPS). The surface roughness of titanium was measured with a profilometer. The surface energy was obtained by measurement of contact angles and calculation with Owens-Wendt-Kaeble's equation. The amount of surface hydroxyl (OH)(s) groups was examined using XPS. The change of binding energy of the some elements on the substrate surface suggested that the interactions between the cells and the titanium involved chemical reactions. The greater surface roughness, higher surface energy and more surface hydroxyl groups resulted in greater numbers of adhered osteoblasts and higher cell activity. Compared to the acidic hydroxyl (OH)(a) groups in (OH)(s) groups and the dispersion component of the total surface energy, the basic hydroxyl (OH)(b) groups and the polar component play more important roles in the osteoblast-titanium interaction.

Alkaline Phosphatase↗
PubMed2002

Effect of water vapor treatment on apatite formation on precalcified titanium and bond strength of coatings to substrates.

In previous investigations, a simple method, precalcification, was developed for bioactivating titanium. After a titanium sample was precalcified in a boiling saturated Ca(OH)(2) solution and then immersed in a calcium phosphate supersaturated solution, an apatite coating rapidly precipitated onto its surface. In the present study, heat-treatment in water vapor was carried out prior to precalcification. Heat-treatment in water vapor stimulated the chemical reaction between titanium, calcium, and phosphate. Coating properties were improved, and the bond strength of the coating to substrate was enhanced.

Apatites↗
PubMed2002

Carbonate apatite coating on titanium induced rapidly by precalcification.

Chemical treatments have been thought to be promised methods for improving bioactivity of titanium. In this work, the effect of precalcification with boiling saturated Ca(OH)2 solution on bioactivation of titanium was investigated. After precalcification and soaking in supersaturated Ca-P solution (SCP), calcium phosphate rapidly precipitated onto the surfaces of titanium, and after only three days an uniform apatite layer was found up to thickness of a few micrometers. The observation using scanning electron microscopy (SEM) showed that the coating was composed of a number of small crystal grains. The investigation by X-ray energy dispersion spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that the coating was Ca-deficient carbonate apatite. Based on the analyses for the surfaces and SCP, a mechanism of precipitation of apatite was proposed in thermal dynamics and kinetics.

Apatites↗
PubMed2002

Characterization of surface oxide films on titanium and bioactivity.

Biological properties of titanium implant depend on its surface oxide film. In the present study, the surface oxide films on titanium were characterized and the relationship between the characterization and bioactivity of titanium was studied. The surface oxide films on titanium were obtained by heat-treatment in different oxidation atmospheres, such as air, oxygen and water vapor. The bioactivity of heat-treated titanium plates was investigated by immersion test in a supersaturated calcium phosphate solution. The surface roughness, energy morphology, chemical composition and crystal structure were used to characterize the titanium surfaces. The characterization was performed using profilometer, scanning electronic microscopy, ssesile drop method, X-ray photoelectron spectroscopy, common Bragg X-ray diffraction and sample tilting X-ray diffraction. Percentage of surface hydroxyl groups was determined by X-ray photoelectron spectroscopy analysis for titanium plates and density of surface hydroxyl groups was measured by chemical method for titanium powders. The results indicated that heat-treatment uniformly roughened the titanium surface and increased surface energy. After heat-treatment the surface titanium oxide was predominantly rutile TiO(2), and crystal planes in the rutile films preferentially orientated in (1 1 0) plane with the highest density of titanium ions. Heat-treatment increased the amount of surface hydroxyl groups on titanium. The different oxidation atmospheres resulted in different percentages of oxygen species in TiO(2), in physisorbed water and acidic hydroxyl groups, and in basic hydroxyl groups on the titanium surfaces. The immersion test in the supersaturated calcium phosphate solution showed that apatite spontaneously formed on to the rutile films. This revealed that rutile could be bioactivated. The analyses for the apatite coatings confirmed that the surface characterization of titanium has strong effect on bioactivity of titanium. The bioactivity of the rutile films on titanium was related not only to their surface basic hydroxyl groups, but also to acidic hydroxyl groups, and surface energy. Heat-treatment endowed titanium with bioactivity by increasing the amount of surface hydroxyl groups on titanium and its surface energy.

Journal Article↗
PubMed2002

Dose-response and time course of specific IgE and IgG after single and repeated topical skin exposure to dry trimellitic anhydride powder in a Brown Norway rat model.

BACKGROUND: Trimellitic anhydride (TMA)-induced occupational asthma is thought to be associated with its ability to acylate proteins and to induce production of TMA-specific immunoglobulin (Ig)E. Though the respiratory tract is considered to be a major exposure route leading to airway sensitization, the potential role of dermal exposure producing asthmatic sensitization is not known. The present study examines the ability of dry TMA powder to sensitize Brown Norway rats when applied, topically, to the skin. METHODS: A patch of hair was carefully clipped with scissors on the rat's back. Dry TMA powder (0.3, 1.25, 5 and 20 mg) was administered on days 0, 7, 14 and 21, and the area occluded with surgical tape overnight after each application. Residual powder recovered from the occluded skin was analyzed by proton nuclear magnetic resonance and was still predominantly TMA. Circulating anti-TMA IgE and IgG were measured by ELISA. RESULTS: TMA elicited dose-dependent production of specific IgE and IgG. Specific antibodies were detectable 2 weeks after the first TMA exposure and peaked between 3 and 4 weeks. CONCLUSION: The data suggest that topical skin exposure to dry TMA powder can induce allergic/immunological sensitization as demonstrated by the production of specific antibodies.

Administration, Topical↗
PubMed2001

Tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis of human melanoma is regulated by smac/DIABLO release from mitochondria.

In previous studies we have shown that the sensitivity of melanoma cell lines to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis was determined largely by the level of expression of death receptor TRAIL receptor 2 on the cells. However, approximately one-third of melanoma cell lines were resistant to TRAIL, despite expression of high levels of TRAIL receptor 2. The present studies show that these cell lines had similar levels of TRAIL-induced activated caspase-3 as the TRAIL-sensitive lines, but the activated caspase-3 did not degrade substrates downstream of caspase-3 [inhibitor of caspase-activated DNase and poly(ADP-ribose) polymerase]. This appeared to be due to inhibition of caspase-3 by X-linked inhibitor of apoptosis (XIAP) because XIAP was bound to activated caspase-3, and transfection of XIAP into TRAIL-sensitive cell lines resulted in similar inhibition of TRAIL-induced apoptosis. Conversely, reduction of XIAP levels by overexpression of Smac/DIABLO in the TRAIL-resistant melanoma cells was associated with the appearance of catalytic activity by caspase-3 and increased TRAIL-induced apoptosis. TRAIL was shown to cause release of Smac/DIABLO from mitochondria, but this release was greater in TRAIL-sensitive cell lines than in TRAIL-resistant cell lines and was associated with down-regulation of XIAP levels. Furthermore, inhibition of Smac/DIABLO release by overexpression of Bcl-2 inhibited down-regulation of XIAP levels. These results suggest that Smac/DIABLO release from mitochondria and its binding to XIAP are an alternative pathway by which TRAIL induces apoptosis of melanoma, and this pathway is dependent on the release of activated caspase-3 from inhibition by XIAP and possibly other inhibitor of apoptosis family members.

Apoptosis↗
PubMed2001

The role of NF-kappa B in TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of melanoma cells.

Previous studies have shown that activation of NF-kappaB can inhibit apoptosis induced by a number of stimuli. It is also known that TNF-related apoptosis-inducing ligand (TRAIL) can activate NF-kappaB through the death receptors TRAIL-R1 and TRAIL-R2, and decoy receptor TRAIL-R4. In view of these findings, we have investigated the extent to which activation of NF-kappaB may account for the variable responses of melanoma lines to apoptosis induced by TRAIL and other TNF family members. Pretreatment of the melanoma lines with the proteasome inhibitor N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal (LLnL), which is known to inhibit activation of NF-kappaB, was shown to markedly increase apoptosis in 10 of 12 melanoma lines with death receptors for TRAIL. The specificity of results for inhibition of NF-kappaB activation was supported by an increase of TRAIL-induced apoptosis in melanoma cells transfected with a degradation-resistant IkappaBalpha. Furthermore, studies with NF-kappaB reporter constructs revealed that the resistance of melanoma lines to TRAIL-induced apoptosis was correlated to activation of NF-kappaB in response to TRAIL. TRAIL-resistant sublines that were generated by intermittent exposure to TRAIL were shown to have high levels of activated NF-kappaB, and resistance to TRAIL could be reversed by LLnL and by the superrepressor form of IkappaBalpha. Therefore, these results suggest that activation of NF-kappaB by TRAIL plays an important role in resistance of melanoma cells to TRAIL-induced apoptosis and further suggest that inhibitors of NF-kappaB may be useful adjuncts in clinical use of TRAIL against melanoma.

Apoptosis↗