Biomedical subjects

J P Li

Publications and source records attributed to J P Li.

At least 19 recordsLinked to original sources

PubMed2006

Cancellous bone from porous Ti6Al4V by multiple coating technique.

A highly porous Ti6Al4V with interconnected porous structure has been developed in our previous study. By using a so-called "Multiple coating" technique, the porous Ti6Al4V can be tailored to resemble cancellous bone in terms of porous structure and mechanical properties. A thin layer of Ti6Al4V slurry was coated on the struts of base porous Ti6Al4V to improve the pore structure. After two additional coating, pore sizes ranged from 100 microm to 700 microm, and the porosity was decreased from approximately 90% to approximately 75%, while the compressive strength was increased from 10.3 +/- 3.3 MPa to 59.4 +/- 20.3 MPa and the Young's modulus increased from 0.8 +/- 0.3 GPa to 1.8 +/- 0.3 GPa. The pore size and porosity are similar to that of cancellous bone, meanwhile the compressive strength is higher than that of cancellous bone, and the Young's modulus is between that of cancellous bone and cortical bone. Porosity, pore size and mechanical properties can be controlled by the parameters in such multiple coating processes. Therefore the porous Ti6Al4V with the characteristics of cancellous bone is expected to be a promising biomaterial for biomedical applications.

Alloys↗

PubMed2006

Heparan sulphate requirement in platelet-derived growth factor B-mediated pericyte recruitment.

HS (heparan sulphate) plays a key role in angiogenesis, by interacting with growth factors required in the process. It has been proposed that HS controls the diffusion, and thus the availability, of platelet-derived growth factor B that is needed for pericyte recruitment around newly formed capillaries. The present paper summarizes our studies on the importance of HS structure in this regulatory process.

Animals↗

PubMed2006

Heparanase neutralizes the anticoagulation properties of heparin and low-molecular-weight heparin.

BACKGROUND: Heparanase is a mammalian endo-D-glucuronidase that cleaves heparan sulfate (HS) in the extracellular matrix and cell surface. It is preferentially expressed by cells of the immune system and tumor cells. Heparanase overexpression in experimental tumor models results in increased angiogenesis and metastasis. Heparin and low-molecular weight heparin (LMWH) inhibit HS degradation by heparanase. OBJECTIVE: To investigate whether heparanase cleaves heparin and LMWH, and elucidate its effect on blood coagulation. METHODS: Heparin and LMWH were incubated with recombinant heparanase and subjected to measurements of molecular size (size exclusion chromatography) and anticoagulant activity (plasma APTT-activated thromboplastin time, and anti-Xa activity). APTT was also measured in plasma samples of transgenic mice overexpressing heparanase, in comparison with control mice. RESULTS: Incubation of heparin and LMWH with heparanase resulted in degradation of these substrates, as revealed by a significant decrease in their molecular weight. This was correlated with a marked suppression of the anticoagulant activity of heparin and LMWH, as indicated by a decreased effect on APTT and anti-Xa activity, respectively, when human plasma was added. Transgenic mice overexpressing heparanase exhibited a significantly shorter APTT than control mice. CONCLUSION: Heparanase is capable of degrading heparin and LMWH, so that its overexpression by tumor cells may contribute to heparin resistance, commonly occurring in cancer patients. In view of the complexity of the currently available heparanase activity assays, we propose an indirect approach to quantify heparanase activity by measuring the decrease in plasma APTT or anti-Xa activity exerted by the enzyme under the defined conditions.

Animals↗

PubMed2005

A novel porous Ti6Al4V: characterization and cell attachment.

For the first time, a highly porous strong Ti6Al4V was produced by using a "polymeric sponge replication" method. A polymeric sponge, impregnated with a Ti6Al4V slurry prepared from Ti6Al4V powders and binders, was subjected to drying and pyrolyzing to remove the polymeric sponge and binders. After sintering at a high temperature and under high vacuum, a porous Ti6Al4V was produced. Optical microscopical observation, environmental scanning electron microscopy observation (with energy-dispersive micro X-ray analysis), mechanical tests, and metallurgical analyses were performed on the obtained porous Ti6Al4V with regard to the porous structure (both macropores and micropores), mechanical properties, chemical composition, phase compositions, and cell attachment behavior. The porous Ti6Al4V made by this method had a three-dimensional trabecular porous structure with interconnected pores mainly ranging from 400 to 700 microm and a total porosity of about 90%. The compressive strength was 10.3 +/- 3.3 MPa and the elastic constant 0.8 +/- 0.3 GPa. MC3T3-E1 cells attached and spread well in the inner surface of pores. Being similar to cancellous bone with regard to both interconnected porous structure and mechanical properties, the resulting porous Ti6Al4V is expected to be a promising biomaterial for biomedical applications.

3T3 Cells↗

PubMed2005

Porous Ti6Al4V scaffolds directly fabricated by 3D fibre deposition technique: effect of nozzle diameter.

3D porous Ti6Al4V scaffolds were successfully directly fabricated by a rapid prototyping technology: 3D fibre deposition. In this study, the rheological properties of Ti6Al4V slurry was studied and the flow rate was analyzed at various pressures and nozzle diameters. Scaffolds with different fibre diameter and porosity were fabricated. ESEM observation and mechanical tests were performed on the obtained porous Ti6Al4V scaffolds with regard to the porous structure and mechanical properties. The results show that these scaffolds have 3D interconnected porous structure and a compressive strength which depends on porosity at constant fibre diameters and on the fibre diameter at constant porosity. These Ti6Al4V scaffolds are expected to be constructs for biomedical applications.

Alloys↗

PubMed2004

Factors having influence on the rheological properties of Ti6A14V slurry.

A highly porous Ti6Al4V could be produced with a porous polymeric sponge and Ti6Al4V slurry. However, the rheological properties of Ti6Al4V slurry appeared to be the key issue in the preparation of porous Ti6Al4V. In this study, factors having influence on the rheological properties of Ti6Al4V slurry were addressed in detail. Ti6Al4V powders, organic thickening agents (binders), dispersants, concentration of powder and pH values were optimised with regard to the rheological properties of Ti6Al4V slurry. The results show that Ti6Al4V powder with a mean diameter of 45 microm and spherical shape is beneficial for the preparation of Ti6Al4V slurry. Meanwhile binders with two ingredients, which decompose at different temperatures, have the advantage to keep the shape after debinding. The optimised procedure, based on the findings, made it possible to produce highly porous Ti6Al4V with reticulate porous structure. Porous Ti6Al4V produced by this way is expected to be a promising biomaterial for tissue engineering scaffolds and orthopaedic implant applications.

Alloys↗

PubMed2002

Building a mouse model hallmarking the congenital human cytomegalovirus infection in central nervous system.

To investigate the mechanisms that human cytomegalovirus (HCMV) can vertically transmit from the placenta of mice to infect their offspring in the central nervous system (CNS) and cause congenital anomalies, and in order to provide basic research for preparing HCMV vaccine, we have developed a new type of mouse model of HCMV congenital CNS infection. Pure strain mice were propagated after being infected with HCMV. Then the degree of infection by HCMV to offspring was determined. The experiment shows that in the infection groups the mortality of fetal mice and the fatality of neonatal mice in one week are higher than that of the control groups (P < or = 0.05). At the same time we investigated the CNS of fetus's mice whose mothers were infected by HCMV. Our results showed: 1. The virus was successfully isolated from their cerebral cortex. 2. The signal of HCMV hybridization print was found in their nervous cell through in situ hybridization. 3. Especially human herpes virus-like particles and inclusion bodies in the plasm of nerve cell were found in the tissue of their brain under the electron microscope. This new type of mouse model of HCMV inherent CNS infection will help prepare HCMV vaccine and research HCMV congenital infection in CNS.

Animals↗

PubMed2001

Characterization of the D-glucuronyl C5-epimerase involved in the biosynthesis of heparin and heparan sulfate.

The murine gene for the glucuronyl C5-epimerase involved in heparan sulfate biosynthesis was cloned, using a previously isolated bovine lung cDNA fragment (Li, J.-P., Hagner-McWhirter, A., Kjellén, L., Palgi, J., Jalkanen, M., and Lindahl, U. (1997) J. Biol. Chem. 272, 28158-28163) as probe. The approximately 11-kilobase pair mouse gene contains 3 exons from the first ATG to stop codon and is localized to chromosome 9. Southern analysis of the genomic DNA and chromosome mapping suggested the occurrence of a single epimerase gene. Based on the genomic sequence, a mouse liver cDNA was isolated that encodes a 618-amino acid residue protein, thus extending by 174 N-terminal residues the sequence deduced from the (incomplete) bovine cDNA. Comparison of murine, bovine, and human epimerase cDNA structures indicated 96-99% identity at the amino acid level. A cDNA identical to the mouse liver species was demonstrated in mouse mast cells committed to heparin biosynthesis. These findings suggest that the iduronic acid residues in heparin and heparan sulfate, despite different structural contexts, are generated by the same C5-epimerase enzyme. The catalytic activity of the recombinant full-length mouse liver epimerase, expressed in insect cells, was found to be >2 orders of magnitude higher than that of the previously cloned, smaller bovine recombinant protein. The approximately 52-kDa, similarly highly active, enzyme originally purified from bovine liver (Campbell, P., Hannesson, H. H., Sandbäck, D., Rodén, L., Lindahl, U., and Li, J.-P. (1994) J. Biol. Chem. 269, 26953-26958) was found to be associated with an approximately 22-kDa peptide generated by a single proteolytic cleavage of the full-sized protein.

Amino Acid Sequence↗

PubMed2001

The response of a thermoluminescent dosimeter to low energy protons in the range 30-100 keV.

This study demonstrates the thermoluminescence (TL) response of CaF2:Tm (commercial name TLD-300) to 30-100 keV protons which were generated by means of a Cockcroft-Walton accelerator. The phenomenon in which the total thermoluminescent output from CaF2:Tm (TLD-300) decreases with proton energy from 30 to 100 keV (with increase of LET) can be interpreted by the track structure theory (TST). The analysis of the glow peaks: P2 (131 degrees C), P3 (153.5 degrees C) and P6 (259 degrees C), of TLD-300 show the oscillatory decreasing phenomenon as a function of incident proton energy, which can be interpreted with the TST and the oscillatory emission of electrons in a thermoluminescent dosimeter (TLD) that is caused by resonant or quasi-resonant charge transfer in ion-atom interactions in this TLD-300.

Humans↗

PubMed2001

Toward a biotechnological heparin through combined chemical and enzymatic modification of the Escherichia coli K5 polysaccharide.

A process to generate glycosaminoglycans with heparin- and heparan sulfate-like sequences from the Escherichia coli K5 capsular polysaccharide is described. This polymer has the same structure as N-acetylheparosan, the precursor in heparin/ heparan sulfate biosynthesis. The process involves chemical N-deacetylation and N-sulfation, enzymatic conversion of up to 60% of the D-glucuronic acid to L-iduronic acid residues, and chemical O-sulfation. Because direct sulfation afforded unwanted 3-O-sulfated (instead of 2-O-sulfated) iduronic acid residues, a strategy involving graded solvolytic desulfation of chemically oversulfated C5-epimerized sulfaminoheparosans was assessed using persulfated heparin and heparan sulfate as model compounds. The O-desulfation process was shown to increase the anti-factor Xa activity of oversulfated heparin.

Animals↗

PubMed2001

Roles of 5-HT receptors in the release and action of secretin on pancreatic secretion in rats.

5-Hydroxytryptamine (serotonin, 5-HT) is a hormone and neurotransmitter regulating gastrointestinal functions. 5-HT receptors are widely distributed in gastrointestinal mucosa and the enteric nervous system. Duodenal acidification stimulates not only the release of both 5-HT and secretin but also pancreatic exocrine secretion. We investigated the effect of 5-HT receptor antagonists on the release of secretin and pancreatic secretion of water and bicarbonate induced by duodenal acidification in anesthetized rats. Both the 5-HT(2) receptor antagonist ketanserin and the 5-HT(3) receptor antagonist ondansetron at 1-100 microg/kg dose-dependently inhibited acid-induced increases in plasma secretin concentration and pancreatic exocrine secretion. Neither the 5-HT(1) receptor antagonists pindolol and 5-HTP-DP nor the 5-HT(4) receptor antagonist SDZ-205,557 affected acid-evoked release of secretin or pancreatic secretion. None of the 5-HT receptor antagonists affected basal pancreatic secretion or plasma secretin concentration. Ketanserin or ondansetron at 10 microg/kg or a combination of both suppressed the pancreatic secretion in response to intravenous secretin at 2.5 and 5 pmol x kg(-1) x h(-1) by 55-75%, but not at 10 pmol x kg(-1) x h(-1). Atropine (50 microg/kg) significantly attenuated the inhibitory effect of ketanserin on pancreatic secretion but not on the release of secretin. These observations suggest that 5-HT(2) and 5-HT(3) receptors mediate duodenal acidification-induced release of secretin and pancreatic secretion of fluid and bicarbonate. Also, regulation of pancreatic exocrine secretion through 5-HT(2) receptors may involve a cholinergic pathway in the rat.

Animals↗

PubMed2001

MEK inhibits secretin release and pancreatic secretion: roles of secretin-releasing peptide and somatostatin.

We investigated the mechanism of action of methionine enkephalin (MEK) on HCl-stimulated secretin release and pancreatic exocrine secretion. Anesthetized rats with pancreatobiliary cannulas and isolated upper small intestinal loops were perfused intraduodenally with 0.01 N HCl while bile and pancreatic juice were diverted. The effect of intravenous MEK on acid-stimulated secretin release and pancreatic exocrine secretion was then studied with or without coinfusion of naloxone, an anti-somatostatin (SS) serum, or normal rabbit serum. Duodenal acid perfusate, which contains secretin-releasing peptide (SRP) activity, was collected from donor rats with or without pretreatment with MEK, MEK + naloxone, or MEK + anti-SS serum, concentrated by ultrafiltration, and neutralized. The concentrated acid perfusate (CAP), which contains SRP bioactivity, was infused intraduodenally into recipient rats. MEK increased plasma SS concentration and inhibited secretin release and pancreatic fluid and bicarbonate secretion dose-dependently. The inhibition was partially reversed by naloxone and anti-SS serum but not by normal rabbit serum. In recipient rats, CAP increased plasma secretin level and pancreatic secretion. CAP SRP bioactivity decreased when it was collected from MEK-treated donor rats; this was partially reversed by coinfusion with naloxone or anti-SS serum. These results suggest that in the rat, MEK inhibition of acid-stimulated pancreatic secretion and secretin release involves suppression of SRP activity release. Thus the MEK inhibitory effect appears to be mediated in part by endogenous SS.

Animals↗

PubMed2001

Pancreatic phospholipase A2 from the small intestine is a secretin-releasing factor in rats.

A secretin-releasing activity exists in the upper small intestine and pancreatic juice in the rat and the dog. Group I pancreatic phospholipase A2 (PLA2) in canine pancreatic juice and porcine pancreatic PLA2 stimulate the release of secretin from both STC-1 cells and a secretin-producing cell (S cell)-enriched preparation isolated from rat duodenal mucosa. We investigated the distribution and release of pancreatic PLA2-like immunoreactivity in the gastrointestinal tract and the role of PLA2 on the release of secretin and pancreatic exocrine secretion in response to duodenal acidification in anesthetized rats. PLA2-like immunoreactivity was detected in the mucosa throughout the gastrointestinal tract. High concentrations of PLA2 were found in both the small intestine and the pancreas. Duodenal acidification significantly increased the release of PLA2 from the upper small intestine (385% over basal secretion). Intravenous infusion of an anti-PLA2 serum (anti-PLA2) dose-dependently inhibited the release of secretin and pancreatic exocrine secretion in response to duodenal acid perfusion. Preincubation of the concentrate of intestinal acid perfusate (10-fold) from donor rats with the anti-PLA2 significantly suppressed its stimulation of secretin release and pancreatic exocrine secretion in recipient rats. We conclude that pancreatic PLA2 also functions as a secretin-releasing factor in the small intestine that mediates acid-stimulated release of secretin in rats.

Animals↗

PubMed2001

Regulation of apoA1 gene expression with acidosis: requirement for a transcriptional repressor.

Serum apolipoprotein A(1) (apoA(1)) concentration is inversely correlated with the risk of premature atherosclerosis. Serum apoA(1) concentrations are regulated, in part, at the transcriptional level. ApoA(1) mRNA is synthesized primarily in the liver and small intestine, under the direction of a number of signaling molecules and tissue-specific regulatory elements. Previously, we demonstrated that extracellular acidosis suppresses apoA(1) mRNA levels at the level of transcription. Here we demonstrate that intracellular acidosis, in the absence of extracellular pH changes, represses apoA(1) promoter activity. Repression occurs through a pH responsive element (pH-RE) located within the apoA(1) gene promoter. Acidosis increases the specific DNA binding activity of a putative repressor protein within the immediate 5'-flanking region of the apoA(1) gene. The cis-element that binds the putative repressor protein contains a negative thyroid hormone response element (nTRE) located 3' and adjacent to the apoA(1) TATA box. Mutation of the nTRE/pH-RE abrogates protein binding and alters the activity of reporter genes controlled by this element. Repression by acidosis did not require de novo mRNA and protein synthesis. Inhibition of tyrosine kinase activity and diacylglycerol-stimulated protein kinase C (PKC) signaling pathways with tyrophostin A47 and phorbol myristate acetate, respectively, did not affect the repression of apoA(1) promoter activity with acidosis. These results suggest that transcriptional repression of the apoA(1) gene by alterations in ambient pH is associated with enhanced DNA binding activity of a repressor protein, through a mechanism which appears to be independent of de novo mRNA and protein synthesis, tyrosine kinase activity, or PKC activation.

Acidosis↗

PubMed2001

[Determination of salvianolic acid B in the radix of Salvia miltiorrhiza Bge. by HPLC].

OBJECTIVE: To develop an HPLC method for determining salvianolic acid B in radix of Salvia miltiorrhiza. METHOD: The sample was extracted with 75% methanol. ODS column was used with methanol-5% acetic acid solution (35:65) as mobile phase. Detection wavelength was 281 nm. RESULT: Salvianolic acid B was separated well. Good linearity of salvianolic acid B was obtained (r = 0.9997) within the range of 0.17-1.7 micrograms. The average recovery was 98.9%. Repeatability was good, and RSD was 1.82%. CONCLUSION: This method can be used for quality control of radix of Salvia miltiorrhiza.

Benzofurans↗

PubMed2000

Effect of amitriptyline on the messenger RNA of thyroid hormone-responsive genes in rat cerebral tissue.

To determine the molecular mechanisms of the potentiating effect of thyroid hormones (TH) on the therapeutic efficacy of tricyclic antidepressants (TCA), the expression of two known TH-responsive mRNAs was measured in control rats and rats treated with triiodothyronine (T3, 10 microg/100 g for 10 days), amitriptyline (10 mg/kg for 10 days), or combined T3 and amitriptyline. Northern blot analysis was carried out to measure the cerebral tissue content of a novel translational repressor (NAT-1) and another thyroid hormone-responsive (THR) mRNA. Rats treated with the combination of T3 and amitriptyline had significantly higher NAT-1 expression (2691.1+/-134.1 arbitrary units) than rats treated with T3 only (1688.5+/-77.8) or with amitriptyline only (1452.5+/-87.5) or the untreated control rats (731.3+/-23.0), P<0.01. Amitriptyline treatment did not alter the expression of THR mRNA or THR protein in either control or T3-treated rats. It is concluded that alterations in the expression of selective T3 responsive genes in cerebral tissue could be a mechanism of the known T3 potentiation of the therapeutic efficacy of TCA.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Interactions between Panax quinquefolium saponins and vitamin C are observed in vitro.

Inasmuch as the oxidation of low-density lipoprotein (Ox-LDL) may play a key role in the initiation and progression of atherosclerosis, it has become increasingly important to identify potential antioxidants. Panax quinquefolium saponins (PQS) are extracted from the stems and leaves of the North American form of ginseng, Panax quinquefolium. Our previous studies have indicated that PQS (0.25-1 mg/ml) can protect against oxidation of LDL in vitro. The purpose of the current work was to investigate the potential interaction of lower concentrations of PQS (1-100 microg/ml) with vitamin C on the reduction of LDL oxidation. LDL was isolated from the plasma of healthy human donors by sequential ultracentrifugation. Native LDL (0.05 or 0.2 mg/ml) was incubated with PQS and/or vitamin C for 30 min at 20 degrees C. Oxidative modification was initiated with 2 microM or 5 microM CuSO4 at 37 degrees C for (0-24 h. Pretreatment with PQS (100 microg/ml) reduced alterations in phospholipids, lipid peroxide levels and relative electrophoretic mobility of Ox-LDL. The presence of vitamin C (1-10 microM) significantly enhanced the protective effects of PQS. Pretreatment with PQS (1-100 microg/ml) resulted in concentration-dependent inhibition of LDL oxidation and prolongation of lag time as determined from measurements of conjugated lipid hydroperoxide content in Ox-LDL samples. Interestingly, the inhibitory actions of lower amounts of PQS (1 and 10 microg/ml) on the formation of conjugated dienes were significantly increased when vitamin C (0.1 or 1 microM) was present. In conclusion, our results suggest that PQS not only have direct antioxidant property but at low concentrations, their actions can be enhanced by vitamin C.

Ascorbic Acid↗

PubMed2000

Biosynthesis of heparin/heparan sulfate: kinetic studies of the glucuronyl C5-epimerase with N-sulfated derivatives of the Escherichia coli K5 capsular polysaccharide as substrates.

The D-glucuronyl C5-epimerase involved in the biosynthesis of heparin and heparan sulfate was investigated with focus on its substrate specificity, its kinetic properties, and a comparison of epimerase preparations from the Furth mastocytoma and bovine liver, which synthesize heparin and heparan sulfate, respectively. New substrates for the epimerase were prepared from the capsular polysaccharide of Escherichia coli K5, which had been labeled at C5 of its D-glucuronic and N-acetyl-D-glucosamine moieties by growing the bacteria in the presence of D-[5-(3)H]glucose. Following complete or partial ( approximately 50%) N-deacetylation of the polysaccharide by hydrazinolysis, the free amino groups were sulfated by treatment with trimethylamine.SO(3)complex, which yielded products that were recognized as substrates by the epimerase and released tritium from C5 of the D-glucuronyl residues upon incubation with the enzyme. Comparison of the kinetic properties of the two substrates showed that the fully N-sulfated derivative was the best substrate in terms of its K(m)value, which was significantly lower than that of its partially N-acetylated counterpart. The V(max)values for the E.coli polysaccharide derivatives were essentially the same but were both lower than that of the O-desulfated [(3)H]heparin used in our previous studies. Surprisingly, the apparent K(m)values for all three substrates increased with increasing enzyme concentration. The reason for this phenomenon is not entirely clear at present. Partially purified C5-epimerase preparations from the Furth mastocytoma and bovine liver, respectively, behaved similarly in terms of their reactivity towards the various substrates, but the variation in apparent K(m)values with enzyme concentration precluded a detailed comparison of their kinetic properties.

Animals↗