Giant panda׳s tooth enamel: Structure, mechanical behavior and toughening mechanisms under indentation.

The giant panda׳s teeth possess remarkable load-bearing capacity and damage resistance for masticating bamboos. In this study, the hierarchical structure and mechanical behavior of the giant panda׳s tooth enamel were investigated under indentation. The effects of loading orientation and location on mechanical properties of the enamel were clarified and the evolution of damage in the enamel under increasing load evaluated. The nature of the damage, both at and beneath the indentation surfaces, and the underlying toughening mechanisms were explored. Indentation cracks invariably were seen to propagate along the internal interfaces, specifically the sheaths between enamel rods, and multiple extrinsic toughening mechanisms, e.g., crack deflection/twisting and uncracked-ligament bridging, were active to shield the tips of cracks from the applied stress. The giant panda׳s tooth enamel is analogous to human enamel in its mechanical properties, yet it has superior hardness and Young׳s modulus but inferior toughness as compared to the bamboo that pandas primarily feed on, highlighting the critical roles of the integration of underlying tissues in the entire tooth and the highly hydrated state of bamboo foods. Our objective is that this study can aid the understanding of the structure-mechanical property relations in the tooth enamel of mammals and further provide some insight on the food habits of the giant pandas.

Possible involvement of protein kinase C and cyclic AMP-dependent protein kinase in the sodium fluoride-mediated inhibition of cyclic nucleotide accumulation in smooth muscle cells.

Treatment of rat thoracic aortic smooth muscle cells (A-10) with sodium fluoride (NaF) resulted in inhibition of beta-adrenergic agonist--and forskolin-induced cAMP and ANF-induced cGMP accumulation and stimulation of diacylglycerol (DAG) accumulation. The concentration of NaF and treatment times required to mediate these inhibitory effects were similar to those observed for stimulation of DAG accumulation. Treatment of the cells with NaF also resulted in a loss of [3H]phorbol dibutyrate (PDBu) binding in the cytosolic portion of the cells. In addition, pre-treatment of the cells with NaF resulted in an increase in the adenylate cyclase activity. Pertussis toxin (PT) pre-treatment of the cells did not significantly affect NaF-mediated effects. Pre-treatment of the cells with protein kinase C (PKC) inhibitor staurosporin partially reversed NaF-mediated inhibition of cyclic nucleotides accumulation. These data suggest that inhibition of the formation of agonist-induced cyclic nucleotides by NaF may be due to the formation of DAG and cAMP which lead to the activation of PKC and cAMP-PK, resulting in phosphorylation of key regulatory protein(s) in the cyclic nucleotides pathway.

Application of membrane-based dendrimer/DNA complexes for solid phase transfection in vitro and in vivo.

In this study a general description of the use of solid support membranes as the device for DNA delivery mediated by PAMAM dendrimers is presented. In contrast to the other DNA carriers, dendrimer/DNA complexes retain the ability to transfect after drying, which enabled coating or incorporation of complexes into poly(DL-lactide-co-glycolide) or collagen-based bioerodable membranes. These studies provide support for the use of this technology for in vitro and in vivo transfection of skin cells. Expression of luciferase or green fluorescent protein from pCF1-Luc and pEGFP1 plasmids indicated that dendrimer/DNA complexes can mediate transfection after dissociation from the solid support and/or when retained on the surface of the membranes. Modification of the membranes by incorporation of an anionic lipid, phosphatidyl glycerol (PG) at 1-5% concentrations, resulted in more efficient in situ transfection, particularly with dendrimer/DNA complexes formed at the low charge ratios (1-5). We also report data supporting the feasibility of membrane-based dendrimer/DNA complexes, particularly formed at lower than neutralizing conditions, for topical in vivo delivery of DNA to hairless mouse skin.

Thrombin-stimulated growth, clustering, and collagen lattice contraction of human gingival fibroblasts is associated with its protease activity.

BACKGROUND: Thrombin is a serine protease produced following gingival tissue injury or inflammation. It regulates the functional behavior of injury-neighboring cells via the activation of specific protease-activated receptors (PAR). Thrombin's role in gingival tissue healing and inflammatory response processes is not yet well understood. METHODS: We investigated the effects of thrombin on gingival fibroblast (GF) growth [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay], collagen lattice contraction, and associated morphological changes. RESULTS: Thrombin (>1 U/ml), but not thrombin receptor (PAR-1) agonist peptide (SFLLRN, single letter amino acid code, abbreviated as TRAP, 1 to 50 microg/ml), stimulated the growth and clustering of cultured human GF in vitro. Growth-stimulatory effects of thrombin were inhibited by D-Phe-Pro-ArgCH2Cl (PPACK), a serine protease inhibitor. By contrast, trypsin (>10 microg/ml), a PAR-2 activator, suppressed the growth of GF. Thrombin (>0.2 U/ml) and TRAP (10 to 25 microg/ml), but not trypsin, prostaglandin E2 (0.01 to 0.5 microg/ml), or bovine serum albumin (BSA) (1 to 80 microg/ml), induced the GF-populated collagen lattice contraction within 30 to 60 minutes of exposure. The thrombin-induced collagen lattice contraction was inhibited by PPACK (20 microg/ml) and an actin filament polymerization inhibitor, cytochalasin B (1 microg/ml). The collagen lattice contraction induced by TRAP was also inhibited by cytochalasin B, but not by PPACK. Using a reverse-transcriptase polymerase chain reaction (RT-PCR), the expression of PAR-1, and to a lesser extent PAR-3, was observed for human GF, although little PAR-2 and PAR-4 expression was noted. CONCLUSIONS: These results indicate that thrombin is important in periodontal wound healing and inflammatory processes by promoting the growth and contraction of GF. The stimulatory effects of thrombin are associated with its protease activation of thrombin receptors.

Electron-capture gas chromatographic determination of cyanide, iodide, nitrite, sulfide, and thiocyanate anions by phase-transfer-catalyzed derivatization with pentafluorobenzyl bromide.

A sensitive gas chromatographic method has been established for the simultaneous determination of biologically active inorganic anions, including cyanide, iodide, nitrite, sulfide, and thiocyanate anions as their volatile organic derivatives. The method is based on the formation of ion pairs from the anions and a complex cryptand and on the resulting neutral ion-pair partition to an organic phase for derivatization with pentafluorobenzyl bromide. Several parameters affecting the partition and derivatization of the anions were investigated. Individual and simultaneous determination of the anions can be achieved at sub-nmol levels with an electron-capture detector. Partial application of the method for the analysis of cyanide, nitrite, and thiocyanate in real samples proved satisfactory.

Determination of thiocyanate anion by high-performance liquid chromatography with fluorimetric detection.

A simple and sensitive high-performance liquid chromatographic (HPLC) method was established for the trace determination of thiocyanate anion as a fluorogenic derivative. The method is based on the chemical derivatization of thiocyanate anion with 3-bromomethyl-7-methoxy-1,4-benzoxazin-2-one. The resulting derivative was separated by a Nova-Pak C18 reversed-phase column. Optimization conditions for the derivatization of thiocyanate anion were investigated by HPLC with fluorimetric detection. The linear range for the quantitation of thiocyanate anion was 1-0.05 nmol in 0.1 mL of sample; the detection limit (with a signal-to-noise ratio of 5) of a 20-microL injected aliquot was approximately 3.3 +/- 1.2 fmol. Application of the method to the analysis of thiocyanate anion in saliva and plasma proved to be feasible.

[Pharmacokinetics of harringtonine liposomes in rabbits].

After i.v. free harringtonine (FH) and harringtonine liposomes (HL) with high and low encapsulation percentage (En%) to rabbits, their blood concentrations were determined by reverse-phase HPLC. The blood concentration-time curves were shown to fit a two-compartments open model. FH: T1/2 alpha = 1.32 +/- 0.24, T1/2 beta = 32 +/- 6 min; Low En % HL: T1/2 alpha = 4.12 +/- 0.25, T1/2 beta = 106 +/- 5 min; High En % HL: T1/2 alpha = 9.4 +/- 1.2, T1/2 beta = 209 +/- 5 min.

Detection of hepatitis C virus RNA in peripheral blood mononuclear cells and in saliva.

The nested polymerase chain reaction (PCR) technique was applied to investigate hepatitis C virus (HCV) RNA in the peripheral blood mononuclear cells (PBMCs), saliva, and serum of patients with chronic type C hepatitis. The specificity of the amplified products was analyzed and confirmed by agarose gel electrophoresis, Southern blot hybridization, and restriction endonuclease pattern analysis. HCV RNA was detectable in the PBMCs of 24% (12/50) of the patients. The HCV RNA detected in PBMCs was not due to the contamination from plasma, since no viral sequences could be detected in the third washing of PBMCs. Of the 12 patients with HCV RNA in PBMCs, five were negative for HCV RNA sequences in the serum. Thus the presence of HCV RNA in PBMCs was not strictly correlated to the results for sera. Among 25 patients with HCV RNA in their saliva, 18 were negative for PBMCs. Among 25 patients without HCV RNA in their saliva, five had HCV RNA in PBMCs. In conclusion, PBMCs are an extrahepatic target for chronic HCV infection. However, we do not suggest that PBMCs act as a vehicle for carrying HCV to saliva, since the presence of HCV RNA in PBMCs and in saliva was not closely correlated.

Determination of thiocyanate anion as an organic derivative by gas chromatography.

A simple and sensitive gas chromatographic method has been established for the determination of biologically active thiocyanate anion as pentafluorobenzyl thiocyanate. The method is based on the partition of an ion-pair from the thiocyanate anion and a complex crypstand to a benzene layer for derivatization with pentafluorobenzyl bromide. The resulting derivative was analyzed by gas chromatography with electron capture detection. The quantitation range for thiocyanate anion was over 0.086 and 3.45 nmol. The detection limit of thiocyanate in 0.2 ml sample is about 34 pmol. The effects of several parameters such as base or acid, reaction time and the amount of pentafluorobenzyl bromide were evaluated for the optimization of partition and derivatization of thiocyanate anion. Application of the method to the analysis of thiocyanate in waste water and human saliva proved to be feasible.

[Distribution of harringtonine positively and negatively charged liposome in rat tissues].

Distribution of harringtonine positively and negatively charged liposome (HL(+), HL(-)) and harringtonine free drug (FH) in rat tissues were measured by HPLC. Their LD50 in mice were compared. The results showed that distribution of HL(+), HL(-), In vivo may be changed, that the amount of HL(+), HL(-) was increased in the liver, lung, and spleen and in these tissues it was 2-30-fold higher than that of HF after iv 2 h. HL(+), HL(-) may aid to permeate through the blood-brain, blood-testicle barrier, and to reduce acute lethal toxicity. Areas under the time curve of HL(+), HL(-) in brain and testis within 2 h were 2-4.5 times as much as those of HF. There were significant differences in the fate between negatively and positively charged liposomes in vivo.

Detection of HCV RNA in saliva, urine, seminal fluid, and ascites.

Approximately half of the patients with type C hepatitis do not have a history of parenteral exposure. The route of nonparenteral infection remains unknown. To evaluate the possible role of body fluids, the existence of hepatitis C virus (HCV) RNA in saliva, urine, seminal fluid, and ascites was examined by "nested" polymerase chain reaction (PCR). Amplification of the HCV 5' noncoding sequences was carried out. The amplified product was confirmed by Southern blot hybridization and restriction endonuclease digestion. Among 34 patients with chronic liver disease who were positive for anti-HCV and serum HCV RNA, the prevalence of HCV RNA in body fluids was 100% (7/7) in ascites, 48% (15/31) in saliva, 24% (4/17) in seminal fluid, and 7% (2/29) in urine. The body fluids collected from 3 healthy subjects and 5 patients with chronic liver disease who were positive for anti-HCV but negative for serum HCV RNA were all negative for HCV RNA. Hence, the potential infectivity of body fluids in patients testing negative for serum HCV RNA can probably be discounted. Conversely, the presence of HCV RNA in saliva and seminal fluid of patients positive for serum HCV RNA suggests sexual and household contact as likely modes of nonparenteral transmission of type C hepatitis. Furthermore, the high prevalence of HCV RNA in ascites and saliva may have important implications in medical and dental practice.

Studies of a novel human thrombomodulin immobilized substrate: surface characterization and anticoagulation activity evaluation.

Immobilization of the anticoagulative or antithrombogenic biomolecule has been considered as one of the important methods to improve the blood compatibility of artificial biomaterials. In this study, a novel immobilization reaction scheme was utilized to incorporate the human thrombomodulin, an endothelial cell associated glycoprotein, onto the cover glass surface with an aim to develop an anticoagulative substrate. Trichlorotriazine and amino-terminated silane were employed as the coupling agents, while the polyethylene glycol with a molecular weight of 1500 was used as the spacer in this reaction scheme. Protein C activation assay indicated the immobilized human thrombomodulin still has this coenzymatic activity but is lower, possibly due to the conformation variation by the coupling agents. In vitro platelet adhesion assay has demonstrated the surface with immobilized human thrombomodulin is much less platelet-activating than others. Therefore, the novel reaction scheme proposed here is very promising for future development of an anticoagulative silicon or cover glass substrate (e.g. implantable sensor or biochip) by the immobilization of antithrombogenic protein, such as the human thrombomodulin in this study.