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At least 127 records · Page 7Linked to original sources
PubMed2006

The effect of crystallinity on strength development of alpha-TCP bone substitutes.

Alpha phase tricalcium phosphates (alpha-TCP) were produced using a solid-state reaction method and milled for various periods of time. The resulting four materials were alpha-TCPs, ranging in crystalline content. Powders were exposed to X-ray diffraction for material identification as well as for use in crystallinity and purity calculations. Powder particle size was investigated using laser diffraction. Materials were mixed with 2.5% Na(2)HPO(4) solution to initiate the hydration of alpha-TCP to calcium-deficient hydroxyapatite (CDHA). Isothermal calorimetry was performed to observe thermal response of the powders over a period of time. During the reaction process, at various time points up to 216 h, the material was compression tested to observe strength development. Materials proved to be predominantly alpha phase, while amorphous content determined by XRD varied. Reactivity, as measured by isothermal calorimetry, varied with crystallinity of the alpha-TCP powder. Speed of strength development did not change except for the most finely ground powder. In addition, crystal size of the CDHA was changed only in the product formed from the most highly ground material. It is proposed that increasing reactivity of alpha-TCP cements does not result in a corresponding increase in rate of strength development until there is sufficient supersaturation to produce significant crystal nucleation.

Bone Substitutes↗
PubMed1996

Studies on the ossification of compound transplantation of porous TCP ceramics and bone marrow.

Following the culture of human red marrow with porous TCP ceramics in vitro, a large amount culturing marrow cells adhered well to the surface and inner wall of TCP ceramics and spread well over the dish bottom 4 weeks after cultivation. After the compound transplantation of porous TCP ceramics with red marrow into quadriceps femoris muscle of rabbits, a huge amount of new bone and marrow formed in these sites on and in the ceramics 4 weeks after transplantation. These results showed an excellent biocompatibility between TCP ceramics and marrow and an excellent osteogenic effect in the compound transplantation. The mechanism of ossification and clinical significance about the compound transplantation were discussed.

Animals↗
PubMed2007

Influence of oxide-based sintering additives on densification and mechanical behavior of tricalcium phosphate (TCP).

In this research, we studied and analyzed the effects of four different oxide-based sintering additives on densification, mechanical behavior, biodegradation and biocompatibility of tricalcium phosphate (TCP) bioceramics. Selective sintering additives were introduced into pure TCP ceramics, in small quantities, through homogeneous mixing, using a mortar and pestle. The consequent powders of different compositions were pressed into cylindrical compacts, uniaxially and sintered at elevated temperatures, 1150 degrees C and 1250 degrees C, separately in a muffle furnace. X-ray powder diffraction technique was used to analyze the phase-purity of TCP after sintering. Hardness of these sintered specimens was evaluated using a Vickers hardness tester. Sintered cylindrical samples were tested under uniaxial compressive loading, as a function of composition to determine their failure strength. Biodegradation studies conducted using simulated body fluid under dynamic environment, revealed that these additives could control the rate of resorption and hardness degradation of TCP ceramics.

Absorbable Implants↗
PubMed1989

Neuroprotective effects of MK-801, TCP, PCP and CPP against N-methyl-D-aspartate induced neurotoxicity in an in vivo perinatal rat model.

Three non-competitive antagonists (MK-801, TCP, PCP) and one competitive antagonist (CPP) of N-methyl-D-aspartate (NMDA) receptors, were compared for their ability to antagonize neurotoxic actions of NMDA injected into the brains of 7-day-old rats. Unilateral intracerebral injection of NMDA (25 nmol/0.5 microliters) into the corpus striatum of pups consistently produced severe confluent neuronal necrosis in the striatum extending into the dorsal hippocampus and overlying neocortex. The distribution of damage corresponded to the topography of NMDA type glutamate receptors in the vulnerable regions. With this lesion in developing brain, the weight of the injected hemisphere 5 days later can be used as a quantitative measure of brain injury. Intraperitoneal administration of MK-801 (0.02-42.0 mumol/kg), TCP (3.5-54.0 mumol/kg), PCP (1.0-41.0 mumol/kg), and CPP (1.0-60.0 mumol/kg) 15 min after NMDA injection had prominent dose-dependent neuroprotective effects. MK-801 was 14 times more potent than other compounds tested and the 50% protective dose (PD50, that dose which reduced damage by 50% relative to untreated NMDA-injected controls) was 0.63 mumol/kg. Corresponding values for CPP, PCP, and TCP were 8.84, 10.85, and 24.05 mumol/kg respectively. The lowest dose of MK-801 that provided significant protection was 0.2 mumol/kg (0.04 mg/kg, 37.9 +/- 4.6% protection). Four mumol/kg (0.8 mg/kg) of MK-801 completely protected against NMDA-mediated damage. The study provides the first direct in vivo comparison of the neuroprotective abilities of these compounds. Systemic administrations of MK-801, TCP, PCP, and CPP all limit NMDA-induced neuronal injury in this model. The susceptibility of the immature brain to the neurotoxicity of NMDA provides a sensitive, reproducible, and quantitative in vivo system for comparing the effectiveness of drugs with protective actions against excitotoxic neuronal injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Genetic organization and sequence of the promoter-distal region of the tcp gene cluster of Vibrio cholerae.

The nucleotide sequence of the promoter distal region of the major operon associated with biosynthesis of TCP, the toxin coregulated pilus of Vibrio cholerae has been determined. The genes tcpR, tcpD, tcpS, tcpT, tcpE and tcpF are organized to permit translational coupling and are followed by an inverted repeat structure which is likely to act as a strong Rho-independent terminator. TcpS and TcpF possess N-terminal signal sequences and would be expected to be periplasm and outer membrane located, respectively. TcpT and, to a lesser extent, TcpE show homology to protein transport and secretion proteins identified in a number of other bacteria. TcpR and TcpD are also predicted to be localized in the membrane based on their hydrophobicity profiles. In the case of TcpD, this may be in the outer membrane, as the N terminus is reminiscent of the TcpA signal sequence processed by TcpJ. Taken together with other data on the tcp region, it is clear that the types of proteins involved in the biogenesis of TCP are, at least in some cases, related to those associated with type-4 pilus biosynthesis but differ markedly from those for other well-described fimbrial systems, such as Type I, K88, K99 or Pap pili. The complete sequence data for TCP biosynthesis-controlling genes are now available and represent the only complete example of a type-4 pilus-like system.

Amino Acid Sequence↗
PubMed1994

Identification of a Vibrio cholerae ToxR-activated gene (tagD) that is physically linked to the toxin-coregulated pilus (tcp) gene cluster.

The toxin-coregulated pilus (TCP)-encoding gene cluster (tcp) specifies a type-IV pilus that is a major colonization determinant of Vibrio cholerae. We have identified a gene 200 bp upstream from the tcp cluster that requires ToxR for expression. We have designated this gene tagD (ToxR-activated gene) and have shown that tagD is encoded on a 600-nt transcript. The deduced tagD product is a 164-amino-acid polypeptide (20 kDa). Interestingly, TagD shares a high degree of similarity to a protein of Streptococcus sanguis 12 that is thought to play a role in fimbriae synthesis or assembly. The high degree of similarity between tagD and the Ss 12 protein provides preliminary evidence that tagD represents an additional member of the tcp cluster.

Amino Acid Sequence↗
PubMed1996

Comparison of the promoter proximal regions of the toxin-co-regulated tcp gene cluster in classical and El Tor strains of Vibrio cholerae O1.

A physical map has been constructed of the 5-kb XbaI fragment encoding the promoter proximal of region the tcp gene cluster encoding the toxin-coregulated pilus (TCP) of Vibrio cholerae. This fragment contains the major regulatory regions for TCP. Comparison of the nucleotide (nt) sequences from strains of the classical and El Tor biotypes demonstrates that the regions are essentially identical, with several notable exceptions. The intergenic regions, between tcpI and tcpP, and between tcpH and tcpA, show significant sequence divergence which may account for the biotype-related differences in TCP, since this is the location of the major promoter sequences. The C-terminal coding regions of the major pilin subunit, TcpA, also differ. Southern hybridization analyses suggest that the tcpA nt sequence is conserved within a biotype, and Western blot analysis suggests that the two forms of TcpA are antigenically different, but related. Besides tcpA, tcpB, tcpH and tcpI, the genes encoding two additional proteins, TcpP and TcpQ, but not previously defined, were also identified. TcpH and TcpI have been previously suggested to be regulatory proteins but homology data imply that TcpI is a methyl-accepting chemotaxis protein (MCP), as recently reported [Harkey et al., Infect. Immun. 62 (1994) 2669-2678], and TcpH is predicted to be a periplasmic or exported protein. TcpP is thought to be a trans-cytoplasmic membrane (CM) protein which may have a regulatory role.

Amino Acid Sequence↗
PubMed1992

Concerted evolution of the mouse Tcp-10 gene family: implications for the functional basis of t haplotype transmission ratio distortion.

The mouse Tcr locus is defined by its central role in the transmission ratio distortion phenotype characteristic of t haplotypes. A molecular candidate for Tcr has been identified in the form of a gene--Tcp-10b--expressed during spermatogenesis. Tcp-10b is one member of a multigene family present in two to four copies on different homologs of chromosome 17. The coding regions of the Tcp-10 genes present within two inbred strains were compared with those of the tw5 haplotype. The various gene family members are highly conserved relative to each other with a minimum nucleotide identity of 98.6% in all pairwise comparisons. Maximal parsimony analysis indicates that the Tcp-10 gene family has evolved in a concerted manner with the obliteration of nearly all individual gene-specific characteristics. As a consequence, the candidate for the full-length mutant Tcr gene product is distinguished by only a single, highly conservative, amino acid change. The data are consistent with the hypothesis that the effector of mutant Tcr activity is a second, alternatively spliced product that is expressed in a haploid- and allele-specific manner.

Alleles↗
PubMed1990

Identification and characterization of a high-affinity glutamate-controlled TCP binding site in rat brain postsynaptic densities.

The kinetic and equilibrium binding parameters of the phencyclidine receptor ligand [3H]N-[1-(2-thienyl)cyclohexyl]piperidine (TCP) to a postsynaptic density (PSD) subcellular fraction from rat brain were investigated. A single site was found, which was identified as the high-affinity TCP binding site by competition with dibenzocycloalkenimine (MK-801). In contrast, [3H]TCP binds to two sites on the plasma membrane fraction used as a precursor for PSD; on both fractions, [3H]TCP binding responds to glutamate by an increase of the association rate, the dissociation constant and the number of sites being unchanged. In the PSD fraction [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), an antagonist specific for the N-methyl-D-aspartate (NMDA) site, bound to high- and low-affinity sites. These results ascertain the presence and identity of synaptic NMDA-gated ion channels, which are assumed in the current hypothesis about excitotoxicity, long-term potentiation and learning.

Animals↗
PubMed2005

Influence of magnesium doping on the phase transformation temperature of beta-TCP ceramics examined by Rietveld refinement.

The influence of Mg doping in Ca(3)(PO(4))(2) on the transformation temperature of beta-tricalcium phosphate (beta-TCP) to alpha-tricalcium phosphate (alpha-TCP) was examined. A maximum substitution by 14 mol% of Mg(2+) on Ca(2+) sites in the beta-TCP structure was determined for powders calcinated at 1025+/-10 degrees C. X-ray powder diffraction analysis (XRPD) in combination with Rietveld method (TOPAS 2.1) was employed for quantitative phase analysis and structural refinement. The synthesized and characterized Mg-doped samples were sintered in air atmosphere in a vertical tube furnace at suitable temperatures ranging from 1460 to 1680 degrees C and subsequently quenched to room temperature, in order to stabilize alpha-TCP. The beta to alpha transformation temperatures were determined by differential temperature analysis and XRPD analysis.

Biocompatible Materials↗
PubMed2006

In vitro biological efficiency of tenocyclidine-TCP and its adamantane derivative TAMORF.

Tenocyclidine-TCP showing a broad spectrum of pharmacological activity including antidotal effect in organophosphorus compounds poisoning, radioprotective and anticancer effects. We investigated in vitro interactions of TCP and its adamantane derivative--TAMORF with human erythrocyte acetylcholinesterase (AChE). Moreover, their genotoxicity and radioprotective activity on human white blood cells were studied using the alkaline comet assay, viability testing and the analysis of the structural chromosome aberrations. The tested compounds were found to be weak inhibitors of AChE, for TCP IC(50)=1 x 10(-5)M and for TAMORF IC(50)>1 x 10(-3)M, without reactivating and protective effects on AChE inhibited by soman. Results suggest that TCP modified by the replacement of the cyclohexyl ring with an adamantly ring and piperidine with morpholine group (TAMORF) have lower toxicity. Both compounds possess low cytotoxicity and radioprotective activity, but TAMORF also shows cell growth inhibitory effects. To clarify differences in their biological efficiency observed in vitro and in vivo, additional analyses are necessary. Since TAMORF was found to significantly inhibit cell growth and proliferation in vitro, it is reasonably to consider it as a source molecule promising for further modifications and development of more potent substances with antitumor properties rather then radioprotector or antidote in organophosphorus poisoning.

Adamantane↗
PubMed2002

Decreased density of [3H]TCP binding following antipsychotic drug withdrawal in rats.

Antipsychotic drugs have been reported to increase the expression of subunits of the NMDA receptor at the level of mRNA but it is not clear whether such effects are apparent at the level of the radioligand binding or receptor protein. Therefore, we examined the effect of treatment of, and withdrawal from, haloperidol, chlorpromazine, olanzapine or clozapine on the binding of [3H]N-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP ) to the open ion channel of the NMDA receptor in rat caudate-putamen, hippocampus and frontal cortex. [3H]TCP binding was not significantly different in the caudate-putamen, hippocampus and cortex after three months of treatment with any antipsychotic drug. There were significant decreases in [3H]TCP binding in rat caudate-putamen and cortex, but not hippocampus, one month after ceasing treatment. Decreases in the caudate-putamen were detected in rats previously treated with chlorpromazine (0.1 mg/kg/day) and clozapine (0.1 and 1.0 mg/kg/day). In the cortex, decreases in [3H]TCP binding were also detected in rats previously treated with olanzapine (0.1 mg/kg/day) for three months. These data suggest that changes in the NMDA receptor associated ion channels occur following antipsychotic drug withdrawal.

Animals↗
PubMed2002

In vitro-cultivation of human periosteum derived cells in bioresorbable polymer-TCP-composites.

Bone replacement materials for reconstruction of bone defects must be biocompatible and biodegradable and must have osteoconductive or even osteogenic potential. Ideally, their shape should also be adaptable to the defect and they should possess long-term adaptability to the biomechanical situation at the implantation site. Human mesenchymal stem cells of the cambium layer of the periosteum were cultivated, placed in a fibrin suspension on a preformed carrier structure (PGLA polymer + beta-TCP), and cultivated under conditions of osteogenic differentiation. After 10, 20, 30, and 40 days, histological examination was performed, alkaline phosphatase activity and levels of osteocalcin, DNA, and collagen were determined, and the influence of addition of TGF-beta1 at a concentration of 5 ng/ml to the culture medium was investigated. Demonstration of bone-specific marker proteins indicated that the in vitro combination of mesenchymal stem cells, PGLA polymer, beta-TCP, and fibrin resulted in de-novo synthesis of human preosseous tissue, while addition of TGF-beta1 resulted in greater new bone formation with significantly higher concentrations of marker proteins. Histological examination showed the presence of newly formed bone at the surface of the implant. As compared with the use of structured TCP or hydroxyapatite implants as in earlier works, use of a combination of autologous cell material, PGLA polymer, and beta-TCP results in a malleable, vital implant that is adaptable to the bone defect. This combination thus may represent a new option for the treatment of bone defects.

Alkaline Phosphatase↗
PubMed1998

Sintering of TCP-TiO2 biocomposites: influence of secondary phases.

TCP-TiO2 ceramic biocomposites with various alpha-to-beta TCP ratios can be prepared by quenching the alpha phase. The presence of dopants (Ca, P, or Na) leads to the precipitation of secondary phases, which decreases the densification of titania. In the system TCP-TiO2, there is a eutectic with a composition of 63 wt% TCP-37 wt% TiO2 at a temperature of 1380 degrees C.

Biocompatible Materials↗
PubMed2001

Effects of thienylphencyclidine (TCP) on seizure activity and brain damage produced by soman in guinea-pigs: ECoG correlates of neurotoxicity.

The capacity of thienylcyclohexylpiperidine (TCP), a non-competitive blocker of the N-methyl-D-aspartate (NMDA) receptor, to counteract the convulsant, lethal, and neuropathological effects of 2 x LD50 of soman (an irreversible inhibitor of cholinesterase) was investigated in guinea-pigs treated by pyridostigmine and atropine sulphate. The effects of a weak dose of TCP (1 mg/kg) used in the present study globally reproduced those previously obtained with a higher dose (2.5 mg/kg; [Neurotoxicology 15 (1994) 837]): TCP was again most protective when given curatively within the first hour of soman-induced seizures. In this condition, (a) paroxysmal activity ceased in 10-20 min, (b) all the animals survived, (c) the majority of them recovered remarkably well and did not show any brain damage 24 h after the intoxication, and (d) the minimal duration of seizure activity normally required for producing soman-induced brain damage in other pharmacological environments was increased from 10 to 40 min to 80 min. Strikingly, when TCP was given 120 min after seizure onset, it failed to show any anticonvulsant activity but still provided neuroprotection in the hippocampus. The present study also gives additional evidence (see [Neurotoxicology 21 (4) (2000) 521]) that in soman poisoning, (a) the development of brain damage depends on the occurrence of ECoG seizures, (b) the topographical distribution of lesions depends on seizure duration, and (c) an increase of the relative power in the lowest (delta) frequency band might be a reliable marker of neuronal degradation. All these findings confirm that (a) glutamatergic NMDA receptors are involved in the mechanisms of soman-induced seizures and brain damage, (b) non-competitive antagonists of NMDA receptors might be promising candidates for post-treatment of soman poisoning, and (c) ECoG parameters from ECoG tracings and power spectrum might serve as useful external predictors for soman-induced neuropathological changes.

Animals↗
PubMed1996

N-Tetrachlorophthaloyl (TCP) for ready protection/deprotection of amino sugar glycosides.

The tetrachlorophthaloyl (TCP) group can be utilized when imidic protection of an amine is desired and durability of the protecting group to conditions ranging from mildly basic to harshly acidic is required. Installation can be accomplished in two steps by treating the free base with the commercially available TCP anhydride, and then closing the imidic ring with acetic anhydride and pyridine. Cleavage is effected by 2-4 eq of ethylenediamine under very mild conditions under which esters and glycopeptides have been shown to be stable, and racemization of amino acid residues does not occur. Unsubstituted phthalimides, even within the same molecule, are also unaffected during TCP cleavage. TCP protecting groups serve as beta-directors on donors and can also be present on acceptor species during electrophilic couplings in oligosaccharide synthesis.

Amino Sugars↗
PubMed1999

Neuroprotection of cultured foetal rat hippocampal cells against glucose deprivation: are GABAergic neurons less vulnerable or more sensitive to TCP protection?

In the rat brain, hippocampal neurons are particularly sensitive to secondary excitotoxic injury induced by ischaemia or hypoglycaemia. To determine some distinctive features of vulnerability among neuronal phenotypes in the hippocampus following a metabolic insult, we used an in vitro model of mild glucose deprivation. Primary cultures from the rat hippocampus (21 days in vitro) were deprived of glucose for 4 h and then were returned to the standard medium for 24 or 48 h. Survival of the GABAergic neuronal population was evaluated both by measuring [3H]GABA uptake and by counting GAD65-immunostained cells. This was compared with the survival of the total neuronal population evaluated by counting the neurofilament-200-immunostained cells. Glucose deprivation for 4 h followed by a recovery period of 48 h induced a decrease of 59% and 40% in the number of GAD65- and neurofilament-200-immunostained cells, respectively. Thus, GABAergic neurons were slightly more vulnerable to glucose deprivation than the other neurons in the hippocampal cell cultures. When the excitotoxic component of cellular death was blocked in the presence of TCP, an NMDA-antagonist, the survival of GABAergic neurons was almost complete after 48 h of recovery. In contrast, measurements of the release of lactate dehydrogenase in the medium indicated that TCP largely protected hippocampal cells after 24 h but was ineffective after 48 h. This observation was confirmed by immunostaining data which showed that after 48 h TCP did not significantly increase the survival of neurofilament-200-immunostained cells. These results indicate that after glucose deprivation and a recovery period of 48 h, GABAergic neurons in hippocampal cell cultures are not more resistant than other neurons but they are more sensitive to TCP protection.

Animals↗
PubMed1994

Two yeast genes with similarity to TCP-1 are required for microtubule and actin function in vivo.

We have isolated cold-sensitive mutations in two genes of the yeast Saccharomyces cerevisiae, BIN2 and BIN3, that cause aberrant chromosome segregation in vivo. BIN2 and BIN3 encode essential proteins that are similar to each other and to TCP-1. TCP-1 and TCP-1-like proteins are components of the eukaryotic cytoplasmic chaperonin that facilitates folding of tubulins and actin in vitro. Mutations in BIN2 and BIN3 cause defects in microtubule and actin assembly in vivo and confer supersensitivity to the microtubule-destabilizing drug benomyl. Overexpression of TCP1, BIN2, BIN3, or ANC2, a fourth member of the TCP-1 family in yeast, does not complement mutations in the other genes, indicating that the proteins have distinct functions. However, all double-mutant combinations are inviable; this synthetic lethality suggests that the proteins act in a common process. These results indicate that Bin2p and Bin3p are components of a yeast cytoplasmic chaperonin complex that is required for assembly of microtubules and actin in vivo.

Actins↗