Hydroxyapatite impregnated bone cement: in vitro and in vivo studies

Hydroxyapatite (HA) particle impregnated polymethylmethacrylate (PMMA) bone cement was fabricated in order to induce bony tissue ingrowth into the pores left behind by resorption of the HA. The amount of HA was 0%, 10%, and 30% by weight. After mixing the HA with bone cement it was cast in a 4 mm inside diameter glass tube (10 mm long). Each specimen was cut into half and used for in vitro and in vivo experiment. Diametral tensile and flexural bend tests were made to evaluate its mechanical properties. SEM (scanning electron microscope) and ESCA (electron spectroscopy for chemical analysis) were used to evaluate the surface characteristics of the specimen. Push-out test and histology studies were made after implanting the specimens for six weeks in the distal portion of rabbit femur. The mechanical test results showed significant decrease of the flexural and diametral tensile strength linear with the increased amount of HA (p < 0.05). The SEM and ESCA analyses showed no definite exposure of HA particles on the surface of the specimens due to the covering by PMMA. The interfacial shear strength of the implanted specimens showed significant increases in the 30% HA specimens compared with the 0% ones but the 10% specimens did not show any difference. Histological observation showed little HA particle apposition to new bone in 10% specimens but more in the 30% ones. In conclusion, this study showed the decreased mechanical properties both by increasing the amount of HA particles and with the bone particles impregnated bone cement. In vivo study showed much lower interfacial shear strength due to implant site compared to other studies but the 30% HA specimens showed statistically significant increase in the push-out strength after implanting into the distal end of rabbit femora.

Induction of tetradecanoyl phorbol acetate-inducible sequence (TIS) genes by electroconvulsive shock in rat brain

We studied the induction of tetradecanoyl phorbol acetate-inducible sequences (TIS)1, 7, 8, 11, and 21 in rat cerebral cortex, hippocampus, and cerebellum after electroconvulsive shock (ECS). These genes were reported to be induced by depolarization in PC-12 cells. Single ECS induced TIS1, 8, 11, and 21, but not TIS7 genes in the rat brain regions examined. In cerebral cortex and hippocampus, induction of TIS1, TIS8, and TIS21 reached peak at 30 or 45 min after ECS. The induced mRNA of TIS1 and 21 decreased rapidly and returned almost to the basal level by 90 min after ECS, whereas those of TIS8 and 11 lasted longer. In cerebellum, TIS genes were induced and disappeared more rapidly than in the other two regions. The 10 and 20 daily ECSs did not affect the inducibility of TIS1, 11, and 21 in cerebellum, but the induction of TIS8 was attenuated by 35% after 20 daily ECSs. Our study indicated that ECS could induce some of the TIS genes in various rat brain regions, but the induction patterns were different depending on the TIS genes and brain regions. Our study also suggested that chronic ECS could not attenuate the induction of some immediate early genes.

Purification, cloning and expression of dehydroascorbic acid-reducing activity from human neutrophils: identification as glutaredoxin

Dehydroascorbic acid-reducing activity in normal human neutrophil lysates was characterized and identified by activity-based purification and measurement of newly synthesized ascorbate by HPLC. The initial reducing activity was non-dialysable and could not be accounted for by the activity of glutathione as a reducing agent. The reducing activity was purified to homogeneity as an 11 kDa protein. The protein had a specific activity of 3 mumol/min per mg of protein and was glutathione dependent. Kinetic experiments showed that the protein had a K(m) for glutathione of 2.0 mM and a K(m) for dehydroascorbic acid of 250 microM. Dehydroascorbic acid reduction by the purified protein was pH dependent and was maximal at pH 7.5. Peptide fragments from the purified protein were analysed for amino acid sequence and the protein was identified as glutaredoxin. By using degenerate oligonucleotides based on the amino acid sequence, glutaredoxin was cloned from a human neutrophil library. Expressed purified glutaredoxin displayed reducing activity and kinetics that were indistinguishable from those of native purified enzyme. Several approaches indicated that glutaredoxin was responsible for the most of the protein-mediated dehydroascorbic acid reduction in lysates. From protein purification data, glutaredoxin was responsible for at least 47% of the initial reducing activity. Dehydroascorbic acid reduction was at least 5-fold greater in neutrophil lysates than in myeloid tumour cell lysates, and glutaredoxin was detected in normal neutrophil lysates but not in myeloid tumour cell lysates by Western blotting. Glutaredoxin inhibitors inhibited dehydroascorbic acid reduction in neutrophil lysates as much as 80%. These findings indicate that glutaredoxin plays a major role in dehydroascorbic acid reduction in normal human neutrophil lysates, and represent the first identification of dehydroascorbic acid reductase in human tissue by activity-based purification.

Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance

Determinants of the recommended dietary allowance (RDA) for vitamin C include the relationship between vitamin C dose and steady-state plasma concentration, bioavailability, urinary excretion, cell concentration, and potential adverse effects. Because current data are inadequate, an in-hospital depletion-repletion study was conducted. Seven healthy volunteers were hospitalized for 4-6 months and consumed a diet containing <5 mg of vitamin C daily. Steady-state plasma and tissue concentrations were determined at seven daily doses of vitamin C from 30 to 2500 mg. Vitamin C steady-state plasma concentrations as a function of dose displayed sigmoid kinetics. The steep portion of the curve occurred between the 30- and 100-mg daily dose, the current RDA of 60 mg daily was on the lower third of the curve, the first dose beyond the sigmoid portion of the curve was 200 mg daily, and complete plasma saturation occurred at 1000 mg daily. Neutrophils, monocytes, and lymphocytes saturated at 100 mg daily and contained concentrations at least 14-fold higher than plasma. Bioavailability was complete for 200 mg of vitamin C as a single dose. No vitamin C was excreted in urine of six of seven volunteers until the 100-mg dose. At single doses of 500 mg and higher, bioavailability declined and the absorbed amount was excreted. Oxalate and urate excretion were elevated at 1000 mg of vitamin C daily compared to lower doses. Based on these data and Institute of Medicine criteria, the current RDA of 60 mg daily should be increased to 200 mg daily, which can be obtained from fruits and vegetables. Safe doses of vitamin C are less than 1000 mg daily, and vitamin C daily doses above 400 mg have no evident value.

Evaluation of inductively heated ferromagnetic alloy implants for therapeutic interstitial hyperthermia

Ferromagnetic alloys heated by magnetic induction have been investigated as interstitial hyperthermia delivery implants for over a decade, utilizing low Curie temperatures to provide thermal self-regulation. The minimally invasive method is attractive for fractionated thermal treatment of tumors which are not easily heated by focused microwave or ultrasound techniques. Past analyses of ferromagnetic seeds by other authors depict poor experimental correlation with theoretical heating predictions. Improvements in computer hardware and commercially available finite element analysis software have simplified the analysis of inductively heated thermal seeds considerably. This manuscript examines end effects of finite length implants and nonlinear magnetic material properties to account for previous inconsistencies. Two alloys, Ni-28 wt% Cu (NiCu) and Pd-6.15 wt% Co (PdCo), were used for comparison of theoretical and experimental calorimetric results. Length to diameter (L/d) ratios of over 20 for cylindrical seeds are necessary for minimization of end effects. Magnetic properties tested for alloys of NiCu and PdCo illustrate considerable nonlinearity of these materials in field strength ranges used for induction heating. Field strength dependent magnetic permeabilities and calorimetric data illustrate that more detailed material information must be included to accurately estimate induction power loss for these implants.

Kinetic studies of Helicobacter pylori urease inhibition by a novel proton pump inhibitor, rabeprazole

Urease is an important virulence factor of pathogenicity of gastric Helicobacter pylori. The inhibition of H. pylori urease by the novel proton pump inhibitor, rabeprazole, was investigated kinetically. It was found to act as an irreversible noncompetitive inhibitor of the enzyme. The inhibitory potency of rabeprazole was dependent on the pH of reaction mixture and its Ki values were 0.14 microM (pH 5.0), 0.34 microM (pH 7.0) and 6.10 microM (pH 8.5). Progressive inactivation of urease by rabeprazole initially proceeded according to pseudo-first-order kinetics with respect to the remaining enzymatic activity at pH 7.0 and 37 degrees C, with a second-order rate constant of 0.0017 microM-1 s-1. When the inactivation half-life was plotted versus the reciprocal of the rabeprazole concentration, a straight line was obtained with a slope of -3.12. From an Arrhenius-plot of the temperature-dependence of the inactivation (over the range of 5-37 degrees C), an activation energy of 13.2 kcal/mol was calculated. Recovery of activity was incomplete for H. pylori urease inhibited by rabeprazole, suggesting that the rabeprazole-urease complex is very stable.

Fatigue properties and stem subsidence in wire coil reinforced PMMA bone cement: a preliminary in vitro study

The longevity of the cemented total hip joint replacement depends on the integrity of the cement fixation with respect to the interfaces of the metal stem and bone, and stress/strain transmission and its distribution. A simple stainless steel wire coil was placed around a tapered stem in a simulated cement mantle to counteract radial- and hoop-stress and dynamic compression-compression tests were performed. The results showed that the wire coil reinforced cement group had a higher fatigue (30%) and strength (35%) up to 10(5) loading cycles. The amount of stem subsidence during fatigue tests of the wire reinforced group was significantly reduced (2.5 times) compared with the control group.

Reinforcement of PMMA bone cement with a continuous wire coil--a 3D finite element study

The changes in the mechanical response of a bone cement reinforcement, comprised of a continuous stainless steel coil imbedded within the PMMA bone cement matrix surrounding the distal tip of the total hip arthroplasty, was investigated. To achieve this, a 3D finite element model depicting two and one half rotations of the coil imbedded within the cement at the distal tip was constructed. Ideally, the wire coil should reduce the radial, and to a greater extent, the hoop stresses developing within the cement and at the cement-stem interface. As a means of comparison, a control model of only bone cement was also built. For the radial stresses, the control had about 4.5 times the compressive stress of the reinforced models (0.039 (+/-0.00065) MPa vs. 0.0087 (+/-0.0012) MPa) at the cement-stem interface. The tensile hoop stresses were also 4.5 times higher (4.272 (+/-0.0147) MPa and 0.95 (+/-0.0052) MPa) for the control than for the reinforced models. This indicates that the wire coil reinforcement is effective in reducing the cement mantle's radial and, more importantly, the hoop stresses which may lead to the failure of both the cement and the implant as a whole.

Determination of optimal vitamin C requirements in humans

Although the recommended dietary allowance provides an estimate for vitamin C ingestion in humans, optimal vitamin C requirements are unknown. We define optimal vitamin C requirements operationally based on the following: dose-function relations, availability in the food supply, steady state concentrations in plasma and tissues achieved at each dose of vitamin C, urinary excretion, bioavailability, toxicity, and epidemiologic observations. Optimal vitamin C requirements can be estimated when information is available for at least some of these criteria.

Changes in G protein levels in the hippocampus and the striatum of rat brain after chronic treatment with haloperidol and sulpiride

Treatment with either haloperidol or sulpiride for 14 days increased the levels of Gs alpha and Gi alpha in the rat hippocampus, but decreased those of Golf alpha and Gi alpha in the rat striatum. Levels of Gq alpha/G11 alpha and Go alpha were not affected by the drugs. These results demonstrate that haloperidol and sulpiride regulate G protein expression in the hippocampus and striatum quite differently.

Helicobacter pylori urease inhibition by rabeprazole, a proton pump inhibitor

We investigated the inhibitory effects of four gastric proton pump inhibitors (PPIs): rabeprazole, a novel benzimidazole PPI, omeprazole, lansoprazole and AG-2000, on the urease activity of Helicobacter pylori (H. pylori). Their 50% inhibitory concentrations (I50s) were found to be 0.29, 5.4, 9.3 and 0.3 microM respectively. Rabeprazole and omeprazole were also potent inhibitors of Jack bean and Proteus mirabilis cellular ureases. The thioether derivative of rabeprazole, one of its metabolites, had no inhibitory effect on H. pylori urease, despite being reported as a more potent inhibitor of H. pylori growth than rabeprazole. The inhibitory effect of rabeprazole was prevented completely and reversed considerably by the addition of sulfhydryl compounds, such as beta-mercaptoethanol, glutathione and dithiothreitol. Moreover, the addition of beta-mercaptoethanol recovered the urease activity inhibited by rabeprazole. From these results, we expected that rabeprazole inhibited H. pylori urease activity by forming disulfide bonds between it and the active site of the enzyme.

Pharmacokinetics and antitumour activity of a new anthracycline, DA-125, after intravenous administration to subcutaneously implanted Lewis-lung-carcinoma-bearing mice

The pharmacokinetics and tissue distribution of M1-M4 were compared after intravenous (i.v.) administration of DA-125, 25 mg kg-1, to BDF1 mice (n = 5 at each sampling time) and subcutaneously implanted Lewis-lung-carcinoma-bearing BDF1 mice (n = 10 at each sampling time. The mean plasma concentrations of M1-M4 were not significantly different between the two groups of mice, and hence similar pharmacokinetic parameters for M1-M4 were obtained. The amount of M1 in the lung was significantly greater in the tumour-bearing mice than in the control mice, resulting in a greater AUAt in the tumour-bearing mice (18,600 against 8940 micrograms min g-1), and vice versa in the liver (962 against 3840 micrograms min g-1). However, the corresponding values for other tissues were comparable between the control and tumour-bearing mice. The amount of M1 was greatest in the lung for up to 2 h in the tumour-bearing mice. M2 was the predominant metabolite among M1-M4 excreted in 24 h urine by both groups of mice; 8.36 and 10.7% of the i.v. dose were excreted in 24 h urine as M2--expressed in terms of DA-125--by the control and tumour-bearing mice, respectively. The amount of M1 in the tumour mass reached a mean Cmax of 3.75 micrograms g-1 immediately after i.v. administration of DA-125 to the tumour-bearing mice, then declined very slowly to an amount that remained almost constant for up to 24 h. This suggested that M1 has high affinity for the subcutaneously implanted Lewis lung carcinoma. The antitumour activity, such as the increase in life span (ILS) and tumour growth inhibition (TGI) of DA-125, 6-48 mg kg-1, and adriamycin (ADM), 3-18 mg kg-1, were also compared in subcutaneously implanted Lewis-lung-carcinoma-bearing BDF1 mice after four weekly i.v. administration of the drugs on days 1,8,15, and 22 following tumour implantation. More than three out of six mice survived as tumour-free for longer than 70 d at a DA-125 dose range of 6-24 mg kg-1, but there were no tumour-free mice at any dose of ADM. Assuming ILS values higher than 30% to be effective, DA-125 doses ranging from 6 to 24 mg kg-1 were effective in increasing the life span, which ADM does only within the dose range of 6-12 mg kg-1.

Periodontal regeneration in class III furcation defects of beagle dogs using guided tissue regenerative therapy with platelet-derived growth factor

We developed an effective regenerative therapy, referred to as platelet-derived growth factor-BB (PDGF-BB)-modulated guided tissue regenerative (GTR) therapy (P-GTR), capable of achieving periodontal regeneration of horizontal (Class III) furcation defects in the beagle dog. To determine its efficacy, repair and regeneration of horizontal furcation defects by P-GTR therapy and GTR therapy were compared. Chronically inflamed horizontal furcation defects were created around the second (P2) and fourth mandibular premolars (P4). After demineralization of the root surfaces with citric acid, the surfaces of left P2 and P4 were treated with PDGF-BB (P-GTR therapy) and those of contralateral teeth were treated with vehicle only (GTR therapy). Periodontal membranes were placed and retained 0.5 mm above the cemento-enamel junction for both groups. The mucoperiosteal flap was sutured in a coronal position and plaque control was achieved by daily irrigation with 2% chlorhexidine gluconate. At 5, 8, and 11 weeks, two animals each were sacrificed by perfusion with 2.5% glutaraldehyde through the carotid arteries, and the lesions were sliced mesio-distally, demineralized, dehydrated, and embedded. Periodontal healing and regeneration after GTR and P-GTR therapy were compared by histomorphometric as well as morphological analysis. Morphometric analysis for each time period was performed on the pooled samples of P2 and P4. Five weeks after both therapies, the lesions were filled primarily by tissue-free area, epithelium, inflamed tissue, and a small amount of newly formed fibrous connective tissue. At 8 and 11 weeks after P-GTR therapy, there was a statistically greater amount of bone and periodontal ligament formed in the lesions. The newly formed bone filled 80% of the lesion at 8 weeks and 87% at 11 weeks with P-GTR therapy, compared to 14% of the lesion at 8 weeks and 60% at 11 weeks with GTR therapy. Also, with P-GTR therapy there was less epithelium and tissue-free area, less inflamed tissue, and less connective tissue. Morphological analysis indicated that the defects around P2 revealed faster periodontal repair and regeneration than those around P4. While the lesions around P2 were effectively regenerated by 11 weeks even after GTR therapy, those around P4 failed to regenerate. On the other hand, P-GTR therapy further promoted periodontal repair and regeneration so that at 8 weeks the lesions around P2 and P4 demonstrated complete and nearly complete regeneration, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Accumulation of vitamin C (ascorbate) and its oxidized metabolite dehydroascorbic acid occurs by separate mechanisms

It is unknown whether ascorbate alone (vitamin C), its oxidized metabolite dehydroascorbic acid alone, or both species are transported into human cells. This problem was addressed using specific assays for each compound, freshly synthesized pure dehydroascorbic acid, the specially synthesized analog 6-chloroascorbate, and a new assay for 6-chloroascorbate. Ascorbate and dehydroascorbic acid were transported and accumulated distinctly; neither competed with the other. Ascorbate was accumulated as ascorbate by sodium-dependent carrier-mediated active transport. Dehydroascorbic acid transport and accumulation as ascorbate was at least 10-fold faster than ascorbate transport and was sodium-independent. Once transported, dehydroascorbic acid was immediately reduced intracellularly to ascorbate. The analog 6-chloroascorbate had no effect on dehydroascorbic acid transport but was a competitive inhibitor of ascorbate transport. The Ki for 6-chloroascorbate (2.9-4.4 microM) was similar to the Km for ascorbate transport (9.8-12.6 microM). 6-Chloroascorbate was itself transported and accumulated in fibroblasts by a sodium-dependent transporter. These data provide new information that ascorbate and dehydroascorbic acid are transported into human neutrophils and fibroblasts by two distinct mechanisms and that the compound available for intracellular utilization is ascorbate.

Pharmacological effects of methanolic extract from the root of Scutellaria baicalensis and its flavonoids on human gingival fibroblast

The methanolic extract from the root of Scutellaria baicalensis Georgi and its flavonoids, wogonin, baicalein, and baicalin were evaluated for anti-inflammatory action and the activatory effect on gingival fibroblasts. In LPS-induced production of IL-1 beta, three flavonoids at 1 microgram/ml expressed a significant (> 50%) inhibitory effect, similar to that of prednisolone. Moreover, the flavonoids inhibited IL-1 beta-induced synthesis of PGE2 and LTB4 considerably, although the effect of wogonin on LTB4 synthesis was marginal. In addition, three flavonoids exerted a moderate inhibition (33-36%) of collagenolytic activity, comparable to 40% inhibition by tetracycline. Meanwhile, the cellular activity of fibroblasts was augmented remarkably (40%) by baicalein (2) and slightly by baicalin (3) or wogonin (1). Consistent with the cellular activation, flavonoids enhanced the synthesis of both collagen and total protein in fibroblasts, in contrast to growth factors which increased only the synthesis of total protein. Although the effects of the methanolic extract resembled those of the flavonoids, the extract expressed a preferential effect on the synthesis of collagen and total protein.

Metabolism of capsaicinoids: evidence for aliphatic hydroxylation and its pharmacological implications

A new metabolic oxidation pathway of capsaicin (N-[(4-hydroxy-3-methoxyphenyl)-methyl]-8-methyl-(E)-6 -nonenamide), a major pungent and pharmacologically active principle of hot peppers, was investigated. Incubation of capsaicin with phenobarbital-induced rat liver postmitochondrial supernatant enriched with NADPH-generating system produced N-(4,5-dihydroxy-3-methoxybenzyl)-(E)-6 -nonenylamide and a more polar metabolite. The latter metabolite was spectrophotometrically and chromatographically identical to authentic omega-hydroxycapsaicin. This new metabolite was also detected in the urine of rabbits given capsaicin by gastric intubation. Other analogs of capsaicin, such as dihydrocapsaicin and nonivamide, also formed similar metabolites via aliphatic hydroxylation. When tested for antinociceptive activity as well as pungency, the above polar metabolites were found to be inactive while their parent compounds exhibited strong sensory effects. Capsaicin interacted irreversibly with heptic drug metabolizing enzymes, thereby inhibiting their activity as indicated by prolongation of pentobarbital sleeping time in rats. Such inhibition of drug metabolism was not observed with omega-hydroxycapsaicin. These findings suggest that metabolism of capsaicinoids via hydroxylation of their side chains plays an important role in the detoxification of these pharmacologically active substances.

Inhibitory effect of beta-glucosyl-phenolic hydroxamic acids against urease in the presence of microfloral beta-glucosidase

Three glucosyl-phenolic hydroxamates, 4-O-(beta-D-glucopyranosyl) benzohydroxamic acid, 4-O-(beta-D-glucopyranosyl)hippuric hydroxamic acid, and 3-[4-O-(beta-D-glucopyranosyl)phenyl]propionohydroxamic acid (Glc-PPHA), were hydrolyzed to their corresponding aglycones by beta-glucosidase of intestinal flora of rat without any major adverse hydrolysis in vitro. Inhibitory potency of these glucosyl-hydroxamates on urease was recovered to the same extent as that of the corresponding aglycone hydroxamates by preincubation for 2h with rat intestinal flora. p-Hydroxyphenylpropionohydroxamic acid inhibited noncompetitively jack-bean urease activity and its glucose-ligated form, Glc-PPHA inhibited it competitively. A single oral dose of Glc-PPHA tended to inhibit urease activity in proximal colon contents of rat at 6 h after administration (p = 0.06). After 14C-urea was orally administered to rat, 14CO2 was collected for to measure the ureolysis in vivo. Expired 14CO2 was limited to 40% by a single oral dose of Glc-PPHA during 6 h, and 75% of intestinal ureolysis was repressed during the first 1 h in the breath test.

Electroconvulsive shock reduces inositol 1,4,5-trisphosphate 3-kinase mRNA expression in rat dentate gyrus

We investigated the expression of inositol 1,4,5-trisphosphate (InsP3) 3-kinase mRNA after a single electroconvulsive shock (ECS) with in situ hybridization histochemistry in rat brain. At 6 h after ECS, the expression was markedly decreased in the dentate gyrus, and the decrease was maintained until 9 h with a slight recovery. The InsP3 3-kinase mRNA content returned to basal levels after 12 h. We could not detect any apparent changes in the expression of InsP3 3-kinase mRNA in the CA1-CA3 areas of hippocampus, the striatum, and the cerebral cortex at any time point examined. In the temporal pattern, the reduction of the expression in the dentate gyrus was preceded by the induction of c-fos after ECS. These observations suggest that the InsP3 3-kinase might be one of the genes whose expression can be altered by ECS.

Activation and tyrosine phosphorylation of 44-kDa mitogen-activated protein kinase (MAPK) induced by electroconvulsive shock in rat hippocampus

Electroconvulsive shock (ECS) has been reported to induce the phosphorylation and activation of 42-kDa, but not 44-kDa, mitogen-activated protein kinase (MAPK) in rat hippocampus. We studied the activation and tyrosine phosphorylation of MAPKs in rat brain after ECS. We observed the increase of the activities of both 42- and 44-kDa MAPKs in rat hippocampus after ECS. The activities reached peak at 2 min and returned to basal levels by 15 min after ECS. We also observed the increased phosphorylation on the tyrosine residue of 42-kDa MAPK in rat hippocampus after ECS, but not on that of 44-kDa MAPK. However, when we examined the immunoprecipitated 44-kDa MAPK, we could demonstrate that the tyrosine phosphorylation of 44-kDa MAPK at 2 min after ECS was markedly increased, in accordance with the increase of kinase activity. These results indicate that ECS induces the transient activation and tyrosine phosphorylation of 44-kDa MAPK, as well as 42-kDa MAPK, in rat hippocampus, although the amount of tyrosine phosphorylation is far less and the kinase activity is lower in 44-kDa MAPK than in 42-kDa MAPK.

Improving mouth guards

Mouth guards and materials were tested to provide information for a more protective yet more comfortable product. Ethylene-vinyl acetate copolymer materials varying in thickness and stiffness were tested for their mechanical, thermal, and water-absorption properties. Thickness was measured before and after fabrication of the mouth guard. During fabrication, thicknesses decreased from 25% to 50% for the custom-fabricated mouth guards and 70% to 99% for the mouth-formed (boil-and-bite), off-the-shelf, over-the-counter mouth guards. The thicker the material is, the greater the resulting energy absorption is. It is therefore essential that the thickness in the occlusal portion of the mouth guard remain optimal after fabrication. A mouth guard with a stiffer insert, which softens at a higher temperature in the occlusal portion, is proposed as a more protective mouth guard.

Phosphorylation and activation of mitogen-activated protein kinase by kainic acid-induced seizure in rat hippocampus

Injection of kainic acid into rat induced a limbic seizure and increased the activities of two protein kinases with Mrs of 42 kDa and 44 kDa in the hippocampus. These two protein kinases were identified as MAP kinases by an anti-MAP kinase antibody. These MAP kinases were phosphorylated at least at a tyrosine residue. The time course of the MAP kinase activation was roughly parallel with that of the seizure. These results indicate that the kainic acid-induced seizure induces MAP kinase activation in rat hippocampus.

Possible presence of the ATP-sensitive K+ channel in isolated spinal dorsal horn neurons of the rat

The ATP-sensitive K+ channel (KATP channel) is a K+ channel inhibited by cytoplasmic ATP. It was originally found in cardiac cells and recently in neuronal cells. Here, we present evidence indicating that the KATP channel also exists in spinal dorsal horn neurons: membrane currents were recorded by whole-cell voltage-clamp in spinal dorsal horn neurons isolated from young rats. The outward current was augmented by KATP channel activators nicorandil and minoxidil and reduced by the blocker glibenclamide. This glibenclamide-induced change in the current was augmented when the intracellular ATP was lowered and the reversal potential was shifted according to the external K+ concentration.

Silymarin and its components are inhibitors of beta-glucuronidase

Silymarin, a commercial crude drug used as a hepatoprotective, was found to inhibit 53% of beta-glucuronidase activity at a final concentration of 0.8 mg/ml. Of three compounds A, silybin and C, which were isolated from silymarin, A and silybin potently inhibited the enzyme activity, followed by C. beta-Glucuronidases of intestinal bacteria, HGU-1 and HGU-2, and E. coli HB101 were noncompetitively inhibited by silybin. beta-Glucuronidase of the feces of a healthy human and of a human with colon cancer were also inhibited by silybin, silymarin and saccharic acid 1,4-lactone at 0.03-0.15 mg/ml. Silymarin and silybin protected the increase in enzyme activity in the serum of the rats treated with CCl4.

A comparison of stress-induced porosity due to conventional and a modified spinal fixation device

A hypothesis that device-related osteopenia can be reduced by decreasing the rigidity of a fixation device was tested through a canine study. Polymer washers were interposed between the integral nut and plate of the variable spinal plating (VSP) system to reduce its rigidity. A solid fusion was observed 6 months postoperatively in all of the animals using VSP or modified systems. The stabilized segment using both systems showed similar load-displacement behaviors immediately after surgery and 6 months postoperatively. Although not significant, 5.6 and 1.8% decreases in volumetric density of mineralized bone were found in the stabilized segments due to VSP and modified systems, respectively. The modified system also increased bone growth around screws. The new concept of using polymer washers, to decrease rigidity of the fixation device over time, may reduce device-related osteopenia.

One-step immunoaffinity purification of human beta 1 thyroid hormone receptor with DNA and hormone binding activity

An efficient and versatile method to purify large amounts of active human beta 1 thyroid hormone receptor (h-TR beta 1) was developed. Using a T7 expression system, h-TR beta 1 was overexpressed in Escherichia coli. Approx. 80% of the expressed receptor protein was concentrated in the insoluble inclusion bodies and approximately 20% was in the soluble form (h-TR beta 1-S). h-TR beta 1-S was conveniently purified by one immunoaffinity chromatographic step. From 1 l of cell culture, approx. 0.1 mg of purified h-TR beta 1-S was obtained. The purified h-TR beta 1-S binds to 3,3',5-triiodo-L-thyronine with a Ka = 2 x 10(9) M-1 and exhibits analog specificity. The purified h-TR beta 1-S also binds to T3 response elements (TRE) with different orientation in the half-sites with differential activity. In addition, binding of h-TR beta 1-S to TREs was enhanced by retinoid X receptor. These results indicate that the purified h-TR beta 1-S retains its hormone and DNA binding activity. The purified h-TR beta 1-S is suitable for structural and functional studies. This method could be used to purify h-TR beta 1 or rat TR beta 1 expressed in insect cells or yeast.

Tyrosine phosphorylation of PLC-gamma 1 induced by electroconvulsive shock in rat hippocampus

ECS has been shown to increase PIP2 breakdown in rat brain, which suggested the possible activation of PLC-signal transduction system by ECS. When we examined the PLC-gamma 1 immunoprecipitated from rat hippocampal tissues after ECS, we found a rapid increase in phosphotyrosine of PLC-gamma 1, which reached peak at 10 minutes after ECS and returned to basal level after 2 hours. There was no change in the amount of PLC-gamma 1 proteins during that period. The tyrosine phosphorylation induced by ECS didn't affect the enzyme activity when assayed in vitro. These results suggested that ECS may activate PLC-gamma 1 by phosphorylation on tyrosine residue, but without changing enzyme activity itself.

The mechanism of c-erbB-2 gene product increase in stomach cancer cell lines

c-erbB-2 oncogene encodes a growth factor receptor whose amino acid sequence has extensive homology with human epidermal growth factor receptor. It is frequently overexpressed in human breast, ovary, lung, and stomach cancers, where its overexpression is related significantly to the prognosis. Tl investigate the possible role of c-erbB-2 oncogene in the oncogenesis of stomach cancer, we examined the genetic alterations of c-erbB-2 oncogene in 4 stomach cancer cell lines, SNU-1, SNU-5, SNU-16 and KATO III. There were no differences in c-erbB-2 mRNA level as well as c-erbB-2 gene copy number among them. But gp185-erbB-2, c-erbB-2 gene product, was increased from 2- to 4-fold in SNU-1 and SNU-5 cells, compared with that in SNU-16 or KATO III cells. Our results suggest that post-transcriptional regulation of gp185erbB-2 expression may underlie gp185erbB-2 overexpression in cancer cells.

Heat shock protein response in a prostate tumor model to interstitial thermotherapy: implications for clinical treatment

Hyperthermia is being utilized individually and in conjunction with other therapies in treating malignant and benign tumors, though few studies have examined cellular effects of elevated temperatures in the prostate model. Highly conserved proteins of the 70 kDa heat shock protein family (HSP 70) are produced in response to environmental stresses, including heat, and are found in all organisms. HSPs are an indicator of cell damage, are associated with thermotolerance, and provide cells with transient resistance to subsequent thermal challenges. Transient thermotolerance is important in the determination of temperature, duration, and sequencing for treatments. This preliminary study analyzes the HSP 70 response of the Dunning R3327 adenocarcinoma model to a single 50 degrees C 1 hr treatment. Elevated HSP levels were found between 10 and 16 hr, returning to baseline by 24 hr. As some fractions of the cells are able to produce HSP 70 following treatment, the data suggest that currently utilized clinical temperatures (42-46 degrees C) administered for 1 hr are inadequate. HSP levels in response to hyperthermia, radiation, and chemotherapy may be useful in finding optimal treatment regimens for prostate cancer.

Glutamate dehydrogenase from the hyperthermophile Pyrococcus furiosus. Thermal denaturation and activation

Pyrococcus furiosus is a marine hyperthermophile that grows optimally at 100 degrees C. Glutamate dehydrogenase (GDH) from P. furiosus is a hexamer of identical subunits and has an M(r) = 270,000 +/- 5500 at 25 degrees C. Electron micrographs showed that the subunit arrangement is similar to that of GDH from bovine liver (i.e. 3/2 symmetry in the form of a triangular antiprism). However, GDH from P. furiosus is inactive at temperatures below 40 degrees C and undergoes heat activation above 40 degrees C. Both NAD+ and NADP+ are utilized as cofactors. Apparently the inactive enzyme also binds cofactors, since the enzyme maintains the ability to bind to an affinity column (Cibacron blue F3GA) and is specifically eluted with NADP+. Conformational changes that accompany activation and thermal denaturation were detected by precision differential scanning microcalorimetry. Thermal denaturation starts at 110 degrees C and is completed at 118 degrees C. delta(cal) = 414 Kcal [mol GDH]-1. Tm = 113 degrees C. This increase in heat capacity indicates an extensive irreversible unfolding of the secondary structure as evidenced also by a sharp increase in absorbance at 280 nm and inactivation of the enzyme. The process of heat activation of GDH from 40 to 80 degrees C is accompanied by a much smaller increase in absorbance at 280 nm and a reversible increase in heat capacity with delta(cal) = 187 Kcal [mol GDH]-1 and Tm = 57 degrees C. This absorbance change as well as the moderate increase in heat capacity suggest that thermal activation leads to some exposure of hydrophobic groups to solvent water as the GDH structure is opened slightly. The increase in absorbance at 280 nm during activation is only 12% of that for denaturation. Overall, GDH appears to be well adapted to correspond with the growth response of P. furiosus to temperature.

Comparison of the X-ray structure of native rubredoxin from Pyrococcus furiosus with the NMR structure of the zinc-substituted protein

The three-dimensional X-ray structures of the oxidized and reduced forms of rubredoxin from Pyrococcus furiosus, determined at -161 degrees C, and the NMR structure of the zinc-substituted protein, determined in solution at 45 degrees C, are compared. The NMR and X-ray structures, which were determined independently, are very similar and lead to similar conclusions regarding the interactions that confer hyperthermostability.

Orthopedic prosthesis fixation

The fixation of orthopedic implants has been one of the most difficult and challenging problems. The fixation can be achieved via: (a) direct mechanical fixation using screws, pins, wires, etc.; (b) passive or interference mechanical fixation where the implants are allowed to move or merely positioned onto the tissue surfaces; (c) bone cement fixation which is actually a grouting material; (d) biological fixation by allowing tissues to grow into the interstices of pores or textured surfaces of implants; (e) direct chemical bonding between implant and tissues; or (f) any combination of the above techniques. This article is concerned with various fixation techniques including the potential use of electrical, pulsed electromagnetic field, chemical stimulation using calcium phosphates for the enhancement of tissue ingrowth, direct bonding with bone by glass-ceramics and resorbable particle impregnated bone cement to take advantages of both the immediate fixation offered by the bone cement and long term fixation due to tissue ingrowth.

X-ray crystal structures of the oxidized and reduced forms of the rubredoxin from the marine hyperthermophilic archaebacterium Pyrococcus furiosus

The structures of the oxidized and reduced forms of the rubredoxin from the archaebacterium, Pyrococcus furiosus, an organism that grows optimally at 100 degrees C, have been determined by X-ray crystallography to a resolution of 1.8 A. Crystals of this rubredoxin grow in space group P2(1)2(1)2(1) with room temperature cell dimensions a = 34.6 A, b = 35.5 A, and c = 44.4 A. Initial phases were determined by the method of molecular replacement using the oxidized form of the rubredoxin from the mesophilic eubacterium, Clostridium pasteurianum, as a starting model. The oxidized and reduced models of P. furiosus rubredoxin each contain 414 nonhydrogen protein atoms comprising 53 residues. The model of the oxidized form contains 61 solvent H2O oxygen atoms and has been refined with X-PLOR and TNT to a final R = 0.178 with root mean square (rms) deviations from ideality in bond distances and bond angles of 0.014 A and 2.06 degrees, respectively. The model of the reduced form contains 37 solvent H2O oxygen atoms and has been refined to R = 0.193 with rms deviations from ideality in bond lengths of 0.012 A and in bond angles of 1.95 degrees. The overall structure of P. furiosus rubredoxin is similar to the structures of mesophilic rubredoxins, with the exception of a more extensive hydrogen-bonding network in the beta-sheet region and multiple electrostatic interactions (salt bridge, hydrogen bonds) of the Glu 14 side chain with groups on three other residues (the amino-terminal nitrogen of Ala 1; the indole nitrogen of Trp 3; and the amide nitrogen group of Phe 29). The influence of these and other features upon the thermostability of the P. furiosus protein is discussed.

Solution-state structure by NMR of zinc-substituted rubredoxin from the marine hyperthermophilic archaebacterium Pyrococcus furiosus

The three-dimensional solution-state structure is reported for the zinc-substituted form of rubredoxin (Rd) from the marine hyperthermophilic archaebacterium Pyrococcus furiosus, an organism that grows optimally at 100 degrees C. Structures were generated with DSPACE by a hybrid distance geometry (DG)-based simulated annealing (SA) approach that employed 403 nuclear Overhauser effect (NOE)-derived interproton distance restraints, including 67 interresidue, 124 sequential (i-j = 1), 75 medium-range (i-j = 2-5), and 137 long-range (i-j > 5) restraints. All lower interproton distance bounds were set at the sum of the van Der Waals radii (1.8 A), and upper bounds of 2.7 A, 3.3 A, and 5.0 A were employed to represent qualitatively observed strong, medium, and weak NOE cross peak intensities, respectively. Twenty-three backbone-backbone, six backbone-sulfur (Cys), two backbone-side chain, and two side chain-side chain hydrogen bond restraints were include for structure refinement, yielding a total of 436 nonbonded restraints, which averages to > 16 restraints per residue. A total of 10 structures generated from random atom positions and 30 structures generated by molecular replacement using the backbone coordinates of Clostridium pasteurianum Rd converged to a common conformation, with the average penalty (= sum of the square of the distance bounds violations; +/- standard deviation) of 0.024 +/- 0.003 A2 and a maximum total penalty of 0.035 A2. Superposition of the backbone atoms (C, C alpha, N) of residues A1-L51 for all 40 structures afforded an average pairwise root mean square (rms) deviation value (+/- SD) of 0.42 +/- 0.07 A. Superposition of all heavy atoms for residues A1-L51, including those of structurally undefined external side chains, afforded an average pairwise rms deviation of 0.72 +/- 0.08 A. Qualitative comparison of back-calculated and experimental two-dimensional NOESY spectra indicate that the DG/SA structures are consistent with the experimental spectra. The global folding of P. furiosus Zn(Rd) is remarkably similar to the folding observed by X-ray crystallography for native Rd from the mesophilic organism C. pasteurianum, with the average rms deviation value for backbone atoms of residues A1-L51 of P. furiosus Zn(Rd) superposed with respect to residues K2-V52 of C. pasteurianum Rd of 0.77 +/- 0.06 A. The conformations of aromatic residues that compose the hydrophobic cores of the two proteins are also similar. However, P. furiosus Rd contains several unique structural elements, including at least four additional hydrogen bonds and three potential electrostatic interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Impact of a primary reader's opinion on the detection of rib fractures

RATIONALE AND OBJECTIVES

The authors assessed the influence of a prior reader's opinion on the detectability of rib fractures.

METHODS

Six pairs of observers read the chest PA radiographs of 92 subjects with rib fracture(s) and 28 normal subjects to detect rib fracture(s) according to a five-point rating of confidence with three methods. In method A, each reader read films as a primary reader. In method B, each reader read films after knowing his or her partner's opinion. In method C, each reader initially observed films and then made the final decision after knowing his or her partner's opinion.

RESULTS

Methods B and C were superior to method A in sensitivity. There was no difference in performance between methods B and C. Method C required a significantly longer time than the other methods.

CONCLUSION

Detection of rib fractures is improved by seeking the opinion of other observers.

Fusion of phospholipid vesicles induced by phospholipase D in the presence of calcium ion

Fusion of phospholipid vesicles composed of various combination of phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid was induced by Ca2+ in the presence or absence of phospholipase D from Streptomyces chromofuscus. For the vesicles composed of 20:50:30 molar ratio of phosphatidylcholine/phosphatidylethanolamine/phosphatidic acid, the initial fusion rate was much faster than the expected value when only the conversion of phosphatidylcholine and phosphatidylethanolamine into phosphatidic acid by phospholipase D is taken into account. These observations are discussed in terms of the involvement of outer monolayer of the vesicles and the enzyme activity itself in the fusion process.

Characterization of an extremely thermostable glutamate dehydrogenase: a key enzyme in the primary metabolism of the hyperthermophilic archaebacterium, Pyrococcus furiosus

Glutamate dehydrogenase (L-glutamate:NAD(P)+ oxidoreductase, deaminating, EC 1.4.1.3) from the hyperthermophilic Archeon Pyrococcus furiosus was purified to homogeneity by chromatography on anion-exchange, molecular-exclusion and hydrophobic-interaction media. The purified native enzyme had an M(r) of 270,000 +/- 15,000 and was shown to be a hexamer with identical subunits of M(r) 46,000. The enzyme was exceptionally thermostable, having a half-life of 3.5 to more than 10 h at 100 degrees C, depending on the concentration of enzyme. The Km of the enzyme for ammonia was high (9.5 mM), indicating that the enzyme is probably active in the deaminating, catabolic direction. The coenzyme utilization of the enzyme resembled the equivalent enzymes from eukaryotes rather than eubacteria, since both NADH and NADPH were recognized with high affinity. The enzyme displayed a preference for NADP+ over NAD+ that was more pronounced at low assay temperatures (50-70 degrees C) compared with the optimal temperature for enzyme activity, 95 degrees C.

The effect of interstitial hyperthermia on the Dunning prostate tumor model

The effect of hyperthermia was examined on the Dunning prostate tumor model in rats. Hyperthermia was created by heating self-regulating interstitial seeds with an external oscillating magnetic field. The seed alloy was comprised of 70% nickel and 30% copper. One treatment with 50C seeds for two hours did not provide significant delay in tumor growth compared to controls. However, regimens with two treatments separated by either 48 hours or one week did cause significant delay (p = 0.0013 and p = 0.0096, respectively). These results suggest that an interstitial hyperthermia seed may provide an efficacious outpatient therapy for prostate cancer. Further, interstitial hyperthermia may be readily combined with existing radiotherapy with interstitial gold coated seeds to provide additive or synergistic anti-tumor effects.

Determinants of protein hyperthermostability: purification and amino acid sequence of rubredoxin from the hyperthermophilic archaebacterium Pyrococcus furiosus and secondary structure of the zinc adduct by NMR

The purification, amino acid sequence, and two-dimensional 1H NMR results are reported for the rubredoxin (Rd) from the hyperthermophilic archaebacterium Pyrococcus furiosus, an organism that grows optimally at 100 degrees C. The molecular mass (5397 Da), iron content (1.2 +/- 0.2 g-atom of Fe/mol), UV-vis spectrophotometric properties, and amino acid sequence (60% sequence identity with Clostridium pasteurianum Rd) are found to be typical of this class of redox protein. However, P. furiosus Rd is remarkably thermostable, being unaffected after incubation for 24 h at 95 degrees C. One- and two-dimensional 1H nuclear magnetic resonance spectra of the oxidized [Fe(III)Rd] and reduced [Fe(II)Rd] forms of P. furiosus Rd exhibited substantial paramagnetic line broadening, and this precluded detailed 3D structural studies. The apoprotein was not readily amenable to NMR studies due to apparent protein oxidation involving the free cysteine sulfhydryls. However, high-quality NMR spectra were obtained for the Zn-substituted protein, Zn(Rd), enabling detailed NMR signal assignment for all backbone amide and alpha and most side-chain protons. Secondary structural elements were determined from qualitative analysis of 2D Overhauser effect spectra. Residues A1-K6, Y10-E14, and F48-E51 form a three-strand antiparallel beta-sheet, which comprises ca. 30% of the primary sequence. Residues C5-Y10 and C38-A43 form types I and II amide-sulfur tight turns common to iron-sulfur proteins. These structural elements are similar to those observed by X-ray crystallography for native Rd from the mesophile C. pasteurianum. However, the beta-sheet domain in P. furiosus Rd is larger than that in C. pasteurianum Rd and appears to begin at the N-terminal residue. From analysis of the secondary structure, potentially stabilizing electrostatic interactions involving the charged groups of residues Ala(1), Glu(14), and Glu(52) are proposed. These interactions, which are not present in rubredoxins from mesophilic organisms, may prevent the beta-sheet from "unzipping" at elevated temperatures.

Potentiometric and electron nuclear double resonance properties of the two spin forms of the [4Fe-4S]+ cluster in the novel ferredoxin from the hyperthermophilic archaebacterium Pyrococcus furiosus

Pyrococcus furiosus ferredoxin contains a single [4Fe-4S] that exists in both S = 1/2 (20%) and S = 3/2 (80%) ground states in the reduced protein. We report here on the temperature-dependent potentiometric properties of the two spin forms, their stability, and on the structural features that differentiate them. The midpoint potential (Em) of the cluster in either spin state was determined at -365 mV (30 degrees C, pH 8.0). By rapidly freezing samples for EPR analyses, it was shown that the Em values of both spin states appear to change by -1.7 mV/degrees C over the range 20 degrees-80 degrees C, and by -6 mV/degrees C between 80 and 89 degrees C. The Em values and the relative amounts of the S = 1/2 and S = 3/2 forms of the cluster were unaffected by pH (6.8-10.5), even at 85 degrees C, and were unchanged by the presence of NaCl (1.0 M), sodium dodecyl sulfate (10%, w/v) or ethylene glycol (50%, v/v), even at 80 degrees C. The S = 1/2 form of the [4Fe-4S]+ cluster was found to exhibit a strongly coupled 1H ENDOR resonance (A = 22 MHz) that was exchangeable with the solvent. Such a large coupling has not been observed in any other iron-sulfur protein. Since a unique feature of this 4Fe-ferredoxin is that only 3 cysteinyl residues appear to be coordinated to the [4Fe-4S] cluster, the ENDOR data are consistent with an H2O molecule being a ligand to the unique Fe site. The S = 3/2 form of the [4Fe-4S]+ cluster exhibited a similar, strongly coupled 1H ENDOR resonance, but in this spin state it was not exchangeable with the solvent. This suggests that the [4Fe-4S]+ cluster exhibiting the S = 3/2, but not the S = 1/2 ground state, is "shielded" from the solvent, presumably by neighboring amino acid residues. In view of the pH dependence of the midpoint potential of the two spin states, the fourth ligand to the cluster and the source of the strongly coupled 1H ENDOR resonance is probably an OH- rather than H2O molecule.

Restenosis rate after percutaneous transluminal coronary angioplasty: a literature overview

In order to elucidate factors affecting the rate of angioplasty restenosis, we reviewed 212 published reports on restenosis after percutaneous transluminal coronary angioplasty. We used five specific methodologic standards to select the 31 reports most likely to produce unbiased results. Sixty one factors judged to be related to restenosis rate were investigated. Only shorter duration of data collection (p=0.0003) was related to higher restenosis rate. This factor may be related to inexperience in choosing subjects or performing procedures. Other factors whose association with restenosis rate did not reach our predetermined level of statistical significance (p less than .01) were angioplasties of the left circumflex artery (p=.02), angioplasty of total occlusions (p=.02) and advanced age (p=.05). The association of shorter data collection with higher restenosis rates suggests that improved outcome may result from consolidation to a few centers specializing in this technique.

Effects of rigidity of an internal fixation device. A comprehensive biomechanical investigation

Internal fixation with instrumentation often accompanies surgical fusion to augment spinal stability, provide temporary fixation while the surgical fusion mass unites, and enhance postoperative mobilization of a patient. Some surgeons, however, feel that the existing plate-screw designs are too rigid and are the primary cause of "iatrogenic" adverse effects clinically observed. A three-part study, involving in vitro experimental protocol, analytical finite-element-based models, and an in vivo canine investigation, was undertaken to study the role of decreasing rigidity of a device on the biomechanical response of the stabilized segments. Two alternatives--the use of one variable screw placement (Steffee plate [unilateral, 1VSP model]) as opposed to two VSP plates (bilateral, 2VSP model) and two VSP plates with polymer washers placed in between the integral nut and plate (2MVSP model)--were considered for achieving a reduction in the rigidity of the conventional VSP system. The load-displacement data obtained from the in vitro experiments and the stress distributions within the stabilized and intact models predicted by the finite-element models revealed that the unilateral VSP system is less rigid and is likely to reduce stress shielding of the vertebral bodies compared with the 2VSP model. The undesirable effects associated with the use of the 1VSP plate system are the presence of coupled motions due to the inherent asymmetry and the likely inability to provide enough rigidity for decompression procedures requiring a complete excision of the disc. The use of two MVSP plates overcomes these deficiencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone-particle-impregnated bone cement: an in vivo weight-bearing study

To evaluate an experimental inorganic-bone-particle-impregnated bone cement, canine hip prostheses were implanted in dogs using a regular bone cement on one side and the experimental bone cement on the other. In a preliminary feasibility study, bone ingrowth into the resorbed bone-particle spaces was established 3 months after implantation in three dogs. In a more detailed study, twenty-eight (28) dogs were divided in four groups to delineate the effects of time on the phenomena of bony ingrowth. One month after implantation, active bone ingrowth into the bone cement was obvious. By 3 months postimplantation, the ingrowth appeared to have traversed the thickness of the bone-particle-impregnated cement. By the fifth month, most of the interconnected inorganic bone particles were replaced by new bone. At the end of a year, the ingrown bone was mature and negligible new bone activity was present. Biomechanical pushout tests closely corroborated the histologic observations. The maximum shear strength of the cement/bone interface of the experimental side reached 3.6 times that of the control side at 5 months postimplantation. No further improvements were seen at 12 months postimplantation. A viable bone/cement interface may result in a better orthopedic implant fixation system by combining the advantages of both cement for immediate rigidity and biological ingrowth for longterm stability.

Combined synergistic antiherpetic effect of acyclovir and chlorhexidine in vitro

The combined effect of acyclovir and chlorhexidine on the replication and DNA synthesis of herpes simplex virus was studied. Acyclovir and chlorhexidine showed synergism in the inhibition of the viral replication by enhancing in part the reduction of viral DNA synthesis. These data indicate that combined therapy with acyclovir and chlorhexidine might be beneficial for the control of intraoral herpetic infections.

The effect of defect size on the stress concentration and fracture characteristics for a tubular torsional model with a transverse hole

The maximum stress location and crack resistance of a tubular torsional model with varying transverse circular defects were determined by the use of experimental and global-local finite element modeling techniques. The experimental results showed that the reduction in torsional strength was inversely proportional to defect size. In addition, the maximum stress location around the defect was closely related to the normalized defect diameter. By measuring the shifted angle associated with each defect ratio, a linear relationship, delta theta = -6.28 + 0.55*(d/D), was determined. Finite element results indicated that the stress concentration factor, Kg, for a single-cortex defect is similar to that of a double-cortex defect of identical dimension. Application of the strain energy density (SED) theory proposed by Sih and Oliveira Faria (Fracture Mechanics Methodology, Martinus Nijhoff, The Hague, 1984), indicated that the fracture toughness, KIC, for large defects was greater than that for small defects. This implies that tubular structures with large defects have a greater resistance to crack initiation and growth.

Spectroscopic characterization of the novel iron-sulfur cluster in Pyrococcus furiosus ferredoxin

Pyrococcus furiosus ferredoxin is the only known example of a ferredoxin containing a single [4Fe-4S] cluster that has non-cysteinyl ligation of one iron atom, as evidenced by the replacement of a ligating cysteine residue by an aspartic acid residue in the amino acid sequence. The properties of the iron-sulfur cluster in both the aerobically and anaerobically isolated ferredoxin have been characterized by EPR, magnetic circular dichroism, and resonance Raman spectroscopies. The anaerobically isolated ferrodoxin contains a [4Fe-4S]+,2+ cluster with anomalous properties in both the oxidized and reduced states which are attributed to aspartate and/or hydroxide coordination of a specific iron atom. In the reduced form, the cluster exists with a spin mixture of S = 1/2 (20%) and S = 3/2 (80%) ground states. The dominant S = 3/2 form has a unique EPR spectrum that can be rationalized by an S = 3/2 spin Hamiltonian with E/D = 0.22 and D = +3.3 +/- 0.2 cm-1. The oxidized cluster has an S = 0 ground state, and the resonance Raman spectrum is characteristic of a [4Fe-4S]2+ cluster except for the unusually high frequency for the totally symmetric breathing mode of the [4Fe-4S] core, 342 cm-1. Comparison with Raman spectra of other [4Fe-4S]2+ centers suggests that this behavior is diagnostic of anomalous coordination of a specific iron atom. The iron-sulfur cluster is shown to undergo facile and quantitative [4Fe-4S] in equilibrium [3Fe-4S] interconversion, and the oxidized and reduced forms of the [3Fe-4S] cluster have S = 1/2 and S = 2 ground states, respectively. In both redox states the [3Fe-4S]0,+ cluster exhibits spectroscopic properties analogous to those of similar clusters in other bacterial ferredoxins, suggesting non-cysteinyl coordination for the iron atom that is removed by ferricyanide oxidation. Aerobic isolation induces partial degradation of the [4Fe-4S] cluster to yield [3Fe-4S] and possibly [2Fe-2S] centers. Evidence is presented to show that only the [4Fe-4S] form of this ferredoxin exists in vivo.