Ability of Ni-containing biomedical alloys to activate monocytes and endothelial cells in vitro

Nickel-containing alloys commonly are used in medical and dental applications that place them into long-term contact with soft tissues. The release of Ni ions from these alloys is disturbing because of the toxic, immunologic, and carcinogenic effects that have been documented for some Ni compounds. In particular, Ni ions in solution recently have been shown to cause expression of inflammatory mediators, such as interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and intercellular adhesion molecules (ICAMs) from keratinocytes, monocytes, and endothelial cells. However, the ability of the solid alloys themselves to induce these inflammatory effects has not been demonstrated. An in vitro system was used to determine if Ni-containing biomedical alloys could cause secretion of either IL-1beta or TNF-alpha from monocytes or expression of ICAMs on endothelial cells. Pure nickel, titanium, and three biomedical alloys-18-8 stainless steel, NiTi, and Rexillium III-were evaluated. First, it was determined whether or not the alloys or pure metals could cause cytotoxicity to THP-1 human monocytes or human microvascular endothelial cells (HMVECs) by measuring the succinic dehydrogenase (SDH) activity of the cells. Then, using identical conditions of exposure, the secretion of IL-1beta or TNF-alpha from monocytes or ICAM-1 expression on the HMVECs was determined. Only pure nickel suppressed (by 48% compared to Teflon controls) the SDH activity of the HMVECs or THP-1 monocytes. No alloy or metal caused the HMVECs to express ICAM-1, but the NiTi alloy caused a significant (ANOVA/Tukey) secretion of IL-1beta from the THP-1 monocytes. Secretion of TNF-alpha induced by NiTi was detectable but not statistically significant. The levels of IL-1beta secretion from monocytes were sufficient to induce ICAM-1 expression on HMVECs. The release of Ni from the NiTi was a logical suspect in causing the IL-1beta secretion by monocytes, but its role was not confirmed since other alloys, such as Rexillium III, released the same quantities of Ni yet did not activate the THP-1 monocytes. Within the limitations of in vitro conditions, our results indicate that NiTi alloys pose a risk of promoting an inflammatory response in soft tissues by activating monocytes. Further study is needed to substantiate this finding in vivo.

Neutron-capture therapy of brain tumours: neutron sources, neutron-capture drugs, biological tests and clinical perspectives in the Czech Republic

The paper reviews neutron sources, chemical compounds and clinical perspectives of the boron neutron-capture therapy of brain tumours. Special attention is paid to the physical characteristics and biological effectiveness of the epithermal neutron beam constructed at the LVR-15 nuclear reactor at Rez near Prague.

Accurate titration of avidin and streptavidin with biotin-fluorophore conjugates in complex, colored biofluids

A new fluorimetric assay is presented for the specific and reliable quantitation of >/=2 nM avidin and streptavidin. The assay is based on pronounced changes in the fluorescence properties of commercial fluorescein-biotin, or of a newly synthesized biotin-poly(ethylene glycol)-pyrene conjugate, which occur upon binding to avidin and streptavidin. Accurate measurement of (strept)avidin in complex, colored biofluids, such as crude egg white or serum relies on a simple titration protocol. Only occasional recalibration of the reagent solution is required. Due to these merits the proposed assay is particularly suited for rapid measurement of few samples on short notice, for functional control of (strept)avidin-containing reagents after storage, and for the monitoring of (strept)avidin concentrations in large scale processes.

Connections between polarization curves and log(a[i]/a[ref])-pe diagram

When reading papers concerning studies of corrosion of dental amalgam and its phases by means of polarization curves, one often finds it difficult to understand the reasons for the chemical reactions proposed from the form of the polarization curve. Thermodynamic data represented in the form of log(a[i]/a[ref])-pe diagrams, i.e., the logarithm of the activity of a metal or an alloy with reference to the activity of the corresponding metal ion, as a function of pe (a recalculated form of the potential), make it possible for one to determine which chemical reactions can occur on the specimen surface or in the solution within the potential difference used in the polarization experiment and to decide which of these reactions is the most probable. The hypothesis examined in this study is that a log(a[i]/a[ref])-pe diagram can be used in the interpretation of polarization curves. Potentiodynamic polarization curves and log(a[i]/a[ref])-pe diagrams were compared for the corrosion of Ag, Hg, and gamma 1 with and without Sn. It was found that there was a connection between the polarization curves and the log(a[i]/a[ref])-pe diagrams. From the composition of the specimens and the solution and by means of thermodynamic data, pe values for solid corrosion products and relative concentrations of soluble complexes at these pe values were obtained independently of the polarization curves. A much more reliable value for the nobility of metals and alloys was attained by use of the log(a[i]/a[ref])-pe diagrams than by use of the potential of the starting point of the polarization curves. It was found that pe corresponding to the potential of the starting point of the polarization curves in de-aerated synthetic saliva was obtained about two pe units before pe of the most insoluble solid compound formed on the specimen surface or in the solution.

The effect of tin in the Ag-Hg phase of dental amalgam on dissolution of mercury

OBJECTIVES

The aim of this study was to determine the relationship between the tin content in the gamma 1 phase of dental amalgam and the kinetics of mercury dissolution.

METHODS

The tested materials were the same eleven commercial amalgams used by Mahler et al. (1994) to study mercury evaporation, which contained from 0.13% to 2.49% Sn in the gamma 1. In one set of tests, specimens were stabilized in air before exposure to synthetic saliva for three 24 h sampling periods. In another set of tests, they were exposed for 2 h immediately after wet-grinding. Solutions were analyzed for mercury by atomic absorption spectrophotometry. The results were analyzed by ANOVA and Turkey tests (p < 0.05).

RESULTS

For air-stabilized specimens, the 24 h Hg loss was independent of the tin content in gamma 1 for 0.92 to 2.49% Sn. The loss was higher for amalgams containing 0.13% and 0.32% Sn. For abraded specimens, the 2 h Hg loss decreased with increasing tin content in gamma 1. It is proposed that tin oxide growth is initially controlled by diffusion of tin to the gamma 1/tin oxide interface, the rate of which increases with increasing Sn content in gamma 1. Later the growth becomes controlled by the electric field across the oxide. Mercury release rate, controlled by diffusion through the oxide, is inversely proportional to the oxide thickness and initially lower for high Sn content in gamma 1. For a steady state oxide thickness, tin diffusion and tin content in gamma 1 no longer affect mercury dissolution. When tin oxide film dissolves, a minimum tin content is required to maintain a barrier against mercury dissolution.

SIGNIFICANCE

The results show the importance of rapid formation of a surface oxide to minimize mercury dissolution. The theoretical analysis provides a quantitative model for explanation of the effects of tin content and time.

Dissolution of mercury vapor in simulated oral environments

OBJECTIVE

The aim of this investigation was to determine the effects of variables on the dissolution of atomic mercury in simulated oral fluids. This study was based on a hypothesis that the rate of mercury vapor dissolution in synthetic saliva is affected by the oxidation power and stirring of the solution.

METHOD

The reference solution was synthetic saliva, and the oxidation power was increased by hydrogen peroxide or decreased by ascorbic acid. Test solutions were exposed to mercury vapor in a sealed container, and the dissolved mercury concentration was determined after exposures ranging from 2 to 48 h. The results were analyzed by ANOVA and Tukey's multiple comparison test (p < 0.05). The effect of stirring was examined for a 24 h exposure. Student t-tests were used to compare this data (p < 0.05). The analysis for mercury was performed by cold-vapor atomic absorption spectrophotometry.

RESULTS

Mercury dissolved much faster in the highly oxidizing solution with hydrogen peroxide than in the other two solutions, which dissolved mercury at the same rate. In the less oxidizing solutions, the dissolved mercury concentration reached a nearly constant value. Stirring the solution increased the rate of mercury dissolution for the highly oxidizing solution but had no effect on the less oxidizing solutions.

SIGNIFICANCE

The results show the importance of the transformation of mercury from the atomic to the ionic state. When dissolving atomic mercury is not oxidized, it may evaporate and be inhaled, but the dissolution rate becomes low. Under more oxidizing conditions, mercury dissolves faster, but does not generate mercury vapor. Diffusion in the liquid affects the mercury dissolution rate only under highly oxidizing conditions.

Basic studies on heterobifunctional biotin-PEG conjugates with a 3-(4-pyridyldithio)propionyl marker on the second terminus

Heterobifunctional poly(ethylene glycol) (PEG) derivatives with a biotin terminus have been synthesized and characterized with respect to avidin binding. Unambiguous measurement of biotinyl and pyridyldithiopropionyl end groups was established by selecting suitable assays and introducing necessary modifications. Functional studies on the binding of biotin-PEG conjugates to avidin tetramers revealed much similarity to known biotin-spacer-peptide conjugates with 7-27 atom spacers: dissociation kinetics of the initially formed 4:1 complexes were multiexponential, the complex with 2 ligands per avidin dissociating rather slowly with half-times of approximately 2 days at 25 degrees C. The observed stability of 3:1 and 2:1 complexes with avidin is particularly significant since it allows exploitation of the additional advantages of PEG spacers, i.e. reduced steric strain in biotin-avidin-biotin bridges, reduced nonspecific adsorption of biotinylated probes and markers, and, especially, uncomparable fluorescence intensities of biotin-PEG-fluorophore conjugates as is demonstrated in the accompanying study (second of three papers in this issue).

Biotin-pyrene conjugates with poly(ethylene glycol) spacers are convenient fluorescent probes for avidin and streptavidin

Conventional biotin-fluorophore conjugates with approximately 14 atom spacers are strongly quenched when bound to avidin or streptavidin, whereas fluorescence becomes insensitive to receptor binding if typical fluorophores are linked to biotin via poly(ethylene glycol) (PEG) chains (Gruber et al., see the second of three papers in this issue). In the present study the antagonism between PEG-PEG repulsion and fluorophore interaction was examined more closely, using biotin-PEG-pyrene conjugates as model compounds. The antagonistic tendencies between hydrophilic PEG chains and hydrophobic pyrene labels were about balanced in the PEG1900 derivative since quenching was approximately 50% in 4:1 complexes with avidin or streptavidin. In contrast, strong quenching and concomitant excimer fluorescence was seen with the biotin-PEG800-pyrene conjugate, providing for a new fluorescence assay to accurately measure avidin and streptavidin concentrations at > or = 40 and > or = 10 nM, respectively. Association/ dissociation kinetics were analyzed from pyrene fluorescence changes, and dissociation constants were deduced. About 3-fold affinities were observed for streptavidin as compared to avidin, and little influence of PEG chain length was seen. All affinities were increased by a factor of approximately 3 when biotin-PEG-tetramethylrhodamine conjugates were used. The observed effect of fluorophore variation upon biotin binding is unexpectedly small; thus, the kinetic/thermodynamic data appear to be representative for biotin-PEG conjugates in general.

Biotin-fluorophore conjugates with poly(ethylene glycol) spacers retain intense fluorescence after binding to avidin and streptavidin

Conventional biotin-fluorophore conjugates with approximately 14 atom spacers lose most of their fluorescence when binding to avidin or streptavidin, as is demonstrated in the present study. This explains the unusual fact that only biotinylated marker enzymes, but not fluorescent biotins, are regularly used in bioanalytic assays. Novel biotin-spacer-fluorophore conjugates are presented that retain intense fluorescence when binding to avidin or streptavidin. Preservation of fluorescence depends upon the use of poly(ethylene glycol) (PEG) spacers, which are shown not to interfere with biotin function. The observed absence of nonspecific interactions may also be attributed to the PEG chain. These novel fluorescent biotins are expected to be excellent new tools in fluorescence microscopy and related techniques.

Dissolution of mercury from dental amalgam at different pH values

Dissolution of mercury from dental amalgam has been shown to be diminished by the formation of a tin oxide film on the surface of the mercury-rich gamma 1 phase (Marek, 1990b). Since tin oxides dissolve at low pH values (Deltombe et al., 1974), acidic conditions in the oral cavity may cause an increase in the mercury release. The purpose of this study was to determine the effect of acidity in the range of pH 1 to pH 8 on the rate of mercury dissolution in synthetic saliva from tin-free and tin-containing gamma 1 phase and two commercial dental amalgams. The tested hypothesis was that pH affects mercury dissolution only when a protective oxide film dissolves in an acidic environment. After exposures of the specimens for 2 hr or 24 hr in sealed glass bottles, the solutions were analyzed by flameless atomic absorption spectrophotometry for mercury and silver. The results have shown pH-independent mercury dissolution in the range of pH 3 to 8, and a much faster dissolution at pH 1. At all pH values, more mercury dissolved from the tin-free phase than from the tin-containing phase, and the rate of dissolution was lowest for the dental amalgams. The results were affected by the length of the test exposure. The pH independence in a wide range of pH values has been attributed to the atomic mechanism of mercury dissolution. The low rate of mercury dissolution from specimens containing tin has been explained by the formation of a barrier tin oxide film, which dissolved only at the lowest pH. Dissolution of silver at low pH values is believed to have accelerated dissolution of mercury from the tin-free gamma 1 phase. Variation of the dissolution rate with concentration of the dissolved species and kinetics of oxide film dissolution caused the effect of the exposure period.

Effect of mercury on corrosion of eta' Cu-Sn phase in dental amalgams

OBJECTIVES

The eta' Cu-Sn phase is the most corrosion-susceptible major component of the microstructure in high-copper dental amalgams, even though metallurgically prepared specimens of the phase are corrosion-resistant. The purpose of this study was to determine if mercury is the cause of the degradation.

METHODS

Specimens of metallurgically prepared eta' Cu-Sn phase were tested in synthetic saliva using electrochemical methods. Mercury was adsorbed on the surface by exposure to mercury vapor, and the changes in the corrosion potential and anodic polarization characteristics were determined. Galvanic currents between eta' specimens and a high-copper dental amalgam were measured for both Hg-free and Hg-contaminated eta' electrodes.

RESULTS

The Hg-free eta' phase showed a wide region of passivity. Exposure to mercury made the eta' phase electrochemically more active, and current peaks appeared on the polarization curves. The Hg-free eta' electrode was a cathode to a high-copper dental amalgam. The Hg-contaminated eta' electrode started also as a cathode, but became anode after a period of exposure.

SIGNIFICANCE

It was concluded that mercury destabilizes the protective passive film on the eta' phase, making the phase more susceptible to corrosion in the oral environment. The results of the galvanic current measurements seem to indicate that the galvanic interaction between eta' and the other phases facilitates the mercury-related degradation.

Spatiotemporal chaos in an electric current driven ionic reaction-diffusion system

Two types of transitions from the time-periodic spatiotemporal patterns to chaotic ones in the spatially one-dimensional ionic reaction-diffusion system forced either with direct or alternating electric field are described and analyzed by numerical techniques. An ionic version of the Brusselator kinetic scheme is considered. The Karhunen-Loeve decomposition technique is shown to be a possible tool for the global representation of dynamic behavior, but fails as a tool in the identification of the route of transition to chaos in the case of direct current forcing. Higher dimensional chaos with two positive Lyapunov exponents has been identified for the case of alternating current forcing. Results of the Karhunen-Loeve analysis are compared to results of classical analysis of local time series (attractor dimensions, Lyapunov exponents).

The effect of the electrode potential on the release of mercury from dental amalgam

The effect of the electrode potential on the rate of mercury dissolution from the matrix phase (gamma 1) of dental amalgam was investigated. Specimens of the Ag-Hg phase, with and without dissolved tin, were exposed to synthetic saliva and maintained at various potentials by means of a potentiostat. The amount of dissolved mercury was determined after 24 h by cold-vapor Atomic Absorption Spectrophotometry. Anodic polarization curves for the gamma 1 specimens and pure silver and mercury were also recorded. The results for the Ag-Hg phase showed a potential-independent dissolution rate between -0.6 and -0.1 V (SCE), followed by a sharp increase. Mercury dissolution from the Ag-Hg-Sn phase was much slower than from the tin-free gamma 1 phase, and potential-independent to +0.05 V (SCE); a sharp increase in mercury dissolution was observed at +0.1 V (SCE). The anodic polarization curves for the Ag-Hg-Sn phase indicated passivity between -0.67 V and +0.1 V (SCE), but no clear passivation for the Ag-Hg specimen, silver, or mercury. The results show that in the potential-independent region, mercury dissolved in the atomic form from both the tin-free and tin-containing gamma 1 phase. The increase in dissolution in the upper range of potentials was tentatively attributed to selective anodic dissolution of silver and an onset of electrochemical dissolution. The results indicate that the rate of mercury release from the gamma 1 phase of dental amalgam was not affected by potential changes due to alloying or galvanic contacts unless the potential exceeded some critical value.

Influence of food deprivation on SCFA and electrolyte transport across sheep reticulorumen

Net absorption rates for SCFA, sodium, chloride, magnesium, and water were measured in the temporarily isolated and washed reticulorumen of sheep. The animals were either fed hay ad lib. plus concentrates once daily or were deprived of food for two days. Food deprivation led to decreased net absorption of all the substances tested. Comparing the solutes, the relative decreases varied between 43% (butyrate) and 56% (acetate). The decrease in solute absorption was accompanied by diminished water absorption. It is concluded that the reduction in absorption may be beneficial for the animal in that energy consumption is diminished and the reservoir function of the forestomach will be maintained longer. However, the reduced absorptive capacity may lead to a deficiency of magnesium, which is thought to be absorbed mainly by the forestomachs.