Effects of DC Magnetic Fields on Magnetoliposomes.

The potential use of magnetic nanoparticles (MNPs) in biomedicine as magnetic resonance, drug delivery, imagenology, hyperthermia, biosensors, and biological separation has been studied in different laboratories. One of the challenges on MNP elaboration for biological applications is the size, biocompatibility, heat efficiency, stabilization in physiological conditions, and surface coating. Magnetoliposome (ML), a lipid bilayer of phospholipids encapsulating MNPs, is a system used to reduce toxicity. Encapsulated MNPs can be used as a potential drug and a gene delivery system, and in the presence of magnetic fields, MLs can be accumulated in a target tissue by a strong gradient magnetic field. Here, we present a study of the effects of DC magnetic fields on encapsulated MNPs inside liposomes. Despite their widespread applications in biotechnology and environmental, biomedical, and materials science, the effects of magnetic fields on MLs are unclear. We use a modified coprecipitation method to synthesize superparamagnetic nanoparticles (SNPs) in aqueous solutions. The SNPs are encapsulated inside phospholipid liposomes to study the interaction between phospholipids and SNPs. Material characterization of SNPs reveals round-shaped nanoparticles with an average size of 12 nm, mainly magnetite. MLs were prepared by the rehydration method. After formation, we found two types of MLs: one type is tense with SNPs encapsulated and the other is a floppy vesicle that does not show the presence of SNPs. To study the response of MLs to an applied DC magnetic field, we used a homemade chamber. Digitalized images show encapsulated SNPs assembled in chain formation when a DC magnetic field is applied. When the magnetic field is switched off, it completely disperses SNPs. Floppy MLs deform along the direction of the external applied magnetic field. Solving the relevant magnetostatic equations, we present a theoretical model to explain the ML deformations by analyzing the forces exerted by the magnetic field over the surface of the spheroidal liposome. Tangential magnetic forces acting on the ML surface result in a press force deforming MLs. The type of deformations will depend on the magnetic properties of the mediums inside and outside the MLs. The model predicts a coexistence region of oblate-prolate deformation in the zone where χ = 1. We can understand the chain formation in terms of a dipole-dipole interaction of SNP.

Ethanol reveals novel mercury detoxification step in tissues.

Volatile mercury was produced de novo by mouse tissue homogenates that contained mercuric ions. Ethanol stimulated the release of tissue mercury into the vapor phase, and the mechanism appears to be an inhibition of reoxidation of volatile mercury. Components responsible for mercury volatilization are heat-labile. The highest volatilizing activity in the liver is associated with the soluble fraction obtained after centrifugation at 105,000g.

The effects of dose of elemental mercury and first-pass circulation time on exhalation and organ distribution of inorganic mercury in rats.

The lung plays a major role in the removal of dissolved elemental mercury (Hg0) from the bloodstream. During the first passage through the lung after an intravenous dose of Hg0 dissolved in aqueous buffer, from 10 to 17% was exhaled depending on the dose (0.11 or 1.1 micrograms Hg/rat) and the injection site (jugular versus tail vein). Furthermore, evidence is presented that subsequent exhalation over the next 50 s, before the rats were killed and the mercury determined in the lung at that time, was largely Hg0-extracted during the first pass. The total mercury extracted during the 60 s period was in the range of 40-49% of the dose. The oxidation of Hg0 to Hg2+ in red cells is important in limiting the availability of Hg0 to certain tissues. Thus, after a short residence time in blood (0.6 s after jugular vein injection), 12.9-17% is exhaled in the first pass as compared to 10.4-12.2% with a longer residence time (1.8 s after tail vein injection). Furthermore, there was a general tendency, even at 60 s after dosing, for certain tissues - lung, brain, and heart - to have higher values after dosing from the jugular vein. It was estimated that the half-time for oxidation was 3.3 s. Our results confirm previous observations that the form of inorganic mercury greatly influences the short-term deposition in certain tissues. Thus as compared to Hg2+, administration of Hg0 increases lung levels 5-10-fold; brain, 4-fold; and heart, 3-fold. Blood levels are lower after Hg0, particularly after the higher dose. Such findings are consistent with a model wherein Hg0 is in part oxidized by red blood cells, the remainder rapidly diffusing in tissues where it is also oxidized to Hg2+.

The effects of carbon disulphide exposure on brain catecholamines in rats.

1. Rats exposed to 2.0 mg/1. carbon disulphide (CS(2)) in the inspired air for 2 days, 4 h a day, showed a 13% decrease in their brain noradrenaline concentration and a 16% increase in their brain dopamine concentration.2. After exposure for 5 or 10 days there was a further decrease in the concentration of noradrenaline in the brain, but brain dopamine returned to the control level.3. In animals treated intraperitoneally with 2.0 mg/kg reserpine and exposed 2 and 3 days later to 2.0 mg/1. CS(2) for 4 h per day, the brain dopamine concentration showed a 77% increase compared with the unexposed reserpinized animals, but the noradrenaline concentration remained unchanged.4. The dopamine concentrations in the adrenals after 10 days' exposure to 2.0 mg/1. CS(2) were 67% to 100% higher than in the control animals. In reserpinized rats, 2 days' exposure to CS(2) nearly trebled the dopamine content of adrenals.5. Exposure to CS(2) had no effect on the tyrosine concentration in the brain, and there was no change in the brain monoamine oxidase (MAO) activity. Tyrosine in the brain showed a 30 to 96% increase in concentration and MAO activity, using kynuramine as substrate, showed an approximately 5% increase 0.5 to 2 h after the subcutaneous administration of 500 mg/kg sodium diethyldithiocarbamate.6. CS(2) at 10(-2)M or lower concentrations had no inhibitory effect on the brain MAO activity in vitro. Diethyldithiocarbamate inhibited MAO at 10(-2)M, but not at 10(-3)M or lower concentrations.

The effects of dimercaptosuccinic acid on the excretion and distribution of mercury in rats and mice treated with mercuric chloride and methylmercury chloride.

1 All five rats in a group survived if dimercaptosuccinic acid (DMSA), a water soluble derivative of 2,3-dimercaptopropanol (BAL), was given in doses of 10-40 mg/kg intraperitoneally 30 min, 4 and 24 h after administration of 2.4 mg/kg Hg as HgCl2, whereas three out of a group of five died if DMSA was not given. DMSA 20 mg/kg increased urinary excretion and decreased the body burden significantly more than 10 mg/kg DMSA, but further doubling of the dose had only marginal effects. 2 DMSA was able to reduce body burden and increase urinary excretion of Hg when intraperitoneal treatment started eight days after the subcutaneous administration of HgCl2. 3 DMSA was effective in decreasing body burden and the brain concentration of Hg in rats dosed orally with methylmercury (MeHgCl) when intraperitoneal treatment started with 40 mg/kg DMSA 24 h after Hg. Increase in the urinary excretion of mercury was responsible for the decrease in body burden. 4 DMSA was effective when given in the drinking water of rats or mice both against inorganic Hg and MeHgCl. In mice treated intraperitoneally with MeHgCl, DMSA 19.5 mug/ml in the drinking water caused a significant decrease in the body burden and increase in the excretion of Hg. 5 DMSA was about four times more efficient than D-penicillamine in decreasing the body burden of Hg. As their toxicity is in the same range, the higher efficiency of DMSA offers a larger margin of safety for the mobilization of Hg.

Combined effect of sodium maleate and some thiol compounds on mercury excretion and redistribution in rats.

1. (+)-Penicillamine in a dose of 193 mumoles/kg given subcutaneously twice a day on the sixth and seventh days after the administration of 100 mug mercury increased the urinary excretion of rats more than the equimolar dose of N-acetyl-(+)-penicillamine but less than 2,3-dimercaptopropanol 48.3 mumoles/kg.2. Sodium maleate in a dose of 156 mumoles/kg given on the sixth and seventh days after the mercury did not influence mercury excretion or redistribution. Sodium maleate in the same dose increased considerably the effect of (+)-penicillamine on the urinary excretion and redistribution of mercury. It increased the effect of N-acetyl-(+)-penicillamine only slightly. There was a tendency to decrease the effect of 2,3-dimercaptopropanol.3. All the complexing agents decreased the kidney content of mercury and increased the liver and blood concentration of mercury. These changes were highest with 2,3-dimercaptopropanol. The combination of sodium maleate with (+)-pencillamine caused higher mercury excretion and lower kidney content but a smaller increase in the liver and blood mercury contents than 2,3-dimercaptopropanol.

Carbon disulphide exposure affects the response of rat adrenal medulla to hypothermia and hypoglycaemia.

The effects of hypothermia and hypoglycaemia on adrenal catecholamines and dopamine-beta-hydroxylase were compared in control and carbon disulphide (CS2) exposed rats 24 h after the last of ten daily 4 h inhalation exposures to CS2, 2 mg 1(-1) air. Animals were either kept in a cold room (0 degrees C) for 210 min with or without immobilization or were injected with insulin 100 u kg-1. Before these treatments CS2 exposed rats had more dopamine and less adrenaline in their adrenals than controls, and CS2 exposure also elevated the adrenal synthesis of catecholamines. Cold with immobilization or insulin treatment depressed the adrenal adrenaline content and increased the plasma concentrations of noradrenaline and adrenaline. There were no consistent differences between control and CS2 exposed rats. The adrenal dopamine content increased during cold exposure with immobilization or after insulin treatment both in CS2 exposed and control rats. The increase was smaller in CS2 exposed rats but the final dopamine values were nearly identical in the two groups. Exposure to cold (without immobilization) increased the adrenal dopamine content and the rate of catecholamine synthesis in control, but not in CS2 exposed rats. The increase in controls was less than the difference between the pre-cold exposure values of control and CS2 exposed rats. It is concluded that the elevation of adrenal dopamine content and catecholamine synthesis in CS2 exposed rats satisfy part of the demand placed on the adrenal medulla by hypothermia and hypoglycaemia. Consequently the changes induced by the latter treatments were smaller in CS2 exposed than in non-exposed rats. Moreover, when CS2 exposed rats were subjected to cold stress without immobilization their catecholamine synthesis was higher than the level measured in control rats after cold exposure.

The dependence of biliary methylmercury secretion on liver GSH and ligandin.

The biliary secretion of methylmercury was investigated in male rats which were given i.p. 400 mumoles/kg azathioprine or 96 mumoles/kg benziodarone 2 hr after the i.v. injection of 5 mumoles/kg MeHgCl. A group of rats were given 400 mg/kg trans-stilbene oxide (TSO) for 4 days before treatment with 10 mumoles/kg MeHgCl. A common link between these three compounds is their interference with ligandin. Azathioprine is a competitive inhibitor of glutathione S-transferase, benziodarone is covalently bound to ligandin and TSO is an inducer of liver ligandin. Although only azathioprine depletes liver GSH stores, both azathioprine and benziodarone inhibited the biliary secretion of methylmercury. As there is published proof that the reaction of MeHg+ with GSH does not require enzymatic help, the inhibitory effect of azathioprine and benziodarone confirms the role of ligandin in the transport of methylmercury or its GSH complex. However, the biliary secretion of methylmercury was increased only slightly by TSO pretreatment, but when 2 hr after the injection of MeHgCl animals received 2 mmoles/kg GSH, secretion increased twice as much in TWO pretreated than in control rats. This indicates the dual dependance of biliary methylmercury secretion on liver GSH and ligandin.

Stimulation of dopamine-beta-hydroxylase in rat adrenals by repeated exposures to carbon disulphide.

The conversion of dopamine to noradrenaline, measured shortly after exposure to carbon disulphide, is reduced in the adrenals of rats. However, alongside this effect, carbon disulphide produces a gradual increase in the adrenal content of dopamine-beta-hydroxylase indicated by the increase of in vitro estimated enzyme activity and by the increased in vivo conversion of dopamine to noradrenaline observed 24 hr after the ninth exposure. Thus, after repeated exposures, the reduced rate of noradrenaline synthesis detectable immediately after the exposure alternates with the increased rate of synthesis.

The stimulation and inhibition of the exhalation of volatile selenium.

Administration of methylmercury (1.5-24 mumol kg-1; s.c.) to female rats simultaneously with Na2 75SO3 (0.25 or 24 mumol kg-1; s.c.) causes a dose-dependent increase in the exhalation of dimethylselenide. At the low selenite dose level, exhalation of 75Se over a 24 hr period is about fourfold greater after treatment with 24 mumol kg-1 methylmercury than that (approximately 0.75% of the dose) in the controls, but excretion by other routes (urine, faeces) and the liver and kidney contents of 75Se are not affected significantly. At the higher selenite dose level (24 mumol kg-1) exhalation of 75Se is correlated with the log dose of methylmercury. The faecal and urinary excretion remains essentially unaffected, and in rats treated with 24 mumol kg-1 methylmercury the 75Se contents of the liver, kidneys and blood are reduced by 78%, 86% and 18% respectively. The effects of the alkylmercurial are not specific since, at this selenite dose level, ethylmercury increases the exhalation and decreases the liver and kidney contents of 75Se approximately to the same extent as an equimolar dose of methylmercury. In methylmercury-treated and control animals dosed with 24 mumol kg-1 Na 75SeO3 the exhalation of 75Se is inhibited to the same extent by periodate-oxidized adenosine (PAD; 15 mumol kg-1, i.p.) in the first 6 hr. Later inhibition is less pronounced in methylmercury-treated rats. Under these conditions PAD has little effect on the renal content, but increases the hepatic content of 75Se. It seems, therefore, that the methylation of selenite occurs mainly in the liver and in both control and methylmercury-treated animals, S-adenosylmethionine is the major methyl donor. It is possible that methylmercury does not affect directly the methylation enzyme system but, by competition for protein sulphydryl groups, increases the availability of the intermediary selenide anion.

Epidemiological and experimental aspects of metal carcinogenesis: physicochemical properties, kinetics, and the active species.

The carcinogenic properties of selected metals and their compounds are reviewed to provide a useful reference for existing knowledge on relationships between physical and chemical forms, kinetics and carcinogenic potential and between epidemiology, bioassays, and short-term tests. Extensive consideration is given to arsenic, beryllium, cadmium, chromium, lead, and nickel. Other metals such as antimony, cobalt, copper, iron, manganese, selenium, and zinc are discussed briefly.

Theoretical and practical considerations on the problem of metal--metal interaction.

The interaction between two metals, which can be either synergistic or antagonistic, implies that the behavior of one is changed by the presence of the other. Possible mechanisms of these interactions, which include chemical association, competition for carriers, metabolic changes, induction of binding proteins, membrane alterations are discussed.

The effect of carbon disulphide on the stereotypic effect of dopamine agonists.

Exposure to CS2 increased the intensity of apomorphine-induced stereotypy in male rats without increasing the reaction time. With amphetamine, an indirect agonist of dopamine, exposure to CS2 had a more intensive effect and significantly prolonged the length of reaction.

Effects of diethyldithiocarbamate on the catabolism of tyrosine in the rat brain.

500 mg/kg sodium diethyldithiocarbamate (DDC) and trace quantities of uniformly labelled 14C-tyrosine were administered simultaneously to male albino rats of Porton-Wistar strain of approximately 210 g body weight. Thirty minutes later total radioactivity, the concentration and the specific activity of free tyrosine were increased both in plasma and in the brain by 40% compared with rats untreated with DDC. The incorporation of 14C from 14C-tyrosine into the fraction corresponding to the elution of glutamine-glutamate from the amberlite resin column was 80% less in the brain 30 min after DDC. The exhalation of 14CO2 was depressed by 80% in the first hour after DDC. When 14C-tyrosine was given 3.5 h after DDC the only differences between experimental and control rats were the increased incorporation of 14C into the glutamine-glutamate and aspartate fractions and the increased exhalation of 14CO2 which became significiant in the third and fourth half hour periods after the injection of 14C-tyrosine. From the experiments it is concluded that DDC, an inhibitor of dopamine-beta-hydroxylase, also interferes with the major catabolic pathway of tyrosine.

The hepatotoxicity of 3-amino-1,2,4-triazole and carbon disulphide in phenobarbitone-treated starved rats.

In phenobarbitone-treated starved male rats 1 g/kg 3-amino-1,2,4-triazole produced moderate liver necorsis and increased the serum glutamic-pyruvic transaminase activity. If half an hour after the administration of aminotriazole animals were exposed for 4 h to 2.0 mg/l CS2, the necrotic damage in the liver was larger and the serum glutamic-pyruvic transaminase activity higher than in rats not exposed to CS2. Carbon-disulphide in phenobarbitone-treated starved male rats caused only a very slight increase in the serum transminase activity in spite of the widespread hydropic degeneration in the liver. These experiments indicated that increase in serum transaminase activity is the consequence of necrosis and not hydropic degeneration; aminotriazole is hepatotoxic in rats when microsomal enzymes are induced and the hepatotoxicity of aminotriazole and carbon disulphide is potentiated by the administration of the other compound.

Maleate induced change in the kidney binding of mercury in rats pretreated with cadmium.

The kidney uptake of Hg2+ was increased by Cd2+-pretreatment when Hg2+ was given intraperitoneally but not subcutaneously. Subsequent s.c. administration of maleate increased Hg2+ release from the kidneys only if Hg2+ was given subcutaneously. Neither the effect of Cd2+, nor that of maleate, on the distribution of Hg2+ among the renal soluble protein fractions was affected by the route of Hg2+ administration. The protective effect of Cd2+-pretreatment against the nephrotoxic effect of Hg2+ was also independent of the route of Hg2+ administration. Maleate given in nephrotoxic doses removed Hg2+ and copper, but not Cd2+ from the renal metallothionein fraction. Mercury in the urine, however, was not complexed by proteins with the molecular weight of thionein, but was bound to high molecular weight proteins and diffusible molecules. These findings are discussed in relation to the role of metallothionein in the interaction between Cd2+ and Hg2+.

Cadmium-thionein and the protection by cadmium against the nephrotoxicity of mercury.

Uptake of Hg2+ into the renal and hepatic metallothioneins of rats is increased by pretreatment with Cd2+. This increased uptake occurs both by displacement of Cd2+ (and of Zn2+) from the presynthesized cadmium-thionein, and by further synthesis of thionein. The former mechanism predominates in the kidney of the male rat, which is more sensitive than the female to Hg2+. The latter mechanism, which occurs particularly in the kidney of the female, also is considered to involve an initial displacement of Cd2+ from cadmium-thionein, but is followed by further synthesis of the metalloprotein, which is induced by the liberated cation. Pretreatment with Cd2+ increases not only the incorporation of Hg2+ into the renal metallothionein, but also the uptake of Hg2+ into other components of the kidney. At dose levels of Hg2+ at which Cd2+-pretreatment gives complete protection against the nephrotoxicity in male and female rats, the increase in Hg2+-uptake into both the particulate components and into the soluble fraction of the kidney is greater than into metallothionein. It is concluded, therefore, that binding of Hg2+ by pre-induced cadmium-thionein alone cannot explain the protection by Cd2+ against the nephrotoxicity of Hg2+.

The interaction of cadium-induced rat renal metallothionein with bivalent mercury in vitro.

Addition of Hg2+ in vitro to metallothionein (Cd : Cu : Zn = 6.5 : 4 : 1) from the kidneys of Cd2+ exposed rats appears to result initially in the replacement of Zn2+, then Cd2+ and finally copper. The ionic stoichiometries between Hg2+-binding and the release of Cd2+ (or Zn2+) and copper are 3 : 2 and 1 : 1 respectively. After treatment with amounts of Hg2+ sufficient to displace completely either the bound Zn2+ and Cd2+, or all of the original cations, the metallothionein has little or no negative charge at pH 8.0 and is not resolved into the two isometallothioneins, which characterize the (Cd, Cu, Zn)-thionein, by ion exchange chromatography at this pH. Cation substitution occurs in both isometallothioneins and there is no evidence that Hg2+ interacts preferentially with one of them. Treatment of the metallothionein with increasing amounts of Hg2+, equivalent to approx. 25% and 50% of the bound cations gives rise to a range of molecular species of progressively decreasing negative charge. The consistent stiochiometry between Hg2+ uptake and Cd2+ or Zn2+ release at all concentrations of Hg2+ indicates that free thiol groups are not formed during the substitution reaction.

The in vivo effects of maleate on the cation-distribution in rat kidney metallothionein sub-fractions after induction by cadmium and/or mercury.

The metallothionein fractions, isolated by gel filtration from the kidneys of rats that have been dosed with Cd2+, Hg2+ or Cd2+ followed by Hg2+, yield very different elution profiles on ion-exchange chromatography. The metallothionein from Cd2+-treated animals is resolved into the isomethallothioneins I and II and a minor, less negatively-charged species (B), which contains Cd2+ and copper, but little Zn2+. The corresponding fraction from the kidneys of rats doses with Hg2+ yields five components, all of which contain Hg2+, Zn2+ and Cu, but in different ratios. Three of these compounds correspond in their elution characteristics from DE-cellulose with the above-mentioned isometallothioneins I and II and fraction B. The last of these, which also is rich in Cu, is the major Hg2+-binding component. The distribution of Hg2+ and of other cations between these five sub-fractions, but not the number of sub-fractions, is altered by Cd2+-pretreatment of the animals. Treatment of Cd2+-dosed rats with sodium maleate has no significant effect on the distribution of cations (Cd2+, Zn2+ and copper) amongst the renal metallothionein subfractions. The same treatment, applied to animals dosed with either Hg2+ only, or Cd2+ followed by Hg2+, causes the elimination of 70--75% of the Hg2+ from the metallothionein fraction. Loss occurs from all subfractions, but is greatest in subfraction B, which also loses copper. Whilst it is possible that Hg2+ may induce metallothionein and other metalloproteins in the kidney, Hg2+ appears to bind to both isometallothioneins I and II, when these are induced by Cd2+-pretreatment. The loss of Hg2+, but not of Cd2+, from these metalloproteins after treatment with sodium maleate may be related to differences in the relative binding affinities of the two cations for thionein and other cellular proteins.