Effects of lanthanum in cellular systems. A review

Lanthanum from a modified clay used in eutrophication control is bioavailable to the marbled crayfish (Procambarus fallax f. virginalis)

To mitigate eutrophication in fresh standing waters the focus is on phosphorus (P) control, i.e. on P inflows to a lake as well as a lake's sediment as internal P source. The in-lake application of the lanthanum (La) modified clays – i.e. La modified bentonite (Phoslock) or La modified kaolinite, aim at dephosphatising the water column and at reducing the release of P from a lake's sediment. Application of these clays raises the question whether La from these clays can become bioavailable to biota. We investigated the bioavailability of La from Phoslock in a controlled parallel groups experiment in which we measured the La in carapace, gills, ovaries, hepatopancreas and abdominal muscle after 0, 14 and 28 days of exposure to Phoslock. Expressing the treatment effect as the difference of the median concentration between the two treatment groups (Phoslock minus control group) yield the following effects, the plus sign (+) indicating an increase, concentrations in µg g⁻¹ dry weight: Day 14: carapace +10.5 µg g⁻¹, gills +112 µg g⁻¹, ovaries +2.6 µg g⁻¹, hepatopancreas +32.9 µg g⁻¹ and abodminal muscle +3.2 µg g⁻¹. Day 28: carapace +17.9 µg g⁻¹; gills +182 µg g⁻¹; ovaries +2.2 µg g⁻¹; hepatopancreas +41.9 µg g⁻¹ and abodminal muscle +7.6 µg g⁻¹, all effects were statistically significant. As La from Phoslock is bio-available to and taken up by the marbled crayfishes (Procambarus fallax f. virginalis), we advocate that the application of in-lake chemical water treatments to mitigate eutrophication should be accompanied by a thorough study on potential side effects.

Temporal analysis of dissolution by-products and genotoxic potential of spherical zinc-silicate bioglass: "imageable beads" for transarterial embolization

Embolization of vascular tumors is an important tool in minimally invasive surgical intervention. Radiopaque, non-degradable, and non-deformable spherical zinc-silicate glass particles were produced in a range of 45-500 μm. Three size ranges (45-150, 150-300, and 300-500 μm) were used in the current study. The glass microspheres were eluted in polar (saline solution) and non-polar (dimethyl sulfoxide) medium, and ion release profiles were recorded using inductively coupled plasma atomic emission spectroscopy. Approximately 80% of Gaussian distribution was achieved by simple sieving. The ions released from the microspheres were dependent upon surface area to volume ratio as well as the nature of elution media. Greater ions were released from smaller particles (45-150 μm) having largest surface area in polar medium. For the genotoxicity bacterial mutation Ames assay, the concentrations of all the ions were well below their therapeutic concentration reported in the literature. No mutagenic effect was observed in the bacterial mutation Ames test. Hence, it can be concluded that the glass microspheres produced herein are non-mutagenic further supporting the materials potential as a suitable embolic agent.

Immune dysfunction and liver damage of mice following exposure to lanthanoids

In an effort to investigate the effects of exposure to lanthanoids (Ln) on the immune response and liver function, mice were orally exposed to LaCl3 , CeCl3 , and NdCl3 at 2, 10, and 20 mg/kg doses for 30 days, respectively; lymphocyte counts, serum IgM level, hematological indices, biochemical parameters of liver functions, and histopathological changes in Ln(3+) -treated mice were assessed. Indeed, 20 mg/kg Ln(3+) significantly inhibited mice growth and reduced the counts of white blood cells, platelets, and reticulocyte in mice blood. Specifically, in these Ln(3+) -treated mice, CD3+, CD4+, CD8+, CD19+ and NK cells, and CD4+/CD8+ ratio as well as serum IgM level were decreased. Furthermore, liver function was disrupted, as evidenced by the increased alanine aminotransferase, total bilirubin, total bile acid and triglycerides, and the decreased glucose and ratio of albumin to globulin. The cytoarchitecture damage and fatty degeneration in liver caused by Ln(3+) at 20 mg/kg dose were also observed. Our findings showed that exposure to Ln affected the cell and humoral immunity and disturbed liver function in mice. In addition, Ce(3+) was found to exhibit higher toxicity than La(3+) and Nd(3+).

Lake responses following lanthanum-modified bentonite clay (Phoslock®) application: an analysis of water column lanthanum data from 16 case study lakes

Phoslock(®) is a lanthanum (La) modified bentonite clay that is being increasingly used as a geo-engineering tool for the control of legacy phosphorus (P) release from lake bed sediments to overlying waters. This study investigates the potential for negative ecological impacts from elevated La concentrations associated with the use of Phoslock(®) across 16 case study lakes. Impact-recovery trajectories associated with total lanthanum (TLa) and filterable La (FLa) concentrations in surface and bottom waters were quantified over a period of up to 60 months following Phoslock(®) application. Both surface and bottom water TLa and FLa concentrations were <0.001 mg L(-1) in all lakes prior to the application of Phoslock(®). The effects of Phoslock(®) application were evident in the post-application maximum TLa and FLa concentrations reported for surface waters between 0.026 mg L(-1)-2.30 mg L(-1) and 0.002 mg L(-1) to 0.14 mg L(-1), respectively. Results of generalised additive modelling indicated that recovery trajectories for TLa and FLa in surface and bottom waters in lakes were represented by 2nd order decay relationships, with time, and that recovery reached an end-point between 3 and 12 months post-application. Recovery in bottom water was slower (11-12 months) than surface waters (3-8 months), most probably as a result of variation in physicochemical conditions of the receiving waters and associated effects on product settling rates and processes relating to the disturbance of bed sediments. CHEAQS PRO modelling was also undertaken on 11 of the treated lakes in order to predict concentrations of La(3+) ions and the potential for negative ecological impacts. This modelling indicated that the concentrations of La(3+) ions will be very low (<0.0004 mg L(-1)) in lakes of moderately low to high alkalinity (>0.8 mEq L(-1)), but higher (up to 0.12 mg L(-1)) in lakes characterised by very low alkalinity. The effects of elevated La(3+) concentrations following Phoslock(®) applications in lakes of very low alkalinity requires further evaluation. The implications for the use of Phoslock(®) in eutrophication management are discussed.

Signal pathway of hippocampal apoptosis and cognitive impairment of mice caused by cerium chloride

Experimental studies have demonstrated that lanthanides could impair cognitive functions of children and animals, but very little is known about the hippocampal apoptosis and its molecular mechanism. The study investigated the signal pathway of hippocampal apoptosis induced by intragastric administration of CeCl(3) for 60 consecutive days. It showed that cerium had been significantly accumulated in the mouse hippocampus, and CeCl(3) caused hippocampal apoptosis and impairment of spatial recognition memory of mice. CeCl(3) effectively activated caspase-3 and -9, inhibited Bcl-2, and increased the levels of Bax and cytochrome c, promoted accumulation of reactive oxygen species in the mouse hippocampus. It implied that CeCl(3)-induced apoptosis in the mouse hippocampus could be triggered via mitochondrion-mediated pathway. Our findings suggest the need for great caution to handle the lanthanides for workers and consumers.

The mechanism of the molecular interaction between cerium (III) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)

The mechanism of the molecular interaction between Ce3+, a member of rare earth elements, and Rubisco in vitro is investigated. The carboxylase activity of Rubisco greatly increased under low concentrations of Ce3+ and decreased under high concentrations of Ce3+. The ultraviolet absorption spectra show that the various concentrations of Ce3+ treatment do not shift the characteristic peaks of Rubisco while the characteristic peak intensity of Rubisco increases with increasing Ce3+ concentration. The Rubisco-Ce3+ interactions also do not cause any noticeable change in the λmax of Rubisco fluorescence spectra. However, the fluorescence intensity of Rubisco is found quenched by the addition of Ce3+, which strongly suggests that Ce3+ could directly bind to the Rubisco protein. and the binding sites is estimated to 1.52 per protein. The binding between Ce3+ and Rubisco is also proved by extended X-ray absorption fine-structure essay; Ce3+ coordinated with eight oxygen atoms of Rubisco in first shells and six oxygen atoms in second shells. The results implied that Ce3+ might improve the microenvironment of Rubisco and, in turn, affected the carboxylase capacity of Rubisco greatly.

Effects of lanthanum chloride administration on detouring learning in chicks

Lanthanum cations are well known for their inhibitory actions on calcium channels, and calcium cations are indispensable for the development of brain. Lanthanum may interfere with the developing central nervous system. Detour learning task in chicks is an excellent model to study the development of central nervous system. In the present study, we examined the effects of lanthanum chloride exposure on the development of spatial cognition using the detour learning task. The data suggest that the chicks injected with lanthanum chloride (10 or 5 mM) had significantly delayed the response latency of detour learning but not the chicks injected with lanthanum chloride (1 mM). The effect of lanthanum exposure on the development of spatial cognition is dose relative.

Lanthanum acetate inhibits vascular calcification induced by vitamin D3 plus nicotine in rats

Lanthanum, a rare earth element, has been used to decrease serum phosphorus level in patients with chronic renal disease and hyperphosphatemia. We aimed to observe the effect and mechanism of two doses of lanthanum acetate (375 and 750 mg/kg/day) on vascular calcification induced by vitamin D3 plus nicotine treatment in rats for 4 weeks. As compared with control rats, rats with calcification showed widespread calcified nodules and irregular elastic fibers in calcified aorta on von Kossa calcium staining and increased aortic calcium and phosphorus contents, alkaline phosphatase (ALP) activity and bone-related protein expressions for osteopontin (OPN) and type III sodium dependent phosphate cotransporter Pit-1 (Pit-1). After treatment with either dose of lanthanum acetate, the calcified nodules and degree of irregular elastic fibers decreased in aortas. Lanthanum acetate at 750 mg/kg/day was more effective than 375 mg/kg/day in lessening vascular calcification by significantly reducing plasma phosphorus level, calcium x phosphorus product and ALP activity, by 30.3%, 28.6%, and 68.6%, respectively; reducing aortic phosphorus and calcium contents and ALP activity, by 48%, 53.1%, and 63.5% (all P < 0.01), respectively; reducing aortic mRNA level of OPN and Pit-1, by 55.8% (P < 0.01) and 38.8% (P < 0.05) and protein level of OPN and Pit-1, by 37.2% and 27.2% (both P < 0.01), respectively; and increasing carboxylated matrix Gla-protein (MGP) protein expression by 33.7% (P < 0.05), as compared with rats treated with vitamin D3 and nicotine alone. Lanthanum acetate could effectively inhibit the pathogenesis of vascular calcification.

Enhancement of lanthanum (III) on sodium currents in acutely isolated hippocampal CA1 neurons of rat

The effects of lanthanum (III) (La(3+)) on voltage-gated sodium channel currents (I (Na)) in freshly dissociated rat hippocampal CA1 neurons were studied using the whole-cell patch clamp techniques. La(3+) reversibly enhanced I (Na) in a concentration- and voltage-dependent manner. The 50% enhancement concentration (EC(50)) of La(3+) on I (Na) was 9.93 microM. In addition, 10 microM La(3+) shifted the steady state activation curve of I (Na) towards positive potential and the steady state inactivation curve towards negative potential without changing the slope factor. These results indicated that La(3+) could increase the amplitudes of I (Na) and change the activation and inactivation courses of I (Na) even in very low concentration.

Effects of lanthanum chloride administration in prenatal stage on one-trial passive avoidance learning in chicks

Lanthanum cations (La 3+) are well known for their inhibitory actions on calcium channels. Prenatal lanthanum exposure may affect the development of embryo and alter the capacity for learning and memory in adults, and the one-trial passive avoidance learning paradigm with day-old chicks is an excellent model to study several mechanisms of memory formation. In the present study, we examined the effects of prenatal lanthanum chloride exposure on memory consolidation using one-trial passive avoidance learning task in day-old chicks. The data suggest that chicks injected with lanthanum chloride (2 mg/kg) daily from E9 to E16 had significantly impaired long-term memory at 120 min after training (p < 0.05) but not the chicks injected with lanthanum chloride (0.1 mg/kg) daily from E9 to E16.

Effects of rare earth elements on the distribution of mineral elements and heavy metals in horseradish

In order to investigate the effects of rare earth elements (REEs) on horseradish, the distribution of the mineral elements and heavy metals in different organs of horseradish have been studied by using inductively coupled plasma-atomic emission spectrometry (ICP-AES). Meanwhile, three variable major parameters, namely the concentration of REEs, the type of REEs, and the growth stage of plant were chosen. The results indicated that the test REEs, Ce(III) and Tb(III), could be accumulated in leaves, stems and roots of horseradish. In addition, we found that the content of mineral elements was increased in horseradish treated with 20mgl(-1) of Ce(III), but not those with the 20mgl(-1) of Tb(III). Moreover, the content of mineral elements in horseradish was decreased with the increasing concentration of REEs (100, 300mgl(-1)). Furthermore, we found that there were the opposite effects on the content of the heavy metals in horseradish treated with REEs. Finally, we found that the effect of REEs on the accumulation of REEs, and the content of mineral elements or heavy metals of horseradish during vigorous growth stage, no matter positive or negative, was more obvious than that of the other growth stages. These results demonstrated that the distribution behaviors of mineral elements and heavy metals in horseradish can be affected by the type and concentration of REEs, and the growth period of plant.

Potentiation of inhibitory amino acid receptors-mediated responses by lanthanum in rat sacral dorsal commissural neurons

Lanthanum is one of rare earth cations with extremely active chemical property and has been reported to influence neuronal transmitter systems. To date, little attention has been directed towards the sacral dorsal commissural nucleus (SDCN), which serves as a relay of sensory information from the pelvic viscera in the spinal cord. Therefore, the effect of lanthanum on the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and glycine (Gly) responses in neurons acutely dissociated from the rat SDCN was investigated using the nystatin-perforated patch-recording configuration under voltage-clamp conditions. At a holding potential of -40 mV, La(3+) reversibly potentiated GABA (3 microM)-activated currents (I(GABA)) in a concentration-dependent manner over the concentration range of 10 microM to 30 mM, with the EC(50) value of 67.3+/-16.4 microM. Similarly, La(3+) reversibly potentiated glycine (10 microM)-activated currents (I(Gly)) in a concentration-dependent manner over the concentration range of 1 microM to 1 mM, with the EC(50) value of 52.3+/-10.9 microM. The effects of La(3+) on I(GABA) and I(Gly) were voltage-independent. Moreover, both of the potentiations were not use-dependent and were overcome by increasing the concentration of agonist. Our results indicate that La(3+) potentiates the inhibitory amino acid receptors-mediated responses in SDCN, which may reduce the transmission of the pelvic visceral information. The information provided by this work may help to elucidate the mechanisms and effects of lanthanum on brain functions.

Progressive accumulation of lanthanum in the liver of normal and uremic rats

BACKGROUND

The loss of renal function in chronic kidney disease (CKD) patients leads to a variety of metabolic disturbances that promote the development of secondary hyperparathyroidism (SH) and bone disease. One of these alterations, hyperphosphatemia, is a persistent problem in patients with CKD and is an important factor in the development and severity of SH as well as coronary artery and cardiac valve calcification. To help control serum phosphorus (P), phosphate binders are used to minimize intestinal absorption of P in these patients. Since the use of aluminum- and calcium-based phosphate binders can result in severe side effects, other phosphate binders have been proposed. One of these is lanthanum (La) carbonate.

METHODS

Since there is some controversy as to the degree La is absorbed by the intestine, whether it is deposited in tissues, and what effect its prolonged use would have in patients with chronic renal failure, we studied normal and uremic rats fed a control diet or a diet with La carbonate (1.5% elemental La) for 45, 90, or 110 days.

RESULTS

As expected, plasma creatinine increased after the induction of uremia and continued to increase with time. At 45 and 90 days, dietary La produced a reduction in plasma P in normal rats (N + La) [45 days: 3.15 +/- 0.35 vs. normal control (NC) 4.41 +/- 0.15 mg/dL, P < 0.01; 90 days: 3.20 +/- 0.30 vs. 4.09 +/- 0.15 mg/dL, P < 0.05], but not at 110 days. Plasma P was initially lower (45 days) in both groups of La-treated rats (U + La: 3.47 +/- 0.28 vs. UC: 4.91 +/- 0.27 mg/dL, P < 0.01), but was not at 90 and 110 days. Whole blood La content was not increased in rats fed the La diet and is, therefore, not a good indicator of the La content of tissue. La was increased in kidney, femur, and especially liver in normal and uremic rats fed the La diet. Uremia markedly enhanced tissue accumulation of La (liver, 110 days: N + La: 849 +/- 152 vs. U + La: 2676 +/- 479 ng/g wet wt, P < 0.01), which increased in a time-dependent manner. The increase in La in the liver of normal rats was 44-fold compared to control and 98-fold in the liver of uremic rats compared to uremic control.

CONCLUSION

La accumulates in tissues, most strikingly in the liver, and renal failure accelerates the accumulation. While this was a relatively short-term study, La accumulation increased in a time-dependent manner. The effect of long-term La treatment on patients with chronic renal insufficiency needs to be evaluated.

La3+-promoted proliferation is interconnected with apoptosis in NIH 3T3 cells

Lanthanum ion (La(3+)) has been reported to affect proliferation or apoptosis of different cells. In the present study, La(3+) was confirmed to promote both proliferation and apoptosis of NIH 3T3 cells at the same concentrations. La(3+) was shown to promote proliferation by helping the cells to pass through the G1/S restriction point and enter S phase, however, the proliferating cells induced by incubation with La(3+) eventually underwent apoptosis. The proliferation and apoptosis of NIH 3T3 cells induced by La(3+) were well correlated with cell cycle alterations. La(3+) caused the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2; while inhibition of ERK phosphorylation by 2'-amino-3'-methoxyflavone (PD98059) suppressed both proliferation and apoptosis induced by La(3+). Based on the above experimental results, we postulated that La(3+)-promoted proliferation of NIH 3T3 cells could be interconnected with the cell apoptosis, possibly through cell cycle machinery. Our results thus support the recent hypothesis that proliferation and apoptosis of cell are intrinsically coordinated.

A reappraisal of the role of cerium in burn wound management

A rare earth element, cerium, was introduced as an antibacterial agent in 1976 but has rarely been used due to the emphasis on wound excision. Used in combination with silver sulphadiazine, it may improve patient survival when excision is not possible.

Inhibition of neuronal nicotinic acetylcholine receptors by La(3+)

A study was made of the effects of La(3+) on neuronal alpha 2 beta 4 nicotinic acetylcholine receptors expressed in Xenopus oocytes. La(3+) by itself (up to 10 microM) did not elicit significant membrane currents. However, La(3+) reversibly inhibited the ionic currents induced by acetylcholine (IC(50)=13.5+/-4.3 microM). When La(3+) and acetylcholine were simultaneously applied onto an oocyte, the level of inhibition of the acetylcholine response was the same as when the oocyte was first preincubated with La(3+) and then exposed to acetylcholine plus La(3+). In the presence of La(3+), the EC(50) decreased from 43.8+/-6.4 to 26.5+/-5.1 microM, suggesting a small increase in the affinity of acetylcholine for the receptors through a noncompetitive mechanism. The inhibition of acetylcholine response was independent of the membrane potential. From these results we conclude that La(3+) regulates nicotinic receptors, reversibly and noncompetitively, presumably by inhibiting allosterically the receptor through interactions at an external domain of the receptor complex.

The acute and chronic toxicity of lanthanum to Daphnia carinata

The rare earth elements (REEs) are increasingly being used as trace supplements in agriculture. This study measured the acute and chronic toxicity of one REE, lanthanum (La), to Daphnia carinata. The 48-h EC50 of La to Daphnia was measured in three media of differing composition and hardness. Lanthanum was most toxic to Daphnia in soft tap water (TW) with an acute 48-h EC50 of 43 microg/l compared with 1180 microg/l in ASTM hard water (ASTM). In the third daphnid growth medium (DW), based on diluted sea water, the acute 48-h EC50 was 49 microg La/l, however, there was significant precipitation of La in this media. The chronic toxicity of La to Daphnia was measured in the DW and ASTM media. Nominal exposure concentrations were 100, 200, 400, 600, 800, and 1000 microg La/l. Mortality was a more sensitive endpoint than growth or reproduction in both chronic experiments. Very little La was detected in either media after 24 h and the measured concentrations below were estimated by logarithmic mean of nominal and measured values. There was 100% mortality at concentrations > or = 80 microg La/l (400 microg/l nominal) by day six of the experiment using DW media, but no effect on survival growth or reproduction at lower concentrations. In the ASTM media, La caused significant mortality to Daphnia at concentrations > or = 39 microg/l (200 microg/l nominal), however, at least one animal survived to the end of the study at each of the tested concentrations. There was no effect of La on growth of surviving daphnids at concentrations < or = 57 microg/l (400 g/l), however, second brood clutch sizes were significantly increased at 30, 39, and 57 microg/l (100, 200, 400 g/l nominal) compared with controls. Lanthanum also caused a delayed maturation in Daphnia.

Cerium and lanthanum promote floral initiation and reproductive growth of Arabidopsis thaliana

The effects of cerium and lanthanum on the vegetative growth, floral initiation and reproductive growth of Arabidopsis thaliana were studied. Addition of cerium nitrate (0.5-10 µM) or lanthanum nitrate (0.5-50 µM) to the culture medium significantly increased the lengths of primary roots, but had no significant effects on the number of rosette leaves produced per plant, plant heights and dry weights during the vegetative growth stage (17 days after seed germination). The percentage of plants bolted was significantly increased with the addition of 0.5-10.0 µM cerium nitrate or lanthanum nitrate. The combination of 0.5 µM cerium nitrate and 0.5 µM lanthanum nitrate was found to be most effective on the induction of floral initiation. The height, dry weight and average number of flower numbers of 35-day-old plants growing in media containing cerium nitrate or/and lanthanum nitrate (0.5-10.0 µM) were found to be significantly higher than those in the control medium. The endogenous levels of cytokinins (zeatin riboside, dihydrozeatin riboside and isopentenyl adenosine) and carbohydrates (sucrose, glucose and fructose) in leaf and root tissues of plants growing in the medium supplemented with 0.5 µM cerium nitrate and 0.5 µM lanthanum nitrate were not significantly different from those of plants in the control medium. Application of 0.5 µM cerium nitrate and 0.5 µM lanthanum nitrate enhanced the effects of 10(-6) M IPA on root growth, plant height and flowering. The role of cerium and lanthanum in promoting floral initiation and reproductive growth and the possibility of developing non-hormonal flowering promoting agents are discussed.

Neurodevelopmental effects of lanthanum in mice

Mice were exposed to lanthanum chloride in drinking water at 0, 125, 250, and 500 mg/liter concentration prior to conception, during gestation, and until 30 days postnatally. Developing mice were assessed for the development of swimming and walking behavior and ear and eye opening. At 30 days of age the mice were assessed with a standard neurologic scale. Differences were found in the emergence of swimming and walking behavior and ear and eye opening. Differences were also found for touch response and visual placing responses. The brains of lanthanum-exposed mice were also smaller than controls. These findings indicate that lanthanum is a potential behavioral teratogen. Possible mechanisms are discussed.

Lanthanides stimulate [3H]tyramine binding in the rat striatum

Low (up to 100 nM) and high (approximately 100 microM) concentrations of lanthanides and Ca2+-ions, respectively, stimulated [3H]tyramine binding ([3H]TY) to rat striatal membranes, a putative marker for the vesicular transporter of dopamine. On the other hand, lanthanides (approximately 100 microM) inhibited or stimulated TY binding in striatal and extrastriatal (cortex, cerebellum) tissues, respectively. The binding increases by lanthanum (La3+) appeared to depend on endogenous Ca2+, whereas, those induced in EDTA-pretreated membranes were Ca2+-independent. The La3+-induced, apparent increase in the Bmax for [3H]TY binding seemed to reflect a retarded rate of dissociation of the ligand from its targets, rather than a larger availability of functionally-relevant, vesicular transport-related TY sites. This indicates uncertain mechanisms of present La3+ effects.

Contrasting actions of lanthanum on different recombinant gamma-aminobutyric acid receptor isoforms expressed in L929 fibroblasts

Functional studies have indicated that, unlike most divalent cations, lanthanum increases both native and recombinant gamma-aminobutyric acid (GABA) receptor (GABAR) currents. In the present study, we have examined whether lanthanum shows subunit-dependent selectivity for modification of currents from different GABAR isoforms. The effects of lanthanum on three different GABAR isoforms, alpha1beta3gamma2L, alpha6beta3gamma2L, and alpha6beta3delta, were determined by transient expression of combinations of alpha1, alpha6, beta3, gamma2L, and delta subunit cDNAs in L929 fibroblasts. Whole-cell recording was used to determine the concentration-response curves for lanthanum for the three different isoforms at submaximal concentrations of GABA. Lanthanum displayed strong potentiation of alpha1beta3gamma2L GABAR currents consistent with earlier reports of potentiation of GABAR currents by lanthanum in neurons and recombinant GABAR isoforms. However, in contrast to the potentiation of alpha1beta3gamma2L GABAR currents by lanthanum, alpha6beta3delta GABAR currents were strongly inhibited and alpha6beta3gamma2L GABAR currents were weakly inhibited by lanthanum. Interaction of lanthanum with GABAR isoforms was competitive, with lanthanum decreasing the EC50 value for GABA of alpha1beta3gamma2L GABARs without changing the maximum current and increasing the EC50 value for GABA of alpha6beta3delta and alpha6beta3gamma2L GABAR currents (greater shift in EC50 value in the alpha6beta3delta compared with the alpha6beta3gamma2L GABARs) without changing the maximum GABAR current. Neither potentiation nor inhibition of GABAR currents by lanthanum showed any voltage dependence. These results suggest that 1) changing the alpha-subunit subtype from alpha1 to alpha6 altered the effect of lanthanum from potentiation to inhibition, 2) changing the gamma2L subunit to the delta-subunit changed the level of maximal inhibition of alpha6 subtype-containing GABAR currents by lanthanum, and 3) the site for interaction with lanthanum probably was on the extracellular surface of GABARs.

Intracerebroventricular La3+ but not Gd3+ inhibits cocaine-induced motor activation in rats

In the present work the effects of i.c.v. administration of La3+ and Gd3+ on the motor stimulant effect of cocaine in rats were studied. Both La3+ and Gd3+ failed to influence basal motor activity. However, the two metal ions differ in modulation of cocaine-induced activation of motor activity. While Gd3+ (10.0, 20.0 and 40.0 mM/1 ml) did not influence significantly the cocaine effect, La3+ (0.1, 1.0 and 10 mM/1 ml) inhibited cocaine-induced motor activation in a dose-dependent manner. The results suggest the possible involvement of La(3+)-but not Gd(3+)-sensitive calcium channels in the locomotor stimulant effect of cocaine.

Biopersistence of cerium in the human respiratory tract and ultrastructural findings

For diagnostic purposes, mineralogical analysis was performed in bronchoalveolar lavage fluid and lung tissue from a 58-year-old patient previously exposed to asbestos and rare earth dusts. No significant retention of asbestos was demonstrated in lung tissue by light microscopy (asbestos bodies) or transmission electron microscopy analysis (uncoated fibers). Particles containing rare earth (cerium, lanthanum) and phosphorus were identified in alveolar macrophages in bronchoalveolar lavage fluid, and cerium-containing particles accounted for 70% of particles observed in the lung tissue. Ultrastructural analysis of lung tissue revealed the presence of particles containing cerium and phosphorus in interstitial macrophages and elastic fibers. These results suggest that rare earth is metabolized and should be considered as biopersistent in the human respiratory tract, since occupational inquiries revealed that exposure to cerium oxide abrasive powder had ceased at least 15 years earlier.

Lung retention of cerium in humans

A retrospective study was conducted to evaluate lung retention of particles containing cerium in subjects with and without previous occupational exposure to mineral dusts. Analytical transmission electron microscopy was performed on 459 samples of bronchoalveolar lavage (BAL) fluid and 75 samples of lung tissue. Study of the distribution of mineralogical species in human samples showed that particles containing cerium were encountered in less than 10% of subjects. The proportion of subjects with particles containing cerium in their biological samples was not different between controls and subjects with previous occupational exposure to fibrous or nonfibrous mineral dusts. This was considered as the background level of lung retention of cerium in the general population. By contrast, determination of the absolute concentration of particles containing cerium in BAL fluid and lung tissue samples showed that 1.2% (from BAL fluid) and 1.5% (from lung tissue) of subjects with previous exposure to mineral particles had high lung retention of particles containing cerium. This study is believed to be the first one in which lung retention of cerium was estimated in the general population.

Differential modulation of GABAA receptor-channel complex by polyvalent cations in rat dorsal root ganglion neurons

The effects of divalent and trivalent cations on the gamma-aminobutyric acid (GABA)-induced chloride current were studied with rat dorsal root ganglion neurons in primary culture using the whole-cell configuration of the patch-clamp technique. Lanthanum (La3+) reversibly potentiated the GABA-induced current with a half-maximal effective concentration (EC50) of 231 microM and the maximal potentiation to about 300% of control. La3+ did not seem to compete with chlordiazepoxide, pentobarbital or picrotoxin for binding sites, which indicated that the La3+ binding site was distinct from any of the benzodiazepine, barbiturate and picrotoxin binding sites on the GABA receptor-channel complex. Copper (Cu2+) reversibly suppressed the current induced by GABA with an EC50 of 19 microM in a non-competitive manner. Zinc (Zn2+) and Cu2+ had a very similar action on GABA response in terms of potency and efficacy. The degree of suppression of GABA-induced current by Cu2+ and Zn2+ was not affected by La3+, whereas Cu2+ antagonized the blocking action of Zn2+ in a concentration-dependent manner. Therefore, La3+ does not interfere with the binding site(s) for Cu2+ and Zn2+, whereas Cu2+ and Zn2+ may share a common site. These results are consistent with the presence of at least two distinct binding sites for polyvalent cations on the GABA-receptor channel complex: one for positive regulation by La3+ and the other for negative regulation by Cu2+ and Zn2+. These two sites are likely to be located at or near the external orifice of the chloride channel.