Integration of Au Nanosheets and GdOF:Yb,Er for NIR-I and NIR-II Light-Activated Synergistic Theranostics

The local hyperthermia (>41 °C) effect of photothermal therapy (PTT) is significantly limited by the efficiency of PTT agents to convert laser energy to heat, and such oncotherapy, similar to conventional chemotherapy, invariably encounters the challenge of nonspecific application. Undue reliance on oxygen sources still poses particular difficulties in photodynamic therapy (PDT) for deep-level clinical applications. Considering these therapeutic issues, in this study, we constructed a versatile but unique nanosystem by encapsulating Au nanosheets in codoped gadolinium oxyfluoride (GdOF):Yb,Er spheres, followed by decoration of a chemotherapeutic drug (doxorubicin), photosensitizer (rose Bengal, RB), and targeted agent (folic acid). This allowed the incorporation of cancer treatment and real-time curative efficacy monitoring into one single theranostic nanoplatform. Benefiting from the dual contribution of the strong absorptions in the NIR-I and NIR-II regions, relevant photothermal-conversion efficiency (η) values pertaining to that final product were 39.2% at 1064 nm irradiation and 35.7% at 980 nm illumination. The fluorescence resonance energy transfer that occurred in the up-converted GdOF:Yb,Er to RB contributed to the high PDT efficacy. Combined with a micromeric acid-responsive drug release in a targeted tumor microenvironment, high-performance synergistic therapy was realized. In addition, up-conversion fluorescence imaging and computed tomography imaging accompanied by multimodal magnetic resonance imaging were simultaneously achieved owing to the doped lanthanide ions and the encapsulated Au nanosheets. Our designed oncotherapy nanosystem provides an alternative strategy to acquire ideal theranostic effects.

The ROS-generating photosensitizer-free NaYF4:Yb,Tm@SiO2upconverting nanoparticles for photodynamic therapy application

In this work we adapt rare-earth-ion-doped NaYF₄nanoparticles coated with a silicon oxide shell (NaYF₄:20%Yb,0.2%Tm@SiO₂) for biological and medical applications (for example, imaging of cancer cells and therapy at the nano level). The wide upconversion emission range under 980 nm excitation allows one to use the nanoparticles for cancer cell (4T1) photodynamic therapy (PDT) without a photosensitizer. The reactive oxygen species (ROS) are generated by Tm/Yb ion upconversion emission (blue and UV light). Thein vitroPDT was tested on 4T1 cells incubated with NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and irradiated with NIR light. After 24 h, cell viability decreased to below 10%, demonstrating very good treatment efficiency. High modification susceptibility of the SiO₂shell allows for attachment of biological molecules (specific antibodies). In this work we attached the anti-human IgG antibody to silane-PEG-NHS-modified NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and a specifically marked membrane model by bio-conjugation. Thus, it was possible to perform a selective search (a high-quality optical method with a very low-level organic background) and eventually damage the targeted cancer cells. The study focuses on therapeutic properties of NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and demonstrates, upon biological functionalization, their potential for targeted therapy.

Yb3+, Er3+ Codoped Cerium Oxide Upconversion Nanoparticles Enhanced the Enzymelike Catalytic Activity and Antioxidative Activity for Parkinson's Disease Treatment

Oxidative stress plays an important role in Parkinson's disease (PD) and is considered a therapeutic target for PD. However, most therapeutic antioxidants show limitations due to their low reactive oxygen species (ROS) catalytic properties and low crossing of blood-brain barrier. Herein, the antioxidative activity of Yb3+ and Er3+ double-doped CeO2-x (Yb/Er/CeO2-x) upconversion nanoparticles (UCNPs) is obtained for PD treatment. Doping of Yb3+ and Er3+ ions increases oxygen vacancies, which leads to higher enzymelike catalytic activities compared to CeO2-x nanoparticles alone. Tyrosine hydroxylase protein and glial fibrillary acidic protein expression in substantia nigra and striatum as well as the open-field activity test indicates that Yb/Er/CeO2-x is effective for treatment of PD. The activities of glutathione peroxidase and total antioxidant capacity increase and the production of ROS decreases with Yb/Er/CeO2-x UCNP treatment compared with MPTP-induced injury. This indicates that the mechanism of PD treatment is to catalyze ROS products. There have been no reports to date on the usage of Yb/Er/CeO2-x as an antioxidant for PD treatment. Yb/Er/CeO2-x UCNPs cross the blood-brain barrier and exhibit biocompatibility and antioxidant catalytic properties, which decrease the ROS and effectively help in treating PD.

Unmodified Rose Bengal photosensitizer conjugated with NaYF4:Yb,Er upconverting nanoparticles for efficient photodynamic therapy

In photodynamic therapy (PDT), photosensitizer (PS) molecules are irradiated by light to generate reactive oxygen species (ROS), the presence of which subsequently leads to cell death. At present, the modality is limited to the treatment of skin diseases because of the low tissue penetration of visible or ultraviolet light required for producing ROS. To increase tissue penetration and extend the therapeutic possibilities of PDT to the treatment of deep-seated cancer, rare-earth doped nanoparticles capable of up-converting infrared to visible light are investigated. These up-converting nanoparticles (UCNPs) are conjugated with PS molecules to efficiently generate ROS. In this work, we employ hexagonal β-NaYF₄:Yb^3 +,Er^3 + as UCNPs and Rose Bengal (RB) as PS molecules and demonstrate efficient in vitro PDT using this nanoformulation. Covalent bonding of the RB molecules is accomplished without their functionalization-an approach which is expected to increase the efficiency of ROS generation by 30%. Spectroscopic studies reveal that our approach results in UCNP surface fully covered with RB molecules. The energy transfer from UCNPs to RB is predominantly non-radiative as evidenced by luminescence lifetime measurements. As a result, ROS are generated as efficiently as under visible light illumination. The in vitro PDT is tested on murine breast 4T1 cancer cells incubated with 250 µg ml^-1 of the nanoparticles and irradiated with NIR light under power density of 2 W cm^-2 for 10 minutes. After 24 hours, the cell viability decreased to 33% demonstrating a very good treatment efficiency. These results are expected to simplify the protocols for preparation of the PDT agents and lead to improved therapeutic effects.

Ultrasmall, water dispersible, TWEEN80 modified Yb:Er:NaGd(WO4)2 nanoparticles with record upconversion ratiometric thermal sensitivity and their internalization by mesenchymal stem cells

This work presents the synthesis by coprecipitation of diamond shaped Yb:Er:NaGd(WO₄)₂ crystalline nanoparticles (NPs) with diagonal dimensions in the 5-7 nm × 10-12 nm range which have been modified with TWEEN80 for their dispersion in water, and their interaction with mesenchymal stem cells (MSCs) proposed as cellular NP vehicles. These NPs belong to a large family of tetragonal Yb:Er:NaT(XO₄)₂ (T = Y, La, Gd, Lu; X = Mo, W) compounds with green (²H_11/2 + ⁴S_3/2 → ⁴I_15/2) Er-related upconversion (UC) efficiency comparable to that of Yb:Er:β-NaYF₄ reference compound, but with a ratiometric thermal sensitivity (S) 2.5-3.5 times larger than that of the fluoride. At the temperature range of interest for biomedical applications (∼293-317 K/20-44 °C) S = 108-118 × 10^-4 K^-1 for 20 at%Yb:5 at%Er:NaGd(WO₄)₂ NPs, being the largest values so far reported using the ²H_11/2/⁴S_3/2 Er intensity ratiometric method. Cultured MSCs, incubated with these water NP emulsions, internalize and accumulate the NPs enclosed in endosomes/lysosomes. Incubations with up to 10 μg of NPs per ml of culture medium maintain cellular metabolism at 72 h. A thermal assisted excitation path is discussed as responsible for the UC behavior of Yb:Er:NaT(XO₄)₂ compounds.

A chimeric protein of aluminum-activated malate transporter generated from wheat and Arabidopsis shows enhanced response to trivalent cations

TaALMT1 from wheat (Triticum aestivum) and AtALMT1 from Arabidopsis thaliana encode aluminum (Al)-activated malate transporters, which confer acid-soil tolerance by releasing malate from roots. Chimeric proteins from TaALMT1 and AtALMT1 (Ta::At, At::Ta) were previously analyzed in Xenopus laevis oocytes. Those studies showed that Al could activate malate efflux from the Ta::At chimera but not from At::Ta. Here, functions of TaALMT1, AtALMT1 and the chimeric protein Ta::At were compared in cultured tobacco BY-2 cells. We focused on the sensitivity and specificity of their activation by trivalent cations. The activation of malate efflux by Al was at least two-fold greater in the chimera than the native proteins. All proteins were also activated by lanthanides (erbium, ytterbium, gadolinium, and lanthanum), but the chimera again released more malate than TaALMT1 or AtALMT1. In Xenopus oocytes, Al, ytterbium, and erbium activated inward currents from the native TaALMT1 and the chimeric protein, but gadolinium only activated currents from the chimera. Lanthanum inhibited currents from both proteins. These results demonstrated that function of the chimera protein was altered compared to the native proteins and was more responsive to a range of trivalent cations when expressed in plant cells.

PEGylated hybrid ytterbia nanoparticles as high-performance diagnostic probes for in vivo magnetic resonance and X-ray computed tomography imaging with low systemic toxicity

Novel nanoparticulate contrast agents with low systemic toxicity and inexpensive character have exhibited more advantages over routinely used small molecular contrast agents for the diagnosis and prognosis of disease. Herein, we designed and synthesized PEGylated hybrid ytterbia nanoparticles as high-performance nanoprobes for X-ray computed tomography (CT) imaging and magnetic resonance (MR) imaging both in vitro and in vivo. These well-defined nanoparticles were facile to prepare and cost-effective, meeting the criteria as a biomedical material. Compared with routinely used Iobitridol in clinic, our PEG-Yb2O3:Gd nanoparticles could provide much significantly enhanced contrast upon various clinical voltages ranging from 80 kVp to 140 kVp owing to the high atomic number and well-positioned K-edge energy of ytterbium. By the doping of gadolinium, our nanoparticulate contrast agent could perform perfect MR imaging simultaneously, revealing similar organ enrichment and bio-distribution with the CT imaging results. The super improvement in imaging efficiency was mainly attributed to the high content of Yb and Gd in a single nanoparticle, thus making these nanoparticles suitable for dual-modal diagnostic imaging with a low single-injection dose. In addition, detailed toxicological study in vitro and in vivo indicated that uniformly sized PEG-Yb2O3:Gd nanoparticles possessed excellent biocompatibility and revealed overall safety.

A facile synthesis of strong near infrared fluorescent layered double hydroxide nanovehicles with an anticancer drug for tumor optical imaging and therapy

In this work, a new multifunctional nanovehicle for tumor optical imaging and therapy was developed using Y2O3:Er(3+),Yb(3+) nanoparticles as near infrared fluorescent nanophosphors, and MgAl-layered double hydroxide (LDH) nanosheets as anticancer drug nanovehicles. Monodispersed Y2O3:Er(3+),Yb(3+) nanophosphors were readily synthesized by the urea assisted homogenous precipitation method. Hierarchically structured LDH nanosheets intercalated with an anticancer drug, fluorouracil (5FU), were deposited on the surface of Y2O3:Er(3+),Yb(3+)@SiO2 by a simple precipitation method followed by hydrothermal treatment. The resultant Y2O3:Er(3+),Yb(3+)@SiO2@LDH-5FU nanovehicles exhibit strong red upconversion fluorescence under the excitation of a 980 nm laser, which allows tracking of the nanovehicles after localization in cancer cells. A better anticancer efficiency was obtained over the nanovehicles than the free drug which can be attributed to their positively charged surfaces for favorable interaction with the negatively charged cell membranes. The multifunctional nanovehicles designed in this work are expected to be promising material candidates for simultaneous tumor optical imaging and therapy.

Multifunctional magnetic-fluorescent eccentric-(concentric-Fe₃O₄@SiO₂@polyacrylic acid core-shell nanocomposites for cell imaging and pH-responsive drug delivery

Multifunctional fluorescent-magnetic pH-responsive eccentric-(concentric-Fe3O4@SiO2)@polyacrylic acid core-double shell nanocomposites (NCs) have been prepared for simultaneous cell imaging and pH-responsive drug delivery. To confirm the universality of the synthetic concept, the synthetic strategy was also extended to fabricate monodisperse eccentric-(concentric-NaYF4:Yb/Er/Gd@SiO2)@polyacrylic acid core-double shell NCs.

Artifacts in magnetic resonance imaging and computed tomography caused by dental materials

BACKGROUND

Artifacts caused by dental restorations, such as dental crowns, dental fillings and orthodontic appliances, are a common problem in MRI and CT scans of the head and neck. The aim of this in-vitro study was to identify and evaluate the artifacts produced by different dental restoration materials in CT and MRI images.

METHODS

Test samples of 44 materials (Metal and Non-Metal) commonly used in dental restorations were fabricated and embedded with reference specimens in gelatin moulds. MRI imaging of 1.5T and CT scan were performed on the samples and evaluated in two dimensions. Artifact size and distortions were measured using a digital image analysis software.

RESULTS

In MRI, 13 out of 44 materials produced artifacts, while in CT 41 out of 44 materials showed artifacts. Artifacts produced in both MRI and CT images were categorized according to the size of the artifact.

SIGNIFICANCE

Metal based restoration materials had strong influence on CT and less artifacts in MRI images. Rare earth elements such as Ytterbium trifluoride found in composites caused artifacts in both MRI and CT. Recognizing these findings would help dental materials manufacturers and developers to produce materials which can cause less artifacts in MRI and CT images.

[Development of a new photosensitizer on the basis of ytterbium porphyrazine complex]

The tetraphenyltetracyanoporphyrazine complex of ytterbium has been studied as a potential photosensitizer for fluorescence diagnostics and photodynamic therapy (PDT) of cancer. It has been shown that the new compound has an intensive absorption and fluorescence in the "tissue optical window". In particular, the absorption maximum of the complex is at the wavelength of 590 nm, and the fluorescence emission maximum is at 640 nm. A strong fluorescence enhancement with a 50-fold increase in the quantum yield has been revealed in blood serum. The experiments on human cancer cells line have demonstrated that the complex penetrates the cells in vitro and is located around the nuclei. The biodistribution and pharmacokinetics of the complex in animals have been investigated in vivo by a new method of transillumination fluorescence imaging using a peculiar setup. It has been found that the period of maximum uptake of the complex in mouse cervical carcinoma is from 3 to 6 h after i.v. injection, with the half-life in the tumor being 24 h. However, the selectivity of the complex in the tumor is not high enough. The time of clearance from the body is about 48 h. The area of the strongest fluorescence in the abdominal cavity in in vivo images is anatomically recognized as the intestine. This indicates that the new compounds undergo mainly the hepatic clearance mainly. The conventional methods ex vivo (confocal microscopy and point spectroscopic measurements) have detected the largest content of the complex in the intestine, liver, skin and tumor tissue. In general, the optical characteristics of the ytterbium porphyrazine complex as well as the features of its interaction with biological objects make it promising drug candidate for the photodynamic therapy and/or fluorescence diagnostics of cancer. However, a search for other novel formulations possessing a higher tumor selectivity remains an urgent problem.

[A differential proteomic study on the influence of ytterbium citrate on HepG2 cells]

OBJECTIVE

To explore the effects of ytterbium citrate on human liver carcinoma HepG2 cell line and the potential mechanisms.

METHODS

The HepG2 cells were cultured with DMEM medium and divided into different groups in the following media, in serum-free medium as control, different concentration (0.01 - 5.00 mmol/L) [YbCit(2)](3-)+serum-free medium as treatment group, MTT assay was used to measure the viability of the cells; 2.00 mmol/L [YbCit(2)](3-)+serum-free medium was used as treatment group, and Hoechst 33258 staining was used to detect apoptosis in HepG2 cells. Differential proteomic analysis, assay of intracellular H(2)O(2) levels and mitochondrial transmembrane potential were performed to study the effects of [YbCit(2)](3-) on HepG2 cells and the potential mechanisms.

RESULTS

The data showed that 72 h treatment of [YbCit(2)](3-) at 2.00 - 5.00 mmol/L significantly inhibited cell proliferation, and the IC(50) was (2.46 ± 0.23) mmol/L. After treatment with 2.00 mmol/L [YbCit(2)](3-) for 48 h and 72 h, Hoechst 33258 staining demonstrated that [YbCit(2)](3-) induced significantly increased apoptosis in HepG2 cells. After treatment with 2.00 mmol/L [YbCit(2)](3-) for 72 h, two dimensional gel electrophoresis and MALDI-TOF mass spectrometry analysis revealed 14 differentially expressed proteins between [YbCit(2)](3-)-treated cells and the control cells. These proteins mainly included cofilin1, peroxiredoxin6, S100 calcium-binding protein A6, and proteasome 26S non-ATPase subunit 13 isoform 3 and so on. These proteins played important roles in the processes of anti-apoptosis, oxidation reduction, cell proliferation and protein degradation. The mitochondrial membrane potential were investigated, the results showed the red and green fluorescence ratio was 2.45 ± 0.28 in the control group, 1.56 ± 0.23 in 24 h group, 1.16 ± 0.18 in 48 h group, compared with the control, the differences were significant (F = 23.97, P = 0.001). The results of H(2)O(2) detection showed the fluorescence intensity was 20.00 ± 2.08 in the control group, 40.00 ± 5.50 in 24 h group, and 48.00 ± 2.03 in 48 h group, compared with the control, the differences were significant (F = 48.40, P = 0.000). The results indicated a significant reduction in mitochondrial transmembrane potential and significant increase in H2O2 generation were observed in [YbCit(2)](3-)-treated cells.

CONCLUSION

These results suggested that [YbCit(2)](3-) could induce apoptosis of HepG2 cells through the mechanisms involving oxidative stress and mitochondrial dysfunction.

Antibacterial Effects of a Monoporphyrinato Ytterbium(III) Complex and Its Free Components onStaphylococcus aureus as Determined by Stop-Flow Microcalorimetry

The antibacterial effect of Yb3+, the free porphyrin base 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (H2TMP; 1), and the corresponding Yb3+ porphyrinato complex [Yb(III)(TMP)(H2O)3]+ Cl- (Yb(TMP); 2) towards Staphylococcus aureus was investigated by stop-flow microcalorimetry. By analyzing the obtained metabolic thermogenic curves, crucial parameters such as rate constant of bacterial growth (k), half inhibitory concentration (IC50), and generation time (t(G)) were determined. The antibacterial activities of the three compounds tested was 2>1>Yb3+, with an IC50 value of 273 mg/l for complex 2. The Yb3+ porphyrinato complex is proposed to benefit from synergetic effects of Yb3+ and the free porphyrin 1.

Aluminium triggers malate-independent potassium release via ion channels from the root apex in wheat

The regulatory mechanisms for the aluminium (Al)-induced efflux of K(+) and malate from the root apex of Al-resistant wheat ( Triticum aestivum L. cv. Atlas) were characterized. Treatment with 20 mM tetraethylammonium (TEA) chloride, a K(+)-channel inhibitor, blocked the Al-induced K(+) efflux by 65%, but blocked the Al-induced malate efflux only slightly. Lanthanum (La(3+)) or ytterbium (Yb(3+)) strongly inhibited the K(+) efflux, but slightly increased malate efflux. These lanthanides applied together with Al did not affect the Al-induced malate efflux, but reduced the Al-induced K(+) efflux by 57% for La(3+) and by 35% for Yb(3+). By contrast, pretreatment with 50 microM niflumic acid, an anion-channel inhibitor, strongly suppressed the Al-induced malate efflux, but did not affect the Al-induced K(+) efflux. The efflux of K(+) uncoupled with that of malate resulted in the alkalization of intracellular pH in the root apex, suggesting that the release of K(+) coupled with malate plays an important role in stabilizing intracellular pH. Copper (Cu(2+)) induced the release of K(+) via a TEA-insensitive pathway without the release of malate in both Al-resistant and Al-sensitive (cultivar Scout) wheat. Simultaneous application of Al and Cu(2+) to the root apices resulted in TEA-sensitive K(+) efflux in Atlas but not in Scout, suggesting that Al competes with Cu(2+) for K(+) efflux. Taken together, these results suggest that Al-induced K(+) efflux is mediated by both TEA- and lanthanide-sensitive K(+) channels, although this induction is not a prerequisite for the induction of the release of malate.

Inhibition of transiently expressed low- and high-voltage-activated calcium channels by trivalent metal cations

Calcium channels are important regulators of neuronal excitability and contribute to transmitter release, calcium dependent gene expression, and oscillatory behavior in many cell types. Under physiological conditions, native low-voltage (T-type)- and high-voltage-activated (HVA) currents are potently inhibited by trivalent cations. However, the presence of multiple calcium channel isoforms has hampered our ability to unequivocally assess the effects of trivalent cations on channel activity. Here, we describe the actions of nine trivalent metal ions on transiently expressed alpha1G (Cav3.1) T-type calcium channels cloned from human brain. In 2 mM external barium solution, yttrium most potently inhibited alpha1G current (IC50 = 28 nM), followed by erbium > gadolinium ~ cerium > holmium > ytterbium > neodymium > lanthanum >> scandium. With the exception of scandium, blocking affinity was loosely correlated with decreasing ionic radius. A detailed characterization of yttrium block revealed a 25-fold decrease in blocking affinity when the external concentration of charge carrier was increased from 2 mM to 20 mM. In 20 mM barium, yttrium also effectively inhibited various types of cloned HVA channels indicating that this ion is a nonselective blocker. For all calcium channels examined, yttrium preferentially inhibited inward over outward current, but block was otherwise voltage independent. In addition to peak current inhibition, P/Q- and L-type channels underwent a unique speeding of the macroscopic time course of inactivation. Whereas peak current block of alpha1A channels was highly sensitive to the external charge carrier concentration, the inactivation effects mediated by yttrium were not, suggesting that the two effects are due to distinct mechanisms. Moreover, the speeding effect was greatly attenuated by manipulations that slowed the inactivation kinetics of the channels. Thus, our evidence suggests that yttrium effects are mediated by two distinct events: peak current block likely occurring by occlusion of the pore, and kinetic speeding arising from yttrium interactions with the channel that alter the state of the inactivation gate.

Dual actions of lanthanides on ACTH-inhibited leak K(+) channels

Bovine adrenal zona fasciculata cells express background K(+) channels (I(AC) channels) whose activity is potently inhibited by ACTH. In whole cell patch clamp recordings, it was discovered that the trivalent lanthanides (Ln(3+)s) lanthanum and ytterbium interact with two binding sites to modulate K(+) flow through these channels. Despite large differences in ionic radii, these Ln(3+)s inhibited I(AC) channels half-maximally with IC(50) values near 50 microM. In addition, these Ln(3+)s blocked and reversed ACTH-mediated inhibition of I(AC) K(+) channels at similar concentrations. The Ln(3+)s did not alter inhibition of I(AC) by angiotensin II or cAMP. Ln(3+)-induced uncoupling of ACTH receptor activation from I(AC) inhibition was prevented by raising the external Ca(2+) concentration from 2 to 10 mM. The divalent cation Ni(2+) (500 microM) also blocked ACTH-dependent inhibition of I(AC) through a Ca(2+)-sensitive mechanism. The results are consistent with a model in which Ln(3+)s produce opposing actions on I(AC) K(+) currents through two separate binding sites. In addition to directly inhibiting I(AC), Ln(3+)s (and Ni(2+)) bind with high affinity to a Ca(2+)-selective site associated with the ACTH receptor. By displacing Ca(2+) from this site, Ln(3+)s prevent ACTH from binding and accelerate its dissociation. These results identify Ln(3+)s as a relatively potent group of noncompetitive ACTH receptor antagonists. Allosteric actions of trivalent and divalent metal cations on hormone binding, mediated through Ca(2+)-specific sites, may be common to a variety of peptide hormone receptors.

X-ray image intensifier performance and patient doses for combinations of supplemental beam filters and vascular contrast agents

We present an investigation of the fluoroscopic imaging and dosimetric performances of iodine- and gadolinium-based vascular contrast agents in combination with K-absorption edge filters of atomic numbers between 50 (tin) and 82 (lead). These combinations were studied using a theoretical model for a range of diagnostic x-ray spectra (55 to 100 kVp) and for water phantoms representative of thin and thick anatomies. Performance was characterized by radiographic contrast, a derived image quality index, the patient integral and entrance skin doses, and the x-ray tube load. For a given thickness of anatomy, an optimum combination of spectrum kVp, contrast agent and supplemental filter was defined by maximum imaging performance for a minimum or tolerable x-ray tube load and patient dose. It was possible to both improve imaging performance and reduce dose by the use of an appropriate combination of spectrum kVp and filter. For gadolinium-based contrast, performance was optimized with tungsten filtration at 90 kVp for both thin and thick anatomies. It was not possible, however, to optimize the iodinated contrast performance with a single combination of supplemental filter and spectrum kVp. The optimal performance for iodinated contrast was achieved with gadolinium filtration at 60 kVp for thin anatomy and with ytterbium filtration at 80 kVp for thick anatomy. The best performance for thin anatomy was that of the combination of iodinated contrast/gadolinium filter at 60 kVp and the best performance for thick anatomy was that of the combination of gadolinium-based contrast/tungsten filter at 90 kVp.

Rare earth elements as nonabsorbable fecal markers in studies of iron absorption

The use of rare earth elements as nonabsorbable fecal markers for studies of iron absorption from sources labeled extrinsically with stable isotopes was evaluated. On 3 successive days 13 healthy fasting adults were given different stable isotopes of iron with samarium, ytterbium, or dysprosium. On day 1, three meals were given with 57Fe (1 mg per meal) plus samarium (0.33 mg per meal); on day 2, identical meals (taken with a calcium supplement to reduce iron bioavailability) were given with equivalent amounts of 58Fe-labeled iron and ytterbium; on day 3, a well-absorbed reference dose of 54Fe (3 mg) was given with 1 mg Dy. A complete fecal collection was carried out for 5-9 d and each stool was analyzed for rare earth elements by inductively coupled plasma-mass spectrometry and iron isotopes by thermal ionization quadrupole mass spectrometry. Mean recovery of rare earth elements was 101%, indicating that they are totally unabsorbed. The excretory pattern of the iron isotopes and the rare earth elements was very similar; the correlation coefficients between samarium and 57Fe, ytterbium and 58Fe, and dysprosium and 54Fe were 0.992, 0.989, and 0.988, respectively (P < 0.001). Iron absorption was calculated as the difference between isotope dose and fecal excretion. Mean (+/-SEM) iron absorption was 16.7 +/- 2.4%, 4.3 +/- 1.6%, and 40.3 +/- 3.1% on days 1-3, respectively. Predicted values estimated from the first 4 d of pooled feces, using the rare earth element recovery data to produce corrected figures for unabsorbed isotope, were in close agreement: 19.1 +/- 2.1%, 4.6 +/- 1.7%, and 40.8 +/- 3.1%, respectively (P < 0.001). With the diet of medium iron bioavailability and with the highly bioavailable reference dose it was possible to predict iron absorption accurately from only one or two stools, provided that they were sufficiently enriched with isotope and a rare earth element.

Effect of lanthanide ions on the phase behavior of dipalmitoylphosphatidylcholine multilamellar liposomes

The effect of lanthanide ions (Ln3+) and their coordination compounds of diethylenetriamine pentaacetic acid (DTPA) on the phase behavior of dipalmitoylphosphatidylcholine (DPPC) multi-lamellar liposomes has been studied by differential scanning calorimetry (DSC), Raman spectroscopy, and freeze-fracture electron microscopic techniques. The displacement of Ca2+ binding on DPPC liposomes by lanthanide ions was also studied. The results show that the binding degree of four kinds of chloride salts with DPPC liposomes is: YbCl3 > GdCl3 > LaCl3 > CaCl2. Lanthanide ions increase the phase transition temperature of DPPC liposomes and decrease the membrane fluidity. Freeze-fracture electron microscopic results show that La3+ enhances the order of DPPC membrane. The effect of coordination compounds of lanthanides with DTPA on the phase behavior of DPPC liposomes is smaller than that of their chlorides. La3+, Gd3+, and Yb3+, can displace Ca2+ binding on DPPC liposomes, but there coordination compounds of DTPA can hardly displace Ca2+. Raman spectroscopic results show that a very slight effect in lateral packing order of DPPC liposomes was observed at various concentrations of lanthanides.

Block of current through T-type calcium channels by trivalent metal cations and nickel in neural rat and human cells

1. The effects of the trivalent cations yttrium (Y3+), lanthanum (La3+), cerium (Ce3+), neodymium (Nd3+), gadolinium (Gd3+), holmium (Ho3+), erbium (Er3+), ytterbium (Yb3+) and the divalent cation nickel (Ni2+) on the T-type voltage gated calcium channel (VGCC) were characterized by the whole-cell patch clamp technique using rat and human thyroid C cell lines. 2. All the metal cations (M3+) studied, blocked current through T-type VGCC (IT) in a concentration-dependent manner. Smaller trivalents were the best T-channel antagonists and potency varied inversely with ionic radii for the larger M3+ ions. Estimation of half-maximal blocking concentrations (IC50s) for IT carried by 10 mM Ca2+ resulted in the following potency sequence: Ho3+ (IC50 = 0.107 microM) approximately Y3+ (0.117) approximately Yb3+ (0.124) > or = Er3+ (0.153) > Gd3+ (0.267) > Nd3+ (0.429) > Ce3+ (0.728) > La3+ (1.015) >> Ni2+ (5.65). 3. Tail current measurements and conditioning protocols were used to study the influence of membrane voltage on the potency of these antagonists. Block of IT by Ni2+, Y3+, La3+ and the lanthanides was voltage independent in the range from -200 to +80 mV. In addition, the antagonists did not affect macroscopic inactivation and deactivation of T-type VGCC. 4. Increasing the extracellular Ca2+ concentration reduced the potency of IT block by Ho3+, indicative of competitive antagonism between this blocker and the permeant ion for a binding site. 5. The results suggest that the mechanism of metal cation block of T-type VGCC is occlusion of the channel pore by the antagonist binding to a Ca2+/M3+ binding site, located out of the membrane electric field. 6. Block of T-type VGCC by Y3+, lanthanides and La3+ differ from the inhibition of high voltage-activated VGCC block in several respects: smaller cations are more potent IT antagonists; block is voltage independent and the antagonists do not permeate T-type channels. These differences suggest corresponding structural dissimilarities in the permeation pathways of low and high voltage-activated Ca2+ channels.

Refined crystal structure of ytterbium-substituted carp parvalbumin 4.25 at 1.5 A, and its comparison with the native and cadmium-substituted structures

The crystal structure of carp parvalbumin 4.25 containing a 1:1 molar ratio of ytterbium chloride to protein has been refined at 1.5 A resolution by restrained least-squares methods to a crystallographic R value of 0.199. The crystal structure confirms the NMR studies, which suggest that low concentrations of ytterbium cause an extensive displacement of calcium from the EF metal binding site. A comparison of the ytterbium-substituted model with the native and cadmium-substituted structure show no significant differences, except around the substituted EF metal-binding region. The displacement of calcium by ytterbium at the EF site has caused a movement in the polypeptide backbone of Ser-91 and Asp-92. This movement resulted in an increase in the number of oxygen ligands bound to ytterbium in the EF site from seven to eight.

Interactions between alpha-latrotoxin and trivalent cations in rat striatal synaptosomal preparations

The interactions between alpha-latrotoxin (alpha-LTx), a neurosecretagogue purified from the venom of the black widow spider, and the trivalent cations Al3+, Y3+, La3+, Gd3+, and Yb3+ were investigated in rat striatal synaptosomal preparations. All trivalent cations tested were inhibitors of alpha-LTx-induced [3H]dopamine [( 3H]DA) release (order of potency: Yb3+ greater than Gd3+ approximately Y3+ greater than La3+ greater than Al3+). Only with Al3+ could inhibition of [3H]DA release be attributed to a block of 125I-alpha-LTx specific binding to synaptosomal preparations. The inhibitory effect of trivalent ions was reversible provided synaptosomes were washed with buffer containing EDTA. Trivalent ions also inhibited alpha-LTx-induced [3H]DA release at times when alpha-LTx-stimulated release was already evident. alpha-LTx-induced synaptosomal membrane depolarization was blocked by La3+, but not affected by Gd3+, Y3+, and Yb3+. alpha-LTx-stimulated uptake of 45Ca2+ was inhibited by all trivalent cations tested. These results demonstrate that there exist at least three means by which trivalent cations can inhibit alpha-LTx action in rat striatal synaptosomal preparations: (1) inhibition of alpha-LTx binding (Al3+); (2) inhibition of alpha-LTx-induced depolarization (La3+); and (3) inhibition of alpha-LTx-induced 45Ca2+ uptake (Gd3+, Y3+, Yb3+, La3+).

[Total proteins levels and embryonic development of eggs of sea urchins (Lytechinus variegatus) treated with YbCl3]

Total proteins levels and the embryonic development of sea urchin (Lytechinus variegatus) eggs treated with 25 micrograms/ml of YbCl3 in sea water for one hour were studied. After the treatment, eggs were let to develop for 24 hours when the total proteins levels were determined and morphological changes as well as the synchronism of the embryonic development have been checked.

Effects of traces of rare earth elements on the protozoan Blepherisma and on mice

The growth of the protozoan Blepherisma is stimulated by Lanthanum (La) at concentrations as low as 0.32 ppm. In mice Yttrium (Y) and Ytterbium (Yb) are absorbed, accumulated, and metabolized. Both rare earth elements (RE) exhibit a high affinity for teeth and bones, accumulation occurs and metabolism is slow. In the livers of RE-exposed mice, concentrations are variable. The liver is apparently capable of absorbing and discharging RE in a manner depending on metabolic activity. The main route of discharge for ingested REs is the alimentary canal. Exposure of pregnant mice to RE leads to rapid placental transfer of RE; 14.1% of the total amount of RE administered was detected in newborn mice. Young, developing organisms appear to be especially susceptible to RE accumulation.

Bilayer asymmetry in lysophosphatidylcholine/cholesterol (1:1) vesicles. A phosphorus-31 NMR study

Prolonged sonication (3 h) of equimolar amounts of lysophosphatidylcholine (lysoPC) and cholesterol (chol) produces small unilamellar vesicles. Phosphorus-31 NMR (32.20 MHz) of the vesicles gave rise to a single peak (40.5 ppm) which was split upon addition of lanthanide ions. An additional, more intense signal appeared downfield near 51.0 ppm due to 2.4 mM Pr3+, upfield near 34.3 ppm due to 5 mM Yb3+. The more intense signals responsive to paramagnetic ions were assigned to lysoPC located in the outer vesicle leaflet; the signal not shifted by the ions was assigned to inside lysoPC. Based on peak intensities, an outside-to-inside lysoPC ratio (Ro/i) of 6.5-6.6 was determined. Essentially the same Ro/i values (6.6-6.8) were obtained when Pr3+ was present only in the vesicle interior or when Pr3+ was on the inside and Pr3+ and Yb3+ were on the outside. Ion leakage did not occur. Our data demonstrate that lysoPC/chol (1:1) vesicles are drastically asymmetric and that lysoPC shows a distinct preference for the outer bilayer leaflet.

Lanthanide ion enhancement of interferon binding to cells

Pretreatment of purified [125I]-labeled human and mouse beta interferons (IFN) with lanthanum chloride (LaCl3) enhanced 20-30 fold the binding of the [125I]-IFNs to human A549 and mouse L cells at 0 degree C and also enhanced antiviral activity in homologous cells. Although lanthanides enhanced cross-species binding of both human and mouse [125I]-IFNs, there was no increase in cross-species antiviral activity. Unlabeled IFN not treated with LaCl3 did not compete with [125I]-IFN treated with LaCl3 for cellular receptors. However, unlabeled IFN treated with LaCl3 did compete with LaCl3-treated [125I]-IFN. These results suggest that lanthanide treated IFNs do not bind to the same receptors as native IFNs.

Ytterbium acetate as a particulate-phase digesta-flow marker

The ability of ytterbium acetabe (Yb acetate) to fulfil the requirements of a particulate-phase digesta-flow marker in a dual-phase marker system, and of the indigestible acid-detergent-fibre fraction of the feed (IADF) to act as a digesta flow marker, were examined using six mature wether sheep given a diet of dried grass (1 kg dry matter (DM)/d). CrEDTA was continuously infused (240 mg chromium/d) into the rumen of all sheep and Yb acetate was also continuously infused (100 mg Yb/d) into the rumen of three of the sheep. At this level of infusion the equilibrium concentration of Yb in rumen, duodenal and ileal digesta and in faeces could be reliably measured by atomic absorption spectrometry. Estimates of faecal DM excretion based on either Yb or IADF did not differ (P greater than 0.05) from that determined by total collection, whereas estimates based on Cr were significantly (P less than 0.05) lower. Urinary excretion accounted for 3.1% of the infused Cr but no Yb was detected in urine. Estimates of ileal DM flow, assuming total marker recovery, were similar (P greater than 0.05) with all three markers, whereas the estimate of duodenal DM flow based on IADF was lower (P less than 0.05) than the estimates based on either Cr or Yb. Compared with the infusion of Cr alone, the infusion of Cr and Yb had no effect (P greater than 0.05) on nutrient flows at the duodenum, ileum and in faeces nor on microbial degradative activity volatile fatty acid production and N metabolism in the rumen. Polyester bag and in vitro studies showed that pre-labelling the dried grass with up to 285 mg Yb/g DM did not affect its susceptibility to microbial degradation. The Yb in rumen, duodenal and ileal digesta was predominantly (greater than 90%) associated with the particulate matter but was not uniformly distributed and its concentration increased as particle size decreased. The use of CrEDTA and Yb acetate as a dual-phase marker system proved more reliable in estimating 'true' duodenal flow than the use of the individual markers when the digesta sample was unrepresentative.

Anti-inflammatory effects of praseodymium, gadolinium and ytterbium chlorides

Anti-inflammatory effects of chloride salts of praseodymium, gadolinium and ytterbium were investigated, using various experimental inflammatory models in rats. The lanthanide salts administered by oral route showed no significant effect, but when injected intraperitoneally they significantly inhibited the carrageenin-induced oedema, proportional to their doses ranging from 15 to 75 mg/kg. They also reduced nystatin-induced oedema and vascular permeability response to histamine and serotonin. Pronounced inhibitory effect of lanthanide salts at the dose of 50 mg/kg, i.p., was observed in histamine- and serotonin-induced changes in vascular permeability. Repeated administration of lanthanide salts in the dose of 20 mg/kg for 13 d significantly inhibited arthritis development. The same dose of these salts for a 6-d period similarly reduced granuloma formation. However, praseodymium, gadolinium and ytterbium chlorides showed no significant difference among themselves and their anti-inflammatory effects were smaller than those from phenylbutazone.

Use of lanthanide-induced nuclear magnetic resonance shifts for determination of protein structure in solution: EF calcium binding site of carp parvalbumin

The binding of the paramagnetic lanthanide ion ytterbium to the calcium binding protein carp parvalbumin results in a series of 1H NMR resonances which are shifted far outside the envelope of the 1H NMR spectrum of the diamagnetic form of the protein; bound Yb3+ also induces shifts in the 13C NMR spectrum of parvalbumin and in the 113Cd NMR spectrum of cadmium-substituted parvalbumin. The interpretation of these lanthanide-shifted resonances in terms of the structure of the protein surrounding the metal binding site requires the determination of the orientation and principal elements of the magnetic susceptibility tensor of the protein-bound Yb3+ ion. A previous comparison [Lee, L., & Sykes, B. D. (1982) Biomolecular Structure Determination by NMR (Bothner-By, A. A., Glickson, J. D., & Sykes, B. D., Eds.) pp 169-188, Marcel Dekker, New York] of the observed Yb3+-shifted 1H NMR spectrum of parvalbumin with a calculated spectrum, based upon the X-ray structure and an initial determination of the magnetic susceptibility tensor, led to the conclusion that there were significant differences between the solution and X-ray structures. In this paper, the magnetic susceptibility tensor has been reevaluated with the aid of newly assigned 13C and 113Cd NMR resonances. The agreement between the calculated and observed spectra is now close overall.

Enamel dissolution. I. Effects of various agents and titanium tetrafluoride

By comparing phosphorus loss from enamel windows during successive exposures in acetic acid buffer, measurements were made of the effects of a number of uncommon fluoride and nonfluoride compounds on enamel dissolution. Acidulated ytterbium chloride and the tetrafluorides of titanium, zirconium, and hafnium gave much more lasting protection against the action of acid than did the fluorides commonly used for caries prophylaxis.

Effects of rare earths and yttrium on striated muscle and the neuromuscular junction

Effects of several rare earths and yttrium on isolated frog sartorius muscles were investigated. Lanthanum (La), praseodymium, neodymium (Nd), samarium, gadolinium, dysprosium, erbium, thulium, ytterbium, and yttrium (Y) inhibited twitch tension of indirectly stimulated preparations. Concentrations required to reduce twitch tension to 50% of control tension in 15 min ranged between 0.52 mM and 1.10 mM (Ringer solution; pH 6.0). Similar concentrations (La, Nd, and Y) also inhibited twitch tension of directly stimulated, curarized preparations. A relationship between effect on twitch tension and atomic number was not found. La (0.3 mM) and Y (0.3 mM) reduced the amplitude, but did not appear to alter the time course, of extracellularly recorded end-plate potentials (E.P.P.'s). Amplitudes of intracellularly recorded E.P.P.'s were reduced by La (0.0125–0.05 mM) and Y (0.0125 and 0.025 mM). Effect on quantal contents of E.P.P.'s indicated that the principal action of both agents was an inhibition of transmitter release. La (0.025 and 0.05 mM) and Y (0.05 mM) significantly increased the frequency of miniature end-plate potentials. It is concluded that the prejunctional membrane does not differentiate significantly between the action of the trivalent rare earth ion lanthanum and the action of the trivalent rare-earth-like ion yttrium.