Strontium-substituted hydroxyapatite nanocrystals

Among the many cations that can substitute for calcium in the structure of hydroxyapatite, strontium provokes an increasing interest because of its beneficial effect on bone formation, and prevention of bone resorption. We have synthesized calcium-strontium hydroxyapatite solid solutions in the whole range of composition by direct synthesis in an aqueous medium. The structural, morphological and chemical characterizations were carried out on the as-obtained products. Strontium is quantitatively incorporated into hydroxyapatite where its substitution for calcium provokes a linear increase in the lattice constants and a linear shift of the infrared absorption bands of the hydroxyl and phosphate groups, coherent with the greater ionic radius of strontium. At variance, the effect of relatively low levels of strontium concentration on the dimensions of the coherent length of the perfect crystalline domains and on the morphology of the nanocrystals is opposite to that observed at high levels of strontium concentration. Similarly, the results of the structure refinements carried out using the Rietveld method indicate that whilst in most of the range of concentration strontium displays a slight preference for the M(2) cation site coherently with its ionic radius, at very low concentrations its occupancy of the smaller M(1) site is slightly higher.     

Brefeldin A disrupts asymmetric spindle positioning in mouse oocytes

Polar body formation in oocytes is an extreme form of asymmetric cell division, but what regulates the asymmetric spindle positioning and cytokinesis is poorly understood. During mouse oocyte maturation, the metaphase I spindle forms at the center but then moves to the cortex prior to anaphase I and first polar body emission. We show here that treating denuded mouse oocytes with brefeldin A, an inhibitor of Golgi-based membrane fusion, abolished the asymmetric positioning of the metaphase I spindle and resulted in the formation of two half-size metaphase II eggs, instead of a full-sized egg and a polar body. The normal metaphase II spindle is similarly asymmetrically positioned in the mature egg, where the spindle lies with its axis parallel to the cortex but becomes perpendicular before anaphase II and emission of the second polar body. When ovulated eggs were activated with strontium in the presence of brefeldin A, the metaphase II spindle failed to assume perpendicular position, and the chromosomes separated without the extrusion of the second polar body. Remarkably, symmetric cytokinesis began following a 3 h delay, forming two half-size eggs each containing a pronucleus. BFA-sensitive intracellular vesicular transport is therefore required for spindle positioning in both MI and MII.     

Improved age control on early Homo fossils from the upper Burgi Member at Koobi Fora,Kenya

To address questions regarding the evolutionary origin, radiation and dispersal of the genus Homo, it is crucial to be able to place the occurrence of hominin fossils in a high-resolution chronological framework. The period around 2 Ma (millions of years ago) in eastern Africa is of particular interest as it is at this time that a more substantial fossil record of the genus Homo is first found. Here we combine magnetostratigraphy and strontium (Sr) isotope stratigraphy to improve age control on hominin-bearing upper Burgi (UBU) deposits in Areas 105 and 131 on the Karari Ridge in the eastern Turkana Basin (Kenya). We identify the base of the Olduvai subchron (bC2n) plus a short isolated interval of consistently normal polarity that we interpret to be the Pre-Olduvai event. Combined with precession-forced (∼20 kyr [thousands of years]) wet–dry climate cycles resolved by Sr isotope ratios, the magnetostratigraphic data allow us to construct an age model for the UBU deposits. We provide detailed age constraints for 15 hominin fossils from Area 131, showing that key specimens such as cranium KNM-ER 1470, partial face KNM-ER 62000 and mandibles KNM-ER 1482, KNM-ER 1801, and KNM-ER 1802 can be constrained between 1.945 ± 0.004 and 2.058 ± 0.034 Ma, and thus older than previously estimated. The new ages are consistent with a temporal overlap of two species of early Homo that can be distinguished by their facial morphology. Further, our results show that in this time interval, hominins occurred throughout the wet–dry climate cycles, supporting the hypothesis that the lacustrine Turkana Basin was a refugium during regionally dry periods. By establishing the observed first appearance datum of a marine-derived stingray in UBU deposits at 2.058 ± 0.034 Ma, we show that at this time the Turkana Basin was hydrographically connected to the Indian Ocean, facilitating dispersal of fauna between these areas. From a biogeographical perspective, we propose that the Indian Ocean coastal strip should be considered as a possible source area for one or more of the multiple Homo species in the Turkana Basin from over 2 Ma onwards.     

Stable isotope ecology of Miocene large mammals from Sandelzhausen,southern Germany

The carbon, oxygen, and strontium isotope composition of enamel from teeth of large Miocene herbivorous mammals from Sandelzhausen (MN5, late Early/early Middle Miocene) in the North Alpine foreland basin, were analyzed to infer diet and habitat. The mean enamel δ¹³C value of −11.4 ± 1.0‰ (n = 53) for the nine taxa analyzed (including proboscideans, cervids, suids, chalicotheres, equids, rhinocerotids) indicates a pure C₃ plant diet for all mammals. ⁸⁷Sr/⁸⁶Sr ratios of ~0.710 higher than those from teeth of the western Molasse Basin (0.708–0.709) seem to indicate preferential feeding of the mammals in the northeastern Molasse Basin. The sympatric herbivores have different mean δ¹³C and δ¹⁸O values which support diet partitioning and/or use of different habitats within a C₃ plant ecosystem. Especially the three sympatric rhinoceroses Plesiaceratherium fahlbuschi, Lartetotherium sansaniense, and Prosantorhinus germanicus show clear partitioning of plants and/or habitats. The palaeomerycid Germanomeryx fahlbuschi was a canopy folivore in moderately closed environments whereas Metaschizotherium bavaricum (Chalicotheriidae) and P. germanicus (Rhinocerotidae) were browsers in more closed forest environments. The horse Anchitherium aurelianense was probably a more generalized feeder than assumed from its dental morphology. The forest hog Hyotherium soemmeringi has the highest δ¹³C and lowest δ¹⁸O value of all analyzed taxa, possibly related to a frugivorous diet. Most taxa were water-dependent browsers that record meteoric water δ¹⁸O values of about −5.6 ± 0.7‰ Vienna Standard Mean Ocean Water (VSMOW). Using a modern-day mean annual air temperature (MAT)– relation a MAT of 19.3 ± 1.5°C can be reconstructed for Sandelzhausen. A Gomphotherium subtapiroideum tusk serially sampled for δ¹⁸O values does not record a clear pattern of seasonality. Thus most taxa were C₃ browsers in a forested and humid floodplain environment in the Molasse Basin, which experienced a warm-temperate to subtropical climate and possibly low seasonality.      

Magnesium and strontium doped octacalcium phosphate thin films by matrix assisted pulsed laser evaporation

Octacalcium phosphate (OCP) is a promising alternative to hydroxyapatite as biomaterial for hard tissue repair. In this study we successfully applied Matrix Assisted Pulsed Laser Evaporation (MAPLE) to deposit Mg and Sr doped OCP (MgOCP and SrOCP), as well as OCP, thin films on titanium substrates. OCP, Mg-substituted and Sr-substituted OCP were synthesized in aqueous medium, then were suspended in deionised water, frozen at liquid nitrogen temperature and used as targets for MAPLE experiments. The depositions were carried out using a KrF* excimer laser source (λ = 248 nm, τ_FWHM = 25 ns) in mild conditions of temperature and pressure. The results of X-ray diffraction, infrared spectroscopy, scanning electron microscopy and energy dispersive spectroscopy investigations revealed that the OCP thin films are deposited in the form of cauliflower-like aggregates and droplets, as well as crystal fragments, with a homogeneous distribution of magnesium and strontium on the surface of the coatings. Human osteoblast-like MG-63 cells were cultured on the different biomaterials up to 14 days. MgOCP and SrOCP coatings promote osteoblast proliferation and differentiation with respect to OCP. Under these experimental conditions, the production of procollagen-type I, transforming growth factor-β1, alkaline phosphatase and osteocalcin indicated that the level of differentiation of the cells grown on the different coatings increased in the order OCP < MgOCP < SrOCP.     

微量元素锶对幼年自发性高血压大鼠血压升高 的预防作用及其作用机制探讨

目的:研究微量元素锶对幼年自发性高血压大鼠(Spontaneously hypertensive rats,SHR)血压升高的预防作用并探讨其作用机制。方法:107只自发性高血压大鼠适应性喂养1周后,随机分为A组纯水对照组22只、B组锶水浓度3mg/L组22只、C组锶水浓度9mg/L组19只、D组锶水浓度18mg/L组22只,E组锶水浓度36mg/L组22只,普通饲料喂养12周。实验开始时测定基础血压,至结束时共测十次血压。实验开始及结束采血两次,检测肝、肾功能,Elisa法检测血清内皮素-1(endothelin-1,ET-1)、肾素(renin)、血管紧张素I(Iangiotensin-II)及去甲肾上腺素(noradrenalin,NA),免疫组化法检测主动脉核因子κB(nuclear factor-kappa B,NF-κB)、血管细胞黏附分子-1(vascular cell adhesion molecule-1,VCAM-1)、细胞间黏附分子-1(intercellular cell adhesion molecule-1,ICAM-1)的表达。结果:(1)SHR成年后,E组与A组相比表现出血压下降趋势(P<0.05);第十、十一、十二周时D、E组血压均显著低于A组(P<0.01);B、C组较A组也有不同程度下降;随锶水浓度增高血压呈逐渐下降的大体趋势,B-E组血压值低于A组(P<0.05,P<0.01);(2)锶水喂养后各组肝、肾功能指标及ET-1、renin、Ang-II、NA变化无明显差异(P>0.05);(3)锶水喂养后,B-E组主动脉NF-κB、VCAM-1;ICAM-1的积分光密度值(IOD)均显著低于A组(P<0.01),且随锶水浓度增高,NF-κB、VCAM-1、ICAM-1的表达呈递减趋势(P<0.01)。结论:微量元素锶可延缓SHR血压升高,减小血压波动,其对高血压的预防作用机制可能是由于抑制NF-κB经典通路,减少VCAM-1、ICAM-1等炎症介质的产生而减轻血管壁损害。     

Synthesis and characterization of bis(4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato) strontium and barium adducts with O- and N- ancillary ligands; crystal structure of Sr(tftb)2(batcp)

Complexes of type [M(tftb)₂L_n] [M=Sr; n=1, L=tetraglyme (4), 2,3-benzo-10-aza-1,4,7,13-tetraoxacyclopentadeca-2-ene (batcp) (5), n=2, L=2,2^′-bipyridine-N,N^′ (bipy) (6); M=Ba; n=1, L=tetraglyme (7), 2,3-benzo-10-aza-1,4,7,13-tetraoxacyclopentadeca-2-ene (batcp) (8); n=2, L=2,2^′-bipyridine-N,N^′ (bipy) (9)] were prepared by in situ reactions of 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htftb) (1) with M(OH)₂ [M=Sr (2a); Ba (2b)] in the presence of the ancillary ligands L (3a: L=tetraglyme; 3b: L=2,3-benzo-10-aza-1,4,7,13-tetraoxacyclopentadeca-2-ene (batcp); 3c: L=2,2^′-bipyridine-N,N^′ (bipy)) in aqueous ethanol. The compounds were obtained in high yields and characterized by elemental analysis, ¹H NMR, mass spectrometry and IR analysis. Molecular structure of the [Sr(tftb)₂(batcp)] (5) has been determined by X-ray single crystal analysis.     

Identifying calcium sources at an acid deposition-impacted spruce forest: a strontium isotope,alkaline earth element multi-tracer approach

Depletion of calcium from forest soils has important implications for forest productivity and health. Ca is available to fine feeder roots from a number of soil organic and mineral sources, but identifying the primary source or changes of sources in response to environmental change is problematic. We used strontium isotope and alkaline earth element concentration ratios of trees and soils to discern the record of Ca sources for red spruce at a base-poor, acid deposition-impacted watershed. We measured ⁸⁷Sr/⁸⁶Sr and chemical compositions of cross-sectional stemwood cores of red spruce, other spruce tissues and sequential extracts of co-located soil samples. ⁸⁷Sr/⁸⁶Sr and Sr/Ba ratios together provide a tracer of alkaline earth element sources that distinguishes the plant-available fraction of the shallow organic soils from those of deeper organic and mineral soils. Ca/Sr ratios proved less diagnostic, due to within-tree processes that fractionate these elements from each other. Over the growth period from 1870 to 1960, ⁸⁷Sr/⁸⁶Sr and Sr/Ba ratios of stemwood samples became progressively more variable and on average trended toward values that considered together are characteristic of the uppermost forest floor. In detail the stemwood chemistry revealed an episode of simultaneous enhanced uptake of all alkaline earth elements during the growth period from 1930 to 1960, coincident with reported local and regional increases in atmospheric inputs of inorganic acidity. We attribute the temporal trends in stemwood chemistry to progressive shallowing of the effective depth of alkaline earth element uptake by fine roots over this growth period, due to preferential concentration of fine roots in the upper forest floor coupled with reduced nutrient uptake by roots in the lower organic and upper mineral soils in response to acid-induced aluminum toxicity. Although both increased atmospheric deposition and selective weathering of Ca-rich minerals such as apatite provide possible alternative explanations of aspects of the observed trends, the chemical buffering capacity of the forest floor-biomass pool limits their effectiveness as causal mechanisms.     

Recycling of Synaptic Vesicles at the Frog Neuromuscular Junction in the Presence of Strontium

Abstract: In these experiments, we followed the exocytosis and endocytosis of synaptic vesicles with the vital dye FM1-43 and asked whether calcium is important for membrane retrieval at the frog neuromuscular junction. We replaced calcium with equimolar amounts of strontium and monitored the staining of recycling vesicles by inducing exocytosis with electrical stimulation. Trains of 2,400 (2 or 20 Hz) or 4,200 (20 Hz) pulses failed to induce FM1-43 internalization in the presence of strontium, but they did in the presence of calcium. This effect of strontium was not due to a decrease in exocytosis, because FM1-43 release was similar in the presence of calcium or strontium. The impairment in endocytosis, observed as inhibition of FM1-43 internalization, could be overcome by longer periods of stimulation (6,000 pulses at 2 or 20 Hz) in the presence of strontium (1.8 m M ) or by increasing the extracellular concentration of strontium to 10 m M (2,400 action potentials at 20 Hz). It is suggested that endocytosis is dependent on calcium influx and that strontium is much less effective in replacing calcium for endocytosis than it is for exocytosis.