Mesoporous silica-coated hollow manganese oxide nanoparticles as positive T1 contrast agents for labeling and MRI tracking of adipose-derived mesenchymal stem cells

Mesoporous silica-coated hollow manganese oxide (HMnO@mSiO(2)) nanoparticles were developed as a novel T(1) magnetic resonance imaging (MRI) contrast agent. We hypothesized that the mesoporous structure of the nanoparticle shell enables optimal access of water molecules to the magnetic core, and consequently, an effective longitudinal (R(1)) relaxation enhancement of water protons, which value was measured to be 0.99 (mM(-1)s(-1)) at 11.7 T. Adipose-derived mesenchymal stem cells (MSCs) were efficiently labeled using electroporation, with much shorter T(1) values as compared to direct incubation without electroporation, which was also evidenced by signal enhancement on T(1)-weighted MR images in vitro. Intracranial grafting of HMnO@mSiO(2)-labeled MSCs enabled serial MR monitoring of cell transplants over 14 days. These novel nanoparticles may extend the arsenal of currently available nanoparticle MR contrast agents by providing positive contrast on T(1)-weighted images at high magnetic field strengths.     

两种新型的MRI造影剂两种新型的MRI造影剂

用动物活体核磁共振T2分布像和T1加权像分别观测了超顺磁性氧化铁造影剂和电中性大分子锰配合物造影剂的实验结果。大白鼠肝部的活体测量结果显示,上述两种造影剂能分别显著地改变生物活体组织的T2和T1值。该实验结果对于磁共振造影剂的研制和人体的临床试验具有参考价值。     

Hydrogels Incorporating GdDOTA: Towards Highly Efficient Dual T(1) /T(2) MRI Contrast Agents

Do not tumble dry: Gadolinium-DOTA encapsulated into polysaccharide nanoparticles (GdDOTA?NPs) exhibited high relaxivity (r(1) =101.7?s(-1) mM(-1) per Gd(3+) ion at 37?°C and 20?MHz). This high relaxation rate is due to efficient Gd loading, reduced tumbling of the Gd complex, and the hydrogel nature of the nanoparticles. The efficacy of the nanoparticles as a T(1) /T(2) dual-mode contrast agent was studied in C6 cells.     

Synthesis and evaluation of a high relaxivity manganese(II)-based MRI contrast agent

The manganese(II) ion has many favorable properties that lead to its potential use as an MRI contrast agent: high spin number, long electronic relaxation time, labile water exchange. The present work describes the design, synthesis, and evaluation of a novel Mn(II) complex (MnL1) based on EDTA and also contains a moiety that noncovalently binds the complex to serum albumin, the same moiety used in the gadolinium based contrast agent MS-325. Ultrafiltration albumin binding measurements (0.1 mM, pH 7.4, 37 degrees C) indicated that the complex binds well to plasma proteins (rabbit: 96 +/- 2% bound, human: 93 +/- 2% bound), and most likely to serum albumin (rabbit: 89 +/- 2% bound, human 98 +/- 2% bound). Observed relaxivities (+/- 5%) of the complex were measured (20 MHz, 37 degrees C, 0.1 mM, pH 7.4) in HEPES buffer (r(1) = 5.8 mM(-)(1) s(-)(1)), rabbit plasma (r(1) = 51 mM(-)(1) s(-)(1)), human plasma (r(1) = 46 mM(-)(1) s(-)(1)), 4.5% rabbit serum albumin (r(1) = 47 mM(-)(1) s(-)(1)), and 4.5% human serum albumin (r(1) = 48 mM(-)(1) s(-)(1)). The water exchange rate was near optimal for an MRI contrast agent (k(298) = 2.3 +/- 0.9 x 10(8) s(-)(1)). Variable temperature NMRD profiles indicated that the high relaxivity was due to slow tumbling of the albumin-bound complex and fast exchange of the inner sphere water. The concept of a high relaxivity Mn(II)-based contrast agent was validated by imaging at 1.5 T. In a rabbit model of carotid artery injury, MnL1 clearly delineated both arteries and veins while also distinguishing between healthy tissue and regions of vessel damage.     

Innovative synthesis of citrate-coated superparamagnetic Fe3O4 nanoparticles and its preliminary applications

In this study, we describe the development of a facile and effective route for the synthesis of Fe(3)O(4)-based T(1) contrast agent, which can be useful for in vivo magnetic resonance (MR) imaging. Citrate-coated Fe(3)O(4) nanoparticles (6 nm) with a narrow size distribution were synthesized by "one-pot green chemistry route" in diethylene glycol (DEG) solvent. The synthesized nanoparticles were characterized by different analytical techniques including XRD, TEM, HRTEM, and FTIR. At room temperature, nanoparticles exhibited superparamagnetic nature with high saturation magnetization. The longitudinal (r(1)) and transverse (r(2)) relaxivities were found to be 35.45 and 51.81 mM(-1)s(-1), respectively. Contrast agent developed by this method showed a relatively higher longitudinal relaxivity (r(1)) and the lowest relaxivity ratio (r(2)/r(1)=1.46) at 3T MR field. The anionic nature of citric acid facilitated non-specific internalization without impairment of cell viability and functionality. The in vitro studies showed both phagocitic and non-phagocytic uptake of these NPs. In vivo MR imaging of swine showed both T(1) and T(2) contrast effect.     

Ultrasmall water-soluble metal-iron oxide nanoparticles as T1-weighted contrast agents for magnetic resonance imaging

Using an improved hydrolysis method of inorganic salts assisted with water-bath incubation, ultrasmall water-soluble metal-iron oxide nanoparticles (including Fe(3)O(4), ZnFe(2)O(4) and NiFe(2)O(4) nanoparticles) were synthesized in aqueous solutions, which were used as T(1)-weighted contrast agents for magnetic resonance imaging (MRI). The morphology, structure, MRI relaxation properties and cytotoxicity of the as-prepared metal-iron oxide nanoparticles were characterized, respectively. The results showed that the average sizes of nanoparticles were about 4 nm, 4 nm and 5 nm for Fe(3)O(4), ZnFe(2)O(4) and NiFe(2)O(4) nanoparticles, respectively. Moreover, the nanoparticles have good water dispersibility and low cytotoxicity. The MRI test showed the strong T(1)-weighted, but the weak T(2)-weighted MRI performance of metal-iron oxide nanoparticles. The high T(1)-weighted MRI performance can be attributed to the ultrasmall size of metal-iron oxide nanoparticles. Therefore, the as-prepared metal-iron oxide nanoparticles with good water dispersibility and ultrasmall size can have potential applications as T(1)-weighted contrast agent materials for MRI.     

Facile preparation of zwitterion-stabilized superparamagnetic iron oxide nanoparticles (ZSPIONs) as an MR contrast agent for in vivo applications

We describe a simple method for synthesizing superparamagnetic nanoparticles (SPIONs) as small, stable contrast agents for magnetic resonance imaging (MRI) based on sulfobetaine zwitterionic ligands. SPIONs synthesized by thermal decomposition were coated with zwitterions to impart water dispersibility and high in vivo stability through the nanoemulsion method. Zwitterion surfactant coating layers are formed easily on oleic acid-stabilized SPIONs via hydrophobic and van der Waals interactions. Our zwitterion-coated SPIONs (ZSPIONs) had ultrathin (～5 nm) coating layers with mean sizes of 12.0 ± 2.5 nm, as measured by dynamic light scattering (DLS). Upon incubation in 1 M NaCl and 10% FBS, the ZSPIONs showed high colloidal stabilities without precipitating, as monitored by DLS. The T2 relaxivity coefficient of the ZSPIONs, obtained by measuring the relaxation rate on the basis of the iron concentration, was 261 mM(-1) s(-1). This value was much higher than that of the commercial T2 contrast agent because of the ultrathin coating layer. Furthermore, we confirmed that ZSPIONs can be used as MR contrast agents for in vivo applications such as tumor imaging and lymph node mapping.     

夹心型锰杂多配合物作为磁共振成像造影剂的研究

以两种夹心型锰杂多配合物K10[Mn4(PW9O34)2]·22H2O和Na16[Mn4(H2O)2(P2W15O56)2]·53H2O作为研究对象, 采用元素分析和红外光谱对其结构进行了表征, 测试其在水中、牛血清白蛋白及运铁蛋白溶液中的弛豫效率, 并进行了大鼠活体成像实验. 结果表明, 这两种锰杂多配合物的弛豫效率高于或接近于目前临床常用的造影剂Gd-DTPA, 对肝脏和肾脏MRI信号具有良好的增强效果, 是比较好的潜在磁共振成像造影剂候选化合物.     

Gd@C82(OH)16的合成及其核磁共振成像

采用电弧放电法合成和HPLC 2步分离法,得到了纯度为95％以上的Gd@C82。以四丁基氢氧化铵(TBAH)为催化剂,用NaOH溶液对Gd@C82进行羟基衍生化,并利用同步辐射XPS分析其C(12)确定Gd@C82羟基化产物的羟基数,得到水溶性的Gd@C82(OH)16。对Gd@C82(OH)16进行了体外弛豫率及体内的核磁共振成像研究。结果表明,与(NMG)2-Gd-DTPA相比,在相同Gd浓度下,Gd@C82(OH)16的质子弛豫率R1提高约3倍,R2提高约7倍。体内核磁成像结果也显示,Gd@C82(OH)16提高了核磁成像对比的效果,其信号在2 h内维持稳定。说明Gd@C82(OH)16在作为磁共振增强剂方面具有较大的潜力。     

In situ detection of PHIP at 48 mT: demonstration using a centrally controlled polarizer

Presented here is a centrally controlled, automated parahydrogen-based polarizer with in situ detection capability. A 20% polarization, corresponding to a 5,000,000-fold signal enhancement at 48 mT, is demonstrated on 2-hydroxyethyl-1-(13)C-propionate-d(2,3,3) using a double-tuned antenna and pulsed polarization transfer. In situ detection is a refinement of first-generation devices enabling fast calibration of rf pulses and B(0), quality assurance of hyperpolarized contrast agents, and stand-alone operation without the necessity of high-field MR spectrometers. These features are essential for biomedical applications of parahydrogen-based hyperpolarization and for clinical translation. We demonstrate the flexibility of the device by recording (13)C signal decay due to longitudinal relaxation of a hyperpolarized contrast agent at 48 mT corresponding to 2 MHz proton frequency. This appears to be the longest recorded T(1) (101 ± 7 s) for a (13)C hyperpolarized contrast agent in water.     

A gadolinium(III) complex with 8-amidequinoline based ligand as copper(II) ion responsive contrast agent

A new Cu(2+)-responsive MRI contrast agent (Gd-QDOTAMA) with a quinoline-based ligand was synthesized and characterized. Relaxivity studies on Gd-QDOTAMA showed that the relaxivity increased from 4.27 mM(-1) s(-1) to 7.29 mM(-1) s(-1) in response to equimolar amounts of copper(II) ion, corresponding to ca. 71% relaxivity enhancement. Distinct changes in relaxivity were undetected upon addition of physiologically relevant alkali metal cations (K(+) or Na(+)), alkaline earth metal cations (Mg(2+) or Ca(2+)), or d-block metal cations (Zn(2+), Cu(+), Fe(2+), Fe(3+)), indicating a high selectivity for Cu(2+) over other biologically relevant metal ions. Moreover, the influence of common biological anions at physiological levels on the Cu(2+)-responsive contrast agent was also studied. Luminescence studies on the Eu counterpart Eu-QDOTAMA suggest that the enhancement in relaxivity for Gd-QDOTAMA in response to Cu(2+) is most likely due to the increased number of inner-sphere water molecules around Gd(3+) upon Cu(2+) binding to the 8-amidequinoline moiety. In vitro T(1)-weighted phantom images of Gd-QDOTAMA confirmed that signal intensity was markedly increased by the addition of equimolar amounts of Cu(2+).     

Synthesis of NanoQ, a copper-based contrast agent for high-resolution magnetic resonance imaging characterization of human thrombus

A new site-targeted molecular imaging contrast agent based on a nanocolloidal suspension of lipid-encapsulated, organically soluble divalent copper has been developed. Concentrating a high payload of divalent copper ions per nanoparticle, this agent provides a high per-particle r1 relaxivity, allowing sensitive detection in T1-weighted magnetic resonance imaging when targeted to fibrin clots in vitro. The particle also exhibits a defined clearance and safety profile in vivo.     

Simple method for quantification of gadolinium magnetic resonance imaging contrast agents using ESR spectroscopy

To develop an estimation method of gadolinium magnetic resonance imaging (MRI) contrast agents, the effect of concentration of Gd compounds on the ESR spectrum of nitroxyl radical was examined. A solution of either 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPONE) or 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) was mixed with a solution of Gd compound and the ESR spectrum was recorded. Increased concentration of gadolinium-diethylenetriamine pentaacetic acid chelate (Gd-DTPA), an MRI contrast agent, increased the peak-to-peak line widths of ESR spectra of the nitroxyl radicals, in accordance with a decrease of their signal heights. A linear relationship was observed between concentration of Gd-DTPA and line width of ESR signal, up to approximately 50 mmol/L Gd-DTPA, with a high correlation coefficient. Response of TEMPONE was 1.4-times higher than that of TEMPOL as evaluated from the slopes of the lines. The response was slightly different among Gd compounds; the slopes of calibration curves for acua[N,N-bis[2-[(carboxymethyl)[(methylcarbamoyl)methyl]amino]ethyl]glycinato(3-)]gadolinium hydrate (Gd-DTPA-BMA) (6.22 μT·L/mmol) and gadolinium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid chelate (Gd-DOTA) (6.62 μT·L/mmol) were steeper than the slope for Gd-DTPA (5.45 μT·L/mmol), whereas the slope for gadolinium chloride (4.94 μT·L/mmol) was less steep than that for Gd-DTPA. This method is simple to apply. The results indicate that this method is useful for rough estimation of the concentration of Gd contrast agents if calibration is carried out with each standard compound. It was also found that the plot of the reciprocal square root of signal height against concentrations of contrast agents could be useful for the estimation if a constant volume of sample solution is taken and measured at the same position in the ESR cavity every time.     

肽类树状大分子磁共振成像探针的合成与功能化

通过优化设计,合成了高产率的DTPA和DOTA配体.通过液相发散法制得第三代肽类树状大分子,其外围氨基分别用两种不同保护基团保护,且两种保护基团的个数比精确控制为18∶6,通过选择性脱去保护基团,其中一种氨基与DTPA、DOTA偶联,或与丁二酸酐反应,并与金属离子钆螯合,制得G3-18Gd-DTPA-6COOH,G3-...     

Water-soluble gadofullerenes: toward high-relaxivity, pH-responsive MRI contrast agents

The water-soluble endohedral gadofullerene derivatives, Gd@C(60)(OH)(x) and Gd@C(60)[C(COOH)(2)](10), have been characterized with regard to their MRI contrast agent properties. Water-proton relaxivities have been measured in aqueous solution at variable temperature (278-335 K), and for the first time for gadofullerenes, relaxivities as a function of magnetic field (5 x 10(-4) to 9.4 T; NMRD profiles) are also reported. Both compounds show relaxivity maxima at high magnetic fields (30-60 MHz) with a maximum relaxivity of 10.4 mM(-1) s(-1) for Gd@C(60)[C(COOH)(2)](10) and 38.5 mM(-1) s(-1) for Gd@C(60)(OH)(x) at 299 K. Variable-temperature, transverse and longitudinal (17)O relaxation rates, and chemical shifts have been measured at three magnetic fields (B = 1.41, 4.7, and 9.4 T), and the results point exclusively to an outer sphere relaxation mechanism. The NMRD profiles have been analyzed in terms of slow rotational motion with a long rotational correlation time calculated to be tau(R)(298) = 2.6 ns. The proton exchange rate obtained for Gd@C(60)[C(COOH)(2)](10) is k(ex)(298) = 1.4 x 10(7) s(-1) which is consistent with the exchange rate previously determined for malonic acid. The proton relaxivities for both gadofullerene derivatives increase strongly with decreasing pH (pH: 3-12). This behavior results from a pH-dependent aggregation of Gd@C(60)(OH)(x) and Gd@C(60)[C(COOH)(2)](10), which has been characterized by dynamic light scattering measurements. The pH dependency of the proton relaxivities makes these gadofullerene derivatives prime candidates for pH-responsive MRI contrast agent applications.     

Stereoselective synthesis of d- and L-carbocyclic nucleosides by enzymatically catalyzed kinetic resolution

An efficient synthesis of (S)- or (R)-3-(benzyloxy-methyl)-cyclopent-3-enol was developed by appling an enzyme-catalyzed kinetic-resolution approach. This procedure allowed the syntheses of the enantiomeric building blocks (S)- and (R)-cyclopentenol with high optical purity (>98?% ee). In contrast to previous approaches, the key advantage of this procedure is that the resolution is done on the level of enantiomers that only contain one stereogenic center. Owing to this feature, it was possible to chemically convert the enantiomers into each other. By using this route, the starting materials for the syntheses of carbocyclic D- and L-nucleoside analogues were readily accessible. 3',4'-Unsaturated D- or L-carbocyclic nucleosides were obtained from the condensation of various nucleobases with (S)- or (R)-cyclopentenol. Functionalization of the double bond in 3'-deoxy-3',4'-didehydro-carba-D-thymidine led to a variety of new nucleoside analogues. By using the cycloSal approach, their corresponding phosphorylated metabolites were readily accessable. Moreover, a new synthetic route to carbocyclic 2'-deoxy-nucleosides was developed, thereby leading to D- and L-carba-dT. D-Carba-dT was tested for antiviral activity against multidrug-resistance HIV-1 strain E2-2 and compared to the known antiviral agent d4T, as well as L-carba-dT. Whilst L-carba-dT was found to be inactive, its D-analogue showed remarkably high activity against the resistant virus and significantly better than that of d4T. However, against the wild-type virus strain NL4/3, d4T was found to be more-active than D-carba-dT.     

Large-scale synthesis of uniform and extremely small-sized iron oxide nanoparticles for high-resolution T1 magnetic resonance imaging contrast agents

Uniform and extremely small-sized iron oxide nanoparticles (ESIONs) of < 4 nm were synthesized via the thermal decomposition of iron-oleate complex in the presence of oleyl alcohol. Oleyl alcohol lowered the reaction temperature by reducing iron-oleate complex, resulting in the production of small-sized nanoparticles. XRD pattern of 3 nm-sized nanoparticles revealed maghemite crystal structure. These nanoparticles exhibited very low magnetization derived from the spin-canting effect. The hydrophobic nanoparticles can be easily transformed to water-dispersible and biocompatible nanoparticles by capping with the poly(ethylene glycol)-derivatized phosphine oxide (PO-PEG) ligands. Toxic response was not observed with Fe concentration up to 100 μg/mL in MTT cell proliferation assay of POPEG-capped 3 nm-sized iron oxide nanoparticles. The 3 nm-sized nanoparticles exhibited a high r(1) relaxivity of 4.78 mM(-1) s(-1) and low r(2)/r(1) ratio of 6.12, demonstrating that ESIONs can be efficient T(1) contrast agents. The high r(1) relaxivities of ESIONs can be attributed to the large number of surface Fe(3+) ions with 5 unpaired valence electrons. In the in vivo T(1)-weighted magnetic resonance imaging (MRI), ESIONs showed longer circulation time than the clinically used gadolinium complex-based contrast agent, enabling high-resolution imaging. High-resolution blood pool MR imaging using ESIONs enabled clear observation of various blood vessels with sizes down to 0.2 mm. These results demonstrate the potential of ESIONs as T(1) MRI contrast agents in clinical settings.     

Synthesis of DTPA analogues derived from piperidine and azepane: potential contrast enhancement agents for magnetic resonance imaging.

Two DTPA derivatives (PIP-DTPA and AZEP-DTPA) as potential contrast enhancement agents in MRI are synthesized. The T1 and T2 relaxivities of their corresponding Gd(III) complexes are reported. At clinically relevant field strengths, the relaxivities of the complexes are comparable to that of the contrast agent, Gd(DTPA) which is in clinical use. The serum stability of the (153)Gd-labeled complexes is assessed by measuring the release of (153)Gd from the ligands. The radiolabeled Gd chelates are found to be kinetically stable in human serum for up to at least 14 days without any measurable loss of radioactivity.     

Local diffusion in paramagnetic solutions by NMR relaxometry at one frequency

The relative diffusion coefficient D of a paramagnetic species and a diamagnetic probe molecule bearing nuclear spins is obtained from their measured relaxation times T1 and T2 (or T1rho). This is achieved by introducing the longitudinal relaxivity, r1, a linear expression of 1/T1, and the mixed relaxivity, rmix, a linear expression of 1/T1 and 1/T2 (or 1/T1rho). Under weak assumptions, D is proportional to (rmix - r1) to the power -2/3 and to rmix to the power -1, with easy-to-determine proportionality factors. The method is noninvasive and easy to use on standard NMR spectrometers and imagers. It is validated through the study of various solutions of a Gd(III)-based contrast agent for magnetic resonance imaging.     

Optimized relaxivity and stability of [Gd(H(2,2)-1,2-HOPO)(H2O)]- for use as an MRI contrast agent

Relaxometry and solution thermodynamic measurements show that Gd(H(2,2)-1,2-HOPO) is a good candidate as a contrast agent for magnetic resonance imaging (MRI-CA). Acidic, octadentate H(2,2)-1,2-HOPO forms a very stable Gd(III) complex [pGd=21.2(2)]. The coordination sphere at the Gd(III) center is completed by one water molecule that is not replaced by common physiological anions. In addition, this ligand is highly selective for Gd(III) binding in the presence of Zn(II) or Ca(II). The symmetric charge distribution of the 1,2-HOPO chelates is associated with favorably long electronic relaxation time T1,2e comparable to those of GdDOTA. This, in addition to the fast water exchange rate typical of HOPO chelates, improves the relaxivity to r1p=8.2 mM-1 s-1 (0.47 T). This remarkably high value is unprecedented for small-molecule, q=1 MRI-CA.