Spin-lattice relaxation time in water/graphene-oxide dispersion.

We present the results of the calculations of the spin-lattice relaxation time of water in contact with graphene oxide by means of all-atom molecular dynamics simulations. We fully characterized the water-graphene oxide interaction through the calculation of the relaxation properties of bulk water and of the contact angle as a function of graphene oxide oxidation state and comparing them with the available experimental data. We then extended the calculation to investigate how graphene oxide alters the dynamical and relaxation properties of water in different conditions and concentrations. We show that, despite the diamagnetic nature of the graphene oxide, the confining effects of the bilayers strongly affect the longitudinal relaxation properties of interfacial water, which presents a reduced dynamics due to hydrogen bonds with oxygen groups on graphene oxide. This property makes graphene oxide an interesting platform to investigate water dynamics in confined geometries and an alternative contrast-agent for magnetic resonance imaging applications, especially in view of the possibility to functionalize graphene oxide from theranostic perspectives.

Hypoxia induces peroxisome proliferator-activated receptor α (PPARα) and lipid metabolism peroxisomal enzymes in human glioblastoma cells.

Glioblastoma multiforme (GBM) represents the most severe type of glioma, the most common brain tumor. Their malignancy shows a relationship with an increased proliferation and a poorly organized tumor vascularization, an event that leads to inadequate blood supply, hypoxic areas and at last to the formation of necrotic areas, a feature of glioblastoma. Hypoxic/necrotic tumors are more resistant to chemotherapy and radiation therapies, thus it is crucial to formulate new therapeutic approaches that can render these tumors more sensitive to the action of conventional therapies. It has been demonstrated that under hypoxia, gliomas accumulate lipid droplets and that this event is positively correlated with the degree of malignancy, glioblastoma being the most endowed with lipid droplets. We have previously demonstrated in ex vivo glioma specimens a grade-dependent lipid metabolism perturbation. Here we studied the lipid pathways and the presence of stemness markers in glioma primary cultures, obtained from surgical specimens of patients affected by glioma at different grade of malignancy, GBM primary cultures cultured under both hypoxic and normoxic conditions, as well as normal human astrocytes. The results obtained demonstrate that hypoxia plays a crucial role in regulating the expression of lipid metabolism peroxisomal enzymes, the lipid droplets accumulation as well as the transcription factor PPARα.

Lipid metabolism impairment in human gliomas: expression of peroxisomal proteins in human gliomas at different grades of malignancy.

Gliomas are histologically graded by cellularity, cytological atypia, necrosis, mitotic figures, and vascular proliferation, features associated with biologically aggressive behaviour. However, abundant evidence suggests the presence of unrecognized, clinically relevant subclasses of the diffuse gliomas, both in respect to their underlying molecular phenotype and their clinical response to therapy. It is well-known that patient prognosis and therapeutic decisions rely on accurate pathological grading. Recently, it was reported that human gliomas accumulate lipid droplets during progression, suggesting a lipid metabolism impairment. Considering the crucial role of peroxisomes in lipid metabolism, in the present work we studied the expression profiles of proteins either exclusively localized to peroxisomes, such as peroxin14 (PEX14), peroxisomal membrane protein 70Kda (PMP70), acyl-CoA oxidase, thiolase, or partially associated to peroxisomes such as Hydroxymethylglutaryl-CoA reductase (HMGCoA-red) and peroxisomal-related proteins, namely PPARalpha, in human glioma specimens at different grades of malignancy. Moreover, Nile red staining of lipid droplets, thin layer chromatography (TLC) and proton nuclear magnetic resonance spectroscopy (NMR) were carried out in order to correlate the biochemical results with the lipid content of tumor tissues. The results obtained indicate that correlating the malignancy grade with the expression of peroxisomal genes and proteins, may constitute a sensitive tool to highlight possible subtypes not recognized by the classical histological techniques.

Practical design of a 4 Tesla double-tuned RF surface coil for interleaved 1H and 23Na MRI of rat brain.

MRI is proving to be a very useful tool for sodium quantification in animal models of stroke, ischemia, and cancer. In this work, we present the practical design of a dual-frequency RF surface coil that provides (1)H and (23)Na images of the rat head at 4 T. The dual-frequency RF surface coil comprised of a large loop tuned to the (1)H frequency and a smaller co-planar loop tuned to the (23)Na frequency. The mutual coupling between the two loops was eliminated by the use of a trap circuit inserted in the smaller coil. This independent-loop design was versatile since it enabled a separate optimisation of the sensitivity and RF field distributions of the two coils. To allow for an easy extension of this simple double-tuned coil design to other frequencies (nuclei) and dimensions, we describe in detail the practical aspects of the workbench design and MRI testing using a phantom that mimics in vivo conditions. A comparison between our independent-loop, double-tuned coil and a single-tuned (23)Na coil of equal size obtained with a phantom matching in vivo conditions, showed a reduction of the (23)Na sensitivity (about 28 %) because of signal losses in the trap inductance. Typical congruent (1)H and (23)Na rat brain images showing good SNR ((23)Na: brain 7, ventricular cerebrospinal fluid 11) and spatial resolution ((23)Na: 1.25 x 1.25 x 5mm(3)) are also reported. The in vivo SNR values obtained with this coil were comparable to, if not better than, other contemporary designs in the literature.

In vivo electron paramagnetic resonance spectroscopy-imaging in experimental oncology: the hope and the reality.

PURPOSE: Low frequency (280 MHz) electron paramagnetic resonance imaging is a new magnetic resonance technique, still being developed, that can map the in vivo spatial distribution of paramagnetic species such as nitroxide free radicals. The reduction rate of these molecules is affected by oxygen concentration. This paper gives some examples of the use of electron paramagnetic resonance imaging methodology in whole rats in the framework of its possible use in experimental oncology. METHODS AND MATERIALS: The 280 MHz apparatus based on a cylindrical 16 pole magnet was developed and designed specifically for 50-200 g laboratory animals. It generates the main field and the three field gradients required for three-dimensional (3-D) projections. A pyrrolidine nitroxyl (2,2,5,5,-tetramethylpyrrolidine-1-oxyl-3-carboxylic acid) was injected intravenously in rats to provide an electron paramagnetic resonance signal for in vivo measurements. Electron paramagnetic resonance X-band spectrometer was used to monitor pyrrolidine nitroxyl decay in an external blood circuit during normoxia and moderate hypoxia (15% O2). RESULTS AND CONCLUSION: One-dimensional (1-D) transversal and longitudinal mapping of this nitroxide free radical distribution in rat whole body was obtained 7-9 min after injection. In circulating blood, nitroxide half-life decreased significantly during hypoxia. The present sensitivity (10(-4)-10(-5) M), spatial resolution (3-10 mm) and collection time (3-5 min) could be drastically improved by narrow linewidth paramagnetic probes and pulsed techniques.

Low field (10 mT) pulsed dynamic nuclear polarization.

EPR irradiation by a train of inverting pulses has potential advantages over continuous-wave EPR irradiation in DNP applications; however, it has previously been used only at high field (5 T). This paper presents the design and testing of an apparatus for performing pulsed DNP experiments at 10 mT with large samples (17 ml). Experimental results using pulsed DNP with an aqueous solution of a narrow-linewidth paramagnetic probe are presented. A maximum DNP enhancement of about -36 with a train of inverting pulses (width 500 ns, repetition time 4 micros) was measured. A preliminary comparison showed that, when the same enhancement value is considered, the pulsed DNP technique requires an average power that is about three times higher than that required with the CW irradiation. However, for in vivo DNP applications it is very important to minimize the average power deposited in the sample. From the experimental results reported in this work, when considering the maximum enhancement, the pulsed technique requires only 2% of the average power necessary with the CW DNP technique. We believe that this reduction in the average power can be important for future DNP studies with large biological samples.

Omega-space adaptive acquisition technique for magnetic resonance imaging from projections.

An omega-space adaptive acquisition technique for MRI from projections is presented. It is based on the evaluation of the information content of a set composed of four initial projections, measured at angles 0 degrees, 45 degrees, 90 degrees, and 135 degrees, followed by the selection of new angles where the information content is maximum. An entropy function is defined on the power spectrum of the projections that is useful for evaluating the information content of each projection. The method makes it possible to reduce the total acquisition time with little degradation of the reconstructed image and it adapts to the arbitrary shape of the sample. For this reason, it can be particularly useful in those applications where acquisition from projections is strongly recommended to save acquisition time, such as functional MRI, imaging of species having very short T(2), or angiography. The method has been tested both on simulated data and on experimental data collected by a commercial MRI apparatus. The method has also been compared to the regular acquisition method, that is, the standard acquisition method in MRI from projections.

Fourier reconstruction as a valid alternative to filtered back projection in iterative applications: implementation of Fourier spectral spatial EPR imaging.

The qualitative equivalence between the Fourier reconstruction (FR) algorithm and the filtered back projection (FBP) algorithm is demonstrated when all the different phase errors that can occur in FR are eliminated. The causes of phase errors are underlined and methods to eliminate them are presented. The practical comparison between FR and FBP has been evaluated on a numerical test image and the results are reported, demonstrating the qualitative equivalence. FR has the advantage of being very computationally efficient. In fact, the time spent to obtain the FR image was 1/20 of that used to obtain the FBP image. Because of the computational efficiency of FR and the good quality of the results obtained, an iterative version of FR has been used to implement the spectral-spatial imaging (SSI) algorithm in the field of electron paramagnetic resonance imaging (EPRI). An experimental example, demonstrating its good performance, is reported.

Optimization of axial RF field distribution in low-frequency EPR loop-gap resonators.

A novel coupling method that optimizes the axial RF distribution of low-frequency EPR loop-gap resonators is presented. It consists of a resonant coupling loop positioned at the centre of a two-section loop-gap resonator. This arrangement ensures a symmetrical distribution of the radio frequency field along the axis of the resonator. The design of a central coupling system suitable for EPR resonators operating at about 220 MHz is described. Experimental results show that with the central coupling system the RF field is symmetrical and has a very good axial homogeneity (100% of the resonator length).

Two-dimensional 220 MHz Fourier transform EPR imaging.

In the last decade radiofrequency continuous-wave EPR spectrometers have been developed to detect and localize free radicals in vivo. Only recently, pulsed radiofrequency EPR spectrometers have been described for imaging applications with small samples. In the present work, we show the first two-dimensional image obtained at 220 MHz on a large phantom (40 ml) that simulates typical conditions of in vivo EPR imaging. This pulsed EPR apparatus has the potential to make the time required for three-dimensional imaging compatible with the biological half-life of normally used paramagnetic probes.

Pulsed EPR imaging: image reconstruction using selective acquisition sequences.

Pulsed nuclear magnetic resonance imaging (NMRI) apparatus has developed very quickly. On the other hand, the development of apparatus for pulsed electron paramagnetic resonance imaging (EPRI) has been very slow. This fact is due to the extremely reduced relaxation times of the paramagnetic probes. EPR linewidths are larger than typical NMR linewidths. These large linewidths are also responsible for a substantial worsening of spatial resolution. Due to the brevity of the electronic relaxation times, not all the acquisition/reconstruction techniques currently used in NMRI (such as spin-echo, gradient-echo, etc) can be applied in pulsed EPRI. In fact, the usable sequences in pulsed EPRI are only acquisitions from projections, where it is possible to use stationary magnetic field gradients. Moreover, the use of high fixed magnetic field gradients induces a short decay time constant T2*. The low T2* value can make it impossible for the analogue to digital conversion system (ADC) to reproduce signal variations during the whole acquisition interval and the resolution can worsen. A new pulsed EPRI acquisition sequence from projections, based on selective reception, is presented that is particularly useful in solving the problems of worsening of spatial resolution associated with the use of an ADC. In order to demonstrate the capabilities of our acquisition method, simulated numerical tests will also be reported.

Nitroxide free radical clearance in the live rat monitored by radio-frequency CW-EPR and PEDRI.

The use of RF (100 to 300 MHz) PEDRI and CW-EPR techniques allows the in vivo study of large animals such as whole rats and rabbits. Recently a PEDRI instrument was modified to also allow CW-EPR spectroscopy with samples of similar size and under the same experimental conditions. In the present study, this CW-EPR and PEDRI apparatus was used to assess the feasibility of the detection of a pyrrolidine nitroxide free radical (2,2,5,5,-tetramethylpyrrolidine-1-oxyl-3-carboxylic acid, PCA) in the abdomen of rats. In particular, we have shown that after the PCA administration (4 mmol kg(-1) b.w.): (i) the PCA EPR linewidth does not show line broadening due to concentration effects; (ii) a similar PCA up-take phase is observed by EPR and PEDRI; and (iii) the PCA half-lives in the whole abdomen of rats measured with the CW-EPR (T1/2=26+/-4 min, mean+/-sd, n=10) and PEDRI (T1/2=29+/-4 min, mean+/-sd, n=4) techniques were not significantly different (p > 0.05). These results show, for the first time, that information about PCA pharmacokinetics obtained by CW-EPR is the same as that from PEDRI under the same experimental conditions.

pH-sensitive imaging by low-frequency EPR: a model study for biological applications.

The use of pH-sensitive nitroxides, in conjunction with low-frequency EPR, offers a unique opportunity for non-invasive assessment of pH values (in the range 0 to 14) in living animals. In the present study, we have investigated the potential use of pH-sensitive nitroxide free radicals in conjunction with EPR imaging techniques at low and very low frequencies (280 MHz-2.1 GHz). In particular, we have measured the hyperfine splitting (hfs) of a pH-sensitive probe at three different EPR frequencies: 280 MHz, 1.1 GHz and 2.1 GHz. We have also developed EPR imaging experiments with phantoms simulating in vivo conditions, using pH-sensitive probes at 280 MHz (spatial-spatial) and 1.1 GHz (spectral-spatial). Finally, we discuss the actual sensitivity/resolution limits of the EPR imaging techniques at low frequencies. Practical applications of this method in the biomedical field are suggested for the continuous and non-invasive localization of pH in vivo.

Compensating for B(1) inhomogeneity using active transmit power modulation.

The effect of poor B(1) homogeneity on MRI images not only affects the appearance of the images, but produces difficulty in automated segmentation and in certain quantification methods. While improved RF coil design is the first line in reducing such artifact, compensation methods can significantly improve the quality of images. Existing methods of compensation typically apply a filter during the image reconstruction. Here a method is presented that compensates for part of the inhomogeneity by actively modulating the RF transmit power as a function of slice position. The method is demonstrated both quantitatively on a phantom and qualitatively on a human brain.

Three-dimensional in vivo ESR imaging in rats.

The first experiment of tridimensional in vivo ESR imaging at 1.2 GHz is described in this paper. The tails of rats weighing 300-350 grams were visualized using 1 cc of a 50 * 10(-3) M solution of nitroxide free radical injected in the caudal vein. In an even distribution of spin label is assumed this would correspond to a final concentration of about 10(-4) M. A reconstruction from projections was used to obtain the images. The apparatus utilizes stationary field gradients. Projections were obtained by sweeping the main field. For 3D reconstructions, the projections were collected along 32 * 8 field gradient orientations. The whole procedure takes approximately 18 minutes.

Effect of picotamide and aspirin, combined or alone, on platelet aggregation in patients with cerebral infarction.

After 7 and 90 days of treatment, we studied the effect of picotamide, a thromboxane synthase inhibitor (450 and 900 mg/day), aspirin (150 mg/day), and aspirin plus picotamide (150 and 450 mg/day respectively) on platelet aggregation, evaluated in platelet rich plasma of 48 patients affected by ischemic stroke. Platelet aggregation, induced by collagen (1.0 and 2.0 micrograms/ml) and adenosine diphosphate (1.0 and 10 micrograms/L), was significantly increased in patients in comparison with healthy controls. Aspirin (150 mg/day) reduced collagen-induced platelet aggregation (1.0 microgram/ml) after 7 days of treatment. Picotamide (450 mg/day) reduced platelet aggregation induced by both concentrations of collagen, while the higher dose (900 mg/day) had no significant effect. Aspirin plus picotamide reduced the aggregation induced by 1.0 microgram/ml collagen and by 10 mumol/L adenosine diphosphate after 90 days of therapy. This study has shown that patients during the acute phase of stroke are characterized by an increased in vitro platelet aggregation. Aspirin may be beneficial in the acute phase of the cerebral ischemic event. Picotamide and picotamide plus aspirin could be useful for reducing platelet aggregation in long term treatment.

Versatile coil design and positioning of transverse-field RF surface coils for clinical 1.5-T MRI applications.

Clinical MRI/MRS applications require radio frequency (RF) surface coils positioned at an arbitrary angle alpha with respect to B(0). In these experimental conditions the standard circular loop (CL) coil, producing an axial RF field, shows a large signal loss in the central region of interest (ROI). We demonstrate that transverse-field figure-of-eight (FO8) RF surface coils design are not subject to the same amount of signal loss in the central ROI as loop coils when their orientations are changed. The 1.5-T CL and FO8 prototypes (diameter = 10 cm) were built on Plexiglas using copper strips (width = 4 mm, thickness = 100 mum). The two linear elements of the FO8 coil were 1 cm apart. Axial spoiled gradient echo (SPGR) images of a phantom containing doped water were acquired with the coil plane at alpha=0 degrees , 45 degrees , and 90 degrees . As alpha increases, the CL images show, in the central ROI, a signal that decreases from a maximum value to zero. Whereas the FO8 images show, in the same ROI, a signal that varies little from the maximum value (20%). Optimized FO8 coils can be oriented with the coil plane positioned along any direction with respect to B(0) without significant signal loss. Transverse RF coil design should be useful for clinical MRS studies and also for parallel imaging techniques where versatile RF coils disposed along arbitrary directions are required.

Whole rat electron paramagnetic resonance imaging of a nitroxide free radical by a radio frequency (280 MHz) spectrometer.

Low frequency (280 MHz) electron paramagnetic resonance spectroscopy has been used to follow uptake, distribution and reduction of the nitroxyl spin label PCA in the rat. No difference of half life was found in seven rats submitted to three administrations of PCA (11.3 +/- 0.4; 11.0 +/- 0.6 and 11.5 +/- 0.7 min). Transversal two-dimensional images of PCA distribution in the rat body were obtained over 6 min by means of field gradients. PCA was observed in three regions by projections along the longitudinal axis of the rat. PCA accumulation was found in the lower abdomen 12 min after the start of the PCA injection.

Water soluble free radicals as biologically responsive agents in electron paramagnetic resonance imaging.

Electron paramagnetic resonance imaging (EPRI) is currently being developed at frequencies between 200 MHz and 2 GHz. EPRI can map the in vivo distribution of paramagnetic species, such as water soluble free radicals; nitroxide free radicals are commonly used. EPR images reflect the complexity of metabolic actions on the exogenous delivered nitroxides. Their reduction rate in vivo is affected by parameters such as oxygen concentration, pH and biodistribution. This paper illustrates the main features of low frequency EPRI and reconstruction techniques. Examples of EPR imaging, such as two-dimensional (2D) spatial mapping of the distribution of a nitroxide free radical in phantoms and in whole rat, are given.