Search

31P NMR was used to assess the influence of two weeks creatine supplementation (21g x d(-1)) on resting muscle PCr concentration, on the rate of PCr repletion (R(depl)), and on the half-time of PCr repletion (t 1/2). Body mass (BM) and volume of body water compartments were also estimated by impedance spectroscopy. Fourteen healthy male subjects (20.8+/-1.9 y) participated in this double-blind study. PCr was measured using a surface coil placed under the calf muscle, at rest and during two exercise bout the duration of which was 1 min. They were interspaced by a recovery of 10 min. The exercises comprised of 50 plantar flexions-extensions against weights corresponding to 40% and 70% of maximal voluntary contraction (MVC), respectively. Creatine supplementation increased resting muscle PCr content by approximately 20% (P= 0.002). R(depl) was also increased by approximately 15% (P< 0.001) and approximately 10% (P = 0.026) during 40% and 70% MVC exercises, respectively. No change was observed in R(repl) and t1/2. BM and body water compartments were not influenced. These results indicate that during a standardized exercise more ATP is synthesized by the CK reaction when the pre-exercise level in PCr is higher, giving some support to the positive effects recorded on muscle performance.

A neuroprotective effect can be obtained with N-[(4-cycloheptylaminopyrid-3-yl)sulphonyl]N'-cycloheptyl urea (BM27), a pyrid-3-yl-sulphonylurea structurally related to torasemide, a loop diuretic. We have investigated the neuroprotective effect of BM27 by magnetic resonance imaging and use of the photothrombotic model of cerebral infarction in the rat. This method enables non-invasive quantification of the extent of the cerebral oedema from T2-weighted spin-echo images. This article reports the evolution of the extent of oedema with time (0.5, 1, 2, 4, 6, 24 and 48 h, 7 and 15 days and 1 month after induction of the lesion) in rats pretreated with 5 mg kg(-1) BM27 or an appropriate control. At all times, the rats treated with BM27 had, on average, smaller lesions than control rats (30% decrease between 2 h and 6 h). These results strongly suggest a significant (P < 0.01) but modest neuroprotective effect of BM27 in ischaemic cerebral stroke. Further investigations should be performed to determine if BM27 or its analogues are of clinical interest.

Creatine kinase reaction studied in human skeletal muscle at rest and during exercise by the saturation transfer method

31P NMR spectroscopy was used to study the energy metabolism of dystrophin-deficient skeletal muscle of mdx mice, an animal model of Duchenne muscular dystrophy, in which expression of a truncated form of utrophin has been obtained through transgenesis technology. Measurements of ATP, phosphocreatine (PCr), inorganic phosphates (Pi) and intracellular pH (pHi) were made at rest, during a fatigue protocol and during the subsequent recovery. Mechanical fatigue of transgenic muscles was similar to normal muscle, while mdx muscle showed larger force loss. At rest, muscles of all groups had similar values for [ATP], [PCr], [Pi] and pHi. During fatigue, [PCr] decreases mirrored [Pi] increases and were similar in all groups. The major difference between mdx muscles and the group of normal and trc-utrophin muscles concerned the values and evolution of pHi. The mdx muscles showed a more severe intracellular acidosis during exercise and a slower and incomplete post-exercise recovery of normal pHi. In contrast, in trc-utrophin muscles, the kinetics and amplitude of pHi changes were remarkably close to normal behaviour. We conclude that the impaired proton washout which is present in mdx muscles, is corrected to a great extent by the expression of trc-utrophin.

The development of oxygen-sensitive paramagnetic materials is being pursued actively because of their potential applications in in vivo EPR oximetry. Among these materials, several charcoals and carbohydrate chars are of special interest because of their desirable EPR properties: high sensitivity of the EPR linewidth to the partial pressure of oxygen, simple EPR spectra, and high spin density. Their potential use in humans, however, is limited by the need to demonstrate that they will not lead to deleterious effects. A strategy was used to optimize the biocompatibility of the oxygen-sensitive materials by decreasing the size of the particles and coating them with suspending or surfactive agents such as arabic gum, poloxamer (Pluriol 6800), and polyvinylpyrrolidone. The coated particles of a carbohydrate char and fusinite were characterized in vitro for their size, stability, and pO2 sensitivity. The feasibility of performing pO2 measurement was examined in vivo by inducing ischemia in the gastrocnemius muscle of mice. The use of arabic gum for coating the fusinite particles preserved the pO2 sensitivity in vivo, whereas the other surfactive agents led to a loss of the pO2 sensitivity in vivo. Small particles of fusinite coated by arabic gum and intravenously administered to mice accumulated in the liver, whereas the uncoated fusinite was toxic when injected intravenously due to the large size and aggregation of the particles. Histological studies performed up to 6 months after the injection in muscles of mice did not indicate any toxicity from the materials used in the present study.

RATIONALE AND OBJECTIVES: The authors compare the potential value of unenhanced and gadoxetate disodium-enhanced spin-echo images for the detection of hepatocellular carcinoma in a rat model. METHODS: Eleven rats with chemically induced hepatocellular carcinoma underwent unenhanced T2-weighted fast spin-echo imaging followed by T1-weighted spin-echo imaging before and at 5 minutes, 30 minutes, 3 hours, 1 day, and 3 days after intravenous administration of 60 micromol/kg gadoxetate disodium at 4.7 tesla. Tumor and liver enhancement, and tumor-to-liver contrast-to-noise (C/N) ratio were calculated. RESULTS: After gadoxetate disodium administration, the tumors showed less enhancement than the liver. Tumor-to-liver C/N ratio increased from 5.5 +/- 0.8% on unenhanced T1-weighted images to 12.9 +/- 2.4% on gadoxetate-enhanced T1-weighted images (P = 0.02). However, the C/N ratio on unenhanced T2-weighted images (23.5 +/- 3.6%) remained higher than that on gadoxetate-enhanced T1-weighted images, a difference that is statistically significant (P < 0.01). CONCLUSIONS: In the experimental setting of our study, the higher tumor-to-liver C/N ratio on unenhanced T2-weighted spin-echo images suggests that unenhanced T2-weighted spin-echo images are superior to gadoxetate disodium-enhanced T1-weighted spin-echo images for the detection of hepatocellular carcinoma.

The herpes simplex virus thymidine kinase gene was transferred into C6 glioma cells by infection with a recombinant adenovirus. In vitro, a 10 microM ganciclovir concentration was able to kill 100% of the infected cells. For in vivo experiments, brain tumors were established by stereotactic injection of C6 glioma cells in the caudate nucleus of rats. Five days later, the recombinant adenovirus was inoculated into the tumors and the animals were treated by intraperitoneal injections of ganciclovir for 14 days. At the end of ganciclovir therapy, histological examination revealed a 28-fold decrease in tumor volumes in the treated animals, as compared with control animals. In long-term studies, the mean survival time of the treated animals were four-fold longer than that of control ones. Magnetic resonance imaging demonstrated an apparent complete tumor regression in 62% of the animals. However, late tumor recurrence was observed in the treated animals. Repeated inoculation of C6 glioma cells in the contralateral hemisphere of long-term surviving animals resulted in either tumor rejection or slowly growing tumors. These findings demonstrate the potential efficacy of adenovirus-mediated transfer of the herpes simplex virus thymidine kinase gene and ganciclovir administration in the treatment of rat gliomas.

To detect reperfused ischemia of the rat intestine, T-2-weighted spin-echo images were acquired, followed by T-1-weighted images before and after administration of polylysine-Gd-DTPA or Gd-DTPA, Before administration of the contrast agent, the reperfused intestine was hyperintense on T-2-weighted images, and to a lesser extent on T-2-weighted images, After administration of polylysine-Gd-DTPA, the reperfused intestine enhanced more than the normal one, giving a significantly better contrast-to-noise (CNR) ratio than on unenhanced images, Gd-DTPA induced the same enhancement of the reperfused and the normal intestine and the CNR was lower than on unenhanced T-2-weighted images, Reperfused intestinal ischemia could thus be better detected on polylysine-Gd-DTPA-enhanced MR images than on unenhanced images or on Gd-DTPA-enhanced images.

A contour detection algorithm for cerebral studies, using the method of Tomitani, has been implemented on a single-photon emission tomographic (SPET) system. It is based on the detetion by threshold of the brain edge in the sinogram and does not depend on the reconstruction algorithm. Thirteen normal subjects underwent an examination on both computed tomography (CT) and SPET using a head holder to ensure the reproducibility of the positioning. The CT scan contour of the brain was drawn manually according to the brain parenchyma limits. The SPET brain contour was obtained by use of the Tomitani algorithm after the threshold had been determined on an active cylindrical phantom. Using a threshold of 37% of the maximum uptake, the length of the contour as well as the area obtained with SPET and CT were not found to be statistically different. The method of Tomitani, which is simpler and faster then previous methods, provides contours which superimpose very well with CT scan images. Application to patients with unilateral pathological defects is possible by requiring that the contour is symmetrical.

The purpose of this study was to assess the potential role of MR imaging with polylysine-Gd-DTPA enhancement in the early detection of acute occlusive intestinal ischemia in a rat model. After devascularization of the distal ileum in 12 rats, T2-weighted fast spin-echo MR images were acquired, followed by T1-weighted images before and after IV administration of 0.1 mmol/kg polylysine-Gd-DTPA. The signal intensity of the ischemic intestine did not differ significantly from that of the normal intestine before the administration of the contrast material. No mucosal or submucosal edema or hemorrhage was found in the ischemic intestine at histologic examination. After the administration of polylysine-Gd-DTPA, the ischemic intestine lacked enhancement and its signal intensity was significantly lower than that of the normal intestine. MR imaging with polylysine-Gd-DTPA enhancement can detect acute occlusive ischemia of the rat intestine at an early stage.

Using a rat C6 brain tumor model, we studied the antitumor effects of Herpes simplex virus type 1 thymidine kinase (HSV-tk) gene transfer followed by ganciclovir treatment. C6 glioma cells were transfected in vitro with the HSV-tk gene, and tested for their sensitivity to ganciclovir. Although there was no surviving cell at a 30 microM ganciclovir concentration, unmodified C6 cells were not affected by the drug. For in vivo experiments, intracerebral tumors were induced in rats by stereotactic injection of 10(4) HSV-tk-modified C6 cells. Ten days later, the animals were treated with intraperitoneal injections of ganciclovir for 21 days. The tumors evolution was evaluated by high resolution magnetic resonance imaging. In 33% of the rats, the signal intensity of the tumors became heterogeneous, with development of highly hyperintense areas, and a complete tumor regression was subsequently noted. Histological examination of successfully treated tumors revealed progressive necrosis with formation of cysts. The survival time of the HSV-tk/ganciclovir treated animals was consistently increased, all rats surviving more than 30 days and 33% of them being still alive after 80 days.

This work reports a low-cost and versatile electronic device designed to trigger NMR acquisitions from the cardiac cycle of an isolated perfused heart, or to perform electrical stimulation of the heart. The triggering is synchronised with the pressure curve of the perfused heart. The cardiac pacing is achieved from pulses of the NMR system, or by an internal pulse generator, in order to be operated separately from the NMR instrument.

RATIONALE AND OBJECTIVES. TO compare the magnetic resonance (MR) imaging characteristics of gadolinium-DTPA (Gd-DTPA), a low-molecular-weight contrast agent, and polylysine-Gd-DTPA, a macromolecular contrast agent, in two types of hepatocarcinomas (HCC) in the rat. METHODS. T1-weighted spin-echo images were obtained in 13 rats with chemically induced HCC and 26 rats with Novikoff HCC before and 3 minutes to 60 hours after administration of either Gd-DTPA or polylysine-Gd-DTPA. RESULTS. Three minutes after polylysine-Gd-DTPA administration, the tumor-to-liver contrast of the two types of HCC increased significantly (positive contrast for chemically induced HCC and negative contrast for Novikoff HCC). At 30 minutes and 60 hours, the tumor-to-liver contrast remained above baseline values in chemically induced HCC and returned progressively to baseline values in Novikoff HCC. No significant increase in tumor-to-liver contrast was observed after Gd-DTPA administration. CONCLUSIONS. These results suggest that polylysine-Gd-DTPA provides a higher and more prolonged increase in tumor-to-liver contrast than Gd-DTPA.

In this study, we report the synthesis and the evaluation as MRI contrast agent of arabinogalactan/pyrrolidinoxyl radicals (PCA) covalent adduct (SLAG:Spin Labelled ArabinoGalactan). Arabinogalactan was used as targeting device, as it is recognized by the asialoglycoprotein receptor specific to the hepatocytes. The higher relaxivity R1 in water of SLAG, compared with small hydrophilic nitroxyl radicals, was explained by the molecular dynamics study using EPR spectroscopy that showed some immobilization of the radical into the polysaccharide. A binding study on isolated hepatocytes revealed that SLAG still recognizes the asialoglycoprotein receptor. MR imaging was performed using spin-echo T1 weighted images on mice to compare the contrast effect obtained with SLAG and PCA after IV injection (1 mmol/kg free radical). The percent signal enhancement observed in the liver 5 min after IV injection was 40 +/- 3% and 13 +/- 5% for SLAG and PCA, respectively. The signal was also dramatically increased in the renal cortex. This latter effect as well as the prolonged duration of the contrast (+/- 3 h), indicates at least a partial nonselective biodistribution; the high concentration needed to obtain a contrast effect could account for the saturation of the asialoglycoprotein receptor and hence for the apparent nonselective biodistribution.

The classical method for31P NMR determination of intracellular free magnesium concentration ([Mg 2+free]) requires an accurate knowledge of the apparent dissociation constant (K D ) of MgATP. There is a large difference between the previously determined values ofK D . Although the value of 50 µM, determined by a31P NMR method, is now largely accepted, a value of 86 µM has more recently been measured with a fitting method derived from the original one, and with a different ionic strength. The purpose of our study was to assess if the cause of the difference between these two previously reportedK D values was due to the measuring method or to the ionic strength value used. Working at pH=7.2,T=37°C, and [KCl]=0.25 M, we performedK D measurements with the original31P NMR method and with the fitting method. The results (67±13 µM and 61±20 µM, respectively) were not significantly different. Then, with the first method, we measured KD at [KCl]=0.12 M and found a value of 19±5 µM. We conclude that the main cause of difference between theK D values measured by31P NMR reside in the disparity of ionic strength values used for their measurement. OurK D measurements at [KCl]=0.25 and 0.12 M demonstrate the importance of the ionic strength value used for imitating the intracellular medium on the absolute value of ([Mg 2+free]) measured by31P NMR spectroscopy.

In this study, we report the synthesis and the evaluation as MRI contrast agent of a new compound (nitroxyl fatty acid, NFA), where a pyrrolidinoxyl radical (3-carboxy-proxyl, PCA) is linked to a fatty acid moiety. Fatty acids were selected as vector because they present a high affinity for the liver, their efficient cellular uptake being the result of a specific interaction with a transmembrane transporter (liver plasma membrane-fatty acid binding protein). The uptake of 3H-oleic acid is inhibited after the injection of 1 mmol/kg of NFA, suggesting that NFA recognizes the same transmembrane transporter as the natural fatty acids. The higher relaxivity R1 of NFA in albumin solutions, compared with PCA, was explained by the immobilization of the nitroxyl radical in the protein. MR imaging was performed using T1-weighted images on mice in order to compare the contrast effect obtained after the injection of 1 mmol/kg of radical. The % signal enhancement in the liver 5 min after intravenous injection was 49 +/- 4 and 14 +/- 5 for NFA and PCA, respectively. NFA allowed a better delimitation of some necrotic tumors (Novikoff hepatocarcinoma) due to its preferential uptake by the nontumorous tissue.

Considering their intrinsic properties of accumulation in the hepatic tissue, we have synthesized nitroxyl-containing lipids as potential organ-specific contrast agents for magnetic resonance imaging (MRI). Their resistance to reduction by ascorbate and in liver homogenates, and their relaxivity in different media were investigated and compared to those of free carboxyl-Proxyl (3-carboxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl) and Tempamaine (4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl). With respect to the reduction rates by ascorbate, the lipid derivatives show the same well-known order of reactivity as carboxy-Proxyl and Tempamine, the five-membered nitroxyls being more stable than the six-membered compounds. However the binding of the piperidinoxyl compounds to the fatty acids confers to those lipid derivatives a markedly increased stability. Similarly, in liver homogenates, the nitroxyl lipids remained unchanged more than 20 min, contrarily to carboxy-Proxyl and Tempamine. The measurements of spin-lattice relaxation time (T1) in biological media have demonstrated a higher relaxivity of nitroxyl lipids, which can be related to their interaction with proteins. Tested in vivo, one of the synthesized compounds (0.75 mmol/kg) produced an enhancement of 44 +/- 12% of the hepatic signal 5 min after intraportal injection in T1-weighted images. The potential applicability of the other nitroxyl lipids as contrast agents for MRI was limited in the in vivo studies by an unexpected toxicity. Work is currently in progress to improve the therapeutic index of the present class of nitroxyl lipids.

To evaluate the accuracy of surface coil gradient-echo (GRE) imaging in the detection of regenerative nodules of hepatic cirrhosis, 53 patients with diffuse liver disease, among whom 31 had cirrhosis, were prospectively investigated. Three GRE sequences acquired with a surface coil were used in the study: a T2*-weighted, a T1-weighted, and a gadopentetate-enhanced sequence. ROC analysis showed that two surface coil GRE sequences were superior to conventional T2-weighted spin-echo imaging acquired with a body coil for the detection of regenerative nodules. The detection of regenerative nodules was also more accurate for the diagnosis of cirrhosis than the measurement of the caudate-to-right lobe ratio. These results suggest that there could be a potential for surface coil GRE imaging in the assessment of the characteristic macroscopic alterations of cirrhosis.

To determine the value of oral magnetic particles (OMP) as a superparamagnetic MR contrast agent for the gastrointestinal tract in lower abdominal and pelvic lesions, 30 patients underwent spin-echo imaging before and after ingestion of OMP at a dose of approximately 80 mg of iron in 800 ml water. The preparation was divided into four portions and taken by the patient over a 2-h period. Two readers independently reviewed the MR images. The contrast material was well tolerated and the distribution of the contrast material was good to excellent in the proximal and pelvic small bowel, but was not sufficient in the colon with the dose and timing used in the study. Postcontrast images showed a significantly better delineation of the lesions, the small bowel, and the paraaortic region, but no significant improvement in the delineation of the colon, the iliac vessels area, the bladder or genital tract. Compared with precontrast images, confidence in defining or excluding disease on postcontrast images was better, equal or worse in 40, 60 and 0% of cases, respectively (P less than 0.001) with a substantial agreement between readers (kappa = 0.71). OMP produced susceptibility artefacts of significant intensity in only one case. These results indicate that OMP may be useful in the delineation of lower abdominal and pelvic lesions at MR imaging. Marking of the colon by a contrast agent might improve the results.

Thirty patients with hemangiomas (n = 6), benign liver cell tumors (n = 7), and primary or metastatic malignant tumors of the liver (n = 17) underwent dynamic MR imaging with Gd-DTPA to determine the value of the procedure in the differentiation of hepatic tumors. The diagnoses were proved by histology or follow-up. Hemangiomas had a significantly greater mean T2 value (192.1 +/- 34.8 msec) than did both benign liver cell tumors (71.9 +/- 16.9 msec; p less than .01) and primary or metastatic malignant tumors (79.7 +/- 21.2 msec; p less than .01), but the T2 values of benign liver cell tumors and malignant tumors were not significantly different. Both hemangiomas and benign liver cell tumors had a significantly greater mean signal-intensity ratio (1.86 +/- 0.60 and 1.77 +/- 0.26, respectively) than did malignant tumors (1.04 +/- 0.34; p less than .01) in the early phase after Gd-DTPA administration, and hemangiomas had a significantly greater signal-intensity ratio (1.59 +/- 0.21) than did both benign liver cell tumors (1.21 +/- 0.08; p less than .01) and malignant tumors (1.06 +/- 0.26; p less than .01) in the delayed phase. These results suggest that dynamic MR images obtained after administration of Gd-DTPA are useful in differentiating hepatic hemangiomas, benign liver cell tumors, and malignant liver lesions.