6-Fluoropyridoxol: a novel probe of cellular pH using 19F NMR spectroscopy

6-Fluoropyridoxol was evaluated as an intracellular pH indicator. This molecule exhibits exceptional sensitivity to changes in pH (approximately 10 ppm acid/base shift) and a pKa approximately 8.2 appropriate for physiological investigations. Using 19F NMR spectroscopy we determined both intra- and extracellular pH in whole blood and confirmed the measurements using traditional techniques: ion-electrodes and 31P NMR spectroscopy.

Fluorinated proteins as potential 19F magnetic resonance imaging and spectroscopy agents

Fluorinated proteins have been synthesized and characterized as potential in vivo 19F magnetic resonance imaging (MRI) and spectroscopy (MRS) agents. Proteins labeled with fluorine include bovine serum albumin, gamma-globulin, and purified immunoglobulin (IgG). The amino groups in proteins were selectively trifluoroacetylated using S-ethyl trifluorothioacetate to synthesize fluorinated proteins (TFA-protein; 1-3). In another approach, trifluoroacetamidosuccinic anhydride has been used to prepare corresponding fluorinated derivatives of proteins (TFASA-protein; 4-6). The fluorinated proteins have been purified by exhaustive dialysis and isolated in good yields (55-76%). The fluorinated proteins exhibit useful NMR characteristics and the biocompatibility for in vivo studies. The initial investigations demonstrate the potential of these new fluorinated proteins as in vivo MRI/MRS probes.

Non-invasive determination of tumor oxygen tension and local variation with growth

PURPOSE

The objective was to develop and demonstrate a novel noninvasive technique of measuring regional pO2 in tumors. The method is based on measuring 19F nuclear magnetic resonance spin-lattice relaxation rate (R1 = 1/T1) of perfluorocarbon (PFC) emulsion discretely sequestered in a tumor.

METHODS AND MATERIALS

We have examined pO2 in the Dunning prostate tumor R3327-AT1 implanted in a Copenhagen rat. Oxypherol blood substitute emulsion was administered intravenously and became sequestered in tissue. Proton magnetic resonance imaging (MRI) showed tumor anatomy and correlated 19F MRI indicated the distribution of perfluorocarbon. Fluorine-19 spectroscopic relaxometry was used to measure pO2 in the tumor and repeated measurements over a period of 3 weeks showed the variation in local pO2 during tumor growth.

RESULTS

Perfluorocarbon initially resided in the vascularized peripheral region of the tumor: 19F nuclear magnetic resonance R1 indicated pO2 approximately 75 torr in a small tumor (approximately 1 cm) in an anesthetized rat. As the tumor grew, the sequestered PFC retained its original distribution. When the tumor had doubled in size the residual PFC was predominantly in the core of the tumor and the pO2 of this region was approximately 1 torr indicating central tumor hypoxia.

CONCLUSION

We have demonstrated a novel noninvasive approach to monitoring regional tumor pO2. Given the critical role of oxygen tension in tumor response to therapy this may provide new insight into tumor physiology, the efficacy of various therapeutic approaches, and ultimately provide a clinical technique for assessing individual tumor oxygenation.

Tumor oxygen tension: measurement using Oxygent as a 19F NMR probe at 4.7 T

We have used Oxygent (an emulsion of perflubron [PFOB]) to measure pO2 in a Dunning prostatic adenocarcinoma non-invasively using 19F NMR spectroscopy. We have confirmed a linear relationship between the spin-lattice relaxation rate (R1) and pO2 and we have assessed the effect of temperature. R1 of the individual resonances of Oxygent is considerably more sensitive to changes in pO2 than other PFC emulsions, whilst being considerably less sensitive to interference from temperature variation. Oxygent has two well resolved resonances (delta delta approximately 18ppm) and these were both exploited to estimate tumor pO2 = 47 +/- 5 torr.

Measurement of intrinsic bone quality in vivo by reflection ultrasound: correction of impaired quality with slow-release sodium fluoride and calcium citrate

The intrinsic (material) quality of cancellous and cortical bone was evaluated in vivo from the measurement of reflection ultrasound velocities in the ulna. In cancellous bone, the reflection ultrasound velocity was inversely correlated with age in normal women (r = -0.48, p = 0.001), with a significantly lower mean value in 32 normal postmenopausal women than in 14 premenopausal women (3124 versus 3341 m/s, p < 0.0001). In 32 untreated osteoporotic women the cancellous bone velocity was lower than in normal postmenopausal subjects (2906 versus 3124 m/s, p = 0.0001). Following treatment with slow-release sodium fluoride plus calcium citrate (mean 2.4 years in 33 osteoporotic patients with no fracture during treatment), the cancellous bone velocity was significantly higher than in untreated osteoporotic women (3082 versus 2906 m/s, p = 0.0002) and was not significantly different from that in normal postmenopausal women. The cortical bone velocity displayed similar trends, but the changes did not attain statistical significance. The measurements were repeated approximately 9 months later in 9 untreated and in 20 treated patients; in 5 additional patients, the measurements were made both before and after 9 months of treatment with slow-release sodium fluoride and calcium citrate. The cancellous bone velocity increased significantly (p = 0.046) in these patients, from 3008 m/s before treatment to 3112 m/s after the first 9 months of treatment. The velocity rose significantly from 3037 to 3167 m/s (p = 0.017) in patients treated for a short time (12-30 months at first measurement), but it did not change in untreated patients or those treated for more than 30 months. Thus, the material quality of cancellous bone decreases with normal aging and is reduced further with the osteoporotic process. This impaired quality may be corrected by treatment with slow-release sodium fluoride plus calcium citrate.

In vivo oxygen tension and temperature: simultaneous determination using 19F NMR spectroscopy of perfluorocarbon

A novel technique is presented to measure in vivo simultaneously oxygen tension and temperature using 19F NMR spectroscopy of perfluorocarbon. This work examines the variation with oxygen tension (pO2) and temperature of the individual spin lattice relaxation rates (R1) of the 19F resonances of the perfluorocarbon emulsion Oxypherol-ET. A linear relationship between R1 and pO2 is confirmed for all the resonances at any specific temperature in the range 27-50 degrees C. Similarly, a linear relationship is determined between R1 and temperature at any specific pO2 in this temperature range. Each resonance behaves uniquely with respect to temperature and pO2 and consideration of 2 or more resonances uniquely defines pO2 and temperature simultaneously, and unambiguously. This concept is demonstrated in vivo in a murine tumor and perfused rat heart, where pO2 and temperature were both determined without prior knowledge.

Glutathione in whole blood: a novel determination using double quantum coherence transfer proton NMR spectroscopy

Double quantum selective coherence transfer proton NMR spectroscopy has been used to observe glutathione in whole blood. The efficient water suppression of this technique avoids the need to resuspend the cells in D2O, hence avoiding equilibrium and kinetic isotope effects. Using this method we estimate the concentration of glutathione in fresh whole rabbit blood at approximately 1.7 mM.

Isolated tumor growth in a surgically formed skin pedicle in the rat: a new tumor model for NMR studies

We have developed a new tumor model, the skin flap pedicle, which is ideally suited for study by such techniques as magnetic resonance imaging (MRI) and spectroscopy (MRS) and positron emission tomography (PET) to evaluate changes in metabolism/physiology in tumors before and after treatment. Heretofore, results from such studies were generally obtained from tumors growing in the thigh or flank region and these sites of growth often compromised the quality of the results, because of the contribution of normal tissues such as muscle and bone. In an attempt to circumvent such problems, we developed a surgical technique for creating a tubular skin pedicle and subsequently transplanting tumors in the lumen of such pedicles. We have successfully grown Dunning Prostate tumors (R-3327) as PEDICLE-TUMORS (PED-TUM). This paper describes the surgical procedure for formation of the skin pedicle, implantation of the tumor, data on the growth and histology and discusses the application of the PED-TUM to research problems. We compare the NMR characteristics of the tumor grown in the traditional SC thigh position with that growth in the pedicle and demonstrate the utility and advantages of the new model for studies of tumor physiological function and structure.

Fluoride-stimulated [3H]thymidine uptake in a human osteoblastic osteosarcoma cell line is dependent on transforming growth factor beta

Controversy exists regarding the effect of fluoride on human osteoblast proliferation. To learn more of the cellular action of fluoride, we chose the clonal osteoblast cell line HOS TE85 as a model system. In these phenotypically osteoblast-like cells, sodium fluoride stimulated [3H]thymidine incorporation in a dose-dependent manner over the concentration range 1 x 10(-5)-2 x 10(-4) M. The fluoride-induced stimulation of [3H]thymidine uptake was dependent on cell density, being optimal at subconfluent cell numbers. Stimulation of [3H]thymidine uptake was inhibited by anti-transforming growth factor beta but not by antibody to insulin-like growth factor I or beta 2-microglobulin. Transforming growth factor beta was shown to be a biphasic stimulator of [3H]thymidine uptake in HOS TE85, with maximal stimulation occurring at 0.5 nM transforming growth factor beta. In the presence of fluoride the cells were more sensitive to stimulation by this growth factor, with maximum effect occurring at 0.1 nM. Fluoride did not increase mRNA for transforming growth factor beta following either 8 or 24 h of exposure. We conclude that fluoride activates osteoblast proliferation by modulating the cellular sensitivity to transforming growth factor beta, a known stimulator of bone growth.

Ultrasound study of bone in vitro

Ultrasound has been investigated as a tool for characterizing the biomechanical competence of bone. The rationale for using ultrasound rests on two points. First, its interaction with tissues can be used to measure their density, velocity, and structure, and thus to characterize the elasticity and to infer the strength of bone. Second, ultrasound may be used to characterize tissue properties over a wide range of spatial dimensions and organizational levels, ranging from its constituents (e.g., trabeculae for cancellous bone) to the entire organ. Different ultrasound techniques can be used to investigate diverse bone properties, but two techniques have emerged as having the potential for providing useful information on problems of current biomedical interest. These measure two parameters, density and velocity, which correlate with the elastic and ultimate properties of bone. In particular, the elasticity E is formally related to the product of density and velocity squared, E = rho v2. Moreover, it has been shown by mechanical testing that there is a single linear correlation between elasticity and strength at all orientations, both in cortical and in cancellous bone, materials with a strong intrinsic anisotropy. At the tissue level, it may therefore be expected that the ultrasound parameters will prove to be useful predictors of bone strength and of its dependence on orientation. In vitro ultrasound studies have shown that these properties can be measured specifically and quantitatively, and that they vary under different physiological conditions.

A noninvasive assessment of myocardial oxygen tension: 19F NMR spectroscopy of sequestered perfluorocarbon emulsion

Fluorine NMR spectroscopy of sequestered perfluorocarbon emulsion has been used to measure myocardial oxygen tension. This novel application provides a rapid noninvasive assessment of changes in oxygen tension in response to ischemia and reperfusion. Rats were predosed with Oxypherol-ET (emulsion of perfluorotributylamine). Following vascular clearance of the emulsion the heart was excised and perfused using the Langendorff retrograde technique. 19F spin-lattice relaxation time measurements provided an accurate estimate of myocardial pO2. Using a two-point determination with a time resolution of 1 s, the loss of oxygen was found to be complete within 40 s of the onset of global ischemia. The fall in oxygen tension correlated closely with an observed loss of ventricular pressure. Magnetic resonance imaging showed that perfluorocarbon was distributed throughout the heart; thus, this reporter molecule provides a global measurement of oxygen tension.

Lack of deleterious effect of slow-release sodium fluoride treatment on cortical bone histology and quality in osteoporotic patients

We evaluated the effects of intermittent slow-release sodium fluoride (SRNaF) and continuous calcium citrate therapy on cortical bone histology, reflection ultrasound velocity (material strength) and back-scattered electron image analysis (BEI) in 26 osteoporotic patients before and following therapy. All measurements were made on transiliac crest bone biopsies obtained before and following 2 years of therapy in each patient. For all 26 patients there were no significant changes in cortical bone histomorphometric parameters. In 15 patients in whom bone material quality was assessed by reflection ultrasound, there was no change in velocity (4000 +/- 227 SD to 4013 +/- 240 m/s). BEI disclosed no mineralization defects or the presence of woven bone. Mean atomic number (density) of bone increased slightly, but significantly (9.261 +/- 0.311 to 9.457 +/- 0.223, P = 0.031). While these changes are less marked than those observed for cancellous bone, they indicate that this form of therapy does not adversely affect cortical bone remodelling.

Oxygent: a novel probe of tissue oxygen tension

We have examined the 19F NMR spectrum and relaxation behavior of Oxygent (an emulsion of perfluorooctylbromide). Each of the resonances exhibits a linear relationship between spin-lattice relaxation rate and oxygen tension at constant temperature. Oxygent provides enhanced sensitivity to changes in oxygen tension compared with other emulsions used previously. We have used Oxygent to determine the oxygen tension in the liver of a mouse.

Measurement of mechanical properties of bone material in vitro by ultrasound reflection: methodology and comparison with ultrasound transmission

An ultrasound reflection technique was designed and implemented to study the mechanical properties of bone material. The technique uses the fact that an ultrasound beam produced in water undergoes total internal reflection off a bone sample at a critical angle formally related to the velocity of a pressure wave in bone. When the plane of scattering is rotated around the normal to the sample surface, the critical angle varies with a periodic dependence dictated by the intrinsic symmetry of the bone structure at the point being examined. Most current measurements of sound velocity are made using transmission techniques. A double-blind intercomparison between this technique and a transmission technique, which was previously validated against tensile mechanical testing, was performed for samples of isotropic materials and of human cortical bone. Strong correlations were found for both sets of samples. For the isotropic materials the velocities were approximately equal, but for bone they were on average 11% higher in reflection than in transmission. This was the result both of the higher frequency employed in reflection (3.5 rather than 2.25 MHz) and of the different effects of sample imperfections on the two measurements. In particular, the reflection technique used in this work studied the surface of the sample, but the ultrasound beam in the transmission method propagated through its interior. In assessing the mechanical properties of bone specimens by ultrasound, the reflection technique samples a discrete bone surface element and the transmission method analyzes the entire volume of the specimen. Thus the reflection technique may yield a measure of the mechanical property of bone trabeculae that is largely unaffected by the mass of the entire specimen, but mass and the structural density of the specimen affect the transmission method.

Tissue oxygenation: a novel determination using 19F surface coil NMR spectroscopy of sequestered perfluorocarbon emulsion

This work examines the variation with oxygen tension (pO2) of the individual spin-lattice relaxation times (T1) of the 19F resonances of the perfluorocarbon emulsion Oxypherol-ET (FC-43). A linear relationship between 1/T1 and pO2 has been confirmed for all four resonances at any specific temperature. Using a saturation recovery sequence, T1 has been successfully measured using surface coil NMR spectroscopy. This has facilitated measurement of T1 in vivo in a subcutaneous murine tumor. Mice were predosed with Oxypherol-ET emulsion: following complete vascular clearance of the perfluorocarbon, 19F signal was observed specifically from material sequestered in tissue, thus avoiding flow artifacts. Comparison of the pO2 estimated from each of the 19F resonances provided an internal consistency check. A pO2 = 0.1 +/- 2.2% was determined in a Meth-A murine tumor. When the mouse breathed carbogen (95% O2, 5% CO2) no significant change in tumor pO2 was detected, whereas the pO2 in the liver showed a distinct increase.

Assessment by reflection ultrasound method of the effect of intermittent slow-release sodium fluoride-calcium citrate therapy on material strength of bone

It has been suggested that fluoride therapy, while increasing bone mass, produces bone with inferior mechanical properties. In the present report this hypothesis was tested using a novel reflection ultrasound technique. Transiliac crest bone biopsies were obtained from 16 patients with osteoporosis and vertebral compression fractures (12 women and 4 men, mean age 56 years) before and after approximately 2 years of intermittent slow-release sodium fluoride therapy (25 mg twice a day) combined with continuous calcium citrate supplementation. Samples were analyzed by a reflection ultrasound method, which analyzes ultrasound velocity with a sample site resolution of 200 microns and thus provides a measure of the mechanical property of single trabeculae (material). For the group, mean fractional change in velocity increased 6.1 +/- 2.3% (SEM) from a mean value of 3303 +/- 80 to 3484 +/- 55 m/s (p = 0.028). A total of 13 patients (81%) demonstrated higher velocities after treatment. Thus reflection ultrasound analysis of bone appears to provide a sensitive means of assessing changes in the material property of bone. Furthermore, these results suggest that the treatment regimen utilized in these patients improves strength of bone at the material or trabecular level largely independently of change in bone mass. The combination therapy also increased spinal (L2-L4) bone density for the group as assessed by dual-photon absorptiometry (5.3 +/- 2.0%). There was no significant correlation between the change in ultrasound velocity and bone density (r = 0.0026, p = 0.996).(ABSTRACT TRUNCATED AT 250 WORDS)

New directions in medical imaging of cancer. Magnetic resonance methods and single photon emission computed tomography

Magnetic resonance methods and single photon emission computed tomography (SPECT) are developing technologies that provide both functional and anatomic information. Their role in the diagnosis and monitoring of cancer is the subject of current clinical research. Magnetic resonance imaging (MRI) delineates organs and tissue heterogeneities using differences in the relaxation parameters of water and fat protons; both protons and other nuclei can be imaged or studied by magnetic resonance spectroscopy (MRS) to provide information on the state of naturally occurring or infused molecules. SPECT quantifies the distribution of radiolabeled agents in tissues and organs; labeled monoclonal antibodies provide highly specific imaging of tumors. Spatial resolution is the limiting technologic factor. Proton MRI provides the highest current resolution, better than 1 mm in vivo in deep tissues, whereas the resolution of MRS and SPECT is limited to several cubic centimeters. Recent advances in these technologies have significantly increased their specificity and ability to detect small, deep lesions.

Effect of homonuclear J modulation on 19F spin-echo images

The effect of homonuclear J modulation on 19F spin-echo images is evidenced by a substantial reduction in signal when the echo time, TE, approaches 1/2J, with a subsequent increase in signal at longer TEs. Suppression of the J-modulation effect is demonstrated using chemical shift-selective 180 degrees refocusing pulses.

Exact solutions to the multiregion time-dependent bioheat equation. II: Numerical evaluation of the solutions

Analytic solutions to the time-dependent multiregion bioheat equation are evaluated numerically for cartesian and spherical models. Principle and alternate branch contributions to the solutions are examined. The calculations include a parametric investigation and analyses of temperature behaviour in idealised upper thigh and tumour models.

Exact solutions to the multiregion time-dependent bioheat equation. I: Solution development

Exact solutions are obtained to the classical time-dependent linear bioheat equation in one-dimensional multiregion cartesian and spherical geometries with temperature-invariant physiological parameters. These solutions enable the study of transient temperature behaviour in an arbitrary number of coupled physiologically distinct regions.

Dose distribution around a 3.0-mm type 6702 I-125 seed

The 3M Company recently produced a special version of the type 6702 seed for use in animal studies of ocular melanoma. The seed consists of a single I-125 impregnated ion exchange resin sphere encapsulated in a 3.0-mm-long titanium cylinder, as opposed to the normal 4.5-mm cylinder containing from three to five resin spheres. Monte Carlo simulations and measurements show that the dose distribution around the 3-mm capsule differs in places by up to 10% from that of the 4.5-mm seed. In addition, the two seed types differ by 12% in the ratio of dose in tissue along the transverse seed axis to apparent activity. These differences must be taken into account when using these seeds.

A novel editing technique for 19F MRI: molecule-specific imaging

A novel technique is proposed to facilitate the selective imaging of specific molecules from a mixture. The application of the technique presented here demonstrates the ability to selectively produce 19F MR images of either trifluoroacetic acid or the perfluorocarbon emulsion Oxypherol-ET (perfluorotributylamine), when both molecules are present simultaneously. Selective detection is based on the presence of homonuclear J-modulation in one molecule and differential spin-spin relaxation time (T2). Perfluorotributylamine, an A3B2 system, is subject to homonuclear J-modulation, which produces a null signal from the antiphase components of the triplet (A3) when an echo time (TE) = 1/2J is used in a spin-echo image. At this echo time the second molecule, in this example trifluoroacetic acid, a non-coupled spin system, is selectively imaged. At longer echo times, e.g., TE = 1/J there is substantial recovery of the J-modulated signal, which may be solely observed due to T2 decay of the trifluoroacetic acid signal. The method is demonstrated both using phantoms and in vivo.

Applications of magnetic resonance techniques to deep tumor hyperthermia

Magnetic resonance imaging and spectroscopy have the potential for supporting clinical hyperthermia advances in the treatment of deep tumors. Current spectroscopic techniques can monitor treatment delivery and effectiveness through changes in metabolism and blood flow. Spectra can be obtained in vivo, repetitively and noninvasively; furthermore, current techniques have been implemented to give spatially resolved information. Further advances in MRI/MRS techniques may make it possible to obtained the information necessary for individualized treatment planning, for qualitative monitoring and assessment of treatment results, and for the measurement of thermal fields in vivo.

Perfluorocarbon imaging in vivo: a 19F MRI study in tumor-bearing mice

Multiresonance perfluorocarbon emulsions (Oxypherol and Fluosol-DA) were imaged in tumor-bearing mice using 19F spin-echo magnetic resonance imaging in vivo. Multiple thin-slice fluorine images free of chemical shift artifacts were obtained in 13 minutes and these were correlated with proton images obtained during the same experiment to delineate the anatomic distribution of perfluorocarbons. Sequential images were used to determine the time course of the distribution and the retention of the compounds in tumors and organs. 19F MR spectroscopy was used ex vivo to determine with high sensitivity the relative concentration of perfluorocarbons in different tissues and organs and to confirm the results obtained from imaging experiments. The fluorine images visually demonstrated the preferential localization of the perfluorocarbons in the liver and spleen; shortly after injection, the images also revealed the highly vascularized tumor-chest wall interface. Imaging and spectroscopy together showed that the perfluorocarbons were removed from the blood pool within hours and remained sequestered in tissues at later times; the highest concentrations were found in the spleen and liver, where the agents were retained without spectral changes for the duration of these studies. The perfluorocarbons accumulated within tumors at dose-dependent concentrations, one to two orders of magnitude smaller than those observed in the spleen and liver.