S. Ramaprasad

Substituent effects in tetrapyrrole subunit reactivity and pinacol-pinacolone rearrangements: Vic-dihydroxychlorins and vic-dihydroxybacteriochlorins

Regiospecificity of pyrrole subunit OsO4 oxidation in porphyrins is affected significantly by the presence of electron-withdrawing groups on the macrocycle, the oxidation taking place at the subunit in the quadrant opposite to the electronegative group. Migratory aptitudes in subsequent pinacol-pinacolone rearrangements of porphyrin and pheophorbide vic-dihydroxy systems are likewise dependent upon the presence of electron-withdrawing functionalities.

Use of presaturation for chemical-shift-selective imaging of individual fluids in sandstone and carbonate cores

Abstract A number of approaches to chemical-shift-selective NMR imaging are possible, and several have been demonstrated in the literature. Many of these methods were originally developed for solvent signal suppression in Fourier transform NMR spectroscopy. We demonstrate here the use of RF presaturation to obtain chemical-shift-selective, fluid-specific images of refined oil and aqueous brine in carbonate and sandstone cores. This method of fluid-selective imaging has not been previously demonstrated for rock cores. In the sandstone case, by injecting perdeuterated isopropanol, it was further possible to obtain fluid-selective images for each of the three fluids present in the core. To our knowledge, this is the first demonstration by either NMR or X-ray CT imaging of fluid-selective images for three individual fluids in a rock. In addition, 3D reconstructions of the fluid-selective slice images are presented for the sandstone core.

In vivo relaxation time measurements on a murine tumor model—Prolongation of T1 after photodynamic therapy

RIF tumors implanted on mice feet were investigated for changes in relaxation times (T1 and T2) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T1s of water protons were observed after PDT treatment. In all experiments, 31P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T1s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T2 values after PDT treatment.

Lithium Distribution in Red Blood Cells and Plasma: NMR Studies of Rat Blood

To understand the interaction of lithium (Li+) with a coadministered drug in both the blood and the brain, we have treated rats with either Li+ alone or Li+ and a codrug. In this paper we address the important problem of quantitation of intra and extracellular Li+ ion contents in blood by the 7Li-NMR technique and the use of a shift reagent (SR). Although Li+ can be studied by atomic absorption techniques, these techniques involve tedious separation of intra- and extracellular components prior to chemical analysis. Magnetic resonance studies on rat blood, in the dose range of 0.5 to 10 meq/kg, indicate that the intracellular red blood cell Li+ predominates in the lower dose range of 0.5-1.0 meq/kg. As the lithium dose increases, a significantly larger amount of Li+ accumulates in the extracellular volume. Our studies on a number of animals at various doses of LiCl indicate that 7Li-NMR of blood samples provide a reliable, noninvasive quantification of red blood cell and plasma Li+ concentrations. The NMR method was further used to study the effect of coadministered drugs such as thioridazine on the intra- and extracellular Li+ concentration of RBCs.

In vivo 7Li NMR studies on shift reagent infused rats

Abstract Lithium (Li+) is used widely in the treatment and prophylaxis of bipolar disorder. The mechanism of action remains unknown. There have been many studies of intracellular lithium and its fluxes in the human red blood cells (RBCs) with a view towards understanding the maintenance of Li+ levels inside the cells and the mechanism of Li+ therapeutic action. Such information is valuable for excitable cells such as neurons, the likely site of therapeutic effects, and muscle, the site of common side effects. As intracellular Li+ may be responsible for both muscle irritability and pathological changes in the electrocardiogram, there is a need to discriminate intra‐, and extracellular Li+ components. To date there is no other human cell for which either intracellular Li+ levels or its fluxes have been measured. The muscle tissue with a large concentration of lithium should serve as a suitable model for infusion studies in an in vivo set up. In addition to the intrinsic importance of muscle as a site of sid...

NMR Studies of Intra- and Extracellular Red Blood Cell Lithium by Transverse Relaxation Measurements and Shift Reagents

Lithium salts are used in the treatment and prophylaxis of bipolar or mood disorders. The mechanism of action by which the cation exerts its therapeutic influence is unknown. A knowledge of brain Li concentration, its distribution in the brain, and its properties in the cellular microenvironment may have a strong influence on the understanding of Li function. The differentiation of lithium in the intra and extracellular environments has been achieved in a noninvasive manner in red blood cell (RBC) model. The two distinct transverse relaxation (T2) components have been observed in the blood sample drawn from lithium treated rats. These results indicate two different environments for Li with a fast (T2f) and a slow (T2s) component in the RBC model corresponding fractions that contribute to each relaxation component. The results compare well with the intra- and extracellular RBC lithium measured using shift reagents. Our studies indicate that the T2 method has utility in estimating the intracellular Li in systems that exhibit similar T2 behavior. The studies performed at different Li doses in the rat model indicate that the method may have utility in following a wide range of intracellular Li.

In vivo 19F MR Studies of Fluorine Labeled Photosensitizers in a Murine Tumor Model

The main focus of this report is the MR spectroscopy of the changes in the concentration of fluorine labeled photosensitizer that occur following the IP administration. This process is studied by (19)F in vivo MR methodology in a murine tumor model. The animal model used in these studies was mice bearing radiation induced fibrosarcoma (RIF) tumor on the foot dorsum. The mice were injected with a solution of approximately 100 micro-moles of the fluorinated photosensitizer and the (19)F MR examination of the photosensitizer in the tumor or the muscle was performed. The pharmacokinetic (PK) profile for each labeled compound was generated using the (19)F MR data at various time points post photosensitizer administration. The pharmacokinetic parameters were analyzed and the relationship of these results to photodynamic therapy is discussed. The (19)F MR methods clearly demonstrate utility in measuring the pharmacokinetic profiles and provide a new approach in the evaluation of appropriate photosensitizers for use in preclinical mammalian systems.

Improved photosensitizers for photodynamic therapy

In order to evaluate the effect of substituents in photosensitizing activity, a series of long wavelength absorbing photosensitizers related to pyropheophorbides, bacteriopheophorbides, and benzoporphyrin derivatives were synthesized. Pheophorbide dimers, covalently joining two molecules of pyropheophorbide-a and bacteriopheophorbide-a with lysine as a cross-link were also prepared. The syntheses and spectroscopic properties of these compounds are discussed. Some of these compounds were tested for in vivo photosensitizing activity vis-a-vis Photofrin IITM, using the standard screening system of DBA/2 mice bearing transplanted SMT/F tumors. The preliminary in vivo results suggest that replacement of substituents at peripheral positions of the macrocycles causes a significant difference in photosensitizing efficacy.

In-vivo NMR studies of deuterium-labeled photosensitizers in mice tumor model

Photodynamic therapy (PDT) has emerged as a promising modality for the treatment of cancer. We are using newly synthesized and chemically defined and characterized porphyrin photosensitizers that are specifically labeled with deuterium to perform in vivo NMR studies in a murine tumor model. In vivo magnetic resonance offers the potential for repetitive, safe, noninvasive evaluation of photosensitizers, tumor metabolism, and the effect of PDT on the tumor metabolism. In an effort to monitor noninvasively the photosensitizers in an in vivo tumor model, we are synthesizing several deuterium labeled photosensitizers which absorb red light at or above 630 nm. Development of methods to test these photosensitizers directly in humans is not feasible at this time, since these photosensitizers are new and we do not yet understand the side effects. In addition, we do not understand the potential benefits compared with Photofrin II, the widely used photosensitizer. To perform our in vivo deuterium NMR studies on mouse foot tumors, we have constructed a solenoid coil which operates at 30.7 MHz for the deuterium nucleus. We have been able to detect the deuterium labeled photosensitizer in the tumor after a direct intra-tumor injection. The use of 31P NMR to predict the possible outcome of PDT in these tumors is also discussed.

Responses to photodynamic therapy in a murine tumor model—31P NMR and water proton relaxation studies

Abstract In this study we report the tumor responses to photodynamic therapy (PDT) as measured by in vivo 31P NMR and water relaxation measurements on a murine tumor model. We evaluate the PDT responses to two new photosensitizers by monitoring the tumor volumes post PDT for one tumor and by in vivo 31P NMR for the other. Both photosensitizers are structurally well defined, pure compounds, unlike Photofrin II (PF II), which is a complex chemical mixture of a variety of porphyrin species. Dramatic increases in inorganic phosphate (Pi) were noticed following PDT treatment. The tumor water relaxation time measurements also suggest corresponding increases in Tl values of water after PDT treatment. From a combined study of relaxation times, 31P NMR, and tumor volumes, we conclude that the relaxation measurements can serve as a useful and sensitive method of monitoring PDT.