Sodium ion distribution in the vitreous body.

We have studied the nuclear magnetic resonance (NMR) relaxation behavior, and thus the dynamic properties, of the sodium ion in the vitreous body at different temperatures. The 23Na NMR spectrum exhibits a resonance, the intensity of which accounts for an ion visibility of 100%. The 23Na longitudinal and transverse relaxation times, at all temperatures but the highest, present two components, suggesting that the sodium ions are present in two states of different mobility, whose populations are in slow exchange on the NMR time scale. The correlation times and quadrupole coupling constants for the two sodium pools have been derived. The faster relaxation of a fraction of the vitreal sodium has tentatively been ascribed to the influence of the macromolecular framework of the vitreous body. The reported information may be of use for the understanding of the diagnostic applications of 23Na magnetic resonance imaging of the ocular structures.

Anthracycline gels. II. Spectroscopic study on doxorubicin-lecithin association products.

Thixotropic and thermally reversible gels have been prepared from doxorubicin-lecithin association products (DL12) by addition of salts to their aqueous solutions. The gel formation and the melting profiles have been followed by several spectroscopic techniques (1H NMR, UV-Vis, Circular Dichroism). The transition temperatures increase as the concentration of both the salt and the DL12 is increased, suggesting a progressive closer approach of the gel forming species. The process of the gel formation is cooperative and causes immobilization of the doxorubicin molecules of DL12.

Phospholipid-based reverse micelles.

Physicochemical investigations on the aggregation of phospholipids (mainly phosphatidylcholines) in organic solvents are reviewed and compared with the aggregation behaviour of phospholipids in aqueous medium. In particular we review the data showing that phosphatidylcholines (lecithins) form reverse micellar structures in certain apolar solvents. In these systems not only low molecular weight compounds but also catalytically active enzymes and entire cells can be solubilized. In addition, highly viscous phosphatidylcholine gels can be obtained in organic solvents upon solubilizing a critical amount of water. Generally, phospholipid-based reverse micelles can be regarded as thermodynamically stable models for inverted micellar lipid structures possibly occurring in biological membranes.

NMR monitoring of the anaerobic metabolism of frog muscle at rest.

The time dependence of Lactate (Lac), H+, Adenosine-triphosphate (ATP), Phosphocreatine (PCr), Hexose-monophosphate (PME), and Inorganic Phosphate (Pi) levels has been obtained for frog muscle at rest in anaerobic conditions by multinuclear NMR. All information has been collected on the same samples alternatively tuning the probehead on 1H- and 31P-NMR frequencies. ATP, PCr and H+ levels show the same time dependence for all the samples, while PME, Pi and Lac levels vary in time differently from one sample to another. No direct correlation between the Lac appearance and the H+ concentration has been found.

1H-NMR relaxation study of the liposome--nuclei interaction.

Phospholipidic liposomes can influence DNA template availability for RNA synthesis when interacting with isolated nuclei by enhancing (when the phospholipids are negatively charged) or by inhibiting (when they are neutral) trascriptional activity. The analysis of the 1H-NMR relaxation behaviour of isolated nuclei, of Small Unilamellar Vesicles (SUV) and of the SUV-Nuclei system has been undertaken to elucidate the mechanism of the interaction between the nuclear core and the phospholipids.

Antitumor effect and cardiotoxicity of a doxorubicin-lecithin association.

A doxorubicin-lecithin preparation was tested in vitro on B16 melanoma and Lewis lung carcinoma cells, and in vivo on C57BL/6 mice inoculated with 3LL cells. Results obtained demonstrated that the preparation possesses the same antitumor activity as doxorubicin. The cardiotoxicity of doxorubicin and of the doxorubicin-lecithin association were studied for 120 days after the end of the treatments in Wistar rats inoculated once a week for 5 weeks with equivalent doses of the drugs. Myocardial lesions were observed in both the groups of animals, but their severity and extent were reduced in rats treated with the doxorubicin-lecithin association, and their onset was also delayed.

Nucleotide pool and the proliferative process: an NMR study of the liver regeneration.

The metabolic changes occurring during liver regeneration after partial hepatectomy have been followed by examination of the perchloric extracts by means of NMR spectroscopy. Proton spectra show an abrupt decrease of glycogen, glucose and nucleotides, which are essentially ribonucleotides, in the first hours after hepatectomy. Nucleotides begin to store up again in the third day after hepatectomy, while glucose and glycogen storage builds up from the second day. 31P data evidence a sharp drop of phosphomonoesters, i.e. monophosphosugars (including AMP) and phosphocholine, and phosphodiesters, i.e. GPC and GPE, soon after hepatectomy and a recovery of the initial levels approximately at the 60th hour and a further increase of PDE at later times. The NMR findings are in agreement with the biochemical knowledge of the course of liver regeneration.

Interactions of ubiquinones with membrane models.

The effect of the insertion of coenzyme Q10 and some of its shorter chain homologues in membrane models (Reverse Micelles, Small Unilamellar Vesicles and Liposomes) has been studied by NMR and IR spectroscopies. By 1H-NMR we have found that the stretched conformation of the isoprenoid side-chain observed in solution is maintained in membrane models. Interaction between the quinonoid moiety of the Q's and the phosphatidic groups of the phospholipids has been evidenced by 31P-NMR. A large effect of this interaction on the water microdynamics and distribution around the charged groups of the phospholipids has been observed by measurements of 1H and 2H relaxation times and by infrared spectra. The 13C-NMR spectra of the backbone of the acyl chains of phospholipids does not seem to be influenced to a noticeable extent by the presence of the Q's.

Proton NMR study of erythrocytes of essential hypertensives.

Proton NMR studies (saturation transfer experiments and longitudinal relaxation time determinations) indicate that substantial differences exist between erythrocytes of essential hypertensives and normotensive subjects. A higher degree of intracellular organization has been found for the hypertensives and several factors are proposed as contributing to the observed behaviour.

Time dependence of the proton relaxation times of regenerating rat liver.

The proton longitudinal relaxation time of regenerating rat liver has been found to increase during the first 24 hours after hepatectomy and to drop back to normal in the following hours. The decreased relaxation rate may be related to the increase of the water mobility due to the expansion of the intercellular spaces during the massive proliferation of the first day, or to the increased cell hydration which is known to occur during active cell proliferation. Equations have been derived for the proliferation process, and the competing inhibition process, active from the 24th hour, which can quantitatively account for the proton relaxation behaviour.

Natural abundance 13C-NMR study of liver regeneration in rats.

13C-NMR spectra of liver samples of partially hepatectomized rats have been obtained at 50 MHz. The tissue specimens, fixed in buffered formaldehyde solution, were obtained for NMR spectroscopy at various time intervals between 6 and 72 hours after hepatectomy. Several metabolites were identified from the spectra and their concentrations were determined as a function of time. Neutral lipids increase dramatically in the first two days, to drop thereafter to normal; glycogen and glucose disappear in the first hours after surgery to appear again around 12-24 hours. The level of beta-hydroxybutyrate decreases almost to zero in the first 48 hours and then increases again, while lactic acid seems to remain essentially constant in the first 24-36 hours and to increase markedly at later times. Several other resonances have been identified. The metabolic changes detected by NMR closely correspond to the known biochemical data on liver regeneration.

Modified proton relaxation behaviour in erythrocytes from spontaneously hypertensive rats.

The proton NMR parameters of suspensions of erythrocytes from normotensive (MNS and WKY strains) and spontaneously hypertensive (MHS and SHR strains) rats have been compared: a marked difference in the relaxation behaviour has been observed for the two classes of strains. Various factors which may give rise to the difference found in dynamic behaviour are discussed.