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Prolonged survival was seen in a carcinoma model in mice intraperitoneally inoculated with B-16 melanoma cells after the intraperitoneal treatment with hybrid liposomes composed of L-a-dimyristoylphosphatidylcholine (DMPC) and polyoxyethylenedodecyl ether (C 12 (EO) n , n＝10 and 23 respectivery) which had a uniform and stable structure. No drug was administered. The therapeutic eŠects of the single-component liposomes composed of lipids with a variety of hydrophilic head groups and diŠerent hydrophobic alkyl chains were investigated. Markedly prolonged survival (248％) of mice was achieved after treatment with DMPC liposomes. However, DMPC liposomes have the disadvantage of an unstable structure, requiring daily sonication. On the other hand, no life-prolonging eŠects or toxicity occured with the admistration of the other single-component liposomes employed in this study. Next, we successfully prepared stable, uniform liposomes composed of 90 mol％ DMPC and 10 mol％ C 12 (EO) n (n＝10 and 23, respectively), which have diameters of 70 nm and 100 nm, respectively. Interestingly, prolonged survival (173-186％) of mice was achieved after treatment with hybrid liposomes of 90 mol％ DMPC/10 mol％ C 12 (EO) n (n＝10 and 23). Finally, we conducted toxicity tests using normal rats to determine hybrid liposome stability. There were no abnormalˆndings in blood chemistry or relative organ weights at autopsy of normal rats after hybrid liposome administration. In addition, hybrid liposomes were metabolized in the liver after intravenous administration to normal mice. These results suggest that hybrid liposomes could be used as a new single chemotherapeutic agent in the treatment of carcinoma with no side eŠects.

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Key points Xenon (Xe) non‐competitively inhibited whole‐cell excitatory glutamatergic current (IGlu) and whole‐cell currents gated by ionotropic glutamate receptors (IAMPA, IKA, INMDA), but had no effect on inhibitory GABAergic whole‐cell current (IGABA). Xe decreased only the frequency of glutamatergic spontaneous and miniature excitatory postsynaptic currents and GABAergic spontaneous inhibitory postsynaptic currents without changing the amplitude or decay times of these synaptic responses. Xe decreased the amplitude of both the action potential‐evoked excitatory and the action potential‐evoked inhibitory postsynaptic currents (eEPSCs and eIPSCs, respectively) via a presynaptic inhibition in transmitter release. We conclude that the main site of action of Xe is presynaptic in both excitatory and inhibitory synapses, and that the Xe inhibition is much greater for eEPSCs than for eIPSCs. Abstract To clarify how xenon (Xe) modulates excitatory and inhibitory whole‐cell and synaptic responses, we conducted an electrophysiological experiment using the ‘synapse bouton preparation’ dissociated mechanically from the rat hippocampal CA3 region. This technique can evaluate pure single‐ or multi‐synapse responses and enabled us to accurately quantify how Xe influences pre‐ and postsynaptic aspects of synaptic transmission. Xe inhibited whole‐cell glutamatergic current (IGlu) and whole‐cell currents gated by the three subtypes of glutamate receptor (IAMPA, IKA and INMDA). Inhibition of these ionotropic currents occurred in a concentration‐dependent, non‐competitive and voltage‐independent manner. Xe markedly depressed the slow steady current component of IAMPA almost without altering the fast phasic IAMPA component non‐desensitized by cyclothiazide. It decreased current frequency without affecting the amplitude and current kinetics of glutamatergic spontaneous excitatory postsynaptic currents and miniature excitatory postsynaptic currents. It decreased the amplitude, increasing the failure rate (Rf) and paired‐pulse rate (PPR) without altering the current kinetics of glutamatergic action potential‐evoked excitatory postsynaptic currents. Thus, Xe has a clear presynaptic effect on excitatory synaptic transmission. Xe did not alter the GABA‐induced whole‐cell current (IGABA). It decreased the frequency of GABAergic spontaneous inhibitory postsynaptic currents without changing the amplitude and current kinetics. It decreased the amplitude and increased the PPR and Rf of the GABAergic action potential‐evoked inhibitory postsynaptic currents without altering the current kinetics. Thus, Xe acts exclusively at presynaptic sites at the GABAergic synapse. In conclusion, our data indicate that a presynaptic decrease of excitatory transmission is likely to be the major mechanism by which Xe induces anaesthesia, with little contribution of effects on GABAergic synapses.

It is well known that liposomes are used as drug carriers: examples are antitumor agents, hormones, and immunomodulation. 1,2) On the other hand, we have recently produced specific hybrid liposomes composed of vesicular and micellar molecules; they are stable for a longer period. The physical properties of these liposomes such as size, membrane fluidity, phase transition temperature, and hydrophobicity can be controlled by changing the constituents and compositional ratios of hybrid liposomes. 3,4) In the course of our study on hybrid liposomes, the following interesting results were obtained. (a) Stereochemical control of the enantioselective hydrolysis of amino acid esters could be established by temperature regulation and by changing the composition of hybrid liposomes. 9) (d) No toxicity of the hybrid liposomes was observed in normal cells in vitro nor in normal rats in vivo. 8,10) In this study, we report on hybrid liposomes composed of L-a -dimyristoylphosphatidylcholine (DMPC) and polyoxyethylenedodecyl ether (C 12 (EO) n : CH 3 (CH 2 ) 11 O(CH 2 CH 2 O) n H) having inhibitory effects on the growth of human breast tumor cells (MDA-MB-453) in vitro along with apoptosis.Hybrid liposomes were prepared by sonication (VELVO VS-N300, 300W) of a mixture containing 95 mol% DMPC and 5 mol% C 12 (EO) n in 5% glucose solution at 45°C with 300W, followed by filtration with a 0.20 mm filter.First, we examined the fifty percent inhibitory concentration (IC 50 ) of hybrid liposomes (HL-n) on the growth of MDA-MB-453 cells in vitro on the basis of WST-1 assay. 11)The tumor cells (5.0ϫ10 4 viable cells/ml) were cultured for 48 h in an incubator at 37°C after adding the sample solutions. WST-1 solutions were added and the absorbance at wavelength of 450 nm was measured by spectrophotometer. The inhibitory concentration was evaluated by A mean / A control , where A mean and A control denote the absorbance of water-soluble formazan, which was useful as an indicator of cell viability, in the presence and absence of sample solutions, respectively. The results are shown in Fig. 1. The IC 50 values of HL-n were from one seventh to a half of those of the DMPC liposomes, indicating that the inhibitory effects of hybrid liposomes are large when compared with those of the DMPC liposomes.Morphology of hybrid liposomes (HL-n) was examined on the basis of dynamic light scattering measurements. Hydrodynamic diameter (d hy ) of HL-n was 80-120 (HL-21 and 23) and 90-110 nm (HL-25), which remained stable for more than three weeks. On the other hand, it was found that DMPC liposomes, HL-4 and HL-10 were unstable. It is worthy to note that HL-n (nϭ21, 23, 25) having a diameter of 100 nm could avoid the clearance by reticular endothelial system in vivo. 12)Second, we examined the mechanism for inhibiting the growth of MDA-MB-453 cells in vitro. Fluorescence micrographs of MDA-MB-453 cells using TUNEL method after the treatment with hybrid liposomes are shown in Fig. 2. The green color (FITC) was observed in the cells after adding hybrid lipos...