Certified reference material for radionuclides in fish flesh sample IAEA-414 (mixed fish from the Irish Sea and North Sea).

A certified reference material (CRM) for radionuclides in fish sample IAEA-414 (mixed fish from the Irish Sea and North Seas) is described and the results of the certification process are presented. Nine radionuclides (40K, 137Cs, 232Th, 234U, 235U, 238U, 238Pu, 239+240Pu and 241Am) were certified for this material. Information on massic activities with 95% confidence intervals is given for six other radionuclides (90Sr, 210Pb(210Po), 226Ra, 239Pu, 240Pu 241Pu). Less frequently reported radionuclides (99Tc, 129I, 228Th, 230Th and 237Np) and information on some activity and mass ratios are also included. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in fish sample, for the development and validation of analytical methods and for training purposes. The material is available from IAEA, Vienna, in 100 g units.

The binding of the radioprotective agent cysteamine with the phospholipidic membrane headgroup-interface region.

The interaction of the aminothiol radioprotector cysteamine (beta-mercaptoethylamine) (CYST) with dipalmitoylphosphatidylcholine (DPPC) artificial membranes has been studied by differential scanning calorimetry (DSC), turbidimetry and spin labeling. This hydrophilic molecule displays a biphasic, concentration-dependent binding to the phospholipidic head groups at neutral pH. In the CYST/DPPC molar ratio 1:160-1:2 (mole/mole) an increasing ordering effect is observed. At high concentrations (over 3:1 ratio), this ordering effect decreases. With the symmetric disulfide dimer cystamine, the biphasic effect is not shown and the membrane rigidity decrease is obtained only at concentration ratio higher than 1:1. The charge repartition of the cysteamine molecule has been shown to be disymmetric, +0.52 e on the NH3 group and +0.19 e on the SH extremity, [38] whereas the cystamine molecule is electrostatically symmetrical. These properties could be related to their membrane effects. With cysteamine, at a low concentration, an electrostatic bridging between the negatively charged phosphate groups of the polar heads induces the increase in membrane stability: the molecules behave like a divalent cation. At high concentrations a displacement of the slightly charged SH extremity by the amine disrupts the bridges and induces the decrease in rigidity: the drug behaves like a monovalent cation. Due to its symmetric charge and its double length, such an effect is not observed with cystamine. This study could bring further information about the interactions between cysteamine and polyelectrolytic structures (ADN for example) and about the radioprotective properties of this drug.

Interaction of vinblastine sulfate with artificial phospholipid membranes. A study by differential scanning calorimetry and spin labeling.

The effect of the antimitotic drug vinblastine sulfate has been studied on fully hydrated dipalmitoylphosphatidylcholine (DPPC) liposomes in the temperature range 0 degrees to 60 degrees using differential scanning calorimetry and electron spin resonance spectroscopy with two fatty acid spin labels. In the gel phase, vinblastine interacts essentially with the DPPC polar heads and induces an important disorganization of the phospholipidic bilayer. The co-operativity of the main thermal transition is decreased. In the crystal-liquid phase, the drug penetrates inside the artificial membrane and induces the formation of domains which increased thermal stability. These effects are opposite to those observed with the drug isaxonine which is used to reduce the axonal degenerating effects due to vinblastine.

Oral administration of liposome-entrapped cysteamine and the distribution pattern in blood, liver and spleen.

Oral administration of liposome-entrapped cysteamine induces an increase in the concentration of exogenous sulphur compounds in blood (plasma), liver and spleen. Among those sulphur compounds, an important amount of plasma thiols can be related to a protection of cysteamine in the digestive tract. This can account for the radioprotective effect of a liposomal-cysteamine suspension in rodents, and clearly demonstrates the interest of such a preparation in radioprotection.

Isaxonine base is a strong perturber of phospholipid bilayer order and fluidity--a differential scanning calorimetry and spin labeling study.

The effects of the neurotropic drug isaxonine on fully hydrated dipalmitoyl-phosphatidyl-choline (DPPC) bilayers has been studied in the temperature range 0 degree-60 degrees, using differential scanning calorimetry and electron spin resonance spectroscopy, with two stearic acid spin labels. At low concentration (1% mol/mol), isaxonine is trapped in the polar interface and enhances the phospholipid multibilayers organization in the gel state. In contrast, at high concentration (30% mol/mol), the drug disorganizes the phospholipidic structures and may induce domain formation by phase separation. The strong interactions of isaxonine at the lipid-water interface change the ionization state of the stearic acid spin labels which become totally ionized. Then isaxonine acts as a modifier of the surface pH of the bilayer. The strong membrane effects of isaxonine may explain in part its pharmacological properties in vivo.