Dov Lichtenberg

New sesquiterpene lactones from Artemisia herba alba

Abstract The structures of herbolides A, B and C, new sesquiterpene lactones isolated from Artermisia herba alba , were determined by chemical and spectroscopic methods.

Characterization of Micellar and Liposomal Dispersions of Gangliosides and Phospholipids

Gangliosides are minor surface components of most mammalian cells, where they are located mainly in the outer leaflet of the lipid bilayer of the plasma membrane (1,2, 3). They are also present in membranes of some enveloped viruses (4). In membranes they serve as receptors for various toxins, viruses, hormones and their pattern is often drastically changed in neoplasia (1, 3, 5). The gangliosides, which are part of the lipid bilayer of the membranes differ in their lyotropic behaviour from the phospholipids and cholesterol which constitute the main lipid components of the membrane (6,38). The membrane phospholipids have two long hydrophobic chains, an interface region and a relatively small inogenic head group. They are classified as “non-soluble swelling amphipaths (6), implying that they do not form micelles but disperse spontaneously in water, forming bilayered multilamellar large liposomes (MLV) or, upon ultrasonic irradiation small unilamellar vesicles (SUV). In contrast, the gangliosides are “soluble amphipaths” (6) which form micelles in water (7). The fact that, in spite of their two long hydrophobic chains the gangliosides are classified as “soluble” amphipaths is explained by their large and highly negatively charged polar head group. Since gangliosides and phospholipids differ in their state of aggregation, their coexistance in membranes may affect or even disturb the bilayered structure. This study aimed to investigate the mutual relations between gangliosides arrl the main lipid components of the membranes. For this purpose the structural and dynamic properties of dispersions composed of well-characterized membrane lipids (either synthetic or of natural sources) and well defined, pure gangliosides were studied with the aid of physical and enzymatic methods.

The Activity of Phospholipase D on Aggregates of Phosphatidylcholine, Dodecylsulfate and Ca2+

Phospholipase D from peanut seeds catalyzes the hydrolysis of phosphatidylcholine (PC) to phosphatidic acid and choline. The catalytically active enzyme has a molecular weight of 200,000. Smaller subunits were obtained upon dilution, low pH or in the presence of certain detergents. Activators and Ca2+ ions are required for the hydrolysis; the amphipath sodium dodecylsulfate (SDS) is the most effective in activating the reaction. The dependence of the reaction on SDS is complex. Some physical properties of the PC — SDS mixed aggregates, as a function of their concentration ratio, were studied. Proton PMR, turbidity and ultracentrifugal data in the absence or presence of Ca2+, indicate that “dispersible” PC — SDS mixed micelles are formed at any SDS to PC molar ratio below 4. Upon the addition of Ca2+ however, optimal dispersibility was demonstrated at SDS to PC molar ratio ranging from 0.25–0.65, probably because high concentrations of the insoluble calcium dodecylsulfate causes a precipitation of the mixed micelles. Kinetic experiments showed that PC in low speed precipitated aggregates is not available for hydrolysis by phospholipase D. On the other hand PC aggregates obtained by high speed centrifugation were degraded by the enzyme. These observations serve as a basis for a partial explanation of the dependence of the enzymatic activity on the presenca of SDS.

Transport of liposome components in rat everted intestinal loops.

inferred that VPA indeed acts via potentiation of GABAergic transmission. However, this interpretation cannot be sustained on the basis of the experiments dealing with the interaction of intraperitoneally given VPA with iontophoresed GABA and of VPA with GABA-mediated transsynaptic inhibition. Assuming that VPA acts through potentiation of GABAergic transmission one would expect a potentiation of GABAergic transsynaptic inhibition when the drug is applied in anticonvulsant doses. However, in our experiments we did not observe such an effect. Thus, in conclusion, our results indicate that the anticonvulsive mode of action of VPA is not mainly due to a potentiation of central inhibitory GABAergic transmission. Alternatively, a direct effect of VPA upon neuronal membrane properties has been suggested recently (Slater & Johnston 1977). February 14, 1979

Assignment of individual signals of aromatic protons in the NMR spectrum of 6-substituted purines

Abstract Assignment of the resonances of ring protons in substituted purines is made by comparison with spectra of compounds in which one of these protons has been substituted by an alkyl group, and by application of the nuclear Overhauser effect to these derivatives in order to identify the signals of protons adjacent to the alkyl substituent. Chemical shifts are given for various ionic forms of the purines in deuterium oxide solution, as well as for the neutral forms.

A nuclear magnetic resonance study of hindered rotation in 8-phenylpurines

Abstract In the PMR spectrum of 8-phenylpurines, the multiplet of the o-protons appears downfield of the multiplet, characteristic for m,p-protons. The separation of the centres of these two signals (Δ-value) diminishes with increasing steric interference between the phenyl ring and substituents in the imidazole moiety. The contribution of the purine ring current to the chemical shifts of the aromatic protons was calculated according to the theory of Johnson and Bovey, and the torsion angles θ between the phenyl ring and the plane of the purine system were derived. For 8-phenylpurines with an NH-group in the imidazole ring, θ is 10–15°; for compounds with an N-methyl group in this ring, θ ≈ 35–45°; in 3,9-dimethyl derivatives, Δ becomes zero, while θ is about 50°.

Surface curvature and mobility in phospholipid bilayers. NMR studies of lecithin-deoxycholate mixed micelles

Abstract In mixed micelles of phospholipids and bile salts, the phospholipids are arranged as a flat bilayer with bile salts distributed along the hydrophobic edges. The linewidths of signals in the proton magnetic resonance spectra of such mixed micelles depend strongly on the size of the micelles, which is a function of the molar ratio of the components. The signals in the spectra of such mixed micelles are much broader than the corresponding signals in the much larger, curved bilayers of lecithin vesicles obtained by ultrasonic irradiation. This result strongly supports the idea that curvature is a prime factor in determining proton NMR linewidths, probably through a disruptive effect of curvature on the molecular packing in phospholipid bilayers.

Attenuation of the Lithium-Induced Diabetes-Insipidus-Like Syndrome by Amiloride in Rats

The effect of amiloride on lithium-induced polydipsia and polyuria and on the lithium concentration in the plasma, brain, kidney, thyroid and red blood cells was investigated in rats, chronically treated with LiCl. Amiloride reduced the drinking and urine volume of rats in an acute (6 or 12 h) and a subacute (3 days) experiment. 6 h after the administration of amiloride, a reduction was observed in the lithium content of the renal medulla but not in the other organs studied. At 12 h, all the tissues showed a slight increase in lithium levels. After 3 days of combined treatment, a marked elevation in plasma and tissue lithium levels accompanied a reduction in water intake. In all the experiments, the attenuation of the lithium-induced diabetes-insipidus-like syndrome by amiloride was accompanied by a reduction of the ratio between the lithium concentration in the renal medulla and its levels in the blood and an elevation in the plasma potassium level. It is concluded that acute amiloride administration to lithium-treated patients suffering from polydipsia and polyuria might relieve these patients but prolonged amiloride supplementation would result in elevated lithium levels and might be hazardous.

Effects of prolonged lithium treatment on the water consumption and lithium content of rats.

Abstract Injection of LiC1 to rats (3.0 mmole/kg/day) caused a marked increase in water intake. The polydipsic effect was maximal after 8 – 10 days of treatment and then gradually declined. This reduction in polydipsia was accompanied by a decrease in Li + content of plasma, red blood cells, liver, spleen, kidney and brain. Furthermore, the ratio of tissue to plasma lithium concentration (lithium index) declined in all tissues examined. The decrease in polydipsia was abolished by increasing the dose of LiC1 by 50%. These results suggest that tolerance to the polydipsic effect of lithium develops in the rat during chronic treatment with LiC1 as a result of a reduction in the cells capacity to accumulate lithium.

The use of phospholipid liposomes for lithium administration. Polydipsic effect and tissue distribution of lithium

Administration of lithium entrapped in phospholipid liposomes increased the lithium‐induced polydipsia, but did not accelerate the onset of this effect. It also resulted in a larger accumulation of lithium in the liver, kidney and spleen, but not in the brain. The time course of polydipsia suggests that it depends on the intracellular lithium concentration. However, the rate of development of this effect depends on some additional factor.