Janina Gabrielska

Effect of phenyltin compounds on lipid bilayer organization

Phenyltin compounds are known to be biologically active. Their chemical structure suggests that they are likely to interact with the lipid fraction of cell membranes. Using fluorescence and NMR techniques, the effect of phenyltin compounds on selected regions of model lipid bilayers formed from phosphatidylcholine was studied. The polarization of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) dipalmitoyl-L-phosphatidylethanolamine and desorption of praseodymium ions was used to probe the polar region, whereas the polarization of 1 - (4 - trimethylammoniumphenyl) - 6 - phenyl -1,3,5-hexatriene p-toluenesulfonate measured the hydrophobic core of the membrane. In addition, changes in the N-(5-fluoresceinthiocarbanoly)dipalmitoyl - L - α - phosphatidyl -ethanolamine fluorescence intensity indicated the amount of charge introduced by organotin compounds to the membrane surface. There were no relevant changes of measured parameters when tetraphenyltin was introduced to the vesicle suspension. Diphenyltin chloride causes changes of the hydrophobic region, whereas the triphenyltin chloride seems to adsorb in the headgroup region of the lipid bilayer. When the hemolytic activity of phenyltin compounds was measured, triphenyltin chloride was the most effective whereas diphenyltin chloride was much less effective. Tetraphenyltin causes little damage. Based on the presented data, a correlation between activity of those compounds to hemolysis (and toxicity) and the location of the compound within the lipid bilayer could be proposed. In order to inflict damage on the plasma membrane, the compound has to penetrate the lipid bilayer. Tetraphenyltin does not partition into the lipid fraction; therefore its destructive effect is negligible. The partition of the compound into the lipid phase is not sufficient enough, by itself, to change the structure of the lipid bilayer to a biologically relevant degree. The hemolytic potency seems to be dependent on the location of the compound within the lipid bilayer. Triphenyltin chloride which adsorbs on the surface of the membrane, causes a high level of hemolysis, whereas diphenyltin chloride, which penetrates much deeper, seems to have only limited potency.

Role of Hydrophobic and Hydrophilic Interactions of Organotin and Organolead Compounds with Model Lipid Membranes

Abstract The present study was conducted to clarify the mechanism of toxicity of organic compounds using lipid model membranes (liposomes and planar lipid membranes). The compounds studied were trialkyltin and trialkyllead chlorides, dialkyltin dichlorides and some inorganic forms of those metals. Two different (anionic and cationic) detergents were also used in the experiments to change the surface properties of liposomes. As a measure of interaction between the compounds studied and model membranes were the release of liposome bound praseodymium and the change in stability of planar membranes under the influence of those compounds. On the basis of the results obtained it was postulated that the mechanism of interaction between tin-and leadorganics and model lipid membranes is a combination of different factors featuring interacting sides. The most important properties determining the behaviour of organic compounds in the interaction were lipophilicity and polarity of different parts of the organics and the steric arrangement they can take in the medium. On the other hand, the surface potential of the lipid bilayer and the environment of the lipid molecules, that play a significant role in the availability of the lipid bilayer to the organics, were important factors in the interaction.

The effect of steric constraints on the adsorption of phenyltin onto the dipalmitoylphosphatidylcholine bilayer.

In this paper, we present studies concerning phenyltin adsorption onto the dipalmitoylphosphatidylcholine bilayer. Phenyltin compounds are known to be biologically active, and their molecular geometry makes it possible to study the effect of steric constraints on their ability to penetrate the model lipid membrane. Using a fluorescence probe as a reporter of the amount of adsorbed compound, we evaluated their affinity to the membrane as a function of the membrane state. The amount of the adsorbed compound was found to depend on the adsorbing molecules geometry and lipid bilayer organization. The fluorescence measurements were supported by the density functional theory (DFT) method of quantum mechanical computations. The penetrant location was correlated with the possible relative positions of its polar and hydrophobic moieties to determine if it could adopt structural requirements of the local membrane environment. Molecules were deformed by a model force, mimicking interactions within the membrane interfacial region. Computations show that the diphenyltin molecule can be deformed to such an extent that it can adopt an amphiphilic conformation. Triphenyltin is different, as its bending requires more energy. Born repulsion energies from hydrophobic fluid into water for phenyltins were also computed in an isodensity-polarized continua model of DFT computation. Our results indicate that the phenyltin compounds incorporate into the interface of the lipid membrane, although diphenyltin integrates more deeply than triphenyltin, which locates on the double layers surface, and this is due to the fact that the main role is played by steric and not electrostatic interactions.

Adsorption of Phenyltin Compounds onto Phosphatidylcholine/Cholesterol Bilayers

Phenyltin compounds are known to be biologically active and, whan widely spread, are potentially hazardous. As their chemical structure suggests, they interact with the lipid fraction of the cell membrane. Their effect on the model phosphatidylcholine/cholesterol bilayer has been studied using fluorescence and 1H NMR techniques. The change in the fluorescein-PE fluorescence intensity indicates the amount of charge added by phenyltin compounds to the membrane surface. Although the presence of cholesterol alone does not alter membrane interface properties measured with fluorescein-PE, 1H NMR measurements show that lipid mobility is altered throughout the hydrophobic core of the membrane. Cholesterol in the phosphatidylcholine bilayer does not alter tetraphenyltin interaction with the membrane, though the effect of diphenyltin dichloride, penetrating deeply into the hydrophobic core of the membrane, is reduced when the amount of cholesterol in the membrane is increased, suggesting decreased compound adsorption. Triphenyltin chloride has a qualitatively different effect on the lipid bilayer, when observed using this fluorescence technique. The adsorption of triphenyltin onto the phosphatidylcholine/cholesterol membrane induces a lateral phase separation of membrane components. Since triphenyltin chloride is known to be adsorbed onto the interface of the lipid bilayer, this separation mechanism must originate in this region and does not seem to be electrostatic in origin. 1H NMR measurements have confirmed the observation that these two active phenyltin compounds interact with the phosphatidylcholine/cholesterol membrane differently, disrupting different regions of the bilayer to a different degree. Copyright

A Synergistic Effect of Select Organotin Compounds and Ionic Surfactants on Liposome Membranes

Organometallic compounds and surfactants constitute a potential threat to the environment. For that reason we have embarked on a study of their joint action on membranes. Model lecithin liposome membranes were modified with the cationic surfactant trimethyldodecylammonium bromide or the anionic surfactant sodium dodecylsulfonate, and the effect of tripropyltin chloride on the process of calcium (Ca 2+ ) and praseodymium (Pr 3+ ) desorption from the liposome membrane was studied. Kinetic constants for the process of Ca 2+ ion desorption from lecithin liposome membranes were determined using the radiotracer method. The percentage of Pr 3+ ion desorption from liposome membranes was measured by the 1 H NMR method. Trimethyltin, triethyltin and tripropyltin alone caused increased Ca 2+ and Pr 3+ desorption from liposome membranes with increasing concentration of the compounds and alkyl chain length. For both the processes studied, a cationic surfactant brought about a lower effectiveness of tripropyltin and an anionic surfactant resulted in a higher effectiveness. The effect observed can be explained by changes in the surface charge of the membrane, induced by the surfactant modifiers and by the concomitant change in the partition coefficient of the organotin. The results obtained indicate a protective or harmful joint action of the surfactants used with tripropyltin on membranes.

Biological Activity of Japanese Quince Extract and Its Interactions with Lipids, Erythrocyte Membrane, and Human Albumin.

The aim of the study was to determine in vitro biological activity of fruit ethanol extract from Chaenomeles speciosa (Sweet) Nakai (Japanese quince, JQ) and its important constituents (−)-epicatechin (EC) and chlorogenic acid (CA). The study also investigated the structural changes in phosphatidylcholine (PC) liposomes, dipalmitoylphosphatidylcholine liposomes, and erythrocyte membranes (RBC) induced by the extract. It was found that the extract effectively inhibits oxidation of RBC, induced by 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH), and PC liposomes, induced by UVB radiation and AAPH. Furthermore, JQ extract to a significant degree inhibited the activity of the enzymes COX-1 and COX-2, involved in inflammatory reactions. The extract has more than 2 times greater activity in relation to COX-2 than COX-1 (selectivity ratio 0.48). JQ extract stimulated growth of the beneficial intestinal bacteria Lactobacillus casei and Lactobacillus plantarum. In the fluorimetric method by means of the probes Laurdan, DPH and TMA-DPH, and 1H-NMR, we examined the structural changes induced by JQ and its EC and CA components. The results show that JQ and its components induce a considerable increase of the packing order of the polar heads of lipids with a slight decrease in mobility of the acyl chains. Lipid membrane rigidification could hinder the diffusion of free radicals, resulting in inhibition of oxidative damage induced by physicochemical agents. JQ extract has the ability to quench the intrinsic fluorescence of human serum albumin through static quenching. This report thus could be of huge significance in the food industry, pharmacology, and clinical medicine.

Antioxidant Protection of Egg Lecithin Liposomes during Sonication

Abstract When model membranes are prepared by ultrasonic treatment of polyunsaturated phospholipids, radical production can induce a partial degradation of the polyunsaturated fatty acyl chains and the formation of lipid hydroperoxides. A suitable antioxidant employed during liposome preparation is able to protect them against lipid peroxidation. This work contains the results of studies on egg lecithin liposomes with incorporated antioxidants that were supposed to play the protective role mentioned. As it has been shown the antioxidant com pounds used ensured a 40-60% , i.e., satisfactory protection of liposomes after 30 min sonication. Possible practical applications are discussed.

A comprehensive study on antioxidant properties of crude extracts from fruits of Berberis vulgaris L., Cornus mas L. and Mahonia aquifolium Nutt.

Abstract The antioxidant capacity of methanolic crude extracts of Berberis vulgaris L., Cornus mas L. and Mahonia aquifolium Nutt. was tested with the thiobarbituric acid reactive substances formation assay, the ferric reducing power (FRAP) and 2,2-diphenyl-2-picrylhydrazyl (DPPH•) radical scavenging assay. The content of antioxidant components in the extracts, their partition coefficient on 1-octanol:water and affinity to liposome membranes were determined as well. The results show that the IC50 parameter connected with the antioxidant activity on phosphatidylcholine liposome membrane decreased as follows: B. vulgaris (0.14±0.01 mg/mL) > M. aquifolium (0.34±0.03 mg/mL) > C. mas (1.13±0.01 mg/mL) for AAPH-induced oxidation and M. aquifolium (0.29±0.03 mg/mL) > C. mas (1.24±0.07 mg/mL) > B. vulgaris (1.50±0.05 mg/mL) for Fe(II)/ascorbic acid-induced oxidation, and M. aquifolium (2.35±0.10 mg/mL) > B. vulgaris (2.69±0.04 mg/mL) > C. mas (6.17±0.06 mg/mL) for UVC irradiation. All the extracts exhibited the ability to quench DPPH• and to reduce Fe(III) ions to Fe(II) via redox reaction. The content of active components in the extracts, the partition coefficient and extracts affinity to membranes correlated well with their antioxidant activities. This study has shown that fruits of B. vulgaris, M. aquifolium and C. mas, from which the extracts were obtained, are attractive for consumption and can potentially be used in production of new processed fruit.

The effect of the dipalmitoylphosphatidylcholine lipid bilayer state on the adsorption of phenyltins

The nonspecific adsorption of amphiphilic molecules onto the membrane depends both on the properties of the adsorbate and the state of the lipid bilayer. Electrostatic interactions drive the adsorption of charged molecules and hydrophobicity determines partition of the adsorbate into the membrane, whereas the steric compatibility of the lipid bilayer and the amphiphilic molecule is an additional factor to be accounted for when considering interaction between the adsorbate and the membrane. The adsorption of phenyltins was evaluated from changes in Fluorescein-PE fluorescence intensity. The pH sensitivity of fluorophore, located at the membrane surface, was utilized to detect charges introduced onto the membrane by adsorbing compounds. It has been shown that the state of the membrane affects phenyltin adsorption in accordance with the number of phenyl rings on the molecule. Furthermore, the membrane surface topology determines interfacially located triphenyltin adsorption, with a much weaker effect on deeply embedded diphenyltin. When the dipalmitoylphosphatidylcholine (DPPC) model membrane is in the ripple phase, with complex surface morphology, phenyltin adsorption is greatly enhanced. Results presented in this paper show that steric constraints imposed on rigid and bulky amphiphilic compounds by ordered alkyl chains and membrane surface topology affect nonspecific molecule adsorption onto the membrane.

The modified action of triphenyllead chloride on UVB-induced effects in albumin and lipids

Previously we have shown a toxic effect of the organometallic compound triphenyllead (TPhPb) on cells. In the present study we evaluated the destructive effect of TPhPb on model systems--serum albumin and liposome membranes--alone and under UVB irradiation. UVB irradiation of bovine serum albumin results in protein S-S bond reduction, free SH- and CO- group formation and decrease in fluorescence intensity of tryptophans. Triphenyllead chloride alone and under UVB irradiation did not induce protein oxidation, measured as formation of carbonyl groups, in serum albumin; however, it decreased the content of SH- groups in both cases (alone and under UVB radiation) in a dose-dependent manner. It was found that triphenyllead chloride alone did not induce lipid peroxidation of liposomes but increased their fluidity. However, under UVB irradiation TPhPb dramatically enhances the pro-oxidant action of UVB in a manner dependent on concentration and intensity of radiation, and these effects were suppressed by Trolox. These results suggest that the toxicity of TPhPb under UVB irradiation is due to formation of radical forms of the compound and its disordered effects on the membrane structure.