[Artificially functionalized polyenoic fatty acids--a new lipid bioregulators]. / Iskusstvenno funktsionalizirovannye polienovye zhirnye kisloty-- novye lipidnye bioreguliatory.

Dopamine, histamine, serotonin, and serotonin analogs were acylated with arachidonic and eicosapentaenoic acids, and the reaction products were named as artificially functionalized fatty acids (AFFA). The amides of arachidonic acid with serotonin, dopamine, and histamine were found to inhibit human platelet aggregation induced by ADP, arachidonic acid and adrenaline. Amides of arachidonic and eicosapentaeonic acids with serotonin and dopamine protect sea urchin early embryos against cytotoxic action of serotonin and histamine antagonists. These effects are not connected with the possible hydrolytic cleavage of AFFA to their constituent polyenoic fatty acids and amines. Arachidonic acid dopaminamide was shown to be a substrate of soybean 15-lipoxygenase, whereas the arachidonic acid amides with serotonin and its derivatives were resistant to this enzyme. Moreover, arachidonic acid serotoninamide turned out to be an irreversible lipoxygenase inhibitor. Considerable amount of hydroxyl radicals (fluorescent assay) were found for the first time to accompany lipoxygenase oxidation of linoleic acid; arachidonic acid serotoninamide blocked this process completely. Therefore, it was concluded that AFFA possess specific biological activity and can be considered as a novel group of lipid bioregulators.

The interaction of prostaglandins with serum low-density lipoproteins.

The interaction of human serum low-density lipoproteins (LDL) with various types of prostaglandins (PG) was studied using equilibrium dialysis, steady-state fluorescence polarization spectroscopy and photolabeling methods. Low concentrations (10(-13)-10(-9) M) of PGE1 and PGF2 alpha were shown to induce specific rearrangements of the lipids on the LDL surface, whereas the closely related PGE2 and PGF1 alpha had no effect. With fluorescent labeled LDL, the PGE1-induced changes of the steady-state fluorescence polarization (P) were shown to be time- and concentration-dependent, saturable and reversible. However, equilibrium dialysis revealed a very low binding capacity of LDL for PGE1 (approx. 1 prostaglandin molecule per 600 LDL particles). Approximately the same PGE1 concentration was sufficient to cause maximal changes of P, to enhance the binding to apolipoprotein B of a photoreactive sphingomyelin analogue inserted into the LDL surface and to alter the thermal phase behavior of the LDL surface lipids. It is proposed that the LDL surface rearrangement caused by prostaglandins is due to the interaction of prostaglandins with apolipoprotein B, resulting in formation of short-lived complexes. The mechanism of this interaction is discussed in terms of the non-equilibrium ligand-receptor interaction model proposed earlier to explain the interaction of prostaglandins with high-density lipoproteins (Bergelson, L.D. et al. (1987) Biochim. Biophys. Acta 921, 182-190). It is suggested that direct prostaglandin-lipoprotein interactions may play a role in the homeostasis of cholesterol.

Binding of specific ligands to muscarinic receptors alters the fluidity of membrane fragments from rat brain. A fluorescence polarization study with lipid-specific probes.

The previously suggested method of following ligand-receptor interactions by measuring ligand-induced changes in membrane fluidity [(1986) FEBS Lett. 194, 313-316] was employed to study the binding of specific ligands of the muscarinic receptor to rat brain membrane fragments containing a fluorescent analogue of phosphatidylcholine (APC) as a membrane probe. Upon addition of carbachol and atropine in low concentrations the fluorescence polarization of the APC-labeled membranes decreased significantly demonstrating that binding of these ligands to the muscarinic receptor increases the fluidity of its lipid environment. The fluidity changes were specific, concentration-dependent and saturable. In comparison with radioligand assays the fluorescent lipid probe method proved to be much more sensitive but the Kd values obtained by the two methods differed considerably.

A new approach to studies of cell-antibody interactions using fluorescent lipid probes.

The interaction of poly- and monoclonal antibodies against the L-chain of human Ig with Burkitt lymphoma EB-3 cells was studied using a fluorescent lipid probe, anthrylvinyl-labelled sphingomyelin, incorporated into the cell plasma membrane. Binding of the antibodies to Ig receptors on the surface was shown to induce changes in the fluorescence polarization of the probe. The high sensitivity of the method allows one to detect less than 100 antibody molecules per cell. The possibility of using cells or liposomes carrying antigens and fluorescent lipids for the determination of antibodies in solution is discussed.

[Interaction of prostaglandins with low-density lipoproteins in human blood]. / Vzaimodeistvie prostaglandinov s lipoproteinami nizkoi plotnosti krovi cheloveka.

Interaction of prostaglandins (PG) with human plasma low density lipoproteins (LDL) was studied, using fluorescent spectroscopy and photoreactive labeling. It was demonstrated that PGE1 at low concentrations (less than 10(-9) M) induces specific lipid rearrangements on the surface of LDL globules. It was assumed that these rearrangements are brought about by the interaction of PG with apolipoprotein B to form short-living complexes. A possible mechanism and biological significance of the observed phenomenon are discussed.

The interaction of prostaglandins with high-density lipoproteins: a non-equilibrium model of ligand-receptor interaction.

Using high-density lipoproteins (HDL) labeled with a fluorescent phospholipid probe (an anthrylvinyl-labeled analogue of sphingomyelin) it was found that low amounts (10(-12) M) of the prostaglandins E1 and F2 alpha induced different structural changes of the HDL surface, whereas prostaglandin E2 had no effect. The effects of prostaglandin E1 on HDL were largely paralleled by those of this prostaglandin on synthetic recombinants prepared from apolipoprotein A1, phospholipids and cholesterol. The prostaglandin E1-HDL interaction resembled that of a ligand with a receptor site because it was specific, reversible, concentration- and temperature-dependent and saturable. However, the maximal HDL retaining capacity for prostaglandin E1 as determined by equilibrium dialysis was very low, and a single prostaglandin E1 molecule was able to induce structural changes in a large number of discrete lipoprotein particles. To explain this remarkable fact, a non-equilibrium model of ligand-receptor interaction is proposed. According to this model in open systems characterized by a short life-time of the ligand-receptor complex, high diffusion rates of the ligand and long relaxation times which exceed the interval between two successive ligand-receptor occupations, the ligand-induced changes will accumulate, resulting in amplification of the primary biological signal. It is emphasized that the low mobility of lipids constituting the environment of the receptor protein plays a critical role in this type of signal amplification.

[Experimental research on the action of isoptin and alkylenediamine derivatives on the aggregation capacity and the membrane-bound calcium level of thrombocytes]. / Eksperimental'noe issledovanie deistviia izoptina i proizvodnykh alkilendiaminov na agregatsionnuiu sposobnost' i uroven' membranosviazannogo kal'tsiia trombotstiov.

It was found in experiments on rabbit platelets that isoptin and derivatives of N,N'-di(beta-phenylisopropyl)polymethylene diamines produce a dose-dependent decrease of the platelet aggregation activity. The effect correlates with a lowering of membrane-bound calcium level in platelets as shown by the fluorescent technique with the use of chlortetracycline probe. The results obtained demonstrate that the derivatives of alkylenediamines significantly suppress platelet aggregation and block membrane-bound calcium at the lower concentrations than those of isoptin.

[DNA-phospholipid interactions. A study using lipid-specific fluorescent and photoreactive probes]. / DNK-fosfolipidnoe vzaimodeistvie. Issledovanie s pomoshch'iu lipidspetsificheskikh fluorestsentnykh i fotoreaktivnykh zondov.

The interaction of phospholipids with phage T7 DNA was investigated using anthryl-vinyl-labeled and photoactivable phosphatidylcholine and sphingomyelin. Fluorescence polarization studies demonstrated that, in the presence of DNA, the fluorophore mobility is diminished as its distance from the polar head-group is increased. Immobilization of lipid chains is enhanced by Ca2+ ions, the effect being more pronounced for sphingomyelin than for phosphatidylcholine derivatives. On the other hand, phospholipids with a photoactivable group could not be crosslinked to DNA in the DNA-phospholipid complexes, evidencing against the presence of contacts between lipids and DNA.

The binding of the B-chain of ricin to Burkitt lymphoma cells. A new approach to ligand-receptor interaction studies.

It is shown that conformational changes of receptor proteins brought about by binding of a ligand induce changes in the lipid environment of the receptor that can be monitored by fluorescent lipid probes. On this basis a new approach to studies of ligand-receptor binding is proposed. Using the interaction of the ricin B-chain with Burkitt lymphoma cells as an example and fluorescent labelled sphingomyelin as a probe, the ligand-induced changes of fluorescence anisotropy were shown to be concentration-dependent and to permit determination of the binding constant and the number of receptor-binding sites. The method was found to be specific and highly sensitive, allowing detection of the action of one RB molecule per cell. Scatchard analysis of the binding of 125I-RB demonstrated the presence on the cell surface of two binding sites with Kd approximately 10(-10) and approximately 10(-8) M, respectively. Only the high-affinity sites were detected by the fluorescence technique. Saturation of these sites resulted in maximum inhibition of protein synthesis.

Influence of cholesterol and prostaglandin E1 on the molecular organization of phospholipids in the erythrocyte membrane. A fluorescent polarization study with lipid-specific probes.

Anthryl-labeled fluorescent probes closely mimicking phosphatidylcholine and sphingomyelin were applied to study the state of these phospholipids in the rabbit erythrocyte membrane. At normal cholesterol levels both probes exhibited higher fluorescence polarization values in the membranes than in phospholipid vesicles of similar lipid composition, indicating a decreased fluidity of the probe environment in erythrocyte ghosts. In ghosts prepared from normal erythrocytes no evidence of lateral separation of phosphatidylcholine and sphingomyelin was found. At higher cholesterol levels, however, these lipids appear to segregate. Probably the effect of cholesterol on the erythrocyte membrane lipids involves lipid-protein interactions. At physiological concentrations, prostaglandin E1 only weakly affects the state of phosphatidylcholine and sphingomyelin in erythrocyte membranes. Cholesterol enrichment amplifies the effect of prostaglandin E1. Although the prostaglandin E1-induced changes depended much upon whether the ghosts were enriched with cholesterol in vitro or in vivo, with both types of ghosts effects of prostaglandin E1 were seen at extremely low effector concentrations that may have presented a few molecules of prostaglandin per ghost. The structural and functional significance of these findings is discussed.

Interaction of prostaglandin E1 with human high density lipoproteins.

Prostaglandin E1 has been shown to interact with serum high density lipoproteins (HDL) in a manner resembling the interaction of a ligand with a high affinity binding site. The presence of 10(-12)-10(-10) M prostaglandin E1 induces a rearrangement of the HDL surface lipids and probably influences the biological functions of the lipoproteins.

[Membrane structure of remantadine-sensitive and remantadine-resistant influenza virus studied with fluorescent phospholipid probes]. / Issledovanie stroeniia membran remantadinchuvstvitel'nogo i remantadinustoichivogo virusa grippa s pomoshch'iu fliuorestsentnykh fosfolipidnykh zondov.

Significant differences in the molecular organization of lipid bilayer in remantadin-resistant and remantadin-sensitive strains of influenza virus were demonstrated by means of fluorescent phospholipid probes, analogues of phosphatidylcholine and sphingomyelin. The data on fluorescence polarization and transfer of excitation energy from protein tryptophanes on probe fluorophores showed phosphatidylcholine and sphingomyelin to be segregated in influenza virion membrane. Gradients of mobility of lipid chains in virion membrane and in phospholipid vesicles have opposite directions. The results indicate that M protein coming inside virion into contact with the lipid bilayer does not penetrate further than its middle. In virions of the resistant strain remantadin destroys the array of the entire bilayer whereas in the sensitive strain the addition of remantadin results in a marked decrease of mobility of the chains in the surface area. It is suggested that the molecular organization of lipids is one of the factors determining influenza virus sensitivity to remantadin.