C. Mestres

Interaction of colistin with lipids in liposomes and monolayers

Abstract Colistin is an antibiotic member of the polymixin family, showing a high amphipathic character. Its mechanism of action has been related to its ability to disrupt phospholipid bilayers of the bacterial membrane. Due to its hydrophobic properties colistin can interact both with the polar heads and the alkyl chains of the phospholipids. Moreover, it has a polycationic structure, so its interactions with phospholipids should be highly dependent on the electric charge of the lipid and the ionisation state of polymixin molecule. In the present paper we report on physicochemical studies to define the type and characteristics of these interactions. The surface activity of colistin has been shown to be highly dependent on the pH of the medium, the less protonated forms being more stable at the air–water interface. Interaction with phospholipid monolayers shows the same tendency. Colistin is also able to form mixed monolayers with phospholipids with small deviations from ideality. Physicochemical studies carried out with fluorescent probes indicate the presence of pure colistin aggregates that can coexist with mixed micelles composed of colistin/phospholipids. In no case did the interaction cause significative changes in the transition temperature of phospholipids.

Interaction energies of mixing phosphatidylserine and phosphatidylcholine monolayers

Abstract The interactions between phosphatidylcholine and phosphatidylserine spread in monolayers of different molecular composition were studied. The influence in these mixtures of Na + and Ca 2+ ions was also determined. By applying the Goodrich, and Pagano and Gershfeld equations, the mixing energies and interactions at intermediate and collapse pressures were calculated. The maximum interaction occurs at higher pressures and in the presence of Ca 2+ ions.

Interaction of GB virus C/hepatitis G virus synthetic peptides with lipid langmuir monolayers and large unilamellar vesicles.

In this paper, we aimed to continue the previous study undertaken with one segment of E1 protein belonging to the GB virus C/hepatitis G virus (GBV-C/HGV), specifically between the 53-66 amino acids and their palmitoyl derivative peptide. The sequence selection has been made on the basis of different prediction algorithms of hydrophobicity and antigenicity. Their interactions between two different in vitro membrane models, lipid Langmuir monolayers and vesicles of different lipidic composition, have been evaluated. For this purpose, different lipids, varying the charge and the unsaturations of the hydrocarbon chain 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DPPG) and 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DOPG), have been selected. Miscibility and peptides/lipids interactions have been analyzed on the basis of surface pressure (pi)-mean molecular area (A) isotherms, which have been recorded for pure and mixed monolayers of different composition spread at the air/water interface. Furthermore, E1(53-66) sequence and PalmE1(53-66) have been labeled with a fluorescent group, succinimidyl 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoate (NBD succinimide), in order to study their behavior in the presence of vesicles. The obtained results are consistent with the existence of electrostatic (attractive) intermolecular interactions between the two positive net charges of the peptides and the polar heads of negative-charged lipids. However, both the lipidic membrane fluidity and the palmitic chain linked to the native peptide play an important role in the balance between the electrostatic forces established at the interface and the hydrophobic ones established inside the membrane. The fluorescence assays have demonstrated that electrostatic forces clearly predominate over the hydrophobic interactions only when the native sequence is retained at the polar interface of DPPG and DOPG vesicles. However, the palmitic tail linked to the peptide helped its penetration in the hydrophobic environment of the membrane, and this process was favored by decreasing the membrane fluidity.

Miscibility of dipalmitoylphosphatidylcholine, oleic acid and cholesterol measured by DSC and compression isotherms of monolayers

Abstract The miscibility of dipalmitoylphosphatidylcholine and oleic acid (DPPC/OA) and of dipalmitoylphosphatidylcholine/oleic acid/cholesterol (DPPC/OA/Chol) in mixed monolayers was determined. According to the thermodynamic calculations, the energy involved in the process is very low, suggesting the lack of strong interactions. Moreover, the presence of oleic acid or cholesterol has little influence on the transition temperature of DPPC.

Physicochemical interaction of opioid peptides with phospholipids and membranes

The surface activity and opioid potency of peptide analogues of enkephalins are described. The molecules under study have as a general formula: Tyr-D · Met-Gly-Phe-Pro-NH-(CH2)n-CH3, n being 5, 9 or 13. The interaction of these peptide-alkylamides with PC, PS, PI and GM1 monolayers and their opioid activity measured by the GPI (guinea pig ileum) test are highly dependent on the hydrophobicity of the molecule. Moreover, the GPI muscle contraction records show a strong hydrophobic interaction between the peptides and the bilayer components, that holds the molecules anchored to the membrane and increases the duration of the effect.

Mixed monolayers composed of PC/PS/Chol. Interaction with opioid molecules

The miscibility of phosphatidylserine, phosphatidylcholine, and cholesterol in monolayers were studied. The influence of sodium and calcium ions in this system was determined. The compression isotherms of mixed monolayers of the above cited three components spread on subphases containing opiate molecules are elucidated. Moreover, the penetration kinetics of opiate molecules in these mixed monolayers was also recorded. The results show that the presence of cholesterol always lowers the penetration of opioid molecules; this effect is weaken for meperidine, the most hydrophobic of the molecules assayed.

Interaction of opioid molecules with PS, PC and PS/PC monolayers

The interaction between opiate molecules and phosphatidylserine (PS) or phosphatidylcholine (PC) has been studied on compression isotherms and penetration kinetics. Phosphatidylcholine-opiate interactions are weak and similar in magnitude for all opiate molecules. On contrary, PS and PS/PC interact strongly and differently with opiate molecules. The differences in penetration are not directly related to the pKa or hydrophobicity of the molecules.

Miscibility of phosphatidylcholine and sulphatide in monolayers

Compression isotherms of mixed monolayers of phosphatidylcholine (PC) and sulphatides (S) were carried out, with the lipids being spread on subphases of different pH and different ionic composition. Several common trends can be observed. All monolayers when compressed reach collapse. Collapse pressures are directly related to the molar fractions of the lipids in the monolayer. Miscibility is not ideal, in general, and is independent on the surface pressure of the monolayer, the mixed monolayers being always (with some exceptions) in a more expanded state than those of the pure components. The thermodynamic parameters corresponding to the mixing interactions have been calculated at the molar composition that gives a maximum deviation from ideality.

Physicochemical interaction of a lipophilic derivative of HAV antigen VP3(110–121) with lipid monolayers

Abstract The synthesis of a palmitoyl derivative of a peptide corresponding to the HAV-VP3(110–121) sequence is described. Physicochemical characterisation was carried out through its surface activity, penetration in monolayers and influence in the miscibility of DPPC/DPPG and DPPC/SA monolayers. This peptide showed a lower surface activity than its parent, non acylated sequence. This fact is attributed to its tendency to form aggregates in water media. The thermodynamic parameters associated to the miscibility of lipids with or without peptide have been calculated, indicating that the energies involved are very low. This implies that the peptide sequence can be inserted to monolayers by means of extension bilayers without altering the packing of these lipids. It was not possible to know if these mixed monolayers were completely miscible or not due to the lack of collapse points in the compression isotherms.

Penetration of morphine and naloxone in phosphatidylserine monolayers

Abstract The interaction between morphine or naloxone and phosphatidylserine (PS), has been studied using monomolecular layers as membrane model. The penetration kinetics of both molecules measured at different monolayer pressures and for increasing opiate concentrations has been determined. The results show that penetration of morphine presents a maximum at 15 mN · m−1 of initial PS pressure whereas that of naloxone has a maximum at 10 mN · m−1.