Danielle Carrier

A Fourier-transform infrared study of the interaction between germ-cell specific sulfogalactosylglycerolipid and dimyristoylglycerophosphocholine

In this study, we investigated structural and dynamic changes of sulfogalactosylglycerolipid (SGG) and dimyristoylglycerophosphocholine (DMPC) in a liposomal system (SGG+DMPC, molar ratio 2:3) by Fourier-transform infrared (FTIR) spectroscopy. Cooling of the preheated SGG liposomes (5-65 degrees C) revealed that the liquid crystalline-to-gel phase transition was centered at 45 degrees C. SGG+DMPC liposomes showed a single phase transition at 28 degrees C. Spectral changes of the ester C&z. dbnd6;O groups of SGG and DMPC in the mixed liposomes indicated a decrease in their interfacial hydrogen bonding intermolecularly and with water. Analysis of SGGs symmetric and antisymmetric CH(2) stretching bands revealed that the insertion of DMPC into SGG bilayers increased the number of gauche conformers in SGGs hydrocarbon chains. Overall, the SGG+DMPC liposomes were homogeneous, with reduced interfacial hydrogen bonding and increased orientational and conformational disorder of SGGs hydrocarbon chains.

Molecular basis of the inhibition of gentamicin nephrotoxicity by daptomycin; an infrared spectroscopic investigation

The lipopeptide daptomycin has been reported to reduce in vivo the nephrotoxicity of aminoglycoside antibiotics (Wood et al. (1989) Antimicrob. Agents Chemother. 33, 1280-1285; Beauchamp et al. (1990) Antimicrob. Agents Chemother. 34, 139-147). A recent dialysis study confirmed the existence of an electrostatic interaction between daptomycin and tobramycin (Couture et al. (1994) Antimicrob. Agents Chemother. 38, 742-749). The interaction of gentamicin with daptomycin and phosphatidylinositol (PI) dispersions was investigated by FTIR spectroscopy. We found no evidence of a direct interaction involving the neutralization of the aspartate groups of daptomycin by gentamicin and the amide I band of daptomycin did not reveal significant conformational changes of its peptidic moiety. On the other hand, daptomycin readily inserts within bilayers of PI, dimyristoylphosphatidylglycerol or dipalmitoylphosphatidylcholine, as judged from its influence on the fluidity of these bilayers. The incorporation of daptomycin into PI bilayers has no significant effect on the lipopeptide amide I band. Gentamicin also binds to PI bilayers and the associated modifications of the lipid bands are consistent with a tightening of the lipid network resulting from head group neutralization by gentamicin. The affinity of the aminoglycoside for PI is slightly increased in the presence of daptomycin, in agreement with the results of the dialysis study mentioned above. The lipid features indicate that its head group is still affected by gentamicin charges, but the thermotropic behavior of the hydrophobic portion becomes similar to that of the pure lipid. It is proposed that the contribution of daptomycin to the membrane charge density and its effect on the lipid packing both combine to counteract the inhibition of phospholipase activity due to aminoglycosides. Further work will attempt to determine how the peptide rings and gentamicin molecules are organized at the bilayer surface, how specific these interactions are and to confirm the influence of daptomycin on the phospholipid catabolism.

Interactions of aminoglycoside antibiotics with phospholipids. A deuterium nuclear magnetic resonance study.

The effect of several aminoglycoside (AG) antibiotics on aqueous multilamellar dispersions of mixtures of phosphatidylinositol (PI) and deuterated phosphatidylcholine (PC) has been studied by deuterium (2H) NMR. Isepamicin and amikacin gave rise to no significant changes in 2H-NMR lineshape relative to that of the lipid mixture without antibiotic. Both kanamycin A and B, which have a greater affinity for PI than the other two antibiotics examined in this study, induced temperature-dependent changes in 2H-NMR lineshapes and associated spectral moments. The results are consistent with an antibiotic-induced lateral phase separation giving rise to PC-enriched domains free of drug and PI-AG domains. These effects are correlated with the inhibitory potency of aminoglycosides towards PC degradation.

Polymorphic phases of galactocerebrosides: spectroscopic evidence of lamellar crystalline structures

Fourier transform infrared spectroscopy was applied to study the structural and thermal properties of bovine brain galactocerebroside (GalCer) containing amide linked non-hydroxylated or alpha-hydroxy fatty acids (NFA- and HFA-GalCer, respectively). Over the temperature range 0-90 degrees C, both GalCer displayed complex thermal transitions, characteristic of polymorphic phase behavior. Upon heating, aqueous dispersions of NFA- and HFA-GalCer exhibited high order-disorder transition temperatures near 80 and 72 degrees C, respectively. En route to the chain melting transition, the patterns of the amide I band of NFA-GalCer were indicative of two different lamellar crystalline phases, whereas those of HFA-GalCer were suggestive of lamellar gel and crystalline bilayers. Cooling from the liquid-crystalline phase resulted in the formation of another crystalline phase of NFA-GalCer and a gel phase of HFA-GalCer, with a phase transition near 62 and 66 degrees C, respectively. Prolonged incubation of GalCer bilayers at 38 degrees C revealed conversions among lamellar crystalline phases (NFA-GalCer) or between lamellar gel and crystalline bilayer structures (HFA-GalCer). Spectral changes indicated that the temperature and/or time induced formation of the lamellar crystalline structures of NFA- and HFA-GalCer was accompanied by partial dehydration and by rearrangements of the hydrogen bonding network and bilayer packing mode of GalCer.

Comparison of the effects of amikacin and kanamycins A and B on dimyristoylphosphatidylglycerol bilayers: An infrared spectroscopic investigation☆

Aminoglycoside antibiotics are very effective against severe Gram-negative infections, but their clinical use is associated with nephrotoxic side-effects. The cascade of events leading to acute renal failure involves an impairment of lysosomal phospholipase activity, which is thought to result from the direct interaction of the drugs with the head group of negative phospholipids. Fourier transform infrared spectroscopy was used to study the effects of three aminoglycosides from the kanamycin family (amikacin and kanamycins A and B) on dimyristoylphosphatidylglycerol (DMPG) bilayers at lysosomal pH. The results obtained were consistent with a tightening of the lipidic network caused by the neutralization of the negative head groups of DMPG by the positive charges of the aminoglycosides. These antibiotics induced an increase of the transition temperature of DMPG, a decrease of both the frequency and relative intensity of the hydrogen-bonded carbonyl component, and a decrease of the phosphate antisymmetric band frequency. Kanamycin B, which is known to be the most nephrotoxic drug of the three, exhibited the greatest effects on the transition temperature and on the carbonyl stretching band. A comparison of the nature and extent of the spectral changes led us to conclude that amikacin lies flat on the bilayer surface, whereas kanamycin B is located between the lipidic head groups and quite close to some of the carbonyl groups. Finally, a possible correlation between the importance of bilayers perturbation and the respective inhibitory potency against phospholipases was examined.

Effect of dehydration and hydrostatic pressure on phosphatidylinositol bilayers: an infrared spectroscopic study

Abstract The influence of hydration and hydrostatic pressure on the conformation and local interactions of phosphatidylinositol (PI) has been investigated using infrared spectroscopy. In hydrated PI bilayers, the phosphate groups and a major proportion of the carbonyl groups undergo strong hydrogen bonding with water molecules. These bonds strengthen upon compression to 5–7 kbar but above that, the proportion of bonded carbonyls decreases dramatically, probably due to water expulsion. In dehydrated PI bilayers, the strong H-bonds of the phosphate, carbonyl and inositol hydroxyl groups weaken rapidly up to 2 kbar. Above 2 kbar, the H-bonds of the hydroxyl and carbonyl groups slowly get stronger. This suggests an extension of the inositol rings from the phosphate group vicinity out to the bilayer surface at elevated pressure. This modulation of the inositol availability at the surface according to the balance between steric factors, hydration forces and intra- and intermolecular interactions might be crucial for PI specific biological roles.

Interaction between sulfogalactosylceramide and dimyristoylphosphatidylcholine increases the orientational fluctuation of their lipid hydrocarbon chains

The objective of this study was to investigate the interaction between sulfogalactosylceramide (SGC) and dimyristoylphosphatidylcholine (DMPC) in a mixed model liposomal system (molar ratio SGC:DMPC, 2:3). Structural and dynamic changes of the liposome components were monitored by Fourier-transform infrared spectroscopy (FTIR). Thermotropic FTIR analysis of the mixed liposomes showed a single gel/liquid crystalline phase transition, centered at approximately 42 degrees C. Spectral changes of the amide and ester C = O bands arising from functional groups at the interfacial region indicated a reduced hydrogen bonding of these groups in the mixed liposomes. Pressure-tuning FTIR of mixed liposomes showed that the methylene chains of SGC and DMPC were more orientationally disordered than those of the individual lipid SGC liposomes or DMPC liposomes. These results suggest that the mixed liposomes (molar ratio SGC:DMPC, 2:3) consisted of a homogeneous mixture of SGC and DMPC molecules in which mutual shielding reduced hydrogen bonding in the interfacial region, with a concurrent increase in the orientational disorder of the hydrocarbon chains of both SGC and DMPC.

Effect of daptomycin on the barotropic behavior of dioleoylphosphatidylglycerol: an infrared spectroscopic investigation

Abstract According to our infrared spectra, the pressure-induced liquid-crystal to gel transition of dioleoylphosphatidylglycerol (DOPG) involves a conformational change making the glycerol Csn−1 − Csn−2 bond more parallel to the bilayer surface and resulting in increased carbonyl groups hydrogen bonding. This conformational change allows a more compact packing of the cis unsaturated acyl chains. The lipopeptide daptomycin, at lipid/daptomycin molar ratios of 4:1, impedes the DOPG conformational change and induces an increase of transition pressure from 5.5 (pure lipid) to 6.8 kbar and a higher disorder in the gel state. The analogue (LY298862) of daptomycin containing a myristoyl instead of a decanoyl chain shifts the phase transition to 7.8 kbar at the same molar ratio and reduces more efficiently the lipid conformational change. The lipopeptide hydrocarbon chain length is thus a critical parameter in the modulation of the physical effects of this type of compounds, often used as antibiotics.