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.

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 SGG's symmetric and antisymmetric CH(2) stretching bands revealed that the insertion of DMPC into SGG bilayers increased the number of gauche conformers in SGG's hydrocarbon chains. Overall, the SGG+DMPC liposomes were homogeneous, with reduced interfacial hydrogen bonding and increased orientational and conformational disorder of SGG's hydrocarbon chains.

FTIR study of the monosialoganglioside GM1 in perdeuterated dimyristoylglycerophosphocholine (DMPCd54) multilamellar bilayers: spectroscopic evidence of a significant interaction between Ca2+ ions and the sialic acid moiety of GM1.

Fourier transform infrared (FTIR) spectroscopy was employed to study bovine brain GM1 and perdeuterated dimyristoylglycerophosphocholine (DMPCd54) multilamellar dispersions (mole fractions of GM1 in DMPCd54: 0.12, 0.15, 0.19, 0.26, 0.34, 0.41, and 0.58), in the absence and presence of 10 mM CaCl2. GM1 micelles did not display a thermal phase transition in the temperature range 5-60 degrees C. Moreover, the ceramide moiety of GM1 inserted into the hydrophobic core of DMPCd54 bilayers and was capable of undergoing a single, cooperative phase transition (Tm = 22-28 degrees C, depending on GM1 content) in a bilayer system. This suggested that the mixed bilayers consisted of a homogeneous mixture and that GM1 was uniformly dispersed in the bilayer plane rather than segregated into regions of relative enrichment. The coexistence of GM1 and DMPCd54 in a bilayer environment induced a rearrangement of the interfacial hydrogen bonding network of the amide I and ester C=O groups, relative to GM1 micelles and DMPCd54 bilayers, respectively. The modifications induced by GM1 might ultimately modulate surface events such as lipid-lipid and/or lipid-protein interactions. The spectroscopic results also suggested that the glycolipid's headgroup surface location and conformation in bilayers allow GM1 to act as a receptor for Ca2+ via its sialic acid moiety.

Modulation of phospholipase A2 activity by aminoglycosides and daptomycin: a Fourier transform infrared spectroscopic study.

The antibiotics known as aminoglycosides are commonly used to treat severe infections caused by Gram-negative bacteria. Unfortunately, they often lead to acute renal failure after their accumulation in the lysosomes of renal cells, where an inhibition of the phospholipid catabolism is observed. The lipopeptidic antibiotic daptomycin has been shown to reduce the nephrotoxicity of aminoglycosides, but the exact mechanism of this protection is still unknown. In the present study, Fourier transform infrared spectroscopy (FTIR) has been used to monitor the hydrolysis of phosphatidylcholine by phospholipase A2 (PLA2) from Naja mocambique mocambique venom in the presence of various aminoglycosides and/or daptomycin. Gentamicin and amikacin inhibited the reaction in its early stage. Kanamycin A, tobramycin, and especially kanamycin B enhanced the initial enzyme activity by reducing the lag time. After the initiation period, the reaction proceeded at a much slower rate in the presence of gentamicin. On the other hand, daptomycin led to dramatic alterations of the hydrolysis profile: the initial latency period was eliminated, and the maximal extent of hydrolysis was reduced. When both daptomycin and any of the aminoglycosides were present, the latency period also disappeared, and the phospholipase activity was higher than with the lipopeptide alone. The most drastic change occurred with gentamicin, which was the most inhibitory aminoglycoside when used alone but worked synergistically with daptomycin to yield the most dramatic activation of PLA2.

[Intraoperative malignant hyperthermia: apropos of a case]. / Hyperthermie maligne per opératoire: à propos d'un cas.

Malignant hyperthermia (MHS) is a rare potentially fatal complication of general anesthesia. Anesthetic agents most frequently incriminated are succinylcholine and halogenated agents. Respiratory acidosis is the most specific and sensitive sign. Hyperthermia per se may occur secondarily or may stay totally absent. Tachycardia and/or arrhythmias often develop due to hyperkalemia and metabolic acidosis. Muscle rigidity whenever present is pathognomonic The "gold standard" test for the diagnosis of MHS is the halothane-caffeine contracture test. Dantrolene is the treatment of choice and prognosis depends on the early administration of this agent.