2 research outputs found
Coating Graphene Oxide with Lipid Bilayers Greatly Decreases Its Hemolytic Properties
Toxicity evaluation for the proper
use of graphene oxide (GO) in
biomedical applications involving intravenous injections is crucial,
but the GO circulation time and blood interactions are largely unknown.
It is thought that GO may cause physical disruption (hemolysis) of
red blood cells. The aim of this work is to characterize the interaction
of GO with model and cell membranes and use this knowledge to improve
GO hemocompatibility. We have found that GO interacts with both neutral
and negatively charged lipid membranes; binding is decreased beyond
a certain concentration of negatively charged lipids and favored in
high-salt buffers. After this binding occurs, some of the vesicles
remain intact, while others are disrupted and spread over the GO surface.
Neutral membrane vesicles tend to break down and extend over the GO,
while vesicles with negatively charged membranes are mainly bound
to the GO without disruption. GO also interacts with red blood cells
and causes hemolysis; hemolysis is decreased when GO is previously
coated with lipid membranes, particularly with pure phosphatidylcholine
vesicles
Fluorescent Polyene Ceramide Analogues as Membrane Probes
Three
ceramide analogues have been synthesized, with sphingosine-like
chains containing five conjugated double bonds. Pentaene I has an <i>N-</i>palmitoyl acyl chain, while the other two pentaenes contain
also a doxyl radical, respectively, at C5 (Penta5dox) and at C16 (Penta16dox)
positions of the <i>N</i>-acyl chain. Pentaene I maximum
excitation and emission wavelengths in a phospholipid bilayer are
353 and 478 nm, respectively. Pentaene I does not segregate from the
other lipids in the way natural ceramide does, but rather mixes with
them in a selective way according to the lipid phases involved. Fluorescence
confocal microscopy studies show that when lipid domains in different
physical states coexist, Pentaene I emission is higher in gel than
in fluid domains, and in liquid-ordered than in liquid-disordered
areas. Electron paramagnetic resonance of the pentaene doxyl probes
confirms that these molecules are sensitive to the physical state
of the bilayer. Calorimetric and fluorescence quenching experiments
suggest that the lipids under study orient themselves in lipid bilayers
with their polar moieties located at the lipid–water interface.
The doxyl radical in the <i>N</i>-acyl chain quenches the
fluorescence of the pentaene group when in close proximity. Because
of this property, Penta16dox can detect gel–fluid transitions
in phospholipids. The availability of probes for lipids in the gel
phase is important in view of novel evidence for the existence of
gel microdomains in cell membranes