Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity (original) (raw)
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Archives of Biochemistry and Biophysics, 1996
gested to have a chemical structure in which the angle between the absorption and emission dipole moments Motional properties of fluorescent substances prois very large. On the basis of these observations, the duced by lipid peroxidation by a time-resolved fluoproduction pathway of fluorophores in oxidized memrescence polarization technique were studied. When branes is discussed. ᭧ 1996 Academic Press, Inc. liposomes containing phosphatidylethanolamine (PE) Key Words: amino phospholipid; anisotropy; fluoand linoleic hydrocarbon chain were incubated at rescence; liposome, peroxidation. 37ЊC, fluorophores absorbing maximally at 360 nm and emitting near 430 nm were produced. Their fluorescence anisotropy decay measured at 23ЊC was fitted well with a sum of a fast relaxation and a time-inde-Lipid peroxidation alters several physical properties pendent residual term. With the increase of oxidation of biomembranes. For example, membrane proteins are degree, the time constant of the relaxation term incrosslinked, and their rotational and translateral mocreased. This may be explained by alteration in the bility is decreased (1). In the lipid domain, lipid peroximembrane structure or by modification of the fluoresdation causes an enhancement of flip-flop movements cent products themselves. Information on the location of phospholipids (2, 3), influences polymorphic phase of the fluorescent products was obtained when their behavior of lipids (4), and alters the membrane fluidity motional property was compared with those of various (5, 6). In addition, peroxidation can inactivate enzymes extrinsic probes that were incorporated at different and cause structural abnormalities of biomembranes. positions of the lipid bilayer. It was found that the Some of the abnormalities are concomitant with formamotional property of the fluorescent oxidation prodtion of fluorescent substances, which are produced ucts is similar to that of 1-(4-trimethylammoniummostly by the reaction of lipid oxidation products with phenyl)-6-phenyl-1,3,5-hexatriene, a rod-shaped hyprimary amino compounds. This reaction has been drophobic probe with a charged terminal. Other shown to be responsible for the accumulation of fluoprobes sensing the polar region or the hydrophobic rescent pigments in aged cells (7, 8). region of the membrane were characterized by a lower So far, three types of model reactions have been proorder parameter. It is suggested that the fluorescent posed to describe production of fluorescent substances oxidation products have a polar moiety located at the by peroxidation in the presence of amino compounds: membrane surface and attached to the amino group of PE while the tail part being buried in the hydrophobic (1) malondialdehyde (MDA), 2 one of the major products region of the membrane. This picture is supported by fluorescence quenching experiments with the aqueous
Journal of Biomedical Optics, 2008
Preferential tumor localization and the aggregation state of photosensitizers ͑PSs͒ can depend on the hydrophilic/hydrophobic nature of the molecule and affect their phototoxicity. In this study, three PSs of different hydrophilicity are introduced in liposomes to understand the structure-photochemistry relationship of PSs in this cellular model system. Absorbance and fluorescence spectra of amphiphilic aluminum ͑III͒ phthalocyanine disulfonate chloride adjacent isomer ͑Al-2͒, hydrophilic aluminum ͑III͒ phthalocyanine chloride tetrasulfonic acid ͑Al-4͒, and lipophilic 2-͑1-hexyloxyethyl͒-2-devinyl pyropheophorbide ͑HPPH͒ are compared in a liposomal confined state with free PS in bulk solution. For fluorescence measurements, a broad range of concentrations of both bulk and liposomal confined PSs are examined to track the transition from monomers to dimers or higher order aggregates. Epifluorescence microscopy, absorbance, and fluorescence measurements all confirm different localization of the PSs in liposomes, depending on their hydrophilicity. In turn, the localization affects the aggregation of molecules inside the liposome cell model. Data obtained with such cellular models could be useful in optimizing the photochemical properties of photosensitizing drugs based on their structure-dependent interactions with cellular media and subcellular organelles.
Fluorescence quenching of fluorescein by Merocyanine 540 in liposomes
Journal of Luminescence, 2011
The fluorescence quenching of fluorescein (FL) by merociyanine 540 (MC540) was examined in L-egg lecithin phosphatidycholine (PC) liposomes using spectroscopic methods. The type of quenching mechanism (dynamic or static) was evaluated using the Stern-Volmer plots. Findings were also supported by the temperature studies and florescence decay measurements. The Stern-Volmer equation was utilized to calculate bimolecular quenching constants (K q ). Furthermore, the bimolecular quenching constant of the quencher in the liposomes (K SV ), partition coefficient (K p ), binding constant (K), and corresponding thermodynamic parameters DH, DS, and DG were calculated. The quenching property was also used in determining quantitatively (K p ) the partition coefficient of Merociyanini 540 in PC liposome.The obtained data indicated that static quenching occurred in the system and the K SV values decreased with increasing lipid concentration. In addition, thermodynamic analysis suggested that van der Waals interactions and hydrogen bonding were the main acting forces between fluorescein and merociyanine 540 molecules in the medium.
A Stability Test of Liposome Preparations Using Steady-State Fluorescent Measurements
Drug Delivery, 2001
The stability of liposome preparations under the action of the nonionic detergent Triton X-100 was measured using the fluorescent molecular probe octadecylrhodamine B (R18). The probe inserted in the lipid bilayer shows a self-quenched fluorescence and the degree of quenching depends both on the probe concentration and the phase state of the lipid membrane. The addition of detergent to the liposomes produces a steep decrease in self-quenching caused by dilution of the probe in the bilayer. The curves of steady-state fluorescence intensity show an abrupt change in slope that corresponds to the point at which liposomes break down into lipid-detergent mixed entities that are different from the earlier liposome-monodisperse population. The lytic process was followed in parallel by dynamic light scattering (DLS), and the analysis of the DLS results agree with the interpretation of the fluorescence measurements. The probe R18 therefore is a useful marker to test the stability of liposome ...
Effects of Drug Hydrophobicity on Liposomal Stability
Chemical Biology & Drug Design, 2007
A major obstacle in drug delivery is the inability to effectively deliver drugs to their intended biological target without deleterious side-effects. Delivery vehicles such as liposomes can minimize toxic side-effects by shielding the drug from reaction with unintended targets while in systemic circulation. Liposomes have the ability to accommodate both hydrophilic and hydrophobic drugs, either in the internal aqueous core or the lipid bilayer, respectively. In the present study, fluorescein and rhodamine have been used to model hydrophilic and hydrophobic drugs, respectively. We have compared the stabilities of liposomes encapsulating these fluorophores as a function of lipid content, time, and temperature. At 25 and 37°C, liposomes containing distearoyl phosphatidylcholine as the major phospholipid component were found to be more stable over time than those containing dipalmitoyl phosphatidylcholine, regardless of the fluorophore encapsulated. Liposomes loaded with fluorescein were found to be more stable than those with rhodamine. Dipalmitoyl phosphatidylcholine liposomes that encapsulated rhodamine were the least stable. The results indicate that the physical properties of the drug cargo play a role in the stability, and hence drug delivery kinetics, of liposomal delivery systems, and desired drug release times can be achieved by adjusting/fine-tuning the lipid compositions.
Unusual Photoinduced Response of mTHPC Liposomal Formulation (Foslip)
Photochemistry and Photobiology, 2009
Liposomal formulations of meso-tetra(hydroxyphenyl)chlorin (mTHPC) have already been proposed with the aim to optimize photodynamic therapy. Spectral modifications of these compounds upon irradiation have not yet been investigated. The objective of this study was to evaluate photobleaching properties of mTHPC encapsulated into dipalmitoylphosphatidylcholine (DPPC) liposomes, Foslip. Fluorescence measurements in DPPC liposomes with different DPPC:mTHPC ratios demonstrated a dramatic decrease in fluorescence anisotropy with increasing local mTHPC concentration, thus suggesting strong interactions between mTHPC molecules in lipid bulk medium. Exposure of Foslip suspensions to small light doses (<50 mJ/cm 2) resulted in a substantial drop in fluorescence, which, however, was restored after addition to the sample of a non-ionic surfactant Triton X-100. We attributed this behavior to photoinduced fluorescence quenching. This effect depended strongly on the molar DPPC:mTHPC ratio and was revealed only for high local mTHPC concentrations. The results were interpreted supposing energy migration between closely located mTHPC molecules with its subsequent dissipation by the molecules of photoproduct acting as excitation energy traps. We further assessed the effect of photoinduced quenching in plasma protein solution. Relatively slow kinetics of photoinduced Foslip response during incubation in the presence of proteins was attributed to mTHPC redistribution from liposomal formulations to proteins. Therefore, changes in mTHPC distribution pattern in biological systems would be consistent with changes in photoinduced quenching and would provide valuable information on mTHPC interactions with a biological environment.
Spectroscopic investigation of fluorinated phenols as pH-sensitive probes in mixed liposomal systems
The pKa values of three fluorinated phenols, 2,4,6-trifluorophenol (3FP), 2,3,5,6-tetrafluorophenol (4FP) and 2,3,4,5,6-pentafluorophenol (5FP) have been measured by using UV-vis and 19F-NMR spectroscopy at 25 °C in water and in the presence of pure POPC, pure DDAB and mixed POPC–DDAB liposomes. The probe–liposome interaction depends on both the equilibrium between the neutral and ionic forms of 3FP, 4FP and 5FP and the charge on the liposomal surface determined by zeta potential measurements in a wide pH range. The data from the two spectroscopic techniques are in good agreement and show that the incorporation of DDAB into the POPC membrane decreases the pKa values of the probes with a non-linear correlation.
Biophysical studies and intracellular destabilization of pH-sensitive liposomes
Lipids, 2000
We examined changes in membrane properties upon acidification of dioleoylphosphatidylethanolamine/cholesterylhemisuccinate liposomes and evaluated their potential to deliver entrapped tracers in cultured macrophages. Membrane permeability was determined by the release of entrapped calcein or hydroxypyrene-1,3,6-trisulfonic acid (HPTS)-p-x ylene-bis-pyridinium bromide (DPX); membrane fusion, by measuring the change in size of the liposomes and the dequenching of octadecylrhodamine-B fluorescence; and change in lipid organization, by 3 1 P nuclear magnetic resonance spectroscopy. Measurement of cell-associated fluorescence and confocal microscopy examination were made on cells incubated with liposomes loaded with HPTS or HPTS-DPX. The biophysical studies showed (i) a lipid reorganization from bilayer to hexagonal phase progressing from pH 8.0 to 5.0, (ii) a membrane permeabilization for pH <6.5, (iii) an increase in the mean diameter of liposomes for pH <6.0, and (iv) a mixing of liposome membranes for pH <5.7. The cellular studies showed (i) an uptake of the liposomes that were brought from pH 7.5-7.0 to 6.5-6.0 and (ii) a release of ~15% of the endocytosed marker associated with its partial release from the vesicles (diffuse localization). We conclude that the permeabilization and fusion of pH-sensitive liposomes occur as a consequence of a progressive lipid reorganization upon acidification. These changes may develop intracellularly after phagocytosis and allow for the release of the liposome content in endosomes associated with a redistribution in the cytosol.
Carotenoids in Liposomes: Photodegradation, Excited State Lifetimes, and Energy Transfer
The Journal of Physical Chemistry B, 2000
DMPC (dimyristoyl-L-R-phosphatidylcholine) liposomes are used as artificial photosynthetic media to study the behavior of carotenoids. 8′-Apo--caroten-8′-al (I) and -carotene (II) degrade faster under irradiation in DMPC liposomes than in organic solvents, which is possibly because vibrational deactivation of carotenoid excited states is less efficient in rigid lipid membranes. The lifetime of the first excited singlet state (S 1 ) of I in DMPC liposomes is 27.2 ps, very close to that in 3-methylpentane (26.4 ps), but longer than its lifetime in EtOH (17.1 ps) or CH 2 Cl 2 (14.1 ps). The lifetime of the S 1 state of I in DMPC liposomes is as expected for an alkane environment. The lifetime of the S 1 state of II in DMPC liposomes is 10.3 ps, very close to its lifetimes in 3-methylpentane (8.1 ps), EtOH (9.2 ps), and CH 2 Cl 2 (8.5 ps). This independence of the S 1 state lifetime of II from the matrix agrees with earlier conclusions. Carotenoid I can suppress the photodegradation of chlorophyll a (Chl a) in liposomes, which shows the protection role of I on Chl a under strong irradiation. In liposomes, Chl a fluorescence quenching by I is observed when using either the Q y band or the Soret band of Chl a as the excitation line.
Tocopheryl Succinate-Induced Structural Changes in DPPC Liposomes: DSC and ANS Fluorescence Studies
Molecules
Recent studies show that alpha-tocopheryl succinate (TS) exhibits selective toxicity against cancer cells. In this study, we investigated the effect of TS’s presence on the physico-chemical and structural properties of DPPC liposomes using fluorescence parameters (intensity, lifetime, and position of emission maximum) of 1-anilino-8-naphtalene sulphonate (ANS), differential scanning calorimetry (DSC) and zeta potential methods. Increasing the TS presence in the DPPC gel phase produced ANS fluorescence enhancement with a hypsochromic shift of the maximum. The zeta potential measurements show an increase in the negative surface charge and confirmed that this process is connected with the hydrophobic properties of dye, which becomes located deeper into the interphase region with a progressing membrane disorder. Temperature dependence studies showed that an increase in temperature increases the ANS fluorescence and shifts the ANS maximum emission from 464 to 475 nm indicating a shift fr...