Characterizing the structural transition of cationic DPPC liposomes from the approach of TEM, SAXS and AFM measurements

Hypericin photodynamic activity in DPPC liposomes - part II: stability and application in melanoma B16-F10 cancer cells

Hypericin (Hyp) is considered a promising photosensitizer for Photodynamic Therapy (PDT), due to its high hydrophobicity, affinity for cell membranes, low toxicity and high photooxidation activity. In this study, Hyp photophysical properties and photodynamic activity against melanoma B16-F10 cells were optimized using DPPC liposomes (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) as a drug delivery system. This nanoparticle is used as a cell membrane biomimetic model and solubilizes hydrophobic drugs. Hyp oxygen singlet lifetime (τ) in DPPC was approximately two-fold larger than that in P-123 micelles (Pluronic™ surfactants), reflecting a more hydrophobic environment provided by the DPPC liposome. On the other hand, singlet oxygen quantum yield values (Φ_Δ¹O₂) in DPPC and P-123 were similar; Hyp molecules were preserved as monomers. The Hyp/DPPC liposome aqueous dispersion was stable during fluorescence emission and the liposome diameter remained stable for at least five days at 30 °C. However, the liposomes collapsed after the lyophilization/rehydration process, which was resolved by adding the lyoprotectant Trehalose to the liposome dispersion before lyophilization. Cell viability of the Hyp/DPPC formulation was assessed against healthy HaCat cells and high-metastatic melanoma B16-F10 cells. Hyp incorporated into the DPPC carrier presented a higher selectivity index than the Hyp sample previously solubilized in ethanol under the illumination effect. Moreover, the IC₅₀ was lower for Hyp in DPPC than for Hyp pre-solubilized in ethanol. These results indicate the potential of the formulation of Hyp/DPPC for future biomedical applications in PDT treatment.

Deciphering the Peculiar Behavior of β-Lapachone in Lipid Monolayers and Bilayers

β-Lapachone (β-Lap) is a promising anticancer drug whose applications have been limited so far because of its poor solubility and stability. Its encapsulation in liposomes has been proposed to overcome these issues. However, surface pressure measurements show that β-Lap exhibits atypical interfacial behavior when mixed with lipids. Although the drug does not seem to be retained in lipid monolayers as deduced from the π-A isotherms, small changes in compressibility moduli suggest that β-Lap actually interacts with lipids, either disorganizing or rigidifying their monolayers. Thermal and structural analyses of lipid bilayers confirm the existence of β-Lap/lipid interactions and show that the drug inserts between hydrophobic chains, close to the polar headgroup in DPPC bilayers and deeper in the acyl chains in POPC bilayers. Molecular dynamics simulations allow a comprehensive description of the drug position and orientation in DOPC and POPC bilayers in the presence or absence of cholesterol.

Hypericin photodynamic activity in DPPC liposome. PART I: biomimetism of loading, location, interactions and thermodynamic properties

Hypericin (Hyp) is a potential photosensitizer drug for Photodynamic Therapy (PDT). However, the high lipophilicity of Hyp prevents its preparation in water. To overcome the Hyp solubility problem, this study uses the liposomal vesicle of DPPC. Otherwise liposome is also one of the most employed artificial systems that mimetizes cell membranes. Our present focus is the interaction of Hyp into DPPC liposome as biomimetic system. We studied the loading, interaction, and localization of Hyp (2.8 μmol L^-1) in DPPC (5.4 mmol L^-1) liposomes, as well as the thermodynamic aspects of Hyp-liposomes. The Hyp addition to the DPPC liposome dispersion showed a Encapsulation Efficiency for [Hyp] = 2.8 μmol L^-1 in [DPPC] = 5.3 mmol L^-1 of 74.3% and 89.3% at 30.0 and 50.0 °C, respectively. The encapsulation profile obeys a pseudo first-order kinetic law, with a rate constant of 1.26 × 10^-3 s^-1 at 30.0 °C. Also the data suggests this reaction is preceded by an extremely rapid step. A study on the binding of Hyp/DPPC liposomes (K_b), performed at several temperatures, showed results of 4.8 and 18.5 × 10³ L mol^-1 at 293 and 323 K, respectively. Additionally, a decrease was observed in the ΔG of the Hyp/DPPC interaction (-20.6 and - 26.4 kL mol^-1 at 293 and 323 K, respectively). The resulting ΔH > 0 with ΔS < 0 shows that the entropy is driven the process. Studies of Hyp location in the liposome at 298 K revealed the existence of two different Hyp populations with a Stern-Volmer constant (K_sv) of 4.65 and 1.87 L mol^-1 using iodide as an aquo-suppressor at concentration ranged from 0 to 0.025 mol L^-1 and from 0.025 to 0.150 mol L^-1, respectively. Furthermore, studies of Fluorescence Resonance Energy Transfer, using DPH as a donor and Hyp as an acceptor, revealed that Hyp is allocated in different binding sites of the liposome. This is dependent on temperature. Thermal studies revealed that the Hyp/DPPC formulation presented reasonable stability. Size and morphological investigations showed that Hyp incorporation increases the average size of DPPC liposomes from 116 to 154 nm. The study demonstrated the ability of the Hyp-DPPC liposome as an interesting system for drug delivery system that can be applied to PDT.

Structural Modifications of DPPC Bilayers upon Inclusion of an Antibacterial Cationic Bolaamphiphile

The emergence of antibiotic-resistant bacterial strains has fostered fundamental research to develop alternative antimicrobial strategies. Among the several systems proposed so far, the association complexes (nanoplexes) formed by transcription factor decoys (TFDs), i.e., short oligonucleotides targeting a crucial bacterial transcription factor, and a bolaform cationic amphiphile, 10,10'-(dodecane-1,12-diyl)-bis-(9-amino-1,2,3,4-tetrahydroacridinium) chloride (12-bis-THA), have demonstrated their potential in vitro and in vivo. The application of these nanoplexes is hampered by a scarce colloidal stability, which can be addressed by including the bolaamphiphile in a liposomal carrier, which is then associated to the TFD. The present study reports an investigation on the effects of 12-bis-THA on the structure of synthetic lipid bilayers to assess the morphology of the mixed assemblies, gain insight into the location of the host within the bilayer, and determine the loading capacity of the carrier. Our results demonstrate that 12-bis-THA promptly inserts within 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) bilayers, bending its C-12 spacer chain to adopt a conelike shape and shifting the gel-liquid crystalline transition of the chains to lower temperatures. The host liposomal structure is retained for a bolaamphiphile concentration of up to 3.2% mol to DPPC, whereas higher concentrations lead to the destabilization by means of a detergency-like mechanism, with the simultaneous existence of different lamellar-based structures, such as liposomes, bicelles, and rafts, in which DPPC and 12-bis-THA could be present in different molar ratios. Overall, these results shed light on the interaction of the bolaamphiphile with a lipid bilayer and provide valuable insight to better formulate the antimicrobial amphiphile in liposomal carriers to circumvent the colloidal instability of nanoplexes.

Cationic liposomal vectors incorporating a bolaamphiphile for oligonucleotide antimicrobials

Antibacterial resistance has become a serious crisis for world health over the last few decades, so that new therapeutic approaches are strongly needed to face the threat of resistant infections. Transcription factor decoys (TFD) are a promising new class of antimicrobial oligonucleotides with proven in vivo activity when combined with a bolaamphiphilic cationic molecule, 12-bis-THA. These two molecular species form stable nanoplexes which, however, present very scarce colloidal stability in physiological media, which poses the challenge of drug formulation and delivery. In this work, we reformulated the 12-bis-THA/TFD nanoplexes in a liposomal carrier, which retains the ability to protect the oligonucleotide therapeutic from degradation and deliver it across the bacterial cell wall. We performed a physical-chemical study to investigate how the incorporation of 12-bis-THA and TFD affects the structure of POPC- and POPC/DOPE liposomes. Analysis was performed using dynamic light scattering (DLS), ζ-potential measurements, small-angle x-ray scattering (SAXS), and steady-state fluorescence spectroscopy to better understand the structure of the liposomal formulations containing the 12-bis-THA/TFD complexes. Oligonucleotide delivery to model Escherichia coli bacteria was assessed by means of confocal scanning laser microscopy (CLSM), evidencing the requirement of a fusogenic helper lipid for transfection. Preliminary biological assessments suggested the necessity of further development by modulation of 12-bis-THA concentration in order to optimize its therapeutic index, i.e. the ratio of antibacterial activity to the observed cytotoxicity. In summary, POPC/DOPE/12-bis-THA liposomes appear as promising formulations for TFD delivery.