Main Phase Transition Temperature Research Articles

Decomposition of mixed DMPC-aescin vesicles to bicelles is linked to the lipid's main phase transition: A direct evidence by using chain-deuterated lipid

This work investigates the conversion of bicelles into larger sheets or closed vesicles upon dilution and temperature increase for a system composed of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and the saponin aescin. Due to its peculiar amphiphilic character, aescin is able to decompose DMPC bilayers into smaller, rim-stabilized bicelles. Aspects of the transition process are analyzed in an aescin content- and temperature-dependent manner by photon correlation spectroscopy (PCS), turbidimetry and small-angle neutron scattering (SANS). Both the conversion of bicelles into vesicles induced by temperature increase and the decomposition process upon cooling are presumably related to the main phase transition temperature Tm of DMPC. Therefore, not only conventional DMPC, but also chain-deuterated d54-DMPC was used due to its significantly lower Tm-value compared to the conventional DMPC. It will be demonstrated that the reconversion of vesicle structures (present at low aescin content) into bicelles shows a strong hysteresis effect whereas this is not observed for the reconversion at high aescin amounts, at which for high temperature still bicelle structures are present. The results indicate formation of a trapped state, correlated with the lipid's Tm and the decomposition of vesicles into bicelles is only possible if the lipid membrane entirely adopts the rigid phase state.

Calcium ions do not influence the Aβ(25–35) triggered morphological changes of lipid membranes

We have studied the effect of calcium ions (Ca2+) at various concentrations on the structure of lipid vesicles in the presence of amyloid-beta peptide Aβ(25–35). In particular, we have investigated the influence of calcium ions on the formation of recently documented bicelle-like structures (BLSs) emerged as a result of Aβ(25–35) triggered membrane disintegration. First, we have shown by using small-angle X-ray and neutron scattering that peptide molecules rigidify the lipid bilayer of gel phase DPPC unilamellar vesicles (ULVs), while addition of the calcium ions to the system hinders this effect of Aβ(25–35). Secondly, the Aβ(25–35) demonstrates a critical peptide concentration at which the BLSs reorganize from ULVs due to heating and cooling the samples through the lipid main phase transition temperature (Tm). However, addition of calcium ions does not affect noticeably the Aβ-induced formation of BLSs and their structural parameters, though the changes in peptide's secondary structure, e.g. the increased α-helix fraction, has been registered by circular dichroism spectroscopy. Finally, according to 31P nuclear magnetic resonance (NMR) measurements, calcium ions do not affect the lipid-peptide arrangement in BLSs and their ability to align in the magnetic field of NMR spectrometer. The influences of various concentrations of calcium ions on the lipid-peptide interactions may prove biologically important because their local concentrations vary widely in in-vivo conditions. In the present work, calcium ions were investigated as a possible tool aimed at regulating the lipid-peptide interactions that demonstrated the disruptive effect of Aβ(25–35) on lipid membranes.

Interaction of Melatonin with Zwitterionic Model Lipid Membranes

Melatonin is a key hormone secreted by the pineal gland in the brain. It interacts strongly with cell membranes and plays a protective role in several diseases such as Alzheimer's disease, cardiovascular diseases, and cancer. Hence, studies on the interaction of melatonin with lipid bilayer membranes have gained importance. In this regard, the present study aims to analyze the influence of different concentrations (0 to 15 mol%) of melatonin on the thermal and structural properties of zwitterionic stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) lipid bilayer model systems by using Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The DSC results have shown that melatonin interacts with the membrane in a concentration-dependent fashion, induces patch formation, and alters the phase behaviour by reducing the main phase transition temperature. FTIR data has shown that increasing the melatonin concentration caused a reduction in the wavenumber of C=O and PO$$_{2}^-$$ antisymmetric stretching vibrations corresponding to the ester carbonyl and phosphate groups of SOPC lipids. This indicates the possibility of strong hydrogen bonding of melatonin with the SOPC lipids and nearby water molecules in the environment, suggesting its preferential location near lipid heads at the interfacial region. These results help to understand the organization and interactions of melatonin with membranes and provide insights to develop safe melatonin-based formulations for pharmaceutical applications.

Long-term shelf-life liposomes for delivery of prednisolone and budesonide

Liposomes are nanoscale drug delivery systems built up from lipid layers and are able to spontaneously self-assemble in an aqueous environment. Both hydrophilic and hydrophobic drugs can be delivered by liposomes and this kind of nanoformulation offers many advantages regarding biodistribution, drug absorption and controlled drug release. Corticosteroids as lipophilic molecules are able to integrate into the lipid bilayer. This novel approach can improve the efficacy of several anti-inflammatory, such as asthma therapy.Our aim was to create liposomes with long shelf-life, which can incorporate and release corticosteroids such as Prednisolone (Pred) and Budesonide (Bud) at the temperature of inflamed tissues. Two kinds of liposome samples were prepared from three different kinds of phospholipids to get unilamellar vesicles with 100 nm in diameter and characterize their physicochemical properties and effect on living cells. Their main phase transition temperature in the physiologically relevant temperature range was measured by differential scanning calorimetry. According to the size distributions determined by dynamic light scattering, all drug-containing liposomes were stable for 6 months. All of the liposome types have a slightly negative zeta potential value. The Fourier-transform infrared spectroscopy revealed no chemical interaction between the drug and lipid molecules. The entrapment efficacy was determined by size-exclusion gel chromatography combined with UV–VIS spectrophotometry and it was very high in both cases (between 70 and 87%). The drug leakage was 35–40% for Pred and 6–8% for Bud in the first 30 min. The effect of liposomal drugs on cell viability was measured on the EBC-1 human lung carcinoma cell line. Neither the free corticosteroids nor their liposomal form were toxic to the cells. The cellular internalization of the liposomes was proved by flow cytometry and confocal microscopy.In summary, these liposomes could be useful in the delivery of corticosteroids (Pred or particularly Bud) in more effective asthma therapy, having fewer side effects due to the nanoformulation.

Arrangement of lipid vesicles and bicelle-like structures formed in the presence of Aβ(25–35) peptide

Our complementary experimental data and molecular dynamics (MD) simulations results reveal the structure of previously observed lipid bicelle-like structures (BLSs) formed in the presence of amyloid-beta peptide Aβ(25–35) below the main phase transition temperature (Tm) of saturated phosphatidylcholine lipids and small unilamellar vesicles (SUVs) above this temperature. First, we show by using solid-state 31P nuclear magnetic resonance (NMR) spectroscopy that our BLSs being in the lipid gel phase demonstrate magnetic alignment along the magnetic field of NMR spectrometer and undergo a transition to SUVs in the lipid fluid phase when heated through the Tm. Secondly, thanks to the BLS alignment we present their lipid structure. Lipids are found located not only in the flat bilayered part but also around its perimeter, which is corroborated by the results of coarse-grained (CG) MD simulations. Finally, peptides appear to mix randomly with lipids in SUVs while assuming predominantly unordered secondary structures revealed by circular dichroism (CD), Raman spectroscopy, and all-atom MD simulations. Importantly, the former is changing little when the system undergoes morphological transitions between BLSs and SUVs. Our structural results then offer a platform for studying and understanding mechanisms of morphological transformations caused by the disruptive effect of amyloid-beta peptides on the lipid bilayer.

Asipimoksun DPPC Model Membranlar Üzerindeki Etkilerinin Kalorimetrik İncelenmesi

Liposomes or model membranes are widely used basic systems which mimic biological membranes. In this study, the physical interaction between dipalmitoyl phosphatidylcholine (DPPC) and the lipid-lowering drug acipimox was investigated using Differential Scanning Calorimetry (DSC) technique depending on different acipimox concentrations and temperature. The changes in the phase transition temperature, phase transition enthalpy and phase transition curve half-height width of the model membranes were taken into account. According to the DSC results, with the addition of acipimox into pure DPPC model membranes, the main phase transition temperature curve, which is around 41 °C, shifted to slightly higher temperatures, while the pre-transition temperature curve, which is around 35 °C, did not disappear. Moreover, increasing acipimox concentrations caused a slight broadening of the DSC thermograms of the model membrane DPPC. Since it is very important to understand the pharmacological activity of drugs in biomembranes, the investigation of the interaction between lipid-lowering drug acipimox and lipids may contribute to the biological effects of acipimox at the molecular level.

Determination of the Main Phase Transition Temperature of Phospholipids by Oscillatory Rheology.

Knowledge of the physical and chemical properties of phospholipids, such as phase transition temperatures (Tc), is of great importance in order to reveal the functionalities of biological and artificial membranes. Our research group developed an oscillatory rheological method for the simple and rapid determination of phase transition temperatures (Tc). The phospholipids constructing the membranes undergo conformational changes at their Tc, which cause alterations of viscoelastic properties of the molecules. The oscillatory technique recommended by us proved to be appropriate to reveal the altered molecular properties of phospholipids as tracking the slightest changes in the viscoelasticity. Our study demonstrates the abrupt changes in rheological properties at Tc for the following phospholipids: 1,2-Dimyristoyl-sn-glycero-3-Phosphocholine (DMPC), 1,2-Dipalmitoyl-sn-glycero-3-Phosphatidylcholine (DPPC), and 1,2-Distearoyl-sn-glycero-3-Phosphocholine (DSPC), proving that the applied methodology is adequate for determining the Tc of phospholipids.

Interactions between DMPC Model Membranes, the Drug Naproxen, and the Saponin β-Aescin.

In this study, the interplay among the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) as a model membrane, the nonsteroidal anti-inflammatory drug naproxen, and the saponin β-aescin are investigated. The naproxen amount was fixed to 10 mol%, and the saponin amount varies from 0.0 to 1.0 mol%. Both substances are common ingredients in pharmaceutics; therefore, it is important to obtain deeper knowledge of their impact on lipid membranes. The size and properties of the DMPC model membrane upon naproxen and aescin addition were characterized with differential scanning calorimetry (DSC), small- and wide-angle X-ray scattering (SAXS, WAXS), and photon correlation spectroscopy (PCS) in a temperature-dependent study. The interaction of all substances was dependent on the lipid phase state, which itself depends on the lipid's main phase transition temperature Tm. The incorporation of naproxen and aescin distorted the lipid membrane structure and lowers Tm. Below Tm, the DMPC-naproxen-aescin mixtures showed a vesicle structure, and the insertion of naproxen and aescin influenced neither the lipid chain-chain correlation distance nor the membrane thickness. Above Tm, the insertion of both molecules instead induced the formation of correlated bilayers and a decrease in the chain-chain correlation distance. The presented data clearly confirm the interaction of naproxen and aescin with DMPC model membranes. Moreover, the incorporation of both additives into the model membranes is evidenced.

Storage stability, heat stability, controlled release and antifungal activity of liposomes as alternative fungal preservation agents

The aim of this study was to investigate the characteristics of liposomes encapsulated ethanolic Cinnamomum verum, Curcuma longa, Zingiber officinale, Syzygium aromaticum and Laurus nobilis extract prepared using lipid phase containing phosphatidylcholine/extract mixture of 10:1. The antifungal activity, size, zeta (ζ) potential, morphology, physical stability, heat stability, release in in-vitro digestion, color and differential scanning calorimetry (DSC) were conducted to determine the characteristics of liposomes. All extract-loaded liposomes showed prominently antifungal activity against Aspergillus sp. and Penicillium sp. The encapsulation efficiency of all samples was 86.60%–92.87%. Curcuma longa loaded liposome had high encapsulation efficiency after freeze dry-rehydration (FD-RH), long-term and freeze-thaw (FT) storage treatment. The thermal stability of Syzygium aromaticum loaded liposomes was higher than the others. The highest release values in the in-vitro gastric and intestinal condition were detected in Laurus nobilis loaded liposome. DSC data of liposomes demonstrated to be the endothermic phase at three different temperature ranges: lipid bilayers transition from gel state to liquid crystal form (1.69–5.31 °C), the pre-phase transition temperature (102.16–133.10 °C) and the main phase transition temperature (116.47–165.22 °C).

Long chain ceramides raise the main phase transition of monounsaturated phospholipids to physiological temperature

Little is known about the molecular mechanisms of ceramide-mediated cellular signaling. We examined the effects of palmitoyl ceramide (C16-ceramide) and stearoyl ceramide (C18-ceramide) on the phase behavior of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) using differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS, WAXS). As previously published, the presence of ceramides increased the lamellar gel-to-lamellar liquid crystalline (Lβ–Lα) phase transition temperature of POPC and POPE and decreased the Lα-to-inverted hexagonal (Lα–HII) phase transition temperature of POPE. Interestingly, despite an ~ 30° difference in the main phase transition temperatures of POPC and POPE, the Lβ–Lα phase transition temperatures were very close between POPC/C18-ceramide and POPE/C18-ceramide and were near physiological temperature. A comparison of the results of C16-ceramide in published and our own results with those of C18-ceramide indicates that increase of the carbon chain length of ceramide from 16 to 18 and/or the small difference of ceramide content in the membrane dramatically change the phase transition temperature of POPC and POPE to near physiological temperature. Our results support the idea that ceramide signaling is mediated by the alteration of lipid phase-dependent partitioning of signaling proteins.

Ruscogenin interacts with DPPC and DPPG model membranes and increases the membrane fluidity: FTIR and DSC studies

Ruscogenin, a kind of steroid saponin, has been shown to have significant anti-oxidant, anti-inflammatory, and anti-thrombotic characteristics. Furthermore, it has the potential to be employed as a medicinal medication to treat a variety of acute and chronic disorders. The interaction of a drug molecule with cell membranes can help to elucidate its system-wide protective and therapeutic effects, and it's also important for its pharmacological activity. The molecular mechanism by which ruscogenin affects membrane architecture is still a mystery. Ruscogenin's interaction with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) and anionic dipalmitoyl phosphatidylglycerol (DPPG) multilamellar vesicles (MLVs) was studied utilizing two non-invasive approaches, including: Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry. Ruscogenin caused considerable alterations in the phase transition profile, order, dynamics and hydration state of head groups and glycerol backbone of DPPC and DPPG MLVs at all concentrations. The DSC results indicated that the presence of ruscogenin decreased the main phase transition temperature (Tm) and enthalpy (ΔH) values of both membranes and increased half height width of the main transition (ΔT1/2). The FTIR results demonstrated that all concentrations (1, 3, 6, 9, 15, 24 and 30 mol percent) of ruscogenin disordered the DPPC MLVs both in the gel and liquid crystalline phases while it increased the order of DPPG MLVs in the liquid crystalline phase. Moreover, ruscogenin caused an increase in the dynamics of DPPC and DPPG MLVs in both phases. Additionally, it enhanced the hydration of the head groups of lipids and the surrounding water molecules implying ruscogenin to interact strongly with both zwitterionic and charged model membranes.

Effect of Distigmasterol-Modified Acylglycerols on the Fluidity and Phase Transition of Lipid Model Membranes.

Plant sterols are known for their health-promoting effects, lowering blood cholesterol levels and alleviating cardiovascular disease. In this work, we continue our research on the asymmetric acylglycerols in which fatty acid residues are replaced by two stigmasterol residues in sn-1 and sn-2 or sn-2 and sn-3 positions as new thermostable carriers of phytosterols for their potential application in foods or as components of new liposomes in the pharmaceutical industry. The aim of this manuscript was to compare and analyze the effects of four distigmasterol-modified acylglycerols (dStigMAs) on the fluidity and the main phase transition temperature of the model phospholipid membrane. Their properties were determined using differential scanning calorimetry (DSC), steady-state fluorimetry and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). The determination of the effect of the tested compounds on the mentioned physicochemical parameters of the model membranes will allow for the determination of their properties and stability, which is essential for their practical application. The results indicated that all compounds effect on the physicochemical properties of the model membrane. The degree of these changes depends on the structure of the compound, especially the type of linker by which stigmasterol is attached to the glycerol backbone, as well as on the type of hydrocarbon chain.

Monitoring lipid phase transition temperatures using fluorescent probes and temperature-dependent fluorescence spectroscopy

The response of fluorescent dyes incorporated in multilamellar liposomes was evaluated for their applicability in monitoring thermal-induced changes in liposomes. Five fluorescent probes, diverse in polarity, lipophilicity, and consequently their position within the lipid multibilayers constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), were used to record temperature-dependent fluorescence spectra of the liposomal suspensions. The responses of the dyes were analysed in a multivariate fashion to determine pre- and main phase transition temperatures of DPPC. Laurdan® and 1-chloro-9,10-bis(phenylethynyl)anthracene register both phase transitions, while 9,10-diphenylanthracene and 9,10-bis(phenylethynyl)anthracene report only pretransition. According to the differential scanning calorimetry (DSC) measurements, all suspensions display both phase transitions that resemble DSC curve of pure DPPC. The positions of the dyes within the bilayers were determined by molecular dynamics simulations.

Shear stress induced lipid order and permeability changes of giant unilamellar vesicles

BackgroundThe permeability of a lipid bilayer is a function of its phase state and depends non-linearly on thermodynamic variables such as temperature, pressure or pH. We investigated how shear forces influence the phase state of giant unilamellar vesicles and their membrane permeability. MethodsWe determined the permeability of giant unilamellar vesicles composed of different phospholipid species under shear flow in a tube at various temperatures around and far off the melting point by analyzing the release of fluorescently labelled dextran. Furthermore, we quantified phase state changes of these vesicles under shear forces using spectral decomposition of the membrane embedded fluorescent dye Laurdan. ResultsWe observed that the membrane permeability follows a step function with increasing permeability at the transition from the gel to the fluid phase and vice versa. Second, there was an all-or-nothing permeabilization near the main phase transition temperature and a gradual dye release far off the melting transition. Third, the Laurdan phase state analysis suggests that shear forces induce a reversible melting temperature shift in giant unilamellar vesicle membranes. Major conclusionsThe observed effects can be explained best in a scenario in which shear forces directly induce membrane pores that possess relatively long pore lifetimes in proximity to the phase transition. General significanceOur study elucidates the release mechanism of thermo-responsive drug carriers as we found that liposome permeabilization is not continuous but quantized. Furthermore, the shear force induced melting temperature shift must be taken into consideration when thermo-responsive liposomes are designed.

Trans-Resveratrol Decreases Membrane Water Permeability: A Study of Cholesterol-Dependent Interactions.

Resveratrol (RSV), a biologically active plant phenol, has been extensively investigated for cancer prevention and treatment due to its ability to regulate intracellular targets and signaling pathways which affect cell growth and metastasis. The non-specific interactions between RSV and cell membranes can modulate physical properties of membranes, which in turn can affect the conformation of proteins and perturb membrane-hosted biological functions. This study examines non-specific interactions of RSV with model membranes having varying concentrations of cholesterol (Chol), mimicking normal and cancerous cells. The perturbation of the model membrane by RSV is sensed by changes in water permeability parameters, using Droplet Interface Bilayer (DIB) models, thermotropic properties from Differential Scanning Calorimetry, and structural properties from confocal Raman spectroscopy, all of which are techniques not complicated by the use of probes which may themselves perturb the membrane. The nature and extent of interactions greatly depend on the presence and absence of Chol as well as the concentration of RSV. Our results indicate that the presence of RSV decreases water permeability of lipid membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), indicating a capability for RSV in stiffening fluidic membranes. When Chol is present, however, (at 4:1 and 2:1mol ratio DOPC to cholesterol), the addition of RSV has no significant effect upon the water permeability. DSC thermograms show that RSV interacts with DOPC and DOPC/Chol bilayers and influences their thermotropic phase behavior in a concentration-dependent manner, by decreasing the main phase transition temperature and enthalpy, with a phase separation shown at the higher concentrations of RSV. Raman spectroscopic studies indicate an ordering effect of RSV on DOPC supported bilayer, with a lesser extent of ordering in the presence of Chol. Combined results from these investigations highlight a differential effect of RSV on Chol-free and Chol-enriched membranes, respectively, which results constitute a bellwether for increased understanding and effective use of resveratrol in disease therapy including cancer.

Influence of melatonin on the structural and thermal properties of SOPC lipid membranes

Melatonin, a hormone secreted by the pineal gland in the brain, plays a key role in the regulation of sleep-wake cycles. Due to its antioxidant and free radical scavenging properties, it has shown promising protective effects against cancer, and neurodegenerative disorders. Studies pertaining to the use of melatonin and its biophysical effects on cell membranes are important for their biomedical implications. The main goal of our study is to investigate the effect of melatonin on the thermal and structural properties of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) phospholipid membranes using sensitive techniques such as Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). For this purpose, SOPC lipid bilayer membranes were prepared with different melatonin concentrations (10–50 mol%). DSC results have indicated that melatonin strongly interacts with the membrane lipids in a concentration-dependent fashion to form domains and alters the phase behavior by reducing the main phase transition temperature, lipid order, and increasing membrane fluidity. FTIR data have shown that increasing the melatonin concentration caused a reduction in the wavenumber of CO and PO2−antisymmetric stretching vibrations, indicating the possibility of strong hydrogen bonding between melatonin and the SOPC lipid with the nearby water molecules in the environment, suggesting its preferential location near lipid head groups at the interfacial region. Understanding the organization of melatonin in membranes and its influence on membrane properties is important to gain thorough knowledge and to develop safe melatonin-based formulations for therapeutic applications.

Spray Dried Rugose Lipid Particle Platform for Respiratory Drug Delivery.

To develop a new lipid-based particle formulation platform for respiratory drug delivery applications. To find processing conditions for high surface rugosity and manufacturability. To assess the applicability of the new formulation method to different lipids. A new spray drying method with a simplified aqueous suspension feedstock preparation process was developed for the manufacture of rugose lipid particles of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). A study covering a wide range of feedstock temperatures and outlet temperatures was conducted to optimize the processing conditions. Aerosol performance was characterized in vitro and in silico to assess the feasibility of their use in respiratory drug delivery applications. The applicability of the new spray drying method to longer-chain phospholipids with adjusted spray drying temperatures was also evaluated. Highly rugose DSPC lipid particles were produced via spray drying with good manufacturability. A feedstock temperature close to, and an outlet temperature lower than, the main phase transition were identified as critical in producing particles with highly rugose surface features. High emitted dose and total lung dose showed promising aerosol performance of the produced particles for use as a drug loading platform for respiratory drug delivery. Two types of longer-chain lipid particles with higher main phase transition temperatures, 1,2-diarachidoyl-sn-glycero-3-phosphocholine (DAPC) and 1,2-dibehenoyl-sn-glycero-3-phosphocholine (22:0 PC), yielded similar rugose morphologies when spray dried at correspondingly higher processing temperatures. Rugose lipid particles produced via spray drying from an aqueous suspension feedstock are promising as a formulation platform for respiratory drug delivery applications. The new technique can potentially produce rugose particles using various other lipids.

Structure of gel phase di-C22:1PC lipid bilayers

There has been a dearth of structural studies of the low temperature bilayer phases of unsaturated phophocholine lipids, partly because most of them have inconveniently low main phase transition temperatures TM as temperature is lowered from the fluid phase. This paper studies the phase behavior of bilayers of the long chain diC22:1PC lipids and the structure at temperatures below the TM of 13 °C. We were curious whether a ripple phase forms below TM, and whether there are gel and subgel phases like those that occur in saturated chain PC lipid bilayers.

The impact of the surfactant type on physicochemical properties, encapsulation, and in vitro biocompatibility of coconut oil nanoemulsions

Background: This study investigated the effects of the three types of surfactants including polyethylene glycol 100-stearate (S-PEG100), hydrogenated soybean lecithin (HL), and dimethyldiocatadecylammonium (DODAB) on the physicochemical characteristics, encapsulation, and in vitro biocompatibility of coconut oil (CO) nanoemulsions (NEs).Methods: Size distribution, zeta-potential, structure, and storage stability of the CO NEs were comprehensively studied. The intra-particle and rheological properties of NEs were assessed by using differential scanning calorimetry, fluorescence polarization analysis, and viscosity measurement. The in vitro biocompatibility and the encapsulation efficiency of CO NEs emulsified with S-PEG100, HL, and DODAB were also evaluated.Significant Findings: The size order was S-PEG100-<HL-<DODAB- CO NEs. The main phase-transition enthalpy, main phase-transition temperature, and intra-particle fluidity of CO NEs with HL and DODAB increased with increasing the surfactant/oil ratio, whereas they decreased for NEs with S-PEG100. Moreover, CO NEs with S-PEG100 and HL exhibited Newtonian fluid behavior, while NEs with DODAB behaved like pseudoplastic fluid. Furthermore, the cytotoxicity of NEs with DODAB was higher than those with S-PEG100 and HL. The encapsulation efficiency of NEs with DODAB was higher than those with S-PEG100 and HL.

The activity of the intrinsically water-soluble enzyme ADAMTS13 correlates with the membrane state when bound to a phospholipid bilayer

Membrane-associated enzymes have been found to behave differently qualitatively and quantitatively in terms of activity. These findings were highly debated in the 1970s and many general correlations and reaction specific models have been proposed, reviewed, and discarded. However, new biological applications brought up the need for clarification and elucidation. To address literature shortcomings, we chose the intrinsically water-soluble enzyme a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) and large unilamellar vesicles with a relative broad phase transition. We here present activity measurements of ADAMTS13 in the freely dissolved state and the membrane associated state for phosphocholine lipids with different acyl-chain lengths (13:0, 14:0 and 15:0) and thus main phase transition temperatures. While the freely dissolved enzyme shows a simple Arrhenius behavior, the activity of membrane associated ADAMTS13 in addition shows a peak. This peak temperature correlates with the main phase transition temperature of the used lipids. These findings support an alternative theory of catalysis. This theory predicts a correlation of the membrane associated activity and the heat capacity, as both are susceptibilities of the same surface Gibb’s free energy, since the enzyme is attached to the membrane.