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PubMed2005

A quantitative assessment of the significance of molecular mobility as a determinant for the stability of lyophilized insulin formulations.

PURPOSE: The purpose was to explore a method for quantitatively assessing the contribution of molecular mobility to the chemical reactivity of amorphous solids. Degradation of insulin in lyophilized formulations containing trehalose and poly(vinylpyrrolidone)(PVP) was chosen as a model system, and the temperature- and glass transition temperature (Tg)-dependence of the degradation rate was analyzed to obtain the relative contributions of molecular mobility and that of the chemical activational barrier reflected in the energy of activation. METHODS: Insulin degradation and dimerization in lyophilized trehalose and PVP formulations were monitored at various relative humidities (6-60% RH) and temperatures (10-60 degrees C) by reverse-phase high-performance liquid chromatography (HPLC) and high-performance size-exclusion chromatography (HP-SEC), respectively. The Tg and fragility parameter of the lyophilized insulin formulations were determined by differential scanning calorimetry (DSC). RESULTS: Insulin degradation in the initial stage was describable with first-order kinetics for both of the trehalose and PVP formulations. The temperature- and Tg-dependence of the degradation rate indicated that the reactivity of insulin in the trehalose formulation is affected by molecular mobility at low humidity (12% RH), such that the ratio of the observed rate constant (k') to the rate constant governed only by the activational barrier (k) was 0.051 at the Tg. At higher humidities, in contrast, the value of k'/k was much higher (0.914, 0.978, and 0.994 for 23% RH, 33% RH, and 43% RH, respectively), indicating that insulin degradation rate is determined predominantly by the activational barrier. For insulin degradation in the PVP formulation at temperatures below Tg, the contribution of molecular mobility to the degradation rate appeared to be negligible, as the extrapolated value of t90 at the Tg exhibited a large difference between the formulations with differing Tg values (because of differing water contents). CONCLUSIONS: The reactivity of insulin in the trehalose and PVP formulations can be described by an equation including factors reflecting the activational barrier (activation energy and frequency coefficient) and factors reflecting the molecular mobility (Tg, fragility parameter and a constant representing the relationship between the molecular mobility and the reaction rate). Thus, analysis of temperature dependence based on the proposed equation allows quantitative assessment of the significance of molecular mobility as a factor affecting chemical reactivity.

Calorimetry, Differential Scanning↗

PubMed1983

Physical separation of the aqueous phase and lipoidal lamellae from multilamellar liposomes: an analytical and preparative procedure.

An efficient and rapid method to separate the aqueous phase from lipoidal lamellae after mechanical disruption of multilamellar liposomes with preservation of the phospholipid bilayer organization has been designed. Liposome suspensions were subjected to a few short bursts of sonication at a temperature below the transition temperature (Tc) of the lowest melting phospholipid component. This was followed by ultracentrifugation. The aqueous supernatant contained more than 90% of the encapsulated aqueous elements (6-carboxyfluorescein, bovine serum albumin) and less than 1% of the lipids. The washed pellet consisted of lipoidal lamellae devoid of any encapsulated aqueous phase. The lipoidal lamellae contained more than 99% phospholipids and were contaminated with less than 0.1% aqueous components. Such a method should allow the localization of any component within the aqueous phase or lipoidal lamellae of the liposomes.

Chemical Phenomena↗

PubMed1987

Anisotropy decay of diphenylhexatriene in melittin-phospholipid complexes by multifrequency phase-modulation fluorometry.

Frequency-domain fluorometry was used to investigate the intensity and anisotropy decays of diphenylhexatriene (DPH) in melittin-lipid complexes. Simulated and experimental data indicate that correlation times ranging from 0.3 to 500 ns can be determined using data from 1 to 200 MHz. For the melittin-lipid complexes the hindered rotator model was not adequate to account for the anisotropy decays, especially at temperatures above the transition temperatures. At high protein-to-lipid ratios the data revealed the formation of small particles (100 A) of melittin and dipalmitoylphosphatidylcholine and the disruption of membrane order in bilayers of dipalmitoylphosphatidic acid.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1988

The binding of 8-anilino-1-naphthalene sulfonate (ANS) to fish myosin and the effect of salts on the thermal transitions of fish myosin-ANS complex.

Myosin prepared from tilapia (Serotherodon aureus) was complexed with 8-anilino-1-naphthalene sulfonate (ANS) and continuously heated at 1 degree C/min. A large increase in fluorescence was observed with a transition temperature of 34 degrees C. The effect of several salts on the transition temperature was tested. A plot based on the equation of E. E. Schrier and E. B. Schrier [(1967) J. Phys. Chem. 71, 1851-1860] gave a value of less than or equal to 500 cal/mol-deg for the change in enthalpy per residue due to exposure to solvent. The ratio of hydrophobic group to amide group exposure to solvent was intermediate compared with the ratio of RNase and gelatin. Fluorescence titrations yielded one high affinity site with a Kb of 2 X 10(6) M-1 and at least 200 low affinity sites with an average value of 1 X 10(5) M-1. The parameters did not change significantly with temperature. We propose that the increase in ANS fluorescence reflects changes in conformation of myosin as monitored by these low affinity sites, resulting in an increase in surface hydrophobicity and representing a small enthalpic change in the conformation of the myosin molecule. As a consequence, the change in conformation accelerates polymerization of myosin oligomers.

Anilino Naphthalenesulfonates↗

PubMed1982

Kinetic characteristics of bicarbonate-chloride exchange across the neonatal human red cell membrane.

The kinetics of HCO-3/Cl- exchange across red cell membrane of newborn infants was studied using a stopped-flow rapid reaction apparatus with a glass pH electrode attached. The measured apparent permeability P is (1.35 +/- 0.08 (S.E.)). 10(-4) cm/s (n = 30) for newborns, compared with (3.1 +/- 0.4) . 10(-4) cm/s (n = 15) for adults. These correspond to half-times of 0.2 s for newborns and 0.1 s for adults indicating that neonatal red cells exchange Cl- for HCO-3 only half as fast as do adult cells. The temperature dependence of the exchange rate was studied from 2 to 42 degrees C. From the Arrhenius plot the activation energy of the exchange process in neonatal red cells changes from 22.9 kcal/mol (low temperature) to 4.8 kcal/mol (physiological temperature) at a transition temperature of 17 degrees C. These values are lower than the corresponding values for adult red cells, 34.7 and 10.2 kcal/mol. HCO-3/Cl- exchanges in both adult and neonatal red cells are inhibited by phlorizin. Inhibition constants Ki are 0.8 mM and 2.5 mM for adults and newborns, respectively. The differences in the value of the HCO-3/Cl- exchange rate constant and the activation energy of the exchange process between neonatal and adult red cells indicate that there is a modification of HCO-3/Cl- transport system in the neonatal red cell membranes.

Adult↗

PubMed1983

Comparison of the enthalpy state of vesicles of different size by their interaction with alpha-lactalbumin.

The characteristics of small unilamellar, large unilamellar and large multilamellar vesicles of dimyristoylphosphatidylcholine and their interaction with alpha-lactalbumin are compared at pH 4. (1) By differential scanning calorimetry and from steady-state fluorescence anisotropy data of the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene it is shown that the transition characteristics of the phospholipids in the large unilamellar vesicles resemble more those of the multilamellar vesicles than of the small unilamellar vesicles. (2) The size and composition of the lipid-protein complex formed with alpha-lactalbumin around the transition temperature of the lipid are independent of the vesicle type used. Fluorescence anisotropy data indicate that in this complex the motions of the lipid molecules are strongly restricted in the presence of alpha-lactalbumin. (3) The previous data and a comparison of the enthalpy changes, delta H, of the interaction of the three vesicle types with alpha-lactalbumin allow us to derive that the enthalpy state of the small unilamellar vesicles just below 24 degrees C is about 24 kJ/mol lipid higher than the enthalpy state of both large vesicle types at the same temperature. The abrupt transition from endothermic to exothermic delta H values around 24 degrees C for large vesicles approximates the transition enthalpy of the pure phospholipid.

Calorimetry, Differential Scanning↗

PubMed1986

Free volume model for lipid lateral diffusion coefficients. Assessment of the temperature dependence in phosphatidylcholine and phosphatidylethanolamine bilayers.

The lipid lateral diffusion coefficients, DT, in fluid-phase phosphatidylcholine and phosphatidylethanolamine bilayers have been analysed in terms of the free-volume diffusion model by fitting the expression: DT = AT exp[- B/(T - T0)] to the observed temperature dependence, where A, B and T0 are the parameters to be optimized. Application of an unconstrained optimization procedure to data obtained from excimer formation (Galla et al. (1979) J. Membrane Biol. 48, 215-236) and from fluorescence photobleaching (Vaz et al. (1985) Biochemistry 24, 781-786) provides statistical evidence for a free-volume model as opposed to a simple Stokes-Einstein model (T0 = 0), only in certain cases. In the instances for which the parameter T0 can be determined with a reasonable degree of accuracy, it is found that this characteristic temperature at which the free volume extrapolates to zero lies below the bilayer gel-to-fluid phase transition temperature and does not coincide with the pre-transition temperature for phosphatidylcholines.

Diffusion↗

PubMed1988

Effect of stereoconfiguration on ripple phases (P beta') of dipalmitoylphosphatidylcholine.

Mixtures of sn-1 (D) and sn-3 (L) enantiomers of fully hydrated dipalmitoylphosphatidylcholine (DPPC) were studied with differential scanning calorimetry and freeze-fracture microscopy. The pretransition temperature of racemic mixtures of DPPC was 1.8 C degrees below that of either pure sn-1 or sn-3 enantiomers, which had similar pretransition temperatures. The main transition temperature of racemic mixtures was also depressed, but to a lesser extent, 0.8 C degrees. Freeze-fracture images of liposomes of sn-1, sn-3, and racemic mixtures of DPPC frozen from the P beta' phase showed well-defined ripples of wavelength 13 nm. Lipid stereoconfiguration had no effect on ripple wavelength, configuration or amplitude, or on the number and nature of surface defects.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1989

Differential affinity of charged local anesthetics to solid-gel and liquid-crystalline states of dimyristoylphosphatidic acid vesicle membranes.

Cationic local anesthetics decreased the transition temperature of the anionic phospholipid (dimyristoylphosphatidic acid, DMPA) vesicles. The counterion concentration changes the electrical double layer effect, and affects the magnitude of temperature depression caused by anesthetics. From the counterion effect on the transition-temperature depression, the partition coefficients of cationic local anesthetics to liquid-crystalline and solid-gel DMPA membranes were separately estimated. The differences in the partition coefficients between solid-gel and liquid-crystalline membranes correlated to the nerve blocking potencies. There are at least two states in the nerve membranes: resting state at higher temperature and excited state at lower temperature. We speculate that the resting state corresponds to the liquid-crystalline state, and the excited state to the solid-gel state. The difference in the partition coefficients to the resting and excited states is the cause of local anesthesia.

Anesthetics, Local↗

PubMed1992

Mechanisms of heterogeneity of Na(+)-Pi cotransport in superficial and juxtamedullary renal cortex.

To explore the mechanisms of axial heterogeneity of proximal tubular Pi transport, brush border membrane vesicles (BBMV) were prepared from superficial (BBMV-SC) and juxtamedullary (BBMV-JM) cortex of rat kidneys. Na+ gradient-dependent Pi transport was measured after the imposition of an inside-negative electrical potential created by either a K+ gradient ([K+]i greater than [K+]o) or a proton gradient ([H+]i greater than [H+]o) in the presence of ionophores. The initial Na(+)-dependent Pi uptake was higher in BBMV-SC than in BBMV-JM, both in the presence and absence of ionophores. Na(+)-dependent D-glucose uptake remained unchanged. We did not find a significant electrogenic transport component in either BBMV population when the non-specific effect of ionophores on Pi transport was taken into account. The stoichiometry of Na(+)-Pi cotransport was 2:1 in BBMV-SC and BBMV-JM. Phosphonoformic acid (PFA) competitively inhibited Pi transport. The inhibitory constant (Ki) for PFA was lower in BBMV-SC (237 +/- 1.7 microM) than in BBMV-JM (409 +/- 53 microM) (P less than 0.05). Arrhenius plots showed a higher rate of Pi uptake in BBMV-SC compared to BBMV-JM at all temperatures. However, the transition temperatures did not differ. We conclude that axial heterogeneity of Pi transport is not due to differences in electrogenicity or stoichiometry of transport.

Animals↗

PubMed1996

Interdigitation of bilayers from ether lipid analogs: (R)-PAF, (R)-Lyso-PAF and the antineoplastic (R)-ET-18-OMe.

The ether lipid analogs (R)-PAF, (R)-ET-18-OMe and (R)-Lyso-PAF can form bilayers. Using differential scanning calorimetry (DSC) and small angle X-ray diffraction, we have investigated bilayers formed entirely of these molecules. Small angle X-ray diffraction experiments strongly indicated that these bilayers are interdigitated at 98% relative humidity in the gel phase. The slight differences in the structures of the ether lipids affect their thermal behavior and packing properties. Of the three, (R)-Lyso-PAF shows the highest phase transition temperature, broadest phase transition peak and smallest enthalpy change. These characteristics may be attributed to hydrogen bonding of the -OH group at sn-2 position of its glycerol backbone to water or to other (R)-Lyso-PAF molecules. The interdigitated structure shows that these bilayers are similar to lipid bilayers and suggests that these molecules could easily insert themselves into membranes to reach their respective active sites or to perturb the membranes. The packing and thermal characteristics of (R)-Lyso-PAF may help explain its biological inactivity.

Antineoplastic Agents↗

PubMed1989

Physico-chemical properties of cholesterol-fed rabbit beta-VLDL are not affected by different dietary oils.

Various oils have been used as vehicles for cholesterol in diets used to produce atherosclerosis in rabbits. Because such oils may affect the physico-chemical properties of the beta-VLDL produced in response to cholesterol feeding, we have studied the physico-chemical characteristics of beta-VLDL isolated from cholesterol-fed rabbits using several different oils as vehicles (corn, safflower, cod liver, and peanut oils). All animals developed severe hypercholesterolemia by 2 weeks. During the second and third weeks on diet the apo beta-containing lipoproteins began to develop thermal transitions due to order-disorder cholesterol ester transitions in the lipoproteins. By 4 weeks the apo beta-containing lipoproteins (overwhelmingly beta-VLDL) had transitions which were quite similar (transition temperatures 41.0-42.5 degrees C). No statistical differences were noted between the transition temperatures or enthalpies of any of the dietary groups. Thus, the physico-chemical properties of the beta-VLDL of rabbits fed cholesterol appear to be quite similar, despite the vehicles used to carry the cholesterol in the diet. Thus other mechanisms must be looked for to explain the different atherogenicity of different oils used as cholesterol carrying vehicles.

Animals↗

PubMed1987

Changes in physicochemical properties of mitochondrial membranes during the formation process of megamitochondria induced by hydrazine.

Changes in some biochemical and physico-chemical properties of rat liver mitochondrial membranes during the formation process of megamitochondria induced by hydrazine were analyzed. Hepatic mitochondria obtained from rats placed on a 1% hydrazine diet for 3 days became slightly enlarged and sometimes elongated, while they became gigantic after 7 days of hydrazine intoxication. Changes were observed in mitochondria from rats treated with hydrazine for 3 days. Total amounts of phospholipids extracted from mitochondria and submitochondrial fractions were increased. Among phospholipid species, relative amounts of acidic phospholipids were increased. Contents of Ca2+ in mitochondria were increased. Differential scanning calorimetric analysis of mitochondria, especially that of the outer membrane fraction, showed that the thermotropic lipid phase transition temperatures were elevated accompanying the broadening of thermograms and the increase in transition enthalpy. Contents of water in mitochondria were increased significantly with the ratio of freezable water to unfreezable water unchanged. Among the changes observed was that the total amount of phospholipids (except for that of the outer membrane fraction) and the contents of water and Ca2+ nearly returned to normal in megamitochondria after 7 days of hydrazine intoxication. Relative amounts of phospholipids and thermotropic lipid phase transition temperatures of megamitochondria did not return to normal levels and yet changes were smaller than those obtained from 3 days of hydrazine intoxication. The fluidity of mitochondrial membranes was not affected by hydrazine treatment. These data would suggest that hydrazine-induced megamitochondrial formation is not due simply to the swelling of mitochondria, but might be due to the fusion of adjacent mitochondria by Ca2+-acidic phospholipid interactions, and once megamitochondria are formed the mitochondrial membranes are stabilized.

Animals↗

PubMed2004

Membrane properties of plant sterols in phospholipid bilayers as determined by differential scanning calorimetry, resonance energy transfer and detergent-induced solubilization.

The increased use of plant sterols as cholesterol-lowering agents warrants further research on the possible effects of plant sterols in membranes. In this study, the effects of the incorporation of cholesterol, campesterol, beta-sitosterol and stigmasterol in phospholipid bilayers were investigated by differential scanning calorimetry (DSC), resonance energy transfer (RET) between trans parinaric acid (tPA) and 2-(6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoyl-1-hexadecanoyl-sn-glycero-3-phosphocholine (NBD-PC), and Triton X-100-induced solubilization. The phospholipids used were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), D-erythro-N-palmitoyl-sphingomyelin (PSM), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). In DSC experiments, it was demonstrated that the sterols differed in their effect on the melting temperatures of both the sterol-poor and the sterol-rich domains in DPPC and PSM bilayers. The plant sterols gave rise to lower temperatures of both transitions, when compared with cholesterol. The plant sterols also resulted in lower transition temperatures, in comparison with cholesterol, when sterol-containing DPPC and PSM bilayers were investigated by RET. In the detergent solubilization experiments, the total molar ratio between Triton X-100 and POPC at the onset of solubilization (R(t,sat)) was higher for bilayers containing plant sterols, in comparison with membranes containing cholesterol. Taken together, the observations presented in this study indicate that campesterol, beta-sitosterol and stigmasterol interacted less favorably than cholesterol with the phospholipids, leading to measurable differences in their domain properties.

Androstanes↗

PubMed2006

Evaluation of the interaction of surfactants with stratum corneum model membrane from Bothrops jararaca by DSC.

The interaction of surfactants sodium dodecyl sulfate (SDS), cetyl trimethyl ammonium chloride (CTAC) and lauryl alcohol ethoxylated (12 mol ethylene oxide) (LAE-12OE) was evaluated on the stratum corneum (SC) of shed snake skins from Bothrops jararaca, used as model membrane, and thermal characterized by differential scanning calorimetry (DSC). Surfactant solutions were employed above of the critical micellar concentration (CMC) with treatment time of 8h. The SDS interaction with the SC model membrane has increased the characteristic transition temperature of 130 degrees C in approximately 10 degrees C for the water loss and keratin denaturation, indicating an augmentation of the water content. Samples treated with CTAC have a decrease of the water loss temperature, while, for the LAE-12OE treated samples, changes on the transition temperature have not been observed.

Animals↗

PubMed2005

Cerebrocrast promotes the cotransport of H+ and Cl- in rat liver mitochondria.

Considering that cerebrocrast stimulates oligomycin-inhibited state 3 respiration simultaneously with mitochondrial transmembrane potential (Deltapsi) dissipation, the mechanism underlying the uncoupler activity of cerebrocrast was assessed by its ability to permeabilize the mitochondrial inner membrane to H(+) or to K(+) or to cotransport anions with H(+). The partition coefficient of cerebrocrast in mitochondrial membrane and its ability to act as a membrane-active compound disturbing membrane lipid organization were also investigated. Cerebrocrast induced no permeabilization of mitochondrial inner membrane to H(+) or K(+), but it was able to transport H(+) in association with Cl(-). Cerebrocrast showed a strong incorporation into the mitochondrial membrane, with a partition coefficient (Kp(m/w)) of 2.7(+/-0.1)x10(5). Cerebrocrast also reduced, in a concentration dependent manner, the phase transition temperature, the cooperative unit size, and the enthalpy associated with the phase transition temperature of DMPC membrane bilayers. It was concluded that the uncoupler activity of cerebrocrast is due to its ability to promote the cotransport of H(+) with Cl(-) through the rat liver mitochondrial inner membrane, and that this cerebrocrast mechanism of action may be potentiated by alterations of membrane lipid organization and membrane lateral heterogeneity.

Adenosine Diphosphate↗

PubMed1987

Dynamic light-scattering study on changes in flexibility of filamentous bacteriophage Pf1 with temperature.

The temperature dependence of the flexibility of bacteriophage Pf1 was investigated by dynamic light scattering, and the following results were obtained: The gamma/K2 values measured at 1 degree-25 degrees C and at various K values were T/eta-scaled to 20 degrees C, where gamma is the first cumulant of the field correlation function of scattered light, K is the length of the scattering vector, T is the absolute temperature, and eta is the solvent viscosity at T. And it was found that the scaled gamma/K2 values at low K values were independent of temperature, whereas those at high K values increased sigmoidally and reversibly against temperature. This suggests that the virion is more flexible at temperatures above the transition temperature Tt. This characteristic temperature Tt depended on the pH of the suspension: Tt = 11 degrees C at pH 6.9 and Tt = 8 degrees C at pH 8.2.

Bacteriophages↗

PubMed1980

Radiation damage of phosphatidylcholine bilayers effects of temperature and hydration.

Structural damage by 100 kV electron irradiation in hydrated and dehydrated lecithin bilayers of different acyl chain lengths were measured by the alteration of electron diffraction patterns. At temperatures below the transition temperatures (Tc), the total diffraction intensities of both hydrated and dehydrated bilayers decreased at similar exponential rates, starting at a cumulative dose of 2 x 10(-4) C/cm2. The intensity anisotropy along diffraction rings was not noticeably altered by radiation. At temperatures less than 6 degrees from Tc, the total diffraction intensity of hydrated bilayers increased initially with radiation, while the intensity anisotropy along diffraction rings was also changed by radiation. Unsupported and hydrated bilayers at temperatures well below Tc ruptured at a cumulative dose of 10(-3) C/cm2, whereas those near or above Tc were more resistant to radiation-induced rupture. The results are discussed in terms of molecular damage, bilayer movement and annealing.

Chemical Phenomena↗