Liposomes Loaded with Cisplatin and Magnetic Nanoparticles: Physicochemical Characterization, Pharmacokinetics, and In-Vitro Efficacy.

With the aim improving drug delivery, liposomes have been employed as carriers for chemotherapeutics achieving promising results; their co-encapsulation with magnetic nanoparticles is evaluated in this work. The objective of this study was to examine the physicochemical characteristics, the pharmacokinetic behaviour, and the efficacy of pegylated liposomes loaded with cisplatin and magnetic nanoparticles (magnetite) (Cis-MLs). Cis-MLs were prepared by a modified reverse-phase evaporation method. To characterize their physicochemical properties, an evaluation was made of particle size, ζ-potential, phospholipid and cholesterol concentration, phase transition temperature (Tm), the encapsulation efficiency of cisplatin and magnetite, and drug release profiles. Additionally, pharmacokinetic studies were conducted on normal Wistar rats, while apoptosis and the cytotoxic effect were assessed with HeLa cells. We present a method for simultaneously encapsulating cisplatin at the core and also embedding magnetite nanoparticles on the membrane of liposomes with a mean vesicular size of 104.4 ± 11.5 nm and a ζ-potential of -40.5 ± 0.8 mV, affording a stable formulation with a safe pharmacokinetic profile. These liposomes elicited a significant effect on cell viability and triggered apoptosis in HeLa cells.

Size product modulation by enzyme concentration reveals two distinct levan elongation mechanisms in Bacillus subtilis levansucrase.

Two levan distributions are produced typically by Bacillus subtilis levansucrase (SacB): a high-molecular weight (HMW) levan with an average molecular weight of 2300 kDa, and a low-molecular weight (LMW) levan with 7.2 kDa. Previous results have demonstrated how reaction conditions modulate levan molecular weight distribution. Here we demonstrate that the SacB enzyme is able to perform two mechanisms: a processive mechanism for the synthesis of HMW levan and a non-processive mechanism for the synthesis of LMW levan. Furthermore, the effect of enzyme and substrate concentration on the elongation mechanism was studied. While a negligible effect of substrate concentration was observed, we found that SacB elongation mechanism is determined by enzyme concentration. A high concentration of enzyme is required to synthesize LMW levan, involving the sequential formation of a wide variety of intermediate size levan oligosaccharides with a degree of polymerization (DP) up to ∼70. In contrast, an HMW levan distribution is synthesized through a processive mechanism producing oligosaccharides with DP <20, in reactions occurring at low enzyme concentration. Additionally, reactions where levansucrase concentration was varied while the total enzyme activity was kept constant (using a combination of active SacB and an inactive SacB E342A/D86A) allowed us to demonstrate that enzyme concentration and not enzyme activity affects the final levan molecular weight distribution. The effect of enzyme concentration on the elongation mechanism is discussed in detail, finding that protein-product interactions are responsible for the mechanism shift.

How solvent determines the molecular reactive conformation and the selectivity: Solvation spheres and energy.

In solution, the solvent determines the molecular conformation and the chemical reaction viability and selectivity. When solvent-solute and solvent-solvent interactions present similar strengths, explicit salvation is the best way to describe a system. The problem to solve is how big the explicit shell should be. In this paper, we want to answer one of the fundamental questions in the implementation of explicit solvation, exactly how many solvent molecules should be added and where they should be placed. Here we determine the first solvent sphere around a molecule and describe how it controls the conformation and selectivity of a selected reaction. NMR experiments were carried out to identify the number of solvent molecules around the solute that constitutes the first solvent sphere, and the interaction between this solvent sphere and the solute was detected using DFT and QTAIM calculations. A new approach to the solvation energy is presented. Finally, we established the role of solvent molecules in the conformation of the solute and in the transition states that produce the two possible products of the reaction.

Dodecamer DNA duplex formation is characterized by second-order kinetics, positive activation energies, and a dependence on sequence and Mg2+ ion concentration.

This study provides quantitative information about the kinetics of formation of a complex between DNA oligomers having 12 bp. The DNA dodecamers were designed in such a way as to avoid the formation of hairpins or slipped duplex structures within single strands. The hybridization was carried out employing stopped-flow techniques. The reaction was studied in different buffers (phosphate or cacodylate), in the presence and absence of Mg2+ ions, and at different temperatures. Under all conditions, the reaction followed second-order kinetics. The association rate constants were on the order of 106 M(-1) s(-1) and were found to increase with an increase in temperature. Both the rate constants and the positive activation energies of the two dodecamers, which differ only by the presence of the TAGG tetrad either at the 3'end or at the 5' end, turned out to be significantly different. The presence of Mg2+ ions had a profound influence on the kinetics of association of either compound by substantially decreasing the activation energy of the process. The dependence on sequence of the kinetics of hybridization was manifest in all parameters under all the experimental conditions.

Thermal unfolding of triosephosphate isomerase from Entamoeba histolytica: dimer dissociation leads to extensive unfolding.

In mesophiles, triosephosphate isomerase (TIM) is an obligated homodimer. We have previously shown that monomeric folding intermediates are common in the chemical unfolding of TIM, where dissociation provides 75% of the overall conformational stability of the dimer. However, analysis of the crystallographic structure shows that, during unfolding, intermonomeric contacts contribute to only 5% of the overall increase in accessible surface area. In this work several methodologies were used to characterize the thermal dissociation and unfolding of the TIM from Entamoeba histolytica (EhTIM) and a monomeric variant obtained by chemical derivatization (mEhTIM). During EhTIM unfolding, sequential transitions corresponding to dimer dissociation into a compact monomeric intermediate followed by unfolding and further aggregation of the intermediate occurred. In the case of mEhTIM, a single transition, analogous to the second transition of EhTIM, was observed. Calorimetric, spectroscopic, hydrodynamic, and functional evidence shows that dimer dissociation is not restricted to localized interface reorganization. Dissociation represents 55% (DeltaH(Diss) = 146.8 kcal mol(-1)) of the total enthalpy change (DeltaH(Tot) = 266 kcal mol(-1)), indicating that this process is linked to substantial unfolding. We propose that, rather than a rigid body process, subunit assembly is best represented by a fly-casting mechanism. In TIM, catalysis is restricted to the dimer; therefore, the interface can be viewed as the final nucleation motif that directs assembly, folding, and function.

Association temperature governs structure and apparent thermodynamics of DNA-gold nanoparticles.

Apparent thermodynamics of association of DNA-modified gold nanoparticles has been characterized by UV spectroscopy and dynamic light scattering (DLS). Extinction coefficients of unlabelled and DNA-labelled gold nanoparticles have been determined to permit quantitative analysis of the absorption measurements. In contrast to previous studies the associating gold nanoparticles were furnished with complementary oligonucleotide DNA single strands. This resulted in direct complex formation between the nanoparticles on mixing without the requirement of a DNA linker sequence for initiation of cluster formation. Melting curves of the nanoparticle assemblies formed at different temperatures were subjected to two-state analysis. A comparison of the apparent thermodynamic parameters obtained for the dissociation of these aggregates suggests that both thermodynamically and structurally different nanoparticle clusters are obtained depending on the temperature at which assembly proceeds. The van't Hoff enthalpies permit an estimate of the DNA duplexes: gold nanoparticle ratio involved in network formation.

Investigation on the self-association of an inorganic coordination compound with biological activity (Casiopeína III-ia) in aqueous solution.

From studies using different experimental techniques employed to determine the presence of aggregates e.g. isothermal titration calorimetry, surface tension, electrical conductivity, UV-Vis spectrophotometry, dynamic and static light scattering, it is clearly demonstrated that the compound [Cu(4, 4'-dimethyl-2, 2'-bipyridine)(acetylacetonato)H2O]NO3 (Casiopeína III-ia), promising member of a family of new generation compounds for cancer treatment, is able to auto associate in aqueous media. Physicochemical properties associated with the formation of the aggregates were determined in pure water and in phosphate buffer media in order to simulate physiological conditions. From isothermal titration calorimetry and electrical conductivity measurements we calculated the dissociation constant of the aggregates, KD . For pure water the values obtained in both techniques are 2.73 × 10-4 and 5.93 × 10-4 M respectively while for the buffer media we obtained 4.61 × 10-4 and 1.57 × 10-3 M. The enthalpy of dissociation, ∆HD , calculated from the calorimetric data shows that the presence of the phosphate ions has an energetic effect on the aggregate stability since in pure water a value of 18.79 kJ mol-1 was obtained in comparison with the buffer media where a value 4 times bigger was found (70.48 kJ mol-1). With the data collected from these techniques the number of monomers calculated which participate in the formation of the aggregates is around two. From our surface tension, electrical conductivity and UV-Vis spectrophotometry measurements the critical aggregate concentration, cac, was determined. For each technique specific concentration ranges were obtained but we can summarize that the cac in pure water is between 3 and 3.5 mM and for the buffer media is between 3.5 and 4 mM. Dynamic light scattering measurements provide us with the hydrodynamic diameter of the aggregates and from static light scattering measurements we determined the molecular weight of the Casiopeína III-ia aggregates to be of 1000.015 g mol-1 which is two times the molecular weight of the Casiopeína III-ia molecule. This value is in agreement with the number of monomers which participate in the formation of the aggregates obtained from isothermal titration calorimetry and electrical conductivity data analysis.

Intrinsic Levanase Activity of Bacillus subtilis 168 Levansucrase (SacB).

Levansucrase catalyzes the synthesis of fructose polymers through the transfer of fructosyl units from sucrose to a growing fructan chain. Levanase activity of Bacillus subtilis levansucrase has been described since the very first publications dealing with the mechanism of levan synthesis. However, there is a lack of qualitative and quantitative evidence regarding the importance of the intrinsic levan hydrolysis of B. subtilis levansucrase and its role in the levan synthesis process. Particularly, little attention has been paid to the long-term hydrolysis products, including its participation in the final levan molecules distribution. Here, we explored the hydrolytic and transferase activity of the B. subtilis levansucrase (SacB) when levans produced by the same enzyme are used as substrate. We found that levan is hydrolyzed through a first order exo-type mechanism, which is limited to a conversion extent of around 30% when all polymer molecules reach a structure no longer suitable to SacB hydrolysis. To characterize the reaction, Isothermal Titration Calorimetry (ITC) was employed and the evolution of the hydrolysis products profile followed by HPLC, GPC and HPAEC-PAD. The ITC measurements revealed a second step, taking place at the end of the reaction, most probably resulting from disproportionation of accumulated fructo-oligosaccharides. As levanase, levansucrase may use levan as substrate and, through a fructosyl-enzyme complex, behave as a hydrolytic enzyme or as a transferase, as demonstrated when glucose and fructose are added as acceptors. These reactions result in a wide variety of oligosaccharides that are also suitable acceptors for fructo-oligosaccharide synthesis. Moreover, we demonstrate that SacB in the presence of levan and glucose, through blastose and sucrose synthesis, results in the same fructooligosaccharides profile as that observed in sucrose reactions. We conclude that SacB has an intrinsic levanase activity that contributes to the final levan profile in reactions with sucrose as substrate.

Modeling Gibbs energies of solution for a non-polar solute in aqueous solutions of the protein stabilizers glycerol and ethylene glycol.

The Hydration Shell Chemical Equilibrium Model (HSCE) has been applied to Gibbs energies of solution data for toluene in aqueous solutions of the protein stabilizers glycerol and ethylene glycol. The HSCE model fits the experimental data to nearly experimental uncertainty. This satisfactory rendering of the data provides certainty on the physical significance of the model parameters and allows a description, from the molecular point of view, of the behaviour of a non-polar solute in aqueous solutions of protein stabilizers. The toluene-stabilizer interchange energy is positive indicating a dislike between toluene and the stabilizer molecules. This dislike is, however, much less pronounced than that between the solute and water, i.e. the non-polar solute prefers to be in contact with the stabilizer rather than with water. The cohesion between water molecules is much larger than that between stabilizer molecules and it remains to be the dominant cause of the hydrophobic behaviour of the non-polar solute. Since the solute-stabilizer interactions are energetically favoured over the solute-water ones, in the vicinity of the solute the stabilizer molecules are preferred over water ones. However, there is no specific interaction leading to a distinct chemical entity (a solute-stabilizer complex). Thus, the non-polar solute-stabilizer interaction is better described by the term 'preferential solvation of the solute by the stabilizer'.

Experiment and prediction: a productive symbiosis in studies on the thermodynamics of DNA oligomers.

Recently, we reported the kinetics of hybridization of cDNA dodecamers (Carrillo-Nava, E., Mejía-Radillo, Y., and Hinz, H.-J. Biochemistry 2008, 47, 13153-13157). In this study, we provide the thermodynamic reaction parameters of those dodecamers as well as a comparison with parameters for 24-mers designed from two identical dodecamers in tandem arrangement. The thermodynamic properties were determined by isothermal titration calorimetry (ITC), differential scanning microcalorimetry (DSC), and UV melting studies. On the basis of the results from our kinetic studies, fitting algorithms of DSC and UV melting profiles employed the two-state assumption for the duplex to a single strand dissociation reaction. The formation of both 12-mer and 24-mer duplexes is strongly enthalpy driven at all temperatures. At identical temperatures, the hybridization enthalpy of the 24-mer is within error limits twice that of the 12-mer. Duplex formation is always associated with a significant negative heat capacity change, ΔC(p), which, on a mass basis, is comparable to that observed for protein folding. Only a small part of the favorable reaction enthalpy appears as a standard Gibbs free energy change due to large compensating negative entropy changes linked to duplex formation. On the basis of the results of the present studies, it appears to be absolutely essential for a proper analysis of thermodynamic parameters of oligonucleotide hybridization reactions to combine low temperature ITC measurements of binding enthalpies with DSC and UV melting studies to obtain an accurate assessment of standard Gibbs energy changes or, equivalently, hybridization constants over a broad temperature range. The experimental thermodynamic parameters were compared with theoretical estimates based on nearest-neighbor approximations employing temperature-independent enthalpies. Good agreement between experimental and predicted ΔG° values is observed at ambient temperatures (20-30 °C), as long as helix formation is associated with small molar heat capacity changes. If the experimental ΔC(p) values determined by ITC are taken into account, significant deviations occur.