L-Asparaginase Conjugates from the Hyperthermophilic Archaea Thermococcus sibiricus with Improved Biocatalytic Properties

This study investigated the effect of polycationic and uncharged polymers (and oligomers) on the catalytic parameters and thermostability of L-asparaginase from Thermococcus sibiricus (TsA). This enzyme has potential applications in the food industry to decrease the formation of carcinogenic acrylamide during the processing of carbohydrate-containing products. Conjugation with the polyamines polyethylenimine and spermine (PEI and Spm) or polyethylene glycol (PEG) did not significantly affect the secondary structure of the enzyme. PEG contributes to the stabilization of the dimeric form of TsA, as shown by HPLC. Furthermore, neither polyamines nor PEG significantly affected the binding of the L-Asn substrate to TsA. The conjugates showed greater maximum activity at pH 7.5 and 85 °C, 10-50% more than for native TsA. The pH optima for both TsA-PEI and TsA-Spm conjugates were shifted to lower pH ranges from pH 10 (for the native enzyme) to pH 8.0. Additionally, the TsA-Spm conjugate exhibited the highest activity at pH 6.5-9.0 among all the samples. Furthermore, the temperature optimum for activity at pH 7.5 shifted from 90-95 °C to 80-85 °C for the conjugates. The thermal inactivation mechanism of TsA-PEG appeared to change, and no aggregation was observed in contrast to that of the native enzyme. This was visually confirmed and supported by the analysis of the CD spectra, which remained almost unchanged after heating the conjugate solution. These results suggest that TsA-PEG may be a more stable form of TsA, making it a potentially more suitable option for industrial use.

Disulfide Cross-Linked Polymeric Redox-Responsive Nanocarrier Based on Heparin, Chitosan and Lipoic Acid Improved Drug Accumulation, Increased Cytotoxicity and Selectivity to Leukemia Cells by Tumor Targeting via "Aikido" Principle

We have developed a micellar formulation of anticancer drugs based on chitosan and heparin grafted with lipoic and oleic acids that can release the cytotoxic cargo (doxorubicin) in response to external stimuli, such as increased glutathione concentration-a hallmark of cancer. Natural polysaccharides (heparin and chitosan) provide the pH sensitivity of the nanocarrier: the release of doxorubicin (Dox) is enhanced in a slightly acidic environment (tumor microenvironment). Fatty acid residues are necessary for the formation of nanoparticles (micelles) and solubilization of cytostatics in a hydrophobic core. Lipoic acid residues provide the formation of a labile S-S cross-linking between polymer chains (the first variant) or covalently attached doxorubicin molecules through glutathione-sensitive S-S bridges (the second variant)-both determine Redox sensitivity of the anticancer drugs carriers stable in blood circulation and disintegrate after intracellular uptake in the tumor cells. The release of doxorubicin from micelles occurs slowly (20%/6 h) in an environment with a pH of 7.4 and the absence of glutathione, while in a slightly acidic environment and in the presence of 10 mM glutathione, the rate increases up to 6 times, with an increase in the effective concentration up to 5 times after 7 h. The permeability of doxorubicin in micellar formulations (covalent S-S cross-linked and not) into Raji, K562, and A875 cancer cells was studied using FTIR, fluorescence spectroscopy and confocal laser scanning microscopy (CLSM). We have shown dramatically improved accumulation, decreased efflux, and increased cytotoxicity compared to doxorubicin control with three tumor cell lines: Raji, K562, and A875. At the same time, cytotoxicity and permeability for non-tumor cells (HEK293T) are significantly lower, increasing the selectivity index against tumor cells by several times.

Impact of Lipid Matrix Composition on Activity of Membranotropic Enzymes Galactonolactone Oxidase from Trypanosoma cruzi and L-Galactono-1,4-Lactone Dehydrogenase from Arabidopsis thaliana in the System of Reverse Micelles

The study of many membrane enzymes in an aqueous medium is difficult due to the loss of their catalytic activity, which makes it necessary to use membrane-like systems, such as reverse micelles of surfactants in nonpolar organic solvents. However, it should be taken into account that the micelles are a simplified model of natural membranes, since membranes contain many different components, a significant part of which are phospholipids. In this work, we studied impact of the main phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), on activity of the membrane enzymes using galactonolactone oxidase from Trypanosoma cruzi (TcGAL) and L-galactono-1,4-lactone dehydrogenase from Arabidopsis thaliana (AtGALDH) as examples. Effect of the structure (and charge) of the micelle-forming surfactant itself on the activity of both enzymes has been studied using an anionic surfactant (AOT), a neutral surfactant (Brij-96), and a mixture of cationic and anionic surfactants (CTAB and AOT) as examples. The pronounced effect of addition of PC and PE lipids on the activity of AtGALDH and TcGAL has been detected, which manifests as increase in catalytic activity and significant change in the activity profile. This can be explained by formation of the tetrameric form of enzymes and/or protein-lipid complexes. By varying composition and structure of the micelle-forming surfactants (AOT, CTAB, and Brij-96) it has been possible to change catalytic properties of the enzyme due to effect of the surfactant on the micelle size, lipid mobility, charge, and rigidity of the matrix itself.

Triphenylphosphine Derivatives of Allylbenzenes Express Antitumor and Adjuvant Activity When Solubilized with Cyclodextrin-Based Formulations

Allylbenzenes (apiol, dillapiol, myristicin and allyltetramethoxybenzene) are individual components of plant essential oils that demonstrate antitumor activity and can enhance the antitumor activity of cytotoxic drugs, such as paclitaxel, doxorubicin, cisplatin, etc. Triphenylphosphine (PPh3) derivatives of allylbenzenes are two to three orders of magnitude more potent than original allylbenzenes in terms of IC50. The inhibition of efflux pumps has been reported for allylbenzenes, and the PPh3 moiety is deemed to be responsible for preferential mitochondrial accumulation and the depolarization of mitochondrial membranes. However, due to poor solubility, the practical use of these substances has never been an option. Here, we show that this problem can be solved by using a complex formation with cyclodextrin (CD-based molecular containers) and polyanionic heparin, stabilizing the positive charge of the PPh3 cation. Such containers can solubilize both allylbenzenes and their PPh3 derivatives up to 0.4 mM concentration. Furthermore, we have observed that solubilized PPh3 derivatives indeed work as adjuvants, increasing the antitumor activity of paclitaxel against adenocarcinomic human alveolar basal epithelial cells (A549) by an order of magnitude (in terms of IC50) in addition to being quite powerful cytostatics themselves (IC50 in the range 1-10 µM). Even more importantly, CD-solubilized PPh3 derivatives show pronounced selectivity, being highly toxic for the A549 tumor cell line and minimally toxic for HEK293T non-tumor cells, red blood cells and sea urchin embryos. Indeed, in many cancers, the mitochondrial membrane is more prone to depolarization compared to normal cells, which probably explains the observed selectivity of our compounds, since PPh3 derivatives are known to act as mitochondria-targeting agents. According to the MTT test, 100 µM solution of PPh3 derivatives of allylbenzenes causes the death of up to 85% of A549 cancer cells, while for HEK293T non-cancer cells, only 15-20% of the cells died. The hemolytic index of the studied substances did not exceed 1%, and the thrombogenicity index was < 1.5%. Thus, this study outlines the experimental foundation for developing combined cytostatic medications, where effectiveness and selectivity are achieved through decreased concentration of the primary ingredient and the inclusion of adjuvants, which are safe or practically harmless substances.

Biomimetic Systems Involving Macrophages and Their Potential for Targeted Drug Delivery

The concept of targeted drug delivery can be described in terms of the drug systems' ability to mimic the biological objects' property to localize to target cells or tissues. For example, drug delivery systems based on red blood cells or mimicking some of their useful features, such as long circulation in stealth mode, have been known for decades. On the contrary, therapeutic strategies based on macrophages have gained very limited attention until recently. Here, we review two biomimetic strategies associated with macrophages that can be used to develop new therapeutic modalities: first, the mimicry of certain types of macrophages (i.e., the use of macrophages, including tumor-associated or macrophage-derived particles as a carrier for the targeted delivery of therapeutic agents); second, the mimicry of ligands, naturally absorbed by macrophages (i.e., the use of therapeutic agents specifically targeted at macrophages). We discuss the potential applications of biomimetic systems involving macrophages for new advancements in the treatment of infections, inflammatory diseases, and cancer.

Biomimetic System Based on Reconstituted Macrophage Membranes for Analyzing and Selection of Higher-Affinity Ligands Specific to Mannose Receptor to Develop the Macrophage-Focused Medicines

Progress in macrophage research is crucial for numerous applications in medicine, including cancer and infectious diseases. However, the existing methods to manipulate living macrophages are labor-intense and inconvenient. Here, we show that macrophage membranes can be reconstituted after storage for months at 4 °C, with their CD206 receptor selectivity and specificity being similar to those in the living cells. Then, we have developed a mannose ligand, specific to CD206, linked with PEG as an IR spectroscopy marker to detect binding with the macrophage receptor. PEG was selected due to its unique adsorption band of the C-O-C group at IR spectra, which does not overlap with other biomolecules' spectroscopic feature. Next, competitive binding assay versus the PEG-bound ligand has enabled the selection of other higher-affinity ligands specific to CD206. Furthermore, those higher-affinity ligands were used to differentiate activated macrophages in a patient's bronchoalveolar (BAL) or nasopharyngeal (NPL) lavage. CD206- control cells (HEK293T) showed only non-specific binding. Therefore, biochips based on reconstituted macrophage membranes as well as PEG-trimannoside as an IR spectroscopic marker can be used to develop new methods facilitating macrophage research and macrophage-focused drug discovery.

Mucosal Adhesive Chitosan Nanogel Formulations of Antibiotics and Adjuvants (Terpenoids, Flavonoids, etc.) and Their Potential for the Treatment of Infectious Diseases of the Gastrointestinal Tract

Bacterial infections are usually found in the stomach and the first part of the small intestine in association with various pathologies, including ulcers, inflammatory diseases, and sometimes cancer. Treatment options may include combinations of antibiotics with proton pump inhibitors and anti-inflammatory drugs. However, all of them have high systemic exposure and, hence, unfavorable side effects, whereas their exposure in stomach mucus, the predominant location of the bacteria, is limited. Chitosan and nanogels based on chitosan presumably are not absorbed from the gastrointestinal tract and are known to adhere to the mucus. Therefore, they can serve as a basis for the local delivery of antibacterial drugs, increasing their exposure at the predominant location of therapeutic targets, thus improving the risk/benefit ratio. We have used E. coli ATCC 25922 (as a screening model of pathogenic bacteria) and Lactobacilli (as a model of a normal microbiome) to study the antibacterial activity of antibacterial drugs entrapped in a chitosan nanogel. Classical antibiotics were studied in a monotherapeutic regimen as well as in combination with individual terpenoids and flavonoids as adjuvants. It has been shown that levofloxacin (LF) in combination with zephirol demonstrate synergistic effects against E. coli (cell viability decreased by about 50%) and, surprisingly, a much weaker effect against Lactobacilli. A number of other combinations of antibiotic + adjuvant were also shown to be effective. Using FTIR and UV spectroscopy, it has been confirmed that chitosan nanogels with the drug are well adsorbed on the mucosal model, providing prolonged release at the target location. Using an ABTS assay, the antioxidant properties of flavonoids and other drugs are shown, which are potentially necessary to minimize the harmful effects of toxins and radicals produced by pathogens. In vivo experiments (on sturgeon fish) showed the effective action of antibacterial formulations developed based on LF in chitosan nanogels for up to 11 days. Thus, chitosan nanogels loaded with a combination of drugs and adjuvants can be considered as a new strategy for the treatment of infectious diseases of the gastrointestinal tract.

Covalent Conjugates of Allylbenzenes and Terpenoids as Antibiotics Enhancers with the Function of Prolonged Action

The drug resistance of pathogenic bacteria is often due efflux pumps-specific proteins that remove foreign compounds from bacterial cells. To overcome drug resistance, adjuvants are often used that can inhibit efflux pumps or other systems that ensure the resistance of bacteria to the action of antibiotics. We assumed that a new level of effectiveness with the use of an antibiotic + an adjuvant pair could be achieved by their joint delivery into the pathogen. To test this hypothesis, we constructed a series of molecular carriers based on poly-(olygo-, dendry)mers based on cyclodextrin-grafted PEI or mannan, as well as glycol chitosan, covalently bound to antibiotic, adjuvant, and the oligosaccharide ligand to the macrophage mannose receptor (CD206), which we studied earlier and showed high efficiency and selectivity of delivery of a therapeutic "cargo" to macrophages. Moxifloxacin was used as an antibiotic, and terpenoid and allylbenzene compounds were used as adjuvants, for which we previously discovered the ability to inhibit bacterial efflux pumps. We show that: (a) the resulting structures were stable in vitro for a long time (up to 10 days); (b) they were adsorbed on bacterial cells, providing a local increase in the concentration of the antibiotic and adjuvant in pathogen cells; (c) they were internalized by bacterial cells, ensuring the accumulation of both antibiotic and adjuvant inside bacterial cells; (d) the adjuvant, after entering the bacterial cell, provided inhibition of the efflux pumps; (e) due to this action of the adjuvant, combined with the targeted delivery by the carrier, the antibiotic's half-life in rats increased by more than 2 times, the effective concentration of the drug in the blood plasma (AUC) increased up to 8-10 times; (f) a significant increase in the effectiveness of the antibacterial action against Gram+ and Gram- cells was achieved (up to 3 times). Potentially, such an approach would significantly increase the effectiveness of therapies for a number of infectious and other diseases, reduce the dosage of antibiotics, shorten the duration of treatment, and reduce the risk of developing bacterial resistance. Moreover, the use of a polymer carrier with covalently bound organic molecules of different structures will avoid problems linked to different (suboptimal) solubility and bio-distribution of the administered molecules, which would be almost inevitable when using the same compounds separately. It would be very difficult to find antibiotic/adjuvant pairs that simultaneously achieve optimal concentrations in the same target cells. In our case, terpenoids and alkylbenzenes used as adjuvants are practically insoluble as individual compounds, and their unacceptable pharmacological properties would not allow them to be used as efflux pump inhibitors.

Fluorescent Probes with Förster Resonance Energy Transfer Function for Monitoring the Gelation and Formation of Nanoparticles Based on Chitosan Copolymers

Nanogel-forming polymers such as chitosan and alginic acid have a number of practical applications in the fields of drug delivery, food technology and agrotechnology as biocompatible, biodegradable polymers. Unlike bulk macrogel formation, which is followed by visually or easily detectable changes and physical parameters, such as viscosity or turbidity, the formation of nanogels is not followed by such changes and is therefore very difficult to track. The counterflow extrusion method (or analogues) enables gel nanoparticle formation for certain polymers, including chitosan and its derivatives. DLS or TEM, which are typically used for their characterization, only allow for the study of the already-formed nanoparticles. Alternatively, one might introduce a fluorescent dye into the gel-forming polymer, with the purpose of monitoring the effect of its microenvironment on the fluorescence spectra. But apparently, this approach does not provide a sufficiently specific signal, as the microenvironment may be affected by a big number of various factors (such as pH changes) including but not limited to gel formation per se. Here, we propose a new approach, based on the FRET effect, which we believe is much more specific and enables the elucidation of nanogel formation process in real time. Tryptophan-Pyrene is suggested as one of the donor-acceptor pairs, yielding the FRET effect when the two compounds are in close proximity to one another. We covalently attached Pyrene (the acceptor) to the chitosan (or PEG-chitosan) polymeric chain. The amount of introduced Pyrene was low enough to produce no significant effect on the properties of the resulting gel nanoparticles, but high enough to detect the FRET effect upon its interaction with Trp. When the Pyr-modified chitosan and Trp are both present in the solution, no FRET effect is observed. But as soon as the gel formation is initiated using the counterflow extrusion method, the FRET effect is easily detectable, manifested in a sharp increase in the fluorescence intensity of the pyrene acceptor and reflecting the gel formation process in real time. Apparently, the gel formation promotes the Trp-Pyr stacking interaction, which is deemed necessary for the FRET effect, and which does not occur in the solution. Further, we observed a similar FRET effect when the chitosan gel formation is a result of the covalent crosslinking of chitosan chains with genipin. Interestingly, using ovalbumin, having numerous Trp exposed on the protein surface instead of individual Trp yields a FRET effect similar to Trp. In all cases, we were able to detect the pH-, concentration- and temperature-dependent behaviors of the polymers as well as the kinetics of the gel formation for both nanogels and macrogels. These findings indicate a broad applicability of FRET-based analysis in biomedical practice, ranging from the optimization of gel formation to the encapsulation of therapeutic agents to food and biomedical technologies.

Combined System for the Simultaneous Delivery of Levofloxacin and Rifampicin: Structural and Functional Properties and Antibacterial Activity

The therapy of resistant forms of tuberculosis requires the simultaneous use of several drugs, in particular, a combination of rifampicin and levofloxacin. In this paper, we aimed to design a combined system for the simultaneous delivery of these drugs for potential inhalation administration. A feature of this system is the incorporation of rifampicin into optimized liposomal vesicles capable of forming a multipoint non-covalent complex with chitosan-β-cyclodextrin conjugates. Levofloxacin is incorporated into cyclodextrin tori by forming a host-guest complex. Here, a comprehensive study of the physicochemical properties of the obtained systems was carried out and special attention was paid to the kinetics of cargo release for individual drugs and in the combined system. The release of levofloxacin in combined system is slow and is described by the Higuchi model in all cases. The release of rifampicin from liposomes during the formation of complexes with polymeric conjugates is characterized by the change of the Higuchi model to the Korsmeyer-Peppas model with the main type of diffusion against Fick's law. Microbiological studies in solid and liquid growth media a consistently high antibacterial activity of the obtained systems was shown against B. subtilis and E. coli.

Polymeric Micelles Formulation of Combretastatin Derivatives with Enhanced Solubility, Cytostatic Activity and Selectivity against Cancer Cells

Combretastatin derivatives is a promising class of antitumor agents, tubulin assembly inhibitors. However, due to poor solubility and insufficient selectivity to tumor cells, we believe, their therapeutic potential has not been fully realized yet. This paper describes polymeric micelles based on chitosan (a polycation that causes pH and thermosensitivity of micelles) and fatty acids (stearic, lipoic, oleic and mercaptoundecanoic), which were used as a carrier for a range of combretastatin derivatives and reference organic compounds, demonstrating otherwise impossible delivery to tumor cells, at the same time substantially reduced penetration into normal cells. Polymers containing sulfur atoms in hydrophobic tails form micelles with a zeta potential of about 30 mV, which increases to 40-45 mV when cytostatics are loaded. Polymers with tails of oleic and stearic acids form poorly charged micelles. The use of polymeric 400 nm micelles provides the dissolution of hydrophobic potential drug molecules. Micelles could significantly increase the selectivity of cytostatics against tumors, which has been shown using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, Fourier transform infrared (FTIR) spectroscopy, flow cytometry and fluorescence microscopy. Atomic force microscopy presented the difference between the unloaded micelles and those loaded with the drug: the size of the former was 30 nm on average, while the latter had a "disc-like" shape and a size of about 450 nm. The loading of drugs into the core of micelles was confirmed by UV and fluorescence spectroscopy methods; shifts of absorption and emission maxima into the long-wavelength region by tens of nm was observed. With FTIR spectroscopy, a high interaction efficiency of micelles with the drug on cells was demonstrated, but at the same time, selective absorption was observed: micellar cytostatics penetrate into A549 cancer cells 1.5-2 times better than the simple form of the drugs. Moreover, in normal HEK293T, the penetration of the drug is reduced. The proposed mechanism for reducing the accumulation of drugs in normal cells is the adsorption of micelles on the cell surface and the preservation of cytostatics to penetrate inside the cells. At the same time, in cancer cells, due to the structural features of the micelles, they penetrate inside, merging with the membrane and releasing the drug by pH- and glutathione-sensitive mechanisms. From a methodological point of view, we have proposed a powerful approach to the observation of micelles using a flow cytometer, which, in addition, allows us to quantify the cells that have absorbed/adsorbed cytostatic fluorophore and distinguish between specific and non-specific binding. Thus, we present polymeric micelles as drug delivery systems in tumors using the example of combretastatin derivatives and model fluorophore-cytostatic rhodamine 6G.

Cyclodextrins and Their Polymers Affect Human Serum Albumin's Interaction with Drugs Used in the Treatment of Pulmonary Infections

Respiratory infectious diseases have challenged medical communities and researchers. Ceftriaxone, meropenem and levofloxacin are widely used for bacterial infection treatment, although they possess severe side effects. To overcome this, we propose cyclodextrin (CD) and CD-based polymers as a drug delivery system for the drugs under consideration. CD polymers demonstrate higher binding affinity for levofloxacin (Ka ≈ 10⁵ M) compared to drug-CD complexes. CDs slightly alter the drugs' affinity for human serum albumin (HSA), whereas CD polymers increase the drugs' binding affinity up to 100 times. The most significant effect was observed for more the hydrophilic drugs ceftriaxone and meropenem. The drug's encapsulation in CD carriers leads to a decrease in the degree of change in the protein's secondary structure. The drug-CD carrier-HSA complexes demonstrate satisfying antibacterial activity in vitro, and even a high binding affinity does not decrease the drug's microbiological properties after 24 h. The proposed carriers are promising for a drug form with a prolonged drug release.

Thermoreversible Gels Based on Chitosan Copolymers as "Intelligent" Drug Delivery System with Prolonged Action for Intramuscular Injection

Thermosensitive gels based on copolymers (PEG-chitosan, chitosan-polyethylenimine, chitosan-arginine and glycol-chitosan-spermine) are presented as promising polycations for the formation of DNA polyplexes and the potential for the development of drugs with prolonged release (up to 30 days). Being in liquid form at room temperature, such compounds can be injected into muscle tissue with rapid gel formation at human body temperature. An intramuscular depot is formed with a therapeutic agent that provides a gradual release of the drug, such as an antibacterial or cytostatic. The physico-chemical parameters of the formation of polyplexes between polycationic polymers of various compositions and molecular architecture and DNA were studied via FTIR, UV-vis and fluorescence spectroscopy using the dyes rhodamine 6G (R6G) and acridine orange (AO). The competitive displacement of AO from AO-DNA complexes showed that, with a ratio of N/P = 1, most of the DNA is bound to a polycation. During the formation of polyplexes, the DNA charge is neutralized by a polycation, which is reflected in electrophoretic immobility. The cationic polymers described in this work at a concentration of 1-4% are capable of forming gels, and the thermoreversible property is most characteristic of pegylated chitosan. BSA, as a model anionic molecule, is released by half in 5 days from the Chit5-PEG5 gel; full release is achieved in 18-20 days. At the same time, in 5 days, the gel is destroyed up to 30%, and in 20 days, by 90% (release of chitosan particles). For the first time, flow cytometry was used to study DNA polyplexes, which showed the existence of fluorescent particles in a much larger number in combination with free DNA. Thus, functional stimulus-sensitive polymers are potentially applicable for the creation of prolonged therapeutic formulations for gene delivery systems, which were obtained. The revealed regularities appear to be a platform for the design of polyplexes with controllable stability, in particular, fulfilling the requirements imposed for gene delivery vehicles.

Achievement of the Selectivity of Cytotoxic Agents against Cancer Cells by Creation of Combined Formulation with Terpenoid Adjuvants as Prospects to Overcome Multidrug Resistance

Oncological diseases are difficult to treat even with strong drugs due to development the multidrug resistance (MDR) of cancer cells. A strategy is proposed to increase the efficiency and selectivity of cytotoxic agents against cancer cells to engage the differences in the morphology and microenvironment of tumor and healthy cells, including the pH, membrane permeability, and ion channels. Using this approach, we managed to develop enhanced formulations of cytotoxic agents with adjuvants (which are known as efflux inhibitors and as ion channel inhibitors in tumors)-with increased permeability in A549 and a protective effect on healthy HEK293T cells. The composition of the formulation is as follows: cytotoxic agents (doxorubicin (Dox), paclitaxel (Pac), cisplatin) + adjuvants (allylbenzenes and terpenoids) in the form of inclusion complexes with β-cyclodextrin. Modified cyclodextrins make it possible to obtain soluble forms of pure substances of the allylbenzene and terpenoid series and increase the solubility of cytotoxic agents. A comprehensive approach based on three methods for studying the interaction of drugs with cells is proposed: MTT test-quantitative identification of surviving cells; FTIR spectroscopy-providing information on the molecular mechanisms inaccessible to study by any other methods (including binding to DNA, surface proteins, or lipid membrane); confocal microscopy for the visualization of observed effects of Dox accumulation in cancer or healthy cells depending on the drug formulation as a direct control of the correctness of interpretation of the results obtained by the two other methods. We found that eugenol (EG) and apiol increase the intracellular concentration of cytostatic in A549 cells by 2-4 times and maintain it for a long time. However, an important aspect is the selectivity of the enhancing effect of adjuvants on tumor cells in relation to healthy ones. Therefore, the authors focused on adjuvant's effect on the control healthy cells (HEK293T): EG and apiol demonstrate "protective" properties from cytostatic penetration by reducing intracellular concentrations by about 2-3 times. Thus, a combined formulation of cytostatic drugs has been found, showing promise in the aspects of improving the efficiency and selectivity of antitumor drugs; thereby, one of the perspective directions for overcoming MDR is suggested.

Smart pH- and Temperature-Sensitive Micelles Based on Chitosan Grafted with Fatty Acids to Increase the Efficiency and Selectivity of Doxorubicin and Its Adjuvant Regarding the Tumor Cells

The main factors that determine the low effectiveness of chemotherapy are the low target bioavailability of antitumor drugs and the efflux process. In attempts to overcome this problem, several approaches are proposed here. Firstly, the development of polymeric micellar systems based on chitosan grafted by fatty acids (different types to optimize their properties), which, on the one hand, increase the solubility and bioavailability of cytostatics and, on the other hand, effectively interact with tumor cells due to the polycationic properties of chitosan, allowing for more effective penetration of cytostatic drugs into the cells. Secondly, the use of adjuvants-synergists of cytostatics (such as eugenol) included in the same micellar formulation-that selectively enhance the accumulation and retention of cytostatics in the tumor cells. pH- and temperature-sensitive polymeric micelles developed show high entrapment efficiency for both cytostatics and eugenol (EG) >60% and release the drug in a prolonged manner for 40 h in a weakly acidic medium corresponding to the microenvironment of tumors. In a slightly alkaline environment, the drug circulates longer (more than 60 h). The thermal sensitivity of micelles is realized due to an increase in the molecular mobility of chitosan, which undergoes a phase transition at 32-37 °C. The effect of the cytostatic drug doxorubicin (Dox) on cancerous A549 cells and model healthy cells of human embryonic renal epithelium (HEK293T) was studied by FTIR spectroscopy and fluorescence microscopy. Micellar Dox penetrates into cancer cells 2-3 times more efficiently when using EG adjuvant, which inhibits efflux, as demonstrated by a significant increase in the ratio of intra- and extracellular concentrations of the cytostatic. However, here it is worth remembering about healthy cells that they should not be damaged: according to changes in the FTIR and fluorescence spectra, the penetration of Dox into HEK293T when using micelles in combination with EG is reduced by 20-30% compared to a simple cytostatic. Thus, experimental developments of combined micellar cytostatic drugs have been proposed to increase the effectiveness of cancer treatment and overcome multiple drug resistance.

Application Prospects of FTIR Spectroscopy and CLSM to Monitor the Drugs Interaction with Bacteria Cells Localized in Macrophages for Diagnosis and Treatment Control of Respiratory Diseases

Visualization of the interaction of drugs with biological cells creates new approaches to improving the bioavailability, selectivity, and effectiveness of drugs. The use of CLSM and FTIR spectroscopy to study the interactions of antibacterial drugs with latent bacterial cells localized in macrophages create prospects to solve the problems of multidrug resistance (MDR) and severe cases. Here, the mechanism of rifampicin penetration into E. coli bacterial cells was studied by tracking the changes in the characteristic peaks of cell wall components and intracellular proteins. However, the effectiveness of the drug is determined not only by penetration, but also by efflux of the drugs molecules from the bacterial cells. Here, the efflux effect was studied and visualized using FTIR spectroscopy, as well as CLSM imaging. We have shown that because of efflux inhibition, eugenol acting as an adjuvant for rifampicin showed a significant (more than three times) increase in the antibiotic penetration and the maintenance of its intracellular concentration in E. coli (up to 72 h in a concentration of more than 2 μg/mL). In addition, optical methods have been applied to study the systems containing bacteria localized inside of macrophages (model of the latent form), where the availability of bacteria for antibiotics is reduced. Polyethylenimine grafted with cyclodextrin carrying trimannoside vector molecules was developed as a drug delivery system for macrophages. Such ligands were absorbed by CD206+ macrophages by 60-70% versus 10-15% for ligands with a non-specific galactose label. Owing to presence of ligands with trimannoside vectors, the increase in antibiotic concentration inside macrophages, and thus, its accumulation into dormant bacteria, is observed. In the future, the developed FTIR+CLSM techniques would be applicable for the diagnosis of bacterial infections and the adjustment of therapy strategies.

Allylpolyalkoxybenzene Inhibitors of Galactonolactone Oxidase from Trypanosoma cruzi

Inhibition of biosynthetic pathways of compounds essential for Trypanosoma cruzi is considered as one of the possible action mechanisms of drugs against Chagas disease. Here, we investigated the inhibition of galactonolactone oxidase from T. cruzi (TcGAL), which catalyzes the final step in the synthesis of vitamin C, an antioxidant that T. cruzi is unable to assimilate from outside and must synthesize itself, and identified allylbenzenes from plant sources as a new class of TcGAL inhibitors. Natural APABs (apiol, dillapiol, etc.) inhibited TcGAL with IC₅₀ = 20-130 µM. The non-competitive mechanism of TcGAL inhibition by apiol was established. Conjugation of APABs with triphenylphosphonium, which ensures selective delivery of biologically active substances to the mitochondria, increased the efficiency and/or the maximum percentage of TcGAL inhibition compared to nonmodified APABs.

Cyclodextrins and Their Polymers Affect the Lipid Membrane Permeability and Increase Levofloxacin’s Antibacterial Activity In Vitro

Cyclodextrins (CDs) are promising drug carriers that are used in medicine. We chose CDs with different substituents (polar/apolar, charged/neutral) to obtain polymers (CDpols) with different properties. CDpols are urethanes with average Mw of ~120 kDa; they form nanoparticles 100–150 nm in diameter with variable ζ-potential. We studied the interaction of CD and CDpols with model (liposomal) and bacterial membranes. Both types of CD carriers cause an increase in the liposomal membrane permeability, and for polymers, this effect was almost two times stronger. The formation of CD/CDpols complexes with levofloxacin (LV) enhances LV’s antibacterial action 2-fold in vitro on five bacterial strains. The most pronounced effect was determined for LV-CD complexes. LV-CDs and LV-CDpols adsorb on bacteria, and cell morphology influences this process dramatically. According to TEM studies, the rough surface and proteinaceous fimbria of Gram-negative E. coli facilitate the adsorption of CD particles, whereas the smooth surface of Gram-positive bacteria impedes it. In comparison with LV-CDs, LV-CDpols are adsorbed 15% more effectively by E. coli, 2.3-fold better by lactobacilli and 5-fold better in the case of B. subtilis. CDs and CDpols are not toxic for bacterial cells, but may cause mild defects that, in addition to LV-CD carrier adsorption, improve LV’s antibacterial properties.

Mannosylated Polymeric Ligands for Targeted Delivery of Antibacterials and Their Adjuvants to Macrophages for the Enhancement of the Drug Efficiency

Bacterial infections and especially resistant strains of pathogens localized in macrophages and granulomas are intractable diseases that pose a threat to millions of people. In this paper, the theoretical and experimental foundations for solving this problem are proposed due to two key aspects. The first is the use of a three-component polymer system for delivering fluoroquinolones to macrophages due to high-affinity interaction with mannose receptors (CD206). Cytometry assay determined that 95.5% macrophage-like cells were FITC-positive after adding high-affine to CD206 trimannoside conjugate HPCD-PEI1.8-triMan, and 61.7% were FITC-positive after adding medium-affine ligand with linear mannose label HPCD-PEI1.8-Man. The second aspect is the use of adjuvants, which are synergists for antibiotics. Using FTIR and NMR spectroscopy, it was shown that molecular containers, namely mannosylated polyethyleneimines (PEIs) and cyclodextrins (CDs), load moxifloxacin (MF) with dissociation constants of the order of 10⁻⁴–10⁻⁶ M; moreover, due to prolonged release and adsorption on the cell membrane, they enhance the effect of MF. Using CLSM, it was shown that eugenol (EG) increases the penetration of doxorubicin (Dox) into cells by an order of magnitude due to the creation of defects in the bacterial wall and the inhibition of efflux proteins. Fluorescence spectroscopy showed that 0.5% EG penetrates into bacteria and inhibits efflux proteins, which makes it possible to increase the maximum concentration of the antibiotic by 60% and maintain it for several hours until the pathogens are completely neutralized. Regulation of efflux is a possible way to overcome multiple drug resistance of both pathogens and cancer cells.

The Influence of Lipid Matrix Composition on the Microenvironment of Levofloxacin in Liposomal Forms

We have studied the interaction of the antibacterial drug levofloxacin with lipid bilayers of various compositions: 100% DPPC and with the addition of 20% cardiolipin. For DPPC liposomes, levofloxacin was found to penetrate into the subpolar region at the lipid-water interface. The role of the anionic lipid in the interaction of an active molecule with a bilayer has been established: levofloxacin enters the microenvironment of the phosphate group, displacing water, and does not penetrate into the hydrophobic part of the bilayer. For the first time, the study of the microenvironment of levofloxacin in the liposome by IR and CD spectroscopy was carried out. Such an approach based on a combination of several spectral methods opens up new prospects for the creation of new medicinal properties and the possibility of predicting the nature of the interaction of active molecules with biomembranes in order to predict their efficacy and potential side effects.

Plant Alkylbenzenes and Terpenoids in the Form of Cyclodextrin Inclusion Complexes as Antibacterial Agents and Levofloxacin Synergists

Allylpolyalkoxybenzenes (APABs) and terpenoids from plant essential oils exhibit a range of remarkable biological effects, including analgesic, antibacterial, anti-inflammatory, antioxidant, and others. Synergistic activity with antibiotics of different classes has been reported, with inhibition of P-glycoprotein and impairment of bacterial cell membrane claimed as probable mechanisms. Clearly, a more detailed understanding of APABs’ biological activity could help in the development of improved therapeutic options for a range of diseases. However, APABs’ poor solubility in water solutions has been a limiting factor for such research. Here, we found that complex formation with β-cyclodextrins (CD) is an efficient way to transform the APABs into a water-soluble form. Using a combination of spectroscopic (FTIR, NMR, UV) methods, we have estimated the binding constants, loading capacity, and the functional groups of both APABs and monoterpenes involved in complex formation with CD: ethylene, aromatic, methoxy and hydroxy groups. In the presence of a molar excess of CD (up to 5 fold) it was possible to achieve the complete dissolution of APABs and terpenoids in an aqueous medium (at 90–98% encapsulation) higher by 10–1000 times. Further, we have demonstrated that CD-APABs, if used in combination with levofloxacin (Lev), can be antagonistic, indifferent, additive, or synergistic, mostly depending on the concentration ratio: at high Lev concentration with the addition of APAB is typically neutral or even antagonistic; while at a Lev concentration below MIC, the addition of CD-APAB is either additive or synergistic (according to FICI criteria). An over three-fold increase in Lev antibacterial activity was observed in combination with eugenol (EG), as per the growth inhibition diameter measurement in agar. Interestingly, a synergistic effect could be observed with both Gram-positive and Gram-negative bacteria. So, obviously, the APAB-CD and terpenoid-CD mechanism of action is not limited to their interaction with the bacterial membrane, which has been shown earlier for CDs. Further research may open new prospects for the development of adjuvants to improve the therapeutic regimens with existing, as well as with new anti-infective drugs.

Spectroscopy Approach for Highly-Efficient Screening of Lectin-Ligand Interactions in Application for Mannose Receptor and Molecular Containers for Antibacterial Drugs

Rational search of a ligand for a specific receptor is a cornerstone of a typical drug discovery process. However, to make it more “rational” one would appreciate having detailed information on the functional groups involved in ligand-receptor interaction. Typically, the 3D structure of a ligand-receptor complex can be built on the basis of time-consuming X-ray crystallography data. Here, a combination of FTIR and fluorescence methods, together with appropriate processing, yields valuable information about the functional groups of both the ligand and receptor involved in the interaction, with the simplicity of conventional spectrophotometry. We have synthesized the “molecular containers” based on cyclodextrins, polyethyleneimines (PEI) or spermine with mannose-rich side-chains of different molecular architecture (reticulated, star-shaped and branched) with variable parameters to facilitate delivery to alveolar macrophages. We have shown that synthetic mannose-rich conjugates are highly affine to the model mannose receptor ConA: K_d ≈ 10⁻⁵–10⁻⁷ M vs. natural ligand trimannoside (10⁻⁵ M). Further, it was shown that molecular containers effectively load levofloxacin (dissociation constants are 5·10⁻⁴–5·10⁻⁶ M) and the eugenol adjuvant (up to 15–80 drug molecules for each conjugate molecule) by including them in the cyclodextrins cavities, as well as by interacting with polymer chains. Promising formulations of levofloxacin and its enhancer (eugenol) in star-shaped and polymer conjugates of high capacity were obtained. UV spectroscopy demonstrated a doubling of the release time of levofloxacin into the external solution from the complexes with conjugates, and the effective action time (time of 80% release) was increased from 0.5 to 20–70 h. The synergy effect of antibacterial activity of levofloxacin and its adjuvants eugenol and apiol on Escherichia coli was demonstrated: the minimum effective concentration of the antibiotic was approximately halved.

Improvement of Biocatalytic Properties and Cytotoxic Activity of L-Asparaginase from Rhodospirillum rubrum by Conjugation with Chitosan-Based Cationic Polyelectrolytes

L-asparaginases (L-ASNases, EC 3.5.1.1) are a family of enzymes that are widely used for the treatment of lymphoblastic leukemias. L-ASNase from Rhodospirillum rubrum (RrA) has a low molecular weight, low glutaminase activity, and low immunogenicity, making it a promising enzyme for antitumor drug development. In our work, the complex formation and covalent conjugation of the enzyme with synthetic or natural polycationic polymers was studied. Among non-covalent polyelectrolyte complexes (PEC), polyethyleneimine (PEI) yielded the highest effect on RrA, increasing its activity by 30%. The RrA-PEI complex had increased stability to trypsinolysis, with an inactivation constant decrease up to 10-fold compared to that of the native enzyme. The covalent conjugation of RrA with chitosan-PEI, chitosan-polyethylene glycol (chitosan-PEG), and chitosan-glycol resulted in an increase in the specific activity of L-asparagine (up to 30%). RrA-chitosan-PEG demonstrated dramatically (by 60%) increased cytotoxic activity for human chronic myeloma leukemia K562 cells in comparison to the native enzyme. The antiproliferative activity of RrA and its conjugates was significantly higher (up to 50%) than for that of the commercially available EcA at the same concentration. The results of this study demonstrated that RrA conjugates with polycations can become a promising strategy for antitumor drug development.

Computer simulation of the Receptor-Ligand Interactions of Mannose Receptor CD206 in Comparison with the Lectin Concanavalin A Model

Computer modeling of complexation of mono- and oligosaccharide ligands with the main (fourth) carbohydrate-binding domain of the mannose receptor CD206 (CRD4), as well as with the model receptor concanavalin A (ConA), was carried out for the first time, using methods of molecular dynamics and neural network analysis. ConA was shown to be a relevant model of CD206 (CRD4) due to similarity of the structural organization of the binding sites and high correlation of the values of free energies of complexation between the literature data and computer modeling (r > 0.9). Role of the main factors affecting affinity of the ligand–receptor interactions is discussed: the number and nature of carbohydrate residues, presence of Me-group in the O1 position, type of the glycoside bond in dimannose. Complexation of ConA and CD206 with ligands is shown to be energetically caused by electrostatic interactions (E) of the charged residues (Asn, Asp, Arg) with oxygen and hydrogen atoms in carbohydrates; contributions of hydrophobic and van der Waals components is lower. Possibility of the additional stabilization of complexes due to the CH–π stacking interactions of Tyr with the Man plane is discussed. The role of calcium and manganese ions in binding ligands has been studied. The values of free energies of complexation calculated in the course of molecular dynamics simulation correlate with experimental data (published for the model ConA): correlation coefficient r = 0.68. The Pafnucy neural network was trained based on the set of PDBbind2020 ligand–receptor complexes, which significantly increased accuracy of the energy predictions to r = 0.8 and 0.82 for CD206 and ConA receptors, respectively. A model of normalization of the complexation energy values for calculating the relevant values of ΔG_bind, K_d is proposed. Based on the developed technique, values of the dissociation constants of a series of CD206 complexes with nine carbohydrate ligands of different structures were determined, which were not previously known. The obtained data open up possibilities for using computer modeling for the development of optimal drug carriers capable of active macrophage targeting, and also determine the limits of applicability of using ConA as a relevant model for studying parameters of the CD206 binding to various carbohydrate ligands.

FTIR-based L-asparaginase activity assay enables continuous measurements in optically dense media including blood plasma

Complex heterogeneous systems, such as micelles or blood plasma, represent a particularly challenging environment to measure the catalytic parameters of some enzymes, including l-asparaginase. Existing methods are strongly interfered by the presence of plasma proteins, amino acids, as well as other components of plasma. Here we show that FTIR spectroscopy enables continuous real-time measurement of catalytic activity of l-asparaginase, in native and in PEG-chitosan conjugated form, in aqueous solutions as well as in heterogeneous non-transparent multicomponent systems, including colloidal systems or blood plasma, with minimal or no sample preparation. The approach developed is potentially applicable to other enzymatic reactions where the spectroscopic properties of substrate and product do not allow direct measurement with absorption or fluorescence spectroscopy.

Moxifloxacin interacts with lipid bilayer, causing dramatic changes in its structure and phase transitions

Most drugs besides their intended activity, express undesired side effects, including those with the engagement of cell membrane. Previously, such undesired nonspecific effects on the membrane have been shown for a number of widely used nonsteroidal anti-inflammatory drugs. In this paper, we study the mechanism of interaction between moxifloxacin (Mox), antibacterial drug of broad specificity, with lipid bilayer of the liposomes of various compositions as a model of cell membrane using a combination of spectroscopy methods, including ATR-FTIR spectroscopy, circular dichroism, UV and fluorescence spectroscopy. The fine structure of the moxifloxacin-liposome complex, localization of the drug in bilayer and the main sites of Mox interaction with lipid membrane were determined. Lipid composition of the liposome plays a key role in the interaction with moxifloxacin, drastically affecting the loading efficiency, strength and character of drug binding, lipid phase segregation and phase transition parameters. In case of anionic liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and cardiolipin (CL^2-) the electrostatic interaction of negatively charged nitrogen in heterocycle moiety of moxifloxacin with cardiolipin phosphate groups is a crucial factor for stable complex formation. The study of moxifloxacin-liposome complex behavior at phase transition in bilayer by DSC method revealed that in DPPC/CL^2- liposomes system two microphases with different content of CL^2- coexist and Mox interacts with both of these microphases resulting in the formation of two types of complexes with different structure and phase transition temperature. This binding stabilized the gel-state of the lipid bilayer with increasing the phase transition temperature Tm up to 3-5 °C. A different situation is observed for neutral DPPC liposomes: drug interaction with bilayer results in defects formation and a fluidization effect in lipid bilayer, resulted to decrease the Tm value by 2-4 °C. Moxifloxacin is not firmly binding in the membrane of DPPC and drug releases rapidly.

Decreased epithelial to corneal thickness ratio in healthy fellow eyes of patients with unilateral bullous keratopathy

PURPOSE

To study the relationship between epithelial thickness (ET) and corneal thickness (CT) in healthy fellow eyes of patients with unilateral bullous keratopathy (BKP) and healthy subjects.

METHODS

Seventeen BKP patients (nine males, eight females, 73.2±10.4 years) and 40 healthy individuals (20 males, 20 females, 69.5±9.8 years) were included. All participants received anterior segment optical coherence tomography and specular microscopy with calculation of endothelial cell density. ET, CT, stromal thickness and ET-to-CT ratio were defined automatically (within 2 mm central area). Central epithelial thickness (CET) and central corneal thickness (CCT) were measured manually at the corneal centre and stromal thickness and CET-to-CCT ratio were calculated.

RESULTS

In healthy fellow eyes of BKP patients compared with eyes of healthy individuals ET was statistically significantly lower (p<0.001) while CT was statistically significantly higher (by 28.9 and 30.9 µm in 2 mm zone and corneal centre, respectively). Both 2 mm ET-to-CT ratio (0.091±0.01 and 0.10±0.004, respectively [p<0.001]) and CET-to-CCT ratio (0.083±0.006 and 0.97±0.005, respectively [p<0.0001]) were statistically significantly lower in healthy fellow eyes of BKP patients compared with eyes of healthy individuals. To identify healthy fellow eyes of BKP patients, area under curve for CET-to-CCT ratio and CET was 0.94 and 0.80, respectively (p=0.01), and for 2 mm ET-to-CT ratio and 2 mm ET was 0.91 and 0.80, respectively (p=0.03).

CONCLUSION

Decreased СET-to-СCT ratio resulting from simultaneous epithelial thinning and stromal thickening without significant corneal thickening indicates subclinical dysfunction of corneal endothelium in healthy fellow eyes in unilateral BKP patients.

"Wet" transepithelial phototherapeutic keratectomy in the management of persistent epithelial defects in the graft

Purpose

This study aimed to evaluate the efficacy of “wet” transepithelial phototherapeutic keratectomy (TE-PTK) for treating persistent epithelial defects (PEDs) in the corneal graft following penetrating keratoplasty (PKP).

Methods

This study describes a noncomparative, prospective interventional case series. Patients with post-PKP graft epithelial defects lasting >3 months despite previous treatments with extensive wear soft contact lenses, amniotic membrane transplantation, and tarsorrhaphy were treated with wet TE-PTK. A wet TE-PTK procedure including a “wet ablation” step was performed using the EC-5000 excimer laser. Follow-up visits were at post-PTK days 3, 5, 10, and 30, and at each month thereafter.

Results

Eight patients (8 eyes; 5 men and 3 women; mean age, 51.3±14.3 years; mean follow-up period, 9.1±3.0 months) were included in this study. The mean best-corrected visual acuity was 1.76±0.28 log minimum angle of resolution (logMAR) at baseline and improved to 1.1±0.22 logMAR at 10 days postoperatively (p=0.0156; the improvement was significant). This effect remained stable throughout the remainder of the follow-up period. The mean time from wet TE-PTK to complete reepithelization was 4.3±1.3 days.

Conclusion

Wet TE-PTK appears to be effective for patients with post-PKP PEDs in the corneal graft who have failed conservative measures or previous surgical interventions.

In Situ Observation of Chymotrypsin Catalytic Activity Change Actuated by Nonheating Low-Frequency Magnetic Field

Magnetomechanical modulation of biochemical processes is a promising instrument for bioengineering and nanomedicine. This work demonstrates two approaches to control activity of an enzyme, α-chymotrypsin immobilized on the surface of gold-coated magnetite magnetic nanoparticles (GM-MNPs) using a nonheating low-frequency magnetic field (LF MF). The measurement of the enzyme reaction rate was carried out in situ during exposure to the magnetic field. The first approach involves α-chymotrypsin-GM-MNPs conjugates, in which the enzyme undergoes mechanical deformations with the reorientation of the MNPs under LF MF (16-410 Hz frequency, 88 mT flux density). Such mechanical deformations result in conformational changes in α-chymotrypsin structure, as confirmed by infrared spectroscopy and molecular modeling, and lead to a 63% decrease of enzyme initial activity. The second approach involves an α-chymotrypsin-GM-MNPs/trypsin inhibitor-GM-MNPs complex, in which the activity of the enzyme is partially inhibited. In this case the reorientation of MNPs in the field leads to disruption of the enzyme-inhibitor complex and an almost 2-fold increase of enzyme activity. The results further demonstrate the utility of magnetomechanical actuation at the nanoscale for the remote modulation of biochemical reactions.

Novel Prodrug of Doxorubicin Modified by Stearoylspermine Encapsulated into PEG-Chitosan-Stabilized Liposomes

Here, we report a new modification of doxorubicin based on an amphiphilic stearoylspermine anchor, enabling loading into liposomal membranes. Doxorubicin is coupled with stearoylspermine through an acid-labile hydrazone linker to ensure the release of the drug in the acidic interstitium of tumors. Using ATR-FTIR spectroscopy (Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy), the mechanism of interaction of doxorubicin with the anionic liposomal membrane was studied: incorporation of stearoyl chains leads to an increase in local microfluidity, and the amino groups of spermine interact with the phosphate groups of lipids. To stabilize liposomes against aggregation, we applied the copolymer PEG-chitosan as a coating: complex formation leads to charge neutralization, and the liposomes grow in size. According to MTT tests and confocal microscopy for cell lines A459 and Caco-2, PEG-chitosan-coated liposomes are as effective as neutral liposomes but are much more stable.

[Cyanocobalamin-containing lubricant for topical therapy of LASIK-associated dry eye]

AIM

to study the effect of topical treatment with Artelac Balance, a cyanocobalamin-containing lubricant, in patients with post-LASIK corneal neuropathy and LASIK-associated dry eye.

MATERIAL AND METHODS

Patients scheduled for LASIK were enrolled. Inclusion criteria were contact lens wear for 5 years or longer and more than 6 diopters of myopia. The patients were divided into 3 groups. Group 1 was prescribed the cyanocobalamin-containing topical lubricant for 3 months before and 1 month after surgery, group 2 - the same cyanocobalamin-containing lubricant, but only for the first month after surgery, and group 3 received a standard preservative-free lubricant for the first month after surgery. Tear osmolarity and production as well as corneal sensitivity were assessed 90±10 days before and 30±3 days after surgery. The percentage of patients with dry eye symptoms and those who required prolonged use of lubricants were also estimated at day 30±3.

RESULTS

Preoperatively, there were no statistically significant differences in demographic characteristics, tear osmolarity, tear production, or corneal sensitivity between the three study groups. At day 30±3 after surgery, tear production and corneal sensitivity were both significantly higher in group 1 than in group 3 (16.8 mm vs. 13.2 mm, p=0.003 and 37.7±3.1 mm vs. 32.4±2.2 mm, p=0.023, respectively). As to the percentage of patients with dry eye symptoms and those who required prolonged use of lubricants, it was lower in group 1 than in group 3 (51.3% vs. 76.3%, p=0.03 and 38.5% vs. 63.2%, p=0.03, respectively). Between the groups 2 and 3, none of the studied parameters differed significantly.

CONCLUSION

Combined pre- and postoperative use of Artelac Balance, a cyanocobalamin-containing lubricant, has been proved effective in restoring corneal sensitivity and reducing dry eye symptoms in patients at high risk for developing LASIK-associated dry eye.

"Reagent-free" L-asparaginase activity assay based on CD spectroscopy and conductometry

A new method to determine the catalytic parameters of L-asparaginase using circular dichroism spectroscopy (CD spectroscopy) has been developed. The assay is based on the difference in CD signal between the substrate (L-asparagine) and the product (L-aspartic acid) of enzymatic reaction. CD spectroscopy, being a direct method, enables continuous measurement, and thus differentiates from multistage and laborious approach based on Nessler's method, and overcomes limitations of conjugated enzymatic reaction methods. In this work, we show robust measurements of L-asparaginase activity in conjugates with PEG-chitosan copolymers, which otherwise would not have been possible. The main limitation associated with the CD method is that the analysis should be performed at substrate saturation conditions (V max regime). For K M measurement, the conductometry method is suggested, which can serve as a complimentary method to CD spectroscopy. The activity assay based on CD spectroscopy and conductometry was successfully implicated to examine the catalytic parameters of L-asparaginase conjugates with chitosan and its derivatives, and for optimization of the molecular architecture and composition of such conjugates for improving biocatalytic properties of the enzyme in the physiological conditions. The approach developed is potentially applicable to other enzymatic reactions where the spectroscopic properties of substrate and product do not enable direct measurement with absorption or fluorescence spectroscopy. This may include a number of amino acid or glycoside-transforming enzymes.

[Bacterial recombinant L-asparaginases: properties, structure and anti-proliferative activity]

For more than 40 years L-asparaginases are used in combined therapy of acute lymphoblastic leukemia in children and the range of tumors sensitive to these enzymes constantly extends. This review summarizes results of studies aimed at creation of new systems for heterological expression of bacterial L-asparaginases as Erwinia carotovora (EwA), Helicobacter pylori (HpA), Yersinia pseudotuberculosis (YpA) and Rhodospirillum rubrum (RrA); special attention is paid to isolation of purified enzymes and their crystallization, modification by chitosan/polyethylene, physicochemical, kinetic and structural properties characterization, and the study of the cytotoxic or anti-proliferative activity of new recombinant L-asparaginases on cell cultures in vitro. The resultant recombinant L-asparaginases (EwA, YpA, HpA и RrA) exhibit reasonable cytotoxic action on the human leukemia cells comparable to the pharmacologically available L-asparaginase EcA and represent practical interest in respect to creation, on their basis, new effective antineoplastic remedies. Further prospects of researches on bacterial L-asparaginases are associated with development of analogs of Rhodospirillum rubrum L-asparaginase (RrA) by means of directed changes of the protein structure using genetic engineering, development of chito-PEGylation for receiving L-asparaginase preparations with improved pharmacokinetic characteristics.

Galactonolactone oxidoreductase from Trypanosoma cruzi employs a FAD cofactor for the synthesis of vitamin C

Trypanosoma cruzi, the aetiological agent of Chagas' disease, is unable to salvage vitamin C (l-ascorbate) from its environment and relies on de novo synthesis for its survival. Because humans lack the capacity to synthesize ascorbate, the trypanosomal enzymes involved in ascorbate biosynthesis are interesting targets for drug therapy. The terminal step in ascorbate biosynthesis is catalyzed by flavin-dependent aldonolactone oxidoreductases belonging to the vanillyl-alcohol oxidase (VAO) protein family. Here we studied the properties of recombinant T. cruzi galactonolactone oxidoreductase (TcGAL), refolded from inclusion bodies using a reverse micelles system. The refolded enzyme shows native-like secondary structure and is active with both l-galactono-1,4-lactone and d-arabinono-1,4-lactone. At odd with an earlier claim, TcGAL employs a non-covalently bound FAD as redox-active cofactor. Moreover, it is shown for the first time that TcGAL can use molecular oxygen as electron acceptor. This is in line with the absence of a recently identified gatekeeper residue that prevents aldonolactone oxidoreductases from plants to act as oxidases.

Monomer formation and function of p-hydroxybenzoate hydroxylase in reverse micelles and in dimethylsulfoxide/water mixtures

It has previously been postulated that the dimeric form of the flavoprotein p-hydroxybenzoate hydroxylase (PHBH) is important for catalysis. Here it is demonstrated that the monomeric form of PHBH is active. In a water/AOT/isooctane reverse micellar system, the function of the monomeric and dimeric forms of PHBH could be observed separately by varying the size of the micelles. A considerable decrease in the K(M) value for p-hydroxybenzoate (POHB) was found for monomeric PHBH, accompanied by a 1.5-fold decrease in enzymatic activity. The same tendency was observed when monomers of PHBH were formed by adding DMSO to the buffer. The FAD in PHBH and PHBH labeled with the fluorescence dye Alexa488 was investigated by time-resolved fluorescence anisotropy to observe monomer formation in water/DMSO mixtures. Monomer formation of PHBH occurred gradually with increasing DMSO content in the mixture. Pure PHBH monomers were detected at DMSO concentrations of 30 % (v/v) and higher.

Molecular details of ovalbumin-pectin complexes at the air/water interface: a spectroscopic study

To stabilize air-water interfaces, as in foams, the adsorption of surface-active components is a prerequisite. An approach to controlling the surface activity of proteins is noncovalent complex formation with a polyelectrolyte in the bulk phase. The molecular properties of egg white ovalbumin in a complex with pectin in the bulk solution and at air/water interfaces were studied using drop tensiometry (ADT) and time-resolved fluorescence anisotropy techniques. The complex formation of ovalbumin with pectin in the bulk resulted in the formation of a compact structure with a different spatial arrangement depending on the protein/pectin ratio. Complex formation did not provide an altered protein structure, whereas the conformational stability was slightly increased in the complex. In excess pectin, an overall condensed complex structure is formed, whereas at limited pectin concentrations the structure of the complex is more "segmental". The characteristics of these structures did not depend on pH in the 7.0 to 4.5 regime. Interaction with pectin in the bulk solution resulted in a significantly slower adsorption of the protein to the air/water interface. The limited mobility of the protein at the interface was found for both ovalbumin and ovalbumin-pectin complexes. From both the rotational dynamics and total fluorescence properties of the protein in the absence and presence of pectin, it was suggested that the complex does not dissociate at the interface. Ovalbumin in the complex retains its initial "aqueous" microenvironment at the interface, whereas in the absence of pectin the microenvironment of the protein changed to a more nonpolar one. This work illustrates a more general property of polyelectrolytes, namely, the ability to retain a protein in its microenvironment. Insight into this property provides a new tool for better control of the surface activity of complex biopolymer systems.

Reversible self-association of ovalbumin at air-water interfaces and the consequences for the exerted surface pressure

In this study the relation between the ability of protein self-association and the surface properties at air-water interfaces is investigated using a combination of spectroscopic techniques. Three forms of chicken egg ovalbumin were obtained with different self-associating behavior: native ovalbumin, heat-treated ov-albumin-being a cluster of 12-16 predominantly noncovalently bound proteins, and succinylated ovalbumin, as a form with diminished aggregation properties due to increased electrostatic repulsion. While the bulk diffusion of aggregated protein is clearly slower compared to monomeric protein, the efficiency of transport to the interface is increased, just like the efficiency of sticking to rather than bouncing from the interface. On a timescale of hours, the aggregated protein dissociates and adopts a conformation comparable to that of native protein adsorbed to the interface. The exerted surface pressure is higher for aggregated material, most probably because the deformability of the particle is smaller. Aggregated protein has a lower ability to desorb from the interface upon compression of the surface layer, resulting in a steadily increasing surface pressure upon reducing the available area for the surface layer. This observation is opposite to what is observed for succinylated protein that may desorb more easily and thereby suppresses the buildup of a surface pressure. Generally, this work demonstrates that modulating the ability of proteins to self-associate offers a tool to control the rheological properties of interfaces.

Solubilization and refolding of inclusion body proteins in reverse micelles

Today, many valuable proteins can be obtained in sufficient amounts using recombinant DNA techniques. However, frequently the expression of recombinant proteins results in the accumulation of the product in dense amorphous deposits inside the cells, called inclusion bodies. The challenge then is to transform these inactive and misfolded protein aggregates into soluble bioactive forms. Although a number of general guidelines have been proposed, the search for proper reconstitution conditions can be very laborious and time consuming. Here, we suggest a new versatile approach for solubilization and refolding of inclusion body proteins using a water-sodium bis-2-ethylhexyl sulfosuccinate-isooctane reverse micellar system. Instead of amorphous aggregates, a transparent solution is obtained, where refolded protein is entrapped inside the micelles. The entrapped enzyme has native-like secondary structure and catalytic activity. This approach has been implemented with Fusarium galactose oxidase and Stigmatella aurantiaca putative galactose oxidase.

Structure and dynamics of egg white ovalbumin adsorbed at the air/water interface

The molecular properties of egg white ovalbumin adsorbed at the air/water interface were studied using infrared reflection absorption spectroscopy (IRRAS) and time-resolved fluorescence anisotropy (TRFA) techniques. Ovalbumin adsorbed at the air/water interface adopts a characteristic partially unfolded conformation in which the content of the beta-sheet is 10% lower compared to that of the protein in bulk solution. Adsorption to the interface leads to considerable changes in the rotational dynamics of ovalbumin. The results indicate that the end-over-end mobility of the ellipsoidal protein becomes substantially restricted. This is likely to reflect a preferential orientation of the protein at the interface. Continuous compression of surface layers of ovalbumin causes local aggregation of the protein, resulting in protein-network formation at the interface. The altered protein-protein interactions contribute to the strong increase in surface pressure observed.

Stabilization and activation of alpha-chymotrypsin in water-organic solvent systems by complex formation with oligoamines

Formation of enzyme-oligoamine complexes was suggested as an approach to obtain biocatalysts with enhanced resistance towards inactivation in water-organic media. Complex formation results in broadening (by 20-40% v/v ethanol) of the range of cosolvent concentrations where the enzyme retains its catalytic activity (stabilization effect). At moderate cosolvent concentrations (20-40% v/v) complex formation activates the enzyme (by 3-6 times). The magnitude of activation and stabilization effects increases with the number of possible electrostatic contacts between the protein surface and the molecules of oligoamines (OA). Circular dichroism spectra in the far-UV region show that complex formation stabilizes protein conformation and prevents aggregation in water-organic solvent mixtures. Two populations of the complexes with different thermodynamic stabilities were found in alpha-chymotrypsin (CT)-OA systems depending on the CT/OA ratio. The average dissociation constants and stoichiometries of both low- and high-affinity populations of the complexes were estimated. It appears that it is the low-affinity sites on the CT surface that are responsible for the activation effect.

Formation of quasi-regular compact structure of poly(methacrylic acid) upon an interaction with alpha-chymotrypsin

Structure and dynamic properties of free poly(methacrylic acid) (PMA) and PMA complexed with alpha-chymotrypsin (CT) were studied using the time resolved fluorescence anisotropy technique. We have found that the interaction of PMA with CT induces the formation of a quasi-regular structure of PMA. At a CT/PMA weight ratio of 4:1 the interaction with CT leads to formation of approximately four equal segments of polyelectrolyte, each binding one CT molecule and characterized by an independent rotational mobility. Increase of the CT/PMA weight ratio above 8:1 gives rise to the overall rotation of the whole enzyme-polyelectrolyte complex. In water-ethanol mixtures the mobility of PMA segments containing CT decreases and the structure of the complex becomes even more rigid due to enhancement of the electrostatic interaction between CT and PMA. Formation of the compact and quasi-regular structure of the complex is perhaps the main reason behind the enhancement of enzyme stability and suppression of enzyme aggregation in water-organic cosolvent mixtures.

The chemical modification of alpha-chymotrypsin with both hydrophobic and hydrophilic compounds stabilizes the enzyme against denaturation in water-organic media

We considered alpha-chymotrypsin (CT) in homogeneous water-organic media as a model system to examine the influence of enzyme chemical modification with hydrophilic and hydrophobic substances on its stability, activity and structure. Both types of modifying agents may lead to considerable stabilization of the enzyme in water-ethanol and water-DMF mixtures: (i) the range of organic cosolvent concentration at which enzyme activity (Vm) is at least 100% of its initial value is broadened and (ii) the range of organic cosolvent concentration at which the residual enzyme activity is observed is increased. We found that for both types of modification the stabilization effect can be correlated with the changes in protein surface hydrophobicity/hydrophilicity brought about by the modification. Circular dichroism studies indicated that the effects of these two types of modification on CT structure and its behavior in water-ethanol mixtures are different. Differential scanning calorimetry studies revealed that after modification two or three fractions or domains, differing in their stability, can be resolved. The least stable fractions (or domains) have properties similar to native CT.