Boris Lakatoš

The effect of boromycin on the Ca2+ homeostasis

A boron-containing antibiotic, boromycin (BM), was found to influence the Ca2+ homeostasis in both excitable and non-excitable cells. In non-excitable cells (human erythrocytes and leucocytes) it inhibited the resting passive45Ca2+ transport in 10−6–10−5 mol/L concentrations. In human erythrocytes, the passive 45Ca2+ transport induced by the presence of 1 mmol/L NaVO3 was inhibited by boromycin (90% inhibition) as well. The inhibitory effect of BM on the NaVO3-induced passive 45Ca2+ transport was diminished in the presence of inhibitory concentrations of nifedipine (10 μmol/L – 60% inhibition) or of those of K+o (75 mmol/L – 20% inhibition). On the other hand, in rat brain synaptosomes, and rat cardiomyocytes, BM stimulated the passive 45Ca2+ transport in ‘resting’ cells at similar concentrations. In rat cardiomyocytes the stimulation was transient. The stimulatory effect on the passive 45Ca2+ transport in rat brain synaptosomes was accompanied with the increase of cytoplasmic Ca2+ concentration measured by means of the entrapped fluorescent Ca2+ chelator fura-2. The stimulatory effect of BM was diminished when synaptosomes were pre-treated with veratridine (10 μmol/L) which itself stimulated the passive 45Ca2+ transport. At saturating concentrations of veratridine, no stimulatory effect of BM was observed. These results could be explained by the indirect interaction of BM with both Ca2+ and Na+ transport systems via transmembrane ionic gradients of monovalent cations and could be useful in determining whether the cells belong to excitable, or non-excitable cells.

Cold plasma treatment triggers antioxidative defense system and induces changes in hyphal surface and subcellular structures of Aspergillus flavus

The cold atmospheric-pressure plasma (CAPP) has become one of the recent effective decontamination technologies, but CAPP interactions with biological material remain the subject of many studies. The CAPP generates numerous types of particles and radiations that synergistically affect cells and tissues differently depending on their structure. In this study, we investigated the effect of CAPP generated by diffuse coplanar surface barrier discharge on hyphae of Aspergillus flavus. Hyphae underwent massive structural changes after plasma treatment. Scanning electron microscopy showed drying hyphae that were forming creases on the hyphal surface. ATR-FTIR analysis demonstrated an increase of signal intensity for C=O and C-O stretching vibrations indicating chemical changes in molecular structures located on hyphal surface. The increase in membrane permeability was detected by the fluorescent dye, propidium iodide. Biomass dry weight determination and increase in permeability indicated leakage of cell content and subsequent death. Disintegration of nuclei and DNA degradation confirmed cell death after plasma treatment. Damage of plasma membrane was related to lipoperoxidation that was determined by higher levels of thiobarbituric acid reactive species after plasma treatment. The CAPP treatment led to rise of intracellular ROS levels detected by fluorescent microscopy using 2′,7′-dichlorodihydrofluorescein diacetate. At the same time, antioxidant enzyme activities increased, and level of reduced glutathione decreased. The results in this study indicated that the CAPP treatment in A. flavus targeted both cell surface structures, cell wall, and plasma membrane, inflicting injury on hyphal cells which led to subsequent oxidative stress and finally cell death at higher CAPP doses.

Silver pyridine-2-sulfonate complex - its characterization, DNA binding, topoisomerase I inhibition, antimicrobial and anticancer response

In the current study the ability of silver pyridine-2-sulfonate complex to exert multiple biological activities is compared with the pharmacological action of silver sulfadiazine (AgSD). Polymeric form of {[Ag(py-2-SO3)]}n (AgPS) was synthesized and characterized by analytical techniques (IR, CHN, TG/DTA, MS) and its molecular formula was established. The crystal structure was determined by X-ray diffraction method and the polymeric complex crystallizes in the triclinic P-1 space group. The stability of Ag(I) complex was verified by 1H and 13C NMR measurements and the interaction with calf thymus DNA through UV-VIS and fluorescence quenching experiments was studied. The Ag(I) complex was able to interact with DNA by dual binding mode: partial intercalation along groove binding. The binding constants were calculated to be in the order of 103 M-1. Topoisomerase I inhibition study have shown that silver complex is inhibiting its activity at concentration of 30 μM. The cytotoxic activity of AgPS and AgSD against mouse leukaemia L1210 S, R and T cell line was also evaluated. AgPS showed higher cytotoxicity than AgSD after 48 h incubation. The results suggest that mechanism of cell death is necrosis with a contribution of late apoptosis. Antimicrobial testing indicates higher growth inhibition effect of AgPS with comparison to commercially available AgSD.

New effects and applications of thioflavins

The thiazol dye Thioflavin T (ThT), which is used to stain amyloid fibrils, was found to have strong inhibitory effects on both growth and conidiation of the deuteromycete Trichoderma viride at concentrations between 10–100 µg/ml (ca. 30–300 µmol/l). Thioflavin S (ThS), also known to stain amyloid fibrils, had no significant effect at these concentrations. Both stains yielded a fluorescence response, but their distributions were different. ThT was non-homogenously distributed throughout the cytoplasm, whereas ThS fluorescence was strongly bound to septal regions. The effect of ThT was studied on several model microorganisms. It exerted a strong inhibitory effect on Staphylococcus aureus (Gram-positive bacterium) (MIC=10 µmol/l), but the effect on Escherichia coli (Gram-negative bacterium) was one order of magnitude less pronounced. The effect on Candida albicans was also very strong (MIC=50 µmol/l). The dermatophytic fungus Microsporum gypseum and deuteromycete Alternaria alternata were less affected by ThT (MIC=250 µmol/l and >500 µmol/l, respectively). These results show that ThT could be a useful inhibitor of selected microorganisms, whereas ThS could be a useful agent for monitoring formation and maintenance of intrahyphal septa without inhibiting the growth of the microorganism.