Influence of pH and plant growth regulators on secondary metabolite production and antioxidant activity of Stevia rebaudiana (Bert)

Background and purpose: Beside being rich with sweet glycosides, Stevia rebaudiana Bertoni is an interesting source of flavonoids and phenols. The current study aimed to assess the potential for increasing total phenols and flavonoids in S. rebaudiana tissue by varying concentrations of plant growth regulators (PGR) and pH levels of media. Materials and methods: The culture was established from seeds and propagated shoots were cultured on media of different pH levels (4.6, 5.8 and 7.4) and PGR. Total polyphenolics and free radical scavenging capability of leaf, callus and root extracts were determined. Shoot height, root length, shoot and root number were also recorded. Results: Shoot elongation and root development was stimulated by singly applied growth regulators though the values of both parameters were also satisfactory in PGR-free media. In the latter media, pH value of 4.6 was a main factor for increasing leaf metabolite levels. A most significant rise in phenols and flavonoids was evident in response to combination of BA either with GA3 or IAA compared to singly applied regulators indicating synergistic effects of PGR (especially of auxins and cytokinins). However, polyphenolics levels and their distribution between different tissues were also influenced by medium pH value. A positive correlation was found between antioxidant activity of S. rebaudiana extracts and phenols and flavonoids. Conclusions: The results show that PGR and medium pH value strongly affect accumulation of secondary metabolites and can lead to significant enhancement in productivity of bioactive polyphenolics in S. rebaudiana plant cultures

Come-back of phenanthridine and phenanthridinium derivatives in 21st century

Phenanthridine derivatives are one of the most intensively studied families of biologically active compounds with efficient DNA binding ; attracting attention about time of DNA structure discovery (1960ies), early recognized as a symbol of DNA intercalative binding, for many decades applied as gold-standard DNA- and RNA-fluorescent markers (ethidium bromide), probes for cell viability (propidium iodide), but also “ill-famed” for various toxic (genotoxic) and mutagenic effects. After two decades of low interest, the discovery of phenanthridine alkaloids and new studies of antiparasitic/antitumour properties of phenanthridine derivatives resulted in the strong increase of the scientific interest about the turn of this century. Here are summarized phenanthridine-related advances in the 21st century (2000-present period) with emphasis on the supramolecular interactions and bioorganic chemistry, as well as novel or improved synthetic approaches

Surface-enhanced Raman scattering study of the binding modes of a dibenzotetraaza[14]annulene derivative with DNA/RNA polynucleotides

Binding modes of a dibenzotetraaza[14]annulene (DBTAA) derivative with synthetic nucleic acids were studied using surface-enhanced Raman spectroscopy (SERS). Changes in SERS intensity and appearance of new bands in spectra were attributed to different complexes formed between the DBTAA molecules and DNA/RNA polynucleotides. A decrease in intensity pointed to intercalation as the dominant binding mode of the annulene derivative with poly dGdC-poly dGdC and poly rA-poly rU, whereas new bands in the spectra at 735 cm−1 and 1345 cm−1 revealed binding within the minor groove of poly dAdT-poly dAdT. When all the dominant binding sites were occupied, SERS spectra implied that small molecules bind on the outside of the DNA analogues, while exist mainly as free molecules in equimolar ratio with the synthetic RNA polynucleotide, thereby indicating higher affinity for DNA than for RNA

Biological Activity of Flavonoids and Rare Sesquiterpene Lactones Isolated From Centaurea ragusina L.

The endemic Croatian species Centaurea ragusina L., like other species from the genus Centaurea, has been traditionally used in Croatia as an antibacterial agent and for the treatment of gastrointestinal and urogenital disorders. In several chromatographic steps, three flavonoids and three sesquiterpene lactones (STLs) were isolated and identified from the most active fractions of the ethanol extract. Two STLs, one for which we created the trivial name ragusinin, and hemistepsin A are here reported for the first time as constituents of the genus Centaurea. All six compounds were screened for their effect on several tumor and one normal cell lines. Among them, ragusinin showed the best bioactivity and high specificity to affect tumor murine SCCVII, human HeLa and Caco-2 cell lines, but not the viability of normal V79 fibroblasts. Due to these characteristics the action of ragusinin was investigated in more detail. Since DNA is the primary target for many drugs with antibacterial and anticancer activity, we studied its interaction with ragusinin. Rather moderate binding affinity to DNA excluded it as the primary target of ragusinin. Due to the possibility of STL interaction with glutathione (GSH), the ubiquitous peptide that traps reactive compounds and other xenobiotics to prevent damage to vital proteins and nucleic acids, its role in deactivation of ragusinin was evaluated. Addition of the GSH precursor N- acetyl-cysteine potentiated the viability of HeLa cells, while the addition of GSH inhibitor L-buthionine sulfoximine decreased it. Moreover, pre-treatment of HeLa cells with the inhibitor of glutathione-S-transferase decreased their viability indicating the detoxifying role of GSH in ragusinin treated cells. Cell death, derived by an accumulation of cells in a G2 phase of the cell cylce, was shown to be independent of poly (ADP-ribose) polymerase and caspase-3 cleavage pointing toward an alternative cell death pathway

Molecular recognition of AT-DNA sequences by the induced CD pattern of dibenzotetraaza[14]annulene (DBTAA) - adenine derivatives

An investigation of the interactions of two novel and several known DBTAA–adenine conjugates with double-stranded DNA and RNA has revealed the DNA/RNA groove as the dominant binding site which is in contrast to the majority of reviously studied DBTAA analogues (DNA/RNA intercalators). Only DBTAA–propyladenine conjugates revealed the molecular recognition of AT-DNA by an ICD band pattern > 300 nm, whereas significant ICD bands did not appear for other ds-DNA/RNA. A structure–activity relation for the studied series of compounds showed that the essential structural features for the ICD recognition are a) the presence of DNA-binding appendages (adenine side chain and positively charged side chain) on both DBTAA side chains, and b) the presence of a short propyl linker, which does not support intramolecular aromatic stacking between DBTAA and adenine. The observed AT-DNA-ICD pattern differs from previously reported ss-DNA (poly dT) ICD recognition by a strong negative ICD band at 350 nm, which allows for the dynamic differentiation between ss-DNA (poly dT) and coupled ds-AT-DNA

Cationic side-chains control DNA/RNA binding properties and antiproliferative activity of dicationic dibenzotetraaza[14]annulene derivatives

Studied dicationic dibenzotetraaza[14]annulene derivatives intercalate into synthetic double stranded DNA and RNA, while their positively charged side-chains additionally interact within the minor groove of polynucleotides, contributing to the overall affinity of compounds and controlling pronounced A-T(U) over G-C sequence preference as well as stronger thermal stabilization of ds-DNA than ds-RNA. Furthermore, all compounds showed moderate to high antiproliferative activity against five human tumour cell lines, whereby clear correlation between structure of the side-chain and cytotoxic activity was observed

Biological Activity of Newly Synthesized Benzimidazole and Benzothizole 2,5‐Disubstituted Furane Derivatives

Newly designed and synthesized cyano, amidino and acrylonitrile 2, 5‐disubstituted furane derivatives with either benzimidazole/benzothiazole nuclei have been evaluated for antitumor and antimicrobial activity. For potential antitumor activity, the compounds were tested in 2D and 3D cell culture methods on three human lung cancer cell lines, A549, HCC827 and NCI‐H358, with MTS cytotoxicity and BrdU proliferation assays in vitro. Compounds 5, 6, 8, 9 and 15 have been proven to be compounds with potential antitumor activity with high potential to stop the proliferation of cells. In general, benzothiazole derivatives were more active in comparison to benzimidazole derivatives. Antimicrobial activity was evaluated with Broth microdilution testing (according to CLSI (Clinical Laboratory Standards Institute) guidelines) on Gram‐negative Escherichia coli and Gram‐positive Staphylococcus aureus. Additionally, Saccharomyces cerevisiae was included in testing as a eukaryotic model organism. Compounds 5, 6, 8, 9 and 15 showed the most promising antibacterial activity. In general, the compounds showed antitumor activity, higher in 2D assays in comparison with 3D assays, on all three cell lines in both assays. In natural conditions, compounds with such an activity profile (less toxic but still effective against tumor growth) could be promising new antitumor drugs. Some of the tested compounds showed antimicrobial activity. In contrast to ctDNA, the presence of nitro group or chlorine in selected furane‐benzothiazole structures did not influence the binding mode with AT‐DNA. All compounds dominantly bound inside the minor groove of AT‐DNA either in form of monomers or dimer and higher‐order aggregates

Recognition of ATT Triplex and DNA:RNA Hybrid Structures by Benzothiazole Ligands

Interactions of an array of nucleic acid structures with a small series of benzothiazole ligands (bis-benzothiazolyl-pyridines—group 1, 2- thienyl/2-benzothienyl-substituted 6-(2- imidazolinyl) benzothiazoles—group 2, and three 2- aryl/heteroaryl-substituted 6-(2- imidazolinyl)benzothiazoles—group 3) were screened by competition dialysis. Due to the involvement of DNA:RNA hybrids and triplex helices in many essential functions in cells, this study’s main aim is to detect benzothiazole based moieties with selective binding or spectroscopic response to these nucleic structures compared to regular (non- hybrid) DNA and RNA duplexes and single-stranded forms. Complexes of nucleic acids and benzothiazoles, selected by this method, were characterized by UV/Vis, fluorescence and circular dichroism (CD) spectroscopy, isothermal titration calorimetry, and molecular modeling. Two compounds (1 and 6) from groups 1 and 2 demonstrated the highest affinities against 13 nucleic acid structures, while another compound (5) from group 2, despite lower affinities, yielded higher selectivity among studied compounds. Compound 1 significantly inhibited RNase H. Compound 6 could differentiate between B- (binding of 6 dimers inside minor groove) and A- type (intercalation) helices by an induced CD signal, while both 5 and 6 selectively stabilized ATT triplex in regard to AT duplex. Compound 3 induced strong condensation-like changes in CD spectra of AT-rich DNA sequences