Interaction of drugs with extranuclear genetic elements and its consequences

Euglenoid flagellates: a multifaceted biotechnology platform

Euglenoid flagellates are mainly fresh water protists growing in highly diverse environments making them well-suited for a multiplicity of biotechnology applications. Phototrophic euglenids possesses complex chloroplasts of green algal origin bounded by three membranes. Euglena nuclear and plastid genome organization, gene structure and gene expression are distinctly different from other organisms. Our observations on the model organism Euglena gracilis indicate that transcription of both the plastid and nuclear genome is insensitive to environmental changes and that gene expression is regulated mainly at the post-transcriptional level. Euglena plastids have been proposed as a site for the production of proteins and value added metabolites of biotechnological interest. Euglena has been shown to be a suitable protist species to be used for production of several compounds that are used in the production of cosmeceuticals and nutraceuticals, such as α-tocopherol, wax esters, polyunsaturated fatty acids, biotin and tyrosine. The storage polysaccharide, paramylon, has immunostimulatory properties and has shown a promise for biomaterials production. Euglena biomass can be used as a nutritional supplement in aquaculture and in animal feed. Diverse applications of Euglena in environmental biotechnology include ecotoxicological risk assessment, heavy metal bioremediation, bioremediation of industrial wastewater and contaminated water.

Protection of selenium on hepatic mitochondrial respiratory control ratio and respiratory chain complex activities in ducklings intoxicated with aflatoxin B₁

To investigate the protection of selenium on hepatic mitochondrial functions, 90 7-day-old ducklings were randomly divided into three groups (groups I-III). Group I was used as a blank control. Group II was administered with aflatoxin B(1) (0.1 mg/kg body weight). Group III was administered with aflatoxin B(1) (0.1 mg/kg body weight) plus selenium (sodium selenite, 1 mg/kg body weight). All treatments were given once daily for 21 days. The results showed that the activities of hepatic mitochondrial complexes I-IV in group II ducklings significantly decreased when compared with group I (P < 0.01). Furthermore, the activities of hepatic mitochondrial complexes I-IV in group III significantly increased when compared with group II (P < 0.05). The hepatic mitochondrial respiratory control ratio (RCR) in group II ducklings significantly decreased when compared with group I (P < 0.01). In addition, the hepatic mitochondrial RCR in group III significantly increased when compared with group II (P < 0.05). These results revealed that the aflatoxin B(1) significantly induced hepatic mitochondrial dysfunction in the activities of hepatic mitochondrial respiratory chain complexes I-IV and the RCR in ducklings. However, sodium selenite could significantly ameliorate the negative effect induced by aflatoxin B(1).

Potential antimutagenic activity of berberine, a constituent of Mahonia aquifolium

BACKGROUND

As part of a study aimed at developing new pharmaceutical products from natural resources, the purpose of this research was twofold: (1) to fractionate crude extracts from the bark of Mahonia aquifolium and (2) to evaluate the strength of the antimutagenic activity of the separate components against one of the common direct-acting chemical mutagens.

METHODS

The antimutagenic potency was evaluated against acridine orange (AO) by using Euglena gracilis as an eukaryotic test model, based on the ability of the test compound/fraction to prevent the mutagen-induced damage of chloroplast DNA.

RESULTS

It was found that the antimutagenicity of the crude Mahonia extract resides in both bis-benzylisoquinoline (BBI) and protoberberine alkaloid fractions but only the protoberberine derivatives, jatrorrhizine and berberine, showed significant concentration-dependent inhibitory effect against the AO-induced chloroplast mutagenesis of E. gracilis. Especially berberine elicited, at a very low dose, remarkable suppression of the AO-induced mutagenicity, its antimutagenic potency being almost three orders of magnitude higher when compared to its close analogue, jatrorrhizine. Possible mechanisms of the antimutagenic action are discussed in terms of recent literature data. While the potent antimutagenic activity of the protoberberines most likely results from the inhibition of DNA topoisomerase I, the actual mechanism(s) for the BBI alkaloids is hard to be identified.

CONCLUSIONS

Taken together, the results indicate that berberine possesses promising antimutagenic/anticarcinogenic potential that is worth to be investigated further.

Antioxidative and antimutagenic activity of yeast cell wall mannans in vitro

Antioxidative and antimutagenic effect of yeast cell wall mannans, in particular, extracellular glucomannan (EC-GM) and glucomannan (GM-C.u.) both from Candida utilis, mannan from Saccharomyces cerevisiae (M-S.c.) and mannan from Candida albicans (M-C.a.) was evaluated. Luminol-dependent photochemical method using trolox as a standard showed that EC-GM, GM-C.u., M-S.c. and M-C.a. have relatively good antioxidative properties. EC-GM exhibited the highest antioxidative activity, followed by GM-C.u. and M-S.c. M-C.a. showed the least antioxidative activity. These mannans were experimentally confirmed to exhibit different, statistically significant antimutagenic activity in reducing damage of chloroplast DNA of the flagellate Euglena gracilis induced by ofloxacin and acridine orange (AO). We suggest that the antimutagenic effect of EC-GM, GM-C.u., M-S.c. and M-C.a. against ofloxacin is based on their ability to scavenge reactive oxygen radicals. With AO, the reduction of the chloroplast DNA lession could be a result of the absorptive capacity of the mannans. The important characteristics of mannans isolated from the yeast cell walls, such as good water solubility, relatively small molecular weight (15-30kDa), and antimutagenic effect exerted through different mode of action, appear to be a promising features for their prospective use as a natural protective (antimutagenic) agents.

Phenolic acids inhibit chloroplast mutagenesis in Euglena gracilis

The mutagenicity (bleaching activity) of ofloxacin (43 microM) and acridine orange (AO) (13.5 microM) in Euglena gracilis is inhibited by plant phenolics. Caffeic acid (CA), p-coumaric acid (PCA), ferulic acid (FA) and gentisic acid (GA) (25, 50, 100 and 250 microM) exhibited a significant concentration-dependent inhibitory effect against ofloxacin-induced mutagenicity, which was very effectively eliminated by the highest concentration of all four of those phenolic acids. The mutagenicity of AO was also significantly reduced in the presence of CA, PCA and FA (25, 50, 100 and 250 microM). However, GA exhibited no significant activity, even at the concentration of 250 microM. Based on the UV spectrophotometric measurements, we suggest that the antimutagenic effect of CA, PCA, FA and GA resulted from the scavenging of reactive oxygen species (ROS) produced by ofloxacin. On the other hand, the reduction of AO-induced mutagenicity correlates with the binding capabilities of CA, PCA and FA, with the exception of GA.

Activity of some 3-formylchromone derivatives on the induction of chloroplast-free mutants in Euglena gracilis

The hereditary bleaching test on Euglena gracilis was used for detecting extranuclear mutations. The highest bleaching activity (induction of the chloroplast-free mutants) was shown by the 6-R-3-formylchromones. On the other hand, bleaching-inactive 6-R-3-formylchromone acylhydrazones (derived from gallic and salicylic acids), added at sufficient concentrations in the case of chloroplast mutagenesis in E. gracilis, act as a potent antimutagen. This effect appeared to be a unique feature of chromone derivatives, but was dependent on the type of mutagen. These substances were very effective against the bleaching activity of acridine orange, and were less effective against N-methyl-N'-nitro-N-nitrosoguanidine. The genotoxic effects of these mutagens was reduced, especially during the first stages of induction of this specific cytoplasmic mutation. The experimental study of mutagenicity and antimutagenicty of 3-formylchromone hydrazones was reinforced by data obtained by the semi-empirical AM1 method and lipophilicity values.

Antimutagenicity of milk fermented by Enterococcus faecium

The diethyl ether extracts isolated from unfermented milk and milk fermented by Enterococcus faecium exhibited dose-dependent inhibition of mutagenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), nitrovin (NIT), 5-nitro-2-furylacrylic acid (NFA) and UV-irradiation on the Ames bacterial test (Salmonella typhimurium strains TA97 and TA100) and the unicellular flagellate Euglena gracilis. Overall, the fermented milk extract was the most active against UV-irradiation, less active against NIT and MNNG, and the least active against NFA on bacteria. The highest antibleaching effects were observed against MNNG. The differences between antimutagenic effects from fermented and unfermented milk extracts were determined to be statistically significant at the 0.95 CI level.

Synthesis, antimicrobial activity and bleaching effect of some reaction products of 4-oxo-4H-benzopyran-3-carboxaldehydes with aminobenzothiazoles and hydrazides

The synthesis of the biologically active novel systems derived from reaction of 3-formylchromones with three types of amino derivatives, 6-R2-2-aminobenzothiazoles, 6-amino-2-R3-thiobenzothiazoles and hydrazide derivatives (derived from cyanoacetic, isonicotine, salicylic and gallic acids) was carried out. The structures of the prepared compounds have been proved by elemental analysis, 1H NMR and IR spectra. Antimicrobial activity was studied against the following microorganisms--bacteria G+ (Staphylococcus aureus 29/58, Bacillus subtilis 18/66), G- (Escherichia coli 326/71, Pseudomonas aeruginosa); yeasts: Candida albicans, Saccharomyces cerevisiae; moulds: Microsporum gypseum, Aspergillus niger, Scopulariopsis brevicaulis; and against typical and atypical mycobacteria: Mycobacterium tuberculosis (H37Rv), Mycobacterium kansasii (PFG 8), Mycobacterium avium (My 80/72), Mycobacterium fortuitum (1021). The hereditary bleaching effect on the plastid system of Euglena gracilis, a unique phenomenon of the biological activity of chromone derivatives, is reported. The bleaching test on E. gracilis is used for detecting extranuclear mutations.

Euglena gracilis as an eukaryotic test organism for detecting mutagens and antimutagens

The unicellular flagellate Euglena gracilis was used in order to assess the inhibition of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitrosourea (MNU) mutagenicities, which induce white mutants due to the irreversible loss of chloroplasts. All tested compounds, including o-aminobenzoic acid and p-aminobenzoic acid, salicylic acid, acetylsalicylic acid, sodium salicylate and p-aminosalicylic acid, were not mutagenic per se and inhibited MNNG mutagenicity by at least 50%. The last two compounds inhibited by at least 50% also MNU mutagenicity.

Antimutagens reduce ofloxacin-induced bleaching in Euglena gracilis

The genotoxic effect of ofloxacin was significantly decreased by standard antimutagens (sodium selenite, ascorbic acid, butylated hydroxyanisole and butylated hydroxytoluene) in the unicellular flagellate Euglena gracilis. The antiofloxacin activity of sodium selenite was also documented by a bacterial test in which the repair-proficient strain Salmonella typhimurium TA102 was used.

Euglena gracilis as a supplementary test organism for detecting biologically active compounds

The mutagenic activity of more than 120 antimicrobial agents and protective components was investigated. Only Kathon showed a consistent increase in revertant counts in the Ames test on Salmonella typhimurium. The hereditary bleaching test on Euglena gracilis used for detecting extranuclear mutations, showed positive results for Kathon, triethanolamine and diamine silver tetraborate.

Antimutagenicity in Euglena gracilis

The genotoxic effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and furadantine (Fu) was significantly decreased by standard antimutagens (ascorbic acid, alpha-tocopherol, chlorophyllin and sodium selenite) in the unicellular flagellate Euglena gracilis. The effects of these compounds were verified also by a bacterial test in which three strains of Salmonella typhimurium, TA97, TA100, and TA102, were used. The above compounds were antimutagenic in strains of bacteria used, except for chlorophyllin which had no effect on strain TA102.

Formation of N-hydroxy-N-arylacetamides from nitroso aromatic compounds by the mammalian pyruvate dehydrogenase complex

Bovine, human and porcine heart mitochondria and isolated porcine heart pyruvate dehydrogenase complex (PDHC) pyruvate-dependently form N-hydroxy-N-arylacetamides from nitroso aromatic compounds, including carcinogenic 4-biphenyl and 2-fluorenyl derivatives. The PDHC-catalysed formation of N-hydroxyacetanilide (N-OH-AA) from nitrosobenzene (NOB), through a Ping Pong mechanism, is optimum at pH 6.8 and is accelerated by thiamin pyrophosphate, but is inhibited by thiamin thiazolone pyrophosphate and ATP. Km pyruvate in the reaction is independent of pH over the range tested, whereas KmNOB increases at lower pH, owing to ionization of an active-site functional group of pKa 6.3. The enzymic ionization decreases log (Vmax/KmNOB). Isolated pyruvate dehydrogenase (E1), a constitutive enzyme of PDHC, forms N-OH-AA by itself and has comparable kinetic parameters to those of the PDHC-catalysed N-OH-AA formation. The catalytic efficiency of PDHC in the formation of N-hydroxy-N-arylacylamides, due to the steric limitation of the active site of E1, is lowered both by bulky alkyl groups of alpha-oxo acids and by p-substituents (but not an o-substituent) on nitrosobenzenes. These nitroso compounds serve as electrophiles in the reaction in which the reductive acetylation step is rate-limiting. The reaction mechanism and other factors affecting N-hydroxy-N-arylacylamide formation are discussed.

Mitochondrial DNA damage by anticancer agents

Mitochondrial DNA (mtDNA) is susceptible to damage by a number of anticancer agents either directly or indirectly. This damage is of little consequence if only a few of the mtDNA molecules are damaged. However, multiple drug treatments could result in a significant effect on a cell's ability to survive. The differential effect of anticancer agents on either organ specific toxicities or selective tumor kill can be partially accounted for by differential mtDNA content of cells and on the basis of differential protective mechanisms within mitochondria of various organs or tumor tissue. The concept of damage to mitochondria, especially its genome, is a subject of active investigation in various laboratories. This area of research may provide mechanism(s) by which organ specific toxicities or tumor specific toxicities may be elaborated. Also, the concept of targeting tumor specific mitochondria and/or mtDNA by anticancer agents is very attractive but has not come to fruition due to a lack of understanding of the regulation of the genome in tumor cells. Future investigations in this arena will enhance our knowledge on the interaction between anticancer agents and extranuclear DNA.