Anticlastogenicity of two derivatives of 1,4-dihydroisonicotinic acid in mouse micronucleus test

Genotoxic and genoprotective effects of 1,4-dihydropyridine derivatives: a brief review

This review summarises current knowledge about the genotoxic and genoprotective effects of 1,4-dihydropyridines (DHP) with the main focus on the water-soluble 1,4-DHPs. Most of these water-soluble compounds manifest very low calcium channel blocking activity, which is considered "unusual" for 1,4-DHPs. Glutapyrone, diludine, and AV-153 decrease spontaneous mutagenesis and frequency of mutations induced by chemical mutagens. AV-153, glutapyrone, and carbatones protect DNA against the damage produced by hydrogen peroxide, radiation, and peroxynitrite. The ability of these molecules to bind to the DNA may not be the only mechanism of DNA protection, as other mechanisms such as radical scavenging or binding to other genotoxic compounds may take place and enhance DNA repair. These uncertainties and reports of high 1,4-DHP concentrations damaging the DNA call for further in vitro and in vivo preclinical research, pharmacokinetic in particular, as it can help pinpoint the exact mechanism(s) of the genotoxic and/or genoprotective action of 1,4-DHPs.

Study of interaction of antimutagenic 1,4-dihydropyridine AV-153-Na with DNA-damaging molecules and its impact on DNA repair activity

Background

1,4-dihydropyridines (1,4-DHP) possesses important biochemical and pharmacological properties, including antioxidant and antimutagenic activities. It was shown that the antimutagenic 1,4-dihydropyridine AV-153-Na interacts with DNA. The aim of the current study was to test the capability of the compound to scavenge peroxynitrite and hydroxyl radical, to test intracellular distribution of the compound, and to assess the ability of the compound to modify the activity of DNA repair enzymes and to protect the DNA in living cells against peroxynitrite-induced damage.

Methods

Peroxynitrite decomposition was assayed by UV spectroscopy, hydroxyl radical scavenging—by EPR spectroscopy. DNA breakage was determined by the “comet method”, activity of DNA repair enzymes—using Glyco-SPOT and ExSy-SPOT assays. Intracellular distribution of the compound was studied by laser confocal scanning fluorescence microscopy. Fluorescence spectroscopy titration and circular dichroism spectroscopy were used to study interactions of the compound with human serum albumin.

Results

Some ability to scavenge hydroxyl radical by AV-153-Na was detected by the EPR method, but it turned out to be incapable of reacting chemically with peroxynitrite. However, AV-153-Na effectively decreased DNA damage produced by peroxynitrite in cultured HeLa cells. The Glyco-SPOT test essentially revealed an inhibition by AV-153-Na of the enzymes involved thymine glycol repair. Results with ExSy-SPOT chip indicate that AV-153-Na significantly stimulates excision/synthesis repair of 8-oxoguanine (8-oxoG), abasic sites (AP sites) and alkylated bases. Laser confocal scanning fluorescence microscopy demonstrated that within the cells AV-153-Na was found mostly in the cytoplasm; however, a stain in nucleolus was also detected. Binding to cytoplasmic structures might occur due to high affinity of the compound to proteins revealed by spectroscopical methods.

Discussion

Activation of DNA repair enzymes after binding to DNA appears to be the basis for the antimutagenic effects of AV-153-Na.

Randomly amplified polymorphic DNA as a tool for genotoxicity: an assessment

Novel short-term assays are required to substantiate the battery of assessment methods for evaluating the genotoxicity of candidate drugs. In this study, an attempt has been made to evaluate randomly amplified polymorphic DNA (RAPD) analysis for its potential to establish genotoxic effect of a known genotoxicant, ie, ethyl methanesulfonate (EMS) in Swiss mice (Mus musculus). Based on the RAPD profiles, genetic damages were detected in EMS-exposed animals, suggesting its usefulness in scanning whole genome for assessing the genotoxic effects of candidate drugs. The profiles were generated using genomic DNA, isolated from liver prior to treatment and from liver, bone marrow and blood after treatment of the genotoxicant. Measurable differences indicative of genetic damages were observed when the pre- and post-treatment profiles were compared. This suggests that RAPD analysis may be useful for assessing the pre-clinical genotoxic effects of candidate drugs.

Genotoxic and antigenotoxic assessment of four newly synthesized dihydropyridine derivatives

The current study aims to determine the genotoxic and antigenotoxic potential of four newly synthesized dihydropyridine derivatives using Escherichia coli WP2 and Ames/ Salmonella bacterial reversion assay systems. The bacterial mutant tester strains, E. coli WP2 uvrA with a point mutation and Salmonella typhimurium TA1537 with a frameshift mutation, were used to determine genotoxic potentials of the test compounds. To determine antigenotoxic potentials of the test compounds, the same strains were also used together with positive mutagens N-methyl- N′-nitro- N-nitrosoguanidine (MNNG) for E. coli WP2 uvrA and 9-aminoacridine (9-AA) for S. typhimurium TA1537. According to the results, neither of the test compounds showed significant genotoxic activity on both tester strains at the tested concentrations. However, except compound 4, all the test compounds showed significant antigenotoxic activity on MNNG- or/and 9-AA-induced mutations. The inhibition rates of mutagenesis ranged from 27.0% (compound 2: 2.5 mM/plate) to 65.0% (compound 2: 0.5 mM/plate) for MNNG and from 30.6% (compound 2: 2 mM/plate) to 58.5% (compound 1: 1 mM/plate) for 9-AA genotoxicity. According to these results, it is concluded that all the test compounds do not have a mutagenic potential on the bacterial strains at the tested concentrations, and some of them have antigenotoxic potentials against MNNG- and 9-AA-induced mutagenesis.

Changes in poly(ADP-ribose) level modulate the kinetics of DNA strand break rejoining

ADP-ribose polymers are rapidly synthesized in cell nuclei by the poly(ADP-ribose) polymerases PARP-1 and PARP-2 in response to DNA strand interruptions, using NAD(+) as precursor. The level of induced poly(ADP-ribose) formation is proportional to the level of DNA damage and can be decreased by NAD(+) or PARP deficiency, followed by poor DNA repair and genomic instability. Here we studied the correlation between poly(ADP-ribose) level and DNA strand break repair in lymphoblastoid Raji cells. Poly(ADP-ribose) synthesis was induced by 100 microM H(2)O(2) and intensified by the 1,4-dihydropyridine derivative AV-153. The level of poly(ADP-ribose) in individual cells was analyzed by quantitative in situ immunofluorescence and confirmed in whole-cell extracts by Western blotting, and DNA damage was assessed by alkaline comet assays. Cells showed a approximately 100-fold increase in poly(ADP-ribose) formation during the first 5 min of recovery from H(2)O(2) treatment, followed by a gradual decrease up to 15 min. This synthesis was completely inhibited by the PARP inhibitor NU1025 (100 microM) while the cells treated with AV-153, at non-genotoxic concentrations of 1 nM-10 microM, showed a concentration-dependent increase of poly(ADP-ribose) level up to 130% after the first minute of recovery. The transient increase in poly(ADP-ribose) level was strongly correlated with the speed and efficiency of DNA strand break rejoining (correlation coefficient r > or = 0.92, p<0.05). These results are consistent with the idea that poly(ADP-ribose) formation immediately after genome damage reflects rapid assembly and efficient functioning of repair machinery.

Bioactive 1,4-dihydroisonicotinic acid derivatives prevent oxidative damage of liver cells

1,4-Dihydroisonicotinic acid derivatives (1,4-DHINA) are compounds closely related to derivatives of 1,4-dihydropyridine, a well-known calcium channel antagonists. 1,4-DHINA we used were derived from a well-known antioxidant Diludin. Although some compounds have neuromodulatory or antimutagenic properties, their activity mechanisms are not well known. This study was performed to obtain data on antioxidant and bioprotective activities of: 2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydroisonicotinic acid (Ia); sodium 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxamido)glutamate (Ib) and sodium 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxamido)ethane-sulphate (Ic). 1,4-DHINA's activities were studied in comparison to Trolox by: N,N-Diphenyl-N'-picrylhydrazyl (DPPH*), deoxyribose degradation, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical scavenging and antioxidative capacity assays; copper-induced lipid peroxidation of cultured rat liver cells (malondialdehyde determination by high performance liquid chromatography and 4-hydroxynonenal-protein conjugates by dot-blot); (3)H-thymidine incorporation and trypan blue assay for liver cells growth and viability. In all assays used Ia was the most potent antioxidant. Ia was also a potent antioxidant at non-toxic concentrations for liver cell cultures. It completely abolished, while Ic only slightly decreased copper-induced lipid peroxidation of liver cells. Thus, antioxidant capacities are important activity principle of Ia, which was even superior to Trolox in the cell cultures used, while activity principles of Ic and Ib remain yet to be determined.

A 1,4-dihydropyridine derivative reduces DNA damage and stimulates DNA repair in human cells in vitro

Compounds of the 1,4-dihydropyridine (1,4-DHP) series have been shown to reduce spontaneous, alkylation- and radiation-induced mutation rates in animal test systems. Here we report studies using AV-153, the 1,4-DHP derivative that showed the highest antimutagenic activity in those tests, to examine if it modulates DNA repair in human peripheral blood lymphocytes and in two human lymphoblastoid cell lines, Raji and HL-60. AV-153 caused a 50% inhibition of growth (IC50) of Raji and HL-60 cells at 14.9+/-1.2 and 10.3+/-0.8mM, respectively, but did not show a cytotoxic effect at concentrations <100 microM. Alkaline single-cell gel electrophoresis (comet) assays showed that AV-153 reduced the number of DNA strand breaks in untreated cells and also in cells exposed to 2 Gy of gamma-radiation, 100 microM ethylmethane sulfonate (EMS), or 100 microM H2O2. DNA damage was reduced by up to 87% at AV-153 concentrations between 1 and 10nM, and a positive dose-effect relationship was seen between 0.01 and 1 nM. Comparison of the kinetics of DNA strand-break rejoining in the presence and absence of AV-153 revealed a considerable influence on the rate of repair. In view of the resemblance of this compound's structure to that of dihydronicotinamide, a substrate for poly(ADP-rybose)polymerase, the modulation of DNA repair by AV-153 could involve an influence on poly(ADP)ribosylation.

Chitosan Oligosaccharide inhibits203HgCl2-induced genotoxicity in mice: Micronuclei occurrence and chromosomal aberration

The purpose of this study was to investigate the safety of chitosan oligosaccharide and the effects of chitosan oligosaccharide on mercury induced genotoxicity in mice using the micronuclei and chromosome aberration. The micronuclei test was performed by microscopic examination (x1,000, stained using a May-Grunwald solution) after administering 0.01, 0.1, and 1% (10 mg/mL) chitosan oligosaccharide for 7, 60, and 180 days ad libitum in mice. Total micronuclei of 1,000 polychromatic erythrocytes were recorded for each group. There was no difference between the untreated and experimental groups. The intake periods and concentrations of chitosan oligosaccharide did not affect the occurrence of micronuclei in bone marrow cells (P>0.05). The chromosomal aberration test was performed by microscopic examination (x1,000, stained using a 4% Giemsa solution) after administering the same concentration of chitosan oligosaccharide to mice, in F1, F2, F3 generations and parents. The frequency of chromosomal aberrations was defined as [Ydr = (D+R)/total number of counted lymphocytes]. Similar to the micronuclei test, there was no difference between the untreated and treated groups. These results showed that the intake periods and concentrations of chitosan oligosaccharide did not affect chromosomal aberrations in bone marrow cells (P>0.05). To investigate the effect of chitosan oligosaccharide on mercury-induced chromosome aberration, mice in each condition were supplied with 203HgCl2 and chitosan oligosaccharide ad libitum. Chitosan oligosaccharide significantly inhibited 203HgCl2-induced chromosome aberration in mice. Based on the results of this study, it may be concluded that the chitosan oligosaccharide is a nontoxic material that could be used as a suppressor of heavy metal-induced genotoxicity.