Modulation of cyclophosphamide mutagenicity by vitamin C in the in vivo rodent micronucleus assay

Assessment of oxidative stress and chromosomal aberration inducing potential of three medical grade silicone polymer materials

Medical expenditures for devices are increasing along with the ageing of human population and the synthesis of materials such as silicone polymers is on upsurge for manufacturing these devices. The International Organization for Standardization (ISO) emphasizes a battery of tests for preclinical assessment of biocompatibility of medical devices. Genotoxicity assays have become an integral component of these test procedures and it employs a set of in vitro and in vivo experiments to detect mutagens. Hence, this study was performed with an intention to investigate the genotoxic potential of the physiological saline extracts of three medical grade silicone polymer materials by the in vitro chromosomal aberration assay using human peripheral blood lymphocytes. Further, the oxidative stress inducing potential of the material extracts was investigated in vivo in mice liver homogenates using cyclophosphamide as positive control. The investigation revealed that none of the three materials were able to produce marked human lymphocyte chromosomal aberration, suggesting the absence of mutagens. The materials also showed negative results in their oxidative stress inducing potential, which was revealed by the normal levels of lipid peroxidation and unaltered levels of glutathione and its metabolizing enzymes in the mice liver tissue homogenates. It was interesting to observe a significant correlation between the genotoxic and antioxidant parameters investigated. Hence, it is suggested that the estimation of antioxidant status would serve as a better preliminary testing procedure prior to evaluating the genetic and molecular toxicity mechanisms of medical devices and/or materials intended for manufacture of such devices.

The genotoxicity of vitamin C in vitro

The genotoxic effects of Vitamin C (ascorbic acid) on human lymphocytes in vitro were estimated by analyzing and identifying various chromosome abnormalities, in relation to the concentration of Vitamin C. Testing concentrations of Vitamin C induced different aberrations including the impairment of spindle function. The spindle disturbances can result in mitotic arrest, multipolar spindles and multipolar segregation, errors in chromosome segregation, formation of chromosome bridges and chromosome laggards. The most frequent irregularities were found in anaphase and telophase. A certain number of lymphocytes were arrested at anaphase or telophase (in colchicine-untreated cultures of human lymphocytes). Testing concentrations of ascorbic acid did not induce a significant increase in the number of aneuploid mitoses and were not clastogenic except at the highest concentration (1,000 microg/ml) in colchicine-treated cultures, and in colchicine-untreated cultures of human lymphocytes the pulverization of chromosome was observed. Vitamin C changed the mitotic index value of lymphocytes notably at the higher concentrations (250, 500 and 1,000 microg/ml).

Antigenotoxic effect of apigenin against anti-cancerous drugs

Mitomycin C and cyclophosphamide are well known anti-tumor drugs. Their genotoxic effects are well established in various test systems. The genotoxic effects in non-tumor cell are of special significance due to the possibility that they may induce secondary tumors in cancer patients. Apigenin is a well known anti-oxidant and possess number of properties that are beneficial in some way to humans. With this view, the present study deals with the effect of apigenin against the genotoxic doses of mitomycin C and cyclophosphamide using chromosomal aberrations, sister chromatid exchanges and cell cycle kinetics as a parameters. The treatment of apigenin results in a significant, dose dependent decrease in the genotoxic damage, induced by mitomycin C and cyclophosphamide. It is concluded that the apigenin is potent in reducing the genotoxic damage, induced by anti-cancerous drugs, thereby reducing the chances of developing secondary tumors during the therapy.

In vivo antimutagenic effect of vitamins C and E against rifampicin-induced chromosome aberrations in mouse bone-marrow cells

-The genotoxic effect of rifampicin (RMP), one of the most active antituberculosis agents is studied. Also, the possible protection provided by the natural antioxidant vitamins C (VC) and E (VE) against the genotoxic effect of RMP is assessed. Mice were orally treated by gavage with 10, 50, 150 and 300 mg RMP kg(-1) body weight (bw). Also, oral treatment was conducted with RMP plus the vitamins. Mice received 300 mg RMP kg(-1) bw plus 100, 200 and 400mg VC or VE kg(-1) bw. Samples were taken 24h after the treatment. Repeated treatments with: (1) the therapeutic dose of RMP (10 mg kg(-1) bw); (2) RMP plus a dose of 25, 50 and 75 mg VC kg(-1); (3) RMP plus 10, 20 and 40 mg VE kg(-1) bw for 30 consecutive days were conducted. The tested doses of RMP induced a significant increase in the percentage of chromosome aberrations. However, a lower percentage of chromosome aberrations was observed when animals were treated with the therapeutic dose for 30 consecutive days. The obtained results revealed that chromosome aberrations induced by RMP decreased to a significant extent when mice were treated with RMP plus VC. The repeated doses of VC reduced the percentage of chromosome aberrations induced by RMP in a significant and dose-dependent manner. On the other hand, repeated doses of VE were not very effective in reducing the percentage of chromosome aberrations induced by RMP. Only the highest dose (3 x 40 mg kg(-1) bw) showed a significant effect (P<0.01). The results on the induction of chromosome damage clearly show that only VC appears able to efficiently protect the bone-marrow cells when given together with RMP, while no significant reduction in the yield of chromosome aberrations was observed for VE in combination with the antituberculosis drug.

Anticlastogenic effect of Vitamin C on cisplatin induced chromosome aberrations in human lymphocyte cultures

Vitamin C (ascorbic acid) is an antioxidant that can scavenge free radicals and protect cellular macromolecules, including DNA, from oxidative damage induced by different agents. The protective effect of Vitamin C on cisplatin induced chromosome aberrations has been determined in the human peripheral lymphocyte chromosome aberration test in vitro. The results of treatments with Vitamin C indicated that it statistically significantly decreases the number of chromosome aberrations and number of metaphases with aberrations induced with cisplatin, but it can not completely protect cells from damage. The test concentrations of Vitamin C (10 and 100 microg/ml) had a limited antimutagen effect on cisplatin (0.5 microg/ml), which can cause genetic damage through free radical mechanisms. The antimutagen effect included the anticlastogenic effect of Vitamin C and its ability to decrease the number of aneuploid mitoses. Vitamin C showed the most efficient anticlastogenic effect during simultaneous treatment with cisplatin. Also, Vitamin C reduced cell toxicity of cisplatin during simultaneous treatment.

Effects of the antioxidants curcumin and vitamin C on cisplatin-induced clastogenesis in Wistar rat bone marrow cells

The use of dietary antioxidants to prevent antitumor agent-induced chromosomal damage in nontumor cells is currently eliciting considerable interest. Curcumin (CMN) is a dietary antioxidant that has been reported to protect against clastogenesis in in vivo and in vitro assays. This study was undertaken to investigate the modulatory effects of CMN on cisplatin-induced chromosomal aberrations in Wistar rat bone marrow cells and whether there is any potentiation of these effects with the combination between CMN and vitamin C (VC), which has been reported to reduce the clastogenic effect of many antitumor agents in in vivo assays. Animals treated with CMN plus a single dose of cisplatin, at 18, 24 or 72 h following treatment, presented a statistically significant reduction in the total amount of chromosomal damage and in the number of abnormal metaphases. The results also indicate that the combination between antioxidants would not be effective in protecting against cisplatin-induced chromosomal damage in animals sacrificed 24 h after cisplatin treatment. Under the present experimental conditions, CMN could prevent cisplatin-induced clastogenesis by acting as a free radical scavenger.

In vivo anticlastogenic effects of L-ascorbic acid in mice

The effects of l-ascorbic acid on the frequency of micronuclei induced by model mutagens, cyclophosphamide (CP), mitomycin-C (MMC) and bleomycin (BLM) hydrochloride were tested using mouse bone marrow. Three doses of ascorbic acid (AsA) viz., 10, 30 and 60 mg/kg b.w. were tested for anticlastogenic effects. The doses of positive mutagens used were, CP-50 mg/kg, MMC-4 mg/kg and BLM-20 mg/kg b.w. Bone marrow sampling was done at 24 h after the treatment. AsA was found to be effective in reducing MN frequency induced by CP and BLM. With MMC only, the highest dose showed a slight inhibitory effect.

Effects of high doses of vitamins C and E against doxorubicin-induced chromosomal damage in Wistar rat bone marrow cells

Doxorubicin (DXR) is one of the major antitumoral agents available for clinical use. In addition to intercalating into the DNA molecule, this drug generates free radicals. Vitamins C (VC) and E (VE) can protect normal cells from the damage caused by radicals without interfering with the cytotoxicity of DXR against tumors. The objective of the present study was to investigate the possible protective effect of VC and/or VE on mammalian cells treated with DXR in vivo. Animals treated with the lowest doses of VC and/or VE, alone or in combination, plus a single dose of DXR presented a statistically significant reduction in total number of chromosome aberrations and in number of abnormal metaphases. The highest vitamin doses tested caused no changes in the parameters analyzed when compared with control. Under the present experimental conditions, the efficiency of VC and/or VE in protecting against chromosome damage was dependent on the dose used.

Effects of beta-carotene, retinal, riboflavin, alpha-tocopherol and vitamins C and K1 on sister-chromatid exchanges induced by 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and cyclophosphamide in human lymphocyte cultures

The vitamins and related compounds cited in the title were investigated for their abilities to modulate sister-chromatid exchanges (SCEs) induced by Trp-P-2 or cyclophosphamide (CP) in human peripheral lymphocyte cultures in the presence of an exogenous metabolizing system from rat liver. When inducer and test substances were given simultaneously, beta-carotene, retinal and alpha-tocopherol caused a dose-dependent decrease of SCE frequencies induced by Trp-P-2 and CP. Vitamin K1, however, brought about an identical effect with Trp-P-2 only, while with CP an initial decrease of SCEs was followed by a statistically significant re-increase at higher concentrations. Vitamin C was ineffective against Trp-P-2, but caused an overall increase of SCEs induced by CP. When blood cultures were preincubated with vitamins before the addition of CP or Trp-P-2, basically identical effects were observed with beta-carotene, retinal, alpha-tocopherol, vitamin K1 and vitamin C. Riboflavin decreased SCEs induced by Trp-P-2 in all treatment schedules, although statistically confirmed minima were observed in the dose-response curves, except in post-treatment experiments. On the other hand, riboflavin only reduced SCEs induced by CP when it was preincubated with lymphocytes. When vitamins were applied in a post-treatment schedule after removal of Trp-P-2 or CP, again, basically identical results against both genotoxins were observed with beta-carotene, retinal and alpha-tocopherol with vitamin K1, however, only with respect to Trp-P-2, and with vitamin C only with respect to CP. In the post-treatment schedule, vitamin K1 caused a decrease of SCE frequencies induced by CP, and vitamin C a decrease of SCEs induced by Trp-P-2.

Inhibition of genotoxic effects of mammalian germ cell mutagens

Germ cell mutagens are among the most important chemicals for which chemopreventive agents should be sought and mechanistically defined. These mutagens may include environmental chemicals as well as drugs. In this investigation, the literature was reviewed for substances antimutagenic (or anticlastogenic) to compounds identified as mutagens in at least two germ cell studies. A complete matrix of test results was prepared to identify commonly tested pairs of germ cell mutagens and antimutagens. The categories of antimutagens most tested included vitamins, fatty acids, thiols, tannins and other phenolics. The most frequently studied mutagens were benzo[a]pyrene, cyclophosphamide, mitomycin C, and bleomycin. Based on the availability of the most relevant data, the analysis presented here focused on in vivo tests, specifically on bone marrow cytogenetics. The results indicated that antimutagens commonly found in the diet or endogenously in the body effectively antagonized the cytogenetic damage induced in the bone marrow by most of the germ cell mutagens studied to date. Bone marrow micronucleus and chromosomal aberration assays, which detect systemically active mutagens, may be predictive of similar mitigating effects in germ cells. Test results from antimutagenicity studies in germ cells, though limited, were comparable to the results from studies in the mouse bone marrow micronucleus test.

Effect of selected antimutagens on the genotoxicity of antitumor agents

Cyclophosphamide (CP), bleomycin (BL), doxorubicin (DOX) and cisplatin (CISP) are potent antitumor drugs used worldwide against many forms of human cancer. As with most such agents, there can be physiological side-effects and the possible induction of mutations and other genotoxic effects in non-tumor cells. It is common for patients to ingest a host of food supplements to diminish the discomforting side-effects of therapy. Because these food supplements are often also rich in antimutagens that could also affect the biological efficacy of the antitumor drugs, we investigated if such antimutagenic agents were indeed antimutagenic to these antitumor drugs. Using the Salmonella/microsome bioassay, we tested CP, BL, DOX, and CP for mutagenicity in the presence and absence of the antimutagens ascorbic acid (AA), chlorophyllin (CHL) and (+)-catechin (CAT). AA was a very effective antimutagen against CISP and less effective against BL and DOX. It was not antimutagenic to CP. CHL was effective as an antimutagen against all four antitumor drugs, and CAT was a strong inhibitor of DOX mutagenicity, but had little effect on BL, CP and CISP. These data now provide a basis for future in vivo antitumor/antimutagen combination studies to determine if these antimutagens function in a manner to reduce genetic effects without having concomitant effects on intended antitumorogenicity of these therapeutic agents.

Cyclophosphamide: review of its mutagenicity for an assessment of potential germ cell risks

Cyclophosphamide (CP) is used to treat a wide range of neoplastic diseases as well as some non-malignant ones such as rheumatoid arthritis. It is also used as an immunosuppressive agent prior to organ transplantation. CP is, however, a known carcinogen in humans and produces secondary tumors. There is little absorption either orally or intravenously and 10% of the drug is excreted unchanged. CP is activated by hepatic mixed function oxidases and metabolites are delivered to neoplastic cells via the bloodstream. Phosphoramide mustard is thought to be the major anti-neoplastic metabolite of CP while acrolein, which is highly toxic and is produced in equimolar amounts, is thought to be responsible for most of the toxic side effects. DNA adducts have been formed after CP treatment in a variety of in vitro systems as well as in rats and mice using 3H-labeled CP. 32P-postlabeling techniques have also been used in mice. However, monitoring of adducts in humans has not yet been carried out. CP has also been shown to induce unscheduled DNA synthesis in a human cell line. CP has produced mutations in base-pair substituting strains of Salmonella tryphimurium in the presence of metabolic activation, but it has been shown to be negative in the E. coli chromotest. It has also been shown to be positive in Saccharomyces cerevisiae in D7 strain for many endpoints but negative in D62.M for aneuploidy/malsegregation. It has produced positive responses in Drosophila melanogaster for various endpoints and in Anopheles stephensi. In somatic cells, CP has been shown to produce gene mutations, chromosome aberrations, micronuclei and sister chromatid exchanges in a variety of cultured cells in the presence of metabolic activation as well as sister chromatid exchanges without metabolic activation. It has also produced chromosome damage and micronuclei in rats, mice and Chinese hamsters, and gene mutations in the mouse spot test and in the transgenic lacZ construct of Muta Mouse. Increases in chromosome damage and gene mutations have been found in the peripheral blood lymphocytes of nurses, pharmacists and female workers occupationally exposured to CP during its production or distribution. Chromosome aberrations, sister chromatid exchanges and gene mutations have been observed in somatic cells of patients treated therapeutically with CP. In general, there is a maximum dose and an optimum time for the detection of genetic effects because the toxicity associated with high doses of CP will affect cell division. In germ cells, CP has been shown to induce genetic damage in mice, rats and hamsters although the vast majority of such studies have used male mice.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of ascorbate in antioxidant protection of biomembranes: interaction with vitamin E and coenzyme Q

One of the vital roles of ascorbic acid (vitamin C) is to act as an antioxidant to protect cellular components from free radical damage. Ascorbic acid has been shown to scavenge free radicals directly in the aqueous phases of cells and the circulatory system. Ascorbic acid has also been proven to protect membrane and other hydrophobic compartments from such damage by regenerating the antioxidant form of vitamin E. In addition, reduced coenzyme Q, also a resident of hydrophobic compartments, interacts with vitamin E to regenerate its antioxidant form. The mechanism of vitamin C antioxidant function, the myriad of pathologies resulting from its clinical deficiency, and the many health benefits it provides, are reviewed.

Genotoxicity assessment of the antifungal antibiotic aureofungin in Salmonella typhimurium and Swiss albino mice

The widely used agricultural antifungal agent aureofungin (ARF) was subjected to genotoxicity assessment using the Ames Salmonella assay as well as the in vivo micronucleus test and dominant lethal test in Swiss mice. In the Ames Salmonella spot test, ARF slightly elevated the number of histidine revertants after metabolic activation over a wide dose range (1-1000 micrograms/plate) in TA102 but not in TA97a, TA98 or TA100. In the preincubation plate incorporation assay with TA102, ARF increased the number of revertants in a dose-dependent manner only after metabolic activation. ARF failed to significantly elevate the frequency of micronucleated polychromatic erythrocytes (PE) in the bone marrow of Swiss mice. It elevated the frequency of dominant lethal mutations in the 7th and 8th weeks at 30 mg/kg body weight, a concentration much higher than the actual concentration used in the field. We conclude that ARF is non-mutagenic in somatic cells in vivo at doses used in the present study, probably mutagenic in stem-cell spermatogonia and may be classified as an equivocal promutagen, possibly acting as a cross-linker.

Micronucleus induction in cytokinesis-blocked mouse bone marrow cells in vitro following in vivo exposure to X-irradiation and cyclophosphamide

A cytokinesis-block micronucleus (MN) method for the simultaneous but separate measurement of chromosome damage in erythroid and myeloid bone marrow cells is described. MN induction in cytokinesis-blocked mouse bone marrow cells in vitro following in vivo exposure to x-ray or cyclophosphamide (CP) was investigated. Immediately after whole body irradiation with acute doses of either 0, 1, 2 or 4 Gy x-rays, or 2 hr after treatment with either 0, 12.5, 25, or 50 mg CP/kg body weight, bone marrow cells were collected and then cultured in medium supplemented with 3.0 micrograms/ml cytochalasin B for 24 hr. The binucleated cells were scored in erythroid, myeloid, lymphoid and other cells. The myeloid/erythroid (M/E) ratio was decreased by x-irradiation or CP treatment in a dose-dependent manner. The dividing index (DI; binucleated cells/binucleated + mononucleated cells; %) was decreased in both erythroid and myeloid cells in the same manner. Dose-dependent increases in MN frequency were observed following x-irradiation in both erythroid and myeloid cells. A similar dose-dependent MN induction was observed with CP. The MN frequency in myeloid cells was much greater than in erythroid cells (about 4-fold following 4 Gy exposure, and more than 10-fold after 50 mg/kg CP). Lymphoid and other cells were not suitable for scoring DI and MN frequency because of insufficient numbers of binucleated cells. These results suggest that micronuclei can be identified in both myeloid and erythroid cells and that myeloid cells are more susceptible to x-ray or CP-induced chromosomal damage than erythroid cells as expressed by MN induction.

Bone marrow micronucleus assay: a review of the mouse stocks used and their published mean spontaneous micronucleus frequencies

We have examined published negative control data from 581 papers on micronucleated bone marrow polychromatic erythrocytes (mnPCE) for differences in mean frequency and the frequency distribution profile among the mouse stocks used with the bone marrow micronucleus assay. For the 55 mouse stocks with published micronucleus assay data, the overall mean frequency is 1.95 mnPCE/1,000 PCE (1.95 mnPCE/1,000); for the 13 stocks most commonly used in the assay, it is 1.88 mnPCE/1,000. During the last 5 years, the mnPCE rate for these 13 major stocks has been 1.74 mnPCE/1,000. This current mean frequency is a substantial decrease from the mean of 3.07 mnPCE/1,000 observed for these 13 stocks for data published prior to 1981. Of the major stocks, the highest mean mnPCE negative control frequencies were observed for MS/Ae > BALB/c > C57Bl/6, and the lowest for CD-1 < Swiss Webster. We note that hybrid mouse stocks appear to have lower and less variable negative control frequencies than either of their parent strains and that the negative control frequency for some progeny stocks have diverged significantly from that of the parent stocks. Overall mean negative control frequencies appear to be correlated with breadth of the frequency distribution profile of published mean negative control values. Furthermore, a possible correlation between negative control frequency in the micronucleus assay and sensitivity to clastogens of different mouse strains may be indicated. The databases generated here allow us to define a range of norms for both the historical mean frequency and individual experimental mean frequencies for most stocks, but in particular, for the more commonly used mouse stocks. Our analysis, for the most part, bears out the recommendation of the first Gene-Tox Report on the micronucleus assay that the historical negative control frequency for a mouse stock should fall between 1 and 3 mnPCE/1,000. Eighty-six percent of the most commonly used mouse stocks have historical mean frequencies within this range. Though individual experimental mean values would not necessarily be expected to fall within the 1-3.00 mnPCE/1,000 range, 65.3% of the 2,327 published negative control values do, and 83.5% are < 3 mnPCE/1,000. The frequency with which an individual experimental mean value lies outside the 1.00 to 3.00 mnPCE/1,000 range differs among stocks and appears related to the mouse mean frequency. We suggest that the recommended range for historical mean frequency be extended slightly, to approximately 3.4 mnPCE/1,000, to accommodate some commonly used strains with overall mean negative control frequencies just above 3.00 mnPCE/1,000.(ABSTRACT TRUNCATED AT 400 WORDS)

The anticlastogenicity of beta-carotene evaluated on human hepatoma cells

The efficiency of beta-carotene as a modulatory agent against clastogenicity induced by cyclophosphamide (CPA), an indirect-acting mutagen, and mitomycin C (MMC), a direct-acting mutagen, was evaluated in human hepatoma cells (Hep G2) using three different treatment regimes. Six doses of beta-carotene, 0.25, 0.5, 1.0, 2.0, 4.0 and 6.0 microM, were tested as pre-treatment, simultaneous treatment and pre- + simultaneous treatment. Since these cells are able to activate mutagens without any exogenous metabolizing system (S9 mix), some problems related to the use of S9 mix were eliminated. The data obtained show a statistically significant decrease in the frequency of micronuclei (MN) induced by CPA when the cells were treated with beta-carotene, for all treatments, and no effect of this provitamin on the clastogenicity of MMC was found. These results reinforce the anticlastogenicity of beta-carotene showing that its action is independent of the treatment regime used. On the other hand, the fact that beta-carotene had a protective action only on CPA-induced MN suggests an effect on activation of the promutagen and emphasizes the important utility of cell lines capable of metabolizing chemical mutagens, in such basic studies.