l-Carnitine protects mammalian cells from chromosome aberrations but not from inhibition of cell proliferation induced by hydrogen peroxide

Cadmium as a male reproductive toxicant and natural and non-natural ways to tackle it: a review

Cadmium (Cd) is a naturally occurring environmental pollutant, a toxic substance that causes oxidative stress. According to epidemiological studies, the data suggested that environmental and occupational Cd exposure may be related to several diseases and severe testicular damage. However, studies are going on to explore the mechanism of Cd-induced male reproductive toxicity and its treatment strategies. Currently, researchers are focusing on naturally occurring bioactive compounds, plant extracts, and biochemical, which have better efficacy, less toxicity, and high bioavailability. This review focuses on the mechanistic effect of Cd on testicular toxicity and different categories of compounds having a beneficial impact on Cd-induced male reproductive toxicity. Some potent bioactive antioxidants are quercetin, caffeic acid phenethyl ester, cyanidin-3-O-glucoside, curcumin, and silymarin. In comparison, plant extracts are Costus afer leaf methanol extract, methanol root extract of Carpolobia lutea, red carrot methanolic extract, Panax ginseng extract, and biochemicals including melatonin, progesterone, glutamine, L-carnitine, and selenium. Advanced and more detailed studies are needed on these compounds to explore their mechanism in attenuating Cd-induced testicular toxicity and can be potential therapeutics in the future.

Nickel toxicity alters growth patterns and induces oxidative stress response in sweetpotato

Nickel (Ni) contaminated soil is a persistent risk to plant growth and production worldwide. Therefore, to explore the Ni toxicity levels in sweetpotato production areas, we investigated the influence of different Ni treatments (0, 7.5, 15, 30, and 60 mg L-1) for 15 days on phenotype, Ni uptake, relative water content, gas exchange, photosynthetic pigments, oxidative stress, osmolytes, antioxidants, and enzymes of sweetpotato plants. The results presented that Ni at higher levels (30 and 60 mg L-1) substantially reduced growth, biomass, and root morphological traits. The Pearson correlation analysis suggested that Ni toxicity causes oxidative injuries as persistent augmentation of hydrogen peroxide (H2O2) and malonaldehyde (MDA) and reduced RWC, gas exchange, and photosynthetic pigment. Furthermore, this study revealed that sweetpotato could tolerate moderate Ni treatment (up to 15 mg L-1) by reducing oxidative stress. The results also indicated that the increase in the activities of mentioned osmolytes, antioxidants, and enzymes is not sufficient to overcome the higher Ni toxicity. Based on these results, we suggest using low Ni-contaminated soil for better growth of sweetpotato and also could be used as a phytoremediator in moderate Ni-contaminated soil.

Exometabolome profiling reveals activation of the carnitine buffering pathway in fed-batch cultures of CHO cells co-fed with glucose and lactic acid

Adjustments to CHO cell physiology were recently observed during implementation of a Raman spectroscopy-based glucose and lactate control strategy. To further understand how these cells, under monoclonal antibody (mAb) production conditions, utilized the extra lactic acid fed, we performed a comprehensive semi-quantitative and time-dependent analysis of the exometabolome. This study focused on the CHO cell's metabolic shift from the fifth day of culture. We compared relative levels of extracellular metabolites in the absence or presence of a 2 g/L lactic acid setpoint while glucose was kept at 4 g/L. Our hypothesis is that extra lactic acid would supply more pyruvate, favoring oxidative phosphorylation. We subsequentially uncovered several carnitine derivatives as biomarkers of the simultaneous activation of TCA anaplerotic pathways as well as a carbon-buffering pathway. CHO cells exhibited a balance between intermediates from (i) amino acid catabolism, (ii) fatty acid β-oxidation, and (iii) pyruvate from glycolysis and lactic acid; and the secretion of their intermediate carnitine derivatives. In addition, 3-hydroxy-methyl-glutaric acid (HMG) and mevalonate syntheses were found as biomarkers of alternative acyl group removal. Together, under a limited capacity to assimilate the surplus of acyl-CoA groups as well as an ability to maintain the acyl-CoA: free CoA ratio for proper and continuous functioning of the TCA cycle, CHO cells activate the carnitine-buffering system, HMG, and mevalonate pathways.

Bisphenol A induces DNA damage in cells exerting immune surveillance functions at peripheral and central level

Bisphenol A (BPA) is a synthetic xenoestrogen diffused worldwide. Humans are chronically exposed to low doses of BPA from food and drinks, thus BPA accumulates in tissues posing human health risk. In this study, we investigated the effects of BPA on peripheral blood mononuclear cells (PBMC) from human healthy donors, and in glia and microglia of rat offspring at postnatal day 17 (17PND) from pregnant females who received BPA soon after coupling and during lactation and weaning. Results indicated that BPA affected Phytoemagglutinin (PHA) stimulated PBMC proliferation causing an S-phase cell cycle accumulation at nanomolar concentrations while BPA was almost ineffective in resting PBMC. Furthermore, BPA induced chromosome aberrations and the appearance of shattered cells characterized by high number of fragmented and pulverized chromosomes, suggesting that the compound could cause a massive genomic rearrangement by inducing catastrophic events. The BPA-induced DNA damage was observed mainly in TCD4+ and TCD8+ subsets of T lymphocytes and was mediated by the increase of ERK1/2 phosphorylation, p21/Waf1 and PARP1 protein expression. Intriguingly, we observed for the first time that BPA-induced effects were associated to a sex specific modulation of ERα and ERβ in human PBMC. Immunofluorescence analysis of rat hippocampus corroborated in vitro findings showing that BPA induced ɣH2AX phosphorylation in microglia and astrocytosis by decreasing ERα expression within the dentate gyrus. Overall these results suggest that BPA can alter immune surveillance functions at both peripheral and central level with a potential risk for cancer, neuroinflammation and neurodegeneration.

L-carnitine increases cell proliferation and amino acid transporter expression via the activation of insulin-like growth factor I signaling pathway in rat trophoblast cells

Early embryo implantation and development is primarily determined by the homeostasis between cellular apoptosis and proliferation as well as placental nutrient transporters. Recent studies showed that L-carnitine enhances female reproductive performance. However, the potential function of L-carnitine on placenta is largely unknown. In our study, primary rat trophoblast cells were separated and cultured for 12 hr in medium containing various concentrations of L-carnitine (0, 1, 10, and 50 mM). Placenta trophoblast cells treated with 50 mM L-carnitine increased the proportion of cells in S phase of the cell cycle (p < .05). In addition, live cell percentage was increased when treated with either 10 mM or 50 mM L-carnitine, which was accompanied with decreased necrotic cells, late apoptotic cells, and early apoptotic cells (p < .05). Compared with the control treatment, the mRNA expression of insulin-like growth factor I (IGF-1) and insulin-like growth factor I receptor (IGF-1R) was higher in rat placenta trophoblasts treated with either 10 mM or 50 mM L-carnitine (p < .05). Similarly, sodium-dependent neutral amino acid transporter (SNAT)-1 and SNAT2 were up-regulated in both mRNA and protein levels when trophoblast cells were treated with 50 mM L-carnitine (p < .05). Inhibiting downstream targets (Akt or ERK signaling pathways) of IGF-1 signaling pathway partially blocked the effect the L-carnitine-induced increase in protein abundances of SNAT1 and SNAT2. Collectively, our data showed protective role of L-carnitine on placenta trophoblast cells through the involvement of IGF-1 signaling pathway.

In vivo protective effects of Ginkgo biloba L. leaf extract against hydrogen peroxide toxicity: cytogenetic and biochemical evaluation

In this study, the protective effects of Ginkgo biloba leaf extract (GbE) against toxicity induced by hydrogen peroxide (H₂O₂) in Swiss albino mice were investigated. Abnormal metaphase number (AMn), mitotic index (MI), micronucleus (MN), and chromosomal abnormalities (CAs) were analyzed for cytogenetic effects. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), blood urea nitrogen (BUN), creatinine, glutathione (GSH), and malondialdehyde (MDA) levels in liver and kidney organs were investigated as indicators of biochemical toxicity. Six experimental groups were formed as a control and treatment group, each containing six animals. The mice in the control group were given tap water, while the mice in the administration group received two different doses of GbE and H₂O₂ for 45 consecutive days. It was observed that H₂O₂ administration caused a significant decrease in MI compared to the control group and caused a significant decrease in the frequency of AMn, MN, and CAs. Chromatid break was the most common type of CAs induced by H₂O₂, and the other CAs types observed in this study were chromosome break, fragment, dicentric, gap, and ring. It has been determined that GbE treatment decreases the clastogenic effects of H₂O₂ and reduces the MN and CAs frequency and causes a re-increase in mitotic cell numbers. It was determined that H₂O₂ administration caused changes in biochemical parameters and resulted in significant increases in serum AST, ALP, ALT, BUN, and creatinine levels. However, the level of MDA, which is an indicator of oxidative damage, increased, and GSH level decreased in liver and kidney tissues. Oxidative damage caused by H₂O₂ in liver and kidney tissues was improved, and all biochemical parameters tested were found to be ameliorated after GbE treatment. This improvement was dependent on the dose of GbE, and improvement in 150 mg/kg bw GbE was found to be more prominent. As a result, the GbE can be used as an antioxidant nutritional supplement to protect against the toxic effects of environmental agents such as H₂O₂.

Exogenous L-Carnitine Promotes Plant Growth and Cell Division by Mitigating Genotoxic Damage of Salt Stress

L-carnitine is a fundamental ammonium compound responsible for energy metabolism in all living organisms. It is an oxidative stress regulator, especially in bacteria and yeast and lipid metabolism in plants. Besides its metabolic functions, l-carnitine has detoxification and antioxidant roles in the cells. Due to the complex interrelationship of l-carnitine between lipid metabolism and salinity dependent oxidative stress, this study investigates the exogenous l-carnitine (1 mM) function on seed germination, cell division and chromosome behaviour in barley seeds (Hordeum vulgare L. cv. Bulbul-89) under different salt stress concentrations (0, 0.25, 0.30 and 0.35 M). The present work showed that l-carnitine pretreatment could not be successful to stimulate cell division on barley seeds under non-stressed conditions compared to stressed conditions. Depending on increasing salinity without pretreatment with l-carnitine, the mitotic index significantly decreased in barley seeds. Pretreatment of barley seeds with l-carnitine under salt stress conditions was found promising as a plant growth promoter and stimulator of mitosis. In addition, pretreatment of barley seeds with l-carnitine alleviated detrimental effects of salt stress on chromosome structure and it protected cells from the genotoxic effects of salt. This may be caused by the antioxidant and protective action of the l-carnitine. Consequently, this study demonstrated that the exogenous application of 1 mM l-carnitine mitigates the harmful effects of salt stress by increasing mitosis and decreasing DNA damage caused by oxidative stress on barley seedlings.

In Vitro Cytogenetic Assays: Chromosomal Aberrations and Micronucleus Tests

Chromosome damage is a very important indicator of genetic damage relevant to environmental and clinical studies. Detailed descriptions of the protocols used for detection of chromosomal aberrations induced by genotoxic agents in vitro both in the presence or absence of rat liver-derived metabolizing systems are given in this chapter. Structural chromosomal aberrations that can be observed and quantified at metaphases are described here. For the detection of chromosomal damage (fragments or whole chromosome) in interphase, the micronucleus test can be used, and a description of this test is also presented. Criteria for determining a positive result using appropriate statistical methods are described.

Pb-inhibited mitotic activity in onion roots involves DNA damage and disruption of oxidative metabolism

Plant responses to abiotic stress significantly affect the development of cells, tissues and organs. However, no studies correlating Pb-induced mitotic inhibition and DNA damage and the alterations in redox homeostasis during root division per se were found in the literature. Therefore, an experiment was conducted to evaluate the impact of Pb on mitotic activity and the associated changes in the oxidative metabolism in onion roots. The cytotoxic effect of Pb on cell division was assessed in the root meristems of Allium cepa (onion). The mitotic index (MI) was calculated and chromosomal abnormalities were sought. Pb-treatment induced a dose-dependent decrease in MI in the onion root tips and caused mitotic abnormalities such as distorted metaphase, fragments, sticky chromosomes, laggards, vagrant chromosomes and bridges. Single Cell Gel Electrophoresis was also performed to evaluate Pb induced genotoxicity. It was accompanied by altered oxidative metabolism in the onion root tips suggesting the interference of Pb with the redox homeostasis during cell division. There was a higher accumulation of malondialdehyde, conjugated dienes and hydrogen peroxide, and a significant increase in the activities of superoxide dismutases, ascorbate peroxidases, guaiacol peroxidases and glutathione reductases in Pb-treated onion roots, whereas catalases activity exhibited a decreasing pattern upon Pb exposure. The study concludes that Pb-induced cytotoxicity and genotoxicity in the onion roots is mediated through ROS and is also tightly linked to the cell cycle. The exposure to higher concentrations arrested cell cycle leading to cell death, whereas different repair responses are generated at lower concentrations, thereby allowing the cell to complete the cell cycle.

The protective role of l-carnitine against cylindrospermopsin-induced oxidative stress in tilapia (Oreochromis niloticus)

Cylindrospermopsin (CYN) is one of the most important cyanotoxins in terms of both human health and environmental quality and is produced by several different species of cyanobacteria, including Aphanizomenon ovalisporum. The principal mechanisms of action of CYN involve inhibition of protein and glutathione synthesis. In addition, CYN-mediated genotoxicity results from DNA fragmentation. The results of both in vivo and in vitro studies suggest that oxidative stress also plays a significant role in CYN pathogenesis in fish. We investigated the protective effects of l-carnitine (LC) pre-treatment on A. ovalisporum-induced oxidative stress in cells containing CYN and deoxy-CYN, or pure standard CYN, in tilapia (Oreochromis niloticus) that had been acutely exposed via oral administration. Various oxidative stress markers, including lipid peroxidation (LPO), protein oxidation, DNA oxidation, and the ratio of reduced glutathione to oxidised glutathione (GSH/GSSG), and the activities of NADPH oxidase, superoxide dismutase (SOD), catalase (CAT), and gamma-glutamyl-cysteine synthetase (γ-GCS), were evaluated in the livers and kidneys of fish in the absence and presence of 400 or 880mgLC/kgfish/day during a 21 day period prior to CYN-intoxication. The results of our study demonstrated for the first time the beneficial antioxidant effects of LC dietary supplementation on oxidative stress status in fish. No pro-oxidant effects were detected at any of the LC doses assayed, suggesting that LC is a chemoprotectant that reduces hepatic and renal oxidative stress and may be effective when used for the prophylaxis and treatment of CYN-related intoxication in fish.

In vitro cytogenetic assays: chromosomal aberrations and micronucleus tests

Chromosome damage is a very important indicator of genetic damage relevant to environmental and clinical studies. Detailed descriptions of the protocols used for detection of chromosomal aberrations induced by unknown agents in vitro both in the presence or the absence of rat liver-derived metabolizing systems are given. Structural chromosomal aberrations that can be observed and quantified at metaphases are described here. For the detection of chromosomal damage (fragments or whole chromosome) in interphase, the micronucleus test can be used and a description of this test is also presented. Criteria for determining a positive result using appropriate statistical methods are described.

Protective effect of l-carnitine against acrylamide-induced DNA damage in somatic and germ cells of mice

Recent findings of acrylamide (AA) in many common foods have sparked renewed interest in assessing human health hazards. AA was evaluated by the International Agency for Research on Cancer as probably carcinogenic to humans. For this reason, the aim of this study is to evaluate the potential genotoxic effect of AA using chromosomal aberration analysis and micronucleus (MN) test in mouse bone-marrow cells and morphological sperm abnormalities. The result of the present work indicated that treatment with a single dose of 10, 20, or 30 mg/kg b.wt. of AA for 24 h and the repeated dose of 10 mg/kg b.wt. for 1and 2 weeks induced a statistically significant increase in the percentage of chromosomal aberrations and micronuclei in bone- marrow cells. These percentages reduced significantly in all groups treated with AA and the protective agent l-carnitine. Also the results indicated that the dose 10, 20 and 30 mg/kg b.wt. of AA induced a statistically significant percentage of morphological sperm abnormalities compared with the control group. Such effect reached its maximum (7.24 ± 0.61) with the highest tested dose which reduced to (4.02 ± 0.58) in the group treated with the same dose of AA and l-carnitine. In conclusion, the results confirm the protective role of LC against the mutagenicity of AA.

Different cytotoxic and clastogenic effects of epigallocatechin gallate in various cell-culture media due to variable rates of its oxidation in the culture medium

Positive genotoxicity results are often observed using mammalian cells in culture with agents that are not in vivo genotoxins. We here illustrate one possible explanation: interaction of test chemicals with the cell-culture media used. We find that the toxicity and clastogenicity of epigallocatechin gallate (EGCG) to Chinese Hamster ovary (CHO) cells is affected by the culture medium used and appears largely or entirely due to variable rates of formation of hydrogen peroxide (H(2)O(2)) by chemical reactions of EGCG with the culture media. Catalase decreased EGCG toxicity substantially. Of seven different types of commonly used media evaluated, F-10 and F-12 nutrient mixtures were the least prone to produce this artefact. Although it generated H(2)O(2) in the culture media, ascorbate was not toxic to CHO cells because the H(2)O(2) levels achieved were insufficient to kill these cells. Thus, the culture medium, the cell type and the presence or absence of catalase (e.g. its variable amounts in S9 fractions) must be taken into account in in vitro genotoxicity testing.

How to reduce false positive results when undertaking in vitro genotoxicity testing and thus avoid unnecessary follow-up animal tests: Report of an ECVAM Workshop

Workshop participants agreed that genotoxicity tests in mammalian cells in vitro produce a remarkably high and unacceptable occurrence of irrelevant positive results (e.g. when compared with rodent carcinogenicity). As reported in several recent reviews, the rate of irrelevant positives (i.e. low specificity) for some studies using in vitro methods (when compared to this "gold standard") means that an increased number of test articles are subjected to additional in vivo genotoxicity testing, in many cases before, e.g. the efficacy (in the case of pharmaceuticals) of the compound has been evaluated. If in vitro tests were more predictive for in vivo genotoxicity and carcinogenicity (i.e. fewer false positives) then there would be a significant reduction in the number of animals used. Beyond animal (or human) carcinogenicity as the "gold standard", it is acknowledged that genotoxicity tests provide much information about cellular behaviour, cell division processes and cellular fate to a (geno)toxic insult. Since the disease impact of these effects is seldom known, and a verification of relevant toxicity is normally also the subject of (sub)chronic animal studies, the prediction of in vivo relevant results from in vitro genotoxicity tests is also important for aspects that may not have a direct impact on carcinogenesis as the ultimate endpoint of concern. In order to address the high rate of in vitro false positive results, a 2-day workshop was held at the European Centre for the Validation of Alternative Methods (ECVAM), Ispra, Italy in April 2006. More than 20 genotoxicity experts from academia, government and industry were invited to review data from the currently available cell systems, to discuss whether there exist cells and test systems that have a reduced tendency to false positive results, to review potential modifications to existing protocols and cell systems that might result in improved specificity, and to review the performance of some new test systems that show promise of improved specificity without sacrificing sensitivity. It was concluded that better guidance on the likely mechanisms resulting in positive results that are not biologically relevant for human health, and how to obtain evidence for those mechanisms, is needed both for practitioners and regulatory reviewers. Participants discussed the fact that cell lines commonly used for genotoxicity testing have a number of deficiencies that may contribute to the high false positive rate. These include, amongst others, lack of normal metabolism leading to reliance on exogenous metabolic activation systems (e.g. Aroclor-induced rat S9), impaired p53 function and altered DNA repair capability. The high concentrations of test chemicals (i.e. 10 mM or 5000 microg/ml, unless precluded by solubility or excessive toxicity) and the high levels of cytotoxicity currently required in mammalian cell genotoxicity tests were discussed as further potential sources of false positive results. Even if the goal is to detect carcinogens with short in vitro tests under more or less acute conditions, it does not seem logical to exceed the capabilities of cellular metabolic turnover, activation and defence processes. The concept of "promiscuous activation" was discussed. For numerous mutagens, the decisive in vivo enzymes are missing in vitro. However, if the substrate concentration is increased sufficiently, some other enzymes (that are unimportant in vivo) may take over the activation-leading to the same or a different active metabolite. Since we often do not use the right enzyme systems for positive controls in vitro, we have to rely on their promiscuous activation, i.e. to use excessive concentrations to get an empirical correlation between genotoxicity and carcinogenicity. A thorough review of published and industry data is urgently needed to determine whether the currently required limit concentration of 10mM or 5000 microg/ml, and high levels of cytotoxicity, are necessary for the detection of in vivo genotoxins and DNA-reactive, mutagenic carcinogens. In addition, various measures of cytotoxicity are currently allowable under OECD test guidelines, but there are few comparative data on whether different measures would result in different maximum concentrations for testing. A detailed comparison of cytotoxicity assessment strategies is needed. An assessment of whether test endpoints can be selected that are not intrinsically associated with cytotoxicity, and therefore are less susceptible to artefacts produced by cytotoxicity, should also be undertaken. There was agreement amongst the workshop participants that cell systems which are p53 and DNA-repair proficient, and have defined Phase 1 and Phase 2 metabolism, covering a broad set of enzyme forms, and used within the context of appropriately set limits of concentration and cytotoxicity, offer the best hope for reduced false positives. Whilst there is some evidence that human lymphocytes are less susceptible to false positives than the current rodent cell lines, other cell systems based on HepG2, TK6 and MCL-5 cells, as well as 3D skin models based on primary human keratinocytes also show some promise. Other human cell lines such as HepaRG, and human stem cells (the target for carcinogenicity) have not been used for genotoxicity investigations and should be considered for evaluation. Genetic engineering is also a valuable tool to incorporate missing enzyme systems into target cells. A collaborative research programme is needed to identify, further develop and evaluate new cell systems with appropriate sensitivity but improved specificity. In order to review current data for selection of appropriate top concentrations, measures and levels of cytotoxicity, metabolism, and to be able to improve existing or validate new assay systems, the participants called for the establishment of an expert group to identify the in vivo genotoxins and DNA-reactive, mutagenic carcinogens that we expect our in vitro genotoxicity assays to detect as well as the non-genotoxins and non-carcinogens we expect them not to detect.

The cannabinoid CB1 receptor antagonist rimonabant (SR141716) inhibits human breast cancer cell proliferation through a lipid raft-mediated mechanism

The endocannabinoid system has been shown to modulate key cell-signaling pathways involved in cancer cell growth. In this study, we show that cannabinoid receptor type 1 (CB1) antagonist Rimonabant (SR141716) inhibited human breast cancer cell proliferation, being more effective in highly invasive metastatic MDA-MB-231 cells than in less-invasive T47D and MCF-7 cells. The SR141716 antiproliferative effect was not accompanied by apoptosis or necrosis and was characterized by a G1/S-phase cell cycle arrest, decreased expression of cyclin D and E, and increased levels of cyclin-dependent kinase inhibitor p27KIP1. We have also shown that SR141716 exerted a significant antiproliferative action, in vivo, by reducing the volume of xenograft tumors induced by MDA-MB-231 injection in mice. On the other hand, at the concentration range in which we observed the antiproliferative effect in tumor cells, we did not observe evidence of any genotoxic effect on normal cells. Our data also indicate that the SR141716 antiproliferative effect requires lipid raft/caveolae integrity to occur. Indeed, we found that CB1 receptor (CB1R) is completely displaced from lipid rafts in SR141716-treated MDA-MB-231 cells, and cholesterol depletion by methyl-beta-cyclodextrin strongly prevented SR141716-mediated antiproliferative effect. Taken together, our results suggest that SR141716 inhibits human breast cancer cell growth via a CB1R lipid raft/caveolae-mediated mechanism.