Projects / Programmes
Cytotoxic and genotoxic effects of cyanobacterial toxins: in vitro studies of the effects of low for environmental contamination relevant concentrations
| Code |
Science |
Field |
Subfield |
| 1.08.00 |
Natural sciences and mathematics |
Control and care of the environment |
|
| Code |
Science |
Field |
| B220 |
Biomedical sciences |
Genetics, cytogenetics |
pollution, cyanobacterial toxin, microcystin, nodularin, genotoxicity, oxidative stress, apoptosis, genomics, gene expression
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
20767 |
PhD Bojana Žegura |
Biology |
Head |
2008 - 2009 |
340 |
Organisations (1)
| no. |
Code |
Research organisation |
City |
Registration number |
No. of publicationsNo. of publications |
| 1. |
0105 |
National Institute of Biology |
Ljubljana |
5055784 |
13,258 |
Abstract
The presence of toxic cyanobacteria and their toxins in surface waters used for drinking water sources and recreation is receiving increasing attention worldwide as a potential health concern. Globally the most frequently found cyanobacterial toxins in blooms from fresh and brackish waters are the cyclic peptide toxins of the microcystin and nodularin family. The primary mechanism of hepatotoxic microcystin (MC) and nodularin (NOD) toxicity is the inhibition of protein phosphatases 1 and 2A, resulting in hyperphosphorylation of proteins. MCs are considered to be tumor promoters, while NODs seem to possess both tumor-initiating and promoting activities. Resent studies indicate that apart to inhibition of phosphatases, oxidative stress might be involved in hepatotoxicity of MCs and NODs. However, the exact mechanisms of their activity are not fully understood.
In several countries, including Slovenia, guidelines are being prepared, the goal of which is human protection against toxic effects of cyanobacterial toxins. In 1998 World Health Organization determined the provisional guideline value only for cyanobacterial toxin microcystin-LR (MCLR) in drinking water at 1 μg/L water. This value has been calculated on the basis of the microcystin acute toxicity data, not taking into account possible delayed effects upon chronic exposure to low doses.
In the proposed project we will use state-of-the art molecular biological methods and in vitro test systems to explore molecular mechanisms of cyanobacterial toxin toxicity. In more detail we will evaluate the genotoxic potential of MCLR and NOD. In our previous studies we showed that MCLR can induce DNA strand breaks, here we will determine the potential of MCLR and NOD to induce apart to DNA strand breaks also structural and numerical chromosomal aberrations and mutations. Recently several studies showed that MCs can induce programmed cell death, but, the exact mechanism by which MCLR triggers apoptosis is not fully elucidated, while there is no information regarding the ability of NOD to induce apoptosis. The underlying mechanisms of genotoxic and apoptotic effects will be revealed by studying the expression of genes involved in oxidative and metabolic stress, apoptosis, cellular response to DNA damage and cell division. Therefore, in the proposed project we intend to explore several aspects of the toxins’ influence on intrinsic and extrinsic pathways of apoptosis as well as on cell cycle. Even though MCs are considered as specific hepatotoxins, data from several studies show that they affect also other organs, therefore, the cytotoxic and genotoxic effects on different cell types will be investigated.
The results obtained in the proposed project will contribute new data on MC and NOD cytotoxicity and genotoxicity. The achieved new knowledge will be important for the formation of future strategies for human and animal protection against the harmful effects of cyanobacterial toxins and for better prediction of consequences of long-term exposure to low toxin doses.
Significance for science
Knowing the cellular and molecular mechanisms of the activity of cyanobacterial toxins enables better understanding of their role in cancer initiation and promotin.
In our studies of the mechanisms of genotoxic activity of compex cyaobacterial extracts and pure cyanotoxins (microcystin-LR and nodularin) showed that the extracts as well as pure toxins induced DNA damage in HepG2 cells. We were the first who showed that increased DNA strand breaks were the consequence of intracellular reactive oxygen species formation after the exposure of cells to the toxins. Furtehrmore, we showed that MCLR induced micronuclei formation and influenced cell division. In the frame of our studies we showed that cyanobacterial toxins MCLR and NOD influenced the experssion of several genes involved in cellular responses to DNA damage and apoptosis and that the gene expression patterns for both tested toxins were not the same. Moreover, we showed that the gene expression profiles varied with time of exposure, which should be carefully considered in toxicogenomic studies where gene expression is usually determined at only one or two time points of exposure.
The results from the study showed different sensitivity of various mammalian cell types towards the effects of non-cytotoxic doses of the cyanobacterial peptide, MCLR. A very important finding was relatively high sensitivity of colon derived CaCo-2 cells towards the genotoxicity of MCLR, which indicates that in addition to liver, colon should also be considered as a target of microcystin toxicity, particularly at long-term sub-lethal exposures.
The results obtained from the proposed research contribute to better knowledge and understanding of microcystin and nodularin activity on cellular processes on molecular level, which can lead to changes in genome integrity and consequently mutations. Moreover, these results importantly contributed to evidence, that microcystins are not only tumor promoters, but also their initiators. The importance of our findings can be seen from regular citing of our research in papers dealing with the mechanisms of microcystine carcinogenicity.
Significance for the country
In Slovenia there are several areas where surface freshwaters are highly eutrophicated and in the majority of these surface water bodies bloom forming cyanobacterial species can be found. In Slovenia massive cyanobacterial blooms are frequent in the North-Eastern region with high agricultural activities and occur almost every year in summer-autumn months. Apart of this region two other locations are important with frequent occurrence of cyanobacteria lake Bled and pond Koseze where high recreational activities are developed.
The cyanobacteria form several cyanotoxins that are released into surrounding water after the cell lysis. Such eutrophicated waters represent a permanent threat to human and environmental health, since they accumulate highly toxic substances. Therefore, human population living in the areas with high cyanobacterial toxin contamination can be cronically exposed to these toxins and it is expected that these people are exposed to elevated risk for cancer. Moreover the possible contamination of drinking water is becoming a serious problem therefore it is essential to know the hazard these contaminants represent in order to introduce adequate preventive measures. This indicates that regular control of the presence of these toxins in drinking water would be necessary.
Recognition of health hazards is an important factor for the development of risk management strategies to reduce problems presented by cyanobacterial toxins and cells in potable and recreational waters. It is considered that there is currently insufficient information to derive guidelines for the use of water contaminated by cyanobacteria or their toxins for drinking purpose, recreation, agricultural production, fisheries and ecosystem protection.
The results of our studies contribute to better understanding of mechanisms and cell pathways involved in toxic/genotoxic activity of microcystins and nodularins. This new data is potentially useful for Slovene regulations for setting the safe concentration values for cyanobacterial toxins in drinking as well as recreational waters. Our results on microcystin/nodularin genotoxic activities were published in international scientific papers and reported on numerous scientific meetings in Slovenia and abroad what could lead to better awareness about toxic potential of cyanobacterial toxins.
Most important scientific results
Annual report
2008,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2008,
final report,
complete report on dLib.si
