Microcystin

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Chemical structure of Microcystin LR

Microcystins are cyclic nonribosomal peptides produced by cyanobacteria (e.g.Microcystis aeruginosa and Planktothrix). They are cyanotoxins and can be very toxic for plants and animals including humans. Their hepatotoxicity may cause serious damage to the liver. Microcystins can strongly inhibit protein phosphatases type 1 (PP1) and 2A (PP2A), and are linked to pansteatitis.[1]

Microcystins consist of several uncommon non-proteinogenic amino acids such as dehydroalanine derivatives and the special β-amino acid ADDA, (all-S,all-E)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid).

Microcystin-LR is one of over 80 known toxic variants and is the most studied by chemists, pharmacologists, biologists and ecologists. Microcystin-containing 'blooms' are a problem worldwide, including China, Brazil, Australia, South Africa,[2][3][4][5][6][7][8][9] the United States and much of Europe. Once ingested, microcystin travels to the liver, via the bile acid transport system, where most is stored; though some remains in the blood stream and may contaminate tissue.[10][11] Microcystin binds covalently to protein phosphatases thus disrupting cellular control processes.

There appears to be inadequate information to assess carcinogenic potential of microcystins by applying EPA Guidelines for Carcinogen Risk Assessment. A few studies suggest that there may be a relationship between liver and colorectral cancers and the occurrence of cyanobacteria in drinking water in China [12][13][14][15](Yu et al., 1989; Zhou et al., 2002). Evidence is, however, limited due to limited ability to accurately assess and measure exposure.

The impact of exposure to microcystin by patients with a compromised immune system is not yet fully known, but is starting to raise some concern.[16]

There is some evidence that the toxin can be transported via irrigation into the food chain [17][18] but this still needs additional verification.

Global warming[edit]

Global warming affects the reproductive and productive rate of cyanobacteria, and studies have linked warming to increase in microcystin production.[19][20] This is being found in Lake Midmar in South Africa.[21]

See also[edit]

References[edit]

  1. ^ http://www.pwrc.usgs.gov/health/rattner/rattner_blackwaternwr.cfm
  2. ^ Bradshaw, D., Groenewald, P., Laubscher, R., Nannan, N., Nojilana, B., Norman, B., Pieterse, D. and Schneider, M. (2003). Initial Burden of Disease Estimates for South Africa, 2000. Cape Town: South African Medical Research Council.
  3. ^ Fatoki, O.S., Muyima, N.Y.O. & Lujiza, N. 2001. Situation analysis of water quality in the Umtata River Catchment. Water SA, (27) Pp 467-474.
  4. ^ Oberholster, P.J., Botha, A-M. & Grobbelaar, J.U. 2004 Microcystis aeruginosa: Source of toxic microcystins in drinking water. Africa Journal of Biotechnology 3: 159-168.
  5. ^ Oberholster, P.J., Botha, A-M. & Cloete, T.E. 2005 An overview of toxic freshwater cyanobacteria in South Africa with special reference to risk, impact and detection by molecular marker tools. Biokem17: 57-71.
  6. ^ Oberholster, P.J. & Botha, A-M. 2007. Use of PCR based technologies for risk assessment of a winter cyanobacterial bloom in Lake Midmar, South Africa. African Journal of Biotechnology. (6) Pp 14-21.
  7. ^ Oberholster, P. 2008. Parliamentary Briefing Paper on Cyanobacteria in Water Resources of South Africa. Annexure “A” of CSIR Report No. CSIR/NRE/WR/IR/2008/0079/C. Pretoria. Council for Scientific and Industrial Research (CSIR).
  8. ^ Oberholster, P.J., Cloete, T.E., van Ginkel, C., Botha, A-M. & Ashton, P.J. 2008. The use of remote sensing and molecular markers as early warning indicators of the development of cyanobacterial hyperscum crust and microcystin-producing genotypes in the hypertrophic Lake Hartebeespoort, South Africa. Pretoria: Council for Scientific and Industrial Research (CSIR).
  9. ^ Oberholster, P.J. & Ashton, P.J. 2008. State of the Nation Report: An Overview of the Current Status of Water Quality and Eutrophication in South African Rivers and Reservoirs. Parliamentary Grant Deliverable. Pretoria: Council for Scientific and Industrial Research (CSIR).
  10. ^ Falconer, I.R. 1998. Algal toxins and human health. In Hrubec, J. (Ed.), Handbook of Environmental Chemistry, Volume 5 (Part C). Berlin: Springer-Verlag. Pp. 53-82.
  11. ^ Falconer, I.R. 2005. Cyanobacterial Toxins of Drinking Water Supplies: Cylindrospermopsins and Microcystins. Florida: CRC Press. 279 pages.
  12. ^ Humpage, A.R., Hardy, S.J., Moore, E.J., Froscio, S.M. & Falconer, I.R. 2000. Microcystins (cyanobacterial toxins) in drinking water enhance the growth of aberrant crypt foci in the colon. Journal of Toxicology and Environmental Health. (61) Pp 101-111.
  13. ^ Ito, E., Kondo, F., Terao, K. & Harada, K.-L. 1997. Neoplastic nodular formation in mouse liver induced by repeated intraperitoneal injection of microcystin-LR. Toxicon. (35) Pp 1453-1457.
  14. ^ Nishiwaki-Matushima, R., Nishiwaki, S., Ohta, T., Yoszawa, S., Suganuma, M., Harada, K., Watanabe, M.F. & Fujiki, H. 1991. Structure-function relationships of microcystins, liver-tumor promoters, in interaction with protein phosphatase. Japanese Journal of Cancer Research. (82) Pp 993-996.
  15. ^ Ueno, Y., Nagata, S., Tsutsumi, T., Hasegawa, A., Watanabe, M.F., Park, H.D., Chen, G.C. & Yu, S. 1996. Detection of microcystins in blue-green algae hepatotoxin in drinking water sampled in Haimen and Fusui, endemic areas of primary liver cancer in China, by highly sensitive immunoassay. Carcinogenesis. (17) Pp 1317-1321.
  16. ^ Doyle P. (1991). The Impact of AIDS on the South African Population. AIDS in South Africa: The Demographics and Economic Implications. Centre for Health Policy, University of the Witwatersrand, Johannesburg, South Africa.
  17. ^ Codd, G.A,, Metcalf, J.S. & Beattie, K.A. 1999. Retention of Microcystis aeruginosa and microcystin by salad lettuce after spray irrigation with water containing cyanobacteria. Toxicon, (37) Pp. 1181-1185.
  18. ^ Abe, T., Lawson, T., Weyers, J.D.B,, & Codd, G.A. 1996. Microcystin-LR inhibits photosynthesis of Phaseolus Vulgaris primary leaves: implications for current spray irrigation practice. New Phytol. 133: 651-658.
  19. ^ http://www.sciencedaily.com/releases/2012/07/120703142609.htm
  20. ^ http://www.sciencedirect.com/science/article/pii/S0043135411007056
  21. ^ Oberholster, P.J. & Botha, A-M. 2007. Use of PCR based technologies for risk assessment of a winter cyanobacterial bloom in Lake Midmar, South Africa. African Journal of Biotechnology. (6) Pp 14-21.
  • National Center for Environmental Assessment. Toxicological Reviews of Cyanobacterial Toxins: Microcystins LR, RR, YR and LA (NCEA-C-1765)
  • Yu, S.-Z. 1989. Drinking water and primary liver cancer. In: Primary Liver Cancer, Z.Y. Tang, M.C. Wu and S.S. Xia, Ed. China Academic Publishers, New York, NY. p. 30-37 (as cited in Ueno et al., 1996 and Health Canada, 2002).
  • Zhou, L., H. Yu and K. Chen. 2002. Relationship between microcystin in drinking water and colorectal cancer. Biomed. Environ. Sci. 15(2):166-171.

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