Abstract
Cyanobacterial extracts have been recently shown to alter two in vitro biomarkers of tumor promotion, namely to cause inhibition of gap-junctional intercellular communication (GJIC) and activation of mitogen-activated protein kinases (Blaha et al., 2010a). In the present study, we investigated GJIC-inhibitory potencies of 10 laboratory strains representing common water bloom-forming cyanobacteria (Anabaena, Aphanizomenon, Cylindrospermopsis, Microcystis and Planktothrix) and six natural water bloom samples (dominated by Aphanizomenon sp. or Microcystis). The most pronounced inhibitions of GJIC in a model rat liver epithelial cell line WB-F344 were caused by methanolic extracts of Anabaena flos-aquae UTEX 1444, Aphanizomenon flos-aquae SAG 31.87, Aphanizomenon gracile RCX 06, Microcystis aeruginosa PCC 7806, Cylindrospermopsis raciborskii SAG 1.97, Planktothrix agardhii CCALA 159 and SAG 32.79, whereas weaker effects were induced by Aphanizomenon klebahnii CCALA 009 and no inhibition was induced by extracts of Aph. flos-aquae PCC 7905 and Aph. gracile SAG 31.79. Exudates of the laboratory cultured strains concentrated by solid phase extraction also induced species-specific inhibitory effects, but they did not necessarily correlate with the inhibitory potencies of extracts from the corresponding species. Interestingly, the GJIC-inhibitory effects may not be restricted to cyanobacteria, since exudates of two green alga species also affected GJIC, although their extracts caused no effects. The extracts from different natural water blooms inhibited GJIC with different potencies without apparent relation to bloom-species composition. Since the observed effects on GJIC did not correlate with the content of cyanotoxins microcystins and cylindrospermopsin in the tested samples, they were most likely induced by unknown compound(s). Our results indicate that putative tumor promoting compound(s) could be associated with different species of bloom-forming cyanobacteria, but their production is probably species- and strain-specific.