Inhibition of gap-junctional intercellular communication and activation of mitogen-activated protein kinases by cyanobacterial extracts – Indications of novel tumor-promoting cyanotoxins?

Abstract

Toxicity and liver tumor promotion of cyanotoxins microcystins have been extensively studied. However, recent studies document that other metabolites present in the complex cyanobacterial water blooms may also have adverse health effects. In this study we used rat liver epithelial stem-like cells (WB-F344) to examine the effects of cyanobacterial extracts on two established markers of tumor promotion, inhibition of gap-junctional intercellular communication (GJIC) and activation of mitogen-activated protein kinases (MAPKs) – ERK1/2. Extracts of cyanobacteria (laboratory cultures of Microcystis aeruginosa and Aphanizomenon flos-aquae and water blooms dominated by these species) inhibited GJIC and activated MAPKs in a dose-dependent manner (effective concentrations ranging 0.5 - 5 mg d.w./mL). Effects were independent of the microcystin content and the strongest responses were elicited by the extracts of Aphanizomenon sp. Neither pure microcystin-LR nor cylindrospermopsin inhibited GJIC or activated MAPKs. Modulations of GJIC and MAPKs appeared to be specific to cyanobacterial extracts since extracts from green alga Chlamydomonas reinhardtii, heterotrophic bacterium Klebsiella terrigena, and isolated bacterial lipopolysaccharides had no comparable effects. Our study provides the first evidence on the existence of unknown cyanobacterial toxic metabolites that affect in vitro biomarkers of tumor promotion, i.e. inhibition of GJIC and activation of MAPKs.

Pro- and anti-inflammatory cytokine expression in carp blood and head kidney leukocytes exposed to cyanotoxin stress – An in vitro study

“…This observation corroborates the suggestion reported by many investigators that environmental samples of cyanotoxins may have more activity and cause greater perturbations in cellular homeostasis than pure toxin samples [33,34].…”

“…It has been reported that p38 MAPK, JNK, and ERK 1/2 were activated by MC-LR in the human liver cell line HL7702 [38], and the monkey kidney-derived cell line Vero-E6 [43]. Similarly, Bláha et al [34] showed that cyanobacteria seem to produce specific metabolites that activate ERK1/2.…”

Baltic cyanobacteria – a source of biologically active compounds

“…Usually, when considering cyanobacterial extracts, either specific enzymatic activities were analysed (see, for example: Haystead et al, 1970;Schönherr & Keir, 1972;Papen et al, 1983Papen et al, , 1986Hai et al, 2001;Chiba et al, 2012) or researchers looked for enzyme inhibitors or activators rather than active proteins (Cannell et al, 1987;Lau et al, 1993;Tang et al, 2007;Taori et al, 2008;Zelík et al, 2009;Bláha et al, 2010;Anas et al, 2012;Malloy et al, 2012;Makhlouf Brahmi et al, 2013). It is interesting, however, that similar richness of enzymatic activities and differences in their occurrence were observed within one cyanobacterial genus, when phenotypic and genotypic variabilities among Microcystis strains were studied (Yoshida et al, 2008).…”

Application of cellular biosensors for detection of atypical toxic bioactivity in microcystin-containing cyanobacterial extracts

“…Numerous studies using bioassays (Bláha et al, 2010), as well as recent work with cellular biosensors of endocrine disruption (Jonas et al, 2014(Jonas et al, , 2015 have also concentrated on demonstrating that microcystins are not responsible for the biological effects observed in these experiments. The present results also showed that focusing on one toxic compound (in environmental monitoring practice this is most commonly microcystin-LR) is not a valid approach to the holistic evaluation of environmental risk for human health from cyanobacterial blooms.…”

“…Presently, following some new reports on the activity of unknown endogenous toxic substances contained in cyanobacterial blooms (Sedmak andŠuput, 2002;Bláha et al, 2010;Štěpánková et al, 2011;Nováková et al, 2011Nováková et al, , 2012Sychrová et al, 2012), a holistic approach to water quality monitoring based on physiological effect of combined toxins and xenobiotics present in the cyanobacterial bloom seems to be a necessary complement for regulatory and monitoring purposes. Such an approach must involve the assessment of toxicity mechanisms on the organism, cellular and molecular level which are physiologically relevant to living components of the environment, especially to human health.…”