Comparative Cellular Toxicity of Hydrophilic and Hydrophobic Microcystins on Caco-2 Cells

Abstract

Microcystins (MC), cyanobacterial peptide hepatotoxins, comprise more than 100 different variants. They are rather polar molecules but some variants contain hydrophobic amino acid residues in the highly variable parts of the molecule. In MC-LF and MC-LW, the more hydrophobic phenylalanine (F) and tryptophan (W), respectively, have replaced arginine (R) in MC-LR. Depending on the structure, microcystins are expected to have different in vivo toxicity and bioavailability, but only a few studies have considered the toxic properties of the more hydrophobic variants. The present study shows that MC-LF and MC-LW have more pronounced cytotoxic effects on Caco-2 cells as compared to those of MC-LR. Treatment of Caco-2 cells with MC-LW and especially MC-LF showed clear apoptotic features including shrinkage and blebbing, and the cell–cell adhesion was lost. An obvious reduction of cell proliferation and viability, assessed as the activity of mitochondrial dehydrogenases, was observed with MC-LF, followed by MC-LW and MC-LR. Cytotoxicity was quantified by measuring lactate dehydrogenase leakage. The more hydrophobic MC-LW and MC-LF induced markedly enhanced lactate dehydrogenase leakage compared to controls and MC-LR, indicating that the plasma membrane was damaged. All of the three toxins examined inhibited protein phosphatase 1, with MC-LF and MC-LW to a weaker extent compared to MC-LR. The higher toxic potential of the more hydrophobic microcystins could not be explained by the biophysical experiments performed. Taken together, our data show that the more hydrophobic microcystin variants induce higher toxicity in Caco-2 cells.

Transfer of microcystin from freshwater lakes to Puget Sound, WA and toxin accumulation in marine mussels (Mytilus trossulus)

“…Since toxicities of MC variants range substantially (Shimizu et al, 2014) and some variants are more toxic than MC-LR (Vesterkvist et al, 2012), WHO TDI may underestimate risk if other variants are present. Based on newer data the United States Environmental Protection Agency (USEPA) suggests a lower chronic exposure criteria value (0.003 mg/kg).…”

Review and analysis of occurrence, exposure and toxicity of cyanobacteria toxins in food

“…The inhibitory capacity of single MC congeners on PP1 and PP2A in vitro is comparable,with IC 50 values in the nanomolar range (Hoeger et al, 2007;Monks et al, 2007;Fischer et al, 2010;Vesterkvist et al,2012).…”

A review of reproductive toxicity of microcystins

“…Different MC variants have varied biological affinities i.e., their potential to enter a certain tissue would be different depending on the affinity of the cell transporters for that MC variant [150][151][152]. Moreover, distinct properties of MC variants in terms of PP1 and PP2A inhibition, cytotoxicity, biotransformation, and detoxification have also been reported [152][153][154][155][156]. However, at present, the toxicological database for MCs is almost exclusively limited to data on a single variant, MC-LR, while data on the other variants is very lacking.…”