Effects of the Amino Acid Constituents of Microcystin Variants on Cytotoxicity to Primary Cultured Rat Hepatocytes

Abstract

Microcystins, which are cyclic heptapeptides produced by some cyanobacterial species from algal blooms, strongly inhibit serine/threonine protein phosphatase and are known as hepatotoxins. Microcystins have many structural variations, yet insufficient information is available on the differences in the cytotoxic potentials among the structural variants. In this study, the cytotoxicities of 16 microcystin variants at concentrations of 0.03–10 μg/mL to primary cultured rat hepatocytes were determined by measuring cellular ATP content, and subsequently determined by their 50% inhibitory concentration (IC50). Differences in the amino acid constituents were associated with differences in cytotoxic potential. [d-Asp3, Z-Dhb7] microcystin-LR exhibited the strongest cytotoxicity at IC50 of 0.053 μg/mL among the microcystin variants tested. Furthermore, [d-Asp3, Z-Dhb7] microcystin-HtyR was also highly cytotoxic. These results suggest that both d-Asp and Z-Dhb residues are important in determining the cytotoxic potential of microcystin variants.

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).…”

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.…”

Persistence of microcystin production ofPlanktothrix agardhiiexposed to different salinity concentrations

“…The characterization of the MC-variant composition was performed by liquid chromatography coupled to electrospray ionisation mass spectrometry (LC/ESI-MS/MS) in order to identify the chemo-type profile of the ‘Brack’ strain under optimal conditions (Fig. S1), as a various MC-diversity may exist within a same species Shimizu et al 2014; Tonk et al 2005). Five MC variants, (two major and three minor variants) were determined from cultured ‘Brack’ strain (Table 2).…”

“…MCs have many structural variations ( i.e. depending on the L-amino acid at the position 2 and 4 respectively from the whole MC architecture), and to date, over 200 MCs variants have been identified (Spoof and Catherine 2017) with different cytotoxic potentials; depending on the tested MCs variants (Shimizu et al 2014). While reports on the biosynthesis and chemical processes of the MCs are constantly in progress, the forces underlying toxin production, i.e.…”