Microcystin (MC)

Microcystins are a diverse family of cyclic heptapeptide toxins produced by various genera of cyanobacteria, most notably Microcystis, Anabaena, and Planktothrix, often occurring during harmful algal blooms. These toxins are characterized by a unique amino acid side chain known as Adda (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid), which is essential for their biological activity and toxicity [1][2]. In humans and animals, microcystins primarily target the liver because they are actively transported into hepatocytes via organic anion transporting polypeptides (OATPs) [2][3]. Inside the cell, microcystins act as potent inhibitors of serine/threonine protein phosphatases 1 (PP1) and 2A (PP2A), leading to unregulated protein phosphorylation, disruption of the actin cytoskeleton, and subsequent liver damage or tumor promotion [4][5]. While microcystins are not therapeutic targets in the traditional sense, they are critical environmental health hazards and are used in biochemical research to study phosphatase-regulated signaling pathways. Exposure to microcystins is associated with acute hepatotoxicity and has been linked to an increased risk of primary liver cancer in populations with contaminated drinking water sources [3][6]. Citations: [1] PubChem CID 100742; [2] EPA Health Effects Support Document (2015); [3] WHO Guidelines for Drinking-water Quality; [4] MacKintosh et al. (1990) FEBS Letters; [5] Zhou et al. (2015) Int. J. Environ. Res. Public Health; [6] IARC Monograph Vol 94.

Other names

CyanoginosinMicrocystin-LRMC-LRCyanobacterial toxinHepatotoxinCyclic heptapeptide toxin

Microcystins exert toxicity by potently and irreversibly inhibiting the catalytic subunits of serine/threonine protein phosphatases 1 (PP1) and 2A (PP2A) through covalent binding. This inhibition leads to a massive hyperphosphorylation of cellular proteins, particularly those involved in maintaining the cytoskeleton, which causes hepatocytes to shrink, lose their shape, and eventually undergo apoptosis or necrotic cell death, leading to intrahepatic hemorrhage.