Biochemical and physiological responses after exposure to microcystins in the crab Chasmagnathus granulatus (Decapoda, Brachyura)

Microcystins are usually the predominant cyanotoxins present in both drinking and recreational waters after cyanobacterial blooms. Their classic toxic effect is hepatotoxicity through inhibition of serine/threonine phosphatases. However, recent studies also reported oxidative stress generation and disruption of ion regulation in aquatic organisms after microcystins exposure. In the present study, aqueous extracts of Microcystis aeruginosa were administered to the estuarine crab Chasmagnathus granulatus (Decapoda, Brachyura) by gavage in variable doses (from 34 to 860 μg kg−1) and exposure times (6, 12, and 72 h). A control group was exposed to saline solution. Analyzed variables included oxygen consumption, lipid peroxidation (LPO), enzyme activities (glutathione S-transferases or GST; alanine aminotransferase or ALT; aspartate aminotransferase or AST; and lactate dehydrogenase or LDH), glycogen, and microcystins content. Oxygen consumption increased in organisms exposed for 12h to 860 μg kg−1 of microcystins and a similar result was observed after 72 h at doses equal to or higher than 34 μg kg−1. LPO levels increased in doses equal to or higher than 34 μg kg−1 after 72 h. GST and LDH activities increased after 12 h (at a dose of 860 μg kg−1), but ALT and AST activities remained unaltered in all experimental conditions. Glycogen content decreased after 72 h exposure at doses equal to or higher than 172 μg kg−1. After 12 h of exposure to 860 μg kg−1 of microcystins, the concentration found in the hepatopancreas of C. granulatus was 13.17±0.56 μg kg−1. In crabs exposed to doses higher than 172 μg kg−1 during 72 h this value raised to 32.14±4.12 μg kg−1. The obtained results indicated that microcystins exposure led the tissue to an oxidative stress condition (high LPO levels), at least in part favored by the augment of oxygen consumption, altering the glycogen metabolism. GST responses were only observed in the short-term experiment (12 h) and no effect on classical markers of vertebrate liver damage (ALT and AST) was observed. Although the hepatopancreas from C. granulatus accumulated a relatively low concentration of toxins, it was enough to induce physiological and biochemical disturbances.