Characterization of Sublethal Microcystin-LR Exposure in Mice

Abstract

Microcystin-LR (MCLR) is a potent hepatotoxin produced by the cyanobacterium Microcystis aeruginosa. The histology of acute lethal toxicity has been well characterized, but histology is limited regarding sublethal exposure. Balb/C mice were given a single sublethal dose of MCLR (45 microg/kg) and euthanized at 2, 4, 12, and 24 hours after exposure. Centrilobular to midzonal hepatocellular hypertrophy with loss of cytosolic vacuolation consistent with glycogen depletion occurred at 2 hours. At 4 hours, central lobular hepatocytes exhibited eccentric areas of eosinophilic cytoplasmic condensation that were partially aggregated around the outer nuclear membrane. The areas were weakly positive for cytokeratin and somewhat resembled the Mallory bodies of alcoholic human hepatitis. Small numbers of apoptotic hepatocytes were seen at 24 hours. The toxin was detectable by immunohistochemistry (IHC) as early as 2 hours and was colocalized with the areas of hepatocellular hypertrophy. Intense nuclear staining occurred at 4 hours; this was no longer evident after 12 hours. Strong staining of apoptotic bodies occurred at 24 hours. Mice that received two daily doses had a marked increase in apoptotic hepatocytes in the centrilobular areas. Lesions at four and seven doses consisted of marked hepatocytomegaly and karyomegaly with parenchymal disarray and cytosolic vacuolation. IHC revealed diffuse staining throughout the liver parenchyma consistent with toxin accumulation. An anti-MCLR monoclonal antibody detected bands at the 40-kDa mark in nuclear extracts that were identified as protein phosphatases 1 and 2A by western blotting, consistent with a covalent interaction between MCLR and nuclear protein phosphatases.

PANSTEATITIS OF UNKNOWN ETIOLOGY ASSOCIATED WITH LARGE-SCALE NILE CROCODILE (CROCODYLUS NILOTICUS) MORTALITY IN KRUGER NATIONAL PARK, SOUTH AFRICA: PATHOLOGIC FINDINGS

“…Liver levels of microcystin toxin are being determined. Typical hepatic necrosis seen in mammalian cases of algae microcystin toxicity 20 was not present in these crocodiles, although species differences in susceptibility and tissue responses to this toxin may occur. In addition, cyanobacteria produce a variety of toxins, the effects of some of which are not well characterized.…”

Hepatic Gene Expression Changes in Mice Associated with Prolonged Sublethal Microcystin Exposure

“…Alterations associated with chronic sublethal exposure to MCLR have also been characterized. Balb/c mice administered sublethal intraperitoneal (45 µg/kg/d) doses of MCLR for 4 or 7 days exhibited marked hepatocytomegaly and karyomegaly with numerous multinucleated cells (Guzman and Solter, 2002). In rats, prolonged sublethal (16, 32, and 48 µg/kg/day) exposure to MCLR for 28 days was found to have multiple dose-dependent hepatotoxic effects including increased hepatic apoptosis, steatosis and centrilobular fibrosis (Solter et al, 1998).…”

Renal accumulation and effects of intraperitoneal injection of extracted microcystins in omnivorous crucian carp (Carassius auratus)

“…The high selectivity to liver is believed to be due to toxin uptake via bile acid carriers (Suchy, 1993;Sahin et al, 1996). Histopathological studies in both fish and mammals revealed serious lesions of the liver including rounding and separation of hepatocytes, disruption of hepatic cords, hepatocyte necrosis and degeneration, and severe intrahepatic hemorrhage leading to lethal hypolovemic shock or liver failure (Guzman and Solter, 2002;Li et al, 2003Li et al, , 2004Malbrouck et al, 2003;Handeland and Ostensvik, 2010).…”