Tumor Necrosis Factor-α Expression and Kupffer Cell Activation in Hepatotoxicity Caused by Microcystin-LR in Mice

The aim of this study was to examine tumor necrosis factor-α (TNF-α) expression and Kupffer cell activation in hepatotoxicity caused by microcystin-LR (MCLR). Mice received a single intraperitoneal injection of 60.0 μg/kg MCLR and were killed at several time points within 24 hours. MCLR caused hemorrhage within 7 hours, followed by hepatocellular necrosis and apoptosis. A real-time quantitative reverse-transcription polymerase chain reaction demonstrated that the level of TNF-α mRNA was 2.3-fold higher than in the controls at 17 hours. The number of TNF-α-immunopositive nonparenchymal cells was 2.6- and 7.7-fold greater than that in the controls at 7 and 17 hours, respectively, and they frequently infiltrated into necrotic areas, probably in association with neutrophil recruitment. Some apoptotic hepatocytes were immunopositive for cleaved caspase-3. To inactivate Kupffer cells, mice were pretreated with a single intravenous injection of gadolinium chloride (GdCl3, 2 mg/mouse). That brought about the apoptosis of sinusoidal cells, which indicated Kupffer cell depletion. GdCl3 pretreatment attenuated MCLR-induced hepatocellular apoptosis by 68%, and likely decreased hepatocellular necrosis. These results suggest that Kupffer cell activation, represented by enhanced TNF-α expression, is involved in the progression of MCLR-induced hepatotoxicity in mice.