Differential hepatotoxic effects of single versus repeated MCLR exposure in control diet and high fat, high cholesterol diet fed rats.

Microcystin-LR (MCLR) is a hepatotoxin that has been connected to development of metabolic dysfunction-associated steatotic liver disease (MASLD) and hepatocellular carcinoma, but the hepatotoxic effect of single versus repeated MCLR exposure in pre-existing MASLD is not known. Understanding how a single exposure versus repeated exposures modulate liver physiology can provide insight into risks associated with different exposure patterns. Sprague Dawley rats were fed a control diet or a high-fat, high-cholesterol (HFHC) diet and administered either single or repeated MCLR exposure(s). Necrosis was more prominent after a single MCLR exposure compared to repeated exposure in both diet groups. Inflammation was also more prominent in the control diet group after a single MCLR exposure compared to repeated exposure, whereas it was equally severe after both exposure scenarios in the HFHC diet group. Repeated MCLR exposure caused a larger number of differentially expressed genes compared to a single exposure in both diet groups, although more genes were differentially expressed in the control diet than in the HFHC diet. KEGG Pathways in cancer and phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway were two pathways with the most upregulated genes in both diet groups after repeated MCLR exposure. Follow-up protein expression analysis confirmed activated Akt and increased c-JUN and cyclin D1 protein levels. The expression of β-catenin increased after repeated MCLR exposure only in the HFHC diet group, suggesting this important cell growth pathway may be activated by MCLR specifically in animals with pre-existing liver disease. This study highlights the differential impact of single versus repeated MCLR on liver pathology in healthy and MASLD conditions.