Pyrrolizidine alkaloids (PAs) are the most common plant constituents that
poison livestock, wildlife and humans.
Riddelliine is a prototype genotoxic PA and has been nominated to be classified as a reasonably anticipated human
carcinogen by the US National Toxicology Program (NTP) in the 12th Report on
Carcinogens.
Riddelliine's nomination is due to the high incidence of liver tumours that were observed in both mice and rats in the NTP tumourigenicity bioassay study. In this current study, we explored whether
riddelliine treatment could alter
microRNA (
miRNA) expression in rat liver and whether the possible deregulation of
miRNA was related to mutagenicity and carcinogenicity of
riddelliine. Groups of six rats were administered
riddelliine at a mutagenic dose of 1 mg/kg
body weight or with control vehicle 5 days a week for 12 weeks. A group of six rats treated with
aristolochic acid, a renal
carcinogen, was used as a tissue-specific negative control. The animals were sacrificed 1 day after the last treatment and the livers were isolated for
miRNA expression analysis using
miRNA microarrays.
miRNA expression was significantly altered by
riddelliine treatment. Principal component analysis and hierarchical clustering analysis showed that the
miRNA expression profiles were clearly classified into two groups,
riddelliine treatment versus other samples. Forty-seven
miRNAs were significantly dysregulated by
riddelliine treatment, among which 38 were up-regulated and 9 were down-regulated. Functional analysis of these differentially expressed
miRNAs by
riddelliine revealed that these
miRNAs were involved in liver carcinogenicity and toxicity, such as liver proliferation, liver
necrosis/cell death,
hepatocellular carcinoma, liver
hepatomegaly, liver
inflammation and
liver fibrosis. These results suggest that
miRNAs actively respond to a mutagenic dose of
riddelliine and the pattern of
miRNA expression has the potential to be used as a
biomarker of genotoxicity and carcinogenicity for
riddelliine and possibly other PAs.