The hepatic endothelial carcinogen riddelliine induces endothelial apoptosis, mitosis, S phase, and p53 and hepatocytic vascular endothelial growth factor expression after short-term exposure.
Riddelliineis a naturally occurring pyrrolizidine alkaloid found in certain poisonous rangeland plants of the western United States. In National Toxicology Program 2-year studies, riddelliine induced high incidences of hemangiosarcoma in the liver of F344/N rats (both sexes) and B6C3F1 mice (males). To understand this pathogenesis, we tested short-term effects of riddelliine. Three groups (control; 1.0 mg/kg/day, high dose used in the 2-year study; and 2.5 mg/kg/day) of seven male F344/N rats per group were terminated after 8 consecutive doses and 30 doses (6 weeks, excluding weekends). Serum vascular endothelial growth factor (VEGF), histological, immunohistochemical [factor VIII-related antigen/von Willebrand factor (fVIII-ra/vWf)], VEGF, VEGF receptor-2 (VEGFR2), glutathione S-transferase-pi, S-phase (BrdU), p53, apoptosis, and ultrastructural evaluations were performed on the liver. Following 8 doses of 1.0 and 2.5 mg/kg/day, increased numbers of apoptotic and S-phase nuclei appeared in hepatocytes and endothelial cells. Following 30 doses of 1.0 and 2.5 mg/kg/day, hepatocytes exhibited reduced mitosis, fewer S-phase nuclei, increased hypertrophy, and fatty degeneration, while endothelial cells showed karyomegaly, cytomegaly, decreased apoptosis, more S-phase nuclei, and p53 positivity. Hepatocytes of treated animals expressed higher VEGF immunopositivity. That altered endothelial cells were fVIII-ra/vWf and VEGFR2 positive confirmed their identity. These changes may have promoted hemangiosarcoma development upon long-term exposure through endothelial adduct formation, apoptosis, proliferation of endothelial cells having undamaged and/or damaged DNA, and mutation. Endothelial proliferation may also have been promoted through endothelial arrest at S phase, which was associated with endothelial karyo- and cytomegaly, resulting in hepatocytic hypoxia, triggering VEGF induction.
Nyska
Abraham
A
Laboratory of Experimental Pathology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA. nyska@niehs.nih.gov
Moomaw
Cindy R
CR
Foley
Julie F
JF
Maronpot
Robert R
RR
Malarkey
David E
DE
Cummings
Connie A
CA
Peddada
Shyamal
S
Moyer
Carolyn F
CF
Allen
David G
DG
Travlos
Greg
G
Chan
Po C
PC
D000284:Administration, Oral; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001973:Bromodeoxyuridine / Q000378:metabolism; D002273:Carcinogens / Q000008:administration & dosage / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D016228:Endothelial Growth Factors / Q000097:blood; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D007124:Immunoenzyme Techniques; D036341:Intercellular Signaling Peptides and Proteins / Q000097:blood; D007728:Kupffer Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008222:Lymphokines / Q000097:blood; D008297:Male; D008938:Mitosis; D011763:Pyrrolizidine Alkaloids / Q000008:administration & dosage / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344; D016196:S Phase / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism; D042442:Vascular Endothelial Growth Factors; D014841:von Willebrand Factor / Q000378:metabolism
D002273:Carcinogens; D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D011763:Pyrrolizidine Alkaloids; D016159:Tumor Suppressor Protein p53; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D014841:von Willebrand Factor; C013672:riddelliine; D040301:Vascular Endothelial Growth Factor Receptor-2; D001973:Bromodeoxyuridine