Pyrrolizidine Alkaloid-Derived DNA Adducts as a Common Biological Biomarker of Pyrrolizidine Alkaloid-Induced Tumorigenicity

Abstract

Pyrrolizidine alkaloid-containing plants are the most common poisonous plants affecting livestock, wildlife, and humans. The U.S. National Toxicology Program (NTP) classified riddelliine, a tumorigenic pyrrolizidine alkaloid, as "reasonably anticipated to be a human carcinogen" in the NTP 12th Report on Carcinogens in 2011. We previously determined that four DNA adducts were formed in rats dosed with riddelliine. The structures of the four DNA adducts were elucidated as (i) a pair of epimers of 7-hydroxy-9-(deoxyguanosin-N(2)-yl)dehydrosupinidine adducts (termed as DHP-dG-3 and DHP-dG-4) as the predominant adducts; and (ii) a pair of epimers of 7-hydroxy-9-(deoxyadenosin-N(6)-yl)dehydrosupinidine adducts (termed as DHP-dA-3 and DHP-dA-4 adducts). In this study, we selected a nontumorigenic pyrrolizidine alkaloid, platyphylliine, a pyrrolizidine alkaloid N-oxide, riddelliine N-oxide, and nine tumorigenic pyrrolizidine alkaloids (riddelliine, retrorsine, monocrotaline, lycopsamine, retronecine, lasiocarpine, heliotrine, clivorine, and senkirkine) for study in animals. Seven of the nine tumorigenic pyrrolizidine alkaloids, with the exception of lycopsamine and retronecine, are liver carcinogens. At 8-10 weeks of age, female F344 rats were orally gavaged for 3 consecutive days with 4.5 and 24 μmol/kg body weight test article in 0.5 mL of 10% DMSO in water. Twenty-four hours after the last dose, the rats were sacrificed, livers were removed, and liver DNA was isolated for DNA adduct analysis. DHP-dG-3, DHP-dG-4, DHP-dA-3, and DHP-dA-4 adducts were formed in the liver of rats treated with the individual seven hepatocarcinogenic pyrrolizidine alkaloids and riddelliine N-oxide. These DNA adducts were not formed in the liver of rats administered retronecine, the nontumorigenic pyrrolizidine alkaloid, platyphylliine, or vehicle control. These results indicate that this set of DNA adducts, DHP-dG-3, DHP-dG-4, DHP-dA-3, and DHP-dA-4, is a common biological biomarker of pyrrolizidine alkaloid-induced liver tumor formation. To date, this is the first finding that a set of exogenous DNA adducts are commonly formed from a series of tumorigenic xenobiotics.

Reaction of Dehydropyrrolizidine Alkaloids with Valine and Hemoglobin

“…35 Further studies demonstrated that DHP−dG-3, DHP−dG-4, DHP−dA-3, and DHP−dA-4 were also formed in the liver of rats treated with seven hepatocarcinogenic pyrrolizidine alkaloids and riddelliine N-oxide. 36 These results indicate that this set of DNA adducts is a common biological biomarker of pyrrolizidine alkaloid-induced liver tumor formation. 36 Although a role for DHP−protein adducts formed in vivo in the liver has been proposed for pyrrolizidine alkaloid-induced hepatotoxicity, 4,7,37,38 the structures of these protein-DHP adducts have not been characterized and it is not clear how these protein−DHP adducts can affect hepatotoxicity.…”

“…36 These results indicate that this set of DNA adducts is a common biological biomarker of pyrrolizidine alkaloid-induced liver tumor formation. 36 Although a role for DHP−protein adducts formed in vivo in the liver has been proposed for pyrrolizidine alkaloid-induced hepatotoxicity, 4,7,37,38 the structures of these protein-DHP adducts have not been characterized and it is not clear how these protein−DHP adducts can affect hepatotoxicity. Our success in determining the structures of DHP−DNA adducts in vivo suggested that the structures of protein−DHP adducts could also be characterized.…”

An in vitro comparison of the cytotoxic potential of selected dehydropyrrolizidine alkaloids and some N-oxides

“…Such information is being developed. An example of this mechanistic work is that of Xia et al (2013) in which various DHPAs were compared in their ability to produce DHPA-derived nucleic acid adducts in the livers of rats that were treated with 24 mM DHPA for 3 days. They found that lasiocarpine produced 25.2; riddelliine 13.2; monocrotaline 12.6; riddelliine-N-oxide 8.5; heliotrine 4.1; and lycopsamine 0.3 total adducts/10 8 nucleotides.…”

Hepatotoxic pyrrolizidine alkaloids in Emilia sonchifolia from Taiwan

“…27 Both in vivo and in vitro analyses have resulted in the 28 identification of DNA adducts caused by these toxic PAs such 29 as riddelline (Xia et al, 2013). 30 Mechanistic studies have indicated that both riddelliine 31 (retronecine-type PA) and clivorine (otonecine-type PA) with 32 1,2-double bonds in their unsaturated necine base induced 33 tumors via a genotoxic mechanism mediated by the formation of 34 a set of 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrroli-35…”

“…The 335 study by Xia et al (2013) has demonstrated that senkirkine is 336 strongly implicated in liver tumor formation. PA-containing herbs 337 that cause hepatotoxicity should depend on the types and 338 quantities of the PAs present.…”