title: Contamination is a frequent confounding factor in toxicology studies with anthraquinone and related compounds.
abstract: Anthraquinone (AQ) (9,10-anthracenedione) is an important compound in commerce. Many structurally related AQ derivatives are medicinal natural plant products. Examples include 1-hydroxyanthraquinone (1-OH-AQ) and 2-hydroxyanthraquinone (2-OH-AQ), which are also metabolites of AQ. Some commercial AQ is produced by the oxidation of anthracene (AQ-OX). In the recent past, the anthracene used was distilled from coal tar and different lots of derived AQ often contained polycyclic aromatic hydrocarbon contaminants, particularly 9-nitroanthracene (9-NA). Many toxicology studies on AQ used contaminated anthracene-derived AQ-OX, including a National Toxicology Program (NTP) 2-year cancer bioassay that reported a weak to modest increase in tumors in the kidney and bladder of male and female F344/N rats and in the livers of male and female B6C3F1 mice. The AQ-OX used in that bioassay was mutagenic and contained 9-NA and other contaminants. In contrast, purified AQ is not genotoxic. The purpose of this paper is to provide additional information to help iterpret the NTP cancer bioassay. This paper describes a quantitative analytical study of the NTP anthracene-derived AQ-OX test material, and presents the results of mutagenicity studies with the 1-OH-AQ and 2-OH-AQ metabolites and the primary contaminant 9-NA. Purified 1-OH-AQ and 2-OH-AQ exhibited only weak mutagenic activity in selected strains of tester bacteria and required S9. Literature reports of potent mutagenic activity for 1-OH-AQ and 2-OH-AQ in bacteria minus S9 are, once again, very likely the result of the presence of contaminants in the test samples. Weak activity and limited production of the 1-OH-AQ and 2-OH-AQ metabolites are possible reasons that AQ fails to exhibit activity in numerous genotoxicity assays. 9-NA was mutagenic in tester strains TA98 and TA100 minus S9. This pattern of activity is consistent with that seen with the contaminated AQ-OX used in the NTP bioassay. Analysis of all the mutagenicity and analytical data, however, indicates that the mutagenic contamination in the NTP bioassay probably resides with compounds in addition to 9-NA. 9-NA exhibited potent mutagenic activity in the L5178Y mammalian cell mutagenicity assay in the presence of S9. The positive response was primarily associated with an increase in small colony mutants suggesting a predominance of a clastogenic mechanism. Quantitative mutagenicity and carcinogenicity potency estimates indicate that it is plausible that the contaminants alone in the NTP AQ-OX bioassay could have been responsible for all of the observed carcinogenic activity. Although AQ-OX is no longer commercially used in the United States, many of the reported genotoxicity and carcinogenicity results in the literature for AQ and AQ derivative compounds must be viewed with caution.
authors.affiliation: Butterworth Consulting, Raleigh, North Carolina, USA. bebutterworth@earthlink.net
authors.forename: Byron E
authors.initials: BE
authors.lastname: Butterworth
authors.forename: Owen B
authors.initials: OB
authors.lastname: Mathre
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Ballinger
authors.forename: Orn
authors.initials: O
authors.lastname: Adalsteinsson
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000145:classification / Q000378:metabolism / Q000633:toxicity; D000880:Anthraquinones / Q000737:chemistry / Q000145:classification / Q000378:metabolism / Q000633:toxicity*; D004340:Drug Contamination; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D005189:False Positive Reactions; D007940:Leukemia L5178 / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D008223:Lymphoma / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D051379:Mice; D009152:Mutagenicity Tests; D009153:Mutagens / Q000737:chemistry / Q000145:classification / Q000633:toxicity*; D009154:Mutation; D051381:Rats; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics
chemical_list: D000873:Anthracenes; D000880:Anthraquinones; D009153:Mutagens; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins; C035016:9-nitroanthracene; C061208:1-hydroxyanthraquinone