Polish Journal of Veterinary Sciences Vol. 14, No. 1 (2011), 159-164 DOI 10.2478/v10181-011-0025-8 Review The carcinogenic effects of benzoquinones produced by the flour beetle Ł.B. Lis1, T. Bakuła1, M. Baranowski1, A. Czarnewicz2 1 Department of Veterinary Prevention and Feed Hygiene Faculty of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Oczapowskiego 13, 10-718 Olsztyn, Poland 2 Veterinary Surgery HelpVet, Plonska 113A, 06-400 Ciechanów, Poland Abstract Humans and animals come into contact with various compounds in their natural environment. Most of the encountered substances are neutral, yet some may carry adverse health effects. The ingested food may be a source of harmful substances, including benzoquinones which, as shown by research results cited in this paper, demonstrate toxic, carcinogenic and enterotoxic activity. This group of compounds is inclusive of 2-methyl-1,4-benzoquinone (MBQ) and 2-ethyl-1,4-benzoquinone (EBQ), defensive secretions of the confused flour beetle (Tribolium confusum J. du V) and the red flour beetle (Tribolium castaneum Herbst). Benzoquinones have a carcinogenic effect, they are inhibi- tors of growth of various microorganisms, they produce a self-defense mechanism in threat situations and affect population aggregation. As noted by the referenced authors, the properties of ben- zoquinones have not been fully researched to this date. Key words: benzoquinones, flour beetles, quinone carcinogenicity Introduction set wider than the eyes of red flour beetle. Both spe- cies have well-formed flight wings, but only the red Flour beetles, including the confused flour beetle flour beetle flies in warm interiors or in a tropical (Tribolium confusum) and the red flour beetle climate. The flour beetle develops at a temperature of (Tribolium castaneum), belong to the family of dark- 28-38oC (optimal 30-33oC) and humidity of 10-100% ling beetles (Tenebrionidae) of the order Coleoptera. (optimal 70%). The length of developmental cycle de- Flour beetles are small insects with body length of 3-5 pends on environmental conditions. At 24oC it lasts 54 mm. The head, pronotum and elytrae are shiny, days, and at 34oC – 26 days. Flour beetles may survive red-brown to dark brown in color. Coloring changes for more than two weeks without nutrition. They live with age. Minor differences are observed between 2-3 or even 4 years. The female lays around 15 eggs species. The antennae are composed of 11 segments. per day, a total of 1200 eggs in her lifetime. In the confused flour beetle, the antennae become White-colored eggs with food particles adhering to wider from the fifth segment, whereas in the red flour the surface have the length of 0.6-0.7 mm and the beetle the last segments form a club. Eye setting is width of 0.3-0.4 mm, and they hatch into larvae. The also a discriminating feature. When viewed from the larvae go through 5-18 growth stages (7-8 on average). ventral side, the eyes of the confused flour beetle are Adult larvae emerge on the surface of infested prod- Correspondence to: Ł.B. Lis, e-mail: [email protected] 160 Ł.B. Lis et al. ucts where they undergo metamorphosis. The pupae zoquinone and 2-ethyl-1,4-benzoquinone. do not feed at this stage, and adults emerge within The specific composition of 2-methyl-1,4-ben- a few days (Roth and Howland 1941). zoquinone and 2-ethyl-1,4-benzoquinone and the Flour beetles are among the most common pest methods of extracting these compounds from T. casta- insects found in stored grain and milled products. neum and T. confusum were determined by Pappas Both adults and larvae feed on kernels, causing dam- and Morrison (1995). The proposed methods were age to the seed and rendering it unfit for sowing pur- further modified by Pappas and Wardrop (1996). In- poses. Flour beetles produce large quantities of dust sects were kept in methanol (HPLC purity) and ana- which prevents seed respiration, contributes to seed lyzed by UV spectroscopy, reversed-phase HPLC and overheating, excessive moisture, the growth of my- GC/MS. Methanol solutions obtained from both cotoxic fungi, bacteria and acarid mites. beetle species contained methyl-1,4-benzoquinone Beetles have defensive glands which secret (MBQ) and ethyl-1,4-benzoquinone (EBQ). No sig- quinones such as 2-methyl-p-benzoquinone, nificant differences in MBQ quantities were deter- 2-ethyl-p-benzoquionone, hydroquinone (Alexander mined between samples. Significantly higher quanti- and Barton 1943, Loconti and Roth 1953, Engelhardt et al. 1965, Ladisch et al. 1967, Blum 1978, Howard ties of EBQ and the MBQ and EBQ mixture were 1987), commonly referred to as benzoquinones. The found in T. castaneum than in T. confusum. The darkling beetle family is the most prolific source of above authors concluded that the applied methods for 2-methyl-1,4-benzoquinone and 2-ethyl-1,4-ben- the isolation, identification and quantitative determi- zoquinone (Omaye et al. 1981). An individual beetle nation of benzoquinone were relatively simple, quick secrets from several micrograms to 0.5 mg of quinones and accurate for determining benzoquinone secre- into the substrate (grain, flour, cereal) (Ladisch and tions from individual beetles. Mcque 1953, Yezerski et al. 2000, 2004). The insects rapidly colonize the infested food, and quinone con- centrations are very high in populations of thousands Structure of individuals. Benzoquinones give grain a characteristic, un- Benzoquinones are chemical derivatives of ben- pleasant odor, and infested flour has a pinkish color zenes. They are cyclic organic unsaturated diketone (Payne 1925). In 1941, Roth and Howland isolated compounds (C6H4O2) that contain two carbonyl the odor excretion from T. confusum by passing dry groups (C=O). Benzoquinones are readily soluble in air over the beetles. The excretion was condensed in organic solvents. Benzoquinones have bright yellow, a dry ice trap, yielding yellow-brown crystals. At room orange or red color and a pungent odor. They are temperature, the collected substance was a volatile commonly found in plants and animals as biologically liquid with a pungent quinone odor that easily reacted active substances, and they are classified into three with KI, H2SO4 and the starch solution, turning groups: monocyclic, including 1,4-benzoquinone and blue-black in color. benzoquinones secreted by the flour beetle, bicyclic As noted by Roth (1943), odor secreting glands on naphthoquinones, including vitamin K, and tricyclic the abdomen and thorax of adult Tribolium casta- anthraquinones, such as alizarin dye. neum, T. confusum and T. destructor (Uyttenb.) 1,4-benzoquinone has CAS registry number beetles contain a pungent, irritating fluid. In a paper 106-51-4, systematic name: 2,5-cyclohexadiene- published in 1943, Alexander and Barton reported on -1,4-dione, synonym: para-benzoquinone. It is a solid ethylquinone secretions in the flour beetle. In 1971, substance with bright yellow color, pungent odor, and Von Endt and Wheeler isolated a new compound, it sublimes even at room temperature. The Interna- 1-pentadecene, in addition to the previously deter- tional Agency for Research on Cancer (IARC 1999) mined 2-methyl-1,4-benzoquinone and 2-ethyl-1,4- has classified 1,4-benzoquinone as a Group 3 sub- -benzoquinone produced by Tribolium confusum, vol- stance: atile compounds that are stored in special containers. – Which is not classifiable as to its carcinogenicity The aliphatic ketone C14H26O had not been previously to humans and for which the evidence of carcino- investigated. 1-pentadecene facilitates absorption of genicity is inadequate in humans and inadequate or the admixed quinones by Tribolium enemies. Howard (1987) performed chemosystematic analysis of defens- limited in experimental animals; ive secretions in 10 insect groups from the darkling – For which the evidence of carcinogenicity is in- beetle family (Tenebrionidae), including of the genus adequate in humans but sufficient in experimental Tribolium represented by the confused flour beetle animals, and substances may be placed in this cat- and the red flour beetle. The author determined the egory when there is strong evidence that the mechan- presence of 15 hydrocarbons, of which five were found ism of carcinogenicity in experimental animals does in all studied insects, including 2-methyl-1,4-ben- not operate in humans. The carcinogenic effects of benzoquinones... 161 Absorption and metabolism The above suggests that benzene exposure can cause aplastic anemia (Post et al. 1985). Benzoquinone is readily absorbed from the gas- Benzene and its metabolites inhibit RNA syn- trointestinal tract and subcutaneous tissue. It is ex- thesis subject to the applied dose, at 50% inhibitory creted partially unchanged and partly as hy- concentration of 5×10-3M for benzene, 2.5×10-3M for droquinone, the major proportion of which is elimin- phenol, 2.5×10-5M for hydroquinone and 6×10-6M for ated as acid conjugates. The application of ben- p-benzoquinone; the phenomenon observed did not zoquinone causes local skin changes, including discol- result from impaired cell viability. RNA synthesis in oration, erythema and the appearance of papules; macrophages is most probably inhibited by benzene necrosis can occur. Exposure to vapors induces seri- which probably blocks uridine transport in macro- ous vision disturbances; injury extends through the phages, and phenol which inhibits their conversion entire conjunctiva and cornea (IARC 1977). into covalent bond forms. The above suggests that 1,4-benzoquinone depresses cellular respiration in benzene and phenol may inhibit the synthesis of he- tissues under in vitro conditions. Large doses induce matopoietic colony-stimulating factors (Post et al. local paralysis, clonic convulsions, decreased blood 1986). pressure and death due to paralysis of the medullary D’Odorico et al. (1997) demonstrated that syn- centers. Signs of kidney damage were observed in se- thetic quinones such as menadione cause DNA dam- verely poisoned animals (IARC 1977).