Article: Pulegone [89-82-7] and One Of Its Metabolites Menthofuran [494-90-6]

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http://ntp-server.niehs.nih.gov/htdocs/Chem_Background/EXECSUMM/Pennyroyal/PennyroyalEXECSUM.html

Pulegone [89-82-7]and One Of Its MetabolitesMenthofuran [494-90-6]

EXECUTIVE SUMMARY

The nomination of pulegone and menthofuran for testing is based on the potential for human exposure and the absence of carcinogenicity data. Pulegone and menthofuran are available from suppliers of laboratory test chemicals while pennyroyal oil with pulegone as a major constituent is commonly available in health food stores. Pulegone can be synthetically produced but no data were found concerning the synthetic production process; pulegone can also be produced by shoot cultures of Mentha piperita grown in fermenters. No data were found on production or import volumes. Pulegone is a major constituent of several essential oils (e.g., peppermint, pennyroyal) used for flavoring foods and drinks. Pennyroyal oil, which has been reported to contain 75-85% pulegone, has also been used as a fragrance agent and as an herbal medicine to induce menstruation and abortion. A number of plant species contain pulegone and menthofuran, including numerous species of mints such as peppermint and spearmint, the pennyroyals, and mountain mints. Menthofuran is present in peppermint and in M. aquatica and its hybrids. Exposure to pulegone and menthofuran is primarily through ingestion of food products (e.g., frozen dairy dessert, candy, baked goods, gelatins, and puddings) and of alcoholic and nonalcoholic beverages flavored with spearmint oil, peppermint oil, or synthetic pulegone. Pulegone was not detected in meat products, processed fruit, confectioner frosting, jams, or jellies. Pulegone was authorized in the U.S. as a synthetic flavoring substance under 21 CFR 172.515. Pennyroyal oil was voluntarily canceled for re-registration as a pesticide. A number of case reports provide evidence that ingestion of pennyroyal oil is associated with acute poisoning. Moderate to severe toxicity to the nervous system, liver, and kidneys with a duration of hours to days was reported; death occurred in some cases. Ingestion of less than 10 mL was generally associated with gastritis and mild central nervous system toxicity, but the effects reported after ingestion of different amounts were variable and depended on emetics or other treatments given. In experimental animals, pulegone was metabolically transformed to menthofuran and other metabolites with formation of glucuronide and glutathione conjugates. In vitro studies with rat and mouse liver microsomes showed that menthofuran is a major metabolite of pulegone with metabolism dependent on phenobarbital-induced cytochrome P-450 isozymes and influenced by exposure to substances that induce or inhibit these isozymes. Pulegone or metabolites were shown to covalently bind to tissue proteins. Ketone and organic acid metabolites were found in the urine of rats orally administered menthofuran, while studies of menthofuran metabolism using mouse liver microsomes showed the formation of a -ketoenal and mint lactone. Acute lethal doses are available for pulegone. An LD50 of 1709 mg/kg (11.23 mmol/kg) was reported for mice given pulegone by the subcutaneous (s.c.) route, while rats exposed by the intraperitoneal (i.p.) route had an LD50 of 150 mg/kg (0.985 mmol/kg). An absolute lethal dose of 330 mg/kg (2.17 mmol/kg) was found in dogs intravenously (i.v.) administered pulegone. No lethal values for menthofuran were found. Most toxicity data are from acute exposure of experimental animals to relatively high doses of pulegone or menthofuran. The primary toxic response was liver toxicity. Rats orally administered pulegone once or once daily for five or six days showed a reduction in hepatic cytochrome P-450 and an increase in serum glutamate pyruvate transaminase (SGPT). Mice treated with pulegone i.p. showed hepatic necrosis in addition to an elevation of SGPT or alanine transferase (ALT) 24 hours after dosing. Similarly, menthofuran administered i.p. to mice also produced hepatic necrosis and increases in plasma levels of SGPT or ALT. Rats given pulegone i.p. developed a decrease in hepatic cytochrome P-450, an increase in ALT, and liver necrosis. Acute hepatic and lung damage in male mice (Swiss-Webster and BALB/c) was seen 24 hours after pennyroyal oil was administered acutely i.p. Pennyroyal oil topically applied to a dog resulted in seizures and death of the dog within 30 hours; pulegone was identified in a liver specimen. Animal experiments also measured the effect of pretreatment with chemicals that influence cytochrome P-450 on the hepatotoxicity of pulegone or menthofuran. Pretreatment of mice or rats with inducers of cytochrome P-450 (e.g., phenobarbital, diethyl maleate) enhanced the hepatotoxicity of pulegone or menthofuran. In contrast, pretreatment of mice or rats with chemicals that inhibit cytochrome P-450 (e.g., cobaltous chloride, piperonyl butoxide) reduced hepatotoxicity. Short-term toxicity studies suggested that pulegone may have neurological effects. Histopathological changes in the white matter of the cerebellum were observed in rats given oral doses of pulegone for 28 days. Only very limited in vitro genotoxicity data on pulegone were located. Pulegone did not induce mutations in Salmonella strains TA1537, TA98, TA1535, and TA100, with and without metabolic activation. Pulegone, but not pennyroyal oil, was weakly mutagenic in Drosphila melanogaster larvae in the wing spot test. Pulegone was shown to have antihistaminic activity on guinea pig ileum, based on its ability to inhibit histamine-induced contractions in vitro. No data were found on chronic exposure, teratogenicity and embryotoxicity, and carcinogenicity. Pulegone inhibited the growth of three bacterial species (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa) and three fungal species (Candida albicans, Aspergillus niger, Mucor mucedo) in an agar diffusion test system. Pulegone demonstrated insecticidal activity based on lethality to D. melanogaster, as did mint oil extracted from the species M. pulegium (European pennyroyal), found to contain 75.7% pulegone. Treatment of human epidermis in vitro with pulegone increased the electrical conductivity, which suggests that pulegone can open new polar pathways across the stratum corneum. Menthone and carvone, both structurally similar to pulegone, induced a conversion of rat cytochrome P-450 to cytochrome P-420 and no loss of heme in microsomes from rats pretreated with phenobarbital. When these two compounds were orally administered to rats for three days, there was no significant decrease in cytochrome P-450 levels in liver microsomes. A study with 16 compounds structurally similar to pulegone indicated that a particular structural feature, -isopropylidene ketone with a methyl positioned para to the isopropylidene group, is necessary for the in vitro destruction of cytochrome P-450. Isopulegone, another terpene identified in pennyroyal oil, was also found to be a hepato- and pulmonary toxicant to mice after administration by i.p. The enantiomer of pulegone, S-(-)-pulegone, produced no lung damage and was one-third less hepatotoxic than its congener.