Myosmine has been regarded as a specific tobacco alkaloid until investigations pointed out that nuts and nut products constitute a significant source of myosmine. In the present study it is shown that the occurrence of myosmine is widespread throughout a large number of plant families. Using a method for extraction practicable for all examined foods, quantitative analysis through internal standard addition showed nanograms per gram amounts. Positively tested edibles were staple foods such as maize, rice, wheat flour, millet, potato, and milk and also cocoa, popcorn, tomato, carrot, pineapple, kiwi, and apples. No myosmine was detectable in other vegetables and fruits such as lettuce, spinach, cucumber, onion, banana, tangerines, and grapes. Myosmine is easily nitrosated giving rise to a DNA adduct identical to the esophageal tobacco carcinogen N-nitrosonornicotine. Therefore, the role of dietary myosmine in esophageal adenocarcinoma should be further investigated.

Myosmine is not only one of the minor tobacco alkaloids but is also present in various foods. Therefore, research on myosmine metabolism and activation has been intensified. 3-Pyridylacetic acid, 4-oxo-4-(3-pyridyl)butanoic acid (keto acid), 3-pyridylmethanol, 3'-hydroxymyosmine, and 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) have been identified as urinary metabolites after oral administration to female Wistar rats. Although N-nitrosation of myosmine, yielding N'-nitrosonornicotine (NNN) and HPB, was considered as a possible in vivo activation route, the formation pathways of most metabolites could not be explained until now. Therefore, under consideration of its high reactivity due to its imine structure, peroxidation of myosmine seemed to be a promising additional activation pathway. In vitro peroxidation using myosmine (8.9 micromol in 200 microL methanol) with a mixture of hydrogen peroxide (57.6 micromol, 5 microL of a 35% solution) and acetic acid anhydride (106 micromol, 10 microL) already showed high yields of reaction products after 30 min ultrasonic treatment. The product pattern was analyzed by HPLC/UV and GC/MS. Besides unchanged myosmine, 3-pyridylacetic acid, keto acid, 3-pyridylmethanol, HPB, and nornicotyrine have been identified as myosmine peroxidation products. Different product patterns were obtained after 24 h and 4 days due to a time-dependent degradation, formation, and conversion of the reaction products. Therefore, peroxidation reaction of myosmine might explain the in vivo formation of 3-pyridylacetic acid, keto acid, 3-pyridylmethanol, and HPB in rats. In addition, because of acetylating conditions using acetic acid anhydride, N-(4-oxo-4-pyridin-3-yl-butyl)acetamide was rapidly formed during the first 30 min of the reaction.

ABSTRACT:The alkaloid myosmine is present not only in tobacco products but also in various foods. Myosmine is easily nitrosated, yielding 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) and the esophageal tobacco carcinogen N-nitrosonornicotine. Due to its widespread occurrence, investigations on the metabolism and activation of myosmine are needed for risk assessment. Therefore, the metabolism of myosmine has been studied in Wistar rats treated with single oral doses of [pyridine-5-3 H]myosmine at 0.001, 0.005, 0.5, and 50 mol/kg body weight. Oral administration was achieved by feeding a labeled apple bite. Radioactivity was completely recovered in urine and feces within 48 h. At the two lower doses, 0.001 and 0.005 mol/kg, a higher percentage of the radioactivity was excreted in urine (86.2 ؎ 4.9% and 88.9 ؎ 1.7%) as compared with the higher doses, 0.5 and 50 mol/kg, where only 77.8 ؎ 7.3% and 75.4 ؎ 6.6% of the dose was found in urine. Within 24 h, urinary excretion of radioactivity was nearly complete with less than 4% of the total urinary output appearing between 24 and 48 h. The two major metabolites accounting for >70% of total radioactivity in urine were identified as 3-pyridylacetic acid (20-26%) and 4-oxo-4-(3-pyridyl)butyric acid (keto acid, 50-63%) using UV-diode array detection and gas chromatography-mass spectrometry measurements. 3-Pyridylmethanol (3-5%), 3-hydroxymyosmine (2%) and HPB (1-3%) were detected as minor metabolites. 3-Hydroxymyosmine is exclusively formed from myosmine and therefore might be used as a urinary biomarker for myosmine exposure in the future.

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Occurrence of the tobacco alkaloid myosmine has been proven in various staple foods, vegetables and fruits. Myosmine can be easily activated by nitrosation yielding 4-hydroxy-1-(3-pyridyl)-butanone (HPB) and the esophageal carcinogen N'-nitrosonornicotine. Most of the reaction products after myosmine peroxidation were also identified as urinary metabolites after oral administration to rats. Whole-body autoradiography with freeze dried or multiple solvent extracted tissue sections was used to trace [2'-(14)C]myosmine (0.1 mCi/kg bw) 0.1, 0.25, 1, 4 and 24 h after i.v. injection in Long-Evans rats. In addition, in vitro binding of radioactivity to esophageal and eye tissue was determined and excretion of radioactivity via urine and feces was quantified. Radioactivity is rapidly eliminated by renal excretion. Approximately 30% of the administered radioactivity was recovered in urine within the first 4 h and excretion with urine (72%) and feces (15%) was nearly complete after 24 h. A rapid concentration of radioactivity can be seen in the stomach and in the salivary and lachrymal glands. Rats killed 1 and 4 h after treatment showed by far the highest labeling in the accessory genital gland. High levels of nonextractable radioactivity were present in esophageal tissue and melanin. The half lives for the disappearance of radioactivity from various tissues are in the order of about 1 h. Eye and esophagus sections both showed nonextractable labeling after in vitro incubation with (14)C-myosmine. In conclusion, the toxicological significance of myosmine accumulation in esophagus and accessory genital gland requires further investigations. Hair analysis might be applicable for myosmine biomonitoring, because of possible enrichment in melanin containing tissues.