Dihydromethysticin from kava blocks tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumorigenesis and differentially reduces DNA damage in A/J mice

Abstract

We have previously shown that kava and its flavokavain-free Fraction B completely blocked 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in A/J mice with a preferential reduction in NNK-induced O (6)-methylguanine (O (6)-mG). In this study, we first identified natural (+)-dihydromethysticin (DHM) as a lead compound through evaluating the in vivo efficacy of five major compounds in Fraction B on reducing O (6)-mG in lung tissues. (+)-DHM demonstrated outstanding chemopreventive activity against NNK-induced lung tumorigenesis in A/J mice with 97% reduction of adenoma multiplicity at a dose of 0.05mg/g of diet (50 ppm). Synthetic (±)-DHM was equally effective as the natural (+)-DHM in these bioassays while a structurally similar analog, (+)-dihydrokavain (DHK), was completely inactive, revealing a sharp in vivo structure-activity relationship. Analyses of an expanded panel of NNK-induced DNA adducts revealed that DHM reduced a subset of DNA adducts in lung tissues derived from 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, the active metabolite of NNK). Preliminary 17-week safety studies of DHM in A/J mice at a dose of 0.5mg/g of diet (at least 10× its minimum effective dose) revealed no adverse effects, suggesting that DHM is likely free of kava's hepatotoxic risk. These results demonstrate the outstanding efficacy and promising safety margin of DHM in preventing NNK-induced lung tumorigenesis in A/J mice, with a unique mechanism of action and high target specificity.

Dietary Dihydromethysticin Increases Glucuronidation of 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanol in A/J Mice, Potentially Enhancing Its Detoxification

“…Four groups were maintained on AIN-G powdered diet, four groups on AIN-G powdered diet supplemented with kava at a dose of 5 mg/g of diet, four groups on AIN-G powdered diet supplemented with DHM at a dose of 1 mg/g of diet and the other four groups AIN-G powdered diet supplemented with DHK at a dose of 1 mg/g of diet. Kava, DHM, or DHK supplemented diets were prepared following our reported procedures (Narayanapillai et al, 2014). After 1 week of consuming the various diets, each mouse was treated with NNK via i.p.…”

“…One group of mice from each treatment regimen was euthanized at 0.5, 1.0, 2.0, or 4.0 hours after NNK exposure, and serum and urine samples were collected. Serum collection and storage followed established procedures (Narayanapillai et al, 2014). For urine collection, each individual mouse was placed on a piece of aluminum foil, and urine was passively released upon CO 2 euthanasia.…”

“…Liver tissues used herein were from previous studies (Narayanapillai et al, 2014). Mouse liver microsomes from control mice (n = 4) and mice treated with NNK, NNK + DHM (1 mg/g of diet), or NNK + DHK (1 mg/g of diet) (n = 3 each) were prepared as previously described elsewhere (von Weymarn and Murphy, 2003).…”

“…1) effectively blocked NNK-induced lung adenoma formation in A/J mice when administered during the initiation phase (Narayanapillai et al, 2014), positioning DHM as a promising candidate for lung cancer prevention. Mechanistically, DHM dose-dependently reduced pulmonary DNA adducts derived from 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), one major metabolite of NNK (Carmella et al, 1993) and a potent pulmonary carcinogen (Upadhyaya et al, 1999).…”

“…Kava was acquired from Gaia Herbs (Brevard, NC) as an ethanol extract of the wild crafted lateral root from Vanuatu, which was standardized to 150 mg/ml total kavalactones. DHM and DHK were isolated from kava following an established procedure (Narayanapillai et al, 2014). All other chemicals and solvents were acquired from Sigma-Aldrich or Fisher Scientific (Fairlawn, NJ) and used without further purification.…”