Nicotine is the major addictive agent in tobacco smoke, and it is metabolized extensively by oxidation and glucuronide conjugation. The contributions of ethnicity and UGT2B10 haplotype on variation in nicotine metabolism were investigated. Nicotine metabolism was evaluated in two populations of smokers. In one population of African American and European American smokers (n ϭ 93), nicotine and its metabolites were analyzed in plasma and 24-h urine over 3 days while participants were abstinent and at steady state on the nicotine patch. In a second study of smokers (n ϭ 84), the relationship of a UGT2B10 haplotype linked with D67Y to nicotine and cotinine glucuronidation levels was determined. We observed that both African American ethnicity and the UGT2B10 D67Y allele were associated with a low glucuronidation phenotype. African Americans excreted less nicotine and cotinine as their glucuronide conjugates compared with European Americans; percentage of nicotine glucuronidation, 18.1 versus 29.3 (p Ͻ 0.002) and percentage of cotinine glucuronidation, 41.4 versus 61.7 (p Ͻ 0.0001). In smokers with a UGT2B10 Tyr67 allele, glucuronide conjugation of nicotine and cotinine was decreased by 20% compared with smokers without this allele. Two key outcomes are reported here. First, the observation that African Americans have lower nicotine and cotinine glucuronidation was confirmed in a population of abstinent smokers on the nicotine patch. Second, we provide the first convincing evidence that UGT2B10 is a key catalyst of these glucuronidation pathways in vivo.

1. Plasma levels of 3H and unchanged drug were measured in the non-anaesthetized male rat after intravenous (i.v.) or oral administration of (+/-)-(R,S)-[propyl-3H]-8-OHD-PAT, at three dose levels per route of administration. The excretion of conjugated metabolites in bile was also studied following i.v. administration. 2. For unchanged 8-OHDPAT following i.v. administration, terminal t1/2 was 1.56 +/- 0.01 h (mean +/- SD, n > or = 4), kelim 0.45 +/- 0.01 h-1, volume of distribution 0.14 +/- 0.02 litres and clearance 1.10 +/- 0.17 mlmin-1. After oral administration, terminal t1/2, kelim, apparent volume of distribution and clearance were essentially the same when bioavailability was taken into account. Neither dose size nor route of administration had any significant effect on either terminal t1/2 or kelim. Comparison of AUCs following i.v. and oral administration yielded a mean for absolute oral bioavailability of 2.60 +/- 0.24%. 3. Comparison of AUCB for total plasma 3H showed that the extent of absorption was 80.1%, indicating that the low oral bioavailability of 8-OHDPAT is due to first-pass metabolism, rather than poor absorption from the GI tract. 4. Following i.v. administration, irrespective of dose, some 10% of the 3H dose was excreted in the bile in 6 h, 8.5% as 8-OHDPAT-glucuronide and 1.5% as the glucuronide of the N-despropylated metabolite, 8-OHDPAT. The majority of the biliary excretion occurred within 3 h of dosing.

1. Male Sprague-Dawley rats given (RS)-[3H]-8-OHDPAT by intraperitoneal (i.p.) or intravenous (i.v.) injection, or orally (p.o.) by gavage, excreted the majority of the dose in the urine (> 80% in 3 days and > 70% in the first 24 h). A smaller proportion of the dose was excreted in the faeces (> 10% in 3 days), mostly in the first 24 h. Total recovery was > 90% (mean: i.p. = 94.9; i.v. = 99 and p.o. = 92.9%). 2. Urinary metabolites were separated by reversed-phase hplc before and after treatment with beta-glucuronidase or sulphatase and quantitated by liquid scintillation spectrometry. Metabolites were identified by hydrolysis by specific enzymes, comparison of hplc retention time with those of authentic standards and by LC-MS. 3. Two major metabolites were identified and quantitated in the 24-h urine, namely 8-OHDPAT-glucuronide, accounting for some 45% of dose, and its N-despropylated metabolite, 8-hydroxy-2-(N-n-propylamino)tetralin, excreted as its glucuronide, which accounted for 15% of dose. Small amounts (< 1%) of two monohydroxylated metabolites were also identified, one eluting slightly earlier than and the other co-eluting with the mono-despropylated metabolite. When analysed by LC-MS-MS, the first of these exhibited a fragmentation pattern consistent with ring hydroxylation and the other appeared to be a side chain oxidized metabolite, which may constitute an intermediate in N-despropylation. However, these metabolites were present at too low a level to allow the exact position of hydroxylation to be determined. 4. These studies suggest that the low oral activity exhibited by 8-OHDPAT is most likely the result of rapid and extensive glucuronidation rather than poor absorption from the gastrointestinal tract.