Task Force Nicotine Uptake
The CORESTA Task Force (TF) Nicotine Uptake (initially called TF “Nicotine Intake”) was established in 2001. The objectives of the TF were:
- To develop a recommended method for nicotine uptake in smokers.
- To evaluate the validity of cotinine as a single biomarker for nicotine uptake.
- To investigate differences in nicotine uptake between various populations.
The main activities of the TF were related to Objective 1. It was agreed that for measuring the nicotine uptake, at least the 6 major nicotine metabolites in urine (nicotine, cotinine, trans-3’hydroxycotinine and their respective glucuronides) should be measured. Urinary nicotine and its five major metabolites are also termed ‘Nicotine+5’ (‘Nic+5’) or ‘Nicotine equivalents’ (‘Niceq’). These 6 metabolites represent ~ 80 % of the absorbed nicotine dose. In principle, nicotine equivalents in urine can be determined by ‘indirect’ methods or by ‘direct’ methods. ‘Indirect’ methods comprise two analytical runs: (1) Determination of the free bases (aglycons) in untreated urine, (2) determination of the aglycons after enzymatic hydrolysis of the urine with ß-glucuronidase. The first determination provides values for the free bases (nicotine, cotinine, trans-3’-hydroxycotinine). The second determination provides values for total bases (free + conjugated metabolite). The difference between the second and first determination represents the amount of the conjugated metabolite. ‘Direct methods’ allow the determination of nicotine equivalents in urine in one run and do not require the enzymatic hydrolysis of the glucuronides prior to their analysis. However, ‘direct’ methods require relatively expensive analytical instrumentation (i.e., liquid chromatography with tandem mass spectrometry, LC-MS/MS).
The TF Nicotine Uptake performed five ring trials on the major urinary nicotine metabolites. The main purpose of this endeavor was to find out whether there are systematic differences between ‘indirect’ and ‘direct’ methods and which method would be most suitable to be tested and proposed as a CORESTA Recommended Method (CRM) for urinary nicotine equivalents. A general conclusion from the results of the ring trials was that there is no systematic influence of the analytical method. Rather, extensive experience of the laboratory appears to be more important for the quality of the results. Furthermore, it was concluded that the use of certified stock solutions and reference materials could improve the agreement between various laboratories. Due to the limited number of laboratories using either the ‘direct’ or ‘indirect’ method for urinary Niceq, no CRM was tested in an inter-lab comparison. Both types of methods were provided as appendices to the Final Report of the TF.
The TF also organized three proficiency tests on salivary cotinine, frequently used as a biomarker for tobacco and tobacco smoke exposure. As a general result, it was observed that the intra-lab variations were good, whereas the inter-lab variations were partly too high (> 25 %). The latter was reduced by applying an embedded calibration. This indicated that, as with the Niceq method, the inter-lab variability could be decreased by using reference materials common to all laboratories.
Objective 2 was discussed within the TF. As a result, a review was prepared. It was concluded that salivary cotinine is a suitable biomarker for the determination of the smoke exposure and the nicotine dose, provided that a sufficient number of individuals is investigated in order to compensate for the inter-individual variation in the nicotine metabolism. This review is also part of the appendices to the Final Report of the TF.
Objective 3 was handled as a joint activity of the CORESTA Task Force Nicotine Uptake and the CORESTA Sub-Group Smoking Behaviour. In the meantime, this objective has been moved to the objectives of the Sub-Group Smoking Behaviour.