Introduction:
Previous preclinical and clinical data from our research group strongly suggest that the multifunction protein clusterin can be considered a candidate biomarker of addiction. Based on these antecedents, we have studied clusterin levels in saliva from smokers under cessation therapy to set up novel starting points for the development of new potential methods for the diagnosis and follow-up of tobacco addiction.

Material and Methods:
Preliminary findings of a prospective ongoing cohort study are presented. Up to the date, 51 patients (20 men, 31 women; 32-85 years of age) have been recruited for an ambulatory smoking cessation program that involved the use of pharmacological and behavioral therapy. The subjects underwent clinical and psychological assessment (including Fagerström tests for nicotine dependence as well as DAST-20 and ASSIST for addiction). Saliva samples were collected at the start of the program and after six months of smoking discontinuation. A comparative study of different analytical tools was performed to finally select a non-competitive ELISA sandwich assay (Invitrogen, Spain) for quantifications. Clusterin concentrations were then compared intra and inter-subjects by using ANCOVA and Wilcoxon statistics.

Results:
Clusterin concentrations significantly correlated with the duration of tobacco consumption, ranging from 6.3 ± 1.0 ng/ml (mean ± SEM) in patients with up to 25 years of tobacco use to 11.0 ± 2.1 in patients exceeding 40 years of consumption (p < 0.05). Clusterin levels subsequently decreased in each patient after 6-months of smoking cessation (from 8.4 ± 1.3 to 4.3 ± 0.5, p < 0.05).

Conclusions:
These preliminary results agree with the idea that clusterin levels might be associated to the degree of tobacco dependence /addiction, which remains to be further established by increasing patient recruitment. According to the biological roles attributed to clusterin, these levels may parallel tissue injuring caused by the current tobacco consumption.

Funding Statement:
This work was supported by Delegación del Gobierno para el Plan Nacional sobre Drogas (PNSD 2016I025) and Fundación Universitaria CEU /Banco de Santander (PI16/01489), Spain.