Evaluation of saliva collection devices for the analysis of steroids, peptides and therapeutic drugs
Introduction
Saliva contains various endogenous substances being interesting for both researchers and clinicians. The analysis of salivary hormones in particular is a proven and accepted alternative to plasma analysis. Steroids pass through cell membranes into the salivary glands by diffusion. Consequently, salivary concentrations reflect the non-protein-bound, physiologically active part of the blood concentration [1]. Amines and peptides, such as melatonin and insulin, enter the saliva by either passive diffusion or active transport. For these hormones, excellent correlation was determined between saliva and blood concentrations [2], [3], [4].
Of special interest are potential inflammatory or tumor markers, such as IL-8 [5] and EGF [6]. Other peptide hormones, such as leptin [7], [8] and ghrelin [9], [10], were proved to be expressed by the salivary glands and are involved in the proliferation of the oral mucosa [9], [11].
With saliva being a major component in oral antibiotic defense it is not surprising that immunglobulins, such as secretory IgA [12], can be analyzed in saliva offering possibilities in epidemiological and vaccination studies. Finally, salivary enzyme activity, such as amylase [13] or lysozym [14], is used in the assessment of metabolic or infectious diseases.
In addition to these endogenous substances, various drugs can be measured in saliva as an excellent option for therapeutic drug monitoring (TDM) [15] or in the assessment of drugs of abuse [16]. In most cases a very strong correlation between salivary and plasma concentrations could be demonstrated. Anticonvulsants in particular, but also cytostatic drugs are promising candidates for salivary TDM [17].
The non-invasive character of sample collection and the retention of the patient's privacy are especially convenient in children or out-patient sampling. Chewing absorbent materials may be preferable to the simpler but less esthetic spitting into tubes or passive drool [18], due to a better standardization of saliva flow and comparability of flow dependent components.
Several collection devices exist, with the Salivette® being commonly used in Europe. In North America, the Quantisal® is used for drug monitoring. In comparison to these adsorption-based systems, Greiner-BioOne introduced an alternative approach using rinsing and collection liquids (Saliva-Collection-System®).
In the present study, we investigated the utility of these devices for the above-mentioned panel of salivary analytes combining spike-recovery experiments, variability in the measurement of endogenous concentrations and an evaluation of practicability for the user.
Section snippets
Collection devices
- (a)
Salivette® (Sarstedt, Fig. 1A) consists of a polypropylene tube with perforated inlay. It contains an absorbent wad produced in three different versions, cotton, polyester, and polyethylene. The wad is taken into the mouth, preferably in the cheek, to collect mixed saliva. Although Sarstedt currently does not provide the polyester version, we added this material from our stock as a reference since we have had considerable experience with it over the years.
- (b)
For the Quantisal® (Immunalysis, Fig. 1
Convenience and practicality of the collection devices
Both the participants and the contributors rated the Salivettes® to be very practical and convenient. Although the new polyethylene wad seems relatively hard in the mouth compared to the soft cotton version, this device was considered best for out-patient collection, e.g. for sports medicine and drug monitoring, as the small containers can be opened easily and used by the patient in training conditions, and in the field.
The Quantisal® is also practical, although a little more elaborate. The
Discussion
One main advantage of saliva is the non-invasive collection, most important in pediatrics, psychiatry or stress research. Another biochemical peculiarity is the lack of specific transport proteins in saliva (e.g. corticosteroid-binding-protein), allowing for the determination of free, physiological active concentrations of steroids [33] or drugs [34] passively diffusing through the epithelia.
Consequently, the FDA keeps up with current developments [35], and supports the search for salivary
Acknowledgments
Grant/funding support: This study was supported by the ELAN fund of the University Hospital Erlangen.
Financial disclosures: None declared.
We gratefully acknowledge the technical assistance of J. Biskupek-Sigwart, N. Meier, P. Stöhr, and P. Schmid for linguistic editing.
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