Night work effects on salivary cytokines TNF, IL-1β and IL-6

ABSTRACT

Shift work is unavoidable in modern societies, but at the same time disrupts biological rhythms and contributes to social distress and disturbance of sleep, health and well-being of shift workers. Shift work has been associated with some chronic diseases in which a chronic inflammatory condition may play a role. However, few studies investigating the association of cytokine and other inflammation markers with shift workers have been published in recent years. In this study we evaluated the effects of permanent night work on the production of tumor necrosis factor (TNF), interleukin-1β (IL-1β), IL-6 and melatonin in saliva. Another aim was to demonstrate the benefit of the use of salivary cytokines for studies in chronobiology, since it is an easy and non-invasive method that allows for sampling at several times. Thirty-eight healthy male workers, being 21 day workers and 17 night workers, agreed to participate in this study. Sleep was evaluated by actigraphy and activity protocols. Saliva was collected during three workdays approximately at the middle of the work shift and at bed and wake times of the main sleep episode. Saliva samples were then analyzed by enzyme-linked immunosorbent assay to measure TNF, IL-1β, IL-6 and melatonin levels, and the results were submitted to non-parametric statistical analysis. The use of saliva instead of blood allowed for a greater number of samples from the same subjects, allowing identifying alterations in the daily production patterns of salivary cytokines TNF, IL-1β and IL-6 that probably are linked to night work. Salivary TNF and IL-1β levels were similar for day and night workers, with higher daily production after awakening, in the morning hours for day workers and in the afternoon for night workers. Both groups presented a significant daily variation pattern of these two cytokines. Day and night workers produced similar amounts of salivary IL-6. Nevertheless, the daily variation pattern observed among day workers, with a peak after awakening, was absent among night workers. Thus, in our study, night workers showed partially adjusted daily variation patterns for salivary TNF and IL-1β, not seen for salivary IL-6. Results for salivary IL-6 could be better explained as a consequence of circadian disruption due to permanent night work. Our results suggest that the whole circadian system, including clocks and pineal gland, is involved in regulating cytokine profile in shift workers and that a coordinated production of these cytokines, important for an adequate inflammatory response, could be disturbed by shift work. The distinct effects that shift work may have on different cytokines could give some cues about the mechanisms involved in this association.

KEYWORDS:

• Night work
• salivary cytokines
• inflammatory responses
• circadian system

Acknowledgements

We thank the research subject volunteers, the owners and administrators of the sanitary metals company, Prof. Dr. Mikko Härmä (Finnish Institute of Occupational Health, Helsinki), Nilson Silva Soares (School of Public Health, University of São Paulo, Brazil) and Eduardo Braga Fernandes (Biosciences Institute, University of São Paulo, Brazil).

Declaration of interest

This study received financial support from Fundacentro and a grant (nr 2011/10503-4) from São Paulo Research Foundation (FAPESP). Érica Lui Reinhardt received a scholarship from CAPES (grant nr 8755-11/6). The opinions, hypotheses and conclusions or recommendations expressed in this text are those of the authors and do not necessarily reflect the views of Fundacentro, FAPESP or CAPES. The authors report no conflicts of interest.