Several hormones, including cortisol, have a circadian rhythm in plasma and saliva. Salivary cortisol is now extensively used for screening and following patients with various conditions where the regulation of hypothalamopituitaryadrenal axis is abnormal, for example in major depression where salivary cortisol levels show a disruption or loss of circadian rhythm. Annexin 1 is a glucocorticoid-induced protein, which is responsible for mediating several anti-inflammatory actions of glucocorticoids as well as being involved in glucocorticoid negative feedback inhibition. Evidence from histological studies of human oral cavity demonstrate that annexin 1 protein is highly expressed in the epithelium of the tongue and oral cavity as well as the submandibular, parotid and small salivary glands.
Our objectives were to investigate (i) if annexin 1 was expressed in saliva and (ii) whether it had a circadian rhythm which correlated with salivary cortisol. All experiments using human saliva were granted local ethical approval. Western blotting data from our laboratory, using an early morning (7 am) saliva sample showed that immunoreactive annexin 1 protein was present in human saliva. Annexin 1 was also found to be stable over the 24 h period used for collection, with no detectable loss of immunoreactivity at either 4 or 22 °C. Furthermore, annexin 1 was also measured using an in-house sandwich ELISA over a period of 24 h on saliva samples from healthy human subjects. Levels of salivary annexin 1 ranged from 56.21±9.65 ng/ml at 7 am to 9.10±1.65 ng/ml at 11 pm. Cortisol was also measured by radioimmunoassay on the same set of samples. The annexin 1 measured in these samples displayed a positive trend with the cortisol diurnal rhythm, suggesting that salivary annexin 1 is under cortisol regulation.
The local physiological role of salivary cortisol has never been fully elucidated and yet it is used extensively as an indicator of systemic disease. The discovery of annexin 1 in saliva, may give physiological significance to the existence of salivary cortisol and suggests a role in host defence.