Adiponectin Could Be Salivary Biomarker in Sjogren’s Syndrome, Study Reports

The hormone adiponectin correlates with disease severity in Sjogren’s syndrome patients, and could be used as a salivary biomarker to diagnose the disease, a Spanish pilot study shows.

The research, “Salivary adiponectin, but not adenosine deaminase, correlates with clinical signs in women with Sjögren’s syndrome: a pilot study,” was published in the journal Clinical Oral Investigations.

Salivary and lacrimal (tear) glands are main targets of the autoimmune attack in Sjogren’s syndrome, leading to tissue disruption and infiltration of activated immune cells, including B- and T-cells.

Adiponectin and the enzyme adenosine deaminase (ADA) are implicated in inflammation and regulation of insulin sensitivity. Studies have reported that the levels of both adiponectin and ADA are elevated in autoimmune diseases, including Sjogren’s syndrome.

Although it is mainly produced and released by adipose tissue, adiponectin also can be secreted by salivary gland cells. Studies in animals and in cells suggested that, besides an anti-inflammatory role, this protein protects salivary gland cells in patients with Sjogren’s syndrome by preventing cell death. However, the possible link between salivary adiponectin levels and clinical variables in Sjogren’s syndrome patients has not been explored.

In turn, ADA plays a protective role by mediating the transformation of adenosine and/or deoxyadenosine, two molecules that are highly toxic to cells. Also, ADA plays a role in immune function, including the development of B- and T-cells.

Reports showed that ADA levels in saliva are changed in patients with distinct cancer types, particularly in cancers of squamous cells (those lining the skin and hollow organs in the body).

The scientists hypothesized for this study that ADA activity could be changed in the saliva of Sjogren’s syndrome patients and correlate with clinical severity.

Their study (NCT03156569) compared levels of adiponectin and ADA in 49 adult women — 17 with Sjogren’s syndrome, 13 healthy controls, and 19 with medication-induced xerostomia (dry mouth), a typical Sjogren’s syndrome. The last group was named the non-Sjogren’s syndrome sicca (dryness) group.

Levels of adiponectin and ADA were higher in Sjogren’s syndrome patients and in non-Sjogren’s syndrome sicca women than in healthy controls. These two groups also showed increased levels of pro-inflammatory molecules IL-1-beta, IL-6, IL-8, and TNF-alpha, as well as higher total protein concentration.

However, when the analysis accounted for the different total protein concentration, only adiponectin was higher in Sjogren’s syndrome patients compared to both controls and non-Sjogren’s syndrome sicca women. ADA, on the other hand, was higher in both Sjogren’s syndrome patients and in non-Sjogren’s syndrome sicca than in controls.

As a result, “salivary adiponectin corrected by total protein can be a potential biomarker ” of Sjogren’s syndrome, the researchers commented.

Patients with Sjogren’s syndrome further exhibited more than twice the amount oxidative stress, as measured by levels of toxins called advanced oxidation protein product.

Patients with Sjogren’s syndrome further demonstrated correlations between levels of adiponectin and those of IL-1-beta, IL-6, IL-8, TNF-alpha, the immune molecule interferon (IFN)-gamma, the anti-inflammatory IL10, and total protein concentration. As for ADA levels in these patients, they were associated with total protein concentration, IFN-gamma, IL-1B-beta, IL-8, and TNF-alpha.

Importantly, in Sjogren’s syndrome patients, the higher the salivary adiponectin level, the greater the xerostomia inventory scores, an assessment of dry mouth symptoms. Women with non-Sjogren’s syndrome sicca showed a trend toward a similar association. In contrast, the ADA level did not correlate with clinical variables.

“Overall, these data suggest that adiponectin can have a particular role in [Sjogren’s syndrome] and could be considered as a potential salivary biomarker … ” the investigators wrote. They added that further studies are warranted to assess if adiponectin can be used both as a biomarker and as a therapeutic target.