Bacterial rhamnolipids (RLs) in saliva of Alzheimer's disease and Mild Cognitive Impairment patients and correlation with neuroinflammation and cognitive state

Alzheimer’s disease (AD) is increasingly affecting the aging population and the estimated prevalence reaches 50 million people worldwide. The need for the discovery of new biomarkers for AD diagnosis is urgent and especially in biological fluids other than cerebrospinal fluid (CSF), as its collection is invasive. Arguments are numerous that chronic bacterial infections might be considered as one of the possible causes of AD. Rhamnolipids (RLs) are bacterial virulence factors, suspicious for dysfunctions and disorders including AD. The aim of this pilot trial was to investigate RLs levels in saliva of Mild Cognitive Impairment (MCI) and AD patients with indirect ELISA. Specifically, salivary RLs were determined in 30 AD patients, 24 MCI patients and 15 cognitively healthy individuals and were found elevated in AD and MCI patients compared to those of the control group. The established biomarkers of AD, tau and Aβ42 amyloid, and the inflammatory markers cyclooxygenases (COX-1 and COX-2) were also determined, to evaluate their possible interdependence from RLs levels. Levels of RLs positively correlate with COX-2 levels and negatively with the mental state according to Mini–Mental State Examination (MMSE) score of donors. Multilinear regression verified the tight interrelation of RLs with COX-2 in saliva of MCI and AD patients. The results of this study stand by the hypothesis of inflammatory involvement in AD and indicate that RLs could be suggested as eventual biomarkers for AD diagnosis using saliva as biological fluid.