GUT-DIRECTED LOCALLY ACTING NLRP3 INFLAMMASOME INHIBITOR AS A SUITABLE PHARMACOLOGICAL STRATEGY TARGETING GUT-BRAIN AXIS FOR THE TREATMENT OF ALZHEIMER'S DISEASE

Introduction. Growing evidence highlights the relevance of gut-brain axis in the pathophysiology of brain disorders, including Alzheimer's disease (AD). In particular, alterations of enteric bacteria, impaired intestinal barrier and enteric immune/inflammatory responses can contribute to brain pathology. In this context, the nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome acts as a bacteria-immune sensor involved in the shaping both enteric and central immune/ inflammatory responses in AD. This study examined the effects of a novel gut-directed locally acting NLRP3 inhibitor (INF176), in a spontaneous model of AD. Methods. Senescenceaccelerated mouse prone 8 (SAMP8) mice (4 months old) were employed as a model that develops spontaneously early learning and memory deficits reflecting those occurring in human AD. SAMR1 mice were used as controls. Animals were treated orally with INF176 50 mg/kg/day, donepezil (DON, used as a standard comparator) 3 mg/kg/day or vehicle for two months (n=6/group) in order to evaluate the effects of a gut-directed therapy from the early phases of learning and memory deficiency up to the mild cognitive impairment phase that precedes the full development of AD. During the last week, mice underwent the Morris water maze test to evaluate the effects of drugs on cognitive functions. Upon sacrifice, brain and colonic tissues were excised and processed for the evaluation of: 1) AD-related protein deposition (western blot for phosphorylated (p)-tau and ELISA for b-amyloid, Ab1-42); 2) activation of inflammasome signalling (western blot of NLRP3, ASC and caspase-1 and ELISA for interleukin-1beta (IL-1b) levels); 3) expression of claudin-1 tight junction protein (western blot). Results. SAMP8 mice displayed cognitive dysfunctions, p-tau and Ab1-42 accumulation in the brain, enteric inflammation, characterized by increased active caspase-1 and IL- 1b levels, and decreased intestinal and brain claudin-1 expression. Treatment with INF176 counteracted cognitive impairment with effects comparable to DON and decreased significantly AD-related protein accumulation in the brain as compared with SAMP8 untreated mice. INF176 also decreased colonic active caspase-1 and IL-1b levels, while it did not modify NLRP3 and ASC expression. In addition, INF176 counteracted the decrease in claudin-1 expression both in brain and colonic tissues. Conclusions. The novel gut-directed NLRP3 inflammasome inhibitor INF176 exerts beneficial effects on AD, through reduction of colonic active caspase-1 and IL-1b levels. These findings substantiate the concept that the pharmacological modulation of NLRP3 inflammasome in the gut can represent a promising strategy to develop novel classes of drugs, targeting the gut-brain axis, for the treatment of AD.