The protective effect of Amitriptyline on experimental colitis through inhibiting TLR4/MD2 signaling pathway.

Amitriptyline, a pleiotropic tricyclic antidepressant, possesses anti-oxidant and anti-inflammatory properties. Despite its diverse benefits, the specific effects of amitriptyline on IBD are not yet well defined. To explore this, we utilized a DSS-induced colitis model to examine the anti-inflammatory effects of amitriptyline and the underlying mechanisms by which it operates. Our research revealed that amitriptyline is effective in alleviating several pathological manifestations associated with colitis. This includes improvements in body weight retention, reductions in DAI, lessening of colon length shortening, and repair of colonic mucosal damage. Treatment with amitriptyline significantly protected mucosal injury by preserving the population of goblet cells and increasing the expression of tight junction proteins. Furthermore, we observed that amitriptyline effectively countered immune cell infiltration, specifically neutrophils and macrophages, while simultaneously lowering the levels of inflammatory cytokines such as TNF-α, IL-1β, and IL-6. Additionally, RNA sequencing analysis pointed to the potential involvement of the TLR pathway in the anti-colitic effects induced by amitriptyline. Subsequent Western blot analysis indicated that amitriptyline significantly inhibited the TLR4-mediated NF-κB signaling pathway. To bolster our findings, in vitro studies demonstrated that amitriptyline down-regulated the TLR4/NF-κB/MAPK signaling cascades in mouse macrophages stimulated with LPS. Further molecular investigations revealed that amitriptyline was able to suppress the elevated expression of MD-2 that LPS stimulation typically induces. In summary, our findings suggest that amitriptyline effectively mitigates DSS-induced colitis in mice through the inhibition of TLR4/MD-2 pathway signaling, indicating its potential repurposing for IBD treatment. Significance Statement The potential of utilizing amitriptyline in treating IBD appears promising, leveraging its established safety and dosing profile as an antidepressant. Our observations show that amitriptyline can alleviate pathological symptoms, inflammation, and intestinal mucosal damage in mice with colitis induced by DSS. The protective effect observed appear to be linked to the inhibition of the TLR4/MD2 signaling pathway. By exploring novel applications for existing medications, we can optimize amitriptyline's efficacy and broaden its impact in both medical and commercial contexts.