Amitriptyline blocks innate immune responses mediated by TLR4 & IL1R: preclinical and clinical evidence in OA and gout.

Background and purpose Osteoarthritis (OA), one of the major causes of disability in developed countries, does not have an efficient treatment. Activation of Toll-like receptor 4 (TLR4) and innate immune response (IIR) factors contribute to OA progressive cartilage degradation. However, there are no clinically available TLR4 inhibitors. Interestingly, the antidepressant amitriptyline could block this receptor. Thus, we evaluated amitriptyline anti-TLR4 effects on human OA chondrocytes (hOCs) in order to repurpose it as an inhibitor of IIR in joint inflammatory pathologies. Experimental approach Through in silico docking analysis, RT-PCR, siRNA, ELISA, proteomics, and clinical data mining of drug consumption, we explored the clinical relevance of amitriptyline blockade of TLR4-mediated IIRs in hOCs. Results Amitriptyline bound TLR4 but not IL1 receptor (IL1R). Interestingly, amitriptyline binding to TLR4 inhibited TLR4- and IL1R-mediated IIRs in hOCs, synoviocytes and osteoblasts cells. Furthermore, amitriptyline reduced basal IIR and promoted anabolic effects on hOCs. Supporting its anti-IIR effects, amitriptyline downregulated basal and induced expression of NLR family pyrin domain containing 3 (NLRP3), an inflammasome member from IL1R signalling linked to OA & gout pathologies. Accordingly, mining of dissociated and aggregated drug consumption data from 107.172 elder patients (>65 years) revealed that amitriptyline consumption was significantly associated with lower colchicine consumption, associated with inflammatory gout flares treatment. Conclusion We demonstrate amitriptyline's ability to block TLR4-, IL1R- & NLRP3-dependent IIRs. This activity together with clinical data suggest that amitriptyline could be repurposed for systemic or local IIR management in diverse joint inflammatory pathologies.