Background
Memantine, which is an FDA-proven drug for the treatment of dementia, exerts its function by blocking the function of NMDA (N-methyl-D-aspartate) receptor, a calcium-permeable ion channel that reduces cytotoxic calcium overload. Chondrocyte senescence is a crucial cellular event that contributes to articular cartilage degeneration during osteoarthritis (OA) development. To date, the effects of memantine and its downstream NMDA receptor on chondrocyte senescence and OA have been rarely reported.
Conclusion
NMDA receptor plays an important role in inflammatory-induced cytotoxic calcium overload in chondrocytes, while memantine can effectively block the NMDA receptor to reduce chondrocyte senescence and retard the development of OA. The translational potential of this article: As a clinically licensed drug used for the treatment of dementia, memantine has shown promising therapeutic effects on OA. Mechanistically, it functions by blocking NMDA receptor from mediating chondrocyte senescence. The protective effects of memantine against OA were verified not only by in vivo and in vitro experiments but also via a propensity score-matched human cohort study. These findings presented robust evidence for repurposing memantine for the treatment of OA.
Methods
The protein levels of NMDA receptor and its agonistic ligand, glutamate, were compared between normal and OA chondrocytes. The quantity of intracellular calcium ions and the level of mitochondrial damage were evaluated using specific fluorescent probes and transmission electron microscopy (TEM), respectively. Chondrocyte senescence was evaluated by senescence-associated β-galactosidase (SA-β-Gal) staining and p16INK4a analysis. The function of NMDA receptor in chondrocyte senescence and OA was tested via agonists activation and gene knockdown experiments. The therapeutic effects of memantine on OA were examined both in vitro and in vivo. Additionally, to verify the findings from animal samples, a propensity score-matched cohort study was conducted using data from a United Kingdom primary care database (i.e., IQVIA Medical Research Database [IMRD]) to compare the risk of OA-related joint replacement involved in memantine initiators versus active comparators (i.e., acetylcholinesterase [AchE] initiators) in patients with dementia.
Results
The protein expression of NMDA receptor and the secretion of glutamate were both significantly increased in OA chondrocytes. NMDA receptor activation was found to stimulate chondrocyte calcium overload, which further led to mitochondrial fragmentation and chondrocyte senescence. Blocking the NMDA receptor with memantine and N-methyl-D-aspartate receptor subunit 1(NR1, the gene encoding NMDA receptor) knockdown resulted in reduced calcium influx, mitochondrial fragmentation, as well as cellular senescence in OA chondrocytes. Intra-articular injection of memantine in OA mice also exhibited protective effects against cartilage degeneration. Moreover, in the 1:5 propensity score-matched cohort study consisting of 6218 patients (n = 1435 in the memantine cohort; n = 4783 in the AchE cohort), the memantine initiator was associated with a lower risk of OA-related joint replacement than AchE initiators (Hazard ratio = 0.56, 95 % confidence interval: 0.34 to 0.99).