Effects of mesenchymal stem cell secretome on osteoclast- and osteogenesis-related markers during orthodontic relapse

The mesenchymal stem cell (MSC) secretome has emerged as a promising cell-free approach for modulating bone remodeling, but its effects during the orthodontic relapse phase remain poorly understood. This study investigated the effects of the human umbilical cord-derived MSC (hUC-MSC) secretome on alveolar bone remodeling during orthodontic relapse.

Forty-one male Wistar rats were randomly assigned to three groups: negative control (C-), positive control (C+), and secretome-treated relapse group (S). S rats were subjected to submucosal injections of the hUC-MSC secretome, whereas the control groups received submucosal injection of phosphate-buffered saline. Orthodontic force was applied for 14 days to move the maxillary first molars mesially. Relapse began on day 14 after the appliance was removed. A retention device was placed only in C- rats. The rats were sacrificed on days 21 and 28, and the expression levels were assessed for cathepsin K (CTSK), tartrate-resistant acid phosphatase (TRAP), osteoprotegerin, receptor activator of nuclear factor-κB ligand, alkaline phosphatase (ALP), and osteocalcin (OCN) via immunohistochemistry.

Quantitative analysis demonstrated that the TRAP and CTSK expression levels were significantly lower in S than C-, but remained comparable to those in C+. In addition, the RANKL/OPG ratio was consistently lowest in S at both time points compared with C- and C+. Furthermore, across both observation periods, the expression levels of ALP and OCN were significantly higher in S compared with C-.

The hUC-MSC secretome may promote a favorable alveolar bone remodeling balance at the tension side during orthodontic relapse by suppressing osteoclastic activity and enhancing osteoblastic activity.