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Background and Objective Cellular damage related to oxidative stress (OS) is implicated in periodontal diseases (PD). Melatonin (MEL) has multiple functions, and it has been described as a potential treatment for PD. We aim at evaluating the protective effects of MEL on an in vitro model of cellular damage triggered by glutamate (GLUT) and DL‐buthionine sulfoximine (BSO), on gingival cells (GCs) in culture. Material and Methods A primary culture of GCs from Wistar rats was developed in order to test the protective property of MEL; BSO and GLUT were administered alone as well as in combination with MEL. The viability and apoptosis were measured with MTT assay and TUNEL, respectively, and the concentration of superoxide anion (O2‐) was measured with the NBT method. Results The combination of BSO and GLUT treatment resulted in a decreased viability of GCs. This was evidenced by the increase in both the production of superoxide anion and apoptosis. After MEL administration, the oxidant and pro‐apoptotic effects of BSO and GLUT were totally counteracted. Conclusions These findings demonstrated that MEL has an effective protective role on GCs subjected to cellular damage in a model of OS and cytotoxicity triggered by BSO and GLUT. Consequently, MEL could be used as a therapeutic agent in PD which begin with a significative loss of GCs.

Melatonin, the primary hormone involved in circadian entrainment, plays a significant role in bone physiology. This study aimed to assess the role of MEK1/2 and MEK5 in melatonin‐mediated actions in mouse and human mesenchymal stem cells (MSCs) and on bone using small‐molecule inhibitors and CRISPR/Cas9 knockout approaches. Consistent with in vitro studies performed in mMSCs and hMSCs, nightly (25 mg/kg, i.p., 45 days) injections with PD184352 (MEK1/2 inhibitor) or Bix02189 (MEK5 inhibitor) or SC‐1‐151 (MEK1/2/5 inhibitor) demonstrated that MEK1/2 and MEK5 were the primary drivers underlying melatonin's actions on bone density, microarchitecture (i.e., trabecular number, separation, and connectivity density), and bone mechanical properties (i.e., ultimate stress) through increases in osteogenic (RUNX2, BMP‐2, FRA‐1, OPG) expression and decreases in PPARγ. Furthermore, CRISPR/Cas9 knockout of MEK1 or MEK5 in mMSCs seeded on PLGA scaffolds and placed into critical‐size calvarial defects in Balb(c) mice (male and female) revealed that treatment with melatonin (15 mg/L; p.o., nightly, 90 days) mediates sex‐specific actions of MEK1 and MEK5 in new bone formation. This study is the first to demonstrate a role for MEK1/2 and MEK5 in modulating melatonin‐mediated actions on bone formation in vivo and in a sex‐specific manner.