Introduction:
Melatonin, an indoleamine synthesized mainly in the pineal gland, plays a key role in regulating the homeostasis of bone and cartilage. Reactive oxygen species (ROS) are released during osteoarthritis (OA) and associated with cartilage degradation. Melatonin is a potent scavenger of ROS.

Material and methods:
We used rat chondrocytes as a research objective in our study and investigated the effect of melatonin. We evaluated cell viability by MTS, cell apoptosis and mitochondrial transmembrane potential (MMP) by flow cytometry, hyaluronic acid (HA) concentrations by ELISA assay, relative gene and protein expression by RT-qPCR and WB assay, the subcellular location of nuclear factor κB (NF-κB) p65 and Rh-123 dye by immunofluorescence, oxygen consumption rate (OCR) by Seahorse equipment.

Results:
MTS and flow cytometry assay indicated that melatonin prevented H2O2-induced cell death. Melatonin suppressed the expression of HAS1 both from mRNA and protein level in time- and dose-dependent manners. Furthermore, melatonin treatment attenuated the decrease in HA production in response to H2O2 stimulation and repressed the expression of cyclooxygenase-2 (COX-2). Melatonin significantly decreased the nuclear volume of p65 and inhibited the expression of p50 induced by H2O2. In addition, melatonin restored the MMP and OCR of mitochondria, exerted mitochondrial protection function.

Conclusions:
Melatonin has a protective effect on chondrocytes, possibly by upregulating HA synthesis and inhibiting the NF-kB signaling.