PGE2 production in cementoblasts and PDL cells by ultrasound stimulation

Objectives: It is well understood that ultrasound (US) therapy can promote bone formation and accelerate fracture healing. It is also well known how prostaglandin E₂ (PGE₂) affects the osteogenic response of osteoblasts, playing an important role in modulating bone metabolism. However, the relationship between PGE₂ and periodontal ligament (PDL) cells or cementoblasts still remains unclear. The aim of the present study was to quantify COX-2 gene expression and PGE₂ production in cementoblasts and PDL cells stimulated by US.

Methods: Cultured human periodontal ligament cell line (HPL) and OCCM-30 cementoblasts (kindly provided by Prof. MJ Somerman) were seeded at a density of 3.5x10⁵ cells/cm² in culture plates and then exposed to US (OSTEOSONIC, ITO Co., Tokyo, Japan. Spatial-average intensity: 30mW/cm² and 150mW/cm²; frequency= 1MHz; pulsed 1:4). The culture medium and cells were collected 1, 4, 12 and 24 hrs after a single US exposure for 15 min. COX-2 gene expression was examined with RT-PCR and quantified by real-time PCR analyses. PGE₂ production was quantified with PGE₂ ELISA kit (Cayman, Co, USA).

Results: US with both intensities enhanced significantly (P<0.01) COX-2 mRNA expression after 1 hr exposure compared to the control groups of both cell lines tested. PGE₂ production also significantly increased 1(P<0.05) and 4 hrs (P<0.01) after single US exposure in OCCM-30, and after 12 hrs (P<0.01) in HPL cells. It is suggested that inducible PGE₂ via COX-2 may play an important role in metabolism of HPL cells and cementoblasts with US stimulation.

Conclusions: Due to the biphasic effects of PGE₂ (anabolic/catabolic), further studies are anticipated for understanding the effects of PGE₂ on the periodontium. However, this study suggests that US exposure is a promising therapy for regeneration of periodontal tissues, from the finding that US increased significantly COX-2 mRNA expression and PGE₂ production in OCCM-30 and HPL cells.