Anti-inflammatory effects of the prostacyclin analogue iloprost in an in vitro model of inflamed human dental pulp cells.

Iloprost's anti-inflammatory effects on human dental pulp stem cells (HDPCs) are currently unknown. We hypothesized that iloprost could downregulate the expression of inflammatory-related genes and protein in an inflamed HDPC in vitro model. To induce inflammation, the HDPCs were treated with a cocktail of interleukin-1 beta, interferon-gamma, and tumour necrosis alpha, at a ratio of 1:10:100. Iloprost (10-6  M) was then added or not to the cultures. Interleukin-6 (IL-6) and interleukin-12 (IL-12) mRNA expression were assessed by real-time polymerase chain reaction. IL-6 protein expression was assessed by enzyme-linked immunosorbent assay. The results were analysed using one-way ANOVA or the Kruskal-Wallis test. The cytokine cocktail induced more robust IL-6 expression than LPS treatment. Iloprost slightly, yet significantly, downregulated IL-6 and IL-12 mRNA expression. These findings suggest that iloprost might be used as a beneficial component in vital pulp therapy.

The Prostacyclin Analog Iloprost Promotes Cementum Formation and Collagen Reattachment of Replanted Molars and Up-regulates Mineralization by Human Periodontal Ligament Cells.

INTRODUCTION: This study evaluated the use of the prostacyclin analog iloprost as a root surface treatment agent in promoting acellular cementum (AC) formation and collagen reattachment after tooth replantation in vivo. In addition, its effect on human periodontal ligament cell (hPDLC) mineralization was assessed in vitro. METHODS: First molars of 8-week-old Wistar rats were extracted. In 1 group, the root surfaces were treated with Hank's balanced salt solution (HBSS), and the other group's root surfaces were treated with 10-6 mol/L iloprost before replantation. At day 30, maxillae were prepared for micro-computed tomographic imaging and histomorphometric analysis. The effect of iloprost on mineralization by hPDLCs was analyzed by mineralized nodule formation and quantitative polymerase chain reaction at 7 and 14 days. RESULTS: Micro-computed tomographic imaging demonstrated a significant higher bone volume in the iloprost groups, whereas the HBSS groups had extensive bone and root resorption. Histologic analysis revealed deposition of a thick AC layer along the root in the iloprost group with well-organized periodontal ligament fibers inserted into the cementum. The HBSS group demonstrated more osteoclasts than the iloprost group. In vitro, iloprost-treated hPDLCs had a significantly increased RUNX2, OSX, BSP, and ALP gene expression that coincided with an increased deposition of mineralized nodules. These effects were abrogated by a PGI2 receptor inhibitor. CONCLUSIONS: Our results revealed that iloprost promoted PDL regeneration in replanted molars. Furthermore, resorption of the roots was decreased, whereas AC deposition was stimulated. Iloprost-treatment increased hPDLC mineralization and was mediated by PGI2 receptor activation. These observations indicate that iloprost may be a promising root surface treatment agent.

Prostacyclin Analog Promotes Human Dental Pulp Cell Migration via a Matrix Metalloproteinase 9-related Pathway.

INTRODUCTION: During dental pulp healing, progenitor cells migrate to the injured site. This study investigated the effect of iloprost (an exogenous prostacyclin [PGI2]) on enhancing human dental pulp cell (HDPC) migration and its underlying mechanism. METHODS: HDPC migration was analyzed using a wound scratch assay. HDPCs were obtained from extracted teeth and cultured in the presence of iloprost for 24 and 72 hours. Immunofluorescent staining for matrix metalloproteinase 9 (MMP-9), quantitative polymerase chain reaction gene expression analysis, gelatin zymography, and enzyme-linked immunosorbent assay of MMP-9 expression were performed. A PGI2 (IP) antagonist, protein kinase A (PKA) inhibitor, and MMP-9 inhibitor were used to inhibit the IP receptor, PKA signaling pathway, and MMP-9 activity, respectively. RESULTS: A mechanically applied scratch in HDPC cultures closed more rapidly in the presence of iloprost. This result coincided with increased MMP-9 messenger RNA and protein expression and higher gelatinase activity. These iloprost-enhanced effects were inhibited by an IP receptor antagonist or a PKA inhibitor. Forskolin, a PKA activator, increased MMP-9 expression concomitant with increased migration. The application of a selective MMP-9 inhibitor resulted in decreased iloprost-induced migration. CONCLUSIONS: MMPs play an important role in cell migration by degrading components of the extracellular matrix. In this study, iloprost accelerated HDPC migration in a wound scratch assay. MMP-9 expression was increased concomitantly by iloprost and appeared to be mediated by the IP-PKA pathway. These observations suggest that iloprost may enhance dental pulp tissue healing by up-regulating MMP-9. The PGI2 analog might be a promising biomolecule in dental pulp regenerative treatment.

Iloprost Induces Dental Pulp Angiogenesis in a Growth Factor-free 3-Dimensional Organ Culture System.

INTRODUCTION: Angiogenesis is a key determinant in dental pulp regeneration. Iloprost is a synthetic prostacyclin that promotes angiogenesis. A three-dimensional culture that mimics the in vivo condition has been used in tissue engineering. This study investigated the effect of iloprost on promoting dental pulp angiogenesis by using the tooth slice organ culture system. METHODS: Tooth slices with intact pulp tissue were cut from molars extracted from 12 patients. Dental pulp tissue viability was determined by live/dead staining. The tooth slices were cultured with iloprost for 1 or 3 days. The microvessel density and expression of vascular endothelial growth factor were determined by immunohistochemical staining. Collagen density was determined by using Masson trichrome and immunofluorescent staining. RESULTS: The pulp tissue in the tooth slices remained viable when cultured in serum-free medium. Iloprost increased the microvessel density as shown by a higher number of von Willebrand factor-positive cells. A significant increase in vascular endothelial growth factor expression was observed in the tooth slices cultured with iloprost. Iloprost stimulated collagen deposition, and this effect was abolished after inhibition of protein kinase A activity. CONCLUSIONS: Human tooth slices provide a valuable and easy-to-obtain model to investigate the effect of bioactive molecules used in dental pulp regeneration. This study showed for the first time that tooth slices could be kept viable under serum-free conditions for up to 3 days. Iloprost promoted angiogenesis, increased new vessel formation, and induced collagen deposition. This study proposes the clinical value of iloprost as a drug for inducing angiogenesis that can increase the success of pulp regeneration.