Zoledronic Acid reduces Heparin-Binding Growth Factor in Endothelial cells

Background: Protracted nitrogen-containing bisphosphonate (n-BIS) treatment is associated with bisphosphonate-related osteonecrosis of the jaws (BRON). BRON is characterized by pain, severe recurrent infections and tooth loss, thereby reducing quality of life. Tooth extraction is a common dental procedure that precedes many documented cases of BRON, implying that wound healing is impaired. Endothelial cells are essential for normal wound and bone healing. For example, endothelial cells contribute chemical mediators, such as heparin-binding growth factor (HB-EGF) during soft and hard tissue repair. N-BIS inhibits farnesyl pyrophosphate synthase. Farnesyl pyrophosphate synthase is a key enzymatic step of the mevalonate pathway in the production of geranylgeranyl pyrophosphate (GGPP). GGPP is necessary for prenylation and consequently the membrane anchoring of small GTPases. Membrane anchored GTPases are critical for proper signal transduction and therefore appropriate cell functions. Objectives: To determine if zoledronic acid (ZOL), a n-BIS, modulates VEGF-stimulated endothelial cell expression of HB-EGF. Methods: Human umbilical endothelial cells (HUVECs) were incubated with or without 12.5µM ZOL for 48hrs. Some HUVECs also received GGPP, an end-product isoprenoid of mevalonate pathway. After the 48hr incubation of ZOL and/or GGPP, the HUVECs were stimulated with 10ng/ml VEGF for either 2hrs to determine the relative amount of HB-EGF-specific mRNA by real-time PCR or for 6hrs to determine the amount of HB-EGF protein by western blot. Results: ZOL significantly reduced VEGF-stimulated HUVECs expression of HB-EGF-specific mRNAs and protein when compared to VEGF-stimulated HUVECs (p=0.001, ANOVA). Addition of GGPP attenuated the inhibitory effect of ZOL on HB-EGF expression in VEGF-stimulated HUVECs. Conclusion: ZOL inhibits HB-EGF expression in VEGF-stimulated endothelial cells. GGPP reduced the inhibitory effect of ZOL on the expression of HB-EGF. Collectively, the data suggests that ZOL inhibits HB-EGF expression by VEGF-stimulated endothelial cells, in part, by inhibition of the mevalonate pathway.