Selection of Angiogenic Markers that Predict the Transition from Bisphosphonate Exposure to MRONJ in a Rat Model

Medication related osteonecrosis of the jaw (MRONJ) is a disorder characterized by loss of blood supply to the jaws and death to the bone. In our previous work, we created a rat model of MRONJ by two injections of 60ug/Kg zoledronic acid (a powerful bisphosphonate abbreviated as ZA) via tail vein followed by extraction of a single first molar. We have shown in this model (ZA-treated rats plus molar extraction) a decrease in the vasculature of the jaws and a delay in bone healing beyond 4 weeks. Purpose: The current study identified angiogenic factors from the jaws of our MRONJ model where expression was altered independent of exposure to ZA alone. Methods: Using RT-PCR arrays containing 84 different gene sequences related to angiogenesis, we screened RNA isolated from the jaws of Control, ZA-treated rats, and our MRONJ rat model (ZA-treated plus first molar extraction), 3 and 6 weeks after extraction. Heat maps of gene expression were analyzed to identify genes where expression was either maximal or lost in MRONJ rats relative to ZA-treated rats without extraction. Results: Our study demonstrates the loss or gain of expression for 22 genes in the MRONJ rat model relative to rats treated with ZA alone. In MRONJ rats, the loss of expression was seen for 10 genes after 3 weeks and 3 additional genes (13 total) after 6 weeks where maximal expression was seen in rats treated with ZA-alone. This study also identified 5 genes that were maximally expressed in MRONJ rats after 3 weeks and an additional 4 genes (9 total) after 6 weeks that were not expressed in rats treated with ZA alone. Conclusions: Our study identifies genes that predict the transition from asymptomatic bisphosphonate exposure to MRONJ.