You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

MMP driven endochondral fracture union proceeds independently of osteoclast activity. As new insights into the complexities of endochondral fracture repair emerge, the temporal role of osteoclast activity remains ambiguous. With numerous anti-resorptive agents available to treat bone disease, understanding their impact on bone repair is vital. Further, in light of recent work suggesting osteoclast activity may not be necessary during early endochondral fracture union, we hypothesize instead a pivotal role of MMP secreting cells in driving this process. While the role of MMPs in fracture healing has been examined, no directly comparative experiments exist. We examined a number of anti-resorptive treatments to either block osteoclast activity, including the potent bisphosphonates zoledronic acid (ZA) and clodronate (CLOD), which work via differing mechanisms, or antagonize osteoclastogenesis with recombinant OPG (HuOPG-Fc), comparing these directly to an inhibitor of matrix metalloproteinase (MMP) activity (MMI270). Endochondral ossification to union occurred normally in all anti-resorptive groups. In contrast, MMP inhibition greatly impaired endochondral union, significantly delaying cartilage callus removal. MMP inhibition also produced smaller, denser hard calluses. Hard callus remodeling was, as expected, delayed with ZA, CLOD and OPG treatment at 4 and 6 weeks, resulting in larger more mineralized calluses at 6 weeks. As a result of reduced hard callus turnover, bone formation was reduced with anti-resorptive agents at these time points. These results confirm that the achievement of endochondral fracture union occurs independently of osteoclast activity. Alternatively, MMP secretion by invading cells is obligatory to endochondral union. This study provides new insight into cellular contributions to bone repair and may abate concerns regarding anti-resorptive therapies impeding initial fracture union. © 2013 American Society for Bone and Mineral Research.
{"Chemical": ["bisphosphonates", "CLOD", "zoledronic acid", "clodronate"]}