Zytotoxische Wirkung von Vertebroplastie- und Kyphoplastiezementen auf die Osteoblastenzelllinie MC3T3-E1

Vertebroplasty and kyphoplasty are minimally invasive, surgical procedures for the treatment of vertebral body fractures of osteoporotic, traumatic or neoplastic origin. Highly viscous cement is injected into the vertebral body under radiological control via a hollow needle, which hardens within a few minutes and thus intrinsically stabilizes the fractured vertebra. The difference between the two procedures is that in kyphoplasty, the vertebral body is also straightened up beforehand using a balloon. Both methods lead to an immediate, significant reduction in pain in the majority of patients and usually allow free-functional mobilization on the first day after the operation. Although these are successful and well-established methods, there have been only few studies to date that deal with the interaction between the used cement and the surrounding tissue. Different types of cements are used in both kyphoplasty and vertebroplasty. The two main groups are: cements with polymethyl methacrylate and cements with calcium phosphate as the main component. This study examined in vitro the potential cytotoxicity of the two cement groups on cells of the murine osteoblastic cell line MC3T3-E1 as well as the effect of concentration and exposure time. To quantify the possible cytotoxicity, the methods microscope camera, neutral red test, xCELLigence Real-Time Cell Analysis and flow cytometry (FACS) were used. With the help of the microscope camera, the adherence, confluence and morphology of the cells could be recorded descriptively. In addition, the cell viability was determined by means of the neutral red test and the flow cytometry analyzed the respective cell cycle phases. The measurements were carried out at defined test times after 24 h, 48 h and 72 h. An xCELLigence Real-time Cell Analyzer was used to determine cell proliferation in real time. To determine a possible concentration effect, nutrient medium was incubated for 72 hours with a defined amount of hardened cement and then added to the cells in concentrations of 1:10 and 1:20. In the test procedures mentioned for the analysis of the cytotoxicity, no significant differences were found in the polymethyl methacrylate cements compared to the control. In contrast, there was a significant reduction in confluence, viability and proliferation and the increased proportion of apoptotic cells in the sub-G1 phase in the calcium phosphate cement tested. The higher concentrations of the medium incubated with cement showed a tendency towards a more toxic effect in all tests; however, this difference did not reach sufficient significance in the statistical testing. With the polymethyl methacrylate cements, the results indicated that the cells had a recovery effect with increasing duration. Confluence, viability and proliferation increased after 48 h and 72 h compared to 24 h, and flow cytometry (FACS) also showed a significant decrease in the number of cells in the sub-G1 phase after 48 h. I the calcium phosphate cements, on the other hand, this effect was not evident and the cytotoxic effect was not reversible in each case. This study describes for the first time cytotoxicity of calcium phosphate cements on cells of the murine ostoeblastic cell line MC3T3-E1 and also the influence of the concentration and exposure time. However, important limitations must also be taken into account before interpretation. In vivo, not only interactions with osteoblasts take place in vertebral bodies, for example, there are significantly more complex regulatory mechanisms for bone formation and degradation, with a wide variety of cell types, a specially mineralized extracellular matrix, growth factors, hormones and buffer systems being involved. Furthermore, the meaningfulness of the results is limited by the limited duration of the experiment. In vivo exposure to the potentially cytotoxic cement often lasts for decades. Further studies, both in vivo and in vitro, over a significantly longer period of time are required in order to develop new cements with optimal biomechanical properties, but above all with a reduced toxic effect on the cells in the bone and the extracellular matrix. This could optimize the established vertebrolasty and kyphoplasty procedures and further improve the treatment outcome for the patient.