Validation of Random Positioning Versus Clinorotation Using a Macrophage Model System

Clinostats and Random Positioning Machines (RPMs) are valuable devices for microgravity simulations in order to study fundamental gravity-dependent mechanisms on ground and in preparation for space flights. Both devices have different modes of operation, which have to be carefully considered and comprehensively discussed with respect to their potential impact on the quality of (simulated) microgravity. Here, we used the well-studied oxidative burst reaction of the immune cell (macrophage) model system, in order to compare clinorotation with random positioning. The RPM was used in a clinorotation mode, rotating the sample with 60 rpm around the horizontal axis and in the “random speed mode” (2-10 rpm) with and without random direction, thus, two axes rotating either bi- or unidirectionally. The production of Reactive Oxygen Species (ROS) during oxidative burst of the macrophages was visualized by the luminescence luminol assay. During clinorotation the cells responded with a reduction of the ROS production which is fully in line with earlier studies (clinostat, parabolic flight). In contrast, the exposure to the two random positioning modes showed that the oxidative burst response during RPM-exposure differs significantly from that observed during clinorotation, i.e. a jittering, more variant form of ROS production. We can conclude from our work, that the RPM is not suitable in its real random mode (with and without random direction; 2-10 rpm) to simulate the conditions of microgravity for the chosen system. We recommend that investigators using microgravity simulators should carefully choose the device and mode of operation specifically for their cellular system of interest.