The biological effect of cobalt chloride mimetic-hypoxia on nucleus pulposus cells and the comparability with physical hypoxia in vitro

Objective : Nucleus pulposus cells (NPCs) are cells extracted from the intervertebral disc and are important for research into intervertebral disc degeneration (IVDD). NPCs live in an avascular and relatively hypoxic environment. Cobalt chloride (CoCl 2 ) has been used in many cell studies to mimic hypoxia. The objective of this study was to explore the possibility of using CoCl 2 o induce mimetic-hypoxia for NPCs and the comparison with hypoxia (1% O 2 ) in vitro . Materials and methods : Rat nucleus pulposus cells of Passage 3-5 were used in this research. Cell viability, rate of cell apoptosis, ROS (reactive oxygen species) generation, cell migration, extracellular pH and extracellular matrix metabolism were determined to compare the influence of hypoxia (1% O 2 ) and CoCl 2 on NPCs. Results : We found that the effects of CoCl 2 on NPCs was dose-dependent. At the proper concentration, CoCl 2 could be used to elicit chemical hypoxia for nucleus pulposus cells in vitro and many biological effects, analogous to physical hypoxia (1% O 2 ), could be achieved such as enhanced cell viability, decreased apoptosis and activated extracellular matrix metabolism. On the other hand, CoCl 2 mimetic-hypoxia did not affect NPCs glycolysis and migration compared to physical hypoxia. In addition, high concentration of CoCl 2 (>200 μM) is harmful to NPCs with high rates of apoptosis and ECM (extracellular matrix) degradation. Conclusions : It is feasible and convenient to use CoCl 2 o induce chemical mimetic hypoxia for culturing NPCs on the premise of appropriate concentration. But in aspects of cell migration and glycolysis, CoCl 2 could not achieve similar results with physical hypoxia. This study may provide a convenient method and enlightenment to induce mimetic-hypoxia for researchers studying NPCs and IVVD.