Conclusion
Our results report a novel mechanism through which P188 exerts its protective effects on cartilage in the model of acute injury. In addition to its effect on cellular membrane, P188 affects stress-related p38 signaling, apoptosis-related GSK3, and inflammation-related IL-6 signaling. Taken together, these findings suggest that P188 alone or in combination with proanabolic agents may have a therapeutic potential in preventing progressive cartilage degeneration and the development of posttraumatic osteoarthritis.
Objective
Because P188 poloxamer is effective in promoting cell survival in models of acute trauma, the objectives were to understand the mechanism of its action focusing on glycogen synthase kinase-3 (GSK3) activation, interleukin-6 (IL-6), and p38 signaling. Design: Sixteen normal human tali were impacted using a 4-mm diameter indenter with an impulse of 1 Ns. Eight-millimeter cartilage plugs containing the 4-mm impacted core and 4-mm adjacent nonimpacted ring were removed and cultured with or without P188. Cell lysates were analyzed using Western blots with antibodies against total and phosphorylated extracellular signal-regulated protein kinase (ERK), c-Jun NH2-terminal kinase (JNK), p38, ATF-2, GSK3, Stat1, and Stat3. Additional tests were performed with the p38 inhibitor (p38i) SB203580.
Results
Studied pathways were activated after impaction with the peak of activity at 1 hour. P188 completely attenuated phosphorylation of Stat1 and ATF-2 and inhibited p38, Stat3, JNK, ERK, and GSK3. The p38i partially offset phosphorylation of Stat3, GSK3, and ERK suggesting a role of p38 in these three pathways. Additionally, the p38i improved cell survival (P = 0.053) and reduced apoptosis (by approximately 20%, P = 0.046, versus almost 40% by P188), thus confirming that P188 acts (at least in part) through the p38 pathway.