Effects of Adipokines and Insulin on Intracellular pH, Calcium Concentration, and Responses to Hypo-Osmolarity in Human Articular Chondrocytes from Healthy and Osteoarthritic Cartilage

Abstract

Objective: To evaluate the effects of adipokines and insulin on intracellular calcium concentration ([Ca2+]i) and pH (pHi) in human articular chondrocytes from healthy (CHC) and osteoarthritic cartilage (COC). Design: pHi and [Ca2+]i were measured using BCECF and Fura-2 fluorometric probes in CHC and COC under control conditions and following a hypotonic shock. The effects of interleukin-1β (IL1β), tumor necrosis factor-α (TNFα), insulin, leptin, resistin, and adiponectin were assessed. Results: pHi was lower in COC than in CHC. Only IL1β β decreased pHi in both cell types; all the agents enhanced pHi recovery following an ammonium prepulse in CHC, effect that was attenuated by Na+–H+ exchanger inhibitors, but they had no effect in COC. Hypotonic shock (HTS) caused a pHi increase, which was significantly smaller in COC. All the hormones attenuated this response and the effect of IL1β was greater. The basal [Ca2+]i was similar in COC and CHC; IL1β, TNFα, and insulin increased the [Ca2+]i, but leptin, resistin, and adiponectin did not. These effects were greater in COC. This [Ca2+]i increase was dependent on extracellular Ca2+ and attenuated by Na+–Ca2+ exchanger inhibitors. HTS caused a [Ca2+]i increase, which was inhibited by transient receptor potential vanilloid blockers and attenuated by all the hormones tested with the exception of adiponectin. Conclusions: These findings may help explain the association between obesity and osteoarthritis, in which these hormones are altered. The responses of CHC and COC are different, which suggests that a modification of pH and Ca2+ homeostasis is part of the osteoarthritis pathophysiology.