L-carnitine promotes intracellular calcium rises and exerts antioxidant effect in primary culture of human osteoblast-like cells

Objectives: L-Carnitine (LC) is a non-protein amino acid known for its ability to increase the endurance capacity and to reduce the oxidative stress in human and animal models. Moreover, LC positively affects mineralization, differentiation and proliferation both in porcine and murine primary or tumor-derived osteoblasts, and in a murine model of osteoporosis. Since cytosolic calcium is a critical signalling messenger regulating osteoblast differentiation and functions whereas oxidative stress is a key element affecting cell fate, we designed the following study to investigate the possible effects of LC on intracellular calcium and oxidative stress in human osteoblasts (hOBs). Methods: hOBs, derived from trabecular bone waste material obtained during orthopedic surgery (Ethics Committee approved), were treated with 5mM LC. Intracellular calcium concentration [Ca2 +]i, at single cell level, and antioxidant activity were monitored, respectively, by Video-imaging using Fura2 and by the cell based antioxidant (CAA) assay. Results: LC was able to stimulate significantly (p\0.01) the extracellular calcium uptake in the 84±24% of the analyzed cells, with a [Ca2+]i increase of 37.8±8.5 nM. This influx was completely inhibited by dihydropyridines, specific channels blockers, indicating the involvement of L-type calcium channels. LC induced also the emptying of the intracellular calcium stores in the 97±5% of the analyzed cells, with a [Ca2+]i increase of 44±9 nM (p\0.01). The emptying of the endoplasmic reticulum occurred via phospholipase C pathway activation, as shown by experiments performed with U73122, a specific inhibitor of this pathway. Finally LC significantly enhanced (p\0.01) the antioxidant capacity of hOBs. Summary & Conclusion: LC treatment was able to rapidly modify the hOBs’ intracellular calcium concentration and antioxidant balance. Since the intracellular calcium signalling together with the redox cell status play a crucial role in regulating osteoblast fate and functions, LC deserves interest as a potential nutraceutical supplement for bone health.