Effect of L-lysine and L-arginine on primary osteoblast cultures from normal and osteopenic rats

A therapeutic role of amino acids L-lysine (Lys) and L-arginine (Arg) in os teoporosis and fracture healing was demonstrated previously by in vivo stud ies. In the present study, primary cultures of osteoblasts were used to inv estigate the effect of amino acids on gene expression (alkaline phosphatase activity, ALP; osteocalcin, OC; type I collagen), nitric oxide production (NO) and proliferation (MTT) of cells. Cells were isolated from the distal femurs of normal and osteopenic rats. Normal and osteopenic bone-derived ce lls were divided into four groups: control, Lys (0.587 mg/mL/d), Arg (0.625 mg/mL/d), and Lys + Arg (0.587 + 0.625 mg/mL/d). No evidence of difference s between normal and osteopenic bone-derived cultures in basal conditions w as observed. A significant (P = 0.002) increase of 10.4% in NO production w as observed in normal bone-derived osteoblasts treated with Lys + Arg when compared to the control group at 7 days. At the same time, normal bone-deri ved osteoblasts treated with Arg and Lys + Arg showed significant increases in type I collagen synthesis of 25.3% and 28.4%, respectively, when compar ed to the control group. Osteopenic bone-derived osteoblasts showed signifi cant (P = 0.002) increases of 27.6% in MTT and 28.7% in cell count at 48 ho urs when treated with Lys + Arg in comparison with the control group. At 7 days, NO production and type I collagen synthesis increased significantly ( P < 0.005) both in osteopenic bone-derived osteoblasts treated with Arg (NO : 18.5%; type I collagen: 34.4%) and Lys + Arg (NO: 23.7%; type I collagen: 20.9%) compared to the control group. Finally, a significant (P = 0.025) d ecrease of 5.8% in OC level was observed in osteopenic bone-derived osteobl asts treated with Arg. Results suggest that the potential therapeutic effec t of Lys and Arg on bone could be related, at least in part, to an improvem ent of NO production and type I collagen synthesis by osteoblasts both in n ormal and in osteopenic bone. In osteopenic bone-derived osteoblasts this s ynthetic phase is preceded by an initial increase of cell proliferation. (C ) 2001 Editions scientifiques et medicales Elsevier SAS.