Glucose-induced inhibition of in vitro bone mineralization

Patients with diabetes tend to have an increased incidence of osteopenia th at may be related to hyperglycemia. However, little is known about how gluc ose may alter bone formation and osteoblast maturation. To determine whethe r glucose affects osteoblastic calcium deposition, MC3T3-E1 cells were incu bated in media containing either a normal (5.5 mmol/L) or high glucose conc entration (15 mmol/L) or mannitol (15 mmol/L), and bone nodule formation wa s examined. Net calcium flux was measured thrice weekly and cumulative calc ium uptake was determined, Compared with control incubations, glucose signi ficantly inhibited daily and cumulative calcium uptake into the nodules, At the time of matrix maturation, cultures undergo a rapid phase of increased calcium deposition; this was significantly inhibited by the presence of gl ucose, Total calcium uptake, determined by acid digestion, was also signifi cantly inhibited by glucose. Area and number of nodules were quantitated at the end of the incubation period (day 30) by staining with Alizarin Red S calcium stain. Compared with both control and mannitol-treated cultures, th e number of nodules was increased by incubation with glucose. Furthermore, both the average total nodular area and calcified nodular area of large nod ules were increased by glucose, Cellular proliferation as well as the relea se of markers of osteoblast activity (osteocalcin and alkaline phosphatase) were determined at the end of the experimental period (day 30), Cellular p roliferation and alkaline phosphatase activity was significantly increased in the presence of glucose, however, the release of osteocalcin into cultur e media was similar in all three groups. In conclusion, the present study s hows that elevated glucose concentration present throughout the development of murine osteoblasts stimulates cellular proliferation while inhibiting c alcium uptake. The result of glucose inhibition of calcium uptake suggests that bone could be structurally altered in diabetes. (C) 2001 by Elsevier S cience Inc. All rights reserved.