Glucose-induced inhibition of in vitro bone mineralization

Patients with diabetes tend to have an increased incidence of osteopenia that may be related to hyperglycemia. However, little is known about how glucose may alter bone formation and osteoblast maturation. To determine whether glucose affects osteoblastic calcium deposition, MC3T3-E1 cells were incubated in media containing either a normal (5.5 mmol/L) or high glucose concentration (15 mmol/L) or mannitol (15 mmol/L), and bone nodule formation was examined. Net calcium flux was measured thrice weekly and cumulative calcium uptake was determined. Compared with control incubations, glucose significantly 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 glucose. Total calcium uptake, determined by acid digestion, was also significantly 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, the number of nodules was increased by incubation with glucose. Furthermore, both the average total nodular area and calcified nodular area of large nodules were increased by glucose. Cellular proliferation as well as the release of markers of osteoblast activity (osteocalcin and alkaline phosphatase) were determined at the end of the experimental period (day 30). Cellular proliferation and alkaline phosphatase activity was significantly increased in the presence of glucose, however, the release of osteocalcin into culture media was similar in all three groups. In conclusion, the present study shows that elevated glucose concentration present throughout the development of murine osteoblasts stimulates cellular proliferation while inhibiting calcium uptake. The result of glucose inhibition of calcium uptake suggests that bone could be structurally altered in diabetes.