The present experiments were carried out to test the hypothesis that arterial calcification is linked to
bone resorption by determining whether the selective inhibition of
bone resorption with
osteoprotegerin will inhibit arterial calcification. In the first test, arterial calcification was induced by treating 22-day-old male rats with
warfarin, a procedure that inhibits the gamma-carboxylation of
matrix Gla protein and causes extensive calcification of the arterial media. Compared with rats treated for 1 week with
warfarin alone, rats treated with
warfarin plus
osteoprotegerin at a dose of 1 mg/kg per day had dramatically reduced
alizarin red staining for calcification in the aorta and in the carotid, hepatic, mesenteric, renal, and femoral arteries, and they had 90% lower levels of
calcium and
phosphate in the abdominal aorta (P<0.001) and in tracheal ring cartilage (P<0.01). More rapid arterial calcification was induced by treating 49-day-old male rats with toxic doses of
vitamin D. Treatment for 96 hours with
vitamin D caused widespread
alizarin red staining for calcification in the aorta and the femoral, mesenteric, hepatic, renal, and carotid arteries, and
osteoprotegerin completely prevented calcification in each of these arteries and reduced the levels of
calcium and
phosphate in the abdominal aorta to control levels (P<0.001). Treatment with
vitamin D also caused extensive calcification in the lungs, trachea, kidneys, stomach, and small intestine, and treatment with
osteoprotegerin reduced or prevented calcification in each of these sites. Measurement of serum levels of cross-linked N-teleopeptides showed that
osteoprotegerin dramatically reduced
bone resorption activity in each of these experiments (P<0.001). Therefore, we conclude that doses of
osteoprotegerin that inhibit
bone resorption are able to potently inhibit the calcification of arteries that is induced by
warfarin treatment and by
vitamin D treatment. These results support the hypothesis that arterial calcification is linked to
bone resorption.