Histomorphometry and bone biomarkers in cynomolgus females: a study in young, mature, and old monkeys

Although ovariectomized cynomolgus monkeys are used extensively for studies examining perimenopausal changes in the skeleton, very little is known about the changes that occur naturally during growth and aging in these animals. To evaluate the changes in bone during growth and aging in female cynomolgus monkeys, 29 monkeys ranging from 3 years to >22 years of age were given a bone fluorochrome label and iliac biopsies were collected. Serum and urine were collected at the time of biopsy to determine alkaline phosphatase (ALP), osteocalcin, tartrate-resistant acid phosphatase (TRAP), serum and urinary calcium, estradiol, urinary creatinine, and urinary CrossLaps levels. The biopsies from 8 young (3–4 years of age), 13 mature (11–16 years of age) and 8 old (>22 years of age) were analyzed histomorphometrically. ALP, TRAP, and urinary CrossLaps levels were lower in the mature and old monkeys when compared with the young group. Urinary calcium/urinary creatinine levels increased with age. Bone volume (BV/TV), trabecular number (Tb.N), bone formation rate (BFR), and activation frequency (Ac.f) were greatest in the young monkeys and declined in the older groups. The biomarker and histomorphometric indices in the young animals reflect the growth that was occurring in this group. The older monkeys do not appear to differ significantly between 10 and 22 years of age.