New approaches to the problems of osteoporosis

Homologous androgen receptor up-regulation in osteoblastic cells may be associated with enhanced functional androgen responsiveness

Although androgens have myriad effects on the skeleton, the regulation of androgen action in bone is not well understood. Androgen receptors (ARs) are known to play an important role in mediating androgen action. We have examined the effects of androgens and other sex steroids on AR levels in osteoblastic cells in vitro using two clonal human cell lines, SaOS-2 and U-2 OS. AR protein levels were quantitated both by specific androgen binding studies and Western analyses, and AR messenger RNA was measured with RNase protection assays. Potential changes in AR functionality was assessed by reporter assays. Treatment of osteoblastic cells with the nonaromatizable androgen 5alpha-dihydrotestosterone (DHT) increased specific androgen binding 2-to 4-fold. Similar increases in AR protein levels were documented by Western analysis in both cell lines. The androgen-mediated increase in receptor levels was time and dose dependent as well as androgen specific. Steady-state AR messenger RNA levels were also increased by DHT. When AR concentrations in osteoblastic cells were elevated with exogenous receptor, there was an enhancement of DHT responsiveness, measured by increased trans-activation of an androgen-responsive promoter. Thus, androgen exposure increased androgen receptor protein levels and specific androgen binding in osteoblastic cells. Androgen action as measured by androgen-mediated transcriptional activation is enhanced in the presence of elevated AR levels. Consequently, these studies have revealed an additional means by which androgens may modulate skeletal metabolism.

Treatment of osteoporosis in the elderly

Fracture risk is adversely related to bone density, wherever it is measured. Women should be screened by bone densitometry around the time of the menopause and treated with calcium or hormones if the density is low. Women with vertebral compression should be treated with calcitriol if calcium absorption is low, with hormones if urine calcium is high, and with calcitriol and hormones if both abnormalities are present. It is uncertain whether newer treatments offer any advantages over this regimen. Vitamin D is indicated in household individuals or others with low levels of 25 OHD to prevent loss from secondary hyperparathyroidism and perhaps also to improve muscle power.

Calcium and calcitriol therapy in osteoporotic postmenopausal women with impaired calcium absorption

The effects of oral calcitriol (0.25 and 0.50 micrograms/d), together with calcium (1 g/d), on calcium absorption and bone resorption were measured in postmenopausal osteoporotic women with calcium malabsorption. Radiocalcium absorption was significantly improved and urinary hydroxyproline/creatinine excretion significantly reduced on both doses, but the higher dose caused an unacceptable incidence of hypercalcemia. In 49 patients treated for an average of 15 months with the lower dose, there was a nonsignificant gain in forearm bone mass of 0.4 +/- 0.3 mg/cm/mo (approximately 1/2% per annum) compared with a significant decrease in 17 untreated patients of 3.8 +/- 1.3 mg/cm/mo (approximately 5% per annum).