Endogenous oestrogen and bone loss following oophorectomy

Mechanism of Action, Pharmacokinetic and Pharmacodynamic Profile, and Clinical Applications of Nitrogen-containing Bisphosphonates

Nitrogen-containing bisphosphonates (nBPs) are bone-specific agents that inhibit farnesyl diphosphate synthase. nBPs’ strong affinity for bone, and not for other tissues, makes them potent inhibitors of bone resorption and bone remodeling activity, with limited potential for side-effects in non-skeletal tissues. Five nBPs are currently approved in the United States. The primary indications are for treatment of osteoporosis (alendronate, ibandronate, and risedronate) and treatment/prevention of skeletal-related events (SREs) in multiple myeloma and breast and prostate cancer patients (ibandronate, pamidronate, and zoledronic acid). nBPs are the most efficacious drugs available for these diseases, reducing osteoporotic fracture risk by 50–60% in persons with low bone mass or prior osteoporotic fracture, and SREs by one-third in cancer patients. The absorbed nBP dose for cancer patients is from seven to ten times that in osteoporosis patients. nBPs are unique in that they first exert profound pharmacodynamic effects long after their blood levels reach zero. Current pharmacokinetic studies indicate that approximately half of any nBP dose reaches the skeleton, with an early half-life of ten days, and a terminal half-life of about ten years. Practical study design limitations and theoretical considerations suggest that both the half-life and the amount of nBP retained in the skeletons of patients on long-term nBP therapy are substantially overestimated by extrapolation directly from current pharmacokinetic data. In fact, the amount of nBP being released from skeletal tissues of long-term-treated patients, particularly in osteoporosis patients, becomes insufficient to maintain full pharmacodynamic efficacy relatively soon after dosing is interrupted.

Combined Effect of Bilateral Ovariectomy and Anterior Cruciate Ligament Transection With Medial Meniscectomy on the Development of Osteoarthritis Model

OBJECTIVE

To investigate the combined effect of bilateral ovariectomy (OVX) and anterior cruciate ligament transection (ACLT) with medial meniscectomy (MM) on the development of osteoarthritis (OA).

METHODS

Twenty female 15-week-old Sprague-Dawley rats were used. Five rats in each group underwent bilateral OVX (OVX group), bilateral ACLT with MM (ACLT with MM group), bilateral OVX plus ACLT with MM (OVX plus ACLT with MM group), and sham surgery (SHAM group). All the rats were subjected to treadmill running for 4 weeks. The behavioral evaluation for induction of OA used the number of rears method, and this was conducted at 1, 2, and 4 weeks post-surgery. Bone mineral density (BMD) was calculated with micro-computerized tomography images and the modified Mankin's scoring was used for the histological changes.

RESULTS

The number of rears in the OVX plus ACLT with MM group decreased gradually and more rapidly in the ACLT with MM group. Histologically, the OVX plus ACLT with MM group had a significantly higher modified Mankin's score than the OVX group (p=0.008) and the SHAM group (p=0.008). BMDs of the OVX plus ACLT with MM group were significantly lower than the SHAM group (p=0.002), and the ACLT with MM group (p=0.003).

CONCLUSION

We found that bilateral OVX plus ACLT with MM induced definite OA change in terms of histology and BMD compared to bilateral OVX and ACLT with MM alone. Therefore, OVX and ACLT with MM was an appropriate degenerative OA rat model.

Serum estradiol and sex hormone-binding globulin and the risk of hip fracture in elderly women: the EPIDOS study

It has been suggested that low serum 17beta-estradiol (E2) and sex hormone-binding globulin (SHBG) may predict hip fracture in postmenopausal women. We have investigated the predictive value of serum E2 and SHBG concentrations and urinary deoxypyridinoline (D-Pyr) and type I collagen breakdown products (CTX) in a large prospective cohort of 7,598 healthy elderly ambulatory women (EPIDOS study), aged 75 years or more. We performed a nested case control study, by matching 212 patients with incident hip fracture with 636 controls. Mean follow-up was 3.3 years (maximum, 4.9 years). Women having serum E2 below the limit of detection (3 pg/ml), that is, 2% of the population, were not at higher risk, with a relative hazard (RH) of 1.59 (95% CI = 0.45-5.55). Women having serum E2 below 5, 6, 7, or 8 pg/ml, in the lowest quartile, or below the median had no increased risk of hip fracture. In contrast, women having serum E2 in the highest quartile (i.e., > or = 10 pg/ml) were protected, with an RH of 0.66 (0.44-0.98) that did not remain significant after adjustment for weight (RH = 0.71 [0.47-1.06]). High serum SHBG values with different cut-offs tended to be associated with an increased risk of hip fracture. Women in the highest quartile had an RH of 2.5 (1.37-4.61), compared with those in the lowest quartile, that decreased markedly after adjustment for body weight (1.61 [0.99 -2.62]). The highest quartile of the ratio E2/SHBG, which is an index of free E2, was associated with a lower hip fracture risk (RH = 0.6 [0.4-0.91]) that was no longer significant after adjustment for weight. In contrast, urinary D-Pyr and CTX, when elevated above the upper limit of premenopausal values, were predictive of hip fracture, with an RH of 2.07 (1.49-2.9) and 1.67 (1.19-2.32), respectively, even after adjustment for body weight, serum E2, and SHBG. We conclude that in healthy elderly French women over 75 years of age, serum E2 and E2/SHBG in the highest quartile are associated with a lower risk of hip fracture and that this association is explained by a higher body weight. In addition, serum levels of E2 and SHBG do not account for the increased risk of hip fracture associated with high levels of bone resorption markers.

Zoledronate prevents the development of absolute osteopenia following ovariectomy in adult rhesus monkeys

This study assessed effects of the bisphosphonate zoledronate (ZLN) on bone density and biochemical markers of bone turnover in ovariectomized (OVX) adult female rhesus monkeys. Forty monkeys were randomly assigned to one control or four OVX groups. The control and one OVX group received saline, and the other three OVX groups received ZLN (0.5, 2.5, or 12.5 microg/kg) by a single weekly subcutaneous injection for 69 weeks. Bone mass of the total body (TB), lumbar spine (LS), distal and central radius (dual-energy X-ray absorptiometry), and skeletal turnover markers were measured at baseline and at 13, 26, 39, 52, and 69 weeks of treatment. Increased skeletal turnover and decreased bone mass (LS and TB) were demonstrable by 13 weeks post-OVX. Maximal bone loss (7-8%) at these sites occurred by 39 weeks after OVX and persisted for the study duration. Long-term ZLN treatment was well tolerated and prevented increased skeletal turnover and bone loss in a dose-dependent fashion. Progressive turnover suppression was not observed with any ZLN dose. In conclusion, after OVX, adult rhesus monkeys develop persistent increased bone turnover and absolute osteopenia of the LS and TB, making them an outstanding model of skeletal behavior in perimenopausal women. These OVX-related skeletal changes are dose-dependently blocked by ZLN.

The preventive and interventional effects of raloxifene analog (LY117018 HCL) on osteopenia in ovariectomized rats

The effects of LY117018 HCL (LY) treatment on bone metabolism, spine bone mineral density (BMD), bone mineral content (BMC), and serum cholesterol were studied in ovariectomized (OVX) rats. Experiment 1 was designed to observe the preventive effects of LY on bone loss due to ovariectomy (OVX; prevention study). The rats were divided into three groups: sham group, OVX + vehicle, and OVX + LY. LY was administrated at the same time of OVX. Experiment 2 was designed to investigate the interventional effects of LY on OVX rats with osteopenia (intervention study). The rats were divided into the sham and OVX groups, first. The OVX rats were allowed to lose bone for 6 weeks. At 6 weeks post-OVX, the OVX rats were divided into two groups: OVX + vehicle and OVX + LY. The longitudinal effects of LY on bone were studied by dual-energy X-ray absorptiometry and biochemical markers including urinary pyridinoline (Pyr), deoxypyridinoline (Dpyr), and serum osteocalcin. Urinary Pyr and Dpyr increased maximally at 6 weeks post-OVX, decreased at 12 and 18 weeks post-OVX, although the OVX rats had significantly higher levels of Pyr and Dpyr than the sham group during the experiment. LY was a very potent inhibitor of Pyr and Dpyr excretion while at the same time only partially reducing the bone loss in the high turnover phase at 6 weeks postovariectomy. However, at the later time points at 12 and 18 weeks, no further bone loss occurred in rats treated with LY, while the vehicle-treated group lost another 10% in spine BMD and BMC. LY also completely blocked further bone loss when used in an intervention protocol. LY significantly reduced serum cholesterol levels in OVX rats. The results suggest that LY is not fully protective during the early rapid bone loss phase, but the compound is fully protective during the later slow phase of bone loss in both the protocols.

Risedronate increases bone mass in an early postmenopausal population: two years of treatment plus one year of follow-up

This double-blind, placebo-controlled study was undertaken to determine 1) the efficacy of oral risedronate for prevention of bone loss in healthy, early postmenopausal patients with normal bone mass, 2) the effect on bone mass when treatment was stopped, and 3) the safety and tolerance of risedronate in this population. A group of 111 patients were randomized to oral placebo, risedronate 5 mg daily, or risedronate 5 mg cyclically, for 2 yr followed by 1 yr off treatment. Measurements included percentage change from baseline in lumbar spine bone mineral density (BMD) at 24 months; percentage change from baseline in BMD of the femoral neck, trochanteric region, and Ward's triangle region of the proximal femur; and changes in biochemical markers of bone turnover. After 2 yr, there was a mean increase in BMD of the lumbar spine of 1.4% from baseline and of 5.7% vs. placebo in the risedronate 5 mg daily group. There were decreases from baseline in BMD of 1.6% and 4.3% in the risedronate 5 mg cyclic and placebo groups, respectively. By the end of 24 months, trochanteric bone mass at the hip increased by 5.4% in the risedronate 5 mg daily group and by 3.3% in the risedronate 5 mg cyclic group vs. placebo. Bone mass was maintained at the femoral neck in the 2 active-treatment groups vs. a 2.4% mean loss with placebo. During the treatment-free follow-up, bone turnover increased toward baseline in both risedronate groups. By the end of that year, lumbar spine bone mass in all 3 groups was lower than at baseline. Oral risedronate was well tolerated. We conclude that risedronate (5 mg daily) increases bone mass and risedronate (5 mg cyclic) appears to prevent bone loss in early postmenopausal women with normal BMD.

Androgens and bone

Androgen receptors are present at low densities in osteoblasts. Androgens are also metabolized in bone. (Non)aromatizable androgens probably induce proliferation of osteoblasts and differentiation. A direct effect of androgens on osteoclasts has not been demonstrated. Androgens may however inhibit bone resorption indirectly, by an inhibition of the recruitment of osteoclast precursors from bone marrow, by decreased secretion of interleukin-6 and/or prostaglandin E2, and/or by an increased sensitivity of marrow cells or osteoblasts for bone resorption stimulating factors such as PTH. The recent demonstration of androgen receptors in bone marrow stromal and osteoclast-like cells opens new perspectives in this respect. During puberty, androgens stimulate bone growth both directly and indirectly. Observations in androgen-resistant animals clearly demonstrated that the sexual dimorphism of bone depends on the presence of a functional androgen receptor. Optimal peak bone mass seems related to an appropriately timed androgen secretion. In adults, androgens are also involved in maintenance of the male skeleton. Androgen replacement may prevent further bone loss in hypogonadal men, however, it seems difficult to fully correct bone mass in these men.

Bone and mineral metabolism in the adult guinea pig: long-term effects of estrogen and androgen deficiency

The effects of androgen and estrogen deficiency on skeletal homeostasis were studied in the guinea pig. Male and female adult (7 months old) guinea pigs were either sham operated (9 females and 7 males) or gonadectomized [9 ovariectomized (OVX) females and 6 orchidectomized (ORX) males] and sacrificed 4 months later for evaluation of bone mass, bone turnover, and serum calcium homeostasis. Parameters of bone turnover, calcium homeostasis, and vitamin D metabolites were similar in all groups except for increased serum IGF-I concentrations (+30%) in males compared to females. Gonadectomy resulted in a 50% decrease in serum IGF-I concentrations in males only (p < 0.001). Volume, total calcium content, and cortical density of the tibia were significant higher in males than in females. Estrogen deficiency had no effect on bone volume or calcium content. Androgen deficiency resulted in a significant lower volume and calcium content of the tibia and in a lower calcium content of the distal lumbar vertebrae. Single-photon absorptiometry of the tibia showed that only cortical, not trabecular bone density of the tibia was decreased after ORX. Histomorphometric studies of the tibial metaphysis also did not show significant differences in trabecular bone volume between sham-operated and ORX males. We conclude that in adult male guinea pigs androgen deficiency results in a decrease in (cortical) bone volume and content concomitant with decreased IGF-I levels. In female guinea pigs of the same age, estrogen deficiency did not affect total or regional bone mass.