The prevention and treatment of osteoporosis: a review

Osteoporosis is a disorder characterized by reduced bone strength, diminished bone density, and altered macrogeometry and microscopic architecture. Adult bone mass is the integral measurement of the bone mass level achieved at the peak minus the rate and duration of subsequent bone loss. There is clearly a genetic predisposition to attained peak bone mass, which occurs by a person's mid-20s. Bone loss with age and menopause are universal, but rates vary among individuals. Both peak bone mass and subsequent bone loss can be modified by environmental factors, such as nutrition, physical activity, and concomitant diseases and medications. Osteoporosis prevention requires adequate calcium and vitamin D intake, regular physical activity, and avoiding smoking and excessive alcohol ingestion. Risk of fracture determines whether medication is also warranted. A previous vertebral or hip fracture is the most important predictor of fracture risk. Bone density is the best predictor of fracture risk for those without prior adult fractures. Age, weight, certain medications, and family history also help establish a person's risk for osteoporotic fractures. All women should have a bone density test by the age of 65 or younger (at the time of menopause) if risk factors are present. Guidelines for men are currently in development. Medications include both antiresorptive and anabolic types. Antiresorptive medications--estrogens, selective estrogen receptor modulators (raloxifene), bisphosphonates (alendronate, risedronate, and ibandronate) and calcitonins--work by reducing rates of bone remodeling. Teriparatide (parathyroid hormone) is the only anabolic agent currently approved for osteoporosis in the United States. It stimulates new bone formation, repairing architectural defects and improving bone density. All persons who have had osteoporotic vertebral or hip fractures and those with a bone mineral density diagnostic of osteoporosis should receive treatment. In those with a bone mineral density above the osteoporosis range, treatment may be indicated depending on the number and severity of other risk factors.     

Impact of aromatase inhibitors on bone health in breast cancer patients

Following the implementation of the third generation aromatase inhibitors in the treatment algorithms for early breast cancer, special attention has been given to the influence of these drugs on bone health. Due to their potent estrogen suppression, the aromatase inhibitors anastrozole and letrozole, as well as the aromatase inactivator exemestane, enhance bone loss in postmenopausal women reflected in decreasing levels of bone mineral density. Moreover, all major phase III trials involving aromatase inhibitors in the adjuvant setting have reported increased fracture rates. All in all, there is no hard evidence to suggest major differences between the individual compounds concerning their side-effects on bone. The consequences of AI therapy on bone are in addition modified by a variety of factors like the BMD level prior to therapy, time since menopause, and vitamin D status. Strategies to avoid bone loss during AI therapy have shown promising results. Thus, bisphosphonates have been shown to prohibit bone loss during AI therapy if used upfront. Novel treatment strategies, like antibodies against RANKL have been developed and promising preliminary results have been published from early trials. Standardized guidelines to avoid or minimize bone loss during AI therapy have been developed, in most countries involving calcium and vitamin D supplementation, as well as BMD measurements to identify patient subgroups demanding bisphosphonate therapy.     

Chemoprevention with aromatase inhibitors--trial strategies

Estrogen and its catechol metabolites from both the circulation and synthesized within the breast are important in the pathogenesis of breast cancer. Blocking estrogen's effects on the breast with selective estrogen receptor modulators (SERMS) is an ongoing strategy. Thus, tamoxifen and raloxifene reduce risk as monotherapy. Aromatase (estrogen synthetase) inhibitors are a logical alternative to SERMS. To date, SERMS have demonstrated reduction only in estrogen–progesterone receptor positive cancers without reduction in receptor negative tumors. By inhibiting the parent estrogens and their catechol metabolites, true prevention of cancer initiation might occur and reduction not only in the receptor positive but also negative tumors might result. Ongoing adjuvant breast cancer trials are exploring aromatase inhibitors as alternatives to tamoxifen, or in sequence or in combination with tamoxifen. Relative efficacies including reduction in contralateral breast cancer, toxicities and end-organ effects and impact on quality of life, are being explored. Data from these trials will help to guide future chemoprevention strategies. Proof of principal trials in ‘high risk’ cohorts such as premalignant breast lesions, dense screening mammograms, high plasma estradiol levels or increased bone density are already ongoing. Issues such as dose, schedule, therapeutic index and mono versus combination therapy are important to define.     

Estrogenic side effects of androgen deprivation therapy

Androgen deprivation therapy (ADT) is part of standard therapy for locally advanced or metastatic prostate cancer and is frequently used in men with a rising prostate-specific antigen following radical prostatectomy or radiation therapy. In some men, ADT may be administered for years or even decades. The intended therapeutic effect of ADT is testosterone deficiency. Because estrogen is a normal metabolite of testosterone, ADT also results in estrogen deficiency. ADT has a variety of adverse effects, many of which are primarily related to estrogen deficiency. Bone mineral density may decrease by 4% to 13% per year in men receiving ADT. The fracture rate for patients on ADT averages 5% to 8% per year of therapy. Hot flashes, gynecomastia, and breast tenderness are common side effects associated with ADT. In the clinic, minimum baseline testing should include weight measurement, blood pressure reading, and fasting lipid panel and serum glucose tests. Currently, there are no large outcome trials in men on ADT testing the available therapies for adverse effects. No therapies are specifically approved for treatment of adverse effects in men on ADT. Although some therapies can be used for a single indication (based upon small studies), there is currently no agent to treat the multiple estrogenic side effects of ADT.     

Selective estrogen receptor modulators to prevent treatment-related osteoporosis

The intended therapeutic effect of gonadotropin-releasing hormone (GnRH) agonists is hypogonadism, which is a leading cause of osteoporosis in men. Consistent with this observation, GnRH agonists decrease bone mineral density and increase fracture risk in men with prostate cancer. GnRH agonists markedly decrease serum levels of both testosterone and estrogen. Estrogens play a central role in homeostasis of the normal male skeleton, and the available evidence suggests that estrogen deficiency rather than testosterone deficiency accounts for the adverse skeletal effects of GnRH agonists. The central role of estrogens in male bone metabolism provides a strong rationale to evaluate selective estrogen receptor modulators for prevention of treatment-related osteoporosis in men with prostate cancer. Preliminary evidence suggests that both raloxifene and toremifene increase bone mineral density in GnRH agonist-treated men. An ongoing pivotal study will evaluate the effects of toremifene on fractures and other complications of GnRH agonists in men with prostate cancer.     

Menopausal hormone therapy and cancer: Changing clinical observations of target site specificity

Menopausal hormone therapy with estrogen plus progestin or estrogen alone (for women with prior hysterectomy) is still used by millions of women for climacteric symptom management throughout the world. Until 2002, hormone therapy influence on cancer risk and other chronic diseases was determined through observational study reports. Since then, results from the Women’s Health Initiative randomized, placebo-controlled hormone therapy trials have substantially changed concepts regarding estrogen plus progestin and estrogen alone influence on the most common cancers in postmenopausal women. In these trials, estrogen plus progestin significantly increased breast cancer incidence and deaths from breast cancer, significantly increased deaths from lung cancer, significantly decreased endometrial cancer, and did not have a clinically significant influence on colorectal cancer. In contrast, estrogen alone use in women with prior hysterectomy significantly reduced breast cancer incidence and deaths from breast cancer without significant influence on colorectal cancer or lung cancer. These complex results are discussed in the context of known potential mediating mechanisms of action involved in interaction with steroid hormone receptors.     

Tamoxifen prevents bone loss in castrated male mice.

The selective estrogen receptor modulator tamoxifen was administered to intact and castrated male mice, and its effects on tibial bones and circulatory calcium, phosphate and testosterone were compared with controls and castrated animals. Tamoxifen in a dose used in humans for treatment of breast cancer decreased the weight of seminal vesicles, an organ which is highly sensitive to the androgenic effect, decreased the concentration of testosterone, but did not have any negative effect on bone density or mineral content in intact mice. When castrated mice with extraordinarily low concentrations of testosterone and weights of seminal vesicles were treated with tamoxifen, the changes in bone density and bone mineral resulting from castration were not only entirely prevented, but increased above the values of intact mice. At the same time, cortical bone was lost in orchidectomized mice, and this decrease in cortical thickness of femur was completely prevented by tamoxifen treatment. Pharmacological therapy with estrogen agonist on bone, tamoxifen in androgen deficient adult male mice prevents bone loss.     

Stéroides sexuels et ostéoporose chez l'homme

Several epidemiological studies have shown that about 25 per cent of hip fractures and 20 per cent of symptomatic vertebral fractures occur in men. The lifetime risk of hip fracture was estimated to be about 6 to 8 per cent and the risk of any osteoporotic fracture was estimated to be about 18 per cent in 50-year-old white men. In about 60% of cases in men, bone loss is secondary to several pathological conditions, such as long-term steroid therapy, severe hypogonadism, smoking or alcohol abuse or gastrointestinal disorders. In 40% of cases, osteoporosis is primary or idiopathic in men between the ages of 40 and 60 years. Genetic factors, a defect of boneforming cells or abnormal serum levels of bioavailable sex steroids could explain bone loss and fragility fractures in these men. It has been shown that hypogonadism is associated with a marked increase in bone remodelling and particularly in bone resorption with a dramatic loss in trabecular bone. It is now known that testosterone is partly transformed into estradiol by aromatase. Testosterone may therefore act on bone in two ways: it directly stimulates bone formation and estradiol regulates bone remodelling and inhibits bone resorption. Finally, in men over the age of 60 without hypogonadism, it has been shown that bone mineral density and fracture risk were better correlated with serum levels of bioavailable estradiol and Sex Hormone Binding Globulin than with serum testosterone levels.     

Managing Bone Health in Breast Cancer

ObjectiveOsteoporosis is a common condition that can be caused or exacerbated by estrogen deficiency.MethodsThis narrative review will discuss optimizing bone health in the setting of adjuvant endocrine treatments for hormone receptor–positive breast cancer and the current use of antiresorptive agents as adjuvant therapy and as bone modifying agents.ResultsAdjuvant endocrine treatments for hormone receptor–positive breast cancer (tamoxifen and aromatase inhibitors) affect bone health. The exact effect depends on the agent used and the menopausal state of the woman. Antiresorptive medications for osteoporosis, bisphosphonates and denosumab, lower the risk of bone loss from aromatase inhibitors. Use of bisphosphonates as adjuvant treatment in breast cancer, regardless of hormone receptor status, is increasing because of benefits seen to cancer relapse and survival.ConclusionOptimizing bone health in women with breast cancer during and after cancer treatment is informed by an understanding of breast cancer treatment and its skeletal effect.     

Aromatase inhibitors and bone

The decrease in estrogen levels with the use of aromatase inhibitors results in an increase in the rate of bone remodelling. This result in an acceleration of bone loss, and probably to an increase in the risk of fractures. The risk of fracture is particularly high in the older woman and in the woman with a low bone mineral density. We have a number of proven treatments for the treatment of postmenopausal osteoporosis and it is likely that some of these, particularly bisphosphonates, could be effective at preventing bone loss with aromatase inhibitors.     

A Retrospective Review of Patients with Atypical Femoral Fractures While on Long-Term Bisphosphonates: Including Pertinent Biochemical and Imaging Studies

ObjectiveTo elucidate the effects of prolonged bisphosphonate (BP) exposure on the development of atypical fragility fractures, and to define the associated risk factors.MethodsApproval was obtained from the institutional review board, and a retrospective chart analysis was performed on 51 patients who had been on BPs for at least 3 years and had complete subtrochanteric or diaphyseal femoral fracture(s) between January 2005 and April 2011. All relevant data were available for 25 patients (mean age, 67.52 years). All fractures included in the study were low- or no-energy. Relevant clinical and demographic data were collected regarding age, gender, ethnicity, height, weight, and comorbid medical conditions. Imaging and laboratory data collected on all patients included: calcium, alkaline phosphatase, 25-hydroxyvitamin D (25-OHD), intact parathyroid hormone, serum c-telopeptide, and urine n-telopeptide levels, bone mineral density, radiography, and magnetic resonance imaging.ResultsMost of the patients in this study were Caucasian, were on alendronate, had bilateral findings, and almost half had prodromal symptoms. The 25-OHD level was suboptimal (<30 ng/mL) in 45.8% of the patients. Mean BP duration was 9.84 years, and mean bone density was in the osteopenic, not osteoporotic, range.ConclusionCharacteristics of patients with atypical BP-related fracture include relatively young age, long duration of BP use, suboptimal 25-OHD level, and bone density in the nonosteoporotic range. All of these may be significant risk factors for insufficiency fracture development. (Endocr Pract. 2013;19:456-461)     

Prediction of osteoporotic fractures by postural instability and bone density.

OBJECTIVE--To investigate the utility of risk factors such as bone mineral density, lifestyle, and postural stability in the prediction of osteoporotic fractures. DESIGN--Longitudinal, epidemiological, and population based survey. SETTING--City of Dubbo, New South Wales. SUBJECTS--All residents of Dubbo aged > or = 60 on 1 January 1989. MAIN OUTCOME MEASURE--Incidence of fracture for individual subjects. RESULTS--The overall incidence of atraumatic fractures in men and women was 1.9% and 3.1% per annum respectively. The predominant sites of fracture were hip (18.9%), distal radius (18.5%), ribs and humerus (11.9% in each case), and ankle and foot (9.1% and 6.6% respectively). Major predictors of fractures in men and women were femoral neck bone mineral density, body sway, and quadriceps strength. Age, years since menopause, height, weight, and lifestyle factors were also correlated with bone mineral density and body sway and hence were indirect risk factors for fracture. Discriminant function analysis correctly identified 96% and 93% (sensitivities 88% and 81%) of men and women, respectively, who subsequently developed atraumatic fractures. Predictions based on this model indicated that a woman with a bone mineral density in the lowest quartile in the hip together with high body sway had a 8.4% probability of fracture per annum. This represented an almost 14-fold increase in risk of fracture compared with a woman in the highest bone mineral density quartile with low postural sway. An individual with all three predictors in the "highest risk" quartile had a 13.1% risk of fracture per annum. CONCLUSIONS--Bone mineral density, body sway, and muscle strength are independent and powerful synergistic predictors of fracture incidence.     

Forkhead proteins are critical for bone morphogenetic protein-2 regulation and anti-tumor activity of resveratrol

Osteoporosis is a major public health problem and the most obvious preventive strategy, hormone replacement therapy, has lost favor due to recent findings of the Women's Health Initiative regarding increased risks of breast cancer and cardiovascular disease. Resveratrol, a naturally occurring compound possessing estrogenic activity, is thought to have considerable potential for therapy of osteoporosis. In the present study, resveratrol was found to exhibit bone-protective effects equivalent to those exerted by hormone replacement therapy and decrease the risk of breast cancer in the in vivo and in vitro models. Forkhead proteins were found to be essential for both effects of resveratrol. The bone-protective effect was attributable to induction of bone morphogenetic protein-2 through Src kinase-dependent estrogen receptor activation and FOXA1 is required for resveratrol-induced estrogen receptor-dependent bone morphogenetic protein-2 expression. The tumor-suppressive effects of resveratrol were the consequence of Akt inactivation-mediated FOXO3a nuclear accumulation and activation. Resveratrol is therefore anticipated to be highly effective in management of postmenopausal osteoporosis without an increased risk of breast cancer.     

Impact of Weight‐Cycling History on Bone Density in Obese Women

Objective: The purpose of this study was to examine the effect of weight cycling (as defined by the frequency and magnitude of intentional weight loss) on bone mineral density and bone mineral content in obese sedentary women. Research Methods and Procedures: Bone mineral content and density measured by DXA, submaximal physical fitness assessment, nutrient intake, oral contraceptive use, and weight‐cycling history were assessed in 195 healthy, overweight sedentary women (age, 21 to 45 years; body mass index, 27 to 40 kg/m²) before beginning a behavioral weight‐loss intervention. Results: After controlling for body weight, multivitamin use, oral contraceptive/estrogen use, and calcium and magnesium intake, women who had a history of weight cycling did not have significantly lower total‐body bone mineral content or density or total femur bone mineral density. In addition, 99% of subjects were above or within one SD of age and gender normative data for total femur bone mineral density. Discussion: It does not seem that a history of weight cycling has an adverse affect on total femur and total‐body bone mineral density in overweight sedentary premenopausal women.     

Long-term effects of aromatase inhibitors on bone

The risk of fracture in the postmenopausal woman given aromatase inhibitors may be increased by up to 60%. This is likely to be true for all third generation drugs, but the clinical trials did not include sufficient fracture events for certainty on this issue. It would appear that most of the excess fracture risk relates to vertebral fracture and in future studies, more effort should be given to ascertaining these fractures. The likely mechanism for the increase in fracture risk is an increase in bone turnover (of about 20%) and an acceleration of bone loss. There is evidence to suggest that the residual levels of oestradiol present in the postmenopausal woman are important for bone health, and thus, the effect of these drugs is to remove this protective effect. Current clinical practice should include the measurement of bone mineral density in postmenopausal women taking these drugs and commencement of antiresorptive therapy if osteoporosis is already present.     

Selective estrogen receptor modulators (SERMs) in the practice

Selective estrogen receptor modulators (SERMs) represent a growing class of compounds that act as either estrogen receptor gonists or ntagonists in tissue-selective manner. SERMs with the appropriate selectivity profile offer the opportunity to dissociate the favorable bone and cardio-vascular effects of estrogen from its unfavorable stimulatory effects on the breast and uterus. The triphenylethylene drug tamoxifen proved to be invaluable to treat and protect against breast cancer and bone loss, probably reduces cardiovascular risk, but had side effects on uterus similar to natural estrogens. The tamoxifen derivate toremifene is also used to treat breast cancer, but has less effect on bone. The non-steroidal benzothiophene derivate, raloxifene, is the best SERM available thus far. It has the potential to prevent breast cancer (like tamoxifen), but has better profile in its actions on bone and cardiovascular system (produces a rapid reduction of serum cholesterol, decreases fibrinogen and lipoprotein, improves the vascular epithelial function, attenuates vascular intimal thickening, etc.). It does not increase the incidence of endometrial cancer. Compounds of this class are the first step in developing the perfect hormone replacement and other multitargeted therapy. This review summarizes the recent important knowledge about SERMs.     

Influence of vitamin D receptor genotype on bone mineral density in postmenopausal women: a twin study in Britain.

OBJECTIVES--To investigate the possible association between vitamin D receptor genotype and bone mineral density in a large group of postmenopausal twins. DESIGN--Cross sectional twin study. SETTING--Twin population based in Britain. SUBJECTS--95 dizygotic (non-identical) pairs of twins and 87 monozygotic (identical) pairs of twins aged 50-69 years, postmenopausal, and free of diseases affecting bone, recruited from a national register of twins and with a media campaign. MAIN OUTCOME MEASURES--Bone mineral density measured at the hip, lumbar spine, forearm, and for the whole body by dual energy x ray absorptiometry in relation to differences in the vitamin D receptor genotype. RESULTS--At all sites the values of bone density among dizygotic twins were more similar in those of the same vitamin D receptor genotype than in those of differing genotype, and the values in the former were closer to the correlations seen in monozygotic twins. Women with the genotype that made them at risk of osteoporotic fracture had an adjusted bone mineral density that was significantly lower by SD 0.5 to 0.6 at the hip, lumbar spine, and for the whole body. The results could not be explained by differences in age, weight, years since menopause, or use of hormone replacement therapy. CONCLUSIONS--The findings that in postmenopausal women in Britain bone density-particularly at the hip and spine-is genetically linked and specifically associated with the vitamin D receptor genotypes should lead to novel approaches to the prevention and treatment of osteoporosis.     

Targeted anti-estrogens to treat and prevent diseases in women

The estrogen receptor has been successfully targeted with the anti-estrogen tamoxifen to treat all stages of breast cancer. Because tamoxifen is a partial agonist, it exhibits target-site specificity: it acts as an anti-estrogen in the breast to inhibit tumor growth, while exhibiting estrogenic effects on bones and lipid metabolism. Therefore, tamoxifen has the added benefit of maintaining bone density and reducing the risk of myocardial infarction in postmenopausal women.However, undesirable side effects of tamoxifen preclude its use as a hormone replacement therapy for otherwise healthy women. New anti-estrogens are currently being developed that may prevent osteoporosis, breast and endometrial cancer, and reduce the risk of myocardial infarction.     

Steroids and human breast cancer.

Normal mammary gland cells are sensitive to a number of hormones, of which estrogen and prolactin exert the most obvious effects. Some breast cancer cells are also sensitive. Cytoplasmic receptor sites for each hormone are responsible for the interaction between the hormone and the cell. The presence of estrogen receptor has been especially studied in humans. Data collected from several sources are reviewed. The prese nce of estrogen receptors has been assayed in 154 primary breast tumors and 72 metastatic breast tumors for correlation with response to endocri ne therapy. Positive values were found in 70% of primary and 58% of metastatic specimens. Of 211 treatment trials, ablative therapy produced objective tumor regressions in 33%. Of the 94 trials with negative receptor values, only 8 were successful while 59 of the 107 trials in patients with positive receptor values succeeded. In those with borderline tumor receptor, values had a 30% response. With additive therapy, 34% of 170 trials showed tumor regression. Of these, 82 had negat ive receptor values but 8% were successful, whereas of 85 with positive receptor values, 60% were favorable. With miscellaneous therapy, 27% of 55 trials gave responses to a variety of endocrine therapies, including antiestrogens. The 32 with negative receptor values gave 16% of favorable responses whereas 43% of 23 trials in those with positive receptor values succeeded. Estrogen receptor assays performed routinely would spare patients with negative results from unnecessary major ablative therapy. Of those with positive findings, 55-60% might be benefited. The fact that all with positive receptor values do not respond is attributed to the fact that this is only part of the hormonal control system. Other biochemical lesions are assumed to have occurred in patients when endocrine therapy fails despite positive estrogen receptor levels as measured.     

Bone material properties and mineral matrix contributions to fracture risk or age in women and men

The strength of bone is related to its mass and geometry, but also to the physical properties of the tissue itself. Bone tissue is composed primarily of collagen and mineral, each of which changes with age, and each of which can be affected by pharmaceutical treatments designed to prevent or reverse the loss of bone. With age, there is a decrease in collagen content, which is associated with an increased mean tissue mineralization, but there is no difference in cross-link levels compared to younger adult bone. In osteoporosis, however, there is a decrease in the reducible collagen cross-links without an alteration in collagen concentration; this would tend to increase bone fragility. In older people, the mean tissue age (MTA) increases, causing the tissue to become more highly mineralized. The increased bone turnover following menopause may reduce global MTA, and would reduce overall tissue mineralization. Bone strength and toughness are positively correlated to bone mineral content, but when bone tissue becomes too highly mineralized, it tends to become brittle. This reduces its toughness, and makes it more prone to fracture from repeated loads and accumulated microcracking. Most approved pharmaceutical treatments for osteoporosis suppress bone turnover, increasing MTA and mineralization of the tissue. This might have either or both of two effects. It could increase bone volume from refilling of the remodeling space, reducing the risk for fracture. Alternatively, the increased MTA could increase the propensity to develop microcracks, and reduce the toughness of bone, making it more likely to fracture. There may also be changes in the morphology of the mineral crystals that could affect the homogeneity of the tissue and impact mechanical properties. These changes might have large positive or negative effects on fracture incidence, and could contribute to the paradox that both large and small increases in density have about the same effect on fracture risk. Bone mineral density measured by DXA does not discriminate between density differences caused by volume changes, and those caused by changes in mineralization. As such, it does not entirely reflect material property changes in aging or osteoporotic bone that contribute to bone's risk for fracture.