The ability of statins to inhibit bone resorption is directly related to their inhibitory effect on HMG-CoA reductase activity

Immunomodulating role of bisphosphonates on human gamma delta T cells: an intriguing and promising aspect of their antitumour activity

Vgamma9Vdelta2 T cells have the ability to produce inflammatory cytokines involved in protective immunity against intracellular pathogens and tumours and to display strong cytolytic as well as bactericidal activities. This suggests a direct involvement of Vgamma9Vdelta2 T lymphocytes in immune control of cancer and infections. These observations have recently aided development of novel immunotherapeutic approaches aimed at Vgamma9Vdelta2 T cell activation. Nitrogen-containing bisphosphonates (N-BPs) play a crucial role in Vgamma9Vdelta2 T lymphocyte activation and in the acquisition of effector functions. The preliminary results of these innovative strategies are encouraging. Moreover, compelling evidence in the literature supports the hypothesis that the antitumour effect of bisphosphonates is exerted through direct as well as indirect mechanisms. An additional and not yet well explored mechanism by which N-BPs may display antineoplastic effect is related to their immunomodulatory properties. It is fascinating that N-BPs influence the immune system in various but interrelated ways, being able to enhance the innate and to promote the adaptive immune responses. For all these reasons, Vgamma9Vdelta2 T lymphocytes represent a particularly interesting target for immunotherapeutic protocols based on N-BP administration. All these unexpected effects of N-BPs on the immune system have opened new and intriguing possibilities of therapeutic use for these drugs.

Distribution of lovastatin to bone and its effect on bone turnover in rats

Statins, the widely used lipid-lowering drugs, are inhibitors of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase, which catalyses a rate-limiting step in the biosynthesis of cholesterol. Many previous reports show that statins can act both as bone anabolic and as anti-resorptive agents but their beneficial effects on bone turnover are still controversial. Considering their high liver specificity and low oral bioavailability, the distribution of statins to the bone microenvironment is questionable. In this study, the distribution of lovastatin and its active metabolites to bone, with respect to plasma and liver compartments, was examined after oral and intravenous administration in female rats. As compared with oral administration, the distribution of lovastatin to the bone compartment was significantly enhanced after intravenous administration. Further, the effect of lovastatin on bone turnover was studied in-vitro and in-vivo to assess its anti-osteoporotic potential. Lovastatin acid but not lovastatin was found to inhibit parathyroid-hormone-induced bone resorption in an in-vitro chick embryo bone assay. Oral, as well as intravenous, short-term lovastatin treatment significantly reduced the serum total cholesterol, serum total alkaline phosphatase and urinary crosslinks in ovariectomized rats. In accordance with its increased distribution to the bone compartment, intravenously administered lovastatin was more effective in reducing the ovariectomy-induced increase in markers of bone metabolism, especially urinary crosslinks. The findings of this study suggest that statins inhibit bone resorption and that their anti-resorptive efficacy can be increased by administering them by routes other than oral so as to achieve their enhanced concentration in bone.

Serum leptin and adiponectin are positively associated with bone mineral density at the distal radius in patients with type 2 diabetes mellitus

There have been several reports about associations of serum leptin or adiponectin with bone mineral density and biochemical markers of bone turnover. However, the precise roles of adipocytokines in bone metabolism have not been fully elucidated. We investigated the associations of serum level of leptin or adiponectin with bone mineral density, serum osteocalcin, and urinary N-terminal telopeptide of type I collagen (NTX) in 40 Japanese patients with type 2 diabetes mellitus. Bone mineral density was measured by using dual-energy x-ray absorptiometry at different sites (distal radius, femoral neck, and lumbar spine) and was expressed as z score. Multiple regression analysis revealed that there were significant positive correlations between serum leptin or adiponectin level and z score at the distal radius, but not at the femoral neck or the lumbar spine. Although no correlation was observed between serum leptin and serum osteocalcin, there was a significant negative correlation between serum leptin and urinary NTX, a marker of bone resorption. No correlation was observed between serum adiponectin and serum osteocalcin or urinary NTX. These results indicate that leptin and adiponectin may have a protective effect on bone metabolism in patients with type 2 diabetes mellitus.

Discovery of a small molecule antagonist of the parathyroid hormone receptor by using an N-terminal parathyroid hormone peptide probe

Once-daily s.c. administration of either human parathyroid hormone (PTH)-(1-84) or recombinant human PTH-(1-34) provides for dramatic increases in bone mass in women with postmenopausal osteoporosis. We initiated a program to discover orally bioavailable small molecule equivalents of these peptides. A traditional high-throughput screening approach using cAMP activation of the PTH/PTH-related peptide receptor (PPR) as a readout failed to provide any lead compounds. Accordingly, we designed a new screen for this receptor that used a modified N-terminal fragment of PTH as a probe for small molecule binding to the transmembrane region of the PPR, driven by the assumption that the pharmacological properties (agonist/antagonist) of compounds that bound to this putative signaling domain of the PPR could be altered by chemical modification. We developed DPC-AJ1951, a 14 amino acid peptide that acts as a potent agonist of the PPR, and characterized its activity in ex vivo and in vivo assays of bone resorption. In addition, we studied its ability to initiate gene transcription by using microarray technology. Together, these experiments indicated that the highly modified 14 amino acid peptide induces qualitatively similar biological responses to those produced by PTH-(1-34), albeit with lower potency relative to the parent peptide. Encouraged by these data, we performed a screen of a small compound collection by using DPC-AJ1951 as the ligand. These studies led to the identification of the benzoxazepinone SW106, a previously unrecognized small molecule antagonist for the PPR. The binding of SW106 to the PPR was rationalized by using a homology receptor model.

The Interleukin-6 inflammation pathway from cholesterol to aging--role of statins, bisphosphonates and plant polyphenols in aging and age-related diseases

We describe the inflammation pathway from Cholesterol to Aging. Interleukin 6 mediated inflammation is implicated in age-related disorders including Atherosclerosis, Peripheral Vascular Disease, Coronary Artery Disease, Osteoporosis, Type 2 Diabetes, Dementia and Alzheimer's disease and some forms of Arthritis and Cancer. Statins and Bisphosphonates inhibit Interleukin 6 mediated inflammation indirectly through regulation of endogenous cholesterol synthesis and isoprenoid depletion. Polyphenolic compounds found in plants, fruits and vegetables inhibit Interleukin 6 mediated inflammation by direct inhibition of the signal transduction pathway. Therapeutic targets for the control of all the above diseases should include inhibition of Interleukin-6 mediated inflammation.

Bisphosphonates: mode of action and pharmacology

The profound effects of the bisphosphonates on calcium metabolism were discovered over 30 years ago, and they are now well established as the major drugs used for the treatment of bone diseases associated with excessive resorption. Their principal uses are for Paget disease of bone, myeloma, bone metastases, and osteoporosis in adults, but there has been increasing and successful application in pediatric bone diseases, notably osteogenesis imperfecta. Bisphosphonates are structural analogues of inorganic pyrophosphate but are resistant to enzymatic and chemical breakdown. Bisphosphonates inhibit bone resorption by selective adsorption to mineral surfaces and subsequent internalization by bone-resorbing osteoclasts where they interfere with various biochemical processes. The simpler, non-nitrogen-containing bisphosphonates (eg, clodronate and etidronate) can be metabolically incorporated into nonhydrolysable analogues of adenosine triphosphate (ATP) that may inhibit ATP-dependent intracellular enzymes. In contrast, the more potent, nitrogen-containing bisphosphonates (eg, pamidronate, alendronate, risedronate, ibandronate, and zoledronate) inhibit a key enzyme, farnesyl pyrophosphate synthase, in the mevalonate pathway, thereby preventing the biosynthesis of isoprenoid compounds that are essential for the posttranslational modification of small guanosine triphosphate (GTP)-binding proteins (which are also GTPases) such as Rab, Rho, and Rac. The inhibition of protein prenylation and the disruption of the function of these key regulatory proteins explains the loss of osteoclast activity. The recently elucidated crystal structure of farnesyl diphosphate reveals how bisphosphonates bind to and inhibit at the active site via their critical nitrogen atoms. Although bisphosphonates are now established as an important class of drugs for the treatment of many bone diseases, there is new knowledge about how they work and the subtle but potentially important differences that exist between individual bisphosphonates. Understanding these may help to explain differences in potency, onset and duration of action, and clinical effectiveness.

Short-term effects of atorvastatin on bone turnover in male patients with hypercholesterolemia

No consensus has been reached on whether the 3-hydroxy 3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, known as statins, have beneficial effects on bone health. The purpose of our study was to evaluate the effects of atorvastatin on bone metabolism by means of measuring bone turnover markers in male patients with hypercholesterolemia both at diagnosis and prospectively after 3 months of treatment. Twenty-two Japanese male patients (mean age 62.36 +/- 10.1 years) with untreated hypercholesterolaemeia were selected for this study. After 3-months treatment of atorvastatin, total cholesterol and low density lipoprotein cholesterol significantly decreased as expected (p<0.001 for both parameters). Bone-specific alkaline phosphatase (BAP) did not change significantly (p = 0.444). However, serum N-terminal telopeptide of type I collagen (NTx) significantly decreased by -19.86 +/- 26.4% (p = 0.020). In addition, delta NTx during the course of this study was negatively correlated with NTx at baseline (r = -0.645, p = 0.0008). Although there was a tendency of positive correlations of delta NTx with delta total cholesterol, delta triglycerides, and delta low density lipoprotein cholesterol, and of negative correlations of delta NTx and delta BAP with delta high density lipoprotein cholesterol, none of them reached statistical significance. Our findings suggest that atorvastatin may have potentially beneficial effects on bone metabolism in patients with hypercholesterolemia mostly by reducing bone resorption rather than by stimulating bone formation. Further studies with more patients and longer duration are warranted to evaluate its effects, if any, on prevention of osteoporosis and subsequent fractures.

Simvastatin and atorvastatin enhance gene expression of collagen type 1 and osteocalcin in primary human osteoblasts and MG-63 cultures

To clarify the mechanism of the stimulatory effect of statins on bone formation, we have assessed the effect of simvastatin and atorvastatin on osteoblast activity by analysing cell proliferation, as well as collagen, osteocalcin, and bone morphogenetic protein-2 (BMP2) gene expression in primary human osteoblast (hOB) and MG-63 cell line cultures. Explants of bone from patients without any metabolic disease under orthopedic hip procedures were used to obtain hOB. Cell cultures were established, synchronized, and different concentrations of simvastatin or atorvastatin were added (10(-9) M, 10(-8) M, 10(-7) M, 10(-6) M) during the experiment. Cell proliferation was analyzed after 24 h. Collagen polypeptide alpha1 type 1 (COL1A1) gene expression, osteocalcin, and BMP2 expression levels were quantified by real-time PCR after 24 h incubation with statins. There was a statistically significant decrease in cell proliferation related to simvastatin or atorvastatin addition at all concentrations in primary hOB compared with those not treated. A significant increase in COL1A1, osteocalcin, and BMP2 gene expression was detected when hOB cultures were treated with simvastatin or atorvastatin at different concentrations. Similar but less significant effects were found on MG-63 cells. After statin treatment we observed both an arrest of proliferation in hOB cells and an increase in collagen, osteocalcin, and BMP2 gene expression, consistent with a stimulatory effect towards mature osteoblast differentiation. These findings support the bone-forming effect of statins, probably through the BMP2 pathway.

Short-term effects of pitavastatin on biochemical markers of bone turnover in patients with hypercholesterolemia

OBJECT

No consensus has been reached whether clinical use of statins has beneficial effects on bone health, partly due to lower statin concentrations because of first-pass metabolism by the liver. We thus evaluated the effects of pitavastatin, which does not undergo first-pass metabolism, on bone metabolism.

METHODS

According to the therapeutic regimen, the subjects were divided into two groups (group A, 66 with pitavastatin; group B, 35 without pitavastatin). Bone-specific alkaline phosphatase (BAP) and serum N-terminal telopeptide of type I collagen (NTx) as bone turnover markers (BTMs) were compared between the two groups and between at baseline and after 3 months of treatment in each group. Correlations between baseline characteristics and deltaBTMs, and between delta lipid profile and deltaBTMs were investigated using both Pearson's correlation analysis and multivariate analysis.

PATIENTS

The subjects were 101 patients with untreated hypercholesterolemia.

RESULTS

After 3 months of treatment, BAP in group A did not change significantly compared with either the baseline value or that in group B. However, NTx in group A significantly decreased compared with both the baseline value and that in group B. In addition, deltaNTx was negatively correlated with NTx at baseline, and the significance of this correlation persisted after multiple regression analysis.

CONCLUSION

Our findings suggest that pitavastatin may have potentially beneficial effects on bone metabolism primarily by reducing bone resorption rather than by stimulating bone formation. Further studies with more patients and longer duration are warranted to evaluate its effects, if any, on prevention of osteoporosis and subsequent fractures.

Molecular mechanisms of action of bisphosphonates: current status

PURPOSE

Bisphosphonates are currently the most important class of antiresorptive agents used in the treatment of metabolic bone diseases, including tumor-associated osteolysis and hypercalcemia. These compounds have high affinity for calcium ions and therefore target bone mineral, where they are internalized by bone-resorbing osteoclasts and inhibit osteoclast function.

EXPERIMENTAL DESIGN

This article reviews the pharmacology of bisphosphonates and the relationship between chemical structure and antiresorptive potency. We also describe new insights into their intracellular molecular mechanisms of action, methods for assessing the effects of bisphosphonates on protein prenylation, and their potential as direct antitumor agents.

RESULTS

Nitrogen-containing bisphosphonates act intracellularly by inhibiting farnesyl diphosphate synthase, an enzyme of the mevalonate pathway, thereby preventing prenylation of small GTPase signaling proteins required for normal cellular function. Inhibition of farnesyl diphosphate synthase also seems to account for their antitumor effects observed in vitro and for the activation of gamma,delta T cells, a feature of the acute-phase response to bisphosphonate treatment in humans. Bisphosphonates that lack a nitrogen in the chemical structure do not inhibit protein prenylation and have a different mode of action that seems to involve primarily the formation of cytotoxic metabolites in osteoclasts.

CONCLUSIONS

Bisphosphonates are highly effective inhibitors of bone resorption that selectively affect osteoclasts in vivo but could also have direct effects on other cell types, such as tumor cells. After >30 years of clinical use, their molecular mechanisms of action on osteoclasts are finally becoming clear but their exact antitumor properties remain to be clarified.

Bisphosphonates: From Bench to Bedside

The discovery and development of the bisphosphonates (BPs) as a major class of drugs for the treatment of bone diseases has been a fascinating journey that is still not over. In clinical medicine, several BPs are established as the treatments of choice for various diseases of excessive bone resorption, including Paget's disease of bone, myeloma and bone metastases, and osteoporosis. Bisphosphonates are chemically stable analogues of inorganic pyrophosphate, and are resistant to breakdown by enzymatic hydrolysis. Bisphosphonates inhibit bone resorption by being selectively taken up and adsorbed to mineral surfaces in bone, where they interfere with the action of the bone-resorbing osteoclasts. Bisphosphonates are internalized by osteoclasts and interfere with specific biochemical processes. Bisphosphonates can be classified into at least two groups with different molecular modes of action. The simpler non-nitrogen-containing bisphosphonates (such as clodronate and etidronate) can be metabolically incorporated into nonhydrolyzable analogues of adenosine triphosphate (ATP) that may inhibit ATP-dependent intracellular enzymes. The more potent, nitrogen-containing bisphosphonates (such as pamidronate, alendronate, risedronate, ibandronate, and zoledronate) are not metabolized in this way but can inhibit enzymes of the mevalonate pathway, thereby preventing the biosynthesis of isoprenoid compounds that are essential for the posttranslational modification of small GTP-binding proteins (which are also GTPases) such as rab, rho, and rac. The inhibition of protein prenylation and the disruption of the function of these key regulatory proteins explain the loss of osteoclast activity and induction of apoptosis. The key target for bisphosphonates is farnesyl pyrophosphate synthase (FPPS) within osteoclasts, and the recently elucidated crystal structure of this enzyme reveals how BPs bind to and inhibit at the active site via their critical N atoms. In conclusion, bisphosphonates are now established as an important class of drugs for the treatment of many bone diseases, and their mode of action is being unraveled. As a result their full therapeutic potential is gradually being realized.

Statins and osteoporosis: new role for old drugs

Osteoporosis is the most common bone disease, affecting millions of people worldwide and leading to significant morbidity and high expenditure. Most of the current therapies available for its treatment are limited to the prevention or slowing down of bone loss rather than enhancing bone formation. Recent discovery of statins (HMG-CoA reductase inhibitors) as bone anabolic agents has spurred a great deal of interest among both basic and clinical bone researchers. In-vitro and some animal studies suggest that statins increase the bone mass by enhancing bone morphogenetic protein-2 (BMP-2)-mediated osteoblast expression. Although a limited number of case-control studies suggest that statins may have the potential to reduce the risk of fractures by increasing bone formation, other studies have failed to show a benefit in fracture reduction. Randomized, controlled clinical trials are needed to resolve this conflict. One possible reason for the discrepancy in the results of preclinical, as well as clinical, studies is the liver-specific nature of statins. Considering their high liver specificity and low oral bioavailability, distribution of statins to the bone microenvironment in optimum concentration is questionable. To unravel their exact mechanism and confirm beneficial action on bone, statins should reach the bone microenvironment in optimum concentration. Dose optimization and use of novel controlled drug delivery systems may help in increasing the bioavailability and distribution of statins to the bone microenvironment. Discovery of bone-specific statins or their bone-targeted delivery offers great potential in the treatment of osteoporosis. In this review, we have summarized various preclinical and clinical studies of statins and their action on bone. We have also discussed the possible mechanism of action of statins on bone. Finally, the role of drug delivery systems in confirming and assessing the actual potential of statins as anti-osteoporotic agents is highlighted.

Statins and bone metabolism

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are potent inhibitors of cholesterol biosynthesis. Cholesterol-lowering therapy using statins significantly reduces the risk of coronary heart disease. However, extensive use of statins leads to increases of other undesirable as well as beneficial effects, so-called pleiotropic effects. With respect to these effects, statins augment the expression of bone morphogenetic protein-2, a potent simulator of osteoblast differentiation and its activity, and promote mineralization by cultured osteoblasts, indicating that statins have an anabolic effect on bone. Chronic administration of statins in ovariectomized (OVX) rats modestly increases bone mineral density (BMD) of cancellous bone but not of compact bone. In clinical studies, there are conflicting results regarding the clinical benefits of this therapy for the treatment of osteoporosis. Observational studies suggest an association between statin use and reduction in fracture risk. Clinical trials reported no effect of statin treatment on BMD in hip and spine, and on bone turnover. Statins also may influence oral osseous tissues. Administration of statins in combination with osteoporosis therapy appears to improve alveolar bone architecture in the mandibles of OVX rats with maxillary molar extraction. Statins continue to be considered as potential therapeutic agents for patients with osteoporosis and possibly with periodontal disease. Development of new statins that are more specific and potent for bone metabolism will greatly increase the usefulness of these drugs for the treatment of bone diseases.

Short-term reduction in bone markers with high-dose simvastatin

The effect of statins on bone mass and fracture rates is uncertain. Therefore, we investigated whether statin therapy acutely altered bone turnover as measured by changes in bone serum markers (bone-specific alkaline phosphatase, osteocalcin, and type I collagen N-telopeptide cross-links). Fasting blood samples were obtained from 55 (M/F 39/16) healthy nonsmoking adults (mean +/- standard deviation: age, 50.4+/-7.5 years; body mass index, 27.8+/-4.9 kg/m(2)) with low-density lipoprotein cholesterol concentrations between 3.38-4.90 mmol/l. Subjects were randomized to four possible 8-week treatment regimens: placebo (n =14), pravastatin 40 mg/daily (n =12), simvastatin 20 mg/daily (n =14) or simvastatin 80 mg/daily (n =15). High-dose simvastatin (80 mg/daily) produced a significant reduction in bone-specific alkaline phosphatase as compared with other treatment regimens (p =0.009). However, there were no changes in urinary N-telopeptide cross-links, a sensitive marker of bone resorption. Short-term use of high-dose simvastatin lowers the level of the serum bone marker bone-specific alkaline phosphatase, which suggests the possibility of reduced bone turnover.

Promotion of bone formation by simvastatin in polyethylene particle-induced osteolysis

The effects of statins on bone formation in periprosthetic osteolysis have not been determined to date. We investigated the effect of the HMG-CoA reductase inhibitor simvastatin on osteoblastic bone formation under conditions of ultra-high molecular weight polyethylene (UHMWPE) particle-induced osteolysis. The murine calvarial osteolysis model was utilized in 21 C57BL/J6 mice randomized to three groups. Group I underwent sham surgery only, group II received UHMWPE particles, and group III, particles and simvastatin treatment. After 2 weeks, calvaria were processed for histomorphometry and stained with Giemsa dye. New bone formation was measured as osteoid tissue area within the midline suture. Bone thickness was quantified as indicator of net bone growth. Statistical analysis was performed using one-way ANOVA and a Student's t-test. New bone formation and bone thickness were significantly enhanced following simvastatin treatment. New bone formation was 0.008+/-0.008 mm2 in sham controls (group I), 0.015+/-0.012 mm2 after particle implantation without further intervention (group II), compared to 0.083+/-0.021 mm2 with particle implantation and simvastatin treatment (group III) (p=0.003). The bone thickness was 0.213+/-0.007 mm in group I, 0.183+/-0.005 mm in group II, and 0.238+/-0.009 mm in group III (p=0.00008). In conclusion, simvastatin treatment markedly promoted bone formation and net bone growth in UHMWPE particle-induced osteolysis in a murine calvarial model. These new findings indicate that simvastatin may have favorable osteoanabolic effects on wear debris-mediated osteolysis after total joint arthroplasty, involving local stimulation of osteoblastic bone formation.

Phosphonocarboxylate inhibitors of Rab geranylgeranyl transferase disrupt the prenylation and membrane localization of Rab proteins in osteoclasts in vitro and in vivo

Nitrogen-containing bisphosphonate drugs such as risedronate act by inhibiting farnesyl diphosphate synthase, thereby disrupting protein prenylation in osteoclasts. We recently found that an anti-resorptive phosphonocarboxylate analogue of risedronate, 3-PEHPC (previously referred to as NE10790), selectively prevents prenylation of Rab GTPases in vitro by specifically inhibiting Rab geranylgeranyl transferase. In this study, we demonstrate that unprenylated Rab6 could be detected in J774 cells after treatment with 3-PEHPC or risedronate for as little as 4 h, and reached 50% after 24 h. Furthermore, treatment of J774 cells or osteoclasts with either 3-PEHPC or risedronate disrupted membrane association of several Rab family proteins. Like risedronate, the effects of 3-PEHPC are likely to be restricted to osteoclasts in vivo, since both risedronate and 3-PEHPC inhibited Rab prenylation in osteoclasts, but not in general bone marrow cells, when administered to rabbits in vivo. Analysis of two new phosphonocarboxylate analogues of 3-PEHPC (3-PEPC and 2-PEPC) revealed that, first, the geminal hydroxyl group is not essential for inhibition of Rab prenylation by phosphonocarboxylates, but does contribute to their anti-resorptive potency, most likely by enhancing their affinity for bone mineral. Second, the position of the nitrogen in the side chain of phosphonocarboxylates is crucial for their ability to inhibit Rab prenylation and hence to inhibit bone resorption. In addition, there is a good correlation between the ability of the phosphonocarboxylates to inhibit Rab prenylation and to inhibit bone resorption in vitro, indicating that these compounds are a new class of pharmacological agents that inhibit bone resorption by specifically preventing prenylation of Rab proteins. Furthermore, although phosphonocarboxylates are analogues of bisphosphonates, the structure-activity relationships of phosphonocarboxylates for inhibiting Rab geranylgeranyltransferase appear to differ from the structure-activity relationships of bisphosphonates for inhibiting farnesyl diphosphate synthase.

The effect of simvastatin on polyethylene particle-induced osteolysis

This study aimed to investigate the effects of the HMG-CoA reductase inhibitor simvastatin on ultra-high molecular weight polyethylene (UHMWPE) particle-induced osteolysis. The murine calvarial osteolysis model was used in 21 C57BL/J6 mice randomized to three groups. Group I underwent sham surgery only, group II received UHMWPE particles, and group III, particles and simvastatin treatment. After two weeks, calvaria were processed for histomorphometry. Bone resorption was measured as resorption within the midline suture using Giemsa staining. Osteoclast numbers were determined per high-power field using TRAP-staining. Statistical analysis was performed using one-way ANOVA and Student's t-test. Bone resorption in midline suture was 0.094+/-0.007 mm(2) in sham controls (group I), 0.25+/-0.025 mm(2) after particle implantation without further intervention (group II), and 0.131+/-0.02 mm(2) with particle implantation and additional simvastatin treatment (group III) (p=0.00003). Osteoclast numbers were 15.3+/-3.6 in group I, 48.7+/-7.1 in group II and 6.2+/-3.1 in group III (p=0.00002). In conclusion, simvastatin treatment markedly decreased UHMWPE particle-induced osteolysis in a murine calvarial model. This finding suggests that simvastatin may have a role for noninvasive prevention and treatment of wear debris-mediated periprosthetic osteolysis after total joint arthroplasty.

Effects of simvastatin on bone mineral density and remodeling parameters in postmenopausal osteopenic subjects: 1-year follow-up study

Observational studies suggest that statin use may be associated with lower incidence of fracture. However, there are conflicting data for their effects on bone remodeling parameters and bone mineral density (BMD). In the present study, we aimed to investigate the effects of simvastatin on bone metabolism and BMD in subjects with hypercholesterolemia (>240 mg/dl). For this purpose, 32 postmenopausal osteopenic subjects who were given simvastatin treatment (20 mg/day) and not on osteoporosis treatment were included in the study. During the 1-year follow-up period, the total cholesterol level decreased from 262.1+/-30.9 to 202.2+/-30.1 mg/dl (p<0.0001). At a period as early as the 3rd month, levels of the anabolic markers, e.g., bone-specific alkaline phosphatase (BSAP) and osteocalcin (OCL), were found to be significantly increased (from 120.8+/-56.6 to 149.5+/-57.6 IU/l, p=0.008, and from 20.8+/-12.6 to 34.7+/-18.4 microg/l, p=0.015, respectively) while no significant change was observed in the resorptive marker of serum N-telopeptide of type I collagen (CTX). At the 6th and 12th month, BSAP and OCL were both found to be decreased below the pretreatment values. While a significant reduction was found in BSAP levels (from 120.8+/-56.6 to 55.9+/-18.8 IU/l, p<0.001), no significant change was observed in CTX levels after the 6-month treatment period. Parathyroid hormone showed a gradual profound increase during the follow-up period (from 62.7+/-41.5 to 108.4+/-51.7 pg/ml, p<0.001). No significant change was found in BMD levels at the spine, femoral neck, Ward's triangle, and trochanter at the end of the 1-year follow-up period. In conclusion, simvastatin treatment showed a short-lasting anabolic effect on bone metabolism. However, this effect was lost by prolongation of therapy. The decrease in both anabolic and resorptive markers at the 6th and 12th month suggests that simvastatin affects bone metabolism mostly in favor of inhibition of the bone turnover in a long-term observation period although this inhibitory effect was not reflected in BMD.

Cholesterol synthesis is the trigger and isoprenoid dependent interleukin-6 mediated inflammation is the common causative factor and therapeutic target for atherosclerotic vascular disease and age-related disorders including osteoporosis and type 2 diabetes

This is a unifying theory that cholesterol metabolites (isoprenoids) are an integral component of the signaling pathway for interleukin-6 (IL-6) mediated inflammation. IL-6 inflammation is the common causative origin for atherosclerosis, peripheral vascular disease, coronary artery disease, and age-related disorders including osteoporosis, dementia, Alzheimer's disease and type 2 diabetes. Therapeutic effects of bisphosphonates and statins are mediated by isoprenoid depletion. Statins and bisphosphonates act in the cholesterol pathway to deplete isoprenoids. Anti-inflammatory properties of statins and bisphosphonates are due to isoprenoid depletion with subsequent inhibition of IL-6 mediated inflammation. Therapeutic targets for the prevention and control of all the above diseases should focus on cholesterol metabolites and IL-6 mediated inflammation. Prevention of atherosclerotic vascular disease and age-related disorders will be by utilization of cholesterol lowering agents or techniques and/or treatment with statins and/or bisphosphonates to inhibit IL-6 inflammation through regulation of cholesterol metabolism.

Atorvastatin stimulates the production of osteoprotegerin by human osteoblasts

Recently, HMG-CoA reductase inhibitors (statins), potent inhibitors of cholesterol biosynthesis, have been linked to protective effects on bone metabolism. Because of their widespread use, prevention of bone loss and fractures would be a desirable side effect. However, the mechanisms how statins may affect bone metabolism are poorly defined. Here, we evaluated the effect of atorvastatin on osteoblastic production of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG), cytokines that are essential for osteoclast cell biology. While RANKL enhances osteoclast formation and activation, thereby, promoting bone loss, OPG acts as a soluble decoy receptor and antagonizes the effects of RANKL. In primary human osteoblasts (hOB), atorvastatin increased OPG mRNA levels and protein secretion by hOB by up to three fold in a dose-dependent manner with a maximum effect at 10(-6) M (P < 0.001). Time course experiments indicated a time-dependent stimulatory effect of atorvastatin on OPG mRNA levels after 24 h and on OPG protein secretion after 48-72 h (P < 0.001). Treatment of hOB with substrates of cholesterol biosynthesis that are downstream of the HMG-CoA reductase reaction (mevalonate, geranylgeranyl pyrophosphate) reversed atorvastatin-induced enhancement of OPG production. Of note, atorvastatin abrogated the inhibitory effect of glucocorticoids on OPG production. Treatment of hOB with atorvastatin enhanced the expression of osteoblastic differentiation markers, alkaline phosphatase and osteocalcin. In summary, our data suggest that atorvastatin enhances osteoblastic differentiation and production of OPG. This may contribute to the bone-sparing effects of statins.

Ein Vergleich der antiresorptiven Effekte von Bisphosphonaten und Statinen auf Polyethylenpartikel-induzierte Osteolysen / A Comparison of the Antiresorptive Effects of Bisphosphonates and Statins on Polyethylene Particle-Induced Osteolysis

An ongoing unraveling of the molecular mechanisms in aseptic loosening of hip arthroplasty has opened up novel potential pharmacological interventions. In this study the antiresorptive effects of the bisphosphonate zoledronate and the statin simvastatin on ultra high molecular weighted polyethylene (UHMWPE) particle-induced osteolysis were compared. Two previous studies of our group based on the murine calvarial model of UHWMPE particle-induced osteolysis were pooled to form four study groups. Animals in group I (n=14) underwent sham surgery only. In groups II (n=14), III (n=7) and IV (n=7) UHMWPE particles were implanted on the calvariae. Animals in groups III and IV were additionally treated with zoledronate (single 25 microg/kg s.c. injection) and simvastatin (120 mg/day p.o. for 14 days), respectively. After two weeks, calvaria were processed for undecalcified histomorphometry. Bone resorption was measured using Giemsa staining. Osteoclast numbers were determined using TRAP-staining. UHMWPE particle implantation resulted in a grossly pronounced osteolytic activity with significantly increased values of bone resorption (p < 0.001) and osteoclast numbers (p < 0.001). Additional treatment with zoledronate or simvastatin counteracted the particle-induced effects. A comparison of the two medical treatments revealed no statistically significant differences in bone resorption (p = 0.63) and osteoclast numbers (p = 0.41). A single dose of the bisphosphonate zoledronate decreased UHMWPE particle-induced osteolysis in a murine calvarial model as effectively as a daily treatment with simvastin. Both drug groups may have a preventive and therapeutic role as antiresorptive agents in wear particle-induced bone resorption following total joint replacement.

From molds and macrophages to mevalonate: a decade of progress in understanding the molecular mode of action of bisphosphonates

Although bisphosphonates were first used as therapeutic agents to inhibit bone resorption in the early 1970s, their mode of action at the molecular level has only become fully clear within the last few years. One of the reasons for this lack of understanding was the difficulty in isolating large numbers of pure osteoclasts for biochemical studies. In the last decade, the identification of appropriate surrogate models that reflected the antiresorptive potencies of bisphosphonates, such as Dictyostelium slime molds and macrophages, helped overcome this problem and proved to be instrumental in elucidating the molecular pathways by which these compounds inhibit osteoclast-mediated bone resorption. This brief review summarizes our current understanding of these pathways.

Age-dependent effects of atorvastatin on biochemical bone turnover markers: a randomized controlled trial in postmenopausal women

The use of HMG-CoA-reductase inhibitors (statins) has been associated with decreased risk of bone fractures in epidemiological studies. In vitro evidence suggests that statins may stimulate bone formation, but the data are still preliminary. We assessed the effects of the HMG-CoA-reductase inhibitor atorvastatin on biochemical parameters of bone metabolism in a multicenter, randomized, double-blind, placebo-controlled trial conducted between October 2001 and October 2002 in three hospital-based outpatient metabolism clinics. Forty-nine postmenopausal women, mean age 61 +/- 5 years, mean time postmenopause 12.6 +/- 8.8 years, were treated with atorvastatin, 20 mg per day ( n=24) or matching placebos ( n=25) for 8 weeks. Comparing the differences to baseline between the groups, there were no statistically significant effects of atorvastatin either on the bone formation markers intact osteocalcin and bone-specific alkaline phosphatase or on the bone resorption markers C-telopeptide and intact parathyroid hormone. The marker of bone fractures, undercarboxylated osteocalcin, was also unchanged. When analyzed in dependence of age, atorvastatin increased C-telopeptide and osteocalcin in the younger subjects, while it decreased them in older subjects. Most interestingly, in older subjects, atorvastatin caused a significant decrease in the ratio of C-telopeptide to osteocalcin, an indicator of bone remodeling, while the ratio was increased in younger subjects, suggesting beneficial effects on bone turnover exclusively in older individuals (approx. >63 years). In summary, the present data suggest that short-term treatment with atorvastatin may have age-dependent effects on biochemical markers of bone turnover in postmenopausal women.

Simvastatin treatment partially prevents ovariectomy-induced bone loss while increasing cortical bone formation

Statins are commonly prescribed drugs that inhibit hepatic cholesterol synthesis and thereby reduce serum cholesterol concentrations. Some of the statins are thought to possess bone anabolic properties. Effects of statin on tibia, femur, and vertebral cortical and cancellous bone were studied in ovariectomized (OVX) rats. Sixty Wistar female rats, 4 months old, were allocated into four groups: baseline control, sham + placebo group, OVX + placebo, OVX + simvastatin. Simvastatin, 20 mg/kg, or placebo was given twice daily by a gastric tube for 3 months. The rats were labeled with tetracycline at day 11 and calcein at day 4 before sacrifice. Concerning cortical bone, the tibial diaphysis bending strength was increased by 8% and the periosteal bone formation rate (BFR) at the mid-diaphysis increased by twofold in the OVX + simvastatin group compared with the OVX + placebo group, in harmony with increased serum osteocalcin concentrations. Simvastatin did not affect the endocortical bone formation. Concerning cancellous bone, the cancellous bone volumes in the proximal tibia and vertebral body were reduced in both OVX groups, but the reduction was less in the OVX + simvastatin group compared with the OVX + placebo group. This reduction in cancellous bone loss is in agreement with the 36% decreased activity of serum tartrate-resistant-acid-phosphatase 5b (TRAP-5b), indicating decreased osteoclast activity in the OVX + simvastatin group compared with the OVX + placebo group. In conclusion, simvastatin induces a moderate increase in cortical bone formation at the periosteal bone surface. The new cortical bone exhibits a normal lamellar structure, and simvastatin seems to respect the regional pattern of bone formation, bone resorption, and drift; for example, no periosteal bone formation is observed in the vertebral canal. Furthermore, simvastatin reduces the loss of cancellous bone induced by ovariectomy.

Effect of D-003, a Mixture of Very High Molecular Weight Aliphatic Acids, on Prednisolone-Induced Osteoporosis in Sprague-Dawley Rats

BACKGROUND

Drugs inhibiting cholesterol biosynthesis may affect bone metabolism through inhibition of the mevalonate pathway resulting in the inhibition of protein prenylation required for osteoclast activity. D-003 is a mixture of high molecular weight aliphatic primary acids purified from sugar-cane (Saccharum officinarum) wax, with cholesterol-lowering effects demonstrated in experimental and clinical studies. D-003 inhibits cholesterol biosynthesis through indirect regulation of HMG-CoA reductase activity. A previous study demonstrated that D-003 prevented bone loss and bone resorption on ovariectomy-induced osteoporosis in rats. Corticosteroid-induced osteoporosis is the result of changes affecting calcium homeostasis, but the hallmark of corticosteroid-induced bone loss is the direct effects on bone cells, such as inhibition of osteoblastogenesis, promotion of apoptosis of osteoblasts and osteocytes, and decrease in bone formation.

OBJECTIVE

To determine whether D-003 could prevent the bone loss induced with prednisolone in Sprague-Dawley rats.

METHODS

Rats were randomly distributed in five groups (ten rats per group): a sham-operated control and four groups orally treated with prednisolone 6 mg/kg for 80 days; a positive control orally treated with vehicle; and three groups orally treated with D-003 at 5, 25 and 200 mg/kg, respectively. Rats were killed, bones removed and histological variables of bone resorption and formation studied for histomorphometry.

RESULTS

Compared with the sham group, prednisolone significantly (p < 0.01) reduced trabecular bone volume (TBV), while D-003 significantly (p < 0.001) and dose-dependently prevented the prednisolone-induced reduction of TBV. Treatment with prednisolone lowered (p < 0.001) trabecular thickness (TbTh) and number (TbN), while increasing (p < 0.001) the gap between trabeculae. D-003 (5, 25 and 200 mg/kg/day) significantly (p < 0.001) and dose-dependently prevented the reduction of TbTh and TbN and the increase of trabecular gap induced with prednisolone. Treatment with prednisolone increased both the surface and number of osteoclasts compared with sham (p < 0.001). D-003 (5-200 mg/day), however, prevented this effect (p < 0.001 for all comparisons). D-003 also prevented (p < 0.001) the reduction of osteoblast surface (ObS/BS) induced by prednisolone. Osteonecrotic areas were observed in all positive controls, but in none of the sham animals. Positive controls showed hypertrophy of bone marrow adipocytes and lipid-laden pluripotential stromal cells in bones. A significant and dose-dependent reduction of the frequency of animals showing prednisolone-induced osteo-necrosis was observed across the doses of D-003 (5, 25 and 200 mg/kg) investigated here.

CONCLUSIONS

D-003 (5, 25 and 200 mg/kg) prevented trabecular bone loss and femoral neck osteonecrosis induced with prednisolone in Sprague Dawley rats, also increasing osteoblast surface and reducing bone resorption parameters. These results suggest that D-003 could be useful for managing corticosteroid-induced osteoporosis.

Disruption of hepatitis C virus RNA replication through inhibition of host protein geranylgeranylation

Hepatitis C virus (HCV) RNA replication depends on viral protein association with intracellular membranes, but the influence of membrane composition on viral replication is unclear. We report that HCV RNA replication and assembly of the viral replication complex require geranylgeranylation of one or more host proteins. In cultured hepatoma cells, HCV RNA replication was disrupted by treatment with lovastatin, an inhibitor of 3-hydroxy-3-methyglutaryl CoA reductase, or with an inhibitor of protein geranylgeranyl transferase I, each of which induced the dissolution of the HCV replication complex. Viral replication was not affected by treatment of cells with an inhibitor of farnesyl transferase. When added to lovastatin-treated cells, geranylgeraniol, but not farnesol, restored replication complex assembly and viral replication. Inasmuch as the HCV genome does not encode a canonical geranylgeranylated protein, the data suggest the involvement of a geranylgeranylated host protein in HCV replication. Inhibition of its geranylgeranylation affords a therapeutic strategy for treatment of HCV infection.

Inhibition of protein geranylgeranylation induces apoptosis in myeloma plasma cells by reducing Mcl-1 protein levels

HMG-CoA reductase is the rate-limiting enzyme of the mevalonate pathway leading to the formation of cholesterol and isoprenoids such as farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP). The inhibition of HMG-CoA reductase by lovastatin induced apoptosis in plasma cell lines and tumor cells from patients with multiple myeloma. Here we show that cotreatment with mevalonate or geranylgeranyl moieties, but not farnesyl groups, rescued myeloma cells from lovastatin-induced apoptosis. In addition, the inhibition of geranylgeranylation by specific inhibition of geranylgeranyl transferase I (GGTase I) induced the apoptosis of myeloma cells. Apoptosis triggered by the inhibition of geranylgeranylation was associated with reduction of Mcl-1 protein expression, collapse of the mitochondrial transmembrane potential, expression of the mitochondrial membrane protein 7A6, cytochrome c release from mitochondria into the cytosol, and stimulation of caspase-3 activity. These results imply that protein geranylgeranylation is critical for regulating myeloma tumor cell survival, possibly through regulating Mcl-1 expression. Our results show that pharmacologic agents such as lovastatin or GGTase inhibitors may be useful in the treatment of multiple myeloma.

Lovastatin inhibits adipogenic and stimulates osteogenic differentiation by suppressing PPARgamma2 and increasing Cbfa1/Runx2 expression in bone marrow mesenchymal cell cultures

The mechanism whereby lovastatin can counteract steroid-induced osteonecrosis and osteoporosis is poorly understood. We assessed the effect of lovastatin on a multipotential cell line, D1, which is capable of differentiating into either the osteoblast or the adipocyte lineage. The expression of bone cell and fat cell transcription factors Cbfa1/Runx2 and PPARgamma2, respectively, were determined. 422aP2 gene expression was analyzed. Osteocalcin promoter activity was measured by cotransfecting the cells with the phOC-luc and pSV beta-Gal plasmids. Lovastatin enhanced osteoblast differentiation as assessed by a 1.8x increase in expression of Cbfa1/Runx2 and by a 5x increase in osteocalcin promoter activity. Expression of PPARgamma2 was decreased by 60%. By enhancing osteoblast gene expression and by inhibiting adipogenesis, lovastatin may shunt uncommitted osteoprogenitor cells in marrow from the adipocytic to the osteoblastic differentiation pathway. Future evaluation of lovastatin and other lipid-lowering drugs will help determine their potential as therapeutic agents for osteonecrosis and osteoporosis.