Statins as modulators of bone formation

The use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) to reduce serum cholesterol is well described. However, the recent finding that statins have direct effects on bone was unexpected. A number of epidemiological studies have recently been published that explore the effects of statins on bone mineral density and risk of fracture in humans. Statins may act by directly stimulating the expression of bone morphogenetic protein-2 and increasing osteoblast differentiation or, like nitrogen-containing bisphosphonates, may have effects on the mevalonate pathway that leads to inhibition of osteoclast activity and osteoblast apoptosis. In addition, the demonstration that statins can inhibit inflammation and encourage angiogenesis offers other possibilities for action.     

Statins as modulators of bone formation

The use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) to reduce serum cholesterol is well described. However, the recent finding that statins have direct effects on bone was unexpected. A number of epidemiological studies have recently been published that explore the effects of statins on bone mineral density and risk of fracture in humans. Statins may act by directly stimulating the expression of bone morphogenetic protein-2 and increasing osteoblast differentiation or, like nitrogen-containing bisphosphonates, may have effects on the mevalonate pathway that leads to inhibition of osteoclast activity and osteoblast apoptosis. In addition, the demonstration that statins can inhibit inflammation and encourage angiogenesis offers other possibilities for action.     

The role of statins as potential targets for bone formation

Inhibitors of the 3-hydroxy-3-methylglutaryl coenzyme A reductase enzyme have recently been shown to stimulate bone formation in rodents both in vitro and in vivo. In bone cells, these inhibitors increase the gene expression of bone morphogenetic protein-2, which is an autocrine-paracrine factor for osteoblast differentiation.The findings that statins increase bone formation and bone mass in rodents suggest a potential new action for these compounds, which may be beneficial in patients with established osteoporosis where marked bone loss has occurred. Recent clinical data suggest that they may reduce the risk of fracture in patients taking these drugs.     

Statin therapy and angiogenesis

PURPOSE OF REVIEW: Clinical studies suggested that 3-hydroxyl-3-methylglutaryl coenzyme A reductase inhibitor (statin) therapy has an additional cardiovascular protective activity that may function independently of the ability of statins to lower serum cholesterol. This paper reviews the available data on these effects and discusses the potential intracellular mechanisms involved. RECENT FINDINGS: Experimental studies have clearly shown that statins protect against ischaemia-reperfusion injury of the heart, and exert pro-angiogenic effects by stimulating the growth of new blood vessels in ischaemic limbs of normocholesterolemic animals. The mechanisms underlying these serum lipid-independent statin effects are not completely understood, but there is increasing evidence that statins improve endothelial function through molecular mechanisms that mediate an increase in endothelium-derived nitric oxide. Recent research has revealed a link between statins and the serine/threonine protein kinase Akt that regulates multiple angiogenic processes in endothelial cells. In contrast to these data, it has also been reported that higher doses of statins can inhibit endothelial cell migration and angiogenesis. SUMMARY: Statins have biphasic potential either to promote or inhibit angiogenesis. Low statin doses induce a pro-angiogenic effect through Akt activation and increase nitric oxide production, whereas high statin doses may decrease protein prenylation and inhibit cell growth. Notwithstanding, the clinical relevance of these serum lipid-independent effects is not fully understood. Further studies on the actions of statins on endothelial cells may lead to the identification of new pharmacological targets for the control of angiogenesis.     

Statins modulate the levels of osteoprotegerin/receptor activator of NFkappaB ligand mRNA in mouse bone-cell cultures.

Statins stimulate bone formation partly by inducing osteoblast differentiation, although there is controversy about the effects of statins on bone mineral density and fracture risk. Several studies have revealed that statins suppress bone resorption. However, the mechanism by which statins inhibit bone resorption is still unclear. The present study was performed to clarify the effects of statins on osteoclast formation as well as the levels of osteoprotegerin (OPG) and receptor activator of NFkappaB ligand (RANKL) mRNA in mouse bone-cell cultures by semiquantitative RT-PCR. 10(-8) M 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] significantly stimulated osteoclast formation and 10(-6) M statins (mevastatin and simvastatin) significantly antagonized osteoclast formation stimulated by 1,25(OH)2D3 in mouse bone-cell cultures, including both osteoblasts and osteoclasts. 10(-6) M mevastatin and simvastatin increased the level of OPG mRNA in mouse bone-cell cultures. On the other hand, 10(-6) M mevastatin and simvastatin inhibited the level of RANKL mRNA in these cultures. In conclusion, the present study demonstrates that statins inhibit osteoclast formation in mouse bone-cell cultures. Moreover, statins also increased and decreased the levels of OPG and RANKL mRNA expression in these cultures, respectively. The modulation of OPG/RANKL may be involved in the inhibition of osteoclast formation by statins.     

Mevalonate-suppressive dietary isoprenoids for bone health

Osteoclastogenesis and osteoblastogenesis, the balancing acts for optimal bone health, are under the regulation of small guanosine triphosphate-binding proteins (GTPases) including Ras, Rac, Rho and Rab. The activities of GTPases require post-translational modification with mevalonate-derived prenyl pyrophosphates. Mevalonate deprivation induced by competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase (e.g., statins) prevents the activation of GTPases, suppresses the expression of the receptor for activation of nuclear factor kappa B (NFκB) ligand (RANKL) and activation of NFκB and, consequently, inhibits osteoclast differentiation and induces osteoclast apoptosis. In contrast, statin-mediated inactivation of GTPases enhances alkaline phosphatase activity and the expression of bone morphogenetic protein-2, vascular epithelial growth factor, and osteocalcin in osteoblasts and induces osteoblast proliferation and differentiation. Animal studies show that statins inhibit bone resorption and increase bone formation. The anabolic effect of statins and other mevalonate pathway-suppressive pharmaceuticals resembles the anti-osteoclastogenic and bone-protective activities conferred by dietary isoprenoids, secondary products of plant mevalonate metabolism. The tocotrienols, vitamin E molecules with HMG CoA reductase-suppressive activity, induce mevalonate deprivation and concomitantly suppress the expression of RANKL and cyclooxygenase-2, the production of prostaglandin E2 and the activation of NFκB. Accordingly, tocotrienols inhibit osteoclast differentiation and induce osteoclast apoptosis, impacts reminiscent of those of statins. In vivo studies confirm the bone protective activity of tocotrienols at nontoxic doses. Blends of tocotrienols, statins and isoprenoids widely found in fruits, vegetables, grains, herbs, spices, and essential oils may synergistically suppress osteoclastogenesis while promoting osteoblastogenesis, offering a novel approach to bone health that warrants clinical studies.     

Mechanisms of statin-induced new-onset diabetes

Statins, with their lipid-lowering properties, are a first-line therapy for the prevention of cardiovascular diseases. Recent evidence, however, suggests that statins can increase the risk of new-onset diabetes (NOD). The molecular mechanisms of statin-induced NOD are not precisely known, although some pathophysiologic mechanisms have been suggested. Specific to the beta cell, these mechanisms include alterations in insulin secretion, changes in ion channels, modulation of signaling pathways, and inflammation/oxidative stress. Outwith the beta cell, other suggested mechanisms involve adipocytes, including alterations in adipocyte differentiation and modulation of leptin and adiponectin, and genetic and epigenetic mechanisms, including alterations in microRNA. The evidence supporting these and other mechanisms will be discussed. Greater understanding of the underlying mechanisms linking the onset of diabetes to statin therapy is essential and clinically relevant, as it may enable novel preventative or therapeutic approaches to be instituted and guide the production of a new generation of statins lacking this side effect.     

Liposomal nanocarriers for statins: A pharmacokinetic and pharmacodynamics appraisal

Statins, inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, are a well-known class of drug with beneficial therapeutic effects in cardiovascular disease and lipid disorders and have potential use against cancer. However, the bioavailability of statins is hampered due to low aqueous solubility and rapid metabolism. To improve pharmacokinetic profiles of statins, development of drug delivery systems is promising. Hence, the use of liposomes for selective delivery of statins to a selected site or for bioavailability enhancement is an effective strategy to increase statin therapeutic effects. Moreover, liposomal delivery can reduce the required dose of statins especially in terms of antitumor effects. Liposomes, because of their unique properties and biphasic and amphiphilic nature, have attracted much interest and can be considered as a suitable choice for delivery of both hydrophilic and lipophilic statins. In this review article, we focus on liposomes and evaluate the effects of different liposomal delivery systems, based on differences in size, phospholipid composition, circulation half-life, and cholesterol content, on statin function.     

Mesenchymal stem/stromal cells-derived exosomes for osteoporosis treatment

Osteoporosis is a systemic bone disease, which leads to decreased bone mass and an increased risk of fragility fractures. Currently, there are many anti-resorption drugs and osteosynthesis drugs, which are effective in the treatment of osteoporosis, but their usage is limited due to their contraindications and side effects. In regenerative medicine, the unique repair ability of mesenchymal stem cells(MSCs) has been favored by researchers. The exosomes secreted by MSCs have signal transduction an...     

Statins restore ischemic limb blood flow in diabetic microangiopathy via eNOS/NO upregulation but not via PDGF-BB expression

3-Hydroxy-3-methyl-glutaryl CoA reductase inhibitors, or statins, have pleiotropic effects and can protect the vasculature in a manner independent of their lipid-lowering effect. The effectiveness of statins in reducing the risk of coronary events has been shown even in patients with diabetes, and their effects on diabetic complications have been reported. Using a model of severe hindlimb ischemia in streptozotocin-induced diabetic mice (STZ-DM), we investigated the effects and mechanisms of statin therapy in diabetic angiopathy in ischemic hindlimbs. As a result, STZ-DM mice frequently lost their hindlimbs after induced ischemia, whereas non-DM mice did not. Supplementation with statins significantly prevented autoamputation. We previously showed that diabetic vascular complications are caused by impaired expression of PDGF-BB, but statin therapy did not enhance PDGF-BB expression. Statins helped enhance endogenous endothelial nitric oxide (NO) synthase (eNOS) expression. Furthermore, the inhibition of NO synthesis by the administration of N(omega)-nitro-l-arginine methyl ester impaired the ability of statins to prevent STZ-DM mouse limb autoamputation, indicating that the therapeutic effect of statins in hindlimb ischemia in STZ-DM mice occurs via the eNOS/NO pathway. A combination therapy of statins and PDGF-BB gene supplementation was more effective for diabetic angiopathy than either therapy alone. In conclusion, these findings indicate that statin therapy might be useful for preventing intractable diabetic foot disease in patients with diabetic angiopathy.     

Statins decrease dendritic arborization in rat sympathetic neurons by blocking RhoA activation

Clinical and experimental evidence suggest that statins decrease sympathetic activity, but whether peripheral mechanisms involving direct actions on post-ganglionic sympathetic neurons contribute to this effect is not known. Because tonic activity of these neurons is directly correlated with the size of their dendritic arbor, we tested the hypothesis that statins decrease dendritic arborization in sympathetic neurons. Oral administration of atorvastatin (20 mg/kg/day for 7 days) significantly reduced dendritic arborization in vivo in sympathetic ganglia of adult male rats. In cultured sympathetic neurons, statins caused dendrite retraction and reversibly blocked bone morphogenetic protein-induced dendritic growth without altering cell survival or axonal growth. Supplementation with mevalonate or isoprenoids, but not cholesterol, attenuated the inhibitory effects of statins on dendritic growth, whereas specific inhibition of isoprenoid synthesis mimicked these statin effects. Statins blocked RhoA translocation to the membrane, an event that requires isoprenylation, and constitutively active RhoA reversed statin effects on dendrites. These observations that statins decrease dendritic arborization in sympathetic neurons by blocking RhoA activation suggest a novel mechanism by which statins decrease sympathetic activity and protect against cardiovascular and cerebrovascular disease.     

Alterations in the self-renewal and differentiation ability of bone marrow mesenchymal stem cells in a mouse model of rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease primarily involving the synovium. Evidence in recent years has suggested that the bone marrow (BM) may be involved, and may even be the initiating site of the disease. Abnormalities in haemopoietic stem cells'' (HSC) survival, proliferation and aging have been described in patients affected by RA and ascribed to abnormal support by the BM microenvironment. Mesenchymal stem cells (MSC) and their progeny constitute important components of the BM niche. In this study we test the hypothesis that the onset of inflammatory arthritis is associated with altered self-renewal and differentiation of bone marrow MSC, which alters the composition of the BM microenvironment.

Methods

We have used Balb/C Interleukin-1 receptor antagonist knock-out mice, which spontaneously develop RA-like disease in 100% of mice by 20 weeks of age to determine the number of mesenchymal progenitors and their differentiated progeny before, at the start and with progression of the disease.

Results

We showed a decrease in the number of mesenchymal progenitors with adipogenic potential and decreased bone marrow adipogenesis before disease onset. This is associated with a decrease in osteoclastogenesis. Moreover, at the onset of disease a significant increase in all mesenchymal progenitors is observed together with a block in their differentiation to osteoblasts. This is associated with accelerated bone loss.

Conclusions

Significant changes occur in the BM niche with the establishment and progression of RA-like disease. Those changes may be responsible for aspects of the disease, including the advance of osteoporosis. An understanding of the molecular mechanisms leading to those changes may lead to new strategies for therapeutic intervention.     

Central control of bone remodeling by neuromedin U

Bone remodeling, the function affected in osteoporosis, the most common of bone diseases, comprises two phases: bone formation by matrix-producing osteoblasts and bone resorption by osteoclasts. The demonstration that the anorexigenic hormone leptin inhibits bone formation through a hypothalamic relay suggests that other molecules that affect energy metabolism in the hypothalamus could also modulate bone mass. Neuromedin U (NMU) is an anorexigenic neuropeptide that acts independently of leptin through poorly defined mechanisms. Here we show that Nmu-deficient (Nmu-/-) mice have high bone mass owing to an increase in bone formation; this is more prominent in male mice than female mice. Physiological and cell-based assays indicate that NMU acts in the central nervous system, rather than directly on bone cells, to regulate bone remodeling. Notably, leptin- or sympathetic nervous system-mediated inhibition of bone formation was abolished in Nmu-/- mice, which show an altered bone expression of molecular clock genes (mediators of the inhibition of bone formation by leptin). Moreover, treatment of wild-type mice with a natural agonist for the NMU receptor decreased bone mass. Collectively, these results suggest that NMU may be the first central mediator of leptin-dependent regulation of bone mass identified to date. Given the existence of inhibitors and activators of NMU action, our results may influence the treatment of diseases involving low bone mass, such as osteoporosis.     

High mobility group box 1 potentiates the pro-inflammatory effects of interleukin-1β in osteoarthritic synoviocytes

Introduction

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease primarily involving the synovium. Evidence in recent years has suggested that the bone marrow (BM) may be involved, and may even be the initiating site of the disease. Abnormalities in haemopoietic stem cells' (HSC) survival, proliferation and aging have been described in patients affected by RA and ascribed to abnormal support by the BM microenvironment. Mesenchymal stem cells (MSC) and their progeny constitute important components of the BM niche. In this study we test the hypothesis that the onset of inflammatory arthritis is associated with altered self-renewal and differentiation of bone marrow MSC, which alters the composition of the BM microenvironment.

Methods

We have used Balb/C Interleukin-1 receptor antagonist knock-out mice, which spontaneously develop RA-like disease in 100% of mice by 20 weeks of age to determine the number of mesenchymal progenitors and their differentiated progeny before, at the start and with progression of the disease.

Results

We showed a decrease in the number of mesenchymal progenitors with adipogenic potential and decreased bone marrow adipogenesis before disease onset. This is associated with a decrease in osteoclastogenesis. Moreover, at the onset of disease a significant increase in all mesenchymal progenitors is observed together with a block in their differentiation to osteoblasts. This is associated with accelerated bone loss.

Conclusions

Significant changes occur in the BM niche with the establishment and progression of RA-like disease. Those changes may be responsible for aspects of the disease, including the advance of osteoporosis. An understanding of the molecular mechanisms leading to those changes may lead to new strategies for therapeutic intervention.     

Simvastatin did not prevent nor restore ovariectomy-induced bone loss in adult rats

Current published results on whether statins have beneficial effects on bone metabolism have been conflicting so far. In order to further investigate if statins were promising candidates for the treatment for osteoporosis, we conducted a study in which rats were ovariectomized (OVX) at 6 months of age, allowed to lose bone for 60 days and followed by oral administration of simvastatin at the dose levels of 0.3-10 mg/kg/d for 60 days. PGE2 (6 mg/kg) was used as a positive control. Study endpoints included bone histomorphometry on the proximal tibial metaphysis (PTM) and the tibial diaphysis (TX), dual-energy X-ray absorptiometry on the right femur and micro computed tomography (ICT) on the 5th lumbar vertebra (LV). After 120 days of OVX, cancellous bone lost by 80% in the PTM and 18% in the LV accompanied by increased bone formation and resorption. Simvastatin at all dose levels did not affect bone volume, bone formation rate and bone erosion surface when compared to 120 day ovariectomized animals at all bone sites studied. By contrast, PGE2 restored cancellous and cortical bone area to sham control levels. In conclusion, this study demonstrated that unlike PGE2, oral administration of simvastatin did not have effects on cancellous or cortical bone formation and resorption; and consequently was not able to prevent further bone loss or restore bone mass in the osteopenic, OVX rats.     

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.     

Streptozotocin, Type I Diabetes Severity and Bone

As many as 50% of adults with type I (T1) diabetes exhibit bone loss and are at increased risk for fractures. Therapeutic development to prevent bone loss and/or restore lost bone in T1 diabetic patients requires knowledge of the molecular mechanisms accounting for the bone pathology. Because cell culture models alone cannot fully address the systemic/metabolic complexity of T1 diabetes, animal models are critical. A variety of models exist including spontaneous and pharmacologically induced T1 diabetic rodents. In this paper, we discuss the streptozotocin (STZ)-induced T1 diabetic mouse model and examine dose-dependent effects on disease severity and bone. Five daily injections of either 40 or 60 mg/kg STZ induce bone pathologies similar to spontaneously diabetic mouse and rat models and to human T1 diabetic bone pathology. Specifically, bone volume, mineral apposition rate, and osteocalcin serum and tibia messenger RNA levels are decreased. In contrast, bone marrow adiposity and aP2 expression are increased with either dose. However, high-dose STZ caused a more rapid elevation of blood glucose levels and a greater magnitude of change in body mass, fat pad mass, and bone gene expression (osteocalcin, aP2). An increase in cathepsin K and in the ratio of RANKL/OPG was noted in high-dose STZ mice, suggesting the possibility that severe diabetes could increase osteoclast activity, something not seen with lower doses. This may contribute to some of the disparity between existing studies regarding the role of osteoclasts in diabetic bone pathology. Examination of kidney and liver toxicity indicate that the high STZ dose causes some liver inflammation. In summary, the multiple low-dose STZ mouse model exhibits a similar bone phenotype to spontaneous models, has low toxicity, and serves as a useful tool for examining mechanisms of T1 diabetic bone loss.     

Statins enhance clonal growth of late outgrowth endothelial progenitors and increase myocardial capillary density in the chronically ischemic heart

Background

Coronary artery disease and ischemic heart disease are leading causes of heart failure and death. Reduced blood flow to heart tissue leads to decreased heart function and symptoms of heart failure. Therapies to improve heart function in chronic coronary artery disease are important to identify. HMG-CoA reductase inhibitors (statins) are an important therapy for prevention of coronary artery disease, but also have non-cholesterol lowering effects. Our prior work showed that pravastatin improves contractile function in the chronically ischemic heart in pigs. Endothelial progenitor cells are a potential source of new blood vessels in ischemic tissues. While statins are known to increase the number of early outgrowth endothelial progenitor cells, their effects on late outgrowth endothelial progenitor cells (LOEPCs) and capillary density in ischemic heart tissue are not known. We hypothesized that statins exert positive effects on the mobilization and growth of late outgrowth EPCs, and capillary density in ischemic heart tissue.

Methodology/Principal Findings

We determined the effects of statins on the mobilization and growth of late outgrowth endothelial progenitor cells from pigs. We also determined the density of capillaries in myocardial tissue in pigs with chronic myocardial ischemia with or without treatment with pravastatin. Pravastatin therapy resulted in greater than two-fold increase in CD31+ LOEPCs versus untreated animals. Addition of pravastatin or simvastatin to blood mononuclear cells increased the number of LOEPCs greater than three fold in culture. Finally, in animals with chronic myocardial ischemia, pravastatin increased capillary density 46%.

Conclusions

Statins promote the derivation, mobilization, and clonal growth of LOEPCs. Pravastatin therapy in vivo increases myocardial capillary density in chronically ischemic myocardium, providing an in vivo correlate for the effects of statins on LOEPC growth in vitro. Our findings provide evidence that statin therapy can increase the density of capillaries in the chronically ischemic heart.     

High bone density and bone health

The aim of this paper is to review the main aspects related to high bone density (HBD) as well as to discuss the physiologic mechanisms involved in bone health. There are still no well-defined criteria for identification of individuals with HBD and there are few studies on the topic. Most studies demonstrate that overweight, male gender, black ethnic background, physical activity, calcium and fluoride intake and use of medications such as statins and thiazide diuretics play a relevant and positive role on bone mineral density. Moreover, it is known that individuals with certain diseases such as obesity, diabetes, estrogen receptor-positive breast or endometrial cancer have greater bone density than healthy individuals, as well as athletes having higher bone density than non-athletes does not necessarily mean that they have healthy bones. A better understanding of risk and protective factors may help in the management of patients with bone frailty and have applicability in the treatment and in the prevention of osteoporosis, especially intervening on non-modifiable risk factors.     

Effect of treadmill exercise on bone mass in female rats.

Increasing peak bone mass at skeletal maturity, minimizing bone loss during middle age and after menopause, and increasing bone mass and preventing falls in advanced age are important measures for preventing osteoporotic fractures in women. Exercise has generally been considered to have a positive influence on bone health. This paper reviews the effects of treadmill exercise on bone in young, adult, ovariectomized, and osteopenic female rats. Treadmill exercise increases cortical and cancellous bone mass of the tibia as a result of increased bone formation and decreased bone resorption in young and adult rats. The increase in lumbar bone mass seems to be more significant when long-term exercise is applied. Treadmill exercise prevents cancellous bone loss at the tibia as a result of suppressed bone resorption in ovariectomized rats, and increases bone mass of the tibia and mechanical strength of the femur, as a result of suppressed bone resorption and increased bone formation in osteopenic rats after ovariectomy. Treadmill exercise transiently decreases the serum calcium level as a result of accumulation of calcium in bone, resulting in an increase in serum 1,25-dihydroxyvitamin D(3) level and a decrease in serum parathyroid hormone level. We conclude that treadmill exercise may be useful to increase bone mass in young and adult rats, prevent bone loss in ovariectomized rats, and increase bone mass and bone strength in osteopenic rats, especially in the long bones at weight-bearing sites. Treadmill exercise may have a positive effect on the skeleton in young, and adult, ovariectomized, and osteopenic female rats.