Simvastatin Attenuates Bone Loss Following Simulated Spaceflight John R. Gardner M.D., Ph.D. Department of Emergency Medicine University of Illinois College

Simvastatin Attenuates Bone Loss Following Simulated SpaceflightSimvastatin Attenuates Bone Loss Following Simulated Spaceflight

John R. Gardner M.D., Ph.D.

Department of Emergency Medicine

University of Illinois College of Medicine

at Peoria

Simvastatin Attenuates Bone Loss Following Simulated Spaceflight

How does this research apply to Emergency Medicine?

• Diseases of bone loss constitute a major health problem• 30 million Americans at risk for osteoporosis, 100 million worldwide• The elderly population is expanding• Significant morbidity and mortality associated with osteoporotic fracture• Loss of specialist coverage• ED overcrowding

Disease prevention is as important as treatment!

Effects of Spaceflight on the Musculoskeletal System

• Decreased Mass and Volume• Decreased Protein Content• Altered Contractile Protein Phenotype• Changes in Functional Properties

Bone

• Decreased Bone Mass• Decreased Bone Mineral Content and Density• Altered Mechanical Strength and Stiffness

Muscle

Effects of Spaceflight on the MusculoskeletalSystem

Why is this important?

• Loss of muscle mass and altered contractile phenotype could prevent the completion of manual tasks on long term spaceflights

• Loss of bone mass and strength could pose a serious health risk during prolonged spaceflight

• Significant difficulty returning to a normal gravity environment

Effects of Spaceflight on the Skeletal System

1. Decreased Bone Mass, Mineral Content, and Density

2. Loss of Cortical and Trabecular Bone Volume

3. Changes in Trabecular bone structure• Decreased Trabecular Number• Decreased Trabecular Thickness• Increased Trabecular Spacing

4. Decreased Bone Strength and Stiffness

A B

C D




Mechanism of Bone Loss?

• Large Decrease in the Synthesis of New Bone• Smaller Decrease in Bone Resorbtion

• Net Loss of Bone• Maturation Deficit of New Bone


• Drugs that inhibit bone resorbtion (bisphosphonates) have been shown to attenuate bone loss in osteoporosis, but have been less successful in other conditions (disuse, denervation spaceflight)

• There are currently no pharmacological agents capable of substantially increasing bone formation in patients that have already suffered significant bone loss


Simvastatin• Mundy et al.,(1999) described simvaststin as a potential bone anabolic agent

• Examined 30,000 compounds using an InVitro BMP-2 expression assay. Simvastatin was the only agent found to enhance BMP-2 expression• Mouse calvarial bone culture experiments increased new bone formation 2-3 fold over controls• Subcutaneous InVivo administration increased calvarial new bone formation by 50%• Systemic administration increased mouse femur trabecular bone

volume 39-94% (dose dependant)

The Model: Hindlimb Suspension

Hindlimb Suspension Faithfully Reproduces the CardinalElements of Spaceflight

• Unloading of the hindlimbs without paralysis or loss of range of motion• Head-down tilt (cephaloid fluid shift)

There Are Greater Than 100 Hindlimb Suspension Studies,Many in Direct Comparison to Actual Spaceflight


The Experiment:• 36 mice were randomly assigned to one of threetreatment groups:

• Weight-bearing control (C )• Hindlimb-suspension vehicle only (SV)• Hindlimb-suspension simvastatin (SS)

• Mice underwent two weeks of hindlimb-suspension as described by McCarthy et al., (1997)

• Hindlimb-Suspended mice received either 10 mg/kg of simvastatin or saline vehicle once daily by oral gavage


The Experiment:

• Following two weeks of hindlimb-suspension the mice were uthanized by CO2 asphixiation• The hindlimb bones were removed and cleaned of all soft tissue• Bones were stored at -80ºc until processing

Bone Mineral Content:

• Tibia/fibula and femur bones were thawed and ashed overnight in a Muffle Furnace (400 ºc) and weighed• The resulting product is entirely inflammable mineral


The Results:

Bone Mineral Content from Control and Hindlimb-Suspended Groups

Group Femur (mg/g) Tibia (mg/g) P Value

C (n=12) 1.120±0.028 0.986 ±0.021 ***

SV (n=10) 0.983 ±0.064 0.907 ±0.023 0.049A 0.019B

SS (n=11) 1.049 ±0.038 0.971 ±0.032 0.144A 0.688B

______________________________________________________________________________________

Reported values are given as mean ± SEM (mg bone mineral/body weight). Afemur vscontrol, Btibia vs control.



Discussion:

• There are no perfect countermeasures for the loss of bone mineral observed during spaceflight

• Currently available pharmacological agents are only partially effective and may be deleterious

• Exercise regimens are equally ineffective and impractical


Discussion:

• Although the mechanism of bone-loss during spaceflight is not fully understood, there is a decrease in net bone formation: a substantial decrease in new bone formation whereas bone resorbtion is unabated

• Currently available agents (bisphosphonates) focus largely on preventing resorbtion

• When bisphophonates are used in spaceflight, bone mineral loss is diminished but the resulting bone is histologically abnormal


Discussion:

• Simvastatin appears to promote bone formation, rather than preventing resorbtion

• Enhances BMP-2 synthesis (potent stimulator of bone synthesis)• Blocks production of isoprenoids (modify Ras and Ras-like proteins)• Upregulates VEGF expression (which is required new bone formation)• Induces osteoblast differentiation and maturation

• Simvastatin is likely a more suitable agent for preventing bone loss in spaceflight


Discussion:

• Simvastatin administration to hindlimb suspended mice significantly impacted loss of bone mineral following two weeks of hindlimb-suspension

• Compared to weight-bearing controls (C ), hindlimb-suspended mice (SV) lost 13.7 and 7.9% of bone mineral content in the femur and tibia respectively• Simvastatin administration (SS) attenuated this loss (7.9 and 1.4% respectively)• The loss of bone mineral content in the (SV) group relative to the (C ) group was statistically significant• There was no significant difference between the (C ) group and simvastatin treatment group (SS)

Discussion:

Future studies will focus on bone morphology, functionalproperties, and the mechanism of action of simvastatin onbones of hindlimb-suspended mice

• Magnetic resonance microscopy• Light microscopy• Dynamic labeling studies• Bone strength and fracture risk



How does this research apply to Emergency Medicine?

• Diseases of bone loss constitute a major health problem• 30 million Americans at risk for osteoporosis, 100 million worldwide• The elderly population is expanding• Significant morbidity and mortality associated with osteoporotic fracture• Loss of specialist coverage• ED overcrowding

Disease prevention is as important as treatment!


Meier et al., (2000)• Asked if use of statins decreased risk of fracture in humans• Population-based, nested case control study• Patients were identified from the UK-based General Practice

Research database (3 Million Patients) • 28,340 patients prescribed lipid-lowering drugs, 13,271 patients diagnosed with hyperlipidemia but not treated, 50,000 patients without the diagnosis of hyperlipidemia• Controlled for body mass, smoking, physician utilization, estrogen use, and corticosteroid use• Current use of statins was associated with a significantly reduced risk of fracture (OR 0.55; 95% CI 0.44-0.69)


Wang et al., (2000)• Examined if statin use was associted with reduced risk of hip fracture• Case-control study• Patients identified through Medicaid or Pharmacy Assistance for the Aged and Disabled Program• 6110 patients, 65 years or older• 1222 patients underwent surgical repair of a hip fracture, 4888 control patients matched for age and sex• Controlled for race, insurance status, psychoactive medications, estrogen, thiazide use, number of medications, DM, ischemic heart disease, cancer, Charlson comorbidity index, recent nursing hone stay, and physician utilization• Use of statins in the prior 180 days (OR 0.50; 95% CI 0.33-0.76) and prior three years (OR 0.57; CI 0.40-0.82) was associated with a significant reduction in the risk of hip fracture• Adjusted for extent of use in the past three years, current use at time of fracture showed a 71% decrease in fracture risk (OR 0.29; CI 0.10-0.81)


Wantanabe et al., (2001)• Examined if treatment with statins affected bone mineral density over a 12 month period• Randomized trial• Postmenopausal patients with hypercholesterolemia who had not been previously treated• 31 patients assigned to either fluvastatin (lipophilic) or pravastatin (hydrophilic) treatment groups• No significant differences in age, years after menopause, body weight body mass index, or baseline bone mineral density between groups• Lumbar bone mineral density decreased in the pravastatin group but but not in the fluvastatin group. Whole body bone mineral density was not significantly different between groups• Lumbar bone mineral density increased in the fluvastatin group at 6 and 12 months

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Simvastatin Attenuates Bone Loss Following Simulated Spaceflight John R. Gardner M.D., Ph.D. Department of Emergency Medicine University of Illinois College