MK-2866 – Ostarine is an orally available, non-steroidal SARM that has demonstrated fascinating results in both preclinical and clinical trials, and it is currently being explored for a number of different indications. It is being investigated clinically and preclinically for a variety of benefits:
increased lean body mass and muscle strength;
prevention of muscle loss;
prevention of osteoporosis;
urinary incontinence due to stress;
and treatment of prostate cancer.
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Ostarine is an orally available, non-steroidal SARM that has demonstrated fascinating results in both preclinical and clinical trials, and it is currently being explored for a number of different indications. It is being investigated clinically and preclinically for a variety of benefits:
Ostarine has been the subject of two different Phase 2 clinical trials each of which produced positive data regarding its ability to increase strength.
The first was a study of cachexia—also known as muscle wasting—which is a complex musculoskeletal condition characterized by loss of appendicular skeletal muscle and a complementary decline in physical function with respect to strength. In this study, which was a 12‐week randomized, double‐blind, placebo‐controlled trial, Ostarine was evaluated in 120 healthy men (>60 years of age) and postmenopausal women, all healthy volunteers without evidence of disease recruited from the general population around the phase I study units in the UK, Northern Ireland, and Germany . The primary goal of the study was to assess changes in total lean body mass (as assessed by dual-energy X‐ray absorptiometry) while the secondary goal was to assess broad physical function, body weight, insulin resistance, and pharmacological safety and tolerability. The volunteers were not allowed to initiate dietary modification or initiate or discontinue any exercise program during the study. No additional dietary supplementation was provided. Volunteers were randomly assigned to one of five different dose groups (doses of 0.1, 0.3, 1.0 and 3.0 mg of Ostarine or placebo) and were instructed to consume the medication every day for 80-90 days at approximately the same time each day, which included a period of approximately 70 days on an outpatient basis. These doses were chosen from the pharmacokinetic, safety and tolerability data from the previous trials with Ostarine, and the clinical trial material was provided by the manufacturer, GTx, Inc. Each dose group contained 24 volunteers and was randomized in equal fashion. Randomization was done in such a way that each dose group contained equivalent numbers of both genders. A baseline pre‐study assessment of the volunteers was completed within 3 days of the first administered dose, and the final assessments were conducted at day 86. Body composition, including bone mineral density, was assessed at baseline, day 30, and day 86 by Xray. Physical function was evaluated using the Stair Climb Test at baseline, day 30, and day 86. Volunteers were asked to climb the stairs, one step at a time as quickly as possible without assistance, and were asked to only use the handrail if they felt like they were losing their balance.
Figure 1. Ostarine increases lean body mass in a dose-dependent fashion.
Percentage change from baseline end of the study in total lean body mass: entire study population, *P < 0.001 3 mg vs. placebo (T-test).
Adapted from J. T. Dalton et al., “The selective androgen receptor modulator Enobosarm improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial.,” J. Cachexia. Sarcopenia Muscle, vol. 2, no. 3, pp. 153–161, Sep. 2011.
Figure 2. Ostarine increases lean body mass decreases fat mass and increases power as measured in stair climb challenge.
A statistically significant decrease in total fat mass was also observed at the 3‐mg dose, with the 1‐mg dose approaching statistical significance (P = 0.085). The differences in changes in fat mass from baseline were similar in males and females with a loss of 0.6 kg relative to placebo. No differences in total body weight were observed.
Adapted from: Adapted from J. T. Dalton et al., “The selective androgen receptor modulator Enobosarm improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial.,” J. Cachexia. Sarcopenia Muscle, vol. 2, no. 3, pp. 153–161, Sep. 2011.
The risk profile of TRT (testosterone replacement therapy) and anabolic steroid use limits their clinical utility for a variety of health conditions that would otherwise benefit from increasing lean mass, improving physical function, and improving insulin resistance. Ostarine is the first SARM to reach advanced clinical trials and demonstrate excellent efficacy and safety . In this randomized, double‐blind, placebo‐controlled study, Ostarine increased total lean body mass and improved physical function with no evidence of androgenic side effects in healthy men and postmenopausal women. The increase in total lean body mass with Ostarine was accompanied by a vast improvement in physical function as evidenced by a clinically-meaningful improved score in the Stair Climb Test.
Ostarine at 3.0 mg also significantly reduced fasting glucose levels, and a trend toward reduction in blood insulin was observed. These effects resulted in a decrease in insulin resistance from baseline in the 1.0 mg and 3.0 mg treatment groups. Of note, such a decrease in insulin resistance was similar to that observed with metformin and glipizide, which are drugs used in the treatment of diabetes , . Low levels of testosterone in men are associated with insulin resistance and type II diabetes, while testosterone therapy is known to improve metabolic parameters –. This observation may have potential implications for the use of SARMs in pre-diabetic or diabetic individuals, as commonly seen in patients with chronic kidney disease, chronic obstructive pulmonary disease, or metabolic syndrome –.
Ostarine was well tolerated with similar adverse events compared to placebo during the 3 months of daily treatment. Compared to placebo, Ostarine decreased total cholesterol, HDL, and triglycerides. These findings are consistent with previous reports that oral anabolic therapy influences serum lipid profiles , . Furthermore, the beneficial effects of Ostarine on insulin sensitivity and triglycerides, combined with the known associations of hypogonadism with metabolic syndrome and cardiovascular risk, as well as the low cardiovascular risk observed in randomized clinical trials of testosterone supplementation , all point to one conclusion: the overall cardiovascular risk/benefit ratio for Ostarine is very favorable.
The pharmacologic effects of Ostarine on serum hormone levels were unremarkable. Notable but expected reductions in serum hormone-binding globulin (SHBG) and total testosterone in men were observed. The reductions in SHBG in men and women (−61% and −80%, respectively, at the 3.0 mg dose) exceed those observed in men treated with a 600‐mg intramuscular testosterone enanthate (−31%). Decreases in total testosterone accompanied the observed decreases in SHBG. However, no significant decreases in free testosterone were observed in men or women at any dose of Ostarine.
In this 3‐month study, Ostarine showed no difference in bone mineral density compared to placebo. However, such effects were not necessarily expected as the treatment period was likely too short to discern any benefit. In preclinical studies, Ostarine demonstrated both anabolic and antiresorptive (ie. bone protecting) activity in bone. Future research is warranted as the potential dual beneficial effects of Ostarine and other SARMs on muscle and bone may provide a unique advantage to currently available agents for osteoporosis that solely modify bone strength.
In the second Phase 2 clinical trial which began in 2007, Ostarine was tested primarily for its ability to increase lean body mass in men and women . Secondary measures included total bodyweight, physical function (stair climb, 6-meter walk, and grip test), bone turnover markers, total body fat mass, hair growth, prostate-specific antigen, hemoglobin, appetite, quality of life (assessed by Functional Assessment of Anorexia/Cachexia Therapy score [FAACT] and Functional Assessment of Chronic Illness Therapy-Fatigue [FACIT-F]), and inflammation markers. Changes in body weight were measured with scale weight on day 1 and day 113 or end of the study. Physical function was assessed at baseline and before day 113 or end of the study. Stair climb time was recorded with electronic step switch pads. Grip strength was measured using a Jamar Hydraulic Hand Dynamometer. The occurrence, severity, duration, and possible mechanistic relation of adverse events to Ostarine were recorded from the first dose through the treatment period. The severity of adverse events was graded according to established criteria, and clinical laboratory results, vital signs, and physical examination findings were also assessed. None of the recorded adverse events were deemed related to study drug Ostarine.
Figure 3. Ostarine/Enobosarm at both study doses increased mean lean body mass.
Adapted from A. S. Dobs et al., “Effects of enobosarm on muscle wasting and physical function in patients with cancer: A double-blind, randomized controlled phase 2 trial,” Lancet Oncol., vol. 14, no. 4, pp. 335–345, Apr. 2013.
Figure 4. Ostarine/Enobosarm improved stair climb speed and power. Adapted from A. S. Dobs et al., “Effects of enobosarm on muscle wasting and physical function in patients with cancer: A double-blind, randomized controlled phase 2 trial,” Lancet Oncol., vol. 14, no. 4, pp. 335–345, Apr. 2013.
Figure 5. Ostarine/Enobosarm improved stair climb speed and power. Mean absolute change from baseline to day 113 or end of the study in stair climb time and power. Adapted from A. S. Dobs et al., “Effects of enobosarm on muscle wasting and physical function in patients with cancer: A double-blind, randomized controlled phase 2 trial,” Lancet Oncol., vol. 14, no. 4, pp. 335–345, Apr. 2013. Notably in this study, there were no significant differences observed between the Ostarine and placebo groups with respect to changes in hair growth in women, or serum prostate-specific antigen (PSA) concentrations in men.
Discussion Both 1.0 mg and 3.0 mg of Ostarine resulted in vital increases in lean body mass in patients compared with baseline measurements. No significant changes from baseline were noted in those who were assigned placebo. Ostarine was generally well tolerated, with the occurrence of adverse events and the overall pattern of adverse events being similar among placebo and treatment groups. Increases in alanine aminotransferase concentrations were transient. Crucially, no patient discontinued treatment because of increased alanine aminotransferase concentrations. Overall, despite the heterogeneity of the patient population, treatment with Ostarine resulted in clinical benefit as shown by statistically significant improvements in lean body mass and stair climb power. The stair climb test is a common measure of physical function in elderly populations or those with physical impairment due to injury. Studies in older adults have shown that reduced lower leg function and low leg power predict subsequent disability and decreased healthspan –. This study is one of the first to report stair climb power as an assessment of physical function after treatment with a SARM. Thus, the stair climb test is a simple and reliable measure of leg power and, more importantly, provides a direct measure of a clinically meaningful activity that takes into consideration several muscle-related attributes (eg, balance, strength, mobility, and endurance) of a major muscle group used for locomotion. Although some have argued that changes in lean body mass do not always temporally coincide with changes in physical function, there was a modest correlation between changes in total lean body mass and stair climb power in this study. Handgrip strength is also commonly used to assess physical function but might not be as reliable because of arthritis, atrophy, inflammation, or compensatory use of the hands and arms by people who are sick or elderly as they become physically impaired. Patients who commonly rely on their arms and hands to assist them as they stand or do other activities of daily living, might delay or lessen muscle wasting in the upper arms or mask the effects of a SARM on handgrip strength in these smaller muscle groups. Physical function tests of walking speed (6-meter walk) and handgrip strength were done during this study as exploratory endpoints but no significant differences were observed. Although this study is perhaps the first to show that a SARM can increase lean body mass and improved physical function in patients with existing muscle loss, the small sample size and heterogeneity of the nutritional status of patients enrolled could be deemed potential limitations. Nonetheless, it would be interesting to know the potentially synergistic effect that could accrue from specific nutritional supplementation in conjunction with Ostarine. Ultimately, the desired profile of any agent developed to treat muscle wasting and concomitant loss of strength would need to demonstrate a strong anabolic effect on skeletal muscle, lean body mass, and metabolic processes, improve the functional capacity of the patient, and exhibit a safe and tolerable side-effect profile. Encouragingly, the data available at the time of study enrollment uncovered in our search suggested that Ostarine was the best candidate to satisfy these requirements.
Key Clinical Findings
Ostarine increases lean body mass and strength in diverse adult populations.
Ostarine demonstrates excellent safety and tolerability.
Preclinical Data Androgen receptor (AR), a member of the steroid receptor superfamily, and its binding partners play important roles in several biological processes such as the development and maintenance of secondary sexual organs, bone, and muscle . Separation of these two effects is desirable for expanded therapeutic application and success of androgens, and one such candidate for improved and selective AR modulation is Ostarine . However, it is not clear if Ostarine and Dihydrotestosterone (DHT) have different binding affinities for AR and exert different pharmacological effects.
Figure 6. Ostarine is a tissue-selective SARM that activates androgen receptor (AR)
Activation of AR by DHT vs Ostarine. HEK-293 cells were transfected with a light-emitting reporter for 24 h. Light was then measured and normalized to determine the activation of AR. More light = more activation. RLU=Relative light units. DHT in the solid black square; Ostarine in open white squares; control in black triangles.
DHT and Ostarine both enhance PSA gene expression. LNCaP cells were starved for 3 d and treated in triplicate with control (white bars), DHT (black bars), or Ostarine (striped bars) for 24 h. PSA gene expression was measured and normalized. *Significance at P < 0.05 from control-treated samples.
Tissue-selective actions of Ostarine in rats. Sprague Dawley rats (n = 5) were treated with control, 1 mg/d DHT (black bars) or Ostarine (striped bars) for 14 d. At the end of 14 d, the animals were euthanized, and the weights of prostate and levator ani muscle (ie. pelvic muscle) were measured and interpreted as percent change from control-treated animals. *Significance at P < 0.05 from control-treated samples.
Adapted from: R. Narayanan, C. C. Coss, M. Yepuru, J. D. Kearbey, D. D. Miller, and J. T. Dalton, “Steroidal androgens and nonsteroidal, tissue-selective androgen receptor modulator, S-22, regulate androgen receptor function through distinct genomic and nongenomic signaling pathways,” Mol. Endocrinol., vol. 22, no. 11, pp. 2448–2465, Nov. 2008. Preclinical Conclusion: Ostarine activates the androgen receptor (AR) and shows tissue specificity for muscle as opposed to the prostate. Safety In clinical trials, Ostarine has been shown to be exceptionally safe and well-tolerated in virtually all patients. Adverse events were infrequent and similar between the experimental group and placebo group at all doses tested. *The information herein is for educational and informational purposes only. THIS PRODUCT IS FOR RESEARCH USE ONLY. For use in animal studies, all research must be conducted with oversight from the appropriate Institutional Animal Care and Use Committee (IACUC) following the guidelines of the Animal Welfare Act (AWA).
Shipping Conditions: Ambient temperature. Storage: Use within 12 months. Keep in a cool and dark location.
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