MK-677 oral dosing raised bone turnover markers up to 29% in elderly adults
Background
Age-related bone loss is driven partly by declining growth hormone (GH) and IGF-1 secretion, which reduces osteoblast activity and shifts bone remodeling toward net resorption. GH itself stimulates osteoblasts in vitro and elevates bone turnover markers when administered directly, but injectable GH carries practical and safety drawbacks for chronic use in elderly populations. A key pathway mediating GH's skeletal effects runs through IGF-1, produced either systemically by the liver or locally within bone tissue. MK-677 is an orally active, non-peptide GH secretagogue (GHSR agonist) that mimics ghrelin signaling to stimulate endogenous GH pulses, offering a convenient oral alternative to exogenous GH injections in aging populations at risk for osteoporosis and functional decline.
Study Design
Three randomized, double-blind, placebo-controlled clinical studies enrolled 187 elderly adults (≥65 years). In the dose-response cohort, MK-677 10 mg or 25 mg orally daily vs. placebo was given for 2 weeks (n = 10–12/group). A second healthy-elderly cohort (n = 50) received 25 mg/day × 2 weeks then 50 mg/day × 2 weeks or placebo for 4 weeks. A third cohort of 105 functionally impaired elderly received 5, 10, or 25 mg/day escalating to 25 mg/day for 9 weeks total (n = 63 MK-677; n = 28 placebo completers). Primary endpoints were urinary NTX (bone resorption), serum osteocalcin and BSAP (bone formation), and serum IGF-I.
Results
In the dose-response study, 10 mg MK-677 raised mean urinary NTX by 10% and 25 mg raised it by 17% (both p < 0.05 vs. placebo) after just 2 weeks. In the healthy elderly cohort, 25/50 mg MK-677 increased mean serum osteocalcin by 8% (p < 0.05) and raised IGF-I by 55–94% across studies. In functionally impaired subjects treated for 9 weeks, combined MK-677 groups showed a mean serum osteocalcin rise of 29.4% and BSAP rise of 10.4% (both p < 0.001 vs. placebo), alongside a 22.6% increase in urinary NTX excretion (p < 0.05 vs. placebo).
The change from baseline serum osteocalcin correlated with the change from baseline serum IGF-I in the MK-677 group (r = 0.37; p < 0.01), suggesting
IGF-1mediates at least part of the bone anabolic signal.
Dose-dependent effects were visible across the 5, 10, and 25 mg escalation arms, reinforcing a pharmacological relationship between GHSR stimulation and skeletal marker responses.
Key Findings
- MK-677 25 mg/day raised urinary NTX (bone resorption) by 17% after 2 weeks (p < 0.05).
- Osteocalcin increased 29.4% and BSAP 10.4% in functionally impaired elderly after 9 weeks (p < 0.001).
- Urinary NTX rose 22.6% in functionally impaired elderly over 9 weeks (p < 0.05).
- Serum IGF-I increased 55–94% across studies with MK-677 treatment.
- Osteocalcin change correlated with IGF-I change in MK-677 group (r = 0.37; p < 0.01).
Why It Matters
Oral MK-677 produced measurable increases in both bone formation and resorption markers, suggesting coupled bone remodeling rather than isolated catabolism — a more favorable skeletal profile than pure resorption-driven signals. For clinicians and researchers, 9 weeks of once-daily oral dosing at 25 mg appears sufficient to elicit significant changes in osteocalcin and BSAP, which are established proxies for osteoblast activity. The IGF-1–osteocalcin correlation anchors the mechanism, implying that protocols targeting bone health should monitor serum IGF-I as a surrogate. Functionally impaired elderly showed amplified responses compared to healthy elderly, which may indicate greater skeletal sensitivity in this population and relevance for frailty-related bone loss protocols.
TitrateLab articles covering MK-677
Written by TitrateLab, separately from the study summarized above.
