MK-677 Raised IGF-1 to Youthful Levels and Increased Fat-Free Mass in Older Adults
Background
Sarcopenia — age-related loss of skeletal muscle mass — accelerates after midpuberty as growth hormone (GH) secretion declines progressively, reducing downstream IGF-1 signaling critical for muscle protein synthesis and maintenance. By late life, this contributes to frailty, functional decline, and loss of independence, yet the precise etiologic contribution of GH deficiency to sarcopenia remains incompletely characterized. Standard care lacks approved pharmacological tools to safely restore physiologic GH pulsatility in aging. Ghrelin mimetics that act on GHSR (growth hormone secretagogue receptor) offer a potential oral route to amplify endogenous GH secretion without bypassing pituitary feedback, making them an attractive mechanistic probe and potential therapeutic.
Study Design
A 2-year, double-blind, randomized, placebo-controlled, modified-crossover clinical trial enrolled 65 healthy older adults (men, women on HRT, and women not on HRT) aged 60–81 years at a general clinical research center within a university hospital. Participants received MK-677 25 mg orally once daily or matching placebo. The co-primary endpoints at 1 year were fat-free mass and abdominal visceral fat, measured alongside GH and IGF-1 levels, body weight, fat mass, insulin sensitivity, lipid panels, cortisol, bone mineral density, limb lean and fat mass, isokinetic strength, function, and quality of life — all assessed at baseline and every 6 months.
Results
Daily MK-677 significantly elevated both GH and IGF-1 levels into the range observed in healthy young adults without serious adverse events. Fat-free mass declined in the placebo group but rose in the MK-677 group (change: -0.5 kg [95% CI, -1.1 to 0.2 kg] vs. +1.1 kg [CI, 0.7 to 1.5 kg]; p < 0.001). Body cell mass, reflected by intracellular water, showed a similar divergence (-1.0 kg vs. +0.8 kg; p = 0.021). Limb fat increased significantly more in the MK-677 group than placebo (1.1 kg vs. 0.24 kg; p = 0.001), though no significant difference was found in abdominal visceral fat or total fat mass. Body weight rose 2.7 kg (CI, 2.0–3.5 kg) in the MK-677 group vs. 0.8 kg in placebo (p = 0.003). Fasting blood glucose increased by an average of 0.3 mmol/L (5 mg/dL) in the MK-677 group (p = 0.015), and insulin sensitivity decreased. LDL cholesterol fell -0.14 mmol/L (-5.4 mg/dL) from baseline in the MK-677 group (p = 0.026), with no between-group differences in total or HDL cholesterol. Cortisol increased 47 nmol/L (1.7 µg/dL) in the MK-677 group.
Fat-free mass increased +1.1 kg with MK-677 versus a decline of -0.5 kg with placebo over one year (p < 0.001), demonstrating a net between-group separation of 1.6 kg in lean tissue.
Key Findings
- Fat-free mass: +1.1 kg (MK-677) vs. -0.5 kg (placebo); p < 0.001
- GH and IGF-1 levels restored to healthy young-adult range with MK-677
- Fasting blood glucose rose 0.3 mmol/L (5 mg/dL) in MK-677 group; p = 0.015
- LDL cholesterol decreased -0.14 mmol/L (-5.4 mg/dL) from baseline; p = 0.026
- Limb fat increased 1.1 kg (MK-677) vs. 0.24 kg (placebo); p = 0.001
Why It Matters
Oral MK-677 at 25 mg/day demonstrably attenuates age-related lean mass loss and restores IGF-1 to youthful concentrations, establishing proof-of-concept that GHSR agonism can counter one measurable dimension of sarcopenia without requiring injections. Clinicians considering GH-axis interventions should weigh the insulin-sensitizing trade-off: a modest fasting glucose rise of 5 mg/dL and decreased insulin sensitivity signal metabolic vigilance — particularly relevant for individuals with pre-diabetes risk. For practitioners or researchers designing protocols, the appetite increase subsided after a few months and edema was mild and transient, suggesting tolerability improves with continued use. The 2-year design with 6-month assessments sets a methodological benchmark for future sarcopenia trials, but the lack of an effect on abdominal visceral fat cautions against positioning MK-677 as a body-recomposition agent without further stratified data.
TitrateLab articles covering MK-677
Written by TitrateLab, separately from the study summarized above.
