MK-677 reduced LDL-C/HDL-C ratio in obese men but left Lp(a) unchanged
Background
Obesity is associated with blunted growth hormone (GH) secretion and an unfavorable lipoprotein profile, including elevated LDL cholesterol, reduced HDL cholesterol, and raised triglycerides — a cluster that elevates cardiovascular risk. GH itself influences hepatic lipoprotein metabolism, so pharmacologically restoring GH pulsatility in obese individuals is a plausible route to improving lipid biomarkers. MK-677 is an oral, non-peptide GH secretagogue that stimulates endogenous GH release via the GHSR (ghrelin receptor), offering a practical alternative to injectable GH or peptide secretagogues. The specific effect of GHSR agonism on lipoprotein(a) [Lp(a)] — a genetically determined, largely treatment-resistant cardiovascular risk marker — was unknown prior to this work.
Study Design
A randomized, double-blind, parallel-group clinical trial enrolled 24 obese males aged 18–50 yr with BMI > 30 kg/m² and waist/hip ratio > 0.95. Participants received either 25 mg MK-677 orally once daily (n = 12) or matched placebo (n = 12) for 8 weeks. Serum lipoproteins — including Lp(a), apolipoprotein A-I (apoA-I), apolipoprotein E (apoE), total cholesterol, LDL-C, HDL-C, triglycerides, and mean LDL particle diameter — were measured at baseline, 2 weeks, and 8 weeks. Lipoprotein lipase (LPL) activity was assessed in both abdominal and gluteal subcutaneous adipose tissue biopsies as a mechanistic endpoint.
Results
MK-677 did not significantly change serum Lp(a) at any time point, confirming the null hypothesis for that endpoint. ApoA-I and apoE were both elevated at 2 weeks (P < 0.001 and P < 0.01 vs. placebo, respectively), but neither remained elevated at 8 weeks. HDL-C was increased at 2 weeks (P < 0.01 vs. placebo) but not at study end. Triglycerides were raised at 2 weeks (P < 0.05 vs. placebo) but normalized by 8 weeks. Mean LDL particle diameter was decreased at 2 weeks (P < 0.05 vs. placebo) yet returned to baseline-comparable values by 8 weeks. Total cholesterol and LDL-C were not significantly changed at either time point. LPL activity in subcutaneous adipose tissue was unaffected by active treatment.
The single durable finding: the LDL-C/HDL-C ratio was reduced at 8 weeks (P < 0.05 vs. placebo), representing the only statistically significant lipoprotein improvement that persisted to study end.
Key Findings
- LDL-C/HDL-C ratio reduced at 8 weeks (P < 0.05 vs. placebo) — the sole durable lipoprotein benefit.
- ApoA-I raised at 2 weeks (P < 0.001 vs. placebo) but not sustained to 8 weeks.
- ApoE raised at 2 weeks (P < 0.01 vs. placebo) but not sustained to 8 weeks.
- HDL-C and triglycerides transiently changed at 2 weeks but normalized by study end.
- Serum Lp(a) not significantly changed at any time point with 25 mg/day MK-677.
Why It Matters
The sustained reduction in the LDL-C/HDL-C ratio is clinically meaningful because this ratio is an independent predictor of cardiovascular events, and oral GH secretagogues are already being explored for body composition in obesity. The transient nature of most other lipoprotein changes — apoA-I, apoE, HDL-C, and triglycerides all reverting by week 8 — suggests that acute GH-driven metabolic shifts are partially offset by counter-regulatory adaptation, a pattern practitioners should not mistake for a durable lipid benefit. For those using MK-677 on protocols hoping to improve full lipid panels, the absence of any Lp(a) reduction is directly relevant, given Lp(a)'s growing prominence as a residual cardiovascular risk marker. The GHSR-agonist mechanism alone appears insufficient to modulate this genetically anchored lipoprotein at the tested dose and duration.
TitrateLab articles covering MK-677
Written by TitrateLab, separately from the study summarized above.
mk-677
ibutamoren
obesity
lipoproteins
cardiovascular
growth hormone secretagogue
