What Is MK-677?
MK-677, also known as ibutamoren, is a synthetic, nonpeptide small molecule classified as a growth hormone secretagogue. It acts as an agonist of the growth hormone secretagogue receptor (GHSR), also known as the ghrelin receptor.
Unlike peptide secretagogues, MK-677 does not consist of an amino acid chain. Its scientific interest comes from its activity at GHSR and its relationship to growth hormone regulation. Research has examined GHSR signaling, growth hormone secretion and the growth hormone–IGF-1 axis.
Research Overview Table
Chemical and Molecular Characteristics
MK-677 (ibutamoren) is a small-molecule, non-peptide compound. The mesylate form combines ibutamoren with methanesulfonic acid. Its structure contains a spiro indole-piperidine system, amide groups, a methylsulfonyl group and a phenylmethoxy side chain.
The mesylate has a molecular formula of C₂₈H₄₀N₄O₈S₂ and a molecular weight of 624.8 g/mol. This defined small molecule structure differs from peptide compounds, which consist of linked amino acids. These chemical features provide the basis for identifying and describing MK-677 as a distinct research compound.
Certificates:
Mechanism of Action Under Investigation
MK-677 binds to the growth hormone secretagogue receptor (GHSR), a G protein-coupled receptor. Structural and mutational studies show that ibutamoren occupies the receptor’s agonist binding pocket and promotes the receptor conformation associated with G protein activation.
GHSR activation initiates intracellular signaling involving G proteins, phospholipase C, inositol phosphate signaling, and intracellular calcium. Other GHSR-linked pathways include cAMP and protein kinase signaling. These signals connect receptor activation with cellular regulation of growth hormone secretion.
The receptor also forms part of the signaling network involving growth hormone-releasing hormone and somatostatin. Research has established GHSR as a regulator of pulsatile growth hormone release but the relative contribution of individual downstream pathways to ibutamoren signaling remains unresolved.
Scientific Research Context
MK-677 has an established presence in the scientific literature. Research spans pharmacological and biological investigations. The evidence base includes in vitro studies, preclinical animal research and human studies. Overall, the literature represents a mixed evidence base, with substantial experimental research and a smaller body of clinical investigation.
MK-677 Biology and Biological Pathways
Primary Biological Function
The main biological system studied with MK-677 is the growth hormone (GH)–IGF-1 axis. GH supports growth, tissue development and metabolic regulation. The liver produces most circulating IGF-1, while other tissues can produce IGF-1 locally. Researchers examine this axis to understand changes in GH related endocrine biology and its effects across different tissues.
Relevant Metabolic or Signalling Pathways
GH uses several intracellular signaling pathways. JAK2–STAT5 plays a major role in GH regulated gene expression and IGF-1 production. GH also activates MAPK/ERK and PI3K-AKT signaling. These pathways link GH activity with changes in gene expression and metabolism. Researchers study them because each pathway contributes different cellular responses to GH.
Tissue-Specific Biology
The hypothalamus and pituitary are key tissues in the GH system. The liver produces most circulating IGF-1 after GH signaling. Skeletal muscle also responds to GH and IGF-1 and can produce IGF-1 within the tissue. These tissues have different roles in GH–IGF-1 biology. so researchers study them separately when examining MK-677 related endocrine research.
Experimental Biomarkers
Researchers commonly measure GH, IGF-1, and IGF-binding protein 3 (IGFBP-3) when examining MK-677-related endocrine biology. These markers provide information about activity within the GH–IGF-1 axis. Studies have also measured glucose and insulin when examining metabolic changes associated with altered GH and IGF-1 signaling.
Laboratory Investigation Methods
Researchers use hormone assays, repeated blood sampling, biochemical measurements and molecular techniques to examine this biology. Human studies have measured GH and IGF-1 concentrations over defined periods, while cell and animal studies can examine gene expression and intracellular signaling proteins. Researchers can therefore examine the GH–IGF-1 axis at the circulating, tissue, and cellular levels.
Experimental Models Used in Published Research
Published MK-677 research includes animal models, human studies, and cell-based systems. Animal models have species-specific limits, human studies may involve small or selected groups and cell systems cannot reproduce whole body biology.
Rat Models
MK-677 studies in rats. Rats are a preclinical animal model but their GH regulation and physiology is different than humans. Therefore, the results obtained in rats cannot be taken as fully representative of the human response.
Dog Models
Published studies have also used dogs including beagle dogs. Dogs are a larger animal model, but their endocrine physiology still differs from that of humans. This limits the direct translation of results from dogs to humans .
Human Studies
MK-677 has been studied in human participants, including healthy adults and older adults. as well as clinical populations. Human studies avoid species differences, but small samples, selected populations and study duration can limit how widely their findings apply.
Cell-Based Models
Other studies of MK 677 have used cultured cells and cell systems expressing receptors. These systems provide a controlled experimental environment but cannot simulate organ interactions or whole body endocrine control. Thus their findings have limited relevance to intact human physiology.
Published Scientific Research
Growth Hormone and IGF-1
Researchers have investigated MK-677 in relation to growth hormone and IGF-1 regulation. Human studies have included older adults, obese adults and children with growth hormone deficiency. Published trials measured circulating GH, IGF-1 and IGFBP-3 over different treatment periods.
Body Composition and Metabolic Research
Several human studies have investigated body composition and energy metabolism. Research has included fat free mass, body fat, energy expenditure, glucose and insulin measurements. Longer studies in older adults also examined body composition over time.
Bone Turnover
Published studies have investigated bone turnover using biochemical markers of bone formation and resorption. Research in older adults and obese men measured markers including osteocalcin, bone specific alkaline phosphatase and collagen breakdown products. These studies focused on biochemical changes rather than long-term changes in bone structure or fracture outcomes.
Sleep Research
Researchers have also examined sleep and related endocrine changes in human studies. This work included controlled studies in healthy adults and assessed sleep related measures alongside GH activity. The published research in this area remains smaller than the literature on GH, IGF-1 and metabolic measures.
Clinical Research
Researchers have tested MK-677 in older adults, people recovering from hip fracture and patients with Alzheimer disease. These studies examined body composition, physical function, and disease related outcomes. The clinical literature includes randomized and placebo-controlled trials but findings differ by population and research question.
Limitations of Current Research
Evidence Is Predominantly Preclinical
This point needs careful wording for MK-677. The compound has a substantial human research record, including randomized controlled trials. Preclinical studies in rats and dogs add supporting evidence, but the MK-677 literature as a whole is not predominantly preclinical.
Human Clinical Evidence
Human studies have examined MK-677 in several populations, including older adults, children with growth hormone deficiency and people recovering from hip fracture. However, participant numbers, populations and study periods vary between trials. Some clinical studies also ended early, which limits the amount of evidence available for certain research questions.
Species Differences
Animal research includes rats and dogs. These models can support preclinical investigation, but their endocrine systems do not fully match human physiology. Differences in growth hormone regulation, metabolism, and tissue responses limit direct application of animal findings to humans.
Study Design Limitations
MK-677 trials have used different doses, treatment periods, participant groups and outcome measures. Some studies included relatively small samples or short follow up periods. These differences make direct comparison between studies difficult and can limit conclusions about effects that require longer observation.
Independent Replication
The published record includes repeated human investigations, but the number of studies differs across research areas. GH and IGF-1 have received much more attention than some other outcomes. Independent studies using similar populations and methods would provide a stronger basis for comparing findings across the literature.
Long-Term Evidence
Long-term evidence remains limited for several outcomes. Some human studies lasted weeks, while longer trials have followed participants for months or up to two years. Even the longer studies do not answer every question about prolonged exposure. Reviews of GH secretagogues also note the limited number of rigorously controlled long-term studies.
Analytical Documentation
HPLC separates the components of a sample and can be used to examine chromatographic purity. Validated HPLC procedures may also provide information about identity and the amount of a particular component.
LC-MS adds mass spectrometric measurement to chromatographic separation. The resulting mass information can help characterize and identify compounds. NMR takes a different approach by examining the chemical environment of nuclei within a molecule. It can therefore provide structural information when the sample is suitable for NMR analysis.
A Certificate of Analysis brings together the analytical results recorded for a specific batch. Depending on the material and testing requirements, this may include identity, purity, composition and other quality specifications. Such documentation helps establish the quality and identity of the material used in laboratory research. It does not demonstrate biological performance.
Storage and Laboratory Handling
Store the MK-677 refrigerated at 2–8°C, following the storage conditions listed on the Certificate of Analysis. During laboratory handling, maintain the vial within this temperature range.
Good laboratory practice includes clean handling and measures that limit contamination of the vial or its contents. Personnel should maintain the specified storage conditions during laboratory handling. The material is intended for laboratory research use only.
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