Injectable YK-11 Research Guide: SARM + Myostatin Inhibitor, Follistatin & Anabolic Muscle Research

YK-11 is a synthetic steroidal compound that occupies a unique position in research pharmacology as both a selective androgen receptor modulator (SARM) and a myostatin inhibitor. First described by Japanese researcher Yuichiro Kanno in 2011, YK-11 binds the androgen receptor (AR) with high affinity while simultaneously inducing follistatin expression, the natural antagonist of myostatin (GDF-8), a transforming growth factor-beta (TGF-β) family member that limits skeletal muscle mass. This dual mechanism has made YK-11 a compelling subject of muscle biology and anabolic research. This guide reviews the science behind YK-11, its known mechanisms, and the current state of preclinical research. All content is strictly for scientific and informational purposes.

What Is YK-11?

YK-11 (chemical name: (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester) is a C19 steroidal compound structurally related to 5α-dihydrotestosterone (DHT), making it distinct from the majority of non-steroidal SARMs. Its steroidal backbone gives it a higher intrinsic binding affinity for the androgen receptor compared to non-steroidal SARMs, while its unique C-17 and C-21 side chain modifications confer the tissue-selective agonist profile and myostatin-suppression properties that define its research interest.

YK-11 is typically produced as a lyophilized or oil-based injectable research compound. The injectable format provides more reliable bioavailability for in vivo research compared to oral administration, where hepatic first-pass metabolism significantly reduces systemic exposure.

Mechanisms of Action

Androgen Receptor Partial Agonism

YK-11 binds the androgen receptor with high affinity (Kd reported in the low nanomolar range) and acts as a partial agonist, activating AR-mediated transcription but with a distinct coactivator recruitment profile compared to full agonists like DHT or testosterone. Research using cell-based luciferase reporter assays has shown that YK-11 induces AR-dependent gene expression more potently than DHT in some assay systems, while showing tissue selectivity consistent with SARM classification. This selectivity profile is attributed to the unique AR conformation induced by YK-11 binding, stabilizing specific AR helix-12 conformations that preferentially recruit muscle-associated coactivators (e.g., SRC-1, TIF-2) over prostate-associated transcriptional programs.

Myostatin Inhibition via Follistatin Induction

The most distinctive aspect of YK-11’s pharmacology is its induction of follistatin expression in skeletal muscle cells. Myostatin (GDF-8) is a TGF-β superfamily ligand that binds Activin Type II receptors (ActRIIA/B) and signals via SMAD2/3 to suppress satellite cell activation, reduce protein synthesis, and limit muscle fiber hypertrophy. Myostatin acts as a biological “ceiling” on muscle mass, animals genetically deficient in myostatin (e.g., myostatin knockout mice, “double-muscled” Belgian Blue cattle) display dramatic muscle hypertrophy.

Follistatin is an endogenous glycoprotein that binds and neutralizes myostatin (and related Activin ligands) with high affinity, preventing receptor engagement and effectively removing the myostatin-mediated growth ceiling. YK-11’s induction of follistatin in C2C12 myoblast cultures and in vivo models represents a mechanism for releasing this constraint on muscle protein accretion, operating synergistically with its direct AR agonism.

This dual pathway, direct anabolic signaling through AR + disinhibition of muscle growth through myostatin neutralization, is what distinguishes YK-11 from conventional SARMs that act solely through androgen receptor pathways.

Wnt Signaling and Bone Research

Recent cell culture studies have identified a third potential mechanism: YK-11 appears to activate Wnt/β-catenin signaling in osteoblast models, stimulating bone-forming activity. This finding positions YK-11 as a potential subject for bone density and anabolic bone metabolism research, separate from its muscle effects, though in vivo bone data remains limited.

Preclinical Research Findings

Myoblast and Muscle Cell Studies

Kanno et al.’s original 2011 paper in Biological and Pharmaceutical Bulletin demonstrated that YK-11 treatment of C2C12 myoblasts induced dose-dependent increases in follistatin mRNA and protein levels, alongside AR-mediated anabolic gene expression. Subsequent studies confirmed that YK-11-treated myoblasts showed enhanced differentiation, increased myotube diameter, and greater expression of myosin heavy chain isoforms compared to DHT-treated controls, suggesting the follistatin component adds measurable anabolic signal beyond AR agonism alone.

In Vivo Muscle Mass and Strength

In vivo rodent studies have demonstrated that YK-11 administration produces statistically significant gains in lean muscle mass and grip strength relative to vehicle controls. Importantly, effects on prostate weight (a surrogate for androgenic side effects) were substantially lower than observed with equivalent anabolic doses of testosterone, consistent with the tissue-selective SARM profile. Dose-response relationships have been characterized in the range of 1–5 mg/kg in rodent models.

Bone Density

Osteoblast studies (Sun et al., 2018) found that YK-11 stimulated Wnt/β-catenin signaling and osteoblast differentiation markers including alkaline phosphatase, osteocalcin, and Runx2. In ovariectomized rat models of osteoporosis, YK-11 treatment preserved femoral bone mineral density significantly better than vehicle controls, suggesting potential applications in anabolic bone research alongside its muscle biology applications.

YK-11 vs. Other Anabolic Research Compounds

Injectable Format Considerations

YK-11’s oral bioavailability is substantially reduced by first-pass hepatic metabolism of its ester groups. Injectable formulations (typically in oil-based vehicle: benzyl benzoate/benzyl alcohol/carrier oil) bypass this limitation and provide more consistent systemic exposure for research purposes. Research-grade injectable YK-11 should be supplied as a sterile, filtered preparation with verified concentration, HPLC purity documentation, and appropriate carrier oil ratios to ensure solubility and injectability.

Disclaimer

YK-11 is an investigational research compound. It has not been approved for human use by the FDA or any equivalent regulatory body. All referenced studies are preclinical (cell culture and rodent models). This guide is for educational and scientific informational purposes only and does not constitute medical advice or endorsement of any use outside of controlled research settings.

References

• Kanno Y, et al. (2011). Activated androgen receptor Induces myogenesis by upregulating follistatin in C2C12 myoblasts. Biological and Pharmaceutical Bulletin, 34(3), 374–379.
• Kanno Y, et al. (2013). In vitro effects of YK11, a selective androgen receptor modulator, on C2C12 myoblasts. Biological and Pharmaceutical Bulletin, 36(7), 1231–1234.
• Sun Q, et al. (2018). Novel androgen receptor modulator YK11 stimulates osteoblastic Wnt signaling. Biochemical and Biophysical Research Communications, 503(4), 2801–2807.
• McPherron AC, Lawler AM, Lee SJ. (1997). Regulation of skeletal muscle mass in mice by a new TGF-β superfamily member. Nature, 387(6628), 83–90.
• Narayanan R, et al. (2018). Identification and mechanistic characterization of selective androgen receptor modulators. ACS Chemical Biology, 3(9), 529–560.

Research-Grade Injectable YK-11 Available

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