Met-Enkephalin
An endogenous opioid pentapeptide that doubles as the opioid growth factor, acting as a tonic brake on cell proliferation and immune activity.
Met-Enkephalin (Tyr-Gly-Gly-Phe-Met) is a naturally occurring pentapeptide that engages classical mu- and delta-opioid receptors for pain modulation and, in its role as opioid growth factor (OGF), binds the nuclear OGF receptor (OGFr, the zeta-opioid receptor) to tonically inhibit cell cycle progression. Through this OGF-OGFr axis it functions as a homeostatic regulator of cell proliferation, wound repair, and immune cell activity. It has no FDA-approved therapeutic use as an exogenous agent and remains a research-only compound characterized largely through preclinical and early-stage work.
Class
Endogenous opioid pentapeptide
Routes
Subcutaneous, Intravenous
Category
Immune & Mitochondrial
Researched benefits
What it's studied for
Immune modulation
As opioid growth factor, Met-Enkephalin influences immune cell regulation through the OGF-OGFr axis, a pathway implicated in modulating immune activity in preclinical and autoimmune-disease models.
Cell proliferation regulation
OGF binds the nuclear OGF receptor to upregulate the cyclin-dependent kinase inhibitors p16 and p21, inhibiting S-phase entry and acting as a tonic homeostatic brake on cell cycle progression.
Anti-inflammatory activity
The OGF-OGFr pathway has been characterized as a regulator of inflammatory processes, providing the mechanistic rationale for proposed low-dose naltrexone-mediated OGF upregulation in inflammatory conditions.
Autoimmune support
Reviews from the Zagon laboratory describe the OGF-OGFr axis as relevant to autoimmune disease, where intermittent opioid receptor blockade may raise endogenous MENK tone and suppress aberrant cell replication.
Wound and tissue repair
The OGF-OGFr axis has been characterized in models of wound repair, corneal repair, and diabetic wound healing, where receptor-blockade duration determines whether tissue growth is inhibited or enhanced.
Mechanism
How it works
Met-Enkephalin acts at classical mu- and delta-opioid receptors, where it contributes to pain modulation as one of the body's endogenous opioid peptides. This analgesic signaling is biologically distinct from its growth-regulatory role.
In its role as opioid growth factor (OGF), Met-Enkephalin binds the OGF receptor (OGFr, the zeta-opioid receptor) located on cell nuclei. There it regulates DNA synthesis and cell proliferation in a tonic, inhibitory manner, upregulating the cyclin-dependent kinase inhibitors p16 and p21 to block S-phase entry.
The OGF-OGFr axis functions as an endogenous homeostatic brake on cell cycle progression, a mechanism characterized in models of wound repair, organ development, and immune cell regulation. Research from the Zagon laboratory frames this axis as a broad homeostatic regulator of cell proliferation with implications for cancer, autoimmune disease, and tissue repair.
The duration of opioid receptor blockade determines the direction of the biotherapeutic response: intermittent low-dose blockade (as with low-dose naltrexone) upregulates receptor expression and endogenous MENK tone and suppresses cell replication, whereas continuous blockade enhances growth. This duration-dependence is the mechanistic basis for proposed low-dose naltrexone strategies in inflammatory and neoplastic conditions.
Evidence
Research & clinical studies (4)
Endogenous opioid peptides in trichotillomania: An exploratory analysis of focused and automatic hair-pulling subtypes
Adults with trichotillomania had significantly lower peripheral met-enkephalin and beta-endorphin than controls, with the focused hair-pulling subtype showing the lowest opioid peptide levels.
PMID 42019415Unraveling the role of iodide in photosensitized oxidation of Met-Enkephalin
Iodide ions competitively quench excited photosensitizer molecules, reducing oxidative damage to Met-enkephalin's methionine and tyrosine residues.
PMID 42019119Duration of opioid receptor blockade determines biotherapeutic response
Summarizes 30 years of evidence that intermittent low-dose blockade suppresses cell replication while continuous blockade enhances growth, with applications in diabetic wound healing, corneal repair, autoimmune disease, and cancer.
PMID 26119823The opioid growth factor-opioid growth factor receptor axis: homeostatic regulator of cell proliferation and its implications for health and disease
Describes how [Met5]-enkephalin (OGF) tonically inhibits cell proliferation via OGFr by modulating cyclin-dependent inhibitory kinase pathways, with implications for cancer, autoimmune disease, and wound healing.
PMID 22687282Combinations
Stacking & blends
Low-dose naltrexone (LDN) approach
Raise endogenous OGF tone for immune and proliferation regulation
Intermittent low-dose opioid receptor blockade upregulates OGFr expression and endogenous Met-Enkephalin tone, suppressing aberrant cell replication in inflammatory, autoimmune, and neoplastic contexts.
Safety
Side effects & considerations
Contraindications & cautions
- Active or prior cancer history
- Pregnancy or nursing
Met-Enkephalin carries a moderate risk profile in research contexts. Because the OGF-OGFr axis directly modulates cell proliferation, its use warrants particular caution where cell growth is a concern. Specific adverse-effect frequencies are not established in the available sources.
FAQ
Met-Enkephalin — common questions
What is Met-Enkephalin?
Methionine enkephalin (Met-enkephalin; opioid growth factor, OGF) is an endogenous pentapeptide (Tyr-Gly-Gly-Phe-Met) that acts at classical mu- and delta-opioid receptors for pain modulation and, in its OGF role, tonically inhibits cell proliferation through the nuclear OGF receptor (OGFr, the zeta-opioid receptor).
What is Met-Enkephalin primarily studied for?
Immune modulation, cell proliferation regulation, anti-inflammatory activity, and autoimmune support.
How does Met-Enkephalin regulate cell growth?
As OGF it binds the nuclear OGF receptor and upregulates the cyclin-dependent kinase inhibitors p16 and p21, blocking S-phase entry and acting as a tonic brake on the cell cycle.
What is the connection to low-dose naltrexone?
Intermittent low-dose opioid receptor blockade upregulates OGFr expression and endogenous Met-Enkephalin tone. The duration of blockade determines the response: intermittent blockade suppresses cell replication while continuous blockade enhances growth.
Is Met-Enkephalin FDA-approved?
No. It has no FDA-approved therapeutic applications as an exogenous agent and is characterized as research-only, with the OGF pathway studied mainly through preclinical and early-stage research.
What are the reported contraindications?
Reported considerations include active cancer history and pregnancy or nursing. This is educational information only; consult a qualified healthcare professional before use.
How is Met-Enkephalin administered in research?
Reported routes are subcutaneous and intravenous, though specific human dosing regimens are not established in the available literature.
