MGF (IGF-1 Ec)

Also known as: Mechano Growth Factor, IGF-1 Ec, IGF-1 splice variant

Evidence: Preclinical

PeptideLab is an educational platform for learning about peptides. The information here is for educational and research purposes only. It is not medical advice, diagnosis, or treatment, and PeptideLab does not claim to diagnose, treat, cure, or prevent any disease or health condition. Many peptides discussed have not been approved for human use by the FDA or other regulatory bodies. Consult a qualified healthcare professional before making any health-related decision.

Overview

The IGF-1Ec splice variant and its synthetic 24-residue E-domain peptide; mRNA rises in loaded human muscle, but the peptide's proliferative effect failed to replicate and no endogenous peptide has been isolated.

MGF is the name given to the IGF-1Ec splice variant (IGF-1Eb in rodents), whose mRNA rises in skeletal muscle after loading or damage; what is sold is the synthetic 24-residue C-terminal E-domain peptide. The mRNA response is documented: it rose after stretch and stimulation in rabbit muscle (McKoy 1999) and after high-resistance exercise in young but not elderly men (Hameed 2003). The peptide's own effects are contested. The original report found the E domain increased myoblast proliferation and delayed differentiation through a receptor other than IGF-1R (Yang 2002). Two pharmaceutical companies then failed to reproduce any effect on human or mouse myoblasts or muscle stem cells up to 500 ng/mL (Fornaro 2014), and no endogenous peptide matching it has been isolated from cells, medium, tissue or fluid (Matheny 2010). No human study of the peptide exists.

Benefits

Increased myoblast proliferation and delayed differentiation in vitro (contested; a two-company replication found no effect); neuroprotection in gerbil brain ischemia (animal); MGF mRNA rises in human muscle after loading, which is expression, not peptide effect. No human data for the peptide

Dosing reference

Research dose: 200 to 500 mcg post-exercise: research-community range, no published human dose and no published animal injection dose for the peptide
Range: 200 to 500 mcg, Post-workout
Reconstitution: 1 mL bacteriostatic water
Common vial sizes: 2 mg, 5 mg

Intramuscular or subcutaneous in community use. Local injection for local growth is not established: no published study has injected this peptide into muscle in any species, and the in vitro proliferative effect itself failed to replicate at up to 500 ng/mL (Fornaro 2014). No measured half-life exists for the peptide.

Mechanism

Alternative splicing of the IGF-1 gene across exons 4, 5 and 6 yields pro-IGF-1 isoforms with different E domains; the IGF-1Ec (rodent Eb) form is upregulated by loading and damage, which is why it was named mechano growth factor (Matheny 2010). The synthetic 24-residue C-terminal E peptide was reported to increase myoblast proliferation and delay terminal differentiation, an effect that persisted when IGF-1R was blocked with an antibody, implying a separate and still unidentified receptor (Yang 2002). That proposed mechanism is disputed: a replication across two companies found no effect on proliferation, differentiation or p-ERK in myoblasts, muscle stem cells or cardiac myocytes up to 500 ng/mL, while IGF-1 and full-length IGF-1Eb worked in the same assays (Fornaro 2014). No analogous peptide product of the gene has been isolated from any biological source.

Evidence

Preclinical: animal or in vitro data only

IGF-1 splice variant mRNA including the MGF form rose after stretch and electrical stimulation in rabbit skeletal muscle (McKoy et al., 1999)
After high-resistance knee-extensor exercise, MGF mRNA rose significantly in young men (25 to 36 y, n=8) but not in elderly men (70 to 82 y, n=7); resting MGF levels were about 100-fold below IGF-1Ea (Hameed et al., 2003)
The synthetic Ec E-domain peptide increased myoblast proliferation and inhibited terminal differentiation in vitro, and the effect survived IGF-1 receptor blockade, implying a different receptor (Yang and Goldspink, 2002)
The same C-terminal peptide was neuroprotective in gerbil transient brain ischemia and in organotypic hippocampal culture, independent of the IGF-1 receptor (Dluzniewska et al., 2005)
A replication across two pharmaceutical companies found no effect of MGF peptide up to 500 ng/mL on proliferation or differentiation of human or mouse myoblasts or primary muscle stem cells, and no p-ERK activation in cardiac myocytes, while IGF-1 and full-length IGF-1Eb worked in the same assays (Fornaro et al., 2014)
Human-trial status: none. No trial of MGF peptide has been published or registered; human data are limited to mRNA expression in muscle biopsies, and no endogenous MGF peptide has been isolated from any tissue or fluid (Matheny et al., 2010)

References

Side effects

No human study of the MGF peptide exists, and no pharmacokinetic or toxicology data are published for it in any species. Localized swelling and injection-site pain are reported by users. Hypoglycemia is the risk usually cited for IGF-1 family peptides through insulin receptor cross-reactivity, but the E-domain peptide is not IGF-1 and its reported effects were IGF-1R-independent, so that concern is inferred rather than measured. Because IGF-1 signaling promotes cell proliferation, use with active or suspected malignancy is inadvisable.

Storage

Storage: Refrigerate 2-8°C (36-46°F)
Lyophilized: 2+ years at room temp, 3+ years refrigerated
Reconstituted: 28-30 days refrigerated

Pharmacology

Half-life: Not measured. No pharmacokinetic study of the MGF peptide has been published in any species
Molecular weight: 2868.16 Da
Sequence: YQPPSTNKNTKSQRRKGSTFEERK (24 aa, C-terminal E domain of human IGF-1Ec)