Mechanism of Action
Melanocortin Receptor Activation
Alpha-MSH activates all five melanocortin receptors (MC1R-MC5R), which are Gs-coupled GPCRs that elevate cAMP. MC1R on melanocytes stimulates melanin synthesis (eumelanin preferentially, increasing skin darkening). MC3R and MC4R in the hypothalamus regulate energy balance and appetite (MC4R is the main anti-obesity target). MC4R in the spinal cord and brain mediates sexual arousal. MC2R (adrenal cortex) drives cortisol synthesis.
Anti-Inflammatory Effects
Alpha-MSH inhibits NF-kB activation and suppresses pro-inflammatory cytokine production (TNF-alpha, IL-6, IL-1beta). These effects occur via MC1R and MC3R on macrophages and dendritic cells. Alpha-MSH reduces fever by inhibiting IL-1 and PGE2 in the hypothalamus. Anti-inflammatory alpha-MSH peptide fragments (tripeptide KPV) retain activity with improved stability.
Research Summary
Sexual Function (Bremelanotide/PT-141)
FDA ApprovedBremelanotide (PT-141, a cyclic heptapeptide analog of alpha-MSH) is FDA-approved as Vyleesi for HSDD in premenopausal women. It acts on MC4R in the brain to increase sexual desire. Unlike sildenafil (which acts on genital vasculature), bremelanotide acts centrally on the sexual motivation circuit. Administered 45 minutes before sexual activity via autoinjector.
Obesity and Energy Balance
PreclinicalMC4R agonists reduce food intake and body weight in rodents; MC4R mutations account for ~5% of severe early-onset human obesity. Alpha-MSH fragment melanotan II and MC4R-selective agonists are extensively studied for anti-obesity effects. The challenge is selectivity: MC1R activation causes skin darkening (melanocyte stimulation), limiting systemic exposure.
Inflammatory Skin Disease
PreclinicalTopical or systemic alpha-MSH reduces inflammation in psoriasis and atopic dermatitis models via MC1R on skin cells and immune cells. KPV (C-terminal tripeptide of alpha-MSH) retains full anti-inflammatory activity with improved stability and BBB penetration, making it a lead for topical and oral anti-inflammatory applications.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Pigmentation increase (melanocyte stimulation) | 0.1-1 mg SC daily | Daily x 1-4 weeks (melanotan II analogs) | Subcutaneous |
| Sexual desire (bremelanotide) | 1.75 mg SC | As needed, 45 min before activity (max 1x/24h) | Subcutaneous (thigh/abdomen) |
| Anti-obesity MC4R agonism (rodent) | 1-5 mg/kg SC or ICV | Daily | Subcutaneous or ICV |
Bremelanotide (Vyleesi) is FDA-approved for HSDD in premenopausal women only. Unapproved melanotan analogs used for tanning or libido enhancement carry significant safety risks. See PT-141 page for full bremelanotide protocols.
Interactions
Safety Profile
Native alpha-MSH has extremely short plasma half-life limiting side effects. Bremelanotide causes nausea (40%), flushing, and transient blood pressure changes. Contraindicated with high cardiovascular risk. Unregulated melanotan analogs used for tanning/libido carry risks of nausea, priapism, spontaneous erections, and unknown long-term MC receptor effects. Alpha-MSH analogs may worsen pre-existing melanoma via MC1R activation. Not WADA-listed; analogs may be assessed case by case.
References
- [1]Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides. 2006;27(4):921-930.
- [2]Simon JA, et al. Efficacy and safety of bremelanotide for the treatment of HSDD in premenopausal women. Obstet Gynecol. 2018;132(5):1111-1120.
- [3]Catania A, et al. The neuropeptide alpha-MSH in host defense. Ann N Y Acad Sci. 1999;885:183-192.