Melanotan II Interactions with Melanocortin Receptors

Melanotan II is a synthetic analog of the naturally occurring 13 amino acids of the alpha-melanocyte-stimulating hormone (α-MSH). While the peptide is based on α-MSH, it has important structural distinctions. Specifically, Melanotan II appears to be a cyclic peptide composed of seven amino acids arranged in a ring-like structure. This cyclic configuration is achieved through a lactam bridge, formed by linking the side-chain carboxyl group of aspartic acid at position two with the side-chain amino group of lysine at position seven.

The cyclic structure of Melanotan II is posited to significantly support its binding affinity to various melanocortin receptors, most notably the melanocortin 1 receptor (MC1R). However, researchers such as Wikberg et al. highlight that the peptide is also not particularly selective and binds to other melanocortin receptors with high affinity, such as the melanocortin 4 receptor (MC4R) subtypes.⁽¹⁾ Melanotan II demonstrates a wider range of potential research implications due to this increased receptor affinity.

Through its interaction with MC1R, Melanotan II may stimulate melanogenesis—the biological process responsible for skin cell pigmentation. Additionally, its binding to MC4R may impact copulatory signaling and metabolic regulation, further broadening its potential physiological impacts. In addition, Melanotan II also appears to interact with the melanocortin 3 and melanocortin 5 receptors, but these interactions are less extensively studied. Below, we will break down the interactions between Melanotan II and different receptors, highlighting the specific research implications that these interactions may allow.

 

Research

Melanotan II and Melanocortin 1 Receptor Activation

The MC1Rs are receptors that may be expressed in the pigment cells called melanocytes, which are found in tissues such as dermal tissues and hair. Melanotan II appears to bind to MC1R with activity that may be greater than that of other α-MSH analogs, as suggested by research from Dorr et al.⁽²⁾ This interaction is posited to trigger a cascade of intracellular signaling events mediated by the so-called G protein pathway. Specifically, activation of MC1R may lead to the stimulation of adenylate cyclase, an enzyme that converts adenosine triphosphate (ATP) into cyclic adenosine monophosphate (cAMP).

Elevated cAMP levels subsequently activate protein kinase A (PKA). The latter typically phosphorylates and activates the cAMP response element-binding protein (CREB) transcription factor. Once activated, CREB may translocate to the melanocyte’s nucleus. It is posited to promote the transcription of several genes crucial for melanogenesis, particularly the gene encoding microphthalmia-associated transcription factor (MITF).

MITF is thought to act as a master regulator of melanogenesis, supporting the transcription of multiple enzymes essential to melanin synthesis, notably tyrosinase, tyrosinase-related protein 1 (TRP1), and dopachrome tautomerase (DCT or TRP2). Tyrosinase, in particular, is a critical enzyme that catalyzes the initial step in melanin biosynthesis, converting the amino acid tyrosine into L-DOPA, which is further converted into dopaquinone. This molecule serves as a precursor for eumelanin, the dark brown or black form of melanin responsible for pigmentation and photoprotection in skin tissues.

Melanotan II and Oxidative Stress Management via the MC1R

Research by Wu et al. also suggests that after binding to MC1R, Melanotan II increases the cellular expression of phosphatase and tensin homolog (PTEN), which is considered an essential regulator of a cell’s antioxidant response.⁽³⁾ PTEN typically counteracts oxidative stress by negatively regulating the PI3K/AKT signaling pathway, a critical cascade involved in cell proliferation, inflammation, and survival. The researchers commented that “MTII dose-dependently increased the phosphatase and tensin homolog (PTEN) protein level while reducing PTEN phosphorylation, which resulted in the inhibition of AKT/nuclear factor kappa B (NFκB) signaling”.

The mechanism by which Melanotan II supports PTEN levels involves a reduction in PTEN phosphorylation, potentially leading to increased stability and activity of the PTEN protein. This may suppress the downstream signaling of AKT and nuclear factor kappa B (NFκB), pathways widely recognized for their roles in inflammatory responses, oxidative stress, and tumor cell progression. NFκB suppression is particularly relevant, given its involvement in inducing cyclooxygenase-2 (COX-2), an enzyme intimately linked to inflammation and oxidative stress through prostaglandin E2 (PGE2) production. Melanotan II experimentation resulted in the concentration-dependent inhibition of COX-2 expression and subsequent reduction in PGE2 production, suggesting a potential anti-inflammatory impact that may indirectly contribute to reduced oxidative stress.

Interestingly, previous research has also posited that α-MSH, through similar MC1R-dependent signaling pathways, may reduce oxidative stress and DNA damage induced by UV radiation in melanocytes. Since Melanotan II is a more stable and potent analogue of α-MSH, it is reasonable to speculate that a similar mechanism may also be activated by Melanotan II, potentially offering protection against UV-induced oxidative damage at the cellular level. However, it is also important to note that some researchers, such as Hjuler et al., suggest Melanotan II may stimulate the proliferative potential of melanocytes and increase the potential risk of melanocyte metaplasia, which is a risk factor for the formation of cancer cells.⁽⁴⁾

Melanotan II and Arousal Regulation via the MC4R

The MC4Rs are another group of melanocortin receptors localized in the central nervous system, most likely in the hypothalamus. These receptors are thought to play a role in regulating two major systems – the systems that regulate hunger hormone signaling and the systems that regulate mating-related signaling and copulatory arousal. Melanotan II appears to bind with the MC4R, consequently impacting multiple neural circuits involving regions such as the medial preoptic area (MPOA), the paraventricular nucleus (PVN), and the arcuate nucleus (Arc) of the hypothalamus. These areas are critical in the initiation and regulation of mating-related signaling. Melanotan II may modulate oxytocinergic signaling, potentially interacting with pathways that directly impact spinal erection centers.

Research by King et al.a also suggests that MC4R mRNA has been identified in various neuronal populations linked to penile erection pathways, implicating spinal sites of action for melanocortin agents such as Melanotan II.⁽⁵⁾ The peptide has reportedly led to increases in spontaneous erections in laboratory models, which were potentially mediated via sympathetic innervation, suggesting that melanocortin agonists like Melanotan II possibly modulate sympathetic pathways. Further research by Wessells et al. has suggested that the peptide may induce increased arousal neuron signaling in more than 80% of cases, compared to only 20% success with a placebo.⁽⁶⁾

Melanotan II Impact on Cell Survival via the MC4R

Researchers like Ter Laak et al.. hypothesized that MC4R activation might play a role in neuronal cell recovery, possibly by facilitating neurite outgrowth.⁽⁷⁾ Neurite outgrowth refers to the process by which neurons extend axons and dendrites, potentially supporting the intrinsic regenerative capacity of neuronal tissue following injury. While the precise signaling pathways remain incompletely defined, current theories frequently highlight the potential involvement of peptides derived from pro-opiomelanocortin (POMC). POMC-derived peptides.

These peptides are speculated to impact neuronal architecture by possibly increasing both the number and the elongation of neurites—thin projections from neurons essential for neural network formation—and might even encourage nerve sprouting in regions experiencing damage. By binding to MC4R, Melanotan II may result in a better-supported environment for nerve fiber regeneration after diverse neuronal insults, including physical injury or neurotoxic damage. Furthermore, Melanotan II may also induce limited neuroprotective actions, potentially mitigating the detrimental impact of toxic neuropathic conditions in laboratory models. Ter Laak et al.. noted that they “observed that Melanotan-II also possesses neuroprotective properties, as it partially protected the nerve from a toxic neuropathy induced by cisplatin.”

Melanotan II and Hunger Hormone Regulation via MC4R

Research by Côté et al. suggested that Melanotan II possibly impacts hunger hormone signaling through its potential action on MC3 and MC4Rs.⁽⁸⁾ The researchers suggest that the peptide may cause a concentration-dependent anorexic response. Specifically, a reduction in caloric intake ranging from approximately 30% to 50% was observed shortly after the experimentation began. However, this hunger hormone signal-suppressing action was transient, returning to baseline levels within 2 to 5 days of continuous exposure. This also indicates possible receptor desensitization or compensatory mechanisms.

Furthermore, another potential mechanism related to Melanotan II may impact energy expenditure pathways, notably thermogenesis and adipose tissue metabolism. The research linked the peptide to a 3-fold increase in uncoupling protein 1 (UCP1) content in interscapular brown adipose tissue (iBAT), indicating potentially better-supported thermogenic capacity. Increased thermogenesis, mediated through the activation of brown adipose tissue, may contribute to fat mass loss and suppressed hunger hormone signaling. The researchers noted an approximate 35% – 55% reduction in fat cell mass. Unfortunately, a reduction in lean mass was also reported, reaching up to 30%.

You can find Melanotan 2 for sale with 99% purity, on our website (available for research use only).

NOTE: These products are intended for laboratory research use only. This peptide is not intended for personal use. Please review and adhere to our Terms and Conditions before ordering.

 

References:

1. Wikberg JE. Melanocortin receptors: perspectives for novel drugs. Eur J Pharmacol. 1999 Jun 30;375(1-3):295-310. doi: 10.1016/s0014-2999(99)00298-8. PMID: 10443584.
2. Dorr RT, Lines R, Levine N, Brooks C, Xiang L, Hruby VJ, Hadley ME. Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sci. 1996;58(20):1777-84. doi: 10.1016/0024-3205(96)00160-9. PMID: 8637402.
3. Wu JC, Tsai HE, Hsiao YH, Wu JS, Wu CS, Tai MH. Topical MTII Therapy Suppresses Melanoma Through PTEN Upregulation and Cyclooxygenase II Inhibition. Int J Mol Sci. 2020 Jan 20;21(2):681. doi: 10.3390/ijms21020681. PMID: 31968661; PMCID: PMC7013727.
4. Hjuler KF, Lorentzen HF. Melanoma associated with the use of melanotan-II. Dermatology. 2014;228(1):34-6. doi: 10.1159/000356389. Epub 2013 Dec 18. PMID: 24355990.
5. King, Stephen H et al. “Melanocortin receptors, melanotropic peptides and penile erection.” Current topics in medicinal chemistry vol. 7,11 (2007): 1098-1106. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2694735/
6. Wessells, H et al. “Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with Melanotan II.” International journal of impotence research vol. 12 Suppl 4 (2000): S74-9. doi: 10.1038/sj.ijir.3900582. https://pubmed.ncbi.nlm.nih.gov/11035391/
7. Ter Laak MP, Brakkee JH, Adan RA, Hamers FP, Gispen WH. The potent melanocortin receptor agonist melanotan-II promotes peripheral nerve regeneration and has neuroprotective properties in the rat. Eur J Pharmacol. 2003 Feb 21;462(1-3):179-83. doi: 10.1016/s0014-2999(02)02945-x. PMID: 12591111.
8. Côté I, Sakarya Y, Kirichenko N, Morgan D, Carter CS, Tümer N, Scarpace PJ. Activation of the central melanocortin system chronically reduces body mass without long-term caloric restriction. Can J Physiol Pharmacol. 2017 Feb;95(2):206-214. doi: 10.1139/cjpp-2016-0290. Epub 2016 Oct 19. PMID: 28051332; PMCID: PMC5572812.