This is a working overview of melanocortin receptors, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-06-28. Anything still debated is marked as such rather than presented as settled.
Research interest has centred on photoprotection and pigmentation, with a smaller body of work on appetite and sexual function. Published human data remain limited to small, frequently uncontrolled studies, and the compound has never received marketing approval from a national medicines regulator. Most laboratory work treats it as a pharmacological tool for probing melanocortin signalling in cell culture or animal models. Whether pigmentation changes observed in people translate into measurable protection against ultraviolet-induced DNA damage remains an open question.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, the naturally occurring peptide involved in pigmentation signalling. Its sequence is conventionally written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, with a lactam bridge joining the aspartate side chain to the lysine side chain. The empirical formula is C50H69N15O9 and the monoisotopic mass lies near 1023.5 daltons. N-terminal acetylation and the D-configured phenylalanine both increase resistance to enzymatic breakdown compared with the parent hormone.
Pharmacologically, melanotan-2 behaves as a non-selective agonist across the melanocortin receptor family. Binding at MC1R on dermal melanocytes promotes eumelanin synthesis, which underlies the tanning response described in early human work. Activity at the centrally expressed MC4R receptor is associated with reported effects on appetite and erectile function. Because the peptide does not discriminate strongly among receptor subtypes, attributing any single observed effect to one receptor pathway is generally not possible without selective antagonists or receptor knockout models.
Routine characterisation relies on reversed-phase high-performance liquid chromatography with ultraviolet detection near 214 nanometres, using a C18 column and a water-acetonitrile gradient containing trifluoroacetic acid. Electrospray ionisation mass spectrometry confirms the expected molecular mass and can reveal truncated or oxidised by-products that co-elute poorly. Sequence and stereochemistry require additional work, such as peptide mapping or amino acid analysis, because a chromatographic purity figure alone does not distinguish a diastereomer from the target peptide. Independent testing of research-grade material frequently shows measured content below the stated label, so a certificate of analysis is best read together with the method that produced it.
Melanotan-2 is handled in the laboratory as a lyophilised powder that dissolves readily in water, dimethyl sulfoxide and dimethylformamide, with limited solubility in ethanol. Stock solutions prepared in an organic solvent often precipitate when diluted into aqueous buffer, so gradual dilution with mixing is standard practice. The peptide carries a tryptophan residue and a histidine residue, both sensitive to oxidation and to alkaline conditions. Working solutions are therefore kept near neutral to slightly acidic pH, protected from light, and consumed within the same working session whenever that is practical.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Melanotan II; MT-II; N-acetyl-norleucyl-cyclo[Asp-His-D-Phe-Arg-Trp-Lys] amide | Naming follows peptide convention; the numeral distinguishes it from melanotan-1 |
| Molecular formula | C50H69N15O9 | Includes the lactam bridge; no counter-ion assumed |
| Monoisotopic mass | 1023.53 Da | Free base; salts and counter-ions shift the observed value |
| Appearance | White to off-white lyophilised powder | Batch-to-batch colour variation is not itself proof of impurity |
| Typical analytical method | RP-HPLC purity determination with ESI-MS identity confirmation | Retention time alone does not establish sequence identity |
Activity is attributed to agonism at melanocortin receptors, particularly MC1R and MC4R. Activation of MC1R on melanocytes increases melanin synthesis, which underlies the reported tanning effect. MC4R engagement in the central nervous system is linked to appetite suppression and to effects on sexual arousal reported in early clinical studies. Those studies were small and were not designed to establish efficacy or long-term safety. Receptor selectivity among the melanocortin subtypes is not absolute, which complicates attribution of any effect to a single pathway.
Regulatory treatment varies between countries. Several national medicines agencies have classified the peptide as unapproved, and customs authorities in some jurisdictions seize shipments on that basis. A few jurisdictions channel supply through prescription-only frameworks that do not list the substance by name. Because the material circulates mainly through online vendors, composition and purity are rarely verified before sale. Surveys of unapproved peptide products have reported labels that did not match measured content in a substantial fraction of samples.
Melanotan II is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation signalling. Its structure substitutes a lactam bridge between side chains to increase stability relative to the native hormone. The compound is also known by the shorthand MT-II and by several non-proprietary synonyms used in research catalogues. It is not an approved therapeutic product in any major jurisdiction; material sold under this name is typically offered as a laboratory reagent rather than as a medicine.
Melanotan-2 appears on the World Anti-Doping Agency prohibited list within the peptide hormone class, and several national regulators treat it as an unapproved prescription substance. Some countries restrict importation or sale for personal use. Because the compound is widely traded as a research chemical, the practical legal picture differs between jurisdictions and shifts over time. Human safety data covering long periods are limited, and whether repeated pigmentation changes carry any lasting risk to melanocytes remains an open question.
Freeze-dried melanotan-2 is normally kept as a desiccated powder at minus twenty degrees Celsius or lower, shielded from light and moisture. Peptides of this size degrade through hydrolysis, oxidation and deamidation, and each pathway accelerates as temperature and water activity rise. Repeated freeze-thaw cycles promote aggregation and loss of material, so aliquoting a stock solution before freezing is standard laboratory practice. Once dissolved, the solution is markedly less stable than the powder. In laboratory work, solutions are generally refrigerated and used within days rather than kept for months.
=== Chemotherapy-induced neutropenia === Chemotherapy can cause myelosuppression and unacceptably low levels of white blood cells (leukopenia), making patients susceptible to infections and sepsis. G-CSF stimulates the production of granulocytes, a type of white blood cell. In oncology and hematology, a recombinant form of G-CSF is used with certain cancer patients to accelerate recovery and reduce mortality from neutropenia after chemotherapy, allowing higher-intensity treatment regimens. It is administered to oncology patients via subcutaneous or intravenous routes. A QSP model of neutrophil production and a PK/PD model of a cytotoxic chemotherapeutic drug (Zalypsis) have been developed to optimize the use of G-CSF in chemotherapy regimens with the aim to prevent mild-neutropenia. G-CSF was first trialled as a therapy for neutropenia induced by chemotherapy in 1988. The treatment was well tolerated and a dose-dependent rise in circulating neutrophils was noted. A study in mice has shown that G-CSF may decrease bone mineral density. G-CSF administration has been shown to attenuate the telomere loss associated with chemotherapy.
This expansion introduced BK's "AM Express" product line, which added new products such as French toast sticks and mini-muffins. As the company expanded both inside and outside the US, it introduced localized versions of its products that conform to regional tastes and cultural or religious beliefs. International variations add ingredients such as teriyaki or beetroot and fried egg to the Whopper; beer in Germany, Italy, and Spain; and halal or kosher products in the Middle East and Israel. To generate additional sales, BK will occasionally introduce limited-time offers (LTOs) that are versions of its core products, or new products intended for either long or short term sales. Items such as the Texas Double Whopper and various sandwiches made with mushrooms and Swiss cheese have been rotated in and out of its menu for several years, while products such as its 1993 Meatloaf Specialty Sandwich offering and accompanying limited table service, along with special dinner platters, failed to generate interest and were discontinued.
== Mechanism of toxicity == Once azinphos-methyl is absorbed it can cause neurotoxic effects, like other organophosphate insecticides. At high concentrations AzM itself can be toxic because it can function as an acetylcholinesterase (AChE) inhibitor. But its toxicity is mainly due to the bioactivation by a cytochrome P450 (CYP450)-mediated desulfuration to its phosphate triester or oxon(gutoxon) (see figure 2). Gutoxon can react with a serine hydroxyl group at the active site of the AChE. The active site is then blocked and AChE is inactivated. Under normal circumstances acetylcholinesterase rapidly and efficiently degrades the neurotransmitter acetylcholine (ACh) and thereby terminates the biological activity of acetylcholine. Inhibition of AChE results in an immediate accumulation of free unbound ACh at the ending of all cholinergic nerves, which leads to overstimulation of the nervous system.
To maintain effectiveness, platelet-mimicking particles have to be engineered to remain stable in the bloodstream long enough to reach tumor sites without being rapidly cleared. Simultaneously, they must also be designed to degrade safely after successful drug delivery to tumor sites to avoid triggering adverse immune reactions. Regulatory issues and mass production also become problematic because safety and efficacy evaluation of the synthetic platelet requires extensive preclinical and clinical testing. Overcoming these deficiencies will advance their integration into standard oncological treatments.
=== China === In July 2007, officials of the People's Republic of China seized US-produced pork for containing ractopamine residues. Further shipments of Canadian ractopamine-fed pork were seized in September 2007. In June 2019, customs inspectors in China detected ractopamine in a shipment of Canadian pork products destined for Chinese consumption. The Chinese government thereupon suspended not only pork, but also beef imports from Canada. Canadian Agriculture Minister Marie-Claude Bibeau stated that the CRFPCP certificate was a forgery and called in the RCMP, while Canadian Public Safety Minister Ralph Goodale stressed that the federal government would vigorously defend Canadian meat producers. It was also revealed that the Canadian Cattlemen's Association said in a statement that "We are fully confident in our meat production systems in Canada and the safeguards we have in place." Meanwhile, holes were found in the CRFPCP programme because the meat packer at the centre of the controversy was a chilled butcher shop only.<what> It was disclosed on 3 July that the Chinese authorities had discovered 188 falsified CRFPCP certificates.
Sources: en.wikipedia.org
The US Central Intelligence Agency (CIA) launched a video and a Telegram channel calling on Russians dissatisfied with the situation in Ukraine as well as the domestic situation to share intelligence with the agency and provided instructions on how to do so.
== Adverse effects == A serious side-effect of heparin is heparin-induced thrombocytopenia (HIT), caused by an immunological reaction that makes platelets a target of immunological response, resulting in the degradation of platelets, which causes thrombocytopenia. This condition is usually reversed on discontinuation, and in general can be avoided with the use of synthetic heparins. Not all patients with heparin antibodies will develop thrombocytopenia. Also, a benign form of thrombocytopenia is associated with early heparin use, which resolves without stopping heparin. Approximately one-third of patients with diagnosed heparin-induced thrombocytopenia will ultimately develop thrombotic complications. Two non-hemorrhagic side effects of heparin treatment are known. The first is an elevation of serum aminotransferase levels, which has been reported in as many as 80% of patients receiving heparin. This abnormality is not associated with liver dysfunction, and it disappears after the drug is discontinued. The other complication is hyperkalemia, which occurs in 5 to 10% of patients receiving heparin, and is the result of heparin-induced aldosterone suppression. The hyperkalemia can appear within a few days after the onset of heparin therapy. More rarely, the side-effects alopecia and osteoporosis can occur with chronic use. As with many drugs, overdoses of heparin can be fatal. In September 2006, heparin received worldwide publicity when three prematurely born infants died after they were mistakenly given overdoses of heparin at an Indianapolis hospital.
β-Endorphin release in response to exercise has been known and studied since at least the 1980s. Studies have demonstrated that serum concentrations of endogenous opioids, in particular β-endorphin and β-lipotropin, increase in response to both acute exercise and training. The release of β-endorphin during exercise is associated with a phenomenon colloquially known in popular culture as a runner's high. Acute aerobic exercise significantly increases circulating β-endorphin concentrations, with elevations closely correlated to exercise intensity and the onset of the 'runner’s high'.
=== Pharmacokinetics === When given orally, rivastigmine is well absorbed, with a bioavailability of about 40% in the 3-mg dose. Pharmacokinetics are linear up to 3 mg twice daily, but nonlinear at higher doses. Elimination is through the urine. Peak plasma concentrations are seen in about one hour, with peak cerebrospinal fluid concentrations at 1.4–3.8 hours. When given by once-daily transdermal patch, the pharmacokinetic profile of rivastigmine is much smoother, compared with capsules, with lower peak plasma concentrations and reduced fluctuations. The 9.5 mg/24 h rivastigmine patch provides comparable exposure to 12 mg/day capsules (the highest recommended oral dose). The compound does cross the blood–brain barrier. Plasma protein binding is 40%. The major route of metabolism is by its target enzymes via cholinesterase-mediated hydrolysis. Elimination bypasses the hepatic system, so hepatic cytochrome P450 (CYP) isoenzymes are not involved. The low potential for drug-drug interactions (which could lead to adverse effects) has been suggested as due to this pathway compared to the many common drugs that use the cytochrome P450 metabolic pathway. A QbD driven HPLC method was developed for the quantification of rivastigmine in rat plasma and brain for its pharmacokinetics study.].
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, containing seven amino acids with a lactam ring and a D-configured phenylalanine residue. It is supplied as a lyophilised powder for laboratory research.
The natural hormone is a linear tridecapeptide that is rapidly degraded in circulation. Melanotan-2 is shortened, cyclised, N-terminally acetylated, and carries a D-amino acid substitution, all of which slow enzymatic breakdown.
No national medicines regulator has approved melanotan-2 for therapeutic or cosmetic use. In several jurisdictions it is treated as an unapproved prescription medicine, and its legal classification differs from country to country.
Purity is normally stated as an area percentage from high-performance liquid chromatography, for example ninety-five or ninety-eight percent. That figure describes the proportion of ultraviolet-absorbing material eluting as the main peak. It says nothing about water content, counterions, residual solvents or mass fraction of the peptide itself.