The short version of afamelanotide fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-07-04. Anything still debated is marked as such rather than presented as settled.
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.
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.
Early published reports described melanotan-2 as a tanning agent without sun protection, which means darkening is not the same as protection against ultraviolet radiation. Later studies explored the peptide in erectile dysfunction, hemorrhagic shock, and some skin conditions. No regulator in the United States or Europe has approved it for clinical use. Many products labelled melanotan-2 are sold without approval and their identity and purity are unverified. Its long-term safety in humans remains an open question.
Melanotan-2, also written Melanotan II, is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and the lactam bridge between the aspartate and lysine side chains constrains the peptide into a ring. This structural change increases receptor affinity and metabolic stability relative to the native hormone. The compound was created in the 1980s as a research tool for studying pigmentation biology.
Melanocytes are the pigment-producing cells of the skin, and they carry melanocortin-1 receptors on their surface. When the receptor is activated, cyclic adenosine monophosphate rises inside the cell and raises the activity of enzymes such as tyrosinase, which increases melanin output. Melanotan-2 binds melanocortin-1 receptors in vitro and in animal models, and this binding is generally described as the basis for the tanning effect. Other receptors account for different effects: melanocortin-4 receptors contribute to appetite and erectile signalling, while melanocortin-3 and melanocortin-5 receptors contribute to energy balance and exocrine function.
| 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 |
Receptor studies place melanotan-2 among non-selective melanocortin agonists, binding MC1R, MC3R, MC4R and MC5R rather than a single subtype. Activation of MC1R on cutaneous melanocytes raises tyrosinase activity and shifts pigment synthesis toward eumelanin, which is darker and more photostable than pheomelanin. Central receptors, particularly MC4R, are associated with appetite suppression and with reported effects on sexual function. Because subtype selectivity is low, the same molecule engages pigment, metabolic and vascular pathways at once, and this breadth is a common explanation offered for the range of adverse events described in user reports.
No regulatory authority has approved melanotan-2 for human use, and several countries classify it as a prescription-only or controlled substance, which restricts lawful supply. Material sold online is generally labelled as a research chemical and is not required to meet pharmaceutical standards of identity or purity. Published human data consist mainly of small uncontrolled studies, case reports and adverse-event notifications, so the evidence base is descriptive rather than confirmatory. Whether repeated melanocyte stimulation alters long-term naevus behaviour remains an open question that no completed trial has resolved.
Published pharmacokinetic information is limited and comes mainly from small studies rather than registrational trials. Plasma half-life is usually described as short, on the order of tens of minutes, followed by rapid tissue distribution and clearance of the intact peptide. Metabolites and low concentrations of parent compound have been reported in urine, a detail relevant to anti-doping and forensic testing. Whether repeated exposure changes receptor sensitivity or clearance over time remains an open question. Values differ noticeably between analytical assays, so published numbers should be read as approximate rather than definitive.
Melanotan II is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, corresponding to a molecular formula of C50H69N15O9 and a monoisotopic mass near 1024 daltons. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, a peptide hormone produced by cleavage of proopiomelanocortin. A lactam bridge between the aspartate and lysine side chains closes the ring, and the C-terminal amide removes a free carboxyl group. Both modifications increase resistance to enzymatic degradation compared with the linear parent hormone. Four substitutions distinguish it from afamelanotide, the linear analogue studied under the name melanotan I.
The compound emerged from research programs in the 1980s that examined analogues of alpha-melanocyte-stimulating hormone for pigmentation and photoprotection. Investigators modified the native sequence to extend activity duration and potency. A related analogue, afamelanotide, was developed within the same broad line of inquiry and eventually gained approval in certain jurisdictions for a rare light-sensitivity condition. Melanotan-2 itself did not progress through the same regulatory route and has no approved therapeutic indication.
Melanocortin receptors comprise five subtypes with distinct tissue distributions and functions. Melanotan-2 is described in the literature as a non-selective agonist that engages several of these subtypes, including MC1R, MC3R, MC4R, and MC5R. MC1R is the subtype most directly linked to melanin production in skin cells. Because the compound is not subtype-selective, its observed effects in experimental settings are generally attributed to activity across multiple receptor pathways rather than to a single target.
=== Anti-thyroid drugs === Treatment with methimazole or propylthiouracil for hyperthyroidism, is commonly associated with an elevation of liver enzymes. To differentiate between hyperthyroidism and drug-related liver injury, it is recommended to check baseline liver enzymes prior to initiation of treatment. If liver injury related to anti-thyroid treatment is significant, switching to the alternative agent can be attempted in most cases. Cases of fulminant liver failure reported with propylthiouracil have led to a regulatory warning, and to guidelines recommending methimazole as the first line anti-thyroid agent.
Other Marvel Comics adaptations have also had success with the Spider-Man and X-Men properties, while films based on Batman and Superman from DC Comics have generally performed well. Beyond the superhero genre, Star Wars, with four films, is the most represented franchise in the nominal earnings chart. Although the nominal earnings chart is dominated by films adapted from pre-existing properties and sequels, it is headed by Avatar, which is an original work. Animated family films have performed consistently well, with Disney films enjoying lucrative re-releases prior to the home-video era. Disney also enjoyed later success with films such as Frozen and its sequel, Zootopia and its sequel, and The Lion King (along with its computer-animated remake), as well as its Pixar division, of which Inside Out 2, Incredibles 2, and Toy Story 3, 4 and 5 have been the best performers. Beyond Disney and Pixar animation, China's Ne Zha 2 (the highest-grossing animated film), and the Despicable Me and Shrek series have met with the most success. While inflation has eroded the achievements of most films from the 1960s and 1970s, there are franchises originating from that period that are still active. Besides the Star Wars franchise, James Bond films are still being released periodically; both are among the highest-grossing franchises. Some of the older films that held the record of highest-grossing film still have respectable grosses by today's standards, but no longer compete numerically against today's top-earners in an era of much higher individual ticket prices.
== O == octreotide - odorant receptor - olfaction - olfactory receptor neuron - oligopeptide - oncogene - oncogene protein - oncogene proteins V-abl - oncogenic retroviridae protein - open reading frame - opioid receptor - opsin - optical isomerism - organ (anatomy) - organelle - organic chemistry - organic compound - organic nomenclature - organic reaction - organism - osmosis - osteocalcin - outer hair cell - outline of biochemical techniques - ovalbumin - oxidation - oxidation number - oxidation state - oxidative decarboxylation - oxidative phosphorylation - oxygen - oxytocin - oxytocin receptor
Water extraction: Coffee beans are soaked in water. The water, which contains many other compounds in addition to caffeine and contributes to the flavor of coffee, is then passed through activated charcoal, which removes the caffeine. The water can then be put back with the beans and evaporated dry, leaving decaffeinated coffee with its original flavor. Supercritical carbon dioxide extraction: Supercritical carbon dioxide is an excellent nonpolar solvent for caffeine, and is safer than the organic solvents that are otherwise used. The extraction process is simple: CO2 is forced through the green coffee beans at temperatures above 31.1 °C and pressures above 73 atm. Under these conditions, CO2 is in a "supercritical" state: It has gaslike properties that allow it to penetrate deep into the beans but also liquid-like properties that dissolve 97–99% of the caffeine. The caffeine-laden CO2 is then sprayed with high-pressure water to remove the caffeine. The caffeine can then be isolated by charcoal adsorption (as above) or by distillation, recrystallization, or reverse osmosis. Extraction by organic solvents: Certain organic solvents such as ethyl acetate present much less health and environmental hazard than chlorinated and aromatic organic solvents used formerly. Another method is to use triglyceride oils obtained from spent coffee grounds. Decaffeination does not happen completely; some caffeine remains in the coffee beans. Some commercially available decaffeinated coffee products contain considerable levels.
The sickness was aggravated by the intense heat and the appalling effluvium arising from the 90 Siberian sledge-dogs we had on deck. These dogs were procured from the Samoyedes in the North of Siberia and were the first dogs ever introduced in Antarctic exploration. On the return trip, the dogs were left on Native Island, New Zealand. Due to quarantine requirements, many of the dogs were killed but a few remained. Nine of the remaining dogs were bought by Ernest Shackleton. Robert Falcon Scott brought twenty Samoyeds with him during his 1902 journey. The dogs struggled under the conditions Scott placed them in, with four dogs pulling heavily loaded sleds through 45 cm (18 in) of snow with bleeding feet. Scott blamed their failure on rotten dried fish.
Sources: en.wikipedia.org
Collagenases are enzymes that break the peptide bonds in collagen. They assist in destroying extracellular structures in the pathogenesis of bacteria such as Clostridium. They are considered a virulence factor, facilitating the spread of gas gangrene. They normally target the connective tissue in muscle cells and other body organs. Collagen, a key component of the animal extracellular matrix, is made through cleavage of pro-collagen by collagenase once it has been secreted from the cell. This stops large structures from forming inside the cell itself. In addition to being produced by some bacteria, collagenase can be made by the body as part of its normal immune response. This production is induced by cytokines, which stimulate cells such as fibroblasts and osteoblasts, and can cause indirect tissue damage.
Such designers included Dave McDermott, who initially ran the Sven Co-op website before becoming a developer of it. Fearon had planned from the onset to include support for cooperatively playing through Half-Life's single-player campaign within Sven Co-op, but this was hampered initially by how the game's engine transitions from map to map, and made it difficult to keep players together in the multiplayer approach. Ultimately, the team was able to work this out, and later added support for Half-Life's two expansions, Half-Life: Opposing Force, and Half-Life: Blue Shift. Around 2004, prior to the release of Half-Life 2, Fearon had been planning to release Sven Co-op on Steam, but didn't due to confusion between the Sven Co-op team and Valve. Further, Fearon and the team had started work on a Sven Co-op 2 in anticipation of using the Source engine from Half-Life 2. Though they had developed a large number of assets for the mod, they were hindered by the lack of the SDK, which had been pushed back along with the release of Half-Life 2. Many of the team members had started to move on to other projects, and Fearon found they lost too many key members to continue development. Around this point Fearon opted to leave the project, giving the project lead over to Josh Polito. McDermott and Polito began negotiations with Valve to gain access to the GoldSrc engine around 2010 and to have Valve change some of the numerical limits originally imposed in the engine's use in Half-Life that would enable them to improve Sven Co-op.
YouTube, Facebook and others use recommender systems to guide users to more content. These AI programs were given the goal of maximising user engagement (that is, the only goal was to keep people watching). The AI learned that users tended to choose misinformation, conspiracy theories, and extreme partisan content, and, to keep them watching, the AI recommended more of it. Users also tended to watch more content on the same subject, so the AI led people into filter bubbles where they received multiple versions of the same misinformation. This convinced many users that the misinformation was true, and ultimately undermined trust in institutions, the media and the government. The AI program had correctly learned to maximise its goal, but the result was harmful to society. After the U.S. election in 2016, major technology companies took some steps to mitigate the problem. In the early 2020s, generative AI began to create images, audio, and texts that are virtually indistinguishable from real photographs, recordings, or human writing, while realistic AI-generated videos became feasible in the mid-2020s. It is possible for bad actors to use this technology to create massive amounts of misinformation and computational propaganda through techniques such as deepfakes. AI pioneer and Nobel Prize-winning computer scientist Geoffrey Hinton expressed concern about AI enabling "authoritarian leaders to manipulate their electorates" on a large scale, among other risks. The ability to influence electorates has been proved in at least one study.
=== Russian reaction === Russia welcomed Trump's tariffs against its NATO allies, with Kremlin officials saying it was evidence that the transatlantic alliance was collapsing. The Russian government newspaper Rossiyskaya Gazeta praised Trump's push to take over Greenland and welcomed the strain it was causing between the US and Europe.
Sources: en.wikipedia.org
Sheep fed by a diet containing bracken develop acute haemorrhagic disease and bright blindness. The main features of the blindness include progressive retinal atrophy and stenosis of the blood vessels. In 1993, Yamada group proved ptaquiloside was the compound causing retinal degeneration.
While the Arrhenius concept is useful for describing many reactions, it is also quite limited in its scope. In 1923, chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid–base reactions involve the transfer of a proton. A Brønsted–Lowry acid (or simply Brønsted acid) is a species that donates a proton to a Brønsted–Lowry base. Brønsted–Lowry acid–base theory has several advantages over Arrhenius theory. Consider the following reactions of acetic acid (CH3COOH), the organic acid that gives vinegar its characteristic taste:
{\displaystyle p\left(r\right)={\frac {Ed}{\pi a\left(1-\nu ^{2}\right)}}\ln \left({\frac {a}{r}}+{\sqrt {\left({\frac {a}{r}}\right)^{2}-1}}\right)={\frac {Ed}{\pi a\left(1-\nu ^{2}\right)}}\cosh ^{-1}\left({\frac {a}{r}}\right)}
=== Cancer === Water-soluble polymer shells are being created to deliver a protein, apoptin, into cancer cells. The protein goes into the nucleus of the cancer cells while leaving healthy cells alone, unlike other conventional therapies as gene therapies and chemotherapy. The capsules are 100 nm in size. Active targeting of cancer cells is also being researched. Through active targeting, the nanocapsules form ligands that bind to malignant cells for cell delivery. This method is especially beneficial for those drugs that are not as permeable through the cell membrane, and where tissues are diseased, the nanoparticles are able to bond easier with the malignant cells.
== Risk factors == There is limited research on LADA and its etiology. As with both T1D and T2D, the risk of developing LADA depends on both genetic and environmental factors. Genetic risk factors for LADA are similar to T1D, e.g. it is affected by the HLA complex, but also genetic variants associated with T2D have been identified in LADA. LADA has several lifestyle risk factors in common with T2D, such as obesity, physical inactivity, smoking and consumption of sweetened beverages, all of which are linked to insulin resistance. Obesity has been shown to increase the risk of LADA in several studies, and one study showed that the risk was particularly high in combination with having diabetes in the family. Less physical activity increases the risk of developing LADA. A Swedish study showed that low birth weight, in addition to increasing the risk of T2D, increases the risk of LADA. Although smoking has been shown to increase the risk of T2D and coffee consumption to decrease it, the results regarding these products and LADA are unclear. However, results from two studies based on the same population seem to indicate that coffee consumption increases the risk of LADA. Sweetened beverages and processed red meat have been shown to increase the risk of LADA, while consumption of fatty fish has been shown to have a protective effect.
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.
No. It is a laboratory-made peptide, while the natural hormone is alpha-melanocyte-stimulating hormone, a longer peptide produced by the pituitary gland and by skin cells. Melanotan-2 mimics only a short active region of that hormone and contains non-natural residues such as D-phenylalanine.