A practical reference on prohibited list: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-12-07. Anything still debated is marked as such rather than presented as settled.
Thymosin beta-4 is a 43-residue actin-binding protein found in most mammalian cell types, where it participates in cytoskeletal regulation and cell migration. TB-500 represents only a short fragment of that protein and does not include the remaining residues. Whether the isolated fragment reproduces the full range of activities reported for the intact protein remains an open question. Researchers commonly treat the two as related but distinct entities when comparing results.
Published work involving this sequence spans actin-binding assays, cell-migration studies, wound-healing models, and cardiovascular or musculoskeletal experiments. Much of the biological rationale derives from in vitro systems and animal models, and the number of controlled human studies is small. Reported outcomes vary across preparations, doses, and routes, which complicates comparison between studies. Reviews generally describe the evidence base as preliminary rather than settled. Mechanistic explanations are often proposed by analogy to the parent protein rather than demonstrated directly.
TB-500 is a synthetic seven-amino-acid peptide with the sequence LKKTETQ, corresponding to residues 17 through 23 of the protein thymosin beta-4. The N-terminus is typically acetylated in the described form, giving a monoisotopic mass near 888.5 Da and an average mass of about 889 Da. The designation TB-500 is a catalogue label rather than a formal chemical name, and the same sequence appears in the literature under several alternative abbreviations. It is handled as a research reagent rather than a pharmaceutical product.
Material is normally supplied as a lyophilised powder in a sealed vial. The powder is hygroscopic, so exposure to humid air leads to water uptake, caking and gradual loss of the fluffy texture that indicates a good freeze-dry. Vials are best kept sealed with desiccant, protected from light and stored cold. Letting a cold vial warm to room temperature before opening reduces condensation on the contents. Purity is normally reported from a chromatographic run, and that figure applies to the batch as tested rather than to the vial after repeated opening.
Once dissolved, the peptide is far less stable than the dry powder. Aqueous solutions are subject to hydrolysis, oxidation at susceptible residues and gradual loss of material through adsorption onto glass and plastic surfaces. Terminal glutamine can cyclise under some conditions, producing a related species that complicates purity assessment. Dilute solutions tend to lose a larger fraction of material to surfaces than concentrated ones. Buffers, pH and ionic strength all influence the rate of change, so stability figures are only meaningful when those parameters are stated alongside the storage interval.
Detection in biological samples relies on mass spectrometry, typically liquid chromatography coupled to tandem mass spectrometry after peptide extraction and enrichment. Intact peptides can also be confirmed by high-resolution mass measurement together with fragmentation data. Detection windows in urine are short because the peptide is degraded by proteases and cleared quickly, and concentrations are low. Many jurisdictions treat the compound as a prohibited substance in sport, grouped with peptide hormones and related factors, while it is not an approved therapeutic product. Identity and purity statements therefore rest on certificates of analysis, ideally issued by an independent laboratory.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Acetylated heptapeptide form |
| Monoisotopic mass | 888.5 Da | Average mass about 889 Da |
| Appearance | White to off-white solid | Usually supplied as lyophilised powder |
| Solubility class | Highly water soluble | Also dissolves in aqueous buffers |
| Common synonyms | Tbeta4 fragment, thymosin beta-4 (17-23) | Refer to the same sequence |
TB-500 is a catalogue name applied to a synthetic peptide related to thymosin beta-4, an actin-binding protein found in most mammalian cells. Suppliers do not use the label consistently: some describe it as the full 43-residue protein, others as a short fragment from the actin-binding region, and others as a related tetrapeptide. Because the name is commercial rather than chemical, two products sold under it may not contain the same molecule. This naming ambiguity is the first point to check in any description of the material.
The most frequently cited identity is a seven-residue fragment with the sequence LKKTETQ, taken from the actin-binding domain of the parent protein. A separate molecule, N-acetyl-seryl-aspartyl-lysyl-proline, often shortened to Ac-SDKP, derives from the same protein's N-terminal region and appears in overlapping literature. Reported molecular masses therefore differ between sources, and a mass value on its own does not establish which fragment is present. Confirmation requires a defined sequence rather than a single number.
Research interest in thymosin beta-4 fragments centres on actin sequestration, cell migration and tissue repair models. Most published work uses cultured cells or animal wound and cardiac preparations, and findings are generally described as preliminary. No fragment of this protein has been approved as a therapeutic product by major regulators. Reviews of the field note inconsistent dosing, delivery routes and outcome measures across studies, which complicates direct comparison. The material is best understood as a laboratory reagent with an active but unresolved research literature.
TB-500 is a shorthand label used in supplier catalogs and online discussion for a short synthetic peptide described as a fragment of thymosin beta-4. Most product listings present it as the N-terminally acetylated heptapeptide Ac-LKKTETQ, a sequence corresponding to the actin-binding region of the parent protein. The name is not a formal chemical designation and does not appear in standard nomenclature systems. Because labeling practices vary between vendors, two products sold under the same name may not contain the same molecule, and the stated sequence should be treated as a claim rather than a fixed definition.
Thymosin beta-4 is a naturally occurring protein of 43 amino acids found in most mammalian cells, where it binds actin monomers and influences filament dynamics. It was first isolated from thymus tissue in the early 1980s, and its actin-binding activity was later mapped to a short region near the N-terminus. The synthetic fragment sold as TB-500 was designed to reproduce that region rather than the full protein. Whether a short fragment reproduces the behavior of the intact molecule remains an open question, since the parent protein carries additional structural elements outside the binding region.
Sports authorities classify the peptide as a prohibited substance, and it appears on the World Anti-Doping Agency list under peptide hormones, growth factors, and related substances. Racing jurisdictions for horses and dogs have issued separate restrictions, and several national bodies treat it as a controlled or prescription-only item. As a research chemical it is sold without a therapeutic indication, and labels usually state that the product is not for human or veterinary use. Regulatory treatment therefore varies by country.
Detection in biological matrices generally relies on liquid chromatography coupled with tandem mass spectrometry, because the peptide lacks a convenient ultraviolet chromophore beyond the amide backbone. Immunoassays have been described, but antibodies raised against the fragment can cross-react with the full-length protein or with unrelated peptides, so findings usually require confirmation by a second technique. Sample preparation typically involves protein precipitation followed by solid-phase extraction. Reported detection windows depend on dose, route, matrix, and instrument sensitivity.
Lyophilised material is stable for extended periods when kept dry and cold, and suppliers typically recommend storage well below freezing. Once dissolved, the peptide is handled at refrigeration temperatures and used within a short period, because peptide bonds and the acetylated terminus can be affected by repeated freeze-thaw cycles, proteases, or extreme pH. Bacteriostatic water and saline are both described as solvents, although preservatives can interfere with some analytical workflows. Reconstituted solutions are inspected for particulates before use.
==== Print media ==== While in Wisconsin covering the primary campaign for the United States presidential election of 1972, gonzo journalist Hunter S. Thompson submitted a satirical article to Rolling Stone accusing Democratic Party candidate Edmund Muskie of being addicted to ibogaine. Many readers, and even other journalists, did not realize that the Rolling Stone piece was facetious. The completely unfounded ibogaine assertion did significant damage to Muskie's reputation, and was cited as a factor in his loss of the nomination to George McGovern. Thompson later said he was surprised that anyone believed it. The article is included in Thompson's post-election anthology, Fear and Loathing on the Campaign Trail '72 (1973). Author and Yippie Dana Beal co-wrote the 1997 book The Ibogaine Story. American author Daniel Pinchbeck wrote about his own experience of ibogaine in his book Breaking Open the Head (2002), and in a 2003 article for The Guardian titled "Ten years of therapy in one night". Author and musician Geoff Rickly based his debut novel Someone Who Isn't Me on his real-life experiences with heroin addiction and an ibogaine clinic in Mexico. American investigative journalist, Rachel Nuwer, published a comprehensive feature for Reason magazine titled Can This Psychedelic Help Cure Opioid Addiction? In the article, Rachel speaks with experts in the field of opioid use disorder (OUD) and how ibogaine shows promising results for effective treatment and recovery. This is particularly true for those patients who also suffer from traumatic brain injuries (TBI).
== Medical uses == Fosaprepitant is indicated for people aged six months of age and older, in combination with other antiemetic agents, for the prevention of acute and delayed nausea and vomiting associated with initial and repeat courses of highly emetogenic cancer chemotherapy including high-dose cisplatin; and for delayed nausea and vomiting associated with initial and repeat courses of moderately emetogenic cancer chemotherapy.
Biodiversity informatics deals with the collection and analysis of biodiversity data, such as taxonomic databases, or microbiome data. Examples of such analyses include phylogenetics, niche modelling, species richness mapping, DNA barcoding, or species identification tools. A growing area is also macro-ecology, i.e. the study of how biodiversity is connected to ecology and human impact, such as climate change.
Sources: en.wikipedia.org
=== Plan Colombia === Plan Colombia was a joint security scheme spearheaded by the US and in cooperation with Colombia from 2000 to 2015. The Plan aimed to decrease drug cultivation in Colombia, decrease drug cartel and left-wing insurgency (FARC) violence, and spur economic growth in Colombia. It involved sending trillions in economic and military support to Colombia. Around 80% of the funding was military aid, and overall, the anti-insurgency component of the plan cost the US $500 billion.Paley argues that this heavily security-focused funding was purposeful, as it developed Colombia into an environment that was much more stable to allow foreign investment into the country's natural resource wealth, something she argues was the plans true intention. The US government justified their militarisation of Colombia and their targeting of the FARC in the plan by accusing them of being drug lords, framing their removal as necessary to protect Americans from FARC-trafficked drugs. US security organisations increasingly labelled them as major traffickers throughout the early 2000s. However, in reality, the FARC were not major contributors to the trade at all- in 2001, the Colombian government estimated that paramilitary groups controlled around 40% of the drug trade in the country, whilst the FARC only controlled 2.5%. Despite the erroneous accusation by the US government, the intensified security efforts of Plan Colombia ultimately reduced FARC numbers by around half.
=== Alzheimer's disease === In November 2025, Novo Nordisk announced top-line results from two large-scale studies, evoke and evoke+. The studies reported failure to slow the progression of Alzheimer's disease versus placebo.
=== Chirality === The carbon atom next to the carboxyl group is called the α–carbon. In proteinogenic amino acids, it bears the amine and the R group or side chain specific to each amino acid, as well as a hydrogen atom. With the exception of glycine, for which the side chain is also a hydrogen atom, the α–carbon is stereogenic. All chiral proteinogenic amino acids have the L configuration, and can therefore be referred to as L-amino acids. They are "left-handed" enantiomers, which refers to the stereoisomers of the alpha carbon. A few D-amino acids ("right-handed") have been found in nature, e.g., in bacterial envelopes, as a neuromodulator (D-serine), and in some antibiotics. Rarely, D-amino acid residues are found in proteins, and are converted from the L-amino acid as a post-translational modification.
Sources: en.wikipedia.org
They tried to generate elemental rubidium by electrolysis of molten rubidium chloride, but instead of a metal, they obtained a blue homogeneous substance, which "neither under the naked eye nor under the microscope showed the slightest trace of metallic substance". They presumed that it was a subchloride (Rb2Cl); however, the product was probably a colloidal mixture of the metal and rubidium chloride. In a second attempt to produce metallic rubidium, Bunsen was able to reduce rubidium by heating charred rubidium tartrate. Although the distilled rubidium was pyrophoric, they were able to determine the density and the melting point. The quality of this research in the 1860s can be appraised by the fact that their determined density differs by less than 0.1 g/cm3 and the melting point by less than 1 °C from the presently accepted values. The slight radioactivity of rubidium was discovered in 1908, but that was before the theory of isotopes was established in 1910, and the low level of activity (half-life greater than 1010 years) made interpretation complicated. The now proven decay of 87Rb to stable 87Sr through beta decay was still under discussion in the late 1940s. Rubidium had minimal industrial value before the 1920s. Since then, the most important use of rubidium is research and development, primarily in chemical and electronic applications. In 1995, rubidium-87 was used to produce a Bose–Einstein condensate, for which the discoverers, Eric Allin Cornell, Carl Edwin Wieman and Wolfgang Ketterle, won the 2001 Nobel Prize in Physics.
=== Microbial growth === Since the main method of microbial decontamination for freeze drying is the low-temperature dehydration process, spoilage organisms and pathogens resistant to these conditions can remain in the product. Although microbial growth is inhibited by the low moisture conditions, it can still survive in the food product. An example of this is a viral hepatitis A outbreak that occurred in the United States in 2016, associated with frozen strawberries. If the product is not properly packaged and/or stored, the product can absorb moisture, allowing the once inhibited pathogens to begin reproducing as well.
Liu Wenhui travelled to Chongqing to negotiate with Liu Xiang, but Liu Xiang would not hand over the confiscated shipment. This was because Liu Xiang had a policy of not allowing any other Sichuanese warlord to gain aircraft (he himself had already acquired a rudimentary air force consisting of several Potez 25 and Breguet 14 bombers). Western sources also agree that Liu Wenhui tried obtaining aircraft, although according to them the aircraft were either seized in Hankou by the central government or crashed en route to Chengdu. The Chinese sources go further by asserting that in May 1931, Liu Wenhui attempted to bribe Liu Xiang's subordinates, including Fan Shaozhen, to join him, but they reported this matter to Liu Xiang, causing Liu to waste 450,000 yuan. An angered Liu supposedly then cut off Liu Xiang's grain supply, forcing the Chongqing warlord to urgently purchase grain from Hunan to prevent hunger. Whatever the matter, it is clear that Liu Wenhui's once-cooperative relationship with his nephew, General Liu Xiang, had soured and turned into a rivalry. On 19 October 1932, Liu Xiang's general, Tang Shizun, and ninety-four other Sichuanese warlords issued a circular telegram to denounce Liu Wenhui. The telegram asserted that Liu was power-hungry, unscrupulous, corrupt, and nepotistic, with no real plans for governing Sichuan and resorting to underhanded tactics such as bribery, backstabbing, and banditry to gain and maintain power. On the eve of war in 1932, Liu Wenhui's armies were estimated at around 120,000 men, slightly outnumbering Liu Xiang's 100,000.
Although trials are commonly conducted at major medical centers, some participants are excluded due to the distance and expenses required for travel, leading to hardship, disadvantage, and inequity for participants, especially those in rural and underserved communities. "Decentralized clinical trials" minimize or eliminates the need for patients to travel to sites, and are now more widespread; a capability improved by telehealth and wearable technologies.
Sources: en.wikipedia.org
No. TB-500 is a short synthetic peptide matching residues 17 to 23 of thymosin beta-4, while the parent protein contains 43 residues. The fragment lacks the rest of the protein sequence, so the two are related but not identical.
It consists of leucine, lysine, lysine, threonine, glutamic acid, threonine, and glutamine in that order. The N-terminal leucine is usually acetylated in the forms described in catalogues.
Controlled human data is limited, and most published findings come from cell culture or animal work. This makes it difficult to state clinical effects with confidence.
Sealed, dry and protected from light at reduced temperature is the usual laboratory convention. Allowing a cold vial to reach room temperature before opening limits condensation. Repeated opening exposes the powder to moisture and should be minimised.