If you have been reading about prohibited list and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2026-01-20. Where a claim depends on a specific study, the study is described rather than over-claimed.
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 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.
No major regulatory agency has approved TB-500 for therapeutic use, and it holds no pharmacopoeial monograph. The name appears on the World Anti-Doping Agency prohibited list within the class covering peptide hormones, growth factors, and related substances. Detection in doping control relies on mass spectrometric methods applied to urine, often after preparation steps that concentrate the analyte. Discussion of TB-500 therefore clusters in biochemistry, sports medicine, and anti-doping literature rather than in registered clinical trials.
TB-500 is a synthetic peptide preparation marketed under a name derived from thymosin beta-4, a 43-residue actin-binding protein first isolated from thymus tissue. The full-length protein has a reported molecular mass near 4963 Da, while material sold as TB-500 is often described as a fragment containing the actin-binding motif LKKTETQ. Because suppliers use the name inconsistently, published sources sometimes refer to the same label as a fragment, a synthetic copy, or a related analog. This naming ambiguity complicates direct comparison of reports across studies.
Laboratory work on thymosin beta-4 describes binding to monomeric actin and effects on cell migration, angiogenesis, and inflammatory signaling in cultured cells. Animal models have examined skin, corneal, and cardiac repair after injury, with outcomes reported mainly in preclinical literature. Most of that evidence concerns the parent protein rather than preparations labelled TB-500, so extrapolation from animal findings to a specific commercial product remains uncertain. Whether the two behave identically in living systems has not been established in controlled human studies.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white lyophilized powder | Typical form for short synthetic peptides |
| Solubility class | Freely soluble in water and aqueous buffer | Dissolution aided by gentle mixing, not vigorous shaking |
| Typical storage temperature | −20 °C, desiccated | −80 °C used for long-term holding |
| Common analytical method | Reverse-phase HPLC with UV detection near 214 nm | Identity confirmed separately by mass spectrometry |
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming varies between suppliers and publications |
The seven-residue chain carries several polar and charged side chains, so it dissolves readily in water and in aqueous buffers near neutral pH. No cysteine is present, so disulphide formation is not a concern and reducing agents are unnecessary. Dilute ammonium hydroxide or acetonitrile-water mixtures are sometimes used for stock solutions when initial dissolution is slow. Strongly alkaline conditions and prolonged contact with oxidising agents are avoided because they can modify lysine-containing stretches, and haze in solution usually signals incomplete dissolution or aggregated material.
Identity and purity are checked with reversed-phase high-performance liquid chromatography, which separates the target sequence from truncated or deletion analogues, and with mass spectrometry, which confirms the expected molecular mass. Amino acid analysis and peptide mapping give orthogonal confirmation but are used less often outside specialist laboratories. Counter-ion content varies: material purified on trifluoroacetic acid gradients retains trifluoroacetate, and ion exchange can convert the salt form. Residual water and solvent are measured by Karl Fischer titration or thermogravimetric analysis, and any purity figure should be read together with the method used to obtain it.
Lyophilised peptide powders are hygroscopic, and the fragment absorbs atmospheric moisture when a vial is opened at room temperature. Weighing and aliquoting are normally done quickly in a dry environment, and stock solutions are divided into single-use portions before freezing. Repeated freeze-thaw cycles are avoided because they promote aggregation and can shift the measured content of a vial. These practices are general to synthetic peptides rather than unique to this sequence, but they matter more for short chains kept for long periods.
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.
Purity is normally assessed by reversed-phase HPLC, with the main peak reported as a percentage of total peak area, while identity is confirmed by mass spectrometry. Electrospray and MALDI-TOF instruments are both used, and the observed mass is compared with the value calculated from the stated sequence. Ion-exchange or size-exclusion methods appear where aggregation or charge variants are of interest. Water content, counter-ion content and residual trifluoroacetate from purification are separate variables that can shift the measured mass and should be weighed when reading a certificate of analysis.
Research peptides are typically supplied as a white to off-white lyophilised powder in a sealed vial. The dry solid is more stable than a solution and is normally kept refrigerated or frozen until use. Dissolution is usually done in water, phosphate-buffered saline or a similar aqueous medium, depending on the assay. Because the material is hygroscopic and easily contaminated, opening vials in a low-humidity environment and recording the lot number before use are standard laboratory practices.
=== Excretion === Bile is the major pathway for the excretion of copper and is vitally important in the control of liver copper levels. Most fecal copper results from biliary excretion; the remainder is derived from unabsorbed copper and copper from desquamated mucosal cells.
=== Biosynthesis === Chloramphenicol is produced by Streptomyces venezuelae. Its biosynthesis has been partially elucidated. A portion of the structure originates from the shikimate pathway, in which aromatic amino acids are formed. The non-proteinogenic amino acid para-aminophenylalanine is also accessible via this pathway (step 1 in the scheme). This intermediate is bound to a peptidyl carrier protein via a thioester (2) and hydroxylated at the benzyl position (3). The amino group is then oxidized to the nitro group (4), the dichloroacetyl group is introduced from an unknown precursor (5), and the intermediate is released as an aldehyde (6). Reduction of the aldehyde group to the alcohol (7) yields chloramphenicol.
=== Effects on inflammation === PGLYRP2 directly and indirectly affects inflammation and plays a role in maintaining anti- and pro-inflammatory homeostasis in the intestine, skin, joints, and brain. Hydrolysis of peptidoglycan by PGLYRP2 diminishes peptidoglycan's pro-inflammatory activity. This effect is likely due to amidase activity of PGLYRP2, which separates the stem peptide from MurNAc in peptidoglycan and destroys the motif required for the peptidoglycan-induced activation of NOD2 (nucleotide-binding oligomerization domain-containing protein 2), one of the proinflammatory peptidoglycan receptors. PGLYRP2-deficient mice are more susceptible than wild type mice to dextran sodium sulfate (DSS)-induced colitis, which indicates that PGLYRP2 protects mice from DSS-induced colitis. Intestinal microbiome is important for this protection, because this increased sensitivity to colitis could be transferred to wild type germ-free mice by microbiome transplant from PGLYRP2-deficient mice. PGLYRP2-deficient mice are more susceptible than wild type mice to the development of experimentally induced psoriasis-like inflammation, which indicates that PGLYRP2 is anti-inflammatory and protects mice from this type of skin inflammation. This pro-inflammatory effect in PGLYRP2-deficient mice is due to the increased numbers and activity of T helper 17 (Th17) cells and decreased numbers of T regulatory (Treg) cells. PGLYRP2-deficient mice are more susceptible than wild type mice to S.
electron electric dipole moment (de) An intrinsic property of an electron such that its potential energy is linearly related to the strength of its electric field; a measure of the distribution of an electron's negative charge within the electric field it creates. See also electric dipole moment.
=== May === 3 May – Astronomers from the University of Warwick report 118 new confirmed exoplanets, with a further 2,000 "high-quality" candidates, detected using machine learning applied to data from NASA's Transiting Exoplanet Survey Satellite (TESS). 4 May The discovery of a thin atmosphere on the trans-Neptunian object (612533) 2002 XV93 is announced. A study published in Communications Sustainability finds that utility-scale solar power and wind power generally provide greater climate and public health benefits per dollar than direct air capture (DAC), based on modelling across 22 U.S. grid regions through 2050. The authors conclude that DAC becomes competitive mainly under a breakthrough scenario in which energy use falls from 5,500 to 800 kWh and cost from US$1,000 to US$100 per tonne of CO2 captured. A meta-analysis of over 20,000 participants concludes that drugs targeting amyloid beta peptides do not meaningfully slow progression of Alzheimer's disease. 6 May – A study in npj Space Exploration, using radar data from India's Chandrayaan-2 orbiter, reports strong evidence for subsurface water ice in four doubly-shadowed craters near the lunar south pole. 8 May – A study published in Aging Cell reports that the exceptional-longevity-associated APOE ε2 allele is associated with enhanced DNA-damage response and repair pathways in human neurons.
Sources: en.wikipedia.org
== COVID-19 pandemic == ADLM members who are frontline laboratory specialists also encounter significant challenges in carrying out such studies. Lack of product selection and research materials as well as personal protective equipment, known as PPE, are the most important of these barriers. In recognition of these obstacles to optimizing research ability, ADLM sent a letter to the Coronavirus Task Force advising the Task Force and White House to minimize supply chain issues, and to identify and organize tools such that doctors, nurses, laboratory personnel and other healthcare staff may do their jobs. ADLM has produced instructional videos demonstrating serology, treatment of polymerase chain reaction (PCR), and more through research in the spotlight during the COVID-19 pandemic.
=== Barriers to access === In the US, the list price for a long-acting injectable form is five to 20 times as much as a daily pill. This has reduced the number of people who are able to get a single monthly dose, instead of daily pills. Some jails consider the more expensive form a positive tradeoff: a single monthly injection may be simpler and easier for the staff to manage than daily trips to the dispensary to have a nurse provide a pill and make sure that it has been swallowed.
Alfentanil, sold under the brand name Alfenta among others, is a potent, short-acting synthetic opioid analgesic drug used for anesthesia in surgery. It is an analogue of fentanyl with around one-fourth to one-tenth the potency, one-third the duration of action, and an onset of action four times faster than that of fentanyl. Alfentanil has a pKa of approximately 6.5, which leads to a very high proportion of the drug being uncharged at physiologic pH, a characteristic responsible for its rapid-onset. It is an agonist of the μ-opioid receptor. While alfentanil tends to cause fewer cardiovascular complications than other similar drugs such as fentanyl and remifentanil, it tends to give stronger respiratory depression and so requires careful monitoring of breathing and vital signs. Almost exclusively used by anesthesia providers during portions of a case where quick, fast-acting (though not long-lasting) pain control is needed (as, for example, during nerve blocks), alfentanil is administered by the parenteral (injected) route for fast-onset and precise control of dosage. Discovered at Janssen Pharmaceutica in 1976, alfentanil is classified as a Schedule II drug in the United States.
A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulating surfaces. This joint unites long bones and permits free bone movement and greater mobility. The synovial cavity/joint is filled with synovial fluid. The joint capsule is made up of an outer layer of fibrous membrane, which keeps the bones together structurally, and an inner layer, the synovial membrane, which seals in the synovial fluid. They are the most common and most movable type of joint in the body. As with most other joints, synovial joints achieve movement at the point of contact of the articulating bones. Joints that are not synovial include fibrous joints such as the joints in the cranium, and cartilaginous joints such as intervertebral discs. Synovial joints originated 400 million years ago in the first jawed vertebrates.
Sources: en.wikipedia.org
In addition, composite materials incorporating MOFs with polymers, carbon materials, or magnetic nanoparticles have been developed to improve mechanical stability, facilitate recovery, and enhance overall treatment efficiency. Despite these promising applications, several challenges remain for the large-scale implementation of MOFs in water treatment systems. These include limited stability in aqueous environments for certain frameworks, the cost and scalability of synthesis, and the need for improved durability under realistic operating conditions . Ongoing research efforts are therefore focused on developing more robust MOF structures and scalable production methods to enable their practical deployment in water purification technologies.
== External links == Amino acid metabolism Chapter on Amino acid catabolism in Biochemistry by Jeremy Berg, John Tymoczko, Lubert Stryer. Fourth ed. by Lubert Stryer. ISBN 0-7167-4955-6 Accessed 2007-03-17 Amino acid metabolism
The CBO forecast in April 2020 that the budget deficit in fiscal year 2020 would be $3.7 trillion (17.9% GDP), versus the January estimate of $1 trillion (4.6% GDP). CBO also forecast the unemployment rate would rise to 16% by Q3 2020 and remain above 10% in both 2020 and 2021.
== Genetics and disease relevance == In humans, enteropeptidase is encoded by the TMPRSS15 gene (also known as ENTK, and previously as PRSS7) on chromosome 21q21. Some nonsense and frameshift mutations in this gene lead to a rare recessive disorder characterised by severe failure to thrive in affected infants, due to enteropeptidase deficiency. Enteropeptidase mRNA expression is limited to the proximal small intestine, and the protein is found in enterocytes of duodenum and proximal jejunum. Upon secretion from the pancreas into the duodenum, trypsinogen encounters enteropeptidase and is activated. Trypsin then cleaves and activates other pancreatic serine protease zymogens (chymotrypsinogen and proelastases), metalloprotease zymogens (procarboxypeptidases) and prolipases. By means of this simple two-step cascade, the destructive activity of these digestive hydrolases is confined to the lumen of the intestine. The physiological importance of this pathway is demonstrated by the severe intestinal malabsorption caused by congenital deficiency of enteropeptidase. This condition can be life-threatening, but responds to oral supplementation with pancreatic extract.
Polling before the election indicated profound dissatisfaction with the state of American democracy. According to an October 25 ABC/Ipsos poll, 49% of Americans saw Trump as a fascist, described as "a political extremist who seeks to act as a dictator, disregards individual rights and threatens or uses force against their opponents". Meanwhile, only 22% saw Harris as a fascist by this definition. Some Republicans were concerned that Trump's former impeachment and four criminal indictments were attempts to influence the election and keep him from office; however, there is no evidence that Trump's criminal trials were "election interference" orchestrated by Biden and the Democratic Party, and Trump also continued to repeat false claims that the 2020 election was "rigged" and stolen from him. Trump's 2024 presidential campaign was criticized by legal experts, historians, and political scientists for making increasingly dehumanizing, violent, and authoritarian statements. Trump's platform called for the vast expansion of presidential powers and the executive branch over every part of the federal government. Trump called for stripping employment protections for thousands of career civil service employees (a provision known as Schedule F appointment that had been adopted by Trump at the end of 2020) and replacing them with political loyalists if deemed an "obstacle to his agenda" within federal agencies, the United States Intelligence Community, State Department, and Department of Defense.
Sources: en.wikipedia.org
TB-500 is a trade-style label for a synthetic peptide connected to thymosin beta-4. It is sold mainly through research-chemical channels and is not a single chemically defined product across suppliers.
Not necessarily. Some vendors use the name for the full 43-residue protein, while others apply it to a short actin-binding fragment or to a related tetrapeptide. The sequence should be confirmed from documentation rather than assumed from the label.
No thymosin beta-4 fragment holds marketing approval as a medicine in major jurisdictions. Material offered for sale is typically labelled for laboratory research only.
Not necessarily. TB-500 is a commercial label that suppliers apply to synthetic peptides described as thymosin beta-4 or a fragment of it. Published research most often studies the full-length protein, so statements about one do not automatically transfer to the other.