prohibited list comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-03-09. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
Proposed activity centers on actin sequestration and on the movement of cells during repair processes. In cell culture and animal models, the fragment has been associated with migration, tube formation, and tissue remodeling. These observations are frequently described as preliminary, because most published work uses rodent or in vitro systems rather than controlled human trials. Whether the short fragment reproduces the effects of the full protein remains an open question, and the relationship between dose, route, and measured outcome is not well characterized.
The compound circulates in the literature as a research reagent rather than an approved therapeutic. Regulatory agencies in several countries have not authorized it for medical use, and sporting bodies list related thymosin beta-4 peptides among prohibited substances. Suppliers typically market it with a purity figure and a certificate of analysis, while peer-reviewed clinical reports remain sparse. Discussions therefore often separate laboratory findings from anecdotal reports, and reviewers tend to note the small size and methodological limits of the available studies.
TB-500 refers to a synthetic peptide fragment derived from the actin-binding region of thymosin beta-4, a protein present in most mammalian cells. The full protein contains forty-three amino acids, while the commonly sold fragment is a much shorter acetylated sequence, often cited as LKKTETQ. The fragment retains part of the actin-binding motif but lacks the remainder of the parent protein. Material sold under this name is usually lyophilized powder intended for laboratory research, and it is not a finished pharmaceutical product.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white solid | Lyophilised cake or powder |
| Solubility class | Freely soluble in water | Aqueous buffers also used |
| Typical storage temperature | About -20 degrees Celsius | Dry, sealed and protected from light |
| Typical analytical method | Reversed-phase HPLC or LC-MS/MS | Used for purity, identity and quantification |
| Common synonyms | Thymosin beta-4 fragment | Also listed under fragment-based descriptions |
Identity and purity are assessed with a small set of standard techniques. Reverse-phase high-performance liquid chromatography gives a purity estimate from peak area, usually recorded at 214 or 220 nanometers, where the peptide bond absorbs. Mass spectrometry confirms the expected molecular mass and can reveal truncated or oxidized species. Amino acid analysis or tandem mass spectrometry sequencing can verify the sequence itself. Additional quality attributes include water content, residual trifluoroacetic acid carried over from purification, and endotoxin where the material is intended for biological work.
The compound is most often distributed as a lyophilized powder, appearing white to off-white and forming a loose cake or fluffy solid. It is hygroscopic to some degree, so brief exposure to humid air can add water weight and complicate weighing. The peptide dissolves readily in water and in neutral aqueous buffers, and aqueous solubility is generally described as high, well above the concentrations used in typical assays. Some polar organic solvents are also usable, which matters when a concentrated stock is prepared before dilution into buffer.
Thymosin beta-4 was isolated from calf thymus in the early 1980s and later characterised as an abundant intracellular actin-sequestering protein. Interest in short synthetic fragments grew once the actin-binding motif had been mapped to the middle of the sequence. TB-500 came out of that line of work as a truncated analogue rather than a natural isolate, and it is now sold mainly to laboratories. Published studies on the fragment have been largely in vitro or in animal models, and controlled human trials remain sparse, so claims about effects in people rest on extrapolation.
Literature and online discussion often conflate TB-500 with full-length thymosin beta-4, even though the two differ in size and are not interchangeable in analytical terms. The fragment is produced by solid-phase peptide synthesis, and the product is a defined seven-residue chain rather than a biological extract. Because the term is a trade-style label, two vendors may supply materials of the same nominal sequence but different counter-ion content, purity, or water content. Comparisons across studies are therefore difficult unless the exact sequence and purity are reported.
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.
[RO−P(O)2−O−P(O)2−O−PO3]4− + H2O → [RO−P(O)2−O−PO3]3− + [HPO4]2− + H+ [RO−P(O)2−O−P(O)2−O−PO3]4− + H2O → [RO−PO3]2− + [HO3P−O−PO3]3− + H+ For ATP hydrolysis that takes place with the physiological concentrations of ATP, ADP, and inorganic phosphate (Pi) within the living cell, the change in Gibbs free energy is given by:
=== Reaction pathways === Diterpenes are commonly synthesized from the precursor molecule geranylgeranyl pyrophosphate (GGPP). GGPP's hydrocarbon backbone can be rearranged into different structures that may be further rearranged or added to in order to create precursors for different families of diterpenoid compounds. This precursor molecule may be synthesized through the mevalonic acid pathway or the deoxyxylulose pathway. These pathways produce isopentenyl pyrophosphate, which can be rearranged into GGPP. The cyclization of GGPP and the subsequent reorganizations into different precursors is controlled by a large family of enzymes known as diterpene syntheses (diTPS). To synthesize sugiol a plant must first synthesize GGPP through either of the previously mentioned pathways, (mevalonic acid or the deoxyxylulose pathway), then rearrange GGPP into the molecule mitiradiene. After formation of an intermediate compound abietatriene, a cytochrome P450 enzyme can then attach an oxygen molecule to the intermediate. This produces ferruginol, which can then be modified to sugiol by sugiol synthase. Sugiol may then be formed through the modification of ferruginol according to the following reaction driven by the enzyme sugiol synthase.
Pedro II of Brazil died of pneumonia at the age of 66 during his exile in France in 1891. He was embalmed on 5 December, the day of his death. During the procedure, six liters (1.585 U.S. gallons) of zinc and aluminum hydrochloride were injected into his common carotid artery. Three coffins were used: an inner coffin of lead lined with white satin; a middle coffin of varnished oak; and an outer coffin of oak covered by black velvet. According to Julie Anne Taddeo, a research professor of history at the University of Maryland, lead helps keep out moisture and preserve the body for longer and prevent smells and toxins from a dead body escaping. Interred in the Royal Pantheon of the House of Braganza in Lisbon on 12 December 1891, Pedro II became a focus of pilgrimage for Brazilians visiting Portugal, with the site attracting numerous visitors. Many would visit late at night, carrying candles provided by a local guard. As they leaned over the crystal-paned inner lead coffin to view the embalmed monarch, candle wax often dripped onto the Brazilian imperial flag draped over it. In the 1910s, Brazilian educator and archivist Luís Gastão d'Escragnolle Dória traveled to Europe on a scholarship to search for historical documents related to Brazil. In a 1912 visit to the Royal Pantheon, he noted that Pedro II's body remained largely well preserved and appeared much as it had been when first placed in the coffin.
==== Greek writers ==== It is assumed that the Hippocratic Corpus bears no direct mention of what we now know as diabetes. However, a number of indirect statements referring to excessive and "watery urine" suggest that Hippocratic writers may have been familiar with the condition. According to On Ancient Medicine, Hippocrates was under the impression that the slumbering and thirst which resulted from high blood sugar was due to the bowels struggling to digest too much food and the weaknesses resulting from low blood sugar were because the body lacked nourishment due to missing a meal.
Sources: en.wikipedia.org
=== Off-targeting === Off-targeting is another challenge to the use of siRNAs as a gene knockdown tool. Here, genes with incomplete complementarity are inadvertently downregulated by the siRNA (in effect, the siRNA acts as a miRNA), leading to problems in data interpretation and potential toxicity. This, however, can be partly addressed by designing appropriate control experiments, and siRNA design algorithms are currently being developed to produce siRNAs free from off-targeting. Genome-wide expression analysis, e.g., by microarray technology, can then be used to verify this and further refine the algorithms. A 2006 paper from the laboratory of Anastasia Khvorova implicates 6- or 7-basepair-long stretches from position 2 onward in the siRNA matching with 3'UTR regions in off-targeted genes. The tool of siRNA off-target prediction is available at http://crdd.osdd.net/servers/aspsirna/asptar.php and published as ASPsiRNA resource.
== Research == Anastrozole is surprisingly ineffective at treating gynecomastia, in contrast to selective estrogen receptor modulators like tamoxifen. Anastrozole was under development for the treatment of female infertility but did not complete development and hence was never approved for this indication. An anastrozole and levonorgestrel vaginal ring (developmental code name BAY 98–7196) was under development for use as a hormonal contraceptive and treatment for endometriosis. Development was discontinued in November 2018, and the formulation was never marketed. Anastrozole increases testosterone levels in males and has been studied as an alternative method of androgen replacement therapy in men with hypogonadism. However, there are concerns about its long-term influence on bone mineral density in this patient population, as well as other adverse effects.
According to Historian of Art Benjamin Rowland, the portraits in Kizil show "that the Tocharians were European rather than Mongol in appearance, with light complexions, blue eyes, and blond or reddish hair, and the costumes of the knights and their ladies have haunting suggestions of the chivalric age of the West". The Chinese named Kuchean kings by adding the prefix "白", meaning "white", probably pointing to the fair complexion of the Kucheans. The Chinese Monk Xuanzang in 645 CE, noted that "they clothe themselves with ornamented garments of silk and embroidery". This cave also shows Central Asian traders encountering various dangers on their way, such as being lost in the dark, and being saved by the Dragon-King Mabi. Another is the story of the good merchant Sabu (萨缚), who, in order to show the way to a party of 500 merchants lost in the darkness, puts his own arms on fire to use them as torches, and successfully rescues them. The story appears in numerous paintings, in which the merchants are in Central Asian garb and accompanied by camels, and Sab has the attributes of a Bodhisattva. Cave 17 is contemporary with the earliest decorated Mogao Caves near Dunhuang (caves 268, 272 and 275), which were built and decorated by the Northern Liang between 419 and 439 CE, before the invasion of the Northern Wei. They have many stylistic characteristics in common.
α (orthorhombic) stable up to 668 °C (1,234 °F). Orthorhombic, space group No. 63, Cmcm, lattice parameters a = 285.4 pm, b = 587 pm, c = 495.5 pm. β (tetragonal) stable from 668 to 775 °C (1,234 to 1,427 °F). Tetragonal, space group P42/mnm, P42nm, or P4n2, lattice parameters a = 565.6 pm, b = c = 1075.9 pm. γ (body-centered cubic) from 775 °C (1,427 °F) to melting point—this is the most malleable and ductile state. Body-centered cubic, lattice parameter a = 352.4 pm.
Typically, these projects make use of re-coded nonsense suppressor tRNA-Aminoacyl tRNA synthetase pairs from other organisms, though in most cases substantial engineering is required. Other researchers investigated protein structure and function by reducing the normal set of 20 amino acids. Limited protein sequence libraries are made by generating proteins where groups of amino acids may be replaced by a single amino acid. For instance, several non-polar amino acids within a protein can all be replaced with a single non-polar amino acid. One project demonstrated that an engineered version of Chorismate mutase still had catalytic activity when only nine amino acids were used. Researchers and companies practice synthetic biology to synthesize industrial enzymes with high activity, optimal yields and effectiveness. These synthesized enzymes aim to improve products such as detergents and lactose-free dairy products, as well as make them more cost effective. The improvements of metabolic engineering by synthetic biology is an example of a biotechnological technique utilized in industry to discover pharmaceuticals and fermentive chemicals. Synthetic biology may investigate modular pathway systems in biochemical production and increase yields of metabolic production. Artificial enzymatic activity and subsequent effects on metabolic reaction rates and yields may develop "efficient new strategies for improving cellular properties ... for industrially important biochemical production".
Sources: en.wikipedia.org
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.
Reported purity reflects the batch tested, the chromatographic method used and whether an independent laboratory performed the work. Values quoted without method detail or a traceable certificate are difficult to compare directly.
Short peptides are rapidly broken down by proteases and appear at low concentrations in urine, so the detection window is narrow. Sensitive extraction combined with tandem mass spectrometry is typically required.
TB-500 is a name used for a short synthetic peptide fragment taken from the actin-binding region of thymosin beta-4. Material sold under this label is usually a lyophilized powder supplied for laboratory research rather than a licensed medicine. The commonly cited sequence is LKKTETQ.