Aib substitution raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-03-19 and is reviewed periodically as new material appears.
Development began in the early 2010s with the goal of extending GLP-1 activity beyond the brief window achieved by native peptide infusion. The earliest approved formulation was a subcutaneous injection given once weekly. A later oral tablet pairs the peptide with an absorption enhancer, sodium N-(8-[2-hydroxybenzoyl] amino) caprylate, usually shortened to SNAC. That carrier lowers local pH and helps the peptide cross gastric tissue. Both routes deliver the same active molecule.
Semaglutide is a synthetic peptide analog of human glucagon-like peptide-1, a gut hormone released after meals. Its backbone retains the GLP-1 sequence but incorporates two substitutions that slow enzymatic breakdown by dipeptidyl peptidase-4. A short polyethylene glycol linker and a C18 fatty diacid are attached to the peptide chain, allowing the molecule to bind serum albumin and remain in circulation far longer than the native hormone. The result is a circulating half-life measured in days rather than the minutes typical of endogenous GLP-1.
Clinical development of this compound followed earlier short-acting GLP-1 analogues that required frequent injection. Once-weekly subcutaneous formulations entered use after 2017, and an oral formulation using a permeation enhancer later became available. The oral version pairs the peptide with sodium N-(8-[2-hydroxybenzoyl] amino) caprylate, a carrier that improves uptake across the gastric epithelium. Interest has expanded from glycaemic control into weight management and metabolic liver disease. Regulatory status and approved indications differ between countries, and the product remains subject to ongoing safety monitoring.
Semaglutide is a synthetic peptide that acts as an agonist at the glucagon-like peptide-1 receptor. It is a structural analogue of human GLP-1(7-37), modified to resist enzymatic degradation by dipeptidyl peptidase-4. The peptide backbone contains alpha-aminoisobutyric acid at position 8, a substitution that stabilises the helix and slows cleavage. A fatty diacid side chain attached through a linker at lysine 34 promotes binding to serum albumin, which extends the circulating half-life. These two modifications together allow less frequent administration than native GLP-1 requires.
| Property | Value | Notes |
|---|---|---|
| Molecular class | Synthetic peptide, GLP-1 receptor agonist | Not a small molecule |
| Backbone substitutions | Non-natural residue at position 8, arginine at position 34 | Slows enzymatic cleavage |
| Side chain | C18 fatty diacid with PEG linker | Enables albumin binding |
| Approximate molecular mass | 4114 Da | Varies slightly with salt form |
| Reported half-life | About one week | Longer than native GLP-1 by orders of magnitude |
Storage guidance for the finished injectable product distinguishes the unused state from the in-use state. Before first use, pens are kept refrigerated between 2 and 8 degrees Celsius, protected from light, and never frozen, since freezing can disrupt the peptide or the device. After first use, label instructions in several markets permit storage at room temperature up to about 30 degrees Celsius for a limited number of days. Solid research-grade material is normally held at or below minus 20 degrees Celsius, often with desiccant, and allowed to equilibrate before opening.
Quantification and purity assessment rely on separation methods coupled to optical or mass detection. Reversed-phase high-performance liquid chromatography resolves the intact peptide from related impurities and is the standard assay technique. Size-exclusion chromatography measures aggregates, while ion-exchange chromatography separates charge variants produced by deamidation. Mass spectrometry confirms identity and detects mass shifts of a few daltons. In biological matrices, liquid chromatography with tandem mass spectrometry is often used because immunoassays can cross-react with endogenous GLP-1 or with circulating fragments.
As a peptide, semaglutide is sensitive to conditions that break amide bonds or modify side chains. Deamidation of asparagine and glutamine residues, oxidation of methionine and tryptophan, and non-covalent aggregation are the main degradation routes described in published stability work. Rate depends strongly on pH, buffer species, ionic strength, temperature and exposure to light. Formulators therefore choose a defined solution pH and often add excipients such as phosphate buffer, propylene glycol and phenol, each of which plays a separate role in pH control, tonicity or preservation.
Lyophilised material appears as a white to off-white cake or powder that is hygroscopic, and containers are usually equilibrated to room temperature before opening to limit condensation. Dissolution is performed in water, phosphate-buffered saline, or a mildly alkaline buffer, since solubility rises above neutral pH. Gentle inversion or low-speed mixing is preferred, because vigorous vortexing can promote surface denaturation and aggregation. Complete dissolution may require several minutes, and brief sonication is sometimes applied. Passing the solution through a 0.22 micrometre membrane removes particulates but does not by itself sterilise the liquid.
Storage at minus 20 degrees Celsius or lower in a desiccated container preserves the peptide for extended periods, while working solutions are commonly held at two to eight degrees Celsius for short intervals. Light exposure and repeated freeze-thaw cycles accelerate degradation, so dividing material into single-use aliquots is generally recommended. Adsorption to glass and plastic surfaces can lower the measured concentration of dilute solutions, particularly below one milligram per millilitre. The degradation routes most often reported for GLP-1 analogues are deamidation, methionine oxidation, and backbone hydrolysis. Relative rates under specific conditions are frequently described only for individual formulations.
市售注射用制剂通常要求在二至八摄氏度冷藏保存，并避免光照与冻结。部分多剂量笔在首次使用后允许在不超过三十摄氏度的环境中存放有限周数，具体期限由辅料与防腐剂体系决定。反复冻融会促进肽链聚集并改变可见颗粒计数，因此应予避免。冻干粉末在干燥、避光、低温条件下更为稳定。溶液配制后宜使用低吸附容器，以减少肽类在塑料或玻璃表面的损失。
纯度评价多采用反相高效液相色谱，流动相常加入三氟乙酸或甲酸作为离子对改性剂，检测波长设在二百一十四纳米或二百二十纳米。分子量确认依靠电喷雾电离质谱或基质辅助激光解吸电离质谱，实测值应与理论值在数 ppm 内吻合。肽图分析通过酶切后液相色谱串联质谱完成，用于核查序列与修饰位点。体积排阻色谱用于定量共价与非共价聚集体。生物基质浓度测定则采用免疫分析或液相色谱串联质谱。
肽类的主要降解路径包括天冬酰胺脱酰胺、甲硫氨酸氧化、天冬氨酸异构化以及由 β-折叠驱动的聚集，这些反应对 pH 与缓冲液种类较为敏感。磷酸盐、丙二醇与苯酚等辅料会影响局部微环境与界面行为。强制降解研究借助高温、强光、氧化剂与极端 pH 暴露来预测产物谱。关于长期室温存放的数据相对有限，超出标签条件的稳定性仍属开放问题，需要在具体制剂中通过实时与加速试验加以确认。
Semaglutide is a synthetic peptide analogue of glucagon-like peptide-1, a gut hormone released by intestinal L cells after food intake. The natural hormone acts on pancreatic and central receptors but is degraded within minutes by dipeptidyl peptidase-4 and other peptidases. Semaglutide belongs to the class of long-acting GLP-1 receptor agonists, a group distinguished by structural changes that slow breakdown and extend circulation time. Its development followed earlier short-acting analogues and reflects a general strategy in peptide drug design: preserve receptor activity while blocking proteolytic clearance.
Three structural changes define the molecule. At position 8 an alpha-aminoisobutyric acid residue replaces alanine, which blocks dipeptidyl peptidase-4 cleavage. At position 34 arginine replaces lysine, and at position 26 a lysine carries a C18 fatty diacid attached through a short linker. The fatty chain binds serum albumin, and this albumin association reduces renal filtration and enzymatic attack. The unchanged backbone retains the receptor contacts that produce signalling. The free base has the formula C187H291N45O59 and a molecular weight near 4114 daltons.
Receptor activation follows the canonical Gs pathway: binding increases intracellular cyclic AMP, which promotes protein kinase A activity. In pancreatic beta cells this amplifies glucose-dependent insulin release, so secretion rises when blood glucose is high and changes little when it is low. The same signalling suppresses glucagon release from alpha cells and slows gastric emptying. Receptors in the hypothalamus and brainstem are thought to contribute to reduced appetite and lower energy intake. Which of these effects dominates clinical outcomes remains an area of active study.
Cleavage at the reactive site results in entrapment of the thrombin protease, with movement of the cleaved reactive site loop together with the bound protease, such that the loop forms an extra sixth strand in the middle of beta sheet A. This movement of the reactive site loop can also be induced without cleavage, with the resulting crystallographic structure being identical to that of the physiologically latent conformation of plasminogen activator inhibitor-1 (PAI-1). For this reason the conformation of antithrombin in which the reactive site loop is incorporated uncleaved into the main body of the protein is referred to as latent antithrombin. In contrast to PAI-1 the transition for antithrombin from a normal or native conformation to a latent conformation is irreversible. Native antithrombin can be converted to latent antithrombin (L-antithrombin) by heating alone or heating in the presence of citrate. However, without extreme heating and at 37 °C (body temperature) 10% of all antithrombin circulating in the blood is converted to the L-antithrombin over a 24-hour period. The structure of L-antithrombin is shown in Figure 6. The 3-dimensional structure of native antithrombin was first determined in 1994. Unexpectedly the protein crystallized as a heterodimer composed of one molecule of native antithrombin and one molecule of latent antithrombin.
"Any individual who is not a member of a federally recognized Cherokee tribe, in academia or otherwise, is hereby discouraged from claiming to speak as a Cherokee, or on behalf of Cherokee citizens, or using claims of Cherokee heritage to advance his or her career or credentials." – Joint Council of the Cherokee Nation and the Eastern Band of the Cherokee Indians The United Keetoowah Band did not sign or approve the resolution. The Cherokee Nation acknowledges the existence of people of Cherokee descent "... in states such as Arkansas, Kansas, Missouri, and Texas," who are Cherokee by ancestry but who are not considered citizens of the Cherokee Nation.
=== Other organizations and programs === HOL LiNK program (Literacy and Numeracy Knowledge), by Hands On Learning Australia Liberty in North Korea (LiNK), a refugee resettling group Link Campus University, Rome, Italy LINKS units, later student volunteering units, of St John Ambulance in England and Wales Local involvement networks (LINks), National Health Service England Project LINK, a UN project to build global macroeconomic models The Link (UK organization) for "Anglo-German friendship", UK pro-Nazi organization, 1937–1939 The Links, a social and service organization of American Black women
Central nervous system medicines Immunology/Allergy medicines Nephrology medicines ESPO / NESP / Aranesp (darbepoetin alfa) REGPARA (cincalcet) Oncology medicines ABSTRAL (fentanyl citrate) GRAN / Peglasta / Neulasta (pegfilgrastim) LEUNASE (asparaginase) Mitomycin-C SANCUSO (granisetron) Diagnostics In vitro diagnostic reagents, analyzers and companion diagnostics
== Prevalence == Over 30% of athletes participating in 2011 World Championships in Athletics admitted having used banned substances during their careers. According to a study commissioned by the World Anti-Doping Agency (WADA), actually 44% of them had used them. Nevertheless, only 0.5% of those tested were caught. The entire Russian track and field team was banned from the 2016 Olympic Games, as the Russian State had sponsored and essentially sanctioned their doping program.
Sources: en.wikipedia.org
Chlorpheniramine is an antihistamine that helps to relieve allergic disorders due to cold, hay fever, itchy skin, insect bites and stings. Chlorpromazine is a tranquilizer that sedates without inducing sleep. It is used to relieve anxiety, excitement, restlessness or even mental disorder. Ephedrine and phenylephrine, as amine hydrochlorides, are used as decongestants. Amphetamine, methamphetamine, and methcathinone are psychostimulant amines that are listed as controlled substances by the US DEA. Thioridazine, an antipsychotic drug, is an amine which is believed to exhibit its antipsychotic effects, in part, due to its effects on other amines. Amitriptyline, imipramine, lofepramine and clomipramine are tricyclic antidepressants and tertiary amines. Nortriptyline, desipramine, and amoxapine are tricyclic antidepressants and secondary amines. (The tricyclics are grouped by the nature of the final amino group on the side chain.) Substituted tryptamines and phenethylamines are key basic structures for a large variety of psychedelic drugs. Opiate analgesics such as morphine, codeine, and heroin are tertiary amines.
is the derivative in the direction y, normal to x, of the flow velocity component u that is oriented along the direction x. In case of a general 2‑D incompressibile flow in the plane x, y, the Newton constitutive equation become:
== Hormones == Estrogens cause the hips to widen and become rounded during puberty in females, and androgens cause the shoulders to broaden in males. Estrogens mediate epiphyseal closure in both males and females. Other hormones implicated in control of bone growth include thyroid hormone, parathyroid hormone, calcitonin, glucocorticoids such as cortisol, and vitamin D (calcitriol). According to menoPAUSE, a blog from University of Rochester, estrogen causes females to have their fat distributed in their breasts, thighs, and along their pelvic area, implying that the fat can be used as an energy source for future pregnancies. For men, androgens (such as testosterone) increases male's muscle-to-fat ratio.Woods J. "What does Estrogen Have to Do with Belly Fat?".
To supply the markets of Southern China, Makassarese trepangers traded with the Aboriginal Australians of Arnhem Land from at least the 18th century and likely considerably earlier. This Makassan contact with Australia is the first recorded example of interaction between the inhabitants of the Australian continent and their Asian neighbours. This contact had a major impact on the Indigenous Australians. The Makassarese exchanged goods such as cloth, tobacco, knives, rice and alcohol for the right to trepang coastal waters and employ local labour. Makassar pidgin became a lingua franca along the north coast among different Indigenous Australian groups who were brought into greater contact with each other by the seafaring Makassan culture. Archeological remains of Makassan contact, including trepang processing plants from the 18th and 19th centuries, are still found at Australian locations such as Port Essington and Groote Eylandt, and the Makassar-planted tamarind trees (native to Madagascar and East Africa).
Sources: en.wikipedia.org
Hogan – the hogan is the traditional dwelling of the Navajo people, constructed from timber, packed earth, and stone. Hogans come in two primary forms: the conical "male" forked-stick hogan used for ceremonies, and the larger circular or polygonal "female" hogan used as a family dwelling. The east-facing entrance aligns with Navajo cosmology, and new hogans are traditionally consecrated with a Blessingway ceremony. Hominy – this is a specialized corn dish known by many North American native people. Today, it is most commonly seen in the Southern United States. Hydraulic pressure – The Maya at Palenque (in modern-day Chiapas, Mexico) engineered the first known pressurized water system in the Americas. By constructing a subterranean aqueduct (the Piedras Bolas aqueduct) that narrowed significantly at the downstream end, they utilized hydraulic principles to create water pressure capable of shooting water upwards to a height of 6 meters (20 ft). This system was likely used for fountains or sanitary purposes, operating without the need for mechanical pumps.
=== Regulation of gene expression === The activated IRS-1 acts as a secondary messenger within the cell to stimulate the transcription of insulin-regulated genes. First, the protein Grb2 binds the P-Tyr residue of IRS-1 in its SH2 domain. Grb2 is then able to bind SOS, which in turn catalyzes the replacement of bound GDP with GTP on Ras, a G protein. This protein then begins a phosphorylation cascade, culminating in the activation of mitogen-activated protein kinase (MAPK), which enters the nucleus and phosphorylates various nuclear transcription factors (such as Elk1).
Age: Testosterone levels gradually reduce as men age. This effect is sometimes referred to as andropause or late-onset hypogonadism. Exercise: Resistance training increases testosterone levels acutely, however, in older men, that increase can be avoided by protein ingestion. Endurance training in men may lead to lower testosterone levels. Nutrients: Vitamin A deficiency may lead to sub-optimal plasma testosterone levels. The secosteroid vitamin D in levels of 400–1000 IU/d (10–25 μg/d) raises testosterone levels. Zinc deficiency lowers testosterone levels but over-supplementation has no effect on serum testosterone. There is limited evidence that low-fat diets may reduce total and free testosterone levels in men. Weight loss: Reduction in weight may result in an increase in testosterone levels. Fat cells synthesize the enzyme aromatase, which converts testosterone, the male sex hormone, into estradiol, the female sex hormone. However no clear association between body mass index and testosterone levels has been found. Miscellaneous: Sleep: (REM sleep) increases nocturnal testosterone levels. Behavior: Dominance challenges can, in some cases, stimulate increased testosterone release in men. Foods: Natural or man-made antiandrogens including spearmint tea reduce testosterone levels. Licorice can decrease the production of testosterone and this effect is greater in females.
Sources: en.wikipedia.org
Native GLP-1 is degraded within minutes by circulating enzymes. The synthetic version carries substitutions at positions that block enzymatic cleavage, plus a fatty acid side chain that promotes albumin binding. These two changes together extend circulation time from minutes to roughly a week.
Albumin binding keeps a large fraction of the compound in a slowly released reservoir within the bloodstream. Plasma levels decline gradually rather than falling sharply after each administration. That profile supports dosing intervals measured in days instead of hours.
The active peptide sequence is the same in both formats. The oral version adds an absorption enhancer that is not present in the injected solution. Differences in excipients and formulation affect uptake rather than the identity of the active molecule.
It belongs to the incretin mimetic class and acts as a long-acting glucagon-like peptide-1 receptor agonist. The class includes several peptides with different half-lives and routes of administration.