incretin is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-05-07. Numbers and descriptions here follow the published literature rather than marketing material.
The company that developed the compound filed it as a long-acting analogue, and it gained first approval in 2017 for type 2 diabetes. Later authorisations from several regulators extended the indication to chronic weight management, and the World Health Organization added the glucagon-like peptide-1 receptor agonist drug class to its model list of essential medicines in 2023. Production uses solid-phase peptide synthesis followed by side-chain conjugation and chromatographic purification. Supply constraints and cost differences across regions are well documented. Literature on long-term outcomes continues to grow, with many trials reporting surrogate endpoints rather than hard clinical endpoints.
Semaglutide is a synthetic peptide of thirty-one amino acids that shares roughly ninety-four percent sequence identity with human glucagon-like peptide-1. Two substitutions resist enzymatic cleavage by dipeptidyl peptidase-4, and a fatty diacid side chain attached through a linker promotes binding to serum albumin. That albumin binding slows renal clearance and extends the circulating half-life from minutes to approximately one week. The structural changes are well established in the published literature. Whether the same modifications affect receptor signalling bias in ways that matter clinically remains an open question.
Pharmacological activity arises from agonism at the glucagon-like peptide-1 receptor, a G protein-coupled receptor expressed in the pancreas, the gastrointestinal tract, and the brainstem. Receptor activation raises intracellular cyclic adenosine monophosphate and enhances insulin release in a glucose-dependent manner, an effect that diminishes when blood glucose concentration is low. Other effects include slowed gastric emptying and hypothalamic satiety signalling. These pathways are described well. Receptor desensitisation rates across tissues, relative to the endogenous hormone, are still under investigation, and reported findings differ between laboratories.
序列层面的改动同时解决了两个问题，即酶解稳定性与肾脏清除速度。天然 GLP-1 在循环中的半衰期仅约两分钟，主要被二肽基肽酶-4 迅速灭活。酰化侧链与白蛋白的可逆结合形成循环储库，使分子缓慢释放并持续激活受体。这种设计思路后来被广泛用于同类长效肽的开发，属于该类药物化学改造的典型范式。
Semaglutide 是一种经结构修饰的胰高血糖素样肽-1 类似物，其主链与内源性 GLP-1(7-36) 约有百分之九十四的序列一致性。第 8 位丙氨酸被 α-氨基异丁酸取代，使二肽基肽酶-4 无法识别原有切割位点。第 34 位赖氨酸换为精氨酸，进一步降低酶解速率。第 26 位赖氨酸经间隔基连接一条含十八个碳的二酸脂肪链，该侧链赋予分子与血浆白蛋白结合的能力。
该分子作为 GLP-1 受体的选择性激动剂发挥作用，受体属于 B 类 G 蛋白偶联受体家族，激活后经 Gs 通路提升细胞内环腺苷酸水平。在胰腺 β 细胞，信号促进葡萄糖依赖性的胰岛素释放，血糖偏低时该作用明显减弱。在胰岛 α 细胞，胰高血糖素分泌受到抑制。中枢神经系统与胃肠道同样存在受体表达，相应信号参与食欲调节以及胃排空速率的降低。
| Property | Value | Notes |
|---|---|---|
| Molecular class | 31-amino-acid peptide | Modified glucagon-like peptide-1 analogue |
| Molecular mass | approximately 4114 Da | Calculated for the free peptide backbone |
| Appearance | white to off-white powder | Typical of purified lyophilised peptide batches |
| Solubility class | freely soluble in water | Aqueous solubility improves at slightly alkaline pH |
| Typical storage | -20 degrees Celsius, dry, dark | Protect from repeated freeze-thaw cycles |
Semaglutide is a synthetic peptide analogue of glucagon-like peptide-1, a gut hormone released after nutrient intake. The molecule contains 31 amino acid residues and differs from the native sequence at several positions. A non-natural residue at position eight resists the enzyme that normally truncates the hormone, while a lysine-linked fatty diacid side chain promotes binding to serum albumin. These two modifications extend the circulating half-life from minutes to roughly one week. The peptide is produced by solid-phase synthesis followed by selective acylation, and its identity and purity are confirmed by spectrometric and chromatographic techniques.
The primary target is the GLP-1 receptor, a class B G protein-coupled receptor expressed on pancreatic beta cells, in the gut, and in several brain regions. Receptor activation raises intracellular cyclic AMP, which potentiates glucose-dependent insulin secretion and lowers glucagon release when blood glucose is elevated. Signalling in the hypothalamus and brainstem is associated with reduced appetite and slower gastric emptying. Because the insulinotropic effect depends on prevailing glucose levels, the hypoglycaemic risk of the peptide alone is described as low in most study settings. The relative contribution of peripheral and central actions remains an active research question.
Activation of the GLP-1 receptor couples to Gs signalling and raises intracellular cyclic AMP in pancreatic beta cells. The resulting insulin release depends on prevailing glucose concentrations, so the effect is greater when glucose is elevated. Receptor engagement also suppresses glucagon secretion and slows gastric emptying, which flattens post-meal glucose excursions. In the central nervous system, signalling in hypothalamic and brainstem regions is associated with reduced appetite and lower energy intake. Studies continue to examine effects on cardiac, renal and hepatic endpoints; whether those benefits are independent of weight change remains an open question.
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.
Semaglutide is a synthetic peptide analog of glucagon-like peptide-1, a hormone released from intestinal L cells after food intake. The molecule is a 31-amino-acid backbone modified at three positions to resist cleavage by dipeptidyl peptidase-4, the enzyme that degrades native GLP-1 within minutes. A lysine residue at position 26 carries a linker and a C18 fatty diacid, which promotes binding to serum albumin and slows renal clearance. These changes extend the circulating half-life from roughly two minutes to about one week in humans.
The sequence incorporates alpha-aminoisobutyric acid at position 8, replacing the alanine found in the natural hormone. This substitution blocks the primary DPP-4 recognition site and contributes most of the enzymatic stability. Albumin binding further protects the peptide and reduces the frequency of administration required to maintain active plasma levels. Because the fatty acid chain increases lipophilicity, the compound is formulated as a solution rather than a simple aqueous buffer. Researchers describe the design as an incremental optimization of earlier GLP-1 analogs rather than a wholly new scaffold.
Reported molecular weight is approximately 4113.6 daltons for the free base, and the peptide is supplied as a lyophilized powder or in buffered liquid form depending on the intended use. It is freely soluble in water when formulated with appropriate excipients, though the unconjugated peptide shows limited stability at neutral pH over long periods. Analytical characterization typically relies on reversed-phase high-performance liquid chromatography and mass spectrometry. Purity specifications for research-grade material commonly exceed ninety-five percent by area. Isotopic and impurity profiles differ between suppliers.
Semaglutide belongs to the glucagon-like peptide-1 receptor agonist class, a group of synthetic peptides that imitate an incretin hormone released by intestinal L cells after food intake. Native GLP-1 circulates for only a few minutes because dipeptidyl peptidase-4 cleaves it rapidly. The hormone acts on pancreatic islets, the gastrointestinal tract, and several brain regions. Because the natural peptide is short-lived, development work concentrated on analogues that keep receptor activity while resisting enzymatic breakdown and renal clearance.
The semaglutide sequence is a 31-residue analogue of human GLP-1, altered at three positions relative to the parent hormone. Aminoisobutyric acid replaces alanine at position 8, arginine replaces lysine at position 34, and a lipophilic diacid is attached to lysine 26 through a short linker. These features are reported consistently in the structural literature. The position 8 substitution blocks recognition by dipeptidyl peptidase-4, while the attached chain drives strong, reversible association with a carrier protein in blood.
Tandem mass spectrometry can be used for protein sequencing. When intact proteins are introduced to a mass analyzer, this is called "top-down proteomics" and when proteins are digested into smaller peptides and subsequently introduced into the mass spectrometer, this is called "bottom-up proteomics". Shotgun proteomics is a variant of bottom up proteomics in which proteins in a mixture are digested prior to separation and tandem mass spectrometry. Tandem mass spectrometry can produce a peptide sequence tag that can be used to identify a peptide in a protein database. A notation has been developed for indicating peptide fragments that arise from a tandem mass spectrum. Peptide fragment ions are indicated by a, b, or c if the charge is retained on the N-terminus and by x, y or z if the charge is maintained on the C-terminus. The subscript indicates the number of amino acid residues in the fragment. Superscripts are sometimes used to indicate neutral losses in addition to the backbone fragmentation, * for loss of ammonia and ° for loss of water. Although peptide backbone cleavage is the most useful for sequencing and peptide identification other fragment ions may be observed under high energy dissociation conditions. These include the side chain loss ions d, v, w and ammonium ions and additional sequence-specific fragment ions associated with particular amino acid residues.
=== Rafts === The Lower Paleolithic Homo erectus possibly invented rafts (c. 840,000 – c. 800,000 BP) to travel over large bodies of water, which may have allowed a group of Homo erectus to reach the island of Flores and evolve into the small hominin Homo floresiensis. However, this hypothesis is disputed within the anthropological community. The possible use of rafts during the Lower Paleolithic may indicate that Lower Paleolithic hominins such as Homo erectus were more advanced than previously believed, and may have even spoken an early form of modern language. Supplementary evidence from Neanderthal and modern human sites located around the Mediterranean Sea, such as Coa de sa Multa (c. 300,000 BP), has also indicated that both Middle and Upper Paleolithic humans used rafts to travel over large bodies of water (i.e. the Mediterranean Sea) for the purpose of colonizing other bodies of land.
=== Christmas Island and the B.P.C. === Following the Nauru Agreement of 2 July 1919 the interests of the PPC in the phosphate deposits in Nauru and Ocean Island were acquired by the governments of the United Kingdom, Australia and New Zealand, which carried out mining under the direction of the Board of Commissioners, which represented the three governments.
== Mechanism == Subunit vaccines contain fragments of the pathogen, such as protein or polysaccharide, whose combinations are carefully selected to induce a strong and effective immune response. Because the immune system interacts with the pathogen in a limited way, the risk of side effects is minimal. An effective vaccine would elicit the immune response to the antigens and form immunological memory that allows quick recognition of the pathogens and quick response to future infections. A drawback is that the specific antigens used in a subunit vaccine may lack pathogen-associated molecular patterns which are common to a class of pathogen. These molecular structures may be used by immune cells for danger recognition, so without them, the immune response may be weaker. Another drawback is that the antigens do not infect cells, so the immune response to the subunit vaccines may only be antibody-mediated, not cell-mediated, and as a result, is weaker than those elicited by other types of vaccines. To increase immune response, adjuvants may be used with the subunit vaccines, or booster doses may be required.
Sources: en.wikipedia.org
Consolidate the rule of the CCP Ensure sovereignty, territorial integrity, internal security and national development of the People's Republic of China Safeguard the country's interests Help maintain world peace China describes its military posture as active defense, defined in a 2015 state white paper as "We will not attack unless we are attacked, but we will surely counterattack if attacked."
=== Conformational distortion === Quantitative studies of enzymatic reactions often found that the acceleration of chemical reaction speed cannot be fully explained by existing theories like the approximation, acid/base catalysis and electrophile/nucleophile catalysis. And there is an obvious paradox: in reversible enzymatic reaction if the active site perfectly fits the substrates then the backward reaction will be slowed since products cannot fit perfectly into the active site. So conformational distortion was introduced and argues that both active site and substrate can undergo conformational changes to fit with each other all the time.
Another major biological process and target of many chemotherapeutic drugs is the disruption of structures and genes involved in DNA replication, which would aim to reduce cancer cell proliferation and survival. However, through gene amplification, a resistance-inducing mechanism in which multiple copies of a gene are produced by cancer cells, the enhanced quantity of gene copy number limit the efficiency of such drugs, therefore allowing cancer cells to restore their proliferative ability and promote uncontrolled cell growth. A target enzyme known as topoisomerase II (Topo II) recognized for its fundamental role in detangling and repairing DNA, has also been proposed as a potentially promising site of action for drugs designed to induce DNA breakage. Here, it was suggested that the inhibition of Topo II would result in enzyme-mediated DNA breakage which without the proper functioning of repairment, would ultimately induce cell stress and apoptosis, or programmed cell death. As resistance to these Topo II poisons emerged, it was determined that cancer cells had developed mechanisms to reduce the expression of the Topo II enzyme, ultimately depriving these drugs from their targets and rendering them ineffective. Cancer cells have developed other resistance mechanisms to mediate the effects of chemotherapy-induced DNA breakage such as the activation of DNA damage repair (DDR) pathways which may recruit and upregulate various genes involved in DNA repair processes, thus countering the effects of many chemotherapeutic drugs.
Sources: en.wikipedia.org
The integument of Sinosauropteryx was closely compared to less controversial evidence of collagen fibers preserved in the ichthyosaur Stenopterygius. Although the collagen hypothesis claimed that the central shafts (rachises) of purported theropod feathers were actually misidentified examples of shaft-like collagen fibers, higher quality imagery showed that these similarities were artificial. The supposed shafts in ichthyosaur collagen were actually scratch marks, cracks, and crevasses created during preparation of one of the ichthyosaur specimens. On the other hand, the shafts in the Sinosauropteryx specimens were legitimate examples of fossilized structures. The collagen hypothesis also claims that Sinosauropteryx integument includes beaded structures similar to structures occasionally found in decaying collagen of modern sea mammals. However, this claim was also unsupported, with Smithwick et al. finding no evidence of the beaded structures which collagen hypothesis proponents identified on the specimens. The study proposes that some areas of the fossil preserved in three dimensions cast shadows which would have resembled beaded structures in low quality photographs. Other examples of purported collagen fibers in the tail area were revealed to be scratches, similar to those on the rest of the specimen. An area of the bone with an irregular surface was considered evidence that some collagen fibers were less decayed than others.
The term reticulin was coined in 1892 by M. Siegfried. Today, the term reticulin or reticular fiber is restricted to referring to fibers composed of type III collagen. However, during the pre-molecular era, there was confusion in the use of the term reticulin, which was used to describe two structures:
Monoclonal antibodies that can be used to block pro-inflammatory cytokines Antigen-specific immunotherapy which allows immune cells to specifically target the abnormal cells that cause autoimmune disease Co-stimulatory blockade that works to block the pathway that leads to the autoimmune response Regulatory T cell therapy that utilizes this special type of T cell to suppress the autoimmune response Thymoquinone, a compound found in the flower Nigella sativa, has been studied for potential in treating several autoimmune diseases due to its effects on inflammation.
Osteoblasts can also be stimulated to increase bone mass through increased secretion of osteoid and by inhibiting the ability of osteoclasts to break down osseous tissue. Increased secretion of osteoid is stimulated by the secretion of growth hormone by the pituitary, thyroid hormone and the sex hormones (estrogens and androgens). These hormones also promote increased secretion of osteoprotegerin. Osteoblasts can also be induced to secrete a number of cytokines that promote reabsorption of bone by stimulating osteoclast activity and differentiation from progenitor cells. Vitamin D, parathyroid hormone and stimulation from osteocytes induce osteoblasts to increase secretion of RANK-ligand and interleukin 6, which cytokines then stimulate increased reabsorption of bone by osteoclasts. These same compounds also increase secretion of macrophage colony-stimulating factor by osteoblasts, which promotes the differentiation of progenitor cells into osteoclasts, and decrease secretion of osteoprotegerin.
Sources: en.wikipedia.org
It is a glucagon-like peptide-1 receptor agonist, often grouped with the incretin mimetics. Its backbone is modified from the human hormone to resist enzymatic degradation and to bind albumin. These two features distinguish it from the native peptide.
No. It shares high sequence identity but carries non-natural modifications that alter its stability and clearance. The naturally occurring hormone is broken down within minutes, while the synthetic analogue circulates far longer.
Attachment to serum albumin reduces renal filtration of the peptide and shields it from enzymatic breakdown. The consequence is a much longer interval between administrations than unmodified peptides allow. The precise contribution of binding affinity to overall duration is still being quantified.
差别集中在三处：第 8 位残基被非天然氨基酸取代，第 34 位换成精氨酸，第 26 位增加一条脂肪酸侧链。前两处改动降低酶解速率，侧链则通过白蛋白结合延长循环时间。综合结果是半衰期从约两分钟延长到约一周。