Amyloidβ(Aβ)

Amyloidβ(Aβ) is a peptide containing 39-43 amino acids produced by hydrolysis of amyloid precursor protein (APP) by beta- and gamma-secretase. It can be produced by a variety of cells and circulates in the blood, cerebrospinal fluid and interstitial fluid. The presence of β-amyloid plaques, extracellular protein deposits, in the brain is a major hallmark of Alzheimer's disease. These plaques are formed by the spontaneous aggregation of monomeric Aβ into soluble Aβ oligomers, which aggregate to form insoluble protofibrils. It is mostly bound to protein molecules, with a few existing in a free state.

The peptide chain of Aβconsists of about 40-43 amino acids. Several mutations occur at the N-terminal and C-terminal ends, and representative Aβs accumulated in senile plaques include Aβ40, which consists of 40 amino acids and ends in the 40th Val residue, and Aβ42, which consists of 42 amino acids and ends in the 42nd Ala residue. Because the extra two amino acids in Aβ1-42 lead to a greater likelihood of misfolding and aggregation, Aβ1-42 is generally considered to have a stronger neurotoxicity. In human cerebrospinal fluid, Aβ was found to be more neurotoxic than Aβ 1-42. In human cerebrospinal fluid, the level of Aβ1-40 is 10 times higher than that of Aβ1-42. Aβ1-40 is 10 times more abundant than Aβ1-42 in human cerebrospinal fluid, and it accumulates early in the formation of senile plaques. Aβ1-42 is more toxic, and is more likely to accumulate and form the core of Aβ deposits, which triggers neurotoxic effects.

KMD Bioscience is a company dedicated to providing high-quality biologically active raw materials such as antigens, antibodies, enzymes and substrates, as well as related technical services. KMD Bioscience has a series of technical platforms for protein recombination, antibody production, purification and diagnostic reagent R&D and production (including immunochromatography, enzyme immunoassay and chemiluminescence); and a group of highly qualified in vitro diagnostic upstream and downstream technicians with rich experience, which provides a guarantee for the company's research and development, and production of high-quality raw materials for in vitro diagnostic reagents and related technologies.

The inventory of reagents associated with amyloidβ that KMD Bioscience can offer:

How Aβ is produced

Aβ is a peptide fragment cut from its precursor protein, APP, a type I unidirectional membrane-penetrating protein that is commonly found in various tissues. According to the different amino acid splicing, it is mainly divided into three types of amino acids: 695/751/770, but APP695, which is 695 amino acids, is more frequently found in the brain. aβ can also be detected in the cerebrospinal fluid of healthy people, which is not a product of the brain lesions of patients with AD disease, but a molecule produced and secreted by APP in the normal process of metabolism. aβ is produced through the splicing of APP2 phase (Fig. 1). Aβ is produced through the shearing of the APP2 phase (Figure 1). First, the extracellular domain of APP is cleaved by β-secretase and the extracellular domain fragment (sAPPβ) is secreted. Then, γ-secretase cleaves the C-terminal fragment (C99) of APP remaining in the cell membrane and produces Aβ and AICD. The C-terminal variant of Aβ is induced by γ-secretase cleavage, which, depending on the site of amino acid cleavage, produces a variety of Aβs, ranging from Aβ37 to Aβ49. Previously, attention was focused on the high production of Aβ40, or the aggregation of Aβ42, which is highly toxic, but the APP metabolism is not as effective as that of Aβ42, which is highly toxic. Previously, attention was focused on the high production of Aβ40 or the high aggregation and toxicity of Aβ42 , but in the metabolic process of APP, in addition to the Aβ-producing pathway, there is also a non-Aβ-producing pathway (Figure 1). The non-Aβ pathway is also divided into two stages of shearing, and the shearing enzyme in the second stage is also γ-secretase, but the shearing enzyme in the first stage is α-secretase. α-secretase cuts between Lys residue No. 16 and Leu residue No. 17 of the inner domain of Aβ on the APP, and produces a fragment of about 3 kDa (p3) that is a polypeptide fragment lacking amino acid 16 of the N-terminal domain of Aβ. The resulting fragment (p3) of about 3 kDa is a peptide fragment lacking the 16 amino acids of the Aβ N-terminal domain. ADAM10 is the main α-secretase in neuronal cells.

Schematic diagram of the Aβ molecule

Clearance of Aβ

Normally, a certain concentration of Aβ in the brain can be maintained by rapidly removing the Aβ produced in the brain. However, in some patients with FAD, the mutation of FAD results in an increase in the amount of Aβ production, which disrupts the Aβ balance in the brain and triggers AD. On the other hand, in a group of patients with episodic AD, it was found that the breakthrough point of AD disease was not the enhancement of Aβ production but the clearance of Aβ. This result suggests that in addition to the process of Aβ production, the study of the detailed molecular mechanism of the Aβ clearance process is also crucial. It was reported that the breakdown of Aβ catabolic enzymes, phagocytosis by glial cells, and efflux transport through the blood-brain barrier (BBB) could be the main mechanisms of Aβ clearance.

Fundamental therapeutic approach to AD with Aβ as a therapeutic target

Based on the amyloid hypothesis, various fundamental treatments for AD have been proposed that use Aβ as a therapeutic target. They are mainly aimed at (1) inhibiting Aβ production, (2) promoting Aβ clearance, and (3) inhibiting Aβ aggregation.

The first method is to inhibit the activity of each secretase that inhibits Aβ production. However, γ-secretase contains various secretion substrates in addition to APP, especially Notch, which can cause great side effects. Therefore, instead of using γ-secretase inhibitors, we are seeking to develop a γ-secretase modulator (GSM) that specifically reduces Aβ42 production by regulating secretase activity. In addition, BACE1 and BACE1 knockout mice, which are β-secretase, do not show the abnormal phenotype of presenilin knockout mice, and β-secretase severance restricts the process of Aβ production, so BACE1 inhibitors are expected to be effective drugs for AD treatment.

The second is to promote Aβ clearance. This point of view in clinical experiments there are anti-Aβ antibody passive immunization method and Aβ vaccine active immunization method. 1999, Schenk et al. put forward the report that immunization of Aβ aggregation in APP transgenic mice can reduce the accumulation of Aβ in the brain. In 1999, Schenk et al. reported that immunization of APP transgenic mice against Aβ aggregation could reduce Aβ accumulation in the brain, and later they suggested that injection of anti-Aβ antibody could achieve the same effect, and that anti-Aβ antibody could also promote Aβ clearance. Although the clearance mechanism has not been completely clarified, it is believed that microglia are activated to phagocytose Aβ and promote the extension of Aβ to the periphery. Detailed mechanisms are needed to explain the differences in effect caused by the transfer of very small amounts of antibody to the brain and antibody epitopes.

KMD Bioscience offers a variety of diagnostic components for infectious diseases, tumors, inflammation, nail function, hormones, and other areas.

KMD Bioscience can provide a wide range of bioactive materials and technical services for IVD, which are widely used by domestic and foreign manufacturers of related reagents. These include, but are not limited to, customized development of antigens and antibodies, antigen-antibody labeling and coupling, antibody pair screening and purification, immunochromatography, enzyme immunoassay and chemiluminescence system optimization and process debugging, and many other technologies.