![]() | |
Names | |
---|---|
IUPAC name (2S)-2-Amino-6-((6R,7S)-2-(((S)-4-amino-4-carboxybutyl)amino)-6,7-dihydroxy-6,7,8,8a-tetrahydroimidazo[4,5-b]azepin-4(5H)-yl)hexanoic acid | |
Other names Glucosepan | |
Identifiers | |
3D model (JSmol) | |
ChemSpider | |
PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
| |
| |
Properties | |
C18H32N6O6 | |
Molar mass | 428.490 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
![]() ![]() ![]() | |
Infobox references | |
Glucosepane is a lysine-arginine protein cross-linking product and advanced glycation end product (AGE) derived from D-glucose. [1] It is an irreversible, covalent cross-link product that has been found to make intermolecular and intramolecular cross-links in the collagen of the extracellular matrix (ECM) and crystallin of the eyes. [2] Covalent protein cross-links irreversibly link proteins together in the ECM of tissues. Glucosepane is present in human tissues at levels 10 to 1000 times higher than any other cross-linking AGE, and is currently considered to be the most important cross-linking AGE. [3]
Aging leads to progressive loss of elasticity and stiffening of tissues rich in the ECM such as joints, cartilage, arteries, lungs and skin. [4] It has been shown that these effects are brought about by the accumulation of cross-links in the ECM on long-lived proteins. [5] Studies done on glucosepane by the Monnier group have shown that the level of glucosepane cross-links in human collagen in the ECM increases progressively with age and at a more rapid pace in people with diabetes, thus suggesting the role of glucosepane in the long-term effects associated with diabetes and aging such as arteriosclerosis, joint stiffening and skin wrinkling. [6] In fact, they report that in the ECM of the skin of a non-diabetic 90-year-old, glucosepane accounts for about 50 times the protein cross-linking as all other forms of protein cross-linking. [7] Further, the build up of cross-links such as glucosepane within and between proteins is shown to reduce proteolytic degradation in the ECM. This leads to increased cross-link accumulation and is thought to be linked to the thickening of basement membranes in capillaries, glomeruli, lens, and lungs. [8]
Atomic-force microscopy experiments identified nanoscale morphologic differences in collagen fibril structures as a function of ageing in skin. A decrease in Young's modulus of the transverse fibril was observed. These changes are thought to be due to the accumulation of glucosepane in tissue. It is proposed that this is due to a change in the fibril density caused by age-related differences in water retention. [9] Computational studies using all-atom simulations revealed that glucosepane results in less tightly held helical structure in the collagen molecule and increase porosity to water. This was confirmed with water content measurement that showed higher content in Achilles and anterior tibias tendon tissue from older individuals compared to young people. [10]
As an AGE, the reaction pathway that leads to glucosepane formation is known as the Maillard Reaction, or non-enzymatic browning. Glucosepane is found to form through a non-oxidative path. [11] The exact mechanism leading to glucosepane has been a challenge for researchers to determine. However, it is currently well characterized up to the ring formation. [12]
The formation of glucosepane within connective tissues has been shown to be site-specific. For example, studies using Molecular Dynamics simulations of a complete collagen fibril revealed energetically favourable locations, particularly within the collagen fibril gap-region. This may be due to the lower protein density and higher intra-fibrillar water content within the gap-region. [13] [14]
The overall pathway of glucosepane formation starts with lysine attacking the reducing sugar D-glucose to form the unstable imine known as a Schiff base, which then rearranges to form the more stable aminoketose Amadori product. [15] From there, the stable Amadori Product slowly degrades to form glucosepane through an α-dicarbonyl intermediate. [16]
The particular reaction path proceeding from the Amadori product to the α-dicarbonyl intermediate that will yield glucosepane was difficult to determine. Initially, researchers hypothesized an α-dicarbonyl intermediate in which the carbonyls were located on C-2 and C-3 of D-Glucose. However, by using glucose with C-1, the carbonyl carbon, marked with the isotope 13C in the reaction, researchers found that the α-dicarbonyl formed has the carbonyls located at C-5 and C-6 of the original glucose backbone. [17] The best mechanism proposed is that the α-dicarbonyl N 6-(2,3-dihydroxy-5,6-dioxohexyl)-L-lysinate, [18] a key intermediate in the glucosepane reaction, forms from the Amadori product through a carbonyl shift all the way down the 6 carbon sugar backbone by keto-enol tautomerism and the elimination of the C-4 hydroxyl. [19] Further, evidence was given for the extent of the hypothesized carbonyl shift by using heavy hydrogen in the solvent water, D2O. [20] Researchers found that all the H-C-OH of the carbon backbone were converted to D-C-OH after the reaction, demonstrating that all the hydrogens got transferred out through keto-enol tautomerism, and thus the carbonyl shift went all the way down the backbone, finally eliminating the C-4 hydroxy group. [21]
It is still relatively unclear how the ring is formed and when. One article suggests, and it seems the current belief, that the ring must form in the step after the α-dicarbonyl is formed. The study hypothesized, and another found correlating evidence, that the most likely mechanism of getting from the α-dicarbonyl to glucosepane is through the intramolecular aldimine 6-(3,4-dihydroxy-6-oxo-3,4,5,6-tetrahydro-2H-azepinium-1-yl) norleucine. [22] The ring is hypothesized to form by a nucleophilic attack of N on C-6 carbonyl, followed by elimination of a water (2). This then condenses with the arginine side chain to yield glucosepane in nucleophilic addition-elimination reactions of the nitrogens of arginine and the electrophilic carbonyls on the ring, eliminating two waters. [23]
Glycation processes that lead to AGEs particularly affect long-lived proteins in the human body, such as collagen in the skin and crystallin in the eyes. [24] Skin collagen, for instance, has a half-life of fifteen years. [25] Because these proteins do not degrade as quickly as other proteins in the body, the Amadori product, which is stable and thus transforms very slowly, has time enough to convert into glucosepane. [26] It has been estimated that 50-60% of the steady state levels of Amadori product is converted into glucosepane in old age. [27] A suspected reason for the prevalence of the glucosepane cross-link product as opposed to others is that the α−dicarbonyl from which it forms, N 6-(2,3-dihydroxy-5,6-dioxohexyl)-L-lysinate, is a persisting glycating agent because it is irreversibly bound through lysine to a protein. [28] Therefore, it is not easily degraded and thus is more commonly available to form a cross-link with arginine, unlike other cross-link α-dicarbonyl intermediates, which are found bound and free and thus more susceptible to being degraded by enzymes in the ECM. [29]
Because of the important role glucosepane has been found to play in many pathologies of aging, many researchers have been investigating ways in which the levels of glucosepane could be reduced in tissues. Various methods of doing so have been examined.
One method attempted to inhibit glucosepane formation is to use an α-dicarbonyl trap molecule, aminoguanidine (AG). AG reacts with the α-dicarbonyl intermediate with a higher affinity than arginine, thus blocking the cross-link. While this method has been seen to have some success, it did not greatly interfere with the normal aging of rats. [30]
Another method that has been investigated is the use of thiazolium salts to break the α-dicarbonyl intermediate, therefore cutting off the reaction pathway that leads to glucosepane. These compounds are thought to act as bidentate nucleophiles that attack the adjacent carbonyls in the alpha-dicarbonyl intermediate, which then leads to the cleaving of the C-C bond between the carbonyls. [31] However, an alternate hypothesis as to how they work is that they act as chelating agents. [32] Two thiazolium molecules, PTB (N-phenacylthiazolium bromide) [33] and ALT-711, [34] have demonstrated success at reducing glucosepane levels in rats.
A completely different approach to reducing cross-links that has been proposed is enhancing the ECM turnover processes, which would force the degradation of cross-linked proteins to replace them with new. However, a potential downside to this would be leaky blood vessels resulting from too far enhanced turnover. [35]
Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, organization of the intracellular cytoskeleton, and movement of new receptors to the cell membrane. The presence of integrins allows rapid and flexible responses to events at the cell surface.
A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to efficiently transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability to withstand significant amounts of tension.
Fibronectin is a high-molecular weight glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. Fibronectin also binds to other extracellular matrix proteins such as collagen, fibrin, and heparan sulfate proteoglycans.
In biology, the extracellular matrix (ECM) is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and biochemical support to surrounding cells. Because multicellularity evolved independently in different multicellular lineages, the composition of ECM varies between multicellular structures; however, cell adhesion, cell-to-cell communication and differentiation are common functions of the ECM.
Advanced glycation end products (AGEs) are proteins or lipids that become glycated as a result of exposure to sugars. They are a bio-marker implicated in aging and the development, or worsening, of many degenerative diseases, such as diabetes, atherosclerosis, chronic kidney disease, and Alzheimer's disease.
Matrigel is the trade name for the solubilized basement membrane matrix secreted by Engelbreth-Holm-Swarm (EHS) mouse sarcoma cells produced by Corning Life Sciences. Matrigel resembles the laminin/collagen IV-rich basement membrane extracellular environment found in many tissues and is used by cell biologists as a substrate for culturing cells.
Alagebrium was a drug candidate developed by Alteon, Inc. It was the first drug candidate to be clinically tested for the purpose of breaking the crosslinks caused by advanced glycation endproducts (AGEs), thereby reversing one of the main mechanisms of aging. Through this effect Alagebrium is designed to reverse the stiffening of blood vessel walls that contributes to hypertension and cardiovascular disease, as well as many other forms of degradation associated with protein crosslinking. Alagebrium has proven effective in reducing systolic blood pressure and providing therapeutic benefit for patients with diastolic heart failure.
Decorin is a protein that in humans is encoded by the DCN gene.
Allysine is a derivative of lysine, used in the production of elastin and collagen. It is produced by the actions of the enzyme lysyl oxidase in the extracellular matrix and is essential in the crosslink formation that stabilizes collagen and elastin.
Platelet membrane glycoproteins are surface glycoproteins found on platelets (thrombocytes) which play a key role in hemostasis. When the blood vessel wall is damaged, platelet membrane glycoproteins interact with the extracellular matrix.
Collagenase 3 is an enzyme that in humans is encoded by the MMP13 gene. It is a member of the matrix metalloproteinase (MMP) family. Like most MMPs, it is secreted as an inactive pro-form. MMP-13 has an predicted molecular weight around 54 kDa. It is activated once the pro-domain is cleaved, leaving an active enzyme composed of the catalytic domain and the hemopexin-like domain PDB: 1PEX. Although the actual mechanism has not been described, the hemopexin domain participates in collagen degradation, the catalytic domain alone being particularly inefficient in collagen degradation. During embryonic development, MMP-13 is expressed in the skeleton as required for restructuring the collagen matrix for bone mineralization. In pathological situations it is highly overexpressed; this occurs in human carcinomas, rheumatoid arthritis and osteoarthritis.
Laminin subunit alpha-1 is a protein that in humans is encoded by the LAMA1 gene.
Matrix metalloproteinase-26 also known as matrilysin-2 and endometase is an enzyme that in humans is encoded by the MMP26 gene.
Discoidin domain-containing receptor 2, also known as CD167b, is a protein that in humans is encoded by the DDR2 gene. Discoidin domain-containing receptor 2 is a receptor tyrosine kinase (RTK).
Collagen alpha-1(XIII) chain is a protein that in humans is encoded by the COL13A1 gene.
von Willebrand factor A domain-containing protein 2, also known as A domain-containing protein similar to matrilin and collagen (AMACO), is a protein that in humans is encoded by the VWA2 gene.
The tripeptide Arg-Gly-Asp (RGD) consists of Arginine, Glycine, and Aspartate. It was originally identified as the amino acid sequence within the extracellular matrix protein fibronectin that mediates cell attachment. The RGD cell binding sequence has since been identified in other extracellular matrix proteins, including vitronectin and laminin. The family of membrane proteins known as integrins act as receptors for these cell adhesion molecules via the RGD motif. A subset of the integrins recognize the RGD motif within their ligands, the binding of which mediates both cell-substratum and cell-cell interactions. These integrins include αvβ3, α5β1 and αIIbβ3.
Collagen α-1 (XXIII) chain is a protein encoded by COL23A1 gene, which is located on chromosome 5q35 in humans, and on chromosome 11B1+2 in mice. The location of this gene was discovered by genomic sequence analysis.
Daniel S. Greenspan is an American biomedical scientist, academic and researcher. He is Kellett professor of Cell and Regenerative Biology at the University of Wisconsin-Madison School of Medicine and Public Health. He has authored over 120 publications. His research has mainly focused on genes encoding proteins of the extracellular space and possible links between defects in such genes and human development and disease.
Collin Yvès Ewald is a Swiss scientist investigating the molecular mechanisms of healthy aging. He is a molecular biologist and a professor at ETH Zurich, where he leads the Laboratory of Extracellular Matrix Regeneration. His research focuses on the remodeling of the extracellular matrix during aging and upon longevity interventions.
{{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link){{cite journal}}
: CS1 maint: multiple names: authors list (link)