Cyclopentenosine, major trifunctional crosslinking amino acid isolated from acid hydrolysate of elastin

Chichibabin/isoChichibabin pyridinium synthesis of ma'edamines C and D

Ma'edamines C and D were isolated from an Okinawan marine sponge and exhibited a unique tetrasubstituted pyridinium skeleton. The proposed biosynthetic pathway is similar to that of desmosine and isodesmosine, which are elastin-crosslinking amino acids. In this study, first total synthesis of ma'edamines C and D was achieved via Pr(OTf)₃-promoted Chichibabin/isoChichibabin pyridinium synthesis starting from the corresponding aldehydes and amine.

Elastic fibers: formation, function, and fate during aging and disease

Elastic fibers are extracellular components of higher vertebrates and confer elasticity and resilience to numerous tissues and organs such as large blood vessels, lungs, and skin. Their formation and maturation take place in a complex multistage process called elastogenesis. It requires interactions between very different proteins but also other molecules and leads to the deposition and crosslinking of elastin's precursor on a scaffold of fibrillin-rich microfibrils. Mature fibers are exceptionally resistant to most influences and, under healthy conditions, retain their biomechanical function over the life of the organism. However, due to their longevity, they accumulate damages during aging. These are caused by proteolytic degradation, formation of advanced glycation end products, calcification, oxidative damage, aspartic acid racemization, lipid accumulation, carbamylation, and mechanical fatigue. The resulting changes can lead to diminution or complete loss of elastic fiber function and ultimately affect morbidity and mortality. Particularly, the production of elastokines has been clearly shown to influence several life-threatening diseases. Moreover, the structure, distribution, and abundance of elastic fibers are directly or indirectly influenced by a variety of inherited pathological conditions, which mainly affect organs and tissues such as skin, lungs, or the cardiovascular system. A distinction can be made between microfibril-related inherited diseases that are the result of mutations in diverse microfibril genes and indirectly affect elastogenesis, and elastinopathies that are linked to changes in the elastin gene. This review gives an overview on the formation, structure, and function of elastic fibers and their fate over the human lifespan in health and disease.

Enzymatic and non-enzymatic crosslinks found in collagen and elastin and their chemical synthesis

This review summarized the enzymatic and non-enzymatic crosslinks found in collagen and elastin and their organic synthesis.

Unique molecular networks: Formation and role of elastin cross-links

Elastic fibers are essential assemblies of vertebrates and confer elasticity and resilience to various organs including blood vessels, lungs, skin, and ligaments. Mature fibers, which comprise a dense and insoluble elastin core and a microfibrillar mantle, are extremely resistant toward intrinsic and extrinsic influences and maintain elastic function over the human lifespan in healthy conditions. The oxidative deamination of peptidyl lysine to peptidyl allysine in elastin's precursor tropoelastin is a crucial posttranslational step in their formation. The modification is catalyzed by members of the family of lysyl oxidases and the starting point for subsequent manifold condensation reactions that eventually lead to the highly cross-linked elastomer. This review summarizes the current understanding of the formation of cross-links within and between the monomer molecules, the molecular sites, and cross-link types involved and the pathological consequences of abnormalities in the cross-linking process.

New pyrone and cyclopentenone derivatives from marine-derived fungus Aspergillus sydowii SCSIO 00305

Two new 2-pyrone derivatives sydowiones A-B (1, 2), one new cyclopentenone derivative sydowione C (3), and one new mycotoxin 6-methoxyl austocystin A (4) along with two known analogues paecilpyrone A (5) and austocystin A (6), were isolated from the marine-derived fungus Aspergillus sydowii SCSIO 00305. The structures of 1-4 were elucidated by extensive spectroscopic analysis. The absolute configuration of C-8 in 1 was established by Mosher method, and further confirmed by calculation of the electronic circular dichroism (ECD) spectra. The absolute configuration of C-11 in 3 was also determined by calculation of ECD spectra. The absolute configuration of 6 was determined by a single-crystal X-ray diffraction experiment for the first time. Compounds 1-4 showed moderate toxicity towards brine shrine naupalii with LC₅₀ values of 19.5, 14.3, 8.3 and 2.9 μM, respectively. And 1 and 2 also showed antioxidant activity against 2,2-diphenyl-picrylhydrazyl (DPPH) radicals with IC₅₀ values of 46.0 and 46.6 μM, respectively.[Formula: see text].

Elastin is heterogeneously cross-linked

Elastin is an essential vertebrate protein responsible for the elasticity of force-bearing tissues such as those of the lungs, blood vessels, and skin. One of the key features required for the exceptional properties of this durable biopolymer is the extensive covalent cross-linking between domains of its monomer molecule tropoelastin. To date, elastin's exact molecular assembly and mechanical properties are poorly understood. Here, using bovine elastin, we investigated the different types of cross-links in mature elastin to gain insight into its structure. We purified and proteolytically cleaved elastin from a single tissue sample into soluble cross-linked and noncross-linked peptides that we studied by high-resolution MS. This analysis enabled the elucidation of cross-links and other elastin modifications. We found that the lysine residues within the tropoelastin sequence were simultaneously unmodified and involved in various types of cross-links with different other domains. The Lys-Pro domains were almost exclusively linked via lysinonorleucine, whereas Lys-Ala domains were found to be cross-linked via lysinonorleucine, allysine aldol, and desmosine. Unexpectedly, we identified a high number of intramolecular cross-links between lysine residues in close proximity. In summary, we show on the molecular level that elastin formation involves random cross-linking of tropoelastin monomers resulting in an unordered network, an unexpected finding compared with previous assumptions of an overall beaded structure.

Elastin in lung development and disease pathogenesis

Elastin is expressed in most tissues that require elastic recoil. The protein first appeared coincident with the closed circulatory system, and was critical for the evolutionary success of the vertebrate lineage. Elastin is expressed by multiple cell types in the lung, including mesothelial cells in the pleura, smooth muscle cells in airways and blood vessels, endothelial cells, and interstitial fibroblasts. This highly crosslinked protein associates with fibrillin-containing microfibrils to form the elastic fiber, which is the physiological structure that functions in the extracellular matrix. Elastic fibers can be woven into many different shapes depending on the mechanical needs of the tissue. In large pulmonary vessels, for example, elastin forms continuous sheets, or lamellae, that separate smooth muscle layers. Outside of the vasculature, elastic fibers form an extensive fiber network that originates in the central bronchi and inserts into the distal airspaces and visceral pleura. The fibrous cables form a looping system that encircle the alveolar ducts and terminal air spaces and ensures that applied force is transmitted equally to all parts of the lung. Normal lung function depends on proper secretion and assembly of elastin, and either inhibition of elastin fiber assembly or degradation of existing elastin results in lung dysfunction and disease.

Oxidative deamination of benzylamine and lysine residue in bovine serum albumin by green tea, black tea, and coffee

Oxidative deamination by various polyphenolic compounds is presumed to be due to the oxidative conversion of polyphenols to the corresponding quinones through autoxidation. Here we examined the oxidative deamination by the polyphenol-rich beverages green tea, black tea, and coffee at a physiological pH and temperature. Green tea, black tea, and coffee extracts oxidatively deaminated benzylamine and the lysine residues of bovine serum albumin to benzaldehyde and alpha-aminoadipic delta-semialdehyde residues, respectively, in sodium phosphate buffer (pH 7.4) at 37 degrees C in both the presence and absence of Cu2+, indicating the occurrence of an amine (lysyl) oxidase-like reaction. We also examined the effects of pH and metal ions on the reaction. The possible biological effects of drinking polyphenol-rich beverages on human are also discussed.

Proteins of the extracellular matrix are sensitizers of photo-oxidative stress in human skin cells

Sensitized production of reactive oxygen species after photo-excitation of endogenous chromophores is thought to contribute to skin photo-oxidative stress. Here we present experimental evidence in support of a potential role of extracellular matrix proteins as skin photosensitizers. Human and bovine type I collagen and elastin sensitized of hydrogen peroxide generation upon irradiation with solar simulated light or ultraviolet A. Induction of intracellular oxidative stress by extracellular matrix-protein sensitization was demonstrated by flow cytometric analysis of fibroblasts preloaded with the intracellular redox dye dihydrorhodamine 123 and exposed to pre-irradiated type I collagen. Pre-irradiated collagen and elastin induced pronounced inhibition of proliferation in cultured keratinocytes and fibroblasts, which was reversed by antioxidant or catalase treatment and reproduced by exposure to concentrations of H2O2 formed during extracellular matrix-protein irradiation. In fibroblasts, chromosomal DNA damage as a consequence of collagen-sensitized H2O2 formation was demonstrated using a single cell electrophoresis assay. The enzymatic cross-links pyridinoline and desmosine were examined as candidate sensitizer chromophores contained in collagen and elastin, respectively. Pyridinoline, but not desmosine, sensitized light-driven H2O2 production and inhibition of fibroblast proliferation. Our results support the hypothesis that extracellular matrix proteins play a functional role in skin photoaging and carcinogenesis by sensitization of photo-oxidative damage.

Oxidative deamination of lysine residue in plasma protein of diabetic rats. Novel mechanism via the Maillard reaction

The levels of alpha-aminoadipic-delta-semialdehyde residue, the oxidative deamination product of lysine residue, in plasma protein from streptozotocin-induced diabetic rats were evaluated. alpha-Aminoadipic-delta-semialdehyde was converted to a bisphenol derivative by acid hydrolysis in the presence of phenol, and determined by high performance liquid chromatography. Analysis of plasma proteins revealed three times higher levels of alpha-aminoadipic-delta-semialdehyde in diabetic subjects compared with normal controls. Furthermore, we explored the oxidative deamination via the Maillard reaction and demonstrated that the lysine residue of bovine serum albumin is oxidatively deaminated during the incubation with various carbohydrates in the presence of Cu2+ at a physiological pH and temperature. This experiment showed that 3-deoxyglucosone and methylglyoxal are the most efficient oxidants of the lysine residue. When the reaction was initiated from glucose, a significant amount of alpha-aminoadipic-delta-semialdehyde was also formed in the presence of Cu2+. The reaction was significantly inhibited by deoxygenation, catalase, and a hydroxyl radical scavenger. The mechanism we propose for the oxidative deamination is the Strecker-type reaction and the reactive oxygen species-mediated oxidation. Based on these findings, we propose a novel mechanism for the oxidative modification of proteins in diabetes, namely the oxidative deamination of the lysine residue via the Maillard reaction.

Mechanism of formation of elastin crosslinks

We examined the formation of quaternary pyridinium crosslinks of elastin formed by condensation of lysine and allysine residues using the model compounds propanal (allysine) and n-butylamine (lysine) under quasi-physiological conditions. The resulting pyridinium compounds were characterized and the structure compared with the known pyridinium crosslinks. Three pyridinium compounds were identified and the structures were identical with the skeleton of the crosslinking amino acids, desmosine (DES), isodesmosine (IDE), and pentasine. We concluded that a non-enzymatic pathway is available for the spontaneous generation of pyridinium crosslinks. To elucidate the intermediates and the mechanism of the formation of DES and IDE, we synthesized model intermediates from propanal and n-butylamine, and they were allowed to react in three kinds of solvents. Then, the products were analyzed by an ion-pair reverse-phase HPLC. The results of this model system indicated that DES and IDE can be formed by condensation of dehydromerodesmosine with dehydrolysinonorleucine and by condensation of allysine with dehydrolysinonorleucine, respectively. We also describe the mechanism of DES and IDE crosslinking.

Two new elastin cross-links having pyridine skeleton. Implication of ammonia in elastin cross-linking in vivo

Isolation and structure analysis of two amino acids from bovine ligamentum nuchae elastin hydrolysates revealed the presence of pyridine cross-links in elastin. The structures of these amino acids were determined to have 3,4,5- and 2,3,5-trisubstituted pyridine skeletons both with three carboxylic acids and a mass of 396 (C(18)H(28)N(4)0(6)) identified as 4-(4-amino-4-carboxybutyl)-3,5-di-(3-amino-3-carboxypropyl)-pyridine and 2-(4-amino-4-carboxybutyl)-3,5-di-(3-amino-3-carboxypropyl)-pyridine. We have named these pyridine cross-links desmopyridine (DESP) and isodesmopyridine (IDP), respectively. Structure analysis of these pyridine cross-links implied that the formation of these cross-links involved the condensation reaction between ammonia and allysine. The elastin incubated with ammonium chloride showed that DESP and IDP levels increased as the allysine content decreased. DESP and IDP were measured by high pressure liquid chromatography (HPLC) with UV detection and were found in a variety of bovine tissues. The DESP/desmosine (DES) and IDP/isodesmosine (IDE) ratios in aorta elastin were higher than in other tissues. DESP and IDP contents in human aorta elastin were found to be gradually increased with age. The concentration of IDP was significantly elevated in aorta elastin of rat with chronic liver cirrhosis induced by carbon tetrachloride (mean +/- S.D.; 11.1 +/- 0.9 nmol/mg elastin) when compared with normal rats (5.9 +/- 1.5 nmol/mg elastin). Although DESP and IDP are present at only trace concentrations in the tissue elastin, these pyridine cross-links may be useful biomarkers for the aortic elastin damaged by ammonia.