High-performance liquid chromatographic quantitation of desmosine plus isodesmosine in elastin and whole tissue hydrolysates

Elastin purification and solubilization

The functional form of elastin is a highly cross-linked polymer that organizes as sheets or fibers in the extracellular matrix. Purification of the mature protein is problematic because its insolubility precludes its isolation using standard wet-chemistry techniques. Instead, relatively harsh experimental approaches designed to remove nonelastin "contaminates" are employed to generate an insoluble product that has the amino acid composition expected of elastin. Although soluble, tropoelastin also presents problems for isolation and purification. The protein's extreme stickiness and susceptibility to proteolysis require careful attention during purification and in tropoelastin-based assays. This chapter describes the most common approaches for purification of elastin and for preparing solubilized forms of the protein.

Methods in elastic tissue biology: elastin isolation and purification

Elastin provides recoil to tissues subjected to repeated stretch, such as blood vessels and the lung. It is encoded by a single gene in mammals and is secreted as a 60-70 kDa monomer called tropoelastin. The functional form of the protein is that of a large, highly crosslinked polymer that organizes as sheets or fibers in the extracellular matrix. Purification of mature, crosslinked elastin is problematic because its insolubility precludes its isolation using standard wet-chemistry techniques. Instead, relatively harsh experimental approaches designed to remove non-elastin 'contaminates' are employed to generate an insoluble product that has the amino acid composition expected of elastin. Although soluble, tropoelastin also presents problems for isolation and purification. The protein's extreme stickiness and susceptibility to proteolysis requires careful attention during purification and in tropoelastin-based assays. This article describes the most common approaches for purification of insoluble elastin and tropoelastin. It also addresses key aspects of studying tropoelastin production in cultured cells, where elastin expression is highly dependent upon cell type, culture conditions, and passage number.

Progress in the methodological strategies for the detection in real samples of desmosine and isodesmosine, two biological markers of elastin degradation

Desmosines are crosslinking amino acids unique to mature elastin in humans. Owing to this unicity, they have been discussed as potentially attractive indicators of connective tissue disorders whose clinical manifestations are mostly the result of elastin degradation. This review covers advances in immunochemical, chromatographic, and electrophoretic procedures applied in the last 25 years to detect and quantitate these crosslinksin a variety of biological samples. Recent applications of CE with LIF detection (CE-LIF) for investigating the content of desmosines in different fluids will also be discussed.

Alteration of cross-linking amino acids of elastin in human aorta in association with dissecting aneurysm: analysis using high performance liquid chromatography

Elastic fiber is one of the major component of the extracellular matrix, which provides the resilience to many tissues. Elasticity is an important property of human aorta, and this elastic property decreases in various pathological conditions such as dissecting aneurysm (DA). Since the cross-linking structures in elastin are responsible for this elasticity, we studied the alteration of various cross-linking amino acids in human aorta associated with DA by a new method using high-performance liquid chromatography (HPLC). Materials were obtained from non-atherosclerotic areas of thoracic aorta of 27 autopsy cases which had no particular aortic disease and 19 cases of DA at replacement operation. After acid hydrolysis, SEP-PAK silica-gel column and Fe3+/activated charcoal column pretreatment were carried out for analysis of desmosine (DES), isodesmosine (ISDES), neodesmosine (NEO), oxodesmosine (OXO) and isooxodesmosine (ISOXO), and for analysis of aldosine (ALD), respectively. These prepared samples were applied to the reversed-phase HPLC column. We also analyzed pyridinoline (PYR), a major cross-linking amino acid of collagen as an index of fibrosis. All crosslinks of elastin were decreased in DA as compared to the age-matched control. The decrease of ISOXO was marked. The increase of PYR and PYR/(DES+ISDES) were not statistically significant. It is suggested oxidative degradation on elastin crosslinks occur in DA, and the ratio of collagen to elastin didn't contribute to the pathogenesis of DA.

Age-related alteration of cross-linking amino acids of elastin in human aorta

It is well known that the elastic property of human aorta decreases gradually with age. Since the cross-linking structures are responsible for this elasticity, age-related changes of cross-linking amino acids in human aorta were studied using a high-performance liquid chromatography (HPLC). Non-atherosclerotic areas of thoracic aorta of 27 autopsy cases which had no particular aortic disease were obtained. After acid hydrolysis, SEP-PAK silica-gel column and Fe3+/activated charcoal column pretreatment were carried out for analysis of desmosine (DES), isodesmosine (ISDES), neodesmosine (NEO), oxodesmosine (OXO) and isooxodesomosine (ISOXO), and for analysis of aldosine (ALD), respectively. These prepared samples were applied to the reversed-phase HPLC column. We also analyzed pyridinoline (PYR), a major cross-linking amino acid of collagen as an index of fibrosis. All cross-linking amino acids of elastin rapidly increased in infancy and then gradually decreased with age. In the middle- and old-age, the amount of OXO showed marked variety. PYR was little detected at 0-year-old, and then gradually increased with age. The crosslinks of elastin were rapidly formed in childhood and then decreased with age. These findings suggest that the relative increase of NEO, OXO or ISOXO to DES and ISDES is associated with age-related weakening and/or damage of elastin, and that the gradual shift from elastin- to collagen-dominant state is a possible cause of the loss of elasticity and the gain of stiffness in the aging aorta.

Separation of elastin cross-links as phenylisothiocyanate derivatives

A method has been developed for the separation and quantitation of desmosines in tissue samples. The tissue is treated with cold 10% trichloroacetic acid to remove collagen and hydrolysed in HCl vapours in sealed vials. Preseparation of desmosines from tissue acid hydrolysates is performed on a cellulose column, first eluted with n-butanol-acetic acid-water to wash out other amino acids and then with water to recover desmosines. Separated desmosines are then derivatized with phenylisothiocyanate and determined by reversed-phase high-performance liquid chromatography using a gradient system with sodium acetate pH 6.4 and acetonitrile. Desmosines were detected spectrophotometrically at 254 nm. The method was applied to the determination of desmosine in elastin, rat aorta and bovine ligamentum nuchae.

Development and validation of a high-performance liquid chromatographic method for the determination of desmosines in tissues

The development and the validation of a general strategy for the simple and accurate analysis of desmosines (isodesmosine and desmosine) in tissues coupled with the determination of collagen (as hydroxyproline) is described. The method is based on simplified sample (i.e., lung) pretreatment which involves, in a PTFE screw-capped Pyrex tube, homogenization, collagen extraction with hot 5% trichloroacetic acid and hydrolysis of the elastin-containing residue with 6 M hydrochloric acid, followed by cellulose minicolumn purification of desmosines from the hydrolysates, dansyl chloride pre-column derivatization of the purified desmosines and reversed-phase high-performance liquid chromatographic (HPLC) analysis of the dansyl derivatives using a Spherisorb ODS-2 column, an on-column enrichment sample device and a linear gradient of organic modifier (acetonitrile) in phosphate buffer. The simple sample pretreatment, the optimized chromatographic conditions and the short HPLC analysis time (less than 15 min) allow the accurate and rapid determination of desmosine and isodesmosine, thus permitting the determination of elastin in several kinds of tissues with a minimum of sample manipulation.

Determination of desmosines in elastin-related skin disorders by isocratic high-performance liquid chromatography

Abnormalities in the amount of skin elastin occur in several cutaneous disorders. The number of elastic fibers is increased in elastotic disorders such as pseudoxanthoma elasticum (PXE) and cutis rhomboidalis nuchae (actinic elastosis, AE) and is decreased in elastolytic disorders such as cutis laxa (CL). We describe a procedure to quantify desmosines and elastin in small amounts of skin using high-performance liquid chromatography (HPLC). Biopsies were obtained from normal, nonsolar exposed skin and from the lesional skin of patients with PXE, cutis rhomboidalis nuchae, and CL. Specimens were subjected to hot alkali treatment and the desmosines were released by acid hydrolysis and quantified by HPLC. The mean value for normal skin was 252 +/- 28 ng desmosines per milligram wet weight (SD, n = 5). The disorders of elastosis (PXE and AE) demonstrated a two- to fivefold increased content of desmosines. In contrast, the elastolytic disorder (CL) had only 20% of the normal content of desmosines. Furthermore, PXE and normal skin elastins had the same amount of desmosines per milligram purified elastin. This method could be used to evaluate the extent of elastosis or elastolysis in a particular lesion.

Determination of desmosine, isodesmosine, and other amino acids by liquid chromatography with electrochemical detection following precolumn derivatization with naphthalenedialdehyde/cyanide

Naphthalenedialdehyde (NDA) in the presence of cyanide (CN) reacts with primary amines to produce fluorescent cyano[f]benzoisoindole (CBI) derivatives. These derivatives have been shown to be substantially more stable than the corresponding o-phthalaldehyde derivatives. However, one drawback of this method is that compounds derivatized at more than one site exhibit quenching, precluding the use of fluorescence detection. The CBI derivatives have been found to be electroactive and are oxidized at a modest oxidation potential (+750 mV). Electrochemical detection is especially useful for the analysis of compounds containing more than one primary amine site because the response is not attenuated as it is in fluorescence detection. Desmosine and isodesmosine were of particular interest because of their importance in elastic fiber and the lack of highly sensitive HPLC methods for the determination of these compounds. Both of these compounds react with NDA/CN to produce electrochemically active derivatives. The combination of derivatization with NDA/CN and electrochemical detection was found to be linear over three orders of magnitude. Detection limits for CBI-lysine and CBI-desmosine were 100 fmol at a S/N of 2. Amino acids in elastin were quantitated using this method. The results correlate well with what has been reported previously in the literature. A significant advantage of the use of liquid chromatography with electrochemical detection with precolumn derivatization with NDA/CN for the analysis of desmosine and isodesmosine is that they can be separated and quantitated individually using this method. In addition, the unique voltammetry of multiderivatized CBI-amino acids can be used to verify peak purity.