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

Cation exchange HPLC analysis of desmosines in elastin hydrolysates

Desmosine crosslinks are responsible for the elastic properties of connective tissues in lungs and cardiovascular system and are often compromised in disease states. We developed a new, fast, and simple cation exchange HPLC assay for the analysis of desmosine and isodesmosine in animal elastin. The method was validated by determining linearity, accuracy, precision, and desmosines stability and was applied to measure levels of desmosines in porcine and murine organs. The detection and quantification limits were 2 and 4 pmol, respectively. The run-time was 8 min. Our cation exchange column does not separate desmosine and isodesmosine, but their level can be quantified from absorbance at different wavelengths. Using this assay, we found that desmosines levels were significantly lower in elastin isolated from various organs of immunodeficient severe combined immunodeficiency mice compared with wild-type animals. We also found that desmosines levels were lower in lung elastin isolated from hyperhomocysteinemic Pcft(-/-) mice deficient in intestinal folate transport compared with wild-type Pcft(+/+) animals.

Quantification of mouse lung elastin during prenatal development

Elastic fibres play a crucial function during the process of lung alveolisation. During the perinatal period, any changes in the elastogenic process during foetal development may result in permanent lifetime defects. In pre-natal life, well-developed pulmonary elastic fibres should favor the pre-natal maturation of the lung and an enhanced alveolisation, which in many species, such as humans begins only after birth. The authors present a quantitative study by image analysis and by high-pressure liquid chromatography (HPLC) of the mouse lungs’ elastic fibre content from the 15th till the 19th gestational day.

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.

Platelet-derived growth factor C induces liver fibrosis, steatosis, and hepatocellular carcinoma

Members of the platelet-derived growth factor (PDGF) ligand family are known to play important roles in wound healing and fibrotic disease. We show that both transient and stable expression of PDGF-C results in the development of liver fibrosis consisting of the deposition of collagen in a pericellular and perivenular pattern that resembles human alcoholic and nonalcoholic fatty liver disease. Fibrosis in PDGF-C transgenic mice, as demonstrated by staining and hydroxyproline content, is preceded by activation and proliferation of hepatic stellate cells, as shown by collagen, alpha-smooth muscle actin and glial fibrillary acidic protein staining and between 8 and 12 months of age is followed by the development of liver adenomas and hepatocellular carcinomas. The hepatic expression of a number of known profibrotic genes, including type beta1 TGF, PDGF receptors alpha and beta, and tissue inhibitors of matrix metalloproteinases-1 and -2, increased by 4 weeks of age. Increased PDGF receptor alpha and beta protein levels were associated with activation of extracellular regulated kinase-1 and -2 and protein kinase B. At 9 months of age, PDGF-C transgenic mice had enlarged livers associated with increased fibrosis, steatosis, cell dysplasia, and hepatocellular carcinomas. These studies indicate that hepatic expression of PDGF-C induces a number of profibrotic pathways, suggesting that this growth factor may act as an initiator of fibrosis. Moreover, PDGF-C transgenic mice represent a unique model for the study of hepatic fibrosis progressing to tumorigenesis.

High levels of desmosines in urine and plasma of patients with pseudoxanthoma elasticum

BACKGROUND

Pseudoxanthoma elasticum (PXE), a rare heritable disorder caused by mutations of the ABCC6 gene, is characterized by fragmentation and mineralization of elastic fibres. We determined the extent of degradation of elastin by measuring and comparing the amount of desmosines in plasma and urine of PXE patients, healthy carriers and normal subjects.

METHODS

Using capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) we measured the amount of desmosines in the urine of 46 individuals (14 PXE patients, 17 healthy carriers and 15 controls) and in the plasma of 56 subjects (18 PXE patients, 23 healthy carriers and 15 controls). Pseudoxanthoma elasticum patients and carriers were identified by clinical, structural and molecular biology analyses.

RESULTS

The urinary excretion of desmosines was two-fold higher in PXE patients than in controls (P < 0.01); the values for healthy carriers were intermediate between those of PXE patients and controls. A very similar trend between patients and their relatives was observed for plasma desmosines. There was a significant correlation between the amount of the desmosines in plasma and urine. Moreover, a positive correlation was observed between urinary desmosine content and age of the patients as well as between urinary desmosine content and severity of clinical manifestations.

CONCLUSIONS

Both the urinary and plasma desmosine concentrations indicate that elastin degradation is higher in PXE patients and, to a lesser extent, in healthy carriers than in normal subjects. Data seem to indicate that the amount of elastin breakdown products correlates with the age of patients as well as with the severity of the disease.

Enrichment and analysis of desmosine and isodesmosine in biological fluids

A method has been developed for the enrichment and analysis of the elastin crosslinks, desmosine and isodesmosine, in biological fluids and tissues. It is adapted from published methods, offering improved recovery, sensitivity, resolution, and speed of analysis. Samples were hydrolyzed in 6 M HCl, after which the desmosines were enriched by CF1 cellulose chromatography and analyzed by HPLC with a C18 column. Isodesmosine and desmosine were quantitated based on absorbance at 275 nm, with a limit of detection of approximately 30 pmol and recovery of approximately 66% in urine. Their tR values on our HPLC system were approximately 9 and 12 min, respectively. This method was used to evaluate the daily and weekly variation in the concentrations of desmosine and isodesmosine in human urine. The results suggest that this method can be used to process large numbers of biological samples for analysis of desmosine and isodesmosine.

Derivatization of posttranslationally modified amino acids

After a brief overview of posttranslational modifications of protein amino acids, the use of various derivatizing reagents for amino acid analysis is discussed. Derivatization and chromatographic separation of hydroxyproline, methylhistidine, and phosphorylated amino acids are discussed in detail to illustrate some of the strategies that can be applied to the analysis of posttranslationally modified amino acids.

Post-translational chemical modifications of proteins--III. Current developments in analytical procedures of identification and quantitation of post-translational chemically modified amino acid(s) and its derivatives

1. The Chemical modifications of amino acids and their derivatives are mainly due to different post-translational enzymatic reactions. 2. The enzymatic reactions resulting in amino acids such as acetylation-, formylation, methylation-phosphorylation-, sulfation-, hydroxylation, ADP ribosylation-, carboxylation-, amidation-, adenylylation-, glycosylation-, ubiquitination-, prenylation and acylation are listed and analytical methods are reported and extensively reviewed. 3. The post-translationally modified cross-linking molecules after maturations such as desmosines, allo-desmosine, hydroxy-, lysylpyridinoline, 3-hydroxypyridinium derivatives, cyclopentenosine recently found in matured elastin, and in collagen, and pulcherosine a novel tyrosine-derived found in fertilization envelope of Sea Urchin embryo, di-tyrosine in resilin, gamma-glutamyl-lysine isopeptide cross-linking molecule etc. are listed and both physico-chemical and analytical methods are extensively reviewed and discussed. 4. Other consequences of post-translational modifications encountered in the analytical procedure such as N-terminal step-wise Edman degradation of glycosylated site(s), phosphorylated-site(s) and or sulfated-site(s) were also reported by us.

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.