Measurement of desmosine and isodesmosine by capillary zone electrophoresis

The onset of left ventricular diastolic dysfunction in SHR rats is not related to hypertrophy or hypertension

Left ventricular (LV) diastolic dysfunction, particularly relaxation abnormalities, are known to be associated with the development of LV hypertrophy (LVH). Preliminary human and animal studies suggested that early LV diastolic dysfunction may be revealed independently of LVH. However, whether LV diastolic dysfunction is compromised before the onset of hypertension and LVH remains unknown. We therefore evaluated LV diastolic function in spontaneously hypertensive rats (SHR) at different ages and tested whether LV diastolic dysfunction is associated with abnormal intracellular calcium homeostasis. LV systolic and diastolic functions were evaluated by invasive and echocardiographic methods in 3-week-old (without hypertension) and 5-week-old (with hypertension) SHR and Wistar-Kyoto control rats. Basal intracytoplasmic calcium and sarcoplasmic reticulum (SR) Ca2+ contents were measured in cardiomyocytes using fura-2 AM. Sarco(endo)plasmic Ca2+-ATPase isoform 2a (SERCA 2a) and phospholamban (PLB) expressions were quantified by Western blot and quantitative RT-PCR techniques. LV relaxation dysfunction was observed in 3-week-old SHR rats before onset of hypertension and LVH. An increase in basal intracytoplasmic Ca2+ and a decrease in SR Ca2+ release were demonstrated in SHR. Decreased expression of SERCA 2a and Ser16 PLB (p16-PLB) protein levels was also observed in SHR rats, whereas mRNA expression was not decreased. For the first time, we have shown that LV myocardial dysfunction precedes hypertension in 3-week-old SHR rats. This LV myocardial dysfunction was associated with high diastolic [Ca2+]i possibly due to decreased SERCA 2a and p16-PLB protein levels. Diastolic dysfunction may be a potential predictive marker of arterial hypertension in genetic hypertension syndromes.

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.

Mechanisms of aortic and cardiac dysfunction in uremic mice with aortic calcification

BACKGROUND

Chronic renal failure (CRF) is associated with cardiac dysfunction and increased aortic stiffness. The mechanisms involved are not clearly understood. We examined changes over time in cardiac and aortic function in a murine CRF model.

METHODS AND RESULTS

Eight-week-old mice were randomly assigned to 1 of 4 groups: wild-type non-CRF, wild-type CRF, apolipoprotein E knockout non-CRF, and apolipoprotein E knockout CRF. Echocardiography was performed and blood samples were taken at baseline and after 6 and 10 weeks of CRF. Vascular reactivity and adhesion molecule expression were studied after 6 and 10 weeks of CRF. Left ventricular hypertrophy, altered left ventricular relaxation, and increased aortic stiffness were observed after 6 weeks of CRF and persisted after 10 weeks. The 4 groups of mice did not significantly differ in terms of arterial blood pressure and aortic structure. The degree of vascular calcification and serum total cholesterol concentration were higher in the CRF groups than in the non-CRF groups. These changes, however, could not explain the cardiac and vascular differences seen in the 2 CRF groups. In contrast, alterations in vascular reactivity, the upregulation of adhesion molecule expression, and CRF status were significantly associated with these changes.

CONCLUSIONS

In a mouse model of CRF, left ventricular hypertrophy, cardiac diastolic dysfunction, and increased aortic stiffness were not related to structural changes in the aorta (including aortic calcification) or high serum cholesterol levels. However, cardiac and aortic abnormalities were associated with the extent of subendothelial dysfunction and the severity of CRF.

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.

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.

The detection and quantitation of free desmosine and isodesmosine in human urine and their peptide-bound forms in sputum

Desmosine (D) and isodesmosine (I), the intramolecular crosslinking amino acids that occur in chains of elastin, have now been found in free form in human urine. Until now, these amino acids (M(r) = 526) were found to occur in urine only as higher molecular weight (M (r) = 1,000-1,500) peptides. Thus, the previously used analytical methods required, as the first step, acid hydrolysis of the urine at elevated temperature to liberate D and I from their peptides. The analytical method described here uses HPLC followed by electrospray ionization MS for the detection and quantitation of free D and I in unhydrolyzed urine. Identities of both D and I were established by their retention times on LC and by their mass ion at 526 atomic mass units, characteristic of each compound. The sensitivity of the method is 0.10 ng. The average values of free D and I in the urine of seven healthy subjects were 1.42 +/- 1.16 and 1.39 +/- 1.04 microg/g of creatinine, respectively. After acid hydrolysis of the urine, the amounts of D and I were 8.67 +/- 3.75 and 6.28+/-2.87 microg/g of creatinine, respectively. The method was also successfully used to measure peptide-bound D and I levels in the sputum of patients with chronic obstructive pulmonary disease.

Withdrawal reveals lack of effect of prolonged antihypertensive treatment on intrinsic aortic wall stiffness in senescent spontaneously hypertensive rats

1. Chronic antihypertensive treatment lowers cardiovascular morbidity and mortality. The beneficial effect on the blood vessel wall may be due to the lowering of blood pressure (BP) and, hence, wall stress (WS), or to a treatment-induced change in wall structure. 2. We have previously shown that, when evaluated at the same level of BP and WS, the stiffness of the aortic wall of old spontaneously hypertensive rats (SHR) is higher than that of young and adult SHR and that of age-matched Wistar-Kyoto (WKY) rats. In the present study, we tested the hypothesis that the intrinsic changes in wall composition and mechanics in old SHR can be modulated by long-term treatment with an angiotensin I-converting enzyme inhibitor (captopril; 40 mg/kg per day) combined with a diuretic (hydrochlorothiazide; 20 mg/kg per day) and that treatment withdrawal would reveal whether such changes are maintained when BP and WS return to pretreatment levels. 3. We evaluated aortic structure and mechanics in SHR following 1 week withdrawal of oral antihypertensive treatment from 3 to 15 months of age (n = 8). Results were compared with age-matched SHR that were maintained on treatment (n = 12) or were not treated (n = 13) and with WKY rats (no treatment n = 11; maintained n = 11; withdrawn n = 10). 4. Isobaric aortic wall stiffness was estimated from the ratio of baseline aortic pulse wave velocity (PWV) to BP and the slope relating aortic PWV to BP following sodium nitroprusside-induced hypotension. Relative wall stiffening was estimated as the ratio of elastic modulus (EM) to WS. We argued that if treatment produced a change in wall elastin or collagen content, with a subsequent decrease in isobaric wall stiffness, then this would be maintained when BP increased following withdrawal of treatment. 5. In old SHR, treatment lowered isobaric wall stiffness (baseline PWV/BP 4.6 +/- 0.3 cm/s per mmHg; slope relating PWV to BP 6.7 +/- 0.4 x 10-3 cm/s per mmHg and EM/WS 4.1 +/- 0.4 vs 6.1 +/- 0.4 cm/s per mmHg, 9.7 +/- 0.9 x 10-3 cm/s per mmHg and 8.9 +/- 1.1, respectively, without treatment; all P < 0.05). After 1 weeks treatment withdrawal, the indices (5.7 +/- 0.2 cm/s per mmHg, 9.1 +/- 0.2 x 10-3 cm/s per mmHg and 7.2 +/- 0.6) increased in parallel with the increase in WS to levels similar to those observed in untreated SHR. There were no significant differences among the WKY rat groups. 6. Treatment increased the elastin and collagen contents of the aortic wall in both SHR (196 +/- 13 and 128 +/- 5 vs 111 +/- 9 and 86 +/- 4 mg/g wet weight, respectively, in untreated; P < 0.05) and WKY rats (190 +/- 19 and 135 +/- 4 vs 115 +/- 7 and 114 +/- 5 mg/g wet weight, respectively, in untreated; P < 0.05). This increase remained following withdrawal (213 +/- 26 and 118 +/- 4 vs 161 +/- 14 and 127 +/- 4 mg/g wet weight in SHR and WKY rats, respectively). 7. In summary, 1 year of treatment with captopril plus hydrochlorothiazide increases wall elastin content and reduces WS and stiffness in old SHR. Following withdrawal, elastin content remains high, but wall stiffness parallels WS in a manner similar to that in untreated SHR.

Aminoguanidine and aortic wall mechanics, structure, and composition in aged rats

With aging, the aortic wall becomes stiffer. This could be because of changes in wall stress or composition. We investigated whether a specific change in wall composition, ie, accumulation of advanced glycation end products (AGEs) on the extracellular matrix, is a major factor. We measured aortic mechanics, geometry, and composition in 3-, 10-, 15-, 20-, and 30-month-old inbred normotensive Wistar-Glaxo/Rijswick rats and in a group of 30-month-old rats treated from 20 months onward with aminoguanidine (AG, 42 mg/kg per day), an inhibitor of AGE formation. Thoracoabdominal aortic (pressure) pulse-wave velocity (PWV) increased progressively with age (44% from 3 to 30 months). This age-related increase in aortic PWV was not related to changes in wall stress. For all ages, central (and peripheral) aortic mean blood pressures were not statistically different. Dilatation occurred (18% increase in internal diameter from 3 to 30 months), but this was accompanied by outward hypertrophic remodeling, with an increase in the medial cross-sectional area of 95% and in the ratio of medial thickness to internal diameter of 29%. Wall stress decreased with age (-34%). There was an increase in the ratio of elastic modulus (calculated from the Moens-Korteweg equation) to wall stress (calculated from the Lamé equation, 117% from 3 to 30 months), suggesting that a change in the composition of the wall is responsible for the age-linked increase in wall stiffness. Dry weight decreased slightly but significantly (-14%) with age. Total protein, elastin, collagen, and nonscleroprotein protein [total-(elastin+collagen)] contents did not change with age, but calculated densities of all 4 were halved (as the medial cross-sectional area doubled). The elastin/collagen ratio was statistically similar at all ages. The only significant effect of AG treatment was a fall in PWV (-20%), leading to a fall in the elastic modulus/wall stress ratio (-27% at 10 months of AG treatment versus 30 months of no treatment). In conclusion, the age-related increase in aortic wall stiffness is prevented by 10 months of treatment with AG, which has no effect on wall stress or composition, suggesting that AG may improve aortic wall stiffness by lowering the degree of AGE-induced cross-linking of the extracellular matrix scleroproteins, such as collagen.

Aortic wall mechanics and composition in a transgenic mouse model of Marfan syndrome

In Marfan syndrome, mutations of the fibrillin gene (FBN1) lead to aneurysm of the thoracic aorta, making the aortic wall more susceptible to dissection, but the precise sequence of events underlying aneurysm formation is unknown. We used a rodent model of Marfan syndrome, the mgR/mgR mouse (with mgR: hypomorphic FBN1 mutation), which underexpresses FBN1, to distinguish between a defect in the early formation of elastic fibers and the later disruption of elastic fibers. The content of desmosine plus isodesmosine was used as an index of early elastogenesis; disruption of elastic fibers was analyzed by histomorphometry. Because disruption of the medial elastic fibers may produce aortic stiffening, so amplifying the aneurysmal process, we measured thoracoabdominal pulse wave velocity as an indicator of aortic wall stiffness. Both mgR/mgR and wild-type (C57BL/6J-129SV) strains were normotensive, and wall stress was not significantly modified because the increase in internal diameter (0.80+/-0.06 vs 0.63+/-0.03 mm in wild type, P<0.05) was accompanied by increased medial cross-sectional area. The aortic wall stiffened (4-fold increase in the elastic modulus-to-wall stress ratio). Desmosine content was not modified (mgR/mgR 432+/-31 vs wild type 492+/-42 microg/mg wet weight, P>0.05). Elastic fibers showed severe fragmentation: the percentage of the media occupied by elastic fibers was 18+/-3% in mgR/mgR mice vs 30+/-1% in wild-type mice, with the number of elastic segments being 1.9+/-0.2 vs 1.4+/-0.1x10(-6)/mm(2) in the wild type (both P<0.05). In conclusion, underexpression of FBN1 in mice leads to severe elastic network fragmentation but no change in cross-linking, together with aortic dilatation. This result suggests that fragmentation of the medial elastic network and not a defect in early elastogenesis is 1 of the determinants of aortic dilatation in Marfan syndrome.

Physical exercise, aortic blood pressure, and aortic wall elasticity and composition in rats

With a training schedule (8 weeks' treadmill running at 30 m/min up a 10% incline 5 d/wk for 90 min/day), we investigated whether exercise modifies aortic wall dimensions, composition (calcium and elastin content), or stiffness in normotensive 6-month-old male Wistar WAG/Rij rats. Maximal oxygen uptake was measured in half of the rats (n=10 per group). Wall stiffness was evaluated in the other half (9 trained and 10 untrained) on the basis of changes in thoracoabdominal pressure pulse wave velocity and differences in amplitude between the peripheral and central aortic pressure signals. Experiments were performed in nonanesthetized, unrestrained rats and then after pithing. The impact of exercise on the oxidative capacity of the plantaris muscles was evaluated with the measurement of citrate synthase activity. Training increased maximal oxygen uptake by 34% and citrate synthase activity by 40%. Mean peripheral aortic pressure increased by 6% and 19% in trained rats, under awake and pithed conditions, whereas mean central aortic pressure increased by 16%, after pithing only. All indexes of aortic stiffness were similar in trained and control rats, as were aortic wall dimensions, composition, cardiac mass, and heart rate. In conclusion, physical exercise in young rats appears to have no effect on aortic stiffness.

Elastic properties and composition of the aortic wall in old spontaneously hypertensive rats

We hypothesized that age-linked changes in the composition and elastic properties of the arterial wall occur earlier in hypertensive than in normotensive rats. We evaluated the consequences of hypertension and aging on aortic mechanics, geometry, and composition in 3-, 9-, and 15-month-old awake Wistar-Kyoto rats (WKY) (normotensive) and spontaneously hypertensive rats (SHR) (hypertensive). The elastic modulus of the thoracic aorta, calculated from aortic pulse wave velocity and geometry, was higher in young and adult SHR than in age-matched WKY, as was wall stress; however, isobaric pulse wave velocity and pulse wave velocity-pressure curves were similar. Elastic modulus, isobaric pulse wave velocity, and the slope of the pulse wave velocity-pressure curve dramatically increased in old SHR compared with age-matched WKY; there was no further elevation of blood pressure or wall thickness. Fibrosis did not develop with age in SHR, and the ratio of elastin to collagen decreased in a similar fashion with aging in both strains. In conclusion, although elastic properties of the aortic wall are not intrinsically modified in young and adult SHR in comparison to age-matched WKY, aging is associated with a dramatic stiffening of the aortic wall in old SHR but not in WKY. Changes in blood pressure, aortic wall geometry, or scleroprotein composition do not appear to explain this age-linked aortic stiffening in SHR, suggesting that other mechanisms of disorganization of the media may be involved.

Cardiac consequences of prolonged exposure to an isolated increase in aortic stiffness

In elderly patients, aortic stiffness is a major determinant of increased end-systolic stress leading to left ventricular (LV) hypertrophy with impaired cardiac performance. However, in a rat model of aortic elastocalcinosis (induced by vitamin D(3)-nicotine [VDN] treatment), brief exposure (1 month) to increased aortic stiffness modified neither cardiac function nor cardiac structure. Here we report the impact of longer exposure (3 months) to aortic stiffness. Three months after induction of aortic stiffness, aortic characteristic impedance was measured in awake rats, 8 control and 10 VDN. Stroke volume was measured (electromagnetic probe) at baseline and after acute volume overload. LV weight/body weight ratio, collagen, and myosin heavy chain (MHC) contents were determined. Although aortic characteristic impedance increased (controls, 32+/-2; VDN rats, 50+/-8 10(3) dyne. s/cm(5); P=0.0248), stroke volume was maintained in VDN rats at baseline (controls, 223+/-18; VDN, 211+/-13 microL) and after volume overload (controls, 378+/-14; VDN, 338+/-15 microL). However, LV weight/body weight ratio (controls, 1.54+/-0.07; VDN, 1.73+/-0.05 g/kg; P=0.0397) and LV collagen content (controls, 31+/-4; VDN, 52+/-4 microgram/g dry wt; P=0.0192) increased. A shift from alpha-MHC (controls, 82+/-2%; VDN, 69+/-3%; P=0.0056) to beta-MHC (controls, 18+/-2%; VDN, 31+/-3%; P=0. 0056) was also observed. Three months' exposure to increased aortic stiffness in VDN rats induced LV hypertrophy with moderate interstitial fibrosis and a shift in the MHC-isoform pattern. Such structural adaptation maintains LV performance.

Micellar electrokinetic chromatography for the determination of urinary desmosine and isodesmosine in patients affected by chronic obstructive pulmonary disease

The presence in urine of desmosine (DES) and isodesmosine (IDES), two crosslinked amino acids unique to the elastic fiber network, can be used as a specific indicator of degradation of mature elastin. Compared to methodologies so far available, the capillary electrophoretic technique reported here seems to be suitable and convenient for determining desmosines in urine of patients affected by chronic obstructive pulmonary disease (COPD). By using 35 mM sodium tetraborate pH 9.3 containing 65 mM SDS as the background electrolyte, the peaks of DES and IDES could be detected in hydrolyzed urine samples from controls and patients. Owing to the simultaneous determination of endogenous urinary creatinine used as appropriate internal standard, the amount of these amino acids could be accurately quantified. The results obtained were of the same order of magnitude as the data already reported in the literature for COPD patients. Thus micellar electrokinetic chromatography (MEKC) may be considered as a reliable technique for studying the turnover of the elastic fiber in clinical conditions.

Calcification of medial elastic fibers and aortic elasticity

We tested the hypothesis that a simple change in wall composition (medial calcium overload of elastic fibers) can decrease aortic elasticity. Calcium overload was produced by hypervitaminosis D plus nicotine (VDN) in the young rat. Two months later, measurement of central aortic mean blood pressure in the unanesthetized, unrestrained rat showed that the VDN rat suffered from isolated systolic hypertension but that mean blood pressure was normal. Wall thickness and internal diameter determined after in situ pressurized fixation were unchanged, as was calculated wall stress. Wall stiffness was estimated from (1) elastic modulus (determined with the Moens-Korteweg equation and values for aortic pulse wave velocity in the unanesthetized, unrestrained rat and arterial dimensions) and (2) isobaric elasticity (= slope relating pulse wave velocity to mean intraluminal pressure in the phenylephrine-infused, pithed rat preparation). Both increased after VDN, and both were significantly correlated to the wall content of calcium and the elastin-specific amino acids desmosine and isodesmosine. Left ventricular hypertrophy occurred in the VDN model, and left ventricular mass was related to isobaric elasticity. In conclusion, elastocalcinosis induces destruction of elastic fibers, which leads to arterial stiffness, and the latter may be involved in the development of left ventricular hypertrophy in a normotensive model.