Localisation of endothelin-1 in rat aortae, the relationship to flow and elastic tissue tears

Protease inhibitor 15, a candidate gene for abdominal aortic internal elastic lamina ruptures in the rat

The inbred Brown Norway (BN) rat develops spontaneous ruptures of the internal elastic lamina (RIEL) of the abdominal aorta (AA) and iliac arteries. Prior studies with crosses of the BN/Orl RJ (susceptible) and LOU/M (resistant) showed the presence of a significant QTL on chromosome 5 and the production of congenic rats proved the involvement of this locus. In this study, we further dissected the above-mentioned QTL by creating a new panel of LOU.BN(chr5) congenic and subcongenic lines and reduced the locus to 5.2 Mb. Then we studied 1,002 heterogeneous stock (HS) rats, whose phenotyping revealed a low prevalence and high variability for RIEL. High-resolution mapping in the HS panel detected the major locus on chromosome 5 (log P > 35) and refined it to 1.4 Mb. Subsequently, RNA-seq analysis on AA of BN, congenics, and LOU revealed expression differences for only protease inhibitor 15 (Pi15) gene and a putative long intergenic noncoding RNA (lincRNA) within the linkage region. The high abundance of lincRNA with respect to reduced Pi15 expression, in conjunction with exertion of longitudinal strain, may be related to RIEL, indicating the potential importance of proteases in biological processes related to defective aortic internal elastic lamina structure. Similar mechanisms may be involved in aneurysm initiation in the human AA.

Increased elastic tissue defect formation in the growth restricted Brown Norway rat: a potential link between in utero condition and cardiovascular disease

Low birth weight for gestational age has been epidemiologically linked to cardiovascular mortality and morbidity in adult life. This study aimed to determine whether in utero growth restriction influences an early feature of atherosclerotic pathology; disruption of the aortic internal elastic lamina (IEL) in the adult Brown Norway (BN) rat. In utero growth restriction was induced by bilateral uterine artery ligation on day 18 of gestation, thereby decreasing newborn BN pup weight by approximately 14%. Restriction surgery significantly increased aortic IEL defect number at 8 wk of age in both sexes compared with no surgery animals (p < 0.002). At 16 wk of age placental restriction surgery significantly increased the number of defects in males compared with both no surgery and sham surgery control groups (p < 0.001). The total number of IEL defects was significantly correlated with several postnatal growth rate parameters, including 72-h postpartum weight. Neither blood pressure was significantly different between treatment groups, nor was it correlated with body weight or IEL defect numbers. The findings of this study seem to support the fetal origins of adult disease hypothesis, by demonstrating that a moderate growth restricting insult dramatically increases aortic elastic tissue defect formation via an apparently blood pressure-independent mechanism.

Elastase-induced suppression of endothelin-mediated Ca2+ entry mechanisms of vascular contraction

Abdominal aortic aneurysm (AAA) is associated with increased endothelin (ET-1), both systemically and locally in the aorta. Also, elastase activity is increased in human AAA, and elastase perfusion of the aorta induces aneurysm formation in animal models of AAA. However, whether elastase directly affects the ET-1-induced mechanisms of aortic smooth muscle contraction is unclear. Isometric contraction and 45Ca2+ influx were measured in aortic strips isolated from male Sprague-Dawley rats and treated with elastase (5 U/mL). To avoid degradation of the extracellular matrix proteins by elastase, experiments were performed in the presence of elastin (10 mg/mL). In normal Krebs solution (2.5 mmol/L Ca2+), ET-1 (10(-7) mol/L) caused contraction of aortic strips that was inhibited by elastase (5 U/mL). The elastase-induced inhibition of ET-1 contraction was slow in onset (4.6+/-0.4 minutes), time-dependent, complete in 34+/-3 minutes, and reversible. In Ca2+-free Krebs solution, caffeine (25 mmol/L) caused a small contraction that was not inhibited by elastase, suggesting that elastase does not inhibit Ca2+ release from the intracellular stores. Membrane depolarization by 96 mmol/L KCl, which stimulates Ca2+ entry from the extracellular space, caused a contraction that was inhibited by elastase in a concentration-dependent, time-dependent, and reversible fashion. The reversible inhibitory effects of elastase, particularly in the presence of elastin, suggest that they are not due to dissolution of the extracellular matrix or smooth muscle contractile proteins. Elastase also inhibited ET-1 and KCl-induced 45Ca2+ influx. Thus, elastase directly inhibits ET-1-induced Ca2+ entry mechanisms of vascular smooth muscle contraction, which may explain the role of elastase and ET-1 during the development of AAA.

Plasma endothelin in patients with acute aortic disease

PURPOSE AND BACKGROUND

We investigated the plasma levels of endothelin 1/2 in patients with acute symptoms relating to a known or newly diagnosed aortic aneurysm in order to investigate the possible role of peptides in the development of the disease.

METHODS

Endothelin 1/2 plasma levels were determined in patients admitted to the emergency unit with suspected acute aortic disease. The history, type of aneurysm, outcome and laboratory findings were determined and compared to endothelin 1/2 levels collected on admission.

RESULTS

In patients with ruptured aneurysm (n=27) or acute aortic dissection (n=18) the endothelin 1/2 median levels were higher 1.1 (25th and 75th quartile 0.7, 1.7) fmol/ml than in patients (n=20) with pre-existing aneurysm 0.7 (0.4, 1.1) fmol/ml (P=0.013). Patients who died had significantly higher endothelin levels 1.3 (0.8, 1.9) fmol/ml than the survivors 0.8 (0.5, 1.4) fmol/ml (P=0.04). In a logistic regression analysis, only a higher blood pressure on admission was an independent predictor of survival.

CONCLUSION

Endothelin 1/2 levels are elevated in patients with acute dissection or ruptured aneurysm, but they are not an independent predictor of survival.

Identification of two susceptibility loci for vascular fragility in the Brown Norway rat

A trait of vascular fragility, characterized by the formation of abrupt defects within the elastic laminae of the abdominal aorta, has been identified in Brown Norway (BN) rats. These lesions are greatly exacerbated in F(1) rats from a BN x New Zealand genetically hypertensive (GH) intercross, implying that the genetic background provided by the GH rat influences lesion severity. The F(2) progeny of the BN x GH intercross were used to identify susceptibility loci for the lesions as well as exacerbating loci. Two major quantitative trait loci (QTLs) for number of internal elastic lamina lesions were identified on rat chromosomes 5 and 10, with the maximum "log of the odds ratio" (LOD) scores at D5Rat119 (LOD 5.0) and at D10Mit2 (LOD 4.5), respectively, together contributing 33.5% to the genetic variance. Further analysis revealed that the chromosome 10 locus exhibits a dominant mode of inheritance, with BN alleles being associated with increased lesion number (P < 0.0002) compared with GH homozygotes. This locus was in epistasis to a modifier locus on rat chromosome 2 at D2Mit14 (LOD score 2.12). A second major locus was identified on chromosome 5, exhibiting a semidominant mode of inheritance, again with the BN allele being significantly associated with increased lesion number (P < 0.0001). Furthermore, a locus influencing lesion severity was identified on chromosome 3 wherein GH alleles associated with increased severity. This is the first study to identify susceptibility loci for vascular elastic tissue fragility.

Plasma endothelin levels in patients with abdominal aortic aneurysms

OBJECTIVES

endothelin 1,2 plays a significant role in the process of atherogenesis and vascular wall injury. The aim of this study was to assess whether plasma endothelin 1,2 levels were elevated in patients with large or symptomatic abdominal aortic aneurysms (AAAs).

DESIGN

a prospective open study.

MATERIALS AND METHODS

plasma endothelin 1,2 levels were measured in 65 consecutive patients with infrarenal aortic aneurysms and compared with the levels in 44 healthy volunteer controls. The data for abdominal aneurysm patients was analysed in four subgroups: (i) small aneurysms (<5 cm), (ii) large aneurysms (>/=5 cm), (iii) asymptomatic aneurysms and (iv) symptomatic aneurysms. Comparisons were made between endothelin 1,2 levels in aneurysm patients and controls and between the different aneurysm subgroups.

RESULTS

a highly significant difference (p<0.0001) was found between aneurysm patients and controls. Patients with large aneurysms had significantly higher levels than patients with small aneurysms (p<0.01). There was no statistical difference in endothelin 1,2 levels between symptomatic and asymptomatic patients; however, the highest levels were found in large, symptomatic aneurysms and the lowest in small, asymptomatic aneurysms.

CONCLUSIONS

plasma endothelin 1,2 is an endogenous marker of aneurysm diameter. Further studies are required to determine whether it relates to the rate of growth of aneurysms.

Venous endothelial changes in therapeutic arteriovenous fistulae

Specimens of veins of therapeutic arteriovenous fistulae from five patients were examined by an en face immunohistochemical technique to investigate endothelial morphology and the presence of the vasoactive peptide endothelin-1 (ET-1). These were compared with control segments of long saphenous veins from six patients. Venous endothelium from the arteriovenous shunts was mostly intact even overlying phlebosclerotic plaques. Occasional small areas of denudation, with associated platelets, were present in the depressions of 'jet' lesion however. The endothelial cells were generally elongated and interspersed with foci of polyhedral cells. The control saphenous veins contained elongated endothelial cells without detectable denudation. Image analysis of histological sections of veins from the shunts indicated significantly less intact elastic tissue than control veins but greater mononucleated endothelial cell density in en face preparations. ET-1 staining was considerably stronger in endothelium from the fistulae than in the control saphenous veins and was most intense over the raised crescentic ridges of jet lesions, stenoses and phlebosclerotic plaques. Endothelial mitoses and cells with hyperchromatic nuclei stained more strongly for ET-1 than surrounding cells. These results indicate that the endothelial cells lining veins associated with arteriovenous fistulae are dynamically altered by the increased haemodynamic stresses associated with these shunts. Furthermore ET-1 may act as a localising factor associated with intimal thickening at sites of 'jet' lesions, stenosis and phlebosclerosis.