Thomas Leurgans

Elastin Organization in Pig and Cardiovascular Disease Patients' Pericardial Resistance Arteries

Peripheral vascular resistance is increased in essential hypertension. This involves structural changes of resistance arteries and stiffening of the arterial wall, including remodeling of the extracellular matrix. We hypothesized that biopsies of the human parietal pericardium, obtained during coronary artery bypass grafting or cardiac valve replacement surgeries, can serve as a source of resistance arteries for structural research in cardiovascular disease patients. We applied two-photon excitation fluorescence microscopy to study the parietal pericardium and isolated pericardial resistance arteries with a focus on the collagen and elastin components of the extracellular matrix. Initial findings in pig tissue were confirmed in patient biopsies. The microarchitecture of the internal elastic lamina in both the pig and patient pericardial resistance arteries (studied at a transmural pressure of 100 mm Hg) is fiber like, and no prominent external elastic lamina could be observed. This microarchitecture is very different from that in rat mesenteric arteries frequently used for resistance artery research. In conclusion, we add three-dimensional information on the structure of the extracellular matrix in resistance arteries from cardiovascular disease patients and propose further use of patient pericardial resistance arteries for studies of the human microvasculature.

25 Years of endothelin research: the next generation

In the past three decades, endothelin and endothelin receptor antagonists have received great scientific and clinical interest, leading to the publication of more than 27,000 scientific articles since its discovery. The Thirteenth International Conference on Endothelin (ET-13) was held on September 8-11, 2013, at Tokyo Campus of the University of Tsukuba in Japan. Close to 300 scientists from 25 countries from around the world came to Tokyo to celebrate the anniversary of the discovery of the endothelin peptide discovered 25 years ago at the University of Tsukuba. This article summarizes some of the highlights of the conference, the anniversary celebration ceremony, and particularly the participation of next generation of endothelin researchers in endothelin science and the anniversary celebration. As a particular highlight, next generation endothelin researchers wrote a haiku (a traditional form of Japanese poetry originating from consisting of no more than three short verses and 27 on, or Japanese phonetic units) to describe the magic of endothelin science which they presented to the conference audience at the anniversary ceremony. The text of each haiku - both in its original language together with the English translation - is part of this article providing in an exemplary fashion how poetry can be bridged with science. Finally, we give an outlook towards the next 25 years of endothelin research.

Endothelin-1 shifts the mediator of bradykinin-induced relaxation from NO to H2 O2 in resistance arteries from patients with cardiovascular disease.

We tested the hypothesis that in resistance arteries from cardiovascular disease (CVD) patients, effects of an endothelium‐dependent vasodilator depend on the contractile stimulus.

Imaging and modeling of acute pressure-induced changes of collagen and elastin microarchitectures in pig and human resistance arteries

The impact of disease-related changes in the extracellular matrix (ECM) on the mechanical properties of human resistance arteries largely remains to be established. Resistance arteries from both pig and human parietal pericardium (PRA) display a different ECM microarchitecture compared with frequently used rodent mesenteric arteries. We hypothesized that the biaxial mechanics of PRA mirror pressure-induced changes in the ECM microarchitecture. This was tested using isolated pig PRA as a model system, integrating vital imaging, pressure myography, and mathematical modeling. Collagenase and elastase digestions were applied to evaluate the load-bearing roles of collagen and elastin, respectively. The incremental elastic modulus linearly related to the straightness of adventitial collagen fibers circumferentially and longitudinally (both R2 ≥ 0.99), whereas there was a nonlinear relationship to the internal elastic lamina elastin fiber branching angles. Mathematical modeling suggested a collagen recruitment strain (means ± SE) of 1.1 ± 0.2 circumferentially and 0.20 ± 0.01 longitudinally, corresponding to a pressure of ~40 mmHg, a finding supported by the vital imaging. The integrated method was tested on human PRA to confirm its validity. These showed limited circumferential distensibility and elongation and a collagen recruitment strain of 0.8 ± 0.1 circumferentially and 0.06 ± 0.02 longitudinally, reached at a distending pressure below 20 mmHg. This was confirmed by vital imaging showing negligible microarchitectural changes of elastin and collagen upon pressurization. In conclusion, we show here, for the first time in resistance arteries, a quantitative relationship between pressure-induced changes in the extracellular matrix and the arterial wall mechanics. The strength of the integrated methods invites for future detailed studies of microvascular pathologies.NEW & NOTEWORTHY This is the first study to quantitatively relate pressure-induced microstructural changes in resistance arteries to the mechanics of their wall. Principal findings using a pig model system were confirmed in human arteries. The combined methods provide a strong tool for future hypothesis-driven studies of microvascular pathologies.

Relaxing Responses to Hydrogen Peroxide and Nitric Oxide in Human Pericardial Resistance Arteries Stimulated with Endothelin-1

In human pericardial resistance arteries, effects of the endothelium‐dependent vasodilator bradykinin are mediated by NO during contraction induced by K+ or the TxA2 analogue U46619 and by H2O2 during contraction by endothelin‐1 (ET‐1), respectively. We tested the hypotheses that ET‐1 reduces relaxing effects of NO and increases those of H2O2 in resistance artery smooth muscle of patients with cardiovascular disease. Arterial segments, dissected from the parietal pericardium of 39 cardiothoracic surgery patients, were studied by myography during amplitude‐matched contractions induced by K+, the TXA2 analogue U46619 or ET‐1. Effects of the NO donor Na‐nitroprusside (SNP) and of exogenous H2O2 were recorded in the absence and presence of inhibitors of cyclooxygenases, NO synthases and small and intermediate conductance calcium‐activated K+ channels. During contractions induced by either of the three stimuli, the potency of SNP did not differ and was not modified by the inhibitors. In vessels contracted with ET‐1, the potency of H2O2 was on average and in terms of interindividual variability considerably larger than in K+‐contracted vessels. Both differences were not statistically significant in the presence of inhibitors of mechanisms of endothelium‐dependent vasodilatation. In resistance arteries from patients with cardiovascular disease, ET‐1 does not selectively modify smooth muscle relaxing responses to NO or H2O2. Furthermore, the candidate endothelium‐derived relaxing factor H2O2 also acts as an endothelium‐dependent vasodilator.

Combined use of β-Blockers and Inhibitors of the Renin-Angiotensin System Decreases the Stiffness of Resistance Arteries from Cardiothoracic Surgery Patients

Introduction: Lymphatic Endothelial Cells (LECs) have been shown to express EPHB4, a receptor tyrosine kinase (TK) which signals via the ephrinB2 ligand. Previous data revealed EPHB4 as a new causative gene for Lymphatic-Related (non-immune) Hydrops Fetalis (LRHF), a form of Generalized Lymphatic Dysplasia, a subgroup of Primary Lymphoedemas. Two missense mutations in EPHB4 were reported to be associated with this phenotype and the receptor was also identified as critical regulator of lymphangiogenesis. This study aims to further investigate the role of EPHB4 in lymphangiogenesis and the mechanisms by which the two specific mutations interfere with EPHB4 signalling and dysregulate lymphangiogenesis.

Structure and Contractile Function of Pericardial Resistance Arteries from Cardiothoracic Surgery Patients; Effects of Anti‐Hypertensive Treatments

Introduction: Lymphatic Endothelial Cells (LECs) have been shown to express EPHB4, a receptor tyrosine kinase (TK) which signals via the ephrinB2 ligand. Previous data revealed EPHB4 as a new causative gene for Lymphatic-Related (non-immune) Hydrops Fetalis (LRHF), a form of Generalized Lymphatic Dysplasia, a subgroup of Primary Lymphoedemas. Two missense mutations in EPHB4 were reported to be associated with this phenotype and the receptor was also identified as critical regulator of lymphangiogenesis. This study aims to further investigate the role of EPHB4 in lymphangiogenesis and the mechanisms by which the two specific mutations interfere with EPHB4 signalling and dysregulate lymphangiogenesis.