Quang Trinh Nguyen

Discovery of new antagonists aimed at discriminating UII and URP‐mediated biological activities: insight into UII and URP receptor activation

Recent evidence suggested that urotensin II (UII) and its paralog peptide UII‐related peptide (URP) might exert common but also divergent physiological actions. Unfortunately, none of the existing antagonists were designed to discriminate specific UII‐ or URP‐associated actions, and our understanding, on how these two endogenous peptides can trigger different, but also common responses, is limited.

Use of Adrenomedullin Derivatives for Molecular Imaging of Pulmonary Circulation

Currently, there is no low-molecular-weight agent for imaging of the pulmonary circulation. Adrenomedullin (AM) is a peptide predominantly cleared by the pulmonary circulation through specific endothelial receptors. We developed human AM derivatives radiolabeled with 99mTc and evaluated their biodistribution, plasma kinetics, and utility as pulmonary vascular imaging agents. Methods: Two derivatives radiolabeled with 99mTc were evaluated: the natural cyclic form of the peptide, to which the chelator diethylenetriaminepentaacetic acid was added (C-DTPA-AM), and the linear form, which allows direct labeling (L-AM). The compounds were injected into dogs, and the activities of the tracers in blood and in organs were determined with a nuclear medicine camera. Single-pass pulmonary clearance was measured by the indicator dilution technique. The capacity to image perfusion defects was evaluated after surgical pulmonary artery ligation. Results: Both derivatives were rapidly cleared from plasma, with elimination half-lives of 42 and 32 min for C-DTPA-AM and L-AM, respectively. The lungs retained most of the activity after 30 min; this activity was higher (P = 0.02) for L-AM (42% ± 5% [mean ± SEM]) than for C-DTPA-AM (27% ± 1%). Lung activity slowly declined over time but was maintained after 2 h at approximately 20% for both tracers. The single-pass pulmonary clearance of plasma L-AM was 414 ± 85 mL/min. There was a higher level of urinary excretion of L-AM than of C-DTPA-AM. After pulmonary artery ligation, perfusion defects were easily detectable by external imaging. Conclusion: AM derivatives are promising compounds for molecular imaging of the pulmonary circulation. L-AM displayed higher levels of initial lung retention and of kidney excretion.

Single measurement of troponin T for early prediction of infarct size, congestive heart failure, and pulmonary hypertension in an animal model of myocardial infarction

BACKGROUND Early prediction of infarct size and of the subsequent development of congestive heart failure (CHF) and pulmonary hypertension (PH) would be useful in therapeutic trials using the rat myocardial infarction (MI) model. METHODS A total of 194 rats were subjected to MI or sham surgery, and plasma cardiac troponin T (cTnT) was measured 24 h after surgery in rats. Echocardiography was performed after 2 and 5 weeks. Hemodynamic and morphometric parameters were evaluated 5 weeks after MI. RESULTS cTnT had strong positive correlations with left ventricular (LV) wall motion abnormalities at 2 and 5 weeks (R=.85 and .89; P<.0001), and with histological infarct size (R=.87, P<.0001). cTnT ≥5.1 μg/l predicted LV wall motion abnormalities ≥ 30% with a sensitivity of 90.9% and specificity of 84.0%. Rats with cTnT≥5.1 μg/l developed PH [right ventricular (RV) systolic pressure 37 ± 3 vs. 23 ± 0.6 mmHg], RV hypertrophy (RV/LV+septum weight 42 ± 4% vs. 24 ± 0.5%), and lung structural remodeling (all P<.01). CONCLUSION Early single cTnT measurement correlates with infarct size in rats, and a cutoff value of 5.1 μg/l provides good sensitivity and specificity to predict CHF with secondary PH. cTnT could be used for treatment allocations in therapeutic trials of secondary pulmonary hypertension using this model.

Molecular Imaging of Monocrotaline-Induced Pulmonary Vascular Disease with Radiolabeled Linear Adrenomedullin

No test currently exists for molecular imaging of pulmonary arterial hypertension (PAH). Adrenomedullin is a vasodilator peptide predominantly cleared by pulmonary endothelial receptors. We developed a linear adrenomedullin derivative radiolabeled with 99mTc (99mTc-AM-L) for imaging of pulmonary circulation and tested its capacity to detect anomalies of pulmonary circulation caused by PAH. Methods: PAH was induced by monocrotaline in rats and compared with controls. After 5 wk, 99mTc-AM-L was injected intravenously. Plasma kinetics were measured, lung activity was determined in vivo after 30 min using a nuclear camera, and lung activity was determined ex vivo in explanted lungs. Expression of adrenomedullin receptors was measured in lung homogenates. Results: The plasma levels of 99mTc-AM-L significantly increased in PAH by approximately 2-fold. Uptake by the lungs was homogeneous but greatly reduced in PAH by about 70%. In vivo retention was 14% ± 1% (mean ± SD) of the injected dose in controls and 4% ± 1% in PAH (P < 0.0001). A similar reduction was measured ex vivo (6.0 ± 1.6 percentage injected dose per gram [%ID/g] vs. 0.95 ± 0.21 %ID/g, P < 0.0001). The expression of the heterodimeric component of the adrenomedullin receptor, receptor activity modifying protein 2, was also greatly reduced in PAH lungs (P < 0.001). Interestingly, right ventricular uptake of 99mTc-AM-L was increased by PAH (P = 0.02) and correlated with the degree of right ventricular hypertrophy (r = 0.83, P = 0.001). Conclusion: Pulmonary uptake of 99mTc-AM-L is greatly reduced in monocrotaline-induced PAH. This novel molecular imaging agent may be useful in the diagnosis and follow-up of pulmonary vascular disorders.

PulmoBind, an Adrenomedullin-Based Molecular Lung Imaging Tool

Previous studies showed that adrenomedullin (AM) could be a promising agent for molecular imaging of the pulmonary circulation, with abundant specific binding sites at the pulmonary vascular endothelium. The purpose of this work was to design an AM-based compound that encompasses the desired imaging properties without posing safety issues for clinical applications. Methods: AM analogs were synthesized through solid-phase peptide synthesis. They were evaluated for 99mTc labeling efficiency and in vivo lung uptake. Biodistribution and hemodynamic characteristics of the lead compound were determined in anesthetized dogs as well as by a dosimetric analysis. Lung perfusion was evaluated in the monocrotaline model of pulmonary arterial hypertension in rats. Results: A cyclic AM (residues 22–52) analog encompassing a polyethylene glycol spacer and a tetrapeptide chelating moiety was found to possess the desired characteristics, with 90.7% ± 0.3% (mean ± SD) labeling efficiency, 40% lung uptake at 10 min after injection, and a favorable safety profile. Lung uptake of the 99mTc-labeled compound was markedly reduced in rats with pulmonary arterial hypertension. Conclusion: This lead compound could be a suitable clinical imaging agent for the molecular diagnosis of disorders of the pulmonary circulation.

Endothelial and Epithelial Cell Transition to a Mesenchymal Phenotype Was Delineated by Nestin Expression

Endothelial and epithelial cell transition to a mesenchymal phenotype was identified as cellular paradigms implicated in the appearance of fibroblasts and development of reactive fibrosis in interstitial lung disease. The intermediate filament protein nestin was highly expressed in fibrotic tissue, detected in fibroblasts and participated in proliferation and migration. The present study tested the hypothesis that the transition of endothelial and epithelial cells to a mesenchymal phenotype was delineated by nestin expression. Three weeks following hypobaric hypoxia, adult male Sprague‐Dawley rats characterized by alveolar and perivascular lung fibrosis were associated with increased nestin protein and mRNA levels and marked appearance of nestin/collagen type I(+)‐fibroblasts. In the perivascular region of hypobaric hypoxic rats, displaced CD31(+)‐endothelial cells were detected, exhibited a mesenchymal phenotype and co‐expressed nestin. Likewise, epithelial cells in the lungs of hypobaric hypoxic rats transitioned to a mesenchymal phenotype distinguished by the co‐expression of E‐cadherin and collagen. Following the removal of FBS from primary passage rat alveolar epithelial cells, TGF‐β1 was detected in the media and a subpopulation acquired a mesenchymal phenotype characterized by E‐cadherin downregulation and concomitant induction of collagen and nestin. Bone morphogenic protein‐7 treatment of alveolar epithelial cells prevented E‐cadherin downregulation, suppressed collagen induction but partially inhibited nestin expression. These data support the premise that the transition of endothelial and epithelial cells to a mesenchymal cell may have contributed in part to the appearance nestin/collagen type I(+)‐fibroblasts and the reactive fibrotic response in the lungs of hypobaric hypoxic rats. J. Cell. Physiol. 231: 1601–1610, 2016.