Strategies for Site-Specific Radiolabeling of Peptides and Proteins

Although anatomical imaging modalities (X-ray, computed tomography (CT), magnetic resonance imaging (MRI)) still have a higher spatial resolution (0.1–1 mm) than molecular imaging modalities (single-photon emission computed tomography (SPECT), positron emission tomography (PET), optical imaging (OI)), the advantage of molecular imaging is that it can detect molecular and cellular changes at the onset of a disease before it leads to morphological tissue changes, which can be detected by anatomical imaging. During the last decades, noninvasive diagnostic imaging has encountered a rapid growth due to the development of dedicated imaging equipment for preclinical animal studies. In addition, the introduction of multimodality imaging (PET/CT, SPECT/CT, PET/MRI) which combines high-resolution conventional anatomical imaging with high sensitivity of tracer-based molecular imaging techniques has led to successful accomplishments in this exciting field. In this book chapter, we will focus on chemical synthesis techniques for site-specific incorporation of radionuclide chelators. Subsequently, radiolabeling based on complexation of a radionuclide with a chelator will be discussed, with focus on: diethylenetriaminepentaacetic acid (DTPA), 1,4,7,10-tetraazacyclododecane-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-triacetic acid (NOTA), hexa-histidine (His-tag), and 6-hydrazinonicotinic acid (HYNIC) that allow the production of peptides labeled with 18F, 68Ga, 99mTc, and 111In – the currently most widely used isotopes

Reduced Vitamin K Status as a Potentially Modifiable Risk Factor of Severe Coronavirus Disease 2019

BACKGROUND: Respiratory failure and thromboembolism are frequent in SARS-CoV-2-infected patients. Vitamin K activates both hepatic coagulation factors and extrahepatic endothelial anticoagulant protein S, required for thrombosis prevention. In times of vitamin K insufficiency, hepatic procoagulant factors are preferentially activated over extrahepatic proteins. Vitamin K also activates matrix Gla protein (MGP), which protects against pulmonary and vascular elastic fiber damage. We hypothesized that vitamin K may be implicated in coronavirus disease 2019 (COVID-19), linking pulmonary and thromboembolic disease. METHODS: 135 hospitalized COVID-19 patients were compared with 184 historical controls. Poor outcome was defined as invasive ventilation and/or death. Inactive vitamin K-dependent MGP (dp-ucMGP) and prothrombin (PIVKA-II) were measured, inversely related to extrahepatic and hepatic vitamin K status, respectively. Desmosine was measured to quantify the rate of elastic fiber degradation. Arterial calcification severity was assessed by computed tomography. RESULTS: Dp-ucMGP was elevated in COVID-19 patients compared to controls (p<0.001), with even higher dp-ucMGP in patients with poor outcomes (p<0.001). PIVKA-II was normal in 82.1% of patients. Dp-ucMGP was correlated with desmosine (p<0.001), and coronary artery (p=0.002) and thoracic aortic (p<0.001) calcification scores. CONCLUSIONS: Dp-ucMGP was severely increased in COVID-19 patients, indicating extrahepatic vitamin K insufficiency, which was related to poor outcome while hepatic procoagulant factor II remained unaffected. These data suggest a mechanism of pneumonia-induced extrahepatic vitamin K depletion leading to accelerated elastic fiber damage and thrombosis in severe COVID-19 due to impaired activation of MGP and endothelial protein S, respectively. A clinical trial could assess whether vitamin K administration improves COVID-19 outcomes

Genetic and Pharmacological Modifications of Thrombin Formation in Apolipoprotein E-deficient Mice Determine Atherosclerosis Severity and Atherothrombosis Onset in a Neutrophil-Dependent Manner

Background: Variations in the blood coagulation activity, determined genetically or by medication, may alter atherosclerotic plaque progression, by influencing pleiotropic effects of coagulation proteases. Published experimental studies have yielded contradictory findings on the role of hypercoagulability in atherogenesis. We therefore sought to address this matter by extensively investigating the in vivo significance of genetic alterations and pharmacologic inhibition of thrombin formation for the onset and progression of atherosclerosis, and plaque phenotype determination. Methodology/principal findings: We generated transgenic atherosclerosis-prone mice with diminished coagulant or hypercoagulable phenotype and employed two distinct models of atherosclerosis. Gene-targeted 50% reduction in prothrombin $(FII^{−/WT}:ApoE^{−/−})$ was remarkably effective in limiting disease compared to control $ApoE^{−/−}$ mice, associated with significant qualitative benefits, including diminished leukocyte infiltration, altered collagen and vascular smooth muscle cell content. Genetically-imposed hypercoagulability in $TM^{Pro/Pro}:ApoE^{−/−}$ mice resulted in severe atherosclerosis, plaque vulnerability and spontaneous atherothrombosis. Hypercoagulability was associated with a pronounced neutrophilia, neutrophil hyper-reactivity, markedly increased oxidative stress, neutrophil intraplaque infiltration and apoptosis. Administration of either the synthetic specific thrombin inhibitor Dabigatran etexilate, or recombinant activated protein C (APC), counteracted the pro-inflammatory and pro-atherogenic phenotype of pro-thrombotic $TM^{Pro/Pro}:ApoE^{−/−}$ mice. Conclusions/significance: We provide new evidence highlighting the importance of neutrophils in the coagulation-inflammation interplay during atherogenesis. Our findings reveal that thrombin-mediated proteolysis is an unexpectedly powerful determinant of atherosclerosis in multiple distinct settings. These studies suggest that selective anticoagulants employed to prevent thrombotic events may also be remarkably effective in clinically impeding the onset and progression of cardiovascular disease

Chemokines and galectins form heterodimers to modulate inflammation

Chemokines and galectins are simultaneously upregulated and mediate leukocyte recruitment during inflammation. Until now, these effector molecules have been considered to function independently. Here, we tested the hypothesis that they form molecular hybrids. By systematically screening chemokines for their ability to bind galectin‐1 and galectin‐3, we identified several interacting pairs, such as CXCL12 and galectin‐3. Based on NMR and MD studies of the CXCL12/galectin‐3 heterodimer, we identified contact sites between CXCL12 β‐strand 1 and Gal‐3 F‐face residues. Mutagenesis of galectin‐3 residues involved in heterodimer formation resulted in reduced binding to CXCL12, enabling testing of functional activity comparatively. Galectin‐3, but not its mutants, inhibited CXCL12‐induced chemotaxis of leukocytes and their recruitment into the mouse peritoneum. Moreover, galectin‐3 attenuated CXCL12‐stimulated signaling via its receptor CXCR4 in a ternary complex with the chemokine and receptor, consistent with our structural model. This first report of heterodimerization between chemokines and galectins reveals a new type of interaction between inflammatory mediators that can underlie a novel immunoregulatory mechanism in inflammation. Thus, further exploration of the chemokine/galectin interactome is warranted

Vascular CXCR4 Limits Atherosclerosis by Maintaining Arterial Integrity Evidence From Mouse and Human Studies

BACKGROUND: The CXCL12/CXCR4 chemokine ligand/receptor axis controls (progenitor) cell homeostasis and trafficking. So far, an atheroprotective role of CXCL12/CXCR4 has only been implied through pharmacological intervention, in particular, because the somatic deletion of the CXCR4 gene in mice is embryonically lethal. Moreover, cell-specific effects of CXCR4 in the arterial wall and underlying mechanisms remain elusive, prompting us to investigate the relevance of CXCR4 in vascular cell types for atheroprotection. METHODS: We examined the role of vascular CXCR4 in atherosclerosis and plaque composition by inducing an endothelial cell (BmxCreERT2-driven)-specific or smooth muscle cell (SMC, SmmhcCreERT2-or TaglnCre-driven)-specific deficiency of CXCR4 in an apolipoprotein E-deficient mouse model. To identify underlying mechanisms for effects of CXCR4, we studied endothelial permeability, intravital leukocyte adhesion, involvement of the Akt/WNT/beta-catenin signaling pathway and relevant phosphatases in VE-cadherin expression and function, vascular tone in aortic rings, cholesterol efflux from macrophages, and expression of SMC phenotypic markers. Finally, we analyzed associations of common genetic variants at the CXCR4 locus with the risk for coronary heart disease, along with CXCR4 transcript expression in human atherosclerotic plaques. RESULTS: The cell-specific deletion of CXCR4 in arterial endothelial cells (n=1215) or SMCs (n=13-24) markedly increased atherosclerotic lesion formation in hyperlipidemic mice. Endothelial barrier function was promoted by CXCL12/\CXCR4, which triggered Akt/WNT/beta-catenin signaling to drive VE-cadherin expression and stabilized junctional VE-cadherin complexes through associated phosphatases. Conversely, endothelial CXCR4 deficiency caused arterial leakage and inflammatory leukocyte recruitment during atherogenesis. In arterial SMCs, CXCR4 sustained normal vascular reactivity and contractile responses, whereas CXCR4 deficiency favored a synthetic phenotype, the occurrence of macrophage-like SMCs in the lesions, and impaired cholesterol efflux. Regression analyses in humans (n=259 796) identified the C-allele at rs2322864 within the CXCR4 locus to be associated with increased risk for coronary heart disease. In line, C/C risk genotype carriers showed reduced CXCR4 expression in carotid artery plaques (n=188), which was furthermore associated with symptomatic disease. CONCLUSIONS: Our data clearly establish that vascular CXCR4 limits atherosclerosis by maintaining arterial integrity, preserving endothelial barrier function, and a normal contractile SMC phenotype. Enhancing these beneficial functions of arterial CXCR4 by selective modulators might open novel therapeutic options in atherosclerosis

Vibrational-rotational structure of the silane molecule in the band of v2+v4 (F2)

In recent years, extensive theoretical studies have been carried out on the silane molecule, namely their vibrational-rotational structure. In this work, we continue our research series and focus on the 28SiD4 isotopologue. The IR-spectrum of the silane molecule was recorded in the range 1250-1450 cm-1 (pentad region) on Bruker IFS 120HR Fourier interferometer. The P, Q, and R branches with Jmax up to 17 were assigned, and spectroscopic constants of the v2+v4 (F2) band were derived for 28SiD4. As a result, a set of spectroscopic parameters was obtained which describe the vibrational-rotational structure of the silane molecule close to the experimental uncertainties

Stimuli of Sensory-Motor Nerves Terminate Arterial Contractile Effects of Endothelin-1 by CGRP and Dissociation of ET-1/ETA-Receptor Complexes

Endothelin-1 (ET-1), a long-acting paracrine mediator, is implicated in cardiovascular diseases but clinical trials with ET-receptor antagonists were not successful in some areas. We tested whether the quasi-irreversible receptor-binding of ET-1 (i) limits reversing effects of the antagonists and (ii) can be selectively dissociated by an endogenous counterbalancing mechanism.-receptor complexes.-receptors by ET-1 (i) occur at an antagonist-insensitive site of the receptor and (ii) are selectively terminated by endogenously released CGRP. Hence, natural stimuli of sensory-motor nerves that stimulate release of endogenous CGRP can be considered for therapy of diseases involving ET-1

TFPI-dependent activities of Protein S

Protein S is an essential anticoagulant protein that acts as a cofactor for full length tissue factor pathway inhibitor (TFPI) and activated protein C (APC) in the down regulation of coagulation. Protein S enhances APC-mediated inactivation of the coagulation factors Va and VIIIa, and it stimulates inhibition of factor (F) Xa by TFPI. Because TFPI is a tight binding, but slow inhibitor of FXa, the TFPI/protein S system fails to regulate FXa generation at high tissue factor/FVIIa concentrations. In this review, we explain how TFPI/protein S can regain its activity at high tissue factor concentrations in the presence of APC, resulting in an intertwinement of TFPI- and APC-cofactor activities of protein S, and making TFPI a major determinant of APC-anticoagulant activity in plasma