Tyler Beebe

Ultrafine particles from diesel engines induce vascular oxidative stress via JNK activation

Exposure to particulate air pollution is linked to increased incidences of cardiovascular diseases. Ambient ultrafine particles (UFP) from diesel vehicle engines have been shown to be proatherogenic in ApoE knockout mice and may constitute a major cardiovascular risk in humans. We posited that circulating nano-sized particles from traffic pollution sources induce vascular oxidative stress via JNK activation in endothelial cells. Diesel UFP were collected from a 1998 Kenworth truck. Intracellular superoxide assay revealed that these UFP dose-dependently induced superoxide (O(2)(-)) production in human aortic endothelial cells (HAEC). Flow cytometry showed that UFP increased MitoSOX red intensity specific for mitochondrial superoxide. Protein carbonyl content was increased by UFP as an indication of vascular oxidative stress. UFP also up-regulated heme oxygenase-1 (HO-1) and tissue factor (TF) mRNA expression, and pretreatment with the antioxidant N-acetylcysteine significantly decreased their expression. Furthermore, UFP transiently activated JNK in HAEC. Treatment with the JNK inhibitor SP600125 and silencing of both JNK1 and JNK2 with siRNA inhibited UFP-stimulated O(2)(-) production and mRNA expression of HO-1 and TF. Our findings suggest that JNK activation plays an important role in UFP-induced oxidative stress and stress response gene expression.

Effect of exposure to atmospheric ultrafine particles on production of free fatty acids and lipid metabolites in the mouse small intestine.

Background: Exposure to ambient ultrafine particulate matter (UFP) is a well-recognized risk factor for cardiovascular and respiratory diseases. However, little is known about the effects of air pollution on gastrointestinal disorders. Objective: We sought to assess whether exposure to ambient UFP (diameter < 180 nm) increased free fatty acids and lipid metabolites in the mouse small intestine. Methods: Ldlr-null mice were exposed to filtered air (FA) or UFP collected at an urban Los Angeles, California, site that was heavily affected by vehicular emissions; the exposure was carried out for 10 weeks in the presence or absence of D-4F, an apolipoprotein A-I mimetic peptide with antioxidant and anti-inflammation properties on a high-fat or normal chow diet. Results: Compared with FA, exposure to UFP significantly increased intestinal hydroxyeicosatetraenoic acids (HETEs), including 15-HETE, 12-HETE, 5-HETE, as well as hydroxyoctadecadienoic acids (HODEs), including 13-HODE and 9-HODE. Arachidonic acid (AA) and prostaglandin D2 (PGD2) as well as some of the lysophosphatidic acids (LPA) in the small intestine were also increased in response to UFP exposure. Administration of D-4F significantly reduced UFP-mediated increase in HETEs, HODEs, AA, PGD2, and LPA. Although exposure to UFP further led to shortened villus length accompanied by prominent macrophage and neutrophil infiltration into the intestinal villi, administration of D-4F mitigated macrophage infiltration. Conclusions: Exposure to UFP promotes lipid metabolism, villus shortening, and inflammatory responses in mouse small intestine, whereas administration of D-4F attenuated these effects. Our findings provide a basis to further assess the mechanisms underlying UFP-mediated lipid metabolism in the digestive system with clinical relevance to gut homeostasis and diseases. Citation: Li R, Navab K, Hough G, Daher N, Zhang M, Mittelstein D, Lee K, Pakbin P, Saffari A, Bhetraratana M, Sulaiman D, Beebe T, Wu L, Jen N, Wine E, Tseng CH, Araujo JA, Fogelman A, Sioutas C, Navab M, Hsiai TK. 2015. Effect of exposure to atmospheric ultrafine particles on production of free fatty acids and lipid metabolites in the mouse small intestine. Environ Health Perspect 123:34–41; http://dx.doi.org/10.1289/ehp.1307036

Moving Domain Computational Fluid Dynamics to Interface with an Embryonic Model of Cardiac Morphogenesis

Peristaltic contraction of the embryonic heart tube produces time- and spatial-varying wall shear stress (WSS) and pressure gradients (∇P) across the atrioventricular (AV) canal. Zebrafish (Danio rerio) are a genetically tractable system to investigate cardiac morphogenesis. The use of Tg(fli1a:EGFP)y1 transgenic embryos allowed for delineation and two-dimensional reconstruction of the endocardium. This time-varying wall motion was then prescribed in a two-dimensional moving domain computational fluid dynamics (CFD) model, providing new insights into spatial and temporal variations in WSS and ∇P during cardiac development. The CFD simulations were validated with particle image velocimetry (PIV) across the atrioventricular (AV) canal, revealing an increase in both velocities and heart rates, but a decrease in the duration of atrial systole from early to later stages. At 20-30 hours post fertilization (hpf), simulation results revealed bidirectional WSS across the AV canal in the heart tube in response to peristaltic motion of the wall. At 40-50 hpf, the tube structure undergoes cardiac looping, accompanied by a nearly 3-fold increase in WSS magnitude. At 110-120 hpf, distinct AV valve, atrium, ventricle, and bulbus arteriosus form, accompanied by incremental increases in both WSS magnitude and ∇P, but a decrease in bi-directional flow. Laminar flow develops across the AV canal at 20-30 hpf, and persists at 110-120 hpf. Reynolds numbers at the AV canal increase from 0.07±0.03 at 20-30 hpf to 0.23±0.07 at 110-120 hpf (p< 0.05, n=6), whereas Womersley numbers remain relatively unchanged from 0.11 to 0.13. Our moving domain simulations highlights hemodynamic changes in relation to cardiac morphogenesis; thereby, providing a 2-D quantitative approach to complement imaging analysis.

Pulsatile shear stress increased mitochondrial membrane potential: Implication of Mn-SOD

Mitochondrial dysfunction is intimately involved in cardiovascular diseases. Mitochondrial membrane potential (DeltaPsi(m)) is coupled with oxidative phosphorylation to drive ATP synthesis. In this study, we examined the effect of physiological pulsatile shear stress (PSS) on DeltaPsi(m) and the role of Mn-SOD expression on DeltaPsi(m). Confluent human aortic endothelial cells (HAEC) were exposed to PSS, and DeltaPsi(m) was monitored using tetramethylrhodamine methyl ester (TMRM(+)), a mitochondrial membrane potential probe. PSS significantly increased DeltaPsi(m) and the change in DeltaPsi(m) was a dynamic process. DeltaPsi(m) returned to baseline level after PSS for 2h followed by static state for 4h. Mitochondrial Mn-SOD expression and activities were also significantly up-regulated in response to PSS. Silencing Mn-SOD attenuated PSS-mediated DeltaPsi(m) increase while adding Mn-SOD mimetic, MnTMPyP, increased DeltaPsi(m) to the similar extent as induced by PSS. Our findings suggest that PSS-increased mitochondrial DeltaPsi(m), in part, via Mn-SOD up-regulation.

Shear Stress–Activated Wnt-Angiopoietin-2 Signaling Recapitulates Vascular Repair in Zebrafish Embryos

Objective— Fluid shear stress intimately regulates vasculogenesis and endothelial homeostasis. The canonical Wnt/&bgr;-catenin signaling pathways play an important role in differentiation and proliferation. In this study, we investigated whether shear stress activated angiopoietin-2 (Ang-2) via the canonical Wnt signaling pathway with an implication in vascular endothelial repair. Approach and Results— Oscillatory shear stress upregulated both TOPflash Wnt reporter activities and the expression of Ang-2 mRNA and protein in human aortic endothelial cells accompanied by an increase in nuclear &bgr;-catenin intensity. Oscillatory shear stress–induced Ang-2 and Axin-2 mRNA expression was downregulated in the presence of a Wnt inhibitor, IWR-1, but was upregulated in the presence of a Wnt agonist, LiCl. Ang-2 expression was further downregulated in response to a Wnt signaling inhibitor, DKK-1, but was upregulated by Wnt agonist Wnt3a. Both DKK-1 and Ang-2 siRNA inhibited endothelial cell migration and tube formation, which were rescued by human recombinant Ang-2. Both Ang-2 and Axin-2 mRNA downregulation was recapitulated in the heat-shock–inducible transgenic Tg(hsp70l:dkk1-GFP) zebrafish embryos at 72 hours post fertilization. Ang-2 morpholino injection of Tg (kdrl:GFP) fish impaired subintestinal vessel formation at 72 hours post fertilization, which was rescued by zebrafish Ang-2 mRNA coinjection. Inhibition of Wnt signaling with IWR-1 also downregulated Ang-2 and Axin-2 expression and impaired vascular repair after tail amputation, which was rescued by zebrafish Ang-2 mRNA injection. Conclusions— Shear stress activated Ang-2 via canonical Wnt signaling in vascular endothelial cells, and Wnt-Ang-2 signaling is recapitulated in zebrafish embryos with a translational implication in vascular development and repair.

Electrochemical impedance spectroscopy to characterize inflammatory atherosclerotic plaques

Despite advances in diagnosis and therapy, atherosclerotic cardiovascular disease remains the leading cause of morbidity and mortality in the Western world. Predicting metabolically active atherosclerotic lesions has remained an unmet clinical need. We hereby developed an electrochemical strategy to characterize the inflammatory states of high-risk atherosclerotic plaques. Using the concentric bipolar microelectrodes, we sought to demonstrate distinct Electrochemical Impedance Spectroscopic (EIS) measurements for unstable atherosclerotic plaques that harbored active lipids and inflammatory cells. Using equivalent circuits to simulate vessel impedance at the electrode-endoluminal tissue interface, we demonstrated specific electric elements to model working and counter electrode interfaces as well as the tissue impedance. Using explants of human coronary, carotid, and femoral arteries at various Stary stages of atherosclerotic lesions (n=15), we performed endoluminal EIS measurements (n=147) and validated with histology and immunohistochemistry. We computed the vascular tissue resistance using the equivalent circuit model and normalized the resistance to the lesion-free regions. Tissue resistance was significantly elevated in the oxLDL-rich thin-cap atheromas (1.57±0.40, n=14, p<0.001) and fatty streaks (1.36±0.28, n=33, p<0.001) as compared with lesion-free region (1.00±0.18, n=82) or oxLDL-absent fibrous atheromas (0.86±0.30, n=12). Tissue resistance was also elevated in the calcified core of fibrous atheroma (2.37±0.60, n=6, p<0.001). Despite presence of fibrous structures, tissue resistance between ox-LDL-absent fibroatheroma and the lesion-free regions was statistically insignificant (0.86±0.30, n=12, p>0.05). Hence, we demonstrate that the application of EIS strategy was sensitive to detect fibrous cap oxLDL-rich lesions and specific to distinguish oxLDL-absent fibroatheroma.

Stretchable electrochemical impedance sensors for intravascular detection of lipid-rich lesions in New Zealand White rabbits

Flexible electronics have enabled catheter-based intravascular sensing. However, real-time interrogation of unstable plaque remains an unmet clinical challenge. Here, we demonstrate the feasibility of stretchable electrochemical impedance spectroscopy (EIS) sensors for endoluminal investigations in New Zealand White (NZW) rabbits on diet-induced hyperlipidemia. A parylene C (PAC)-based EIS sensor mounted on the surface of an inflatable silicone balloon affixed to the tip of an interrogating catheter was deployed (1) on the explants of NZW rabbit aorta for detection of lipid-rich atherosclerotic lesions, and (2) on live animals for demonstration of balloon inflation and EIS measurements. An input peak-to-peak AC voltage of 10 mV and sweeping-frequency from 300 kHz to 100 Hz were delivered to the endoluminal sites. Balloon inflation allowed EIS sensors to be in contact with endoluminal surface. In the oxidized low-density-lipoprotein (oxLDL)-rich lesions from explants of fat-fed rabbits, impedance magnitude increased significantly by 1.5-fold across the entire frequency band, and phase shifted ~5° at frequencies below 10 kHz. In the lesion-free sites of the normal diet-fed rabbits, impedance magnitude increased by 1.2-fold and phase shifted ~5° at frequencies above 30 kHz. Thus, we demonstrate the feasibility of stretchable intravascular EIS sensors for identification of lipid rich lesions, with a translational implication for detecting unstable lesions.

Angiopoeitin-2 modulates Survivin expression in OxLDL-induced endothelial cell apoptosis

Angiopoeitin-2 (Ang-2) antagonizes Angiopeitin-1 (Ang-1)-mediated Tie-2 signaling. Ang-1 is reported to up-regulate anti-apoptotic Survivin expression. Here, we investigated the interplay between Ang-2 and Survivin in response to oxidized low density lipoprotein (OxLDL)-induced apoptosis. We demonstrate that treatment of human aortic endothelial cells (HAEC) with 100 μg/ml of OxLDL down-regulated Ang-2 expression as early as 4h after treatment and persisted up to 24h (p<0.05, n=3), but did not down-regulate Survivin until the 24h point. Further, treatment of HAEC with recombinant Ang-2 up-regulated Survivin expression (at Ang-2 ≥200 ng/ml, p<0.05, n=3) and attenuated the OxLDL-mediated down-regulation of Survivin (p<0.05, n=3). Knockdown of Ang-2 further down-regulated Survivin expression, whereas over-expression of Survivin attenuated OxLDL-induced HAEC apoptosis (p<0.05, n=3). Hence, Ang-2 mediated Survivin expression in response to OxLDL-induced endothelial apoptosis.

Flexible and Waterproof Micro-Sensors to Uncover Zebrafish Circadian Rhythms: The Next Generation of Cardiac Monitoring for Drug Screening

Flexible electronics are the next generation of sensors for mobile health and implantation. Zebrafish (Danio rerio) is an emergent strategy for pre-clinical drug development and toxicity testing. To address the confounding effects from sedation of fish and removal from the aquatic habitat for micro-electrocardiogram (µECG) measurements, we developed waterproof and wearable sensors to uncover the circadian variation in heart rate (HR) and heart rate variability (HRV) (Massin et al., 2000). The parylene-C based ECG sensor consisted of an ultra-soft silicone integrated jacket designed to wrap around the fish during swimming. The Youngs modulus of this silicone jacket matched with the fish surface, and an extended parylene cable connected the underwater chest electrodes with the out-of water electronics. In addition, embedded micro-glass spheres in the silicone effectively reduced the effective density of the jacket to ~1 g cm(-3). These innovations enabled physiological ECG telemetry in the fishs natural habitat without the need for sedation. Furthermore, a set of non-linear signal processing techniques filtered out the breathing and electromagnetic artifacts from the recorded signals. We observed a reduction in mean HR and an increase in HRV over 24h at 10 dpa, accompanied by QT prolongation as well as diurnal variations, followed by normalization in mean HR and QT intervals at 26 days post ventricular amputation (dpa). We revealed Amiodarone-mediated QTc prolongation, HR reduction and HRV increase otherwise masked by sedation. The novel features of the flexible silicon jacket for µECG telemetry unraveled the biological clock and normalization of QT intervals at 26 dpa, providing the first evidence of new physiological phenomena during cardiac injury and repair as well as cardiac drug-mediated aberrant rhythms. Thus, the light weight and waterproof design holds promise to advance the next generation of mobile health and drug discovery.

Automated Segmentation of Light-Sheet Fluorescent Imaging to Characterize Experimental Doxorubicin-Induced Cardiac Injury and Repair.

This study sought to develop an automated segmentation approach based on histogram analysis of raw axial images acquired by light-sheet fluorescent imaging (LSFI) to establish rapid reconstruction of the 3-D zebrafish cardiac architecture in response to doxorubicin-induced injury and repair. Input images underwent a 4-step automated image segmentation process consisting of stationary noise removal, histogram equalization, adaptive thresholding, and image fusion followed by 3-D reconstruction. We applied this method to 3-month old zebrafish injected intraperitoneally with doxorubicin followed by LSFI at 3, 30, and 60 days post-injection. We observed an initial decrease in myocardial and endocardial cavity volumes at day 3, followed by ventricular remodeling at day 30, and recovery at day 60 (P < 0.05, n = 7–19). Doxorubicin-injected fish developed ventricular diastolic dysfunction and worsening global cardiac function evidenced by elevated E/A ratios and myocardial performance indexes quantified by pulsed-wave Doppler ultrasound at day 30, followed by normalization at day 60 (P < 0.05, n = 9–20). Treatment with the γ-secretase inhibitor, DAPT, to inhibit cleavage and release of Notch Intracellular Domain (NICD) blocked cardiac architectural regeneration and restoration of ventricular function at day 60 (P < 0.05, n = 6–14). Our approach provides a high-throughput model with translational implications for drug discovery and genetic modifiers of chemotherapy-induced cardiomyopathy.