Contribution of isoprene-derived organosulfates to free tropospheric aerosol mass

Recent laboratory studies have demonstrated that isoprene oxidation products can partition to atmospheric aerosols by reacting with condensed phase sulfuric acid, forming low-volatility organosulfate compounds. We have identified organosulfate compounds in free tropospheric aerosols by single particle mass spectrometry during several airborne field campaigns. One of these organosulfates is identified as the sulfate ester of IEPOX, a second generation oxidation product of isoprene. The patterns of IEPOX sulfate ester in ambient data generally followed the aerosol acidity and NOx dependence established by laboratory studies. Detection of the IEPOX sulfate ester was most sensitive using reduced ionization laser power, when it was observed in up to 80% of particles in the tropical free troposphere. Based on laboratory mass calibrations, IEPOX added > 0.4% to tropospheric aerosol mass in the remote tropics and up to 20% in regions downwind of isoprene sources. In the southeastern United States, when acidic aerosol was exposed to fresh isoprene emissions, accumulation of IEPOX increased aerosol mass by up to 3%. The IEPOX sulfate ester is therefore one of the most abundant single organic compounds measured in atmospheric aerosol. Our data show that acidity-dependent IEPOX uptake is a mechanism by which anthropogenic SO2 and marine dimethyl sulfide emissions generate secondary biogenic aerosol mass throughout the troposphere

Reactive intermediates revealed in secondary organic aerosol formation from isoprene

Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX = β-IEPOX + δ-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low- and high-NO_x conditions, respectively. Isoprene low-NO_x SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NO_x conditions, isoprene SOA formation occurs through oxidation of its second-generation product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NO_x SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO_2 and NO_2, respectively) could be a substantial source of “missing urban SOA” not included in current atmospheric models

Endothelial and cardiomyocyte PI3Kβ divergently regulate cardiac remodelling in response to ischaemic injury

AIMS: Cardiac remodeling in the ischemic heart determines prognosis in patients with ischemic heart disease (IHD), while enhancement of angiogenesis and cell survival has shown great potential for IHD despite translational challenges. Phosphoinositide 3-kinase (PI3K)/Akt signaling pathway plays a critical role in promoting angiogenesis and cell survival. However, the effect of PI3Kβ in the ischemic heart is poorly understood. This study investigates the role of endothelial and cardiomyocyte PI3Kβ in post-infarct cardiac remodeling. METHODS AND RESEARCH: PI3Kβ catalytic subunit-p110β level was increased in infarcted murine and human hearts. Using cell type-specific loss-of-function approaches, we reported novel and distinct actions of p110β in endothelial cells versus cardiomyocytes in response to myocardial ischemic injury. Inactivation of endothelial p110β resulted in marked resistance to infarction and adverse cardiac remodeling with decreased mortality, improved systolic function, preserved microvasculature, and enhanced Akt activation. Cultured endothelial cells with p110β knockout or inhibition displayed preferential PI3Kα/Akt/eNOS signaling that consequently promoted protective signaling and angiogenesis. In contrast, mice with cardiomyocyte p110β-deficiency exhibited adverse post-infarct ventricular remodeling with larger infarct size and deteriorated cardiac function, which was due to enhanced susceptibility of cardiomyocytes to ischemia-mediated cell death. Disruption of cardiomyocyte p110β signaling compromised nuclear p110β and phospho-Akt levels leading to perturbed gene expression and elevated pro-cell death protein levels, increasing the susceptibility to cardiomyocyte death. A similar divergent response of PI3Kβ endothelial and cardiomyocyte mutant mice was seen using a model of myocardial ischemia-reperfusion injury. CONCLUSIONS: These data demonstrate novel, differential, and cell-specific functions of PI3Kβ in the ischemic heart. While loss of endothelial PI3Kβ activity produces cardioprotective effects, cardiomyocyte PI3Kβ is protective against myocardial ischemic injury

The Construction of an X-Ray Diffraction Unit and the Analysis of the Characteristic Spectrum of Tungsten

The method of obtaining the x-ray spectrum of a substance by means of an oscillating crystal, originated with the Braggs in 1914. It is this principle that is employed in the operation of this unit. It is sincerely hoped that this x-ray diffraction unit will serve as a basis for later diffraction experiments

Abstract 333: MED13-dependent Regulation of Cardiac Thyroid Hormone Signaling

Thyroid hormone (TH) is a key regulator of cardiac metabolism. While hypothyroidism is known to result in adverse cardiac effects, the molecular mechanisms that modulate TH signaling are not completely understood. Mediator is a multiprotein complex that coordinates signal dependent transcription factors with basal transcriptional machinery. Mediator complex protein, MED13, was previously demonstrated to repress numerous thyroid receptor (TR) response genes in the heart. Furthermore, we have previously demonstrated that mice overexpressing cardiac MED13 (MED13cTg) treated with propylthiouracil (PTU), an inhibitor of T3 biosynthesis, were resistant to PTU-dependent decreases in cardiac contractility. Here we demonstrate that MED13 expression is induced in the hearts of mice in response to a PTU diet. To elucidate the role of MED13 in transcriptional regulation of cardiac TH signaling, cardiac-specific Med13 knockout mice (MED13cKO) and control mice were placed on a PTU diet or normal chow diet for 4 weeks. An additional group of mice on PTU diet were treated acutely with thyroid hormone (T3). While heart weight to body weight ratios did not differ between genotypes, RNA sequencing was performed from hearts of these mice to understand the role of MED13 in TR-dependent transcription. Echocardiography was performed to assess cardiac function in these mice. In addition, histology was performed to evaluate cardiac structure and fibrosis. These studies demonstrate that MED13 is induced in response to hypothyroidism and further deciphers molecular mechanisms of MED13 regulation of TR-dependent transcription.</jats:p

Assessing the potential for diol and hydroxy sulfate ester formation from the reaction of epoxides with tropospheric aerosols

Polyols and sulfate esters have recently been identified in the secondary organic aerosol (SOA) formed in the photooxidation of biogenic hydrocarbons both in the laboratory and under ambient atmospheric conditions. In the present study, the potential role of the reactions of epoxides in SOA to form diols and hydroxy sulfate esters is explored. Nuclear magnetic resonance methods were used to monitor the bulk reaction kinetics of the epoxide hydrolysis reactions for a number of simple epoxides. The experiments were carried out at various acid concentrations in order to confirm the acid-catalysis rate order and to determine the second-order rate constants for such reactions in aerosols under the previously studied laboratory conditions and under ambient atmospheric conditions. The measured rate constants depended systematically on the carbon substitution nature of the epoxide ring, with the tertiary epoxides characterized by the largest rate constants. The hydroxy sulfate yield was observed to depend linearly on the total sulfate concentration, with yields as high as 30% observed at high sulfate concentrations. Due to the large values of the observed rate constants, these reactions are expected to be efficient even for mostly neutralized tropospheric SOA, let alone the much more acidic SOA particles previously studied in laboratory experiments. Therefore, the epoxide hydrolysis mechanism appears to be a kinetically feasible route to the formation of the diols and hydroxy sulfate esters observed in the SOA resulting from the photooxidation of biogenic hydrocarbons

Kinetics of the reactions of isoprene-derived epoxides in model tropospheric aerosol solutions

Polyols and organic sulfates have recently been identified in the secondary organic aerosol (SOA) formed in the photooxidation of isoprene in both the laboratory and under ambient atmospheric conditions. Nuclear magnetic resonance methods were used to monitor the bulk reaction kinetics of acid-catalyzed hydrolysis reactions for isoprene- and 1,3-butadiene-derived epoxides in order to determine the rates for such reactions in aerosols under the previously studied laboratory conditions and under ambient atmospheric conditions. The measured rate constants were found to vary over 7 orders of magnitude. For the fast case of the hydrolysis of 1,2-epoxyisoprene, the lifetime at neutral pH was found to be only 3 min. On the other hand, for the relatively slow reaction of 1,2-epoxy-3,4-hydroxybutane, the lifetime at the most acidic conditions commonly observed in tropospheric aerosols (pH 1.5) was found to be 7.7 h, a value that is still less than the several day lifetime of tropospheric aerosols. Therefore, the present results suggest that, despite a wide range in reactivities, several possible reactions of isoprene-derived epoxides should be kinetically efficient on atmospheric SOA. The reactions were also studied with the elevated sulfate concentrations that are often characteristic of tropospheric aerosols, and sulfate products were identified for all species except 1,2-epoxyisoprene. Other nucleophiles that may be present in aerosols (nitrate, chloride, bromide, and iodide) were also investigated, and it was found that nitrate and sulfate have similar nucleophilic strength, while the halides are much stronger nucleophiles in their reactions with epoxides. Therefore, aerosols which contain significant concentrations of these species may be expected to readily form species similar to those already identified for the reactions of epoxides with sulfate