BackgroundExposure to traffic-derived particulate matter (PM), such as diesel exhaust particles (DEP), is a leading environmental cause of cardiovascular disease (CVD), and may contribute to endothelial dysfunction and development of atherosclerosis. It is still debated how DEP and other inhaled PM can contribute to CVD. However, organic chemicals (OC) adhered to the particle surface, are considered central to many of the biological effects. In the present study, we have explored the ability of OC from DEP to reach the endothelium and trigger pro-inflammatory reactions, a central step on the path to atherosclerosis.ResultsExposure-relevant concentrations of DEP (0.12 μg/cm2) applied on the epithelial side of an alveolar 3D tri-culture, rapidly induced pro-inflammatory and aryl hydrocarbon receptor (AhR)-regulated genes in the basolateral endothelial cells. These effects seem to be due to soluble lipophilic constituents rather than particle translocation. Extractable organic material of DEP (DEP-EOM) was next fractionated with increasing polarity, chemically characterized, and examined for direct effects on pro-inflammatory and AhR-regulated genes in human microvascular endothelial (HMEC-1) cells and primary human endothelial cells (PHEC) from four healthy donors. Exposure-relevant concentrations of lipophilic DEP-EOM (0.15 μg/cm2) induced low to moderate increases in IL-1α, IL-1β, COX2 and MMP-1 gene expression, and the MMP-1 secretion was increased. By contrast, the more polar EOM had negligible effects, even at higher concentrations. Use of pharmacological inhibitors indicated that AhR and protease-activated receptor-2 (PAR-2) were central in regulation of EOM-induced gene expression. Some effects also seemed to be attributed to redox-responses, at least at the highest exposure concentrations tested. Although the most lipophilic EOM, that contained the majority of PAHs and aliphatics, had the clearest low-concentration effects, there was no straight-forward link between chemical composition and biological effects.ConclusionLipophilic and semi-lipophilic chemicals seemed to detach from DEP, translocate through alveolar epithelial cells and trigger pro-inflammatory reactions in endothelial cells at exposure-relevant concentrations. These effects appeared to be triggered by AhR agonists, and involve PAR-2 signaling.Electronic supplementary materialThe online version of this article (10.1186/s12989-018-0257-1) contains supplementary material, which is available to authorized users.

Exposure to diesel exhaust particles (DEPs) affects endothelial function and may contribute to the development of atherosclerosis and vasomotor dysfunction. As intracellular calcium concentration [Ca2+]i is considered important in myoendothelial signalling, we explored the effects of extractable organic matter from DEPs (DEP-EOM) on [Ca2+]i and membrane microstructure in endothelial cells. DEP-EOM of increasing polarity was obtained by pressurized sequential extraction of DEPs with n-hexane (n-Hex-EOM), dichloromethane (DCM-EOM), methanol, and water. Chemical analysis revealed that the majority of organic matter was extracted by the n-Hex- and DCM-EOM, with polycyclic aromatic hydrocarbons primarily occurring in n-Hex-EOM. The concentration of calcium was measured in human microvascular endothelial cells (HMEC-1) using micro-spectrofluorometry. The lipophilic n-Hex-EOM and DCM-EOM, but not the more polar methanol- and water-soluble extracts, induced rapid [Ca2+]i increases in HMEC-1. n-Hex-EOM triggered [Ca2+]i increase from intracellular stores, followed by extracellular calcium influx consistent with store operated calcium entry (SOCE). By contrast, the less lipophilic DCM-EOM triggered [Ca2+]i increase via extracellular influx alone, resembling receptor operated calcium entry (ROCE). Both extracts increased [Ca2+]i via aryl hydrocarbon receptor (AhR) non-genomic signalling, verified by pharmacological inhibition and RNA-interference. Moreover, DCM-EOM appeared to induce an AhR-dependent reduction in the global plasma membrane order, as visualized by confocal fluorescence microscopy. DCM-EOM-triggered [Ca2+]i increase and membrane alterations were attenuated by the membrane stabilizing lipid cholesterol. In conclusion, lipophilic constituents of DEPs extracted by n-hexane and DCM seem to induce rapid AhR-dependent [Ca2+]i increase in HMEC-1 endothelial cells, possibly involving both ROCE and SOCE-mediated mechanisms. The semi-lipophilic fraction extracted by DCM also caused an AhR-dependent reduction in global membrane order, which appeared to be connected to the [Ca2+]i increase.

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Aromatic and aliphatic hydrocarbons were analyzed in extracts from 105 rock core samples collected from 16 wells across the Bakken Petroleum System in the Williston Basin, North Dakota (USA). Crude oil hydrocarbons recovered from the Upper (UBS) and Lower (LBS) Bakken shale source rocks had consistently higher proportions of aromatic hydrocarbons compared to aliphatic hydrocarbons than were found in the adjacent Middle Bakken (MB) and Three Forks (TF) target drilling zones. The higher aromatic/aliphatic (Ar/Al) ratios in the UBS and LBS source zones as compared to the adjacent MB and TF producing zones and the near molecular-sized nanometer pore throats in the UBS and LBS rocks suggest that primary migration of the aromatic hydrocarbons out of the source shale pores was (and still is) inhibited by the rounded, flat, and rigid "turtle" shape of the aromatic hydrocarbons significantly more than by the linear and flexible "snake" shape of the aliphatic hydrocarbons. Additional evidence for inhibited primary migration of aromatics versus aliphatics based on molecular shape was shown in laboratory experiments by comparing their recovery rates from the "as-received" UBS, LBS, and MB rock core samples from three wells using supercritical CO 2 and supercritical ethane under reservoir conditions of 34.5 MPa and 110 °C. CO 2 and ethane gave similar aromatic hydrocarbon recovery rates with all the rock samples regardless of whether recoveries from the individual rocks were slow or fast. Since CO 2 as a solvent can better disrupt polar interactions between aromatics and the shale organic matrix than ethane, the similarity in recovery rates comparing CO 2 and ethane indicates that sorption of the aromatics to the source shale organic matrix was not the primary reason for their inhibited migration. However, the recovery of aromatics as compared to the same-sized aliphatics (same carbon number) was much more inhibited from the UBS and LBS samples than from the MB samples, results which provide further evidence that shapeselective filtration during primary migration out of the source shale nanopores is the dominant mechanism for lower Ar/Al ratios in the oil-producing MB and TF zones than in the source UBS and LBS zones.

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