Modulation of antigen-induced responses by serotonin and prostaglandin E2 via EP1 and EP4 receptors in the peripheral rat lung

Differential Cytotoxicity and Inflammatory Responses to Particulate Matter Components in Airway Structural Cells

Particulate matter (PM) is a major component of ambient air pollution. PM exposure is linked to numerous adverse health effects, including chronic lung diseases. Air quality guidelines designed to regulate levels of ambient PM are currently based on the mass concentration of different particle sizes, independent of their origin and chemical composition. The objective of this study was to assess the relative hazardous effects of carbonaceous particles (soot), ammonium nitrate, ammonium sulfate, and copper oxide (CuO), which are standard components of ambient air, reflecting contributions from primary combustion, secondary inorganic constituents, and non-exhaust emissions (NEE) from vehicular traffic. Human epithelial cells representing bronchial (BEAS-2B) and alveolar locations (H441 and A549) in the airways, human lung fibroblasts (HFL-1), and rat precision-cut lung slices (PCLS) were exposed in submerged cultures to different concentrations of particles for 5-72 h. Following exposure, cell viability, metabolic activity, reactive oxygen species (ROS) formation, and inflammatory responses were analyzed. CuO and, to a lesser extent, soot reduced cell viability in a dose-dependent manner, increased ROS formation, and induced inflammatory responses. Ammonium nitrate and ammonium sulfate did not elicit any significant cytotoxic responses but induced immunomodulatory alterations at very high concentrations. Our findings demonstrate that secondary inorganic components of PM have a lower hazard cytotoxicity compared with combustion-derived and indicative NEE components, and alveolar epithelial cells are more sensitive to PM exposure. This information should help to inform which sources of PM to target and feed into improved, targeted air quality guidelines.

Precision cut lung slices: an integrated ex vivo model for studying lung physiology, pharmacology, disease pathogenesis and drug discovery

Precision Cut Lung Slices (PCLS) have emerged as a sophisticated and physiologically relevant ex vivo model for studying the intricacies of lung diseases, including fibrosis, injury, repair, and host defense mechanisms. This innovative methodology presents a unique opportunity to bridge the gap between traditional in vitro cell cultures and in vivo animal models, offering researchers a more accurate representation of the intricate microenvironment of the lung. PCLS require the precise sectioning of lung tissue to maintain its structural and functional integrity. These thin slices serve as invaluable tools for various research endeavors, particularly in the realm of airway diseases. By providing a controlled microenvironment, precision-cut lung slices empower researchers to dissect and comprehend the multifaceted interactions and responses within lung tissue, thereby advancing our understanding of pulmonary pathophysiology.

Anti-Inflammatory Effects of Serotonin Receptor and Transient Receptor Potential Channel Ligands in Human Small Intestinal Epithelial Cells

Intestinal inflammation and dysbiosis can lead to inflammatory bowel diseases (IBD) and systemic inflammation, affecting multiple organs. Developing novel anti-inflammatory therapeutics is crucial for preventing IBD progression. Serotonin receptor type 2A (5-HT2A) ligands, including psilocybin (Psi), 4-Acetoxy-N,N-dimethyltryptamine (4-AcO-DMT), and ketanserin (Ket), along with transient receptor potential (TRP) channel ligands like capsaicin (Cap), curcumin (Cur), and eugenol (Eug), show promise as anti-inflammatory agents. In this study, we investigated the cytotoxic and anti-inflammatory effects of Psi, 4-AcO-DMT, Ket, Cap, Cur, and Eug on human small intestinal epithelial cells (HSEIC). HSEIC were exposed to tumor necrosis factor (TNF)-α and interferon (IFN)-γ for 24 h to induce an inflammatory response, followed by treatment with each compound at varying doses (0-800 μM) for 24 to 96 h. The cytotoxicity was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and protein expression by Western blot (WB) analysis. As single treatments, Psi (40 μM), Cur (0.5 μM), and Eug (50 μM) significantly reduced COX-2 levels without cytotoxic effects. When combined, Psi (40 μM) and Cur (0.5 μM) exhibited synergy, resulting in a substantial decrease in COX-2 protein levels (-28× fold change), although the reduction in IL-6 was less pronounced (-1.6× fold change). Psi (20 μM) and Eug (25 μM) demonstrated the most favorable outcomes, with significant decreases in COX-2 (-19× fold change) and IL-6 (-10× fold change) protein levels. Moreover, the combination of Psi and Eug did not induce cytotoxic effects in vitro at any tested doses. This study is the first to explore the anti-inflammatory potential of psilocybin and 4-AcO-DMT in the intestines while highlighting the potential for synergy between the 5-HT2A and TRP channel ligands, specifically Psi and Eug, in alleviating the TNF-α/IFN-γ-induced inflammatory response in HSEIC. Further investigations should evaluate if the Psi and Eug combination has the therapeutic potential to treat IBD in vivo.

Uncovering the cytotoxic effects of air pollution with multi-modal imaging of in vitro respiratory models

Annually, an estimated seven million deaths are linked to exposure to airborne pollutants. Despite extensive epidemiological evidence supporting clear associations between poor air quality and a range of short- and long-term health effects, there are considerable gaps in our understanding of the specific mechanisms by which pollutant exposure induces adverse biological responses at the cellular and tissue levels. The development of more complex, predictive, in vitro respiratory models, including two- and three-dimensional cell cultures, spheroids, organoids and tissue cultures, along with more realistic aerosol exposure systems, offers new opportunities to investigate the cytotoxic effects of airborne particulates under controlled laboratory conditions. Parallel advances in high-resolution microscopy have resulted in a range of in vitro imaging tools capable of visualizing and analysing biological systems across unprecedented scales of length, time and complexity. This article considers state-of-the-art in vitro respiratory models and aerosol exposure systems and how they can be interrogated using high-resolution microscopy techniques to investigate cell-pollutant interactions, from the uptake and trafficking of particles to structural and functional modification of subcellular organelles and cells. These data can provide a mechanistic basis from which to advance our understanding of the health effects of airborne particulate pollution and develop improved mitigation measures.

A tunable physiomimetic stretch system evaluated with precision cut lung slices and recellularized human lung scaffolds

Breathing exposes lung cells to continual mechanical stimuli, which is part of the microenvironmental signals directing cellular functions together with the extracellular matrix (ECM). Therefore, developing systems that incorporate both stimuli is urgent to fully understand cell behavior. This study aims to introduce a novel in vitro culture methodology combining a cyclic stretch that simulates in vivo breathing with 3D cell culture platforms in the form of decellularized lung slices (DLS) and precision cut lung slices (PCLS). To this end, we have constructed a device that mimics the amplitudes and frequencies of distensions seen in the breathing human lung. For its validation, we cultured H441 lung epithelial cells in human DLS exposed to 16 stretch cycles per minute with a 10% stretch amplitude. Cell viability (resazurin reduction), proliferation (Ki-67) and YAP1 activation were evaluated at 24 and 96 h by immunohistochemistry, while the expression of SFTPB, COL3A1, COL4A3 and LAMA5 was evaluated by qPCR. Cyclic stretch induced an increase in SFTPB expression after 24 h without a concomitant increase in the stretch responsive gene YAP1. Moreover, the ECM milieu lowered the expression of the basement membrane protein genes COL4A3 and LAMA5 compared to tissue culture plastic control cultures, but no effect was observed by the mechanical stimuli. The device also confirmed good compatibility with PCLS culture, showing preserved morphology and metabolism in rat PCLS after 72 h of mechanical stretch. Thus, we present a novel device and methodology for the easy assembling and study of lung tissue slice cultures subjected to physiomimetic mechanical stimuli, which shows promise for future studies of cell and tissue function in a lung ECM milieu with physiological or pathological mechanical stimuli.

Pathological Insight into 5-HT2B Receptor Activation in Fibrosing Interstitial Lung Diseases

Interstitial lung disease (ILD) encompasses a heterogeneous group of more than 200 conditions, of which primarily idiopathic pulmonary fibrosis (IPF), idiopathic nonspecific interstitial pneumonia, hypersensitivity pneumonitis, ILD associated with autoimmune diseases and sarcoidosis may present a progressive fibrosing (PF) phenotype. Despite different aetiology and histopathological patterns, the PF-ILDs have similarities regarding disease mechanisms with self-sustaining fibrosis, which suggests that the diseases may share common pathogenetic pathways. Previous studies show an enhanced activation of serotonergic signaling in pulmonary fibrosis, and the serotonin (5-HT)₂ receptors have been implicated to have important roles in observed profibrotic actions. Our research findings in support by others, demonstrate antifibrotic effects with 5-HT_2B receptor antagonists, alleviating several key events common for the fibrotic diseases such as myofibroblast differentiation and connective tissue deposition. In this review, we will address the potential role of 5-HT and in particular the 5-HT_2B receptors in three PF-ILDs: ILD associated with systemic sclerosis (SSc-ILD), ILD associated with rheumatoid arthritis (RA-ILD) and IPF. Highlighting the converging pathways in these diseases discloses the 5-HT_2B receptor as a potential disease target for PF-ILDs, which today have an urgent unmet need for therapeutic strategies.

Effects of 5-Hydroxytryptamine Class 2 Receptor Antagonists on Bronchoconstriction and Pulmonary Remodeling Processes

Serotonin [5-hydroxytryptamine (5-HT)] is associated with several chronic pulmonary diseases, recognizing 5-HT₂ receptor antagonists as potential inhibitors of tissue remodeling. However, the effects of 5-HT₂ receptors, especially 5-HT_2B receptors on airway function and remodeling, are unclear. We investigated the role of 5-HT_2B receptors on airway smooth muscle contractility and remodeling processes. Murine precision-cut lung slices were pretreated with 5-HT_2B receptor antagonists (EXT5, EXT9, RS 127445, and PRX 08066), as well as ketanserin (5-HT_2A/2C receptor antagonist) (1, 10 μmol/L), before addition of cumulative concentrations of 5-HT to induce bronchoconstriction. Remodeling effects after treatment with 10 μmol/L 5-HT and 5-HT₂ receptor antagonists were further studied in distal lung tissue by examining release of profibrotic transforming growth factor (TGF)-β1 and proliferation of human bronchial smooth muscle cells (HBSMCs). 5-HT-induced bronchoconstriction was significantly reduced by EXT5, EXT9, and ketanserin, but not by RS 127445 or PRX 08066. The 5-HT_2B receptor antagonists significantly reduced TGF-β1 release. 5-HT, in combination with TGF-β1, increased proliferation of HBSMCs, a process reduced by EXT5 and EXT9. Our results indicate that EXT5 and EXT9 may relieve bronchoconstriction in murine airways and serve as an add-on effect in attenuating pulmonary remodeling by improving airway function. The antiproliferative effect on HBSMCs and the inhibition of TGF-β1 release further support a role of 5-HT_2B receptors in pathologic remodeling processes.

5-HT2B receptor antagonists attenuate myofibroblast differentiation and subsequent fibrotic responses in vitro and in vivo

Pulmonary fibrosis is characterized by excessive accumulation of connective tissue, along with activated extracellular matrix (ECM)‐producing cells, myofibroblasts. The pathological mechanisms are not well known, however serotonin (5‐HT) and 5‐HT class 2 (5‐HT₂) receptors have been associated with fibrosis. The aim of the present study was to investigate the role of 5‐HT_2B receptors in fibrosis, using small molecular 5‐HT_2B receptor antagonists EXT5 and EXT9, with slightly different receptor affinity. Myofibroblast differentiation [production of alpha‐smooth muscle actin (α‐SMA)] and ECM synthesis were quantified in vitro, and the effects of the receptor antagonists were evaluated. Pulmonary fibrosis was also modeled in mice by subcutaneous bleomycin administrations (under light isoflurane anesthesia), and the effects of receptor antagonists on tissue density, collagen‐producing cells, myofibroblasts and decorin expression were investigated. In addition, cytokine expression was analyzed in serum. Lung fibroblasts displayed an increased α‐SMA (P < 0.05) and total proteoglycan production (P < 0.01) when cultured with TGF‐β1 together with 5‐HT, which were significantly reduced with both receptor antagonists. Following treatment with EXT5 or EXT9, tissue density, expression of decorin, number of collagen‐producing cells, and myofibroblasts were significantly decreased in vivo compared to bleomycin‐treated mice. Receptor antagonization also significantly reduced systemic levels of TNF‐α and IL‐1β, indicating a role in systemic inflammation. In conclusion, 5‐HT_2B receptor antagonists have potential to prevent myofibroblast differentiation, in vitro and in vivo, with subsequent effect on matrix deposition. The attenuating effects of 5‐HT_2B receptor antagonists on fibrotic tissue remodeling suggest these receptors as novel targets for the treatment of pulmonary fibrosis.

Induction of angiotensin-converting enzyme after miR-143/145 deletion is critical for impaired smooth muscle contractility

MicroRNAs have emerged as regulators of smooth muscle cell phenotype with a role in smooth muscle-related disease. Studies have shown that miR-143 and miR-145 are the most highly expressed microRNAs in smooth muscle cells, controlling differentiation and function. The effect of miR-143/145 knockout has been established in the vasculature but not in smooth muscle from other organs. Using knockout mice we found that maximal contraction induced by either depolarization or phosphatase inhibition was reduced in vascular and airway smooth muscle but maintained in the urinary bladder. Furthermore, a reduction of media thickness and reduced expression of differentiation markers was seen in the aorta but not in the bladder. Supporting the view that phenotype switching depends on a tissue-specific target of miR-143/145, we found induction of angiotensin-converting enzyme in the aorta but not in the bladder where angiotensin-converting enzyme was expressed at a low level. Chronic treatment with angiotensin type-1 receptor antagonist restored contractility in miR-143/145-deficient aorta while leaving bladder contractility unaffected. This shows that tissue-specific targets are critical for the effects of miR-143/145 on smooth muscle differentiation and that angiotensin converting enzyme is one such target.

Pharmacological characterization of the late phase reduction in lung functions and correlations with microvascular leakage and lung edema in allergen-challenged Brown Norway rats

Late phase airflow obstruction and reduction in forced vital capacity are characteristic features of human asthma. Airway microvascular leakage and lung edema are also present in the inflammatory phase of asthma, but the impact of this vascular response on lung functions has not been precisely defined. This study was designed to evaluate the role of increased lung microvascular leakage and edema on the late phase changes in forced vital capacity (FVC) and peak expiratory flow (PEF) in allergen-challenged Brown Norway rats using pharmacological inhibitors of the allergic inflammatory response. Rats were sensitized and challenged with ovalbumin aerosol and forced expiratory lung functions (FVC, PEF) and wet and dry lung weights were measured 48 h after antigen challenge. Ovalbumin challenge reduced FVC (63% reduction) and PEF (33% reduction) and increased wet (65% increase) and dry (51% increase) lung weights. The antigen-induced reduction in FVC and PEF was completely inhibited by oral treatment with betamethasone and partially attenuated by inhibitors of arachidonic acid metabolism including indomethacin (cyclooxygenase inhibitor), 7-TM and MK-7246 (CRTH2 antagonists) and montelukast (CysLT1 receptor antagonist). Antagonists of histamine H1 receptors (mepyramine) and 5-HT receptors (methysergide) had no significant effects indicating that these pre-formed mast cell mediators were not involved. There was a highly significant (P < 0.005) correlation for the inhibition of FVC reduction and increase in wet and dry lung weights by these pharmacological agents. These results strongly support the hypothesis that lung microvascular leakage and the associated lung edema contribute to the reduction in forced expiratory lung functions in antigen-challenged Brown Norway rats and identify an important role for the cyclooxygenase and lipoxygenase products of arachidonic acid metabolism in these responses.