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Frontiers in Immunology 2023Acute respiratory distress syndrome (ARDS) is marked by damage to the capillary endothelium and alveolar epithelium following edema formation and cell infiltration.... (Review)
Review
Acute respiratory distress syndrome (ARDS) is marked by damage to the capillary endothelium and alveolar epithelium following edema formation and cell infiltration. Currently, there are no effective treatments for severe ARDS. Pathologies such as sepsis, pneumonia, fat embolism, and severe trauma may cause ARDS with respiratory failure. The primary mechanism of edema clearance is the epithelial cells' Na/K-ATPase (NKA) activity. NKA is an enzyme that maintains the electrochemical gradient and cell homeostasis by transporting Na and K ions across the cell membrane. Direct injury on alveolar cells or changes in ion transport caused by infections decreases the NKA activity, loosening tight junctions in epithelial cells and causing edema formation. In addition, NKA acts as a receptor triggering signal transduction in response to the binding of cardiac glycosides. The ouabain (a cardiac glycoside) and oleic acid induce lung injury by targeting NKA. Besides enzymatic inhibition, the NKA triggers intracellular signal transduction, fostering proinflammatory cytokines production and contributing to lung injury. Herein, we reviewed and discussed the crucial role of NKA in edema clearance, lung injury, and intracellular signaling pathway activation leading to lung inflammation, thus putting the NKA as a protagonist in lung injury pathology.
Topics: Humans; Lung Injury; Pneumonia; Respiratory Distress Syndrome; Sodium-Potassium-Exchanging ATPase; Edema
PubMed: 38299144
DOI: 10.3389/fimmu.2023.1287512 -
Clinical and Experimental... May 2024The distribution and extent of excitable spiral ganglion neurons (SGNs) have been investigated using the electrically evoked auditory brainstem response (EABR) during...
OBJECTIVES
The distribution and extent of excitable spiral ganglion neurons (SGNs) have been investigated using the electrically evoked auditory brainstem response (EABR) during preoperative and perioperative periods. In this study, we investigated the EABR with extracochlear stimulation (eEABR) as a preoperative test to estimate these factors.
METHODS
Sixteen male Sprague-Dawley rats were used in this study. Experiments were conducted in nine rats with normal hearing and seven rats that were partially deafened with ouabain treatment. Each experiment involved the following steps: extracochlear stimulating electrode placement at three different sites along the axis of the cochlea and eEABR recordings; cochleostomy and four-channel intracochlear array implantation, followed by EABR recordings with various electrode pair combinations; and after electrophysiological measurements, harvest of the cochleae for histopathological evaluation. The slope characteristics of the amplitude growth function measured from eEABR and EABR, frequency-specific auditory thresholds, and the density of SGNs were compared.
RESULTS
Similar trends were observed in slope changes on different sites of stimulation with both types of stimulation in normal-hearing animals-specifically, a monotonically increasing slope with increasing distance between bipolar pairs. In addition, eEABR slopes showed significant correlations with EABR slopes when the expected cochlear regions of stimulation were similar in normal-hearing animals. In partially deaf animals, the auditory thresholds at several frequencies had a significant correlation with the eEABR slopes of each extracochlear electrode at the apical, middle, and basal cochlear positions. This indicated that increasing the regions of cochlear stimulation had a differential impact on eEABR slopes, depending on the neural conditions.
CONCLUSION
Our results indicated that eEABR slopes showed significant spatial correlations with the functionality of the auditory nerve. Therefore, eEABR tests at various cochlear positions might be used for estimating the extent of excitable SGNs in cochlear implant candidates prior to implantation.
PubMed: 38273767
DOI: 10.21053/ceo.2023.00034 -
American Journal of Physiology. Cell... Apr 2024Cardiotonic steroids (CTS), used by certain insects, toads, and rats for protection from predators, became, thanks to Withering's trailblazing 1785 monograph, the... (Review)
Review
Cardiotonic steroids (CTS), used by certain insects, toads, and rats for protection from predators, became, thanks to Withering's trailblazing 1785 monograph, the mainstay of heart failure (HF) therapy. In the 1950s and 1960s, we learned that the CTS receptor was part of the sodium pump (NKA) and that the Na/Ca exchanger was critical for the acute cardiotonic effect of digoxin- and ouabain-related CTS. This "settled" view was upended by seven revolutionary observations. First, subnanomolar ouabain sometimes stimulates NKA while higher concentrations are invariably inhibitory. Second, endogenous ouabain (EO) was discovered in the human circulation. Third, in the DIG clinical trial, digoxin only marginally improved outcomes in patients with HF. Fourth, cloning of NKA in 1985 revealed multiple NKA α and β subunit isoforms that, in the rodent, differ in their sensitivities to CTS. Fifth, the NKA is a cation pump and a hormone receptor/signal transducer. EO binding to NKA activates, in a ligand- and cell-specific manner, several protein kinase and Ca-dependent signaling cascades that have widespread physiological effects and can contribute to hypertension and HF pathogenesis. Sixth, all CTS are not equivalent, e.g., ouabain induces hypertension in rodents while digoxin is antihypertensinogenic ("biased signaling"). Seventh, most common rodent hypertension models require a highly ouabain-sensitive α2 NKA and the elevated blood pressure is alleviated by EO immunoneutralization. These numerous phenomena are enabled by NKA's intricate structure. We have just begun to understand the endocrine role of the endogenous ligands and the broad impact of the ouabain-binding site on physiology and pathophysiology.
Topics: Humans; Rats; Animals; Ouabain; Sodium-Potassium-Exchanging ATPase; Ligands; Digoxin; Cardiotonic Agents; Hypertension; Heart Failure; Enzyme Inhibitors; Calcium Signaling; Binding Sites
PubMed: 38223926
DOI: 10.1152/ajpcell.00273.2023 -
European Journal of Applied Physiology Mar 2024This historical review traces key discoveries regarding K and Na ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na,K-ATPase... (Review)
Review
A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na,K-ATPase, Na and K ions, and on plasma K concentration-historical developments.
This historical review traces key discoveries regarding K and Na ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na,K-ATPase (NKA) and exercise effects on plasma [K] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal muscle showed K loss and gains in Na, Cl and H0, then subsequently bidirectional muscle K and Na fluxes. After NKA discovery in 1957, methods were developed to quantify muscle NKA activity via rates of ATP hydrolysis, Na/K radioisotope fluxes, [H]-ouabain binding and phosphatase activity. Since then, it became clear that NKA plays a central role in Na/K homeostasis and that NKA content and activity are regulated by muscle contractions and numerous hormones. During intense exercise in humans, muscle intracellular [K] falls by 21 mM (range - 13 to - 39 mM), interstitial [K] increases to 12-13 mM, and plasma [K] rises to 6-8 mM, whilst post-exercise plasma [K] falls rapidly, reflecting increased muscle NKA activity. Contractions were shown to increase NKA activity in proportion to activation frequency in animal intact muscle preparations. In human muscle, [H]-ouabain-binding content fully quantifies NKA content, whilst the method mainly detects α isoforms in rats. Acute or chronic exercise affects human muscle K, NKA content, activity, isoforms and phospholemman (FXYD1). Numerous hormones, pharmacological and dietary interventions, altered acid-base or redox states, exercise training and physical inactivity modulate plasma [K] during exercise. Finally, historical research approaches largely excluded female participants and typically used very small sample sizes.
Topics: Humans; Rats; Animals; Sodium-Potassium-Exchanging ATPase; Ouabain; Muscle, Skeletal; Muscle Contraction; Hormones; Protein Isoforms; Ions
PubMed: 38206444
DOI: 10.1007/s00421-023-05335-9 -
International Journal of Molecular... Dec 2023Ionizing radiation (IR) causes disturbances in the functions of the gastrointestinal tract. Given the therapeutic potential of ouabain, a specific ligand of the...
Ionizing radiation (IR) causes disturbances in the functions of the gastrointestinal tract. Given the therapeutic potential of ouabain, a specific ligand of the Na,K-ATPase, we tested its ability to protect against IR-induced disturbances in the barrier and transport properties of the jejunum and colon of rats. Male Wistar rats were subjected to 6-day intraperitoneal injections of vehicle or ouabain (1 µg/kg/day). On the fourth day of injections, rats were exposed to total-body X-ray irradiation (10 Gy) or a sham irradiation. Isolated tissues were examined 72 h post-irradiation. Electrophysiological characteristics and paracellular permeability for sodium fluorescein were measured in an Ussing chamber. Histological analysis and Western blotting were also performed. In the jejunum tissue, ouabain exposure did not prevent disturbances in transepithelial resistance, paracellular permeability, histological characteristics, as well as changes in the expression of claudin-1, -3, -4, tricellulin, and caspase-3 induced by IR. However, ouabain prevented overexpression of occludin and the pore-forming claudin-2. In the colon tissue, ouabain prevented electrophysiological disturbances and claudin-2 overexpression. These observations may reveal a mechanism by which circulating ouabain maintains tight junction integrity under IR-induced intestinal dysfunction.
Topics: Male; Rats; Animals; Claudin-2; Ouabain; Rats, Wistar; Sodium-Potassium-Exchanging ATPase; Intestines
PubMed: 38203449
DOI: 10.3390/ijms25010278 -
BMC Research Notes Jan 2024Silicosis is an irreversible occupational lung disease resulting from crystalline silica inhalation. Previously, we discovered that Western diet (HFWD)-consumption...
OBJECTIVES
Silicosis is an irreversible occupational lung disease resulting from crystalline silica inhalation. Previously, we discovered that Western diet (HFWD)-consumption increases susceptibility to silica-induced pulmonary inflammation and fibrosis. This study investigated the potential of HFWD to alter silica-induced effects on airway epithelial ion transport and smooth muscle reactivity.
METHODS
Six-week-old male F344 rats were fed a HFWD or standard rat chow (STD) and exposed to silica (Min-U-Sil 5, 15 mg/m, 6 h/day, 5 days/week, for 39 d) or filtered air. Experimental endpoints were measured at 0, 4, and 8 weeks post-exposure. Transepithelial potential difference (V), short-circuit current (I) and transepithelial resistance (R) were measured in tracheal segments and ion transport inhibitors [amiloride, Na channel blocker; NPPB; Cl- channel blocker; ouabain, Na, K-pump blocker] identified changes in ion transport pathways. Changes in airway smooth muscle reactivity to methacholine (MCh) were investigated in the isolated perfused trachea preparation.
RESULTS
Silica reduced basal I at 4 weeks and HFWD reduced the I response to amiloride at 0 week compared to air control. HFWD + silica exposure induced changes in ion transport 0 and 4 weeks after treatment compared to silica or HFWD treatments alone. No effects on airway smooth muscle reactivity to MCh were observed.
Topics: Male; Rats; Animals; Amiloride; Silicon Dioxide; Diet, Western; Rats, Inbred F344; Epithelium; Ion Transport; Methacholine Chloride; Muscle, Smooth
PubMed: 38172968
DOI: 10.1186/s13104-023-06672-w -
Cells Dec 2023Inflamed and infected tissues can display increased local sodium (Na) levels, which can have various effects on immune cells. In macrophages, high salt (HS) leads to a...
Inflamed and infected tissues can display increased local sodium (Na) levels, which can have various effects on immune cells. In macrophages, high salt (HS) leads to a Na/Ca-exchanger 1 (NCX1)-dependent increase in intracellular Na levels. This results in augmented osmoprotective signaling and enhanced proinflammatory activation, such as enhanced expression of type 2 nitric oxide synthase and antimicrobial function. In this study, the role of elevated intracellular Na levels in macrophages was investigated. Therefore, the Na/K-ATPase (NKA) was pharmacologically inhibited with two cardiac glycosides (CGs), ouabain (OUA) and digoxin (DIG), to raise intracellular Na without increasing extracellular Na levels. Exposure to HS conditions and treatment with both inhibitors resulted in intracellular Na accumulation and subsequent phosphorylation of p38/MAPK. The CGs had different effects on intracellular Ca and K compared to HS stimulation. Moreover, the osmoprotective transcription factor nuclear factor of activated T cells 5 (NFAT5) was not upregulated on RNA and protein levels upon OUA and DIG treatment. Accordingly, OUA and DIG did not boost nitric oxide (NO) production and showed heterogeneous effects toward eliminating intracellular bacteria. While HS environments cause hypertonic stress and ionic perturbations, cardiac glycosides only induce the latter. Cotreatment of macrophages with OUA and non-ionic osmolyte mannitol (MAN) partially mimicked the HS-boosted antimicrobial macrophage activity. These findings suggest that intracellular Na accumulation and hypertonic stress are required but not sufficient to mimic boosted macrophage function induced by increased extracellular sodium availability.
Topics: Humans; Sodium; Cardiac Glycosides; Ouabain; Macrophages; Sodium Chloride; Sodium Chloride, Dietary; Caffeine; Anti-Infective Agents
PubMed: 38132136
DOI: 10.3390/cells12242816 -
International Journal of Molecular... Nov 2023Ouabain, a substance originally obtained from plants, is now classified as a hormone because it is produced endogenously in certain animals, including humans. However,...
Ouabain, a substance originally obtained from plants, is now classified as a hormone because it is produced endogenously in certain animals, including humans. However, its precise effects on the body remain largely unknown. Previous studies have shown that ouabain can influence the phenotype of epithelial cells by affecting the expression of cell-cell molecular components and voltage-gated potassium channels. In this study, we conducted whole-cell clamp assays to determine whether ouabain affects the activity and/or expression of TRPV4 channels. Our findings indicate that ouabain has a statistically significant effect on the density of TRPV4 currents (dI), with an EC50 of 1.89 nM. Regarding treatment duration, dI reaches its peak at around 1 h, followed by a subsequent decline and then a resurgence after 6 h, suggesting a short-term modulatory effect related to on TRPV4 channel activity and a long-term effect related to the promotion of synthesis of new TRPV4 channel units. The enhancement of dI induced by ouabain was significantly lower in cells seeded at low density than in cells in a confluent monolayer, indicating that the action of ouabain depends on intercellular contacts. Furthermore, the fact that U73122 and neomycin suppress the effect caused by ouabain in the short term suggests that the short-term induced enhancement of dI is due to the depletion of PIP2 stores. In contrast, the fact that the long-term effect is inhibited by PP2, wortmannin, PD, FR18, and IKK16 suggests that cSrc, PI3K, Erk1/2, and NF-kB are among the components included in the signaling pathways.
Topics: Humans; Animals; Ouabain; TRPV Cation Channels; Signal Transduction; Epithelial Cells; Sodium-Potassium-Exchanging ATPase
PubMed: 38069012
DOI: 10.3390/ijms242316687 -
Journal of Chemical Ecology Feb 2024The brilliant red Lilioceris merdigera (Coleoptera, Chrysomelidae) can spend its entire life cycle on the cardenolide-containing plant Convallaria majalis (lily of the...
The brilliant red Lilioceris merdigera (Coleoptera, Chrysomelidae) can spend its entire life cycle on the cardenolide-containing plant Convallaria majalis (lily of the valley) and forms stable populations on this host. Yet, in contrast to many other insects on cardenolide-containing plants L. merdigera does not sequester these plant toxins in the body but rather both adult beetles and larvae eliminate ingested cardenolides with the feces. Tracer feeding experiments showed that this holds true for radioactively labeled ouabain and digoxin, a highly polar and a rather apolar cardenolide. Both compounds or their derivatives are incorporated in the fecal shields of the larvae. The apolar digoxin, but not the polar ouabain, showed a deterrent effect on the generalist predatory ant Myrmica rubra, which occurs in the habitat of L. merdigera. The deterrent effect was detected for digoxin both in choice and feeding time assays. In a predator choice assay, a fecal shield derived from a diet of cardenolide-containing C. majalis offered L. merdigera larvae better protection from M. rubra than one derived from non-cardenolide Allium schoenoprasum (chives) or no fecal shield at all. Thus, we here present data suggesting a new way how insects may gain protection by feeding on cardenolide-containing plants.
Topics: Animals; Larva; Cardenolides; Ouabain; Coleoptera; Insecta; Digoxin
PubMed: 38062246
DOI: 10.1007/s10886-023-01465-8 -
Redox Biology Feb 2024Empagliflozin (EMPA) ameliorates reactive oxygen species (ROS) generation in human endothelial cells (ECs) exposed to 10 % stretch, but the underlying mechanisms are...
BACKGROUND
Empagliflozin (EMPA) ameliorates reactive oxygen species (ROS) generation in human endothelial cells (ECs) exposed to 10 % stretch, but the underlying mechanisms are still unclear. Pathological stretch is supposed to stimulate protein kinase C (PKC) by increasing intracellular calcium (Ca), therefore activating nicotinamide adenine dinucleotide phosphate oxidase (NOX) and promoting ROS production in human ECs. We hypothesized that EMPA inhibits stretch-induced NOX activation and ROS generation through preventing PKC activation.
METHODS
Human coronary artery endothelial cells (HCAECs) were pre-incubated for 2 h before exposure to cyclic stretch (5 % or 10 %) with either vehicle, EMPA or the PKC inhibitor LY-333531 or PKC siRNA. PKC activity, NOX activity and ROS production were detected after 24 h. Furthermore, the Ca chelator BAPTA-AM, NCX inhibitor ORM-10962 or NCX siRNA, sodium/potassium pump inhibitor ouabain and sodium hydrogen exchanger (NHE) inhibitor cariporide were applied to explore the involvement of the NHE/Na/NCX/Ca in the ROS inhibitory capacity of EMPA.
RESULTS
Compared to 5 % stretch, 10 % significantly increased PKC activity, which was reduced by EMPA and PKC inhibitor LY-333531. EMPA and LY-333531 showed a similar inhibitory capacity on NOX activity and ROS generation induced by 10 % stretch, which was not augmented by combined treatment with both drugs. PKC-β knockdown inhibits the NOX activation induced by Ca and 10 % stretch. BAPTA, pharmacologic or genetic NCX inhibition and cariporide reduced Ca in static HCAECs and prevented the activation of PKC and NOX in 10%-stretched cells. Ouabain increased ROS generation in cells exposed to 5 % stretch.
CONCLUSION
EMPA reduced NOX activity via attenuation of the NHE/Na/NCX/Ca/PKC axis, leading to less ROS generation in HCAECs exposed to 10 % stretch.
Topics: Humans; Endothelial Cells; Reactive Oxygen Species; Coronary Vessels; Protein Kinase C; Ouabain; Oxidative Stress; Sodium-Hydrogen Exchangers; RNA, Small Interfering; Guanidines; Indoles; Glucosides; Maleimides; Sulfones; Benzhydryl Compounds
PubMed: 38061206
DOI: 10.1016/j.redox.2023.102979