A potassium ionophore (Nigericin) inhibits stimulation of human lymphocytes by mitogens

Protein corona formation on supramolecular polymer nanoparticles causes differential endosomal sorting resulting in an attenuated NLRP3 inflammasome activation

Upon introduction into biological environments, nanoparticles undergo the spontaneous formation of a dynamic protein corona, which continually evolves and significantly modifies their physicochemical properties and interactions with biological systems. This evolving protein corona can critically impact the nanoparticles' endocytic pathways and targeting efficiency, potentially altering their functional characteristics and obscuring their intended therapeutic effects. Despite considerable focus on the characterization of corona proteins and their impact on nanoparticle uptake, the intracellular processes and their effects on immunogenicity are not yet thoroughly understood. Supramolecular polymer nanoparticles (SNPs) with a highly hydrophobic core are recognized for triggering NLRP3 inflammasome activation, a key component of the innate immune system. Here, it is reported that the protein corona formation on SNPs exerts an inhibitory effect on the activation pathway of NLRP3 inflammasome. The protein corona impairs the intrinsic capacity of SNPs to induce lysosomal membrane rupture, thereby diminishing the cellular stress signals necessary for the formation of the NLRP3 inflammasome complex. Furthermore, the cells transport SNPs with an attached protein corona to recycling endosomes, where they are sorted and prepared for exocytosis. Conversely, nascent SNPs are primarily confined to late endosomes and lysosomes, leading to lysosomal rupture and inflammasome activation. This differential routing reflects the significant impact of the protein corona on the cellular handling and subsequent biological activity of nanoparticles. In summary, this study elucidates the fundamental role of the protein corona in shaping the intracellular disposition of nanoparticles, with implications for modulating their interactions with the immune system.

Cytotoxicity Study of Ionophore-Based Membranes: Toward On-Body and in Vivo Ion Sensing

We present the most complete study to date comprising in vitro cytotoxicity tests of ion-selective membranes (ISMs) in terms of cell viability, proliferation, and adhesion assays with human dermal fibroblasts. ISMs were prepared with different types of plasticizers and ionophores to be tested in combination with assays that focus on the medium-term and long-term leaching of compounds. Furthermore, the ISMs were prepared in different configurations considering (i) inner-filling solution-type electrodes, (ii) all-solid-state electrodes based on a conventional drop-cast of the membrane, (iii) peeling after the preparation of a wearable sensor, and (iv) detachment from a microneedle-based sensor, thus covering a wide range of membrane shapes. One of the aims of this study, other than the demonstration of the biocompatibility of various ISMs and materials tested herein, is to create an awareness in the scientific community surrounding the need to perform biocompatibility assays during the very first steps of any sensor development with an intended biomedical application. This will foster meeting the requirements for subsequent on-body application of the sensor and avoiding further problems during massive validations toward the final in vivo use and commercialization of such devices.

The Role of Early Bioelectric Signals in the Regeneration of Planarian Anterior/Posterior Polarity

Axial patterning during planarian regeneration relies on a transcriptional circuit that confers distinct positional information on the two ends of an amputated fragment. The earliest known elements of this system begin demarcating differences between anterior and posterior wounds by 6 h postamputation. However, it is still unknown what upstream events break the axial symmetry, allowing a mutual repressor system to establish invariant, distinct biochemical states at the anterior and posterior ends. Here, we show that bioelectric signaling at 3 h is crucial for the formation of proper anterior-posterior polarity in planaria. Briefly manipulating the endogenous bioelectric state by depolarizing the injured tissue during the first 3 h of regeneration alters gene expression by 6 h postamputation and leads to a double-headed phenotype upon regeneration despite confirmed washout of ionophores from tissue. These data reveal a primary functional role for resting membrane potential taking place within the first 3 h after injury and kick-starting the downstream pattern of events that elaborate anatomy over the following 10 days. We propose a simple model of molecular-genetic mechanisms to explain how physiological events taking place immediately after injury regulate the spatial distribution of downstream gene expression and anatomy of regenerating planaria.

Hyperpolarization by N-(3-oxododecanoyl)-l-homoserine-lactone, a quorum sensing molecule, in rat thymic lymphocytes

To study the adverse effects of N-(3-oxododecanoyl)-l-homoserine-lactone (ODHL), a quorum sensing molecule, on mammalian host cells, its effect on membrane potential was examined in rat thymic lymphocytes using flow cytometric techniques with a voltage-sensitive fluorescent probe. As 3-300 μM ODHL elicited hyperpolarization, it is likely that it increases membrane K⁺ permeability because hyperpolarization is directly linked to changing K⁺ gradient across membranes, but not Na⁺ and Cl^- gradients. ODHL did not increase intracellular Ca²⁺ concentration. ODHL also produced a response in the presence of an intracellular Zn²⁺ chelator. Thus, it is unlikely that intracellular Ca²⁺ and Zn²⁺ are attributed to the response. Quinine, a non-specific K⁺ channel blocker, greatly reduced hyperpolarization. However, because charybdotoxin, tetraethylammonium chloride, 4-aminopyridine, and glibenclamide did not affect it, it is pharmacologically hypothesized that Ca²⁺-activated K⁺ channels, voltage-gated K⁺ channels, and ATP-sensitive K⁺ channels are not involved in ODHL-induced hyperpolarization. Although the K⁺ channels responsible for ODHL-induced hyperpolarization have not been identified, it is suggested that ODHL can elicit hyperpolarization in mammalian host cells, disturbing cellular functions.

Pyroptosis is driven by non-selective gasdermin-D pore and its morphology is different from MLKL channel-mediated necroptosis

Necroptosis and pyroptosis are two forms of programmed cell death with a common feature of plasma membrane rupture. Here we studied the morphology and mechanism of pyroptosis in comparison with necroptosis. Different from necroptosis, pyroptosis undergoes membrane blebbing and produces apoptotic body-like cell protrusions (termed pyroptotic bodies) prior to plasma membrane rupture. The rupture in necroptosis is explosion-like, whereas in pyroptosis it leads to flattening of cells. It is known that the execution of necroptosis is mediated by mixed lineage kinase domain-like (MLKL) oligomers in the plasma membrane, whereas gasdermin-D (GSDMD) mediates pyroptosis after its cleavage by caspase-1 or caspase-11. We show that N-terminal fragment of GSDMD (GSDMD-N) generated by caspase cleavage also forms oligomer and migrates to the plasma membrane to kill cells. Both MLKL and GSDMD-N are lipophilic and the N-terminal sequences of both proteins are important for their oligomerization and plasma membrane translocation. Unlike MLKL which forms channels on the plasma membrane that induces influx of selected ions which osmotically swell the cells to burst, GSDMD-N forms non-selective pores and does not rely on increased osmolarity to disrupt cells. Our study reveals the pore-forming activity of GSDMD and channel-forming activity of MLKL determine different ways of plasma membrane rupture in pyroptosis and necroptosis.

Metabolic dysfunction in lymphocytes promotes postoperative morbidity

Perioperative lymphopenia has been linked with an increased risk of postoperative infectious complications, but the mechanisms remain unclear. We tested the hypothesis that bioenergetic dysfunction is an important mechanism underlying lymphopenia, impaired functionality and infectious complications. In two cohorts of patients (61-82 years old) undergoing orthopaedic joint replacement (n=417 and 328, respectively), we confirmed prospectively that preoperative lymphopenia (≤1.3 x 10(9)·l(-1); <20% white cell count; prevalence 15-18%) was associated with infectious complications (relative risk 1.5 (95% confidence interval 1.1-2.0); P=0.008) and prolonged hospital stay. Lymphocyte respirometry, mitochondrial bioenergetics and function were assessed (n=93 patients). Postoperative lymphocytes showed a median 43% fall (range: 26-65%; P=0.029; n=13 patients) in spare respiratory capacity, the extra capacity available to produce energy in response to stress. This was accompanied by reduced glycolytic capacity. A similar hypometabolic phenotype was observed in lymphocytes sampled preoperatively from chronically lymphopenic patients (n=21). This hypometabolic phenotype was associated with functional lymphocyte impairment including reduced T-cell proliferation, lower intracellular cytokine production and excess apoptosis induced by a range of common stressors. Glucocorticoids, which are ubiquitously elevated for a prolonged period postoperatively, generated increased levels of mitochondrial reactive oxygen species, activated caspase-1 and mature interleukin (IL)-1β in human lymphocytes, suggesting inflammasome activation. mRNA transcription of the NLRP1 inflammasome was increased in lymphocytes postoperatively. Genetic ablation of the murine NLRP3 inflammasome failed to prevent glucocorticoid-induced lymphocyte apoptosis and caspase-1 activity, but increased NLRP1 protein expression. Our findings suggest that the hypometabolic phenotype observed in chronically lymphopenic patients and/or acquired postoperatively increases the risk of postoperative infection through glucocorticoid activation of caspase-1 via the NLRP1 inflammasome.

Nigericin is a potent inhibitor of the early stage of vaccinia virus replication

Poxviruses remain a significant public health concern due to their potential use as bioterrorist agents and the spread of animal borne poxviruses, such as monkeypox virus, to humans. Thus, the identification of small molecule inhibitors of poxvirus replication is warranted. Vaccinia virus is the prototypic member of the Orthopoxvirus genus, which also includes variola and monkeypox virus. In this study, we demonstrate that the carboxylic ionophore nigericin is a potent inhibitor of vaccinia virus replication in several human cell lines. In HeLa cells, we found that the 50% inhibitory concentration of nigericin against vaccinia virus was 7.9 nM, with a selectivity index of 1038. We present data demonstrating that nigericin targets vaccinia virus replication at a post-entry stage. While nigericin moderately inhibits both early vaccinia gene transcription and translation, viral DNA replication and intermediate and late gene expression are severely compromised in the presence of nigericin. Our results demonstrate that nigericin has the potential to be further developed into an effective antiviral to treat poxvirus infections.

Effect of ionophores on lymphocyte cellular metabolism

The effect of valinomycin, nigericin, gramicidin S and D, A23187 and X537A on respiration and cellular ATP content of rat spleen lymphocytes is presented. It has been found that while valinomycin and nigericin interfere with mitochondrial functions gramicidin D does not show an appreciable effect. These results are explained in terms of different ability of ionophores to re-distribute among intracellular membranes. A23187 and X537A, added with Ca2+, strongly enhanced O2 consumption and reduced cellular ATP content.

Effect of monovalent cation ionophores on lymphocyte cellular metabolism

The effect of valinomycin, nigericin and gramicidin on the cellular O2 consumption and on ATP content has been investigation. It has been found that while valinomycin and nigericin interfere with mitochondrial functions, gramicidin D does not show any appreciable effect. These results are explained in terms of the differing abilities of ionophores to redistribute among intracellular membranes.

Membrane potential changes during mitogenic stimulation of mouse spleen lymphocytes

By monitoring differences in accumulation of the lipophilic cation [(3)H]tetraphenylphosphonium in media containing low or high potassium concentrations [Lichtshtein, D., Kaback, H. R. & Blume, A. J. (1979) Proc. Natl. Acad. Sci. USA 76, 650-654], the membrane potential of lymphocytes from various sources has been estimated. On the basis of this method, the potential of normal mouse spleen lymphocytes (T and B cells) is -65 +/- 2 mV (mean +/- SEM, interior negative). During the course of mitogenic stimulation by concanavalin A, lipopolysaccharide, or fetal calf serum, the membrane potential of murine spleen lymphocytes changes systematically according to the following pattern: (i) early depolarization lasting 2-3 hr, (ii) repolarization over the next 7 hr, and (iii) a final hyperpolarization phase during the last 24-48 hr. During repolarization and hyperpolarization, moreover, there is a direct correlation between the membrane potential and DNA synthesis, as judged by [(3)H]thymidine incorporation. By using isolated T and B cells, it is observed that concanavalin A depolarizes T cells only, whereas lipopolysaccharide depolarizes B cells only. Thus, both mitogens exhibit the same specificity for depolarization as for mitogenic stimulation. On the basis of these observations, it is suggested that the transition of lymphocytes from a resting state to mitotic activity is initiated by depolarization of the plasma membrane.

Concanavalin A induces an intraluminal alkalinization of thymocyte membrane vesicles

Weak acid distribution methods demonstrate that mitogenic levels of concanavalin A induce an intravesicular alkalinization of isolated thymocyte membrane vesicles. Experiments with chemical reagents that crosslink the high affinity concanavalin A receptor and extensive correlation with known cellular events suggest that a "membrane Bohr effect" may participate in the initiation of mitogenesis.

Transmembrane electrical and pH gradients across human erythrocytes and human peripheral lymphocytes

Transmembrane electrical and pH gradients have been measured across human erythrocytes and peripheral blood lymphocytes using equilibrium distributions of radioactively labelled lipophilic ions, and of weak acids and weak bases, respectively. The distributions of methylamine, trimethylamine, acetic acid and trimethylacetic acid give calculated transmembrane pH gradients (pHe-pHi) for erythrocytes of between 0.14-0.21 for extracellular pH values of 7.28-7.16. The distributions of trimethylacetic acid. DMO and trimethylamine were determined for lymphocytes, establishing upper and lower limits of the calculated pH gradient over the external pH range of 6.7 to 7.7. Tritiated triphenylmethyl phosphonium ion (TPMP) and 14C-thiocyanate ion (SCN) equilibrium distributions were measured in order to calculate transmembrane electrical potentials, using tetraphenylboron as a catalyst to facilitate TPMP equilibrium. Transmembrane potentials of -7 to -10 mV were calculated from SCN and TPMP, respectively for red cells, and -35 to -52 mV respectively, in the case of lymphocytes. Distributions of TPMP and potassium ions were determined in the presence of valinomycin over a wide range of extracellular potassium concentrations for red cells and the calculated Nernst potentials for TPMP compared to the calculated potential using the Goldman equation for chloride and potassium ions. Distributions of TPMP, SCN and potassium ions were also determined for lymphocyte suspensions as a function of extracellular potassium and the calculated Nernst potentials for TPMP and SCN compared to the calculated potassium diffusion potential.

Lymphocyte response to phytohemagglutinin: intracellular volume and intracellular [K+]

The effect of phytohemagglutinin (PHA) on lymphocytes was examined with respect to free intracellular water volume and intracellular [K+]. At a cell concentration of 30 X 10(6) lymphocytes/ml in modified Hank's Buffered Salt Solution (HBSS) in the presence of 10% human AB serum, addition of PHA at 3 mg/ml resulted in a 24-27% decrease in free intracellular water space within 30 to 60 minutes and a return to control level after three hours. A larger change in intracellular water (44%) was observed under similar conditions in the absence of serum. The absolute intracellular K+ content did not change after PHA addition, but the cell water volume decrease arising from PHA addition resulted in a 29% increase in intracellular [K+] at 60 minutes. The decrease in lymphocyte water volume induced by PHA was also observed for concanavalin A which stimulates lymphocyte proliferation, but not for wheat germ lectin, an agglutinating agent which is not mitogenic. Thus, volume regulation may be closely associated with the mitogenicity of these compounds.