Pharmaceutical agent cetylpyridinium chloride inhibits immune mast cell function by interfering with calcium mobilization

Cetylpyridinium chloride (CPC) is an antimicrobial used in numerous personal care and janitorial products and food for human consumption at millimolar concentrations. Minimal information exists on the eukaryotic toxicology of CPC. We have investigated the effects of CPC on signal transduction of the immune cell type mast cells. Here, we show that CPC inhibits the mast cell function degranulation with antigen dose-dependence and at non-cytotoxic doses ∼1000-fold lower than concentrations in consumer products. Previously we showed that CPC disrupts phosphatidylinositol 4,5-bisphosphate, a signaling lipid critical for store-operated Ca2+ entry (SOCE), which mediates degranulation. Our results indicate that CPC inhibits antigen-stimulated SOCE: CPC restricts Ca2+ efflux from endoplasmic reticulum, reduces Ca2+ uptake into mitochondria, and dampens Ca2+ flow through plasma membrane channels. While inhibition of Ca2+ channel function can be caused by alteration of plasma membrane potential (PMP) and cytosolic pH, CPC does not affect PMP or pH. Inhibition of SOCE is known to depress microtubule polymerization, and here we show that CPC indeed dose-dependently shuts down formation of microtubule tracks. In vitro data reveal that CPC inhibition of microtubules is not due to direct CPC interference with tubulin. In summary, CPC is a signaling toxicant that targets Ca2+ mobilization.

Pharmaceutical agent cetylpyridinium chloride inhibits immune mast cell function by interfering with calcium mobilization

Cetylpyridinium chloride (CPC) is an antimicrobial used in numerous personal care and janitorial products and food for human consumption at millimolar concentrations. Minimal information exists on the eukaryotic toxicology of CPC. We have investigated the effects of CPC on signal transduction of the immune cell type mast cells. Here, we show that CPC inhibits the mast cell function degranulation with antigen dose-dependence and at non-cytotoxic doses ∼1000-fold lower than concentrations in consumer products. Previously we showed that CPC disrupts phosphatidylinositol 4,5-bisphosphate, a signaling lipid critical for store-operated Ca 2+ entry (SOCE), which mediates degranulation. Our results indicate that CPC inhibits antigen-stimulated SOCE: CPC restricts Ca 2+ efflux from endoplasmic reticulum, reduces Ca 2+ uptake into mitochondria, and dampens Ca 2+ flow through plasma membrane channels. While inhibition of Ca 2+ channel function can be caused by alteration of plasma membrane potential (PMP) and cytosolic pH, CPC does not affect PMP or pH. Inhibition of SOCE is known to depress microtubule polymerization, and here we show that CPC indeed dose-dependently shuts down formation of microtubule tracks. In vitro data reveal that CPC inhibition of microtubules is not due to direct CPC interference with tubulin. In summary, CPC is a signaling toxicant that targets Ca 2+ mobilization.

Cetylpyridinium chloride (CPC) reduces zebrafish mortality from influenza infection: Super-resolution microscopy reveals CPC interference with multiple protein interactions with phosphatidylinositol 4,5-bisphosphate in immune function

The COVID-19 pandemic raises significance for a potential influenza therapeutic compound, cetylpyridinium chloride (CPC), which has been extensively used in personal care products as a positively-charged quaternary ammonium antibacterial agent. CPC is currently in clinical trials to assess its effects on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) morbidity. Two published studies have provided mouse and human data indicating that CPC may alleviate influenza infection, and here we show that CPC (0.1 μM, 1 h) reduces zebrafish mortality and viral load following influenza infection. However, CPC mechanisms of action upon viral-host cell interaction are currently unknown. We have utilized super-resolution fluorescence photoactivation localization microscopy to probe the mode of CPC action. Reduction in density of influenza viral protein hemagglutinin (HA) clusters is known to reduce influenza infectivity: here, we show that CPC (at non-cytotoxic doses, 5-10 μM) reduces HA density and number of HA molecules per cluster within the plasma membrane of NIH-3T3 mouse fibroblasts. HA is known to colocalize with the negatively-charged mammalian lipid phosphatidylinositol 4,5-bisphosphate (PIP2); here, we show that nanoscale co-localization of HA with the PIP2-binding Pleckstrin homology (PH) reporter in the plasma membrane is diminished by CPC. CPC also dramatically displaces the PIP2-binding protein myristoylated alanine-rich C-kinase substrate (MARCKS) from the plasma membrane of rat RBL-2H3 mast cells; this disruption of PIP2 is correlated with inhibition of mast cell degranulation. Together, these findings offer a PIP2-focused mechanism underlying CPC disruption of influenza and suggest potential pharmacological use of this drug as an influenza therapeutic to reduce global deaths from viral disease.

Triclosan disrupts immune cell function by depressing Ca2+ influx following acidification of the cytoplasm

Triclosan (TCS) is an antimicrobial agent that was effectively banned by the FDA from hand soaps in 2016, hospital soaps in 2017, and hand sanitizers in 2019; however, TCS can still be found in a few products. At consumer-relevant, non-cytotoxic doses, TCS inhibits the functions of both mitochondria and mast cells, a ubiquitous cell type. Via the store-operated Ca2+ entry mechanism utilized by many immune cells, mast cells undergo antigen-stimulated Ca2+ influx into the cytosol, for proper function. Previous work showed that TCS inhibits Ca2+ dynamics in mast cells, and here we show that TCS also inhibits Ca2+ mobilization in human Jurkat T cells. However, the biochemical mechanism behind the Ca2+ dampening has yet to be elucidated. Three-dimensional super-resolution microscopy reveals that TCS induces mitochondrial swelling, in line with and extending the previous finding of TCS inhibition of mitochondrial membrane potential via its proton ionophoric activity. Inhibition of plasma membrane potential (PMP) by the canonical depolarizer gramicidin can inhibit mast cell function. However, use of the genetically encoded voltage indicators (GEVIs) ArcLight (pH-sensitive) and ASAP2 (pH-insensitive), indicates that TCS does not disrupt PMP. In conjunction with data from a plasma membrane-localized, pH-sensitive reporter, these results indicate that TCS, instead, induces cytosolic acidification in mast cells and T cells. Acidification of the cytosol likely inhibits Ca2+ influx by uncoupling the STIM1/ORAI1 interaction that is required for opening of plasma membrane Ca2+ channels. These results provide a mechanistic explanation of TCS disruption of Ca2+ influx and, thus, of immune cell function.

Molecular evolution of the maize sex-determining gene TASSELSEED2 in Bouteloua (Poaceae)

The majority of angiosperms produce hermaphrodite flowers, while a lesser number (20-30%) produce unisexual flowers. Little is known about the molecular biology of sex-determination in angiosperms, however, a few sex-determining genes have been cloned from the model system Zea mays. One of these genes is Tasselseed2 (Ts2) which has been shown to be involved in the arrest of developing pistils in male flowers. In this study, we sequenced a putative homologue of Ts2 in species of Bouteloua, a genus in the grass subfamily Chloridoideae. We found significant genetic variation at Ts2 in Bouteloua relative to other developmental genes characterized in maize and other grass species. We also found that in Bouteluoua, Ts2 is evolving non-neutrally in the hermaphrodite-flowered Bouteloua hirsuta while no difference from neutral expectation was detected at Ts2 in the monoecious/dioecious Bouteloua dimorpha. The putatively neutral gene Alcohol Dehydrogenase1 (Adh1) was also examined for the same species of Bouteloua, and no departure from neutral expectation was detected. Our results suggest that purifying selection may be acting on Ts2 in the hermaphrodite-flowered B. hirsuta while no evidence of selection was detected at Ts2 in the monoecious/dioecious B. dimorpha.

Changes in length and disk shedding rate of Xenopus rod outer segments associated with metamorphosis

Histological examination of the retinae of Xenopus tadpoles undergoing the extensive transformations of metamorphic climax revealed a progressive and dramatic decrease in the length of rod outer segments (r. o. s.) (by 1.22 µm/day), which was reversed after the completion of metamorphosis, when r. o. s. grew longer (by 1.11 µm/day). The rate of r. o. s. disk addition during these two periods was determined by examining the incorporation of [ 3 H]-leucine by light microscopic autoradiography. The band of labelled protein in r. o. s. was displaced sclerally at a rate of 1.70 µm/day during the first half of metamorphic climax, and of 1.56 µm/day in young juveniles during the second month after metamorphosis. The similarity of the rate of band displacement at these times indicates that the changes in r. o. s. length associated with metamorphosis result from major changes in the rate of disk shedding and/or phagocytosis, which was about 2.92 µm/day pre-metamorphically and 0.45 µm/day post-metamorphically. E. m. observation at these stages and during the final stages of metamorphic climax revealed no significant alterations in the cellular organization or ultrastructure of rods or pigment epithelium, even though some r. o. s. were only 3 µm long. This large change in r. o. s. length undoubtedly influences the animal’s scotopic sensitivity and the relative mesopic activity of its rods and cones, and may have important effects on the animal’s visual physiology.

The photoreceptors and pigment epithelium of the larval Xenopus retina: morphogenesis and outer segment renewal

Light microscopic autoradiography and electron microscopy were used to examine outer segment renewal and the development of photoreceptors and pigment epithelium in the larvalXenopusretina. Following the injection of [3H]-leucine at stages 37/38–40 (when outer segments first develop) or 53–54 (when rod outer segments (r. o. s.) attain adult length), a band of label accumulated at the base of r. o. s. and was displaced sclerally with time, whereas label was diffusely distributed in cone outer segments (c. o. s.). By taking into account the change in shape of r. o. s. from conical to cylindrical around stage 46, and calculating outer segment growth (determined from the rate of band displacement) asvolumeof material added with time, we found a constant rate of membrane addition (1.59 μm/day) from the time of initial outer segment formation. The changes observed in r. o. s. length therefore indicate variations in the rate of disk shedding and phagocytosis, which is minimal before stage 46 and rises to 1.19 μm/day after stages 53–54. Ultrastructural observation showed that although all photoreceptor outer segments form by the repeated evagination of the plasma membrane of the connecting cilium, r. o. s. and c. o. s. are distinguishable by differences in membrane appearance even before they develop divergent membrane topologies. Fibrous granules near the basal body of young receptors may be precursors to the elongating ciliary microtubules. Clusters of cisternae observed near the ciliary base in photoreceptor inner segments may represent a stage in the transport of newly-synthesized opsin to the outer segment base.

The photoreceptors and pigment epithelim of the adult Xenopus retina: morphology and outer segment renewal

Outer segment renewal and the fine structure of photoreceptors and pigment epithelium (p. e.) were studied in the adult Xenopus retina by light microscopic autoradiography and electron microscopy. Following the injection of [ 3 H]leucine, the pattern of labelling observed in receptor outer segments was typical of that reported in other adult retinae: only diffuse labelling was found in cones, but in rods a discrete band of label accumulated at the base of the outer segment and migrated sclerally with time. The rate of band displacement and thus disk addition in Xenopus rods was 1.86 μm/day (or 78 disks/day), which is more than twice that reported for red rods in Rana under similar experimental conditions, although these species have similar metabolic rates. Average rod outer segment (r. o. s.) length did not change, demonstrating a balance between disk addition and shedding. R. o. s. renewal time was about 24 days, corresponding to the time when labelled phagosomes were first found in the p. e. Ultrastructurally, one kind of (red) rod and one kind of cone were found whose outer segments differed in membrane topology. Although microfilaments were found in the apical processes of the p. e. and its cytoplasm contained both pigment granules and myeloid bodies, pigment granules did not migrate into these processes during light adaptation. In addition to possible morphological evidence for phago­somes of cone origin, both large and small rod phagosomes were observed in the p. e. The latter appear to represent small stacks of partial disks shed from individual r. o. s. scallops.