Diethylstilbestrol and other nonsteroidal estrogens: novel class of store-operated calcium channel modulators

Antibacterial and Antibiofilm Efficacy of Repurposing Drug Hexestrol against Methicillin-resistant Staphylococcus aureus

There has been an explosion in the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) because of the indiscriminate use of antibiotics. In this study, we repurposed hexestrol (HXS) as an antibacterial agent to fight planktonic and biofilm-related MRSA infections. HXS is a nonsteroidal synthetic estrogen that targets estrogen receptors (ERα and ERβ) and has been used as a hormonal antineoplastic agent. In our work, the minimum inhibitory concentrations (MICs) were determined using the antimicrobial susceptibility of MSSA and MRSA strains. Anti-biofilm activity was evaluated using biofilm inhibition and eradication assays. Biofilm-related genes were analyzed with or without HXS treatment using RTqPCR analysis of S. aureus. HXS was tested using the checkerboard dilution assay to identify antibiotics that may have synergistic effects. Measurement of ATP and detection of ATPase allowed the determination of bacterial energy metabolism. As shown in the results, HXS showed effective antimicrobial activity against S. aureus, including both type strains and clinical isolations, with MICs of 16 µg/mL. Sub-HXS strongly inhibited the adhesion of S. aureus. The content of extracellular polymeric substances (EPS) and the relative transcription levels of eno, sacC, clfA, pls and fnbpB were reduced after HXS treatment. HXS showed antibacterial effects against S. aureus and synergistic activity with aminoglycosides by directly interfering with cellular energy metabolism. HXS inhibits adhesion and biofilm formation and eradicates biofilms formed by MRSA by reducing the expression of related genes. Furthermore, HXS increases the susceptibility of aminoglycosides against MRSA. In conclusion, HXS is a repurposed drug that may be a promising therapeutic option for MRSA infection.

Aberrant calcium signalling downstream of mutations in TP53 and the PI3K/AKT pathway genes promotes disease progression and therapy resistance in triple negative breast cancer

Triple-negative breast cancer (TNBC) is characterized as an aggressive form of breast cancer (BC) associated with poor patient outcomes. For the majority of patients, there is a lack of approved targeted therapies. Therefore, chemotherapy remains a key treatment option for these patients, but significant issues around acquired resistance limit its efficacy. Thus, TNBC has an unmet need for new targeted personalized medicine approaches. Calcium (Ca²⁺) is a ubiquitous second messenger that is known to control a range of key cellular processes by mediating signalling transduction and gene transcription. Changes in Ca²⁺ through altered calcium channel expression or activity are known to promote tumorigenesis and treatment resistance in a range of cancers including BC. Emerging evidence shows that this is mediated by Ca²⁺ modulation, supporting the function of tumour suppressor genes (TSGs) and oncogenes. This review provides insight into the underlying alterations in calcium signalling and how it plays a key role in promoting disease progression and therapy resistance in TNBC which harbours mutations in tumour protein p53 (TP53) and the PI3K/AKT pathway.

Naphthalene Exchange in [Re(η6 -napht)2 ]+ with Pharmaceuticals Leads to Highly Functionalized Sandwich Complexes [M(η6 -pharm)2 ]+ (M=Re/99m Tc)

Bis‐arene sandwich complexes are generally prepared by the Fischer‐Hafner reaction, which conditions are incompatible with most O‐ and N‐ functional groups. We report a new way for the synthesis of sandwich type complexes [Re(η⁶‐arene)₂]⁺ and [Re(η⁶‐arene)(η⁶‐benzene)]⁺ from [Re(η⁶‐napht)₂]⁺ and [Re(η⁶‐napht)(η⁶‐benzene)]⁺, with functionalized arenes and pharmaceuticals. N‐methylpyrrolidine (NMP) facilitates the substitution of naphthalene with the incoming arene. A series of fully characterized rhenium sandwich complexes with simple arenes, such as aniline, as well as with active compounds like lidocaine and melatonin are presented. With these rhenium compounds in hand, the radioactive sandwich complexes [^99mTc(η⁶‐pharm)₂]⁺ (pharm=pharmaceutical) can be unambiguously confirmed. The direct labelling of pharmaceuticals with ^99mTc through η⁶‐coordination to phenyl rings and the confirmation of the structures with the rhenium homologues opens a path into molecular theranostics.

Development of Store-Operated Calcium Entry-Targeted Compounds in Cancer

Store-operated Ca²⁺ entry (SOCE) is the major pathway of Ca²⁺ entry in mammalian cells, and regulates a variety of cellular functions including proliferation, motility, apoptosis, and death. Accumulating evidence has indicated that augmented SOCE is related to the generation and development of cancer, including tumor formation, proliferation, angiogenesis, metastasis, and antitumor immunity. Therefore, the development of compounds targeting SOCE has been proposed as a potential and effective strategy for use in cancer therapy. In this review, we summarize the current research on SOCE inhibitors and blockers, discuss their effects and possible mechanisms of action in cancer therapy, and induce a new perspective on the treatment of cancer.

Resveratrol inhibits Ca2+ signals and aggregation of platelets

Background

Resveratrol has been shown to inhibit platelet aggregation. However, the mechanism for this action of resveratrol remains to be clarified. The purpose of this study was to elucidate the Ca²⁺-related mechanism for the inhibitory action of resveratrol on platelet aggregation.

Methods

Ca²⁺ entry and subsequent aggregation of human platelets induced by different stimulants including thrombin, thapsigargin, and 1-oleoyl-2-acetylglycerol (OAG) were measured by the fluorescence method and light transmittance method, respectively. Each stimulant was added to a nominally Ca²⁺-free medium containing platelets, and then CaCl₂ was added to the medium to induce Ca²⁺ influx into platelets.

Results

Thapsigargin-induced Ca²⁺ entry into platelets and subsequent platelet aggregation were significantly inhibited in the presence of resveratrol at 6.25 μM or higher concentrations, while OAG-induced Ca²⁺ entry and subsequent platelet aggregation were not affected by resveratrol at concentrations up to 50 μM. In the nominally Ca²⁺-free medium, thrombin induced a small transient increase in intracellular Ca²⁺ concentrations, which was attenuated in the presence of resveratrol at 12.5 μM or higher concentrations. Thrombin-induced Ca²⁺ entry into platelets and subsequent platelet aggregation were significantly inhibited in the presence of resveratrol at 12.5 μM or higher concentrations.

Conclusions

The results suggest that resveratrol inhibits thrombin-induced platelet aggregation through decreasing Ca²⁺ release from its stores and inhibiting store-operated Ca²⁺ influx into platelets.

Puberty visualized: sexual maturation in the transparent Casper zebrafish

Transparent Casper zebrafish allow studies of vertebrate sexual maturation and gonad development in vivo. Casper gonad dynamics can be observed longitudinally over time and non-invasively. Gonad maturation and reproduction are complex processes subject to disruption by endocrine-disrupting chemicals (EDCs), such as diethylstilbestrol (DES). DES was used as a 'proof of principle' to ascertain the usefulness of the Casper model to determine EDC effects on gonad maturation. Puberty onset in control juvenile Casper zebrafish (N = 43) averaged 13.2 weeks post fertilization (WPF) for females and included increased vent size, while in males puberty occurred at 11.7 WPF along with maintenance of small vents. DES treatment for 6 days in early juveniles (N = 20) induced an average delay in puberty of 5 weeks in females and 10 weeks in males. DES induced loss of breeding tubercles and vent enlargement in post-pubescent males. Puberty in control fish was correlated with an average body length of 1.7 cm for males and 1.8 cm for females. Increased testes opacity, small vent and breeding tubercles denoted male puberty. Puberty in females was defined as ovarian follicle diameters reaching 400 µm with increasingly opaque follicles and by an increased vent size. These results are like those for wild-type zebrafish and indicate that the Casper model is a useful system for studying gonad dynamics in vivo. Future use of transgenic reporter lines in Casper will allow new avenues of investigation into the reproductive biology of this vertebrate model.

In vivo assessment of gonad status, secondary sex characteristics and spawning in transparent Casper zebrafish

Important aspects of vertebrate reproduction, such as gametogenesis, involve changes in organs found deep internally and thus not easily studied directly in most living vertebrates due to obscuring pigment and overlying tissues. Transparent lines of zebrafish, especially the Casper double mutant, allow direct observation and analysis of reproductive events in the gonads in vivo. The natural production of fertilized eggs in zebrafish is a complex process involving oogenesis, spermatogenesis, mating behavior, endocrine and neurological processes with inputs from the environment including light, temperature and nutrition. While these factors play important roles, the hypothalamic-pituitary-gonadal axis (HPGA) is central in the regulation of embryo output. Endocrine disrupting compounds (EDCs) include a variety of pollutants often present in the environment. EDCs may have direct effects on the HPGA or indirect effects through toxic action on supporting organs such as the liver or kidney. Estrogenic compounds such as diethylstilbestrol (DES) have been reported to affect reproduction in a variety of species including man. In this study, the effects of DES on reproduction were determined in a novel way by using transparent Casper zebrafish that allow direct visualization of gonad status over time. Changes in gonad status with DES treatment were correlated with effects on secondary sex characteristics (i.e., genital vent size and breeding tubercles) spawning and embryo production. The results suggest that the Casper zebrafish is a useful model for studying dynamics of reproductive events in vertebrate gonads in vivo and for determining effects of EDCs on zebrafish reproduction.

Transient Receptor Potential Canonical 3 and Nuclear Factor of Activated T Cells C3 Signaling Pathway Critically Regulates Myocardial Fibrosis

AIMS

Cardiac fibroblasts (CFs) are emerging as major contributors to myocardial fibrosis (MF), a final common pathway of many etiologies of heart disease. Here, we studied the functional relevance of transient receptor potential canonical 3 (TRPC3) channels and nuclear factor of activated T cells c3 (NFATc3) signaling in rodent and human ventricular CFs, and whether their modulation would limit MF.

RESULTS

A positive feedback loop between TRPC3 and NFATc3 drove a rat ventricular CF fibrotic phenotype. In these cells, polyphenols (extract of grape pomace polyphenol [P.E.]) decreased basal and angiotensin II-mediated Ca²⁺ entries through a direct modulation of TRPC3 channels and subsequently NFATc3 signaling, abrogating myofibroblast differentiation, fibrosis and inflammation, as well as an oxidative stress-associated phenotype. N(ω)-nitro-l-arginine methyl ester (l-NAME) hypertensive rats developed coronary perivascular, sub-epicardial, and interstitial fibrosis with induction of embryonic epicardial progenitor transcription factors in activated CFs. P.E. treatment reduced ventricular CF activation by modulating the TRPC3-NFATc3 pathway, and it ameliorated echocardiographic parameters, cardiac stress markers, and MF in l-NAME hypertensive rats independently of blood pressure regulation. Further, genetic deletion (TRPC3^-/-) and pharmacological channel blockade with N-[4-[3,5-Bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl]-4-methyl-benzenesulfonamide (Pyr10) blunted ventricular CF activation and MF in l-NAME hypertensive mice. Finally, TRPC3 was present in human ventricular CFs and upregulated in MF, whereas pharmacological modulation of TRPC3-NFATc3 decreased proliferation and collagen secretion. Innovation and Conclusion: We demonstrate that TRPC3-NFATc3 signaling is modulated by P.E. and critically regulates ventricular CF phenotype and MF. These findings strongly argue for P.E., through TRPC3 targeting, as potential and interesting therapeutics for MF management.

Flavonoids and Platelet-Derived Thrombotic Disorders

:

Thrombotic disorders are characterized by an increase in the probability of the formation of unnecessary thrombi that might be due to the activation of the coagulation cascade or the circulating platelets. Platelets or thrombocytes play an essential role in hemostasis but abnormal platelet function leads to the development of a number of cardiovascular complications, including thrombotic disorders. Under pathological conditions, platelets are associated with the development of different thrombotic disorders, including atherosclerosis, arterial thrombosis and stroke, deep venous thrombosis and pulmonary embolism; therefore, platelets are the target of a number of anti-thrombotic strategies. Flavonoids, a large group of polyphenols ubiquitously expressed in fruits and vegetables that have attracted considerable attention because of their benefits in human health, including the reduction of the risk of cardiovascular disease. Flavonoids have been reported to reduce platelet activity by attenuating agonist-induced GPIIb/IIIa receptor activation, mobilization of intracellular free Ca2+, granule exocytosis, as well as activation of different signaling molecules such as mitogen- activated protein kinases or phospholipases. This review summarizes the current studies concerning the modulation of platelet activation by flavonoids, giving especial attention to those events associated to thrombotic disorders.

Recovery of fertility in quinestrol-treated or diethylstilbestrol-treated mice: Implications for rodent management

Fertility control is an alternative strategy to traditional culling for the management of rodent pests. Previous studies have demonstrated that quinestrol is a potential contraceptive for male rodents, but the recovery of fertility in quinestrol-treated rodents has not been evaluated. This study used C57BL/6J mice to evaluate the recovery rate of male fertility after the administration of quinestrol. Diethylstilbestrol (DES), a non-steroid estrogenic compound, was used for comparison. Different groups of mice were treated with 1 mg/kg quinestrol, 1 mg/kg DES, or castor oil separately for 7 days. These mice were then killed on days 8, 22 and 50 respectively. Our results indicated that the weight of epididymides and seminal vesicles decreased significantly on days 8 and 22 in quinestrol/DES-treated mice, with extensive histological changes in the seminiferous tubules. Sperm concentrations in the cauda epididymal fluid were significantly reduced on days 8 and 22 in both quinestrol and DES treatment groups and on day 50 for the DES, but not the quinestrol group. Further analysis revealed that DES-treated mice exhibited a higher proportion of abnormal sperm accumulation in the epididymis, indicating that the normal sperm transportation to the cauda epididymis was blocked. Our results indicate that the anti-fertility effects on male mice given quinestrol were of shorter duration than for those receiving DES at the dose of 1 mg/kg body weight.

Molecular signaling mechanisms behind polyphenol-induced bone anabolism

For millennia, in the different cultures all over the world, plants have been extensively used as a source of therapeutic agents with wide-ranging medicinal applications, thus becoming part of a rational clinical and pharmacological investigation over the years. As bioactive molecules, plant-derived polyphenols have been demonstrated to exert many effects on human health by acting on different biological systems, thus their therapeutic potential would represent a novel approach on which natural product-based drug discovery and development could be based in the future. Many reports have provided evidence for the benefits derived from the dietary supplementation of polyphenols in the prevention and treatment of osteoporosis. Polyphenols are able to protect the bone, thanks to their antioxidant properties, as well as their anti-inflammatory actions by involving diverse signaling pathways, thus leading to bone anabolic effects and decreased bone resorption. This review is meant to summarize the research works performed so far, by elucidating the molecular mechanisms of action of polyphenols in a bone regeneration context, aiming at a better understanding of a possible application in the development of medical devices for bone tissue regeneration.

Resveratrol and calcium signaling: molecular mechanisms and clinical relevance

Resveratrol is a naturally occurring compound contributing to cellular defense mechanisms in plants. Its use as a nutritional component and/or supplement in a number of diseases, disorders, and syndromes such as chronic diseases of the central nervous system, cancer, inflammatory diseases, diabetes, and cardiovascular diseases has prompted great interest in the underlying molecular mechanisms of action. The present review focuses on resveratrol, specifically its isomer trans-resveratrol, and its effects on intracellular calcium signaling mechanisms. As resveratrol's mechanisms of action are likely pleiotropic, its effects and interactions with key signaling proteins controlling cellular calcium homeostasis are reviewed and discussed. The clinical relevance of resveratrol's actions on excitable cells, transformed or cancer cells, immune cells and retinal pigment epithelial cells are contrasted with a review of the molecular mechanisms affecting calcium signaling proteins on the plasma membrane, cytoplasm, endoplasmic reticulum, and mitochondria. The present review emphasizes the correlation between molecular mechanisms of action that have recently been identified for resveratrol and their clinical implications.

Resveratrol Interferes with Fura-2 Intracellular Calcium Measurements

Resveratrol, a naturally occurring polyphenol found in some fruits and especially in grapes, has been reported to provide diverse health benefits. Resveratrol's mechanism of action is the subject of many investigations, and some studies using the ratiometric calcium indicator Fura-2 suggest that it modulates cellular calcium responses. In the current study, contradictory cellular calcium responses to resveratrol applied at concentrations exceeding 10 μM were observed during in vitro imaging studies depending on the calcium indicator used, with Fura-2 indicating an increase in intracellular calcium while Fluo-4 and the calcium biosensor YC3.60 indicated no response. When cells loaded with Fura-2 were treated with 100 μM resveratrol, excitation at 340 nm resulted in a large intensity increase at 510 nm, but the expected concurrent decline with 380 nm excitation was not observed. Pre-treatment of cells with the calcium chelator BAPTA-AM did not prevent a rise in the 340/380 ratio when resveratrol was present, but it did prevent an increase in 340/380 when ATP was applied, suggesting that the resveratrol response was an artifact. Cautious data interpretation is recommended from imaging experiments using Fura-2 concurrently with resveratrol in calcium imaging experiments.

Inhibition of STIM1 phosphorylation underlies resveratrol-induced inhibition of store-operated calcium entry

Resveratrol, a natural phytoalexin that shows health-promoting benefits, is an inhibitor of store-operated calcium entry (SOCE). Knowledge of the molecular mechanism underlying this inhibition is required for the proper design of therapies that include resveratrol or related stilbenoids, but remains largely unknown. To unravel this mechanism, using HEK293 cells as a model, we found that resveratrol inhibited the ERK1/2 activation triggered by Ca²⁺ store depletion. As a consequence, resveratrol inhibited STIM1 phosphorylation at residues Ser575, Ser608, and Ser621. Because this phosphorylation regulates the dissociation of STIM1 from the microtubule plus-end binding protein EB1 under store depletion conditions, resveratrol inhibited STIM1-EB1 dissociation. This inhibition had downstream effects such as inhibition of STIM1 multimerization in response to store depletion, and a significant impairment in the binding of STIM1 to ORAI1. Although additional targets for resveratrol in the molecular mechanism that governs SOCE cannot be discarded, the present results demonstrate that ERK1/2 pathway is a major target for resveratrol, and that the impairment of its activation produces a significant inhibition of SOCE.

Waterborne exposure of zebrafish embryos to micromole concentrations of ioxynil and diethylstilbestrol disrupts thyrocyte development

The herbicide ioxynil (IOX) and synthetic estrogen diethylstilbestrol (DES) are common aquatic contaminants with an endocrine disrupting action. In juvenile teleost fish IOX and DES disrupt the hypothalamic-pituitary-thyroid (HPT) axis. To assess how IOX and DES influence the developing HPT axis prior to establishment of central regulation of thyroid hormones, zebrafish embryos were exposed to low concentrations of the chemicals in water. IOX and DES (1 and 0.1 μM) exposure failed to modify hypothalamic development but had a negative effect on thyrocyte development. Specifically, IOX and DES caused a significant (p<0.05) reduction in the size of the thyroid anlagen by decreasing the mRNA expression field of both nk2.1a and thyroglobulin (Tg) genes. Inhibition of thyroid gland development by IOX and DES (0.1 μM) was strongly associated with altered heart morphology. To test if the effect of IOX and DES on the thyroid was a consequence of altered cardiac development a morpholino (MO) against zebrafish cardiac troponin I (zcTnI) was microinjected. The zcTnI morphants had modified heart function, a small thyroid anlagen and a reduction in the mRNA expression of nk2.1a and Tg genes similar to that of zebrafish exposed to IOX (1 and 0.1 μM) and DES (0.1 μM). Collectively the data indicate that IOX and DES alter thyroid development in zebrafish and chemicals that alter heart development and function can have an indirect endocrine disrupting action on the thyroid in teleosts.

Regulation of STIM1/Orai1-dependent Ca2+ signalling in platelets

Platelet secretion and aggregation as well as thrombus formation of blood platelets critically depend on increase of cytosolic Ca2+ concentration ([Ca2+]i) mainly resulting from intracellular Ca2+ release followed by store operated Ca2+ entry (SOCE) through Ca2+ release activated channels (CRAC). SOCE is in part accomplished by the pore forming unit Orai and its regulator stromal interaction molecule (STIM). Orai1 and STIM1 transcription is stimulated by NF-κB (nuclear factor kappa B). Serum- and glucocorticoid-inducible kinase 1 (SGK1) up-regulates NF-κB-activity in megakaryocytes and thus Orai1-expression and SOCE in platelets. SGK1 is thus a powerful regulator of platelet Ca2+-signalling and thrombus formation and presumably participates in the regulation of platelet activation by a variety of hormones as well as clinical conditions (e.g. type 2 diabetes or metabolic syndrome) associated with platelet hyperaggregability and increased risk of thromboocclusive events. SOCE in platelets is further regulated by scaffolding protein Homer and chaperone protein cyclophilin A (CyPA). Additional potential regulators of Orai1/STIM1 and thus SOCE in platelets include AMP activated kinase (AMPK), protein kinase A (PKA), reactive oxygen species, lipid rafts, pH and mitochondrial Ca2+ buffering. Future studies are required defining the significance of those mechanisms for platelet Orai1 abundance and function, for SOCE into platelets and for platelet function in cardiovascular diseases.

Lysophosphatidic acid promotes cell migration through STIM1- and Orai1-mediated Ca2+(i) mobilization and NFAT2 activation

Lysophosphatidic acid (LPA) enhances cell migration and promotes wound healing in vivo, but the intracellular signaling pathways regulating these processes remain incompletely understood. Here we investigated the involvement of agonist-induced Ca²⁺ entry and STIM1 and Orai1 proteins in regulating nuclear factor of activated T cell (NFAT) signaling and LPA-induced keratinocyte cell motility. As monitored by Fluo-4 imaging, stimulation with 10 μℳ LPA in 60 μℳ Ca²⁺_o evoked Ca²⁺_i transients owing to store release, whereas addition of LPA in physiological 1.2 mℳ Ca²⁺_o triggered store release coupled to extracellular Ca²⁺ entry. Store-operated Ca²⁺ entry (SOCE) was blocked by the SOCE inhibitor diethylstilbestrol (DES), STIM1 silencing using RNA interference (RNAi), and expression of dominant/negative Orai1^R91W. LPA induced significant NFAT activation as monitored by nuclear translocation of green fluorescent protein-tagged NFAT2 and a luciferase reporter assay, which was impaired by DES, expression of Orai1^R91W, and inhibition of calcineurin using cyclosporin A (CsA). By using chemotactic migration assays, LPA-induced cell motility was significantly impaired by STIM1, CsA, and NFAT2 knockdown using RNAi. These data indicate that in conditions relevant to epidermal wound healing, LPA induces SOCE and NFAT activation through Orai1 channels and promotes cell migration through a calcineurin/NFAT2-dependent pathway.

Tamoxifen promotes superoxide production in platelets by activation of PI3-kinase and NADPH oxidase pathways

BACKGROUND

Tamoxifen is a selective estrogen receptor antagonist that is widely used for treatment and prevention of breast cancer. However, tamoxifen use can lead to an increased incidence of thrombotic events. The reason for this adverse event remains unknown. Previous studies showed that tamoxifen and its active metabolite Z-4-hydroxytamoxifen rapidly increased intracellular free calcium ([Ca(2+)](i)) in human platelets by a non-genomic mechanism that involved the activation of phospholipase C. Platelets play a pivotal role in thrombosis and Ca(2+) elevation is a central event in platelet activation. Therefore the mechanism by which tamoxifen activated Ca(2+) entry into platelets was investigated.

METHODS

[Ca(2+)](i) was measured using the fluorescent indicator fura-2 and reactive oxygen species were measured using lucigenin in isolated human platelets.

RESULTS

Tamoxifen analogs E-4-hydroxytamoxifen, with weak activity at the nuclear estrogen receptor and Z-4-hydroxytamoxifen, with strong activity at nuclear estrogen receptor, were equally active at increasing [Ca(2+)](i) and synergizing with ADP and thrombin to increase [Ca(2+)](i) in platelets. This result suggests that the effects of tamoxifen and E- and Z-4-hydroxytamoxifen to increase [Ca(2+)](i) are not mediated by the classical genomic estrogen receptor. The effects of tamoxifen to increase [Ca(2+)](i) were strongly inhibited by apocynin and apocynin dimer. This suggests that tamoxifen activates NADPH oxidase which leads to superoxide generation and in turn caused an increase in [Ca(2+)](i). Free radical scavengers TEMPO and TEMPOL also inhibited tamoxifen-induced [Ca(2+)](i) elevation. Inhibition of phosphoinositide-3-kinase (PI3-kinase), an upstream effector of NADPH oxidase with wortmannin and LY-294,002 also caused substantial inhibition of tamoxifen-induced elevation of [Ca(2+)](i).

CONCLUSION

Tamoxifen increases [Ca(2+)](i) in human platelets by a non-genomic mechanism. Tamoxifen activates phospholipase Cγ as well as PI3-kinase and NADPH oxidase pathway to generate superoxide which causes the release of Ca(2+) from the endoplasmic reticulum, and promotes Ca(2+) influx into the platelets.

TRPC5 channel sensitivities to antioxidants and hydroxylated stilbenes

Transient receptor potential canonical 5 (TRPC5) forms cationic channels that are polymodal sensors of factors including oxidized phospholipids, hydrogen peroxide, and reduced thioredoxin. The aim of this study was to expand knowledge of the chemical-sensing capabilities of TRPC5 by investigating dietary antioxidants. Human TRPC5 channels were expressed in HEK 293 cells and studied by patch clamp and intracellular Ca(2+) recording. GFP- and HA-tagged channels were used to quantify plasma membrane localization. Gallic acid and vitamin C suppressed TRPC5 activity if it was evoked by exogenous hydrogen peroxide or lanthanide ions but not by lysophosphatidylcholine or carbachol. Catalase mimicked the effects, suggesting that lanthanide-evoked activity depended on endogenous hydrogen peroxide. Trans-resveratrol, by contrast, inhibited all modes of TRPC5, and its effect was additive with that of vitamin C, suggesting antioxidant-independent action. The IC(50) was ∼10 μM. Diethylstilbestrol, a related hydroxylated stilbene, inhibited TRPC5 with a similar IC(50), but its action contrasted sharply with that of resveratrol in outside-out membrane patches where diethylstilbestrol caused strong and reversible inhibition and resveratrol had no effect, suggesting indirect modulation by resveratrol. Resveratrol did not affect channel surface density, but its effect was calcium-sensitive, indicating an action via a calcium-dependent intermediate. The data suggest previously unrecognized chemical-sensing properties of TRPC5 through multiple mechanisms: (i) inhibition by scavengers of reactive oxygen species because a mode of TRPC5 activity depends on endogenous hydrogen peroxide; (ii) direct channel blockade by diethylstilbestrol; and (iii) indirect, antioxidant-independent inhibition by resveratrol.