Inhibition of Kv1.3 Channels in Human Jurkat T Cells by Xanthohumol and Isoxanthohumol

High throughput clone screening on overexpressed hERG1 and Kv1.3 potassium channels using ion channel reader (ICR) label free technology

Pharmacological studies aimed at the development of newly synthesized drugs directed against ion channels (as well as genetic studies of ion channel mutations) involve the development and use of transfected cells. However, the identification of the best clone, in terms of transfection efficiency, is often a time consuming procedure when performed through traditional methods such as manual patch-clamp. On the other hand, the use of other faster techniques, such as for example the IF, are not informative on the effective biological functionality of the transfected ion channel(s). In the present work, we used the high throughput automated ion channel reader (ICR) technology (ICR8000 Aurora Biomed Inc.) that combine atomic absorption spectroscopy with a patented microsampling process to accurately measure ion flux in cell-based screening assays. This technology indeed helped us to evaluate the transfection efficiency of hERG1 and hKv1.3 channels respectively on the HEK-293 and CHO cellular models. Moreover, as proof of the validity of this innovative method, we have corroborated these data with the functional characterization of the potassium currents carried out by the same clones through patch-clamp recordings. The results obtained in our study are promising and represent a valid methodological strategy to screen a large number of clones simultaneously and to pharmacologically evaluate their functionality within an extremely faster timeframe.

Flavonoids as Modulators of Potassium Channels

Potassium channels are widely distributed integral proteins responsible for the effective and selective transport of K+ ions through the biological membranes. According to the existing structural and mechanistic differences, they are divided into several groups. All of them are considered important molecular drug targets due to their physiological roles, including the regulation of membrane potential or cell signaling. One of the recent trends in molecular pharmacology is the evaluation of the therapeutic potential of natural compounds and their derivatives, which can exhibit high specificity and effectiveness. Among the pharmaceuticals of plant origin, which are potassium channel modulators, flavonoids appear as a powerful group of biologically active substances. It is caused by their well-documented anti-oxidative, anti-inflammatory, anti-mutagenic, anti-carcinogenic, and antidiabetic effects on human health. Here, we focus on presenting the current state of knowledge about the possibilities of modulation of particular types of potassium channels by different flavonoids. Additionally, the biological meaning of the flavonoid-mediated changes in the activity of K+ channels will be outlined. Finally, novel promising directions for further research in this area will be proposed.

Co-Application of Statin and Flavonoids as an Effective Strategy to Reduce the Activity of Voltage-Gated Potassium Channels Kv1.3 and Induce Apoptosis in Human Leukemic T Cell Line Jurkat

Voltage-gated potassium channels of the Kv1.3 type are considered a potential new molecular target in several pathologies, including some cancer disorders and COVID-19. Lipophilic non-toxic organic inhibitors of Kv1.3 channels, such as statins and flavonoids, may have clinical applications in supporting the therapy of some cancer diseases, such as breast, pancreas, and lung cancer; melanoma; or chronic lymphocytic leukemia. This study focuses on the influence of the co-application of statins-simvastatin (SIM) or mevastatin (MEV)-with flavonoids 8-prenylnaringenin (8-PN), 6-prenylnarigenin (6-PN), xanthohumol (XANT), acacetin (ACAC), or chrysin on the activity of Kv1.3 channels, viability, and the apoptosis of cancer cells in the human T cell line Jurkat. We showed that the inhibitory effect of co-application of the statins with flavonoids was significantly more potent than the effects exerted by each compound applied alone. Combinations of simvastatin with chrysin, as well as mevastatin with 8-prenylnaringenin, seem to be the most promising. We also found that these results correlate with an increased ability of the statin-flavonoid combination to reduce viability and induce apoptosis in cancer cells compared to single compounds. Our findings suggest that the co-application of statins and flavonoids at low concentrations may increase the effectiveness and safety of cancer therapy. Thus, the simultaneous application of statins and flavonoids may be a new and promising anticancer strategy.

Midazolam's Effects on Delayed-Rectifier K+ Current and Intermediate-Conductance Ca2+-Activated K+ Channel in Jurkat T-lymphocytes

Midazolam (MDZ) could affect lymphocyte immune functions. However, the influence of MDZ on cell’s K⁺ currents has never been investigated. Thus, in the present study, the effects of MDZ on Jurkat T lymphocytes were studied using the patch-clamp technique. Results showed that MDZ suppressed the amplitude of delayed-rectifier K⁺ current (I_K(DR)) in concentration-, time-, and state-dependent manners. The IC₅₀ for MDZ-mediated reduction of I_K(DR) density was 5.87 μM. Increasing MDZ concentration raised the rate of current-density inactivation and its inhibitory action on I_K(DR) density was estimated with a dissociation constant of 5.14 μM. In addition, the inactivation curve of I_K(DR) associated with MDZ was shifted to a hyperpolarized potential with no change on the slope factor. MDZ-induced inhibition of I_K(DR) was not reversed by flumazenil. In addition, the activity of intermediate-conductance Ca²⁺-activated K⁺ (IK_Ca) channels was suppressed by MDZ. Furthermore, inhibition by MDZ on both I_K(DR) and IK_Ca-channel activity appeared to be independent from GABAA receptors and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes. In conclusion, MDZ suppressed current density of I_K(DR) in concentration-, time-, and state-dependent manners in Jurkat T-lymphocytes and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes.

Actions of FTY720 (Fingolimod), a Sphingosine-1-Phosphate Receptor Modulator, on Delayed-Rectifier K+ Current and Intermediate-Conductance Ca2+-Activated K+ Channel in Jurkat T-Lymphocytes

FTY720 (fingolimod), a modulator of sphingosine-1-phosphate receptors, is known to produce the immunomodulatory actions and to be beneficial for treating the relapsing multiple sclerosis. However, whether it exerts any effects on membrane ion currents in immune cells remains largely unknown. Herein, the effects of FTY720 on ionic currents in Jurkat T-lymphocytes were investigated. Cell exposure to FTY720 suppressed the amplitude of delayed-rectifier K⁺ current (I_K(DR)) in a time- and concentration-dependent manner with an IC₅₀ value of 1.51 μM. Increasing the FTY720 concentration not only decreased the I_K(DR) amplitude but also accelerated the inactivation time course of the current. By using the minimal reaction scheme, the effect of FTY720 on I_K(DR) inactivation was estimated with a dissociation constant of 3.14 μM. FTY720 also shifted the inactivation curve of I_K(DR) to a hyperpolarized potential with no change in the slope factor, and recovery from I_K(DR) became slow during the exposure to this compound. Cumulative inactivation for I_K(DR) in response to repetitive depolarizations was enhanced in the presence of FTY720. In SEW2871-treated cells, FTY720-induced inhibition of I_K(DR) was attenuated. This compound also exerted a stimulatory action on the activity of intermediate-conductance Ca²⁺-activated K⁺ channels in Jurkat T-lymphocytes. However, in NSC-34 neuronal cells, FTY720 did not modify the inactivation kinetics of KV3.1-encoded I_K(DR), although it suppressed I_K(DR) amplitude in these cells. Collectively, the perturbations by FTY720 on different types of K⁺ channels may contribute to the functional activities of immune cells, if similar findings appear in vivo.

Immunosuppressive effects of a novel potassium channel toxin Ktx-Sp2 from Scorpiops Pocoki

Background

The cDNA Library of venomous animals could provide abundant bioactive peptides coding information and is an important resource for screening bioactive peptides that target and regulate disease-related ion channels. To further explore the potential medicinal usage of the transcriptome database of Scorpiops Pocoki’s venom gland, this research identified the function of a new potassium channel toxin Ktx-Sp2, whose gene was screened from the database by sequence alignment.

Results

The mature peptide of Ktx-Sp2 was obtained by genetic engineering. Whole-cell patch-clamp experiment showed that Ktx-Sp2 peptide could effectively block three types of exogenous voltage-gated potassium channels—Kv1.1, Kv1.2 and Kv1.3, among which, the blocking activity for Kv1.3 was relatively high, showing selectivity to some extent. Taking Jurkat T cells as the cell model, this study found that Ktx-Sp2 peptide could also effectively block endogenous Kv1.3, significantly reduce the free calcium concentration in Jurkat T cells, inhibit the activation of Jurkat T cells and reduce the release of inflammatory cytokines IL-2, showing a strong immunosuppressant effect.

Conclusions

This study further proves that the transcriptome database of the Scorpiops Pocoki venom gland is an important resource for discovery of novel bioactive polypeptide coding genes. The newly screened Kv1.3 channel blocker Ktx-Sp2 expanded the range of leading compounds for the treatment of autoimmune diseases and promoted the development and application of scorpion toxin peptides in the field of biomedicine.

Voltage-Gated Potassium Channel Kv1.3 as a Target in Therapy of Cancer

Voltage-gated potassium channel Kv1.3 is an integral membrane protein, which is selectively permeable for potassium ions and is activated upon a change of membrane potential. Channel activation enables transportation of potassium ions down their electrochemical gradient. Kv1.3 channel is expressed in many cell types, both normal and cancer. Activity of the channel plays an important role in cell proliferation and apoptosis. Inhibition of Kv1.3 channel may be beneficial in therapy of several diseases including some cancer disorders. This review focuses on Kv1.3 channel as a new potentially attractive molecular target in cancer therapy. In the first part, changes in the channel expression in selected cancer disorders are described. Then, the role of the channel activity in cancer cell proliferation and apoptosis is presented. Finally, it is shown that some low molecular weight organic inhibitors of the channel including selected biologically active plant-derived polycyclic compounds may selectively induce apoptosis of Kv1.3-expressing cancer cells while sparing normal cells and healthy organs. These compounds may be promising candidates for putative application in therapy of some cancer disorders, such as melanoma, pancreatic ductal adenocarcinoma (PDAC), or B-type chronic lymphocytic leukemia (B-CLL).

The Influence of 6-Prenylnaringenin and Selected Non-prenylated Flavonoids on the Activity of Kv1.3 Channels in Human Jurkat T Cells

The influence of a prenylated flavonoid-6-prenylnaringenin (6-PR) and selected non-prenylated flavonoids: acacetin, chrysin, baicalein, wogonin, and luteolin on the activity of voltage-gated potassium channels Kv1.3 was investigated in human leukemic Jurkat T cells. Electrophysiological measurements were accompanied by studies on the cytotoxic effect of the examined compounds on Jurkat T cells. Electrophysiological studies were performed using the whole-cell patch-clamp technique. Cell viability was determined using the MTT assay. 6-PR inhibited Kv1.3 channels in Jurkat T cells in a concentration-dependent manner. The estimated value of the half-blocking concentration (EC₅₀) was about 5.76 µM. Among non-prenylated flavonoids, acacetin and chrysin inhibited Kv1.3 channels in Jurkat T cells when applied at the concentration of 30 µM, whereas baicalein, wogonin, and luteolin were ineffective at this concentration. The inhibitory effects of acacetin and chrysin on Kv1.3 channels were significantly less potent than the inhibition caused by 6-PR. All tested compounds inhibited growth of Jurkat T cells in a concentration-dependent manner. Wogonin and chrysin were the most cytotoxic flavonoids tested, whereas baicalein and 6-PR were the least cytotoxic compounds. In accordance to our hypothesis the prenylated flavonoid (6-PR) was much more effective inhibitor of Kv1.3 channels than non-prenylated compounds selected for this study. The inhibition of Kv1.3 channels by 6-PR, acacetin, and chrysin was not related to cytotoxicity of these compounds. The channels' inhibition might be involved in anti-proliferative and pro-apoptotic effects of 6-PR, acacetin and chrysin observed in cancer cell lines expressing these channels.