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Site and Mechanism of Action of Resin Acids on Voltage-Gated Ion Channels
Linköping University, Department of Clinical and Experimental Medicine, Divison of Neurobiology. Linköping University, Faculty of Medicine and Health Sciences.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Voltage-gated ion channels are pore-forming membrane proteins that open or close their gates when the voltage across the membrane is changed. They underlie the electrical activity that enables the heart to pump blood and the brain to receive and send signals. Changes in expression, distribution, and functional properties of voltage-gated ion channels can lead to diseases, such as epilepsy, cardiac arrhythmia, and pain-related disorders. Drugs that modulate the function of voltage-gated ion channels control these diseases in some patients, but the existing drugs do not adequately help all patients, and some also have severe side effects.

Resin acids are common components of pine resins, with a hydrophobic three-ringed motif and a negatively charged carboxyl group. They open big-conductance Ca2+-activated K+ (BK) channels and voltage-gated potassium (KV) channels. We aimed to characterize the binding site and mechanism of action of resin acids on a KV channel and explore the effect of a resin acid by modifying the position and valence of charge of the carboxyl group. We tested the effect on several voltage-gated ion channels, including two KV channels expressed in Xenopus laevis oocytes and several voltage-gated ion channels expressed in cardiomyocytes. For this endeavour different electrophysiological techniques, ion channels, and cell types were used together with chemical synthesis of about 140 resin-acid derivatives, mathematical models, and computer simulations.

We found that resin acids bind between the lipid bilayer and the Shaker KV channel, in the cleft between transmembrane segment S3 and S4, on the extracellular side of the voltage-sensor domain. This is a fundamentally new interaction site for small-molecule compounds that otherwise usually bind to ion channels in pockets surrounded by water. We also showed that the resin acids open the Shaker KV channel via an electrostatic mechanism, exerted on the positively charged voltage sensor S4. The effect of a resin acid increased when the negatively charged carboxyl group (the effector) and the hydrophobic three-ringed motif (anchor in lipid bilayer) were separated by three atoms: longer stalks decreased the effect. The length rule, in combination with modifications of the anchor, was used to design new resin-acid derivatives that open the human M-type (Kv7.2/7.3) channel. A naturally occurring resin acid also reduced the excitability of cardiomyocytes by affecting the voltage-dependence of several voltage-gated ion channels. The major finding was that the resin acid inactivated sodium and calcium channels, while it activated KV channels at more negative membrane voltages. Computer simulations confirmed that the combined effect on different ion channels reduced the excitability of a cardiomyocyte. Finally, the resin acid reversed induced arrhythmic firing of the cardiomyocytes.

In conclusion, resin acids are potential drug candidates for diseases such as epilepsy and cardiac arrhythmia: knowing the binding site and mechanism of action can help to fine tune the resin acid to increase the effect, as well as the selectivity.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. , p. 50
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1620
National Category
Biophysics Biochemistry and Molecular Biology Pharmaceutical Sciences Medicinal Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-147838DOI: 10.3384/diss.diva-147838ISBN: 9789176853184 (print)OAI: oai:DiVA.org:liu-147838DiVA, id: diva2:1205916
Public defence
2018-06-05, Hasselquistsalen, Campus US, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-15Bibliographically approved
List of papers
1. A drug pocket at the lipid bilayer-potassium channel interface
Open this publication in new window or tab >>A drug pocket at the lipid bilayer-potassium channel interface
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2017 (English)In: Science Advances, ISSN 0036-8156, E-ISSN 2375-2548, Vol. 3, no 10, article id e1701099Article in journal (Refereed) Published
Abstract [en]

Many pharmaceutical drugs against neurological and cardiovascular disorders exert their therapeutic effects by binding to specific sites on voltage-gated ion channels of neurons or cardiomyocytes. To date, all molecules targeting known ion channel sites bind to protein pockets that are mainly surrounded by water. We describe a lipid-protein drug-binding pocket of a potassium channel. We synthesized and electrophysiologically tested 125 derivatives, analogs, and related compounds to dehydroabietic acid. Functional data in combination with docking and molecular dynamics simulations mapped a binding site for small-molecule compounds at the interface between the lipid bilayer and the transmembrane segments S3 and S4 of the voltage-sensor domain. This fundamentally new binding site for small-molecule compounds paves the way for the design of new types of drugs against diseases caused by altered excitability.

Place, publisher, year, edition, pages
AMER ASSOC ADVANCEMENT SCIENCE, 2017
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-144164 (URN)10.1126/sciadv.1701099 (DOI)000417998700021 ()29075666 (PubMedID)
Note

Funding Agencies|Swedish Research Council; Swedish Brain Foundation; Swedish Heart-Lung Foundation; Swedish National Infrastructure for Computing

Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2018-05-15
2. Atom-by-atom tuning of the electrostatic potassium-channel modulator dehydroabietic acid
Open this publication in new window or tab >>Atom-by-atom tuning of the electrostatic potassium-channel modulator dehydroabietic acid
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2018 (English)In: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 150, no 5, p. 731-750Article in journal (Refereed) Published
Abstract [en]

Dehydroabietic acid (DHAA) is a naturally occurring component of pine resin that was recently shown to open voltage-gated potassium (KV) channels. The hydrophobic part of DHAA anchors the compound near the channel’s positively charged voltage sensor in a pocket between the channel and the lipid membrane. The negatively charged carboxyl group exerts an electrostatic effect on the channel’s voltage sensor, leading to the channel opening. In this study, we show that the channel-opening effect increases as the length of the carboxyl-group stalk is extended until a critical length of three atoms is reached. Longer stalks render the compounds noneffective. This critical distance is consistent with a simple electrostatic model in which the charge location depends on the stalk length. By combining an effective anchor with the optimal stalk length, we create a compound that opens the human KV7.2/7.3 (M type) potassium channel at a concentration of 1 µM. These results suggest that a stalk between the anchor and the effector group is a powerful way of increasing the potency of a channel-opening drug.

Place, publisher, year, edition, pages
New York, United States: Rockefeller Institute for Medical Research, 2018
National Category
Physiology
Identifiers
urn:nbn:se:liu:diva-147837 (URN)10.1085/jgp.201711965 (DOI)000434417800008 ()2-s2.0-85046705149 (Scopus ID)
Note

Funding agencies: Swedish Research Council [2016-02615]; Swedish Heart-Lung Foundation [20150672]; Swedish Brain Foundation [2016-0326]

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-06-28Bibliographically approved
3. Isopimaric acid - a multi-targeting ion channel modulator reducing excitability and arrhythmicity in a spontaneously beating mouse atrial cell line
Open this publication in new window or tab >>Isopimaric acid - a multi-targeting ion channel modulator reducing excitability and arrhythmicity in a spontaneously beating mouse atrial cell line
2018 (English)In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 222, no 1, article id e12895Article in journal (Refereed) Published
Abstract [en]

AimAtrial fibrillation is the most common persistent cardiac arrhythmia, and it is not well controlled by present drugs. Because some resin acids open voltage-gated potassium channels and reduce neuronal excitability, we explored the effects of the resin acid isopimaric acid (IPA) on action potentials and ion currents in cardiomyocytes. MethodsSpontaneously beating mouse atrial HL-1 cells were investigated with the whole-cell patch-clamp technique. Results1-25 mol L-1 IPA reduced the action potential frequency by up to 50%. The effect of IPA on six different voltage-gated ion channels was investigated; most voltage-dependent parameters of ion channel gating were shifted in the negative direction along the voltage axis, consistent with a hypothesis that a lipophilic and negatively charged compound binds to the lipid membrane close to the positively charged voltage sensor of the ion channels. The major finding was that IPA inactivated sodium channels and L- and T-type calcium channels and activated the rapidly activating potassium channel and the transient outward potassium channel. Computer simulations of IPA effects on all of the ion currents were consistent with a reduced excitability, and they also showed that effects on the Na channel played the largest role to reduce the action potential frequency. Finally, induced arrhythmia in the HL-1 cells was reversed by IPA. ConclusionLow concentrations of IPA reduced the action potential frequency and restored regular firing by altering the voltage dependencies of several voltage-gated ion channels. These findings can form the basis for a new pharmacological strategy to treat atrial fibrillation.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
Keywords
arrhythmia; atrial fibrillation; ion channels; isopimaric acid; patch clamp; resin acid
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-144564 (URN)10.1111/apha.12895 (DOI)000419864000009 ()28514017 (PubMedID)
Note

Funding Agencies|Swedish Research Council; Swedish Heart-Lung Foundation; Swedish Brain Foundation; ALF

Available from: 2018-01-29 Created: 2018-01-29 Last updated: 2018-05-15

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