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Deak AT, Belić K, Meissl AM, Artinger K, Eller K, Rechberger B, Niedrist T, Graier WF, Malli R, Bischof H, Burgstaller S, Blass S, Avian A, Rosenkranz AR, Kirsch AH. Salivary potassium measured by genetically encoded potassium ion indicators as a surrogate for plasma potassium levels in hemodialysis patients-a proof-of-concept study. Nephrol Dial Transplant 2023; 38:757-763. [PMID: 35700151 DOI: 10.1093/ndt/gfac195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Hyperkalemia is a common complication in cardiorenal patients treated with agents interfering with renal potassium (K+) excretion. It frequently leads to discontinuation of potentially life-saving medication, which has increased the importance of K+ monitoring. Non-invasive means to detect hyperkalemia are currently unavailable, but would be of potential use for therapy guidance. The aim of the present study was to assess the analytical performance of genetically encoded potassium-ion indicators (GEPIIs) in measuring salivary [K+] ([K+]Saliva) and to determine whether changes of [K+]Saliva depict those of [K+]Plasma. METHODS We conducted this proof-of-concept study: saliva samples from 20 healthy volunteers as well as plasma and saliva from 29 patients on hemodialysis (HD) before and after three consecutive HD treatments were collected. We compared [K+]Saliva as assessed by the gold standard ion-selective electrode (ISE) with GEPII measurements. RESULTS The Bland-Altmann analysis showed a strong agreement (bias 0.71; 95% limits of agreement from -2.79 to 4.40) between GEPII and ISE. Before treatment, patients on HD showed significantly higher [K+]Saliva compared with healthy controls [median 37.7 (30.85; 48.46) vs 23.8 (21.63; 25.23) mmol/L; P < .05]. [K+]Plasma in HD patients decreased significantly after dialysis. This was paralleled by a significant decrease in [K+]Saliva, and both parameters increased until the subsequent HD session. Despite similar kinetics, we found weak or no correlation between [K+]Plasma and [K+]Saliva. CONCLUSION GEPIIs have shown an excellent performance in determining [K+]Saliva. [K+]Plasma and [K+]Saliva exhibited similar kinetics. To determine whether saliva could be a suitable sample type to monitor [K+]Plasma, further testing in future studies are required.
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Affiliation(s)
- Andras T Deak
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
| | - Katarina Belić
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
| | - Anna-Maria Meissl
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
| | - Katharina Artinger
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
| | - Kathrin Eller
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
| | - Bernd Rechberger
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
| | - Tobias Niedrist
- Clinical Institute of Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Graz, Austria
| | - Wolfgang F Graier
- Gottfried Schatz Research Center (for Cell Signaling, Metabolism and Aging, Division of Molecular Biology and Biochemistry), Medical University of Graz, Graz, Austria
| | - Roland Malli
- Gottfried Schatz Research Center (for Cell Signaling, Metabolism and Aging, Division of Molecular Biology and Biochemistry), Medical University of Graz, Graz, Austria
| | - Helmut Bischof
- Gottfried Schatz Research Center (for Cell Signaling, Metabolism and Aging, Division of Molecular Biology and Biochemistry), Medical University of Graz, Graz, Austria
| | - Sandra Burgstaller
- Gottfried Schatz Research Center (for Cell Signaling, Metabolism and Aging, Division of Molecular Biology and Biochemistry), Medical University of Graz, Graz, Austria
| | - Sandra Blass
- Gottfried Schatz Research Center (for Cell Signaling, Metabolism and Aging, Division of Molecular Biology and Biochemistry), Medical University of Graz, Graz, Austria
| | - Alexander Avian
- Institute for Medical Informatics, Statistics and Documentation, Medical University of Graz, Graz, Austria
| | - Alexander R Rosenkranz
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
| | - Alexander H Kirsch
- Division of Nephrology, Department of Internal Medicine, Medical University of Graz, Graz, Austria
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Burgstaller S, Bischof H, Rauter T, Schmidt T, Schindl R, Patz S, Groschup B, Filser S, van den Boom L, Sasse P, Lukowski R, Plesnila N, Graier WF, Malli R. Immobilization of Recombinant Fluorescent Biosensors Permits Imaging of Extracellular Ion Signals. ACS Sens 2021; 6:3994-4000. [PMID: 34752056 PMCID: PMC8630794 DOI: 10.1021/acssensors.1c01369] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
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Given the importance
of ion gradients and fluxes in biology, monitoring
ions locally at the exterior of the plasma membrane of intact cells
in a noninvasive manner is highly desirable but challenging. Classical
targeting of genetically encoded biosensors at the exterior of cell
surfaces would be a suitable approach; however, it often leads to
intracellular accumulation of the tools in vesicular structures and
adverse modifications, possibly impairing sensor functionality. To
tackle these issues, we generated recombinant fluorescent ion biosensors
fused to traptavidin (TAv) specifically coupled to a biotinylated
AviTag expressed on the outer cell surface of cells. We show that
purified chimeras of TAv and pH-Lemon or GEPII 1.0, Förster
resonance energy transfer-based pH and K+ biosensors, can
be immobilized directly and specifically on biotinylated surfaces
including glass platelets and intact cells, thereby remaining fully
functional for imaging of ion dynamics. The immobilization of recombinant
TAv–GEPII 1.0 on the extracellular cell surface of primary
cortical rat neurons allowed imaging of excitotoxic glutamate-induced
K+ efflux in vitro. We also performed micropatterning of
purified TAv biosensors using a microperfusion system to generate
spatially separated TAv–pH-Lemon and TAv–GEPII 1.0 spots
for simultaneous pH and K+ measurements on cell surfaces.
Our results suggest that the approach can be greatly expanded by immobilizing
various biosensors on extracellular surfaces to quantitatively visualize
microenvironmental transport and signaling processes in different
cell culture models and other experimental settings.
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Affiliation(s)
- Sandra Burgstaller
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, Graz 8010, Austria
- Department of Pharmacology, Toxicology and Clinical Pharmacy, Institute of Pharmacy, Eberhard Karls University of Tuebingen, Auf der Morgenstelle 8, Tuebingen 72076, Germany
- NMI Natural and Medical Sciences Institute at the University of Tuebingen, Reutlingen 72770, Germany
| | - Helmut Bischof
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, Graz 8010, Austria
- Department of Pharmacology, Toxicology and Clinical Pharmacy, Institute of Pharmacy, Eberhard Karls University of Tuebingen, Auf der Morgenstelle 8, Tuebingen 72076, Germany
| | - Thomas Rauter
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, Graz 8010, Austria
| | - Tony Schmidt
- Gottfried Schatz Research Center, Biophysics, Medical University of Graz, Neue Stiftingtalstraße 6/6, Graz 8010, Austria
| | - Rainer Schindl
- Gottfried Schatz Research Center, Biophysics, Medical University of Graz, Neue Stiftingtalstraße 6/6, Graz 8010, Austria
| | - Silke Patz
- Department of Neurosurgery, Medical University of Graz, Auenbruggerplatz 29, Graz 8036, Austria
| | - Bernhard Groschup
- Laboratory of Experimental Stroke Research, Institute for Stroke and Dementia Research, University of Munich Medical Center, Munich 81377, Germany
| | - Severin Filser
- Laboratory of Experimental Stroke Research, Institute for Stroke and Dementia Research, University of Munich Medical Center, Munich 81377, Germany
| | - Lucas van den Boom
- Institute of Physiology I, Medical Faculty, University of Bonn, Bonn 53127, Germany
| | - Philipp Sasse
- Institute of Physiology I, Medical Faculty, University of Bonn, Bonn 53127, Germany
| | - Robert Lukowski
- Department of Pharmacology, Toxicology and Clinical Pharmacy, Institute of Pharmacy, Eberhard Karls University of Tuebingen, Auf der Morgenstelle 8, Tuebingen 72076, Germany
| | - Nikolaus Plesnila
- Laboratory of Experimental Stroke Research, Institute for Stroke and Dementia Research, University of Munich Medical Center, Munich 81377, Germany
- Munich Cluster for Systems Neurology (SyNergy), Feodor-Lynen-Str. 17, Munich 81377, Germany
| | - Wolfgang F. Graier
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, Graz 8010, Austria
- BioTechMed Graz, Mozartgasse 12/II, Graz 8010, Austria
| | - Roland Malli
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, Graz 8010, Austria
- BioTechMed Graz, Mozartgasse 12/II, Graz 8010, Austria
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