Abstract
In sickle cell disease (SCD), the pathological shift of red blood cells (RBCs) into distorted morphologies under hypoxic conditions follows activation of a cationic leak current (Psickle) and cell dehydration. Prior work showed sickling was reduced by 5-hydroxylmethyl-2-furfural (5-HMF), which stabilized mutant hemoglobin and also blocked the Psickle current in RBCs, though the molecular basis of this 5-HMF-sensitive cation current remained a mystery. Work here is the first to test the hypothesis that Aquaporin-1 (AQP1) cation channels contribute to the monovalent component of Psickle. Human AQP1 channels expressed in Xenopus oocytes were evaluated for sensitivity to 5-HMF and four derivatives known to have differential efficacies in preventing RBC sickling. Ion conductances were measured by two-electrode voltage clamp, and osmotic water permeability by optical swelling assays. Compounds tested were: 5-HMF; 5-PMFC (5-(phenoxymethyl)furan-2-carbaldehyde); 5-CMFC (5-(4-chlorophenoxymethyl)furan-2-carbaldehyde); 5-NMFC (5-(2-nitrophenoxymethyl)-furan-2-carbaldehyde); and VZHE006 (tert-butyl (5-formylfuran-2-yl)methyl carbonate). The most effective anti-sickling agent, 5-PMFC, was the most potent inhibitor of the AQP1 ion conductance (98% block at 100 µM). The order of sensitivity of the AQP1 conductance to inhibition was 5-PMFC > VZHE006 > 5-CMFC ≥ 5-NMFC, which corresponded with effectiveness in protecting RBCs from sickling. None of the compounds altered AQP1 water channel activity. Combined application of a selective AQP1 ion channel blocker AqB011 (80 µM) with a selective hemoglobin modifying agent 5-NMFC (2.5 mM) increased anti-sickling effectiveness in red blood cells from human SCD patients. Another non-selective cation channel known to be expressed in RBCs, Piezo1, was unaffected by 2 mM 5-HMF. Results suggest that inhibition of AQP1 ion channels and capacity to modify hemoglobin are combined features of the most effective anti-sickling agents. Future therapeutics aimed at both targets could hold promise for improved treatments for SCD.
Highlights
Sickle cell disease (SCD) results from an inherited mutation in the oxygen-carrying molecule hemoglobin in red blood cells
Electrophysiological analyses tested the effects of four furan derivatives, 5-PMFC, VZHE006, 5-NMFC, and 5-CMFC at 0.5 mM each, on the 8CTP-cGMP-activated ionic conductance in human AQP1-expressing oocytes (Figure 1), and confirmed block by the original scaffold compound 5-HMF at 0.5 mM
Compounds structurally related to 5-HMF were shown previously by Abdulmalik and others to protect SCD cells from sickling, with differences in efficacies thought to be due to levels of modification of hemoglobin carrying the SCD mutation (HbS) and oxygen affinity (Xu et al, 2017)
Summary
Sickle cell disease (SCD) results from an inherited mutation in the oxygen-carrying molecule hemoglobin in red blood cells. Unlike wild type hemoglobin (Hb), hemoglobin carrying the SCD mutation (HbS) polymerizes more readily in low oxygen conditions into stiff strands which distort red blood cell morphology into diagnostic dysfunctional shapes. HbS molecules aggregate into rigid polymers, changing red blood cell shape, and increasing fragility, solute loss and stickiness (Pauling et al, 1949; Joiner 1993). Current interventions include blood transfusions to alleviate symptoms, and hydroxyurea treatment to reduce pain crises and anemia, but chronic side effects and variability in individual responsiveness to hydroxyurea limit its usefulness (Perutz and Mitchison 1950; Charache et al, 1987; Segal et al, 2008). Transplanting stem cells from donor bone marrow is the only cure for SCD (Saraf and Rondelli 2019), an option not available to most patients around the world
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
