Evidence for the Capability of Roxadustat (FG-4592), an Oral HIF Prolyl-Hydroxylase Inhibitor, to Perturb Membrane Ionic Currents: An Unidentified yet Important Action

Abstract

Roxadustat (FG-4592), an analog of 2-oxoglutarate, is an orally-administered, heterocyclic small molecule known to be an inhibitor of hypoxia inducible factor (HIF) prolyl hydroxylase. However, none of the studies have thus far thoroughly investigated its possible perturbations on membrane ion currents in endocrine or heart cells. In our studies, the whole-cell current recordings of the patch-clamp technique showed that the presence of roxadustat effectively and differentially suppressed the peak and late components of IK(DR) amplitude in response to membrane depolarization in pituitary tumor (GH3) cells with an IC50 value of 5.71 and 1.32 μM, respectively. The current inactivation of IK(DR) elicited by 10-sec membrane depolarization became raised in the presence of roxadustatt. When cells were exposed to either CoCl2 or deferoxamine (DFO), the IK(DR) elicited by membrane depolarization was not modified; however, nonactin, a K+-selective ionophore, in continued presence of roxadustat, attenuated roxadustat-mediated inhibition of the amplitude. The steady-state inactivation of IK(DR) could be constructed in the presence of roxadustat. Recovery of IK(DR) block by roxadustat (3 and 10 μM) could be fitted by a single exponential with 382 and 523 msec, respectively. The roxadustat addition slightly suppressed erg-mediated K+ or hyperpolarization-activated cation currents. This drug also decreased the peak amplitude of voltage-gated Na+ current with a slowing in inactivation rate of the current. Likewise, in H9c2 heart-derived cells, the addition of roxadustat suppressed IK(DR) amplitude in combination with the shortening in inactivation time course of the current. In high glucose-treated H9c2 cells, roxadustat-mediated inhibition of IK(DR) remained unchanged. Collectively, despite its suppression of HIF prolyl hydroxylase, inhibitory actions of roxadustat on different types of ionic currents possibly in a non-genomic fashion might provide another yet unidentified mechanism through which cellular functions are seriously perturbed, if similar findings occur in vivo.

Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents

“…Indeed, previous studies have demonstrated the presence of I h and I K(DR) in endocrine cells, such as pancreatic αor β-cells [4][5][6]11,39]. The I K(DR) presented herein (i.e., K V 2.1-encoded current) has been reported to be functionally enriched in different types of heart cells [25,26,40,41]. Consequently, it is possible that the mediation by CIL of I K(DR) inhibition influences the heart function to a certain extent, as previously reported with respect to the effectiveness of aconitine, a potent cardiotoxin, in the amplitude and gating of depolarization-triggered I K(DR) in heart cells [41].…”

“…This type of ionic current has been regarded to be carried by channels of the hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) gene family, which belongs to the superfamily of voltage-gated K + channels and cyclic nucleotide-gated channels [8,12,18,20].Voltage-gated K + (K V ) channels play essential roles in determining membrane excitability, and the delayed rectifier K + channels, such as K V 3 (KCNC) and K V 2 (KCNB) channels, are ubiquitous in endocrine cells [21][22][23][24]. A causal relationship between the K V 3 or K V 2 channel and the delayed rectifier K + current (I K(DR) ) has been previously established [21,23,25,26]. The K V channels from the K V 3.1-K V 3.2 types, the biophysical properties of which exhibit to have positively shifted voltage dependency and fast deactivation rate, are the major determinants of I K(DR) identified in the pituitary tumor (GH 3 ) cells [23,24,26].…”

“…A causal relationship between the K V 3 or K V 2 channel and the delayed rectifier K + current (I K(DR) ) has been previously established [21,23,25,26]. The K V channels from the K V 3.1-K V 3.2 types, the biophysical properties of which exhibit to have positively shifted voltage dependency and fast deactivation rate, are the major determinants of I K(DR) identified in the pituitary tumor (GH 3 ) cells [23,24,26]. However, to the best of our knowledge, whether and how CIL or other structurally similar compounds affect any modifications on these types of K + currents (e.g., I K(DR) ) remains largely unexplored.Therefore, in light of the above-described considerations, we intended to address the possibility that CIL exerts the perturbing actions on different types of ionic currents, which include hyperpolarization-activated cation current (I h ), delayed-rectifier K + current (I K(DR) ), and voltage-gated Na + current (I Na ) identified in pituitary tumor (GH 3 ) cells.…”

Evidence for the Effectiveness of Remdesivir (GS-5734), a Nucleoside-Analog Antiviral Drug in the Inhibition of IK(M) or IK(DR) and in the Stimulation of IMEP

“…The causal link between the delayed-rectifier K + current ( I K(DR) ) and K V 3/K V 2 channels has been previously disclosed ( Yeung et al., 2005 ; Wang et al., 2008 ; Huang et al., 2013 ; Chang et al., 2019 ; Lu et al., 2019 ). The biophysical characteristics of K V 3.1-K V 3.2 channels, which are the dominant factors of I K(DR) identified in pituitary tumor (GH 3 ) cells ( Chang et al., 2019 ; Lu et al., 2019 ; So et al., 2019 ), show a positively shifted voltage dependency as well as fast deactivation rate. However, whether and how RDV effects the adjustments on the amplitude and kinetic gating of above-stated types of K + currents still requires investigations.…”

“…Specifically, K V 3 (KCNC) and K V 2 (KCNB), two delayed-rectifier K + channels, are widespread in different excitable cells such as endocrine cells (Lien and Jonas, 2003;Wang et al, 2008;Fletcher et al, 2018;Kuo et al, 2018;Lu et al, 2019;So et al, 2019). The causal link between the delayedrectifier K + current (I K(DR) ) and K V 3/K V 2 channels has been previously disclosed (Yeung et al, 2005;Wang et al, 2008;Huang et al, 2013;Chang et al, 2019;Lu et al, 2019). The biophysical characteristics of K V 3.1-K V 3.2 channels, which are the dominant factors of I K(DR) identified in pituitary tumor (GH 3 ) cells (Chang et al, 2019;Lu et al, 2019;So et al, 2019), show a positively shifted voltage dependency as well as fast deactivation rate.…”