Abstract
SM-102 (1-octylnonyl 8-[(2-hydroxyethyl)[6-oxo-6-(undecyloxy)hexyl]amino]-octanoate) is an amino cationic lipid that has been tailored for the formation of lipid nanoparticles and it is one of the essential ingredients present in the ModernaTM COVID-19 vaccine. However, to what extent it may modify varying types of plasmalemmal ionic currents remains largely uncertain. In this study, we investigate the effects of SM-102 on ionic currents either in two types of endocrine cells (e.g., rat pituitary tumor (GH3) cells and mouse Leydig tumor (MA-10) cells) or in microglial (BV2) cells. Hyperpolarization-activated K+ currents in these cells bathed in high-K+, Ca2+-free extracellular solution were examined to assess the effects of SM-102 on the amplitude and hysteresis of the erg-mediated K+ current (IK(erg)). The SM-102 addition was effective at blocking IK(erg) in a concentration-dependent fashion with a half-maximal concentration (IC50) of 108 μM, a value which is similar to the KD value (i.e., 134 μM) required for its accentuation of deactivation time constant of the current. The hysteretic strength of IK(erg) in response to the long-lasting isosceles-triangular ramp pulse was effectively decreased in the presence of SM-102. Cell exposure to TurboFectinTM 8.0 (0.1%, v/v), a transfection reagent, was able to inhibit hyperpolarization-activated IK(erg) effectively with an increase in the deactivation time course of the current. Additionally, in GH3 cells dialyzed with spermine (30 μM), the IK(erg) amplitude progressively decreased; moreover, a further bath application of SM-102 (100 μM) or TurboFectin (0.1%) diminished the current magnitude further. In MA-10 Leydig cells, the IK(erg) was also blocked by the presence of SM-102 or TurboFectin. The IC50 value for SM-102-induced inhibition of IK(erg) in MA-10 cells was 98 μM. In BV2 microglial cells, the amplitude of the inwardly rectifying K+ current was inhibited by SM-102. Taken together, the presence of SM-102 concentration-dependently inhibited IK(erg) in endocrine cells (e.g., GH3 or MA-10 cells), and such action may contribute to their functional activities, assuming that similar in vivo findings exist.