Effect of the cardiac glycoside, digoxin, on neuronal viability, serotonin production and brain development in the embryo

Abstract

Digoxin has been known as a treatment for chronic heart failure for over 200 years. Its effect on the heart itself has been extensively studied and its inotropic effect well established. The inotropic effect of digoxin is the result of its inhibition of the membrane sodium pump or Na+/K+-ATPase, which plays an important role in maintaining the resting membrane potential across the plasma membrane through constantly pumping Na+ and K+ across the plasma membrane. Na+/K+-ATPase is not found exclusively in heart muscle. It is also found extensively throughout the brain. As digoxin is the drug of choice for pregnant woman with chronic heart failure, this study aimed to examine how digoxin affects brain development and neurons in culture. The well established chicken embryo animal model was used in this study. To probe for deviations from normal brain development, chicken embryos were exposed in ovo. Brains were examined using both transmission and scanning electron microscopy. Microscopy indicated significant damage to the neurons, specifically membranes and mitochondria, as well as cellular death by means of aponecrosis. An unexpected result was premature myelinogenesis in the brain. Chick embryo neurons (CEN) were exposed to digoxin in vitro and cell viability was assessed by performing crystal violet (CV) assays. Results showed that cell number increased over time. This is however, impossible as CEN are non-dividing cells and results were therefore interpreted as an increase in protein synthesis over time, correlating with the myelinogenesis results seen with electron microscopy. To assess membrane integrity, fluorescence microscopy was performed using propidium iodide as stain. Results from this experiment showed a sharp increase in propidium iodide uptake in exposed cells indicative of the membrane damage caused by digoxin. These results also correlated with the aponecrosis seen with electron microscopy, as the nuclei indicated apoptosis while propidium iodide is normally only absorbed by cells undergoing necrosis. Finally, a literature search was conducted to shed some light on the role that digoxin plays in serotonin production and levels in the brain. From the literature it seems that digoxin could increase serotonin production and elevate serotonin levels in the brain, which may influence normal brain development and may therefore play a role in myelinogenesis in the brain.