Effect of short and long-term cadmium exposure on behaviour and cardiac function in Drosophila

Cadmium is a non-essential heavy metal and environmental pollutant that causes a range of pathologies across different species. In humans, cadmium exposure has recently been directly linked to heart disease. Understanding how long-term cadmium exposure affects cardiac physiology is therefore important. In this work we employed a tractable Drosophila melanogaster model to study the effects of cadmium exposure on behaviour, lifespan and cardiac physiology. Dietary experiments established that cadmium at 10 μM and 100 μM was tolerated for several weeks, whereas doses in the mM range caused lethality within days. It was estimated that 10 μM dietary exposure represented an approximately 60-fold excess of the maximum exposure recommended for humans. Although 10 μM cadmium had no impact on lifespan compared to the control diet, it did cause significant daytime hyperactivity. Direct exposure of the heart to cadmium caused reversible cardiac arrest and disrupted calcium signalling. Compared to controls, 10 μM dietary cadmium had no impact on the rate of cardiac ageing over a six-week period. The higher dose of 100 μM shortened the flies' lifespan but it slowed the rate of cardiac ageing. The findings indicate that Drosophila can be used to model the direct effects of cadmium on cardiomyocyte function and also demonstrate the existence of cardioprotective pathways triggered by dietary cadmium exposure. The data also indicate that cadmium at doses that do not affect lifespan or heart function, do cause daytime hyperactivity. Identifying the cardioprotective mechanisms of cadmium and understanding the hyperactivity phenotype in Drosophila may yield important findings of applied relevance to insects in general, as well as humans exposed to cadmium.