Lithium affects sodium balance but not intestinal microbiota - studies in Drosophila melanogaster

The trace element lithium (Li) is known for its therapeutic mood-stabilizing application in humans, but also for its various bioactivities, which have been uncovered in model organisms. According to the literature, Li may interfere with the homeostasis of other minerals in mammals, namely sodium, calcium and magnesium. In addition, Li was found to influence the composition and diversity of the intestinal microbiota in vertebrates, an observation that may be related to the many bioactivities of Li.

Based on these previous findings, we employed the model organism Drosophila melanogaster to decipher whether Li exhibits similar bioactivities in invertebrates. First, we examined the influence of increasing dietary Li supply (0 -100 mM LiCl) on the status of Li and ten other minerals via Inductively coupled plasma - mass spectrometry (ICP-MS) in heads and remaining body parts of the three wildtype strains w¹¹¹⁸, Oregon-R-C and Canton-S. In addition, we investigated the potential impact of Li feeding (0, 0.1, 1 mM LiCl) on the total bacterial load, α- and β-diversity via real-time quantitative polymerase chain reaction (RT q-PCR) and 16S rDNA sequencing in the intestines of female w¹¹¹⁸.

Our observations revealed that Li accumulates linearly in both sexes and all body parts of the three Drosophila strains as the dietary Li supply increases. While the status of most elements remained unchanged, the sodium levels of the fly also correlated positively with the Li content of the diet. The intestinal microbiota, however, remained largely unaffected by Li feeding in terms of both, bacterial load and diversity.

These findings support the hypothesis that elevating the Li supply affects sodium homeostasis in Drosophila, a finding coherent with observations in mammals. Furthermore, our data opposes a possible involvement of the bacterial intestinal colonization in the bioactivity of Li in Drosophila.