In view of the call by the World Health Organization (WHO) for elimination of
schistosomiasis as a public health problem by 2025, use of molluscicides in snail control to supplement
chemotherapy-based control efforts is likely to increase in the coming years. The mechanisms of action of
niclosamide, the active ingredient in the most widely used molluscicides, remain largely unknown. A better understanding of its toxicology at the molecular level will both improve our knowledge of snail biology and may offer valuable insights into the development of better chemical control methods for snails. We used a recently developed Biomphalaria glabrata
oligonucleotide microarray (31K features) to investigate the effect of sublethal exposure to
niclosamide on the transcriptional responses of the snail B. glabrata relative to untreated snails. Most of the genes highly upregulated following exposure of snails to
niclosamide are involved in biotransformation of
xenobiotics, including genes encoding
cytochrome P450s (CYP),
glutathione S-
transferases (GST), and
drug transporters, notably multi-drug resistance
protein (efflux transporter) and solute linked carrier (influx transporter).
Niclosamide also induced stress responses. Specifically, six
heat shock protein (HSP) genes from three super-families (HSP20, HSP40 and HSP70) were upregulated. Genes encoding
ADP-ribosylation factor (ARF),
cAMP response element-binding protein (CREB) and coatomer, all of which are involved in vesicle trafficking in the Golgi of mammalian cells, were also upregulated. Lastly, a
hemoglobin gene was downregulated, suggesting
niclosamide may affect
oxygen transport. Our results show that snails mount substantial responses to sublethal concentrations of
niclosamide, at least some of which appear to be protective. The topic of how
niclosamide's lethality at higher concentrations is determined requires further study. Given that
niclosamide has also been used as an
anthelmintic drug for decades and has been found to have activity against several types of
cancer, our findings may be of relevance in understanding how both parasites and neoplastic cells respond to this compound.