Integrated strategies for investigating endocrine mechanisms in Biomphalaria Glabrata as a test organism for androgenic chemical testing

Abstract

Endocrine and metabolic disease or dysfunctions are of growing concern in modern societies across the globe, underlining the need for continued focus on the development of pharmaceuticals. Subsequent scientific research has revealed a trend in the increase of such abnormalities and expansion of chemical industries, highlighting concerns that these disorders may, in part, be caused by exposure to environmental pollutants. This has led to changes in legislation concerning chemicals safety testing involving an increasing number of vertebrate animal tests as a part of environmental risk assessment process, at significant financial and ethical costs. A solution that is appropriate and aligned with the three R’s (reduction, refinement and replacement) in relation to animal research is to exploit the use of small invertebrate organisms as possible replacements for mammals. In line with the above approach/solution, this thesis is based on the null hypothesis that common genes, proteins and processes in gastropod molluscs and humans underlie the response of male reproductive organs to androgenic chemicals. Using a freshwater pulmonate snail, Biomphalaria glabrata, physiological effects of two steroid androgens on the development of mollusc secondary sexual organs were studied. Furthermore, an exhaustive investigation on the mollusc nuclear receptor repertoire and reproductive type neuropeptides was conducted. This also included the study of the evolutionary degree of conservation of these genes in non-model molluscs. The results obtained suggest that the snails did not respond to, and were not affected by exposure to the androgens. These results were supported by the absence of the members of subfamily 3C of nuclear receptors, which includes some of the “vertebrate” steroid hormone targets, suggesting that this mollusc may be an inappropriate model for steroid hormone mediated mammalian endocrine function. The nuclear receptor (NR) repertoire of B. glabrata comprised of 39 nuclear receptors representing all the known subfamilies of the NR superfamily. 21 reproductive type neuropeptide genes were identified encoding precursors that are predicted to release over 124 bioactive cleavage products. The consequence of these findings is significant in the context of the development of alternative model organisms for chemical testing as well as elucidating the taxonomic scope of nuclear receptor mediated endocrine disruption.