Publication Abstract

Using the stickleback to monitor androgens and anti-androgens in the aquatic environment

I. Katsiadaki

Over the past few years there has been increasing evidence of the hormone-like effects of environmental chemicals, such as pesticides and industrial chemicals, in both wildlife and humans. These so-called endocrine disruptive chemicals (EDCs) mainly act by mimicking or antagonising the effect of the endogenous hormones estradiol and testosterone but may also disrupt the synthesis and metabolism of endogenous hormones and/or their receptors. A large number of compounds have been reported to possess endocrine modulating activity. These include natural products, pesticides, fungicides and insecticides, medical drugs and commercial and/or industrial chemicals. Although a causal relationship between exposure to these substances and human/wildlife reproductive health has not been fully established, the characterisation of the adverse effects of EDCs, at environmentally relevant concentrations, is very desirable. Much research appears to have been done already on the role of estrogenic xenobiotics. The most widely used biomarker for estrogenic exposure is the presence of the female specific protein, vitellogenin in the plasma, liver or whole body homogenates of male fish. The role of androgenic xenobiotics has not been studied in nearly so much detail, despite the fact that there is an increasing concern for clinical implications of these chemicals in humans. One of the clearest observations of androgenicity in the aquatic environment has been made in female mosquitofish (Gambusia sp.), living downstream of kraft mill effluent discharges. While the detection of androgenic compounds in the environment is presently restricted to pulp mill effluents and Sewage Treatment Works without secondary treatment, compounds with anti-androgenic activity appear to be more widespread. At the moment, the only in vivo test able to provide information on the androgenic or anti-androgenic effect of suspected chemicals is the Hershberger castrated male rat assay.

The three-spined stickleback (Gasterosteus aculeatus) offers a great potential for the assessment of reproductive disturbances caused by androgenic xenobiotics due to its pronounced androgen-dependent male secondary sexual characters that present during its breeding season (late spring and summer). These characters include development of nuptial coloration, kidney hypertrophy, territorial and nest-building behaviour. The kidney hypertrophies under the control of androgens to produce a 'glue' protein that is used to build the nest out of algae, plant material, sand and detritus. This glue protein was first characterised by Jakobsson and co-workers and was given the name spiggin from the name of the stickleback in Swedish, the spigg. Spiggin is assembled from three subunits in the urinary bladder and is deposited on suitable nest material by contractions of the urinary bladder. The production of the glue protein by the male stickleback has potential as a biomarker for androgenic and anti-androgenic xenobiotics because a) it is well established that is androgen-dependent and b) it has easily measurable response parameters that include kidney weight changes (nephrosomatic index), histological changes on the height of the epithelial cells, spiggin changes and spiggin mRNA changes.

To date, spiggin is the only androgen-induced protein that has been isolated from fish. Recent research at CEFAS (Centre for Environment, Fisheries and Aquaculture Science) has firmly established that female stickleback kidneys can produce spiggin in response to several model androgens such as 17-Methyl-testosterone (17-MT), Dihydro-testosterone (DHT), Testosterone (T) and 11-Ketotestosterone (11-KT), added to the ambient water. As we show in this chapter, spiggin production is inhibited in males (and in 17-MT-stimulated females) by flutamide (a well-known anti-androgenic drug that is used in the treatment of prostate cancer. A number of other xenobiotics with suspected anti-androgenic activity have been tested and most showed clear inhibition of spiggin production.

Reference:

I. Katsiadaki (2005). Using the stickleback to monitor androgens and anti-androgens in the aquatic environment. Techniques in aquatic toxicology; (2) 339-356.