Interaction of cadmium and oestradiol-17β on metallothionein and vitellogenin synthesis in rainbow trout (Oncorhynchus mykiss)

Abstract

The induction of metallothionein and vitellogenin synthesis in rainbow trout liver was studied after injection of oestradiol-17 beta alone or in combination with cadmium or zinc. Intraperitoneal injection of oestradiol-17 beta increased the liver somatic index, with subsequent induction of vitellogenin synthesis. Oestradiol-17 beta did not induce metallothionein synthesis. Injection of cadmium induced the synthesis of metallothionein mRNA and metallothionein. Injection of oestradiol-17 beta in combination with cadmium resulted in inhibition of transcription and translation of both vitellogenin and metallothionein. Chromatography of liver cytosols revealed that cadmium, when co-injected with oestradiol-17 beta, did not bind to metallothionein but would initially bind to high-molecular-mass (HMr) cytosolic proteins. In fish injected with cadmium in combination with oestradiol-17 beta, cadmium was gradually redistributed from HMr proteins to metallothionein. This resulted in induction of metallothionein synthesis and in binding of most of the cadmium to metallothionein. Induction of vitellogenin mRNA was observed 15 days after injection, as cadmium was being redistributed to newly synthesized metallothionein. These findings indicate that cadmium inhibits the transcription of vitellogenin. The binding of cadmium to these non-metallothionein proteins represses the induction of metallothionein and results in increased toxicity of the metal. Preinduction of metallothionein by zinc injections resulted in decreased cadmium sensitivity of the fish and a decrease in the repression of vitellogenin mRNA. Furthermore, a role for metallothionein in the detoxification of cadmium is indicated by the induction of vitellogenin synthesis that occurs once metallothionein has begun sequestering cadmium.

Effects of steroid hormones on reproduction- and detoxification-related gene expression in adult male mosquitofish, Gambusia affinis

“…In the present study, all hormone treatments did not result in the significant change of MT mRNA expression in the liver of male mosquitofish as compared with the control. The lack of induction of MT mRNA by the steroid hormones is in accordance with some previous studies on rainbow trout (Olsson et al, 1995) and Arctic Char (Gerpe et al, 2000). However, the changes of MT mRNA in the testis were different from those in the liver of male mosquitofish exposed to steroid hormones.…”

“…MT mRNA expression showed significant decrease in the testis of mosquitofish in response to P, E2, T + E2 and P + T + E2. Previous studies have shown that (xeno)estrogens may inhibit MT expression at the transcriptional and/or translational level by altering the Zn utilization in the liver during the synthesis of Vtg (Olsson et al, 1995;Werner et al, 2003). It is unclear whether MT mRNA expression decline in the spermaries of mosquitofish in response to steroid hormones is due to the induction of Vtg mRNA expression, or whether the testis is more sensitive than the liver to regulate MT mRNA.…”

Regulation of reproduction- and biomarker-related gene expression by sex steroids in the livers and ovaries of adult female western mosquitofish (Gambusia affinis)

“…Moreover, Costa et al (2010) showed that the levels of MT decreased in the liver of mature male fish (Rhamdia quelen) exposed to the highest E2 dose with a higher E2 level in plasma. Previous studies showed that E2 or other estrogenic compounds might inhibit MT expression by reducing free intracellular Zn being available to bind to the metal responsive elements in the promoters of MTs during Vtg synthesis (Olsson et al, 1995;Gerpe et al, 2000;Werner et al, 2008). In the present study, MT mRNA expression was also significantly inhibited in the livers of mosquitofish exposed to P or T alone.…”

“…MT has been shown to be regulated during the period of sexual maturation as well as during early embryonic development (Olsson et al, 1995). Tissue-specific regulation of MT mRNA in mosquitofish has been observed following steroid hormone exposure.…”

Estradiol uptake, toxicity, metabolism, and adverse effects on cadmium-treated amphibian embryos.

“…A deficiency in the expression of MTs could augment Cd 2+ toxicity. Olsson et al (1995) have reported this effect in the salmon, Oncorhynchus mykiss, in which the combined treatment with E 2 and Cd 2+ caused an inhibition of transcription and translation of MT mRNA in the liver. This was also observed in mammals; in ovariectomized mice, E 2 reduces MT-I mRNA expression induced by Cd 2+ (Sogawa et al 2001).…”