Effects of cadmium on the reproductive axis of Japanese medaka (Oryzias latipes)

Cadmium (Cd) is a ubquitous element and a significant inorganic pollutant that has previously been found to bioaccumulate in reproductive organs of fish and disrupt important endocrine processes, especially those involved in synthesis, release and metabolism of hormones. Clearly, there is potential for reproductive effects in fish populations exposed to Cd, however, few studies have investigated the non-lethal consequences of Cd in fish. To this extent, adult male and female Japanese medaka were exposed to 0-10 ppb Cd for 7 weeks. Reproductive endpoints were monitored during weeks 6 and 7 of exposure and compared to physiological responses along the hypothalamus-pituitary-gonadal (HPG) axis, including plasma vitellogenin (VTG), hepatic estrogen receptor (ER), plasma steroids, gonadal-somatic indices (GSI), and gonadal steroid release. There were no observed effects on VTG and ER by long-term Cd exposure. However, gonadal steroid release was significantly decreased in males and females at all exposure concentrations and female plasma estradiol levels were significantly altered at concentrations higher than 5 ppb Cd. Overall, responses along the HPG axis were more sensitive to Cd exposure than the reproductive and developmental endpoints, which were not affected in this study, indicating that higher level impairment in fish might be relatively protected.     

Changes in zinc,copper and metallothionein contents during oocyte growth and early development of the teleost Danio rerio (zebrafish)

In the present report, we investigated zinc, copper and metallothionein (MT) contents in zebrafish oocytes and embryos. Our results demonstrate that the metal content increases during oocytes maturation. Zinc increases from 30 ng/oocyte (stage-1 oocytes) to 100 ng/oocyte (stage-3 oocytes); copper varied from 1 ng/oocyte (stage-1 oocytes) to 3.5 ng/oocyte (stage-3 oocytes). During embryogenesis, zinc and copper contents dramatically increase after fertilisation around the 512-cells stage, then slowly decrease until the mid-gastrula stage. During oocyte growth, the changes in the MT level are proportional to metal content, whereas during embryogenesis the pattern of MT accumulation does not parallel that of the two metals. Indeed, the maternal pool of MT decreases steadily during the early stages of the development until the gastrula stage. We have examined the effect of cadmium on the expression of MT during zebrafish development. After cadmium exposure, MT content increases in embryos at the blastula stage, whereas no induction occurs in embryos at the gastrula stage. However, pre-treatment of embryos at the gastrula stage with 5-aza-2'-deoxycytidine induces MT synthesis following exposure to cadmium. These observations show that changes in metal levels are not correlated to MT content in the embryo, whereas DNA methylation is one of the factors regulating MT expression.     

Increasing intracellular cAMP and cGMP inhibits cadmium-induced oxidative stress in rat submandibular saliva

The effect of cadmium on induction of oxidative stress in rat submandibular saliva and protective role of increasing intracellular cAMP and cGMP by use of specific phosphodiesterase inhibitors, theophylline and sildenafil were investigated. Pure submandibular saliva was collected intraorally by micro polyethylene cannula from anaesthetized rats using pilocarpine as secretagogue. Acute administration of cadmium (10 mg/kg) caused significant oxidative stress by increasing lipid peroxidation by-products (thiobarbituric reactive substances, TBARS) and decreasing total thiols and total antioxidant power of the saliva. Concurrent therapy of rats by theophylline (25 mg/kg) and sildenafil (5 mg/kg) prevented cadmium-induced oxidative stress in saliva. Theophylline and sildenafil inhibited cadmium-induced increase in lipid peroxidation and decrease in total thiols and antioxidant power. It is concluded that cadmium administration results in oxidative stress in rat submandibular saliva, which can be protected by concurrent administration of specific cyclic nucleotide phosphodiesterase inhibitors.     

Cytoplasmic expression of a soluble synthetic mammalian metallothionein-α domain in Escherichia coli

Bacteria are commonly used for bioremediation of heavy metal pollution and strategies to improve their performance in this respect are desirable. In this study, an Escherichia coli strain was engineered to express a common metallothionein-α domain. The metallothionein-α domain was over-expressed in the cytoplasm of E. coli as a fusion to the carboxyl terminal of maltose binding protein. The fusion protein was highly soluble in the cytoplasm of E. coli. When grown in the presence of cadmium, cells expressing the metallothionein-α fusion protein showed increased viability compared with control cells. Cells expressing the metallothionein-α also demonstrated increased accumulation of cadmium.     

A cadmium resistance plasmid, pXU5, in Staphylococcus aureus, strain ATCC25923

A 25.9-kb plasmid, pXU5, encoding high level cadmium resistance was isolated from Staphylococcus aureus strain ATCC25923. A labelled cadA probe from plasmid pI258 hybridised to a 2.3-kb EcoRI fragment of pXU5. pXU5 was incompatible with an S. aureus incompatibility group 1 plasmid.     

Cellular compartmentation of cadmium and zinc in relation to other elements in the hyperaccumulator Arabidopsis halleri

The cellular compartmentation of elements was analysed in the Zn hyperaccumulator Arabidopsis halleri (L.) O'Kane & Al-Shehbaz (=Cardaminopsis halleri) using energy-dispersive X-ray microanalysis of frozen-hydrated tissues. Quantitative data were obtained using oxygen as an internal standard in the analyses of vacuoles, whereas a peak/background ratio method was used for quantification of elements in pollen and dehydrated trichomes. Arabidopsis halleri was found to hyperaccumulate not only Zn but also Cd in the shoot biomass. While large concentrations of Zn and Cd were found in the leaves and roots, flowers contained very little. In roots grown hydroponically, Zn and Cd accumulated in the cell wall of the rhizodermis (root epidermis), mainly due to precipitation of Zn/Cd phosphates. In leaves, the trichomes had by far the largest concentrations of Zn and Cd. Inside the trichomes there was a striking sub-cellular compartmentation, with almost all the Zn and Cd being accumulated in a narrow ring in the trichome base. This distribution pattern was very different from that for Ca and P. The epidermal cells other than trichomes were very small and contained lower concentrations of Zn and Cd than mesophyll cells. In particular, the concentrations of Cd and Zn in the mesophyll cells increased markedly in response to increasing Zn and Cd concentrations in the nutrient solution. This indicates that the mesophyll cells in the leaves of A. halleri are the major storage site for Zn and Cd, and play an important role in their hyperaccumulation. Received: 4 April 2000 / Accepted: 16 May 2000     

Effects of cadmium administration on the endogenous metal balance in rats

The concentrations of cadmium and other metal ions in selected organs, urine, and blood of female rats were measured after exposure to cadmium chloride through their diet or by oral or intravenous administration. The hematological and urinary variations were followed for 4 wk. Body weight gain and the weights of livers and kidneys from all treated groups were not significantly different from the controls. No gross morphological changes were observed in any of the tissues studied at necropsy. The accumulation of cadmium occurred in the liver and kidney. The zinc levels in these organs were elevated relative to controls, in all treated groups regardless of dose and exposure route. Copper was elevated in the liver, kidney, bone, and blood of animals subject to intravenous administration of cadmium. Hepatic iron was decreased in the dietary and orally treated groups, but was not affected in the intravenous study group. The level of magnesium in kidney was increased for all exposure routes, but that of liver was increased only in the intravenously injected groups. The changes in the concentrations of sodium, potassium, calcium, and phosphorus did not follow a specific pattern and varied from organ to organ, depending on the exposure route. The discussion includes a relationship between tissue injury and the alteration of tissue essential element concentrations.     

Responses of Glutathione and Glutathione S-Transferase to Cadmium and Mercury Exposure in Pedunculate Oak (Quercus robur) Leaf Discs

Changes in chlorophyll, non-protein thiol and glutathione (GSH) levels, and the activity of glutathione S-transferase (GST) were investigated in cadmium(ll) and mercury(ll) cchloride treated leaf discs of mature pedunculate oak trees (Quercus robur). Both heavy metals caused decreases in chlorophyll content, but mercury was more toxic than cadmium. Cadmium treatments (30–250μiM) resulted in increasing non-protein thiol levels after 3d, but GSH contents decreased. Mercury (1–20μM) led to a concentration-dependent decline in both non-protein thiol and GSH levels. GST activities were not modified significantly by cadmium, but mercury treatments caused a dose- and time-dependent enzyme induction. Both the phytotoxic- and GST-inducing effect of mercury could be prevented by the cysteine precursor L-2-oxo-4-thiazolidinecarboxylic acid.     

Improved methods for the extraction of polyphenol oxidase from d'anjou pears

The conditions for extracting polyphenol oxidase (PPO, monophenol monooxygenase, EC 1.14.18.1) from d'Anjou pears have been studied. Water extracts of pear PPO contained artefacts which were present as additional bands on polyacrylamide-gel electrophoresis. Buffer extracts of an acetone powder did not remove sufficient endogenous phenolics to prevent browning of the extract. The following phenolic absorbents, arranged in order of increasing efficiency, reduced the formation of artefacts in extracts of PPO: PVPP, Amberlite XAD-4, Bio-Rad AG 1-X8, and Bio-Rad AG 2-X8. Greatest activity was extracted within a pH range of 5.6–5.9. Anion exchange resins were particularly effective in removing phenolics. XAD-4, AG 1-X8, or AG 2-X8 did not adsorb PPO and reduced the electrophoretically separable bands of PPO activity from 11 in water extracts to 3. The properties of the crude PPO were also studied.