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Zinc is an essential trace element with various functions in all living organisms. Its bioavailability is tightly controlled by a combination of nutritional availability, binding to proteins, location in cellular organelles, and the presence of zinc transporters. In humans, changes in zinc homeostasis, such as zinc deficiency, have varied impacts on individuals. Zinc affects growth, fertility, immune cell functioning, and disease progression. Zinc homeostasis is compromised in aging, whereby abnormal metabolism contributes to sub-clinical changes and cellular dysfunction that may underlie the early onset of (neuro-)degenerative diseases. Therefore, a better understanding of the normal function of this trace element in health and diseases is highly desired.

Goldfish (Carassius auratus) fry (80 mg) were fed purified diets based on casein as a protein source and containing different levels of supplementary zinc (0, 30, 60, 90, 120, 150 mg Zn/kg diet) for nine weeks. There were overt signs of zinc deficiency (suppressed growth, high mortality) in fish fed the zinc-deficient control diet, while the highest growth was obtained in fish fed the 60 mg Zn/kg diet. Alkaline phosphatase (ALP) activity in the muscle and super-oxide dismutase (SOD) activity in the liver were highest in fish fed the 60 mg Zn/kg diet and did not significantly improve beyond this level. Muscle and whole body zinc concentrations increased proportionately with the dietary zinc supplementation but iron and copper concentrations in fish tissue were not affected by the supplementary zinc. After the 9-week trial, twelve fish were subjected to thermal stress (28-32°C) for another four weeks to observe growth and the physiological response of the stress enzyme, SOD. After thermal stress, growth improved with the increase in zinc. Likewise, SOD activity in the fish liver increased, indicating that fish utilize more zinc in high temperatures to counteract stress.

Goldfish (Carassius auratus) fry (80 mg) were fed purified diets based on casein as a protein source and containing different levels of supplementary zinc (0, 30, 60, 90, 120, 150 mg Zn/kg diet) for nine weeks. There were overt signs of zinc deficiency (suppressed growth, high mortality) in fish fed the zinc-deficient control diet, while the highest growth was obtained in fish fed the 60 mg Zn/kg diet. Alkaline phosphatase (ALP) activity in the muscle and super-oxide dismutase (SOD) activity in the liver were highest in fish fed the 60 mg Zn/kg diet and did not significantly improve beyond this level. Muscle and whole body zinc concentrations increased proportionately with the dietary zinc supplementation but iron and copper concentrations in fish tissue were not affected by the supplementary zinc. After the 9-week trial, twelve fish were subjected to thermal stress (28-32°C) for another four weeks to observe growth and the physiological response of the stress enzyme, SOD. After thermal stress, growth improved with the increase in zinc. Likewise, SOD activity in the fish liver increased, indicating that fish utilize more zinc in high temperatures to counteract stress.

Goldfish (Carassius auratus) fry (80 mg) were fed purified diets based on casein as a protein source and containing different levels of supplementary zinc (0, 30, 60, 90, 120, 150 mg Zn/kg diet) for nine weeks. There were overt signs of zinc deficiency (suppressed growth, high mortality) in fish fed the zinc-deficient control diet, while the highest growth was obtained in fish fed the 60 mg Zn/kg diet. Alkaline phosphatase (ALP) activity in the muscle and super-oxide dismutase (SOD) activity in the liver were highest in fish fed the 60 mg Zn/kg diet and did not significantly improve beyond this level. Muscle and whole body zinc concentrations increased proportionately with the dietary zinc supplementation but iron and copper concentrations in fish tissue were not affected by the supplementary zinc. After the 9-week trial, twelve fish were subjected to thermal stress (28-32°C) for another four weeks to observe growth and the physiological response of the stress enzyme, SOD. After thermal stress, growth improved with the increase in zinc. Likewise, SOD activity in the fish liver increased, indicating that fish utilize more zinc in high temperatures to counteract stress.

Eukaryotic cells respond to stressful environmental stimuli, such as toxic concentrations of heavy metals, by rapidly synthesising defence proteins: the metallothioneins (MT) and the heat shock protein 70 (Hsp70). In this study we have analysed how the human hepatoblastoma cell line HepG2 responds to exposure to excess copper (30 mug/ml) and zinc (50 mug/ml) for long exposure times (48 and 72 h). Accumulation of the two metals, as measured by ICP-AES, was time-dependent reaching a plateau after 72 It. HepG2 cells responded by dramatically increasing levels of MT during stress, mostly during zinc exposure. A time tag in Hsp70 induction was observed as the levels of this protein increased only after removal of the stress from culture medium (recovery) for 24 h, thus suggesting that the two defence mechanisms are not coordinated in a metal-induced stress response. Moreover in HepG2 cells, immunochemical and fluorescence techniques showed the presence and the localisation of the zinc membrane exporter ZnT-1 as a further mechanism of defence/homeostasis against zinc toxicity.