Combined toxic effects of cadmium and environmental microplastics in Aphanius fasciatus (Pisces, Cyprinodontidae).

Microplastics (MPs), plastic particles smaller than 5 mm in diameter, have received extensive attention as new environmental pollutants with still unexplored potential ecological risks. The main objective of the present study is to see if the concomitant exposure to MPs and Cd is more toxic than that to MPs or Cd separately in Aphanius fasciatus. Immature female were exposed to Cd and/or MPs for 21 days, and the subsequent effects were monitored by a combination of biochemical, histological and molecular toxicity markers. Exposure to Cd, but not to MPs, increased metallothioneins content and mRNA levels of the metallothioneins gene MTA both in liver and gills. In addition, we observed a significant oxidative stress response at histological, enzymatic (Catalase and Superoxide dismutase), non-enzymatic (proteins sulfhydryl and malondialdehyde) and gene expression levels to both toxicants in both tissues, particularly in gills, but no clear evidence for interaction between the two factors. Our results indicate a major effect of MPs on gills at different organizational levels. Finally, exposure to both MPs and Cd induced spinal deformities, although bone composition was only altered by the latter, whereas MTA mRNA bone levels were only increased realtive to controls in doubly-exposed samples. Interestingly, the simultaneous use of both pollutants produced the same effects as Cd and MPs alone, probably due to reduced bioavailability of this heavy metal.

Interference with zinc homeostasis and oxidative stress induction as probable mechanisms for cadmium-induced embryo-toxicity in zebrafish.

The present study was conducted to provide new insights into the mechanisms that may be responsible for cadmium (Cd)-induced toxicity in zebrafish larvae as well as the role of the trace element zinc (Zn) in reversing Cd harmful effects. For this purpose, zebrafish eggs were exposed to Cd or/and Zn for 96 h. The effects on morphological aspect; mortality rate; Cd, Zn, and metallothionein (MT) levels; oxidative stress biomarkers; as well as molecular expression of some genes involved in Zn metabolism (Zn-MT, ZIP10, and ZnT1) and in antioxidant defense system (Cu/Zn-SOD, CAT and GPx) were examined. Our results showed that Cd toxicity was exerted, initially, by an interference with Zn metabolism. Thus, Cd was able to modify the expression of the corresponding genes so as to ensure its intracellular accumulation at the expense of Zn, causing its depletion. An oxidative stress was then generated, representing the second mode of Cd action which resulted in developmental anomalies and subsequently mortality. Interestingly, significant corrections have been noted following Zn supplementation based, essentially, on its ability to interact with the toxic metal. The increases of Zn bioavailability, the improvement of the oxidative status, as well as changes in Zn transporter expression profile are part of the protection mechanisms. The decrease of Cd-induced MTs after Zn supplement, both at the protein and the mRNA level, suggests that the protection provided by Zn is ensured through mechanisms not involving MT expression but which rather depend on the oxidative status.

Effect of melatonin and folic acid supplementation on the growth performance, antioxidant status, and liver histology of the farmed gilthead sea bream (Sparus aurata L.) under standard rearing conditions.

The present study aimed to investigate the effect of dietary of melatonin (MLT) and folic acid (FA) administrations on growth performance, antioxidant status, and liver histological structure of juvenile gilthead sea bream, Sparus aurata L. under standard rearing conditions. Four diets were considered: a basal diet considered a control and three diets supplemented with 40 mg/kg of melatonin (MLT), 2 mg/kg of folic acid (FA), and with the mixture of melatonin and folic acid (MLT + FA). Each diet was randomly allocated to triplicate groups of fish (mean initial weight was 2.99 ± 0.55 g) for 41 days. The obtained results clearly indicated that the melatonin-supplemented diet decreased significantly the growth performance parameters (final body weight, weight gain rate, and specific growth rate) and IGF-1 level of the gilthead sea bream, while the folic acid-supplemented diet has no significant effect on these parameters. The mixture supplementation of melatonin and folic acid has no significant effect on the growth parameters due to the possible interaction between melatonin and folic acid effects. Furthermore, fish fed with all experimental diets showed significantly higher superoxide dismutase activity (SOD) and protein sulfhydryl level (PSH) and lower lipid peroxidation level (TBARS) and catalase activity (CAT) which confirm their powerful antioxidant role. The acetylcholinesterase activity (ACHE) decreased in fish fed with all experimental diets. The underlying mechanisms of driving melatonin and folic acid to reduce acetylcholinesterase activity require further studies. The histological structure of liver of control S. aurata fish shows severe hepatic lipid accumulation in large vacuoles that diminished after dietary individual or mixture folic acid and melatonin supplementations over 41 days. This work proved that 2 mg/kg of dietary folic acid has a positive effect on the growth performance, oxidative stress defense, and hepatic lipid accumulation reduction in the gilthead sea bream fish. Under our experimental conditions, melatonin failed to improve the growth indexes WGR, SGR, and IGF-I. This study recommends the diet supplementation with a dose lower than 2 mg/kg of food due to the observed effects on tissue ACHE activity.

First evidence on protective effect of exogenous melatonin supplementation against disruption of the estrogenic pathway in bone metabolism of killifish (Aphanius fasciatus).

This study was carried out to investigate the effects of exposure to estrogen antagonist nafoxidine hydrochloride (NH) and/or melatonin (Mlt) on certain bone metabolism parameters in killifish Aphanius fasciatus, a species suggested to be a suitable model for studying spinal deformities such as scoliosis. Immature females of A. fasciatus receiving 10 µg/L NH and/or 100 µg/L of Mlt were used and were sacrificed 30 days after the treatment. The spinal column, brain, and liver were collected and analyzed by various histological, biochemical, chemical, and molecular investigations. NH exposure increased frequency of histological alterations and caused signs of spinal column demineralization such as significant decrease in the percentage of nonorganic components content and calcium concentration. These changes were accompanied by decreased alkaline phosphatase activity (AP), hepatic insulin growth factor-1 (IGF-1) content, and, interestingly, cerebral Mlt concentration. Concomitant treatment with Mlt and NH enhanced expression of the gene encoding the Mlt receptor "mtnr1aa"and significantly restored the normal skeletal histology and the normal metabolism bone parameters. Our data suggest that disturbance of estrogen pathway in A. fasciatus induces cerebral Mlt depletion and, then, causes skeletal tissue alterations and bone demineralization and that exogenous Mlt supplementation has a protective effect. Thus, estrogen receptor antagonists and Mlt become important compounds to consider for the accurate prediction and assessment of bone physiology and spinal deformities in fish.

Effects of cadmium and high temperature on some parameters of calcium metabolism in the killifish (Aphanius fasciatus).

This study aims to investigate the influence of high temperature on cadmium (Cd) toxicity in Aphanius fasciatus (Pisces: Cyprinodontidae). For this reason, Cd, mineral, and organic content in the vertebral column as well as the histological structure of gills and bone were compared in fishes exposed for 30 days to Cd (2 mg/L CdCl2) and/or high temperature (26 °C). Cd exposure caused a negative correlation between Cd and Ca concentrations (r = 0.98, p < 0.05), as well as a significant decrease in inorganic components (p < 0.05) and ash weight/dry weight ratio (p < 0.05) in the vertebral column. These changes were accompanied by an increased frequency of histological alterations in gills and bone. Concomitant treatment with Cd and high temperature increases Cd accumulation and Ca depletion in the skeletal tissue and increases the frequency and the severity of histological alterations. These results confirm that temperature increases Cd toxicity and needs to be taken into account for the accurate prediction and assessment of Cd-induced spinal deformities in fish.

Influence of cadmium exposure on growth and fecundity of freshwater mosquitofish Gambusia affinis: in situ and in vivo studies.

This study aims to investigate the effect of cadmium (Cd) exposure on growth and fecundity of mosquitofish Gambusia affinis. For this purpose, two natural populations of pregnant females of G. affinis captured from two sites were differently contaminated with Cd (S1 present Cd levels 5-fold higher than S2) and a sublethal exposure to 0.4 mg CdCl(2)/L (10% of LC(50)) during 56 days was conducted in vivo. The length-weight regression revealed a significant difference in the growth between these two populations. A significant difference in fecundity was also noted between the two populations. Indeed, the embryo numbers in pregnant females captured from S1 are significantly higher than those noted in pregnant females from S2 (21.17±5 and 7.97±2.12, respectively; p<0.05). Following Cd exposure, we noted a growth perturbation resulting in lower values of both indices BWG and SGR following 7 and 21 days (-5.21 and -1.18 for BWG, and -2.09 and -0.46 for SGR, respectively) and a recuperation of growing weight at 42 and 56 days (1.32 and 1.71 for BWG, and 0.45 and 0.54 for SGR, respectively). For CF index, we observed a significant difference (p<0.05) between control and Cd groups at 7 and 21 days of exposure, and at 21 and 56 days respectively for HSI and GSI indices. Furthermore, Cd contents in both tissues (liver and yolk sac) and fractions (cytosolic and membrane) are significantly different between groups during experimentation. In addition, the Cd contents noticed in the liver membrane fraction are significantly higher than those noted in the yolk sac tissue. The MTs levels revealed a significant difference between the control and Cd groups. In liver tissue, a significant difference was noted, in MTs levels, during the Cd exposure (7, 21, 42, and 56 days) while in the yolk sac tissue the difference was noted at 42 days of exposure. Taken together, these results imply the potential negative effect of Cd on physiological status of G. affinis as evidenced by decreasing growth and fecundity rate.

Influence of high temperature on cadmium-induced skeletal deformities in juvenile mosquitofish (Gambusia affinis).

The aim of this study was to assess the effect of high temperature on cadmium (Cd)-induced skeletal deformities in juvenile Mosquitofish, Gambusia affinis. For this purpose, 188 juveniles (1 day old) were equally divided into the control group, which was maintained in Cd-free water at 24 degrees C, and three treated groups exposed either to Cd (0.4 mg/l as Cd Cl(2)) at 24 degrees C, to high temperature (32 degrees C), or to Cd at 32 degrees C for 30 days. The results showed that Cd exposure at 24 degrees C significantly increased the Cd accumulation (P < 0.0001) in the whole tissues of juveniles as well as the incidence of skeletal deformities (P < 0.01) compared with control animals. Exposure to high temperature also led to a significant increase in the incidence of skeletal deformities (P < 0.01) with respect to the control group. Interestingly, our results showed that the combined exposure to Cd and high temperature led to a more significant increase in Cd accumulation and in the frequency of spinal deformities than exposure to Cd or high temperature alone. These results confirm that temperature increases Cd toxicity and needs to be taken into account for the accurate prediction and assessment of Cd-induced spinal deformities in fish.