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.

Aphanius fasciatus: a molecular model of scoliosis?

STUDY DESIGN: Observational study of Killifish with spinal deformities OBJECTIVE: To evaluate the morphology and molecular biology of Aphanius fasciatus with severe spine deformities. Idiopathic Scoliosis affects 3% of the population and is an abnormal three-dimensional curvature of the spine with unknown cause. The lack of a model system with naturally occurring spinal curvatures has hindered research on the etiology of IS. METHODS: The Mediterranean killifish Aphanius fasciatus, collected from the coast of Sfax (Tunisia), which has an inborn skeletal deformity was chosen. We used morphologic features to evaluate the severity of scoliosis according to the different types and performed a biochemical analysis using factors previously studied in humans (estradiol, melatonin and Insulin Growth Factor 1 "IGF-1"). RESULTS: We have detected relevant molecular deviations that occur in Killifish deformities and the fish with severe scoliosis are smaller and less old than the ones with milder scolioses. Furthermore, a significant change in levels of ovarian estradiol, liver IGF-1 and brain melatonin was noted between deformed and normal fish. CONCLUSIONS: Aphanius fasciatus could be used as a molecular model system to study the etiology of IS in humans as the characterization of the Aphanius fasciatus scoliosis syndrome has revealed morphological and biochemical parallels to IS. However, it is important to note the limitations of the proposed model, including the short lifespan of the fish. LEVEL OF EVIDENCE: III.

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.