Futuristic Approach to Alternative Model Organisms: Hydra Stakes Its Claim

Abstract

The use of mammalian models for toxicological risk assessment of chemicals has been a widespread practice for well over 50 years. This has remained controversial in view of the species differences. Further, the advances in molecular biology techniques have revolutionized the toxicological risk assessment scenario by creating demand for rapid, less expensive and highly relevant methods to risk-evaluate chemical substances quickly. In order to take advantage of these advances the US EPA funded the National Research Council to develop a strategy and vision for toxicity testing in 21 st century (Tox21). Tox21 envisions a paradigm shift in toxicity testing and proposes the use of emerging technologies based on non-animal methods for better understanding of chemical-environment interaction, and also emphasizes the adoption of animals belonging to lower levels of taxonomic hierarchy, which are less sentient, in in vivo toxicity testing. Adoption of this shift would perhaps benefit translation of the REACH Legislation, which otherwise greatly relies on animal experiments for chemical risk assessment. We aimed at establishing Hydra, a simple organism belonging to Phylum Cnidaria, as a model organism for toxicity testing of environmental chemicals. Besides, Hydra offers advantages such as easy to culture, reproduces fast, cost-effective and highly sensitivity to inorganic pollutants. Moreover, the whole genome sequence of hydra revealed that most of the genes are conserved in which sense it offers advantage over even in the most routinely used other invertebrate model organisms. We standardized several assay methods which formed the nucleus of several publications. Herein we show that Hydra can be used as a viable bio-indicator for early warning of aquatic pollutants.

Polymethylmethacrylate nanoplastics effects on the freshwater cnidarian Hydra viridissima

“…At intermediate concentrations of PMMA-NPLs (5 and 10 mg /L), morphological alterations started to be registered after 48h of exposure, whereas at the lowest tested concentration (1 mg/L) malformations were only detected after 72h of exposure. However, the malformations detected at these treatments (1, 5 and 10 mg PMMA-NPLs/L) had no correspondence on the Wilby's classification table of morphological changes (Wilby, 1988;Tino et al, 2011;Traversetti et al, 2017;Murugadas et al, 2019). They were associated with tentacle structure: curled-tips; elbow-like structure; doubled-tip (Fig.…”

“…Scoring of malformations (or morphological changes) was based on the classification of Wilby's (1988) -Toxicity to polyp phasefrom 0 to 10, where 10 is the score attributed to healthy, green hydras, while 0 is attributed to dead/disintegrated hydras. Also, malformations scored below 6 are considered irreversible (Wilby, 1988;Tino et al, 2011;Traversetti et al, 2017;Murugadas et al, 2019).…”

“…During the exposure period, medium renewal was not performed, nor food provided. The regeneration assessment of columnae was performed every 24h J o u r n a l P r e -p r o o f until the end of the assay under a magnifying glass and scoring of the regeneration phases performed according to Wilby's (1988) -Inhibition of the Regeneration phasefrom 0 to 10, where 10 is the score attributed to a complete regenerated hydra, while 0 is attributed to dead/disintegrated hydras (Wilby, 1988;Tino et al, 2011;Traversetti et al, 2017;Murugadas et al, 2019). The duration of exposure was set to 96h because hydras may regenerate a whole specimen within 4 days (Wilby, 1988;Tino et al, 2011;Traversetti et al, 2017;Murugadas et al, 2019).…”

Assessing the risks of capecitabine and its active metabolite 5-fluorouracil to freshwater biota

“…The toxicity of CAP and 5-FU was assessed using freshwater species representative of two functional groups of freshwater ecosystems: the green microalgae R. subcapitata (producer), the cnidarian H. viridissima , and the fish D. rerio (both secondary consumers). These are well-known and studied species recommended/suggested by several guidelines to be used in aquatic toxicity assays (OECD 2011 , 2013 ; Traversetti et al 2017 ; Murugadas et al 2019 ). The choice of two secondary consumers here — one invertebrate and one vertebrate — was related to potential different exposure pathways.…”

“…The scoring of the morphological changes was performed based on the classification of Wilby's (1988), in which scores ranges from 10 (healthy green hydras) to 0 (dead/disintegrated hydras). Organisms scored with 5 (tulip phase) or lower were considered to be in an irreversible morphological and physiological state and, thus, considered as dead at the end of the assay (Murugadas et al 2019;Wilby 1988).…”