# Has the Toxicity of Therapeutic Deep Eutectic Systems
## 3 Animal Models  
Regarding the toxicity of DESs, to date, these compounds have been tested mainly in invertebrates and animal models (rodents). Studies in invertebrate animals included _Daphnia magna_, _Artemia salina_, and _Hydra sinensis_ with mixed results in the toxicity of the DES use. In reference to the _Daphnia magna_toxicity test, only two studies evaluated different DESs [70] or NADESs [71], and none of the tested combinations induced significant toxicity toward this model. [PERSON] et al. tested different DESs in _Artemia salina_ to determine the toxicity and the mortality. The results of the assays indicated that the toxicity of DESs was higher than their individual components, suggesting that the toxicity can be influenced by the composition of DESs by varying the salt/HBD combination and molar ratio [42,47]. The study of _Hydra sinensis_ concluded that the survival times of _Hydra sinensis_ were significantly shortened by exposure to a DES-containing aqueous solution, suggesting that the DES exhibited a toxic effect on the hydras. It was suspected that depending on the type of HBD of the eutectic mixtures, the charge will be delocalized in the HBA and modify the toxicity [72]. Regarding more complex animal models, [PERSON] et al. also tested the toxic potential of ammonium-based DESs in vivo in a murine model. As in _Artemia salina_ had shown previously, in mice tests, DESs were relatively more toxic in comparison to their individual components [38]. Consequently, [PERSON] et al. tested the toxicity of DESs and NADESs in mice, showing that NADESs presented higher toxicity than DESs, and induced liver failure due to their viscosity, which made the circulation of the mixture difficult [50]. In the same line, [PERSON] et al. administered phenolic NADES extract from green coffee beans to Wistar rats, and its oral administration induced mortality in two rats, and short-term side effects such as excessive water consumption, weight loss, hepatomegaly, and plasma oxidative stress associated with hyperlipemia [73]. On the other hand, more recent articles observed less toxicity on the DESs studied. [PERSON] et al. investigated the toxicity of oral CAGE (Choline bicarbonate and Geranic acid) administration in rats treated for 30 days. The results obtained indicate that the CAGE formulation was well tolerated, that no changes were found in the red blood cells and platelet count of treated rats compared with the controls [74]. [PERSON] et al. used metabolites of _Coptidis rhizoma_ extract to artificially prepare the NADES. Then, the toxicity in the mice was evaluated, showing that after the oral administration of the NADES, the mice became irritable and presented dyskinesia, which means that the NADES itself showed an acute toxicity to the mice. However, the mice that were given 10% dilution of the NADES in water showed no toxicity, and none died after oral administration [75]. Different NADESs/DESs were used to improve the bioavailability and/or biocompatibility of different compounds [36,76,77,78,79,80]. [PERSON] et al. developed a novel hydrogel system incorporating an amino acid-based DES. The DESs were integrated into Carbomer(r) 940 hydrogels for the skin delivery of \"sanwujiaowan\" extract, a Chinese herbal medicine. Sanwujiaowan is composed of six ingredients, some of them with a certain degree of toxicity. By preparing the DES extract complex, it demonstrated good dissolution and skin permeability of the ingredients in the extracts. The authors used a collagen-induced-arthritis rat model, and the hydrogel with the DES extract complex exerted an enhanced therapeutic effect that reduced the inflammatory response with systemic toxicity of the extracts [32]. Due to their high stabilization and solubilization power, DESs offer the ability to tune the solubility, permeation, and absorption of APIs. For that, APIs with low solubility or permeability could be improved by including these solvents on their formulation in in vivo studies.