Gadolinium Accumulation and Toxicity on In Vitro Grown Stevia rebaudiana: A Case-Study on Gadobutrol

Abstract

Gadolinium-based contrast agents are molecular complexes which are extensively used for diagnostic purposes. Apart from their tremendous contribution to disease diagnostics, there are several issues related to their use. They are extremely stable complexes and potential contaminants of surface and ground waters, an issue which is documented worldwide. The irrigation of fields with contaminated surface waters or their fertilization with sludge from wastewater treatment plants can lead to the introduction of Gd into the human food supply chain. Thus, this study focused on the potential toxicity of Gd on plants. For this purpose, we have studied the molecular effects of gadobutrol (a well-known MRI contrast agent) exposure on in vitro-grown Stevia rebaudiana. The effects of gadobutrol on plant morphology, on relevant plant metabolites such as chlorophylls, carotenoids, ascorbic acids (HPLC), minerals (ICP-OES), and on the generation of free radical species (MDA assay and EPR) were assessed. Exposures of 0.01, 0.05, 0.1, 1, and 3 mM gadobutrol were used. We found a correlation between the gadobutrol dose and the plant growth and concentration of metabolites. Above the 0.1. mM dose of gadobutrol, the toxic effects of Gd⁺³ ions became significant.

Keywords: accumulation; carotenoids; chlorophylls; free radicals; gadobutrol; growth; toxicity.

Figure 1

Top: (a) S. rebaudiana plants after being grown for 28 days in control growth media and media exposed to 1 mM and 3 mM gadobutrol (from left to right); Bottom: (b) mean and SE shoot length (n = 30), (c) mean and SE root length (n = 30) and (d) mean and SE dry weight plant biomass (n = 30) of S. rebaudiana plants after being exposed for 28 days to different concentrations of gadobutrol of 0–3 mM. (ns for p-value range > 0.05; ** for p-value range 0.001–0.01; *** for p-value range 0.0001–0.01; **** for p-value range <0.0001).

Figure 2

Ascorbic (a) and dehydroascorbic acids (b) concentrations in S. rebaudiana plants exposed to GB in concentrations of 0–3 mM. The concentrations are represented as mean and SD. (ns for p-value range > 0.05; * for p-value range 0.01–0.05; ** for p-value range 0.001–0.01; *** for p-value range 0.0001–0.01; **** for p-value range <0.0001).

Figure 3

Concentration of carotenoids in S. rebaudiana plants treated with GB in concentrations 0–3 mM; lutein (a), zeaxanthin (b), β-carotene (c) (ns for p-value range > 0.05; ** for p-value range 0.001–0.01; *** for p-value range 0.0001–0.01; **** for p-value range <0.0001).

Figure 4

Uptake of Gd ions in the S. rebaudiana plant tissues exposed to GB in concentrations 0–3 mM, quantified by ICP-OES. The results are presented as mean and SD.

Figure 5

Characteristic UV-Vis spectra of the compounds resulted from the MDA assay (a) and the evolution of the absorbances of the 450 and 532 nm peaks with the increase in the Gd exposure (b).

Figure 6

EPR spectra of the S. rebaudiana plants exposed to GB in concentration 0–3 mM and a Gd standard at 330 µg in capillary, at room temperature, 9.46 mW power. The g-values of the signals are indicated (a); radical intensity of the S. rebaudiana plants exposed to GB measured by peak-to-peak difference at I_3513G–I_3527G (b).