Shinya S et al. (2023), Characteristics of tissue distribution, metabol...

XB-ART-59596

Aquat Toxicol 2023 Apr 01;257:106437. doi: 10.1016/j.aquatox.2023.106437.

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Characteristics of tissue distribution, metabolism, effects on brain catecholamines, and environmental exposure of frogs to neonicotinoid insecticides.

Shinya S , Nishibe F , Yohannes YB , Ishizuka M , Nakayama SM , Ikenaka Y .

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Pesticide exposure is considered to be one important factor responsible for declining amphibian populations worldwide. The usage of neonicotinoid insecticides (NNIs) has markedly increased in recent years, and there are concerns regarding the effects of NNI-induced toxicity on the development and behavior of amphibians. However, there have been few reports on the metabolism, distribution, and neurotoxicity of NNIs in amphibians. In this study, we exposed the Western clawed frog (Silurana tropicalis) to clothianidin (CLT) in water. After 24 h of exposure, the highest concentrations were detected in the skin, indicating that frogs are at a high risk of absorbing CLT through their skin along with water. Excretion of CLT was estimated based on the concentrations of CLT metabolites in the water until 48 h of exposure. The findings showed that frogs had higher CLT metabolic ability than zebrafish. Serotonin levels in the brain were lower in the high-concentration CLT exposure group than in the control group, although the difference was not statistically significant. This suggested that catecholamine-related effects of CLT on the brain cannot be disregarded. In addition, quantitative analyses of NNI residue in wild frogs, soil, and water in agricultural areas in Hokkaido, Japan, were performed and four NNIs were detected. These results indicated the possible risk of NNI-induced toxicity in frogs. This is the first report of the characteristics of tissue distribution and metabolism of NNIs in frogs, which may facilitate the design of appropriate conservation programs for amphibians.

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Species referenced: Xenopus tropicalis Xenopus laevis
GO keywords: response to insecticide [+]

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	Fig. 1. Concentrations of clothianidin in the organs of Western clawed frogs exposed to clothianidin for 24 h Western clawed frogs were exposed to clothianidin concentrations of 10 ppb, 100 ppb, and 500 ppb. Clothianidin concentrations were measured in eight tissues (brain, liver, kidney, muscle, skin, stomach, intestine, and testis). Data are shown as the mean ± SD (n = 9). *P < 0.05: Significantly different between groups indicated by lines (Tukey–Kramer test).
	Fig. 2. Concentrations of desmethyl-clothianidin in the organs of Western clawed frogs exposed to clothianidin for 24 h Western clawed frogs were exposed to clothianidin at concentrations of 10 ppb, 100 ppb, and 500 ppb. Desmethyl clothianidin concentrations were measured in eight tissues (brain, liver, kidney, muscle, skin, stomach, intestine, and testis). Data are shown as the mean ± SD (n = 9). *P < 0.05: Significantly different between groups indicated by lines (Tukey–Kramer test).
	Fig. 3. Concentrations of clothianidin metabolites in the rearing water. Western clawed frogs were exposed to clothianidin (10 ppb, 100 ppb, and 500 ppb) for 48 h. (3-A) Concentration of desmethyl-clothianidin. (3-B) Concentrations of clothianidin-urea. (3-C) Concentration of desnitro-clothianidin. Data are shown as the mean ± SD (n = 4).
	Fig. 4. Concentrations of desmethyl-clothianidin in the rearing water, including excretion, of Western clawed frogs exposed to 500 ppb of clothianidin for 48 h The approximate straight line was obtained based on this polygonal line.
	Fig. 5. Concentrations of catecholamines in the brains of Western clawed frogs exposed to clothianidin for 24 h Western clawed frogs were exposed to clothianidin at concentrations of 0 ppb, 10 ppb, 100 ppb, and 500 ppb. (A) Dopamine, (B) 3-methoxytyramine, and (C) serotonin were analyzed. Data are shown as the mean ± SD (n = 9).