Enhanced cytotoxicity of imidacloprid by biotransformation in isolated hepatocytes and perfused rat liver.

Imidacloprid (IMD) is a neonicotinoid insecticide widely used in crops, pets, and on farm animals for pest control, which can cause hepatotoxicity in animals and humans. In a previous study using isolated rat liver mitochondria, we observed that IMD inhibited the activity of FoF1-ATP synthase. The aim of this study was to evaluate the effects of IMD on rat isolated hepatocytes and perfused rat liver, besides the influence of its biotransformation on the toxicological potential. For the latter goal, rats were pretreated with dexamethasone or phenobarbital, two classical cytochrome P-450 stimulators, before hepatocytes isolation or liver perfusion. IMD (150 and 200 µM) reduced state 3 mitochondrial respiration in digitonin-permeabilized cells that were energized with glutamate plus malate but did not dissipate the mitochondrial membrane potential. In intact (non-permeabilized) hepatocytes, the intracellular ATP concentration and cell viability were reduced when high IMD concentrations were used (1.5-3.0 mM), and only in cells isolated from dexamethasone-pretreated rats, revealing that IMD biotransformation increases its toxicity and that IMD itself affects isolated mitochondria or mitochondria in permeabilized hepatocytes in concentrations that do not affect mitochondrial function in intact hepatocytes. Coherently, in the prefused liver, IMD (150 and 250 µM) inhibited gluconeogenesis from alanine, but without affecting oxygen consumption and urea production, indicating that such effect was not of mitochondrial origin. The gluconeogenesis inhibition was incomplete and occurred only when the rats were pretreated with phenobarbital, signs that IMD biotransformation was involved in the observed effect. Our findings reveal that changes in hepatic energy metabolism may be acutely implicated in the hepatotoxicity of IMD only when animals and humans are exposed to high levels of this compound, and that IMD metabolites seem to be the main cause for its toxicity.

Imidacloprid affects rat liver mitochondrial bioenergetics by inhibiting FoF1-ATP synthase activity.

Imidacloprid (IMD) is a neonicotinoid insecticide widely used in crops, pets, and on farm animals for pest control. Several studies were conducted examining the adverse effects of IMD on animals often exhibiting hepatic damage. The aim of this study was to determine the effects of IMD on bioenergetics of mitochondria isolated from rat liver. Imidacloprid (50-200 µM) produced a concentration-dependent decrease in oxygen consumption and ATP production without markedly affecting mitochondrial membrane potential (MMP). Oxygen consumption experiments showed that IMD did not significantly affect the respiratory chain, and this was similar to findings with oligomycin and carboxyatractyloside, suggesting a direct action on FoF1-ATP synthase and/or the adenine nucleotide translocator (ANT). Imidacloprid inhibited FoF1-ATP synthase activity only in disrupted mitochondria and induced a partial inhibition of ADP-stimulated depolarization of the MMP. Our results indicate that IMD interacts specifically with FoF1-ATP synthase resulting in functional inhibition of the enzyme with consequent impairment of mitochondrial bioenergetics. These effects of IMD on mitochondrial bioenergetics may be related to adverse effects of this insecticide on the liver.