Bees have a crucial role in pollination; therefore, it is important to determine the causes of their recent decline. Fipronil and imidacloprid are insecticides used worldwide to eliminate or control insect pests. Because they are broad-spectrum insecticides, they can also affect honeybees. Many researchers have studied the lethal and sublethal effects of these and other insecticides on honeybees, and some of these studies have demonstrated a correlation between the insecticides and colony collapse disorder in bees. The authors investigated the effects of fipronil and imidacloprid on the bioenergetic functioning of mitochondria isolated from the heads and thoraces of Africanized honeybees. Fipronil caused dose-dependent inhibition of adenosine 5'-diphosphate-stimulated (state 3) respiration in mitochondria energized by either pyruvate or succinate, albeit with different potentials, in thoracic mitochondria; inhibition was strongest when respiring with complex I substrate. Fipronil affected adenosine 5'-triphosphate (ATP) production in a dose-dependent manner in both tissues and substrates, though with different sensitivities. Imidacloprid also affected state-3 respiration in both the thorax and head, being more potent in head pyruvate-energized mitochondria; it also inhibited ATP production. Fipronil and imidacloprid had no effect on mitochondrial state-4 respiration. The authors concluded that fipronil and imidacloprid are inhibitors of mitochondrial bioenergetics, resulting in depleted ATP. This action can explain the toxicity of these compounds to honeybees.

BackgroundGossypol is a chemical present in the seeds of cotton plants (Gossypium sp.) that reduces fertility in farm animals. Vitamin E is an antioxidant and may help to protect cells and tissues against the deleterious effects of free radicals. The aim of this study was to evaluate the mechanisms of reproductive toxicity of gossypol in rats and the protective effects of vitamin E. Forty Wistar rats were used, divided into four experimental groups (n = 10): DMSO/saline + corn oil; DMSO/saline + vitamin E; gossypol + corn oil; and gossypol + vitamin E.ResultsFertility was significantly reduced in male rats treated with gossypol in that a significant decrease in epididymal sperm count was observed (P < 0.05) and the number of offspring was significantly reduced in females mated with them (P < 0.05). This dysfunction was prevented by vitamin E. Gossypol caused a significant increase in the activity of the enzymes glutathione peroxidase (P < 0.01) and glutathione reductase (P < 0.01), but vitamin E did not reduce the enzyme activities (P > 0.05). The levels of reduced glutathione and pyridine nucleotides in testis homogenate were significantly reduced by gossypol (P < 0.05 and P < 0.01, respectively) and this reduction was accompanied by increased levels of oxidized glutathione (P < 0.05). Vitamin E showed a preventive effect on the changes in the levels of these substances. Gossypol significantly increased the levels of malondialdehyde (P < 0.01), a lipid peroxidation indicator, whereas treatment with vitamin E inhibited the action of the gossypol. Vitamin E prevented a decrease in mitochondrial ATP induced by gossypol (P < 0.05).ConclusionsThis study suggests that the reproductive dysfunction caused by gossypol may be related to oxidative stress and mitochondrial bioenergetic damage and that treatment with vitamin E can prevent the infertility caused by the toxin.

Abamectin (ABA) is a macrocyclic lactone of the avermectin family used worldwide as an antiparasitic agent in farm animals and pets and as the active ingredient of insecticides and nematicides. In this study, the effects of abamectin on the bioenergetics of mitochondria isolated from rat liver were evaluated. Mitochondria are responsible for converting the energy released by electron transport and stored as the binding energy molecule ATP. Xenobiotics that interfere with its synthesis or utilization can be acutely or chronically toxic. Abamectin (5-25μM) caused concentration-dependent inhibition of the respiratory chain without affecting the membrane potential or the activity of enzymes NADH dehydrogenase or succinate dehydrogenase. This behavior is similar to oligomycin and carboxyatractyloside and suggests direct action on F(o)F(1)-ATPase and/or the adenine nucleotide translocator (ANT). ABA more pronouncedly inhibited ATPase phosphohydrolase activity in intact, uncoupled mitochondria than in freeze-thawed disrupted mitochondria. ADP-stimulated depolarization of the mitochondrial membrane potential was also inhibited by ABA. Our results indicate that ABA interacts more specifically with the ANT, resulting in functional inhibition of the translocator with consequent impairment of mitochondrial bioenergetics. This effect could be involved in the ABA toxicity to hepatocytes.

BackgroundThe liver is an important organ for its ability to transform xenobiotics, making the liver tissue a prime target for toxic substances. The carotenoid bixin present in annatto is an antioxidant that can protect cells and tissues against the deleterious effects of free radicals. In this study, we evaluated the protective effect of bixin on liver damage induced by carbon tetrachloride (CCl4) in rats.ResultsThe animals were divided into four groups with six rats in each group. CCl4 (0.125 mL kg-1 body wt.) was injected intraperitoneally, and bixin (5.0 mg kg-1 body wt.) was given by gavage 7 days before the CCl4 injection. Bixin prevented the liver damage caused by CCl4, as noted by the significant decrease in serum aminotransferases release. Bixin protected the liver against the oxidizing effects of CCl4 by preventing a decrease in glutathione reductase activity and the levels of reduced glutathione and NADPH. The peroxidation of membrane lipids and histopathological damage of the liver was significantly prevented by bixin treatment.ConclusionTherefore, we can conclude that the protective effect of bixin against hepatotoxicity induced by CCl4 is related to the antioxidant activity of the compound.

The clinical management of head and neck squamous cell carcinoma (HNSCC) commonly involves chemoradiotherapy, but recurrences often occur that are associated with radioresistance. Using human SQD9 laryngeal squamous cell carcinoma cancer cells as a model, we aimed to identify metabolic changes associated with acquired radioresistance. In a top-down approach, matched radiosensitive and radioresistant SQD9 cells were generated and metabolically compared, focusing on glycolysis, oxidative phosphorylation (OXPHOS) and ROS production. The cell cycle, clonogenicity, tumor growth in mice and DNA damage-repair were assessed. Mitochondrial DNA (mtDNA) was sequenced. In a bottom-up approach, matched glycolytic and oxidative SQD9 cells were generated using FACS-sorting, and tested for their radiosensitivity/radioresistance. We found that acquired radioresistance is associated with a shift from a glycolytic to a more oxidative metabolism in SQD9 cells. The opposite was also true, as the most oxidative fraction isolated from SQD9 wild-type cells was also more radioresistant than the most glycolytic fraction. However, neither reduced hexokinase expression nor OXPHOS were directly responsible for the radioresistant phenotype. Radiosensitive and radioresistant cells had similar proliferation rates and were equally efficient for ATP production. They were equally sensitive to redox stress and had similar DNA damage repair, but radioresistant cells had an increased number of mitochondria and a higher mtDNA content. Thus, an oxidative switch is associated with but is not responsible for acquired radioresistance in human SQD9 cells. In radioresistant cells, more abundant and fitter mitochondria could help to preserve mitochondrial functions upon irradiation.

Prosopis juliflora, popularly known as Algaroba, is a major problem because the lack of food during the driest times of the year and its high palatability and nutritional value make its fruits (pods) much appreciated by cattle, goats, sheep and other animals. However, the consumption of this plant for long periods can cause a disease called cara-torta (pie face), which is characterized by cranial nerve dysfunction, mainly due to the degeneration and disappearance of neurons in the trigeminal motor nucleus. Algaroba contains piperidine alkaloids that have been suggested as being responsible for its toxicity; one of these alkaloids is juliprosopine. This study was conducted to evaluate the mechanisms of action of juliprosopine in isolated rat brain mitochondria to evaluate the potential mechanisms that lead to neurotoxicity in animals intoxicated by algaroba. Juliprosopine stimulated state-4 respiration at concentrations of 10-25 μM, affected the membrane potential at all concentrations studied (5-25 μM) and affected ATP production only at higher concentrations (15 and 25 μM). Juliprosopine cannot be classified as a member of the protonophoric class of uncouplers, such as 2,4-dinitrophenol or CCCP (m-chlorophenylhydrazone), due to its inability to promote mitochondrial swelling in the hyposmotic medium of potassium acetate. In addition, carboxyatractyloside, Mg(2+), cyclosporine A and dithiothreitol did not protect the uncoupling induced by juliprosopine. Because juliprosopine increased the fluorescence responses of mitochondria labeled with 1-aniline-8-naphthalene sulfonate (ANS) and DPH (1,6-diphenyl-1,3,5-hexatriene), we suggested that its uncoupling action must be attributed to a modification of the arrangement of the inner mitochondrial membrane.

Abamectin (ABA), which belongs to the family of avermectins, is used as a parasiticide; however, ABA poisoning can impair liver function. In a previous study using isolated rat liver mitochondria, we observed that ABA inhibited the activity of adenine nucleotide translocator and FoF1-ATPase. The aim of this study was to characterize the mechanism of ABA toxicity in isolated rat hepatocytes and to evaluate whether this effect is dependent on its metabolism. The toxicity of ABA was assessed by monitoring oxygen consumption and mitochondrial membrane potential, intracellular ATP concentration, cell viability, intracellular Ca(2+) homeostasis, release of cytochrome c, caspase 3 activity and necrotic cell death. ABA reduces cellular respiration in cells energized with glutamate and malate or succinate. The hepatocytes that were previously incubated with proadifen, a cytochrome P450 inhibitor, are more sensitive to the compound as observed by a rapid decrease in the mitochondrial membrane potential accompanied by reductions in ATP concentration and cell viability and a disruption of intracellular Ca(2+) homeostasis followed by necrosis. Our results indicate that ABA biotransformation reduces its toxicity, and its toxic action is related to the inhibition of mitochondrial activity, which leads to decreased synthesis of ATP followed by cell death.

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