Does acute exposure to thimerosal, an organic mercury compound, affect the mitochondrial function of an infant model?

BACKGROUND: Thimerosal (TM) is a toxic, organometallic mercury compound (which releases ethyl-mercury-containing compounds in aqueous solutions) used as a preservative in vaccines. Mitochondria are organelle which are highly vulnerable to many chemical compounds, including mercury (Hg) and its derivatives. METHOD: Wistar rats (at 21 days of age) were used to model a child's TM exposure following childhood vaccination, divided in two groups: TM exposed (20 µg/kg/day) and unexposed controls (saline solution), both for 24 h. Atomic Fluorescence Spectrometry was used to quantify the amounts of mercury in tissues. The electron transport chain (ETC) from isolated mitochondria was evaluated using an oxygen electrode. The mitochondrial membrane potential and H2O2 production were analyzed using selective fluorescence probes. The activity of some enzymes (SOD, CAT, GPx, and AChE) and secondary markers of oxidative stress (GSH, GSSG, total free thiol) were also examined in tissues. RESULTS: Hg accumulation in the brain and liver was higher in exposed animals when compared to the control. Liver-isolated mitochondria showed that TM improved respiratory control by 23%; however, states 3 and 4 of the ETC presented a decrease of 16% and 37%, respectively. Furthermore, brain-isolated mitochondria presented an improvement of 61% in respiratory control. Brain enzyme activities were significantly impacted in TM-exposed rats compared to unexposed rats as follows: decreases in SOD (32%) and AChE (42%) and increases in GPx (79%) and CAT (100%). GPx enzyme activity in the liver was significantly increased (37%). Among secondary oxidative stress markers, the brain's total reduced thiol (SH) concentration was significantly increased (41%). CONCLUSION: Acute TM treatment exposure in a Wistar rat model mimicking TM exposure in an infant following childhood vaccination significantly damaged brain bioenergetic pathways. This study supports the ability of TM exposure to preferentially damage the nervous system.

Effects of pyriproxyfen on zebrafish brain mitochondria and acetylcholinesterase.

Pyriproxyfen is an insecticide used worldwide that acts as a biomimetic of juvenile hormone. This study investigated metabolic and synaptic impairments triggered by pyriproxyfen using zebrafish acetylcholinesterase (zbAChE) and mitochondria as markers. A brain zbAChE assay was performed in vitro and in vivo covering a range of pyriproxyfen concentrations (0.001-10 µmol/L) to assess inhibition kinetics. Docking simulations were performed to characterize inhibitory interactions. Zebrafish male adults were acutely exposed to 0.001, 0.01 and 0.1 µg/mL pyriproxyfen for 16 h. Mitochondrial respiration of brain tissues was assessed. ROS generation was estimated using H2DCF-DA and MitoSOX. Calcium transport was monitored by Calcium Green™ 5 N. NO synthesis activity was estimated using DAF-FM-DA. Brain acetylcholinesterase showed an in vivo IC20 of 0.30 µmol/L pyriproxyfen, and an IC50 of 92.5 µmol/L. The inhibitory effect on zbAChE activity was competitive-like. Respiratory control of Complex I/II decreased significantly after insecticide exposure. The MitoSOX test showed that O2- generation had a pyriproxyfen dose-dependent effect. Brain tissue lost 50% of Ca2+ uptake capacity at 0.1 µg/mL pyriproxyfen. Ca2+ release showed a clear mitochondrial impairment at lower pyriproxyfen exposures. Thus, Ca2+ transport imbalance caused by pyriproxyfen may be a novel deleterious mechanism of action. Overall, the results showed that pyriproxyfen can compromise multiple and interconnected pathways: (1) zbAChE impairment and (2) the functioning of the electron transport chain, ROS generation and calcium homeostasis in zebrafish brain mitochondria. Considering the many similarities between zebrafish and human, more caution is needed when pyriproxyfen is used in both urban and agricultural pest control.

Mitochondria as targets for toxicity and metabolism research using zebrafish.

BACKGROUND: The study of mitochondrial functions in zebrafish was initiated before the 1990s and has effectively supported many of the recent scientific advances in the functional studies of mitochondria. SCOPE OF REVIEW: This work elaborates various peculiarities and general advances in the study of mitochondria using this animal model. MAJOR CONCLUSIONS: The inclusion of zebrafish models in scientific research was initiated with structural studies of mitochondria. Then, toxicological studies involving chemical compounds were undertaken. Currently, there is a decisive tendency to use zebrafish to understand how chemicals impair mitochondrial bioenergetics. Zebrafish modeling has been fruitful for the analysis of ion homeostasis, especially for Ca2+ transport, since zebrafish and mammals have the same set of Ca2+ transporters and mitochondrial membrane microdomains. Based on zebrafish embryo studies, our understanding of ROS generation has also led to new insights. GENERAL SIGNIFICANCE: For the study of mitochondria, a new era was begun with the inclusion of zebrafish in bioenergetics research.

The Cratylia mollis seed lectin induces membrane permeability transition in isolated rat liver mitochondria and a cyclosporine a-insensitive permeability transition in Trypanosoma cruzi mitochondria.

Previous results provided evidence that Cratylia mollis seed lectin (Cramoll 1,4) promotes Trypanosoma cruzi epimastigotes death by necrosis via a mechanism involving plasma membrane permeabilization to Ca(2+) and mitochondrial dysfunction due to matrix Ca(2+) overload. In order to investigate the mechanism of Ca(2+) -induced mitochondrial impairment, experiments were performed analyzing the effects of this lectin on T. cruzi mitochondrial fraction and in isolated rat liver mitochondria (RLM), as a control. Confocal microscopy of T. cruzi whole cell revealed that Cramoll 1,4 binding to the plasma membrane glycoconjugates is followed by its internalization and binding to the mitochondrion. Electrical membrane potential (∆Ψm ) of T. cruzi mitochondrial fraction suspended in a reaction medium containing 10 µM Ca(2+) was significantly decreased by 50 µg/ml Cramoll 1,4 via a mechanism insensitive to cyclosporine A (CsA, membrane permeability transition (MPT) inhibitor), but sensitive to catalase or 125 mM glucose. In RLM suspended in a medium containing 10 µM Ca(2+) this lectin, at 50 µg/ml, induced increase in the rate of hydrogen peroxide release, mitochondrial swelling, and ∆Ψm disruption. All these mitochondrial alterations were sensitive to CsA, catalase, and EGTA. These results indicate that Cramoll 1, 4 leads to inner mitochondrial membrane permeabilization through Ca(2+) dependent mechanisms in both mitochondria. The sensitivity to CsA in RLM characterizes this lectin as a MPT inducer and the lack of CsA effect identifies a CsA-insensitive MPT in T. cruzi mitochondria.