Abstract
BackgroundSilica nanoparticles (nanoSiO2) are promising systems that can deliver biologically active compounds to tissues such as the heart in a controllable manner. However, cardiac toxicity induced by nanoSiO2 has been recently related to abnormal calcium handling and energetic failure in cardiomyocytes. Moreover, the precise mechanisms underlying this energetic debacle remain unclear. In order to elucidate these mechanisms, this article explores the ex vivo heart function and mitochondria after exposure to nanoSiO2.ResultsThe cumulative administration of nanoSiO2 reduced the mechanical performance index of the rat heart with a half-maximal inhibitory concentration (IC50) of 93 μg/mL, affecting the relaxation rate. In isolated mitochondria nanoSiO2 was found to be internalized, inhibiting oxidative phosphorylation and significantly reducing the mitochondrial membrane potential (ΔΨm). The mitochondrial permeability transition pore (mPTP) was also induced with an increasing dose of nanoSiO2 and partially recovered with, a potent blocker of the mPTP, Cyclosporine A (CsA). The activity of aconitase and thiol oxidation, in the adenine nucleotide translocase, were found to be reduced due to nanoSiO2 exposure, suggesting that nanoSiO2 induces the mPTP via thiol modification and ROS generation. In cardiac cells exposed to nanoSiO2, enhanced viability and reduction of H2O2 were observed after application of a specific mitochondrial antioxidant, MitoTEMPO. Concomitantly, CsA treatment in adult rat cardiac cells reduced the nanoSiO2-triggered cell death and recovered ATP production (from 32.4 to 65.4%). Additionally, we performed evaluation of the mitochondrial effect of nanoSiO2 in human cardiomyocytes. We observed a 40% inhibition of maximal oxygen consumption rate in mitochondria at 500 μg/mL. Under this condition we identified a remarkable diminution in the spare respiratory capacity. This data indicates that a reduction in the amount of extra ATP that can be produced by mitochondria during a sudden increase in energy demand. In human cardiomyocytes, increased LDH release and necrosis were found at increased doses of nanoSiO2, reaching 85 and 48%, respectively. Such deleterious effects were partially prevented by the application of CsA. Therefore, exposure to nanoSiO2 affects cardiac function via mitochondrial dysfunction through the opening of the mPTP.ConclusionThe aforementioned effects can be partially avoided reducing ROS or retarding the opening of the mPTP. These novel strategies which resulted in cardioprotection could be considered as potential therapies to decrease the side effects of nanoSiO2 exposure.
Highlights
Silica nanoparticles have been widely studied for biomedical and biotechnological applications [44], those of amorphous nature, which arise from several synthetic preparation methods
In cardiac cells exposed to nanoSiO2, enhanced viability and reduction of H2O2 were observed after application of a specific mitochondrial antioxidant, MitoTEMPO
We observed a 40% inhibition of maximal oxygen consumption rate in mitochondria at 500 μg/mL. Under this condition we identified a remarkable diminution in the spare respiratory capacity. This data indicates that a reduction in the amount of extra ATP that can be produced by mitochondria during a sudden increase in energy demand
Summary
Silica nanoparticles (nanoSiO2) have been widely studied for biomedical and biotechnological applications [44], those of amorphous nature, which arise from several synthetic preparation methods. NanoSiO2 is unintentionally present in silica powders typically used in the industry for food, cosmetic and health applications [7] Given this wide range of applications, it is clear that intended or unintended exposure to amorphous nanoSiO2 is likely to occur, which depending on the route of administration and its physicochemical properties, may translocate into the bloodstream and become available to interact with tissues and organs. Exposure to amorphous nanoSiO2 resulted in a functional loss of contraction caused by a dysregulation of intracellular Ca2+ handling, due in part to an increased oxidative stress production and reduced mitochondrial membrane potential (Δψm), resulting in impaired ATP production [24]. In order to elucidate these mechanisms, this article explores the ex vivo heart function and mitochondria after exposure to nanoSiO2.
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