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A general mechanism for intracellular toxicity of metal-containing nanoparticles.

Sabella S, Carney RP, Brunetti V, Malvindi MA, Al-Juffali N, Vecchio G, Janes SM, Bakr OM, Cingolani R, Stellacci F, Pompa PP - Nanoscale (2014)

Bottom Line: We show that particles known to pass directly through cell membranes become more toxic when modified so as to be mostly internalized by endocytosis.Furthermore, using experiments with chelating and lysosomotropic agents, we found that the toxicity mechanism for different metal containing NPs (such as metallic, metal oxide, and semiconductor NPs) is mainly associated with the release of the corresponding toxic ions.Finally, we show that particles unable to release toxic ions (such as stably coated NPs, or diamond and silica NPs) are not harmful to intracellular environments.

View Article: PubMed Central - PubMed

Affiliation: Istituto Italiano di Tecnologia, Center for Bio-Molecular Nanotechnologies@UniLe, Via Barsanti, 73010 Arnesano (Lecce), Italy. pierpaolo.pompa@iit.it.

ABSTRACT
The assessment of the risks exerted by nanoparticles is a key challenge for academic, industrial, and regulatory communities worldwide. Experimental evidence points towards significant toxicity for a range of nanoparticles both in vitro and in vivo. Worldwide efforts aim at uncovering the underlying mechanisms for this toxicity. Here, we show that the intracellular ion release elicited by the acidic conditions of the lysosomal cellular compartment--where particles are abundantly internalized--is responsible for the cascading events associated with nanoparticles-induced intracellular toxicity. We call this mechanism a "lysosome-enhanced Trojan horse effect" since, in the case of nanoparticles, the protective cellular machinery designed to degrade foreign objects is actually responsible for their toxicity. To test our hypothesis, we compare the toxicity of similar gold particles whose main difference is in the internalization pathways. We show that particles known to pass directly through cell membranes become more toxic when modified so as to be mostly internalized by endocytosis. Furthermore, using experiments with chelating and lysosomotropic agents, we found that the toxicity mechanism for different metal containing NPs (such as metallic, metal oxide, and semiconductor NPs) is mainly associated with the release of the corresponding toxic ions. Finally, we show that particles unable to release toxic ions (such as stably coated NPs, or diamond and silica NPs) are not harmful to intracellular environments.

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Schematic of the general toxicity mechanism induced by NPs when they enter cells by active internalization mechanisms, compared to endocytosis-free NPs. NPs that enter the cells by energy-dependent processes (mediated by clathrin, caveolin, lipid raft formations and others)59 are rapidly confined in vesicular structures, endosomes, and finally in lysosomes. The acidic lysosomal pH triggers a lysosome-enhanced Trojan horse effect (LETH effect) that combines the abundant cellular internalization of the NPs via active processes with the consequent enhanced release of the relatively toxic ions (e.g., Ag+, Cd2+, Fe2+/3+, Au1+/3+ ions). The significant amount of intracellularly leaked ions may then exert ion-specific toxicity (e.g., enzyme depletion/inactivation, protein denaturation, etc.) against some cellular targets (e.g., mitochondria, RER) and/or lysosomal damage/dysfunction. This finally results in increased ROS levels, apoptosis, DNA and membrane damage.
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fig7: Schematic of the general toxicity mechanism induced by NPs when they enter cells by active internalization mechanisms, compared to endocytosis-free NPs. NPs that enter the cells by energy-dependent processes (mediated by clathrin, caveolin, lipid raft formations and others)59 are rapidly confined in vesicular structures, endosomes, and finally in lysosomes. The acidic lysosomal pH triggers a lysosome-enhanced Trojan horse effect (LETH effect) that combines the abundant cellular internalization of the NPs via active processes with the consequent enhanced release of the relatively toxic ions (e.g., Ag+, Cd2+, Fe2+/3+, Au1+/3+ ions). The significant amount of intracellularly leaked ions may then exert ion-specific toxicity (e.g., enzyme depletion/inactivation, protein denaturation, etc.) against some cellular targets (e.g., mitochondria, RER) and/or lysosomal damage/dysfunction. This finally results in increased ROS levels, apoptosis, DNA and membrane damage.

Mentions: We have, therefore, identified a key toxicity mechanism that we define as a “Lysosome-Enhanced Trojan Horse effect (LETH effect)” (Fig. 7). Such a mechanism may be valid for all those NPs that are actively and efficiently taken up by cells (i.e., almost all NPs < 100 nm), whose acidic corrosion results in the generation of toxic ions. The LETH effect thus combines the abundant cellular internalization of the NPs via active processes with the consequent enhanced release of the relatively toxic ions (e.g., Ag+, Cd2+, Fe2+/3+, Au1+/3+ ions) in the cytoplasm elicited by the acidic lysosomal environment. The induced cellular toxicity can be therefore mainly ascribed to that of the corresponding ions (as also recently suggested in Cd-based QDs and ZnO NPs26,48,49), with resulting oxidative stress and apoptosis. More generally, the significant amount of intracellularly leaked ions may exert ion-specific toxicity (e.g., enzyme inactivation as demonstrated for gold ions) against cellular targets (e.g., mitochondria, RER, etc.) and/or lysosomal damage/dysfunction, in line with recent findings with other types of NPs.20,22,23


A general mechanism for intracellular toxicity of metal-containing nanoparticles.

Sabella S, Carney RP, Brunetti V, Malvindi MA, Al-Juffali N, Vecchio G, Janes SM, Bakr OM, Cingolani R, Stellacci F, Pompa PP - Nanoscale (2014)

Schematic of the general toxicity mechanism induced by NPs when they enter cells by active internalization mechanisms, compared to endocytosis-free NPs. NPs that enter the cells by energy-dependent processes (mediated by clathrin, caveolin, lipid raft formations and others)59 are rapidly confined in vesicular structures, endosomes, and finally in lysosomes. The acidic lysosomal pH triggers a lysosome-enhanced Trojan horse effect (LETH effect) that combines the abundant cellular internalization of the NPs via active processes with the consequent enhanced release of the relatively toxic ions (e.g., Ag+, Cd2+, Fe2+/3+, Au1+/3+ ions). The significant amount of intracellularly leaked ions may then exert ion-specific toxicity (e.g., enzyme depletion/inactivation, protein denaturation, etc.) against some cellular targets (e.g., mitochondria, RER) and/or lysosomal damage/dysfunction. This finally results in increased ROS levels, apoptosis, DNA and membrane damage.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4120234&req=5

fig7: Schematic of the general toxicity mechanism induced by NPs when they enter cells by active internalization mechanisms, compared to endocytosis-free NPs. NPs that enter the cells by energy-dependent processes (mediated by clathrin, caveolin, lipid raft formations and others)59 are rapidly confined in vesicular structures, endosomes, and finally in lysosomes. The acidic lysosomal pH triggers a lysosome-enhanced Trojan horse effect (LETH effect) that combines the abundant cellular internalization of the NPs via active processes with the consequent enhanced release of the relatively toxic ions (e.g., Ag+, Cd2+, Fe2+/3+, Au1+/3+ ions). The significant amount of intracellularly leaked ions may then exert ion-specific toxicity (e.g., enzyme depletion/inactivation, protein denaturation, etc.) against some cellular targets (e.g., mitochondria, RER) and/or lysosomal damage/dysfunction. This finally results in increased ROS levels, apoptosis, DNA and membrane damage.
Mentions: We have, therefore, identified a key toxicity mechanism that we define as a “Lysosome-Enhanced Trojan Horse effect (LETH effect)” (Fig. 7). Such a mechanism may be valid for all those NPs that are actively and efficiently taken up by cells (i.e., almost all NPs < 100 nm), whose acidic corrosion results in the generation of toxic ions. The LETH effect thus combines the abundant cellular internalization of the NPs via active processes with the consequent enhanced release of the relatively toxic ions (e.g., Ag+, Cd2+, Fe2+/3+, Au1+/3+ ions) in the cytoplasm elicited by the acidic lysosomal environment. The induced cellular toxicity can be therefore mainly ascribed to that of the corresponding ions (as also recently suggested in Cd-based QDs and ZnO NPs26,48,49), with resulting oxidative stress and apoptosis. More generally, the significant amount of intracellularly leaked ions may exert ion-specific toxicity (e.g., enzyme inactivation as demonstrated for gold ions) against cellular targets (e.g., mitochondria, RER, etc.) and/or lysosomal damage/dysfunction, in line with recent findings with other types of NPs.20,22,23

Bottom Line: We show that particles known to pass directly through cell membranes become more toxic when modified so as to be mostly internalized by endocytosis.Furthermore, using experiments with chelating and lysosomotropic agents, we found that the toxicity mechanism for different metal containing NPs (such as metallic, metal oxide, and semiconductor NPs) is mainly associated with the release of the corresponding toxic ions.Finally, we show that particles unable to release toxic ions (such as stably coated NPs, or diamond and silica NPs) are not harmful to intracellular environments.

View Article: PubMed Central - PubMed

Affiliation: Istituto Italiano di Tecnologia, Center for Bio-Molecular Nanotechnologies@UniLe, Via Barsanti, 73010 Arnesano (Lecce), Italy. pierpaolo.pompa@iit.it.

ABSTRACT
The assessment of the risks exerted by nanoparticles is a key challenge for academic, industrial, and regulatory communities worldwide. Experimental evidence points towards significant toxicity for a range of nanoparticles both in vitro and in vivo. Worldwide efforts aim at uncovering the underlying mechanisms for this toxicity. Here, we show that the intracellular ion release elicited by the acidic conditions of the lysosomal cellular compartment--where particles are abundantly internalized--is responsible for the cascading events associated with nanoparticles-induced intracellular toxicity. We call this mechanism a "lysosome-enhanced Trojan horse effect" since, in the case of nanoparticles, the protective cellular machinery designed to degrade foreign objects is actually responsible for their toxicity. To test our hypothesis, we compare the toxicity of similar gold particles whose main difference is in the internalization pathways. We show that particles known to pass directly through cell membranes become more toxic when modified so as to be mostly internalized by endocytosis. Furthermore, using experiments with chelating and lysosomotropic agents, we found that the toxicity mechanism for different metal containing NPs (such as metallic, metal oxide, and semiconductor NPs) is mainly associated with the release of the corresponding toxic ions. Finally, we show that particles unable to release toxic ions (such as stably coated NPs, or diamond and silica NPs) are not harmful to intracellular environments.

Show MeSH
Related in: MedlinePlus