Probing the Outer Mitochondrial Membrane in Cardiac Mitochondria with Nanoparticles

Abstract

The outer mitochondrial membrane (OMM) is the last barrier between the mitochondrion and the cytoplasm. Breaches of OMM integrity result in the release of cytochrome c oxidase, triggering apoptosis. In this study, we used calibrated gold nanoparticles to probe the OMM in rat permeabilized ventricular cells and in isolated cardiac mitochondria under quasi-physiological ionic conditions and during permeability transition. Our experiments showed that under control conditions, the OMM is not permeable to 6-nm particles. However, 3-nm particles could enter the mitochondrial intermembrane space in mitochondria of permeabilized cells and isolated cardiac mitochondria. Known inhibitors of the voltage-dependent anion channel (VDAC), König polyanion, and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid inhibited this entrance. Thus, 3-nm particles must have entered the mitochondrial intermembrane space through the VDAC. The permeation of the isolated cardiac mitochondria OMM for 3-nm particles was approximately 20 times that in permeabilized cells, suggesting low availability of VDAC pores within the cell. Experiments with expressed green fluorescent protein showed the existence of intracellular barriers restricting the VDAC pore availability in vivo. Thus, our data showed that 1), the physical diameter of VDAC pores in cardiac mitochondria is >or=3 nm but <or=6 nm, and 2), permeability transition-related mitochondrial swelling results in breaching and disruption of the OMM.

Nanocarriers’ entry into the cell: relevance to drug delivery

“…While access to the mitochondrial intermembrane is highly restricted by the small size of the voltage-dependent anion channels (3-6 nm) [157], it has been suggested to take advantage of the mitochondrial fusion events [158,159] to deliver nanoparticles to these organelles. Nucleus targeting of nanoparticles is actively investigated for gene delivery.…”

Oxidative Stress and Nanomaterial-Cellular Interactions

“…Studies using well defi ned gold nanoparticles suggest that there is a strict permeability size limit (<6 nm) by which nanoparticles can pass though ion channels of the outer mitochondrial membrane [ 119 ]. These observations raise the question of whether the disruption of mitochondrial permeability by ENMs is primarily mediated by dissolved metal ions that are small enough to transit across mitochondrial pores.…”

Mitochondria-selective photodynamic tumor therapy using globular PEG nanoparticles

“…5,[15][16][17] It is known that mitochondria regulate vital and lethal functions of cells such as ATP synthesis, reactive oxygen species (ROS) production, programmed cell death (apoptosis), and oxidative phosphorylation. 19 Mitochondrial damage can lead to extensive cell death mechanisms, including bioenergetic dysfunctions and the cytosolic release of proapoptotic proteins. 5,[15][16][17][18][19] Therefore, pursuing the versatile design of mitochondria-targeting nano-sized drug carriers may be crucial for advanceing PDT.…”

“…19 Mitochondrial damage can lead to extensive cell death mechanisms, including bioenergetic dysfunctions and the cytosolic release of proapoptotic proteins. 5,[15][16][17][18][19] Therefore, pursuing the versatile design of mitochondria-targeting nano-sized drug carriers may be crucial for advanceing PDT. Recently, there have been several efforts to engineer mitochondria-targeting drug carrier systems.…”