© 2003 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003

15.6.3.3 Intracellular Microspheres and Crystals

Various particulate substances have been introduced intracellularly to observe the effects on the cell. In one study [4556], up to 500 polystyrene 0.26-micron beads were injected into a tissue cell and this 4.6-micron³ load did not affect the cell’s ability to transport the particles around inside as if they were tiny organelles or vesicles. A few micron³/cell of engineered nanoparticles are tolerated by living cells when employed as intracellular fluorescent labels [4238]. Cholesterol crystals have been induced to grow inside living J774 mouse peritoneal macrophages, reaching a concentration of ~120 µg cholesterol/mg protein or ~2.4% intracellular crystals by volume [4557] without lethality. However, excessive intracellular crystallization (e.g., of drug molecules) can lead to problems such as acute renal failure [4558], and intracellular crystals have been found inside chondrocytes in certain crystal deposition diseases [4559]. Cholesterol crystals in macrophage foam cells may also contribute to atherosclerosis [5481]. A useful and simple experiment that could be done today would be to microinject cells with progressively larger loads of chemically inert diamond particles or polystyrene spheres, noting the effect on cell motility, behavior, and metabolic function. Other intracellular crystal deposition diseases are known such as mitochondrial crystalline inclusions [6147-6149] and intermembrane inclusion bodies [6150], polyglucosan bodies [6151], and Fardeau-Engel bodies [6152] involved in peripheral neuropathies.

Interestingly, Pseudomonas stutzeri AG259, a species of bacterium isolated from silver mines, protects itself from the usual bactericidal effect of silver ions by sequestering triangular and hexagonal insoluble nanocrystals of Ag₀ and Ag₂S (believed to be acanthite, a stable crystalline form of silver sulfide) intracellularly in vacuole-like granules in the periplasmic space [4560]. In one photomicrograph, several crystals ranging from 90-200 nm in diameter are visible inside a living bacterial cell ~800 nm in diameter, suggesting a total inert particulate ~13% volumetric intrusiveness.

Last updated on 30 April 2004