Gradient centrifugation of infected Red Blood Cells

Percoll is a reagent consisting of

colloidal A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others exten ...

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

particles used in

cell biology Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living an ...

and other laboratory settings. It was first formulated by Pertoft and colleagues, and commercialized by Pharmacia Fine Chemicals. Percoll is used for the isolation of cells,

organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...

s, or

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

es by density centrifugation. Percoll was developed from previously reported uses of colloidal silica nanoparticles coated with polysaccharides or polymers for rate zonal, isopycnic, or equilibrium centrifugal separations. Percoll itself specifically consists of polydisperse silica nanoparticles 15–30 nm diameter (23% w/w in water) which have been coated with

polyvinylpyrrolidone Polyvinylpyrrolidone (PVP), also commonly called povidone, is a water-soluble polymer compound made from the monomer ''N''-vinylpyrrolidone. PVP is available in a range of molecular weights and related viscosities, and can be selected according ...

(PVP). Percoll is well suited for density gradient experiments because it possesses a low

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

compared to alternatives, a low

osmolarity Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/ ...

, and no toxicity towards cells and their constituents. Percoll is a registered trademark of Cytiva.

Characteristics

Percoll does not notably diffuse over time, resulting in the formation of very stable gradients. Therefore, both discontinuous and continuous Percoll density gradients can be prepared weeks in advance, allowing great reproducibility & ease of use.

Past use in artificial reproduction

Percoll was previously used in

assisted reproductive technology Assisted reproductive technology (ART) includes medical procedures used primarily to address infertility. This subject involves procedures such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), and cryopreservation of ga ...

(ART) to select

sperm Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm ...

from

semen Semen, also known as seminal fluid, is a bodily fluid that contains spermatozoon, spermatozoa which is secreted by the male gonads (sexual glands) and other sexual organs of male or hermaphrodite, hermaphroditic animals. In humans and placen ...

by density gradient centrifugation, for use in techniques such as ''in vitro'' fertilization or intrauterine insemination. However, in 1996,

Pharmacia Pharmacia was a pharmaceutical and biotechnological company in Sweden that merged with the American pharmaceutical company Upjohn in 1995. History Pharmacia company was founded in 1911 in Stockholm, Sweden by pharmacist Gustav Felix Grönfel ...

sent out a letter to laboratories stating that Percoll should be used for research purposes only, not clinical. Pharmacia had not marketed it as a sperm preparation product; it had been repackaged and sold as such by third-party manufacturers. The

FDA Warning Letter An FDA warning letter is an official message from the United States Food and Drug Administration (FDA) to a manufacturer or other organization that has violated some rule in a federally regulated activity. The FDA defines an FDA warning letter as: ...

was due to concerns that PVP might cause damage to sperm (an unknown issue), and also that some batches of Percoll contained high levels of

endotoxin Lipopolysaccharide (LPS), now more commonly known as endotoxin, is a collective term for components of the outermost membrane of the cell envelope of gram-negative bacteria, such as '' E. coli'' and ''Salmonella'' with a common structural archit ...

(a known issue). The latter concern also applies to the use of Percoll with any other cells that might be injected back into a patient, since endotoxin can cause severe inflammation and fever. Since then it has been replaced with other colloids in the ART industry.

References

{{reflist Biochemistry