The technology of C₂N Diagnostics uses in vivo stable isotope labeling to follow the production and clearance of proteins and other biomolecules in the human cerebrospinal fluid and brain.

Pulse - Chase

Pulse-chase experiments have been used in biology for decades to measure the rates of production and clearance of biomolecules. This type experiment involves the labeling of newly synthesized molecules with a radioactive or otherwise labeled building block. The rate of production is measured by the rate of incorporation of the label into the biomolecule. Rate of degradation is measured by the disappearance of the label from the biomolecule once the labeled building block is withdrawn and or excess unlabeled building block is added.

In vivo labelling

To measure production and clearance rates of biomolecules in humans - C₂N uses carbon 13 (¹³C) - a naturally occurring non-radioactive carbon isotope to label newly synthesized proteins and biomolecules. ¹³C is one Dalton heavier than regular ¹²C and this difference in weight can be resolved by tandem mass spectrometry, allowing the calculation of a ratio of labeled to unlabeled biomolecule. By measuring this ratio at different time points following infusion of a ¹³C labeled building block it is possible to measure the fractional synthetic rate of a given biomolecule. The fractional clearance rate can be calculated by stopping the ¹³C labeled building block infusion and measuring the decrease in the ratio of labeled to unlabeled biomolecule.

The first application of this technology was the labeling of the amyloid precursor protein with ¹³C leucine (Bateman et al. 2006). This allowed the calculation of the fractional synthetic and clearance rates of the amyloid beta peptide in the human cerebrospinal fluid, which is produced in the brain.

References:

Bateman RJ, Munsell LY, Chen X, Holtzman DM, Yarasheski KE (2007)
"Stable isotope labeling tandem mass spectrometry (SILT) to quantify protein production and clearance rates", J Am Soc Mass Spectrom. 18(6):997-1006

Bateman RJ, Wen G, Morris JC, Holtzman DM. (2007)
"Fluctuations of CSF amyloid-beta levels: implications for a diagnostic and therapeutic biomarker", Neurology. 68(9):666-9

Bateman RJ, Munsell LY, Morris JC, Swarm R, Yarasheski KE, Holtzman DM. (2006)
"Human amyloid-beta synthesis and clearance rates as measured in cerebrospinal fluid in vivo", Nature Med. 12(7):856-61