Figure 2.

The duration of ¹³C₆-labeling does not affect Aβ production estimates, and plasma better reflects the ¹³C₆-leucine precursor for Aβ compared with CSF. A, B, Rhesus monkeys (n = 3) were infused with ¹³C₆-leucine (8 mg/kg/h) for either 21 h (black, solid circle) or 12 h (red, solid triangle). The ratio of ¹³C-Aβ to ¹²C-Aβ from CSF was measured by LC-MS, and normalized to the ¹³C₆-leucine precursor enrichment measured in either CSF (A) or plasma (B). Values >1 indicate incorrect estimates. Error bars represent SEM.