Figure 3

The cellular CO/AA ratio is the most sensitive amino acid-based biomarker of LPS activation. The relative sensitivity of the CO/AA ratio to varying concentrations of LPS was compared to total media nitrate/nitrite (NOx), Gln/Glu, SAM/SAH, GSH/GSSG, AND Spd/Spm ratios. Raw cells (2 × 10⁶ cells) were either left untreated or incubated with 0.1, 1,10, 100 and 1000 ng/ml LPS at 37°C for 24 hrs. Media NOx concentrations and metabolite ratios obtained were normalized to baseline levels in untreated cells and the % changes from baseline were plotted (mean ± SD; N = 6). The CO/AA ratio was the sole indicator that was significantly changed, even at 0.1 ng/ml LPS, and further increased at higher LPS concentrations in a dose-dependent manner. At all concentrations of LPS tested, the changes in CO/AA ratio were greater than other metabolic indices of macrophage activation. * denotes p < 0.05; ** denotes p < 0.001.