Figure 4.

Analysis of ¹³C and D isotopologues of Ser and Gly reveals reduced Ser/Gly uptake but enhanced Ser–Gly one-carbon exchanges in human CA versus matched NC lung tissues ex vivo. UK022 patient sample treatment, processing, extraction, and ECF derivatization were as described under “Experimental procedures.” The respective level (a and b) and fractional enrichment (c and d) in ¹³C and d isotopologues of Ser or Gly in tissues and uptake or release of these Ser or Gly species in the medium (e and f) were obtained from UHR-FTMS analysis, as described under “Experimental procedures.” D₁, D₂-Ser in a, c, and e and D₁-Gly in b, d, and f represented D-scrambled Ser and Gly, respectively. no D, [¹³C₆]Glc only; DSer, D₃-Ser + [¹³C₆]Glc; DGly, D₂-Gly + [¹³C₆]Glc. Using the two-tailed unpaired t test, the absolute levels of D₁-, D₂-, and D₃-serine differed between CA versus NC tissues (n = 3 each) (a) 2-fold for D₁ (p = 0.01, t = 4.472), 3-fold for D₂ (p = 0.002, t = 70.7), and 0.27 for D₃ (p = 0.0032, t = 6.31). The fractional enrichment differed for CA versus NC tissues with (c) 7-fold for D₁ (p = 0.0042, t = 5.884), 3.5-fold for D₂ (p = 0.001, t = 8.575), and 0.27-fold for D₃ (p = 0.0001, t = 19.677). For D₁- and D₂-glycine, the fractional enrichments differed between CA versus NC tissues (d) 0.3-fold for D₁ (p = 0.0001, t = 24.748) and 0.07-fold for D₂ (p = 0.0029, t = 6.492). The absolute levels in b were too low for reliable statistical testing. Because of large standard errors, the difference (4.4-fold) in the uptake of D₃-serine from the medium did not reach statistical significance between CA versus NC tissues (e), but the differential uptakes (4.2–5.2-fold) of unlabeled (¹²C) Ser between the two tissue types were statistically significant (*, p = 0.018, t = 4.695). The uptake of D₂-Gly decreased 23-fold in CA versus NC tissues (f) (*, p = 0.02, t = 6.856).