Table 4– Changes in amino acid concentration in Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage IV patients versus control subjects, measured by liquid chromatography with tandem mass spectrometry

	Control subjects	GOLD IV patients
Decreasing amino acid in concentration nM
ABA	655.8±178.2	543.7±191.9
4-HYP	12258.7±11552.1	8600.4±7001.7
AAA^#	50.1±19.2	40.9±17.3
Pro^#	3478.3±490.1	3049.1±965.1
Ile	1963.7±408.1	1814.1±585.2
Leu	3730.0±725.5	3361.6±1110.7
Val	4642.1±1292.4	4190.2±1319.8
Increasing amino acid concentrations nM
AIB^#	56.1±22.5	80.3±42.9
1-MH^#	242.4±54.6	282.5±126.8
3-MH^#	166.5±182.9	461.7±675.5
Asp^#	239.3±82.5	296.1±176.3
Glu	8805.3±1158.8	9198.0±2716.4
GABA	9.2±3.2	10.0±3.4

Data are presented as mean±sd. ABA: α-aminobutyrate; 4-HYP: 4-hydroxyproline; AAA: aminoadipate; Pro: proline; Ile: isoleucine, Leu: leucine; Val: valine, AIB: aminoisobutyrate; 1-MH: 1-methyhistidine; 3-MH: 3-methylhistidine; Asp: aspartate; Glu: glutamine; GABA: γ-aminobutyrate. Principal component (PC)1 and PC2 R²=37.5% and Q²=26.2%; PC3–PC5 R²=63.9%, Q²=36.3. ^#: amino acids with p-values <0.1 (adjusted for using Benjamini–Hochberg test, false discovery rate α=0.1).