Identification and validation of serum amino acids as diagnostic biomarkers for diabetic peripheral neuropathy

Table 2 Serum levels of twenty amino acids among diabetic peripheral neuropathy patients, type 2 diabetes mellitus patients and normal individuals in the two cohorts

Variable	Training cohort			Validation cohort
	DPN	T2DM	Normal	DPN	T2DM	Normal
Number	84	82	50	112	93	58
Glycine (μmol/L)	214.10 ± 50.54	216.41 ± 54.63	211.89 ± 58.25	221.68 ± 52.99	222.36 ± 54.04	219.34 ± 48.68
Serine (μmol/L)	121.10 ± 23.46	122.02 ± 24.47	121.12 ± 25.73	119.64 ± 25.01	120.37 ± 23.59	119.69 ± 28.05
Asparagine (μmol/L)	46.16 ± 12.30	47.80 ± 13.41	46.83 ± 10.54	45.61 ± 11.60	46.49 ± 14.25	44.85 ± 9.45
Arginine (μmol/L)	29.28 ± 12.61a,b	40.87 ± 15.21c	52.37 ± 11.73	27.44 ± 12.61a,b	39.11 ± 12.64c	55.55 ± 15.48
Alanine (μmol/L)	423.49 ± 121.55	429.40 ± 132.01	460.38 ± 137.59	442.13 ± 107.48	431.17 ± 137.76	451.38 ± 135.83
Homoproline (μmol/L)	28.37 ± 10.15b	29.84 ± 12.01c	21.73 ± 7.11	28.30 ± 10.28b	29.14 ± 9.97c	20.07 ± 6.90
Proline (μmol/L)	221.19 ± 79.16	223.31 ± 77.11	215.75 ± 82.67	235.44 ± 83.14	236.59 ± 96.97	238.85 ± 86.01
Valine (μmol/L)	276.17 ± 83.42b	291.84 ± 89.69c	239.45 ± 40.91	282.59 ± 88.93b	280.52 ± 94.10c	240.93 ± 60.67
Methionine (μmol/L)	25.91 ± 9.51	25.69 ± 8.81	25.32 ± 6.73	25.11 ± 8.83	27.13 ± 9.11	25.96 ± 7.74
Tyrosine (μmol/L)	65.77 ± 21.19a,b	78.88 ± 20.77	77.39 ± 23.50	64.41 ± 20.13a,b	74.66 ± 22.64	75.66 ± 16.40
Phenylalanine (μmol/L)	71.55 ± 16.70	72.38 ± 14.26	72.35 ± 15.88	71.81 ± 14.25	72.94 ± 16.05	70.58 ± 14.97
Isoleucine (μmol/L)	84.24 ± 27.50b	86.90 ± 22.27c	72.19 ± 24.26	83.39 ± 26.38b	84.29 ± 24.99c	70.21 ± 21.54
Leucine (μmol/L)	158.37 ± 31.22b	164.74 ± 28.92c	139.76 ± 26.81	153.83 ± 33.57b	160.42 ± 30.52c	132.30 ± 33.26
Hydroxyproline (μmol/L)	15.85 ± 5.75	15.39 ± 5.81	13.56 ± 5.57	15.35 ± 6.06	15.05 ± 6.48	16.74 ± 7.30
Threonine (μmol/L)	129.93 ± 30.88	129.25 ± 27.54	126.58 ± 31.02	122.08 ± 29.83	124.13 ± 28.55	126.92 ± 29.13
Tryptophane (μmol/L)	70.48 ± 29.87	66.63 ± 28.17	66.52 ± 25.53	67.34 ± 26.72	72.24 ± 26.78	67.85 ± 26.64
Glutamic acid (μmol/L)	186.17 ± 49.22a,b	170.51 ± 37.05	156.29 ± 31.89	185.28 ± 48.05a,b	169.88 ± 44.30	163.73 ± 35.35
Aspartic acid (μmol/L)	12.23 ± 4.53	11.82 ± 4.35	11.34 ± 3.35	11.45 ± 3.93	11.90 ± 4.36c	10.11 ± 3.02
Histidine (μmol/L)	89.34 ± 14.46	92.49 ± 15.19c	85.45 ± 12.98	89.37 ± 14.93	89.04 ± 17.64	85.43 ± 14.38
Lysine (μmol/L)	209.86 ± 54.74b	203.83 ± 60.96	181.47 ± 39.72	191.68 ± 49.90	195.68 ± 55.03c	174.38 ± 40.86

^aP < 0.05, comparison of diabetic peripheral neuropathy (DPN) patients with type 2 diabetes mellitus (T2DM) patients was significantly different.

^bP < 0.05, comparison of DPN patients with normal controls was significantly different.

^cP < 0.05, comparison of T2DM patients with normal controls was significantly different.

T2DM: Type 2 diabetes mellitus; DPN: Diabetic peripheral neuropathy.