Serum Osteopontin, KL-6, and Syndecan-4 as Potential Biomarkers in the Diagnosis of Coal Workers’ Pneumoconiosis: A Case–Control Study

Figures & data

Table 1 Basic Characteristics of the Study Population

Characteristics	Health Controls	DEWs	CWPs	p-value
Age, years	60.45±9.07	61.56±9.09	62.71±8.86	0.115
BMI	23.60±2.95	23.75±3.39	22.88±3.25	0.062
Smoking status (N, %)				<0.001
Non-smokers	30 (30.00)	17 (17.00)	19 (8.00)
Smokers	70 (70.00)	83 (83.00)	181 (92.00)
Smoking index	21.55±19.19	26.28±24.55	29.45±23.20*	0.012
Duration of exposure, years	NA	22.64±8.53	23.61±7.83	0.222
Pulmonary function
FVC observed (L)	3.72±0.65	3.48±0.85	2.82±0.84*^#	<0.001
FVC% predicted	95.15±13.30	91.32±19.27	79.30±20.42*^#	<0.001
FEV1 observed (L)	2.84±0.54	2.55±0.75*	1.80±0.73*^#	<0.001
FEV1% predicted	91.66±13.30	84.50±21.83*	64.84±23.70*^#	<0.001
FEV1/FVC (%)	76.20±4.17	72.51±9.15*	62.34±13.55*^#	<0.001

Notes: p value was computed by Kruskal–Wallis test among HCs, DEWs, and CWPs; p value was calculated by Mann–Whitney test between two groups. *Compared with Health controls, p < 0.05; ^#Compared with DEWs, p < 0.05. Data are presented as mean ±SD.

Abbreviations: BMI, body mass index; FEV1, forced expiratory volume in one second; FVC, forced vital capacity; DEWs, dust-exposed workers; CWPs, coal workers’ pneumoconiosis; N, number.

Figure 1 Comparison of serum concentrations of biomarkers among the HCs, DEWs and CWPs groups. (A) Osteopontin; (B) KL-6; (C) Syndecan-4; (D) Gremlin-1; (E) Osteopontin; (F) KL-6; (G) Syndecan-4; (H) Gremlin-1. *Compared with HCs, p < 0.05; ^#Compared with DEWs, p < 0.05. p value was computed by Kruskal–Wallis test among different stage of CWPs in Osteopontin, KL-6, Syndecan-4 and Gremlin-1. p >0.05. Bars represent median with interquartile 25–75, min-maximum.

Figure 2 (A) Correlations among Osteopontin, KL-6, Gremlin-1 and Syndecan-4 in all participants. (B) Correlations between Osteopontin, KL-6, Gremlin-1, and Syndecan-4 and pulmonary function parameters in all participants. The numbers represent the value of Pearson coefficient.

Table 2 Correlations Between Biomarkers and Pulmonary Function Among All Participants

Characteristics	Univariate Analysis			Multivariable Analysis
	β	95% CI	P value	β	95% CI	P value
FEV1/FVC
Osteopontin	−1.12	-(1.41–0.84)	<0.001	−0.87	-(1.21–0.54)	<0.001
KL-6	−16.79	-(21.86–11.72)	<0.001	−12.38	-(17.97–6.80)	<0.001
Syndecan-4	−1.84	-(2.48–1.20)	<0.001	−1.21	-(1.91–0.50)	0.001
Gremlin-1	−10.70	-(15.15–0.62)	<0.001	−5.54	-(10.33–0.74)	0.024
FEV1
Osteopontin	−0.08	-(0.09–0.06)	<0.001	−0.05	-(0.07–0.03)	<0.001
KL-6	−1.32	-(1.65–0.99)	<0.001	−0.90	-(1.25–0.55)	<0.001
Syndecan-4	−0.15	-(0.19–0.11)	<0.001	−0.09	-(0.13–0.04)	<0.001
Gremlin-1	−0.87	-(1.16–0.57)	<0.001	−0.44	-(0.74–0.13)	0.005
FVC
Osteopontin	−0.06	-(0.08–0.04)	<0.001	−0.03	-(0.06–0.01)	0.002
KL-6	−1.18	-(1.55–0.82)	<0.001	−0.77	-(1.15–0.39)	<0.001
Syndecan-4	−0.14	-(0.18–0.09)	<0.001	−0.08	-(0.12–0.03)	0.001
Gremlin-1	−0.80	-(1.12–0.48)	<0.001	−0.41	-(0.73–0.08)	0.014

Notes: Univariate analysis: single factor logistic regression; Multivariable analysis: adjusted for age, BMI, duration of exposure and smoking index.

Table 3 The Association Between Serum Biomarkers and CWP by Univariate and Multivariate Analysis

Characteristics	Model 1		Model 2		Model 3
	OR (95% CI)	P value	OR (95% CI)	P value	OR (95% CI)	P value
CWP vs HC
Osteopontin	3.09 (2.28–4.19)	<0.001	3.15 (2.29–4.32)	<0.001	3.88 (2.34–6.42)	<0.001
KL-6	1.01 (1.00–1.01)	<0.001	1.01 (1.00–1.01)	<0.001	1.01 (1.01–1.02)	<0.001
Syndecan-4	3.51 (2.66–4.64)	<0.001	3.66 (2.73–4.91)	<0.001	4.26 (2.78–6.52)	<0.001
Gremlin-1	1.01 (1.00–1.01)	<0.001	1.01 (1.00–1.01)	<0.001	1.01 (1.00–1.01)	<0.001
CWP vs DEW
Osteopontin	1.55 (1.37–1.75)	<0.001	1.55 (1.37–1.75)	<0.001	1.53 (1.34–1.75)	<0.001
KL-6	1.01 (1.00–1.01)	<0.001	1.01 (1.00–1.01)	<0.001	1.01 (1.00–1.01)	<0.001
Syndecan-4	1.43 (1.21–1.67)	<0.001	1.42 (1.20–1.67)	<0.001	1.40 (1.16–1.69)	<0.001
Gremlin-1	1.00 (1.00–1.01)	0.078	1.00 (1.00–1.01)	0.101	1.00 (1.00–1.01)	0.134

Notes: Model 1 was univariate analysis; Model 2 adjusted for age, BMI and smoking index; Model 3 adjusted for age, BMI and smoking index and pulmonary function.

Table 4 Cut-Off Values and the Identifying Ability of Osteopontin, KL-6, Syndecan-4, and Gremlin-1 by ROC Curve Analysis

Variables	Identifying HCs				Identifying DEWs
	Osteopontin	KL-6	Syndecan-4	Gremlin-1	Osteopontin	KL-6	Syndecan-4	Gremlin-1
AUC	0.970	0.924	0.917	0.868	0.788	0.823	0.643	0.547
95% CI	0.954–0.985	0.895–0.954	0.886–0.947	0.828–0.909	0.734–0.842	0.777–0.869	0.577–0.709	0.479–0.615
Cut-off	10.58 ng/mL	674.83 U/mL	5.76 ng/mL	777.3 ng/mL	12.16 ng/mL	745.63 U/mL	6.06 ng/mL	–
Sensitivity, %	85.5	82.0	77.5	89.5	70.0	64.5	72.5	–
Specificity, %	93.0	94.0	93.0	67.0	79.0	88.0	48.0	–

Abbreviations: HCs, health controls; DEWs, dust-exposed workers; AUC, area under the curve; 95% CI, 95% confidence interval.

Figure 3 (A) ROC curve analysis to differentiate patients with CWP from HCs. (B) ROC curve analysis to differentiate patients with CWP from DEWs. (C) Combined ROC curve analysis to differentiate patients with CWP from HCs. (D) Combined ROC curve analysis to differentiate patients with CWP from DEWs. a+b: combined Osteopontin and KL-6; a+c: combined Osteopontin and Syndecan-4; b+c: combined KL-6 and Syndecan-4; a+b+c: combined Osteopontin, KL-6 and Syndecan-4. a: Osteopontin; b: KL-6; c: Syndecan-4.

Table 5 Cut-Off Values and the Identifying Ability of Combined Osteopontin, KL-6, and Syndecan-4 by ROC Curve Analysis

Variables	Identifying HCs				Identifying DEWs
	Model 1	Model 2	Model 3	Model 4	Model 1	Model 2	Model 3	Model 4
AUC	0.991	0.993	0.935	0.994	0.867	0.802	0.812	0.867
95% CI	0.984–0.998	0.987–0.999	0.907–0.964	0.988–0.999	0.826–0.908	0.748–0.855	0.765–0.859	0.827–0.908
Sensitivity, %	94.0	96.5	89.5	96.5	76.0	86.5	58.0	73.0
Specificity, %	99.0	97.0	95.0	98.0	85.0	61	93.0	89.0

Notes: Model 1: Osteopontin + KL-6; Model 2: Osteopontin + Syndecan-4; Model 3: KL-6 + Syndecan-4; Model 4: Osteopontin + KL-6 + Syndecan-4.

Abbreviations: HCs, health controls; DEWs, dust-exposed workers; AUC, area under the curve; 95% CI, 95% confidence interval.