Inter-alpha-trypsin inhibitor heavy chain 4: a novel biomarker for environmental exposure to particulate air pollution in patients with chronic obstructive pulmonary disease

Abstract

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory disease that is correlated with environmental stress. Particulate matter ≤10 μm (PM10) is considered to be a risk factor for COPD development; however, the effects of PM10 on the protein levels in COPD remain unclear. Fifty subjects with COPD and 15 healthy controls were recruited. Gene ontology analysis of differentially expressed proteins identified immune system process and binding as the most important biological process and molecular function, respectively, in the responses of PM10-exposed patients with COPD. Biomarkers for PM10 in COPD were identified and compared with the same in healthy controls and included proteoglycan 4 (PRG4), inter-alpha-trypsin inhibitor heavy chain 4 (ITIH4), and apolipoprotein F (APOF). PRG4 and ITIH4 were associated with a past 3-year PM10 exposure level. The receiver operating characteristic curve analysis showed that ITIH4 is a sensitive and specific biomarker for PM10 exposure (area under the curve [AUC] =0.690, P=0.015) compared with PRG4 (AUC =0.636, P=0.083), APOF (AUC =0.523, P=0.766), 8-isoprostane (AUC =0.563, P=0.405), and C-reactive protein (CRP; AUC =0.634, P=0.086). ITIH4 levels were correlated with CRP (r=0.353, P=0.005), suggesting that ITIH4 may be involved in an inflammatory mechanism. In summary, serum ITIH4 may be a PM10-specific biomarker in COPD and may be related to inflammation.

Keywords: C-reactive protein; air pollution; apolipoprotein F; inflammation; oxidative stress; proteoglycan 4.

Figure 1

Protein expression and biological process and molecular functions determined by PANTHER. Notes: (A) Venn diagram of proteins that are common among or unique to patients with COPD exposed to low ambient particles (LAP; range: 35.4–43.9 μg/m³) and high ambient particles (HAP; range: 63.2–64.5 μg/m³) compared with healthy controls exposed to either LAP or HAP. Six proteins were commonly expressed in the serum samples: proteoglycan 4 (PRG4), inter-alpha-trypsin inhibitor heavy chain 4 (ITIH4), apolipoprotein F (APOF), Ig kappa chain V-I region DEE, type I cytoskeletal 16 keratin, and type II cytoskeletal 6A keratin. (B) The biological processes and molecular functions of the unique proteins identified in the LAP and HAP groups. Immune system process and binding are the important biological process and molecular function, respectively, in response to PM₁₀ in COPD. Abbreviation: COPD, chronic obstructive pulmonary disease.

Figure 2

Serum PRG4, ITIH4, and APOF levels in healthy controls, smokers, and subjects with COPD. Notes: The PRG4 levels in subjects with COPD were significantly higher than in healthy controls and smokers, whereas the ITIH4 level in COPD was lower than in healthy controls (*P<0.05). Abbreviations: APOF, apolipoprotein F; COPD, chronic obstructive pulmonary disease; ITIH4, inter-alpha-trypsin inhibitor heavy chain 4; PRG4, proteoglycan 4.

Figure 3

The relationship of serum PRG4, ITIH4, and APOF levels to 1-year, 2-year, and 3-year changes in PM₁₀ levels. Notes: Study subjects were divided equally based on quintiles of PM₁₀. The values in parentheses along the X-axis represent the mean PM₁₀ values for each quintile group. Spearman’s rank correlation coefficient was used to examine the correlation of quintiles of PM₁₀ with PRG4, ITIH4, and APOF. PRG4 levels were correlated with the 2-year (r=0.278, P=0.033) and 3-year PM₁₀ averages (r=0.349, P=0.007), whereas the ITIH4 levels were correlated with the 1-year (r=−0.325, P=0.012), 2-year (r=−0.401, P=0.002), and 3-year (r=−0.342, P=0.008) PM₁₀ averages. Abbreviations: APOF, apolipoprotein F; ITIH4, inter-alpha-trypsin inhibitor heavy chain 4; PM₁₀, particulate matter ≤10 μm; PRG4, proteoglycan 4.

Figure 4

Diagnostic performance of serum 8-isoprostane, CRP, PRG4, ITIH4, and APOF in receiver operating characteristic (ROC) curve analyses. Notes: ROC curve of the sensitivity and specificity of PRG4, ITIH4, and APOF levels for discriminating between the ≥50 μg/m³ and <50 μg/m³ average 3-year PM₁₀ value in COPD. The area under the curve value was 0.563 (95% CI: 0.413–0.713, P=0.405) for 8-isoprostane, 0.634 (95% CI: 0.486–0.782, P=0.086) for CRP, 0.636 (95% CI: 0.492–0.780, P=0.083) for PRG4, 0.690 (95% CI: 0.545–0.836, P=0.015) for ITIH4, and 0.523 (95% CI: 0.376–0.671, P=0.766) for APOF. Abbreviations: APOF, apolipoprotein F; CI, confidence interval; COPD, chronic obstructive pulmonary disease; CRP, C-reactive protein; ITIH4, inter-alpha-trypsin inhibitor heavy chain 4; PM₁₀, particulate matter ≤10 μm; PRG4, proteoglycan 4.

Figure 5

Correlation of 8-isoprostane and CRP to PRG4, ITIH4, and APOF in subjects with COPD. Notes: The Spearman’s rank correlation coefficient for CRP and ITIH4 was r=0.353 (P=0.005). Abbreviations: APOF, apolipoprotein F; COPD, chronic obstructive pulmonary disease; CRP, C-reactive protein; ITIH4, inter-alpha-trypsin inhibitor heavy chain 4; PM₁₀, particulate matter ≤10 μm; PRG4, proteoglycan 4.