Peripheral blood proteins predict mortality in idiopathic pulmonary fibrosis

Abstract

Rationale: Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease of unknown etiology with a variable and unpredictable course.

Objectives: The aim of this study was to identify and validate plasma proteins that are predictive of outcome in IPF.

Methods: Plasma samples were available for 241 patients with IPF (140 derivation and 101 validation). In the derivation cohort, concentrations of 92 proteins were analyzed using a multiplex bead-based immunoassay and concentrations of matrix metalloproteinase (MMP)-7, MMP-1, and surfactant protein D were assessed by ELISA. In the validation cohort concentrations of intercellular adhesion molecule (ICAM)-1, IL-8, and vascular cell adhesion molecule (VCAM)-1 were assessed by bead-based multiplex assay, and S100A12 and MMP-7 by ELISA. Associations of biomarkers with mortality, transplant-free survival, and disease progression were tested in the derivation and validation cohorts using nonparametric methods of survival analysis and the Cox proportional hazards model, and an integrated risk prediction score was derived and tested.

Measurements and main results: High concentrations of MMP-7, ICAM-1, IL-8, VCAM-1, and S100A12 predicted poor overall survival, poor transplant-free survival, and poor progression-free survival in the derivation cohort. In the independent validation cohort high concentrations of all five were predictive of poor transplant-free survival; MMP-7, ICAM-1, and IL-8 of overall survival; and ICAM-1 of poor progression-free survival. The personal clinical and molecular mortality prediction index derived in the derivation cohort was highly predictive of mortality in the validation cohort.

Conclusions: Our results suggest that plasma proteins should be evaluated as a tool for prognosis determination in prioritization of patients for lung transplantation and stratification in drug studies.

Figure 1.

Patient outcomes of the derivation and validations cohorts. Red indicates the Kaplan-Meier plot of mortality. The only admissible event is death without lung transplantation. Any patient undergoing lung transplantation is censored. The dotted black line at 0.5 on the y axis intersects the survival curve at the median mortality. Blue indicates the Kaplan-Meier plot of transplant-free survival, which is similar to mortality, except that lung transplantation is treated as an event, rather than being censored. Green indicates the Kaplan-Meier plot of progression-free survival. Disease progression event is defined as a relative decline of at least 10% in FVC % predicted within any 1-year interval during follow-up. Death with no recorded disease progression is also counted as an event. A patient receiving a lung transplant during follow-up is censored at transplant date. Patients with no follow-up record of pulmonary function tests are excluded from this analysis. Black indicates the Kaplan-Meier plot of progression-free transplant-free survival: progression-free survival where lung transplant is treated as an event. (A) The derivation cohort with median time-to-event (Greenwood 95% confidence interval). (B) The validation cohort with median time-to-event (Greenwood 95% confidence interval).

Figure 2.

Peripheral blood biomarkers strongly predict idiopathic pulmonary fibrosis outcomes in the derivation cohort. For each biomarker, red indicates the Kaplan-Meier plot of overall survival (OS) by peripheral blood concentration dichotomized at an optimal threshold as described in the text and related to OS by the log-rank test. Blue indicates the Kaplan-Meier plot of transplant-free survival, by peripheral blood concentration dichotomized at an optimal threshold and related to transplant-free survival by the log-rank test. For each outcome and biomarker, high concentrations, above the threshold, are indicated by a solid line, low concentrations, below the threshold, by a broken line. The log-rank P values comparing high with low concentrations are shown in the appropriate color for OS and transplant-free survival are shown above each plot. The markers shown are (A) matrix metalloproteinase-7, (B) intercellular adhesion molecule-1, (C) IL-8, (D) vascular cell adhesion molecule-1, and (E) S100A12.

Figure 3.

Prediction of idiopathic pulmonary fibrosis. Outcome is largely validated in an independent validation set. As in Figure 2 , red indicates the Kaplan-Meier plot of overall survival by peripheral blood concentration dichotomized at an optimal threshold by profile likelihood, and blue indicates transplant-free survival. All line styles are identical to those in Figure 2 , and log-rank P values are listed at the top of each plot. As in Figure 2 , the markers shown are (A) matrix metalloproteinase-7, (B) intercellular adhesion molecule-1, (C) IL-8, (D) vascular cell adhesion molecule-1, and (E) S100A12.

Figure 4.

Peripheral blood risk index (PCMI) predicts mortality in idiopathic pulmonary fibrosis. (A) Kaplan-Meier curve for mortality of patients in validation cohort grouped by the mortality-associated PCMI derived in the derivation cohort. Black is low risk (PCMI <330) and red is high risk (PCMI ≥330). (B) Time-dependent receiver operating characteristic curves for predicting idiopathic pulmonary fibrosis mortality by PCMI. True-positive rate is plotted versus false-positive rate, for all possible thresholds in the validation set, of the PCMI derived in the derivation set. Each line is for predicting mortality within a specified time point after blood draw. The predictive performance of this combined index is high: area under the curve ranges from 0.74–0.84, C statistic from 0.73–0.84.