Surfactant protein a in cystic fibrosis: supratrimeric structure and pulmonary outcome

Abstract

Background: The state of oligomerization of surfactant associated protein-A (SP-A) monomers differs between individuals. This likely affects SP-A's functional properties and could thereby influence clinical status in patients with lung diseases. In this study we focus on SP-A structure in cystic fibrosis (CF) compared to both healthy subjects and disease controls.

Methods: SP-A composition and function were assessed in both bronchoalveolar lavage (BAL) fluid and serum of 46 CF patients with mild disease, 25 patients with chronic bronchitis and 22 healthy subjects by gel chromatography and a functional agglutination assay. Relation of SP-A agglutination ability to disease severity of the subjects was explored.

Results: SP-A was present in seven major oligomeric forms with the majority of SP-A being structurally organized as complex oligomeric forms. More complex oligomeric forms were associated with better SP-A function with regard to its agglutination ability. These forms were more frequently observed in BAL than in serum, but there were no differences between disease groups. In CF patients, more complex forms of SP-A were associated with better lung function.

Conclusions: Organizational structure of SP-A affects its functional activity and is linked to disease severity in CF.

Figure 1. Illustration of the column characteristics for the separation of SP-A present in bronchoalveolar lavage or serum samples.

Samples from different patients were run on the column and SP-A content of each fraction was determined and plotted, normalized to its total amount eluting from the column. Here, selected samples from three different subjects, each with a distinct extreme pattern of elution, are shown (patient A (squares), having mainly one initial peak around fraction 10 contains 18-mers and larger; patient B (triangles), having mainly a peak around fraction 15 with SP-A 6–12-mers; and patient C (circles), having mainly the lower molecular weight forms of SP-A).

Figure 2. Relationship between different structure compositions of SP-A and their agglutination ability (A,B) as well as their association with lung function (C,D).

The graphs illustrate the agglutination ability differences between different oligomeric structure compositions (forms) in BAL (A) and serum (B) analyzed by gel chromatography. 42 BAL samples and 31 serum samples of CF patients were analyzed. In serum only the 010 and 110 forms showed a significant difference regarding the agglutination ability compared to other forms. In BAL the 100 form agglutinated significantly better than the 111, 110 and 101 form and the 101 form significantly better than the 111 and 101 form. The graphs (C,D) plot the relation between the lung function (y-axis) and the oligomeric SP-A distribution in BAL (C) and in serum (D). For analysis One way ANOVA with Tukey as post-test was used and in all cases with a significant result (P<0.05), post hoc tests were calculated. Differences between groups are indicated by dotted (P<0.05) or solid (P<0.01) lines.

Figure 3. Correlation between agglutinate size and FEV1 (% pred.)_age20 and ΔFEV1 (% pred.)/year.

The graphs show on the x-axis the SP-A agglutination size in whole, non-size fractionated BAL (A, C) and serum (B, D) in Pixel and in the y-axis the FEV1 (% pred.)_age20 (A, B), and accordingly ΔFEV1 (% pred.)/year (C, D). 28 BAL samples and 12 serum samples of CF patients were used for the graphs a and b and 26 BAL samples and 14 serum samples of CF patients could be included in the graphs C and D. The p-values analyzed by linear regression were 0.0076 (r² = 0.2438) for BAL (A) and 0.0417 (r² = 0.2819) for serum (B) as well as 0.0147 (r² = 0.2156) for BAL (C) and 0.0343 (r² = 0.3006) for serum (D).