Lipid metabolism impairment in patients with sepsis secondary to hospital acquired pneumonia, a proteomic analysis

Abstract

Background: Sepsis is a dysregulated host response to infection and a major cause of death worldwide. Respiratory tract infections account for most sepsis cases and depending on the place of acquisition, i.e., community or hospital acquired infection, differ in etiology, antimicrobial resistance and outcomes. Accordingly, the host response may be different in septic patients secondary to community-acquired pneumonia and hospital acquired pneumonia (HAP). Proteomic analysis is a useful approach to evaluate broad alterations in biological pathways that take place during sepsis. Here we evaluated plasma proteome changes in sepsis secondary to HAP.

Methods: Plasma samples were obtained from patients (n = 27) at admission and after 7 days of follow-up, and were analyzed according to the patients' outcomes. The patients' proteome profiles were compared with healthy volunteers (n = 23). Pooled plasma samples were labeled with isobaric tag for relative and absolute quantitationand analyzed by LC-MS/MS. We used bioinformatics tools to find altered functions and pathways. Results were validated using biochemical estimations and ELISA tests.

Results: We identified 159 altered proteins in septic patients; most of them were common when comparing patients' outcomes, both at admission and after 7 days. The top altered biological processes were acute inflammatory response, response to wounding, blood coagulation and homeostasis. Lipid metabolism emerged as the main altered function in patients, with HDL as a central node in the network analysis, interacting with downregulated proteins, such as APOA4, APOB, APOC1, APOL1, SAA4 and PON1. Validation tests showed reduced plasma levels of total cholesterol, HDL-C, LDL-C, non-HDL cholesterol, apolipoproteins ApoA1 and ApoB100, and Paraoxonase 1 in HAP patients.

Conclusion: Proteomic analysis pointed to impairment of lipid metabolism as a major change in septic patients secondary to HAP, which was further validated by the reduced levels of cholesterol moieties and apolipoproteins in plasma. Our results stress the involvement of lipids in the pathogenesis of sepsis, which is in accordance with previous reports supporting the role of lipid moieties in pathogen toxin clearance and in modulating inflammatory responses.

Keywords: Cholesterol; Hospital-acquired pneumonia; Lipid metabolism; Proteome; Sepsis.

Fig. 1

Schematic flow chart of the patient enrollment and selection. Patients admitted to intensive care units with severe sepsis and/or septic shock were selected based on criteria that included blood sampling, source and site of infection, and were assigned to groups according to their outcomes (survivors and nonsurvivors)

Fig. 2

A Venn diagram showing differential proteome expression between the septic patient groups. I shows the differential protein expression levels in survivors and nonsurvivors at admission (Ia) and at D7 (Ib), and the differential expression levels at D0 and D7 in survivors and in nonsurvivors (Ic). II demonstrates the differential expression levels between community-acquired pneumonia and hospital-acquired pneumonia (a–d). CAP, community-acquired pneumonia; HAP, hospital-acquired pneumonia. D0S and D7S, admission and follow-up samples in survivors, and D0NS and D7 NS, admission and follow-up samples in nonsurvivors

Fig. 3

Gene ontology annotations for the identified differentially expressed proteins. Altered molecular functions (a), biological processes (b) and cellular components (c) in septic survivors and nonsurvivors at admission and after 7 days. The altered functions are represented as − log10 (P value) with the highlighted dots representing the group with maximum changes for a function. The white squares represent P values that were not included in the range selected for each analysis

Fig. 4

Protein-protein interactions and functional networks. The red color represents upregulation and the green color represents downregulation. a–d corresponds to the D0 survivors, D0 nonsurvivors, D7 survivors and D7 nonsurvivors, respectively

Fig. 5

Expression of lipid metabolism related proteins. The bar chart represents log₂-fold-changes (patients vs. healthy volunteers) of altered proteins related to lipid metabolism. The dashed line represents the fold-change cut-off (log₂-fold-change │0.3785│, corresponding to fold-change ± 1.3)