Plasma Lipidomic Signature of Rectal Adenocarcinoma Reveals Potential Biomarkers

Abstract

Background: Rectal adenocarcinoma (RAC) is a common malignant tumor of the digestive tract and survival is highly dependent upon stage of disease at diagnosis. Lipidomic strategy can be used to identify potential biomarkers for establishing early diagnosis or therapeutic programs for RAC.

Objective: To evaluate the lipoperoxidation biomarkers and lipidomic signature in the plasma of patients with RAC (n = 23) and healthy controls (n = 18).

Methods: Lipoperoxidation was evaluated based on malondialdehyde (MDA) and F₂-isoprostane levels and the lipidomic profile obtained by gas chromatography and high resolution mass spectrometry (ESI-q-TOF) associated with a multivariate statistical technique.

Results: The most abundant ions identified in the RAC patients were those of protonated phosphatidylcholine and phosphatidylethanolamine. It was found that a lisophosphatidylcholine (LPC) plasmalogen containing palmitoleic acid [LPC (P-16:1)], with highest variable importance projection score, showed a tendency to be lower in the cancer patients. A reduction of n - 3 polyunsaturated fatty acids was observed in the plasma of these patients. MDA levels were higher in patients with advanced cancer (stages III/IV) than in the early stages groups and the healthy group (p < 0.05). No differences in F₂-isoprostane levels were observed among these groups.

Conclusion: This study shows that the reduction in plasma levels of LPC plasmalogens associated with an increase in MDA levels may indicate increased oxidative stress in these patients and identify the metabolite LPC (P-16:1) as a putatively novel lipid signature for RAC.

Keywords: biomarkers; lipidomic; lipoperoxidation; mass spectrometry; rectal adenocarcinoma.

Figure 1

Representative (+) ESI-MS (q-ToF) mass spectra of plasma from (A) a healthy volunteer and (B) a rectal adenocarcinoma patient. (B) Representation of the molecular structure (C₂₄H₄₈NO₆P) m/z 478 identified as lisophosphatidylcholine [LPC (P-16:1)].

Figure 2

(A) PLS-DA scores plot of healthy volunteers (red) and rectal adenocarcinoma patients (green). 36.5 and 19.2% are the scores of the component 1 and 2, respectively. (B) Loadings plot for components 1 and 2. (C) Cross validation showing the performance measures (prediction accuracy, R², and Q²). *best values of Q² (0.97). (D) The permutation test statistics (p < 5e⁻⁴). PLS score (T-score) explains Y and maximizes the relation between X and Y.

Figure 3

Important metabolite ions selected on the basis of variable importance in projection (VIP) score. The colored boxes on the right indicate relative bin integrals for healthy volunteers and rectal adenocarcinoma patients. VIP score is a weighted sum of squares of the PLS-DA loadings taking into account the amount of explained Y-variation in each dimension.

Figure 4

Malondialdehyde (A) and F₂-isoprostane (B) levels of the healthy volunteers and rectal adenocarcinoma patients in the different cancer stages. *p < 0.05 compared to the healthy volunteers. ^#p < 0.05 compared to stage 0; ANOVA followed by Tukey test. 1. Healthy volunteers, 2. Stages 0, 3. Stages I/II, 4. Stages III/IV.