Altered Plasma Apolipoprotein Modifications in Patients with Pancreatic Cancer: Protein Characterization and Multi-Institutional Validation

Abstract

BackgroundAmong the more common human malignancies, invasive ductal carcinoma of the pancreas has the worst prognosis. The poor outcome seems to be attributable to difficulty in early detection.MethodsWe compared the plasma protein profiles of 112 pancreatic cancer patients with those of 103 sex- and age-matched healthy controls (Cohort 1) using a newly developed matrix-assisted laser desorption/ionization (oMALDI) QqTOF (quadrupole time-of-flight) mass spectrometry (MS) system.ResultsWe found that hemi-truncated apolipoprotein AII dimer (ApoAII-2; 17252 m/z), unglycosylated apolipoprotein CIII (ApoCIII-0; 8766 m/z), and their summed value were significantly decreased in the pancreatic cancer patients [P = 1.36×10−21, P = 4.35×10−14, and P = 1.83×10−24 (Mann-Whitney U-test); area-under-curve values of 0.877, 0.798, and 0.903, respectively]. The significance was further validated in a total of 1099 plasma/serum samples, consisting of 2 retrospective cohorts [Cohort 2 (n = 103) and Cohort 3 (n = 163)] and a prospective cohort [Cohort 4 (n = 833)] collected from 8 medical institutions in Japan and Germany.ConclusionsWe have constructed a robust quantitative MS profiling system and used it to validate alterations of modified apolipoproteins in multiple cohorts of patients with pancreatic cancer.

Serum Protein Signatures Differentiating Autoimmune Pancreatitis versus Pancreatic Cancer

“…One reason could be the posttranslational modification of the proteins. Investigations of other groups and our own studies have demonstrated that modifications and truncated forms of proteins such as apolipoproteins and transthyretin may represent disease-specific signatures [17], [41]–[43]. The modified protein forms are binding with a low affinity, or not at all, to the immobilised antibodies on the depletion columns and, therefore, are not efficiently removed.…”

CA19‐9 and apolipoprotein‐A2 isoforms as detection markers for pancreatic cancer: a prospective evaluation

“…In healthy subjects, 3 basic isoforms are found which we labeled ApoA2‐ATQ/ATQ, ApoA2‐ATQ/AT and ApoA2‐AT/AT), by the lengths of each of the homomers. Patients with PDAC show additional isomers formed through two aberrant processing patterns of ApoA2i: a hyper‐processing pattern of ApoA2i, which leads to predominantly light isoforms such as ApoA2‐AT/AT, ApoA2‐AT/A and ApoA2‐A/A, and a hypo‐processing pattern which leads to a predominance of heavy isoforms such as ApoA2‐ATQ/ATQ . The aberrant processing is likely a consequence of abnormal expression and release of carboxypeptidase A, a digestive enzyme that is primarily synthesized by the pancreas, and leads to a reduction in plasma levels of ApoA2‐ATQ/AT, the major intermediate isoform of ApoA2i, in comparison with healthy subjects.…”

“…The aberrant processing is likely a consequence of abnormal expression and release of carboxypeptidase A, a digestive enzyme that is primarily synthesized by the pancreas, and leads to a reduction in plasma levels of ApoA2‐ATQ/AT, the major intermediate isoform of ApoA2i, in comparison with healthy subjects. Aberrant processing of ApoA2 is observed not only in relation to pancreatic malignancies (including early‐stage cancers), but also in individuals with intraductal papillary mucinous neoplasia (IPMN) and other pancreatic conditions (e.g., chronic pancreatitis) predisposing to pancreatic cancer development …”

“…8,9 Recently, we identified unique processing patterns of cterminal amino acids of apolipoprotein A2 (ApoA2) in patients with pancreatic cancer. [10][11][12] In the bloodstream ApoA2 can be found in 5 dimeric isoforms (ApoA2i). [10][11][12][13] In healthy subjects, 3 basic isoforms are found which we labeled ApoA2-ATQ/ ATQ, ApoA2-ATQ/AT and ApoA2-AT/AT), by the lengths of each of the homomers.…”

Potential Usefulness of Apolipoprotein A2 Isoforms for Screening and Risk Stratification of Pancreatic Cancer

“…The AUC value of apoA2-ATQ/AT in the German cohort was 0.958, and the diagnostic accuracy to distinguish PDAC from healthy controls was confirmed by the German cohort [35]. …”