Use of MALDI Mass Spectrometry Imaging to Identify Proteomic Signatures in Aortic Aneurysms after Endovascular Repair

Abstract

Endovascular repair (EVAR) has become the standard procedure in treating thoracic (TAA) or abdominal aortic aneurysms (AAA). Not entirely free of complications, a persisting perfusion of the aneurysm after EVAR, called Endoleak (EL), leads to reintervention and risk of secondary rupture. How the aortic wall responds to the implantation of a stentgraft and EL is mostly uncertain. We present a pilot study to identify peptide signatures and gain new insights in pathophysiological alterations of the aortic wall after EVAR using matrix-assisted laser desorption or ionization mass spectrometry imaging (MALDI-MSI). In course of or accompanying an open aortic repair, tissue sections from 15 patients (TAA = 5, AAA = 5, EVAR = 5) were collected. Regions of interest (tunica media and tunica adventitia) were defined and univariate (receiver operating characteristic analysis) statistical analysis for subgroup comparison was used. This proof-of-concept study demonstrates that MALDI-MSI is feasible to identify discriminatory peptide signatures separating TAA, AAA and EVAR. Decreased intensity distributions for actin, tropomyosin, and troponin after EVAR suggest impaired contractility in vascular smooth muscle cells. Furthermore, inability to provide energy caused by impaired respiratory chain function and continuous degradation of extracellular matrix components (collagen) might support aortic wall destabilization. In case of EL after EVAR, this mechanism may result in a weakened aortic wall with lacking ability to react on reinstating pulsatile blood flow.

Risk factors for elective and urgent open conversion after EVAR—a retrospective observational study

“…Furthermore, the continuing degradation of extracellular matrix proteins, such as collagen, might support this structural instability. 28 As long as EVAR is performed successfully without persisting perfusion of the aneurysm, these structural alteration problems will be limited and not cause significant trouble. However, this can change if EL occurs.…”

“…However, recently, increasing interest has developed on pathological alterations inside the aortic wall as a reaction to an inserted stent graft. In the case of EL, various theories [25][26][27][28] suggest decreased structural and functional resistance to persistent blood flow inside the aneurysm. Structural atrophy and thinning of the aortic wall complemented by alterations in extracellular matrix components, such as collagen, may contribute to lower structural resistance.…”

Molecular analysis of the extracellular microenvironment: from form to function

“…Considerations for customizing sample preparation include the type of tissue being imaged, the enzymes used for targeting the ECM proteins or PTMs and required spatial resolution. MALDI ECM-MSI has been done on fresh-frozen tissues, formalin-fixed paraffin-embedded (FFPE) [68,[176][177][178] tissues, and tissue microarrays (TMAs) [179][180][181][182][183]. Embedded tissues or TMAs are sectioned with a typical thickness of 3-7 μm for FFPE tissues and 8-10 μm for fresh-frozen tissues [173,184].…”

“…Deglycosylation greatly improves access to the ECM protein structure for increased detection of ECM proteins [194]. Spatial studies reporting ECM expression have used either trypsin [176][177][178]182,195] or collagenase Type III [68,180,181,191,194,[196][197][198] in combination with deglycosylation.…”

“…Targeted identification can be done by on-tissue MALDI-MS/MS [179,199], or by using an in silico reference library [182,183]. Using the same tissue section, an untargeted reference library may be created by LC-MS/MS from either locally-digested, liquid-extracted peptides [177] or insolution-digested peptides from homogenized whole tissue [178,196] or homogenized macrodissected regions of interest [176].…”