Van der Waals Force between Protein-linked Oligosaccharide and N-alkanes Determining Disease Status of Colonic Neuroendocrine Tumor using FTIR Imaging

Neuroendocrine tumors (NETs) frequently occur in gastrointestinal tract, arising from cells of the neuroendocrine systems. The finalized grade and disease state are determined after morphology examination of biopsy inspected by a pathologist team. Good prognosis is always expected for patients with grade 1 NET after tumor excision; rapid progressing multiple metastases was, however, found for ones with grade 3 neuroendocrine carcinoma (NEC) even after aggressive treatment. The mechanisms of NETs still remain unclear and the interobserver variability of diagnosis exists. Previous studies1-3 showed that protein glycosylation is considered strongly relating with cell proliferation, differentiation and carcinogenesis; furthermore, neo-synthesis and incomplete synthesis of oligosaccharide residues of glycoprotein were proved during cancerization4. Herein the alteration of oligosaccharide residues of glycoprotein within NET tissues was investigated by using FTIR imaging. The differentiation of van der Waals (VDW) force between specific carbon number n-alkane as oligosaccharide adsorbent and tissue section surface was found and suggested being strongly correlated with the IR absorbance ratio of the residue of n-alkyl waxes adhering onto the surface of colonic grade 1 NET and grade 3 NEC tissue sections in the spectral range of 3000-2800 cm-1. The FTIR imaging results of NET tissue sections for both grade 1 and grade 3 showed that the IR absorbance ratio of Abs (carbon number N n-alkane)/ Abs (carbon number M n-alkane) and N > M of waxes adhering onto tissue sections was referred to VDW force and significantly increased in grade 1 NET compared with normal colon epithelium and grade 3 NEC. On the basis of our findings, FTIR imaging demonstrated that VDW force between protein-linked oligosaccharide and n-alkanes is an innovative and a potential target for discriminating the NET grade 1 from NEC grade 3. This is the first study to demonstrate the elongation and diagnostic role of surface protein-linked glycans residues using FTIR imaging in NETs.