Pancreatic cancer induced diabetes mellitus: relevance of the S100A8 N-terminal peptide (Nt-S100A8).

Background: After isolating NT-S100A8 from pancreatic cancer (PC) tissue of diabetic patients, we verified whether this peptide alters PC cell growth and invasion and/or insulin release and [Ca2+]i oscillations of insulin secreting cells and/or insulin signalling. We verified also whether this peptide is treaceble in serum to detect pancreatic cancer induced diabetes mellitus. Methods: BxPC3, Capan1, MiaPaCa2, Panc1 (PC cell lines) cell growth and invasion were assessed in the absence or presence of 50, 200 and 500 nM NT-S100A8. In NTS100A8 stimulated b-TC6 (insulinoma cell line) culture medium, insulin and [Ca2+] were measured at 2,3,5,10,15,30 and 60 minutes, and [Ca2+]i oscillations were monitored (epifluorescence) for three minutes. Results: 500 nM NT-S100A8 stimulated BxPC3 cell growth only and dose dependently reduced MiaPaCa2 and Panc1 invasion. 500 nM NT-S100A8 induced a rapid insulin release and enhanced b-TC6 [Ca2+]i oscillations after both one (F=6.05, p<0.01) and two minutes (F=7.42, p<0.01). In the presence of NT-S100A8, [Ca2+] in b-TC6 culture medium significantly decreased with respect to control cells (F=6.3, p<0.01). NT-S100A8 did not counteract insulin induced phosphorylation of the insulin receptor, Akt and IkB-a, but it independently activated Akt and NF-kB signalling in PC cells. To verify whether NT-S100A8 is traceable in serum as a potential index of pancreatic cancer induced diabetes mellitus, sera from 42 pancreatic patients (17 with and 25 without diabetes mellitus) and from 11 healthy controls were subjected to discontinuous SDS-PAGE in the same conditions which allowed NT-S100A8 to be isolated from pancreatic cancer tissues. At analysis of the low molecular weight (from about 15,000 to about 1,000 Da), nine protein bands were identified in sera. Only the band with an approximate molecular weight of 14,200 Da was correlated with the diagnosis of pancreatic cancer, being present in 10/11 controls and absent in 37/42 cancer cases (χ2=26.8, p<0.001). Two bands with an approximate molecular weight of 10,000 and 1,000 Da respectively, were correlated with each other (χ2=4.8, p<0.05) and, in cancer cases, their disappearance was closely correlated with the presence of diabetes mellitus (χ2=8.6, p<0.01 and χ2=6.6, p<0.05). Conclusion: NT-S100A8 exerts a mild effect on PC cell growth, while it reduces PC cell invasion, possibly by Akt and NF-kB signalling, NT-S100A8 enhances [Ca2+]i oscillations and insulin release, probably by inducing Ca2+ influx from the extracellular space, but it does not interfere with insulin signalling. New potential serum biomarkers for pancreatic cancer and pancreatic cancer induced diabetes mellitus diagnosis were also identified.