An Unidentified Pancreatic Cancer Cell Product Alters Some Intracellular Pathways of Glucose Metabolism in Isolated Rat Hepatocytes

Abstract

In this study we assessed whether conditioned media from a human pancreatic cancer cell line (MIA PaCa 2) can interfere with some intracellular pathways involved in glucose metabolism in isolated rat hepatocytes. The hepatocytes. isolated from Male Wistar rats, were incubated with MIA PaCa 2-conditioned or nonconditioned media. Conditioned and nonconditioned hepatocytes were run for 120 min in the presence or absence of insulin (100 m M ) and were sampled at fixed time intervals. Supernatant glucose levels decreased to a similar extent over time in both conditioned and nonconditioned hepatocytes, while lactate levels significantlly increased in nonconditioned hepatocytes with respect to conditioned hepatocytes. A pyruvate kinase activity increase was observed only in nonconditioned hepatocytcs and was biphasic in nature, since this increased activity was dctccted both after a few and after 30 min following insulin stimulation. The cyclic A M P level increase was significantly higher in conditioned than in nonconditioned hepatocytes. It appears that MIA PaCa 2 cells produce a factor(s) that may interfere with one of the insulin-mediated intracellular pathways of glucose metabolism, namely, glycolysis. This detrimental effect on glycolysis is supported by the blunted rise in lactate concentration in the medium after the glucose challenge. This substance(s) probably transfers its signal inside the target cells, activating the adenylate cyclase pathway. These results support the hypothesis that pancreatic cancer is the cause rather than the consequence of diabetes mellitus. Key Words: Pancreatic cancer-Diabetes mellitus-MIA PaCa 2.Severall literature studies demonstrate a link between paincreatic cancer and altered glucose homeostasis (1-11). Overt diabetes mellitus and/or a reduced glucose tolerance are found in -80% of patients with pancreatic cancer (2,5,7). Several in vivo and in viiro studies attempted to identify the pathophysiological mechanism(s) responsible for the association between pancreatic cancer and diabetes mellitus. It hlas been shown that pancreatic cancerassociated diabetes does not depend on the destruction of pancreatic p cells (5,7,9) but, rather, on the Manuscript Address corrcspondence and reprint requcsts to Dott. M. Plebani.

Abnormal Differentiation of Islet Cells in Pancreatic Cancer

“…Abnormalities in the serum levels of islet hormones indicate deregulation in islet cell function. The results of some studies have suggested that yet unknown substances released from tumor cells are, at least in part, responsible for this phenomenon [1,[4][5][6]. This possibility was confirmed by our recent observation that in pancreatic cancer patients the abnormalities in the hormonal contents of islets occurs predominantly in the immediate area of cancers but to a much lesser extent in tissues remote from cancer [7].…”

“…Recent studies in our laboratories [7] and elsewhere [21] have demonstrated a significant reduction in the number of ß cells in the islets of pancreatic cancer patients. Because these changes were more pronounced in islets within and in the immediate area of cancer, it was postulated that a substance or substances released by cancer cells affect the islet cell function by a paracrine pathway [5,6,22].…”

Quantitative analysis of the low molecular weight serum proteome using 18O stable isotope labeling in a lung tumor xenograft mouse model

“…An interesting feature of many of the diagnostic studies that have employed various proteomic strategies is that, consistently, proteins (and/or their fragments) that are considered diagnostic for the disease of interest possess low molecular weights, suggesting that the LMW serum proteome may contain an unexplored archive of histopathological information and provide useful biomarkers for disease detection. Indeed, LMW serum proteins, peptides, and other small components have been associated with pathological conditions such as cancer [12], diabetes [13], cardiovascular, and infectious diseases [14]. A simple method for the enrichment of the LMW components in serum has previously been developed in our laboratory and used in conjunction with multidimensional chromatographic fractionation and MS analysis to better characterize this unexplored fraction [2].…”

An investigation into the human serum “interactome”

“…Indeed, the LMW components (i.e., proteins, metabolites, etc.) of human serum have been associated with histopathologies ranging from cancer [10] to diabetes [11] and cardiovascular and infectious diseases [12]. Recent studies of serum using surfaceenhanced laser/desorption ionization (SELDI)-time of flight (TOF)-mass spectrometry (MS), when combined with advanced bioinformatic techniques, have identified many key species with putative molecular masses below 15 kDa that serve to distinguish the onset of cancer [10,[13][14][15][16][17][18].…”