Metabolite Changes Associated with Resectable Pancreatic Ductal Adenocarcinoma

Abstract

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is insidious, with only 15-20% of those diagnosed suitable for surgical resection as it is either too advanced and has invaded local structures or has already spread to distant sites. The associated tumor microenvironment provides a protective shield which limits the efficacy of chemotherapeutic agents, but also impairs the delivery of nutrients required for the PDAC cells. To compensate for this, metabolic adaptions occur to provide alternative sources of fuel. The aim of this study is to explore metabolomic differences between participants with resectable PDAC compared to healthy volunteers (HV). The objectives were to use nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) to determine if resectable PDAC induces sufficient metabolic adaptations and variations which could be used to discriminate between the two groups.

Methods: Plasma samples were collected from fasted individuals with resectable PDAC (n = 23, median age 68 [IQR 56-75], 69.6% male) and HV (n = 24, median age 63 [IQR 58-71], 54.2% male). Samples were analyzed using NMR and the Biocrates MxP Quant 500 kit at University Hospital Southampton.

Results: NMR spectroscopy identified six independent metabolites that significantly discriminated between the PDAC and HV groups, including elevated plasma concentrations of 3-hydroxybutyrate and citrate, with decreased amounts of glutamine and histidine. MS analysis identified 84 metabolites with a significant difference between the PDAC and HV cohorts. The metabolites with a fold change (FC) > 1.5 in the PDAC population were conjugated bile acids (taurocholic acid, glycocholic acid, and glycochenodexoycholic acid).

Discussion: In conclusion, using metabolomics, biochemical differences between resectable PDAC and HV were detected. These differences indicate metabolic plasticity and utilization of alternative fuel sources.

Keywords: PDAC; adenocarcinoma; metabolite; metabolomics; pancreatic.

Figure 1

OPLS-DA model comparing the circulating metabolic profiles from participants with pancreatic ductal adenocarcinoma (PDAC) vs. healthy volunteers measured by ¹H NMR spectroscopy (Q²Y = 0.30, p = 0.001). The coefficients plot indicates covariance with class, with positive peaks having a greater abundance in PDAC plasma compared to healthy volunteers and negative peaks being present in lower amounts. Red spectral peaks indicate metabolites significantly associated with class membership. PEG, polyethylene-glycol.

Figure 2

Receiver operating characteristic curve predicting pancreatic ductal adenocarcinoma vs. healthy volunteers based on the metabolomic profile derived from 3-hydroxybutyrate, N-acetylglycoproteins, glutamine, citrate, glucose, and histidine.

Figure 3

Volcano plot demonstrating the difference in log fold change of metabolites identified using mass spectrometry between participants with pancreatic ductal adenocarcinoma vs. healthy volunteers.

Figure 4

Metabolomic alterations induced by pancreatic ductal adenocarcinoma (PDAC) detected using nuclear magnetic resonance (NMR) spectroscopy. The paraneoplastic effect of PDAC impairs systemic insulin sensitivity, which increases plasma glucose levels. This process is influenced by inflammatory mediators such as the cytokines interleukin-1 and interleukin-6, which also drive the production of N-acetylglycoprotein. As a result of reduced intracellular glucose, alternative fuel sources are utilized, such as fatty acid oxidation to produce acetyl-CoA. This is used by the tricarboxylic acid (TCA) cycle, to produce citrate. Mitochondrial citrate can move into the cytoplasm where it is then used in the formation of cholesterol and fatty acids for cell membrane synthesis, a KRAS-driven hallmark of PDAC. Glutamine and histidine abundance were both reduced because of their conversion into glutamate, which is used to maintain α-ketoglutarate and propagate the TCA cycle. To maintain alternative fuel sources, ketogenesis occurs in the liver and converts acetyl-CoA into ketone bodies, such as 3-hydroxybutyrate, thus increasing the plasma concentration of this metabolite. This latter process can be upregulated if there is a scarcity of oxaloacetate, as is the case with increased citrate production. Solid arrows represent successful pathways, dashed arrows represent impaired pathways.