Abstract
Purpose[S-methyl-11C]-L-methionine ([11C]MET) uptake in the pancreas might be a central indicator of beta cell function. Since gastric emptying was recently shown to influence glycemic control in subjects after pancreaticoduodenectomy (PD, the surgical treatment of neoplasms of the pancreas head), we looked for imaginable relationships between gastric emptying, pre- and postprandial insulin concentrations, and [11C]MET uptake.MethodsNineteen tumor-free survivors after PD (age mean ± SD: 61 ± 8.7 yrs.; 10 male, 9 female) and 10 healthy controls (age: 27 ± 8.7 yrs.; 7 male, 3 female) were given a mixed test meal. One gram of paracetamol was ingested with the meal to evaluate the speed of gastric emptying. Insulin, glucose, and paracetamol plasma concentrations were measured before and over 180 minutes after ingestion. Beta cell function was calculated from fasting glucose and insulin plasma concentrations. Simultaneously, 800 MBq of [11C]MET were administered and the activity (maximum tissue standardized uptake values [SUVmax]) over the pancreas was measured at 15, 30, and 60 minutes after injection. Total integrated SUVmax (area under the curve [AUC]) and incremental SUVmax were calculated.ResultsThe uptake of [11C]MET in the pancreas was significantly higher (p < 0.0001) in controls compared to the PD group. Gastric emptying was significantly slower in controls compared to pancreatectomy subjects (p < 0.0001). Paracetamol AUC30 correlated with the SUVmax increment between 15 and 30 minutes (R2 = 0.27, p = 0.0263), suggesting a relationship between gastric emptying and the uptake of [11C]MET. Total integrated SUVmax correlated with insulin AUC60 (R2 = 0.66,p < 0.0001) in patients after PD. Multivariate regression analysis revealed insulin AUC60 and beta cell function, calculated from the fasting insulin to glucose ratio, as independent predictors of 11C-methionine uptake, i.e. total integrated SUVmax, in patients after PD (R2 = 0.78, p < 0.0001).ConclusionPostprandial [11C]MET uptake may represent basal and postprandial beta cell function. The findings suggest a possible usefulness of this imaging procedure for further studying beta cell function.
Highlights
Positron emission tomography (PET) is widely used to measure amino acid metabolism and protein synthesis rates in vivo. [S-methyl-11C]-L-methionine ([11C]MET), a PET tracer, radiolabeled with short-lived carbon-11 without any alteration to the molecular structure, is an universal donor of transmethyl reactions that participates in the synthesis of DNA and RNA.Eur J Nucl Med Mol Imaging (2017) 44:509–516Methionine is mainly incorporated in the liver, brain, pancreas, and in tumors, where its main metabolic pathway is protein incorporation [1, 2]
Paracetamol AUC over 30 minutes (AUC30) correlated with the SUVmax increment between 15 and 30 minutes (R2 = 0.27, p = 0.0263), suggesting a relationship between gastric emptying and the uptake of [11C]MET
Total integrated SUVmax correlated with insulin AUC over 60 minutes (AUC60) (R2 = 0.66,p < 0.0001) in patients after PD
Summary
Positron emission tomography (PET) is widely used to measure amino acid metabolism and protein synthesis rates in vivo. [S-methyl-11C]-L-methionine ([11C]MET), a PET tracer, radiolabeled with short-lived carbon-11 without any alteration to the molecular structure, is an universal donor of transmethyl reactions that participates in the synthesis of DNA and RNA.Eur J Nucl Med Mol Imaging (2017) 44:509–516Methionine is mainly incorporated in the liver, brain, pancreas, and in tumors, where its main metabolic pathway is protein incorporation [1, 2]. Comar et al suggested the use of [11C]MET PET imaging for the examination of the pancreas in 1976 [3]. Various studies have addressed the relationship between tracer uptake, beta cell function, and exocrine pancreatic function [2, 4,5,6,7,8,9,10,11]. Syrota et al studied [11C]MET uptake and protein incorporation in duodenal aspirate in patients with chronic pancreatitis, and observed a diminished uptake and incorporation of the tracer. Takasu et al found a close relationship between tracer uptake and the secretininduced volume of duodenal secretions as well as its amylase and HCO3− content [10, 11]
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