Glutamine is the most abundant free amino acid in the body and is known to play a regulatory role in several cell specific processes including metabolism (e.g., oxidative fuel, gluconeogenic precursor, and lipogenic precursor), cell integrity (apoptosis, cell proliferation), protein synthesis, and degradation, contractile protein mass, redox potential, respiratory burst, insulin resistance, insulin secretion, and extracellular matrix (ECM) synthesis. Glutamine has been shown to regulate the expression of many genes related to metabolism, signal transduction, cell defense and repair, and to activate intracellular signaling pathways. Thus, the function of glutamine goes beyond that of a simple metabolic fuel or protein precursor as previously assumed. In this review, we have attempted to identify some of the common mechanisms underlying the regulation of glutamine dependent cellular functions.

Aims/hypothesis. Pancreatic islet cells and clonal betacell lines can metabolise L-glutamine at high rates. The pathway of L-glutamine metabolism has traditionally been described as L-glutamine→L-glutamate→2-oxoglutarate→oxidation in TCA cycle following conversion to pyruvate. Controversially, the metabolism of D-glucose to L-glutamate in beta cells is not widely accepted. However, L-glutamate has been proposed to be a stimulation-secretion coupling factor in glucose-induced insulin secretion. We aimed to investigate the metabolism of glutamine and glucose by using 13 C NMR analysis. Methods. BRIN-BD11 cells were incubated in the presence of 16.7 mmol/l [1-13 C]glucose, 2 mmol/l [2-13 C]L-glycine or 2 mmol/l [1,2-13 C]glutamine in the presence or absence of other amino acids or inhibitors. After an incubation period the cellular metabolites were extracted using a PCA extract procedure. After neutralisation, the extracts were prepared for analysis using 13 C-NMR spectroscopy.Results. Using 13 C NMR analysis we have shown that L-glutamine could be metabolised in BRIN-BD11 cells via reactions constituting part of the γ-glutamyl cycle producing glutathione. Moderate or high activities of the enzymes required for these pathways of metabolism including glutaminase, γ-glutamyltransferase and γ-glutamylcysteine synthetase were observed. We additionally report significant D-glucose metabolism to L-glutamate. Addition of the aminotransferase inhibitor, aminooxyacetate, attenuated Lglutamate production from D-glucose. Conclusion/interpretation. We propose that L-glutamine metabolism is important in the beta cell for generation of stimulus-secretion coupling factors, precursors of glutathione synthesis and for supplying carbon for oxidation in the TCA cycle. D-glucose, under appropriate conditions, can be converted to L-glutamate via an aminotransferase catalysed step. [Diabetologia (2003[Diabetologia ( ) 46:1512[Diabetologia ( -1521 Keywords Pancreatic beta cells, NMR, γ-glutamyl cycle, L-glutamine, L-glutamate, glutathione. Diabetologia (2003( ) 46:1512( -1521( DOI 10.1007( /s00125-003-1184 13 C NMR analysis reveals a link between L-glutamine metabolism, D-glucose metabolism and γ-glutamyl cycle activity in a clonal pancreatic beta-cell line

We have investigated the effects of prolonged exposure (24 h) to the amino acid L-glutamine, on gene and protein expression using clonal BRIN-BD11 b-cells. Expression profiling of BRIN-BD11 cells was performed using oligonucleotide microarray analysis. Culture for 24 h with 10 mM L-glutamine compared with 1 mM resulted in substantial changes in gene expression with 148 genes upregulated more than 1$8-fold, and 18 downregulated more than 1$8-fold, including many genes involved in cellular signaling, metabolism, gene regulation, and the insulin-secretory response. Subsequent functional experiments confirmed that L-glutamine increased the activity of the Ca 2C regulated phosphatase calcineurin and the transcription factor Pdx1. Additionally, we demonstrated that b-cell-derived L-glutamate was released into the extracellular medium at high rates. As calcineurin is a regulator of the glutamate N-methyl-Daspartate (NMDA) receptor activity, we investigated the action of NMDA on nutrient-induced insulin secretion, and demonstrated suppressed insulin release. These observations indicate important long-term effects of L-glutamine in regulating b-cell gene expression, signaling, and secretory function.