Assessment of glutamine synthetase activity by [¹³N]ammonia uptake in living rat brain

Abstract

Glutamine synthetase (GS) plays an important role in glutamate neurotransmission or neurological disorder in the brain. [(13) N]Ammonia blood flow tracer has been reported to be metabolically trapped in the brain via the glutamate-glutamine pathway. The present study investigated the effect of an inhibitor of GS on [(13) N]ammonia uptake in order to clarify the feasibility of measuring GS activity in the living brain. l-Methionine sulfoximine (MSO), a selective GS inhibitor was microinjected into the ipsilateral striatum in rats. [(13) N]Ammonia uptake was quantified by autoradiography method as well as small animal positron emission tomography (PET) scans. The GS activity of the brain homogenate was assayed from the γ-glutamyl transferase reaction. Autoradiograms showed a decrease of [(13) N]ammonia radioactivity on the MSO-injected side compared with the saline-injected side of the striatum. This reduction could be detected with a small animal PET scanner. MSO had no effect on cerebral blood flow measured by uptake of [(15) O]H2 O. The reduction of [(13) N]ammonia uptake was closely related to the results of GS activity assay. These results indicated that [(13) N]ammonia may enable measurement of GS activity in the living brain.

Hypoxic Preconditioning Maintains GLT-1 Against Transient Global Cerebral Ischemia Through Upregulating Cx43 and Inhibiting c-Src

“…Under ischemic conditions, the released glutamate from neurons and astrocytes shall be mainly taken up into astrocytes by GLT-1 and converted to glutamine by glutamine synthetase (GS), a key enzyme for the regulation of the extracellular glutamate in the glutamate-glutamine cycle localized primarily in astrocytes. This disorder of glutamate-glutamine cycle related to a metabolic trafficking mechanism between glia and neurons plays an important role in neuronal death after cerebral ischemia (Wang et al, 2013 ; Momosaki et al, 2015 ). The loss of GS would increase the level of brain glutamate (Wang et al, 2013 ).…”

Evaluation of [13N]ammonia positron emission tomography as a potential method for quantifying glutamine synthetase activity in the human brain

“…Coloured circles and lines (blue, green, red, magenta and cyan, for subjects 1-5, respectively) and grey symbols and lines (triangle/solid, square/dashed, diamond/dotted for subjects 6-8, respectively). All fits for all subjects are shown in Additional file 1: Figure S5 Kinetic modelling in these subjects was unable to reliably estimate the rate constant relating to GS activity (k 3 ) from that related [34]. In kinetic modelling of dynamic [ 13 N]ammonia PET images of the human brain, GS activity would be captured by the rate constant k 3 in an irreversible two tissue compartment model.…”

Therapeutic effects of astragaloside IV and Astragalus spinosus saponins against bisphenol A-induced neurotoxicity and DNA damage in rats

“…The specific activity of glutaminase (GA) in the brain regions was assayed according to the procedure described in Blanco et al (2015) . Glutamine synthetase (GS) activity was assayed in brain regions according to the modified method of Momosaki et al (2015) and expressed as mM of γ-glutamyl hydroxamate/min/mg protein. The concentration of glutamate (Glu) in different brain regions was measured enzymatically using glutamate dehydrogenase according to the method of Bernt & Bergmeyer (1974) .…”