Feasibility of direct mapping of cerebral fluorodeoxy‐D‐glucose metabolism in situ at subcellular resolution using soft X‐ray fluorescence

Abstract

Glucose metabolism is difficult to image with cellular resolution in mammalian brain tissue, particularly with 18 fluorodeoxy-D-glucose (FDG) positron emission tomography (PET). To this end, we explored the potential of synchrotron-based low-energy X-ray fluorescence (LEXRF) to image the stable isotope of fluorine (F) in phosphorylated FDG (DG-6P) at 1 lm 2 spatial resolution in 3-lm-thick brain slices. The excitation-dependent fluorescence F signal at 676 eV varied linearly with FDG concentration between 0.5 and 10 mM, whereas the endogenous background F signal was undetectable in brain. To validate LEXRF mapping of fluorine, FDG was administered in vitro and in vivo, and the fluorine LEXRF signal from intracellular trapped FDG-6P over selected brain areas rich in radial glia was spectrally quantitated at 1 lm 2 resolution. The subsequent generation of spatial LEXRF maps of F reproduced the expected localization and gradients of glucose metabolism in retinal Mü ller glia. In addition, FDG uptake was localized to periventricular hypothalamic tanycytes, whose morphological features were imaged simultaneously by X-ray absorption. We conclude that the high specificity of photon emission from F and its spatial mapping at 1 lm resolution demonstrates the ability to identify glucose uptake at subcellular resolution and holds remarkable potential for imaging glucose metabolism in biological tissue. V V C 2012 Wiley Periodicals, Inc.

Effect of selectively knocking down key metabolic genes in Müller glia on photoreceptor health

“…It was previously reported that only Müller glia took up radioactively labeled d ‐glucose in guinea pig retinas (C. Poitry‐Yamate & Tsacopoulos, 1991). This finding was recently reproduced in rat retinas using Positron Emission Tomography (PET) to image a stable isotope of fluorine after an intravenous injection of 18 fluorodeoxy‐ d ‐glucose (C. Poitry‐Yamate et al, 2013). The investigators observed high uptake and phosphorylation of 18 fluorodeoxy‐ d ‐glucose in Müller glial end feet and the inner synaptic cell layer, suggesting Müller glia can take up glucose.…”

“…Whether Müller glia can take up glucose at all is also controversial and depends on how it is studied (Kanow et al, 2017; C. Poitry‐Yamate et al, 2013; C. Poitry‐Yamate & Tsacopoulos, 1991). It was previously reported that only Müller glia took up radioactively labeled d ‐glucose in guinea pig retinas (C. Poitry‐Yamate & Tsacopoulos, 1991).…”

GABA and Glutamate Uptake and Metabolism in Retinal Glial (Müller) Cells

“…In the retina, glucose uptake and metabolism occurs predominantly in the inner processes of Müller cells, localized to the inner plexiform and ganglion cell layers (Poitry-Yamate et al, 2013) where glutamatergic signaling occurs. Müller cells produce substrates for the oxidative metabolism of photoreceptors and neurons including glutamine, lactate, pyruvate, alanine, and α-ketoglutarate (Figure 3) (Poitry-Yamate et al, 1995; Tsacopoulos et al, 1997).…”

Towards a multi‐element silicon drift detector system for fluorescence spectroscopy in the soft X‐ray regime

“…Because those are the main constituents of organic matter, their detection may be of paramount importance when studying biological systems. [1][2][3][4][5][6][7][8][9] Although diffraction grating-based LEXRF possesses excellent energy resolution better than 0.2 eV at Al-L emission on Al metal, [10] its use is limited to narrow energy windows and to certain geometries. LEXRF systems relying on the intrinsic energy resolution of spectroscopic, solid-state X-ray detectors such as silicon drift detectors (SDDs) offer more flexibility and faster specimen mapping at the expenses of an inferior energy resolution.…”

“…The low‐energy X‐ray fluorescence (XRF) (LEXRF) technique maximizes the detection and excitation of light elements, such as C, N, and O. Because those are the main constituents of organic matter, their detection may be of paramount importance when studying biological systems . Although diffraction grating‐based LEXRF possesses excellent energy resolution better than 0.2 eV at Al‐L emission on Al metal, its use is limited to narrow energy windows and to certain geometries.…”