Magnetic resonance spectroscopy of the occipital cortex and the cerebellar vermis distinguishes individual cats affected with alpha-mannosidosis from normal cats

Abstract

A genetic deficiency of lysosomal alpha-mannosidase causes the lysosomal storage disease alpha-mannosidosis (AMD), in which oligosaccharide accumulation occurs in neurons and glia. The purpose of this study was to evaluate the role of magnetic resonance spectroscopy (MRS) in detecting the oligosaccharide accumulation in AMD. Five cats with AMD and eight age-matched normal cats underwent in vivo MRS studies with a single voxel short echo time (20 ms) STEAM spectroscopy sequence on a 4.7T magnet. Two voxels were studied in each cat, from the cerebellar vermis and the occipital cortex. Metabolites of brain samples from these regions were extracted with perchloric acid and analyzed by high resolution NMR spectroscopy. A significantly elevated unresolved resonance signal between 3.4 and 4. ppm was observed in the cerebellar vermis and occipital cortex of all AMD cats, which was absent in normal cats. This resonance was shown to be from carbohydrate moieties by high resolution NMR of tissue extracts. Resonances from the Glc-NAc group (1.8-2.2 ppm) along with anomeric proton signals (4.6-5.4 ppm) from undigested oligosaccharides were also observed in the extract spectra from AMD cats. This MRS spectral pattern may be a useful biomarker for AMD diagnosis as well as for assessing responses to therapy.

Copyright (c) 2009 John Wiley & Sons, Ltd.

Figures

Figure 1

In vivo MR spectra of AMD (a, c) and normal (b, d) cat brains. The spectra were acquired from the cerebellar vermis (a, b) and the occipital cortex regions (c, d) of the brain. Increased resonances due to accumulation of oligosaccharides can be clearly observed from the spectra of AMD cats.

Figure 2

Normalized signal intensity (peak area/water area ratio) of the resonances at 1.8–2.2 and 3.4–4.3 ppm regions from the cerebellar vermis (a) and occipital cortex (b) regions of normal and AMD cats. A significant increase in signal intensity from AMD animals due to increased oligosaccharides (3.4–4.3 ppm region) and due to NAA +Glc-NAc (1.8–2.2 ppm region) is apparent. * indicates significant differences between the two groups (p <0.01).

Figure 3

High resolution NMR spectrum of brain extract from occipital cortex of AMD (a) and normal (b) cats. The presence of a broad resonance due to the mannose rich oligosaccharide (H-C-OH) protons is evident from the AMD spectrum. Asp, Aspartate; Cho, Choline; Cr, Creatine; Gln, Glutamine; Glu, Glutamate; Ins, Myo-Inositol; Lac, lactate; NAA, N Acetyl Aspartate; Tau, Taurine; TSP – 3, (trimethylsilyl)-[2,2,3,3,-2H4]-1-propionate.

Figure 4

High resolution NMR spectra showing the 1.95–2.2 ppm and the 5.0–5.5 ppm region of the spectra shown in Figure 3. The spectrum from the occipital cortex of AMD cat is shown in (a) and that from the same anatomical region of normal cat is shown in (b). Increased peaks due to the N-CH3 protons of Glc-NAc group of oligosaccharides is clear in the AMD spectrum (peaks 1–3). Additionally the anomeric protons signals from undigested oligosaccharides can also be seen in the AMD spectrum (peaks 4–9), which were not observed from the normal brain spectrum. Chemical shifts (ppm) are: 1 =2.046; 2 =2.063–2.065; 3 =2.085; 4 =5.052; 5 =5.109; 6 =5.193–5.199; 7 =5.217–5.237; 8 =5.314–5.37; 9 =5.359.

Figure 5

2D-TOCSY spectrum from the of brain extract of an AMD cat. Two prominent groups of cross peaks are observed, those close to the diagonal connecting carbohydrate ring protons in the 3.4–4.3 ppm region, and those connecting the carbohydrate ring protons to the anomeric oligosaccharide protons in the 4.6–5.4 ppm regions (circled).