Introduction

Hypoxia causes disorders in brain energy metabolism. One of perspective ways of treatment having an anti-hypoxic effect is hyperbaric oxygenation (HBO). There are clinical and laboratory studies that have demonstrated the effectiveness of HBO in different cases, for example, after CO poisoning¹. The in vivo studies of HBO influence on energy metabolism might be of interest, and ³¹P MR spectroscopy is a unique noninvasive method for it. The aim of this study is to reveal the effect of one low-pressure (1.2 atmosphere absolute, ATA) HBO session on ³¹P MRS metabolites of the normal human brain.

Materials and methods

Eleven healthy subjects with no contraindications to MR methods and HBO became the participants of this study. Each subject has passed diagnostic MRI (T1-, T2-weighted, FLAIR, DTI) that revealed no abnormalities. Philips Achieva 3.0T, ³¹P/¹H Dual bird-cage coil by Rapid Biomed and hyperbaric chamber Sechrist 3200 were used. The plan of the study is as follows: 1) in MRI scanner survey images (30 seconds), axial (1 minute), sagittal (1 minute) T2-weighted images and 2D ³¹P MRS (10 minutes) data were obtained; 2) the subject proceeded to the hyperbaric chamber for 50 minutes (5 minutes for achieving constant 1.2 ATA mode, 40 minutes at the mode and 5 minutes for decompression); after that step 1) was repeated. The axial and sagittal images were used for 2D ³¹P MRS voxels location, as it is demonstrated on figures 1 and 2. The match of spectroscopy voxels location before and after HBO session was provided by placing the spectroscopy slice symmetrically in relation to fissura longitudinalis cerebri on axial images, and by keeping the same distances from genu and splenium of corpus callosum to several spectroscopy voxels (see figure 1). The parameters of 2D ³¹P MRS: slice thickness = 30 mm, FOV = 200x200 mm, voxel size = 40x40 mm. Spectroscopy data was obtained with ISIS pulse sequence (TE = 0.3 ms, TR = 1900 ms, NSA = 16, FA = 35°, broadband NOE (mix time = 1560 ms) and decoupling).

Data processing

The 2D ³¹P data obtained preprocessing and quantification was performed in jMRUI 5.2 program. The FIDs of voxels that were completely located in the brain of a subject (shown on fig.2 with red frames) were averaged, two spectra remained for each subject: before and after HBO session. The integral intensities of spectral peaks were quantified using AMARES algorithm. For each subject in spectra before and after HBO session the intensities of individual peaks were normalized to the sum of integral intensities of all peaks (total ³¹P). The pH value before and after HBO session was calculated from PCr-Pi chemical shift difference. The statistical processing was performed in STATISTICA 12 program using Mann-Whitney U-criterion.

Results

The typical spectrum obtained in this study is demonstrated on figure 3. After HBO session there was a statistically significant (p<0.05) increase of α-ATP peak integral intensity relative to total ³¹P (see figure 4). No changes in other peak integral intensities relative to total ³¹P were revealed. HBO also had no effect on pH value.

Discussion

The revealed increase of α-ATP peak integral intensity while β-ATP remains unchanged testifies to the increase in intensities of signals that compose α-ATP peak besides ATP: α-ADP, nicotinamide adenine dinucleotide (NAD+ and NADH), uridine diphosphate glucose (UDPG). UDPG signal has two resonance frequencies: one of them is overlapped by an α-ATP peak, the second is at -9.72 ppm relative to PCr². Since this peak cannot be picked out of noise neither in spectrum before, nor in spectrum after HBO session, we may conclude that UDPG does not make a substantial contribution to α-ATP change discovered in this study. Change in ADP concentration can also hardly be a reason of α-ATP intensity increase because no change in γ-ATP peak intensity (that is a superposition of γ-ATP and β-ADP) stimulated by HBO session is revealed. The only hypothesis remaining is that the effect is caused by [NAD+] and/or [NADH] increase. The HBO is known to change chemical equilibrium of [NAD+]/[NADH] to increase [NAD+]³, however, the spectral resolution at 3T does not allow to separately analyze NAD+ and NADH, and to detach them from α-ATP peak. The nature of [NAD(H)] increase phenomenon revealed in this study is a subject of future research. Nonetheless, since [NAD(H)] plays an important role in cell energy metabolism⁴, we suppose that the result obtained might be a confirmation of HBO effectiveness even at low pressures (p=1.2 ATA) in the context of energy metabolism stimulation in human brain.

Acknowledgements

No acknowledgement found.