Assessment of a one-week ketogenic diet on brain glycolytic metabolism and on the status epilepticus stage of a lithium-pilocarpine rat model

Abstract

The ketogenic diet (KD) has been shown to be effective in refractory epilepsy after long-term administration. However, its interference with short-term brain metabolism and its involvement in the early process leading to epilepsy remain poorly understood. This study aimed to assess the effect of a short-term ketogenic diet on cerebral glucose metabolic changes, before and after status epilepticus (SE) in rats, by using [¹⁸F]-FDG PET. Thirty-nine rats were subjected to a one-week KD (KD-rats, n = 24) or to a standard diet (SD-rats, n = 15) before the induction of a status epilepticus (SE) by lithium-pilocarpine administrations. Brain [¹⁸F]-FDG PET scans were performed before and 4 h after this induction. Morphological MRIs were acquired and used to spatially normalize the PET images which were then analyzed voxel-wisely using a statistical parametric-based method. Twenty-six rats were analyzed (KD-rats, n = 15; SD-rats, n = 11). The 7 days of the KD were associated with significant increases in the plasma β-hydroxybutyrate level, but with an unchanged glycemia. The PET images, recorded after the KD and before SE induction, showed an increased metabolism within sites involved in the appetitive behaviors: hypothalamic areas and periaqueductal gray, whereas no area of decreased metabolism was observed. At the 4th hour following the SE induction, large metabolism increases were observed in the KD- and SD-rats in areas known to be involved in the epileptogenesis process late-i.e., the hippocampus, parahippocampic, thalamic and hypothalamic areas, the periaqueductal gray, and the limbic structures (and in the motor cortex for the KD-rats only). However, no statistically significant difference was observed when comparing SD and KD groups at the 4th hour following the SE induction. A one-week ketogenic diet does not prevent the status epilepticus (SE) and associated metabolic brain abnormalities in the lithium-pilocarpine rat model. Further explorations are needed to determine whether a significant prevention could be achieved by more prolonged ketogenic diets and by testing this diet in less severe experimental models, and moreover, to analyze the diet effects on the later and chronic stages leading to epileptogenesis.

Figure 1

Study design. D-8 and D-1 are defined as eight and one day before status epilepticus (SE) respectively, H+4 is defined as four hours after SE.

Figure 2

Representation of the spatial normalization pipeline. The PET images are normalized using non-linear transformations estimated between the SIGMA MRI (used to create the Atlas) and the individual MRI of each rat. PET images were previously registered to their individual MRI.

Figure 3

Anatomical localization of the areas of increased metabolic activity between Day (-8) and Day (-1) and for KD subjects (n = 11). The SPM-T maps were obtained using a paired test (p < 0.001, uncorrected, k > 50 voxels) then projected onto two-dimensional slices of T1-weighted MRI. The colorbar represents the T-values.

Figure 4

Areas of increased [¹⁸F]-FDG uptake observed at the 4th hour after induction of SE (i.e., with a paired comparison between the PET images recorded before SE and at the 4^th hours after SE induction) in the 11 SD-rats (left panel) and 15 KD-rats (right panel). SPM-T maps are displayed with a Z score-based color scale, projected on T1-weighted MRI slices, and with the following parameters: p < 0.001 (no correction for multiple comparisons), and k > 38 voxels. The colorbar represents the T-values.