The pathophysiological role of the gut microbiota in epilepsy: from preclinical to clinical evidence

A dysfunctional gut microbiota-brain axis is emerging as a novel pathogenic mechanism in epilepsy. To study which gut-related modifications are specifically linked to epileptogenesis, we used a multi-omics approach in a rat model of acquired epilepsy with 56% epilepsy incidence. The presence of spontaneous seizures was assessed in rats (n=46) at 5 months after status epilepticus induced by intra-amygdala kainate by 2 weeks (24/7) EEG monitoring: 26 rats developed epilepsy (Epi) while the remaining 20 rats (No-Epi) did not display spontaneous seizures. At the end of EEG monitoring, all rats were sacrificed for quantitative histopathological and immunohistochemical analyses of the gut structure, as well as for RTqPCR analysis of inflammation/oxidative stress markers. By comparing Epi (n=26), No-Epi rats (n=20), and sham controls (n=8), we found significant structural, cellular, and molecular alterations reflecting a dysfunctional gut, which were specifically associated with epileptogenesis. In particular, the villus height-to-crypt depth ratio and number of Goblet cells were reduced in the duodenum of Epi rats vs No-Epi rats and sham controls (p<0.01). Notably, villus height in the duodenum and jejunum (p<0.01) and crypt depth in the jejunum (p<0.05) were increased in No-Epi vs both Epi and sham controls. We also detected an enhanced Iba1-positive signal in macrophages, as well as increased IL1b and NFE2L2 transcripts in the small intestine of Epi vs both No-Epi and sham control rats (p<0.01), denoting the presence of inflammation and oxidative stress. Astroglial GFAP-immunostaining was similar in all groups. The metagenomic analysis showed that the ratio of two main dominant phyla (Bacteroidota-to-Firmicutes) was increased similarly in Epi and No-Epi rats vs sham control rats, likely reflecting changes related to status epilepticus. Notably, the relative abundance of families, genera and species associated with SCFA production was different in Epi vs No-Epi rats, depicting a bacterial fingerprint associated with epileptogenesis. Furthermore, Epi rats displayed a peripheral metabolic signature characterized by changes in lipid metabolism compared to both No-Epi and sham control rats.