A prospective pilot study of gut microbiome in cerebral vasospasm and delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage

A recent systematic review indicated that gut-microbiota-brain axis contributes to growth and rupture of intracranial aneurysms. However, gaps were detected in the role of intestinal microbiome in cerebral vasospasm (CVS) after aneurysmal subarachnoid hemorrhage (aSAH). This is the first pilot study aiming to test study feasibility and identify differences in gut microbiota between subjects with and without CVS following aSAH. A prospective nested case-control pilot study with 1:1 matching was conducted recruiting subjects with aSAH: cases with CVS; and controls without CVS based on the clinical picture and structured bedside transcranial Doppler (TCD). Fecal samples for microbiota analyses by means of 16S rRNA gene amplicon sequencing were collected within the first 96 h after ictus. Operational taxonomic unit tables were constructed, diversity metrics calculated, phylogenetic trees built, and differential abundance analysis (DAA) performed. At baseline, the groups did not differ significantly in basic demographic and aneurysm-related characteristics (p > 0.05). Alpha-diversity (richness and Shannon Index) was significantly reduced in cases of middle cerebral artery (MCA) vasospasm (p < 0.05). In DAA, relative abundance of genus Acidaminococcus was associated with MCA vasospasm (p = 0.00013). Two butyrate-producing genera, Intestinimonas and Butyricimonas, as well as [Clostridium] innocuum group had the strongest negative correlation with the mean blood flow velocity in anterior cerebral arteries (p < 0.01; rho = - 0.63; - 0.57, and - 0.57, respectively). In total, 16 gut microbial genera were identified to correlate with TCD parameters, and two intestinal genera correlated with outcome upon discharge. In this pilot study, we prove study feasibility and present the first preliminary evidence of gut microbiome signature associating with CVS as a significant cause of stroke in subjects with aSAH.