Modulation of fecal miRNA highlights the preventive effects of a Mediterranean Low-Inflammatory Dietary Intervention in patients with Familial Adenomatous Polyposis (sRNA-Seq)

Diet can regulate gene and microRNA (miRNA) expression and various biological processes in the gut. Dietary interventions have been proposed as therapeutic approaches for several diseases, including cancer. In a pilot study, we showed that a low-inflammatory Mediterranean diet reduced markers of local and systemic inflammation in 27 patients with Familial Adenomatous Polyposis (FAP). We evaluated the changes induced by a low-inflammatory Mediterranean dietary intervention on fecal miRNome and intestinal tissue transcriptome in FAP subjects and assessed whether these changes could be associated with the beneficial effects observed in the pilot study. The diet modulated 41 fecal miRNAs, and this modulation remained for three months after the intervention. miR-5092-5p, miR-4527, and miR-3612-3p were positively correlated with adherence to the Mediterranean diet, while miR-6867-5p and miR-760-5p were negatively correlated with serum calprotectin levels. The altered miRNAs target genes mainly related to inflammatory pathways, DNA repair, metabolism, and cytoskeleton organization. Seventy genes were differentially expressed between adenoma and normal tissue. Most were different before the dietary intervention, but reached similar levels after the diet. Functional enrichment analysis identified the proinflammatory ERK1/2, cell cycle regulation and nutrient response pathways as commonly regulated by differentially expressed miRNAs and genes. These findings suggest that fecal miRNAs modulated by the diet reflect an epigenetic regulation occurring in tissues that seems to influence inflammatory pathways. miRNAs and genes with oncogenic and tumor suppressor functions are also regulated, highlighting the potential cancer-preventive effect of the low-inflammatory Mediterranean diet. Overall design: The study was a prospective nonrandomized pilot single-arm trial aimed at evaluating the effects of a low-inflammatory Mediterranean diet on FAP patients. Briefly, FAP individuals aged >18 years, who underwent prophylactic colectomy and were involved in the surveillance program at the Fondazione IRCCS Istituto Nazionale Tumori of Milan (INT), were eligible. Participants participated in dietary intervention activities that included 12 days of training, cookery, supportive education, and meals. The intervention lasted three months and was followed by another three months in which subjects continued the diet at home. The participants signed informed consent and were asked to donate blood and stool samples at baseline, at the end of the three-month dietary intervention, and at six months (respectively, T0, T1 and T2). They were also asked to complete a questionnaire on Mediterranean diet adherence (MEDAS). Finally, they underwent endoscopy at T0 and T2, in which tissue samples of healthy rectal mucosa and adenomas (when present) were collected as formalin-fixed and paraffin-embedded (FFPE) specimens.