Urolithin metabotype A remodels the transcriptome of M2 macrophages towards a non-inflammatory profile

Background. In humans, ellagitannins (ETs), polyphenols present in nuts, seeds and some fruits such as pomegranates, can be metabolised by intestinal microbiota to urolithins (UTs), which controversial evidence [1] associates to anti-inflammatory and anti-oxidant properties. According to microbiota composition, humans metabolise ETs in line with one of three different metabolic phenotypes or metabotypes: metabotype A (urolithin A and conjugates), metabotype B (conjugates of urolithin B and isourolithin A, in addition to urolithin A), and metabotype 0 (not producing urolithins) [2]. Macrophages play a pivotal role in inflammatory diseases, including atherosclerosis, and differentiate in either M1 macrophages (with pro-inflammatory properties) or M2 macrophages (with anti-inflammatory properties) in response to the cytokine milieu. We hypothesised that ET metabotypes could differently affect macrophages, and hence may display a different potential for prevention of and protection from inflammatory diseases. Aim. To assess the effect(s) of physiological doses of UTs, mimicking the three different human metabotypes of ETs, on gene expression profile in human M1 and M2 polarised macrophages. Methods. Monocytes were isolated from healthy donors’ buffy coats and then stimulated to induce M1 or M2 phenotypes, in the presence or absence of different UT combinations, reproducing the A, B, and 0 metabotypes. The gene expression profile was analysed with whole human genome microarray technology. Gene expression data were analysed with GeneSpring GX v11.5; Differentially expressed genes were identified by Moderated t-test (Benjamini Hochberg correction p-value < 0.05). Gene enrichment analysis was applied on the significant differentially expressed list of genes. Results. The transcriptome of M1 macrophages was minimally influenced by UT metabotypes. In contrast, in M2 macrophages, metabotype A UTs induced extensive significant changes in gene expression of M2 macrophages, apparently enhancing their anti-inflammatory properties, by downregulating the focal adhesion and transendothelial migration pathways, and also amplifying their anti-senescence mechanisms, by upregulating lysosomal activity and DNA repair pathways. Metabotype B reduced the expression of key genes involved in leukocyte transendothelial migration. Conclusions. These findings indicate that metabotype A UTs cause an extensive remodelling of the transcriptomic platform of M2 macrophages, whereas metabotype B UTs induce relatively minor changes. These changes are compatible with an enhancement in M2 macrophages of anti-inflammatory properties and, only for metabotype A UTs, of anti-senescence mechanisms, including autophagy. These data suggest that the people with metabotype A may receive a much greater benefit from high ET intake towards organ damage/clinical events due to inflammatory diseases, in particular, atherosclerosis. Real time PCR validation will be performed to confirm these results. Acknowledgments. This study was supported by the Italian Ministry of Education, University and Research MIUR – SIR programme (no. RBSI14LHMB). References. [1]. Danesi F, Ferguson LR. Could pomegranate juice help in the control of inflammatory diseases? Nutrients. 2017; 9(9):E958. [2]. Tomás-Barberán FA, García-Villalba R, González-Sarrías A, Selma MV, Espín JC. Ellagic acid metabolism by human gut microbiota: consistent observation of three urolithin phenotypes in intervention trials, independent of food source, age, and health status. Journal of Agricultural and Food Chemistry. 2014; 62(28):6535–8.