Gut Microbiome Mediates Metformin’s Effects on Choroidal Neovascularization

Abstract

Purpose : Data show that metformin may prevent age-related macular degeneration (AMD) along with other age-related diseases. While the underlying mechanism of metformin’s antiaging properties is unknown, gut microbiome modulation has been proposed as a key pathway. We aim to assess if metformin prevents AMD via microbiome modulation using the germ free (GF) and fecal microbial transplantation (FMT) gnotobiotic models of laser-induced choroidal neovascularization (CNV).

Methods : GF C57Bl/6 male mice (GF-MET) were treated daily with metformin (300 mg/kg) or vehicle (GF-CTR) via oral gavage for seven days prior to laser and remained on same regimen for 7 days till mice were sacrificed for a total duration of 2 weeks. For the FMT groups, GF mice (GF-FMT-MET) or mice with eliminated microbiome with antibiotic/antifungal treatment (Abx-FMT-MET) were colonized with FMT from mice with conventional microbiome (SPF) treated with metformin for 2 weeks or FMT from vehicle gavaged SPF mice. Laser-induced CNV size and macrophage/microglia infiltration were evaluated with isolectin/Iba1 immunostaining of choroidal flatmounts. Fecal DNA extracted from fecal pellets was analyzed with PCR for sterility in GF groups and 16srRNA sequencing in FMT groups to ensure colonization.

Results : Metformin did not suppress CNV in GF mice (13009um2 +/- 3954 vs 11949+/-2564, p>0.05). Colonization with metformin-derived FMT decreased CNV by 2-fold compared to colonization with FMT from control mice in both GF and Abx groups. (26850nm2±5781 vs 13330nm2±4814, 20889±3208 vs 11384nm2±1663 respectively, p<0.05). Metformin derived FMT also suppressed Iba1+_macrophages/microglia infiltration in both GF and Abx groups within CNV (29.4±4.4 vs 13.9±4.1, 50.4±3.3 vs 40.1±3.8 respectively, p<0.05) as well as around CNV (5.5±1.3 vs 2.2±0.6, 2.9±0.8 vs 2.0±0.3 respectively, p<0.05). Fecal 16SrRNA confirmed successful transplantation with increased abundance of Bacteroidetes, Verrucomicrobiota, and decreased Clostridiales in mice receiving metformin derived FMTs.

Conclusions : These data suggest that microbiome modulation mediates metformin’s ability to suppress CNV, the hallmark lesion of advanced neovascular AMD and further support the crucial role of gut microbiome in CNV. Further studies are necessary to understand metformin-microbiome-CNV interactions.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.