Glycine-Conjugated Bile Acids Protect RPE Tight Junctions against Oxidative Stress and Inhibit Choroidal Endothelial Cell Angiogenesis In Vitro

Abstract

We previously demonstrated that the bile acid taurocholic acid (TCA) inhibits features of age-related macular degeneration (AMD) in vitro. The purpose of this study was to determine if the glycine-conjugated bile acids glycocholic acid (GCA), glycodeoxycholic acid (GDCA), and glycoursodeoxycholic acid (GUDCA) can protect retinal pigment epithelial (RPE) cells against oxidative damage and inhibit vascular endothelial growth factor (VEGF)-induced angiogenesis in choroidal endothelial cells (CECs). Paraquat was used to induce oxidative stress and disrupt tight junctions in HRPEpiC primary human RPE cells. Tight junctions were assessed via transepithelial electrical resistance and ZO-1 immunofluorescence. GCA and GUDCA protected RPE tight junctions against oxidative damage at concentrations of 100–500 µM, and GDCA protected tight junctions at 10–500 µM. Angiogenesis was induced with VEGF in RF/6A macaque CECs and evaluated with cell proliferation, cell migration, and tube formation assays. GCA inhibited VEGF-induced CEC migration at 50–500 µM and tube formation at 10–500 µM. GUDCA inhibited VEGF-induced CEC migration at 100–500 µM and tube formation at 50–500 µM. GDCA had no effect on VEGF-induced angiogenesis. None of the three bile acids significantly inhibited VEGF-induced CEC proliferation. These results suggest glycine-conjugated bile acids may be protective against both atrophic and neovascular AMD.

Microbiota mitochondria disorders as hubs for early age-related macular degeneration

“…In vitro, TUDCA promoted RPE cell integrity and diminished VEGF-induced choroidal endothelial cell migration and tube formation [ 242 ], as well as protecting RPE tight junctions and inhibiting choroidal neovascularization in an in vitro model of neovascular AMD [ 243 ]. Systemic administration of UDCA and TUDCA significantly suppressed rat models of laser-induced choroidal neovascularization, and the VEGF levels in the retina were lower in the treated group as compared to controls, which might be associated with anti-inflammatory action [ 244 ]. Furthermore, systemic administration of UDCA and TUDCA also preserved photoreceptors after retinal detachment and upregulated antiapoptotic, antioxidant, and anti-inflammatory genes, suggesting that their oral administration may be a potential neuroprotective adjuvant therapy in retinal detachment and other retinal degenerative diseases like AMD [ 245 , 246 ].…”

Mitochondrial Dysfunction and Endoplasmic Reticulum Stress in Age Related Macular Degeneration, Role in Pathophysiology, and Possible New Therapeutic Strategies

“…CA, DCA, and UDCA are conjugated with glycine to form glycocholic acid (GCA), glycodeoxycholic acid (GDCA), and glycoursodeoxycholic acid (GUDCA), respectively, and UDCA is conjugated with taurine to form tauroursodeoxycholic acid (TUDCA). In addition to increasing hydrophilicity, conjugation of bile acids with taurine or glycine increases solubility and limits passive diffusion across the cell membrane [ 110 , 111 ].…”

“…In two independent studies, Warden et al recently assessed the ability of glycine and taurine-conjugated bile acids at different concentrations, to inhibit features of AMD modeled in vitro. On the one hand they evaluated their capacity to protect human primary RPE cells tight junction integrity, assessed by ZO-1 immunofluorescence and transepithelial electrical resistance measurements, against paraquat-induced oxidative damage; and on the other hand, they tested their ability to inhibit VEGF-induced choroidal endothelial cells angiogenesis, evaluated through cell proliferation, cell migration, and tube formation assays in immortalized macaque choroidal endothelial cells [ 111 ]. With these experiments, authors found that GCA, GDCA, and GUDCA preserved RPE tight junctions’ function and structure under oxidative stress conditions.…”

“…With these experiments, authors found that GCA, GDCA, and GUDCA preserved RPE tight junctions’ function and structure under oxidative stress conditions. While none of the studied bile acids affected VEGF-induced choroidal endothelial cells’ proliferation, GCA and GUDCA, but not GDCA, significantly inhibited VEGF-induced cell migration and tubulogenesis [ 111 ].…”

“…A bile acid transporter called OATP1B3 has been found to be expressed in the retina and has been shown to prefer taurine- and glycine-conjugated bile acids over unconjugated bile acids [ 133 , 134 ]. Additionally, conjugated bile acids have been shown to activate other receptors like TGR5 and S1P2, suggesting that differences in hydrophobicity are relevant and can alter the effect of bile acids on endothelial cells [ 111 ].…”