BACKGROUND:Both host and microbe metabolism of tryptophan (Trp) is altered in diabetes; however, the molecular mechanisms are incompletely understood. OBJECTIVE:We used strategies to increase either angiotensin converting enzyme-2 (ACE-2) dependent or independent Trp absorption in a model of type 2 diabetes, db/db mice, and tested whether the strategies could prevent development of diabetic retinopathy (DR), the most common microvascular complication of diabetes. Additionally, we investigated levels of Trp metabolites in humans with and without DR. DESIGN:Enhanced ACE-2 dependent Trp absorption was achieved with gavage of genetically modified bacteria that preserved intestinal ACE2:sodium coupled neutral amino acid transporter expression. ACE-2 independent Trp absorption was achieved by gavage of the Trp dipeptide (Isoleucine-Trp; IW) absorbed via solute carrier family 15 member 1. Both strategies were used either as a prevention (6 months treatment) or intervention (3 months treatment) and at the conclusion, intestinal, metabolic and retinal studies were performed including spatial mass spectroscopy (MS). Plasma Trp metabolites and gut permeability markers were measured in individuals with T2D with (n=30) and without (n=40) DR and compared with healthy controls (n=35). RESULTS:Lactobacillus paracasei-ACE2 or IW treatment prevented DR, corrected dysbiosis, enriched Trp-metabolising bacteria, improved gut barrier integrity, boosted incretin secretion and restored glucose homeostasis in db/db mice. Spatial MS identified indole propionic acid (IPA) as a metabolite in the retinal pigment epithelial layer protecting the posterior blood retinal barrier. T2D individuals with DR demonstrated elevated serum markers of endotoxemia and intestinal barrier disruption while showing reduced levels of the beneficial metabolite IPA and elevated levels of the toxic metabolite indole sulfate. CONCLUSION:Nutraceutical strategies that restore Trp metabolism or IPA serve as both a biomarker and a treatment for DR.

Reduction–oxidation factor-1 or apurinic/apyrimidinic endonuclease 1 (Ref-1/APE1) is a crucial redox-sensitive activator of transcription factors such as NF-κB, HIF-1α, STAT-3 and others. It could contribute to key features of ocular neovascularization including inflammation and angiogenesis; these underlie diseases like neovascular age-related macular degeneration (nAMD). We previously revealed a role for Ref-1 in the growth of ocular endothelial cells and in choroidal neovascularization (CNV). Here, we set out to further explore Ref-1 in neovascular eye disease. Ref-1 was highly expressed in human nAMD, murine laser-induced CNV and Vldlr−/− mouse subretinal neovascularization (SRN). Ref-1’s interaction with a redox-specific small molecule inhibitor, APX2009, was shown by NMR and docking. This compound blocks crucial angiogenic features in multiple endothelial cell types. APX2009 also ameliorated murine laser-induced choroidal neovascularization (L-CNV) when delivered intravitreally. Moreover, systemic APX2009 reduced murine SRN and downregulated the expression of Ref-1 redox regulated HIF-1α target carbonic anhydrase 9 (CA9) in the Vldlr−/− mouse model. Our data validate the redox function of Ref-1 as a critical regulator of ocular angiogenesis, indicating that inhibition of Ref-1 holds therapeutic potential for treating nAMD.

Purpose: We previously reported that the systemic administration of preprogrammed mouse hematopoietic bone marrow-derived progenitor cells (HSPCs) improved visual function and restored a functional retinal pigment epithelial (RPE) layer. Here, we investigated the potential impact of donor vs. host age on systemic cellular therapy in a murine model of retinal degeneration. Methods: HSPCs from young (8 weeks) and old (15 months) mice were programmed ex vivo with a lentiviral vector expressing the RPE65 gene (LV-RPE65) and systemically administering into young or old SOD2 KD mice. Visual loss and pathological changes were evaluated by electroretinogram (ERG), optical coherence tomography (OCT), histology, and immunohistochemistry. Results: Old donor HSPCs administered to old manganese superoxide dismutase (SOD2) knockdown (KD) recipient mice offered the least benefit. This was exemplified by the reduced recruitment and incorporation of LV-RPE65 HSPC into the RPE layer, as well as decreased improvement in visual function, retinal thinning, and limited reduction in oxidative damage and microglial activation. LV-RPE65 HSPC from young mice incorporated into the RPE layer of old SOD2 KD mice, though to a lesser extent than young cells administered to young hosts, offered some level of protection. By contrast, LV-RPE65 HSPCs from old mice, located to the subretinal space of young host mice, reduced visual loss, although some retinal pathology was observed. Conclusions: The administration of LV-RPE65 HSPC from old donors to old SOD2 KD mice offered the least improvement. Translational Relevance: Our findings highlight how both donor and recipient age impact the success of HSPC-based retinal therapy and using cells from aged donors for AMD treatment may have some limitations.

Purpose:We evaluated the safety and bioactivity of carboxyamidotriazole (CAI) using two approaches, a polymeric CAI-PLGA nanoemulsion in the mouse model of choroidal neovascularization (CNV) and CAI-loaded bioresorbable intravitreal implant in a rabbit model of vascular leakage. Methods:Mice underwent laser rupture of Bruch's membrane to induce CNV followed by a single (2 µL volume) intravitreal injection of either vehicle (n = 11); CAI nanoparticles (0.5 µg, 1 µg, 2 µg, 400 nM, 800 nM, and 1.6 µM, respectively); aflibercept 10 µg; or CAI nanoparticles (1 µg) + aflibercept 10 µg. New Zealand white rabbits underwent either sham intravitreal injection, aflibercept 500 µg injection, or CAI-PLGA intravitreal implant. Vascular leakage was induced with injections of VEGF on days 23 and 53. On days 30 and 60, all groups underwent vitreous fluorophotometry and fundus imaging. On day 60, the rabbits were euthanized, and their eyes were enucleated. Results:Intravitreal injection of the CAI-Nano at the dose of 1 µg significantly decreased choroidal neovascular volume, to 25% of saline on day 7 and 30% on day 14, which was comparable to aflibercept. Vitreous fluorophotometry revealed significantly lower levels of fluorescein in the aflibercept and CAI implant groups compared to the sham group on day 30. On day 60, the CAI implant group showed significantly reduced neovascularization as compared with the aflibercept groups. No toxicity was observed in any group. Conclusions:CAI in nanoparticle formulation or as a sustained release bioresorbable implant showed potent efficacy and caused no retinal toxicity in murine and rabbit models. Translational Significance:CAI demonstrates strong potential as a sustained release anti-angiogenic therapy with effective long-term durability.

AIMS/HYPOTHESIS:Within the small intestine, neutrophils play an integral role in preventing bacterial infection. Upon interaction with bacteria or bacteria-derived antigens, neutrophils initiate a multi-staged response of which the terminal stage is NETosis, formation of protease-decorated nuclear DNA into extracellular traps. NETosis has a great propensity to elicit ocular damage and has been associated with diabetic retinopathy and diabetic macular oedema (DME) progression. Here, we interrogate the relationship between gut barrier dysfunction, endotoxaemia and systemic and intestinal neutrophilia in diabetic retinopathy. METHODS:In a cohort of individuals with type 2 diabetes (n=58) with varying severity of diabetic retinopathy and DME, we characterised the abundance of circulating neutrophils by flow cytometry and markers of gut permeability and endotoxaemia by plasma ELISA. In a mouse model of type 2 diabetes, we examined the effects of diabetes on abundance and function of intestinal, blood and bone marrow neutrophils, gut barrier integrity, endotoxaemia and diabetic retinopathy severity. Pharmacological inhibition of NETosis was achieved by i.p. injection of the peptidyl arginine deiminase 4 inhibitor (PAD4i) GSK484 daily for 4 weeks between 6 and 7 months of type 2 diabetes. RESULTS:In human participants, neutrophilia was unique to individuals with type 2 diabetes with diabetic retinopathy and DME and was accompanied by heightened circulating markers of gut permeability. At late-stage diabetes, neutrophilia and gut barrier dysfunction were seen in db/db mice. The db/db mice exhibited an increase in stem-like pre-neutrophils in the intestine and bone marrow and a decrease in haematopoietic vascular reparative cells. In the db/db mouse intestine, enhanced loss of gut barrier integrity was associated with elevated intestinal NETosis. Inhibition of NETosis by the PAD4i GSK484 resulted in decreased abundance of premature neutrophils in the intestine and blood and resulted in neutrophil retention in the bone marrow compared with vehicle-treated db/db mice. Additionally, the PAD4i decreased senescence within the gut epithelium and yielded a slowing of diabetic retinopathy progression. CONCLUSIONS/INTERPRETATION:Severity of diabetic retinopathy and DME were associated with peripheral neutrophilia, gut barrier dysfunction and endotoxaemia in the human participants. db/db mice exhibited intestinal neutrophilia, specifically stem-like pre-neutrophils, which was associated with elevated NETosis and decreased levels of vascular reparative cells. Chronic inhibition of NETosis in db/db mice reduced intestinal senescence and NETs in the retina. These changes were associated with reduced endotoxaemia and an anti-inflammatory bone marrow milieu with retention of pre-neutrophils in the bone marrow and increased gut infiltration of myeloid angiogenic cells. Collectively, PAD-4i treatment decreased gut barrier dysfunction, restoring physiological haematopoiesis and levels of haematopoietic vascular reparative cells.

Retinal neovascularization impairs visual function and is a hallmark of several neovascular eye diseases, including retinopathy of prematurity (ROP) and proliferative diabetic retinopathy (PDR). Current treatments include intravitreal injections of anti-vascular endothelial growth factor (VEGF) biologics, but these therapeutics are often accompanied by high treatment burden and resistance to therapy. Prior studies indicate that APE1/Ref-1, a multifunctional protein with both endonuclease (APE1) and redox-mediated transcriptional regulatory activity (Ref-1), activates multiple pro-angiogenic and pro-inflammatory signaling pathways by chemically reducing key cysteine residues in transcription factors, thereby activating them. Here, we investigated the previously unexplored role of Ref-1 in retinal neovascularization. We demonstrate that Ref-1 is highly expressed in endothelial cells in human PDR and in the oxygen-induced retinopathy (OIR) mouse model of retinal neovascularization. Ref-1 is also highly expressed in microglia and astrocytes in OIR. A small molecule Ref-1 redox inhibitor, APX2009, decreased retinal neovascularization in OIR after systemic delivery. In vitro, hypoxic endothelial cells did not exhibit upregulation of Ref-1 but rather increased Ref-1 nuclear localization. APX2009 decreased hypoxic endothelial cell proliferation and HIF-1 alpha transcriptional activation. Thus, Ref-1 redox activity may be a novel therapeutic target for the treatment of retinal neovascularization, making APX2009 a promising systemic therapeutic approach for the treatment of vascular retinopathies such as ROP and PDR.

Ocular neovascular diseases including neovascular age-related macular degeneration (nvAMD) are widespread causes of blindness. Patients’ non-responsiveness to currently used biologics that target vascular endothelial growth factor (VEGF) poses an unmet need for novel therapies. Here, we identify protein arginine methyltransferase 5 (PRMT5) as a novel therapeutic target for nvAMD. PRMT5 is a well-known epigenetic enzyme. We previously showed that PRMT5 methylates and activates a proangiogenic and proinflammatory transcription factor, the nuclear factor kappa B (NF-κB), which has a master role in tumor progression, notably in pancreatic ductal adenocarcinoma and colorectal cancer. We identified a potent and specific small molecule inhibitor of PRMT5, PR5-LL-CM01, that dampens the methylation and activation of NF-κB. Here for the first time, we assessed the antiangiogenic activity of PR5-LL-CM01 in ocular cells. Immunostaining of human nvAMD sections revealed that PRMT5 is highly expressed in the retinal pigment epithelium (RPE)/choroid where neovascularization occurs, while mouse eyes with laser induced choroidal neovascularization (L-CNV) showed PRMT5 is overexpressed in the retinal ganglion cell layer and in the RPE/choroid. Importantly, inhibition of PRMT5 by PR5-LL-CM01 or shRNA knockdown of PRMT5 in human retinal endothelial cells (HRECs) and induced pluripotent stem cell (iPSC)-derived choroidal endothelial cells (iCEC2) reduced NF-κB activity and the expression of its target genes, such as tumor necrosis factor α (TNF-α) and VEGF-A. In addition to inhibiting angiogenic properties of proliferation and tube formation, PR5-LL-CM01 blocked cell cycle progression at G1/S-phase in a dose-dependent manner in these cells. Thus, we provide the first evidence that inhibition of PRMT5 impedes angiogenesis in ocular endothelial cells, suggesting PRMT5 as a potential therapeutic target to ameliorate ocular neovascularization.

Purpose:Sulforaphane (SFN) is an isothiocyanate derived from cruciferous vegetables that has therapeutic efficacy in numerous animal models of human disease, including mouse models of retinal degeneration. However, despite dozens of clinical trials, the compound remains to be tested as a clinical treatment for ocular disease. Numerous cellular activities of SFN have been identified, including the activation of Nrf2, a transcription factor that induces a battery of target gene products to neutralize oxidative and xenobiotic stresses. As Nrf2 expression and function reportedly decrease with aging, we tested whether the loss of the transcription factor limits the therapeutic efficacy of SFN against retinal degeneration.Methods:Six- to 8-month-old wild-type and Nrf2 knockout mice were treated with SFN beginning 1 month after ribozyme-mediated knockdown of superoxide dismutase 2 (SOD2) mRNA in the RPE. The impacts of MnSOD (the protein product of SOD2) knockdown and the efficacy of SFN were evaluated using a combination of electroretinography (ERG), spectral domain optical coherence tomography (SD-OCT), and postmortem histology.Results:SFN restored the ERG photopic b-wave suppressed by MnSOD loss in wild-type mice, but not in the Nrf2 knockout mice. In contrast, ERG scotopic a- and b-wave loss was not restored for either genotype. SFN significantly improved retinal thickness in the Nrf2 knockout mice with MnSOD knockdown, but this was not observed in the wild-type mice. In both genotypes, SFN treatment reduced morphological markers of RPE atrophy and degeneration, although these improvements did not correlate proportionally with functional recovery.Conclusions:These findings highlight the capacity of SFN to preserve cone function, as well as the potential challenges of using the compound as a standalone treatment for age-related retinal degeneration under conditions associated with reduced Nrf2 function.

Neovascular or “wet” age-related macular degeneration (nAMD) is a leading cause of blindness among older adults. Choroidal neovascularization (CNV) is a major pathological feature of nAMD, in which abnormal new blood vessel growth from the choroid leads to irreversible vision loss. There is a critical need to develop novel therapeutic strategies to address limitations of the current anti-vascular endothelial growth factor biologics. Previously, we identified soluble epoxide hydrolase (sEH) as a possible therapeutic target for CNV through a forward chemical genetic approach. The purpose of this study was to validate sEH as a target by examining retinal expression of sEH protein and mRNA by immunohistochemistry and RNAscope in situ hybridization, respectively, and to assess the efficacy of an adeno-associated virus (AAV) vector designed to knock down the sEH gene, Ephx2, in the murine laser-induced (L-) CNV model. nAMD patient postmortem eye tissue and murine L-CNV showed overexpression of sEH in photoreceptors and retinal pigment epithelial cells. Ephx2 knockdown significantly reduced CNV and normalized mRNA expression levels of CNV-related inflammatory markers. Thus, this study further establishes sEH as a promising therapeutic target against CNV associated with nAMD.

The vascular endothelial growth factor receptors (VEGFRs) can shape the neovascular phenotype of vascular endothelial cells when translocated to the nucleus, however the spatial and temporal changes in the intracellular distribution and translocation of VEGFRs to the nucleus and the organelles involved in this process is unclear. This study reports the effect of exogenous VEGF on translocation of VEGFRs and organelles in micro- and macrovascular endothelial cells. We showed that VEGF is responsible for: a rapid and substantial nuclear translocation of VEGFRs; VEGFR1 and VEGFR2 exhibit distinct spatial, temporal and structural translocation characteristics both in vitro and in vivo and this determines the nuclear VEGFR1:VEGFR2 ratio which differs between microvascular and macrovascular cells; VEGFR2 nuclear translocation is associated with the endosomal pathway transporting the receptor from Golgi in microvascular endothelial cells; and an increase in the volume of intracellular organelles. In conclusion, the nuclear translocation of VEGFRs is both receptor and vessel (macro versus micro) dependent and the endosomal pathway plays a key role in the translocation of VEGFRs to the nucleus and the subsequent export to the lysosomal system. Modulating VEGF-mediated VEGFR1 and VEGFR2 intracellular transmigration pathways may offer an alternative for the development of new anti-angiogenic therapies.

BACE1 is a key enzyme facilitating the generation of neurotoxic β-amyloid (Aβ) peptide. However, given that BACE1 has multiple substrates we explored the importance of BACE1 in the maintenance of retinal pigment epithelial (RPE) cell homeostasis under oxidative stress. Inhibition of BACE1 reduced mitochondrial membrane potential, increased mitochondrial fragmentation, and increased cleaved caspase-3 expression in cells under oxidative stress. BACE1 inhibition also resulted in significantly lower levels of mitochondrial fusion proteins OPA1 and MFN1 suggesting a higher rate of mitochondrial fission while increasing the levels of mitophagic proteins Parkin and PINK1 and autophagosome numbers. In contrast, BACE2 had minimal effect on cellular response to oxidative stress. In summary, our results emphasize the importance of BACE1 in augmenting cellular defense against oxidative stress by protecting mitochondrial dynamics.

Low doses of nitrite, close to physiological levels, increase blood flow in normal and ischemic tissues through a nitric oxide (NO) dependent mechanism. Given that nitrite therapy and dietary supplementation with vegetables high in nitrate (e.g. beets) are gaining popularity we decided to determine if low doses of nitrite impact the development of choroidal neovascularization (CNV), a key feature of wet age related macular degeneration (AMD). Sodium nitrite (at 50 mg/L, 150 mg/L, and 300 mg/L), nitrate (1 g/L) or water alone were provided in the drinking water of C57BL/6 J mice aged 2 or 12 months. Mice were allowed to drink ad libitum for 1 week at which time laser-induced choroidal neovascularization (L-CNV) was induced. The mice continued to drink the supplemented water ad libitum for a further 14 days at which point optical coherence tomography (OCT) was performed to determine the volume of the CNV lesion. Blood was drawn to determine nitrite and nitrate levels and eyes taken for histology. CNV volume was 2.86 × 107 μm3 (±0.4 × 107) in young mice on water alone but CNV volume more than doubled to >6.9 × 107 μm3 (±0.8 × 107) in mice receiving 300 mg/L nitrite or 7.34 × 107 μm3 (±1.4 × 107) in 1 g/L nitrate (p < 0.01). A similar trend was observed in older mice. CNV volume was 5.3 × 107 μm3 (±0.5 × 107) in older mice on water alone but CNV volume almost doubled to approximately 9.3 × 107 μm3 (±1.1 × 107) in mice receiving 300 mg/L nitrite or 8.7 × 107 μm3 (±0.9 × 107) 1 g/L nitrate (p < 0.01). Plasma nitrite levels were highest in young mice receiving 150 mg/L in the drinking water with no changes in plasma nitrate observed. In older mice, drinking water nitrite did not significantly change plasma nitrite, but plasma nitrate was increased. Plasma nitrate was elevated in both young and old mice provided with nitrate supplemented drinking water. Our data demonstrate that the CNV lesion is larger in older mice compared to young and that therapeutic levels of oral nitrite increase the volume of CNV lesions in both young and older mice. Therapeutic nitrite or nitrate supplementation should be used with caution in the elderly population prone to CNV.

Purpose Previously, we reported that the intravenous injection of bone marrow-derived cells (BMDC) infected with lentivirus expressing the human RPE65 gene resulted in the programming of BMDC to promote visual recovery in a mouse model of age-related macular degeneration (AMD). The aim of this study was to characterize the spatial and temporal recruitment of these programmed BMDC to the retinal pigment epithelial (RPE) layer. Methods C57BL/6J female mice received a subretinal injection of AAV1-SOD2 ribozyme to knock down (KD) superoxide dismutase 2 (SOD2) and induce AMD-like pathology. BMDC were isolated from-GFP(+) mice and infected with a lentivirus expressing RPE65. One month after SOD2 KD, fifty thousand-GFP(+) RPE65-BMDC were injected in the mouse tail vein. Animals were terminated at different time points up to 60 min following cell administration, and localization of-GFP(+) cells was determined by fluorescence microscopy of neural retina and RPE flat mounts and tissue sections. Results GFP(+) RPE65-BMDC were observed in SOD2 KD neural retina and RPE as early as 1 min following administration. With increasing time, the number of cells in the neural retina decreased, while those in the RPE increased. While the number of cells in peripheral and central retina remained similar at each time point, the number of BMDC recruited to the central RPE increased in a time-dependent manner up to a maximum by 60 min post administration. Immunohistochemistry of cross-sections of the RPE layer confirmed the incorporation of donor-GFP(+) BMDC into the RPE layer and that these -GFP(+) human RPE65 expressing cells co-localized with murine RPE65. No-GFP(+) cells were observed in the neural retina or RPE layer of normal uninjured control eyes. Conclusions Our study shows that systemically administered-GFP(+) RPE65-BMDC can reach the retina within minutes and that the majority of these BMDC are recruited to the injured RPE layer by 60 min post injection.

Reduction of salivary nitrate to nitrite by oral nitrate reductase (NR) expressing bacteria has emerged as an integral pathway in regulating nitric oxide (NO) homeostasis and signaling. The oral microbiome is critical for this pathway. Variations in this pathway may underlie variable responses in the magnitude by which dietary or therapeutic nitrate modulates NO-signaling. The relationships between oral microbes and NR activity, and the factors that affect this relationship remain unclear however. Using a cross-sectional study design, the objective of this study was to determine the relationships between oral microbes and oral NR activity using a protocol that directly measures initial NR activity. Tongue swabs were collected from 28 subjects ranging in age from 21 to 73y. Initial NR activity showed a bell-shaped dependence with age, with activity peaking at ~40-50y and being lower but similar between younger (20-30y) and older (51–73) individuals. Microbiome relative abundance and diversity analyses, using 16s sequencing, demonstrated differences across age and identified both NR expressing and non-expressing bacteria in modulating initial NR activity. Finally, initial NR activity was measured in 3mo and 13mo old C57BL/6J mice. No differences in bacterial number were observed. However initial NR activity was significantly (80%) lower in 13mo old mice. Collectively, these data suggest that age is a variable in NR activity and may modulate responsiveness to dietary nitrate.