Mineralocorticoid Receptor Pathway and Its Antagonism in a Model of Diabetic Retinopathy

RAAS in diabetic retinopathy: mechanisms and therapies

Diabetic retinopathy (DR) is a complication of diabetes with a complex pathophysiology and multiple factors involved. Recently, it has been found that the upregulation of the renin-angiotensin-aldosterone system (RAAS) leads to overexpression of angiotensin II (Ang II), which induces oxidative stress, inflammation, and angiogenesis in the retina. Therefore, RAAS may be a promising therapeutic target in DR. Notably, RAAS inhibitors are often used in the treatment of hypertension. Still, the potential role and mechanism of DR must be further studied. In this review, we discuss and summarize the pathology and potential therapeutic goals of RAAS in DR.

Review of lipocalin-2-mediated effects in diabetic retinopathy

BACKGROUND

Studies have uncovered LCN2 as a marker of inflammation strongly related to obesity, insulin resistance, and abnormal glucose metabolism in humans, and is involved in vascular diseases, inflammatory diseases, and neurological diseases. In recent years, studies have shown that elevated levels of LCN2 have a strong association with diabetic retinopathy (DR), but the pathogenesis is unknown. Here, we reviewed the relevant literature and compiled the pathogenesis associated with LCN2-induced DR.

METHODS

We searched PubMed and Web of Science electronic databases using "lipocalin-2, diabetic retinopathy, retinal degeneration, diabetic microangiopathies, diabetic neuropathy and inflammation" as subject terms.

RESULTS

In diabetic retinal neuropathy, LCN2 causes impaired retinal photoreceptor function and retinal neurons; in retinal microangiopathy, LCN2 induces apoptosis of retinal vascular endothelial cells and promotes angiogenesis; in retinal inflammation, increased secretion of LCN2 recruits inflammatory cells and induces pro-inflammatory cytokines. Moreover, LCN2 has the potential as a biomarker for DR. Recent studies have shown that retinal damage can be attenuated by silencing LCN2, which may be associated with the inhibition of caspase-1-mediated pyroptosis, and LCN2 may be a new target for the treatment of DR.

CONCLUSIONS

In conclusion, LCN2, involved in the development of diabetic retinopathy, is a key factor in diabetic retinal microangiopathy, neurodegeneration, and retinal inflammation. LCN2 is likely to be a novel molecular target leading to DR, and a more in-depth study of the pathogenesis of DR caused by LCN2 may provide considerable benefits for clinical research and potential drug development.

Association between lipocalin-2 levels and diabetic retinopathy in patients with overweight/obese type 2 diabetes mellitus

AIMS

The study aimed to investigate the association between lipocalin-2 (LCN-2) levels and diabetic retinopathy (DR) in patients with overweight/obese type 2 diabetes mellitus(T2DM), and to explore the mechanism of LCN-2 in overweight/obese DR.

METHODS

The study involved 237 T2DM inpatients divided into the normal group and overweight/obese group, and the two groups were further divided into two subgroups according to the presence or absence of DR. The demographic data and biochemical parameters were measured.

RESULTS

LCN-2 levels in overweight/obese groups were higher than those in normal groups (P < 0.001 for all), and patients with DR had higher levels of LCN-2 than those without DR(P < 0.05 for all) in normal groups and overweight/obese groups. Binary logistic regression analysis showed that no significant significance was observed for LCN-2 levels compared to those below the median in the normal group, but individuals with LCN-2 levels above the median had 4.198 times higher risk of developing DR than those below the median (OR = 4.198, 95% CI = 1.676-10.516) after adjustment for potential confounding factors in the overweight/obese group. In the total, normal and overweight/obese groups, the prediction capacity of LCN-2 for DR was 1.56, 1.58 and 1.65 times, respectively. Conclusionsː In conclusion, our study found that LCN-2 levels were higher in overweight/obese patients with DR, and LCN-2 was an independent predictor of DR in T2DM patients with overweight/obese. In addition, LCN-2 may be a valuable predictor of DR-like factors such as the duration of diabetes and hypertension.

Spironolactone Eyedrop Favors Restoration of Corneal Integrity after Wound Healing in the Rat

Abnormal corneal wound healing can compromise corneal transparency and lead to visual impairment. Mineralocorticoid receptor antagonists (MRA) are promising candidates to promote corneal remodeling with anti-inflammatory properties and lack gluococorticoids-associated side effects. In this preclinical study, a new polymer-free hydroxypropyl-gamma-cyclodextrin-based eyedrop containing 0.1% spironolactone (SPL), a potent but non-water-soluble MRA, was investigated for its ocular surface tolerance and efficacy in a rat model of corneal wound healing. SPL eyedrops were stable for up to 9 months at 4 °C. The formulation was well-tolerated since no morphological changes or inflammatory reactions were observed in the rat cornea after multiple daily instillations over 7 days. SPL eyedrops accelerated rat corneal wound healing, reduced corneal edema and inflammation, enhanced epithelial integrity, and improved nerve regeneration, suggesting restoration of corneal homeostasis, while potassium canrenoate, an active and soluble metabolite of SPL, had no effect. SPL eyedrops could benefit patients with impaired corneal wound healing, including that secondary to glucocorticoid therapy. Repurposing known drugs with known excipients will expedite translation to the clinic.

Diabetic Retinopathy - a Common Disease

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus and one of the leading causes of visual impairment in working age individuals in the western world. The treatment of DR depends on its severity, so it is of great importance to detect patients as early as possible, in order to initiate early treatment and preserve vision. Despite currently insufficient screening participation, patients with diabetes already visit ophthalmological practices and clinics above average. Their medical care, including DR diagnostics and treatment has been making up an increasing proportion of ophthalmic activity for years. Since the prevalence of diabetes is increasing dramatically worldwide and a further increase is also predicted for Germany, the challenge for ophthalmologists is likely to grow considerably. As the same time, the diagnostic possibilities for differentiating DR and the therapeutic measures, especially with IVOM therapy, are becoming more and more complex, which increases the time burden in everyday clinical practice. The hope to avoid healthcare deficits and to further improve screening rates and visual acuity prognosis in patients with DR is based, among other things, on camera-assisted screening supported by artificial intelligence. Better diabetes management to reduce the prevalence of DR, as well as longer-acting drugs to treat DR, could also improve the care and help reduce the burden on ophthalmology practices.

Ocular steroidome in human eyes and in eyes with complex central serous chorioretinopathy (CSCR)

The exact link between systemic and ocular endogenous corticoids (steroidome) is unclear and whether the ocular steroidome is altered in CSCR eyes is unknown. The aims of this study were to analyze the human steroidome in the aqueous humor as a function of age, sex and time of the day, to correlate systemic and ocular steroidome and to analyze the ocular steroidome in long lasting complex inactive CSCR. Based on our results, we present two CSCR cases treated by the combination of oral mineralocorticoid antagonist and glucocorticoids drops. In a cross-sectional study, aqueous humor (AH) was collected between 8am and 6 pm from 50 unaffected individuals (25 men and 25 women) and from 14 patients with chronic CSCR, during cataract surgery. In addition, simultaneous serum and AH were collected from 27 individuals undergoing cataract surgery and, simultaneous AH and vitreous were collected from 9 patients undergoing cataract and vitrectomy to estimate corticoids levels in the different compartments. The steroidome was determined using a LC-MS/MS method that quantifies 13 endogenous corticoids from the gluco, mineralocorticoid and androgen pathways. In AH and vitreous, the highest corticoid level is reached by cortisol (F), that represents less than 10% of F serum level. The cortisol levels in the serum did not correlate with ocular cortisol levels. Serum and ocular cortisone (E) levels correlate, although less than 5% of circulating E reaches the eye. The only mineralocorticoids measured in the AH were corticosterone (B) and its inactive form, the 11-desoxycorticosterone (A). There was no influence of circadian rhythm on cortisol ocular levels and there was no correlation between the age or the sex and the level of F, E, A, and B. In eyes with chronic inactive CSCR, the levels of the active glucocorticoid form F was lower than in control eyes and the F/E ratio was reduced by 50% but the B/A ratio was higher indicating imbalance towards active mineralocorticoids. Base on this observation, we propose to combine an antagonist of the mineralocorticoid receptor together with topical glucocorticoids in two CSCR patients, resistant to all other treatments, with favorable outcome. Our results indicate that the ocular psteroidome is highly regulated suggesting a local metabolism of ocular corticoids. In eyes with long-lasting complex inactive CSCR, the steroidome analysis shows lower active glucocorticoids and higher active mineralocorticoids.

Topical Spironolactone in the Treatment of Evaporative Dry Eye Disease

Meibomian gland dysfunction (MGD) is associated with evaporative dry eye syndrome, which is characterized by a reduction in meibum secretion and tear film instability. Present treatments provide only temporary relief, thereby necessitating the exploration of novel therapeutic strategies for chronic treatment. This study aims to evaluate topical spironolactone, a medication with anti-mineralocorticoid, anti-androgenic, and anti-inflammatory properties, in treating dry eye. A retrospective observational study was performed on the medical records of 102 patients diagnosed with dry eye disease. These patients were categorized into two groups based on their Schirmer's tear test scores. Various clinical indicators, including subjective global assessment scores, visual acuity, keratitis, conjunctival staining scores, and lid margin health, were evaluated prior to and following treatment with topical spironolactone eye drops. The group with higher Schirmer's scores exhibited improvement in self-reported global assessment scores after treatment. Significant improvements were also observed in keratitis and conjunctival staining scores, visual acuity, and lid margin inflammation. Similarly, the group with lower Schirmer's scores demonstrated improvements in self-reported global assessment scores and visual acuity after treatment. Topical spironolactone may improve tear film quality and address the inflammatory processes associated with MGD and evaporative dry eye. Moreover, the topical administration of spironolactone in an ocular vehicle appears to be well tolerated and may mitigate the risk of systemic adverse effects. Further studies are warranted to explore the long-term effects of topical spironolactone in the treatment of evaporative dry eye disease.

Finerenone, a Non-Steroidal Mineralocorticoid Receptor Antagonist, Reduces Vascular Injury and Increases Regulatory T-Cells: Studies in Rodents with Diabetic and Neovascular Retinopathy

Vision loss in diabetic retinopathy features damage to the blood-retinal barrier and neovascularization, with hypertension and the renin-angiotensin system (RAS) having causal roles. We evaluated if finerenone, a non-steroidal mineralocorticoid receptor (MR) antagonist, reduced vascular pathology and inflammation in diabetic and neovascular retinopathy. Diabetic and hypertensive transgenic (mRen-2)27 rats overexpressing the RAS received the MR antagonist finerenone (10 mg/kg/day, oral gavage) or the angiotensin-converting enzyme inhibitor perindopril (10 mg/kg/day, drinking water) for 12 weeks. As retinal neovascularization does not develop in diabetic rodents, finerenone (5 mg/kg/day, i.p.) was evaluated in murine oxygen-induced retinopathy (OIR). Retinal vasculopathy was assessed by measuring gliosis, vascular leakage, neovascularization, and VEGF. Inflammation was investigated by quantitating retinal microglia/macrophages, pro-inflammatory mediators, and anti-inflammatory regulatory T-cells (Tregs). In diabetes, both treatments reduced systolic blood pressure, gliosis, vascular leakage, and microglial/macrophage density, but only finerenone lowered VEGF, ICAM-1, and IL-1ß. In OIR, finerenone reduced neovascularization, vascular leakage, and microglial density, and increased Tregs in the blood, spleen, and retina. Our findings, in the context of the FIDELIO-DKD and FIGARO-DKD trials reporting the benefits of finerenone on renal and cardiovascular outcomes in diabetic kidney disease, indicate the potential of finerenone as an effective oral treatment for diabetic retinopathy.

Aldosterone as a Possible Contributor to Eye Diseases

Aldosterone, an effector molecule of the renin-angiotensin-aldosterone system (RAAS), has been receiving more attention in the field of ophthalmology because of its possible role in the pathogenesis of various eye diseases or abnormalities; it may even become a target for their treatment. Primary aldosteronism, a typical model of a systemic aldosterone excess, may cause vision loss due to various ocular diseases, such as retinal vein occlusion, central serous chorioretinopathy, and, possibly glaucoma. RAAS components are present in various parts and types of cells present in the eye. Investigations of the local RAAS in various animal models of diabetic macular edema, retinal vein occlusion, retinopathy of prematurity, central serous chorioretinopathy, and glaucoma have found evidence that aldosterone or mineralocorticoid receptors may exacerbate the pathology of these disorders. Further studies are needed to elucidate whether the modulation of aldosterone or mineralocorticoid receptors is an effective treatment for preventing vision loss in patients with eye diseases.

Nonsteroidal Mineralocorticoid Receptor Antagonism by Finerenone—Translational Aspects and Clinical Perspectives across Multiple Organ Systems

Perception of the role of the aldosterone/mineralocorticoid receptor (MR) ensemble has been extended from a previously renal epithelial-centered focus on sodium and volume homeostasis to an understanding of their role as systemic modulators of reactive oxygen species, inflammation, and fibrosis. Steroidal MR antagonists (MRAs) are included in treatment paradigms for resistant hypertension and heart failure with reduced ejection fraction, while more recently, the nonsteroidal MRA finerenone was shown to reduce renal and cardiovascular outcomes in two large phase III trials (FIDELIO-DKD and FIGARO-DKD) in patients with chronic kidney disease and type 2 diabetes, respectively. Here, we provide an overview of the pathophysiologic role of MR overactivation and preclinical evidence with the nonsteroidal MRA finerenone in a range of different disease models with respect to major components of the aggregate mode of action, including interfering with reactive oxygen species generation, inflammation, fibrosis, and hypertrophy. We describe a time-dependent effect of these mechanistic components and the potential modification of major clinical parameters, as well as the impact on clinical renal and cardiovascular outcomes as observed in FIDELIO-DKD and FIGARO-DKD. Finally, we provide an outlook on potential future clinical indications and ongoing clinical studies with finerenone, including a combination study with a sodium–glucose cotransporter-2 inhibitor.

The Mineralocorticoid receptor signal could be a new molecular target for the treatment of diabetic retinal complication

BACKGROUND

Activation of the mineralocorticoid receptor (MR) is involved in the pathophysiology of diabetic vascular complications. In recent years, it has been indicated that the MR expressed in retinal Müller cells plays an important role in regulating the potassium and water balance in the retina. Therefore, it has also been speculated that abnormal MR signaling contributes to edematous diseases of the retina.

RESEARCH DESIGN AND METHODS

We examined the effect of high-glucose conditions on MR protein and mRNA levels in human retinal Müller cells and changes in cell size in vitro. We also investigated MR transcriptional activity and signaling in high-glucose conditions.

RESULTS

The MR protein increased by 2.2-fold with high-glucose treatment. Additionally, high-glucose treatment induced Müller cell swelling. Aldosterone-induced MR transcriptional activity was enhanced in high-glucose conditions, resulting in the upregulation of αENaC, AQP4 and Kir4.1 mRNA. Treatment with an MR antagonist led to the suppression of aldosterone-induced cell swelling, MR transcriptional activity and upregulation of the target genes in high-glucose conditions.

CONCLUSIONS

High glucose induces Müller cell swelling through activation of MR signaling, which could be associated with aggravation of macular edema. Thus, Müller cell swelling and diabetic macular edema may represent a target for treatment with MR antagonists.

Chronic Systemic Dexamethasone Regulates the Mineralocorticoid/Glucocorticoid Pathways Balance in Rat Ocular Tissues

Central serous chorioretinopathy (CSCR) is a retinal disease affecting the retinal pigment epithelium (RPE) and the choroid. This is a recognized side-effect of glucocorticoids (GCs), administered through nasal, articular, oral and dermal routes. However, CSCR does not occur after intraocular GCs administration, suggesting that a hypothalamic-pituitary-adrenal axis (HPA) brake could play a role in the mechanistic link between CSCR and GS. The aim of this study was to explore this hypothesis. To induce HPA brake, Lewis rats received a systemic injection of dexamethasone daily for five days. Control rats received saline injections. Baseline levels of corticosterone were measured by Elisa at baseline and at 5 days in the serum and the ocular media and dexamethasone levels were measured at 5 days in the serum and ocular media. The expression of genes encoding glucocorticoid receptor (GR), mineralocorticoid receptors (MR), and the 11 beta hydroxysteroid dehydrogenase (HSD) enzymes 1 and 2 were quantified in the neural retina and in RPE/ choroid. The expression of MR target genes was quantified in the retina (Scnn1A (encoding ENac-α, Kir4.1 and Aqp4) and in the RPE/choroid (Shroom 2, Ngal, Mmp9 and Omg, Ptx3, Plaur and Fosl-1). Only 10% of the corticosterone serum concentration was measured in the ocular media. Corticosterone levels in the serum and in the ocular media dropped after 5 days of dexamethasone systemic treatment, reflecting HPA axis brake. Whilst both GR and MR were downregulated in the retina without MR/GR imbalance, in the RPE/choroid, both MR/GR and 11β-hsd2/11β-hsd1 ratio increased, indicating MR pathway activation. MR-target genes were upregulated in the RPE/ choroid but not in the retina. The psychological stress induced by the repeated injection of saline also induced HPA axis brake with a trend towards MR pathway activation in RPE/ choroid. HPA axis brake causes an imbalance of corticoid receptors expression in the RPE/choroid towards overactivation of MR pathway, which could favor the occurrence of CSCR.

Mineralocorticoid pathway in retinal health and diseases

In the retina, the mineralocorticoid receptor (MR) is expressed in retinal and choroidal vessels and in cells from neural and glial origins. Like in the brain, the major ligand of the MR is cortisol and the MR/glucocorticoid receptor (GR) balance regulates the activation of the MR pathway. Experimental MR pathway activation using either pharmacological agents or transgenic manipulation favors retinal and choroidal pathology. In various models of retinal diseases, such as glaucomatous neuropathy, retinopathy of prematurity, ischemic retinopathies, diabetic retinopathy and choroidal neovascularization, MR antagonism exerts beneficial effects, demonstrating its potential in the treatment of major blinding retinal diseases. But specific formulations are required to optimize the bioavailability of MR antagonists in various compartments of the eye and molecular biomarkers of MR pathway activation remain to be identify in humans to select patients amenable to clinical trials.