Chronic low-dose isotretinoin treatment limits renal damage in subtotally nephrectomized rats

Disparate roles of retinoid acid signaling molecules in kidney disease

Retinoid acid (RA) is synthesized mainly in the liver and has multiple functions in development, cell differentiation and proliferation, and regulation of inflammation. RA has been used to treat multiple diseases, such as cancer and skin disorders. The kidney is a major organ for RA metabolism, which is altered in the diseased condition. RA is known to have renal-protective effects in multiple animal models of kidney disease. RA has been shown to ameliorate podocyte injury through induction of expression of differentiation markers and regeneration of podocytes from its progenitor cells in animal models of kidney disease. The effects of RA in podocytes are mediated mainly by activation of the cAMP/PKA pathway via RA receptor-α (RARα) and activation of its downstream transcription factor, Kruppel-like factor 15. Screening of RA signaling molecules in human kidney disease has revealed RAR responder protein 1 (RARRES1) as a risk gene for glomerular disease progression. RARRES1, a podocyte-specific growth arrest gene, is regulated by high doses of both RA and TNF-α. Mechanistically, RARRES1 is cleaved by matrix metalloproteinases to generate soluble RARRES1, which then induces podocyte apoptosis through interaction with intracellular RIO kinase 1. Therefore, a high dose of RA may induce podocyte toxicity through upregulation of RARRES1. Based on the current findings, to avoid potential side effects, we propose three strategies to develop future therapies of RA for glomerular disease: 1) develop RARα- and Kruppel-like factor 15-specific agonists, 2) use the combination of a low dose of RAR-α agonist with phosphodiesterase 4 inhibitors, and 3) use a combination of RARα agonist with RARRES1 inhibitors.NEW & NOTEWORTHY Retinoic acid (RA) exerts pleotropic cellular effects, including induction of cell differentiation while inhibiting proliferation and inflammation. These effects are mediated by both RA responsive element-dependent or -independent pathways. In kidneys, RA confers renoprotection by signaling through podocyte RA receptor (RAR)α and activation of cAMP/PKA/Kruppel-like factor 15 pathway to promote podocyte differentiation. Nevertheless, in kidney disease settings, RA can also promote podocyte apoptosis and loss through downstream expression of RAR responder protein 1, a recently described risk factor for glomerular disease progression. These disparate roles of RA underscore the complexity of its effects in kidney homeostasis and disease, and a need to target specific RA-mediated pathways for effective therapeutic treatments against kidney disease progression.

Repurposing existing drugs for COVID-19: an endocrinology perspective

BACKGROUND

Coronavirus Disease 2019 (COVID-19) is a multi-systemic infection caused by the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), that has become a pandemic. Although its prevailing symptoms include anosmia, ageusia, dry couch, fever, shortness of brief, arthralgia, myalgia, and fatigue, regional and methodological assessments vary, leading to heterogeneous clinical descriptions of COVID-19. Aging, uncontrolled diabetes, hypertension, obesity, and exposure to androgens have been correlated with worse prognosis in COVID-19. Abnormalities in the renin-angiotensin-aldosterone system (RAAS), angiotensin-converting enzyme-2 (ACE2) and the androgen-driven transmembrane serine protease 2 (TMPRSS2) have been elicited as key modulators of SARS-CoV-2.

MAIN TEXT

While safe and effective therapies for COVID-19 lack, the current moment of pandemic urges for therapeutic options. Existing drugs should be preferred over novel ones for clinical testing due to four inherent characteristics: 1. Well-established long-term safety profile, known risks and contraindications; 2. More accurate predictions of clinical effects; 3. Familiarity of clinical management; and 4. Affordable costs for public health systems. In the context of the key modulators of SARS-CoV-2 infectivity, endocrine targets have become central as candidates for COVID-19. The only endocrine or endocrine-related drug class with already existing emerging evidence for COVID-19 is the glucocorticoids, particularly for the use of dexamethasone for severely affected patients. Other drugs that are more likely to present clinical effects despite the lack of specific evidence for COVID-19 include anti-androgens (spironolactone, eplerenone, finasteride and dutasteride), statins, N-acetyl cysteine (NAC), ACE inhibitors (ACEi), angiotensin receptor blockers (ARB), and direct TMPRSS-2 inhibitors (nafamostat and camostat). Several other candidates show less consistent plausibility. In common, except for dexamethasone, all candidates have no evidence for COVID-19, and clinical trials are needed.

CONCLUSION

While dexamethasone may reduce mortality in severely ill patients with COVID-19, in the absence of evidence of any specific drug for mild-to-moderate COVID-19, researchers should consider testing existing drugs due to their favorable safety, familiarity, and cost profile. However, except for dexamethasone in severe COVID-19, drug treatments for COVID-19 patients must be restricted to clinical research studies until efficacy has been extensively proven, with favorable outcomes in terms of reduction in hospitalization, mechanical ventilation, and death.

Estrogen Receptor α Signaling Exacerbates Immune-Mediated Nephropathies through Alteration of Metabolic Activity

Glomerulonephritis is one of the most serious manifestations of systemic lupus erythematous (SLE). Because SLE is ≥10 times more common in women, a role for estrogens in disease pathogenesis has long been suspected. Estrogen receptor α (ERα) is highly expressed in renal tissue. We asked whether ERα expression contributes to the development of immune-mediated nephropathies like in lupus nephritis. We tested the overall effects of estrogen receptors on the immune response by immunization with OVA and induction of chronic graft-versus-host disease in female ERα-knockout mice. We used nephrotoxic serum nephritis as a model of immune-mediated nephropathy. We investigated the influence of ERα on molecular pathways during nephritis by microarray analysis of glomerular extract gene expression. We performed RNA sequencing of lupus patient whole blood to determine common pathways in murine and human nephritis. Absence of ERα protects female mice from developing nephritis, despite the presence of immune complexes and the production of proinflammatory cytokines in the kidneys and normal humoral responses to immunization. Time-course microarray analysis of glomeruli during nephrotoxic serum nephritis revealed significant upregulation of genes related to PPAR-mediated lipid metabolism and downregulation of genes in the retinol metabolism in wild-type females compared with ERα-knockout females. Similarly, RNA sequencing of lupus patient blood revealed similar expression patterns of these same pathways. During nephritis, the altered activity of metabolic pathways, such as retinol metabolism, occurs downstream of ERα activation and is essential for the progression to end-stage renal failure.

The safety of isotretinoin in patients with lupus nephritis: a comprehensive review

Oral isotretinoin (13-cis-retinoinc acid) is a derivative of vitamin A and belongs to the first generation of retinoids, which act as synthetic isomers of retinoic acid (RA). It is a very effective agent in a treatment of acne vulgaris; however, multiple side effects related to therapy with retinoids preclude the use of isotretinoin in less severe acne vulgaris. A significant limitation for the administration of isotretinoin appears in case of concomitant kidney disease with a special attention regarding the safety of the agent in patients with lupus nephritis (LN). The aim of this review is an assessment of the safety of isotretinoin for the treatment of acne vulgaris in patients with LN. We searched both MEDLINE and SCOPUS databases, as well as several dermatological textbooks, to present all limitations and benefits of therapy with isotretinoin or its isomer (ATRA) for patients with kidney diseases. Several mouse models of SLE revealed a significant modulatory influence of retinoids on autoimmune injury of the glomerular unit. Retinoids were demonstrated to affect mononuclear cell infiltrations of renal tissue allowing for a reduction in the overall glomerular damage. Presumptively, they can affect a synthesis of autoantibodies significantly limiting their deposition in the glomerular unit. Moreover, retinoids were also shown to affect the synthesis of different cytokines specific both for lymphocytes Th1 (IL-2, IL-12, INFγ) ant Th2 (IL-4, IL-10). The influence of retinoids on the course of LN seems to be more multidimensional than only restricted to immune aspects and these synthetic RA isomers manifest also antiproteinuric activity in comparable extent to steroidal agents. The agents were demonstrated to counteract a loss of podocytes after the injury of the glomerular unit. They can promote a differentiation of renal progenitor cells (RPCs) within the Bowman capsule into mature podocytes leading to regeneration of podocyte number. Additionally, retinoids can probably protect podocytes from injury limiting their apoptosis, as well as reducing foot process effacement. Although, an endogenous production of RA isomers increases after the injury of the glomerular unit aiming to the restoration of podocyte number, it can be significantly impaired by a loss of albumins into urine. RA isomers are progressively sequestered by albumin within the Bowman's space and therefore, they are quickly eliminated with urine. It was demonstrated that the administration of exogenous RA isomers (retinoids) can bypass the activity of albumins enhancing the regeneration of podocytes. Finally, retinoids can regulate the production of vasoactive substances influencing on different vascular functions in the kidney. They can beneficially change a balance of angiotensin metabolites through by down-regulation of angiotensin-converting enzyme type 1 and the enhancement of an expression of angiotensin-converting enzyme type 2. Another studies revealed that retinoids could also alter the activity of renal endothelin pathway; however, the significance of this effect requires further elucidation. Taken all these presented effects of retinoids in the kidney into consideration, we can conclude that isotretinoin can be the safe treatment option of acne vulgaris in patients with LN.

An in vitro model for the pro-fibrotic effects of retinoids: mechanisms of action

BACKGROUND AND PURPOSE

Retinoids, including all-trans retinoic acid (tRA), have dose-dependent pro-fibrotic effects in experimental kidney diseases. To understand and eventually prevent such adverse effects, it is important to establish relevant in vitro models and unravel their mechanisms.

EXPERIMENTAL APPROACH

Fibrogenic effects of retinoids were assessed in NRK-49F renal fibroblasts using picro-Sirius red staining for collagens and quantified by spectrophotometric analysis of the eluted stain. Other methods included RT-qPCR, immunoassays and matrix metalloproteinase (MMP) activity assays.

KEY RESULTS

With or without TGF-β1, tRA was dose-dependently pro-fibrotic, notably increasing collagen accumulation. tRA and TGF-β1 additively suppressed expression of mRNA for MMP2, 3 and 13 and suppressed MMP activity. tRA, in the presence of TGF-β1, induced plasminogen activator inhibitor-1 (PAI-1) mRNA and they additively induced PAI-1 protein expression. A PAI-1 inhibitor, a pan-retinoic acid receptor (RAR) antagonist and a pan-retinoid X receptor (RXR) antagonist each partially prevented the pro-fibrotic effect of tRA. The dose-dependent pro-fibrotic effects of a pan-RXR agonist were similar to those of tRA. A pan-RAR agonist showed weaker, less dose-dependent pro-fibrotic effects and the pro-fibrotic effects of RARα and RARβ-selective agonists were even smaller. An RARγ-selective agonist did not affect fibrogenesis.

CONCLUSIONS AND IMPLICATIONS

An in vitro model for the pro-fibrotic effects of retinoids was established in NRK-49F cells. It was associated with reduced MMP activity and increased PAI-1 expression, and was probably mediated by RXR and RAR. To avoid or antagonize the pro-fibrotic activity of tRA, further studies on RAR isotype-selective agonists and PAI-1 inhibitors might be of value.

Retinoid and TGF-β families: crosstalk in development, neoplasia, immunity, and tissue repair

Transforming growth factor-β (TGF-β) isoforms are profibrotic cytokines, par excellence, and have complex multifunctional effects on many systems, depending on the biologic setting. Retinoids are vitamin A derivatives that also have diverse effects in development, physiology, and disease. The interactions between these classes of molecules are, not surprisingly, highly complex and are dependent on the tissue, cellular, and molecular settings.

13-cis-Retinoic acid specific down-regulation of angiotensin type 1 receptor in rat liver epithelial and aortic smooth muscle cells

Transcriptional repression through cis- and trans-acting factors enabling an alternate approach to control angiotensin type 1 receptor (AT1 or AGTR1 as listed in the MGI database) expression has not been studied. In previous investigations, treatment with retinoic acid was found to be associated with enhanced insulin sensitivity. In our previous study, expression of AT1 was found to be inversely correlated with intracellular glucose concentrations. Therefore, we hypothesized that 13-cis-retinoic acid (13cRA), an antioxidant, enhances insulin-sensitive glucose-mediated down-regulation of the AT1. In this study, we used continuously passaged rat liver epithelial cells. Our study shows that cells exposed to 13cRA specifically down-regulated the AT1 protein in a dose- and time-dependent manner, independently of any change in receptor affinity. Down-regulation of the AT1 expression leads to reduced AngII-mediated intracellular calcium release, a hallmark of receptor-mediated intracellular signaling. Similarly with receptor down-regulation, we observed a significant reduction in AT1 mRNA; however, the AT1 down-regulation was independent of insulin-sensitive glucose uptake and retinoic acid receptor activation (RAR/RXR). Treatment with 13cRA resulted in phosphorylation of p42/p44 MAP kinases in these cells. Subsequent studies using MEK inhibitor PD98059 prevented 13cRA-mediated AT1 down-regulation and restored AngII-mediated intracellular calcium response. Furthermore, 13cRA-mediated inhibitory effects on AT1 were validated in primary rat aortic smooth muscle cells. In summary, our results demonstrate for the first time that 13cRA has a glucose- and RAR/RXR-independent mechanism for transcriptional inhibition of AT1, suggesting its therapeutic potential in systems in which AT1 expression is deregulated in insulin-sensitive and -insensitive tissues.

Amelioration of glomerulosclerosis with all-trans retinoic acid is linked to decreased plasminogen activator inhibitor-1 and α-smooth muscle actin

AIM

To examine the effects of all-trans retinoic acid (atRA) on renal morphology and function as well as on renal plasminogen activator inhibitor-1 (PAI-1) expression and plasmin activity in rats with 5/6 nephrectomy.

METHODS

Adult male Sprague Dawley rats were given 5/6 nephrectomy or sham operation. Renal function was measured 2 weeks later. The nephrectomized rats were assigned to groups matched for proteinuria and treated with vehicle or atRA (5 or 10 mg/kg by gastric gavage once daily) for the next 12 weeks. Rats with sham operation were treated with vehicle. At the end of the treatments, kidneys were collected for histological examination, Western blot analysis, and enzymatic activity measurements.

RESULTS

The 5/6 nephrectomy promoted hypertension, renal dysfunction, and glomerulosclerosis. These changes were significantly reduced in the atRA-treated group. The expressions of PAI-1 and α-smooth muscle actin (α-SMA) were significantly increased in the vehicle-treated nephrectomized rats. Treatment with atRA significantly reduced the expressions of PAI-1 and α-SMA. However, plasmin activity remained unchanged following atRA treatment.

CONCLUSION

Treatment with atRA ameliorates glomerulosclerosis and improves renal function in rats with 5/6 nephrectomy. This is associated with a decrease in PAI-1 and α-SMA, but not with a change in plasmin activity.

Kidneys of Alb/TGF-beta1 transgenic mice are deficient in retinoic acid and exogenous retinoic acid shows dose-dependent toxicity

BACKGROUND

Alb/TGF-beta(1) transgenic mice overexpress active transforming growth factor-beta(1) (TGF-beta(1)) in the liver, leading to increased circulating levels of the cytokine and progressive renal fibrosis. This study was designed to explore if exogenous all-trans retinoic acid (tRA) prevents renal fibrosis in this animal model.

METHODS

The retinoid profile in kidney and liver of wild-type and Alb/TGF-beta(1) transgenic mice was examined by high-performance liquid chromatography and slow-release pellets containing different amounts of tRA were implanted subcutaneously to treat the Alb/TGF-beta(1) transgenic mice, starting at 1 week of age; mice were sacrificed 2 weeks later.

RESULTS

Kidneys of 3-week-old wild-type mice had abundant tRA, which was completely absent in kidneys of the transgenic mice. Low doses of tRA (6-10.7 mg/kg/day) failed to affect renal fibrosis although it tended to suppress the mRNA expression of some molecular markers of fibrosis and retinal dehydrogenase 2 (RALDH2), a gene encoding a key tRA-synthesising enzyme. These tendencies disappeared, mortality tended to increase and RALDH2 and connective tissue growth factor (CTGF) mRNAs significantly increased in the medium-dose group (12.7-18.8 mg/kg/day). High doses (20.1-27.4 mg/kg/day) showed even higher toxicity with increased renal fibrosis and significant mortality.

CONCLUSIONS

Alb/TGF-beta(1) transgenic mice are characterised by depletion of endogenous renal tRA. Exogenous tRA dose-dependently increases mortality and kidney fibrosis, which is associated with dose-dependent regulation of renal RALDH2 and CTGF mRNA expression.