The best-laid plans

Key pathways in renal disease progression of experimental diabetes

Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes mellitus and the leading cause of end-stage kidney disease. Both diabetes and chronic kidney disease are risk factors for cardiovascular disease, and diabetic patients with renal involvement are three times more likely to eventually die of cardiovascular disease than diabetic patients without signs of renal failure. In type 2 diabetes, microalbuminuria is a marker of renal dysfunction and a crucial predictor of cardiovascular disease. Inhibitors of angiotensin II synthesis/activity, while preventing micro- or macroalbuminuria, also reduced cardiovascular events in diabetic patients. However, the effectiveness of renin angiotensin system blocking agents depends on the time when treatment is started, and imperfect renoprotection may occur if therapy begins at an advanced disease phase. This raises the need to identify novel multidrug approaches that simultaneously inhibit additional pathways other than angiotensin II for those diabetic patients who remain at high risk of both poor renal and cardiovascular outcomes. Studies in animal models of diabetes have contributed to defining relevant cellular mechanisms underlying the pathogenesis of DN that could represent possible targets for therapies. The pathogenesis of DN is multifactorial, involving a complex series of molecular processes. In this review, we report evidence obtained in experimental models of DN on some specific processes and pathways implicated in DN that may be crucial for managing this disease.

Characterization of RA839, a Noncovalent Small Molecule Binder to Keap1 and Selective Activator of Nrf2 Signaling

The activation of the transcription factor NF-E2-related factor 2 (Nrf2) maintains cellular homeostasis in response to oxidative stress by the regulation of multiple cytoprotective genes. Without stressors, the activity of Nrf2 is inhibited by its interaction with the Keap1 (kelch-like ECH-associated protein 1). Here, we describe (3S)-1-[4-[(2,3,5,6-tetramethylphenyl) sulfonylamino]-1-naphthyl]pyrrolidine-3-carboxylic acid (RA839), a small molecule that binds noncovalently to the Nrf2-interacting kelch domain of Keap1 with a Kd of ∼6 μM, as demonstrated by x-ray co-crystallization and isothermal titration calorimetry. Whole genome DNA arrays showed that at 10 μM RA839 significantly regulated 105 probe sets in bone marrow-derived macrophages. Canonical pathway mapping of these probe sets revealed an activation of pathways linked with Nrf2 signaling. These pathways were also activated after the activation of Nrf2 by the silencing of Keap1 expression. RA839 regulated only two genes in Nrf2 knock-out macrophages. Similar to the activation of Nrf2 by either silencing of Keap1 expression or by the reactive compound 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid methyl ester (CDDO-Me), RA839 prevented the induction of both inducible nitric-oxide synthase expression and nitric oxide release in response to lipopolysaccharides in macrophages. In mice, RA839 acutely induced Nrf2 target gene expression in liver. RA839 is a selective inhibitor of the Keap1/Nrf2 interaction and a useful tool compound to study the biology of Nrf2.

Novel effective drugs for diabetic kidney disease? or not?

INTRODUCTION

Diabetes mellitus is increasingly common worldwide and is expected to affect 592 million people by 2035. The kidney is often involved. A key goal in treating diabetes is to reduce the risk of development of kidney disease and, if kidney disease is already present, to delay the progression to end-stage renal disease (ESRD). This represents a social and ethical issue, as a significant proportion of patients reaching ESRD in developing countries do not have access to renal replacement therapy.

AREAS COVERED

The present review focuses on novel therapeutic approaches for diabetic nephropathy (DN), implemented on the basis of recent insights on its pathophysiology, which might complement the effects of single inhibition of the renin-angiotensin-aldosterone system (RAAS), the cornerstone of renoprotective interventions in diabetes, along with glycemic and blood pressure control.

EXPERT OPINION

Although a plethora of new treatment options has arisen from experimental studies, the number of novel renoprotective molecules successfully implemented in clinical practice over the last two decades is disappointingly low. Thus, new investigational strategies and diagnostic tools - including the appropriate choice of relevant renal end points and the study of urinary proteome of patients - will be as important as new therapeutic interventions to fight DN. Finally, in spite of huge financial interests in replacing the less expensive ACE inhibitors and angiotensin II receptor blockers with newer drugs, any future therapeutic approach has to be tested on top of - rather than instead of - optimal RAAS blockade.

The Nrf2 pathway in the progression of renal disease

The Nrf2/Keap1 system regulates the transcription of antioxidant and cytoprotective genes through direct Nrf2 binding to responsive elements in the promoter region of target genes or via Keap1-induced NF-kB inhibition. The association between oxidative stress and inflammation with progression of chronic kidney diseases (CKDs) directed attention towards bardoxolone methyl and its analogues, potent Nrf2/Keap1 inducers, as a potential modality of renoprotective intervention. In a phase II clinical trial (BEAM), bardoxolone methyl was shown to increase the estimated glomerular filtration rate (eGFR) in patients with CKD associated with type 2 diabetes. The study generated great interest but raised concerns as well, on the adverse event profile of the drug. Experiments in rats with type 2 diabetic nephropathy treated with bardoxolone methyl analogues reproduced some drawbacks of bardoxolone methyl therapy in humans. Despite these warnings, a long-term phase III trial (BEACON) was started that was prematurely terminated because of an excess serious adverse events and mortality. Lessons from the above studies suggest that before jumping into use in clinical practice, adequately designed experiments in animal models are needed to provide insights into pathogenetic mechanisms as well as unexpected side effects.