ADPKD and metformin: from bench to bedside

Renal ciliopathies: promising drug targets and prospects for clinical trials

INTRODUCTION

Renal ciliopathies represent a collection of genetic disorders characterized by deficiencies in the biogenesis, maintenance, or functioning of the ciliary complex. These disorders, which encompass autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and nephronophthisis (NPHP), typically result in cystic kidney disease, renal fibrosis, and a gradual deterioration of kidney function, culminating in kidney failure.

AREAS COVERED

Here we review the advances in basic science and clinical research into renal ciliopathies which have yielded promising small compounds and drug targets, within both preclinical studies and clinical trials.

EXPERT OPINION

Tolvaptan is currently the sole approved treatment option available for ADPKD patients, while no approved treatment alternatives exist for ARPKD or NPHP patients. Clinical trials are presently underway to evaluate additional medications in ADPKD and ARPKD patients. Based on preclinical models, other potential therapeutic targets for ADPKD, ARPKD, and NPHP look promising. These include molecules targeting fluid transport, cellular metabolism, ciliary signaling and cell-cycle regulation. There is a real and urgent clinical need for translational research to bring novel treatments to clinical use for all forms of renal ciliopathies to reduce kidney disease progression and prevent kidney failure.

Retarding Progression of Chronic Kidney Disease in Autosomal Dominant Polycystic Kidney Disease with Metformin and Other Therapies: An Update of New Insights

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent single-gene disorder leading to renal failure. Current therapies are aimed to treat renal and extrarenal complications of ADPKD, but improved knowledge of the pathophysiological mechanisms leading to the generation and growth of cysts has permitted the identification of new drug candidates for clinical trials. Among these, in this review, we will examine above all the role of metformin, hypothesized to be able to activate the AMP-activated protein kinase (AMPK) pathway and potentially modulate some mechanisms implicated in the onset and the growth of the cysts.

Autosomic dominant polycystic kidney disease and metformin: Old knowledge and new insights on retarding progression of chronic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common congenital kidney disorder, generally caused by mutations in the PKD1 and PKD2 genes, coding for polycystins 1 and 2. Its pathogenesis is accompanied by alterations of the cAMP, mTOR, MAPK/ERK, and JAK/STAT pathways. ADPKD is clinically characterized by the formation of many growing cysts with kidney enlargement and a progressive damage to the parenchyma, up to its complete loss of function, and the onset of end-stage renal disease (ESRD). The current aim of ADPKD therapy is the inhibition of cyst development and retardation of chronic kidney disease progression. Several drugs have been recently included as potential therapies for ADPKD including metformin, the drug of choice for the treatment of type 2 diabetes mellitus, according to its potential inhibitory effects on cystogenesis. In this review, we summarize preclinical and clinical evidence endorsing or rejecting metformin administration in ADPKD evolution and pathological mechanisms. We explored the biology of APDKD and the role of metformin in slowing down cystogenesis searching PubMed and Clinical Trials to identify relevant data from the database inception to December 2020. From our research analysis, evidence for metformin as emerging cure for ADPKD mainly arise from preclinical studies. In fact, clinical studies are still scanty and stronger evidence is awaited. Its effects are likely mediated by inhibition of the ERK pathway and increase of AMPK levels, which are both linked to ADPKD pathogenesis.

Therapeutic advances in ADPKD: the future awaits

Autosomal dominant polycystic kidney disease (ADPKD) is a heterogeneous genetic disorder included in ciliopathies, representing the fourth cause of end stage renal disease (ESRD), with an estimated prevalence between 1:1000 and 1:2500. It is mainly caused by mutations in the PKD1 and PKD2 genes encoding for polycystin 1 (PC1) and polycystin 2 (PC2), which regulate differentiation, proliferation, survival, apoptosis, and autophagy. The advances in the knowledge of multiple molecular pathways involved in the pathophysiology of ADPKD led to the development of several treatments which are currently under investigation. Recently, the widespread approval of tolvaptan and, in Italy, of long-acting release octreotide (octreotide-LAR), represents but the beginning of the new therapeutic management of ADPKD patients. Encouraging results are expected from ongoing randomized controlled trials (RCTs), which are investigating not only drugs acting on the calcium/cyclic adenosin monoposphate (cAMP) pathway, the most studied target so far, but also molecules targeting specific pathophysiological pathways (e.g. epidermal growth factor (EGF) receptor, AMP-activated protein kinase (AMPK) and KEAP1-Nrf2) and sphingolipids. Moreover, studies on animal models and cultured cells have also provided further promising therapeutic strategies based on the role of intracellular calcium, cell cycle regulation, MAPK pathway, epigenetic DNA, interstitial inflammation, and cell therapy. Thus, in a near future, tailored therapy could be the key to changing the natural history of ADPKD thanks to the vigorous efforts that are being made to implement clinical and preclinical studies in this field. Our review aimed to summarize the spectrum of drugs that are available in the clinical practice and the most promising molecules undergoing clinical, animal, and cultured cell studies.

Metformin: the updated protective property in kidney disease

Metformin is a frontline hypoglycemic agent, which is mainly prescribed to manage type 2 diabetes mellitus with obesity. Emerging evidence suggests that metformin also exerts protective effects against various kidney diseases. Some postulate that kidney disease is actually a metabolic disease, accompanied by nonresolving pathophysiologic pathways controlling oxidative stress, endoplasmic reticulum stress, inflammation, lipotoxicity, fibrosis, and senescence, as well as insufficient host defense mechanisms such as AMP-activated protein kinase (AMPK) signaling and autophagy. Metformin may interfere with these pathways by orchestrating AMPK signaling and AMPK-independent pathways to protect the kidneys from injury. Furthermore, the United States Food and Drug Administration declared metformin is safe for patients with mild or moderate kidney impairment in 2016, assuaging some conservative attitudes about metformin management in patients with renal insufficiency and broadening the scope of research on the renal protective effects of metformin. This review focuses on the molecular mechanisms by which metformin imparts renal protection and its potential in the treatment of various kidney diseases.