Pulsed oral sirolimus in advanced autosomal-dominant polycystic kidney disease (Vienna RAP Study): study protocol for a randomized controlled trial

Shared pathobiology identifies AMPK as a therapeutic target for obesity and autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common Mendelian kidney disease, affecting approximately one in 1,000 births and accounting for 5% of end-stage kidney disease in developed countries. The pathophysiology of ADPKD is strongly linked to metabolic dysregulation, which may be secondary to defective polycystin function. Overweight and obesity are highly prevalent in patients with ADPKD and constitute an independent risk factor for progression. Recent studies have highlighted reduced AMP-activated protein kinase (AMPK) activity, increased mammalian target of rapamycin (mTOR) signaling, and mitochondrial dysfunction as shared pathobiology between ADPKD and overweight/obesity. Notably, mTOR and AMPK are two diametrically opposed sensors of energy metabolism that regulate cell growth and proliferation. However, treatment with the current generation of mTOR inhibitors is poorly tolerated due to their toxicity, making clinical translation difficult. By contrast, multiple preclinical and clinical studies have shown that pharmacological activation of AMPK provides a promising approach to treat ADPKD. In this narrative review, we summarize the pleiotropic functions of AMPK as a regulator of cellular proliferation, macromolecule metabolism, and mitochondrial biogenesis, and discuss the potential for pharmacological activation of AMPK to treat ADPKD and obesity-related kidney disease.

The PI3K/Akt/mTOR pathway in polycystic kidney disease: A complex interaction with polycystins and primary cilium

Over-activation of the PI3K/Akt/mTOR network is a well-known pathogenic event that leads to hyper-proliferation. Pharmacological targeting of this pathway has been developed for the treatment of multiple diseases, including cancer. In polycystic kidney disease (PKD), the mTOR cascade promotes cyst growth by boosting proliferation, size and metabolism of kidney tubule epithelial cells. Therefore, mTOR inhibition has been tested in pre-clinical and clinical studies, but only the former showed positive results. This review reports recent discoveries describing the activity and molecular mechanisms of mTOR activation in tubule epithelial cells and cyst formation and discusses the evidence of an upstream regulation of mTOR by the PI3K/Akt axis. In particular, the complex interconnections of the PI3K/Akt/mTOR network with the principal signaling routes involved in the suppression of cyst formation are dissected. These interactions include the antagonism and the reciprocal negative regulation between mTOR complex 1 and the proteins whose deletion causes Autosomal Dominant PKD, the polycystins. In addition, the emerging role of phopshoinositides, membrane components modulated by PI3K, will be presented in the context of primary cilium signaling, cell polarization and protection from cyst formation. Overall, studies demonstrate that the activity of various members of the PI3K/Akt/mTOR network goes beyond the classical transduction of mitogenic signals and can impact several aspects of kidney tubule homeostasis and morphogenesis. These properties might be useful to guide the establishment of more effective treatment protocols to be tested in clinical trials.

Recent Advances of mTOR Inhibitors Use in Autosomal Dominant Polycystic Kidney Disease: Is the Road Still Open?

Autosomal Dominant Polycystic Kidney Disease (ADPKD), the most common monogenic kidney disease, is caused by mutations in the PKD1, PKD2 or, in a very limited number of families, GANAB genes. Although cellular and molecular mechanisms of this disease have been understood in the past 20 years, specific therapy approaches remain very little. Both experimental and clinical studies show that the mammalian or mechanistic target of rapamycin (mTOR) pathway plays an important role during cyst formation and enlargement in ADPKD. Studies in rodent models of ADPKD showed that mTOR inhibitors had a significant and long-lasting decrease in kidney volume and amelioration in kidney function. In the past over ten years, researchers have been devoting continuously to test mTOR inhibitors efficacy and safety in both preclinical studies and clinical trials in patients with ADPKD. In this review, we will discuss the mTOR pathway thoroughly, mainly focusing on current advances in understanding its role in ADPKD, especially the recent progress of mTOR inhibitors use in preclinical studies and clinical trials.

Roles of mTOR complexes in the kidney: implications for renal disease and transplantation

The mTOR pathway has a central role in the regulation of cell metabolism, growth and proliferation. Studies involving selective gene targeting of mTOR complexes (mTORC1 and mTORC2) in renal cell populations and/or pharmacologic mTOR inhibition have revealed important roles of mTOR in podocyte homeostasis and tubular transport. Important advances have also been made in understanding the role of mTOR in renal injury, polycystic kidney disease and glomerular diseases, including diabetic nephropathy. Novel insights into the roles of mTORC1 and mTORC2 in the regulation of immune cell homeostasis and function are helping to improve understanding of the complex effects of mTOR targeting on immune responses, including those that impact both de novo renal disease and renal allograft outcomes. Extensive experience in clinical renal transplantation has resulted in successful conversion of patients from calcineurin inhibitors to mTOR inhibitors at various times post-transplantation, with excellent long-term graft function. Widespread use of this practice has, however, been limited owing to mTOR-inhibitor- related toxicities. Unique attributes of mTOR inhibitors include reduced rates of squamous cell carcinoma and cytomegalovirus infection compared to other regimens. As understanding of the mechanisms by which mTORC1 and mTORC2 drive the pathogenesis of renal disease progresses, clinical studies of mTOR pathway targeting will enable testing of evolving hypotheses.

Interventions for preventing the progression of autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited disorder causing kidney disease. Current clinical management of ADPKD focuses primarily on symptom control and reducing associated complications, particularly hypertension. In recent years, improved understanding of molecular and cellular mechanisms involved in kidney cyst growth and disease progression has resulted in new pharmaceutical agents to target disease pathogenesis to prevent progressive disease.

OBJECTIVES

We aimed to evaluate the effects of interventions for preventing ADPKD progression on kidney function, kidney endpoints, kidney structure, patient-centred endpoints (such as cardiovascular events, sudden death, all-cause mortality, hospitalisations, BP control, quality of life, and kidney pain), as well as the general and specific adverse effects related to their use.

SEARCH METHODS

We searched the Cochrane Renal Group's Specialised Register to 6 June 2015 using relevant search terms.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing any interventions for preventing the progression of ADPKD with other interventions or placebo were considered for inclusion without language restriction.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study risks of bias and extracted data. We summarised treatment effects on clinical outcomes, kidney function and structure and adverse events using random effects meta-analysis. We assessed heterogeneity in estimated treatment effects using the Cochran Q test and I(2) statistic. Summary treatment estimates were calculated as a mean difference (MD) or standardised mean difference (SMD) for continuous outcomes and a risk ratio (RR) for dichotomous outcomes together with their 95% confidence intervals.

MAIN RESULTS

We included 30 studies (2039 participants) that investigated 11 pharmacological interventions (angiotensin-converting enzyme inhibitors (ACEi), angiotensin receptor blockers (ARBs), calcium channel blockers, beta blockers, vasopressin receptor 2 (V2R) antagonists, mammalian target of rapamycin (mTOR) inhibitors, somatostatin analogues, antiplatelet agents, eicosapentaenoic acids, statins and vitamin D compounds) in this review.ACEi significantly reduced diastolic blood pressure (9 studies, 278 participants: MD -4.96 mm Hg, 95% CI -8.88 to -1.04), but had uncertain effects on kidney volumes (MD -42.50 mL, 95% CI -115.68 to 30.67), GFR (MD -3.41 mL/min/1.73 m(2), 95% CI -15.83 to 9.01), and SCr (MD -0.02 mg/dL, 95% CI -0.14 to 0.09), in data largely restricted to children. ACEi did not show different effects on GFR (MD -8.19 mL/min/1.73 m(2), 95% CI -29.46 to 13.07) and albuminuria (SMD -0.19, 95% CI -1.77 to 1.39) when compared with beta-blockers, or SCr (MD 0.00 mg/dL, 95% CI -0.09 to 0.10) when compared with ARBs.Data for effects of V2R antagonists on kidney function and volumes compared to placebo were limited to narrative information within a single study while these agents increased thirst (1444 participants: RR 2.70, 95% CI 2.24 to 3.24) and dry mouth (1455 participants: RR 1.33, 95% CI 1.01 to 1.76).Compared with no treatment, mTOR inhibitors had uncertain effects on kidney function (2 studies, 115 participants: MD 4.45 mL/min/1.73 m(2), 95% CI -3.20 to 12.11) and kidney volume (MD -0.08 L, 95% CI -0.75 to 0.59) but in three studies (560 participants) caused angioedema (RR 13.39, 95% CI 2.56 to 70.00), oral ulceration (RR 6.77, 95% CI 4.42 to 10.38), infections (RR 1.14, 95% CI 1.04 to 1.25) and diarrhoea (RR 1.70, 95% CI 1.26 to 2.29).Somatostatin analogues (6 studies, 138 participants) slightly improved SCr (MD -0.43 mg/dL, 95% CI -0.86 to -0.01) and total kidney volume (MD -0.62 L, 95% CI -1.22 to -0.01) but had no definite effects on GFR (MD 9.50 mL/min, 95% CI -4.45 to 23.44) and caused diarrhoea (RR 3.72, 95% CI 1.43 to 9.68).Data for calcium channel blockers, eicosapentaenoic acids, statins, vitamin D compounds and antiplatelet agents were sparse and inconclusive.Random sequence generation was adequate in eight studies, and in almost half of the studies, blinding was not present or not specified. Most studies did not adequately report outcomes, which adversely affected our ability to assess this bias. The overall drop-out rate was over 10% in nine studies, and few were conducted using intention-to-treat analyses.

AUTHORS' CONCLUSIONS

Although several interventions are available for patients with ADPKD, at present there is little or no evidence that treatment improves patient outcomes in this population and is associated with frequent adverse effects. Additional large randomised studies focused on patient-centred outcomes are needed.