Treatment strategies and clinical trial design in ADPKD

Cross-Species Insights into Autosomal Dominant Polycystic Kidney Disease: Provide an Alternative View on Research Advancement

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a prevalent hereditary disorder that affects the kidneys, characterized by the development of an excessive number of fluid-filled cysts of varying sizes in both kidneys. Along with the progression of ADPKD, these enlarged cysts displace normal kidney tissue, often accompanied by interstitial fibrosis and inflammation, and significantly impair renal function, leading to end-stage renal disease. Currently, the precise mechanisms underlying ADPKD remain elusive, and a definitive cure has yet to be discovered. This review delineates the epidemiology, pathological features, and clinical diagnostics of ADPKD or ADPKD-like disease across human populations, as well as companion animals and other domesticated species. A light has been shed on pivotal genes and biological pathways essential for preventing and managing ADPKD, which underscores the importance of cross-species research in addressing this complex condition. Treatment options are currently limited to Tolvaptan, dialysis, or surgical excision of large cysts. However, comparative studies of ADPKD across different species hold promise for unveiling novel insights and therapeutic strategies to combat this disease.

The value of soluble suppression of tumorigenesis-2 (sST2) in the maintenance of hemodialysis patients with heart failure

BACKGROUND

Patients with end-stage renal disease are prone to develop heart failure (HF). The N-terminal pro-brain natriuretic peptide (NT-proBNP, BNP) is regarded as the gold standard for diagnosing HF. However, its prognostic sensitivity in patients with end-stage renal disease is sub-optimal. Soluble suppression of tumorigenesis-2 (sST2) has been well studied in HF but rarely in patients with maintenance hemodialysis (MHD). This study aimed to evaluate the value of sST2 in predicting HF in MHD patients.

METHODS

Twenty-three patients with New York Heart Association (NYHA) class III-IV were included in the HF group and 88 NYHA class I-II patients in the non-heart failure (NHF) group. sST2 and laboratory indexes were compared between the two groups.

RESULTS

The HF group, compared with the NHF group, presented with higher sST2, more advanced age, higher incidence of coronary heart disease (CHD), left ventricle end-diastolic diameter (LVEDD), and pulmonary artery pressure (PAP), and unchanged parathyroid hormone (iPTH). The HF group also had lower ejection fraction (EF), uric acid, inorganic phosphorus, 25-OH VitD3, and serum albumin. Multivariate logistic regression indicated that age, BNP, and sST2 were independent risk factors of HF in MHD patients. Spearman analysis defined that sST2 was positively correlated with PAP (r =0.283, p =0.003) and C-reactive protein (r =0.354, p <0.001); and negatively correlated with sex (r =-0.255, p =0.007), albumin (r =-0.366, p <0.001), uric acid (r =-0.213, p =0.025), 25-OH VitD3 (r =-0.216, p =0.04), calcium (r =-0.219, p =0.021), and inorganic phosphorus (r =-0.256, p =0.007). Receiver operating characteristic curve analysis determined a positive association between BNP and sST2 (r =0.373, p <0.001), with the area under the curve (AUC) of BNP being 0.822 (sensitivity: 0.783, specificity: 0.830) and the AUC of sST2 being 0.841 (sensitivity: 0.913, specificity: 0.761). The AUC of sST2 was 0.841, and the cut-value was 42.840 (sensitivity: 0.913, specificity: 0.761).

CONCLUSION

sST2 can predict HF in MHD patients and facilitate early diagnosis and prevention of HF in MHD patients. HIPPOKRATIA 2022, 26 (1):19-24.

Diverse Receptor Tyrosine Kinase Phosphorylation in Urine-Derived Tubular Epithelial Cells from Autosomal Dominant Polycystic Kidney Disease Patients

BACKGROUNDS

The clinical features of autosomal dominant polycystic kidney disease (ADPKD) differ among patients even if they have the same gene mutation in PKD1 or PKD2. This suggests that there is diversity in the expression of other modifier genes or in the underlying molecular mechanisms of ADPKD, but these are not well understood.

METHODS

We primarily cultured solute carrier family 12 member 3 (SLC12A3)-positive urine-derived distal tubular epithelial cells from 6 ADPKD patients and 4 healthy volunteers and established immortalized cell lines. The diversity in receptor tyrosine kinase (RTK) phosphorylation by phospho-RTK array in immortalized tubular epithelial cells was analyzed.

RESULTS

We noted diversity in the activation of several molecules, including Met, a receptor of hepatocyte growth factor (HGF). Administration of golvatinib, a selective Met inhibitor, or transfection of small interfering RNA for Met suppressed cell proliferation and downstream signaling only in the cell lines in which hyperphosphorylation of Met was observed. In three-dimensional culture of Madin-Darby canine kidney (MDCK) cells as a cyst formation model of ADPKD, HGF activated Met, resulting in an increased total cyst number and total cyst volume. Administration of golvatinib inhibited these phenotypes in MDCK cells.

CONCLUSION

Analysis of urine-derived tubular epithelial cells demonstrated diverse RTK phosphorylation in ADPKD, and Met phosphorylation was noted in some patients. Considering the difference in the effects of golvatinib on immortalized tubular epithelial cells among patients, this analysis may aid in selecting suitable drugs for individual ADPKD patients.

Clinical burden of autosomal dominant polycystic kidney disease

There are no specific therapies for autosomal dominant polycystic kidney disease (ADPKD), and clinical data evaluating the effects of non-specific therapies on ADPKD patients are scarce. We therefore evaluated those effects using data from a longitudinal health insurance database collected from 2000-2010. We individually selected patients with and without ADPKD from inpatient data files as well as from the catastrophic illness registry in Taiwan based on 1:5 frequency matching for sex, age, and index year. The hazard ratios (HR) of all-cause mortality, ischemic stroke, hemorrhagic stroke and end-stage renal disease (ESRD) in ADPKD inpatients were elevated as compared to the controls. Similarly, ADPKD patients from the catastrophic illness registry had an increased risk of hemorrhagic stroke and ESRD. Allopurinol users also had an increased risk of all-cause mortality. The HR for developing ESRD after medication exposure was 0.47-fold for statin and 1.93-fold for pentoxifylline. These results reveal that patients with ADPKD (either inpatient or from the catastrophic illness registry) are at elevated risk for hemorrhagic stroke and ESRD, and suggest that allopurinol and pentoxifylline should not be prescribed to ADPKD patients due to possible adverse effects.

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.

Glutamine metabolism via glutaminase 1 in autosomal-dominant polycystic kidney disease

Background

Metabolism of glutamine by glutaminase 1 (GLS1) plays a key role in tumor cell proliferation via the generation of ATP and intermediates required for macromolecular synthesis. We hypothesized that glutamine metabolism also plays a role in proliferation of autosomal-dominant polycystic kidney disease (ADPKD) cells and that inhibiting GLS1 could slow cyst growth in animal models of ADPKD.

Methods

Primary normal human kidney and ADPKD human cyst-lining epithelial cells were cultured in the presence or absence of two pharmacologic inhibitors of GLS1, bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide 3 (BPTES) and CB-839, and the effect on proliferation, cyst growth in collagen and activation of downstream signaling pathways were assessed. We then determined if inhibiting GLS1 in vivo with CB-839 in the Aqp2-Cre; Pkd1fl/fl and Pkhd1-Cre; Pkd1fl/fl mouse models of ADPKD slowed cyst growth.

Results

We found that an isoform of GLS1 (GLS1-GAC) is upregulated in cyst-lining epithelia in human ADPKD kidneys and in mouse models of ADPKD. Both BPTES and CB-839 blocked forskolin-induced cyst formation in vitro. Inhibiting GLS1 in vivo with CB-839 led to variable outcomes in two mouse models of ADPKD. CB-839 slowed cyst growth in Aqp2-Cre; Pkd1fl/fl mice, but not in Pkhd1-Cre; Pkd1fl/fl mice. While CB-839 inhibited mammalian target of rapamycin (mTOR) and MEK activation in Aqp2-Cre; Pkd1fl/fl, it did not in Pkhd1-Cre; Pkd1fl/fl mice.

Conclusion

These findings provide support that alteration in glutamine metabolism may play a role in cyst growth. However, testing in other models of PKD and identification of the compensatory metabolic changes that bypass GLS1 inhibition will be critical to validate GLS1 as a drug target either alone or when combined with inhibitors of other metabolic pathways.

Angiotensinogen and interleukin 18 in serum and urine of children with kidney cysts

BACKGROUND

The most common disease associated with the presence of kidney cysts in the population is autosomal dominant polycystic kidney disease (ADPKD), which finally leads to end-stage renal disease.

METHOD

The study evaluated serum and urinary concentration of angiotensinogen (AGT) and interleukin 18 (IL-18) in a group of 39 children with renal cysts of different aetiology.

RESULTS

Serum and urinary AGT concentration in children with renal cysts was higher compared to controls, regardless of the underlying background and gender. Serum IL-18 concentration was lower, in contrast, and the concentration of IL-18 in the urine did not differ between affected and healthy children. Negative correlation between urinary IL-18 concentration and systolic and mean arterial blood pressure was noted.

CONCLUSIONS

Higher AGT levels in serum and urine in children with renal cysts may indicate the activation of the renin-angiotensin-aldosterone system, including its intrarenal part, even before the onset of hypertension. Lower serum concentration of IL-18 in children with kidney cysts may indicate the loss of the protective role of this cytokine with the occurrence of hypertension.

Autosomal dominant polycystic kidney disease: Disrupted pathways and potential therapeutic interventions

Autosomal dominant polycystic kidney disease (ADPKD) is a monogenic inherited renal cystic disease that occurs in different races worldwide. It is characterized by the development of a multitude of renal cysts, which leads to massive enlargement of the kidney and often to renal failure in adulthood. ADPKD is caused by a mutation in PKD1 or PKD2 genes encoding the proteins polycystin-1 and polycystin-2, respectively. Recent studies showed that cyst formation and growth result from deregulation of multiple cellular pathways like proliferation, apoptosis, metabolic processes, cell polarity, and immune defense. In ADPKD, intracellular cyclic adenosine monophosphate (cAMP) promotes cyst enlargement by stimulating cell proliferation and transepithelial fluid secretion. Several interventions affecting many of these defective signaling pathways have been effective in animal models and some are currently being tested in clinical trials. Moreover, the stem cell therapy can improve nephropathies and according to studies were done in this field, can be considered as a hopeful therapeutic approach in future for PKD. This study provides an in-depth review of the relevant molecular pathways associated with the pathogenesis of ADPKD and their implications in development of potential therapeutic strategies.

Discoidin Domain Receptor 1 (DDR1) tyrosine kinase is upregulated in PKD kidneys but does not play a role in the pathogenesis of polycystic kidney disease

Tolvaptan is the only drug approved to slow cyst growth and preserve kidney function in patients with autosomal dominant polycystic kidney disease (ADPKD). However, its limited efficacy combined with significant side effects underscores the need to identify new and safe therapeutic drug targets to slow progression to end stage kidney disease. We identified Discoidin Domain Receptor 1 (DDR1) as receptor tyrosine kinase upregulated in vivo in 3 mouse models of ADPKD using a novel mass spectrometry approach to identify kinases upregulated in ADPKD. Previous studies demonstrating critical roles for DDR1 to cancer progression, its potential role in the pathogenesis of a variety of other kidney disease, along with the possibility that DDR1 could provide new insight into how extracellular matrix impacts cyst growth led us to study the role of DDR1 in ADPKD pathogenesis. However, genetic deletion of DDR1 using CRISPR/Cas9 failed to slow cyst growth or preserve kidney function in both a rapid and slow mouse model of ADPKD demonstrating that DDR1 does not play a role in PKD pathogenesis and is thus a not viable drug target. In spite of the negative results, our studies will be of interest to the nephrology community as it will prevent others from potentially conducting similar experiments on DDR1 and reinforces the potential of performing unbiased screens coupled with in vivo gene editing using CRISPR/Cas9 to rapidly identify and confirm new potential drug targets for ADPKD.

The expression of somatostatin receptor 2 decreases during cyst growth in mice with polycystic kidney disease

IMPACT STATEMENT

Somatostatin (SST) analogs have been shown to halt cyst growth and progression of autosomal dominant polycystic kidney disease by several clinical trials. However, two studies suggest that the effect of the SST analog octreotide on kidney growth during the first year of treatment is reduced in the subsequent follow-ups and the kidney enlargement resumes. This biphasic change in kidney growth during octreotide treatment may be partially explained by alterations in SSTR2 expression. Here, we found that SSTR2 is mainly expressed in distal tubules and collecting ducts in murine kidneys, and the expression of SSTR2 decreases during cyst growth in two PKD mouse models. Our data may thus provide possible explanations for the lack of efficacy in long-term treatment with SST analogs.

Should kidney volume be used as an indicator of surgical occasion for patients with autosomal dominant polycystic kidney disease?

To investigate the best surgical occasion of laparoscopic cyst decortications (LCDs) in patients with autosomal dominant polycystic kidney disease (ADPKD), in accordance with the renal volume (RV). We retrospectively analyzed 135 (65 male and 70 female) patients with ADPKD who underwent LCD between June 2011 and October 2015. Patients were divided into 4 groups according to the volume of the operated kidney measured from computed tomography scans: group A (28 patients, RV < 500 mL), group B (63 patients, RV = 500-1000 mL), group C (30 patients, RV = 1000-1500 mL), and group D (14 patients, RV > 1500 mL). We studied postoperative indicators at least 1-year follow-up. For each RV group, therapeutic responses of LCD in these patients with ADPKD were assessed by improvement of clinical parameters and manifestations. A significant glomerular filtration rate (GFR) improvement was found in RV group B (31.8 ± 11.1 mL/min; final GFR 36.9 ± 12.7 mL/min; P < 0.01), and RV group C (21.1 ± 8.7 mL/min; final GFR 27.4 ± 9.2 mL/min; P < 0.01). RV group C had much higher GFR improvements than did RV group B (P < 0.01). In addition, refractory pain in patients of RV groups B, C, and D was much relieved by LCD treatment. Compared with other RV groups, blood pressures in patients with ADPKD of RV group D were also improved (P < 0.01). Our study indicates that RV could be used to evaluate LCD clinical outcomes in patients with ADPKD. The results of LCD for patients with ADPKD with RV between 500 and 1500 mL were encouraging, especially with regards to renal function improvement and pain relief. Therefore, RV may become a useful marker to predict the timing of LCD surgery in patients with ADPKD.

Increased soluble ST2 and IL‑4 serum levels are associated with disease severity in patients with membranous nephropathy

The interleukin (IL)‑33/suppression of tumorigenicity 2 (ST2) axis regulates Th2 reactivity, and ST2 is the receptor for IL‑33. In this study, the roles of IL‑33 and soluble ST2 (sST2) in the pathogenesis of membranous nephropathy (MN), and their association with disease severity were evaluated. Serum levels of IL‑33 and sST2 in 93 patients, and 34 healthy controls (HCs) were measured by enzyme‑linked immunosorbent assays. Clinical characteristics were recorded and the estimated glomerular filtration rates (eGFRs) were computed. In addition, the association between serum IL‑33 and sST2 levels, and clinical measurements in patients with MN was analyzed. No difference in the serum levels of IL‑33 was identified between the patients with MN and HCs. However, the serum levels of sST2 were considerably higher in the MN patients compared with in the HCs at every stage. Higher concentrations of serum IL‑2, IL‑4, IL‑10, IL‑17A, and IFN‑γ were measured in the MN patients compared with in the HCs. Serum sST2 concentrations were negatively correlated with IL‑4 concentrations in the patients with MN. Furthermore, serum sST2 levels were negatively correlated with the eGFRs and serum calcium levels. Serum sST2 levels, but not IL‑33 levels, were positively correlated with the 24‑h urine protein and serum phosphorus levels. Following treatment, serum sST2 levels were considerably reduced, whereas serum IL‑4 and IL‑10 levels were significantly increased. These data suggest that sST2 and IL‑4, but not IL‑33, contribute to the pathogenesis of MN.

Lysine methyltransferase SMYD2 promotes cyst growth in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is driven by mutations in PKD1 and PKD2 genes. Recent work suggests that epigenetic modulation of gene expression and protein function may play a role in ADPKD pathogenesis. In this study, we identified SMYD2, a SET and MYND domain protein with lysine methyltransferase activity, as a regulator of renal cyst growth. SMYD2 was upregulated in renal epithelial cells and tissues from Pkd1-knockout mice as well as in ADPKD patients. SMYD2 deficiency delayed renal cyst growth in postnatal kidneys from Pkd1 mutant mice. Pkd1 and Smyd2 double-knockout mice lived longer than Pkd1-knockout mice. Targeting SMYD2 with its specific inhibitor, AZ505, delayed cyst growth in both early- and later-stage Pkd1 conditional knockout mouse models. SMYD2 carried out its function via methylation and activation of STAT3 and the p65 subunit of NF-κB, leading to increased cystic renal epithelial cell proliferation and survival. We further identified two positive feedback loops that integrate epigenetic regulation and renal inflammation in cyst development: SMYD2/IL-6/STAT3/SMYD2 and SMYD2/TNF-α/NF-κB/SMYD2. These pathways provide mechanisms by which SMYD2 might be induced by cyst fluid IL-6 and TNF-α in ADPKD kidneys. The SMYD2 transcriptional target gene Ptpn13 also linked SMYD2 to other PKD-associated signaling pathways, including ERK, mTOR, and Akt signaling, via PTPN13-mediated phosphorylation.

RAPAMYCIN INCREASES LENGTH AND MECHANOSENSORY FUNCTION OF PRIMARY CILIA IN RENAL EPITHELIAL AND VASCULAR ENDOTHELIAL CELLS

Primary cilia arebiophysically-sensitive organelles responsible for sensing fluid-flow and transducing this stimulus into intracellular responses. Previous studies have shown that the primary cilia mediate flow-induced calcium influx, and sensitivity of cilia function to flow is correlated to cilia length. Cells with abnormal cilia length or function can lead to a host of diseases that are collectively termed as ciliopathies. Rapamycin, a potent inhibitor of mTOR (mammalian target of rapamycin), has been demonstrated to be a potential pharmacological agent against the aberrant mTOR signaling seen in ciliopathies such as polycystic kidney disease (PKD) and tuberous sclerosis complex (TSC). Here we look at the effects of rapamycin on ciliary length and function for the first time. Compared to controls, primary cilia in rapamycin-treated porcine renal epithelial and mouse vascular endothelial cells showed a significant increase in length. Graded increases in fluid-shear stress further indicates that rapamycin enhances cilia sensitivity to fluid flow. Treatment with rapamycin led to G0 arrest in porcine epithelial cells while no significant change in cell cycle were observed in rapamycin-treated mouse epithelial or endothelial cells, indicating a species-specific effect of rapamycin. Given the previousin vitro and in vivo studies establishing rapamycin as a potential therapeutic agent for ciliopathies, such as PKD and TSC, our studies show that rapamycin enhances ciliary function and sensitivity to fluid flow. The results of our studies suggest a potential ciliotherapeutic effect of rapamycin.

Effects of TORC1 Inhibition during the Early and Established Phases of Polycystic Kidney Disease

The disease-modifying effects of target of rapamycin complex 1 (TORC1) inhibitors during different stages of polycystic kidney disease (PKD) are not well defined. In this study, male Lewis Polycystic Kidney Disease (LPK) rats (a genetic ortholog of human NPHP9, phenotypically characterised by diffuse distal nephron cystic growth) and Lewis controls received either vehicle (V) or sirolimus (S, 0.2 mg/kg by intraperitoneal injection 5 days per week) during the early (postnatal weeks 3 to 10) or late stages of disease (weeks 10 to 20). In early-stage disease, sirolimus reduced kidney enlargement (by 63%), slowed the rate of increase in total kidney volume (TKV) in serial MRI by 78.2% (LPK+V: 132.3±59.7 vs. LPK+S: 28.8±12.0% per week) but only partly reduced the percentage renal cyst area (by 19%) and did not affect the decline in endogenous creatinine clearance (CrCl) in LPK rats. In late-stage disease, sirolimus reduced kidney enlargement (by 22%) and the rate of increase in TKV by 71.8% (LPK+V: 13.1±6.6 vs. LPK+S: 3.7±3.7% per week) but the percentage renal cyst area was unaltered, and the CrCl only marginally better. Sirolimus reduced renal TORC1 activation but not TORC2, NF-κB DNA binding activity, CCL2 or TNFα expression, and abnormalities in cilia ultrastructure, hypertension and cardiac disease were also not improved. Thus, the relative treatment efficacy of TORC1 inhibition on kidney enlargement was consistent at all disease stages, but the absolute effect was determined by the timing of drug initiation. Furthermore, cystic microarchitecture, renal function and cardiac disease remain abnormal with TORC1 inhibition, indicating that additional approaches to normalise cellular dedifferentiation, inflammation and hypertension are required to completely arrest the progression of PKDs.

Protein- and diabetes-induced glomerular hyperfiltration: role of glucagon, vasopressin, and urea

A single protein-rich meal (or an infusion of amino acids) is known to increase the glomerular filtration rate (GFR) for a few hours, a phenomenon known as “hyperfiltration.” It is important to understand the factors that initiate this upregulation because it becomes maladaptive in the long term. Several mediators and paracrine factors have been shown to participate in this upregulation, but they are not directly triggered by protein intake. Here, we explain how a rise in glucagon and in vasopressin secretion, directly induced by protein ingestion, might be the initial factors triggering the hepatic and renal events leading to an increase in the GFR. Their effects include metabolic actions in the liver and stimulation of sodium chloride reabsorption in the thick ascending limb. Glucagon is not only a glucoregulatory hormone. It is also important for the excretion of nitrogen end products by stimulating both urea synthesis in the liver (along with gluconeogenesis from amino acids) and urea excretion by the kidney. Vasopressin allows the concentration of nitrogenous end products (urea, ammonia, etc.) and other protein-associated wastes in a hyperosmotic urine, thus allowing a very significant water economy characteristic of all terrestrial mammals. No hyperfiltration occurs in the absence of one or the other hormone. Experimental results suggest that the combined actions of these two hormones, along with the complex intrarenal handling of urea, lead to alter the composition of the tubular fluid at the macula densa and to reduce the intensity of the signal activating the tubuloglomerular feedback control of GFR, thus allowing GFR to raise. Altogether, glucagon, vasopressin, and urea contribute to set up the best compromise between efficient urea excretion and water economy.

Total Kidney Volume in Autosomal Dominant Polycystic Kidney Disease: A Biomarker of Disease Progression and Therapeutic Efficacy

Autosomal dominant polycystic kidney disease (ADPKD) is the most common potentially life-threatening monogenic disorder in humans, characterized by progressive development and expansion of fluid-filled cysts in the kidneys and other organs. Ongoing cyst growth leads to progressive kidney enlargement, whereas kidney function remains stable for decades as a result of hyperfiltration and compensation by unaffected nephrons. Kidney function irreversibly declines only in the late stages of the disease, when most of the parenchyma is lost to cystic and fibrotic tissue and the remaining compensatory capacity is overwhelmed. Hence, conventional kidney function measures, such as glomerular filtration rate, do not adequately assess disease progression in ADPKD, especially in its early stages. Given the recent development of potential targeted therapies in ADPKD, it has become critically important to identify relevant biomarkers that can be used to determine the degree of disease progression and evaluate the effects of therapeutic interventions on the course of the disease. We review the current evidence to provide an informed perspective on whether total kidney volume (TKV) is a suitable biomarker for disease progression and whether TKV can be used as an efficacy end point in clinical trials. We conclude that because cystogenesis is the central factor leading to kidney enlargement, TKV appears to be an appropriate biomarker and is gaining wider acceptance. Several studies have identified TKV as a relevant imaging biomarker for monitoring and predicting disease progression and support its use as a prognostic end point in clinical trials.

Urine Fetuin-A is a biomarker of autosomal dominant polycystic kidney disease progression

Background

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by numerous fluid-filled cysts that frequently result in end-stage renal disease. While promising treatment options are in advanced clinical development, early diagnosis and follow-up remain a major challenge. We therefore evaluated the diagnostic value of Fetuin-A as a new biomarker of ADPKD in human urine.

Results

We found that renal Fetuin-A levels are upregulated in both Pkd1 and Bicc1 mouse models of ADPKD. Measurement by ELISA revealed that urinary Fetuin-A levels were significantly higher in 66 ADPKD patients (17.5 ± 12.5 μg/mmol creatinine) compared to 17 healthy volunteers (8.5 ± 3.8 μg/mmol creatinine) or 50 control patients with renal diseases of other causes (6.2 ± 2.9 μg/mmol creatinine). Receiver operating characteristics (ROC) analysis of urinary Fetuin-A levels for ADPKD rendered an optimum cut-off value of 12.2 μg/mmol creatinine, corresponding to 94% of sensitivity and 60% of specificity (area under the curve 0.74 ; p = 0.0019). Furthermore, urinary Fetuin-A levels in ADPKD patients correlated with the degree of renal insufficiency and showed a significant increase in patients with preserved renal function followed for two years.

Conclusions

Our findings establish urinary Fetuin-A as a sensitive biomarker of the progression of ADPKD. Further studies are required to examine the pathogenic mechanisms of elevated renal and urinary Fetuin-A in ADPKD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0463-7) contains supplementary material, which is available to authorized users.

Prophages in enterococcal isolates from renal transplant recipients: renal failure etiologies promote selection of strains

Infections caused by commensal bacteria may be fatal for the patients under immunosuppressive therapy. This results also from difficulty in identification of high risk strains. Enterococcal infections are increasingly frequent but despite many studies on virulence traits, the difference between commensal and pathogenic strains remains unclear. Prophages are newly described as important elements in competition between strains during colonization, as well as pathogenicity of the strains. Here we evaluate a difference in presence of pp4, pp1, and pp7 prophages and ASA (aggregation substance) gene expression in enterococcal isolates from renal transplant recipients (RTx) with different etiology of the end-stage renal failure. Prophages sequence was screened by PCR in strains of Enterococcus faecalis isolated from urine and feces of 19 RTx hospitalized at Medical University of Gdansk and 18 healthy volunteers. FLOW-FISH method with use of linear locked nucleic acid (LNA) probe was used to assess the ASA gene expression. Additionally, ability of biofilm formation was screened by crystal violet staining method. Presence of prophages was more frequent in fecal isolates from immunocompromised patients than in isolates from healthy volunteers. Additionally, both composition of prophages and ASA gene expression were related to the etiology of renal disease.

Pharmacological management of polycystic kidney disease

INTRODUCTION

Autosomal-dominant polycystic kidney disease (ADPKD) represents a therapeutic challenge as effective treatment to retard the growth of cysts in the kidneys and the liver has not been available despite decades of intense basic and clinical research.

AREAS COVERED

Several clinical trials have been performed in recent years to study the effect of diverse drugs on the growth of renal and hepatic cysts, and on functional deterioration of the glomerular filtration rate. The drug classes that have been tested in randomized clinical trials include the mammalian target of rapamycin (mTOR) inhibitors, sirolimus and everolimus, the somatostatin analogues (octreotide, lanreotide, pasireotide), and most recently, the vasopressin V2 receptor antagonist, tolvaptan. The results with the mTOR inhibitors were disappointing, but more encouraging with the somatostatin analogues and with tolvaptan. Additional drugs are being tested, which include among others, the SRC-ABL tyrosine kinase inhibitor, bosutinib, and the traditional Chinese herbal medication, triptolide. Additional therapeutic strategies to retard cyst growth aim at blood pressure control via inhibition of the renin-angiotensin system and the sympathetic nervous system.

EXPERT OPINION

Given the accumulated knowledge, it is currently uncertain whether drugs will become available in the near future to significantly change the course of the relentlessly progressing polycystic kidney disease.

Rationale and design of the DIPAK 1 study: a randomized controlled clinical trial assessing the efficacy of lanreotide to Halt disease progression in autosomal dominant polycystic kidney disease

BACKGROUND

There are limited therapeutic options to slow the progression of autosomal dominant polycystic kidney disease (ADPKD). Recent clinical studies indicate that somatostatin analogues are promising for treating polycystic liver disease and potentially also for the kidney phenotype. We report on the design of the DIPAK 1 (Developing Interventions to Halt Progression of ADPKD 1) Study, which will examine the efficacy of the somatostatin analogue lanreotide on preservation of kidney function in ADPKD.

STUDY DESIGN

The DIPAK 1 Study is an investigator-driven, randomized, multicenter, controlled, clinical trial.

SETTING & PARTICIPANTS

We plan to enroll 300 individuals with ADPKD and estimated glomerular filtration rate (eGFR) of 30-60 mL/min/1.73 m(2) who are aged 18-60 years.

INTERVENTION

Patients will be randomly assigned (1:1) to standard care or lanreotide, 120 mg, subcutaneously every 28 days for 120 weeks, in addition to standard care.

OUTCOMES

Main study outcome is the slope through serial eGFR measurements starting at week 12 until end of treatment for lanreotide versus standard care. Secondary outcome parameters include change in eGFR from pretreatment versus 12 weeks after treatment cessation, change in kidney volume, change in liver volume, and change in quality of life.

MEASUREMENTS

Blood and urine will be collected and questionnaires will be filled in following a fixed scheme. Magnetic resonance imaging will be performed for assessment of kidney and liver volume.

RESULTS

Assuming an average change in eGFR of 5.2 ± 4.3 (SD) mL/min/1.73 m(2) per year in untreated patients, 150 patients are needed in each group to detect a 30% reduction in the rate of kidney function loss between treatment groups with 80% power, 2-sided α = 0.05, and 20% protocol violators and/or dropouts.

LIMITATIONS

The design is an open randomized controlled trial and measurement of our primary end point does not begin at randomization.

CONCLUSIONS

The DIPAK 1 Study will show whether subcutaneous administration of lanreotide every 4 weeks attenuates disease progression in patients with ADPKD.

CFTR inhibitors

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a cAMP-regulated Cl- channel whose major function is to facilitate epithelial fluid secretion. Loss-of-function mutations in CFTR cause the genetic disease cystic fibrosis. CFTR is required for transepithelial fluid transport in certain secretory diarrheas, such as cholera, and for cyst expansion in autosomal dominant polycystic kidney disease. High-throughput screening has yielded CFTR inhibitors of the thiazolidinone, glycine hydrazide and quinoxalinedione chemical classes. The glycine hydrazides target the extracellular CFTR pore, whereas the thiazolidinones and quinoxalinediones act at the cytoplasmic surface. These inhibitors have been widely used in cystic fibrosis research to study CFTR function at the cell and organ levels. The most potent CFTR inhibitor has IC50 of approximately 4 nM. Studies in animal models support the development of CFTR inhibitors for antisecretory therapy of enterotoxin-mediated diarrheas and polycystic kidney disease.

Novel role of ouabain as a cystogenic factor in autosomal dominant polycystic kidney disease

The classic role of the Na-K-ATPase is that of a primary active transporter that utilizes cell energy to establish and maintain transmembrane Na(+) and K(+) gradients to preserve cell osmotic stability, support cell excitability, and drive secondary active transport. Recent studies have revealed that Na-K-ATPase located within cholesterol-containing lipid rafts serves as a receptor for cardiotonic steroids, including ouabain. Traditionally, ouabain was viewed as a toxin produced only in plants, and it was used in relatively high concentrations to experimentally block the pumping action of the Na-K-ATPase. However, the new and unexpected role of the Na-K-ATPase as a signal transducer revealed a novel facet for ouabain in the regulation of a myriad of cell functions, including cell proliferation, hypertrophy, apoptosis, mobility, and metabolism. The seminal discovery that ouabain is endogenously produced in mammals and circulates in plasma has fueled the interest in this endogenous molecule as a potentially important hormone in normal physiology and disease. In this article, we review the role of the Na-K-ATPase as an ion transporter in the kidney, the experimental evidence for ouabain as a circulating hormone, the function of the Na-K-ATPase as a signal transducer that mediates ouabain's effects, and novel results for ouabain-induced Na-K-ATPase signaling in cystogenesis of autosomal dominant polycystic kidney disease.

Genomic instability in patients with autosomal-dominant polycystic kidney disease

OBJECTIVE

Autosomal-dominant polycystic kidney disease (ADPKD) is a systemic disorder affecting multiple organs that results in renal and extrarenal cysts. Patients with ADPKD may have genomic instability, making them more vulnerable to developing cancer. This study aimed to investigate latent genomic instability in patients with ADPKD, using single-cell gel electrophoresis (comet assay).

METHODS

The susceptibility of peripheral blood lymphocytes to DNA damage induced by X-ray treatment (0.5 Gy) was tested in 20 patients with ADPKD using single-cell gel electrophoresis. The percentage of DNA in the comet tail (TDNA%) before and after irradiation was compared between patients with ADPKD and 20 sex- and age-matched healthy control subjects.

RESULTS

Renal and extrarenal cysts were observed in patients with ADPKD. A significantly higher mean TDNA% was determined in patients with ADPKD compared with control subjects (8.85% versus 7.50%). After in vitro irradiation, DNA damage was significantly increased in all participants, but the increase was significantly greater in patients with ADPKD compared with control subjects.

CONCLUSION

These data suggest that patients with ADPKD have genomic instability, which may trigger renal and extrarenal cyst formation.

Clinical utility of PKD2 mutation testing in a polycystic kidney disease cohort attending a specialist nephrology out-patient clinic

Background

ADPKD affects approximately 1:1000 of the worldwide population. It is caused by mutations in two genes, PKD1 and PKD2. Although allelic variation has some influence on disease severity, genic effects are strong, with PKD2 mutations predicting later onset of ESRF by up to 20 years. We therefore screened a cohort of ADPKD patients attending a nephrology out-patient clinic for PKD2 mutations, to identify factors that can be used to offer targeted gene testing and to provide patients with improved prognostic information.

Methods

142 consecutive individuals presenting to a hospital nephrology out-patient service with a diagnosis of ADPKD and CKD stage 4 or less were screened for mutations in PKD2, following clinical evaluation and provision of a detailed family history (FH).

Results

PKD2 mutations were identified in one fifth of cases. 12% of non-PKD2 patients progressed to ESRF during this study whilst none with a PKD2 mutation did (median 38.5 months of follow-up, range 16–88 months, p < 0.03). A significant difference was found in age at ESRF of affected family members (non-PKD2 vs. PKD2, 54 yrs vs. 65 yrs; p < 0.0001). No PKD2 mutations were identified in patients with a FH of ESRF occurring before age 50 yrs, whereas a PKD2 mutation was predicted by a positive FH without ESRF.

Conclusions

PKD2 testing has a clinically significant detection rate in the pre-ESRF population. It did not accurately distinguish those individuals with milder renal disease defined by stage of CKD but did identify a group less likely to progress to ESRF. When used with detailed FH, it offers useful prognostic information for individuals and their families. It can therefore be offered to all but those whose relatives have developed ESRF before age 50.

Caffeine intake by patients with autosomal dominant polycystic kidney disease

Because caffeine may induce cyst and kidney enlargement in autosomal dominant polycystic kidney disease (ADPKD), we evaluated caffeine intake and renal volume using renal ultrasound in ADPKD patients. Caffeine intake was estimated by the average of 24-h dietary recalls obtained on 3 nonconsecutive days in 102 ADPKD patients (68 females, 34 males; 39 ± 12 years) and compared to that of 102 healthy volunteers (74 females, 28 males; 38 ± 14 years). The awareness of the need for caffeine restriction was assessed. Clinical and laboratory data were obtained from the medical records of the patients. Mean caffeine intake was significantly lower in ADPKD patients versus controls (86 vs 134 mg/day), and 63% of the ADPKD patients had been previously aware of caffeine restriction. Caffeine intake did not correlate with renal volume in ADPKD patients. There were no significant differences between the renal volumes of patients in the highest and lowest tertiles of caffeine consumption. Finally, age-adjusted multiple linear regression revealed that renal volume was associated with hypertension, chronic kidney disease stage 3 and the time since diagnosis, but not with caffeine intake. The present small cross-sectional study indicated a low level of caffeine consumption by ADPKD patients when compared to healthy volunteers, which was most likely due to prior awareness of the need for caffeine restriction. Within the range of caffeine intake observed by ADPKD patients in this study (0-471 mg/day), the renal volume was not directly associated with caffeine intake.

Educational paper: ciliopathies

Cilia are antenna-like organelles found on the surface of most cells. They transduce molecular signals and facilitate interactions between cells and their environment. Ciliary dysfunction has been shown to underlie a broad range of overlapping, clinically and genetically heterogeneous phenotypes, collectively termed ciliopathies. Literally, all organs can be affected. Frequent cilia-related manifestations are (poly)cystic kidney disease, retinal degeneration, situs inversus, cardiac defects, polydactyly, other skeletal abnormalities, and defects of the central and peripheral nervous system, occurring either isolated or as part of syndromes. Characterization of ciliopathies and the decisive role of primary cilia in signal transduction and cell division provides novel insights into tumorigenesis, mental retardation, and other common causes of morbidity and mortality, including diabetes mellitus and obesity. New technologies ("Next generation sequencing/NGS") have considerably improved genetic research and diagnostics by allowing simultaneous investigation of all disease genes at reduced costs and lower turn-around times. This is undoubtedly a result of the dynamic development in the field of human genetics and deserves increased attention in genetic counselling and the management of affected families.

Systematic review: the pathophysiology and management of polycystic liver disease

BACKGROUND

Polycystic liver diseases (PCLD) represent a group of genetic disorders in which cysts occur solely in the liver, or together with renal cysts. Most of the patients with PCLD are asymptomatic, however, in some patients, expansion of liver cysts causes invalidating abdominal symptoms.

AIM

To provide a systemic review on the pathophysiology and management of PCLD.

METHODS

A PubMed search was undertaken to identify relevant literature using search terms including polycystic liver disease, pathophysiology, surgical and medical management.

RESULTS

The most common complication in patients with PCLD is extensive hepatomegaly, which may lead to malnutrition and can be lethal. Conservative surgical approaches are only partially effective and do not change the natural course of the disease. Liver transplantation has been successfully performed in PCLD, however, in an era of organ shortage, medical management needs to be evaluated. A better understanding of the pathophysiology and the availability of animal models have already identified promising drugs. Abnormalities in cholangiocyte proliferation/apoptosis and enhanced fluid secretion are key factors in the pathophysiology. It has been demonstrated in rodents and in humans that somatostatin analogues diminish liver volume. The role of the inhibitors of the mammalian target of rapamycin (mTOR) in the management of PCLD is still under investigation.

CONCLUSIONS

The exact pathophysiology of polycystic liver disease still remains unclear. In symptomatic patients, none of the currently available surgical options except liver transplantation have been shown to change the natural course of the disease. The use of somatostatin analogues has been shown to diminish liver volume.

mTOR signaling in polycystic kidney disease

Polycystic kidney diseases (PKDs) comprise a large group of genetic disorders characterized by formation of cysts in the kidneys and other organs, ultimately leading to end-stage renal disease. Although PKDs can be caused by mutations in different genes, they converge on a set of common molecular mechanisms involved in cystogenesis and ciliary dysfunction, and can be qualified as ciliopathies. Recent advances in understanding the mechanisms regulating disease progression have led to the development of new therapies that are being tested in both preclinical and clinical trials. In this article, we briefly review a network of molecular pathways of cystogenesis that are regulated by ciliary functions. We discuss the mTOR pathway in depth, highlighting recent progress in understanding its role in PKD and the current results of clinical trials.

Potent, metabolically stable benzopyrimido-pyrrolo-oxazine-dione (BPO) CFTR inhibitors for polycystic kidney disease

We previously reported the discovery of pyrimido-pyrrolo-quinoxalinedione (PPQ) inhibitors of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and showed their efficacy in an organ culture model of polycystic kidney disease (PKD) (J. Med. Chem. 2009, 52, 6447-6455). Here, we report related benzopyrimido-pyrrolo-oxazinedione (BPO) CFTR inhibitors. To establish structure-activity relationships and select lead compound(s) with improved potency, metabolic stability, and aqueous solubility compared to the most potent prior compound 8 (PPQ-102, IC(50) ∼ 90 nM), we synthesized 16 PPQ analogues and 11 BPO analogues. The analogues were efficiently synthesized in 5-6 steps and 11-61% overall yield. Modification of 8 by bromine substitution at the 5-position of the furan ring, replacement of the secondary amine with an ether bridge, and carboxylation, gave 6-(5-bromofuran-2-yl)-7,9-dimethyl-8,10-dioxo-11-phenyl-7,8,9,10-tetrahydro-6H-benzo[b]pyrimido [4',5':3,4]pyrrolo [1,2-d][1,4]oxazine-2-carboxylic acid 42 (BPO-27), which fully inhibited CFTR with IC(50) ∼ 8 nM and, compared to 8, had >10-fold greater metabolic stability and much greater polarity/aqueous solubility. In an embryonic kidney culture model of PKD, 42 prevented cyst growth with IC(50) ∼ 100 nM. Benzopyrimido-pyrrolo-oxazinediones such as 42 are potential development candidates for antisecretory therapy of PKD.

Sudden death of a young male with previously undiagnosed autosomal dominant polycystic kidney disease (ADPKD)

Autosomal dominant polycystic kidney disease (ADPKD) is one of the best known genetic diseases. However, in only very rare cases does it present as an abnormal death followed by clarification of its genetic background. We experienced a case in which ADPKD first became evident from the results of forensic autopsy, on the basis of which all potentially affected family members were offered genetic and other medical examinations. In this way, forensic medicine was able not only to determine the cause of death but to contribute to preventive medicine as well.

Drug discovery for polycystic kidney disease

In polycystic kidney disease (PKD), a most common human genetic diseases, fluid-filled cysts displace normal renal tubules and cause end-stage renal failure. PKD is a serious and costly disorder. There is no available therapy that prevents or slows down the cystogenesis and cyst expansion in PKD. Numerous efforts have been made to find drug targets and the candidate drugs to treat PKD. Recent studies have defined the mechanisms underlying PKD and new therapies directed toward them. In this review article, we summarize the pathogenesis of PKD, possible drug targets, available PKD models for screening and evaluating new drugs as well as candidate drugs that are being developed.

Proteomics in chronic kidney disease: The issues clinical nephrologists need an answer for

A growing number of patients are recognised to have chronic kidney disease (CKD). However, only a minority will progress to end-stage renal disease requiring dialysis or transplantation. Currently available diagnostic and staging tools frequently fail to identify those at higher risk of progression or death. Furthermore within specific disease entities there are shortcomings in the prediction of the need for therapeutic interventions or the response to different forms of therapy. Kidney and urine proteomic biomarkers are considered as promising diagnostic tools to predict CKD progression early in diabetic nephropathy, facilitating timely and selective intervention that may reduce the related health-care expenditures. However, independent groups have not validated these findings and the technique is not currently available for routine clinical care. Furthermore, there are gaps in our understanding of predictors of progression or need for therapy in non-diabetic CKD. Presumably, a combination of tissue and urine biomarkers will be more informative than individual markers. This review identifies clinical questions in need of an answer, summarises current information on proteomic biomarkers and CKD, and describes the European Kidney and Urine Proteomics initiative that has been launched to carry out a clinical study aimed at identifying urinary proteomic biomarkers distinguishing between fast and slow progressors among patients with biopsy-proven primary glomerulopathies.

Cilium, centrosome and cell cycle regulation in polycystic kidney disease

Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

ADPKD: Prototype of Cardiorenal Syndrome Type 4

The cardiorenal syndrome type 4 (Chronic Renocardiac Syndrome) is characterized by a condition of primary chronic kidney disease (CKD) that leads to an impairment of the cardiac function, ventricular hypertrophy, diastolic dysfunction, and/or increased risk of adverse cardiovascular events. Clinically, it is very difficult to distinguish between CRS type 2 (Chronic Cardiorenal Syndrome) and CRS type 4 (Chronic Renocardiac Syndrome) because often it is not clear whether the primary cause of the syndrome depends on the heart or the kidney. Autosomal dominant polycystic kidney disease (ADPKD), a genetic disease that causes CKD, could be viewed as an ideal prototype of CRS type 4 because it is certain that the primary cause of cardiorenal syndrome is the kidney disease. In this paper, we will briefly review the epidemiology of ADPKD, conventional and novel biomarkers which may be useful in following the disease process, and prevention and treatment strategies.