Autosomal dominant polycystic kidney disease: recent advances in pathogenesis and potential therapies. Clin Exp Nephrol. 2013;17:317-326. [PMID: 23192769 DOI: 10.1007/s10157-012-0741-0]

Association of hyperphosphatemia with renal prognosis in patients with autosomal dominant polycystic kidney disease

BACKGROUND

Serum phosphate (P) levels are generally lower in autosomal dominant polycystic kidney disease (ADPKD) than in other kidney disorders, potentially masking the clinical significance of hyperphosphatemia. This study aimed to determine if serum P levels can predict renal outcomes in ADPKD patients.

METHODS

We included 235 patients with ADPKD who were not taking drugs to treat hyperphosphatemia. Survival analysis was performed for the renal outcome of a 50% reduction in estimated glomerular filtration rate or initiation of renal replacement therapy.

RESULTS

Multivariable Cox regression analyses revealed that serum P (1 mg/dL increase, HR = 2.03, P < 0.0001) was a significant risk factor for kidney disease progression. Similarly, hyperphosphatemia (P > 3.5 mg/dL, HR = 2.05; P > 4.0 mg/dL, HR = 1.90; P > 4.5 mg/dL, HR = 2.78; P > 5.0 mg/dL, HR = 27.22) was significantly associated with renal prognosis. Kaplan-Meier analysis showed significantly lower kidney survival rates in patients with P > 3.5 mg/dL than in those without hyperphosphatemia (log-rank test, P < 0.0001), and similar Kaplan-Meier analysis results were found for P > 4.0 mg/dL, P > 4.5 mg/dL, and P > 5.0 mg/dL. The 2 year kidney survival rate for ADPKD patients with P > 3.5 mg/dL was 66.7% overall and 41.4% in those with stage 4-5 CKD. For patients with P > 4.0 mg/dL, the survival rate dropped to 46.8% overall and 28.2% in those with stage 4-5 CKD, indicating a very poor prognosis.

CONCLUSION

Hyperphosphatemia was associated with renal prognosis in patients with ADPKD. In these patients, attention should be paid to even mild serum P elevation of > 3.5 or > 4.0 mg/dL.

Elevated hemoglobin levels in renal transplant recipients with polycystic kidney disease versus other etiologies: exploring mechanisms and implications for outcomes

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD)-related end-stage kidney disease (ESKD) often necessitates transplantation. However, the impact of ADPKD on post-transplant outcomes, specifically hemoglobin levels, remains unknown.

METHODS

We retrospectively analyzed 513 Kidney Transplant Recipients (KTRs), of whom 81 had ESKD due to ADPKD (20 with pre-transplant native nephrectomy and 61 without). Hemoglobin levels were evaluated at multiple time intervals post-transplant.

RESULTS

Kidney transplant recipients with ADPKD vs. KTRs with ESKD due to other causes exhibited significantly higher hemoglobin levels in repeated measurement analysis. Multivariable analyses confirmed ADPKD as an independent predictor for elevated hemoglobin levels. In a multivariable logistic regression analysis, the odds for maximum hemoglobin > 15 mg/dL at 3-12 months post-transplant were more than twice as high in ADPKD patients vs. all the other KTRs (Odds Ratio [OR] 2.31, 95% Confidence Interval [CI] 1.3-4.13, p < 0.001). Pre-transplant native nephrectomy revealed a trend toward lower hemoglobin levels. Elevated hemoglobin levels were linked to improved estimated glomerular filtration rate (eGFR) at one year post-transplant. Patient survival was enhanced among KTRs with ADPKD compared to other ESKD causes.

CONCLUSIONS

Kidney transplant recipients with ADPKD exhibited elevated hemoglobin levels post-transplant, possibly due to prolonged native kidney erythropoietin production. These elevated hemoglobin levels were linked to improved outcomes, including allograft function and patient survival. Future research should further investigate the underlying mechanisms driving favorable ADPKD KTR outcomes.

Factors associated with early-onset intracranial aneurysms in patients with autosomal dominant polycystic kidney disease

BACKGROUND

Recently, the importance of attribute-based medicine has been emphasized. The effects of early-onset intracranial aneurysms on patients can be significant and long-lasting. Herein, we compared the factors associated with intracranial aneurysms in patients with autosomal dominant polycystic kidney disease (ADPKD) according to age categories (≥ 50 years, < 50 years).

METHODS

We included 519 ADPKD patients, with a median age of 44 years, estimated glomerular filtration rate of 54.5 mL/min/1.73 m2, and total follow-up duration of 3104 patient-years. Logistic regression analyses were performed to determine factors associated with intracranial aneurysms.

RESULTS

Regarding the presence of intracranial aneurysm, significant interactions were identified between the age category (age ≥ 50 years), female sex (P = 0.0027 for the interaction) and hypertension (P = 0.0074 for the interaction). Female sex and hypertension were associated with intracranial aneurysm risk factors only in patients aged ≥ 50 years. The presence of intracranial aneurysm was significantly associated with chronic kidney disease (CKD) stages 4-5 (odds ratio [OR] = 3.87, P = 0.0007) and family history of intracranial aneurysm or subarachnoid hemorrhage (OR = 2.30, P = 0.0217) in patients aged < 50 years. For patients aged ≥ 50 years, in addition to the abovementioned factors [OR = 2.38, P = 0.0355 for CKD stages 4-5; OR = 3.49, P = 0.0094 for family history of intracranial aneurysm or subarachnoid hemorrhage], female sex (OR = 4.51, P = 0.0005), and hypertension (OR = 5.89, P = 0.0012) were also associated with intracranial aneurysm.

CONCLUSION

Kidney dysfunction and family history of intracranial aneurysm or subarachnoid hemorrhage are risk factors for early-onset intracranial aneurysm. Patients aged < 50 years with a family history of intracranial aneurysm or subarachnoid hemorrhage or with CKD stages 4-5 may be at an increased risk of early-onset intracranial aneurysm.

Activation of farnesoid X receptor retards expansion of renal collecting duct cell-derived cysts via inhibition of CFTR-mediated Cl- secretion

The transcription factor farnesoid X receptor (FXR) regulates energy metabolism. Specifically, FXR functions to regulate cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl- secretion in intestinal epithelial cells. Therefore, this study aimed to investigate the role of FXR in CFTR-mediated Cl- secretion in renal tubular cells and to further elucidate its effects on renal cyst formation and growth. CFTR-mediated Cl- transport was evaluated via short-circuit current (ISC) measurements in Madin-Darby canine kidney (MDCK) cell monolayers and primary rat inner medullary collecting duct cells. The role of FXR in renal cyst formation and growth was determined by the MDCK cell-derived cyst model. Incubation with synthesized (GW4064) and endogenous (CDCA) FXR ligands reduced CFTR-mediated Cl- secretion in a concentration- and time-dependent manner. The inhibitory effect of FXR ligands was not due to the result of reduced cell viability and was attenuated by cotreatment with an FXR antagonist. FXR activation significantly decreased CFTR protein but not its mRNA. In addition, FXR activation inhibited CFTR-mediated Cl- secretion in primary renal collecting duct cells. FXR activation decreased ouabain-sensitive ISC without altering Na+-K+-ATPase mRNA and protein levels. Furthermore, FXR activation significantly reduced the number of cysts and renal cyst expansion. These inhibitory effects were correlated with a decrease in the expression of protein synthesis regulators mammalian target of rapamycin/S6 kinase. This study shows that FXR activation inhibits Cl- secretion in renal cells via inhibition of CFTR expression and retards renal cyst formation and growth. The discoveries point to a physiological role of FXR in the regulation of CFTR and a potential therapeutic application in polycystic kidney disease treatment.NEW & NOTEWORTHY The present study reveals that farnesoid X receptor (FXR) activation reduces microcyst formation and enlargement. This inhibitory effect of FXR activation is involved with decreased cell proliferation and cystic fibrosis transmembrane conductance regulator-mediated Cl- secretion in renal collecting duct cells. FXR might represent a novel target for the treatment of autosomal dominant polycystic kidney disease.

Mammalian target of rapamycin inhibition impacts energy homeostasis and induces sex-specific body weight loss in humans

BACKGROUND

Previous data from a 2-year randomized controlled trial (CRAD001ADE12) indicated that mammalian target of rapamycin (mTOR) inhibition by everolimus slowed cyst growth in patients with autosomal-dominant polycystic kidney disease (ADPKD). During the trial, we noted body weight loss in some patients, particularly in women. We hypothesized that everolimus causes body weight reduction by reduced food intake and/or metabolic changes, which could lead to cachexia.

METHODS

Within a sub-analysis of the CRAD001ADE12 trial, body weight course was investigated regarding sex-specific differences in 433 adult ADPKD patients (everolimus, n = 215; placebo, n = 218). One hundred four out of 111 patients who participated in the clinical trial centre in Berlin were evaluated under everolimus/placebo therapy (on drug: everolimus, n = 48; placebo, n = 56) and after therapy (off drug: everolimus, n = 15; placebo, n = 18). Eating habits and nutrient/caloric intake were evaluated by validated questionnaires. Systemic and local metabolism was evaluated in four patients after an oral glucose load (OGL) by using calorimetry and adipose/muscle tissue microdialysis.

RESULTS

Within the 2-year CRAD001ADE12 trial, a significant body weight loss was observed in female patients on everolimus versus placebo (P = 0.0029). Data of the Berlin Cohort revealed that weight loss was greater in women on everolimus versus men (P < 0.01). After 9 months, women and men had lost 2.6 ± 3.8 and 0.8 ± 1.5 kg (P < 0.05) in body weight, respectively, and after 21 months, they had lost 4.1 ± 6.6 and 1.0 ± 3.3 kg (P < 0.05), respectively. On everolimus, caloric intake was significantly lower in women versus men (1510 ± 128 vs. 2264 ± 216 kcal/day, P < 0.05), caused mainly by a lower fat and protein intake in women versus men. Cognitive restraints, disinhibition and hunger remained unchanged. In a subgroup of patients resting metabolic rate was unchanged whereas OGL-induced thermogenesis was reduced (7 ± 2 vs. 11 ± 2 kcal, P < 0.05). Fasting and OGL-induced fat oxidation was increased (P < 0.05) on versus off everolimus. In adipose tissue, fasting lipolytic activity was increased, but lipolytic activity was inhibited similarly after the OGL on versus off everolimus, respectively. In skeletal muscle, postprandial glucose uptake and aerobic glycolysis was reduced in patients on everolimus.

CONCLUSIONS

mTOR inhibition by everolimus induces body weight reduction, specifically in female patients. This effect is possibly caused by a centrally mediated reduced food (fat and protein) intake and by centrally/peripherally mediated increased fat oxidation (systemic) and mobilization (adipose tissue). Glucose uptake and oxidation might be reduced in skeletal muscle. This could lead to cachexia and, possibly, muscle wasting. Therefore, our results have important implications for patients recieving immune-suppressive mTOR inhibition therapy.

Case Report: Guanfacine and methylphenidate improved chronic lower back pain in autosomal dominant polycystic kidney disease with comorbid attention deficit hyperactivity disorder and autism spectrum disorder

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited renal disease characterized by the bilateral development of multiple cysts in the kidneys. Pain management is a clinically important issue, especially because approximately 60% of patients with ADPKD experience chronic pain related to hemorrhage from renal cysts, which significantly reduces their daily life. The cystic fibrosis transmembrane conductance regulator, the molecule responsible for cyst formation in ADPKD, is also the cause of cystic fibrosis. Since attention deficit hyperactivity disorder (ADHD) is known to occur frequently in conjunction with cystic fibrosis, ADPKD may be associated with ADHD. However, to our knowledge, no study has investigated 1) ADHD or autism spectrum disorder (ASD) as comorbidities with ADPKD, 2) the effects of ADHD medications on chronic pain in ADPKD, or 3) cerebral blood flow corresponding to guanfacine (GF) or methylphenidate (MP) treatment for chronic pain. We report the case of a 15-year-old girl with ADPKD, who had chronic back pain associated with ADPKD and had to withdraw from high school because the pain interfered with her daily life. Although she took antihypertensive medications to prevent bleeding, they did not provide adequate blood pressure control. The patient was referred to a child psychiatrist and diagnosed with ASD; however, the pain did not improve. Subsequently, she was referred to our pain center. The diagnosis of ADHD was confirmed and treatment with ADHD medications was initiated. Monotherapy with MP, atomoxetine, and GF resulted in hypertension and hypotension as side effects; however, a combination of MP 18 mg and GF 4 mg provided pain relief and moderate blood pressure control, and the patient was able to go on to college. During the course of treatment, there was an improvement in the distribution of cerebral blood flow in the prefrontal and insular cortices. Confirmation of an ADHD diagnosis comorbid with ASD enabled the use of ADHD medications. The combination of MP and GF improved chronic back pain and high blood pressure due to ADPKD and cerebral blood flow. Screening for ADHD is important in the treatment of ADPKD.

Public support for patients with intractable diseases in Japan: impact on clinical indicators from nationwide registries in patients with autosomal dominant polycystic kidney disease

BACKGROUND

Clinical practice guidelines recommend antihypertensive and tolvaptan therapies for patients with autosomal dominant polycystic kidney disease (ADPKD) in Japan. However, tolvaptan therapy may pose an economic burden. The Japanese Ministry of Health, Labour and Welfare supports patients with intractable diseases. This study aimed to confirm the impact of the intractable disease system in Japan on the clinical treatment of ADPKD.

METHODS

We analyzed the data of 3768 patients with ADPKD having a medical subsidy certificate from the Japanese Ministry of Health, Labour and Welfare in 2015-2016. The following quality indicators were use: the adherence rate to the 2014 clinical practice guideline for polycystic kidney disease (prescription rates of antihypertensive agents and tolvaptan in this cohort) and the number of Japanese patients with ADPKD nationwide started on renal replacement therapy in 2014 and 2020.

RESULTS

Compared with new applications from 2015 to 2016, the prescription rates of antihypertensives and tolvaptan for the indicated patients at the 2017 renewal application increased by 2.0% (odds ratio = 1.41, p = 0.008) and 47.4% (odds ratio = 10.1, p > 0.001), respectively. These quality indicators improved with antihypertensive treatment, especially in patients with chronic kidney disease stages 1-2 (odds ratio = 1.79, p = 0.013) and in those aged < 50 years (odds ratio = 1.70, p = 0.003). The number of patients with ADPKD who were started on renal replacement therapy in Japan decreased from 999 in 2014 to 884 in 2020 in the nationwide database (odds ratio = 0.83, p < 0.001).

CONCLUSIONS

The Japanese public intractable disease support system contributes to improvement of ADPKD treatment.

Impact of kidney function and kidney volume on intracranial aneurysms in patients with autosomal dominant polycystic kidney disease

Presently, only personal or family history of intracranial aneurysm/subarachnoid hemorrhage (IA/SAH) has been established as a risk factor for IA in autosomal dominant polycystic kidney disease (ADPKD). This study aimed to verify the association between kidney function/volume and IAs in patients with ADPKD. This study included 519 patients with ADPKD. At baseline IA screening, the median age and estimated glomerular filtration rate were 44 years and 54.5 mL/min/1.73 m², respectively. Family IA/SAH history was confirmed in 18.1% of the patients, and 54.3% of the patients had hypertension. The IA point prevalence was 12.5%. During clinical follow up of 3104 patient-years, de novo IA was detected in 29 patients (0.93% patient-years). The IA period prevalence was 18.1% (median age, 60 years). Multivariable logistic regression demonstrated that total kidney volume (TKV) ≥ 1000 mL (odds ratio [OR] = 2.81), height-adjusted TKV ≥ 500 mL (OR = 2.81), Mayo imaging classification Class 1D-1E (OR = 2.52), and chronic kidney disease stages 3-5 (OR = 2.31) were significantly associated with IA formation. IAs in patients with ADPKD may be associated not only with general risk factors for IAs but also with declining kidney function and increased KV. Kidney disease progression may contribute to effective IA screening and treatment planning in patients with ADPKD.

Germline Mutations for Kidney Volume in ADPKD

Introduction

Valid prediction models or predictors of disease progression in children and young patients with autosomal dominant polycystic kidney disease (ADPKD) are lacking. Although total kidney volume (TKV) and Mayo imaging classification are generally used to predict disease progression in patients with ADPKD, it remains unclear whether germline mutation types are associated with these factors. We therefore investigated the association between mutation type and TKV and Mayo imaging classification among patients with ADPKD.

Methods

A total of 129 patients with ADPKD who underwent genetic analyses were enrolled in the study. The associations between the severity of PKD (TKV ≥ 1000 ml and Mayo classes 1C–1E) and the PKD1 mutation types (nonsense mutation, frameshift or splicing mutation, and substitution) were evaluated.

Results

Among the mutation types, only PKD1 splicing/frameshift mutation had significant associations with TKV ≥ 1000 ml in sex-adjusted and multivariable logistic analyses. Similarly, only the PKD1 splicing/frameshift mutation was significantly associated with Mayo 1C–1E in sex-adjusted and multivariable logistic analyses. PKD1 nonsense mutation, PKD1 substitution, or PKD1 mutation position had no significant association with TKV ≥ 1000 ml or Mayo 1C–1E.

Conclusion

Kidney cyst severity differs according to the mutation types in PKD1. Patients with PKD1 splicing mutations or PKD1 frameshift mutations are associated with TKV ≥ 1000 ml or Mayo 1C–1E. Detailed assessment of mutation types may be useful for predicting renal prognosis in patients with ADPKD and may especially contribute to the care of a high-risk group of children with ADPKD.

Aggressive advanced gastric cancer in a patient with autosomal dominant polycystic kidney disease

A 60-year-old man with autosomal dominant polycystic kidney disease presented with malaise, melena, and epigastric discomfort. Esophagogastroduodenoscopy revealed a massive elevated gastric cancer lesion involving the cardia. Histopathological evaluation of a biopsy specimen showed poorly differentiated adenocarcinoma. Fluorodeoxyglucose-positron emission tomography revealed significant fluorodeoxyglucose uptake in the stomach, liver, bones, and bone marrow. He was diagnosed with metastatic gastric cancer resistant to chemotherapy, and he developed bone marrow carcinomatosis and disseminated intravascular coagulation and died 8 weeks after disease onset. A statistically significant association is reported between autosomal dominant polycystic kidney disease and gastric cancer. Moreover, the specific clinical features observed in our patient could be attributed to the molecular disorders like PC-1 and mechanistic target of rapamycin that are known to occur in autosomal dominant polycystic kidney disease.

A Multitubular Kidney-on-Chip to Decipher Pathophysiological Mechanisms in Renal Cystic Diseases

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major renal pathology provoked by the deletion of PKD1 or PKD2 genes leading to local renal tubule dilation followed by the formation of numerous cysts, ending up with renal failure in adulthood. In vivo, renal tubules are tightly packed, so that dilating tubules and expanding cysts may have mechanical influence on adjacent tubules. To decipher the role of this coupling between adjacent tubules, we developed a kidney-on-chip reproducing parallel networks of tightly packed tubes. This original microdevice is composed of cylindrical hollow tubes of physiological dimensions, parallel and closely packed with 100-200 μm spacing, embedded in a collagen I matrix. These multitubular systems were properly colonized by different types of renal cells with long-term survival, up to 2 months. While no significant tube dilation over time was observed with Madin-Darby Canine Kidney (MDCK) cells, wild-type mouse proximal tubule (PCT) cells, or with PCT Pkd1 +/- cells (with only one functional Pkd1 allele), we observed a typical 1.5-fold increase in tube diameter with isogenic PCT Pkd1 -/- cells, an ADPKD cellular model. This tube dilation was associated with an increased cell proliferation, as well as a decrease in F-actin stress fibers density along the tube axis. With this kidney-on-chip model, we also observed that for larger tube spacing, PCT Pkd1 -/- tube deformations were not spatially correlated with adjacent tubes whereas for shorter spacing, tube deformations were increased between adjacent tubes. Our device reveals the interplay between tightly packed renal tubes, constituting a pioneering tool well-adapted to further study kidney pathophysiology.

Predicting liver cyst severity by mutations in patients with autosomal-dominant polycystic kidney disease

BACKGROUND

Most patients with autosomal-dominant polycystic kidney disease (ADPKD) develop liver cysts and polycystic liver disease as they age. To date, no simple clinical indicator has been confirmed to predict polycystic liver disease exacerbation. Furthermore, the effect of the type and location of mutation on disease progression of polycystic liver disease remains unclear. Here, we aimed to establish a simple liver cyst indicator for clinical practice and investigate whether gene mutations determined liver phenotype in patients with autosomal-dominant polycystic kidney disease.

METHODS

In total, 129 patients with ADPKD were enrolled and liver cyst indicators were assessed based on mutation type (truncating mutation: nonsense, frameshift, and splicing mutation; non-truncating mutation: substitution) and mutation position. Liver cyst severity was determined using Gigot and Drenth classifications, based on their number, maximum diameter, and area ratio with the liver.

RESULTS

We observed an overall prevalence of 62.8% for polycystic liver disease. Patients with PKD1 nonsense mutations, a type of PKD1 truncating mutation, exhibited more severe liver disease phenotypes than those without the mutation. We identified maximum diameter as a potential liver cyst indicator. Moreover, a subgroup analysis that included a PKD1 nonsense mutation cohort revealed that genetic mutations located closer to the 5' end of PKD1 were associated with a maximum diameter index value ≥ 6 cm.

CONCLUSION

PKD1 nonsense mutations were associated with liver cyst severity, which along with maximum diameter index as a simple clinical indicator for liver cysts, may improve the treatment of polycystic liver disease associated with ADPKD.

Exceptionally Large Kidneys in Autosomal Dominant Polycystic Disease in India

We report a case of exceptionally large kidneys in autosomal dominant polycystic kidney disease (ADPKD) in India. A 43-year-old male with a family history of ADPKD presented with abdominal pain, intermittent fever, and a sense of bilateral fullness in both flanks. On examination, he had bilaterally enlarged kidneys extending towards iliac fossae. The serum metabolic panel revealed elevated serum creatinine and blood urea nitrogen. Ultrasound abdomen and pelvis showed enlarged kidneys with parenchyma replaced by multiple varying-sized cysts and few cysts in both the kidneys leading to hemorrhagic transformation. CT abdomen showed bulky bilateral kidneys with multiple non-communicating cysts, with few cysts showing the hemorrhagic and calcific transformation. The right kidney measured 30.3 x 15 cm, weighing 9 lb, was resected. The left kidney measured 37.0 x 14.0 cm and was resected three months later. The specimen weighed 19.8 lb. Histopathological examination showed a gross specimen with a bossellated surface composed of sub-capsular multiple cysts of varying sizes. Both the enlarged kidneys were resected due to cyst hemorrhage and infection. The patient is currently on hemodialysis until he receives a renal graft.

Novel Potential Application of Chitosan Oligosaccharide for Attenuation of Renal Cyst Growth in the Treatment of Polycystic Kidney Disease

Chitosan oligosaccharide (COS), a natural polymer derived from chitosan, exerts several biological activities including anti-inflammation, anti-tumor, anti-metabolic syndrome, and drug delivery enhancer. Since COS is vastly distributed to kidney and eliminated in urine, it may have a potential advantage as the therapeutics of kidney diseases. Polycystic kidney disease (PKD) is a common genetic disorder characterized by multiple fluid-filled cysts, replacing normal renal parenchyma and leading to impaired renal function and end-stage renal disease (ESRD). The effective treatment for PKD still needs to be further elucidated. Interestingly, AMP-activated protein kinase (AMPK) has been proposed as a drug target for PKD. This study aimed to investigate the effect of COS on renal cyst enlargement and its underlying mechanisms. We found that COS at the concentrations of 50 and 100 µg/mL decreased renal cyst growth without cytotoxicity, as measured by MTT assay. Immunoblotting analysis showed that COS at 100 µg/mL activated AMPK, and this effect was abolished by STO-609, a calcium/calmodulin-dependent protein kinase kinase beta (CaMKKβ) inhibitor. Moreover, COS elevated the level of intracellular calcium. These results suggest that COS inhibits cyst progression by activation of AMPK via CaMKKβ. Therefore, COS may hold the potential for pharmaceutical application in PKD.

High Serum Phosphate Level as a Risk Factor to Determine Renal Prognosis in Autosomal Dominant Polycystic Kidney Disease: A Retrospective Study

Background: Serum phosphate levels, which are associated with the progression of renal dysfunction in chronic kidney disease, in patients with autosomal dominant polycystic kidney disease (ADPKD) are lower than those in patients with other kidney diseases. However, their role in ADPKD remains unclear. This study aimed to determine whether serum phosphate levels could have an association with renal prognoses among patients with ADPKD. Methods: In total, 55 patients with PKD1 or PKD2 mutations but not undergoing dialysis were evaluated. Data regarding serum phosphate levels were collected, and Cox regression analyses were used to calculate hazard ratios (HRs) with renal replacement therapy as the endpoint. Results: The median (quartile 1; quartile 3) serum phosphate concentration was 3.4 (3.1; 3.9) mg/dL, and the estimated glomerular filtration rate (eGFR) was 39.5 (17.6; 65.7) mL/min/1.73 m². The multivariate analysis that included age, PKD1 mutation, eGFR, urinary protein excretion, hyperuricemia, and serum phosphate determined that eGFR (HR, 0.82; 95% confidence interval (CI), 0.74-0.90; p < 0.0001) and serum phosphate (HR, 6.78; 95% CI, 1.94-34.02; p = 0.0021) were independently associated with renal replacement therapy. Conclusions: We found that serum phosphate levels were significantly associated with poor renal prognoses in patients with ADPKD.

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.

Association between anemia and renal prognosis in autosomal dominant polycystic kidney disease: a retrospective study

BACKGROUND

Though anemia is a sign of poor renal prognosis in chronic kidney disease (CKD), hemoglobin (Hb) levels are typically higher in autosomal dominant polycystic kidney disease (ADPKD) than in other kidney diseases, and anemia has not been examined as a potential prognosticator. Thus, we investigated anemia as a factor for renal prognosis in ADPKD.

METHODS

In total, 115 non-dialysis patients, 48 men and 67 women, with ADPKD were evaluated. The renal outcome of a 50% reduction in the estimated glomerular filtration rate or renal replacement therapy was examined using the Cox regression analysis and Kaplan-Meier analysis.

RESULTS

Patients were followed for a median of 5.5 years and 50 patients had reached the end point. The mean age of the patients at the first visit was 45.9 ± 13.3 years. The overall mean Hb was 12.90 ± 1.85 g/dL, and the mean Hb in men and women was 13.82 ± 1.72 g/dL and 12.25 ± 1.65 g/dL, respectively. Hb levels and uric protein content were statistically significant factors for poor renal prognosis, while hypertension and genetic mutations failed to reach significance. Furthermore, statistical significance was found in men with Hb < 12 g/dL and in women with Hb < 11 g/dL. Anemia had significant association with kidney disease progression in patients with ADPKD.

CONCLUSIONS

We found that anemia might be a factor for poor renal prognosis in ADPKD. Furthermore, a sex difference was found, wherein men with Hb < 12 g/dL and women with Hb < 11 g/dL were at risk of renal disease progression.

Renal transplant outcomes in patients with autosomal dominant tubulointerstitial kidney disease

INTRODUCTION

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a rare genetic cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD). We aimed to compare renal transplant outcomes in people with ESRD due to ADTKD to those with other causes of renal failure.

METHODS

Patients with clinical characteristics consistent with ADTKD by the criteria outlined in the 2015 KDIGO consensus were included. We compared ADTKD transplant outcomes with those of 4633 non-ADTKD renal transplant recipients.

RESULTS

We included 31 patients who met diagnostic criteria for ADTKD in this analysis, 23 of whom had an identified mutation (28 were categorized as definite-ADTKD and 3 as suspected ADTKD). Five patients received a second transplant during follow-up. In total, 36 grafts were included. We did not identify significant differences between groups in terms of graft or patient survival after transplantation. Twenty-five transplant biopsies were performed during follow-up, and none of these showed signs of recurrent ADTKD post-transplant.

CONCLUSION

In patients with ESRD due to ADTKD, we demonstrate that transplant outcomes are comparable with the general transplant population. There is no evidence that ADTKD can recur after transplantation.

Mutation analyses by next-generation sequencing and multiplex ligation-dependent probe amplification in Japanese autosomal dominant polycystic kidney disease patients

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD), one of the most common hereditary kidney diseases, causes gradual growth of cysts in the kidneys, leading to renal failure. Owing to the advanced technology of next-generation sequencing (NGS), genetic analyses of the causative genes PKD1 and PKD2 have been improved.

METHODS

We performed genetic analyses of 111 Japanese ADPKD patients using hybridization-based NGS and long-range (LR)-PCR-based NGS. Additionally, genetic analyses in exon 1 of PKD1 using Sanger sequencing because of an extremely low coverage of NGS and those using multiplex ligation-dependent probe amplification (MLPA) were performed.

RESULTS

The detection rate using NGS for 111 patients was 86.5%. One mutation in exon 1 of PKD1 and five deletions detected by MLPA were identified. When combined, the total detection rate was 91.9%.

CONCLUSION

Although NGS is useful, we propose the addition of Sanger sequencing for exon 1 of PKD1 and MLPA as indispensable for identifying mutations not detected by NGS.

PKD1 mutation may epistatically ameliorate nephronophthisis progression in patients with NPHP1 deletion

We report a patient with adult-onset nephronophthisis (NPHP) that was identified a homozygous full gene deletion of NPHP1 and a heterozygous PKD1 mutation. We suggest that the PKD1 mutation may have epistatically ameliorated NPHP disease progression and that the screening of larger cohorts for similar possible epistatic effects is needed.

Elevation of the serum liver enzyme levels during tolvaptan treatment in patients with autosomal dominant polycystic kidney disease (ADPKD)

BACKGROUND

In 2014, tolvaptan, a vasopressin receptor antagonist, was approved for the treatment of autosomal dominant polycystic kidney disease (ADPKD) in Japan. Clinical trials of tolvaptan revealed frequent occurrence of the liver function abnormality. According to the package insert in Japan, liver function tests should be performed once a month in patients receiving tolvaptan. Furthermore, immediate discontinuation of tolvaptan is recommended in the appearance of liver function abnormalities.

METHODS

Seven patients of ADPKD who was discontinued tolvaptan because of elevation of the serum liver enzyme levels were described in detail and analyzed.

RESULTS

None of them fulfilled the criteria for applicability of Hy's law, which predicts a high risk of severe, potentially fatal, drug-induced liver injury (DILI). In our patients, the rate of increase of total kidney volume (TKV) significantly decreased during tolvaptan administration, but increased after discontinuation; in Cases 1-5, mean annual growth rate of TKV during administration was - 10.15%/year, and during discontinuation was + 23.72%/year. After the serum liver enzyme levels returned to normal range, tolvaptan was resumed in six patients with informed consent. Except one patient, tolvaptan has been continued without increase of the serum liver enzyme levels.

CONCLUSION

In patients with mild elevation of the serum liver enzyme, as is less than three times the upper limit of normal (ULN), resumption of tolvaptan may be considered after the serum liver enzyme levels return to normal range.

A case of unilateral nephrectomy performed for autosomal dominant polycystic kidney disease with marked unilateral enlargement

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the occurrence of multiple cysts that increase the size of both kidneys, progressively reducing kidney function. Usually the cysts occur bilaterally, and there is no difference in the degree of cyst enlargement between the left and right. Here, we report a case of ADPKD in which kidney size increased markedly on the left side and was accompanied by severe abdominal distension and discomfort. Renal dynamic scintigraphy revealed a severe reduction in function of the left kidney compared with the right. Open left nephrectomy was performed. No change in renal function was observed postoperatively [preoperative estimated glomerular filtration rate (eGFR): 57.6 mL/min/1.73 m², 3-month postoperative eGFR: 56.4 mL/min/1.73 m²], and the abdominal symptoms subsided. When one kidney is markedly larger than the other, the cause and status of the laterality should be evaluated by using renal dynamic scintigraphy in addition to other examinations such as computed tomography or magnetic resonance imaging. Unilateral nephrectomy should be considered as a potential treatment.

Actualización en enfermedad renal poliquística

Introducción. La enfermedad renal poliquística (PKD, por su sigla en inglés) es una enfermedad genética frecuente en la que se desarrollan de forma progresiva lesiones quísticas que reemplazan el parénquima renal. Es una causa de insuficiencia renal terminal y una indicación común para diálisis y trasplante renal. Existen dos presentaciones de esta enfermedad que se distinguen por sus patrones de herencia: la enfermedad renal poliquística dominante (ADPKD, por su sigla en inglés) y la enfermedad renal poliquística recesiva (ARPKD, por su sigla en inglés).Objetivo. Resumir los aspectos más relevantes de la enfermedad renal: epidemiología, fisiopatología, diagnóstico, manifestaciones clínicas, tratamiento y pronóstico.Materiales y métodos. Revisión sistemática de la literatura en las bases de datos PubMed, Lilacs, UptoDate y Medline con los siguientes términos: enfermedades renales poliquísticas, riñón poliquístico autosómico dominante y riñón poliquístico autosómico recesivo.Resultados. Se encontraron 271 artículos y se escogieron 64 con base en su importancia.Conclusiones. Todo paciente con enfermedad renal poliquística en insuficiencia renal grado V debe ser estudiado para un trasplante renal; en la gran mayoría de los casos no se encontrará contraindicación para realizarlo.

Combined renin-angiotensin-aldosterone system blockade and statin therapy effectively reduces the risk of cerebrovascular accident in autosomal dominant polycystic kidney disease: a nationwide population-based cohort study

Fairly limited data reported the incidence and risk of cerebrovascular accident (CVA) in autosomal dominant polycystic kidney disease (ADPKD). Additionally, little is known regarding the therapeutic impact of renin-angiotensin-aldosterone system (RAAS) blockade and statin on reducing the occurrence of CVA in ADPKD. We utilized the data from Taiwan National Health Insurance Research Database (NHIRD) to perform a population-based cohort study (1997-2013). A total of 2,647 patients with ADPKD were selected from 1,000,000 general population after excluding patients with age<18, renal replacement therapy and concomitant diagnosis of CVA. Additionally, non-ADPKD subjects were assigned as comparison group by matching study cohort with age, gender, income and urbanization in 1:10 ratio (n=26,470). The results showed that ADPKD group had significantly higher frequency rate and cumulative incidence of CVA as compared with the non-ADPKD group (8.73% v.s. 3.93%, p<0.0001). Furthermore, the frequencies of both hemorrhagic and ischemic strokes were also significantly higher in the ADPKD than non-ADPKD group (all p-values <0.0001). After adjusting for age, gender and atherosclerotic risk factors with multivariate analysis, ADPKD independently carried 2.34- and 5.12-fold risk for occurrence of CVA and hemorrhagic stroke (95% CI: 2.02-2.72 and 4.01-6.54), respectively. Combination therapy [adjusted (a) HR=0.19, 95% CI: 0.11-0.31] was superior to either RAAS blockade (aHR=0.37, 95% CI, 0.28-0.5) or statin (aHR=0.44, 95% CI, 0.24-0.79) alone for reducing the CVA occurrence in the ADPKD population. In conclusion, ADPKD was associated with an increased risk of CVA occurrence. Combined RAAS blockade and statin therapy effectively reduces the risk of CVA in ADPKD.

Targeting TRPM2 in ROS-Coupled Diseases

Under pathological conditions such as inflammation and ischemia-reperfusion injury large amounts of reactive oxygen species (ROS) are generated which, in return, contribute to the development and exacerbation of disease. The second member of the transient receptor potential (TRP) melastatin subfamily, TRPM2, is a Ca(2+)-permeable non-selective cation channel, activated by ROS in an ADP-ribose mediated fashion. In other words, TRPM2 functions as a transducer that converts oxidative stress into Ca(2+) signaling. There is good evidence that TRPM2 plays an important role in ROS-coupled diseases. For example, in monocytes the influx of Ca(2+) through TRPM2 activated by ROS contributes to the aggravation of inflammation via chemokine production. In this review, the focus is on TRPM2 as a molecular linker between ROS and Ca(2+) signaling in ROS-coupled diseases.

Live Donor Renal Transplant With Simultaneous Bilateral Nephrectomy for Autosomal Dominant Polycystic Kidney Disease Is Feasible and Satisfactory at Long-term Follow-up

BACKGROUND

Timing of bilateral nephrectomy (BN) is controversial in patients with refractory symptoms of autosomal dominant polycystic kidney disease (APKD) in need of a renal transplant.

METHODS

Adults who underwent live donor renal transplant (LRT) + simultaneous BN (SBN) from August 2003 to 2013 at a single transplant center (n = 66) were retrospectively compared to a matched group of APKD patients who underwent LRT alone (n = 52). All patients received general health and polycystic kidney symptom surveys.

RESULTS

Simultaneous BN increased operative duration, estimated blood loss, transfusions, intravenous fluid, and hospital length of stay. Most common indications for BN were pain, loss of abdominal domain, and early satiety. There were more intraoperative complications for LRT + SBN (6 vs 0, P = 0.03; 2 vascular, 2 splenic, and 1 liver injury; 1 reexploration to adjust graft positioning). There were no differences in Clavien-Dindo grade I or II (39% vs 25%, P = 0.12) or grade III or IV (7.5% vs 5.7%, P = 1.0) complications during the hospital course. There were no surgery-related mortalities. There were no differences in readmission rates (68% vs 48%, P = 0.19) or readmissions requiring procedures (25% vs. 20%, P = 0.51) over 12 months. One hundred percent of LRT + SBN allografts functioned at longer than 1 year for those available for follow-up. Survey response rate was 40% for LRT-alone and 56% for LRT + SBN. One hundred percent of LRT + SBN survey responders were satisfied with their choice of having BN done simultaneously.

CONCLUSIONS

Excellent outcomes for graft survival, satisfaction, and morbidity suggest that the combined operative approach be preferred for patients with symptomatic APKD to avoid multiple procedures, dialysis, and costs of staged operations.

Stop chronic kidney disease progression: Time is approaching

Progression of chronic kidney disease (CKD) is inevitable. However, the last decade has witnessed tremendous achievements in this field. Today we are optimistic; the dream of withholding this progression is about to be realistic. The recent discoveries in the field of CKD management involved most of the individual diseases leading the patients to end-stage renal disease. Most of these advances involved patients suffering diabetic kidney disease, chronic glomerulonephritis, polycystic kidney disease, renal amyloidosis and chronic tubulointerstitial disease. The chronic systemic inflammatory status and increased oxidative stress were also investigated. This inflammatory status influences the anti-senescence Klotho gene expression. The role of Klotho in CKD progression together with its therapeutic value are explored. The role of gut as a major source of inflammation, the pathogenesis of intestinal mucosal barrier damage, the role of intestinal alkaline phosphatase and the dietary and therapeutic implications add a novel therapeutic tool to delay CKD progression.

CaMKII as a pathological mediator of ER stress, oxidative stress, and mitochondrial dysfunction in a murine model of nephronophthisis

Polycystic kidney diseases (PKDs) are genetic diseases characterized by renal cyst formation with increased cell proliferation, apoptosis, and transition to a secretory phenotype at the expense of terminal differentiation. Despite recent progress in understanding PKD pathogenesis and the emergence of potential therapies, the key molecular mechanisms promoting cystogenesis are not well understood. Here, we demonstrate that mechanisms including endoplasmic reticulum stress, oxidative damage, and compromised mitochondrial function all contribute to nephronophthisis-associated PKD. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is emerging as a critical mediator of these cellular processes. Therefore, we reasoned that pharmacological targeting of CaMKII may translate into effective inhibition of PKD in jck mice. Our data demonstrate that CaMKII is activated within cystic kidney epithelia in jck mice. Blockade of CaMKII with a selective inhibitor results in effective inhibition of PKD in jck mice. Mechanistic experiments in vitro and in vivo demonstrated that CaMKII inhibition relieves endoplasmic reticulum stress and oxidative damage and improves mitochondrial integrity and membrane potential. Taken together, our data support CaMKII inhibition as a new and effective therapeutic avenue for the treatment of cystic diseases.

Comparison of volume-reductive therapies for massive polycystic liver disease in autosomal dominant polycystic kidney disease

AIM

Polycystic liver disease (PLD) in autosomal dominant polycystic kidney disease (ADPKD) patients can induce massive hepatomegaly-related symptoms. Volume-reductive therapies for symptomatic PLD include transcatheter arterial embolization (TAE), liver resection and liver transplantation; however, consensus has not been reached regarding treatment selection. We compared three volume-reductive therapies for a better understanding of PLD treatment strategies.

METHODS

We retrospectively analyzed 28 ADPKD patients who underwent TAE, liver resection or liver transplantation for PLD at a single center, and compared their outcomes.

RESULTS

Of 18 TAE patients, five required repeat TAE, and five required rescue liver transplantation or liver resection because of refractory symptoms or hepatic failure. The treatment failure rate for TAE was high (69.6%). Nine underwent liver resection, and the degree of volume reduction in the liver resection group was greater than that in the TAE group (52.4% vs 7.6%, P < 0.001). One liver resection patient required rescue liver transplantation because of hepatic failure. Seven patients underwent liver transplantations. All liver transplant patients had successfully controlled symptoms or hepatic failure, and had good graft function. Three patients in the TAE group died of infections or hepatic failure, whereas no mortality occurred after surgical therapy.

CONCLUSION

Liver resection is a good first-line therapy in patients that have severe symptoms, cyst involvement in several segments with some spared segments and preserved liver function. Liver transplantation is a preferred first-line therapy in patients with poor liver function or whole-liver involvement. Liver transplantation is also a good rescue therapy following TAE or liver resection.

Current management of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD), the most frequent cause of genetic renal disease affecting approximately 4 to 7 million individuals worldwide and accounting for 7%-15% of patients on renal replacement therapy, is a systemic disorder mainly involving the kidney but cysts can also occur in other organs such as the liver, pancreas, arachnoid membrane and seminal vesicles. Though computed tomography and magnetic resonance imaging (MRI) were similar in evaluating 81% of cystic lesions of the kidney, MRI may depict septa, wall thickening or enhancement leading to upgrade in cyst classification that can affect management. A screening strategy for intracranial aneurysms would provide 1.0 additional year of life without neurological disability to a 20-year-old patient with ADPKD and reduce the financial impact on society of the disease. Current treatment strategies include reducing: cyclic adenosine monophosphate levels, cell proliferation and fluid secretion. Several randomised clinical trials (RCT) including mammalian target of rapamycin inhibitors, somatostatin analogues and a vasopressin V2 receptor antagonist have been performed to study the effect of diverse drugs on growth of renal and hepatic cysts, and on deterioration of renal function. Prophylactic native nephrectomy is indicated in patients with a history of cyst infection or recurrent haemorrhage or to those in whom space must be made to implant the graft. The absence of large RCT on various aspects of the disease and its treatment leaves considerable uncertainty and ambiguity in many aspects of ADPKD patient care as it relates to end stage renal disease (ESRD). The outlook of patients with ADPKD is improving and is in fact much better than that for patients in ESRD due to other causes. This review highlights the need for well-structured RCTs as a first step towards trying newer interventions so as to develop updated clinical management guidelines.

Association of arginine vasopressin surrogate marker urinary copeptin with severity of autosomal dominant polycystic kidney disease (ADPKD)

BACKGROUND

Experimental studies suggest a detrimental role for cyclic adenosine monophosphate (cAMP) and vasopressin in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). It is unknown, however, whether urinary cAMP and copeptin concentration are associated with disease severity in patients with ADPKD.

METHODS

Urinary cAMP (u-cAMP) and copeptin concentration (u-copeptin) were measured by immunoassay in ADPKD patients with CKD stage ≤4. We compared our measurements with clinical parameters including estimated glomerular filtration rate (eGFR), total kidney volume (TKV), and height-adjusted TKV (htTKV). Logarithmic transformation of all variables was performed to fulfill the requirement of equal distribution of the residuals.

RESULTS

We included 50 patients in this study (24 females and 26 males; mean age: 49.3 years). The median eGFR and TKV were 53.2 ml/min/1.73 m(2) (interquartile range: IQR; 29.4-68.45) and 1138.1 ml (IQR; 814.7-2065.0), respectively. The median u-copeptin level was 12.19 (IQR; 6.91-22.32) ng/ml. Although u-cAMP/u-Cr was not significantly correlated with TKV (R = -0.006, p = 0.967) and eGFR (R = 0.077, p = 0.602), urinary copeptin/u-Cr was statistically associated with the various markers of disease severity in ADPKD [positively with TKV (R = 0.351, p = 0.014), htTKV (R = 0.383, p = 0.008) and negatively with eGFR (R = -0.304, p = 0.036)].

CONCLUSIONS

In ADPKD subjects, a higher u-copeptin is associated with disease progression, suggesting that u-copeptin may be a new surrogate marker to predict renal prognosis in ADPKD.

The effect of tolvaptan on autosomal dominant polycystic kidney disease patients: a subgroup analysis of the Japanese patient subset from TEMPO 3:4 trial

BACKGROUND

Japan is the first country in the world to approve tolvaptan for the treatment of autosomal dominant polycystic kidney disease (ADPKD), which was based on the results of Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes (TEMPO) 3:4 trial. To evaluate the safety and efficacy of tolvaptan, we performed a subgroup analysis in the participating Japanese ADPKD patient population.

METHODS

The primary outcome was the annual rate of percentage change in the total kidney volume (TKV). The secondary endpoint was the rate of kidney function change.

RESULTS

The tolvaptan and placebo groups included 118 and 59 patients, respectively. The annual rate of percentage changes in TKV were 1.3 % [95 % confidence interval (CI) 0.4-2.1] in the tolvaptan group, and 5.0 % (95 % CI 3.9-6.2) in the placebo group (P < 0.001). The annual estimated glomerular filtration rate change was -3.83 mL/min/1.73 m(2) in the tolvaptan group and -5.05 mL in the placebo group for a treatment effect of +1.22 mL/min/1.73 m(2) (95 % CI 0.41-2.02: P = 0.003). Hepatic function abnormal as a serious adverse event was observed in 3 patients (2.5 %) in the tolvaptan group.

CONCLUSIONS

Administration of tolvaptan in the Japanese sub-population reduced the annual rate of TKV growth and slowed the rate of kidney function decline over 36 months compared to patients on placebo, thus providing a novel and effective therapy for the treatment of ADPKD. (TEMPO 3:4 ClinicalTrials.gov number, NCT00428948).

Massive cystic degeneration of a uterine leiomyoma in a patient with autosomal dominant polycystic kidney disease

BACKGROUND

A uterine cyst occurring as an extrarenal manifestation of autosomal dominant polycystic kidney disease (ADPKD) is extremely rare.

CASE

A 46-year-old Japanese woman was referred with a large abdominal mass causing severe abdominal distension. A large uterine cyst as an extrarenal manifestation of ADPKD was strongly suspected. First, we managed this patient by aspirating the cyst fluid through a small laparotomy. A year later, the cyst recurred and the patient underwent hysterectomy. Massive cystic degeneration of a uterine leiomyoma was diagnosed histologically.

CONCLUSION

We described the rare case of massive cystic degeneration of a uterine leiomyoma in a patient with ADPKD, in which a causal relationship was suspected.

Determinants of renal tissue hypoxia in a rat model of polycystic kidney disease

Renal tissue oxygen tension (Po2) and its determinants have not been quantified in polycystic kidney disease (PKD). Therefore, we measured kidney tissue Po2 in the Lewis rat model of PKD (LPK) and in Lewis control rats. We also determined the relative contributions of altered renal oxygen delivery and consumption to renal tissue hypoxia in LPK rats. Po2 of the superficial cortex of 11- to 13-wk-old LPK rats, measured by Clark electrode with the rat under anesthesia, was higher within the cysts (32.8 ± 4.0 mmHg) than the superficial cortical parenchyma (18.3 ± 3.5 mmHg). Po2 in the superficial cortical parenchyma of Lewis rats was 2.5-fold greater (46.0 ± 3.1 mmHg) than in LPK rats. At each depth below the cortical surface, tissue Po2 in LPK rats was approximately half that in Lewis rats. Renal blood flow was 60% less in LPK than in Lewis rats, and arterial hemoglobin concentration was 57% less, so renal oxygen delivery was 78% less. Renal venous Po2 was 38% less in LPK than Lewis rats. Sodium reabsorption was 98% less in LPK than Lewis rats, but renal oxygen consumption did not significantly differ between the two groups. Thus, in this model of PKD, kidney tissue is severely hypoxic, at least partly because of deficient renal oxygen delivery. Nevertheless, the observation of similar renal oxygen consumption, despite markedly less sodium reabsorption, in the kidneys of LPK compared with Lewis rats, indicates the presence of inappropriately high oxygen consumption in the polycystic kidney.

Polycystic kidney disease - where gene dosage counts

Gene dosage effects have emerged as playing a central role in the pathogenesis of polycystic kidney disease. Yet, how gene dosage can ultimately have an impact on the formation of kidney cysts remains unknown. In this commentary we review the evidence for the role of gene dosage effects versus the “2-hit” mutation model in polycystic kidney disease (PKD), and also discuss how gene networks may potentially make intertwined contributions to PKD.

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.

Osteocytes: master orchestrators of bone

Osteocytes comprise the overwhelming majority of cells in bone and are its only true "permanent" resident cell population. In recent years, conceptual and technological advances on many fronts have helped to clarify the role osteocytes play in skeletal metabolism and the mechanisms they use to perform them. The osteocyte is now recognized as a major orchestrator of skeletal activity, capable of sensing and integrating mechanical and chemical signals from their environment to regulate both bone formation and resorption. Recent studies have established that the mechanisms osteocytes use to sense stimuli and regulate effector cells (e.g., osteoblasts and osteoclasts) are directly coupled to the environment they inhabit-entombed within the mineralized matrix of bone and connected to each other in multicellular networks. Communication within these networks is both direct (via cell-cell contacts at gap junctions) and indirect (via paracrine signaling by secreted signals). Moreover, the movement of paracrine signals is dependent on the movement of both solutes and fluid through the space immediately surrounding the osteocytes (i.e., the lacunar-canalicular system). Finally, recent studies have also shown that the regulatory capabilities of osteocytes extend beyond bone to include a role in the endocrine control of systemic phosphate metabolism. This review will discuss how a highly productive combination of experimental and theoretical approaches has managed to unearth these unique features of osteocytes and bring to light novel insights into the regulatory mechanisms operating in bone.

Evidence for a role of proteins, lipids, and phytochemicals in the prevention of polycystic kidney disease progression and severity

Polycystic kidney disease (PKD) is a heritable disease characterized by renal cysts and is a leading cause of end-stage renal disease. Dietary intervention offers a potentially efficacious, cost-effective, and safe therapeutic option for PKD. The aim of this article was to review studies investigating the effect of dietary components on PKD and potential mechanisms of action. Low-protein diets are commonly recommended for PKD patients, but inconsistent findings in human and animal PKD studies suggest that the type rather the amount of protein may be of greater importance. Dietary soy protein has been shown to have renal protective effects in various animal models of PKD. Other than dietary proteins, studies investigating the role of the amount and type of dietary lipids on PKD progression are increasing. The omega-3 polyunsaturated fatty acids can alter multiple steps in PKD pathogenesis. Phytoestrogens and phytochemicals are other dietary compounds shown to attenuate cyst pathogenesis in animal studies. A better understanding of the role of nutrition in PKD can contribute to the development of dietary recommendations and diet-based therapies to reduce PKD progression and severity.

Centrosomal abnormalities characterize human and rodent cystic cholangiocytes and are associated with Cdc25A overexpression

Hepatic cystogenesis in polycystic liver diseases is associated with abnormalities of cholangiocyte cilia. Given the crucial association between cilia and centrosomes, we tested the hypothesis that centrosomal defects occur in cystic cholangiocytes of rodents (Pkd2(WS25/-) mice and PCK rats) and of patients with polycystic liver diseases, contributing to disturbed ciliogenesis and cyst formation. We examined centrosomal cytoarchitecture in control and cystic cholangiocytes, the effects of centrosomal abnormalities on ciliogenesis, and the role of the cell-cycle regulator Cdc25A in centrosomal defects by depleting cholangiocytes of Cdc25A in vitro and in vivo and evaluating centrosome morphology, cell-cycle progression, proliferation, ciliogenesis, and cystogenesis. The cystic cholangiocytes had atypical centrosome positioning, supernumerary centrosomes, multipolar spindles, and extra cilia. Structurally aberrant cilia were present in cystic cholangiocytes during ciliogenesis. Depletion of Cdc25A resulted in i) a decreased number of centrosomes and multiciliated cholangiocytes, ii) an increased fraction of ciliated cholangiocytes with longer cilia, iii) a decreased proportion of cholangiocytes in G1/G0 and S phases of the cell cycle, iv) decreased cell proliferation, and v) reduced cyst growth in vitro and in vivo. Our data support the hypothesis that centrosomal abnormalities in cholangiocytes are associated with aberrant ciliogenesis and that accelerated cystogenesis is likely due to overexpression of Cdc25A, providing additional evidence that pharmacological targeting of Cdc25A has therapeutic potential in polycystic liver diseases.

Emerging key roles for P2X receptors in the kidney

P2X ionotropic non-selective cation channels are expressed throughout the kidney and are activated in a paracrine or autocrine manner following the binding of extracellular ATP and related extracellular nucleotides. Whilst there is a wealth of literature describing a regulatory role of P2 receptors (P2R) in the kidney, there are significantly less data on the regulatory role of P2X receptors (P2XR) compared with that described for metabotropic P2Y. Much of the historical literature describing a role for P2XR in the kidney has focused heavily on the role of P2X1R in the autoregulation of renal blood flow. More recently, however, there has been a plethora of manuscripts providing compelling evidence for additional roles for P2XR in both kidney health and disease. This review summarizes the current evidence for the involvement of P2XR in the regulation of renal tubular and vascular function, and highlights the novel data describing their putative roles in regulating physiological and pathophysiological processes in the kidney.

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.