The pathogenesis of hypertension in autosomal dominant polycystic kidney disease

Cardiovascular Manifestations and Management in ADPKD

Cardiovascular disease (CVD) is the major cause of mortality in autosomal dominant polycystic kidney disease (ADPKD) and contributes to significant burden of disease. The manifestations are varied, including left ventricular hypertrophy (LVH), intracranial aneurysms (ICAs), valvular heart disease, and cardiomyopathies; however, the most common presentation and a major modifiable risk factor is hypertension. The aim of this review is to detail the complex pathogenesis of hypertension and other extrarenal cardiac and vascular conditions in ADPKD drawing on preclinical, clinical, and epidemiological evidence. The main drivers of disease are the renin-angiotensin-aldosterone system (RAAS) and polycystin-related endothelial cell dysfunction, with the sympathetic nervous system (SNS), nitric oxide (NO), endothelin-1 (ET-1), and asymmetric dimethylarginine (ADMA) likely playing key roles in different disease stages. The reported rates of some manifestations, such as LVH, have decreased likely due to the use of antihypertensive therapies; and others, such as ischemic cardiomyopathy, have been reported with increased prevalence likely due to longer survival and higher rates of chronic disease. ADPKD-specific screening and management guidelines exist for hypertension, LVH, and ICAs; and these are described in this review.

Blood pressure response to exercise in unaffected relatives of autosomal dominant polycystic kidney disease patients: an observational study

INTRODUCTION

Hypertension is an early finding of autosomal dominant polycystic kidney disease (ADPKD) and is related to different mechanisms. Cyst expansion-related renin secretion or early endothelial dysfunctions are some of these hypotheses. In addition, the underlying genetic factor is thought to play a role in the inheritance of hypertension. The differential course of hypertension in ADPKD preoccupies that relatives of ADPKD patients may also be at risk for this underlying mechanisms with a genetically determined abnormal endothelial-vascular state. In this study, we aimed to evaluate blood pressure response to exercise as an initial vascular problem in unaffected and normotensive relatives of hypertensive ADPKD patients.

METHODS

This is an observational study including unaffected and normotensive relatives (siblings and children) of ADPKD patients (relative group) and healthy controls (control group) who performed an exercise stress test. A 6-lead electrocardiogram was recorded and blood pressure was measured automatically with a cuff worn on the right arm, immediately before the test and every 3 min during the exercise and the recovery phase. Participants continued the test until their age-specific target heart rate was reached or symptoms occurred that required discontinuation of the test. The highest blood pressure and pulse values during exercise were noted. In addition, as a marker for endothelial function, nitric oxide (NO) and asymmetric dimethylarginine (ADMA) levels were measured at baseline and post-exercise.

RESULTS

There were 24 participants in the relative group (16 female, mean age 38.45 years) and 30 participants in the control group (15 female, mean age 37.96 years). Two groups were similar in terms of age, gender, body mass index (BMI), smoking status, resting systolic blood pressure (SBP)/diastolic blood pressure (DBP) and biochemical parameters. Mean SBP and DBP were similar in both groups during 1st, 3rd and 9th minutes of exercise (1st minute: 136.25 ± 19.71 mmHg vs 140.36 ± 30.79 mmHg for SBP, p = 0.607, 84.05 ± 14.75 mmHg vs 82.60 ± 21.60 mmHg for DBP, p = 0.799; 3rd minute: 150.75 ± 30.39 mmHg vs 148.54 ± 27.30 mmHg for SBP, p = 0.801, 98.95 ± 26.92 mmHg vs 85.92 ± 17.93 mmHg for DBP, p = 0.062; 9th minute: 156.35 ± 30.84 mmHg vs 166.43 ± 31.90 mmHg for SBP, p = 0.300, 96.25 ± 21.99 mmHg vs 101.78 ± 33.11 mmHg for DBP, p = 0.529 for control and relatives, respectively). During the recovery phase, SBP decreased in both groups in 6th minute (119.85 ± 14.06 mmHg vs 122.86 ± 16.76 mmHg, p = 0.538 for control and relatives respectively); however, in the relatives of ADPKD patients DBP remained high at the end of the 6th minute (78.95 ± 11.29 mmHg vs 86.67 ± 9.81 mmHg p = 0.025 for control and relatives, respectively). Baseline and post-exercise NO and ADMA levels were similar in both groups (Baseline p = 0.214 and p = 0.818, post-exercise p = 0.652 and p = 0.918 for NO and ADMA, respectively).

CONCLUSION

Abnormal blood pressure response to exercise was observed in unaffected normotensive relatives of ADPKD. Although its clinical significance needs to be demonstrated by additional research, it is an important finding that unaffected relatives of ADPKD may be at risk for an altered arterial vascular network. Furthermore, these data are the first to demonstrate that relatives of ADPKD patients may also be under risk with a genetically determined abnormal vascular state.

Ciliotherapy: Remote Control of Primary Cilia Movement and Function by Magnetic Nanoparticles

Patients with polycystic kidney disease (PKD) are characterized with uncontrolled hypertension. Hypertension in PKD is a ciliopathy, an abnormal function and/or structure of primary cilia. Primary cilia are cellular organelles with chemo and mechanosensory roles. In the present studies, we designed a cilia-targeted (CT) delivery system to deliver fenoldopam specifically to the primary cilia. We devised the iron oxide nanoparticle (NP)-based technology for ciliotherapy. Live imaging confirmed that the CT-Fe₂O₃-NPs specifically targeted primary cilia in cultured cells in vitro and vascular endothelia in vivo. Importantly, the CT-Fe₂O₃-NPs enabled the remote control of the movement and function of a cilium with an external magnetic field, making the nonmotile cilium exhibit passive movement. The ciliopathic hearts displayed hypertrophy with compromised functions in left ventricle pressure, stroke volume, ejection fraction, and overall cardiac output because of prolonged hypertension. The CT-Fe₂O₃-NPs significantly improved cardiac function in the ciliopathic hypertensive models, in which the hearts also exhibited arrhythmia, which was corrected with the CT-Fe₂O₃-NPs. Intraciliary and cytosolic Ca²⁺ were increased when cilia were induced with fluid flow or magnetic field, and this served as a cilia-dependent mechanism of the CT-Fe₂O₃-NPs. Fenoldopam-alone caused an immediate decrease in blood pressure, followed by reflex tachycardia. Pharmacological delivery profiles confirmed that the CT-Fe₂O₃-NPs were a superior delivery system for targeting cilia more specifically, efficiently, and effectively than fenoldopam-alone. The CT-Fe₂O₃-NPs altered the mechanical properties of nonmotile cilia, and these nano-biomaterials had enormous clinical potential for ciliotherapy. Our studies further indicated that ciliotherapy provides a possibility toward personalized medicine in ciliopathy patients.

Recent advances in the molecular diagnosis of polycystic kidney disease

INTRODUCTION

Polycystic kidney disease (PKD) is clinically and genetically heterogeneous and constitutes the most common heritable kidney disease. Most patients are affected by the autosomal dominant form (ADPKD) which generally is an adult-onset multisystem disorder. By contrast, the rarer recessive form ARPKD usually already manifests perinatally or in childhood. In some patients, however, ADPKD and ARPKD can phenotypically overlap with early manifestation in ADPKD and only late onset in ARPKD. Progressive fibrocystic renal changes are often accompanied by severe hepatobiliary changes or other extrarenal abnormalities. Areas covered: A reduced dosage of disease proteins disturbs cell homeostasis and explains a more severe clinical course in some PKD patients. Cystic kidney disease is also a common feature of other ciliopathies and genetic syndromes. Genetic diagnosis may guide clinical management and helps to avoid invasive measures and to detect renal and extrarenal comorbidities early in the clinical course. Expert Commentary: The broad phenotypic and genetic heterogeneity of cystic and polycystic kidney diseases make NGS a particularly powerful approach. Interpretation of data becomes the challenge and bench and bedside benefit from digitized multidisciplinary interrelationships.

Heterotrimeric G protein signaling in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a signalopathy of renal tubular epithelial cells caused by naturally occurring mutations in two distinct genes, polycystic kidney disease 1 (PKD1) and 2 (PKD2). Genetic variants in PKD1, which encodes the polycystin-1 (PC-1) protein, remain the predominant factor associated with the pathogenesis of nearly two-thirds of all patients diagnosed with PKD. Although the relationship between defective PC-1 with renal cystic disease initiation and progression remains to be fully elucidated, there are numerous clinical studies that have focused upon the control of effector systems involving heterotrimeric G protein regulation. A major regulator in the activation state of heterotrimeric G proteins are G protein-coupled receptors (GPCRs), which are defined by their seven transmembrane-spanning regions. PC-1 has been considered to function as an unconventional GPCR, but the mechanisms by which PC-1 controls signal processing, magnitude, or trafficking through heterotrimeric G proteins remains to be fully known. The diversity of heterotrimeric G protein signaling in PKD is further complicated by the presence of non-GPCR proteins in the membrane or cytoplasm that also modulate the functional state of heterotrimeric G proteins within the cell. Moreover, PC-1 abnormalities promote changes in hormonal systems that ultimately interact with distinct GPCRs in the kidney to potentially amplify or antagonize signaling output from PC-1. This review will focus upon the canonical and noncanonical signaling pathways that have been described in PKD with specific emphasis on which heterotrimeric G proteins are involved in the pathological reorganization of the tubular epithelial cell architecture to exacerbate renal cystogenic pathways.

Chronic kidney pain in autosomal dominant polycystic kidney disease: a case report of successful treatment by catheter-based renal denervation

Chronic pain is a common concern in patients with autosomal dominant polycystic kidney disease (ADPKD). We report what to our knowledge is the first catheter-based renal denervation procedure in a patient with ADPKD resulting in successful management of chronic pain. The patient was a 43-year-old woman whose chronic pain could not be controlled by pain medication or splanchnic nerve blockade. Transluminal radiofrequency renal denervation was performed as an experimental therapeutic option with an excellent result, indicating that this procedure should be considered for chronic pain management in ADPKD.

Localized cystic disease of the kidney: a rare cause of hypertension in a young adult

Localized cystic disease of kidney (LCDK) is a rare, non-familial, non-progressive renal disorder that is not associated with cysts or disorders in other organs. Only a few cases have been reported in the literature. While this condition is morphologically identical to the autosomal dominant form of polycystic kidney disease, it is not inherited and is not associated with significant deterioration of renal function. We present a case of a 16-year-old male patient who suffered from hypertension for over two years. On imaging we found several, variable-sized cysts in the upper half of the right kidney. The left kidney and lower segment of the right kidney were normal. Selective renal vein catheterization and sampling showed markedly elevated renin level in the right upper segmental vein (92 pg/ml, normal value: 11-33 pg/ml). The patient underwent a right upper heminephrectomy and histopathology was suggestive of LCDK. After surgery, the patient's blood pressure returned to normal levels without any need of antihypertensive medication and he is under follow-up on outpatient basis for the past two years.

Dissection of Iliac Artery in a Patient With Autosomal Dominant Polycystic Kidney Disease: A Case Report

Autosomal dominant polycystic kidney disease (ADPKD) is a risk factor for several cardiovascular disorders such as intracranial aneurysm or aortic dissection, preferentially occurring at the thoracic or abdominal level. A 47-year-old man suffering from ADPKD had renal transplantation. Sixteen hours after surgery, he presented with left leg pain. Clinical and ultrasound examination revealed thrombosis of the external left iliac artery. Therefore, we decided to perform intra-arterial angiography to evaluate the possibility of an endovascular treatment. Aorto-femorography showed an obstruction of the external left iliac artery that was found during emergency surgery, consecutive to a dissection, which occurred following the surgery for kidney transplantation. The resected segment of the dissected vessel was analyzed by histology. Collagen fibers organization and density in the adventitia and smooth muscle cells density in the media were similar in the dissected and a normal artery from a healthy donor. By contrast, an almost complete disappearance and fragmentation of elastic lamellae were observed in the media of the dissected artery, most likely responsible for the weakening of the arterial wall and its dissection. Association between ADPKD and single dissection of the iliac artery has been rarely reported. Relationship between inactivation of polycystin/PKD genes and elastic fibers degradation through elevated TGFβ signaling and matrix metalloproteinase 2 (MMP2) elastolytic activity, as recently reported in ADPKD, would be worth investigating.

Urinary excretion of AQP2 and ENaC in autosomal dominant polycystic kidney disease during basal conditions and after a hypertonic saline infusion

Renal handling of sodium and water is abnormal in chronic kidney diseases. To study the function and regulation of the aquaporin-2 water channel (AQP2) and the epithelial sodium channel (ENaC) in autosomal dominant polycystic kidney disease (ADPKD), we measured urinary excretion of AQP2 (u-AQP2), the β-subunit of ENaC (u-ENaC(β)), cAMP (u-cAMP), and prostaglandin E(2) (u-PGE(2)); free water clearance (C(H2O)); fractional sodium excretion (FE(Na)); and plasma vasopressin (p-AVP), renin (p-Renin), angiotensin II (p-ANG II), aldosterone (p-Aldo), and atrial and brain natriuretic peptide (p-ANP, p-BNP) in patients with ADPKD and healthy controls during 24-h urine collection and after hypertonic saline infusion during high sodium intake (HS; 300 mmol sodium/day) and low sodium intake (LS; 30 mmol sodium/day). No difference in u-AQP2, u-ENaC(β), u-cAMP, u-PGE(2), C(H2O), and vasoactive hormones was found between patients and controls at baseline, but during HS the patients had higher FE(Na). The saline caused higher increases in FE(Na) in patients than controls during LS, but the changes in u-ENaC(β), p-Aldo, p-ANP, p-BNP, p-Renin, and p-ANG II were similar. Higher increases in u-AQP2 and p-AVP were seen in patients during both diets. In conclusion, u-AQP2 and u-ENaC(β) were comparable in patients with ADPKD and controls at baseline. In ADPKD, the larger increase in u-AQP2 and p-AVP in response to saline could reflect an abnormal water absorption in the distal nephron. During LS, the larger increase in FE(Na) in response to saline could reflect a defective renal sodium retaining capacity in ADPKD, unrelated to changes in u-ENaC(β).

The mechanosensory role of primary cilia in vascular hypertension

Local regulation of vascular tone plays an important role in cardiovascular control of blood pressure. Aside from chemical or hormonal regulations, this local homeostasis is highly regulated by fluid-shear stress. It was previously unclear how vascular endothelial cells were able to sense fluid-shear stress. The cellular functions of mechanosensory cilia within vascular system have emerged recently. In particular, hypertension is insidious and remains a continuous problem that evolves during the course of polycystic kidney disease (PKD). The basic and clinical perspectives on primary cilia are discussed with regard to the pathogenesis of hypertension in PKD.

Clinical effects of calcium channel blockers and renin-angiotensin-aldosterone system inhibitors on changes in the estimated glomerular filtration rate in patients with polycystic kidney disease

BACKGROUND

In the tubular cells of patients with polycystic kidney disease (PKD), a reduced intracellular Ca(2+) level accelerates cell proliferation, resulting in cyst formation. Thus, whether calcium channel blockers (CCB) are useful for the treatment of hypertension in patients with PKD is questionable.

METHODS

Thirty-two outpatients with autosomal dominant PKD (ADPKD) were treated at Tokyo Women's Medical University between 2003 and 2008; these patients were studied retrospectively. Periods during which the antihypertensive drug prescriptions for CCB and/or renin-angiotensin-aldosterone system inhibitors (RAAS-I; including angiotensin converting enzyme inhibitor and angiotensin II receptor blocker) had not been changed for at least 1 year and during which time a diuretic agent had not been prescribed were selected from among the clinical histories of the 32 outpatients. Consequently, 31 periods of 31 patients were analyzed, and mean treatment duration was 2.4 years in this study. The estimated glomerular filtration rate (eGFR) was used to evaluate renal function. To evaluate the influence of CCB and RAAS-I with respect to the decrease of the eGFR, analysis of covariance (ANCOVA), including confounding factors [baseline eGFR, mean systolic blood pressure (SBP), mean diastolic blood pressure (DBP)], was used. Only CCB significantly contributed to a reduction in ∆eGFR in both a univariable ANCOVA and a multivariable ANCOVA. None of the confounding factors, RAAS-I, the baseline eGFR, or blood pressure, contributed to reductions in ∆eGFR.

CONCLUSION

These results suggest that from a renoprotective perspective, CCB should possibly be avoided in patients with PKD unless treatment for resistant hypertension is necessary.

Hypertension in autosomal dominant polycystic kidney disease

Hypertension is common and occurs in a majority of autosomal dominant polycystic kidney disease (ADPKD) patients before the loss of kidney function. Hypertension relates to progressive kidney enlargement and is a significant independent risk factor for progression to ESRD. The pathogenesis of hypertension in ADPKD is complex and dependent on many factors that influence each other. Pkd1 and Pkd2 expression levels are highest in the major vessels and are present in the cilia of endothelial cells and in vascular smooth muscle cells. Decreased or absent polycystin 1 or 2 expression is associated with abnormal vascular structure and function. Pkd1/Pkd2 deficiency results in reduced nitric oxide (NO) levels, altered endothelial response to shear stress with attenuation in vascular relaxation. Ten percent to 20% of ADPKD children show hypertension and the majority of adults are hypertensive before any loss of kidney function. Cardiac abnormalities such as left ventricular hypertrophy and carotid intimal wall thickening are present before the development of hypertension in ADPKD. The activation of the renin-angiotensin-aldosterone system occurs in ADPKD because of decreased NO production as well as bilateral cyst expansion and intrarenal ischemia. With increasing cyst size, further activation of the RAAS occurs, blood pressure increases, and a vicious cycle ensues with enhanced cyst growth and hypertension ultimately leading to ESRD. The inhibition of the angiotensin aldosterone system is possible with angiotensin converting enzyme inhibitors and angiotensin receptor blockers. However, interventional studies have not yet shown benefit in slowing progression to renal failure in ADPKD. Currently, large multicenter studies are being performed to determine the beneficial effects of RAAS inhibition both early and late in ADPKD.

Mechanosensitive TRP channels in cardiovascular pathophysiology

Transient receptor potential (TRP) proteins constitute a large non-voltage-gated cation channel superfamily, activated polymodally by various physicochemical stimuli, and are implicated in a variety of cellular functions. Known activators for TRP include not only chemical stimuli such as receptor stimulation, increased acidity and pungent/cooling agents, but temperature change and various forms of mechanical stimuli such as osmotic stress, membrane stretch, and shear force. Recent investigations have revealed that at least ten mammalian TRPs exhibit mechanosensitivity (TRPC1, 5, 6; TRPV1, 2, 4; TRPM3, 7; TRPA1; TRPP2), but the mechanisms underlying it appear considerably divergent and complex. The proposed mechanisms are associated with lipid bilayer mechanics, specialized force-transducing structures, biochemical reactions, membrane trafficking and transcriptional regulation. Many of mechanosensitive (MS)-TRP channel likely undergo multiple regulations via these mechanisms. In the cardiovascular system in which hemodynamic forces constantly operate, the impact of mechanical stress may be particularly significant. Extensive morphological and functional studies have indicated that several MS-TRP channels are expressed in cardiac muscle, vascular smooth muscle, endothelium and vasosensory neurons, each differentially contributing to cardiovascular (CV) functions. To further complexity, the recent evidence suggests that mechanical stress may synergize with neurohormonal mechanisms thereby amplifying otherwise marginal responses. Furthermore, the currently available data suggest that MS-TRP channels may be involved in CV pathophysiology such as cardiac arrhythmia, cardiac hypertrophy/myopathy, hypertension and aneurysms. This review will overview currently known mechanisms for mechanical activation/modulation of TRPs and possible connections of MS-TRP channels to CV disorders.

Asymmetric dimethylarginine and lipid peroxidation products in early autosomal dominant polycystic kidney disease

BACKGROUND

Patients with autosomal dominant polycystic kidney disease (ADPKD) with normal renal function have endothelial dysfunction and decreased nitric oxide synthase activity in subcutaneous resistance vessels. We investigated asymmetric dimethylarginine (ADMA) as a marker of an inhibitor of nitric oxide synthase and the lipid peroxidation product 13-hydroxyoctadecadienoic acid (HODE) as a marker of oxidative stress in patients with early ADPKD.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

Patients with early ADPKD (n = 27) and age-matched volunteers (n = 30) from a single academic medical center.

FACTOR

Patients with ADPKD versus controls.

OUTCOMES & MEASUREMENT

Plasma (P) levels, urinary (U) excretion, and urinary clearance (C) of ADMA and HODE. Because of multiple comparisons, P for significance is considered less than 0.0167.

RESULTS

Patients with ADPKD had significantly increased P(ADMA) levels (604 +/- 131 versus 391 +/- 67 nmol/L; P < 0.01) and U(ADMA) excretion (22 +/- 4 versus 15.2 +/- 3 nmol/micromol creatinine; P = 0.01), decreased C(ADMA) (25 +/- 3 versus 33 +/- 4 mL/min; P = 0.01), increased P(HODE) levels (316 +/- 64 versus 230 +/- 38 nmol/L; P < 0.01) and U(HODE) excretion (467 +/- 67 versus 316 +/- 40 nmol/micromol creatinine; P < 0.01), and decreased plasma nitrite plus nitrate (P(NOx)) levels (21 +/- 5 versus 32 +/- 6 micromol/L; P < 0.01) and U(NOx) excretion (59 +/- 7 versus 138 +/- 27 micromol/micromol creatinine; P < 0.01).

LIMITATIONS

Small sample size, cross-sectional nature of study, and limited number of markers of oxidative stress.

CONCLUSIONS

P(ADMA) and P(HODE) levels are increased in patients with early ADPKD. Increased P(ADMA) level is related to decreased C(ADMA) and is accompanied by oxidative stress.

Potential pharmacological interventions in polycystic kidney disease

Polycystic kidney diseases (autosomal dominant and autosomal recessive) are progressive renal tubular cystic diseases, which are characterised by cyst expansion and loss of normal kidney structure and function. Autosomal dominant polycystic kidney disease (ADPKD) is the most common life- threatening, hereditary disease. ADPKD is more prevalent than Huntington's disease, haemophilia, sickle cell disease, cystic fibrosis, myotonic dystrophy and Down's syndrome combined. Early diagnosis and treatment of hypertension with inhibitors of the renin-angiotensin-aldosterone system (RAAS) and its potential protective effect on left ventricular hypertrophy has been one of the major therapeutic goals to decrease cardiac complications and contribute to improved prognosis of the disease. Advances in the understanding of the genetics, molecular biology and pathophysiology of the disease are likely to facilitate the improvement of treatments for these diseases. Developments in describing the role of intracellular calcium ([Ca(2+)](i)) and its correlation with cellular signalling systems, Ras/Raf/mitogen extracellular kinase (MEK)/extracellular signal-regulated protein kinase (ERK), and interaction of these pathways with cyclic adenosine monophosphate (cAMP) levels, provide new insights on treatment strategies. Blocking the vasopressin V(2) receptor, a major adenylyl cyclase agonist, demonstrated significant improvements in inhibiting cytogenesis in animal models. Because of activation of the mammalian target of rapamycin (mTOR) pathway, the use of sirolimus (rapamycin) an mTOR inhibitor, markedly reduced cyst formation and decreased polycystic kidney size in several animal models. Caspase inhibitors have been shown to decrease cytogenesis and renal failure in rats with cystic disease. Cystic fluid secretion results in cyst enlargement and somatostatin analogues have been shown to decrease renal cyst progression in patients with ADPKD. The safety and efficacy of these classes of drugs provide potential interventions for experimental and clinical trials.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Selective COX-2 inhibition markedly slows disease progression and attenuates altered prostanoid production in Han:SPRD-cy rats with inherited kidney disease

Selective cyclooxygenase-2 (COX-2) inhibitors appear to have beneficial renoprotective effects in most, but not all, renal disease conditions. The objective of our study was to examine the effects of COX-2 inhibition in a rat model of polycystic kidney disease. Four-week-old Han:SPRD-cy rats were given a standard rodent diet containing NS-398 (3 mg.kg body wt(-1).day(-1)) or a control diet without NS-398 for 7 wk. In diseased rats, selective COX-2 inhibition resulted in 18% and 67% reduction in cystic expansion and interstitial fibrosis, respectively, but no change in renal function. NS-398 also ameliorated disease-associated pathologies, such as renal inflammation, cell proliferation, and oxidant injury (by 33, 38, and 59%, respectively). Kidney disease was associated with elevated renal COX-1 and COX-2 enzyme activities, and NS-398 blunted the increase in COX-2 enzyme activity (as indicated by 21 and 28% lower renal thromboxane B2 and PGE2 levels, respectively). NS-398 reduced urinary excretion of prostanoid metabolites in diseased rats. In summary, COX-2 inhibition attenuated renal injury, reduced the elevated renal COX-2 activity, and ameliorated disease-related alterations in prostanoid production in this rat model of chronic renal disease.

Temporal relationship between renal cyst development, hypertension and cardiac hypertrophy in a new rat model of autosomal recessive polycystic kidney disease

BACKGROUND/METHODS

We have examined the hypothesis that cyst formation is key in the pathogenesis of cardiovascular disease in a Lewis polycystic kidney (LPK) model of autosomal-recessive polycystic kidney disease (ARPKD), by determining the relationship between cyst development and indices of renal function and cardiovascular disease.

RESULTS

In the LPK (n = 35), cysts appear at week 3 (1.1 +/- 0.1 mm) increasing to week 24 (2.8 +/- 2 mm). Immunostaining for nephron-specific segments indicate cysts develop predominantly from the collecting duct. Cyst formation preceded hypertension (160 +/- 22 vs. Lewis control 105 +/- 20 mm Hg systolic blood pressure (BP), n = 12) at week 6, elevated creatinine (109 +/- 63 vs. 59 +/- 6 micromol/l, n = 16) and cardiac mass (0.7 vs. 0.4% bodyweight, n = 15) at week 12, and left ventricular hypertrophy (2,898 +/- 207 vs. 1,808 +/- 192 mum, n = 14) at week 24 (all p < or = 0.05). Plasma-renin activity and angiotensin II were reduced in 10- to 12-week LPK (2.2 +/- 2.9 vs. Lewis 11.9 +/- 4.9 ng/ml/h, and 25.0 +/- 19.1 vs. 94.9 +/- 64.4 pg/ml, respectively, n = 26, p < or = 0.05). Ganglionic blockade (hexamethonium 3.3 mg/kg) significantly reduced mean BP in the LPK (52 vs. Lewis 4%, n = 9, p < or = 0.05).

CONCLUSION

Cyst formation is a key event in the genesis of hypertension while the sympathetic nervous system is important in the maintenance of hypertension in this model of ARPKD.

Cardiovascular polycystins: insights from autosomal dominant polycystic kidney disease and transgenic animal models

Mutations in the PKD1 and PKD2 polycystin genes are responsible for autosomal dominant polycystic kidney disease (ADPKD), one of the most prevalent genetic kidney disorders. ADPKD is a multisystem disease characterized by the formation of numerous fluid-filled cysts in the kidneys, the pancreas, and the liver. Moreover, major cardiovascular manifestations are common complications in ADPKD. Intracranial aneurysms and arterial hypertension are among the leading causes of mortality in this disease. In the present review, we summarize our current understanding of the role of polycystins in the development, maintenance, and function of the cardiovascular system.

Autosomal dominant polycystic kidney disease: role of the renin-angiotensin system in raised blood pressure in progression of renal and cardiovascular disease

Raised blood pressure (BP) is extremely common in individuals with autosomal dominant polycystic kidney disease (ADPKD) and is almost invariably raised once they develop renal failure. The underlying mechanisms for the rise in BP in individuals with ADPKD are unclear. The progressive number and enlargement of renal cysts, causing structural damage to the kidneys and, thereby, affecting tubular function as well as causing distortion of the glomeruli and renal ischaemia, is likely to be of primary importance. There is some evidence from animal models that there may be over-activity of the intra-renal renin-angiotensin system (RAS) that could account for the rise in BP. Studies in man have shown conflicting results, but a recent more carefully controlled study using both measurements of activity and pharmacological blockade of the RAS clearly demonstrated no evidence of over-activity of the circulating RAS in ADPKD compared to matched individuals with essential hypertension. A more likely explanation for the rise in BP that occurs in ADPKD is retention of sodium and water due to tubular damage. Disappointingly, in spite of good evidence that RAS blocking drugs slow the progression of other renal, particularly glomerular, diseases, there is little evidence to suggest this is true for patients with ADPKD. Nevertheless, there is no doubt that lowering BP in ADPKD is just as important, if not more important, as in essential hypertension to prevent cardiovascular disease and strokes, with a recommended BP target of < 120/80 mmHg.

Flow-associated dilatory capacity of the brachial artery is intact in early autosomal dominant polycystic kidney disease

BACKGROUND/AIMS

Autosomal dominant polycystic kidney disease is associated with endothelial dysfunction of resistance arteries. This study tested whether endothelial dysfunction is also present in the conduit arteries in patients with preserved renal function.

METHODS

Twenty-seven patients (9 females and 18 males, age 36 +/- 10 years) with polycystic kidney disease and normal renal function were compared to 27 healthy controls. The dilatory responses of the brachial artery to postischemic increased blood flow [endothelium-dependent flow-associated dilatation (FAD)] and to nitroglycerin [endothelium-independent nitroglycerin-induced dilatation (NID)] were measured by external ultrasound. Plasma concentrations of the stable end products of nitric oxide nitrate/nitrite (NOx) and of the endothelial markers vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1, E-selectin and von Willebrand factor antigen were also measured.

RESULTS

No differences in FAD or NID were found between patients and controls (104.6 +/- 4.2 vs. 105.3 +/- 3.9%, mean +/- SD, p = 0.55, and 117.0 +/- 8.4 vs. 117.5 +/- 7.6%, p = 0.75). However, the plasma concentration of VCAM-1 was elevated and the plasma concentration of NOx was reduced in patients with polycystic kidney disease.

CONCLUSION

Biochemical markers confirm an association between polycystic kidney disease and endothelial dysfunction. However, a normal FAD of the brachial artery suggests that the endothelial dysfunction does not involve the conduit arteries.

Calcium channel blocker versus angiotensin II receptor blocker in autosomal dominant polycystic kidney disease

BACKGROUND

Although hypertension is commonly found in patients with autosomal dominant polycystic kidney disease (ADPKD), there is no consensus about which antihypertensive agents are most appropriate. The effects of calcium channel blockers (CCB) and angiotensin II receptor blockers (ARB) on blood pressure and renoprotection were compared in hypertensive patients with ADPKD.

METHODS

We randomly assigned 49 participants to CCB amlodipine-based (2.5-10 mg/day) or ARB candesartan-based (2-8 mg/day) regimens. Twenty-five patients (13 males and 12 females) received amlodipine, and 24 patients (13 males and 11 females) received candesartan. This was followed up for 36 months.

RESULTS

Baseline characteristics were similar, and blood pressure was well controlled in both groups throughout the study period. Six out of 25 (24.0%) amlodipine and 1 out of 24 (4.2%) candesartan patients were terminated from the protocol due to a twofold increase in serum creatinine and/or decrease in creatinine clearance (Ccr) to half of the baseline. The renal event-free survival rate was significant (p < 0.05, Breslow-Gehan-Wilcoxon test). Serum creatinine was higher in the amlodipine group than in the candesartan group at 24 and 36 months (p < 0.05). The decrease in Ccr at 36 months was larger in the amlodipine group than in the candesartan group (DeltaCcr: -20.9 +/- 13.1 vs. -4.8 +/- 13.8 ml/min, p < 0.01). Urinary protein excretion was significantly lower in the candesartan group than in the amlodipine group at 36 months. Urinary albumin excretion was significantly lower in the candesartan group than in the amlodipine group at 12, 24 and 36 months.

CONCLUSIONS

The renoprotective effect of candesartan is considered more favorable than amlodipine in the treatment of ADPKD. This is independent of the antihypertensive effect per se.

Pathogenesis of hypertension in renal failure: role of the sympathetic nervous system and renal afferents

1. The kidney receives a dense innervation of sympathetic and sensory fibres and can be both a target of sympathetic activity and a source of signals that drive sympathetic tone. In the normal state, interactions between the kidney and sympathetic nervous system (SNS) serve to maintain blood pressure and glomerular filtration rate within tightly controlled levels. In renal failure, a defect in renal sodium excretory function leads to an abnormal pressure natriuresis relationship and activation of the renin-angiotensin-aldosterone system, contributing to the development of hypertension and progression of kidney disease. 2. Evidence now strongly indicates a role for the SNS in the pathogenesis of hypertension in renal failure. Hypertension occurs commonly and early in renal disease and is paralleled by increases in SNS activity, as indicated by increased muscle sympathetic nerve activity and circulating catecholamines. This appears to be driven by the diseased kidneys, because nephrectomy or denervation has been shown to correct blood pressure and SNS activity in human and animal studies. 3. Afferent signals from the kidney, detected by chemoreceptors and mechanoreceptors, feed directly into central nuclei of the SNS, including the hypothalamus and circumventricular organs, in addition to the stimulus provided by circulating and brain-derived angiotensin II. Therefore, the pathogenesis of hypertension in renal failure is complex and arises from the interaction of haemodynamic and neuroendocrine factors. 4. Increased SNS activity has significant implications with regard to increased risk of cardiovascular disease and is an important consideration in the treatment of renal failure.

Recent advances in understanding the pathogenesis of polycystic kidney disease: therapeutic implications

Hereditary polycystic kidney disease (PKD) is a common cause of renal failure. Increasing knowledge is available regarding mechanisms of cyst development and progression, and renal functional deterioration in PKD. On the basis of this information and theories regarding the pathophysiology of these processes, studies to alter progression and potentially treat PKD have been reported. Cyst development and progression requires epithelial cell proliferation, transepithelial fluid secretion and extracellular matrix remodelling. Several interventions designed to inhibit cell proliferation or alter fluid secretion modify the progression of PKD in selected animal models. Renal functional deterioration appears to involve interstitial inflammation and fibrosis, and tubular apoptosis. Glucocorticoids with anti-inflammatory and antifibrotic properties slow the progression of cystic disease and renal functional deterioration in animal models of PKD. Other interventions, such as dietary modification and angiotensin antagonism, shown to be of benefit in non-PKD models of slowly progressive renal disease, are also of benefit in animal models of PKD. Caution should be used in extrapolating interventional studies in one animal model to another model and certainly to human disease, since examples exist in which treatments in one model of PKD have different effects in another model. Nonetheless, early attempts to determine whether potential treatments are tolerated and of potential benefit in patients with PKD are beginning to appear. Ultimately, treatment of PKD may involve efforts to identify patients at greatest risk for disease progression, thus allowing targeted therapy, use of surrogate markers for disease progression to assist assessment of therapeutic efficacy, and combination therapy to retard disease progression and renal functional deterioration in this common hereditary cause of chronic renal failure.

The intrarenal renin-angiotensin system in autosomal dominant polycystic kidney disease

Hypertension is a common complication of autosomal dominant polycystic kidney disease (ADPKD), often present before the onset of renal failure. A role for the renin-angiotensin system (RAS) has been proposed, but studies of systemic RAS have failed to show a correlation between plasma renin activity and blood pressure in ADPKD. Ectopic renin expression by cyst epithelium was first reported in 1992 (Torres VE, Donovan KA, Sicli G, Holley KE, Thibodeau ST, Carretero OA, Inagami T, McAteer JA, and Johnson CM. Kidney Int 42: 364-373, 1992). It is not known, however, whether other RAS components are also expressed by cysts in ADPKD. We show that, in addition to renin, angiotensinogen (AGT) is produced by some cysts and dilated tubules. Angiotensin-converting enzyme, ANG II type 1 receptor, and ANG II peptide are also present within cysts and in many tubules; and some cyst fluids contain high ANG II concentrations. Additionally, cyst-derived cells in culture continue to express the components of the RAS at both the protein and mRNA levels. We further show that renin is expressed primarily in cysts of distal tubule origin and in cyst-derived cells with distal tubule characteristics, whereas AGT is expressed primarily in cysts of proximal tubule origin and in cyst-derived cells with proximal tubule characteristics. Renin production by cyst-derived cells appears to be regulated by extracellular Na+ concentration. Based on these observations, we propose a model of an autocrine/paracrine RAS in polycystic kidney disease, whereby overactivity of the intrarenal system results in sustained increases in intratubular ANG II concentrations.

Endothelial dysfunction and reduced nitric oxide in resistance arteries in autosomal-dominant polycystic kidney disease

BACKGROUND

Patients with autosomal-dominant polycystic kidney disease (ADPKD) have defective endothelium-dependent relaxation (EDR). We investigated the relationship between endothelial dysfunction and nitric oxide generation in hypertension and chronic renal insufficiency (CRI) in ADPKD.

METHODS

We contrasted acetylcholine (ACh)-induced EDR, 3-morphollinosydnonimine (SIN-1)-induced endothelium-independent relaxation (EIDR) and constitutive nitric oxide synthase (cNOS) activity in subcutaneous resistance vessels and plasma levels and excretion of NO2-/NO3- (NOX) in normal, control (N = 10) patients with ADPKD or essential hypertension.

RESULTS

EDR was decreased significantly in normotensive ADPKD (N = 9), but more severely in hypertensive ADPKD (N = 6), or those with CRI (N = 5) and in essential hypertension (N = 9). The increases in EDR with l-arginine and decreases with LG-nitro-l-arginine methyl ester (L-NAME) were lost in all groups of patients with ADPKD and in essential hypertension except for a modest effect of L-NAME in normotensive ADPKD. EIDR was unimpaired throughout. Vascular cNOS activity and renal NOX excretion were reduced profoundly in patients with all categories of ADPKD and especially in those with hypertension.

CONCLUSION

EDR in resistance vessels from patients with ADPKD is impaired even in the absence of hypertension or CRI, but becomes more marked as hypertension develops. Patients with ADPKD have defective nitric oxide generation from diminished cNOS activity. Endothelial dysfunction and impaired cNOS activity in ADPKD may predispose to hypertension whose occurrence is accompanied by a further sharp deterioration in EDR.

ETA receptor blockade induces tubular cell proliferation and cyst growth in rats with polycystic kidney disease

Tissue concentrations of ET-1 are markedly elevated in the kidneys of Han:Sprague-Dawley (Han:SPRD) rats, a model of human autosomal dominant polycystic kidney disease (ADPKD). This study analyzed whether disease progression might be attenuated by endothelin receptor antagonists. Heterozygous Han:SPRD rats received an ETA receptor antagonist (LU 135252), a combined ETA/ETB receptor antagonist (LU 224332), or placebo for 4 mo. Glomerulosclerosis, protein excretion, and GFR remained unchanged, whereas interstitial fibrosis was enhanced by both compounds. BP was not reduced by both compounds in Han:SPRD rats. Renal blood flow (RBF) decreased in ADPKD rats treated with the ETA receptor antagonist. Long-term ETA receptor blockade furthermore increased markedly the number of renal cysts (ADPKD rats, 390 +/- 119 [cysts/kidney section +/- SD]; LU 135252-treated APKD rats, 1084 +/- 314; P < 0.001), cyst surface area (ADPKD rats, 7.97 +/- 2.04 [% of total section surface +/- SD]; LU 135252-treated ADPKD rats, 33.83 +/- 10.03; P < 0.001), and cell proliferation of tubular cells (ADPKD rats, 42.2 +/- 17.3 [BrdU-positive cells/1000 cells]; LU 135252-treated ADPKD rats, 339.4 +/- 286.9; P < 0.001). The additional blockade of the ETB receptor attenuated these effects in Han:SPRD rats. Both endothelin receptor antagonists had no effect on BP, protein excretion, GFR, and kidney morphology in Sprague-Dawley rats without renal cysts. It is concluded that ETA receptor blockade enhances tubular cell proliferation, cyst number, and size and reduces RBF in Han:SPRD rats. This is of major clinical impact because endothelin receptor antagonists are upcoming clinically used drugs.

Cardiac and renal effects of standard versus rigorous blood pressure control in autosomal-dominant polycystic kidney disease: results of a seven-year prospective randomized study

This study sought to investigate the cardiac and renal effects of rigorous versus standard BP control on autosomal-dominant polycystic kidney disease (ADPKD). A prospective, randomized, 7-yr study was performed to examine the effect of rigorous (<120/80 mmHg) versus standard (135-140/85-90 mmHg) BP control on left ventricular mass index (LVMI) and kidney function in 75 hypertensive ADPKD patients with left ventricular hypertrophy. LVMI was measured by echocardiogram at baseline and at 1 and 7 yr. Renal function was assessed by measuring serum creatinine and 24-h creatinine clearance every 6 mo for 3 yr, then annually for an additional 4 yr. The baseline characteristics were comparable in the two groups. During the study, average mean arterial pressure was 90 +/- 5 mmHg for the rigorous group and 101 +/- 4 mmHg for the standard group (P < 0.0001). The LVMI decreased by 21% in the standard group and by 35% in the rigorous group. A mixed model longitudinal data analysis revealed that rigorous BP control was significantly more effective in decreasing LVMI (P < 0.01). There was no statistically significant difference in renal function between the two groups. In conclusion, left ventricular hypertrophy, a major cardiovascular risk factor, was decreased to a significantly greater extent by rigorous than standard BP control. This finding has particular clinical importance because cardiovascular complications are the most common cause of death in ADPKD patients.

Immunohistochemical study on hypoxia in spontaneous polycystic liver and kidney disease in rats

Hypoxia-inducible factor (HIF) mediates homeostatic responses to hypoxia and activates transcription of hypoxia-inducible genes including vascular endothelial growth factor (VEGF). The aim of this study was to examine the expressions of VEGF, HIF-1alpha and HIF-3alpha in spontaneously occurring hepatorenal polycystic lesions in two Sprague-Dawley (Crj:CD) rats. Hepatic multiple cysts were derived from the interlobular and large bile ducts, while renal cysts were from the collecting ducts and distal tubuli. These findings were confirmed by a lectin peanut agglutinin (PNA) histochemistry. In the polycystic liver, VEGF immunoreaction was strongly evident in the cytoplasm of hepatocytes, whereas expression of HIF-3alpha, but not HIF-1alpha, was found in a few nuclei of hepatocytes. In the polycystic kidney, VEGF immunoreaction was increased in the cytoplasm of collecting ducts and distal tubuli, whereas nuclear expression of HIF-1alpha and HIF-3alpha was evident in the proximal tubuli and thin loop of Henle, respectively. The results suggest that hypoxia-related molecules may be induced by cystic alterations in a heterogeneous appearance.

Progression of autosomal-dominant polycystic kidney disease in children

BACKGROUND

Although many case reports describe manifestations of autosomal-dominant polycystic kidney disease (ADPKD) in children, no longitudinal studies have examined the natural progression or risk factors for more rapid progression in a large number of children from ADPKD families.

METHODS

Since 1985, we have studied 312 children from 131 families with a history, a physical examination, blood and urine chemistries, an abdominal ultrasonography, and gene linkage analysis. One hundred fifteen of 185 affected children were studied multiple times for up to 15 years. Renal volumes were determined by ultrasound imaging. Graphs of mean renal volumes according to age were compared between affected and unaffected children, ADPKD children with and without early severe disease, and children with and without high blood pressure.

RESULTS

Affected children had faster renal growth than unaffected children. ADPKD children with severe renal enlargement at a young age continued to experience faster renal growth than those with mild enlargement or normal kidney size for their age, and affected children with high blood pressure had faster renal growth than those with lower blood pressure. Glomerular filtration rate did not decrease in any children except for two with unusually severe early onset disease.

CONCLUSIONS

The progression of ADPKD clearly occurs in childhood and manifests as an increase in cyst number and renal size. This study identifies children at risk for rapid renal enlargement who may benefit the most from future therapeutic interventions.

Contractility and endothelium-dependent relaxation of resistance vessels in polycystic kidney disease rats

Hypertension and vascular disease are common complications in autosomal-dominant polycystic kidney disease (ADPKD). The role of changes in morphology and reactivity of resistance vessels in this disease have not previously been studied. Mesenteric resistance arteries were dissected from 8- to 14-week-old heterozygous Han:SPRD polycystic kidney disease (PKD) rats, homozygous normal Han:SPRD littermates (HSPRD) and Sprague-Dawley rats (SD). The morphology, noradrenaline (NA) contractility, endothelium-dependent acetylcholine (ACh) relaxation before and after incubation with L(G)-nitro-L-arginine methyl ester (L-NAME), and endothelium-independent 3-morphollino-sydnonimine (SIN-1) relaxation were studied with the Mulvany-Halpern myograph. Blood pressure and morphology of vessels were the same in all groups of rats, apart from a slightly higher media/lumen ratio in heterozygous PKD rats (p < 0.05). Active wall tension and contractile sensitivity to NA were higher in both heterozygous PKD rats and HSPRD than SD rats (p < 0. 05). The maximum endothelium-dependent relaxation rate was markedly decreased in heterozygous PKD (19 +/- 9%) and HSPRD (34 +/- 12%) compared to SD rats (75 +/- 11%) (p < 0.05). After incubation with L-NAME, ACh-induced relaxation was significantly attenuated in SD rats, less attenuated in HSPRD, and not significantly changed in heterozygous PKD rats. SIN-1-induced endothelium-independent relaxation was similar in all three groups. In conclusion, hyperreactivity to NA and impaired endothelium-dependent relaxation were present in resistance vessels from Han:SPRD rats, especially in animals with PKD. These abnormalities in resistance vessels from PKD rats may be important for the development of hypertension and vascular disease.

Familial phenotype differences in PKD11

Familial phenotype differences in PKD1.

BACKGROUND

Mutations within the PKD1 gene are responsible for the most common and most severe form of autosomal dominant polycystic kidney disease (ADPKD). Although it is known that there is a wide range of disease severity within PKD1 families, it is uncertain whether differences in clinical severity also occur among PKD1 families.

METHODS

Ten large South Wales ADPKD families with at least 12 affected members were included in the study. From affected members, clinical information was obtained, including survival data and the presence of ADPKD-associated complications. Family members who were at risk of having inherited ADPKD but were proven to be non-affected were included as controls. Linkage and haplotype analysis were performed with highly polymorphic microsatellite markers closely linked to the PKD1 gene. Survival data were analyzed by the Kaplan-Meier method and the log rank test. Logistic regression analysis was used to test for differences in complication rates between families.

RESULTS

Haplotype analysis revealed that each family had PKD1-linked disease with a unique disease-associated haplotype. Interfamily differences were observed in overall survival (P = 0.0004), renal survival (P = 0.0001), hypertension prevalence (P = 0.013), and hernia (P = 0.048). Individuals with hypertension had significantly worse overall (P = 0.0085) and renal (P = 0.03) survival compared with those without hypertension. No statistically significant differences in the prevalence of hypertension and hernia were observed among controls.

CONCLUSION

We conclude that phenotype differences exist between PKD1 families, which, on the basis of having unique disease-associated haplotypes, are likely to be associated with a heterogeneous range of underlying PKD1 mutations.