Factors affecting the progression of renal disease in autosomal-dominant polycystic kidney disease

Reliability of magnetic resonance imaging for measuring the volumetric indices in autosomal-dominant polycystic kidney disease: correlation with hypertension and renal function

BACKGROUND

The purpose of this study was to determine if renal volumetric indices can be accurately measured using MRI, and if these volumetric indices are associated with hypertension and renal function in patients with autosomal-dominant polycystic kidney disease (ADPKD).

METHODS

For testing the accuracy of the MRI-based volume measurements that we proposed for clinical trial, we designed phantoms to simulate cysts within the kidney. Fifty-six patients with ADPKD were included in this study, and their respiratory compensated T2-weighted fast spin-echo images were acquired. The total kidney volume (Vt), cyst volume (Vc), and noncystic parenchymal volume (Vp) were measured and the percent cyst volume (Pc) was calculated. These volumetric indices were compared with the disease progression in the ADPKD patients.

RESULTS

The MRI measures of the phantoms were accurate. The Vt, Vc and Pc were significantly greater in the hypertensive group (n = 35) than in the normotensive group (n = 21) (p < 0.01). The Vt, Vc and Pc were significantly greater in the renal failure group (n = 23) than in the normal renal function group (n = 33) (p < 0.01). The Vt, Vc, and Pc were inversely correlated with the creatinine clearance.

CONCLUSION

MRI is a reliable method to measure renal volumetric indices. The MRI-based volume measurements can be employed as useful markers for the progression of disease in ADPKD patients.

Renal and extrarenal manifestations of autosomal dominant polycystic kidney disease

The objective of the present study was to determine the frequency of the most common clinical features in patients with autosomal dominant polycystic kidney disease in a sample of the Brazilian population. The medical records of 92 patients with autosomal dominant polycystic kidney disease attended during the period from 1985 to 2003 were reviewed. The following data were recorded: age at diagnosis, gender, associated clinical manifestations, occurrence of stroke, age at loss of renal function (beginning of dialysis), and presence of a family history. The involvement of abdominal viscera was investigated by ultrasonography. Intracranial alterations were prospectively investigated by magnetic resonance angiography in 42 asymptomatic patients, and complemented with digital subtraction arteriography when indicated. Mean age at diagnosis was 35.1 +/- 14.9 years, and mean serum creatinine at referral was 2.4 +/- 2.8 mg/dL. The most frequent clinical manifestations during the disease were arterial hypertension (63.3%), lumbar pain (55.4%), an abdominal mass (47.8%), and urinary infection (35.8%). Loss of renal function occurred in 27 patients (mean age: 45.4 +/- 9.5 years). The liver was the second organ most frequently affected (39.1%). Stroke occurred in 7.6% of the patients. Asymptomatic intracranial aneurysm was detected in 3 patients and arachnoid cysts in 3 other patients. In conclusion, the most common clinical features were lumbar pain, arterial hypertension, abdominal mass, and urinary infection, and the most serious complications were chronic renal failure and stroke. Both intracranial aneurysms and arachnoid cysts occurred in asymptomatic patients at a frequency of 7.14%.

Sonographic assessment of the severity and progression of autosomal dominant polycystic kidney disease: the Consortium of Renal Imaging Studies in Polycystic Kidney Disease (CRISP)

BACKGROUND

The accuracy and precision of ultrasonography (US) in assessing the severity of autosomal dominant polycystic kidney disease (ADPKD) is unknown.

METHODS

US and magnetic resonance imaging (MRI) were performed at baseline and 1 year on 230 subjects with ADPKD. Ellipsoid volume was calculated from US length, width, and depth, and sequential transverse images were used to measure total and cystic volume directly. These were compared with MRI measurements of kidney volume and cystic volume.

RESULTS

Variability between different sonographers ranged from 18% to 42%. Correlations between US and MRI volume were 0.88 and 0.89. The SD of the discrepancy from MRI ranged from 21% to 33% and was unrelated to kidney size or body mass. Kidney length was the most reproducible measurement, and its correlation with MRI volume was 0.84. All patients with an US volume less than 700 cm3 had an MRI volume less than 1,000 cm3, and all patients with an US volume greater than 1,700 cm3 had an MRI volume greater than 1,000 cm3. Increases in volume after 1 year were 12% +/- 36% for the ellipsoid method, 6% +/- 29% for the direct method, and 4.2% +/- 7.2% for MRI. Correlation between US and MRI measurement of fractional cyst volume was 0.80.

CONCLUSION

Sonographic measurement of kidney volume in patients with ADPKD is inaccurate and lacks the precision necessary to measure short-term disease progression. However, sonography can provide an estimate of kidney volume that reflects severity and prognosis in individual patients.

Autosomal-dominant polycystic kidney disease in infancy and childhood: progression and outcome

BACKGROUND

The natural history of autosomal-dominant polycystic kidney disease (ADPKD) has not been well described in children and infants.

METHODS

The present study analyzed the characteristics of 46 ADPKD children diagnosed before 18 months of life (VEO) and 153 children diagnosed between 18 months of age and 18 years of age (non-VEO).

RESULTS

VEO children had more cysts and larger renal volumes than non-VEO children when adjusted for age. In both VEO and non-VEO children, the presence of signs or symptoms at the time of diagnosis as well as the presence of hematuria or proteinuria at the study visit were associated with larger renal volumes. Children diagnosed early (VEO) or diagnosed due to signs or symptoms were also more likely to have high blood pressure. Two VEO children and no non-VEO children reached end-stage renal disease during follow-up.

CONCLUSION

In contrast to many published case reports suggesting the occurrence of early end-stage renal disease in VEO children, the results of the present study were much more optimistic. Over 90% of the VEO children maintained preserved renal function well into childhood.

Biventricular diastolic dysfunction in patients with autosomal-dominant polycystic kidney disease

BACKGROUND

Left ventricular diastolic dysfunction has been shown in patients with autosomal-dominant polycystic kidney disease (ADPKD). However, there is no study evaluating right ventricular functions in these patients.

METHODS

In the present study, diastolic functions of both ventricles in normotensive and hypertensive ADPKD patients with well-preserved renal function were investigated. Fifteen hypertensive and 16 normotensive patients with ADPKD with well-preserved renal function, 16 patients with essential hypertension, and 24 healthy subjects were included in the study. Conventional left and right ventricular echocardiographic measurements were performed in all subjects. Left and right ventricular functions were investigated both by myocardial performance index (MPI) [calculated by dividing the sum of isovolumic contraction time and isovolumic relaxation time (IVRT) by ejection time] and by tissue Doppler imaging (TDI).

RESULTS

Left ventricular deceleration time and IVRT were significantly prolonged in hypertensive patients with ADPKD compared with patients with essential hypertension and even in normotensive patients with ADPKD compared with healthy subjects. Left and right MPIs were significantly higher in patients with ADPKD compared with healthy subjects, showing systolic and diastolic dysfunction. Moreover, by using TDI, the peak early diastolic mitral annular velocity (Em) to peak late diastolic mitral annular velocity (Am) ratio and the peak early diastolic tricuspid annular velocity (Et) to peak late diastolic tricuspid annular velocity (At) ratio were decreased in patients with ADPKD, suggesting biventricular diastolic dysfunction.

CONCLUSION

Both hypertensive and normotensive patients with ADPKD show significant biventricular diastolic dysfunction, suggesting cardiac involvement very early in the course of ADPKD.

Aberrant expression of SPARC and its impact on proliferation and apoptosis in ADPKD cyst-lining epithelia

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) results from a combination of environmental and genetic factors. Secreted protein acidic and rich in cysteine (SPARC) can be expressed by many different cell types and is associated with development, remodelling, cell turnover and tissue repair. The analysis of SPARC would help evaluate the effect of the unique matricellular glycoprotein on renal disease progression in ADPKD.

METHODS

The concentration of SPARC was measured with an enzyme-linked immunosorbent assay (ELISA); distribution and expression levels were measured with in situ hybridization, immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) and western blot assays. Apoptosis was assessed by morphological observation and fluorescence-activated cell sorting (FACS) apoptosis index (AI) analysis. Cell cycle phase was examined by FACS analysis. Cell proliferation was studied using bromodeoxyuridine (BrdU) incorporation ELISA.

RESULTS

The SPARC level in the renal cyst fluid of patients with ADPKD was greater than that in patients with simple renal cyst (SRC), and also greater than that found in the plasma and urine of patients with either ADPKD or SRC and normal subjects. SPARC mRNA and protein levels in polycystic renal tissue were greater than that in normal renal tissue. Additionally, SPARC could inhibit cyst-lining epithelial cell proliferation, bring about cell cycle arrest in the G0/G1 phase and induce apoptosis in vitro. SPARC treatment resulted in decreased mRNA levels of PCNA (proliferating cell nuclear antigen), MCM2 (minichromosome maintenance protein 2), ClnD1 and Bcl-2, but an increased mRNA level of p21(Waf1) in cyst-lining epithelial cells.

CONCLUSION

Our findings suggest that the increased SPARC expression in ADPKD renal tissue may provide negative feedback in ADPKD patients.

Gender hormones and the progression of experimental polycystic kidney disease

BACKGROUND

Male gender is a risk factor for progression of autosomal-dominant polycystic kidney disease (ADPKD), clinically and in the Han:SPRD rat model. Orchiectomy limits progression, but mechanisms of the detrimental effect of androgen, and/or beneficial effects of estrogen, are not known. This protocol tested the hypothesis that male gender (intact androgen status) promotes progression, while female gender (intact estrogen status) is protective; and that these disease-modifying effects are due to changes in expression of known fibrotic mediators.

METHODS

Studies were performed in male and female noncystic control (+/+) and cystic (+/-) rats subjected to orchiectomy, ovariectomy, or sham operation. At 12 weeks of age, renal function was measured. Blood and kidneys were taken for measurement of plasma and renal renin, endothelin (ET-1), endothelial nitric oxide synthase (eNOS), and vascular endothelial growth factor (VEGF), using biochemical, protein expression, and immunohistochemical methods.

RESULTS

Cystic male rats exhibited significantly reduced glomerular filtration (GFR) and effective renal plasma flow (ERPF) rates, with suppression of plasma and renal renin, up-regulation of renal ET-1 and eNOS, and down-regulation of renal VEGF expression. Orchiectomy attenuated the fall in GFR and ERPF, while numerically limiting changes in eNOS and VEGF. Female rats exhibited less cystic growth, with normal renin status, lesser elevation of renal ET-1, and proportionately lesser changes in VEGF and eNOS. Ovariectomy led to higher blood pressure and reduced GFR and ERPF, with a trend toward upregulation of ET-1, and significant down-regulation of VEGF and eNOS.

CONCLUSION

Female gender is protective, but ovariectomy attenuates the protective effect of female gender, in association with changes in renal expression of ET-1, VEGF, and eNOS. The accelerated disease in male rats can be attenuated by orchiectomy and consequent changes in expression of disease mediators.

Volume Progression in Autosomal Dominant Polycystic Kidney Disease: The Major Factor Determining Clinical Outcomes

Autosomal dominant polycystic kidney disease (PKD) is a hereditary condition characterized by the progressive enlargement of innumerable renal cysts that contribute to life-altering morbidity early in the course of the disease. Evidence indicates that the rate of increase in kidney volume can be reliably measured by magnetic resonance or computed tomography imaging, thus providing objective means to judge the effectiveness of therapies that are targeted to the aberrant growth of renal tubules. It is now possible, therefore, to monitor the effectiveness of potential therapies on the signature abnormality in autosomal dominant PKD before irreversible damage has been done by the cysts. Evidence accumulated from human cross-sectional and longitudinal studies and longitudinal studies of PKD models in animals provide strong support for the view that reducing the rate of kidney volume enlargement will ameliorate the late-stage development of renal insufficiency.

Earlier Diagnosis of Autosomal Dominant Polycystic Kidney Disease: Importance of Family History and Implications for Cardiovascular and Renal Complications

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common and serious cause of hereditary renal disease. The emerging possibilities to intervene early in the disease course elevate the importance of both accurate and early diagnosis of ADPKD. Family history analysis is a simple and inexpensive approach to identifying individuals at risk for ADPKD. We hypothesized that advances in knowledge of and potential interventions for ADPKD have led to increased use of family history screening.

METHODS

We distributed surveys to 1,527 subjects from our ADPKD research database to determine the extent to which examination of family history was used to diagnose ADPKD, by birth cohort.

RESULTS

Six hundred thirty-seven subjects with ADPKD (42%) completed and returned surveys. Family history analysis led to the initial ADPKD diagnosis in 49% of all subjects overall. In the birth-cohort analysis, ADPKD was more likely to have been diagnosed in individuals born between 1951 and 1974 because of family history (55% versus 38%; P < 0.0002) and patients were younger at diagnosis (27 versus 39 years; P < 0.0001) than individuals born before 1951.

CONCLUSION

In a large cohort of subjects with ADPKD, we found increased use of family history analysis as a tool for diagnosing ADPKD and earlier age of diagnosis in the more recent birth cohort. This trend may reflect increased overall awareness of ADPKD by physicians, as well as encouraging hypertension and proteinuria treatment outcome data that may depend on intervening early in the course of disease.

Androgen Receptor Pathway in Rats with Autosomal Dominant Polycystic Kidney Disease

Androgens have been implicated in mediating disease escalation in autosomal dominant polycystic kidney disease (ADPKD). Dihydrotestosterone (DHT), an agonist, and flutamide (FLT), an antagonist, were administered to Han:SPRD rats with ADPKD, and the role of androgen receptor (AR) abundance and activation on the enlargement and function of cystic kidneys was evaluated. Renal AR abundance determined by immunoblots in 8- to 10-wk-old Cy/+ male rats was naturally increased four-fold above that of littermate +/+ controls. In male Cy/+, castration decreased AR abundance below control +/+ by -89.4%, and AR expression within cyst mural epithelial cells was strikingly decreased. Castration of Cy/+ male rats also reduced the usual increases in kidney weight by -49.7%, kidney cyst area by -34.0%, and serum urea nitrogen by -72.8%; these indices were restored to precastration levels by DHT. In Cy/+ male rats, FLT administration reduced the increase in kidney weight by -27.6% and serum urea nitrogen by -53.7% and decreased the increment in AR expression by -84.2% in comparison with untreated +/+ controls. There was no effect of FLT in female rats. Immunoblot expression of phospho-extracellular signal-regulated kinase 1/2 (P-ERK) and B-Raf, key intermediates in the mitogen-activated protein kinase pathway that are abnormally elevated in Cy/+, was unaffected by castration and/or administration of DHT or FLT. AR was not expressed in renal epithelial cell nuclei of androgen-deficient rats but was displayed in most tubule and mural cyst cell nuclei of androgen-replete rats. In androgen-deficient Cy/+, 80.6% of renal epithelial cells that had entered the cell cycle (proliferating cell nuclear antigen positive) also expressed P-ERK. In androgen-replete rats, proliferating cell nuclear antigen-positive cells co-expressed AR (12.7%), P-ERK (36.4%), and P-ERK + AR (45.0%); 5.9% were probably stimulated by other mitogenic mechanisms. It is concluded that androgens potentiate renal cell proliferation and cyst enlargement through ERK1/2-dependent and ERK1/2-independent signaling mechanisms in Han:SPRD. It is suggested that the basal rate of cell proliferation is determined by ERK1/2 signaling to a major extent and that androgens have additive effects.

Molecular basis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a serious, life-threatening genetic disease in which extensive epithelial-lined cysts develop in the kidneys and, to a lesser extent, in other organs such as liver, pancreas, and ovaries. In a majority of cases (80-85%), the gene involved is PKD1, which is located on chromosome 16 (16q13.3) and encodes polycystin-1, a large receptor-like integral membrane protein that contains several extracellular motifs indicative of cell-cell and cell-matrix interaction. In the remaining (10-15%) cases, the disease is milder and is caused by mutational changes in another gene (PKD2), which is located at chromosome 4 (4q21-23) and encodes polcystin-2, a transmembrane protein, which acts as a nonspecific calcium-permeable channel. Both polycystins function together in a nonredundant fashion, through a common pathway, and produce cellular responses that regulate proliferation, migration, differentiation, and kidney morphogenesis. Through combined function of polycystins, normal tubular cells are maintained in a state of terminal differentiation, and their proliferation is strictly controlled. Loss of function of either protein due to gene mutations results in the tubular cells reverting to a less differentiated state, which is more prone to proliferation. Patients with ADPKD carry a germ-line mutation in PKD1 or PKD2. A second somatic mutation in some of the tubular cells results in loss of both normal alleles, leading to loss of polycystin function. The affected cells lose the normal terminally differentiated state, revert to less differentiated phenotype, and undergo proliferation, which leads to cyst formation. As the cysts enlarge over many decades, the normal renal parenchyma is progressively destroyed, leading to renal failure. Recently, the crucial role of primary cilia in modulating proliferation, migration, and differentiation of tubular epithelium has been recognized. Most of the tubular cells have one or two primary cilia projecting from the apical surface into the luminal space. The cilia act as mechanoreceptors as they bend with the urinary flow within the tubules. Both polycystins are strategically located within the cilia and act as important mediators of ciliary mechanosensation. Loss of this important function due to mutational changes in PKD1 or PKD2 leads to loss of normal control over cellular proliferation, resulting in cyst formation. Several other ciliary proteins have recently been found to contribute directly to a wide spectrum of human kidney diseases with cystic phenotype, thus underscoring the pivotal role the primary cilia play in maintaining the normal structure and function of the tubular cells and probably other cells in the body.

Design and baseline characteristics of participants in the study of antihypertensive therapy in children and adolescents with autosomal dominant polycystic kidney disease (ADPKD)

In this manuscript, we describe our ongoing randomized clinical trial to assess the efficacy of blood pressure control with angiotensin converting enzyme (ACE) inhibition on renal cyst growth over a 5-year study period in children and young adults aged 4-21 years with autosomal dominant polycystic kidney disease (ADPKD). Baseline demographic and laboratory data for the study groups are reported. Results of this study could significantly impact the standard of care for management of ADPKD in this population.

Modifier genes play a significant role in the phenotypic expression of PKD111See Editorial by Pei, p. 1630

BACKGROUND

Polycystic kidney disease type 1 (PKD1) is characterized by extreme variation in the severity and progression of renal and extrarenal phenotypes. There are significant familial phenotype differences; but it is not clear if this is due to differences in PKD1 mutations, differences in genetic background, or both.

METHODS

A total of 315 affected relatives (83 PKD1 families) without end-stage renal disease (ESRD) were evaluated for disease markers, including renal volume, creatinine clearance, proteinuria, liver cysts, and hypertension. Of these patients, 19% progressed to ESRD within 1 to 10 years after the initial examination. Nested analysis of variance was used to investigate interfamilial and intrafamilial differences in these phenotypes. Heritability analyses were used to estimate the effect of the genetic background on phenotypic variability. The age of onset of ESRD was also analyzed with an additional 389 family members from the same PKD1 families without clinical evaluation but with data on age of onset of ESRD (or age without ESRD).

RESULTS

There were significant phenotype differences between patients with the same mutation and different genetic backgrounds. The phenotypic variation between patients with different mutations and different genetic backgrounds was not significantly greater than the variation between patients with the same mutation and different genetic backgrounds. However, when the 389 family members were included, both the mutation and modifier genes had significant effects on the age of onset of ESRD. Inherited differences in genetic background were estimated to account for 18% to 59% of the phenotypic variability in PKD1 disease markers in patients prior to ESRD and in the subsequent progression to ESRD (43% heritability) in the 315 patients who were clinically evaluated.

CONCLUSION

Modifier loci in the genetic background are important factors in inter- and intrafamilial variability in the phenotypic expression of PKD1. The extreme intrafamilial phenotype differences are consistent with the hypothesis that one or a few modifier genes have a major effect on the progression and severity of PKD1.

Transplantation of a cadaveric polycystic kidney in a patient with autosomal dominant polycystic kidney disease: long-term outcome

INTRODUCTION

Kidneys from donors affected by autosomal dominant polycystic kidney disease (ADPKD) were considered unusable for transplantation. To the best of our knowledge, seven cases worldwide have now been described in the English literature since 1967 suggesting such donor organs may be acceptable under certain conditions. Most of these reports have only short-term follow-up.

METHODS

We provide a review of these patients and share our experience with an ADPKD patient who had a cadaveric ADPKD transplant and has been closely followed for 10 years.

RESULTS

During the 10-year period, the patient had three transplant biopsies without complication. This creatinine is currently 1.2 mg/dL. Serial computed tomography imaging indicated that the cystic disease slowly progressed during this time period. He eventually developed intractable pain in his native left kidney and underwent a laparoscopic nephrectomy.

CONCLUSIONS

Normal functioning cadaveric kidneys that show early signs of polycystic kidney disease should be considered acceptable for renal donation. These organs provide the recipient a safe, reasonable period of graft survival and have not been shown to cause adverse effects.

Autosomal dominant polycystic kidney disease (ADPKD, MIM 173900, PKD1 and PKD2 genes, protein products known as polycystin-1 and polycystin-2)

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited nephropathy affecting over 1:1000 of the worldwide population. It is a systemic condition with frequent hepatic and cardiovascular manifestations in addition to the progressive development of renal cysts that eventually result in loss of renal function in the majority of affected individuals. The diagnosis of ADPKD is typically made using renal imaging despite the identification of mutations in PKD1 and PKD2 that account for virtually all cases. Mutations in PKD1 are associated with more severe clinical disease and earlier onset of renal failure. Most PKD gene mutations are loss of function and a 'two-hit' mechanism has been demonstrated underlying focal cyst formation. The protein products of the PKD genes, the polycystins, form a calcium-permeable ion channel complex that regulates the cell cycle and the function of the renal primary cilium. Abnormal cilial function is now thought to be the primary defect in several types of PKD including autosomal recessive polycystic kidney disease and represents a novel and exciting mechanism underlying a range of human diseases.

The role of parental hypertension in the frequency and age of diagnosis of hypertension in offspring with autosomal-dominant polycystic kidney disease

BACKGROUND

Hypertension in autosomal-dominant polycystic kidney disease (ADPKD) patients is associated with more rapid progression of renal disease and a high incidence of left ventricular hypertrophy (LVH). The present study was undertaken to examine the role of parental hypertension in the occurrence of hypertension in 475 ADPKD offspring.

METHODS

Adult subjects participating in an ongoing study of the natural history of ADPKD were included in the analysis if they were diagnosed with ADPKD, had a known affected parent, and knew the hypertensive status of both parents.

RESULTS

When the affected parent was hypertensive, the ADPKD male (82% versus 62%, P < 0.05) and female (61% versus 37%, P < 0.005) offspring had a significantly higher frequency of hypertension than when the ADPKD-affected parent was normotensive. The median age of diagnosis of hypertension was also significantly earlier in both male (33 years versus 40 years, P < 0.05) and female (38 years versus 50 years, P < 0.05) ADPKD patients when their affected parents were hypertensive as compared with normotensive. These effects of hypertension in the affected parent on hypertension in the ADPKD offspring were independent of age, renal volume, and renal function in the offspring. Hypertension in unaffected parents also increased the frequency of hypertension in the ADPKD female (69% versus 53%, P < 0.01), but not male (89% versus 77%, NS) subjects.

CONCLUSION

The results indicate that parental hypertension influences the frequency of hypertension in ADPKD patients.

The expression and activity of renal nitric oxide synthase and circulating nitric oxide in polycystic kidney disease rats

Nitric oxide (NO) influences tubular fluid and electrolyte transport, and hence possibly also fluid accumulation in renal cysts. The expression and activity of intrarenal constitutive NO synthase (cNOS) [neuronal NOS, nNOS and endothelial NOS, eNOS] and inducible NOS (iNOS) and plasma nitrite/nitrate (PNOx) concentration were assessed in homozygous Han:SPRD polycystic kidney disease (PKD) rats (cy/cy), heterozygous Han:SPRD PKD rats (cy/+), homozygous normal Han:SPRD littermates (+/+) and Sprague Dawley rats (sd). The results showed: 1) nNOS expression was decreased in proximal tubules and thick ascending limbs of the loop of Henle in cy/cy and cy/+ rats compared to +/+ and sd rats (p<0.05). nNOS was weakly expressed in the epithelium of small cysts and unexpressed in epithelium of large cysts. 2) iNOS expression was increased in proximal tubular epithelial cells in cy/+ rats compared to +/+ rats and sd rats (p<0.01). iNOS expression in cyst epithelium was decreased in cy/+ rats (p<0.05) and absent in cy/cy rats. 3) eNOS expression was similar in the endothelium of intrarenal arteries in all groups. 4) The activity of renal cNOS was decreased in cy/cy and cy/+ rats; the activity of iNOS was decreased only in cy/cy rats, with no significant difference among the other three groups. 5) PNOx concentration was higher in cy/cy rats than in the other three groups, and correlated positively with plasma creatinine and urea. In conclusion, NOS expression and activity decreased as cysts developed, suggesting that NO downregulation is involved in the pathogenesis of PKD.

Characterization of microsatellite markers to diagnose ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) maps to chromosome 16p13.3 (PKD1) and to chromosome 4q21-23 (PKD2), with the likelihood of a third unmapped locus. The size and genomic complexity of the PKD1 gene make it impractical to detect mutations for prenatal diagnosis. Therefore, pedigree-based linkage analysis remains useful for diagnosis of ADPKD. Since, the complete genome sequences of chromosome 16p13.3 and 4q21-23 including PKD1 and PKD2, respectively, were reported very recently, in order to do more precise diagnosis of ADPKD, we tried to find microsatellite markers. We performed database searches of 2000 kb of genome sequence across the 16p13.3 and the 4q21-23. To determine the distribution of alleles and the degree of polymorphism of the microsatellites, genotyping experiments were performed on 48 Korean individuals. We found novel 14 microsatellite markers around ADPKD that are more polymorphic and closer to PKD1 or PKD2 than the known markers. The novel microsatellite markers were applied to diagnose ADPKD families. These novel microsatellite markers are not only useful for presymptomatic and prenatal diagnosis of ADPKD, but also applicable in the study of positional cloning, human evolution and tumor biology.

Effects of gender, Helicobacter pylori and hepatitis B virus serology status on cardiovascular and renal complications in Chinese type 2 diabetic patients with overt nephropathy

BACKGROUND

The aim of this study was to investigate whether chronic infections with Helicobacter pylori and hepatitis B virus (HBV) might affect clinical outcomes in Chinese type 2 diabetic patients with advanced nephropathy.

METHODS

A prospective study of 97 type 2 diabetic patients with clinical proteinuria and renal insufficiency (median serum creatinine 200 micro mol/l).

RESULTS

During a median follow-up period of 2 years, 34 developed end-stage renal disease (ESRD), 28 had cardiovascular endpoints and 11 patients had died (seven men and four women), and 52.7% developed a combined endpoint. Female patients had longer disease duration, higher blood pressure, lower body weight but higher serum creatinine and spot urine albumin : creatinine ratio as well as lower haemoglobin than male patients. On logistic regression analysis, female gender (hazard ratio: 5.91, p = 0.02), negative H. pylori serology (8.39, p = 0.004), baseline serum creatinine (1.04, p = 0.001) and haemoglobin (1.86, p = 0.01) were independent predictors for ESRD. Systolic blood pressure (1.04, p = 0.003), prior treatment with angiotensin-converting enzyme inhibitors or angiotensin II receptor antagonists (3.41, p = 0.04) and positive hepatitis B surface antigen (4.88, p = 0.025) were independent predictors for cardiovascular endpoints. Female gender (7.89, p = 0.002) and baseline serum creatinine (1.05, p < 0.001) were independent predictors for combined death and cardio-renal endpoints.

CONCLUSIONS

In Chinese type 2 diabetic patients with clinical proteinuria renal insufficiency, there were high rates of death and cardio-renal outcomes. Female gender, low haemoglobin and negative H. pylori serology were important predictors for ESRD, whereas chronic HBV infection was associated with increased cardiovascular risks.

Ambulatory blood pressure correlates with renal volume and number of renal cysts in children with autosomal dominant polycystic kidney disease

OBJECTIVE

In adult patients with autosomal dominant polycystic kidney disease (ADPKD) renal volume was found to be significantly greater in hypertensive compared to normotensive patients. The purpose of this study was to find out if blood pressure (BP) is related to renal size also in children with ADPKD, for example, in an early stage of the disease.

METHOD AND RESULTS

Sixty-two children with ADPKD and normal renal function (mean age 12.3+/-4.3 years) were examined by renal ultrasound and ambulatory BP monitoring (ABPM). Twenty-two children were hypertensive and 40 normotensive. Mean renal volume was significantly greater in hypertensive than in normotensive children (2.7+/-2.3 SDS versus 1.2+/-2.5 SDS, P<0.01) despite similar anthropometric data and renal function. Similarly the mean number of cysts was significantly higher in hypertensive patients than in normotensive (35+/-15 cysts versus 23+/-14 cysts, P<0.01). Renal volume correlated with daytime as well as with night-time systolic and diastolic BP (r=0.41-0.47, P<0.01). Correlations with renal length and the number of renal cysts were somewhat less (r=0.29-0.43, P<0.05 and 0.01, respectively).

CONCLUSIONS

This study revealed a significant relationship between renal volume, renal length and number of renal cysts and BP. It is suggested that children with ADPKD should regularly be checked for BP changes by ABPM, especially those who show increased renal size or a high number of renal cysts on ultrasound. All these children are at high risk for development of hypertension.

Modulation of renal injury in pcy mice by dietary fat containing n−3 fatty acids depends on the level and type of fat

Low-fat diets and diets containing n-3 fatty acids (FA) slow the progression of renal injury in the male Han:Sprague-Dawley (SPRD)-cy rat model of polycystic kidney disease. To determine whether these dietary fat effects are similar in females and in another model of renal cystic disease, in this study we used both male and female pcy mice to examine the effects of fat level and type on disease progression. Adult pcy mice were fed 4, 10, or 20 g soybean oil/100 g diet for 130 d in study 1. In study 2, weanling pcy mice were fed high or low levels of fat rich in 18:2n-6 (corn oil, CO), 18:3n-3 (flaxseed oil/CO 4:1 g/g, FO), or 22:6n-3 (algal oil/CO 4:1 g/g, DO) for 8 wk. In adult pcy mice, low- compared with high-fat diets lowered kidney weights (2.4 +/- 0.2 vs. 3.1 +/- 0.2 g/100 g body weight, P = 0.006) and serum urea nitrogen (SUN) (9.6 +/- 0.6 vs. 11.9 +/- 0.6 mmol/L, P = 0.009), whereas in young pcy mice it reduced renal fibrosis volumes (0.44 +/- 0.04 vs. 0.62 +/- 0.04 mL/kg body weight, P < 0.0001). FO feeding in young pcy mice mitigated the detrimental effects of high fat on fibrosis while not altering kidney size, function, and oxidative damage when compared with the CO-fed mice. In contrast, DO- compared with CO-fed mice had higher kidney weights (2.64 +/- 0.07 vs. 2.24 +/- 0.08 g/100 g body weight, P = 0.005), SUN (9.4 +/- 0.57 vs. 7.0 +/- 0.62 mmol/L, P < 0.0001), and cyst volumes (7.9 +/- 0.28 vs. 6.2 +/- 0.30 mL/kg body weight, P < 0.0001) and similar levels of oxidative damage and fibrosis. The FA compositions of the diets were reflected in the kidneys: 18:2n-6, 18:3n-3, and 22:6n-3 were the highest in the CO, FO, and DO diets, respectively. Dietary effects on kidney disease progression were similar in males and females. A low-fat diet slows progression of renal injury in male and female pcy mice, consistent with findings in the male Han:SPRD-cy rat. Dietary fat type also influenced renal injury, with flaxseed oil diets rich in 18:3n-3 slowing early fibrosis progression compared with diets rich in 18:2n-6 or in 22:6n-3.

Renal Vascular Resistance and Renin-Angiotensin System in the Pathogenesis of Early Hypertension in Autosomal Dominant Polycystic Kidney Disease

Activation of the renin-angiotensin system (RAS) has been proposed to increase renal vascular resistance (RVR) and to play a role in the development of hypertension in autosomal dominant polycystic kidney disease (ADPKD). The aim of this study was to investigate the relationship among RVR, RAS and blood pressure (BP) profile in patients without renal impairment. Thirty-four ADPKD patients underwent ambulatory blood pressure monitoring (ABPM) over a 24-h period and were divided into two groups: 17 hypertensive (group A, day-systolic BP > or = 135 mmHg and/or day-diastolic BP > or = 85 mmHg) and 17 normotensive (group B, day-BP < 135/85 mmHg) patients. The two groups were comparable with respect to age, sex, and renal function. None of the patients assumed therapy. In all subjects the plasma renin activity (PRA) was measured, and the RVR was assessed by measuring resistivity indices (RI). RI was significantly higher in the hypertensive than in normotensive patients (0.67 +/- 0.05 vs. 0.62 +/- 0.03), while PRA was normal in all subjects, and showed no statistical difference between the two groups. Taking all the patients together (group A + group B), a significant positive correlation between RI and 24-h mean arterial pressure (MAP) was discovered, but no correlation was found between RI and PRA or between MAP and PRA. We conclude that in ADPKD patients without renal impairment the MAP values are strictly correlated with the RVR, but not with PRA. Thus factors other than RAS probably contribute to the increase of the RVR and to the early development of hypertension.

Renal structure in early autosomal-dominant polycystic kidney disease (ADPKD): The Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) cohort

BACKGROUND

Autosomal-dominant polycystic kidney disease (ADPKD) is characterized by gradual renal enlargement and cyst growth prior to loss of renal function. Standard radiographic imaging has not provided the resolution and accuracy necessary to detect small changes in renal volume or to reliably measure renal cyst volumes. The Consortium for Radiologic Imaging Studies in Polycystic Kidney Disease (CRISP) is longitudinally observing ADPKD individuals using high-resolution magnetic resonance (MR) imaging to determine if change in renal and cyst volumes can be detected over a short period of time, and if they correlate with decline in renal function early in disease.

METHODS

Standardization studies were conducted in phantoms and four subjects at each participating clinical center. After, in the full-scale protocol, healthy ADPKD individuals 15 to 45 years old with creatinine clearance>70 mL/min underwent standardized MR renal imaging, renal iothalamate clearance, comprehensive clinical evaluation, and determination of 24-hour urinary albumin and electrolyte excretion. Stereology was used from T1-weighted images to quantify renal volume, and region-growing thresholding was used from T2-weighted images to determine cyst volume. Renal structures were evaluated in relation to demographic, clinical, and biochemical variables using means/medians, standard deviations, and Pearson correlations.

RESULTS

Reliability coefficients for MR renal and cyst volume measurements in phantoms were 99.9% and 89.2%, respectively. In the full-scale protocol, 241 ADPKD individuals (145 women and 96 men) were enrolled. Total renal, cyst, and % cyst volume were significantly greater in each decade group. Hypertensive individuals demonstrated greater renal, cyst, and % cyst volume than normotensive subjects. Age-adjusted renal (r = -0.31, P < 0.0001), cyst (r = -0.36, P < 0.0001), and % cyst volume (r = -0.35, P < 0.0001) were inversely related to glomerular filtration rate (GFR). Age-adjusted renal volume (r = 0.42, P < 0.0001), cystic (r = 0.39, P < 0.0001, and % cyst volume (r = 0.41, P < 0.0001) were related with urinary albumin excretion.

CONCLUSION

MR measures of renal and cyst volume are reliable and accurate in patients with ADPKD. ADPKD is characterized by significant cystic involvement that increases with age. Structure (renal and cyst volume) and function (GFR) are inversely related and directly related with the presence of hypertension and urinary albumin excretion in individuals with normal renal function.

Laparoscopic cyst decortication in autosomal dominant polycystic kidney disease: impact on pain, hypertension, and renal function

BACKGROUND AND PURPOSE

In patients with autosomal dominant polycystic kidney disease (ADPKD), laparoscopic cyst decortication (LCD) has been proposed as a means to relieve chronic cyst-related pain. We present our 7-year experience with LCD for ADPKD with regard to pain relief, hypertension, and renal function.

PATIENTS AND METHODS

Between August 1994 and February 2001, 29 ADPKD patients with chronic pain (N=29), hypertension (N=21), and renal insufficiency (N=10) underwent 35 LCD procedures. Every detectable cyst within 2 mm of the renal surface was treated. Pain relief was assessed using a pain analog scale; relative pain relief (RPR) equaled (preoperative pain score) - (postoperative pain score)/(preoperative pain score). Hypertension was evaluated using the antihypertensive therapeutic index (ATI): [(dose of blood pressure medication 1/max dose 1) + (dose med 2/max dose 2) + etc.] x 10. Renal function was assessed using the Cockcroft and Gault formula for creatinine clearance.

RESULTS

The mean operating room time was 4.9 hours (range 2.6-6.6 hours) with no conversions to open surgery. An average of 220 cysts (range 4-692) were treated per patient. The mean follow-up was 32.3 months (range 6-72 months). The RPR was 58%, 47%, and 63% at 12, 24, and 36 months, respectively. At 12, 24, and 36 months, 73%, 52%, and 81% of patients, respectively, noted >50% improvement in their pain compared with the preoperative situation. Five patients became normotensive, and patients improved their ATI by an average of 49% (range 11%-93%). However, six patients had worsening hypertension, with an ATI increase averaging 53% (range 11%-122%), and one patient who was not hypertensive preoperatively has since developed hypertension. The creatinine clearance changed +4%, +7%, and -2% at 12, 24, and 36 months, respectively. Only one patient had a >20% increase in creatinine clearance. The only patients with a >20% decrease in creatinine clearance were those who had a creatinine clearance <30 mg/dL preoperatively (average decrease 34% [range 20%-51%]).

CONCLUSIONS

For ADPKD patients with debilitating pain, extensive LCD can provide durable relief. In the majority of patients with pain and hypertension, a marked improvement in blood pressure also occurs. Cyst decortication was not associated with worsening renal function; indeed, renal function remained largely unchanged over the 3-year follow-up period.

Risk factors for progressive chronic kidney disease

The occurrence of chronic kidney disease and subsequent rate of loss of renal function are highly variable among individuals with the same underlying cause of renal injury or degree of functional impairment. Individual variability of risk is typical of complex diseases and reflects the multifactorial nature of the biologic mechanisms that are involved in the underlying disease process. The utility of the risk factor concept in developing CKD prevention and control strategies includes identifying individuals at high risk for the occurrence and progression of CKD, defining at-risk populations, elucidating potential targets for intervention, and generating explanatory hypotheses for the variable risk of CKD noted in different populations. Future application of the risk factor concept in the prevention and control of CKD will entail developing multivariate prediction equations; using spatial and temporal, as well as personal, characteristics, to define at-risk populations; identifying biomarkers for complex risk factors like race; and translating this information into testable interventions. This should include active extension of our current understanding of health care, social, and economic risk factors at both the individual and the community level.

Renal activation of extracellular signal-regulated kinase in rats with autosomal-dominant polycystic kidney disease

BACKGROUND

Abnormal proliferation of renal tubule epithelial cells is a central factor in the biogenesis and sustained expansion of cysts in autosomal-dominant polycystic kidney disease (ADPKD). Recent evidence from in vitro studies of human cyst wall epithelial cells has implicated a role for the mitogen-activated protein (MAP) kinase pathway in this aberrant proliferation. To determine the extent to which this signaling pathway is involved in cyst pathogenesis in vivo, we measured the expression of select components of the MAP kinase cascade in Han:SPRD rats with ADPKD at an early stage of the disease.

METHODS

Kidneys of 8-week-old normal Han:SPRD rats (+/+) or rats heterozygous (Cy/+) for ADPKD were examined by Western blot analysis and immunohistochemistry to determine the expression of extracellular-regulated kinase (ERK), phosphorylated ERK (P-ERK), Raf-1 (MAPKKK), phosphorylated Raf-1 (P-Raf-1), B-Raf, Rap-1 and phosphorylated protein kinase A (P-PKA).

RESULTS

P-ERK was expressed to a greater extent in Cy/+ kidneys (3.74 +/- 1.07 fold) than in normal kidneys, whereas ERK abundance was not different. P-Raf-1 levels were higher in Cy/+ than in +/+ kidneys (1.53 +/- 0.08 fold) consistent with upstream stimulation of receptor tyrosine kinase. B-Raf and Raf-1 abundances were greater in Cy/+ than in +/+ (1.74 +/- 0.25 and 1.27 +/- 0.08 fold, respectively). In Cy/+, immunohistochemistry showed increased P-ERK and B-Raf expression in the abnormal mural epithelial cells within cysts. These findings, together with the detection of P-PKA and the small G protein, Rap-1, in cyst epithelial cells, implicate a potential role for cyclic adenosine monophosphate (AMP) in the activation of ERK in ADPKD cells.

CONCLUSIONS

We conclude that the MAP kinase pathway is activated to the level of ERK in the abnormal mural epithelial cells lining cysts in animals with a dominantly inherited type of polycystic kidney disease. We suggest that cAMP, acting through PKA, Rap-1 and B-Raf, may contribute to the activation of ERK in a way that complements receptor tyrosine kinase-mediated agonists in the promotion of cyst enlargement.

Epidemiological study of kidney survival in autosomal dominant polycystic kidney disease

BACKGROUND

It is unknown whether the substantial increase in research, identification of risk factors for renal progression, greater antihypertensive armamentarium including inhibitors of the renin-angiotensin-aldosterone system (RAAS) and enhanced educational information have impacted the progression of autosomal dominant polycystic kidney disease (ADPKD) renal disease.

METHODS

An epidemiological study involving 513 ADPKD subjects was performed. The hypothesis tested was that over two separate periods, 1985 to 1992 versus 1992 to 2001, a significant slowing of renal function loss in ADPKD patients would be demonstrated in association with improved blood pressure (BP) control and inhibition of the RAAS as instituted by their primary care physicians.

RESULTS

ADPKD males and females in the later cohort (1992 to 2001) had longer mean and median survival times to ESRD than males and females in the earlier cohort (1985 to 1992). Analysis revealed that both males and females in the later cohort had significantly lower diastolic blood pressure (DBP) and mean arterial pressure (MAP) values than males and females in the earlier cohort. ADPKD male and female patients in the later cohort used significantly more angiotensin converting enzyme inhibitors (ACEIs) than ADPKD male and female patients in the earlier cohort.

CONCLUSIONS

These results demonstrate a significant slowing of ADPKD renal progression in both male and female patients that was associated with a significantly lower MAP and increased use of ACEIs in the later cohort (1992 to 2001) as compared to the early cohort (1985-1992).

Cystic disease in women: clinical characteristics and medical management

Autosomal dominant polycystic kidney disease (ADPKD) is a dominantly inherited systemic disorder equally inherited in men and women characterized by renal cyst development and expansion ultimately leading to renal failure. ADPKD women have a slower rate of progression to renal failure, with a later age of entry into end-stage renal disease (ESRD) as compared with men. Renal cyst growth and renal expansion are the hallmarks of ADPKD, and women will develop renal insufficiency with smaller renal volume than their male counterparts. As well, women have different rates of occurrence of renal and extrarenal complications in ADPKD. Renal complications related to ADPKD, including hypertension and gross hematuria, occur more frequently in men than in women, whereas liver cystic disease occurs earlier and more frequently in women than in men. The presence of polycystic liver disease is related to pregnancy number and oral contraceptive pill use in ADPKD women. Importantly, massive polycystic liver disease requiring surgical intervention occurs primarily in ADPKD women. ADKPD women have a highly successful reproductive course. The chance of a successful pregnancy is excellent in ADPKD women and comparable to healthy unaffected women as long as prepregnancy blood pressure and renal function are normal. Fetal complication rates are no greater than in the general population; however, maternal complication rates in ADPKD women are high with an increased frequency of new or worsening hypertension as well as an increased occurrence of preeclampsia and preterm deliveries. Finally, increasing pregnancy number has minimal or no effect on renal outcome in ADPKD women.

The role of gender in the progression of renal disease

The rate of progression of certain renal diseases in animals is greater in men than in women. In various animal models of renal disease, investigators have concluded that the presence of testosterone explains the worse course in men compared with women, whereas in other diseases, estrogen seems to confer protection for women. The gender disparity in renal disease progression found in animals is seen in certain human renal diseases, including chronic renal disease, membranous nephropathy, immunoglobin A nephropathy, and polycystic kidney disease. In humans, the differences between the genders in renal disease progression cannot be fully explained by differences in blood pressure or serum cholesterol levels. The underlying mechanisms for this gender disparity are potentially related to differences between the sexes in glomerular structure, glomerular hemodynamics, diet, variations in the production and activity of local cytokines and hormones, and/or the direct effect of sex hormones on kidney cells. Further investigation into the contribution of gender to renal disease progression may aid us in developing strategies for slowing this pathological process.

Recent advances in the cell biology of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a significant familial disorder, crossing multiple ethnicities as well as organ systems. The goal of understanding and, ultimately, curing ADPKD has fostered collaborative efforts among many laboratories, mustered on by the opportunity to probe fundamental cellular biology. Here we review what is known about ADPKD including well-accepted data such as the identification of the causative genes and the fact that PKD1 and PKD2 act in the same pathway, fairly well-accepted concepts such as the "two-hit hypothesis," and somewhat confusing information regarding polycystin-1 and -2 localization and protein interactions. Special attention is paid to the recently discovered role of the cilium in polycystic kidney disease and the model it suggests. Studying ADPKD is important, not only as an evaluation of a multisystem disorder that spans a lifetime, but as a testament to the achievements of modern biology and medicine.

The ENOS polymorphism is not associated with severity of renal disease in polycystic kidney disease 1

BACKGROUND

The renal phenotype in autosomal dominant polycystic kidney disease (ADPKD) is highly variable. Although genetic and allelic heterogeneity explain part of this variability, significant intrafamilial differences in time to end-stage renal disease (ESRD) indicate that genetic modifiers and the environment influence renal phenotype. Previously, a glutamic acid to aspartic acid polymorphism at residue 298 (E/D298) of the endothelial nitric oxide synthase (eNOS) gene ENOS was associated with disease severity in males with ADPKD.

METHODS

We typed the E/D298 polymorphism in 215 mutation-defined polycystic kidney disease 1 (PKD1) patients from 80 families. In this population, 96 patients had ESRD, with a median time to renal failure of 53 years.

RESULTS

Distribution of ENOS genotypes was 86 (40%), 106 (49.3%), and 23 (10.7%) for EE, ED, and DD, respectively. The occurrence of hypertension was not significantly different between genotypes. Kaplan-Meier renal survival analysis showed no significant difference between genotypes, with a median age to ESRD of 53 years for all genotypes in the total population and 52, 52, and 51 years (men) and 57, 53, and 55 years (women) for DD, DE, and EE, respectively.

CONCLUSION

Although the D298 ENOS allele may be associated with lower vascular activity of eNOS, this did not correlate with severity of renal disease in this PKD1 population. An important difference between this study and one finding a modifying role for ENOS was the rigor in defining the PKD1 population. This study shows the importance of using mutation-characterized populations for association studies in ADPKD.

Does type 2 diabetes mellitus delay renal failure in autosomal dominant polycystic kidney disease?

Autosomal dominant polycystic kidney disease (ADPKD) is a common renal disease without an effective therapeutic intervention to delay renal failure. Within kindreds, renal dysfunction often develops at a similar age in affected individuals, although there are known modifying factors. Two kindreds with ADPKD have shown a striking pattern of delayed onset of renal insufficiency in those individuals also suffering from type 2 diabetes mellitus. Eight nondiabetic patients with ADPKD had onset of dialysis or renal death at ages 38-52 years, (mean +/- SEM 46 +/- 1.9, n = 7) as compared with four diabetics who started dialysis or are still off dialysis at the age of 61 +/- 2.8 years (p < 0.01). Two of the four diabetics still have reasonable renal function at age 61 and 66. The diabetes was diagnosed at age 32 +/- 2 years and was treated with oral hypoglycemics for 19 +/- 2 years before institution of insulin. Cardiovascular disease dominated the clinical picture in the diabetics. In conclusion, onset of renal failure in ADPKD was delayed for over 15 years in individuals who also suffered from type 2 diabetes mellitus, in two ADPKD kindreds. Possible mechanisms are discussed, including glibenclamide inhibition of the cystic fibrosis transmembrane conductance regulator. The striking delay associated with type 2 diabetes mellitus in ADPKD induced renal failure should be evaluated further.

Renal ultrasonographic and computed tomographic appearance, volume, and function of cats with autosomal dominant polycystic kidney disease

The purpose of this study was to describe the ultrasonographic (US) and computed tomographic (CT) appearance of autosomal dominant polycystic kidney disease (ADPKD) in cats; to compare renal volume in cats with ADPKD (n = 5; mean age 59 +/- 10 months)) and normal cats (n = 5; mean age 66 +/- 10 months) using 2 imaging modalities, US and CT; and to calculate cyst volume using CT. Glomerular filtration rate (GFR) was determined by 2 methods: 99mTc-diethylene-triaminepentaacetic acid (99mTc-DPTA) scintigraphic uptake and 99-Tc-DTPA plasma clearance. Sonographically, ADPKD affected kidneys were characterized by multiple anechoic to hypoechoic, round to irregularly shaped structures with variation in size. Affected kidneys had indistinct corticomedullary junctions and foci of mineralization. Intravenous (IV) contrast medium administration allowed more definitive identification of cysts with CT, and identification of distortion of renal pelves by cysts. A significant difference (Welch ANOVA, P = 0.05) was detected between the US-estimated renal volumes of normal and affected cats. No statistically significant differences were detected in CT volume (between the normal and affected cats, or between US and CT volume measurements) or the 2 GFR methods. In this group of clinically normal, middle-aged ADPKD cats, renal function was within normal limits and not significantly different than normal.

Altered expression pattern of polycystin-2 in acute and chronic renal tubular diseases

Polycystin-2 represents one of so far two proteins found to be mutated in patients with autosomal-dominant polycystic kidney disease. Evidence obtained from experiments carried out in cell lines and with native kidney tissue strongly suggests that polycystin-2 is located in the endoplasmic reticulum. In the kidney, polycystin-2 is highly expressed in cells of the distal and connecting tubules, where it is located in the basal compartment. It is not known whether the expression of polycystin-2 in the kidney changes or whether it can be manipulated under certain instances. Therefore, the distribution of polycystin-2 under conditions leading to acute and chronic renal failure was analyzed. During ischemic acute renal failure, which affects primarily the S3 segment of the proximal tubule, a pronounced upregulation of polycystin-2 and a predominantly combined homogeneous and punctate cytoplasmic distribution in damaged cells was observed. After thallium-induced acute injury to thick ascending limb cells, polycystin-2 staining assumed a chicken wire-like pattern in damaged cells. In the (cy/+) rat, a model for autosomal-dominant polycystic kidney disease in which cysts originate predominantly from the proximal tubule, polycystin-2 immunoreactivity was lost in some distal tubules. In kidneys from (pcy/pcy) mice, a model for autosomal-recessive polycystic kidney disease in which cyst formation primarily affects distal tubules and collecting ducts, a minor portion of cyst-lining cells cease to express polycystin-2, whereas in the remaining cells, polycystin-2 is retained in their basal compartment. Data show that the expression and cellular distribution of polycystin-2 in different kinds of renal injuries depends on the type of damage and on the nephron-specific response to the injury. After ischemia, polycystin-2 may be upregulated by the injured cells to protect themselves. It is unlikely that polycystin-2 plays a role in cyst formation in the (cy/+) rat and in the (pcy/pcy) mouse.

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.

Activity and functional significance of the renal kallikrein-kinin-system in polycystic kidney disease of the rat

Activity and functional significance of the renal kallikrein-kinin-system in polycystic kidney disease of the rat.

BACKGROUND

The kallikrein-kinin-system is a complex multienzymatic system that has been implicated in the control of systemic blood pressure, glomerular filtration rate, and proteinuria. The present study investigated its functional role in rat polycystic kidney disease (PKD), which is characterized by progressive renal failure and proteinuria in the absence of systemic hypertension and stimulated renin-angiotensin-system.

METHODS

Kallikrein and bradykinin levels were measured in plasma and urine of rats with polycystic kidneys and compared to non-affected controls (SD) and rats with reduced renal mass. The functional relevance of the kallikrein-kinin system (KKS) was assessed by the effects of a short-term treatment with either a selective bradykinin (BK) B1-receptor antagonist (des-Arg9-[Leu8]-BK), a B2-receptor antagonist (HOE 140), an angiotensin converting enzyme inhibitor (ramipril), or an angiotensin II-receptor blocker (HR 720) on systemic and renal parameters.

RESULTS

Urine levels of kallikrein were increased threefold in 9-month-old PKD, and BK excretion was increased tenfold in 3-month and 30-fold in 9-month-old PKD compared to age-matched SD rats. Blood pressure in 9-month-old PKD rats was decreased to the same degree by ramipril and HR 720. In contrast, only ramipril and HOE 140 significantly reduced proteinuria and albuminuria, independent from creatinine clearance. This effect was accompanied by an increased excretion of bradykinin. The B1 receptor antagonist had no influence on functional renal parameters.

CONCLUSIONS

The present study demonstrates an age-dependent activation of the renal KKS in rats with polycystic kidney disease. The bradykinin B2-receptor is involved in the pathogenesis of proteinuria, independent from systemic blood pressure or creatinine clearance. The antiproteinuric effect of ramipril in this model is angiotensin II-independent and related to its influence on the renal KKS.

Relationship between renal volume growth and renal function in autosomal dominant polycystic kidney disease: a longitudinal study

In autosomal dominant polycystic kidney disease (ADPKD), renal function remains normal for many years into adult life while cysts form and expand progressively, starting in childhood. The longitudinal relationships between renal volume growth, hypertension, and renal function loss have not been examined in detail. At the University of Colorado (Denver, CO), 229 adult subjects with ADPKD participated in a longitudinal study from 1985 to 2001. Sequential ultrasound examinations were performed at a mean interval of 7.8 +/- 3.1 years (range, 2.6 to 15.1 years). Renal volume was calculated using a standard formula for a modified ellipsoid. The Modified Diet in Renal Disease equation was used to calculate glomerular filtration rate (GFR). The mean annual increase in renal volume was 46 +/- 55 cm3, and mean annual decline in GFR was 2.4 +/- 2.8 mL/min/1.73 m2. Men had faster renal growth, more severe hypertension, and a faster decline in GFR than women of similar ages. Multiple linear regression showed a significant relationship between rate of change in GFR and renal volume growth rate, initial renal volume, proteinuria, and age at entry. Correlational analysis showed a significant correlation between GFR and renal volume over time (R = -0.53) and between follow-up renal volume and follow-up GFR (R = -0.50) for both men and women. We conclude that renal volume and rate of renal volume growth may be useful markers for disease progression in early stages of ADPKD when GFR is preserved.

Mutations of the human polycystic kidney disease 2 (PKD2) gene

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited nephropathy, usually of late onset (onset between third to seventh decade), primarily characterized by the formation of fluid-filled cysts in the kidneys. It is one of the most frequent inherited conditions affecting approximately 1:1,000 Caucasians. Two major genes have been identified and characterized in detail: PKD1 and PKD2, mapping on chromosomes 16p13.3 and 4q21-23, respectively. A third gene, PKD3, has been implicated in selected families. Polycystic kidney disease of types 1 or 2 follows a very similar course of symptoms, both being multisystem pleiotropic disorders of indistinguishable picture on clinical grounds. The only difference is that patients with PKD2 mutations run a milder course compared to PKD1 carriers, with an average 10-20 years later age of onset and lower probability to reach end-stage-renal failure. The proteins polycystin-1 and -2 are trans-membranous glycoproteins hypothesized to participate in a common signaling pathway, interacting with each other and with other proteins, and coordinately expressed in normal and cystic tissue. Renal cysts most probably arise after a second somatic event, which inactivates the inherited healthy allele of the same gene, or perhaps one of the alleles of the other gene counterpart, generating a trans-heterozygous state. This article reviews the reported mutations in PKD2. Mutations of all kinds have been reported over the entire sequence of the PKD2 gene, with no apparent significant clustering and with some evidence of genotype/phenotype correlation. Most families harbor their own private mutations but a few recurrent events have been reported in unrelated families.

Impaired endocytosis may represent an obstacle to gene therapy in polycystic kidney disease

BACKGROUND

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease and a frequent cause of chronic renal failure. The cloning of the PKD1 and PKD2 genes, which are mutated in the great majority of patients with this disease, opens up the opportunity for somatic gene therapy by introduction of the wild-type gene or cDNA. Several publications have provided evidence, that many portions of the nephron and the collecting duct can form cysts, including the proximal tubule. Alterations in the proximal tubule may prevent the efficient endocytosis of filtered proteins and thus contribute to proteinuria, a frequent symptom in patients with polycystic kidney disease. At the same time this may also negatively affect various gene therapy strategies, since endocytosis is important for the uptake of foreign DNA at least under some circumstances. In the (cy/+) rat, a widely used animal model for ADPKD, cysts almost exclusively develop from proximal tubules, and we have therefore investigated whether proteinuria and defective endocytosis also occur in this model.

METHODS

Proteinuria was demonstrated by direct measurement and by protein gel electrophoresis of urines from 16 week-old (cy/+) rats. Endocytosis was investigated by injection of FITC-dextran and immunohistochemical staining with anti-ClC-5 and anti-megalin antibodies.

RESULTS

Similar to the observations made in ADPKD patients, proteinuria also develops in the (cy/+) rat. Using FITC-labeled dextran as an in vivo tracer for renal tubular endosomal function, we could show that portions of cyst-lining epithelia from proximal tubules have lost the ability to endocytose, which is necessary for the reabsorption of albumin and lower-molecular-weight proteins. By immunohistochemistry the expression of other proteins implicated in endocytosis, such as the chloride channel ClC-5 and the albumin receptor megalin, correlated well with the presence and absence of FITC-dextran in cyst wall epithelia.

CONCLUSION

These data indicate that proteinuria and albuminuria in the (cy/+) rat model for ADPKD are due to a loss of the endocytic machinery in epithelia of proximal tubular cysts. Such a defect may also reduce the efficacy of certain gene therapy protocols.

Increased renal expression of monocyte chemoattractant protein-1 and osteopontin in ADPKD in rats

BACKGROUND

Human autosomal-dominant polycystic kidney disease (ADPKD) is variable in the rate of deterioration of renal function, with end-stage renal disease (ESRD) occurring in only approximately 50% of affected individuals. Evidence suggests that interstitial inflammation may be important in the development of ESRD in ADPKD. Han:SPRD rats manifest ADPKD that resembles the human disease. Homozygous cystic (Cy/Cy) rats develop rapidly progressive PKD and die near age 3 weeks. Heterozygous (Cy/+) females develop slowly progressive PKD without evidence of renal dysfunction until the second year of life, whereas heterozygous (Cy/+) males develop more aggressive PKD with renal failure beginning by 8 to 12 weeks of age.

METHODS

To examine the relationship between proinflammatory chemoattractants and the development of interstitial inflammation and ultimately renal failure in ADPKD, we evaluated monocyte chemoattractant protein-1 (MCP-1) and osteopontin mRNAs and proteins in kidneys from Han:SRPD rats.

RESULTS

MCP-1 and osteopontin mRNAs, expressed at low levels in kidneys from normal (+/+) animals at all ages, were markedly elevated in kidneys from 3-week-old Cy/Cy animals. In kidneys from heterozygous (Cy/+) adults of either gender, MCP-1 and osteopontin mRNAs were more abundant than normal; MCP-1 mRNA was more abundant in Cy/+ males than in females. Thus, chemoattractant mRNA expression correlated with the development of renal failure in Cy/Cy and Cy/+ rats. Osteopontin mRNA, localized by in situ hybridization, was moderately expressed in the renal medulla of normal animals; however, this mRNA was expressed at very high levels in the cystic epithelia of Cy/+ and Cy/Cy animals. MCP-1 and osteopontin proteins, localized by immunohistochemistry, were weakly detected in +/+ kidneys but were densely expressed in Cy/Cy and in adult Cy/+ kidneys, primarily over cystic epithelium. Increased expression of chemoattractants was associated with the accumulation of ED-1 positive cells (macrophages) in the interstitium of cystic kidneys.

CONCLUSIONS

We suggest that proinflammatory chemoattractants have a role in the development of interstitial inflammation and renal failure in ADPKD.

Chronic caffeine consumption exacerbates hypertension in rats with polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder frequently associated with renal failure, hypertension, and other abnormalities. The present study determined whether chronic caffeine intake in an animal model of this disease would affect renal structure and function and blood pressure. Heterozygous male Han:Sprague-Dawley rats with ADPKD and normal littermates were provided with either tap water or solutions of caffeine to drink, starting at 1 month of age. When rats were aged 6 months, glomerular filtration rate (GFR) and mean arterial blood pressure (MAP) were measured under Inactin (Byk Gulden, Konstanz, Germany) anesthesia. Caffeine intake had no effect on GFR or cyst development in rats with PKD. MAP was greater in rats with PKD than normal rats and was increased more by caffeine. The hypertensive effect of chronic caffeine intake could not be ascribed to direct pressor effects of angiotensin II. Based on our finding that caffeine exacerbates hypertension in rats with PKD, it may be prudent for patients with ADPKD to limit coffee consumption to four or fewer cups of caffeinated coffee per day, pending studies of humans.

Effect of simvastatin on renal function in autosomal dominant polycystic kidney disease

BACKGROUND

In animal models, HMG-CoA reductase inhibitors were able to improve renal function and endothelium-dependent vascular reactivity. In various experimental renal diseases, including autosomal dominant polycystic kidney disease (ADPKD), HMG-CoA reductase inhibitors improved the rate of decline in renal function. We studied the effect of simvastatin on ADPKD patients.

METHODS

In a double-blind cross-over study, 10 normocholesterolaemic ADPKD patients were treated in random order for 4 weeks with 40 mg simvastatin or placebo daily. After each treatment period, we investigated the effect of simvastatin on renal blood flow and endothelium-dependent vascular reactivity. These periods were separated by a 4-week wash-out period.

RESULTS

After treatment with simvastatin, glomerular filtration rate (GFR) significantly increased from 124+/-4 ml/min to 132+/-6 ml/min (P<0.05). Simultaneously, effective renal plasma flow (ERPF) increased significantly from 494+/-30 ml/min to 619+/-67 ml/min after simvastatin treatment (P<0.05). These renal effects were accompanied by a significantly enhanced vasodilator response to acetylcholine in the forearm after simvastatin treatment. Total serum cholesterol levels were significantly reduced after treatment with simvastatin, from 4.24+/-0.32 to 3.17+/-0.22 mmol/l (P<0.001).

CONCLUSION

We concluded that simvastatin treatment can ameliorate renal function in ADPKD patients, by increasing renal plasma flow, possibly via improvement of endothelial function. Long-term clinical trials with HMG-CoA reductase inhibitors are needed to confirm these results and to establish a chronic inhibiting effect of HMG-CoA reductase inhibitors on the progression towards end-stage renal disease in ADPKD patients.

Polycystic kidney disease: from the bedside to the gene and back

Collated in this highly personal commentary are the most important research findings of the past 10 years that deal primarily with the renal manifestations of inherited polycystic kidney diseases. Progress in understanding these complex disorders has followed two major concurrent and convergent lines of investigation: genes and genetic mechanisms, and pathogenesis and progression. The field has moved from descriptive pathobiology to the elucidation of molecular mechanisms consequent to genetic and epigenetic events. Doubtless, the favorite works of some who have labored diligently in this field have not been fully exalted, and for this I apologize. Were I the editor, this entire celebratory volume would be used to extol the thrilling growth of knowledge during the tenure of this polycystic kidney disease watcher.

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.

Nanobacteria: controversial pathogens in nephrolithiasis and polycystic kidney disease

Nanobacteria are unconventional agents 100-fold smaller than common bacteria that can replicate apatite-forming units. Nanobacteria are powerful mediators of biogenic apatite nucleation (crystal form of calcium phosphate) and crystal growth under conditions simulating blood and urine. Apatite is found in the central nidus of most kidney stones and in mineral plaques (Randall's plaques) in renal papilla. The direct injection of nanobacteria into rat kidneys resulted in stone formation in the nanobacteria-injected kidney during one month follow-up, but not in the control kidney injected with vehicle. After intravenous administration in rats and rabbits, nanobacteria are rapidly excreted from the blood into the urine, as a major elimination route, and damage renal collecting tubuli. Nanobacteria are cytotoxic to fibroblasts in vitro. Human kidney cyst fluids contain nanobacteria. Nanobacteria thus appear to be potential provocateurs and initiators of kidney stones, tubular damage, and kidney cyst formation. It is hypothesized that nanobacteria are the initial nidi on which kidney stone is built up, at a rate dependent on the supersaturation status of the urine. Those individuals having both nanobacteria and diminished defences against stone formation (i.e. genetic factors, diet and drinking habits) could be at high risk. Kidney cyst formation is hypothesized to involve nanobacteria-induced tubular damage and defective tissue regeneration yielding cyst formation, the extent of which is dependent on genetic vulnerability.

A possible role for metalloproteinases in renal cyst development

The expansion of cysts in polycystic kidneys bears several similarities to the invasion of the extracellular matrix by benign tumors. We therefore hypothesized that cyst-lining epithelial cells produce extracellular matrix-degrading metalloproteinases and that the inhibition of these enzymes may represent a potential target for therapeutic intervention. Using in situ hybridization, we first analyzed the expression of membrane-type metalloproteinase 1 (MMP-14), an essential matrix metalloproteinase, of its inhibitor TIMP-2, and of the cytokine transforming growth factor (TGF)-beta2 in the (cy/+) rat model of autosomal-dominant polycystic kidney disease. Upregulated MMP-14 mRNA was predominantly located in cyst-lining epithelia and distal tubules, whereas TIMP-2 mRNA was confined almost exclusively to fibroblasts. TGF-beta2, a cytokine known to regulate the expression of matrix metalloproteinases and their inhibitors, was also expressed by cyst wall epithelia. We then treated (cy/+) rats with the metalloproteinase inhibitor batimastat for a period of 8 wk. The treatment with the metalloproteinase inhibitor batimastat resulted in a significant reduction of cyst number and kidney weight. Our study suggests that metalloproteinase inhibitors represent a new therapeutic tool against polycystic kidney disease, which should be applicable independently of the background of the disease.

Lack of association of ACE/angiotensinogen genotype with renal function in autosomal dominant polycystic kidney disease

ACE polymorphisms have recently been shown to associate with worse renal and or cardiovascular outcome, with the D allele widely reported as a risk factor for cardiovascular disease. In autosomal dominant polycystic kidney disease (ADPKD), there are conflicting reports of an association between ACE polymorphisms and disease phenotype. There are no previous reports of any association between angiotensinogen polymorphisms and clinical phenotype in ADPKD. We examined the ACE I/D and angiotensinogen M235T polymorphisms in 176 patients with ADPKD. Patients are categorized into three groups according to the reason for initial investigation. Clinical history and examination findings were recorded at the time of first referral. A cohort of 17 patients had progressive renal impairment observed after 3 or more years of follow-up. Reciprocal creatinine against time was plotted in this group. From the patient population of 176, a total of 33 patients reached end-stage renal failure (ESRF) or a serum creatinine greater than 500 microm/liter. ACE genotype and M235T polymorphism frequencies were compared across groups. Serum creatinine and presence of hypertension and onset of ESRF were taken as outcome variables; age and source of referral were taken as confounding variables. There was no association of any genotype or allele with either creatinine, inverse creatinine, hypertension, or age at end-stage renal failure. These findings do not support the proposition that ACE genotype or angiotensinogen polymorphisms are associated with a worse prognosis in patients with ADPKD.

Dietary soy protein effects on disease and IGF-I in male and female Han:SPRD-cy rats

BACKGROUND

Dietary soy protein compared with casein retards disease progression in a gender-specific manner in the pcy mouse. In this model of polycystic kidney disease (PKD), kidney insulin-like growth factor-I (IGF-I) levels are elevated. The present study examined the gender-specific effects of soy protein feeding on disease and IGF-I in Han:SPRD-cy rats.

METHODS

Normal (+/+) and affected (cy/+) weanling male and female Han:SPRD-cy rats were given either casein- or soy protein-based diets for six weeks. Renal size, water content, cyst size and IGF-I, serum creatinine, urea and IGF-I, and creatinine clearance were determined.

RESULTS

Soy protein-fed cy/+ animals had lower kidney weight, water content and cyst size, lower serum urea and creatinine, and higher creatinine clearance. In cy/+ females, dietary soy protein resulted in normalized serum creatinine and creatinine clearance. Kidney IGF-I levels (ng/kidney) were 32 to 76% higher in cy/+ compared with +/+ groups (P < 0.001). Soy protein feeding resulted in lower kidney IGF-I in cy/+ males (1123 vs. 1496 ng/kidney, P < 0.001) and cy/+ females (816 vs. 943 ng/kidney, P < 0.05). In males, soy protein feeding resulted in lower serum IGF-I concentrations in +/+ (1439 vs. 1708 ng/mL, P < 0.05) and in cy/+ (1483 vs. 2073 ng/mL, P < 0.001) animals.

CONCLUSIONS

Dietary soy protein compared with casein delays the progression of disease in male and female Han:SPRD-cy rats. Overall, IGF-I was lower in +/+ animals, in females, and in animals consuming the soy protein diet, supporting a role for IGF-I in the pathogenesis of disease in the Han:SPRD-cy rat and an ameliorating role for dietary soy protein.