Endothelial-derived vasoactive mediators in 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.

Pathogenesis of Congenital Malformations: Possible Role of Oxidative Stress

OBJECTIVE

Congenital anomalies are important causes of morbidity and mortality in children. Oxidative stress (OS) is involved in the physiopathology of pregnancy-related congenital malformations. This review summarizes the role of OS in the pathogenesis of congenital malformations; in particular, its purpose is to describe how OS influences the development of heart congenital malformations, oesophageal atresia, biliary atresia, diaphragmatic hernia, and autosomal dominant polycystic kidney disease.

STUDY DESIGN

Systematic review of previous studies about the role of OS in pregnancy and its possible effects in developing of congenital malformations. One electronic database (PubMed) was searched and reference lists were checked.

RESULTS

An imbalance between the production of reactive oxygen species (ROS) and antioxidant defense can occur early in pregnancy and continue in the postnatal life, producing OS. It may destroy the signaling pathways needed for a correct embryogenesis leading to birth defects. In fact, cell functions, especially during embryogenesis, needs specific signaling pathways to regulate the development. These pathways are sensitive to both endogenous and exogenous factors; therefore, they can produce structural alterations of the developing fetus.

CONCLUSION

Because OS plays a significant role in pathogenesis of congenital malformations, studies should be developed in order to better define their OS mechanisms and the beneficial effects of supplemental therapeutic strategies.

KEY POINTS

· Oxidative stress is involved in the pathogenesis of congenital malformations.. · Heart malformations, oesophageal atresia, biliary atresia, diaphragmatic hernia, and autosomal dominant polycystic kidney are analyzed.. · A knowledge of pathomechanism of OS-related congenital malformations could be useful to prevent them..

Long-term dietary nitrate supplementation does not reduce renal cyst growth in experimental autosomal dominant polycystic kidney disease

Augmentation of endogenous nitric oxide (NO) synthesis, either by the classical L-arginine-NO synthase pathway, or the recently discovered entero-salivary nitrate-nitrite-NO system, may slow the progression of autosomal dominant polycystic kidney disease (ADPKD). To test this hypothesis, the expression of NO in human ADPKD cell lines (WT 9–7, WT 9–12), and the effect of L-arginine on an in vitro model of three-dimensional cyst growth using MDCK cells, was examined. In addition, groups of homozygous Pkd1^RC/RC mice (a hypomorphic genetic ortholog of ADPKD) received either low, moderate or high dose sodium nitrate (0.1, 1 or 10 mmol/kg/day), or sodium chloride (vehicle; 10 mmol/kg/day), supplemented drinking water from postnatal month 1 to 9 (n = 12 per group). In vitro, intracellular NO, as assessed by DAF-2/DA fluorescence, was reduced by >70% in human ADPKD cell lines, and L-arginine and the NO donor, sodium nitroprusside, both attenuated in vitro cyst growth by up to 18%. In contrast, in Pkd1^RC/RC mice, sodium nitrate supplementation increased serum nitrate/nitrite levels by ~25-fold in the high dose group (P<0.001), but kidney enlargement and percentage cyst area was not altered, regardless of dose. In conclusion, L-arginine has mild direct efficacy on reducing renal cyst growth in vitro, whereas long-term sodium nitrate supplementation was ineffective in vivo. These data suggest that the bioconversion of dietary nitrate to NO by the entero-salivary pathway may not be sufficient to influence the progression of renal cyst growth in ADPKD.

Cardiovascular Risk and Quality of Life in Autosomal Dominant Polycystic Kidney Disease Patients on Therapy With Tolvaptan: A Pilot Study

INTRODUCTION

Cardiovascular (CV) complications are the most frequent cause of morbidity and mortality in autosomal dominant polycystic kidney disease (ADPKD) patients. In 2017, the Italian Medicines Agency authorised tolvaptan, a vasopressin V2 receptor antagonist, for the treatment of ADPKD, based on the Tolvaptan Phase 3 Efficacy and Safety Study in ADPKD (TEMPO 3: 4), TEMPO 4: 4 and Replicating Evidence of Preserved Renal Function: An Investigation of Tolvaptan Safety and Efficacy (REPRISE) studies.

AIM OF THE STUDY

The aim of the study was to assess the impact of tolvaptan on CV risk and quality of life, evaluated by nutritional, inflammatory, metabolic, instrumental parameters and psychocognitive tests on ADPKD patients.

METHODS AND MATERIALS

We evaluated 36 patients with ADPKD; 10 patients (7 males, mean age 42.5±7.0 years) treated with tolvaptan and 26 controls (11 males, mean age 36.7±9.1 years). They underwent, at T0, monthly, and at T1 (1 year) clinical, laboratory and instrumental evaluation, in addition to psychocognitive tests.

RESULTS

In ADPKD patients treated with tolvaptan, we found at T1, a decrease in carotid intima-- media thickness (p=0.048), epicardial adipose tissue thickness (p=0.002), C-reactive protein (p=0.026), sympathovagal balance during night (p=0.045) and increased flow-mediated dilation (p=0.023) with a reduction in depression (Hamilton and Beck tests, p=0.008 and p=0.002, respectively) compared with controls.

CONCLUSION

These preliminary results suggest that treatment with tolvaptan could improve early atherosclerosis and endothelial dysfunction markers and improve mood in ADPKD patients (probably by acting on endothelial cell and adipocyte V2 receptors).

Hypoxia and Endothelial Dysfunction in Autosomal-Dominant Polycystic Kidney Disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most prevalent inherited kidney disease, characterized by growth of bilateral renal cysts, hypertension, and multiple extrarenal complications that eventually can lead to renal failure. It is caused by mutations in PKD1 or PKD2 genes encoding the proteins polycystin-1 and polycystin-2, respectively. Over the past few years, studies investigating the role of primary cilia and polycystins, present not only on the surface of renal tubular cells but also on vascular endothelial cells, have advanced our understanding of the pathogenesis of ADPKD and have shown that mechanisms other than cyst formation also contribute to renal functional decline in this disease. Among them, increased oxidative stress, endothelial dysfunction, and hypoxia may play central roles because they occur early in the disease process and precede the onset of hypertension and renal functional decline. Endothelial dysfunction is linked to higher asymmetric dimethylarginine levels and reduced nitric oxide bioavailability, which would cause regional vasoconstriction and impaired renal blood flow. The resulting hypoxia would increase the levels of hypoxia-inducible-transcription factor 1α and other angiogenetic factors, which, in turn, may drive cyst growth. In this review, we summarize the existing evidence for roles of endothelial dysfunction, oxidative stress, and hypoxia in the pathogenesis of ADPKD.

Effect of Statin Therapy on the Progression of Autosomal Dominant Polycystic Kidney Disease. A Secondary Analysis of the HALT PKD Trials

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) commonly results in end-stage renal disease (ESRD), yet a long-term treatment that is well tolerated is still lacking. In a small randomized trial in children and adolescents pravastatin administration for 3 years was associated with reduced renal cyst growth, but no large trial has tested the effect of statins in adults.

METHODS

We performed a post-hoc analysis of the HALT PKD trials to compare outcomes of participants who never used statins with those who used statin for at least 3 years. Because statins were not randomly allocated, we used propensity score models with inverse probability of treatment weighting to account for imbalances between the groups. For subjects in Study A (preserved renal function, n=438) relevant outcomes were percent change in total kidney and liver volume and the rate of decline in estimated glomerular filtration rate (eGFR); for those in Study B (reduced renal function, n=352) we compared time to the composite endpoint of death, ESRD or 50% decline in eGFR. Follow-up was 5-8 years.

RESULTS

There was no difference in any outcome between the 2 groups. However, limitations of this analysis are the small number of statin users in Study A, different statin drugs and doses used, non-randomized allocation and advanced disease stage in Study B.

CONCLUSION

Although this post-hoc analysis of the HALT PKD trials does not demonstrate a benefit of statin therapy, conclusions remain preliminary. A larger randomized trial in young people with ADPKD is necessary to answer the question whether statins can slow renal cyst growth and preserve kidney function.

Cost-effectiveness of angiotensin-converting enzyme inhibitors versus angiotensin II receptor blockers as first-line treatment in autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a rare kidney disorder impacting ∼1:2,500 individuals among the general US population. Hypertension is a significant predictor of ADPKD progression, and a risk factor for development of cardiovascular disease (CVD), the most common cause for mortality among ADPKD patients. Angiotensin-converting enzymes inhibitors (ACE-I) are widely used as first-line treatment in ADPKD for the management of hypertension. However, their cost-effectiveness relative to other hypertensive medications, such as angiotensin II receptor blockers (ARB), has never been assessed.

OBJECTIVE

To determine if ARB are more cost-effective than ACE-Is as first-line treatment in ADPKD.

METHODS

A Markov-state decision model was constructed for estimation of cost and outcome benefits in hypertensive ADPKD patients. Transition probabilities were extrapolated from a retrospective cohort study comparing chronic kidney disease (CKD) stage transitions in ADPKD patients. Annual pharmaceutical costs per average daily dose per CKD stage were extracted from a US healthcare claims database. Median total healthcare costs per CKD stage or transplant were extracted from the published literature. The time horizon was set to 30 years, with 1-year duration to cycle shift. A cost-effectiveness analysis was conducted to estimate the incremental cost-effectiveness ratio (ICER) of ACE-I vs ARB per additional year of prevented transplant and/or death. A one-way probabilistic sensitivity analysis was conducted, with 10% variation in probabilities and cost.

RESULTS

Total annual healthcare costs accrued after 30 years among ADPKD patients taking ACE-Is was estimated to be $3,505,028.41, compared to ARB at $3,644,327.65. Life expectancy was increased by 1.39 years among patients taking ACE-I. Approximate 10-year survival in patients taking ACE-Is was 47% compared to ARB at 34%.

CONCLUSIONS

ACE-I dominated ARB and displayed greater cost-effectiveness due to lower cost and increased capacity to prolong years of life without transplant or death among hypertensive ADPKD patients. This model strengthens the value of ACE-I over ARB as first-line treatment for hypertension management in ADPKD patients.

Baseline predictors of aortic stiffness progression among multi-ethnic Asians with type 2 diabetes

BACKGROUND AND AIMS

This 3-year prospective study aimed to identify baseline parameters that predicted the progression of carotid-femoral pulse wave velocity (cf-PWV), which was used to evaluate aortic stiffness, among Singapore's multi-ethnic Asians with type 2 diabetes (T2DM).

METHODS

The cf-PWV was measured by the gold-standard tonometry method in 994 T2DM subjects at baseline and follow-up. The annual rate of cf-PWV change was calculated, and individuals above the 90^th percentile with rate≥1.42 m/s per year were regarded as rapid progressors (n = 104). In a subgroup analysis of subjects with normal cf-PWV at 1^st visit (n = 611), incident aortic stiffness was defined as follow-up cf-PWV≥10 m/s (n = 188).

RESULTS

The total cohort (mean age:57 ± 10 years; 53.4% Chinese, 20.4% Malay, 22.9% Indian, 3.2% 'Others') displayed a median annual cf-PWV progression rate of 0.2 m/s. Adjusted multivariate regression analyses showed that baseline age, cf-PWV and body mass index (BMI) constantly predicted follow-up cf-PWV, annual cf-PWV progression rate, rapid cf-PWV progression, and incident aortic stiffness. Paradoxically, lower baseline cf-PWV was associated with elevated annual cf-PWV progression rate and rapid progressors. This inverse relationship remained significant across ethnicities after ethnic stratification. Higher BMI independently predicted cf-PWV progression in Chinese and Indians, but not in Malay and 'Others' ethnic groups. Increased age was a significant predictor in Chinese and 'Others' ethnicities.

CONCLUSIONS

We demonstrated that baseline BMI is a modifiable independent risk factor of cf-PWV progression and incident aortic stiffness. Therefore, better obesity management may impede aortic stiffness in Singapore's T2DM patients, especially in the Chinese and Indians.

Polycystin deficiency induces dopamine-reversible alterations in flow-mediated dilatation and vascular nitric oxide release in humans

Autosomal dominant polycystic kidney disease (ADPKD) is a renal hereditary disorder associated with increased cardiovascular mortality, due to mutations in polycystin-1 and polycystin-2 genes. Endothelial polycystin-deficient cells have an altered mechanosensitivity to fluid shear stress and subsequent deficit in calcium-induced nitric oxide release, prevented by dopamine receptor stimulation. However, the impact of polycystin deficiency on endothelial function in ADPKD patients is still largely unknown. Here we assessed endothelium-dependent flow-mediated dilatation in 21 normotensive ADPKD patients and 21 healthy control subjects, during sustained (hand skin heating) and transient (postischemic hyperemia) flow stimulation. Flow-mediated dilatation was less marked in ADPKD patients than in controls during heating, but it was similar during postischemic hyperemia. There was no difference in endothelium-independent dilatation in response to glyceryl trinitrate. Local plasma nitrite, an indicator of nitric oxide availability, increased during heating in controls but not in patients. Brachial infusion of dopamine in a subset of ADPKD patients stimulated plasma nitrite increase during heating and improved flow-mediated dilatation. Thus, ADPKD patients display a loss of nitric oxide release and an associated reduction in endothelium-dependent dilatation of conduit arteries during sustained blood flow increase. The correction of these anomalies by dopamine suggests future therapeutic strategies that could reduce the occurrence of cardiovascular events in ADPKD.

Mechanisms and management of hypertension in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most commonly inherited kidney disease, characterized by progressive cyst growth and renal enlargement, resulting in renal failure. Hypertension is common and occurs early, prior to loss of kidney function. Whether hypertension in ADPKD is a primary vasculopathy secondary to mutations in the polycystin genes or secondary to activation of the renin-angiotensin-aldosterone system by cyst expansion and intrarenal ischemia is unclear. Dysregulation of the primary cilium causing endothelial and vascular smooth muscle cell dysfunction is a component of ADPKD. In this article, we review the epidemiology, pathophysiology and clinical characteristics of hypertension in ADPKD and give specific recommendations for its treatment.

Hypertension and left ventricular hypertrophy in autosomal dominant polycystic kidney disease

Hypertension is a common problem in patients with autosomal dominant polycystic kidney disease affecting both renal and patient survival. Activation of the renin-angiotensin-aldosterone system due to cyst expansion and local renal ischemia has been proposed to play an important role in the development of hypertension in autosomal dominant polycystic kidney disease. Left ventricular hypertrophy, a major cardiovascular risk factor, is also common in patients with autosomal dominant polycystic kidney disease. Both hypertension and the activation of the renin-angiotensin-aldosterone system play a role in the development of left ventricular hypertrophy in these patients. Prospective randomized results indicate that aggressive control of blood pressure is important for the optimal reversal of left ventricular hypertrophy, thereby diminishing a major risk factor for cardiovascular morbidity and mortality of patients with autosomal dominant polycystic kidney disease. There is also substantial epidemiological support for aggressive control of blood pressure in slowing renal disease progression in autosomal dominant polycystic kidney disease patients. Blockade of the renin-angiotensin-aldosterone system should be the initial approach in the treatment of hypertension in these patients.

Polycystic kidneys have decreased vascular density: a micro-CT study

OBJECTIVE

Polycystic kidney disease (PKD) is a common cause of end-stage renal failure and many of these patients suffer vascular dysfunction and hypertension. It remains unclear whether PKD is associated with abnormal microvascular structure. Thus, this study examined the renovascular structure in PKD.

METHODS

PKD rats (PCK model) and controls were studied at 10 weeks of age, and mean arterial pressure (MAP), renal blood flow, and creatinine clearance were measured. Microvascular architecture and cyst number and volume were assessed using micro-computed tomography, and angiogenic pathways evaluated.

RESULTS

Compared with controls, PKD animals had an increase in MAP (126.4 ± 4.0 vs. 126.2 ± 2.7 mmHg) and decreased clearance of creatinine (0.39 ± 0.09 vs. 0.30 ± 0.05 mL/min), associated with a decrease in microvascular density, both in the cortex (256 ± 22 vs. 136 ± 20 vessels per cm2) and medullar (114 ± 14 vs. 50 ± 9 vessels/cm2) and an increase in the average diameter of glomeruli (104.14 ± 2.94 vs. 125.76 ± 9.06 mm). PKD animals had increased fibrosis (2.2 ± 0.2 fold vs. control) and a decrease in the cortical expression in hypoxia inducible factor 1-α and vascular endothelial growth factor.

CONCLUSIONS

PKD animals have impaired renal vascular architecture, which can have significant functional consequences. The PKD microvasculature could represent a therapeutic target to decrease the impact of this disease.

Serum uric acid levels and endothelial dysfunction in patients with autosomal dominant polycystic kidney disease

BACKGROUND/AIMS

Patients with autosomal dominant polycystic kidney disease (ADPKD) exhibit endothelial dysfunction (ED) despite normal levels of renal function. Hyperuricemia occurs in these patients and has been postulated to affect ED through the generation of oxidative stress. We therefore investigated the prevalence of ED and its association with serum uric acid levels in early-stage ADPKD.

METHODS

A cross-sectional design was used for the assessment of prevalent patients with early-stage (normal renal function) ADPKD (n = 91) from two academic medical centers. ED was assessed using ischemia-induced forearm flow-mediated vasodilation (FMD). Serum uric acid levels were evaluated using an Olympus AU2700 autoanalyzer.

RESULTS

ADPKD patients with higher serum uric acid levels had a higher asymmetric dimethylarginine (ADMA) level (1.19 ± 0.2 vs. 1.47 ± 0.3, p < 0.001) and lower FMD rates (8.1 ± 1.3 vs. 6.8 ± 0.7, p < 0.001). In multiple regression analysis for predictors of cohort FMD, uric acid (β = -0.32, p < 0.001), ADMA (β = -0.36, p < 0.001), high-sensitivity C reactive protein (CRP; β = -0.32, p < 0.001) and estimated glomerular filtration rate (eGFR; β = 0.33, p < 0.001) all predicted FMD.

CONCLUSIONS

In early-stage ADPKD patients, uric acid levels, serum ADMA and eGFR all independently predict ED in a similar manner. Future studies are needed to investigate the causes of elevated serum uric acid, ADMA and CRP in these patients.

Suppression of microRNA-29 expression by TGF-β1 promotes collagen expression and renal fibrosis

Synthesis and deposition of extracellular matrix (ECM) within the glomerulus and interstitium characterizes renal fibrosis, but the mechanisms underlying this process are incompletely understood. The profibrotic cytokine TGF-β1 modulates the expression of certain microRNAs (miRNAs), suggesting that miRNAs may have a role in the pathogenesis of renal fibrosis. Here, we exposed proximal tubular cells, primary mesangial cells, and podocytes to TGF-β1 to examine its effect on miRNAs and subsequent collagen synthesis. TGF-β1 reduced expression of the miR-29a/b/c/family, which targets collagen gene expression, and increased expression of ECM proteins. In both resting and TGF-β1-treated cells, ectopic expression of miR-29 repressed the expression of collagens I and IV at both the mRNA and protein levels by targeting the 3'untranslated region of these genes. Furthermore, we observed low levels of miR-29 in three models of renal fibrosis representing early and advanced stages of disease. Administration of the Rho-associated kinase inhibitor fasudil prevented renal fibrosis and restored expression of miR-29. Taken together, these data suggest that TGF-β1 inhibits expression of the miR-29 family, thereby promoting expression of ECM components. Pharmacologic modulation of these miRNAs may have therapeutic potential for progressive renal fibrosis.

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.

Aortic stiffness is independently associated with rate of renal function decline in chronic kidney disease stages 3 and 4

Aortic stiffness and chronic kidney disease are closely linked by shared risk factors and associated increased cardiovascular mortality. At lower levels of renal function, aortic stiffness is independently associated with glomerular filtration rate. However, the longitudinal impact of aortic stiffness on renal function has not been reported previously. A cohort of 133 patients with chronic kidney disease stages 3 and 4 (estimated glomerular filtration rate: 15 to 59 mL/min per 1.73 m(2)) underwent prospective measurement of arterial stiffness parameters and monitoring of renal function. Aortic pulse wave velocity measurement was performed in 120 patients. The mean age was 69+/-12 years (mean+/-SD; 103 men, 30 women, and 23.3% diabetic). Mean systolic blood pressure was 155+/-21 mm Hg, and mean diastolic blood pressure was 83+/-11 mm Hg. The mean Modification of Diet in Renal Disease estimated glomerular filtration rate was 32+/-11 mL/min per 1.73 m(2). Change in renal function was measured using reciprocal creatinine plots and the dichotomous combined end point of > or = 25% decline in renal function or start of renal replacement therapy. After stepwise multivariate analysis, aortic pulse wave velocity was independently associated with gradient of reciprocal creatinine plot (r=0.46; P=0.014). In multivariate analysis of the end point of > or = 25% decline in renal function or start of renal replacement therapy, independent predictors were aortic pulse wave velocity (r=0.48; P=0.002), systolic blood pressure (r=0.17; P=0.039), and urine protein:creatinine ratio (r=0.20; P=0.021). We, therefore, conclude that aortic stiffening is independently associated with rate of change in renal function in patients with chronic kidney disease stages 3 and 4.

Cardiovascular abnormalities in autosomal-dominant polycystic kidney disease

Cardiovascular problems are a major cause of morbidity and mortality in patients with autosomal-dominant polycystic kidney disease (ADPKD). Hypertension is a common early symptom of ADPKD, and occurs in approximately 60% of patients before renal function has become impaired. Hypertension is associated with an increased rate of progression to end-stage renal disease and is the most important potentially treatable variable in ADPKD. Left ventricular hypertrophy, which is a powerful, independent risk factor for cardiovascular morbidity and mortality, also occurs frequently in patients with ADPKD. Both hypertension and left ventricular hypertrophy have important roles in cardiovascular complications in these individuals. Moreover, biventricular diastolic dysfunction, endothelial dysfunction, increased carotid intima-media thickness, and impaired coronary flow velocity reserve are present even in young patients with ADPKD who have normal blood pressure and well-preserved renal function. These findings suggest that cardiovascular involvement starts very early in the course of ADPKD. Intracranial and extracranial aneurysms and cardiac valvular defects are other potential cardiovascular problems in patients with ADPKD. Early diagnosis and treatment of hypertension, with drugs that block the renin-angiotensin-aldosterone system, has the potential to decrease the cardiovascular complications and slow the progression of renal disease in ADPKD.

Mechanism of alcohol-induced oxidative stress and neuronal injury

Neuro-cognitive deficits, neuronal injury, and neurodegeneration are well documented in alcoholics, yet the underlying mechanisms remain elusive. Oxidative damage of mitochondria and cellular proteins intertwines with the progression of neuroinflammation and neurological disorders initiated by alcohol abuse. Here, we present the evidence that metabolism of ethanol in primary human neurons by alcohol dehydrogenase (ADH) or cytochrome P450-2E1 (CYP2E1) generates reactive oxygen species (ROS) and nitric oxide (NO) via induction of NADPH/xanthine oxidase (NOX/XOX) and nitric oxide synthase (NOS) in human neurons. The acetaldehyde-mediated increase in NOX, XOX, or NOS activity is regulated as a transcriptional rather than a translational process. Marked increase in the lipid peroxidation product (4-hydroxynonenal) and enhanced ROS generation coincides with decreased neuronal viability and diminished expression of neuronal marker (neurofilaments). Novel quantitative methods of ROS and NO detection help dissect the mechanisms of alcohol-induced neurodegeneration. Uncovering the basic mechanisms of oxidative neuronal injury will serve as the basis for development of new therapies.

Improvement of endothelial dysfunction with simvastatin in patients with autosomal dominant polycystic kidney disease

Cardiovascular problems are a major cause of morbidity and mortality in patients with autosomal dominant polycystic kidney disease (ADPKD). Endothelial dysfunction (ED), which is an early manifestation of vascular injury, has been shown in patients with ADPKD. Statins have a beneficial effect in the reversal of ED. The aim of this study was to investigate the effects of a statin, simvastatin, on ED in patients with ADPKD. Sixteen patients with ADPKD having well-preserved renal function were included in the study. Endothelial function of the brachial artery was evaluated by using high-resolution vascular ultrasound. Endothelial-dependent dilatation (EDD) was expressed as the percentage change in the brachial artery diameter from baseline to reactive hyperemia. After the baseline evaluations of EDDs, patients were started treatment with simvastatin at a dose of 40 mg/day and were treated for six months. EDDs were recalculated after one and six months of therapy. Interleukin-6 (IL-6) and high-sensitivity C-reactive protein were also measured as markers of inflammation. Baseline EDD was 11.3 +/- 6.9% in patients with ADPKD. After one month of simvastatin treatment, EDD increased significantly to 14.6 +/- 4.6 % (P = 0.016 versus baseline). Endothelial-dependent dilatation further increased significantly to 18.9 +/- 7.5 % (P = 0.011 versus baseline, P = 0.048 versus first month) after six months of therapy. There was also a significant decrease in the level of IL-6 from 21.6 +/- 21.7 pg/mL to 9.1 +/- 3.5 pg/mL (P= 0.002). Six months of simvastatin therapy resulted in a significant improvement of ED in patients with ADPKD. This finding may be in part related to the pleiotropic effects of simvastatin.

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.

Late dietary intervention limits benefits of soy protein or flax oil in experimental polycystic kidney disease

BACKGROUND/AIMS

Dietary soy protein and flax oil retard kidney disease progression when initiated in the early stages of disease in several experimental models, including the Han:SPRD-cy rat. However, individuals with kidney disease often do not become aware of their condition until injury to the kidney is extensive. The objective of this study was to determine whether initiating these interventions in established disease would alter further progression of renal injury.

METHODS

Two-month-old adult male Han:SPRD-cy rats were given either a flax oil diet (7% flax oil), a soy protein diet (20% soy protein) or a control diet (7% corn oil, 20% casein) for 4 months. Renal disease progression was assessed by examining morphological, immunohistochemical and biochemical parameters.

RESULTS

Compared to controls, there was 21-24% less staining of proliferating cells, 21-24% less oxidative damage and 13-15% less renal inflammation in kidneys from rats given dietary soy protein and flax oil. Renal cystic growth and fibrosis and serum creatinine levels were not altered by these dietary treatments.

CONCLUSIONS

Late intervention with dietary soy protein and flax oil reduces some disease-associated pathologies in established renal disease in Han:SPRD-cy rats. The potential benefits of the antioxidant and anti-inflammatory effects on ultimate renal disease outcome in the long term remains to be determined.

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.

Pulse wave reflection is amplified in normotensive patients with autosomal-dominant polycystic kidney disease and normal renal function

BACKGROUND

In young ADPKD patients, we have previously found an impaired endothelium-dependent relaxation in small resistance vessels but a normal flow-mediated dilatation of the brachial artery. The present study investigated arterial stiffness in early ADPKD by pulse-wave analysis (PWA) and measurement of pulse-wave velocity (PWV).

METHODS

18 young normotensive ADPKD patients with normal renal function and 18 controls were studied by applanation tonometry with the SphygmoCor equipment. Parameters included an estimate of aortic blood pressure, augmentation index (AIx), AIx standardized to heart rate 75 (AIx(HR75)) and PWV. Glomerular filtration rate (GFR) was measured by the 51Cr-EDTA plasma clearance method. Statistical comparisons were made with t tests and multiple linear regression analysis.

RESULTS

GFR was the same in the two groups. Brachial diastolic blood pressure was slightly but significantly higher in ADPKD patients than in controls (81 +/- 9 vs. 73 +/- 9 mm Hg, p < 0.05). No significant difference was present in brachial systolic blood pressure. AIx was significantly higher in ADPKD than in controls: 21.6 +/- 11.3 vs. 11.4 +/- 11.2%, p < 0.02. AIx(HR75) and estimated aortic systolic and diastolic blood pressure was likewise significantly higher in ADPKD than in controls. Multiple linear regression analysis showed AIx and AIx(HR75) to be independently correlated to group (ADPKD/control), p < 0.02 and p < 0.05, respectively. No difference was found between PWV in the two groups.

CONCLUSION

Reflection of the pulse wave was amplified in young normotensive ADPKD patients, demonstrating early pathology in the arterial system.

Renal protection in hypertensive patients: selection of antihypertensive therapy

Hypertension is common in chronic renal disease and is a risk factor for the faster progression of renal damage, and reduction of blood pressure (BP) is an efficient way of preventing or slowing the progression of this damage. International guidelines recommend lowering BP to 140/90 mm Hg or less in patients with uncomplicated hypertension, and to 130/80 mm Hg or less for patients with diabetic or chronic renal disease. The attainment of these goals needs to be aggressively pursued with multidrug antihypertensive regimens, if needed. The pathogenesis of hypertensive renal damage involves mediators from various extracellular systems, including the renin-angiotensin system (RAS). Proteinuria, which occurs as a consequence of elevated intraglomerular pressure, is also directly nephrotoxic. As well as protecting the kidneys by reducing BP, antihypertensive drugs can also have direct effects on intrarenal mechanisms of damage, such as increased glomerular pressure and proteinuria. Antihypertensive drugs that have direct effects on intrarenal mechanisms may, therefore, have nephroprotective effects additional to those resulting from reductions in arterial BP. Whereas BP-lowering effects are common to all antihypertensive drugs, intrarenal effects differ between classes and between individual drugs within certain classes. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARB) have beneficial effects on proteinuria and declining renal function that appear to be mediated by factors additional to their effects on BP. These RAS inhibitors are recommended as a first-line antihypertensive approach in patients with chronic kidney disease. The addition of diuretics and calcium channel antagonists to RAS inhibitor therapy is also considered to be a rational strategy to reduce BP and preserve renal function. Calcium channel antagonists are a highly heterogeneous class of compounds, and it appears that some agents are more suitable for use in patients with chronic renal disease than others. Manidipine is a third-generation dihydropyridine (DHP) calcium channel antagonist that blocks both L and T-type calcium channels. Unlike older-generation DHPs, which preferentially act on L-type channels, manidipine has been shown to have beneficial effects on intrarenal haemodynamics, proteinuria and other measures of renal functional decline in the first clinical trials involving hypertensive patients with chronic renal failure. Preliminary results from a trial in diabetic patients who had uncontrolled hypertension and microalbuminuria despite optimal therapy with an ACE inhibitor or an ARB suggest that manidipine may be an excellent antihypertensive drug in combination with RAS inhibitor treatment in order to normalise BP and albumin excretion in patients with diabetes.

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.

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.

The potential of endothelin antagonism as a therapeutic approach

Endothelin (ET) is a pivotal physiological regulator of blood pressure through its effects on blood vessels, heart, lung and kidneys, and the ET system can be overactive in disorders such as pulmonary hypertension, heart failure and renal disease. Such observations stimulated interest among scientists and pharmaceutical companies that have set up high-throughput screens to search for antagonists of ET receptors. The emerging compounds have been tested in animals with exciting results, leading to great hope that such inhibitors could be translated into human drugs with desirable therapeutic activities and few side effects. This review will describe the most relevant results obtained in experimental animals in a wide variety of disease conditions and focus on the data of selected compounds that have been employed in clinical trials.

Selectivity of cyclooxygenase isoform activity and prostanoid production in normal and diseased Han:SPRD-cy rat kidneys

Renal prostanoids are important regulators of normal renal function and maintenance of renal homeostasis. In diseased kidneys, renal cylooxygenase (COX) expression and prostanoid formation are altered. With the use of the Han:Sprague-Dawley-cy rat, the aim of this study was to determine the relative contribution of renal COX isoforms (protein, gene expression, and activity) on renal prostanoid production [thromboxane B(2) (TXB(2), stable metabolite of TXA(2)), prostaglandin E(2) (PGE(2)), and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha), stable metabolite of PGI(2))] in normal and diseased kidneys. In diseased kidneys, COX-1-immunoreactive protein and mRNA levels were higher and COX-2 levels were lower compared with normal kidneys. In contrast, COX activities were higher in diseased compared with normal kidneys for both COX-1 [0.05 +/- 0.02 vs. 0.45 +/- 0.11 ng prostanoids x min(-1) x mg protein(-1) (P < 0.001)] and COX-2 [0.64 +/- 0.10 vs. 2.32 +/- 0.22 ng prostanoids x min(-1).mg protein(-1) (P < 0.001)]. As the relative difference in activity was greater for COX-1, the ratio of COX-1/COX-2 was higher in diseased compared with normal kidneys, although the predominant activity was still due to the COX-2 isoform in both genotypes. Endogenous and steady-state in vitro levels of prostanoids were approximately 2-10 times higher in diseased compared with normal kidneys. The differences between normal and diseased kidney prostanoids were in the order of TXB(2) > 6-keto-PGF(1alpha) > PGE(2), as determined by higher renal prostanoid levels and COX activity ratios of TXB(2)/6-keto-PGF(1alpha), TXB(2)/PGE(2), and 6-keto-PGF(1alpha)/PGE(2). This specificity in both the COX isoform type and for the prostanoids produced has implications for normal and diseased kidneys in treatments involving selective inhibition of COX isoforms.

Functional imaging in small animals using X-ray computed tomography--study of physiologic measurement reproducibility

X-ray computed tomography (CT) has been traditionally used for morphologic analysis and in the recent past has been used for physiology imaging. This paper seeks to demonstrate functional CT as an effective tool for monitoring changes in tissue physiology associated with disease processes and cellular and molecular level therapeutic processes. We investigated the effect of noise and sampling time on the uncertainty of tissue physiologic parameters. A whole body compartmental model of mouse was formulated to simulate tissue time density curves and study the deviation of tissue physiologic parameters from their true values. These results were then used to determine the appropriate scanning protocols for the experimental studies. Dynamic contrast enhanced CT (DCE-CT) was performed in mice following the injection of hydrophilic iodinated contrast agent (CA) at three different injection rates, namely 0.5 ml/min, 1 ml/min, and 2.0 ml/min. These experiments probed the Nyquist sampling limit for reproducibility of tissue physiologic parameters. Separate experiments were performed with three mice at four different X-ray tube currents corresponding to different image noise values. A two-compartment model (2CM) model was formulated to describe the contrast kinematics in the kidney cortex. Three different 2CMs were implemented namely the 4-parameter (4P), 5-parameter (5P), and the 6-parameter (6P) model. The tissue kinematics is fitted to the models by using the Levenberg-Marquardt algorithm implemented in IDL (RSI Inc.) programming language to minimize the weighted sum of squares. The relevant tissue physiologic parameters extracted from the models are the renal blood flow (RBF), glomerular filtration rate (GFR), fractional plasma volume, fractional tubular volumes and urine formation rates. The experimental results indicate that the deviation of the tissue physiologic parameters is within the limits required for tracking disease physiology in vivo and thus small animal functional X-ray CT would be able to determine changes in tissue physiology in vivo.

Exercise blood pressure, cardiac structure, and diastolic function in young normotensive patients with polycystic kidney disease: a prehypertensive state

BACKGROUND

Increased left ventricular mass (LVM) and left ventricular hypertrophy have been found in early stages of autosomal dominant polycystic kidney disease (ADPKD). The mechanisms that lead to an increase in LVM in this population are unknown. The aim of this study is to evaluate blood pressure (BP) response to exercise and very early alterations in cardiac structure and diastolic function in young normotensive patients with ADPKD.

METHODS

Color Doppler echocardiography and exercise treadmill testing according to the Bruce protocol were performed in 18 young normotensive patients with ADPKD and 18 healthy subjects.

RESULTS

LVM index was greater and isovolumic relaxation time (IVRT) was longer in patients with ADPKD than controls (93.3 +/- 21.4 versus 77.5 +/- 18.6 g/m2; P = 0.02; 100 +/- 20.2 versus 80 +/- 9.7 milliseconds; P = 0.001, respectively). Exercise capacity in metabolic equivalents was similar in both groups. Systolic BP response during exercise and recovery were similar in both groups. Diastolic BP decreased during exercise, but the magnitude of decrease was lower in patients with ADPKD than controls (P = 0.01). During recovery, patients with ADPKD showed a greater sustained diastolic BP than controls (P = 0.02). Patients with ADPKD with an exaggerated systolic BP response had a greater LVM index than those with a normal response (112.1 +/- 10.4 versus 84 +/- 19.2 g/m2; P = 0.001). Multivariate regression analysis showed that exercise systolic BP and diastolic BP were independent predictors of LVM index and IVRT, respectively.

CONCLUSION

Young normotensive patients with ADPKD showed increased LVM index and prolonged IVRT, which are related to exercise BP response. Exaggerated diastolic BP response during exercise suggests an impaired capacity for exercise-induced vasodilatation and may indicate a greater risk for the development of future hypertension.

Changes of tissue endothelin-1 and nitric oxide synthase in a sheep model of large intestinal obstruction

Large intestinal obstruction (LIO) in farm animals can cause a ischaemic necrosis of intestinal tissue, eventually leading to death. The roles of endothelin-1 (ET-1) and nitric oxide (NO) are not well understood in the process of LIO, but evidence suggests that endothelial-derived mediators may participate. In the present study, ET-1 concentration and total nitric oxide synthase (NOS) activity were measured in heart, liver, pancreas, lung and kidney in a model of LIO in sheep. Our data demonstrated that ET-1 concentration and NOS activity were altered, with significant increases of ET-1 in heart, lung and kidney and of NOS activity in pancreas and kidney, but a marked decline of NOS activity in liver (p < 0.05). It is postulated that these alterations in NOS activity and ET-1 concentration may contribute to the progressive loss of organ function, and finally lead to death in LIO in sheep.

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.