Imed Helal

Glomerular hyperfiltration: definitions, mechanisms and clinical implications

Glomerular hyperfiltration is a phenomenon that can occur in various clinical conditions including kidney disease. No single definition of glomerular hyperfiltration has been agreed upon, and the pathophysiological mechanisms, which are likely to vary with the underlying disease, are not well explored. Glomerular hyperfiltration can be caused by afferent arteriolar vasodilation as seen in patients with diabetes or after a high-protein meal, and/or by efferent arteriolar vasoconstriction owing to activation of the renin–angiotensin–aldosterone system, thus leading to glomerular hypertension. Glomerular hypertrophy and increased glomerular pressure might be both a cause and a consequence of renal injury; understanding the renal adaptations to injury is therefore important to prevent further damage. In this Review, we discuss the current concepts of glomerular hyperfiltration and the renal hemodynamic changes associated with this condition. A physiological state of glomerular hyperfiltration occurs during pregnancy and after consumption of high-protein meals. The various diseases that have been associated with glomerular hyperfiltration, either per nephron or per total kidney, include diabetes mellitus, polycystic kidney disease, secondary focal segmental glomerulosclerosis caused by a reduction in renal mass, sickle cell anemia, high altitude renal syndrome and obesity. A better understanding of the mechanisms involved in glomerular hyperfiltration could enable the development of new strategies to prevent progression of kidney disease.

Prevalence of cardiovascular events in patients with autosomal dominant polycystic kidney disease.

Background: This study evaluates the prevalence of cardiovascular events in autosomal dominant polycystic kidney disease (ADPKD) patients. Methods: We distributed surveys to 1,439 subjects from our ADPKD research database. In total, 426 subjects completed and returned surveys; 7 of these were from children and were excluded from the study. Results: The patients who responded were female (63.2%), nonHispanic (88.1%) and white (93.6%). The mean age of the total group was 53.2 ± 13.7 years; 82.8% had a family history of ADPKD and 32.5% had reached end-stage renal disease (ESRD). With respect to cardiovascular risk factors, 86.6% were hypertensive with a mean age at diagnosis of 36.9 ± 12.9 years and hypertension was significantly more prevalent in males. In addition, 19.6% of the subjects were obese, 20.8% were smokers, 8.7% had diabetes, 45.7% had high cholesterol and 17.8% were sedentary. The most prevalent self-reported cardiovascular events were arrhythmias (25.9%), evidence of peripheral vascular disease (16.5%), heart valve problems (14.4%), cardiac enlargement (9.5%), stroke or cerebral bleeding (7.5%), myocardial infarction (6%) and brain aneurysm (5.0%). The most commonly used antihypertensive medications were renin-angiotensin inhibitors used by 75% of ADPKD patients. Older ADPKD patients and those at ESRD had a significantly higher incidence of cardiovascular events. Conclusion: These findings support the high prevalence of cardiovascular risk factors and events in ADPKD patients which contribute to a greater mortality risk. Due to the prevalence of cardiovascular risk factors in the ADPKD population, early diagnosis and clinical intervention are recommended.

Glomerular Hyperfiltration and Renal Progression in Children with Autosomal Dominant Polycystic Kidney Disease

BACKGROUND AND OBJECTIVES The purpose of this study was to determine whether glomerular hyperfiltration (GH) occurring early in autosomal dominant polycystic kidney disease (ADPKD) is indicative of more rapid disease progression in children. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS One hundred eighty children with ADPKD (ages 4 to 18 years) with normal renal function were examined by renal ultrasound. Renal volume was calculated using a standard formula for a modified ellipsoid. Creatinine clearance was calculated from serum creatinine and 24-hour urine creatinine. GH was defined as creatinine clearance ≥140 ml/min per 1.73 m(2). RESULTS Thirty-two children had GH (mean age 11.4 ± 3.6 years) and 148 had normal renal function (mean age 10.8 ± 3.9 years). Patients with GH at baseline demonstrated an increased rate of total renal volume growth (β: rate of change = +19.3 ± 10.8 cm(3)/year) over 5 years compared with those without GH at baseline (β = -4.3 ± 7.7 cm(3)/year), P = 0.008. Those with GH at baseline experienced a faster decline in creatinine clearance in subsequent years (β = -5.0 ± 0.8 ml/min per 1.73 m(2) per year) compared with those without GH at baseline (β = +1.0 ± 0.4 ml/min per 1.73 m(2) per year), P < 0.0001. CONCLUSIONS This study revealed that occurrence of GH in ADPKD children is associated with a significantly faster decline in renal function and higher rate of kidney enlargement over time. GH combined with the increased renal volume may therefore be used as an early marker for a more severe progression of ADPKD in children.

Emergent early markers of renal progression in autosomal-dominant polycystic kidney disease patients: implications for prevention and treatment.

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common single cause of end-stage renal disease after diabetes, hypertension and glomerulonephritis. The clinical course of ADPKD is highly variable. Even with optimal care and therapy monitoring, currently the progression of ADPKD is slowed but not stopped. Newer treatments will no doubt become available in the future, but their side effect profiles will always need to be considered. Therefore, markers to distinguish ADPKD patients with a poor versus a good prognosis will be helpful. Several risk factors influencing kidney disease progression in ADPKD have been identified in the current era. The present review will discuss the spectrum of early markers of ADPKD renal disease progression. Specifically, the volume of total kidney, hypertension, glomerular hyperfiltration, renal blood flow, microalbuminuria, uric acid, and urinary molecular markers will be discussed. On this background, implications for the prevention and treatment of kidney disease progression in ADPKD are also discussed.

Serum uric acid, kidney volume and progression in autosomal-dominant polycystic kidney disease

BACKGROUND Hyperuricemia has been implicated in the development and progression of chronic kidney disease, both in animal experiments and in clinical studies. As a potentially modifiable risk factor, we examined whether serum uric acid levels correlate with early hypertension, kidney volume and progression to end-stage renal disease (ESRD) in autosomal-dominant polycystic kidney disease (ADPKD). METHODS Retrospective analysis of a prospective observational study of the natural history of ADPKD, conducted at the University of Colorado between 1985 and 2005. Included are 680 ADPKD adults who provided data on blood pressure, renal volume, renal function, uric acid, age at the onset of ESRD or last known age without ESRD. Serum uric acid levels were examined as a continuous variable and as gender-specific quartiles. The main outcome of interest was age at the onset of ESRD; secondary outcomes were hypertension onset before age 30 years and total kidney volume (TKV) at the study visit. RESULTS Subjects with early-onset hypertension had higher age-adjusted serum uric acid levels than those with no or late-onset hypertension despite similar creatinine clearance. After adjusting for age, gender and creatinine clearance, there was a 5.8% increase in TKV and 4.1% increase in TKV/body surface area for every 1 mg/dL increase in uric acid (P = 0.007). The multivariate-adjusted Cox regression demonstrated a greater hazard ratio for ESRD for subjects in the 4th and 3rd quartiles of uric acid compared with the 1st [4.8 (2.6-8.9; P < 0.001) and 2.9 (1.6-5.3; P < 0.001)]. CONCLUSIONS Higher serum uric acid levels are associated with earlier onset of hypertension, larger kidney volume and increased hazard for ESRD in ADPKD independent of gender, body mass index and renal function at the study visit. Randomized interventional studies will be necessary to examine whether treating hyperuricemia has a protective role in ADPKD.

Changing Referral Characteristics of Patients with Autosomal Dominant Polycystic Kidney Disease

OBJECTIVE Autosomal dominant polycystic kidney disease is the most frequent life-threatening hereditary disease. The study objective was to assess whether the clinical characteristics of patients with autosomal dominant polycystic kidney disease who are referred to a major autosomal dominant polycystic kidney disease center have changed over time. METHODS The clinical characteristics of patients with autosomal dominant polycystic kidney disease were compared between period A (1961-1990) and period B (1991-2011). The study took place at the Autosomal Dominant Polycystic Kidney Disease Center at the University of Colorado. A total of 837 patients referred with autosomal dominant polycystic kidney disease were included. Blood pressure control and renin-angiotensin-aldosterone system inhibition were instituted. Renal function, blood pressure, end-stage renal disease, and mortality were analyzed. RESULTS The results in period B compared with period A demonstrated an earlier age of autosomal dominant polycystic kidney disease diagnosis (29 vs 35 years, P < .001), lower mean blood pressure (129/82 vs 142/91 mm Hg, P < .001), better estimated glomerular filtration rate (63.6 vs 44.6 mL/min, P < .001), and more therapy with angiotensin-converting enzyme inhibition (42.5% vs 13.6%, P < .001). Time from birth to end-stage renal disease (52.8 ± 0.6 vs 49.1 ± 0.6 years, P < .001) and birth to death (63.5 ± 1.5 years vs 57.2 ± 1.0 years, P < .001) was longer in period B compared with period A when adjusted for age at diagnosis, sex, and estimated glomerular filtration rate. The study was retrospective, which is a limitation. CONCLUSIONS In period B, there was significantly better blood pressure control, more renin-angiotensin-aldosterone system inhibition, better preservation of renal function, and a longer period from birth to end-stage renal disease and death.

Renin-Angiotensin-Aldosterone System in Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease is the most frequent life-threatening hereditary disease. Prognostic factors for progressive renal impairment have been identified such as gender, race, age, proteinuria, hematuria, hypertension. Hypertension is the only risk factor for renal dysfunction in autosomal dominant polycystic kidney disease, which is presently treatable. Better understanding of the pathophysiology of hypertension will help in defining appropriate interventions. The renin-angiotensin-aldosterone-system is the pivotal factor in the pathogenesis of hypertension in autosomal dominant polycystic kidney disease. Basic research and clinical studies in autosomal dominant polycystic kidney disease implicated activation of the renin-angiotensin-aldosterone-system. Therapy of hypertension in autosomal dominant polycystic kidney disease with angiotensin-converting enzyme inhibitors or angiotensin receptor blocker has the potential to prevent cardiovascular complications and slow the progression of renal disease. The results of two large multicenter double-blind placebo controlled randomized clinical trials (the HALT-PKD trials) possibly will elucidate the beneficial effects of the renin-angiotensin-aldosterone-system inhibition in autosomal dominant polycystic kidney disease.

The impact of type II diabetes mellitus in patients with autosomal dominant polycystic kidney disease

BACKGROUND The epidemic of obesity and diabetes is increasing within the USA and worldwide. We have previously shown that body mass index has increased significantly in autosomal dominant polycystic kidney disease (ADPKD) subjects seen at our center in more recent years. However, the impact of Type II diabetes in ADPKD patients has not been well studied. METHODS This retrospective cohort study compared clinical characteristics in 44 pre-renal transplant patients with ADPKD and diabetes and 88 age- and sex-matched non-diabetic patients with ADPKD who were seen at the University of Colorado between 1977 and 2008. The primary outcomes in this study were renal volume determined by renal ultrasonography, renal function assessed by estimated glomerular filtration rate and time to onset of end-stage renal disease or death by Kaplan-Meier analyses. RESULTS Diabetic patients had significantly larger kidney volumes than those with ADPKD alone [geometric mean (95% confidence interval (CI)]: 2456 (1510-3992) versus 1358 (1186-1556) cm3, P=0.02. Among those whose age at hypertension diagnosis was known, the diabetic ADPKD patients had earlier median (95% CI) age at onset of hypertension compared to those with ADPKD alone: 32.5 (28-40) versus 38 (35-42) years, P=0.04. Diabetic ADPKD patients tended to have an earlier median age of death than those with ADPKD alone. CONCLUSIONS Patients with ADPKD and type II diabetes have larger renal volumes, earlier age at diagnosis of hypertension and may die at a younger age compared to those patients with ADPKD alone. This study emphasizes the importance of diabetes risk management in ADPKD.

Short- and long-term outcomes of kidney donors: A report from Tunisia

Kidney transplantation remains the best treatment option of end-stage renal disease. Kidney donations are of particular interest with the currently increasing practice of living-donor transplantation. The purpose of this study was to analyze retrospectively the general health status as well as renal and cardiovascular consequences of living-related kidney donation. A total of 549 living-related kidney donors had donated their kidneys between 1986 and 2007. We attempted to contact all donors to determine short- and long-term outcome following kidney donation. All kidney donors who responded underwent detailed clinical and biochemical evaluation. The data were compared with age-matched health tables of the Tunisian general population. In all, 284 donors (52%) had a complete evaluation. They included 117 men and 167 women with a mean age of 42 ± 12 years. The major peri-operative complications that occurred in these donors included four cases of pneumothorax, six cases of surgical site infection, one case of phlebitis and one case of pulmonary embolism. None of the study cases died. The median length of hospital stay after donor nephrectomy was 6.5 days (range: 3-28 days). The median follow-up period was eight years. The mean creatinine clearance after donation was 90.4 ± 25 mL/min in men and 81.5 ± 27.2 mL/min in women. Proteinuria was >300 mg/24 h in 17 cases (5.9%). Fifty-eight (20.4%) donors became hypertensive and 19.6% of the men and 37.2% of the women became obese. Diabetes mellitus developed in 24 (8.4%), and was more common in patients who had significant weight gain. Our study suggests that kidney donors have minimal adverse effects on overall health status. Regular follow-up identifies at-risk populations and potentially modifiable factors. Creation of a national registry of living donors and their monitoring are an absolute necessity.

Autosomal dominant polycystic kidney disease: new insights into treatment.

Autosomal dominant polycystic kidney disease (ADPKD) is the worlds most common inherited kidney disease. An increasing number of animal and human studies have enhanced our understanding of the molecular and cellular pathology of ADPKD. New treatment options are being tested in clinical trials in spite of the failure of mammalian target of rapamycin inhibitor therapy. The main and most effective therapy remains control of hypertension by renin-angiotensin-aldosterone system (RAAS) blockade. This review focuses only on promising therapies, including dual inhibition of RAAS, vasopressin receptor antagonists, increased fluid intake, and blockade of certain receptors of cyclic adenosine monophosphate. Also, the paper reviews what these advances mean to patients and clinicians and elaborates on how these changes can be immediately applied to clinical practice. There is an urgent need for discovery of new therapies targeted toward ADPKD in comparison with therapeutic progress of all other renal diseases.