Abstract
Introduction: Cardiovascular complications are the leading cause of death in patients with autosomal dominant polycystic kidney disease (ADPKD) and there is a high incidence of hypertension in ADPKD patients with early disease. Endothelial dysfunction (ED) is an early marker of cardiovascular complications and this has also been reported in ADPKD. However, published studies have included a significant number of patients with later stage disease and other known comorbidities that are also associated with ED including hypertension. The major aim of this thesis was therefore to test the hypothesis that ED was present in ADPKD patients with early disease.
Method: A cross-sectional study was first performed using retrospective serum samples obtained from 60 ADPKD patients, 40 patients with other forms of chronic kidney disease (OCKD) and 36 healthy volunteers. In a subsequent prospective study, 20 ADPKD patients with eGFR ≥60ml/min/1.73m2 attending the PKD clinic at the Sheffield Kidney Institute were recruited. Exclusion criteria included hypertension, current smokers, age above 50 years, high body mass index (>30kg/m2) and concurrent use of medications known to be associated with ED. A total of 20 age, sex and eGFR matched healthy volunteers were also recruited. Endothelial function was assessed non-invasively by reactive hyperaemia index (RHI). Serum concentrations of asymmetric dimethyl arginine (ADMA), matrix metalloproteinase 2, and nitrite/nitrate were measured as markers of ED while 8 isoprostane and PGE2 were measured as markers of oxidative stress. Blood was collected for routine biochemistry and urine for 24hr protein and creatinine measurements. Finally, tissue quantification of oxidative stress was assessed by immunohistochemistry in Pkd2 heterozygous mice subjected to ischemia reperfusion injury (IRI) to mesenteric vessels (detecting β hydroxyl deoxyguanosine, β OHdG protein) or kidney (detecting matrix metalloproteinase 2, MMP2, β OHdG, superoxide dismutase 2, SOD2 and heme oxygenase 1, HO-1 proteins).
Results: In the initial retrospective cross-sectional study, markers of oxidative stress (serum 8 isoprostane) and ED (serum ADMA) were significantly higher in ADPKD patients than in HV but were similarly elevated in patients with OCKD. In the prospective study, there was a significant difference in diastolic blood pressure (DBP) and proteinuria between PKD and HV groups despite the absence of diagnosed hypertension or difference in eGFR (p<0.001). RHI was not significantly different between PKD patients and controls. Similarly, no difference in 8 isoprostane, ADMA, MMP2 and PGE2 were found. Conversely, serum nitrite/nitrate was lower in ADPKD patients than in controls. Immunohistochemistry of mesenteric vessels and kidneys of Pkd2 heterozygous mice subjected to IRI revealed greater oxidative stress compared to wild type mice.
Conclusions: Although baseline endothelial function was normal as measured by RHI and some serum biomarkers in ADPKD patients with early disease (eGFR>60ml/min/1.73m2), the presence of increased proteinuria, lowered serum nitrite/nitrate concentrations correlating with higher DBP suggest some features of ED may be present in early PKD. The detection of similar increases in ADMA and 8-isoprostane in ADPKD with late disease (eGFR<60ml/min) and OCKD suggests similar mechanisms for ED and oxidative stress in both groups rather than a PKD specific pathway of ED. Finally, Pkd2 heterozygous animals appear to be more sensitive to oxidative stress experimentally, suggesting a genetic predisposition to oxidant injury which may be relevant to ED in human disease.
