Cutaneous Microcirculation Is Impaired in Early Autosomal Dominant Polycystic Kidney DiseaseRamunni A.a · Brescia P.a · Quaranta D.b · Bianco M.S.b · Ranieri P.c · Dolce E.d · Coratelli P.a
aDivision of Nephrology, Department of Internal and Public Medicine, bDivision of Dermatology, cCoagulation Laboratory and dDivision of Internal Medicine and Clinical Oncology, University of Bari, Bari, Italy Corresponding Author
Background/Aims: An endothelial dysfunction has been described in autosomal dominant polycystic kidney disease (ADPKD) before the development of hypertension and renal impairment. The aim of this work was to verify the existence of a microvascular reactivity in the early stages of ADPKD. Methods: Fifteen ADPKD normotensive patients with normal renal function underwent laser Doppler examination of the cutaneous microcirculation in basal conditions and after the warm test, as well as evaluation of plasma concentrations of some endothelial activation parameters [total cholesterol and fractions, fibrinogen, von Willebrand factor, Lp(a)]. The results were compared with those in 15 healthy subjects, 15 essential hypertensive patients and 15 hypertensive ADPKD patients with normal renal function. Results: Both basal and post-warm-test values were significantly lower in normotensive ADPKD subjects than controls (3.2 ± 1 vs. 5.8 ± 1.3 AU, p = 0.0001; 35.2 ± 10.9 vs. 50.5 ± 10.8 AU, p = 0.005, respectively). All evaluated parameters were within normal limits and comparable between normotensive ADPKD subjects and controls, except for LDL cholesterol (125 ± 18 vs. 101 ± 22 mg/dl, p = 0.01) and Lp(a), which was significantly higher in the ADPKD subjects (52.2 ± 36 vs. 6.0 ±4 mg/dl, p = 0.0006). Conclusion: Our study confirms the existence of a systemic microcirculation defect in ADPKD. The presence of high levels of Lp(a) could contribute to causing the high incidence of cardiovascular events in ADPKD.
Copyright © 2009 S. Karger AG, Basel
Patients affected by autosomal dominant polycystic kidney disease (ADPKD) have an increased incidence of cardiovascular complications [1, 2]. This can be explained by the onset of renal failure, in itself an important cardiovascular risk factor [3,4,5]. Moreover, the presence of arterial hypertension [6, 7] and left ventricular hypertrophy [8, 9] already by the early stages of ADPKD is consistent with the high rate of cardiovascular morbidity and mortality in these patients.
Although ADPKD manifests itself prevalently at the renal level, its variegated clinical features highlight its systemic nature . In fact, being caused by mutations in PKD1 and PKD2 , genes controlling the production of the proteins polycystin 1 and polycystin 2, ADPKD must be considered a multisystem disorder affecting the liver, blood vessels and heart valves.
Confirming its systemic nature, polycystin 1 has been detected in endothelial and vascular smooth muscle cells [12, 13], being considered an essential element for maintaining the integrity of blood vessels . It has been suggested that the reduced nitric oxide synthase observed in the resistance arteries of patients affected by ADPKD may be determined by close interactions between eNOS and polycystin 1 . Since normal blood flow is guaranteed by a physiological balance between endothelial-derived constricting and relaxing factors, the presence of a dysfunction of the NO system, associated with the reported upregulation of endothelin 1 , confirms the existence of an endothelial dysfunction .
This endothelial dysfunction seems to be the common denominator according to which different risk factors can foster the onset of cardiovascular complications . The aim of this work was to verify to what extent this endothelial dysfunction is expressed in the cutaneous microcirculation in the early stages of ADPKD and whether it is associated with increased plasma concentrations of some endothelial activation markers.
The protocol was approved by the medical ethics committee of our hospital and all patients gave their informed consent before entering the study.
Fifteen healthy control subjects (CTS), 15 normotensive ADPKD patients (NP), 15 hypertensive ADPKD patients (HP), all with normal renal function (Cockcroft creatinine clearance/1.73 m2 >80 ml/min), and 15 essential hypertensive (EH) patients were studied (table 1).
|Table 1. Characteristics of the patients|
None of the subjects was diabetic, a smoker or affected by familial hypercholesterolemia.
All cases of ADPKD were diagnosed by renal ultrasound showing 5 or more renal cysts distributed in both kidneys. Most patients had a positive family history of ADPKD. NP patients had systolic blood pressure values consistently <140 mm Hg and/or diastolic values consistently <90 mm Hg.
All the HP subjects were taking ACE inhibitors (ramipril). For those who still did not achieve adequate blood pressure control (<140/90 mm Hg), angiotensin receptor blockers were added (telmisartan; 4/15). In just 1 patient, in addition to these 2 drugs, a calcium antagonist (amlodipin) also needed to be added.
The EH patients were taking ramipril (7/15), ramipril and losartan (5/15), and ramipril and nifedipine (3/15).
No drugs were being taken by the NP or the control subjects.
No statin was being taken by the patients.
Laser Doppler flowmetry (LDF) makes a semiquantitative assessment of microvascular blood perfusion expressed in arbitrary units (AU). LDF measurements from the skin reflect the perfusion in capillaries, arterioles, venules and dermal vascular plexa. The technique was used to measure skin perfusion of the hands by LDF (PF3; Perimed, Stockholm, Sweden) in both basal conditions and after the warm test, heating the probe to 44°C to achieve the maximum tolerable vasodilatation.
The probe has 2 fibers: one delivers light to the site under observation, and the other collects the backscattered light which contains the Doppler-shifted frequency information.
The serum concentrations of total, LDL and HDL cholesterol and triglycerides were assayed by standard routine methods on the automatic analyzer. The von Willebrand factor was analyzed with the enzyme-linked fluorescent assay technique (VIDAS® vWF; BioMerieux SA, Marcy l’Etoile, France), and fibrinogen was determined using the Biopool Assay Kit (Trinity Biotech plc, Bray, Ireland), according to Clauss. Lp(a) lipoprotein was measured with a monoclonal-antibody-based enzyme-linked immunosorbent assay (Immunodiagnostic Systems Inc., Fountain Hills, Ariz., USA).
Data are expressed as means ± SD. Data between groups were compared by means of Student’s t test, after confirming by the Shapiro-Wilk test that they were normally distributed, and by means of Mann-Whitney U test for skewed variables.
Statistical significance was defined as p < 0.05. StatView software (version 5.0; SAS Institute Inc., Cary, N.C., USA) was used for all statistical analyses.
Table 2 shows the mean values of the endothelial activation factors assayed in the 4 populations examined. No differences were found for total cholesterol, HDL cholesterol, triglycerides, von Willebrand factor and fibrinogen. LDL cholesterol was higher in NP ADPKD patients than CTS (125 ± 18 vs. 101 ± 22 mg/dl, p = 0.01) and also in EH patients than CTS (129.2 ± 11 vs. 101 ± 22 mg/dl, p = 0.01), although these values were in any case within normal limits for ADPKD subjects not presenting other cardiovascular risk factors apart from the basic disease. Instead, Lp(a) lipoprotein was much higher in both groups of ADPKD patients, NP and HP, than in CTS, this difference being statistically significant (52 ± 36 mg/dl in NP and 26.2 ± 19.7 in HP vs. 6 ± 4 mg/dl for CTS).
|Table 2. Endothelial activation markers in the 4 groups|
The basal LDF value was significantly lower in all patient groups than in CTS (3.2 ± 1 AU in NP, 2.8 ± 1.5 AU in HP and 3.8 ± 0.8 in EH vs. 5.8 ± 1.3 AU in CTS; table 3). After the warm test, this value remained significantly lower only in the NP group as compared to CTS (35.2 ± 10.9 AU vs. 50.5 ± 10.8 AU, p = 0.005; table 3).
|Table 3. Laser Doppler flowmetry in the 4 groups|
The results of our study demonstrate a reduced blood flow in the cutaneous microcirculation of patients affected by ADPKD compared to an age- and sex-matched population of CTS. This phenomenon is present right from the early stages of ADPKD, when arterial hypertension and renal failure are still absent. The latter 2 conditions could each in themselves justify the onset of an endothelial dysfunction [3,4,5, 6, 7]. It is known that any cardiovascular risk factor, either traditional or nontraditional, will wreak its aggression on the vessel walls through the endothelium, causing endothelial dysfunction.
Several works have shown that endothelial dysfunction is a prelude to the onset of cardiovascular disease [17,18,19,20]. Since the endothelium is a true organ that can control hemostatic processes and maintain correct vascular tone thanks to nitric oxide synthesis, the assessment of endothelial function is clinically relevant  as a means of defining the existence of a cardiovascular risk.
Until recently, the detection of endothelial dysfunction has depended on surrogate markers, such as elevated levels of C-reactive protein , circulating adhesion molecules , homocysteine  and so on. Although all these tests have some value, none is capable of directly measuring the microcirculation status and regulation function. This gap in the physician’s armamentarium of tests of the microcirculatory profile is being filled by studies using noninvasive LDF. Therefore, to provide direct evidence of microvascular endothelial dysfunction, LDF techniques for noninvasive assessment of cutaneous blood flow were adopted. In fact, laser Doppler measurements correlate well with angiographically demonstrated coronary artery disease  and offer a sensitive characterization of endothelial dysfunction which may improve cardiovascular risk assessment in renal disease patients .
In addition, it has been shown that the basal cutaneous blood flow is partly mediated by nitric oxide . Since a defective endothelium-dependent relaxation mechanism has been demonstrated in the resistance arteries of patients affected by ADPKD, sustained by a reduced synthesis of nitric oxide , it could be hypothesized that at the cutaneous microcirculation level, too, a deficient nitric oxide synthesis could have an important role in reducing the blood flow.
The data in our study show that the existence of a circulation deficit in patients with ADPKD extends to the cutaneous microcirculation and confirm the cardiovascular risk in these patients, regardless of the presence of arterial hypertension or renal failure (table 3).
After the onset of arterial hypertension, both in HP ADPKD and in EH patients, the deficient blood flow observed at basal laser Doppler measurement persists, whereas after the warm test this value is comparable in these hypertensive patients to that in healthy CTS (table 3). This behavior could be explained by the antihypertensive drugs taken by these subjects, which could alter vascular reactivity favoring a microcirculation response to high temperature through endothelium-independent mechanisms.
While the existence of a reduced responsiveness of the cutaneous microcirculation has already been demonstrated in EH patients , this study shows a similar deficit of the cutaneous blood flow in NP ADPKD patients.
In support of the idea of a defective endothelium-dependent relaxation sustained by a reduced NO synthesis, in a previous work we found an increased intrarenal vascular resistance in patients with ADPKD still unaffected by hypertension or renal failure . In these subjects, the normal values of circulating renin led us to hypothesize that, at least under baseline conditions, PRA was not involved in the increase in RVR, thus upholding the notion of a reduced NO synthesis .
In this assessment of endothelial dysfunction, besides testing the cutaneous microcirculation, we assayed the plasma concentrations of some endothelial activation markers. None of the parameters examined showed significant differences among the 4 groups, with the exception, in the NP and in the EH group, of mildly increased LDL cholesterol levels but still below 130 mg/dl (table 2), and above all, in both ADPKD patient groups, a consistent, significant increase in Lp(a) lipoprotein as compared to CTS.
We know that Lp(a) lipoprotein is a low-density lipoprotein particle in which apolipoprotein B-100 is linked by a simple interchain disulfide bridge to a unique glycoprotein, apoprotein (a) . Lp(a) lipoprotein has been associated with endothelial dysfunction  and, in view of its structural homology with plasminogen, it could have a thrombogenic effect by interfering with intrinsic fibrinolysis .
A number of case-control [34,35,36] and prospective studies  have indicated that elevated serum Lp(a) lipoprotein concentrations are a risk factor for coronary heart disease in the general population.
To our knowledge, this is the first time that high concentrations of Lp(a) lipoprotein have been reported in patients affected by ADPKD, a finding that suggests that this factor could contribute to the pathogenesis of endothelial dysfunction and to the high incidence of cardiovascular complications observed in these subjects.
In conclusion, in the early stages of ADPKD a deficient blood flow seems to be present in the microcirculation, associated with the previously described deficit in the resistance arteries . On the basis of these observations it seems likely that alterations in vascular tone may develop even before the onset of arterial hypertension and/or renal failure, and could foster the development of the cardiovascular complications so frequently observed in these patients.
Due to the small number of patients studied, we are aware of the possibility of a statistic bias and a type I error. Investigation in a larger case series should provide confirmation of the results obtained in this pilot study.
The existence of an abnormal microvascular reactivity in such an early stage of the disease should urge the patients on the strictest adherence to a healthy way of living, avoiding smoking, keeping an ideal weight, doing physical activity constantly, and so on, in the attempt of improving their microvascular reactivity.
Moreover, administration of drugs capable of ameliorating endothelial dysfunction, like statins, could be tested, in order to improve the microvascular reactivity.
Furthermore, our findings support the measurement of serum Lp(a) lipoprotein as a screening tool for cardiovascular risk in ADPKD. If a hyperlipoproteinemia (a) should be confirmed in a larger case series, a therapeutic approach to the reduction of this cardiovascular risk factor, like niacin, should be taken into account.
Support and Financial Disclosure Declaration
The study was conducted with the aid of the funds awarded to the University of Bari by the Ministry of Education, the Universities and Research.
Alfonso Ramunni, MD
Division of Nephrology, Department of Internal and Public Medicine
University of Bari, Piazza Giulio Cesare, 11
IT–70124 Bari (Italy)
Tel. +39 08 0547 8383, Fax +39 08 0547 8675, E-Mail email@example.com
Received: August 14, 2008
Accepted: January 14, 2009
Published online: July 14, 2009
Number of Print Pages : 5
Number of Figures : 0, Number of Tables : 3, Number of References : 37
Nephron Clinical Practice
Vol. 113, No. 2, Year 2009 (Cover Date: September 2009)
Journal Editor: El Nahas M. (Sheffield)
ISSN: 1660-2110 (Print), eISSN: 1660-2110 (Online)
For additional information: http://www.karger.com/NEC