487565 2013

DVD13310.1177/1474651413487565The British Journal of Diabetes & Vascular DiseaseGaber and El-Attar

Achieving Best Practice

The relationship between dopamine and renalase in type 2 diabetic patients with and without diabetic nephropathy

The British Journal of Diabetes & Vascular Disease 13(3) 130­–137 © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1474651413487565 dvd.sagepub.com

Eman W Gaber1 and Hoda A El-Attar2

Abstract Background: Diabetes clustered with hypertension and nephropathy is the commonest cause of end stage renal disease. Dopamine, an ancestral catecholamine, is involved in the regulation of sodium homeostasis and blood pressure. Renalase metabolises circulating catecholamines and is thought to regulate blood pressure. This study aimed to assess the relationship between dopamine and renalase in type 2 diabetic patients with and without diabetic nephropathy. Methods: This study was conducted on 80 subjects. Group 1 included 10 healthy subjects as controls, group 2 included 60 type 2 diabetic patients with normal or increased albumin excretion rate (AER) and group 3 included 10 type 2 diabetic patients on maintenance hemodialysis (HD).Thorough clinical assessment and laboratory investigations included estimation of serum levels of fasting glucose (FSG), creatinine, urea, calcium, phosphorus, cholesterol (total and high and low-density lipoprotein) and triglycerides. Urinary albumin/creatinine ratio (ACR) was estimated to assess AER and plasma dopamine and serum renalase were estimated. Results: There were no significant differences in the mean dopamine levels between the three studied groups. Renalase level was significantly higher in HD patients than controls and other diabetic patients. Diabetic patients with increased AER had significantly higher systolic blood pressure, serum creatinine and renalase levels than diabetic patients with normal AER. Diabetic patients with increased serum creatinine ≥ 1.5 mg/dl had significantly longer duration of diabetes and higher systolic and diastolic blood pressures.They also had significantly higher AER, FSG, dopamine and renalase levels than diabetic patients with serum creatinine < 1.5 mg/dl. ACR was positively correlated with duration of diabetes, systolic and diastolic blood pressure and serum creatinine and negatively correlated with the use of angiotensin converting enzyme inhibitors or angiotensin receptor blockers. Renalase was positively correlated with diastolic blood pressure, ACR, serum creatinine, phosphorus and dopamine Conclusion: Serum levels of renalase are increased in type 2 diabetic patients with renal dysfunction. Renalase levels may be increased to compensate for the increase in dopamine level. The higher renalase level in HD patients may be due to much lower renalase clearance, higher production or slower degradation in these patients. Keywords dopamine; renalase; sympathetic over activity; type 2 diabetes

Abbreviations: ACR albumin/creatinine ratio AER albumin excretion rate CKD chronic kidney disease CVD cardiovascular disease ESRD end-stage renal disease FSG serum levels of fasting glucose HD hemodialysis HDL-C high-density lipoprotein cholesterol LDL-C low-density lipoprotein cholesterol RAAS renin angiotensin aldosterone system

1Internal

Medicine, Medical Research Institute, Alexandria University, Alexandria, Egypt 2Professor of Chemical Pathology, Medical Research Institute, Alexandria University, Alexandria, Egypt Corresponding author: Dr Eman Wagdy Gaber, Assistant Professor of Internal Medicine, Medical Research Institute, Alexandria University, 10 kamal El deen Salah Street, Smoha, Alexandria, Egypt. Email: [email protected]

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Introduction

Subjects and methods

Diabetes mellitus is a chronic metabolic disorder that can lead to micro-vascular and macro-vascular complications including nephropathy and cardiovascular complications.1 Hypertension, which occurs in an estimated 70% of type 2 diabetic patients, is a major risk factor for these complications. The coexistence of diabetes and hypertension triples the risk of cardiovascular disease. Moreover, the presence of hypertension accelerates diabetic nephropathy and contributes to the extremely high occurrence of ESRD in type 2 diabetic patients.2 There is accumulating experimental and clinical evidence suggesting a crucial role for sympathetic activation in the development of hypertension and the progression of renal damage in patients with CKD.3 Understanding the contribution of sympathetic nervous system hyperactivity to the onset and maintenance of renal injury might aid in the prevention and treatment of renal injury in type 2 diabetic patients. Dopamine, a precursor of norepinephrine biosynthesis, is synthesised within the renal proximal tubules and is recognised as an important regulator of sodium homeostasis and blood pressure.4 Activation of dopamine D1 receptors results in inhibition of Na/K-ATPase and the Na/H exchanger in the proximal tubule, leading to an increase in sodium excretion. Dopamine is metabolised in the kidney and excreted into urine.5 Renalase is a flavin adenine dinucleotide-containing amine oxidase that is highly expressed in kidney and is expressed at a lower level in heart, skeletal muscle and small intestine.6 In vitro study has shown that renalase can degrade catecholamines and has the strongest enzymatic hydrolysis action against dopamine, followed by adrenaline and noradrenaline. In vivo studies indicate that catecholamines activate renalase precursor which promotes deactivation of catecholamines and regulation of cardiovascular function.7 Another study showed that renalase preferentially metabolises circulating epinephrine and the dopamine precursor l-3,4-dihydroxyphenylalanine and has low activity against dopamine.8 Renalase lowers blood pressure by decreasing cardiac contractility and heart rate and by preventing the expected compensatory increase in peripheral vascular tone. Abnormalities in the renalase pathway are evident in animal models of CKD and hypertension.6 There are still some controversies concerning the plasma catecholamine levels in diabetic patients and their possible role in the pathogenesis of renal complications of diabetes mellitus.9 Some investigators have described normal or elevated plasma catecholamines,10 and other have reported a reduction in the circulating concentrations of plasma catecholamines.11 The goal of the present study is to assess the relationship between dopamine and renalase in type 2 diabetic patients with and without diabetic nephropathy

After approval by the Ethical Committee of the Medical Research Institute, the present study was conducted on 80 subjects recruited from the Internal Medicine Department of the Medical Research Institute, Alexandria, Egypt. Written informed consent was obtained from all subjects and they were divided into three groups: Group 1 included 10 apparently healthy volunteers (six women) with a mean age of 54.21±10.81 years as controls. Group 2 included 60 type 2 diabetic patients (42 women) with a mean age of 54.88±9.17 years. These patients were subdivided as follows: • Patients with normal renal function (they had normal urinary albumin to creatinine ratio (ACR < 30 mg/g) and normal serum creatinine < 1.5 mg/dl).12 • Patients with renal dysfunction (they had increased ACR or increased serum creatinine ≥ 1.5 mg/dl). Group 3 included 10 type 2 diabetic patients (six women) on maintenance hemodialysis. The mean duration of diabetes of all studied diabetic patients was 12.82±8.31 years. For all participants the following tests were made and information recorded: 1. Detailed history and thorough clinical examination with special stress on diabetic complications and measurement of blood pressure. Blood pressure was measured in the hemodialysis group after hemodialysis in three consecutive dialysis sessions, and the average of three measurements taken was used for the analysis. 2. Twelve-lead electrocardiogram. 3. Laboratory investigations – the blood for the laboratory investigations in the hemodialysis group was taken before the hemodialysis session in the middle of three dialysis sessions. These investigations included the following. a. Estimation of FSG, urea, creatinine, uric acid, sodium, potassium, calcium, inorganic phosphorus, cholesterol (total, HDL-C and LDLC) and triglycerides.13 b. Estimation of urinary creatinine, albumin and calculation of ACR to assess AER.14 ACR < 30 mg/g was considered as normoalbuminuria, and all abnormal tests were confirmed in two samples collected over a 3-weeks period, due to the known day-to-day variability in AER.

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Table 1.  Clinical and laboratory data for all subjects. Item/Group Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Urinary albumin/creatinine ratio (mg/g) Number of hypertensive cases Number of cases with cardiovascular disease Number of cases with hypotensive therapy  

Mean±SD Mean±SD Median Min – Max

β–blockers ACEI or AT1RB

Controls (Group 1) (n=0)

Diabetic patients (Group 2) (n=60)

Hemodialysis patients (Group 3) (n=10)

114±5.2 73±4.8 11.25 3.1–23 0 0

139.6±23* 87±10.2* 181.8* 11.6–3844 32 (53.3%) 23 (38.3%) 8 29

131.11±12.7* 84.4±5.3* Not available

0

8 (80%) 2 (20%) 3 7

Key: ACEI: angiotensin converting enzyme inhibitors inhibitors; AT1RB: angiotensin 1 receptor blockers. *Significant results between each group and control group.

Table 2.  Laboratory data for all subjects. Item/group

Controls (Group 1) (n=0)

Diabetic patients (Group 2) (n=60)

Hemodialysis patients (Group 3) (n=10)

P

P1

P2

FSG (mg/dl) Mean±SD Urea (mg/dl) Mean±SD Cr (mg/dl) Mean±SD UA (mg/dl) Mean±SD Dopamine (ng/ml) Mean±SD Renalase (ng/ml) Mean±SD

100.2±13 26.6±8.1 1.0±0.1 5.2±0.9 5.7±3.0 6.0±2.9

262.5±184.1 73.1±61.9 1.77±0.5 6.7±2.5 4.85±7.1 10.0±7.6

194.9±107.2 126.0±49.2 8.3±2.9 7.0±1.6 5.3±4.0 28.9±18.8

0.051 0.001 0.000 0.017 NS 0.000

0.006 NS NS NS NS NS

NS 0.025 0.000 NS NS 0.004

Key: Cr: serum creatinine; FSG: fasting serum glucose; UA: serum uric acid. P = Significance between group 3 and group 1. P1 = Significance between group 2 and group 1. P2 = Significance between group 3 and group 2.

c. Estimation of plasma dopamine using ELISA FAST TRACK BA E-6300 kit, Labor Diagnostika Nord GmbH & Co.KG. d. Estimation of serum renalase using E 92845 Hu ELISA kit (Uscn Life Science Inc.).

Statistical analysis Statistical analysis was performed using SPSS software (version 11.5, SPSS Inc Chicago, USA). The KolmogorovSmirnov test was used to verify the normality of distribution of variables. Data which were normally distributed were represented as mean±standard deviation and data which were abnormally distributed were represented as median and range. Statistical comparisons of the three groups were made using ANOVA test with post hoc comparisons. Correlations between variables were done with Pearson’s correlation test for parametric variables and Spearman‘s correlation test for non-parametric variables. P