Coenzyme Q₁₀ and its Relation with Oxidant and Antioxidant System Markers in Patients with End-Stage Renal Disease

Abstract

Rationale and objectives: Oxidative stress is increased in chronic kidney disease (CKD) patients and end-stage renal disease (ESRD) patients undergoing dialysis treatment. Coenzyme Q₁₀ (CoQ₁₀) is a ubiquitous and strong antioxidant. Role of CoQ₁₀ is not fully evaluated in renal patients. We aimed to investigate the relationship of CoQ₁₀ with oxidant and antioxidant system markers in patients with renal disease. Material and methods: Forty patients with CKD (stages 3–5) who were managed conservatively without dialysis treatment, 40 hemodialysis, and 60 chronic ambulatory peritoneal dialysis (CAPD) patients were included in the study. Biochemical and whole blood analyses were done using hospital auto-analyzers from stored samples. Serum CoQ₁₀, malondialdehyde (MDA), superoxide dismutase (SOD), and antioxidant activity (AOA) levels were determined. Main findings: There was no difference among the groups in terms of serum CoQ₁₀ levels. However, other components of antioxidant system, namely, SOD and AOA were significantly higher in CAPD patients when compared to CKD patients. MDA levels were not significantly different among the groups. Principal conclusion(s): The results of this study showed no difference among CKD, CAPD, and hemodialysis patients in terms of serum CoQ₁₀ levels.

Keywords:

• Antioxidant system
• chronic kidney disease
• coenzyme Q₁₀
• hemodialysis
• malondialdehyde
• oxidative stress
• peritoneal dialysis

INTRODUCTION

Oxidative stress is increased in chronic kidney disease (CKD) patients and end-stage renal disease (ESRD) patients undergoing dialysis treatment.¹ A number of studies have linked oxidative stress to uremia and increased inflammation.^2,3 In addition, it is now well established that cardiovascular morbidity and mortality are closely related to increased oxidative stress and resultant endothelial dysfunction in patients with renal insufficiency.⁴ Precise mechanisms of increased oxidative stress in patients with renal disease largely remain speculative at this time despite some experimental data showing role of renin-angiotensin system⁵ and immune modulation.⁶ In patients with ESRD, the balance between reactive oxygen species (ROS) and antioxidant system is deranged in favor of ROS. To date, it has been clearly demonstrated that different markers of oxidative stress such as glyoxal, F₂-isoprostanes, and malondialdehyde (MDA) are increased in patients with decreased kidney function.^7,8 In addition, several markers of the antioxidant system have been studied in CKD patients including vitamins A and E, carotenoids, and glutathione.⁹ However, only a few studies evaluated the role of coenzyme Q₁₀ (CoQ₁₀) as a component of antioxidant system in CKD patients.^10–12 To our knowledge, no study in the literature looked at the relation of serum CoQ₁₀ and markers of oxidative stress and antioxidant system in CKD and dialysis (peritoneal dialysis, PD, and hemodialysis, HD) patients.

Previous studies ^11,12 have showed that the most severe oxidative stress was present in patients with CKD and then in a decreasing order in HD and PD patients. The ongoing elevated levels of oxidative markers in dialysis patients, despite an adequate dialysis, led to questioning of dialysis modalities and techniques as a way of increasing oxidative stress. Some studies ¹³ showed improved oxidative stress marker profile with improvements in membrane material and design. The exact explanation for why dialysis does not normalize oxidative markers and why dialysis modalities differ in this respect is not available for the time being.

To our opinion the difference between HD and PD modalities with respect to oxidative stress levels may be due to differences in antioxidant system as well as oxidative stress. CoQ₁₀ is a ubiquitous and strong antioxidant.¹⁴ CoQ₁₀ is the only lipid-soluble antioxidant synthesized endogenously and prevents oxidation of proteins, lipids, and DNA.¹⁵ In some disease states, such as cancer and diabetes, tissue levels of CoQ₁₀ are elevated.¹⁶ This increase is considered as an adaptive defense mechanism against increased oxidative stress in these disease states. A few previous studies^10,11 showed decreased levels of CoQ₁₀ in patients with uremia and in patients undergoing HD. However, to our knowledge, the status of CoQ₁₀ in PD patients is yet to be defined. We hypothesize that the difference in the reserve of CoQ₁₀ may account for the differences in oxidative stress markers observed in HD and PD patients.

We aimed to investigate levels and associations of various markers of oxidative stress and members of antioxidant system including superoxide dismutase (SOD), antioxidant activity (AOA), MDA, and CoQ₁₀ in CKD, HD, and PD patients.

MATERIAL AND METHODS

This is a cross-sectional cohort study. Forty patients with CKD (stages 3–5, mean estimated Glomerular filtration rate (eGFR): 35.48 ± 13.6 mL/min/1.73 m²) who were managed conservatively without dialysis treatment, 40 HD, and 60 chronic ambulatory peritoneal dialysis (CAPD) patients were included in the study. CKD patients were consecutive patients who fulfilled the inclusion criteria and being followed at our outpatient nephrology clinic. HD and CAPD patients were randomly selected (using a computer random number generator) among patients at our HD unit and CAPD outpatient clinic, respectively.

Inclusion criteria were as follows: diagnosis of CKD (GFR between 15 and 60 mL/min/1.73 m²), maintenance HD for at least 3 months for HD patients, manual exchange of —four to five 2000 PD bags during a day for at least 3 months for CAPD patients. Exclusion criteria included age below 18 years, hospitalization due to systemic infection in the preceding 3 months, unwillingness to participate in the study, active neoplasm, liver cirrhosis, diabetes mellitus, congestive heart failure, overt coronary artery disease, and dialysis inadequacy based on guideline targets (weekly Kt/V values <1.9 and <3.6 for PD and HD patients, respectively).

All CKD, HD, and CAPD patients fulfilling these criteria were asked to take part in the study and were included in the study after signing informed consent forms. The study protocol was approved by the local ethics committee. Peripheral venous blood samples were taken after an overnight fasting from CKD patients and CAPD patients. HD patients gave blood samples after the longest interval between the two HD sessions after an overnight fast. Venous blood samples were obtained from each patient’s forearm and serum samples were separated from blood cells by centrifugation (3200 rpm for 15 min at 4°C) and stored at –80°C until time of analysis. Biochemical and whole blood analyses were done using hospital auto-analyzer (Synchron LX20 system, Beckman Coulter, Fullerton, CA, USA) from stored samples. PTH was analyzed with Beckman Coulter chemiluminescent immunoassay using Beckman Coulter UniCel DXI 800 immunoassay analyzer.

MDA levels (total) were determined via thiobarbituric acid method as defined by Wasowicz and coworkers¹⁷ and expresses as millimoles per liter. SOD levels (U/mL) were determined via the method first defined by Sun and coworkers¹⁸ and modified by Durak et al.¹⁹ AOA levels (mmol/L) were determined by the method of Koracevic and colleagues.²⁰

CoQ₁₀ levels were determined by high performance liquid chromatography (HPLC) using the commercially available kits according to the manufacturer’s (Immuchrom GmbH, Heppenheim, Germany) instructions and expressed as milligrams per liter.

Statistical Analysis

The data were evaluated using SPSS 15 (Statistical Package for the Social Sciences, Inc., Chicago, IL, USA) statistical program. Student’s t-test was used to compare the means of normally distributed variables and the Mann–Whitney U-test was used for variables that were not normally distributed. Differences among categorical variables were analyzed using the chi-square test or the two-tailed Fisher’s exact test as appropriate. The level of significance was p < 0.05 for all comparisons.

RESULTS

Epidemiologic and laboratory characteristics of the patients in all three study groups are shown in Table 1. There was no difference in the mean age of the groups. However, inflammation (defined as serum CRP concentrations) in the CKD group was higher than those of HD and PD groups (Table 1). PD patients were on dialysis much shorter than HD counterparts. Also, it was noteworthy that PD group had higher serum total cholesterol and low density lipoprotein cholesterol (LDL) and lower total protein and albumin values compared to HD patients.

Table 1. Demographic and laboratory characteristics of hemodialysis, peritoneal dialysis, and chronic kidney disease patients.

Parameter	Hemodialysis	Peritoneal dialysis	CKD
Patient number	40	60	40
Age (years)	54.8 ± 15.1	53.2 ± 14.1	57.8 ± 14.5
Dialysis vintage (months)	70.3 ± 44.2^a	46.7 ± 23.8
Hemoglobin (g/L)	11.0 ± 1.3^b	11.5 ± 1.7^c	12.5 ± 1.8
Hematocrit (%)	35.9 ± 4.3	34.8 ± 5.3^c	37.9 ± 5.2
BUN (mg/dL)	132.9 ± 23.5^a,^b	101.5 ± 29.3^c	81.4 ± 34.6
Creatinine (mg/dL)	8.8 ± 2^b	7.9 ± 2.8^c	2.5 ± 0.9
Calcium (mg/dL)	8.8 ± 1.1^b	9.1 ± 0.9	9.4 ± 0.4
Phosphorus (mg/dL)	4.8 ± 1.1^a,^b	3.8 ± 0.9	3.5 ± 0.6
iPTH (pg/mL)	237.1 ± 167.5^a,^b	513.6 ± 465.3^c	154.6 ± 86.6
Total protein (mg/dL)	7.4 ± 0.5^a	6.8 ± 0.7^c	7.2 ± 0.6
Albumin (mg/dL)	3.9 ± 0.3^a	3.8 ± 0.4^c	4.1 ± 0.4
CRP (mg/dL)	13.9 ± 21.3^b	19.7 ± 13.0^c	30.2 ± 14.9
Total cholesterol (mg/dL)	179.7 ± 38.4^a	200.1 ± 53.2^c	172.2 ± 40.3
Triglycerides (mg/dL)	184.6 ± 137.1	158.2 ± 75.2	153.8 ± 91.6
HDL (mg/dL)	37.2 ± 11.7	41.3 ± 14.1	36.8 ± 10.6
LDL (mg/dL)	109.6 ± 36.6^a	127.5 ± 44.6^c	104.0 ± 32.2

Notes: ^aSignificant difference (p < 0.05) between HD and PD.

^bSignificant difference (p < 0.05) between HD and CKD.

^cSignificant difference (p < 0.05) between PD and CKD.

Table 2. Serum levels of malondialdehyde, uric acid, CoQ₁₀, superoxide dismutase, and antioxidant capacity in CKD, hemodialysis, and peritoneal dialysis patients.

	CKD	Hemodialysis	Peritoneal dialysis
Malondialdehyde (μmol/L)	10.80 ± 3.34	9.97 ± 3.39	11.58 ± 3.95
Uric acid (mg/dL)	8.26 ± 2.80	6.37 ± 1.76^a	5.86 ± 1.25^a
Superoxide dismutase (U/mL)	0.86 ± 0.19	0.99 ± 0.42	1.03 ± 0.22^a
Antioxidant activity (mmol/L)	1.13 ± 0.24	0.75 ± 0.24^a	1.24 ± 0.25^a,^b
Coenzyme Q10 (mg/L)	0.47 ± 0.15	0.49 ± 0.12	0.46 ± 0.17

Notes: ^aCompared with CKD (p < 0.05).

^bCompared with hemodialysis (p < 0.05).

Serum levels of uric acid, MDA, SOD, AOA, and CoQ₁₀ are depicted in Table 2. There was no difference among the groups in terms of CoQ₁₀ levels. However, other components of antioxidative system, namely SOD and AOA were significantly higher in PD patients when compared to CKD patients (p < 0.05).

DISCUSSION

The main result of this study was that CoQ₁₀ levels were not different among the groups although other members of the antioxidant system such as SOD and AOA were higher in patients undergoing PD compared to CKD patients.

One can suppose that serum CoQ₁₀ levels in response to increased oxidative stress would be higher in CKD and dialysis patients in an attempt to counterbalance increased oxidative stress burden. On the other hand, one can assume that CoQ₁₀ levels may be found decreased due to their consumption in balancing oxidative stress. However, when considering the ubiquitous nature of CoQ₁₀ in the body, the latter assumption seems less likely. A few previous studies showed that serum CoQ₁₀ levels were significantly decreased in HD and CKD patients compared to healthy controls as lending support for the former hypothesis.^10,11 In another study, CoQ₁₀ concentrations were found to be decreased in patients with mildly reduced creatinine clearance, however no further reduction was observed in HD patients.¹²

No study in the literature examined the level of serum CoQ₁₀ level in PD patients to date. It has been shown in a number of studies that serum levels of various oxidative stress markers were higher in HD patients compared to PD patients.^21–23 On the other hand, other studies ^24,25 showed equal severity of oxidative stress in HD and PD patients. In addition to these, a number of previous studies investigated some members of antioxidant system including total antioxidant capacity and SOD showed that levels of these antioxidant molecules were not different between PD and HD patients.^24,26 Precise mechanisms of why PD confers such an advantage over HD have not been clearly demonstrated. Presence of larger amounts of residual renal function for longer periods than HD may in part account for this difference between the dialysis modalities. Another factor may be due to selection bias while deciding incident dialysis modality as such patients with more comorbidity are directed toward HD. Consequently, comorbid diseases, such as cardiovascular disease, contribute to higher oxidative stress status in these patients regardless of dialysis modality selected. In fact, the process of HD per se is a source of increased inflammation and oxidative stress due to bioincompatible membranes and volume fluctuations.²³ Another factor responsible for this difference may be the study of myriad markers of oxidative stress and antioxidant system in different studies. Use of different markers and methodologies makes the picture more complicated. We hypothesized that another factor responsible for the different patterns of oxidative stress markers in different dialysis modalities might be due to differences in serum levels of CoQ₁₀ in these patients while keeping the aforementioned concerns in mind.

However, our results did not show such a favorable effect in CAPD patients. Their serum CoQ₁₀ levels were not different from those of CKD and HD groups. On the other hand, other markers of antioxidant capacity, SOD and AOA, were found to be higher in CAPD patients. The possible explanation for lack of difference in serum CoQ₁₀ levels among the groups may be due to the fact that measurement of blood levels of CoQ₁₀ provides only limited information concerning its actual levels in organs and cells.¹⁴

During the oxidative deterioration of polyunsaturated lipids several end-products are formed such as aldehydes, mainly MDA. Thus, in a conceptual framework we can assume that CoQ₁₀, with its unique abilities to prevent lipid peroxidation and placement in the cell membrane, should be closely interrelated. However, results of our study did not demonstrate such a reciprocal relationship between MDA and CoQ₁₀. MDA levels have been shown to be increased in CKD and dialysis patients. However, previous studies reported conflicting results regarding MDA levels in different dialysis modalities.^22,24,27,28 These variable results may be due to some confounding factors related to the method of study of MDA.²⁹ Another factor which should be taken into account is that MDA is found in two forms: bound and free MDA. While chemically reactive free MDA is an index of recent and potential damage, bound MDA, excreted by the kidney, is a marker of an older injury. Almost all studies to date investigated total MDA levels in CKD and dialysis patients. On the other hand, De Vecchi et al.³⁰ studied free and bound MDA levels as well as total levels in CKD, HD, PD patients, and normal controls. They found that total and bound MDA concentrations were significantly higher in patients than in controls (ESRD>HD>PD) and free MDA levels were similar in HD and PD patients and significantly higher than CKD patients.

In conclusion, this is the first study investigating levels of serum CoQ₁₀ in CKD, HD, and PD patients. Our results supported the null hypothesis and did not show a difference among the groups in terms of serum CoQ₁₀ levels. Given important therapeutic implications of exogenous CoQ₁₀ in different disease states such as diabetes, cancer, and some neurological diseases, exact status of CoQ₁₀ levels in renal patients is of paramount importance to develop a replacement regimen in case of detection of any deficiency. Conducting studies with larger sample sizes and with meticulous methodologies is a clear research need.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.