The effect of Omega-3 fatty acids on serum paraoxonase activity, vitamins A, E, and C in type 2 diabetic patients.

BACKGROUND: Diabetes mellitus is a heterogeneous metabolic disorder characterized by hyperglycemia. Studies showed paraoxonase activity, and vitamin C and A levels are decreased in diabetes. The effect of omega-3 fatty acids on serum paraoxonase activity and vitamins A, E, C in patients with type 2 diabetes is not fully understood. This study aimed to determine the effect of omega-3 fatty acids on paraoxonase activity, vitamins C, A and E levels in type 2 diabetic patients.
METHODS: In a double-blind, placebo controlled trial, 80 type 2 diabetic patients were randomly enrolled into the study. Study subjects received daily 2714 mg of omega-3 fatty acids or placebo for 8 weeks. Ten milliliter fasting blood was collected before and after treatments. Serum paraoxonase activity and vitamin C levels were measured by spectrophotometry. Vitamin A and vitamin E were measured using high performance liquid chromatography. Nutrient intake was estimated using 24-hours dietary recall questionnaire (for 2 days) before and after treatments. Dietary data were analyzed using FPII. To compare the means of variables between the two groups, independent t-test was employed. Differences between variables before and after interventions were calculated using paired t-test.
RESULTS: Serum levels of paraoxonase activity were significantly increased after omega-3 intake (126.47 IU/ml vs. 180.13 IU/ml). However, omega-3 intake caused no significant change in serum vitamin A, C, and E.
CONCLUSIONS: Supplementation of omega-3 fatty acids was found to increase paraoxonase activity in diabetic patients.

RCT Entities:   Population Interventions Outcomes

Diabetes is a complex metabolic disease characterized by high blood glucose level.1 Its macrovascular complications include atherosclerosis, and its microvascular complications include damage to the kidney, nerves and eyes.2 Oxidative stress is increased in diabetes,3 therefore, it is considered as a cause of development of atherosclerosis.4 In diabetic patients, atherosclerosis is one of the most important causes of mortality.5 Human paraoxonase (PON-1) which is an antioxidant (via scavenging of free radicals),6 is synthesized in the liver and secreted into blood, where it is associated with high density lipoprotein (HDL) levels,7 and serum paraoxonase levels are inversely related to the risk of cardiovascular disease.89 Some studies found that PON-1 activity is decreased in cardiovascular and diabetes mellitus.1011

Vitamin C is an important antioxidant in human,1213 however, several studies showed vitamin C level in diabetic patients is decreased.1415 Vitamin A is a hydrophobic antioxidant1617 which is decreased in diabetes causes retinopathy.18 Also, vitamin E is a hydrophobic antioxidant which is found in membranes as well as lipoproteins and can afford primary as well as secondary stage protection against ROS activity.1219 Many studies showed the association between intake of omega-3 fatty acids and decreased risk of coronary heart disease2021 and its mortality.21 Studies with evaluation of the metabolic effect of omega-3 fatty acids on serum vitamins A, E, C in patients with type 2 diabetes are rare in literature. In addition, the metabolic effect of omega-3 fatty acids in patients with type 2 diabetes is not fully clear. There is also no evidence about the effect of omega-3 fatty acids in patients with type 2 diabetes in Iranian population. The aim of this study was to determine the effect of omega-3 fatty acids on paraoxonase activity, as well as the levels of vitamin A, C and E in Iranian diabetic type 2 patients.

Methods

Study design

The present study was a randomized double blind placebo-controlled study financially supported by Tehran University of Medical Science (research project number: 2296). Study subjects included 80 type 2 diabetic patients (aged 45-80 years) with at least 2 years of diagnosed diabetes since onset of the condition. The subjects had a written consent to enroll into the study from Iranian Diabetes Association, Tehran, Iran using written announcement. They were divided randomly into two groups (experiment and control, n = 41 and n = 40, respectively) using computer's random numbers. Subjects had their routine medication regimens. Patients did not take omega-3 fatty acid supplements and/or medications interacting with lipid profile, did not have hepatic or renal disease, and had no history of cancer or myocardial infarction. Each patient received 3 capsules per day for 8 weeks. The dose of the supplements was chosen from other studies22. The supplement was obtained from PBL Company, US. Omega-3 fatty acid dose was 2714 mg (EPA= 1548 mg, DHA= 828 mg and 338 mg of other omega-3 fatty acids) via 3 gel capsules. Placebo consisted of 3 capsules containing 2100 mg sunflower oil (12% SFA, 65% linoleic acid, and 23% MUFA). Placebo capsules looked identical and were prepared for this study by Zakaria Inc., Tehran, Iran.

Data collection

Anthropometric data, medical and drug history were obtained via face-to-face interviews. Ten milliliter blood was collected from each patient after 12-14 hours overnight fasting, before taking oral hypoglycemia drugs, between 8-10 a.m., at the beginning and at the end of 8 weeks. Fasting blood sugar was measured. Paraoxonase (PON-1) activity and vitamin C were measured by spectrophotometry; and vitamin E and A were measured using HPLC. Daily nutrient intakes were estimated using 24-hour dietary recall questionnaires at the beginning and at the end of the study for 2 days. Dietary data were analyzed using Food Processor version 2 software. The patients were asked not to change their usual diets, activity and medications throughout the study.

Statistical analysis

Differences between the two groups of supplemented and control groups were calculated using independent t-test. Differences between variables before and after interventions were calculated using paired t-test. Statistical analyses were performed using SPSS 11 (compatible with Microsoft Windows). The results are expressed as mean ± SD (standard deviation). For statistical evaluations, P value of less than 0.05 was considered as a significant change.

Results

The clinical and demographic characteristics of subjects are shown in Table 1. Participants in case or control groups had equal age, sex, BMI, glucose and duration of diabetes at the beginning of the study (P > 0.05). As shown in Table 2, energy and nutrient intake before and after intervention were also equal. Table 3 shows that there was no significant difference in serum paraoxonase activity between the two groups before and after intervention, but after 8 weeks of omega-3 supplementation, serum paraoxonase activity was increased compared to its activity before treatment (P=0.002). Table 4 presents the serum concentration of vitamins (A, E and C) in subjects before and after supplementation. At the beginning of the study, 2 groups were similar by the means of vitamins level. Following 2 months of supplementation, serum levels of vitamins A, E, C were not significantly changed in the case group.

Table 1

Demographic and clinical characteristic of the study groups

Table 2

Comparison of dietary intake of macro- and micro-nutrients between two groups of study

Table 3

Paraoxonase (arylesterase) (IU/mL) activity before and after 2 months omega-3 supplementation in type 2 diabetic patients

Table 4

Levels of vitamin A, E (μmol/L) and vitamin C (mg/dl) before and after 2 months omega-3 supplementation in type 2 diabetic patients

Table 4 presents the serum concentration of vitamins (A, E and C) in subjects before and after supplementation. At the beginning of the study, two groups were similar by the means of vitamin levels. Following 2 months of supplementation, serum levels of vitamins A, E, C were not significantly changed in the case group.

Discussion

It is believed that oxidative stress plays an important role in the pathogenesis of type II diabetes.23 Many studies on diabetes mellitus have showed that free radicals can cause chronic complications such as cardiovascular disease.24 Paraoxonase protects low density lipoprotein (LDL) and high density lipoprotein (HDL) against oxidative modification.25 It is believed that the oxidation of LDL is the first stage of development of atherosclerosis.26 Mackness and Karabina found that paraoxonase activity decreases in cardiovascular disease as well as in diabetes mellitus.1011 Omega-3 fatty acids are a class of polyunsaturated fatty acids that found in fish and fish oils.27 Omega-3 fatty acids from seafood and plant sources can reduce coronary heart disease.28 Our previous studies showed that omega-3 PUFA can decrease the inflammation in a cell culture model.29 The possible mechanism of anti-inflammatory effect of omega-3 PUFA is the decreased levels of arachidonic acid inflammatory pathway in the cells.30 However, it is believed that these fatty acids has no antioxidant activity and increase the utilization of the antioxidants.30 In our study, it is found that paraoxonase activity increased following omega-3 supplements. The changes in paraoxonase activity were observed after 8 weeks of supplementation of omega-3 by Calabresi.31 In other studies, it has been found that plasma concentration of HDL-bound antioxidant paraoxonase enzyme increased by 10% after omega-3 supplementation31 which is in the same track of our study.

Increased oxidative stress in diabetes could contribute to depletion of antioxidants.32 Several studies showed decreased basal vitamin C levels (a potent water phase antioxidant) in diabetic patients.3334 There are conflicting reports regarding plasma vitamin concentrations in diabetes mellitus. Merzouk found no alteration in the levels of serum vitamin C, whereas the levels of vitamin A and E were lower in type I and type II diabetes mellitus patients with or without complications than in control subjects.35 Studies also reported that plasma vitamin C and E in type II diabetic patients were not significantly different from those in control groups, while vitamin A levels were significantly lower.3637 On the other hand, Sundaram reported low levels of vitamin E and C in diabetic patients.38 Basu showed that the concentration of serum vitamin A and its binding protein, RBP, were lower in patients with diabetes than in normal control subjects.39 The present study demonstrated no significant change in vitamin A, C and E after consumption of omega-3 fatty acids. Zhou demonstrated that α-linolenic acid deficiency decreased DHA and elevated Osbond acid (OA) levels in tissue membranes, and dietary vitamin A deficiency had an important effect on membrane DHA and OA in rat tissues.4041 However, the effect of omega-3 on vitamin A, C and E in diabetic patients has not been studied recently.

Conclusion

The present study demonstrated for the first time, that there was no significant change in vitamin A, C and E after consumption of omega-3 fatty acids. We concluded that omega-3 fatty acid supplementation (3 g/per day) in the form of capsules can increase paraoxonase activity in diabetic patients. The metabolic effect of omega-3 fatty acid in diabetic patients is less studied.

Authors’ Contributions

All the authors have carried out the study, participated in the design of the study and acquisition of data performed the statistical analysis and wrote the manuscript. All authors read and approved the final manuscript.