Elsevier

Nutrition

Volume 72, April 2020, 110644
Nutrition

Basic nutritional investigation
Eicosapentaenoic acid prevents salt sensitivity in diabetic rats and decreases oxidative stress

https://doi.org/10.1016/j.nut.2019.110644Get rights and content

Highlights

  • Salt Sensitivity prevention in Diabetes Mellitus.

  • Hypertension is an important risk factor for cardiovascular disease and mortality, characterized by a slow inflammation process.

  • Activation of Nrf-2 via eicosapentaenoic acid supplementation may be a strategy in diabetes mellitus to prevent renal oxidative stress generation and finally the development of Hypertension.

Abstract

Objectives

Salt sensitivity (SS) is associated with increased cardiovascular risk in patients with Type 2 diabetes mellitus (T2-DM) due to an increase in renal oxidation. ω-3 polyunsaturated fatty acids have shown antioxidant effects, but a typical Western diet contains limited content. In particular, ω-3 polyunsaturated fatty acids are able to activate nuclear factor erythroid 2-related factor 2 (Nrf-2) to prevent diabetes mellitus–related complications by mitigating oxidative stress. Therefore, we hypothesized that eicosapentaenoic acid (EPA; ω-3) modulates SS in rats with T2-DM by decreasing renal oxidative stress via Nrf-2 activation and enhancing the antiinflammatory response via interleukin (IL) 6 modulation.

Methods

Three-month-old male rats (n = 40) were fed with a Normal Na-diet (NNaD) and randomly selected into four groups: Healthy Wistar nondiabetic rats (Wi), diabetic controls (eSS), arachidonic acid-treated eSS (AA; ω-6), and EPA-treated eSS (ω-3). After 1 year, rats were placed in metabolic cages for 7 d and fed a NNaD, followed by a 7-d period with a High Na-diet (HNaD). Systolic blood pressure, body weight, serum IL-6 and reactive oxygen species (ROS) levels were determined at the end of each 7-d period. Glycated hemoglobin (HbA1c), triacylglycerol, creatinine, and cholesterol levels were determined. ROS levels and Nrf-2 expression in kidney lysates were also assayed. Histologic changes were evaluated. A t test or analysis of variance was used for the statistical analysis.

Results

After a HNaD, systolic blood pressure increased in both the control eSS and AA groups, but not in the EPA and Wi groups. However, HbA1c levels remained unchanged by the treatments, which suggests that the observed beneficial effect was independent of HbA1c levels. The IL-6 levels were higher in the eSS and AA groups, but remained unaltered in EPA and Wi rats after a HNaD diet. Interestingly, EPA protected against serum ROS in rats fed the HNaD, whereas AA did not. In kidney lysates, ROS decreased significantly in the EPA group compared with the eSS group, and Nrf-2 expression was consistently higher compared with the AA and eSS groups. Diabetic rats presented focal segmental sclerosis, adherence to Bowman capsule, and mild-to-moderate interstitial fibrosis. EPA and AA treatment prevented kidney damage.

Conclusions

An adequate ω3-to-ω6 ratio prevents SS in diabetic rats by a mechanism that is independent of glucose metabolism but associated with the prevention of renal oxidative stress generation. These data suggest that EPA antioxidant properties may prevent the development of hypertension or kidney damage.

Introduction

Diabetes mellitus (DM) is a major cause of death and disability worldwide and a strong risk factor for cardiovascular disease. In particular, diabetic nephropathy (DN) remains a significant problem despite efforts to limit its impact on end-organ damage. In a complex milieu where no single treatment can halt DN progression, interactions have been found between metabolic and hemodynamic factors involved in the development of renal lesions in patients with DM [1].

Salt sensitivity (SS), defined as an increase of >10% of blood pressure and secondary to sodium load, is one of the initial changes observed during the development of hypertension in DM. According to the classic concept by Guyton and Coleman [2], high salt intake increases a circulating volume, which leads to an increase in renal perfusion pressure, immediately followed by an increase in natriuresis that restores the circulating volume. This pressure-natriuresis mechanism prevents an increase in blood pressure (BP) that could arise from a transient increase of circulating volume. Thus, the deterioration of this mechanism increases the circulating volume and blood pressure leading to hypertension [3].

Several studies have reported the infiltration of macrophages and proinflammatory cells in the kidney at different stages of DN. The inflammatory infiltrate produces reactive oxygen species (ROS) and proinflammatory cytokines, which lead to an upregulation of chronic systemic inflammation and mediate DN progression [4]. As a consequence of the inflammation, various cytokines and acute phase proteins are released to augment or attenuate the inflammatory response. The main inflammatory cytokines involved in the development of DN are interleukin (IL) 6, as well as IL-1β, IL-18, and tumor necrosis factor-α that may contribute to the progression of renal injury, either directly or indirectly [5]. Thus, chronic inflammation of kidney tissue contributes to DN, not only as a consequence of a direct effect of proinflammatory mediators on cellular signaling, but also by creating a state of oxidative stress, and sodium reabsorption is increases under these conditions [6].

In recent years, substantial evidence has implicated nuclear factor erythroid 2-related factor 2 (Nrf2), a redox-sensitive transcription factor, in inflammation and associated disorders. In this setting, the therapeutic potential of Nrf2 activation in DM as relating to the control of oxidative stress has been described [7,8]. Chronic inflammation and oxidative stress contribute not only to DN development, but also to increased sodium reabsorption and enhancing circulatory volume [6], a condition associated with abnormal pressure natriuresis. It is widely believed that abnormal pressure natriuresis is the initial abnormality observed before the fully development of hypertension [9]. In this setting, the relative contribution of interindividual differences on the basis of genetic background, nutrition, physical activity, and other environmental factors has not been fully elucidated.

Understanding how these factors interact is necessary to tackle the global burden of hypertension triggered by DM. In particular, the pathophysiological effects of diets have drawn attention in response to the increasing worldwide adoption of the Western diet and the accompanying increase in the incidence rate of obesity, which is an associated outcome of DM [10]. Particularly, a high intake of ω-6 polyunsaturated fatty acids (PUFAs) and lower intake of ω-3 PUFAs, which is typical of a Western diet, exert several functions that play significant roles in inflammation, metabolism, and the regulation of intracellular processes. The supplementation of eicosapentaenoic acid (EPA 20:5, ω-3) especially is an important regulator of cardiovascular health because of the decrease in the levels of markers and mediators of inflammation, such as cytokines interleukin-1β and tumor necrosis factor α [11]. Therefore, we hypothesized that nutritional supplementation with EPA 20:5 ω-3 prevents the increase of blood pressure owing to sodium load in rats with Type 2 DM (T2-DM) by decreasing renal oxidative stress via Nrf2 activation and decreasing IL-6 release.

Section snippets

Experimental design

Diabetic rats (eSS) are a stable strain derived from Wistar rats a model of T2-DM that is characterized by fasting hyperglycemia, glucose intolerance, hyperinsulinemia, and early hypertriacylglycerolmia. Diabetic symptoms in this model worsen with age as insulin release decreases and closely resembles T2-DM in adult humans. eSS rats were kindly provided by Professors Tarres and Martinez from the University of Rosario in Argentina [12]. Three-month-old male Wistar (healthy control) or eSS rats

HNaD increased and EPA prevented blood systolic pressure in diabetic rats

Wi rats weighed 37% more than eSS rats of the same age; however, no difference was observed in basal SBP. As expected, rats with T2-DM showed higher HbA1c levels (+43%) compared with those in the Wi group. Additionally, the eSS group showed higher postprandial glucose, Chol, and TAG levels. All rats with T2-DM that were treated had lower serum lipid levels compared with those in the eSS group. Renal functions were similar between the groups. Table 1 shows the physiological parameters of each

Discussion

Our results show that EPA treatment minimized inflammation and oxidative stress in rats with T2-DM through Nrf2 activation during sodium load, which are effects associated with less glomerular sclerosis and less interstitial fibrosis. This effectively prevented SS observed in untreated diabetic rats and was independent of glucose homeostasis because HbA1c levels did not change. Particularly, EPA supplementation prevented the deleterious outcome by improving endothelial function and preventing

Conclusions

Overall, this study provides compelling evidence that adequate ω-3 supplementation can minimize inflammation as well as oxidative stress through Nrf2 activation in T2-DM after Na overload. EPA effectively prevented SS observed in untreated diabetic rats independent of glucose homeostasis because the HbA1c levels did not change. In particular, EPA supplementation did not present any deleterious effect because EPA improved endothelial function and thus prevented increased blood pressure in DM

Acknowledgments

The authors are grateful to Mr. Ricardo Mattos (Facultad de Ciencias Médicas, Universidad Nacional de Córdoba) and Clarisa Lagares (Consejo Nacional de Investigaciones Científicas y Técnicas) for animal care. Néstor H. Garcia acknowledges the support from the Consejo Nacional de Investigaciones Científicas y Técnicas.

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