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Nutzen-Risiko-Bewertung von Mineralstoffen und Spurenelementen

 | 
Andrea Hartwig
, 
Beate Köberle
, 
Bernhard Michalke

Posterbeiträge

Influence of selenium deficiency and sulforaphane on lipid metabolism in growing rats

Nicole M. Blum, Kristin Mueller et Andreas S. Mueller

Entrées d'index

Note de l’éditeur

Running title: Selenium deficiency and lipid metabolism

Texte intégral

Introduction

1In recent years the trace element selenium (Se) was subject to a critical discussion regarding its role in lipid metabolism and diabetes. Some studies with animal models have shown positive effects of Se in the treatment of obesity, diabetes and hyperlipidemia. However, only high supranutritive selenate concentrations were effective [1, 2]. More recent studies in humans have shown that a high selenium status is associated with hyperlipidemia, including both increased cholesterol (Chol) and increased triglycerides (TG) [3, 4]. In contrast, data of our group revealed that feeding a Se deficient diet to rats reduced liver TG and Chol compared to their companions fed diets with adequate or slightly supranutritive Se [5, 6].

2One very recent investigation suggested beneficial effects of sulforaphane (SFN), the main isothiocyanate in broccoli, on cholesterol metabolism in hamsters [7]. Furthermore, the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which can be activated via SFN, seems to be a negative regulator of lipid synthesis [8].

3Consequently the aim of our study was to investigate if SFN can counteract negative effects of Se supplementation on lipid metabolism in a similar manner like Se deficiency.

Materials and Methods

Rats and diets

428 weaned albino rats (initial body weight: 63.1 ± 1.25 g) were divided into 4 groups of 7. The basal diet was a high fat diet (20% lard, 0.15% cholesterol) with 1.5% methionine. The rats of the positive control group (PC) were fed a Se deficient diet. The diets of the other 3 groups (NC = negative control, SFN50, SFN100) contained 150 µg Se/kg. The rats of groups SFN50 and SFN100 received 2 single oral SFN doses of 50 µmol SFN and 100 µmol SFN 2 days before the end of the experiment. After 6 weeks of feeding, the animals were decapitated under CO2 anesthesia for blood and organ sampling.

TG and Chol concentration in liver and plasma

5TG and Chol concentration in liver and plasma were analyzed photometrically using commercial test kits (DiaSys Diagnostic Systems GmbH, Germany).

Relative mRNA concentration of ABCG8 and LDLR

6Liver RNA was extracted using the acid guanidinium thiocyanate-phenolchloroform extraction method [9]. Reverse transcription of 1.2 µg of total RNA and real-time RT-PCR of ABCG8 and LDLR were performed as described previously [10]. Amplification data were analysed with the Rotor-Gene 6000™ series software using the ΔΔCt method [11]. For normalization the mean value of β-Actin and Rpl13a expression was used. Relative mRNA expression levels are expressed as x-fold changes relative to group PC = 1.0.

Statistical anaylsis

7The data were analysed by one-way ANOVA using the SPSS Statistics Package 19.0 for Windows.

Results

8Liver TG were significantly lower in Se deficient PC rats than in the Se sufficient NC group and in group SFN50 (Figure 1A). Liver Chol was reduced in Se deficient rats (PC) compared to all other groups (Figure 1B). SFN administration did not influence liver Chol concentration compared to the Se-sufficient control group NC. Plasma TG concentration was significantly reduced in group SFN100 compared to all other groups (Figure 1C). Plasma Chol was lower in tendency in SFN50 rats and in SFN100 rats than in both control groups (Figure 1D).

Figure 1 (A-D): Total Chol and TG concentrations in liver (A, B) and plasma (C, D). Values are means ± SEM. Different small letters indicate significant differences between means (p ≤ 0.05).

9SFN treatment at both concentrations increased relative liver LDLR mRNA concentration about 1.5-fold compared to PC and NC rats (Figure 2). Liver ABCG8 mRNA expression was about 2 to 4-fold higher in groups PC, SFN50 and SFN100 than in NC rats.

Figure 2: Relative mRNA concentrations of LDLR and ABCG8 in the liver. Values are means ± SEM. Different small letters indicate significant differences between means (p ≤ 0.05).

Discussion

10The aim of our study was to investigate if SFN can counteract negative effects of Se supplementation on lipid metabolism in a similar manner like Se deficiency. Our results confirmed the findings of previous studies that Se deficiency decreases TG [6] and Chol [5] in the liver. In contrast to Se deficiency, SFN efficiently reduced TG and Chol in the plasma but not in the liver. A reason for the missing effect of Se deficiency on plasma TG and Chol could be the lower mRNA level of LDLR and the subsequent lowered import of Chol into the liver. Simultaneously the export of Chol from the liver by ABCG8 was similar between the Se deficient rats and the SFN supplemented groups. To explain the strong effect of SFN on plasma TG further analysis are needed.

Bibliographie

References

[1] Mueller AS, Pallauf J. Compendium of the antidiabetic effects of supranutritional selenate doses. In vivo and in vitro investigations with type II diabetic db/db mice. J Nutr Biochem. 2006; 17: 548-560.

[2] Mueller AS, Pallauf J, Rafael J. The chemical form of selenium affects insulinomimetic properties of the trace element: investigations in type II diabetic dbdb mice. J Nutr Biochem. 2003; 14: 637-647.

[3] Bleys J, Navas-Acien A, Stranges S, Menke A, Miller ER 3rd, Guallar E. Serum selenium and serum lipids in US adults. Am J Clin Nutr. 2008; 88: 416-423.

[4] Stranges S, Laclaustra M, Ji C, Cappuccio FP, Navas-Acien A, Ordovas JM, Rayman M, Guallar E. Higher selenium status is associated with adverse blood lipid profile in British adults. J Nutr. 2010; 140: 81-87.

[5] Wolf NM, Mueller K, Hirche F, Most E, Pallauf J, Mueller AS. Study of molecular targets influencing homocysteine and cholesterol metabolism in growing rats by manipulation of dietary selenium and methionine concentrations. Br J Nutr. 2010; 104: 520-532.

[6] Mueller AS, Klomann SD, Wolf NM, Schneider S, Schmidt R, Spielmann J, Stangl G, Eder K, Pallauf J. Redox regulation of protein tyrosine phosphatase 1B by manipulation of dietary selenium affects the triglyceride concentration in rat liver. J Nutr. 2008; 138: 2328-2336.

[7] Rodríguez-Cantú LN, Gutiérrez-Uribe JA, Arriola-Vucovich J, Díaz-De La Garza RI, Fahey JW, Serna-Saldivar SO. Broccoli ( Brassica oleracea var. italica) sprouts and extracts rich in glucosinolates and isothiocyanates affect cholesterol metabolism and genes involved in lipid homeostasis in hamsters. J Agric Food Chem. 2011; 59: 1095-1103.

[8] Vomhof-Dekrey EE, Picklo MJ Sr. The Nrf2-antioxidant response element pathway: a target for regulating energy metabolism. J Nutr Biochem. 2012 Jul 20. [Epub ahead of print].

[9] Chomczynski P, Sacchi N. The single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction: twenty-something years on. Nat Protoc. 2006 1: 581-585.

[10] Blum NM, Mueller K, Hirche F, Lippmann D, Most E, Pallauf J, Linn T, Mueller AS. Glucoraphanin does not reduce plasma homocysteine in rats with sufficient Se supply via the induction of liver ARE-regulated glutathione biosynthesis enzymes. Food Funct. 2011; 2: 654-664.

[11] Livak KJ, Schmittgen TD. Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method. Methods. 2001; 25: 402-408.

Table des illustrations

Légende Figure 1 (A-D): Total Chol and TG concentrations in liver (A, B) and plasma (C, D). Values are means ± SEM. Different small letters indicate significant differences between means (p ≤ 0.05).
URL http://books.openedition.org/ksp/docannexe/image/183/img-1.jpg
Fichier image/jpeg, 184k
Légende Figure 2: Relative mRNA concentrations of LDLR and ABCG8 in the liver. Values are means ± SEM. Different small letters indicate significant differences between means (p ≤ 0.05).
URL http://books.openedition.org/ksp/docannexe/image/183/img-2.jpg
Fichier image/jpeg, 106k

Auteurs

Institution: Martin Luther University Halle Wittenberg, Institute of Agricultural and Nutritional Sciences, Preventive Nutrition Group, Von-Danckelmann-Platz 2, 06120 Halle (Saale), Germany

Institution: Martin Luther University Halle Wittenberg, Institute of Agricultural and Nutritional Sciences, Preventive Nutrition Group, Von-Danckelmann-Platz 2, 06120 Halle (Saale), Germany

Institution: Martin Luther University Halle Wittenberg, Institute of Agricultural and Nutritional Sciences, Preventive Nutrition Group, Von-Danckelmann-Platz 2, 06120 Halle (Saale), Germany
Email: andreas.mueller@landw.uni-halle.de

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