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Magnesium deficiency stimulated mRNA expression of tumor necrosis factor-α in skeletal muscle of rats
Nutrition Research 27 (2007) 66 – 68 www.elsevier.com/locate/nutres
Communication
Magnesium deficiency stimulated mRNA expression of tumor necrosis factor-a in skeletal muscle of rats Tohru Matsui4, Hiroshi Kobayashi, Shizuka Hirai, Hiroyuki Kawachi, Hideo Yano Laboratory of Animal Nutrition, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8502, Japan Received 3 June 2006; revised 12 September 2006; accepted 21 September 2006
Abstract Tumor necrosis factor-a (TNF-a) has been known to induce insulin resistance in adipose tissue and skeletal muscle as a local and systemic factor. The objective of this study was to determine the effect of magnesium deficiency on mRNA expression of TNF-a in the tissues related to hypoglycemic action of insulin, such as skeletal muscle, adipose tissue, and liver, and on plasma TNF-a concentration. Twelve male rats were divided into 2 groups and given a magnesium-deficient diet or control diet for 4 weeks. Although magnesium deficiency did not affect the expression of TNF-a mRNA in liver and adipose tissue, magnesium deficiency increased TNF-a mRNA expression in skeletal muscle. Plasma TNF-a was higher in the magnesium-deficient diet group than in the control group, but the circulating TNF-a level was unlikely to be sufficient for causing insulin resistance in the magnesium-deficient rat. This study suggests that magnesium deficiency stimulates TNF-a production in skeletal muscle, which may cause local insulin resistance in rats. D 2007 Elsevier Inc. All rights reserved. Keywords:
Magnesium deficiency; Tumor necrosis factor-a; Skeletal muscle; Adipose tissue; Liver; Rat
1. Introduction Tumor necrosis factor-a (TNF-a) is a proinflammatory cytokine that is implicated in the pathogenesis of inflammatory disorders. In addition, adipose tissue produces large amounts of TNF-a in obese rodents and humans, which locally interferes with insulin-stimulated glucose uptake [1]. The expression of TNF-a in skeletal muscle was negatively correlated with insulin sensitivity in rats given a high fructose diet [2]. This result suggests that the increasing TNF-a production in skeletal muscle induces insulin resistance. Some studies on humans indicate that magnesium deficiency is associated with insulin resistance [3,4]. Magnesium deficiency was shown to induce insulin
4 Corresponding author. Tel.: +81 75 753 6056; fax: +81 75 753 6344. E-mail address: [email protected] (T. Matsui). 0271-5317/$ – see front matter D 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.nutres.2006.09.008
resistance in the hindquarter of rats, which might suggest that magnesium deficiency suppresses insulin sensitivity in skeletal muscle [5]. Suarez et al [6] found whole-body and muscular insulin resistance in magnesium-deficient rats. An in vitro experiment also showed that magnesium deficiency impaired insulin sensitivity in skeletal muscle of rats [7]. Plasma TNF-a concentration was increased by magnesium deficiency in rats [8]. Magnesium-deficient media stimulated the production of TNF-a in the cells derived from adipose tissue [9]. Thus, it is possible that the production of TNF-a locally and/or systemically impairs insulin sensitivity in magnesium-deficient animals. However, the effect of magnesium deficiency on production of TNF-a was not clarified in tissues related to the hypoglycemic action of insulin. In the present experiment, we investigated the expression of TNF-a mRNA in skeletal muscle, adipose tissue and liver, and plasma TNF-a concentration in magnesium-deficient rats.
T. Matsui et al. / Nutrition Research 27 (2007) 66–68
2. Methods and materials 2.1. Animals and diets All studies were performed with the approval of the Animal Care Committee at the Graduate School of Agriculture, Kyoto University, Kyoto, and conformed to the Guide for the Care and Use of Laboratory Animals (Kyoto University). Twelve male Sprague-Dawley rats aged 4 weeks were purchased from Japan SLC, Inc (Shizuoka, Japan). The rats were individually housed in metabolism cages in a room with controlled temperature (228C), relative humidity (60%), and lighting (a 12-hour light/dark cycle). They were allowed free access to diet and demineralized water throughout the experiment. The diets contained the following (in g/kg): casein 200, cornstarch 529.5, sucrose 100, corn oil 70, cellulose powder 50, mineral mixture (based on AIN-93G) with or without magnesium 35, vitamin mixture (AIN-93) 10, l-cystine 3, choline bitartrate 2.5. The concentration of magnesium was 507 and 43 mg/kg in the control and the magnesium-deficient diets, respectively. The control diet satisfied the magnesium requirement (500-mg/kg diet), and the magnesium-deficient diet contained magnesium at approximately 8% of the required level. Each rat was given the control diet for 1 week and then randomly divided into control and magnesium-deficient groups. Each group was given the corresponding diet for 4 weeks. 2.2. Sample collection Blood was collected from the ventral artery of the rat under diethyl ether anesthesia at the end of feeding period, and heparinized plasma was obtained. Plasma samples were stored at 808C until analyzed. Liver, perirenal adipose tissue, and musculi biceps femoris were collected after exsanguination. The tissue samples were immediately frozen in liquid nitrogen and stored at 808C until RNA isolation. 2.3. Analyses Magnesium concentration in diets and in plasma samples was determined as described by Takasugi et al [10]. Briefly, the diets and plasma samples were digested by concentrated nitric acid and perchloric acid. The acid-digested samples
67
were diluted by 0.1 mol/L nitric acid to appropriate concentration for measuring magnesium concentration using an inductively coupled plasma emission spectrometer (ICPS-1000II, Shimadzu, Kyoto, Japan). Plasma TNF-a concentration was determined by a commercial ELISA kit (rTNFa-US, Biosource, Calif, USA). Total RNAs were prepared from the tissues using TRIZOL reagent (Invitrogen, Calif, USA) according to the manufacturer’s instructions. The extracted RNA was dissolved in diethyl pyrocarbonate treated water, and RNA concentration was determined spectrophotometrically at 260 nm. Single-strand cDNA was synthesized using oligo (dT)12-18 and SuperScript II reverse transcriptase (Invitrogen) according to the manufacturer’s instructions. To quantify mRNA level, polymerase chain reaction (PCR) was performed using a quantitative real-time PCR system (LightCycler System, Roche Diagnostics, Mannheim, Germany). The oligonucleotide primer sets for rat TNF-a (GenBank accession number X66539) were forward (5V- CAGACCCTCACACTCAGATCA-3V) and reverse (5V-TCTCCTGGTATGAAGTGGCA-3V), and for rat glyceraldehyde-3-phosphate dehydrogenase (GAPDH, GenBank accession number X02231) were forward (5V-TGAACGGG A A G C TC A C T G G - 3V) an d r e v e r s e (5 V-TC C A C CACCCTGTTGCTGTA-3V). Amplification was performed according to the published protocols [11]. The expression of TNF-a mRNA was calculated as described by Takahashi et al [12]. Briefly, each PCR product, amplified from the mRNA of liver, was subcloned into pCRII-TOPO vector (Invitrogen) using as standard plasmid. The copy number of each standard plasmid was calculated from the absorbance at 260 nm and the molecular weight of each plasmid. Standard curves were calculated with the LightCycler software version 3 (Roche Diagnostics) using a 10-fold dilution series of standard plasmid DNAs. The copy number of each sample was obtained as the mean value of 4 replicated analyses compared to the standard curves. The expression of TNF-a mRNA was shown as the ratio of TNF-a copy number to GAPDH copy number. Data were expressed as means F SEM. The statistical difference between means was assessed with a 2-tailed Student t test using Excel (Microsoft Inc, Redmond, Wash, USA). Differences were considered significant at P b .05.
Fig. 1. Expression of tumor necrosis factor-a mRNA in liver, adipose tissue, and skeletal muscle of magnesium-deficient rats (V) or control rats (5). The copy number of TNF-a was multiplied by 1000 and was expressed as the ratio to that of GAPDH for each sample. Data are expressed as means F SEM for 6 rats. *Significantly different from control rats ( P b .01).
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T. Matsui et al. / Nutrition Research 27 (2007) 66–68
3. Results and discussion Plasma magnesium concentration was higher ( P b .05) in the control group (17.8 F 1.4 mg/L) compared with that in the magnesium-deficient group (4.8 F 1.6 mg/L). The magnesium-deficient group had hyperemia of ear in the present experiment (data not shown). The hyperemia of the ear is a clinical sign of magnesium deficiency in rats [13]. Although dietary magnesium did not affect TNF-a mRNA expression in adipose tissue and in liver, mRNA expression of TNF-a in skeletal muscle was significantly higher ( P b .01) in the magnesium-deficient group than in the control group (Fig. 1). A high fructose diet was reported to stimulate TNF-a production in skeletal muscle, which induced insulin resistance [2]. Some researchers showed that magnesium deficiency led to insulin resistance in skeletal muscles of rats [5,6]. Therefore, we propose that magnesium deficiency increases TNF-a production in skeletal muscle, which may cause local insulin-insensitivity. Plasma TNF-a concentration was significantly higher ( P b .05) in the magnesium-deficient group (10.5 F 1.1 pg/mL) than in the control group (4.8 F 1.6 pg/mL). These results were in accordance with a previous report [8]. The expression of TNF-a mRNA was remarkably lower in skeletal muscle than in the other tissues, irrespective of the dietary magnesium level. Although magnesium deficiency increased TNF-a mRNA expression in skeletal muscle, the magnesium-deficient group showed a 40-fold higher expression of TNF-a mRNA in liver and 4-fold higher expression in adipose tissue than in skeletal muscle. A previous study showed that TNF-a concentration was largely lower in skeletal muscles than in adipose tissue and liver of rats [14]. Therefore, it is unlikely that the upregulation of TNF-a mRNA in skeletal muscle can explain the high concentration of plasma TNF-a in magnesiumdeficient rats. Magnesium deficiency induces inflammatory responses in rats, and the inflammatory state is not restricted to localized tissue reactions [8]. Thus, magnesium deficiency results in generalized inflammatory state, which may increase plasma TNF-a concentration. Although obese mice had high plasma TNF-a level (20-200 pg/mL), the levels were still below that required to suppress insulin action in cultured adipocytes [15]. Furthermore, TNF-a caused whole body insulin resistance when circulating TNF-a level reached the range from 150 to 500 pg/mL [14]. We believe that the increasing level of plasma TNF-a is not sufficient for inducing insulin resistance in magnesium-deficient rats because plasma TNF-a concentration was 10 pg/mL in this group. Magnesium deficiency has been reported to induce whole-body insulin resistance in rats [6] and humans [3,4], which may result from local insulin insensitivity
induced by increasing TNF-a production in skeletal muscle and not by increasing TNF-a level in circulation. Reis et al [16] reported that magnesium deficiency did not affect insulin signaling in skeletal muscle of rats but enhanced insulin signaling in liver. Further studies are necessary to clarify whether the stimulation of TNF-a production in skeletal muscle decreases local and whole body insulin insensitivity in magnesium-deficient rats. References [1] Coppack SW. Pro-inflammatory cytokines and adipose tissue. Proc Nutr Soc 2001;60:349 - 56. [2] Togashi N, Ura N, Higashiura K, Murakami H, Shimamoto K. The contribution of skeletal muscle tumor necrosis factor-a to insulin resistance and hypertension in fructose-fed rats. J Hypertens 2000;18: 1605 - 10. [3] Huerta MG, Roemmich JN, Kington ML, Bovbjerg VE, Weltman AL, Holmes VF, et al. Magnesium deficiency is associated with insulin resistance in obese children. Diabetes Care 2005;28:1175 - 81. [4] Laires MJ, Moreira H, Monteiro CP, Sardinha L, Limao F, Veiga L, et al. Magnesium, insulin resistance and body composition in healthy postmenopausal women. J Am Coll Nutr 2004;23:510S - 3S. [5] Balon TW, Jasman A, Scott S, Meehan WP, Rude RK, Nadler JL. Dietary magnesium prevents fructose-induced insulin insensitivity in rats. Hypertension 1994;23:1036 - 9. [6] Suarez A, Pulido N, Casla A, Casanova B, Arrieta FJ, Rovira A. Impaired tyrosine-kinase activity of muscle insulin receptors from hypomagnesaemic rats. Diabetologia 1995;38:1262 - 70. [7] Stefikova K, Spustova V, Sebekova K, Dzurik R. Magnesium deficiency impairs rat soleus muscle glucose utilization and insulin sensitivity. Mater Med Pol 1992;24:215 - 6. [8] Weglicki WB, Phillips TM, Freedman AM, Cassidy MM, Dickens BF. Magnesium deficiency elevates circulating levels of inflammatory cytokines and endothelin. Mol Cell Biochem 1992;110:169 - 73. [9] Tchoukalova YD, Grider A, Mouat MF, Hausman GJ. Priming with magnesium-deficient media inhibits preadipocyte differentiation via potential upregulation of tumor necrosis factor-a. Biol Trace Elem Res 2000;74:11 - 21. [10] Takasugi S, Matsui T, Yano H. The effects of excess calcium as different form on mineral metabolism in rats. Anim Sci J 2005;76:469 - 74. [11] Rasmussen R. Quantification on the light cycler. In: Meuer S, Wittwer C, Nakagawara K, editors. Rapid Cycle Real-time PCR. Berlin7 Springer; 2001. p. 21 - 34. [12] Takahashi N, Kawada T, Goto T, Yamamoto T, Taimatsu A, Matsui N, et al. Dual action of isoprenols from herbal medicines on both PPARc and PPARa in 3T3-L1 adipocytes and HepG2 hepatocytes. FEBS Lett 2002;514:315 - 22. [13] Nishio A, Ishiguro S, Ikegaki I, Matsumoto S, Yoshimitsu F, Miyazaki A. Histamine metabolism and pinnal hyperaemia during magnesium deficiency in rats. Magnes Res 1988;1:155 - 61. [14] Borst SE, Bagby GJ. Adipose tumor necrosis factor-a is reduced during onset of insulin resistance in Sprague-Dawley rats. Cytokine 2004;26:217 - 22. [15] Hotamisligil GS, Shargill NS, Spiegelman BM. Adipose expression of tumor necrosis factor-a: direct role in obesity-linked insulin resistance. Science 1993;259:87 - 91. [16] Reis MA, Reyes FG, Saad MJ, Velloso LA. Magnesium deficiency modulates the insulin signaling pathway in liver but not muscle of rats. J Nutr 2000;130:133 - 8.
Communication
Magnesium deficiency stimulated mRNA expression of tumor necrosis factor-a in skeletal muscle of rats Tohru Matsui4, Hiroshi Kobayashi, Shizuka Hirai, Hiroyuki Kawachi, Hideo Yano Laboratory of Animal Nutrition, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8502, Japan Received 3 June 2006; revised 12 September 2006; accepted 21 September 2006
Abstract Tumor necrosis factor-a (TNF-a) has been known to induce insulin resistance in adipose tissue and skeletal muscle as a local and systemic factor. The objective of this study was to determine the effect of magnesium deficiency on mRNA expression of TNF-a in the tissues related to hypoglycemic action of insulin, such as skeletal muscle, adipose tissue, and liver, and on plasma TNF-a concentration. Twelve male rats were divided into 2 groups and given a magnesium-deficient diet or control diet for 4 weeks. Although magnesium deficiency did not affect the expression of TNF-a mRNA in liver and adipose tissue, magnesium deficiency increased TNF-a mRNA expression in skeletal muscle. Plasma TNF-a was higher in the magnesium-deficient diet group than in the control group, but the circulating TNF-a level was unlikely to be sufficient for causing insulin resistance in the magnesium-deficient rat. This study suggests that magnesium deficiency stimulates TNF-a production in skeletal muscle, which may cause local insulin resistance in rats. D 2007 Elsevier Inc. All rights reserved. Keywords:
Magnesium deficiency; Tumor necrosis factor-a; Skeletal muscle; Adipose tissue; Liver; Rat
1. Introduction Tumor necrosis factor-a (TNF-a) is a proinflammatory cytokine that is implicated in the pathogenesis of inflammatory disorders. In addition, adipose tissue produces large amounts of TNF-a in obese rodents and humans, which locally interferes with insulin-stimulated glucose uptake [1]. The expression of TNF-a in skeletal muscle was negatively correlated with insulin sensitivity in rats given a high fructose diet [2]. This result suggests that the increasing TNF-a production in skeletal muscle induces insulin resistance. Some studies on humans indicate that magnesium deficiency is associated with insulin resistance [3,4]. Magnesium deficiency was shown to induce insulin
4 Corresponding author. Tel.: +81 75 753 6056; fax: +81 75 753 6344. E-mail address: [email protected] (T. Matsui). 0271-5317/$ – see front matter D 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.nutres.2006.09.008
resistance in the hindquarter of rats, which might suggest that magnesium deficiency suppresses insulin sensitivity in skeletal muscle [5]. Suarez et al [6] found whole-body and muscular insulin resistance in magnesium-deficient rats. An in vitro experiment also showed that magnesium deficiency impaired insulin sensitivity in skeletal muscle of rats [7]. Plasma TNF-a concentration was increased by magnesium deficiency in rats [8]. Magnesium-deficient media stimulated the production of TNF-a in the cells derived from adipose tissue [9]. Thus, it is possible that the production of TNF-a locally and/or systemically impairs insulin sensitivity in magnesium-deficient animals. However, the effect of magnesium deficiency on production of TNF-a was not clarified in tissues related to the hypoglycemic action of insulin. In the present experiment, we investigated the expression of TNF-a mRNA in skeletal muscle, adipose tissue and liver, and plasma TNF-a concentration in magnesium-deficient rats.
T. Matsui et al. / Nutrition Research 27 (2007) 66–68
2. Methods and materials 2.1. Animals and diets All studies were performed with the approval of the Animal Care Committee at the Graduate School of Agriculture, Kyoto University, Kyoto, and conformed to the Guide for the Care and Use of Laboratory Animals (Kyoto University). Twelve male Sprague-Dawley rats aged 4 weeks were purchased from Japan SLC, Inc (Shizuoka, Japan). The rats were individually housed in metabolism cages in a room with controlled temperature (228C), relative humidity (60%), and lighting (a 12-hour light/dark cycle). They were allowed free access to diet and demineralized water throughout the experiment. The diets contained the following (in g/kg): casein 200, cornstarch 529.5, sucrose 100, corn oil 70, cellulose powder 50, mineral mixture (based on AIN-93G) with or without magnesium 35, vitamin mixture (AIN-93) 10, l-cystine 3, choline bitartrate 2.5. The concentration of magnesium was 507 and 43 mg/kg in the control and the magnesium-deficient diets, respectively. The control diet satisfied the magnesium requirement (500-mg/kg diet), and the magnesium-deficient diet contained magnesium at approximately 8% of the required level. Each rat was given the control diet for 1 week and then randomly divided into control and magnesium-deficient groups. Each group was given the corresponding diet for 4 weeks. 2.2. Sample collection Blood was collected from the ventral artery of the rat under diethyl ether anesthesia at the end of feeding period, and heparinized plasma was obtained. Plasma samples were stored at 808C until analyzed. Liver, perirenal adipose tissue, and musculi biceps femoris were collected after exsanguination. The tissue samples were immediately frozen in liquid nitrogen and stored at 808C until RNA isolation. 2.3. Analyses Magnesium concentration in diets and in plasma samples was determined as described by Takasugi et al [10]. Briefly, the diets and plasma samples were digested by concentrated nitric acid and perchloric acid. The acid-digested samples
67
were diluted by 0.1 mol/L nitric acid to appropriate concentration for measuring magnesium concentration using an inductively coupled plasma emission spectrometer (ICPS-1000II, Shimadzu, Kyoto, Japan). Plasma TNF-a concentration was determined by a commercial ELISA kit (rTNFa-US, Biosource, Calif, USA). Total RNAs were prepared from the tissues using TRIZOL reagent (Invitrogen, Calif, USA) according to the manufacturer’s instructions. The extracted RNA was dissolved in diethyl pyrocarbonate treated water, and RNA concentration was determined spectrophotometrically at 260 nm. Single-strand cDNA was synthesized using oligo (dT)12-18 and SuperScript II reverse transcriptase (Invitrogen) according to the manufacturer’s instructions. To quantify mRNA level, polymerase chain reaction (PCR) was performed using a quantitative real-time PCR system (LightCycler System, Roche Diagnostics, Mannheim, Germany). The oligonucleotide primer sets for rat TNF-a (GenBank accession number X66539) were forward (5V- CAGACCCTCACACTCAGATCA-3V) and reverse (5V-TCTCCTGGTATGAAGTGGCA-3V), and for rat glyceraldehyde-3-phosphate dehydrogenase (GAPDH, GenBank accession number X02231) were forward (5V-TGAACGGG A A G C TC A C T G G - 3V) an d r e v e r s e (5 V-TC C A C CACCCTGTTGCTGTA-3V). Amplification was performed according to the published protocols [11]. The expression of TNF-a mRNA was calculated as described by Takahashi et al [12]. Briefly, each PCR product, amplified from the mRNA of liver, was subcloned into pCRII-TOPO vector (Invitrogen) using as standard plasmid. The copy number of each standard plasmid was calculated from the absorbance at 260 nm and the molecular weight of each plasmid. Standard curves were calculated with the LightCycler software version 3 (Roche Diagnostics) using a 10-fold dilution series of standard plasmid DNAs. The copy number of each sample was obtained as the mean value of 4 replicated analyses compared to the standard curves. The expression of TNF-a mRNA was shown as the ratio of TNF-a copy number to GAPDH copy number. Data were expressed as means F SEM. The statistical difference between means was assessed with a 2-tailed Student t test using Excel (Microsoft Inc, Redmond, Wash, USA). Differences were considered significant at P b .05.
Fig. 1. Expression of tumor necrosis factor-a mRNA in liver, adipose tissue, and skeletal muscle of magnesium-deficient rats (V) or control rats (5). The copy number of TNF-a was multiplied by 1000 and was expressed as the ratio to that of GAPDH for each sample. Data are expressed as means F SEM for 6 rats. *Significantly different from control rats ( P b .01).
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T. Matsui et al. / Nutrition Research 27 (2007) 66–68
3. Results and discussion Plasma magnesium concentration was higher ( P b .05) in the control group (17.8 F 1.4 mg/L) compared with that in the magnesium-deficient group (4.8 F 1.6 mg/L). The magnesium-deficient group had hyperemia of ear in the present experiment (data not shown). The hyperemia of the ear is a clinical sign of magnesium deficiency in rats [13]. Although dietary magnesium did not affect TNF-a mRNA expression in adipose tissue and in liver, mRNA expression of TNF-a in skeletal muscle was significantly higher ( P b .01) in the magnesium-deficient group than in the control group (Fig. 1). A high fructose diet was reported to stimulate TNF-a production in skeletal muscle, which induced insulin resistance [2]. Some researchers showed that magnesium deficiency led to insulin resistance in skeletal muscles of rats [5,6]. Therefore, we propose that magnesium deficiency increases TNF-a production in skeletal muscle, which may cause local insulin-insensitivity. Plasma TNF-a concentration was significantly higher ( P b .05) in the magnesium-deficient group (10.5 F 1.1 pg/mL) than in the control group (4.8 F 1.6 pg/mL). These results were in accordance with a previous report [8]. The expression of TNF-a mRNA was remarkably lower in skeletal muscle than in the other tissues, irrespective of the dietary magnesium level. Although magnesium deficiency increased TNF-a mRNA expression in skeletal muscle, the magnesium-deficient group showed a 40-fold higher expression of TNF-a mRNA in liver and 4-fold higher expression in adipose tissue than in skeletal muscle. A previous study showed that TNF-a concentration was largely lower in skeletal muscles than in adipose tissue and liver of rats [14]. Therefore, it is unlikely that the upregulation of TNF-a mRNA in skeletal muscle can explain the high concentration of plasma TNF-a in magnesiumdeficient rats. Magnesium deficiency induces inflammatory responses in rats, and the inflammatory state is not restricted to localized tissue reactions [8]. Thus, magnesium deficiency results in generalized inflammatory state, which may increase plasma TNF-a concentration. Although obese mice had high plasma TNF-a level (20-200 pg/mL), the levels were still below that required to suppress insulin action in cultured adipocytes [15]. Furthermore, TNF-a caused whole body insulin resistance when circulating TNF-a level reached the range from 150 to 500 pg/mL [14]. We believe that the increasing level of plasma TNF-a is not sufficient for inducing insulin resistance in magnesium-deficient rats because plasma TNF-a concentration was 10 pg/mL in this group. Magnesium deficiency has been reported to induce whole-body insulin resistance in rats [6] and humans [3,4], which may result from local insulin insensitivity
induced by increasing TNF-a production in skeletal muscle and not by increasing TNF-a level in circulation. Reis et al [16] reported that magnesium deficiency did not affect insulin signaling in skeletal muscle of rats but enhanced insulin signaling in liver. Further studies are necessary to clarify whether the stimulation of TNF-a production in skeletal muscle decreases local and whole body insulin insensitivity in magnesium-deficient rats. References [1] Coppack SW. Pro-inflammatory cytokines and adipose tissue. Proc Nutr Soc 2001;60:349 - 56. [2] Togashi N, Ura N, Higashiura K, Murakami H, Shimamoto K. The contribution of skeletal muscle tumor necrosis factor-a to insulin resistance and hypertension in fructose-fed rats. J Hypertens 2000;18: 1605 - 10. [3] Huerta MG, Roemmich JN, Kington ML, Bovbjerg VE, Weltman AL, Holmes VF, et al. Magnesium deficiency is associated with insulin resistance in obese children. Diabetes Care 2005;28:1175 - 81. [4] Laires MJ, Moreira H, Monteiro CP, Sardinha L, Limao F, Veiga L, et al. Magnesium, insulin resistance and body composition in healthy postmenopausal women. J Am Coll Nutr 2004;23:510S - 3S. [5] Balon TW, Jasman A, Scott S, Meehan WP, Rude RK, Nadler JL. Dietary magnesium prevents fructose-induced insulin insensitivity in rats. Hypertension 1994;23:1036 - 9. [6] Suarez A, Pulido N, Casla A, Casanova B, Arrieta FJ, Rovira A. Impaired tyrosine-kinase activity of muscle insulin receptors from hypomagnesaemic rats. Diabetologia 1995;38:1262 - 70. [7] Stefikova K, Spustova V, Sebekova K, Dzurik R. Magnesium deficiency impairs rat soleus muscle glucose utilization and insulin sensitivity. Mater Med Pol 1992;24:215 - 6. [8] Weglicki WB, Phillips TM, Freedman AM, Cassidy MM, Dickens BF. Magnesium deficiency elevates circulating levels of inflammatory cytokines and endothelin. Mol Cell Biochem 1992;110:169 - 73. [9] Tchoukalova YD, Grider A, Mouat MF, Hausman GJ. Priming with magnesium-deficient media inhibits preadipocyte differentiation via potential upregulation of tumor necrosis factor-a. Biol Trace Elem Res 2000;74:11 - 21. [10] Takasugi S, Matsui T, Yano H. The effects of excess calcium as different form on mineral metabolism in rats. Anim Sci J 2005;76:469 - 74. [11] Rasmussen R. Quantification on the light cycler. In: Meuer S, Wittwer C, Nakagawara K, editors. Rapid Cycle Real-time PCR. Berlin7 Springer; 2001. p. 21 - 34. [12] Takahashi N, Kawada T, Goto T, Yamamoto T, Taimatsu A, Matsui N, et al. Dual action of isoprenols from herbal medicines on both PPARc and PPARa in 3T3-L1 adipocytes and HepG2 hepatocytes. FEBS Lett 2002;514:315 - 22. [13] Nishio A, Ishiguro S, Ikegaki I, Matsumoto S, Yoshimitsu F, Miyazaki A. Histamine metabolism and pinnal hyperaemia during magnesium deficiency in rats. Magnes Res 1988;1:155 - 61. [14] Borst SE, Bagby GJ. Adipose tumor necrosis factor-a is reduced during onset of insulin resistance in Sprague-Dawley rats. Cytokine 2004;26:217 - 22. [15] Hotamisligil GS, Shargill NS, Spiegelman BM. Adipose expression of tumor necrosis factor-a: direct role in obesity-linked insulin resistance. Science 1993;259:87 - 91. [16] Reis MA, Reyes FG, Saad MJ, Velloso LA. Magnesium deficiency modulates the insulin signaling pathway in liver but not muscle of rats. J Nutr 2000;130:133 - 8.