Importance of Magnesium in Nutrient Metabolism

Bull. Soc. Sea Water Sci., Jpn., 64, 202–210 (2010)Bulletin of the Society of Sea Water Science, Japan

Special Issue: Nutritional Research on Magnesium in Foods, with a Focus on “Nigari” (General Review)

Importance of Magnesium in Nutrient MetabolismMariko Uehara ＊1, Tomoko Ishijima ＊2, Ichiro Matsumoto ＊2, Shinji Okada ＊2, Soichi Arai ＊3, Keiko Abe ＊2, Shin-ichi Kasumata ＊1, Hiroshi Matsuzaki ＊4, Kazuharu Suzuki ＊1

Magnesium (Mg) is essential for a wide range of physiological functions because it participates in numerous biochemical processes within the body. Mg deficiency, whether due to insufficient intake or excessive excretion, is often suspected to contribute to the development of various symptoms and diseases. The nutritional and physiological significance of Mg has been well established. Mg has been recognized as particularly effective in preventing several conditions, including cardiovascular disease and metabolic disorders such as obesity, diabetes, and hypertension. Recent studies and meta-analyses have confirmed these findings. Moreover, multiple studies have reported the effects of Mg deficiency on the metabolism of carbohydrates, lipids, proteins, vitamins, and minerals. This review discusses the effects of dietary Mg deficiency on proteins, lipids, ascorbic acid, and mineral metabolism, including kidney calcification and bone loss in rodents. Additionally, we performed transcriptome analyses using DNA microarrays to comprehensively understand the impact of dietary Mg deficiency in rat livers and femora.

Keywords: Magnesium, Protein, Lipid, Ascorbic Acid, DNA Microarray

1. Introduction

Magnesium (Mg) is an essential mineral for the body, indispensable for life-sustaining biochemical reactions. In particular, Mg is required as a cofactor in the phosphate transfer reactions involved in adenosine triphosphate (ATP) synthesis and utilization during energy metabolism (Fig.1)¹. Mg is also crucial in glycolysis², the activity of ion pumps and excitable cells such as neurons and muscles¹,³, and intracellular signal transduction⁴. Mg deficiency, which compromises these life-supporting functions, is known to manifest in various clinical symptoms. Epidemiological and clinical studies investigating Mg intake, serum Mg levels, and disease occurrence have indicated that Mg intake reduces the risk of developing conditions such as diabetes, hypertension, metabolic syndrome, acute ischemic events, and myocardial infarction⁵–⁷. Numerous reports have examined Mg deficiency and its relationship to the metabolism of the five major nutrients. This review summarizes, mainly from the authors’ previous work using experimental animals, the relationships between Mg deficiency and the metabolism of proteins, lipids, ascorbic acid, and other minerals, particularly phosphorus (P). It also provides an overview of comprehensive gene expression analysis in Mg-deficient rat livers and bones using DNA microarrays.

2. Magnesium Deficiency and Protein Metabolism

Mg deficiency reduces food intake and body weight gain, thereby inhibiting growth in rats. This growth inhibition—i.e., weight loss due to Mg deficiency—occurs even when Mg-sufficient rats are restricted to match the food intake of Mg-deficient rats, suggesting impaired protein metabolism under Mg deficiency. Juvenile male rats were divided into two groups: a Mg-normal diet (C) group and a Mg-deficient diet (MD) group based on AIN-93G purified diet. Observations were made over 28 days. Half of the Mg-deficient group was switched to a Mg-normal diet to create a recovery (R) group for 7 or 14 days. After 28 days, the MD group showed reduced final body weight, weight gain, and feed efficiency (Fig.2), as well as lower Mg absorption, retention, and serum Mg levels. Urinary nitrogen excretion increased, while nitrogen retention and serum albumin decreased (Fig.3). In the recovery group, Mg absorption, retention, and serum Mg levels increased, but body weight and feed efficiency remained lower than in the MD group (Fig.2). Nitrogen retention improved by day 14, and serum albumin increased by days 7 and 14 (Fig.3). These results suggest that Mg deficiency impairs protein utilization, and while partial recovery occurs with Mg-normal diets, growth delay is not fully reversed within 14 days.

3. Magnesium Deficiency and Lipid Peroxidation

Mg deficiency also affects lipid metabolism, leading to tissue damage associated with lipid peroxidation of cellular membranes¹⁰–¹². In Mg-deficient animals, increased levels of thiobarbituric acid reactive substances (TBARS), indicative of malondialdehyde (MDA) formation, have been observed, though the details of oxidative damage remain unclear. The authors investigated changes in phosphatidylcholine hydroperoxide (PCOOH) and phosphatidylethanolamine hydroperoxide (PEOOH), primary lipid peroxidation products, in relation to tissue Mg, calcium (Ca), iron (Fe), and copper (Cu) distribution.

4. Ascorbic Acid Supplementation in Mg Deficiency and Lipid Metabolism

Hus et al.¹⁸ reported reduced liver ascorbic acid (AsA) levels in Mg-deficient rats. AsA plays a critical role in many biological reactions and acts as an antioxidant, cooperating with α-tocopherol. Reduced liver AsA due to Mg deficiency may contribute to lipid peroxidation in Mg-deficient rats. The authors hypothesized that Mg-deficient rats have an increased AsA requirement and investigated the effects of AsA supplementation. Juvenile male rats were divided into three groups: Mg-normal diet (control), Mg-deficient diet, and Mg-deficient diet with AsA supplementation, observed over 42 days.

Mg deficiency increased liver Fe concentrations, which can initiate lipid peroxidation via Fenton or Haber-Weiss reactions. Two mechanisms were suggested:

1. Mg deficiency enhances Fe absorption in the intestine.

2. Hemolysis releases Fe from hemoglobin.

A positive correlation between Fe and PCOOH in the liver (r=0.837, p=0.001) and heart (r=0.780, p=0.003) was observed (Fig.4). Mg deficiency is linked to cardiovascular disease, partially via increased intracellular Ca leading to lipid peroxidation. AsA supplementation normalized serum AsA levels and suppressed PCOOH increase.

Mg deficiency also alters lipoprotein metabolism, increasing VLDL and decreasing HDL, partly due to Mg’s role in lecithin-cholesterol acyltransferase (LCAT) activation. Mg deficiency further increases triacylglycerol (TG) in lipoproteins while reducing apoprotein content. AsA plays a role in cholesterol metabolism; its deficiency or secondary reduction in Mg-deficient animals can impair cholesterol catabolism. In the study, AsA normalized liver cholesterol and TG but did not affect serum levels.

5. Magnesium Deficiency and Kidney Calcification

Mg deficiency impacts other mineral metabolism. Renal calcification is a typical example. Previous studies reported increased kidney Ca and P in Mg-deficient rats, though results varied based on dietary P levels. Using AIN-93G diets with P levels of 3, 5, or 7 g/kg, the authors confirmed that kidney calcification occurred at 5-P and 7-P but not 3-P, indicating dietary P is a critical factor in Mg deficiency-induced nephrocalcinosis (Table 2).

Table 1　 Changes of serum AsA, PCOOH, TG and TC and liver TG and TC in control rats (C), Mg-defi cient rats (D) and Mg-defi cientrats supplemented with AsA (DA).

Table 2　Kidney mineral concentration and degree of nephrocalcinosis in rats fed on six experimental diets. Normal-Mg diet Mg-defi cient diet

6. DNA Microarray Analysis of Liver and Femur in Magnesium-Deficient Rats

Background

As described in the previous section, magnesium (Mg) deficiency induces significant changes in nutrient metabolism. However, a comprehensive understanding of the relationship between these biochemical changes and the associated alterations in gene expression has not yet been achieved. Therefore, we aimed to clarify the overall regulatory mechanisms of metabolism by performing a comprehensive analysis of gene expression changes related to physiological functions under Mg-deficient conditions using DNA microarrays.

Methods

• Young male rats were fed an Mg-deficient diet (AIN-93G composition without Mg oxide) for 28 days.

• A control group received normal Mg supplementation. To account for reduced food intake in the Mg-deficient group, a pair-fed control group was used.

• RNA was extracted from the livers of three animals per group with similar body weights, purified, and converted to cDNA and cRNA. These were hybridized onto a GeneChip Rat Genome Array 230 2.0 containing 31,099 probes.

• After staining and scanning, GeneChip Operating Software (GCOS) was used for single analysis (quantification of fluorescence signals), scatter plot generation, Pearson correlation, and cluster analysis (Fig. 5).

• A separate set of animals was fed an Mg-deficient diet for 35 days (MD35 group), with normal Mg-fed (C35) and recovery (R) groups, where rats were fed Mg-deficient diet for 28 days followed by 7 days of normal diet. Analysis was performed in the same manner.

• Femurs were collected after 6 weeks of Mg-deficient feeding, RNA was extracted, and DNA microarray analysis was performed.

• Statistical analysis: From 31,042 normalized probes, 13,729 probes not expressed in ≥2 samples per group were excluded. 1,144 probes with ≥2-fold changes were analyzed using GeneSpring GX7.3 (Agilent Technologies), log-transformed, and Student t-tests were conducted with FDR < 0.05 considered significant. For recovery analysis, probes showing significant changes in both 28- and 35-day Mg-deficient diets were used. One-way ANOVA followed by Tukey’s multiple comparison test was applied for significant probes.

• Gene ontology (GO) analysis was used to classify genes showing changes, and Fisher’s exact test (P < 0.05) was applied to identify enriched functional categories.

Results – Liver

• Mg deficiency caused extensive changes in hepatic gene expression. Of 31,099 probes, 734 showed ≥2-fold significant changes.

• Affected genes were involved in carbohydrate, lipid, protein/amino acid, vitamin, and nucleotide metabolism, xenobiotic detoxification, immune response, transport, cell proliferation, and transcriptional regulation (Table 3).

• Carbohydrate metabolism: Mg deficiency increased expression of genes in the pentose phosphate pathway and decreased glycogen synthase expression.

• Lipid metabolism: Genes involved in fatty acid synthesis and long-chain fatty acid transport were upregulated, while β-oxidation in mitochondria/peroxisomes and cholesterol catabolism genes were downregulated.

• Transcription factors: SREBP-1 expression increased, while PPARα decreased, affecting downstream target genes; this change had not been reported previously.

• Protein metabolism: Ubiquitin–proteasome-related proteolysis genes were upregulated, whereas translation initiation-related genes were downregulated.

• Amino acid metabolism: Genes related to cysteine synthesis, glycine, cystine, and cysteine degradation were upregulated, suggesting a decrease in total body protein, potentially contributing to reduced body weight gain and growth suppression.

• Comparison of 28- and 35-day Mg-deficient feeding showed no major differences in liver gene expression patterns, suggesting that prolonged Mg deficiency maintains a relatively stable altered state. Approximately 50% of genes with significant expression changes were common to both periods (Fig. 6).

• Genes affected by Mg deficiency were particularly enriched in lipid metabolism, with the 35-day group showing stronger effects.

Recovery Analysis

• After 28 days of Mg-deficient feeding, switching to normal diet for 7 days restored gene expression patterns closer to normal levels (Fig. 7).

• About 80% of genes significantly altered by Mg deficiency returned to normal expression levels. However, some genes either did not fully recover or overshot normal levels.

• Functional analysis showed that immune-related genes were slower to respond to dietary Mg restoration, whereas genes involved in cell division responded more rapidly.

• Overall, liver gene expression related to nutrient metabolism is dynamically regulated by dietary Mg levels.

Femur

• Mg-deficient rats showed previously reported decreases in bone density and strength, along with altered bone metabolism markers.

• DNA microarray analysis of femur RNA showed fewer and smaller expression changes compared to liver. Only genes with ≥1.5-fold changes were considered.

• Notable changes included:

  • Ca sensing receptor (CaSR, Casr): 3.7-fold increase; Mg acts as a CaSR agonist, and Mg deficiency may elevate intracellular Ca²⁺, potentially promoting osteoclast differentiation via NFATc1 activation.

  • Tnfrsf6: 1.8-fold increase; as a TNF receptor family member, upregulation may contribute to Mg deficiency-induced bone resorption.

  • BMP-related genes: Bmp2k and Gdf10 decreased (~1.5-fold), while Bmper-predicted increased 4.3-fold.

  • PKC family (pkcb) decreased ~2-fold; Cox-VIC-1 increased ~2-fold; Camk2b increased 1.5-fold; Camk2d decreased ~1.6-fold.

• Other bone metabolism regulators (RANKL, OPG, TGF, IL, IGF families) showed no significant changes.

• Overall, Mg deficiency had less pronounced effects on femoral gene expression than in liver, though some genes related to Ca sensing, bone formation, and resorption were affected.

Fig.5　 Scatter plotting (A), and Peason’s correlation coeffi cient analysis and cluster analysis (B)Gene expression differences were observed to a greater or lesser extent between the control (C) and the Mg-defi cient (MD) group.

Table 3　Signifi cant classifi cation of up-and down regulated genes by dietary magnesium-defi ciency Metabolism Up Down Total Functions Up Down Total

Proteins 28 23 51 Transcription 16 27 43

Carbohydrates 5 10 15 Immune Response 18 ＊ 9 27

Lipids 19＊＊ 18 37＊＊ Nerve system 10 11 21

Amino Acids 3 6 9 Circadian Rhythm 1 5 6

Vitamins 3 2 5 Transport 25 31 56

Cofactors 2 7 9 Cell Proliferation 11 8 19

DNA 3 3 6 Cell Death 13 5 18

Nucleotide 3 2 5 Cell Cycle 12 5 17

Active Oxygens 2 3 5 Cell Growth 5 4 9

Xenobiotic detoxication 1 4 5 Cell Division 6 ＊ 2 8

Cell Homeostasis 4 3 7

＊ p ＜ 0.05, ＊＊ p ＜ 0.01 in Fisher’s exact test

Fig.6　 Changed gene expressions by feeding Mg-defi cient diet

for 28 or 35 days

7. Conclusion

• Magnesium is essential for life and plays a crucial role in nutrient metabolism.

• Comprehensive DNA microarray analysis revealed that Mg deficiency induces changes in enzyme and transcription factor gene expression, explaining many observed biochemical and physiological phenomena.

• These findings provide further scientific evidence supporting the role of Mg intake in reducing lifestyle-related disease risks.

Acknowledgments

• Section 6 of this review is based on research supported by the Salt Science Research Foundation. The authors gratefully acknowledge this support.

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Received July 2, 2010.

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Bull. Soc. Sea Water Sci., Jpn., 64, 202 － 210（2010） B