The term micronutrients encompasses a wide range of vitamins and trace elements. For the purposes of this review, we will focus on genetic variants that affect folate, selenium, zinc and carotenoid metabolism.
Hyperhomocysteinemia is now regarded as an independent risk factor in the development of cerebrovascular and coronary heart disease as well as venous thrombosis . Methylenetetrahydrofolate reductase (MTHFR) is a key regulatory enzyme in folate and homocysteine metabolism, and the C677T (Ala222Val) variant has become recognized as the most common genetic factor associated with hyperhomocysteinemia and reduced folate concentrations [3,5•]. However, another common MTHFR variant, A1298C (Glu3Ala), also affects the enzyme activity and interacts with the C677T polymorphism . Although MTHFR is certainly the best characterized candidate gene within the homocysteine-related metabolic pathway, more recent studies have also reported variants in methionine synthase (MTR; A2756G), MTR reductase (MTRR; A66G), cystathionine β-synthase (68 bp insertion at base 844) and transcobalamin (TCN2; C776G) [5•]. Combinations of genotypes can act together to increase the risk of disease, and in relation to blood levels of homocysteine, the presence of the MTRR 66 G allele has been reported to increase the effect of MTHFR 677 TT [5•]. It is reasonable to believe that other gene–gene interactions are involved in the regulation of serum homocysteine concentration; however, further large-scale studies are needed to investigate them [4,5•].
It is well known that a SNP within the coding region of the gene encoding the selenoprotein glutathione peroxidase 1 leads to an amino-acid change (Pro to Leu) that leads to lower enzyme activity . Although some disease association studies suggest that the Leu variant increases susceptibility to lung, breast and bladder cancer, possibly when combined with the influence of either a SNP in the gene encoding the antioxidant defense protein manganese superoxide dismutase or environmental factors such as alcohol consumption and smoking [14,15,16•], no direct demonstration of altered function in vivo has been demonstrated.
Recently, three SNPs in regulatory regions of selenoprotein genes have been shown to have functional consequences (see Table 1). In the promoter region of the GPx3 gene, there are eight linked variants in two haplotype groups, and gene reporter studies have suggested differences in promoter activity between the two haplotypes . An SNP within the region of the GPx4 gene corresponding to the 3′UTR at position 718 (rs713041) was found in Caucasians a few years ago , but recently evidence has accumulated to indicate that this SNP is functionally significant. Reporter gene studies in transfected cells have shown that the C variant promotes reporter gene activity, presumably reflecting greater SeCys incorporation into the deiodinase reporter, and in-vitro studies show that transcripts corresponding to the T and C variants differ in their ability to form RNA–protein complexes [12,19•]. Furthermore, data from a Se supplementation trial showed that this SNP affected responses of GPx4, GPx1 and GPx3 protein expression or activity in response to Se supplementation or withdrawal [19•]. Two small disease association studies suggest that the T variant is associated with a lower risk of ulcerative colitis  and colon cancer , and results from a large association study suggest a link between genotype at this SNP and susceptibility to breast cancer .
SEPP contains multiple SeCys and is found in plasma in which it contributes the majority of functionally available Se . As it is thought that SEPP plays a central role in Se transport throughout the body, potential variants in the SePP gene could have significant functional consequences. Three variants in the SePP gene appear to be functionally significant. First, a variant in a TC repeat sequence in the promoter region of the SePP gene has been reported to lower promoter activity in reporter gene constructs expressed in hepatoma cells . Second, a G/A variant found in Caucasians in the coding region causes an amino-acid change from Ala to Thr at codon 234 (rs3877899) [24•]. Interestingly, the variant is not found in Chinese, indicating the added complexity of ethnicity in micronutrient–gene interaction studies. In a Se supplementation trial of prospectively genotyped volunteers, baseline plasma SEPP levels were found to be influenced by rs24731 [24•]. Third, a G/A variant is found within the 3′UTR at position 25 191 (rs7579), and this has been reported to affect plasma and lymphocyte glutathione peroxidise activities and plasma concentrations of SePP after supplementation [24•].
Several lines of work indicate links between Se, selenoproteins and lipid metabolism. Eicosapentaenoic and docosahexaenoic acids regulate both GPx1 and GPx4 expression and activity in human endothelial cells [28,29]. Furthermore, several studies have linked GPxs, particularly GPx4, and lipoxygenase activity in metabolism of arachidonic acid. GPx4 has been suggested to inhibit 5′-lipoxygenase activity in lymphocytes and basophils, and, recently, studies of a conditional GPx4 knockout mouse have suggested that GPx4 regulates generation of a 12/15-lipoxygenase-dependent proapoptotic signal in response to oxidative stress . The value of considering such GPx4–lipoxygenase interactions in genetic studies is shown by the finding that individuals homozygous for C or T allele of the SNP in the 3′UTR of GPx4 show different levels of lipoxygenase metabolites in their lymphocytes . Polyunsaturated fatty acid (PUFA) and Se metabolism should be considered together in relationship to identifying SNPs for experimental genotyping and choosing metabolic biomarkers for such studies. In addition, SePP appears linked to apolipoprotein metabolism. The low brain Se content and neurological symptoms found in SEPP knockout mice are similar to the phenotypic changes observed in knockout mice lacking the apolipoprotein receptor ApoER2 , and these changes could be overcome in both cases by feeding a diet supplemented with Se.
The enzyme responsible for provitamin A conversion into retinal is β-carotene 15,15′-monoxygenase (BCMO1), and approximately 95% of retinoids arising from β-carotene are produced by this pathway in vivo. Studies using BCMO1 knockout mice have provided evidence for the fundamental role of this enzyme in producing vitamin A from dietary β-carotene [48,49••,50]. Furthermore, altered tissue distribution and isomer patterns of lycopene were observed in the same mouse model after feeding lycopene in combination with low levels of vitamin A . It is estimated that about 55–75% of absorbed β-carotene is cleaved with the rest being secreted as intact β-carotene . However, variations in cleavage efficiency between different individuals vary considerably . Our laboratory recently identified two common nonsynonymous SNPs (R267S; rs12934922 and A379V; rs7501331) in the BCMO1 gene with variant allele frequencies of 42 and 24%, respectively [53••]. Results of the functional analysis of these SNPs revealed that the recombinant 267S + 379V double mutant had a reduced catalytic activity of 57% in vitro, and assessment of the responsiveness to a pharmacological dose of β-carotene in female volunteers confirmed that carriers of both the 379V and 267S+379V variant alleles had a reduced ability to convert β-carotene by 32 and 69%, respectively [53••]. These results may provide an explanation for the molecular basis of the poor converter phenotype within the population.
When considering micronutrient-related genes, the first challenge is to identify SNPs that alone, or in conjunction with other SNPs or nutritional factors, bring about functional changes in metabolism. Knowledge of genetic variants that affect micronutrient metabolism and responses to micronutrient supplementation was until recently largely limited to MTHFR. However, identification of novel functional SNPs in BCMO1[53••], the critical enzyme of β-carotene metabolism, and in several key selenoproteins [17,19•] indicates the potential importance of micronutrient–gene interactions in worldwide populations.
Nutrition is by nature an integrative discipline, and attention is now being directed at how nutrients affect not single enzymes but how they influence networks of biochemical pathways – ‘nutritional systems biology’. As illustrated schematically in Fig. 3, this integrative view emphasizes that in order to understand how genetics and micronutrient status could affect metabolism synergistically, functional knowledge of SNPs not in a single micronutrient-related gene, but at least in a physiological pathway and preferably in a wider physiological network including downstream targets is required [5•,60]. Despite the recent advances highlighted in this review, further research is needed to identify SNPs in other genes and to assess SNP functionality in terms of the whole functional pathway together with haplotype effects. The importance of such a pathway approach to nutrient–gene interaction studies is illustrated by reports that cancer risk is affected by the combination of two SNPs in different genes that both encode antioxidant enzymes, one in GPx1 and a second in manganese superoxide . Recent studies with micronutrient-related SNPs also indicate that effects of genetic variants on response to micronutrients can be modulated by sex [19•,24•,53••], emphasizing the importance of considering such factors as age, ethnicity, sex and BMI when examining interactions of genes and micronutrients.
The well defined pathways of micronutrient function, the importance of micronutrient intake in relation to disease susceptibility and the increasing number of micronutrient-related SNPs together emphasize the need to have a fuller understanding of micronutrient –gene interactions. Building on the recent expansion in known functional SNPs that affect micronutrient metabolism and function, this need is being recognized by the new International Micronutrient Genetic Project (www.nugo.org/micronutrient).
The work in the authors' laboratories has been supported by Food Standards Agency, BBSRC and NuGO, a EU-funded Network of Excellence.
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Additional references related to this topic can also be found in the Current World Literature section in this issue (p. 142).
1 Joost HG, Gibney MJ, Cashman KD, et al
. Personalised nutrition: status and perspectives. Br J Nutr 2007; 98:26–31.
2 Ordovas JM. Nutrigenetics, plasma lipids, and cardiovascular risk. J Am Diet Assoc 2006; 106:1074–1081.
3 Leclerc D, Rozen R. Molecular genetics of MTHFR: polymorphisms are not all benign. Med Sci (Paris) 2007; 23:297–302.
4 Loktionov A. Common gene polymorphisms and nutrition: emerging links with pathogenesis of multifactorial chronic diseases (review). J Nutr Biochem 2003; 14:426–451.
5• Haggarty P. B-vitamins, genotype and disease causality. Proc Nutr Soc 2007; 66:539–547. A comprehensive review describing the effect of single and multiple SNP combinations on B-vitamin status.
6 Koubaa N, Nakbi A, Smaoui M, et al
. Hyperhomocysteinemia and elevated ox-LDL in Tunisian type 2 diabetic patients: role of genetic and dietary factors. Clin Biochem 2007; 40:1007–1014.
7 Frelut ML, Emery-Fillon N, Guilland JC, et al
. Alanine amino transferase concentrations are linked to folate
intakes and methylenetetrahydrofolate reductase polymorphism in obese adolescent girls. J Pediatr Gastroenterol Nutr 2006; 43:234–239.
8 Taylor R. Pathogenesis of type 2 diabetes: tracing the reverse route from cure to cause. Diabetologia 2008; 51:1781–1789.
9 Tchantchou F, Graves M, Shea TB. Expression and activity of methionine cycle genes are altered following folate
and vitamin E deficiency under oxidative challenge: modulation by apolipoprotein E-deficiency. Nutr Neurosci 2006; 9:17–24.
10 Kryukov GV, Castellano S, Novoselov SV, et al
. Characterization of mammalian selenoproteomes. Science 2003; 300:1439–1443.
11 Hatfield DL, Gladyshev VN. How selenium
has altered our understanding of the genetic code. Mol Cell Biol 2002; 22:3565–3576.
12 Bermano G, Pagmantidis V, Holloway N, et al
. Evidence that a polymorphism within the 3′UTR of glutathione peroxidase 4 is functional and is associated with susceptibility to colorectal cancer. Genes Nutr 2007; 2:225–232.
13 Forsberg L, de Faire U, Marklund SL, et al
. Phenotype determination of a common Pro-Leu polymorphism in human glutathione peroxidase 1. Blood Cells Mol Dis 2000; 26:423–426.
14 Cox DG, Tamimi RM, Hunter DJ. Gene x gene interaction between MnSOD and GPX-1 and breast cancer risk: a nested case-control study. BMC Cancer 2006; 6:217.
15 Raaschou-Nielsen O, Sorensen M, Hansen RD, et al
. GPX1 Pro198Leu polymorphism, interactions with smoking and alcohol consumption, and risk for lung cancer. Cancer Lett 2007; 247:293–300.
16• Ravn-Haren G, Olsen A, Tjonneland A, et al
. Associations between GPX1 Pro198Leu polymorphism, erythrocyte GPX activity, alcohol consumption and breast cancer risk in a prospective cohort study. Carcinogenesis 2006; 27:820–825. The above article illustrates interaction of a micronutrient-related SNP with environmental factors.
17 Voetsch B, Jin RC, Bierl C, et al
. Promoter polymorphisms in the plasma glutathione peroxidase (GPx-3) gene: a novel risk factor for arterial ischemic stroke among young adults and children. Stroke 2007; 38:41–49.
18 Villette S, Kyle JA, Brown KM, et al
. A novel single nucleotide polymorphism in the 3′untranslated region of human glutathione peroxidase 4 influences lipoxygenase metabolism. Blood Cells Mol Dis 2002; 29:174–178.
19• Meplan C, Crosley LK, Nicol F, et al
. Functional effects of a common single-nucleotide polymorphism
(GPX4c718t) in the glutathione peroxidase 4 gene: interaction with sex. Am J Clin Nutr 2008; 87:1019–1027. The above article reports further evidence from both in-vivo and in-vitro
20 Qatatsheh A, Seal CJ, Jowet SL, et al
. Patients with ulcerative colitis show an altered frequency distribution of a single nucleotide polymorphism (SNP) in the gene encoding phospholipid hydroperoxide glutathione peroxidise (GPx4). Proc Nutr Soc 2005; 64:20A.
21 Udler M, Maia AT, Cebrian A, et al
. Common germline genetic variation in antioxidant defense genes and survival after diagnosis of breast cancer. J Clin Oncol 2007; 25:3015–3023.
22 Burk RF, Hill KE. Selenoprotein P: an extracellular protein with unique physical characteristics and a role in selenium
homeostasis. Annu Rev Nutr 2005; 25:215–235.
23 Al-Taie OH, Seufert J, Mork H, et al
. A complex DNA-repeat structure within the Selenoprotein P promoter contains a functionally relevant polymorphism and is genetically unstable under conditions of mismatch repair deficiency. Eur J Hum Genet 2002; 10:499–504.
24• Meplan C, Crosley LK, Nicol F, et al
. Genetic polymorphisms in the human selenoprotein P gene determine the response of selenoprotein markers to selenium
supplementation in a gender-specific manner (the SELGEN study). FASEB J 2007; 21:3063–3074. The first report that two SNPs in region of the
25 Hu YJ, Korotkov KV, Mehta R, et al
. Distribution and functional consequences of nucleotide polymorphisms in the 3′-untranslated region of the human Sep15 gene. Cancer Res 2001; 61:2307–2310.
26• Curran JE, Jowett JB, Elliott KS, et al
. Genetic variation in selenoprotein S influences inflammatory response. Nat Genet 2005; 37:1234–1241. The first description of effects of a SNP in promoter of
27 Gao Y, Feng HC, Walder K, et al
. Regulation of the selenoprotein SelS by glucose deprivation and endoplasmic reticulum stress - SelS is a novel glucose-regulated protein. FEBS Lett 2004; 563:185–190.
28 Crosby AJ, Wahle KW, Duthie GG. Modulation of glutathione peroxidase activity in human vascular endothelial cells by fatty acids and the cytokine interleukin-1 beta. Biochim Biophys Acta 1996; 1303:187–192.
29 Sneddon AA, Wu HC, Farquharson A, et al
. Regulation of selenoprotein GPx4 expression and activity in human endothelial cells by fatty acids, cytokines and antioxidants. Atherosclerosis 2003; 171:57–65.
30 Seiler A, Schneider M, Forster H, et al
. Glutathione peroxidase 4 senses and translates oxidative stress into 12/15-lipoxygenase dependent- and AIF-mediated cell death. Cell Metab 2008; 8:237–248.
31 Burk RF, Hill KE, Olson GE, et al
. Deletion of apolipoprotein E receptor-2 in mice lowers brain selenium
and causes severe neurological dysfunction and death when a low-selenium
diet is fed. J Neurosci 2007; 27:6207–6211.
32 Giacconi R, Bonfigli AR, Testa R, et al
. +647 A/C and +1245 MT1A polymorphisms in the susceptibility of diabetes mellitus and cardiovascular complications. Mol Genet Metab 2008; 94:98–104.
33• Perry JR, Frayling TM. New gene variants alter type 2 diabetes risk predominantly through reduced beta-cell function. Curr Opin Clin Nutr Metab Care 2008; 11:371–377. A genome-wide association (GWA) study identifying an SNP in zinc
transporter SLC30A8 as associated with diabetes.
34• Tabara Y, Osawa H, Kawamoto R, et al
. Replication study of candidate genes associated with type 2 diabetes based on genome-wide screening. Diabetes 2009; 58:493–498. A GWA study confirming in a second population that an SNP in zinc
transporter SLC30A8 as associated with diabetes.
35 Mocchegiani E, Malavolta M. Zinc
-gene interaction related to inflammatory/immune response in ageing. Genes Nutr 2008; 3:61–75.
36 Lunetta JM, Zulim RA, Dueker SR, et al
. Method for the simultaneous determination of retinol and beta-carotene concentrations in human tissues and plasma. Anal Biochem 2002; 304:100–109.
37 Bowen PE, Garg V, Stacewiczsapuntzakis M, et al
. Variability of serum carotenoids
in response to controlled diets containing 6 servings of fruits and vegetables per day. Ann N Y Acad Sci 1993; 691:241–243.
38 Brown ED, Micozzi MS, Craft NE, et al
. Plasma carotenoids
in normal men after a single ingestion of vegetables or purified beta-carotene. Am J Clin Nutr 1989; 49:1258–1265.
39 During A, Dawson HD, Harrison EH. Carotenoid transport is decreased and expression of the lipid transporters SR-BI, NPC1L1, and ABCA1 is downregulated in Caco-2 cells treated with ezetimibe. J Nutr 2005; 135:2305–2312.
40 During A, Doraiswamy S, Harrison EH. Xanthophylls are preferentially taken up compared with beta-carotene by retinal cells via a SRBI-dependent mechanism. J Lipid Res 2008; 49:1715–1724.
41 During A, Hussain MM, Morel DW, Harrison EH. Carotenoid uptake and secretion by CaCo-2 cells: beta-carotene isomer selectivity and carotenoid interactions. J Lipid Res 2002; 43:1086–1095.
42 Moussa M, Landrier JF, Reboul E, et al
. Lycopene absorption in human intestinal cells and in mice involves scavenger receptor class B type I but not Niemann-Pick C1-like 1. J Nutr 2008; 138:1432–1436.
43 Reboul E, Abou L, Mikail C, et al
. Lutein transport by Caco-2 TC-7 cells occurs partly by a facilitated process involving the scavenger receptor class B type I (SR-BI). Biochem J 2005; 387:455–461.
44• Borel P, Moussa M, Reboul E, et al
. Human plasma levels of vitamin E and carotenoids
are associated with genetic polymorphisms in genes involved in lipid metabolism. J Nutr 2007; 137:2653–2659. The first publication identifying a range of genes involved in lipid metabolism to influence carotenoid plasma concentrations.
45• Borel P, Moussa M, Reboul E, et al.
Human fasting plasma concentrations of vitamin E and carotenoids
, and their association with genetic variants in apo C-III, cholesteryl ester transfer protein, hepatic lipase, intestinal fatty acid binding protein and microsomal triacylglycerol transfer protein. Br J Nutr 2008 [Epub ahead of print]. doi:10.1017/S0007114508030754.
This article gives further evidence of lipid–carotenoid interactions modified by common SNPs.
46• Herbeth B, Gueguen S, Leroy P, et al
. The lipoprotein
lipase serine 447 stop polymorphism is associated with altered serum carotenoid concentrations in the Stanislas Family Study. J Am Coll Nutr 2007; 26:655–662. This publication shows a very clear role of LPL on carotenoid plasma concentrations.
47 Barua AB, Olson JA. Beta-carotene is converted primarily to retinoids in rats in vivo. J Nutr 2000; 130:1996–2001.
48 Fierce Y, de Morais Vieira M, Piantedosi R, et al
. In vitro and in vivo characterization of retinoid synthesis from beta-carotene. Arch Biochem Biophys 2008; 472:126–138.
49•• Hessel S, Eichinger A, Isken A, et al
. BCMO1 deficiency abolishes vitamin A production from beta-carotene and alters lipid metabolism in mice. J Biol Chem 2007; 282:33553–33561. The first publication indicating that BCMO1 deficiency influences lipid metabolism.
50 Lindshield BL, King JL, Wyss A, et al
. Lycopene biodistribution is altered in 15,15′-carotenoid monooxygenase knockout mice. J Nutr 2008; 138:2367–2371.
51 Hickenbottom SJ, Lemke SL, Dueker SR, et al
. Dual isotope test for assessing beta-carotene cleavage to vitamin A in humans. Eur J Nutr 2002; 41:141–147.
52 Tang G, Qin J, Dolnikowski GG, et al
. Short-term (intestinal) and long-term (postintestinal) conversion of beta-carotene to retinol in adults as assessed by a stable-isotope reference method. Am J Clin Nutr 2003; 78:259–266.
53•• Leung W, Hessel S, Méplan C, et al.
Two common single nucleotide polymorphisms in the gene encoding β-carotene 15,15′-monoxygenase alter β-carotene metabolism in female volunteers. FASEB J 2008 [Epub ahead of print] PMID: 19103647.
The first publication indicating that common SNPs in BCMO1 influence β-carotene conversion and fasting β-carotene plasma concentrations in female volunteers.
54 Suruga K, Mochizuki K, Suzuki R, et al
. Regulation of cellular retinol-binding protein type II gene expression by arachidonic acid analogue and 9-cis retinoic acid in caco-2 cells. Eur J Biochem 1999; 262:70–78.
55 Gong X, Tsai SW, Yan B, Rubin LP. Cooperation between MEF2 and PPARgamma in human intestinal beta,beta-carotene 15,15′-monooxygenase gene expression. BMC Mol Biol 2006; 7:7.
56• Ziouzenkova O, Orasanu G, Sharlach M, et al
. Retinaldehyde represses adipogenesis and diet-induced obesity. Nat Med 2007; 13:695–702. The key publication indicating the important role of retinaldehyde in adipogenesis.
57 Ziouzenkova O, Orasanu G, Sukhova G, et al
. Asymmetric cleavage of beta-carotene yields a transcriptional repressor of retinoid X receptor and peroxisome proliferator-activated receptor responses. Mol Endocrinol 2007; 21:77–88.
58 Goodman M, Bostick RM, Ward KC, et al
. Lycopene intake and prostate cancer risk: effect modification by plasma antioxidants and the XRCC1 genotype. Nutr Cancer 2006; 55:13–20.
59 Ratnasinghe DL, Yao SX, Forman M, et al
. Gene-environment interactions between the codon 194 polymorphism of XRCC1 and antioxidants influence lung cancer risk. Anticancer Res 2003; 23:627–632.
60 Hesketh J. Nutrigenomics and selenium
: gene expression patterns, physiological targets and genetics. Ann Rev Nutr 2008; 28:157–177.