Uterine microvascular sensitivity to nanomaterial inhalation: An in vivo assessment

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Nutrition Research 32 (2012) 71 – 77 www.nrjournal.com

Serum levels of polyunsaturated fatty acids are low in Chinese men with metabolic syndrome, whereas serum levels of saturated fatty acids, zinc, and magnesium are high Yinghua Yua, b , Zhenzhen Caia , Jusheng Zhenga , Jiezhong Chenb , Xu Zhangc , Xu-Feng Huangb , Duo Lia,⁎ a

Department of Food Science and Nutrition, Zhejiang University, Zhejiang Province 310058, China b School of Health Sciences, University of Wollongong, Australia c Ningbo College of Health, Zhejiang Province, China Received 30 June 2011; revised 9 December 2011; accepted 12 December 2011

Abstract The purpose of this study was to examine the hypothesis that serum levels of phospholipid (PL) fatty acids (FA) and minerals are associated with the components of metabolic syndrome (MetS) in the Chinese population and the profiles of changes may differ from patients with MetS from Western countries. The levels of serum PL, FA, and minerals were examined in 201 subjects (52 with MetS and 149 healthy controls without any MetS components) in China. The saturated FA proportion in serum was significantly higher, whereas the proportion of total polyunsaturated FA (PUFA), n-3 and n-6 PUFA (22:6n-3: −16%, P = .006; 20:4n-6: −36%, P b .001), and estimated δ-5 desaturase were significantly lower in the MetS group compared with those that are not MetS. Subjects with MetS had higher levels of serum Zn (P = .037) and Mg (P b .001) than subjects without MetS. The proportion of n-3 PUFA was significantly negatively correlated with body mass index and waist circumference. In conclusion, serum PL FA composition and serum minerals in Chinese men with MetS differed significantly from that of healthy individuals, reflecting a decrease in n-3 and n-6 PUFA, especially 22:6n-3 and 20:4n-6, and an increase in saturated FA, magnesium, and zinc. These changes may reflect improper dietary intake in subjects with MetS, and dietary modification could be useful to prevent MetS and as an adjunctive therapy. © 2012 Elsevier Inc. All rights reserved. Keywords: Abbreviations:

Metabolic syndrome; Fatty acids; Minerals; Desaturase; Chinese men BMI, body mass index; Ca, calcium; Cu, copper; D5D, δ-5 desaturase; D6D, δ-6 desaturase; FA, fatty acids; Fe, iron; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; MetS, metabolic syndrome; Mg, magnesium; PG, prostaglandin; PL, phospholipids; PUFA, polyunsaturated FA; SFA, saturated FA; Zn, zinc.

1. Introduction Metabolic syndrome (MetS) is a clustering of abnormalities including obesity, dyslipidemia, hyperglycemia, and hypertension [1]. The major components of MetS are ⁎ Corresponding author. Tel.: +86 571 88982024; fax: +86 571 88982024. E-mail address: [email protected] (D. Li). 0271-5317/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.nutres.2011.12.004

associated with genetic predisposition and lifestyle factors. In the last 2 decades with rapid economic growth and change in diet and lifestyle, MetS has become one of the most widespread health challenges in China, with a prevalence of 9.8% and 17.8% in men and women, respectively [2]. The fatty acid (FA) composition of serum phospholipids (PLs) can be used to track dietary intake of FA for a period of a few weeks and also reflects endogenous FA metabolism

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[3], regulated by different enzymes, such as desaturases and elongases [4]. The FA composition in serum can be used as an indicator for the risks of some metabolic and cardiovascular diseases [4]. High proportions of palmitic acid (16:0) and dihomo-γ-linolenic acid (20:3n-6) and low concentrations of linoleic acid (18:2n-6) in serum cholesteryl esters are characteristic of these populations in Western countries [5]. Furthermore, several enzymes, including δ-5 desaturase (D5D), δ-9 desaturase (D9D), δ-6 desaturase (D6D), and elongase, are involved in the endogenous synthesis of polyunsaturated FAs (PUFA), and thus, their activities can be estimated by the product precursor ratios of individual FAs in human tissues [4]. The serum minerals, zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), and iron (Fe), are associated with MetS [6,7]. Hypomagnesemia has been demonstrated in various experimental models of hypertension [8]. Zinc has been positively correlated with total cholesterol and low-density lipoprotein cholesterol (LDL-C) [9]. Furthermore, trace elements, such as Zn and Mg, are important cofactors for normal activities of desaturases and elongases in endogenous FA synthesis [10,11]. Therefore, the alteration of serum mineral levels in individuals with MetS may influence the activities of these enzymes and, hence, the regulation of FA metabolism and production of PUFA. Alterations of serum FA composition or minerals of subjects with MetS have been reported in Western countries [12-14]. Serum FA composition predicts the long-term development of MetS [12,13] and is related to components of MetS. Low serum Mg levels are related to MetS and its components [14]. The research of FA and minerals in Chinese population is sparse. Our hypothesis is that altered PL FA composition and minerals in serum are correlated with the components of MetS. The changes may differ from that in subjects with MetS in Western countries. The lifestyle factors and genetic phenotype differ dramatically between Chinese and Western populations, which may influence the intake of FAs and minerals and their metabolism in the blood. We performed a cross-sectional study to compare the serum FA composition and mineral levels of male subjects with MetS in the eastern coastal area of China. The levels of FAs in serum PLs were determined by gas-liquid chromatography, whereas the levels of serum minerals were detected by a Perkin-Elmer Flame Atomic Absorption Spectroscopy (Perkin Elmer AAnalyst 800; Perkin-Elmer, Beaconsfield, United Kingdom).

2. Methods and materials 2.1. Definition of the MetS We used the Chinese Diabetes Society's definition of MetS [15]. Metabolic syndrome was considered present when 3 or more of the following components were met: (1) overweight or obesity: body mass index (BMI) 25 or more; (2) Hyperglycemia: fasting blood glucose 6.1 mmol/L or

more and/or 2-hour postprandial blood glucose 7.8 mmol/L or more, and/or diabetic patient under treatment; (3) hypertension: systolic/diastolic blood pressure 140/90 mm Hg or greater and/or patients with hypertension under treatment; and (4) dyslipidemia: fasting blood triacylglycerol (TG) 1.7 mmol/L or more and/or blood high-density lipoprotein cholesterol (HDL-C) (fasting) less than 0.9 mmol/L (male) and less than 1.0 mmol/L (female). 2.2. Subjects Subjects provided informed consent. The study protocol was approved by the Ethics Committee, Zhejiang University, China. There were 379 male participants aged 24 to 57 years in the study, recruited through a health check program in 2 sanatoriums of Hangzhou, China. In the 2 months before the study, the participants did not smoke and had no acute diseases, operations, or chronic medication. Of the 379 participants, there were (1) 120 subjects with 1 component of MetS (31.7%), (2) 58 subjects with 2 components of MetS (15.3%), (3) 43 subjects with 3 components of MetS (11.3%), and (4) 9 subjects with 4 components of MetS (2.4%). The subjects with 3 or 4 components of MetS were selected as MetS group (52 subjects, 13.7%). The 149 subjects who did not have any components of MetS were selected as the control group. 2.3. Blood sampling and blood biochemical parameters analysis Blood samples were taken from the antecubital vein after the subjects fasted overnight (N12 hours). All samples were processed within 3 hours of sampling, and serum samples were divided into aliquots for immediate analysis or for longterm storage at −80 °C. Serum biochemical parameters were measured by Olympus AU2700 chemistry-immuno analyzer (Olympus America Inc, Melville, NY). 2.4. Serum PLs FA and serum minerals The total lipid of serum was extracted with chloroform: methanol 1:1 (C:M, vol/vol) containing 10 mg/L of butylated hydroxytoluene and 10 mg/L of C17:0 PL (diheptadecanoyl) (Nu-Chek-Prep, Inc, Minn) as the internal standard [16,17]. The serum PL fractions were separated by thin-layer chromatography. The methyl esters of the FA were prepared by saponification using potassium hydroxide (KOH) (0.68 mol/L in methanol), followed by transesterification with 20% boron trifluoride (BF3) in methanol. The FA compositions of serum PL were determined by gas-liquid chromatography as described previously [16,17]. Levels of serum minerals were quantified using a Perkin-Elmer Flame Atomic Absorption Spectroscopy according to the standard method [18]. 2.5. Estimation of desaturase activity The desaturase activity was estimated as the productprecursor ratio of individual FAs in serum PL according to

Y. Yu et al. / Nutrition Research 32 (2012) 71–77

the following: D9D-18 = 18:1/18:0, D5D = 20:4n-6/20:3n-6, D6D = 18:3n-6/18:2n-6. 2.6. Statistical analyses Data were analyzed using the SPSS 11.5 for windows statistical package (SPSS, Chicago, Ill). Characteristics of the participants, blood biochemical parameters, serum FA composition, and minerals were analyzed by 1-way analysis of variance. Values were expressed as means ± SD, and P b .05 was regarded as statistically significant. The association of serum FA proportion with the risk of MetS was explored by univariant logistic regression. Odds ratio (OR) greater than 1 and P b .05 were considered as a positive association with the risk of MetS; OR less than 1 and P b .05 were considered as a negative association with risk of the MetS. Two-tailed partial correlations were used to analyze the correlation of the serum PL FAs and mineral concentration and components of MetS adjusted for BMI and age.

3. Results 3.1. Subject characteristics and blood biochemical parameters The body weight, BMI, and waist circumference of subjects with MetS were significantly higher than subjects without MetS (Table 1). Both systolic and diastolic blood Table 1 Characteristics and blood biochemical parameters of the subjects with or without MetS Without MetS MetS (n = 52) P (n = 149) Age (y) 39.3 ± 6.3 42.4 ± 7.8 Height (m) 171.7 ± 4.8 172.1 ± 3.7 Body weight (kg) 68.0 ± 4.8 75.2 ± 4.2 23.07 ± 1.29 25.41 ± 1.36 BMI (kg/m2) Waist circumference (cm) 86.74 ± 5.05 90.51 ± 2.67 Hip circumference (cm) 96.03 ± 3.27 98.51 ± 0.53 Wasit-to-Hip Ratio 0.90 ± 0.05 0.92 ± 0.02 Systolic blood pressure (mm Hg) 119.08 ± 9.33 140.71 ± 13.01 Diastolic blood pressure (mm Hg) 78.06 ± 5.75 92.06 ± 7.37 Blood biochemical parameters Glucose (mmol/L) 4.91 ± 0.44 6.92 ± 2.38 Triacylglycerols (mmol/L) 1.00 ± 0.36 2.55 ± 1.03 Total cholesterol (mmol/L) 4.96 ± 0.91 5.57 ± 1.13 HDL-C (mmol/L) 1.47 ± 0.21 1.44 ± 0.17 LDL-C (mmol/L) 3.24 ± 0.67 3.89 ± 0.91 HDL-C/LDL-C 0.47 ± 0.13 0.39 ± 0.10 Creatinine level(μmol/L) 86.39 ± 19.71 84.88 ± 11.77 Uric acid (μmol/L) 292.35 ± 64.65 337.90 ± 73.79 ALP (U/L) 77.33 ± 15.46 83.86 ± 15.23 ALT (U/L) 24.79 ± 11.96 46.98 ± 27.08 AST (U/L) 22.51 ± 4.82 30.13 ± 15.30 AST/ALT 1.04 ± 0.38 0.80 ± 0.14

.071 .553 b.001 b.001 .039 .098 .378 b.001 b.001 b.001 b.001 b.001 .415 b.001 b.001 .634 .001 .324 b.001 .002 .017

ALP indicates alkaline phosphatase; ALT, alanine amino transferase; AST, aspartate amino transferase; TP, total protein; ALB, albumin; GLB, globulin. Data are expressed as means ± SD.

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pressures were higher in the MetS group than the withoutMetS group. Serum biochemical parameters also differed between the groups. Serum glucose, TGs, total cholesterol, LDL-C, uric acid, alkaline phosphatase, and aspartate amino transferase were significantly higher in the MetS group compared with the control group. 3.2. Composition and ratio of FAs in serum PLs according to MetS status The proportions of total saturated FA (SFA), 16:0 and 18:0, were significantly higher in subjects with MetS than in those without MetS (total SFA: P b .001; 16:0: P = .027; 18:0: P = .002) (Table 2). Individuals with MetS had a lower proportion of PUFA compared with those without MetS (P b .001). The proportion of total n-3 PUFA, 22:6n-3, and 22:5n-3 was significantly lower in MetS subjects than in those without MetS (n-3 PUFA: −18%, P = .002; 22:6n-3: −16%, P = .006; 22:5n-3: −30%, P = .022). Similarly, the proportion of total n-6 PUFA and 20:4n-6 were also significantly lower in MetS subjects compared with subjects without MetS (total n-6 PUFA: P = .009; 20:4n-6: −36%; P b .001) (Table 2). The estimation of D5D, the ratio of 20:4n-6 to 20:3n-6, was significantly lower in individuals with MetS than in those without MetS (P = .009) (Table 2). There was no significant difference in the estimation of D9D-18 and D6D between the MetS group and control group.

Table 2 Fatty acid composition in serum PLs of subjects with or without MetS (% of total FA)

Total SFA 16:0 18:0 Total MUFA 16:1 18:1 Total PUFA Total n-3 PUFA 18:3n-3 20:5n-3 22:5n-3 22:6n-3 Total n-6 PUFA 18:2n-6 18:3n-6 20:3n-6 20:4n-6 n-6 PUFA/n-3 PUFA PUFA/SFA Ratio of 18:1 to 18:0 (D9D-18) Ratio of 18:3n-6 to 18:2n-6 (D6D) Ratio of 20:4n-6 to 20:3n-6 (D5D)

Without MetS MetS (n = 149) (n = 52)

P

48.11 ± 31.11 ± 14.81 ± 10.11 ± 0.54 ± 8.47 ± 41.78 ± 5.77 ± 0.23 ± 0.72 ± 1.37 ± 3.44 ± 36.01 ± 23.71 ± 0.19 ± 1.71 ± 9.42 ± 6.59 ± 0.87 ± 0.61 ± 7.28 ± 5.63 ±

b.001 .027 .002 .440 .330 .525 b.001 .002 .988 .938 .022 .006 .009 .091 .226 .912 b.001 .800 b.001 .068 .543 .009

2.63 2.36 1.76 2.02 0.25 1.78 2.77 1.24 0.09 0.37 0.72 0.85 3.07 3.75 0.20 0.57 1.59 1.77 0.01 0.21 4.91 1.87

50.73 ± 3.63 32.38 ± 2.19 16.30 ± 1.33 10.50 ± 1.09 0.48 ± 0.19 8.75 ± 1.38 38.77 ± 2.87 4.73 ± 0.78 0.23 ± 0.09 0.71 ± 0.36 0.96 ± 0.50 2.83 ± 0.37 34.03 ± 2.43 25.28 ± 4.26 0.26 ± 0.12 1.73 ± 0.32 5.99 ± 3.98 7.34 ± 0.99 0.77 ± 0.03 0.54 ± 0.12 8.62 ± 2.83 4.10 ± 1.92

MUFA indicates monounsaturated FAs. Data are expressed as means ± SD.

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3.3. Serum mineral concentrations in MetS group and control group The serum levels of Zn and Mg were significantly higher in subjects with MetS compared with subjects without MetS (Zn: P = .037, Mg: P b .001) (Table 3). There was no significant difference in serum Ca, Fe, and Cu levels between the MetS and without-MetS groups. The ratio of serum Zn/Cu of subjects with MetS was higher compared with that of subjects without MetS (P = .032), whereas the ratio of serum Ca/Mg was lower (P b .001). 3.4. Analysis of serum FAs and the risk of MetS In univariate logistic regression analysis (Table 4), the proportion of SFA and 18:0 were positively associated with the risk of MetS (SFA: OR, 1.301; confidence interval [CI], 1.083-1.563; P = .005; 18:0: OR, 1.967; CI, 1.3052.964; P = .001), although total PUFA, total n-3 PUFA, and total n-6 PUFA were negatively associated with the risk of MetS (Table 4). The proportion of 22:6n-3 and 20:4n-6 in the serum was also significantly negatively associated with the risk of MetS (Table 4). 3.5. The correlation between FA composition, the estimate of D5D, levels of serum minerals, and components of MetS Both total n-3 PUFA and 22:6n-3 were negatively correlated with BMI (P = .001) (Table 5). Total n-6 PUFA was negatively correlated with systolic blood pressure (P = .030) and waist circumference (P = .019). The proportion of 20:4n-6 was negatively correlated with blood glucose (P = .003), diastolic blood pressure (P = .002), and TGs (P = .003). Estimated D5D was negatively correlated with BMI (P b .001), blood glucose (P = .007), and diastolic blood pressure (P = .011). The systolic and diastolic blood pressures were positively correlated with serum Mg and Zn (Table 6). 4. Discussion Our study showed that total SFA in the serum PL was higher in the Chinese male population with MetS, whereas total n-3 and n-6 PUFA were lower, especially in 22:6n-3 and 20:4n-6 compared with subjects without MetS. The estimated D5D activity decreased in subjects with MetS Table 3 Serum mineral concentrations of subjects with or without MetS (mg/L)

Without MetS (n = 149)

MetS (n = 52)

P

Ca (mg/L) Mg (mg/L) Fe (mg/L) Cu (mg/L) Zn (mg/L) Ca/Mg Zn/Cu

110.97 ± 10.16 19.30 ± 2.84 1.47 ± 0.99 1.10 ± 0.24 1.05 ± 0.32 5.89 ± 0.78 0.98 ± 0.29

110.45 ± 10.15 20.87 ± 2.79 1.46 ± 0.92 1.06 ± 0.17 1.17 ± 0.31 5.37 ± 0.76 1.11 ± 0.32

.340 b.001 .950 .358 .037 b.001 .032

Data are expressed as means ± SD.

Table 4 Univariate logistic regression analysis of serum FAs as factors that may be associated with risks of MetS OR

Total SFA 16:0 18:0 Total MUFA 16:1 18:1 Total PUFA Total n-3 PUFA 18:3n-3 20:5n-3 22:5n-3 22:6n-3 Total n-6 PUFA 18:2n-6 20:4n-6 n-6/n-3 PUFA

95.0% CI for OR

1.301 1.236 1.967 1.118 0.303 1.104 0.734 0.393 0.955 0.931 0.380 0.175 0.832 1.143 0.579 1.287

P

Lower

Upper

1.083 0.996 1.305 0.843 0.025 0.809 0.612 0.214 0.002 0.218 0.158 0.052 0.707 0.964 0.431 0.951

1.563 1.534 2.964 1.481 3.679 1.508 0.880 0.722 3.686 3.983 0.914 0.593 0.978 1.354 0.778 1.742

.005 .054 .001 .439 .348 .533 .001 .003 .988 .923 .031 .005 .026 .124 b.001 .102

Positive correlation: OR N 1, P b .05; Negative correlation: OR b 1, P b .05.

and was negatively associated with the components of MetS, including BMI, fasting blood glucose, and diastolic blood pressure. The levels of serum Mg and Zn were higher in subjects with MetS than in controls. These findings confirmed our hypothesis that serum levels of FAs and minerals were altered in Chinese men with MetS, but the profile was different to subjects with MetS in Western countries. Table 5 Age- and BMI-adjusted Spearman correlation of serum FAs composition and components of MetS in study participants

Total SFA

R P Total MUFA R P Total PUFA R P Total n-3 PUFA R P 22:5n-3 R P 22:6n-3 R P Total n-6 PUFA R P 20:4n-6 R P Estimate of D5D R P n-6/n-3 R P

BMI ⁎

GLU ⁎⁎ SP ⁎⁎

DP ⁎⁎

TG ⁎⁎

WC ⁎⁎

0.077 .337 0.222 .005 −0.215 .007 −0.264 .001 −0.067 .406 −0.265 .001 −0.099 .215 −0.063 .432 −0.279 b.001 0.185 .020

−0.152 .059 0.269 .001 −0.035 .670 −0.003 .974 −0.107 .187 −0.072 .378 −0.033 .683 −0.239 .003 −0.217 .007 −0.020 .810

0.259 .001 −0.139 .085 −0.153 .058 −0.108 .182 0.028 .732 −0.074 .362 −0.104 .200 −0.248 .002 −0.203 .011 0.007 .930

0.048 .550 0.007 .929 −0.049 .538 0.019 .810 0.021 .792 −0.031 .696 −0.057 .478 −0.237 .003 −0.155 .054 −0.045 .577

0.244 .062 0.151 .255 −0.305 .019 −0.283 .030 −0.207 .116 −0.208 .114 −0.203 .124 −0.037 .782 −0.235 .073 0.135 .309

0.209 .008 −0.040 .616 −0.169 .033 0.014 .865 0.118 .140 −0.014 .861 −0.173 .030 −0.055 .494 −0.018 .822 −0.091 .255

GLU indicates fasting blood glucose; SP, systolic blood pressure; DP, diastolic blood pressure; WC, waist circumference. P b .05 was regarded as statistically significant correlation. The associations of 201 subjects (59 subjects with MetS and 142 subjects without any MetS components) were evaluated using 2-tailed partial correlation adjusted by age or BMI. ⁎ Adjusted for age. ⁎⁎ Adjusted for BMI and age.

Y. Yu et al. / Nutrition Research 32 (2012) 71–77 Table 6 Age- and BMI-adjusted Spearman correlations of serum mineral concentrations and components of MetS in the study participants

Ca Mg Fe Cu Zn Ca/Mg Zn/Cu

R P R P R P R P R P R P R P

BMI ⁎

GLU ⁎⁎

SP ⁎⁎

DP ⁎⁎

TG ⁎⁎

WC ⁎⁎

−0.045 .397 −0.054 .313 −0.001 .979 0.054 .315 0.080 .150 0.014 .790 0.110 .047

−0.083 .120 0.051 .341 −0.086 .107 −0.087 .105 0.052 .348 −0.098 .066 0.098 .076

−0.002 .966 0.176 .001 0.021 .701 0.002 .966 0.149 .007 −0.168 .002 0.027 .632

−0.014 .786 0.205 b.001 −0.037 .494 0.011 .841 0.142 .010 −0.196 b.001 0.100 .070

−0.068 .201 0.043 .425 0.083 .123 −0.023 .672 0.083 .133 −0.067 .209 0.047 .398

−0.200 .130 0.228 .082 0.087 .514 −0.063 .635 0.019 .885 −0.326 .012 0.119 .370

P b .05 was regarded as statistically significant correlation. The associations of 201 subjects (59 subjects with MetS and 142 subjects without any MetS components) were evaluated using 2-tailed partial correlation adjusted by age or BMI. ⁎ Adjusted for age. ⁎⁎ Adjusted for BMI and age.

High levels of serum SFA in MetS positively contributed to MetS components, such as BMI, serum glucose, blood pressure, and TGs, in Chinese men. Our findings are consistent with previous investigations in the Western population [5,13], in which SFA in serum lipid and erythrocytes were positively associated with MetS. Our results suggest that the increased SFA in serum PL is also common in Chinese men with MetS. Fatty acid composition of serum, platelet, and erythrocyte PLs reflects an individual's type of dietary fat intake [16,19]. Therefore, compositions of serum PL FAs can be used as a surrogate marker of dietary intake of FAs. The increased serum PL SFA in the MetS group may represent an increased dietary intake of SFA. The present study found that n-3 PUFA, especially the proportion 22:6n-3, was decreased and negatively contributed to the risk of MetS in Chinese men. We also found a negative correlation between total n-3 PUFA and 22:6n-3 in serum PL and BMI. Furthermore, total n-3 PUFA was negatively correlated with waist circumference. These findings suggest that n-3 PUFA of serum PL is negatively correlated with obesity, especially central obesity. Our data are consistent with findings in an Australian population, where obese individuals had significantly lower plasma lipid n-3 PUFA [20]. Furthermore, the concentration of n-3 PUFA in serum PL was significantly lowered in obese vs lean, agematched, females [21]. These findings including ours may indicate that the intake of n-3 PUFA is lowered in individuals with MetS, especially with obesity. Previous studies indicate that n-3 PUFA intake plays an important role in preventing weight gain and improving weight loss [22,23]. The potential mechanisms underlying the relationship between n-3 PUFA and adiposity in MetS are not fully understood. However, previous studies have shown that n-3 PUFA can

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increase basal fat oxidation to reduce fat mass in severely obese women [24]. High dietary 22:6n-3 increases messenger RNA expression of mitochondrial uncoupling protein leading to thermogenesis and provides a defense against obesity in mice [25]. A high intake of 22:6n-3 increased levels of phosphorylated Akt in mouse brain [26], which is the signaling pathway of leptin and insulin to promote negative energy balance [27]. In the present study, the proportion of 20:4n-6 was decreased in the serum PL of subjects with MetS and negatively correlated with serum glucose and TG. These findings are consistent with the previous studies of 20:4n-6 and MetS-related disorders. The level of 20:4n-6 in plasma, liver, and muscle decreases at an early phase during the development of insulin resistance in rats [28]. Plasma 20:4n-6 concentrations are lower in humans with type 2 diabetes than in healthy subjects [29]. Moreover, 20:4n-6 is involved in many of the functions of insulin in liver, muscle, and fat, including stimulating glucose utilization and stimulating glucose uptake [30]. In vivo, 20:4n-6 can be converted into prostaglandin (PG) E1 and PGE2, which are reported to improve insulin sensitivity in soleus muscle of rat [31]. Therefore, the decreased proportion of 20:4n-6 in serum PL may contribute to the elevated fasting blood glucose in Chinese men with MetS. Although 20:4n-6 treatment decreases the glucose-insulin index and blood TG in insulinresistant rats induced by high-fat diet [32], there are also some reports about the adverse effects of 20:4n-6 on the effect of insulin [33,34]. Because 20:4n-6 can be a PG precursor, excessive 20:4n-6 may interfere with PG action as competitor of PG binding sites [35]. Furthermore, 20:4n-6 has a direct effect on the activation of inflammation signaling via IKKβ/NF-κB [36], which can promote obesity and type 2 diabetes [37]. Therefore, it is important to maintain adequate but not excessive 20:4n-6 intake for individuals with MetS. Furthermore, a change in the ratio of n-6/n-3 PUFA in the diet from 5:1 to 2:1 has shown a beneficial effect in preventing and treating chronic disease [38]. Sweden has recommended that the ratio be 5:1 in the diet [39], and Japan has revised the recommended ratio from 4:1 to 2:1 [40]. Decreasing the dietary n-6/n-3 PUFA ratio for 6 months has been shown to lower fasting and postprandial TG concentrations [41]. The n-6/n-3 PUFA ratio (estimated 10-25:1) in the Western diet has increased in parallel with the prevalence of obesity, diabetes, and cardiovascular diseases [42]. In deaths from cardiovascular disease, the ratios of n-6/n-3 PUFA in thrombocyte PLs are 50:1 (Europe and United States) and 12:1 (Japan) [38]. In the present study, the ratio of n-6/n-3 PUFA of serum PL in Chinese men (control group: 6.59:1 and MetS group: 7.34:1, respectively) was higher than the recommended ratio. Therefore, a lower ratio of dietary n-6/n-3 PUFA is desirable for the population described in this study. In the present study, the estimated D5D was negatively correlated with BMI, blood glucose, and diastolic blood pressure. D5D and D6D catalyze the synthesis of n-3 and n-6 PUFA. Therefore, we hypothesize that the lower activity

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of the D5D may induce alterations in PUFA desaturation processes and contribute to components of MetS. δ-5 desaturase messenger RNA expression decreased in the liver of streptozotocin diabetic rats with hypoinsulinemia [43]. Single nucleotide polymorphisms in the FADS1 and FADS2 gene encoding D5D and D6D were highly associated with a decrease of 20:4n-6 and 22:5n-3 in erythrocytes of the European population [44]. Recently, FADS1 and FADS2 genotypes have been considered to have a modulating effect on PUFA composition in PLs, which is related to MetS [45]. In the present study, the decreased estimate of D5D and its metabolites of PUFAs in the MetS group require future genetic studies to clarify if desaturase gene variants contribute to the development of MetS in the Chinese population. In the present study, serum Mg was found to be higher in the MetS group and positively associated with blood pressure. Some studies of the Chinese population have also found that the serum Mg increased in subjects with MetS components, obesity, hypertension, and hyperlipidemia [46,47]. Increased level of serum Mg may be caused by increased dietary intake of Mg in Chinese subjects with MetS. However, hypomagnesemia is positively associated with the presence of MetS in studies on populations of Western countries [14]. The different findings in serum Mg levels of MetS groups between Chinese and Western populations may be caused by the difference in habitual diets. The optimal concentrations of serum Mg are critical to the activities of desaturase enzymes [10,11]. Deficiency of Mg has been shown to decrease the D5D activities and is considered as a pathogenic factor of MetS in Western populations [14]. In the present study, the higher serum Mg levels in the subjects with MetS of the Chinese population could also affect D5D activity and be involved in the hypertension in subjects with MetS. The present study also showed that serum Zn and Zn/Cu increased in MetS compared with subjects without MetS. The levels of serum Zn were positively correlated with both systolic and diastolic blood pressure. Increased Zn absorption from the alimentary tract was found in patients with primary arterial hypertension, and decreased Zn absorption in these patients contributed to the antihypertensive effect of perindopril [48]. Zn and Zn/Cu were elevated in spontaneous hypertensive rat model with low level of serum Cu [49]. Therefore, the elevated serum Zn and Zn/Cu may be involved in the significantly higher blood pressure, both systolic and diastolic blood pressure in Chinese males with MetS. In conclusion, total PUFA, especially n-3 PUFA (22:6n-3) and n-6 PUFA (20:4n-6), and estimated D5D were lower in the serum PLs, whereas total SFA level, Mg, and Zn were higher in Chinese men with MetS compared with healthy population. However, Mg and 18:2n-6 are low, whereas 20:3n-6 is high in MetS subjects of Western countries. The total PUFA, n-3 PUFA, and n-6 PUFA were negatively associated with the MetS, whereas the SFA was positively

associated with MetS in Chinese male population. Our results may reflect improper dietary intake in these MetS subjects and thus dietary adjustment may have therapeutic significance for Chinese men with MetS. However, environmental factors, such as dietary intake and physical activity, have not been taken into consideration in the present study. Furthermore, it is not known whether a diet high in SFA and low in polyunsaturated fat acids can lead to the development of the MetS or whether the genes that predispose to the development of MetS are also associated with preference for a diet high in SFA and low in polyunsaturated fat acids. The combined effects of environmental and genetic factors need to be considered in future investigations of dietary FA and MetS. Acknowledgment This study was funded by the National Natural Science Foundation of China (No. 30972464), the National Basic Research Program of China (973 Program: 2011CB504002), and National Health and Medical Research Council of Australian Government (573441). The authors state that there are no conflicts of interest. References [1] Alberti KGMM, Zimmet P, Shaw J. The metabolic syndrome-a new worldwide definition. The Lancet 2005;366(9491):1059-62. [2] Gu D, Reynolds K, Wu X, Chen J, Duan X, Reynolds R, Whelton P, He J. Prevalence of the metabolic syndrome and overweight among adults in China. Lancet 2005;365:1398-405. [3] Skeaff CM, Hodson L, McKenzie JE. Dietary-induced changes in fatty acid composition of human plasma, platelet, and erythrocyte lipids follow a similar time course. J Nutr 2006;136(3):565-9. [4] Vessby B, Gustafsson I, Tengblad S. Desaturation and elongation of fatty acids and insulin action. Ann N Y Acad Sci 2002;967:183-95. [5] Warensjo E, Sundstrom J, Lind L, Vessby B. Factor analysis of fatty acids in serum lipids as a measure of dietary fat quality in relation to the metabolic syndrome in men. Am J Clin Nutr 2006;84(2):442-8. [6] Aguilar MV, Saavedra P, Arrieta FJ, Mateos CJ, González MJ, Meseguer I. MC. M-P. Plasma mineral content in type-2 diabetic patients and their association with the metabolic syndrome. Ann Nutr Metab 2007;51(5):402-6. [7] Song C, Choi W, Oh H, Kim K. Associations of serum minerals with body mass index in adult women. Eur J Clin Nutr 2007;61(5):682-5. [8] Laurant P, Kantelip JP, Berthelot A. Dietary magnesium supplementation modifies glood bressure and cardiovascular function in mineralocorticoid-salt hypertensive rats but Not in Normotensive Rats. J Nutr 1995;125(4):830-41. [9] Hughes S, Samman S. The effect of zinc supplementation in humans on plasma lipids, antioxidant status and thrombogenesis. J Am Coll Nutr 2006;25(4):285-91. [10] Clejan S, Castro-Magana M, Collipp P, Jonas E, Maddaiah V. Effects of Zinc deficiency and castration on fatty acid composition and desaturations in rats. Lipids 1982;17(3):129-35. [11] Mahfouz M, Kummerow F. Effect of Magnesium defficiency on Delta 6 desaturase activity and fatty acid composition rat liver microsomes. Lipids 1989;24(8):727-32. [12] Warensjo E, Riserus U, Vessby B. Fatty acid composition of serum lipids predicts the development of the metabolic syndrome in men. Diabetologia 2005;48(10):1999-2005. [13] Kabagambe EK, Tsai MY, Hopkins PN, Ordovas JM, Peacock JM, Borecki IB, Arnett DK. Erythrocyte fatty acid composition and the

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