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Effects of a flaxseed-derived lignan supplement on C-reactive protein, IL-6 and retinol-binding protein 4 in type 2 diabetic patients

Published online by Cambridge University Press:  08 September 2008

An Pan
Affiliation:
Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, 294 Tai-Yuan Road, Shanghai200031, China
Wendy Demark-Wahnefried
Affiliation:
Department of Behavioral Science, The University of Texas-MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
Xingwang Ye
Affiliation:
Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, 294 Tai-Yuan Road, Shanghai200031, China
Zhijie Yu
Affiliation:
Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, 294 Tai-Yuan Road, Shanghai200031, China
Huaixing Li
Affiliation:
Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, 294 Tai-Yuan Road, Shanghai200031, China
Qibin Qi
Affiliation:
Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, 294 Tai-Yuan Road, Shanghai200031, China
Jianqin Sun
Affiliation:
Huadong Hospital, Fudan University, 221 West Yan-An Road, 200040, Shanghai, China
Yanqiu Chen
Affiliation:
Huadong Hospital, Fudan University, 221 West Yan-An Road, 200040, Shanghai, China
Xiafei Chen
Affiliation:
Huadong Hospital, Fudan University, 221 West Yan-An Road, 200040, Shanghai, China
Yong Liu
Affiliation:
Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, 294 Tai-Yuan Road, Shanghai200031, China
Xu Lin*
Affiliation:
Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, 294 Tai-Yuan Road, Shanghai200031, China
*
*Corresponding author: Dr Xu Lin, fax +86 21 54920249, email xlin@sibs.ac.cn
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Abstract

Elevated C-reactive protein (CRP), IL-6 and retinol-binding protein 4 (RBP4) levels are associated with insulin resistance and diabetes mellitus. Phytoestrogens (including lignans and isoflavones) may enhance the management of diabetes and are hypothesized to act through inflammation pathways. The present study explored the effects of flaxseed-derived lignan on inflammatory factors and RBP4 concentrations in type 2 diabetics, who have higher levels of these biomarkers. Seventy community-dwelling diabetic patients (twenty-six men and forty-four post-menopausal women) with mild hypercholesterolaemia completed a randomized, double-blind, placebo-controlled, cross-over trial of supplementation with flaxseed-derived lignan capsules (360 mg/d) or placebo for 12 weeks, separated by an 8-week wash-out period. The participants maintained their habitual diets and levels of physical activity. Baseline to follow-up concentrations of CRP increased significantly within the placebo group (1·42 (sem 0·19) v. 1·96 (sem 0·22) mg/l, P < 0·001), but were comparatively unchanged in the lignan-supplemented group (1·67 (sem 0·19) v. 1·90 (sem 0·26) mg/l, P = 0·94); a significant difference was observed between treatments ( − 0·45 (95 % CI − 0·76, − 0·08) mg/l, P = 0·021). This effect was confined to women (P = 0·016), but not observed in men (P = 0·49). No between-treatment differences were found with regard to IL-6 or RBP4; though IL-6 concentrations increased significantly from baseline to follow-up in both groups (P = 0·004 and P < 0·001 following lignan and placebo treatments, respectively). The study suggests that lignan might modulate CRP levels in type 2 diabetics. These results need to be confirmed by further large clinical trials of longer duration.

Type
Short Communication
Copyright
Copyright © The Authors 2008

Several studies suggest that chronic inflammation, as indicated by elevated levels of inflammatory factors such as C-reactive protein (CRP) and IL-6, plays an important role in the pathogenesis of diabetes mellitus(Reference Plutzky1Reference Duncan, Schmidt, Pankow, Ballantyne, Couper, Vigo, Hoogeveen, Folsom and Heiss3). Recently, retinol-binding protein 4 (RBP4), a protein product of hepatocytes and adipocytes, has been associated with insulin resistance, diabetes(Reference Polonsky4, Reference Qi, Yu and Ye5) and inflammation(Reference Balagopal, Graham, Kahn, Altomare, Funanage and George6).

A growing body of evidence suggests that certain chronic disorders, including diabetes, dyslipidaemia and CVD, are responsive to dietary phytoestrogens (isoflavones and lignans)(Reference Bhathena and Velasquez7, Reference Bloedon and Szapary8), which may modulate disease risk through inflammatory pathways(Reference Si and Liu9). Flaxseed is the richest food source of the plant lignan, secoisolariciresinol diglucoside(Reference Kurzer and Xu10). In a recent study of twenty-two healthy post-menopausal women, Hallund et al. (Reference Hallund, Tetens, Bugel, Tholstrup and Bruun11) observed significantly lower CRP concentrations in participants receiving a lignan complex (500 mg secoisolariciresinol diglucoside/d) for 6 weeks compared to those on placebo. Hall et al. (Reference Hall, Vafeiadou and Hallund12) also detected beneficial effects on CRP with 8-week supplementation of isolated isoflavones (50 mg/d) in 170 healthy post-menopausal women. However, other studies using isoflavones have produced null findings(Reference Nikander, Metsa-Heikkila, Tiitinen and Ylikorkala13Reference Hanson, Engelman, Alekel, Schalinske, Kohut and Reddy16).

We have previously reported that a flaxseed-derived lignan supplement moderately decreased glycated Hb levels in type 2 diabetics(Reference Pan, Sun and Chen17). The present study is a secondary analysis, and is aimed at exploring the impact of lignan supplementation on CRP, IL-6 and RBP4 levels in an effort to better understand the effects of lignan on diabetes.

Methods

Study design and participants

The methods of the parent study were detailed elsewhere(Reference Pan, Sun and Chen17). Briefly, seventy-three type 2 diabetic patients (twenty-eight men and forty-five post-menopausal women) aged 50–79 years were consented and randomized in a crossover design to a double-blind, placebo-controlled study with 12-week supplementation of lignan or placebo capsules separated by an 8-week washout period. Randomization was performed using stratification factors of gender and tertiled LDL-cholesterol concentrations (the primary end-point of the parent study).

Intervention

The lignan capsules (LinumLife™ Extra; Frutarom Netherlands BV, Veenendaal, The Netherlands) provided a daily dose of 360 mg flaxseed-derived secoisolariciresinol diglucoside. The three capsules provided 15·5 kJ and were comprised of 20 % secoisolariciresinol diglucoside, 30 % carbohydrate, 15·6 % fat, 3·2 % protein and 2·6 % fibre. The placebo was an identical capsule of rice flour devoid of soluble fibre. The participants took three capsules per day (1·8 g) which contributed minimally to their daily energy and nutrient intake. Adherence was assessed by pill counts and urinary concentrations of lignan metabolites(Reference Pan, Sun and Chen17). While on study, participants were required to take their regularly prescribed medications, and maintain their habitual diets and physical activity levels.

Measurements

Fasting venous blood samples were collected at the beginning and completion of each intervention period. Serum CRP was measured via a high-sensitive immunoturbidimetric assay on a Hitachi 7080 automatic analyser using commercial kits (Roche Diagnostics, Mannheim, Germany). IL-6 was measured by a high-sensitive ELISA (R&D Systems, Minneapolis, USA). Plasma RBP4 was measured by an in-house-developed sandwich ELISA, detailed elsewhere(Reference Qi, Yu and Ye5). Fasting morning urine samples (50 ml) were collected at identical time-points using plastic jugs containing 50 mg ascorbic acid. Urinary lignan metabolites were analysed using HPLC as reported previously(Reference Pan, Sun and Chen17).

Statistical analyses

The power calculations of our previous study were based on serum lipids and were described previously(Reference Pan, Sun and Chen17). In the present exploratory secondary analysis, a total of sixty participants provide 80 % power with an α level of 0·05 (two-sided) to detect between-treatment differences of 0·30 mg/l, 0·30 pg/ml and 14·6 μg/ml on CRP, IL-6 and RBP4, respectively.

Data were analysed in Stata 9.2 (Stata™; Texas, USA); the two-sided P value ≤ 0·05 was considered statistically significant. For all biomarkers, the data were natural-logarithmically transformed prior to analysis. Paired Student's t tests were used to compare differences between baseline and end of treatment. Differences between values after the 12-week intervention were analysed using a mixed model analysis of covariance with treatment and period as fixed factors, participants as random factors and baseline values as covariates. Further fixed terms corresponding to treatment–period and treatment–baseline value interactions were included. Given the weight-dependent nature of the study end-points, baseline weight and weight changes during treatment also were incorporated as covariates. The analyses were further stratified by gender to explore differential effects in males and females.

Participants with extremely high levels of CRP ( ≥ 10 mg/l) or IL-6 ( ≥ 10 pg/ml) were considered to have acute inflammation and were excluded from the final mixed models. Sixty-four participants remained for CRP analyses and sixty-seven remained for IL-6 analyses.

Results

Of the seventy-three participants consented, three participants dropped out for reasons described previously(Reference Pan, Sun and Chen17). Seventy (twenty-six men and forty-four women) completed the study and were available for analyses. The mean age of the sample was 62·9 (sd 7·5) years.

Significant increases in CRP concentrations were found from baseline to follow-up within the placebo group (P < 0·001), while those in the lignan treatment group did not experience increases of similar magnitude (P = 0·94). Thus, compared to placebo, increases in CRP with the lignan supplement were significantly lower (P = 0·021). These differences were primarily observed in women (P = 0·016), and not in men (P = 0·49) (Table 1).

Table 1 Baseline and 12-week follow-up levels of C-reactive protein (CRP), IL-6 and retinol-binding protein 4 (RBP4) in placebo v. lignan-supplemented study groups

(Mean values with their standard errors)

Mean values were significantly different from those of the baseline: *P < 0·05, **P < 0·01, ***P < 0·001.

For details of subjects and procedures, see Methods.

P values are shown for the treatment effect analysed using a mixed model analysis of covariance.

In contrast, IL-6 concentrations significantly increased from baseline to follow-up in both groups, with no between-treatment difference observed. Likewise, no between-treatment difference was detected in levels of RBP4, which remained at fairly stable levels throughout the study period. Additionally, urinary excretion of lignan metabolites increased significantly after lignan treatment. As reported previously, no significant differences were observed for energy and nutrient intake, and physical activity between treatment phases over time(Reference Pan, Sun and Chen17).

Discussion

The CRP concentrations in the placebo group increased significantly over the study period. This is an unexpected finding, and the exact reasons are unclear. Elevated levels of CRP, however, have been documented among diabetic patients and correlated with both glycaemic control and complications(Reference Plutzky1). Speculation exists that increased CRP concentrations may reflect aggravated diabetes management within these individuals. Furthermore, some participants had medication changes during the study period, which also might have influenced their inflammatory status. Although CRP levels increased slightly in the lignan-treated group, this increase was not statistically significant. The present findings are similar to a recent study by Hallund et al. (Reference Hallund, Tetens, Bugel, Tholstrup and Bruun11) which also employed a crossover design delivering placebo v. a lignan supplement (500 mg secoisolariciresinol diglucoside/d) among twenty-two healthy post-menopausal women. They also found greater increases in CRP during the placebo period (from 0·80 to 1·10 mg/l) than during lignan treatment (from 0·88 to 0·92 mg/l) (P = 0·028). Similarly, Teede et al. (Reference Teede, Dalais and McGrath18) also found increased CRP levels over 3-month treatments of soya (from 1·91 to 2·33 mg/l) and placebo (from 1·39 to 1·87 mg/l) in fifty healthy post-menopausal women, however no between-treatment difference was observed.

The present findings of moderate protective effects on CRP are consistent with the results of five previous trials that either tested isolated lignans(Reference Hallund, Tetens, Bugel, Tholstrup and Bruun11) or isoflavones(Reference Hall, Vafeiadou and Hallund12), flaxseed flour(Reference Faintuch, Horie, Barbeiro, Barbeiro, Soriano, Ishida and Cecconello19) or soya protein(Reference Azadbakht, Atabak and Esmaillzadeh20, Reference Azadbakht, Kimiagar, Mehrabi, Esmaillzadeh, Hu and Willett21). However, the present findings differ from studies which tested isolated isoflavones(Reference Nikander, Metsa-Heikkila, Tiitinen and Ylikorkala13Reference Hanson, Engelman, Alekel, Schalinske, Kohut and Reddy16) or whole flaxseed(Reference Dodin, Cunnane and Masse22, Reference Bloedon, Balikai and Chittams23), which found no differences with respect to CRP. It must be borne in mind that the difference that we observed between placebo and lignan-treated groups in the present study was primarily due to increased levels of CRP following the placebo period, rather than a direct reduction by lignan treatment. Therefore, given the exploratory nature of the present study, it remains premature to draw the conclusion that lignan can actually lower CRP levels.

Furthermore, stratified analysis found that the significant between-treatment difference of CRP concentrations was confined to females. One potential explanation is the relatively small sample of males. For detecting a between-treatment difference of 0·20 mg/l, 126 participants would be required to have a power of 80 %. The second possibility may be that although not statistically significant, post-menopausal women had moderately higher CRP levels than men, therefore, they were more likely to be responsive to phytoestrogens. Previous studies suggest that the metabolism and excretion of phytoestrogens differ between men and women(Reference Lu and Anderson24); however, it is currently unknown whether gender variation in the phytoestrogen bioavailability plays a role in CRP response.

The present findings of no effect on IL-6 are consistent with data from another study in which forty-two post-menopausal women with metabolic syndrome consumed soya protein or soy nuts (30 g/d containing 84–102 mg isoflavones) for 8 weeks(Reference Azadbakht, Kimiagar, Mehrabi, Esmaillzadeh, Hu and Willett21). In contrast, Jenkins et al. (Reference Jenkins, Kendall, Connelly, Jackson, Parker, Faulkner and Vidgen25) found that IL-6 levels increased significantly after 1 month of a high soya diet (containing 73 mg isoflavones/d) compared to control among eighteen hypercholesterolaemic post-menopausal women. In the present study, the results of CRP and IL-6 did not follow the same pattern, which is also found in previous reports using lignan(Reference Hallund, Tetens, Bugel, Tholstrup and Bruun11) or flaxseed(Reference Bloedon, Balikai and Chittams23). A possible explanation for the present finding is that although IL-6 is the major inducer of CRP in the liver, other pro-inflammatory factors could also induce CRP production in other cell types(Reference Calabro, Willerson and Yeh26).

RBP4 is a newly recognized adipokine associated with obesity, insulin resistance and diabetes(Reference Polonsky4, Reference Qi, Yu and Ye5). A previous study showed that RBP4 levels decreased in parallel to weight loss and increased LDL-cholesterol catabolism after a 16-week intervention of a hypoenergetic low-fat diet in men with metabolic syndrome(Reference Ng, Watts, Barrett, Rye and Chan27). In our previous study, we found no effects of lignan supplementation on weight, lipid profiles and insulin resistance(Reference Pan, Sun and Chen17). Therefore, it is possible that RBP4 levels were not affected. Since whole or defatted flaxseed has consistently shown to be effective in improving insulin resistance, and lowering total and LDL-cholesterol(Reference Bhathena and Velasquez7, Reference Bloedon and Szapary8), its potential impact on RBP4 levels needs to be elucidated in future.

In conclusion, flaxseed lignan may suppress CRP elevation in type 2 diabetics without affecting IL-6 and RBP4 concentrations compared to placebo. However, further studies are needed to validate the present results and explore the efficacy of phytoestrogens on inflammatory factors before consensus is achieved.

Acknowledgements

This study was funded by the Knowledge Innovation Program Project of the Chinese Academy of Sciences (KSCX1-YW-02, KSCX2-YW-R-116), the Science and Technology Commission of Shanghai Municipality (04DZ14007) and the Ministry of Science and Technology of China (973 Program, Grant 2006CB503902). We thank Dr Marian Verbruggen of Frutarom Netherlands BV and Mrs Guo Peilin of Jarrow Formulas Inc. for their kind donation of study capsules. A. P., W. D.-W., Z. Y., H. L., J. S., Y. C., X. C., Y. L. and X. L. contributed to the conception and design of the study. A. P., X. Y., Z. Y. and Y. C. contributed to the data collection and management of the study subjects. A. P., X. Y., H. L. and Q. Q. conducted the biomarkers measurement. A. P., X. Y. and Z. Y. carried out the statistical analyses. A. P. wrote the first draft of the manuscript with help from W. D.-W., X. Y., H. L., Z. Y. and X. L. All authors participated in the writing of the final draft of the manuscript and the final interpretation of the data. None of the authors had any conflicts of interest.

References

1Plutzky, J (2004) Inflammation in atherosclerosis and diabetes mellitus. Rev Endocr Metab Disord 5, 255259.Google Scholar
2Hu, FB, Meigs, JB, Li, TY, Rifai, N & Manson, JE (2004) Inflammatory markers and risk of developing type 2 diabetes in women. Diabetes 53, 693700.Google Scholar
3Duncan, BB, Schmidt, MI, Pankow, JS, Ballantyne, CM, Couper, D, Vigo, A, Hoogeveen, R, Folsom, AR & Heiss, G (2003) Low-grade systemic inflammation and the development of type 2 diabetes: the atherosclerosis risk in communities study. Diabetes 52, 17991805.Google Scholar
4Polonsky, KS (2006) Retinol-binding protein 4, insulin resistance, and type 2 diabetes. N Engl J Med 354, 25962598.Google Scholar
5Qi, Q, Yu, Z, Ye, X, et al. (2007) Elevated retinol-binding protein 4 levels are associated with metabolic syndrome in Chinese people. J Clin Endocrinol Metab 92, 48274834.Google Scholar
6Balagopal, P, Graham, TE, Kahn, BB, Altomare, A, Funanage, V & George, D (2007) Reduction of elevated serum retinol binding protein in obese children by lifestyle intervention: association with subclinical inflammation. J Clin Endocrinol Metab 92, 19711974.Google Scholar
7Bhathena, SJ & Velasquez, MT (2002) Beneficial role of dietary phytoestrogens in obesity and diabetes. Am J Clin Nutr 76, 11911201.Google Scholar
8Bloedon, LT & Szapary, PO (2004) Flaxseed and cardiovascular risk. Nutr Rev 62, 1827.Google Scholar
9Si, H & Liu, D (2007) Phytochemical genistein in the regulation of vascular function: new insights. Curr Med Chem 14, 25812589.Google Scholar
10Kurzer, MS & Xu, X (1997) Dietary phytoestrogens. Annu Rev Nutr 17, 353381.Google Scholar
11Hallund, J, Tetens, I, Bugel, S, Tholstrup, T & Bruun, JM (2008) The effect of a lignan complex isolated from flaxseed on inflammation markers in healthy postmenopausal women. Nutr Metab Cardiovasc Dis 18, 497502.Google Scholar
12Hall, WL, Vafeiadou, K, Hallund, J, et al. (2005) Soy-isoflavone-enriched foods and inflammatory biomarkers of cardiovascular disease risk in postmenopausal women: interactions with genotype and equol production. Am J Clin Nutr 82, 12601268.Google Scholar
13Nikander, E, Metsa-Heikkila, M, Tiitinen, A & Ylikorkala, O (2003) Evidence of a lack of effect of a phytoestrogen regimen on the levels of C-reactive protein, E-selectin, and nitrate in postmenopausal women. J Clin Endocrinol Metab 88, 51805185.Google Scholar
14D'Anna, R, Baviera, G, Corrado, F, Cancellieri, F, Crisafulli, A & Squadrito, F (2005) The effect of the phytoestrogen genistein and hormone replacement therapy on homocysteine and C-reactive protein level in postmenopausal women. Acta Obstet Gynecol Scand 84, 474477.Google Scholar
15Ryan-Borchers, TA, Park, JS, Chew, BP, McGuire, MK, Fournier, LR & Beerman, KA (2006) Soy isoflavones modulate immune function in healthy postmenopausal women. Am J Clin Nutr 83, 11181125.Google Scholar
16Hanson, LN, Engelman, HM, Alekel, DL, Schalinske, KL, Kohut, ML & Reddy, MB (2006) Effects of soy isoflavones and phytate on homocysteine, C-reactive protein, and iron status in postmenopausal women. Am J Clin Nutr 84, 774780.Google Scholar
17Pan, A, Sun, J, Chen, Y, et al. (2007) Effects of a flaxseed-derived lignan supplement in type 2 diabetic patients: a randomized, double-blind, cross-over trial. PLoS ONE 2, e1148.Google Scholar
18Teede, HJ, Dalais, FS & McGrath, BP (2004) Dietary soy containing phytoestrogens does not have detectable estrogenic effects on hepatic protein synthesis in postmenopausal women. Am J Clin Nutr 79, 396401.Google Scholar
19Faintuch, J, Horie, LM, Barbeiro, HV, Barbeiro, DF, Soriano, FG, Ishida, RK & Cecconello, I (2007) Systemic inflammation in morbidly obese subjects: response to oral supplementation with alpha-linolenic acid. Obes Surg 17, 341347.Google Scholar
20Azadbakht, L, Atabak, S & Esmaillzadeh, A (2008) Soy protein intake, cardiorenal indices, and C-reactive protein in type 2 diabetes with nephropathy: a longitudinal randomized clinical trial. Diabetes Care 31, 648654.Google Scholar
21Azadbakht, L, Kimiagar, M, Mehrabi, Y, Esmaillzadeh, A, Hu, FB & Willett, WC (2007) Soy consumption, markers of inflammation, and endothelial function: a cross-over study in postmenopausal women with the metabolic syndrome. Diabetes Care 30, 967973.Google Scholar
22Dodin, S, Cunnane, SC, Masse, B, et al. (2008) Flaxseed on cardiovascular disease markers in healthy menopausal women: a randomized, double-blind, placebo-controlled trial. Nutrition 24, 2330.Google Scholar
23Bloedon, LT, Balikai, S, Chittams, J, et al. (2008) Flaxseed and cardiovascular risk factors: results from a double blind, randomized, controlled clinical trial. J Am Coll Nutr 27, 6574.Google Scholar
24Lu, LJ & Anderson, KE (1998) Sex and long-term soy diets affect the metabolism and excretion of soy isoflavones in humans. Am J Clin Nutr 68, Suppl. 6, S1500S1504.Google Scholar
25Jenkins, DJ, Kendall, CW, Connelly, PW, Jackson, CJT, Parker, T, Faulkner, D & Vidgen, E (2002) Effects of high- and low-isoflavone (phytoestrogen) soy foods on inflammatory biomarkers and proinflammatory cytokines in middle-aged men and women. Metabolism 51, 919924.Google Scholar
26Calabro, P, Willerson, JT & Yeh, ET (1997) Inflammatory cytokines stimulated C-reactive protein production by human coronary artery smooth muscle cells. Circulation 21, (108), 19301932.Google Scholar
27Ng, TW, Watts, GF, Barrett, PH, Rye, KA & Chan, DC (2007) Effect of weight loss on LDL and HDL kinetics in the metabolic syndrome: associations with changes in plasma retinol-binding protein-4 and adiponectin levels. Diabetes Care 30, 29452950.Google Scholar
Figure 0

Table 1 Baseline and 12-week follow-up levels of C-reactive protein (CRP), IL-6 and retinol-binding protein 4 (RBP4) in placebo v. lignan-supplemented study groups†(Mean values with their standard errors)