Skip Navigation


NDT Advance Access originally published online on June 9, 2006
Nephrology Dialysis Transplantation 2006 21(8):2239-2246; doi:10.1093/ndt/gfl169
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
21/8/2239    most recent
gfl169v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (5)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Fanti, P.
Right arrow Articles by Franke, A. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fanti, P.
Right arrow Articles by Franke, A. A.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author [2006]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Original Articles: Dialysis and Transplantation

Positive effect of dietary soy in ESRD patients with systemic inflammation—correlation between blood levels of the soy isoflavones and the acute-phase reactants

Paolo Fanti1, Reto Asmis1, Tammy J. Stephenson2, B. Peter Sawaya3 and Adrian A. Franke4

1 Division of Nephrology, University of Texas Health Science Center, San Antonio, TX, 2 Department of Nutrition and Food Science, 3 Division of Nephrology, Bone and Mineral Metabolism, University of Kentucky, Lexington, KY and 4 Cancer Research Center, University of Hawaii, Honolulu, HI, USA

Correspondence and offprint requests to: Paolo Fanti, MD, Division of Nephrology – MC 7882, University of Texas, Health Science Center at San Antonio, 7703, Floyd Curl Drive, San Antonio, TX 78229, USA. Email: fanti{at}uthscsa.edu



   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Background. Inflammation is commonly associated with malnutrition and cardiovascular disease in end-stage renal failure patients. Anti-inflammatory properties of the isoflavones, a micronutrient component of soy, have been reported in several experimental models and disease conditions, but never in renal failure. We hypothesized that dietary soy isoflavones correct laboratory evidence of systemic inflammation in haemodialysis (HD) patients with underlying high blood levels of C-reactive protein (CRP).

Methods. End-stage renal disease patients on chronic HD, with elevated CRP (>10.0 mg/l) were enrolled in this pilot study. The subjects were double-blind randomly distributed with 2 : 1 ratio to receive isoflavone-containing soy-based nutritional supplements (soy group) or isoflavone-free milk protein (control group) for 8 weeks. Serum isoflavone, inflammatory markers and nutrition markers were assessed at baseline and at the end of the treatment.

Results. Thirty-two subjects were enrolled. Fifteen subjects in the soy group and 10 in the control group completed the study; five dropouts were due to acute illness and two due to food intolerance. After intervention, blood isoflavone levels were 5- to 10-fold higher in the soy group than in the control group [e.g. median genistein (25–75th percentile): 337.9 (175.5–1007) nM in the soy group vs 41.4 (22.9–100.4) nM in the control group; P < 0.001]. However, the isoflavone levels ranged widely in the soy group (e.g. genistein: 33–1868 nM) and, depending on the individual compound, four to seven subjects had end-of-treatment levels that were not different from baseline. Variation from baseline of the individual serum isoflavone levels ({Delta}-isoflavone) and CRP displayed a strong inverse correlation in the soy group (R = –0.599, P < 0.02). In addition, {Delta}-isoflavone correlated positively with the variation of albumin (R = 0.522, P = 0.05) and insulin-like growth factor-1 (R = 0.518, P < 0.05). Group levels of CRP were not statistically different after intervention although a trend towards lower levels was noted in the soy group [18.2 (12.7–29.1) mg/l at baseline vs 9.7 (5.2–20.7) mg/l at week 8; NS] but not in the control group [20.6 (9.2–38.5) vs 17.6 (9.1–40.7) mg/l].

Conclusion. These data suggest the possibility of beneficial effects of isoflavone-rich soy foods on the inflammatory and nutritional status of HD patients with underlying systemic inflammation.

Keywords: albumin; C-reactive protein; daidzein; genistein; IGF-1; phytochemicals



   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Inflammation is a common problem and an important predictor of morbidity and mortality in Western European and North American end-stage renal disease (ESRD) patients [1]. The negative impact of chronic inflammation in renal failure seems to result primarily from its association with poor nutritional status and accelerated cardiovascular disease [2,3]. The clinical significance of this problem is magnified by the fact that the therapeutic options for reducing inflammation, and thus preventing malnutrition and accelerated cardiovascular disease, are very limited. No effective strategies are available for improving survival rates.

Epidemiological evidence suggests that Southeast Asian ESRD patients have lower morbidity and mortality than their counterparts in Western countries [4]. For example, Japanese dialysis patients had 50% lower 1 year mortality rates than US patients, an advantage that appears unrelated to the quality of dialysis therapy or medical care [5]. It is currently unknown whether this advantage may be explained by genetic differences between the two populations or whether social factors such as lifestyle and diet play a role. Human consumption of soy as food is one of the dietary practices that set the Southeast Asian and Western populations apart. There is evidence that Southeast Asian dialysis patients eat soy, as inferred from diet questionnaires and blood isoflavone levels [6]. Soybeans, besides being an important traditional source of protein and energy for the Southeast Asian populations, have been recognized more recently as the only human food rich in isoflavones, a unique class of micronutrients [7]. The isoflavones are biologically active heterocyclic phenols that are absorbed by the intestine, circulate systemically and are eliminated by the kidneys and liver [8]. Genistein and daidzein, the most abundant and most extensively investigated isoflavones, have been attributed the ability of modulating the reproductive function and of preventing cardiovascular disease, osteoporosis and cancer [7]. Biological features of the isoflavones that may be particularly relevant to renal failure patients are their anti-inflammatory effects [9,10].

Because of the anti-inflammatory effects of isoflavones demonstrated both in in vitro and in vivo models with preserved renal function, we have formulated the hypothesis that dietary intake of soy isoflavones may significantly reduce inflammation in ESRD patients.



   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
Patient population and protocol
Sixty-two adult ESRD patients suspected of suffering from inflammation without a clinically identifiable cause were enrolled. The suspicion of inflammation was based on the presence of at least one of the following features: serum albumin ≤3.5 g/dl, ferritin ≥800 ng/ml, C-reactive protein (CRP) ≥10 mg/l, erythropoietin-resistant anaemia and/or body weight >10% below ideal. Subjects were excluded from the study if clinical causes of inflammation (e.g. active infection, immune dysfunction, inflammatory bowel disease, collagen vascular disease and malignancy) were discovered during the screening interview, complete physical examination and review of the medical record. Other exclusion criteria were enlistment in the chronic haemodialysis (HD) programme for <4 months, and use of antibiotics or hospital admissions during the 2 months prior to screening or at any time during the study. After enrolment, inflammation was confirmed by the detection of CRP levels ≥10.0 mg/l in two specimens that were collected just before consecutive dialytic sessions via the venous HD needle. This CRP concentration is 2.5 SD above the mean of the reference normal population and, thus, it is higher than our laboratory upper limit of normal (8.0 mg/l). This concentration was chosen empirically to increase the likelihood that the recruited subjects suffered from inflammation. Out of 62 subjects, 32 fulfilled all criteria and were randomly distributed with a 2:1 ratio to the 8-week double-blind intervention with isoflavone-containing soy-based nutritional supplements (soy group: n = 19) or with isoflavone-free milk-based supplements (control group; n = 13). All subjects were dialysed three times per week with reused low-flux Fresenius F6 or F8 polysulfone membranes (Fresenius Medical Care, Lexington, MA). The average treatment duration was 3.96 ± 0.12 h, with blood flow 385 ± 12 ml/min and dialysate flow 800 ml/min. The single-pool Kt/V was 1.48 ± 0.06. To test the primary hypothesis, two blood specimens were collected during the week preceding initiation of intervention (baseline) and during week 8 of intervention (end of treatment). To calculate the normalized protein catabolic rate (nPCR), blood samples were obtained immediately before and at the end of the mid-week dialysis treatment with stop flow/stop pump technique [11], 2 weeks prior to starting the intervention and at weeks 0, 2, 4, 6 and 8 of intervention. Clinical information was collected weekly by patient interview and by review of the out-patient dialysis medical record. Dietary intake was assessed monthly using a 24-h diet recall and nutrient intake was calculated using Nutritionist V software (First Data Bank, San Jose, CA). Records of all out-patient clinic and emergency room encounters and hospital admissions were reviewed and the pertinent information recorded. The study was approved by the University of Kentucky, Office of Research Integrity. Written informed consent was obtained from every potential subject before the screening interview.

Dietary intervention
Dietary intervention consisted of intake of a protein drink under direct supervision, during each scheduled dialysis session, and of a protein snack bar or a cereal-like breakfast product on each non-dialysis day. All products were packaged as single servings and code-labelled to ensure that investigators and subjects were blinded to the active ingredients. The soy products were made with soy protein isolate (Supro®Soy; The Solae Company; St Louis, MO) that retained the isoflavone content of the whole bean. The control products were made with milk protein (casein plus whey). As shown in Table 1, the supplement composition differed exclusively in the protein quality (soy or milk protein) and in the presence of isoflavones in the soy-based but not in the milk-based supplement. The drinks were prepared on the day of consumption by reconstituting the powder supplement with 200 ml of soft drink or juice. The snack bars and the cereal-like products contained approximately the same calories but half the protein and isoflavones of the aforementioned drinks and were chocolate, vanilla or lemon flavoured. Each product lot was tested for isoflavone content in our laboratory, prior to initiation of intervention. Compliance was checked weekly by snack bar and cereal box count. The investigational food was intended as a dietary supplement and, therefore, the patients were otherwise instructed to follow a self-selected, standard renal diet throughout the duration of the study.


View this table:
[in this window]
[in a new window]
  		Table 1. Nutrient composition of the protein powder, cereal-like product and energy bar

 
Ex vivo incubation of whole blood for analysis of interleukin-6 (IL-6) and tumour necrosis factor-{alpha} (TNF-{alpha}) production
The method described by Nerad et al. [12] was followed with minor modification. Seven millilitres of blood were drawn into sterile vacuum tubes with the anticoagulant EDTA [15% EDTA(K3) 11.7 µl/ml blood; Vacutainer®, Becton-Dickinson, Franklin Lakes, NJ]. The samples were kept at constant room temperature until processing, which occurred within 3 h. Two 3 ml aliquots were transferred into sterile non-pyrogenic polypropylene tubes (Becton-Dickinson) and incubated for 24 h at 36°C with either 50 ng/ml lipopolysaccharide (LPS, E. Coli 0111; B4; Sigma Chemicals, St Louis, MO) or vehicle (10 µl/ml phosphate-buffered saline). Following incubation, the samples were centrifuged for 10 min at 1500 r.p.m. and the plasma was collected and stored at –70°C.

Laboratory analysis
Serum CRP and pre-albumin were analysed by immunonephelometry using specific antibodies and the BN-100 nephelometer (Dade Behring Diagnostics, Deerfield, IL). For CRP, the measuring range was 0.2–1100 mg/l with sample dilution between 1 : 20 and 1 : 2000. The assay lowest calibration point was 0.2 mg/l. The coefficient of variation was 3.5% within assay and 3.2% between assays. The normal range (mean ± 2 SD) for our laboratory was <0.2–8.0 mg/l. Serum albumin was analysed with the bromocresol purple (BCP) colorimetric reaction (Vitros 950, Ortho Clinical Diagnostics, Raritan, NJ). Serum insulin-like growth factor-1 (IGF-1), ex vivo peripheral blood IL-6 and TNF-{alpha} were analysed using ELISA kits (R&D Systems, Minneapolis, MN) and the µQuant microplate reader (Biotech Instruments, Winooski, VT). The IGF-1 analysis included sample pre-treatment with an acidic solution to release IGF-1 from binding proteins. Serum isoflavones were analysed with liquid chromatography mass spectrometry as described previously [6]. Genistein, dihydrogenistein, daidzein, dihydrodaidzein, glycitein, equol and O-desmethylangolensin were detected and their composite constitutes the total isoflavones (see subsequently). Recovery of analytes through the whole procedure varied from 84 to 100% for genistein, from 79 to 100% for daidzein, from 96 to 100% for glycitein and from 77 to 100% for O-desmethylangolensin. Mean detection limits in dialysis patient serum (20 µl injection volume) were 1.08 pmol for daidzein, 4.2 pmol for equol, 0.015 pmol for glycitein, 0.86 pmol for genistein and 0.081 pmol for O-desmethylangolensin. Detection limits of pure standards were lower by a factor of 5–20. Inter-assay coefficients of variations for these analytes were 8–22% at levels below 20 nM, 7–14% at levels 20–100 nM and 3–12% at levels over 100 nM. To analyse the isoflavone content of the food supplement, 1 g aliquots of protein supplement were processed with a methanol-based extraction solution, followed by high-pressure liquid chromatography-photo diode array analysis [13]. The normalized Protein Catabolic Rate (nPCR) was used to estimate dietary protein intake. The PCR was calculated based on the single-pool, variable-volume model, mid-week formula ‘C0/{25.8 +[(1.15/(spKt/V)] + (56.4)/(spKt/V)} + 0.168’ [11], in which C0 = pre-dialysis blood urea nitrogen (BUN); spKt/V = –ln(R – 0.008 x t) + [4 – (3.5 x R)] x UF/W; R = post-dialysis/pre-dialysis BUN ratio; t = duration of the dialysis session in hours; UF = ultrafiltration volume in litres; W = post-dialysis weight in kilograms. PCR was normalized (nPCR) using the formula (urea nitrogen volume of distribution)/0.58 [11].

Statistical analysis
Individual serum CRP values are the average of two determinations at the start of consecutive HD treatments. All other values are single-point determinations. The Kolgomorov–Smirnov test was used to assess normality of distribution and the Levene test to assess homogeneity of variance. Variables are expressed as means ± SEM or medians (25–75th percentile), as appropriate. The transformation functions for non-normally distributed variables were selected based on normal probability plots. Two-tailed t-test for independent samples and univariate analysis of variance for repeated measurements were used for comparisons. Pearson correlation coefficient with two-tailed test of significance was utilized to analyse the association between blood isoflavone levels and inflammation and nutrition variables. SPSS 10.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis.



   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
Patient characteristics
The baseline clinical characteristics of all 25 subjects who completed the study and of the intervention groups are shown in Table 2. On average, the study subjects were 61.0 ± 2.9 years old and were moderately overweight. Of them, 40% were females and 60% African-Americans. The primary cause of ESRD was diabetes mellitus in 44% and hypertension in 36%. Intake of medications that could influence the immuno-inflammatory response, including aspirin, statins, angiotensin converting enzyme (ACE) inhibitors and calcitriol or analogues, was comparable between the two groups. The serum CRP ranged from 8.4 to 52.4 mg/l. The serum albumin, serum IGF-1, protein and energy intake, and the nPCR were low despite well-preserved serum pre-albumin and body mass index. The intervention groups were well balanced with respect to all variables.


View this table:
[in this window]
[in a new window]
  		Table 2. Baseline clinical characteristics

 
Effects of dietary intervention on nutrition and isoflavone levels
The effect of 8-week dietary intervention on nutrition and soy isoflavone levels is reported in Table 3. Dietary intervention resulted in just 6% increase in total protein intake, even through the nutritional supplements added 20–25% protein to the baseline daily intake. This suggests that the study subjects may have adapted to the nutritional supplements by decreasing the spontaneous protein intake. The calorie intake decreased by 7% in the controls and increased by 15% in the soy group, but these variations were not statistically significant. The protein and energy intake and the nPCR were not different between the control and the soy group, and between the baseline and end of treatment. At baseline, the isoflavone levels were low and not significantly different between the two groups. A 5- to 10-fold increase in mean isoflavone level was observed (P < 0.001) in the soy group at the end of the treatment. Despite this marked increase, the individual levels varied widely with seven subjects showing end-of-treatment daidzein concentrations within two standard deviations of the baseline and four subjects with similar findings for genistein and total isoflavones (Figure 1). The control group demonstrated no change in isoflavone levels at the end of the treatment.


View this table:
[in this window]
[in a new window]
  		Table 3. Dietary intake (A) and blood concentration of isoflavones, inflammation markers and nutrition markers (B) at baseline and at the end of 8 week intake of soy-based or milk-based supplements

 

Figure 1
View larger version (9K):
[in this window]
[in a new window]
  		Fig. 1. Individual fasting blood levels of genistein, daidzein and the total isoflavone pool in 15 HD patients, before and after 8 week intake of isoflavone-containing supplements. The dotted lines indicate the upper 95% confidence interval limit of the baseline mean concentration for the respective isoflavone.

 
Effects of dietary intervention on inflammation markers
Levels of markers of inflammation are reported in Table 3. Serum CRP was comparable between the groups at baseline and was not significantly affected by the dietary intervention (Table 3, P = 0.09). After treatment, CRP levels had fallen to within the normal range (<9.5 mg/l) in 7/15 soy-fed subjects (47%) vs 3/10 casein-fed subjects (30%). Figure 2B shows a significant inverse correlation between individual variation from baseline of CRP ({Delta}-CRP; end of treatment—baseline) and of total isoflavones ({Delta}-isoflavones) in the soy group (R = –0.599, P = 0.02). Comparison of Figure 2A and B shows that the range of {Delta}-CRP values (y-axis) was similar in the control and soy groups, although it was shifted more towards negative values in the soy group. In the same figures, the {Delta}-isoflavone values (x-axis) spanned from –1 to 7 µM in the soy group but were close to 0 µM in the control group. {Delta}-CRP also displayed an inverse correlation with {Delta}-genistein and {Delta}-daidzein, albeit not as strongly as with {Delta}-isoflavones. Similar to CRP, the mean concentration of secreted IL-6 and TNF-{alpha} in unstimulated whole-blood samples tended to decrease after soy intake (Table 3). The IL-6 and TNF-{alpha} concentrations increased 50–250-folds when LPS was added to the overnight incubation. The dietary intervention had no obvious effect on LPS-stimulated IL-6 and TNF-{alpha} (Table 3). As expected, individual variation from baseline of IL-6 ({Delta}-IL-6) displayed a strong positive correlation with that of TNF-{alpha} ({Delta}-TNF-{alpha}) in the soy group (R = 0.762, P < 0.01), but neither {Delta}-IL-6 nor {Delta}-TNF-{alpha} correlated with {Delta}-isoflavones concentrations. None of the inflammation markers displayed correlation with variation from baseline of energy intake ({Delta}-energy intake) or nPCR ({Delta}-nPCR). As expected, no correlation was present in the control group.


Figure 2
View larger version (15K):
[in this window]
[in a new window]
  		Fig. 2. Correlations between the individual variation from baseline of total isoflavone concentration ({Delta}-isoflavones) and CRP concentration ({Delta}-CRP) in the control group (A, open triangle) and soy group (B, closed triangle).

 
Effects of dietary intervention on nutritional markers
The albumin, IGF-1 and pre-albumin levels were comparable at baseline and did not change substantially after 8 weeks of dietary supplements (Table 3). However, the variation from baseline of albumin ({Delta}-albumin) displayed positive correlation with {Delta}-genistein, {Delta}-daidzein and {Delta}-total isoflavones, in the soy group (Figure 3B). A positive correlation was also present between {Delta}-albumin and {Delta}-nPCR, although the latter did not correlate with any of the isoflavones. In addition, variation in IGF-1 ({Delta}-IGF-1) showed significant positive correlations with {Delta}-genistein and {Delta}-total isoflavones, in the soy group (Figure 3D). No correlation was present in the control group between {Delta}-genistein, {Delta}-daidzein or {Delta}-total isoflavones and {Delta}-albumin (Figure 3A) or {Delta}-IGF-1 (Figure 3C). The isoflavones displayed a weaker correlation with change in pre-albumin.


Figure 3
View larger version (16K):
[in this window]
[in a new window]
  		Fig. 3. Correlations between the individual variation from baseline of total isoflavone concentration ({Delta}-isoflavones) and albumin ({Delta}-albumin) in the control group (A, open circle) and in the soy group (B, closed circle), and between {Delta}-isoflavones and the variation of IGF-1 ({Delta}-IGF-1) in the control group (C, open diamond) and in the soy group (D, closed diamond).

 
Study flow and tolerance of intervention
Thirty-two subjects participated and seven did not complete the study (four in the soy group and three in the control group). Five of these seven were eliminated because of protocol violations including extended hospital admission and use of antibiotics; one subject (soy group) withdrew because of the development of gastrointestinal symptoms that he attributed to the supplements; and one (control group) withdrew because of acquired distaste for the protein drinks. Compliance with the protein drinks during the dialysis sessions was 97% in the soy group and 94% in the control group. Compliance with the snack bars and the cereal-like product on the non-dialysis days was 77% in the soy group and 65% in the control group. Four subjects in the soy group and two in the control group requested switching between drinks, protein bars and cereal-like snacks to add variety to the supplement intake. The remaining subjects had no obvious preference for any one type of supplement.



   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
We report that blood levels of the micronutrient isoflavones correlate inversely with markers of inflammation and positively with markers of nutrition following 8-week intervention with soy food supplements in HD patients with underlying systemic inflammation. This pilot study is the first prospective investigation of the effect of soy foods on surrogate endpoints of clinical outcome in chronic renal failure.

The demographics and general characteristics of the study cohort were representative of both regional and national statistics, if not for a high number of African-Americans [14]. As expected, the study subjects displayed low serum albumin, a trait associated with increased morbidity and mortality in the ESRD population [1]. These findings are consistent with the main inclusion criterion of presence of underlying inflammation, as indicated by high CRP levels.

The study was based on the premise that high tissue levels of dietary isoflavones are necessary to elicit biological activity. Compliance with the food supplements was closely monitored and it was generally good. Nevertheless, seven out of 15 subjects had fasting levels of genistein below 300 nM, a concentration probably insufficient to elicit any significant biological effect [7]. In retrospect, failure of several patients to develop the desired rise in isoflavone levels is consistent with prior reports [8] and with the metabolism of other lipophilic micronutrients [15]. A multiplicity of factors may be involved in causing this variability: (i) intake of foods and medications that affect micronutrient assimilation [15]; (ii) gastrointestinal problems that commonly affect HD patients, e.g. altered intestinal transit time, microflora colonization, and altered integrity of the small intestine wall; (iii) presence of isoflavone degradation pathways in target tissues [16]; and (iv) genetic variation of such pathways. We reported before that the HD treatment does not affect blood isoflavone levels [8].

Despite a lack of group differences in markers of inflammation and nutrition at the end of intervention, the hypothesis that soy isoflavones are biologically active is supported by the robust inverse correlation between blood total isoflavones and the inflammation marker CRP. The positive correlation between blood total isoflavones, genistein and daidzein and the nutritional parameters albumin and IGF-1 further supports beneficial effects from these micronutrients. Concomitant interaction of the isoflavones with both markers of inflammation and nutrition is explained by the fact that albumin and IGF are not only nutritional markers but also negative acute-phase reactants [2]. The specific mechanisms of actions of the isoflavones in ESRD patients were not investigated in the current study and they remain objects of speculation. Blockade of tyrosine kinase activity and antioxidant activity are the known effects of isoflavones. Other reported activities of these micronutrients, such as activation of the estrogen receptor-{alpha} or -ß, activation of the peroxisome proliferator-activated receptor and direct interaction with several intracellular enzymes, are also candidate contributors to the observed response [10,17].

IGF-1 is a potent anabolic hormone which inhibits protein degradation and stimulates protein synthesis [18]. The peripheral levels of IGF-1 correlate inversely with systemic inflammation, both in subjects with preserved renal function and in the ESRD population [19]. Prior studies reported either modest or null effects of the isoflavones on peripheral blood IGF-1 [20]. It is likely, however, that the impact of the isoflavones on this hormone will depend on the underlying pathophysiological state. Subjects with marked suppression of peripheral blood IGF-1 concentration, such as our inflamed ESRD subjects, may therefore experience larger response to isoflavone exposure.

An intriguing aspect of this research is that the total isoflavones, but not genistein and/or daidzein, correlated individually with CRP, while all the aforesaid agents correlated with albumin and IGF-1. These discrepancies could be due to the small sample size. As an alternative, it should be noted that the total isoflavone pool includes several less-well studied, lower concentration compounds. It is possible that one or more of these compounds participate in the reduction of circulating CRP. For example, it was suggested recently that the daidzein metabolite equol has beneficial effects in cardiovascular disease [17]. Since only 30–50% of humans are capable of converting daidzein to equol, it is unclear to what extent this metabolite might have impacted the study outcome. The prevalence of equol producers is unknown among renal failure patients.

Also, somewhat surprising is the observation that the blood isoflavone levels correlated with CRP but not with two other markers of inflammation, i.e. IL-6 and TNF-{alpha}. These inconsistent findings may be explained by the relatively poor precision of the circulating levels of inflammatory cytokines, vis-à-vis the acute-phase reactant levels, as markers of inflammation in HD patients [21]. The small size of our patient sample may also have contributed to uncovering differences in precision between these markers. Another possible explanation is that the liver, i.e. the major producer of CRP, is exposed through the portal circulation to higher isoflavone concentrations than other tissues and organs. Conversely, the peripheral blood mononuclear leucocytes that we tested for production of IL-6 and TNF-{alpha} are exposed to relatively lower isoflavone concentrations. Lastly, IL-6 and TNF-{alpha} are just two of the cytokines involved in the inflammatory response. It is possible that the isoflavones selectively modulate other pro-inflammatory cytokines that are produced by the peripheral blood mononuclear cells but they were not tested in the current study.

The study has several limitations including the small size of the population sample and the lack of enrolment screening regarding individual ability to generate high blood isoflavone levels in response to diet. In addition, the active treatment and the control groups received dietary supplements with different protein base (milk vs soy isolates). Thus, although the strong correlation between blood isoflavone levels and the outcome markers of inflammation and nutrition points to these micronutrients as the major effectors, the study cannot resolve whether the effect of the soy supplement should be attributed to the isoflavones or the soy protein itself, or some other component.

In conclusion, this pilot study supports an anti-inflammatory, pro-nutritional effect of dietary soy in ESRD patients with underlying systemic inflammation and poor nutrition. The potential role of soy isoflavones needs further investigation in clinical trials of larger scope.



   Acknowledgments
 
This work was supported by grants from NIH (AT00205 and AT00323 to P.F., CA71789 to A.A.F. and HL70963 to R.A.), the University of Kentucky GCRC (M01-RR02602), the NKF-Council of Renal Nutrition (to T.J.S) and the Kentucky Soybean Association. We would like to thank Lois Hill, RD, Darreldean Winkler, RD and Kyleen Ward, RD for facilitating the collection of the dietary record; the research coordinators Karen Meekins, RN, Mary Wethington, RN, and Kathy Holbrook, RN for conduction of the clinical trial; the research analyst Jason Stevens for excellent technical assistance; and Susan Gardner (VA Hospital Central Laboratory) for allowing access to her laboratory equipment. Part of this work was presented at the ASN 36th Annual Meeting, San Diego, CA, 2003 and 37th Annual Meeting, St Louis, MO, 2004, and the Fifth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, Orlando, FL, November 2003.

Conflict of interest statement. None declared.



   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

  1. Stenvinkel P, Heimburger O, Paultre F, et al. Strong association between malnutrition, inflammation, and atherosclerosis in chronic renal failure. Kidney Int 1999; 55: 1899–1911[CrossRef][ISI][Medline]
  2. Kalantar-Zadeh K, Ikizler TA, Block G, Avram MM, Kopple JD. Malnutrition-inflammation complex syndrome in dialysis patients: causes and consequences. Am J Kidney Dis 2003; 42: 864–881[ISI][Medline]
  3. Kaysen GA. The microinflammatory state in uremia: causes and potential consequences. J Am Soc Nephrol 2001; 12: 1549–1557[Abstract/Free Full Text]
  4. Goodkin DA, Bragg-Gresham JL, Koenig KG, et al. Association of comorbid conditions and mortality in hemodialysis patients in Europe, Japan, and the United States: the Dialysis Outcomes and Practice Patterns Study (DOPPS). J Am Soc Nephrol 2003; 14: 3270–3277[Abstract/Free Full Text]
  5. Wong J, Port F, Hulbert-Shearon T, et al. Survival advantage in Asian American end-stage renal disease patients. Kidney Int 1999; 55: 2515–2523[CrossRef][ISI][Medline]
  6. Fanti P, Stephenson TJ, Kaarianinen IM, et al. Serum isoflavones and soya food intake in Japanese, Thai and American end-stage renal disease patients on chronic haemodialysis. Nephr Dial Transplant 2003; 18: 1862–1868[Abstract/Free Full Text]
  7. Adlercreutz H, Mazur W. Phyto-oestrogens and western diseases. Ann Med 1997; 29: 95–120[ISI][Medline]
  8. Fanti P, Sawaya B, Custer L, Franke A. Serum levels and metabolic clearance of the isoflavones genistein and daidzein in hemodialysis patients. J Am Soc Nephr 1999; 10: 864–871[Abstract/Free Full Text]
  9. Akiyama T, Ishida J, Nakagawa S, et al. Genistein, a specific inhibitor of tyrosine-specific protein kinase. J Biol Chem 1987; 262: 5592–5595[Abstract/Free Full Text]
  10. Chacko BK, Chandler RT, Mundhekar A, et al. Revealing anti-inflammatory mechanisms of soy isoflavones by flow: modulation of leukocyte-endothelial cell interactions. Am J Physiol Heart Circ Physiol 2005; 289: H908–H915[Abstract/Free Full Text]
  11. National Kidney Foundation – Disease Outcome Quality Initiative. Clinical Practice Guidelines for Hemodialysis Adequacy: K/DOQI Update http://www.kidney.org/professionals/kdoqi/guidelines_updates/doqi_uptoc.html#hd, 2000
  12. Nerad JL, Griffiths JK, Van der Meer JW, et al. Interleukin-1 beta (IL-1 beta), IL-1 receptor antagonist, and TNF alpha production in whole blood. J Leukoc Biol 1992; 52: 687–692[Abstract]
  13. Franke AA, Hankin JH, Yu MC, Maskarinec G, Low SH, Custer LJ. Isoflavone levels in soy foods consumed by multiethnic populations in Singapore and Hawaii. J Agric Food Chem 1999; 47: 977–986[CrossRef][Medline]
  14. US Renal Data System. Incidence and prevalence of ESRD. Bethesda, MD: National Institute of Health, National Institute of Diabetes and Digestive and Kidney Diseases, 2003: 47–60
  15. Borel P. Factors affecting intestinal absorption of highly lipophilic food microconstituents (fat-soluble vitamins, carotenoids and phytosterols). Clin Chem Lab Med 2003; 41: 979–994[CrossRef][ISI][Medline]
  16. Kulling SE, Honig DM, Metzler M. Oxidative metabolism of the soy isoflavones daidzein and genistein in humans in vitro and in vivo. J Agric Food Chem 2001; 49: 3024–3033[Medline]
  17. Setchell K, Cassidy A. Dietary isoflavones: biological effects and relevance to human health. J Nutrition 1999; 129: 758s–767s[Medline]
  18. Fouque D, Peng SC, Shamir E, Kopple JD. Recombinant human insulin-like growth factor-1 induces an anabolic response in malnourished CAPD patients. Kidney Int 2000; 57: 646–654[ISI][Medline]
  19. Fernandez-Reyes MJ, Alvarez-Ude F, Sanchez R, et al. Inflammation and malnutrition as predictors of mortality in patients on hemodialysis. J Nephrol 2002; 15: 136–143[ISI][Medline]
  20. Adams KF, Newton KM, Chen C, et al. Soy isoflavones do not modulate circulating insulin-like growth factor concentrations in an older population in an intervention trial. J Nutr 2003; 133: 1316–1319[Abstract/Free Full Text]
  21. Tsirpanlis G, Bagos P, Ioannou D, et al. The variability and accurate assessment of microinflammation in haemodialysis patients. Nephrol Dial Transplant 2004; 19: 150–157[Abstract/Free Full Text]
  22. ARUP Laboratories. ARUP: User's Guide, 2004
  23. National Kidney Foundation – Disease Outcome Quality Initiative. Management of protein and energy intake: K/DOQI Update http://www.kidney.org/professionals/kdoqi/guidelines_updates/nut_a15.html, 2000
Received for publication: 23. 9.05
Accepted in revised form: 15. 3.06


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?



This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
21/8/2239    most recent
gfl169v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (5)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Fanti, P.
Right arrow Articles by Franke, A. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fanti, P.
Right arrow Articles by Franke, A. A.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?