Black Soybean Extract Improves Lipid Profiles in Fenofibrate-Treated Type 2 Diabetics with Postprandial Hyperlipidemia

Abstract

Black soybeans (Glycine max (L.) Merr.) are known to be rich in polyphenols, including anthocyanins, and they have been consumed since ancient times for their beneficial effects on health. In addition, it has been reported that black soybean (BS) seed coat may ameliorate obesity and insulin resistance. In the present study, we administered BS extract to type 2 diabetics for 2 months to investigate the effects of BS on glycemic control and lipid metabolism parameters. In addition, we administered BS and antihyperlipidemic agent, fenofibrate, to patients with type 2 diabetes complicated by postprandial hyperlipidemia for 2 months and assessed the combined effects of fenofibrate and BS on serum lipid profile. The results showed that administration of the BS alone had no effect on the blood glucose or lipid levels, but that administration of fenofibrate alone and fenofibrate in combination with the BS significantly lowered their serum triglyceride (TG) level at fasting state, and the percent decrease in the serum TG level after combined administration was significantly higher than in the subjects who received fenofibrate alone. Furthermore, the serum LDL cholesterol concentration, which did not decrease when fenofibrate was administered alone, decreased significantly when the BS and fenofibrate were administered in combination. These results suggest that combined administration of the BS with fenofibrate enhanced the antihyperlipidemic action of fenofibrate, and the results of this study demonstrated the usefulness of the BS in clinical practice.

Introduction

Black soybeans (Glycine max (L.) Merr.) have primarily been consumed as food in East Asia, including in Japan. Black soybean (BS) seed coats are rich in polyphenols, including anthocyanins, and their use as Chinese herbal medicine dates back to ancient times.^1,2 The antiobesity anti-inflammatory, and antioxidant actions through inhibition of the production of inflammatory cytokines and reactive oxygen species by BS seed coat-derived components have been demonstrated in several in vitro and in vivo experiments.^2

–7 In addition, administration of black soy peptide to patients with prediabetes and type 2 diabetes for 12 weeks has been reported to improve glucose tolerance in glucose tolerance tests.⁸ However, little is known about the effect of BS extract on glycemic control in type 2 diabetes patients and its effect on blood lipids has never been elucidated.

Fenofibrate, on the other hand, is an antihyperlipidemic drug that improves lipid metabolism by activating the peroxisome proliferator-activated receptor α in hepatocytes, and it has been reported to have an ameliorating effect on postprandial hyperlipidemia and an antihyperlipidemic effect in patients with type 2 diabetes complicated by lipid metabolism disorders.^9,10

In the present study, we investigated the effect of consuming a BS extract on the lipid metabolism parameters of type 2 diabetes patients and the effect of combined administration with fenofibrate.

Subjects and Methods

Study population

We divided 36 type 2 diabetes patients, 26 males [54±11 years old] and 10 females [62±12 years old], into three groups: a BS extract administration group of 18 patients (12 males, 6 females), a fenofibrate administration (FEN) group of 11 patients (10 males, 1 female), and a BS extract and fenofibrate combined administration (BS+FEN) group of 7 patients (4 males, 3 females). The FEN group and BS+FEN group in this study consisted of patients who exhibited postprandial hyperlipidemia (nonfasting serum triglyceride level ≥225 mg/dL). Before the study, none of the subjects was using either fenofibrate or BS extract, and the blood glucose levels were being controlled with a dipeptidyl peptidase-4 inhibitor. Patients who deviated from the dosing protocol were regarded as dropouts from the present study.

The purpose of this study was approved by the Ethics Committee of Aichi Medical University and it was conducted in accordance with the Declaration of Helsinki.

Agents and administration methods

The whole BS (“Iwaikuro”) extract used in the present study was fortified with polyphenols derived from additional BS hull extract. The compositions of nutrients and polyphenols in the BS extract are shown in Table 1.

Table 1.

Nutrient and Polyphenol Composition in Black Soybean Extract (for One Dose)

Nutrient composition
Energy	8.9 kcal
Protein	90 mg
Fat	5.0 mg
Carbohydrate	2.1 g
Ash	108 mg
Fiber	70 mg
Sodium	0.8 mg
Potassium	45 mg
Polyphenol composition
Soy isoflavone	8.3 mg
Soy saponin	3.0 mg
Proanthocyanidin	465 mg
Cyanidin-3-glucoside	56 mg

The BS group was given a BS extract (Kuromagen 600; Kikuchi Foods Industry, Tokyo, Japan), 2.5 g a day, after breakfast. A 2.5 g dose of the BS extract used in this study contained 465 mg of proanthocyanidin and 62 mg of anthocyanin (of which 56 mg was cyanidin-3-glucoside) as BS seed coat-derived polyphenols.

The FEN group was given an 80–160 mg dose of fenofibrate (Lipidil^® Tablets; Kaken Pharmaceutical, Tokyo, Japan), once daily, after breakfast.

The BS+FEN group was given an 80–160 mg dose of fenofibrate plus a 2.5 g dose of the BS extract after breakfast.

The period of administration in all three groups was 2 months.

Blood analyses

Blood was drawn before the start of the study and 2 months after the start of the study at fasting state, and body–mass index (BMI) was calculated at the same times. The Health Care Center, Medical Association of Handa City (Handa, Japan) measured blood glucose and the lipid metabolism parameters (serum triglyceride [TG], total cholesterol [TC], HDL cholesterol [HDL-C], and LDL cholesterol [LDL-C] levels), and the measurements were made by an enzymatic method using an automated analyzer (JCA-BM8000 series; JEOL, Tokyo, Japan). Hemoglobin A_1c (HbA_1c) levels were measured by high-performance liquid chromatography with an automated glycohemoglobin analyzer (Tosoh, Tokyo, Japan).

Statistical analyses

Data are reported as mean±SD. The three groups were tested for significant differences at baseline by one-way ANOVA and Tukey–Kramer post hoc test. The two-sided paired Student's t-test was used to test for significant differences between values before and after the study. Logarithmic values were used to test for significant differences between TG levels. Percentage decreases in TG levels (ΔTG) were compared by means of the one-sided unpaired Welch's t-test only on groups in which significant differences in TG levels were detected.

Results

Body composition and glycemic control

The results of the comparisons between the data before the start of the study and 2 months after the start of the study are shown in Table 2.

Table 2.

Effect of Combined Administration of Black Soybean Extract and Fenofibrate on Body Weight, Body–Mass Index, HbA1c, Serum Glucose, and Serum Lipid Levels

	BS		FEN		BS+FEN
Fasting levels	Before	2 months after	Before	2 months after	Before	2 months after
Body weight (kg)	72.0±16.6	71.6±16.2	83.3±29.7	83.7±29.0	72.4±8.4	71.6±10.0
Body mass index (kg/m²)	26.1±3.2	25.9±3.1	28.2±5.9	28.4±5.9	27.9±2.7	27.6±3.0
Blood glucose (mg/dL)	103±19	112±21	142±50	114±11	121±35	111±12
HbA1c (%)	5.8±0.7	5.7±0.7	7.1±1.7	6.8±0.7	6.7±1.0	6.8±1.1
Total cholesterol (mg/dL)	177±36	180±33	192±56	182±34	184±36	173±36
HDL cholesterol (mg/dL)	59±12	60±15	47±8	49±8	53±11	59±17
LDL cholesterol (mg/dL)	104±32	103±24	98±24	97±21	107±29	91±32^*
Triglyceride (mg/dL)	113±52	98±39	281±129	202±172^*	206±58	119±62^**

Data are expressed as mean±SD. BS, black soybean extract administered patients (n=18, male/female=12/6); FEN, fenofibrate administered patients (n=11, male/female=10/1); BS+FEN, black soybean and fenofibrate administered patients (n=7, male/female=4/3); “Before,” before administration. ^** P<.01, ^* P<.05 versus before administration.

No significant differences were seen between the body weight, BMI, blood glucose, or HbA1c levels before the start of the study and 2 months after the start of the study in any of the three groups.

Serum lipids

The results for the serum lipid levels are shown in Table 2. There were no significant changes in TC or HDL-C levels before and after the study in any of the three groups, but although the difference in the TG level 2 months after the start of the study in the BS group was not significant, the TG levels in the FEN group and the BS+FEN group were significantly lower than before the start of the study (FEN: P<.05, BS+FEN: P<.01). When ΔTG was compared between the FEN group and BS+FEN group, both exhibited significantly lower TG levels before and after the study, and the results showed that the percentage decrease in the BS+FEN group was higher than in the FEN group (FEN: −22.6%±46.1% vs. BS+FEN: −50.1%±17.0%, P<.05). There was no significant change in the LDL-C level before and after the study when the BS extract or fenofibrate was administered alone, but there was a significant decrease when fenofibrate and the BS extract were administered in combination.

Discussion

BSs, which are rich in polyphenols, including anthocyanins, are said to have health benefits in a variety of conditions, and they have been used as food or as Chinese herbal medicine in East Asia since ancient times.^1,2 In addition, BS seed coats have been reported to be instrumental in inhibiting the secretion of inflammatory cytokines and improving glucose and lipid metabolism in vivo.^2,4,5,11 In the present study, a BS extract was administered to type 2 diabetes patients and its effects on lipid metabolism was assessed. Fenofibrate, an antihyperlipidemic agent, was also administered to patients with type 2 diabetes complicated by postprandial hyperlipidemia to investigate the effects of fenofibrate when administered in combination with BS extract.

When the BS extract was administered alone in this study, it had no effect on the subjects' body weight, BMI, blood glucose or HbA1c levels, or serum TG, LDL-C, or HDL-C levels.

The results of administering fenofibrate to patients with type 2 diabetes complicated by postprandial hyperlipidemia showed that it significantly lowered their TG levels. Both Sandoval et al. and Reyes-Soffer et al. have reported that fenofibrate improves postprandial hyperlipidemia,^12,13 and their reports are consistent with the decrease in TG levels in the present study. On the other hand, the TG levels also decreased in the patients given fenofibrate and the BS extract in combination, and the ΔTG was significantly higher than in the FEN-alone group. In other words, in the present study, the TG-lowering action of fenofibrate was found to be enhanced by administering it in combination with BS extract. Kanamoto et al. reported that BS seed coat extract decreases the expression of genes, which regulates inflammatory cytokines such as TNF-α, MCP-1, and IL-6 in adipose tissue in high-fat-fed mice.² Because an increase in these cytokines suppresses the lipoprotein lipase activity and then leads to hyperlipidemia,¹⁴ activation of β-oxidation by fenofibrate and reduction of inflammatory cytokines by BS extract might have occurred simultaneously in the BS+FEN group.

Fenofibrate has been shown to lower LDL-C levels in clinical practice,¹⁵ but no decrease in LDL-C in response to administration for 2 months was seen in the present study. A significant increase in HDL-C and significant decrease in LDL-C were confirmed after administration of fenofibrate for 4 months in the FIELD study, which was conducted on type 2 diabetes patients,¹⁶ and the 2-month administration period set in the present study may have been too short for fenofibrate to exert its effects on these parameters. When fenofibrate and BS extract were administered in combination, on the other hand, there was a significant decrease in the LDL-C level. These results suggested that BS extract may enhance the action of fenofibrate in lowering serum LDL-C levels as well as in lowering serum TG levels.

In conclusion, BS extract alone did not affect the serum lipids of type 2 diabetes patients. However, BS extract in combination with fenofibrate exerted stronger TG- and LDL-C-lowering effects than did fenofibrate alone in patients with diabetes complicated by postprandial hyperlipidemia. BS extract administration is useful for serum lipid control in diabetes patients.

Footnotes

Acknowledgment

The authors thank the Kikuchi Foods Industry Co., Ltd. for providing the black soybean extract without accepting compensation.

Author Disclosure Statement

No competing financial interests exist.

References

Choung

, Baek

, Kang

, et al.: Isolation and determination of anthocyanins in seed coats of black soybean (Glycine max (L.) Merr.). J Agric Food Chem, 2001; 49:5848–5851.

Kanamoto

, Yamashita

, Nanba

, et al.: A black soybean seed coat extract prevents obesity and glucose intolerance by up-regulating uncoupling proteins and down-regulating inflammatory cytokines in high-fat diet-fed mice. J Agric Food Chem, 2011; 59:8985–8993.

Jang

, Moon

, Ko

, et al.: Novel black soy peptides with antiobesity effects: activation of leptin-like signaling and AMP-activated protein kinase. Int J Obes, 2008; 32:1161–1170.

Tsoyi

, Park

, Kim

, et al.: Anthocyanins from black soybean seed coats inhibit UVB-induced inflammatory cylooxygenase-2 gene expression and PGE₂ production through regulation of the nuclear factor-κB and phosphatidylinositol 3-kinase/Akt pathway. J Agric Food Chem, 2008; 56:8969–8974.

Jang

, Ko

, Ahn

, et al.: In vivo and in vitro application of black soybean peptides in the amelioration of endoplasmic reticulum stress and improvement of insulin resistance. Life Sci, 2010; 86:267–274.

, Chang

: Antioxidant capacity of seed coat, dehulled bean, and whole black soybeans in relation to their distributions of total phenolics, phenolic acids, anthocyanins, and isoflavones. J Agric Food Chem, 2008; 56:8365–8373.

Kim

, Chung

, Ha

, et al.: Neuroprotective effects of black soybean anthocyanins via inactivation of ASK1-JNK/p38 pathways and mobilization of cellular sialic acids. Life Sci, 2012; 90:874–882.

Kwak

, Lee

, Ahn

, et al.: Black soy peptide supplementation improves glucose control in subjects with prediabetes and newly diagnosed type 2 diabetes mellitus. J Med Food, 2010; 13:1307–1312.

Rosenson

, Wolff

, Huskin

, Helenowski

, Rademaker

: Fenofibrate therapy ameliorates fasting and postprandial lipoproteinemia, oxidative stress, and the inflammatory response in subjects with hypertriglyceridemia and the metabolic syndrome. Diabetes Care, 2007; 30:1945–1951.

10.

Lalloyer

, Wouters

, Baron

, et al.: Peroxisome proliferator-activated receptor-α gene level differently affects lipid metabolism and inflammation in apolipoprotein E2 knock-in mice. Arterioscler Thromb Vasc Biol, 2011; 31:1573–1579.

11.

Kurimoto

, Shibayama

, Inoue

, et al.: Black soybean seed coat extract ameliorates hyperglycemia and insulin sensitivity via the activation of AMP-activated protein kinase in diabetic mice. J Agric Food Chem, 2013; 61:5558–5564.

12.

Sandoval

, Nakagawa-Toyama

, Masuda

, et al.: Fenofibrate reduces postprandial hypertriglyceridemia in CD36 knockout mice. J Atheroscler Thromb, 2010; 17:610–618.

13.

Reyes-Soffer

, Lovato

, Holleran

, et al.: Fenofibrate reduces postprandial triglycerides levels in subjects in the ACCORD lipid trial. Diabetes, 2010; 59(Suppl. 1):A288.

14.

Ohara

, Tsutsumi

, Ohsawa

: Suppression of carcass weight loss in cachexia in rats bearing Leydig cell tumor by the novel compound NO-1886, a lipoprotein lipase activator. Metabolism, 1998; 47:101–105.

15.

Chapman

: Fibrates in 2003: therapeutic action in atherogenic dyslipidaemia and future perspectives. Atherosclerosis, 2003; 171:1–13.

16.

Taskinen

, Barter

, Ehnholm

, et al.: Ability of traditional lipid ratios and apolipoprotein ratios to predict cardiovascular risk in people with type 2 diabetes. Diabetologia, 2010; 53:1846–1855.