Effects of diacylglycerol ingestion on postprandial hyperlipidemia in diabetes
Introduction
A greatly enhanced risk for coronary heart disease (CHD) has been reported in diabetes [1], [2]. Lipid abnormalities in diabetes, including elevated plasma triacylglycerol (TAG), low cholesterol in high-density lipoproteins (HDL), an increase in small, dense low-density lipoproteins (LDL), and postprandial hyperlipidemia contribute to this increased risk [3], [4], [5], [6]. Among them, postprandial increase in remnant lipoproteins (remnants) has been recognized as a powerful CHD risk not only for diabetic but also for nondiabetic subjects [7], [8], [9], [10], [11], [12].
Remnants are the metabolites of TAG-rich lipoproteins, such as chylomicrons (CM) and very-low-density lipoproteins (VLDL), and are formed in the circulation by the effect of lipoprotein lipase. These remnants are readily incorporated into endothelial macrophages, leading to the accumulation of cholesterol in these cells, consequently forming a premature atherosclerotic lesion [9], [12], [13], [14].
Therapeutic approaches to reduce remnant levels in the postprandial phase are believed to be important for the management of patients with diabetes and also with metabolic syndrome [5]. We have previously reported [15] that the substitution of diacylglycerol (DAG) oil intake for TAG oil significantly suppressed postprandial increases in serum TAG and lipids in remnants measured by the method of Nakajima et al. [16] in healthy male volunteers. Therefore, we had an interest whether this favorable effect of DAG intake on postprandial hyperlipidemia can be applied to diabetic subjects without any serious adverse phenomenon.
Diacylglycerol is a natural component of various edible oils and consists mainly of the 1,3-species. The intake of DAG has been reported to reduce fasting serum TAG concentration and hemoglobin A1c (HbA1c) levels in type 2 diabetics and to prevent the accumulation of body fat in experimental animals and in humans [17], [18]. Decreased activities of enzymes of fatty acid synthesis and increased activities of enzymes involved in the β-oxidation pathway by DAG ingestion have also been reported [18].
The objectives of this study were to investigate the effects of oral DAG loading on postprandial changes in serum lipids, related parameters including ketone bodies, and changes in remnants in moderately controlled diabetics.
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Subjects
The subjects were six patients with type 2 diabetes mellitus (five females and one male; aged 46–70 years) who had moderately controlled HbA1c levels that were <8%. The study was performed in accordance with the principle of the Helsinki Declaration. The subjects were fully informed concerning the study and gave their informed consent. The clinical characteristics of subjects are shown in Table 1. All of them were not receiving insulin therapy, but they were medicated as follows: one was taking
Changes in serum lipids and apolipoproteins
Table 3 shows changes in serum lipids, LDL-C, HDL-C, and RLP lipids. Serum total cholesterol, LDL-C, and HDL-C did not change during TAG or DAG loading. However, serum TAG increased, peaking at 4 h after the loading with either oil and decreased at 6 h. Increases (Δ: shown in the parentheses in Table 3) in serum TAG from the initial value were significantly smaller during DAG loading than those observed during TAG loading (p=0.005), as determined by two-way ANOVA. No significant difference in
Discussion
The effects of DAG loading on postprandial changes in serum lipids and lipid parameters in diabetic patients were examined. Although the subject number of this study was small, the findings again showed the suppressed postprandial increases in serum TAG, RLP-TAG, and RLP-C in the DAG intake when compared with TAG intake in diabetic subjects as previously reported in healthy volunteers [15].
Increased fasting RLP-C concentrations have been reported in individuals with impaired glucose tolerance
Acknowledgement
A part of this study was supported by Health and Labor Sciences Research Grants for Comprehensive Research on Aging and Health (H15-Choju-012), Japan.
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Current address: Department of Food and Nutrition, Toita Woman's College, 2-21-17 Shiba, Minato-ku, Tokyo, 105-0014 Japan.