Effect of acute oral chlorogenic acid ingestion on the inhibition of blood glucose excursions following glucose to-lerance testing ()
1. INTRODUCTION
Over 15 million people worldwide contract type 2 diabetes mellitus [1]. Diabetes is associated with a state of increased free radical production induced by chronic inflammation along with hyperglycemia, resulting in an imbalance between radical-generating and radical-scavenging systems [2]. Oxygen free radicals are known to be associated with a variety of cellular functions, but they can be both essential and highly toxic to cellular homeostasis [3]. Due to the damaging effects of increased oxidative stress observed during complications of diabetes mellitus, a countermeasure for relieving symptoms of diabetic complications and preventing the onset of symptoms is important [4].
Because type 2 diabetes is heterogeneous in nature, current therapies are unable to modify the natural history of this disorder. Therefore, it is necessary to explore new antidiabetic therapies. Polyphenol, an antioxidant found in many plants, fruits, vegetables, coffee, red wine, and tea, has been studied widely to examine its effect in reducing oxidative stress at the cellular level, thereby inhibiting the disease [5-7]. Coffee and wine are known to have a higher polyphenol content than other foods [8]. Until recently, it was reported that chlorogenic acid (CGA) inhibits blood glucose increase after a meal as well as reduces cholesterol and triacylglycerol levels; however, all prior studies examined the effect in vivo in rat models. Therefore, it is not clear if similar effects may be observed in human subjects [9,10].
This study aimed to examine the effect of acute oral CGA ingestion on the inhibition of blood glucose increase following glucose tolerance.
2. METHODS
2.1. Subjects
Ten healthy young male adults without past type 2 diabetes history participated in this study (age: 25.9 ± 5.4 years; height: 171.2 ± 6.1 cm; body mass: 70.7 ± 8.9 kg). Written informed consent was obtained from all subjects after a full explanation of the experimental purpose and protocol was provided. Moreover, the experimental protocol was approved by the Ethics Committee on Human Experimentation of Faculty of Human Science, Kanazawa University (authorization number: 2012-10).
2.2. Experimental Design
The experimental design was a double-blind, cross-over study. Subjects received both CGA and placebo ingestion over the course of the study, with a 1-week washout period. Moreover, the test condition order was counter balanced to eliminate order effect. In addition, subjects were instructed to refrain from intensive exercise for two days before the experiment and to fast the evening before the experiment. Subjects were also instructed to refrain from consuming beverages or food containing CGA and cold remedies.
2.3. Experimental Condition
CGA was ingested at a ratio of 0.1 g/kg body weight. CGA is one of the polyphenol and their effect looks like tannin. It contains 5% - 10% within coffee beans and its content is greater than caffeine (1% - 2%). Antioxidative effect has been expected by its ability to entrap radical, and it is suggested to include the effect of delay glucose absorption. Both CGA and placebo were administered in capsules. Each capsules were administered with 75 g glucose (Partial hydrolysate of starch), which dissolved with 150 g water.
2.4. Experimental Procedure and Protocol
Subjects reported to the study laboratory twice during the experiment; the standard protocol for glucose tolerance testing was followed (Figure 1) with administration of glucose along with ingestion of either CGA or placebo at each visit. In addition, height, body weight, and body composition were measured at the first visit before engaging in the experimental protocol. Subjects rose at 7:00 hours following an overnight fast from 20:00 hours, and reported to the study lab. Approximately 30 minutes after reporting to the study lab, a baseline blood sample was obtained. The study subjects then were administered 75 g of glucose, which dissolved with 150 g water and CGA or a placebo capsules. Four blood samples were collected over a 120-minute rest period at 30 min intervals.
2.5. Parameters
Blood samples collected over the 120-min rest period
were analyzed for blood glucose and insulin. This was accomplished by transferring 3 mL of blood into a blood sampling tube containing sodium fluoride to assess blood glucose concentration and 7 mL of blood into a tube for analysis of insulin. These processes were carried out within 30 s of the blood collection. The samples were immediately centrifuged, and the supernatants were placed in chilled containers and stored at −80˚C until analyzed. Plasma glucose concentrations were analyzed by enzymatically. The inter-assay and intra-assay coefficients of variation (CV) were 0.2% and 0.9%, respectively. The samples for insulin were analyzed by high performance liquid chromatography (HPLC) using the HPLC system (Shimazu and Hitachi, Japan). Sensitivity, inter-assay, and intra-assay coefficients of variation (CV) of this assay were 5.92 nmoL/L, 4.94%, and 0.00%, respectively.
2.6. Statistical Analysis
Two-way repeated measures analysis of variance (ingestion condition × measurement time) was used to examine the mean difference between CGA and placebo ingestion conditions for each parameter. When showing a significant main or interaction effect, Tukey’s honestly significant difference (HSD) was used as post hoc analysis to examine specific mean differences. An alpha concentration of 0.05 was used for all experiments.
3. RESULTS
Figure 2 compares serum insulin concentration before 30, 60, 90, and 120 min after administration of 75 g glucose along with either CGA or placebo. The significant main effect of time (F = 17.6, P < 0.001) was found, and serum insulin concentration on and after 30 min of glucose injection was significantly greater than that before ingestion in both conditions. No significant effect of ingestion and interaction were found (F = 1.3, P = 0.291