The objective of the present study was to evaluate
Diabetes is a disease that seriously threatens human health, with more than 200 million people suffering from the disease worldwide. The World Health Organization estimates that the number of patients with diabetes will exceed 360 million by 2030 [
Nopal (NP, plant genus
Dietary fiber is classified into water-soluble dietary fiber and non-water-soluble dietary fiber. Water-soluble dietary fiber is composed of mucus, gum, pectin, and hemicelluloses, while non-water-soluble dietary fiber is composed of cellulose, lignin, and a large hemicellulose fraction. The gel in the three-dimensional structure formed by water-soluble dietary fiber is known to prolong the passage of food through the intestine.
However, most preceding studies used samples from NP which was dried and powdered by the sun. Therefore, the purpose in our study was to investigate the evaluation for the prevention and treatment of antidiabetic effect from water extracts of fresh NP stem on the blood glucose control effect by conducting glucose tolerance experiments in the STZ-induced diabetic animal model fed a high-fat diet, as well as the
Streptozotocin (STZ), acarbose,
Plant material used in this study was dried
Insoluble dietary fiber was quantified according to the method of Prosky et al. [
Ten milliliters of filtrate and water with washed sediments was acquired from the process of measuring insoluble dietary fiber content, adjusted to 50 g with water, and moved to a beaker, to which 200 mL of 95% ethanol heated to 60°C was added. This was left for 60 min so that sediments could form at room temperature. The sediments of a 1 G3 filtering crucible with constant weight that included celite soaked in 78% celite ethanol were vacuum-filtered and washed in the order of 30 mL of 78% ethanol, 10 mL of 95% ethanol, and 10 mL of acetone and then dried in a 70°C vacuum oven for 12 h. The weights of sediments were acquired by weighing the glass crucible cooled in the desiccators, and ash and protein contents were weighed with the same method as insoluble dietary fiber. The same procedures were used to measure the blank samples.
After the completion of the above process, content of dietary fiber was calculated as follows:
Inhibitory activity of
Experimental animals used in this study were male Sprague Dawley rats with body weight of 180–200 g purchased from Koatech Inc. They were adapted to a breeding environment of
Experiments were conducted in order to verify the difference in the blood glucose reduction effect between NPDP and NPWE. Animals adapted to the breeding room were supplied with a high-fat diet for 4 weeks, fasted for 12 h, and separated into the following three groups, with ten animals in each group: a group with no extract injected (control), a group injected with 100 mg/kg NPDP, and a group injected with 100 mg/kg NPWE. Thirty minutes after injection of test samples, 2 g/kg of glucose was orally administered.
After supplying rats with a high-fat diet for 4 weeks, 34 mg/kg STZ (in 0.1 M citrate buffer) was administered by intraperitoneal injection in experimental animals that had been fasted for 12 h. After 1 week, animals with fasting blood glucose of 250 mg/dL were selected for experiments, by measuring blood glucose of blood from the tail vein with a blood glucose monitoring device (Accu-Chek, Germany). Animals were separated into four experimental groups, with ten rats per group. The groups were as follows: a positive control group which was supplied with normal diet with no test samples (RD-Control), a negative control group supplied with a high-fat diet with STZ administration and no test samples (HF-STZ-Control), a group supplied with a high-fat diet with STZ administration and 100 mg/kg of orally administered NPWE (HF-STZ-NPWE), and a group supplied with a high-fat diet with STZ administration and 10 mg/kg of rosiglitazone as comparison medication (HF-STZ-Rosiglitazone). The animal group that was not administered test sample or medication was instead administered carboxymethyl cellulose (CMC, Sigma, USA) solution, which was used in test sample dilution, while each test sample was orally administered at 4 p.m. each day. Test samples and comparison medications were orally administered in all experimental animal groups every day for 4 weeks. Then, the animals were fasted for 12 h, and 2 g/kg of glucose was orally administered.
At time points of 0 min, 30 min, 1 h, 2 h, and 3 h after glucose administration, blood was collected from the tail vein and blood glucose was measured with a blood glucose monitoring device and blood was collected from the orbital vein of animals fasted for 15 h and contained in SST Vacutainers. Plasma was centrifuged at 3,000 rpm for 15 min and then analyzed with a biochemical measuring instrument for blood index.
Data are expressed as mean values ± SD and comparisons among data were carried out using Student’s unpaired
Contents of dietary fiber contained in NP stems are presented in Table
Concentration of soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) in Nopal dry powder (NPDP) and water extract (NPWE).
Dietary fibers | Nopal dry powder (%) | Nopal water extract (%) |
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The inhibitory activity of NP of
Inhibitory effect of
Extracts | Concentration ( |
Inhibition (%) | IC50 ( |
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Nopal dry powder | 100 | 43.59 |
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50 | 41.50 | ||
25 | 23.52 | ||
10 | 8.67 | ||
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Nopal water extract | 100 | 53.23 |
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50 | 47.22 | ||
25 | 44.65 | ||
10 | 28.89 | ||
5 | 19.02 | ||
2.5 | 5.12 | ||
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Acarbose(2) | 100 | 68.39 |
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50 | 59.41 | ||
25 | 49.34 | ||
10 | 39.32 | ||
5 | 34.41 | ||
2.5 | 16.46 |
Although NP had lower inhibitory activity than acarbose (which was used as comparison medication), it was judged that NP has a significant effect in the body even in small amounts. Usually, the intake of the starch is decomposed to monosaccharide by
Commercially available
Glucose tolerance tests conducted for each experimental group are presented in Figure
Single-term oral glucose tolerance tests (a) of Nopal dry powder (NPDP) and water extract (NPWE) after 12 h food deprivation in SD rats fed a high-fat diet. (b) Area under the blood glucose concentration curve was measured over 180 min (AUC-180 min). Values are expressed as the mean ± SE (
As shown in Figure
Long-term oral glucose tolerance tests (a) of Nopal water extract (NPWE) after 12 h food deprivation in STZ-induced SD rats fed a high-fat diet. (b) Area under the blood glucose concentration curve was measured over 180 min (AUC-180 min). Values are expressed as the mean ± SE (
Blood indices for each experimental group were analyzed, and results of analysis are presented in Table
Analytical methods of blood plasma chemistry items.
Biomarker | Raw diet (mg/dL) | High fat diet-STZ (mg/dL) | ||
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RD-Control | HF-STZ-Control | HF-STZ-NPWE | HF-STZ-Rosiglitazone | |
Albumin |
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Total protein |
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AST(1) |
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ALT(2) |
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Cholesterol |
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Triglyceride |
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HDL-cholesterol |
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LDL-cholesterol |
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Creatine |
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Uric acid |
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Values are expressed as the mean ± SE (
The HDL-cholesterol level of the RD-Control was 54.70 mg/dL and that of the HF-STZ-Control was 56.60 mg/dL, while the HF-STZ-NPWE showed a level of 49.17 mg/dL, which is close to the normal level. Even though HF-STZ-Rosiglitazone showed ALT levels of 113.90 mg/dL, this was still higher than the level of ALT of HF-STZ-NPWE. The blood creatine concentration was high, but no significant difference was observed.
The creatine is measured as indicators reflecting the status of renal function prior to diabetic nephropathy, with creatine being a substance that is generated as a result of the creatine phosphate metabolism in the muscle. Under normal conditions, creatine is isolated from the muscle at a relatively constant speed, so the blood creatine concentration is constant when filtered through the glomerulus, and is neither reabsorbed nor metabolized. In a chronic kidney disease due to diabetes, the glomerular filtration rate decreases and the concentration of blood creatine increases. In the present study, the creatine concentration tended to increase in the diabetes-induced group, but there was no significant difference. The degradation of kidney function can be assumed, but no serious complications appeared.
While the content of the soluble dietary fiber in the NPDP test sample was 4.99%, the content increased to 45.92% as a result of water extraction. On the contrary, content of insoluble dietary fiber was eliminated through the water extraction process. The results of the
NP and dietary fibers have been previously reported on the antihyperglycemic effect included in STZ-induced diabetic rats [
In the prevention and treatment of diabetes, it is important to control blood glucose after eating. Hyperglycemia after feeding is known to be a symptom not only of severe diabetes, but also of slight diabetes, in which high glucose levels on an empty stomach are not a symptom [
Following the suggestion that deficiency of dietary fiber may be a cause of diabetes, Lee et al. reported that a high carbohydrate, high fiber diet decreases blood glucose and insulin requirements in insulin-dependent or insulin-independent diabetics and lowers concentrations of lipids in the blood [
Our study has several strengths. First, we analyzed concentration of dietary fiber in NP stem extract used as dietary supplements. We fed animals with a high-fat diet that might cause prediabetes condition in humans supplemented with NPWE, allowing us to calculate intake of dietary fiber from food intake. Third, in an experimental approach we have adapted, diabetes is induced by a single intraperitoneal STZ injection in citrate buffer in an amount of 15–90 mg/kg of animal body weight. This model has been commonly used to study the pathophysiology for humans with type 2 diabetes model. However, our study has some limitations. First, we did not perform morphological examination to further substantiate the beneficial effect of NPWE on pancreatic
In conclusion, the study demonstrates that NPWE significantly improves deranged carbohydrate metabolism in STZ-induced diabetic rats fed a high-fat diet. The results suggest that, at least in part, NPWE preparations can be used as a nutraceutical agent to ameliorate diabetes type 2 and are necessary to further elucidate the antidiabetic of action of NPWE.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2015R1D1A1A01059199) and the Ministry of Trade, Industry and Energy (MOTIE), and Korea Institute for Advancement of Technology (KIAT) through the Center for Efficacy Assessment and Development of Functional Foods and Drugs at Hallym University (B0008864), Korea.