Journal Search Engine
Search Advanced Search Adode Reader(link)
Download PDF Export Citaion korean bibliography PMC previewer
ISSN : 1738-7248(Print)
ISSN : 2287-7428(Online)
Korean Journal of Food Preservation Vol.20 No.1 pp.1-6
DOI : https://doi.org/10.11002/kjfp.2013.20.1.1

SD계 랫트와 db/db 마우스에서 Curcuma longa L.가 비만과 인슐린저항성에 미치는 영향

유미경1, 김민숙1, 류동영2, 김현아1†
1목포대학교 식품영양학과, 2목포대학교 한약자원학과

Effect of Curcuma longa L. on the Obesity and Insulin Resistance in Sprague-Dawley Rats and db/db Mice

Hyeon-A Kim1†, Mi-Kyoung You1, Min-Sook Kim1, Dong-Young Rhyu2
1Department of Food & Nutrition, Mokpo National University
2Deparrtment of Oriental Medicine Resources, Mokpo National University

Abstract

In this study, the effect of Curcuma longa L. on obesity and insulin resistance was investigated in animals feda moderate high fat diet. The animals used in this study were normal weight Spargue-Dawley (SD) rats and type2 diabetic obese db/db mice. Accumulation of abdominal adipose tissue and weight gain were inhibited in theanimals fed the C. longa extract. C. longa decreased fasting insulin and HOMA-IR in the SD rats, and effectivelydecreased blood glucose and hemoglobin A1c in db/db mice. C. longa decreased serum free fatty acid (FFA) levelin the SD rats. FFA in db/db mice fed C. longa tended to decrease. C. longa significantly decreased serum triglyceridelevel. Our results collectively represent that C. longa prevented fat accumulation and insulin resistance in bothnormal weight SD rats and type 2 diabetic obese db/db mice fed a moderate high fat diet.

food-20-1- t 1.jpg113.1KB

Introduction

Obesity is a risk factor for coronary artery disease, dyslipidemia, hypertension, stroke and type 2 diabetes (1,2). It has been reported that the risk of diabetes increases by 7.3% for each kilogram of weight gained (3). In addition to general obesity, greater visceral adipose tissue has been shown to be independently associated with insulin resistance, which is a major factor for the metabolic syndrome in older men and women (4). Even normal weight elderly may be at risk for metabolic abnormalities if they have inordinate amounts of visceral abdominal fat. Insulin resistance along with β‐cell failure is the major contributor to the development of type 2 diabetes. Insulin resistance occurs early in the course of type 2 diabetes, typically when glucose values are still within the normal glucose tolerance range (5). Even without diabetes, insulin resistance is a major risk factor for cardiovascular disease and early mortalit (6,7). Although there is a significant correlation between obesity and insulin resistance as well as type 2 diabetes, the pathophysiology of these relationships is not well established.

Curcuma longa L. has been used as a spice and food coloring agent in several foods, including curry, mustard, and potato chips (8). Numerous biological effects of Curcuma longa L. have been associated with curcumin. Several studies have demonstrated its beneficial biological activity, including anti‐inflammatory, antioxidant, anti-carcinogenic, antiviral, anti-infectious and anti-diabetic activities (9,10). Curcumin produced a potential hypoglycemic effect in streptozotocininduced diabetic animals (11). El-Moselhy et al. (12) observed a hypoglycemic effect of curcumin in rats fed a 40% fat diet and suggested that this effect was associated with the anti-inflammatory activity. However, the mechanism by which curcumin lowers blood glucose is still not known. 

In this study, we investigated the effect of Curcuma longa L. on the body weight and insulin resistance in Sprague Dawley (SD) rats and db/db mice fed a moderate high fat diet. We used two different animal models to compare the effect of Curcuma longa L. on obesity and insulin resistance; those with normal body weight and those with overweight. The db/db mouse has been used as a genetic model of type 2 diabetes. This genetic model has defects in the receptor for the obese gene product, leptin (13), which results in diabetes with hyperinsulinemia, hyperglycemia and extreme obesity (14). We fed the animals a moderate high fat diet, which consisted of 15% fat by weight (about 30% by calorie). This was selected because total fat is allowed to range from 15~25% of total energy in Dietary reference intakes of Koreans (15). We also used Curcuma longa L. extracts instead of curcumin to investigate its effect as a food ingredient. 

Materials and Methods

Preparation of Curcuma longa L. extract

Curcuma longa L. powder (50 g) was immersed in 5 L of 50% ethanol at room temperature for 24 h, and this procedure was repeated three times. The extract was concentrated under reduced pressure using a rotary evaporator (Daesin machine industry, Korea) at 60℃ and then freeze-dried. The yield obtained by ethanol extraction was 15.6%. 

Animals

Male Sprague–Dawley (SD) rats, 21 days of age, were obtained from Central Laboratory Animal Inc. (SLC, Inc., Japan) Animals were housed in a climate-controlled room (22±2℃, 50±10% relative humidity) under a 12 h light/dark cycle and provided diet and water ad libitum. The rats were acclimated to a pellet diet for 3 days and then divided into four groups. Animals in the control group were provided a modified AIN-93G control diet (15% fat by weight). Three groups of animals were fed a diet containing 0.5, 1 or 1.5% of the ethanol extract of Curcuma longa L. powder for eight weeks (Table 1). 

Table. 1. Composition of diet.

Six week old male db/db mice were also obtained from Central Laboratory Animal Inc (SLC, Inc, Japan). Animals were housed in a climate‐controlled room (22±2℃, 50±10% relative humidity) under a 12 h light/dark cycle and provided diet and water ad libitum. The mice were acclimated to a pellet diet for 3 days and then divided into two groups. Animals in the control group were provided a modified AIN-93G control diet (15% fat by weight). The other groups of animals were fed a diet containing 1.5% of the ethanol extract (Table 1). 

Body weight and abdominal adipose tissue

The weight of the animals was recorded every week. Abdominal adipose tissues were removed and weighed after sacrifice. 

Biochemical analysis

Fasting blood glucose levels were measured in blood taken from the tail vein using a kit (Medisense 2, Korea) every week. Hemoglobin A1c (in2it analyser, Bio-Rad) was determined in the blood obtained from the heart after sacrifice. Serum insulin (Shibayagi, Japan), free fatty acid, triglyceride and total cholesterol (Asan, Seoul) were determined using kits. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated according to the homeostasis of assessment, as follows (16,17). 

Statistical analysis

All data are expressed as the mean±SE. Statistical analyses were performed using the SPSS program (Version SPSS 17, Chicago, IL, USA). Group comparisons were carried out using variance analysis followed by the Duncan's multiple range test. Statistical significance was considered at p<0.05. 

Results and Discussion

Effect of Curcuma longa L. on the obesity and insulin resistance in SD rats

Body weight and abdominal adipose tissue

In this study, we investigated the effect of Curcuma longa L. on obesity and insulin resistance in SD rats and db/db mice. High fat diet has been long used to study glucose tolerance and metabolism and insulin sensitivity in experimental animals and for type 2 diabetes. In Dietary reference intakes for Koreans (15), the total fat intake should range from 15~25% of total energy. For many years, the National cholesterol education program (NCEP) and the American Heart Association (AHA) (18) recommended a fat intake of <30% of total energy. Therefore, we fed animals a 15% fat diet by weight (about 30% by calorie) to investigate the effect of Curcuma longa L. on obesity and insulin resistance induced by a moderate high fat diet. 

At the termination of the experiment, a significant decrease in the body weight gain of SD rats fed the Curcuma longa L. extract diet was observed, but no significant differences were observed among the groups fed the diet containing different levels of Curcuma longa L. extract (Fig. 1). The weight of adipose tissue was significantly lower in SD rats fed the 1.5% Curcuma longa L. extract diet than that of animals fed the control diet. While there was a tendency toward lower adipose tissue weight in the 0.5% and 1% Curcuma longa L. extract diet group at the 8th week. However, no significant differences were detected among control, 0.5 and 1% Curcuma longa L. extract groups (Fig. 1). 

Fig 1. Effect of Curcuma longa L. extract on body weight (a) and adipose tissue weight (b) in Sprague-Dawley rats.Means with the same letter are not significantly different by Duncan’s multiple range test (p<.05). CON, control; CL, Curcuma Longa L. supplemented group

Blood glucose, Serum insulin and HOMA-IR

In the SD rats, no significant difference in blood glucose levels was observed among the groups at the termination of the experiment (Table 2). Fasting serum insulin levels were significantly lower in the SD rats fed the 1.5% Curcuma longa L. extract diet than those in the rats fed the control diet (Table 2). Accordingly, HOMA-IR was significantly lower in the 0.5% and 1.5% Curcuma longa L. diet groups than in the control group. Insulin resistance is considered as a major etiologic factor of the metabolic syndrome (19,20). Hyperinsulinemia has also been suggested as a marker for a cluster of metabolic abnormalities in individuals that do not have diabetes (7). There was no significant difference in the fasting blood glucose levels among the SD rat groups (Table 2). However, Curcuma longa L. effectively decreased fasting insulin and thereby HOMA-IR. The HOMA model has been used to estimate insulin sensitivity and β-cell function from fasting insulin and glucose concentrations (16). 

Table. 2. Effect of Curcuma longa L. on the fasting blood glucose, serum insulin levels, HOMA-IR and serum lipids in high fat fed SD rats

Serum lipids

The Curcuma longa L. extract diet lowered serum triglyceride levels in a dose dependent manner. Serum triglyceride levels in the SD rats fed the 1.5% Curcuma longa L. extract diet were significantly lower than that of SD rats fed the control diet (Table 2). However, there was no significant difference in serum total cholesterol levels among the groups (Table 2). Sumner and Cowie (21) demonstrated that fasting TG concentrations could be used to identify insulin resistance in humans, even though ethnic differences in TG levels should be considered. 

Effect of Curcuma longa L. on the obesity and insulin resistance in db/db mice

Body weight and abdominal adipose tissue

No significant difference in body weight between the control diet and 1.5% Curcuma longa L. extract diet groups were observed during the experimental period (Fig. 2). However, the Curcuma longa L. extract significantly lowered the adipose tissue weight (Fig. 2). It has been suggested that maintenance of normal homeostasis of the abdominal adipose tissue is important for the prevention of the metabolic syndrome (22-24). Furthermore, excess accumulation of either visceral abdominal or muscle adipose tissue was reported to be associated with a higher prevalence of metabolic syndrome, particularly in those who are of normal body weight (4,24). Therefore, Curcuma longa L. could prevent high fat diet induced metabolic syndrome in both the normal weight and the obese by prevention of abdominal adipose tissue accumulation. 

Fig 2. Effect of Curcuma long L. extract on the body weight (a) and the adipose tissue weight (b) in db/db mice.*Significantly different with control (p<.05). CON, control; C L, Curcuma Longa L.supplemented group

Blood glucose, Hemoglobin A1c, Serum insulin, HOMA-IR and free fatty acid

As shown in Fig. 3, the 1.5% Curcuma longa L. extract effectively reduced fasting blood glucose levels in db/db mice during the entire experimental period. Glycosylated hemoglobin was lowered by the Curcuma longa L. extract. At the termination of experiment, fasting blood glucose levels were significantly lowered by 41% in the Curcuma longa L. extract diet group; however, the fasting serum insulin level was increased by 14.6%, which was not statistically significant compared to the control (Table 3). Accordingly, the HOMA‐IR was lower in the 1.5% Curcuma longa L. diet groups than in the control group, but the difference was not statistically significant (Table 3). Insulin resistance occurs even when glucose values are still within the normal glucose tolerance range in the course of type 2 diabetes (4). In the present study Curcuma longa L. was shown to reduce insulin resistance by preventing weight gain and abdominal fat accumulation even in normal weight animals. Curcuma longa L. significantly decreased hemoglobin A1c as well as blood glucose in leptin receptor defected db/db mice (Fig. 3). In type 2 diabetes, hyperglycemia was induced when increased insulin secretion no longer compensates for insulin resistance. Therefore, increased insulin alone was not sufficient to cause diabetes (6,22). Fasting insulin levels were higher in db/db mice fed Curcuma longa L., which contributed to decreased glucose concentrations and hemoglobin A1c. The final outcome was that Curcuma longa L. significantly decreased blood glucose levels, which reduced HOMA-IR in db/db mice. Serum free fatty acid was also lowered by the 1.5% Curcuma longa L. diet, but the difference did not reach statistical significance (Table 2). Excess abdominal obesity results in an increased flux of FFA to the liver, leading to an increase in insulin resistance (25). In addition, a high level of plasma FFA also causes a further decrease in insulin sensitivity at the cellular level, impair insulin signaling and augment hepatic glucose production. Therefore, Curcuma longa L. can decrease the risk of type 2 diabetes by decreasing free fatty acid flux to the liver and insulin resistance. Hypertriglyceridemia is not absolutely required for diagnosis of the metabolic syndrome. Nevertheless, due to the strong relationship between insulin resistance and hypertriglyceridemia, hypertriglyceridemia is considered one of the most important metabolic syndrome criteria (20,25,26). In conclusion, Curcuma longa L. prevented fat accumulation and insulin resistance in SD rats fed a moderate high fat diet and improved hyperglycemia by decreasing fat accumulation and increasing serum insulin levels in type 2 diabetic obese db/db mice. 

Fig 3. Effect of Curcuma long L. extract on the fasting blood glucose and HbA1c in db/db mice.*Significantly different with control (p<.05). CON, control; CL, Curcuma Longa L.supplemented group

Table. 3. Effect of Curcuma longa L. on the fasting blood glucose and serum insulin levels, HOMA-IR and serum free fatty acid in high fat fed db/db mice

Acknowledgements

This work(Grants No. 08-01-86) was supported by Business for Cooperative R&D between Industry and Academy Corperation Laboratory funded Korea Small and Medium Business Administration in 2008 

Reference

1.Gower BA, Munoz J, Desmond R, Hailey RH, Jiao X (2006) Changes in intra-abdominal fat in early postmenopausal women: effects of hormone use. Obesity, 14, 1046-1055
2.Castejon MG, Casado AR (2011) Dietary phytochemicals and their potential effects on obesity: A review. Pharmacol Res, 64, 438-455
3.Koh-Banerjee p, Wang Y, Hu FB, Spoegelman D, Willett WC, Rimm EB (2004) Changes in cody weight and body fat distribution as risk factors for clinical diabetes in us men. Am J Epidemiol, 159, 1150-1159
4.Goodpaster BH, Krishmaswami S, Harris TB, Katsiaras A, Kritchevsky SB, Simonsick EM, Mevitt M, Holvoet P, Newman AB (2005) Obesity, regional fat distribution and the metabolic syndrome in older men and women. Arch Int Med, 165, 777-783
5.Leahy HK (2005) Pathogenesis of type 2 diabetes Mellitus. Archi Med Res, 36, 197-209
6.Yang Q, Graham TE, Mody N, Preitner F, Peroni OD, Zabolotny JM, Kotan K, Quadro L, Kahn BB (2005) Serum retinol binding protein 4 contributes to insulin resistance in obesity and type 2 diabetes. Nature, 436, 356-362
7.Despres, JP, Lamarche B, Mauriege P, Cantin B, Dagenais GR, Moorjani S, Lupien PJ (1996) Hyperinsulinemia as an independant risk factor for ischemic heart disease. N Engl J Med, 334, 952-957
8.Okada K, Wangpoentrakul C, Tanaka T, Toyokuni S, Uchida K, Isawa T (2001) Curcumin and especially tetrahydrocurcumin ameliorate oxidative stress-induced renal injury in mice. J Nutr, 131, 2090-2095
9.Sharma S, Kulkarni SK, Chopra K (2006) Curcumin, the active principle of turmeric (Curcuma longa), ameliorates diabetic nephropathy in rats. Clin Exp Pharmacil Physio, 33, 940-945
10.Shishodia S, Singh T, Chatuvedi MM (2007) Modulation of transcription factors by curcumin. Adv Exp Biol, 595, 127-148
11.Pari L, Murugan P (2005) Effect of tetrahydrocurcumin on blood glucose, plasma insulin and hepatic key enzymes in streptozotocin induced diabetic rats. J Basic Clin Physiol Pharmacol, 16, 257-274
12.El‐Moselhy M, Taye A, Sharkawi SS, El-Sisi SFI, Ahmed AF (2011) The antihyperglycenic effect of curcumin in high fat diet fed rats. Role of TNF-α and free fatty acids. Food Chem Toxidol, 49, 1123-1140
13.Tartaglia LA, Dembski M, Weng X, Deng N, Culpepper J, Devos R (1995) Identification and expression cloning of a leptin receptor, OB-R. Cell, 83, 1263-1271
14.Coleman DL (1978) Ovese and diabetes: Two mutant genes causing diabetes-obesity syndroms in mice. Diabetologia, 14, 141-148
15.The Korean Nutrition Society (2010) Dietary reference intakes for Koreans. 1st revision 2010. Seoul: The Korean Nutrition Society.
16.Matthews DR, Hosker JP, Rudenski A, Naylor BA, Treacher DF, Turner RC (1985) Homeostasis model assessment: insulin resistance and geta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia, 28, 412-419
17.Matsuzawa Y, Funahashi T, Kihara S, Shimomura I (2004) Adiponectin and metabolic syndrome. Arterioscler Thromb Vasc Biol, 24, 29-33
18.Expert pannel in detecton evaluation and treatment of high Blood cholesterol in adults. (2001) Executive summary of the third report of the national cholesterol education program(NCEP) expert panel in detection, evaluation, and treatment of high blood cholesterol in adults(Adult treatment panel III). JAMA, 285, 2486-2497
19.Alberti KG, Zimmet P, Shaw J (2005) The metabolic syndrome-a new world-side definition: IDF epidemiology task force consensus group. Lancet, 366, 1059-1062.
20.Eckel RH, Grundy SM, Zimmet PZ (2005) The metabolic syndrome, Lancet, 365, 1415-1428
21.Sumner AE, Cowie CC (2008) Ethnic differences in the ability of triglyceride levels to identify insulin resisrance. Atherosclerosis, 196, 696-703
22.Berg AH, Combs TP, Scherer PE (2002) ACRP30/ adiponectin: An adipokine regulating glucose and lipid metabolism. Trends Endocrinol Metab, 13, 84-89
23.Tsao TS, Lodish HF, Fruebis J (2002) ACRP 30, a new hormone controlling fat and glucose metabolism. European J Pharm, 440, 213-221
24.Goodpaster BH, Krishnaswami S, Resnick H, Kelley DE, Haggerty C, Harris TB, Schwartx AV, Kritchevsky S, Newman AB (2003) Association between regional adipose tissue distribution and both type 2 diabetes and impaired glucose tolerance in elderly men and women. Diabetes care, 165, 372-379
25.Bergman RN, Ader M (2000) Free fatty acid and pathogenesis of type 2 diabetes mellitus. Trends Endocrinol Metabol, 11, 351-356
26.Avramiglu RK, Basciano H, Adeli K (2006) Lipid and lipid protein dysregulation in insulin resistant states. Clin Clim Acta, 368, 1-19