Nutrition Reserch nd Prctice 2015;9(5):472-479 c2015 The Koren Nutrition Society nd the Koren Society of Community Nutrition http://e-nrp.org Srgssum corenum extrct llevites hyperglycemi nd improves insulin resistnce in db/db dibetic mice Mi Hw Prk 1, Young Hw Nm 2 nd Ji-Sook Hn 3 1 Deprtment of Food nd Nutrition, College of Medicl nd Life Science, Sill University, Busn 617-736, Kore 2 Deprtment of Food Science nd Nutrition, Pusn Ntionl University, Busn 609-735, Kore 3 Deprtment of Food Science nd Nutrition & Reserch Institute of Ecology for the Elderly, Pusn Ntionl University, 63 Beon-gil 2, Busndehg-ro, Geumjeong-gu, Busn 609-735, Kore BACKGROUND/OBJECTIVES: The gol of this study ws to exmine the effect of Srgssum corenum extrct (SCE) on blood glucose concentrtion nd insulin resistnce in C57BL-KsJ-db/db mice. MATERIALS/METHODS: For 6 weeks, mle C57BL/KsJ-db/db mice were dministrted SCE (0.5%, w/w), nd rosiglitzone (0.005%, w/w). RESULTS: A supplement of the SCE for 6 weeks induced significnt reduction in blood glucose nd glycosylted hemoglobin concentrtions, nd it improved hyperinsulinemi compred to the dibetic control db/db mice. The glucokinse ctivity in the heptic glucose metbolism incresed in the SCE-supplemented db/db mice, while phosphoenolpyruvte crboxykinse nd glucose-6-phosphtse ctivities in the SCE-supplemented db/db mice were significntly lower thn those in the dibetic control db/db mice. The homeosttic index of insulin resistnce ws lower in the SCE-supplemented db/db mice thn in the dibetic control db/db mice. CONCLUSIONS: These results suggest tht supplement of the SCE lowers the blood glucose concentrtion by ltering the heptic glucose metbolic enzyme ctivities nd improves insulin resistnce. Nutrition Reserch nd Prctice 2015;9(5):472-479; doi:10.4162/nrp.2015.9.5.472; pissn 1976-1457 eissn 2005-6168 Keywords: Anti-dibetic effects, Srgssum corenum extrct, C57BL/KsJ-db/db mice, hyperglycemi, insulin resistnce INTRODUCTION 4) Dibetes mellitus is chronic disese representing one of the world s most serious helth concerns. Primrily, dibetes mellitus hs been clssified into type 1 dibetes nd type 2 dibetes. The incidence of type 2 dibetes is incresing round the globe [1]. Type 2 dibetes is mostly defect tht is chrcterized by high blood glucose due to insulin resistnce nd reduced sensitivity to insulin in muscle, dipose, nd liver cells [2,3]. Currently vilble drugs for type 2 dibetes include insulin secretgogues, such s sulfonylure, nd insulin sensitizers, such s thizolinedione [4]. However, phrmcologicl gents for type 2 dibetes exhibit number of limittions, such s side effects nd high rtes of secondry filure [5]. Thus, person with dibetes nd helthcre professionls re interested in lterntive therpies nd nturl products with the therpeutic potentil to tret dibetes, prticulrly those derived from mrine lge or plnts becuse these sources re regrded to be less toxic with fewer side effects compred to their synthetic counterprts. Mrine lge re known to generte n bundnce of bioctive compounds with gret potentil in the phrmceuticl, food, nd biomedicl industries. In prticulr, brown lge hve mny different bioctive compounds, including phycocolloids, pigments, nd polyphenolic compounds (e.g., phlorotnnins) [6]. The brown lg Srgssum corenum is produced on Jeju Islnd in Kore [7]. It hs mny biologicl benefits, including its ntioxidnt effects in free-rdicl medited oxidtive systems [8] nd its inhibitory effect on humn immunodeficiency virus [9]. However, the effect of S. corenum extrct on type 2 dibetes hs not yet been investigted, especilly with respect to lleviting blood glucose concentrtion, improving insulin resistnce, nd its effect on the ctivities of the enzymes involved in heptic glucose metbolism. Therefore, the present study ws conducted to investigte whether S. corenum extrct llevites hyperglycemi nd improves insulin resistnce in type 2 dibetes mellitus mice. The efficcy ws compred with n orl nti-dibetic gent, rosiglitzone (n insulin sensitizer), for type 2 dibetes. This work ws supported by the Bsic science Reserch Progrm through the Ntionl Reserch Foundtion of Kore (NRF) funded by the Ministry of Eduction, Science nd Technology (grnt number 2013027365). Corresponding Author: Ji-Sook Hn, Tel. 82-51-510-2836, Fx. 82-51-583-3648, Emil. hnjs@pusn.c.kr Received: November 24, 2014, Revised: Februry 8, 2015, Accepted: April 13, 2015 This is n Open Access rticle distributed under the terms of the Cretive Commons Attribution Non-Commercil License (http://cretivecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercil use, distribution, nd reproduction in ny medium, provided the originl work is properly cited.
Mi Hw Prk et l. 473 MATERIALS AND METHODS Preprtion of Srgssum corenum extrct S. corenum were collected from the cost of Jeju Islnd, Kore. The smples were initilly wshed 3 times with tp wter to remove slt, epiphytes, nd snd ttched to the surfce nd then crefully rinsed with fresh wter. Therefter, the smples were lyophilized nd homogenized with grinder. The dried S. corenum powder ws extrcted 3 times with 80% methnol nd then filtered. Subsequently, the methnol extrct ws filtered through Whtmn No.1 filter pper nd evported under vcuum t 40 C, nd 30 g of extrct per 200 g of powdered S. corenum ws obtined. After freeze-drying, the S. corenum extrct ws powdered nd used in the experiment. Animls nd diets Mle C57BL/KsJ-db/db mice were purchsed from Jpn SLC (Hmmtsu, Jpn). The 5-week-old db/db mice were fed pelletized commercil chow diet for 2 weeks fter rrivl. The mice were then rndomly divided into 3 groups (n = 8). For 6 weeks, the db/db mice in the control of dibetes mellitus group were fed stndrd semi-synthetic diet (AIN-93G), while those in the other 2 groups were fed stndrd AIN-93G diet with either rosiglitzone (0.005%, w/w) or S. corenum extrct (SCE; 0.5%, w/w) (Tble 1). Rosiglitzone nd SCE doses were bsed on references nd dosge for humn type 2 dibetes ptients. Type 2 dibetic ptients (BW: 60 kg) tke 2 tblet rosiglitzone dy (1 tblet: 2 mg). In mouse dosge terms (BW: 30 g), the dily food intke is 0.002 mg. And then, we were multiply tht by humn sfety index 100. The mice were fed stndrd AIN-93G diet with either rosiglitzone (0.005%, w/w). Also, we multiply drug dosge by sfety index 100 to decide SCE dose. The mice were fed stndrd AIN-93G diet with either SCE (0.5%, w/w). The mice were housed individully in stinless steel cges with rndomized complete block design t temperture of 23 ± 1 C nd humidity of 53 ± 2% in light-controlled room with 12 h light-drk cycle. The mice hd ccess to food nd wter d libitum. Food nd wter intkes were mesured Tble 1. Composition of the experimentl diets DMC SCE Rosiglitzone Csein 20 20 20 Cornstrch 39.7486 39.7486 39.7486 Dyetrose 13.2 13.2 13.2 Sucrose 10 9.5 9.995 Cellulose 5 5 5 Soyben Oil 7 7 7 t-butylhydroquinone 0.0014 0.0014 0.0014 Slt Mix 3.5 3.5 3.5 Vitmin Mix 1 1 1 L-Cystine 0.3 0.3 0.3 Choline Bitrtrte 0.25 0.25 0.25 Srgssum corenum extrct 0.5 Rosiglitzone 0.005 Totl (%) 100 100 100 DMC: C57BL/KsJ-db/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). periodiclly mnully. After defined time elpses (24 h), the food nd wter were reweighed nd the mount consumed ws clculted by difference. At the end of the experimentl period, the mice were nesthetized with ether fter withholding food for 12 h, nd blood smples were tken from the inferior ven cv to determine the level of plsm biomrkers. Furthermore, the liver ws removed fter collecting the blood nd ws rinsed with physiologicl sline solution. All procedures were pproved by the niml ethics committee of pusn ntionl university (PNU-2012-0078). Blood glucose nd glycosylted hemoglobin concentrtions Glucose concentrtion in the venous blood drwn from the til vein ws determined using glucometer (Roche Dignostics GmbH, Mnnheim, Germny) once week for 6 weeks fter 12 h fst. The nticogulted whole blood specimen ws hemolyzed nd the blood glycosylted hemoglobin concentrtion ws mesured. Glycosylted hemoglobin levels were determined by immunoturbidimetry. Plsm insulin concentrtion Blood smples from the inferior ven cv were collected into heprin-coted. After centrifugtion t 1000 g for 15 min t 4 C, the plsm ws crefully removed from the smple. The levels of plsm insulin were determined by rdioimmunossy with n enzyme-linked immunosorbent ssy kit (Linco Reserch Inc., Billeric, MA, USA). Homeosttic index of insulin resistnce nd quntittive insulin sensitivity check index The homeosttic index of insulin resistnce (HOMA-IR) [10] nd quntittive insulin sensitivity check index (QUICKI) [11] were determined s surrogtes of insulin sensitivity. The HOMA-IR ws clculted by using the homeostsis model ssessment s follows: Eq. (1): HOMA-IR = [fsting glucose (mmol/l) fsting insulin (IU/mL)]/22.51 QUICKI ws derived by using the inverse of the sum of the logrithms of fsting insulin nd fsting glucose s follows: Eq. (2): QUICKI = 1/[log (fsting glucose (mg/dl)) + log (fsting insulin (U/mL))] Intrperitonel glucose tolernce test An intrperitonel glucose tolernce test (IPGTT) ws performed during the lst week of the experimentl period. Twelve-hourfsted mice received n intrperitonel injection of glucose (0.5 mg of glucose/g of body weight), nd blood smples in the dibetes mellitus control (DMC), SCE, nd rosiglitzone db/db mice groups were obtined for glucose mesurement t 0, 30, 60, nd 120 min. The glucose concentrtion in the venous blood drwn from the til vein ws determined using glucometer (Roche Dignostics GmbH, Mnnheim, Germny) every week fter 12 h fst. Heptic tissue processing The livers were perfused vi the portl vein with cold 0.25 M sucrose nd then excised, blotted, weighed, minced, nd homogenized in 9 volumes of 0.25 M sucrose. Ech homogente
474 Antidibetic effect of Srgssum corenum ws subjected to cell frctiontion. The cytosolic, mitochondril, nd microsoml frctions were isolted by sucrose liner density-grdient centrifugtion method [12] nd stored t -80 C. All of the isoltion procedures were performed t 2-4 C. The cytosolic, mitochondril, nd microsoml frctions (heptic subcellulr frctions) were used for the enzyme ssys. Heptic glucose metbolic enzyme ctivities Glucokinse ctivity ws determined by continuous spectrophotometric ssy, s described by Dvidson nd Arion [13] with slight modifiction, wherein the formtion of glucose-6- phosphtse t 37 C ws coupled to its oxidtion by glucose-6- phosphte dehydrogense nd NAD+. The glucose-6-phosphtse ctivity ws determined ccording to the method of Alegre et l. [14] with slight modifiction; the ctivity ws determined using spectrophotometric ssy contining 100 mmol/l sodium Hepes (ph 6.5), 26.5 mmol/l glucose-6- phosphte, nd 1.8 mmol/l EDTA (djusted to ph 6.5), 2 mmol/l NADP+, 0.6 IU/mL mutrotse, nd 6 IU/mL glucose dehydrogense. The phosphoenolpyruvte crboxykinse ctivity in the direction of oxlocette synthesis ws estimted using the spectrophotometric ssy developed by Bentle nd Lrdy [15] with slight modifiction; 1-mL finl volume of the purified enzyme ws pipetted into rection mixture (ph 7.0) contining 50 mmol/l sodium Hepes, 1mmol/L IDP, 1mmol/L MnCl 2, 1 mmol/l dithiothreitol, 0.25 mmol/l NADH, 2 mmol/l phosphoenolpyruvte, 50 mmol/l NHCO 3, nd 7.2 units of mlic dehydrogense. The enzyme ctivity ws then mesured t 25 C bsed on decrese in the bsorbnce t 340 nm. Heptic glycogen ssy The glycogen concentrtion ws determined s previously described by Seifter et l. with some modifictions [16]. Briefly, the liver tissue ws homogenized in 5 volumes of 30% (w/v) ice-cold KOH solution nd dissolved in boiling wter bth (100 C) for 30 min. The glycogen ws precipitted with ethnol nd then pelleted, wshed, nd resolubilized in distilled wter. This solution ws treted with n nthrone regent [2 g nthrone/1 L of 95% (v/v) H 2SO 4, nd its bsorbnce ws mesured t 620 nm. Plsm lipid concentrtion The plsm totl cholesterol (TC), HDL-cholesterol (HDL-C) nd triglyceride concentrtions were determined using n enzymtic method (Asin Phrmceuticl Corp., Kore), while the plsm free ftty cid (FFA) concentrtion ws determined using n enzymtic colorimetric method (Wko, Jpn). Heptic function tests Asprte minotrnsferse nd lnine minotrnsferse ctivities were determined using kit (Asin Phrm Co., Kore) by the modified Reitmn-Frnkel method. Sttisticl nlysis of dt The dt were represented s the men ± SD. Sttisticl nlyses were performed using the SAS softwre. The vlues were evluted by one-wy nlysis of vrince (ANOVA) followed by post-hoc Duncn s multiple rnge tests. RESULTS Body weight nd food nd wter intke At the strt of the study, the db/db mice did not differ significntly in their body weight mong the control of dibetes mellitus, rosiglitzone-supplemented, nd SCE-supplemented db/db mice groups. During the 6-week period, body weight incresed grdully. The body weights of the control of dibetes mellitus, rosiglitzone-supplemented, nd SCE-supplemented db/db mice were significntly different t the end of the study. The rosiglitzone-supplemented db/db mice hd higher body weight compred to the control of dibetes mellitus nd SCE-supplemented db/db mice (Tble 2). The dily food intke of these db/db mice did not differ significntly. The rosiglitzonend SCE-supplemented db/db mice hd significntly lower dily intke of wter thn the control of dibetes mellitus db/db mice. Blood glucose nd glycted hemoglobin concentrtions The effects of the SCE nd rosiglitzone supplement on blood glucose concentrtions re shown in Fig. 1. There were no significnt differences in blood glucose concentrtions mong the groups t the beginning of the experiment. Throughout the experimentl period, the blood glucose concentrtions of the control of dibetes mellitus db/db mice incresed steeply, Tble 2. The effects of SCE supplement on food intke nd body weight in C57BL/KsJ-db/db mice DMC SCE Rosiglitzone Food intke (g/dy) 6.09 ± 0.33 NS 5.09 ± 0.69 4.61 ± 1.36 Wter intke (ml/dy) 20.98 ± 1.47 13.89 ± 2.49 b 6.16 ± 1.95 c Body weights (g) Initil 34.34 ± 1.45 NS 33.51 ± 1.01 34.82 ± 1.87 Finl 42.07 ± 4.48 NS 43.90 ± 1.95 49.92 ± 3.11 Vlues re men±sd (n=8). Superscripts in the sme row not shring common superscript re significntly different between groups (P < 0.05). DMC: C57BL/KsJdb/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). Fsting blood glucose (mmol/l) 30 25 20 15 10 5 0 NS DMC SCE rosiglitzone NS * b b b b b c 0 1 2 3 4 5 6 Feeding durtion (wks) Fig. 1. Chnges in the blood glucose concentrtions of C57BL/KsJ-db/db mice supplemented with SCE for 6 weeks. DMC: C57BL/KsJ-db/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). Vlues re men ± SD (n = 8); Superscripts with different lphbets in sme time point differ significntly t P < 0.05 s nlyzed vi ANOVA with Duncn s multiple rnge test. b
Mi Hw Prk et l. 475 Tble 3. The effects of SCE supplement on glycted hemoglobin, plsm insulin, fsting blood glucose, nd insulin resistnce in C57BL/KsJ-db/db mice DMC SCE Rosiglitzone HbA1c (mmol/mol Hb) 112.24 ± 6.30 74.08 ± 9.18 b 59.02 ± 4.83 b Plsm insulin (pmol/l) 239.65 ± 34.51 168.70 ± 16.97 b 158.57 ± 29.46 b Fsting blood glucose (mmol/l) 23.73 ± 3.03 18.16 ± 2.05 b 6.81 ± 1.04 c HOMA-IR 25.50 ± 1.32 13.54 ± 2.29 b 7.05 ± 0.01 b QUICKI 0.25 ± 0.01 b 0.27 ± 0.01 0.29 ± 0.01 Vlues re men±sd (n=8). Superscripts in the sme row not shring common superscript re significntly different between groups (P < 0.05). DMC: C57BL/KsJdb/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). HOMA-IR: homeosttic index of insulin resistnce; QUICKI: quntittive insulin sensitivity check index. but those of SCE-supplemented db/db mice incresed grdully nd to lesser extent thn the control of dibetes mellitus db/db mice. The blood glycted hemoglobin concentrtion ws significntly lower in the SCE-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. The blood glycted hemoglobin concentrtion ws effectively reduced in the SCE-supplemented db/db mice, even if the level in these db/db mice ws higher thn tht of the rosiglitzone-supplemented db/db mice (Tble 3). Homeosttic index of insulin resistnce, quntittive insulin sensitivity check index, nd intrperitonel glucose tolernce test Tble 3 shows tht the plsm insulin concentrtions of the SCE- nd rosiglitzone-supplemented db/db mice were significntly lower thn tht of the control of dibetes mellitus db/db Fig. 2. The effect of SCE supplement on glucose tolernce test in C57BL/ KsJ-db/db mice. After 12 h fst, mle mice were intrperitonelly injected with glucose (0.5 g/kg body weight). The blood glucose concentrtion ws mesured t the indicted times nd presented s ctul vlue injection. DMC: C57BL/KsJ-db/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). Vlues re men ± SD (n = 8); Superscripts with different lphbets in sme time point differ significntly t P < 0.05 s nlyzed vi ANOVA with Duncn s multiple rnge test. mice. Furthermore, the homeosttic index of insulin resistnce nd quntittive insulin sensitivity check index were significntly different mong the control of dibetes mellitus, rosiglitzone-supplemented, nd SCE-supplemented db/db mice. The homeosttic index of insulin resistnce ws significntly lower in the SCE- nd rosiglitzone-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. In ddition, the quntittive insulin sensitivity check index ws significntly (A) (B) (C) (D) Fig. 3. The effects of SCE supplementtion on the heptic glucokinse (A), glucose-6-phosphtse (B), nd phosphoenolpyruvte crboxykinse ctivities (C), nd glycogen content (D) in C57BL/KsJ-db/db mice. DMC: C57BL/KsJ-db/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). Vlues re men ± SD (n = 8); Superscripts with different lphbets differ significntly t P < 0.05 s nlyzed vi Duncn s multiple rnge test.
476 Antidibetic effect of Srgssum corenum Tble 4. The effects of SCE supplement on plsm lipid concentrtion in C57BL/KsJ-db/db mice DMC SCE Rosiglitzone Totl cholesterol (mg/dl) 327.15 ± 69.61 198.30 ± 53.79 b 184.05 ± 21.87 b Triglyceride (mg/dl) 289.47 ± 17.92 216.87 ± 21.35 b 199.03 ± 21.80 b FFA (mmol/l) 1.02 ± 0.13 0.42 ± 0.12 b 0.49 ± 0.15 b HDL-C (mg/dl) 49.13 ± 9.86 b 104.12 ± 7.63 78.01 ± 16.30 b LDL-C (mg/dl) 220.12 ± 56.17 74.06 ± 68.56 b 70.02 ± 25.22 b AI (mg/dl) 5.66 ± 0.31 1.14 ± 0.13 b 1.41 ± 0.22 b Vlues re men±sd (n=8). Superscripts in the sme row not shring common superscript re significntly different between groups (P < 0.05). DMC: C57BL/KsJdb/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). AI: Atherogenic index. Tble 5. The effects of SCE supplement on heptic function tests in C578BL/ KsJ-db/db mice DMC SCE Rosiglitzone ALT (krmen/ml) 14.06 ± 0.55 NS 13.09 ± 0.51 13.14 ± 0.17 AST (krmen/ml) 12.24 ± 0.67 NS 11.90 ± 0.61 12.48 ± 0.21 Vlues re men ± SD (n = 8). DMC: C57BL/KsJ-db/db mice supplemented with AIN-93G diet; rosiglitzone: C57BL/KsJ-db/db mice supplemented with rosiglitzone (0.005 g/100 g diet); SCE: C57BL/KsJ-db/db mice supplemented with SCE (0.5 g/100 g diet). ALT: lnine minotrnsferse; AST: sprtte minotrnsferse; NS: not significnt. higher in the SCE- nd rosiglitzone-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. Glucose tolernce ws monitored by n intrperitonel glucose tolernce test t 6 weeks fter supplementtion with SCE or rosiglitzone (Fig. 2). There ws significnt difference in the progression of nonliner ptterns mong the control of dibetes mellitus, rosiglitzone-supplemented, nd SCE-supplemented db/db mice. In terms of the chnge point nlysis, it ws confirmed tht the SCE- nd rosiglitzone-supplemented db/db mice hd chnge point t 60 min. Specificlly, the blood glucose concentrtions in the rosiglitzone-supplemented db/db mice peked t 60 min nd lmost recovered to the bsl vlue t 120 min. Similrly, the blood glucose concentrtions in SCE-supplemented db/db mice peked t 60 min nd presented with declined vlue t 120 min. However, the blood glucose concentrtions in the control of dibetes mellitus db/db mice grdully incresed nd remined t constnt, high level with miniml chnges occurring over the course of 30-120 min. In other words, when the mice were injected with glucose, the rtes of increse in the blood glucose concentrtion were similr mong the groups during the first 60 min. Subsequently, the blood glucose concentrtion becme significntly higher in the control of dibetes mellitus db/db mice compred to the SCE- nd rosiglitzone-supplemented db/db mice. Heptic glucose regulting enzyme ctivities nd glycogen levels Heptic glucokinse ctivity ws significntly higher in the SCE- nd rosiglitzone-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. In contrst, glucose-6- phosphtse ctivity ws remrkbly lower in the SCE- nd rosiglitzone-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. Phosphoenolpyruvte crboxykinse ctivity ws lso significntly lower in the SCE- nd rosiglitzonesupplemented db/db mice thn in the control of dibetes mellitus db/db mice. The heptic glycogen levels in the SCEnd rosiglitzone-supplemented db/db mice were significntly higher thn tht in the control of dibetes mellitus db/db mice (Fig. 3). Plsm lipid The plsm triglyceride, free ftty cid, totl cholesterol, LDL-cholesterol, nd therogenic index levels of the SCE- nd rosiglitzone-supplemented db/db mice were significntly lower thn those of the control of dibetes mellitus db/db mice, while the plsm HDL-cholesterol ws significntly higher in the SCE- nd rosiglitzone-supplemented db/db mice thn in the control of dibetes mellitus db/db mice (Tble 4). Heptic function The levels of ALT nd AST were not significntly different mong the control of dibetes mellitus, rosiglitzone-supplemented, nd SCE-supplemented db/db mice groups (Tble 5). The ALT nd AST levels of ech were within the norml rnge. DISCUSSION Type 2 dibetes mellitus nd its relted complictions hve risen s serious helth problems in modern societies. In this study, we demonstrted the nti-dibetic effect of SCE supplementtion in C57BL/KsJ-db/db mice. These db/db mice hve chrcteristics tht re similr to humn type 2 dibetes, including hyperglycemi, obesity, nd insulin resistnce [16-18]. The body weights incresed in db/db mice fter 6 weeks. The rosiglitzone-supplemented db/db mice experienced significntly greter body weight gin compred to the SCE-supplemented nd control of dibetes mellitus db/db mice. These results my be due to incresed dipose tissue mss, which hs been shown for rodents nd humns receiving rosiglitzone tretment [5]. Food intke did not hve significnt effect on the groups, but wter intke ws significntly lower in the SCE- nd rosiglitzone-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. The typicl symptoms of type 2 dibetes re polyphgi, polyuri, nd polydipsi. Supplements of SCE nd rosiglitzone improved the symptoms of type 2 dibetes compred to the control of dibetes mellitus db/db mice; prticulrly polydipsi. Rosiglitzone is n nti-dibetic drug in the thizolinedione clss, nd ws used s the positive control for SCE in the present study. Rosiglitzone works s n insulin sensitizer by binding to the Peroxisome prolifertor-ctivted receptor receptors in ft cells nd mking the cells more responsive to insulin [19]. Tht is, it increses insulin sensitivity nd improves glycemic control in type 2 dibetes. However, this compound induces dipogenesis in cell culture systems [20] nd rises weight gin in rodents nd humns [5]. In ddition, it hs severl side effects, such s hedches, hypoglycemi, edem, hypertension, nd liver toxicity [21]. Hyperglycemi is crucil fctor in the onset of type 2 dibetes nd the complictions ssocited with the disese [22]. Thus, the effective control of hyperglycemi is key for preven-
Mi Hw Prk et l. 477 ting dibetic complictions nd improving the qulity of life in ptients with type 2 dibetes [23]. Hyperglycemi is n independent risk fctor for vsculr compliction disese, nd therpeutic mediction my be required in order to rech hyperglycemic control trgets in ptients who hve type 2 dibetes [24]. Fsting blood glucose concentrtion in the control of dibetes mellitus db/db mice incresed steeply, but the concentrtion in the SCE-supplemented db/db mice incresed grdully up to the second week of the experimentl diet. Also, rosiglitzone supplementtion slowly decresed the fsting blood glucose concentrtion over 6-week period. It is well known tht rosiglitzone supplement improves glycemic control in db/db mice [20]. The SCE supplement in the db/db mice significntly llevited rising blood glucose levels compred to the control of dibetes mellitus db/db mice over the entire experimentl period. In ddition, the SCE supplement in the db/db mice significntly lowered the glycted hemoglobin concentrtions compred to the control of dibetes mellitus db/db mice. Glycted hemoglobin is primrily mesured to identify verge blood glucose concentrtions over prolonged periods of time. This serves s mrker for verge blood glucose concentrtions over the previous months nd is useful for monitoring glycemic control in ptients with type 2 dibetes [25]. The findings in this study suggest tht the SCE supplement improved blood glucose concentrtion in type 2 dibetes mellitus mice. In generl, db/db mice exhibit n initil phse of hyperinsulinemi nd progressively develop insulinopeni with ge, feture tht is commonly observed in the lte stges of type 2 dibetes [26]. The results of this study showed tht the plsm insulin level in the control of dibetes mellitus db/db mice ws higher thn those in the SCE- nd rosiglitzone-supplemented db/db mice, indicting tht hyperinsulinemi ws still expressed in the control of dibetes mellitus db/db mice. It hs been reported tht rosiglitzone improves the ctions of insulin, thereby meliorting glucose tolernce nd lowering hyperinsulinemi in nimls nd humns with type 2 dibetes [27]. The homeosttic index of insulin resistnce nd the quntittive insulin sensitivity check index re simple indexes of insulin resistnce. These were clculted using insulin nd fsting glucose levels. The homeosttic index of insulin resistnce is used s biomrker of insulin resistnce; vlues should increse with incresing insulin resistnce. It is useful index of insulin resistnce [28]. Even though the homeosttic index of insulin resistnce hs severl limittions in terms of ccurcy nd relibility [12], it essentilly expresses insulin resistnce [29]. The quntittive insulin sensitivity check index is n index of insulin sensitivity; vlues should decrese with incresing insulin resistnce. In this study, the blood glucose level, plsm insulin level, nd homeosttic index of insulin resistnce were significntly lower in the SCE-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. The intrperitonel glucose tolernce test ws performed fter supplementing SCE in db/db mice for 6 weeks. Twelvehour-fsted mice received n intrperitonel injection of glucose, nd blood smples in the control of dibetes mellitus, rosiglitzone-supplemented, nd SCE-supplemented db/db mice were obtined for glucose mesurement t 0, 30, 60, nd 120 min. The rosiglitzone-supplemented db/db mice results indicted ner recovery of blood glucose levels t 120 min fter glucose loding when expressed s ctul vlues. SCE lso improved the glucose-hndling bility of db/db mice by lowering blood glucose level t 120 min, wheres glucose tolernce in the control of dibetes mellitus db/db mice becme impired. Thus, the SCE- nd rosiglitzone-supplemented db/db mice meliorted their glucose tolernce when the dt were presented s ctul blood glucose levels in the intrperitonel glucose tolernce test. Subjects with impired glucose tolernce generlly hve heightened risk of mcrovsculr disese [30-32]. The dignosis of impired glucose tolernce hs importnt prognostic implictions for crdiovsculr disese risk fctors with respect to detecting hypertension, dyslipidemi, nd centrl obesity [33]. Abnorml heptic glucose metbolism is mjor symptom of type 2 dibetes, nd it contributes to postprndil hyperglycemi [34]. Elevted heptic glucose production is criticl for the occurrence of fsting nd postprndil hyperglycemi [35]. While the level of plsm insulin in the db/db mice ws high, heptic glucose production ws elevted, indicting reltive insensitivity of the liver to insulin [36]. Heptic glucokinse plys mjor role in controlling blood glucose homeostsis nd its ctivity is low in type 2 dibetes [37]. Glucose-6-phosphtse is key enzyme controlling heptic gluconeogenesis nd glucose output in the liver, nd is normlly suppressed by the ctions of insulin [38]. Due to their strtegic positions in heptic glucose metbolism, both glucokinse nd glucose-6-phophtse re the trget enzymes regulting heptic glucose production [39]. In this study, heptic glucokinse ctivity ws significntly higher in the SCE-supplemented db/db mice thn in the control of dibetes mellitus db/db mice. Furthermore, heptic glucose- 6-phosphtse ctivity ws significntly lower in the SCE-supplemented db/db mice thn in the control of dibetes mellitus db/db mice, thereby decresing heptic gluconeogenesis. The SCE supplement in db/db mice lso lowered the ctivity of heptic phosphoenolpyruvte crboxykinse compred with the control of dibetes mellitus db/db mice. Thus, the hypoglycemic effects of the SCE supplement my be prtly controlled through enhnced glucokinse ctivity nd suppressed glucose-6- phosphtse nd phosphoenolpyruvte crboxykinse ctivity in the liver of db/db mice. Both lipolysis nd circulting free ftty cids increse in n insulin resistnce condition [19,40]. Also, elevted plsm free ftty cid levels ccount for up to 50% of insulin resistnce in obese ptients with type 2 dibetes [41]. In the present study, the SCE supplement significntly lowered the plsm free ftty cid, triglyceride, totl cholesterol, nd LDL-cholesterol levels compred to the control of dibetes mellitus db/db mice. A few studies hve reported tht free ftty cid nd LDLcholesterol levels were significntly reduced by supplementtion with nturl products contining polyphenol in type 2 dibetes mellitus nimls [42-44]. In this study, the results lso indicte tht SCE supplementtion enhnces the meliorting effect of insulin resistnce by decresing plsm lipid levels in db/db mice. In conclusion, we investigted the nti-dibetic effect of SCE on blood glucose concentrtion nd insulin resistnce in mle C57BL/KsJ-db/db mice. Fsting blood glucose level, glycted
478 Antidibetic effect of Srgssum corenum hemoglobin concentrtion, nd insulin resistnce were meliorted in the SCE-supplemented db/db mice compred to those in the control of dibetes mellitus db/db mice. Furthermore, SCE supplementtion elevted the ctivity of glucokinse, while the ctivities of glucose-6-phosphtse nd phosphoenolpyruvte crboxykinse were significntly reduced in the SCE-supplemented db/db mice compred to the control of dibetes mellitus db/db mice. The plsm lipid level ws lso improved in the SCE-supplemented db/db mice compred to the control of dibetes mellitus db/db mice. These results suggest tht SCE diet supplementtion lowers the blood glucose concentrtion nd improves insulin resistnce. Thus, it seems likely tht SCE, the extrct from Srgssum corenum, is potentil ntidibetic resource tht will be helpful for the lleviting the symptoms of type 2 dibetes. REFERENCES 1. Zimmet P, Alberti KG, Shw J. Globl nd societl implictions of the dibetes epidemic. Nture 2001;414:782-7. 2. 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