Prophylactic efficacy and possible mechanisms of oligosaccharides based standardized fenugreek seed extract on high-fat diet-induced insulin resistance in C 57 BL / 6 mice

Article history: Received on: 02/12/2014 Revised on: 30/12/2014 Accepted on: 18/01/2015 Available online: 28/03/2015 The present work was aimed to study the efficacy and possible mechanism of oligosaccharides based standardized fenugreek seed extract (SFSE-OS) on high-fat diet (HFD)-induced insulin resistance in male C57BL/6 mice. The effects of 12 weeks of oral administration of SFSE-OS (30, 60 and 100 mg/kg, twice daily) were evaluated on HFD fed mice for anthropomorphic, glycemic, gene expression related and histopathological parameters. Separate groups of mice with vehicle co-administered with HFD and low-fat diet (LFD) were maintained as HFD control and LFD control respectively. Twelve weeks of SFSE-OS (60 and 100 mg/kg, p.o.) administration showed significant prophylactic effects on HFD induced insulin resistance in terms of body weight, plasma glucose and insulin levels, glycated hemoglobin, insulin resistance (IR), area under the curve (AUC) of plasma glucose during oral glucose tolerance and intraperitoneal insulin tolerance. Furthermore, HFDinduced mRNA expression changes in adipose tissue, liver and skeletal muscle were prevented by SFSE-OS coadministration. Histology of sections of the pancreas showed the normal architecture in all groups of mice. SFSE-OS showed promising efficacy in prevention of HFD-induced insulin resistance through modulation of Glut-2, Glut-4, IRS-2 and SREBP-1c expression.


INTRODUCTION
Diabetes mellitus (DM) is the most common endocrine disorder of the 21st century.The prevalence of DM is more than 194 million people worldwide (Liao et al., 2010) and estimated to increase to 333 million by 2025 (Zhu et al., 2010).Lifestyle modification measures such as diet control and exercise have been found useful in short term control of body weight and T2D management.However, long-term solution is still elusive.Existing oral anti-diabetic medications including insulin sensitizers and exogenous insulin therapy address hyperglycemia but leads to many side effects such as increased body weight, osteoporosis sodium retention, hypoglycemia and lactic acidosis (Chiang et al., 2007, Hamza et al., 2010, Stades et al., 2004).The type 2 DM (T2DM) is characterized by insulin resistance in .target tissues due to both insulin action and insulin secretion with subsequent pancreatic β-cell dysfunction (Nyenwe et al., 2011).Insulin resistance (IR) is a physiological condition in which cells fail to respond to the normal actions of the hormone insulin.
The body produces insulin, but the cells in the body become resistant to insulin and are unable to use it effectively, leading to hyperglycemia.High plasma levels of insulin and glucose due to IR are a major component of the metabolic syndrome.The association between obesity and IR is well established (Hardy et al., 2012, Masuo et al., 2010).
IR is undoubtedly known as a hallmark of feature of obesity that compromises function of the pancreatic β-cell so as to cause insufficient insulin secretion and leads to T2DM (Das et al., 2013, McGarry, 2002).Strongly association between IR and microvascular (Groop et al.,2005), cardiovascular (Fontbonne, 1996) and renal (Masuo et al.,2010) complications of DM and obesity is also established.
Therefore, safer medications with effective control on both arms (blood glucose and IR) in DM are in need (Turner etal., 1998).In recent years, many new plant derived natural products have demonstrated the potential for treatment of T2DM and its complications (Matsui et al., 2006).One such promising plant is Fenugreek (Trigonella foenum-graecum L., family: Fabaceae).Plethora of evidence confirmed beneficial effects of fenugreek seeds powder and extract on glucose and fat metabolism in animal models and patients of DM (Roberts, 2011).Fenugreek seeds reported to cause improvement in glycemic control by decreasing IR in mild T2DM patients (Gupta et al., 2001).Fenugreek seed extract in various forms demonstrated promising effects on highfat (Chaturvedi et al., 2013, Hamza et al., 2012a, Handa et al., 2005) and high sucrose (Muraki et al., 2012) diet-induced hyperlipidemia.However, the responsible component of fenugreek seed extract and its mode of action for beneficial effects on IR not been elucidated.
Among all bioactive phytoconstituents of fenugreek seeds, only component that showed efficacy towards effective restoration of both glucose and fat metabolism in DM is its fibre component (Roberts, 2011)).The endosperm of the fenugreek seed is a rich source of fiber (20%) and gum (32.4 %) (Sharma, 1986, Sharma et al., 1990) which include water soluble (low molecular weight) and insoluble (high molecular weight) fibres.Interestingly, only water soluble low molecular weight soluble fibre fraction of fenugreek seeds demonstrated excellent efficacy in glucose and lipid management in animal and human studies (Ali et al., 1995, Evans et al., 1992).Recently, we have reported promising and dose-dependent anti-hyperglycemic effects of water-soluble low molecular weight soluble fibre fraction in diabetic mice (Kamble et al., 2013).
The soluble fibres of fenugreek seeds contain oligosaccharides along with Pinitol (methylated cyclic alcohol derivative of sugar).Oliosugers with structural similarity with a synthetic anti-diabetic oligosaccharide compound, acrabose (an αglucosidase inhibitor).Oligosaccharides from various natural sources have been shown anti-diabetic potential in animal studies by effective control of glucose and fat metabolism (Costa et al., 2012, Jo et al., 2014, Lee et al., 2003, Zhang et al., 2004).Furthermore, eleutheroside E (an oligosaccharide component of Eleutherococcus senticosus) was shown to ameliorates IR in animal model of type 2 diabetic db/db mice (Ahn et al., 2013).On the other hand, Pinitol obtained from other plant sources is reported to have good potential against IR for maintenance of glycemic control (Dang et al., 2010, Hernandez-Mijares et al., 2013, Kim et al., 2012, Kim et al., 2005a) through alternations in glucose (Kang et al., 2006, Kim et al., 2007) and fat metabolism (Choi et al., 2009, Geethan andPrince, 2008).The combination of naturally occurring oligosaccharide with pinitol in fenugreek seeds offers a unique option for management of insulin resistance (IR) and effective glycemic control (Watson and Preedy, 2010).
Recently, effects of oliosugers based standardized fenugreek seeds extract (SFSE-OS) containing oligosaccharide (with eleutheroside-C, methyl-α-D-galactoside), Pinitol (methylated cyclic alcohol derivative of sugar) has been reported against experimental neuropathy models in rats (Bhaskaran and Vishwaraman, 2014).However, potential of SFSE-OS to achieve effective control of glycemia and/or IR is not been explored yet.Therefore, we undertook present study with an objective to evaluate efficacy and probable mechanism of action SFSE-OS on high-fat diet (HFD)-induced IR in C57BL/6 mice.

Animals
Male C57BL/6 mice (age 4-weeks, 20-22 g) were used for the study.They were housed in cages at a temperature of 19.1-23.6 °C, and relative humidity 56-66 %, with 12 h fluorescent light and 12 h dark cycle in an accredited animal facility (Bioneeds, Bangalore, India).The mice had free access to water ad libitum throughout the study duration except during actual measurements.All experiments were carried out between 09:00 h and 17:00 h.Institutional Animal Ethics Committee (IAEC) of Bioneed (Bangalore, India) approved the experimental protocol (BIO-IAEC-477).The experiments were performed in accordance with the guidelines on animal experimentation recommended by the Committee for Control and Supervision of Experimentation on Animals (CPCSEA), Government of India.

The test compound
The test compound, SFSE-OS supplied by Indus Biotech Private Limited (Pune, India) after preparation and characterization (HPLC and LC-MS) as per reported procedure (Bhaskaran and Vishwaraman, 2014).The sample of SFSE-OS used for the present study was standardized to Eleutheroside-C (30%), Pinitol (48%), Sucrose (6%), Raffinose (6.5%), and Stachyose (9.5%).As SFSE-OS was water soluble, the solution was freshly prepared daily as 1% w/v in distilled water and orally administered twice a day to mice in volume of 10 mg/kg.The doses of SFSE-OS (30, 60 and 100 mg/kg, twice a day, oral) were derived from LD50 dose of 2000 mg/kg found during acute oral toxicity (AOT) study (Bodhankar et al., 2013).The vehicle or SFSE-OS were orally administered twice daily with difference of approximately 8 h between morning and evening administration using intragastric tube for 12 weeks.
Body weights of individual mouse were recorded before grouping and three times a week thereafter, during the treatment period.At end of treatment period of 12-weeks, 100 µL blood were withdrawn from the retro-orbital plexus and used for glycated hemoglobin (HbA1c) levels measurement using mouse hemoglobin A1c kit (Crystal Chem, Inc., Downers Grove, IL, USA) as per manufacturer's instructions.

Oral Glucose Tolerance Test (OGTT)
On the next day of HbA1c measurement, mice were fasted for 12 h and OGTT was performed as per reported procedure (Gallou-Kabani et al., 2007).At 0 h (before administration of glucose) fasting plasma glucose (FPG) was measured using Accu-Chek Performa Blood Glucose Meter (Roche Diagnostics India Private Ltd, Mumbai, India) and glucose load (2 g/kg) was administered orally.Blood was withdrawn at 30, 60, 120, and 180 min, plasma was obtained after centrifugation and PG measurements were done.Additional blood was collected at 0 and 120 min, plasma was separated and used for insulin measurement with mouse insulin ELISA kit (ALPCO Diagnostics, Salem, NH, USA).
From the values of FPG and fasting insulin, the HOMA-IR was calculated as per reported formula (Matsuda and DeFronzo, 1999).The graph of PG levels versus time (min) was plotted and area under the OGTT curve (AUC-OGTT) was calculated with the help of Prism v6.0 (GraphPad Software Inc, La Jolla, CA, USA).

Intraperitoneal Insulin Tolerance Test (IPITT)
Three days after OGTT, 6 mice per group were selected for IPITT.Mice were fasted for 4 h and FPG was measured using Accu-Chek Performa Blood Glucose Meter (Roche Diagnostics India Private Ltd).After 30 min, mice were administered intraperitoneally with insulin (0.5 IU/kg, Actrapid ® , Novo Nordisk India Pvt Ltd, Bangalore, India).PG was measured at 30, 60, and 120 min from insulin administration.The graph of PG levels versus time (min) was plotted and area under the IPITT curve (AUC-IPITT) was calculated with the help of Prism v6.0 (GraphPad Software Inc, La Jolla, CA, USA).

Gross Necropsy
At end of the experimental period, all mice were sacrificed using CO 2 asphyxiation and subjected to gross necropsy.Four samples of adipose tissues, liver, pancreas and skeletal muscle from each group were preserved in liquid nitrogen for gene expression analysis by reverse transcriptase-polymerase chain reaction (RT-PCR).Two samples of pancreas from each group were preserved in 10% neutral buffered formalin for histopathology.

Gene expression analysis by RT-PCR
Four tissue samples of adipose tissue, liver, pancreas and skeletal muscle from each group was used for RT-PCR analysis using kits (Biotools B & M Labs, Spain) according to manufacturer's instructions.Total RNA was extracted from each tissue.The PCR mixture was amplified in a DNA thermal cycler (Eppendorf India Ltd, Chennai, India) by using gene specific primers (Table 1).PCR products were run on 1 % agarose gels, stained with ethidium bromide.The expression of all the genes was assessed by generating densitometry data for band intensities in different sets of experiments and was generated by analyzing the gel images on the Image J program (Version 1.33, Wayne Rasband, National Institutes of Health Bethesda, MD, USA).The band intensities were compared with constitutively expressed βactin which served as a control for sample loading and integrity.The intensity of mRNAs was standardized against that of the βactin mRNA from each sample, and the results were expressed in a quantitative manner as PCR-product/β-actin mRNA ratio.

Histopathology
The samples from pancreas were embedded in paraffin wax, sectioned at 4 µm and stained with haematoxylin and eosin (H&E) and observed under compound microscope using a Zeiss intravital microscopy setup (Zeiss Axioscope A1, Carl Zeiss MicroImaging, Jena, Germany) with a 40X magnification for histological examinations.

Statistical analysis
All statistical analysis was performed using GraphPad Prism 6.0 (GraphPad Software, Inc, La Jolla, CA, USA).Data of body weight and biochemical measurements was analyzed by separate One-way ANOVA followed by Dunnett's test separately for each parameter.A value of P < 0.05 was considered to be statistically significant.

Effect on body weight and Glycemic parameters
The data of effects of treatments on body weight and glycemic parameters (fasting glucose level, OGTT and IPITT, plasma insulin, HOMA-IR and HbA1c levels) are presented in Table 2.At the end of study (12-weeks), significant gain in the body weight (P < 0.05) and HbA1c (P < 0.001) was observed in HFD control mice as compared to LFD control mice (Table 2).The mean body weights in LFD fed mice was 20.66 g whereas that of HFD control mice were was 33.40 g (gain of increase 4.74 g., 17.7%).
The body weights of HFD mice co-administered with SFSE-OS (60) group showed significant (P < 0.01) reduction by 3.73 g (15.17%) as compared to HFD control group.At the end of 12-week of study period, HFD control group showed significant ( P < 0.001) increase in mean HbA1c values of 5.43% as compared to HBA1c values of LFD control mice (2.94%).Mean HbA1c levels of HFD mice co-administered with SFSE-OS (30, 60 and 100 mg/kg, p.o.) were 4.11%, 2.96% and 3.13% respectively.These values were significantly (P < 0.001) less as compared to HFD control mice (5.43%).
Fasting insulin levels of SFSE-OS (60 and 100 mg/kg, p.o.) co-administrated HFD mice showed significantly less values of 0.70 and 0.57 μg/L (37.5% and 49.10% less) as compared to that of HFD control mice.However, fasting plasma insulin levels of SFSE-OS (30 mg/kg) co-administered mice show values of 0.89, (20.53% less) which was not significant as compared HFD control mice.The values of 2 h post-glucose plasma insulin was not significantly different in any of SFSE-OS co-administrated group as compared to HFD control mice.
The values of AUC-OGTT in SFSE-OS (60 and 100 mg/kg) co-administrated mice were 33290 and 36336.30respectively.These values were significantly (P < 0.001 and P < 0.01) less by 22.52% and 15.43% as compared to that of HFD control group.However, SFSE-OS (30 mg/kg) co-administrated mice showed reduction of 6.74% in AUC-OGTT which was not significant as compared with that of HFD control group (42967).

Effect on mRNA expressions in adipose tissues
The effects of SFSE-OS on mRNA expressions of Glut-2, Glut-4, IRS-2 and SREBP-1c in adipose tissue are presented as Fig. 1.There was significant down-regulation in the mRNA expressions of Glut-2, Glut-4 and IRS-2 in adipose tissues of HFD control mice (P < 0.01, P < 0.05 and P < 0.001 respectively) as compared with LFD control mice.Treatment with SFSE-OS (100 mg/kg, p.o.) significantly up-regulated the mRNA expression of Glut-2 (P < 0.01) in adipose tissue as compared to HFD control mice.The mRNA expression of Glut-4 in adipose tissue was significantly up-regulated (P < 0.01 and P < 0.01, resp.) in SFSE-OS (60 and 100 mg/kg, p.o.) treated mice as compared to HFD control mice.As compared with HFD control mice, the mRNA expression of IRS-2 in adipose tissue was significantly upregulated (P< 0.01) by SFSE-OS (100 mg/kg, p.o.) treatment.
On the other hand, SFSE-OS (30 mg/kg, p.o.) failed to produce any significant up-regulation in mRNA expression of Glut-2, Glut-4 and IRS-2 in adipose tissue when compared with HFD control mice (Fig. 1A, 1B, 1C and 1D).The level of SREBP-1c mRNA expression in adipose tissue of HFD control mice was significantly up-regulated (P < 0.001) as compared to LFD control mice.Up-regulation in SREBP-1c mRNA expression was significantly reduced (P < 0.001) by the SFSE-OS (100 mg/kg, p.o.) treatment when compared with HFD control mice.But when compared with HFD control mice, the SREBP-1c mRNA expression in adipose tissue of SFSE-OS (30 mg/kg, p.o.) treated mice was not significantly down-regulated (Fig. 1E).

Effect of SFSE-OS on mRNA expressions in liver
The effects of SFSE-OS on gene expressions of Glut-2, Glut-4, IRS-2 and SREBP-1c in liver are presented as Fig. 2. The mRNA expression of Glut-2 and IRS-2 in liver was significantly down-regulated (P < 0.001) in HFD control mice as compared to LFD control mice.This down-regulated mRNA expression of Glut-2 and IRS-2 in liver was significantly up-regulated (P < 0.001) by the SFSE-OS (100 mg/kg, p.o.) treatment as compared to HFD control mice.However, treatment with SFSE-OS (30 and 60 mg/kg, p.o.) did not produce any significant up-regulation in the mRNA expression level of Glut-2 and IRS-2 in liver as compared to HFD control mice.Moreover, the Glut-4 mRNA expression was non-significantly down-regulated in HFD control mice as compared to LFD control mice and SFSE-OS (30, 60 and 100 mg/kg, p.o.) treated mice also did not show any significant change in Glut-4 mRNA expression as compared to HFD control mice (Fig. 2A, 2B, 2C and 2D).The liver SREBP-1c mRNA expression of HFD control mice was significantly up-regulated (P < 0.001) as compared to LFD control mice.When compared with HFD control mice, the liver SREBP-1c mRNA expression was significantly and dose dependently down-regulated (P < 0.01, P < 0.001 and P < 0.001, resp.) by SFSE-OS (30, 60 and 100 mg/kg, p.o.) treatment (Fig. 2A and 2E)..00± 673.00***Data are expressed as mean ± S.E.M. and analyzed by one-way ANOVA followed by Dunnett's test for each parameter separately.ns -not significant, ###P < 0.001 as compared to LFD control and ns1 -not significant, *P < 0.05, **P < 0.01, ***P < 0.001 as compared to HFD control.

Effect of SFSE-OS on mRNA expression in skeletal muscle
The effects of SFSE-OS on gene expression of IRS-2 in skeletal muscle are presented as Fig. 3.There was significant down-regulation (P < 0.001) in skeletal muscle IRS-2 mRNA expression in HFD control mice as compared to LFD control mice.Treatment with SFSE-OS (60 and 100 mg/kg, p.o.) significantly and dose dependently up-regulated (P < 0.001) the mRNA expression of IRS-2 in skeletal muscle as compared to HFD control mice.However, SFSE-OS (30 mg/kg, p.o.) treated mice failed to produce any significant up-regulation in IRS-2 mRNA expression in skeletal muscle when compared with HFD control mice (Fig. 3A and 3B).

Effect of SFSE-OS on m-RNA expressions in pancreas
The effects of SFSE-OS on gene expression of SREBP-1c in pancreas are presented as Fig. 3.The pancreatic SREBP-1c mRNA expression of HFD control mice did not differ significantly as compared to LFD control mice and SFSE-OS (30, 60 and 100 mg/kg, p.o.) treatment also did not produce any significant change in the pancreatic SREBP-1c mRNA expression as compared to HFD control mice (Fig. 3C and 3D).

Effect on histopathological alteration in mice pancreas
The effects of treatments on histopathological alternations found during histology of pancreatic tissues are presented as Fig. 4. The sections of pancreas from LFD control, HFD control mice and SFSE-OS (30, 60 and 100 mg/kg, p.o.) treated mice showed no histopathological alterations in pancreatic tissue and showed normal size and shape of acini and islet of Langerhans.

DISCUSSION
In the etiology of IR, diet played a important role.Features like weight and fat mass gain, polydipsia and hyperglycemia are hallmark of progressive worsening of IR.
Several reports of postprandial blood glucose reduction and improved insulin sensitivity by fenugreek seed extracts in nondiabetic (Fairchild et al., 1996, Jenkins et al., 1980, O'Connor et al., 1981) and diabetic (Gupta et al., 2001, Losso et al., 2009, Mohan and Balasubramanyam, 2001, Roberts, 2011) subjects exist.The combination of naturally occurring oligosaccharide with pinitol from fenugreek seeds unique and offers excellent potential for management of IR.Therefore, the present study was aimed at evaluation of efficacy and mechanism of SFSE-OS, a unique composition with oligosaccharide and pinitol, in well-validated animal model of diet induced IR (HFD in C57/BL6 mice).Recent advance in preclinical pharmacology allow us to mimic human obese condition in laboratory animals with ease of weight gain as well as IR.HFD feeding for 12 weeks is known to mimic modern fat rich dietary conditions (Surwit et al., 1988).HFD induced IR model is well validated and known to have excellent predictive validity (Buettner et al., 2007, Pagliassotti et al., 1994).This model exhibits an array of features of IR including hyperglycemia and hyperinsulinemia (Ahren and Pacini, 2002).In the present study, 12-weeks of HFD feeding resulted in increase in body weight, and FPG and insulin levels in HFD control mice as compared to LFD control mice.Our observations of weight gain, hyperglycemia, and hyperinsulinemia in mice confirmed induction of IR and in line with earlier reports (Azman et al., 2012, Veerapur et al., 2012, Zhang et al., 2010).
Treatment with SFSE-OS showed significant antihyperglycemic effects with prevention of weight gain despite of HFD feeding.Prevention of body weight gain shown by SFSE-OS can be attributed to balance between fat burning catabolic (reduction of weight) effect and anabolic (increased muscle mass) effect.In our study during OGTT, HFD control mice showed elevated plasma insulin levels, which represent important characteristics of IR.The elevated insulin levels during the OGTT represents reduced glucose elimination and impaired insulin utilization (Fonseca, 2003).Furthermore, HFD control mice exhibited higher AUC than LFD control mice similar to earlier reports (Abdin et al., 2010, Zhang et al., 2010).In the present study, SFSE-OS co-administration with HFD prevented hyperglycemia during OGTT and IPITT and better utilization of exogenous insulin during IPITT.Administration of SFSE-OS showed time-dependent suppression of increased blood glucose and insulin levels as shown by reduced AUC-OGTT and AUC-IPITT.The results of present study are also consistent with the earlier reports of beneficial effects of chronic administration of fenugreek seeds significantly decreased plasma insulin, AUC of OGTT and HOMA-IR (Hamza et al., 2012b).
These observation can be attributed oligosaccharide content of SFSE-OS similar to reports of slowing glucose intestinal glucose absorption either by carbohydrate hydrolyzing enzyme inhibition (Jo et al., 2014) or induction of intestinal gluconeogenesis (Mithieux and Gautier-Stein, 2014).Another probable mechanism behind observed effects during present study can be increased utilization of insulin-regulated glucose into peripheral tissues.This notion is supported by past reports of activation of an insulin-signaling pathway by fenugreek seed extract in general (Vijayakumar et al., 2005) .The reports of insulinotropic activity of oligosaccharides (Kim et al., 2009, Kim et al., 2005b, Lee et al., 2003) and pinitol (Bates et al., 2000, Dang et al., 2010, Kim et al., 2012) suggested their major role in reduction of blood glucose and IR observed in the present study.
To explore molecular mechanism of action in further details we have analyzed mRNA expression important targets in organs related to IR namely skeletal muscle, liver and white adipose tissue (WAT) (Fischer-Posovszky et al., 2007, Korenblat et al., 2008).Skeletal muscle is primary site for IR because insulin-stimulated glucose uptake takes place in skeletal muscle (DeFronzo and Tripathy, 2009).Impairment of insulin signaling transduction pathways leads to IR (Leturque et al., 2009, Previs et al., 2000).Insulin receptor substrate-2 (IRS-2) is known to regulate insulin signaling in liver.In liver, IRS-2 play central role in hepatic nutrient homeostasis via anabolic effects of insulin through the activation of phosphatidylinositol 3-kinase/Akt) pathway cascade (Andersson et al., 2004, Hirashima et al., 2003), inhibit gluconeogenesis, apoptosis (Valverde et al., 2003, Valverde et al., 2004) and GLUT-2 translocation to the plasma membrane, resulting in hepatic IR (Pessin and Saltiel, 2000).Fasted state increases and feeding (and weight increase) reduces expression of IRS-2 (Kubota et al., 2000).In the present study, adipose tissue, liver and skeletal muscles of HFD control mice showed reduced levels of IRS-2 expression whereas pancreatic IRS-2 expression was unaltered.The findings from histology of pancreas are also in line with mRNA expression findings.SFSE-OS co-administration with HFD prevented decrease in the expression of IRS-2 in target organs (adipose tissue, liver and skeletal muscles) and expectedly prevented weight gain and fasting insulin elevation (hyperinsulinemia) in the present study.IRS2 and downstream PI-3K/Akt-->Foxo1 signaling cascade play key roles in many functions of insulin/Insulin like growth factor -1 (IGF-1) that plays important role in control of DM and its complications (Guo, 2013).In the present study, SFSE-OS coadministration with HFD, down regulated the mRNA expression of two important integral isoforms of glucose transporter proteins namely of Glut-2 and Glut-4 in liver and adipose tissues.Glut-2 plays critical role in glucose transport and metabolism to regulate body glucose homeostasis whereas Glut-4 is a key gene that mainly responsible for insulin-stimulated glucose transport in tissues (Charron et al., 1999).Insulin-dependent translocation of Glut-2 resulted in regulation of glucose homeostasis via activation of insulin PI3K/phosphorylated protein kinase B (p-Akt) pathway (Watson et al., 2004).HFD fed mice are known to decrease Glut-2 mRNA expression in liver and adipose tissue to cause hyperglycemia (Azman et al., 2012, Yang et al., 2012).Glut-4 is mainly expressed in liver as well as adipocytes.Clinical evidence of decreased Glut-4 expression in obese and DM patients confirmed its role in glucose homeostasis (Berger et al., 1989, Cushman and Wardzala, 1980, Sivitz et al., 1989).Glut-4 increases insulin sensitivity through glucose uptake via a pathway where insulin binds to its cell surface receptors to facilitate glucose transport in tissue (Kwon et al., 2007) whereas increased expression of Glut-4 in adipose tissue improves glucose disposal and insulin sensitivity in vivo (Shepherd et al., 1993, Yang et al., 2012).Moreover, up-regulation in the Glut-4 gene expression in transgenic db/db mice was found to be correlated with amelioration of insulin resistance (Brozinick et al., 2001).Therefore, SFSE-OS is suggested to increase insulin sensitivity and glucose uptake in skeletal muscles through Glut 2 upregulation.The molecular mechanism of insulin resistance in diabetes involves impaired Glut-4 gene expression via sterol regulatory element binding proteins 1c (SREBP-1c) pathway (Horton et al., 2002, Kang et al., 2010).SREBP-1c gene is one of the responsible factors for development of IR in many organs (Letexier et al., 2003).Up-regulated SREBP-1c expression in HFD control mice in the liver and adipose tissues are in line with earlier reports of up-regulation in SREBP-1c mRNA in HFDinduced insulin resistance mice and subsequent induction of insulin resistance (Horton et al., 2002, Shimomura et al., 2000).
Over-expression of SREBPs, the membrane-bound transcription factors, are implicated in biosynthesis of fatty acids and triglycerides (Foufelle andFerré, 2002, Osborne, 2000).SREBP-1c play vital role in insulin signaling by inhibiting IRS-2 expression in the liver and adipose tissue (Takahashi et al., 2005) and modulation of glucose-stimulated Glut-2 gene expression (Andersson et al., 2004).In the present study, SFSE-OS administration caused down-regulation in expression of SREBP-1c in liver and adipose tissue that may enhance expression of Glut-2 as well as Glut-4 to facilitate insulin-stimulated glucose transporter in target organ to improve insulin sensitivity.Our study results are in support with earlier reports on mechanism of fenugreek seeds against IR (Vijayakumar et al., 2010, Vijayakumar et al., 2005) and suggested SFSE-OS is a responsible component for action against IR.In the past, dietary oligosaccharides were reported to improve insulin sensitivity in obese horses (Respondek et al., 2011).In addition, dietary pinitol is reported to have antihyperglycemic effects be mediated via the insulin signaling pathway (Do et al., 2008) and reported as an insulin sensitizer or insulin mediator in 3T3-L1 preadipocytes in vitro (Do et al., 2008).Therefore, oligosaccharides and pinitol can be envisaged as responsible for efficacy of SFSE-OS against hyperglycemia and IR in the present study.The stimulation of glucose uptake by SFSE-OS against HFD induced IR can be contributed by possible prevention of fat mass accumulation by SFSE-OS.In the past, oligosaccharide (Smith et al., 2010, Wang et al., 2011) and pinitol (Choi et al., 2009, Geethan and Prince, 2008) from other sources demonstrated beneficial effects on lipid and cholesterol metabolism.However, more investigations directed towards effects of SFSE-OS on obesity-induced IR are required to confirm such possibilities.CONCLUSIONS SFSE-OS administration showed promising prophylactic efficacy against HFD-induced IR development suggested good potential for management of obese and prediabetes population.This effect, at least in part, mediated through the improved insulin sensitivity and improvement in glucose transport to target organs.The up-regulation of IRS2, Glut2 and Glut4 and downregulation of SREBP-1c in liver and adipose tissues, perhaps plays crucial role in the mechanism of action of SFSE-OS.

Table 2 :
Effect of SFSE-OS on body weight and glycemic parameters (fasting glucose level, OGTT and IPITT, plasma insulin, HOMA-IR and HbA1c levels) in mice.