Fructose-induced Insulin Resistance Rats Research Articles

Reversal of insulin resistance to combat type 2 diabetes mellitus by newer thiazolidinedione's in fructose induced insulin resistant rats

In our pursuit of discovering new antidiabetic agents to manage type 2 diabetes mellitus (T2DM), our approach aimed to identify the bioactive feature/pharmacophore responsible for PPAR-γ expression, as it is accountable for the glucose homeostasis and lipid metabolism. This was achieved by pharmacophore model generation, screening of rationally designed newer thiazolidinedione's library, identifying synthesizing and characterizing the top ten molecules (5a-5j) for their (Invitro &invivo) antidiabetic activity. Preliminary screening of all the ligands by Invitro glucose uptake assay in L6 myotubes (skeletal muscle cell line of rats) revealed compound 5b and 5f stimulated the glucose uptake with 79.29 ± 1.02 % and 74.58 ± 1.02 % respectively compared to pioglitazone with 82.36 ± 0.98 %. This was validated by PPAR-γ TF expression assay, which highlighted a dose dependent increase in transactivation of PPAR-γ. These compounds 5b and 5f were evaluated in fructose induced insulin resistance rat model. Where the treatment with 5b and 5f markedly increased the exogenous clearance of glucose and exogenous insulin via OGTT and ITT respectively, also improved the glucose utilization by significantly increasing content of glycogen and uptake of glucose in rat hemidiaphragm and reversed insulin resistance. Likewise a significant decreased in the VLDL and triglyceride levels was seen in 5b and 5f treated groups compared to insulin resistant (IR) group. It improved glycogenesis by catabolism of glucose and maintained glycaemic control. Similarly it had marked action on enzymatic oxidative biomarkers. Compound 5b displayed better, improved T1/2 (half-life) of 4.21 h and Kel (elimination constant) of 0.381 was noticed in comparison to compound 5f indicating the pharmacokinetic profile. Insilico studies like DFT calculations refined the geometry of 5b and 5f ligands, docking and molecular simulation provided the insights in binding affinity, dynamic behaviour and stability of ligands in PPAR-γ ligand binding domain. MM/GBSA provided the energetics of 5b and 5f in binding pocket. Finally network pharmacology identified ADIPOQ (adiponectin), NR1C3 (PPAR-γ), SLC2A4 (GLUT4), and LEP (leptin) proteins associate with compound 5b and 5f and enriched in Adipocytokine pathway, and PPAR-γ signaling pathway.

Insulin sensitization by Feronia elephantum in fructose-induced hyperinsulinemic rats: Insights from computational and experimental pharmacology

Ethnopharmacological relevanceFeronia elephantum corr. (synonym: Feronia limonia, Murraya odorata, Schinus Limonia, or Limonia acidissima; common names: Bela, Kath, Billin, and Kavitha), belonging to the family Rutaceae has been known for clinical conditions such as pruritus, diarrhea, impotence, dysentery, heart diseases, and is also used as a liver tonic. However, the effect of the fruit pulp of F. elephantum on insulin resistance has yet not been reported. Aim of the studyThe present study aimed to assess the effect of hydroalcoholic extract/fraction of F. elephantum fruit pulp on fasting blood glucose, oral glucose tolerance test, and glucose uptake in fructose-induced insulin-resistant rats and predict the gene-set enrichment of lead hits of F. elephantum with targets related to insulin resistance. Material and methodsSystem biology tools were used to predict the best category of fraction and propose a possible mechanism. Docking was carried out with adiponectin and its receptor (hub genes). Further, fructose supplementation was used for the induction of insulin resistance. Later, three doses of extract (400, 200, and 100 mg/kg) and a flavonoid-rich fraction (63 mg/kg) were used for treatment along with metformin as standard. The physical parameters like body weight, food intake, and water intake were measured along with oral glucose tolerance test, insulin tolerance test, glycogen content in skeletal muscles and liver, glucose uptake by rat hemidiaphragm, lipid profiles, anti-oxidant biomarkers, and histology of the liver and adipose tissue. ResultsNetwork pharmacology reflected the potency of F. elephantum to regulate adiponectin which may promote the reversal of insulin resistance and inhibit α-amylase and α-glucosidase. Vitexin was predicted to modulate the most genes associated with diabetes mellitus. Further, F. elephantum ameliorated the exogenous glucose clearance, promoted insulin sensitivity, reduced oxidative stress, and improved glucose and lipid metabolism. HPLC profiling revealed the presence of apigenin and quercetin in the extract for the first time. ConclusionThe fruit pulp of F. elephantum reverses insulin resistance by an increase in glucose uptake and a decrease in gluconeogenesis which may be due to the regulation of multiple proteins via multiple bio-actives.

Duranta repens L. reverses hepatic and peripheral insulin resistance in fructose-induced hyperinsulinaemic rats – Experimental and computational findings

The present study investigated the effect of hydroalcoholic extract of Duranta repens Linn over gluconeogenesis, glycolysis, glycogenesis, leptin, and dipeptidyl peptidase-4 regulation in fructose-induced insulin-resistant rats. Initially, hyperinsulinemia was induced by supplementing fructose in drinking water for fifty-four days. Glucose intolerance was confirmed using oral glucose tolerance test and subjected for extract treatment for next thirty days. After thirty days of treatment, animals fasted and an oral glucose tolerance test was performed followed by an insulin tolerance test. After that, animals were overdosed with anesthetic ether, blood was collected to separate plasma and serum. Further, multiple biochemical parameters i.e. lipid profile, hepatic enzymes, enzymatic and non-enzymatic antioxidant biomarkers, glycogen content, leptin, and the glucagon-like peptide-1 level were quantified. Additionally, the glucose uptake in rat hemidiaphragm and hepatic histology were performed. Further, molecular docking was performed using AutoDock Vina and the ligand pose with minimum binding energy was chosen to visualize the ligand-protein interaction. After the thirty days of treatment with extract, it was observed to ameliorate the fructose-induced alterations in body weight, food intake, and water intake. Further, it improved glucose tolerance. This was confirmed via the quantification of the total triglycerides and assessing oral glucose and insulin tolerance test. Additionally, it also improved the level of hepatic enzymes involved in gluconeogenesis and glycolysis. Also, it upregulated the leptin pathway; however, did not influence the dipeptidyl peptidase-4-glucagon-like peptide-1. Similarly, a docking study predicted scutellarein, pseudo-ginsenoside-RT1, repennoside, and durantanin I as probable lead hits from Duranta repens as prime regulators of gluconeogenesis. Additionally, molecular docking revealed scutellarein, pseudo-ginsenoside-RT1, repennoside, and durantanin I as the probable lead hits in regulating the enzymes involved in hepatic glucose catabolism and anabolism. Treatment with the hydroalcoholic extract of Duranta repens extract ameliorated fructose-induced gluconeogenesis, glycolysis, glycogenesis, and leptin regulation; however, did not influence the dipeptidyl-peptidase 4- glucagon-like peptide-1 pathway.

Reversal of insulin resistance by Ficus benghalensis bark in fructose-induced insulin-resistant rats

Ethnopharmacological relevanceBark of Ficus benghalensis L. (family: Moraceae), commonly known as Banyan is recorded as Nyagrodha in Ayurvedic Pharmacopeia of India to manage burning sensation, obesity, diabetes, bleeding disorders, thirst, skin diseases, wounds, and dysmenorrhoea. However, the effect of F. benghalensis bark over glycolysis, gluconeogenesis, and appetite regulation in insulin-resistant pathogenesis has not been reported yet. Aim of the studyThe present study aimed to investigate the effect of hydroalcoholic extract of F. benghalensis bark in gluconeogenesis, glycolysis, and appetite regulation in fructose-induced insulin resistance in experimental rats. Materials and methodsMale Wister rats were supplemented with fructose in drinking water (10% w/v for 42 days and 20% w/v for next 12 days; a total of 54 days); insulin resistance was confirmed via the elevated area under the curve of the glucose during oral glucose tolerance test after 54 days and was subjected with extract treatment for next 30 days. After 30 days of treatment, animals were fasted to perform oral glucose and insulin tolerance test to estimate glucose and insulin levels. The blood sample was collected for biochemical estimation and the liver homogenate was prepared to estimate hepatic enzymes and enzymatic and non-enzymatic anti-oxidant biomarkers followed by histopathological evaluation. Also, glycogen content was quantified in gastrocnemius muscle and liver homogenates. Further, reported bioactives from the F. benghalensis were retrieved from the ChEBI database and docked against hexokinase, phosphofructokinase, glucose-6-phosphatase, lactate dehydrogenase, and fructose-1,6-biphosphatase to identify the probable lead hits against the enzymes involved in gluconeogenesis. ResultsTreatment with the F. benghalensis bark extract significantly increased the body weight and food intake and significantly decreased fructose supplemented water intake. Further, treatment with extract significantly increased the exogenous glucose clearance and well responded to the exogenous insulin. Further, extract treatment improved lipid metabolism, ameliorated plasma leptin, and multiple enzymatic and non-enzymatic antioxidant biomarkers. Likewise, it also improved gluconeogenesis mediated pathogenesis of non-alcoholic fatty liver injury. Additionally, molecular docking also identified mucusisoflavone A and B as lead hits in downregulating gluconeogenesis. ConclusionHydroalcoholic extract of F. benghalensis bark may prevent insulin resistance by downregulating gluconeogenesis and improving the appetite in fructose-induced insulin-resistant rats.

Inhibition of tumor necrosis factor-α enhanced the antifibrotic effect of empagliflozin in an animal model with renal insulin resistance

Insulin resistance (IR) has emerged as one of the main risk factors for renal fibrosis (RF) that represents a common stage in almost all chronic kidney disease. The present study aims to investigate the inhibitory effect of empagliflozin (EMPA "a sodium-glucose co-transporter 2 inhibitor") and infliximab [IFX "a tumor necrosis factor-α (TNF-α) antibody"] on RF in rats with induced IR. IR was induced by adding 10% fructose in drinking water for 20weeks. Thereafter, fructose-induced IR rats were concurrently treated with EMPA (30mg/kg), IFX (1 dose 5mg/kg), or EMPA + IFX for 4weeks, in addition to IR control group (received 10% fructose in water) and normal control (NC) group. Rats with IR displayed hyperglycemia, deterioration in kidney functions, glomerulosclerosis, and collagen fiber deposition in renal tissues as compared to NC. This was associated with downregulation of the renal sirtuin 1 (Sirt 1) expression along with higher renal tissue TNF-α and transforming growth factor-β1 (TGF-β1) levels. Both EMPA and IFX significantly modulated the aforementioned fibrotic cytokines, upregulated the renal Sirt 1 expression, and attenuated RF compared to IR control group. Of note, IFX effect was superior to that of EMPA. However, the combination of EMPA and IFX alleviated RF to a greater extent surpassing the monotherapy. This may be attributed to the further upregulation of renal Sirt 1 in addition to the downregulation of fibrotic cytokines. These findings suggest that the combination of EMPA and IFX offers additional benefits and may represent a promising therapeutic option for RF.

Neuronal and Endothelial Nitric Oxide Synthases in the Paraventricular Nucleus Modulate Sympathetic Overdrive in Insulin-Resistant Rats.

A central mechanism participates in sympathetic overdrive during insulin resistance (IR). Nitric oxide synthase (NOS) and nitric oxide (NO) modulate sympathetic nerve activity (SNA) in the paraventricular nucleus (PVN), which influences the autonomic regulation of cardiovascular responses. The aim of this study was to explore whether the NO system in the PVN is involved in the modulation of SNA in fructose-induced IR rats. Control rats received ordinary drinking water, whereas IR rats received 12.5% fructose-containing drinking water for 12 wks to induce IR. Basal SNA was assessed based on the changes in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) in response to chemicals administered to the PVN. We found an increased plasma norepinephrine level but significantly reduced NO content and neuronal NOS (nNOS) and endothelial NOS (eNOS) protein expression levels in the PVN of IR rats compared to Control rats. No difference in inducible NOS (iNOS) protein expression was observed between the two groups. In anesthetized rats, the microinjection of sodium nitroprusside (SNP), an NO donor, or Nω-nitro-L-arginine methyl ester (L-NAME), a non-selective inhibitor of NOS, into the PVN significantly decreased and increased basal SNA, respectively, in both normal and IR rats, but these responses to SNP and L-NAME in IR rats were smaller than those in normal rats. The administration of selective inhibitors of nNOS or eNOS, but not iNOS, to the PVN significantly increased basal SNA in both groups, but these responses were also smaller in IR rats. Moreover, IR rats exhibited reduced nNOS and eNOS activity in the PVN. In conclusion, these data indicate that the decreased protein expression and activity levels of nNOS and eNOS in the PVN lead to a reduction in the NO content in the PVN, thereby contributing to a subsequent enhancement in sympathoexcitation during IR.

Insulin plant (Costus pictus) extract improves insulin sensitivity and ameliorates atherogenic dyslipidaemia in fructose induced insulin resistant rats: Molecular mechanism

The preventative effect of insulin plant (Costus pictus) leaf extract on hyperglycaemia, insulin sensitivity and dyslipidaemia in fructose-fed insulin resistant rats was investigated in the present study, further the possible underlying mechanism was also explored. It was observed that under insulin resistant condition this plant extract decreases hyperinsulinaemia by improving insulin sensitivity at the peripheral level through its antioxidant and anti-inflammatory effects. At molecular level decreased activation of molecules involved in stress sensitive signalling cascade and down regulation of pro-inflammatory cytokines were noticed. Furthermore the effects of this plant extract on adipokine profile and plasma homocysteine were evaluated. The possible active components responsible for the beneficial effect exerted by this plant extract have also been identified and quantified. To the best of our knowledge this is the first study on insulin plant extract on the aforementioned animal model.

Antidiabetic Effects of Some Tropical Fruit Extracts in Fructose Induced Insulin Resistant Wistar Rats

Aim: Fruit extracts of Apple (Malus domestica), coconut (Cocos nucifera) and cucumber (Cucumis sativus) were tested for their antidiabetic potential in rats with fructose-induced insulin resistance for 28 days. Study Design: In-vivo antidiabetic study using fructose-induced insulin resistant rats. Place and Duration of Study: Department of Biochemistry, Lagos State University, Ojo, Lagos, Nigeria, between March and May 2014. Methodology: Wistar rats were randomized into 5 groups comprising 5 animals each. Group A (control) was fed on standard rat chow and distilled water ad libitum while Groups B-E were fed standard rat chow and 10% w/v fructose. Groups C-E were also administered 500 mg/kg body weight of apple, coconut and cucumber extracts for 28 days. At the end of the experiment, all animals were sacrificed and the serum glucose, lipid profile and electrolytes were determined. Results: The fructose-fed rats had significantly decreased weight and increased blood glucose concentration (P < 0.05), when compared to the control rats. The fructose-fed rats also witnessed significant increase (P < 0.05) in total cholesterol and low density lipoprotein cholesterol (LDLC) concentration as well as significant decrease (P < 0.05) in the high density lipoprotein (HDLC) and serum electrolytes concentration compared to control. Administration of the aqueous extracts of apple, coconut and cucumber to the fructose-fed rats significantly increase (P < 0.05) their body weights, HDLC and serum electrolytes’ concentration in the rats while significantly reducing (P < 0.05) blood glucose, total cholesterol and LDLC. Conclusions: Aqueous extracts of apple, coconut and cucumber displayed antidiabetic effect, but apple exhibited the most potent effect as it ameliorates most of the derangements observed in insulin-resistant rats.

Effect of carnosine alone or combined with α-tocopherol on hepatic steatosis and oxidative stress in fructose-induced insulin-resistant rats

A diet high in fructose (HFr) induces insulin resistance in animals. Free radicals are involved in the pathogenesis of HFr-induced insulin resistance. Carnosine (CAR) is a dipeptide with antioxidant properties. We investigated the effect of CAR alone or in combination with α-tocopherol (CAR + TOC) on HFr-induced insulin-resistant rats. Rats fed with HFr containing 60% fructose received CAR (2 g/L in drinking water) with/without TOC (200 mg/kg, i.m. twice a week) for 8 weeks. Insulin resistance, serum lipids, inflammation markers, hepatic lipids, lipid peroxides, and glutathione (GSH) levels together with glutathione peroxidase (GSH-Px) and superoxide dismutase 1 (CuZnSOD; SOD1) activities and their protein expressions were measured. Hepatic histopathological examinations were performed. HFr was observed to cause insulin resistance, inflammation and hypertriglyceridemia, and increased triglyceride and lipid peroxide levels in the liver. GSH-Px activity and expression decreased, but GSH levels and SOD1 activity and expression did not alter in HFr rats. Hepatic marker enzyme activities in serum increased and marked macro- and microvesicular steatosis were seen in the liver. CAR treatment did not alter insulin resistance and hypertriglyceridemia, but it decreased steatosis and lipid peroxidation without any change in the antioxidant system of the liver. However, CAR + TOC treatment decreased insulin resistance, inflammation, hepatic steatosis, and lipid peroxidation and increased GSH-Px activity and expression in the liver. Our results may indicate that CAR + TOC treatment is more effective to decrease HFr-induced insulin resistance, inflammation, hepatic steatosis, and dysfunction and pro-oxidant status in rats than CAR alone.

The protective effect and underlying mechanism of metformin on neointima formation in fructose-induced insulin resistant rats

BackgroundInsulin resistance is strongly associated with the development of type 2 diabetes and cardiovascular disease. However, the underlying mechanisms linking insulin resistance and the development of atherosclerosis have not been fully elucidated. Moreover, the protective effect of antihyperglycemic agent, metformin, is not fully understood. This study investigated the protective effects and underlying mechanisms of metformin in balloon-injury induced stenosis in insulin resistant rats.MethodsAfter 4 weeks high fructose diet, rats received balloon catheter injury on carotid arteries and were sacrificed at 1 and 4 weeks post injury. Biochemical, histological, and molecular changes were investigated.ResultsPlasma levels of glucose, insulin, total cholesterol, triglyceride, free fatty acids, and methylglyoxal were highly increased in fructose-induced insulin resistant rats and treatment with metformin significantly improved this metabolic profile. The neointimal formation of the carotid arteries was enhanced, and treatment with metformin markedly attenuated neointimal hyperplasia. A significant reduction in BrdU-positive cells in the neointima was observed in the metformin-treated group (P < 0.01). Insulin signaling pathways were inhibited in insulin resistant rats while treatment with metformin enhanced the expression of insulin signaling pathways. Increased expression of JNK and NFKB was suppressed following metformin treatment. Vasoreactivity was impaired while treatment with metformin attenuated phenylephrine-induced vasoconstriction and enhanced methacholine-induced vasorelaxation of the balloon injured carotid arteries in insulin resistant rats.ConclusionThe balloon-injury induced neointimal formation of the carotid arteries is enhanced by insulin resistance. Treatment with metformin significantly attenuates neointimal hyperplasia through inhibition of smooth muscle cell proliferation, migration, and inflammation as well as by improvement of the insulin signaling pathway.

New drug for treatment of insulin-resistant complication?

Diabetes is an increasing epidemic and more than 500 million people are expected to have diabetes within the nearest 20 years (Whiting et al., 2011). The disease is poly-factorial, and both genetic and life-style factors contribute to the risk of developing the disease. The pathogenesis involves impaired insulin secretion and insulin resistance and is associated with both macro- and microvascular complications. In the work by Zhou et al. (2013) in this issue of ACTA Physiologia, the therapeutic effects of adrenomedullin (ADM) on vascular calcification in fructose-induced insulin resistance rats have been investigated. Calcification of the media of the arterial wall is a common feature in patients with increased glucose levels and is associated with increased risk of nephropathy, retinopathy, coronary heart disease and mortality (Jeffcoate et al., 2009). The process includes active ossification and bone formation. The bone formation is initiated by bone morphogenetic proteins (BMPs) secreted from mesenchymal stem cells that activate transcription factors such as transcription factor core-binding protein (Cbafa1). BMPs belong to the TGF-beta family of proteins, and BMP-2 and BMP-4 are the BMPs suggested to be associated with vascular calcification. Calcification of the arterial wall also involves the cytokine osteopontin (OPN). Type 2 diabetes patients with calcification-related complications have been demonstrated to have higher circulating levels of OPN (Jeffcoate et al., 2009). Moreover, it was recently demonstrated that hyperglycaemia increases the level of OPN in smooth muscle cells (Nilsson-Berglund et al., 2010). In agreement with current published work, Zhou et al. (2013) demonstrate that increased calcification through fructose-induced insulin resistance and hyperglycaemia is accompanied by increased protein levels of BMP2, OPN and Cbfa-1. They further demonstrate that the levels of BMP2 and Cbfa-1 are reduced after addition of ADM, whereas levels of OPN continue to increase. Adrenomedullin is a member of the calcitonin gene–related peptide (CGRP)/amylin family. It is widely distributed in peripheral tissue and in the brain, where it has been shown to have both autocrine and paracrine effects. In type 2 diabetes, ADM has been associated with the pathogenesis of diabetic vasculopathy (Lim et al., 2007). Levels of ADM are increased in patients with heart failure and the precursor of ADM, pro-ADM, has been investigated as a possible biomarker of cardiac heart disease (CHD) (Melander et al. 2009). In line with previous studies, Zhoe et al. demonstrate an increased level of ADM due to fructose-induced insulin resistance. This study further contributes by demonstrating direct beneficial effects of ADM on the levels of key proteins in the bone formation associated by arterial calcification. The work by Zhou is one of the first studies demonstrating the positive effects of exogenous added ADM on vascular calcification associated with insulin resistance. In addition, earlier studies have demonstrated that ADM reduces fructose-induced insulin resistance and associated myocardial hypertrophy (Zhang et al., 2011). Thus, the multiple positive effects make administration of ADM a most likely and favourable therapeutic approach for patients with diabetes, at least insulin resistance associated. The multiple positive effects make ADM reminiscent of incretins, such as GLP-1 and GIP. These endogenous produced hormones increase insulin secretion in beta cells and glucose uptake in target tissue. In addition, GLP-1 has been proven to increase cardio protection and cardiac function (Baggio and Drucker, 2007). Agonist of GLP-1 and antagonists of DPPIV (the enzyme that breaks down GLP-1 and GIP) are today widely used in the treatment of type 2 diabetes due to their effects on both insulin secretion and complications. Most of the genetic risk variants of type 2 diabetes discovered today is associated with insulin secretion and it remains to be investigated whether ADM, as the incretins, has beneficial effects also on insulin secretion. The work by Zhou et al. (2013) has added one piece to the large puzzle of ADM as a possible treatment for diabetes and its complications. None.

Adrenomedullin attenuates vascular calcification in fructose‐induced insulin resistance rats

To determine the therapeutic effects of adrenomedullin (ADM) on vascular calcification and related molecular mechanism in fructose-induced insulin resistance rats. Rats received ordinary drinking water or 10% fructose in drinking water for 12 weeks and subcutaneous injection of normal saline or ADM (3.6 μg kg(-1) ) twice a day for the last 4 weeks. Levels of ADM, calcitonin receptor-like receptors (CRLR), receptor activity-modifying proteins (RAMP) as well as calcium content, alkaline phosphatase (ALP) activity, osteoblastic and contractile smooth muscle markers in aortic media were measured. The levels of ADM, CRLR, RAMP2 and RAMP3 in aortic media were increased in fructose-fed rats. ADM treatment attenuated the fructose-induced insulin resistance, increased blood pressure, fasting glucose, insulin, triglycerides and cholesterol levels. It improved VSMCs proliferation and disordered arrangement and hyperplasia of elastic fibres in fructose-fed rats. Calcium deposits, calcium content and ALP activity in the aortic media were increased in fructose-fed rats, which were attenuated by ADM treatment. The osteoblastic markers such as osteopontin (OPN), bone morphogenetic protein 2 (BMP2) proteins and core binding factor alpha-1 (Cbfα-1) protein and mRNA expressions were increased in fructose-fed rats. ADM treatment increased the OPN protein expression, but reduced the BMP2 protein, Cbfα-1 protein and mRNA expression. Contractile smooth muscle markers such as α-actin and smooth muscle 22α (SM-22α) were downregulated in fructose-fed rats, which were recovered by ADM treatment. Administration of ADM attenuates insulin resistance, calcium deposition and osteogenic transdifferentiation in aortic media in fructose-fed rats.

The Mechanism of Calcitonin Gene-Related Peptide–Containing Nerve Innervation

Calcitonin gene-related peptide (CGRP) is a major neurotransmitter and CGRP-containing primary sensory neurons play an important role in nociception and potent vasodilation. CGRP-containing nerves in mesenteric arteries are decreased in pathological animal models (hypertension, diabetes, and atherosclerosis). In apolipoprotein E–knockout mice, which have atherosclerosis and peripheral sensory nerve defects, nerve growth factor (NGF)-mediated CGRP nerve facilitation was down-regulated, which may have been caused by the impairment of the Akt–NO–cGMP pathway. In addition, NGF-mediated CGRP neurite outgrowth was decreased in fructose-induced insulin-resistant rats. We recently discovered that renin–angiotensin inhibitors improved CGRP innervation in spontaneously hypertensive rats, indicating that rescuing CGRP nerve innervation might improve pathophysiological conditions. To find a novel reagent that facilitates CGRP nerves, a new model, phenol-injured perivascular nerve model rats, was established. Adrenomedullin, hepatocyte growth factor, and angiotensin II type 2 receptor activation induced CGRP nerve distribution in phenol-injured rats. Furthermore, in insulin-resistant model rats, the down-regulation of CGRP nerves was likely due to the depression of phosphoinositide 3-kinase (PI3K)-dependent Akt activation. Administration of candesartan improves CGRPergic function via the PI3K–Akt pathway in insulin-resistant rats. Thus, clarification of the mechanisms of CGRP nerve defects may constitute future therapeutic targets.

Swim Training Reduces Metformin Levels in Fructose-Induced Insulin Resistant Rats

Regular exercise training and metformin medication are widely considered to increase insulin sensitivity and protect against type 2 diabetes, however, evaluating the effect of exercise training on the disposition and pharmacokinetics of metformin is unclear. We investigated the effect of a 4-wk swim training program (45 min/day, 5 days/wk) on the pharmacokinetics for the use of metformin in fructose-induced insulin resistant rats. Fructose-induced insulin resistant rats were assigned into two groups (n=6/group): swim training with metformin (SM), and non-swim training with metformin (CM). Blood samples were collected from 12 h-fasted rats at baseline and at 0.25, 0.5, 0.75, 1, 2, 3, 4, 6, 8, 10, and 12 h after an oral glucose tolerance test (OGTT) with administration of a single dose of metformin (450 mg/kg). Our study revealed that both glucose and insulin levels in the SM group were significantly lower than those in the CM group at 15 min following OGTT. The maximum concentration (C(max)) and area under the serum concentration-time curve (AUC) for the SM group were significantly lower than CM group. The apparent distribution volume (Vd) and the time-averaged total body clearance (CL) for the SM group were significantly higher than those for the CM group. There were no significant differences in the time to maximum concentration (T(max)) or the time to half-life concentration (t(1/2)) between the two groups. Our data demonstrate that swim training reduces metformin serum levels.

Atorvastatin Protects against Ischemia-Reperfusion Injury in Fructose-Induced Insulin Resistant Rats

High fructose (HFr) intake is known to cause insulin resistance syndrome (IRS), however its effect against acute coronary events remains elusive. The present study was undertaken to evaluate the effect of HFr (60%) diet on myocardial ischemia-reperfusion (MI-RP) injury and its modulation by atorvastatin treatment. Wistar rats kept on HFr/chow feeding for 10weeks, received atorvastatin (30mg/kg, per oral) or vehicle for two additional weeks followed by MI-RP injury. MI-RP injury was significantly augmented in HFr fed rats, as evident by the increase in infarct size (IS, 65 ± 5% vs. 43 ± 7%) and activities of cardiac injury biomarkers [serum lactate dehydrogenase (LDH, 698 ± 57 vs. 444 ± 26 U/L), creatinine kinase (CK-MB, 584 ± 58 vs. 435 ± 28 U/L) and tissue myeloperoxidase (MPO, 235 ± 15 vs. 101 ± 11μM/min/100mg tissue)]. Insulin resistance (plasma glucose, 64 ± 5 vs. 100 ± 5mg/dl; AUC (0-120 min), p < 0.05), MI-RP injury (IS 20 ± 5%, LDH 292 ± 28 U/L, CK-MB 257 ± 13 U/L, MPO 95 ± 5μM/min/100mg tissue) and triglyceride (TG) level were significantly reduced, while myocardial Akt, p-Akt, eNOS, p-eNOS and iNOS protein expression were significantly enhanced following atorvastatin treatment in comparison to HFr fed rats. Oxidative stress marker, malondialdehyde and circulating levels of inflammatory cytokines (CRP, IL-6, IFN-γ and TNF) were significantly reduced, while total nitrite content in the tissue and plasma was significantly augmented in atorvastatin treated rats. Atorvastatin also ameliorated endothelial dysfunction and significantly enhanced aortic Akt and eNOS protein expression. Atorvastatin conferred significant protection against MI-RP injury and alleviated HFr induced IRS possibly by increasing NOS expression through Akt dependent pathway.

Antiproliferation of cardamonin is involved in mTOR on aortic smooth muscle cells in high fructose-induced insulin resistance rats

The objective of this study was to determine possible effects and potential mechanisms of cardamonin on improving insulin resistance and vascular proliferative lesions in the rat's model system. Fed with 60% fructose-enriched diet for 12 weeks, male Sprague–Dawley (SD) rats developed insulin resistance and hyperinsulinemia. They also showed excessive proliferation of the vascular smooth muscle cells (VSMCs) and activation of the mammalian target of rapamycin (mTOR)/translation control proteins p70 ribosomal S6 kinase (P70S6K1)/eukaryotic initiation factor 4E binding protein 1 (4E-BP1) signaling in the rat thoracic aorta. From weeks 9–12, cardamonin was injected into the peritoneal cavity once daily. Under the detection of microscopy and electron microscopy, cardamonin improved hyperinsulinemia and inhibited proliferation of VSMCs in the thoracic aorta of rats in a dose-dependent manner. By the Real-Time RT-PCR, mRNA expression of mTOR, P70S6K1 and 4E-BP1 was significantly reduced in cardamonin treated rats. Similarly, protein over-expression of mTOR and p-P70S6K1 was obviously inhibited by immunohistochemical analyses. These findings suggest that cardamonin may play a role in ameliorating insulin resistance and smooth muscle hyperplasia of major vessels in fructose-induced rats, possibly via a mechanism that involves the modulation of insulin/mTOR signaling.

Swimming Training Reduced Metformin Concentration after Single Dosage of Administration in Insulin Resistance Rats

Previous study has shown that performing a single bout of swimming before administration of metformin can improve insulin sensitivity and the rate of metformin absorption. We here extended knowledge to examine the effects of swimming training on the absorption, distribution, metabolism, and excretion for the use of metformin. PURPOSE: To investigate the effect of 1 month swimming training (5days/week, 45min/day) on the pharmacokinetics for the use of metformin in fructose-induced insulin resistance rats. METHODS: Twelve fructose-induced rats were assigned to two groups: administration metformin without swimming training (M, n=6) and administration metformin with swimming training (MS, n=6). After 12 hrs fasting, blood samples (0.5 mL) were collected before administration of metformin and at 15, 45, 60, 120, 180, 240, 360, 480, 600, 720-min after dosing (450mg/kg). Plasma metformin concentrations were determined by high performance liquid chromatography (HPLC, Hypersil Cps 3-0679 column (250mm×4.6mm I.D.). The flow rate kept constant at 1mL/min, and the temperature maintained at 40°C. A mixture of acetonitrile and 0.01M potassium dihydrogen phosphate (40:60) (pH 5.5) was used as the mobile phase with UV detection at 234 nm. RESULTS: Cmax,AUC, Vd and CL for the MS group were significantly lower than M group. There were no significant differences in Tmax and t1/2 between two groups. CONCLUSIONS: Swimming training may decrease the accumulation of metformin, which would reduce the risk of side effects.

Hypoglycemic Effect of Aqueous Shallot and Garlic Extracts in Rats with Fructose-Induced Insulin Resistance

The present study has been carried out to investigate the effect of aqueous extract of shallot (Allium ascalonicum) and garlic (Allium satium) on the fasting insulin resistance index (FIRI) and intraperitoneal glucose tolerance test (IPGTT) of fructose-induced insulin resistance rats. Male albino Wistar rats were fed either normal or high-fructose diet for a period of eight weeks. Fasting blood glucose level, fasting blood triglyceride level, FIRI, and the area under the glucose tolerance curve were significantly elevated in fructose-fed animals. Fructose-induced insulin resistance rats treated by aqueous shallot or garlic extract (500 mg/kg body weight/day, i.p.) for duration of eight weeks. Control animals only received normal saline (0.9%). The results showed that neither shallot nor garlic extracts significantly altered the FIRI and the IPGTT at the fourth week after treatment. The fasting blood glucose in fructose-induced insulin resistance animals has been significantly decreased in 8-week treated animals by both shallot and garlic extracts. Shallot extract administration, but not garlic extract, for a period of eight weeks can significantly improve the intraperitoneal glucose tolerance and diminish the FIRI. These results indicate that shallot and garlic extracts have a hypoglycemic influence on the fructose-induced insulin resistance animals and aqueous shallot extract is a stronger hypoglycemic agent than the garlic extract.

Stress and vascular responses: oxidative stress and endothelial dysfunction in the insulin-resistant state.

Although insulin-resistant states have been associated with endothelial dysfunction due to increased vascular oxidative stress, the underlying mechanisms are pooly understood. Recent experimental evidence suggests that tetrahydrobiopterin (BH(4)), the natural and essential cofactor of NO synthases (NOS), plays a crucial role not only in increasing the rate of NO generation by NOS but also in controlling the formation of superoxide anion (O(2)(-)) in endothelial cells. Because insulin resistance has been suggested to be a significant contributing factor in the development of abnormal pteridine metabolism and endothelial dysfunction, we investigated pteridine content and NO/O(2)(-) production with the use of isolated thoracic aortas obtained from fructose-induced insulin-resistant rats. Under insulin-resistant conditions where BH(4) levels are suboptimal, the production of O(2)(-) by NOS leads to endothelial dysfunction. Furthermore, oral supplementation of BH(4) restores endothelial function and relieved oxidative tissue damage, at least in part, through activation of endothelial NOS (eNOS) in the aorta of insulin-resistant rats. These results indicate that insulin resistance may be a pathogenic factor for endothelial dysfunction through impaired eNOS activity and increased oxidative breakdown of NO due to enhanced formation of O(2)(-), which are caused by relative deficiency of BH(4) in vascular endothelial cells.