Patchareewan Pannangpetch

Mulberry leaf extract restores arterial pressure in streptozotocin-induced chronic diabetic rats

Free radical-induced vascular dysfunction plays a key role in the pathogenesis of vascular disease found in chronic diabetic patients. Morus alba (MA) leaf extract is promoted for good health especially in diabetic patients. Interestingly, antidiabetic and antioxidant activities of MA have been reported in experimental animals. Thus, the hypothesis of this study was that the long-term treatment with MA could improve vascular reactivity of chronic diabetic rats. To test this hypothesis, we examined the effect of long-term treatment with MA on the vascular responses to vasoactive agents in streptozotocin-induced chronic diabetic rats. The diabetic rats were either orally administered with distilled water, MA (0.25, 0.5 and 1 g/kg per day) or subcutaneously injected with insulin (4 U/kg per day) for 8 weeks. After each treatment, the fasting blood glucose, blood pressure, vascular responses to vasoactive agents and tissue malondialdehyde were examined. Morus alba at the doses of 0.5 and 1 g/kg, which significantly reduced blood glucose level, also significantly decreased the high blood pressure in diabetic rats. Vascular responses of the chronic diabetic rats to vasodilators, acetylcholine (3-30 nmol/kg) and sodium nitroprusside (1-10 nmol/kg) were significantly suppressed by 26% to 44% and 45% to 77% respectively, whereas those to vasoconstrictor, phenylephrine (0.01-0.1 micromol/kg) were significantly increased by 23% to 38% as compared to normal rats. Interestingly, the administration of 0.5 and 1 g/kg MA or 4 U/kg insulin significantly restored the vascular reactivities of diabetic rats. Moreover, 8 weeks of diabetes resulted in the elevation of malondialdehyde content in tissues (liver, kidney, heart, and aorta), and MA treatment significantly lessened this increase. These results provide the first evidence for the efficacy of MA in restoring the vascular reactivity of diabetic rats, the mechanism of which may associate with the alleviation of oxidative stress.

Mulberry leaf extract stimulates glucose uptake and GLUT4 translocation in rat adipocytes.

Mulberry (Morus alba L.) leaf tea is promoted for its health benefits and the control of diabetes in Asian nations. The blood glucose lowering activity of mulberry leaf extract (MA) has been proven; however, the molecular basis underlying this effect remains unclear. The aim of the present work is to elucidate its mechanism of the antihyperglycemic action, by examining the effect of MA on glucose uptake and the translocation of glucose transporter 4 protein (GLUT4) to the plasma membrane of adipocytes isolated from diabetic rats. The incubation of adipocytes with 5-45 μg/ml MA resulted in 31-54% increase of glucose uptake in a dose-dependent manner. This glucose uptake enhancing effect was inhibited by the phosphoinositol 3-kinase (PI3-K) inhibitor, wortmannin (100 nM). The GLUT4 protein on the plasma membrane fraction of adipocytes was markedly increased after treatment with 15 μg/ml MA extract. Interestingly, gallic acid, one of the phenolic compounds found in MA extract, increased glucose uptake and enhanced the translocation of GLUT4 at concentrations comparable to the amount of gallic acid in the effective concentration ranges of MA. Thus, it is likely that gallic acid contributes, at least in part, to its antihyperglycemic activity. The present results suggest that the antihyperglycemic action of MA is mediated by increasing glucose uptake via the activation of PI3-K signaling pathway and translocation of GLUT4 to the plasma membrane. These findings are the first molecular evidence supporting the mulberry tea as herbal medicine for diabetic patients.

Curcumin improves vascular function and alleviates oxidative stress in non-lethal lipopolysaccharide-induced endotoxaemia in mice

Oxidative stress is implicated in various pathological conditions, including septic shock, and other diseases associated with local or systemic inflammation. Curcumin, a major component from turmeric (Curcuma longa), possesses diverse anti-inflammatory, anti-tumour and antioxidant properties. The aim of this study was to investigate the effect of curcumin on modulation of vascular dysfunction and oxidative stress induced by lipopolysaccharide (LPS) in mice. Male ICR mice were treated with curcumin (50 or 100 mg/kg), administered intragastrically, either before or after intraperitoneal injection of LPS (10 mg/kg). Fifteen hours after LPS administration, arterial blood pressure was measured and vascular response to vasoactive agents were assessed. Aortic tissues and blood samples were taken for assays of antioxidant and oxidative stress markers. LPS caused marked hypotension, tachycardia and vascular hyporeactivity. The mean arterial pressures in responses to phenylephrine, acetylcholine, and sodium nitroprusside of LPS-treated mice were significantly decreased when compared with the untreated controls. Curcumin modulated heart rate and restored arterial blood pressure in a dose-dependent manner in both protectively- and therapeutically-treated regimens. Furthermore, the vascular responsiveness of LPS-treated mice was improved by curcumin. Interestingly, the improvements of haemodynamics and vascular response during endotoxaemia were related to alleviation of oxidative stress by reducing aortic-derived superoxide production, suppression of lipid peroxidation and protein oxidation, and decrease in urinary nitric oxide metabolites with preservation of the ratio of glutathione/glutathione disulfide. This study provides the first evidence for the potential role of curcumin in prevention and treatment of vascular dysfunction in mice with endotoxaemia elicited by LPS.

Curcumin improves endothelial dysfunction and vascular remodeling in 2K-1C hypertensive rats by raising nitric oxide availability and reducing oxidative stress.

Oxidative stress plays a role in maintaining high arterial blood pressure and contributes to the vascular changes that lead to hypertension. Consumption of polyphenol-rich foods has demonstrated their beneficial role in the prevention and treatment of hypertension. Curcumin (CUR), a phenolic compound present in the rhizomes of turmeric, possesses cardiovascular protective, anti-inflammatory and antioxidant properties. The present study was designed to investigate the protective effect of CUR on 2kidney-1clip (2K-1C)-induced hypertension, endothelial dysfunction, vascular remodeling and oxidative stress in male Sprague-Dawley rats. Sham operated or 2K-1C rats were treated with CUR at a dose of 50 or 100 mg/kg/day (or vehicle). After 6 weeks of treatment, CUR ameliorated hemodynamic performance in 2K-1C hypertensive rats (P< 0.05), by reducing blood pressure, increasing hindlimb blood flow and decreasing hindlimb vascular resistance. Hemodynamic restoration was associated with a reduction in plasma angiotensin converting enzyme level. Endothelium-dependent vasorelaxation, in response to acetylcholine, of aortic rings isolated from 2K-1C hypertensive rats-treated with CUR was significantly increased (P< 0.05). CUR also attenuated hypertension-induced oxidative stress and vascular structural modifications. These effects were associated with elevated plasma nitrate/nitrite, upregulated eNOS expression, downregulated p47phox NADPH oxidase and decreased superoxide production in the vascular tissues. The overall findings of this study suggest the mechanisms responsible for the antihypertensive action of CUR in 2K-1C hypertension-induced endothelial dysfunction and vascular remodeling involve the improvement NO bioavailability and a reduction in oxidative stress.

Mulberry leaf extract increases adiponectin in murine 3T3-L1 adipocytes

We have previously shown that mulberry leaf extract (MA) causes blood glucose levels to decrease in rats with streptozotocin-induced diabetes while enhancing glucose uptake by isolated fat cells. We hypothesized that the antidiabetic activity of MA is mediated via enhancement of adiponectin secretion and adipogenesis, which consequently decreases blood glucose. In the present study, we aimed to elucidate the molecular basis for the observed antidiabetic activity using murine 3T3-L1 preadipocyte cultures. We found that treatment of differentiating 3T3-L1 cells with MA at concentrations of 5, 15, and 45 μg/mL increased expression of adiponectin messenger RNA from 1.4-fold (control) to 1.5-, 1.95-, and 2.2-fold above basal values, respectively, while causing adiponectin secretion to increase from 70 ± 7.4 ng/mL to 100 ± 1.4, 138 ± 2.0, and 176 ± 21.4 ng/mL, respectively. Furthermore, we observed an increase in both lipid accumulation and messenger RNA expression of transcription factors, such as CCAAT/enhancer-binding protein α and peroxisome proliferator-activated receptor γ; and of the fatty acid-binding protein aP2 in differentiated 3T3-L1 cells pretreated with MA. Our findings indicate that the stimulatory effects of mulberry leaf extract on adipocyte proliferation and differentiation likely occur through up-regulation of adipogenic transcription factors and downstream gene expression. Such effects of mulberry leaf extract on adiponectin secretion and adipocyte activity may account for, at least in part, the antidiabetic effects of consumption of beverages containing mulberry leaves.

Curcumin Protects against Cadmium-Induced Vascular Dysfunction, Hypertension and Tissue Cadmium Accumulation in Mice

Curcumin from turmeric is commonly used worldwide as a spice and has been demonstrated to possess various biological activities. This study investigated the protective effect of curcumin on a mouse model of cadmium (Cd)—induced hypertension, vascular dysfunction and oxidative stress. Male ICR mice were exposed to Cd (100 mg/L) in drinking water for eight weeks. Curcumin (50 or 100 mg/kg) was intragastrically administered in mice every other day concurrently with Cd. Cd induced hypertension and impaired vascular responses to phenylephrine, acetylcholine and sodium nitroprusside. Curcumin reduced the toxic effects of Cd and protected vascular dysfunction by increasing vascular responsiveness and normalizing the blood pressure levels. The vascular protective effect of curcumin in Cd exposed mice is associated with up-regulation of endothelial nitric oxide synthase (eNOS) protein, restoration of glutathione redox ratio and alleviation of oxidative stress as indicated by decreasing superoxide production in the aortic tissues and reducing plasma malondialdehyde, plasma protein carbonyls, and urinary nitrate/nitrite levels. Curcumin also decreased Cd accumulation in the blood and various organs of Cd-intoxicated mice. These findings suggest that curcumin, due to its antioxidant and chelating properties, is a promising protective agent against hypertension and vascular dysfunction induced by Cd.

Ferulic Acid Alleviates Changes in a Rat Model of Metabolic Syndrome Induced by High-Carbohydrate, High-Fat Diet

Metabolic syndrome is a cluster of metabolic abnormalities characterized by obesity, insulin resistance, hypertension and dyslipidemia. Ferulic acid (FA) is the major phenolic compound found in rice oil and various fruits and vegetables. In this study, we examined the beneficial effects of FA in minimizing insulin resistance, vascular dysfunction and remodeling in a rat model of high-carbohydrate, high-fat diet-induced metabolic changes, which is regarded as an analogue of metabolic syndrome (MS) in man. Male Sprague-Dawley rats were fed a high carbohydrate, high fat (HCHF) diet and 15% fructose in drinking water for 16 weeks, where control rats were fed with standard chow diet and tap water. FA (30 or 60 mg/kg) was orally administered to the HCHF and control rats during the last six weeks of the study. We observed that FA significantly improved insulin sensitivity and lipid profiles, and reduced elevated blood pressure, compared to untreated controls (p < 0.05). Moreover, FA also improved vascular function and prevented vascular remodeling of mesenteric arteries. The effects of FA in HCHF-induced MS may be realized through suppression of oxidative stress by down-regulation of p47phox, increased nitric oxide (NO) bioavailability with up-regulation of endothelial nitric oxide synthase (eNOS) and suppression of tumor necrosis factor-α (TNF-α). Our results suggest that supplementation of FA may have health benefits by minimizing the cardiovascular complications of MS and alleviating its symptoms.

Peptides-Derived from Thai Rice Bran Improves Endothelial Function in 2K-1C Renovascular Hypertensive Rats

In recent years, a number of studies have investigated complementary medical approaches to the treatment of hypertension using dietary supplements. Rice bran protein hydrolysates extracted from rice is a rich source of bioactive peptides. The present study aimed to investigate the vasorelaxation and antihypertensive effects of peptides-derived from rice bran protein hydrolysates (RBP) in a rat model of two kidney-one clip (2K-1C) renovascular hypertension. 2K-1C hypertension was induced in male Sprague-Dawley rats by placing a silver clip around the left renal artery, whereas sham-operated rats were served as controls. 2K-1C and sham-operated rats were intragastrically administered with RBP (50 mg·kg−1 or 100 mg·kg−1) or distilled water continuously for six weeks. We observed that RBP augmented endothelium-dependent vasorelaxation in all animals. Administration of RBP to 2K-1C rats significantly reduced blood pressure and decreased peripheral vascular resistance compared to the sham operated controls (p < 0.05). Restoration of normal endothelial function and blood pressure was associated with reduced plasma angiotensin converting enzyme (ACE), decreased superoxide formation, reduced plasma malondialdehyde and increased plasma nitrate/nitrite (p < 0.05). Up-regulation of eNOS protein and down-regulation of p47phox protein were found in 2K-1C hypertensive rats-treated with RBP. Our results suggest that RBP possesses antihypertensive properties which are mainly due to the inhibition of ACE, and its vasodilatory and antioxidant activity.

Rice Bran Protein Hydrolysates Improve Insulin Resistance and Decrease Pro-inflammatory Cytokine Gene Expression in Rats Fed a High Carbohydrate-High Fat Diet

A high carbohydrate-high fat (HCHF) diet causes insulin resistance (IR) and metabolic syndrome (MS). Rice bran has been demonstrated to have anti-dyslipidemic and anti-atherogenic properties in an obese mouse model. In the present study, we investigated the beneficial effects of rice bran protein hydrolysates (RBP) in HCHF-induced MS rats. After 12 weeks on this diet, the HCHF-fed group was divided into four subgroups, which were orally administered RBP 100 or 500 mg/kg, pioglitazone 10 mg/kg, or tap water for a further 6 weeks. Compared with normal diet control group, the MS rats had elevated levels of blood glucose, lipid, insulin, and HOMA-IR. Treatment with RBP significantly alleviated all those changes and restored insulin sensitivity. Additionally, RBP treatment increased adiponectin and suppressed leptin levels. Expression of Ppar-γ mRNA in adipose tissues was significantly increased whereas expression of lipogenic genes Srebf1 and Fasn was significantly decreased. Levels of mRNA of proinflammatory cytokines, Il-6, Tnf-α, Nos-2 and Mcp-1 were significantly decreased. In conclusion, the present findings support the consumption of RBP as a functional food to improve insulin resistance and to prevent the development of metabolic syndrome.

Ferulic acid improves lipid and glucose homeostasis in high‐fat diet‐induced obese mice

Ferulic acid (FA) is a plant phenolic acid that has several pharmacological effects including antihyperglycaemic activity. Thus, the objective of this study is to investigate the effect of FA on glucose and lipid metabolism in high‐fat diet (HFD)‐induced obese mice. Institute for Cancer Research (ICR) mice were fed a HFD (45 kcal% fat) for 16 weeks. At the ninth week of induction, the obese mice were orally administered with daily FA doses of 25 and 50 mg/kg for the next eight weeks. The results show that FA significantly reduced the elevated blood glucose and serum leptin levels, lowered the insulin resistance, and increased the serum adiponectin level. Moreover, serum lipid level, and liver cholesterol and triglyceride accumulations were also reduced. The histological examination showed clear evidence of a decrease in the lipid droplets in liver tissues and smaller size of fat cells in the adipose tissue in the obese mice treated with FA. Interestingly, FA reduced the expression of hepatic lipogenic genes such as sterol regulatory element‐binding protein 1c (SREBP1c), fatty acid synthase (FAS), and acetyl‐CoA carboxylase (ACC). It could also up‐regulate hepatic carnitine palmitoyltransferase 1a (CPT1a) gene and peroxisome proliferator‐activated receptor alpha (PPARα) proteins. The FA treatment was also found to suppress the protein expressions of hepatic gluconeogenic enzymes, phosphoenolpyruvate carboxylase (PEPCK) and glucose‐6‐phosphatase (G6Pase). In conclusion, the findings of this study demonstrate that FA improves the glucose and lipid homeostasis in HFD‐induced obese mice probably via modulating the expression of lipogenic and gluconeogenic genes in liver tissues.