Новые доказательства фармакологической активности и возможных молекулярных мишеней полисахаридов ягоды Годжи
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Hypoglycemic effectsDiabetes mellitus is a group of complicated metabolic disorders characterized by high blood glucose level and inappropriate insulin secreting capacity due to decreased glucose metabolism and pancreatic cell mass or dysfunction of cells. Based on the data from the 2011 National Diabetes Fact Sheet in the US, 25.8 million children and adults (ie, 8.3% of the population) have diabetes and 1.9 million new cases of diabetes were diagnosed in people aged 20 years and older in 2010. A total of 25.6 million or 11.3% of US people aged 20 years and older have diabetes. In adults, type 2 diabetes (previously called non-insulin-dependent diabetes mellitus or adult-onset diabetes; T2DM) accounts for about 90%–95% of all diagnosed cases of diabetes. T2DM is a chronic metabolic disorder characterized by progressive hyperglycemia secondary to declining β-cell function, and usually accompanied by a reduced sensitivity to insulin in peripheral tissues, such as liver and muscle.103 If untreated or not well managed, long-term hyperglycemia can lead to increased risk of macrovasulcar (cardiovascular, cerebrovascular, and peripheral vascular disease) and microvasulcar (nephropathy, neuropathy, and retinopathy) complications. Improving glucose metabolism and preserving β-cell mass and function represent the major strategies for the treatment of T2DM. High glucose concentrations and fatty acid levels stimulate excessive accumulation of ROS, which can cause tissue injury and insulin resistance in peripheral metabolic tissues.104 Several studies have showed that LBPs had significant hypoglycemic effects and insulin-sensitizing activity by increasing antioxidation, glucose metabolism, and insulin secretion and by promoting pancreatic β-cell proliferation.17,105–110 Streptozotocin- or alloxan-induced diabetesLuo et al107 compared the hypoglycemic effects of LBF water decoction, crude polysaccharide extracts (crude LBPs), and purified polysaccharide fractions (LBPs) in alloxan-induced diabetic rabbits. All the three LBF extracts/fractions significantly reduced blood glucose levels in rabbits.107 The hypoglycemic effect of LBPs was more significant than those of water decoction and crude LBPs, but water and methanolic fruit extracts and crude polysaccharide extracts exhibited stronger antioxidant activity than purified polysaccharide fractions. Zhao et al108 conducted an animal study to examine the hypoglycemic activity of LBPs in male Wistar rats with experimental diabetes. Rats were fed with HD for 3 weeks and administered intraperitoneal injection of 50 mg/kg streptozotocin to induce diabetes. Fasting plasma levels of glucose, lipids, and insulin were monitored. The content of glucose transporter type-4 (GLUT4) in gastrocnemius skeletal muscle was determined. Under anabolic condition, GLUT4 is the main carrier that transports blood glucose into muscle and adipose cells.111,112 In the nonstimulated state, GLUT4 is efficiently sequestered intracellularly. This retention prevents GLUT4 from reaching the cell surface and transporting glucose into muscle and fat cells when blood glucose levels are low.112 After a meal, when blood glucose levels rise, insulin is secreted by the pancreas, which triggers an intracellular signaling cascade, leading to the translocation of GLUT4 from intracellular compartments to the cell surface, resulting in glucose uptake and normalization of the blood glucose levels.111,112 Oral treatment of 10 mg/kg/day LBP for 3 weeks resulted in a significant decrease in the concentration of plasma triglyceride and weight in diabetic rats.108 Furthermore, LBPs markedly decreased the plasma cholesterol levels, fasting plasma insulin levels, and the postprandial glucose level at 30 minutes during oral glucose tolerance test and significantly increased the insulin sensitivity index in diabetic rats.108 Moreover, LBPs increased the level of GLUT4 in skeletal muscle under insulin stimulation. LBPs can alleviate abnormal glucose and lipid metabolism and ameliorate insulin resistance, and the mechanism may be involved in upregulation of GLUT4 and improved GLUT4 trafficking and intracellular insulin signaling. The effect of oral LBP treatment on blood glucose, oxidative stress, and DNA damage was examined by Wu et al106 in male Wistar rats with experimental diabetes. Rats were fed with HD for 3 weeks and administered intraperitoneal injection of 50 mg/kg streptozotocin to induce diabetes. Oral administration of 10 mg/kg/day LBP for 4 weeks led to decreased levels of blood glucose.106 Serum MDA and NO levels were decreased by LBPs in fasting diabetic rats, and the serum level of SOD was increased by LBPs in diabetic rats.106 LBPs reduced cellular DNA damage in peripheral lymphocytes of the diabetic rats as determined by the single cell gel assay. These results suggest that LBPs can improve glucose metabolism via inhibition of oxidative stress in diabetes. Li17 reported that in streptozotocin-induced diabetic rats, treatment of 50–200 mg/kg LBP for 30 days significantly decreased blood glucose level and increased blood plasma insulin level. The hypoglycemic effects of LBPs are strongly related to their antioxidative effects. HD-induced insulin resistanceNrf2 is a master regulator for the expression of Phase II detoxifying enzymes such as HO-1, SOD, and CAT.113 Upon stimulation by oxidative stress, Nrf2 is translocated into the nucleus and induces the expression of antioxidant enzymes by binding antioxidant response element. JNK activation is a crucial mediator of ROS-induced insulin resistance.114 Suppression of JNK activation prevents insulin receptor substrate-1 (IRS-1) degradation and promotes insulin signaling and insulin-dependent glucose uptake. Yang et al110 investigated the mechanisms involved in LBP-mediated phosphatidylinositol 3-kinase (PI3K)/Akt/Nrf2 pathway against high-fat-induced insulin resistance in human hepatoma HepG2 cells and male C57BL/6J mice. HepG2 cells were incubated with LBPs for 12 hours in the presence of palmitate. C57BL/6J mice were fed an HD together with 100 mg/kg LBPs for 24 weeks. Liver glucokinase (GCK) and pyruvate kinase (PK) activities were monitored. The mRNA levels of GCK, PK, phosphoenolpyruvate carboxykinase (PEPCK), glucose 6-phosphatase (G6Pase), IL-6, TNF-α, and monocyte chemotactic protein 1 (MCP-1) were determined using quantitative real-time PCR. The protein expression levels of Nrf2 and phosphorylated (p)-Nrf2 at Ser40; HO-1, SOD, CAT, JNK, glycogen synthase kinase 3β (GSK3β), and p-GSK3β at Ser9; IRS-1, p-IRS-1 at Ser307; PI3K and p-PI3K at Tyr458/199; Akt and p-Akt at Ser473; and JNK and p-JNK at Thr183/Tyr were determined by Western blotting assay.110 The results showed that oral treatment with 100 mg/kg LBPs for 24 weeks lowered blood glucose and insulin concentrations and increased pyruvate concentration compared with high fat-fed mice. In the liver, LBPs increased hepatic GCK and PK mRNA levels but decreased liver PEPCK and G6Pase mRNA levels. LBPs treatment of mice significantly enhanced the phosphorylation of IRS-1, PI3K, and Akt in liver. In HepG2 cells, incubation of 100–600 µg/mL LBPs for 12 hours significantly promoted the phosphorylation of IRS-1, PI3K, and Akt. In in vivo experiment, administration of LBPs effectively inhibited the phosphorylation of JNK but increased the phosphorylation of GSK3β in the liver of high-fat diet-fed mice. LBPs also lowered the mRNA levels of liver MCP-1, IL-6, and TNF-α. In HepG2 cells, LBPs significantly increased the phosphorylation of GSK3β but reduced the phosphorylation of JNK. When HepG2 cells were pretreated with 10 µM LY294002 and 2 µM wortmannin (both PI3K/Akt inhibitors) for 2 hours, and then treated with 300 µg/mL LBPs for 12 hours, the inhibitor-induced p-JNK level was suppressed by LBPs, and inhibitor-suppressed p-GSK3β level was reversed by LBPs.110 LBPs regulated phosphorylation levels of GSK3β and JNK through PI3K/Akt signaling. In HepG2 cells, 300 µg/mL LBPs caused the nuclear translocation of p-Nrf2. LBPs significantly induced the phosphorylation of Nrf2 through PI3K/Akt signaling in vitro and in vivo.110 LBPs increased the expression of hepatic HO-1, SOD, and CAT and reduced intracellular ROS level via PI3K/Akt/Nrf2 axis in mice.110 These data indicate that LBPs significantly reversed glycolytic and gluconeogenic gene expression via the activation of Nrf2-mediated cytoprotective effects and that LBPs reverse insulin resistance induced by HD via activation of PI3K/Akt/Nrf2-mediated antioxidative pathway. Spontaneous diabetesSeveral spontaneous or genetically derived diabetic rat models are commonly used in pharmacological and pathological studies, including Zucker fatty rats, ZDF rats, SHR/N-cp rats, JCR/LA-cp rats, and Otsuka Long Evans Tokushima fatty (OLETF) rats.115 The OLETF rats show typical symptoms of T2DM, including hyperinsulinemia, hyperglycemia, insulin resistance, hypertriglycemia, and mild obesity. A recent study by Zhao et al109 further reported that LBPs improved insulin resistance via translocation and activation of GLUT4 in OLETF rats. The results showed that LBPs caused translocation of the GLUT4 to the cell surface, which in turn stimulated glucose uptake, and the effect was sensitive to wortmannin, an inhibitor of PI3K, and SB203580, an inhibitor of p38 mitogen-activated protein kinase (p38 MAPK).109 Furthermore, the effects of LBPs on p38 MAPK activities were abrogated by pretreatment of rat adipocytes using SB203580. LBPs improved insulin resistance via translocation and activation of GLUT4 in OLETF rats, and the activation of PI3K and p38 MAPK contributed to these effects.109 Clinical studyAmagase and Nance116 investigated the effect of GoChi consumption on caloric expenditure and changes in morphometric parameters (waist circumference) in healthy adults. Two separate randomized, double-blind, placebo-controlled, small clinical studies were conducted using GoChi and assessing its effects on resting metabolic rate and postprandial energy expenditure as measured by indirect calorimetry after single-bolus intake of three doses of GoChi (30 mL, 60 mL, and 120 mL) and placebo; and waist circumference and other morphometric changes in a 14-day intervention trial (120-mL daily intake) in the subjects (age =34 years, body mass index =29 kg/m2).116 A single bolus of GoChi intake increased postprandial energy expenditure 1–4 hours post-intake over the baseline level in a dose-dependent manner and was significantly higher than the placebo group by 10% at 1 hour post-intake of 120 mL. In a 14-day intervention trial, GoChi was found to significantly decrease waist circumference by 5.5±0.8 cm (n=15) compared with the preintervention measurements and placebo group at postintervention day 15.116 In contrast, the changes in the placebo group (n=14) from preinterventions was 0.9±0.8 cm, which was not statistically significant. These results show that GoChi consumption can increase metabolic rate and reduce the waist circumference. Summary of the hypoglycemic activities of LBPsLBPs significantly promote glucose uptake involving several signaling pathways in the liver and muscle (Figure 8). LBPs increase the content of GLUT4 and promote the translocation of GLUT4 from cytosol to cell membrane, enhancing glucose uptake in Wistar rats muscle. LBPs also increase the phosphorylation of PI3K/Akt/Nrf2 and repress the activation of JNK, promoting insulin-signaling pathway and insulin-dependent glucose uptake in C57BL/6J mice liver. Furthermore, LBPs activate PI3K- and p38MAPK-mediated signaling pathway, improving insulin sensitivity in rats. Moreover, consumption of GoChi, a standardized Goji juice containing 13.6 mg/mL LBPs, promotes caloric expenditure and reduces waist circumference in healthy subjects. Figure 8 
Possible mechanisms for the hypoglycemic effects of LBPs. Notes: LBPs significantly promote glucose uptake involving several signaling pathways in the liver and muscle. LBPs increase the content of GLUT4 and promote the translocation of GLUT4 from cytosol to cell membrane, enhancing glucose uptake in Wistar rats muscle. LBPs also increase the phosphorylation of PI3K/Akt/Nrf2 and repress the activation of JNK, promoting insulin-signaling pathway and insulin-dependent glucose uptake in C57BL/6J mice liver. Furthermore, LBPs activate PI3K- and p38MAPK-mediated signaling pathway, improving insulin sensitivity in rats. Moreover, consumption of GoChi, a standardized Goji juice containing 13.6 mg/mL LBPs promotes caloric expenditure and reduces waist circumference in healthy subjects. Abbreviations: LBPs, Lycium barbarum polysaccharides; JNK, Jun N-terminal kinases; Nrf2, nuclear factor erythroid 2-related factor; PI3K, phosphatidylinositol 3-kinase; p38 MAPK, p38 mitogen activated protein kinase; GLUT4, glucose transporter type-4; IRS-1, insulin receptor substrate-1; HO-1, heme oxygenase-1; SOD, superoxide dismutase; GSK3β, glycogen synthase kinase 3β. |