Enantioselective hydrolysis of 2-carboxyethyl-3-cyano-5-methylhexanoic acid (CNDE) is the key step in chemoenzymatic synthesis of pregabalin. We purified an intracellular carboxyl esterase from Morganella morganii ZJB-09203, which exhibited high enantioselectivity and activity towards CNDE. The carboxyl esterase was purified to electrophoretic homogeneity by ammonium sulfate fraction precipitation, Phenyl Sepharose 6 FF hydrophobic interaction chromatography, anion exchange with DEAE Sephadex A-50 and Bio-Scale CHT column. The purified enzyme was a monomer with molecular mass of 68 kDa determined by SDS-PAGE and gel chromatography. Substrate specificity of the enzyme towards p-nitrophenyl esters suggested that the purified enzyme was an esterase. The optimal reaction pH for CNDE hydrolysis was 9.0, and optimal temperature was 45 degrees C. The esterase was stable between pH 7.0 and 9.0, and at 40 degrees C. The enzyme activity was enhanced by Ca2+, Cu2+ and Mn2+, whereas strongly inhibited by Co2+, Fe3+, Ni2+ and EDTA. Meanwhile, we investigated the kinetic parameters of the esterase towards p-nitrophenyl esters and effect of CNDE concentration on conversion. The present study reported the esterase capable of stereospecific hydrolysis of CNDE for the first time. Our research will provide foundations for industrial production of Pregabalin using the new biocatalyst.
Chromatography, Gel ; Electrophoresis, Polyacrylamide Gel ; Esterases ; metabolism ; Hydrogen-Ion Concentration ; Kinetics ; Molecular Weight ; Morganella morganii ; enzymology ; Substrate Specificity ; Temperature

AIM To investigate whether the relaxation characteristics of phytoestrogens resveratrol and phloretin on contractile response of aortic strips are similar to that of estrogen and the mechanisms underground. METHODS Aortic strips from rabbits were suspended in organ baths containing Krebs solution, and then isometric tension was measured. RESULTS Resveratrol and phloretin inhibited the contractile responses to norepinephrine (NE), KCl and CaCl2, shifted their concentration-response curves rightward with pD2′ values of 2.89, 3.34, 3.37 for resveratrol and 3.23, 3.52, 3.77 for phloretin respectively. Also both of them concentration-dependently relaxed KCl-precontracted aortic strip. The relaxing response of resveratrol but not of phloretin in aortic strip was significantly reduced by removal of endothelium or incubation with Nω-L-nitro-arginine and methylthioninium chloride, however both their relaxant effects were not affected by indometacin and propranolol. In Ca2+-free Krebs solution containing 0.01 mmol·L-1 EGTA, resveratrol and phloretin inhibited NE-induced contraction which was caused by Ca2+ release from intracellular store, but did not affect the contraction which was induced by Ca2+ influx. CONCLUSION Resveratrol and phloretin can induce vasorelaxations which may relate to inhibition of Ca2+ influx through potential-dependent calcium channels and Ca2+ release from intracellular stores, and the relaxing response of resveratrol is endothelium-dependent in part, but of phloretin is not endothelium-dependent.

BACKGROUND: Cassia seed acts on decreasing blood pressure and blood lipid, protecting liver and inhibiting bacteria. It is worth to carry on a further discussion on its effect of weight loss.OBJECTIVE: To observe the influence of cassia seed decoction drunk naturally on body mass of nutritional obese rats in physiological state.DESIGN: Completely randomized grouping was designed, in which, control experiment, analysis of variance and q test were applied in comparison among groups.SETTING: Cardiovascular Institute, Second Affiliated Hospital, Henan University of Science and Technology.MATERIALS: The experiment was performed in Cardiovascular Instutute,Second Affiliated Hospital, Henan University of Science and Technology from March 2004 to September 2004, in which, 27 male SD rats were employed and randomized into 3 groups, named normal control group, model group and cassia seed group, 9 rats in each one.METHODS: [1] In normal control, the rats were bred with basic forage(the contents of protein, fat, carbohydrate were 18.2%, 4.5% and 55.2%successively, with 14.54 kJ caloric each gram) and drank water naturally.In model group, the rats were bred with high nutritive forage (the contents of protein, fat, carbohydrate were 23.7%, 21.6% and 39.0% successively,with 19.56 kJ caloric each gram) and drank water naturally. In cassia seed group, the rats were bred with high nutritive forage and drank cassia seed decoction of various concentration naturally. The concentration of cassia seed decoction started at 10 g/L (equally contained 10 mg raw cassia seed each milliliter) and was increased by 100% concentration each day (10 g/L)till to 60 g/L on the 6th day. Since the 7th day, the concentration of 60 g/L was maintained till to the 7th weekend. [2] It was to record appetite and drinking quantity at definite time every day and calculate absorbed caloric(intake mass × caloric contained each gram). It was to measure body mass at definite time each week. On the 7th weekend, the body length of rat was measured and Lee's index was calculated [ 3√body mass (g)×103/body length (cm)]MAIN OUTCOME MEASURES: Influences of cassia seed on body mass, Lee's index, appetite, caloric and drinking quantity in nutritional obese rats.RESULTS: Twenty-seven rats all entered result analysis. [1] Body mass:that in model group from the 3rd to 7th week in experiment group was higher remarkably than normal control group (P ＜ 0.05-0.01). That in cassia seed group from the 2nd to 7th week was lower remarkably than that in the model group (P ＜ 0.05-0.01). [2] Lee's index: that in model group and cassia seed group on the 7th week of experiment was higher remarkably than that in the normal control group [(358.60±8.55), (341.84±7.29), (322.00±6.89) g/cm, P ＜ 0.05-0.01] and that in cassia seed group was lower remarkably than that in the model group (P ＜ 0.05). [3] Appetite: that in model group and cassia seed group was lower remarkably than that in the normal control group (P ＜ 0.05-0.01) and that in cassia seed group was near to the control group (P ＞ 0.05). [4] Absorbed caloric: that in model group and cassia seed group was higher remarkably than that in the normal control group (P ＜ 0.05-0.01) and that in cassia seed group was near to the control group (P ＞ 0.05). [5] Drinking quantity: that in cassia seed group was basically near to that in the model group and the control group (P ＞ 0.05) and that in model group was near to the control group. It was indicated that cassia seed decoction at mass concentration of 60 g/L did not affect appetite.CONCLUSION: Cassia seed decoction at mass concentration of 60 g/L inhibits remarkably the increased body mass of nutritional obese rats and is free from influence on appetite.

BACKGROUND: Gastrodin (GAS) is widely used as adjuvant therapy for vertigo, headache and hypertension. However, it is recently noticed that GAS might be used as an agent for treating obesity.OBJECTIVE: To set up obese rats of high-fat diet to observe the effects of different concentrations of GAS on body mass and serum metabolite levels and to analyze its possible mechanism.DESIGN: A randomized and controlled animal experiment.SETTING: Institute of Physiology and Psychology, School of Basic Medical Science, Lanzhou University.MATERIALS: This study was performed at the Institute of Physiology and Psychology, School of Basic Medical Science, Lanzhou University and Gansu Provincial Key Laboratory of Pre-clinical Study for New Drugs from June to August in 2007. Forty-four healthy one-week-old male SD rats, weighing (99.57±2.13)g, were purchased from Shanghai SILAIKE Laboratory Animal Co., Ltd. Disposal of animals was in accordance with the animal ethics standards. Basic animal feed was provided by Suzhou Shuangshi Laboratory Animal Feed Science and Technology Co., Ltd. High-fat forage were self-made in the authors' laboratory. Each 100 gram of high-fat forage consisted of basic feed (57.5g), egg yolk powder (11.79g), lard (10g), pig bile salt (0.2g), casein (7g), milk power (13g), salt(0.085g), and yeast powder (0.425g), and the 100 gram of high-fat forage contained of fat (22.07g), protein (23.7g), carbohydrate (39g), and quantity of heat (472.16 calorie). GAS (98% in purity) was purchased from Shaanxi Xuhuang Botanical Science & Technology Development Co., Ltd. Malondialdehyde (MDA) and total antioxidative capability (T-AOC) kits were purchased from Jiancheng Bioengineering Institute, Nanjng, Jiangsu Province.MAIN OUTCOME MEASURES: The body mass was measured every seven days. The food intake in each group was monitored in every morning. At the end of the experiment, femoral artery blood samples were collected to determine the blood glucose, the serum levels of MDA, T-AOC, Insulin, free fatty acid (FFA), glutamate-pyruvate transaminase (GPT), glutamic oxalacetic transaminase (GOT) and blood lipid profile. Insulin resistance index (IRI) and insulin sensitivity index (ISI) were calculated as IRI=(FBG×FINS)/22.5 and ISI=1/(FINS×FBG).RESULTS: All 44 rats were included in the final analysis. Body mass: The body mass in the HFFC group was significantly higher than in the NC group from 4th-8th weeks (P＜0.01), while the body mass in GAS groups was lower compared to HFFC group (P＜0.05-0.01). There were no significant differences among the GAS-H, GAS-M, and GAS-L groups (P＞0.05). Therefore, GAS had no dose-dependent relationship in inhibiting the body mass of obese rats of high-fat diet. Caloric intake: The caloric intake was significantly higher in the HFFC group than in the NC group (P＜0.01), and was significantly decreased in GAS group compared to NFFC group from the 4th week (P＜0.05-0.01). Serum levels of MDA, T-AOC, GPT and GOT: The serum level of T-AOC was decreased and that of MDA, GPT were increased significantly in the HFFC group compared with NC group (P＜0.01, P＜0.05). In the GAS-L group, T-AOC, level was significantly increased and MDA level was significantly decreased compared to HFFC group (both P＜0.01). Levels of blood glucose and insulin: In the HFFC group, blood glucose level and IRI were significantly increased, and ISI was obviously decreased compared to NC group (P＜0.05-0.01). In the GAS-L group, blood glucose level and IRI were significantly decreased, and ISI was significantly increased compared to HFFC group (P＜0.05-0.01). FFA and lipoprotein cholesterol levels: In the HFFC group, FFA and low-density lipoprotein cholesterol levels were increased and high-density lipoprotein cholesterol level was decreased compared to NC group (P＜0.05-0.01).CONCLUSION: GAS may play an important role in inhibiting rats' body mass of high-fat diet. The mechanism of action may be related to GAS regulating the metabolism of blood glucose and FFA, improving IRI and elevating T-AOC.

BACKGROUND: Salvia miltiorrhiza is widely used to treat angina cordis, ischemic stroke and other ischemic cardiovascular diseases. However, the effects of Salvia miltiorrhiza on ovariectomized rats remain unclear.OBJECTIVE: To observe the effects of Salvia miltiorrhiza on the body mass, food intake, and levels of blood lipids and malondialdehyde (MDA) in ovariectomized rats.DESIGN: A completely randomized and controlled experiment.SETTING: Institute of Physiology and Psychology, School of Basic Medical Sciences, Lanzhou University.MATERIALS: The experiment was performed in the Key Laboratory of Pre-clinical Study for New Drugs of Gansu Province and the laboratory of Institute of Physiology and Psychology, School of Basic Medical Sciences, Lanzhou University from November 2005 to December 2006. Twenty-four healthy female SD rats of 3 months old and (220±2) g were selected. Salvia miltiorrhiza water decoction (equal to 1 g/mL crude drug) was identified and extracted by Drug Control Institute of Gansu Province; MDA kit was purchased from Nanjing Jiancheng Institute of Bioengineering.METHODS: ①The rats were randomly divided into three groups with 8 rats in each group: sham-operated group,ovariectomized group and Salvia miltiorrhiza group. The rats were underwent a bilateral ovariectomy except those in the sham-operated group, which were subjected to a removal of bilateral fat as much as ovariectomized group with the ovaries remained. Rats in sham-operated group and ovariectomized group freely drank water; rats in Salvia miltiorrhiza group freely took 1% water extracts from Salvia miltiorrhiza postoperatively, and the concentration of Salvia miltiorrhiza gradually increased to 12% on the eighth day, which was lasted until the end of the experiment (55 days). ②The food intake of rats in each group was monitored daily, and the body mass was measured every five days. At the end of the experiment, femoral artery blood samples of rats were collected to determine the levels of blood lipids. At the same time,MDA was measured according to the kit.MAIN OUTCOME MEASURES: The body mass, food intake, levels of blood lipids and malondialdehyde in each group.RESULTS: Twenty-four rats all entered the result analysis. ①The body mass of rats in 3 groups was nearly the same before operation (P ＞ 0.05). While the body mass in ovariectomized group on the postoperatively 10th, 20th, 25th, and 55th days was significantly higher than those in sham-operated group (P ＜ 0.01). The body mass in Salvia miltiorrhiza group on the postoperatively 20th, 25th, and 55th days was significantly lower than those in ovariectomized group (P ＜0.05-0.01). ②The food intake in ovariectomized group on the postoperatively 15th, 40th, and 55th days was significantly higher than those in sham-operated group (P ＜ 0.05-0.01), and that in Salvia miltiorrhiza group was significantly lower than those in ovariectomized group at those 3 time points (P ＜ 0.05-0.01). ③At the end of the experiment, the levels of total cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol and triglyceride in ovariectomized group were significantly higher than those in sham-operated group (P ＜ 0.05-0.01). The levels of triglyceride and MDA in Salvia miltiorrhiza group were significantly lower than those in ovariectomized group (P＜0.01, 0.05).CONCLUSION: Salvia miltiorrhiza can significantly reduce the body mass and levels of triglyceride and MDA in ovariectomized rats.

BACKGROUND: Ephedra, a Chinese medicine, is often used to treat obesity with relatively satisfying results recently. However, the effects of Ephedra on the perimenopausal and postmenopausal obese women remain unclear.OBJECTIVE: To observe the effects of oral Ephedra decoction on body mass and the levels of blood lipids, blood glucose and hormone in ovarietomized obese rats.DESIGN: A completely randomized and controlled experiment.SETTING: Institute of Physiology and Psychology, School of Basic Medical Sciences, Lanzhou University.MATERIALS: The experiment was performed in the Key Laboratory of Pre-clinical Study for New Drugs of Gansu Province and the Laboratory of Institute of Physiology and Psychology, School of Basic Medical Sciences,Lanzhou University from February 2006 to June 2006. Forty-four healthy female SD rats were randomly divided into four groups with 11 rats in each group, namely sham-operated group, ovariectomized group, estrogen replacement therapy group and Ephedra group.METHODS: ① After having been narcotized by cloraminone (110 mg/kg),rats were underwent a bilateral ovariectomy except those in the sham-operated group, which were also operated, but their ovaries were not cut off. ②Rats in the sham-operated group and ovariectomized group were subcutaneously injected with sesame oil (0.2 mL/each rat) every day postoperatively till the end of the experiment. ③ The rats in the estrogen replacement therapy group were given estradiol (1 mg/kg) by subcutaneous injection every day postoperatively till the end of the experiment. ④ The rats in the Ephedra group freely drank 1% water extracts from Ephedra postoperatively, later the concentration of Ephedra gradually increased to 8% on the sixth day, which lasted until the end of the experiment. ⑤ The food intake was monitored daily, and body mass was measured every ten days. ⑥ At the end of the experiment, all the rats were fasted for 12 hours and collected blood samples for the measurement of serum indexes. The body mass and body length were measured to calculate the Lee's index [(g)×103/body length (cm)] at the same time.MAIN OUTCOME MEASURES: ① Body mass and Lee's index at different time points in each group. ② Food intake at different time points in each group. ③ Levels of blood lipids and blood glucose in each group. ④Levels of estrogen, progesterone and insulin in each group.RESULTS: Forty-four rats all entered the analysis of results. ① Result of body mass and Lee's index at different time points: The body masses on the 20th, 30th, 40th and 50th days in the ovariectomized group were (256.4±14.3),(271.3±16.1), (276.4±12.7), (285.7±24.2) g, which were significantly higher than those in the sham-operated group [(226.5±11.5), (241.8±12.6),(243.1±13.5), (251.1±22.4) g, P ＜ 0.05-0.01], and the Lee's index in the ovariectomized group was greater than that in the sham-operated group(317.2±13.5, 280.4±11.2, P ＜ 0.01). The body masses on the 40th and 50th days in the estrogen replacement therapy group were (243.7±14.8) and(246.2±11.9) g, which were significantly lower than those in the ovariectomized group (P ＜ 0.05-0.01), and the Lee's index (289.9±13.5) was lower than that in the ovariectomized group (P ＜ 0.01). The body masses on the 40th and 50th days in the Ephedra group were (245.4 ±14.1) and(252.4±14.9) g, and the Lee's index was 294.4±11.0, which were all lower than those in the ovariectomized group (P ＜ 0.05). ② Result of Food in take at different time points: The food intakes on the 30th, 40th and 50th days in the Ephedra group were (17.8±2.4), (22.3±3.9), (26.1±3.5) g per day,which were decreased as compared with those in the ovariectomized group[(25.9±4.7), (28.5±5.3), (32.8±5.5) g per day, P ＜ 0.05]. ③ Levels of blood lipids and blood glucose: The levels of triglyceride, cholesterol and low density lipoprotein cholesterol (LDL-C) in the ovariectomized group were (1.73±0.32), (1.45±0.50), (0.78±0.19) mmol/L, which were higher than those in the sham-operated group [(0.94±0.29), (1.05±0.30), (0.08±0.11) mmol/L, P ＜ 0.01]. After the estrogen replacement therapy, the levels of triglyceride, cholesterol, LDL-C and blood glucose were (1.10±0.34),(1.14±0.30), (0.17±0.05), (5.88±1.21) mmol/L, which were lower than those in the ovariectomized group (P ＜ 0.05-0.01), but the level of high density lipoprotein cholesterol (HDL-C) was higher than that in the ovariectomized group [(1.11±0.31), (0.88±0.21) mmol/L, P ＜ 0.05]. The levels of triglyceride, cholesterol, LDL-C and HDL-C in the Ephedra group were (0.97±0.16), (1.11±0.20), (0.59±0.07) and (0.45±0.061) mmol/L, which were lower than those in the ovariectomized group (P ＜ 0.05-0.01). ④ The serum levels of estrogen, progesterone and insulin in each group: The serum levels of estrogen and progesterone in the ovariectomized group were lower than those in the sham-operated group [(17.09±9.00), (28.51 ±7.99) μg/L;(58.69±12.11), (62.73±10.93) μg/L, P ＜ 0.01], the serum level of insulin was higher than that in the sham-operated group [(31.74±6.69),(23.75±6.66) mU/L, P ＜ 0.01]. The serum levels of estrogen in the estro gen replacement therapy and Ephedra group were (36.03±8.83) and (30.18±8.61) ng/L, which were higher than those in the ovariectomized group(P ＜ 0.05-0.01), the level of insulin were (21.34±4.57), (24.86±6.20) mU/L,which were lower than those in the ovariectomized group (P ＜ 0.05-0.01).The serum level of progesterone in the Ephedra group [(17.68±6.19) μg/L]was lower than that in the ovariectomized group (P ＜ 0.01).CONCLUSION: Ephedra can promote loss of body mass, reduce levels of the blood lipids and insulin, and increase the serum levels of hormones in ovariectomized obese rats.

BACKGROUND: Ramulus Uncariae et Uncus can be used to treat many diseases of cardiovesculer and neurosystem by calming and protecting endothelium and neuron.OBJECTIVE: To study the effects of drinking water extracts of Ramulus Uncariae et Uncus on body mass, food intake, energy intakes, serum glucose, insulin, total antioxidative ability of high-fat-fed rats.DESIGN: A completely randomized and controlled experiment.SETTING: Institute of Physiology, Foundational Medical College of Lanzhou University.MATERIALS: The experiment which is Gansu Province Key Labor of Pre-clinical Research for Chinese Herbs & New Drugs was carried out at the Physiological Laboratory of Institute of Foundational Medical College of Lanzhou University from March 2003 to May 2003. Twenty-seven healthy male SD rats were randomly divided into the following three groups (9 rats each group): namely, the normal control group, the high-fat-fed group and the Ramulus Uncariae et Uncus group.METHODS: [1] The rats of control group were fed with referenced diets(Protein, fat and carbohydrate was made up fore18.2%, 4.5%, 55.2% respectively), while the rats of high-fat-fed and the Ramulus Uncariae et Uncus group were fed with high-fat diets in which protein, fat and carbohydrate accounted for 23.7%, 21.6%, 39.0% respectively. [2]The rats in control and high-fat group could drink water freely every day while the rats in Ramulus Uncariae et Uncus group drank freely one percent water extract of Ramulus Uncariae et Uncus at the first day of the experiment, later the concentration of Ramulus Uncariae et Uncus increased gradually to six percent at the sixth day, which lasted until the end of the experiment. [3]Food intake was monitored daily, and body mass weekly at set time, the energy intake was calculated on basis of food intake. We calculated the Lee's Index [(body mass)1/3 (g) × 103 / body length (cm)]. [4] At the end of the seventh week, all rats were fasted for twelve hours to collect blood for the measure of some serum items. The serum levels of glucose were determined with hexokinase. The levels of insulin was measured by Radioimmunology methods. Malondiadehyde was measured by thiobarbituricbased colorimetric assay. Total antioxidative ability and free fatty acid were evaluated by colorimetric assay. [5] The difference of quantity data among the tree groups were statistically analyzed by F analysis, while the difference between two groups was analyzed by LSD methods. The main indexes of the experiment were body mass, food intake, energy intake, serum glucose after fasting, insulin, free fatty acid, malondialdehyde and total antioxidative ability respectively.RESULTS: Twenty-seven rats date was analyzed and nine rats in every group. [1] Body mass: Compared with the high-fat-fed group, body mass in rats of the control group and the Ramulus Uncariae et Uncus group were less from the end of the third week to the end of the experiment (P ＜ 0.05-0.01).As compared between the Ramulus Uncariae et Uncus group and the control group, there was no significant difference from the first week to the sixth week (P ＞ 0.05), while the body mass of the former group was bigger than that of the latter at the end of the seventh week (P ＜ 0.01). [2] Lee's Index of the rats in high-fat-fed group was significantly higher than those of the rats in the control and Ramulus Uncariae et Uncus group (P ＜ 0.01).[3] Food intake: From the first week, compared with the control group, the food intake of rats in Ramulus Uncariae et Uncus group was less (P ＜ 0.01)and lower than that in high-fat-fed group at the end of the third, fifth, sixth and seventh week, too (P ＜ 0.05-0.01). [4] Energy intake: As the food was high-fat, the Energy intake of rats in the Ramulus Uncariae et Uncus group was higher than that of the control group at the end of the first, second and forth week (P ＜ 0.05-0.01), while less than that of the high-fat-fed group at the end of the third, fifth, sixth and seventh week (P ＜ 0.01). [5] The serum glucose: There was no statistical significance among the three groups. [6]The level of serum insulin and malondiadehyde of the rats in high-fat-fed group were higher than that of the control group and the Ramulus Uncariae et Uncus (P ＜ 0.01). [7] The level of free fatly acid of rats in high-fat-fed group was higher than that of the control group (P ＜ 0.05), while there wasno statistical difference compared with the Ramulus Uncariae et Uncus group. [8] The level of total antioxidative of the rats in high-fat group was lower than that of the Ramulus Uncariae et Uncus group (P ＜ 0.01).CONCLUSION: [1] Drinking water extracts of Ramulus Uncariae et Uncus could inhibit the weight gain and food intake, [2] reduce level of free radical and insulin of serum, which could be caused by the dec lining of free fatty acid. [3] In the same time, increase the total antioxidative ability of the obese rats caused by high-fat diets.

ObjectiveTo study effects of gastrodine (GAS) on insulinoma (INS-1) cells and the protection of INS-1 ceils from steptozotocin (STZ) injury by gaatrodine. MethodsThe experiment was carried out in 5 groups: normal control group ( NC), GAS group (GAS), streptozotocin group (STZ), GAS protection group ( GAS +STZ) and GAS repair group (STZ +GAS). INS-1 cells were cultured, the cell viability was determined by tetrazolium (MTT) assay, insulin concentration was detected by radioimmunoassay, and malondialdehyde (MDA)concentration and total antioxidant capacity (T-AOC) of the culture medium were measured by colorimetry. Results GAS promoted insulin release of INS-1 cells (P＜0.05, P＜O.01). Low-concentration GAS could increase viability of INS-1 cells ( P ＜ 0.01 ). GAS could increase viability of the injured INS-1 cells (P ＜ 0.01 ). High concentration GAS contributed in repair of INS-1 cells injured by STZ and promoted insulin serection ( P ＜ 0.01 ). GAScould decrease MDA concentration (P ＜0.01 ) and significantly increase T-AOC capacity of INS-1 cells injured by STZ (P ＜0.01 ). ConclusionsGAS can increase INS-1 viability, promote insulin secretion of INS-1 cells, alleviate INS-1 cells injury caused by STZ, and strengthen the antioxidant capacity of INS-1 cells injured by STZ.