Antiglycation effect of gliclazide on in vitro AGE formation from glucose and methylglyoxal

Gliclazide, a sulfonylurea widely used for treatment of diabetes mellitus, is known to scavenge reactive oxygen species. To clarify whether its antioxidative ability interferes with the glycation processes, we incubated bovine serum albumin (BSA) with 1 M glucose or 1 mM methylglyoxal, in the presence or absence of gliclazide, and observed the formation of advanced glycation end products (AGEs). AGE production was assessed by AGE-specific fluorescence, an enzyme-linked immunosorbent assay (ELISA), and Western blotting. The fluorescence at excitation/emission wavelengths of 320/383 nm and 335/385 nm was definitely increased by incubating BSA with 1 M glucose or 1 mM methylglyoxal, and 1 mM gliclazide significantly blunted the fluorescent augmentation, in both wavelengths, in a dose-dependent fashion. Gliclazide almost equaled to aminoguanidine, a putative antiglycation agent, in the inhibitory effect on the glucose-induced fluorescence, while the methylglyoxal-derived fluorescent formation was less suppressed by gliclazide than by aminoguanidine. The AGE concentrations determined by ELISA showed similar results. Incubation of BSA with 1 M glucose or 1 mM methylglyoxal yielded an apparent increase in carboxymethyllysine or argpyrimidine. Both AGEs were significantly lowered by 1 mM gliclazide and a reduction of glucose-derived carboxymethyllysine was comparable to that caused by aminoguanidine. The results of Western blotting supported the findings in ELISA. To our knowledge, the present study provides the first evidence of the antiglycation effect of gliclazide on in vitro AGE formation from glucose and methylglyoxal.     

Antioxidative and anti-diabetic effects of amaranth (Amaranthus esculantus) in streptozotocin-induced diabetic rats

The anti-diabetic and antioxidative effect of amaranth grain (AG) and its oil fraction (AO) was studied in streptozotocin-induced diabetic rats. Male Sprague-Dawley rats were divided into four groups after induction of STZ-diabetes: normal control; diabetic control; diabetic-AG supplement (500 g kg(-1) diet); diabetic-AO supplement (100 g kg(-1) diet) and fed experimental diets for 3 weeks. Serum glucose, insulin, activities of serum marker enzymes of liver function and liver cytosolic antioxidant enzymes were measured. The AG and AO supplement significantly decreased the serum glucose and increased serum insulin level in diabetic rats. Serum concentration of liver function marker enzymes, GOT and GPT, were also normalized by AG and AO treatment in diabetic rats. Liver cytosolic SOD and GSH-reductase activities were significantly increased, and catalase, peroxidase and GSH-Px activities were decreased in diabetic rats. AG and AO supplement reverted the antioxidant enzyme activities to near normal values. Hepatic lipid peroxide product was significantly higher, and GSH content was decreased in diabetic rats. However, AG and AO supplement normalized these values. Our data suggest that AG and AO supplement, as an antioxidant therapy, may be beneficial for correcting hyperglycaemia and preventing diabetic complications.     

Effects of aminoguanidine Schiff's base on biomarkers of the oxidative stress, 4-hydroxy-2-nonenal and conjugated dienes,in the model diabetes mellitus

Diabetes mellitus evoked by streptozotocine in rats is associated with the oxidative stress. We examined the effect of Schiff's base 2,5-dihydroxybenzaldehyde with a well-known antidiabetic drug aminoguanidine, 2,5-dihydroxybenzilideneaminoguanidine (BAG) on the production of markers of oxidative stress such as 4-hydroxy-2-nonenal (4HNE) and conjugated dienes in diabetic rats. BAG administration did not affect glucose level in diabetic rats but significantly decreased the production of 4HNE and conjugated dienes. On the other hand, BAG caused the elevation of conjugated dienes and an insignificant increase of 4HNE levels in the control animals.     

Aminoguanidine pyridoxal adduct is superior to aminoguanidine for preventing diabetic nephropathy in mice.

Aminoguanidine inhibits the formation of advanced glycation end-products, and has been extensively examined in animals. However, administration of aminoguanidine decreases the hepatic content of pyridoxal phosphate. In order to avoid this problem, we developed an aminoguanidine pyridoxal Schiff base adduct and examined its efficacy in vitro as well as in a model of diabetic nephropathy. Mice with streptozotocin-induced diabetes were treated with aminoguanidine or aminoguanidine pyridoxal adduct for 9 weeks. An in vitro study was also performed to assess the antioxidant activity of aminoguanidine and its pyridoxal adduct. Neither drug altered glycemic control. Aminoguanidine pyridoxal adduct significantly improved urinary albumin excretion by 78.1 % compared with the diabetic control, and also had a better preventive effect on the progression of renal pathology than aminoguanidine did. Inhibition of glycation by both drugs was similar, but the antioxidant activity of the pyridoxal adduct was far superior. These findings suggest that aminoguanidine pyridoxal adduct may be superior to aminoguanidine, as it not only prevents vitamin B6 deficiency but is also better at controlling diabetic nephropathy, as this adduct inhibits oxidation as well as glycation.     

Protective effect of aminoguanidine against oxidative stress and bladder injury in cyclophosphamide‐induced hemorrhagic cystitis in rat

Cyclophosphamide (CP) is an antineoplastic agent that is used for the treatment of many neoplastic diseases. Hemorrhagic cystitis (HC) is a major dose limiting side effect of CP. Recent studies show that aminogaunidine, an inhibitor of inducible nitric oxide synthase is a potent antioxidant and prevents changes caused by oxidative stress such as depletion of antioxidant activity and tissue injury. The purpose of the study is to investigate the effect of aminoguanidine on parameters of oxidative stress, antioxidant enzymes and bladder injury caused by CP. Adult male rats were randomly divided into four groups. Control rats were administered saline; the AG control group received 200 mg/kg body wt of aminoguanidine; The CP group received a single injection of CP at the dose of 150 mg/kg body wt intraperitoneally. The CP + AG group received aminoguanidine (200 mg/kg body wt) intraperitoneally 1 h before the administration of CP. The rats were sacrificed 16 h after CP/saline administration. The bladder was used for light microscopic studies and biochemical studies. The markers of oxidative damage including protein carbonyl content, protein thiol, malondialdehyde and conjugated dienes were assayed in the homogenates along with the activities of the antioxidant enzymes, superoxide dismutase, glutathione peroxidase, catalase, and glutathione reductase and glutathione S transferase. In the bladders of CP treated rats edema of lamina propria with epithelial and sub‐epithelial hemorrhage was seen. All the parameters of oxidative stress that were studied were significantly elevated in the bladders of CP treated rats. The activities of the antioxidant enzymes were significantly lowered in the bladders of CP treated rats. Aminoguanidine pretreatment prevented CP‐induced oxidative stress, decrease in the activities of anti‐oxidant enzymes and reduced bladder damage. The results of the present study suggest the antioxidant role for aminoguanidine in CP‐induced bladder damage. Copyright © 2008 John Wiley & Sons, Ltd.     

Detection of 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal after gavage of trans-4-hydroxy-2-nonenal or induction of lipid peroxidation with carbon tetrachloride in F344 rats

The 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal (HNE-dGp-adducts) were quantitated in tissues of rats treated with trans-4-hydroxy-2-nonenal (HNE) or carbon tetrachloride, respectively, using a 32P-postlabeling method. The method development was based on chemically synthesized HNE-1,N2-propanodeoxyguanosine adduct standard, which was characterized by NMR and mass spectra. The adducts were enriched by Nuclease P1. They were subsequently reacted with gamma-32P-ATP to give the respective 3'-5'-bisphosphates, which were two-directionally separated on PEI-cellulose-TLC and quantitated by autoradiography. The labeling efficiency for the adduct standard was 27%, and the recovery of spiked amounts of adduct standard in the enzymatical procedure was about 80%. Internal standard was used to eliminate methodological variations. The determination of the limit of quantitation in DNA from rat tissues by spiking of HNE-dGp-adduct standard revealed a sensitivity of about 20 HNE-dGp-adducts/10(9) normal nucleotides. Background levels of HNE-dGp-adducts in tissues of rats including liver, kidney, lung, colon and forestomach were found in the range of 18-158 adducts/10(9) nucleotides with relatively high adduct levels in the liver and low adduct levels in kidney, lung and colon. These background levels were statistically significantly increased by the factor of 2 in liver, lung, colon and forestomach after induction of lipid peroxidation by carbon tetrachloride. The finding that background HNE-dGp-adduct levels may be in context with different metabolic activities of the tissues and the increase of HNE-dGp-adduct levels after application of carbon tetrachloride indicate that HNE-dGp-adducts are an endogenous lesion and that they are probably formed from radical initiated lipid peroxidation.     

Trigonelline and curcumin alone,but not in combination,counteract oxidative stress and inflammation and increase glycation product detoxification in the liver and kidney of mice with high-fat diet-induced obesity

The development of obesity-associated complications is related to various pathogenic events including chronic inflammation, oxidative stress and generation of advanced glycation end products (AGEs). Due to their antioxidant, anti-inflammatory and antiglycation properties, trigonelline and curcumin are interesting candidates to counteract complications of obesity and diabetes mellitus. The current study aimed to investigate the effects of treatment with curcumin or trigonelline mixed into yoghurt, alone or in combination, on mice fed high-fat diet (HFD); the focus was mainly on the potential of these phytochemicals to counteract oxidative and glycative stress. Yoghurt alone improved glucose tolerance and reduced proinflammatory cytokine levels in HFD mice; however, it did not affect the antioxidant status. Trigonelline-enriched yoghurt prevented fat accumulation in adipose tissue, improved both insulin sensitivity and glucose tolerance and exerted anti-inflammatory and antiglycation activities (reduced AGEs and AGE receptor levels and increased the levels of components related to AGE detoxification) in liver and kidney of HFD mice. Curcumin-enriched yoghurt exerted anti-inflammatory and potent antioxidant properties (increased antioxidant enzyme activities and decreased lipid peroxidation) in liver and kidney of HFD mice. However, several beneficial effects were nullified when trigonelline and curcumin were administered in combination. Trigonelline and curcumin have emerged as promising complementary therapy candidates for liver and kidney complications associated with obesity. However, the administration of these phytochemicals in combination, at least in HFD mice, was not effective; inhibition of biotransformation processes and/or the reaching of toxic doses during combined treatment may be prevailing over the individual pharmacodynamic actions of these phytochemicals.     

Lipoic acid decreases lipid peroxidation and protein glycosylation and increases (Na(+) + K(+))- and Ca(++)-ATPase activities in high glucose-treated human erythrocytes

Lipoic acid supplementation has been found to be beneficial in preventing neurovascular abnormalities in diabetic neuropathy. Insufficient (Na(+) + K(+))-ATPase activity has been suggested as a contributing factor in the development of diabetic neuropathy. This study was undertaken to test the hypothesis that lipoic acid reduces lipid peroxidation and glycosylation and can increase the (Na(+) + K(+))- and Ca(++)-ATPase activities in high glucose-exposed red blood cells (RBC). Washed normal human RBC were treated with normal (6 mM) and high glucose concentrations (45 mM) with 0-0.2 mM lipoic acid (mixture of S and R sterioisomers) in a shaking water bath at 37 degrees C for 24 h. There was a significant stimulation of glucose consumption by RBC in the presence of lipoic acid both in normal and high glucose-treated RBC. Lipoic acid significantly lowered the level of glycated hemoglobin (GHb) and lipid peroxidation in RBC exposed to high glucose concentrations. High glucose treatment significantly lowered the activities of (Na(+) + K(+))- and Ca(++)-ATPases of RBC membranes. Lipoic acid addition significantly blocked the reduction in activities of (Na(+) + K(+))- and Ca(++)-ATPases in high glucose- treated RBC. There were no differences in lipid peroxidation, GHb and (Na(+) + K(+))- and Ca(++)-ATPase activity levels in normal glucose-treated RBC with and without lipoic acid. Thus, lipoic acid can lower lipid peroxidation and protein glycosylation, and increase (Na(+) + K(+))- and Ca(++)-ATPase activities in high-glucose exposed RBC, which provides a potential mechanism by which lipoic acid may delay or inhibit the development of neuropathy in diabetes.     

Antihyperglycemic activity of Woodfordia fruticosa (Kurz) flowers extracts in glucose metabolism and lipid peroxidation in streptozotocin-induced diabetic rats

The ethanolic extract of W. fruticosa flowers (250 and 500 mg/kg) significantly reduced fasting blood glucose level and increased insulin level after 21 days treatment in streptozotocin diabetic rats. The extract also increased catalase, superoxide dismutase, glutathione reductase, glutathione peroxidase activities significantly and reduced lipid peroxidation. Glycolytic enzymes showed a significant increase in their levels while a significant decrease was observed in the levels of the gluconeogenic enzymes in ethanolic extract treated diabetic rats. The extract has a favourable effect on the histopathological changes of the pancreatic beta-cells in streptozotocin induced diabetic rats. The results suggest that W. fruticosa possess potential antihyperglycemic effect by regulating glucose homeostasis and antioxidant efficacy in streptozotocin-induced diabetic rats.     

Antioxidant activity of a Schiff base of pyridoxal and aminoguanidine

We recently reported that PL-AG, a Schiff base of pyridoxal and aminoguanidine, was more effective than aminoguanidine (AG), a well-known anti-diabetic-complication compound, in preventing nephropathy in diabetic mice and presented brief data indicating the antioxidant activity of the adduct. In the present study, we additionally investigated the inhibitory activity of PL-AG in comparison with that of AG against in vitro and in vivo oxidation. PL-AG was more potent than AG and reference compounds such as pyridoxal and pyridoxamine in any of the five antioxidant activities examined in vitro, i.e., hydrogen peroxide-scavenging, hydroxyl radical-scavenging, superoxide radical-scavenging, ascorbic acid-autoxidation inhibitory, and low-density lipoprotein (LDL)-oxidation inhibitory activities, the last two of which were assessed in the presence of Cu(2+). Unlike AG, PL-AG did not show the pro-oxidant activity. The inhibitory activity of PL-AG against lipid peroxidation in diabetic rats was higher than that of AG, for example, the amounts of malondialdehyde in erythrocytes (nmol/g hemoglobin; mean +/- SD) in normal, untreated diabetic, AG-treated diabetic, and PL-AG-treated diabetic rats were 3.53 +/- 0.35, 4.99 +/- 0.23, 4.65 +/- 0.45, and 4.06 +/- 0.35, respectively. A fluorescent substance different from PL-AG was found in the plasma and urine of rats treated with PL-AG. The chemical structure of this substance, i.e., oxidized PL-AG, was determined by a combination of nuclear magnetic resonance, mass, and infrared spectrometry. AG dramatically decreased the pyridoxal phosphate level in the diabetic rat liver, whereas PL-AG only moderately affected it. Our results indicate that the antioxidant activity of PL-AG is due to its chelation with transition metal ions and to scavenging of reactive oxygen species. They also suggest that PL-AG is more promising for the treatment of diabetic complications than AG.     

The botanical extracts of Achyrocline satureoides and Ilex paraguariensis prevent methylglyoxal-induced inhibition of plasminogen and antithrombin III

Endogenously produced dicarbonyls, such as methylglyoxal (MG), are involved in advanced glycation end-product formation and thus linked to the pathophysiology of diabetic chronic complications. While the search for synthetic new antiglycation agents continues, little attention has been paid to putative antiglycation agents in natural compounds. Given the link between glycation and oxidation, in this work, we study the effects of methylglyoxal on two model systems; plasminogen and antithrombin III (AT III), then we set out to unravel a possible antiglycation effect for extracts of the flavonoid-rich common herbal species Achyrocline satureoides (AS) and Ilex paraguariensis (IP). Using SAR-PRO-ARG-pNA as a specific thrombin substrate, we show that incubation of plasma with MG decreases heparin activation of AT III by up to a 70%, in a dose-dependent manner. A parallel dose-dependent decrease in plasminogen activity reaching more than 50% was shown using D-BUT-CHT-lys-pNA as a plasmin-specific substrate. Extracts of AS and IP display a dose dependent inhibition of the action of the dicarbonyl, already significant at a 1/100 dilution of the herbal infusions. The inhibition was comparable to that obtained by using millimolar concentrations of known AGE inhibitors such as aminoguanidine and carnosine as well as micromolar concentrations of the antioxidant ascorbic acid. We believe our system of whole plasma glycation over 16 h with micromolar concentrations of MG, coupled with the measurement of activities of plasminogen and AT III by specific substrates provides a straightforward, practical method for monitoring the action of putative antiglycation agents. If predictably milder glycated forms of AT III and plasminogen were to be secreted in vivo, the loss of activities shown here could act synergistically to generate hyperthrombicity.     

A novel insulin-releasing substance, phanoside, from the plant Gynostemma pentaphyllum

Extracts from Gynostemma pentaphyllum Makino (Cucurbitaceae), a Southeast Asian herb, has been reported to affect numerous activities resulting in antitumor, cholesterol-lowering, immunopotentiating, antioxidant, and hypoglycemic effects. We have isolated one active compound by ethanol extraction, distribution in n-butyl alcohol/water, solid phase extraction/separation, and several rounds of reverse phase high pressure liquid chromatography. We have shown by NMR and mass spectrometry that this active compound is a novel saponin, a gypenoside, which we have named phanoside (21-,23-epoxy-,3beta-,20-,21-trihydroxydammar-24-ene-3-O-([alpha-d-rhamnopyranosyl(1-->2)]-[beta-d-glycopyranosyl(1-->3)]-beta-d-lyxopyranoside)), with a molecular mass of 914.5 Da. Phanoside is a dammarane-type saponin, and four stereoisomers differing in configurations at positions 21 and 23 were identified, each of which were found to stimulate insulin release from isolated rat pancreatic islets. We have also found that the stereoisomers are interconvertible. Dose-dependent insulin-releasing activities at 3.3 and 16.7 mM glucose levels were determined for the racemic mixture containing all four stereoisomers. Phanoside at 500 microM stimulates insulin release in vitro 10-fold at 3.3 mM glucose and potentiates the release almost 4-fold at 16.7 mM glucose. At these glucose levels, 2 microm glibenclamide stimulates insulin release only 2-fold. Interestingly, beta-cell sensitivity to phanoside is higher at 16.7 mM than at 3.3 mM glucose, although insulin responses were significantly increased by phanoside below 125 microM only at high glucose levels. Also when given orally to rats, phanoside (40 and 80 mg/ml) improved glucose tolerance and enhanced plasma insulin levels at hyperglycemia.     

Oxidative stress in streptozotocin-induced diabetic rats: effects of garlic oil and melatonin

In the present study, oxidative stress in diabetic model and the effect of garlic oil or melatonin treatment were examined. Streptozotocin (60 mg/kg body weight, i.p.)-induced diabetic rats, showed a significant increase of plasma glucose, total lipids, triglyceride, cholesterol, lipid peroxides, nitric oxide and uric acid. Concomitantly, significant decreases in the levels of antioxidants ceruloplasmin, albumin and total thiols were found in the plasma of diabetic rats. Lipid peroxide levels were significantly increased in erythrocyte lysate and in homogenates of liver and kidney, while superoxide dismutase (SOD) activities were decreased in tissue homogenates of liver and kidney. Treatment of diabetic rats with garlic oil (10 mg/kg i.p.) or melatonin (200 microg/kg i.p.) for 15 days significantly increased plasma levels of total thiol, ceruloplasmin activities, albumin. Lipid peroxides, uric acid, blood glucose, total lipid, triglyceride and cholesterol were decreased significantly after treatment with garlic oil or melatonin. Nitric oxide levels were decreased significantly in rats treated with melatonin only. In erythrocytes lysate, glutathione S-transferase (GST) activities were increased significantly in rats treated with garlic oil or melatonin, while lipid peroxides decreased significantly and total thiol increased significantly in melatonin or garlic oil treatment, respectively. In liver homogenates of rats treated with garlic or melatonin, lipid peroxides were decreased significantly, and GST activities increased significantly, while SOD activities were increased significantly in liver and kidney after garlic or melatonin treatment. The results suggest that garlic oil or melatonin may effectively normalize the impaired antioxidants status in streptozotocin induced-diabetes. The effects of these antioxidants of both agents may be useful in delaying the complicated effects of diabetes as retinopathy, nephropathy and neuropathy due to imbalance between free radicals and antioxidant systems. Moreover, melatonin may be more powerful free radical scavenger than garlic oil.     

Efficacy of lower doses of vanadium in restoring altered glucose metabolism and antioxidant status in diabetic rat lenses

Vanadium compounds are potent in controlling elevated blood glucose levels in experimentally induced diabetes. However the toxicity associated with vanadium limits its role as therapeutic agent for diabetic treatment. A vanadium compound sodium orthovanadate (SOV) was given to alloxan-induced diabetic Wistar rats in lower doses in combination withTrigonella foenum graecum, a well-known hypoglycemic agent used in traditional Indian medicines. The effect of this combination was studied on lens morphology and glucose metabolism in diabetic rats. Lens, an insulin-independent tissue, was found severely affected in diabetes showing visual signs of cataract. Alterations in the activities of glucose metabolizing enzymes (hexokinase, aldose reductase, sorbitol dehydrogenase, glucose-6-phosphate dehydrogenase) and antioxidant enzymes (glutathione peroxidase, glutathione reductase) besides the levels of related metabolites, [sorbitol, fructose, glucose, thiobarbituric acid reactive species (TBARS) and reduced glutathione (GSH)]were observed in the lenses from diabetic rats and diabetic rats treated with insulin (2 IU/day), SOV (0.6 mg/ml),T. f. graecum seed powder (TSP, 5%) and TSP (5%) in combination with lowered dose of vanadium SOV (0.2 mg/ml), for a period of 3 weeks. The activity of the enzymes, hexokinase, aldose reductase and sorbitol dehydrogenase was significantly increased whereas the activity of glucose-6-phosphate dehydrogenase, glutathione peroxidase and glutathione reductase decreased significantly in lenses from 3 week diabetic rats. Significant increase in accumulation of metabolites, sorbitol, fructose, glucose was found in diabetic lenses. TBARS measure of peroxidation increased whereas the levels of antioxidant GSH decreased significantly in diabetic condition. Insulin restored the levels of altered enzyme activities and metabolites almost to control levels. Sodium orthovanadate (0.6 mg/ml) andTrigonella administered separately to diabetic animals could partially reverse the diabetic changes, metabolic and morphological, while vanadate in lowered dose in combination withTrigonella was found to be the most effective in restoring the altered lens metabolism and morphological appearance in diabetes. It may be concluded that vanadate at lowered doses administered in combination withTrigonella was the most effective in controlling the altered glucose metabolism and antioxidant status in diabetic lenses, these being significant factors involved in the development of diabetic complications, that reflects in the reduced lens opacity     

Evaluation of the anti-atherogenic potential of chrysin in Wistar rats

Hypercholesterolemia is one of the major risk factors that precipitate coronary heart disease and atherosclerosis. Oxidative stress is believed to contribute to the pathogenesis of hypercholesterolemic atherosclerosis; hence, various antioxidant compounds are being evaluated for potential anti-atherogenic effects. In the present study, the putative anti-atherogenic and antioxidant efficacy of a flavonoid, chrysin, was evaluated in an experimental model of atherosclerosis. In male, albino Wistar rats fed an atherogenic diet for 45 days and treated with saline, significantly higher mean levels of serum lipid profile parameters (total cholesterol, triglycerides, low-density, and very low-density lipoprotein cholesterol), lower mean levels of high-density lipoprotein cholesterol and higher mean serum levels of hepatic marker enzymes (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and lactate dehydrogenase) were observed when compared with the levels in rats fed a control diet. In addition, significantly lower mean hepatic levels of lipoprotein lipase, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, antioxidant enzymes (catalase, superoxide dismutase, and glutathione peroxidase) and non-enzymatic antioxidants (reduced glutathione, and vitamins C and E), and a significantly higher mean level of hepatic malondialdehyde (MDA) were noted in comparison to the values in control rats. In atherogenic diet-fed rats that received chrysin orally (200 mg/kg b.wt) for 15 days, starting 30 days after the start of the atherogenic diet, significantly lower mean serum levels of lipid profile parameters (except for HDL-cholesterol which was elevated), hepatic marker enzymes, and significantly higher mean hepatic levels of LPL, HMG-CoA reductase, enzymatic, and non-enzymatic antioxidants and significantly lower mean levels of hepatic MDA were noted, compared to the values in atherogenic diet-fed, saline-treated rats. Histopathological studies appeared to suggest the protective effect of chrysin on the hepatic tissue and aorta of atherosclerotic rats. These results suggest that chrysin has anti-atherogenic potential in an experimental setting.     

Effects of simvastatin treatment on oxidant/antioxidant state and ultrastructure of streptozotocin-diabetic rat lung

In the present study, we investigated the effects of simvastatin, a 3-hydroxy-3-methyl-glutaryl coenzyme A reductase inhibitor, on lipid metabolism, lipid peroxidation, antioxidant enzyme activities and ultrastructure of diabetic rat lung. Diabetes was induced by a single injection of streptozotocin (45 mg kg(-1), i.p.). After 8 weeks induction of diabetes, some control and diabetic rats were treated with simvastatin (10 mg kg(-1) rat day(-1); orally) for 4 weeks. Diabetes resulted in significantly high levels of blood glucose and plasma lipids. Malondialdehyde levels were unchanged after 12-week-old diabetic rats, whereas catalase activity significantly decreased in the lung. Glutathione peroxidase activity and nitric oxide level were significantly elevated in the diabetic lung. Histological analysis of the diabetic lung revealed some deterioration in the structure. Simvastatin treatment reduced plasma lipid levels and partially decreased the severity of hyperglycaemia. Catalase, glutathione peroxidase activities and nitric oxide levels were partially restored and accompanied by improved structure in diabetic lung by the simvastatin treatment. These results suggest that structural disturbances and alteration of antioxidative enzyme activities occurred in diabetic lung. Simvastatin treatment may provide some benefits in the maintenance of antioxidant status and structural organization of diabetes-induced injury of lung.     

Antidiabetic and Pancreas-Protective Effects of Zinc Threoninate Chelate in Diabetic Rats may be Associated with its Antioxidative Stress Ability

Zinc exerts a wide range of important biological roles. The present study was carried out to investigate the effects of zinc threoninate chelate in blood glucose levels, lipid peroxidation, activities of antioxidant defense systems and nitrite concentration, and histology of the pancreas in diabetic rats. Wistar rats were intravenously injected with a single dose of streptozotocin to induce diabetes. Then, diabetic rats were administrated orally with zinc threoninate chelate (3, 6, and 9 mg/kg body weight) once daily for 7 weeks. Fasting blood glucose was monitored weekly. At the end of the experimental period, the diabetic rats were killed, and levels of serum insulin, malondialdehyde, and nitric oxide, activities of glutathione peroxidase, total superoxide dismutase, copper/zinc-superoxide dismutase, and nitric oxide synthase were determined; pancreas was examined histopathologically as well. Zinc threoninate chelate significantly reduced the blood glucose levels and significantly increased the serum insulin levels in diabetic rats. In addition, zinc threoninate chelate caused a significant increase in activities of antioxidant enzymes and significant decrease in nitrite concentration and malondialdehyde formation in the pancreas and serum of diabetic rats. These biochemical observations were supplemented by histopathological examination of the pancreas. These results suggested that the antidiabetic effect of zinc threoninate chelate may be related to its antioxidative stress ability in diabetic rats.     

Glucose-induced cataract in CuZn-SOD null lenses: An effect of nitric oxide?

Lenses from mice lacking the antioxidant enzyme copper-zinc superoxide dismutase (SOD1) show elevated levels of superoxide radicals and are prone to developing cataract when exposed to high levels of glucose in vitro. As superoxide may react further with nitric oxide, generating cytotoxic reactive nitrogen species, we attempted to evaluate the involvement of nitric oxide in glucose-induced cataract. Lenses from SOD1-null and wild-type mice were incubated with high or normal levels of glucose (55.6 and 5.56 mM). A nitric oxide synthase inhibitor (L-NAME) or a nitric oxide donor (DETA/NO) was added to the culture medium. Cataract development was assessed using digital image analysis of lens photographs and cell damage by analyzing the leakage of lactate dehydrogenase. The levels of superoxide radicals in the lenses were also measured. L-NAME was found to reduce cataract development and cell damage in the SOD1-null lenses exposed to high glucose. On the other hand, DETA/NO accelerated cataract development, especially in the SOD1-null lenses. These lenses also showed a higher leakage of lactate dehydrogenase than wild-type controls. We conclude that a combination of high glucose and absence of SOD1 increases the formation of cataract and that nitric oxide probably contributes to this process.     

Influence of beta-resorcylidene aminoguanidine on selected metabolic parameters and antioxidant status of rats with diabetes mellitus

We studied the effects of administration of beta-resorcylidene aminoguanidine (RAG) to Wistar strain rats with experimental diabetes mellitus (DM) induced by streptozotocin. The effects studied included antioxidant levels in plasma and the liver, oxidative damage of lipids represented by the formation of substances reacting with thiobarbituric acid (TBARP) and selected biochemical indicators. The administration of RAG did not significantly affect antioxidant status of diabetic rats or hemoglobin glycation and plasma concentration of fructosamine. In diabetic rats, application of RAG decreased formation of TBARP in plasma but not in the liver. Moderate steatosis of liver and increased plasma levels of triacylglycerols in diabetic rats were significantly improved by application of RAG.     

Glucose induces lipid peroxidation and inactivation of membrane-associated ion-transport enzymes in human erythrocytes in vivo and in vitro.

Erythrocytes of diabetic subjects (non-insulin dependent) were found to have eight- to ten-fold higher levels of endogenously formed thiobarbituric acid reactive malonyldialdehyde (MDA), thirteen-fold higher levels of phospholipid-MDA adduct, 15-20% reduced Na(+)-K(+)-ATPase activity with unchanged Ca+2-ATPase activity, as compared with the erythrocytes from normal healthy individuals. Incubation of normal erythrocytes with elevated concentrations (15-35 mM) of glucose, similar to that present in diabetic plasma, led to the increased lipid peroxidation, phospholipid-MDA adduct formation, reduction of Na(+)-K(+)-ATPase (25-50%) and Ca+2-ATPase (50%) activities. 2-doxy-glucose was 80% as effective as glucose in the lipid peroxidation and lipid adduct formation. However, other sugars, such as fructose, galactose, mannose, fucose, glucosamine and 3-O-methylmannoside, and sucrose, tested at a concentration of 35 mM, resulted in reduced (20-30%) lipid peroxidation without the formation of lipid-MDA adduct. Kinetic studies show that reductions in Na(+)-K(+)-ATPase and Ca+2-ATPase activities precede the lipid peroxidation as the enzyme inactivation occur within 30 min of incubation of erythrocytes with high concentration (15-35 mM) of glucose, while lipid peroxidation product, MDA appears at 4 hr and lipid-MDA adducts at 8 hr. The lipoxygenase pathway inhibitors, 5,8,11-eicosatriynoic acid and Baicalein (5,6,7-trihydroxyflavone), reduced the glucose-induced lipid peroxidation by 30% and MDA-lipid adduct formation by 26%. Indomethacin, a cyclooxygenase pathway inhibitor, had no discernible effect on the lipid peroxidation in erythrocytes. However, the inhibitors of lipid peroxidation, 3-phenylpyrazolidone, metyrapone, and the inhibitors of lipoxygenase pathways did not ablate the glucose-induced reduction of Na(+)-K(+)-ATPase and Ca+2-ATPase activities in erythrocytes. Erythrocytes produce 15-HETE (15-hydroxy-eicosatetraenoic acid), which is augmented by glucose. These results suggest that the formation of lipoxygenase metabolites potentiate the glucose-induced lipid peroxidation and that the inactivation of Na(+)-K(+)-ATPase and Ca+2-ATPase occurs as a result of non-covalent interaction of glucose with these enzymes.