Modification of renal oxidative stress and lipid peroxidation in streptozotocin-induced diabetic rats treated with extracts from Gongronema latifolium leaves

Exploring the Oxidative Stress Regulation of Mice with Hyperglycemia by Lactiplantibacillus plantarum SCS4

The aim of this study was to evaluate the effects of Lactiplantibacillus plantarum SCS4 (L. plantarum SCS4) on oxidative stress in streptozocin-induced hyperglycemic mice. After establishment of the hyperglycemic model, control group mice were gavaged daily with phosphate-buffered saline, while different experimental groups (AG, BG, and CG) mice were gavaged with L. plantarum SCS4 suspension, cellular inclusion suspension, and inactivated inclusion suspension for 10 weeks, respectively. Compared with the model group (MG) group, the results showed that fasting blood glucose levels in BG and CG groups decreased, and postprandial 2-h blood glucose levels in BG groups decreased, whereas glucose tolerance improved. Meanwhile, ROS and MDA levels in serum of AG mice were decreased significantly (P < 0.05). Compared with the MG group, serum levels of GPx, HO-1, and NQO1 were increased in the BG group, whereas serum levels of CAT, HO-1, and GSH were increased in the CG group. Our results indicate that L. plantarum SCS4 can alleviate oxidative stress induced by hyperglycemia, and there may be synergistic effects among the different treatments.

Protective role of diosgenin against hyperglycaemia-mediated cerebral ischemic brain injury in zebrafish model of type II diabetes mellitus

Impairment in glucose regulation is an indicatory effect capable of mediating multiple dysfunction such as cerebrovascular disorder with ischemia and brain damage inclusive. This study aims at investigating the glucose-lowering and neuroprotective capability of Diosgenin (DG) towards hyperglycemia-induced cerebral injury in a developed type 2 diabetes mellitus (T2DM) Zebrafish (ZF) model. T2DM was developed in ZF with 20 mg/kg body weight (b.w) multiple-low dose (MLD) Streptozotocin (STZ) for 28 days. Different doses of 20 mg/kg b.w (DG1) and 40 mg/kg b.w (DG2) DG was intraperitoneally administered twice in 7 days for a period of 28 days after T2DM was completely developed. Weight and behavioral changes were monitored and the catalytic activity including the plasma glucose level of diseased and treated ZF was spectrometrically estimated. Histopathological studies were employed to image the brain pathological condition during disease and treatment. SPSS was used as the statistical tool for result analysis and comparison of data obtained. STZ significantly (^###p < 0.001) induced hyperglycemia when compared to control as plasma glucose increases from 101.56 ± 4.52 mgdL⁻¹ to 175.87 ± 6.00 mg/dL. Our results have indicated a marked reduction in glucose concentration from a mean average of 175.87 ± 6.00 mgdL⁻¹ to 105.68 ± 4.48 mgdL⁻¹ and 82.06 ± 7.27 mgdL⁻¹ in DG 1 and DG 2 respectively. Catalytic activity significantly decreases (p < 0.05) from 206.42 ± 30.77 unit/mL to 123.85 ± 29.99 unit/mL at a minimum and maximum value of 103.21 and 275.23 in diseased ZF respectively. On DG treatment, catalytic activity significantly (p < 0.01) rise from 101.58 ± 11.29 and 130.73 ± 27.52 to 130.98 ± 17.13 and 255.96 ± 30.34 with DG1 and DG2 treatment respectively. Studies on the behavioral pattern of STZ-induced anxiolytic effect on ZF confirmed changes in the number of transitions and time spent in both Novel tank test (NTT) and Dark/light test (LDT). Histopathological analysis confirmed the cerebral cortex with inflammatory brain cells in the diseased condition and an attenuation of damage posed revealed in diseased state was largely reversed with DG. As compared to the normal control, a significant (^#p < 0.05 and ^###p < 0.001) changes in weight of fishes were recorded and DG1 and DG2 significantly promotes (***p < 0.001) body weight and improves the irregularities in weight of ZF during disease progression. Our study confirms that the potential of DG towards the management of hyperglycemia and hyperglycemia–mediated cerebral ischemic injury is through its blood glucose-lowering properties, anti-inflammatory activity, antioxidant effect, and anxiolytic capabilities.

Phosphocreatine Improves Cardiac Dysfunction by Normalizing Mitochondrial Respiratory Function through JAK2/STAT3 Signaling Pathway In Vivo and In Vitro

Diabetic cardiomyopathy (DCM) is one of the common cardiovascular complications in patients with diabetes. Accumulating evidence has demonstrated that DCM is thoroughly related to mitochondrial energy impairment and increases the generation of reactive oxygen species (ROS). Therefore, an ongoing study is developing strategies to protect cardiac mitochondria from diabetic complications, especially from hyperglycemia. Phosphocreatine (PCr) plays a major metabolic role in cardiac muscular cells including intracellular concentration of ATP which affects the activity of the myocardium. We hypothesized that PCr might improve oxidative phosphorylation and electron transport capacity in mitochondria impaired by hyperglycemia in vivo and in vitro. Also, we aimed to evaluate the protective effect of PCr against DCM through the JAK2/STAT3 signaling pathway. The mitochondrial respiratory capacity from rats and H9C2 cells was measured by high-resolution respirometry (HRR). Expressions of proteins Bax, Bcl-2, caspase 3, caspase 9, cleaved caspase 3, and cleaved caspase 9, as well as JAK2/STAT3 signaling pathways, were determined by western blotting. ROS generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Type 1 diabetes mellitus was induced in Wistar male rats by a single intraperitoneal injection of streptozotocin (STZ) (80 mg/kg body weight). Our results revealed that PCr possessed protective effects against DCM injury by improving the mitochondrial bioenergetics and by positively exerting protective effects against DCM in vivo and in vitro, not only improving diabetes symptom, resulting in changes of cardiac tissue using hematoxylin and eosin (H&E) stain, but also ameliorating biochemical changes. Moreover, PCr increased Bcl-2, caspase 3, and caspase 9 protein expressions and decreased Bax, cleaved caspase 3, and cleaved caspase 9 expressions as well as the JAK2/STAT3 signaling pathway. In conclusion, PCr improves mitochondrial functions and exerts an antiapoptotic effect in vivo and in vitro exposed to oxidative stress by hyperglycemia through the JAK2/STAT3 signaling pathway. Our findings suggest that PCr medication is a possible therapeutic strategy for cardioprotection.

Blood pressure-reducing activity of Gongronema latifolium Benth. (Apocynaeceae) and the identification of its main phytochemicals by UHPLC Q-Orbitrap mass spectrometry

Background Gongronema latifolium Benth. (family Apocynaceae) leaves (GL) has interesting medicinal properties. The effects of extracts from G. latifolium on blood pressure (BP) and the possible mechanisms of action were also investigated. Methods The ultrahigh resolution liquid chromatography orbitrap MS analysis was used to identify the phytochemicals present. Normotensive Wistar rats were anesthetized with sodium pentobarbitone (40 mg/kg) intraperitoneally, and the jugular vein was cannulated for infusion of drugs while the carotid artery was cannulated for direct BP measurement. GL extract (5-20 mg) alone or with nifedipine (10 mg/kg), atropine (2 mg/kg), L-NAME (5 mg/kg), methyl blue (3 mg/kg) and propranolol (1 mg/kg) were administered intravenously to Wistar rats and direct BP measurements were carried out. Results Systolic and diastolic BP levels (128/90 mm Hg; MAP 103 ± 3 mm Hg) and heart rates were all significantly (p < 0.01) decreased after GL administration. Raised mean arterial pressure (MAP) and heart rate by atropine, L-NAME and methyl blue were significantly (p < 0.01) reduced after GL administration, while propranolol significantly (p < 0.01) inhibited hypotension caused by GL. Infusion of GL reduced MAP (95 ± 3 mm Hg) comparable with nifedipine (93 ± 2 mm Hg), a calcium channel blocker. The phytochemicals identified were 34 compounds, including oleanolic acid derivatives, flavonoids, antioxidant fatty acids, 2 coumarins and 2 iridoids. Conclusions These results suggest that G. latifolium has hypotensive properties mediated by the synergistic activity of the compounds, probably via the β-adrenergic blockade mechanism.

Extract of Rhus verniciflua stokes protects against renal ischemia-reperfusion injury by enhancing Nrf2-mediated induction of antioxidant enzymes

Ischemia-reperfusion injury (IRI) may cause acute kidney disease (AKD) by mediating the oxidative stress-induced apoptosis of parenchymal cells. The extract of Rhus verniciflua Stokes (RVS) is used as a traditional herbal medicine as it exhibits anti-oxidant, anti-apoptotic and anti-inflammatory properties. Therefore, the current study investigated the therapeutic effect and the underlying mechanism of RVS on IRI-induced AKD in vivo and in vitro. The current study assessed the effects of RVS on a mouse model of renal IRI and in hypoxic human renal tubular epithelial HK-2 cells. The results demonstrated that the IRI-induced elevation of blood urea nitrogen, serum creatinine and lactate dehydrogenase was significantly attenuated by the intraoral administration of RVS (20 mg/kg/day) for 14 days prior to surgery. It was demonstrated that IRI surgery induced histological damage and cellular apoptosis in renal parenchyma, which were attenuated by pretreatment with RVS. Furthermore, in HK-2 cells incubated with 300 µM CoCl₂ to induce chemical hypoxia, it was demonstrated that RVS treatment significantly inhibited cell death and the production of reactive oxygen species (ROS). Furthermore, RVS treatment upregulated the levels of endogenous antioxidant enzymes, including heme oxygenase-1 and catalase, as well as their upstream regulator nuclear factor erythroid 2-related factor 2, in HK-2 cells. Taken together, these results suggested that the intraoral administration of RVS induces a therapeutic effect on IRI-induced AKD. These effects are at least partly due to the attenuation of ROS production via upregulation of the antioxidant defense system in renal tubular cells.

Phytochemical characterization of the Vochysia rufa (Vochysiaceae) extract and its effects on oxidative stress in the pancreata of streptozotocin-induced diabetic rats

Aqueous extract of macerated Vochysia rufa stem bark has been commonly used in the treatment of diabetes. Therefore, we evaluated the antihyperglycemic and antioxidant effects of an extract of V. rufa on the pancreata of streptozotocin (STZ)-induced diabetic rats. Animals received one of the following treatments daily by oral gavage: water (diabetic-control), V. rufa extract (diabetic-V. rufa), or glibenclamide (diabetic-GBD). Total antioxidant capacity; levels of thiobarbituric acid reactive substances, reduced glutathione, and sulfhydryls; and superoxide dismutase, catalase, and glutathione peroxidase (GPx) activities were measured in the pancreas. Biochemical analysis of serum total cholesterol and fractions, triglycerides, creatinine, urea, acid uric, ALP, γ-GT, AST, and ALT was performed, and pancreatic β-cells positive for insulin were evaluated by immunohistochemistry. Rats treated with extract exhibited a decrease in fasting blood glucose compared with levels in diabetic control rats. GPx activity and sulfhydryl levels were significantly lower in diabetic-V. rufa rats compared with those of diabetic-control rats. V. rufa extract acted to normalize the biochemical alterations found in diabetic rats (diabetic-controls), as demonstrated by increases in urea, HDL, ALP, AST, and ALT. Reduction in blood glucose was independent of an increase in insulin. The V. rufa extract was found to be composed of free sugars (inositol, galactose, glucose, mannose, sucrose, arabinose, and ribose) as the main metabolites. Thus, aqueous extract of the stem bark of V. rufa is capable of reducing blood glucose, resulting in an antioxidant effect on the pancreatic tissue of STZ-diabetic rats.

Therapeutic insight into molsidomine, a nitric oxide donor in streptozotocin-induced diabetic nephropathy in rats

BACKGROUND

Diabetes-induced oxidative stress and hypertension play a major role in the development of nephropathy. Hence, the present study was undertaken to evaluate the protective effects of molsidomine, a nitric oxide donor in streptozotocin (STZ)-induced diabetic nephropathy (DN) in rats.

MATERIALS AND METHODS

Type 1 diabetes was induced through a single dose of STZ (52 mg/kg, i.p.) in male Wistar rats and then treated with molsidomine (5 and 10 mg/kg; p.o.) for 8 weeks. Physical parameters, vital and renal function test including blood glucose, albuminuria, blood urine nitrogen, serum creatinine, and kidney index were determined. Oxidative stress and lipid peroxidation were assessed in the kidney homogenate by means of antioxidant enzymes and malondialdehyde levels.

RESULTS

DN rats exhibited a significant renal dysfunction with a reduction in body weight, excessive oxidative stress, and pathological changes. Molsidomine treatment significantly improved vital sign, renal functions, and oxidative stress in DN rats in a dose-dependent manner. The protective effect of molsidomine was also substantiated by pathological changes in the architect of the kidney.

CONCLUSION

Molsidomine shows a significant beneficial effect in Type 1 DN in rats.

THE PURVIEW OF PHYTOTHERAPY IN THE MANAGEMENT OF KIDNEY DISORDERS: A SYSTEMATIC REVIEW ON NIGERIA AND SOUTH AFRICA

BACKGROUND

The kidney is tasked with a number of metabolic functions in the body. In its role as a detoxifier and primary eliminator of xenobiotics, it becomes vulnerable to developing injuries. Currently, over 1 million people in the world are living on renal replacement therapies (RRTs). The case in sub-Sahara African countries like Nigeria and South Africa is not any better than the global trend.

MATERIALS AND METHODS

A systematic review of medicinal plants used in the treatment of kidney disorders was conducted. Information were gathered from published scientific journals, books, reports from national, regional and international institutions, conference proceedings and other high profile intellectual resources. MeSH words like 'prevalence of kidney disorders in Africa', 'renal replacement therapy', 'nephrotoxins or nephrotoxicants', 'nephroprotective plants', 'nephroprotective plants in Nigeria or South Africa' and 'nephroprotective phytocompounds' were used to retrieve information from online databases (Google, Pubmed, MEDLINE, Science Direct, Scopus and SID).

RESULTS

Interestingly, our findings revealed that phytotherapy has emerged and is being employed to protect renal functions and delay progression of renal pathological conditions into end episodes where the last resort is RRT. In fact, in recent times, Phytotherapists are not only interested in developing relatively safe, more affordable, easily accessible and potent nephroprotective formulations but also increasing awareness on the prevalence of the disease and educating the populace on the probable preventive measures. More importantly, efforts at scientifically elucidating the pharmacological efficacy of the identified nephroprotective plants yet to be validated must be intensified through informed expert opinions. Till date, there is paucity of information on the concept of nephroprotection in most developing countries where kidney disorder is a major threat. Although, the concept is just emerging in South Africa, evidences have given credence to its application in complementary and alternative system of medicine in Nigeria.

CONCLUSION

This review, therefore, reawaken researchers' consciousness in the continuous search for auspicious nephroprotective plants that could potentially be excellent candidates in developing new lead drugs to manage and treat renal disorders.

A Soxhlet Extract of Gongronema latifolium Retains Moderate Blood Glucose Lowering Effect and Produces Structural Recovery in the Pancreas of STZ-Induced Diabetic Rats

BACKGROUND

Gongronema latifolium Benth. (GL) possesses considerable glucose lowering effects able to be utilized on a large-scale. This paper investigates the effects of a Soxhlet extract on hyperglycemia, Langerhans islets and glucose uptake by abdominal muscles.

METHODS

Ethanol and a Soxhlet apparatus were used to obtain GL ethanolic Soxhlet extract (GLES). It was then administered to randomly-segregated male Sprague-Dawley, normal and STZ-induced diabetic rats, using oral gavage to evaluate blood glucose levels (BGLs), serum lipid profile, insulin levels and the pancreas post-treatment.

RESULTS

GLES significantly (p < 0.05) decreased BGLs of normal rats in glucose tolerance testing at a dose of 2 g/kg b.w. but failed to do so in diabetic rats undergoing acute 7-h treatment. Given twice-daily, 1 g/kg b.w. of GLES moderately controlled diabetic BGLs starting from day 10. After 14 days of treatment, 1 g/kg and 0.5 g/kg b.w. of GLES caused 44% and 50% respective increases in the average area of Langerhans islets compared to DC. Using isolated rat abdominal muscle, GLES was found to be a mild insulin-sensitizer. GC-MS analysis revealed the presence of the known glucose-lowering phytosterol, Sitostenone.

CONCLUSION

Despite retaining moderate antidiabetic activity, Soxhlet extraction of Gongronema latifolium probably leads to the destruction of active heat-liable compounds.

Herbal therapy: A review of emerging pharmacological tools in the management of diabetes mellitus in Africa

BACKGROUND

Diabetes mellitus is a chronic physiological glucose metabolic disorder. It has affected millions of people all over the world thereby having a significant impact on quality of life. The management of diabetes includes both nonpharmacological and conventional interventions. Drawbacks in conventional therapy have led to seeking alternative therapy in herbal medicine. Therefore, the need to review, elucidate and classify their mode of action in therapy for diabetes disease arises.

MATERIALS AND METHODS

Comprehensive literature reports were used to review all conventional agents and herbal therapy used in the management of diabetes. An online database search was conducted for medicinal plants of African origin that have been investigated for their antidiabetic therapeutic potentials.

RESULTS

The results showed that of the documented sixty five plants used, fourteen inhibit intestinal absorption of glucose, three exhibit insulin-mimetic properties, seventeen stimulate insulin secretion from pancreatic beta cells, twelve enhance peripheral glucose uptake, one promotes regeneration of beta-cell of islets of Langerhans, thirteen ameliorate oxidative stress and twenty induces hypoglycemic effect (mode of action is still obscure). Thirteen of these plants have a duplicate mode of actions while one of them has three modes of actions. These agents have a similar mechanism of action as the conventional drugs.

CONCLUSION

In conclusion, antidiabetic activities of these plants are well established; however, the molecular modulation remains unknown. It is envisaged that the use of herbal therapy will promote good health and improve the status of diabetic patients.

Pyrroloquinoline quinone (PQQ) has potential to ameliorate streptozotocin-induced diabetes mellitus and oxidative stress in mice: A histopathological and biochemical study

Enhanced oxidative stress and hyperglycemia are associated with diabetes mellitus (DM). As pyrroloquinoline quinone (PQQ) is known to protect cells from oxidative stress, the present study was undertaken to reveal the hitherto unknown effects of PQQ in DM and associated problems in different tissues. Forty two mice were randomly divided into six groups. Group I receiving only citrate buffer served as the normal control, while group II animals were injected with citrate buffer and PQQ at 20 mg/kg for 15 days and served as test drug control. Animals of groups III-VI were rendered diabetic by single dose of streptozotocin (STZ, 150 mg/kg body weight), following which PQQ at a dose of 5, 10 and 20 mg/kg, was injected to the animals of group IV, V and VI respectively for 15 days. At the end, alterations in serum indices such as glucose, different lipids, insulin, amylase, urea, uric acid, serum glutamate pyruvate transaminase and serum glutamate oxaloacetate transaminase; tissue antioxidants and histopathological alterations in liver, kidney and pancreas were evaluated. STZ-treated animals developed oxidative stress as indicated by a significant increase in tissue lipid peroxidation (LPO) and lipid hydroperoxide, serum glucose, total cholesterol, triglyceride and urea, with a parallel decrease in the levels of serum insulin and tissue antioxidants. When diabetic animals received different doses of PQQ, these adverse effects were ameliorated. However, 20 mg/kg of PQQ appeared to be most effective. Findings revealed for the first time that PQQ has the potential to mitigate STZ-induced DM and oxidative damage in different organs of mice, suggesting that it may ameliorate diabetes mellitus and associated problems.

Yacon roots (Smallanthus sonchifolius) improve oxidative stress in diabetic rats

CONTEXT

Smallanthus sonchifolius (Poepp. and Endl.) H. Robinson, Asteraceae (yacon) roots are a natural product recognized by the traditional medicine to treat diabetes-related problems. There are no reports concerning the potential of yacon roots to reduce oxidative stress and ameliorate diabetes complications in diabetic animals.

OBJECTIVE

This work analyzes the in vivo antioxidant activity and beneficial effects of yacon roots, using a model of streptozotocin-induced diabetes in rats.

MATERIALS AND METHODS

Lipid peroxidation and other indicators of oxidative stress were determined in liver and kidney homogenates from non-diabetic rats, untreated diabetic rats, and diabetic rats treated orally with yacon flour (340 mg fructooligosaccharide/kg/d) as a diet supplement for 90 d. Biochemical parameters were determined in liver, kidney, and blood at the end of the experimental period.

RESULTS

Yacon supplementation to diabetic rats produced a significant decrease in malondialdehyde levels in both liver (-30.97%) and kidney (-19.15%). Hepatic superoxide dismutase and catalase activities were significantly lower in diabetic-treated rats (-13.46 and -64.33%, respectively) compared with diabetic controls. Similar results were observed in kidney. The treatment of diabetic rats produced an increase of glutathione peroxidase and glutathione levels in liver (172.50 and 35.91%, respectively) and kidney (177.78 and 57.76%, respectively). Plasma cholesterol and triacylglycerol levels and liver fatty acid composition, which were altered in diabetic rats, reverted back to nearly normal with yacon treatment.

CONCLUSIONS

These results indicate that yacon root flour is a potential diet supplement with high in vivo antioxidant activity.

Arginase inhibition alleviates hypertension in the metabolic syndrome

BACKGROUND AND PURPOSE

We have previously shown that arginase inhibition alleviates hypertension associated with in a diabetic animal model. Here, we investigated the protective effect of arginase inhibition on hypertension in metabolic syndrome.

EXPERIMENTAL APPROACH

Metabolic syndrome was induced in rats by administration of fructose (10% in drinking water) for 12 weeks to induce vascular dysfunction. Three arginase inhibitors (citrulline, norvaline and ornithine) were administered daily in the last 6 weeks of study before and tail BP was recorded in conscious animals. Concentration response curves for phenylephrine (PE), KCl and ACh in addition to ACh-induced NO generation were obtained in thoracic aorta rings. Serum glucose, insulin, uric acid and lipid profile were determined as well as reactive oxygen species (ROS) and arginase activity.

KEY RESULTS

Arginase activity was elevated in metabolic syndrome while significantly inhibited by citrulline, norvaline or ornithine treatment. Metabolic syndrome was associated with elevations in systolic and diastolic BP, while arginase inhibition significantly reduced elevations in diastolic and systolic BP. Metabolic syndrome increased vasoconstriction responses of aorta to PE and KCl and decreased vasorelaxation to ACh, while arginase inhibition completely prevented impaired responses to ACh. In addition, arginase inhibition prevented impaired NO generation and exaggerated ROS formation in metabolic syndrome. Furthermore, arginase inhibition significantly reduced hyperinsulinaemia and hypertriglyceridaemia without affecting hyperuricaemia or hypercholesterolaemia associated with metabolic syndrome.

CONCLUSIONS AND IMPLICATIONS

Arginase inhibition alleviates hypertension in metabolic syndrome directly through endothelial-dependent relaxation/NO signalling protection and indirectly through inhibition of insulin resistance and hypertriglyceridaemia.

Characterization of vascular complications in experimental model of fructose-induced metabolic syndrome

Vascular dysfunction is an important complication associated with metabolic syndrome (MS). Here we fully characterized vascular complications in a rat model of fructose-induced MS. MS was induced by adding fructose (10%) to drinking water to male Wistar rats of 6 weeks age. Blood pressure (BP) and isolated aorta responses phenylephrine (PE), KCl, acetylcholine (ACh), and sodium nitroprusside (SNP) were recorded after 6, 9, and 12 weeks of fructose administration. In addition, serum levels of glucose, insulin, uric acid, tumor necrosis factor α (TNFα), lipids, advanced glycation end products (AGEs), and arginase activity were determined. Furthermore, aortic reactive oxygen species (ROS) generation, hemeoxygenase-1 expression, and collagen deposition were examined. Fructose administration resulted in a significant hyperinslinemia after 6 weeks which continued for 12 weeks. It was also associated with a significant increase in BP after 6 weeks which was stable for 12 weeks. Aorta isolated from MS animals showed exaggerated contractility to PE and KCl and impaired relaxation to ACh compared with control after 6 weeks which were clearer at 12 weeks of fructose administration. In addition, MS animals showed significant increases in serum levels of lipids, uric acid, AGEs, TNFα, and arginase enzyme activity after 12 weeks of fructose administration. Furthermore, aortae isolated from MS animals were characterized by increased ROS generation and collagen deposition. In conclusion, adding fructose (10%) to drinking water produces a model of MS with vascular complications after 12 weeks that are characterized by insulin resistance, hypertension, disturbed vascular reactivity and structure, hyperuricemia, dyslipidemia, and low-grade inflammation.

Fenugreek Prevents the Development of STZ-Induced Diabetic Nephropathy in a Rat Model of Diabetes

The present study aims to examine the protective effect of fenugreek and the underlying mechanism against the development of diabetic nephropathy (DN) in streptozotocin- (STZ-) induced diabetic rats. A rat model of diabetes was successfully established by direct injection of STZ and then the rats were administered an interventional treatment of fenugreek. Parameters of renal function, including blood glucose, albuminuria, hemoglobin A1c (HbA1c), dimethyl formamide (DMF), blood urine nitrogen (BUN), serum creatinine (Scr), and kidney index (KI), were detected in the three groups (Con, DN, and DF). Oxidative stress was determined by the activity of antioxidase. Extracellular matrix (ECM) accumulation and other morphological alterations were evaluated by means of immunohistochemistry and electron microscope. Quantitive (q)PCR was employed to detect the mRNA expression of transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF) and protein expression was determined with western blot analysis. DN rats in the present study demonstrated a significant renal dysfunction, ECM accumulation, pathological alteration, and oxidative stress, while the symptoms were evidently reduced by fenugreek treatment. Furthermore, the upregulation of TGF-β1 and CTGF at a transcriptional and translational level in DN rats was distinctly inhibited by fenugreek. Consequently, fenugreek prevents DN development in a STZ-induced diabetic rat model.

Evaluation of Antioxidant, Immunomodulatory Activities, and Safety of Ethanol Extract and Fractions of Gongronema latifolium Fruit

Gongronema latifolium fruit has wide application in ethnomedicine, especially in maintaining healthy living and general body healing. We therefore investigated the antioxidant, immunomodulatory activities, and safety of its ethanol extract and fractions. The in vitro antioxidant activities of the extract and fractions were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) test while in vivo activities were determined using carbon tetrachloride (CCL₄) induced oxidative stress. Cell and humoral mediated immune responses were also evaluated together with toxicity studies. The extract, ethyl acetate, and methanol fractions showed inhibition of DPPH radical with IC₅₀s 120, 90, and 60 μg/mL, respectively. Methanol fraction at 200 mg/kg produced significant (P < 0.05) inhibition of lipid peroxidation (MDA conc. 1.2 μmol/L) compared to control (2.8 μmol/L). Both ethyl acetate and methanol fractions at 200 mg/kg produced significant (P < 0.05) phagocytic index of 0.021 and 0.025, respectively, compared with control (0.01). Significant (P < 0.05) elevations of white blood cells, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase were noticed on the 91st day at higher doses. Generally, this study justified the traditional use of G. latifolium fruit for general body healing and maintenance of healthy living. Long term administration is safe on the haematological and biochemical systems especially at lower doses and its toxicity at higher doses is reversible.

Acute restraint stress induces rapid and prolonged changes in erythrocyte and hippocampal redox status

The onset and consequential changes in reduction-oxidation (redox) status that take place in response to short-term stress have not been well defined. This study utilized erythrocytes and neural tissue from male Wistar rats to demonstrate the rapid redox alterations that occur following an acute restraining stress. Serial blood samples collected from catheterized animals were used to measure prolactin, corticosterone, glucose, general oxidative status, and glutathione/glutathione disulfide ratios. Restraint increased prolactin concentration by approximately 300% at 30 min and rapidly returned to baseline values by 120 min of stress. Baseline blood glucose and corticosterone increased during stress exposure by approximately 25% and 150% respectively. Over the experimental period, the erythrocytic oxidative status of restrained animals increased by approximately 10% per hour which persisted after stress exposure, while changes in the glutathione redox couple were not observed until 120 min following the onset of stress. Application of restraint stress increased hippocampal oxidative status by approximately 17% while no change was observed in the amygdala. It was concluded that while endocrine and metabolic markers of stress rapidly increase and habituate to stress exposure, redox status continues to change following stress in both peripheral and neural tissue. Studies with longer post-restraint times and the inclusion of several brain regions should further elucidate the consequential redox changes induced by acute restraint stress.

Management of diabetic complications: a chemical constituents based approach

ETHNOPHARMACOLOGICAL RELEVANCE

Long term hyperglycemia leads to development of complications associated with diabetes. Diabetic complications are now a global health problem without effective therapeutic approach. Hyperglycemia and oxidative stress are important components for the development of diabetic complications. Over the past few decades, herbal medicines have attracted much attention as potential therapeutic agents in the prevention and treatment of diabetic complications due to their multiple targets and less toxic side effects. This review aims to assess the current available knowledge of medicinal herbs for attenuation and management of diabetic complications and their underlying mechanisms.

MATERIAL AND METHODS

Bibliographic investigation was carried out by scrutinizing classical text books and peer reviewed papers, consulting worldwide accepted scientific databases (SCOPUS, PUBMED, SCIELO, NISCAIR, Google Scholar) to retrieve available published literature. The inclusion criteria for the selection of plants were based upon all medicinal herbs and their active compounds with attributed potentials in relieving diabetic complications. Moreover, plants which have potential effect in ameliorating oxidative stress in diabetic animals have been included.

RESULTS

Overall, 238 articles were reviewed for plant literature and out of the reviewed literature, 127 articles were selected for the study. Various medicinal plants/plant extracts containing flavonoids, alkaloids, phenolic compounds, terpenoids, saponins and phytosterol type chemical constituents were found to be effective in the management of diabetic complications. This effect might be attributed to amelioration of persistent hyperglycemia, oxidative stress and modulation of various metabolic pathways involved in the pathogenesis of diabetic complications.

CONCLUSION

Screening chemical candidate from herbal medicine might be a promising approach for new drug discovery to treat the diabetic complications. There is still a dire need to explore the mechanism of action of various plant extracts and their toxicity profile and to determine their role in therapy of diabetic complications. Moreover, a perfect rodent model which completely mimics human diabetic complications should be developed.

Evaluation of ethnomedical claim III: anti-hyperglycemic activities of Gongronema latifolium root and stem

BACKGROUND

The insulinotropic activity of the combined root and stem of Gongronema latifolium (Asclepiadaceae) was evaluated to justify its African ethnomedicinal use in the management of diabetes.

METHODS

A methanolic extract and its chromatographic fractions (A1 -A6 ) were tested for glucose-reducing and in vitro insulin-stimulating abilities using glucose-loaded rats and INS-1 cells, respectively. In vivo insulin-releasing activities for the significantly (P<0.05) active antihyperglycemic A5 and A6 and in vitro insulinotropic activity of the C1 fraction and its isolated constituents were also similarly determined.

RESULTS

The extract (100 mg/kg) had higher in vivo antihyperglycemic activity than the individual A1 -A6 , indicating a synergistic effect of the plant constituents. Higher in vivo insulin release in response to A5 (100 mg/kg) than A6 , agreed with their in vivo antihyperglycemic activities and confirmed insulin release as a mechanism of action of the plant. Compared with 5.6 mmol/L glucose (negative control), the extract and the A3 , A6 , and C1 (all at 100.0 μg/mL) elicited significantly higher in vitro insulin release that was similar to that of glibenclamide (1.0 μg/mL; P>0.05). Fraction C1 yielded a 1:1 mixture of α-amyrin and β-amyrin cinnamates (1a:1b), lupenyl cinnamate (2), lupenyl acetate (3), and two unidentified triterpenoids, Y and Z. The 1a:1b mixture (100.0 μg/mL) demonstrated the highest insulinotropic activity that was comparable (P>0.05) to that of glibenclamide (1.0 μg/mL).

CONCLUSIONS

The results confirm pancreatic activity as a mechanism underlying the antidiabetic action of G. latifolium and justify its ethnomedical use.

The effects of medicinal plants on renal function and blood pressure in diabetes mellitus

Abstract

Diabetes mellitus is one of the most common chronic global diseases affecting children and adolescents in both the developed and developing nations. The major types of diabetes mellitus are type 1 and type 2, the former arising from inadequate production of insulin due to pancreatic β-cell dysfunction, and the latter from reduced sensitivity to insulin in the target tissues and/or inadequate insulin secretion. Sustained hyperglycaemia is a common result of uncontrolled diabetes and, over time, can damage the heart, eyes, kidneys and nerves, mainly through deteriorating blood vessels supplying the organs. Microvascular (retinopathy and nephropathy) and macrovascular (atherosclerotic) disorders are the leading causes of morbidity and mortality in diabetic patients. Therefore, emphasis on diabetes care and management is on optimal blood glucose control to avert these adverse outcomes.

Studies have demonstrated that diabetic nephropathy is associated with increased cardiovascular mortality. In general, about one in three patients with diabetes develops end-stage renal disease (ESRD) which proceeds to diabetic nephropathy (DN), the principal cause of significant morbidity and mortality in diabetes. Hypertension, a well-established major risk factor for cardiovascular disease contributes to ESRD in diabetes. Clinical evidence suggests that there is no effective treatment for diabetic nephropathy and prevention of the progression of diabetic nephropathy. However, biomedical evidence indicates that some plant extracts have beneficial effects on certain processes associated with reduced renal function in diabetes mellitus. On the other hand, other plant extracts may be hazardous in diabetes, as reports indicate impairment of renal function. This article outlines therapeutic and pharmacological evidence supporting the potential of some medicinal plants to control or compensate for diabetes-associated complications, with particular emphasis on kidney function and hypertension.

Heme oxygenase-1 induction protects against hypertension associated with diabetes: effect on exaggerated vascular contractility

Disturbances in vascular reactivity are important components of diabetes-evoked hypertension. Heme oxygenase-1 (HO-1) is a homeostatic enzyme upregulated in stress. This study aims to investigate the protective effect of HO-1 against diabetes-evoked hypertension. Rats were left 8 weeks after diabetes induction with streptozotocin to induce vascular dysfunction in the diabetic groups. HO-1 inducers, hemin and curcumin, were daily administrated in the last 6 weeks in the treated groups after 2 weeks of induction. Then, at the end of the study (8 weeks), HO-1 protein level was assessed by immunofluorescence; blood pressure (BP) was recorded; isolated aorta reactivity to phenylephrine (PE) and KCl was studied; reactive oxygen species (ROS) generation was determined; and serum level of glucose, advanced glycation end products (AGEs), and tumor necrosis factor alpha (TNF-α) were determined. While not affected by diabetes, HO-1 protein expression was strongly induced by hemin or curcumin administration. Compared with control animals, diabetes increased systolic and pulse BP. Induction of HO-1 by hemin or curcumin significantly reduced elevated systolic BP and abolished elevated pulse BP without affecting the developed hyperglycemia or AGEs level. The possibility that alterations in vascular reactivity contributed to diabetes-HO-1 BP interaction was investigated. Diabetes increased contractile response of the aorta to PE and KCl, while HO-1 induction by curcumin or hemin prevented aorta-exaggerated response to PE and KCl. Furthermore, the competitive HO inhibitor, tin protoporphyrin, abolished the protective effect of hemin. Diabetes was accompanied with elevated level of TNF-α and ROS generation, while HO-1 induction abrogated increased TNF-α and ROS generation. Collectively, induction of HO-1 protects against hypertension associated with diabetes via ameliorating exaggerated vascular contractility by reducing TNF-α and aortic ROS levels.

Antioxidant role of coumarin on streptozotocin-nicotinamide-induced type 2 diabetic rats

The purpose of this study was to investigate the antioxidant role of coumarin on streptozotocin-nicotinamide-induced Type 2 diabetic rats. In experimental rats, the levels of plasma glucose, insulin, and the levels of thiobarbituric acid reactive substances, lipid hydroperoxides, conjugated dienes, and the activities of superoxide dismutase, catalase, glutathione-S-transferase, and glutathione peroxidase were assayed in liver and kidney. Diabetic rats showed elevated levels of plasma glucose and lipid peroxidation markers and reduced plasma insulin and antioxidant enzymes. Oral administration of coumarin resulted in a significant reduction in the plasma glucose and lipid peroxides and a significant increase in the plasma insulin and antioxidant enzymes. Chronic treatment of coumarin remarkably restored the normal status of the histopathological changes observed in the selected tissues. It can be concluded that coumarin has antioxidant effect in Type 2 diabetic rats.

Protective Effect of Proanthocyanidin against Diabetic Oxidative Stress

We investigated the antidiabetic potential of proanthocyanidin and its oligomeric form in STZ-induced diabetic model rats and db/db type 2 diabetic mice. Proanthocyanidin ameliorated the diabetic condition by significant decreases of serum glucose, glycosylated protein, and serum urea nitrogen as well as decreases of urinary protein and renal-AGE in STZ-induced diabetic rats and decrease of serum glucose as well as significant decrease of glycosylated protein in db/db type 2 diabetic mice. The suppression of ROS generation and elevation of the GSH/GSSG ratio were also observed in the groups administered proanthocyanidin. Moreover, proanthocyanidin, especially its oligomeric form, affected the inflammatory process with the regulation of related protein expression, iNOS, COX-2 and upstream regulators, NF-κB, and the IκB-α. In addition, it had a marked effect on hyperlipidemia through lowering significant levels of triglycerides, total cholesterol, and NEFA. Moreover, expressions in the liver of SREBP-1 and SREBP-2 were downregulated by the administration of proanthocyanidins. The protective effect against hyperglycemia and hyperlipidemia in type 1 and 2 diabetic models was significantly strong in the groups administered the oligomeric rather than polymeric form. This suggests that oligomers act as a regulator in inflammatory reactions caused by oxidative stress in diabetes.

Iridoid extracts from Ajuga iva increase the antioxidant enzyme activities in red blood cells of rats fed a cholesterol-rich diet

The lyophilized aqueous extract of Ajuga iva (Ai) is able to reduce oxidative stress, which may prevent lipid peroxidation in hypercholesterolemic rats. Iridoids (I) were isolated from Ai. We hypothesized that the antioxidant defense status in red blood cells (RBC) and tissues in rats fed a cholesterol-rich diet and treated with Ai may be correlated to these compounds. Male Wistar rats (n = 32) weighing 120 +/- 5 g were fed a diet containing 1% cholesterol for 15 days. After this phase, hypercholesterolemic (HC) rats were divided into groups, fed the same diet, and received either the same or different doses (5, 10, or 15 mg/kg body weight by intraperitoneal injection) of I for 15 days. Compared with the HC group, total cholesterol value was 1.4- and 1.2-fold lower in the I(5)-HC and I(10)-HC groups. Serum thiobarbituric acid reactive substance content was 2.3-, 2.9-, and 3-fold lower in the I(5)-HC, I(10)-HC, and I(15)-HC groups compared with the HC group. In RBC, glutathione peroxidase, glutathione reductase, and superoxide dismutase activities were significantly higher in the I(5)-HC, I(10)-HC, and I(15)-HC groups than the HC group. Liver, heart, and muscle glutathione peroxidase and superoxide dismutase activities were significantly higher in the groups treated with I than the HC group. Muscle glutathione reductase activity was increased 1.4-fold in the I(5)-HC, 1.5-fold in the I(10)-HC, and 1.5-fold in the I(15)-HC group. In HC rats, different doses of I increase the antioxidant enzyme activities in RBC and act differently in tissues. Treatment with I may play an important role in suppressing oxidative stress caused by dietary cholesterol and, thus, may be useful for the prevention and/or early treatment of hypercholesterolemia.

The chronological characteristics of SOD1 activity and inflammatory response in the hippocampi of STZ-induced type 1 diabetic rats

Because it appears that oxidative stress and inflammation are implicated with disease pathogenesis in the diabetic brain, many researchers have used streptozotocin (STZ)-induced diabetic animals to study superoxide production and the effects of superoxide scavengers like Cu,Zn-superoxide dismutase (SOD1). However, many studies have been conducted without considering temporal changes after STZ injection. Interestingly, though SOD activities were not significantly different among the groups, SOD1 and 4-hydroxy-2-nonenal (4-HNE) immunoreactivities were significantly enhanced at 3 weeks after an STZ injection (STZ3w) versus only marginal levels in sham controls, whereas microglial activity was remarkably reduced in injected rats at this time. However, SOD1 immunoreactivity and microglial activities were only at the sham level at STZ4w. The present study provides important information concerning cell damage by ROS generated by STZ. Microglial response was found to be inactivated at STZ3w and neuronal cells (NeuN) showed a non-significant tendency to be reduced in number at STZ4w except in the dentate gyrus. We speculated that the above oxidative stress-related events should be accomplished at STZ3w in the brains of STZ-induced diabetes animal models. Therefore, the aim of the present study was to investigate chronological changes in SOD1 immunoreactivity associated with lipid peroxidation and inflammatory responses in the hippocampi of STZ-induced type I diabetic rats.

Bacopa monnieri modulates antioxidant responses in brain and kidney of diabetic rats

Role of oxidative stress has been reported in various diabetic complications including neuropathy, nephropathy and cardiopathy. This study was undertaken to evaluate the protective effect of Bacopa monnieri, a medicinal plant, on tissue antioxidant defense system and lipid peroxidative status in streptozotocin-induced diabetic rats. Extract of B. monnieri was administered orally, once a day for 15 days (at doses 50, 125 and 250mg/(kgbw)) to diabetic rats. Activity of antioxidant enzymes (SOD, Catalase, and GPx), levels of GSH and lipid peroxidation were estimated in kidney, cerebrum, cerebellum and midbrain of diabetic rats and compared to reference drug, Glibenclamide. Administration of plant extract to diabetic rats showed significant reversal of disturbed antioxidant status and peroxidative damage. Significant increase in SOD, CAT, GPx activity and levels of GSH was observed in extract treated diabetic rats. The present study indicates that extract of B. monnieri modulates antioxidant activity, and enhances the defense against ROS generated damage in diabetic rats.

Protective Effects of Glurenorm (Gliquidone) Treatment on the Liver Injury of Experimental Diabetes

Oxidative stress plays an important role in chronic complications of diabetes mellitus, and hence the regulation of free radicals is essential in the treatment of diabetes. The aim of the current study is to investigate the effect of glurenorm (10 mg/kg) on liver tissue in experimental diabetes. Diabetes was induced by intraperitoneal injection of 65 mg/kg streptozotocin. Glurenorm was administered to one diabetic and one control group separately, from days 14 to 42. On day 42, cardiac blood samples and liver tissue were taken from each rat. In diabetic rats, blood glucose, serum alkaline phosphatase and serum amino transferase activities, serum uric acid, serum sodium and potassium levels, liver nonenzymatic glycosylation, and lipid peroxidation increased, whereas body weight and liver glutathione levels decreased. The diabetic group given glurenorm blood glucose, serum alkaline phosphatase and aminotransferase activities, serum uric acid, sodium and potassium, liver nonenzymatic glycosylation, and lipid peroxidation levels decreased, and liver glutathione levels increased. As a result of all the biochemical findings obtained, it was concluded that glurenorm has a protective effect on damage of liver of streptozotocin-induced diabetes in rats.

Synthesis, characterization and antidiabetic properties of N(1)-2,4-dihydroxybenzylidene-N(4)-2-hydroxybenzylidene-S-methyl-thiosemicarbazidato-oxovanadium(IV)

A new oxovanadium(IV) chelate [VOL] (L: N(1)-2,4-dihydroxybenzylidene-N(4)-2-hydroxybenzylidene-S-methyl-thiosemicarbazidato) was synthesized and characterized by elemental analysis, conductivity and magnetic measurements, UV-vis, IR, EPR spectroscopy and mass spectrometry. The biochemical and immunohistochemical effects of the administration of the vanadium complex (VOL) into the pancreas of normal and streptozotocin-induced diabetic rats were profoundly investigated. The animals were randomly divided into four groups. Group I: control (intact) animals. Group II: control animals administered with VOL. Group III: STZ-induced diabetic animals. Group IV: STZ-induced diabetic animals administered with VOL. VOL was given to some of the experimental animals by gavage at a dose of 0.2mM/kg every day for 12 days. Blood samples were collected from animals, on 0 and 1, 6 and 12 days after STZ injection. On day 12, the pancreatic tissues were taken from the animals. The tissue sections were labelled with streptavidin biotin peroxidase technique for insulin. In the diabetic group, the blood glucose levels, aspartate and alanine transaminases, alkaline phosphatase activities were increased. But, in the diabetic+VOL groups, the blood glucose levels, aspartate and alanine transaminases, alkaline phosphatase activities were reduced. In the diabetic group, a decrease in the pancreatic glutathione levels, glutathione peroxidase and superoxide dismutase activities and an increase in the pancreatic lipid peroxidation level and catalase activities were observed. The administration of VOL to the diabetic rats reversed this diabetic effect due to its insulinomimetic effects. According to the immunohistochemical and biochemical results obtained, it was concluded that VOL can regenerate B cells of the pancreas in experimental diabetes and has an antidiabetic and protective effects on the pancreas.

Oxidative stress in the testis of hyperglycemic rabbits treated with repaglinide

In the present study, the induction of oxidative stress was examined in the testis of alloxan-induced diabetic rabbits. In addition, the protective effect of repaglinide, an oral anti-diabetic, at a dose of 1 mg daily was studied after four and eight weeks of the treatment. For these purposes, the levels of superoxide dismutase (Cu,Zn-SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-R), glutathione (GSH), ascorbic acid (AA), lipid peroxidation products (LPO) and protein carbonyl groups (PCG) were quantified. Hyperglycemia resulted in significant increases in the antioxidative enzymes, Cu, Zn-SOD, CAT, GSH-Px, and GSSG-R after four and eight weeks, respectively. There was also an increase in GSH level, and a decrease in the level of AA. These effects were accompanied by an elevation in testicular LPO levels and PCG levels. Repaglinide was found to normalize the activity of GSSG-R and levels of GSH and AA, and blunted the increased lipid peroxidation, however no decrease in PCG levels were observed. In conclusion, some oxidative changes provoked in the testis of rabbits by hyperglycemia, were found to be reduced with repaglinide treatment at therapeutic dose.

Ameliorative effects of proanthocyanidin on oxidative stress and inflammation in streptozotocin-induced diabetic rats

Recent evidence strongly suggests that oxidative stress due to redox imbalance is causally associated with inflammatory processes and various diseases including diabetes. We examined the effects of proanthocyanidin from persimmon peel, using both oligomers and polymers, against oxidative stress with elucidation of the underlying mechanisms in streptozotocin-induced diabetic rats. The elevation of lipid peroxidation in the kidney and serum under the diabetic condition was decreased by the administration of proanthocyanidin. The suppression of reactive oxygen species generation and elevation of the reduced glutathione/oxidized glutathione ratio were observed in the groups administered proanthocyanidin. These results support the protective role of proanthocyanidin from oxidative stress induced by diabetes. Moreover, proanthocyanidin, especially its oligomeric form, affected the inflammatory process with regulation of related protein expression, inducible nitric oxide synthase, cyclooxygenase-2, and upstream regulators, nuclear factor kappaB, and inhibitor-binding protein kappaB-alpha. Proanthocyanidin ameliorated the diabetic condition by decreases of serum glucose, glycosylated protein, serum urea nitrogen, urinary protein, and renal advanced glycation endproducts. In particular, oligomeric proanthocyanidin exerted a stronger protective activity than the polymeric form. This suggests that the polymerization of proanthocyanidin has an effect on its protective effect against diabetes. The present study supports the beneficial effect of proanthocyanidin against diabetes and oxidative stress-related inflammatory processes.

Attenuation of plasma dyslipidemia and oxidative damage by dietary caloric restriction in streptozotocin-induced diabetic rats

Oxidative stress has been proposed as the pathogenic mechanism linking insulin resistance with endothelial dysfunction during diabetes. The present study investigated the attenuation of plasma dyslipidemia and oxidative damage by caloric restriction in experimental diabetes. Forty male Wistar rats were divided into ad libitum and calorie-restricted groups. The calorie-restricted group was subjected to 30% caloric restriction for 63 days before induction of diabetes to 50% of both groups. Caloric restriction significantly (p<0.01) reduced the body weights, reactive oxygen species (ROS), catalase, total cholesterol levels and non-significantly reduced SOD activities in non-diabetic and diabetic rats. Caloric restriction was also found to improve blood glucose levels, glycated hemoglobin, malondialdehyde, triglyceride, oxidized glutathione and reduced glutathione levels and significantly (p<0.05) increased GPx and GR activities in the experimental animals. The non-diabetic rats fed ad libitum had the most significant increases in body weight which could be due to dyslipidemia. These results indicate that dietary caloric restriction attenuates the oxidative damage and dyslipidemia exacerbated during diabetes as evidenced by the significant reduction in their body weights, ROS, total cholesterol levels and the increases in GPx activity and redox status.

Antihyperglycemic effect of a new thiazolidinedione analogue and its role in ameliorating oxidative stress in alloxan-induced diabetic rats

Thiazolidinediones (TZDs) are a new class of antidiabetic drugs, having an insulin sensitizing effect in patients with type 2 diabetes. The contribution of oxidative stress from the standpoint of lipid and protein damage, alteration in endogenous antioxidant enzymes and effects of newly synthesized compounds, 5-[4-2-(6,7-Dimethyl-1,2,3,4-tetrahydro-2-oxo-4-quinoxalinyl)ethoxy]phenyl]methylene]thiazolid- ine-2,4-dione, (C(1)) in normal/alloxan-induced diabetic rats form the focus area of this study. Its effect was compared to two well-known TZDs, namely pioglitazone and rosiglitazone. It has been concluded from results that after thirty days of administration of C(1), Pg and Rg in alloxan-induced diabetic animal groups, the blood glucose level decreased, more remarkably in C(1) treated group. Also oxidative damage has been studied by estimating hepatic superoxide dismutase (SOD) activity, which was found to be increased (p<0.001 vs. control). An inverse change in SOD values between hepatic and pancreatic/kidney tissues were observed. Treatment with the test compounds lowered the activity of SOD in liver while increased its activity in kidney and pancreas. Similar normalizing effect of C(1) on liver, pancreatic and renal catalase (CAT)/ glutathione peroxidase (GPx) activities were pronounced in diabetic rats (p<0.001 vs. diabetic rats). Decreased reduced glutathione (GSH) content, found in diabetic animals, was significantly elevated to normal levels by C(1) treatment. The treatment with C(1) also decreased the levels of nitric oxide and increased the activities of glutathione-s-transferase and glutathione reductase, as compared to diabetic animals. Evidence of oxidative damage to lipids and proteins was shown through the quantification of protein carbonyl (in tissues) and malondialdehyde levels (both serum and tissues). It was observed that the protein/lipid damage in diabetic rats was improved by treatment with C(1). Total antioxidant activity (TAA) was found to be enhanced in C(1) treated rats (p>0.05 vs. group3, p<0.001 vs. group2, p<0.001 vs. group 4). These results suggest that the newly synthesized TZD derivative (C(1)) has a potential to act as antihyperglycemic and antioxidant agent. In addition, for all parameters checked, it has better efficacy than rosiglitazone and is as effective as pioglitazone.

Eucommia ulmoidesOliver Leaf Extract Increases Endogenous Antioxidant Activity in Type 2 Diabetic Mice

Eucommia ulmoides Oliver (Du-zhong) leaf extract was investigated for its antioxidant effects in type 2 diabetic animals, C57BL/KsJ-db/db mice. Du-zhong extract equivalent to 1% dried whole Du-zhong leaf (0.187 g of extract/100 g of diet) was added to the experimental diets for 6 weeks. The Du-zhong extract supplement significantly lowered blood glucose concentrations and elevated plasma paraoxonase activity compared with the control group. The activities of erythrocyte superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were significantly higher in the Du-zhong group compared with the control group, while glutathione reductase (GR) activity was not different between groups. The activities of SOD, GSH-Px, and GR in liver and kidney were not affected by Du-zhong extract supplementation, whereas the CAT activity was significantly higher in the Du-zhong group than in the control group. Du-zhong extract supplementation resulted in lower levels of hydrogen peroxide and lipid peroxide in erythrocytes, liver, and kidney. These results suggest that the antioxidant activity of Du-zhong extract is potentially beneficial for the prevention and management of complications of type 2 diabetes.

Dietary caloric restriction improves the redox status at the onset of diabetes in hepatocytes of streptozotocin-induced diabetic rats

Enhanced production of free radicals and oxidative stress induced by hyperglycemia play a central role in the pathogenesis of diabetes and its complications. This study assessed the attenuation by dietary caloric restriction on the oxidative and lipid peroxidative effects of diabetes in the liver through reduction in body and organ weights and concomitant metabolic changes. Three-month-old male Wistar rats were subjected to ad libitum feeding and 30% caloric restriction for 9 weeks before induction of diabetes by intraperitoneal injection of 35 mg/kg body weight streptozotocin. The animals were sacrificed 2 weeks after streptozotocin treatment depicting the onset of diabetes. Caloric restriction significantly reduced the organ weights (p<0.01), malondialdehyde (p<0.01) and catalase activity (p<0.01), but significantly increased glutathione reductase activity (p<0.01), and GSH/GSSG ratios (p<0.05). Caloric restriction also non-significantly reduced reactive oxygen species, superoxide dismutase and oxidized glutathione but increased glutathione peroxidase activity and reduced glutathione levels in the diabetic rats. Our data indicate a decrease in lipid peroxidation, improvement in the antioxidant defense systems and restoration of the redox status in the liver by caloric restriction. Therefore, this could provide a non-invasive antioxidant therapy early in diabetes to prevent the development of the complications associated with the disease.

Ameliorative effects of dietary caloric restriction on oxidative stress and inflammation in the brain of streptozotocin-induced diabetic rats

BACKGROUND

There is a strong association between oxidative stress and inflammation in the pathologies of diabetes. Recent evidence suggests that these phenomena could impair brain function. We investigated the potential role of dietary caloric restriction in ameliorating the effects of both oxidative stress and inflammation in the brain of streptozotocin-induced type 2 diabetic rats.

METHODS

Forty male Wistar rats were subjected to 30% caloric restriction (20 animals) and ad libitum feeding (20 animals) for 9 weeks before the induction of diabetes in 20 animals (10 from each group) by intraperitoneal injection of 35 mg/kg body weight streptozotocin.

RESULTS

Caloric restriction was able to significantly (p>0.05) reduce triglyceride, ROS, IL6, TNF-alpha and body weights in diabetic rats. However, no significant differences were obtained in the antioxidant enzyme (SOD, CAT and GPx) activities except in GPx where caloric restriction increased the levels in both non-diabetic and diabetic rats.

CONCLUSION

Caloric restriction was found to ameliorate the oxidative and inflammatory effects of diabetes in the brain. Non-diabetic rats feeding ad libitum were found to have increased levels of oxidative stress and inflammatory biomarkers and these could, in part, be due to their increased body weights.

Croton cajucara BENTH. Leaf Extract Scavenges the Stable Free Radical DPPH and Protects Against Oxidative Stress Induced by Paraquat

Antioxidant effects of extracts from Croton cajucara BENTH. leaves was investigated in different in vitro and in vivo models. Extracts showed inhibitory radical scavenging activity against the stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) (75%, 43% and 25% of the standard trolox at 1, 10 and 100 mg/ml, respectively; IC50 218 mg/ml). Percentage survival of Saccharomyces cerevisiae cells treated with 10 mM paraquat increased by 21% and 55%, when 1 mg/ml and 10 mg/ml concentrations of the extract, respectively, were added. The cytosolic concentration of TBARS increased in animals treated with paraquat (+283%), while values did not significantly differ from the controls in rats additionally receiving the leaf extract. Paraquat administration also induced a significant increase in hydroperoxide-initiated chemiluminiscence (+76%), that was partially prevented by the leaf extract (+31%). Liver SOD activity was a 158% higher in animals receiving paraquat as compared to the controls. This effect was abolished by administration of the leaf extract. Paraquat administration did not significantly modify the activity of GPx or catalase. Croton cajucara extract increased GPx and catalase activities in paraquat treated-animals by 342% and 70%, respectively. Our results confirm that Croton cajucara leaf extract present radical scavenging activity and reduce oxidative stress induced by paraquat, suggesting the beneficial use as a potential source of antioxidant agents of natural origin.

Kidney expression of glutathione peroxidase-1 is not protective against streptozotocin-induced diabetic nephropathy

In many diseases, including progressive renal disorders, tissue injury and pathological intracellular signaling events are dependent on oxidative stress. Glutathione peroxidase-1 (Gpx1) is an antioxidant enzyme that is highly expressed in the kidney and removes peroxides and peroxynitrite that can cause renal damage. Therefore, we examined whether this abundant renal antioxidant enzyme limits renal damage during the development of type 1 diabetic nephropathy. Wild-type (Gpx1+/+) and deficient (Gpx1−/−) mice were made diabetic by intraperitoneal injection of streptozotocin (100 mg/kg) on 2 consecutive days. Diabetic Gpx1+/+ and −/− mice with equivalent blood glucose levels (23 ± 4 mM) were selected and examined after 4 mo of diabetes. Compared with normal mice, diabetic Gpx1+/+ and −/− mice had a two- to threefold increase in urine albumin excretion at 2 and 4 mo of diabetes. At 4 mo, diabetic Gpx1+/+ and −/− mice had equivalent levels of oxidative renal injury (increased kidney reactive oxygen species, kidney lipid peroxidation, urine isoprostanes, kidney deposition of advanced glycoxidation, and nitrosylation end products) and a similar degree of glomerular damage (hypertrophy, hypercellularity, sclerosis), tubular injury (apoptosis and vimentin expression), and renal fibrosis (myofibroblasts, collagen, TGF-β excretion). A lack of Gpx1 was not compensated for by increased levels of catalase or other Gpx isoforms in diabetic kidneys. Contrary to expectations, this study showed that the high level of Gpx1 expressed in the kidney is not protective against the development of renal oxidative stress and nephropathy in a model of type 1 diabetes.

Alterations in antioxidant enzyme activities in the eyes, aorta and kidneys of diabetic rats relevant to the onset of oxidative stress

Profound changes in antioxidant enzyme activities were observed in a number of vascular tissues during the development of streptozotocin-induced diabetes in rats. In the eyes, there was an increase in superoxide dismutase activity at week 4 of diabetes. However, no difference in superoxide dismutase activity was observed between the control and diabetic animals at week 8. On the other hand, the diabetic state did not seem to affect the catalase activity in the eyes. There was a generalized increase in catalase activity of the eyes from week 4 to week 8 irrespective of the diabetic state. For glutathione peroxidase in the eyes, a decreased activity was observed in the diabetic animals at week 8, but not in week 4. A different pattern of enzyme activity changes was observed in the aorta where an increase in superoxide dismutase activity was observed in the diabetic group at week 4 but not in week 8. On the other hand, an increase in catalase activity was observed only at week 8 but not at week 4. Whereas there was no observed difference between the control and diabetic animals in glutathione peroxidase activity in the aorta, except for a generalized decrease from week 4 to week 8 in both groups of animals. In big contrast to the eyes and aorta where an increase in superoxide dismutase activity was observed at week 4 of diabetes, no change in kidney superoxide dismutase activity was noted at week 4 and a decrease was observed at week 8. A similar pattern of enzyme activity changes was observed for glutathione peroxidase in the kidneys. The catalase activity in the kidneys was not affected at all by the diabetic state at both week 4 and week 8. These results clearly demonstrate the active involvement of these antioxidant enzymes during the development of diabetes, and could be rationalized by the differential response of the tissues towards the different extent of oxidative stress imposed by the diabetic state on the different tissues.

Effects of repaglinide on oxidative stress in tissues of diabetic rabbits

In this study, the antioxidative properties of repaglinide were examined in tissues of alloxan-induced diabetic rabbits. Glutathione (GSH), glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-R) and protein carbonyl groups (PCG) were measured after 4 and 8 weeks treatment with repaglinide (0.3 mg/kg daily). In liver, diabetic versus control values (mean +/- S.E.M., p<0.05) for GSH-Px were 181.0 +/- 5.4 mU/mg protein versus 203.1 +/- 1.9 mU/mg protein and 187.4 +/- 6.6 mU/mg protein versus 240.9 +/- 18.8 mU/mg protein. The respective values for GSH were 33.7 +/- 0.4 nmol/mg protein versus 49.0 +/- 1.6 nmol/mg protein and 37.7 +/- 1.0 nmol/mg protein versus 41.2 +/- 0.7 nmol/mg protein. In diabetic kidney, GSSG-R activity (20.6 +/- 1.6 mU/mg protein versus 32.4 +/- 1.5 mU/mg protein and 23.6 +/- 0.6 mU/mg protein versus 36.3 +/- 0.3 mU/mg protein) and GSH level (16.6 +/- 0.5 nmol/mg protein versus 23.2 +/- 0.9 nmol/mg protein and 17.9 +/- 0.5 nmol/mg protein versus 23.2 +/- 0.6 nmol/mg protein) were reduced compared to control. PCG level was elevated in diabetic liver (0.58 +/- 0.02 nmol/mg protein versus 0.16 +/- 0.03 nmol/mg protein at 4 weeks and 0.64 +/- 0.04 nmol/mg protein versus 0.16 +/- 0.03 nmol/mg protein at 8 weeks) and in diabetic kidney (0.32 +/- 0.03 nmol/mg protein versus 0.11 +/- 0.02 nmol/mg protein and 0.35 +/- 0.03 nmol/mg protein versus 0.16 +/- 0.03 nmol/mg protein). Repaglinide did not affect the glucose level but reduced to some extent the oxidative stress enhanced by chronic hyperglycemia. In diabetic kidney, it restored to control values GSSG-R activity (45.4 +/- 2.0 mU/mg protein at 4 weeks and 41.1 +/- 0.07 mU/mg protein at 8 weeks), GSH level (27.0 +/- 0.8 and 26.8 +/- 0.9 nmol/mg protein), and partly PCG level (0.17 +/- 0.02 nmol/mg protein at 8 weeks). The treatment partly affected GSH-Px activity (262.7 +/- 17.6 mU/mg protein) and GSH level (40.4 +/- 1.4 nmol/mg protein) in diabetic liver. This study shows that repaglinide produces measurable antioxidative effects at therapeutic dose.

The effects of dietary caloric restriction on antioxidant status and lipid peroxidation in mild and severe streptozotocin-induced diabetic rats

BACKGROUND

Dietary caloric restriction (CR) without malnutrition is effective in the control of diabetes mellitus by stabilizing glucose homeostasis and enhancing glycemic control. Mild and severe streptozotocin-induced diabetic and non-diabetic rats were subjected to caloric restriction and ad libitum feeding to evaluate their effects on oxidative stress and lipid profile in the plasma of experimental animals.

METHODS

Mild and severe diabetes were induced in Male Wistar rats by intraperitoneal injection of 35 and 65 mg/kg streptozotocin respectively. The experimental animals were subjected to 40% caloric restriction and ad libitum feeding for 9 weeks.

RESULTS

CR was effective in significantly reducing body weight, blood glucose, HbA IC and TG concentrations (all p < 0.001) in mild diabetic rats and non-significantly improving the plasma HDL-cholesterol concentrations. However, CR did not produce any significant effect on the antioxidant enzyme activities and MDA concentrations in all the groups nor in any of the parameters measured in non-diabetic rats except their overall weight change. There were significant (p < 0.001) decreases in body weight and non-significant fluctuating results in HbA IC and HDL-cholesterol in severe diabetic animals.

CONCLUSIONS

These results demonstrate that caloric restriction is most effective in mild than in non-diabetic or severe diabetic animals.