Effects of Stobadine and Vitamin E in Diabetes-Induced Retinal Abnormalities: Involvement of Oxidative Stress

Background. Because hyperglycemia-induced oxidative stress may be a cause of retinopathy, this study examined the hypothesis that administration of exogenous antioxidants, stobadine (ST) and vitamin E (vitE), can restore retinal abnormalities in experimental diabetes. Methods. Normal and streptozotocin (STZ)-induced male Wistar rats received daily intraoral doses of ST (24.7 mg/kg) and vitE (a-dl-tocopherol acetate, 400e500 IU/kg) individually or in combinations for 8 months. The biochemical parameters including aldose reductase enzyme (AR) activity and lipid peroxidation (MDA), and histopathological changes such as retinal capillary basement membrane thickness (RCBMT) and vascular endothelial growth factor (VEGF) expression were evaluated. Results. A 37.99% increase in RCBMT was observed in rats after 8 months diabetes duration. The increase in RCBMT was 12.34% in diabetic rats treated with ST and 23.07% in diabetic rats treated with vitE. In diabetic rats treated with antioxidant combination, just a 4.38% increase was observed in RCBMT. The excess VEGF immunoreactivity and increased MDA and AR activity determined in diabetic retina were significantly attenuated by individual antioxidant treatments. Although both antioxidants decreased blood glucose, HbA1c, fructosamine and triglyceride levels in diabetic rats, poor glycemic control was maintained in all experimental groups during the treatment period. However, the antioxidant combination led to almost complete amelioration in retinal MDA and RCBMT in diabetic rats. Conclusions. The ability of antioxidant combination to arrest retinal abnormalities and lipid peroxidation even in the presence of poor glycemic control might advocate the key role of direct oxidative damage and the protective action of antioxidants in retinal alterations associated with diabetic retinopathy. Ó 2007 IMSS. Published by Elsevier Inc

Redox status related activation of endoplasmic reticulum stress and apoptosis caused by 4-hydroxynonenal exposure in INS-1 cells

4-Hydroxynonenal (HNE), a diffusible aldehyde product of membrane lipid peroxidation, can be produced by oxidative stress and has been detected in several diseases such as diabetes. In this study, we investigated the effects of HNE exposure on cytotoxicity, intracellular redox status, endoplasmic reticulum (ER) stress and apoptosis in insulinoma cell line (INS-1). Short-term (1 h) incubation of INS-1 cells with 0-50 mu M HNE decreased cell viability and caused depletion in reduced glutathione (GSH) levels and increased intracellular HNE-histidine adducts in a concentration-dependent manner. HNE activated the ER stress, leading to an increase in inositol-requiring enzyme-1a IRE1-alpha, phosphorylation of protein kinase-like ER kinase, phosphorylation of c-Jun N-terminal kinase (JNK) and increased the expression of CCAAT/enhancer binding protein (CHOP). Western blot analysis showed that HNE exposure induced dose-dependent activation of caspase 9 and caspase 3. These data indicate a potential role for HNE promoting deleterious effects toward pancreatic beta cell redox status and beta cell mass which may be important for the pathogenesis in diabetes

Impaired Na+,K+-ATPase activity as a mechanism of reactive nitrogen species-induced cytotoxicity in guinea pig liver exposed to lipopolysaccharides

In animal models of endotoxin, the excess production of NO and the reactive nitrogen species (RNS), are potent oxidant and nitrating agents, lead to lipid peroxidation, apoptosis, tissue dysfunction and injury and inactivate enzymes in many cell types. Although liver functions are well known to deteriorate following bacterial infection, the underlying specific mechanism(s) remain a matter of considerable debate. Therefore, the aim of the present study was to determine the in vivo effect of bacterial lipopolysaccharides (LPS) on Na+, K+-ATPase activity of guinea pig liver, and to investigate the possible contribution of RNS by measuring of iNOS activity and 3-nitrotyrosine (nTyr) levels. Liver Na+, K+-ATPase activity were maximally inhibited 6 h after LPS injection (p < 0.001). nTyr was not detectable in liver of normal control animals, but was detected markedly in LPS exposed animals. LPS treatment significantly increased iNOS activity of liver (p < 0.001). The regression analysis revealed a very close correlation between Na+, K+-ATPase activity and nTyr levels of LPS treated animals (r = -0.863, p < 0.001). Na+, K+-ATPase activity were also negatively correlated with iNOS activity (r = -0.823, p < 0.003) in inflamed tissues. Our results have strongly suggested that bacterial LPS disturbs activity of membrane Na+, K+-ATPase that may be an important component leading to the pathological consequences such as hepatocyte cell loss and dysfunction in which the production of RNS are increased as in the case of LPS challenge

Effects of olive leaf polyphenols against H₂O₂ toxicity in insulin secreting β-cells

In pancreatic β-cells, although H₂O₂ is a metabolic signal for glucose stimulated insulin secretion, it may induce injury in the presence of increased oxidative stress (OS) as in the case of diabetic chronic hyperglycemia. Olea europea L. (olive) leaves contain polyphenolic compounds that may protect insulin-secreting cells against OS. The major polyphenolic compound in ethanolic olive leaf extract (OLE) is oleuropein (about 20%), thus we compared the effects of OLE with the effects of standard oleuropein on INS-1 cells. The cells were incubated with increasing concentrations of OLE or oleuropein for 24 h followed by exposure to H₂O₂ (0.035 mM) for 45 min. H₂O₂ alone resulted in a significantly decreased viability (MTT assay), depressed glucose-stimulated insulin secretion, increased apoptotic and necrotic cell death (AO/EB staining), inhibited glutathione peroxidase activity (GPx) and stimulated catalase activity that were associated with increased intracellular generation of reactive oxygen species (ROS) (fluorescence DCF). OLE and oleuropein partly improved the viability, attenuated necrotic and apoptotic death, inhibited the ROS generation and improved insulin secretion in H₂O₂-exposed cells. The effects of oleuropein on insulin secretion were more pronounced than those of OLE, while OLE exerted a stronger anti-cytotoxic effect than oleuropein. Unlike OLE, oleuropein had no significant preserving effect on GPx; however, both compounds stimulated the activity of catalase in H₂O₂-exposed cells. These findings indicate different modulatory roles of polyphenolic constituents of olive leaves on redox homeostasis that may have a role in the maintenance of β-cell physiology against OS

Development of Novel Indole-Based Bifunctional Aldose Reductase Inhibitors/Antioxidants as Promising Drugs for the Treatment of Diabetic Complications

Aldose reductase (AR, ALR2), the first enzyme of the polyol pathway, is implicated in the pathophysiology of diabetic complications. Aldose reductase inhibitors (ARIs) thus present a promising therapeutic approach to treat a wide array of diabetic complications. Moreover, a therapeutic potential of ARIs in the treatment of chronic inflammation-related pathologies and several genetic metabolic disorders has been recently indicated. Substituted indoles are an interesting group of compounds with a plethora of biological activities. This article reviews a series of indole-based bifunctional aldose reductase inhibitors/antioxidants (ARIs/AOs) developed during recent years. Experimental results obtained in in vitro, ex vivo, and in vivo models of diabetic complications are presented. Structure–activity relationships with respect to carboxymethyl pharmacophore regioisomerization and core scaffold modification are discussed along with the criteria of ‘drug-likeness”. Novel promising structures of putative multifunctional ARIs/AOs are designed

A pyridoindole antioxidant SMe1EC2 regulates contractility, relaxation ability, cation channel activity, and protein-carbonyl modifications in the aorta of young and old rats with or without diabetes mellitus

We studied the effects of treatment with SMe1EC, a hexahydropyridoindole antioxidant, on vascular reactivity, endothelial function, and oxidonitrosative stress level of thoracic aorta in young and old rats with or without diabetes mellitus. The rats were grouped as young control (YC 3 months old), old control (OC 15 months old), young diabetic (YD), old diabetic (OD), young control treated (YCT), old control treated (OCT), young diabetic treated (YDT), and old diabetic treated (ODT). Diabetes was induced by streptozotocin injection and subsequently SMe1EC2 (10 mg/kg/day, p.o.) was administered to YCT, OCT, YDT, and ODT rats for 5 months. In young and old rats, diabetes resulted in hypertension, weight loss, hyperglycemia, and hypertriglyceridemia, which were partially prevented by SMe1EC2. SMe1EC2 also inhibited the diabetes-induced increase in aorta levels of AGEs (advanced glycosylation end-protein adducts), 4-HNE (4-hydroxy-nonenal-histidine), 3-NT (3-nitrotyrosine), and RAGEs (receptors for AGEs). The contractions of the aorta rings to phenylephrine (Phe) and KCL did not significantly change, but acetylcholine (ACh) and salbutamol relaxations were reduced in OC compared to YC rats. Diabetes induction increased Phe contractions in YC and OC rats, KCL contractions in YC rats, and did not cause further inhibition in already inhibited ACh and salbutamol relaxations in OC rats. We have achieved the lowest levels of ACh relaxation in YD rats compared to other groups. SMe1EC2 did not change the response of aorta to ACh, salbutamol and Phe in YC rats, and ameliorated ACh relaxations in OC and YD but not in OD rats. In YDT and ODT rats, increased Phe and KCL contractions, high blood pressure, and impaired salbutamol relaxations were amended by SMe1EC2. Phe contractions observed in YD and OD rats as well as KCl contractions observed in OC rats were the lowest levels when the rats were treated with SMe1EC2. When the bath solution was shifted to cyclopiazonic acid (CYP) or CYP plus Ca2+-free medium, the contraction induced by a single dose of Phe (3 x 10(-6) M) was more inhibited in YD and OD than in YC but not in OC rats. In SMe1EC2-treated rats, neither the presence of CFM nor CFM plus CYP exhibited a significant change in response of aorta to a single dose of Phe. These findings suggest that alpha 1-adrenergic receptor signaling is activated in both age groups of diabetic rats, diabetes activates K+-depolarization and calcium mobilization via Ca-V especially in the aorta of young rats, and sensitizes the aorta of old rats to the regulating effect of SMe1EC2. ACh relaxations were inhibited in YC rats, increased in OC rats and unchanged in YD and OD rats when aortic rings pretreated with TEA, an inhibitor of calcium-activated K+ channels (K-Ca), or 4-aminopyridine (4-AP), an inhibitor of voltage-sensitive K+ channels (K-V). ACh relaxations were inhibited in YCT, OCT, and YDT rats in the presence of 4-AP or TEA. In ODT rats, 4-AP did not change ACh relaxation but TEA inhibited. These findings suggest that the contribution of K-v and K-Ca to ACh relaxation is likely upregulated by SMe1EC2 when the relaxations were inhibited by aging or diabetes. We conclude that SMe1EC2 might be a promising agent for aging and diabetes related vascular disorders

Bacopa Monnieri Protects the Directly Affected Organ as Well as Distant Organs Against I/R Injury by Modulating Anti-Inflammatory and Anti-Nitrosative Pathways in A Rat Model for Infra-Renal Aortic Occlusion

Objective: To investigate the protective effect and underlying mechanisms of B. monnieri, a medicinal plant, on kidney and skeletal muscle injury induced by infra-renal abdominal aorta clamping for 2-hours (ischemia) and following removal of the clamp (reperfusion, 2-hours). Methods: Rats were divided into four groups (n = 6): (I) animals given only saline (sham-control); (II) animals given B. monnieri extract for 10-days (300 mg/kg/day) (Bacopa-treated sham); (III) animals subjected to ischemia/reperfusion (I/R); (IV) animals given B. monnieri extract and then subjected to I/R. Kidneys and lower extremity muscles were examined for GPx, CAT, iNOS, 3-NT, IL-1 beta and TNF-alpha. Apoptosis and injury were evaluated by TUNEL and H&E staining, respectively. Results: I/R resulted in TUNEL positive cells, periarterial edema and glomerular capillary dilatation, decreased GPx activity, unchanged CAT, iNOS, 3-NT, IL-1 beta and TNF-alpha in kidney. B. monnieri minimized renal remote reperfusion injury, and Group IV showed a lower degree of renal histopathology score when compared to the others. B. monnieri mitigated muscle I/R injury, decreased muscle hypertrophy, myofibril abnormalities and apoptosis. Muscle 3-NT and cytokine levels were increased by I/R, and B. monnieri inhibited iNOS and 3-NT both in sham-control and I/R groups. Muscle GPx unaffected by I/R or B. monnieri, but CAT was inhibited only in B. monnieri-treated I/R group. Muscle iNOS, 3-NT, IL-1 beta, TNF-alpha levels and CAT activity of B. monnieri-treated I/R rats were lower than those in sham-control or Bacopa-treated sham. Conclusions: B. monnieri can protect the directly affected organ as well as distant organs against I/R injury by modulating anti-inflammatory and anti-nitrosative pathways