Increased activity of H2O2 in aorta isolated from chronically streptozotocin-diabetic rats: effects of antioxidant enzymes and enzymes inhibitors

Phytochemical Analysis and hypoglycemic potential of Filago hurdwarica (Wall. ex DC.) Wagenitz in alloxan induced diabetic mice

Abstract Plants have profound therapeutic benefits, more economical treatments, fewer side effects, and a relatively cheap cost, making them a source of drugs for protective, preventative, curative, or conducive purposes and creating novel phytomedicines. Plant derived medicines are relatively safe compared to synthetic medicines. Many plants have proved to successfully aid in the treatment of diabetes including Filago hurdwarica (Wall. ex DC.) Wagenitz. The current investigations were therefore designed to assess the phytochemical, antioxidant, antidiabetic, and antihyperlipidemic activities of F. hurdwarica. The phytochemical investigations and antioxidant activities of different extracts were carried out using standard chemical tests, DPPH, and H2O2 scavenging assays. F. hurdwarica plant extract in Hydromethanolic solution were prepared by Soxhletation method and stored in refrigerator at 4°C for two days before use. Swiss Albino mice were made diabetic by a single dose of alloxan (150 mg/kg). Hydromethanolic plant extract and fractions of F. hurdwarica were screened for antidiabetic activity and given to the alloxan-induced diabetic mice at a concentration of 150-250 mg/kg of body weight in different groups of 6 diabetic mice each orally once a day for 15 days. Glibenclamide is also given to another group to as a standard drug to support the result at a dose of 10 mg/kg of body weight orally once a day for 15 days. Blood glucose levels and body weights of mice were measured on 0, 4, 7, 11 and 15th days. The study found that the extract was safe up to the dose level of 2000 mg/kg and the dose response effect of chloroform extract (150-250 mg/kg) of F. hurdwarica showed expressive antihyperglycemic effects and also improved other altered biochemical parameters associated with diabetes. The FTIR and XRD spectra demonstrated the occurrence of phenols, alcohols, alkenes, alkyl halides, ketones, and aromatic compounds and confirmed the amorphous nature of the extract. GC-MS spectral analysis showed the tentative presence of 31 phytochemical constituents in the chloroform extract of F. hurdwarica with different retention time. To conclude, the chloroform extract (250 mg/kg) of F. hurdwarica revealed considerable antioxidant, antihyperglycemic, and antihyperlipidemic potential and is safe for treating diabetes and related complications.

Phytochemical Investigation and Therapeutical Potential of Cotinus coggygria Scop. in Alloxan-Induced Diabetic Mice

Plants are a significant source for the development of new phytomedicines due to their great clinical benefits, efficiency, cost-effectiveness, fewer side effects, and more affordable therapies. Numerous plants used in traditional treatments, such as Cotinus coggygria Scop., have been effective in the treatment of diabetes mellitus (DM). Therefore, the study is aimed at assessing the phytochemical, antioxidant, and antidiabetic properties of C. coggygria. The hypoglycemic and hypolipidemic activity was evaluated in Swiss male Albino mice by administering an oral dose of 150-250 mg/kg of C. coggygria extracts in alloxan-induced diabetic mice for 15 days. The antioxidant activity and phytochemical composition of the extracts were assessed by using α, α diphenyl-β-picrylhydrazyl (DPPH) and hydrogen peroxide scavenging assays and through standard chemical procedures. The effects of extracts on blood glucose, body weight, lipid profile, and biochemical parameters like total cholesterol (TC), triglyceride (TG), low-density lipids (LDL), high-density lipids (HDL), plasma insulin, liver glycogen, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), urea, and creatinine were determined according to standard procedures. The activities of antioxidant enzymes such as superoxide-dismutase (SOD), peroxidase (POD), and catalase (CAT) were also analyzed spectrophotometrically. The hypoglycemic and hypolipidemic effects with chloroform extracts of 250 mg/kg were found significant in the treatment of diabetes in alloxanised mice compared to the diabetic group. The haematological parameters such as TC, TG, HDL, LDL, creatinine, urea, AST, ALT, and ALP were significantly improved (p < 0.01) by the chloroform extract of 250 mg/kg compared to the diabetic group. Treatment for 15 days showed significant elevation (p < 0.01) of antioxidant enzymes. Fourier-transform infrared spectroscopic (FTIR) and gas chromatography-mass spectrometry (GC-MS), column chromatography (CC), and nuclear magnetic resonance (NMR) analyses tentatively identified different phytoconstitutents and metabolites in C. coggygria leaves, which have been reported to possess antihyperglycemic properties. In conclusion, the chloroform extract of 250 mg/kg of C. coggygria possesses significant hypoglycemic and hypolipidemic potential which may prove the claimed use of the plant in amelioration of diabetes and associated complications in folkloric medicine. Additional studies are required for the purification, characterization, and structural elucidation of bioactive compounds.

A mitochondria-targeted rhodol fluorescent probe for imaging of hydrogen peroxide in living cells

Hydrogen peroxide (H₂O₂) is a main member of reactive oxygen species (ROS) in cells that has a significant impact on various physiological and pathological processes of organisms. Here, we designed and synthesized a new type of fluorescent probe Rhodol-OAc for the specific detection of H₂O₂. The probe had good water solubility, high selectivity and sensitivity to H₂O₂, low cytotoxicity, excellent mitochondrial targeting ability, etc. It was successfully applied in the imaging of exogenous and endogenous H₂O₂ in living cells. In addition, theoretical calculations were carried out to clarify the luminescence mechanism of the probe. More importantly, we successfully applied the probe to indirectly detect xanthine and glucose, the metabolism of which generates H₂O₂, and achieved satisfactory results.

Investigation of healing effects of lemon (Citrus limonum) seeds lyophilized extracts on experimental diabetic rats

In this study, the effects of lemon seed lyophilised extract (LSLE) were investigated on the diabetic rats. Groups were conducted as normal control (NC), diabetic control (DC), diabetic + 20 mg acarbose/kg bw (DAC)), diabetic + 100 mg LSLE/kg bw (DLSLE1), diabetic + 200 LSLE mg/kg bw (DLSLE2) and diabetic + 400 LSLE mg/kg bw (DLSLE4). The protective and antioxsidant effects of LSLE on experimental diabetes complications were evaluated by measuring hepatic and renal damage biomarkers (HRDBs), antioxidant defence system constituents (ADSCs), diabetes biomarkers and MDA content in tissues of diabetic rats. Glucose, HRDBs, HbA1c, lipid profile (LP) levels increased in DC compared to NC whereas these parameters of the supplementation groups showed a significant decreas compared to DC. Also, it was determined an increase MDA content and fluctuate ADSCs in the DC tissues whereas the LSLE restored the parameters towards to the NC. It can be said that LSLE is may have healings effects against diabetic complications.

Redox-active phytoconstituents ameliorate cell damage and inflammation in rat hippocampal neurons exposed to hyperglycemia+Aβ1-42 peptide

Alzheimer's disease (AD) is the most common dementia causing progressive loss of memory and compromised cognitive functions. Although the neurotoxic mechanisms underlying AD have yet to be fully elucidated, hyperglycemia seems to trigger oxidative and inflammatory responses in the brain of afflicted patients. Removal of free radicals reduces the neurotoxic effects of hyperglycemia in AD models. In this study we investigated the neuroprotective effects of the antioxidant phytoconstituents oleuropein (OLE), rutin (RUT), luteolin (LUT) and S-allylcysteine (SAC) in an experimental model combining the exposure to high glucose (HG, mimicking chronic hyperglycemia) plus amyloid-β peptide 1-42 (Aβ_1-42, mimicking AD) in primary hippocampal neurons. Cells were pre-treated with OLE, RUT, LUT or SAC (10-1000 nM), and then co-treated with high glucose (GLU, 150 mM) for 24 h plus 500 nM oligomeric Aβ_1-42 for 24 h more. Cell viability and reactive oxygen species (ROS) formation were assessed as indices of survival/toxicity and oxidative stress, respectively. Activity/expression of antioxidant enzymes, toxic adducts, inflammatory molecules, mitochondrial membrane potential (ΔΨm) and the pattern of amyloid aggregation were also assessed. The GLU + Aβ_1-42 treatment significantly decreased cell viability, increased ROS formation, reduced superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase activities, augmented Advanced Glycation End Products- and 4-hydroxynonenal-adducts generation, increased 3-nitrotyrosine and inflammatory outcomes such as inducible nitric oxide synthase, interleukin 1β and Tumor Necrosis Factor α, decreased MMP and augmented amyloid aggregation. All phytoconstituents reduced in a differential manner all toxic endpoints, with SAC showing the highest efficacy in preventing loss of cell viability and oxidative damage, whereas RUT was most efficacious in mitigating inflammatory endpoints. Combined, the results of this study suggest that protection afforded by these compounds against GLU + Aβ_1-42-induced cell damage in hippocampal neurons is attributable to their properties as redox modulators, which might act through a concerted mechanism oriented to reduce oxidative stress and neuroinflammation.

Multidrug resistance associated protein-1 (MRP1) deficiency attenuates endothelial dysfunction in diabetes

AIM

The multidrug resistance associated protein-1 (MRP1) is the main transporter of oxidized glutathione in endothelial cells, and blockade of MRP1 improves endothelial cell dysfunction induced by reactive oxygen species. We therefore investigated the role of MRP1 in hyperglycemia-induced endothelial dysfunction and ROS production.

METHODS AND RESULTS

Diabetes was induced in 12 week old male MRP1(-/-)- or corresponding FVB wild-type (wt) mice by injection of streptozotocin (50mg/kg for 5 days). Eight weeks thereafter acetylcholine-induced endothelium-dependent vasorelaxation was blunted in aortic rings from diabetic wt mice (blood glucose levels >250 mg/dl) compared with nondiabetic animals (Rmax 74 ± 2% vs. 94 ± 2%, p<0.001). However in aortae from diabetic mice lacking MRP1, endothelium-dependent vasorelaxation was only mildly impaired (Rmax 87 ± 3%, p<0.001 vs. wt). Endothelium-independent relaxation induced by DEA-NONOate was not different among the groups. Streptozotocin-induced diabetes significantly increased aortic superoxide anion and hydrogen peroxide production in wild-type but not in MRP1(-/-) mice. Aortic levels of glutathione were significantly diminished in STZ-treated FVB mice, while preserved in MRP1(-/-) mice. Further, in cultured human aortic endothelial cells, high glucose levels (30 mmol/l) over 5 days significantly increased superoxide production which was inhibited by downregulation of MRP1 via siRNA.

CONCLUSIONS

These data indicate that MRP1 plays an important role for endothelial dysfunction and reactive oxygen species production in diabetes and under conditions of hyperglycemia. MRP1 therefore may represent a therapeutic target in treatment of diabetes induced vascular dysfunction.

Carbonyl stress in aging process: role of vitamins and phytochemicals as redox regulators

There is a growing scientific agreement that the cellular redox regulators such as antioxidants, particularly the natural polyphenolic forms, may help lower the incidence of some pathologies, including metabolic diseases like diabetes and diabesity, cardiovascular and neurodegenerative abnormalities, and certain cancers or even have anti-aging properties. The recent researches indicate that the degree of metabolic modulation and adaptation response of cells to reductants as well as oxidants establish their survival and homeostasis, which is linked with very critical balance in imbalances in cellular redox capacity and signaling, and that might be an answer the questions why some antioxidants or phytochemicals potentially could do more harm than good, or why some proteins lose their function by increase interactions with glyco- and lipo-oxidation mediates in the cells (carbonyl stress). Nonetheless, pursue of healthy aging has led the use of antioxidants as a means to disrupt age-associated physiological dysfunctions, dysregulated metabolic processes or prevention of many age-related diseases. Although it is still early to define their exact clinical benefits for treating age-related disease, a diet rich in polyphenolic or other forms of antioxidants does seem to offer hope in delaying the onset of age-related disorders. It is now clear that any deficiency in antioxidant vitamins, inadequate enzymatic antioxidant defenses can distinctive for many age-related disease, and protein carbonylation can used as an indicator of oxidative stress associated diseases and aging status. This review examines antioxidant compounds and plant polyphenols as redox regulators in health, disease and aging processes with hope that a better understanding of the many mechanisms involved with these distinct compounds, which may lead to better health and novel treatment approaches for age-related diseases.

Chronic supplementation of paeonol combined with danshensu for the improvement of vascular reactivity in the cerebral basilar artery of diabetic rats

One of the leading causes of death in the world is cerebrovascular disease. Numerous Chinese traditional medicines, such as Cortex Moutan (root bark of Paeonia suffruticosa Andrew) and Radix Salviae miltiorrhizae (root and rhizome of Salvia miltiorrhiza Bunge), protect against cerebrovascular diseases and exhibit anti-atherosclerotic effects. Traditional medicines have been routinely used for a long time in China. In addition, these two herbs are prescribed together in clinical practice. Therefore, the pharmacodynamic interactions between the active constituents of these two herbs, which are paeonol (Pae) and danshensu (DSS), should be particularly studied. The study of Pae and DSS can provide substantial foundations in understanding their mechanisms and empirical evidence to support clinical practice. This study investigated the effects and possible mechanisms of the pharmacodynamic interaction between Pae and DSS on cerebrovascular malfunctioning in diabetes. Experimental diabetes was induced in rats, which was then treated with Pae, DSS, and Pae + DSS for eight weeks. Afterward, cerebral arteries from all groups were isolated and equilibrated in an organ bath with Krebs buffer and ring tension. Effects of Pae, DSS, and Pae + DSS were observed on vessel relaxation with or without endothelium as well as on the basal tonus of vessels from normal and diabetic rats. Indexes about oxidative stress were also determined. We report that the cerebral arteries from diabetic rats show decreased vascular reactivity to acetylcholine (ACh) which was corrected in Pae, DSS, and Pae + DSS treated groups. Furthermore, phenylephrine (PE)-induced contraction response decreased in the treated groups. Phenylephrine and CaCl(2)-induced vasoconstrictions are partially inhibited in the three treated groups under Ca2+-free medium. Pre-incubated with tetraethylammonium, a non-selective K+ channel blocker, the antagonized relaxation responses increased in DSS and Pae + DSS treated diabetic groups compared with those in diabetic and Pae-treated diabetic groups. In addition, superoxide dismutase activity and thiobarbituric acid reactive substances content significantly changed in the presence of Pae + DSS. We therefore conclude that both Pae and DSS treatments prevent diabetes-induced vascular damage. Furthermore, Pae + DSS prove to be the most efficient treatment regimen. The combination of Pae and DSS produce significant protective effects through the reduction of oxidative stress and through intracellular Ca2+ regulatory mechanisms.

Osmotic stress induced oxidative damage: possible mechanism of cataract formation in diabetes

Chronic hyperglycemia causes increased level of reactive oxygen species which is thought to be involved in the pathogenesis of diabetes associated complications including cataract. In diabetic cataractous lens, over production of free radicals and decreased capacity of antioxidant defense system are the major contributors to oxidative damage by polyol pathway and advanced glycation end products. The current study focused on analysis of factors associated with osmotic imbalance and oxidative stress in aging and diabetic human cataractous lenses. We examined activities of polyol pathway enzymes, G6PD and glutathione system in lenses from subjects suffering from cataract due to aging and diabetes. We observed elevated activities of aldose reductase and sorbitol dehydrogenase while G6PD and glutathione system enzyme activities were found to be lower in cataractous subjects suffering from diabetes. The findings from the current study support the premise that osmotic imbalance, AGEs formation and oxidative stress contribute synergistically to the development of lens opacity in hyperglycemia.

Evaluation of antidiabetic and antioxidant activity of Moringa oleifera in experimental diabetes

BACKGROUND

Moringa oleifera, a widely cultivated species in India, is an exceptionally nutritious vegetable with a variety of potential uses in treating rheumatism, venomous bites, and microbial infections. In the present study, we investigated the antidiabetic and antioxidant effects of methanol extracts of M. oleifera pods (MOMtE) in streptozotocin (STZ)-induced diabetic albino rats.

METHODS

Diabetic rats were treated with 150 or 300 mg/kg MOMtE for 21 days and the antidiabetic effects of the extract were evaluated by measuring changes in biochemical parameters in the serum and pancreatic tissue. Two phytoconstituents, namely quercetin and kaempferol, were isolated from the MOMtE extract and their structures were determined using nuclear magnetic resonance and infrared spectroscopy.

RESULTS

The progression of diabetes was significantly reduced after MOMtE treatment. In treated rats, both doses of MOMtE induced a significant reduction in serum glucose and nitric oxide, with concomitant increases in serum insulin and protein levels. Furthermore, MOMtE treatment increased antioxidant levels in pancreatic tissue, with concomitant decreases in levels of thiobarbituric acid-reactive substances. Histologic examination of the pancreas from diabetic rats showed degenerative changes in β-cells; MOMtE treatment significantly reversed the histoarchitectural damage to the islets cells.

CONCLUSION

In conclusion, M. oleifera exerts protective effects against STZ-induced diabetes. The MOMtE exhibited significant antidiabetic and antioxidant activity and active constituents may be isolated from the extract for evaluation in future clinical studies.

Glycoxidative stress and cardiovascular complications in experimentally-induced diabetes: effects of antioxidant treatment

Diabetes mellitus (DM) is a common metabolic disease, representing a serious risk factor for the development of cardiovascular complications, such as coronary heart disease, peripheral arterial disease and hypertension. Oxidative stress (OS), a feature of DM, is defined as an increase in the steady-state levels of reactive oxygen species (ROS) and may occur as a result of increased free radical generation and/or decreased anti-oxidant defense mechanisms. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage in DM, either through repeated acute changes in cellular glucose metabolism, or through long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs are formed by the Maillard process, a non-enzymatic reaction between ketone group of the glucose molecule or aldehydes and the amino groups of proteins that contributes to the aging of proteins and to the pathological complications of DM. In the presence of uncontrolled hyperglycemia, the increased formation of AGEs and lipid peroxidation products exacerbate intracellular OS and results in a loss of molecular integrity, disruption in cellular signaling and homeostasis, followed by inflammation and tissue injury such as endothelium dysfunction, arterial stiffening and microvascular complications. In addition to increased AGE production, there is also evidence of multiple pathways elevating ROS generation in DM, including; enhanced glucose auto-oxidation, increased mitochondrial superoxide production, protein kinase C-dependent activation of NADPH oxidase, uncoupled endothelial nitric oxide synthase (eNOS) activity, increased substrate flux through the polyol pathway and stimulation of eicosanoid metabolism. It is, therefore, not surprising that the correction of these variables can result in amelioration of diabetic cardiovascular abnormalities. A linking element between these phenomena is cellular redox imbalance due to glycoxidative stress (GOS). Thus, recent interest has focused on strategies to prevent, reverse or retard GOS in order to modify the natural history of diabetic cardiovascular abnormalities. This review will discuss the links between GOS and diabetes-induced cardiovascular disorders and the effect of antioxidant therapy on altering the development of cardiovascular complications in diabetic animal models.

Reactive oxygen-derived free radicals are key to the endothelial dysfunction of diabetes

Vascular complications are an important pathological issue in diabetes that lead to the further functional deterioration of several organs. The balance between endothelium-dependent relaxing factors and endothelium-dependent contracting factors (EDCFs) is crucial in controlling local vascular tone and function under normal conditions. Diabetic endothelial dysfunction is characterized by reduced endothelium-dependent relaxations and/or enhanced endothelium-dependent contractions. Elevated levels of oxygen-derived free radicals are the initial source of endothelial dysfunction in diabetes. Oxygen-derived free radicals not only reduce nitric oxide bioavailability, but also facilitate the production and/or action of EDCFs. Thus, the endothelial balance tips towards vasoconstrictor responses over the course of diabetes.

The effects of Yucca schidigera and Quillaja saponaria on DNA damage, protein oxidation, lipid peroxidation, and some biochemical parameters in streptozotocin-induced diabetic rats

The aim of this study was to examine the effects of Yucca schidigera, Quillaja saponaria, and a mixture of both plants on streptozotocin-induced diabetic rats. Animals were allocated into five groups with 10 rats each. The control (C) and diabetic control group (D) were fed with standard rat feed (SRF). The other diabetic groups, the Y. schidigera group (DY), the Q. saponaria group (DQ), and the mix group (DQY), were fed ad libitum using SRF+100 ppm Y. schidigera powder (Sarsaponin 30), SRF+100 ppm Q. saponaria powder (Nutrafito), and SRF+100 ppm Y. schidigera-Q. saponaria powder (Nutrafito Plus), respectively, for 3 weeks. The blood glucose level was found to be significantly lower in the DY and DQ groups than in the D and DQY groups (P<.001). The insulin levels increased in the DY and DQY groups (P<.05). Plasma cholesterol and triglyceride levels in the DY, DQ, and DQY groups significantly decreased compared to those of the D group (P<.01, P<.001, respectively). HDL in the diabetic groups significantly increased in the DQ and DQY groups (P<.05), while LDL did not show any significant change. Mononuclear leukocyte DNA damage, plasma malondialdehyde, and plasma protein carbonyl levels were found to be significantly lower (P<.001, P<.001, P<.05, respectively) in the DY, DQ, and DQY groups according to the D group. The low level of nitric oxide in diabetic rats increased in the DQ group (P<.01). Total antioxidant capacity between groups did not differ. Our results thus suggested that Q. saponaria and Y. schidigera powders could help in the treatment of the disease owing to their hypoglycemic, hypocholesterolemic, and antioxidant effects.

Oxidative stress and COX cause hyper-responsiveness in vascular smooth muscle of the femoral artery from diabetic rats

BACKGROUND AND PURPOSE

To investigate the dysfunction of vascular smooth muscle in streptozotocin-induced diabetic rats.

EXPERIMENTAL APPROACH

Rings without endothelium of femoral arteries were suspended in organ chambers for isometric tension recording. The production of oxygen-derived free radicals was measured with 2',7'-dichlorodihydrofluorescein diacetate using confocal microscopy. The protein expressions were measured by western blotting.

KEY RESULTS

The concentration-response curves to U46619 and phenylephrine, but not that to KCl, were shifted to the left, suggesting a hypersensitivity of cell membrane receptors in diabetes. Exogenous oxygen-derived free radicals induced greater vasoconstrictions in the femoral artery from diabetic rats. Chronic treatment with apocynin (inhibitor of NADPH oxidase) and acute exposure to MnTMPyP (SOD/catalase mimetic) normalized the response. The catalase activity and the total glutathione level were reduced in arteries from streptozotocin-treated rats, confirming a redox abnormality. The basal oxidative state was higher in arteries from streptozotocin-treated rats and reduced in arteries from apocynin- and streptozotocin-treated rats, suggesting that the functional changes in diabetes are due to a chronic increase in oxidative stress. In the arteries of streptozotocin-treated rats, inhibitors of COX-1 and/or COX-2 prevented the hypersensitivity and reduced the increase in oxidative stress caused by phenylephrine and U46619, suggesting that both isoforms contribute to the smooth muscle dysfunction. The expression of proteins for COX-1 and COX-2 was increased in arteries of streptozotocin-treated rats and reduced in preparations of apocynin- and streptozotocin-treated rats.

CONCLUSIONS AND IMPLICATIONS

Chronic diabetes and the resulting increased oxidative stress activate the production of COX-derived vasoconstrictor prostanoids causing hypersensitivity of vascular smooth muscle.

Oxygen-derived free radicals mediate endothelium-dependent contractions in femoral arteries of rats with streptozotocin-induced diabetes

BACKGROUND AND PURPOSE

The present experiments were designed to study the contribution of oxygen-derived free radicals to endothelium-dependent contractions in femoral arteries of rats with streptozotocin-induced diabetes.

EXPERIMENTAL APPROACH

Rings with and without endothelium were suspended in organ chambers for isometric tension recording. The production of oxygen-derived free radicals in the endothelium was measured with 2',7'-dichlorodihydrofluorescein diacetate using confocal microscopy. The presence of protein was measured by western blotting.

KEY RESULTS

In the presence of L-NAME, the calcium ionophore A23187 induced larger endothelium-dependent contractions in femoral arteries from diabetic rats. Tiron, catalase, deferoxamine and MnTMPyP, but not superoxide dismutase reduced the response, suggesting that oxygen-derived free radicals are involved in the endothelium-dependent contraction. In the presence of L-NAME, A23187 increased the fluorescence signal in femoral arteries from streptozotocin-treated, but not in those from control rats, confirming that the production of oxygen-derived free radicals contributes to the enhanced endothelium-dependent contractions in diabetes. Exogenous H2O2 caused contractions in femoral arterial rings without endothelium which were reduced by deferoxamine, indicating that hydroxyl radicals contract vascular smooth muscle and thus could be an endothelium-derived contracting factor in diabetes. The reduced presence of Mn-SOD and the decreased activity of catalase in femoral arteries from streptozotocin-treated rats demonstrated the presence of a redox abnormality in arteries from rats with diabetes.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that the redox abnormality resulting from diabetes increases oxidative stress which facilitates and/or causes endothelium-dependent contractions.

Stobadine protects rat kidney against ischaemia/reperfusion injury

1. Ischaemia-reperfusion (I/R) injury, one of the main causes of acute renal failure, still needs satisfactory treatment for routine clinical application. Stobadine, a novel synthetic pyridoindole anti-oxidant, has the ability to reduce tissue injury induced by mechanisms involving reactive oxygen species during I/R. The aim of the present study was to determine the effects of stobadine on renal I/R injury. 2. Forty male Wistar rats were randomly divided into four groups as follows: sham, I/R, stobadine treated and I/R + stobadine treated. Stobadine (2 mg/kg, i.v.) was given intravenously to two groups of rats. The stobadine-treated group was treated with stobadine following sham operation before the abdominal wall was closed, whereas the I/R + stobadine group received stobadine at the beginning of reperfusion. Renal I/R was achieved by occluding the renal arteries bilaterally for 40 min, followed by 6 h reperfusion. Immediately thereafter, blood was drawn and tissue samples were harvested to assess: (i) serum levels of blood urea nitrogen and creatinine; (ii) serum and/or tissue levels of malondialdehyde (MDA), glutathione (GSH), glucose 6-phosphate dehydrogenase (G-6PD), 6-phosphogluconate dehydrogenase (6-PGD), glutathione reductase (GR) and glutathione peroxidase (GPx); (iii) renal morphology; and (iv) immunohistochemical staining for P-selectin. 3. Stobadine was able to significantly attenuate the renal dysfunction as a result of renal I/R injury. Ischaemia-reperfusion resulted in a significant increase in serum and kidney MDA levels and a decrease in serum and kidney GSH. Stobadine treatment at the beginning of reperfusion attenuated both the increased MDA levels and decreased GSH secondary to I/R injury. In addition, the decreased G-6PD activity observed after I/R was significantly attenuated by stobadine treatment. Stobadine did not alter 6-PGD activity after I/R. Neither GR nor GPx activity was significantly changed in the I/R alone or the I/R + stobadine groups compared with the sham group. In addition, stobadine decreased the morphological deterioration and high P-selectin immunoreactivity secondary to renal I/R injury. 4. A pyridoindole anti-oxidant, stobadine exerts a renal protective effect in renal I/R injury, which is probably due to its radical-scavenging and anti-oxidant activities.

Hydrogen peroxide modulates angiotensin II-induced contraction of mesenteric arteries from streptozotocin-induced diabetic rats

Hydrogen peroxide (H(2)O(2)) contributes in the regulation of vascular tone, especially in pathological states. The role of H(2)O(2) and superoxide anion free radicals in angiotensin II (Ang II)-induced contraction of diabetic tissues was examined with the aim of elucidating the underlying mechanisms. Isometric tension in response to various drug treatments was measured in isolated superior mesenteric arteries of streptozotocin (STZ)-induced diabetic WKY rats using the Mulvany wire myograph. Compared to the normal (euglycaemic) arteries, the Ang II-induced contraction was significantly reduced in diabetic arteries. Superoxide dismutase (SOD; converts superoxide to H(2)O(2)) significantly reduced the contraction in both types of arteries -- an effect abolished by catalase (H(2)O(2) scavenger), suggesting that the SOD effect was mediated by H(2)O(2). Treatment with catalase had no effect on the Ang II contraction in euglycaemic arteries, but it raised the contraction in diabetic arteries to euglycaemic levels. This increase was similar to that observed with diabetic arteries incubated with L-NAME. Combined catalase and L-NAME treatment further enhanced the contraction in diabetic arteries, suggesting that the catalase effect was not mediated by nitric oxide (NO). The catalase effect was abolished by indomethacin treatment. These results suggest that attenuation of Ang II-induced contraction in diabetic tissues is modulated by endogenous H(2)O(2), the scavenging of which unmasks an indomethacin-sensitive (and therefore cyclooxygenase product-mediated) Ang II-induced contraction.

Protective effect of Lycium barbarum polysaccharides on streptozotocin-induced oxidative stress in rats

Fruit from Lycium barbarum L. in the family Solanaceae is well-known in traditional Chinese herbal medicine. Lycium barbarum polysaccharides (LBP) have been identified as one of the active ingredients responsible for its biological activities. We isolated polysaccharides from dried Lycium barbarum fruits by boiling water extraction. In the study, 50 animals were divided into two groups: a nondiabetic control (n=10) and a diabetic group (n=40). Diabetes was induced by a single injection of streptozotocin (50mg/kg BW; Sigma, USA) freshly dissolved in a 0.1 mol/L citrate buffer (pH 4.5) into the intraperitonium. The normal control rats and the untreated diabetic control rats were only injected with the citrate buffer. Treated diabetic rats were administrated with LBP in drinking water through oral gavage for 30 days. At the end of experiment, oxidative indice in blood, liver and kidney of all groups were examined. The results show that administration of LBP can restore abnormal oxidative indice near normal levels. Therefore, we may assume that LBP is effective in the protection of liver and kidney tissue from the damage of STZ-induced diabetic rats and that the LBP may be of use as a antihyperglycemia agent.

Acrolein generation stimulates hypercontraction in isolated human blood vessels

Increased risk of vasospasm, a spontaneous hyperconstriction, is associated with atherosclerosis, cigarette smoking, and hypertension-all conditions involving oxidative stress, lipid peroxidation, and inflammation. To test the role of the lipid peroxidation- and inflammation-derived aldehyde, acrolein, in human vasospasm, we developed an ex vivo model using human coronary artery bypass graft (CABG) blood vessels and a demonstrated acrolein precursor, allylamine. Allylamine induces hypercontraction in isolated rat coronary artery in a semicarbazide-sensitive amine oxidase activity (SSAO) dependent manner. Isolated human CABG blood vessels (internal mammary artery, radial artery, saphenous vein) were used to determine: (1) vessel responses and sensitivity to acrolein, allylamine, and H(2)O(2) exposure (1 microM-1 mM), (2) SSAO dependence of allylamine-induced effects using SSAO inhibitors (semicarbazide, 1 mM; MDL 72274-E, active isomer; MDL 72274-Z, inactive isomer; 100 microM), (3) the vasoactive effects of two other SSAO amine substrates, benzylamine and methylamine, and (4) the contribution of extracellular Ca(2+) to hypercontraction. Acrolein or allylamine but not H(2)O(2), benzylamine, or methylamine stimulated spontaneous and pharmacologically intractable hypercontraction in CABG blood vessels that was similar to clinical vasospasm. Allylamine-induced hypercontraction and blood vessel SSAO activity were abolished by pretreatment with semicarbazide or MDL 72274-E but not by MDL 72274-Z. Allylamine-induced hypercontraction also was significantly attenuated in Ca(2+)-free buffer. In isolated aorta of spontaneously hypertensive rat, allylamine-induced an SSAO-dependent contraction and enhanced norepinephrine sensitivity but not in Sprague-Dawley rat aorta. We conclude that acrolein generation in the blood vessel wall increases human susceptibility to vasospasm, an event that is enhanced in hypertension.

Endothelium-dependent smooth muscle hyperpolarization: do gap junctions provide a unifying hypothesis?

An endothelium-derived hyperpolarizing factor (EDHF) that is distinct from nitric oxide (NO) and prostanoids has been widely hypothesized to hyperpolarize and relax vascular smooth muscle following stimulation of the endothelium by agonists. Candidates as diverse as K(+) ions, eicosanoids, hydrogen peroxide and C-type natriuretic peptide have been implicated as the putative mediator, but none has emerged as a 'universal EDHF'. An alternative explanation for the EDHF phenomenon is that direct intercellular communication via gap junctions allows passive spread of agonist-induced endothelial hyperpolarization through the vessel wall. In some arteries, eicosanoids and K(+) ions may themselves initiate a conducted endothelial hyperpolarization, thus suggesting that electrotonic signalling may represent a general mechanism through which the endothelium participates in the regulation of vascular tone.

Decreased oxidative stress in prehepatic portal hypertensive rat livers following the induction of diabetes

1. Oxidative stress (OS) is a biological entity indicated as being responsible for several pathologies, including diabetes. Diabetes can also be associated with human cirrhosis. Portal hypertension (PH), a major syndrome in cirrhosis, produces hyperdynamic splanchnic circulation and hyperaemia. The present study was designed to investigate the occurrence of OS in prehepatic PH rat livers following the induction of diabetes. 2. Five groups of rats were used: control, sham operated, chronic diabetes (induced with a single dose of streptozotocin at 60 mg/kg, i.p.), prehepatic PH and chronic diabetic plus prehepatic PH. The occurrence of OS was determined in liver homogenates by measuring hydroperoxide-initiated chemiluminescence and the activity of anti-oxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase). 3. Prehepatic PH produced a significant increase in hydroperoxide-initiated chemiluminescence in the liver compared with control and sham-operated rats, whereas the liver in chronic diabetic rats showed no difference. However, chemiluminescence values decreased almost by 50% in the chronic diabetic plus prehepatic PH group. Concomitantly, the activities of the anti-oxidant enzymes in chronic diabetes, prehepatic PH and chronic diabetic plus prehepatic PH groups were decreased (P < 0.05 vs control and sham-operated groups). 4. Livers from the chronic diabetic group did not show any evidence of the occurrence of OS, whereas the prehepatic PH group showed the occurrence of OS. The association of PH and chronic diabetes resulted in a significant decrease in the occurrence of OS, which could be explained by an anti-oxidant response to an OS.

Low micromolar concentrations of copper augment the impairment of endothelium-dependent relaxation of aortae from diabetic rabbits

Both diabetes mellitus (DM) and elevated plasma copper concentrations are risk factors for cardiovascular disease (CVD). DM is associated with impaired endothelial nitric oxide (NO) and with excess superoxide (O2*-) formation. Copper is also elevated in DM and is also associated with the generation of O2*-. To explore possible interactions between DM and copper, the effect of exogenous copper (CuCl2) on endothelium-dependent relaxation and cyclic guanosine monophosphate (GMP) formation was investigated in aortae from diabetic rabbits. Rabbits were rendered diabetic by intravenous injection of alloxan. Six months after induction of DM, the aortae were excised, cut into rings, and mounted in an organ bath for isometric measurement of acetylcholine (Ach)-evoked relaxation in rings precontracted with phenylephrine (PE). In parallel studies, cyclic (c)GMP formation by aortic rings following stimulation with Ach, calcium ionophore A23187 (A23187) and sodium nitroprusside (SNP) was assessed using radioimmunoassay. The effect of copper on these parameters was then studied using the same methods. Ach-evoked relaxation and Ach- and A23187-evoked cGMP formation were significantly impaired in aortae from diabetic rabbits compared to controls, effects that were reversed with superoxide dismutase (SOD) and catalase (CAT). In contrast, there were no significant differences in SNP-stimulated relaxation or cGMP formation in aortae from diabetic rabbits compared to controls. Copper (1 to 10 micromol/L) promoted a further significant inhibition of Ach-stimulated relaxation in aortae from diabetic but not control rabbits. This reduction by copper was again reversed by SOD and CAT. We conclude that copper augments the reduction of NO bioavailability, which is already impaired in aortae from diabetic rabbits due to excess production of O2*- and H2O2. These results indicate that patients with DM may be susceptible to copper-mediated vasculopathy at much lower concentrations than those that promote vasculopathy in nondiabetic patients.

Mechanisms of hydroxyl radical-induced contraction of rat aorta

The present study was designed to investigate the effects of hydroxyl radicals (*OH), generated via the Fe2+-mediated Fenton reaction, on isolated rat aortic rings with and without endothelium. In the absence of any vasoactive agent, generation of *OH alone elicited an endothelium-independent contraction in rat aortic rings in a concentration-dependent manner. Hydroxyl radical-induced contractions of denuded rat aortic rings appeared, however, to be slightly stronger than those on intact rat aortic rings. The contractile responses to *OH were neither reversible nor reproducible in the same ring; even small concentrations of *OH radicals resulted in tachyphylaxis. Removal of extracellular calcium ions (Ca2+) or buffering intracellular Ca2+ with 10 microM acetyl methyl ester of bis(o-aminophenoxy) ethane-N,N,N',N',-tetraacetic acid (BAPTA-AM) significantly attenuated the contractile actions of *OH radicals. The presence of 1 microM staurosporine, 1 microM bisindolylmaleimide I, 1 microM Gö6976 [inhibitor of protein kinase C (PKC)], 2 microM PD-980592 (inhibitor of ERK), 10 microM genistein, and 1 microM wortmannin significantly inhibited the contractions induced by *OH. Proadifen (10 microM), on the other hand, significantly potentiated the hydroxyl radical-induced contractions. Exposure of primary cultured aortic smooth muscle cells to *OH produced significant, rapid rises of intracellular free Ca2+ ([Ca2+]i). Several, specific antagonists of possible endogenously formed vasoconstrictors did not inhibit or attenuate either hydroxyl radical-induced contractions or the elevation of [Ca2+]i. Our new results suggest that hydroxyl radical-triggered contractions on rat aortic rings are Ca2+-dependent. Several intracellular signal transduction systems seem to play some role in hydroxyl radical-induced vasoconstriction of rat aortic rings.

Vasoactive effects of methylamine in isolated human blood vessels: role of semicarbazide-sensitive amine oxidase, formaldehyde, and hydrogen peroxide

It is hypothesized that methylamine (MA) and semicarbazide-sensitive amine oxidase (SSAO) activity are involved in the cardiovascular complications in human diabetics. To test this, we 1) determined the acute vasoactive effects of MA (1-1,000 micromol/l) in uncontracted and norepinephrine (NE; 1 micromol/l)-precontracted human blood vessels used for coronary artery bypass grafts [left internal mammary artery (LIMA), radial artery (RA), and right saphenous vein (RSV)]; 2) tested whether MA effects in LIMA and RSV were dependent on SSAO activity using the SSAO inhibitor semicarbazide (1 mmol/l, 15 min); 3) determined the effects of MA metabolites formaldehyde and hydrogen peroxide in LIMA and RSV; 4) tested whether the MA response was nitric oxide, prostaglandin, or hyperpolarization dependent; 5) measured the LIMA and RSV cGMP levels after MA exposure; and 6) quantified SSAO activity in LIMA, RA, and RSV. In NE-precontracted vessels, MA stimulated a biphasic response in RA and RSV (rapid contraction followed by prolonged relaxation) and dominant relaxation in LIMA (mean +/- SE, %relaxation: 55.4 +/- 3.9, n = 30). The MA-induced relaxation in LIMA was repeatable, nontoxic, and age independent. Semicarbazide significantly blocked MA-induced relaxation (%inhibition: 82.5 +/- 4.8, n = 7) and SSAO activity (%inhibition: 98.1 +/- 1.3, n = 26) in LIMA. Formaldehyde (%relaxation: 37.3 +/- 18.6, n = 3) and H(2)O(2) (%relaxation: 55.6 +/- 9.0, n = 9) at 1 mmol/l relaxed NE-precontracted LIMA comparable with MA. MA-induced relaxation in LIMA was nitric oxide, prostaglandin, and possibly cGMP independent and blocked by hyperpolarization. We conclude that vascular SSAO activity may convert endogenous amines, like MA, to vasoactive metabolites.

Distinct hyperpolarizing and relaxant roles for gap junctions and endothelium-derived H2O2 in NO-independent relaxations of rabbit arteries

We have compared the contributions of gap junctional communication and chemical signaling via H2O2 to NO-independent relaxations evoked by the Ca2+ ionophore A23187 and acetylcholine (ACh) in rabbit ilio-femoral arteries. Immunostaining confirmed the presence of connexins (Cxs) 37 and 40 in the endothelium and Cxs 40 and 43 in smooth muscle. Maximal endothelium-dependent subintimal smooth muscle hyperpolarizations evoked by A23187 and ACh were equivalent (approximately 20 mV) and almost abolished by an inhibitory peptide combination targeted against Cxs 37, 40, and 43. However, maximal NO-independent relaxations evoked by A23187 were unaffected by such peptides, whereas those evoked by ACh were depressed by approximately 70%. By contrast, the enzyme catalase, which destroys H2O2, attenuated A23187-induced relaxations over a broad range of concentrations, but only minimally depressed the maximum response to ACh. Catalase did not affect A23187- or ACh-evoked hyperpolarizations. After loading with an H2O2-sensitive probe, A23187 caused a marked increase in endothelial fluorescence that correlated temporally with relaxation, whereas only a weak delayed increase was observed with ACh. In arteries without endothelium, the H2O2-generating system xanthine/xanthine oxidase induced a catalase-sensitive relaxation that mimicked the gap junction-independent response to A23187 as it was maximally equivalent to approximately 80% of induced tone, but associated with a smooth muscle hyperpolarization <5 mV. We conclude that myoendothelial gap junctions underpin smooth muscle hyperpolarizations evoked by A23187 and ACh, but that A23187-induced relaxation is dominated by extracellular release of H2O2. Endothelium-derived H2O2 may thus be regarded as a relaxing factor, but not a hyperpolarizing factor, in rabbit arteries.

Pentose phosphate pathway, glutathione-dependent enzymes and antioxidant defense during oxidative stress in diabetic rodent brain and peripheral organs: effects of stobadine and vitamin E

The aim of the present study was to investigate the effects of treatment with antioxidant stobadine (ST) on the activities of enzymes related with pentose phosphate pathway and glutathione-dependent metabolism and the other markers of oxidative stress in brain and peripheral organs of diabetic rats, and to compare the effects of ST treatment alone with the effects of treatments with another antioxidant vitamin E and ST plus vitamin E. Rats were made diabetic by the injection of streptozotocin (STZ; 55 mg/kg IP), and, 2 days later, some control and diabetic rats were left untreated or treated with ST (24.7 mg/kg/day, orally), vitamin E (400-500 U/kg/day, orally), or both substances together. In the brain, although 6-phosphogluconate dehydrogenase activity (6-PGD) did not change, glucose-6-phosphate dehydrogenase activity (G-6PD) was markedly increased in diabetic rats compared with controls; only combined treatment with ST and vitamin E produced a partial prevention on this alteration. The aorta G-6PD and 6-PGD of diabetic rats were 52% and 36% of control values, respectively. Neither single treatments with each antioxidant nor their combination altered the G-6PD and 6-PGD in aorta of diabetic rats. Glutathione peroxidase (GSHPx) activity was increased by STZ-diabetes in brain, heart, and kidney. In diabetic brain, vitamin E alone or combination with ST kept GSHPx at normal levels. Diabetes-induced stimulation in GSHPx did not decrease in response to the treatment with vitamin E in heart and kidney, but was greatly prevented by ST alone. The activity of glutathione reductase (GR) was decreased in brain and heart of diabetic rats. The treatment with each antioxidant or with a combination of both agents completely prevented this deficiency and resulted in further activation of GR in diabetic tissues. Glutathione S-transferase (GST) activity did not significantly change in diabetic brain and aorta. GST was stimulated by all treatment protocols in the brain of diabetic rats and was depressed in aorta of control rats. Catalase (CAT) was activated in diabetic heart but depressed in diabetic kidney. Diabetes-induced abnormalities in CAT activity did not respond to vitamin E alone in heart, was moderately ameliorated by the treatment with this vitamin in kidney, and was completely prevented by ST alone in both tissues. Superoxide dismutase (SOD) activity of brain and heart was unchanged by the diabetes but inhibited in diabetic kidney after the treatment ST alone or ST plus vitamin E. The lipid peroxidation (MDA) was increased in diabetic brain and heart. ST or vitamin E alone partly prevented diabetes-induced increase in MDA in brain and heart; however, antioxidant combination achieved a completely amelioration in MDA of these tissues of diabetic rats. Kidney MDA levels were similar in control and untreated diabetic animals. ST and vitamin E treatments, when applied separately or together, significantly reduced kidney MDA in both control and diabetic rats; and the combined effect of antioxidants was greater than that of each alone. These results are consistent with the degenerative role of hyperglycemia on cellular reducing equivalent homeostasis and antioxidant defense, and provide further evidence that pharmacological intervention of different antioxidants may have significant implications in the prevention of the prooxidant feature of diabetes and protects redox status of the cells.

Effects of vitamin E on microsomal Ca(2+) -ATPase activity and calcium levels in streptozotocin-induced diabetic rat kidney

Vitamin E treatment has been found to be beneficial in preventing or reducing diabetic nephropathy. Increased tissue calcium and abnormal microsomal Ca(2+)-ATPase activity have been suggested as contributing factors in the development of diabetic nephropathy. This study was undertaken to test the hypothesis that vitamin E reduces lipid peroxidation and can prevent the abnormalities in microsomal Ca(2+)-ATPase activity and calcium levels in kidney of streptozotocin (STZ)-induced diabetic rats. Male rats were rendered diabetic by a single STZ injection (55 mg x kg(-1) i.p.). After diabetes was verified, diabetic and age-matched control rats were untreated or treated with vitamin E (400-500 IU kg(-1) x day(-1), orally) for 10 weeks. Ca(2+)-ATPase activity and lipid peroxidation (MDA) were determined spectrophotometrically. Blood glucose levels increased approximately five-fold (> 500 mg x dl(-1)) in untreated-diabetic rats but decreased to 340+/-27 mg x dl(-1) in the vitamin E treated-diabetic group. Kidney MDA levels did not significantly change in the diabetic state. However, vitamin E treatment markedly inhibited MDA levels in both control and diabetic animals. Ca(2+)-ATPase activity was 0.483+/-0.008 U l(-1) in the control group and significantly increased to 0.754+/-0.010 U l(-1) in the STZ-diabetic group (p < 0.001). Vitamin E treatment completely prevented the diabetes-induced increase in Ca(2+)-ATPase activity (0.307+/-0.025 U l(-1), p < 0.001) and also reduced the enzyme activity in normal control rats. STZ-diabetes resulted in approximately two-fold increase in total calcium content of kidney. Vitamin E treatment led to a significant reduction in kidney calcium levels of both control and diabetic animals (p < 0.001). Thus, vitamin E treatment can lower blood glucose and lipid peroxidation, which in turn prevents the abnormalities in kidney calcium metabolism of diabetic rats. This study describes a potential biochemical mechanism by which vitamin E supplementation may delay or inhibit the development of cellular damage and nephropathy in diabetes.

Effects of cod liver oil on tissue antioxidant pathways in normal and streptozotocin-diabetic rats

Lipid disorders and increased oxidative stress may exacerbate some complications of diabetes mellitus. Previous studies have implicated the beneficial effects of some antioxidants, omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the protection of cells from the destructive effect of increased lipids and lipid peroxidation products. This study, therefore, was designed to investigate the effects of cod liver oil (CLO, Lysi Ltd. Island), which comprises mainly vitamin A, PUFAs, EPA and DHA. Effects were monitored on plasma lipids, lipid peroxidation products (MDA) and the activities of antioxidant enzymes, glutathione peroxidase (GSHPx) and catalase in heart, liver, kidney and lung of non-diabetic control and streptozotocin (STZ)-induced-diabetic rats. Two days after STZ-injection (55 mg kg(-1) i.p.), non-diabetic control and diabetic rats were divided randomly into two groups as untreated or treated with CLO (0.5 ml kg(-1) rat per day) for 12 weeks. Plasma glucose, triacylglycerol and cholesterol concentrations were significantly elevated in 12-week untreated-diabetic animals; CLO treatment almost completely prevented these abnormalities in triacylglycerol and cholesterol, but hyperglycaemia was partially controlled. CLO also provided better weight gain in diabetic animals. In untreated diabetic rats, MDA markedly increased in aorta, heart and liver but was not significantly changed in kidney and lung. This was accompanied by a significant increase in both GSHPx and catalase enzyme activities in aorta, heart, and liver of diabetic rats. In kidney and lung, diabetes resulted in reduced catalase while GSHPx was significantly activated. In aorta, heart, and liver, diabetes-induced changes in MDA were entirely prevented by CLO treatment. In the tissues of CLO-treated diabetic animals, GSHPx activity paralleled those of control animals. CLO treatment also caused significant improvements in catalase activities in every tissue of diabetic rats, but failed to affect MDA and antioxidant activity in control animals. The current study suggests that the treatment of diabetic rats with CLO provides better control of glucose and lipid metabolism, allows recovery of normal growth rate, prevents oxidative/peroxidative stress and ameliorates endogenous antioxidant enzyme activities in various tissues. Because CLO contains a plethora of beneficial compounds together, its use for the management of diabetes-induced complications may provide important advantages.

Histomorphometric evaluation of the effect of doxycycline on the healing of bone defects in experimental diabetes mellitus: a pilot study

PURPOSE

Bone healing is impaired in diabetes mellitus, particularly due to increased collagen breakdown. Recently, tetracyclines have been used to treat experimental bone defects because they have anticollagenolytic properties, and positive effects on the healing process have been obtained. The objective of this study was to develop a computer-assisted histomorphometric technique to quantitatively determine the amount of regenerating bone within experimental bone defects in a diabetic rodent model.

MATERIALS AND METHODS

This study examined the effects of systemic doxycycline administration on the healing of tibial bone defects in healthy albino rats and in experimentally induced diabetic rats. Twenty-four female albino rats were assigned to 4 groups: diabetic, diabetic plus doxycycline, control, or control plus doxycycline. The standardized bone defects were histomorphometrically examined 10 and 30 days postoperatively. Histomorphometric analysis of the amount of new bone formation was performed using the Zeiss Vision image analysis program KS 400 (Kontron Elektron GmbH, Eching, Germany).

RESULTS

At 10 days of healing, the diabetic groups exhibited inferior healing compared with the control groups in terms of the amount of new bone formation within the defects. However, the effect of doxycycline administration to the diabetic and control groups was not statistically different. At 30 days of healing, there were no statistically significant differences between the amount of newly formed bone in any of the groups.

CONCLUSIONS

This study found that doxycycline administration did not significantly alter the amount of new bone formation during the healing of bone defects in control and diabetic rats.

Effects of vitamin A and insulin on the antioxidative state of diabetic rat heart: a comparison study with combination treatment

Because elevated oxidative stress may exacerbate cardiovascular complications of diabetes mellitus, the current study aimed to investigate the effects of treatment with either vitamin A, an antioxidant, or with insulin on lipid peroxidation products and antioxidant enzyme activities of diabetic rat heart. Also to evaluate whether a combination of vitamin A and insulin exerts more beneficial effects than treatment with each agent alone. Rats were made diabetic with a single injection of streptozotocin (STZ, 55 mg kg(-1) i.p.). Two days after STZ-injection, one group of diabetic rats was treated with vitamin A (retinol acetate, 30 mg kg(-1) day(-1) i.o.) for 12 weeks. A second group of diabetic rats was untreated for 6 weeks and then treated for another 6 weeks with insulin (8-10 IU rat(-1) day(-1) s.c.). Both therapies were applied to another group of diabetic rats for assessment of combined therapy with vitamin A plus insulin. Hearts from 12-week untreated diabetic animals showed about a four-fold increase in the level of thiobarbituric acid reactive substances (TBARS), indicative of increased lipid peroxidation. This was accompanied by approximately 100% increase in both catalase and glutathione peroxidase (GSHPx) enzyme activities. Therapy with insulin alone caused a small but significant improvement in plasma TBARS as well as GSHPx activities, but no significant change in plasma catalase in diabetic animals. Diabetes-induced disturbance in TBARS was almost completely prevented by vitamin A therapy. Although, a similar degree of activities for GSHPx was determined in diabetic animals treated with each agent alone, combination therapy was found to be more effective than single therapies in the recovery of GSHPx of diabetic heart. In contrast to insulin single therapy, vitamin A alone significantly prevented an increase in catalase activity of diabetic heart, and a combination of these agents did not supply any further benefit. Superoxide dismutase (SOD) activity was not found significantly different among the experimental groups. STZ-diabetes also resulted in less plasma retinol and retinol-binding protein (RBP), which was significantly improved by insulin single therapy while vitamin A used alone, failed to increase plasma retinol and RBP levels of diabetic animals. Our findings suggest that single therapy with insulin is unable to preclude oxidative reactions in diabetic heart to the same extent as obtained by vitamin A therapy alone, in spite of allowing recovery of normal growth rate and improved vitamin A metabolism in diabetic rats. A combination of insulin with vitamin A may provide more benefits than use of either agent alone in the treatment of general characteristics of diabetes and the maintenance of antioxidant defence of diabetic heart and thus in the reduction of peroxidative stress-induced cardiac injury.

Elimination of *O(2)(-)/H(2)O(2) by alpha-lipoic acid mediates the recovery of basal EDRF/NO availability and the reversal of superoxide dismutase-induced relaxation in diabetic rat aorta

AIM

The aims of this study were to ascertain the mechanism(s) of relaxant action of exogenous superoxide dismutase (SOD) in aortic rings obtained from 12-week, streptozotocin(STZ)-diabetic and age-matched control rats, and to examine the effects of alpha-lipoic acid (ALA) treatment (for 6 weeks, after 6 weeks of untreated diabetes) on SOD-induced relaxations.

MATERIALS AND METHODS

Thoracic aorta rings were suspended to isolated tissue chamber, and the changes in isometric tension were recorded.

RESULTS

SOD produced a greater relaxation in untreated-diabetic rings compared with control rings. ALA treatment partially reversed SOD-induced relaxation in diabetic aorta. Pretreatment of rings with N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microm) inhibited SOD-induced relaxation. This effect of L-NAME was markedly observed in control and ALA-treated-diabetic rings compared with untreated-diabetic rings. SOD-induced relaxation was also inhibited by catalase (60 U/ml) in untreated-diabetic rings but not in ALA-treated-diabetic and control rings. Pretreatment with the cyclooxygenase inhibitor, indomethacin, or the catalase inhibitor, aminotriazole, had no effect on SOD-induced relaxation in any ring.

CONCLUSION

Findings suggested that: (i) in normal physiological conditions, the relaxant effect of SOD is related to the inhibition of superoxide anion radicals (*O(2)(-))-induced endothelium-derived relaxing factor/nitric oxide (EDRF/NO) destruction in the rat aorta; (ii) in diabetic state, excess *O(2)(-) increasingly inhibits basal EDRF/NO, and the dismutation of excess *O(2)(-) to H(2)O(2) is enhanced by exogenous SOD. H(2)O(2) a vasorelaxant molecule, which probably accounts for the increased responsiveness of diabetic rings to exogenous SOD; and (iii) the reversal effect of in vivo ALA treatment on SOD-induced relaxation in diabetic aorta is probably linked with the elimination of *O(2)(-)/H(2)O(2), which mediates the recovery of basal EDRF/NO availability.

Short-term gemfibrozil treatment reverses lipid profile and peroxidation but does not alter blood glucose and tissue antioxidant enzymes in chronically diabetic rats

In this study, we investigated the efficiency of short-term treatment with gemfibrozil in the reversal of diabetes-induced changes on carbohydrate and lipid metabolism, and antioxidant status of aorta. Diabetes was induced by a single injection of streptozotocin (45 mg/kg, i.p.). After 12 weeks of induction of diabetes, the control and diabetic rats were orally gavaged daily with a dosing vehicle alone or with 100 mg/kg of gemfibrozil for 2 weeks. At 14 weeks, there was a significant increase in blood glucose, plasma cholesterol and triglyceride levels of untreated-diabetic animals. Diabetes was associated with a significant increase in thiobarbituric acid reactive substances (TBARS) in both plasma and aortic homogenates, indicating increased lipid peroxidation. Diabetes caused an increase in vascular antioxidant enzyme activity, catalase, indicating existence of excess hydrogen peroxide (H2O2). However, superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) activities in aortas did not significantly change in untreated-diabetic rats. In diabetic plus gemfibrozil group both plasma lipids and lipid peroxides showed a significant recovery. Gemfibrozil treatment had no effect on blood glucose, plasma insulin and vessel antioxidant enzyme activity of diabetic animals. Our findings suggest that the beneficial effect of short-term gemfibrozil treatment in reducing lipid peroxidation in diabetic animals does not depend on a change of glucose metabolism and antioxidant status of aorta, but this may be attributed to its decreasing effect on circulating lipids. The ability of short-term gemfibrozil treatment to recovery of metabolism and peroxidation of lipids may be an effective strategy to minimize increased oxidative stress in diabetic plasma and vasculature.

Time course of changes in endothelium-dependent and -independent relaxation of chronically diabetic aorta: role of reactive oxygen species

In the present study, the role of reactive oxygen species and the contribution of antioxidant defence in the time course of changes in acetylcholine-stimulated endothelium-dependent and sodium nitroprusside-stimulated endothelium-independent relaxation were investigated in aortic rings isolated from 6-month streptozotocin-diabetic and age-matched control rats. Although there were no significant differences in the degree of the peak relaxations produced by a single administration of acetylcholine (1 microM) or sodium nitroprusside (0.01 microM) between control and diabetic rings, the endothelium-dependent and -independent relaxant responses were more transient and the time required to reach a peak relaxation after addition of acetylcholine was shorter in diabetic vessels. Pretreatment of diabetic vessels with superoxide dismutase (100 U/ml) normalized the recovery phases of endothelium-dependent and -independent relaxations, but had no effect on the peak responses to acetylcholine and sodium nitroprusside. In the presence of diethyldithiocarbamate (5 mM), an inhibitor of superoxide dismutase, the transient nature of the relaxant response to acetylcholine or sodium nitroprusside was more marked and the peak relaxations were inhibited; these effects of diethyldithiocarbamate were more pronounced in diabetic than in control rings. Catalase, 160 U/ml, decreased the peak relaxant response to acetylcholine and accelerated fading of the relaxation in diabetic aorta. Similar results were obtained for control aorta with a higher concentration of catalase (550 U/ml). Pretreatment with 3-amino-1,2,4 triazole (5 mM), a catalase inhibitor, inhibited the peak relaxant response to acetylcholine in diabetic rings. The combination of superoxide dismutase (100 U/ml) plus 3-amino-1,2,4 triazole (5 mM) produced an increase of the transient nature of endothelium-dependent relaxation of diabetic rings greater than that with 3-amino-1,2,4 triazole alone. Neither catalase nor 3-amino-1,2,4 triazole affected the characteristics of sodium nitroprusside-induced relaxation. Desferrioxamine, an inhibitor of hydroxyl radical (.OH) production, or mannitol, a.OH scavenger, had no effect on the characteristics of either acetylcholine- or sodium nitroprusside-induced relaxation in control and diabetic rings. Biochemical measurements revealed an inhibited superoxide dismutase activity in diabetic aorta together with activated catalase. Our findings suggest that, during the chronic phase of streptozotocin-diabetes, excess superoxide (O(2)(. -)) is responsible for the enhanced transient nature of endothelium-dependent and -independent relaxation of aorta via a reduction in bioavailable concentrations of nitric oxide (NO). However, the involvement of hydrogen peroxide (H(2)O(2)) in the establishment of acetylcholine-stimulated relaxation may be increased, which is likely to account for the maintenance of the relaxant effect of acetylcholine in chronically diabetic vessels.