Comparative investigation of kidney mesangial cells from increased oxidative stress-induced diabetic rats by using different microscopy techniques

High glucose and increased oxidative stress levels are the known important mediators of diabetic nephropathy. However, the effects of these mediators on tissue damage basically due to extracellular matrix expansion in mesangial cells have yet to be fully examined within the context of early stage diabetic nephropathy. In this study, we attempted to characterize changes in mesangial cells of streptozotocin-induced diabetic rats with a comparative investigation of kidney tissue by using different microscopy techniques. The serum levels of urea and creatinine of diabetic rats, as biomarkers of kidney degeneration, decreased significantly compared to those of age-matched controls. In diabetic rats, there are increased malondialdehyde and oxidized-glutathione levels as well as reduced-glutathione and glutathione-peroxidase activity levels in renal tissue compared to those of the controls. By using light and electron microscopies, we showed that there were marked thickening in Bowman's membrane and glomerular capillary wall, increased amount of extracellular matrix often occupying Bowman's space, degenerations in tubules, an increased number of mesangial cells in the network of glomerular capillary walls, and increased amount of lipid accumulation in proximal tubules in the renal tissue of diabetic rats. Our confocal microscopy data confirmed also the presence of irregularity and widened in glomerular capillaries, their attachment to the Bowman's capsule, degenerated heterochromatin, thickening in foci of glomerular basement membrane, and marked increase in mesangial cells. These results suggest that a detailed structural investigation of kidney tissue provides further information on the important role of mesangial cells in pathogenesis of diabetic nephropathy.

ß-blocker timolol prevents arrhythmogenic Ca²⁺ release and normalizes Ca²⁺ and Zn²⁺ dyshomeostasis in hyperglycemic rat heart

Defective cardiac mechanical activity in diabetes results from alterations in intracellular Ca(2+) handling, in part, due to increased oxidative stress. Beta-blockers demonstrate marked beneficial effects in heart dysfunction with scavenging free radicals and/or acting as an antioxidant. The aim of this study was to address how β-blocker timolol-treatment of diabetic rats exerts cardioprotection. Timolol-treatment (12-week), one-week following diabetes induction, prevented diabetes-induced depressed left ventricular basal contractile activity, prolonged cellular electrical activity, and attenuated the increase in isolated-cardiomyocyte size without hyperglycemic effect. Both in vivo and in vitro timolol-treatment of diabetic cardiomyocytes prevented the altered kinetic parameters of Ca(2+) transients and reduced Ca(2+) loading of sarcoplasmic reticulum (SR), basal intracellular free Ca(2+) and Zn(2+) ([Ca(2+)]i and [Zn(2+)]i), and spatio-temporal properties of the Ca(2+) sparks, significantly. Timolol also antagonized hyperphosphorylation of cardiac ryanodine receptor (RyR2), and significantly restored depleted protein levels of both RyR2 and calstabin2. Western blot analysis demonstrated that timolol-treatment also significantly normalized depressed levels of some [Ca(2+)]i-handling regulators, such as Na(+)/Ca(2+) exchanger (NCX) and phospho-phospholamban (pPLN) to PLN ratio. Incubation of diabetic cardiomyocytes with 4-mM glutathione exerted similar beneficial effects on RyR2-macromolecular complex and basal levels of both [Ca(2+)]i and [Zn(2+)]i, increased intracellular Zn(2+) hyperphosphorylated RyR2 in a concentration-dependent manner. Timolol also led to a balanced oxidant/antioxidant level in both heart and circulation and prevented altered cellular redox state of the heart. We thus report, for the first time, that the preventing effect of timolol, directly targeting heart, seems to be associated with a normalization of macromolecular complex of RyR2 and some Ca(2+) handling regulators, and prevention of Ca(2+) leak, and thereby normalization of both [Ca(2+)]i and [Zn(2+)]i homeostasis in diabetic rat heart, at least in part by controlling the cellular redox status of hyperglycemic cardiomyocytes.

Evaluation of pathogenic Escherichia coli occurrence in vegetable samples from district bazaars in Istanbul using real-time PCR

In this study, a total of 180 vegetable samples collected from several district bazaars of Istanbul were investigated for the occurrence of Escherichia coli using a culture-based method. The isolates were subjected to real-time PCR detection of Shiga-toxin-producing E. coli (STEC) using primers specific for the Shiga toxin (stx1 and stx2) and intimin (eae) virulence genes. The prevalences of E. coli in the samples were 93·3% in spinach, 93·3% in lettuce, 86·6% in parsley, 43·3% in carrot, 33·3% in cucumber and 13·3% in tomato. Of 180 samples, 13 contained STEC (six parsley, three carrots, three lettuces and one cucumber of 30 samples of each). Among 13 STEC-positive isolates, presence of stx1, stx2 and eae was detected in only one sample, stx2 and eae in two samples, and stx2 in ten samples. Serotype O157 was found in parsley, lettuce and carrot; O26 in lettuce, parsley, cucumber and carrot; and O111 and O113 in parsley only. In conclusion, STEC was present in vegetable samples marketed in several district bazaars in Istanbul; this might represent a route of transmission of pathogenic STEC to humans and be harmful to public health.

SIGNIFICANCE AND IMPACT OF THE STUDY

We assessed the occurrence of virulent Escherichia (E.) coli and Shiga-toxin-producing E. coli (STEC) virulent populations in the vegetable samples collected from several district bazaars in Istanbul, Turkey. The results indicated that the vegetables from the bazaars had poor microbial quality and represented a potential health risk to customers.

Role of ROCK upregulation in endothelial and smooth muscle vascular functions in diabetic rat aorta

Background

The RhoA/ROCK signaling pathway mediates vascular smooth muscle contraction while endogenous NO induces vasodilation through its inhibition. Since myosin light chain phosphatase (MLCP) and eNOS are targeted by RhoA/ROCK upregulation then turn to lead abnormalities in vasculature, we aimed to examine whether less endothelial NO-production and inhibited eNOS together with an upregulation of RhoA/ROCK signaling pathway in thoracic aorta can play an important role in vascular dysfunction under hyperglycemia.

Methods

We used streptozotocin-injected rats, as a model of type 1 diabetes, and their lean controls to investigate the role of ROCK upregulation in the function of toracic aorta by using electrophysiological and biochemical techniques.

Results

The protein level of ROCK isoform ROCK2 was found to be 2.5-fold higher in endothelium-intact aortic rings of the diabetic rats compared to those of the controls while its level in endothelium-denuded rings was similar among these two groups. Phosphorylation level of eNOS in endothelium-intact rings from the diabetics was 50% less compared to that of the control. ROCK inhibitors, either Y27632 or HA1077, induced concentration-dependent relaxation with a marked left-shift in phenylephrine pre-contracted endothelium-intact rings from either diabetics or high glucose incubated controls while pretreatment of these rings with L-NAME abolished this shift, fully. Moreover, phosphorylation levels of both MLCP and MLC in endothelium-denuded rings were markedly higher in the diabetics than the controls.

Conclusion

We demonstrated that diabetes-induced vascular dysfunction can arise due to either inbition of eNOS, thereby less endothelial NO-production, either directly or indirectly, in part, due to an upregulation of ROCK2 by hyperglycemia. Additionally, our data demonstrate that high phosphorylation levels of both MLC and MLCP in endothelium-denuded rings can be due to a less endothelial NO-production dependent ROCK upregulation in the smooth muscle cells under hyperglycemia, as well.

Fourier transform infrared study of the effect of diabetes on rat liver and heart tissues in the CH region

Diabetes mellitus is characterized by hyperglycemia, a relative lack of insulin. The metabolic disturbances in diabetic patients are often associated with cardiac and liver dysfunctions. Generally, experimental diabetic models in animals have been used to study diabetes-related changes in organ function, but the complexity of intact tissues can cause contradictory results. For this reason, different techniques have been used to understand the mechanisms of these dysfunctions in diabetic organs. The purpose of the present study is to investigate the effects of streptozotocin (STZ)-induced diabetes on rat liver and heart tissues at the molecular level by Fourier Transform Infrared (FTIR) spectroscopy. Wistar rats of both sexes, weighing 200-250 g, were made diabetic by a single injection of 50 mg kg(-1) intraperitoneal (i.p.) streptozotocin dissolved in 0.05 M citrate buffer (pH 4.5) and they were kept for 4-5 weeks. The diabetes status was checked by measuring the blood glucose level. In the complex FTIR spectra, the bands in the CH region for example the CH(2) antisymmetric and symmetric stretching, the CH(3) symmetric and asymmetric stretching vibrations due to lipids and proteins in the 3000-2800 cm(-1) region and CH(2) scissoring around 1464 cm(-1) and the CH(3) scissoring at 1454 cm(-1) were analyzed. Characteristic spectral bands of these diabetic samples were compared with those of control group to confirm the effect of diabetes on liver and heart tissues. The FTIR spectra revealed dramatic differences in the band positions and bandwidths, signal intensity values and signal intensity ratios between diabetic and control tissues. Similar differences were observed for diabetic liver and heart tissues. A significant increase in the bandwidth of the CH(2) symmetric and antisymmetric stretching and the CH(3) symmetric and asymmetric stretching bands has been observed for both tissue types. The wavenumber of the CH(3) asymmetric stretching band shifts to lower values, indicating an increase in the order in the deep interior part of the lipid chains. The ratio of the CH(2) symmetric to CH(3) symmetric stretching band (lipid/protein ratio) decreases by 13% for diabetic heart and liver tissues. A decrease is also detected in the ratio of the CH(2) scissoring to the CH(3) scissoring mode. The overall intensity of these bands is seen to increase for diabetic tissues.

Vitamin E in oxidant stress-related cardiovascular pathologies: focus on experimental studies

The scope of this review is to summarize the important roles of vitamin E family members as protective agents in cardiovascular pathologies of different types of disease states and particularly in diabetes, including some of our research results, to illustrate how this recent knowledge is helping to better understand the roles of the vitamin E family in biology, in animals and humans specifically. Cardiovascular disease, a general name for a wide variety of diseases, disorders and conditions, is caused by disorders of the heart and blood vessels. Cardiovascular disease is the world's largest killer, claiming 17.1 million lives a year. Cardiovascular complications result from multiple parameters including glucotoxicity, lipotoxicity, fibrosis. Obesity and diabetes mellitus are also often linked to cardiovascular disease. In fact, cardiovascular disease is the most life-threatening of the diabetic complications and diabetics are 2- to 4-fold more likely to die of cardiovascular-related causes than non-diabetics. In order to prevent the tendency of cardiovascular disease, primary prevention is needed by modifying risk factors. Several recent studies, besides earlier ones, have reported beneficial effects of therapy with antioxidant agents, including trace elements, vitamins (E and/or C), other antioxidants, against the cardiovascular dysfunction. Hence, the use of peroxisome proliferator activated receptor-α (PPARα) agonists to reduce fatty acid oxidation, of trace elements such as selenium as antioxidant and other antioxidants such as vitamins E and C, contributes to the prevention of these dysfunctions. Moreover, therapy with antioxidants and the above vitamins to prevent or delay the onset and development of cardiovascular complications in diabetic patients and animal models has been investigated although these studies showed inconsistent results.

Ryanodine receptor: a new therapeutic target to control diabetic cardiomyopathy

Diabetes mellitus is a major risk factor for cardiovascular complications. Intracellular Ca(2+) release plays an important role in the regulation of muscle contraction. Sarcoplasmic reticulum Ca(2+) release is controlled by dedicated molecular machinery, composed of a complex of cardiac ryanodine receptors (RyR2s). Acquired and genetic defects in this complex result in a spectrum of abnormal Ca(2+) release phenotypes in heart. Cardiovascular dysfunction is a leading cause for mortality of diabetic individuals due, in part, to a specific cardiomyopathy, and to altered vascular reactivity. Cardiovascular complications result from multiple parameters, including glucotoxicity, lipotoxicity, fibrosis, and mitochondrial uncoupling. In diabetic subjects, oxidative stress arises from an imbalance between production of reactive oxygen and nitrogen species and capability of the system to readily detoxify reactive intermediates. To date, the etiology underlying diabetes-induced reductions in myocyte and cardiac contractility remains incompletely understood. However, numerous studies, including work from our laboratory, suggest that these defects stem in part from perturbation in intracellular Ca(2+) cycling. Since the RyR2s are one of the well-characterized redox-sensitive ion channels in heart, this article summarizes recent findings on redox regulation of cardiac Ca(2+) transport systems and discusses contributions of redox regulation to pathological cardiac function in diabetes.

Role of antioxidants in redox regulation of diabetic cardiovascular complications

Cardiovascular dysfunction is leading cause for the mortality of diabetic individuals, in part due to a specific cardiomyopathy, and due to altered endothelial dependent/independent vascular reactivity. Cardiovascular complications result from multiple parameters including glucotoxicity, lipotoxicity, fibrosis and mitochondrial uncoupling. Oxidative stress arises from an imbalance between the production of reactive oxygen and nitrogen species (ROS and RNS) and the capability of biological system to readily detoxify reactive intermediates. Several studies have reported beneficial effects of a therapy with antioxidant agents, including trace elements and other antioxidants, against the cardiovascular system dysfunction due to the diabetes. Antioxidants act through different mechanisms to prevent oxidant-induced cell damages acting either directly or indirectly. They can reduce the generation of ROS, scavenge ROS, or interfere with ROS-induced alterations. Modulating mitochondrial activity is an important possibility to control ROS production. Hence, the use of PPARα agonist to reduce fatty acid oxidation and of trace elements such as selenium as antioxidant and other antioxidants such as vitamins E and C, contribute to the prevention of diabetes-induced cardiovascular dysfunction. The paradigm that, inhibiting the overproduction of superoxides and peroxides would prevent cardiac dysfunction in diabetes has been difficult to verify using conventional antioxidants like vitamins E and C. That led to use of catalytic antioxidants such as SOD/CAT mimetics. Hence, well-tuned, balanced and responsive antioxidant defence systems are vital for proper prevention against diabetic damage. Myocardial cell death is observed in the hearts of diabetic patients and animal models; however, its importance in the development of diabetic cardiomyopathy is not completely understood. This review aims to summarize our present knowledge on various strategies to control oxidative stress and antagonize cardiovascular dysfunction during diabetes. In here, we consider aspects of redox signaling in the cardiovascular system, focusing on the molecular basis of redox sensing by proteins and the array of post-translational oxidative modifications that can occur. In addition, we discuss studies identify redox-sensitive cardiac proteins, as well as those assessing redox signalling in cardiovascular disease.

Profound cardioprotection with timolol in a female rat model of aging-related altered left ventricular function

Increasing evidence shows a marked beneficial effect with β-blockers in heart dysfunction via scavenging reactive oxygen species. Previously we showed that chronic treatment with either timolol or propranolol possessed similar beneficial effects for heart function in male rats as age increased, whereas only timolol exerted similar benefits in female rats. Therefore, in this study, we aimed first to examine the cellular bases for age-related alterations in excitation–contraction coupling in ventricular myocytes from female rats and, second, to investigate the hypothesis that age-related changes in [Ca2+]ihomeostasis and receptor-mediated system can be prevented with chronic timolol treatment. Chronic timolol treatment of 3-month-old female rats abolished age-related decrease in left ventricular developed pressure and the attenuated responses to β-adrenoreceptor stimulation. It also normalized the altered parameters of [Ca2+]itransients, decreased Ca2+loading of sarcoplasmic reticulum and increased basal [Ca2+]i, and decreased L-type Ca2+currents in 12-month-old female rats compared with the 3-month-old group. Adenylyl cyclase activity, β-adrenoreceptor affinity to its agonist, and β-adrenoreceptor density of the 12-month-old group are normalized to those of the 3-month-old group. Moreover, timolol treatment prevented dysfunction of the antioxidant system, including increased lipid peroxidation, decreased ratio of reduced glutathione to oxidized glutathione, and decreased activities of thioredoxin reductase and glucose-6-phosphate dehydrogenase, in the left ventricle of hearts from the 12-month-old group. Our data confirmed that aging-related early myocardial impairment is primarily related to a dysfunctional antioxidant system and impairment of Ca2+homeostasis, which can be prevented with chronic timolol treatment.

Treatments with sodium selenate or doxycycline offset diabetes-induced perturbations of thioredoxin-1 levels and antioxidant capacity

Diabetes is associated with increased oxidative stress and impaired antioxidant defenses. Thioredoxin-1 (TRX-1) is a cytosolic thiol antioxidant and redox-active protein which plays a vital role in the maintenance of reduced intracellular redox state. In this study, the authors examined whether 4-week treatments with sodium selenate and doxycycline--a metalloproteinase-2 inhibitor which also has antioxidant-like effects--offset perturbations in oxidative stress and antioxidant protection in rat liver and skeletal muscle in streptozotocin-induced diabetes (SID) model. Experimental diabetes decreased TRX-1 levels in skeletal muscle and liver. On the other hand, SID increased oxidative stress marker protein carbonyl levels and decreased oxygen radical absorbance capacity (ORAC), an indicator of antioxidant capacity, in liver. A 4-week treatment of sodium selenate to diabetic rats decreased blood glucose levels moderately, while doxycycline treatment caused a reduction in weight loss of diabetic rats. Both doxycycline and sodium selenate prevented diabetes-induced decrease of TRX-1 levels in skeletal muscle, whereas only doxyxycline was effectively preventing diabetes-induced decrease of TRX-1 in liver. Furthermore, both treatments prevented diabetes-induced altered levels of protein carbonyls and ORAC in liver, and restored free and total protein thiol levels in both skeletal muscle and liver. In conclusion, the data of this study provides further evidence that sodium selenate and doxycycline treatments may control oxidative stress and improve antioxidant defense in diabetes.

Intracellular free zinc during cardiac excitation-contraction cycle: calcium and redox dependencies

AIMS

Zinc exists in biological systems as bound and histochemically reactive free Zn(2+). It is an essential structural constituent of many proteins, including enzymes from cellular signalling pathways, in which it functions as a signalling molecule. In cardiomyocytes at rest, Zn(2+) concentration is in the nanomolar range. Very little is known about precise mechanisms controlling the intracellular distribution of Zn(2+) and its variations during cardiac function.

METHODS AND RESULTS

Live-cell detection of intracellular Zn(2+) has become feasible through the recent development of Zn(2+)-sensitive and -selective fluorophores able to distinguish Zn(2+) from Ca(2+). Here, in freshly isolated rat cardiomyocytes, we investigated the rapid changes in Zn(2+) homeostasis using the Zn(2+)-specific fluorescent dye, FluoZin-3, in comparison to Ca(2+)-dependent fluo-3 fluorescence. Zn(2+) sparks and Zn(2+) transients, in quiescent and electrically stimulated cardiomyocytes, respectively, were visualized in a similar manner to known rapid Ca(2+) changes. Both Zn(2+) sparks and Zn(2+) transients required Ca(2+) entry. Inhibiting the sarcoplasmic reticulum Ca(2+) release or increasing the Ca(2+) load in a low-Na(+) solution suppressed or increased Zn(2+) movements, respectively. Mitochondrial inhibitors slightly reduced both Zn(2+) sparks and Zn(2+) transients. Oxidation by H₂O₂ facilitated and acidic pH inhibited the Ca(2+)-dependent Zn(2+) release.

CONCLUSION

It is proposed that Zn(2+) release during the cardiac cycle results mostly from intracellular free Ca(2+) increase, triggering production of reactive oxygen species that induce changes in metal-binding properties of metallothioneins and other redox-active proteins, aside from ionic exchange on these proteins.

Antioxidant treatment protects diabetic rats from cardiac dysfunction by preserving contractile protein targets of oxidative stress

BACKGROUND

Animal studies suggest that reactive oxygen species (ROS) play an important role in the development of diabetic cardiomyopathy.

HYPOTHESIS

Matrix metalloproteinase-2 (MMP-2) is activated by ROS and contributes to the acute loss of myocardial contractile function by targeting and cleaving susceptible proteins including troponin I (TnI) and alpha-actinin.

METHODS

Using the streptozotocin-induced diabetic rat model, we evaluated the effect of daily in vivo administration of sodium selenate (0.3 mg/kg; DMS group), or a pure omega-3 fish oil with antioxidant vitamin E (omega-3E; 50 mg/kg; DMFA group), which has antioxidant-like effects, for 4 weeks on heart function and on several biochemical parameters related to oxidant stress and MMP-2.

RESULTS

Although both treatments prevented the diabetes-induced depression in left ventricular developed pressure (LVDP) as well as the rates of changes in developed pressure (+/-dP/dt) (P<.001), the improvement in LVDP of the DMS group was greater compared to that of the DMFA group (P<.001). Moreover, these treatments reduced the diabetes-induced increase in myocardial oxidized protein sulfhydryl and nitrite concentrations (P<.001). Gelatin zymography and Western blot data indicated that the diabetes-induced changes in myocardial levels of MMP-2 and tissue inhibitor of matrix metalloproteinase-4 (TIMP-4) and the reduction in TnI and alpha-actinin protein levels were improved in both the DMS and DMFA groups (P<.001).

CONCLUSIONS

These results suggest that diabetes-induced alterations in MMP-2 and TIMP-4 contribute to myocardial contractile dysfunction by targeting TnI and alpha-actinin and that sodium selenate or omega-3E could have therapeutic benefits in diabetic cardiomyopathy.

Omega-3E treatment regulates matrix metalloproteinases and prevents vascular reactivity alterations in diabetic rat aorta

It is known that increased generation of oxidants and (or) reduced endogenous antioxidant defense mechanisms are associated with the etiology of diabetic vascular complications. Although a close correlation exists between increased oxidative stress and the activation of matrix metalloproteinases (MMPs), little is known about the effect of hyperglycemia on the regulation and contribution of MMPs in the vascular system. Therefore, we aimed to examine whether omega-3E (50 mg/kg per day for 4 weeks), a long-chain (n-3) polyunsaturated fatty acid enriched with vitamin E, has a beneficial effect on vascular dysfunction via affecting MMPs in streptozotocin-diabetic rat aorta. Omega-3E treatment improved the diabetes-induced impairment of phenylephrine-induced contraction and isoproterenol-induced relaxation responses of aorta. It also exhibited marked protection against diabetes-induced degenerative changes in smooth muscle cell morphology. Biochemical data showed that this treatment significantly prevented important changes, such as inhibition of MMP-2 and MMP-9 activity, loss of tissue inhibitor of matrix metalloproteinase-4 (TIMP-4) protein, increase in tissue levels of thiol oxidation, endothelin-1, protein kinase C (PKC), and cAMP production, and decrease in tissue level of nitrite. These results indicated that omega-3E significantly improved impaired vascular responses and regulated the activity of MMPs via preventing oxidative injury. Overall, the data suggest that omega-3E ameliorates or prevents vascular reactivity alterations in diabetes. Such an observation provides preliminary evidence for omega-3E's potential as a therapeutic agent for the prevention of vascular disorders in diabetes.

Selenium restores defective beta-adrenergic receptor response of thoracic aorta in diabetic rats

Increased oxidative stress is one of the basic contributors to the development of the cardiovascular complications in diabetes. Both endothelial and vascular smooth muscle cell dysfunctions are the main sign involved in the pathogenesis of diabetic cardiovascular dysfunction. Matrix metalloproteinases (MMPs) are expressed in the vasculature, and participate in tissue remodeling under pathological conditions such as increased oxidative stress, whereas little is known about effect of hyperglycemia on regulation of MMPs in vascular system. Therefore, we aimed to evaluate the effect of an antioxidant, sodium selenate treatment (0.3 mg/kg for 4 weeks) on function of streptozotocin-diabetic rat aorta. Sodium selenate treatment improved significantly impaired isoproterenol-induced relaxation responses and contraction responses of the aortic strips, and exhibited marked protection against diabetes-induced degenerative changes in the smooth muscle cell morphology. Biochemical data showed that sodium selenate treatment induced a significant regulation of MMP-2 activity and protein loss as well as normalization of increased levels of tissue nitrite and protein thiol oxidation. In addition, this treatment restored diabetes-induced increased levels of endothelin-1, PKC, and cAMP production in the aortic tissue. Taken together, our data demonstrate that these beneficial effects of sodium selenate treatment in diabetics are related to be not only inhibition of increased oxidative stress but also prevention of both receptor- and smooth muscle-mediated dysfunction of vasculature, in part, via regulation of MMP-2. Such an observation provides evidence for potential therapeutic usage of selenium compounds for the amelioration of vascular disorders in diabetes.