Ashraf Taye

Oxidative Stress and Endothelial Dysfunction in Aortas of Aged Spontaneously Hypertensive Rats by NOX1/2 Is Reversed by NADPH Oxidase Inhibition

Arterial hypertension is associated with increased levels of reactive oxygen species, which may scavenge endothelium-derived NO and thereby diminish its vasorelaxant effects. However, the quantitatively relevant source of reactive oxygen species is unclear. Thus, this potential pathomechanism is not yet pharmacologically targetable. Several enzymatic sources of reactive oxygen species have been suggested: uncoupled endothelial NO synthase, xanthine oxidase, and NADPH oxidases. Here we show that increased reactive oxygen species formation in aortas of 12- to 14-month–old spontaneously hypertensive rats versus age-matched Wistar Kyoto rats is inhibited by the specific NADPH oxidase inhibitor VAS2870 but neither by the xanthine oxidase inhibitor oxypurinol nor the NO synthase inhibitor NG-nitro-l-arginine methyl ester. NADPH oxidase activity, as well as protein expression of its catalytic subunits, NOX1 and NOX2, was increased in the aortas of spontaneously hypertensive rats, whereas the expression of NOX4 protein, the most abundant NOX isoform, was not significantly changed. Impaired acetylcholine-induced relaxation of spontaneously hypertensive rat aortas was significantly improved by VAS2870. In conclusion, NOX1 and NOX2 but not NOX4 proteins are increased in aged spontaneously hypertensive rat aortas. Importantly, these NOX isoforms, in particular, ectopic expression of NOX1 in endothelial cells, appear to affect vascular function in an NADPH oxidase inhibitor-reversible manner. NADPH oxidases may, thus, be a novel target for the treatment of systemic hypertension.

The antihyperglycemic effect of curcumin in high fat diet fed rats. Role of TNF-α and free fatty acids

This study was conducted to investigate the effect of curcumin, obtained from Curcuma longa, in comparison with rosiglitazone on the progression of insulin resistance and type 2 diabetes mellitus (T2DM) and the mechanisms underlying this effect. Insulin resistance and T2DM was induced in male Sprague Dawley rats by high fat diet (HFD) feeding for 60 and for 75 days representing two regimens of the study, protection and treatment. Prophylactic oral administration of curcumin (80 mg/kg), rosiglitazone (1 mg/kg), their combination, or vehicle (in control groups) was started along with HFD feeding in different groups. Treatment is achieved by oral administration of the previously mentioned agents in the last 15 days of HFD feeding after induction of insulin resistance and T2DM in rats. Curcumin showed an anti-hyperglycemic effect and improved insulin sensitivity, and this action may be attributed at least in part to its anti-inflammatory properties as evident by attenuating TNF-α levels in HFD fed rats, and its anti-lipolytic effect as evident by attenuating plasma free fatty acids. The curcumin effects are comparable to those of rosiglitazone, which indicate that they may act similarly. Finally we can say that, curcumin could be a beneficial adjuvant therapy in patients with T2DM.

Effect of apocynin on NADPH oxidase-mediated oxidative stress-LOX-1-eNOS pathway in human endothelial cells exposed to high glucose

Hyperglycemia-induced generation of reactive oxygen species contributes to the development of proatherogenic changes and vasculopathy in diabetes. NADPH oxidase has been recognized as a major source of reactive oxygen species in the vasculature and the lectin-like oxLDL receptor-1 (LOX-1) appears to play a crucial role in the pathogenesis of diabetic endothelial dysfunction. The present study aimed to examine the relationships between the hyperglycemia-mediated NADPH oxidase-LOX-1 pathway activation and nitric oxide-mediated endothelial function. In addition, we investigated effect of the NADPH oxidase inhibitor, apocynin on these consequences. In human umbilical artery endothelial cells (HUAECs), the effect of high glucose on expressional regulations and functional consequences of NADPH oxidase subunits, LOX-1 and endothelial nitric oxide synthase (eNOS), in the absence and presence of apocynin (10 micromol/l) were evaluated. HUAECs were cultured under normal (5.5 mmol/l) or high glucose (30mmol/l) concentrations for 48 h in the absence and presence of apocynin. Our results showed that high glucose significantly enhanced the activity and the protein expression of NADPH oxidase subunits, Nox2 and p47(phox). High glucose markedly increased LOX-1 mRNA level and this was functionally reflected on the augmented uptake of Dil-labelled LDL (5 micromol/l, 3h) by HUAECs. Furthermore, high glucose attenuated eNOS protein and total nitrite levels. However, apocynin inhibited all these changes. Collectively, our study demonstrates that high glucose-induced oxidative stress via NADPH oxidase activation and this contributed to LOX-1 upregulation and eNOS downregulation in human endothelial cells. Apocynin efficiently reversed these consequences, suggesting its potential role as a vasculoprotective agent.

Quercetin augments the protective effect of losartan against chronic doxorubicin cardiotoxicity in rats

The present study aimed to examine whether the co-administration of quercetin (QRN) and losartan (LOS) can produce additional protective effects against chronic DOX cardiotoxicity. Cardiotoxicity in rats was induced by intraperitoneal injection of doxorubicin (DOX) in a cumulative dose of 15mg/kg for two weeks. Results revealed that DOX administration exhibited elevated serum levels of TNF-α, creatine kinase (CK-MB), lactate dehydrogenase (LDH) in addition to increased myocardial lipid peroxide (MDA) and nitric oxide (NO) alongside attenuating cardiac antioxidant defense system of superoxide dismutase (SOD) and catalase (CAT) activities. DOX produced leukocyte infiltration and myocardial lesions. Pretreatment with QRN (10mg/kg, orally) solely or in combination with LOS (0.7mg/kg, orally) for 6 weeks markedly ameliorated all these biochemical characteristics, and substantially reduced the myocardium peroxidative damage. The protective effects obtained by LOS were more pronounced by its combination with QRN. Our results suggest that quercetin potentially augmented the cardioprotective effect of losartan against chronic DOX cardiotoxicity via its antioxidant and anti-inflammatory properties.

Lectin‐like oxidized low‐density lipoprotein receptor 1 pathways

The role of lectin‐like oxidized low‐density lipoprotein receptor (LOX)‐1 has been implicated in the pathogenesis of different diseases, including atherosclerosis, hypertension, obesity, diabetes mellitus and metabolic syndrome. To date, several studies aimed at partially investigating the mechanistic role of LOX‐1 in these various pathologies. Still, so far, the precise signal transduction pathways involving LOX‐1 have not yet been elucidated.

Cardioprotective Effects of Nicorandil, a Mitochondrial Potassium Channel Opener against Doxorubicin-Induced Cardiotoxicity in Rats

Doxorubicin is a chemotherapeutic drug used to treat solid and haematopoietic tumours. Its use is limited by a major side effect of cardiotoxicity. It was reported that doxorubicin‐induced cardiotoxicity is mediated through oxidative stress coupled with impaired NO bioavailability and NF‐κB activation. Nicorandil, a mitochondrial ATP‐dependent potassium (KATP) channel opener, was reported to be cardioprotective on ischaemic myocardium. However, the effect of nicorandil against doxorubicin‐induced cardiotoxicity has not yet been clarified. Accordingly, six groups of rats were used. The first three groups were injected with vehicle, nicorandil (3 mg/kg) orally and doxorubicin (a single intraperitoneal injection of 20 mg/kg), respectively. Group four was treated with nicorandil, whereas group five was treated with glibenclamide and then nicorandil starting 2 days before doxorubicin and continued for five consecutive days. Group six was treated with glibenclamide alone. At the end of the experiment, the rats were killed. Cardiac enzyme indexes were measured in serum. Heart tissues were processed for determination of nitrite/nitrate, NF‐κB protein expression, glutathione (GSH), lipid peroxide (TBARS) levels and superoxide production. In addition to body‐weight reduction, doxorubicin produced cardiotoxicity as indicated from the increase in lactate dehydrogenase (LDH), creatine kinase (CK) activities, TBARS, superoxide production, NF‐κB expression and caspase‐3 activity. Moreover, doxorubicin decreased GSH and nitrite/nitrate levels. Histopathological examination of doxorubicin‐treated hearts revealed degenerative changes. On the other hand, nicorandil protected cardiac tissues against doxorubicin cardiotoxicity as demonstrated from normalization of cardiac biochemical and oxidative stress parameters and amelioration of histopathological changes. Glibenclamide, a blocker of the KATP channel, reversed most of the cardiac effects of nicorandil.

Combination therapy with spironolactone and candesartan protects against streptozotocin-induced diabetic nephropathy in rats

Diabetic nephropathy is one of the most common causes of end-stage kidney disease. Aldosterone and angiotensin II appear to play a crucial role in the pathogenesis of this disease. The present study aimed to investigate effects of the combination therapy with spironolactone and candesartan on diabetic nephropathy and elucidate the underlying mechanism(s) involved. Diabetes was induced in rats by a single intraperitoneal injection of streptozotocin (STZ) (55 mg/kg). The diabetic rats were orally treated with spironolactone (50 mg/kg/day) and/or candesartan (1 mg/kg/day) for 8 weeks. Administration of STZ caused a marked elevation in the serum level of creatinine, urea and urinary albumin-creatinine ratio (ACR). This was associated with upregulated renal protein levels of nuclear factor-kappa B (NF-κB), transforming growth factor (TGF)-β, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) alongside increasing the renal superoxide anion (O2(-)) production, malondialdehyde (MDA) level and the systolic blood pressure. There was a marked decrease in nitric oxide (NO) bioavailability and antioxidant enzyme capacity. The combined therapy of spironolactone and candesartan significantly normalized the oxidative stress and fibrotic/inflammatory alterations. Additionally, the elevated blood pressure was attenuated by administration of candesartan alone or in combination. This was associated with improving the renal function parameters. The combined therapy exhibited more profound response compared to the monotherapy. In conclusion, our results demonstrate that the combined therapy of spironolactone and candesartan can confer an additive benefit over the use of either drug alone against STZ-induced diabetic nephropathy, presumably via attenuating the inflammatory responses and oxidative status markers.

Activation of renal haeme oxygenase-1 alleviates gentamicin-induced acute nephrotoxicity in rats.

This study aimed to investigate whether activation of haeme oxygenase (HO)‐1 enzyme by haemin would have beneficial effects on the functional and histological outcome against gentamicin‐induced renal damage in rats and sought to elucidate the underlying mechanisms of the therapeutic action.

Combination therapy with losartan and L-carnitine protects against endothelial dysfunction of streptozotocin-induced diabetic rats.

Endothelial dysfunction is a critical factor during the initiation of diabetic cardiovascular complications and angiotensin II appears to play a pivotal role in this setting. The present study aimed to investigate whether the combination therapy with losartan and the nutritional supplement, L-carnitine can provide an additional protection against diabetes-associated endothelial dysfunction and elucidate the possible mechanism(s) underlying this effect. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ) (60 mg/kg) in rat. Effects of losartan (20 mg/kg, orally, 3 months) and L-carnitine (200 mg/kg, orally, 3 months) on tumor necrosis factor (TNF)-α, oxidative stress parameters, endothelial nitric oxide synthase expression (eNOS), and vascular function were evaluated. Our results showed a marked increase in aortic superoxide anion (O2(-)) production and serum malondialdehyde (MDA) level alongside attenuating antioxidant enzyme capacities in diabetic rats. This was associated with a significant increase in anigiotensin II type 1 receptor gene expression and TNF-α serum level of diabetic rats alongside reducing aortic eNOS gene expression and nitric oxide (NO) bioavailability. The single or combined administration of losartan and L-carnitine significantly inhibited these changes. Additionally, the vascular endothelium-dependent relaxation with acetylcholine (ACh) in aortic diabetic rat was significantly ameliorated by the single and combined administration of losartan or L-carnitine. Noteworthy, the combination therapy exhibited a more profound response over the monotherapy. Collectively, our results demonstrate that the combined therapy of losartan and L-carnitine affords additive beneficial effects against diabetes-associated endothelial dysfunction, possibly via normalizing the dysregulated eNOS and reducing the inflammation and oxidative stress in diabetic rats.

Comparative study between atorvastatin and losartan on high fat diet-induced type 2 diabetes mellitus in rats.

Obesity is often associated with chronic inflammatory state which contributes to the development of insulin resistance (IR) and type 2 diabetes mellitus (T2DM). This study investigated the effects of single and combined administration of atorvastatin (ATOR, lipid‐lowering drug) and losartan (LOS, angiotensin receptor antagonist) on metabolic disorders and inflammatory status that are implicated in the development of T2DM with the use of pioglitazone (PIO) as a standard antidiabetic drug. T2DM was induced in male rats by high‐fat diet (HFD) feeding for 16 weeks. Oral administrations of ATOR (10 mg/kg), LOS (20 mg/kg), PIO (3 mg/kg), their binary combinations, or vehicle were started in the last 4 weeks. Fasting serum glucose, oral glucose tolerance, fasting serum insulin, IR, serum lipid profile, serum TNF‐α and body composition index were determined. Results showed that all drugs and their combinations had positive impact effect on all measured parameters, and better results were achieved from binary drug combinations than administration of each drug alone. Combination of PIO with either ATOR or LOS provided better improvements on T2DM‐associated metabolic abnormalities and inflammatory status with respect to each drug alone. However, the most pronounced effects of drugs and their combinations regarding the above parameters were attributed to LOS + PIO combination. In conclusion, this study indicates that combination of ATOR + PIO and, in particular, LOS + PIO can be used as promising effective therapies in the management of HFD‐induced T2DM. This concept may be attributed to the combined effects of the respective monotherapies to improve lipid profile, insulin sensitivity, and TNF‐α level.