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

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

We studied the effects of treatment with SMe1EC, a hexahydropyridoindole antioxidant, on vascular reactivity, endothelial function, and oxidonitrosative stress level of thoracic aorta in young and old rats with or without diabetes mellitus. The rats were grouped as young control (YC 3 months old), old control (OC 15 months old), young diabetic (YD), old diabetic (OD), young control treated (YCT), old control treated (OCT), young diabetic treated (YDT), and old diabetic treated (ODT). Diabetes was induced by streptozotocin injection and subsequently SMe1EC2 (10 mg/kg/day, p.o.) was administered to YCT, OCT, YDT, and ODT rats for 5 months. In young and old rats, diabetes resulted in hypertension, weight loss, hyperglycemia, and hypertriglyceridemia, which were partially prevented by SMe1EC2. SMe1EC2 also inhibited the diabetes-induced increase in aorta levels of AGEs (advanced glycosylation end-protein adducts), 4-HNE (4-hydroxy-nonenal-histidine), 3-NT (3-nitrotyrosine), and RAGEs (receptors for AGEs). The contractions of the aorta rings to phenylephrine (Phe) and KCL did not significantly change, but acetylcholine (ACh) and salbutamol relaxations were reduced in OC compared to YC rats. Diabetes induction increased Phe contractions in YC and OC rats, KCL contractions in YC rats, and did not cause further inhibition in already inhibited ACh and salbutamol relaxations in OC rats. We have achieved the lowest levels of ACh relaxation in YD rats compared to other groups. SMe1EC2 did not change the response of aorta to ACh, salbutamol and Phe in YC rats, and ameliorated ACh relaxations in OC and YD but not in OD rats. In YDT and ODT rats, increased Phe and KCL contractions, high blood pressure, and impaired salbutamol relaxations were amended by SMe1EC2. Phe contractions observed in YD and OD rats as well as KCl contractions observed in OC rats were the lowest levels when the rats were treated with SMe1EC2. When the bath solution was shifted to cyclopiazonic acid (CYP) or CYP plus Ca²⁺-free medium, the contraction induced by a single dose of Phe (3 × 10^-6 M) was more inhibited in YD and OD than in YC but not in OC rats. In SMe1EC2-treated rats, neither the presence of CFM nor CFM plus CYP exhibited a significant change in response of aorta to a single dose of Phe. These findings suggest that α1-adrenergic receptor signaling is activated in both age groups of diabetic rats, diabetes activates K⁺-depolarization and calcium mobilization via Ca_V especially in the aorta of young rats, and sensitizes the aorta of old rats to the regulating effect of SMe1EC2. ACh relaxations were inhibited in YC rats, increased in OC rats and unchanged in YD and OD rats when aortic rings pretreated with TEA, an inhibitor of calcium-activated K⁺ channels (K_Ca), or 4-aminopyridine (4-AP), an inhibitor of voltage-sensitive K⁺ channels (K_V). ACh relaxations were inhibited in YCT, OCT, and YDT rats in the presence of 4-AP or TEA. In ODT rats, 4-AP did not change ACh relaxation but TEA inhibited. These findings suggest that the contribution of K_v and K_Ca to ACh relaxation is likely upregulated by SMe1EC2 when the relaxations were inhibited by aging or diabetes. We conclude that SMe1EC2 might be a promising agent for aging and diabetes related vascular disorders.

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.

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.

Effect of 17beta-oestradiol replacement on vascular responsiveness in ovariectomized diabetic rats

1. Women with functional ovaries exhibit a gender advantage in terms of the prevalence of cardiovascular diseases. However, whether this gender bias pertains in diabetes is unknown. 2. The aim of the present study was to examine the effects of 17beta-oestradiol (E2) on vascular responsiveness in normal and diabetic ovariectomized (OVX) rats. Aged-matched female rats were divided into four groups as follows: (i) OVX; (ii) OVX + E2 treated; (iii) diabetic OVX; and (iv) diabetic OVX + E2 treated. Bilateral ovariectomy was performed and streptozotocin was used to induce experimental diabetes. Rats were treated with 1 mg/kg per day, p.o., E2 for 8 weeks. 3. Although E2 treatment had no effect on blood glucose levels in normal and diabetic OVX rats, it significantly reduced systolic blood pressure and prevented diabetes-induced loss of bodyweight gain. 4. In segments of the thoracic aorta, concentration-dependent vasoconstrictor responses to KCl and phenylephrine were significantly attenuated following E2 treatment in both the normal and diabetic groups. The sarcoplasmic/endoplasmic reticulum calcium ATPase inhibitor thapsigargin (10(-6) mol/L) and the Ca(2+) channel blocker nifedipine (10(-6) mol/L) inhibited the transient vasoconstriction to PE in all groups. The constrictor effect of PE was increased by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME; 10(-6) mol/L), but was reduced by superoxide dismutase (SOD; 100 U/mL) and the cyclo-oxygenase inhibitor indomethacin (10(-6) mol/L) in all groups. Responses to acetylcholine (ACh; 10(-6) mol/L) demonstrated reduced endothelium-dependent relaxation in non-E2-treated groups. Relaxation responses to ACh were increased by 100 U/mL SOD and 10(-6) mol/L indomethacin, but were reduced by 10(-6) mol/L l-NAME in all groups. There were no differences among the four groups in terms of relaxation responses to sodium nitroprusside (10(-11) to 10(-6) mol/L). 5. In conclusion, the results of the present study suggest that oestrogen treatment has beneficial effects on vascular function in both diabetic and non-diabetic OVX rats due to Ca(2+) regulation and anti-oxidation.

Reactive Oxygen Species Mediate Caspase Activation and Apoptosis Induced by Lipoic Acid in Human Lung Epithelial Cancer Cells through Bcl-2 Down-Regulation

The antioxidant alpha-lipoic acid (LA) is a naturally occurring compound that has been shown to possess promising anticancer activity because of its ability to preferentially induce apoptosis and inhibit proliferation of cancer cells relative to normal cells. However, the molecular mechanisms underlying the apoptotic effect of LA are not well understood. We report here that LA induced reactive oxygen species (ROS) generation and a concomitant increase in apoptosis of human lung epithelial cancer H460 cells. Inhibition of ROS generation by ROS scavengers or by overexpression of antioxidant enzymes glutathione peroxidase and superoxide dismutase effectively inhibited LA-induced apoptosis, indicating the role of ROS, especially hydroperoxide and superoxide anion, in the apoptotic process. Apoptosis induced by LA was found to be mediated through the mitochondrial death pathway, which requires caspase-9 activation. Inhibition of caspase activity by the pan-caspase inhibitor (z-VAD-FMK) or caspase-9-specific inhibitor (z-LEHD-FMK) completely inhibited the apoptotic effect of LA. Likewise, the mitochondrial respiratory chain inhibitor rotenone potently inhibited the apoptotic and ROS-inducing effects of LA, supporting the role of mitochondrial ROS in LA-induced cell death. LA induced down-regulation of mitochondrial Bcl-2 protein through peroxide-dependent proteasomal degradation, and overexpression of the Bcl-2 protein prevented the apoptotic effect of LA. Together, our findings indicate a novel pro-oxidant role of LA in apoptosis induction and its regulation by Bcl-2, which may be exploited for the treatment of cancer and related apoptosis disorders.

Thioctic acid for patients with symptomatic diabetic polyneuropathy: a critical review

Diabetic neuropathy represents a major health problem, as it is responsible for substantial morbidity, increased mortality, and impaired quality of life. Near-normoglycemia is now generally accepted as the primary approach to prevention of diabetic neuropathy, but is not achievable in a considerable number of patients. A growing body of evidence suggests that oxidative stress resulting from enhanced free-radical formation and/or defects in antioxidant defense is implicated in the pathogenesis of diabetic neuropathy. Markers of oxidative stress such as superoxide anion and peroxynitrite production are increased in diabetic patients in relation to the severity of polyneuropathy. In experimental diabetic neuropathy, oxygen free-radical activity in the sciatic nerve is increased, and treatment with thioctic acid, a potent lipophilic antioxidant, results in prevention or improvement of the diabetes-induced neurovascular and metabolic abnormalities in various organ systems. Pharmacodynamic studies have shown that thioctic acid favorably influences the vascular abnormalities of diabetic polyneuropathy such as impaired microcirculation, increased indices of oxidative stress, and increased levels of markers for vascular dysfunction, such as thrombomodulin, albuminuria, and nuclear factor-kappaB. Thus far, seven controlled randomized clinical trials of thioctic acid in patients with diabetic neuropathy have been completed (Alpha-Lipoic Acid in Diabetic Neuropathy [ALADIN I-III], Deutsche Kardiale Autonome Neuropathie [DEKAN], Oral Pilot [ORPIL], Symptomatic Diabetic Neuropathy [SYDNEY], Neurological Assessment of Thioctic Acid in Neuropathy [NATHAN] II) using different study designs, durations of treatment, doses, sample sizes, and patient populations. Recently, a comprehensive analysis was undertaken of trials with comparable designs that met specific eligibility criteria for a meta-analysis to obtain a more precise estimate of the efficacy and safety of thioctic acid (600mg intravenously for 3 weeks) in diabetic patients with symptomatic polyneuropathy. This meta-analysis included the largest sample of diabetic patients (n = 1258) ever to have been treated with a single drug or class of drugs to reduce neuropathic symptoms, and confirmed the favorable effects of thioctic acid based on the highest level of evidence (Class Ia: evidence from meta-analyses of randomized, controlled trials). The following conclusions can be drawn from these trials: (i) short-term treatment for 3 weeks using intravenous thioctic acid 600 mg/day reduces the chief symptoms of diabetic polyneuropathy to a clinically meaningful degree; (ii) this effect on neuropathic symptoms is accompanied by an improvement of neuropathic deficits, suggesting potential for the drug to favorably influence underlying neuropathy; (iii) oral treatment for 4-7 months tends to reduce neuropathic deficits and improve cardiac autonomic neuropathy; and (iv) clinical and postmarketing surveillance studies have revealed a highly favorable safety profile of the drug. Based on these findings, a pivotal long-term multicenter trial of oral treatment with thioctic acid (NATHAN I) is being conducted in North America and Europe to investigate effects on progression of diabetic polyneuropathy, using a clinically meaningful and reliable primary outcome measure that combines clinical and neurophysiological assessment.

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.

Alpha-lipoic acid ameliorates myocardial toxicity induced by doxorubicin

The effect of alpha-lipoic acid (LA) on the cardiotoxicity induced by doxorubicin (DOX) was investigated. A single dose of DOX (15 mg kg(-1), i.p) induced cardiotoxicity manifested biochemically by a significant elevation of serum creatine phosphokinase (CK; EC: 2.7.3.2) and lactate dehydrogenase (LDH; EC: 1.1.1.27) 48 h later. Moreover, cardiotoxicity was further confirmed by the significant increase in lipid peroxides measured as malondialdehyde (MDA), and significant decrease in protein thiols (Protein-SH) content in heart tissues. Administration of LA (100 mg kg(-1)) orally for 5 days before and 2 days after DOX injection produced a significant protection against cardiotoxicity induced by DOX. The amelioration of cardiotoxicity was evident by significant reductions in serum CK and LDH. Moreover, LA prevented the rise of MDA as well as the significant reduction of Protein-SH. These results may suggest that LA has a protective effect against cardiotoxicity induced by DOX and it may, therefore, improve the therapeutic index of DOX.