Excess Amounts Of Free Radicals Research Articles

The Third-Generation Beta-Blocker

In this issue of the Journal, Khan et al1 study the third-generation beta-blocker, nebivolol, in a rat model of aldosterone/salt treatment–induced hypertensive heart disease and show that myocyte necrosis is incited by oxidative stress secondary to an increase in cytosolic free calcium and mitochondrial calcium overload—a process that overwhelms the endogenous zinc (Zn)-based antioxidants. Using the first-generation beta-blocker atenolol as a control, treatment with nebivolol induced activation of endothelial nitric oxide synthase, nitric oxide (NO) generation, and a marked increase in intracellular Zn. Conversely, there was a concomitant decrease in intracellular and subsarcolemmal mitochondrial calcium levels. Likewise, there was attenuation of mitochondrial hydrogen peroxide production and lipid peroxidation, inhibition of microscopic myocardial scarring, and a reduction in collagen volume fractions. They postulate an intriguing pathophysiologic phenomenon whereby nebivolol, acting as a β3 agonist, increases NO formation leading to a rise in cytosolic free Zn. This inhibits intracellular and mitochondrial calcium overload, which ameliorates many of the detrimental effects of reactive oxygen species (ROS), lipid peroxidation, and the eventual myocardial scarring. Several important points can be gleaned from this study. First, this animal model of hypertensive cardiomyopathy serves as an effective model of sudden cardiac death as both myocardial fibrosis and adverse remodeling are key features of this disease process. This hypothesis, originally formulated by Weber and others, served as a fundamental basis for the RALES and EPHESUS trials. This concept was recently reviewed and confirmed by Esposito et al2 in a canine model of pacing-induced systolic heart failure, interstitial fibrosis, and myocardial electrical activation delays. They showed that mineralocorticoid receptor antagonism played a key role in preventing the activation of inflammatory pathways and in the development of ventricular arrhythmogenic foci. It is interesting to speculate that nebivolol may also induce similar cardioprotection. Nebivolol is approved for the treatment of hypertension in the United States and is marketed as Bystolic. In Europe, it is approved for the treatment of both hypertension and left ventricular failure. At low doses, it is a selective β1-receptor blocker, and as the dose is up-titrated, it loses its selectivity. It is unique in that unlike carvedilol (Coreg), it has a NO potentiating ability, a property that Khan et al1 have effectively shown in their study. Another plausible mechanism for the drug's efficacy is that it may act primarily within the mitochondria at the site of ROS production or as a ROS scavenger, inhibiting superoxide anion or hydrogen peroxide. Accordingly, the sequelae of pathology associated with excessive ROS production in hypertensive cardiomyopathy can effectively be targeted. Nebivolol is not the first beta-blocker to demonstrate antioxidant properties. Carvedilol, the first of the third-generation beta-blockers, has been shown in a number of studies to be both an antioxidant and free radical scavenger.3 Its antioxidant property resides in its carbazole moiety, a property partly shared by nebivolol. The apparent underlying protective mechanism of carvedilol is through inhibition of lipid peroxidation primarily through free radical scavenging. Khan et al1 showed that nebivolol could similarly protect against lipid peroxidation. This unique property has not received a great deal of attention from our clinical colleagues, except in the burgeoning field of Cardio-Oncology. The chemotherapeutic anthracyclines are known to be one of the most effective anticancer treatments available but produce an excessive amount of free radicals within the myocardium, leading to cardiotoxicity and heart failure. It is of no surprise then that carvedilol is currently considered the “beta-blocker of choice” for patients suffering from anthracycline-induced heart failure. Perhaps, it is time when nebivolol was investigated for its antioxidant properties in oxidative pathological conditions also? The use of the term “third-generation beta-blocker,” is a method we use to explain the hierarchy of beta-blockers in terms of development. Atenolol is a first-generation beta-blocker in terms of age, a drug known to have no antioxidant properties and a characteristic Khan et al1 use for control experiments. The second-generation beta-blockers include metoprolol, which although has cardioprotective effects, does not have any antioxidant effects. The current third-generation beta-blockers include carvedilol, a drug with antioxidant effects and free radical scavenging ability.4 Nebivolol can now be added to this list. It is rather interesting to recall that over the last several decades, both laboratory and clinical research with endogenous antioxidants such as superoxide dismutase, vitamin E, and catalase were all fraught with failure and frustration. Conceivably, the elusive and effective antioxidant has been right in front us for the past 20 years, and we were just a little slow in recognizing the potential expedient effects of these drugs.

English

OBJECTIVES: Cigarette smoking and alcohol consumption has multiple effects on the thyroid gland. Ingestion of alcohol produces striking of metabolic imbalance in the liver, it leads to formation of reactive oxygen species, cigarette smoke is known to stimulate the alveolar macrophages to release excessive amount of free radicals which causes pathogenicity. Our study was designed to assess the thyroid status in smoking & alcoholism, also oxidant and antioxidant status in smokers and alcoholics. MATERIALS & METHODS: The study was conducted in50 smokers & alcoholics, they smoke 10-15 cigarettes per day and all are having history of alcohol intake from past 10-15years, as well as 25 healthy non-smoker volunteers served as controls. All the subjects are attended to O.P.D and admitted in medicine department P.E.S. Medical College & Hospital, Kuppam, A.P. The study was done by assessing thyroid profile (FreeT3,FreeT4,TSH) by ELISA method and oxidative stress parameters protein carbonylation, reduced glutathione were studied in RBC by colorimetric method. RESULTS: There is slightly elevated levels of TSH compared with controls (p=0.005). Free T3 levels slightly lowered compared with controls (p=0.001). Free T4 levels are normal in range for smokers and alcoholics. Reduced glutathione levels are decreased slightly compared with controls (P=0.076). Protein carbonylation is increased compared with controls (P=0.001). CONCLUSIONS: The above findings suggest that there is fall in thyroid action due to alcoholic liver damage, Antioxidants levels are decreased and oxidant levels are increased due to oxidative damage.

Urinary Biopyrrins: Potential Biomarker for Monitoring of the Response to Treatment with Anxiolytics

During periods of psychological stress, excess amounts of free radicals are produced. Bilirubin oxidative metabolites (biopyrrins; BOM) are generated from bilirubin as a result of its scavenging action against free radicals. We investigated whether the urinary excretion of biopyrrins is altered by anxiolytics. In the present study, mice were immobilized for a period of 6hr. Alprazolam (0.1-1mg/kg of body-weight) was administered 30min. before subjecting the animals to acute stress. The BOM concentrations in urine and the corticosterone levels in serum were measured by ELISA with an anti-bilirubin antibody and EIA, respectively. We observed an increase in urinary biopyrrins in stressed mice in comparison with non-stressed mice and a decrease after the treatment of stressed animals with alprazolam. A correlation between urinary BOM and serum corticosterone levels was found. Urinary levels of biopyrrins might be used to assess the response to anxiolytics prescribed during acute stress periods.

Dietary Antioxidants as Potential Pharmacological Agents for Ischemic Stroke

Acute ischemic stroke is a leading cause of death and severe disability in industrialised countries and also in many developing countries. An excessive amount of free radicals is generated during cerebral ischemia, which significantly contributes to brain damage. Therefore, an increasing interest has been devoted to the potential benefits of antioxidant compounds in ischemic stroke patients. In this review, we examined the most relevant observational studies concerning the relationship between dietary antioxidants and ischemic stroke as well as clinical trials investigating the effects of single or multiple antioxidant supplementation in the prevention or treatment of acute ischemic stroke. Furthermore, we reviewed the most promising antioxidant compounds, i.e. dehydroascorbic acid, alpha-tocotrienol, gamma-tocopherol, flavonoids, resveratrol and gingko biloba, tested in animal models of acute ischemic stroke. Finally, we carefully evaluated the reasons for the discrepancy between experimental and clinical studies, and provided recommendations to improve the translation of the results obtained in animal models to patients with acute ischemic stroke.

Increased urinary excretion of biopyrrins, oxidative metabolites of bilirubin, in patients with schizophrenia

During periods of psychological stress, excess amounts of free radicals are produced, and they play an important role in the pathophysiological process. Bilirubin oxidative metabolites, biopyrrins, are generated from bilirubin as a result of this scavenging action against free radicals. We investigated whether the urinary excretion of biopyrrin is altered during the psychotic state in patients with schizophrenia. Biopyrrin concentrations in urine of 15 patients with schizophrenia and 100 age-matched healthy subjects were measured by enzyme-linked immunosorbent assay with an anti-bilirubin antibody. Urine samples were obtained from the patients on first admission (acute state), 1 month after admission (sub-acute state), and on discharge (remission state). Urinary concentrations of biopyrrins in patients with schizophrenia on admission were significantly higher than those in the controls. Response to treatment was associated with a significant decrease in the concentrations of biopyrrins. Moreover, urinary concentrations of biopyrrins were still significantly higher in patients with schizophrenia in the sub-acute and remission states than in the controls. These results demonstrated an increase in urinary biopyrrins in patients with schizophrenia and a decrease with recovery from the psychotic state. These findings indicate that the urinary biopyrrin level is a possible indicator that can be useful in the continuous monitoring of psychotic states in clinical practice.

Megamitochondria formation - physiology and pathology.

Mitochondria undergo structural changes simultaneously with their functional changes in both physiological and pathological conditions. These structural changes of mitochondria are classified into two categories: simple swelling and the formation of megamitochondria (MG). Data have been accumulated to indicate that free radicals play a crucial role in the mechanism of the MG formation induced by various experimental conditions which are apparently various. These include ethanol-, chloramphenicol- and hydrazine-induced MG formation. Involvement of free radicals in the mechanism of MG formation is showed by the fact that MG formation is successfully suppressed by free radical scavengers such as alpha-tocopherol, coenzyme Q(10), and 4-OH-TEMPO. Detailed mechanisms and pathophysiological meanings of MG formation still remain to be investigated. However, a body of evidence strongly suggests that enormous changes in physicochemical and biochemical properties of the mitochondrial membranes during MG formation take place and these changes are favorable for membrane fusion. A recent report showed that continous exposure of cells with MG to free radicals induces apoptosis, finding which suggests that MG formation is an adaptative process to unfavorable environments at the level of intracellular organelles. Mitochondria try to decrease intracellular reactive oxygen species (ROS) levels by decreasing the consume of oxygen via MG formation. If mitochondria succeed to suppress intracellular ROS levels, MG return to normal both structurally and functionally, and they restore the ability to actively synthesize ATP. If cells are additionally exposed to excess amounts of free radicals, MG become swollen, membrane potential of mitochondria (DeltaPsim) decreases, cytochrome c is released from mitochondria, leading to activation of caspases and apoptosis is induced.

Increased Urinary Excretion of Bilirubin Oxidative Metabolites in Septic Patients: A New Marker for Oxidative Stress in Vivo

Background. Bilirubin oxidative metabolites (BOMs) are generated from bilirubin as a result of its scavenging action against free radicals. During sepsis, excess amounts of free radicals are produced, and they play an important role in the pathophysiological process. We studied whether urinary excretion of BOMs would increase under septic conditions in humans and compared BOM levels with other well-established clinical parameters of inflammation.Methods. In 19 septic patients and 28 nonseptic control patients, the BOM concentrations in urine were measured by enzyme-linked immunosorbent assay with an anti-bilirubin antibody.Results. Urinary BOM levels in septic patients were much higher than those in control patients (21.6 ± 2.5 vs 1.4 ± 0.4 μmol/g creatinine, P < 0.001). Although there was a linear correlation between urinary BOM and serum total bilirubin levels (r = 0.392, P = 0.008), serum bilirubin levels were not significantly higher in the septic group than in the control group (P = 0.072). BOM levels correlated with body temperature (r = 0.801, P < 0.001), white blood cell counts in the peripheral blood (r = 0.590, P < 0.001), serum C-reactive protein (r = 0.653, P < 0.001), and the acute physiological and chronic health evaluation (APACHE II) score (r = 0.467, P = 0.003).Conclusions. These results demonstrated a urinary increase in BOMs in septic patients. This increase indicates that urinary BOM level is a possible marker for continuous monitoring of sepsis severity in clinical practice.

Calpain Activation and Not Oxidative Damage Mediatesl-2-Chloropropionic Acid-Induced Cerebellar Granule Cell Necrosis

Possible biochemical events involved inl-2-chloropropionic acid (L-CPA)-induced delayed cerebellar granule cell necrosis followingN-methyl-d-aspartate activation were studiedin vivo.We examined whether the calcium-sensitive proteolytic enzymes, the calpains, may be activated by L-CPA or whether the generation of excess quantities of cytotoxic free radicals may play a role in the neurotoxicity produced by oral administration of L-CPA (750 mg/kg, pH 7.0). Evidence for free radical-induced cellular damage was examined using biochemical approaches such as examining brains from L-CPA-treated rats for increased lipid peroxidation, DNA damage, or protein oxidation. Second, the ability of antioxidants to provide neuroprotective activity against L-CPA-induced neurotoxicity was examinedin vivo.Western blotting using antibodies against spectrin (α-fodrin) demonstrated evidence for calpain (EC 3.4.22.17) activation in the cerebellum, but not in the cerebral cortex of L-CPA-treated rats at 36 and 48 hr after L-CPA dosing. In contrast, there was no evidence for oxidative damage to cerebellar proteins or lipids in L-CPA-treated rat brains compared to controls. We also could not find evidence for DNA damage using the TUNEL method for the detection of single- and/or double-strand breakagein situin L-CPA-treated brains. We examined whether a number of reported antioxidants may be effective against L-CPA-induced neurotoxicity. The aminosteroids U74389G and U83836E, the free radical scavengers 3-methyl-1-phenylpyrazolin-5-one andN-tert-butylphenylnitrone, and the iron chelatorN-ethoxy-2-ethyl-3-hydroxypyridin-4-one were all ineffective in attenuating L-CPA neurotoxicity. We suggest that L-CPA-induced cerebellar necrosis is the result of calpain activation which results in the degradation of cytoskeletal proteins and other proteins necessary for cellular biochemistry. We could find no evidence of oxidative damage to cerebellar proteins, lipids, or DNA as a result of excess amounts of free radicals, and selective antioxidants were unable to provide neuroprotection against L-CPA neurotoxicity, suggesting that oxidative stress does not play a role in the granule cell necrosis.

Involvement of free radical mechanism in the toxic effects of alcohol: implications for fetal alcohol syndrome.

The role of free-radicals in alcohol-induced organ damage is still a matter of debate, in spite of decades of research. Moreover, during the last few years, great advances have been made in our understanding of the mechanisms of ethanol-induced enhancement of oxidative damage in liver and certain extrahepatic tissues. These advances have led to promising therapeutic approaches for the prevention of ethanol-induced oxidative stress. The present review focuses on the ethanol-induced production of pro-oxidant reactive species in different organs, an on the factors involved in ethanol metabolism that contribute to the generation of excess amounts of free radicals. Finally, the possible contribution of free radical generation to alcohol-induced fetal effects (fetal alcohol syndrome) are also discussed.KeywordsLipid PeroxidationAlcoholic Liver DiseaseFree Radical GenerationChronic EthanolFetal Alcohol SyndromeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Antagonists of the NMDA receptor and allopurinol protect the olfactory cortex but not the striatum after intra-cerebral injection of kainic acid

Overstimulation of the NMDA receptor, as well as generation of excessive amounts of free radicals, has been implicated in excitotoxic brain injuries. We report here that two antagonists of the NMDA receptor and an inhibitor of the free radical-generating enzyme, xanthine oxidase, protect the olfactory cortex but not the striatum after intrastriatal injection of kainic acid. Our results suggest the existence of a precise link between excitotoxic activation of the NMDA receptor and neuropathology related to excessive amounts of free radicals. The focal point of this link may be the entry of Ca 2+ through the NMDA receptor and the consequent activation of proteases and free radical-generating systems.