Production Of Hydroxyl Free Radicals Research Articles

Yielding hydroxyl radicals in the Fenton-like reaction induced by manganese (II) oxidation determines Cd mobilization upon soil aeration in paddy soil systems

As a redox-sensitive element, manganese (Mn) plays a critical role in Cd mobilization, especially in paddy soil. In an anoxic environment, the precipitation of Mn(II)-hydroxides specifically favors Cd retention, while draining the paddy fields results in substantial remobilization of Cd. However, how the change in Mn redox states during the periodical transit of anoxic to oxic systems affects Cd mobility remains unclear. In this study, we demonstrate that the radical effect generated during the oxidation of Mn(II)-hydroxides exerts a significant effect on the oxidative dissolution of Cd during the aeration of paddy soils. The extractable Cd concentration decreased rapidly during the reduction phases but increased upon oxidation, while Cd availability produced the opposite effect with soil pe + pH and the extractable Mn concentration. Inhibiting the oxidation of Mn(II)-containing phases by microbes suppressed the production of hydroxyl free radicals (•OH) and Cd mobilization in the drainage phase. Analysis of X-ray absorption spectroscopy and sequential extraction demonstrated that the transformation from the Mn phase of Mn(II) to Mn(III/IV) determines Cd solubility. Altogether, the oxidization of Mn(II)-hydroxides was associated with the generation of significant amounts of •OH. The dissolution of Mn(II)- incorporating phases lead to a net release of Cd into soils during soil aeration.

Effect of Quercetin on Dexamethasone-Induced C2C12 Skeletal Muscle Cell Injury.

Glucocorticoids are widely used anti-inflammatory drugs in clinical settings. However, they can induce skeletal muscle atrophy by reducing fiber cross-sectional area and myofibrillar protein content. Studies have proven that antioxidants can improve glucocorticoid-induced skeletal muscle atrophy. Quercetin is a potent antioxidant flavonoid widely distributed in fruits and vegetables and has shown protective effects against dexamethasone-induced skeletal muscle atrophy. In this study, we demonstrated that dexamethasone significantly inhibited cell growth and induced cell apoptosis by stimulating hydroxyl free radical production in C2C12 skeletal muscle cells. Our results evidenced that quercetin increased C2C12 skeletal cell viability and exerted antiapoptotic effects on dexamethasone-treated C2C12 cells by regulating mitochondrial membrane potential (ΔΨm) and reducing oxidative species. Quercetin can protect against dexamethasone-induced muscle atrophy by regulating the Bax/Bcl-2 ratio at the protein level and abnormal ΔΨm, which leads to the suppression of apoptosis.

Intensifying ozonation treatment of municipal secondary effluent using a combination of microbubbles and ultraviolet irradiation.

Ozonation treatment of municipal secondary effluent is complicated by the low solubility of ozone and inefficient production of hydroxyl free radicals from ozone decomposition. To resolve these problems, this study investigated methods for intensifying ozonation treatment, using a combination of microbubbles and ultraviolet (UV) irradiation (UV/MBO). The high efficiency of the method was illustrated by treating river water containing refractory components derived from secondary effluent in a wastewater treatment plant. The results showed that the ozone mass transfer coefficient in a microbubble system was an order of magnitude compared with a conventional macrobubble system at the initial stage. The amount of ·OH generated during the treatment was quantified using a fluorescent probe analysis. The amount of ·OH in the UV/MBO system was almost 2-6 times more than the amount found with conventional ozonation using macrobubbles (CO), CO with UV irradiation (UV/CO), and microbubble ozonation (MBO) units. The UV/MBO system achieved chemical oxygen demand (COD), UV254, and UV400 removal performance rates of up to 37.50%, 81.15%, and 94.74% respectively. These levels were 2-36% higher than those in other systems. The coupling UV/MBO treatment significantly reduced all five categories of substances according to EEM spectra and fluorescence regional integration. The distribution of fractions with different molecular weights (MW) was altered and the UV254 of MW (< 500Da) increased by 15.8%. The biodegradability of the water was significantly improved, as indicated by the TOC/UV254. This is ascribed to the enhanced degradation of refractory organics in the water. The combination of the UV/microbubble technique with ozonation could provide an efficient approach for advanced wastewater treatment. Graphical abstract.

Removal of Refractory Organic Compounds from Wastewater by Various Advanced Oxidation Process - A Review

Per capita average annual freshwater availability is gradually reduced due to increasing population, urbanization and affluent lifestyles. Hence, management of wastewater is of great concern. The wastewater from different industries can be treated by various conventional treatment methods but these conventional treatment technologies seem to be ineffective for the complete removal of pollutants especially refractory organic compounds that are not readily biodegradable in nature. Detergents, detergent additives, sequestering agents like EDTA, Pesticides, Polycyclic aromatic hydrocarbons, etc. are some of the recalcitrant organic compounds found in the wastewater. One of the treatment technologies for the removal of recalcitrant organic compounds is Advanced Oxidation Process (AOP). The production of hydroxyl free radical is the main mechanism for the AOP. AOP is a promising technology for the treatment of refractory organic compounds due to its low oxidation selectivity and high reactivity of the radical. Hydrogen peroxide (H2O2), Ozonation, Ultra-violet (UV) radiation, H2O2/UV process and Fenton’s reaction are extensively used for the removal of refractory organic compounds thus reducing Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), phenolic compounds, dyes etc. to great extent. From the studies, we found that Fenton’s reagents appear to be most economically practical AOP systems for almost all industries with respect to high pollutant removal efficiency and it is also economical. From the energy point of view, the ozone based process proves to be more efficient but it is costlier than the Fenton’s process.

Radio-Fluorogenic Gel Dosimetry with Coumarin.

Gel dosimeters are attractive detectors for radiation therapy, with properties similar to biological tissue and the potential to visualize volumetric dose distributions. Radio-fluorogenesis is the yield of fluorescent chemical products in response to energy deposition from ionizing radiation. This report shares the development of a novel radio-fluorogenic gel (RFG) dosimeter, gelatin infused with coumarin-3-carboxlyic acid (C3CA), for the quantification of imparted energy. Aqueous solutions exposed to ionizing radiation result in the production of hydroxyl free radicals through water radiolysis. Interactions between hydroxyl free radicals and coumarin-3-carboxylic acid produce a fluorescent product. 7-hydroxy-coumarin-3-carboxylic acid has a blue (445 nm) emission following ultra-violet (UV) to near UV (365–405 nm) excitation. Effects of C3CA concentration and pH buffers were investigated. The response of the RFG was explored with respect to strength, type, and exposure rate of high-energy radiation. Results show a linear dose response relationship independent of energy and type, with a dose-rate dependency. This report demonstrates increased photo-yield with high pH and the utility of gelatin-RFG for phantom studies of radiation dosimetry.

Chemical Colitis From a Hydrogen Peroxide Enema

Constipation is one of the most common complaints among patients. Many resort to “natural” therapies described by complimentary and alternative medicine. Hydrogen peroxide enemas, ranging from 3-10% solutions, are one of the promoted remedies. We present a case of chemical colitis after using a hydrogen peroxide enema. A 26-year-old female with chronic constipation, presented with bright red blood per rectum for 2 days. It started immediately after using a 35% hydrogen peroxide enema for constipation. She had used herbal enemas previously, and this was the first time she had used hydrogen peroxide. She had large-volume rectal bleeding with fresh blood that quickly slowed down. She had abdominal pain with vomiting, decreased appetite, and tenesmus. Initial assessment revealed an afebrile, normotensive young woman, with diffuse abdominal tenderness most severe in the left lower quadrant, without rebound tenderness or rigidity. Laboratory evaluation was significant for leukocytosis (17.09 x 103/μL) and slightly elevated C-reactive protein (3.0 mg/dL). Her hemoglobin was normal on presentation 12.8 g/dL. Fecal calprotectin was greater than 1250 μg/g with fecal leukocytes present. Her lactic acid was within normal limits. Computed tomography of the abdomen and pelvis revealed diffuse left transverse and left colonic thickening and submucosal edema up to the mid-transverse colon, suggestive of colitis (Image 1). She was admitted and was managed conservatively with intravenous hydration, electrolytes correction, serial abdominal examinations, and hemoglobin checks. Colonoscopy was deferred due to risk of perforation. Rectal bleeding stopped after 3 days; she clinically improved with supportive care only. The patient was discharged and advised to avoid chemical enemas in the future. At a 3-month follow up, she denied any episodes of rectal bleeding. There are a few reported cases of chemical-induced colitis in patients experimenting with hydrogen peroxide enemas to self-treat chronic constipation. Hydrogen peroxide enemas are an increasing “home remedy” that are made popular on alternative medicine websites. The production of hydroxyl free radicals from hydrogen peroxide causes cell death. Macroscopically, it leads to corrosive injury of the colonic mucosa. With increasing availability of information on the Internet, it is critical to caution and inform patients of potentially dangerous therapies that are not medically approved.Figure: Diffuse submucosal edema up to mid-transverse colon, suggestive of colitis.

M\xf6ssbauer spectroscopy and the understanding of the role of iron in neurodegeneration

The possible role of iron in neurodegeneration may be related to the oxidative stress, triggered by Fenton reaction. In this reaction hydroxyl free radical production is generated by divalent iron. Motor symptoms of Parkinson’s disease depend on the destruction of substantia nigra (SN). As the substantive questions were: 1/ what is the concentration of iron in the samples, 2/ what is the proportion of divalent vs. trivalent iron in the samples, and 3/ what is the iron-binding compound, it seemed appropriate to use Mössbauer spectroscopy to answer those questions. We found no difference in the concentration of total iron between PD and control, with the ratio of iron in PD vs. control being 1.00 ± 0.13. The divalent iron could not exceed 5% of the total iron. The main iron-binding compound in SN, both in PD and control is ferritin. Our further studies of ferritin in parkinsonian SN demonstrated a decrease, compared to control, of L-ferritin involved in the storage of iron within ferritin. This could allow an efflux of iron from the ferritin shell and an increase of non-ferritin iron in PD SN, which was confirmed by us. Mössbauer studies in Alzheimer showed slightly higher concentration of iron in hippocampal cortex with significantly higher concentrations of L and H ferritins compared to control. In atypical parkinsonism, progressive supranuclear palsy, higher concentration of iron was found in globus pallidus and SN compared to control. Mössbauer spectroscopy may play crucial role in further studies of human neurodegeneration.

Tyrosine isomers and hormonal signaling: A possible role for the hydroxyl free radical in insulin resistance.

Oxidative stress processes play a major role in the development of the complications associated with diabetes and other diseases via non-enzymatic glycation, the hexosamine pathway, the polyol pathway and diacylglycerol-protein kinase C. Oxidative stress may lead to the production of hydroxyl free radicals, which can attack macromolecules, such as lipids, nucleic acids or amino acids. Phenylalanine (Phe) can be enzymatically converted to the physiological para-tyrosine (p-Tyr); however, a hydroxyl free radical attack on Phe may yield meta- and ortho-tyrosine (m- and o-Tyr, respectively) in addition to p-Tyr. Hence, m- and o-Tyr may be regarded as markers of hydroxyl free radical-induced damage. Their accumulation has been described; e.g., this accumulation has been found in the urine of patients with diabetes mellitus (DM) and/or chronic kidney disease, in cataract lenses, in vessel walls, in irradiated food and in amniotic fluid, and it may serve as an indicator of oxidative stress. The use of resveratrol to treat patients with type 2 DM led to a decrease in the urinary excretion of o-Tyr and concomitantly led to an improvement in insulin signaling and insulin sensitivity. Literature data also suggest that m- and o-Tyr may interfere with intracellular signaling. Our group has shown that erythropoietin (EPO) has insulin-like metabolic effects on fat cells in addition to its ability to promote the proliferation of erythroid precursor cells. We have shown that the supplementation of cell culture medium with m- and o-Tyr inhibits erythroblast cell proliferation, which could be ameliorated by p-Tyr. Additionally, in vivo, the o-Tyr/p-Tyr ratio is higher in patients with renal replacement therapy and a greater need for EPO. However, the o-Tyr/p-Tyr ratio was an independent determinant of EPO-resistance indices in our human study. The o-Tyr content of blood vessel walls inversely correlates with insulin- and acetylcholine-induced vasodilation, which could be further impaired by artificial oxidative stress and improved by the use of antioxidants. In rats that receive o-Tyr supplements, decreased vasorelaxation is detected in response to insulin. Additionally, o-Tyr supplementation led to the incorporation of the unnatural amino acid into cellular proteins and caused a decrease in the insulin-induced phosphorylation of endothelial nitric oxide synthase. Our data suggest that m- and o-Tyr may not only be markers of oxidative stress; instead, they may also be incorporated into cellular proteins, leading to resistance to insulin, EPO and acetylcholine.

Silica Decorated TiO2 for Virus Inactivation in Drinking Water – Simple Synthesis Method and Mechanisms of Enhanced Inactivation Kinetics

A new method of modifying TiO2 photocatalysts with SiO2 is developed in which SiO2 nanoparticles are simply mixed with TiO2 in water under ambient conditions. This method does not require the use of toxic solvents or significant energy input. Although the SiO2 modification slightly reduces hydroxyl free radical production, the composite SiO2-TiO2 nanomaterials have markedly higher photocatalytic inactivation rates for a common surrogate virus, bacteriophage MS2 (up to 270% compared to the unmodified TiO2), due to the greatly improved adsorptive density and dark inactivation of MS2. The Langmuir isotherm describes the adsorption data well and shows that the TiO2 modified with 5% SiO2 has a maximum adsorption density qmax 37 times that of the unmodified TiO2. The Langmuir-Hinshelwood model fits the photocatalytic inactivation kinetic data well. The SiO2-TiO2 material produces a greater maximum initial inactivation rate yet a lower intrinsic surface reaction rate constant, consistent with the reduced hydroxyl radical production and enhanced adsorption. These results suggest that modifying photocatalyst surface to increase contaminant adsorption is an important strategy to improve photocatalytic reaction efficiency. Simple and cheap synthesis methods such as that used in this study bring photocatalysis closer to being a viable water treatment option.

Coating rice seeds with reduced iron powder induces the production of hydroxyl free radicals, leading to antimicrobial activity

Coating rice seeds with reduced iron powder induces the production of hydroxyl free radicals, leading to antimicrobial activity

Hydroxyl free radical production during torsional phacoemulsification

To quantitate free radical generation during phacoemulsification using an ultrasonic phacoemulsification device that includes a torsional mode and evaluate tip designs specific to the torsional mode. Chemistry and Biochemistry Department, Utah State University, Logan, Utah, USA. Experimental study. Experiments were performed using the Infiniti Vision System and OZil handpiece. Hydroxyl radical concentrations in the aspirated irrigation solution during torsional phacoemulsification were quantitated as nanomolar malondialdehyde (nM MDA) and determined spectrophotometrically using the deoxyribose assay. The mean free radical production during phacoemulsification with torsional modality at 100% amplitude was 30.1 nM MDA ± 5.1 (SD) using a 0.9 mm 45-degree Kelman tapered ABS tip. With other tip designs intended for use with the torsional modality, free radical production was further reduced when fitted with the 0.9 mm 45-degree Kelman mini-flared ABS tip (13.2 ± 5.6 nM MDA) or the 0.9 mm 45-degree OZil-12 mini-flared ABS tip (14.3 ± 6.7 nM MDA). Although the measurements resulting from the use of the latter 2 tips were not statistically significantly different (P ≈ .25), they were different from those of the tapered tip (P<.0001). The MDA concentration in the aspirated irrigation solution using the torsional modality was approximately one half that reported for the handpiece's longitudinal modality in a previous study using the same bent-tip design (Kelman tapered, P<.0001). The level of MDA was further reduced approximately one half with torsional-specific tips.

Virus inactivation by silver doped titanium dioxide nanoparticles for drinking water treatment

Photocatalytic inactivation of viruses and other microorganisms is a promising technology that has been increasingly utilized in recent years. In this study, photocatalytic silver doped titanium dioxide nanoparticles (nAg/TiO2) were investigated for their capability of inactivating Bacteriophage MS2 in aqueous media. Nano-sized Ag deposits were formed on two commercial TiO2 nanopowders using a photochemical reduction method. The MS2 inactivation kinetics of nAg/TiO2 was compared to the base TiO2 material and silver ions leached from the catalyst. The inactivation rate of MS2 was enhanced by more than 5 fold depending on the base TiO2 material, and the inactivation efficiency increased with increasing silver content. The increased production of hydroxyl free radicals was found to be responsible for the enhanced viral inactivation.

Fenton Activity and Cytotoxicity Studies of Iron-Loaded Carbon Particles

The chemical and biological properties of iron-loaded manufactured carbon nanoparticles (Flammruss 101) were contrasted with those of an iron-loaded synthetic carbon particle. X-ray photoelectron spectroscopy was used to characterize the iron on the carbon particles. Production of hydroxyl free radicals via the Fenton reaction was monitored by electron paramagnetic resonance spectroscopy. The iron-loaded synthetic carbon particles produced a positive Fenton response, whereas the iron-loaded manufactured carbon particles did not. The source of the Fenton activity of the synthetic carbon particles is proposed to be a soluble iron compound that was formed during the synthesis of the particle. A likely candidate for the soluble iron species is Fe2F5, which was synthesized and its properties were examined. Higher toxicity of Fe2F5 toward murine macrophages compared with other simple iron salts was attributed to soluble iron that was stabilized by the fluoride ligand. The cytotoxicity of manufactured carbon particles toward murine macrophages decreased or remained unaltered upon impregnation with iron compounds.

Escherichia coli FtnA acts as an iron buffer for re-assembly of iron–sulfur clusters in response to hydrogen peroxide stress

Iron-sulfur clusters are one of the most ubiquitous redox centers in biology. Ironically, iron-sulfur clusters are highly sensitive to reactive oxygen species. Disruption of iron-sulfur clusters will not only change the activity of proteins that host iron-sulfur clusters, the iron released from the disrupted iron-sulfur clusters will further promote the production of deleterious hydroxyl free radicals via the Fenton reaction. Here, we report that ferritin A (FtnA), a major iron-storage protein in Escherichia coli, is able to scavenge the iron released from the disrupted iron-sulfur clusters and alleviates the production of hydroxyl free radicals. Furthermore, we find that the iron stored in FtnA can be retrieved by an iron chaperon IscA for the re-assembly of the iron-sulfur cluster in a proposed scaffold IscU in the presence of the thioredoxin reductase system which emulates normal intracellular redox potential. The results suggest that E. coli FtnA may act as an iron buffer to sequester the iron released from the disrupted iron-sulfur clusters under oxidative stress conditions and to facilitate the re-assembly of the disrupted iron-sulfur clusters under normal physiological conditions.

Acceleration of Maturity of Young Sorghum (Kaoliang) Spirits by Linking Nanogold Photocatalyzed Process to Conventional Biological Aging—a Kinetic Approach

With an aim to effectively shorten the ageing period and reduce process cost, a nanogold photocatalyzed process was developed. This process successfully accelerated maturity of young sorghum spirit less than 120 min at ambient temperature. Process parameters relevant to process design were determined to be (1) the amount of acetic acid (≥1.53 g/100 ml); (2) an operation temperature ≤37°C; (3) a degree of mineralization ≤4.87%. Kinetic analysis indicated that to cautiously control dissolved oxygen (DO) to facilitate optimum production of hydroxyl free radical [-OH] could be a crucial step, while the kinetic equations elucidated to indicate production of ethyl acetate and acetic acid could be applicable to reactor scale-up. More importantly, this process provides several benefits including container-saving, space-saving, labor-saving, and no storage-loss due to evaporation; hence, a huge amount of cost reduction (20–24%) in a 4-year aging period could be attainable for each batch cycle.

Distinct Iron Binding Property of Two Putative Iron Donors for the Iron-Sulfur Cluster Assembly: IscA AND THE BACTERIAL FRATAXIN ORTHOLOG CyaY UNDER PHYSIOLOGICAL AND OXIDATIVE STRESS CONDITIONS

Frataxin, a small mitochondrial protein linked to the neurodegenerative disease Friedreich ataxia, has recently been proposed as an iron donor for the iron-sulfur cluster assembly. An analogous function has also been attributed to IscA, a key member of the iron-sulfur cluster assembly machinery found in bacteria, yeast, and humans. Here we have compared the iron binding property of IscA and the frataxin ortholog CyaY from Escherichia coli under physiological and oxidative stress conditions. In the presence of the thioredoxin reductase system, which emulates the intracellular redox potential, CyaY fails to bind any iron even at a 10-fold excess of iron in the incubation solution. Under the same physiologically relevant conditions, IscA efficiently recruits iron and transfers the iron for the iron-sulfur cluster assembly in a proposed scaffold IscU. In the presence of hydrogen peroxide, however, IscA completely loses its iron binding activity, whereas CyaY becomes a competent iron-binding protein and attenuates the iron-mediated production of hydroxyl free radicals. Hydrogen peroxide appears to oxidize the iron binding thiol groups in IscA, thus blocking the iron binding in the protein. Once the oxidized thiol groups in IscA are re-reduced with the thioredoxin reductase system, the iron binding activity of IscA is fully restored. On the other hand, hydrogen peroxide has no effect on the iron binding carboxyl groups in CyaY, allowing the protein to bind iron under oxidative stress conditions. The results suggest that IscA is capable of recruiting intracellular iron for the iron-sulfur cluster assembly under normal physiological conditions, whereas CyaY may serve as an iron chaperon to sequester redox active free iron and alleviate cellular oxidative damage under oxidative stress conditions.

Master equation simulations of competing unimolecular and bimolecular reactions: application to OH production in the reaction of acetyl radical with O2

Master equation calculations were carried out to simulate the production of hydroxyl free radicals initiated by the reaction of acetyl free radicals (CH3(C=O).) with molecular oxygen. In particular, the competition between the unimolecular reactions and bimolecular reactions of vibrationally excited intermediates was modeled by using a single master equation. The vibrationally excited intermediates (isomers of acetylperoxyl radicals) result from the initial reaction of acetyl free radical with O2. The bimolecular reactions were modeled using a novel pseudo-first-order microcanonical rate constant approach. Stationary points on the multi-well, multi-channel potential energy surface (PES) were calculated at the DFT(B3LYP)/6-311G(2df,p) level of theory. Some additional calculations were carried out at the CASPT2(7,5)/6-31G(d) level of theory to investigate barrierless reactions and other features of the PES. The master equation simulations are in excellent agreement with the experimental OH yields measured in N2 or He buffer gas near 300 K, but they do not explain a recent report that the OH yields are independent of pressure in nearly pure O2 buffer gas.

Flumazenil Mimics whereas Midazolam Abolishes Ischemic Preconditioning in a Rabbit Heart Model of Ischemia–Reperfusion

The goal of the current study was to assess the effects of flumazenil, a benzodiazepine receptor antagonist, in limiting infarct size and in reducing hydroxyl free radical production. After intravenous salicylate (100 mg/kg) administration, rabbits were subjected to 40 min of regional myocardial ischemia and 2 h of reperfusion. In one group, flumazenil (0.05 mg/kg) and, in another, midazolam (0.05 mg/kg) was administered 15 min before 40 min of ischemia. Ischemic preconditioning (IP) was elicited by 5 min of ischemia followed by 10 min of reperfusion (before the 40-min ischemia period). In two other groups, midazolam was added to flumazenil and IP. Infarct size was determined using triphenyl tetrazolium chloride staining. The authors quantified the hydroxyl-mediated conversion of salicylate to its 2,3- and 2,5-dihydroxybenzoate derivatives during reperfusion by high-performance liquid chromatography coupled with electrochemical detection. Results are expressed as mean +/- SEM. Flumazenil, like IP, significantly decreased infarct size (23 +/- 4 and 22 +/- 5%, respectively, vs. 57 +/- 6% in control group; P < 0.01). Midazolam inhibited the effects of flumazenil and IP. Flumazenil and IP significantly limited the increase in the normalized concentrations of 2,3- and 2,5-dihydroxybenzoic acids. With midazolam, however, the increase was comparable to that of the control group. 5-Hydroxydecanoate, a selective mitochondrial adenosine triphosphate-sensitive K channel blocker, given with flumazenil, abolished the protection obtained with the latter. Flumazenil mimics preconditioning to decrease infarct size and hydroxyl radical production during reperfusion. Midazolam, however, abolishes these effects. Blockade of benzodiazepine receptors is upstream to the mitochondrial adenosine triphosphate-sensitive K channels in the preconditioning cascade.

Ischemic preconditioning decreases the reperfusion-related formation of hydroxyl radicals in a rabbit model of regional myocardial ischemia and reperfusion: The role of KATP channels

The objective of this study was to assess the effects of ischemic preconditioning (IP) on hydroxyl free radical production in an in vivo rabbit model of regional ischemia and reperfusion. Another goal was to determine whether KATP channels are involved in these effects.The hearts of anesthetized and mechanically ventilated New Zealand White rabbits were exposed through a left thoracotomy. After IV salicylate (100 mg/kg) administration, all animals underwent a 30-min stabilization period followed by 40 min of regional ischemia and 2 h of reperfusion. In the IP group, IP was elicited by 5 min of ischemia followed by 10 min of reperfusion (prior to the 40-min ischemia period). Glibenclamide, a KATP channel blocker, was administered prior to the preconditioning stimulus. Infarct size was measured by 2,3,5-triphenyl tetrazolium chloride (TTC) staining. We quantified the hydroxyl-mediated conversion of salicylate to its 2,3 and 2,5-dihydroxybenzoate derivatives during reperfusion by high performance liquid chromatography coupled with electro-chemical detection.IP was evidenced by reduced infarct size compared to control animals: 22% vs. 58%, respectively. Glibenclamide inhibited this cardioprotective effect and infarct size was 53%. IP limited the increase in 2,3 and 2,5-dihydroxybenzoic acid to 24.3 and 23.8% above baseline, respectively. Glibenclamide abrogated this effect and the increase in 2,3 and 2,5-dihydroxybenzoic acid was 94.3 and 85% above baseline levels, respectively, similar to the increase in the control group. We demonstrated that IP decreased the formation of hydroxyl radicals during reperfusion. The fact that glibenclamide inhibited this effect, indicates that KATP channels play a key role in this cardioprotective effect of IP.

Left Ventricular Dysfunction After Acute Intracranial Hypertension is Associated with Increased Hydroxyl Free Radical Production, Cardiac Ryanodine Hyperphosphorylation, and Troponin I Degradation

In addition to generating free radicals, stress-induced activation of the sympathetic nervous system results in hyperphosphorylation of the cardiac ryanodine receptor (RyR2)/calcium (Ca2+) release channel on the sarcoplasmic reticulum, causing leaky channels. These events may contribute to cytosolic Ca2+ overload and activation of Ca2+-dependent cytotoxic processes. Because myocardial dysfunction associated with intracranial hypertension is catecholamine mediated, we sought to determine in a rat model if hemodynamic changes are associated with an increase in oxidative stress, hyperphosphorylation of RyR2, and degradation of myofilament protein cardiac troponin I (TnI). In halothane-anesthetized rats treated with saline, dimethyl sulfoxide (DMSO), or the synthetic calpain inhibitor calpeptin (3,500 microg), a subdural balloon catheter was inflated to induce intracranial hypertension. Hearts were excised, and RyR2 phosphorylation status and TnI degradation was determined with Western blot analysis. In separate experiments, treated rats were challenged with increasing doses of dobutamine 30 minutes after subdural balloon inflation. Elevating the intracranial pressure resulted in an increase in plasma catecholamines, as well as in 3,4-dihydroxybenzoic acid (DHBA), an indirect marker of HO. radical production, and left ventricular dysfunction in rats treated with saline or DMSO. There was evidence of hyperphosphorylation of RyR2 and TnI degradation (27 kD immunoreactive band). Calpeptin treatment improved left ventricular function; however, this had no effect on the phosphorylation status of RyR2 or TnI degradation levels. In addition, the myocardial responsiveness to dobutamine was augmented in rats with depressed myocardial function. The present findings demonstrate that hemodynamic instability after intracranial hypertension is associated with oxidative stress and post-translational changes to RyR2 and TnI degradation. Despite this, the myocardial responsiveness to beta1 adrenergic stimulation is preserved in rats with depressed myocardial function.