Inhibition of H2O2 generation in rat liver mitochondria by radical quenchers and phenolic compounds

Isoproterenol-induced cardiac ischemia and fibrosis: Plant-based approaches for intervention

Heart is the most active and incumbent organ of the body, which maintains blood flow, but due to various pathological reasons, several acute and chronic cardiac complications arise out of which myocardial infarction is one of the teething problems. Isoproterenol (ISP)-induced myocardial ischemia is a classical model to screen the cardioprotective effects of various pharmacological interventions. Phytochemicals present a novel option for treating various human maladies including those of the heart. A large number of plant products and their active ingredients have been screened for efficacy in ameliorating ISP-induced myocardial ischemia including coriander, curcumin, Momordica, quercetin, and Withania somnifera. These phytochemicals constituents may play key role in preventing disease and help in cardiac remodeling. Reactive oxygen species scavenging, antiinflammatory, and modulation of various molecular pathways such as Nrf2, NFкB, p-21 activated kinase 1 (PAK1), and p-smad2/3 signaling modulation have been implicated behind the claimed protection. In this review, we have provided a focused overview on the utility of ISP-induced cardiotoxicity, myocardial ischemia, and cardiac fibrosis for preclinical research. In addition, we have also surveyed molecular mechanism of various plant-based interventions screened for cardioprotective effect in ISP-induced cardiotoxicity, and their probable mechanistic profile is summarized.

Some radical queries

A little over 500 years ago, Vasco da Gama arrived on the west coast of India after the first direct sea voyage from Portugal with the intention of developing trade in spices, particularly in black pepper. Portugese took the merchandise, and much more; they ended up colonizing Goa. In 1999 delegates from all over the world came to this fabulous Goa for a symposium on antioxidants, some of which are natural products found in spices. Some views and queries on the interaction of antioxidants and radicals are presented.

Quinone mediated electron transport system in the filarial parasite Setaria digitata

Setaria digitata, a cattle filarial parasite, is known to have peculiarities such as hydrogen peroxide (H2O2) production, cyanide insensitivity, absence of cytochromes and presence of quinones. Estimation of mitochondrial H2O2 with different substrates and inhibitors showed that salicylhydroxamic acid (SHAM), the alternative oxidase inhibitor, inhibited the H2O2 production maximally. Based on the inhibitory studies with rotenone, antimycin A, o-hydroxydiphenyl, SHAM and 2 thenoyltrifluoroacetone, a mechanism for the electron transport is proposed. Quinone Q8 seems to have a central role, hence inhibitors at the level of quinones might prove to be effective in designing drugs for filariasis.

Decrease of oxidative activities in brown adipose tissue mitochondria of cold acclimated rats on short term exposure to heat stress

Exposure of rats to the cold (4-5 degrees C) caused large (2-3-fold) increases in the mass of interscapular brown adipose tissue (BAT), its mitochondrial content and the basal metabolic rate of the animals. The rate of substrate oxidation by BAT mitochondria also increased about 3-fold. When cold-acclimated animals were exposed to heat (37 degrees C), the BMR decreased by half in 3 h, the earliest time interval tested. Mitochondrial substrate oxidation, as well as substrate-dependent H2O2 generation, showed a proportionate decrease in rates. In these mitochondria, activities of cytochrome c reductases, but not dehydrogenases with NADH, alpha-glycerophosphate and succinate as substrates, also showed a significant decrease. The concentration of cytochromes aa3 and b, but not cytochrome c, also decreased in BAT mitochondria from 12-h heat-exposed animals, while the change in concentration of cytochrome b alone was found as early as 3 h of heat exposure. These results identify the change in cytochromes as a mechanism of regulation of oxidative activities in BAT mitochondria under conditions of acute heat stress.

The scopoletin assay for hydrogen peroxide. A review and a better method

Scopoletin, 7-hydroxy-6-methoxy-2H-1-benzopyran-2-one, a naturally occurring component in cotton leaf and citrus peel is a fluorescent substrate for peroxidase which has been used by many investigators for the determination of hydrogen peroxide concentration. The technical details of these investigations are application-specific and rather critical, making it difficult to apply the scopoletin assay to alternative systems without extensive modification. Although such factors as interfering substances and optimum conditions have been discussed in many publications, these discussions tend to be application-specific. The present paper attempts to provide a technical review of scopoletin applications, add a few new experimental observations, and discuss general parameters which must be carefully controlled for reliable results.

Oxidative activities in mitochondria-like particles from Setaria digitata, a filarial parasite

The oxidative metabolic potential of Setaria digitata, a filarial parasite found in the intraperitoneal cavity of cattle, was investigated. These worms showed active wriggling movements which were not affected by respiratory poisons such as cyanide, rotenone and malonate. They also possessed cyanide-insensitive and glucose-independent oxygen consumption pathways. By differential centrifugation of sucrose homogenates, a fraction containing mitochondria-like particles was obtained in which the activity of the marker enzyme, succinate dehydrogenase, was recovered. This fraction catalysed succinate- and NADH-dependent reduction of both cytochrome c and dyes. Oxygen uptake found with succinate, NADH and ascorbate as substrates was not sensitive to cyanide. Cytochromes could not be detected in either this fraction or homogenates of the worms. H2O2 generation with a number of substrates and lipid peroxidation by measuring malondialdehyde formed as well as by accompanying oxygen uptake were demonstrated in the mitochondria-like particles. A lipid quinone, possibly with a short side chain and related to ubiquinone, was detected in the worms. The results suggested the existence of two cyanide-insensitive oxygen-consuming reactions in Setaria: one respiratory substrate-independent lipid peroxidation, and a second substrate-dependent reaction that requires an auto-oxidizable quinone but not a cytochrome system.

Generation of hydrogen peroxide by brown adipose tissue mitochondria

This is the first report on the generation of H2O2 by brown adipose tissue mitochondria. Flavin dehydrogenase-linked substrates like succinate, glycerol-1-phosphate, and fatty acyl CoA were good substrates for the reaction, while NAD+-linked substrates were less effective. In cold-acclimated animals the activity showed a substantial increase (2.5-fold). The Km and Vmax of the reaction were considerably lower than those of the respective dehydrogenase. Metal ions, particularly Cu2+ and Fe2+ were potent inhibitors of the reaction. Nucleoside diphosphates, which were inhibitors by themselves, potentiated the inhibitory action of Fe2+ ions. In most of the properties, the H2O2 generator of brown adipose tissue mitochondria resembled that of liver mitochondria.

Generation of H2O2 in brain mitochondria

Generation of H2O2 by rat brain mitochondria using succinate and glycerol-1-phosphate as substrates has been demonstrated. Earlier workers were unable to detect this activity in sucrose-Tris buffer. We found that this was due to a lag in the expression of activity in sucrose medium. Using phosphate buffer (50 mM), good rates are now obtained. Generation of H2O2 by rat brain mitochondria required the presence of antimycin A and was dependent on the substrates succinate and glycerol-1-phosphate. Low rates were obtained with NAD+-linked substrates and none with choline, glutamate, and NADH. The Km and Vmax values for H2O2 generation were considerably lower than the corresponding values for the respective dehydrogenase activity, measured by dye reduction. Oxygen-radical scavengers inhibited H2O2 generation, suggesting oxygen radical involvement. Depletion of ubiquinone from mitochondria resulted in loss of H2O2 generation. Reconstitution of such depleted particles with ubiquinone restored the capacity to generate H2O2 in a concentration-dependent manner. Levels of H2O2 production were found to be maximal in cerebellum. Brain mitochondria from rabbit, hamster, mouse, and guinea pig also have the capacity to generate H2O2 on oxidation of glycerol-1-phosphate.

Antioxidant action of natural health products and Chinese herbs

The scavenging effects of reactive oxygen species (ROS) by two natural health products, antioxidant analogs (AOA), and green magma (GM), and 16 medical Chinese herbs were investigated in two in vitro ROS-generating systems, activated neutrophils and xanthine-xanthine oxidase. Native, unheated AOA and GM products significantly reduced ROS levels, while unheated Chinese herbs had a negligible effect on ROS levels. In contrast, heat-extracted Chinese herbs and AOA markedly, and GM mildly, suppressed the levels of ROS in both systems. The ROS scavenging activity of these native, unheated products was unaffected by dialysis, but that of heated products was markedly diminished by dialysis. Further, the incubation of these products with gastric juice obtained by a gastric tube from healthy volunteers revealed results comparable to those induced by heat treatment with or without dialysis. Although the antioxidant activity of these natural products appears to be partly due to enzymes such as superoxide dismutase (SOD), the predominant factor seems to be low-molecular-weight ROS scavengers that are liberated or activated by gastric juice digestion as observed after heat treatment.

Heat exposure and hypothyroid conditions decrease hydrogen peroxide generation in liver mitochondria

Exposure of rats to heat (39 +/- 1 degree C) decreased H2O2 generation in mitochondria of the liver, but not of the kidney or the heart. The effect was obtained with three substrates, succinate, glycerol 1-phosphate and choline, with a decrease to 50% in the first 2-3 days of exposure, and a further decrease on longer exposure. The dehydrogenase activity with only glycerol 1-phosphate decreased, which is indicative of the hypothyroid condition, whereas choline dehydrogenase activity remained unchanged and that of succinate dehydrogenase decreased on long exposure. The serum concentration of thyroxine decreased in heat-exposed rats. Thyroxine treatment of rats increased H2O2 generation. Hypothyroid conditions obtained by treatment with propylthiouracil or thyroidectomy caused a decrease in H2O2 generation and changes in dehydrogenase activities similar to those with heat exposure. Treatment of heat-exposed or thyroidectomized rats with thyroxine stimulated H2O2 generation by a mechanism apparently involving fresh protein synthesis. The results indicate that H2O2 generation in mitochondria of heat-exposed animals is determined by thyroid status.

Generation of hydrogen peroxide on oxidation of NADH by hepatic plasma membranes

The oxidation of NADH by mouse liver plasma membranes was shown to be accompanied by the formation of H2O2. The rate of H2O2 formation was less than one-tenth the rate of oxygen uptake and much slower than the rate of reduction of artificial electron acceptors. The optimum pH for this reaction was 7.0 and the Km value for NADH was found to be 3 X 10(-6) M. The H2O2-generating system of plasma membranes was inhibited by quinacrine and azide, thus distinguishing it from similar activities in endoplasmic reticulum and mitochondria. Both NADH and NADPH served as substrates for plasma membrane H2O2 generation. Superoxide dismutase and adriamycin inhibited the reaction. Vanadate, known to stimulate the oxidation of NADH by plasma membranes, did not increase the formation of H2O2. In view of the growing evidence that H2O2 can be involved in metabolic control, the formation of H2O2 by a plasma membrane NAD(P)H oxidase system may be pertinent to control sites at the plasma membrane.