The toxic effects of oxygen on brain metabolism and on tissue enzymes; tissue enzymes

Review of the Brain's Behaviour after Injury and Disease for Its Application in an Agent-Based Model (ABM)

The brain is the most complex organ in the human body and, as such, its study entails great challenges (methodological, theoretical, etc.). Nonetheless, there is a remarkable amount of studies about the consequences of pathological conditions on its development and functioning. This bibliographic review aims to cover mostly findings related to changes in the physical distribution of neurons and their connections-the connectome-both structural and functional, as well as their modelling approaches. It does not intend to offer an extensive description of all conditions affecting the brain; rather, it presents the most common ones. Thus, here, we highlight the need for accurate brain modelling that can subsequently be used to understand brain function and be applied to diagnose, track, and simulate treatments for the most prevalent pathologies affecting the brain.

670 nm light mitigates oxygen-induced degeneration in C57BL/6J mouse retina

Background

Irradiation with light wavelengths from the far red (FR) to the near infrared (NIR) spectrum (600 nm -1000 nm) has been shown to have beneficial effects in several disease models. In this study, we aim to examine whether 670 nm red light pretreatment can provide protection against hyperoxia-induced damage in the C57BL/6J mouse retina. Adult mice (90–110 days) were pretreated with 9 J/cm² of 670 nm light once daily for 5 consecutive days prior to being placed in hyperoxic environment (75% oxygen). Control groups were exposed to hyperoxia, but received no 670 nm light pretreatment. Retinas were collected after 0, 3, 7, 10 or 14 days of hyperoxia exposure (n = 12/group) and prepared either for histological analysis, or RNA extraction and quantitative polymerase chain reaction (qPCR). Photoreceptor damage and loss were quantified by counting photoreceptors undergoing cell death and measuring photoreceptor layer thickness. Localization of acrolein, and cytochrome c oxidase subunit Va (Cox Va) were identified through immunohistochemistry. Expression of heme oxygenase-1 (Hmox-1), complement component 3 (C3) and fibroblast growth factor 2 (Fgf-2) genes were quantified using qPCR.

Results

The hyperoxia-induced photoreceptor loss was accompanied by reduction of metabolic marker, Cox Va, and increased expression of oxidative stress indicator, acrolein and Hmox-1. Pretreatment with 670 nm red light reduced expression of markers of oxidative stress and C3, and slowed, but did not prevent, photoreceptor loss over the time course of hyperoxia exposure.

Conclusion

The damaging effects of hyperoxia on photoreceptors were ameliorated following pretreatment with 670 nm light in hyperoxic mouse retinas. These results suggest that pretreatment with 670 nm light may provide stability to photoreceptors in conditions of oxidative stress.

Effect of inhibitors on the activity of soluble succinic dehydrogenase and on the reconstitution of the succinic dehydrogenase-cytochrome system from its components

The succinic dehydrogenase-cytochrome system, which catalyzes the oxidation of suecinate to fumarate by molecular oxygen, was successfully reconstituted from soluble succinic dehydrogenase, soluble cytochrome c and a particulate heart-muscle preparation which is deprived of these components but contains cytochromes a 3 , a , c 1 and b and has a strong cytochrome oxidase activity. Although succinic dehydrogenase isolated in a soluble form by Singer and by Wang with their co-workers was identified by them as a flavoprotein compound containing one modified flavin adenine dinucleotide and 2 or 4 iron atoms, neither the function of the iron nor the structure and function of the flavin group have so far been satisfactorily elucidated. Soluble succinic dehydrogenase, unlike its endogenous form, is very unstable and catalyzes the oxidation of succinate by phenazine methosulphate or ferricyanide but not by cytochrome c or methylene blue. However, when soluble enzyme is re-incorporated within the particles of the heart-muscle preparation deprived of this enzyme, it becomes an integral part of the respiratory chain and re-acquires all the properties of its endogenous form, that is insolubility, stability and reactivity towards the cytochrome system and methylene blue. The succinic dehydrogenase-cytochrome system thus reconstituted, on addition of cytochrome c , actively catalyzes the oxidation of succinate by molecular oxygen. It shows normal oxidation and reduction of its cytochrome components and is susceptible to all inhibitors in the same way as is the succinic oxidase system of an untreated heart-muscle preparation. The comparative study of a soluble succinic dehydrogenase and a particulate succinic oxidase system revealed: (i) that pyrophosphate, like malonate and oxalacetate, acts as a competitive inhibitor of the succinic dehydrogenase itself; (ii) that narcotics have two sites of action: like antimycin they break the link between cytochromes b and c 1 and, unlike antimycin, they also inhibit, but to a lesser degree, the activity of succinic dehydrogenase; and (iii) that cyanide can react with three components of this system in three different ways: a rapid and perfectly reversible reaction with cytochrome oxidase, a slow and still reversible reaction with oxidized soluble cytochrome c and a slow, irreversible reaction with the succinic dehydrogenase itself. It was previously shown (Tsou 1951) that the incubation of heart-muscle preparation with cyanide irreversibly inhibited the oxidation of succinate via the cytochrome system or methylene blue. Although cyanide treatment of soluble succinic dehydrogenase does not inhibit its catalytic activity in the oxidation of succinate by phenazine methosulphate, it prevents the dehydrogenase from anchoring itself within the particles of the heart-muscle preparation deprived of this enzyme, and so the reconstitution of the particulate succinic oxidase system does not take place. As the cyanide effect of Tsou is slow, irreversible, sensitive to temperature, complete and can be prevented by reducing substances, such as succinate acting as a hydrogen donor, or sodium dithionite, but not by malonate or pyrophosphate, we postulated: (i) that this effect is due to an irreversible reduction by cyanide of a disulphide group of succinic dehydrogenase to one thiol and one thiocyanate group, and (ii) th at this disulphide group originates by a reversible oxidation of a dithiol group which is present in addition to, and differs in several respects from the dithiol group of Hopkins.

Studies in the respiratory and carbohydrate metabolism of plant tissues - X. The influence of oxygen at high pressures as a stimulant and inhibitor of certain pathways of respiration in carrots

In contrast with the behaviour of peas (Turner & Quartley 1956; Pritchard 1959, 1961) but like that of various tissues (Johannsen 1888; Cass 1947; Barker, Quartley & Turner 1960), the rate of CO 2 output of whole carrots was stimulated initially in oxygen at a pressure of 5 atm prior to the strong inhibition characteristic of oxygen poisoning. The inhibition was associated with an accumulation of citrate together with a decrease in the contents of α -ketoglutarate, succinate, malate and oxaloacetate; later pyruvate, alcohol and acetate also increased. As in the earlier work with potatoes, peas and apples (Barker & Mapson 1955; Turner & Quartley 1956; Barker et al . 1960), these changes in the acids were attributed in part to the production of an enzymic ‘block’ first in the tricarboxylic acid cycle between citrate and α -ketoglutarate and later in the oxidation of pyruvate. The earlier observations of the activity of the tricarboxylic acid cycle in carrot slices were thus confirmed (Pritchard 1959; ap Rees & Beevers 1960). The ‘total carbon traffic’, representing the sum of the observed CO 2 output in high oxygen and the calculated amounts of CO 2 that would be derived by oxidation of the accumulations of citrate, pyruvate, alcohol and acetate, increased initially in high oxygen to a rate which was about double that of the CO 2 output in air. Considered in relation to this increased carbon traffic in respiration, there was thus initially in high oxygen a large inhibition of the CO 2 output. Oxygen at high pressures thus produced simultaneous stimula­tory and inhibitory effects on certain phases of the respiratory process in carrots. Initially in high oxygen only a small part of the CO 2 output could be accounted for by the observed concentration changes: e. g. the accumulation of citrate; a part of the ‘unknown’ CO 2 output is provisionally attributed, without direct evidence, to operation of the pentose phosphate pathway, earlier shown to be active in carrot slices (Beevers & Gibbs 1954; ap Rees & Beevers 1960).

Dependence of Escherichia coli hyperbaric oxygen toxicity on the lipid acyl chain composition

This study examines certain membrane-related aspects of oxygen poisoning in Escherichia coli K1060 (fabB fadE lacI) and its parent strain, K-12 Ymel. Cells were grown to exponential or stationary phase in a minimal medium and exposed to air plus 300 lb/in2 of O2 as a suspension in minimal salts. After an initial lag, both strains lost viability with apparent first-order kinetics. Hypebaric oxygen was more toxic to cells harvested during the exponential phase of growth than to cells harvested from the stationary phase of growth for both strains K-12 Ymel and K1060. Control suspensions exposed to air plus 300 lb/in2 of N2 did not lose viability during a 96-h exposure. The sensitivity of the unsaturated fatty acid auxotroph, strain K1060, to hyperbaric oxygen increased as the degree of unsaturation of the fatty acid supplement increased. Cells grown with a cyclopropane fatty acid (9,10=methylenoctadecanoate) were the most resistant; cells grown with a monounsaturated fatty acid (oleate) were intermediate; and those grown with polyunsaturated fatty acids (linoleate and linolenate) were most sensitive to hyperbaric oxygen. The parent strain, K-12 Ymel, lost viability in hyperbaric oxygen most similarly to strain K1060 supplemented with oleate. To determine the relative effect of hyperbaric oxygen on the survival of E. coli with saturated membranes, substrains of K1060 were selected for growth on 12-methyltetrade-canoate or on 9 or 10-monobromostearate. Substrains grown with a saturated fatty acid supplement were equally or more sensitive to hyperbaric oxygen than when the same substrains were grown with a cyclopropane fatty acid supplement. The lipid acyl chain composition was determined in E. coli K1060 before and after exposure to hyperbaric oxygen or hyperbaric nitrogen. The proportion of nonsaturated acyl chain lipid of either the oleate- or the 9,10-methyleneoctade-canoate-supplemented K1060 remained unchanged after hyperbaric gas exposure. In strain K1060 supplemented with linoleate and grown to stationary phase, however, the relative unsaturated acyl chain content after hyperbaric exposure decreased in both gases. This finding prompted an investigation of the role of lipid oxidation in hyperbaric oxygen toxicity. Assays of potential lipid oxidation products were performed with linoleate-grown cells. The lipid hydroperoxide and peroxide content of the lipid extract increased by 6.9 times after 48 h of air plus 300 lb/in2 of O2; malondialdehyde and fluorescent complex lipid oxidation products showed much smaller or no changes. Lipid extracts from hyperbaric oxygen-exposed cells were not toxic to viable E. coli K1060, nor did they increase the rate of loss of viability in cells simultaneously exposed to hyperbaric oxygen. Linoleic acid hydroperoxide at 1.0 mM had no effect on the viability of E. coli K-12 Ymel and only marginally decreased the viability of E. coli K1060 supplemented with linoleate. We conclude that the kinetics of oxygen toxicity in E...

The effect of oxygen tension on the growth and metabolism of WI-38 cells

The effect of oxygen tension on cellular growth and metabolism was studied in actively growing WI-38 cells [greater than 90% labeled nuclei (LN)] grown under atmospheres containing 5% CO2 and various combinations of O2 and N2. Cells grown under a partial pressure of oxygen (PO2) of 7.8 +/- 3.5 mm Hg had a significantly slower growth rate, lower saturation densities and higher rates of glucose consumption and lactate production than did cells grown under a PO2 of 44 +/- 7 mm Hg. There were no significant differences in saturation density or the rates of glucose consumption or lactate production between cells grown under PO2 26 +/- 4 mm Hg, 44 +/- 7 mm Hg, or 134 +/- 11 mm Hg. Population doubling time was slightly prolonged at a PO2 of 134 mm Hg compared to a PO2 of 44 mm Hg. Cells grown under a PO2 of 291 +/- 25 mm Hg showed only 20-30% of the growth rate and 10-20% of the saturation density of cells grown under a PO2 of 134 mm Hg. Despite this reduced growth, cells grown under a PO2 of 291 mm Hg consumed four to six times as much glucose and produced four to six times as much lactate per cell as cells grown at a PO2 of 134 mm Hg. Cells grown under a PO2 of 560 +/- 38 mm Hg attached but did not proliferate. This toxic effect of oxygen on cell proliferation was reversible and was not due to an effect of oxygen on the media.

A STUDY OF INTERMEDIATE CARBOHYDRATE METABOLISM IN RATS EXPOSED TO HIGH OXYGEN PRESSURES

Exposure of male rats to 100% oxygen at 6 atmospheres for 20 minutes produced an increase in the concentration of fructose-1,6-diphosphate in the liver and muscle, but not in the brain. The activities of aldolase and glyceraldehyde phosphate dehydrogenase were measured in the liver and muscle. The change in the activity of these enzymes indicated that they had not become rate-limiting during exposure. The relation of these data to the Pasteur effect is considered.

Effect of oxygen on developing retinal vessels with particular reference to the problem of retrolental fibroplasia

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