Mediation of the antilipolytic and lipogenic effects of insulin in adipocytes by intracellular accumulation of hydrogen peroxide.
01 May 1980-Biochemical Pharmacology (Elsevier)-Vol. 29, Iss: 9, pp 1239-1246
TL;DR: Endogenous H 2 O 2 appears to satisfy the manifold criteria for a ‘second messenger’ of insulin, and increasing availability of d -glucose may counterbalance these effects by replenishing the reducing equivalents.
Abstract: Exposure of rat adipocytes to insulin causes activation of a pyridine nucleotide oxidase at the internal side of the plasma membrane, generating hydrogen peroxide (S. P. Mukherjee and W. S. Lynn, Fedn Proc. 35 , 1694 (1976); S. P. Mukherjee and W. S. Lynn, Archs Biochem. Biophys. 184 , 69 (1977). Evidence was also presented that intracellular utilization of H 2 O 2 by the peroxidative pathways of glutathione peroxidase and catalase is coupled with glucose oxidation via the pentose phosphate pathway [S. P. Mukherjee, R. H. Lane and W. S. Lynn, Biochem. Pharmac. 27 , 2589 (1978)]. The relationship between the glucose-independent insulin effect on H 2 O 2 production and its metabolic role is evaluated on the basis of formate oxidation, lipogenesis, antagonism of lipase activity and lowering of cellular levels of cyclic 3',5'-adenosine monophosphoric acid (cAMP). These measures of the effects of insulin, observed at low concentrations of glucose, were reversed at higher concentrations of glucose (over 0.3 mM). Exogenous H 2 O 2 had metabolic effects similar to insulin. Addition of H 2 O 2 (10 −4 M and higher) to the extracellular medium caused a substantial inhibition of epinephrine-stimulated and adrenocorticotropin-stimulated depot-fat lipase activity in these cells, measured by net glycerol production. H 2 O 2 also increased lipogenesis by increasing the provision of the substrates and cofactor (NADPH) and activating pyruvate dehydrogenase in the same manner as insulin. Exogenous catalase (16 μg/ml) abolished the insulin-like effects of H 2 O 2 (but not of insulin itself) on glucose oxidation, the contribution of glucose carbons to glyceride fatty acids and glyceride glycerol, the inhibition of lipolysis, and the time-dependent decline in the cAMP content of the cells. The data suggest that, while insulin-stimulated H 2 O 2 production from the plasma membrane may bring about some glucose-independent metabolic effects through a lowering of cytoplasmic redox potential, increasing availability of d -glucose may counterbalance these effects by replenishing the reducing equivalents. Endogenous H 2 O 2 appears, therefore, to satisfy the manifold criteria for a ‘second messenger’ of insulin.
TL;DR: Results strongly suggest that UCP2 is sensitive to GDP and that the UCPs, particularly U CP2, are able to modulate H2O2 mitochondrial generation, which supports a role for UCP1 in cellular (patho‐) physiological processes involving free radicals generated by mitochondria, such as oxidative damage, inflammation, or apoptosis.
Abstract: According to the state of mitochondrial respiration, the respiratory chain generates superoxide anions converted into hydrogen peroxide. Two uncoupling proteins (UCP) able to modulate the coupling between the respiratory chain and ATP synthesis are now identified and could be involved in mitochondrial H2O2 generation. UCP1 is specific to brown adipose tissue (BAT) whereas UCP2 is expressed in numerous tissues, particularly in monocytes/macrophages. Preincubation of BAT mitochondrial fractions with GDP, an inhibitor of UCP1, induced a rise in mitochondrial membrane potential (assessed by rhodamine 123 uptake) and H2O2 production. An uncoupling agent reversed this effect. Liver mitochondria exhibited a similar phenotype. GDP was also able to raise membrane potential and H2O2 production of the mitochondria from nonparenchymal cells expressing UCP2, but was completely ineffective on mitochondria from hepatocytes deprived of UCP2. The GDP effect was also observed with mitochondrial fractions of the spleen or thymus, which highly expressed UCP2. Altogether, these results strongly suggest that UCP2 is sensitive to GDP and that the UCPs, particularly UCP2, are able to modulate H2O2 mitochondrial generation. This supports a role for UCP2 in cellular (patho-) physiological processes involving free radicals generated by mitochondria, such as oxidative damage, inflammation, or apoptosis.
Cites background from "Mediation of the antilipolytic and ..."
...cies to mimick insulin effect or promote adipose differentiation (30, 31)....
TL;DR: Results suggest that H2O2 produced by hamster sperm plays a significant role during capacitation, possibly in membrane reorganization to facilitate the fusion that takes place during exocytosis of the acrosomal contents.
Abstract: We have investigated the possibility that the generation of hydrogen peroxide (H2O2) by spermatozoa plays a physiological role during capacitation. Capacitation is defined as the incubation period required for fertilization in mammals. Capacitation culminates in an exocytotic event, the acrosome reaction (AR). Mammalian sperm generate H2O2 during aerobic incubation and do not contain catalase, the enzyme that promotes scavenging of H2O2. In the present work we show that added catalase inhibited the AR, while glucose oxidase (GO), an enzyme that generates H2O2, accelerated the onset of the AR. Direct addition of H2O2 also stimulated the AR; catalase inhibited both the stimulation by GO and by H2O2. The onset of the AR was always preceded by the appearance of hyperactivated motility. The stimulation of the AR by H2O2 was manifest 1-2 h after the addition of H2O2. Catalase added at 3 h of incubation was less effective in inhibiting the AR than catalase added at the beginning. Incubation of sperm with catalase prevented the induction of the AR by the membrane-perturbing lipid, lysophosphatidyl choline. Taken together, these results suggest that H2O2 produced by hamster sperm plays a significant role during capacitation, possibly in membrane reorganization to facilitate the fusion that takes place during exocytosis of the acrosomal contents.
TL;DR: This chapter highlights physiological and metabolic effects on enzyme activities of vanadium, affecting the transition state of phosphate, which seems to have an affinity for the binding sites on these enzymes.
Abstract: Publisher Summary This chapter highlights physiological and metabolic effects on enzyme activities. Vanadium, a group V element, belongs to the first transition series and can form compounds mainly in valence states 3+, 4+, and 5+, both anionic and cationic species. Several criteria of essentiality of an element are satisfied by the properties of vanadium such as low molecular weight, excellent catalytic activity, appropriate atomic structure, its position as a transition metal, ability to form chelates potentially with biologically active compounds, ubiquity in the geosphere and possibly in the biosphere, homeostatic regulation by controlled accumulation and rapid excretion, deficiency in animals and plants showing characteristic symptoms, and low toxicity on oral intake. At least three significant enzymes of the plasma membrane are affected by vanadate—Na, K-ATPase is inhibited in nanomolar concentrations and adenylate cyclase and NADH oxidase are activated in micro-molar to milli-molar concentrations. These enzymes are interrelated. ATP is the substrate for the first two, and both substrates are nucleotides. Vanadate, affecting the transition state of phosphate, seems to have an affinity for the binding sites on these enzymes.
TL;DR: The insulin-like effects of ionic zinc (Zn2+) in adipocytes are caused not only by direct effects of the ion on intracellular metabolism but also by indirect effects related to H2O2 generation.
Abstract: The insulin-like effects of ionic zinc (Zn2+) were studied in isolated rat adipocytes. Concentrations of Zn2+ between 250 and 1000 microM stimulated 3-O-methylglucose transport and glucose metabolism to CO2, glyceride-fatty acid, and glyceride-glycerol. Selective stimulation of the pentose phosphate cycle was observed since a Zn2+-induced increase in glucose carbon 1 oxidation persisted even when glucose transport was blocked with 50 microM cytochalasin B or when transport was no longer rate-limiting for metabolism at high concentrations of glucose. Enhanced pentose phosphate cycle activity may have been due to a selective inhibition of glutathione reductase by the ion, which was also accompanied by a fall in cellular glutathione content. Zn2+ also inhibited lipolysis stimulated by the beta-adrenergic agent ritodrine in the absence of glucose. The effects of Zn2+ on glucose oxidation and stimulated rates of lipolysis were inhibited by extracellular catalase, indicating that they were largely a result of H2O2 generation. The H2O2 production appeared for the most part to be caused by zinc-catalyzed autoxidation of sulfhydryl groups present on external cell membranes, although involvement of sulfhydryl groups on bovine serum albumin in the buffer could also have contributed. The insulin-like effects of Zn2+ in adipocytes are therefore caused not only by direct effects of the ion on intracellular metabolism but also by indirect effects related to H2O2 generation.
TL;DR: Under aerobic conditions generation of H202 by a Variety of biomembranes has now been found to be a physiological event interlinked with phenomena such as phagocytosis, transport processes and thermogenesis in some as yet unidentified way.
Abstract: Knowledge of the generation of H202 in cellular oxidations has existed for many years. It has been assumed that H202 is tOxiC tO cells and the presence of catalase is indicative of a detoxication mechanism. Other radicals of oxygen were recently recognized to be more potent destructive agents of biological material than H202. Also catalase and other peroxidases utilize H202 in some cellular oxidation processes leading to several important metabolites. Thus, the generation of H202 in cellular processes seems to be purposeful and H202 can not be dismissed as a mere undesirable byproduct. Biological formation of H202 is not limited to the previously known flavoproteins and some copper enzymes, but other redox systems, particularly heme and non-heme iron proteins, are now found to undergo auto-oxidation yielding H202. The capacity for generation of H202 is now found to be widespread in a variety of organisms and in the organdies of the cells. The reduction of oxygen to H20 by mitochondrial cytochrome oxidase being the predominant oxygen-utilizing reaction had over-shadowed the importance of the quantitatively minor pathways. Under aerobic conditions generation of H202 by a Variety of biomembranes has now been found to be a physiological event interlinked with phenomena such as phagocytosis, transport processes and thermogenesis in some as yet unidentified way. The underlying mechanisms of these processes seem to involve generation and utilization of H202 in mitochondria, microsomes, peroxisomes or plasma membranes. This review gives an account of the potential of biomembranes to generate H202 and its implication in the cellular processes.
01 Feb 1964
TL;DR: This article marks the beginning of Rodbell's interest in cell receptors and related his discovery that fat cells could be isolated from other cells by treating them with preparations of collagenase, and also found that insulin could stimulate glucose uptake.
Abstract: This article marks the beginning of Rodbell's interest in cell receptors. In it, he related his discovery that fat cells could be isolated from other cells by treating them with preparations of collagenase, and also found that insulin could stimulate glucose uptake. This had far-reaching implications for the treatment of various diseases, as it was the first demonstration that insulin acted on individual cells.