Intra-dimer cooperativity between the active site cysteines during the oxidation of peroxiredoxin 2

Peroxiredoxin 2 (Prdx2) and other typical 2-Cys Prdxs function as homodimers in which hydrogen peroxide oxidizes each active site cysteine to a sulfenic acid which then condenses with the resolving cysteine on the alternate chain. Previous kinetic studies have considered both sites as equally reactive. Here we have studied Prdx2 using a combination of non-reducing SDS-PAGE to separate reduced monomers and dimers with one and two disulfide bonds, and stopped flow analysis of tryptophan fluorescence, to investigate whether there is cooperativity between the sites. We have observed positive cooperativity when H₂O₂ is added as a bolus and oxidation of the second site occurs while the first site is present as a sulfenic acid. Modelling of this reaction showed that the second site reacts 2.2 ± 0.1 times faster. In contrast, when H₂O₂ was generated slowly and the first active site condensed to a disulfide before the second site reacted, no cooperativity was evident. Conversion of the sulfenic acid to the disulfide showed negative cooperativity, with modelling of the exponential rise in tryptophan fluorescence yielding a rate constant of 0.75 ± 0.08 s^-1 when the alternate active site was present as a sulfenic acid and 2.29 ± 0.08-fold lower when it was a disulfide. No difference in the rate of hyperoxidation at the two sites was detected. Our findings imply that oxidation of one active site affects the conformation of the second site and influences which intermediate forms of the protein are favored under different cellular conditions.

Peroxiredoxin expression and redox status in neutrophils and HL-60 cells

Peroxiredoxins (Prxs) are thiol peroxidases with a key role in antioxidant defense and redox signaling. They could be important in neutrophils for handling the large amount of oxidants that these cells produce. We investigated the redox state of Prx1 and Prx2 in HL-60 promyelocytic cells differentiated to neutrophil-like cells (dHL-60) and in human neutrophils. HL-60 cell differentiation with dimethyl sulfoxide caused a large decrease in expression of both Prxs, and all-trans retinoic acid also decreased Prx1 expression. Prx1 was mostly reduced in dHL-60 cells. NADPH oxidase activation by phorbol myristate acetate (PMA) or ingestion of Staphylococcus aureus induced rapid oxidation to disulfide-linked dimers, and eventually hyperoxidation. The NADPH oxidase inhibitor, diphenyleneiodonium, prevented Prx1 dimerization in stimulated dHL-60 cells, and decreased the extent of oxidation under resting conditions. In contrast, Prx1 and Prx2 were present in neutrophils from human blood as disulfides, and PMA or S. aureus caused no further oxidation. They remained oxidized on incubation with diphenyleneiodonium in media. Although this suggests that Prx redox cycling could be deficient in neutrophils, thioredoxin expression and thioredoxin reductase activity were similar in neutrophils and dHL-60 cells. Additionally, neutrophil thioredoxin was initially reduced and underwent oxidation after PMA activation. Thus, although the Prxs respond to oxidant generation in dHL-60 cells, in neutrophils they appear "locked" as disulfides. On this basis we propose that neutrophil Prxs are inefficient antioxidants and contribute little to peroxide removal during the oxidative burst, and speculate that they might be involved in other cell processes.

Phaseolin ingestion affects vesicular traffic causing oxidative stress in the midgut of Callosobruchus maculatus larvae

It has been reported that phaseolin, the major storage globulin of the common bean (Phaseolus vulgaris), is toxic to Callosobruchus maculatus larvae, an Old World bruchid beetle that is not capable of infesting this New World edible bean. It has also been demonstrated that vicilin, the major storage globulin found in cowpea (Vigna unguiculata) seeds, is absorbed through receptor-mediated endocytosis in the insect midgut. A putative vicilin receptor has been purified and showed high homology to α-tocopherol transfer protein. However, the ingestion of a variant vicilin purified from C. maculatus resistant seeds inhibits transcytosis, resulting in the accumulation of vicilins in the midgut cells and ultimately antibiosis. In the present work, we studied the cellular up-take of phaseolin in C. maculatus larvae with the aim of discovering if this protein is also capable of inhibiting endocytic traffic in the enterocytes. FITC-labelled vicilin and FITC-labelled phaseolin were incorporated into the diet of the larvae at a physiological concentration of 0.5% w/w. The fate of labelled and non-labelled globulins was monitored by confocal microscopy. Here we demonstrated that phaseolin is also endocytosed by enterocytes causing an accumulation of endocytic vesicles in the midgut when compared to the ingestion of vicilin obtained from a susceptible V. unguiculata cultivar. From the results obtained for HNE, MDA and TBARS, a pro-oxidative scenario was established in the intestinal epithelial cells of the larvae, which may explain the deleterious effect observed in larvae developing inside P. vulgaris seeds.

Interaction of curcumin with manganese may compromise metal and neurotransmitter homeostasis in the hippocampus of young mice

Manganese (Mn) exposure is related to industrial activities, where absorption by inhalation has high relevance. Manganism, a syndrome caused as a result of excessive accumulation of Mn in the central nervous system, has numerous symptoms similar to those seen in idiopathic Parkinson disease (IPD). Some of these symptoms, such as learning, memory, sensorial, and neurochemical changes, appear before the onset of motor deficits in both manganism and IPD. The aim of this study was to evaluate the possible neuroprotective effects of curcumin against behavioral deficits induced by Mn toxicity in young (2 months old) Swiss mice. We evaluated the effect of chronic inhalation of a Mn mixture [Mn(OAc)3 and MnCl2 (20:40 mM)], 1 h/session, three times a week, over a 14-week period on behavioral and neurochemical parameters. Curcumin was supplemented in the diet (500 or 1,500 ppm in food pellets). The Mn disrupted the motor performance evaluated in the single-pellet reach task, as well as the short- and long-term spatial memory evaluated in the step-down inhibitory avoidance task. Surprisingly, curcumin also produced similar deleterious effects in such behavioral tests. Moreover, the association of Mn plus curcumin significantly increased the levels of Mn and iron, and decreased the levels of dopamine and serotonin in the hippocampus. These alterations were not observed in the striatum. In conclusion, the current Mn treatment protocol resulted in mild deficits in motor and memory functions, resembling the early phases of IPD. Additionally, curcumin showed no beneficial effects against Mn-induced disruption of hippocampal metal and neurotransmitter homeostasis.

Antidepressant-like action of the bark ethanolic extract from Tabebuia avellanedae in the olfactory bulbectomized mice

ETHNOPHARMACOLOGICAL RELEVANCE

Tabebuia avellanedae Lorentz ex Griseb is a plant employed in tropical America folk medicine for the treatment of several diseases, including depressive disorders.

AIM OF THE STUDY

To investigate the ability of Tabebuia avellanedae ethanolic extract (EET) administered chronically to cause an antidepressant-like effect in the tail suspension test (TST), a predictive test of antidepressant activity, and to reverse behavioral (hyperactivity, anhedonic-like behavior and increased immobility time in the TST) and biochemical changes induced by olfactory bulbectomy (OB), a model of depression, in mice.

MATERIALS AND METHODS

Mice were submitted to OB to induce depressive-related behaviors, which were evaluated in the open-field test (hyperactivity), splash test (loss of motivational and self-care behavior indicative of an anhedonic-like behavior) and TST (increased immobility time). Phosphorylation levels of Akt, GSK-3β, ERK1/2 and CREB, as well as BDNF immunocontent, were evaluated in the hippocampus of bulbectomized mice or sham-operated mice treated for 14 days by p.o. route with EET or vehicle.

RESULTS

EET (10 and 30mg/kg) given 14 days by p.o route to mice reduced the immobility time in the TST without altering locomotor activity, an indicative of an antidepressant-like effect. EET per se increased both CREB (Ser(133)) and GSK-3β (Ser(9)) phosphorylation (at doses of 10-30 and 30mg/kg, respectively) in sham-operated mice. OB caused hyperactivity, loss of motivational and self-care behavior, increased immobility time in the TST and an increase in CREB and ERK1 phosphorylation, as well as BDNF immunocontent. EET abolished all these OB-induced alterations except the increment of CREB phosphorylation. Akt (Ser(473)) and ERK2 phosphorylation levels were not altered in any group.

CONCLUSIONS

EET ability to abolish the behavioral changes induced by OB was accompanied by modulation of ERK1 and BDNF signaling pathways, being a promising target of EET. Results indicate that this plant could constitute an attractive strategy for the management of depressive disorders, once more validating the traditional use of this plant.