Hydrogen sulfide:A novel component in Arabidopsis peroxisomes which triggers catalase inhibition

Plant peroxisomes have the capacity to generate different reactive oxygen and nitrogen species(ROS and RNS),such as H_2O_2,superoxide radical(O_2~-),nitric oxide and peroxynitrite(ONOO~-).These organelles have an active nitrooxidative metabolism which can be exacerbated by adverse stress conditions.Hydrogen sulfide(H_2S)is a new signaling gasotransmitter which can mediate the posttranslational modification(PTM)persulfidation.We used Arabidopsis thaliana transgenic seedlings expressing cyan fluorescent protein(CFP)fused to a canonical peroxisome targeting signal 1(PTS1)to visualize peroxisomes in living cells,as well as a specific fluorescent probe which showed that peroxisomes contain H_2S.H_2S was also detected in chloroplasts under glyphosate-induced oxidative stress conditions.Peroxisomal enzyme activities,including catalase,photorespiratory H_2O_2-generating glycolate oxidase(GOX)and hydroxypyruvate reductase(HPR),were assayed in vitro with a H_2S donor.In line with the persulfidation of this enzyme,catalase activity declined significantly in the presence of the H_2S donor.To corroborate the inhibitory effect of H_2S on catalase activity,we also assayed pure catalase from bovine liver and pepper fruit-enriched samples,in which catalase activity was inhibited.Taken together,these data provide evidence of the presence of H_2S in plant peroxisomes which appears to regulate catalase activity and,consequently,the peroxisomal H_2O_2 metabolism.     

The synthetic varespladib molecule is a multi-functional inhibitor for PLA2 and PLA2-like ophidic toxins

BackgroundThe treatment for snakebites is early administration of antivenom, which can be highly effective in inhibiting the systemic effects of snake venoms, but is less effective in the treatment of extra-circulatory and local effects. To complement standard-of-care treatments such as antibody-based antivenoms, natural and synthetic small molecules have been proposed for the inhibition of key venom components such as phospholipase A₂ (PLA₂) and PLA₂-like toxins. Varespladib (compound LY315920) is a synthetic molecule developed and clinically tested aiming to block inflammatory cascades of several diseases associated with high PLA₂s. Recent studies have demonstrated this molecule is able to potently inhibit snake venom catalytic PLA₂ and PLA₂-like toxins.MethodsIn vivo and in vitro techniques were used to evaluate the inhibitory effect of varespladib against MjTX-I. X-ray crystallography was used to reveal details of the interaction between these molecules. A new methodology that combines crystallography, mass spectroscopy and phylogenetic data was used to review its primary sequence.ResultsVarespladib was able to inhibit the myotoxic and cytotoxic effects of MjTX-I. Structural analysis revealed a particular inhibitory mechanism of MjTX-I when compared to other PLA₂-like myotoxin, presenting an oligomeric-independent function.ConclusionResults suggest the effectiveness of varespladib for the inhibition of MjTX-I, in similarity with other PLA₂ and PLA₂-like toxins.General significanceVarespladib appears to be a promissory molecule in the treatment of local effects led by PLA₂ and PLA₂-like toxins (oligomeric dependent and independent), indicating that this is a multifunctional or broadly specific inhibitor for different toxins within this superfamily.     

Ovarian structure and oogenesis of the oviparous goodeids Crenichthys baileyi (Gilbert, 1893) and Empetrichthys latos Miller, 1948 (teleostei,Cyprinodontiformes)

The cyprinodontiform family Goodeidae comprises two biogeographically disjunct subfamilies: the viviparous Goodeinae endemic to the Mexican Plateau, and the oviparous Empetrichthyinae, known only from relict taxa in Nevada and California. Ovarian characteristics of two oviparous species of goodeid, Crenichthys baileyi and Empetrichthys latos, studied using museum collections, are compared with those of viviparous species of goodeids. Both subfamilies have a single, cystovarian ovary. The ovary in the viviparous Goodeinae has an internal septum that divides the ovarian lumen into two compartments, and it may possess oogonia. There is no ovarian septum in the oviparous C. baileyi and E. latos. Oogenesis is similar in both subfamilies with regard to the proliferation of oogonia, initiation of meiosis, primary growth and development of an oocyte during secondary growth in which fluid yolk progressively fuses into a single globule. Notably, eggs of C. baileyi and E. latos are approximately double the size of those of the viviparous Goodeinae in which embryos develop inside the ovarian lumen and are nourished, in part, by nutrients transferred from the maternal tissues, a mode of embryo development called matrotrophy. Egg envelopes of the two subfamilies differ in that those of C. baileyi and E. latos have a relatively thick zona pellucida, attachment fibrils or filaments that develop between the follicle cells during oogenesis, and a micropyle observed only in E. latos. In contrast, viviparous goodeid eggs have a relatively thin zona pellucida, but lack adhesive fibrils, and a micropyle was not observed. These reproductive characters are compared with those of species of the eastern North American Fundulus, a representative oviparous cyprinodontiform. One newlyrecognized shared, derived character, a single, median ovoid ovary with no obvious external evidence of fusion, supports monophyly of the Goodeidae. Differences among the goodeid subfamilies and Fundulus are interpreted relative to the oviparous versus viviparous modes of reproduction. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.     

Ca2+ ionophoretic activity of oligomers of prostaglandin B1 with isolated hepatocytes

Chemically synthesized oligomers (dimers, trimers and tetramers) of 15-dehydroprostaglandin B1 and 16,16'dimethyl-15-dehydroprostaglandin B1 (16,16'diMePGB1) are effective Ca2+ ionophores with isolated mitochondria and in artificial systems. The trimer of 16, 16'diMePGB1 mediated a dose dependent Ca2+ efflux from intact rat hepatocytes; at 9.2 microM oligomer, Ca2+ was released primarily from the mitochondrial pool but at higher concentrations from other cellular pools. The 16, 16'diMePGB1 trimer did not alter Ca2+ release mediated by epinephrine suggesting that the PGB1 oligomer interacts at a different site. The oligomer also caused an activation of phosphorylase similar to that mediated by epinephrine.     

Effect of oligomeric derivatives of prostaglandin B1 on oxidative phosphorylation and their Ca2+ ionophoretic activity

Dimers, trimers and tetramers of 15-dehydro-PGB1 and of 16,16'-dimethyl-15-dehydro-PGB1 have been synthesized and their effect on mitochondrial function evaluated. The trimers and tetramers, and to a lesser extent the dimers, of both series, protected isolated mitochondria from the loss of phosphorylating capacity during in vitro incubation. The monomers were inactive. The trimers and tetramers inhibited between 40 and 50% the F1F0-ATPase of submitochondrial particles. All of the oligomers, but not the monomers, had Ca2+ ionophoretic activity with isolated mitochondria. These activities are qualitatively similar to that reported for the oligomeric mixture of 15-dehydro-PGB1, termed PGBX.     

Kinetic Modelling of in Vitro Lipid Peroxidation Experiments - 'Low Level' Validation of a Model of in Vivo Lipid Peroxidation

Kinetic modelling overcomes some of the drawbacks of purely intuitive thinking in integrating information accumulated on chemical reactions involved in oxidative stress. However, it is important to assess if current knowledge about the reactions that mediate lipid peroxidation already allows satisfactory modelling of this process in near-to-physiological conditions. In this paper, a set of increasingly complex in vitro experiments on antioxidants (a-tocopherol and ascorbate) and lipid peroxidation in heterogeneous systems is simulated. Quantitative to semiquantitative agreement is found between experimental and simulation results. In addition, this theoretical analysis provided useful insights, suggested new hypotheses and experiments and pointed out relevant aspects needing further research. The results encourage and serve as partial validation for the formulation of relatively detailed mathematical models of in vivo lipid peroxidation. Some important aspects of the formulation and analysis of such models are discussed.