Prevention of arsenic-induced hepatic apoptosis by concomitant administration of garlic extracts in mice

Garlic is well known as a folk remedy for a variety of ailments since ancient times, however, very few studies are available suggesting its beneficial role against arsenic toxicity pertaining to its ability to eliminate arsenic from the blood and soft tissues and in reversal of arsenic-induced oxidative stress in affected tissues. The present study was planned to investigate the protective efficacy of aqueous garlic extract using two different doses on parameters suggestive of hepatic injury, tissue oxidative stress and mobilization of arsenic. Further, an attempt to understand the mechanism of arsenic in inducing hepatic apoptosis was also studied. Results of the present study suggested that arsenic administration in mice caused generation of reactive oxygen species (ROS) causing apoptosis through mitochondria-mediated pathway. The ROS generation in hepatic tissue reverted to normal values after co-administration of garlic extracts. The study provides significant evidence that garlic extracts contain strong anti-oxidant property which could be beneficial in preventing arsenic-induced toxicity in cells. However, further research is required to determine whether the results from animal studies are applicable to humans before garlic can be recommended as a putative agent against arsenic toxicity.     

Ligand Reduces Galectin-1 Sensitivity to Oxidative Inactivation by Enhancing Dimer Formation

Galectin-1 (Gal-1) regulates leukocyte turnover by inducing the cell surface exposure of phosphatidylserine (PS), a ligand that targets cells for phagocytic removal, in the absence of apoptosis. Gal-1 monomer-dimer equilibrium appears to modulate Gal-1-induced PS exposure, although the mechanism underlying this regulation remains unclear. Here we show that monomer-dimer equilibrium regulates Gal-1 sensitivity to oxidation. A mutant form of Gal-1, containing C2S and V5D mutations (mGal-1), exhibits impaired dimerization and fails to induce cell surface PS exposure while retaining the ability to recognize carbohydrates and signal Ca²⁺ flux in leukocytes. mGal-1 also displayed enhanced sensitivity to oxidation, whereas ligand, which partially protected Gal-1 from oxidation, enhanced Gal-1 dimerization. Continual incubation of leukocytes with Gal-1 resulted in gradual oxidative inactivation with concomitant loss of cell surface PS, whereas rapid oxidation prevented mGal-1 from inducing PS exposure. Stabilization of Gal-1 or mGal-1 with iodoacetamide fully protected Gal-1 and mGal-1 from oxidation. Alkylation-induced stabilization allowed Gal-1 to signal sustained PS exposure in leukocytes and mGal-1 to signal both Ca²⁺ flux and PS exposure. Taken together, these results demonstrate that monomer-dimer equilibrium regulates Gal-1 sensitivity to oxidative inactivation and provides a mechanism whereby ligand partially protects Gal-1 from oxidation.Immunological homeostasis relies on efficient contraction of activated leukocytes following an inflammatory episode. Several factors, including members of the galectin and tumor necrosis factor families (1, 2), regulate leukocyte turnover by inducing apoptotic cell death. In contrast, several galectin family members, in particular galectin-1 (Gal-1),² uniquely regulate neutrophil turnover by inducing phosphatidylserine (PS) exposure, which normally sensitizes apoptotic cells to phagocytic removal (3, 4), independent of apoptosis, a process recently termed preaparesis (5).Previous studies suggested that dimerization may be required for Gal-1-induced PS exposure, as a mutant form of Gal-1 (mGal-1) containing two point mutations within the dimer interface, C2S and V5D (C2S,V5D), displays impaired Gal-1 dimerization and fails to induce PS exposure (6). However, the manner in which monomer-dimer equilibrium regulates Gal-1 signaling remains unclear. Previous studies suggest that dimerization may be required for efficient cross-linking of functional receptors or the formation of signaling lattices (7–9). Consistent with this, monomeric mutants of several other galectins fail to induce PS exposure or signal leukocytes (4, 8). Gal-1 signaling of PS exposure requires initial signaling events, such as mobilization of intracellular Ca²⁺ followed by sustained receptor engagement (10). Although mGal-1 fails to induce PS exposure (6), whether mGal-1 can induce these initial signaling events remains unknown (10).In addition to directly regulating signaling, monomer-dimer equilibrium may also regulate other aspects of Gal-1 function. Unlike many other proteins involved in the regulation of immunity, Gal-1 displays unique sensitivity to oxidative inactivation (11–15). Although engagement of ligand partially protects Gal-1 from oxidation (15), the impact of Gal-1 oxidation on signaling remains enigmatic. During oxidation, Gal-1 forms three distinct intramolecular disulfide bridges that facilitate profound conformational changes that preclude ligand binding and Gal-1 dimerization (12–14), suggesting that monomerdimer equilibrium may also regulate Gal-1 sensitivity to oxidative inactivation.Previous studies utilized dithiothreitol (DTT) in treatment conditions to protect Gal-1 from oxidative inactivation (16, 17). Indeed, failure to include DTT precluded Gal-1-induced death in T cells (3, 18), suggesting that Gal-1 undergoes rapid oxidation in vivo in the absence of reducing conditions. However, DTT itself can induce apoptosis in leukocytes (19), leaving questions regarding the impact of Gal-1 oxidation on these signaling events. In contrast, recent studies utilizing iodoacetamide-alkylated Gal-1 (iGal-1), previously shown to protect Gal-1 from oxidative inactivation (20–29), demonstrated that DTT actually primes cells to become sensitive to Gal-1-induced apoptosis regardless of Gal-1 sensitivity to oxidation (5).As the engagement of leukocyte ligands requires glycan recognition and oxidation precludes this binding (11, 15), understanding the impact of oxidation on Gal-1 signals will facilitate a greater appreciation of the factors that govern Gal-1 oxidation and therefore function. Our results demonstrate that Gal-1 monomer-dimer equilibrium provides a key regulatory point controlling both Gal-1 sensitivity to oxidation and its ability to signal PS exposure in leukocytes. These results provide novel insights into Gal-1 function and explain at a biochemical level the mechanisms regulating Gal-1 oxidative inactivation and signaling.     

Population genetic structure of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) based on mitochondrial cytochrome oxidase (COI) gene sequences

Population genetic structure of melon fly analysed with mitochondrial cytochrome oxidase I gene suggested that melon fly populations across the globe is homogeneous with non-significant variation of 0.000-0.003 base substitutions per site. Test isolates representing various geographic situations across the world were placed in 26 mitochondrial haplotypes based on variations associated with a maximum of three mutational steps and the predominant haplotype i.e. H1 was present in all melon fly populations except Hawaiian population. Evolution of mtCOI gene suggested that the fly could have originated some 0.4 million years ago. The present study also indicated that the B. cucurbitae population expansion is an event of post Pleistocene warm climatic conditions with small number of founder population. The invasion of B. cucurbitae in Hawaii was associated with the large population size and the global presence of the fly is associated with human mediated dispersal. The very low genetic variation suggested that the fly management might be possible by large scale sterile insect techniques programme.     

NSs Encoded by Groundnut Bud Necrosis Virus Is a Bifunctional Enzyme

Groundnut bud necrosis virus (GBNV), a member of genus Tospovirus in the family Bunyaviridae, infects a large number of leguminosae and solanaceae plants in India. With a view to elucidate the function of nonstructural protein, NSs encoded by the small RNA genome (S RNA), the NSs protein of GBNV- tomato (Karnataka) [1] was over-expressed in E. coli and purified by Ni-NTA chromatography. The purified rNSs protein exhibited an RNA stimulated NTPase activity. Further, this activity was metal ion dependent and was inhibited by adenosine 5′ (β, γ imido) triphosphate, an ATP analog. The rNSs could also hydrolyze dATP. Interestingly, in addition to the NTPase and dATPase activities, the rNSs exhibited ATP independent 5′ RNA/DNA phosphatase activity that was completely inhibited by AMP. The 5′ α phosphate could be removed from ssDNA, ssRNA, dsDNA and dsRNA thus confirming that rNSs has a novel 5′ α phosphatase activity. K189A mutation in the Walker motif A (GxxxxGKT) resulted in complete loss of ATPase activity, but the 5′ phosphatase activity was unaffected. On the other hand, D159A mutation in the Walker motif B (DExx) resulted in partial loss of both the activities. These results demonstrate for the first time that NSs is a bifunctional enzyme, which could participate in viral movement, replication or in suppression of the host defense mechanism.