Factors influencing lethality of Bacillus thuringiensis kurstaki toxin for eggs and larvae of Trichostrongylus colubriformis (Nematoda)

A toxin from Bacillus thuringiensis kurstaki was lethal to eggs and first- and second-stage larvae of the ruminant nematode Trichostrongylus colubriformis. Sheathed and exsheathed third-stage larvae were also killed by the toxin. However, susceptibility of the ova to the toxin decreased after several hours of development. Heating at 65 C for 1 hr or freezing at 0 C for 3 mo did not affect stability of the toxin. Ovicidal activity of the toxin was not altered by treatment with 13 microbial or mammalian enzymes, but toxicity was reduced by the antibiotics streptomycin or penicillin G and the enzyme inhibitor L-1-tosylamide 2-phenylethylchloromethyl ketone. Cuprous, ferrous, and zinc chlorides also inhibited the ovicidal activity of the toxin. Increased osmolarity of the assay media or solubilization of the toxin from pH 3 to 11 had no effect on toxicity for eggs. The membrane agents sodium vanadate and 4,4'-diisothiocyano-2,2' disulfonic acid stilbene increased (9-fold) and decreased (333-fold) toxicity, respectively. N-acetylneuraminic acid was the only tested sugar that reduced the toxicity of B. t. kurstaki.     

In vitro reconstitution and analysis of the chain initiating enzymes of the R1128 polyketide synthase.

Biosynthesis of the carbon chain backbone of the R1128 substances is believed to involve the activity of a ketosynthase/chain length factor (ZhuB/ZhuA), an additional ketosynthase (ZhuH), an acyl transferase (ZhuC), and two acyl carrier proteins (ACPs; ZhuG and ZhuN). A subset of these proteins initiate chain synthesis via decarboxylative condensation between an acetyl-, propionyl-, isobutyryl-, or butyryl-CoA derived primer unit and a malonyl-CoA derived extender unit to yield an acetoacetyl-, beta-ketopentanoyl-, 3-oxo-4-methylpentanoyl-, or beta-ketohexanoyl-ACP product, respectively. To investigate the precise roles of ZhuH, ZhuC, ZhuG, and ZhuN, each protein was expressed in Escherichia coli and purified to homogeneity. Although earlier reports had proposed that ZhuC and its homologues played a role in primer unit selection, direct in vitro analysis of ZhuC showed that it was in fact a malonyl-CoA:ACP malonyltransferase (MAT). The enzyme could catalyze malonyl transfer but not acetyl- or propionyl-transfer onto R1128 ACPs or onto ACPs from other biosynthetic pathways, suggesting that ZhuC has broad substrate specificity with respect to the holo-ACP substrate but is specific for malonyl-CoA. Thus, ZhuC supplies extender units to both the initiating and elongating ketosynthases from this pathway. To interrogate the primer unit specificity of ZhuH, the kinetics of beta-ketoacyl-ACP formation in the presence of various acyl-CoAs and malonyl-ZhuG were measured. Propionyl-CoA and isobutyryl-CoA were the two most preferred substrates of ZhuH, although acetyl-CoA and butyryl-CoA could also be accepted and elongated. This specificity is not only consistent with earlier reports demonstrating that R1128B and R1128C are the major products of the R1128 pathway in vivo, but is also in good agreement with the properties of the ZhuH substrate binding pocket, as deduced from a recently solved crystal structure of the enzyme. Finally, to investigate the molecular logic for the occurrence of not one but two ACP genes within the R1128 gene cluster, the inhibition of ZhuH-catalyzed formation of beta-ketopentanoyl-ACP was quantified in the presence of apo-ZhuG or apo-ZhuN. Both apo-proteins were comparable inhibitors of the ZhuH catalyzed reaction, suggesting that the corresponding apo-proteins can be used interchangeably during chain initiation. Together, these results provide direct biochemical insights into the mechanism of chain initiation of an unusual bacterial aromatic PKS.     

Oral iron and the bioavailability of zinc.

The oral bioavailability of zinc was studied in nonpregnant adults before and 24 hours after two weeks of oral supplementation with iron and folic acid. Bioavailability was greatly reduced, and the shape of the plasma curves suggested that this was due to impairment of the intestinal absorption of zinc. The findings suggest that the reduced bioavailability of zinc occurs because of interelement competition in the bowel wall. This might induce zinc depletion.     

Endothelial Nitric Oxide Synthase Deficient Mice Are Protected from Lipopolysaccharide Induced Acute Lung Injury

Lipopolysaccharide (LPS) derived from the outer membrane of gram-negative bacteria induces acute lung injury (ALI) in mice. This injury is associated with lung edema, inflammation, diffuse alveolar damage, and severe respiratory insufficiency. We have previously reported that LPS-mediated nitric oxide synthase (NOS) uncoupling, through increases in asymmetric dimethylarginine (ADMA), plays an important role in the development of ALI through the generation of reactive oxygen and nitrogen species. Therefore, the focus of this study was to determine whether mice deficient in endothelial NOS (eNOS^-/-) are protected against ALI. In both wild-type and eNOS^-/- mice, ALI was induced by the intratracheal instillation of LPS (2 mg/kg). After 24 hours, we found that eNOS^-/-mice were protected against the LPS mediated increase in inflammatory cell infiltration, inflammatory cytokine production, and lung injury. In addition, LPS exposed eNOS^-/- mice had increased oxygen saturation and improved lung mechanics. The protection in eNOS^-/- mice was associated with an attenuated production of NO, NOS derived superoxide, and peroxynitrite. Furthermore, we found that eNOS^-/- mice had less RhoA activation that correlated with a reduction in RhoA nitration at Tyr³⁴. Finally, we found that the reduction in NOS uncoupling in eNOS^-/- mice was due to a preservation of dimethylarginine dimethylaminohydrolase (DDAH) activity that prevented the LPS-mediated increase in ADMA. Together our data suggest that eNOS derived reactive species play an important role in the development of LPS-mediated lung injury.     

Fructose Mediated Non-Alcoholic Fatty Liver Is Attenuated by HO-1-SIRT1 Module in Murine Hepatocytes and Mice Fed a High Fructose Diet

Background

Oxidative stress underlies the etiopathogenesis of nonalcoholic fatty liver disease (NAFLD), obesity and cardiovascular disease (CVD). Heme Oxygenase-1 (HO-1) is a potent endogenous antioxidant gene that plays a key role in decreasing oxidative stress. Sirtuin1 (SIRT1) belongs to the family of NAD-dependent de-acyetylases and is modulated by cellular redox.

Hypothesis

We hypothesize that fructose-induced obesity creates an inflammatory and oxidative environment conducive to the development of NAFLD and metabolic syndrome. The aim of this study is to determine whether HO-1 acts through SIRT1 to form a functional module within hepatocytes to attenuate steatohepatitis, hepatic fibrosis and cardiovascular dysfunction.

Methods and Results

We examined the effect of fructose, on hepatocyte lipid accumulation and fibrosis in murine hepatocytes and in mice fed a high fructose diet in the presence and absence of CoPP, an inducer of HO-1, and SnMP, an inhibitor of HO activity. Fructose increased oxidative stress markers and decreased HO-1 and SIRT1 levels in hepatocytes (p<0.05). Further fructose supplementation increased FAS, PPARα, pAMPK and triglycerides levels; CoPP negated this increase. Concurrent treatment with CoPP and SIRT1 siRNA in hepatocytes increased FAS, PPARα, pAMPK and triglycerides levels suggesting that HO-1 is upstream of SIRT1 and suppression of SIRT1 attenuates the beneficial effects of HO-1. A high fructose diet increased insulin resistance, blood pressure, markers of oxidative stress and lipogenesis along with fibrotic markers in mice (p<0.05). Increased levels of HO-1 increased SIRT1 levels and ameliorated fructose-mediated lipid accumulation and fibrosis in liver along with decreasing vascular dysfunction (p<0.05 vs. fructose). These beneficial effects of CoPP were reversed by SnMP.

Conclusion

Taken together, our study demonstrates, for the first time, that HO-1 induction attenuates fructose-induced hepatic lipid deposition, prevents the development of hepatic fibrosis and abates NAFLD-associated vascular dysfunction; effects that are mediated by activation of SIRT1 gene expression.     

Bub3p Facilitates Spindle Checkpoint Silencing in Fission Yeast

Although critical for spindle checkpoint signaling, the role kinetochores play in anaphase promoting complex (APC) inhibition remains unclear. Here we show that spindle checkpoint proteins are severely depleted from unattached kinetochores in fission yeast cells lacking Bub3p. Surprisingly, a robust mitotic arrest is maintained in the majority of bub3Δ cells, yet they die, suggesting that Bub3p is essential for successful checkpoint recovery. During recovery, two defects are observed: (1) cells mis-segregate chromosomes and (2) anaphase onset is significantly delayed. We show that Bub3p is required to activate the APC upon inhibition of Aurora kinase activity in checkpoint-arrested cells, suggesting that Bub3p is required for efficient checkpoint silencing downstream of Aurora kinase. Together, these results suggest that spindle checkpoint signals can be amplified in the nucleoplasm, yet kinetochore localization of spindle checkpoint components is required for proper recovery from a spindle checkpoint-dependent arrest.     

Variable nuclear markers for a Sonoran Desert bark beetle, Araptus attenuatus Wood (Curculionidae: Scolytinae), with applications to related genera

We report eight new co-dominant nuclear markers for population genetics of the bark beetle Araptus attenuatus Wood. Several loci include introns from low-copy genes, and four cross-amplify in one or more related genera. The markers show moderate levels of polymorphism (2–19 alleles per locus), and no loci showed significant deviations from Hardy–Weinberg or linkage equilibrium across both of the two populations examined, consistent with Mendelian inheritance patterns.