Sphingomyelinase D Activity in Model Membranes: Structural Effects of in situ Generation of Ceramide-1-Phosphate

The toxicity of Loxosceles spider venom has been attributed to a rare enzyme, sphingomyelinase D, which transforms sphingomyelin to ceramide-1-phosphate. The bases of its inflammatory and dermonecrotic activity, however, remain unclear. In this work the effects of ceramide-1-phosphate on model membranes were studied both by in situ generation of this lipid using a recombinant sphingomyelinase D from the spider Loxosceles laeta and by pre-mixing it with sphingomyelin and cholesterol. The systems of choice were large unilamellar vesicles for bulk studies (enzyme kinetics, fluorescence spectroscopy and dynamic light scattering) and giant unilamellar vesicles for fluorescence microscopy examination using a variety of fluorescent probes. The influence of membrane lateral structure on the kinetics of enzyme activity and the consequences of enzyme activity on the structure of target membranes containing sphingomyelin were examined. The findings indicate that: 1) ceramide-1-phosphate (particularly lauroyl ceramide-1-phosphate) can be incorporated into sphingomyelin bilayers in a concentration-dependent manner and generates coexistence of liquid disordered/solid ordered domains, 2) the activity of sphingomyelinase D is clearly influenced by the supramolecular organization of its substrate in membranes and, 3) in situ ceramide-1-phosphate generation by enzymatic activity profoundly alters the lateral structure and morphology of the target membranes

Treatment with the Interleukin-17A-Blocking Antibody Secukinumab Does Not Interfere with the Efficacy of Influenza and Meningococcal Vaccinations in Healthy Subjects: Results of an Open-Label, Parallel-Group, Randomized Single-Center Study

Our objective was to evaluate the efficacy of influenza and meningococcal vaccinations in healthy subjects exposed to the anti-interleukin-17A (IL-17A) monoclonal antibody (MAb) secukinumab. We used an open-label, parallel-group, randomized single-center study of 50 healthy subjects. Subjects received a single 150-mg dose of secukinumab or no treatment, followed by vaccination with inactivated trivalent subunit influenza virus and conjugate group C meningococcal vaccine (Agrippal and Menjugate, respectively) 2 weeks later. Primary efficacy variables were responses of ≥4-fold increases in antibody titer (hemagglutination inhibition [HI; for influenza virus] and serum bactericidal assay [SBA; for Neisseria meningitides]) for meningococcus and influenza (at least two out of three serotypes), both at 4 weeks postvaccination. All subjects randomized to secukinumab (n = 25) or the control (n = 25) completed the study. Antibody responses to vaccinations measured at 4 weeks were comparable in both groups, with ≥4-fold increased responses following influenza virus vaccination of 20/25 (80%) for both groups and following meningococcal vaccination of 19/25 (76%) for the secukinumab group and 18/25 (72%) for the control group. Differences between groups were 0% (90% confidence intervals [CI], 19 and 19%) and 4% (90% CI, 16 and 24%) for influenza virus and meningococcal vaccines, respectively. Antibody responses were comparable between the 2 groups at different time points. Headache was the most frequently reported adverse effect. No deaths or serious adverse events were reported. Blockade of IL-17A by secukinumab does not appear to interfere with efficacy of influenza and meningococcal vaccinations, as assessed by the achievement of protective antibody levels. A protective (≥4-fold) immune response to both vaccinations at 4 weeks was achieved in 80 and 76% of subjects exposed to secukinumab and the control, respectively

Suramin inhibits macrophage activation by human group IIA phospholipase A(2), but does not affect bactericidal activity of the enzyme

Suramin is a polysulphonated napthylurea antiprotozoal and anthelminitic drug, which also presents inhibitory activity against a broad range of enzymes. Here we evaluate the effect of suramin on the hydrolytic and biological activities of secreted human group IIA phospholipase A(2) (hsPLA(2)GIIA). The hsPLA(2)GIIA was expressed in E. coli, and refolded from inclusion bodies. The hydrolytic activity of the recombinant enzyme was measured using mixed dioleoylphosphatidylcholine/dioleoylphosphatidylglycerol (DOPC/DOPG) liposomes. The activation of macrophage cell line RAW 264.7 by hsPLA(2) GIIA was monitored by NO release, and bactericidal activity against Micrococcus luteus was evaluated by colony counting and by flow cytometry using the fluorescent probe Sytox Green. The hydrolytic activity of the hsPLA(2) GIIA was inhibited by a concentration of 100 nM suramin and the activation of macrophages by hsPLA(2) GIIA was abolished at protein/suramin molar ratios where the hydrolytic activity of the enzyme was inhibited. In contrast, both the bactericidal activity of hsPLA(2) GIIA against Micrococcus luteus and permeabilization of the bacterial inner membrane were unaffected by suramin concentrations up to 50 mu M. These results demonstrate that suramin selectively inhibits the activity of the hsPLA(2) GIIA against macrophages, whilst leaving the anti-bacterial function unchanged.CNPq[471509/2006-0]Universidade de São Paulo - Pró-Reitoria de Pesquisa PRP-USPFAPESP[05/50379-0]FAPESP[01/00279-8

Calcium-Independent Membrane Damage by Venom Phospholipases A(2)

Many snake venom phospholipase A(2)s (vPLA(2)s) present biological effects that are independent of hydrolytic activity. Here we review the evidence for the calcium-independent membrane damaging activity of vPLA(2)s, the possible relevance of this activity on their biological effects, and models for the mechanism of membrane permeabilization by these proteins.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP