Structural determinants of antimicrobial activity in polymers which mimic host defense peptides

Antimicrobial polymers, designed to mimic the salient structural features of host defense peptides, are an emerging class of materials with potential for applications to combat infectious disease. Because the putative mode of action relies on physiochemical parameters of peptides such as hydrophobicity and cationic charge, rather than specific receptor-mediated interactions, the activity of the polymers can be modulated by tuning key structural parameters. While a wide diversity of chemical structures have been reported as antimicrobial polymers, a precise understanding of the structural factors which control their activity is a subject of current investigations. In this mini-review, we will outline the design principles that have been developed so far to fine tune the activity of these antimicrobial agents. The roles played by specific structural features such as cationic charge, hydrophobicity, and molecular weight will be discussed. Future directions of the field and potential challenges will be proposed.     

Isolation of elatol from Laurencia microcladia and its palatability to the sea urchin Echinometra lucunter

Elatol was isolated as the major compound from the red alga Laurencia microcladia Kütz. collected in Southern Brazil. This is the first report of elatol in this species. We also investigated the herbivore behaviour of the black sea urchin Echinometra lucunter (Linnaeus, 1758) towards L. microcladia, Ulva fasciata Delile and Gracilaria domingensis (Kütz.) Sond. ex Dickie through live algal multiple-choice feeding assay, as well as artificial feeding assay. The sea urchins ate the crude algae L. microcladia and pellets containing the powdered algae, extract and all tested concentrations of elatol, suggesting that this seaweed and its main compound are palatable for E. lucunter.     

Soluble fibrinogen modulates neutrophil functionality through the activation of an extracellular signal-regulated kinase-dependent pathway

The integrin family not only mediates the recruitment of polymorphonuclear leukocytes (PMN) to sites of inflammation but also regulates several effector functions by binding to specific ligands. We have recently demonstrated that soluble fibrinogen (sFbg) is able to trigger an activating signal in PMN through an integrin-dependent mechanism. This activation results in degranulation, phagocytosis enhancement, and apoptosis delay. The aim of the present work was to further elucidate the molecular events that follow sFbg interaction with CD11b in human PMN, and the participation of this signaling pathway in the regulation of neutrophil functionality. We demonstrate that sFbg triggers a cascade of intracellular signals that lead to focal adhesion kinase and extracellular signal-regulated kinase 1/2 tyrosine phosphorylation. The activation of this mitogen-activated protein kinase pathway plays a central role in the sFbg modulation of secondary granule degranulation, Ab-dependent phagocytosis, and apoptosis. However, fibrinogen-induced secretory vesicle degranulation occurs independently of the signaling transduction pathways investigated herein. In the context of an inflammatory process, the intracellular signal pathway activated by sFbg may be an early event influencing the functionality of PMN.     

Mutagenicity of methyl methanesulfonate and cyclophosphamide in resting and growing Saccharomyces cerevisiae D7 cells.

In order to evaluate the optimal experimental conditions and to identify the best growth phase for yeast genotoxicity studies, comparative experiments were performed with stationary and growing cells. Methyl methanesulfonate (MMS) and cyclophosphamide (CP) were used as chemical mutagens and strain D7 of Saccharomyces cerevisiae as detector of induced mitotic gene conversion (trp+ convertants) and point reverse mutation (ilv+ revertants) in log or stationary phase cells after either 4 or 16 h of treatment. The highest MMS-induced toxicity and genotoxicity were observed after 16 h of exposure in a suspension test with log phase cells, which is consistent with the greater permeability and sensitivity of growing yeast cells. The maximal induction of genetic effects and toxicity by CP was conversely obtained after 16 h of treatment in stationary phase cells. This may be ascribed to the greater ability of detoxication of growing cells as compared to resting cells. Our results suggest that in evaluating the mutagenicity of chemicals in yeast systems it is important to consider factors such as growth phase and exposure time.     

Melampolides from Argentinean Acanthospermum australe

The investigation of the ethanol extract of Acanthospermum australe, collected in the province of Misiones, Argentina, yielded eight melampolides (1–8) of the acanthospermal type. Two of them, 8β-hydroxy-9α-(2-methylbutyryloxy)-14-oxo-acanthospermolide (3) and 9α-hydroxy-8β-(2-methylbutyryloxy)-14-oxo-acanthospermolide (7) are new compounds. Two other compounds (4 and 8) have been previously reported, and the NMR data of 4 are corrected. Compounds 1, 2, 5 and 6 have not been previously reported, but are probably artifacts formed during extraction. Compounds 3, 6 and 7 showed slight antibiotic activity against Gram-positive bacteria.     

A novel protein with similarities to Rb binding protein 2 compensates for loss of Chk1 function and affects histone modification in fission yeast

The conserved protein kinase Chk1 mediates cell cycle progression and consequently the ability of cells to survive when exposed to DNA damaging agents. Cells deficient in Chk1 are hypersensitive to such agents and enter mitosis in the presence of damaged DNA, whereas checkpoint-proficient cells delay mitotic entry to permit time for DNA repair. In a search for proteins that can improve the survival of Chk1-deficient cells exposed to DNA damage, we identified fission yeast Msc1, which is homologous to a mammalian protein that binds to the tumor suppressor Rb (RBP2). Msc1 and RBP2 each possess three PHD fingers, domains commonly found in proteins that influence the structure of chromatin. Msc1 is chromatin associated and coprecipitates a histone deacetylase activity, a property that requires the PHD fingers. Cells lacking Msc1 have a dramatically altered histone acetylation pattern, exhibit a 20-fold increase in global acetylation of histone H3 tails, and are readily killed by trichostatin A, an inhibitor of histone deacetylases. We postulate that Msc1 plays an important role in regulating chromatin structure and that this function modulates the cellular response to DNA damage.     

Xenogeneic transplantation of human spermatogonia

In the last 3 years, several studies have shown that xenogeneic transplantation of rodent spermatogonia is feasible. The treatment of infertile patients with spermatogenic arrest using the injection of immature germ cells has yielded only poor results. We attempted to establish a complete spermatogenetic line in the testes of mutant aspermatogenic (W/Wv) and severe combined immunodeficient mice (SCID) transplanted with germ cells from azoospermic men. Spermatogenic cells were obtained from testicular biopsy specimens of men (average age of 34.3 +/- 9 years) undergoing infertility treatment because of obstructive and non-obstructive azoospermia. Testicular tissue was digested with collagenase to promote separation of individual spermatogenic cells. The germ cells were injected into mouse testicular seminiferous tubules using a microneedle (40 microm inner diameter) on a 10 ml syringe. To assess the penetration of the cell suspension into the tubules, trypan blue was used as an indicator. Mice were maintained for 50 to 150 days to allow time for germ cell colonisation and development prior to them being killed. Testes were then fixed for histological examination and approximately 100 cross-sectioned tubules were examined for human spermatogenic cells. A total of 26 testicular cell samples, 16 frozen and 10 fresh, were obtained from 24 men. The origin of the azoospermia was obstructive (OA) in 16 patients and non-obstructive (NOA) in 8 patients. The concentration of spermatogenic cells in the OA group was 6.6 x 10(6) cells/ml, and 1.3 x 10(6) cells/ml in the NOA group (p < 0.01). The different spermatogenic cell types were distributed equally in the OA samples, ranging from spermatogenia to fully developed spermatozoa, but in the NOA group the majority of cells were spermatogonia and spermatocytes. A total of 23 testes from 14 W/Wv mice and 24 testes from 12 SCID mice were injected successfully, as judged by the presence of spermatogenic cells in histological sections of testes removed immediately after the injection. However, sections from the remaining testes examined up to 150 days after injection showed tubules lined with Sertoli cells and xenogeneic germ cells were not found. The reason why the two strains of mouse used as recipients did not allow the implantation of human germ cells is probably due to interspecies specificity involving non-compatible cell adhesion molecules and/or immunological rejection.