GATEKEEPING, GATEWATCHING, REALIMENTAÇÃO EM TEMPO REAL: novos desafios para o Jornalismo

Faz vários anos que se sabe como os blogueiros e outros comentaristas on-line independentes criticam, corrigem, e de outra maneira desafiam o jornalismo convencional, porém isto ainda não foi plenamente aceito pelos jornalistas; as hostilidades entre as empresas de mídia e a nova geração de jornalistas cidadãos continuam a irromper de vez em quando. O antigo monopólio de gatekeeping mantido pela mídia de massa tem sido desafiado pela nova prática de gatewatching: feita pelos blogueiros individuais e pelas comunidades de comentaristas que podem não fazer reportagem das notícias de primeira mão, porém fazem a curation e avaliam as notícias e outras informações fornecidas pelas fontes oficiais, e assim prestam um serviço importante. E isto ocorre atualmente com cada vez mais rapidez, quase em tempo real: usando as redes sociais mais recentes, que divulgam, compartilham, comentam, questionam e desacreditam as matérias noticiosas dentro de minutos, e usando plataformas adicionais que possibilitam a colaboração ad hoc rápida e eficaz entre os usuários. Quando centenas de voluntários podem provar dentro de alguns poucos dias que um ministro alemão foi culpado de plágio sério, quando o mundo inteiro fica sabendo de terremotos e tsunamis pelo Twitter – como é que o jornalismo consegue acompanhar tudo isto?

Anti-proliferative and cytotoxic activity of pentadactylin isolated from Leptodactylus labyrinthicus on melanoma cells

Nowadays, the emergence of resistance to the current available chemotherapeutic drugs by cancer cells makes the development of new agents imperative. The skin secretion of amphibians is a natural rich source of antimicrobial peptides (AMP), and researchers have shown that some of these wide spectrum molecules are also toxic to cancer cells. The aim of this study was to verify a putative anticancer activity of the AMP pentadactylin isolated for the first time from the skin secretion of the frog Leptodactylus labyrinthicus and also to study its cytotoxic mechanism to the murine melanoma cell line B16F10. The results have shown that pentadactylin reduces the cell viability of B16F10 cells in a dose-dependent manner. It was also cytotoxic to normal human fibroblast cells; nevertheless, pentadactylin was more potent in the first case. The studies of action mechanism revealed that pentadactylin causes cell morphology alterations (e.g., round shape and shrinkage morphology), membrane disruption, DNA fragmentation, cell cycle arrest at the S phase, and alteration of mitochondrial membrane potential, suggesting that B16F10 cells die by apoptosis. The exact mechanism that causes reduction of cell viability and cytotoxicity after treatment with pentadactylin is still unknown. In conclusion, as cancer cells become resilient to death, it is worthwhile the discovery of new drugs such as pentadactylin that induces apoptosis.

The crude skin secretion of the pepper frog leptodactylus labyrinthicus is rich in metallo and serine peptidases

Peptidases are ubiquitous enzymes involved in diverse biological processes. Fragments from bioactive peptides have been found in skin secretions from frogs, and their presence suggests processing by peptidases. Thus, the aim of this work was to characterize the peptidase activity present in the skin secretion of Leptodactylus labyrinthicus. Zymography revealed the presence of three bands of gelatinase activity of approximately 60 kDa, 66 kDa, and 80 kDa, which the first two were calcium-dependent. These three bands were inhibited either by ethylenediaminetetraacetic acid (EDTA) and phenathroline; thus, they were characterized as metallopeptidases. Furthermore, the proteolytic enzymes identified were active only at pH 6.0–10.0, and their activity increased in the presence of CHAPS or NaCl. Experiments with fluorogenic substrates incubated with skin secretions identified aminopeptidase activity, with cleavage after leucine, proline, and alanine residues. This activity was directly proportional to the protein concentration, and it was inhibited in the presence of metallo and serine peptidase inhibitors. Besides, the optimal pH for substrate cleavage was determined to be 7.0–8.0. The results of the in gel activity assay showed that all substrates were hydrolyzed by a 45 kDa peptidase. Gly-Pro-AMC was also cleaved by a peptidase greater than 97 kDa. The data suggest the presence of dipeptidyl peptidases (DPPs) and metallopeptidases; however, further research is necessary. In conclusion, our work will help to elucidate the implication of these enzymatic activities in the processing of the bioactive peptides present in frog venom, expanding the knowledge of amphibian biology.