Composição química e atividades biológicas de extratos e frações de Guadua chacoensis (Rojas) Londoño & P.M. Peterson / Chemical composition and biological activities of extracts and fractions of Guadua chacoensis (Rojas) Londoño & P.M. Peterson

O Brasil é o país que possui a maior diversidade de bambus em todo o continente americano, com mais de 200 espécies catalogadas. Devido à alta resistência e durabilidade, essas espécies são muito utilizadas na construção civil e confecção de móveis e utensílios. No entanto, faltam estudos que investiguem a composição química e as atividades biológicas. Neste projeto foram avaliados extratos etanólicos de folhas e colmos de Guadua chacoensis (Rojas) Londoño & P.M. Peterson e frações em hexano, clorofórmio, acetato de etila e n-butanol. Também se obteve o óleo volátil, mas com um rendimento extremamente baixo (0,00079%). As frações dos extratos apresentaram teores de compostos fenólicos variando entre 1,92 e 15,80 µg EAG/mg. Esses compostos mostraram-se mais abundantes nas amostras de colmos. Em relação ao teor de flavonoides, as folhas apresentaram maior quantidade, variando entre 0,39 e 1,18 µg EQ/mg contra 0,17 a 0,34 µg EQ/mg nos colmos. Investigou-se a atividade antimicrobiana dos extratos, frações e óleo volátil frente cinco microrganismos: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans e Aspergillus brasiliensis. As amostras demonstraram potencial inibitório moderado a bom contra S. aureus e C. albicans, porém fraca para as demais espécies. Testou-se a capacidade antioxidante frente o radical DPPH e os resultados indicaram atividade antioxidante significativa, especialmente as frações acetato e butanol de colmos. As folhas apresentaram EC50 variando entre 67,5 e 124,0 µg/mL e os colmos entre 40,2 e 124 µg/mL. A inibição da enzima tirosinase, que está associada à produção de melanina, também se mostrou boa a uma concentração de 1 mg/mL, com o extrato bruto de colmos apresentando 43% de inibição, seguido pelas frações acetato (36%) e n-butanol (38%) de folhas. As análises por CG-MS detectaram pelo menos 44 compostos diferentes no óleo volátil, com vários terpenos e sesquiterpenos, e com ß-ionona sendo o componente majoritário (8,75%). As amostras de colmos e folhas apontaram grande diversidade de compostos, cerca de 20 para cada fração, onde os ácidos graxos como ácido palmítico e linoleico e seus ésteres derivados foram os mais abundantes. A análise dos perfis cromatográficos por CCD e CLAE revelaram a presença de ácido p-cumárico nos colmos de G. chacoensis. Esse composto tem relevante atividade antioxidante e de inibição da tirosinase. Também foi possível identificar a quercetagetina-7-O-glicosídeo, uma flavona glicosilada, com propriedades anti-inflamatorias e antidiabéticas. Desta forma, constatou-se que G. chacoensis apresenta grande diversidade de metabólitos secundários com atividades biológicas relevantes, como atividade antioxidante e clareadora, abrindo caminho para investigações mais profundas de suas aplicações, especialmente no segmento de cosméticos e produtos naturais

Brazil is the country with the greatest diversity of bamboo in the entire American continent, with more than 200 species catalogued. Due to their high resistance and durability, they are widely used in home construction and manufacture of furniture and utensils. However, studies investigating chemical composition and biological activities are absent. In this project, ethanol extracts from leaves and stems of Guadua chacoensis (Rojas) Londoño & P.M. Peterson and fractions in hexane, chloroform, ethyl acetate and n-butanol were evaluated. Volatile oil was also obtained, but with an extremely low yield (0.00079%). The fractions of the extracts presented contents of phenolic compounds varying between 1.92 and 15.80 µg GAE/mg. These compounds were more abundant in culm samples. In relation to the flavonoid content, leaves showed a greater amount, varying between 0.39 and 1.18 µg QE/mg against 0.17 to 0.34 µg QE/mg in culms. The antimicrobial activity of extracts, fractions and volatile oil were investigated against five microorganisms: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus brasiliensis. The samples showed moderate to good inhibitory potential against S. aureus and C. albicans, but weak for the other species. The antioxidant capacity was tested against the DPPH radical and the results indicated significant antioxidant activity, especially acetate and butanol culm fractions. The leaves presented EC50 varying between 67.5 and 124.0 µg/mL and culms between 40.2 and 124 µg/mL. The inhibition of the enzyme tyrosinase, which is associated with the production of melanin, was also shown to be good at a concentration of 1 mg/mL, with the raw culm extract showing 43% inhibition, followed by acetate (36%) and n-butanol (38%) fractions of leaves. CG-MS analysis detected at least 44 different compounds in volatile oil, with several terpenes and sesquiterpenes, and with ß-ionone being the major component (8.75%). Culm and leaf samples showed great diversity of compounds, about 20 for each fraction, where fatty acids such as palmitic and linoleic acid and their derivative esters were the most abundant. The analysis of the chromatographic profiles by TLC and HPLC revealed the presence of p-coumaric acid in culms of G. chacoensis. This compound has relevant antioxidant and tyrosinase inhibiting activity. It was also possible to identify quercetagetine-7-O-glucoside, a glycosylated flavone, with anti-inflammatory and anti-diabetic properties. Thus, it was found that G. chacoensis presents a great diversity of secondary metabolites with relevant biological activities, such as antioxidant and whitening activity, opening ways for deeper investigations of its applications, especially in the segment of cosmetics and natural products

Pseudomonas aeruginosa pyoverdine maturation enzyme PvdP has a noncanonical domain architecture and affords insight into a new subclass of tyrosinases.

Pyoverdines (PVDs) are important chromophore-containing siderophores of fluorescent pseudomonad bacteria such as the opportunistic human pathogen Pseudomonas aeruginosa in which they play an essential role in host infection. PVD biosynthesis encompasses a complex pathway comprising cytosolic nonribosomal peptide synthetases that produce a polypeptide precursor that periplasmic enzymes convert to the final product. The structures of most enzymes involved in PVD chromophore maturation have been elucidated, but the structure of the essential tyrosinase PvdP, a monooxygenase required for the penultimate step in PVD biosynthesis, is not known. Here, we closed this gap by determining the crystal structure of PvdP in an apo and tyrosine-complexed state at 2.1 and 2.7 Å, respectively. These structures revealed that PvdP is a homodimer, with each chain consisting of a C-terminal tyrosinase domain and an N-terminal eight-stranded ß-barrel reminiscent of streptavidin that appears to have a structural role only. We observed that ligand binding leads to the displacement of a "placeholder" tyrosine that blocks the active site in the apo structure. This exposes a large, deep binding site that seems suitable for accommodating ferribactin, a substrate of PvdP in PVD biosynthesis. The binding site consists almost exclusively of residues from the tyrosinase domain. Of note, we also found that this domain is more closely related to tyrosinases from arthropods rather than to tyrosinases from other bacteria. In conclusion, our work unravels the structural basis of PvdP's activity in PVD biosynthesis, observations that may inform structure-guided development of PvdP-specific inhibitors to manage P. aeruginosa infections.

Global patterns of diversity and selection in human tyrosinase gene.

Global variation in skin pigmentation is one of the most striking examples of environmental adaptation in humans. More than two hundred loci have been identified as candidate genes in model organisms and a few tens of these have been found to be significantly associated with human skin pigmentation in genome-wide association studies. However, the evolutionary history of different pigmentation genes is rather complex: some loci have been subjected to strong positive selection, while others evolved under the relaxation of functional constraints in low UV environment. Here we report the results of a global study of the human tyrosinase gene, which is one of the key enzymes in melanin production, to assess the role of its variation in the evolution of skin pigmentation differences among human populations. We observe a higher rate of non-synonymous polymorphisms in the European sample consistent with the relaxation of selective constraints. A similar pattern was previously observed in the MC1R gene and concurs with UV radiation-driven model of skin color evolution by which mutations leading to lower melanin levels and decreased photoprotection are subject to purifying selection at low latitudes while being tolerated or even favored at higher latitudes because they facilitate UV-dependent vitamin D production. Our coalescent date estimates suggest that the non-synonymous variants, which are frequent in Europe and North Africa, are recent and have emerged after the separation of East and West Eurasian populations.

Tyrosinase inhibitors from natural and synthetic sources: structure, inhibition mechanism and perspective for the future.

Tyrosinase is known to be a key enzyme in melanin biosynthesis, involved in determining the color of mammalian skin and hair. Various dermatological disorders, such as melasma, age spots and sites of actinic damage, arise from the accumulation of an excessive level of epidermal pigmentation. In addition, unfavorable enzymatic browning of plant-derived foods by tyrosinase causes a decrease in nutritional quality and economic loss of food products. The inadequacy of current conventional techniques to prevent tyrosinase action encourages us to seek new potent tyrosinase inhibitors. This article overviews the various inhibitors obtained from natural and synthetic sources with their industrial importance.

Allozyme differentiation among nine populations of the corn borer (Ostrinia) in China.

To test the hypothesis of the migration of the corn borer, the allozymes of nine populations of the corn borer (Ostrinia) in China were checked using vertical-slab polyacrylamide gel electrophoresis. Eight loci of six allozymes were analyzed. The mean of the genetic identities among the nine populations calculated from the allele frequencies was 0.99068, much closer than that of other species and geographical populations. The mean (0.97955) of the genetic identities between the XJYN population (Ostrinia nubilalis Hübner, collected from Yining, Xinjiang Autonomous Region) and each of the other eight populations (O. furnacalis Guenée) was significantly smaller than that between the pairs of the eight populations (0.99386; t test, P < 0.01). Although the population XJYN clearly deviates from the other eight populations in the dendrogram, the relationship of the two species of corn borer was very close. It is possible that the speciation of corn borer may have resulted from single-gene substitutions.