Xanthones for melanogenesis inhibition: Molecular docking and QSAR studies to understand their anti-tyrosinase activity.

The human skin is constantly exposed to external factors that affect its integrity, UV radiation being one of the main stress factors. The repeated exposure to this radiation leads to increased production of Reactive Oxygen Species (ROS) which activate a series of processes involved in photoaging. Excessive UV exposure also exacerbates melanin production leading to a variety of pigmentation disorders. Xanthones are reported to exhibit properties that prevent deleterious effects of UV exposure and high levels of ROS in the organism, so in this work a wide library of xanthones with different patterns of substitution was synthesized and tested for their inhibitory activity against the skin enzymes tyrosinase, elastase, collagenase and hyaluronidase, many of which were evaluated for the first time. Most of the compounds were tyrosinase inhibitors, with the best one (xanthone 27) presenting an IC50 of 1.9 µM, which is approximately 6 times lower than the IC50 of the positive control kojic acid. Concerning the other enzymes, only one compound presented IC50 lower than 150 µM in elastase inhibition (xanthone 14 = 91.8 µM) and none in collagenase and hyaluronidase inhibition. A QSAR model for tyrosinase inhibitory activity was built using six molecular descriptors, with a partial negative surface area descriptor and the relative number of oxygen atoms being positively contributing to the tyrosinase inhibitory activity. Docking using AutoDock Vina shows that all the tested compounds have more affinity to mushroom tyrosinase than kojic acid. Docking results implied that the tyrosinase inhibitory mechanisms of xanthonic derivatives are attributed to an allosteric interaction. Taken together, these data suggest that xanthones might be useful scaffolds for the development of new and promising candidates for the treatment of pigmentation-related disorders and for skin whitening cosmetic products.

Assessing microbial activities in metal contaminated agricultural volcanic soils--An integrative approach.

Volcanic soils are unique naturally fertile resources, extensively used for agricultural purposes and with particular physicochemical properties that may result in accumulation of toxic substances, such as trace metals. Trace metal contaminated soils have significant effects on soil microbial activities and hence on soil quality. The aim of this study is to determine the soil microbial responses to metal contamination in volcanic soils under different agricultural land use practices (conventional, traditional and organic), based on a three-tier approach: Tier 1 - assess soil microbial activities, Tier 2 - link the microbial activity to soil trace metal contamination and, Tier 3 - integrate the microbial activity in an effect-based soil index (Integrative Biological Response) to score soil health status in metal contaminated agricultural soils. Our results showed that microbial biomass C levels and soil enzymes activities were decreased in all agricultural soils. Dehydrogenase and ß-glucosidase activities, soil basal respiration and microbial biomass C were the most sensitive responses to trace metal soil contamination. The Integrative Biological Response value indicated that soil health was ranked as: organic>traditional>conventional, highlighting the importance of integrative biomarker-based strategies for the development of the trace metal "footprint" in Andosols.

Volatile compounds in samples of cork and also produced by selected fungi.

The production of volatile compounds by microbial communities of cork samples taken during the cork manufacturing process was investigated. The majority of volatiles were found in samples collected at two stages: resting after the first boiling and nontreated cork disks. Volatile profiles produced by microbiota in both stages are similar. The releasable volatile compounds and 2,4,6-trichloroanisole (TCA) produced in cork-based culture medium by five isolated fungal species in pure and mixed cultures were also analyzed by gas chromatography coupled with mass spectrometry (GC-MS).The results showed that 1-octen-3-ol and esters of fatty acids (medium chain length C8-C20) were the main volatile compounds produced by either pure fungal species or their mixture. Apparently, Penicillium glabrum is the main contributor to the overall volatile composition observed in the mixed culture. The production of releasable TCA on cork cannot be attributed to any of the assayed fungal isolates.

Variation of the antimicrobial susceptibility profiles of Burkholderia cepacia complex clonal isolates obtained from chronically infected cystic fibrosis patients: a five-year survey in the major Portuguese treatment center.

The treatment of cystic fibrosis (CF) patients chronically infected with Burkholderia cepacia complex (Bcc) bacteria requires extensive and aggressive antibiotics therapy, exposing these bacteria to prolonged antibiotics-selective pressure. In the present study, we have compared the susceptibility patterns to 13 antimicrobials of 94 Bcc isolates obtained from 15 Portuguese CF patients in the course of chronic infection during a five-year survey. These isolates were previously genotyped and represent 11 different strains of the species B. cenocepacia (subgroups A and B), B. cepacia, B. multivorans, and B. stabilis. The results are consistent with the notion that CF Bcc isolates are resistant to the most clinically relevant antimicrobials and suggest an uneven distribution of resistance rates among the different species, with B. cenocepacia subgroup A isolates being the most resistant. Phenotypic variants exhibiting differences in the antimicrobial susceptibility patterns were obtained from the sputum samples of clinically deteriorated CF patients during chronic lung infection. The isolation of resistant variants coincided with periods of pulmonary exacerbation and antibiotics therapy.