Plant-derived antimicrobials to fight against multi-drug-resistant human pathogens

Antibiotic resistance is becoming a pivotal concern for public health that has accelerated the search for new antimicrobial molecules from nature. Numbers of human pathogens have inevitably evolved to become resistant to various currently available drugs causing considerable mortality and morbidity worldwide. It is apparent that novel antibiotics are urgently warranted to combat these life-threatening pathogens. In recent years, there have been an increasing number of studies to discover new bioactive compounds from plant origin with the hope to control antibiotic-resistant bacteria. This review attempts to focus and record the plant-derived compounds and plant extracts against multi-drug-resistant (MDR) pathogens including methicillin-resistant Staphylococcus aureus (MRSA), MDR-Mycobacterium tuberculosis and malarial parasites Plasmodium spp. reported between 2005 and 2015. During this period, a total of 110 purified compounds and 60 plant extracts were obtained from 112 different plants. The plants reviewed in this study belong to 70 different families reported from 36 countries around the world. The present review also discusses the drug resistance in bacteria and emphasizes the urge for new drugs

Evaluation of the Antioxidant Activity of the Marine Pyrroloiminoquinone Makaluvamines

Makaluvamines are pyrroloiminoquinones isolated from Zyzzya sponges. Until now, they have been described as topoisomerase II inhibitors with cytotoxic effects in diverse tumor cell lines. In the present work, seven makaluvamines were tested in several antioxidant assays in primary cortical neurons and neuroblastoma cells. Among the alkaloids studied, makaluvamine J was the most active in all the assays. This compound was able to reduce the mitochondrial damage elicited by the well-known stressor H2O2. The antioxidant properties of makaluvamine J are related to an improvement of the endogenous antioxidant defenses of glutathione and catalase. SHSY5Y assays proved that this compound acts as a Nrf2 activator leading to an improvement of antioxidant defenses. A low concentration of 10 nM is able to reduce the reactive oxygen species release and maintain a correct mitochondrial function. Based on these results, non-substituted nitrogen in the pyrrole plus the presence of a p-hydroxystyryl without a double bond seems to be the most active structure with a complete antioxidant effect in neuronal cells

Aurantoside K, a New Antifungal Tetramic Acid Glycoside from a Fijian Marine Sponge of the Genus Melophlus

A new tetramic acid glycoside, aurantoside K, was isolated from a marine sponge belonging to the genus Melophlus. The structure of the compound was elucidated on the basis of spectroscopic analysis (1H NMR, 1H–1H COSY, HSQC, and HMBC, as well as high-resolution ESILCMS). Aurantoside K did not show any significant activity in antimalarial, antibacterial, or HCT-116 cytotoxicity assays, but exhibited a wide spectrum of antifungal activity against wild type Candida albicans, amphotericin-resistant C. albicans, Cryptococcus neoformans, Aspergillus niger, Penicillium sp., Rhizopus sporangia and Sordaria sp

LC-HRMS-Database Screening Metrics for Rapid Prioritization of Samples to Accelerate the Discovery of Structurally New Natural Products

In order to accelerate the isolation and characterization of structurally new or novel secondary metabolites, it is crucial to develop efficient strategies that prioritize samples with greatest promise early in the workflow so that resources can be utilized in a more efficient and cost-effective manner. We have developed a metrics-based prioritization approach using exact LC-HRMS, which uses data for 24 618 marine natural products held in the PharmaSea database. Each sample was evaluated and allocated a metric score by a software algorithm based on the ratio of new masses over the total (sample novelty), ratio of known masses over the total (chemical novelty), number of peaks above a defined peak area threshold (sample complexity), and peak area (sample diversity). Samples were then ranked and prioritized based on these metric scores. To validate the approach, eight marine sponges and six tunicate samples collected from the Fiji Islands were analyzed, metric scores calculated, and samples targeted for isolation and characterization of new compounds. Structures of new compounds were elucidated by spectroscopic techniques, including 1D and 2D NMR, MS, and MS/MS. Structures were confirmed by computer-assisted structure elucidation methods (CASE) using the ACD/Structure Elucidator Suite

Five new species of Sarcophyton (Coelenterata: Octocorallia) from the Fiji Islands

This paper describes five new species of the soft coral genus Sarcophyton which were identified by their morphological characters (colony form and sclerite shape). The five species have been named: S. aalbersbergi sp. nov., S. aldersladei sp. nov., S. alexanderi sp. nov., S. skeltoni sp. nov and S. soapiae sp. nov. For the first time it is documented that there is a Sarcophyton species that does not have sclerites in the interior of the disc

Antimicrobial and cytotoxic activities of marine plants and invertebrates from the coast of Espirito Santo in Vanuatu

Marine invertebrates and algae collected off the coast of Espirito Santo in Vanuatu were investigated for antimicrobial and cytotoxic activities. The combined crude methanol-dichloromethane extracts from 52 sponges, 5 algae, 17 soft corals (cnidaria) and 5 other samples of various marine invertebrates were screened for cytotoxicity, antibacterial and antifungal properties. The cytotoxicity of the samples was determined using a brine shrimp lethality test and, notably, 78% of the invertebrate and algae samples showed cytotoxic activity against brine shrimps with the sponge Crella spinulata displaying the strongest activity. Antimicrobial activity was determined against three resistant bacterial strains and two fungal strains. A total of 42% of the samples tested showed antimicrobial activity against at least one of the five strains. The most potent antibacterial activities were recorded for the sponges Lamellodysidea herbacea, Phyllospongia sp., a sponge in the order Halichondrida and Hippospongia metachromia. A Theonella sp. sponge displayed the strongest antifungal activity

Papuamides E and F, cytotoxic depsipeptides from the marine sponge

Two known papuamides C (1) and D (2) together with two new depsipeptides, papuamides E (3) and F (4), were isolated from an undescribed sponge of the genus Melophlus collected in the Solomon Islands. The planar structures of the compounds were elucidated on the basis of spectroscopic studies. Papuamides C–F (1–4) showed cytotoxicity against brine shrimp with LD50 values between 92 and 106 μg/mL

Papuamides E and F, cytotoxic depsipeptides from the marine sponge Melophlus sp.

Two known papuamides C (1) and D (2) together with two new depsipeptides, papuamides E (3) and F (4), were isolated from an undescribed sponge of the genus Melophlus collected in the Solomon Islands. The planar structures of the compounds were elucidated on the basis of spectroscopic studies. Papuamides C-F (1-4) showed cytotoxicity against brine shrimp with LD values between 92 and 106 μg/mL