Onnamide A suppresses the severe acute respiratory syndrome-coronavirus 2 infection without inhibiting 3-chymotrypsin-like cysteine protease.

Given the continuous emergence of new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the development of new inhibitors is necessary to enhance clinical efficacy and increase the options for combination therapy for the coronavirus disease 2019. Because marine organisms have been a resource for the discovery of numerous bioactive molecules, we constructed an extract library of marine invertebrates collected from the Okinawa Islands. In this study, the extracts were used to identify antiviral molecules against SARS-CoV-2. Using a cytopathic effect (CPE) assay in VeroE6/TMPRSS2 cells, an extract from the marine sponge Theonella swinhoei was found to reduce virus-induced CPE. Eventually, onnamide A was identified as an antiviral compound in the extract using column chromatography and NMR analysis. Onnamide A inhibited several SARS-CoV-2 variant-induced CPEs in VeroE6/TMPRSS2 cells as well as virus production in the supernatant of infected cells. Moreover, this compound blocked the entry of SARS-CoV-2 pseudo-virions. Taken together, these results demonstrate that onnamide A suppresses SARS-CoV-2 infection, which may be partially related to entry inhibition, and is expected to be a candidate lead compound for the development of anti-SARS-CoV-2 drugs.

Okichromanone, a new antiviral chromanone from a marine-derived Microbispora.

Okichromanone (1), a new chromanone, was isolated from the culture extract of a sponge-derived actinomycete Microbispora, along with known 1-hydroxyphenazine (2). Compound 1 was elucidated to exist as a mixture of two isomeric structures (1a and 1b) at a ratio of nearly 3:2. Compounds 1 and 2 showed anti HSV-I activity with IC50 values 40 and 86 µM, respectively, and anti HSV-II activity with IC50 values 59 and 123 µM, respectively.

Membrane-Vesicle-Mediated Interbacterial Communication Activates Silent Secondary Metabolite Production.

Most bacterial biosynthetic gene clusters (BGCs) are "silent BGCs" that are expressed poorly or not at all under normal culture conditions. However, silent BGCs, even in part, may be conditionally expressed in response to external stimuli in the original bacterial habitats. The growing knowledge of bacterial membrane vesicles (MVs) suggests that they could be promising imitators of the exogenous stimulants, especially given their functions as signaling mediators in bacterial cell-to-cell communication. Therefore, we envisioned that MVs added to bacterial cultures could activate diverse silent BGCs. Herein, we employed Burkholderia multivorans MVs, which induced silent metabolites in a wide range of bacteria in Actinobacteria, Bacteroidetes and Proteobacteria phyla. A mechanistic analysis of MV-induced metabolite production in Xenorhabdus innexi suggested that the B. multivorans MVs activate silent metabolite production by inhibiting quorum sensing in X. innexi. In turn, the X. innexi MVs carrying some MV-induced peptides suppressed the growth of B. multivorans, highlighting the interspecies communication between B. multivorans and X. innexi through MV exchange.

Geographical parthenogenesis in the brown alga Scytosiphon lomentaria (Scytosiphonaceae): Sexuals in warm waters and parthenogens in cold waters.

Geographical parthenogenesis, a phenomenon where parthenogens and their close sexual relatives inhabit distinct geographical areas, has been considered an interesting topic in evolutionary biology. Reports of geographical parthenogenesis from land and freshwater are numerous, but this occurrence has been rarely reported from the sea. Brown algae are mostly marine and are thought to include numerous obligate parthenogens; still, little is known about the distribution, origin and evolution of parthenogens in this group. Here we report a novel pattern of geographical parthenogenesis in the isogamous brown alga Scytosiphon lomentaria. Sex ratio investigation demonstrated that, in Japan, sexual populations grew in the coast along warm ocean currents, whereas female-dominant parthenogenetic populations grew mainly in the coast along a cold ocean current. In the two localities where sexual and parthenogenetic populations were parapatric, parthenogens grew in more wave-exposed areas than sexuals. Population genetic and phylogenetic analyses, including those based on genome-wide single nucleotide polymorphism data, indicated that parthenogens have initially evolved at least twice and subsequent hybridizations between the parthenogens and sexuals have generated multiple new parthenogenetic lineages. The origin of the initial parthenogens is not clear, except that it would not be interspecies hybridization. Interestingly, we found that the production of sex pheromones, which attract male gametes, has been independently lost in the initial two parthenogenetic lineages. This parallel loss of the sexual trait may represent the direct origin of parthenogens, or the regressive evolution of a useless trait under asexuality.

Insights into phosphatase-activated chemical defense in a marine sponge holobiont.

Marine sponges often contain potent cytotoxic compounds, which in turn evokes the principle question of how marine sponges avoid self-toxicity. In a marine sponge Discodermia calyx, the highly toxic calyculin A is detoxified by the phosphorylation, which is catalyzed by the phosphotransferase CalQ of a producer symbiont, "Candidatus Entotheonella" sp. Here we show the activating mechanism to dephosphorylate the stored phosphocalyculin A protoxin. The phosphatase specific to phosphocalyculin A is CalL, which is also encoded in the calyculin biosynthetic gene cluster. CalL represents a new clade and unprecedently coordinates the heteronuclear metals Cu and Zn. CalL is localized in the periplasmic space of the sponge symbiont, where it is ready for the on-demand production of calyculin A in response to sponge tissue disruption.

Mycobacterium smegmatis alters the production of secondary metabolites by marine-derived Aspergillus niger.

It is generally accepted that fungi have a number of dormant gene clusters for the synthesis of secondary metabolites, and the activation of these gene clusters can expand the diversity of secondary metabolites in culture. Recent studies have revealed that the mycolic acid-containing bacterium Tsukamurella pulmonis activates dormant gene clusters in the bacterial genus Streptomyces. However, it is not clear whether the mycolic acid-containing bacteria activate dormant gene clusters of fungi. We performed co-culture experiments using marine-derived Aspergillus niger with Mycobacterium smegmatis, a mycolic acid-containing bacteria. The co-cultivation resulted in the production of a pigment by A. niger and increased cytotoxic activity of the extract against human prostate cancer DU145 cells. An analysis of secondary metabolites in the extract of the co-culture broth revealed that the increase in cytotoxic activity was caused by the production of malformin C (1), and that TMC-256A1 (2), desmethylkotanin (3), and aurasperone C (4) were selectively produced under co-culture conditions. In addition, further study suggested that direct interaction between the two microorganisms was necessary for the production of the pigment and the cytotoxic compound malformin C (1) from A. niger. Given the biological activities of malformin C, including cytotoxic activity, our approach for increasing the production of bioactive secondary metabolites has important practical applications and may facilitate structural analyses of novel bioactive compounds.

Scrobiculosides A and B from the deep-sea sponge Pachastrella scrobiculosa.

Two new steroidal saponins, scrobiculosides A and B, were isolated from the deep-sea sponge Pachastrella scrobiculosa, collected at a depth of 200 m off Miura Peninsula, Japan. The aglycones of scrobiculosides A and B feature a vinylic cyclopropane and a ∆24,25 exomethylene on the side chains, respectively. Both saponins have a common sugar moiety composed of ß-D-galactopyranosyl-(1 → 2)-6-acetyl-ß-D-glucopyranoside, with the exception of an acetyl group on C6″ in scrobiculoside A. Scrobiculoside A exhibited cytotoxicity against HL-60 and P388 cells, with IC50 values of 52 and 61 µM, respectively.

Peridinin, a carotenoid, inhibits proliferation and survival of HTLV-1-infected T-cell lines.

Human T-cell leukemia virus type 1 (HTLV-1) causes either adult T-cell leukemia (ATL) or chronic inflammatory disorders such as HTLV-1-associated myelopathy/tropical spastic paraparesis. These diseases are not curable as yet; therefore new agents for treatment and prevention are needed. Carotenoids are natural plant compounds with anti-carcinogenic activities. Peridinin is one of the most abundant carotenoids found in nature. Based on a series of past experiments, here we investigated the effects of peridinin extracted from Okinawan coral Isis hippuris on the proliferation and survival of HTLV-1-infected T-cell lines. The results of water-soluble tetrazolium-8 assay indicated that peridinin dose-dependently inhibits cell proliferation and viability of HTLV-1-infected T-cell lines. Flow cytometry showed that low concentration of peridinin induced cell cycle arrest at G1 phase, while higher concentration induced apoptosis. Peridinin caused cleavage of caspase-3, -8 and -9. Peridinin significantly reduced the expression of G1 cell cycle regulators, including cyclin D1, cyclin D2, CDK4, CDK6 and c-Myc, and anti-apoptotic proteins, including survivin, XIAP and Bcl-2, in a dose-dependent manner. Peridinin suppressed DNA binding of NF-κB. Peridinin inhibited phosphorylation of IκBα, RelA, Akt and p70 S6 kinase, and reduced protein expression level of 3-phosphoinositide-dependent protein kinase 1. Thus, peridinin exerts its anti-proliferative and pro-apoptotic effects by suppressing NF-κB and Akt signaling in HTLV-1-infected T cells. Peridinin also reduced tumor growth in mice harboring ATL xenograft tumors. The results suggested that peridinin is a potentially suitable therapeutic agent against HTLV-1-associated diseases.

Pattern recognition analysis for 1H NMR spectra of plasma from hemodialysis patients.

1H NMR spectroscopic and pattern recognition-based methods (NMR-PR) were applied to the metabolic profiling studies on hemodialysis (HD). Plasma samples were collected from 37 patients before and after HD and measured by 600 MHz NMR spectroscopy. Each spectrum was data-processed and subjected to principal component analysis for pattern recognition. Spectral patterns of plasma between pre- and post-dialyses were clearly discriminated, together with significant fluctuations in the levels of creatinine, trimethylamine-N-oxide, glucose, lactate, and acetate, which were quantitated. We have first observed the significant elevation of lactate levels in post-dialysis plasma. The present study has demonstrated the high feasibility of NMR-PR method for monitoring the dialysis condition and comprehensive profiling of the change of low-molecular-weight metabolites in HD.