Won-Gon Kim

Fatty acid synthesis is a target for antibacterial activity of unsaturated fatty acids

Long‐chain unsaturated fatty acids, such as linoleic acid, show antibacterial activity and are the key ingredients of antimicrobial food additives and some antibacterial herbs. However, the precise mechanism for this antimicrobial activity remains unclear. We found that linoleic acid inhibited bacterial enoyl‐acyl carrier protein reductase (FabI), an essential component of bacterial fatty acid synthesis, which has served as a promising target for antibacterial drugs. Additional unsaturated fatty acids including palmitoleic acid, oleic acid, linolenic acid, and arachidonic acid also exhibited the inhibition of FabI. However, neither the saturated form (stearic acid) nor the methyl ester of linoleic acid inhibited FabI. These FabI‐inhibitory activities of various fatty acids and their derivatives very well correlated with the inhibition of fatty acid biosynthesis using [14C] acetate incorporation assay, and importantly, also correlated with antibacterial activity. Furthermore, the supplementation with exogenous fatty acids reversed the antibacterial effect of linoleic acid, which showing that it target fatty acid synthesis. Our data demonstrate for the first time that the antibacterial action of unsaturated fatty acids is mediated by the inhibition of fatty acid synthesis.

Sesquiterpene O-naphthoquinones from the root bark of Ulmus davidiana

Three new sesquiterpene ortho-naphthoquinones, davidianones A, B and C, together with four known compounds, mansonones E, F, H and I, were isolated from the root bark of Ulmus davidiana. On the basis of spectral data including pulse field gradient two-dimensional NMR spectroscopy, the structures of new compounds were established as 3-hydroxymethyl-6,9-dimethylnaphtho(1,8-b,c)pyran-7,8-dione, 6-methoxycarbonyl-3,9-dimethylnaphtho(1,8-b,c)pyran-7,8-dione, 6-dimethoxymethyl-3,9-dimethylnaphtho(1.8-b,c)pyran-7,8-d ion e, respectively. Their antioxidative activities were evaluated by a thiobarbituric acid method using rat liver microsomes, with mansonone F showing the greatest activity.

Nuclear receptor Nurr1 agonists enhance its dual functions and improve behavioral deficits in an animal model of Parkinson’s disease

Significance Parkinson’s disease (PD) is the most prevalent movement disorder with no available treatments that can stop or slow down the disease progress. Although the orphan nuclear receptor Nurr1 is a promising target for PD, it is thought to be a ligand-independent transcription factor and, so far, no small molecule has been identified that can bind to its ligand binding domain. Here, we established high throughput cell-based assays and successfully identified three Nurr1 agonists among FDA-approved drugs, all sharing an identical chemical scaffold. Remarkably, these compounds not only directly bind to Nurr1 but also ameliorate behavioral defects in a rodent model of PD. Thus, our study shows that Nurr1 could serve as a valid drug target for neuroprotective therapeutics of PD. Parkinson’s disease (PD), primarily caused by selective degeneration of midbrain dopamine (mDA) neurons, is the most prevalent movement disorder, affecting 1–2% of the global population over the age of 65. Currently available pharmacological treatments are largely symptomatic and lose their efficacy over time with accompanying severe side effects such as dyskinesia. Thus, there is an unmet clinical need to develop mechanism-based and/or disease-modifying treatments. Based on the unique dual role of the nuclear orphan receptor Nurr1 for development and maintenance of mDA neurons and their protection from inflammation-induced death, we hypothesize that Nurr1 can be a molecular target for neuroprotective therapeutic development for PD. Here we show successful identification of Nurr1 agonists sharing an identical chemical scaffold, 4-amino-7-chloroquinoline, suggesting a critical structure–activity relationship. In particular, we found that two antimalarial drugs, amodiaquine and chloroquine stimulate the transcriptional function of Nurr1 through physical interaction with its ligand binding domain (LBD). Remarkably, these compounds were able to enhance the contrasting dual functions of Nurr1 by further increasing transcriptional activation of mDA-specific genes and further enhancing transrepression of neurotoxic proinflammatory gene expression in microglia. Importantly, these compounds significantly improved behavioral deficits in 6-hydroxydopamine lesioned rat model of PD without any detectable signs of dyskinesia-like behavior. These findings offer proof of principle that small molecules targeting the Nurr1 LBD can be used as a mechanism-based and neuroprotective strategy for PD.

Long-term suppression of tyrosinase by terrein via tyrosinase degradation and its decreased expression

Abstract:  Previously, we reported that a fungal metabolite, terrein, decreases melanin synthesis via downregulation of microphthalmia‐associated transcription factor (MITF). In the present study, we further investigated the long‐term hypopigmenting action of terrein in a spontaneously immortalized mouse melanocyte cell line, Mel‐Ab. Treatment with terrein at a concentration of 50 μm strongly decreased melanogenesis in a time‐dependent manner. Interestingly, the decreased tyrosinase protein levels lasted for at least 7 days, even though the MITF protein levels were restored after 3 days of treatment. In accordance with the results of Western blot analyses, the tyrosinase mRNA levels were found to be continuously decreased for at least 7 days, even though recovery of the MITF mRNA levels began after 3 days of terrein treatment. Therefore, we evaluated tyrosinase downregulation to determine if it is caused by proteasomal degradation. We found that the reduction in tyrosinase levels that was induced by terrein was clearly recovered by MG‐132, a proteasome inhibitor. Moreover, ubiquitination of tyrosinase increased following treatment with terrein in the presence of MG‐132. Taken together, these results suggest that terrein decreases melanogenesis through ubiquitin‐dependent proteasomal degradation as well as via decreased expression of its mRNA.

Atromentin and Leucomelone, the First Inhibitors Specific to Enoyl-ACP Reductase (FabK) of Streptococcus pneumoniae

Two potent inhibitors of FabK, the enoyl-acyl carrier protein (ACP) reductase of Streptococcus pneumoniae, were isolated from the solid state fermentation of an unidentified fungus F010248. Their structures were identified to be atromentin and leucomelone by various spectral analysis. Atromentin and leucomelone inhibited the FabK with IC50 values of 0.24 and 1.57 μM, respectively, while did not inhibit FabI, the enoyl-ACP reductase of either Escherichia coli or Staphylococcus aureus, even at 200 μM. Atromentin and leucomelone are the first inhibitors specific to the enoyl-ACP reductase (FabK) of Streptococcus pneumoniae.

Benzastatins E, F, and G: New indoline alkaloids with neuronal cell protecting activity from Streptomyces nitrosporeus

Abstract Three new indoline alkaloids, benzastatins E (5), F (6), and G (7), were isolated from the culture broth of Streptomyces nitrosporeus 30643 as neuronal cell protecting substances. Their structures were elucidated on the basis of spectral data. 5, 6 and 7 suppressed glutamate toxicity in N18-RE-105 cells with EC50 values of 1.7, 3.6, and 12.2 μM, respectively.

Flavimycins A and B, dimeric 1,3-dihydroisobenzofurans with peptide deformylase inhibitory activity from Aspergillus flavipes.

Flavimycins A (1) and B (2), novel dimeric 1,3-dihydroisobenzofurans, were isolated as inhibitors of peptide deformylase from cultures of Aspergillus flavipes. Their chemical structures were established by NMR and MS data analysis. Compounds 1 and 2 exist as epimeric mixtures at C-1 through fast hemiacetal-aldehyde tautomerism. Compounds 1 and 2 inhibited Staphylococcus aureus peptide deformylase with IC₅₀ values of 35.8 and 100.1 μM, respectively. Consistent with their PDF inhibition, 1 showed two times stronger antibacterial activity than 2 on S. aureus including MRSA, with MIC values of 32-64 μg/mL.

Vinaxanthone, a new FabI inhibitor from Penicillium sp.

OBJECTIVES Bacterial enoyl-ACP reductase (FabI) has been validated as a novel antibacterial target for tackling infections caused by multidrug-resistant pathogens. A few FabI inhibitors, however, are known. This study isolated a new FabI inhibitor from Penicillium sp. METHODS A screening programme led to the selection of a Penicillium sp. producing a strong FabI-inhibitory metabolite. The chemical structure of the isolated FabI inhibitor was elucidated by mass spectrometry and nuclear magnetic resonance spectral data. The antibacterial target of the inhibitor was validated by overexpression assays. RESULTS The isolated FabI inhibitor was elucidated to be vinaxanthone. It selectively inhibited Staphylococcus aureus FabI with an IC(50) of 0.9 microM; it did not affect FabK, an enoyl-ACP reductase of Streptococcus pneumoniae. Consistent with its inhibition of FabI, the inhibitor prevented intracellular fatty acid synthesis while it did not affect protein biosynthesis. It also prevented the growth of S. aureus as well as methicillin-resistant S. aureus (MRSA) and quinolone-resistant S. aureus. Importantly, fabI-overexpressing S. aureus showed reduced susceptibility to the inhibitor compared with the wild-type strain, demonstrating that its antibacterial action is mediated by inhibition of FabI. CONCLUSIONS Vinaxanthone is a new FabI-directed antibacterial of natural origin that could have potential for further development as a new anti-MRSA agent.

Talosins A and B: New isoflavonol glycosides with potent antifungal activity from Kitasatospora kifunensis MJM341. II. Physicochemical properties and structure determination

In our screening program for new antifungal agents from microbial secondary metabolites, two new isoflavonol glycosides with potent antifungal activity, talosins A and B, were isolated from the culture broth of Kitasatospora kifunensis MJM341. Talosins A and B were determined to be genistein 7-α-L-6-deoxy-talopyranoside and genistein 4′,7-di-α-L-6-deoxy-talopyranoside, respectively, by spectroscopic studies. They are the first flavonoid glycosides incorporating 6-deoxy-talose as a sugar component.

Agrocybenine, novel class alkaloid from the Korean mushroom Agrocybe cylindracea

Abstract A new type alkaloid agrocybenine was isolated from mushroom Agrocybe cylindracea . The structure of agrocybenine was elucidated by spectroscopic methods, especially 15 N-NMR studies using pulsed field gradient(PFG)-HMBC and HMQC techniques.