Antibacterial and NF-κB Inhibitory Lumazine Peptides, Aspochalasin, γ-Butyrolactone Derivatives, and Cyclic Peptides from a Hawaiian Aspergillus flavipes

Biosynthesis of the fungal nonribosomal peptide penilumamide A and biochemical characterization of a pterin-specific adenylation domain

We report the characterization of the penilumamide biosynthetic cluster from Aspergillus flavipes CNL-338. In vitro reconstitution experiments demonstrated that three nonribosomal peptide synthetases are required for constructing the tripeptide and studies with dissected adenylation domains allowed for the first biochemical characterization of a domain that selects a pterin-derived building block.

Butyrolactone I attenuates inflammation in murine NASH by inhibiting the NF-κB signaling pathway

Nonalcoholic steatohepatitis (NASH) is the development of non-alcoholic fatty liver disease (NAFLD) and a key element in the exacerbation of NAFLD. Since there are currently no drugs approved by the U.S. Food and Drug Administration to treat this disease, the search for treatments that can be translated into clinical use is urgent. Butyrolactone I (BLI), isolated from Aspergillus terreus, is an active compound possessing multiple biological activities. However, the effects of BLI on NASH have never been reported. In this study, RAW264.7 cells stimulated by lipopolysaccharide (LPS) were applied to study the anti-inflammatory effect and the underlying mechanisms of BLI in vitro. Following this, mice fed with high-fat and -fructose diet (HFFD) were used to explore the alleviation of NASH by BLIin vivo. We found that BLI attenuated inflammation in LPS-induced RAW264.7 cells by inhibiting the NF-κB signaling pathway and downregulating the expression of iNOS and COX-2. Moreover, results of experiments in vivo demonstrated that BLI reduced serum transaminase levels, decreased hepatic fat accumulation, inhibited inflammation, suppressed oxidative stress, and ameliorated liver fibrosis. For the first time, we investigated the role of BLI in the treatment of murine NASH. We found that BLI alleviates NASH partly by inhibiting the NF-κB pathway of signaling. Given its hepatoprotective effects and non-toxic properties, BLI can be a novel and effective drug for NASH patients.

Polyketides, diketopiperazines and an isochromanone from the marine-derived fungal strain Fusarium graminearum FM1010 from Hawaii

The fungal strain Fusarium graminearum FM1010 was isolated from a shallow-water volcanic rock known as "live rock" at the Richardson's Beach, Hilo, Hawaii. Eleven specialised metabolites, including two undescribed diketopiperazines, three undescribed polyketides, and one undescribed isochromanone, along with five known fusarielin derivatives were obtained from F. graminearum FM1010. The structures of the six undescribed compounds were elucidated by extensive analysis of NMR spectroscopy, HRESIMS, chemical reactions, and electronic circular dichroism (ECD) data. Kaneoheoic acids G-I showed mild inhibitory activity against S. aureus with the MIC values in the range of 20-40 μg/mL when assayed in combination with chloramphenicol (half of the MIC, 1 μg/mL), an FDA approved antibiotic. Kaneoheoic acid I exhibited both anti-proliferative activity against ovarian cancer cell line A2780 and TNF-α induced NF-κB inhibitory activity with the IC₅₀ values of 18.52 and 15.86 μM, respectively.

New and bioactive polyketides from Hawaiian marine-derived fungus Trichoderma sp. FM652

Two new sorbicillinoid derivatives (1 and 2), together with ten other related compounds (3-12) were isolated from a Hawaiian marine fungal strain Trichoderma sp. FM652. The structures of compounds 1 and 2, including the absolute configuration, were elucidated by extensive analysis of NMR spectroscopy, HRESIMS and electronic circular dichroism (ECD) data. Compounds 6-12 exhibited significant anti-proliferative activity against ovarian cancer cell line A2780, with the IC₅₀ values ranging from 0.5 to 8.07 μM. Moreover, compounds 1, 7 and 8 showed significant inhibition against NF-κB with IC₅₀ values of 13.83, 24.40 and 14.63 µM, respectively. Compounds 6, 9 and 12 also demonstrated moderate inhibitory activity against S. aureus and methicillin resistant S. aureus with the MIC values in the range of 10-40 μg/mL.

A validated high-throughput method for assaying rat lungworm (Angiostrongylus cantonensis) motility when challenged with potentially anthelmintic natural products from Hawaiian fungi

Parasitic nematodes devastate human and animal health. The limited number of anthelmintics available is concerning, especially because of increasing drug resistance. Anthelmintics are commonly derived from natural products, e.g. fungi and plants. This investigation aimed to develop a high-throughput whole organism screening method based on a motility assay using the wMicroTracker system. Anthelmintic activity of extracts from Hawaiian fungi was screened against third-stage larvae of the parasitic nematode Angiostrongylus cantonensis , categorized according to the degree of motility reduction. Of the 108 crude samples and fractionated products, 48 showed some level of activity, with 13 reducing motility to 0–25% of the maximum exhibited, including two pure compounds, emethacin B and epicoccin E, neither previously known to exhibit anthelmintic properties. The process of bioassay-guided fractionation is illustrated in detail based on analysis of one of the crude extracts, which led to isolation of lamellicolic anhydride, a compound with moderate activity. This study validates the wMicroTracker system as an economical and high-throughput option for testing large suites of natural products against A. cantonensis , adds to the short list of diverse parasites for which it has been validated and highlights the value of A. cantonensis and Hawaiian fungi for discovery of new anthelmintics.

Isolation and characterisation of antibacterial and anti-inflammatory compounds from Gnaphalium polycaulon

ETHNO-PHARMACOLOGICAL RELEVANCE

Gnaphalium polycaulon commonly known as "cudweed" has been used throughout South America as an infusion to treat colds, bronchitis, fever or pneumonia.

AIM OF THE STUDY

This study aimed to determine the antibacterial and anti-inflammatory activities of the aqueous extract of Gnaphalium polycaulon and identify the related compounds.

MATERIALS AND METHODS

A bio-guided isolation of the active compounds of Gnaphalium polycaulon was carried out, selecting the fractions depending on their antibacterial, anti-inflammatory and cytotoxic activities. The antibacterial effect was studied against Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus and Streptococcus pneumoniae; and the anti-inflammatory study was performed by measuring the inhibition of NF-κB in BEAS-2B and IMR-90 cell cultures.

RESULTS

Three compounds were obtained and characterised by nuclear magnetic resonance and mass spectrometry. These compounds are 2-(4-(1-H-tetrazol-1-yl) phenyl)-2-aminopropanoic acid (1), N-phenyl-4-(3-phenyl-1,2,4-thiadiazol-5-yl) piperazine-1-carboxamide (2) and N-(4-ethoxyphenyl)-4-(2-methylimidazo-[1,2-α] pyridine-3-yl) thiazol-2-amine (3). All compounds showed antibacterial activity with MIC values of 44.80-44.85, 0.017-0.021 and 0.0077-0.0079 μM, respectively, in the Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus and Streptococcus pneumoniae strains, while the positive control, Ofloxacin, had a MIC value of 27.64-27.67 μM. This was corroborated through a zone inhibition assay, where compound 3 (11.36-11.67 mm) was much more active than the positive control (Ofloxacin, 23.41-24.12 mm), while compounds 2 (26.47-27.64 mm) and 1 (28.39-29.76 mm) displayed similar antibacterial potential to the positive control. Finally, all the compounds presented NF-κB inhibitory activity, compounds 3 (IC₅₀ = 0.0071-0.0073 μM) and 2 (IC₅₀ = 0.016-0.019 μM) being the most promising. Compound 1 (IC₅₀ = 44.24-44.26 μM) had less anti-inflammatory potential, being also the closest to the values displayed by the positive control (Celastrol, IC₅₀ = 7.41 μM).

CONCLUSION

In the present study, three compounds were isolated for the first time from the aqueous extract of Gnaphalium polycaulon. Their antibacterial and anti-inflammatory potential was tested and showcased.

NF-κB inhibitory, antimicrobial and antiproliferative potentials of compounds from Hawaiian fungus Aspergillus polyporicola FS910

Bioassay-guided experimental design and chromatographic analysis led to the isolation and identification of ten compounds (1-10) including two unusual sulfur-containing curvularin macrolides (1 and 2) from a Hawaiian fungal strain Aspergillus polyporicola FS910. Compounds 1 and 2 are rare curvularin macrolides each with a five-membered cyclic sulfur-containing moiety. The structures of the compounds were identified by HRESIMS, NMR spectroscopy, X-ray crystallography, ECD and DFT energy calculation, as well as comparing with previous literatures. Compounds 4, 6 and 8 were active against TNF-α-induced NF-κB inhibitory activity with IC₅₀ values of 26.45, 5.41 and 15.8 µM, respectively. Compounds 3 and 5-8 exhibited anti-proliferative activity against HT1080, T46D, and A2780S cell lines, with IC₅₀ values ranging from 2.48 to 29.17 μM. Additionally, Compound 3 showed promising antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis, Escherichia coli and Candida albicans. Moreover, when tested in combination with antibiotic adjuvant disulfiram [4 µg/mL], compounds 4, 5 and 10 also displayed significant antibacterial activity against S. aureus.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02877-7.

Aspochalasin H1: A New Cyclic Aspochalasin from Hawaiian Plant-Associated Endophytic Fungus Aspergillus sp. FT1307

Aspergillus is one of the most diverse genera, and it is chemically profound and known to produce many biologically active secondary metabolites. In the present study, a new aspochalasin H1 (1), together with nine known compounds (2-10), were isolated from a Hawaiian plant-associated endophytic fungus Aspergillus sp. FT1307. The structures were elucidated using nuclear magnetic resonance (NMR) (1H, 1H-1H COSY, HSQC, HMBC, ROESY and 1D NOE), high-resolution electrospray ionization mass spectroscopy (HRESIMS), and comparisons with the reported literature. The absolute configuration of the new compound was established by electronic circular dichroism (ECD) in combination with NMR calculations. The new compound contains an epoxide moiety and an adjacent trans-diol, which has not been reported before in the aspochalasin family. The antibacterial screening of the isolated compounds was carried out against pathogenic bacteria (Staphylococcus aureus, Methicillin-resistant S. aureus and Bacillus subtilis). The antiproliferative activity of compounds 1-10 was evaluated against human breast cancer cell lines (MCF-7 and T46D) and ovarian cancer cell lines (A2780).

Asperflaloids A and B from Aspergillus flavipes DZ-3, an Endophytic Fungus of Eucommia ulmoides Oliver

The fungus strain DZ-3 was isolated from twigs of the well-known medicinal plant Eucommia ulmoides Oliver and identified as Aspergillus flavipes. Two new alkaloids, named asperflaloids A and B (1 and 2), together with 10 known compounds (3-12) were obtained from the EtOAc extract of the strain. Interestingly, the alkaloids 1-4 with different frameworks are characterized by the presence of the same anthranilic acid residue. The structures were established by detailed analyses of the spectroscopic data. The absolute configuration of asperflaloids A and B was resolved by quantum chemistry calculation. All compounds were screened for their inhibitions against α-glucosidase and the antioxidant capacities. The results were that compound 3 had an IC50 value of 750.8 μM toward α-glucosidase, and the phenol compounds 7 and 8 exhibited potent antioxidant capacities with IC50 values 14.4 and 27.1 μM respectively.

Prenylated phenylbutyrolactones from cultures of a marine sponge-associated fungus Aspergillus flavipes KUFA1152

Four undescribed prenylated phenylbutyrolactones, aspulvinones R, S, T and U, were isolated together with the previously reported aspulvinones A, B', H and 4-hydroxy-3,5-bis(3-methylbut-2-en-1-yl)benzaldehyde, from cultures of the marine sponge-derived fungus Aspergillus flavipes KUFA1152. The structures of the undescribed compounds were established on the basis of extensive analysis of 1D and 2D NMR and HRMS spectra. In the case of aspulvinone T, the absolute configuration of its stereogenic carbon was established by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. The structure of the previously reported compounds were elucidated by 1D and 2D NMR analysis as well as comparison of their ¹H or/and ¹³C NMR data with those reported in the literature. Aspulvinones B', H, R, S, T and a mixture of aspulvinones A and U exhibited antibacterial activity against reference strains and multidrug-resistant isolates from the environment as well as capacity to inhibit biofilm formation in the reference strains. However, none of the tested compounds showed potential synergy with clinically relevant antibiotics on multidrug-resistant isolates.

Secondary Metabolites from the Leather Coral-Derived Fungal Strain Xylaria sp. FM1005 and Their Glycoprotein IIb/IIIa Inhibitory Activity

Five new tyrosine derivatives (1-5), one new phenylacetic acid derivative (6), two new quinazolinone analogues (7 and 8), one new naphthalenedicarboxylic acid (9), and one new 3,4-dihydroisocoumarin derivative (10), together with seven known compounds, were isolated from the fungus Xylaria sp. FM1005, which was isolated from Sinularia densa (leather coral) collected in the offshore region of the Big Island, Hawaii. The structures of compounds 1-10 were elucidated by extensive analysis of NMR spectroscopy, HRESIMS, and ECD data. Due to their structure similarity to the antiplatelet drug tirofiban, compounds 1-5 together with 6 were investigated for their antithrombotic activities. Compounds 1 and 2 strongly inhibited the binding of fibrinogen to purified integrin IIIb/IIa in a dose-dependent manner with the IC50 values of 0.89 and 0.61 μM, respectively, and compounds 1 and 2 did not show any cytotoxicity against A2780 and HEK 293 at 40 μM.

Antibacterial kaneoheoic acids A-F from a Hawaiian fungus Fusarium sp. FM701

Alarming rate of resistance to the existing antibiotics exhibits the importance of developing new antibiotic molecules from relatively under explored sources as well as implementing alternative approaches like antibiotic adjuvants. Six previously undescribed fungal polyketides, kaneoheoic acids A-F (1-6) were isolated from a fungal strain Fusarium sp. FM701 which was collected from a muddy sample of Hawaiian beach. The structures of these six compounds were elucidated by spectroscopic interpretation, including HRESIMS and NMR, and electronic circular dichroism (ECD) analysis. All six compounds that were inactive when tested alone showed significant antibacterial activity against Staphylococcus aureus and Bacillus subtilis, in the range of 10-80 μg/mL when assayed in combination with either chloramphenicol (half of the MIC, 1 μg/mL), an FDA approved antibiotic or disulfiram (6 μg/mL), an established antibiotic adjuvant that augmented the activity of antibiotics.