Melastoma malabathricum L. Suppresses Neutrophil Extracellular Trap Formation Induced by Synthetic Analog of Viral Double-Stranded RNA Associated with SARS-CoV-2 Infection.

Platelet hyper-reactivity and neutrophil extracellular trap (NET) formation contribute to the development of thromboembolic diseases for patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This study investigated the pathophysiological effects of SARS-CoV-2 surface protein components and the viral double-stranded RNA (dsRNA) on platelet aggregation and NET formation. Traditional Chinese medicine (TCM) with anti-viral effects was also delineated. The treatment of human washed platelets with SARS-CoV-2 spike protein S1 or the ectodomain S1 + S2 regions neither caused platelet aggregation nor enhanced agonists-stimulated platelet aggregation. Moreover, NET formation can be induced by polyinosinic-polycytidylic acid (poly(I:C)), a synthetic analog of viral dsRNA, but not by the pseudovirus composed of SARS-CoV-2 spike, envelope, and membrane proteins. To search for TCM with anti-NET activity, the plant Melastoma malabathricum L. which has anticoagulant activity was partially purified by fractionation. One of the fractions inhibited poly(I:C)-induced NET formation in a dose-dependent manner. This study implicates that SARS-CoV-2 structural proteins alone are not sufficient to promote NET and platelet activation. Instead, dsRNA formed during viral replication stimulates NET formation. This study also sheds new insight into using the active components of Melastoma malabathricum L. with anti-NET activity in the battle of thromboembolic diseases associated with SARS-CoV-2 infection.

Polysaccharide-containing fraction from Artemisia argyi inhibits tumor cell-induced platelet aggregation by blocking interaction of podoplanin with C-type lectin-like receptor 2.

Tumor cell-induced platelet aggregation (TCIPA) is a mechanism that involves the protection of tumor cells in the circulation and the promotion of tumor cell invasion and metastases. The C-type lectin-like receptor 2 (CLEC-2) that binds podoplanin (PDPN) is on the platelet surface and facilitates the TCIPA. Selective blockage of the PDPN-mediated platelet-tumor cell interaction is thereby a plausible strategy for inhibiting metastases. In a search for antagonists of PDPN- and tumor cell-induced platelet aggregation, traditional Chinese medicines were screened and it was found that the water extract of Artemisia argyi leaves selectively inhibited the PDPN-induced platelet aggregation. Bioactivity-guided fractionation analysis was performed for defining a polysaccharide-containing fraction (AAWAP) characterized by inhibition of PDPN activity and tumor cell-induced platelet aggregation. The pharmacological effects of AAWAP on PDPN-activated CLEC-2 signaling were determined by using Western blot and alpha screening analyses. AAWAP was non-toxic to the cells and platelets and it suppressed PDPN- and tumor cell-induced platelet aggregation by irreversibly blocking the interaction between PDPN and CLEC-2 in a dose-dependent manner. These findings indicate that AAWAP is an antagonist of the PDPN-CLEC-2 interaction. This action by AAWAP may result in the prevention of tumor cell metastases, and if so, could become an effective pharmacological agent in treating cancer patients.

Four New 2-(2-Phenylethyl)-4H-chromen-4-one Derivatives from the Resinous Wood of Aquilaria sinensis and Their Inhibitory Activities on Neutrophil Pro-Inflammatory Responses.

Four new 2-(2-phenylethyl)-4H-chromen-4-one derivatives, 6-hydroxy-5-methoxy-2-[2-(4'-methoxyphenyl)ethyl]chromone (1: ), 6,7-dimethoxy-2-[2-(2'-hydroxyphenyl)ethyl]chromone (2: ), 5-hydroxy-6-methoxy-2-[2-(3'-methoxyphenyl)ethyl]-chromone (3: ), and 7-chloro-8-hydroxy-2-[2-(4'-methoxyphenyl)ethyl]chromone (4: ), have been isolated from the resinous wood of Aquilaria sinensis, together with 16 known compounds (5: -20: ). Among these, 7-methoxy-2-[2-(4'-methoxyphenyl)ethyl]chromone (5: ) was isolated from a natural source for the first time. The structures of the new compounds were established by spectroscopic analyses (1D and 2D NMR, HR-ESI-MS, IR, UV). Nine compounds, including 1: showed more than 80% inhibition of superoxide anion generation by human neutrophils in response to formyl-L-methionyl-L-leucyl-L-phenylalanine at 50 µM.

Naphthofuranone derivatives and other constituents from Pachira aquatica with inhibitory activity on superoxide anion generation by neutrophils.

Two new naphthofuranone derivatives, 11-hydroxy-2-O-methylhibiscolactone A (1) and O-methylhibiscone D (2), have been isolated from the stems of Pachira aquatica, together with 18 known compounds (3-20). The structures of two new compounds were determined through spectroscopic and MS analyses. Among the isolated compounds, 11-hydroxy-2-O-methylhibiscolactone A (1), isohemigossylic acid lactone-7-methyl ether (4), gmelofuran (6), and 5-hydroxyauranetin (8) exhibited inhibition (IC50≤28.84µM) of superoxide anion generation by human neutrophils in response to N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP).

New Sesquiterpenoids and Anti-Platelet Aggregation Constituents from the Rhizomes of Curcuma zedoaria.

Two new sesquiterpenoids-13-hydroxycurzerenone (1) and 1-oxocurzerenone (2)-have been isolated from the rhizomes of Curcuma zedoaria, together with 13 known compounds (3-15). The structures of two new compounds were determined through spectroscopic and MS analyses. Among the isolated compounds, 13-hydroxycurzerenone (1), 1-oxocurzerenone (2), curzerenone (3), germacrone (4), curcolone (5), procurcumenol (6), ermanin (7), curcumin (8), and a mixture of stigmast-4-en-3,6-dione (12) and stigmasta-4,22-dien-3,6-dione (13) exhibited inhibition (with inhibition % in the range of 21.28%-67.58%) against collagen-induced platelet aggregation at 100 µM. Compounds 1, 5, 7, 8, and the mixture of 12 and 13 inhibited arachidonic acid (AA)-induced platelet aggregation at 100 µM with inhibition % in the range of 23.44%-95.36%.

Limonoids from the Seeds of Swietenia macrophylla and Their Anti-Inflammatory Activities.

A new limonoid, swietemacrophin (1), was isolated from the seeds of Swietenia macrophylla, together with five known compounds 2-6. The structure of 1 was determined through extensive 1D/2D-NMR and mass-spectrometric analyses. Swietemacrophin (1), humilinolide F (2), 3,6-O,O-diacetylswietenolide (3), 3-O-tigloylswietenolide (4), and swietemahonin E (5) exhibited inhibition (IC50 values≤45.44 µM) of superoxide anion generation by human neutrophils in response to formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP). Compounds 1, 4, 5, and swietenine (6) showed potent inhibition with IC50 values≤36.32 µM, against lipopolysaccharide (LPS)-induced nitric oxide (NO) generation.

New pterosin sesquiterpenes and antitubercular constituents from Pteris ensiformis.

Two new pterosin sesquiterpenes, (2S)-13-hydroxypterosin A (1) and (2S,3S)-12-hydroxypterosin Q (2), were isolated from the whole plants of Pteris ensiformis, together with six known compounds. The structures of 1 and 2 were determined through extensive 1D/2D-NMR and MS analyses. Compound 2 exhibited antitubercular activity (MIC 6.25 µg/ml) against Mycobacterium tuberculosis H37 Rv in vitro.