Diarylheptanoid‐flavanone Hybrids as Multiple‐target Antidiabetic Agents from Alpinia katsumadai

Antidiabetic constituents of Kaempferiae rhizoma: Previously undescribed O-linked diarylheptanoid dimers promoting GLP-1 secretion via PKA-CREB pathway

Glucagon-like peptide-1 (GLP-1) is a fascinating target for the treatment of diabetes to avoid hypoglycemia. Kaempferiae Rhizoma (KR), the dried rhizomes of Kaempferia galanga, is a famous pungent medicine used for activating Qi, warming interior, removing digestion and relieving pain in China. In order to characterize the antidiabetic effects of KR, 21 previously undescribed O-linked diarylheptanoid dimers, kaemgalangins A1-A4 (1-4), B1-B13 (5-17) and C1-C4 (18-21), were isolated from the ethyl acetate fraction. Their structures were determined by extensive spectroscopic analyses, quantum computation and chemical methods. All compounds were tested for their GLP-1 stimulating effects on NCI-H716 cells, most of which showed obvious activity representing a new type of antidiabetic constituents. Especially, compounds 1, 2 and 16 showed spectacular GLP-1 stimulation with promoting rates of 146.6 ± 31.1 %, 159.0 ± 16.6 % and 142.9 ± 2.7 %, more potent than the positive control. Mechanism study manifested that kaemgalangin A1 (1) promoted GLP-1 secretion through up-regulating the mRNA expression of Gcg and Pc1/3, and the phosphorylation of PKA and CREB, but independent on TGR5 and GPR119 receptors. Furthermore, network pharmacology analysis suggested that the GLP-1 secretion induced by 1 was closely related to MAPK and PI3K-Akt signaling pathways. This investigation first revealed that KR was rich in diarylheptanoid dimers with GLP-1 promoting effects, which provides scientific basis for the antidiabetic application of K. galanga.

Isospongian Diterpenoids from the Leaves of Amomum tsao-ko Promote GLP-1 Secretion via Ca2+/CaMKII and PKA Pathways and Inhibit DPP-4 Enzyme

Three uncommon isospongian diterpenoids including a new one, 3-epi-kravanhin A (2), were isolated from the leaves of Amomum tsao-ko. Compounds 2 and 3 dose-dependently promoted GLP-1 secretion on STC-1 cells with promotion ratios of 109.7 % and 186.1 % (60 μM). Mechanism study demonstrated that the GLP-1 stimulative effects of 2 and 3 were closely related with Ca2+/CaMKII and PKA pathways, but irrelevant to GPBAR1 and GPR119 receptors. Moreover, compound 1 showed DPP-4 inhibitory activity with an IC50 value of 311.0 μM. Molecular docking verified the binding affinity of 1 with DPP-4 by hydrogen bonds between the γ-lactone carbonyl (C-15) and Arg61 residue. Bioinformatics study indicated that compound 1 exerted antidiabetic effects by improving inflammation, oxidative stress and insulin resistance. This study first disclosed the presence of isospongian diterpenoids in A. tsao-ko, which showed antidiabetic potency by promoting GLP-1 secretion and inhibiting DPP-4 activity.

New labdane diterpenoids from Alpinia galanga: A new type of GLP-1 secretagogues targeting the PKA-CREB and PI3K-Akt signaling axes

Glucagon-like peptide-1 (GLP-1) secretagogues are fascinating pharmacotherapies to overcome the defects of GLP-1 analogs and dipeptidyl peptidase-4 (DPP-4) inhibitors in treating diabetes and obesity. To discover new GLP-1 secretagogues from natural sources, alpigalangols A-Q (1-17), 17 new labdane diterpenoids including four unusual nor-labdane and N-containing ones, were isolated from the fruits of Alpinia galanga. Most of the isolates showed GLP-1 promotive effects in NCl-H716 cells, of which compounds 3, 4, 12, and 14-17 were revealed with high promoting rates of 246.0%-413.8% at 50 µM. A mechanistic study manifested that the most effective compound 12 upregulated the mRNA expression of Gcg and Pcsk1, and the protein phosphorylation of PKA, CREB, and GSK3β, but was inactive on GPBAR and GPR119 receptors. Network pharmacology analysis indicated that the PI3K-Akt pathway was involved in the GLP-1 stimulation of 12, which was highly associated with AKT1, CASP3, PPARG, and ICAM1 proteins. This study suggests that A. galanga is rich in diverse labdane diterpenoids with GLP-1 promoting effects, representing a new type of antidiabetic candidates from natural sources.

Monoterpene-chalcone conjugates and diarylheptanoids isolated from the seeds of Alpinia katsumadai Hayata with cytotoxic activity

Five undescribed monoterpene-chalcone conjugates (1-5), one undescribed hypothetical precursor of diarylheptanoid (6), two undescribed diarylheptanoids (7-8), and fourteen known compounds (9-22) were isolated from the seeds of Alpinia katsumadai. Their structures were elucidated through the interpretation of HRESIMS, NMR, ECD, and X-ray diffraction data. MTT assays on human cancer cell lines (HepG2, A549, SGC7901, and SW480) revealed that compounds 3-8, 11, and 13 exhibited broad-spectrum antiproliferative activities with IC50 values ranging from 3.59 to 21.78 μM. B cell lymphoma 2 was predicted as the target of sumadain C (11) by network pharmacology and verified by homogeneous time-resolved fluorescence assay and molecular docking.

Sesquiterpenoids from Alpinia oxyphylla with GLP-1 Stimulative Effects through Ca2+/CaMKII and PKA Pathways and Multiple-Enzyme Inhibition

Six new sesquiterpenoids (1-6), a pair of enantiomers (7a and 7b), and six known ones (8-13) were isolated from the fruits of Alpinia oxyphylla. The structures of the new compounds were elucidated by extensive spectroscopic data and ECD calculations. The stereochemistry of 7a and 7b was reported for the first time. All compounds showed significant GLP-1 stimulation in NCI-H716 cells with promoting ratios ranging from 90.4 to 668.9% at 50 μM. Mechanism study indicated that compound 6 stimulated GLP-1 secretion mainly by regulating the transcription and the shearing process of proglucagon, while compound 13 exerted its effects through up-regulating prkaca levels. Interestingly, the GLP-1 stimulative effects of 6 and 13 were both closely related with Ca2+/CaMKII and PKA pathways but irrelevant to TGR5 and GPR119 receptors. Moreover, most compounds exhibited inhibitory activity against α-glucosidase and PTP1B at concentrations of 100 and 200 μM, while showing no activity against GPa. Compounds 3, 9, 11, and 13 could suppress α-glucosidase with IC50 values of 190.0, 204.0, 181.8, and 159.6 μM, equivalent to acarbose (IC50 = 212.0 μM). This study manifests that A. oxyphylla contains diverse sesquiterpenoids with multiple activities.

Acyclic Triterpenoids from Alpinia katsumadai Seeds with Proprotein Convertase Subtilisin/Kexin Type 9 Expression and Secretion Inhibitory Activity

Cholesterol is one of the primary causes of cardiovascular disease. Investigating and developing potential drugs to effectively treat hypercholesterolemia are therefore of critical importance. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors have been developed to lower the levels of low-density lipoprotein cholesterol in patients with hypercholesterolemia. In this study, we aimed to identify compounds that inhibit the PCSK9 mRNA expression and secretion. The bioassay-guided investigation of Alpinia katsumadai seeds utilizing a PCSK9 mRNA expression monitoring assay yielded the isolation and identification of seven new compounds. Among these were three acyclic triterpenoids (1-3), an acyclic sesquiterpenoid (5), one arylpentanoid (6), and two diarylheptanoids (7 and 8), alongside 10 known compounds. The structures of these compounds were determined using nuclear magnetic resonance (NMR) spectroscopy, vibrational circular dichroism (VCD), and electronic circular dichroism (ECD). The absolute configurations of compounds 1 and 2 were identified by comparing the calculated and experimental VCD data as the ECD method was unable to distinguish the diastereomers. All the isolated compounds were evaluated for their regulatory effects on the low-density lipoprotein receptor (LDLR) and PCSK9 mRNA expression, as well as PCSK9 secretion. Of the tested compounds, two of the acyclic triterpenoids (1 and 2) demonstrated potent effects in downregulating PCSK9 at both the mRNA and protein levels, compared with the positive control (berberine chloride). Additionally, compound 1 inhibited PCSK9 secretion to a level comparable to that of berberine chloride. This study identifies compounds that inhibit PCSK9 mRNA expression and secretion, offering significant contributions to the development of novel drugs for the effective treatment of hypercholesterolemia..

Semisynthesis, biological activities, and mechanism studies of Mannich base analogues of magnolol/honokiol as potential α-glucosidase inhibitors

Magnolol and honokiol, derived from a Magnolia officinalis Rehd. et Wils, are a class of natural biphenolic lignans. Currently, the discovery of new α-glucosidase inhibitors from natural analogues is of interest. Here, four series of thirty new Mannich base analogues of magnolol/honokiol were prepared and evaluated for their α-glucosidase inhibitory activities. Among these Mannich base analogues of magnolol/honokiol, 3k and 3l exhibited more potent inhibitory effects on α-glucosidase than the reference drug acarbose, and their IC50 values were 14.94 ± 0.17 µM and 13.78 ± 1.42 µM, respectively. Some interesting structure-activity relationships (SARs) were also analyzed. The enzyme inhibition kinetics indicated that 3k and 3l were noncompetitive inhibitors. This result was in agreement with molecular docking studies, where the binding sites of 3k and 3l to α-glucosidase were different from that of the competitive inhibitor acarbose to α-glucosidase. Moverover, compounds 3k and 3l exhibited low toxicity to normal cells (LO2). Thus, analogues 3k and 3l could be deeply developed for the discovery of natural products based antidiabetic candidates.

Norlignans as potent GLP-1 secretagogues from the fruits of Amomum villosum

The dried fruit of Amomum villosum (Amomi Fructus) is an important spices and traditional Chinese medicine. In this study, the EtOH extract of Amomi Fructus was revealed with hypoglycemic effects on db/db mice by increasing plasma insulin levels. After extracted with EtOAc, the EtOAc fraction showed increased activity in stimulating glucagon-like peptide-1 (GLP-1) secretion compared with the EtOH extract. In order to clarify the antidiabetic constituents, four undescribed norlignans, amovillosumins A‒D, were isolated from the EtOAc fraction, and the subsequent chiral resolution yielded three pairs of enantiomers. Their structures were determined by extensive spectroscopic data (1D and 2D NMR, HRESIMS, IR, UV and [α]_D) and ECD calculations. Amovillosumins A and B significantly stimulated GLP-1 secretion by 375.1% and 222.7% at 25.0 μM, and 166.9% and 62.7% at 12.5 μM, representing a new type of GLP-1 secretagogues.

New ent-kaurane diterpenoid acids from Nouelia insignis Franch and their anti-inflammatory activity

Eleven undescribed ent-kaurane-type diterpenoid acids, namely noueinsiancins A–K (1–11), together with sixteen related known analogs (12–27) were isolated from Nouelia insignis Franch. The chemical structures and absolute configurations of the new compounds were confirmed by the extensive spectroscopic data, electronic circular dichroism (ECD) data analysis and single crystal X-ray diffraction. Additionally, the anti-inflammatory assay was applied to estimate the nitric oxide (NO) inhibitory activities of all compounds by using lipopolysaccharide (LPS)-induced RAW 264.7 cells in vitro. The results revealed that 4–7 and 13–17 significantly inhibited NO production at the concentrations of 2.5 μM, 5.0 μM and 10.0 μM. Meanwhile, compounds 6 and 7 were found to down-regulate the protein expression levels of IL-6 and TNF-α in RAW 264.7 cells induced by LPS in a dose-dependent manner. In conclusion, these findings provided the reference values for exploring the new chemicals with biological activities from this genus.

Eleven undescribed ent-kaurane-type diterpenoid acids, namely noueinsiancins A–K (1–11), together with sixteen related known analogs (12–27) were isolated from Nouelia insignis Franch.

Synthesis and biological evaluation of (20S,24R)-epoxy-dammarane-3β,12β,25-triol derivatives as α-glucosidase and PTP1B inhibitors

The dammarane triterpenoid (20S,24R)-epoxy-dammarane-3β,12β,25-triol obtained from Cyclocarya paliurus in our previous study showed inhibitory activity on α-glucosidase in vitro with an inhibitory ratio of 32.2% at the concentration of 200 μM. In order to reveal the structure-activity relationships (SARs) and get more active compounds, 42 derivatives of (20S,24R)-epoxy-dammarane-3β,12β,25-triol were synthesized by chemical modification on the hydroxyls (C-3 and C-12), rings A and E, and assayed for their α-glucosidase and PTP1B inhibitory activities. Two compounds (8, 26) increased activity against α-glucosidase, and four compounds (8, 15, 26, 42) significantly inhibited PTP1B. It was noted that compounds 8 and 26 could inhibit both α-glucosidase and PTP1B as dual-target inhibitors with IC₅₀ values of 489.8, 467.7 μM (α-glucosidase) and 319.7, 269.1 μM (PTP1B). Compound 26 was revealed to be a mix-type inhibitor on α-glucosidase and a noncompetitive-type inhibitor on PTP1B based on enzyme kinetic study. Furthermore, compound 42 could selectively inhibited PTP1B as a mix-type inhibitor with IC₅₀ value of 134.9 μM, which was 2.5-fold higher than the positive control, suramin sodium (IC₅₀ 339.0 μM), but not inhibit α-glucosidase.

Six New 3,5-Dimethylcoumarins from Chelonopsis praecox, Chelonopsis odontochila and Chelonopsis pseudobracteata

Ten 3,5-dimethylcoumarins (1-6 and 8‒11) involving six new ones (1-6), together with a known 3-methylcoumarin (7), were isolated from the aerial parts of three Chelonopsis plants, C. praecox, C. odontochila, and C. pseudobracteata. The structures of the new compounds were determined by extensive HRESIMS, 1D and 2D NMR spectroscopic analyses. According to the substitution at C-5, these coumarins were classified into 5-methyl, 5-hydroxymethyl, 5-formyl, and 5-nor types. All the isolates were assayed for their inhibition on α-glucosidase, protein tyrosine phosphatase 1B, and T-cell protein tyrosine phosphatase in vitro.