Potential anti-hepatocellular carcinoma properties and mechanisms of action of clerodane diterpenes isolated from Polyalthia longifolia seeds.

Diterpenes are secondary metabolites that have attracted much attention due to their potential biological activities including anti-cancer potential. The aim of the current study is to assess the anticancer potential of the six known clerodane diterpenes (1-6) isolated from Polyalthia longifolia seeds and their underlying molecular mechanisms. These compounds were evaluated for their cytotoxicity in vitro by using MTT assays. The "two-phase model" with NDEA and PB ad libitum was used for induction of HCC and sorafenib was used as the standard drug. Prophylactic studies were carried out for compounds 4/6 at both low (5 mg/kg b.w) and high (10 mg/kg b.w) doses. Based on the MTT assay results, the two best compounds, 4 and 6, were selected for in vivo studies. The results showed that treatment with compound 4/6 significantly restored the changes in biochemical parameters and liver morphology observed in (NDEA + PB)-induced HCC rats. Additionally, the docking studies showed that compound 4/6 interacted with several key proteins such as MDM2, TNF-α, FAK, thereby inhibiting these proteins and reversing the negative impacts of NDEA. In conclusion, our results suggested that compounds 4 and 6 are potential therapeutic agents for HCC, mostly due to their ability to control typical cancer pathways.

Anti-proliferative Activity of Labdane Diterpenes Isolated from Polyalthia cerasoides and their Molecular Interaction Studies.

BACKGROUND: Polyalthia cerasoides is well known for its therapeutic effects and is extensively used by the tribal people of South India and Africa to treat infertility, toothache, inflammation, rheumatism, fever, and to combat stress. OBJECTIVE: In the present research, the anti-proliferative potential of two bioactive compounds isolated from the stem bark of P. cerasoides (Roxb.) Bedd. of the Annonaceae family was investigated. METHODS: The dried stem bark was powdered and subjected to extraction using methanol and further partitioned using petroleum ether. Yellow viscous oil was isolated from the petroleum ether fraction using column and preparative thin-layer chromatography. The chromatographic fractions were characterized using GC-MS. The anti-proliferative effect of the isolated compounds was assessed against HepG2 Cells using MTT- Cytotoxicity test. Furthermore, comparative in-silico docking studies were performed to predict the binding pattern of isolated molecules individually, as well as simultaneously with α, ß-tubulin, a critical protein involved in the molecular mechanism of microtubule formation. RESULTS: GC-MS analysis of yellow viscous oil from petroleum fraction confirmed the presence of two labdane diterpenes that were identified as 12E-3,4-Seco-labda-4(18),8(17),12,14-tetraen-3-oic acid, and methyl harvadate C by mass fragmentation analysis. The MTT-cytotoxicity assay showed the dose-dependent cytotoxic effect on HepG2 Cells. The comparative docking studies of the isolated compounds exhibited strong interactions with the α, ß-tubulin protein. CONCLUSION: The prominent anti-proliferative effect exhibited by the isolated compounds, along with effective binding to α, ß-tubulin protein, encourages their future utilization as prominent anti-cancer molecules.

In vitro antiaging activity of polyphenol rich Polyalthia longifolia (Annonaceae) leaf extract in Saccharomyces cerevisiae BY611 yeast cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Polyalthia longifolia var. angustifolia Thw. (Annonaceae) is commonly used in traditional medicine as a tonic for rejuvenation and exhibiting good antioxidant activities. AIM OF THE STUDY: To evaluate P. longifolia methanolic leaf extract (PLME) antiaging activity at 1 mg/mL in Saccharomyces cerevisiae BY611 yeast. MATERIALS AND METHODS: The antiaging effect of PLME was studied via replicative lifespan assay, antioxidative stress assays, reactive oxygen species (ROS) determination, reduced glutathione (GSH) determination, superoxide dismutase (SOD) and Sirtuin 1 (SIRT1) genes regulation studies and SOD and SIRT1 proteins activities. RESULTS: The PLME treatment increased the growth and prolonged the lifespan of the yeast significantly (p < 0.05) compared to the untreated yeast group. Besides, the PLME also protected the yeast from oxidative stress induced by 4-mM-H2O2 via decreasing (p < 0.05) the ROS from 143.207 to 127.223. The antioxidative action of PLME was proved by spot assay. Phloxine B staining was further confirmed the PLME antioxidative action of PLME, where more whitish-pink live yeast cells were observed. In addition, the PLME also enhanced GSH content significantly (p < 0.05) in yeast treated with PLME from 16.81 to 25.31 µmol. Furthermore, PLME increased the SOD and SIRT1 genes expression significantly (p < 0.05) with ΔCt values of 1.11 and 1.15, respectively. The significantly (p < 0.05) elevated SOD and SIRT1 protein activities were recorded as 51.54 U/mg Prot and 1716 ng/mL, respectively. CONCLUSIONS: PLME exhibited good antiaging activities in S. cerevisiae, by modulating oxidative stress, enhancing GSH content, and increasing SOD and SIRT1 genes expression.

Phytoconstituents and renoprotective effect of Polyalthia longifolia leaves extract on radiation-induced nephritis in rats via TGF-ß/smad pathway.

Renoprotectors are highly demanded due to environmental nephrotoxic factors. P. longifolia leaves extract alleviating effect was assessed in nephritic-induced rats by whole body shot dose of γ-radiation. Many biomarkers were detected using several assays. Renohistopathological examinations were performed. Moreover, the extract phytoconstituents were identified using spectroscopic analysis. In-vitro anti-inflammatory activity of some compounds was examined using histamine release assay. Post-irradiation treatment with the extract significantly ameliorated all elevated biomarker levels. Creatinine and urea were adjusted, TGF-ß/Smad signaling was suppressed causing down-regulation to microRNA-21. Nitric oxide, reactive oxygen species, glutathione and kidney injury molecule-1 were normalized in comparison with the γ-irradiated group. The renohistopathological analysis was consistent with the biochemical study. Phytochemical analysis resulted in the isolation of two diterpenoids (γ-methoxybutenolide clerodane diterpene and 16(R/S)-hydroxycleroda-3,13-dien-16,15-olide-2-one), aporphine alkaloid (anonaine) and flavonol (kaempferol-3-O-rutinoside). The latter two showed moderate anti-histaminic activities. Our results indicated that P. longifolia reduced oxidative stress and nephropathy in rats due to its anti-inflammatory principles.

Antiproliferative, apoptotic, and antimutagenic properties of stem bark and seed fractions of Polyalthia cerasoides (Roxb.).

AIMS: The aim was to compare the anticancer and antimutagenic potency of Polyalthia cerasoides seeds and stem bark. AIM OF THE STUDY: The aim of this study was to investigate the antiproliferative, apoptotic, antioxidation to DNA, and antimutagenic activity of alcoholic (PS-1 and PS-3) and petroleum ether (PS-2 and PS-4) stem bark and seed fractions of P. cerasoides. METHODS: P. cerasoides stem bark and seeds were extracted with ethanol: water mixture (9:1 ratio v: v) and fractionated with petroleum ether. Fractions were investigated for antiproliferative effect using cell by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, a tetrazole assay (cell line used liver [HepG2] and cervical [HeLa] cancer cell lines), DNA damage protection using hydroxyl radical and antimutagenic effect using chromosome aberration test. RESULTS: PS-1 (IC50 10 µg/ml) and PS-3 (IC50 11 µg/ml) showed maximum antiproliferative activity against HepG2 cell lines, whereas, PS-1 (IC50 10 µg/ml), PS-2 (IC50 24 µg/ml), and PS-3 (IC50 11 µg/ml) showed better antiproliferative activity against HeLa cell lines. PS-3 and PS-4 were protective against oxidation to the supercoiled DNA molecule. Further, petroleum ether extract of both seed (PS-2) and stem bark (PS-4) showed good antimutagenicity as revealed by the less chromosomal aberrations compared to PS-1 and PS-3 fractions. CONCLUSIONS: This study demonstrated the beneficial effect of fractions against oxidation of DNA, antiproliferative, apoptotic, and antimutagenic activity. Probably, this property would be attributable by their phenolic and steroid constituents. Therefore, this plant could be used as a potential source of nutraceutical agents.

Phytochemicals from Polyalthia Species: Potential and Implication on Anti-Oxidant, Anti-Inflammatory, Anti-Cancer, and Chemoprevention Activities.

Polyalthia belong to the Annonaceae family and are a type of evergreen tree distributed across many tropical and subtropical regions. Polyalthia species have been used long term as indigenous medicine to treat certain diseases, including fever, diabetes, infection, digestive disease, etc. Recent studies have demonstrated that not only crude extracts but also the isolated pure compounds exhibit various pharmacological activities, such as anti-oxidant, anti-microbial, anti-tumor, anti-cancer, etc. It is known that the initiation of cancer usually takes several years and is related to unhealthy lifestyle, as well as dietary and environmental factors, such as stress, toxins and smoking. In fact, natural or synthetic substances have been used as cancer chemoprevention to delay, impede, or even stop cancer growing. This review is an attempt to collect current available phytochemicals from Polyalthia species, which exhibit anti-cancer potentials for chemoprevention purposes, providing directions for further research on the interesting agents and possible clinical applications.

Cleroda-4(18),13-dien-15,16-olide as novel xanthine oxidase inhibitors: An integrated in silico and in vitro study.

In the present study, in silico predictions and molecular docking were performed on five clerodane diterpenes (1-5) from Polyalthia longifolia seeds to evaluate their potential as xanthine oxidase (XO) inhibitors. The initial screening was conducted by target prediction using TargetNet web server application and only compounds 3 and 4 showed a potential interaction with XO. Compounds 3 and 4 were subsequently subjected to in silico analyses on XO protein structure (PDB: 1N5X) using Schrödinger Release 2020-3 followed by structural modeling & molecular simulation studies to confirm the initial prediction result and identify the binding mode of these compounds to the XO. Molecular docking results revealed that compounds 3 (-37.3 kcal/mol) and 4 (-32.0 kcal/mol) binds more stably to XO than the reference drug allopurinol (-27.0 kcal/mol). Interestingly, two residues Glu 802 and Thr 1010 were observed as the two main H-bond binding sites for both tested compounds and the allopurinol. The center scaffold of allopurinol was positioned by some π-π stacking with Phe 914 and Phe 1009, while that of compounds 3 and 4 were supported by many hydrophobic interactions mainly with Leu 648, Phe 649, Phe 1013, and Leu 1014. Additionally, the docking simulation predicted that the inhibitory effect of compounds 3 and 4 was mediated by creating H-bond with particularly Glu 802, which is a key amino acid for XO enzyme inhibition. Altogether, in vitro studies showed that compounds 3 and 4 had better inhibitory capacity against XO enzyme with IC50 values significantly (p < 0.001) lower than that of allopurinol. In short, the present study identified cleroda-4(18),13-dien-15,16-olide as novel potential XO inhibitors, which can be potentially used for the treatment of gout.

Essential Oils of Polyalthia suberosa Leaf and Twig and Their Cytotoxic and Antimicrobial Activities.

Essential oils from the leaf and twig of Polyalthia suberosa (Roxb.) Thwaites were analyzed using GC/MS/FID. A total of sixty-three constituents were namely identified accounting for 96.03 and 94.12 % in the hydrodistilled oils of the leaf and twig, respectively. Monoterpenes, monoterpenoids, sesquiterpenes, and sesquiterpenoids were characteristic derivatives of P. suberosa essential oils. Sesquiterpenes bicyclogermacrene (26.26 %) and (E)-caryophyllene (7.79 %), and monoterpene ß-pinene (12.71 %) were the major constituents of the leaf oil. Sesquiterpenes (E)-caryophyllene (17.17 %) and α-humulene (9.55 %), sesquiterpenoid caryophyllene oxide (9.41 %), and monoterpenes camphene (8.16 %) and tricyclene (6.35 %) were to be main components in the twig oil. The leaf oil indicated cytotoxic activity against three cancer cell lines HepG2, MCF7 and A549 with the IC50 values of 60.96-69.93 µg/mL, while the twig oil inhibited MCF7 with the IC50 value of 66.70 µg/mL. Additionally, the twig oil successfully suppressed the growth of the negative Gram bacterium Pseudomonas aeruginosa, fungus Aspergillus niger, and yeast Candida albicans with the same MIC value of 50 µg/mL, whereas the leaf oil had the same result on the negative Gram bacterium Escherichia coli.

Flavonoids from Polyalthia longifolia prevents advanced glycation end products formation and protein oxidation aligned with fructose-induced protein glycation.

Advanced glycation end products (AGEs) are reactive chemical entities formed by non-enzymatic reaction between reducing sugars and amino group of proteins. Enhanced accumulation of AGEs and associated protein oxidation contribute to pathogenesis of diabetes-associated complications. Here, we evaluated the inhibitory activity of flavonoid compounds isolated from the leaves of Polyalthia longifolia on formation of AGEs and protein oxidation. Antiglycation activity was determined by measuring the formation of AGE fluorescence intensity, Nε-(carboxymethyl) lysine, and level of fructosamine. Protein oxidation was examined using levels of protein carbonyls and thiol group. Compounds significantly (p < 0.001) restricted the formation of fluorescent AGEs in fructose- BSA and methylglyoxal-BSA systems. Furthermore, there was a decrease in levels of fructosamine and protein carbonyls, and elevation in level of thiol group in fructose-BSA in presence of flavonoids. In summary, flavonoids from Polyalthia longifolia inhibit fructose-mediated protein glycation and oxidation, and can be potential agent for preventing AGE-mediated diabetic complications.

Terpenes isolated from Polyalthia simiarum and their cytotoxic activities.

Two new C31 triterpenes, polysimiaric acid A (1) and B (2) as well as one new clerodane diterpenoid, 16,16-dimethoxy-cleroda-3,13Z-dien-15-oic acid (3), together with six known compounds were isolated from Polyalthia simiarum. Their structures were determined by analysis of 1D and 2D NMR data. Three new compounds were tested for their cytotoxicity against five human tumour cell lines. Compound 3 showed cytotoxic activities against SMMC-7721 with the IC50 value of 22.43 µM.

Dual COX and 5-LOX inhibition by clerodane diterpenes from seeds of Polyalthia longifolia (Sonn.) Thwaites.

Natural metabolites with their specific bioactivities are being considered as a potential source of materials for pharmacological studies. In this study, we successfully isolated and identified five known clerodane diterpenes, namely 16-oxo-cleroda-3,13(14)E-dien-15-oic acid (1), 16-hydroxy-cleroda-3,13-dien-15-oic acid (2), 16-hydroxy-cleroda-4(18),13-dien-16,15-olide (3), 3α,16α-dihydroxy-cleroda-4(18),13(14)Z-dien-15,16-olide (4), and 16α-hydroxy-cleroda-3,13(14)Z-dien-15,16-olide (5) from the methanolic extract of seeds of Polyalthia longifolia. Initially, all the isolated metabolites were investigated for COX-1, COX-2, and 5-LOX inhibitory activities using the standard inhibitory kits. Of which, compounds 3, 4, and 5 exhibited to be potent COX-1, COX-2, and 5-LOX inhibitors with the IC50 values similar or lower to those of the reference drugs. To understand the underlying mechanism, these compounds were subjected to molecular docking on COX-1, COX-2, and 5-LOX proteins. Interestingly, the in silico study results were in high accordance with in vitro studies where compounds 3, 4, and 5 hits assumed interactions and binding pattern comparable to that of reference drugs (indomethacin and diclofenac), as a co-crystallized ligand explaining their remarkable dual (COX/LOX) inhibitor actions. Taken together, our findings demonstrated that compounds 3, 4, and 5 functioned as dual inhibitors of COX/5-LOX and can contribute to the development of novel, more effective anti-inflammatory drugs with minimal side-effects.

Evaluation of mechanical, thermal and water absorption behaviors of Polyalthia longifolia seed reinforced vinyl ester composites.

This study presented a novel utilization of biomass solid waste, named Polyalthia longifolia (Mast tree) seed as a reinforcement in a composite, using a compression molding technique. An attempt was made to reinforce vinyl ester matrix (VE) with Polyalthia longifolia seed filler (PLSF), ranging from 5 to 50 wt% loadings. Mechanical properties of the fabricated Polyalthia longifolia seed filler/vinyl ester (PLSF-VE) composite samples were tested and analyzed. The results showed that the PLSF-VE composite exhibited optimum mechanical properties at 25 % wt of filler loading; ultimate tensile strength and modulus were approximately 32.50 MPa and 1.23 GPa, respectively. The ultimate flexural, impact strengths and hardness were observed around 125 MPa, 31.09 kJ/m2 and 36.50, respectively. The heat deflection test and thermo-gravimetric analysis depicted that the PLSF-VE composites withstood up to 66 °C and 430 °C, respectively. Furthermore, the PLSF and its various composite samples were studied, using energy-dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM).

Chemical composition of the essential oils of four Polyalthia species from Malaysia.

Polyalthia is one of the largest genera in the Annonaceae family, and has been widely used in folk medicine for the treatment of rheumatic fever, gastrointestinal ulcer, and generalized body pain. The present investigation reports on the extraction by hydrodistillation and the composition of the essential oils of four Polyalthia species (P. sumatrana, P. stenopetalla, P. cauliflora, and P. rumphii) growing in Malaysia. The chemical composition of these essential oils was determined by gas chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The multivariate analysis was determined using principal component analysis (PCA) and hierarchical clustering analysis (HCA) methods. The results revealed that the studied essential oils are made up principally of bicyclogermacrene (18.8%), cis-calamenene (14.6%) and ß-elemene (11.9%) for P. sumatrana; α-cadinol (13.0%) and δ-cadinene (10.2%) for P. stenopetalla; δ-elemene (38.1%) and ß-cubebene (33.1%) for P. cauliflora; and finally germacrene D (33.3%) and bicyclogermacrene for P. rumphii. PCA score and HCA plots revealed that the essential oils were classified into three separated clusters of P. cauliflora (Cluster I), P. sumatrana (Cluster II), and P. stenopetalla, and P. rumphii (Cluster III) based on their characteristic chemical compositions. Our findings demonstrate that the essential oil could be useful for the characterization, pharmaceutical, and therapeutic applications of Polyalthia essential oil.

Discovery of a Natural Product That Binds to the Mycobacterium tuberculosis Protein Rv1466 Using Native Mass Spectrometry.

Elucidation of the mechanism of action of compounds with cellular bioactivity is important for progressing compounds into future drug development. In recent years, phenotype-based drug discovery has become the dominant approach to drug discovery over target-based drug discovery, which relies on the knowledge of a specific drug target of a disease. Still, when targeting an infectious disease via a high throughput phenotypic assay it is highly advantageous to identifying the compound's cellular activity. A fraction derived from the plant Polyalthia sp. showed activity against Mycobacterium tuberculosis at 62.5 µge/µL. A known compound, altholactone, was identified from this fraction that showed activity towards M. tuberculosis at an minimum inhibitory concentration (MIC) of 64 µM. Retrospective analysis of a target-based screen against a TB proteome panel using native mass spectrometry established that the active fraction was bound to the mycobacterial protein Rv1466 with an estimated pseudo-Kd of 42.0 ± 6.1 µM. Our findings established Rv1466 as the potential molecular target of altholactone, which is responsible for the observed in vivo toxicity towards M. tuberculosis.

α-Glucosidase inhibitory and nitric oxide production inhibitory activities of alkaloids isolated from a twig extract of Polyalthia cinnamomea.

The first phytochemical investigation of Polyalthia cinnamomea led to the isolation and identification of two new oxoprotoberberine alkaloids, (-)-(13aS)-polyalthiacinnamines A and B, together with eleven known compounds. The structures of the new compounds were elucidated by extensive spectroscopic methods. The absolute configuration of miliusacunine E and consanguine B was established by X-ray diffraction analysis using Cu Kα radiation and ECD spectra, whereas the absolute configurations of polyalthiacinnamines A and B were established by comparison of their ECD spectra and specific rotations with those of miliusacunine E and consanguine B. Compounds 1-4, 6, and 8 exhibited α-glucosidase inhibitory activities (IC50 values ranging from 11.3 to 57.9 µM) better than a positive control (acarbose, IC50 83.5 µM). Compound 2 also exhibited NO production inhibitory activity with an IC50 value of 24.4 µM (indomethacin, a positive control, IC50 = 32.2 µM).

Three new methylated Δ8-pregnene steroids from the Polyalthia laui-derived fungus Stemphylium sp. AZGP4-2.

Three new methylated Δ8-pregnene steroids, stemphylisteroids A-C (1-3) were isolated from the medicinal plant Polyalthia laui-derived fungus Stemphylium sp. AZGP4-2. Their structures were elucidated by the detailed analysis of comprehensive spectroscopic data. The absolute configuration of 1 was determined by X-ray crystallographic analysis. Compound 1 show antibacterial activity against Escherichia coli with the MIC value of 6.25 µg/mL, and 2 exhibited a broad spectrum of antibacterial activities against six pathogenic bacteria with the MIC values ranging from 12.5 to 50 µg/mL. The discovery of three methylated Δ8-pregnene steroids 1-3 are a further addition to diverse and complex array of methylated steroids.

Polyalthia longifolia Extract Triggers ER Stress in Prostate Cancer Cells Concomitant with Induction of Apoptosis: Insights from In Vitro and In Vivo Studies.

Plant-based therapies are being explored to prevent or treat several cancer types. The antioxidant properties of Polyalthia longifolia plant are well established. In our previous work, we demonstrated the presence of cytotoxic compounds in the methanol extract of Polyalthia longifolia (MEP) with potent activity against human leukemia cells. In the present study, we evaluated the efficacy of MEP against prostate cancer (PCa) and established the molecular basis of its effect in in vitro and in vivo models. We observed that MEP treatment resulted in a significant decrease in the growth and viability of PCa cells, associated with arrest in the G1/S phase of the cell cycle. Apoptosis was confirmed as the primary mode of MEP-induced cell death through activation of the intrinsic apoptotic machinery. Proteomic and biochemical studies identified BiP as an important target of MEP with the activation of the ER stress pathway, as a potential mechanism driving MEP-induced apoptosis. The extract exhibited strong efficacy in the PCa xenograft mouse model with significant inhibition of tumor growth and reduced tumor burden. Taken together, our findings indicate that MEP-induced apoptosis in PCa cells concomitant with the activation of the ER stress pathways results in the inhibition of tumor growth, in vitro and in vivo. Our studies provide initial evidence of the efficacy of MEP against PCa and advocate for in-depth studies in other preclinical models for its possible use in clinical settings.

Functional Validation of DownRegulated MicroRNAs in HeLa Cells Treated with Polyalthia longifolia Leaf Extract Using Different Microscopic Approaches: A Morphological Alteration-Based Validation.

Several microscopy methods have been developed to assess the morphological changes in cells in the investigations of the mode of cell death in response to a stimulus. Our recent finding on the treatment of the IC50 concentration (26.67 µg/mL) of Polyalthia longifolia leaf extract indicated the induction of apoptotic cell death via the regulation of miRNA in HeLa cells. Hence, the current study was conducted to validate the function of these downregulated microRNAs in P. longifolia-treated HeLa cells using microscopic approaches. These include scanning electron microscope (SEM), transmission electron microscope (TEM), and acridine orange/propidium iodide (AO/PI)-based fluorescent microscopy techniques by observing the morphological alterations to cells after transfection with mimic miRNA. Interestingly, the morphological changes observed in this study demonstrated the apoptotic hallmarks, for instance, cell blebbing, cell shrinkage, cytoplasmic and nuclear condensation, vacuolization, cytoplasmic extrusion, and the formation of apoptotic bodies, which proved the role of dysregulated miRNAs in apoptotic HeLa cell death after treatment with the P. longifolia leaf extract. Conclusively, the current study proved the crucial role of downregulated miR-484 and miR-221-5p in the induction of apoptotic cell death in P. longifolia-treated HeLa cells using three approaches-SEM, TEM, and AO/PI-based fluorescent microscope.

Polyalthia Clerodane Diterpene Potentiates Hypoglycemia via Inhibition of Dipeptidyl Peptidase 4.

Serine protease dipeptidyl peptidase 4 (DPP-4) is involved in self/non-self-recognition and insulin sensitivity. DPP-4 inhibitors are conventional choices for diabetic treatment; however, side effects such as headache, bronchus infection, and nasopharyngitis might affect the daily lives of diabetic patients. Notably, natural compounds are believed to have a similar efficacy with lower adverse effects. This study aimed to validate the DPP-4 inhibitory activity of clerodane diterpene 16-hydroxycleroda-3,13-dien-15,16-olide (HCD) from Polyalthia longifolia, rutin, quercetin, and berberine, previously selected through molecular docking. The inhibitory potency of natural DPP-4 candidates was further determined by enzymatic, in vitro Caco-2, and ERK/PKA activation in myocyte and pancreatic cells. The hypoglycemic efficacy of the natural compounds was consecutively analyzed by single-dose and multiple-dose administration in diet-induced obese diabetic mice. All the natural-compounds could directly inhibit DPP-4 activity in enzymatic assay and Caco-2 inhibition assay, and HCD showed the highest inhibition of the compounds. HCD down-regulated LPS-induced ERK phosphorylation in myocyte but blocked GLP-1 induced PKA expression. For in vivo tests, HCD showed hypoglycemic efficacy only in single-dose administration. After 28-days administration, HCD exhibited hypolipidemic and hepatoprotective efficacy. These results revealed that HCD performed potential antidiabetic activity via inhibition of single-dose and long-term administrations, and could be a new prospective anti-diabetic drug candidate.

3,4- seco-Norclerodane Diterpenoids from the Roots of Polyalthia laui.

Ten new clerodane diterpenoids, polylauioids A-J (1-10), and five known analogues (11-15) were isolated from the roots of Polyalthia laui. Among the new compounds, 3 and 8 are artifacts. The structures were elucidated using spectroscopic methods and by comparison with published NMR spectroscopic data. The absolute configurations of 4, 5, and 7 were defined based on single-crystal X-ray diffraction and electronic circular dichroism data. Compounds 1 and 2 represent the first examples of rearranged 3,4- seco-norclerodane diterpenoids, and a putative biosynthesis pathway for these compounds is proposed. Compounds 1, 4, 6, 7, 9, and 10 showed anti-HIV activities with EC50 values ranging from 12.2 to 35.2 µM.