Xanthone and benzophenone glycosides from the stems of Cratoxylum formosum ssp. pruniflorum

Characterization of Antioxidant and α-Glucosidase Inhibitory Compounds of Cratoxylum formosum ssp. pruniflorum and Optimization of Extraction Condition

Cratoxylum formosum ssp. pruniflorum (Kurz.) Gogel (Guttiferae), called kuding tea, is widely distributed in Southeast Asia. In this study, the constituents and biological activity of C. formosum ssp. pruniflorum were investigated. Extract of its leaves, roots and stems showed antioxidant and α-glucosidase inhibitory activity. Interestingly, comparison of the metabolite profiles of leaves, roots and stems of C. formosum ssp. pruniflorum by LC-MS analysis showed a great difference between the roots and leaves, whereas the roots and stems were quite similar. Purification of the roots and leaves of C. formosum ssp. pruniflorum through various chromatographic techniques resulted in the isolation of 25 compounds. The structures of isolated compounds were elucidated on the basis of spectroscopic analysis as 18 xanthones, 5 flavonoids, a benzophenone and a phenolic compound. Among them, a xanthone (16) and a benzophenone (19) were first reported from nature. Evaluation of biological activity revealed that xanthones had a potent α-glucosidase inhibitory activity, while flavonoids were responsible for the antioxidant activity. To maximize the biological activity, yield and total phenolic content of C. formosum ssp. pruniflorum, extraction conditions such as extraction solvent, time and temperature were optimized using response surface methodology with Box-Behnken Design (BBD). Regression analysis showed a good fit of the experimental data, and the optimal condition was obtained as MeOH concentration in EtOAc, 88.1%; extraction time, 6.02 h; and extraction temperature 60.0 °C. α-Glucosidase inhibitory activity, yield and total phenolic content under the optimal condition were found to be 72.2% inhibition, 10.3% and 163.9 mg GAE/g extract, respectively. These results provide useful information about C. formosum ssp. pruniflorum as functional foods for oxidative stress-related metabolic diseases.

Biotransformation of Benzoate to 2,4,6-Trihydroxybenzophenone by Engineered Escherichia coli

The synthesis of natural products by E. coli is a challenging alternative method of environmentally friendly minimization of hazardous waste. Here, we establish a recombinant E. coli capable of transforming sodium benzoate into 2,4,6-trihydroxybenzophenone (2,4,6-TriHB), the intermediate of benzophenones and xanthones derivatives, based on the coexpression of benzoate-CoA ligase from Rhodopseudomonas palustris (BadA) and benzophenone synthase from Garcinia mangostana (GmBPS). It was found that the engineered E. coli accepted benzoate as the leading substrate for the formation of benzoyl CoA by the function of BadA and subsequently condensed, with the endogenous malonyl CoA by the catalytic function of BPS, into 2,4,6-TriHB. This metabolite was excreted into the culture medium and was detected by the high-resolution LC-ESI-QTOF-MS/MS. The structure was elucidated by in silico tools: Sirius 4.5 combined with CSI FingerID web service. The results suggested the potential of the new artificial pathway in E. coli to successfully catalyze the transformation of sodium benzoate into 2,4,6-TriHB. This system will lead to further syntheses of other benzophenone derivatives via the addition of various genes to catalyze for functional groups.

Assessment of the anti-diabetic potential of the Cratoxylum formosum subsp. formosum extracts via carbohydrate hydrolyzing enzymes inhibitory activities

Introduction: This research aims to evaluate the anti-diabetic activity of the extracts from different parts of Cratoxylum formosum subsp. formosum.Methods: The in vitro inhibitory activities of the hexane (HEX), dichloromethane (DCM) and ethyl acetate (EtOAc) extracts from the flowers, leaves, roots and stems on pancreatic α-amylase (pAA), Saccharomyces α-glucosidase (SAG), rat intestinal maltase (rIM), and sucrase (rIS) were investigated. Results: The DCM and EtOAc extracts from the flowers (IC50 5.4 ± 1.5 and 10.5 ± 0.6 µg/mL) displayed the similar inhibitory activities as acarbose (IC50 7.2 ± 0.4 µg/mL) in the pAA assay. The inhibitory activities of the DCM and EtOAc extracts from the flowers (IC50 56.7 ± 8.9 and 20.4 ± 0.4 µg/mL), EtOAc extract from leaves (IC50 45.0 ± 3.5 µg/mL), DCM and EtOAc extracts from roots (IC50 35.0 ± 6.7 and 16.7± 3.6 µg/mL), and EtOAc extract from stems (IC50 31.1 ± 7.3 µg/mL) were more potent than acarbose (IC50 431.4 ± 16.7 µg/mL) on SAG inhibitory assay (P<0.05). In the rIM assay, DCM and EtOAc extracts from the flowers (IC50 8.5 ± 0.2 and 12.4 ± 0.3 µg/mL) exhibited stronger inhibitory activity than acarbose (IC50 38.5 ± 7.2 µg/mL) (P<0.05). Moreover, the inhibitory activity of DCM extract from the flowers (IC50 16.9 ± 1.5 µg/ mL) was comparable to the acarbose (IC50 15.5 ± 1.2 µg/mL) on rIS assay. Conclusion: The DCM and EtOAc extracts from the flowers were more active than the leaves, roots and stems in the inhibition of our defined target enzymes.

Cytotoxic Components from Hypericum elodeoides Targeting RXRα and Inducing HeLa Cell Apoptosis through Caspase-8 Activation and PARP Cleavage

To find small-molecule regulators of RXRα, a phytochemical study of Hypericum elodeoides was conducted. Fifteen compounds, including the new 1 and 6, were isolated from the whole plant of H. elodeoides. The absolute configuration of 1 was assigned by comparison of experimental and calculated ECD data. Compounds 1 and 6 exhibited concentration-dependent inhibitory effects on RXRα transcription and selectively inhibited the proliferation of HeLa cells. Western blot analysis suggested that 1 and 6 induced apoptosis of HeLa cells with time- and dose-dependent PARP cleavage. A caspase activation assay indicated that these two compounds triggered caspase-8 activation to induce apoptosis by the extrinsic pathway. Molecular docking results suggested that 1 and 6 interacted with the Arg319 moiety of RXRα-LBD. Ligands binding to RXRα have shown promise in the discovery of anticancer drugs. A fluorescence quenching assay indicated the binding of 1 and 6 to the RXRα with the binding constant ( K_D) fitted as 68.3 and 14.0 μM, respectively. A preliminary SAR study of the isolates was conducted to enhance the knowledge of the RXRα ligands. Thus, 1 and 6 might act as the small-molecule regulators of RXRα, which target RXRα and mediate HeLa cell apoptosis through the extrinsic pathways.

Bioactive prenylated xanthones from the stems of Cratoxylum cochinchinense

Cochinchinones M-U (1-9), together with 12 known compounds (10-21), were isolated from the stems of Cratoxylum cochinchinense (Lour.) Blume. Their structures were determined on the basis of extensive spectroscopic data analyses. In addition, their retinoid X receptor-α transcriptional activities were evaluated using an in vitro assay.

Cratoxylum formosum (Jack) Dyer ssp. pruniflorum (Kurz) Gogel. (Hóng yá mù) extract induces apoptosis in human hepatocellular carcinoma HepG2 cells through caspase-dependent pathways

BACKGROUND

Cratoxylum formosum (Jack) Dyer ssp. pruniflorum (Kurz) Gogel. (Hóng yá mù) (CF) has been used for treatment of fever, cough, and peptic ulcer. Previously, a 50% ethanol-water extract from twigs of CF was shown highly selective in cytotoxicity against cancer cells. This study aims to investigate the molecular mechanisms underlying the apoptosis-inducing effect of CF.

METHODS

The cytotoxicity of CF was evaluated in the human hepatocellular carcinoma (HCC) HepG2 cell line in comparison with a non-cancerous African green monkey kidney epithelial cell line (Vero) by a neutral red assay. The apoptosis induction mechanisms were investigated through nuclear morphological changes, DNA fragmentation, mitochondrial membrane potential alterations, and caspase enzyme activities.

RESULTS

CF selectively induced HepG2 cell death compared with non-cancerous Vero cells. A 1.5-fold higher apoptotic effect compared with melphalan was induced by 120 μg/mL of the 50% ethanol-water extract of CF. The apoptotic cell death in HepG2 cells occurred via extrinsic and intrinsic caspase-dependent pathways in dose- and time-dependent manners by significantly increasing the activities of caspase 3/7, 8, and 9, decreasing the mitochondrial membrane potential, and causing apoptotic body formation and DNA fragmentation.

CONCLUSIONS

CF extract induced a caspase-dependent apoptosis in HepG2 cells.

Inhibition of nitric oxide production in lipopolysaccharide-activated RAW264.7 macrophages by isolated xanthones from the roots of Cratoxylum formosum ssp. pruniflorum

The inhibitory activity of extract and compounds isolated from the roots of Cratoxylum formosum ssp. pruniflorum against nitric oxide (NO) was evaluated using RAW264.7 cells. Isolation of the CH2Cl2 extract of C. formosum ssp. pruniflorum roots afforded ten known xanthones including six tri-oxygenated xanthones (1-6) and four tetra-oxygenated xanthones (7-10), respectively. Compound 7 showed the highest inhibitory activity against NO release with an IC50 value of 3.9 μM, followed by compound 8 with an IC50 value of 4.3 μM, respectively. In order to understand the mechanism of this anti-inflammatory activity, the transcriptional level of 7 was found to down regulate mRNA expressions of iNOS and COX-2 in dose-dependent manners, whereas 8 inhibited only iNOS mRNA expression but did not affect on that of COX-2 gene. Xanthones might be the main anti-inflammatory components in C. formosum ssp. pruniflorum.

Structural diversity and bioactivities of natural benzophenones

Natural benzophenones are a class of compounds with more than 300 members, mainly in the Clusiaceae family. We review key benzophenones, and provide an in-depth discussion of their great structural diversity and biological activity.

Targeting truncated retinoid X receptor-α by CF31 induces TNF-α-dependent apoptosis

A truncated version of retinoid X receptor-α, tRXR-α, promotes cancer cell survival by activating the phosphoinositide 3-kinase (PI3K)/AKT pathway. However, targeting the tRXR-α-mediated survival pathway for cancer treatment remains to be explored. We report here our identification of a new natural product molecule, CF31, a xanthone isolated from Cratoxylum formosum ssp. pruniflorum, and the biologic evaluation of its regulation of the tRXR-α-mediated PI3K/AKT pathway. CF31 binds RXR-α and its binding results in inhibition of RXR-α transactivation. Through RXR-α mutational analysis and computational studies, we show that Arg316 of RXR-α, known to form salt bridges with certain RXR-α ligands, such as 9-cis-retinoic acid (9-cis-RA), is not required for the antagonist effect of CF31, showing a distinct binding mode. Evaluation of several CF31 analogs suggests that the antagonist effect is mainly attributed to an interference with Leu451 of helix H12 in RXR-α. CF31 is a potent inhibitor of AKT activation in various cancer cell lines. When combined with TNF-α, it suppresses TNF-α activation of AKT by inhibiting TNF-α-induced tRXR-α interaction with the p85α regulatory subunit of PI3K. CF31 inhibition of TNF-α activation of AKT also results in TNF-α-dependent activation of caspase-8 and apoptosis. Together, our results show that CF31 is an effective converter of TNF-α signaling from survival to death by targeting tRXR-α in a unique mode and suggest that identification of a natural product that targets an RXR-mediated cell survival pathway that regulates PI3K/AKT may offer a new therapeutic strategy to kill cancer cells.

Xanthones from the stems of Cratoxylum cochinchinense

Four new xanthones, 1-methoxy-3,7,8-trihydroxyxanthone (1), 1-methoxy-4,7,8-trihydroxyxanthone (2), 1-methoxy-4,7-dihydroxyxanthone (3), and 1,4-dimethoxy-2,7-dihydroxyxanthone (4) were isolated from the stems of Cratoxylum cochinchinense along with four known xanthones (5-8). The structures of new compounds were determined by extensive spectroscopic analyses, mainly 1D and 2D NMR and HRESIMS data.

Furocoumarin derivatives from radix Angelicae dahuricae and their effects on RXRα transcriptional regulation

A novel furocoumarin derivative named oxyalloimperatorin (1), together with seventeen furocoumarins 2–18 were isolated from the radix of Angelica dahurica. The chemical structure of new metabolite was characterized by analysis of IR, NMR, and HR-ESI-MS spectroscopic data. Among the isolated compounds, 13, 16, and 18 (each at 20 μM) could significantly promote the gene transcriptional function of nuclear receptor RXRα. While 7–9, 13, 14, and the new structure 1 (each at 20 μM) showed significant reduction in RXRα gene transcriptional activities induced by 9-cis-retinoid acid. The findings indicated that these furocoumarin skeleton derivatives might hold beneficial effects on many intractable diseases, such as cancer and metabolic diseases, due to their potential activities on regulating the transcriptional activation function of RXRα.