The natural secolignan peperomin E induces apoptosis of human gastric carcinoma cells via the mitochondrial and PI3K/Akt signaling pathways in vitro and in vivo

Phytochemicals and mitochondria: Therapeutic allies against gastric cancer

BACKGROUND

Mitochondria are the energy factories of cells with the ability to modulate the cell cycle, cellular differentiation, signal transduction, growth, and apoptosis. Existing drugs targeting mitochondria in cancer treatment have disadvantages of drug resistance and side effects. Phytochemicals, which are widely found in plants, are bioactive compounds that could facilitate the development of new drugs for gastric cancer. Studies have shown that some phytochemicals can suppress the development of gastric cancer.

METHODS

We searched for data from PubMed, China National Knowledge Infrastructure, Web of Science, and Embase databases from initial establishment to December 2021 to review the mechanism by which phytochemicals suppress gastric cancer cell growth by modulating mitochondrial function. Phytochemicals were classified and summarized by their mechanisms of action.

RESULTS

Phytochemicals can interfere with mitochondria through several mechanisms to reach the goal of promoting apoptosis in gastric cancer cells. Some phytochemicals, e.g., daidzein and tetrandrine promoted cytochrome c spillover into the cytoplasm by modulating the members of the B-cell lymphoma-2 protein family and induced apoptotic body activity by activating the caspase protein family. Phytochemicals (e.g., celastrol and shikonin) could promote the accumulation of reactive oxygen species and reduce the mitochondrial membrane potential. Several phytochemicals (e.g., berberine and oleanolic acid) activated mitochondrial apoptotic submission via the phosphatidylinositol-3-kinase/Akt signaling pathway, thereby triggering apoptosis in gastric cancer cells. Several well-known phytochemicals that target mitochondria, including berberine, ginsenoside, and baicalein, showed the advantages of multiple targets, high efficacy, and fewer side effects.

CONCLUSIONS

Phytochemicals could target the mitochondria in the treatment of gastric cancer, providing potential directions and evidence for clinical translation. Drug discovery focused on phytochemicals has great potential to break barriers in cancer treatment.

Bioactive Phenolic Compounds from Peperomia obtusifolia

Peperomia obtusifolia (L.) A. Dietr., native to Middle America, is an ornamental plant also traditionally used for its mild antimicrobial properties. Chemical investigation on the leaves of P. obtusifolia resulted in the isolation of two previously undescribed compounds, named peperomic ester (1) and peperoside (2), together with five known compounds, viz. N-[2-(3,4-dihydroxyphenyl)ethyl]-3,4-dihydroxybenzamide (3), becatamide (4), peperobtusin A (5), peperomin B (6), and arabinothalictoside (7). The structures of these compounds were elucidated by 1D and 2D NMR techniques and HREIMS analyses. Compounds 1–7 were evaluated for their anthelmintic (against Caenorhabditis elegans), antifungal (against Botrytis cinerea, Septoria tritici and Phytophthora infestans), antibacterial (against Bacillus subtilis and Aliivibrio fischeri), and antiproliferative (against PC-3 and HT-29 human cancer cell lines) activities. The known peperobtusin A (5) was the most active compound against the PC-3 cancer cell line with IC₅₀ values of 25.6 µM and 36.0 µM in MTT and CV assays, respectively. This compound also induced 90% inhibition of bacterial growth of the Gram-positive B. subtilis at a concentration of 100 µM. In addition, compound 3 showed anti-oomycotic activity against P. infestans with an inhibition value of 56% by using a concentration of 125 µM. However, no anthelmintic activity was observed.

Peperomin E Induces Apoptosis and Cytoprotective Autophagy in Human Prostate Cancer DU145 Cells In Vitro and In Vivo

Peperomin E was first isolated from Peperomia dindygulensis, an anticarcinogenic herb, and exhibited anticancer activity in many cancer cell lines. To date, it is unknown whether peperomin E has an effect on human prostate cancer DU145 cells in vitro and in vivo. In this study, we used MTT to assess the proliferation inhibition activity of peperomin E in DU145 cells in vitro and observed the cell morphological changes by a phase contrast microscope. A DU145 cell xenograft tumor mouse model was used to evaluate the efficacy of peperomin E in vivo. Apoptosis rates were measured by flow cytometry, and protein expression levels were analyzed by western blot. The results showed that peperomin E significantly inhibited the proliferation of DU145 cells in vitro and reduced the weight and volume of tumors in vivo. Peperomin E also significantly induced the apoptosis and autophagic response of DU145 cells. The autophagic inhibitors LY294002 and chloroquine enhanced peperomin E-mediated inhibition of DU145 cell proliferation and induction of DU145 cell apoptosis. The results also showed that the Akt/mTOR pathway participated in peperomin E-induced autophagy in DU145 cells. In summary, our finding showed that peperomin E had an effect on DU145 cells in vitro and in a nude mouse DU145 cell xenograft model in vivo, demonstrated that peperomin E could significantly induce apoptosis and the autophagic response in DU145 cells and that autophagy played a cytoprotective role in peperomin E-treated DU145 cells. These results suggest that the combination of peperomin E treatment and autophagic inhibition has potential for the treatment of prostate cancer.

Sanggenon O induced apoptosis of A549 cells is counterbalanced by protective autophagy

Sanggenon O (SO) is a Diels-Alder type adduct extracted fromMorus alba, which has been used for its anti-inflammatory action in the Oriental medicine. However, whether it has regulatory effect on human cancer cell proliferation and what the underlying mechanism remains unknown. Here, we found that SO could significantly inhibit the growth and proliferation of A549 cells and induce its pro-apoptotic action through a caspase-dependent pathway. It could also impair the mitochondria which can be reflected by mitochondrial membrane permeabilization. Besides, SQSTM1 up-regulation and autophagic flux measurement demonstrated that exposure to SO led to autophagosome accumulation, which plays a protective role in SO-treated cells. In addition, knocking down of LC3B increased SO triggered apoptotic cell rates. These results indicated that SO has great potential as a promising candidate combined with autophagy inhibitor for the treatment of NSCLC. In conclusion, our results identified a novel mechanism by which SO exerts potent anticancer activity.

Peperomin E (PepE) protects against high fat diet-induced atherosclerosis in Apolipoprotein E deficient (ApoE-/-) mice through reducing inflammation via the suppression of NLRP3 signaling pathway

Peperomin E (PepE) is a type of secolignan, a major component of the plant Peperomia dindygulensis. It has been shown to exert anti-inflammatory effects; however, the effects of PepE on human atherosclerosis remain unexplored. In the study, we investigated the role of PepE in high fat diet (HFD) induced atherosclerosis using apolipoprotein E defcient (ApoE^-/-) mice. Elevated serum homocyteine, cholesterol, and triglyceride levels, accelerated progression of atherosclerosis and exacerbated macrophage infiltration into atherosclerotic lesions were observed in HFD-fed ApoE^-/- mice, which were attenuated by PepE treatment. ApoE^-/- mice fed with HFD exhibited significantly high levels of inflammation-associated regulators in artery tissues, accompanied with an increased expression of p-inhibitor of κBα (IκBα) and p-nuclear factor-kappa B (NF-κB), and the process was blocked by PepE administration. Further, we found NOD-like receptor pyrin 3 (NLRP3) inflammasome activation in artery tissues of HFD-fed ApoE^-/- mice. In vitro, silencing NLRP3 using small interfering RNA efficiently inhibited oxidized-low-density lipoprotein (oxLDL)-induced ASC and Caspase-1 expressions, interleukin (IL)-1β and IL-18 production in human aortic endothelial cells (HAECs). Further experiments indicated that NLRP3-ASC pathway was activated by reactive oxygen species (ROS), since ROS scavenger of N-acetyl-cysteine (NAC) prevented, which was further reduced by PepE addition. However, the anti-inflammatory effects of PepE on oxLDL-incubated HAECs were abolished by over-expression NLRP3. Together, our study revealed that PepE inhibited atherosclerosis development in HFD-fed ApoE^-/- mice by suppressing NLRP3 inflammatory signaling pathway, and suggested that PepE might be a potential therapeutic strategy in the prevention of atherosclerosis.

-Chemical profiling and biological activity of Peperomia blanda (Jacq.) Kunth

Background

Peperomia belongs to the family of Piperaceae. It has different uses in folk medicine and contains rare compounds that have led to increased interest in this genus. Peperomia blanda (Jacq.) Kunth is used as an injury disinfectant by Yemeni people. In addition, the majority of Yemen’s population still depend on the traditional remedy for serious diseases such as cancer, inflammation and infection. Currently, there is a deficiency of scientific evidence with regards to the medicinal plants from Yemen. Therefore, this study was performed to assess the chemical profile and in vitro antioxidant and cytotoxic activities of P. blanda.

Methods

Chemical profiling of P. blanda was carried out using gas chromatography mass spectrometry (GCMS) followed by isolation of bioactive compounds by column chromatography. DPPH• and FRAP assays were used to evaluate antioxidant activity and the MTT assay was performed to estimate the cytotoxicity activity against three cancer cell lines, namely MCF-7, HL-60 and WEHI-3, and three normal cell lines, MCF10A, WRL-68 and HDFa.

Results

X-ray crystallographic data for peperomin A is reported for the first time here and N,N′-diphenethyloxamide was isolated for the first time from Peperomia blanda. Methanol and dichloromethane extracts showed high radical scavenging activity with an IC₅₀ of 36.81 ± 0.09 µg/mL, followed by the dichloromethane extract at 61.78 ± 0.02 µg/mL, whereas the weak ferric reducing activity of P. blanda extracts ranging from 162.2 ± 0.80 to 381.5 ± 1.31 µg/mL were recorded. In addition, petroleum ether crude extract exhibited the highest cytotoxic activity against all the tested cancer cell lines with IC₅₀ values of 9.54 ± 0.30, 4.30 ± 0.90 and 5.39 ± 0.34 µg/mL, respectively. Peperomin A and the isolated mixture of phytosterol (stigmasterol and β-sitosterol) exhibited cytotoxic activity against MCF-7 and WE-HI cell lines with an IC₅₀ of (5.58 ± 0.47, 4.62 ± 0.03 µg/mL) and (8.94 ± 0.05, 9.84 ± 0.61 µg/mL), respectively, compared to a standard drug, taxol, that has IC₅₀ values of 3.56 ± 0.34 and 1.90 ± 0.9 µg/mL, respectively.

Conclusion

The activities of P. blanda extracts and isolated compounds recorded in this study underlines the potential that makes this plant a valuable source for further study on anticancer and antioxidant activities.

Loss of Tctn3 causes neuronal apoptosis and neural tube defects in mice

Tctn3 belongs to the Tectonic (Tctn) family and is a single-pass membrane protein localized at the transition zone of primary cilia as an important component of ciliopathy-related protein complexes. Previous studies showed that mutations in Tctn1 and Tctn2, two members of the tectonic family, have been reported to disrupt neural tube development in humans and mice, but the functions of Tctn3 in brain development remain elusive. In this study, Tctn3 knockout (KO) mice were generated by utilizing the piggyBac (PB) transposon system. We found that Tctn3 KO mice exhibited abnormal global development, including prenatal lethality, microphthalmia, polysyndactyly, and abnormal head, sternum, and neural tube, whereas Tctn3 heterozygous KO mice did not show abnormal development or behaviors. Further, we found that the mRNA levels of Gli1 and Ptch1, downstream signaling components of the Shh pathway, were significantly reduced. Likewise, neural tube patterning-related proteins, such as Shh, Foxa2, and Nkx2.2, were altered in their distribution. Interestingly, Tctn3 KO led to significant changes in apoptosis-related proteins, including Bcl-2, Bax, and cleaved PARP1, resulting in reduced numbers of neuronal cells in embryonic brains. Tctn3 KO inhibited the PI3K/Akt signaling pathway but not the mTOR-dependent pathway. The small molecule SC79, a specific Akt activator, blocked apoptotic cell death in primary mouse embryonic fibroblasts from Tctn3 KO mice. Finally, NPHP1, a protein with anti-apoptotic ability, was found to form a complex with Tctn3, and its levels were decreased in Tctn3 KO mice. In conclusion, our results show that Tctn3 KO disrupts the Shh signaling pathway and neural tube patterning, resulting in abnormal embryonic development, cellular apoptosis, and prenatal death in mice.

Eucalrobusone C suppresses cell proliferation and induces ROS-dependent mitochondrial apoptosis via the p38 MAPK pathway in hepatocellular carcinoma cells

BACKGROUND

Eucalyptus extracts have anti-cancer activity against various cancer cells. Formyl-phloroglucinol meroterpenoids (FPMs), which are typical secondary metabolites of the genera Eucalyptus, have many important pharmacological activities.

PURPOSE

Eucalrobusone C (EC), a new bioactive phytochemical, was first isolated from the leaves of Eucalyptus robusta in our laboratory. EC is a FPM, and our previous research revealed that EC showed strongest cytotoxicity in three cancer models than other compounds isolated from the leaves of E. robusta. This study investigated its anti-tumor effects on human hepatocellular carcinoma (HCC) and its underlying mechanisms.

METHODS

Cell viability was measured by MTT assay. Cell cycle, apoptosis and mitochondrial transmembrane potential were determined by flow cytometry. Immunofluorescence was determined by a laser scanning confocal microscope. Protein levels were analyzed by Western blotting.

RESULTS

Our results showed that EC exerted strong anti-proliferative activity against HCC cells in a concentration- and time-dependent manner. EC markedly induced apoptosis through the caspase-dependent mitochondrial pathway, and the cell cycle was arrested at S phase. SB203580, a p38 MAPK inhibitor, effectively decreased cell death caused by EC. Moreover, the ROS scavenger N-acetyl cysteine (NAC) significantly attenuated apoptosis induced by EC and reversed EC-induced p38 MAPK activation.

CONCLUSION

Our findings indicate that EC induces mitochondrial-dependent apoptosis in HCC cells through ROS generation and p38 MAPK activation, making EC a promising candidate for further development as an anticancer agent for HCC cells.

Determination of a natural DNMT1 inhibitor, peperomin E, in rat plasma by UFLC-MS/MS and method application in a pharmacokinetic study

Peperomin E (PepE), a naturally occurring secolignan isolated from Peperomia dindygulensis, has drawn much attention recently owing to its anticancer and DNA methyltransferase 1 (DNMT1) inhibitory activity. Here, a simple and sensitive ultra-fast liquid chromatography-tandem mass spectrometry method was developed and validated for the determination of PepE in rat plasma for the first time. Samples were prepared by simple protein precipitation. Separation was performed on an XBridge™ C₁₈ column using a mobile phase of acetonitrile and 0.1% (v/v) aqueous formic acid. PepE and the internal standard arctigenin were detected in a positive-ion mode using multiple reaction monitoring of the transitions at m/z 413.2 → 261.0 and 373.2 → 137.2, respectively. The calibration curve for PepE was linear over the range of concentrations of 1.46-6000 ng/mL, with a lower limit of quantitation of 1.46 ng/mL. Both intra- and interday precisions were within 11.05%, and the accuracy ranged from -11.5 to 5.51%. The extraction recovery and matrix effect were within acceptable limits. Stability tests showed that PepE remained stable throughout the analytical procedure. The validated method was then used to analyze the pharmacokinetics of PepE administered to rats orally (12.5 and 25 mg/kg) or intravenously (6.25 and 12.5 mg/kg).

Peperomin E and its synthetic amino derivatives: potent agents targeting leukaemia stem cells

A series of amino derivatives of Peperomin E have been synthesized. Compound 6, derived from N-methylethanolamine, exhibited exclusive cytotoxicity against leukaemia stem cells (IC₅₀ = 0.5 μM) and low toxicity against normal bone marrow cells.