Isolation and identification of two new polyynes from a North American ethnic medicinal plant--Oplopanax horridus (Smith) Miq

Efforts in Bioprospecting Research: A Survey of Novel Anticancer Phytochemicals Reported in the Last Decade

Bioprospecting natural products to find prominent agents for medical application is an area of scientific endeavor that has produced many clinically used bioactive compounds, including anticancer agents. These compounds come from plants, microorganisms, and marine life. They are so-called secondary metabolites that are important for a species to survive in the hostile environment of its respective ecosystem. The kingdom of Plantae has been an important source of traditional medicine in the past and is also enormously used today as an exquisite reservoir for detecting novel bioactive compounds that are potent against hard-to-treat maladies such as cancer. Cancer therapies, especially chemotherapies, are fraught with many factors that are difficult to manage, such as drug resistance, adverse side effects, less selectivity, complexity, etc. Here, we report the results of an exploration of the databases of PubMed, Science Direct, and Google Scholar for bioactive anticancer phytochemicals published between 2010 and 2020. Our report is restricted to new compounds with strong-to-moderate bioactivity potential for which mass spectroscopic structural data are available. Each of the phytochemicals reported in this review was assigned to chemical classes with peculiar anticancer properties. In our survey, we found anticancer phytochemicals that are reported to have selective toxicity against cancer cells, to sensitize MDR cancer cells, and to have multitarget effects in several signaling pathways. Surprisingly, many of these compounds have limited follow-up studies. Detailed investigations into the synthesis of more functional derivatives, chemical genetics, and the clinical relevance of these compounds are required to achieve safer chemotherapy.

Anticholinesterase Compounds from Endemic Prangos uechtritzii

In this study, the anticholinesterase effects of the extracts and isolated compounds from the roots of endemic Prangos uechtritzii Boiss & Hausskn (Apiaceae) are reported. A novel polyacetylenic compound; (+)-8-O-methyloplopantriol A along with two known polyacetylenes; (-)-panaxynol, (+)-falcarindiol and fifteen known coumarin derivatives; umbelliferone, 6-formylumbelliferone, suberosin, 7-demethylsuberosin, (+)-ulopterol, tamarin, psoralen, imperatorin, (+)-oxypeucedanin, (+)-oxypeucedanin hydrate, (+)-oxypeucedanin methanolate, (+)-marmesin, (-)-prantschimgin, (+)-decursinol, and (-)-adicardin were isolated from the hexane (Pu-HE), chloroform (Pu-CE), and methanol (Pu-ME) extracts of P. uechtritzii roots. (-)-Panaxynol, (+)-falcarindiol, 6-formylumbelliferone, (+)-decursinol, and (-)-adicardin were obtained from the genus Prangos for the first time. (+)-8-O-Methyloplopantriol A inhibited both AChE (IC50 =194.5±5.8 μM) and BChE (IC50 =51.9±2.96 μM) enzymes. (+)-Falcarindiol, 6-formylumbelliferone, 7-demethylsuberosin, tamarin, and imperatorin also exhibited BChE-specific inhibitory activities (IC50 =27.88-93.86 μM). (+)-Falcarindiol (IC50 =27.88±0.91 μM) and imperatorin (IC50 =30.89±1.40 μM) as the most active components could be led compounds to develop new BChE inhibitors with further research against Alzheimer's disease.

Human intestinal microbiota derived metabolism signature from a North American native botanical Oplopanax horridus with UPLC/Q-TOF-MS analysis

Oplopanax horridus, widely distributed in North America, is an herbal medicine traditionally used by Pacific indigenous peoples for various medical conditions. After oral ingestion, constituents in O. horridus extract (OhE) could be converted to their metabolites by the enteric microbiome before absorption. In this study, in order to mimic gut environment, the OhE was biotransformed using the enteric microbiome of healthy human subjects. For accurate and reliable data collection with optimized approaches in sample preparation and analytical conditions, ultra-performance liquid chromatography and quadrupole time-of-flight mass spectrometry were used to characterize parent constituents and their metabolites. In the extract, 20 parent compounds were identified including polyynes, sesquiterpenes, monoterpeondids, phenylpropanoids and phenolic acids. After the biotransformation, a total of 78 metabolites were identified, of which 37 belonged to polyynes metabolites. The common biotransformation pathways are hydroxylation, acetylization, methylation and demethylation. Based on the pathway distributions, the metabolism signature of OhE has been explored. The metabolism pathways of OhE compounds are dependent on their structural classifications and hydrophilic/hydrophobic properties. In summary, with comprehensive analysis, we systematically investigated human microbiome-derived OhE metabolites. The enteric microbial metabolism signature provides novel information for future effective use of O. horridus.

Bioactive C17 and C18 Acetylenic Oxylipins from Terrestrial Plants as Potential Lead Compounds for Anticancer Drug Development

Bioactive C₁₇ and C₁₈ acetylenic oxylipins have shown to contribute to the cytotoxic, anti-inflammatory, and potential anticancer properties of terrestrial plants. These acetylenic oxylipins are widely distributed in plants belonging to the families Apiaceae, Araliaceae, and Asteraceae, and have shown to induce cell cycle arrest and/or apoptosis of cancer cells in vitro and to exert a chemopreventive effect on cancer development in vivo. The triple bond functionality of these oxylipins transform them into highly alkylating compounds being reactive to proteins and other biomolecules. This enables them to induce the formation of anti-inflammatory and cytoprotective phase 2 enzymes via activation of the Keap1–Nrf2 signaling pathway, inhibition of proinflammatory peptides and proteins, and/or induction of endoplasmic reticulum stress, which, to some extent, may explain their chemopreventive effects. In addition, these acetylenic oxylipins have shown to act as ligands for the nuclear receptor PPARγ, which play a central role in growth, differentiation, and apoptosis of cancer cells. Bioactive C₁₇ and C₁₈ acetylenic oxylipins appear, therefore, to constitute a group of promising lead compounds for the development of anticancer drugs. In this review, the cytotoxic, anti-inflammatory and anticancer effects of C₁₇ and C₁₈ acetylenic oxylipins from terrestrial plants are presented and their possible mechanisms of action and structural requirements for optimal cytotoxicity are discussed.

Polyacetylenes from Oplopanax horridus and Panax ginseng: Relationship between Structure and PPARγ Activation

Oplopanax horridus and Panax ginseng are members of the plant family Araliaceae, which is rich in structurally diverse polyacetylenes. In this work, we isolated and determined structures of 23 aliphatic C17 and C18 polyacetylenes, of which five are new compounds. Polyacetylenes have a suitable scaffold for binding to PPARγ, a ligand-activated transcription factor involved in metabolic regulation. Using a reporter gene assay, their potential was investigated to activate PPARγ. The majority of the polyacetylenes showed at least some PPARγ activity, among which oplopantriol B 18-acetate (1) and oplopantriol B (2) were the most potent partial PPARγ activators. By employing in silico molecular docking and comparing the activities of structural analogues, features are described that are involved in PPARγ activation, as well as in cytotoxicity. It was found that the type of C-1 to C-2 bond, the polarity of the terminal alkyl chain, and the backbone flexibility can impact bioactivity of polyacetylenes, while diol structures with a C-1 to C-2 double bond showed enhanced cytotoxicity. Since PPARγ activators have antidiabetic and anti-inflammatory properties, the present results may help explain some of the beneficial effects observed in the traditional use of O. horridus extracts. Additionally, they might guide the polyacetylene-based design of future PPARγ partial agonists.

Devil's Club Falcarinol-Type Polyacetylenes Inhibit Pancreatic Cancer Cell Proliferation

Natural falcarinol-type (FC-type) polyacetylenes are known to show anticancer activities. We studied the bioactivity of synthetic FC, 1,2-dihydrofalcarinol (FCH) and 3-acetoxyfalcarinol (FCA) and compared them with the natural bioactive polyacetylene [9,17-octadecadiene-12,14-diyne-1,11,16-triol,1-acetate] (DCA) isolated from Devil's club (DC) Oplopanax horridus. Antiproliferation activity of these polyacetylenes, along with DC inner stem bark 70% ethanol and water extracts, was tested on human pancreatic ductal adenocarcinoma cell lines PANC-1 and BxPC-3. Chemically synthesized FC and FCA showed consistent IC₅₀ (50% inhibition concentration) and higher potency than DCA. FC and DCA's mechanism of action investigated by antibody array on apoptosis-associated genes, and cellular features confirmed by microscopy demonstrated that both compounds modulated genes related to pro-apoptosis, antiapoptosis, apoptosis, cell cycle, stress related, and death receptors. FC-type polyacetylenes with a terminal double bond (FC, FCA, and DCA) are potent inhibitors of pancreatic cancer cell proliferation compared to FCH with a terminal single bond. Liquid chromatography mass spectrometry confirmed the presence of FC and FCH in the inner stem bark of DC. For potential applications of FC-type polyacetylenes as anticancer agents, preparing them by chemical synthesis may provide an advantage over the labor intensive extraction process from raw plant material.

Oplopanax horridus: Phytochemistry and Pharmacological Diversity and Structure-Activity Relationship on Anticancer Effects

Oplopanax horridus, well-known as Devil's club, is probably the most important ethnobotanical to most indigenous people living in the Pacific Northwest of North America. Compared with the long history of traditional use and widespread distribution in North America, the study of O. horridus is relatively limited. In the past decade, some exciting advances have been presented on the phytochemistry and pharmacological diversity and structure-activity relationship on anticancer effects of O. horridus. To date, no systematic review has been drafted on the recent advances of O. horridus. In this review, the different phytochemicals in O. horridus are compiled, including purified compounds and volatile components. Animal and in vitro studies are also described and discussed. Especially, the potential structural-activity relationship of polyynes on anticancer effects is highlighted. This review aimed to provide comprehensive and useful information for researching O. horridus and finding potential agents in drug discovery.

Screening and identifying antioxidants from Oplopanax elatus using 2,2'-diphenyl-1-picrylhydrazyl with off-line two-dimensional HPLC coupled with diode array detection and tandem time-of-flight mass spectrometry

The root of Oplopanax elatus (Nakai) Nakai has a well-known history of use for the treatment of diseases such as neurasthenia, cardiovascular disorders, and cancer by the native people in northeast China. It is important to screen and identify the bioactive molecules from its root rapidly. Hereby, an off-line two-dimensional high performance liquid chromatography coupled with diode array detection and tandem time-of-flight mass spectrometry together with 2,2'-diphenyl-1-picrylhydrazyl was established to screen antioxidants from the root of O. elatus. A Waters cyanogen column (150 × 3.9 mm, id, 4 μm) was used for the first dimensional liquid chromatography, while a Hypersil BDS-C18 column (250 × 4.6 mm, id, 5 μm) was installed for the second dimension liquid chromatographic analysis. Twenty-eight compounds had been tentatively identified from the methanol extract of the air-dried root of O. elatus including six polyynes and eight phenolic derivatives were screened with antioxidant activity. The developed method could be expedient for screening and identifying antioxidants from O. elatus.

Determination of six polyynes in Oplopanax horridus and Oplopanax elatus using polyethylene glycol modified reversed migration microemulsion electrokinetic chromatography

A PEG-modified reversed migration MEEKC method was developed for simultaneous determination of six polyynes, including oplopandiol, falcarindiol, oplopandiol acetate, (11S, 16S, 9Z)-9,17-octadecadiene-12,14-diyne-1,11,16-triol,1-acetate, oplopantriol B, and oplopantriol A, in Oplopanax horridus and Oplopanax elatus. The running buffer containing 0.8% v/v ethyl acetate, 3.8% w/v SDS, 6.6% v/v n-butanol in 20 mM phosphate buffer (pH 2.5), followed by mixing with propan-2-ol at 30% v/v and PEG-1000 at 15% w/v, was applied in the analysis. The proposed method was successfully applied to determine the six polyynes in five samples of Oplopanax horridus and one of O. elatus. The result showed that the types and amounts of polyynes present were obviously different when comparing the two herbs. Besides, the developed PEG-modified reversed MEEKC method might be suitable for the analysis of hydrophobic analytes in herbal medicines.

Phenolic Derivatives from the Root Bark of Oplopanax horridus

Four new phenolic derivatives, including two phenylpropanoid glycosides, one benzoate glycoside, and one lignan glycoside, together with one known glyceride, were isolated from the root bark of Oplopanax horridus. The structures of the new compounds were elucidated as 3-{4-[(6-O-acetyl-β-D-glucopyranosyl) oxy]-3,5-dimethoxyphenylpropanoic acid (1), (+)-[5,6,7,8-tetrahydro-7- (hydroxylmethyl)-10,11-dimehoxydibenzo[a,c][8]annulen-6-yl]methyl β-D-glucopyranoside (2), (+)-methyl 4-[6-O-{3-hydroxy-3-methyl-5-(1-methylpropyl)oxy]-5-oxopentanoyl}-4-O-(β-D-glucopyranosyl)-β-D-glucopyranosyl)oxy]-3-methoxybenzoate (3), and 2-methoxy-4-[(1E)-3-methoxy-3-oxoprop-1-en-1-yl]phenyl 6-O-{3-hydroxy-3-methyl-5-[(1-methylpropyl)oxy]-5-oxopentanoyl-4-O-β-D-glucopyranosyl-β-D-glucopyranoside (4) on the basis of spectroscopic techniques including NMR and MS analyses. The known compound was identified as glycer-2-yl ferulate (5) by comparing its physical and spectral data with those reported in the literature.

Chemopreventive effects of oplopantriol A, a novel compound isolated from Oplopanax horridus, on colorectal cancer

Oplopanax horridus is a North American botanical that has received limited investigations. We previously isolated over a dozen of the constituents from O. horridus, and among them oplopantriol A (OPT A) is a novel compound. In this study, we firstly evaluated the in vivo chemoprevention activities of OPT A using the xenograft colon cancer mouse model. Our data showed that this compound significantly suppressed tumor growth with dose-related effects (p < 0.01). Next, we characterized the compound's growth inhibitory effects in human colorectal cancer cell lines HCT-116 and SW-480. With OPT A treatment, these malignant cells were significantly inhibited in both a concentration- and time-dependent manner (both p < 0.01). The IC50 was approximately 5 µM for HCT-116 and 7 µM for SW-480 cells. OPT A significantly induced apoptosis and arrested the cell cycle at the G2/M phase. From further mechanism explorations, our data showed that OPT A significantly upregulated the expression of a cluster of genes, especially the tumor necrosis factor receptor family and caspase family, suggesting that the tumor necrosis factor-related apoptotic pathway plays a key role in OPT A induced apoptosis.

Anticancer activities of polyynes from the root bark of Oplopanax horridus and their acetylated derivatives

Six polyynes OH-1~6, some of which are occur naturally in acetylated form, had been isolated and identified from the root bark of Oplopanax horridus (Devil’s Club), a natural dietary supplement and medicinal plant in North America. During the evaluation of the polyynes’ potential anticancer activities, sixteen more acetylated derivatives OHR-1~16 have synthesized and their anti-proliferation activity on MCF-7, MDA-MB-231, A549, HepG2 and LO2 cells assayed to elucidate their structure-activity relationships. The results showed that OH-1 ((3S, 8S)-falcarindiol) had the most potent anticancer activity, with IC₅₀ values of 15.3, 23.5, 7.7 and 4.7 μM on MCF-7, A549, HepG2 and MDA-MB-231 cells, respectively. For the primary structure-activity relationship, the anticancer activities of polyynes become weaker if their hydroxyl groups are acetylated, the terminal double bonds transformed into single bonds or they contain one more methylene group in the main skeleton chain.

Anticancer compound Oplopantriol A kills cancer cells through inducing ER stress and BH3 proteins Bim and Noxa

Oplopantriol-A (OPT) is a natural polyyne from Oplopanax horridus. We show here that OPT preferentially kills cancer cells and inhibits tumor growth. We demonstrate that OPT-induced cancer cell death is mediated by excessive endoplasmic reticulum (ER) stress. Decreasing the level of ER stress either by inactivating components of the unfolded protein response (UPR) pathway or by expression of ER chaperone protein glucose-regulated protein 78 (GRP78) decreases OPT-induced cell death. We show that OPT induces the accumulation of ubiquitinated proteins and the stabilization of unstable proteins, suggesting that OPT functions, at least in part, through interfering with the ubiquitin/proteasome pathway. In support of this, inhibition of protein synthesis significantly decreased the accumulation of ubiquitinated proteins, which is correlated with significantly decreased OPT-induced ER stress and cell death. Finally, we show that OPT treatment significantly induced the expression of BH3-only proteins, Noxa and Bim. Knockdown of both Noxa and Bim significantly blocked OPT-induced cell death. Taken together, our results suggest that OPT is a potential new anticancer agent that induces cancer cell death through inducing ER stress and BH3 proteins Noxa and Bim.

Identification of potential anticancer compounds from Oplopanax horridus

Oplopanax horridus is a plant native to North America. Previous reports have demonstrated that this herb has antiproliferative effects on cancer cells but study mostly focused on its extract or fractions. Because there has been limited phytochemical study on this herb, its bioactive compounds are largely unknown. We recently isolated and identified 13 compounds, including six polyynes, three sesquiterpenes, two steroids, and two phenolic acids, of which five are novel compounds. In this study, we systemically evaluated the anticancer effects of compounds isolated from O. horridus. Their antiproliferative effects on a panel of human colorectal and breast cancer cells were determined using the MTS assay. Cell cycle distribution and apoptotic effects were analyzed by flow cytometry. The in vivo antitumor effect was examined using a xenograft tumor model. Among the 13 compounds, strong antiproliferative effects were observed from falcarindiol and a novel compound oplopantriol A. Falcarindiol showed the most potent antiproliferative effects, significantly inducing pro-apoptosis and cell cycle arrest in the S and G2/M phases. The anticancer potential of falcarindiol was further verified in vivo, significantly inhibiting HCT-116 tumor growth in an athymic nude mouse model at 15 mg/kg. We also analyzed the relationship between polyyne structures and their pharmacological activities. We observed that both the terminal hydroxyl group and double bond obviously affected their anticancer potential. Results from this study supplied valuable information for future semi-synthesis of polyyne derivatives to develop novel cancer chemopreventive agents.

The antitumor natural compound falcarindiol promotes cancer cell death by inducing endoplasmic reticulum stress

Falcarindiol (FAD) is a natural polyyne with various beneficial biological activities. We show here that FAD preferentially kills colon cancer cells but not normal colon epithelial cells. Furthermore, FAD inhibits tumor growth in a xenograft tumor model and exhibits strong synergistic killing of cancer cells with 5-fluorouracil, an approved cancer chemotherapeutic drug. We demonstrate that FAD-induced cell death is mediated by induction of endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). Decreasing the level of ER stress, either by overexpressing the ER chaperone protein glucose-regulated protein 78 (GRP78) or by knockout of components of the UPR pathway, reduces FAD-induced apoptosis. In contrast, increasing the level of ER stress by knocking down GRP78 potentiates FAD-induced apoptosis. Finally, FAD-induced ER stress and apoptosis is correlated with the accumulation of ubiquitinated proteins, suggesting that FAD functions at least in part by interfering with proteasome function, leading to the accumulation of unfolded protein and induction of ER stress. Consistent with this, inhibition of protein synthesis by cycloheximide significantly decreases the accumulation of ubiquitinated proteins and blocks FAD-induced ER stress and cell death. Taken together, our study shows that FAD is a potential new anticancer agent that exerts its activity through inducing ER stress and apoptosis.

Chemical and pharmacological studies of Oplopanax horridus, a North American botanical

Oplopanax horridus (OH), or Devil's club, is an ethnobotanical used by the indigenous people native to the Pacific Northwest of North America. There are three species in the genus Oplopanax, and OH is the only species that is distributed in North America. Compared with the extensive research on OH's "cousin," American ginseng, there is comparatively little reported about the chemical makeup and pharmacological effects of OH. Nevertheless, there has been some research over the past few years that shows promise for the future usage perspectives of OH. To date, 17 compounds were isolated and elucidated, including polyynes, glycosides, lignans, and polyenes, with most of the attention being paid to the polyynes. Gas chromatography (GC) and high-performance liquid chromatography (HPLC) were used to determine the contents of volatile compounds and polyynes in the essential oil and extracts of OH. For the pharmacological studies, antibacterial and antidiabetes effects of polyynes were reported. Our recent study has focused more on the anticancer effects of OH and the involved mechanisms of action. In this review, we will summarize the research status in the botany, phytochemistry, and pharmacology of OH.

Ginsenosides from American ginseng: chemical and pharmacological diversity

Ginseng occupies a prominent position in the list of best-selling natural products in the world. Compared to the long history of use and widespread research on Asian ginseng, the study of American ginseng is relatively limited. In the past decade, some promising advances have been achieved in understanding the chemistry, pharmacology and structure-function relationship of American ginseng. To date, there is no systematic review of American ginseng. In this review, the different structures of the ginsenosides in American ginseng are described, including naturally occurring compounds and those resulting from steaming or biotransformation. Preclinical and clinical studies published in the past decade are also discussed. Highlighted are the chemical and pharmacological diversity and potential structural-activity relationship of ginsenosides. The goal is that this article is a useful reference to chemists and biologists researching American ginseng, and will open the door to agents in drug discovery.

Hydrophobic constituents and their potential anticancer activities from Devil's Club (Oplopanax horridus Miq.)

ETHNOPHARMACOLOGICAL RELEVANCE

Devil's Club (Oplopanax horridus) is one of the most important spiritual and medicinal plants to many indigenous peoples of Alaska and the Pacific Northwest. It is widely used for external and internal infections as well as arthritis, respiratory ailments, digestive tract ailments, broken bones, fever, headaches, and cancer.

AIM OF THE STUDY

To investigate hydrophobic constituents and their potential anticancer activity from Devil's Club, Oplopanax horridus.

MATERIALS AND METHODS

The root bark extract of Oplopanax horridus was isolated by chromatographic techniques. Structures of isolated compounds were identified by spectroscopic methods and comparison with published data. The anti-proliferation of isolated hydrophobic constituents in human breast cancer MCF-7 cells, human colon cancer SW-480 and HCT-116 cells were tested. The potential mechanism of anti-proliferation was also investigated using cell cycle and apoptosis assays.

RESULTS AND DISCUSSION

Six compounds were isolated and structurally identified as 9,17-octadecadiene-12,14-diyne-1,11,16-triol, 1-acetate (1), oplopandiol acetate (2), falcarindiol (3), oplopandiol (4), trans-nerolidol (5) and t-cadinol (6). These compounds showed potential anticancer activities on human breast cancer and colon cancer cells, of which compound 3 possesses the strongest activity. Further cell cycle and apoptosis tests by flow cytometry showed the polyacetylenes 1-4 induced HCT-116 cell arresting in G2/M phase and inhibited proliferation by the induction of apoptosis at both earlier and later stages.

CONCLUSION

These results provide promising baseline information for the potential use of Oplopanax horridus, as well as some of the isolated compounds in the treatment of cancer.

American ginseng: potential structure-function relationship in cancer chemoprevention

Ginseng has a prominent position on the list of best-selling herbal products in the world, and its main active constituents are thought to be ginsenosides. Compared with the long history of use and widespread research on Asian ginseng, studies of American ginseng are relatively limited, especially regarding cancer chemoprevention. In recent studies of American ginseng, steaming or heating altered the ginsenoside profile and thereby increased anticancer effects. Yet the ginsenoside structures and their activities have not been systematically elucidated. In this commentary, we introduce the different ginsenosides in American ginseng, both the naturally occurring compounds and those resulting from steaming or biotransformation. We briefly review American ginseng's reported anticancer effects and their mechanisms of action, and explore the possible structural-function relationship with a focus on sugar molecules, hydroxyl groups and stereoselectivity in ginsenosides. Understanding these relationships may produce insights into chemical and pharmacological approaches for enhancing the chemopreventive effects of ginsenoside and for developing novel anticancer agents.

Quantitative analysis of six polyynes and one polyene in Oplopanax horridus and Oplopanax elatus by pressurized liquid extraction and on-line SPE-HPLC

A pressurized liquid extraction and on-line SPE-HPLC method was developed for simultaneous determination of six polyynes, including falcarindiol, oplopandiol, (11S,16S,9Z)-9,17-octadecadiene-12,14-diyne-1,11,16-triol,1-acetate, oplopandiol acetate, oplopantriol A, oplopantriol B, and one polyene, (S,E)-nerolidol, in Oplopanax horridus and Oplpanax elatus. The analysis was conducted on a Grace Prevail C(18) column (3 microm, 7 mm x 33 mm) with gradient elution of acetonitrile and water after the sample loaded and washed with 42%ACN in 0.3 min on a phenomenex Strata-X on-line Extraction Cartridge SPE column (2.5 microm, 2.0 x 20 mm). All calibration curves of seven analytes showed good linearity within the test ranges. The validated method was successfully applied to quantify six polyynes and one polyene in two species of Oplopanax, O. horridus and O. elatus.