Isolation, structural identification and cytotoxic activity of hexanic extract, cyperenoic acid, and jatrophone terpenes from Jatropha ribifolia roots

Abstract

The cytotoxicity of a hexanic fraction produced from the ethanolic crude extract, obtained from Jatropha ribifolia (Pohl) Baill, Euphorbiaceae, roots was evaluated against ten human cancer cell lines (MCF-7, NCI-ADR/RES, OVCAR-3, PC-3, HT-29, NCI-H460,786-O, UACC-62, K-562, U251) compared with doxorrubicine as positive control. Compounds jatrophone and cyperenoic acid were isolated from the hexanic extract and characterized by spectroscopic techniques (NMR of ¹H, 13C and IR). The in vitro antiproliferative activity of jatrophone showed selectivity in a concentration dependent way with Total Inhibition growth of: glioma 0.57 µg mL-1 (U251), breast cancer 9.2 µg mL-1 (MCF-7), adriamycin-resistant ovarian cancer 0.96 µg mL-1 (NCI-ADR/RES), kidney 4.2 µg mL-1 (786-0), prostate cancer 8.4 µg mL-1 (PC-3), colon cancer 16.1 µg mL-1 (HT29) and leukemia 0.21 µg mL-1 (K-562).

cytotoxic activity; diterpene; Euphorbiaceae; Jatropha ribifolia; sesquiterpene

Isolation, structural identification and cytotoxic activity of hexanic extract, cyperenoic acid, and jatrophone terpenes from Jatropha ribifolia roots

Elaine de S. Fernandes^I; Fátima A. Rodrigues^I; Danilo Tófoli^II; Paulo M. Imamura^III; João E. de Carvalho^IV; Ana L. T. G. Ruiz^IV; Mary A. Foglio^IV; Sandro Minguzzi^I; Rogério C. L. SilvaI, ^*

^IDepartamento de Química, Unidade Universitária de Naviraí, Universidade Estadual de Mato Grosso do Sul, Brazil

^IIDepartamento de Química, Universidade Federal de Mato Grosso do Sul, Centro de Ciências Exatas e Tecnologia, Universidade Federal de Mato Grosso do Sul, Brazil

^IIIDepartamento de Química, Universidade Estadual de Campinas, Brazil

^IVCentro Pluridisciplinar de Pesquisas Químicas, Biológicas e Agrícolas, Universidade Estadual de Campinas, Brazil

ABSTRACT

The cytotoxicity of a hexanic fraction produced from the ethanolic crude extract, obtained from Jatropha ribifolia (Pohl) Baill, Euphorbiaceae, roots was evaluated against ten human cancer cell lines (MCF-7, NCI-ADR/RES, OVCAR-3, PC-3, HT-29, NCI-H460,786-O, UACC-62, K-562, U251) compared with doxorrubicine as positive control. Compounds jatrophone and cyperenoic acid were isolated from the hexanic extract and characterized by spectroscopic techniques (NMR of ¹H, ¹³C and IR). The in vitro antiproliferative activity of jatrophone showed selectivity in a concentration dependent way with Total Inhibition growth of: glioma 0.57 µg mL^-1 (U251), breast cancer 9.2 µg mL^-1 (MCF-7), adriamycin-resistant ovarian cancer 0.96 µg mL^-1 (NCI-ADR/RES), kidney 4.2 µg mL^-1 (786-0), prostate cancer 8.4 µg mL^-1 (PC-3), colon cancer 16.1 µg mL^-1 (HT29) and leukemia 0.21 µg mL^-1 (K-562).

Keywords: cytotoxic activity; diterpene; Euphorbiaceae; Jatropha ribifolia; sesquiterpene

Introduction

Bioactive terpenes have a significant importance for the pharmaceutical industry which covers a wide range of diverse chemical compounds, providing opportunities for synthesis (Wang & Bidigare, 2005). The genus Jatropha is recognized as an important source of secondary metabolites, with mainly terpenes that are fairly known to this genus (Can-Aké et al., 2004).

Jatropha ribifolia (Pohl) Baill (Euphorbiaceae) is found throughout the Brazilian northeastern region, popularly known as "pinhão-de-purga" (purgin nut). The latex is used by folkmedicine for treatment of snake bites and to treat upper tract decongestions. No previous reports were found describing the phytochemical studies of this species that is considered endemic in the state of Mato Grosso do Sul and known in Navirai as "minâncora-do-campo" (Souza & Rodal, 2010). Herein we report the isolation and structure elucidation of the compounds jatrophone and cyperenoic acid with in vitro antiproliferative activity.

Materials and Methods

Plant material

Material was collected at Naviraí, Mato Grosso do Sul, Brazil. Voucher specimen (CGMS 31.481) was deposited at the Herbarium of the Institute of de Botany of São Paulo at the University of São Paulo, Brazil.

Isolation procedures

Fresh roots (1.5 kg) of Jatropha ribifolia (Pohl) Baill., Euphorbiaceae, were ground, and extracted with EtOH at room temperature. The solvent was removed under reduced pressure yielding 386 g (25.7%) of crude ethanol extract. The crude extract was further partitioned with n-hexane and MeOH-H₂O (9:1). The crude dried n-hexane-soluble fraction (7.75 g) was purified by silica gel column chromatography using gradients of n-hexane/EtOAc and EtOAc. Fractions eluted with n-hexane:EtOAc (20 and 25%) were grouped and purified by column chromatography yielding jatrophone compound 1 (431.3 mg). Cyperenoic acid was isolated from the crude n-hexane extract obtained from freshly picked roots (660 g) further extracted with n-hexane under reflux. After removal of the organic solvent under reduced pressure, 8 g of the extract was purified by silica gel column chromatography affording 475.8 mg of compound 2. The active compounds were monitored by the in vitro antiproliferative assay.

Spectroscopic analysis

The structures determination were based mainly on spectroscopic investigation of ¹H and ¹³C NMR studies including HMBC (hetero nuclear multiple bond correlation) and COSY (proton-proton correlation) experimental. Infrared (IR) spectroscopy was utilized for identifying absorption band and gas chromatography coupled mass spectrometry for the structure mass-charge (m/z).

Biological tests

In vitro antiproliferative assay in human cancer cell lines

For the in vitro antiproliferative activity screening, ten cell lines were selected from human tumors, designated as: strains K562 (leukemia), MCF-7 (breast), NCI-ADR/RES (ovarian phenotype of resistance to multiple drugs), UACC-62 (melanoma), NCI-H460 (lung), PC 3 (prostate), HT29 (colon), OVCAR-3 (ovarian), 786-0 (kidney) and U251 (glioma), and a normal cell lines: VERO (monkey kidney) later replaced by HaCat (human keratinocyte). All cell lines were provided by the National Cancer Institute (NCI), USA. The experimental procedures were performed according with the literature (Skehan et al., 1990; Monks et al., 1991; Rubinstein et. al., 1990).

Stock solution of the n-hexanic extract, jatrophone (1) and cyperenoic acid (2) compounds (100 mg mL^-1) were prepared in dimethylsulfoxide (DMSO). Cell culture DMSO was diluted 400 times in RPMI/FBS/gentamicin, to avoid toxicity. After dilution, 100 µL of medium containing the extract and compounds to be tested were added to a 96 compartments (except for the control) at concentrations of 0.25, 2.5, 25 and 250 µg mL^-1. The plates were incubated for 24 h at 37 °C in a 5% CO₂ in a humid environment.

Cells were cultured in RPMI-1640 medium (10 mL), supplemented with 5% fetal calf serum (SFB). The vials were centrifuged (2000 g) by 4 min at 4 ºC. The supernatant was collected and discarded and precipitated of cells were resuspended in 5 mL culture medium. After 48 h, the plate T0 was fixed by adding 50 µL trichloroacetic acid (TCA) 50 % determining the actual amount of cells present at the time the samples were applied. After 48 h treatment 50 µL of TCA (50%) was added and incubated for 1 h at 4 ºC. Then the plates were subjected to four successive washes with water to remove residues of TCA, medium, SFB and secondary metabolites, and then stored at room temperature until complete drying with further adition of 50 µL of sulforhodamine B (SRB) to 0.4% (weight/volume) dissolved in 1% acetic acid, and incubated at room temperature for 30 min. After wards the plates were washed four times consecutively with a solution of 1% acetic acid for complete removal of residues of SRB. After complete drying the plates at room temperature, the protein bound dye was solubilized by adding 150 µL of 10 µM Trizma Base in pH 10.5. The cells were then fixed with 50% trichloroacetic acid. Cell proliferation was determined by spectrophotometric quantification at 540 nm using the sulforhodamine B as dyeing reagent. Doxorubicin chloridate (0.025 to 25 µg mL^-1) was used as positive control (Table 3).

Date analysis

The averages of the absorbance were calculated discounting the value the white and total growth inhibition (TGI) was determined by the equation: if T>C the drug stimulated the growth and showed not IC; if T≥T_o and <C, the drug was cytostatic and the equation used was 100 x [(T-T_o)/(C-T_o)]; is T<T_o and drug was cytocidal equation used was 100 x [(T-T_o)/(T_o)], being T the absorbance of treated cell, C the cell control and To control cells on day of addition of the drugs, the results was subtracted from 100% to yield the percentage of growth. The absorbance data were analyzed and compiled in constructing graphs using the Origin 7.5 software correlating the percentage of inhibition or cell death at the concentration of extract and terpenes.

Results and Discussion

Isolation and structural identification

The antitumor properties of species of the genus Jatropha have been targets of phytochemical studies. No previous reports on in vitro antiprolifrative activity on human cancer cell lines Jatropha ribifolia (Pohl) Baill., Euphorbiaceae, were found. Compound 1 (Figure 1) was obtained as colorless crystals with mp 142-144 °C. The GC/MS spectrum gave an [M-H] ion at m/z 312.1, corresponding to the molecular formula C₂₀H₂₄O₃. The FTIR spectrum showed absorption at OH 3449 cm^-1 indicating the presence of OH group and carbonyl group at 1697 cm^-1. The ¹H and ¹³C NMR spectroscopy and 2D NMR technique (Table 1) were compared with data reported by Goulart et al., (1993) and Taylor et al. (1983) confirming the structure which is a common compound among the genus Jatropha. Compound 2 (Figure 2) was obtained as colorless crystals with mp 162-164 °C. The GC/MS spectrum gave an [M-H] ion at m/z 234.1 corresponding to the molecular formula C₁₅H₂₂O₂. The FTIR spectrum showed a broad absorption at 3430 cm^-1 due to the presence of OH group and carbonyl group at 1674 cm^-1 indicating the presence of carboxylic acid. The ¹H and ¹³C NMR spectroscopy and 2D NMR technique (Table 2) were compared with the data reported by Pertino (2006) for cyperenoic acid, confirming the chemical structure. This is the first time where the presence of this compound was described in this specie. The NOESY spectrums of jatrophone and cyperenoic acid showed the H groups in proximity (Figure 1 and 2) confirming the stereochemical aspects observed by X-ray, for both compounds. (Pertino et. al., 2006; Jacobs et al., 1987).

In vitro antitumour activity

This is the first report exploring the in vitro antiproliferative activities effect of J. ribifolia extract and two isolated terpenic compounds, jatrophone and cyperenoic acid against ten human cells lines and normal monkey cells (VERO). A range of J. ribifolia roots extract and terpenes concentration (0.25 µg mL^-1 to 250 µg mL^-1) were used to investigate the relative degree of TGI against the following cell line: glioma (U251), melanoma (UACC-62), breast cancer (MCF7), adriamycin-resistant ovarian cancer (NCI-ADR/RES), kidney (786-0), non-small lung cancer (NCl-H460), ovarian cancer (OVCAR-3), prostate cancer (PC-3), colon cancer (HT29), leukemia (K-562) and normal green monkey kidney cells (VERO). Figure 3 shows the curves of the concentration response for the doxorrubicin control drug, hexanic extract, cyperenoic acid and jatrophone terpenes against human tumor cells. Table 3 presents the results determined by the in vitro antiproliferative assay with human cancer cell lines.

The activity of hexanic extract was efficient for seven cell lines tested, when compared with doxorrubicine, with an in vitro antiproliferative activity ranging from 1.2 to 26.5 µg mL^-1. The hexanic extract's cytocidal activity against tumoral cells growth was significantly efficient for seven strains. The necessary concentration for Total growth Inhibition (TGI) for tumoral cells were 1.2 µg mL^-1 (U251), 15.5 µg mL^-1 (MCF-7), 9.5 µg mL^-1 (NCI-ADR/RES), 9.1 µg mL^-1 (786-0), 12.3 µg mL^-1 (PC-3), 26.5 µg mL^-1 (HT29) and 2.4 µg mL^-1 (K-562). The best selectivity was observed with glioma (U251) with 1.2 µg mL^-1, above this concentration was observed cell death of VERO cells (normal cell) with 1.7 µg mL^-1. The activity on tumoral cells was also observed for the crude hexane extract due to the presence of jatrophone and cyperenoic acid. The terpenes when isolated also showed significant results in the bioassay under study. The cytocidal activity for cyperenoic acid against tumoral growth cells was efficient for three tested cells. The TGI for tumoral cells were 11.4 µg mL^-1 (U251), 25.1 µg mL^-1 (PC-3) and 10.5 µg mL^-1 (K-562). For VERO cells 9.5 µg mL^-1 was the concentration determined. Better results were noted for jatrophone (1) with selectivity in a concentration dependent way determined as 0.57 µg mL^-1 (U251), 9.2 µg mL^-1 (MCF-7), 0.96 µg mL^-1 (NCI-ADR/RES), 4.2 µg mL^-1 (786-0), 8.4 µg mL^-1 (PC-3), 16.1 µg mL^-1 (HT-29) and 0.21 µg mL^-1 (K-562) and VERO (normal cells). Doxorubicin drug was efficient to total growth inhibition in concentration 25 µg mL^-1.

Further studies are necessary to better understand the toxic effects toward normal cells. These terpenes were isolated in other Euphorbiaceae species (Pertino et al., 2006), nevertheless no antiproliferative activities test were reported for cell lines mentioned herein. Previous authors evaluated activities against epithelial gastric cell line (AGS) and gastroprotecion effect (Pertino et al., 2006; Fröhlich et al., 2010). Cyperenoic acid (2) has been also isolated from different species of plants as Sandwithia guyanensis (Jacobs et al., 1987) Croton crassifolius (Boonyaratavej et al., 1988) and from Joannesia princeps which was evaluated for antifungic activity (Fröhlich et al., 2010). The preliminary results presented here show that jatrophone (1) and cyperenoic acid (2) could be a promising molecule to study for the development of a new cancer treatment.

Acknowledgment

The authors are grateful to Dr. Lauro E. S. Barata and the University of Campinas for the chemical analysis.

Authors' contributions

ESF, FAR, and DT (graduation students) contributed in collecting plant sample and identification and isolation, purification of the extracts of the isolated compounds. PMI contributed to purification and spectroscopic analysis. JEC, ALTGR and MAF contributed to in vitro antiproliferative assay and interpretation. SM and RCLS contributed to EF student orientation and analysis of the results and writing of the manuscript. All the authors have read the final manuscript and approved the submission.

Received 18 Sep 2012

Accepted 23 Jan 2013

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Publication Dates

• Publication in this collection
  26 Mar 2013
• Date of issue
  June 2013

History

• Received
  18 Sept 2012
• Accepted
  23 Jan 2013