Plant material and extraction
The stem bark of A. cadamba (Roxb.) Miq. (Rubiaceae) was collected from the middle hill region of Sikkim in the month of September 2010 and authenticated by Botanical Survey of India, Gangtok, India. A voucher specimen (SHRC-5/5/2010/Tech.47A) was deposited at Phytotherapy and Pharmacology Research Laboratory, Department of Pharmaceutical Technology, Jadavpur University, Kolkata. First the collected stem bark was shade dried at room temperature for 7 days and then powdered in a mechanical grinder. Next, the powdered plant material (1 Kg) was successively extracted by methanol using Soxhlet extraction apparatus. Then solvent was completely evaporated under reduced pressure, in vacuo at 40 °C to render the methanol extract (MEAC; 200 g; 20.0% w/w).
Phytochemical analysis of MEAC
Qualitative screening
The presence of various phytoconstituents such as glycosides, steroids, saponins, alkaloids, tannins, phenolics and flavonoid were analyzed by using standard protocols (
10).
Quantification of total phenolic and flavonoid contents
The quantities of phenolics and flavonoids compound were measured by the method described in our previous study (
11). The Folin–Ciocalteu method and aluminium trichloride colormetric assay were applied for the determination of phenolics and flavonoids compound, respectively.
Animals
Swiss albino mice of about 8 weeks of age with an average body weight of 20-25 g were used for the experiment. The mice were grouped and housed in poly acrylic cages (38 cm × 23 cm × 10 cm) with not more than six animals per cage.
The animals were maintained under standard laboratory conditions (temperature 25-30 °C and 55-60% relative humidity with dark/light cycle 14/10 h) and were allowed to free access of standard dry pellet diet and water ad libitum. The mice were acclimatized to laboratory conditions for 7 days before commencement of the experiment.
Acute toxicity study
The acute oral toxicity of MEAC in Swiss albino mice was performed as per OECD guideline 425 (OECD, 2008). The extract was safe up to the dose of 2 g/Kg b.w. p.o. for mice. Generally 1/5th to 1/10th of the lethal dose has taken for effective dose calculation. So, 200 and 400 mg/Kg b.w. doses were used in the present study (
9).
Cell culture
DLA cells were obtained from Chittaranjan National Cancer Institute, Kolkata, India. Ascitic fluid was drawn out from DLA tumor bearing mouse at the log phase (days 7–8 of tumor bearing) of the tumor cells. The DLA cells were maintained in-vivo in Swiss albino mice by intraperitoneal transplantation of 2×106 cells per mouse after every 10 days and it is used for both in-vivo and in-vitro study.
Cell viability assay
Cell viability was determined by using the3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay (
12). Briefly, 0.1 mL of cell suspension was seeded in 96-well plates (Greiner, Frickenhausen, Germany) with a seeding density of 1×10
4 cells/well. The cells were treated with different concentrations of MEAC (10, 25, 50, 100, 150 and 200 μg/mL) and incubated for 24 h at 37 °C, 5% CO
2 with 98% relative humidity. After incubation, 20 μL of MTT (5 mg/mL) in phosphate buffered saline (PBS) were added to each well and the plates were incubated for 4 h at 37 °C. The colored formazan crystals which were produced from MTT were dissolved in 150 μL of dimethyl sulfoxide (DMSO) and the absorbance was measured at a wavelength of 570 nm by ELISA plate reader. All determinations were carried out in triplicate. Concentrations of MEAC showing 50% reduction in cell viability (ie, IC
50 values) were then calculated.
Treatment schedulefor assessment of antitumor potential
Swiss albino mice (20–25 g) were divided in to four groups (
n = 12). Except Group-I all the animals in each groups were being injected DLA cells (2×10
6 cells/mouse, i.p.). This was marked as day ‘0’. Group-I served as normal saline control (5 mL/Kg, i.p.) and group-II served as DLA control. After 24 h, DLA transplanted Group-III and IV were being injected MEAC (200 and 400 mg/Kg b.w, i.p.) once daily for 14 consecutive days (
9). After administration of last dose, 6 mice from each group were kept fasting for 18 h and blood was collected by direct cardiac puncture for the estimation of hematological parameters determination and then those animals were sacrificed for collection of DLA cells to check the apoptogenic properties of stem bark of
A. cadamba. Rest of the animals in each groups were kept alive with food and water
ad libitum to check percentage increase in life span of the tumor host to determine the mean survival time (MST).
Antitumor activity of MEAC was assessed by observation of changes with respect to the following parameters (
13).
Tumor volume and weight
The mice were dissected and the ascitic fluid was collected from the peritoneal cavity. Volume of the fluid was measured by taking it in a graduated centrifuge tube and expressed in milliliter (mL). Tumor weight was measured by taking the weight of the mice before and after the collection of the ascitic fluid from peritoneal cavity and expressed in gram (g).
Percentage increase life span (% ILS)
The effect of MEAC on tumor growth was monitored by recording the mortality of the experimental mice. Percentage increase in life span (%ILS) was calculated by the following formula.
Mean survival time (MST) in days = (Day of the first death + Day of the last death) / 2
ILS (%) = [(MST of the treated group / MST of the control group) – 1] × 100
Tumor cell (Viable/nonviable) count
The ascitic fluid was taken in a WBC pipette and diluted upto 20 times with PBS solution. Then a drop of the diluted cell suspension was placed on the Neubauer’s counting chamber and the numbers of cells in the 64 small squares were counted.
The viability and non-viability of the cell were determined by trypan blue assay. The cells were stained with trypan blue (0.4% in normal saline) dye. The cells that did not take up the dye were viable and those that took the dye were nonviable. These viable and nonviable cells were counted by using the under-scribbled formula.
Cell count = (Number of cells × dilution factor) / (Area × thickness of liquid film)
Hematological parameters
Collected blood was used for the estimation of hemoglobin (Hb), red blood cell (RBC) and white blood cell (WBC) count by standard procedures (
14).
Detection of apoptosis
Isolation of DLA from mice peritoneal cavity
The DLA cells were isolated from the peritoneal cavity of tumor-bearing mice (control or treated). 3 mL of sterile PBS was injected into the peritoneal cavity of the mice and the peritoneal fluid containing the tumor cells was withdrawn, collected in sterile Petri dish and incubated at 37 °C for 2 h. The cells of macrophage lineage adhered to the bottom of the Petri dishes. The non-adherent population was aspirated out gently and repeatedly washed with PBS. The viability of DLA was assessed by trypan blue exclusion test. The viable DLA cells were processed for further experiments (
15).
Acridine orange (AO) and ethidium bromide (EB) double staining
DNA binding dyes AO and EB (Sigma Aldrich, USA) were used for the morphological detection of apoptotic and necrotic cells (
16). DLA cells (1×10
6) were collected from sacrificed mice. The cells were detached, washed by cold PBS and then stained with a mixture of AO (100 μg/mL) and EB (100 μg/mL) at room temperature for 5 min. The stained cells were observed by a fluorescence microscope (Leica DM 3000, Germany) at 40X magnifications. The cells were divided into four categories as follows: living cells (normal green nucleus), early apoptotic (bright green nucleus with condensed or fragmented chromatin), late apoptotic (orange-stained nuclei with chromatin condensation or fragmentation) and necrotic cells (uniformly orange-stained cell nuclei). In each experiment, more than 300 cells/sample were counted for % of apoptotic cells count.
Comet Assay
The extent of DNA was quantified by alkaline single cell gel electrophoresis (SCGE), also known as the comet assay. Briefly, cells suspended in 0.5% (w/v) low melting agarose were layered over a frosted microscopic slide coated with a layer of 1% normal melting agarose. The slides were left in a lysing solution overnight at 4 °C. Electrophoresis was carried out for 30 min (280 mA, 20 V) at 4 °C. The slides were washed thrice with neutralizing buffer (Tris 0.4 M, pH 7.5), stained with EB, examined under a fluorescence microscope (Leica DM3000, Germany) and subjected to image analysis using CometScore software (
17).
Flow cytometric analysis (FACS) assay
Assay was performed using procedure described in the reagent-kit purchased from BD Biosciences and protocol was followed by manufacturer’s instruction. To distinguish between apoptosis and necrosis, in a double labeling system, DLA cells from untreated or MEAC treated tumor-bearing mice were washed twice with cold PBS and then re-suspended in 1X binding buffer at a concentration of 1×106 cells/mL. Then 100 µL of the cell suspension was transferred to the 5 mL culture tube. Afterward, added 25 µL of Annexin V-FITC and/or propidium iodide (PI) solution to the cell suspension. The cell were gently mixed by vortexing and incubated for 15 min at 37 °C. Then 400 µL of 1X binding buffer was added to each tube and analyzed by FACS within one hour using flowcytometer (BD LSRFortessaTM Cell analyzer, USA).
Analysis of protein expression by Western blotting
DLA lysate was loaded into a 10% Sodium dodecyl sulfate (SDS)-polyacrylamide gel. After electrophoresis, the gel was transferred to nitrocellulose membrane and blocked with 5% Bovin serum albumin (BSA) in 1X tris buffer saline (TBS). The membrane was then incubated with specific primary antibody of anti-Bax, anti-Bcl-2 and β-actin (1:1000) for overnight at 4 °C. The protein of interest was visualized by treating with alkaline phosphatase (ALP) conjugated specific secondary antibody. The target protein band was then visualized using bromochloroindolyl phosphate (BCIP) and nitrobluetetrazolium (NBT) substrates. Equal loading of protein in each lane was established by β-actin antibody probing (
1).
Statistical analysis
Data was statistically analyzed by using one way analysis of variance (ANOVA) followed by Dunnett’s post hoc test by GraphPad Prism software (Version 5.0, GraphPad Prism software Inc., San Diego, CA). p<0.01 was considered as statistically significant.
| Fractions | Steroid | Glycoside | Alkaloid | Saponin | Tannin | Phenolicmg GAE/g | Flavonoidmg QE/g |
|---|
| MEAC | + | + | + | + | - | 164.75 ± 3.8 | 51.20 ± 2.1 |
| Parameters | Normal control (5ml/kg) | DLA control(2× 106 cell/ml) | DLA + MEAC(200 mg/kg) | DLA + MEAC(400 mg/kg) |
|---|
| Tumor volume | - | 2.99 ± 0.40 | 1.66 ± 0.28 b,* | 1.26 ± 0.15 b,* |
| Tumor weight | - | 2.85 ± 0.21 | 1.37 ± 0.18 b,* | 0.91 ± 0.07 b,* |
| Viable cell | - | 9.12 ± 0.45 | 3.99 ± 0.39 b,* | 1.76 ± 0.28 b,* |
| Nonviable cell | - | 0.38 ± 0.07 | 1.24 ± 0.15 b,* | 3.03 ± 0.72 b,* |
| MST (days) | - | 20.00 | 30.50 | 37.00 |
| % ILS | - | 00 | 52.50 | 80.00 |
| RBC | 5.63 ± 0.19 | 2.46 ± 0.60 a,* | 4.01 ± 0.18 b,* | 4.96 ± 0.42 b,* |
| WBC | 5.11 ± 0.39 | 10.16 ± 1.05 a,* | 7.43 ± 0.31 b,* | 6.13 ± 0.86 b,* |
| Hemoglobin | 11.50 ± 1.01 | 5.12 ± 0.91 a,* | 9.05 ± 0.90 b,* | 9.91 ± 0.80 b,* |
DLA control group vs normal group,
treated groups vs DLA control group,
p<0.01.
Morphological changes in DLA cells after 14 days treatment with MEAC extract. For DLA control group (A), MEAC 200 mg/kg (B) and MEAC 400 mg/kg (C). The cells were stained with acridine orange and ethidium bromide. Blue arrows next to "L" point to live cells; Yellow arrows next to "A" indicate apoptotic cells; and Red arrows next to "N" indicate necrotic cells (magnification at 40X).
The DNA damage was measured by comet assay after treatment of DLA cells with MEAC extract. The cells were left untreated (A) or treated with MEAC 200 mg/kg (B) or MEAC 400 mg/kg (C). The extent of DNA damage was expressed in terms of comet % tail length (D). Data are the mean ± SD from three replicate measurements. Treated groups vs. DLA control group, ***p<0.001
Flow cytometry analysis for apoptosis inducing activity of MEAC on DLA cells were labeled with PI and Annexin-V FITC Fluos and then fixed and analyzed on a Flowcytometer. DLA control group (A), MEAC 200 mg/kg (B) and MEAC 400 mg/kg (C). Dual parameter dot plot of FITC-fluorescence (x-axis) versus PI-fluorescence (y-axis) has been shown in logarithmic fluorescence intensity. Quadrants: lower left, live cells; lower right, apoptotic cells; upper right, necrotic cells
DLA lysates [Lane 1- DLA control; Lane 2- MEAC treated 200 mg/kg and Lane 3- MEAC treated 400 mg/kg] were subjected to western blot analysis. Pro-apoptotic proteins Bax and anti-apoptotic protein Bcl-2 and visualized by ALP-conjugated secondary antibody. The β-actin band confirmed equal protein loading (A). Quantitative bar diagram showing Bcl-2/Bax expression and ratio (B), Data are the mean ± SD from three replicate measurements. Treated groups vs. DLA control group, NS= non significant, *p<0.05 and **p<0.01