Experimental design
An interventional study was performed on L6 (Rat skeletal muscle myoblast) cell line, purchased from Pasteur Institute, Iran. The BPA (Merck, Germany), adiponectin (Abnova, Taiwan), and quercetin (Sigma, USA) were purchased and prepared in different concentrations. The cells were divided into the following groups:
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Cells with no treatment as the control group
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Cells treated with BPA (50 and 100 µM)
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Cells treated with BPA (50 and 100 µM) and quercetin (10 and 25 ng/ml)
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Cells treated with BPA (50 and 100 µM) and adiponectin (10 and 100 ng/ml)
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Cells treated with BPA (50 and 100 µM), quercetin (10 and 25 ng/ml), and adiponectin (10 and 100 ng/ml)
Mtt Assay
The L6 cells were cultured in DMEM medium supplemented with 10% FBS (Gibco) to reach suitable confluency. 7000 cells were cultured into 96 wells plate. 24 h later, each medium was replaced by the prepared mediums containing BPA, quercetin, and adiponectin according to the mentioned groups. 24 and 48 h after treatment, cells were incubated with (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) MTT solution (5mg/ml of DMEM) for 3 h. Next, the supernatant was taken away, and DMSO solvent was added. The absorbance of suspension was then read at 570 nm using a microplate reader.
Prooxidant-antioxidant Balance (Pab) Assay
The PAB test has been performed in two different reactions, including enzymatic and chemical reactions. In the enzymatic reaction, the pro-oxidants oxidize the chromogen TMB to a color cation, while in the chemical reaction, the antioxidants reduce the TMB cation to a colorless compound. First, by dissolving the TMB powder in DMSO, the TMB/DMSO solution was prepared. Next, 1 ml of TMB/DMSO solution was added to acetate buffer (50 mL, pH 4.5). Then, chloramine T (175 µL, 100 mM) to prepare the TMB cation solution incubated in a dark place for 2 hours at room temperature. Also, 16.5 µL of peroxidase enzyme solution was added and placed at -20 ºC.
TMB solution was prepared by adding 200 µL of TMB/DMSO to the acetate buffer (10 mL, pH 5.6). As the working solution, the third solution was prepared by adding 1 ml of TMB cation solution to 10 ml of TMB solution and, after 6 min incubation in the dark place at room temperature, freshly used. Also, the standard solutions are obtained by mixing different ratios of hydrogen peroxide at a concentration of 500 µM (as peroxidants) with a solution of 3 mM Uric acid in 10 mM NaOH (as antioxidants).
To perform the PAB test and evaluate the oxidant and antioxidant activity of the cells, 50,000 cells were cultured in 24 well plates according to the mentioned groups for 24 and 48 h. 200µL of the working solution was added to each well and incubated in a dark place at 37oC for 12 min. Then, 5 µL of HCL 2N was added to wells, and the optical density (OD) was read at 450 nm (the reference wavelength was 620 nm).
Catalase Activity Assay
For catalase activity evaluation, hydrogen peroxide, and ammonium molybdate solutions were prepared. Briefly, 102 µl of 30% hydrogen peroxide solution (Mw: 34.01, 9.79 N) was diluted with PBS to 50 ml, and 10 g of ammonium molybdate was diluted to 250 ml with distilled water to prepare 20 mM hydrogen peroxide solution and 32.4 mM ammonium molybdate, respectively. Different catalase reagents were designed and are shown in Table 1.
Table 1
Preparation of catalase reagents
Reagent | Test | Control test | Standard | Blank |
Serum | 100 µl | 100 µl | - | - |
Distilled water | - | 1000 µl | 100 µl | 1100 µl |
hydrogen peroxide | 1000 µl | - | 1000 µl | - |
The reagents were gently mixed with the vortex. After incubation at 37 ° C for 3 minutes, 4 ml of ammonium molybdate was added to the tubes and read at 374 nm using a spectrophotometer. Formula 1 is used to obtain the activity of the catalase enzyme based on (KU / L) KU.
$$Catalase activity=2.303/t \times \left(log \right(S.)/(S-M\left)\right)\times VT/VS$$
Formula 1. Calculating catalase activity, in which t: time, VT: Total volume of test tube reagents, S০: Standard absorption, S: Sample absorption, VS: Test sample volume
Qrt-pcr
L6 cells were cultured and treated with BPA, adiponectin, and quercetin for 24 h. According to the protocol instruction, the total RNA was extracted using the trizol Reagent (Total RNA Isolation Reagent) according to the protocol instruction. The purity and amount of RNA were measured by NanoDrop 2000c (Thermo Scientific, Pittsburgh, PA, USA). Complementary DNA (cDNA) was synthesized using cDNA synthesis kit (Yektatajhiz, Co, Iran) according to the instruction. RealQ Plus 2x Master Mix green was used for realtime PCR analysis based on its instruction. RTqPCR was done using Applied Biosystems Real-Time PCR Instrument. Primers for GAPDH: the housekeeping gene, Nrf2, and KEAP1 genes, are shown in Table 2. Real time-PCR was performed by the 10-min at 95 ˚ C for enzyme activation, followed by 35 cycles of 15 seconds for denaturation at 95 ˚ C, 60 seconds for annealing at 54.5 ˚ C, and 25 seconds for the extension at 72 ˚ C. The 2−ΔΔCt method was used to calculate relative expression levels.
Table 2
Specific primers for evaluated genes
Primers | | Sequans | Size (bp) | Tm |
GAPDH | forward | TGACTGTGCCGTTGAACTTG | 224 | 54.5˚ C |
reverse | GAGACAGCCGCATCTTCTTG |
Keap1 | forward | CAGCGTGGAGAGATATGAG | 158 | 57˚ C |
reverse | AGTAACATTCTGCCGAGTT | 53˚ C |
Nrf2 | forward | ACAACTGGATGAAGAGACCG | 101 | 58˚ C |
reverse | TGTGGGCAACCTGGGAGTAG | 63˚ C |