4.1 Animals and experimental protocol
The C57BL/6 mice were purchased from Shanghai model organisms (Shanghai, China). These mice were fed under SPF-condition in Zhejiang University Center of Drug Safety Evaluation and Research. The mouse studies experimental procedures were approved by IACUC (IACUC-s21-013) of Zhejiang University.
To induce RM-AKI by glycerol, the mice were divided into two groups: glycerol (10 mL/kg, 50%, im) group (n = 9) and vehicle group (n = 3). Deprived of water for 16 h, the mice were injected glycerol to manufacture the incidence of AKI model. Glycerol was injected into both hind limbs of each mouse. Each three mice were sacrificed at three time points 6 h, 12 h and 24 h after glycerol injection, and three mice in the vehicle group were sacrificed at 24 h. We collected the kidney tissues and serum of the mice. To investigate CN128 protective effect in AKI, mice were divided into three groups randomly i) vehicle group; ii) glycerol group; and iii) glycerol + CN128 (50 mg/kg) group. CN128 were intraperitoneally (i.p.) every 12 h for 5 times of the experiment, glycerol administration one hour after the sixth time injection. Same drug evaluation method in AKI-02: mice were respectively divided into four groups (vehicle group, glycerol group, glycerol + 50 mg/kg DFP group, glycerol + 12.5 mg/kg or 25 mg/kg AKI-02 group) with five mice in each group. Mice were sacrificed 24 h as described above.
4.2 Cell culture
The HK-2 cell line were purchased from the Shanghai Institute of Biochemistry and Cell Biology (Shanghai, China). Cell culture was used RPMI-1640 medium (SH30809, HyClone) with 10% fetal bovine serum (SV30160, HyClone). And the cell maintained at 37°C, 5% CO2 humidified atmospher. Cell line HK-2 was authenticated by STR profiling.
4.3 Growth inhibition assay
Using the sulforhodamine B (SRB, #S1402, Sigma-Aldrich, St. Louis, MO, USA) measured cell growth inhibition. The monolayers of cell were fixed with 10% (wt/vol) trichloroacetic acid (TCA) for 30 min, then washed repeatedly with 1% (vol/vol) acetic acid. The protein binding dye was dissolved in 10 mM Tris base solution and determined for the OD value at 510 nm using Multiskan Spectrum (Thermo).
4.4 Assessment of kidney function
Kidney function was assessed by BUN and serum creatinine. The serum samples were collected at 24 h after administration, and the BUN and serum creatinine were quantified via Roche automatic biochemical analyzer (COBASC 311).
4.5 Renal tissue H&E staining
Renal tissues were collected and fixed with 4% PFA, followed cut into 5 µm thickness sections. 1) Hematoxylin-eosin (H&E) staining (C0105S, Beyotime, China). 2) Prussian blue staining was dyed with freshly prepared 10% potassium ferrocyanide and 20% hydrochloric acid. The histopathological changes of the renal tissue were observed and photographed using light microscope.
4.6 Determination of renal malondialdehyde
The renal tissue supernatant MDA was measured by Malondialdehyde assay kit (A003-1-2, Nanjing Jiancheng Bioengineering Institute, Hangzhou, China). MDA reacted with thiobarbituric acid to form a red-pink color compound. The compond absorbance was measured at 532 nm with the microplate reader and the result was presented as µmol MDA/mg protein.
4.7 RT-PCR analysis
Total RNA in renal tissue samples was extracted using TRIzol Reagent. The mRNA expression level of Gpx4, Nrf2, Ptgs2 and Acls4 was measured by RT-PCR.
Actin forward, ACTGCCGCATCCTCTTCCT and reverse, TCAACGTCACACTTCATGATGGA;
Gpx4 forward, CTTATCCAGGCAGACCATGTGC and reverse, CCTCTGCTGCAAGAGCCTCCC;
Nrf2 forward, AAAATCATTAACCTCCCTGTTGAT and reverse, CGGCGACTTTATTCTTACCTCTC;
Ptgs2 forward, TGCCTGGTCTGATGATGTATG and reverse, GGGGTGCCAGTGATAGAGTG;
Acls4 forward, CCACACTTATGGCCGCTGTT and reverse, GGGCGTCATAGCCTTTCTTG;
Actinb forward, ACTGCCGCATCCTCTTCCT and reverse, TCAACGTCACACTTCATGATGGA.
4.8 Measure of tissue non-heme iron
We used chromogen method determine kidney non-heme iron levels (44). The tissue from each groups were collected and digested in 10% trichloroacetic acid in 3M HCl for 70 h at 60 oC. The results were expressed in iron per gram micrograms of wet tissue weight.
4.9 ICP-MS detection
The kidney total element iron was measured using inductively coupled plasma mass spectrometry (ICP-MS) (45). Kidneys from each groups were collected, weighted and lyophilized. Then kidneys were digested in nitric acid (65%, w/w, AR grade) for 2 h at 110 oC. The results are expressed in iron per milligram micrograms of dry tissue weight.
4.10 Lipid peroxidation assay
i) In the six-well plates, 1 × 105 cells per well were seeded prior to the experiment. Cells were treated with the ferroptosis inducers for 14h the next day and incubated with Liperfluo (DojinDo, L248, Kumamoto, Japanese) 2 μM for 1 h at 37°C. Subsequently, cells were resuspended in PBS strained and analyzed by CytoFLEX LX flow cytometer (Beckman Coulter) and FACSCanto™ flow cytometer with FACSDiva 6.1.3 software (BD Biosciences). Cell Data was performed using the Flowjo program (Verify Software House, Topsham, ME).
ii) 1 × 105 cells in 6-well dishes were treated with the ferroptosis inducers for 12h, then harvested by trypsinization, re-suspended in PBS containing 2 μM C11 BODIPY (#D3861, Invitrogen, Carlsbad, CA, USA), and cells incubated at 37 °C for 30 min. The cells were re-suspended in PBS and analyzed using a flow cytometer as mentioned above.
4.11 Statistical analysis
Statistical analyses were performed by Prism 6 (GraphPad Software). Statistical comparisons among groups were calculated by one-way ANOVA, and t-test. P < 0.05 was considered significant.