Annexin V-FITC Staining Protocol for Apoptosis Detection

Apoptosis or programmed cell death is an important biological process involved in various physiological and pathological conditions. It plays a vital role in embryogenesis, tissue homeostasis, immune response, and elimination of damaged or unwanted cells in the body. The detection of apoptosis can be used in the research of different types of pathological specimens including tumor cells and tissues, clinical diagnosis and treatment, new drug development, biological product development, tumor radiotherapy and chemotherapy, and other fields. Annexin V-FITC staining is currently a widely used method for detecting apoptosis.

Understand Apoptosis Execution Pathway

Principles of Annexin V-FITC Staining

The Annexin V-FITC staining protocol is based on the selective binding of Annexin V, a calcium-dependent phospholipid-binding protein, to phosphatidylserine (PS) residues exposed on the outer leaflet of apoptotic cells. In healthy cells, PS is predominantly located on the inner leaflet of the plasma membrane. However, during apoptosis, PS translocates to the outer surface, providing an early and specific marker for apoptotic cells. By utilizing the high affinity of Annexin V for exposed PS, apoptotic cells can be easily identified and quantified.

Propidium Iodide (PI) is a nucleic acid dye that cannot penetrate the complete cell membrane, but due to the increase in the permeability of the cell membrane in the middle and late stages of apoptosis and dead cells, PI can penetrate the cell membrane and stain the nucleus red. Therefore, the matching of Annexin V and PI can distinguish cells in different apoptotic stages.

Fig. 1 Representative flow cytometry plots using Annexin V-FITC/PI staining for apoptosis. (Park H J, et al., 2017)

Protocol of Annexin V-FITC Staining

The Annexin V-FITC staining protocol consists of the following steps:

Cell Incubation with Annexin V-FITC:

Induce apoptosis in the desired cell population using appropriate methods.
Collect 1-5 x 10⁵ cells and resuspend them in 500 µL 1 x Annexin V binding buffer.
Add 5 µL Annexin V-FITC and PI to the cell suspension (PI, optional).
Incubate the cells at room temperature in the dark for a specific duration.

Note: To prepare adherent cells for Annexin V-FITC staining:

Gently detach the cells using trypsin.
Wash the cells once with serum-containing media.
Proceed with the incubation step using Annexin V-FITC.

Browse the Cell Counting Kit

Analysis of Annexin V-FITC Binding:

Analyze annexin V-FITC binding using flow cytometry, utilizing the FITC signal detector.
If PI was added, analyze PI staining using the phycoerythrin emission signal detector.

Observation of Cell Staining:

For visual confirmation, transfer the stained cells onto a glass slide.
Cover the cells with a glass coverslip and observe under a fluorescence microscope.
Use a fluorescence microscope with a dual filter set for FITC and rhodamine to observe the cells.

Precautions

PI is toxic, can be absorbed through the skin, and is irritating to the eyes. Gloves should be worn when using it.
Annexin V-FITC and PI are photosensitive substances, so care should be taken to avoid light during operation. During the incubation period, wrap the container in aluminum foil or place it in a drawer. After the cells were labeled, they were observed with a microscope in a dark room.
During the whole operation process, the action should be as gentle as possible, not blow or beat the cells hard, and try to operate at 4°C to avoid affecting the state of the cells.
To prevent fluorescence decay, flow detection should be performed within 1 hour.
If the PI staining time is too long, the detected apoptosis rate may be too high. It is recommended to perform Annexin V-FITC staining first, and then add PI staining at least 5 minutes before using the machine.
If the sample is from blood, platelets need to be removed from the blood. Because platelets contain PS, they can combine with Annexin V, thereby interfering with the experimental results.

In summary, the Annexin V-FITC staining protocol is a powerful tool for the detection of apoptosis, enabling researchers to study the complex processes underlying programmed cell death. As a leading provider of innovative life science solutions, Creative Diagnostics offers a range of high-quality products and services related to Annexin V-FITC staining for apoptosis detection and empowers researchers to explore the intricate mechanisms of apoptosis.

References

Park H J, et al. Phellinus linteus grown on germinated brown rice increases cetuximab sensitivity of KRAS-mutated colon cancer. International Journal of Molecular Sciences. 2017, 18(8): 1746.