Tracking Cell Death with Apoptosis Assays from Elabscience®

An average adult loses approximately 50 to 70 billion cells per day through programmed cell death [1]. At first glance, this may seem like an enormous number. However, considering that the human body contains on average more than 13 trillion cells (1.3 x 10¹³), this accounts for only about 0.5 % of all body cells [2]. Nevertheless, cell death in self-renewing tissues such as the skin, gut, and bone marrow is essential to make room for the billions of new cells produced each day. The morphological “ritual” that cells undergo during this process is known as apoptosis and is controlled by a family of intracellular proteases called caspases. In contrast to necrosis – the accidental and often “chaotic” form of cell death caused by trauma – apoptosis is tightly regulated. During this process, the cell breaks down into small, membrane-bound fragments (apoptotic bodies) that are rapidly engulfed and cleared by phagocytes. As a result, no inflammatory reactions or tissue scarring occur – essentially a “clean” cellular cleanup process [1]. 

If apoptosis fails, cancer cells can survive and proliferate uncontrollably. Conversely, excessive apoptosis can contribute to neurodegenerative diseases such as Alzheimer’s disease [3]. It is therefore hardly surprising that this central biological process receives significant attention in research. Our partner Elabscience® supports scientists in apoptosis research with a broad range of products for investigating and detecting apoptotic processes [4]. The portfolio spans from Annexin V and caspase assays to TUNEL assays and JC-1 assays – ensuring that you can find the right kit for every question in your apoptosis research. 

1) Annexin V – A Sensitive Marker for Early Apoptosis

2) Caspases – The Molecular Scissors of Apoptosis

3) TUNEL Assays – Established in situ Method for Apoptosis Detection

4) JC-1 – The Color Indicator for Mitochondrial Health

Annexin V – A Sensitive Marker for Early Apoptosis

In the early phase of apoptosis, the essential phospholipid phosphatidylserine (PS) translocates from the cytoplasmic inner leaflet of the plasma membrane to the outer membrane surface of the dying cell (Fig. 1). Annexin V is a calcium-dependent protein with a molecular weight of approximately 35-36 kDa that binds PS with high affinity and can therefore be used to detect early apoptotic cells [5]. Elabscience® has developed Annexin V apoptosis kits that combine 15 fluorochromes and three nucleic acid dyes to meet diverse research requirements. The assays employ a conjugate of Annexin V and a fluorescent marker, combined with nuclear DNA staining, for example using propidium iodide (PI), 7-aminoactinomycin D (7-AAD), or 4’,6-diamidino-2-phenylindole (DAPI). This approach enables reliable discrimination between viable, apoptotic, and necrotic cells. Detection is typically performed by flow cytometry.

Figure1:  Principle of Annexin V apoptosis kits. During apoptosis, phosphatidylserine (PS) translocates from the inner leaflet of the plasma membrane to the outer surface. Ca²⁺-dependent Annexin V conjugated to a fluorescent marker (here APC) can then bind PS, enabling detection of apoptotic cells by flow cytometry [5].  

Key Advantages of Annexin V Apoptosis Kits at a Glance: 

• Multiple options: 15 fluorochromes combined with 3 nucleic acid dyes
• High accuracy: Ideal for detecting early apoptosis without fixation-related false positives
• Fast and simple workflow: Only 15-20 minutes of hands-on time
• Strict quality control: Developed in-house with traceable and reliable quality 
  
  

Caspases – The Molecular Scissors of Apoptosis

Caspases are a family of cysteine proteases that act as central regulators of programmed cell death as well as certain inflammatory processes. They cleave target proteins specifically after aspartate residues, leading either to the orderly dismantling of the cell or to the maturation of inflammatory cytokines [6]. With the caspase assays from Elabscience®, the activity of different caspases can be measured with high specificity using either colorimetric or fluorescence-based methods. 

The colorimetric method employs caspase-specific peptide substrates conjugated to the yellow chromophore p-nitroanilide (pNA) (Fig. 2). Upon caspase activation, the enzyme cleaves the substrate, thereby releasing the yellow chromophore. The absorbance of the liberated pNA can subsequently be measured using a spectrophotometer or a microplate reader at wavelengths of approximately 400-405 nm [6]. 

Figure 2:  Principle of the colorimetric caspase assay method. The activated caspase cleaves the acetylated (Ac) peptide substrate, thereby releasing the yellow chromophore p-nitroanilide (pNA). Its absorbance can then be measured using a spectrophotometer or a microplate reader [6].   

In contrast, the fluorescence-based method uses caspase-specific peptide substrates conjugated to a high-affinity DNA fluorochrome (Fig. 3). These substrates are capable of penetrating the cell membrane and entering the cytoplasm. In their intact form, they are non-fluorescent and, due to electrostatic repulsion, do not bind to DNA. Following caspase activation, the substrate is cleaved and the high-affinity DNA fluorochrome is released. This fluorochrome can then bind to DNA and generate a strong fluorescent signal. Consequently, this method enables both the detection of caspase activity and the visualization of morphological changes in the nucleus during apoptosis [6]. 

Figure 3:  Principle of the fluorescence-based caspase assay method. The peptide substrates, conjugated to a DNA fluorochrome, enter the cytoplasm, where they are cleaved by activated caspases. The released DNA fluorochrome can then enter the nucleus, bind to DNA, and generate a strong fluorescent signal [6].  

Key Advantages of Caspase Apoptosis Kits at a Glance: 

• Easy to use: One-step staining saves time and effort
• Safe and non-toxic: Low cytotoxicity and does not interfere with the apoptosis process
• Cost-effective: Key components are developed in-house, ensuring stable quality at a more affordable price
• Wide applicability: Suitable for various cell types and compatible with other assay kits  
  
  

TUNEL Assays – Established in situ Method for Apoptosis Detection

A key feature of late-stage apoptosis is DNA fragmentation. In the TUNEL assay, the exposed 3’-OH ends of fragmented DNA can be enzymatically labeled with fluorochrome-conjugated deoxyuridine triphosphate (dUTP) by terminal deoxynucleotidyl transferase (TdT). This labeling can then be detected using fluorescence microscopy or flow cytometry. If the 3’-OH groups are labeled with biotin-conjugated dUTP under TdT catalysis and subsequently coupled with HRP-conjugated streptavidin, the signal can be visualized via DAB color development catalyzed by HRP. In this case, apoptotic cells can be detected using a conventional light microscope [7].   

Elabscience® has developed a series of TUNEL apoptosis kits, including the One-step TUNEL In Situ Apoptosis Kit, the One-step TUNEL Flow Cytometry Apoptosis Kit, and the TUNEL In Situ Apoptosis Kit (HRP-DAB method). These kits can be used to detect apoptosis in both tissue samples (paraffin-embedded and frozen sections) and cell samples (cell smears, culture preparations, as well as suspension and adherent cells) [7]. 

Key Advantages of TUNEL Apoptosis Kits at a Glance: 

• Multiple options: Kits available with a variety of fluorescent dyes (FITC / Elab Fluor® 488 / Elab Fluor® 594 / Elab Fluor® Violet 450 / Elab Fluor® 647 / Elab Fluor® 555)
• Easy to use: One-step staining saves time and effort
• Broad applicability: Suitable for a variety of cell and tissue samples
• High sensitivity: Apoptosis can be detected at the single-cell level
• Methodological flexibility: Compatible with both flow cytometry and fluorescence microscopy   
  
  

JC-1 – The Color Indicator for Mitochondrial Health

A decrease in mitochondrial membrane potential (ΔΨm) is a marker event in the early stages of apoptosis and occurs before nuclear apoptotic features such as chromatin condensation and DNA fragmentation appear. Once the mitochondrial membrane potential collapses, apoptosis becomes irreversible. JC-1 is a fluorescent probe commonly used to measure mitochondrial membrane potential. In healthy cells, the mitochondrial membrane potential is high; JC-1 accumulates in the mitochondrial matrix and forms aggregates (polymers) that emit red fluorescence. In the early stages of apoptosis, the mitochondrial membrane potential decreases, preventing JC-1 from accumulating in the mitochondrial matrix. In its monomeric form, JC-1 emits green fluorescence. 

The decrease in membrane potential can therefore be detected by the shift of JC-1 fluorescence from red to green; this color change serves as an early indicator of apoptosis [8]. The Elabscience® Mitochondrial Membrane Potential Assay Kit (with JC-1) is easy to use, and the results are straightforward to interpret, making it an effective tool for assessing apoptotic status [9].

With Elabscience® apoptosis kits, you are perfectly equipped for your research. Take advantage of our exclusive 10% discount on all Elabscience® cell apoptosis kits and expand your toolkit for precise apoptosis analyses. 

Curious to learn more? Explore the full range of apoptosis assays and other products from Elabscience® here.  

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Sources

[1] Reed JC. Dysregulation of apoptosis in cancer. J Clin Oncol. 1999 Sep;17(9):2941-53. doi: 10.1200/JCO.1999.17.9.2941. PMID: 10561374.

[2] Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2015). Molecular Biology of the Cell (6th ed.). Garland Science. p. 2. ISBN 978-0-8153-4432-2.

[3] Hug, H. (2000), Apoptose: die Selbstvernichtung der Zelle als Überlebensschutz. Biologie in unserer Zeit, 30: 128-135.

[4] https://www.elabscience.com/products/cell-function-assays?srsltid=AfmBOoq-4JeaxxFRo6azA0AxpQIWezlviWVqnP6DsbX0IeP6EkTdZK7A, 08.02.2026

[5] https://www.elabscience.com/products/annexin-assay-kits, 08.02.2026

[6] https://www.elabscience.com/products/caspase-assay-kits, 09.02.2026

[7] https://www.elabscience.com/products/tunel-assay-kits, 09.02.2026

[8] https://www.elabscience.com/p/mitochondrial-membrane-potential-assay-kit-with-jc-1--e-ck-a301, 09.02.2026

[9] https://www.elabscience.com/search?category=mitochondrial-assay-kits, 09.02.2026

Preview Image: https://commons.wikimedia.org/wiki/File:HeLa-IV.jpg, 08.02.2026