Workflow of FFPE-Based Proteomic Analysis

Formalin-fixed paraffin-embedded (FFPE) samples are widely used in clinical and research settings due to their importance in tissue preservation and long-term storage. Proteomic analysis of FFPE samples can provide crucial insights into tumor biology, disease mechanisms, and potential therapeutic targets.

Sample Preparation

Sample preparation is the first step in proteomic analysis, and FFPE samples require deparaffinization and rehydration. This process typically includes the following steps:

1. Deparaffinization

Using xylene or other organic solvents to remove the paraffin. Samples are usually immersed in xylene multiple times to ensure complete deparaffinization.

2. Rehydration

Gradually immersing the deparaffinized samples in different concentrations of ethanol, finally transitioning to deionized water to rehydrate the tissue.

3. Sectioning

Cutting the samples into appropriate thickness slices, typically 5-10 micrometers, to facilitate protein extraction.

Protein Extraction

Following deparaffinization and rehydration, protein extraction is necessary. Common extraction buffers include solutions containing urea, thiourea, and phosphate-buffered saline, which effectively disrupt cell membranes and release intracellular proteins. The extraction steps typically include:

1. Homogenization

Placing the samples in a homogenizer to mechanically break down the tissue.

2. Centrifugation

Centrifuging the homogenate to remove cellular debris, collecting the supernatant containing the proteins.

3. Quantification

Using the BCA or Bradford assay to quantify the extracted proteins, ensuring consistent protein concentrations for subsequent experiments.

Enzymatic Digestion

After protein extraction, samples usually require enzymatic digestion to generate small peptides suitable for analysis. Trypsin is commonly used, and the specific steps are as follows:

1. Digestion Reaction

Mixing the extracted proteins with trypsin at a ratio of 1:50, typically incubating at 37°C overnight.

2. Termination of Reaction

Using trifluoroacetic acid (TFA) or other chemicals to terminate the digestion reaction, preventing over-digestion.

3. Purification

Purifying the small peptides through solid-phase extraction (SPE) or reverse-phase liquid chromatography (RP-HPLC) to remove undigested proteins and enzymes.

Labeling

1. TMT (Tandem Mass Tag) Labeling

Using TMT reagents for isotope labeling of small peptides, allowing multiple samples to be compared within the same experiment.

2. iTRAQ (Isobaric Tags for Relative and Absolute Quantification) Labeling

Similar to TMT, iTRAQ allows relative quantification of up to eight samples.

Separation

1. Liquid Chromatography (LC)

Separating small peptides through reverse-phase or normal-phase chromatography, typically using C18 columns for efficient separation.

2. Gradient Elution

Optimizing separation by altering the composition of the eluent (e.g., increasing the proportion of organic phase).

Detection

1. MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time of Flight)

Suitable for analyzing large molecules and complex samples.

2. LC-MS/MS (Liquid Chromatography Tandem Mass Spectrometry)

Combining the separation capability of liquid chromatography with the detection sensitivity of mass spectrometry, providing high-quality proteomic data.

The workflow for proteomic analysis based on FFPE samples encompasses multiple key steps, from sample preparation to mass spectrometry detection. Through careful experimental design and rigorous execution, researchers can obtain valuable proteomic information from FFPE samples, supporting the study of disease mechanisms and the discovery of potential therapeutic targets..