Lipofuscin is a granular, yellowish-brown pigment composed of lipid-containing residues and lysosomal digestates. It is believed to be generated by the oxidation of lipids and lipoproteins-a slow, progressive process that results in the pigment exhibiting variable staining reactions, colors, shapes, and sizes. Lipofuscin is found in the liver, kidneys, myocardium, adrenal glands, neurons, and ganglion cells, and is mostly distributed around the cell nucleus. It can be categorized into early-stage lipofuscin and late-stage lipofuscin. Early-stage lipofuscin retains all lipid characteristics and stains grayish-black with the Sudan Black B method. Late-stage lipofuscin is a fully oxidized pigment that loses sudanophilia but possesses stronger reducing power, and is primarily visualized using the Schmorl ferric-ferricyanide reduction method. Currently, common staining methods for lipofuscin include the PAS method, Schmorl ferric-ferricyanide reduction method, and Gomori aldehyde-fuchsin method.
Melanin is a group of non-hematogenous endogenous pigments ranging in color from light brown to black. It typically occurs in the skin, eyes, substantia nigra of the brain, and hair follicles. Melanin is a highly stable substance that is insoluble in both organic solvents and water. It can chelate ferrous ions to form melanin-ferrous complexes, which react with potassium ferricyanide to produce a blue color. Melanin can reduce ammoniacal silver solutions to metallic silver and can be bleached by strong oxidizing agents such as potassium permanganate. Numerous methods are available for identifying melanin and melanocytes, with the most reliable being: reduction methods (e.g., Masson-Fontana silver technique and Schmorl ferric-ferricyanide reduction method); enzymatic methods (e.g., dopa reaction); fluorescence methods; and immunohistochemistry.
The staining principle of Melanin-Lipofuscin Staining Solution (Schmorl Method) is Both melanin and lipofuscin have strong reducing properties, capable of reducing ferric ions to ferrous ions, which then react with potassium ferricyanide to yield a dark blue color. This method detects all substances that can reduce ferric compounds and is therefore not specific for melanin and lipofuscin. However, differentiation can be assisted based on tissue/cell type, pigment location and distribution, and staining intensity. Comparative observations can also be performed alongside methods such as the ammoniacal silver method, aldehyde-fuchsin method, and periodic acid-Schiff (PAS) method.This reagent is intended for research use only and not for clinical diagnosis or other purposes.
A1508695
| Component | 2×50 mL | Storage | | A1508695A | Ferric salt solution
| 45 mL | RT. | | A1508695B | Potassium ferricyanide solution
| 5 mL | 2-8℃. Store in the dark. | | A1508695C | Nuclear counterstain solution
| 50 mL | RT. Store in the dark. |
|
Just before use, mix Solution A and Solution B at a ratio of 9:1 to prepare Schmorl Stain. Do not prepare the stain in advance.
Materials to Be Prepared by the User
Fixatives (10% neutral buffered formalin, 10% formalin, etc.), Graded ethanol solutions, 1% acetic acid aqueous solution
Procedure (For Reference Only)
(1) Paraffin Section Staining
1. Fix tissues in 10% neutral buffered formalin, then process for routine dehydration and embedding.
2. Cut sections at a thickness of 4 μm. Deparaffinize sections with xylene or a deparaffinization solution and hydrate to distilled water; rinse with distilled water for 1 min.
3. Immerse sections in Schmorl stain (see Note 3) for 1-5 min; rinse with distilled water for 2 min.
4. (Optional) Rinse sections in 1% acetic acid aqueous solution for 1-3 min to thoroughly remove residual ferricyanide; rinse with distilled water for 2 min.
5. Counterstain with nuclear counterstain for 3-10 min; rinse with distilled water for 1-2 min.
6. Dehydrate sections routinely, clear with xylene or a deparaffinization solution, and mount with neutral mounting medium.
(2) Frozen Section Staining
1. Skip deparaffinization; rinse sections quickly with distilled water for 2-3 min.
2. Follow the staining and mounting steps for paraffin sections, with appropriate reduction of incubation times.
(3) Cell Staining
1. Fix cells with 4% paraformaldehyde for 10-20 min.
2. Rinse with tap water twice, 2 min each time.
3. Rinse with distilled water twice, 2 min each time.
4. Follow the staining and mounting steps for paraffin sections, with appropriate extension of incubation times.
Staining Results
Lipofuscin, Melanin Greenish: blue to dark blue
Cell Nuclei, Other Tissues: Red
Precautions
1. Ensure complete deparaffinization of sections.
2. Use distilled or deionized water throughout the procedure to avoid interference from reducing impurities in water.
3. Prepare Schmorl stain fresh immediately before use; it is stable for approximately 2 hours. Do not over-incubate sections in the stain. Generally, melanin stains faster than lipofuscin and should show a positive reaction within 2 min. Prolonged staining will cause heavy background coloration, impairing observation contrast.
4. The 1% acetic acid rinse step is optional and helps remove residual ferricyanide.
5. For frozen section and cell staining, optimize experimental conditions according to specific sample types.
6. This method detects all ferric ion-reducing substances and lacks specificity for lipofuscin. Differentiation of lipofuscin can be aided by tissue/cell type, pigment location/distribution, and staining intensity. Comparative observations with the ammoniacal silver method, aldehyde-fuchsin method, and PAS method are recommended.
7. Most tissues exhibit inherent reducing properties that can cause background staining. Therefore, strictly control staining time to achieve clear visualization of lipofuscin with minimal background.
8. For safety and health, wear a lab coat and disposable gloves during operation.
9. Use the reagent promptly after opening to avoid compromising experimental results.
K2610352