From: A blood–brain barrier overview on structure, function, impairment, and biomarkers of integrity
Marker | Size (Da) | Binding | Advantage | Disadvantage | |
---|---|---|---|---|---|
Protein | Tissue | ||||
Radiolabeled-mannitol | 182 | No | No | No interaction with proteins Metabolically stable Uncharged No interaction with BBB transporters Suitable for small molecules permeability prediction | Contains lipophilic impurities Requires a radioactive license High cost It cannot be visualized |
Biotin ethylenediamine | 286 | No | No | It can be measured quantitatively with HPLC Visual qualification is feasible | It has a low binding to plasma proteins |
Radiolabeled-sucrose | 342 | No | No | No interaction with proteins Metabolically stable Uncharged No interactions with BBB transporters Suitable for small molecules permeability prediction | Contains lipophilic impurities Over-time degradation Requires a radioactive license High cost It cannot be visualized |
13C12 sucrose | 354 | No | No | Non-radioactive A sensitive and specific method of detection No interaction with BBB transporters Metabolically stable No interaction with protein Suitable for small molecules permeability prediction | Requires LC–MS/MS device for detection High cost It cannot be visualized |
Sodium fluorescein | 376 | Weak | NR | Easy detection method Freely diffusible Detectable in very low concentrations Inexpensive Non-radioactive Nontoxic It can be visually assessed Suitable for small molecules permeability prediction | Interaction with BBB transporters Weekly binds to plasma proteins |
Evans blue | 961 | Yes | Yes | Visual investigation and qualification are feasible using different microscope techniques Allow assessment of vascular permeability to macromolecules due to binding to its extensive binding to albumin | Quantification is unreliable It strongly binds to serum albumin in vivo and in vitro and, thereby, becomes a high molecular weight protein tracer (69 kDa) Potential in vivo toxicity Not suitable for small molecules permeability prediction |
Trypan blue | 961 | Yes | Yes | Visual evaluation is feasible | Quantification is unreliable Binds to plasma proteins Not suitable for small molecules permeability prediction |
Radio-inulin | 7000 | No | No | Quantification is feasible No protein binding | Contains lipophilic impurities Requires a radioactive license High cost It cannot be visualized |
Horseradish peroxidase | 44,000 | NR | NR | Can be easily visualized under light and electron microscopy | The possibility of diffusion artifacts resulted in a distribution of the reaction product that may not reflect actual protein Found to be toxic in large doses Not suitable for small molecules permeability prediction Quantification is unreliable Species-specific degranulation of mast cells and histamine release |
Albumin | 69,000 | No | No | It is widely used in the radiolabeled or fluorescently labeled form The fluorescent-labeled version could be used for morphological studies The radiolabeled version allows for accurate quantification | Requires radioactive license Not suitable for small molecules permeability prediction |
Dextrans | 1500 to 70,000 | No | No | It can be used for a broad range of molecular weights Can be visualized with both light microscopic and electron microscopic level due to conjugation with biotin of FITC | Not suitable for small molecules permeability prediction Stability issue May be toxic at high concentrations |